Small Lag Research Articles

Angular acceleration estimation and feedback control: An experimental investigation

Angular acceleration estimation and its application in acceleration feedback control are investigated experimentally in the paper. In combination of Newton Predictor (NP) with Kalman Filter (KF), a new predictive estimator for angular acceleration, called Newton Predictor Enhanced Kalman Filter (NPEKF) is proposed. This estimator provides a wide bandwidth and a small phase lag of the estimated acceleration while attenuating noises. Based on the estimated acceleration an acceleration feedback control (AFC) is presented for multiple degree-of-freedom (DOF) mechatronic system. The design of AFC is specified in terms of its stability and ability in suppressing dynamic disturbances. Experiments are conducted on a 2-DOF direct-drive manipulator. The frequency responses of the acceleration estimated by NP, KF and NPEKF are compared with those of the measured acceleration via linear accelerometer. The performance of AFC using the estimated acceleration is assessed against that using the measured acceleration. This study has shown that the proposed NPEKF estimator is able to supply the AFC with reliable required acceleration.

The Matérn variogram model: Implications for uncertainty propagation and sampling in geostatistical surveys

The Matérn variogram model has been advocated because it is flexible and can represent varied behaviour at small lags. We show how the constraints on the spherical and exponential variogram at short lags ignore a possible source of uncertainty in the variogram and so in kriging surveys, that the Matérn model can describe. Matérn, spherical and exponential variogram models were fitted by maximum likelihood to a set of log 10(K) observations made on a regular grid at Broom's Barn Farm, Suffolk, England. The likelihood profiles of the Matérn parameter estimates were asymmetric. Thus the uncertainty of these estimates could only be adequately assessed by a Bayesian approach. The uncertainty of estimated parameters of the Matérn variogram was larger than for the exponential variogram. This is an indication that the assumption of an exponential model limits the behaviour that may be described by the variogram. Thus uncertainty analyses where an exponential variogram is assumed may underestimate the uncertainty of kriged estimates. Bayesian analysis of the kriged estimates of log 10(K) at Broom's Barn Farm using the Matérn variogram revealed an observable component of uncertainty due to variogram uncertainty. When an exponential variogram model was used, the estimate of this component of uncertainty was negligible. The Matérn variogram should therefore be used rather than the exponential model when assessing the adequacy of a variogram estimate. A method of designing sample schemes which is suitable for both estimating a Matérn variogram and interpolation is suggested.

Field statistics and correlation functions for stochastically growing waves

Bursty waves are common in laboratory and space plasmas. This paper simulates the generation of bursty waves using stochastic differential equations, calculating the field statistics and correlation functions with and without thermal effects, linear instability, nonlinear processes, intrinsic spatiotemporal inhomogeneities (clumps), and different sampling techniques. Driven thermal waves are shown to have field statistics that agree very well with an analytic prediction (typically power-law above a low field peak near the thermal level, but whose peak can be moved to high fields with appropriate fine tuning of parameters) and are robust against changes in sampling and inclusion of clumping effects. Purely stochastically growing waves, expected to have the log normal statistics observed in multiple applications, only do so under stringent conditions and inclusion of spatiotemporal clumping effects. These conditions have similar forms to ones derived previously using analytic arguments. Deviations from a log normal can be due to sampling and clumping effects, rather than due to the nonlinear and convolution effects inferred previously. Correlation functions are predicted and observed to have an exponential decrease at small lags, with time constant equal to the inverse effective growth rate, provided stochastic effects are relatively small and sufficient averaging is possible. Extraction of the wave, stochastic, and clump parameters from observed field statistics and correlation functions appears viable. An evolutionary transition must exist between driven thermal waves and stochastically driven waves, since their field statistics have different functional forms, dependencies, and sensitivity to clump effects, but still requires identification.

