Distribution by Scientific Domains
Distribution within Engineering

Terms modified by Nonlinear

  • nonlinear absorption
  • nonlinear analysis
  • nonlinear association
  • nonlinear behavior
  • nonlinear behaviour
  • nonlinear characteristic
  • nonlinear component
  • nonlinear continuous-time system
  • nonlinear control
  • nonlinear control system
  • nonlinear controller
  • nonlinear coupling
  • nonlinear dependence
  • nonlinear differential equation
  • nonlinear discrete-time system
  • nonlinear disturbance
  • nonlinear dynamic model
  • nonlinear dynamic models
  • nonlinear dynamic system
  • nonlinear dynamics
  • nonlinear effects
  • nonlinear equation
  • nonlinear fashion
  • nonlinear function
  • nonlinear h
  • nonlinear increase
  • nonlinear interaction
  • nonlinear manner
  • nonlinear mixed effects modelling
  • nonlinear mixed-effect model
  • nonlinear model
  • nonlinear modeling
  • nonlinear models
  • nonlinear nature
  • nonlinear optical
  • nonlinear optical activity
  • nonlinear optical crystal
  • nonlinear optical property
  • nonlinear optical response
  • nonlinear optics
  • nonlinear optimal control problem
  • nonlinear ordinary differential equation
  • nonlinear parameter
  • nonlinear partial differential equation
  • nonlinear perturbation
  • nonlinear phase shift
  • nonlinear plant
  • nonlinear predictive control
  • nonlinear problem
  • nonlinear process
  • nonlinear programming
  • nonlinear programming problem
  • nonlinear reaction
  • nonlinear refractive index
  • nonlinear regime
  • nonlinear regression
  • nonlinear regression analysis
  • nonlinear relation
  • nonlinear relationship
  • nonlinear relationships
  • nonlinear response
  • nonlinear schrödinger equation
  • nonlinear seismic response
  • nonlinear selection
  • nonlinear simulation
  • nonlinear source
  • nonlinear static analysis
  • nonlinear structure
  • nonlinear system
  • nonlinear term
  • nonlinear theory
  • nonlinear time series
  • nonlinear transformation
  • nonlinear uncertain system
  • nonlinear uncertainty
  • nonlinear wave
  • nonlinear wave equation

  • Selected Abstracts

    Nonlinear balanced model residualization via neural networks

    AICHE JOURNAL, Issue 6 2002
    Juergen Hahn
    First page of article [source]

    Synthesis and nonlinear optical properties of methacrylate polymers based on 2-[4-(N -methyl,N -hydroxyethylamino)phenylazo]-phenyl-6-nitrobenzoxazole chromophore

    Paola Persico
    Abstract Methacrylate polymers containing different molar contents of nonlinear optical (NLO) active molecular segments based on 2-[4-(N -methyl,N -hydroxyethylamino)phenylazo]-phenyl-6-nitrobenzoxazole chromophores were synthesized, and their phase behavior and second-order NLO properties were investigated. Polymers containing 6,17 mol % chromophore segments allowed the preparation of amorphous and optically clear thin films. Some mesomorphic structuration was exhibited by a polymer with 33 mol % chromophoric units. However, this feature did not prevent the possibility of investigating the NLO properties. Nonlinear resonance-enhanced d33 coefficients were determined by second harmonic generation experiments on spin-coated, corona-poled thin films at , = 1064 nm. Values ranging from 40 to 60 pm/V were measured with increasing chromophore molar contents. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1841,1847, 2003 [source]

    Nonlinear ,(3) -lasing in the tetragonal RbH2PO4 crystal

    LASER PHYSICS LETTERS, Issue 12 2007
    A.A. Kaminskii
    Abstract Raman-induced Stokes and anti-Stokes generation in RbH2PO4 crystal with nanosecond pumping has been observed. All recorded nonlinear-laser wavelengths in the visible and near-IR regions are identified and attributed to the ,(3) -promoting vibration mode of this tetragonal acentric phosphate. (© 2007 by Astro Ltd., Published exclusively by WILEY-VCH Verlag GmbH & Co. KGaA) [source]

