Relative Dispersion Research Articles

Effects of spraying pressure and installation angle of nozzles on atomization characteristics of external spraying system at a fully-mechanized mining face

Aiming to effectively suppress excessively high dust concentration around the drums during coal cutting and the related dust particle dispersion issues at a fully-mechanized mining face, the present study employed experiments, numerical simulations, and field measurements to carry out an in-depth investigation of the dust suppression performance of an external spraying system. Firstly, the atomization characteristics of the nozzles with optimized macro-atomization performances were tested. According to the experimental results, hybrid nozzles with an orifice diameter of 2.0 mm and an X-shaped diversion core (type-B nozzles) delivered the best overall atomization performances at a spraying pressure of 8 MPa; in this case, the spraying angle and the effective spraying range were approximately 81.9° and 2.56 m, respectively. Next, numerical simulations were conducted to assess the dust suppression performances of an external spraying system, using ANSYS Fluent software. The results showed that, when the nozzles were installed at an inclination angle of 30° and operated at a spraying pressure of 8 MPa, the spray field formed could cover the whole dust-producing region around the drum. Meanwhile, the spray field near the coal cutter drum was not affected by airflow, which prevented dust particles being dispersed by the airflow, leading to a mitigation of pollution. Finally, field testing at the No. 30106 mining face of the Shiquan Coal Mine indicated that the mean overall dust suppression efficiency could reach up to 90.10%, i.e. the dust particles at this fully-mechanized mining face were effectively settled. To conclude, the dust pollution issues at a fully-mechanized mining face during the coal cutting process were adequately addressed by the measures investigated here.

Developing an index to assess human toxicity potential of sugarcane industry

Despite the importance and characteristics sugar-energy industry, the specialized literature does not present studies to analyze specifically the human toxicity of residues and by-products generated by this industry. Therefore, the objective of this article is the proposal of an unprecedented Human Toxicity Potential Index (Htpi) applied to the sugar-energy industry in order to evaluate its environmental performance based on the human toxicity potential. The Htpi indicator developed in this work takes into account, for each residue and by-product generated: i) the relative weighting of the potential impact on human health; (ii) the relative quantity produced over a given period of time; (iii) the relative geographical coverage or relative spatial dispersion that each residue/by-product can achieve; and iv) the evaluation of the suitability of the final destination of each residue/by-product practiced by the company, since each company can use adequate or inadequate means in the final disposal. Regarding the potential impact on human health, the results pointed out that the residues/by-products with the highest relative weight are vinasse (35.57%), filter cake (29.15%) and bagasse-burning ashes (27.38%). The proposed index was tested in a large Brazilian sugar-energy enterprise in which, despite the large amount of residues and by-products generated, the result achieved was environmentally friendly. The Htpi index resulted in 93.97%, which means that 93.97% of the residues and by-products generated by this company have an adequate environmental allocation when considering its human toxicity potential.

Dimensional response analysis of bilinear SDOF systems under near-fault ground motions with intrinsic length scale

This paper proposes an intrinsic length scale with unambiguous physical significance for dimensional response analysis of inelastic systems, and establishes a versatile regression model for the self-similar response spectra of bilinear single-degree-of-freedom (SDOF) under near-fault ground motions. Firstly, according to the dimensional analysis of elastic SDOF systems subjected to analytical pulses, the intrinsic length scale is proposed to compare with the widely used energetic length scale. It is shown that the normalized displacement with respect to the intrinsic length scale is compatible with the analytical solution, and the overall absolute dispersion in the normalized responses is effectively reduced and is more evenly distributed in the entire frequency-ratio range. Then, the intrinsic length scale is adopted in the case of bilinear SDOF systems under analytical pulses, and similar results are observed. Finally, 30 near-fault ground motion records are selected as seismic input of the bilinear SDOF systems. Results indicate that both overall absolute and relative dispersions associated with intrinsic length scale are smaller than those with energetic length scale, when the normalized yield displacement is large. Therefore, the intrinsic length scale is recommended as an alternative length scale for dimensional analysis of elastoplastic structures. Moreover, it is illustrated that there exist two states of complete similarity in the normalized yield displacement. Accordingly, a versatile regression model is suggested for self-similar response spectrum, which can predict structural response.

