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

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 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

The Effect of Drying Conditions on ASA Sized Paper

The object of this study is to determine the roles of the drying variable and solids content of the sheet in the ASA sizing mechanism. Handsheets were produced according to the Western Michigan University Standard Hardsheet Procedure for Alkenyl Succinic Anhydride (ASA) sized sheets. A control value of 346 seconds was set drying sheets in a forced draft oven at 221◦F (105◦C) for 60 minutes. Additional handsheets were then dried on a hot plate at one of the following temperatures: 100-120◦F, 200-210◦F, 317◦F or 475◦F, and they experienced vastly reduced sizing levels. Sheets were also fed into the drying stage at varied solids levels. Tests indicated the dependency of the resulting sizing level on drying temperature and rate of water removal. Also indicated by the results was the necessity of cationic starch as a retention aid. The data showed conclusively that ASA sized handsheets are two-sided and that the higher degree of sizing is obtained on the wire side. Also, the level of water resistance imparted to a sheet is dependent on the solids content of the sheet going in to the drying stage. Handsheets of higher solids content result in better sized sheets. Keywords: Internal sizing, alkenyl succinic, anhydride, drying temperature, web moisture, alkaline papermakin