The effect of sudden source buoyancy flux increases on turbulent plumes

Building upon the recent experimentally verified modelling of turbulent plumes which are subject to decreases in their source strength (Scase et al., J. Fluid Mech., vol. 563, 2006b, p. 443), we consider the complementary case where the plume's source strength is increased. We consider the effect of increasing the source strength of an established plume and we also compare time-dependent plume model predictions for the behaviour of a starting plume to those of Turner (J. Fluid Mech., vol. 13, 1962, p. 356)

Understanding Needs and Concerns of Black Students in Pursuit of Higher Education

The problem of this study was to increase the general publics\u27 awareness of the difficulties Black Americans faced in pursuit of higher education. The procedure was a twofold process. First, the writer reviewed some of the pre-college variables that affected the Black student. Second, the needs and concerns of the Black student at a predominantly White University were studied by the use of a questionnaire. The questionnaire was distributed to three groups on the Eastern Illinois University Campus. The first group was comprised of twenty-five Black students that were currently enrolled in the University. The second group was twenty Black faculty and administrators and the third twenty-five White faculty and administrators. The writer designed twenty questions based on his review of the literature concerning Black students needs and concerns at predominantly White Universities. Each individual respondent was asked to answer the questions according to his or her perception of the specific need or concern. The writer has drawn the following conclusions from his study of the problems Black Americans faced in pursuit of higher education. (1) Black students responded they felt alienated by their environment; (2) Black faculty and administrators also indicated this viewpoint; (3) White faculty and administrators indicated they were in favor of increasing resources to Black elementary and secondary schools and promoting pre-college remedial and tutorial programs; (4) Black students indicated a concern over the limited number of Black faculty and administrators; (5) Black students also indicated that minority counseling and racial interaction were important needs and concerns for Black students in pursuit of higher education. The writer would like to propose the following recommendations as a result of this study: (1) an increase in Black faculty and administrators to serve as role models for the Black students; (2) improved remedial and tutorial programs for Black students; (3) an increase in minority counseling services to aid the disadvantaged Black students; (4) a more open discussion of racial issues to increase the overall awareness of the general public, faculty, and students

Creating Pathways For High School Students To BHCC

Nursing, without a doubt, is one of the most popular programs at the community colleges today. If predictions are correct, there will be shortages in this field approaching a possible crisis situation. While community colleges educate 60% ofthe registered nurses and 63% of the allied health workers, it is not enough. Our colleges are faced with faculty shortages, a lack of clinical training sites, skyrocketing programs costs, regulations and compliances that they must fulfill, and to top all of this, students enroll at rates far exceeding their ability to accommodate. And, a group of people seemingly standing on the outside looking in, that could help alleviate the shortages if trained and educated early, are high school healthcare career majors. A collaborative effort on the part of the colleges, the high schools, students and parents must be established to help solve these problems of our nation

A variational framework for flow optimization using semi-norm constraints

When considering a general system of equations describing the space-time evolution (flow) of one or several variables, the problem of the optimization over a finite period of time of a measure of the state variable at the final time is a problem of great interest in many fields. Methods already exist in order to solve this kind of optimization problem, but sometimes fail when the constraint bounding the state vector at the initial time is not a norm, meaning that some part of the state vector remains unbounded and might cause the optimization procedure to diverge. In order to regularize this problem, we propose a general method which extends the existing optimization framework in a self-consistent manner. We first derive this framework extension, and then apply it to a problem of interest. Our demonstration problem considers the transient stability properties of a one-dimensional (in space) averaged turbulent model with a space- and time-dependent model "turbulent viscosity". We believe this work has a lot of potential applications in the fluid dynamics domain for problems in which we want to control the influence of separate components of the state vector in the optimization process.Comment: 30 page

Optical implementation of systolic array processing

Algorithms for matrix vector multiplication are implemented using acousto-optic cells for multiplication and input data transfer and using charge coupled devices detector arrays for accumulation and output of the results. No two dimensional matrix mask is required; matrix changes are implemented electronically. A system for multiplying a 50 component nonnegative real vector by a 50 by 50 nonnegative real matrix is described. Modifications for bipolar real and complex valued processing are possible, as are extensions to matrix-matrix multiplication and multiplication of a vector by multiple matrices

Seismic imaging of rapid onset of stratified turbulence in the South Atlantic Ocean

