Prior Knowledge (prior + knowledge)

Distribution by Scientific Domains

Kinds of Prior Knowledge

  • student prior knowledge

  • Selected Abstracts

    Prior knowledge processing for initial state of Kalman filter

    E. Suzdaleva
    Abstract The paper deals with a specification of the prior distribution of the initial state for Kalman filter. The subjective prior knowledge, used in state estimation, can be highly uncertain. In practice, incorporation of prior knowledge contributes to a good start of the filter. The present paper proposes a methodology for selection of the initial state distribution, which enables eliciting of prior knowledge from the available expert information. The proposed methodology is based on the use of the conjugate prior distribution for models belonging to the exponential family. The normal state-space model is used for demonstrating the methodology. The paper covers processing of the prior knowledge for state estimation, available in the form of simulated data. Practical experiments demonstrate the processing of prior knowledge from the urban traffic control area, which is the main application of the research. Copyright © 2009 John Wiley & Sons, Ltd. [source]

    Radiographic Recognition of Dental Implants as an Aid to Identifying the Deceased

    John W. Berketa B.D.S.
    Abstract:, This study was undertaken to determine if dental implants can be radiographically differentiated by company type to aid forensic identification of the deceased. Recognition of dental implants on intraoral radiographic images was assessed in a blind study using a radiographic examination guide to highlight differences between dental implants. Inter- and intra-examiner comparisons were conducted and a computer program (Implant Recognition System®) was evaluated to see whether it improved the accuracy of implant recognition. The study found that dental implants could be radiographically differentiated by company type. The Implant Recognition System® in its current form was of little benefit for radiographic assessment of dental implants for forensic odontologists. Prior knowledge of implant types, with a McNemar's statistical value of 92.9, proved to be most significant in identification. [source]

    Undersampled radial MRI with multiple coils.

    Iterative image reconstruction using a total variation constraint
    Abstract The reconstruction of artifact-free images from radially encoded MRI acquisitions poses a difficult task for undersampled data sets, that is for a much lower number of spokes in k-space than data samples per spoke. Here, we developed an iterative reconstruction method for undersampled radial MRI which (i) is based on a nonlinear optimization, (ii) allows for the incorporation of prior knowledge with use of penalty functions, and (iii) deals with data from multiple coils. The procedure arises as a two-step mechanism which first estimates the coil profiles and then renders a final image that complies with the actual observations. Prior knowledge is introduced by penalizing edges in coil profiles and by a total variation constraint for the final image. The latter condition leads to an effective suppression of undersampling (streaking) artifacts and further adds a certain degree of denoising. Apart from simulations, experimental results for a radial spin-echo MRI sequence are presented for phantoms and human brain in vivo at 2.9 T using 24, 48, and 96 spokes with 256 data samples. In comparison to conventional reconstructions (regridding) the proposed method yielded visually improved image quality in all cases. Magn Reson Med 57:1086,1098, 2007. © 2007 Wiley-Liss, Inc. [source]

    How multiple external representations are used and how they can be made more useful

    Rolf Schwonke
    In two studies, students' difficulties in using multiple external representations were effectively addressed. In a first explorative study (N,=,16), we investigated the allocation of visual attention (as assessed by gaze data) on external representations, its relation to learning and learners' beliefs on the representations' functions. Results confirmed that students were not aware of the functions. In a subsequent experiment (N,=,30), we analysed effects of informing students about the function of diagrams in worked examples on learning, mediating effects of visual attention and moderating effects of prior knowledge. The instruction had strong effects on learning, which were partially mediated by visual attention. Prior knowledge moderated both, the effects of the instruction on visual attention and of visual attention on learning. Implications for research into multiple representations and instructional design are discussed. Copyright © 2008 John Wiley & Sons, Ltd. [source]

