Analysis of nonlinear gain-induced effects on short-pulse amplification in doped fibers by use of an extended power equation

Optical pulse amplification in doped fibers is studied using an extended power transport equation for the coupled pulse spectral components. This equation includes the effects of gain saturation, gain dispersion, fiber dispersion, fiber nonlinearity, and amplified spontaneous emission. The new model is employed to study nonlinear gain-induced effects on the spectrotemporal characteristics of amplified subpicosecond pulses, in both the anomalous and the normal dispersion regimes.

Simulation of Drosophila circadian oscillations, mutations, and light responses by a model with VRI, PDP-1, and CLK.

A model of Drosophila circadian rhythm generation was developed to represent feedback loops based on transcriptional regulation of per, Clk (dclock), Pdp-1, and vri (vrille). The model postulates that histone acetylation kinetics make transcriptional activation a nonlinear function of [CLK]. Such a nonlinearity is essential to simulate robust circadian oscillations of transcription in our model and in previous models. Simulations suggest that two positive feedback loops involving Clk are not essential for oscillations, because oscillations of [PER] were preserved when Clk, vri, or Pdp-1 expression was fixed. However, eliminating positive feedback by fixing vri expression altered the oscillation period. Eliminating the negative feedback loop in which PER represses per expression abolished oscillations. Simulations of per or Clk null mutations, of per overexpression, and of vri, Clk, or Pdp-1 heterozygous null mutations altered model behavior in ways similar to experimental data. The model simulated a photic phase-response curve resembling experimental curves, and oscillations entrained to simulated light-dark cycles. Temperature compensation of oscillation period could be simulated if temperature elevation slowed PER nuclear entry or PER phosphorylation. The model makes experimental predictions, some of which could be tested in transgenic Drosophila.

Specimen specific parameter identification of ovine lumbar intervertebral discs: On the influence of fibre-matrix and fibre-fibre shear interactions.

Numerical models of the intervertebral disc, which address mechanical questions commonly make use of the difference in water content between annulus and nucleus, and thus fluid and solid parts are separated. Despite this simplification, models remain complex due to the anisotropy and nonlinearity of the annulus and regional variations of the collagen fibre density. Additionally, it has been shown that cross-links make a large contribution to the stiffness of the annulus. Because of this complex composite structure, it is difficult to reproduce several sets of experimental data with one single set of material parameters. This study addresses the question to which extent the ultrastructure of the intervertebral disc should be modelled so that its moment-angle behaviour can be adequately described. Therefore, a hyperelastic constitutive law, based on continuum mechanical principles was derived, which does not only consider the anisotropy from the collagen fibres, but also interactions among the fibres and between the fibres and the ground substance. Eight ovine lumbar intervertebral discs were tested on a custom made spinal loading simulator in flexion/extension, lateral bending and axial rotation. Specimen-specific geometrical models were generated using CT images and T2 maps to distinguish between annulus fibrosus and nucleus pulposus. For the identification of the material parameters the annulus fibrosus was described with two scenarios: with and without fibre-matrix and fibre-fibre interactions. Both scenarios showed a similar behaviour on a load displacement level. Comparing model predictions to the experimental data, the mean RMS of all specimens and all load cases was 0.54±0.15° without the interaction and 0.54±0.19° when the fibre-matrix and fibre-fibre interactions were included. However, due to the increased stiffness when cross-links effects were included, this scenario showed more physiological stress-strain relations in uniaxial and biaxial stress states. Thus, the present study suggests that fibre-matrix and fibre-fibre interactions should be considered in the constitutive law when the model addresses questions concerning the stress field of the annulus fibrosus.

VIS-NIR reflectance of water ice/regolith analogue mixtures and implications for the detectability of ice mixed within planetary regoliths

Permanently shadowed regions at the poles of the Moon and Mercury have been pointed out as candidates for hosting water ice at their surface. We have measured in the laboratory the visible and near infrared spectral range (VIS-NIR) bidirectional reflectance of intimate mixtures of water ice and the JSC-1AF lunar simulant for different ice concentrations, particle sizes, and measurement geometries. The nonlinearity between the measured reflectance and the amount of ice in the mixture can be reproduced to some extent by the mixing formulas of standard reflectance models, in particular, those of Hapke and Hiroi, which are tested here. Estimating ice concentrations from reflectance data without knowledge of the mixing coefficientsstrongly dependent on the size/shape of the grainscan result in large errors. According to our results, it is possible that considerable amounts of water ice might be intimately mixed in the regolith of the Moon and Mercury without producing noticeable photometric signatures.

Intrinsic characteristics of the proton pump in the luminal membrane of a tight urinary epithelium. The relation between transport rate and delta mu H.

