Numerical Calculations (numerical + calculation)

Distribution by Scientific Domains
Distribution within Engineering

Selected Abstracts

Numerical Calculations of Spray Roasting Reactors of the Steel Industry with Special Emphasis on Fe2O3 -Particle Formation

M. Beck
Abstract This work presents numerical calculations for the lay-out of spray roasting reactors for the steel industry. In these reactors, a pickling liquor based on water and HCl containing FeCl2 is regenerated in a combustor leading to the formation of Fe2O3 particles. For the lay-out of these reactors, detailed knowledge of the flow and temperature field, the associated gas phase reactions, and especially, of the formation of the Fe2O3 particles is required. An extended particle formation model is presented which is based on earlier work. Finally, results for an industrial spray roasting reactor are given showing the potential of the numerical tools developed for the improvement of the technical lay-out of such thermal reactors. [source]

Laser diodes semicircular side-pumped laser rod with a round-sharped output

Y. X. Guo
Abstract In order to keep the symmetric of the pump geometry and obtain a low-level, high quality laser output, the temperature of the side-pumped laser rod is more often be controlled by a water cooling system than a conduction cooling system in the diode-pumped solid-state lasers. But the use of the water cooling system increases the volume and decreases the mobility. To solve the confliction between the beam quality and the mobility of the laser system, a novel, compact and all-solid design of the pump structure is applied to the side-pumped laser system. The Nd:YAG rod is pumped by semicircular mounted LD arrays inthe pump module, and two pump modules are working together to compensate each other. Numerical calculation and experiment are performed, the output laser has a round-sharped beam with a beam waist of 5 mm and a divergence angle less than 7 mrad, and a maxim output pulse energy of 75.8 mJ is obtained under the working frequency of 20Hz, the slope efficiency is 35.8%. (© 2006 by Astro, Ltd. Published exclusively by WILEY-VCH Verlag GmbH & Co. KGaA) [source]

Numerical calculations of the pH of maximal protein stability

FEBS JOURNAL, Issue 1 2004
The effect of the sequence composition, three-dimensional structure
A large number of proteins, found experimentally to have different optimum pH of maximal stability, were studied to reveal the basic principles of their preferenence for a particular pH. The pH-dependent free energy of folding was modeled numerically as a function of pH as well as the net charge of the protein. The optimum pH was determined in the numerical calculations as the pH of the minimum free energy of folding. The experimental data for the pH of maximal stability (experimental optimum pH) was reproducible (rmsd = 0.73). It was shown that the optimum pH results from two factors , amino acid composition and the organization of the titratable groups with the 3D structure. It was demonstrated that the optimum pH and isoelectric point could be quite different. In many cases, the optimum pH was found at a pH corresponding to a large net charge of the protein. At the same time, there was a tendency for proteins having acidic optimum pHs to have a base/acid ratio smaller than one and vice versa. The correlation between the optimum pH and base/acid ratio is significant if only buried groups are taken into account. It was shown that a protein that provides a favorable electrostatic environment for acids and disfavors the bases tends to have high optimum pH and vice versa. [source]

A numerical study of natural convection in a vertical cylinder bundle

Yuji Isahai
Abstract Natural convection in a bundle of vertical cylinders, arranged in equilateral triangular spacing, has been investigated numerically using a boundary-fitted coordinate system. Numerical calculations for center-to-center distance between cylinders S/D = 1.1 to 1.9, 3.0, 4.0, and 7.0 were made of natural convection of air at modified Grashof numbers Gr* from 10 to 108. Local Nusselt number Nu for uniform wall heat flux indicates the same value at the axial locations except for the thermal entrance region. The region for respective cylinder spacing is noted to diminish with decreasing Grashof number. Numerical values of local Nusselt number Nui are in relatively good agreement with those obtained from the experiment for air. © 2003 Wiley Periodicals, Inc. Heat Trans Asian Res, 32(4): 330,341, 2003; Published online in Wiley InterScience ( DOI 10.1002/htj.10095 [source]

