Simple Cascade Research Articles

Evaluation of a scaling cascade model for temporal rain- fall disaggregation

Abstract. The possibility of modelling the temporal structure of rainfall in southern Sweden by a simple cascade model is tested. The cascade model is based on exact conservation of rainfall volume and has a branching number of 2. The weights associated with one branching are 1 and 0 with probability P(1/0), 0 and 1 with P(0/1), and Wx/x, and 1 - Wx/x, 0 < Wx/x, < 1, with P(x/x), where Wx/x is associated with a theoretical probability distribution. Furthermore, the probabilities p are assumed to depend on two characteristics of the rainy time period (wet box) to be branched: rainfall volume and position in the rainfall sequence. In the first step, analyses of 2 years of 8-min data indicates that the model is applicable between approximately 1 hour and 1 week with approximately uniformly distributed Wx/x values. The probabilities P show a clear dependence on the box characteristics and a slight seasonal nonstationarity. In the second step, the model is used to disaggregate the time series from 17- to 1-hour resolution. The model-generated data reproduce well the ratio between rainy and nonrainy periods and the distribution of individual volumes. Event volumes, event durations, and dry period lengths are fairly well reproduced, but somewhat underestimated, as was the autocorrelation. From analyses of power spectrum and statistical moments the model preserves the scaling behaviour of the data. The results demonstrate the potential of scaling-based approaches in hydrological applications involving rainfall disaggregation.

Valence intersubband lasers with inverted light-hole effective mass

We propose a novel intersubband laser based on transition between the ground-state heavy-hole subband (HH1) and light-hole subband (LH1) in a k-space region where the light-hole effective mass is inverted. The laser structure can be electrically pumped with a simple quantum cascade scheme. Our calculation shows that with only a small fraction of the carrier population in the upper subband (LH1), it is possible to achieve population inversion between the two subbands locally in K space where the light-hole effective mass is inverted. Optical gain in excess of 150/cm can be achieved with a pumping current density on the order to 100 A/cm2 at the temperature of liquid nitrogen.

Neural interactions between cone photoreceptors and horizontal cells in the turtle (Mauremys caspica) retina.

Horizontal cells and cone photoreceptors in the vertebrate retina are interconnected by a complex network of synapses leading to the generation of color-coded responses in chromaticity horizontal cells. A simple cascade model of excitatory feedforward and inhibitory feedback synapses had been suggested to underlie these observations. In this study, the photoresponses of cones and horizontal cells were recorded intracellularly from the turtle eyecup. Three different approaches were adopted in order to test quantitatively the cascade model. Comparing linearity functions between these neurons indicated multiple excitatory inputs to each type of horizontal cells. The depolarizing photoresponses of R/G C-type horizontal cells were considerably faster than those of L-type horizontal cells but slower than those recorded from L-cones. This observation disagrees with the basic assumption of the cascade model that assign the depolarizing photoresponses of R/G C-type horizontal cells to a negative feedback pathway from L-type horizontal cells onto M-cones. Finally, the action spectra of each of the three types of horizontal cells could not be solely accounted for by input from one spectral type of cones. Only by assuming excitatory and inhibitory inputs from all spectral types of cones, the action spectra of all types of horizontal cells could be reconstructed. These findings suggest that the negative feedback pathways from horizontal cells onto cones in the turtle retina cannot solely account for the chromatic properties of the horizontal cells and support a direct inhibitory inputs from cones to turtle horizontal cells.

Multinucleon pion absorption on4He into thepppnfinal state

Results from a 4π solid angle measurement of the reaction π+4He→pppn at incident pion energies of Tπ+= 70, 118, 162, 239, and 330 MeV are presented. Integrated cross sections are given for the reactions where three nucleons participate, leading to energetic (ppp) or (ppn) final states, and for states where four nucleons are involved (pppn). The two three-nucleon absorption modes were investigated in particular, and an energy dependent isospin ratio of the cross sections of σppn/σppp=3.6±1.3, 2.6±0.5, 1.8±0.3, 1.4±0.2, and 1.8±0.6 was determined from 70 to 330 MeV. The differential cross sections were described by a complete set of eight independent variables and compared to simple cascade and phase space models. From this analysis the contributions from initial state interactions to the multinucleon absorption cross sections were found to be more important at higher pion energies, while those from final state interactions are stronger at lower energies. However, both mechanisms combined were found to account for not more than one-third of the total pppn multinucleon yield. The remaining strength is reasonably well reproduced by phase space models, but shows a dependence on the incident pion's orbital angular momentum. The isospin structure of the (ppp) and (ppn) final states is not understood, nor are some structures in their distributions. The four-nucleon yield (pppn) was found to be weak (1–8 % of the total absorption cross section) and shows no evidence for a “double-Δ” excitation.Received 18 June 1997DOI:https://doi.org/10.1103/PhysRevC.56.1872©1997 American Physical Society

