Tetroon evaluation program

The actual volume of a constant volume superpressured tetrahedron shaped balloon changes as the amount of superpressure is changed. The experimental methods used to measure these changes in volume are described and results are presented. The basic equations used to determine the amount of inflation gas required for a tetroon to float at a predetermined flight level are presented and inflation techniques discussed

Substituent effects on the nitrogen-15 and carbon-13 shieldings of some N-arylguanidinium chlorides

The 13C and 15N chemical shifts of five N-arylguanidinium chlorides carrying polar substituents, ranging in character from 4-methoxy to 4-nitro groups, have been determined by NMR spectroscopy at the natural-abundance level of 13C and 15N in dimethyl sulfoxide solution. Comparison of the 13C shifts of these salts with those of monosubstituted benzenes shows that the guanidinium group induces an average downfield shift of -5.8 ppm of the resonance of the aryl carbon to which it is attached (C1), an average upfield shift of +4.2 ppm for C2 and C6, and a small upfield shift of +1.9 ppm for C4. The shifts of C3 and C5 are small and erratic relative to the corresponding carbons in monosubstituted benzenes. The 15N resonances of the guanidinium nitrogens are quite sensitive to electric effects resulting from substitution of polar groups at C4. The 15N shift of the ==NAr nitrogen relative to that of the salts suggests that the predominant tautomer for N-arylguanidines is (H2N)2C==NAr. The 15N shifts of the (NH2) 2 nitrogens correlate rather well with σp- parameters, whereas the shifts of the -NHAr nitrogens seem to correlate only with R values derived from the σp- substituent constants

Interferometric Astrometry of the Low-mass Binary Gl 791.2 (= HU Del) Using Hubble Space Telescope Fine Guidance Sensor 3: Parallax and Component Masses

With fourteen epochs of fringe tracking data spanning 1.7y from Fine Guidance Sensor 3 we have obtained a parallax (pi_abs=113.1 +- 0.3 mas) and perturbation orbit for Gl 791.2A. Contemporaneous fringe scanning observations yield only three clear detections of the secondary on both interferometer axes. They provide a mean component magnitude difference, Delta V = 3.27 +- 0.10. The period (P = 1.4731 yr) from the perturbation orbit and the semi-major axis (a = 0.963 +- 0.007 AU) from the measured component separations with our parallax provide a total system mass M_A + M_B = 0.412 +- 0.009 M_sun. Component masses are M_A=0.286 +- 0.006 M_sun and M_B = 0.126 +- 0.003 M_sun. Gl 791.2A and B are placed in a sparsely populated region of the lower main sequence mass-luminosity relation where they help define the relation because the masses have been determined to high accuracy, with errors of only 2%.Comment: 19 pages, 5 figures. The paper is to appear in August 2000 A

Current evaluation of the tripropellant concept

An analytical study was conducted to determine the specific-impulse advantages of adding metals to conventional liquid-bipropellant systems. These tripropellant systems theoretically offer higher specific impulse and increased propellant density compared with bipropellant systems. Metals considered were Be, Li, and Al. Bipropellant systems were H2/O2, N2H4/N2O4, RP-1/O2, and H2/F2. Thermochemical calculations were performed for sea-level expansion from 6.895-MN/sq. m. (1000-psia) chamber pressure over a wide range of mixture ratios and propellant compositions. Three-dimensional plots characterize the specific impulse of each tripropellant system. Technology issues pertinent to metallized propellant systems are discussed

Wandering Poles in the Last 2000 Years

In this activity students will plot the location of the north magnetic pole for the last 2000 years on a map and explore how it has changed location. They will discover that before igneous rocks cool and harden, the liquid magma is acted on by the magnetic field of Earth and that this causes some of the iron atoms in the rock to align with the magnetic field and "point" toward the North Geomagnetic Pole of Earth. Students also learn that when scientists analyzed rocks formed at different times in the past, they found that the magnetic pointers did not point to the same location on the Earth and that they interpreted this to mean that the position of the magnetic North Pole had moved over time. They will come to realize that the magnetic North Pole is still moving today and, using modern instruments, this movement can be measured from year to year. Educational levels: High school

Energy and Environmental Analysis of a Linear Concentrating Photovoltaic System

The world is facing an imminent energy supply crisis. In order to sustain and increase our energy supply in an environmentally-conscious manner, it is necessary to advance renewable technologies. Despite this urgency, however, it is paramount to consider the larger environmental effects associated with using renewable energy resources. This research is meant to better understand linear concentrating photovoltaics (LCPVs) from an engineering and environmental standpoint. In order to analyze the LCPV system, a simulation and life cycle assessment (LCA) were developed. The LCPV system serves two major purposes: it produces electricity, and waste heat is collected for heating use. There are three parts to the LCPV simulation. The first part simulates the multijunction cell output so as to calculate the temperature-dependent electricity generation. The second part simulates the cell cooling and waste heat recovery system using a model consisting of heat transfer and fluid flow equations. The waste heat recovery in the LCPV system was linked to a hot water storage system, which was also modeled. Coupling the waste heat recovery simulation and the hot water storage system gives an overall integrated system that is useful for system design, optimization, and acts as a stepping stone for future multijunction cell Photovoltaic/Thermal (PV/T) systems. Finally, all of the LCPV system components were coded in Engineering Equation Solver (EES) and were used in an energy analysis under actual weather and solar conditions for the Phoenix, AZ, region.The life cycle assessment (LCA) for the LCPV system allowed for an environmental analysis of the system where areas of the highest environmental impact were pinpointed. While conducting the LCA research, each component of the system was analyzed from a resource extraction, production, and use standpoint. The collective production processes of each LCPV system component were gathered into a single inventory of materials and energy flows. From these parameters, an analysis was conducted to identify areas of high environmental impact. This area identification can lead to the optimizing of the corresponding processes or materials so as to reduce the overall impact of the system

Direct quark transition potential for ΛN→NN\Lambda N \to NN decay

The weak $\Lambda N\to NN$ transition is studied in the valence quark model approach. The quark component of the two baryon system is described in the quark cluster model and the weak transition potential is calculated by evaluating the matrix elements of the $\Delta S=1$ effective weak Hamiltonian. The transition potential is applied to the decay of hypernuclei and the results are compared with available experimental data. The results indicate that direct quark process is significant and qualitatively different when compared with those in conventional meson-exchange calculations. The direct quark mechanism predicts the violation of the $\Delta I = 1/2$ rule for this transition.Comment: 36 pages, LaTeX, 2 figures (uuencoded Postscript) included using epsf.te