A discrete adaptive guidance system for a roving vehicle
NASA Technical Reports Server (NTRS)
Miller, J. A.
19770101
An adaptive guidance technique which provides a selfcorrecting path following capability in an environment sensitive semiautonomous roving robot is described. A realtime maneuver planning function performs tradeoffs between speed, magnitude of expected deviations and accelerations to best satisfy the design goals of vehicle safety and reliability, subsystem autonomy, performance accuracy and operational efficiency. The appropriate combination of maneuver parameters is selected through an iterative process using knowledge of vehicle performance characteristics, environmental model updates and vehicle state
An adaptive guidance algorithm for aerospace vehicles
NASA Astrophysics Data System (ADS)
Bradt, J. E.; Hardtla, J. W.; Cramer, E. J.
The specifications for proposed space transportation systems are placing more emphasis on developing reusable avionics subsystems which have the capability to respond to vehicle evolution and diverse missions while at the same time reducing the cost of ground support for mission planning, contingency response and verification and validation. An innovative approach to meeting these goals is to specify the guidance problem as a multipoint boundary value problen and solve that problem using modern control theory and nonlinear constrained optimization techniques. This approach has been implemented as Gamma Guidance (Hardtla, 1978) and has been successfully flown in the Inertial Upper Stage. The adaptive guidance algorithm described in this paper is a generalized formulation of Gamma Guidance. The basic equations are presented and then applied to four diverse aerospace vehicles to demonstrate the feasibility of using a reusable, explicit, adaptive guidance algorithm for diverse applications and vehicles.
Light Adaptation of Discrete Waves in the Limulus Photoreceptor
Srebro, Richard; Behbehani, Mahmood
19720101
Light adaptation affects discrete waves in two ways. It reduces their average size and decreases the probability that a photon incident at the cornea causes a discrete wave. There is no effect of light adaptation on the latency of discrete waves, or on their timecourse. PMID:5042025
Averaging analysis for discrete time and sampled data adaptive systems
NASA Technical Reports Server (NTRS)
Fu, LiChen; Bai, ErWei; Sastry, Shankar S.
19860101
Earlier continuous time averaging theorems are extended to the nonlinear discrete time case. Theorems for the study of the convergence analysis of discrete time adaptive identification and control systems are used. Instability theorems are also derived and used for the study of robust stability and instability of adaptive control schemes applied to sampled data systems. As a by product, the effects of sampling on unmodeled dynamics in continuous time systems are also studied.
An averaging analysis of discretetime indirect adaptive control
NASA Technical Reports Server (NTRS)
Phillips, Stephen M.; Kosut, Robert L.; Franklin, Gene F.
19880101
An averaging analysis of indirect, discretetime, adaptive control systems is presented. The analysis results in a signaldependent stability condition and accounts for unmodeled plant dynamics as well as exogenous disturbances. This analysis is applied to two discretetime adaptive algorithms: an unnormalized gradient algorithm and a recursive leastsquares (RLS) algorithm with resetting. Since linearization and averaging are used for the gradient analysis, a local stability result valid for small adaptation gains is found. For RLS with resetting, the assumption is that there is a long time between resets. The results for the two algorithms are virtually identical, emphasizing their similarities in adaptive control.
Discretetime adaptive control of robot manipulators
NASA Technical Reports Server (NTRS)
Tarokh, M.
19890101
A discretetime model reference adaptive control scheme is developed for trajectory tracking of robot manipulators. Hyperstability theory is utilized to derive the adaptation laws for the controller gain matrices. It is shown that asymptotic trajectory tracking is achieved despite gross robot parameter variation and uncertainties. The method offers considerable design flexibility and enables the designer to improve the performance of the control system by adjusting free design parameters. The discretetime adaptation algorithm is extremely simple and is therefore suitable for realtime implementation.
Adaptive pattern for autonomous UAV guidance
NASA Astrophysics Data System (ADS)
Sung, ChenKo; Segor, Florian
20130901
The research done at the Fraunhofer IOSB in Karlsruhe within the AMFIS project is focusing on a mobile system to support rescue forces in accidents or disasters. The system consists of a ground control station which has the capability to communicate with a large number of heterogeneous sensors and sensor carriers and provides several open interfaces to allow easy integration of additional sensors into the system. Within this research we focus mainly on UAV such as VTOL (Vertical takeoff and Landing) systems because of their ease of use and their high maneuverability. To increase the positioning capability of the UAV, different onboard processing chains of image exploitation for real time detection of patterns on the ground and the interfacing technology for controlling the UAV from the payload during flight were examined. The earlier proposed static ground pattern was extended by an adaptive component which admits an additional visual communication channel to the aircraft. For this purpose different components were conceived to transfer additive information using changeable patterns on the ground. The adaptive ground pattern and their application suitability had to be tested under external influence. Beside the adaptive ground pattern, the onboard process chains and the adaptations to the demands of changing patterns are introduced in this paper. The tracking of the guiding points, the UAV navigation and the conversion of the guiding point positions from the images to real world coordinates in video sequences, as well as use limits and the possibilities of an adaptable pattern are examined.
NASA Technical Reports Server (NTRS)
Kantor, A. V.; Timonin, V. G.; Azarova, Y. S.
19740101
The method of adaptive discretization is the most promising for elimination of redundancy from telemetry messages characterized by signal shape. Adaptive discretization with associative sorting was considered as a way to avoid the shortcomings of adaptive discretization with buffer smoothing and adaptive discretization with logical switching in onboard information compression devices (OICD) in spacecraft. Mathematical investigations of OICD are presented.
A local adaptive discretization algorithm for Smoothed Particle Hydrodynamics
NASA Astrophysics Data System (ADS)
Spreng, Fabian; Schnabel, Dirk; Mueller, Alexandra; Eberhard, Peter
20140601
In this paper, an extension to the Smoothed Particle Hydrodynamics (SPH) method is proposed that allows for an adaptation of the discretization level of a simulated continuum at runtime. By combining a local adaptive refinement technique with a newly developed coarsening algorithm, one is able to improve the accuracy of the simulation results while reducing the required computational cost at the same time. For this purpose, the number of particles is, on the one hand, adaptively increased in critical areas of a simulation model. Typically, these are areas that show a relatively low particle density and high gradients in stress or temperature. On the other hand, the number of SPH particles is decreased for domains with a high particle density and low gradients. Besides a brief introduction to the basic principle of the SPH discretization method, the extensions to the original formulation providing such a local adaptive refinement and coarsening of the modeled structure are presented in this paper. After having introduced its theoretical background, the applicability of the enhanced formulation, as well as the benefit gained from the adaptive model discretization, is demonstrated in the context of four different simulation scenarios focusing on solid continua. While presenting the results found for these examples, several properties of the proposed adaptive technique are discussed, e.g. the conservation of momentum as well as the existing correlation between the chosen refinement and coarsening patterns and the observed quality of the results.
Missile guidance law design using adaptive cerebellar model articulation controller.
Lin, ChihMin; Peng, YaFu
20050501
An adaptive cerebellar model articulation controller (CMAC) is proposed for command to lineofsight (CLOS) missile guidance law design. In this design, the threedimensional (3D) CLOS guidance problem is formulated as a tracking problem of a timevarying nonlinear system. The adaptive CMAC control system is comprised of a CMAC and a compensation controller. The CMAC control is used to imitate a feedback linearization control law and the compensation controller is utilized to compensate the difference between the feedback linearization control law and the CMAC control. The online adaptive law is derived based on the Lyapunov stability theorem to learn the weights of receptivefield basis functions in CMAC control. In addition, in order to relax the requirement of approximation error bound, an estimation law is derived to estimate the error bound. Then the adaptive CMAC control system is designed to achieve satisfactory tracking performance. Simulation results for different engagement scenarios illustrate the validity of the proposed adaptive CMACbased guidance law. PMID:15940993
Inherent robustness of discretetime adaptive control systems
NASA Technical Reports Server (NTRS)
Ma, C. C. H.
19860101
Global stability robustness with respect to unmodeled dynamics, arbitrary bounded internal noise, as well as external disturbance is shown to exist for a class of discretetime adaptive control systems when the regressor vectors of these systems are persistently exciting. Although fast adaptation is definitely undesirable, so far as attaining the greatest amount of global stability robustness is concerned, slow adaptation is shown to be not necessarily beneficial. The entire analysis in this paper holds for systems with slowly varying return difference matrices; the plants in these systems need not be slowly varying.
A discretetime adaptive control scheme for robot manipulators
NASA Technical Reports Server (NTRS)
Tarokh, M.
19900101
A discretetime model reference adaptive control scheme is developed for trajectory tracking of robot manipulators. The scheme utilizes feedback, feedforward, and auxiliary signals, obtained from joint angle measurement through simple expressions. Hyperstability theory is utilized to derive the adaptation laws for the controller gain matrices. It is shown that trajectory tracking is achieved despite gross robot parameter variation and uncertainties. The method offers considerable design flexibility and enables the designer to improve the performance of the control system by adjusting free design parameters. The discretetime adaptation algorithm is extremely simple and is therefore suitable for realtime implementation. Simulations and experimental results are given to demonstrate the performance of the scheme.
Discretetime minimal control synthesis adaptive algorithm
NASA Astrophysics Data System (ADS)
di Bernardo, M.; di Gennaro, F.; Olm, J. M.; Santini, S.
20101201
This article proposes a discretetime Minimal Control Synthesis (MCS) algorithm for a class of singleinput singleoutput discretetime systems written in controllable canonical form. As it happens with the continuoustime MCS strategy, the algorithm arises from the family of hyperstabilitybased discretetime model reference adaptive controllers introduced in (Landau, Y. (1979), Adaptive Control: The Model Reference Approach, New York: Marcel Dekker, Inc.) and is able to ensure tracking of the states of a given reference model with minimal knowledge about the plant. The control design shows robustness to parameter uncertainties, slow parameter variation and matched disturbances. Furthermore, it is proved that the proposed discretetime MCS algorithm can be used to control discretised continuoustime plants with the same performance features. Contrary to previous discretetime implementations of the continuoustime MCS algorithm, here a formal proof of asymptotic stability is given for generic ndimensional plants in controllable canonical form. The theoretical approach is validated by means of simulation results.
A SelfAdaptive Missile Guidance System for Statistical Inputs
NASA Technical Reports Server (NTRS)
Peery, H. Rodney
19600101
A method of designing a selfadaptive missile guidance system is presented. The system inputs are assumed to be known in a statistical sense only. Newton's modified Wiener theory is utilized in the design of the system and to establish the performance criterion. The missile is assumed to be a beam rider, to have a g limiter, and to operate over a flight envelope where the openloop gain varies by a factor of 20. It is shown that the percent of time that missile acceleration limiting occurs can be used effectively to adjust the coefficients of the Wiener filter. The result is a guidance system which adapts itself to a changing environment and gives essentially optimum filtering and minimum miss distance.
An adaptive mesh refinement algorithm for the discrete ordinates method
Jessee, J.P.; Fiveland, W.A.; Howell, L.H.; Colella, P.; Pember, R.B.
19960301
The discrete ordinates form of the radiative transport equation (RTE) is spatially discretized and solved using an adaptive mesh refinement (AMR) algorithm. This technique permits the local grid refinement to minimize spatial discretization error of the RTE. An error estimator is applied to define regions for local grid refinement; overlapping refined grids are recursively placed in these regions; and the RTE is then solved over the entire domain. The procedure continues until the spatial discretization error has been reduced to a sufficient level. The following aspects of the algorithm are discussed: error estimation, grid generation, communication between refined levels, and solution sequencing. This initial formulation employs the step scheme, and is valid for absorbing and isotopically scattering media in twodimensional enclosures. The utility of the algorithm is tested by comparing the convergence characteristics and accuracy to those of the standard singlegrid algorithm for several benchmark cases. The AMR algorithm provides a reduction in memory requirements and maintains the convergence characteristics of the standard singlegrid algorithm; however, the cases illustrate that efficiency gains of the AMR algorithm will not be fully realized until threedimensional geometries are considered.
