A combined reflectometry and quartz crystal microbalance with dissipation setup for surface interaction studies

We have developed an instrument for surface interaction studies, which combines a newly invented four detector optical reflectometry setup with quartz crystal microbalance with dissipation (QCM-D) monitoring. The design is such that data from both techniques can be obtained simultaneously on the same sensor surface, with the same signal-to-noise ratio and time resolution, as for the individual techniques. In addition, synchronized information about structural transformations, molecular mass, and the hydration of thin films on solid surfaces can be obtained on the same specimen, as validated by monitoring the formation of supported lipid bilayers on a silica-coated QCM sensor surface. We emphasize that the optical (molecular) mass can be separated from the acoustic mass including hydrodynamically coupled solvent, which means, in turn, that the amount of solvent sensed by the QCM-D technique can be dynamically resolved during adsorption processes. In addition, the advantage/necessity to use four, compared to two, detector reflectometry is emphasized.     

用石灰及水泥土柱稳定边坡和深开挖

本文介绍用生石灰粉或水泥与软粘土就地搅拌在地基内形成土柱以稳定沟槽,深开挖以及边坡的设计与施工方法。石灰土柱具有石灰用量低,施工振动小,挤土扰动少,透水性好的优点。文中讨论了石灰土的强度机理,石灰土柱的受力及破坏形式,给出了计算图式及应取的安全系数值。全文结合瑞典工程实例阐述。     

Early identification of reading difficulties using heterogeneous developmental trajectories.

Serious conceptual and procedural problems associated with current diagnostic methods call for alternative approaches to assessing and diagnosing students with reading problems. This study presents a new analytic model to improve the classification and prediction of children's reading development. Growth mixture modeling was used to identify the presence of 10 different heterogeneous developmental patterns. In all, 411 children in kindergarten through Grade 2 from 3 elementary schools in Texas were administered measures of phonological awareness, word recognition, and rapid naming skills 4 times a year. The mean ages were 5.8 years (SD = 0.35) for the kindergartners, 6.9 years (SD = 0.39) for Grade 1, and 8.0 years (SD = 0.43) for Grade 2; the percentage of boys was 50%. The results indicate that precursor reading skills such as phonological awareness and rapid naming are highly predictive of word reading (word recognition) and that developmental profiles formed in kindergarten are directly associated with development in Grades 1 and 2. Students identified as having reading-related difficulties in kindergarten exhibited slower development of word recognition skills in subsequent years of the study. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Liquid side heat transfer and pressure drop in finned-tube cooling-coils operated with secondary refrigerants

In this study full-scale experiments with two different conventional cooling-coils aimed for display cabinets were performed. Heat transfer and pressure drop on the liquid side for three different single phase secondary refrigerants were studied and compared to predictions by existing correlations. Predominantly, the laminar flow regime was studied. The results show that when predicting the heat transfer performance on the liquid side of a cooling-coil the Gnielinski correlation for thermally developing flow and uniform wall temperature boundary conditions (T) leads to good agreement for 0.0014 < x^* < 0.017 if 50 < Re < 1700, assuming a new entrance length is formed after each U-bend. In addition, these entrance lengths must also be accounted for, when predicting the pressure drop on the liquid side of the cooling-coil. The uncertainty of measurement can be a problem in this type of investigations and this has been taken into consideration when analysing the results.     

Measurements of Some Characteristics of Thermal Radiation in a 400-kW Grate-Fired Furnace Combusting Biomass

A comprehensive experimental investigation relevant to thermal radiation has been performed in a grate-fired test furnace. Thermal radiation is the dominating mode of heat transfer in the grate-fired furnace and yet only a few studies have focused on thermal radiation. No previous works, to the authors' knowledge, have been carried out concerning measurements on radiative heat transfer in grate-fired furnaces. In this work measurements of temperature have been carried out for all boundaries and the flue gases at a large number of locations. The gas species volume fraction, particle mass–size distributions, and wall irradiation have also been measured at a number of spatial locations. These data are useful in a computational framework to describe the radiative heat transfer reaching the boundaries. Comparing modeled wall irradiation to the measured one makes it possible to obtain a deeper insight into the thermal radiative transport inside the grate-fired furnace.     

