Relative Dispersion Research Articles

From the butterfly effect to spontaneous stochasticity in singular shear flows

The butterfly effect is today commonly identified with the sensitive dependence of deterministic chaotic systems upon initial conditions. However, this is only one facet of the notion of unpredictability pioneered by Lorenz, who actually predicted that multiscale fluid flows could spontaneously lose their deterministic nature and become intrinsically random. This effect, which is radically different from chaos, have remained out of reach for detailed physical observations. Here we show that this scenario is inherent to the elementary Kelvin–Helmholtz hydrodynamical instability of an initially singular shear layer. We moreover provide evidence that the resulting macroscopic flow displays universal statistical properties that are triggered by, but independent of specific physical properties at micro-scales. This spontaneous stochasticity is interpreted as an Eulerian counterpart to Richardson’s relative dispersion of Lagrangian particles, giving substance to the intrinsic nature of randomness in turbulence.

Analysis of the Surface Dispersion in the Mediterranean Sub-Basins

Surface dispersion properties give an immediate characterization of the spreading of passive and active tracers in the ocean, like pollutant and marine species. The Mediterranean sub-basins (Tyrrhenian, Adriatic, Ionian, Levantine and Aegean) are known as complex dynamic regions due to the presence of coherent structures on different motion scales. This paper focus on dispersion of the surface Mediterranean flow using the surface current data derived from two different drifter designs: the Coastal Ocean Dynamics Experiment (CODE) and the Surface Velocity Program (SVP) drifters. The absolute dispersion for small time scales (15 days) and spatial scale larger than DI, our results emphasize a similarity in all the sub-basins with the presence of a quasi Random-walk regime and a quasi diffusive regime for the absolute and relative dispersion, respectively.

Can statistics of turbulent tracer dispersion be inferred from camera observations of SO<sub>2</sub> in the ultraviolet? A modelling study

Abstract. Atmospheric turbulence and in particular its effect on tracer dispersion may be measured by cameras sensitive to the absorption of ultraviolet (UV) sunlight by sulfur dioxide (SO2), a gas that can be considered a passive tracer over short transport distances. We present a method to simulate UV camera measurements of SO2 with a 3D Monte Carlo radiative transfer model which takes input from a large eddy simulation (LES) of a SO2 plume released from a point source. From the simulated images the apparent absorbance and various plume density statistics (centre-line position, meandering, absolute and relative dispersion, and skewness) were calculated. These were compared with corresponding quantities obtained directly from the LES. Mean differences of centre-line position, absolute and relative dispersions, and skewness between the simulated images and the LES were generally found to be smaller than or about the voxel resolution of the LES. Furthermore, sensitivity studies were made to quantify how changes in solar azimuth and zenith angles, aerosol loading (background and in plume), and surface albedo impact the UV camera image plume statistics. Changing the values of these parameters within realistic limits has negligible effects on the centre-line position, meandering, absolute and relative dispersions, and skewness of the SO2 plume. Thus, we demonstrate that UV camera images of SO2 plumes may be used to derive plume statistics of relevance for the study of atmospheric turbulent dispersion.

Asymptotic normality of the test statistics for the unified relative dispersion and relative variation indexes

Dispersion indexes with respect to the Poisson and binomial distributions are widely used to assess the conformity of the underlying distribution from an observed sample of the count with one or the other of these theoretical distributions. Recently, the exponential variation index has been proposed as an extension to nonnegative continuous data. This paper aims to gather to study the unified definition of these indexes with respect to the relative variability of a nonnegative natural exponential family of distributions through its variance function. We establish the strong consistency of the plug-in estimators of the indexes as well as their asymptotic normalities. Since the exact distributions of the estimators are not available in closed form, we consider the test of hypothesis relying on these estimators as test statistics with their asymptotic distributions. Simulation studies globally suggest good behaviours of these tests of hypothesis procedures. Applicable examples are analysed, including the lesser-known references such as negative binomial and inverse Gaussian, and improving the very usual case of the Poisson dispersion index. Concluding remarks are made with suggestions of possible extensions.