Taiwan-Specific Model forVS30Prediction Considering Between-Proxy Correlations

Ergodic site response models are generally conditional on the time-averaged shear wave velocity in the upper 30 m ( VS30). Ground motion databases contain many recordings from Taiwan, and because of site characterization efforts, 56% of recording sites have VS30derived from measurements. We develop proxy-based VS30prediction models, one application of which is for the remaining 44% of Taiwan sites. Our approach, which can be suitable for other regions, differs from previous studies in which proxies are based on detailed geologic categories and possible within-category topographic gradient effects. Instead, we use three broad, age-based geologic categories, and for the youngest category of Holocene and Quaternary undivided sediments, we propose models conditioned on gradient and elevation. We also adapt a geomorphic terrain-based method, thus providing two VS30-prediction models. We describe a model weighting scheme that combines the models in consideration of their relative dispersions and correlation, producing a weighted mean and standard deviation natural-log VS30. Included as an electronic supplement is a profile database file and a site database with site parameters for Taiwan ground motion stations.

Scale Dependence of Cloud Microphysical Response to Turbulent Entrainment and Mixing

AbstractThe dynamics and lifetime of atmospheric clouds are tightly coupled to entrainment and turbulent mixing. This paper presents direct numerical simulations of turbulent mixing followed by droplet evaporation at the cloud‐clear air interface in a meter‐sized volume, with an ensemble of up to almost half a billion individual cloud water droplets. The dependence of the mixing process on domain size reveals that inhomogeneous mixing becomes increasingly important as the domain size is increased. The shape of the droplet size distribution varies strongly with spatial scale, with the appearance of a pronounced negative exponential tail. The increase of relative dispersion during the transient mixing process is strongly dependent on the scale of the mixing and therefore on the Damköhler number, defined as the turbulence large‐eddy time scale divided by the cloud supersaturation relaxation time.

Effect of thermally reduced graphene oxides obtained at different temperatures on the barrier and mechanical properties of polypropylene/TRGO and polyamide‐6/TRGO nanocomposites

Polypropylene (PP) and polyamide‐6 (PA6) nanocomposites containing thermally reduced graphene oxide (TRGO), obtained either at 600°C (TRGO600) or 800°C (TRGO800), were prepared by melt mixing in order to study the effect of the thermal treatments on their barrier and mechanical properties. Transmission electron microscopy images of nanocomposites showed a relative good dispersion of TRGO in polymer matrices with some agglomerations. Differential scanning calorimetry analyses showed a slight reduction in crystallinity for both polymers in the presence of TRGO. The permeability to oxygen and water vapor was decreased in almost all nanocomposites due to a more tortuous path to gas permeation, being more evident for PP/TRGO800. Tensile stress–strain tests showed that all nanocomposites had higher elastic modulus, but PA6/TRGO600 nanocomposites showed better mechanical properties. These findings indicated that TRGO obtained at a higher temperature imparts better barrier and mechanical properties to PP, while TRGO obtained at a lower temperature imparts better barrier and mechanical properties to PA6. POLYM. COMPOS., 40:E1746–E1756, 2019. © 2018 Society of Plastics Engineers

Effects of the Reynolds number on a scale-similarity model of Lagrangian velocity correlations in isotropic turbulent flows