    Web Discovery and Filtering Based on Textual Relevance Feedback Learning

    Wai Lam
    We develop a new approach for Web information discovery and filtering. Our system, called WID, allows the user to specify long-term information needs by means of various topic profile specifications. An entire example page or an index page can be accepted as input for the discovery. It makes use of a simulated annealing algorithm to automatically explore new Web pages. Simulated annealing algorithms possess some favorable properties to fulfill the discovery objectives. Information retrieval techniques are adopted to evaluate the content-based relevance of each page being explored. The hyperlink information, in addition to the textual context, is considered in the relevance score evaluation of a Web page. WID allows users to provide three forms of the relevance feedback model, namely, the positive page feedback, the negative page feedback, and the positive keyword feedback. The system is domain independent and does not rely on any prior knowledge or information about the Web content. Extensive experiments have been conducted to demonstrate the effectiveness of the discovery performance achieved by WID. [source]

    SecondSkin: An interactive method for appearance transfer

    A. Van Den Hengely
    Abstract SecondSkin estimates an appearance model for an object visible in a video sequence, without the need for complex interaction or any calibration apparatus. This model can then be transferred to other objects, allowing a non-expert user to insert a synthetic object into a real video sequence so that its appearance matches that of an existing object, and changes appropriately throughout the sequence. As the method does not require any prior knowledge about the scene, the lighting conditions, or the camera, it is applicable to video which was not captured with this purpose in mind. However, this lack of prior knowledge precludes the recovery of separate lighting and surface reflectance information. The SecondSkin appearance model therefore combines these factors. The appearance model does require a dominant light-source direction, which we estimate via a novel process involving a small amount of user interaction. The resulting model estimate provides exactly the information required to transfer the appearance of the original object to new geometry composited into the same video sequence. [source]

    Borderline nuclear change; can a subgroup be identified which is suspicious of high-grade cervical intraepithelial neoplasia, i.e. CIN 2 or worse?

    CYTOPATHOLOGY, Issue 5 2002
    J. M. Edwards
    Borderline nuclear change; can a subgroup be identified which is suspicious of high-grade cervical intraepithelial neoplasia, i.e. CIN 2 or worse? Only 10% of first borderline smears are associated with a histological high-grade (HG) abnormality, i.e. CIN 2,3, invasive malignancy or glandular neoplasia on subsequent investigation. The advantages of highlighting this subgroup are obvious but is this possible? From 1996 and 1997, 242 borderline smears with histological follow-up were examined by two independent experienced observers (observer 1 and 2) without prior knowledge of further investigation results. For each smear a profile of nuclear details was produced, also noting the type of cell mainly affected by the process; then the observers were asked to assess the degree of worry of HG disease for each smear i.e. whether the smear fell into group 1 borderline changes indicative of low-grade (normal, inflammatory, CIN1/HPV) disease (BL/LG) or group 2 difficult borderline smear, HG disease (CIN 2,3, invasive neoplasia or glandular neoplasia) cannot be excluded (BL/HG). Observer 1 selected a group of BL/HG with a PPV for HG disease of 38%, with observer 2 having a PPV of 50%; this compared with the overall laboratory HG disease PPV for borderline smears of 14%. Both observers found the most useful criterion to be the increase in nuclear:cytoplasmic ratio. Our results show that it is possible to separate a small group of borderline smears which should be classified as ,borderline/high grade lesion difficult to exclude' (BL/HG). Both observers had some success in arriving at this classification although their method of selecting out this group was quite different. [source]

    Technology Entrepreneurs' Human Capital and Its Effects on Innovation Radicalness

    Matthew R. Marvel
    Radical innovations transform existing markets, create new markets, and stimulate economic growth. This study investigates how the experience, education, and prior knowledge of technology entrepreneurs relate to innovation radicalness. Findings from a sample of 145 technology entrepreneurs operating within university-affiliated incubators suggest that general and specific human capital are both vital to innovation outcomes. Innovation radicalness was positively associated with formal education and prior knowledge of technology, but negatively associated with prior knowledge of ways to serve markets. This suggests a counterintuitive conclusion,the less technology entrepreneurs know about ways to serve a market, the greater their chances of using technology knowledge to create breakthrough innovations within it. Finally, we discuss configurations of human capital that are likely to bestow unique advantages in the construction of radical innovations. [source]

