Semi-implicit and fully implicit shock-capturing methods for hyperbolic conservation laws with stiff source terms

Some numerical aspects of finite-difference algorithms for nonlinear multidimensional hyperbolic conservation laws with stiff nonhomogenous (source) terms are discussed. If the stiffness is entirely dominated by the source term, a semi-implicit shock-capturing method is proposed provided that the Jacobian of the soruce terms possesses certain properties. The proposed semi-implicit method can be viewed as a variant of the Bussing and Murman point-implicit scheme with a more appropriate numerical dissipation for the computation of strong shock waves. However, if the stiffness is not solely dominated by the source terms, a fully implicit method would be a better choice. The situation is complicated by problems that are higher than one dimension, and the presence of stiff source terms further complicates the solution procedures for alternating direction implicit (ADI) methods. Several alternatives are discussed. The primary motivation for constructing these schemes was to address thermally and chemically nonequilibrium flows in the hypersonic regime. Due to the unique structure of the eigenvalues and eigenvectors for fluid flows of this type, the computation can be simplified, thus providing a more efficient solution procedure than one might have anticipated

Experimental perfect-gas study of expansion-tube flow characteristics

Results of an experimental investigation of expansion tube flow characteristics performed with helium test gas and acceleration gas are presented. The use of helium, eliminates complex real gas chemistry in the comparison of measured and predicted flow quantities. The driver gas was unheated helium at a nominal pressure of 33 MN sq m. The quiescent test gas pressure and quiescent acceleration gas pressure were varied from 0.7 to 50 kN/sq m and from 2.5 to 53 N/sq m, respectively. The effects of tube-wall boundary layer growth and finite secondary diaphragm opening time were examined through the variation of the quiescent gas pressures and secondary diaphragm thickness. Optimum operating conditions for helium test gas were also defined

Green's function methods in heavy ion shielding

An analytic solution to the heavy ion transport in terms of Green's function is used to generate a highly efficient computer code for space applications. The efficiency of the computer code is accomplished by a nonperturbative technique extending Green's function over the solution domain. The computer code can also be applied to accelerator boundary conditions to allow code validation in laboratory experiments

Land use change detection with LANDSAT-2 data for monitoring and predicting regional water quality degradation

The author has identified the following significant results. Comparison between LANDSAT 1 and 2 imagery of Arkansas provided evidence of significant land use changes during the 1972-75 time period. Analysis of Arkansas historical water quality information has shown conclusively that whereas point source pollution generally can be detected by use of water quality data collected by state and federal agencies, sampling methodologies for nonpoint source contamination attributable to surface runoff are totally inadequate. The expensive undertaking of monitoring all nonpoint sources for numerous watersheds can be lessened by implementing LANDSAT change detection analyses

Laser ablation for the synthesis of carbon nanotubes

Single walled carbon nanotubes are produced in a novel apparatus by the laser-induced ablation of moving carbon target. The laser used is of high average power and ultra-fast pulsing. According to various preferred embodiments, the laser produces and output above about 50 watts/cm.sup.2 at a repetition rate above about 15 MHz and exhibits a pulse duration below about 10 picoseconds. The carbon, carbon/catalyst target and the laser beam are moved relative to one another and a focused flow of "side pumped", preheated inert gas is introduced near the point of ablation to minimize or eliminate interference by the ablated plume by removal of the plume and introduction of new target area for incidence with the laser beam. When the target is moved relative to the laser beam, rotational or translational movement may be imparted thereto, but rotation of the target is preferred

Laser ablation for the synthesis of carbon nanotubes

Single walled carbon nanotubes are produced in a novel apparatus by the laser-induced ablation of moving carbon target. The laser used is of high average power and ultra-fast pulsing. According to various preferred embodiments, the laser produces an output above about 50 watts/cm.sup.2 at a repetition rate above about 15 MHz and exhibits a pulse duration below about 10 picoseconds. The carbon, carbon/catalyst target and the laser beam are moved relative to one another and a focused flow of side pumped, preheated inert gas is introduced near the point of ablation to minimize or eliminate interference by the ablated plume by removal of the plume and introduction of new target area for incidence with the laser beam. When the target is moved relative to the laser beam, rotational or translational movement may be imparted thereto, but rotation of the target is preferred

Understanding Afghan Opinion Leaders’ Viewpoints About Post-Conflict Foreign Agricultural Development: A Case Study in Herāt Province, Afghanistan

This investigation sprang from a yearlong immersion in post-conflict agricultural development environments in Herāt Province Afghanistan and from observing an array of NGO development projects. The purpose was to understand better the viewpoints of Afghan opinion leaders regarding the adoption–integration of foreign agricultural development. Objectives included (a) the identification of perceived strengths of foreign agricultural development, (b) perceived weaknesses, (c) opportunities, (d) threats, (e) anomalies, and (f)incentives and barriers. The case method fit the qualitative research design, and IRB approved the protocols. Researchers selected 15 opinion leaders (OLs) based on their knowledge, experience, and positional responsibilities. An interview guide framed 13 open-ended questions. A researcher fluent in Farsi/Pashto/English assisted with each interview. The findings from 15 interviews emerged as 11 themes. Fourteen OLs recognized agriculture and natural resources as strengths for development. Opinion leaders recognize government, infrastructure, and corruption as fundamental weaknesses. Opinion Leaders were slow to identify opportunities but generally identified opportunities to exploit labor, land, and water coupled with improving management and mechanization.They universally recognized threats related to to personal security and safety but had difficulty separating internal weaknesses from external threats. Two anomalies emerged as incongruous expectations about Afghan government and foreign NGOs. Improving market chains and increasing governmental subsidies were incentives for development. The authors conclude that indigenous knowledge is a fundamental resource and a foundation for local level decision making and sustainability. Opinion Leaders serve as channels to move the society from poverty and conflict toward security and peacebuilding. The tension between Maslow’s hierarchy of needs and Max Neef’s interrelated and interactive needs should be explore