A number of tight urinary epithelia, as exemplified by the turtle bladder, acidify the luminal solution by active transport of H+ across the luminal cell membrane. The rate of active H+ transport (JH) decreases as the electrochemical potential difference for H+ [delta mu H = mu H(lumen) - mu H(serosa)] across the epithelium is increased. The luminal cell membrane has a low permeability for H+ equivalents and a high electrical resistance compared with the basolateral cell membrane. Changes in JH thus reflect changes in active H+ transport across the luminal membrane. To examine the control of JH by delta mu H in the turtle bladder, transepithelial electrical potential differences (delta psi) were imposed at constant acid-base conditions or the luminal pH was varied at delta psi = 0 and constant serosal PCO2 and pH. When the luminal compartment was acidified from pH 7 to 4 or was made electrically positive, JH decreased as a linear function of delta mu H as previously described. When the luminal compartment was made alkaline from pH 7 to 9 or was made electrically negative, JH reached a maximal value, which was the same whether the delta mu H was imposed as a delta pH or a delta psi. The nonlinear JH vs. delta mu H relation does not result from changes in the number of pumps in the luminal membrane or from changes in the intracellular pH, but is a characteristic of the H+ pumps themselves. We propose a general scheme, which, because of its structural features, can account for the nonlinearity of the JH vs. delta mu H relations and, more specifically, for the kinetic equivalence of the effects of the chemical and electrical components of delta mu H. According to this model, the pump complex consists of two components: a catalytic unit at the cytoplasmic side of the luminal membrane, which mediates the ATP-driven H+ translocation, and a transmembrane channel, which mediates the transfer of H+ from the catalytic unit to the luminal solution. These two components may be linked through a buffer compartment for H+ (an antechamber).

Assessing time-by-covariate interactions in Cox proportional hazards regression models using cubic spline functions

This dissertation develops and explores the methodology for the use of cubic spline functions in assessing time-by-covariate interactions in Cox proportional hazards regression models. These interactions indicate violations of the proportional hazards assumption of the Cox model. Use of cubic spline functions allows for the investigation of the shape of a possible covariate time-dependence without having to specify a particular functional form. Cubic spline functions yield both a graphical method and a formal test for the proportional hazards assumption as well as a test of the nonlinearity of the time-by-covariate interaction. Five existing methods for assessing violations of the proportional hazards assumption are reviewed and applied along with cubic splines to three well known two-sample datasets. An additional dataset with three covariates is used to explore the use of cubic spline functions in a more general setting. ^

Territory and Infrastructure : Strategic Identification and Project Pondering

El Territorio hoy es visto como una totalidad organizada que no puede ser pensada separando cada uno de los elementos que la componen; cada uno de ellos es definido por su relación con los otros elementos. Así, un pensamiento que integra diferentes disciplinas y saberes comienza a manejar una realidad que lejos está de definir certezas inamovibles, y comienza a vislumbrar horizontes estratégicos. La adaptación a la no linealidad de las relaciones que se dan sobre el territorio, y la diferencia de velocidades en las que actúan los distintos actores, nos exige hacer de la flexibilidad una característica esencial de la metodología de planificación estratégica. La multi-causalidad de los fenómenos que estructuran el territorio nos obliga a construir criterios cualitativos, entendiendo que nos es imposible la medición de estas cadenas causales y su reconstrucción completa en el tiempo; sin dejar por ello de edificar un marco profundo de acción y transformación que responda a una realidad cierta y veraz. Los fenómenos producidos sobre el territorio nunca actúan de manera aislada, lo que implica una responsabilidad a la hora de comprender las sinergias y la restricción que afectan los resultados de los procesos desatados. La presente ponencia corresponde a la Segunda Fase del proceso de identificación estratégica de los proyectos Plan Estratégico Territorial (PET) que se inició en el año 2005; dicho Plan es llevada a cabo por la Subsecretaría de Planificación Territorial del Ministerio de Planificación Federal y fue abordado sobre la base de tres pretensiones: institucionalizar el ejercicio del pensamiento estratégico, fortalecer la metodología de trabajo transdisciplinaria y multisectorial, y diseñar un sistema de ponderación de proyectos estratégicos de infraestructura, tanto a nivel provincial como nacional, con una fuerte base cualitativa. Este proceso dio como resultado una cartera ponderada de proyectos de infraestructura conjuntamente con una metodología que permitió consolidar los equipos provinciales de planificación, tanto en su relación con los decisores políticos como con los actores de los múltiples sectores del gobierno, y en estos resultados consolidar y reforzar una cultura del pensamiento estratégico sobre el territorio