Heat transfer characteristics in a two-dimensional channel with an oscillating wall

Masahide Nakamura
Abstract Numerical calculations have been carried out for the laminar heat transfer in a two-dimensional channel bounded by a fixed wall and an oscillating wall. In this calculation, the moving boundary problem was transformed into a fixed boundary problem using the coordinate transformation method, and the fully implicit finite difference method was used to solve the mass, momentum, and energy conservation equations. The calculated results are summarized as follows: (i) The wall oscillation has an effect of enhancing the heat transfer and an effect of increasing the additional pressure loss. (ii) An optimum Strouhal number for the enhancement of heat transfer exists, and this optimum value is strongly affected by the amplitude of wall oscillation. © 2001 Scripta Technica, Heat Trans Asian Res, 30(4): 280,292, 2001 [source]

A numerical solution for the equation of the lifting surface in ground effects

r Drago
Abstract Using the Gauss-type quadrature formulas one discretizes the 2d integral equation of the lifting surface in ground effects. Numerical calculations of the aerodynamical coefficients are performed for the elliptical and rectangular wings. Copyright 2002 John Wiley & Sons, Ltd. [source]

Generalized nodes and high-performance elements

Rong Tian
Abstract The paper concerns the development of robust and high accuracy finite elements with only corner nodes using a partition-of-unity-based finite-element approximation. Construction of the partition-of-unity-based approximation is accomplished by a physically defined local function of displacements. A 4-node quadratic tetrahedral element and a 3-node quadratic triangular element are developed. Eigenvalue analysis shows that linear dependencies in the partition-of-unity-based finite-element approximation constructed for the new elements are eliminable. Numerical calculations demonstrate that the new elements are robust, insensitive to mesh distortion, and offer quadratic accuracy, while also keeping mesh generation extremely simple. Copyright © 2005 John Wiley & Sons, Ltd. [source]

Comparative study of the continuous phase flow in a cyclone separator using different turbulence models,

H. Shalaby
Abstract Numerical calculations were carried out at the apex cone and various axial positions of a gas cyclone separator for industrial applications. Two different NS-solvers (a commercial one (CFX 4.4 ANSYS GmbH, Munich, Germany, CFX Solver Documentation, 1998), and a research code (Post-doctoral Thesis, Technical University of Chemnitz, Germany, September, 2002)) based on a pressure correction algorithm of the SIMPLE method have been applied to predict the flow behaviour. The flow was assumed as unsteady, incompressible and isothermal. A k,, turbulence model has been applied first using the commercial code to investigate the gas flow. Due to the nature of cyclone flows, which exhibit highly curved streamlines and anisotropic turbulence, advanced turbulence models such as Reynolds stress model (RSM) and large eddy simulation (LES) have been used as well. The RSM simulation was performed using the commercial package activating the Launder et al.'s (J. Fluid. Mech. 1975; 68(3):537,566) approach, while for the LES calculations the research code has been applied utilizing the Smagorinsky model. It was found that the k,, model cannot predict flow phenomena inside the cyclone properly due to the strong curvature of the streamlines. The RSM results are comparable with LES results in the area of the apex cone plane. However, the application of the LES reveals qualitative agreement with the experimental data, but requires higher computer capacity and longer running times than RSM. This paper is organized into five sections. The first section consists of an introduction and a summary of previous work. Section 2 deals with turbulence modelling including the governing equations and the three turbulence models used. In Section 3, computational parameters are discussed such as computational grids, boundary conditions and the solution algorithm with respect to the use of MISTRAL/PartFlow-3D. In Section 4, prediction profiles of the gas flow at axial and apex cone positions are presented and discussed. Section 5 summarizes and concludes the paper. Copyright © 2005 John Wiley & Sons, Ltd. [source]

Numerical solutions of 2-D steady incompressible driven cavity flow at high Reynolds numbers