A scale-similarity model of a two-point two-time Lagrangian velocity correlation (LVC) was originally developed for the relative dispersion of tracer particles in isotropic turbulent flows (HE, G. W., JIN, G. D., and ZHAO, X. Scale-similarity model for Lagrangian velocity correlations in isotropic and stationary turbulence. Physical Review E, 80, 066313 (2009)). The model can be expressed as a two-point Eulerian space correlation and the dispersion velocity V. The dispersion velocity denotes the rate at which one moving particle departs from another fixed particle. This paper numerically validates the robustness of the scale-similarity model at high Taylor micro-scale Reynolds numbers up to 373, which are much higher than the original values (Rλ = 66, 102). The effect of the Reynolds number on the dispersion velocity in the scale-similarity model is carefully investigated. The results show that the scale-similarity model is more accurate at higher Reynolds numbers because the two-point Lagrangian velocity correlations with different initial spatial separations collapse into a universal form compared with a combination of the initial separation and the temporal separation via the dispersion velocity. Moreover, the dispersion velocity V normalized by the Kolmogorov velocity Vη ≡ η/τη in which η and τη are the Kolmogorov space and time scales, respectively, scales with the Reynolds number Rλ as $$V/V_\eta\propto{R_\lambda^{1.39}}$$ obtained from the numerical data.

The Effect of Barotropic and Baroclinic Tides on Three‐Dimensional Coastal Dispersion

AbstractThe effects of barotropic and baroclinic tides on three‐dimensional (3‐D) coastal dispersion are examined with realistic, 200‐m horizontal resolution simulations of the Central Californian continental shelf during upwelling. Over multiple tidal cycles, the horizontal relative dispersion and vertical dispersion of 3‐D drifters are similar between simulations with no tides and with barotropic tides. In contrast, baroclinic tides, which dissipate across the shelf and induce vertical mixing, result in a factor of 2–3 times larger horizontal and vertical dispersion. The increase in horizontal dispersion with vertical mixing is qualitatively consistent with weak‐mixing shear dispersion. Without shear dispersion, horizontal dispersion of surface‐trapped (2‐D) drifters was similar in all simulations. However, 2‐D drifter trajectory differences relative to no tide simulations are 3–4 times larger with baroclinic tides than barotropic tides alone. These results demonstrate the need to include baroclinic tides and 3‐D tracking for coastal passive tracer dispersion.

Dispersion Aerosol Indirect Effect in Turbulent Clouds: Laboratory Measurements of Effective Radius.

Cloud optical properties are determined not only by the number density n d and mean radius of cloud droplets but also by the shape of the droplet size distribution. The change in cloud optical depth with changing n d , due to the change in distribution shape, is known as the dispersion effect. Droplet relative dispersion is defined as . For the first time, a commonly used effective radius parameterization is tested in a controlled laboratory environment by creating a turbulent cloud. Stochastic condensation growth suggests d independent of n d for a nonprecipitating cloud, hence nearly zero albedo susceptibility due to the dispersion effect. However, for size-dependent removal, such as in a laboratory cloud or highly clean atmospheric conditions, stochastic condensation produces a weak dispersion effect. The albedo susceptibility due to turbulence broadening has the same sign as the Twomey effect and augments it by order 10%.

A structural subgrid-scale model for relative dispersion in large-eddy simulation of isotropic turbulent flows by coupling kinematic simulation with approximate deconvolution method

A kinematic simulation with an approximate deconvolution (KSAD) hybrid model is proposed to predict the Lagrangian relative dispersion of fluid particles in a large eddy simulation (LES) of isotropic turbulent flows. In the model, a physical connection between the resolved and subgrid scales is established through the energy flux rate at the filter width scale. Due to the lack of subgrid-scale (SGS) turbulent structures and SGS model errors, the LES cannot accurately predict the two- and multi-point Lagrangian statistics of the fluid particles. To improve the predictive capability of the LES, we use an approximate deconvolution model to improve the resolved scales near the filter width and a kinematic simulation to recover the missing velocity fluctuations beneath the subgrid scales. To validate the proposed hybrid model, we compare the Lagrangian statistics of two- and four-particle dispersion with the corresponding results from the direct numerical simulation and the conventional LES. It is found that a significant improvement in the prediction of the Lagrangian statistics of fluid particles is achieved through the KSAD hybrid model. Furthermore, a parametric study regarding the wavenumbers and orientation wavevectors is conducted to reduce the computational cost. Good results can be obtained using a small number of wavenumber modes and orientation wavevectors. Thus, we can improve the prediction of the Lagrangian dispersion of fluid particles in the LES by applying the KSAD hybrid model at an acceptable computational cost.