Tide-induced groundwater head fluctuation in coastal multi-layered aquifer systems with a submarine outlet-capping

This paper considered the tide-induced head fluctuations in two coastal multi-layered aquifer systems. Model I comprises two semi-permeable layers and a confined aquifer between them. Model II is a four-layered aquifer system including an unconfined aquifer, an upper semi-permeable layer, a confined aquifer and a lower semi-permeable layer. In each model, the submarine outlet of the confined aquifer is covered with a skin layer (“outlet-capping”). Analytical solutions of the two models are derived. In both models, leakages of the semi-permeable layers decrease the tidal head fluctuations. The outlet-capping reduces the aquifer’s head fluctuation by a constant factor and shifts the phase by a positive constant. The solution to Model II explains the inconsistency between the relatively small lag time and the strong amplitude damping effect of the tidal head fluctuations reported by Trefry and Johnston [Ground Water 1998;36:427–33] near the Port Adelaide River, Australia.

Estimating the adoption of Bt eggplant in India: Who Benefits from public–private partnership?

The study analyzes ex ante the adoption of insect-resistant Bt eggplant technology in India. Farmers’ willingness to pay (WTP) is estimated using the contingent valuation method. Given the economic importance of insect pests in eggplant cultivation, the average WTP for Bt hybrids is more than four times the current price of conventional hybrid seeds. Since the private innovating firm has also shared its technology with the public sector, proprietary hybrids will likely get competition through public open-pollinated Bt varieties after a small time lag. This will reduce farmers’ WTP for Bt hybrids by about 35%, thus decreasing the scope for corporate pricing policies. Nonetheless, ample private profit potential remains. Analysis of factors influencing farmers’ adoption decisions demonstrates that public Bt varieties will particularly improve technology access for resource-poor eggplant producers. The results suggest that public–private partnership can be beneficial for all parties involved.

Can fabric sensors monitor breast motion?

To establish whether conducting polymer-coated fabric sensors could be used to monitor breast motion, vertical breast motion of two large breasted women (C+ bra cup) was simultaneously monitored using an OPTO TRAK ® 3020 motion analysis system (200 Hz) and polymer-coated fabric sensors linked to a custom-made Bluetooth telemetry system (100 Hz) as the subjects walked and ran on a treadmill (7–10 km h −1). Sensor strain, change in resistance and vertical breast displacement relative to trunk movement were output for analysis. It was concluded that, although polymer-coated fabric sensors may exhibit a small response lag due to textile geometry changes, they were able to accurately and reliably represent changes in the amplitude of vertical breast displacement during treadmill gait.

Role of the Gouy Phase in the Coherent Phase Control of the Photoionization and Photodissociation of Vinyl Chloride

We demonstrate theoretically and experimentally that the Gouy phase of a focused laser beam may be used to control the photoinduced reactions of a polyatomic molecule. Quantum mechanical interference between one- and three-photon excitation of vinyl chloride produces a small phase lag between the dissociation and ionization channels on the axis of the molecular beam. Away from the axis, the Gouy phase introduces a much larger phase lag that agrees quantitatively with theory without any adjustable parameters.

A model-independent test for the presence of regulatory equilibrium and non-random structure in island species trajectories

Aims To test a key prevision of the dynamic equilibrium theory of island biogeography, namely that changes in species numbers on islands over time (hereafter, species trajectories) are equilibrial, and to characterize aspects of the dynamical properties of species change over time using a model-independent test. Methods We tested for regulatory equilibrium and non-random structure in species numbers through time by comparing observed correlation coefficients at lag-k for species trajectories from four true islands and two habitat islands. First, we estimated the shape of the autocorrelation function for each observed species trajectory by calculating correlation coefficients of the observed data between pairs of values Nt)k and Nt separated by lag-k (k ¼ 1, 2, …, N ) 1). Second, we tested the observed correlation coefficients at each lag against a distribution of correlation coefficients generated by randomly ordering observed numbers in the species trajectories. Results The patterns of autocorrelation functions for all but one of the observed species trajectories did not exhibit evidence of regulatory equilibrium, and, in fact, closely matched what would be expected from a non-stationary or ‘random walk’ process. The majority of the correlation coefficients generated from the observed species trajectories did not deviate significantly from correlation coefficients produced by the randomized trajectories. However, there was strong evidence of unusual positive autocorrelation at small time lags for birds on islands measured annually (2- to 4-year lags) and for arthropods on islands measured weekly (7- to 8-week lags), suggesting some degree of structure in change in species richness over time. Main conclusions The autocorrelation function patterns for all but one of the observed species trajectories showed various forms of non-stationarity. These types of patterns suggest that the numbers of species through time gradually wandered away from their initial sizes. Our model-independent test of individual correlation coefficients revealed significant structure in the observed species trajectories. These trajectories appear to be non-random at relatively short lag intervals, indicating a process with short memory.