    Computer programs for estimating substrate flux into steady-state biofilms from pseudoanalytical solutions

    Chetan T. Goudar
    Abstract Fixed-film processes employing microorganisms attached to an inert surface (biofilms) are widely used for biological treatment of municipal and industrial wastewater. For optimal design and analysis of these processes, mathematical models are necessary that describe the dynamics of contaminant transport within these biofilms and the associated contaminant utilization by the microorganisms. However, these governing equations that typically involve Fickian diffusion for contaminant transport and Monod kinetics for contaminant utilization are inherently nonlinear and have no closed form solutions except under special conditions. This can restrict their use in the classroom as cumbersome numerical techniques must be used for their solution. This problem is well documented in the literature and several authors have presented pseudoanalytical solutions that replace numerical solutions with algebraic equations. In the present study, we present pseudoanalytical solution-based computer programs for estimating substrate flux and biofilm thickness for a steady-state biofilm. Depending upon the intended end use, these programs can either partially or totally automate the solution process. In the partial automation mode, they can serve to enhance student understanding of important concepts related to steady-state biofilms, while complete automation can help bring more challenging and realistic problems associated with steady-state biofilms into the classroom. The programs have been tested on MATLAB version 5.0 and are available as freeware for educational purposes. © 2002 Wiley Periodicals, Inc. Comput Appl Eng Educ 10: 26,32, 2002; Published online in Wiley InterScience (; DOI 10.1002/cae.10017 [source]

    User-Controllable Color Transfer

    Xiaobo An
    This paper presents an image editing framework where users use reference images to indicate desired color edits. In our approach, users specify pairs of strokes to indicate corresponding regions in both the original and the reference image that should have the same color "style". Within each stroke pair, a nonlinear constrained parametric transfer model is used to transfer the reference colors to the original. We estimate the model parameters by matching color distributions, under constraints that ensure no visual artifacts are present in the transfer result. To perform transfer on the whole image, we employ optimization methods to propagate the model parameters defined at each stroke location to spatially-close regions of similar appearance. This stroke-based formulation requires minimal user effort while retaining the high degree of user control necessary to allow artistic interpretations. We demonstrate our approach by performing color transfer on a number of image pairs varying in content and style, and show that our algorithm outperforms state-of-the-art color transfer methods on both user-controllability and visual qualities of the transfer results. [source]

    Near-Term Travel Speed Prediction Utilizing Hilbert,Huang Transform

    Khaled Hamad
    In this study, we propose an innovative methodology for such prediction. Because of the inherently direct derivation of travel time from speed data, the study was limited to the use of speed only as a single predictor. The proposed method is a hybrid one that combines the use of the empirical mode decomposition (EMD) and a multilayer feedforward neural network with backpropagation. The EMD is the key part of the Hilbert,Huang transform, which is a newly developed method at NASA for the analysis of nonstationary, nonlinear time series. The rationale for using the EMD is that because of the highly nonlinear and nonstationary nature of link speed series, by decomposing the time series into its basic components, more accurate forecasts would be obtained. We demonstrated the effectiveness of the proposed method by applying it to real-life loop detector data obtained from I-66 in Fairfax, Virginia. The prediction performance of the proposed method was found to be superior to previous forecasting techniques. Rigorous testing of the distribution of prediction errors revealed that the model produced unbiased predictions of speeds. The superiority of the proposed model was also verified during peak periods, midday, and night. In general, the method was accurate, computationally efficient, easy to implement in a field environment, and applicable to forecasting other traffic parameters. [source]


    CRIMINOLOGY, Issue 4 2003
    Sociologists and criminologists have become increasingly concerned with nonlinear relationships and interaction effects. For example, some recent studies suggest that the positive relationship between neighborhood disadvantage and violent crime is nonlinear with an accelerating slope, whereas other research indicates a nonlinear decelerating slope. The present paper considers the possibility that this inconsistency in findings is partially caused by lack of attention to an important methodological concern. Specifically, we argue that researchers have not been sensitive to the ways in which logarithmic transformation of the dependent variable can bias tests for nonlinearity and statistical interaction. We illustrate this point using demographic and violent crime data for urban neighborhoods, and we propose an alternative procedure to log transformation that involves the use of weighted least-squares regression, heteroscedasticity consistent standard errors, and diagnostics for influential observations. [source]

