Processing of Carbon Fibers: Texture Enhancement Induced by Hot Stretching

A synchrotron radiation source has been used to monitor the x-ray diffraction patterns of a series of experimental PAN-based carbon fibers. The use of the synchrotron made feasible the collection of a substantial quantity of data on a reasonable time scale, by reducing the required exposure times by more than three orders of magnitude. The fibers considered in this report were hot stretched at temperatures in the range 2700°C to 3000°C for 5 minutes with stretching stresses between 5 MPa and 85 MPa. Measurement of the azimuthal and radial widths of the (00.2) reflections led to evaluation of figures for the preferred orientation parameter, Z, and the “apparent” crystallite size perpendicular to the graphitic rafts, L_c. The results showed that large increases in texturing can be achieved by hot stretching, so that from a starting value of ~38°, Z was reduced to between ~19° (2700°C and 5 MPa) and ~10° (3000°C and 85 MPa). Measurement of L_c was not possible for the as-received libers, since reflections were too diffuse, but the corresponding values for processed fibers were ~ 8 nm and ~11 nm respectively. It was found that the microstructural parameters depended on both the processing temperature and the stretching stress. Z showed substantial variation with both parameters, whereas Lc was far more sensitive to temperature than stress. Although the preferred orientation depended on a combination of extension and temperature, a close correlation was found between Z and the reduction in cross sectional area that occurred during processing. Similarly, within the range of conditions considered, Z varied approximately linearly with final fiber diameter, independently of the precise combination of processing parameters. A close correlation was also observed between the preferred orientation and Young's modulus of hot stretched fibers over the full range from ~330 GPa to ~690 GPa, compared with the untreated modulus value of ~180 GPa     

Using fuzzy sets to assign metallurgical grades to steel

To optimize the productivity and yield of a modern high-speed continuous casting operation, it is desirable to minimize the number of metallurgical grades that have to be melted to satisfy a collection of customer orders. This problem has been addressed through the development of an expert system for selecting the set of all potential grades for each order and an optimal selection algorithm for determining the actual grades that would be required to produce all orders. As a further refinement, a fuzzy formulation with a membership function based on the likelihood of a grade meeting the customer’s specifications without difficulty has been added. This enables the plate mill to trade off minimizing the number of grades used against maximizing the likelihood that the customer specifications will be met without difficulty.     

Neuropsychological changes in children with cancer: the treatment of missing data in longitudinal studies

Researchers conducting longitudinal studies with children or adults are inevitably confronted with problems of attrition and missing data. Missing data in longitudinal studies is frequently handled by excluding from analyses those cases for whom data are incomplete. This approach to missing data is not optimal. On the one hand, if data are missing at random, then dropping incomplete cases ignores information collected on those cases that could be used to improve estimates of population parameters (e.g., means, variances, covariances, and growth rates) and improve the power of significance tests of statistical hypotheses. On the other hand, if data are not missing at random, then dropping incomplete cases leads to biased parameter estimates and hypothesis tests that may be internally and externally invalid. This study uses three years of follow-up data from a longitudinal investigation of neuropsychological outcomes of cancer in children to demonstrate the problems presented by missing data in repeated measures designs and some solutions. In evaluating potential biasing effects of attrition, the study extends previous research on neuropsychological outcomes in pediatric cancer by inclusion of patients whose disease had relapsed, and by comparison of surviving and nonsurviving patients. Although the data presented have specific relevance to the study of neuropsychological outcome in pediatric cancer, the problems of missing data and the solutions presented are relevant to a wide variety of diseases and conditions of interest to researchers in child and adult neuropsychology.     

The interaction of arginine 106 of human prostaglandin G/H synthase-2 with inhibitors is not a universal component of inhibition mediated by nonsteroidal anti-inflammatory drugs