Discrete optimal control approach to a fourdimensional guidance problem near terminal areas
NASA Technical Reports Server (NTRS)
Nagarajan, N.
19740101
Description of a computeroriented technique to generate the necessary control inputs to guide an aircraft in a given time from a given initial state to a prescribed final state subject to the constraints on airspeed, acceleration, and pitch and bank angles of the aircraft. A discretetime mathematical model requiring five state variables and three control variables is obtained, assuming steady wind and zero sideslip. The guidance problem is posed as a discrete nonlinear optimal control problem with a cost functional of Bolza form. A solution technique for the control problem is investigated, and numerical examples are presented. It is believed that this approach should prove to be useful in automated air traffic control schemes near large terminal areas.
An adaptive synchronization protocol for parallel discrete event simulation
Bisset, K.R.
19981201
Simulation, especially discrete event simulation (DES), is used in a variety of disciplines where numerical methods are difficult or impossible to apply. One problem with this method is that a sufficiently detailed simulation may take hours or days to execute, and multiple runs may be needed in order to generate the desired results. Parallel discrete event simulation (PDES) has been explored for many years as a method to decrease the time taken to execute a simulation. Many protocols have been developed which work well for particular types of simulations, but perform poorly when used for other types of simulations. Often it is difficult to know a priori whether a particular protocol is appropriate for a given problem. In this work, an adaptive synchronization method (ASM) is developed which works well on an entire spectrum of problems. The ASM determines, using an artificial neural network (ANN), the likelihood that a particular event is safe to process.
Discrete adaptive zone light elements (DAZLE): a new approach to adaptive imaging
NASA Astrophysics Data System (ADS)
Kellogg, Robert L.; Escuti, Michael J.
20070901
New advances in Liquid Crystal Spatial Light Modulators (LCSLM) offer opportunities for large adaptive optics in the midwave infrared spectrum. A light focusing adaptive imaging system, using the zeroorder diffraction state of a polarizerfree liquid crystal polarization grating modulator to create millions of high transmittance apertures, is envisioned in a system called DAZLE (Discrete Adaptive Zone Light Elements). DAZLE adaptively selects large sets of LCSLM apertures using the principles of coded masks, embodied in a hybrid Discrete Fresnel Zone Plate (DFZP) design. Issues of system architecture, including factors of LCSLM aperture pattern and adaptive control, image resolution and focal plane array (FPA) matching, and tradeoffs between filter bandwidths, background photon noise, and chromatic aberration are discussed.
ADGS2100 Adaptive Display and Guidance System Window Manager Analysis
NASA Technical Reports Server (NTRS)
Whalen, Mike W.; Innis, John D.; Miller, Steven P.; Wagner, Lucas G.
20060101
Recent advances in modeling languages have made it feasible to formally specify and analyze the behavior of large system components. Synchronous data flow languages, such as Lustre, SCR, and RSMLe are particularly well suited to this task, and commercial versions of these tools such as SCADE and Simulink are growing in popularity among designers of safety critical systems, largely due to their ability to automatically generate code from the models. At the same time, advances in formal analysis tools have made it practical to formally verify important properties of these models to ensure that design defects are identified and corrected early in the lifecycle. This report describes how these tools have been applied to the ADGS2100 Adaptive Display and Guidance Window Manager being developed by Rockwell Collins Inc. This work demonstrates how formal methods can be easily and costefficiently used to remove defects early in the design cycle.
Adaptive model reduction for nonsmooth discrete element simulation
NASA Astrophysics Data System (ADS)
Servin, Martin; Wang, Da
20160301
A method for adaptive model order reduction for nonsmooth discrete element simulation is developed and analysed in numerical experiments. Regions of the granular media that collectively move as rigid bodies are substituted with rigid bodies of the corresponding shape and mass distribution. The method also support particles merging with articulated multibody systems. A model approximation error is defined and used to derive conditions for when and where to apply reduction and refinement back into particles and smaller rigid bodies. Three methods for refinement are proposed and tested: prediction from contact events, trial solutions computed in the background and using split sensors. The computational performance can be increased by 550 times for model reduction level between 7095 %.
Computerized adaptive control weld skate with CCTV weld guidance project
NASA Technical Reports Server (NTRS)
Wall, W. A.
19760101
This report summarizes progress of the automatic computerized weld skate development portion of the Computerized Weld Skate with Closed Circuit Television (CCTV) Arc Guidance Project. The main goal of the project is to develop an automatic welding skate demonstration model equipped with CCTV weld guidance. The three main goals of the overall project are to: (1) develop a demonstration model computerized weld skate system, (2) develop a demonstration model automatic CCTV guidance system, and (3) integrate the two systems into a demonstration model of computerized weld skate with CCTV weld guidance for welding contoured parts.
PFC design via FRIT Approach for Adaptive Output Feedback Control of Discretetime Systems
NASA Astrophysics Data System (ADS)
Mizumoto, Ikuro; Takagi, Taro; Fukui, Sota; Shah, Sirish L.
This paper deals with a design problem of an adaptive output feedback control for discretetime systems with a parallel feedforward compensator (PFC) which is designed for making the augmented controlled system ASPR. A PFC design scheme by a FRIT approach with only using an input/output experimental data set will be proposed for discretetime systems in order to design an adaptive output feedback control system. Furthermore, the effectiveness of the proposed PFC design method will be confirmed through numerical simulations by designing adaptive control system with adaptive NN (Neural Network) for an uncertain discretetime system.
NASA Astrophysics Data System (ADS)
Abedini, Mohammad; Nojoumian, Mohammad Ali; Salarieh, Hassan; Meghdari, Ali
20150801
In this paper, model reference control of a fractional order system has been discussed. In order to control the fractional order plant, discretetime approximation methods have been applied. Plant and reference model are discretized by GrünwaldLetnikov definition of the fractional order derivative using "Short Memory Principle". Unknown parameters of the fractional order system are appeared in the discrete time approximate model as combinations of parameters of the main system. The discrete time MRAC via RLS identification is modified to estimate the parameters and control the fractional order plant. Numerical results show the effectiveness of the proposed method of model reference adaptive control.
Adaptive guidance and control for future remote sensing systems
NASA Technical Reports Server (NTRS)
Lowrie, J. W.; Myers, J. E.
19800101
A unique approach to onboard processing was developed that is capable of acquiring high quality image data for users in near real time. The approach is divided into two steps: the development of an onboard cloud detection system; and the development of a landmark tracker. The results of these two developments are outlined and the requirements of an operational guidance and control system capable of providing continuous estimation of the sensor boresight position are summarized.
Experimental and simulation study results of an Adaptive Video Guidance System /AVGS/
NASA Technical Reports Server (NTRS)
Schappell, R. T.; Knickerbocker, R. L.
19750101
Studies relating to stellarbody exploration programs have pointed out the need for an adaptive guidance scheme capable of providing automatic realtime guidance and site selection capability. For the case of a planetary lander, without such guidance, targeting is limited to what are believed to be generally benign areas in order to ensure a reasonable landingsuccess probability. Typically, the Mars Viking Lander will be jeopardized by obstacles exceeding 22 centimers in diameter. The benefits of onboard navigation and realtime selection of a landing site and obstacle avoidance have been demonstrated by the Apollo lunar landings, in which man performed the surface sensing and steering functions. Therefore, an Adaptive Video Guidance System (AVGS) has been developed, breadboarded, and flown on a sixdegreeoffreedom simulator.
Federal Register 2010, 2011, 2012, 2013, 2014
20100226
... HUMAN SERVICES Food and Drug Administration Draft Guidance for Industry on Adaptive Design Clinical... entitled ``Adaptive Design Clinical Trials for Drugs and Biologics.'' The draft guidance provides sponsors... Evaluation and Research (CBER) with information regarding adaptive design clinical trials when used in...
Micropylar pollen tube guidance and burst: adapted from defense mechanisms?
Dresselhaus, Thomas; Márton, Mihaela L
20091201
After the first description of fertilization in flowering plants some 125 years ago (Strasburger E: NeueUntersuchungen über den Befruchtungsvorgang bei den Phanerogamen als Grundlage für eine Theorie der Zeugung. Gustav Fischer; 1884), we are finally beginning to understand the various molecular mechanisms leading to sperm delivery and discharge inside the hidden micropylar region of the female gametophyte (embryo sac). The last phase of pollen tube guidance culminating in tube burst and explosive release of tube contents requires extensive crosstalk between both male and female gametophytes. The first molecules identified that play key roles in these processes represent highly polymorphic proteins, similar to major components of the plant innate immune system. Here we summarize recent advances and briefly discuss the underlying molecular mechanisms also in respect to prezygotic barriers of reproductive isolation. PMID:19896414
Deng, Hua; Li, HanXiong; Wu, YiHu
20080901
A new feedbacklinearizationbased neural network (NN) adaptive control is proposed for unknown nonaffine nonlinear discretetime systems. An equivalent model in affinelike form is first derived for the original nonaffine discretetime systems as feedback linearization methods cannot be implemented for such systems. Then, feedback linearization adaptive control is implemented based on the affinelike equivalent model identified with neural networks. Pretraining is not required and the weights of the neural networks used in adaptive control are directly updated online based on the inputoutput measurement. The deadzone technique is used to remove the requirement of persistence excitation during the adaptation. With the proposed neural network adaptive control, stability and performance of the closedloop system are rigorously established. Illustrated examples are provided to validate the theoretical findings. PMID:18779092
ERIC Educational Resources Information Center
Kanar, Adam M.; Bell, Bradford S.
20130101
Adaptive guidance is an instructional intervention that helps learners to make use of the control inherent in technologybased instruction. The present research investigated the interactive effects of guidance design (i.e., framing of guidance information) and individual differences (i.e., pretraining motivation and ability) on learning basic and…
Adaptive Discrete Equation Method for injection of stochastic cavitating flows
NASA Astrophysics Data System (ADS)
Geraci, Gianluca; Rodio, Maria Giovanna; Iaccarino, Gianluca; Abgrall, Remi; Congedo, Pietro
20141101
This work aims at the improvement of the prediction and of the control of biofuel injection for combustion. In fact, common injector should be optimized according to the specific physical/chemical properties of biofuels. In order to attain this scope, an optimized model for reproducing the injection for several biofuel blends will be considered. The originality of this approach is twofold, i) the use of cavitating twophase compressible models, known as Baer & Nunziato, in order to reproduce the injection, and ii) the design of a global scheme for directly taking into account experimental measurements uncertainties in the simulation. In particular, stochastic intrusive methods display a high efficiency when dealing with discontinuities in unsteady compressible flows. We have recently formulated a new scheme for simulating stochastic multiphase flows relying on the Discrete Equation Method (DEM) for describing multiphase effects. The setup of the intrusive stochastic method for multiphase unsteady compressible flows in quasi 1D configuration will be presented. The target testcase is a multiphase unsteady nozzle for injection of biofuels, described by complex thermodynamics models, for which experimental data and associated uncertainties are available.
