Artificial Dispersion Research Articles

Lagomorph biology: evolution, ecology, and conservation

Palaeontology and Evolution.- to the Lagomorpha.- Prehistoric and Historic Artificial Dispersal of Lagomorphs on the Mediterranean Islands.- The Lagomorph Fossil Record and the Origin of the European Rabbit.- Inferring the Evolutionary History of the European Rabbit (Oryctolagus cuniculus) from Molecular Markers.- Phylogenetic Aspects of Nuclear and Mitochondrial Gene-Pool Characteristics of South and North African Cape Hares (Lepus capensis) and European Hares (Lepus europaeus).- Population Ecology and Dynamics.- The World of Pikas.- When? Where? and for How Long? Census Design Considerations for an Alpine Lagomorph, the Collared Pika (Ochotona collaris).- Weather Effects on Reproduction, Survival, and Body Mass of European Rabbits in a Temperate Zone Habitat.- Ecosystem Engineering Effects of European Rabbits in a Mediterranean Habitat.- Forest-Fire Regime: The Missing Link to Understand Snowshoe Hare Population Fluctuations?.- Introduced Lagomorphs as a Threat to Native Lagomorphs: The Case of the Eastern Cottontail (Sylvilagus floridanus) in Northern Italy.- Testing Multiple Hypotheses to Identify Causes of the Decline of a Lagomorph Species: The New England Cottontail as a Case Study.- Physiology and Behaviour.- Many Common Odour Cues and (at Least) One Pheromone Shaping the Behaviour of Young Rabbits.- Mother-Young and Within-Litter Relations in the European Rabbit Oryctolagus cuniculus.- Fertility and Infertility in the European Hare Lepus europaeus in Australia.- A Review of Competition between Rabbits (Oryctolagus cuniculus) and Hares (Lepus europaeus).- Diseases.- European Brown Hare Syndrome.- How Many Caliciviruses are there in Rabbits? A Review on RHDV and Correlated Viruses.- Geographic and Seasonal Variation in the Impact of Rabbit Haemorrhagic Disease on European Rabbits, Oryctolagus cuniculus, and Rabbit Damage in Australia.- Conservation and Management.- Conservation of Endangered Lagomorphs.- Managing the European Rabbit: Converging Interests Between Australian Research for Rabbit Control and European Research for their Conservation.- Improving Rabbit Restocking Success: A Review of Field Experiments in France.- Recovering the Endangered Riparian Brush rabbit (Sylvilagus bachmani riparius): Reproduction and Growth in Confinement and Survival after Translocation.- Conservation of Critically Endangered Lagomorphs: The Tehuantepec Jackrabbit (Lepus flavigularis) as an Example.- A Review of the Biology and Conservation of the Amami Rabbit (Pentalagus furnessi).- Concluding Remarks.- Overview of Lagomorph Research: What we have learned and what we still need to do.

Measurement of the dispersion induced by a slow-light system based on coupled active-resonator-induced transparency

We demonstrate experimentally coupled active-resonator-induced transparency in a fiber system. We show that the use of ${\mathrm{Er}}^{3+}$-doped fibers can compensate for the optical losses leading to a high transparency of the system. Using a Mach-Zehnder fiber interferometer, we measure the dispersion properties of our coupled active resonators under different pumping rates. We show that the active feature of the system allows us to engineer the different orders of its artificial dispersion. This experimental demonstration shows the potential of active coupled resonators for dispersion tailoring and slow-light applications.

A finite volume‐based high‐order, Cartesian cut‐cell method for wave propagation

AbstractComputational aeroacoustics requires numerical techniques capable of yielding low artificial dispersion and dissipation to preserve the amplitude and the frequency characteristics of the physical processes. Furthermore, for engineering applications, the techniques need to handle irregular geometries associated with realistic configurations. We address these issues by developing an optimized prefactored compact finite volume (OPC‐fv) scheme along with a Cartesian cut‐cell technique. The OPC‐fv scheme seeks to minimize numerical dispersion and dissipation while satisfying the conservation laws. The cut‐cell approach treats irregularly shaped boundaries using divide‐and‐merge procedures for the Cartesian cells while maintaining a desirable level of accuracy. We assess these techniques using several canonical test problems, involving different levels of physical and geometric complexities. Richardson extrapolation is an effective tool for evaluating solutions of no high gradients or discontinuities, and is used to evaluate the performance of the solution technique. It is demonstrated that while the cut‐cell method has a modest effect on the order of accuracy, it is a robust method. The combined OPC‐fv scheme and the Cartesian cut‐cell technique offer good accuracy as well as geometric flexibility. Copyright © 2008 John Wiley & Sons, Ltd.