Turbulent Behavior of Stock Exchange Indices and Foreign Currency Exchange Rates

The time evolution of stock exchange indices and foreign currency exchange rates has many similarities with turbulent flows. In particular, the probability densities of price changes are non-Gaussian and develop stretched exponential tails, quite similar to the densities of velocity differences measured in fully developed hydrodynamical turbulence. We show that a simple cascade model, based on a self-similar, hierarchical dynamics of price changes, describes the observed probability densities of the financial indices in a quantitatively correct way.

An information-theoretic approach to the design of a distributed cascade of sensors

We consider a new approach to the design of a cascade of distributed sensors for the detection of a target when the individual sensors in the cascade have different measurement reliabilities. To obtain specific results, we consider a Rayleigh scattering target model and independent additive Gaussian noise at each sensor. Because of the intractability of the general solution in the case where we are free to order the sensors in the cascade, we introduce a new, and more analytically tractable, information-theoretic approach to the design of the distributed sensor cascade. We compare the performance of this approach to the classical optimal design for the simple two-stage cascade. We note that although the classical design is more robust to changes in the sensor order in the cascade, if the sensors in the cascade are ordered from least reliable to most reliable, the information-theoretic approach yields performance with only a negligible degradation over the optimal classical approach. The approach holds the potential for providing near optimal designs for large cascades with only a fraction of the design complexity.

Butterflies in the spotlight

AbstractRecent advances in our understanding of developmental phenomena has come from highly interdisciplinary studies where molecular biology, ecology and evolution converge to elucidate fundamental mechanisms, how they change through time, and what function they actually have in the context of the niche of the organism. A recent study on butterfly eyespots(1) pinpoints the surprisingly simple regulatory cascade controlling such an apparently complex phenotype. The implications go beyond the elucidation of a fascinating developmental pathway, into the mechanisms and tempo of speciation and macroevolution.

The Cost-Effectiveness of Semi-Lagrangian Advection

The purpose of this paper is to ascertain the cost-effectiveness of semi-Lagrangian advection schemes for a wide variety of geophysical flows at all scales. The approach used is first to determine the minimum computational overhead associated with these schemes and then to examine temporal variability in the Lagrangian and Eulerian frames by employing simple turbulent cascade phenomenologies. The goal is to evaluate whether the Lagrangian variability is sufficiently slower than that of the Eulerian frame to overcome the computational overhead. It is found that the most efficient semi-Lagrangian schemes require a factor of 5–10 times more floating point operations per grid point per time step than the classic second-order leapfrog scheme. In the enstrophy cascade of 2D or quasigeostrophic turbulence, evolution of flow quantities is considerably slower in the Lagrangian frame and semi-Lagrangian advection schemes can be very cost-effective. In an energy cascade such as the Kolmogorov range of 3D turbulence or the inverse cascade of QG or 2D turbulence, the Lagrangian evolution remains slower than the Eulerian evolution. However, the difference is very much less than in the enstrophy cascade. Since the computational overhead of semi-Lagrangian schemes is considerable, they are at best marginally cost-effective at current resolutions for these flows, which prevail in the atmosphere at scales below 300–400 km. In the presence of stationary forcing fields in the Eulerian frame, the time step must respect the advective timescale even in the Lagrangian frame, at length scales where the forcing is significant. Here semi-Lagrangian schemes are not recommended.

