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Perturbation Analysis (perturbation + analysis)
Selected AbstractsPerturbation analysis of fiber surface plasma resonance sensorMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 12 2006F. G. Sun Abstract Perturbation method is used to calculate the resonance wavelength shift and the sensitivity of fiber surface plasma resonance sensor. We show that the resonance wavelength always shifts to long wavelength direction as the sensed medium dielectric index increases. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 2425,2427, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21956 [source] Population viability and perturbation analyses in remnant populations of the Andean catfish Astroblepus ubidiaiECOLOGY OF FRESHWATER FISH, Issue 2 2005L. A. Vélez-Espino Abstract ,Astroblepus ubidiai (Actinopterygii; Siluriformes), which is the only native fish of the highlands of the Province of Imbabura, Ecuador, was abundant in the past in the Imbakucha watershed and adjacent drainages but currently it is restricted to a few isolated refuges. Population viability analysis (PVA) was used to detect critical aspects in the ecology and conservation biology of this unique fish. The annual population growth rate (,) was estimated for six remnant populations of this Andean catfish using a deterministic matrix population model. Sensitivity and elasticity analyses complemented the PVA by providing constructive insights into vital rates affecting projections and extinction probabilities. Positive population growth rates were found in all the study populations. The high contributions of juvenile survival to the variance of , and its high elasticity indicated that A. ubidiai population dynamics are highly sensitive to the transition values of this vital rate, which can promptly respond to management or antagonistic perturbations. Allowing fish to survive until the age of first reproduction and permitting the successful reproduction of these individuals will facilitate positive population growth rates, however the very small areas of occupancy, small extent of occurrence and severe fragmentation may still contribute to the extinction risk. Resumen 1. Astroblepus ubidiai (Actinopterygii; Siluriformes), el único pez nativo de los altos Andes en la Provincia de Imbabura, Ecuador, era abundante en el pasado en la cuenca de Imbakucha y en las cuencas adyacentes, pero actualmente existe en unos cuantos refugios geográficamente aislados. 2. Un Análisis de Viabilidad Poblacional (AVP) fue necesario para detectar los aspectos críticos en la ecología y biología de conservación de la especie. La tasa anual de crecimiento poblacional (,) se estimó en seis poblaciones remanentes de este pez andino usando un modelo matricial de población. Análisis de sensitividad y elasticidad permitieron la complementación de interpretaciones derivadas del AVP mediante la facilitación de exploraciones constructivas de los efectos relativos de las tasas vitales en proyecciones demográficas y probabilidades de extinción. 3. Todas las poblaciones estudiadas presentaron tasas positivas de crecimiento poblacional a pesar de que factores determinísticos tales como la pérdida de hábitat y fragmentación han llevado la ocurrencia de esta especie a pequeños fragmentos. La alta contribución a la varianza de , y la alta elasticidad de la supervivencia juvenil indicaron que las dinámicas poblacionales de A. ubidiai son altamente sensibles a los valores de transición de esta tasa vital, la cual puede responder con facilidad a actividades de manejo o perturbaciones antagónicas. 4. Facilitando que los peces sobrevivan hasta la edad de primera reproducción y permitiendo la reproducción exitosa de estos individuos son condiciones determinantes para mantener tasas positivas de crecimiento. Sin embargo, aún existe la necesidad de confrontar el riesgo de extinción derivado de pequeñas áreas de ocupación, limitada extensión de ocurrencia, y fragmentación severa. En este artículo también se discute la manera en que el conocimiento de estas circunstancias específicas es esencial para tomar acciones efectivas de conservación. [source] Backward perturbation analysis for scaled total least-squares problemsNUMERICAL LINEAR ALGEBRA WITH APPLICATIONS, Issue 8 2009X.-W. Chang Abstract The scaled total least-squares (STLS) method unifies the ordinary least-squares (OLS), the total least-squares (TLS), and the data least-squares (DLS) methods. In this paper we perform a backward perturbation analysis of the STLS problem. This also unifies the backward perturbation analyses of the OLS, TLS and DLS problems. We derive an expression for an extended minimal backward error of the STLS problem. This is an asymptotically tight lower bound on the true minimal backward error. If the given approximate solution is close enough to the true STLS solution (as is the goal in practice), then the extended minimal backward error is in fact the minimal backward error. Since the extended minimal backward error is expensive to compute directly, we present a lower bound on it as well as an asymptotic estimate for it, both of which can be computed or estimated more efficiently. Our numerical examples suggest that the lower bound gives good order of magnitude approximations, while the asymptotic