Hardware for studying the demixing of aqueous polymer two-phase systems in low gravity

The gravity-free demixing behavior of aqueous polymer two-phase systems (APTPS) has been studied on Earth, and onboard KC-135 aircraft and the Space Shuttle. Results suggest a good correlation between the demixing behavior of isopycnic systems on Earth and the low g behavior of systems exhibiting phase density differences. The short term (20 s) behavior of APTPS onboard KC-135 aircraft has been shown to mimic their initial demixing behavior in space. It appears that the few minutes of low g provided by parabolic rocket flight will be sufficient to study all but the later stages of demixing of APTPS. We are therefore turning our attention toward the design and use of hardware for studying the demixing of APTPS onboard sounding rockets. This seminar will discuss the evolution of hardware and research from hand-held KC-135 and Shuttle hardware through to automated hardware designed for utilization of KC-135, sounding rocket, and Space Shuttle Mid-deck Locker flight opportunities

Separation of biological materials in microgravity

Partition in aqueous two phase polymer systems is a potentially useful procedure in downstream processing of both molecular and particulate biomaterials. The potential efficiency of the process for particle and cell isolations is much higher than the useful levels already achieved. Space provides a unique environment in which to test the hypothesis that convection and settling phenomena degrade the performance of the partition process. The initial space experiment in a series of tests of this hypothesis is described

Demixing kinetics of phase separated polymer solutions in microgravity

Phase separated solutions of two neutral polymers in buffer provide a useful and versatile medium for the partition separation of biological cells. However, the efficiency of such separations is orders of magnitude lower than the thermodynamic limit. To test the hypothesis that this inefficiency is at least partially due to the convection and sedimentation that occur during the gravity driven demixing that follows introduction of cells to the systems, a series of experiments were begun aimed at performing cell partition in a low g environment. Demixing of isopycnic three polymer solvent systems was studied, experiments were performed on KC-135 aircraft and one shuttle middeck experiment was completed. Analysis of the results of these experiments and comparisons with the predictions of scaling relations for the dependence of phase domain size on time, derived for a number of possible demixing mechanisms, are presented

Demixing of aqueous polymer two-phase systems in low gravity

When polymers such as dextran and poly(ethylene glycol) are mixed in aqueous solution biphasic systems often form. On Earth the emulsion formed by mixing the phases rapidly demixes because of phase density differences. Biological materials can be purified by selective partitioning between the phases. In the case of cells and other particulates the efficiency of these separations appears to be somewhat compromised by the demixing process. To modify this process and to evaluate the potential of two-phase partitioning in space, experiments on the effects of gravity on phase emulsion demixing were undertaken. The behavior of phase systems with essentially identical phase densities was studied at one-g and during low-g parabolic aircraft maneuvers. The results indicate the demixing can occur rather rapidly in space, although more slowly than on Earth. The demixing process was examined from a theoretical standpoint by applying the theory of Ostwald ripening. This theory predicts demizing rates many orders of magnitude lower than observed. Other possible demixing mechanisms are considered

) Maceil, C. E.; In The Encyclopedia of Nuclear Magnetic Resonance

Evanescent-wave cavity ring-down spectroscopy has been applied to a planar fused-silica surface covered with crystal violet (CV + ) cations to characterize the silanol groups indirectly. A radiation-polarization dependence of the adsorption isotherm of CV + at the CH 3 CN/silica interface is measured and fit to a two-site Langmuir equation to determine the relative populations of two different types of isolated silanol groups. CV + binding at type I sites yields a free energy of adsorption of -29.9 ( 0.2 kJ/mol and a saturation surface density of (7.4 ( 0.5) × 10 12 cm -2 , whereas the values of -17.9 ( 0.4 kJ/mol and (3.1 ( 0.4) × 10 13 cm -2 are obtained for the type II sites. The CV + cations, each with a planar area of ∼120 Å 2 , seem to be aligned randomly while lying over the SiOtype I sites, thereby suggesting that this type of site may be surrounded by a large empty surface area (>480 Å 2 ). In contrast, the CV + cations on a type II sites are restricted with an average angle of ∼40°tilted off the surface normal, suggesting that the CV + cations on these sites are grouped closely together. The average tilt angle increases with increasing concentration of crystal violet so that CV + cations may be separated from each other to minimize the repulsion of nearby CV + and SiOH sites. Adsorption behavior of organic molecules on silica surfaces has been the major theme of interface studies for improving the efficiency of chromatographic separations. When cationic molecules are involved, the strong electrostatic interaction with the negatively charged silanol (SiOH) groups on the surface of the stationary-phase silica may cause unwanted peak broadening and tailing, mainly from a slow kinetic response of the electrostatic adsorption. [1][2][3][4][5][6] The surface charge density is one of the primary factors influencing the strength of electrostatics. Accordingly, insight into how the cationic molecules interact with the local silanol groups of the silica surface should aid in the improvement of the design of surface modifications. Silanol groups play the main role in influencing the interfacial adsorption behavior, possessing an average surface density of ∼4.9 × 10 14 cm -2 on the silica surface 7-9 or an average surface area of 20.4 Å 2 per silanol group. As compared to silica sol particles, which have higher surface areas of (0.1-5) × 10 22 Å 2 /g, 7-9 only a few studies focus on characterization of silanol groups on a planar silica surface. 10-12 Ong et al. 10 first reported that isolated and vicinal silanol groups both exist at the water/silica interface possessing different pK a values of 4.9 and 8.5, with corresponding surface populations of 19 and 81%, respectively. These results were confirmed by means of cross-polarization magic angle spinning NMR 13 and fluorescence microscopy. 14 The isolated silanol groups with pK a ) 4.9 are anticipated to be separated far from each other (>5.5 Å), permitting proton dissociation. The vicinal silanol groups are located so closely as to form hydrogen bonds directly with their neighbors (<3.3 Å), which share 46% of the surface population, or through a water-molecule bridge (3.5-5.5 Å), which covers ∼35% of the surface population. 12,[15][16][17] By using second harmonic generation (SHG) with a cationic crystal violet (CV + ) molecular probe to investigate the local density distribution of the isolated silanols (pK a ) 4.9) on the planar fusedsilica surface, Xu and co-workers 12 classified them into two types. The first type of silanol group is anticipated to be surrounded by a large empty surface area (g120 Å 2 ) with a surface density o

Application of a model-based fault detection system to nuclear plant signals

To assure the continued safe and reliable operation of a nuclear power station, it is essential that accurate online information on the current state of the entire system be available to the operators. Such information is needed to determine the operability of safety and control systems, the condition of active components, the necessity of preventative maintenance, and the status of sensory systems. To this end, ANL has developed a new Multivariate State Estimation Technique (MSET) which utilizes advanced pattern recognition methods to enhance sensor and component operational validation for commercial nuclear reactors. Operational data from the Crystal River-3 (CR-3) nuclear power plant are used to illustrate the high sensitivity, accuracy, and the rapid response time of MSET for annunciation of a variety of signal disturbances