Role of droplet size classes on the cloud droplet spectral dispersion as observed over the Western Ghats

The aerosol indirect effects (AIE) on cloud microphysical properties have been studied using ground-based in-situ measurements. Aerosol and cloud microphysical properties were collected from a high altitude site in the Western Ghats region of India, where clouds pass over the surface during South West monsoon. The AIE was estimated using cloud droplet number concentration (AIEn) and cloud droplet effective radius (AIEs) at different fixed liquid water content (LWC) bins. The AIE varied in the range 0.01–0.13 for LWC between 0.04 g m−3 and 0.26 g m−3. The maximum AIEn and AIEs (0.125 and 0.119) were observed at the lower LWC bin (0.06–0.07 g m−3). An overestimation in AIEn is due to the dispersion effect. The offset was reduced and AIEn became close to AIEs after dispersion correction. Hence for the correct estimation of AIE using cloud droplet number concentration (Nc), dispersion correction should be considered. At the same time, the AIE estimate obtained using Reff does not need correction as the dispersion effect is implicitly included. Relative dispersion can be viewed not only as the combined effects of σ and Rm, but also as the combined effects of cloud droplets of different sizes. Further, for the first time in India, the relative contribution by the smaller and medium size droplets to the total dispersion of cloud droplet size distribution (CDSD) at lower and higher LWC bins were studied. In lower LWC, the smaller size droplets are contributing maximum (71%) to the total Nc, whereas the medium size droplets are contributing maximum (61%) to the total dispersion. At higher LWC, the contribution to total Nc by the smaller size droplets was reduced by 20%, however contribution by the medium size droplets increased by 17%, compared to the lower LWC case. Hence at higher LWC, both smaller (42%) and medium (55%) size droplets have a significant role in the total dispersion of CDSD.

Historical demography and climate driven distributional changes in a widespread Neotropical freshwater species with high economic importance

The Neotropical region exhibits the greatest worldwide diversity and the diversification history of several clades is related to the puzzling geomorphologic and climatic history of this region. The freshwater Amazon ecoregion contains the main hydrographic basins of the Neotropical region that are highly dendritic and ecologically diverse. It contains a rich and endemic fish fauna, including one of its most iconic and economically important representatives, the bony‐tongue Arapaima gigas (Teleostei, Osteoglossiformes). Here, we evaluated the projected distribution of the genus in different historical periods (Present, Last Glacial Maximum, Last Interglacial Maximum and Near Future) and interpreted these results in light of the genomic diversity and modeled historical demography. For that, we combined species distribution models, population genetic analysis using SNPs and deep learning model selection. We analyzed a representative sample of the genus from the two basins where it naturally occurs, four localities in the Amazon (Am) and three in the Tocantins‐Araguaia (To‐Ar) basin, as well as individuals from three fish farms. We inferred a potentially smaller distribution in the glacial period, with a possible refuge in central Am. Our genetic data agrees with this result, suggesting a higher level of genetic diversity in the Am basin, compared to that observed in To‐Ar. Our deep learning model comparison indicated that the To‐Ar basin was colonized by the population from the Am basin. Considering a global warming scenario in the near future, A. gigas could reach an even larger range, especially if anthropogenic related dispersal occurs, potentially invading new areas and impacting their communities.

1011-P: Effect of Fluctuating Temperature on Pump Delivery

Background: Accuracy of continuous subcutaneous insulin infusion (CSII) is essential for glycaemic control. Our study presents results of accuracy assessment of three off-the-shelves CSII under fluctuating temperature at 0,5UI/h. Methods: CSII systems accuracy was assessed by a double measurement approach utilizing a direct mass flow meter and a time-stamped micro-gravimetric test bench combined with a Kalman mathematical filter. CSII was placed inside a chamber of fluctuating temperature: 8h-tests were composed of successions of 1h at 32°C, 1h at 5°C, and compared to 8-hour tests at a 22°C fixed temperature. Accuracy was evaluated using mean of dose error. Mean absolute relative dispersion (MARD) of error was also computed for 15min time-windows. Stroke regularity was assessed in terms of frequency and volume. Tests were conducted both with insulin and medical water. Results: Delivery errors follow temperature profile. MARD of error is significantly higher with fluctuating temperature (85.2%, 44.4%, 20.4% according to each of the 3 CSII pump models) vs. fixed temperature (13.3%, 9.5%, 12.7%). No difference was observed between insulin and medical water. Stroke volume is affected by temperature changes rather than stroke frequency. Conclusion: Temperature and its fluctuations may affect the accuracy and amounts of insulin delivered by CSII. The clinical impact of the difference in insulin intake requires clinical investigations. Disclosure S. Girardot: Employee; Self; Air Liquide. Employee; Spouse/Partner; Air Liquide. P. Jacquemier: Employee; Self; Air Liquide. F. Mousin: Employee; Self; Air Liquide. C. Rendekeu: Employee; Self; Air Liquide. S. Hardy: None. J. Riveline: None.