estimate is an excellent estimate. We show how to use our results to easily obtain the corresponding results for the OLS and DLS problems in the literature. Copyright © 2009 John Wiley & Sons, Ltd. [source] Sensitivity analysis of transient population dynamicsECOLOGY LETTERS, Issue 1 2007Hal Caswell Abstract Short-term, transient population dynamics can differ in important ways from long-term asymptotic dynamics. Just as perturbation analysis (sensitivity and elasticity) of the asymptotic growth rate reveals the effects of the vital rates on long-term growth, the perturbation analysis of transient dynamics can reveal the determinants of short-term patterns. In this article, I present a completely new approach to transient sensitivity and elasticity analysis, using methods from matrix calculus. Unlike previous methods, this approach applies not only to linear time-invariant models but also to time-varying, subsidized, stochastic, nonlinear and spatial models. It is computationally simple, and does not require calculation of eigenvalues or eigenvectors. The method is presented along with applications to plant and animal populations. [source] A perturbation analysis of harmonic generation from saturated elements in power systemsELECTRICAL ENGINEERING IN JAPAN, Issue 4 2010Teruhisa Kumano Abstract Nonlinear phenomena such as saturation of magnetic flux have considerable effects in power systems analysis. It is reported that a failure in a real 500-kV system triggered islanding operation, where resultant even harmonics caused malfunctions in protective relays. It is also reported that the major origin of this wave distortion is nothing but unidirectional magnetization of the transformer iron core. Time simulation is widely used today to analyze phenomena of this type, but it has basically two shortcomings. One is that the time simulation takes too much computing time in the vicinity of inflection points in the saturation characteristic curve because certain iterative procedures such as N-R (Newton,Raphson) must be used and such methods tend to be caught in an ill-conditioned numerical hunting. The other is that such simulation methods sometimes do not aid an intuitive understanding of the studied phenomenon because all of the nonlinear equations are treated in matrix form and are not properly divided into understandable parts, as is done in linear systems. This paper proposes a new computation scheme that is based on the so-called perturbation method. Magnetic saturation of iron cores in a generator and a transformer are taken into account. The proposed method has a special feature to deal with the first shortcoming of the N-R-based time simulation method stated above. The proposed method does not use an iterative process to reduce the equation residue, but uses perturbation series, so that it is free of the ill-conditioning problem. The user need only calculate the perturbation terms one by one until the necessary accuracy is attained. In a numerical example treated in the present paper, first-order perturbation can achieve reasonably high accuracy, which means very fast computing time. In a numerical study, three nonlinear elements are considered. The calculation results are almost identical to the conventional N-R-based time simulation, which shows the validity of the method. The proposed method can be effectively used in screening where many case studies are needed. © 2009 Wiley Periodicals, Inc. Electr Eng Jpn, 170(4): 35,42, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20895 [source] Stochastic computational modelling of highly heterogeneous poroelastic media with long-range correlationsINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 1 2004Diego G. Frias Abstract The compaction of highly heterogeneous poroelastic reservoirs with the geology characterized by long-range correlations displaying fractal character is investigated within the framework of the stochastic computational modelling. The influence of reservoir heterogeneity upon the magnitude of the stresses induced in the porous matrix during fluid withdrawal and rock consolidation is analysed by performing ensemble averages over realizations of a log-normally distributed stationary random hydraulic conductivity field. Considering the statistical distribution of this parameter characterized by a coefficient of variation governing the magnitude of heterogeneity and a correlation function which decays with a power-law scaling behaviour we show that the combination of these two effects result in an increase in the magnitude of effective stresses of the rock during reservoir depletion. Further, within the framework of a perturbation analysis we show that the randomness in the hydraulic conductivity gives rise to non-linear corrections in the upscaled poroelastic equations. These corrections are illustrated by a self-consistent recursive hierarchy of solutions of the stochastic poroelastic equations parametrized by a scale parameter representing the fluctuating log-conductivity standard deviation. A classical example of land subsidence caused by fluid extraction of a weak reservoir is numerically simulated by performing Monte Carlo simulations in conjunction with finite elements discretizations of the poroelastic equations associated with an ensemble of geologies. Numerical results