    A cost analysis of ranked set sampling to estimate a population mean

    ENVIRONMETRICS, Issue 3 2005
    Rebecca A. Buchanan
    Abstract Ranked set sampling (RSS) can be a useful environmental sampling method when measurement costs are high but ranking costs are low. RSS estimates of the population mean can have higher precision than estimates from a simple random sample (SRS) of the same size, leading to potentially lower sampling costs from RSS than from SRS for a given precision. However, RSS introduces ranking costs not present in SRS; these costs must be considered in determining whether RSS is cost effective. We use a simple cost model to determine the minimum ratio of measurement to ranking costs (cost ratio) necessary in order for RSS to be as cost effective as SRS for data from the normal, exponential, and lognormal distributions. We consider both equal and unequal RSS allocations and two types of estimators of the mean: the typical distribution-free (DF) estimator and the best linear unbiased estimator (BLUE). The minimum cost ratio necessary for RSS to be as cost effective as SRS depends on the underlying distribution of the data, as well as the allocation and type of estimator used. Most minimum necessary cost ratios are in the range of 1,6, and are lower for BLUEs than for DF estimators. The higher the prior knowledge of the distribution underlying the data, the lower the minimum necessary cost ratio and the more attractive RSS is over SRS. Copyright © 2005 John Wiley & Sons, Ltd. [source]

    Chemical mass balance when an unknown source exists

    ENVIRONMETRICS, Issue 8 2004
    Nobuhisa Kashiwagi
    Abstract A chemical mass balance method is proposed for the case where the existence of an unknown source is suspected. In general, when the existence of an unknown source is assumed in statistical receptor modeling, unknown quantities such as the composition of an unknown source and the contributions of assumed sources become unidentifiable. To estimate these unknown quantities avoiding the identification problem, a Bayes model for chemical mass balance is constructed in the form of composition without using prior knowledge on the unknown quantities except for natural constraints. The covariance of ambient observations given in the form of composition is defined in several ways. Markov chain Monte Carlo is used for evaluating the posterior means and variances of the unknown quantities as well as the likelihood for the proposed model. The likelihood is used for selecting the best fit covariance model. A simulation study is carried out to check the performance of the proposed method. Copyright © 2004 John Wiley & Sons, Ltd. [source]

    Learner-control vs. program-control instructional multimedia: a comparison of two interactions when teaching principles of orthodontic appliances

    M. Aly
    Abstract Background:, Many studies have compared computer assisted learning (CAL) to more traditional learning formats and have shown CAL to be as effective as or superior to the alternative resources. However, there are only scarce attempts to show which style of CAL leads to the best learning outcomes in orthodontics. Aim:, To compare the effectiveness of a learner-control (group A) vs. program-control (group B) multimedia learning environment courseware packages regarding knowledge, understanding and transfer of content when applied to teaching principles of orthodontic appliances to undergraduate students. Methods:, Pre- and post-test assessments of undergraduate dental students (n = 30) who either studied a learner-control multimedia learning environment courseware package (n = 15) or a program-control version (n = 15) on equivalent material of the orthodontic appliances curriculum. Both groups were evaluated by means of multiple-choice questions covering knowledge, understanding and application. A one-way ANOVA was carried out in order to check for statistical difference between the two groups. The P -value was set at 0.05. Results:, There was no difference in prior knowledge between both groups at baseline. Although, both groups significantly improved their scores after having studied the course, no significant difference was found between both groups in relation to answers to questions about knowledge, understanding and application. Conclusions:, In this study, the learner-control instructional multimedia program was found to be as effective as the program-control version when teaching principles of the orthodontic appliances to undergraduate students. The focus needs to be on improving the value of CAL. Comparative evaluations of how different CAL approaches compare with or complement one another are certainly needed. [source]

    Adaptive group detection for DS/CDMA systems over frequency-selective fading channels,