Electrocatalytic hydrogenation of cinnamaldehyde in a PEM cell: The role of sodium hydroxide and platinum loading

In order to improve the electrocatalytic performance of Vulcan XC-72 supported Pt catalyst used as a cathode towards the electrocatalytic hydrogenation of cinnamaldehyde in a PEM cell, two different studies were carried out. In the first stage, the influence of the cathode Pt loading was evaluated. In a second study the influence of the pH during the cathode synthesis procedure (by modifying the required amount of NaOH) was explored. Results from physicochemical and electrochemical characterization and PEM essays showed that both pH and metal loading play a direct role on the obtained active particle size, basicity as well as on the electrochemical surface area, Pt facets and degradation of the samples. As a consequence, the electrochemical hydrogenation activity and selectivity are highly modified by both parameters. Hence, the cathode prepared with 15 wt.% of Pt using a 0.2 M NaOH solution showed the best electrocatalytic performance due to its relative basicity and suitable metal dispersion, which provide adequate ECSA value, deactivation degree and selectivity to the value-added compounds.

DISTRIBUTION OF THERMODYNAMIC PARAMETERS IN THE DISCRETE DISORDERED POTT’S MODEL. RESULTS OF COMPUTER SIMULATION

Using the Monte Carlo method, we study the distribution of thermodynamic parameters in a strongly disordered Potts model with the number of spin states q = 4. For this model, relative dispersions of magnetization Rm and susceptibility R are calculated. It is shown that in this model, the relative dispersions of Rm and R lead to nonzero values, which in-dicates poor self-averaging for magnetization and susceptibility in a strongly diluted mod-el. Averaging the thermodynamic parameters in a strongly diluted regime over an ensem-ble of disordered spin systems with different disorder implementations requires a signifi-cant increase in the number of disordered impurity configurations. Computer simulation was performed for spin systems with periodic boundary conditions at a spin concentration of p = 0.65. Systems with linear dimensions L  L  L= N, L = 60 were investigated.

Enemy-free space and the distribution of ants, springtails and termites in the soil of one tropical rainforest

The soil fauna of tropical rainforests is difficult to study because of its extreme species richness and taxonomic impediment. Studies of multi-taxon assemblages in the soil of tropical rainforests are relatively rare and studies of interspecific interactions, such as predation, even rarer. Here we attempt to infer prey predator interactions and enemy-free space from the faunal composition of 100 litter/soil samples obtained from Barro Colorado Island in Panama during the dry and wet seasons. We focused on assemblages of ants (assigned to categories of non-predators, potential and confirmed predators), springtails and termites, which were characterized by their Barcode Index Numbers. Overall in 0.2 m3 of soil/litter we collected 2129 ants, 5592 springtails and 260 termites, which represented 80, 104 and 15 species, respectively. The faunal composition of confirmed ant predators was spatially coincident with that of Collembola. However, despite considerable seasonal shifts in the rank abundance of Collembola species, seasonal shifts of confirmed ant predators were low, resulting in a poor match of seasonal shifts between ants and their prey items. No location could be considered as being relatively free of ant enemies for springtails or termites, but the dry season supported higher prey-predator ratios than the wet season. We inferred only 4 possible prey-predator interactions, out of 7616 potential interactions in the study system. The relative dispersion of confirmed ant predators, which only weakly influenced springtail and termite assemblages, suggests low specificity in ant-prey interactions. This confirms that “brown food webs” may be structured by bottom-up effects rather than by top-down effects.

Performance of laterally elongated pillar array columns in capillary electrochromatography mode.

In the present study, cylindrical and laterally elongated pillar array columns were investigated for use in capillary electrochromatography. Minimal theoretical plate heights of H = 1.90 and 1.46μm (in absence of sidewall effect) were obtained for coumarin C440 under unretained conditions for cylindrical and rectangular (laterally elongated, aspect ratio 4) pillar array columns, respectively. By comparing dispersion at the entire channel width to that at the central zone only, it appears that sidewall related dispersion significantly contributes to overall dispersion. A 40% reduction of the plate height was observed by taking into account only the central channel zone. A kinetic plot analysis was performed to evaluate the potential of the studied geometries by considering a maximum operating voltage of 20kV as limiting parameter. It was demonstrated that rectangular radially elongated pillars produce a higher efficiency than cylindrical pillars and other microfabricated column structures for microchip capillary electrochromatography previously studied.