Comparison of the solutions of a phase-lagging heat transport equation and damped wave equation with a heat source

In this article, we study the difference between the solutions of the phase-lagging equation (PLE), a new heat conduction equation, and the damped wave equation (DWE) with a heat source. The exact solution of the PLE is obtained using the Laplace transform method, and is approximated using an approximate analytical method when the time lag is small since the exact solution is practically not computable for the small time lag case. Results show that the DWE is a good approximation to the PLE when the time lag is small.

Spatial distributions of perchloroethylene reactive transport parameters in the Borden Aquifer

We determined the descriptive statistical and spatial geostatistical properties of the perchloroethene ln Kd and the ln k of a 1.5 m thick by 10 m horizontal transect of the Borden aquifer near the location of the Stanford‐Waterloo (SW) tracer experiment. The ln Kd distribution is not normal and is right skewed because of a few high values that occur localized in two regions of the transect. In contrast, the ln k data can be characterized by a normal distribution. A linear regression of ln Kd on ln k yields a statistically significant positive correlation, also shown at small lags in the cross correlogram. No significant vertical or horizontal trend in the ln Kd data was detected. The semivariogram ranges of ln k and ln Kd differ from one another in the vertical direction (0.33 ± 0.06 m and 0.20 ± 0.04 m, respectively) and are much less than the horizontal ranges (a few meters). Despite significant effort the horizontal range of ln Kd remains poorly characterized because of limitations of the sample locations. Many of the characteristics described above do not match those assumed in prior theoretical studies that examined the importance of various aquifer characteristics on SW tracer transport. We suggest that there is knowledge to be gained by revisiting the conclusions of these prior studies in light of the new information presented here.

Probing turbulence with infrared observations in OMC1

A statistical analysis is presented of the turbulent velocity structure in the Orion Molecular Cloud at scales ranging from 70 AU to AU. Results are based on IR Fabry-Perot interferometric observations of shock and photon-excited H2 in the K-band S(1) line at 2.121 μm and refer to the dynamical characteristics of warm perturbed gas. Data consist of a spatially resolved image with a measured velocity for each resolution limited region () in the image. The effect of removal of apparent large scale velocity gradients is discussed and the conclusion drawn that these apparent gradients represent part of the turbulent cascade and should remain within the data. Using our full data set, observations establish that the Larson size-linewidth relation is obeyed to the smallest scales studied here extending the range of validity of this relationship by nearly 2 orders of magnitude. The velocity probability distribution function (PDF) is constructed showing extended exponential wings, providing evidence of intermittency, further supported by the skewness (third moment) and kurtosis (fourth moment) of the velocity distribution. Variance and kurtosis of the PDF of velocity differences are constructed as a function of lag. The variance shows an approximate power law dependence on lag, with exponent significantly lower than the Kolmogorov value, and with deviations below 2000 AU which are attributed to outflows and possibly disk structures associated with low mass star formation within OMC1. The kurtosis shows strong deviation from a Gaussian velocity field, providing evidence of velocity correlations at small lags. Results agree accurately with semi-empirical simulations in Eggers & Wang (1998). In addition, 170 individual H2 emitting clumps have been analysed with sizes between 500 and 2200 AU. These show considerable diversity with regard to PDFs and variance functions (related to second order structure functions) displaying a variety of shapes of the PDF and different values of the scaling exponent within a restricted spatial region. However, a region associated with an outflow from a deeply embedded O-star shows high values of the scaling exponent of the variance function, representing a strong segregation of high and low exponent clumps. Our analysis constitutes the first characterization of the turbulent velocity field at the scale of star formation and provide a dataset which models of star-forming regions should aim to reproduce.