    Causal mapping as a tool to mechanistically interpret phenomena in cell motility: Application to cortical oscillations in spreading cells

    CYTOSKELETON, Issue 9 2006
    Gabriel E. Weinreb
    Abstract Biological processes that occur at the cellular level and consist of large numbers of interacting elements are highly nonlinear and generally involve multiple time and spatial scales. The quantitative description of these complex systems is of great importance but presents large challenges. We outline a new systems biology approach, causal mapping (CMAP), which is a coarse-grained biological network tool that permits description of causal interactions between the elements of the network and overall system dynamics. On one hand, the CMAP is an intermediate between experiments and physical modeling, describing major requisite elements, their interactions and paths of causality propagation. On the other hand, the CMAP is an independent tool to explore the hierarchical organization of cell and the role of uncertainties in the system. It appears to be a promising easy-to-use technique for cell biologists to systematically probe verbally formulated qualitative hypotheses. We apply the CMAP to study the phenomenon of contractility oscillations in spreading cells in which microtubules have been depolymerized. The precise mechanism by which these oscillations are governed by a complex mechano-chemical system is not known but the data observed in experiments can be described by a CMAP. The CMAP suggests that the source of the oscillations results from the opposing effects of Rho activation leading to a decreased level of myosin light chain phosphatase and a cyclic calcium influx caused by increased membrane tension and leading to a periodically enhanced activation of myosin light chain kinase. Cell Motil. Cytoskeleton 2006. © 2006 Wiley-Liss, Inc. [source]

    An electro-optic monitor of the behavior of Chlamydomonas reinhardtii cilia

    CYTOSKELETON, Issue 2 2005
    Keith Josef
    Abstract The unicellular green alga Chlamydomonas reinhardtii steers through water with a pair of cilia (eukaryotic flagella). Long-term observation of the beating of its cilia with controlled stimulation is improving our understanding of how a cell responds to sensory inputs. Here we describe how to record ciliary motion continuously for long periods. We also report experiments on the network of intracellular signaling that connects the environment inputs with response outputs. Local spatial changes in ciliary response on the time scale of the underlying biochemical dynamics are observed. Near-infrared light monitors the cells held by a micropipette. This condition is tolerated well for hours, not interfering with ciliary beating or sensory transduction. A computer integrates the light stimulation of the eye of Chlamydomonas with the ciliary motion making possible long-term correlations. Measures of ciliary responses include the beating frequency, stroke velocity, and stroke duration of each cilium, and the relative phase of the cis and trans cilia. The stationarity and dependence of the system on light intensity was investigated. About 150,000,000 total beat cycles and up to 8 h on one cell have been recorded. Each beat cycle is resolved so that each asynchronous beat is detected. Responses extend only a few hundred milliseconds, but there is a persistence of momentary changes that last much longer. Interestingly, we see a response that is linear with absolute light intensity as well as different kinds of response that are clearly nonlinear, implying two signaling pathways from the cell body to the cilia. Cell Motil. Cytoskeleton 61:83,96, 2005. © 2005 Wiley-Liss, Inc. [source]

    Nonlinear epigenetic variance: review and simulations

    Kees-Jan Kan
    We present a review of empirical evidence that suggests that a substantial portion of phenotypic variance is due to nonlinear (epigenetic) processes during ontogenesis. The role of such processes as a source of phenotypic variance in human behaviour genetic studies is not fully appreciated. In addition to our review, we present simulation studies of nonlinear epigenetic variance using a computational model of neuronal network development. In each simulation study, time series for monozygotic and dizygotic twins were generated and analysed using conventional behaviour genetic modelling. In the results of these analyses, the nonlinear epigenetic variance was subsumed under the non-shared environmental component. As is commonly found in behaviour genetic studies, observed heritabilities and unique environmentabilities increased with time, whereas common environmentabilities decreased. The fact that the phenotypic effects of nonlinear epigenetic processes appear as unsystematic variance in conventional twin analyses complicates the identification and quantification of the ultimate genetic and environmental causes of individual differences. We believe that nonlinear dynamical system theories provide a challenging perspective on the development of individual differences, which may enrich behaviour genetic studies. [source]