Effect of 3B Group in Rings on Special Dispersion of B2O3-SiO2-ZrO2-Ta2O5-Na2O System Glass

Borosilicate glasses, with xB2O3-(60-x)SiO2-8ZrO2-8Ta2O5-24Na2O (7≤x≤59 mol%) composition, were fabricated by melt-quenching technique. NMR, UV-Vis, Raman and IR spectroscopic studies were utilized to investigate the structure of fabricated glasses. The NMR spectrum was deconvoluted into five Gaussian bands, assigned to 4B(0B,4Si), 4B(1B,3Si), 4B(2B,2Si), 3B(rings) and 3B(loose), to get their quantitative information. The relative dispersion deviation ΔPg,F was attributed to the relative quantity of 3B (rings) but not all 3B groups, and B2O3 existed mainly as [BO3] in rings firstly, and then as [BO3] in loose condition. The UV-Vis spectra revealed that the quantity of non-bridging oxygen increased firstly and then decreased with increasing concentration of B2O3. Acting as complementary techniques, Raman and IR measurements revealed that four-coordinated boron and silica mainly existed as 4B-O-B, and Si-O-Si in Q2, respectively, as chain structure but not framework structure, and [BO4] units prefered connections with borate rather than with silicate entities of the glass network in these studied glasses. In addition, the conclusion also certified that 3B in “loose” condition located in lower wavenumbers between 1 200-1 600 cm-1 in Raman spectra.

Relative Dispersion of Surface Drifters in the Benguela Upwelling Region

AbstractWe examine the relative dispersion of surface drifters deployed in groups of triplets at the boundaries of a filament in the upwelling region off Namibia for both the entire ensemble and the two main subgroups. For the drifters in the group released at the northern boundary of the filament, close to the upwelling front, we find that the mean-square pair separation 〈s2(t)〉 shows the characteristic distinct dispersion regimes [nonlocal, local (Richardson), and diffusive] of an ocean surface mixed layer. We confirm the different dispersion regimes by a rescaled presentation of the moments 〈sn(t)〉 and thereby also explain the anomalous slow decay of the kurtosis in the transient regime. For the drifter group released at the southern boundary, 〈s2(t)〉 remains constant for a short period, followed by a steep “Richardson like” increase and an asymptotic diffusive increase. In contrast to the northern release, the corresponding moments reveal a narrow distribution of pair separations for all regimes. The analysis of finite-size Lyapunov exponents (FSLEs) reveals consistent results when applied to the two releases separately. When applied to the entire drifter ensemble, the two measures yield inconsistent results. We relate the breakdown of consistency to the impact of the different dynamics on the respective averages: whereas, because of separation in scale, 〈s2(t)〉 is dominated by the northern release, the decay of the FSLEs for small distances reflects the drifter dynamics within the filament.

Box–Cox elliptical distributions with application

We propose and study the class of Box–Cox elliptical distributions. It provides alternative distributions for modeling multivariate positive, marginally skewed and possibly heavy-tailed data. This new class of distributions has as a special case the class of log-elliptical distributions, and reduces to the Box–Cox symmetric class of distributions in the univariate setting. The parameters are interpretable in terms of quantiles and relative dispersions of the marginal distributions and of associations between pairs of variables. The relation between the scale parameters and quantiles makes the Box–Cox elliptical distributions attractive for regression modeling purposes. Applications to data on vitamin intake are presented and discussed.

