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991.
992.
Prior studies of two series of segmented polyurethanes based on 2, 4 toluene cliisocyanate (2, 4 TDI) or 2, 8 TDI, butanediol, and a 1000 molecular weight polytetramethyleneoxide (PTMO-1000) soft segment revealed a rapid increase in soft segment glass transition temperature (Tg) with increasing urethane content in the 2, 4 TDI series. The change in Tg couldbe correlated with estimates of hard segment-soft segment phase mixing obtained by infrared analysis of the urethane NH and carbonyl bands. In the present paper, the infrared data have been reevaluated using improved procedures for resolving the carbonyl band into H-bonded and nonbonded components, and the relation between the estimated extent of phase mixing and Tg has been reexamined. The transition behavior in an extensive series of related polymers has also been determined, including 2, 4 TDI arid 2, 6 TDI samples with PTMO2000 as well as polybutyleneadipate (PBA-1000 and PBA-2000) soft segments. The results indicate the effectiveness, of increased soft segment molecular weight in promoting phase segregation, imply that much greater phase mixing occurs in polyester than polyether samples, suggest that anchoring the ends of the soft segments has only a small effect on Tg, and provide some evidence that H-bonding not only increases Tg but can also impede soft segment crystallization. 相似文献
993.
Spin-lattice relaxation times T1 of 13C and 1H nuclei, as well as nuclear Overhauser enhancement (NOE) values of stereoregular poly(methyl methacrylates) (PMMA) in CD3CN and CDCl3 were measured. Analysis of these data has shown that the mobility of PMMA in solution is affected by stereoregularity of PMMA and by solvent. Comparison of 13C and 1H n.m.r. relaxation data has further shown that the solvent affects also the local conformational structure of stereoregular PMMA in solution; this conclusion is supported by preliminary measurements of infra-red spectra. Based on this finding, the effect of solvent upon formation of the ordered structure of the so-called stereocomplex of PMMA is discussed. 相似文献
994.
Epoxidations with Peracetic Acid I: The Peracetic Acid and Related Epoxidations of Soybean Oil Progressive formation of peracetic acid by the action of hydrogen peroxide on acetic acid was studied. In the presence of ethyl acetate and by employing acetic anhydride, water free peracetic acid was obtained. In the epoxidation of soybean oil the maximum epoxide content of the same is dependent on the reaction conditions, especially on the degree of homogeneity of the reaction partners and the acidic catalyst. 相似文献
995.
Soft X-ray microscopy employs the photoelectric absorption contrast between water and protein in the 2.34-4.38 nm wavelength region to visualize protein structures down to 30 nm size without any staining methods. Due to the large depth of focus of the Fresnel zone plates used as X-ray objectives, computed tomography based on the X-ray microscopic images can be used to reconstruct the local linear absorption coefficient inside the three-dimensional specimen volume. High-resolution X-ray images require a high specimen radiation dose, and a series of images taken at different viewing angles is needed for computed tomography. Therefore, cryo microscopy is necessary to preserve the structural integrity of hydrated biological specimens during image acquisition. The cryo transmission X-ray microscope at the electron storage ring BESSY I (Berlin) was used to obtain a tilt series of images of the frozen-hydrated green alga Chlamydomonas reinhardtii. The living specimens were inserted into borosilicate glass capillaries and, in this first experiment, rapidly cooled by plunging into liquid nitrogen. The capillary specimen holders allow image acquisition over the full angular range of 180 degrees. The reconstruction shows for the first time details down to 60 nm size inside a frozen-hydrated biological specimen and conveys a clear impression of the internal structures. This technique is expected to be applicable to a wide range of biological specimens, such as the cell nucleus. It offers the possibility of imaging the three-dimensional structure of hydrated biological specimens close to their natural living state. 相似文献
996.