NASA Astrophysics Data System (ADS)
Wang, Tong; Ding, Yongsheng; Zhang, Lei; Hao, Kuangrong
20160801
This paper considered the synchronisation of continuous complex dynamical networks with discretetime communications and delayed nodes. The nodes in the dynamical networks act in the continuous manner, while the communications between nodes are discretetime; that is, they communicate with others only at discrete time instants. The communication intervals in communication period can be uncertain and variable. By using a piecewise LyapunovKrasovskii function to govern the characteristics of the discrete communication instants, we investigate the adaptive feedback synchronisation and a criterion is derived to guarantee the existence of the desired controllers. The globally exponential synchronisation can be achieved by the controllers under the updating laws. Finally, two numerical examples including globally coupled network and nearestneighbour coupled networks are presented to demonstrate the validity and effectiveness of the proposed control scheme.
NASA Technical Reports Server (NTRS)
Karmarkar, J. S.
19720101
Proposal of an algorithmic procedure, based on mathematical programming methods, to design compensators for hyperstable discrete modelreference adaptive systems (MRAS). The objective of the compensator is to render the MRAS insensitive to initial parameter estimates within a maximized hypercube in the model parameter space.
NASA Technical Reports Server (NTRS)
Grantham, Katie
20030101
Reusable Launch Vehicles (RLVs) have different mission requirements than the Space Shuttle, which is used for benchmark guidance design. Therefore, alternative Terminal Area Energy Management (TAEM) and Approach and Landing (A/L) Guidance schemes can be examined in the interest of cost reduction. A neural network based solution for a finite horizon trajectory optimization problem is presented in this paper. In this approach the optimal trajectory of the vehicle is produced by adaptive critic based neural networks, which were trained offline to maintain a gradual glideslope.
Fuzzy Adaptive Control Design and Discretization for a Class of Nonlinear Uncertain Systems.
Zhao, Xudong; Shi, Peng; Zheng, Xiaolong
20160601
In this paper, tracking control problems are investigated for a class of uncertain nonlinear systems in lower triangular form. First, a statefeedback controller is designed by using adaptive backstepping technique and the universal approximation ability of fuzzy logic systems. During the design procedure, a developed method with less computation is proposed by constructing one maximum adaptive parameter. Furthermore, adaptive controllers with nonsymmetric deadzone are also designed for the systems. Then, a sampleddata control scheme is presented to discretize the obtained continuoustime controller by using the forward Euler method. It is shown that both proposed continuous and discrete controllers can ensure that the system output tracks the target signal with a small bounded error and the other closedloop signals remain bounded. Two simulation examples are presented to verify the effectiveness and applicability of the proposed new design techniques. PMID:26208376
Espinosa, Felipe; Santos, Carlos; MarrónRomera, Marta; Pizarro, Daniel; Valdés, Fernando; Dongil, Javier
20110101
This paper describes a relative localization system used to achieve the navigation of a convoy of robotic units in indoor environments. This positioning system is carried out fusing two sensorial sources: (a) an odometric system and (b) a laser scanner together with artificial landmarks located on top of the units. The laser source allows one to compensate the cumulative error inherent to deadreckoning; whereas the odometry source provides less pose uncertainty in short trajectories. A discrete Extended Kalman Filter, customized for this application, is used in order to accomplish this aim under real time constraints. Different experimental results with a convoy of Pioneer P3DX units tracking nonlinear trajectories are shown. The paper shows that a simple setup based on low cost laser range systems and robot builtin odometry sensors is able to give a high degree of robustness and accuracy to the relative localization problem of convoy units for indoor applications. PMID:22164079
Espinosa, Felipe; Santos, Carlos; MarrónRomera, Marta; Pizarro, Daniel; Valdés, Fernando; Dongil, Javier
20110101
This paper describes a relative localization system used to achieve the navigation of a convoy of robotic units in indoor environments. This positioning system is carried out fusing two sensorial sources: (a) an odometric system and (b) a laser scanner together with artificial landmarks located on top of the units. The laser source allows one to compensate the cumulative error inherent to deadreckoning; whereas the odometry source provides less pose uncertainty in short trajectories. A discrete Extended Kalman Filter, customized for this application, is used in order to accomplish this aim under real time constraints. Different experimental results with a convoy of Pioneer P3DX units tracking nonlinear trajectories are shown. The paper shows that a simple setup based on low cost laser range systems and robot builtin odometry sensors is able to give a high degree of robustness and accuracy to the relative localization problem of convoy units for indoor applications. PMID:22164079
Ren, Shenghan; Hu, Haihong; Li, Gen; Cao, Xu; Zhu, Shouping; Chen, Xueli; Liang, Jimin
20160101
Bioluminescence tomography (BLT) has been a valuable optical molecular imaging technique to noninvasively depict the cellular and molecular processes in living animals with high sensitivity and specificity. Due to the inherent illposedness of BLT, a priori information of anatomical structure is usually incorporated into the reconstruction. The structural information is usually provided by computed tomography (CT) or magnetic resonance imaging (MRI). In order to obtain better quantitative results, BLT reconstruction with heterogeneous tissues needs to segment the internal organs and discretize them into meshes with the finite element method (FEM). It is timeconsuming and difficult to handle the segmentation and discretization problems. In this paper, we present a fast reconstruction method for BLT based on multiatlas registration and adaptive voxel discretization to relieve the complicated data processing procedure involved in the hybrid BLT/CT system. A multiatlas registration method is first adopted to estimate the internal organ distribution of the imaged animal. Then, the animal volume is adaptively discretized into hexahedral voxels, which are fed into FEM for the following BLT reconstruction. The proposed method is validated in both numerical simulation and an in vivo study. The results demonstrate that the proposed method can reconstruct the bioluminescence source efficiently with satisfactory accuracy. PMID:27446674
Ren, Shenghan; Hu, Haihong; Li, Gen; Cao, Xu; Zhu, Shouping; Chen, Xueli; Liang, Jimin
20160401
Bioluminescence tomography (BLT) has been a valuable optical molecular imaging technique to noninvasively depict the cellular and molecular processes in living animals with high sensitivity and specificity. Due to the inherent illposedness of BLT, a priori information of anatomical structure is usually incorporated into the reconstruction. The structural information is usually provided by computed tomography (CT) or magnetic resonance imaging (MRI). In order to obtain better quantitative results, BLT reconstruction with heterogeneous tissues needs to segment the internal organs and discretize them into meshes with the finite element method (FEM). It is timeconsuming and difficult to handle the segmentation and discretization problems. In this paper, we present a fast reconstruction method for BLT based on multiatlas registration and adaptive voxel discretization to relieve the complicated data processing procedure involved in the hybrid BLT/CT system. A multiatlas registration method is first adopted to estimate the internal organ distribution of the imaged animal. Then, the animal volume is adaptively discretized into hexahedral voxels, which are fed into FEM for the following BLT reconstruction. The proposed method is validated in both numerical simulation and an in vivo study. The results demonstrate that the proposed method can reconstruct the bioluminescence source efficiently with satisfactory accuracy. PMID:27446674
Chen, Yingping; Chen, ChaoHong
20100101
An adaptive discretization method, called splitondemand (SoD), enables estimation of distribution algorithms (EDAs) for discrete variables to solve continuous optimization problems. SoD randomly splits a continuous interval if the number of search points within the interval exceeds a threshold, which is decreased at every iteration. After the split operation, the nonempty intervals are assigned integer codes, and the search points are discretized accordingly. As an example of using SoD with EDAs, the integration of SoD and the extended compact genetic algorithm (ECGA) is presented and numerically examined. In this integration, we adopt a local search mechanism as an optional component of our back end optimization engine. As a result, the proposed framework can be considered as a memetic algorithm, and SoD can potentially be applied to other memetic algorithms. The numerical experiments consist of two parts: (1) a set of benchmark functions on which ECGA with SoD and ECGA with two wellknown discretization methods: the fixedheight histogram (FHH) and the fixedwidth histogram (FWH) are compared; (2) a realworld application, the economic dispatch problem, on which ECGA with SoD is compared to other methods. The experimental results indicate that SoD is a better discretization method to work with ECGA. Moreover, ECGA with SoD works quite well on the economic dispatch problem and delivers solutions better than the best known results obtained by other methods in existence. PMID:20210600
Ray, Jaideep; Lefantzi, Sophia; Najm, Habib N.; Kennedy, Christopher A.
20060101
Blockstructured adaptively refined meshes (SAMR) strive for efficient resolution of partial differential equations (PDEs) solved on large computational domains by clustering mesh points only where required by large gradients. Previous work has indicated that fourthorder convergence can be achieved on such meshes by using a suitable combination of highorder discretizations, interpolations, and filters and can deliver significant computational savings over conventional secondorder methods at engineering error tolerances. In this paper, we explore the interactions between the errors introduced by discretizations, interpolations and filters. We develop general expressions for highorder discretizations, interpolations, and filters, in multiple dimensions, using a Fourier approach, facilitating the highorder SAMR implementation. We derive a formulation for the necessary interpolation order for given discretization and derivative orders. We also illustrate this order relationship empirically using one and twodimensional model problems on refined meshes. We study the observed increase in accuracy with increasing interpolation order. We also examine the empirically observed order of convergence, as the effective resolution of the mesh is increased by successively adding levels of refinement, with different orders of discretization, interpolation, or filtering.
Discrete cosine transformbased local adaptive filtering of images corrupted by nonstationary noise
NASA Astrophysics Data System (ADS)
Lukin, Vladimir V.; Fevralev, Dmitriy V.; Ponomarenko, Nikolay N.; Abramov, Sergey K.; Pogrebnyak, Oleksiy; Egiazarian, Karen O.; Astola, Jaakko T.
20100401
In many imageprocessing applications, observed images are contaminated by a nonstationary noise and no a priori information on noise dependence on local mean or about local properties of noise statistics is available. In order to remove such a noise, a locally adaptive filter has to be applied. We study a locally adaptive filter based on evaluation of image local activity in a ``blind'' manner and on discrete cosine transform computed in overlapping blocks. Two mechanisms of local adaptation are proposed and applied. The first mechanism takes into account local estimates of noise standard deviation while the second one exploits discrimination of homogeneous and heterogeneous image regions by adaptive threshold setting. The designed filter performance is tested for simulated data as well as for reallife remotesensing and maritime radar images. Recommendations concerning filter parameter setting are provided. An area of applicability of the proposed filter is defined.
Charging Guidance of Electric Taxis Based on Adaptive Particle Swarm Optimization
Niu, Liyong; Zhang, Di
20150101
Electric taxis are playing an important role in the application of electric vehicles. The actual operational data of electric taxis in Shenzhen, China, is analyzed, and, in allusion to the unbalanced time availability of the charging station equipment, the electric taxis charging guidance system is proposed basing on the charging station information and vehicle information. An electric taxis charging guidance model is established and guides the charging based on the positions of taxis and charging stations with adaptive mutation particle swarm optimization. The simulation is based on the actual data of Shenzhen charging stations, and the results show that electric taxis can be evenly distributed to the appropriate charging stations according to the charging pile numbers in charging stations after the charging guidance. The even distribution among the charging stations in the area will be achieved and the utilization of charging equipment will be improved, so the proposed charging guidance method is verified to be feasible. The improved utilization of charging equipment can save public charging infrastructure resources greatly. PMID:26236770
Charging Guidance of Electric Taxis Based on Adaptive Particle Swarm Optimization.