The response regulator-like protein Pos9/Skn7 ofSaccharomyces cerevisiae is involved in oxidative stress resistance

We have isolated mutants of Saccharomyces cerevisiae with an increased sensitivity to oxidative stress. All pos9 mutants (pos for peroxide sensitivity) were hypersensitive to methylviologene, hyperbaric oxygen or hydrogen peroxide, but grew similarly to the wild-type under all other conditions tested. Isolation and sequencing of the respective POS9 gene revealed that it was identical to SKN7. The predicted Skn7/Pos9 protein possesses a domain with high homology to prokaryotic response regulators. These regulatory proteins are part of a simple signalling cascade termed a "two-component system", where a phosphorylation signal of a histidine kinase is transferred to a conserved aspartate residue of the response regulator. To test the functional role of the respective aspartate residue of Skn7/Pos9 protein in oxidative stress, we mutagenized this residue in vitro to alanine, arginine and glutamate. Only the glutamate allele (D427 to E) was able to rescue the hydrogen peroxide-sensitivity of pos9 mutants. By fusion experiments with the Gal4 DNA-binding domain we identified the isolated response regulator-like domain as a novel eukaryotic domain sufficient for gene activation. Whereas this hybrid protein activated transcription of a lacZ reporter gene under aerobic conditions, no activation was observed under anaerobic conditions, indicating that the response regulator domain is involved in a signalling reaction. Two-hybrid investigations also suggest an oligomerization of the Pos9 protein. Our results indicate that a two-component system is involved in the oxidative-stress response of yeast.

Temperature Cascade Control of Distillation Columns

This paper examines how difficult control tasks are enhanced by introducing secondary measurements, creating control cascades. Temperature is much used as secondary measurement because of cheap implementation and quick and accurate response. Distillation is often operated in this manner due to slow or lacking composition measurements, although the benefits have hardly been investigated closely, especially for multivariable control applications. We therefore use distillation as the example when quantifying improvements in interaction and disturbance rejection. We also give analytical expressions for the secondary controller gain. The improvements are reached through simple cascade operation of the control system and require no complicated estimator function.

Cell-vertex adaptive Euler method for cascade flows

This paper is concerned with the numerical solution of the two-dimensional steady Euler equations, using a multidimensional upwind cell-vertex residual distribution scheme. A solution-adaptive grid-refinement procedure is proposed, which combines with an efficient multigrid strategy based on an optimally smoothing explicit multistage scheme. A very accurate treatment of solid wall boundaries and a general approach for guaranteeing conservation on patched grids are developed within the present context of cell-vertex residual distribution schemes. The proposed approach is shown to be very efficient and sufficiently accurate to compute the transonic flow past a high-turning turbine cascade. N the last few years, a large effort has been devoted to the development of numerical methods for solving the multidimensional Euler equations with improved discontinuity-capturing capability. Classical upwind methods, based on the application of one-dimensional Riemann solvers along grid dependent directions, experience a loss of resolution in the presence of discontinuiti es not aligned with the mesh. In order to overcome such a difficulty, two different approaches have been proposed that introduce a truly multidimensional modeling of the propagation phenomena dominating the behavior of compressible flows. The Euler system is decomposed either into an equivalent set of five-to-six simple wave equations1 or into a system of four optimally decoupled compatibility equations.2 The scalar equations are solved using one of the newly developed multidimensional fluctuation splitting (FS) space discretization schemes,3 that send the residual calculated over each cell-vertex triangular element to its downstream nodes. The more robust methodology introduced by Roe1 and further developed in Refs. 4—6 has been widely used by the authors in combination with the linear first-order accurate space discretization AT-scheme.3 A standard full approximation scheme (FAS) multigrid strategy with an optimally smoothing explicit three-stage scheme57 has been employed to obtain a very efficient genuinely multidimensional Euler solver. The compact space discretization and the explicit time integration make the resulting methodology ideally suited for adaptive mesh refinement as well as for vector and parallel computers. In particular, the use of a solution-adaptive grid-refinement strategy is expected to further improve the efficiency of the method, as well as to make it sufficiently accurate for computing two-dimensional complex Euler flows. In this paper, after reviewing the basic multidimensional upwind FS Euler solver, a multigrid adaptive strategy is proposed that effectively combines a solution-adapt ive grid-refinement procedure with the FAS multigrid approach based on the optimally smoothing explicit scheme.6'7 Furthermore, the solid wall boundary conditions based on isentropic simple radial equilibrium (ISRE)8 are generalized to the present context of cell-vertex distribution schemes, and a general approach for guaranteeing conservation on patched grids is developed. Finally, results are presented for two transonic cascade flows. A simple cascade of NACA 0012 airfoils is used to demonstrate the accuracy improvement obtained using the ISRE wall boundary conditions with respect to the standard characteristic ones. A severe high-turning turbine blade cascade is employed to