    Stefano Buzzi
    In this paper we consider the problem of group detection for asynchronous Direct-Sequence Code Division Multiple Access (DS/CDMA) systems operating over frequency-selective fading channels. A two-stage near-far resistant detection structure is proposed. The first stage is a linear filter, aimed at suppressing the effect of the unwanted user signals, while the second stage is a non-linear block, implementing a maximum likelihood detection rule on the set of desired user signals. As to the linear stage, we consider both the Zero-Forcing (ZF) and the Minimum Mean Square Error (MMSE) approaches; in particular, based on the amount of prior knowledge on the interference parameters which is available to the receiver and on the affordable computational complexity, we come up with several receiving structures, which trade system performance for complexity and needed channel state information. We also present adaptive implementations of these receivers, wherein only the parameters from the users to be decoded are assumed to be known. The case that the channel fading coefficients of the users to be decoded are not known a priori is also considered. In particular, based on the transmission of pilot signals, we adopt a least-squares criterion in order to obtain estimates of these coefficients. The result is thus a fully adaptive structure, which can be implemented with no prior information on the interfering signals and on the channel state. As to the performance assessment, the new receivers are shown to be near-far resistant, and simulation results confirm their superiority with respect to previously derived detection structures. Copyright © 2003 AEI. [source]

    A Bayesian approach to estimating tectonic stress from seismological data

    Richard Arnold
    SUMMARY Earthquakes are conspicuous manifestations of tectonic stress, but the non-linear relationships between the stresses acting on a fault plane, its frictional slip, and the ensuing seismic radiation are such that a single earthquake by itself provides little information about the ambient state of stress. Moreover, observational uncertainties and inherent ambiguities in the nodal planes of earthquake focal mechanisms preclude straightforward inferences about stress being drawn on the basis of individual focal mechanism observations. However, by assuming that each earthquake in a small volume of the crust represents a single, uniform state of stress, the combined constraints imposed on that stress by a suite of focal mechanism observations can be estimated. Here, we outline a probabilistic (Bayesian) technique for estimating tectonic stress directions from primary seismological observations. The Bayesian formulation combines a geologically motivated prior model of the state of stress with an observation model that implements the physical relationship between the stresses acting on a fault and the resultant seismological observation. We show our Bayesian formulation to be equivalent to a well-known analytical solution for a single, errorless focal mechanism observation. The new approach has the distinct advantage, however, of including (1) multiple earthquakes, (2) fault plane ambiguities, (3) observational errors and (4) any prior knowledge of the stress field. Our approach, while computationally demanding in some cases, is intended to yield reliable tectonic stress estimates that can be confidently compared with other tectonic parameters, such as seismic anisotropy and geodetic strain rate observations, and used to investigate spatial and temporal variations in stress associated with major faults and coseismic stress perturbations. [source]

    Development of a stable isotope index to assess decadal-scale vegetation change and application to woodlands of the Burdekin catchment, Australia

    Abstract Forty-four study sites were established in remnant woodland in the Burdekin River catchment in tropical north-east Queensland, Australia, to assess recent (decadal) vegetation change. The aim of this study was further to evaluate whether wide-scale vegetation ,thickening' (proliferation of woody plants in formerly more open woodlands) had occurred during the last century, coinciding with significant changes in land management. Soil samples from several depth intervals were size separated into different soil organic carbon (SOC) fractions, which differed from one another by chemical composition and turnover times. Tropical (C4) grasses dominate in the Burdekin catchment, and thus ,13C analyses of SOC fractions with different turnover times can be used to assess whether the relative proportion of trees (C3) and grasses (C4) had changed over time. However, a method was required to permit standardized assessment of the ,13C data for the individual sites within the 13 Mha catchment, which varied in soil and vegetation characteristics. Thus, an index was developed using data from three detailed study sites and global literature to standardize individual isotopic data from different soil depths and SOC fractions to reflect only the changed proportion of trees (C3) to grasses (C4) over decadal timescales. When applied to the 44 individual sites distributed throughout the Burdekin catchment, 64% of the sites were shown to have experienced decadal vegetation thickening, while 29% had remained stable and the remaining 7% had thinned. Thus, the development of this index enabled regional scale assessment and comparison of decadal vegetation patterns without having to rely on prior knowledge of vegetation changes or aerial photography. [source]