Territory and Infrastructure : Strategic Identification and Project Pondering

El Territorio hoy es visto como una totalidad organizada que no puede ser pensada separando cada uno de los elementos que la componen; cada uno de ellos es definido por su relación con los otros elementos. Así, un pensamiento que integra diferentes disciplinas y saberes comienza a manejar una realidad que lejos está de definir certezas inamovibles, y comienza a vislumbrar horizontes estratégicos. La adaptación a la no linealidad de las relaciones que se dan sobre el territorio, y la diferencia de velocidades en las que actúan los distintos actores, nos exige hacer de la flexibilidad una característica esencial de la metodología de planificación estratégica. La multi-causalidad de los fenómenos que estructuran el territorio nos obliga a construir criterios cualitativos, entendiendo que nos es imposible la medición de estas cadenas causales y su reconstrucción completa en el tiempo; sin dejar por ello de edificar un marco profundo de acción y transformación que responda a una realidad cierta y veraz. Los fenómenos producidos sobre el territorio nunca actúan de manera aislada, lo que implica una responsabilidad a la hora de comprender las sinergias y la restricción que afectan los resultados de los procesos desatados. La presente ponencia corresponde a la Segunda Fase del proceso de identificación estratégica de los proyectos Plan Estratégico Territorial (PET) que se inició en el año 2005; dicho Plan es llevada a cabo por la Subsecretaría de Planificación Territorial del Ministerio de Planificación Federal y fue abordado sobre la base de tres pretensiones: institucionalizar el ejercicio del pensamiento estratégico, fortalecer la metodología de trabajo transdisciplinaria y multisectorial, y diseñar un sistema de ponderación de proyectos estratégicos de infraestructura, tanto a nivel provincial como nacional, con una fuerte base cualitativa. Este proceso dio como resultado una cartera ponderada de proyectos de infraestructura conjuntamente con una metodología que permitió consolidar los equipos provinciales de planificación, tanto en su relación con los decisores políticos como con los actores de los múltiples sectores del gobierno, y en estos resultados consolidar y reforzar una cultura del pensamiento estratégico sobre el territorio

Territory and Infrastructure : Strategic Identification and Project Pondering

El Territorio hoy es visto como una totalidad organizada que no puede ser pensada separando cada uno de los elementos que la componen; cada uno de ellos es definido por su relación con los otros elementos. Así, un pensamiento que integra diferentes disciplinas y saberes comienza a manejar una realidad que lejos está de definir certezas inamovibles, y comienza a vislumbrar horizontes estratégicos. La adaptación a la no linealidad de las relaciones que se dan sobre el territorio, y la diferencia de velocidades en las que actúan los distintos actores, nos exige hacer de la flexibilidad una característica esencial de la metodología de planificación estratégica. La multi-causalidad de los fenómenos que estructuran el territorio nos obliga a construir criterios cualitativos, entendiendo que nos es imposible la medición de estas cadenas causales y su reconstrucción completa en el tiempo; sin dejar por ello de edificar un marco profundo de acción y transformación que responda a una realidad cierta y veraz. Los fenómenos producidos sobre el territorio nunca actúan de manera aislada, lo que implica una responsabilidad a la hora de comprender las sinergias y la restricción que afectan los resultados de los procesos desatados. La presente ponencia corresponde a la Segunda Fase del proceso de identificación estratégica de los proyectos Plan Estratégico Territorial (PET) que se inició en el año 2005; dicho Plan es llevada a cabo por la Subsecretaría de Planificación Territorial del Ministerio de Planificación Federal y fue abordado sobre la base de tres pretensiones: institucionalizar el ejercicio del pensamiento estratégico, fortalecer la metodología de trabajo transdisciplinaria y multisectorial, y diseñar un sistema de ponderación de proyectos estratégicos de infraestructura, tanto a nivel provincial como nacional, con una fuerte base cualitativa. Este proceso dio como resultado una cartera ponderada de proyectos de infraestructura conjuntamente con una metodología que permitió consolidar los equipos provinciales de planificación, tanto en su relación con los decisores políticos como con los actores de los múltiples sectores del gobierno, y en estos resultados consolidar y reforzar una cultura del pensamiento estratégico sobre el territorio

Carbon isotopes, hydrography, and nutrients measured at hydrographic stations from a transatlantic section near 40° N

14C concentrations, as well as 14C, hydrographic and nutrient data are reported for 5 hydrographic stations that form a transatlantic section near 40° N ("Meteor" cruise no. 23, 1971). Precision (for 14C ± 0.3 ? or better) and comparability with literature data are specified. A planned intercomparison with the US GEOSECS program within the Newfoundland Basin deep water failed because of variability of water characteristics. The observed 14C values decrease from about Delta 14C = + 80 ? at the surface to -70 ? at 2000 m depth. Deeper down, the values west of the Midatlantic Ridge remain similar, whereas those east of the ridge decrease further, to about - 110 ?. It is shown that bomb-14C is prominent down to about 1500 m depth. Beyond this depth the bomb 14C component is small and is negligible in the eastern basin below 2800 m. On the basis of the 14C-tritium correlation, the distribution of natural 14C below about 1500 m depth is derived from the observations. In the deep and bottom water east of the ridge the 14C-salinity relationship seemingly is non-linear. Contrary to expectation, the 14C concentration in the bottom water is not lower than found on an US GEOSECS station near 10° N. Apparently, lateral concentration differences in the Northeast Atlantic bottom water as well as nonlinearity of the 14C-salinity relationship at 40° N do not exceed 10 ? in Delta 14C.