Structure identification of non-linear models for QMB polymer-coated sensors

This article deals with the representation of quartz-microbalance (QMB) polymer-coated sensors by block-structured models, their structural identification and their functional identification. The block-structured modelling approach is one of the techniques available for obtaining a complete description of the dynamic behaviour of a non-linear sensing device without having detailed information about its inner structure. A QMB sensor, employed for the detection of mixtures of n-octane and toluene, is studied at the high concentration range (up to 100000 ppm), where a non-linear behaviour is expected. The sensor is exposed to time-varying concentrations of toluene and n-octane having quasi-white power spectral density. It is recognized that the sensor is very likely to admit a special model structure, called the ′Wiener model′, which is a simple non-linear cascade consisting of sequential dynamic linear, static non-linear and dynamic linear processes. The model is completely identified and gives a good approximation to the response of the sensor to any time-varying concentration. Our approach has not yet been widely applied because of the complication of the structure testing procedure, but it is demonstrated that the method is well suited for the study of most chemical transducers provided certain considerations and preliminary analyses are made, as described in this paper.

Wavelet correlations in the p model.

We suggest applying the concept of wavelet transforms to the study of correlations in multiparticle physics. Both the usual correlation functions as well as the wavelet transformed ones are calculated for the p model, which is a simple but tractable random cascade model. For this model, the wavelet transform decouples correlations between fluctuations defined on different scales. The advantageous properties of factorial moments are also shared by properly defined factorial wavelet correlations.

Application of Cascade theory to the description of microphase-separated biopolymer gels

Studies of the kinetics of gelation of an acid-modified waxy maize amylopectin have been performed using gel-time measurements and small- and wide-angle X-ray diffraction. The gel time–concentration relationship for gels set at 5 °C showed a high negative C–5.2 power law dependence over most of the concentration range considered (ca. 14–55% w/w), with a decrease in this exponent to –7.4 as the gelation temperature increased to 20 °C. The effective critical concentrations, at which the gel time–concentration relationships diverged, shifted from ca. 14 to 25% w/w for this temperature increases. For the 5 °C gels, changes in X-ray scattering continued over periods in excess of one month, with the kinetics of this process showing a C–4.1 concentration dependence. Comparison of the X-ray results at low and wide scattering angles showed a clear correlation between the growth of B-form starch crystallinity in the gels, and the aggregation of individual amylopectin molecules. From these, and some microscopical observations, a picture emerges of the gelation in such systems, involving the rate-determining formation of large semi-crystalline aggregates (of diameter 0.1–1.0 µm) which subsequently percolate. The simple cascade theory approach to biopolymer gelation will require substantial modification if it is to provide a realistic description of this situation.

A characteristic‐based method for incompressible flows

AbstractA new characteristic‐based method for the solution of the 2D laminar incompressible Navier‐Stokes equations is presented. For coupling the continuity and momentum equations, the artificial compressibility formulation is employed. The primitives variables (pressure and velocity components) are defined as functions of their values on the characteristics. The primitives variables on the characteristics are calculated by an upwind diffencing scheme based on the sign of the local eigenvalue of the Jacobian matrix of the convective fluxes. The upwind scheme uses interpolation formulae of third‐order accuracy. The time discretization is obtained by the explicit Runge–Kutta method. Validation of the characteristic‐based method is performed on two different cases: the flow in a simple cascade and the flow over a backwardfacing step.

Spin-polarized electron capture for the Na+3He2+ system at a 3He2+ impact energy of 5.33-9.33 keV/amu.