Interannual Variation of Freshwater in the Yellow and East China Seas: Roles of the Changjiang Discharge and Wind Forcing

The interannual variation of the behavior of Changjiang freshwater has been investigated using the Princeton Ocean Model (POM). Five experiments are described in this study. Three basic experiments (Exps. B1, B2 and B3) were performed to examine the freshwater behavior in response to annual variations of the Changjiang discharge in normal, wet and dry years, respectively. Thereafter, the freshwater variation was investigated with the model forced by primary-interannual variations of river discharge with an 8-year period (Exp. I1) and a wind field with a 3.6-year period (Exp. I2). In Exp. B1, the average residence time of freshwater is roughly estimated to be 681.4 days in the Yellow Sea (YS) and 353.4 days in the combined area of the East China Sea (ECS) and the Chinese Coast (CC). This difference is attributed to the current pattern in each region and freshwater exchange among the regions. The interannual variation of freshwater volume in Exp. I1 has a large amplitude and long phase lag in the YS (38 km3 and 1.6-year against primary-interannual discharge variation), while there are relatively small amplitudes and short phase lags in the ECS (18 km3 and 0.7-year) and the CC (14 km3 and 0.5-year). It is concluded that the difference in the freshwater behavior results from the difference in the average residence time in each region.

Fluviodeltaic response to sea level perturbations: Amplitude and timing of shoreline translation and coastal onlap

Alluvial river systems respond to changing sea level by adjusting channel length through shoreline translation and coastal onlap/offlap at the alluvial basement transition. The magnitude and timing of shoreline translation and coastal onlap/offlap relative to the driving sea level signal depend on the dynamics of the fluvial system and have important implications for interpreting ancient fluviodeltaic deposits. I obtain analytical solutions to a diffusive geometric model of fluviodeltaic response to sea level perturbations that treats the shoreline and alluvial basement transition as moving boundaries. Fluviodeltaic behavior is most sensitive to the ratio of the period of eustatic cycling to the fluvial response time, which varies with the length and water discharge of the fluvial system. The square root of this ratio provides a first‐order estimate of the fraction of the fluvial long profile affected by eustatic forcing. The fluviodeltaic system behaves as a low‐pass filter with respect to eustatic cycling: The amplitude of both shoreline translation and coastal onlap/offlap increase with increasing cycle period within a relatively narrow bandwidth in which the fluvial response time is comparable to the cycle period. Only small time lags develop between shoreline response and eustatic forcing. The time lag between maximum coastal onlap and maximum sea level increases without bound as the forcing period decreases relative to the fluvial response time. Model predictions agree with experimental data and differ considerably from the model predictions of Pitman (1978) and Angevine (1989), which suggest that fluviodeltaic systems are strong high‐pass filters to sea level cycling.

Fractional Brownian description of aggregate surfaces within undisturbed soil samples using penetration resistance measurements

Soil structure exerts a major influence on physical processes but its description is still a challenge for soil scientists. Methods commonly used to describe soil structure are based on soil fragmentation. Yet, for a more holistic approach of soil properties modeling, one should describe the variability of soil as found in situ. In this study, we applied a fractional Brownian model to penetration resistance measurements within undisturbed soil samples from two tillage systems, no-tillage (NT) and moldboard plow (MP). Semivariograms were estimated for 92 penetration resistance series for MP and 100 samples for NT. Surface fractal dimension ( D s) and crossover length ( l) were estimated from the slope and intercept of the log–log semivariograms plots at small lags. The mean ± 95% confidence intervals D s for both treatments were similar, averaging 1.65 ± 0.03 for MP and 1.64 ± 0.03 for NT. The geometric mean crossover lengths ( l) were, however, significantly different, with NT presenting higher value (5.9 ± 1.15 mm) compared to MP (2.9 ± 1.13 mm). Also, soil samples for NT presented significantly higher bulk density and geometric mean diameter (GMD) compared to MP treatment. Mean ± 95% confidence intervals GMD were 6.8 ± 0.30 and 10.8 ± 0.40 mm for MP and NT treatments, respectively. At the same time, organic matter content and water content at a fixed head were not significantly different between treatments and should not influence the penetration resistance results in this study. Higher values of log e( l) indicate that NT penetrometer series presented a rougher surface compared to MP, suggesting component microaggregate coalescence within the year following tillage. The use of fractal analysis of penetration resistance series appears to be a useful tool to describe aggregate surfaces in an undisturbed soil sample.