Niu, Liyong; Zhang, Di
20150101
Electric taxis are playing an important role in the application of electric vehicles. The actual operational data of electric taxis in Shenzhen, China, is analyzed, and, in allusion to the unbalanced time availability of the charging station equipment, the electric taxis charging guidance system is proposed basing on the charging station information and vehicle information. An electric taxis charging guidance model is established and guides the charging based on the positions of taxis and charging stations with adaptive mutation particle swarm optimization. The simulation is based on the actual data of Shenzhen charging stations, and the results show that electric taxis can be evenly distributed to the appropriate charging stations according to the charging pile numbers in charging stations after the charging guidance. The even distribution among the charging stations in the area will be achieved and the utilization of charging equipment will be improved, so the proposed charging guidance method is verified to be feasible. The improved utilization of charging equipment can save public charging infrastructure resources greatly. PMID:26236770
An adaptive discretization of incompressible flow using a multitude of moving Cartesian grids
NASA Astrophysics Data System (ADS)
English, R. Elliot; Qiu, Linhai; Yu, Yue; Fedkiw, Ronald
20131201
We present a novel method for discretizing the incompressible NavierStokes equations on a multitude of moving and overlapping Cartesian grids each with an independently chosen cell size to address adaptivity. Advection is handled with first and second order accurate semiLagrangian schemes in order to alleviate any time step restriction associated with small grid cell sizes. Likewise, an implicit temporal discretization is used for the parabolic terms including NavierStokes viscosity which we address separately through the development of a method for solving the heat diffusion equations. The most intricate aspect of any such discretization is the method used in order to solve the elliptic equation for the NavierStokes pressure or that resulting from the temporal discretization of parabolic terms. We address this by first removing any degrees of freedom which duplicately cover spatial regions due to overlapping grids, and then providing a discretization for the remaining degrees of freedom adjacent to these regions. We observe that a robust second order accurate symmetric positive definite readily preconditioned discretization can be obtained by constructing a local Voronoi region on the fly for each degree of freedom in question in order to obtain both its stencil (logically connected neighbors) and stencil weights. Internal curved boundaries such as at solid interfaces are handled using a simple immersed boundary approach which is directly applied to the Voronoi mesh in both the viscosity and pressure solves. We independently demonstrate each aspect of our approach on test problems in order to show efficacy and convergence before finally addressing a number of common test cases for incompressible flow with stationary and moving solid bodies.
Nonlinear Adaptive Control and Guidance for Unstart Recovery for a Generic Hypersonic Vehicle
NASA Astrophysics Data System (ADS)
Gunbatar, Yakup
This work presents the development of an integrated flight controller for a generic model of a hypersonic airbreathing vehicle. The flight control architecture comprises a guidance and trajectory planning module and a nonlinear innerloop adaptive controller. The emphasis of the controller design is on achieving stable tracking of suitable reference trajectories in the presence of a specific engine fault (inlet unstart), in which sudden and drastic changes in the vehicle aerodynamics and engine performance occur. First, the equations of motion of the vehicle for a rigid body model, taking the rotation of the Earth into account, is provided. Aerodynamic forces and moments and engine data are provided in lookuptable format. This comprehensive model is used for simulations and verification of the control strategies. Then, a simplified controloriented model is developed for the purpose of control design and stability analysis. The design of the guidance and nonlinear adaptive control algorithms is first carried out on a longitudinal version of the vehicle dynamics. The design is verified in a simulation study aiming at testing the robustness of the innerloop controller under significant model uncertainty and engine failures. At the same time, the guidance system provides reference trajectories to maximize the vehicle's endurance, which is cast as an optimal control problem. The design is then extended to tackle the significantly more challenging case of the 6degreeoffreedom (6DOF) vehicle dynamics. For the full 6DOF case, the adaptive nonlinear flight controller is tested on more challenging maneuvers, where values of the flight path and bank angles exceed the nominal range defined for the vehicle. Simulation studies show stable operation of the closedloop system in nominal operating conditions, unstart conditions, and during transition from sustained scramjet propulsion to engine failure mode.
ERIC Educational Resources Information Center
Rolleri, Lori A.; Fuller, Taleria R.; FirpoTriplett, Regina; Lesesne, Catherine A.; Moore, Claire; Leeks, Kimberly D.
20140101
Evidencebased interventions (EBIs) are effective in preventing adolescent pregnancy and sexually transmitted infections; however, prevention practitioners are challenged when selecting and adapting the most appropriate programs. While there are existing adaptation frameworks, there is little practical guidance in applying research in the field.…
Discretetime entropy formulation of optimal and adaptive control problems
NASA Technical Reports Server (NTRS)
Tsai, Yweting A.; Casiello, Francisco A.; Loparo, Kenneth A.
19920101
The discretetime version of the entropy formulation of optimal control of problems developed by G. N. Saridis (1988) is discussed. Given a dynamical system, the uncertainty in the selection of the control is characterized by the probability distribution (density) function which maximizes the total entropy. The equivalence between the optimal control problem and the optimal entropy problem is established, and the total entropy is decomposed into a term associated with the certainty equivalent control law, the entropy of estimation, and the socalled equivocation of the active transmission of information from the controller to the estimator. This provides a useful framework for studying the certainty equivalent and adaptive control laws.
NASA Technical Reports Server (NTRS)
Spratlin, Kenneth Milton
19870101
An adaptive numeric predictorcorrector guidance is developed for atmospheric entry vehicles which utilize lift to achieve maximum footprint capability. Applicability of the guidance design to vehicles with a wide range of performance capabilities is desired so as to reduce the need for algorithm redesign with each new vehicle. Adaptability is desired to minimize missionspecific analysis and planning. The guidance algorithm motivation and design are presented. Performance is assessed for application of the algorithm to the NASA Entry Research Vehicle (ERV). The dispersions the guidance must be designed to handle are presented. The achievable operational footprint for expected worstcase dispersions is presented. The algorithm performs excellently for the expected dispersions and captures most of the achievable footprint.
NASA Astrophysics Data System (ADS)
Palaniswamy, Sumithra; Duraisamy, Prakash; Alam, Mohammad Showkat; Yuan, Xiaohui
20120401
Automatic speech processing systems are widely used in everyday life such as mobile communication, speech and speaker recognition, and for assisting the hearing impaired. In speech communication systems, the quality and intelligibility of speech is of utmost importance for ease and accuracy of information exchange. To obtain an intelligible speech signal and one that is more pleasant to listen, noise reduction is essential. In this paper a new Time Adaptive Discrete Bionic Wavelet Thresholding (TADBWT) scheme is proposed. The proposed technique uses Daubechies mother wavelet to achieve better enhancement of speech from additive non stationary noises which occur in real life such as street noise and factory noise. Due to the integration of human auditory system model into the wavelet transform, bionic wavelet transform (BWT) has great potential for speech enhancement which may lead to a new path in speech processing. In the proposed technique, at first, discrete BWT is applied to noisy speech to derive TADBWT coefficients. Then the adaptive nature of the BWT is captured by introducing a time varying linear factor which updates the coefficients at each scale over time. This approach has shown better performance than the existing algorithms at lower input SNR due to modified soft level dependent thresholding on time adaptive coefficients. The objective and subjective test results confirmed the competency of the TADBWT technique. The effectiveness of the proposed technique is also evaluated for speaker recognition task under noisy environment. The recognition results show that the TADWT technique yields better performance when compared to alternate methods specifically at lower input SNR.
Convergence of a discretized selfadaptive evolutionary algorithm on multidimensional problems.
Hart, William Eugene; DeLaurentis, John Morse
20030801
We consider the convergence properties of a nonelitist selfadaptive evolutionary strategy (ES) on multidimensional problems. In particular, we apply our recent convergence theory for a discretized (1,{lambda})ES to design a related (1,{lambda})ES that converges on a class of seperable, unimodal multidimensional problems. The distinguishing feature of selfadaptive evolutionary algorithms (EAs) is that the control parameters (like mutation step lengths) are evolved by the evolutionary algorithm. Thus the control parameters are adapted in an implicit manner that relies on the evolutionary dynamics to ensure that more effective control parameters are propagated during the search. Selfadaptation is a central feature of EAs like evolutionary stategies (ES) and evolutionary programming (EP), which are applied to continuous design spaces. Rudolph summarizes theoretical results concerning selfadaptive EAs and notes that the theoretical underpinnings for these methods are essentially unexplored. In particular, convergence theories that ensure convergence to a limit point on continuous spaces have only been developed by Rudolph, Hart, DeLaurentis and Ferguson, and Auger et al. In this paper, we illustrate how our analysis of a (1,{lambda})ES for onedimensional unimodal functions can be used to ensure convergence of a related ES on multidimensional functions. This (1,{lambda})ES randomly selects a search dimension in each iteration, along which points generated. For a general class of separable functions, our analysis shows that the ES searches along each dimension independently, and thus this ES converges to the (global) minimum.
Development of the Adaptive Collision Source (ACS) method for discrete ordinates
Walters, W.; Haghighat, A.
20130701
We have developed a new collision source method to solve the Linear Boltzmann Equation (LBE) more efficiently by adaptation of the angular quadrature order. The angular adaptation method is unique in that the flux from each scattering source iteration is obtained, with potentially a different quadrature order. Traditionally, the flux from every iteration is combined, with the same quadrature applied to the combined flux. Since the scattering process tends to distribute the radiation more evenly over angles (i.e., make it more isotropic), the quadrature requirements generally decrease with each iteration. This allows for an optimal use of processing power, by using a high order quadrature for the first few iterations that need it, before shifting to lower order quadratures for the remaining iterations. This is essentially an extension of the first collision source method, and we call it the adaptive collision source method (ACS). The ACS methodology has been implemented in the TITAN discrete ordinates code, and has shown a relative speedup of 1.52.5 on a test problem, for the same desired level of accuracy. (authors)
Policy iteration adaptive dynamic programming algorithm for discretetime nonlinear systems.
Liu, Derong; Wei, Qinglai
20140301
This paper is concerned with a new discretetime policy iteration adaptive dynamic programming (ADP) method for solving the infinite horizon optimal control problem of nonlinear systems. The idea is to use an iterative ADP technique to obtain the iterative control law, which optimizes the iterative performance index function. The main contribution of this paper is to analyze the convergence and stability properties of policy iteration method for discretetime nonlinear systems for the first time. It shows that the iterative performance index function is nonincreasingly convergent to the optimal solution of the HamiltonJacobiBellman equation. It is also proven that any of the iterative control laws can stabilize the nonlinear systems. Neural networks are used to approximate the performance index function and compute the optimal control law, respectively, for facilitating the implementation of the iterative ADP algorithm, where the convergence of the weight matrices is analyzed. Finally, the numerical results and analysis are presented to illustrate the performance of the developed method. PMID:24807455
NASA Technical Reports Server (NTRS)
Malin, Jane T.; Basham, Bryan D.
19890101
CONFIG is a modeling and simulation tool prototype for analyzing the normal and faulty qualitative behaviors of engineered systems. Qualitative modeling and discreteevent simulation have been adapted and integrated, to support early development, during system design, of software and procedures for management of failures, especially in diagnostic expert systems. Qualitative component models are defined in terms of normal and faulty modes and processes, which are defined by invocation statements and effect statements with time delays. System models are constructed graphically by using instances of components and relations from objectoriented hierarchical model libraries. Extension and reuse of CONFIG models and analysis capabilities in hybrid rule and modelbased expert faultmanagement support systems are discussed.
Zhong, Xiangnan; He, Haibo; Zhang, Huaguang; Wang, Zhanshan
20141201
In this paper, we develop and analyze an optimal control method for a class of discretetime nonlinear Markov jump systems (MJSs) with unknown system dynamics. Specifically, an identifier is established for the unknown systems to approximate system states, and an optimal control approach for nonlinear MJSs is developed to solve the HamiltonJacobiBellman equation based on the adaptive dynamic programming technique. We also develop detailed stability analysis of the control approach, including the convergence of the performance index function for nonlinear MJSs and the existence of the corresponding admissible control. Neural network techniques are used to approximate the proposed performance index function and the control law. To demonstrate the effectiveness of our approach, three simulation studies, one linear case, one nonlinear case, and one single link robot arm case, are used to validate the performance of the proposed optimal control method. PMID:25420238
Finiteapproximationerrorbased discretetime iterative adaptive dynamic programming.