AbstractBroadband measurements of the internal wavefield will help to unlock an understanding of the energy cascade within the oceanic realm. However, there are challenges in acquiring observations with sufficient spatial resolution, especially in horizontal dimensions. Seismic reflection profiling can achieve a horizontal and vertical resolution of order meters. It is suitable for imaging thermohaline fine structure on scales that range from tens of meters to hundreds of kilometers. This range straddles the transition from internal wave to turbulent regimes. Here, the authors analyze an 80-km-long seismic image from the Falkland Plateau and calculate vertical displacement spectra of tracked reflections. First, they show that these spectra are consistent with the Garrett–Munk model at small horizontal wavenumbers (i.e., kx ≲ 3 × 10−3 cpm). There is a transition to stratified turbulence at larger wavenumbers (i.e., kx ≳ 2 × 10−1 cpm). This transition occurs at length scales that are significantly larger than the Ozmidov length scale above which stratification is expected to modify isotropic Kolmogorov turbulence. Second, the authors observe a rapid onset of this stratified turbulence over a narrow range of length scales. This onset is consistent with a characteristic energy injection scale of stratified turbulence with a forward cascade toward smaller scales through isotropic turbulence below the Ozmidov length scale culminating in microscale dissipation. Finally, they estimate the spatial pattern of diapycnal diffusivity and show that the existence of an injection scale can increase these estimates by a factor of 2.M.F. is supported by the Department of Earth Sciences. Research activity of C.P.C. is supported by EPSRC Programme Grant EP/K034529/1 (“Mathematical Underpinnings of Stratified Turbulence”). We thank C. Bond, A. Dickinson, K. Gunn, S. Holbrook, J. Klymak, J. Moum and S. Thorpe for their help. We are very grateful to J. Klymak for generously making available his MATLAB toolbox for calculating Garrett-Munk spectra. Department of Earth Sciences contribution number esc.XXXX.This is the author accepted manuscript. The final version is available from the American Meteorological Society via http://dx.doi.org/10.1175/JPO-D-15-0140.

Mixing and entrainment are suppressed in inclined gravity currents

We explore the dynamics of inclined temporal gravity currents using direct numerical simulation, and find that the current creates an environment in which the flux Richardson number $\mathit{Ri}_{f}$, gradient Richardson number $\mathit{Ri}_{g}$ and turbulent flux coefficient \unicode[STIX]{x1D6E4} are constant across a large portion of the depth. Changing the slope angle \unicode[STIX]{x1D6FC} modifies these mixing parameters, and the flow approaches a maximum Richardson number $\mathit{Ri}_{max}\approx 0.15$ as \unicode[STIX]{x1D6FC}\rightarrow 0 at which the entrainment coefficient $E\rightarrow 0$. The turbulent Prandtl number remains $O(1)$ for all slope angles, demonstrating that $E\rightarrow 0$ is not caused by a switch-off of the turbulent buoyancy flux as conjectured by Ellison (J. Fluid Mech., vol. 2, 1957, pp. 456–466). Instead, $E\rightarrow 0$ occurs as the result of the turbulence intensity going to zero as \unicode[STIX]{x1D6FC}\rightarrow 0, due to the flow requiring larger and larger shear to maintain the same level of turbulence. We develop an approximate model valid for small \unicode[STIX]{x1D6FC} which is able to predict accurately $\mathit{Ri}_{f}$, $\mathit{Ri}_{g}$ and \unicode[STIX]{x1D6E4} as a function of \unicode[STIX]{x1D6FC} and their maximum attainable values. The model predicts an entrainment law of the form $E=0.31(\mathit{Ri}_{max}-\mathit{Ri})$, which is in good agreement with the simulation data. The simulations and model presented here contribute to a growing body of evidence that an approach to a marginally or critically stable, relatively weakly stratified equilibrium for stratified shear flows may well be a generic property of turbulent stratified flows.</jats:p

The Dimer Model for k-phase Organic Superconductors

We prove that the upper electronic bands of k-phase BEDT-TTF salts are adequately modeled by an half-filled tight-binding lattice with one site per cell. The band parameters are derived from recent ab-initio calculations, getting a very simple but extremely accurate one-electron picture. This picture allows us to solve the BCS gap equation adopting a real-space pairing potential. Comparison of the calculated superconducting properties with the experimental data points to isotropic s_0-pairing. Residual many-body or phonon-mediated interactions offer a plausible explanation of the large variety of physical properties observed in k-phase BEDT-TTF salts.Comment: 8 pages, 6 PostScript figures, uses RevTe