E. Erturk
Abstract Numerical calculations of the 2-D steady incompressible driven cavity flow are presented. The Navier,Stokes equations in streamfunction and vorticity formulation are solved numerically using a fine uniform grid mesh of 601 × 601. The steady driven cavity flow solutions are computed for Re , 21 000 with a maximum absolute residuals of the governing equations that were less than 10,10. A new quaternary vortex at the bottom left corner and a new tertiary vortex at the top left corner of the cavity are observed in the flow field as the Reynolds number increases. Detailed results are presented and comparisons are made with benchmark solutions found in the literature. Copyright © 2005 John Wiley & Sons, Ltd. [source]

Numerical calculations of erosion in an abrupt pipe contraction of different contraction ratios

M. A. Habib
Abstract Erosion predictions in a pipe with abrupt contraction of different contraction ratios for the special case of two-phase (liquid and solid) turbulent flow with low particle concentration are presented. A mathematical model based on the time-averaged governing equations of 2-D axi-symmetric turbulent flow is used for the calculations of the fluid velocity field (continuous phase). The particle-tracking model of the solid particles is based on the solution of the governing equation of each particle motion taking into consideration the effect of particle rebound behaviour. Models of erosion were used to predict the erosion rate in mg/g. The effect of Reynolds number and flow direction with respect to the gravity was investigated for three contraction geometries considering water flow in a carbon steel pipe. The results show that the influence of the contraction ratio on local erosion is very significant. However, this influence becomes insignificant when the average erosion rates over the sudden contraction area are considered. The results also indicate the significant influence of inlet velocity variations. The influence of buoyancy is significant for the cases of low velocity of the continuous flow. A threshold velocity below which erosion may be neglected was indicated. Copyright © 2004 John Wiley & Sons, Ltd. [source]

Performance analysis of gas liquefaction cycles

Mehmet Kanoglu
Abstract Relations are developed for first- and second-law analyses of the simple Linde,Hampson cycle used in gas liquefaction systems. An expression for the minimum work requirement, which is applicable to any gas liquefaction system, is developed with the help of a Carnot refrigerator. It is shown that the minimum work depends only on the properties of the incoming and outgoing gas streams and the environment temperature. Numerical calculations are performed to obtain the performance parameters of different gases while parametric studies are done to investigate the effects of liquefaction and inlet gas temperatures on various first- and second-law performance parameters. As the liquefaction temperature increases and the inlet gas temperature decreases, the liquefied mass fraction, the coefficient of performance (COP) and the exergy efficiency increase while actual and reversible work consumptions decrease. The exergy efficiency values appear to be low, indicating significant potential exists for improving efficiency and thus decreasing the required work consumption for a specified amount of liquefaction. Copyright © 2007 John Wiley & Sons, Ltd. [source]

The Marginal Costs and Benefits of Redistributing Income and the Willingness to Pay for Status

The effect of status on aggregate welfare is ambiguous for marginal reforms that redistribute income. If average consumption falls, the change in relative consumption increases household utility but reinforces the decrease in household labor supply, raising welfare cost. For parameterizations of the model developed here, reforms which lower average consumption increase aggregate welfare. Numerical calculations show that status increases marginal welfare cost and marginal net benefit for a demogrant reform. Redistributing to high income households may increase aggregate welfare depending on the definition of average consumption and if the willingness to pay for status increases with income. [source]

The source of energy of the comet 29P/Schwassmann-Wachmann 1 outburst activity: the test of the summary

P. Gronkowski
ABSTRACT The comet 29P/Schwassmann-Wachmann 1 is an exceptional comet as far as cometary outbursts are concerned. Despite its large distance from the Sun (about 6 au), it shows quasi-regular outburst activity, usually once or twice a year. Up to now there has not been a generally accepted model that explains this phenomenon. In the first part of this paper, the most well-known hypotheses that attempt to explain the outburst activity of this comet are presented and critically analysed. The main aim of this paper is to present a model for the outburst activity of this comet. The model is based on the global analysis of the internal structure and physical and chemical processes that take place in the cometary nucleus. Numerical calculations were carried out for reasonable assumed values of a large range of cometary characteristics. The obtained results are consistent with observational data. [source]

