A Laplace-domain method is proposed to predict time-domain motion responses of floating structures. As a theoretical contribution, two techniques of generalising transfer functions of floating ...structures (GTFF) are developed, which are symbolic-based and Fourier transform-based techniques. Three cases are employed in this study: The first case involves a single degree-of-freedom system to demonstrate the correctness of the derived GTFF, which is assumed to have a purely analytical retardation function. The second case involves a truncated cylinder subjected to random waves that are defined by a Jonswap spectrum. Numerical results show that the symbolic approach simultaneously offers a perfect estimation of the transfer functions of a system, while the inverse Fourier-transform-based approach has some discrepancies at the first short parts of the phases. To further investigate potential applications, a floating platform is employed, and comparisons are drawn by using the commercial software SESAM, which found consistently estimated motion responses.
Interpreting the fate of wastewater contaminants in streams is difficult because their inputs vary in time and several processes synchronously affect reactive transport. We present a method to ...disentangle the various influences by performing a conservative-tracer test while sampling a stream section at various locations for chemical analysis of micropollutants. By comparing the outflow concentrations of contaminants with the tracer signal convoluted by the inflow time series, we estimated reaction rate coefficients and calculated the contaminant removal along a river section. The method was tested at River Steinlach, Germany, where 38 contaminants were monitored. Comparing day-time and night-time experiments allowed distinguishing photo-dependent degradation from other elimination processes. While photo-dependent degradation showed to be highly efficient for the removal of metroprolol, bisoprolol, and venlafaxine, its impact on contaminant removal was on a similar scale to the photo-independent processes when averaged over 24 h. For a selection of compounds analyzed in the present study, bio- and photodegradation were higher than in previous field studies. In the Steinlach study, we observed extraordinarily effective removal processes that may be due to the higher proportion of treated wastewater, temperature, DOC and nitrate concentrations, but also a higher surface to volume ratio from low flow conditions that favorizes photodegradation through the shallow water column and a larger transient storage than observed in comparable studies.
Display omitted
•Studying reactive processes in river channels is inherently difficult.•Tracer tests allowed separating conservative transport from the measured signal.•Comparison of day and night experiments highlighted photodegradation.•Photodegradation is weaker than photo-independent elimination on the long term.
Given the closed-form expression of the mass transfer function pertaining to one-dimensional mass transport conditions in the electrolyte, the voltammetric response of one-step reversible ...electrochemical (Er) reactions to a linear potential ramp can be derived first as an infinite series well suited to formal analysis, and then as an integral formulation well suited to numerical calculation. This approach applies in this article to the Er reaction studied on a uniformly accessible Rotating Disk Electrode (RDE). Using three closed-form approximations of the mass transfer function, three infinite series and three integral formulations can be derived for the Faradaic current response versus the electrode potential. Discrimination of the approximating formulations of the voltammetric response can be performed by comparison to benchmark voltammetric data obtained using the numerical method of lines to solve the relevant partial differential equation for diffusion-convection at RDE. Once the best approximating model is selected, based on its voltammetric features, the appropriate mass transfer function can be used together with the inverse Laplace transformation to derive the kernel function involved in the Integral Equation method. Application to the E reaction investigated by cyclic voltammetry on RDE is an illustration example in this article, first disregarding and then taking into account Ohmic drop and double-layer charging effects with capacitive or pseudo-capacitive (constant phase element) interfacial behaviour.
•Infinite series formulations of the voltammetric response for the Erreaction on RDE.•Integral formulations of the voltammetric response for the Erreaction on RDE.•Derivation of a new kernel function for the dissolved species reacting on RDE.•Application to the Integral Equation method for cyclic voltammetry on RDE.•Voltammetric modelling of Ohmic drop and double-layer (capacitance/CPE) effects.
Historically, high-performance infrared (IR) detectors have been fabricated out of materials such as InSb or HgCdTe. These semiconductors have material properties that are isotropic, e.g., the hole ...mobilities along the in-plane and growth directions are equal. However, IR absorbing materials with anisotropic material properties, such as type-II superlattice (T2SL) materials, based on InAs/GaInSb or InAs/InAsSb, have become increasingly prevalent. Specifically, the hole mobility is much larger along the in-plane direction than the growth direction, which directly impacts detector performance. The impact of utilizing T2SL materials with anisotropic material properties is assessed by simulating the crosstalk and modulation transfer function (MTF) in sequential two-color MW/LW T2SL focal plane arrays. The MTF is a key figure of merit (FOM) in all cameras which describes how well an optical system reproduces an object's contrast in the image at different spatial frequencies. The detector MTF depends on numerous parameters, especially material transport parameters such as the mobility, and as such the MTF is sensitive to the mobility anisotropy. This dependence, and the MTF already being a valuable FOM, makes the MTF a natural metric to assess the impacts of adopting an absorbing material with anisotropic material properties.
Discomfort evoked by stereoscopic depth has been widely concerned. Previous studies have proposed a comfortable disparity range and considered that disparities exceed this range would cause visual ...discomfort. Brain activity recordings including Electroencephalograph (EEG) monitoring enable better understanding of perceptual and cognitive processes related to stereo depth-induced visual comfort.