An approximated method for the solution of elliptic problems in thin domains: Application to nonlinear internal waves

Realistic numerical simulations of nonlinear internal waves (NLIWs) have been hampered by the need to use computationally expensive nonhydrostatic models. In this paper, we show that the solution to the elliptic problem arising from the incompressibility condition can be successfully approximated by a few terms (three at most) of an expansion in powers of the ratio (horizontal grid spacing)/(total depth). For an n dimensional problem, each term in the expansion is the sum of a function that satisfies a one-dimensional second-order ODE in the vertical direction plus, depending on the surface boundary condition, the solution to an n - 1 dimension elliptic problem, an evident saving over having to solve the original n-dimensional elliptic problem. This approximation provides the physically correct amount of dispersion necessary to counteract the nonlinear steepening tendency of NLIWs. Experiments with different types of NLIWs validate the approach. Unlike other methods, no ad hoc artificial dispersion needs to be introduced.

Electrical Characterization Techniques of Dielectric Thin Films Using Metal–Insulator–Metal Structures

In this paper, we describe an electrical characterization technique of dielectric thin films using metal–insulator–metal (MIM) structures and an LCR meter. It is demonstrated theoretically and experimentally that the equivalent parallel conductance and equivalent parallel capacitance of MIM capacitors necessarily show artificial frequency dispersions due to the effects of series resistance, owing to electrode and probing contact resistances. A procedure to extract the true equivalent parallel conductance and capacitance from measured admittance data is presented.

A physically based flux limiter for QUICK calculations of advective scalar transport

AbstractTransient, advective transport of a contaminant into a clean domain will exhibit a moving sharp front that separates contaminated and clean regions. Due to ‘numerical diffusion’—the combined effects of ‘cross‐wind diffusion’ and ‘artificial dispersion’—a numerical solution based on a first‐order (upwind) treatment will smear out the sharp front. The use of higher‐order schemes, e.g. QUICK (quadratic upwinding) reduces the smearing but can introduce non‐physical oscillations in the solution. A common approach to reduce numerical diffusion without oscillations is to use a scheme that blends low‐order and high‐order approximations of the advective transport. Typically, the blending is based on a parameter that measures the local monotonicity in the predicted scalar field. In this paper, an alternative approach is proposed for use in scalar transport problems where physical bounds CLow⩽C⩽CHigh on the scalar are known a priori. For this class of problems, the proposed scheme switches from a QUICK approximation to an upwind approximation whenever the predicted upwind nodal value falls outside of the physical range [CLow, CHigh]. On two‐dimensional steady‐state and one‐dimensional transient test problems predictions obtained with the proposed scheme are essentially indistinguishable from those obtained with monotonic flux‐limiter schemes. An analysis of the modified equation explains the observed performance of first‐ and second‐order time‐stepping schemes in predicting the advective transport of a step. In application to the transient two‐dimensional problem of contaminate transport into a streambed, predictions obtained with the proposed flux‐limiter scheme agree with those obtained with a scheme from the literature. Copyright © 2007 John Wiley & Sons, Ltd.

Using the material‐point method to model sea ice dynamics

The material‐point method (MPM) is a numerical method for continuum mechanics that combines the best aspects of Lagrangian and Eulerian discretizations. The material points provide a Lagrangian description of the ice that models convection naturally. Thus properties such as ice thickness and compactness are computed in a Lagrangian frame and do not suffer from errors associated with Eulerian advection schemes, such as artificial diffusion, dispersion, or oscillations near discontinuities. This desirable property is illustrated by solving transport of ice in uniform, rotational and convergent velocity fields. Moreover, the ice geometry is represented by unconnected material points rather than a grid. This representation facilitates modeling the large deformations observed in the Arctic, as well as localized deformation along leads, and admits a sharp representation of the ice edge. MPM also easily allows the use of any ice constitutive model. The versatility of MPM is demonstrated by using two constitutive models for simulations of wind‐driven ice. The first model is a standard viscous‐plastic model with two thickness categories. The MPM solution to the viscous‐plastic model agrees with previously published results using finite elements. The second model is a new elastic‐decohesive model that explicitly represents leads. The model includes a mechanism to initiate leads, and to predict their orientation and width. The elastic‐decohesion model can provide similar overall deformation as the viscous‐plastic model; however, explicit regions of opening and shear are predicted. Furthermore, the efficiency of MPM with the elastic‐decohesive model is competitive with the current best methods for sea ice dynamics.