Diamagnetic and nonlinear Zeeman shifts in spatially separated electron and hole layers of semiconductor heterostructures with disorder

J. Desforges
Abstract The effect of the diamagnetic shift on the formation of excitons is investigated for double layer semiconductor systems in which electrons and holes are spatially separated. The effect of disorder due to interface roughness of the double layer structures is included in the calculation of exciton density. Numerical calculations are performed based on an effective lattice-gas model where the electron,hole system is divided into unit cells. The exciton density is calculated by using the partition function method. The effect of the nonlinear Zeeman splitting is also included in the numerical calculations. It is found that the density of the optically allowed exciton states (excitons with Sz = 0) increases under the influence of either or both the diamagnetic and the nonlinear Zeeman shifts. [source]

Phase modulation effects in X-ray diffraction from a highly deformed crystal with variable strain gradient

M. Shevchenko
The X-ray interbranch scattering by lattice distortions is studied for a thin crystal whose thickness is appreciably less than the conventional X-ray extinction length. The concept of interbranch phase modulation of the X-ray wavefield is extended to the case of a large gradient which depends on depth inside the crystal. The prominent interbranch features of the diffracted intensity are also established within this concept. Numerical calculations of the diffracted intensity are presented for an exponential strain gradient model to illustrate this. Diffraction (extinction) contrast is discussed for a strongly deformed specimen containing a single dislocation. It is predicted that for large values of the X-ray extinction length the extinction contrast may arise even in the case of a very thin crystal. This effect, owing to the interbranch phase changes of the waves scattered in the deformed matrix, is observed in experiments with protein crystals. [source]

The destruction of cometary grains and changes in the luminosity of comets

P. Gronkowski
Abstract One explanation of the sudden changes in the brightness of comets is proposed based on the author's earlier suggestions involving the fragmentation of cometary grains. Within the inner coma, a core-mantle model of the structure of grains is assumed. The proposed mechanism is a combination of electrostatic stress and thermodynamical fragmentation of the cometary grains water-ice mantle. It has been shown that the vapour pressure of volatile inclusions placed in the waterice mantle of grains can increase sufficiently to cause their fragmentation. It takes place before grains can completely sublime into the vacuum away. Numerical calculations have been carried out for a large range of values of probable physical characteristics of cometary material. The proposed approach yields increases in cometary brightness consistent with observations of typical cometary outbursts. It is concluded that this approach can provide an explanation of the sudden change in activity of comets for a wide range of heliocentric distances (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

The effect of the electrical anisotropy on the response of helicopter-borne frequency-domain electromagnetic systems

Changchun Yin
ABSTRACT Helicopter electromagnetic (HEM) systems are commonly used for conductivity mapping and the data are often interpreted using an isotropic horizontally layered earth model. However, in regions with distinct dipping stratification, it is useful to extend the model to a layered earth with general anisotropy by assigning each layer a symmetrical 3 × 3 resistivity tensor. The electromagnetic (EM) field is represented by two scalar potentials, which describe the poloidal and toroidal parts of the magnetic field. Via a 2D Fourier transform, we obtain two coupled ordinary differential equations in the vertical coordinate. To stabilize the numerical calculation, the wavenumber domain is divided into two parts associated with small and large wavenumbers. The EM field for small wavenumbers is continued from layer to layer with the continuity conditions. For large wavenumbers, the EM field behaves like a DC field and therefore cannot be sensed by airborne EM systems. Thus, the contribution from the large wavenumbers is simply ignored. The magnetic fields are calculated for the vertical coaxial (VCX), horizontal coplanar (HCP) and vertical coplanar (VCP) coil configurations for a helicopter EM system. The apparent resistivities defined from the VCX, VCP and HCP coil responses, when plotted in polar coordinates, clearly identify the principal anisotropic axes of an anisotropic earth. The field example from the Edwards Aquifer recharge area in Texas confirms that the polar plots of the apparent resistivities identify the principal anisotropic axes that coincide well with the direction of the underground structures. [source]

