Tough,transparent heat- and flame-resistant thermoplastics via silicone block-modified bisphenol fluorenone polycarbonate

Bisphenol fluorenone carbonate–dimethylsiloxane block polymers have been synthesized by interfacial condensation of phosgene with various mixtures of BPF-endcapped silicone oligomers and free BPF or its monosodium salt. The multisequence block polymers described here contain 7% to 27% silicone consisting of blocks of number-average degree of polymerization 10 to 40. Cast films are clear and colorless. Two glass temperatures are evident in each resin, one at about ?100°C for the silicone microdomains and one at temperatures as high as 275°C for the polycarbonate matrix. While BPF polycarbonate is brittle, block polymers with as little as 10% silicone yield by shear deformation before breaking. Ultimate elongations are increased by preorientation at silicone contents above 15%. At temperatures far removed from BPF carbonate domain T_g's, both modulus and yield stress decrease with increasing silicone content, independent of block length, in a manner rationalized quantitatively by hard phase–soft phase continuum models. Ultimate tensile elongation, impact toughness, and plane strain stress intensity factors increase with silicone content, through a stress whitening mechanism. At higher silicone contents, shear deformation enhances tensile elongation and impact toughness. Heat distortion temperatures of 200°C or more are achieved. Flame resistance exceeds that of any known nonhalogenated resin. The resins are extrudable and injection moldable with only minor changes in color, transparency, and strength properties. Resins with 15% to 20% silicone can have a balance of properties that makes them attractive as tough, transparent heat- and flame- resistant engineering plastics.     

Shape factors of narrow size range samples of respirable coal mine dust

Respirable coal mine dust samples from three different U.S. mines were aerodynamically classified in a Bahco centrifugal classifier to yield four particle size fractions. Fractions were analyzed for density, particle size by optical microscopy, random and oriented projected area, and specific surface area (BET). These measures enabled us to define additional characterizing parameters which yielded insight into the physical nature of the size fractions. Differences in parameters for size fractions obtained form the same sample and from samples collected in different mines are discussed. It is suggested that to understand the differences in reported incidences of coal workers' pneumoconiosis in different mines, analyses of this type, together with the dust chemical composition as a function of particle size within the respirable size range, will be necessary.     

The internal oxidation of Nb-Hf alloys

The internal oxidation of some binary Nb-Hf and several commercial Nb alloys containing Hf was studied at 1568 and 1755°C in oxygen pressures ranging from 5×10 ^–5 to 1×10^–3 torr.The reaction kinetics were linear, suggesting that diffusion of oxygen in the substrate was not rate-controlling. The dependence of the reaction rate on oxygen pressure was linear also. Well-defined reaction fronts were observed at higher pressures and the lower temperature, whereas ill-defined fronts occurred at lower pressures and at the higher temperature. The solubility product was much higher than normally encountered in Wagnerian-type behavior and gave rise to varying solute content across the internal-reaction zone. The solute-concentration profiles (EPMA/WDS) of the matrix between particles exhibited a sigmoidal shape for well-defined reaction fronts, whereas the profiles showed a gradual decrease in solute with distance near the front for ill-defined fronts, dropping fairly abruptly at the metal/gas interface. The solute concentration never reached zero at the surface for any condition studied. In contrast to classical, Wagnerian behavior, solute continued to precipitate out after the reaction zone had passed, leading to a variation in the mole fraction of oxide in the zone. SEM/EDXA and XRD showed that precipitation occurred by the formation of precursors (Hf-rich regions surrounded by Hf-depleted regions), followed by precipitation of tetragonalHfO₂,which in some cases transformed to monoclinicHfO₂ and subsequently coarsened. The precipitate morphology varied with solute concentration, temperature, oxygen pressure, and location within the reaction zone. High temperature and high oxygen pressure favored a Widmanstätten structure, whereas low temperature and low oxygen pressure favored a spheroidal precipitate structure. Widmanstätten plates were observed to spheroidize at longer times, suggesting that the interfacial energy between particles and matrix was very high. The presence of a small amount of Y (0.11 w/o in C129) always resulted in spheroidal particles. It appears that Y markedly increased the particle/matrix interfacial energy. Microhardness profiles showed decreasing values with distance into the sample for some conditions and alloys but increasing values in other cases. Hardness increases in the substrate in advance of the interface showed that oxygen activity did not reach zero at the reaction front, once again contrary to classical behavior but consistent with high solubility products of the oxide. Results are analyzed in terms of oxygen-trapping by reactive solutes as noted in the literature for both lattice-parameter measurements and oxygen diffusivity studies.     

