Computer program for solving laminar, transitional, or turbulent compressible boundary-layer equations for two-dimensional and axisymmetric flow

A numerical algorithm and computer program are presented for solving the laminar, transitional, or turbulent two dimensional or axisymmetric compressible boundary-layer equations for perfect-gas flows. The governing equations are solved by an iterative three-point implicit finite-difference procedure. The software, program VGBLP, is a modification of the approach presented in NASA TR R-368 and NASA TM X-2458, respectively. The major modifications are: (1) replacement of the fourth-order Runge-Kutta integration technique with a finite-difference procedure for numerically solving the equations required to initiate the parabolic marching procedure; (2) introduction of the Blottner variable-grid scheme; (3) implementation of an iteration scheme allowing the coupled system of equations to be converged to a specified accuracy level; and (4) inclusion of an iteration scheme for variable-entropy calculations. These modifications to the approach presented in NASA TR R-368 and NASA TM X-2458 yield a software package with high computational efficiency and flexibility. Turbulence-closure options include either two-layer eddy-viscosity or mixing-length models. Eddy conductivity is modeled as a function of eddy viscosity through a static turbulent Prandtl number formulation. Several options are provided for specifying the static turbulent Prandtl number. The transitional boundary layer is treated through a streamwise intermittency function which modifies the turbulence-closure model. This model is based on the probability distribution of turbulent spots and ranges from zero to unity for laminar and turbulent flow, respectively. Several test cases are presented as guides for potential users of the software

Single-cycle THz pulses with amplitudes exceeding 1 MV/cm generated by optical rectification in LiNbO3

Using the tilted-pulse-intensity-front scheme, we generate single-cycle terahertz (THz) pulses by optical rectification of femtosecond laser pulses in LiNbO3. In the THz generation setup, the condition that the image of the grating coincides with the tilted-optical-pulse front is fulfilled to obtain optimal THz beam characteristics and pump-to-THz conversion efficiency. The designed focusing geometry enables tight focus of the collimated THz beam with a spot size close to the diffraction limit, and the maximum THz electric field of 1.2 MV/cm is obtained

Finite element computation of a viscous compressible free shear flow governed by the time dependent Navier-Stokes equations

A finite element algorithm for solution of fluid flow problems characterized by the two-dimensional compressible Navier-Stokes equations was developed. The program is intended for viscous compressible high speed flow; hence, primitive variables are utilized. The physical solution was approximated by trial functions which at a fixed time are piecewise cubic on triangular elements. The Galerkin technique was employed to determine the finite-element model equations. A leapfrog time integration is used for marching asymptotically from initial to steady state, with iterated integrals evaluated by numerical quadratures. The nonsymmetric linear systems of equations governing time transition from step-to-step are solved using a rather economical block iterative triangular decomposition scheme. The concept was applied to the numerical computation of a free shear flow. Numerical results of the finite-element method are in excellent agreement with those obtained from a finite difference solution of the same problem

DIRECT PRODUCE PROFIT FOR SMALL AND INTERMEDIATE SIZE GROCERY RETAILERS

Direct product profit (DPP) is a retailing tool used to analyze product sales performance. Although the concept is over 20 years old, its widespread use in grocery stores is a fairly recent phenomena. A product's DPP is calculated as its adjusted gross margin less its direct selling costs, which normally include transportation, warehousing, and retailing or store costs. A product's DPP and sales volume classifies it in one of four categories to assist in merchandising options. Fifteen small and intermediate size grocery retailers cooperated with a study of produce DPP. Based on weekly produce sales, the stores were separated into three groups. As store group produce sales increased, produce adjusted gross margin and DPP increased. Based on produce sales volume and DPP level, various merchandising strategies are suggested.Agribusiness,

Scattering Models and Basic Experiments in the Microwave Regime

The objectives of research over the next three years are: (1) to develop a randomly rough surface scattering model which is applicable over the entire frequency band; (2) to develop a computer simulation method and algorithm to simulate scattering from known randomly rough surfaces, Z(x,y); (3) to design and perform laboratory experiments to study geometric and physical target parameters of an inhomogeneous layer; (4) to develop scattering models for an inhomogeneous layer which accounts for near field interaction and multiple scattering in both the coherent and the incoherent scattering components; and (5) a comparison between theoretical models and measurements or numerical simulation

The reversibility of sea ice loss in a state-of-the-art climate model

Rapid Arctic sea ice retreat has fueled speculation about the possibility of threshold (or ‘tipping point’) behavior and irreversible loss of the sea ice cover. We test sea ice reversibility within a state-of-the-art atmosphere–ocean global climate model by increasing atmospheric carbon dioxide until the Arctic Ocean becomes ice-free throughout the year and subsequently decreasing it until the initial ice cover returns. Evidence for irreversibility in the form of hysteresis outside the envelope of natural variability is explored for the loss of summer and winter ice in both hemispheres. We find no evidence of irreversibility or multiple ice-cover states over the full range of simulated sea ice conditions between the modern climate and that with an annually ice-free Arctic Ocean. Summer sea ice area recovers as hemispheric temperature cools along a trajectory that is indistinguishable from the trajectory of summer sea ice loss, while the recovery of winter ice area appears to be slowed due to the long response times of the ocean near the modern winter ice edge. The results are discussed in the context of previous studies that assess the plausibility of sea ice tipping points by other methods. The findings serve as evidence against the existence of threshold behavior in the summer or winter ice cover in either hemisphere

The Persistence Of Community College Students: A Single Site Case Study

Only 22% of all students who enroll in community colleges complete an associate degree within three years, and only 16% of students at urban community colleges earn a degree in the same time frame. Community college administrators recognize that a majority of their student population desires to earn a degree, but many lack the knowledge, skills, and support to complete college. The purpose of this single site qualitative case study was to understand how community college students perceive wraparound services and how these services impact students’ persistence. Deil-Amen (2011) was used as the theoretical underpinning for this study. The setting was a community college in the Midwest. Twelve interview questions and three instruments were used in this study. The instruments included a demographic questionnaire, a semi-structured interview, and a personal artifact form. The population was defined as eight (N = 8) second year community college students. The sample mean age was 21 (M = 21) and 50% of the sample were male (n = 4) and 50% were female (n = 4). Using NVivo 12 Pro, 50 nodes were found, nine overarching themes were expressed, and eight findings were noted. These findings included: • tutoring is essential, • motivation is not inherent and must be fostered, • coaching can promote persistence, • overcoming social and academic barriers promotes the motivation to stay on track, • life assistance helps grow financial stability, • resources and services help students achieve stability, • professor support encourages participation in social and academic activities and maintains confidence, and • use of wraparound services is need driven and helps student persistence. Findings from this study provide recommendations for students, which included: • use wraparound services often and as needed,• learn transformative leadership skills to overcome social and academic barriers, • take advantage of life assistance for food and shelter to avoid insecurities in these areas, and • learn to utilize professors’ support when offered and when needed