illustrate the effects of the spatial variability and fractal character of the permeability distribution upon the evolution of the Mohr,Coulomb function of the rock. Copyright © 2004 John Wiley & Sons, Ltd. [source] On Marangoni effects in a heated thin fluid layer with a monolayer surfactant.INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 1 2005Part I: model development, stability analysis Abstract We develop a model for surface tension driven flow induced by an insoluble surfactant monolayer on a heated thin fluid layer. The mathematical model is based on a perturbation analysis for a thin fluid layer. The resulting model involves coupling of flow and heat transfer to an additional transport equation for surfactant concentration on the surface. We develop the stability analysis of this coupled system. We characterize the stability behaviour and induced wave motion into four parametric regions based on linear stability analysis. A finite element formulation and numerical studies of the behaviour in the various stability regimes are given in Part II. Copyright © 2004 John Wiley & Sons, Ltd. [source] QOS and call admission control of multimedia traffic in a PCS networkINTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 6 2004Duan-Shin Lee Abstract In this paper we study the quality of service of integrated voice and data services in a wireless network. The voice traffic is transmitted in circuit-switched mode and data traffic is transmitted in packet-switched mode. Voice traffic has high transmission priority and data packets are transmitted only when there are available channels not used by the voice traffic. Otherwise, the data packets wait in a data buffer. We consider two schemes to reduce the forced termination probability for the handoff voice calls. The two schemes are the reserved channel scheme and the queueing priority scheme. We apply a fluid analysis to study the performance of the data buffer under the two handoff schemes and the basic system in which there is no arrangement to reduce the forced termination probability of handoff calls. From this analysis, we derive admission controls for voice traffic as well as for data traffic. This analysis also enables us to conclude that the reserved channel scheme not only is more effective in reducing the forced termination probability of handoff calls, it is also more effective in providing the QOS guarantee for the data traffic. Another contribution of this paper is to develop a perturbation analysis to solve the fluid models efficiently and quickly. Copyright © 2004 John Wiley & Sons, Ltd. [source] First-order perturbation analysis of the best rank-(R1, R2, R3) approximation in multilinear algebraJOURNAL OF CHEMOMETRICS, Issue 1 2004Lieven De Lathauwer Abstract In this paper we perform a first-order perturbation analysis of the least squares approximation of a given higher-order tensor by a tensor having prespecified n -mode ranks. This work generalizes the classical first-order perturbation analysis of the matrix singular value decomposition. We will show that there are important differences between the matrix and the higher-order tensor case. We subsequently address (1) the best rank-1 approximation of supersymmetric tensors, (2) the best rank-(R1, R2, R3) approximation of arbitrary tensors and (3) the best rank-(R1, R2, R3) approximation of arbitrary tensors. Copyright © 2004 John Wiley & Sons, Ltd. [source] Convection, diffusion, and exothermic zero-order reaction in a porous catalyst slab: Scaling and perturbation analysisAICHE JOURNAL, Issue 10 2009João P. Lopes Abstract The analysis of the interaction between transport phenomena and chemical reaction inside large-pore catalyst particles needs to include intraparticular convection as an additional mass/heat transfer mechanism. In this work, we describe by a 3D regime diagram the global behavior of a permeable catalyst slab, where an exothermic, zero-order reaction is occurring. An order of magnitude estimate for the maximum temperature change is obtained by scaling techniques in each regime of operation. Specific operating regimes of fast mass/heat transport, dominant reaction and strong intraparticular convection, are then studied in more detail using perturbation analysis. The results include approximate concentration and temperature profiles, which allow the estimation of both the effectiveness factor and maximum temperature attained inside the catalyst in these regimes. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source] Tidal mass loss from collisionless systemsMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 3 2007Marios Kampakoglou ABSTRACT We examine the problem tidally induced mass loss from collisionless systems, such as dark matter haloes. We develop a model for tidal mass loss, based upon the phase-space distribution of particles, which accounts for how both tidal and Coriolis torques perturb the angular momentum of each particle in the system. This allows us to study how both the density profile and velocity anisotropy affect the degree of mass loss , we present basic results from such a study. Our model predicts that mass loss is a continuous process even in a static tidal field, a consequence of the fact that mass loss weakens the potential of the system making it easier for further mass loss to occur. We compare the predictions of our model with N -body simulations of idealized systems in order to check its validity. We find reasonable agreement with the N -body simulations except for in the case of very strong tidal fields, where our results suggest that a higher order perturbation analysis may be required. The continuous tidally induced mass loss predicted by our model can lead to substantial reduction in satellite mass in cases where the traditional treatment predicts no mass loss. As such, our results may have important consequences for the orbits and survival of low-mass satellites in dark matter haloes. [source] Backward perturbation analysis for scaled total least-squares problemsNUMERICAL LINEAR ALGEBRA WITH APPLICATIONS, Issue 8 2009X.