Wei, Qinglai; Wang, FeiYue; Liu, Derong; Yang, Xiong
20141201
In this paper, a new iterative adaptive dynamic programming (ADP) algorithm is developed to solve optimal control problems for infinite horizon discretetime nonlinear systems with finite approximation errors. First, a new generalized value iteration algorithm of ADP is developed to make the iterative performance index function converge to the solution of the HamiltonJacobiBellman equation. The generalized value iteration algorithm permits an arbitrary positive semidefinite function to initialize it, which overcomes the disadvantage of traditional value iteration algorithms. When the iterative control law and iterative performance index function in each iteration cannot accurately be obtained, for the first time a new "design method of the convergence criteria" for the finiteapproximationerrorbased generalized value iteration algorithm is established. A suitable approximation error can be designed adaptively to make the iterative performance index function converge to a finite neighborhood of the optimal performance index function. Neural networks are used to implement the iterative ADP algorithm. Finally, two simulation examples are given to illustrate the performance of the developed method. PMID:25265640
NASA Technical Reports Server (NTRS)
Blissit, J. A.
19860101
Using analysis results from the post trajectory optimization program, an adaptive guidance algorithm is developed to compensate for density, aerodynamic and thrust perturbations during an atmospheric orbital plane change maneuver. The maneuver offers increased mission flexibility along with potential fuel savings for future reentry vehicles. Although designed to guide a proposed NASA Entry Research Vehicle, the algorithm is sufficiently generic for a range of future entry vehicles. The plane change analysis provides insight suggesting a straightforward algorithm based on an optimized nominal command profile. Bank angle, angle of attack, and engine thrust level, ignition and cutoff times are modulated to adjust the vehicle's trajectory to achieve the desired endconditions. A performance evaluation of the scheme demonstrates a capability to guide to within 0.05 degrees of the desired plane change and five nautical miles of the desired apogee altitude while maintaining heating constraints. The algorithm is tested under offnominal conditions of + or 30% density biases, two density profile models, + or 15% aerodynamic uncertainty, and a 33% thrust loss and for various combinations of these conditions.
Camley, Brian A.; Zimmermann, Juliane; Levine, Herbert; Rappel, WouterJan
20160101
Single eukaryotic cells commonly sense and follow chemical gradients, performing chemotaxis. Recent experiments and theories, however, show that even when single cells do not chemotax, clusters of cells may, if their interactions are regulated by the chemoattractant. We study this general mechanism of “collective guidance” computationally with models that integrate stochastic dynamics for individual cells with biochemical reactions within the cells, and diffusion of chemical signals between the cells. We show that if clusters of cells use the wellknown local excitation, global inhibition (LEGI) mechanism to sense chemoattractant gradients, the speed of the cell cluster becomes nonmonotonic in the cluster’s size—clusters either larger or smaller than an optimal size will have lower speed. We argue that the cell cluster speed is a crucial readout of how the cluster processes chemotactic signals; both amplification and adaptation will alter the behavior of cluster speed as a function of size. We also show that, contrary to the assumptions of earlier theories, collective guidance does not require persistent cellcell contacts and strong short range adhesion. If cellcell adhesion is absent, and the cluster cohesion is instead provided by a coattraction mechanism, e.g. chemotaxis toward a secreted molecule, collective guidance may still function. However, new behaviors, such as cluster rotation, may also appear in this case. Coattraction and adaptation allow for collective guidance that is robust to varying chemoattractant concentrations while not requiring strong cellcell adhesion. PMID:27367541
NASA Astrophysics Data System (ADS)
Gehb, Christopher M.; Platz, Roland; Melz, Tobias
20150401
In many applications, kinematic structures are used to enable and disable degrees of freedom. The relative movement between a wheel and the body of a car or a landing gear and an aircraft fuselage are examples for a defined movement. In most cases, a springdamper system determines the kinetic properties of the movement. However, unexpected high load peaks may lead to maximum displacements and maybe to locking. Thus, a hard clash between two rigid components may occur, causing acceleration peaks. This may have harmful effects for the whole system. For example a hard landing of an aircraft can result in locking the landing gear and thus damage the entire aircraft. In this paper, the potential of adaptive auxiliary kinematic guidance elements in a springdamper system to prevent locking is investigated numerically. The aim is to provide additional forces in the auxiliary kinematic guidance elements in case of overloading the springdamper system and thus to absorb some of the impact energy. To estimate the potential of the load redistribution in the springdamper system, a numerical model of a twomass oscillator is used, similar to a quartercarmodel. In numerical calculations, the reduction of the acceleration peaks of the masses with the adaptive approach is compared to the Acceleration peaks without the approach, or, respectively, when locking is not prevented. In addition, the required force of the adaptive auxiliary kinematic guidance elements is calculated as a function of the masses of the system and the drop height, or, respectively, the impact energy.
Discretetime GeoX/G/1 queue with unreliable server and multiple adaptive delayed vacations
NASA Astrophysics Data System (ADS)
Tang, Yinghui; Yun, Xi; Huang, Shujuan
20081001
In this paper we consider a discretetime GeoX/G/1 queue with unreliable server and multiple adaptive delayed vacations policy in which the vacation time, service time, repair time and the delayed time all follow arbitrary discrete distribution. By using a concise decomposition method, the transient and steadystate distributions of the queue length are studied, and the stochastic decomposition property of steadystate queue length has been proved. Several common vacation policies are special cases of the vacation policy presented in this study. The relationship between the generating functions of steadystate queue length at departure epoch and arbitrary epoch is obtained. Finally, we give some numerical examples to illustrate the effect of the parameters on several performance characteristics.
Adaptive critic designs for discretetime zerosum games with application to H(infinity) control.
AlTamimi, Asma; AbuKhalaf, Murad; Lewis, Frank L
20070201
In this correspondence, adaptive critic approximate dynamic programming designs are derived to solve the discretetime zerosum game in which the state and action spaces are continuous. This results in a forwardintime reinforcement learning algorithm that converges to the Nash equilibrium of the corresponding zerosum game. The results in this correspondence can be thought of as a way to solve the Riccati equation of the wellknown discretetime H(infinity) optimal control problem forward in time. Two schemes are presented, namely: 1) a heuristic dynamic programming and 2) a dualheuristic dynamic programming, to solve for the value function and the costate of the game, respectively. An H(infinity) autopilot design for an F16 aircraft is presented to illustrate the results. PMID:17278575
NASA Astrophysics Data System (ADS)
Sun, Zhiyong; Hao, Lina; Chen, Wenlin; Li, Zhi; Liu, Liqun
20130901
Ionic polymermetal composite (IPMC), also called artificial muscle, is an EAP material which can generate a relatively large deformation with a low driving voltage (generally less than 5 V). Like other EAP materials, IPMC possesses strong nonlinear properties, which can be described as a hybrid of backrelaxation (BR) and hysteresis characteristics, which also vary with water content, environmental temperature and even the usage consumption. Nowadays, many control approaches have been developed to tune the IPMC actuators, among which adaptive methods show a particular striking performance. To deal with IPMCs’ nonlinear problem, this paper represents a robust discrete adaptive inverse (AI) control approach, which employs an online identification technique based on the BR operator and PrandtlIshlinskii (PI) hysteresis operator hybrid model estimation method. Here the newly formed control approach is called discrete adaptive slidingmodelike control (DASMLC) due to the similarity of its design method to that of a sliding mode controller. The weighted least mean squares (WLMS) identification method was employed to estimate the hybrid IPMC model because of its advantage of insensitivity to environmental noise. Experiments with the DASMLC approach and a conventional PID controller were carried out to compare and demonstrate the proposed controller’s better performance.
NASA Astrophysics Data System (ADS)
Xin, Yizhong; Ren, Xiangshi
Continuous pen pressure can be used to operate multistate widgets such as menus in pen based user interfaces. The number of levels into which the pen pressure space is divided determines the number of states in the multistate widgets. To increase the optimal number of divisions of the pen pressure space and achieve greater pen pressure usability, we propose a new discretization method which divides the pen pressure space according to a personal pen pressure use profile. We present here four variations of the method: discretization according to personal/aggregation pen pressure use profile with/without visual feedback of uniform level widths and the traditional even discretization method. Two experiments were conducted respectively to investigate pen pressure use profile and to comparatively evaluate the performance of these methods. Results indicate that the subjects performed fastest and with the fewest errors when the pen pressure space was divided according to personal profile with visual feedback of uniform level widths (PU) and performed worst when the pen pressure space was divided evenly. With PU method, the optimal number of divisions of the pen pressure space was 8. Visual feedback of uniform level widths enhanced performance of uneven discretization. The findings of this study have implications for humanoriented pen pressure use in pen pressure based user interface designs.
Zhang, Huaguang; Qin, Chunbin; Jiang, Bin; Luo, Yanhong
20141201
The problem of H∞ state feedback control of affine nonlinear discretetime systems with unknown dynamics is investigated in this paper. An online adaptive policy learning algorithm (APLA) based on adaptive dynamic programming (ADP) is proposed for learning in realtime the solution to the HamiltonJacobiIsaacs (HJI) equation, which appears in the H∞ control problem. In the proposed algorithm, three neural networks (NNs) are utilized to find suitable approximations of the optimal value function and the saddle point feedback control and disturbance policies. Novel weight updating laws are given to tune the critic, actor, and disturbance NNs simultaneously by using data generated in realtime along the system trajectories. Considering NN approximation errors, we provide the stability analysis of the proposed algorithm with Lyapunov approach. Moreover, the need of the system input dynamics for the proposed algorithm is relaxed by using a NN identification scheme. Finally, simulation examples show the effectiveness of the proposed algorithm. PMID:25095274
NASA Astrophysics Data System (ADS)
Yoshimura, Toshio
20160201
This paper presents the design of an adaptive fuzzy sliding mode control (AFSMC) for uncertain discretetime nonlinear dynamic systems. The dynamic systems are described by a discretetime state equation with nonlinear uncertainties, and the uncertainties include the modelling errors and the external disturbances to be unknown but nonlinear with the bounded properties. The states are measured by the restriction of measurement sensors and the contamination with independent measurement noises. The nonlinear uncertainties are approximated by using the fuzzy IFTHEN rules based on the universal approximation theorem, and the approximation error is compensated by adding an adaptive complementary term to the proposed AFSMC. The fuzzy inference approach based on the extended single input rule modules is proposed to reduce the number of the fuzzy IFTHEN rules. The estimates for the unmeasurable states and the adjustable parameters are obtained by using the weighted least squares estimator and its simplified one. It is proved that under some conditions the estimation errors will remain in the vicinity of zero as time increases, and the states are ultimately bounded subject to the proposed AFSMC. The effectiveness of the proposed method is indicated through the simulation experiment of a simple numerical system.