Mid-latitude convective boundary-layer electricity: A study by large-eddy simulation

This paper reports the first investigations of the mid-latitude convective boundary layer (CBL) electricity above the homogeneous land surface using a large-eddy simulation (LES). Our approach uses LES together with a subgrid kinematic model for relative dispersion of scalar to calculate Lagrangian trajectories of notional particles carrying radioactive nuclei, small atmospheric ions, and charged aerosol particles. This technique opens up new possibilities for quantifying the influence of various environmental conditions on the formation of the electrical state of the undisturbed lower atmosphere. We examine the altitude distribution of principal atmospheric electrical quantities in the CBL and lower free weakly stable atmosphere without clouds depending on surface turbulent heat flux, geostrophic wind speed, mixed-layer height, ionospheric potential, and various ion production rates due to cosmic rays and radioactive gases.

Slope matched highly birefringent hybrid dispersion compensating fiber over telecommunication bands with low confinement loss

This article reveals a best possible design for hybrid dispersion compensating fiber with high birefringence established on modified broadband compensating structure through S, C and L telecommunication bands. The simulation outcome exhibits relatively higher birefringence of 3.76 × 10−2 at wavelength of 1550 nm. The suggested fiber also has dispersion compensation characteristics in an inclusive series of wavelengths which covers 1400–1625 nm. The reported design can achieve dispersion quantity of − 606 ps/(nm·km) at 1550 nm effective wavelength. The reported fiber design matches the relative dispersion slope 0.003694 nm−1 similar to single-mode fiber at 1550 nm operating wavelength. This fiber demonstrates negatively flattened effective dispersion of − 2.703 ± 0.734 ps/(nm·km) within 180 nm flat band ranging from 1460 to 1640 nm wavelength. It is also convenient to optical high bit rate communication systems. The low confinement loss is found 3.756 × 10−10 dB/m at the operating wavelength. This design also achieves highly nonlinear coefficient of 50.34 W−1 km−1. In some cases, it can also be used in sensing applications.

Reconciling Contrasting Relationships Between Relative Dispersion and Volume‐Mean Radius of Cloud Droplet Size Distributions

AbstractCloud droplet spectral relative dispersion is critical to parameterizations of cloud radiative properties, warm‐rain initiation, and aerosol‐cloud interactions in models; however, there is no consistent relationship between relative dispersion and volume‐mean radius in literature, which hinders improving relative dispersion parameterization and calls for physical explanation. Here we show, by analyzing aircraft observations of cumulus clouds during Routine AAF [Atmospheric Radiation Measurement (ARM) Aerial Facility] Clouds with Low Optical Water Depths (CLOWD) Optical Radiative Observations, that the correlation between relative dispersion and volume‐mean radius changes from positive to negative as volume‐mean radius increases. With the new observation, we postulate that the sign of the correlation is determined by whether or not condensation (evaporation) occurs simultaneously with significant new activation (deactivation). The hypothesis is validated by simulations of both an adiabatic cloud parcel model and a parcel model accounting for entrainment‐mixing. A new quantity, first bin strength, is introduced to quantify this new observation. Theoretical analysis of truncated gamma and modified gamma size distributions further supports the hypothesis and reconciles the contrasting relationships between relative dispersion and volume‐mean radius, including the results in polluted fog observations. The results could shed new light on the so‐called “twilight zone” between cloudy and cloud‐free air, which in turn affects evaluation of aerosol‐cloud interactions and retrieval of aerosol optical depth.

Non-Kolmogorov scaling for two-particle relative velocity in two-dimensional inverse energy-cascade turbulence

Herein,we numerically examine the relative dispersion of Lagrangian particle pairs in two-dimensional inverse energy-cascade turbulence. Behind the Richardson-Obukhov $t^3$ law of relative separation, we discover that the second-order moment of the relative velocity have a temporal scaling exponent different from the prediction based on the Kolmogorov's phenomenology. The results also indicate that time evolution of the probability distribution function of the relative velocity is self-similar. The findings are obtained by enforcing Richardson-Obukhov law either by considering a special initial separation or by conditional sampling. In particular, we demonstrate that the conditional sampling removes the initial-separation dependence of the statistics of the separation and relative velocity. Furthermore, we demonstrate that the conditional statistics are robust with respect to the change in the parameters involved, and that the number of the removed pairs from the sampling decreases when the Reynolds number increases. We also discuss the insights gained as a result of conditional sampling.