    Characterization of a Multilayer Aquifer Using Open Well Dilution Tests

    GROUND WATER, Issue 1 2007
    L. Jared West
    An approach to characterization of multilayer aquifer systems using open well borehole dilution is described. The approach involves measuring observation well flow velocities while a nearby extraction well is pumped by introducing a saline tracer into observation wells and collecting dilution vs. depth profiles. Inspection of tracer profile evolution allows discrete permeable layers within the aquifer to be identified. Dilution profiles for well sections between permeable layers are then converted into vertical borehole flow velocities and their evolution, using an analytic solution to the advection-dispersion equation applied to borehole flow. The dilution approach is potentially able to measure much smaller flow velocities that would be detectable using flowmeters. Vertical flow velocity data from the observation wells are then matched to those generated using a hydraulic model of the aquifer system, "shorted" by the observation wells, to yield the hydraulic properties of the constituent layers. Observation well flow monitoring of pumping tests represents a cost-effective alternative or preliminary approach to pump testing each layer of a multilayer aquifer system separately using straddle packers or screened wells and requires no prior knowledge of permeable layer depths and thicknesses. The modification described here, of using tracer dilution rather than flowmeter logging to obtain well flow velocities, allows the approach to be extended to greater well separations, thus characterizing a larger volume of the aquifer. An example of the application of this approach to a multilayer Chalk Aquifer in Yorkshire, Northeast England, is presented. [source]

    Psychological aspects and coping styles of parents with Haemophilic child undergoing a programme of counselling and psychological support

    HAEMOPHILIA, Issue 3 2007
    A. M. BOTTOS
    Summary., Parents of children affected by haemophilia must face, often without prior knowledge, the difficult challenge imposed by such a pathology. To satisfy the need of information, guideline and psychological support for a better quality of life, 30 parents with haemophiliac children have participated in a programme of counselling and psychological support. Such a programme has the aim of guiding the group trough a process of discovery, comparison and personal growth and stimulating adaptive processes of problem,solving and decision,making. The aim of this paper was to verify how the programme influenced coping strategies and other psychological constructs such as depression and anxiety. Subjects of this study were administered the following psychological tests: COPE (coping, orientation to problems experienced), BDI (beck depression inventory), STAI-Y form (state,trait anxiety inventory) at the beginning and at the end of the programme. The results show that by the end of the programme subjects are characterized by a greater use of problem,focused coping strategies, typical of individuals who think that the situation is susceptible to change, and a minor use of emotion,focused coping strategies, related to individuals who regard the situation as immutable. The use of avoidance ,focused coping strategies seems to remain at the same level even if it was low. Also the other psychological aspects investigated, namely depression and anxiety, did receive a positive influence. The results show how significant such programme has been for parents. [source]

    Sensitivity analysis of prior model probabilities and the value of prior knowledge in the assessment of conceptual model uncertainty in groundwater modelling

    Rodrigo Rojas
    Abstract A key point in the application of multi-model Bayesian averaging techniques to assess the predictive uncertainty in groundwater modelling applications is the definition of prior model probabilities, which reflect the prior perception about the plausibility of alternative models. In this work the influence of prior knowledge and prior model probabilities on posterior model probabilities, multi-model predictions, and conceptual model uncertainty estimations is analysed. The sensitivity to prior model probabilities is assessed using an extensive numerical analysis in which the prior probability space of a set of plausible conceptualizations is discretized to obtain a large ensemble of possible combinations of prior model probabilities. Additionally, the value of prior knowledge about alternative models in reducing conceptual model uncertainty is assessed by considering three example knowledge states, expressed as quantitative relations among the alternative models. A constrained maximum entropy approach is used to find the set of prior model probabilities that correspond to the different prior knowledge states. For illustrative purposes, a three-dimensional hypothetical setup approximated by seven alternative conceptual models is employed. Results show that posterior model probabilities, leading moments of the predictive distributions and estimations of conceptual model uncertainty are very sensitive to prior model probabilities, indicating the relevance of selecting proper prior probabilities. Additionally, including proper prior knowledge improves the predictive performance of the multi-model approach, expressed by reductions of the multi-model prediction variances by up to 60% compared with a non-informative case. However, the ratio between-model to total variance does not substantially decrease. This suggests that the contribution of conceptual model uncertainty to the total variance cannot be further reduced based only on prior knowledge about the plausibility of alternative models. These results advocate including proper prior knowledge about alternative conceptualizations in combination with extra conditioning data to further reduce conceptual model uncertainty in groundwater modelling predictions. Copyright © 2009 John Wiley & Sons, Ltd. [source]

    Estimating the snow water equivalent on the Gatineau catchment using hierarchical Bayesian modelling