Liu, YanJun; Tong, Shaocheng
20150301
In the paper, an adaptive tracking control design is studied for a class of nonlinear discretetime systems with deadzone input. The considered systems are of the nonaffine purefeedback form and the deadzone input appears nonlinearly in the systems. The contributions of the paper are that: 1) it is for the first time to investigate the control problem for this class of discretetime systems with deadzone; 2) there are major difficulties for stabilizing such systems and in order to overcome the difficulties, the systems are transformed into an nstepahead predictor but nonaffine function is still existent; and 3) an adaptive compensative term is constructed to compensate for the parameters of the deadzone. The neural networks are used to approximate the unknown functions in the transformed systems. Based on the Lyapunov theory, it is proven that all the signals in the closedloop system are semiglobally uniformly ultimately bounded and the tracking error converges to a small neighborhood of zero. Two simulation examples are provided to verify the effectiveness of the control approach in the paper. PMID:24968366
Numerous strategies but limited implementation guidance in US local adaptation plans
NASA Astrophysics Data System (ADS)
Woodruff, Sierra C.; Stults, Missy
20160801
Adaptation planning offers a promising approach for identifying and devising solutions to address local climate change impacts. Yet there is little empirical understanding of the content and quality of these plans. We use content analysis to evaluate 44 local adaptation plans in the United States and multivariate regression to examine how plan quality varies across communities. We find that plans draw on multiple data sources to analyse future climate impacts and include a breadth of strategies. Most plans, however, fail to prioritize impacts and strategies or provide detailed implementation processes, raising concerns about whether adaptation plans will translate into ontheground reductions in vulnerability. Our analysis also finds that plans authored by the planning department and those that engaged elected officials in the planning process were of higher quality. The results provide important insights for practitioners, policymakers and scientists wanting to improve local climate adaptation planning and action.
Evaluation of discretization procedures for transition elements in adaptive mesh refinement
NASA Technical Reports Server (NTRS)
Park, K. C.; Levit, Itzak; Stanley, Gary M.
19910101
Three transition interpolation schemes for use in hor rrefinement have been analyzed in terms of accuracy, implementation ease and extendability. They include blendingfunction interpolation, displacement averaging, and strain matching at discrete points along the transition edge lines. The results suggest that the choice of matching depends strongly on the element formulations, (viz. displacement or assumed strain, etc.) and mesh refinement criteria employed, and to a lesser extent the choice of computer architecture (serial vs. parallel) and the equation solution procedures. A recommended pairing of some of the elements with the choice factors is suggested.
Qin, An; Sun, Ying; Liang, Jian; Yan, Di
20150401
Purpose: To evaluate online/offline imageguided/adaptive treatment techniques for prostate cancer radiation therapy with daily conebeam CT (CBCT) imaging. Methods and Materials: Three treatment techniques were evaluated retrospectively using daily pre and posttreatment CBCT images on 22 prostate cancer patients. Prostate, seminal vesicles (SV), rectal wall, and bladder were delineated on all CBCT images. For each patient, a pretreatment intensity modulated radiation therapy plan with clinical target volume (CTV) = prostate + SV and planning target volume (PTV) = CTV + 3 mm was created. The 3 treatment techniques were as follows: (1) Daily Correction: The pretreatment intensity modulated radiation therapy plan was delivered after online CBCT imaging, and position correction; (2) Online Planning: Daily online inverse plans with 3mm CTVtoPTV margin were created using online CBCT images, and delivered; and (3) Hybrid Adaption: Daily Correction plus an offline adaptive inverse planning performed after the first week of treatment. The adaptive plan was delivered for all remaining 15 fractions. Treatment dose for each technique was constructed using the daily posttreatment CBCT images via deformable image registration. Evaluation was performed using treatment dose distribution in target and critical organs. Results: Treatment equivalent uniform dose (EUD) for the CTV was within [85.6%, 100.8%] of the pretreatment planned target EUD for Daily Correction; [98.7%, 103.0%] for Online Planning; and [99.2%, 103.4%] for Hybrid Adaptation. Eighteen percent of the 22 patients in Daily Correction had a target dose deficiency >5%. For rectal wall, the mean ± SD of the normalized EUD was 102.6% ± 2.7% for Daily Correction, 99.9% ± 2.5% for Online Planning, and 100.6% ± 2.1% for Hybrid Adaptation. The mean ± SD of the normalized bladder EUD was 108.7% ± 8.2% for Daily Correction, 92.7% ± 8.6% for Online Planning, and 89.4% ± 10.8% for Hybrid
Liu, YanJun; Gao, Ying; Tong, Shaocheng; Chen, C L Philip
20160101
In this paper, an effective adaptive control approach is constructed to stabilize a class of nonlinear discretetime systems, which contain unknown functions, unknown deadzone input, and unknown control direction. Different from linear dead zone, the dead zone, in this paper, is a kind of nonlinear dead zone. To overcome the noncausal problem, which leads to the control scheme infeasible, the systems can be transformed into a m stepahead predictor. Due to nonlinear deadzone appearance, the transformed predictor still contains the nonaffine function. In addition, it is assumed that the gain function of deadzone input and the control direction are unknown. These conditions bring about the difficulties and the complicacy in the controller design. Thus, the implicit function theorem is applied to deal with nonaffine deadzone appearance, the problem caused by the unknown control direction can be resolved through applying the discrete Nussbaum gain, and the neural networks are used to approximate the unknown function. Based on the Lyapunov theory, all the signals of the resulting closedloop system are proved to be semiglobal uniformly ultimately bounded. Moreover, the tracking error is proved to be regulated to a small neighborhood around zero. The feasibility of the proposed approach is demonstrated by a simulation example. PMID:26353383
Wang, FeiYue; Jin, Ning; Liu, Derong; Wei, Qinglai
20110101
In this paper, we study the finitehorizon optimal control problem for discretetime nonlinear systems using the adaptive dynamic programming (ADP) approach. The idea is to use an iterative ADP algorithm to obtain the optimal control law which makes the performance index function close to the greatest lower bound of all performance indices within an εerror bound. The optimal number of control steps can also be obtained by the proposed ADP algorithms. A convergence analysis of the proposed ADP algorithms in terms of performance index function and control policy is made. In order to facilitate the implementation of the iterative ADP algorithms, neural networks are used for approximating the performance index function, computing the optimal control policy, and modeling the nonlinear system. Finally, two simulation examples are employed to illustrate the applicability of the proposed method. PMID:20876014
Turing pattern dynamics and adaptive discretization for a superdiffusive LotkaVolterra model.
Bendahmane, Mostafa; RuizBaier, Ricardo; Tian, Canrong
20160501
In this paper we analyze the effects of introducing the fractionalinspace operator into a LotkaVolterra competitive model describing population superdiffusion. First, we study how cross superdiffusion influences the formation of spatial patterns: a linear stability analysis is carried out, showing that cross superdiffusion triggers Turing instabilities, whereas classical (self) superdiffusion does not. In addition we perform a weakly nonlinear analysis yielding a system of amplitude equations, whose study shows the stability of Turing steady states. A second goal of this contribution is to propose a fully adaptive multiresolution finite volume method that employs shifted Grünwald gradient approximations, and which is tailored for a larger class of systems involving fractional diffusion operators. The scheme is aimed at efficient dynamic mesh adaptation and substantial savings in computational burden. A numerical simulation of the model was performed near the instability boundaries, confirming the behavior predicted by our analysis. PMID:26219250
NASA Astrophysics Data System (ADS)
Zhou, Di; Zhang, YongAn; Duan, GuangRen
The twostep filter has been combined with a modified SageHusa timevarying measurement noise statistical estimator, which is able to estimate the covariance of measurement noise on line, to generate an adaptive twostep filter. In many practical applications such as the bearingsonly guidance, some model parameters and the process noise covariance are also unknown a priori. Based on the adaptive twostep filter, we utilize multiple models in the firststep filtering as well as in the time update of the secondstep filtering to handle the uncertainties of model parameters and process noise covariance. In each timestep of the multiple model filtering, probabilistic weights punishing the estimates of firststep state from different models, and their associated covariance matrices are acquired according to Bayes’ rule. The weighted sum of the estimates of firststep state and that of the associated covariance matrices are extracted as the ultimate estimate and covariance of the firststep state, and are used as measurement information for the measurement update of the secondstep state. Thus there is still only one iteration process and no apparent enhancement of computation burden. A motion tracking slidingmode guidance law is presented for missiles with nonnegligible delays in actual acceleration. This guidance law guarantees guidance accuracy and is able to enhance observability in bearingsonly tracking. In bearingsonly cases, the multiple model adaptive twostep filter is applied to the motion tracking slidingmode guidance law, supplying relative range, relative velocity, and target acceleration information. In simulation experiments satisfactory filtering and guidance results are obtained, even if the filter runs into unknown target maneuvers and unknown timevarying measurement noise covariance, and the guidance law has to deal with a large time lag in acceleration.
ERIC Educational Resources Information Center
Lieberman, Lauren; Lucas, Mark; Jones, Jeffery; Humphreys, Dan; Cody, Ann; Vaughn, Bev; Storms, Tommie
20130101
"Helping General Physical Educators and Adapted Physical Educators Address the Office of Civil Rights Dear Colleague Guidance Letter: Part IVSport Groups" provides the the following articles: (1) "Sport Programming Offered by Camp Abilities and the United States Association for Blind Athletes" (Lauren Lieberman and Mark…
Conformational adaptation of apolipoprotein AI to discretely sized phospholipid complexes.
Bhat, Shaila; SorciThomas, Mary G; Tuladhar, Rubina; Samuel, Michael P; Thomas, Michael J
20070701
The conformational constraints for apoAI bound to recombinant phospholipid complexes (rHDL) were attained from a combination of chemical crosslinking and mass spectrometry. Molecular distances were then used to refine models of lipidbound apoAI on both 80 and 96 A diameter rHDL particles. To obtain molecular constraints on the protein bound to phospholipid complexes, three different lysineselective homobifunctional crosslinkers with increasing spacer arm lengths (i.e., 7.7, 12.0, and 16.1 A) were reacted with purified, homogeneous recombinant 1palmitoyl2oleoylsnglycero3phosphocholine (POPC) apoAI rHDL complexes of each diameter. Crosslinked dimeric apoAI products were separated from monomeric apoprotein using 12% SDSPAGE, then subjected to ingel trypsin digest, and identified by MS/MS sequencing. These studies aid in the refinement of our previously published molecular model of two apoAI molecules bound to approximately 150 molecules of POPC and suggest that the protein hydrophobic interactions at the N and Cterminal domains decrease as the number of phospholipid molecules or "lipidation state" of apoAI increases. Thus, it appears that these incremental changes in the interaction between the N and Cterminal ends of apoAI stabilize its tertiary conformation in the lipidfree state as well as allowing it to unfold and sequester discrete amounts of phospholipid molecules. PMID:17563120
NASA Astrophysics Data System (ADS)
Axente, Marian
Accelerated tumor cell repopulation during radiation therapy is one of the leading causes for low survival rates of headandneck cancer patients. The therapeutic effectiveness of radiotherapy could be improved by selectively targeting proliferating tumor subvolumes with higher doses of radiation. Positron emission tomography (PET) imaging with 3'deoxy3 '18Ffluorothymidine (FLT) has shown great potential as a noninvasive approach to characterizing the proliferation status of tumors. This thesis focuses on histopathological validation of FLT PET imaging specifically for imageguidance applications in biologically adaptive radiotherapy. The lack of experimental data supporting the use of FLT PET imaging for radiotherapy guidance is addressed by developing a novel methodology for histopathological validation of PET imaging. Using this new approach, the spatial concordance between the intratumoral pattern of FLT uptake and the spatial distribution of cell proliferation is demonstrated in animal tumors. First, a twodimensional analysis is conducted comparing the microscopic FLT uptake as imaged with autoradiography and the distribution of active cell proliferation markers imaged with immunofluorescent microscopy. It was observed that when tumors present a pattern of cell proliferation that is highly dispersed throughout the tumor, even highresolution imaging modalities such as autoradiography could not accurately determine the extent and spatial distribution of proliferative tumor subvolumes. While microscopic spatial coincidence between high FLT uptake regions and actively proliferative subvolumes was demonstrated in tumors with highly compartmentalized/aggregated features of cell proliferation, there were no conclusive results across the entire set of utilized tumor specimens. This emphasized the need for addressing the limited resolution of FLT PET when imaging microscopic patterns of cell proliferation. This issue was emphasized in the second part of the
NASA Astrophysics Data System (ADS)
Lei, Yu; Wu, Qiuwen
20100401
Offline adaptive radiotherapy (ART) has been used to effectively correct and compensate for prostate motion and reduce the required margin. The efficacy depends on the characteristics of the patient setup error and interfraction motion through the whole treatment; specifically, systematic errors are corrected and random errors are compensated for through the margins. In online imageguided radiation therapy (IGRT) of prostate cancer, the translational setup error and interfractional prostate motion are corrected through pretreatment imaging and couch correction at each fraction. However, the rotation and deformation of the target are not corrected and only accounted for with margins in treatment planning. The purpose of this study was to investigate whether the offline ART strategy is necessary for an online IGRT protocol and to evaluate the benefit of the hybrid strategy. First, to investigate the rationale of the hybrid strategy, 592 conebeamcomputed tomography (CBCT) images taken before and after each fraction for an online IGRT protocol from 16 patients were analyzed. Specifically, the characteristics of prostate rotation were analyzed. It was found that there exist systematic interfractional prostate rotations, and they are patient specific. These rotations, if not corrected, are persistent through the treatment fraction, and rotations detected in early fractions are representative of those in later fractions. These findings suggest that the offline adaptive replanning strategy is beneficial to the online IGRT protocol with further margin reductions. Second, to quantitatively evaluate the benefit of the hybrid strategy, 412 repeated helical CT scans from 25 patients during the course of treatment were included in the replanning study. Both lowrisk patients (LRP, clinical target volume, CTV = prostate) and intermediaterisk patients (IRP, CTV = prostate + seminal vesicles) were included in the simulation. The contours of prostate and seminal vesicles were
NASA Technical Reports Server (NTRS)
Tolmadzheva, T. A.; Kantor, A. V.; Rozhkovskiy, L. V.