Influence of ground substrate on establishment of reindeer lichen after artificial dispersal

Methods to improve the recovery of reindeer lichen after soil disturbance or overgrazing are being sought for areas where reindeer are herded. The effects of four substrates – mineral soil, moss, twigs and pine bark – on the establishment of lichen fragments after total removal of the vegetation were thus studied in a middle-aged pine stand and a clear-cut, both located in a lichen-rich pine-heath. Cladina mitis fragments of two sizes were manually dispersed in 1 m quadrats and their movements from their respective dispersal points were registered after one year. The natural re-establishment of lichens in the quadrats was monitored over three years by using digital pictures. In the forest stand, no significant differences were detected in either the fragment movement or the lichen establishment between the different substrates, but the fragment size had positive effects on both parameters. In the clear-cut, the moss substrate was the most suitable not only for the artificially dispersed lichens to fasten to, but also for the natural settlement of lichens from the surrounding lichen mat. More lichen thalli fastened to the bark and twigs substrates than to the mineral soil, but the settlement of lichens from the surrounding was greater on bare mineral soil substrate. The results indicate that artificial dispersal of lichen thalli on an appropriate substrate could be a successful strategy for promoting lichen recovery.2

Positive Solution of Two‐Dimensional Solute Transport in Heterogeneous Aquifers

The transport of contaminants in aquifers is usually represented by a convection-dispersion equation. There are several well-known problems of oscillation and artificial dispersion that affect the numerical solution of this equation. For example, several studies have shown that standard treatment of the cross-dispersion terms always leads to a negative concentration. It is also well known that the numerical solution of the convective term is affected by spurious oscillations or substantial numerical dispersion. These difficulties are especially significant for solute transport in nonuniform flow in heterogeneous aquifers. For the case of coupled reactive-transport models, even small negative concentration values can become amplified through nonlinear reaction source/sink terms and thus result in physically erroneous and unstable results. This paper includes a brief discussion about how nonpositive concentrations arise from numerical solution of the convection and cross-dispersion terms. We demonstrate the effectiveness of directional splitting with one-dimensional flux limiters for the convection term. Also, a new numerical scheme for the dispersion term that preserves positivity is presented. The results of the proposed convection scheme and the solution given by the new method to compute dispersion are compared with standard numerical methods as used in MT3DMS.

Optimally Accurate Second-Order Time-Domain Finite-Difference Scheme for Acoustic, Electromagnetic, and Elastic Wave Modeling

Abstract. Numerical methods are extremely useful in solving real-life problems with complex materials and geometries. However, numerical methods in the time domain suffer from artificial numerical dispersion. Standard numerical techniques which are second-order in space and time, like the conventional Finite Difference 3-point (FD3) method, Finite-Difference Time-Domain (FDTD) method, and Finite Integration Technique (FIT) provide estimates of the error of discretized numerical operators rather than the error of the numerical solutions computed using these operators. Here optimally accurate time-domain FD operators which are second-order in time as well as in space are derived. Optimal accuracy means the greatest attainable accuracy for a particular type of scheme, e.g., second-order FD, for some particular grid spacing. The modified operators lead to an implicit scheme. Using the first order Born approximation, this implicit scheme is transformed into a two step explicit scheme, namely predictor-corrector scheme. The stability condition (maximum time step for a given spatial grid interval) for the various modified schemes is roughly equal to that for the corresponding conventional scheme. The modified FD scheme (FDM) attains reduction of numerical dispersion almost by a factor of 40 in 1-D case, compared to the FD3, FDTD, and FIT. The CPU time for the FDM scheme is twice of that required by the FD3 method. The simulated synthetic data for a 2-D P-SV (elastodynamics) problem computed using the modified scheme are 30 times more accurate than synthetics computed using a conventional scheme, at a cost of only 3.5 times as much CPU time. The FDM is of particular interest in the modeling of large scale (spatial dimension is more or equal to one thousand wave lengths or observation time interval is very high compared to reference time step) wave propagation and scattering problems, for instance, in ultrasonic antenna and synthetic scattering data modeling for Non-Destructive Testing (NDT) applications, where other standard numerical methods fail due to numerical dispersion effects. The possibility of extending this method to staggered grid approach is also discussed. The numerical FD3, FDTD, FIT, and FDM results are compared against analytical solutions.