    Ousmane Seidou
    Abstract One of the most important parameters for spring runoff forecasting is the snow water equivalent on the watershed, often estimated by kriging using in situ measurements, and in some cases by remote sensing. It is known that kriging techniques provide little information on uncertainty, aside from the kriging variance. In this paper, two approaches using Bayesian hierarchical modelling are compared with ordinary kriging; Bayesian hierarchical modelling is a flexible and general statistical approach that uses observations and prior knowledge to make inferences on both unobserved data (snow water equivalent on the watershed where there is no measurements) and on the parameters (influence of the covariables, spatial interactions between the values of the process at various sites). The first approach models snow water equivalent as a Gaussian spatial process, for which the mean varies in space, and the other uses the theory of Markov random fields. Although kriging and the Bayesian models give similar point estimates, the latter provide more information on the distribution of the snow water equivalent. Furthermore, kriging may considerably underestimate interpolation error. Copyright © 2006 Environment Canada. Published by John Wiley & Sons, Ltd. [source]

    Use of neural networks for the prediction of frictional drag and transmission of axial load in horizontal wellbores

    Tanvir Sadiq
    Abstract The use of mud motors and other tools to accomplish forward motion of the bit in extended reach and horizontal wells allows avoiding large amounts of torque caused by rotation of the whole drill string. The forward motion of the drill string, however, is resisted by excessive amount of friction. In the presence of large compressive axial loads, the drill pipe or coiled tubing tends to buckle into a helix in horizontal boreholes. This causes additional frictional drag resisting the transmission of axial load (resulting from surface slack-off force) to the bit. As the magnitude of the frictional drag increases, a buckled pipe may become ,locked-up' making it almost impossible to drill further. In case of packers, the frictional drag may inhibit the transmission of set-up load to the packer. A prior knowledge of the magnitude of frictional drag for a given axial load and radial clearance can help avoid lock-up conditions and costly failure of the tubular. In this study a neural network model, for the prediction of frictional drag and axial load transmission in horizontal wellbores, is presented. Several neural network architectures were designed and tested to obtain the most accurate prediction. After cross-validation of the Back Propagation Neural Network (BPNN) algorithm, a two-hidden layer model was chosen for simultaneous prediction of frictional drag and axial load transmission. A comparison of results obtained from BPNN and General Regression Neural Network (GRNN) algorithms is also presented. Copyright © 2002 John Wiley & Sons, Ltd. [source]

    Prior knowledge processing for initial state of Kalman filter

    E. Suzdaleva
    Abstract The paper deals with a specification of the prior distribution of the initial state for Kalman filter. The subjective prior knowledge, used in state estimation, can be highly uncertain. In practice, incorporation of prior knowledge contributes to a good start of the filter. The present paper proposes a methodology for selection of the initial state distribution, which enables eliciting of prior knowledge from the available expert information. The proposed methodology is based on the use of the conjugate prior distribution for models belonging to the exponential family. The normal state-space model is used for demonstrating the methodology. The paper covers processing of the prior knowledge for state estimation, available in the form of simulated data. Practical experiments demonstrate the processing of prior knowledge from the urban traffic control area, which is the main application of the research. Copyright © 2009 John Wiley & Sons, Ltd. [source]

    Semi-adaptive control of convexly parametrized systems with application to temperature regulation of chemical reactors

    Alexander Fradkov
    In this paper, we are interested in the problem of adaptive control of non-linearly parametrized systems. We investigate the viability of defining a stabilizing parameter update law for the case when the plant model is convex on the uncertain parameters. We show that, when the only prior knowledge is convexity, there does not exist an adaptation law,derivable from the standard separable Lyapunov function technique of Parks,applicable for all the state space. Therefore, we propose a semi-adaptive state feedback controller where adaptation takes place only in the region of the state space where convexity can be used to reduce parameter uncertainty. In the remaining part of the state space we freeze the adaptation and switch to a robust controller. This scheme ensures semi-global stability for convexly parametrized non-linear systems with matched uncertainty. The proposed controller is then applied to the problem of temperature regulation of continuous stirred exothermic chemical reactors where reaction heat is convex in the uncertain parameters. Copyright © 2001 John Wiley & Sons, Ltd. [source]