Groutability of cement-based grout with consideration of viscosity and filtration phenomenon

Jong-Sun Kim
Abstract The groutability depends on the properties of the grout, its injection processes, and on the mechanical properties of the soil formation. During the process of pouring cement-based grouting into a porous medium, a variation with time occurs in the viscosity of grout suspension. In addition, the particle filtration phenomenon will limit the expansion of the grouted zone because cement particles are progressively stagnant within the soil matrix. In this paper, a closed-form solution was derived by implementing the mass balance equations and the generalized phenomenological filtration law, which can be used to evaluate the deposition of cement-based grout in the soil matrix. The closed-form solution relevant to a particular spherical flow was modified by a step-wise numerical calculation, considering the variable viscosity caused by a chemical reaction, and the decrease in porosity resulting from grout particle deposition in the soil pores. A series of pilot-scale chamber injection tests was performed to verify that the developed step-wise numerical calculation is able to evaluate the injectable volume of grout and the deposition of grout particles. The results of the chamber injection tests concurred well with that of the step-wise numerical calculation. Based on the filtration phenomenon, a viable approach for estimating the groutability of cement-based grout in a porous medium was also suggested, which might facilitate a new insight in the design of the grouting process. Copyright © 2009 John Wiley & Sons, Ltd. [source]

A posteriori pointwise error estimation for compressible fluid flows using adjoint parameters and Lagrange remainder

A. K. Alekseev
Abstract The pointwise error of a finite-difference calculation of supersonic flow is discussed. The local truncation error is determined by a Taylor series with the remainder being in a Lagrange form. The contribution of the local truncation error to the total pointwise approximation error is estimated via adjoint parameters. It is demonstrated by numerical tests that the results of the numerical calculation of gasdynamics parameter at an observation point may be refined and an error bound may be estimated. The results of numerical tests for the case of parabolized Navier,Stokes are presented as an illustration of the proposed method. Copyright © 2004 John Wiley & Sons, Ltd. [source]

Efficiency in the calculation of absorption corrections for cylinders

Takashi Ida
Efficiency in the numerical calculation of absorption corrections for cylinders has been examined. Two mathematical expressions for the correction factors have been evaluated by two methods for numerical integration. It has been found that the Gauss,Legendre quadrature applied to the formula proposed by Thorkildsen & Larsen [Acta Cryst. (1998), A54, 172,185] gives results with relative errors ,10,6, using 12,×,12 terms in the numerical integration. The conventional approach, using Simpson's method in conjunction with the formula given by Dwiggins [Acta Cryst. (1975), A31, 146,148] for the absorption correction, is far less efficient. [source]

Systematic and statistical error in histogram-based free energy calculations

Mark N. Kobrak
Abstract A common technique for the numerical calculation of free energies involves estimation of the probability density along a given coordinate from a set of configurations generated via simulation. The process requires discretization of one or more reaction coordinates to generate a histogram from which the continuous probability density is inferred. We show that the finite size of the intervals used to construct the histogram leads to quantifiable systematic error. The width of these intervals also determines the statistical error in the free energy, and the choice of the appropriate interval is therefore driven by the need to balance the two sources of error. We present a method for the construction of the optimal histogram for a given system, and show that the use of this technique requires little additional computational expense. We demonstrate the efficacy of the technique for a model system, and discuss how the principles governing the choice of discretization interval could be used to improve extended sampling techniques. © 2003 Wiley Periodicals, Inc. J Comput Chem 24: 1437,1446, 2003 [source]