施耐德电气 《仪器仪表标准化与计量》2007,(2):I0006-I0007
上海震旦大厦的BMS集成系统采用基于LONWORKS技术平台开发的TAC—I/A系列产品。具有集成子系统多、控制点多的特点,实现了无缝集成,体现了LONNORKS技术开放性和互操作性的优点和LONMARK开放式系统的优势。 相似文献
997.
A number of measurements were made to help define the thermal and flow conditions in a 9 × 18 meter pool fire that was used to simulate a transportation accident. Temperatures were measured at twenty-eight locations throughout the continuous flame region. Velocities were measured at four vertical stations near the centerline of the pool. Heat fluxes were estimated from thermal measurements on and near vertical steel plates. As is often the case in fires of this size, the effects of mild, ambient winds on the measurements were pronounced. Attempts have been made to mitigate these effects by the application of conditional sampling. Temperatures and velocities are compared with other experimental results as well as results of modeling efforts. 相似文献
998.
Schneider T Sundell J Bischof W Bohgard M Cherrie JW Clausen PA Dreborg S Kildesø J Kaergaard SK Løvik M Pasanen P Skyberg K 《Indoor air》2003,13(1):38-48
The relevance of particle mass, surface area or number concentration as risk indicators for health effects in non-industrial buildings has been assessed by a European interdisciplinary group of researchers (called EUROPART) by reviewing papers identified in Medline, Toxline, and OSH. Studies dealing with dermal effects or cancer or specifically addressing environmental tobacco smoke, house dust-mite, cockroach or animal allergens, microorganisms and pesticides were excluded. A total of 70 papers were reviewed, and eight were identified for the final review: Five experimental studies involving mainly healthy subjects, two cross-sectional office studies and one longitudinal study among elderly on cardiovascular effects. From most studies, no definite conclusions could be drawn. Overall, the group concluded that there is inadequate scientific evidence that airborne, indoor particulate mass or number concentrations can be used as generally applicable risk indicators of health effects in non-industrial buildings and consequently that there is inadequate scientific evidence for establishing limit values or guidelines for particulate mass or number concentrations. 相似文献
999.
Carletto JS Roux KC Maltez HF Martendal E Carasek E 《Journal of hazardous materials》2008,157(1):88-93
This study presents the development of an on-line preconcentration system for zinc(II) determination in aqueous samples. The analyte was trapped in a mini-column filled with a chelating resin based on a chitosan biopolymer modified with 8-hydroxyquinoline obtained by the diazotization reaction. Flow and chemical variables of the system, as well as the potential interference ions, were optimized through a multivariate procedure. The factors selected were sample pH, eluent concentration (HNO(3)), and sample and eluent flow rates. It was verified through a full factorial design that the sample pH and eluent flow rate factors were statistically significant at the 95% confidence level. A final optimization of the significant factors was carried out using a Doehlert matrix. The preconcentration system was linear between 2.5 and 75 microgL(-1), with a regression coefficient of 0.9995. The enrichment factor was 17.6. The limits of detection and quantification were 0.8 and 2.5 microgL(-1), respectively. The repeatability and the analytical frequency were, respectively, 2.7 (25.0 microgL(-1), n=8) and 18 samples per hour. Results for recovery tests using mineral water samples were between 85 and 93%. Certified reference materials were analyzed in order to check the accuracy of the proposed method. 相似文献
1000.
We present a study of the growth, morphology and optical properties of Al(x)Ga(1-x-y)In(y)As quantum dots (QDs) for a wide range of Al and In concentrations (0≤x≤0.34 and 0.43≤y≤0.60). Short emission wavelengths between 660 and 940?nm and QD surface densities up to 1.1 × 10(11)?cm(-2) have been achieved. Our results show that by varying both the Al concentration and the In concentration an independent adjustment of strain and QD band gap is possible. This additional degree of freedom can be employed for tailoring AlGaInAs QDs with the desired emission wavelength, surface density and average size. AlGaInAs QDs thus offer new possibilities for future QD device design. 相似文献