Stability of the flow around a cylinder: The spin-up problem

A concern is the flow around an infinite cylinder, which at a certain instant impulsively starts to spin. The growth of vortices in the resulting boundary layer occurring outside the cylinder is investigated. This layer is essentially a Rayleigh layer which grows with time, so the mechanism involved is similar to that studied in Hall (1983). Vortices with wavenumber comparable to the layer thickness are shown to be described by partial differential equations that govern the system numerically. It is assumed that the Rayleigh layer is thin, so particles are confined to move in a path with radius of curvature the same as the cylinder. The Goertler number is a function of time, so the time scale which produces an order, is considered one Goertler number. The right hand branch calculation is considered by letting the time tend to infinity, also inviscid Goertler modes are considered

Analysis of phase transitions in the mean-field Blume-Emery-Griffiths model

In this paper we give a complete analysis of the phase transitions in the mean-field Blume-Emery-Griffiths lattice-spin model with respect to the canonical ensemble, showing both a second-order, continuous phase transition and a first-order, discontinuous phase transition for appropriate values of the thermodynamic parameters that define the model. These phase transitions are analyzed both in terms of the empirical measure and the spin per site by studying bifurcation phenomena of the corresponding sets of canonical equilibrium macrostates, which are defined via large deviation principles. Analogous phase transitions with respect to the microcanonical ensemble are also studied via a combination of rigorous analysis and numerical calculations. Finally, probabilistic limit theorems for appropriately scaled values of the total spin are proved with respect to the canonical ensemble. These limit theorems include both central-limit-type theorems when the thermodynamic parameters are not equal to critical values and non-central-limit-type theorems when these parameters equal critical values.Comment: 33 pages, revtex

Institutions and the transition to adulthood: Implications for fertility tempo in low-fertility settings

The number of countries experiencing very low fertility has been rising in recent years, garnering increasing academic, political and media attention. There is now widespread academic agreement that the postponement of fertility is a major contributing factor in the very low levels of fertility that have occurred, and yet most policy discussions have been devoted to increasing the numbers of children women have. We discuss factors in three institutions--the educational system, the labour market and the housing market--that may inadvertently have led to childbearing postponement. We highlight important components of the timing of childbearing, including its changing place within the transition to adulthood across countries and the significance of the demands of childbearing versus childrearing. Using illustrations from Europe, North America, Japan, Australia and New Zealand, we argue that the following all lead to younger childbearing: 1) an open education system whereby it is relatively easy to return to school after having dropped out for a while; 2) a shorter, smoother, easier school-to-work transition; 3) easier re-entry into the labour market after having taken time out for childrearing or any other reason; 4) greater capability of integrating childrearing into a career; 5) easier ability to obtain a mortgage with a moderately small down payment, moderately low interest rate and a long time period over which to repay the loan; and 6) easier ability to rent a dwelling unit at an affordable price. Conversely, reversing any or all of these factors would lead, other things being equal, to postponement of childbearing.

Design and fabrication of a full-size landing impact test model of the Mars legged lander configuration Master agreement, task order three

Design and fabrication of full size landing impact test model of Mars legged lander configuratio

Fully nonlinear development of the most unstable goertler vortex in a three dimensional boundary layer

The nonlinear development is studied of the most unstable Gortler mode within a general 3-D boundary layer upon a suitably concave surface. The structure of this mode was first identified by Denier, Hall and Seddougui (1991) who demonstrated that the growth rate of this instability is O(G sup 3/5) where G is the Gortler number (taken to be large here), which is effectively a measure of the curvature of the surface. Previous researchers have described the fate of the most unstable mode within a 2-D boundary layer. Denier and Hall (1992) discussed the fully nonlinear development of the vortex in this case and showed that the nonlinearity causes a breakdown of the flow structure. The effect of crossflow and unsteadiness upon an infinitesimal unstable mode was elucidated by Bassom and Hall (1991). They demonstrated that crossflow tends to stabilize the most unstable Gortler mode, and for certain crossflow/frequency combinations the Gortler mode may be made neutrally stable. These vortex configurations naturally lend themselves to a weakly nonlinear stability analysis; work which is described in a previous article by the present author. Here we extend the ideas of Denier and Hall (1992) to the three-dimensional boundary layer problem. It is found that the numerical solution of the fully nonlinear equations is best conducted using a method which is essentially an adaption of that utilized by Denier and Hall (1992). The influence of crossflow and unsteadiness upon the breakdown of the flow is described

Application of Artificial Intelligence in Transportation Demand Management: Development and Implementation of E-sutra

Allowing traffic to grow to a level at which there is extensive and regular congestion is economically inefficient. Although the construction of additional roads can alleviate some of the effects of congestion, the benefits may be counterbalanced unless the growth in traffic volumes can be restrained. Therefore, another alternative is by implementing Transportation Demand Management (TDM), which means people still travel but at the same time the private car USAge is reduced. This paper presents the development of an expert system for sustainable transportation (E-SUTRA) through implementation of TDM. The overall result of 69% accuracy indicates the high possibility of the E-SUTRA system to be used as an advisory tool for sustainable transportation through TDM

Optical properties of current carrying molecular wires

We consider several fundamental optical phenomena involving single molecules in biased metal-molecule-metal junctions. The molecule is represented by its highest occupied and lowest unoccupied molecular orbitals, and the analysis involves the simultaneous consideration of three coupled fluxes: the electronic current through the molecule, energy flow between the molecule and electron-hole excitations in the leads and the incident and/or emitted photon flux. Using a unified theoretical approach based on the non-equilibrium Green function method we derive expressions for the absorption lineshape (not an observable but a ueful reference for considering yields of other optical processes) and for the current induced molecular emission in such junctions. We also consider conditions under which resonance radiation can induce electronic current in an unbiased junction. We find that current driven molecular emission and resonant light induced electronic currents in single molecule junctions can be of observable magnitude under appropriate realizable conditions. In particular, light induced current should be observed in junctions involving molecular bridges that are characterized by strong charge transfer optical transitions. For observing current induced molecular emission we find that in addition to the familiar need to control the damping of molecular excitations into the metal substrate the phenomenon is also sensitive to the way in which the potential bias si distributed on the junction.Comment: 56 pages, 8 figures; submitted to JC