    Dynamic systems with high damping rubber: Nonlinear behaviour and linear approximation

    Andrea Dall'Asta
    Abstract High damping rubber (HDR) shows a quite complex constitutive behaviour, which is nonlinear with respect to strain and is dependent on the strain rate. In addition, it exhibits a transient response during which the material properties change (scragging or more generally the Mullins effect). A number of recent works were dedicated to analysing and modelling material behaviour. This paper studies the nonlinear dynamics of systems with restoring force produced by HDR-based devices in order to propose a procedure to define equivalent linear models considering both transient and stationary behaviours. The reliability of these linear models is tested by evaluating the upper and lower bounds of the seismic response of a structural system equipped with HDR-based devices (structural system with dissipative bracings and isolated systems). Copyright © 2008 John Wiley & Sons, Ltd. [source]

    Use of collision shear walls to minimize seismic separation and to protect adjacent buildings from collapse due to earthquake-induced pounding

    S. A. Anagnostopoulos
    Abstract The use of collision shear walls (bumper-type), acting transversely to the side subject to pounding, as a measure to minimize damage of reinforced concrete buildings in contact, is investigated using 5-story building models. The buildings were designed according to the Greek anti-seismic and reinforced concrete design codes. Owing to story height differences potential pounding in case of an earthquake will occur between floor slabs, a case specifically chosen because this is when pounding can turn out to be catastrophic. The investigation is carried out using nonlinear dynamic analyses for a real earthquake motion and also a simplified solution for a triangular dynamic force of short duration, comparable to the forces caused by pounding. For such analyses, nonlinear, prismatic beam,column elements are used and the effects of pounding are expressed in terms of changes in rotational ductility factors of the building elements. The local effects of pounding on the collision shear walls are investigated using a detailed nonlinear finite element model of the shear walls and results are expressed in terms of induced stresses. It is found that pounding will cause instantaneous acceleration pulses in the colliding buildings and will somewhat increase ductility demands in the members of the top floor, but all within tolerable limits. At the same time the collision walls will suffer repairable local damage at the points of contact, but will effectively protect both buildings from collapse, which could occur if columns were in the place of the walls. Copyright © 2008 John Wiley & Sons, Ltd. [source]

    Sensitivity analysis of transient population dynamics

    ECOLOGY LETTERS, Issue 1 2007
    Hal Caswell
    Abstract Short-term, transient population dynamics can differ in important ways from long-term asymptotic dynamics. Just as perturbation analysis (sensitivity and elasticity) of the asymptotic growth rate reveals the effects of the vital rates on long-term growth, the perturbation analysis of transient dynamics can reveal the determinants of short-term patterns. In this article, I present a completely new approach to transient sensitivity and elasticity analysis, using methods from matrix calculus. Unlike previous methods, this approach applies not only to linear time-invariant models but also to time-varying, subsidized, stochastic, nonlinear and spatial models. It is computationally simple, and does not require calculation of eigenvalues or eigenvectors. The method is presented along with applications to plant and animal populations. [source]

    Symbolic dynamics for identifying similarity between rhythms of ecological time series

    ECOLOGY LETTERS, Issue 9 2004
    Bernard Cazelles
    Abstract Explaining the associations between animal populations or between population and environmental signals is an important challenge. The time series that quantify animal populations are often complex, nonlinear, noisy and non-stationary. These characteristics may make it inappropriate to use traditional techniques when analysing these time series and their mutual dependencies. Here I propose to use symbolic dynamics and techniques from Information Theory to evaluate the degree of dynamic cohesion between time series fluctuations. The main idea is to check whether two (or more) signals tend to oscillate simultaneously, rising and falling together with the same rhythm. Based on synthetic and real time series, I demonstrate that this method is robust to the presence of noise and to the short length of the analysed time series and gives relevant information about the weak relationships between different series. Furthermore, this method appears as simple as classical cross-correlation and outperforms it in the analysed examples. [source]