THE INFLUENCE OF PRE-CULTURAL CONDITIONS ON THE INDIVIDUAL CELL LAG PHASE AND GENERATION TIME OF LISTERIA MONOCYTOGENES

In this study, we assessed the impact of pre-cultural temperature and pH on the lag phase of individual Listeria monocytogenes cells at 7 degrees C. In a first step, the pre-cultural temperature effect (37, 15, 10, 7, 4 and 2 degrees C) was investigated on a subsequent growth at 7 degrees C and pH 7.4. In a second step, low pre-cultural temperatures (10, 7 and 4 degrees C) were combined with a controlled pH at 7.4 and 5.7 with a subsequent growth at 7 degrees C and different pH values (7.4, 6.0 and 5.5). Growth was monitored by OD measurements at 600 nm. For all temperature-pH combinations, the individual cell lag phase and the subsequent growth rate were determined using a three-phase linear growth model. Around 100 replications were made for each set of conditions. The results were plotted as histograms, and distributions were fitted to these data. It was observed that at low pre-cultural temperatures, a high proportion of L. monocytogenes cells was able to grow with almost no lag phase. Regarding the pH effect, the pH transition from the pre-cultural to a growth media was proportional to the mean values of the lag phases. There was no remarkable effect observed on the generation time. Regarding the statistical distributions, the exponential distribution yielded the best fit in most cases, as the highest probability was observed for very small lag phases and decreased with lag phase increase. To apply the results obtained at an industrial level, a simulation in @RISK to predict the distribution of the lag phase of L. monocytogenes at different transitions of temperature was performed. These findings have important consequences to estimate the possible risks concerned L. monocytogenes for refrigerated food products.

Regional climate and glacial control on high‐resolution oxygen isotope records from Ain el Beida (latest Miocene, northwest Morocco): A cyclostratigraphic analysis in the depth and time domain

High‐resolution benthic and planktonic stable oxygen isotope records are presented for the upper Miocene Ain el Beida (AEB) section in northwestern Morocco and reveal the clear imprint of the (climatic) precession, obliquity, and eccentricity cycles in the interval between 6.5 and 5.5 Ma. The δ18O depth series were transformed into time series using astronomical tuning of the sedimentary color cycles to the 65°N summer insolation curve of the La93 solution with present‐day values for tidal dissipation and dynamical ellipticity. Spectral analysis and band‐pass filtering show that the ratios of the astronomically related spectral peaks are not consistent in the depth and time domain. The inconsistencies are mainly due to variations in sedimentation rate that are positively correlated with precession amplitude (i.e., modulated by eccentricity). In addition, they result from a long‐term trend in sedimentation rate. A simple model of nonlinear response of the sedimentation rate to the eccentricity modulation of precession was used to simulate the observed shifts in the relative position of the spectral peaks in the depth domain. Cross‐spectral analysis was carried out on the δ18O time series and a combined eccentricity, tilt (obliquity), and precession (ETP) curve. The precession‐controlled δ18O signal varies in‐phase with ETP partly as a result of the tuning procedure, while the obliquity related signal reveals a small lag of 2–3 kyr relative to obliquity. This lag is slightly reduced at the time of the Messinian Salinity Crisis (MSC) and increases to 5–6 kyr if the tidal dissipation term in the astronomical solution is reduced to half its present‐day value. The obliquity‐related lag is most likely associated with the slow buildup of ice caps, whereas the precession signal is interpreted as to dominantly reflect regional climate changes comparable to those associated with Mediterranean sapropels. Finally, the benthic δ18O record is compared with open ocean records and discussed in terms of an astronomically tuned oxygen isotope stratigraphic framework.