-W. Chang Abstract The scaled total least-squares (STLS) method unifies the ordinary least-squares (OLS), the total least-squares (TLS), and the data least-squares (DLS) methods. In this paper we perform a backward perturbation analysis of the STLS problem. This also unifies the backward perturbation analyses of the OLS, TLS and DLS problems. We derive an expression for an extended minimal backward error of the STLS problem. This is an asymptotically tight lower bound on the true minimal backward error. If the given approximate solution is close enough to the true STLS solution (as is the goal in practice), then the extended minimal backward error is in fact the minimal backward error. Since the extended minimal backward error is expensive to compute directly, we present a lower bound on it as well as an asymptotic estimate for it, both of which can be computed or estimated more efficiently. Our numerical examples suggest that the lower bound gives good order of magnitude approximations, while the asymptotic estimate is an excellent estimate. We show how to use our results to easily obtain the corresponding results for the OLS and DLS problems in the literature. Copyright © 2009 John Wiley & Sons, Ltd. [source] Numerical Analysis of Isothermal Gaseous Flows in MicrochannelCHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 1 2006B. Cao Abstract Two-dimensional compressible momentum equations were solved by a perturbation analysis and the PISO algorithm to investigate the effects of compressibility and rarefaction on the local flow resistance of isothermal gas flow in circular microchannels. The computations were performed for a wide range of Reynolds numbers and inlet Mach numbers. The explicit expression of the normalized local Fanning friction factor along the microchannel was derived in the present paper. The results reveal that the local Fanning friction factor is a function of the inlet Mach number, the Reynolds number and the length-diameter ratio of the channel. For larger Reynolds and inlet Mach numbers, the friction coefficient in the microchannel is higher than the value in a macrotube, and the gas flow in the microchannel is dominated only by compressibility. For smaller Reynolds and inlet Mach numbers, the Fanning friction factor of gas flow in the microchannel is lower than that in a circular tube of conventional size due to slip flow at the wall and thus, rarefaction has a significant effect on the fluid flow characteristics in a microchannel. [source] On the continuum limit of a discrete inverse spectral problem on optimal finite difference gridsCOMMUNICATIONS ON PURE & APPLIED MATHEMATICS, Issue 9 2005Liliana Borcea We consider finite difference approximations of solutions of inverse Sturm-Liouville problems in bounded intervals. Using three-point finite difference schemes, we discretize the equations on so-called optimal grids constructed as follows: For a staggered grid with 2 k points, we ask that the finite difference operator (a k × k Jacobi matrix) and the Sturm-Liouville differential operator share the k lowest eigenvalues and the values of the orthonormal eigenfunctions at one end of the interval. This requirement determines uniquely the entries in the Jacobi matrix, which are grid cell averages of the coefficients in the continuum problem. If these coefficients are known, we can find the grid, which we call optimal because it gives, by design, a finite difference operator with a prescribed spectral measure. We focus attention on the inverse problem, where neither the coefficients nor the grid are known. A key question in inversion is how to parametrize the coefficients, i.e., how to choose the grid. It is clear that, to be successful, this grid must be close to the optimal one, which is unknown. Fortunately, as we show here, the grid dependence on the unknown coefficients is weak, so the inversion can be done on a precomputed grid for an a priori guess of the unknown coefficients. This observation leads to a simple yet efficient inversion algorithm, which gives coefficients that converge pointwise to the true solution as the number k of data points tends to infinity. The cornerstone of our convergence proof is showing that optimal grids provide an implicit, natural regularization of the inverse problem, by giving reconstructions with uniformly bounded total variation. The analysis is based on a novel, explicit perturbation analysis of Lanczos recursions and on a discrete Gel'fand-Levitan formulation. © 2005 Wiley Periodicals, Inc. [source] | ||||||||||||||||||||||||||||