$^{3}\mathrm{He}^{+}$ atomic polarizations following the spin-polarized electron capture process for the Na\ensuremath{\rightarrow}(3s)${+}^{3}$${\mathrm{He}}^{2+}$ system were measured at $^{3}\mathrm{He}^{2+}$ impact energies from 5.33 to 9.33 keV/amu. The magnitude of the $^{3}\mathrm{He}^{+}$ atomic polarizations was deduced from the $^{3}\mathrm{He}^{+}$ nuclear polarization measured by means of beam-foil spectroscopy. The observed polarization transfer coefficient ${\mathit{P}}_{\mathit{T}}$ defined by the ratio of the $^{3}\mathrm{He}^{+}$ atomic polarization to the sodium one showed a pronounced reduction from unity, which was qualitatively explained by the prediction of a simple cascade photon decay model. Evidence for a further reduction of ${\mathit{P}}_{\mathit{T}}$ from the above model and a possible impact energy dependence of ${\mathit{P}}_{\mathit{T}}$ suggested an excessive depolarization due to the presence of the collision alignment parameter ${\mathit{A}}_{0}^{\mathrm{col}}$ of $^{3}\mathrm{He}^{+}$ formed by the electron capture process. In order to see this more closely, the observed ${\mathit{P}}_{\mathit{T}}$'s were examined theoretically using the semiclassical impact parameter method, in which an 18-state molecular expansion was employed, and atomic-type electron translation effects were rigorously taken into account. Ensuring that both the absolute values and the impact energy dependence of the observed capture cross sections were remarkably well reproduced by the calculations in which the states up to 4f in $^{3}\mathrm{He}^{+}$ were introduced, it was demonstrated that the calculated results for ${\mathit{P}}_{\mathit{T}}$ qualitatively reproduced not only the absolute values of the observed ${\mathit{P}}_{\mathit{T}}$'s but also their gentle decrease with increasing impact energy. Production of nuclear polarizations resulting from the polarized electron capture processes between multicharged heavy ions and alkaline-earth-metal atoms is offered as one of the promising applications to the future project of universal polarized heavy-ion sources.

Two new cascade resonator-in-a-loop filter configurations for tracking multiple sinusoids

Two adaptive configuration arrangements for tracking multiple sinusoids are introduced: a simple cascade of resonators-in-loops and a more elaborately interconnected structure. Simulation results demonstrate that these structures can successfully track and enhance multiple sinusoids, especially effectively when using the latter adaptive configuration. >

Multi-step rhodopsin inactivation schemes can account for the size variability of single photon responses in Limulus ventral photoreceptors.

Limulus ventral photoreceptors generate highly variable responses to the absorption of single photons. We have obtained data on the size distribution of these responses, derived the distribution predicted from simple transduction cascade models and compared the theory and data. In the simplest of models, the active state of the visual pigment (defined by its ability to activate G protein) is turned off in a single reaction. The output of such a cascade is predicted to be highly variable, largely because of stochastic variation in the number of G proteins activated. The exact distribution predicted is exponential, but we find that an exponential does not adequately account for the data. The data agree much better with the predictions of a cascade model in which the active state of the visual pigment is turned off by a multi-step process.

A cascade interpretation of Lundgren’s stretched spiral vortex model for turbulent fine structure

Lundgren’s [Phys. Fluids 25, 2193 (1982)] model for turbulent fine structure comprises coherent vortices which wind up vorticity variations into spiral structures; simultaneously the vortices are stretched axially by a background strain field. The model predicts a k−5/3 energy spectrum and is remarkably robust to the form of the coherent vortices and the form of the vorticity variations. To understand this the present article introduces a simple cascade argument which illuminates how the dynamical processes of vortex stretching and reduction of scale conspire to give this Kolmogorov spectrum. Some generalizations are considered.

Genetics of differentiation in Streptomyces.

The use of mutants and molecular genetics has begun to reveal how differentiation is brought about in multicellular, mycelial Streptomyces spp. Alternative pathways to aerial mycelium formation may be activated on different media. In some cases, extracellular signals are transmitted or exchanged. Extracellular proteins may act as morphogens in the erection of aerial hyphae. A rare codon, UUA, is apparently confined to mRNAs from a few genes important only for early stages of differentiation; it is absent from vegetative or developmentally late mRNAs. Sporulation of aerial hyphae involves at least four specific regulatory proteins, including a sigma factor and an unusual small protein. A complex interplay between the sporulation regulatory genes, rather than a simple linear dependence cascade, is emerging.