    Estimation of Nonlinear Models with Measurement Error

    ECONOMETRICA, Issue 1 2004
    Susanne M. Schennach
    This paper presents a solution to an important econometric problem, namely the root n consistent estimation of nonlinear models with measurement errors in the explanatory variables, when one repeated observation of each mismeasured regressor is available. While a root n consistent estimator has been derived for polynomial specifications (see Hausman, Ichimura, Newey, and Powell (1991)), such an estimator for general nonlinear specifications has so far not been available. Using the additional information provided by the repeated observation, the suggested estimator separates the measurement error from the "true" value of the regressors thanks to a useful property of the Fourier transform: The Fourier transform converts the integral equations that relate the distribution of the unobserved "true" variables to the observed variables measured with error into algebraic equations. The solution to these equations yields enough information to identify arbitrary moments of the "true," unobserved variables. The value of these moments can then be used to construct any estimator that can be written in terms of moments, including traditional linear and nonlinear least squares estimators, or general extremum estimators. The proposed estimator is shown to admit a representation in terms of an influence function, thus establishing its root n consistency and asymptotic normality. Monte Carlo evidence and an application to Engel curve estimation illustrate the usefulness of this new approach. [source]

    A Parametric Approach to Flexible Nonlinear Inference

    ECONOMETRICA, Issue 3 2001
    James D. Hamilton
    This paper proposes a new framework for determining whether a given relationship is nonlinear, what the nonlinearity looks like, and whether it is adequately described by a particular parametric model. The paper studies a regression or forecasting model of the form yt=,(xt)+,t where the functional form of ,(,) is unknown. We propose viewing ,(,) itself as the outcome of a random process. The paper introduces a new stationary random field m(,) that generalizes finite-differenced Brownian motion to a vector field and whose realizations could represent a broad class of possible forms for ,(,). We view the parameters that characterize the relation between a given realization of m(,) and the particular value of ,(,) for a given sample as population parameters to be estimated by maximum likelihood or Bayesian methods. We show that the resulting inference about the functional relation also yields consistent estimates for a broad class of deterministic functions ,(,). The paper further develops a new test of the null hypothesis of linearity based on the Lagrange multiplier principle and small-sample confidence intervals based on numerical Bayesian methods. An empirical application suggests that properly accounting for the nonlinearity of the inflation-unemployment trade-off may explain the previously reported uneven empirical success of the Phillips Curve. [source]

    Credibility, Irreversibility of Investment, and Liberalization Reforms in LDCs

    ECONOMIC NOTES, Issue 2 2006
    Andrea Bassanini
    Empirical evidence of the impact of policy uncertainty on aggregate investment is mixed. However, if the relationship between policy uncertainty and investment performance is nonlinear, linear regression exercises might not capture the effect of policy uncertainty. In this paper, I present a simple model with investment irreversibility which shows that, in the presence of legal constraints on investment in foreign assets, domestic real investment performance is poorer when liberalization reforms are only partially incredible. [source]

    Smooth Transition Models and Arbitrage Consistency

    ECONOMICA, Issue 287 2005
    David A. Peel
    Slow adjustment of real exchange rate towards equilibrium in linear models has long puzzled researchers, stimulating the adoption of nonlinear models. The exponential smooth transition model has been particularly successful, providing faster adjustment speeds. This paper discusses some of its theoretical limitations, for example that expectations are adaptive. We propose a new nonlinear model conceptually superior to the ESTAR model since it is consistent with rational expectations. One of its advantages is that it can be solved and estimated by nonlinear least squares. Using monthly post-1973 real exchange rate data, we show that the model implies even faster speeds of adjustment. [source]