    Model-based shape from shading for microelectronics applications

    A. Nissenboim
    Abstract Model-based shape from shading (SFS) is a promising paradigm introduced by Atick et al. [Neural Comput 8 (1996), 1321,1340] in 1996 for solving inverse problems when we happen to have a lot of prior information on the depth profiles to be recovered. In the present work we adopt this approach to address the problem of recovering wafer profiles from images taken using a scanning electron microscope (SEM). This problem arises naturally in the microelectronics inspection industry. A low-dimensional model, based on our prior knowledge on the types of depth profiles of wafer surfaces, has been developed, and based on it the SFS problem becomes an optimal parameter estimation. Wavelet techniques were then employed to calculate a good initial guess to be used in a minimization process that yields the desired profile parametrization. A Levenberg,Marguardt (LM) optimization procedure has been adopted to address ill-posedness of the SFS problem and to ensure stable numerical convergence. The proposed algorithm has been tested on synthetic images, using both Lambertian and SEM imaging models. © 2006 Wiley Periodicals, Inc. Int J Imaging Syst Technol, 16, 65,76, 2006 [source]

    Multicriteria second-order neural networks approach to imaging through turbulence

    Yuanmei Wang
    Abstract Atmospheric turbulence can greatly limit the spatial resolution in optical images obtained of space objects when imaged with ground-based telescopes. Two widely used algorithms to remove atmospheric turbulence in this class of images are blind de-convolution and speckle imaging. Both algorithms are effective in removing atmospheric turbulence, but they use different types of prior knowledge and have different strengths and weaknesses. We have developed a multicriteria cross entropy minimization approach to imaging through atmospheric turbulence and a second-order neural network implementations. Our simulations illustrated the efficiency of our method. © 2003 Wiley Periodicals, Inc. Int J Imaging Syst Technol 13, 146,151, 2003; Published online in Wiley InterScience ( DOI 10.1002/ima.10037 [source]

    Tracking of multiple target types with a single neural extended Kalman filter

    Kathleen A. Kramer
    The neural extended Kalman filter is an adaptive state estimation routine that can be used in target-tracking systems to aid in the tracking through maneuvers without prior knowledge of the targets' dynamics. Within the neural extended Kalman filter, a neural network is trained using a Kalman filter training paradigm that is driven by the same residual as the state estimator. The difference between the a priori model used in the prediction steps of the estimator and the actual target dynamics is approximated. An important benefit of the technique is its versatility because little if any a priori knowledge of the target dynamics is needed. This allows the technique to be used in a generic tracking system that will encounter various classes of targets. In this paper, the neural extended Kalman filter is applied simultaneously to three separate classes of targets, each with different maneuver capabilities. The results show that the approach is well suited for use within a tracking system with multiple possible or unknown target characteristics. © 2010 Wiley Periodicals, Inc. [source]

    Design of the fuzzy multiobjective controller based on the eligibility method

    Hwan-Chun Myung
    A multiobjective control problem has been handled in many different ways such as fuzzy, neural network and reinforcement learning, etc. Among them, a reinforcement learning method solves a multiobjective control problem without any prior knowledge. In this article, a new reinforcement learning method for a multiobjective control problem is proposed in consideration of its convergence. The proposed method, in which objective eligibility is considered for handling multirewards, reformulates a multiobjective control problem in a form of a reinforcement learning problem under non-Markov environment. Using a similar relation to eligibility, the proposed method dealt with the previous research results of eligibility and was implemented with the concept of a decoupled fuzzy sliding mode control (DFSMC). © 2003 Wiley Periodicals, Inc. [source]

    An adaptive load balancing scheme for web servers

    Dr. James Aweya
    This paper describes an overload control scheme for web servers which integrates admission control and load balancing. The admission control mechanism adaptively determines the client request acceptance rate to meet the web servers' performance requirements while the load balancing or client request distribution mechanism determines the fraction of requests to be assigned to each web server. The scheme requires no prior knowledge of the relative speeds of the web servers, nor the work required to process each incoming request. Copyright © 2002 John Wiley & Sons, Ltd. [source]

    Observer-based adaptive robust control of a class of nonlinear systems with dynamic uncertainties,