The three-dimensional cocrystal structures of ovine prostaglandin G/H synthase-1 (PGHS-1) with S-flurbiprofen and murine PGHS-2 with S-flurbiprofen and indomethacin reveal that the carboxylate acid groups of these nonsteroidal anti-inflammatory drugs (NSAIDs) form a salt bridge with the guanidinium group of Arg120 in PGHS-1 and Arg106 in PGHS-2. Mutagenesis studies confirmed that the Arg120 residue of PGHS-1 is critical for binding of substrate and inhibitors through ionic interactions of its guanidinium group with the carboxylate moieties of arachidonic acid and certain NSAIDs. We report here that the analogous R106E substitution in human PGHS-2 results in a catalytically active enzyme with a 30-fold higher Km value for arachidonic acid. Comparison of the inhibition of hPGHS-2(R106E) with wild-type hPGHS-2 by 11 structurally diverse selective and nonselective PGHS inhibitors revealed a 0-1000-fold decrease in inhibitory potency on the mutant enzyme. The loss of inhibitory potency of NSAIDs on hPGHS-2(R106E) could not be correlated with the presence or absence of a carboxylate functional group in the inhibitor, as was demonstrated previously for the PGHS-1(R120E) mutant, or with the selective or nonselective nature of the PGHS inhibitor. The decreases in the inhibitory potencies on hPGHS-2(R106E) by the carboxylate-containing NSAIDs flurbiprofen, indomethacin, meclofenamic acid, and diclofenac on hPGHS-2(R106E) were 965-, 48-, 5.5-, and 4.5-fold, respectively. The nonuniversal requirement for interaction of the carboxylate group of certain NSAIDs with the Arg106 residue in hPGHS-2 is supported by the observation that the methyl ester derivative of indomethacin was a more potent inhibitor than indomethacin on both hPGHS-2 and hPGHS-2(R106E). The greatest loss of potency for inhibition of hPGHS-2(R106E) was observed with the hPGHS-2-selective sulfonamide-containing inhibitors NS-398 and flosulide. The PGHS-2-selective inhibitor DuP697 and a desbromo-sulfonamide analogue of DuP697 displayed equivalent potency on hPGHS-2(R106E) and hPGHS-2. The change in inhibitory potency of NS-398 on hPGHS-2(R106E) was due to a difference in the kinetics of inhibition, with NS-398 displaying time-dependent inhibition of hPGHS-2 but time-independent inhibition of PGHS-2(R106E). The time-dependent inhibition of hPGHS-2 by DuP697 was not affected by the presence of the R106E mutation. We conclude that the Arg106 residue of hPGHS-2 is involved in binding arachidonic acid and certain NSAIDs, but interactions with Arg106 are not a universal requirement for inhibition by either carboxylate-containing NSAIDs or PGHS-2-selective inhibitors.     

Water mollusc communities and bioindication of lower salzach floodplain waters

The lower Salzach River lost its natural river dynamics as a result of channelization, which caused its bed to deepen, its groundwater table to be lowered, and its floodplains to gradually dry out. These changes of the floodplain have lead to a loss of natural biotopes with their biocoenoses. By using water mollusc communities as bioindicators these losses are detectable at a landscape level. A numerical analysis of a water mollusc survey in 1989 defined six water mollusc communities identifying six water-body types: three flowing (streams, ditches, and rivers) and three standing (young former meanders, large deep groundwater-influenced backwaters and small shallow groundwater-influenced backwaters) within the lower Salzach valley. These communities and water-body types are interpreted using results from water mollusc communities of other floodplain systems and by comparison with earlier water mollusc surveys in the lower Salzach valley. Then predictions are made on the future fate of the investigated floodplain water. Finally the investigated water bodies are evaluated for nature conservation in the face of plans to impound the lower Salzach River.     

SIMULTANEOUS WATER AND SOLUTE TRANSPORT IN SHRINKING MEDIA - PART 2

A simple compartmental model of simultaneous water and solute transport was developed on agar gel cubes, for particular situations in which high water loss is accompanied by shrinkage and flux interaction. The model provided a good fit for the different situations tested, and proved to behave adequately in a wider application field. Furthermore, it made it possible to obtain a simulation of the evolution of the solute contents in both compartments which was consistent with the previous studies.     

Extinguishing class B fires with dry chemicals: Scaling studies

In a continuing study of flame extinguishment,^1,2,3,4 we report on scaling studies for dry chemicals on larger heptane diffusion flames (0.29 m² and 2.32 m² pans). We demonstrate again that small particle sizes extinguish most effectively. Extinguishment is related to heat absorption by decomposing or vaporizing particles. We show that the limiting particle size for each dry chemical—that is, the maximum size which completely decomposes or vaporizes in the flame—is independent of flame size for the systems studied. We broaden and apply the concept of latent or maximum effectiveness^2,3 to pan fires of all sizes. Finally, we describe and characterize an aerodynamic effect in the transport of powders, where large particles with their higher momentum entrain and drag smaller, more effective particles into the flame.We also show that extinction curves, involving the ratio of real-to-latent extinction weight and the proportion of small to large particles, have predictable shapes and predictable quantitative levels for most dry chemicals. We have developed the real-to-latent concept along with scaling equations for agent mixtures and for a wide spectrum of agents and particle sizes.     

Axonal dysfunction and disability in a relapse of multiple sclerosis: longitudinal study of a patient

In a 6-year longitudinal study of a patient with relapsing progressive multiple sclerosis (MS), we used proton magnetic resonance spectroscopy to assess N-acetylaspartate (NAA) from a large central brain volume to evaluate the relationship between this marker of neuronal integrity and clinical disability. During the follow-up period, there was one major relapse and its subsequent partial remission. Changes in the brain NAA to creatine ratio correlated strongly with clinical disability (Spearman rank coefficient = -0.73, p < 0.001). We interpret this as evidence that axonal dysfunction or loss contributes to functional impairment of patients with MS. Because the NAA signal in the large volume of interest originated predominantly from white matter that appeared normal on conventional MRI, these results also suggest that some degree of axonal dysfunction may be widespread in acute, severe relapses.