Managing information technology in academic medical centers: a "multicultural" experience

Based on a session at the 1997 conference on Information Resources and Academic Medicine sponsored by the Association of American Medical Colleges, this article illustrates how the beliefs and concerns of academic medicine's diverse professional cultures affect the management of information technology. Two scenarios--one dealing with the standardization of desktop PCs, the other with publication of syllabi on an institutional intranet--form the basis of this exercise. Four prototypical members of a hypothetical medical center community--the chairman of surgery, a senior basic scientist, the chief information officer of an affiliated hospital, and the chief administrative officer--offer their perspectives on each scenario. Their statements illustrate many of the challenges of planning, deploying, and maintaining effective information technology in the "multicultural" environment of academic medical centers.     

Technically accurate intracavitary insertions improve pelvic control and survival among patients with locally advanced carcinoma of the uterine cervix

The purpose of this study was to document whether the technical qualities of a brachytherapy application impacts on the outcome of patients with locally advanced cervix cancer treated by definitive irradiation. A previous report from the patterns of care study demonstrated the importance of brachytherapy in the treatment of locally advanced cervix cancer. Locally advanced disease was defined as FIGO stages Ib (if tumor diameter was < or = 4 cm), IIb (if disease was bilateral or involved the lateral aspect of either parametrium), and III. Localization films from 128 patients with locally advanced squamous cell carcinoma of the cervix were reviewed by a radiation physicist and a radiation oncologist with expertise in gynecologic radiotherapy. All patients received external beam irradiation followed by one brachytherapy application (median point A dose = 8040 cGy; range, 4083-10,020 cGy). Brachytherapy parameters assessed were (a) the distance between the right colpostat source and the distal tandem source, (b) the distance between the left colpostat source and the distal tandem source, and (c) the symmetry of colpostat placement. Implants were scored as "ideal" (n = 8) when all three parameters were deemed satisfactory, "unacceptable" (n = 17) when none of the parameters was deemed satisfactory, and "adequate" (n = 41) in all other cases. Significantly improved 5-year local control was seen when comparing ideal and adequate placements to unacceptable placements (68% vs 34%, P = 0.02). A strong trend toward improved 5-year survival was also noted among the group with ideal and adequate implants as opposed to unacceptable implants (60% vs 40%). Multivariate analysis showed that the technical adequacy of the brachytherapy implant was the most important prognostic discriminant of local control. In conclusion, these analyses demonstrate the direct influence of competent technical implant performance on tumor control and even survival. While only a small fraction of implants for cervical cancer are performed poorly in the United States, there is a need for continued emphasis of the principles for proper implant technique.     

Determination of ribonuclease H surface enzyme kinetics by surface plasmon resonance imaging and surface plasmon fluorescence spectroscopy