19740101
Digital computer modeling of the process of adaptive discretization with associative sorting of actual multichannel telemetry information is discussed. The main task in modeling is production of initial data for determination of dependences describing the operation of the onboard information compression device. Conclusions are presented including the shortcomings of telemetric information used in modeling.
Parallel Implementation and Scaling of an Adaptive Mesh Discrete Ordinates Algorithm for Transport
Howell, L H
20041129
Blockstructured adaptive mesh refinement (AMR) uses a mesh structure built up out of locallyuniform rectangular grids. In the BoxLib parallel framework used by the Raptor code, each processor operates on one or more of these grids at each refinement level. The decomposition of the mesh into grids and the distribution of these grids among processors may change every few timesteps as a calculation proceeds. Finer grids use smaller timesteps than coarser grids, requiring additional work to keep the system synchronized and ensure conservation between different refinement levels. In a paper for NECDC 2002 I presented preliminary results on implementation of parallel transport sweeps on the AMR mesh, conjugate gradient acceleration, accuracy of the AMR solution, and scalar speedup of the AMR algorithm compared to a uniform fullyrefined mesh. This paper continues with a more indepth examination of the parallel scaling properties of the scheme, both in singlelevel and multilevel calculations. Both sweeping and setup costs are considered. The algorithm scales with acceptable performance to several hundred processors. Trends suggest, however, that this is the limit for efficient calculations with traditional transport sweeps, and that modifications to the sweep algorithm will be increasingly needed as job sizes in the thousands of processors become common.
Highperformance oscillators employing adaptive optics comprised of discrete elements
NASA Astrophysics Data System (ADS)
Jackel, Steven M.; Moshe, Inon; Lavi, Raphael
19990501
Flashlamp pumped oscillators utilizing Nd:Cr:GSGG or Nd:YAG rods were stabilized against varying levels of thermal focusing by use of a Variable Radius Mirror (VRM). In its simplest form, the VRM consisted of a lens followed by a concave mirror. Separation of the two elements controlled the radius of curvature of the reflected phase front. Addition of a concaveconvex variableseparation cylindrical lens pair, allowed astigmatism to be corrected. These distributed optical elements together with a computer controlled servo system formed an adaptive optic capable of correcting the varying thermal focusing and astigmatism encountered in a Nd:YAG confocal unstable resonator (0  30 W) and in Nd:Cr:GSGG stable (hemispherical or concave convex) resonators so that high beam quality could be maintained over the entire operating range. By utilizing resonators designed to eliminate birefringence losses, high efficiency could also be maintained. The ability to eliminate thermally induced losses in GSGG allows operating power to be increased into the range where thermal fracture is a factor. We present some results on the effect of surface finish (fine grind, grooves, chemical etch strengthening) on fracture limit and high gain operation.
Shih, ChengTing; Lin, HsinHon; Chuang, KehShih; Wu, Jay; Chang, ShuJun
20140815
Purpose: Several positron emission tomography (PET) scanners with special detector block arrangements have been developed in recent years to improve the resolution of PET images. However, the discontinuous detector blocks cause gaps in the sinogram. This study proposes an adaptive discrete cosine transformbased (aDCT) filter for gapinpainting. Methods: The gapcorrupted sinogram was morphologically closed and subsequently converted to the DCT domain. A certain number of the largest coefficients in the DCT spectrum were identified to determine the lowfrequency preservation region. The weighting factors for the remaining coefficients were determined by an exponential weighting function. The aDCT filter was constructed and applied to two digital phantoms and a simulated phantom introduced with various levels of noise. Results: For the SheppLogan head phantom, the aDCT filter filled the gaps effectively. For the Jaszczak phantom, no secondary artifacts were induced after aDCT filtering. The percent mean square error and mean structure similarity of the aDCT filter were superior to those of the DCT2 filter at all noise levels. For the simulated striatal dopamine innervation study, the aDCT filter recovered the shape of the striatum and restored the striatum to reference activity ratios to the ideal value. Conclusions: The proposed aDCT filter can recover the missing gap data in the sinogram and improve the image quality and quantitative accuracy of PET images.
Avci, Derya; Leblebicioglu, Mehmet Kemal; Poyraz, Mustafa; Dogantekin, Esin
20140201
So far, analysis and classification of urine cells number has become an important topic for medical diagnosis of some diseases. Therefore, in this study, we suggest a new technique based on Adaptive Discrete Wavelet Entropy Energy and Neural Network Classifier (ADWEENN) for Recognition of Urine Cells from Microscopic Images Independent of Rotation and Scaling. Some digital image processing methods such as noise reduction, contrast enhancement, segmentation, and morphological process are used for feature extraction stage of this ADWEENN in this study. Nowadays, the image processing and pattern recognition topics have come into prominence. The image processing concludes operation and design of systems that recognize patterns in data sets. In the past years, very difficulty in classification of microscopic images was the deficiency of enough methods to characterize. Lately, it is seen that, multiresolution image analysis methods such as Gabor filters, discrete wavelet decompositions are superior to other classic methods for analysis of these microscopic images. In this study, the structure of the ADWEENN method composes of four stages. These are preprocessing stage, feature extraction stage, classification stage and testing stage. The Discrete Wavelet Transform (DWT) and adaptive wavelet entropy and energy is used for adaptive feature extraction in feature extraction stage to strengthen the premium features of the Artificial Neural Network (ANN) classifier in this study. Efficiency of the developed ADWEENN method was tested showing that an avarage of 97.58% recognition succes was obtained. PMID:24493072
Kertzscher, Gustavo Andersen, Claus E.; Tanderup, Kari
20140515
Purpose: This study presents an adaptive error detection algorithm (AEDA) for realtimein vivo point dosimetry during high dose rate (HDR) or pulsed dose rate (PDR) brachytherapy (BT) where the error identification, in contrast to existing approaches, does not depend on an a priori reconstruction of the dosimeter position. Instead, the treatment is judged based on dose rate comparisons between measurements and calculations of the most viable dosimeter position provided by the AEDA in a data driven approach. As a result, the AEDA compensates for false error cases related to systematic effects of the dosimeter position reconstruction. Given its nearly exclusive dependence on stable dosimeter positioning, the AEDA allows for a substantially simplified and time efficient realtime in vivo BT dosimetry implementation. Methods: In the event of a measured potential treatment error, the AEDA proposes the most viable dosimeter position out of alternatives to the original reconstruction by means of a data driven matching procedure between dose rate distributions. If measured dose rates do not differ significantly from the most viable alternative, the initial error indication may be attributed to a mispositioned or misreconstructed dosimeter (false error). However, if the error declaration persists, no viable dosimeter position can be found to explain the error, hence the discrepancy is more likely to originate from a misplaced or misreconstructed source applicator or from erroneously connected source guide tubes (true error). Results: The AEDA applied on twoin vivo dosimetry implementations for pulsed dose rate BT demonstrated that the AEDA correctly described effects responsible for initial error indications. The AEDA was able to correctly identify the major part of all permutations of simulated guide tube swap errors and simulated shifts of individual needles from the original reconstruction. Unidentified errors corresponded to scenarios where the dosimeter position was
George, Libin; Gargiulo, Gaetano Dario; Lehmann, Torsten; Hamilton, Tara Julia
20160601
This paper presents the design of a reconfigurable buckboost switchedcapacitor DCDC converter suitable for use in a wide range of biomedical implants. The proposed converter has an extremely small footprint and uses a novel control method that allows coarse and fine control of the output voltage. The converter uses adaptive gain control, discrete frequency scaling and pulseskipping schemes to regulate the power delivered to a range of output voltages and loads. Adaptive gain control is used to implement variable switching gain ratios from a reconfigurable power stage and thereby make coarse steps in output voltage. A discrete frequency scaling controller makes discrete changes in switching frequency to vary the power delivered to the load and perform fine tuning when the output voltage is within 10% of the target output voltage. The control architecture is predominately digital and it has been implemented as part of a fullyintegrated switchedcapacitor converter design using a standard bulk CMOS 0.18 μm process. Measured results show that the converter has an output voltage range of 1.0 to 2.2 V, can deliver up to 7.5 mW of load power and efficiency up to 75% using an active area of only 0.04 mm (2), which is significantly smaller than that of other designs. This lowarea, lowcomplexity reconfigurable power converter can support lowpower circuits in biomedical implant applications. PMID:26600247
NASA Astrophysics Data System (ADS)
Sandhu, Amit
A sequential quadratic programming method is proposed for solving nonlinear optimal control problems subject to general path constraints including mixed statecontrol and state only constraints. The proposed algorithm further develops on the approach proposed in [1] with objective to eliminate the use of a high number of time intervals for arriving at an optimal solution. This is done by introducing an adaptive time discretization to allow formation of a desirable control profile without utilizing a lot of intervals. The use of fewer time intervals reduces the computation time considerably. This algorithm is further used in this thesis to solve a trajectory planning problem for higher elevation Mars landing.
ERIC Educational Resources Information Center
Wood, Milton E.
The purpose of the effort was to determine the benefits to be derived from the adaptive training technique of automatically adjusting task difficulty as a function of a student skill during early learning of a complex perceptual motor task. A digital computer provided the task dynamics, scoring, and adaptive control of a secondorder, twoaxis,…
NASA Astrophysics Data System (ADS)
Krüger, Alexander; Hansen, Anja; Matthias, Ben; Ripken, Tammo
20140201
Although fslaser surgery is clinically established in the field of corneal flap cutting for laser in situ keratomileusis, surgery with fslaser in the posterior part of the eye is impaired by focus degradation due to aberrations. Precise targeting and keeping of safety distance to the retina also relies on an intraoperative depth resolved imaging. We demonstrate a concept for image guided fslaser surgery in the vitreous body combining adaptive optics (AO) for focus reshaping and optical coherence tomography (OCT) for focus position guidance. The setup of the laboratory system consist of an 800 nm fslaser which is focused into a simple eye model via a closed loop adaptive optics system with HartmannShack sensor and a deformable mirror to correct for wavefront aberrations. A spectral domain optical coherence tomography system is used to target phantom structures in the eye model. Both systems are set up to share the same scanner and focusing optics. The use of adaptive optics results in a lowered threshold energy for laser induced breakdown and an increased cutting precision. 3D OCT imaging of porcine retinal tissue prior and immediately after fslaser cutting is also demonstrated. In the near future OCT and AO will be two essential assistive components in possible clinical systems for fslaser based eye surgery beyond the cornea.