Recursive Relations for Multistep Prediction of a Stationary Time Series

Pascal Bondon
Recursive relations are established between the coefficients of the finite past multistep linear predictors of a stationary time series. These relations generalize known results when the prediction is based on infinite past and permit simplification of the numerical calculation of the finite past predictors. [source]

An optimal memory-reduced procedure for calculating adjoints of the instationary Navier-Stokes equations

Michael Hinze
Abstract This paper discusses approximation schemes for adjoints in control of the instationary Navier,Stokes system. It tackles the storage problem arising in the numerical calculation of the appearing adjoint equations by proposing a low-storage approach which utilizes optimal checkpointing. For this purpose, a new proof of optimality is given. This new approach gives so far unknown properties of the optimal checkpointing strategies and thus provides new insights. The optimal checkpointing allows a remarkable memory reduction by accepting a slight increase in run-time caused by repeated forward integrations as illustrated by means of the Navier,Stokes equations. In particular, a memory reduction of two orders of magnitude causes only a slow down factor of 2,3 in run-time. Copyright © 2005 John Wiley & Sons, Ltd. [source]

Polarization properties in deep-ultraviolet AlGaN quantum wells with various substrate orientations

A. Atsushi Yamaguchi
Abstract It is known that emission polarization in AlGaN quantum wells (QWs) on c-plane substrates switches from in-plane polarization to c -axis polarization with increasing Al composition. This behaviour is unfavourable for light extraction from c-plane based light emitting diodes (LEDs). Previously, we proposed theoretically that this unfavourable polarization can be changed into favourable in-plane polarization by decreasing well width and/or introduction of compressive strain in c-oriented AlGaN-QWs. In this work, we have investigated the substrate orientation dependence of polarization properties in such AlGaN QWs by numerical calculation using the 6,×,6 k·p Hamiltonian. It is shown that even small inclination of c-plane substrate makes a drastic change in the polarization characteristics and that the use of the vicinal substrates as well as semipolar and nonpolar substrates could be beneficial in improving optical device performance. [source]

Ultrafast coherent vibronic oscillations in regioregular poly(3-alkylthiophene)

Katsuichi Kanemoto
Abstract Ultrafast degenerate four-wave mixing (DFWM) signals of the regioregular (RR) poly(3-hexylthiophene) (P3HT) film have been investigated by the experiments using sub-20 fs pulses generated from a noncollinear optical parametric amplifier (NOPA) system. Strong DFWM signals were observed owing to a large third-order nonlinear susceptibility ,(3) of the RR-P3HT film. The time profile of the DFWM signals exhibits clear coherent oscillation on a decaying signal. The oscillation turn out to be caused by the C=C stretching mode that gives strong Raman signal. The time profile of the DFWM signal is simulated by a numerical calculation. The result of simulation reveals that decay constants of electronic population and of vibronic oscillation are 200 fs and 210 fs, respectively. This is the first determination of the decay constants for the RR-P3HT film. The obtained result demonstrates that the ,(3) signal of the RR-P3HT film decays very rapidly. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Photoreflectance investigations of energy level structure of InAs quantum dashes embedded in InGaAs/InGaAlAs quantum well grown on InP substrate

W. Rudno-Rudzi
Abstract Photoreflectance (PR) and photoluminescence measurements have been performed on molecular beam epitaxy grown InAs quantum dashes (QDash) of various sizes, embedded in In0.53Ga0.47As/In0.53Ga0.23Al0.24As quantum well (QW), grown on InP substrate. PR response from all relevant parts of the structure, i.e InAs/In0.53Ga0.47As QDashes, InAs/In0.53Ga0.47As/In0.53Ga0.23Al0.24As QW, and In0.53Ga0.23Al0.24As barriers, has been obtained. The lowest energy transition related to the ground state transition in QDashes shifts towards red with the increase in QDash sizes (amount of deposited InAs material) reaching wavelengths longer than for structures without the intermediate QW. The experimental data on the energies of optical transitions combined with the numerical calculation within the effective mass approximation has allowed determining the energy level structure of the entire system, including the values of conduction band offset between InGaAs and InGaAlAs layers. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Coupled thermo-mechanical analysis for plastic thermoforming