Larval transport pathways from Cuban snapper (Lutjanidae) spawning aggregations based on biophysical modeling

The potential linkages among Cuba and geographically associated northwestern Caribbean locations were examined through simulated transport of snapper larvae for 5 harvested snapper species. The analyses are based on a coupled biophysical model incorporating realistic, intra-annual varying currents from a single year (1984), a Lagrangian stochastic scheme, and larval behaviors to find settlement habitat. Sequential runs centered on peak spawning months and lunar phases estimated the degree to which each spawning event contributes larvae to distant populations or to neighboring populations on the complex Cuban shelf. Results suggest that considerable levels of self-recruitment (ca. 37 to 80% total recruitment) structure Cuban snapper populations, in partic- ular, those from the southern and north-central regions. The northern snapper populations exported larvae to the southern Bahamas, specifically to Cay Sal Bank (ca. 11 to 28% total recruitment), while, for more distant locations, the import of larvae from Cuba was negligible depending on the species. Regional oceanographic regimes for cubera, dog and gray snappers and site utilization (e.g. shelf geomorphology) for mutton snapper caused most within-species recruitment variability. However, a small lag in peak spawning times contributed significantly to high recruitment variability among species. Active virtual larvae stand a better chance of reaching settlement habitat, whereas spatial distribution of recruitment is similar but less structured (i.e. homogeneous low abundance) for passive larvae. This modeling approach produces spatio-temporal predictions of larval pathways with explicit measures of variance. Further, it allows for the quantification of relative levels of connectivity, a component needed in the design of marine reserve networks.

Second order coefficients for storage routing

Concentrated linear storage routing is represented as a first order differential equation and routing coefficients are analytically derived for the case of inflow defined by a quadratic in time. Routing with these coefficients, continuity is preserved at a coarser timestep than is possible with the Nash coefficients. This may be useful in daily timestep basin-wide routing models and for flood routing through catchments with small lags

Coherent spike-wave oscillations in the cortex and subthalamic nucleus of the freely moving rat

The basal ganglia play a critical role in controlling seizures in animal models of idiopathic non-convulsive (absence) epilepsy. Inappropriate output from the substantia nigra pars reticulata (SNr) is known to exacerbate seizures, but the precise neuronal mechanisms underlying abnormal activity in SNr remain unclear. To test the hypothesis that cortical spike-wave oscillations, often considered indicative of absence seizures, propagate to the subthalamic nucleus, an important afferent of SNr, we simultaneously recorded local field potentials from the frontal cortex and subthalamic nucleus of freely moving rats. Spontaneous spike-wave oscillations in cortex (mean dominant frequency of 7.4 Hz) were associated with similar oscillations in the subthalamic nucleus (mean of 7.9 Hz). The power of oscillations at 5–9 Hz was significantly higher during spike-wave activity as compared with rest periods without this activity. Importantly, spike-wave oscillations in cortex and subthalamic nucleus were significantly coherent across a range of frequencies (3–40 Hz), and the dominant (7–8 Hz) oscillatory activity in the subthalamic nucleus typically followed that in cortex with a small time lag (mean of 2.7 ms). In conclusion, these data suggest that ensembles of subthalamic nucleus neurons are rapidly recruited into oscillations during cortical spike-wave activity, thus adding further weight to the importance of the subthalamic nucleus in absence epilepsy. An increase in synchronous oscillatory input from the subthalamic nucleus could thus partly underlie the expression of pathological activity in SNr that could, in turn, aggravate seizures. Finally, these findings also reiterate the importance of oscillations in these circuits in normal behaviour.

Fundamental mechanisms for tsunami generation by submarine mass flows in idealised geometries

Tsunami generation from submarine gravity mass flows is investigated using linear two-dimensional analytical models, a simplified slide geometry, and a prescribed sub-critical slide velocity. Slide characteristics as maximum slide velocity, initial acceleration, slide length, and thickness, are all found to determine the characteristics of the tsunami. Effects of dispersion usually turn out to be of minor practical importance. Tsunamis due to retrogressive slides are generally smaller than for a similar fixed shaped slide with the same characteristics due to an increased duration of slide mass mobilisation. However, above the rear of the slide, the surface elevation can also be increased for small time lags.