A NOVEL EOR POLYMER (Ⅱ)——INVESTIGATION ON IN-SITU GELATION OF SMRF SYSTEM IN BEREA CORE

In-situ gelation of aqueous sulfomethylated resorcinol formaldehyde (SMRF) system inBerea core has been investigated. Two sets of displacement experiments were conducted with thissystem (containing 5% NaCl, 0. 036% CaCl_2. 2H_2O). The brine permeabilities of the coreswere reduced significantly from about 600 to 0.1 md. The in-situ gelation in Berea core occurreda little bit earlier than gelation anticipated from bulk test in the experiments. The gel time waseasier to control at initial pH between 6 and 8. During injection of SMRF system, the apparentviscosity was less than 1 mPa·s at 41℃.     

Inaccessible hydroxyl groups on silica are accessible in supercritical CO2

The three main types of hydroxyl groups on a silica surface are classified as isolated, hydrogen bonded, and inaccessible. The isolated and hydrogen bonded groups are the most important as these readily exchange with D(2)O and thus are exposed to reactant molecules. However, it has generally been accepted that the inaccessible groups do not participate in surface reactions as only a small fraction of these groups exchange with D(2)O. It is shown that the inaccessible hydroxyl groups on nonporous fumed silica and mesoporous MCM-48 silica powders and films fully exchange with D(2)O and are reactive with octadecylydimethylchlorosilane when supercritical CO(2) is used as the solvent. Furthermore, it is found that the CO(2) penetrating the regions containing the inaccessible groups is not removed by simple evacuation but rather slowly diffuses from the silica over periods of months.     

Atomic layer deposition of PbZrO3 thin films

In this paper, we report on the preparation of lead zirconate films for the first time using atomic layer deposition in an attempt to investigate some of the film properties and also to evaluate possible use of the precursor combination to prepare more complex lead titanate zirconate. In the depositions tetraphenyl lead (Ph₄Pb) was used as the lead and zirconium 2,2,6,6-tetramethyl-3,5-heptadionato (Zr(thd)₄) as the zirconium precursor, while ozone was used as the oxygen source. Film growth, stoichiometry and quality were studied using different pulsing ratios at deposition temperatures of 275 and 300 °C. According to X-ray diffraction, the crystalline perovskite phase was observed when films deposited on SrTiO₃(1 0 0) were annealed at 600 °C. Surface roughness was reduced for lead deficient films as well as in annealed samples.     

A single‐crystal neutron diffraction study of RbTiOAsO4

A rubidium titanyl arsenate single‐crystal has been studied by neutron diffraction (λ = 1.207 Å). The polished sample used was 5 × 3 × 2 mm and was cut from a crystal made by top‐seeded solution growth. The crystal showed severe extinction. It was, however, possible to obtain a structural model with well defined oxy­gen sites and reasonable anisotropic displacement parameters.     

Characterization of the first beta-class carbonic anhydrase from an arthropod (Drosophila melanogaster) and phylogenetic analysis of beta-class carbonic anhydrases in invertebrates

Background

The β-carbonic anhydrase (CA, EC 4.2.1.1) enzymes have been reported in a variety of organisms, but their existence in animals has been unclear. The purpose of the present study was to perform extensive sequence analysis to show that the β-CAs are present in invertebrates and to clone and characterize a member of this enzyme family from a representative model organism of the animal kingdom, e.g., Drosophila melanogaster.

Results

The novel β-CA gene, here named DmBCA, was identified from FlyBase, and its orthologs were searched and reconstructed from sequence databases, confirming the presence of β-CA sequences in 55 metazoan species. The corresponding recombinant enzyme was produced in Sf9 insect cells, purified, kinetically characterized, and its inhibition was investigated with a series of simple, inorganic anions. Holoenzyme molecular mass was defined by dynamic light scattering analysis and gel filtration, and the results suggested that the holoenzyme is a dimer. Double immunostaining confirmed predictions based on sequence analysis and localized DmBCA protein to mitochondria. The enzyme showed high CO₂ hydratase activity, with a k_cat of 9.5 × 10⁵ s^-1 and a k_cat/K_M of 1.1 × 10⁸ M^{- 1}s^{- 1}. DmBCA was appreciably inhibited by the clinically-used sulfonamide acetazolamide, with an inhibition constant of 49 nM. It was moderately inhibited by halides, pseudohalides, hydrogen sulfide, bisulfite and sulfate (K_I values of 0.67 - 1.36 mM) and more potently by sulfamide (K_I of 0.15 mM). Bicarbonate, nitrate, nitrite and phenylarsonic/boronic acids were much weaker inhibitors (K_Is of 26.9 - 43.7 mM).

Conclusions

The Drosophila β-CA represents a highly active mitochondrial enzyme that is a potential model enzyme for anti-parasitic drug development.     

Overwinter changes to near-surface bulk density, penetration resistance and infiltration rates in compacted soil

Previous studies at Yakima Training Center (YTC), in Washington State, suggest freeze-thaw (FT) cycles can ameliorate soil compacted by tracked military vehicles [J. Terramechanics 38 (2001) 133]. However, we know little about the short-term effects of soil freezing over a single winter. We measured bulk density (BD), soil penetration resistance (SPR), and steady-state runoff rates in soil newly tracked by an Abrams tank and in uncompacted soil, before and after a single winter at YTC. We similarly measured BD, SPR and saturated hydraulic conductivity (k_fs) in simulated tank tracks at another site near Lind Washington. Average BD was significantly greater in tank ruts at YTC and in simulated tracks at the Lind site than in uncompacted soil soon after tracking and did not change significantly during the winter of 1997–1998. Measurements of SPR were strongly influenced by soil moisture. When soil was moist or tracks were newly formed, SPR was significantly higher in tank ruts than in uncompacted soil from the surface to a depth of about 10–15 cm. The greatest average SPR in compacted soil was observed between 4 and 6 cm depth. We observed less difference in SPR between tank ruts and uncompacted soil near-surface at YTC as the time after trafficking increased. We observed highest SPR ratios (compacted rut:undisturbed) in fresh tracks near the surface, with lower ratios associated with increasing track age or soil depth, indicating that some recovery had occurred at YTC near-surface. However, we did not observe a similar over-winter change in SPR profiles at the Lind site. Rainfall simulator data from YTC showed higher steady-state runoff rates in tank ruts than over uncompacted soil both before and after winter. However, more time was required to reach steady-state flow in tank ruts and the proportion of runoff was slightly lower in May 1998 than in August 1997. At the Lind site, k_fs was lower in newly compacted soil than in one-year old compacted soil or uncompacted soil. Our data suggest that indices of water infiltration such as steady-state runoff rates or k_fs, are more sensitive indicators of soil recovery after compaction than are BD or SPR.     

Blitzlampe für Lichtpulse im Nanosekundenbereich

Ohne Zusammenfassung     

Handling errors as they arise in whole-class interactions

There has been a long history of research into errors and their role in the teaching and learning of mathematics. This research has led to a change to pedagogical recommendations from avoiding errors to explicitly using them in lessons. In this study, 22 mathematics lessons were video-recorded and transcribed. A conversation analytic (CA) approach was then taken to examine how mathematical errors are treated by teachers and students when they arise in interaction. Despite pedagogical recommendations, in these interactions, errors continue to be predominantly treated as something to avoid. There is a tension between the affective aspects of managing errors in interactions and the cognitive aspects. Close examination of classroom interactions enable us to see how these tensions are managed both by teachers and students.