The effect of osmotic pressure on the flow of solutions through semi-permeable hollow fibers

We study the laminar flow of binary liquid mixture, whose components are a Newtonian fluid (solvent) and a solute, in a hollow fiber. The fiber walls are porous, but the pores size is small enough preventing the solute molecules to be transported across the membrane. This produces an osmotic pressure that offers resistance (in many cases non negligible) to the fluid cross flow.     

Inlet length by laminar flow of elastico-viscous liquids through straight channel and circular tube

The inlet lengths in a straight channel and a circular tube by the laminar flow of an elastico-viscous liquid have been determined in this paper. Expressions for the inlet lengths have been obtained by the kinetic energy end correction method. For a given pressure drop, the elasticity of the liquid increases the inlet length only if the liquid possesses cross-viscosity. But cross-viscosity which decreases the inlet length has an independent effect on it.     

Rectilinear laminar flow of a visco-elastic fluid

Zusammenfassung Eine inkompressible viskoelastische Flüssigkeit fliesst zwischen zwei parallelen, starren, unendlichen Wänden. Es wird unter der Voraussetzung, dass die eine Wand fest ist und die andere sich mit einer exponentiell abklingenden Geschwindigkeit bewegt, das zur Aufrechterhaltung einer speziellen laminaren Strömung nötige Kraftfeld bestimmt.     

Heat transfer for laminar flow through parallel porous disks of different permeability

The problem of temperature distribution and heat transfer for laminar flow through two parallel porous disks of different permeability, has been investigated when the flow is entirely due to injection and/or suction at the two disks. Viscous dissipation terms have been included in the energy equation and the injection and/or suction velocities at the two disks are assumed to be small. The boundaries are kept at constant temperatures. The variation of temperature and Nusselt numbers at the two disks has been graphically depicted for various values of the injection and suction velocities.     

Constructing a covering triangulation by means of a nowhere-zero dual flow

Tutte conjectured that every graph with no isthmus can be provided with an integral nowhere-zero flow with no absolute value greater than k=5. As yet the result is established for k=6, and it is used for proving that the existence of a triangular imbedding of a graph G in a surface S implies the existence of a triangular imbedding of G_(m) in a surface $\text{S}\text{?}$ with the same orientability characteristic as S. G_(m) stands for the composition of G by an independent set of m vertices.     

Numerical simulation of laminar flow past a circular cylinder

The present paper focuses on the analysis of two- and three-dimensional flow past a circular cylinder in different laminar flow regimes. In this simulation, an implicit pressure-based finite volume method is used for time-accurate computation of incompressible flow using second order accurate convective flux discretisation schemes. The computation results are validated against measurement data for mean surface pressure, skin friction coefficients, the size and strength of the recirculating wake for the steady flow regime and also for the Strouhal frequency of vortex shedding and the mean and RMS amplitude of the fluctuating aerodynamic coefficients for the unsteady periodic flow regime. The complex three dimensional flow structure of the cylinder wake is also reasonably captured by the present prediction procedure.     

The stability of time-dependent laminar flow: Parallel flows

Zusammenfassung In dieser Arbeit wird das allgemeine Problem der Stabilität inkompressibler, instationärer, paralleler und laminarer Strömungen zwischen zwei unendlichen Ebenen untersucht. Dabei werden sowohl die klassische linearisierte Theorie für Störungen mit kleiner Amplitude als auch eine Variationsmethode für Störungen endlicher Grösse angewandt. Die grundlegenden Lehrsätze der linearen Theorie werden, soweit dies für das allgemeine Problem möglich ist, erweitert und ihre Konsequenzen aufgezeigt. Unter Anwendung der Variationsmethode werden für mehrere besondere instationäre Strömungen quantitative Ergebnisse gezeigt, aber die hier entwickelten Gleichungen können ebenso auf jedwede parallele Strömung angewendet werden. Das stationäre Problem ist als ein besonderer Grenzfall behandelt.     

Analytic continuations of a general algebraic function by means of Puiseux series

A complete list of power series (centered at the point x = 0) is obtained for the solution y(x) of the general reduced algebraic equation $y^n x_s y^{n_s } + ... + x_1 y^{n_1 } - 1 = 0$ . The domains of convergence of these series are described in terms of the amoeba of the discriminant of the equation. Sectorial domains through which one selected series is analytically continued to the other series are explicitly described.     