Yuhua Song
An FEM software ARVIP-3D was developed to simulate the process of 3-D plastic thermoforming. The coupled thermo-mechanical analysis, thermal stress and warpage analysis for plastic thermoforming was carried out by means of this software. Rigid visco-plastic formula was adopted to simulate the deforming process. During this process, the method of comparing velocity, time and area was adopted as the contact algorithm at different nodes and triangular elements. Sticking contact was assumed when the nodes become in contact with tool surface. The Arrhenius equation and the Williams equation were employed to ascertain the temperature dependence of material properties. In order to analyze the temperature field of plastic thermoforming, the Galerkin FEM code and the dynamic heat conduction boundary condition were adopted; latent heat and deformation heat were treated as dynamic internal heat sources. Based on the above, the model of coupled thermomechanical analysis was established. Assuming that the thermal deformation occurs under elastic conditions, the thermal stress and the warpage following the cooling stage were estimated. Experiments of plastic thermoforming were made for high-density polyethylene (HDPE). An infrared thermometer was used to record the temperature field and a spiral micrometer was used to measure the thickness of the part. Results of numerical calculation for thickness distribution, temperature field and warpage were in good agreement with experimental results. [source]

Variation mode and effect analysis: an application to fatigue life prediction

Pär Johannesson
Abstract We present an application of the probabilistic branch of variation mode and effect analysis (VMEA) implemented as a first-order, second-moment reliability method. First order means that the failure function is approximated to be linear around the nominal values with respect to the main influencing variables, while second moment means that only means and variances are taken into account in the statistical procedure. We study the fatigue life of a jet engine component and aim at a safety margin that takes all sources of prediction uncertainties into account. Scatter is defined as random variation due to natural causes, such as non-homogeneous material, geometry variation within tolerances, load variation in usage, and other uncontrolled variations. Other uncertainties are unknown systematic errors, such as model errors in the numerical calculation of fatigue life, statistical errors in estimates of parameters, and unknown usage profile. By treating also systematic errors as random variables, the whole safety margin problem is put into a common framework of second-order statistics. The final estimated prediction variance of the logarithmic life is obtained by summing the variance contributions of all sources of scatter and other uncertainties, and it represents the total uncertainty in the life prediction. Motivated by the central limit theorem, this logarithmic life random variable may be regarded as normally distributed, which gives possibilities to calculate relevant safety margins. Copyright © 2008 John Wiley & Sons, Ltd. [source]

Ruin theory for classical risk process that is perturbed by diffusion with risky investments

Xiang Lin
Abstract In this paper, we study the ruin theory for classical risk process that is perturbed by diffusion with risky investments. We obtain the upper bound for the minimal ruin probability. We also investigate the relationships between the adjustment coefficient and the diffusion volatility parameter, the risk-free rate and the correlation coefficient by numerical calculation. We give the relationships between ruin and investment. Copyright © 2008 John Wiley & Sons, Ltd. [source]

Modeling normal and altered human erythrocyte shapes by a new parametric equation: Application to the calculation of induced transmembrane potentials

S. Muñoz San Martín
Abstract We present simple parametric equations in terms of Jacobi elliptic functions that provide a realistic model of abnormal variations in size which maintain the biconcave shape of a normal erythrocyte (anisocytosis) and abnormal variations in shape which maintain the original volume of the erythrocyte (poikilocytosis), as well as continuous deformations from the normal to the altered shapes. We illustrate our results with parameterizations of microcytes, macrocytes, and stomatocytes, and we apply these parameterizations to the numerical calculation of the induced transmembrane voltage in microcytes, macrocytes, and stomatocytes exposed to an external electromagnetic field of 1800 MHz. Bioelectromagnetics 27:521,527, 2006. © 2006 Wiley-Liss, Inc. [source]