A topologically consistent class of 3-D higher order curvilinear FDTD schemes for dispersion-optimized EMC and material modeling

An enhanced higher order finite-difference time-domain (FDTD) algorithm for the precise analysis of complex 3-D electromagnetic compatibility (EMC) structures and arbitrary interface material distributions in general curvilinear, skewed and stretching lattices is presented in this paper. Introducing a systematic topological tessellation, the novel methodology develops a family of robust higher order non-standard forms, which exactly represent the material properties and significantly suppress the artificial dispersion errors. To handle inherent mesh deficiencies an enhanced low-pass filtering procedure is implemented, while a consistent class of self-adaptive compact operators ensures the correct evaluation of electromagnetic components near boundary walls. Moreover, for more involved media interfaces that do not follow the lines of the grid, a convergent transformation around these discontinuities leads to precise simulations. Therefore, this optimal field-preserving technique along with suitably tuned perfectly matched layers (PMLs), achieve high levels of accuracy, decrease the required number of points per wavelength and provide considerable computational savings, as indicated by extensive numerical results addressing 3-D EMC and hard-to-model material applications.

Photonic band structure and related properties of photonic crystal waveguides in nonlinear optical polymers with metallic cladding

We examined the photonic band structure of a photonic crystal (PC) slab waveguide formed out of a nonlinear optical (NLO) polymer with metallic cladding by angle-dependent optical reflectivity and generated a theoretical photonic band structure by three-dimensional finite-difference time-domain calculations. The observed band dispersions determined from resonant features between the in-plane photonic band modes and incident light agree well with the theoretical band structure. We performed numerical simulations of the field distributions and decay rates of the observed photonic band modes in the waveguide and found that the observed modes are well confined in the patterned core when metal cladding is used, and have a longer lifetime than when a low refractive-index dielectric cladding is used. These results indicate that we can design artificial optical dispersions of band modes with strong waveguide confinement using this NLO polymer PC waveguide with metallic cladding.

Artificial dispersal of endangered epiphytic lichens: a tool for conservation in boreal forest landscapes

Due to increasing fragmentation of the boreal forests of Fennoscandia, a number of epiphytic lichens are now becoming threatened. Since these species typically are limited by a poor ability of dispersal, one possible but largely unexplored strategy for conservation is to disperse lichen material artificially into suitable habitats. Therefore, the objective of this study was to evaluate survival and vitality in lichen fragments from Evernia divaricata (L.) Ach. and Ramalina dilacerata (Hoffm.) Hoffm. after transplantation into three different stand types situated in northern Sweden, using different fragment sizes and modes of transplantation. After one year, survival ranged between 85% and 97.5%, and new growth occurred at all transplantation sites. The study has shown that transplantations of small fragments might constitute a resource-efficient option for establishment of new populations of endangered lichen species, or for enlarging their populations at the present sites of occurrence. In addition, the mode of transplantation was of importance for fragment vitality.

Flux-based method of characteristics for contaminant transport in flowing groundwater

A numerical method for treating advection-dominated contaminant transport in flowing groundwater is described. This method combines advantages of numerical discretizations by finite volume methods (like local mass conservation and the positivity of solutions) and by methods of characteristics (like larger time steps and reduced artificial numerical dispersion). For one-dimensional problems the method can produce equivalent algebraic systems as the finite volume Eulerian–Lagrangian localized adjoint method [13] and the flux-based modified method of characteristics [23] (and some other methods). An extension of the “flux-based methods of characteristics” for complex transport problems on multidimensional unstructured computational grids is the main contribution of this paper. Numerical results are included for a well established test example using a flux-based method of characteristics with aligned finite volumes.