The kinetics of the ribonuclease H (RNase H) surface hydrolysis of RNA-DNA heteroduplexes formed on DNA microarrays was studied using a combination of real-time surface plasmon resonance imaging (SPRI) and surface plasmon fluorescence spectroscopy (SPFS). Time-dependent SPRI and SPFS data at various enzyme concentrations were quantitatively analyzed using a simple model that couples diffusion, enzyme adsorption, and surface enzyme kinetics. This model is characterized by a set of three rate constants, enzyme adsorption (k(a)), enzyme desorption (k(d)), enzyme catalysis (k(cat)), and one dimensionless diffusion parameter (beta). Values of k(a) = 3.15 (+/-0.20) x 10(6) M(-1).s(-1), k(d) = 0.10 (+/-0.05) s(-1), and k(cat) = 0.95 (+/-0.10) s(-1) were determined from fitting all of the SPRI and SPFS data sets. One of the most interesting kinetic parameters is the surface RNase H hydrolysis reaction rate constant (k(cat)), which was found to be approximately 10 times slower than that observed in solution, but approximately 100 times faster than that recently observed for the exonuclease III surface hydrolysis of double-stranded DNA microarrays (k(cat) = 0.009 s(-1)). Moreover, the surface coverage of the intermediate enzyme-substrate complex (ES) was found to be extremely small during the course of the reaction because k(cat) is much larger than the product of k(a) and the bulk enzyme concentration.     

Characterization and optimization of peptide arrays for the study of epitope-antibody interactions using surface plasmon resonance imaging

The characterization of peptide arrays on gold surfaces designed for the study of peptide-antibody interactions using surface plasmon resonance (SPR) imaging is described. A two-step process was used to prepare the peptide arrays: (i) a set of parallel microchannels was used to deliver chemical reagents to covalently attach peptide probes to the surface by a thiol-disulfide exchange reaction; (ii) a second microchannel with a wraparound design was used as a small-volume flow cell (5 microL) to introduce antibody solutions to the peptide surface. As a demonstration, the interactions of the FLAG epitope tag and monoclonal anti-FLAG M2 were monitored by SPR imaging using a peptide array. This peptide-antibody pair was studied because of its importance as a means to purify fusion proteins. The surface coverage of the FLAG peptide was precisely controlled by creating the peptide arrays on mixed monolayers of alkanethiols containing an amine-terminated surface and an inert alkanethiol. The mole fraction of peptide epitopes was also controlled by reacting solutions containing FLAG peptide and the non-interacting peptide HA or cysteine. By studying variants based on the FLAG binding motif, it was possible to distinguish peptides differing by a single amino acid substitution using SPR imaging. In addition, quantitative analysis of the signal was accomplished using the peptide array to simultaneously determine the binding constants of the antibody-peptide interactions for four peptides. The binding constant, K(ads), for the FLAG peptide was measured and found to be 1.5 x 10(8) M(-1) while variants made by the substitution of alanine for residues based on the binding motif had binding constants of 2.8 x 10(7), 5.0 x 10(6), and 2.0 x 10(6) M(-1).     

Evolution of the North Carolina Information Highway

As the first information highway of its kind, the North Carolina Information Highway is likely to set an example for ATM broadband deployment not only in the BellSouth region but also in the rest of the country. The article outlines an evolutionary path for new network architectural features and additional video and data services that can be supported by the NCIH. These architectures will support the introduction of on-demand video services (e.g. the distance learning service), and other associated vertical services. As standard procedures are developed, users will be able to use data services like TCP/IP and frame relay over large-bandwidth ATM connections. In addition, they will have opportunities to use their existing applications in the legacy LANs, as well as with ATM endpoints. As ATM standards agreements are realized over the next few years, and the ATM technology cost curve continues to improve, the NCIH will prove to be a very cost-effective and high-performance alternative for all the high-speed communication needs of the North Carolina State Government     

Quality control of hospital discharge data

Data based on medical records of discharged hospital patients are widely used. However, recent studies of the reliability of discharge data have found error rates which appear to be high, in view of the important data uses. In this paper, the procedures reportedly followed to control the quality of discharge data by private abstracting services, the national Hospital Discharge Survey and the Medicare system are described. Some weaknesses of the quality controls of the existing systems are identified. Recommendations are made for reducing duplicate data collection efforts, and for studies of the relative effectiveness and costs of various quality control procedures.