Mode Structure of Diffusive Transport in Hydroxypropylcellulose:Water

A systematic analysis of the mode structure of diffusive relaxations in 1 MDa hydroxypropylcellulose(HPC):water is presented. New methods and data include (1) use of integral spectral moments to characterize nonexponential decays, (2) spectra of small probes in concentrated HPC solutions, (3) temperature dependence of the mode structure, and (4) comparison of optical probe spectra and spectra of probe-free polymer solutions. We find that (1) probe and polymer relaxations are in general not the same; (2) the apparent viscometric crossover near ct≈6 g/l is echoed by probe behavior; (3) our HPC solutions have a characteristic dynamic length, namely the 50 nm length that matches the polymer’s hydrodynamic radius; (4) characterization of spectral modes with their mean relaxation time affords simplifications relative to other characterizations; and (5) contrary to some expectations, Stokes–Einsteinian behavior (diffusion rate determined by the macroscopic viscosity) is not observed, even for large probes in relatively concentrated solutions. We propose that the viscometric and light scattering effects found in HPC solutions at elevated concentrations reflect the incipient formation of a generalized Kivelson [S. A. Kivelson et al., J. Chem. Phys. 101, 2391 (1994)] glass

Mode Structure of Diffusive Transport in Hydroxypropylcellulose:Water

A systematic analysis of the mode structure of diffusive relaxations in 1 MDa hydroxypropylcellulose(HPC):water is presented. New methods and data include (1) use of integral spectral moments to characterize nonexponential decays, (2) spectra of small probes in concentrated HPC solutions, (3) temperature dependence of the mode structure, and (4) comparison of optical probe spectra and spectra of probe-free polymer solutions. We find that (1) probe and polymer relaxations are in general not the same; (2) the apparent viscometric crossover near ct≈6 g/l is echoed by probe behavior; (3) our HPC solutions have a characteristic dynamic length, namely the 50 nm length that matches the polymer’s hydrodynamic radius; (4) characterization of spectral modes with their mean relaxation time affords simplifications relative to other characterizations; and (5) contrary to some expectations, Stokes–Einsteinian behavior (diffusion rate determined by the macroscopic viscosity) is not observed, even for large probes in relatively concentrated solutions. We propose that the viscometric and light scattering effects found in HPC solutions at elevated concentrations reflect the incipient formation of a generalized Kivelson [S. A. Kivelson et al., J. Chem. Phys. 101, 2391 (1994)] glass

The Design and Management of a Low Cost Scientific STEDI Mission

The release of the Student Explorer Demonstration Initiative (STEDI) Opportunity of Announcement in May 1994 generated a tremendous amount of excitement and activity within the small satellite community. To meet the very tight constraints of the STEDI program (2 years, $4 million) a new paradigm for small science satellites must be created which centers on university involvement. This paper describes the collaborative process for the three university CATSAT project and focuses on some of the issues that are important for a successful university small satellite program. These points include: running a program from within a university environment, creating a model for low cost and reliable distributed design and technical oversight, and the development of a simple and effective communication and documentation process. CATSAT is a small astrophysical science satellite which is currently being funded to serve as the alternate for the two primary STEDI missions

Low-Cost Attitude Determination and Control for Small Satellites

This paper addresses the need to develop small satellite technology which will enable small satellites to perform large satellite missions. The Center for Aerospace Technology (CAST) at Weber State University (WSU) has an 18 year history of small satellite innovation. Previous satellites include: NUSAT, WEBERSAT, and PHASE 3d. CAST is currently fabricating two new small satellites with advanced capabilities. CATSAT, a USRA program, will determine the origin of gamma-ray bursts and is a joint project with the University of New Hampshire and the University of Leicister in England. JAWSAT, a joint project with the U.S. Air Force Academy, will be the first payload launched by a converted minuteman missile. Both missions require active attitude determination and control previously unavailable for satellites of this class. In support of these two missions CAST has undertaken the task of developing satellite instrumentation designed specifically for small satellite applications. Size, weight, power consumption and cost minimization were incorporated into the design philosophy. New enabling technology includes the use of the State-Sampled Network for sensor integration, attitude determination and attitude control. The overall development history is chronicled with emphasis relating to issues of reliability and acceptance testing

The CATSAT Student Explorer Mission

CATSAT (Cooperative Astrophysical and Technology SATellite) is one of three missions being developed under NASA/USRA\u27s Student Explorer Demonstration Initiative (STEDI) for launch in 1997-98. STEDI is a pilot program to assess the efficacy of smaller, low-cost spaceflight missions ... that is matched to the traditional process of research and development at universities . This program allows $4 million and 2-3 years for all aspects of the mission, i.e. instrument and satellite development, integration, testing, mission operations and data analysis. CATSAT is an astrophysics mission being developed in collaboration by three university teams. Its mission is to study the nature and distance scale of Cosmic Gamma Ray Bursters. Its prime instrumentation is a Soft X-Ray spectrometer (0.5-15 keV), with a total area of 190 cm2 and 5.5 sr. FOV, to measure the photoelectric absorption along the line-of-sight and thus determine a distance scale to the burst source. This sensor is supported by three context sensors to determine intensity, spectral and directional information. These include four Hard X-Ray spectrometers (15-400 keV, 4x45 cm2 ), a Directional Gamma-ray Spectrometer (0.3-6 MeV, 135 cm2) and an array of nine X-ray Albedo sensors (15-400 keV, 9x80 cm2 ) which are also sensitive to polarization in the burst\u27s x-ray emissions. The science payload will generate 24 Mbytes of data per 12 hours. CATSAT is expected to be launched in mid 1998 into a 550 Km polar sun synchronous 6am-6pm orbit. The mission form factor is a rectangular box with a base of 72 cm, a height of 102 cm and a launch mass of 135 Kg. A combination of body mounted cells and deployable solar panels produce a total of 150 watts. The mission is 3-axis stabilized utilizing reaction wheels and magnetic torquers to provide continuous solar-(near zenith) pointing to 5°, in orbits up to 30° from its initial terminator orbit. Solar and earth-horizon sensors are used for attitude determination and will provide after-the-fact knowledge to 1°. An onboard GPS receiver will provide universal time and orbital navigation data. The GPS information together with an onboard three-axis magnetometer will be used for a coarse attitude solution during the initial turn-on as well as other orbital emergencies, and also act as a backup for the primary sensors. Commanding and science data retrieval will take place every 12 hours by student operating teams at the university sites. A 10 watt low power standby mode is included to manage orbital emergencies between contacts

Application of harmonic analysis of water levels to determine vertical hydraulic conductivities in clay-rich aquitards

A harmonic analysis method was used to determine vertical hydraulic conductivities (Kv) in geologic media between vertically separated piezometers using water level measurements. In this method, each water level time series was filtered and then decomposed using harmonic analysis into a sum of trigonometric components. The phase and amplitude of each harmonic function were calculated. These data were used to estimate Kv values between vertically separated data sets assuming one-dimensional transient flow. The method was applied to water level data collected from nested piezometers at two thick clay-rich till aquitards in Saskatchewan, Canada. At one site, routine water levels were measured in 12 piezometers (installed between 1 and 29 m below ground surface) since installation (1995). At the other site, water levels were measured in seven piezometers (installed between 4 and 53 m below ground surface) since installation (1998–1999). The Kv calculated using harmonic analysis decreased with depth below the water table at both sites, approaching matrix estimates of hydraulic conductivity between 10 and 11 m and between 21 and 43 m below ground surface. These depths reflected the depth of extensive vertical fracturing at the sites and showed that the depth of fracturing may be site specific