Rein, Robert; Davids, Keith; Button, Chris
20100301
The identification of attractors is one of the key tasks in studies of neurobiological coordination from a dynamical systems perspective, with a considerable body of literature resulting from this task. However, with regards to typical movement models investigated, the overwhelming majority of actions studied previously belong to the class of continuous, rhythmical movements. In contrast, very few studies have investigated coordination of discrete movements, particularly multiarticular discrete movements. In the present study, we investigated phase transition behavior in a basketball throwing task where participants were instructed to shoot at the basket from different distances. Adopting the ubiquitous scaling paradigm, throwing distance was manipulated as a candidate control parameter. Using a cluster analysis approach, clear phase transitions between different movement patterns were observed in performance of only two of eight participants. The remaining participants used a single movement pattern and varied it according to throwing distance, thereby exhibiting hysteresis effects. Results suggested that, in movement models involving many biomechanical degrees of freedom in degenerate systems, greater movement variation across individuals is available for exploitation. This observation stands in contrast to movement variation typically observed in studies using more constrained bimanual movement models. This degenerate system behavior provides new insights and poses fresh challenges to the dynamical systems theoretical approach, requiring further research beyond conventional movement models. PMID:19851763
Zhang, Guoqing; Zhang, Xianku
20150501
Around the waypointbased pathfollowing control for marine ships, a novel dynamic virtual ship (DVS) guidance principle is developed to implement the assumption "the reference path is generated using a virtual ship", which is critical for applying the current theoretical studies in practice. Taking two steerable variables as control inputs, the robust adaptive scheme is proposed by virtue of the robust neural damping and dynamic surface control (DSC) techniques. The derived controller is with the advantages of concise structure and being easytoimplement for its burdensome superiority. Furthermore, the low frequency learning method improves the applicability of the algorithm. Finally, the comparison experiments with the lineofsight (LOS) based fuzzy scheme are presented to demonstrate the effectiveness of our results. PMID:25579375
ERIC Educational Resources Information Center
Redondo, Miguel A.; Bravo, Crescencio; Ortega, Manuel; Verdejo, M. Felisa
20070101
Experimental learning environments based on simulation usually require monitoring and adaptation to the actions the users carry out. Some systems provide this functionality, but they do so in a way which is static or cannot be applied to problem solving tasks. In response to this problem, we propose a method based on the use of intermediate…
NASA Astrophysics Data System (ADS)
Lausch, Anthony; Chen, Jeff; Ward, Aaron D.; Gaede, Stewart; Lee, TingYim; Wong, Eugene
20141101
Parametric response map (PRM) analysis is a voxelwise technique for predicting overall treatment outcome, which shows promise as a tool for guiding personalized locally adaptive radiotherapy (RT). However, image registration error (IRE) introduces uncertainty into this analysis which may limit its use for guiding RT. Here we extend the PRM method to include an IRErelated PRM analysis confidence interval and also incorporate multiple graded classification thresholds to facilitate visualization. A Gaussian IRE model was used to compute an expected value and confidence interval for PRM analysis. The augmented PRM (APRM) was evaluated using CTperfusion functional image data from patients treated with RT for glioma and hepatocellular carcinoma. Known rigid IREs were simulated by applying one thousand different rigid transformations to each image set. PRM and APRM analyses of the transformed images were then compared to analyses of the original images (ground truth) in order to investigate the two methods in the presence of controlled IRE. The APRM was shown to help visualize and quantify IRErelated analysis uncertainty. The use of multiple graded classification thresholds also provided additional contextual information which could be useful for visually identifying adaptive RT targets (e.g. subvolume boosts). The APRM should facilitate reliable PRM guided adaptive RT by allowing the user to identify if a patient’s unique IRErelated PRM analysis uncertainty has the potential to influence target delineation.
Narendra, Ajay; Greiner, Birgit; Ribi, Willi A; Zeil, Jochen
20160815
Ants of the Australian genus Myrmecia partition their foraging niche temporally, allowing them to be sympatric with overlapping foraging requirements. We used histological techniques to study the light and dark adaptation mechanisms in the compound eyes of diurnal (Myrmecia croslandi), crepuscular (M. tarsata, M. nigriceps) and nocturnal ants (M. pyriformis). We found that, except in the dayactive species, all ants have a variable primary pigment cell pupil that constricts the crystalline cone in bright light to control for light flux. We show for the nocturnal M. pyriformis that the constriction of the crystalline cone by the primary pigment cells is light dependent whereas the opening of the aperture is regulated by an endogenous rhythm. In addition, in the lightadapted eyes of all species, the retinular cell pigment granules radially migrate towards the rhabdom, a process that in both the dayactive M. croslandi and the nightactive M. pyriformis is driven by ambient light intensity. Visual system properties thus do not restrict crepuscular and nightactive ants to their temporal foraging niche, while dayactive ants require high light intensities to operate. We discuss the ecological significance of these adaptation mechanisms and their role in temporal niche partitioning. PMID:27535985
NASA Technical Reports Server (NTRS)
Swenson, Harry N.; Zelenka, Richard E.; Hardy, Gordon H.; Dearing, Munro G.
19920101
A computer aiding concept for lowaltitude helicopter flight was developed and evaluated in a realtime piloted simulation. The concept included an optimal control trajectorygeneration algorithm based upon dynamic programming and a helmetmounted display (HMD) presentation of a pathwayinthesky, a phantom aircraft, and flightpath vector/predictor guidance symbology. The trajectorygeneration algorithm uses knowledge of the global mission requirements, a digital terrain map, aircraft performance capabilities, and advanced navigation information to determine a trajectory between mission way points that seeks valleys to minimize threat exposure. The pilot evaluation was conducted at NASA ARC moving base Vertical Motion Simulator (VMS) by pilots representing NASA, the U.S. Army, the Air Force, and the helicopter industry. The pilots manually tracked the trajectory generated by the algorithm utilizing the HMD symbology. The pilots were able to satisfactorily perform the tracking tasks while maintaining a high degree of awareness of the outside world.
ERIC Educational Resources Information Center
Gartrell, Dan
20050101
In this column, the author shares and comments on early childhood educators' use of guidance to foster young children's development and learning. He defines guidance as the commitment a teacher makes to teaching children how to solve their problems, rather than punishing them for having problems they haven't yet learned how to solve. The focus of…
Broom, Donald M
20060101
The term adaptation is used in biology in three different ways. It may refer to changes which occur at the cell and organ level, or at the individual level, or at the level of gene action and evolutionary processes. Adaptation by cells, especially nerve cells helps in: communication within the body, the distinguishing of stimuli, the avoidance of overload and the conservation of energy. The time course and complexity of these mechanisms varies. Adaptive characters of organisms, including adaptive behaviours, increase fitness so this adaptation is evolutionary. The major part of this paper concerns adaptation by individuals and its relationships to welfare. In complex animals, feed forward control is widely used. Individuals predict problems and adapt by acting before the environmental effect is substantial. Much of adaptation involves brain control and animals have a set of needs, located in the brain and acting largely via motivational mechanisms, to regulate life. Needs may be for resources but are also for actions and stimuli which are part of the mechanism which has evolved to obtain the resources. Hence pigs do not just need food but need to be able to carry out actions like rooting in earth or manipulating materials which are part of foraging behaviour. The welfare of an individual is its state as regards its attempts to cope with its environment. This state includes various adaptive mechanisms including feelings and those which cope with disease. The part of welfare which is concerned with coping with pathology is health. Disease, which implies some significant effect of pathology, always results in poor welfare. Welfare varies over a range from very good, when adaptation is effective and there are feelings of pleasure or contentment, to very poor. A key point concerning the concept of individual adaptation in relation to welfare is that welfare may be good or poor while adaptation is occurring. Some adaptation is very easy and energetically cheap and
NASA Astrophysics Data System (ADS)
Bargatze, L. F.
20151201
Active Data Archive Product Tracking (ADAPT) is a collection of software routines that permits one to generate XML metadata files to describe and register data products in support of the NASA Heliophysics Virtual Observatory VxO effort. ADAPT is also a philosophy. The ADAPT concept is to use any and all available metadata associated with scientific data to produce XML metadata descriptions in a consistent, uniform, and organized fashion to provide blanket access to the full complement of data stored on a targeted data server. In this poster, we present an application of ADAPT to describe all of the data products that are stored by using the Common Data File (CDF) format served out by the CDAWEB and SPDF data servers hosted at the NASA Goddard Space Flight Center. These data servers are the primary repositories for NASA Heliophysics data. For this purpose, the ADAPT routines have been used to generate data resource descriptions by using an XML schema named Space Physics Archive, Search, and Extract (SPASE). SPASE is the designated standard for documenting Heliophysics data products, as adopted by the Heliophysics Data and Model Consortium. The set of SPASE XML resource descriptions produced by ADAPT includes highlevel descriptions of numerical data products, display data products, or catalogs and also includes lowlevel "Granule" descriptions. A SPASE Granule is effectively a universal access metadata resource; a Granule associates an individual data file (e.g. a CDF file) with a "parent" highlevel data resource description, assigns a resource identifier to the file, and lists the corresponding assess URL(s). The CDAWEB and SPDF file systems were queried to provide the input required by the ADAPT software to create an initial set of SPASE metadata resource descriptions. Then, the CDAWEB and SPDF data repositories were queried subsequently on a nightly basis and the CDF file lists were checked for any changes such as the occurrence of new, modified, or deleted
ERIC Educational Resources Information Center
Rosenstein, Joseph G., Ed.; Franzblau, Deborah S., Ed.; Roberts, Fred S., Ed.
This book is a collection of articles by experienced educators and explains why and how discrete mathematics should be taught in K12 classrooms. It includes evidence for "why" and practical guidance for "how" and also discusses how discrete mathematics can be used as a vehicle for achieving the broader goals of the major effort now underway to…
Defn: Guidance Document  A peerreviewed document stating overarching principles and practices to be followed (also includes handbook documents).
Internet Guidance.
ERIC Educational Resources Information Center Savage, Frank X. 19990101 States that children need proper guidance and boundaries to reap the benefits of the Internet. Focuses on two issues: how parents can protect their children from the Internet's potential dangers and how they can help their children use the Internet to get work done. Includes suggestions for teachers to help parents meet these challenges. (VWC) NASA Astrophysics Data System (ADS) Vivaldi, Franco 20151201 The concept of resonance has been instrumental to the study of Hamiltonian systems with divided phase space. One can also define such systems over discrete spaces, which have a finite or countable number of points, but in this new setting the notion of resonance must be reconsidered from scratch. I review some recent developments in the area of arithmetic dynamics which outline some salient features of linear and nonlinear stable (elliptic) orbits over a discrete space, and also underline the difficulties that emerge in their analysis. NASA Astrophysics Data System (ADS) Vivaldi, Franco The concept of resonance has been instrumental to the study of Hamiltonian systems with divided phase space. One can also define such systems over discrete spaces, which have a finite or countable number of points, but in this new setting the notion of resonance must be reconsidered from scratch. I review some recent developments in the area of arithmetic dynamics which outline some salient features of linear and nonlinear stable (elliptic) orbits over a discrete space, and also underline the difficulties that emerge in their analysis.
