A numerical method for the prediction of high-speed boundary-layer transition using linear theory

A method is described of estimating the location of transition in an arbitrary laminar boundary layer on the basis of linear stability theory. After an examination of experimental evidence for the relation between linear stability theory and transition, a discussion is given of the three essential elements of a transition calculation: (1) the interaction of the external disturbances with the boundary layer; (2) the growth of the disturbances in the boundary layer; and (3) a transition criterion. The computer program which carried out these three calculations is described. The program is first tested by calculating the effect of free-stream turbulence on the transition of the Blasius boundary layer, and is then applied to the problem of transition in a supersonic wind tunnel. The effects of unit Reynolds number and Mach number on the transition of an insulated flat-plate boundary layer are calculated on the basis of experimental data on the intensity and spectrum of free-stream disturbances. Reasonable agreement with experiment is obtained in the Mach number range from 2 to 4.5

Numerical Investigation of Second Mode Attenuation over Carbon/Carbon Surfaces on a Sharp Slender Cone

We have carried out axisymmetric numerical simulations of a spatially developing hypersonic boundary layer over a sharp 7$^{\circ{}}$-half-angle cone at $M_\infty=7.5$ inspired by the experimental investigations by Wagner (2015). Simulations are first performed with impermeable (or solid) walls with a one-time broadband pulse excitation applied upstream to determine the most convectively-amplified frequencies resulting in the range 260kHz -- 400kHz, consistent with experimental observations of second-mode instability waves. Subsequently, we introduce harmonic disturbances via continuous periodic suction and blowing at 270kHz and 350kHz. For each of these forcing frequencies complex impedance boundary conditions (IBC), modeling the acoustic response of two different carbon/carbon (C/C) ultrasonically absorptive porous surfaces, are applied at the wall. The IBCs are derived as an output of a pore-scale aeroacoustic analysis -- the inverse Helmholtz Solver (iHS) -- which is able to return the broadband real and imaginary components of the surface-averaged impedance. The introduction of the IBCs in all cases leads to a significant attenuation of the harmonically-forced second-mode wave. In particular, we observe a higher attenuation rate of the introduced waves with frequency of 350kHz in comparison with 270kHz, and, along with the iHS impedance results, we establish that the C/C surfaces absorb acoustic energy more effectively at higher frequencies.Comment: AIAA-SciTech 201

Absolute and convective instabilities of an inviscid compressible mixing layer: Theory and applications

This study aims to examine the effect of compressibility on unbounded and parallel shear flow linear instabilities. This analysis is of interest for industrial, geophysical, and astrophysical flows. We focus on the stability of a wavepacket as opposed to previous single-mode stability studies. We consider the notions of absolute and convective instabilities first used to describe plasma instabilities. The compressible-flow modal theory predicts instability whatever the Mach number. Spatial and temporal growth rates and Reynolds stresses nevertheless become strongly reduced at high Mach numbers. The evolution of disturbances is driven by Kelvin -Helmholtz instability that weakens in supersonic flows. We wish to examine the occurrence of absolute instability, necessary for the appearance of turbulent motions in an inviscid and compressible two-dimensional mixing layer at an arbitrary Mach number subject to a three-dimensional disturbance. The mixing layer is defined by a parametric family of mean-velocity and temperature profiles. The eigenvalue problem is solved with the help of a spectral method. We ascertain the effects of the distribution of temperature and velocity in the mixing layer on the transition between convective and absolute instabilities. It appears that, in most cases, absolute instability is always possible at high Mach numbers provided that the ratio of slow-stream temperature over fast-stream temperature may be less than a critical maximal value but the temporal growth rate present in the absolutely unstable zone remains small and tends to zero at high Mach numbers. The transition toward a supersonic turbulent regime is therefore unlikely to be possible in the linear theory. Absolute instability can be also present among low-Mach-number coflowing mixing layers provided that this same temperature ratio may be small, but nevertheless, higher than a critical minimal value. Temperature distribution within the mixing layer also has an effect on the growth rate, this diminishes when the slow stream is heated. These results are applied to the dynamics of mixing layers in the interstellar medium and to the dynamics of the heliopause, frontier between the interstellar medium, and the solar wind. (C) 2009 American Institute of Physics