    Modelling Monetary Policy: Inflation Targeting in Practice

    ECONOMICA, Issue 282 2004
    Christopher Martin
    This paper estimates a simple structural model of monetary policy in the UK focusing on the policy of inflation targeting introduced in 1992. We find that: (i) the adoption of inflation targeting led to significant changes in monetary policy; (ii) post-1992 monetary policy is asymmetric as policy-makers respond more to upward deviation of inflation away from the target; (iii) post-1992 policy-makers may be attempting to keep inflation within the 1.4%,2.6% range rather than pursuing a point target of 2.5% and (iv) the response of monetary policy to inflation is nonlinear as interest rates respond more when inflation is further from the target. [source]

    New structures of vector control systems for permanent magnet synchronous motors with core loss

    Shinji Shinnaka
    Abstract This paper investigates and proposes new system structures for vector control of permanent-magnet synchronous motors (PMSMs) with core loss. The proposed vector control systems have the following versatile features. (a) The systems employ the structures allowing control of the stator current through control of the load current. (b) The systems employ unique "stator voltage feedback-use" structures in order to accomplish simply the load current control. (c) The produced torque is directly related to the load current, and the precise torque control can be attained through the load current control. (d) The relation between produced torque and the load current is nonlinear for salient-pole PMSMs similar to the case of no core loss, and a variety of the load current commands can be selected from viewpoints of minimum loss and/or wide speed range drives. The system structures add no constraint to the selection of the load current commands. (e) In addition to the torque control, the speed control can be allowed, where linearity between output of the speed controller and produced torque is kept. The validity of versatile features is verified through the numerical experiments. © 2009 Wiley Periodicals, Inc. Electr Eng Jpn, 170(3): 28,39, 2010; Published online in Wiley InterScience (www.interscience. DOI 10.1002/eej.20910 [source]

    Development of a high-speed electromagnetic repulsion mechanism for high-voltage vacuum circuit breakers

    Mitsuru Tsukima
    Abstract This paper presents a design and testing of a new high-speed electromagnetic driving mechanism for a high-voltage vacuum circuit breaker (VCB). This mechanism is based on a high-speed electromagnetic repulsion and a permanent magnet spring (PMS). This PMS is introduced instead of the conventional disk spring due to its low spring energy and more suitable force characteristics for VCB application. The PMS has been optimally designed by the 3D nonlinear finite-elements magnetic field analysis and investigated its internal friction and eddy-current effect. Furthermore, we calculated the dynamic of this mechanism coupling with the electromagnetic field and circuit analysis, in order to satisfy the operating characteristics,contact velocity, response time, and so on, required for the high-speed VCB. A prototype VCB, which was built based on the above analysis, shows sufficient operating performance. Finally, the short circuit interruption tests were carried out with this prototype breaker, and we have been able to verify its satisfying performance. © 2008 Wiley Periodicals, Inc. Electr Eng Jpn, 163(1): 34,40, 2008; Published online in Wiley InterScience ( DOI 10.1002/eej.20398 [source]

    Capillary sieving electrophoresis and micellar electrokinetic capillary chromatography produce highly correlated separation of tryptic digests

    ELECTROPHORESIS, Issue 14 2010
    Jane A. Dickerson
    Abstract We perform 2-D capillary electrophoresis on fluorescently labeled proteins and peptides. Capillary sieving electrophoresis (CSE) was performed in the first dimension and MEKC was performed in the second. A cellular homogenate was labeled with the fluorogenic reagent FQ and separated using the system. This homogenate generated a pair of ridges; the first had essentially constant migration time in the CSE dimension, while the second had essentially constant migration time in the MEKC dimension. In addition, a few spots were scattered through the electropherogram. The same homogenate was digested using trypsin, and then labeled and subjected to the 2-D separation. In this case, the two ridges observed from the original 2-D separation disappeared and were replaced by a set of spots that fell along the diagonal. Those spots were identified using a local-maximum algorithm and each was fit using a 2-D Gaussian surface by an unsupervised nonlinear least squares regression algorithm. The migration times of the tryptic digest components were highly correlated (r=0.862). When the slowest migrating components were eliminated from the analysis, the correlation coefficient improved to r=0.956. [source]

    Combined use of chiral ionic liquid and CD for MEKC: Part II.