EEG data was collected using a stereo-visual evoked potential (VEP) test system by providing visual stimulus to subjects aged from 21 to 25 with normal stereoscopic vision. For each type of visual stimulus, data were processed using directed transfer function (DTF) and adaptive directed transfer function (ADTF) in combination with subjective feedbacks (comfort or discomfort). The topographies of information flow were constructed to compare responses stimulated by different stereoscopic depth, and to determine the difference in comfort and discomfort situations upon stimulation with same stereoscopic depth.
Based on EEG analysis results, we found that the occipital P270 was moderately related to the disparity. Moreover, the ADTF of P270 showed that the information flows at frontal lobe and central-parietal lobe changed when stimulation with different stereoscopic depth applied. As to the stereo images with same stereoscopic depth, the DTF outflows at the temporal and temporal-parietal lobes in δ band, central and central-parietal lobes in α and θ bands, and the comparison of inflows in these three bands could be considered as discriminated indexes for matching the stereoscopic effect with viewers' comfort or discomfort state impacted by disparity. The subjective feedbacks indicated that the comfort judgments remained as a result of cumulative effect.
This study proposed a short-term stereo-VEP experiment that shorted the duration of each stimulus in the experimental scheme to minimize the interference from other factors except the disparity. The occipital P270 had a mid-relevance to the disparity and its ADTF showed the affected areas when viewers are receiving stimulations with different disparities. DTF could be considered as discriminated indexes for matching the stereoscopic effect with viewers' comfort or discomfort state induced by disparity. This study proposed a preferable experiment to observe the single effect of disparity and provided an intuitive and easy-to-read result in a more convenient manner.
Despite the ubiquity of nonlinear functional relationships in nature we tend to characterize mechanisms in science using more tractable linear functions. In demographic modeling, transfer function ...analysis is used to calculate the nonlinear response of population growth rate to a theoretical perturbation of one or more matrix elements. This elegant approach is not yet popular in ecology. Inconveniently, using transfer function without care can produce erroneous results without warning. We used a large matrix projection model database to explore the potential pitfalls to be avoided in using transfer function analysis. We asked a fundamental population control question, what matrix element perturbation would be needed to reach a minimum goal of replacement population growth? We then tracked instances in which transfer function yields erroneous output and explored these cases in detail to measure how frequently it occurs. We developed a phylogenetically‐corrected mixed effects logistic regression model in a Bayesian framework to test the effect of species traits and the identity of matrix elements on the probability that transfer function yields errors. We found in 16% of cases the transfer function yielded erroneous outcomes. These errors were more likely when perturbing demographic stasis and also for shrubs more than any other life form. Errors in transfer function analysis were often due to perturbing matrix elements beyond their biological limits, even when this is still mathematically correct. To use transfer function analysis properly in demographic modeling and avoid erroneous results, input must be carefully selected to include only a biologically admissible set of perturbations.
In a size‐ age‐ or stage‐structured population, how the population growth rate (λ) responds to a change (δ) in a single demographic rate is often nonlinear. Due to biological and/or mathematical boundaries inherent in a species' biology and its projection matrix, reaching a target growth rate may sometimes be out of reach. The mathematical behavior of a perturbed matrix may be unexpected for many biologists. In this brief article, we map the underlying relationships between all matrix eigenvalues (λ) and changes (δ) to matrix entries to reveal potential pitfalls when using the transfer function to calculate future population growth with hypothetical changes in demographic rates.
Transfer functions with a high translational gain can increase the range of walking in virtual reality. These functions determine how much virtual movements are amplified compared to the ...corresponding physical movements. However, it is unclear how the design of these functions influences the user’s gait and experience when walking with high gain values. In a mixed-methods study with 20 users, we find that their best transfer functions are nonlinear and asymmetrical for starting and stopping. We use an optimization approach to determine individually optimized functions that are significantly better than a common approach of using a constant gain. Based on interviews, we also discuss what qualities of walking matter to users and how these vary across different functions. Our work shows that it is possible to create high-gain walking techniques that offer dramatically increased range of motion and speed but still feel like normal walking.
The Mediterranean region is expected to be highly impacted by global warming, although the uncertainty of future scenarios, particularly about precipitation patterns remains quite large. To better ...predict shifts in its current climate system and to test models, more regional climate records are needed spanning longer than the instrumental period. Here we provide a high-resolution reconstruction of autumn precipitation for the Central Pyrenees since 1500 CE based on annual calcite sublayer widths from Montcortès Lake (Central southern Pyrenees) varved sediments.
The 500-yr calcite data series was detrended and calibrated with instrumental climate records by applying correlations and cross-correlations to regional precipitation anomalies. Highest relationships were obtained between a composite calcite series and autumn precipitation anomalies for the complete calibration period (1900–2002) and for the two halves of the full period. Applied statistical tests were significant, evidencing that the climatic signal could be reconstructed.