Radial position–momentum uncertainties for the infinite spherical well and the Fisher entropy

We present the analytical expression of the product of the radial position and momentum uncertainties and for the infinite spherical well. We find a few interesting features. First, the uncertainty increases with the radius R and the quantum number n, the nth root of the spherical Bessel function, but finally arrives at a constant for a large n and decreases with the angular momentum number l. It is seen that the becomes imaginary, which arises from the fact that the moving particle is shifted to axis y suddenly from the original axis x as the quantum number n increases. Furthermore, the becomes zero when the n increases for a given l. This means that the particle is spiraling around a circle whose radius r < R changes between a varying radius and a constant but with an increasing radius r as the n increases. Finally, the particle moves around a circle with a maximum radius R. Second, the relative dispersion is independent of the radius R, and it increases with the quantum number n but decreases with the quantum number l. Third, the radial momentum uncertainty decreases with the radius R and increases with the quantum numbers l > 0 and n. We notice that there exists a turning point for the uncertainty when l = 1 and n > 1. This also leads to the product . Fourth, the product is independent of the radius R and increases with the quantum numbers l > 0 and n. Finally, we obtain the analytical expression of the Fisher entropy and notice that it decreases with the radius R but increases with the quantum numbers l and n. We also find that the Cramer–Rao uncertainty relation is satisfied, and it increases with the quantum numbers l and n.

Sea Breeze Sensitivity to Coastal Upwelling and Synoptic Flow Using Lagrangian Methods

AbstractSea breezes occur nearly daily in the U.S. Mid‐Atlantic summer during high electricity demand periods, and thus have important implications for the burgeoning U.S. offshore wind energy industry. The sea breeze's offshore component is poorly understood and ill defined relative to its onshore counterpart. Here a new Lagrangian method not yet readily used to study the sea breeze, relative dispersion, was validated and applied to a validated Weather Research and Forecasting model in the U.S. Mid‐Atlantic. This Lagrangian method is used to characterize the onshore convergent and offshore divergent sea breeze extents and intensities, and test their sensitivities to both atmospheric synoptic flow and oceanic coastal upwelling, another common summer season regional phenomenon. It was found that offshore‐directed synoptic flow impacted the sea breeze onshore extent more than offshore extent, and that coastal upwelling did not significantly impact sea breeze onshore or offshore extent for these carefully selected case studies. Upwelling, however, produced an earlier sea breeze onset (~5 hr), and a shallower, sharper, and more intense offshore/onshore sea breeze during strong offshore synoptic flow, consistent with past studies. The offshore side of the sea breeze cell—with stronger intensity during upwelling—crossed the New Jersey Wind Energy Area at ~1900 UTC, regardless of synoptic wind or upwelling conditions. Results overall are consistent with dynamic linear sea breeze theory. Uncertain projected trends in coastal upwelling/sea breezes in a warming world highlight the importance of continued study of coastal air‐sea interactions for improved offshore wind energy assessment and prediction.

Tasseled cap transformation for assessing hurricane landfall impact on a coastal watershed

Tasseled cap transformation (TCT) has been used to observe relationships among soil moisture, vegetation cover, and canopy condition. Time series Landsat satellite images of high resolution may provide continuous and accurate observations of the land surface, which can be further analyzed using the TCT for natural hazard events. This study explores the use of a unique dispersion phenomenon of TCT for observing the dynamics of vegetation cover and landscape changes due to a major hurricane landfall in the United States. This is based on the Landsat images taken during the Hurricane Bob event, during which the hurricane made landfall in the highly developed New England area in late August 1991. A unique comparison of the TCT time series plots illustrating the relative TCT dispersion phenomenon, which addresses the landfall’s profound impact on the Mattapoisett River watershed in 1991, reflects the interactions among biosphere, atmosphere, hydrosphere, and lithosphere in hurricane-prone regions. This analysis can be done without the use of ground truth data and can be further supported by the multitemporal and multidimensional change detection of box plots in terms of brightness and greenness to gain more biophysical interpretation. Findings unveil an inherent earth system process via the varying levels of dispersion among brightness, greenness, and wetness over the coastal watershed with environmental sustainability implications.