Elastoplastic consolidation at finite strain. Part 2: finite element implementation and numerical examples

A mathematical model for finite strain elastoplastic consolidation of fully saturated soil media is implemented into a finite element program. The algorithmic treatment of finite strain elastoplasticity for the solid phase is based on multiplicative decomposition and is coupled with the algorithm for fluid flow via the Kirchhoff pore water pressure. A two-field mixed finite element formulation is employed in which the nodal solid displacements and the nodal pore water pressures are coupled via the linear momentum and mass balance equations. The constitutive model for the solid phase is represented by modified Cam—Clay theory formulated in the Kirchhoff principal stress space, and return mapping is carried out in the strain space defined by the invariants of the elastic logarithmic principal stretches. The constitutive model for fluid flow is represented by a generalized Darcy's law formulated with respect to the current configuration. The finite element model is fully amenable to exact linearization. Numerical examples with and without finite deformation effects are presented to demonstrate the impact of geometric nonlinearity on the predicted responses. The paper concludes with an assessment of the performance of the finite element consolidation model with respect to accuracy and numerical stability.

Cryptographic properties of Boolean functions defining elementary cellular automata

In this work, the algebraic properties of the local transition functions of elementary cellular automata (ECA) were analysed. Specifically, a classification of such cellular automata was done according to their algebraic degree, the balancedness, the resiliency, nonlinearity, the propagation criterion and the existence of non-zero linear structures. It is shown that there is not any ECA satisfying all properties at the same time.

Column Generation Algorithms for Nonlinear Optimization II: Numerical Investigations

García et al. present a class of column generation (CG) algorithms for nonlinear programs. Its main motivation from a theoretical viewpoint is that under some circumstances, finite convergence can be achieved, in much the same way as for the classic simplicial decomposition method; the main practical motivation is that within the class there are certain nonlinear column generation problems that can accelerate the convergence of a solution approach which generates a sequence of feasible points. This algorithm can, for example, accelerate simplicial decomposition schemes by making the subproblems nonlinear. This paper complements the theoretical study on the asymptotic and finite convergence of these methods given in [1] with an experimental study focused on their computational efficiency. Three types of numerical experiments are conducted. The first group of test problems has been designed to study the parameters involved in these methods. The second group has been designed to investigate the role and the computation of the prolongation of the generated columns to the relative boundary. The last one has been designed to carry out a more complete investigation of the difference in computational efficiency between linear and nonlinear column generation approaches. In order to carry out this investigation, we consider two types of test problems: the first one is the nonlinear, capacitated single-commodity network flow problem of which several large-scale instances with varied degrees of nonlinearity and total capacity are constructed and investigated, and the second one is a combined traffic assignment model

Stabilization in a two-species chemotaxis system with logistic source

We study a system of three partial differential equations modelling the spatiotemporal behaviour of two competitive populations of biological species both of which are attracted chemotactically by the same signal substance. For a range of the parameters the system possesses a uniquely determined spatially homogeneous positive equilibrium (u?, v?) globally asymptotically stable within a certain nonempty range of the logistic growth coefficients.

Revisiting the method to obtain the mechanical properties of hydrided fuel cladding in the hoop direction

The method reported in the literature to calculate the stress–strain curve of nuclear fuel cladding from ring tensile test is revisited in this paper and a new alternative is presented. In the former method, two universal curves are introduced under the assumption of small strain. In this paper it is shown that these curves are not universal, but material-dependent if geometric nonlinearity is taken into account. The new method is valid beyond small strains, takes geometric nonlinearity into consideration and does not need universal curves. The stress–strain curves in the hoop direction are determined by combining numerical calculations with experimental results in a convergent loop. To this end, ring tensile tests were performed in unirradiated hydrogen-charged samples. The agreement among the simulations and the experimental results is excellent for the range of concentrations tested (up to 2000 wppm hydrogen). The calculated stress–strain curves show that the mechanical properties do not depend strongly on the hydrogen concentration, and that no noticeable strain hardening occurs. However, ductility decreases with the hydrogen concentration, especially beyond 500 wppm hydrogen. The fractographic results indicate that as-received samples fail in a ductile fashion, whereas quasicleavage is bserved in the hydrogen-charged samples.