    Bin Yao
    Abstract In this paper, a discontinuous projection-based adaptive robust control (ARC) scheme is constructed for a class of nonlinear systems in an extended semi-strict feedback form by incorporating a nonlinear observer and a dynamic normalization signal. The form allows for parametric uncertainties, uncertain nonlinearities, and dynamic uncertainties. The unmeasured states associated with the dynamic uncertainties are assumed to enter the system equations in an affine fashion. A novel nonlinear observer is first constructed to estimate the unmeasured states for a less conservative design. Estimation errors of dynamic uncertainties, as well as other model uncertainties, are dealt with effectively via certain robust feedback control terms for a guaranteed robust performance. In contrast with existing conservative robust adaptive control schemes, the proposed ARC method makes full use of the available structural information on the unmeasured state dynamics and the prior knowledge on the bounds of parameter variations for high performance. The resulting ARC controller achieves a prescribed output tracking transient performance and final tracking accuracy in the sense that the upper bound on the absolute value of the output tracking error over entire time-history is given and related to certain controller design parameters in a known form. Furthermore, in the absence of uncertain nonlinearities, asymptotic output tracking is also achieved. Copyright © 2001 John Wiley & Sons, Ltd. [source]

    Earnings Surprise "Materiality" as Measured by Stock Returns

    William Kinney
    Ranked earnings surprise portfolios formed from First Call files for 1992,97 are used to assess the annual earnings surprise magnitude for an individual firm sufficient to expect a "significant market reaction." We find that, for an individual firm, the maximum probability of a gain from trading on prior knowledge of any surprise magnitude is .622. The lack of probable trading gains is due to the S,shaped surprise/return relation and the large variance of returns for a given magnitude of surprise. In turn, we find that the S,shape is related empirically to the dispersion of analyst forecasts. Thus, factors underlying dispersion differences are related to the importance or "materiality" of earnings surprise as measured by stock returns and explain at least part of the S,shaped surprise/return relation. [source]

    How Should Clinicians Describe Hospice to Patients and Families?

    David J. Casarett MD
    Objectives: To describe hospice enrollment from the perspective of bereaved family members and to identify information about hospice that would encourage patients and families to enroll sooner. Design: Cross-sectional interviews. Setting: Three Medicare-certified hospice organizations. Participants: One hundred family members of 100 patients who died in hospice. Measurements: Semistructured interviews assessed prior knowledge of hospice, patients' and physicians' involvement in the enrollment process, features of hospice that motivated enrollment, and features that patients and families wished they had learned about sooner. Results: Almost all family members (n=92) and patients (n=71) knew about hospice before the patient's illness. Almost half the patients (n=44) were not involved at all in the hospice enrollment decision. The patient's physician (n=51) or the patient or family (n=34) initiated most hospice discussions, but patients and families usually obtained information about hospice from a hospice representative (n=75) rather than from the patient's physician (n=22). Family members identified several kinds of information about hospice that were particularly helpful in deciding whether to enroll and described several aspects of hospice that they wished they had known about sooner. Conclusion: Many patients and families learn about hospice from someone other than the patient's physician, and most learn about valuable hospice features and services only after enrollment. By providing more information about hospice earlier in the illness course, clinicians may be able to facilitate more-informed and more-timely decisions about hospice enrollment. [source]

    FBR: a robust method to determine the basis matrix of the Bravais lattice from oscillation images

    Klaus Döhring
    The FBR (Fourier basis reconstruction) method described in this paper has been designed to determine the basis matrix of the Bravais lattice with respect to the laboratory frame of reference and without prior knowledge of cell constants, particularly for protein crystals of comparatively low quality. It is based on Fourier analysis of a three-dimensional intensity distribution in reciprocal space, which is directly obtained from observed intensity distributions, provided that they are recorded by the rotation method using a fixed X-ray wavelength, resulting in a direct-space determination of the basis vectors. After a description of the motivation and theory behind the method, it is tested by application to numerically generated images of a virtual sample crystal and to experimental data of a lysozyme crystal with well known cell constants. Finally, FBR is applied to a set of images of bacteriorhodopsin crystals suffering from strong anisotropic spot broadening; this case provided the original motivation for the present work. [source]