The reconstructed precipitation anomalies show interdecadal shifts, and rainfall decrease within the coldest period of the LIA and during the second half of the 20th century, probably associated to current Global Warming. Neither increasing nor decreasing linear trends or periods of extreme precipitation events were identified. Our results are coherent with other palaeohydrological reconstructions for northern Iberian Peninsula. Correlations between the predicted autumn precipitation and the main teleconnections –NAO, ENSO and WEMO– were weak, although a potential relationship with the Atlantic Multidecadal Oscillation (AMO) pattern is suggested.
The obtained reconstruction provides the first estimations of regional autumn precipitation shifts in the Central Pyrenees and is one of the few reconstructions that cover annual-to-century scale climate variability of precipitation in the Mediterranean region from the end of the Litte Ice Age (LIA) to the current period of Global Warming.
Display omitted
•A reconstruction of autumn precipitation for the Central Pyrenees since 1500 CE•Lacustrine varve calcite sublayer width is a precipitation proxy.•A model based on varve width captures the documented temporal precipitation variability of the LIA.•The model reflects the 20th century drier conditions related to Global Warming.•The reconstructed series indicates a link between AMO variability and precipitation shifts.
Operators of mobile platforms that employ hydraulic actuation, such as excavators, seek more efficient power transfer from source to load. Pump-controlled architectures achieve greater efficiency ...than valve-controlled architectures but exhibit poor tracking performance. We present a system-design optimization technique that ensures compliance with design requirements and minimizes peak input power, which correlates inversely with efficiency. We utilize the optimization technique to size a valve-controlled hydraulically actuated stabilized mount on a mobile platform. Our optimization framework accounts for the disturbance spectrum, a stabilization performance measure, the system dynamics, and control system design. Our technique features automated requirement derivation in the form of a parameter estimation, which supports design decisions under constraints. Our results show that one of four inequality constraints is active. This constraint represents a common design rule and results in limiting efficiency. We show that relaxing this constraint is practically feasible and leads to higher efficiency in achieving the required performance. We propose adding an inerter to justify the relaxed constraint and present the resulting open-loop servo transfer function.
Purpose
The purpose of this study was to quantify location and direction‐dependent variations in the 3D modulation transfer function (MTF) of a high‐resolution CT scanner with selectable focal spot ...sizes and resolution modes.
Methods
The Aquilion Precision CT scanner (Canon Medical Systems) has selectable 0.25 mm or 0.5 mm detectors (by binning) in both the axial (x‐y) and detector array width (z) directions. For the x‐y and z orientations, detectors are configured (x–y) = 0.5 mm/(z) = 0.5 mm for normal resolution (NR), 0.25/0.5 mm for high resolution (HR), and 0.25/0.25 mm for super high resolution (SHR). Six focal spots (FS1‐FS6) range in size from 0.4 (x‐y) × 0.5 mm (z) for FS1 to 1.6 × 1.4 mm for FS6. Phantoms fabricated from spherical objects were positioned at radial distances of 0, 4.0, 7.5, 11.0, 14.5, and 18.5 cm. Axial and helical acquisitions were utilized and reconstructed using filtered back projection with the FC18 “Body,” FC30 “Bone,” and FC81 “Bone Sharp” kernels. The reconstructions were used to measure a 1D slice of the 3D MTF by oversampling the 3D ESF in the axial plane MTF(fr); φ = 0°), 45° out of the axial plane MTF(fr); φ = 45°), in the longitudinal direction MTF(fr); φ = 80°), and along the radial and azimuthal directions within the axial plane.
Results
The MTF(fr); φ = 45°) drops to 10% (f10) at 1.20, 1.45, and 2.06 mm−1 for NR, HR, and SHR, respectively, for a helical acquisition with FS1, FC30, and r = 4 cm from the isocenter. The MTF(fr); φ = 45°) includes contributions of both the axial‐plane MTF (f10 = 1.10, 2.04, and 2.01 mm−1) and the longitudinal MTF (f10 = 1.17, 1.18, and 1.82 mm−1) for the NR, HR, and SHR modes, respectively. For SHR, the axial scan mode showed a 15–25% improvement over helical mode in the longitudinal resolution. Helical pitch, ranging from 0.569 to 1.381, did not appreciably affect the 3D resolution (<2%). The radial MTFs across the axial field of view (FOV) showed dependencies on the focal spot length in z; for example, for SHR with FS2 (0.6 × 0.6 mm), f10 at r = 11 cm was within 17% of the value at r = 4 cm, but for SHR with FS3 (0.6 × 1.3), the reduction in f10 was 46% from 4 to 11 cm from the isocenter. The azimuthal MTF also decreased as r increased but less so for longer gantry rotation times and smaller focal spot dimensions in the axial plane. The longitudinal MTF was minimally affected (<11%) by position in the FOV and was principally affected by the focal spot length in the z‐dimension.
Conclusions
The 3D MTF was measured throughout the FOV of a high‐resolution CT scanner, quantifying the advantages of different resolution modes and focal spot sizes on the axial‐plane and longitudinal MTF. Reconstruction kernels were shown to impact axial‐plane resolution, imparting non‐isotropic 3D resolution characteristics. Focal spot size (both in x‐y and in z) and gantry rotation time play important roles in preserving the high‐resolution characteristics throughout the field of view for this new high‐resolution CT scanner technology.
PDF
