Ignition and combustion in a laminar mixing zone

The analytic investigation of laminar combustion processes which are essentially two- or three-dimensional present some mathematical difficulties. There are, however, several examples of two-dimensional flame propagation which involve transverse velocities that are small in comparison with that in the principal direction of flow. Such examples occur in thc problem of flame quenching by a cool surface, flame stabilization on a heated flat plate, combustion in laminar mixing zones, etc. In these cases the problem may be simplified by employing what is known in fluid mechanics as the boundary-layer approximation, since it was applied first by Prandtl in his treatment of the viscous flow over a flat plate. Physically it consists in recognizing that if the transverse velocity is small, the variations of flow properties along the direction of main flow are small in comparison with those in a direction normal to the main flow. The analytic description of the problem simplifies accordingly. The present analysis considers the ignition and combustion in the laminar mixing zone between two parallel moving gas streams. One stream consists of a cool combustible mixture, the second is hot combustion products. The two streams come into contact at a given point and a laminar mixing process follows in which the velocity distribution is modified by viscosity, and the temperature and composition distributions by conduction, diffusion, and chemical reaction. The decomposition of the combustible stream is assumed to follow first-order reaction kinetics with temperature dependence according to the Arrhenius law. For a given initial velocity, composition, and temperature distribution, the questions to be answered are: (1) Does the combustible material ignite; and (2) how far downstream of the initial contact point does the flame appear and what is the detailed process of development. Since the hot stream is of infinite extent, it is found that ignition always takes place at some point of the stream. However, when the temperature of the hot stream drops below a certain value, the distance required for ignition increases so enormously that it essentially does not occur in a physical apparatus of finite dimension. The complete development of the laminar flame front is computed using an approximation similar to the integral technique introduced by von Kármán into boundary layer theory

3-D mesoscale MHD simulations of magnetospheric cusp-like configurations: cusp diamagnetic cavities and boundary structure

We present results from mesoscale simulations of the magnetospheric cusp region for both strongly northward and strongly southward interplanetary magnetic field (IMF). Simulation results indicate an extended region of depressed magnetic field and strongly enhanced plasma β which exhibits a strong dependence on IMF orientation. These structures correspond to the Cusp Diamagnetic Cavities (CDC's). The typical features of these CDC's are generally well reproduced by the simulation. The inner boundaries between the CDC and the magnetosphere are gradual transitions which form a clear funnel shape, regardless of IMF orientation. The outer CDC/magnetosheath boundary exhibits a clear indentation in both the x-z and y-z planes for southward IMF, while it is only indented in the x-z plane for northward, with a convex geometry in the y-z plane. The outer boundary represents an Alfvénic transition, mostly consistent with a slow-shock, indicating that reconnection plays an important role in structuring the high-altitude cusp region

'Female heroes': celebrity executives as postfeminist role models

This article explores the significance of contemporary celebrity businesswomen as role models for women aspiring to leadership in business. We explore the kind of gendered ideals they model and promote to women through their autobiographical narratives, and analyze how these ideals map against contemporary postfeminist sensibility to further understand the potential of these role models to redress the under-representation of women in management and leadership . Our findings show that celebrity businesswomen present a role model that we call the ‘female hero’, a figure characterized by 3Cs: confidence to jump over gendered barriers, control in managing these barriers, and courage to push through them. We argue that the ‘female hero’ role model is deeply embedded in the contemporary postfeminist sensibility; it offers exclusively individualized solutions by calling on women to change themselves to succeed, and therefore has limited capacity to challenge the current gendered status quo in management and leadership. The article contributes to current literature on role models by generating a more differentiated and socially-situated understanding of distant female role models in business and extending our understanding of their potential to generate sustainable and long-term change in advancing gendered change in management and leadership

Automatic navigation of a long range rocket vehicle

The flight of a rocket vehicle in the equatorial plane of a rotating earth is considered with possible disturbances in the atmosphere due to changes in density, in temperature, and in wind speed. These atmospheric disturbances together with possible deviations in weight and in moment of inertia of the vehicle tend to change the flight path away from the normal flight path. The paper gives the condition for the proper cut-off time for the rocket power, and the proper corrections in the elevator angle so that the vehicle will land at the chosen destination in spite of such disturbances. A scheme of tracking and automatic navigation involving a high-speed computer and elevator servo is suggested for this purpose

A General Quantum Mechanical Method to Predict Positron Spectroscopy

The nuclear-electronic orbital (NEO) method was modified and extended to positron systems. NEO - second-order Moeller-Plesset perturbation (MP2) energies and annihilation rates were calculated for the positronium hydride (PsH) system, and the effects of basis set size on correlation energies captured with the NEO-MP2 and NEO-full configuration interaction (FCI) methods are compared and discussed. Equilibrium geometries and vibrational energy levels were computed for the LiX and e+LiX (X = H, F, Cl) systems at the MP2 and NEO-MP2 levels. It was found that anharmonicity plays a significant role, specifically in the differences between the vibrational energy levels of the LiX and e+LiX systems. The implications of these results with respect to VFR for these systems is discussed. The positron lifetime in potassium dodecahydrododecaborate methanolate, K2B12H12·CH3OH, was measured to be 0.2645±0.0077 ns. Quantum mechanical calculations reveal a spherically symmetric positronic wavefunction, with a peak in the positron density at the outside edge of the hydrogen atom cage. The experimentally determined annihilation rate corresponds to an effective number of electrons of 1.88, indicating that there is significant positron density both inside and outside of the B12H122- cage

Preferential Land Assessment In Virginia

The post-World War II land boom has seen cities and many towns snake outward into the countryside, engulfing millions of acres of formerly open land and developing them into suburbs. Cities have expanded not merely in numbers of people; they have over the past several decades also swallowed up vast areas of heretofore rural and farm land as city dwellers have fled to the suburbs