Former Employees\u27 Right to Relief under the Americans with Disabilities Act

The Americans with Disabilities Act (ADA) does not state whether a former employee may sue a former employer regarding post-employment fringe benefits. Some courts have held that former employees who are retired or have total disabilities have no right to relief under the statute because they do not meet the ADA\u27s requirement that a claimant be a qualified individual with a disability. Other courts have concluded that former employees receiving post-employment benefits do have a right to relief under the statute. These courts reasoned that an internal ambiguity in the statute requires courts to look to the legislative history and purpose of the ADA, and construe the statute in accord with its broad remedial purpose. This Comment argues that post-employment benefits recipients have a right to relief under the ADA. The ADA expressly prohibits discrimination in terms, conditions, and privileges of employment; individuals must have legal recourse when faced with this type of discrimination. By broadly construing the employment relationship to include individuals who no longer work but continue to receive benefits from a former employer, the qualified individual with a disability requirement is satisfied and does not stand as an artificial barrier to relief under the ADA

Why Biography?

Reading for Pleasure (Essay Review

Perceptions of African-american Seniors Regarding Factors of Institutional Support at Three Predominantly White Tennessee State-supported Institutions of Higher Education

This study of African-American seniors at East Tennessee State University, Middle Tennessee State University, and the University of Tennessee at Knoxville was conducted to solicit student responses about the perceptions of their schools, university services, and experiences at those institutions. The study employed quantitative data and descriptive analysis was performed. Data collected in this study described the demographic characteristics of the students and their perceptions, attitudes, experiences and level of involvement in the campus environment for African-American seniors. Data in this study indicated perceptions that Tennessee must be committed to increasing financial support to the universities. Universities must be committed to increase faculty and student involvement, create a culturally diverse environment and expand existing recruitment and retention programs

Social Networking Privacy: a Qualitative Study of the Risks and Effects of Sharing Data to a Global Environment Via Facebook

Young women have placed themselves at risk by disclosing private and sensitive data on their Facebook accounts. Privacy settings which can help prevent unauthorized access of this data exist, but some women choose to ignore them. This study is an attempt to gain an understanding of this phenomenon and answer the question of why young women choose to share personal information. Qualitative interviews of college students were conducted and the results interpreted in this paper. The results of this interview are intended to supply research for future studies which aim to minimize problems caused to individuals who choose to share such private information to a semi-global audience

Multi-Frequency Study of the B3-VLA Sample II. The Database

We present total flux densities of 1049 radio sources in the frequency range from 151 MHz to 10.6 GHz. These sources belong to the B3-VLA sample, which is complete down to 100 mJy at 408 MHz. The data constitute a homogeneous spectral database for a large sample of radio sources, 50 times fainter than the 3C catalogue, and will be used to perform a spectral ageing analysis, which is one of the critical points in understanding the physics and evolution of extragalactic radio sources.Comment: 14 pages, 3 figures, accepted for publication in Astronomy & Astrophysics Supplement Series, gzipped postscript file also available at http://multivac.jb.man.ac.uk:8000/ceres/papers/papers.html or http://gladia.astro.rug.nl:8000/ceres/papers/papers.htm

Cultivating Culturally Responsive Elementary Teachers in a Suburban Title I School

Research suggests increased enrollment of students with diverse cultural, racial, linguistic, and social backgrounds will continue in schools across the United States over the coming years; thereby, imposing a challenge for some teachers with differing backgrounds to instruct culturally and linguistically diverse students. Without adequate professional development focused on culturally responsive teaching, it has been purported teachers will continue to adopt deficit perceptions and subpar practices that negatively impact students of culturally and linguistically diverse backgrounds. Thus, this study aimed to explore how a series of in-service professional development focused on culture, race, and pedagogy may influence teacher perceptions and practices regarding culturally and linguistically diverse students served in a suburban Title I elementary school. The study was also conducted to determine beneficial components of the professional development. A collective case study involving interviews, questionnaire surveys, and reflective journaling was conducted over a 6-week period to gain insight into eight teacher participants’ perceptions and practices before, during, and after engaging in the professional development designed to promote transformation of their thoughts and actions through the processes of critical reflection and rational discourse. The study revealed how the reflective nature of the professional development fostered notable changes in the participants’ perceptions and practices. The findings also yielded implications and recommendations for stakeholders – teachers, teacher leaders, school leaders, district leaders, teacher preparation programs, and policymakers – regarding the significance of prioritizing the learning needs of all students by maximizing opportunities for ongoing professional development intended to cultivate and sustain a culturally responsive teacher workforce