A semigroup approach to the study of a general stochastic epidemic

A general stochastic epidemic, with immigration, in a large population is examined, introducing exponentially distributed latent and incubation periods. By means of semigroups, existence and uniqueness are proved for the solution of the initial-value problem arising from the stochastic model proposed. Equations for expected values of the random variables describing the epidemic are derived rigorously from the Kolmogorov equations of the process. Conditions for the extinction of the epidemic are also obtained.     

Smooth exact penalty functions: a general approach

In the article, we present a new perspective on the method of smooth exact penalty functions that is becoming more and more popular tool for solving constrained optimization problems. In particular, our approach to smooth exact penalty functions allows one to apply previously unused tools (namely, parametric optimization) to the study of these functions. We give a new simple proof of local exactness of smooth penalty functions that significantly generalizes all similar results existing in the literature. We also provide new necessary and sufficient conditions for a smooth penalty function to be globally exact.     

Distribution management by means of cutoff order size: a case study

We present a case study on physical distribution management for a production company in Western Europe. The company delivers finished goods both from distribution centres and directly from plants to its customers. The lead time from distribution centres is shorter, but higher costs are involved. The choice for delivery of an individual order is based on the so-called stockmix and cutoff order size. The stockmix is the set of products stocked at the distribution centre, which for efficiency reasons is restricted. Orders smaller than the cutoff order size are delivered from the distribution centre closest to the customer, provided that the product ordered is present in its stockmix. Otherwise they are delivered from the production plant that makes the product. In this paper we develop methods to determine both the stockmix and the cutoff order size for each distribution centre. The objective considered is the minimisation of distribution and handling costs subject to service constraints.     

On the Potential Flow of an Ideal Incompressible Fluid through a Porous Boundary

The potential flow of an incompressible fluid is considered.The fluid is supposed to be ideal except on the porous boundarywhere the normal velocity is proportional to the pressure. Thisleads to the Laplace equation with the square of the gradientin the boundary condition. The linearized problem (small velocities)is trivially solvable by the variational method in the usualenergy space. The nonlinearity of the boundary condition beingtoo strong for that space, the stationary problem is treatedin some Banach algebras of functions defined on the boundaryof . The existence and uniqueness of the solution are provedfor small flows or for large boundary resistances.     

Solving the response time variability problem by means of a psychoclonal approach

The response time variability problem (RTVP) is a combinatorial scheduling problem that has recently appeared in the literature. This problem has a wide range of real life applications in fields such as manufacturing, hard real-time systems, operating systems and network environments. Originally, the RTVP occurs whenever products, clients or jobs need to be sequenced in such a way that the variability in the time between the instants at which they receive the necessary resources is minimized. Since the RTVP is hard to solve, heuristic techniques are needed for solving it. Three metaheuristic—multi-start, GRASP and PSO—algorithms proposed for solving the RTVP in two previous studies have been the most efficient to date in solving non-small instances of the RTVP. We propose solving the RTVP by means of a psychoclonal algorithm based approach. The psychoclonal algorithm inherits its attributes from Maslow’s hierarchy of needs theory and the artificial immune system (AIS) approach, specifically the clonal selection principle. In this paper, we compare the proposed psychoclonal algorithm with the three aforementioned metaheuristic algorithms and show that, on average, the psychoclonal algorithm strongly improves on the results obtained.     

Homogenization in general periodically perforated domains by a spectral approach

In this article we study the asymptotic behaviour as tends to 0 of the Neumann problem $-\Delta u_\epsilon+u_\epsilon=\epsilon$-periodic bounded open set of . The period cell of is equal to where is a regular open subset of the d-dimensional torus. We prove that if there exists a smallest integer such that the n-th non-zero eigenvalue of the spectral problem in satisfies , the limiting problem is a linear system of second order p.d.e.'s, of size n. By this spectral approach we extend in the periodic framework a result due to Khruslov without making strong geometrical assumptions on the perforated domain . Received: 20 December 2000 / Accepted: 11 May 2001 / Published online: 19 October 2001