Lagrangian Dispersion Characteristics in The Western Mediterranean

Dispersion characteristics in the Western Mediterranean are analyzed using data from Coastal Ocean Dynamics Experiment (CODE) and Surface Velocity Program (SVP) surface drifters deployed in the period 1986–2017. Results are presented in terms of absolute dispersion A2 (mean-squared displacement of drifter individuals) and of relative dispersion (D2; mean square separation distance of drifter pairs). Moreover, the dispersion characteristics are estimated for different initial separation distances (D0) between particles: smaller, larger, or comparable with the internal Rossby radius of deformation. Results show the presence of a quasiballistic regime for absolute dispersion at small time scales and the nonlocal relative dispersion regime related to the submesoscale activities for scales smaller than the internal Rossby radius. At intermediate times, two anomalous absolute dispersion regimes (elliptic and hyperbolic regimes) related with the flow topology are observed, although the relative dispersion involves the Richardson and shear/ballistic regimes only for D0 smaller than the Rossby radius. During the subsequent 20–30 days, absolute dispersion shows quasirandom walk regime and relative dispersion follows the diffusive regime for scales larger than 100 km for which pair velocities are uncorrelated.

Influence of Turbulent Fluctuations on Cloud Droplet Size Dispersion and Aerosol Indirect Effects.

Cloud droplet relative dispersion, defined as the standard deviation over the mean cloud droplet size, is of central importance in determining and understanding aerosol indirect effects. In recent work, it was found that cloud droplet size distributions become broader as a result of supersaturation variability and that the sensitivity of this effect is inversely related to cloud droplet number density. The subject is investigated in further detail using an extensive dataset from a laboratory cloud chamber capable of producing steady-state turbulence. An extended stochastic theory is found to successfully describe properties of the droplet size distribution, including an analytical expression for the relative dispersion. The latter is found to depend on the cloud droplet removal time, which in turn increases with the cloud droplet number density. The results show that relative dispersion decreases monotonically with increasing droplet number density, consistent with some recent atmospheric observations. Experiments spanning fast to slow microphysics regimes are reported. The observed dispersion is used to estimate time scales for autoconversion, demonstrating the important role of the turbulence-induced broadening effect on precipitation development. An initial effort is made to extend the stochastic theory to an atmospheric context with a steady updraft, for which autoconversion time is the controlling factor for droplet lifetime. As in the cloud chamber, relative dispersion is found to increase with decreasing cloud droplet number density.

Circular photonic crystal fiber supporting 110 OAM modes

We propose a new circular photonic crystal fiber (CPCF), which can support orbital angular momentum (OAM) modes as many as 110 in C and L communication bands. Using finite element method (FEM), the characteristics of the CPCF for different OAM modes are systematically studied. The numerical analysis shows that most eigenmodes effective index differences are at the order of 10−3, which is helpful to reduce the mode coupling and ensure stable OAM modes transmission. Moreover, the nonlinear coefficient is relatively low, with the values for most modes are within 2.80 W−1∕km at 1.55 μm. In addition, the confinement loss of most eigenmodes possesses low values under 10−7 dB/m. Besides, all of the OAM modes have relative flat dispersion. In brief, the designed CPCF features large effective index contrast, small nonlinear coefficient, low confinement loss and relatively flat dispersion, which could find potential application in high capacity OAM mode division multiplexing (MDM) fiber communication systems.

Off-host longevity of the winged dispersal stage of Carnus hemapterus (Insecta: Diptera) modulated by gender, body size and food provisioning.

Highlighting the dispersal ecology of parasites is important for understanding epidemiological, demographic and coevolutionary aspects of host-parasite interactions. Yet, critical aspects of the dispersal stage of parasites, such as longevity and the factors influencing it, are poorly known. Here we study the lifespan of the dispersal stage of an ectoparasitic dipteran, Carnus hemapterus, and the impact of gender, body size and food provisioning on longevity. We found that freshly emerged imagoes survive at most less than 4 days. Longevity increased with body size and, since this parasite exhibits sexual size dimorphism, the bigger females lived longer than males. However, controlling for body size suggests that males lived relatively longer than females. Furthermore, a humid environment and food provisioning (flowers) significantly increased individual life spans. We discuss the relative importance of spatial and temporal dispersal in relation to the infectious potential of this parasite.