As2Se3-Ge11.5As24Se64.5 based mid-infrared dual nano-slot optical waveguide with huge and wavelength tunable dispersion

An As2Se3-Ge11.5As24Se64.5 based dual nano-slot waveguide with huge chromatic dispersion at mid-infrared is proposed. The large chromatic dispersion at the target wavelength is achieved induced by resonance interaction. The characteristics of dispersion are investigated by employing the FDTD method. The simulation results indicate that by optimizing the geometrical parameters, the maximum dispersion of -3.48×105 ps·nm-1·km-1 over a full width at FWHM of 2 nm at 3000 nm has been attained. A flat and ultra-large dispersion of -3.48×105 ps·nm-1·km-1 from 2980 to 3010 nm is achieved by cascading the dual-slot waveguides. The relative dispersion magnitude fluctuation is less than 1.85%.

Variation in juvenile steelhead (Oncorhynchus mykiss) dispersal in relation to age and growth performance

AbstractVolitional dispersal is a ubiquitous strategy characteristic of species across major faunal groups. Dispersal during the juvenile life stage is of interest because early performance can be critical for determining future success (survival/reproduction). For salmonids, dispersal can influence local density, competition, individual growth and survival, though drivers of dispersal at meso‐scales are rarely quantified. Here, we evaluate dispersal of tagged juvenile steelhead (Oncorhynchus mykiss) through habitat units in extended stream reaches (500 m) at sites across a watershed from July to October 2017. Our aim was to quantify the frequency and spatial extent of dispersal, identify links to biotic and abiotic factors, evaluate the implications for individual growth and test for associations between dispersal and migration initiation. Dispersal rates varied between sites, but were consistently higher for age 1+ than for age 0 steelhead (avg. 21% vs. 6% respectively). Age 1+ dispersal probability was positively correlated with time between recapture events and body mass, and negatively correlated with growth rate, maximum temperature experienced and age 1+ density. At sites where there appeared to be growth benefits to remaining sedentary compared to moving, proportionally fewer fish performed dispersal. We found no links between dispersal and timing or probability of migration initiation the following spring. Our results support the hypothesis that although dispersal over intermediate scales (10–1,000 m) might be rare, it could be an important strategy that permits fish to seek out better opportunities (foraging, shelter or otherwise) in underutilised areas.

The theory of collectivity of drinking cultures: how alcohol became everyone's problem.

The theory of collectivity of drinking cultures: how alcohol became everyone's problem.

Structure, Morphology, and Faceting of TiO2 Photocatalysts by the Debye Scattering Equation Method. The P25 and P90 Cases of Study.

Characterization of functional nanocrystalline materials in terms of quantitative determination of size, size dispersion, type, and extension of exposed facets still remains a challenging task. This is particularly the case of anisotropically shaped nanocrystals (NCs) like the TiO2 photocatalysts. Here, commercially available P25 and P90 titania nanopowders have been characterized by wide-angle X-ray total scattering techniques. Synchrotron data were modelled by the reciprocal space-based Debye scattering equation (DSE) method using atomistic models of NC populations (simultaneously carrying atomic and nanoscale structural features) for both anatase and rutile phases. Statistically robust descriptors are provided of size, morphology, and {101} vs. {001} facet area of truncated tetragonal bipyramids for anatase, jointly to polymorph quantification. The effects of using the proper NC shape on the X-ray diffraction pattern are analyzed in depth through DSE simulations by considering variable bipyramid aspect ratios (resulting in different {101} vs. {001} surface) and relative dispersion in a bivariate manner. We demonstrate that using prismatic NCs having equal volume and aspect ratio as bipyramids provides reasonably accurate sizes and {101} and {001} surface areas of the parent morphology.

Practical Applications of Performance Dispersion Risk Assessment in Alternatives and Active Strategies

Practical Applications In Performance Dispersion Risk Assessment in Alternatives and Active Strategies from the Spring 2020 issue of The Journal of Alternative Investments, author Amit Soni of New York Life Investments addresses the fact that traditional portfolio optimization models underestimate the risk of investing in alternative asset classes, and therefore overallocate assets to them. They do this in part by ignoring the fact that individual alternative funds are more likely than traditional funds to perform much better or worse than average—a phenomenon called performance dispersion risk. Portfolio managers need a way to measure this type of risk, and the author provides one by using the cross-sectional volatility of the performance of all the managers in a particular investment category. He then provides a simple approach that utilizes the interquartile or interdecile performance range to approximate the cross-sectional volatility. He measures the relative performance dispersion risk of alternative funds by comparing it to the performance dispersion of traditional funds like US large-cap equities. The author finds that including such data in portfolio modeling calculations yields portfolios that are better balanced between alternative and traditional investments. This is likely to improve investor satisfaction. TOPICS:Real assets/alternative investments/private equity, statistical methods, performance measurement