Colloidal systems containing free radical-forming particles and composites on their basis

Controlled surface activity and reactivity of new carbon-chain functional surface-active oligoperoxides (FSAP) and derived metal complexes (OMC) with side and end di-tertiary and tert-alkyl (aryl) peroxidic, respectively, and other active functional groups cause the possibility of their tailored utilization as emulsifiers, surface-active initiators and modifiers of the phase boundaries of liquid, solid and mixed phases in different colloidal systems in a wide temperature range. New materials can be developed such as water and hydrocarbon polymer dispersions, artificial water dispersions of unsaturated polyesters and alkyd resins, polymer/polymeric blends, active glass and carbon fibers, dispersed fillers, reinforced and filled polymer composites with the definite special properties. Methods for the obtaining and the application of these materials are described.

テンサイの花粉に関する研究 : 第2報 風洞実験における花粉の飛散特性

テンサイの花粉に関する研究 : 第2報 風洞実験における花粉の飛散特性

Optimized Petrov–Galerkin model for advective–dispersive transport

Petrov–Galerkin finite element models (PGFEMs) appear to be the preferred choice for simulating advective–dispersive transport of chemicals in the natural environment for their ability to provide oscillation-free results. The PGFEM, however, provides oscillation-free results at the expense of introducing significant artificial dispersion. Introduction of artificial dispersion may lead to erroneous prediction of faster movement of the chemical and underestimation of the peak concentration. The objective of this paper is to develop an optimized PGFEM (OPGFEM). The OPGFEM developed is found to predict advective–dispersive transport of chemicals more accurately than the PGFEM.

DYNAMIC STABILITY AND SIZES OF CHAIN-LIKE CLUSTERS IN WIDE GAP NON-CRYSTALLINE SEMICONDUCTORS

In As y S 1-y glasses with the growth of the average coordination 2.1z<2.4 the decrease in the intensity of low-frequency (LF) boson maximum in Raman spectra and a “ violet “ shift of (0 B , the reduction in dimensions of chain clusters ( L ) and rise in dynamic stability has been observed. Linear dimensions L agree well with the diameter of zeolite pores at artificial dispersion of a chalcogenide into clusters. In the variety of As 2 S 3 (z=2.4) - GeS 2 (2.66)-Ge 2 S 3 (2.8) L varies as 1.42-2.24-1.25 nm, correspondingly. The smaller value of dynamic stability of glasses corresponds to the larger value of L.Based on the analysis of the Raman spectra and quantum-mechanical calculations of vibration frequencies for chalcogenide clusters by ab initio method it has been established that narrow windows in a zeolite of A­type stimulate the penetration of only linear clusters of As 2 S 3 and As 2 S 5 -type into the pores. While injecting clusters the dimensions of windows confine the penetration of branched clusters (As 2 S 3 )n, n=2-3 and molecules S 8 into the pores whose dimensions are larger than those of zeolite windows. The branched system of clusters is formed in the pores of a zeolite of X-typewith wide windows. The Raman spectra of zeolite matrix with dispersed into clusters x-As 22 S 78 chalcogenide and c-As 22 S 78 bulk glass in the region of valence vibrations are similar.

Computer Modeling of Oil Spill Trajectories With a High Accuracy Method

This paper proposes a high accuracy numerical method to model oil spill trajectories using a particle-tracking algorithm. The Euler method, used to calculate oil trajectories, can give adequate solutions in most open ocean applications. However, this method may not predict accurate particle trajectories in certain highly non-uniform velocity fields near coastal zones or in river problems. Simple numerical experiments show that the Euler method may also introduce artificial numerical dispersion that could lead to overestimation of spill areas. This article proposes a fourth-order Runge–Kutta method with fourth-order velocity interpolation to calculate oil trajectories that minimize these problems. The algorithm is implemented in the OilTrack model to predict oil trajectories following the “Nissos Amorgos” oil spill accident that occurred in the Gulf of Venezuela in 1997. Despite lack of adequate field information, model results compare well with observations in the impacted area.

Simulating advective-dispersive transport in groundwater: an accurate finite difference model

Finite difference models (FDMs) may provide oscillatory results when employed to predict contaminant transport in groundwater. The oscillation is usually avoided by adapting upwind methods. The upwind methods are reported to introduce large artificial dispersion. An improved FDM has been developed to provide oscillation free results with the introduction of minimum artificial dispersion. The improvement has been achieved by developing an expression of the minimum artificial dispersion needed to provide accurate results. The improved FDM provides results in excellent agreement with the analytical solution. Further, the improved FDM can easily be extended to two- or three-dimensional problems.