    ELECTROPHORESIS, Issue 16 2009
    Determination of binding constants
    Abstract A competitive inhibition mechanism is proposed to investigate the interactions among 2,3,6-tri- O -methyl-,-CD (TM-,-CD), cationic ionic liquid type surfactants, N -undecenoxy-carbonyl- L -leucinol bromide (L -UCLB) and profens using affinity CE. The apparent binding constant of TM-,-CD to L -UCLB was estimated by nonlinear and linear plotting methods. The binding constants of one representative profen (e.g. fenoprofen) to TM-,-CD and L -UCLB were estimated by a secondary plotting approach. The R - and S -fenoprofens have different binding constant values, resulting in the enantioseparation due to the synergistic effect of the two chiral selectors, TM-,-CD and L -UCLB. [source]

    Characterization of voltage degradation in dynamic field gradient focusing

    ELECTROPHORESIS, Issue 5 2008
    Jeffrey M. Burke
    Abstract Dynamic field gradient focusing (DFGF) is an equilibrium gradient method that utilizes an electric field gradient to simultaneously separate and concentrate charged analytes based on their individual electrophoretic mobilities. This work describes the use of a 2-D nonlinear, numerical simulation to examine the impact of voltage loss from the electrodes to the separation channel, termed voltage degradation, and distortions in the electric field on the performance of DFGF. One of the design parameters that has a large impact on the degree of voltage degradation is the placement of the electrodes in relation to the separation channel. The simulation shows that a distance of about 3,mm from the electrodes to the separation channel gives the electric field profile with least amount of voltage degradation. The simulation was also used to describe the elution of focused protein peaks. The simulation shows that elution under constant electric field gradient gives better performance than elution through shallowing of the electric field. Qualitative agreement between the numerical simulation and experimental results is shown. The simulation also illustrates that the presence of a defocusing region at the cathodic end of the separation channel causes peak dispersion during elution. The numerical model is then used to design a system that does not suffer from a defocusing region. Peaks eluted under this design experienced no band broadening in our simulations. Preliminary experimental results using the redesigned chamber are shown. [source]

    Kinetics of cadmium accumulation in periphyton under freshwater conditions,

    Philippe Bradac
    Abstract The aim of the present study was to investigate the kinetics of cadmium (Cd) accumulation (total and intracellular) in periphyton under freshwater conditions in a short-term microcosm experiment. Periphyton was precolonized in artificial flow-through channels supplied with natural freshwater and then exposed for 26.4 h to nominal Cd concentrations of 5 and 20 nM added to natural freshwater. Labile Cd in water determined with diffusion gradient in thin films was 60 to 69% of total dissolved Cd in the exposure channels and 11% in the control channel. Intracellular Cd concentrations in periphyton increased rapidly and linearly during the first 71 min. Initial intracellular uptake rates were 0.05 and 0.18 nmol of Cd/g of dry weight × min in the 5 nM and 20 nM exposures, respectively. The subsequent intracellular uptake was slower, approaching steady state at the end of Cd exposure. Uptake kinetics of Cd was slower when compared to experiments with planktonic algal cultures, probably due to diffusion limitations. Intracellular Cd uptake during the entire exposure was modeled with a nonlinear, one-compartment model from which uptake and clearance rate constants, as well as bioconcentration factors, were obtained. The release of Cd from periphyton after the end of Cd exposure was slow when compared to the initial uptake rates. [source]

    Bilinear estimation of pollution source profiles and amounts by using multivariate receptor models

    ENVIRONMETRICS, Issue 7 2002
    Eun Sug Park
    Abstract Multivariate receptor models aim to identify the pollution sources based on multivariate air pollution data. This article is concerned with estimation of the source profiles (pollution recipes) and their contributions (amounts of pollution). The estimation procedures are based on constrained nonlinear least squares methods with the constraints given by nonnegativity and identifiability conditions of the model parameters. We investigate several identifiability conditions that are appropriate in the context of receptor models, and also present new sets of identifiability conditions, which are often reasonable in practice when the other traditional identifiability conditions fail. The resulting estimators are consistent under appropriate identifiability conditions, and standard errors for the estimators are also provided. Simulation and application to real air pollution data illustrate the results. Copyright © 2002 John Wiley & Sons, Ltd. [source]


    EVOLUTION, Issue 7 2008
    Leonardo D. Bacigalupe
    Sexual selection requires social interactions, particularly between the sexes. When trait expression is influenced by social interactions, such traits are called interacting phenotypes and only recently have the evolutionary consequences of interacting phenotypes been considered. Here we investigated how variation in relative fitness, or the opportunity for sexual selection, affected the evolutionary trajectories of interacting phenotypes. We used experimentally evolved populations of the naturally promiscuous Drosophila pseudoobscura, in which the numbers of potential interactions between the sexes, and therefore relative fitness, were manipulated by altering natural levels of female promiscuity. We considered two different mating interactions between the sexes: mating speed and copulation duration. We investigated the evolutionary trajectories of means and (co)variances (P) and also the influence of genetic drift on the evolutionary response of these interactions. Our sexual selection treatments did not affect the means of either mating speed or copulation duration, but they did affect P. We found that the means of both traits differed among replicates within each selection treatment whereas the Ps did not. Changes as a consequence of genetic drift were excluded. Our results show that although variable potential strengths of sexual interactions influence the evolution of interacting phenotypes, the influence may be nonlinear. [source]


    EVOLUTION, Issue 12 2006
    Josh Van Buskirk
    Abstract Inbreeding is known to reduce heterozygosity of neutral genetic markers, but its impact on quantitative genetic variation is debated. Theory predicts a linear decline in additive genetic variance (VA) with increasing inbreeding coefficient (F) when loci underlying the trait act additively, but a nonlinear hump-shaped relationship when dominance and epistasis are important. Predictions for heritability (h2) are similar, although the exact shape depends on the value of h2 in the absence of inbreeding. We located 22 published studies in which the level of genetic variation in [source]

    Lessons from the past: the collapse of Jamaican coral reefs

    FISH AND FISHERIES, Issue 2 2009
    Marah J. Hardt
    Abstract Since Pre-Columbian times, humans have exploited Jamaican marine ecosystems with significant consequences for flora and fauna. This study focuses on the history of reef fish exploitation in Jamaica, from first human occupation to the present day, to determine how past fishing activities contributed to subsequent declines in the coral reef ecosystem. The pattern of declining reef fish populations was nonlinear. Reef fish first declined in prehistoric times but then potentially recovered, following genocide of the native human population. Reduced fishing pressure lasted until the mid-19th century. At that time, depletion of reef fish populations again occurred with a precipitous decline from the 1850s to the 1940s. The final shift from relatively abundant to overfished marine fauna corresponded to subtle changes in fish trap design as well as development of recreational fishing. Government subsidies throughout the second half of the 20th century exacerbated the declines. This analysis shows that local artisanal fisheries with relatively low levels of effort and seemingly subtle shifts in technology can significantly impact the coral reef ecosystem and that declines occurred decades to centuries before modern ecological studies began. This research shows how historical analysis can be a powerful tool to minimize shifted baselines and establish realistic targets for recovery and sustainable management of marine ecosystems. [source]

    Towards effective Lagrangians for adelic strings

    Article first published online: 20 MAR 200, B. Dragovich
    Abstract p-Adic strings are important objects of string theory, as well as of p-adic mathematical physics and nonlocal cosmology. By a concept of adelic string one can unify and simultaneously study various aspects of ordinary and p-adic strings. By this way, one can consider adelic strings as a very useful instrument in the further investigation of modern string theory. It is remarkable that for some scalar p-adic strings exist effective Lagrangians, which are based on real instead of p-adic numbers and describe not only four-point scattering amplitudes but also all higher ones at the tree level. In this work, starting from p-adic Lagrangians, we consider some approaches to construction of effective field Lagrangians for p-adic sector of adelic strings. It yields Lagrangians for nonlinear and nonlocal scalar field theory, where spacetime nonlocality is determined by an infinite number of derivatives contained in the operator-valued Riemann zeta function. Owing to the Riemann zeta function in the dynamics of these scalar field theories, obtained Lagrangians are also interesting in themselves. [source]