Poly(ethylene‐graft‐ethylene oxide) (PE‐PEO) and poly(ethylene‐co‐acrylic acid) (PEAA) as compatibilizers in blends of LDPE and polyamide‐6

In a blend of two immiscible polymers a controlled morphology can be obtained by adding a block or graft copolymer as compatibilizer. In the present work blends of low‐density polyethylene (PE) and polyamide‐6 (PA‐6) were prepared by melt mixing the polymers in a co‐rotating, intermeshing twin‐screw extruder. Poly(ethylene‐graft‐polyethylene oxide) (PE‐PEO), synthesized from poly(ethylene‐co‐acrylic acid) (PEAA) (backbone) and poly(ethylene oxide) monomethyl ether (MPEO) (grafts), was added as compatibilizer. As a comparison, the unmodified backbone polymer, PEAA, was used. The morphology of the blends was studied by scanning electron microscopy (SEM). Melting and crystallization behavior of the blends was investigated by differential scanning calorimetry (DSC) and mechanical properties by tensile testing. The compatibilizing mechanisms were different for the two copolymers, and generated two different blend morphologies. Addition of PE‐PEO gave a material with small, well‐dispersed PA‐spheres having good adhesion to the PE matrix, whereas PEAA generated a morphology characterized by small PA‐spheres agglomerated to larger structures. Both compatibilized PE/PA blends had much improved mechanical properties compared with the uncompatibilized blend, with elongation at break (ε_b) increasing up to 200%. Addition of compatibilizer to the PE/PA blends stabilized the morphology towards coalescence and significantly reduced the size of the dispersed phase domains, from an average diameter of 20 μm in the unmodified PE/PA blend to approximately 1 μm in the compatibilized blends. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 2416–2424, 2000     

Influence of seed polymer molecular weight on polymerization kinetics and particle morphology of structured styrene–butadiene latexes

Heterogeneous film‐forming latexes were prepared using two‐stage, seeded emulsion polymerization. The polymerization was performed in a calorimetric reactor with a control unit that monitored the reaction rate and controlled the charging rate of the monomers. Three types of styrene seed latexes were prepared at 70°C. The first was an unmodified polystyrene (PS) latex. The second had the molecular weight lowered by the use of carbon tetrachloride (CCl₄) as a chain‐transfer agent, added at the start of the polymerization. For the third one, divinylbenzene (DVB) was used as a comonomer. DVB was added under starved conditions near the end of the polymerization to achieve crosslinked particle shells and to introduce double bonds as possible grafting sites. The second polymerization step was performed at 80°C as a batch operation in a 200‐mL calorimeter reactor. The second‐stage polymer was poly(styrene‐co‐butadiene‐co‐methacrylic acid) (S/B/MAA). A fixed S/B ratio was used together with varying small amounts of MAA. Particle morphology and particle‐size distributions were examined after the second stage using TEM after staining with osmium tetroxide. The particle morphology was found to depend on both the seed composition and the amount of MAA used in the second stage. Molecular weight and crosslinking of the DVB‐containing seed influenced the internal particle viscosity, which gave differences in the polymerization rate and the particle morphology. Crosslinking of the second‐stage polymer decreased the monomer concentration in the particles, which could be detected as a change in the slope the pressure/conversion curve. This phenomenon was used to indicate the critical conversion for crosslinking of the second‐stage polymer. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 297–311, 2000     

Influence of spacer groups on grafting ability,curing ability,and film properties of water-based radiation curable latexes

Film-forming polystyrene/poly(n-butyl acrylate-co-glycidyl methacrylate) [PS/P(BA-co-GMA)] core–shell latex particles were prepared via a two-stage emulsion polymerization procedure using a PS latex seed. A delayed addition of GMA was used to locate the functional epoxy groups near the surface of the particles. The surface-bound epoxy groups were used as grafting sites for unsaturated carboxyl functional monomers having the unsaturated groups and the carboxylic group separated by 1, 5, or 10 oxyethylene units. Grafting and curing characteristics and film properties after irradiation were investigated as a function of the number of oxyethylene units. A BA-GMA [P(BA-co-GMA)] copolymer was used as a model system for the core–shell latex particles for quantification of the grafting reactions. The grafting was demonstrated by FTIR and ¹H-NMR spectroscopy. The effects of crosslinking was studied by thermal mechanical analysis and dynamical mechanical analysis. Differential photocalorimetry was also used for evaluation of the curing ability. It was demonstrated that the reagent having five oxyethylene units in the spacer group was grafted onto the polymer backbones to a larger extent than the other two reagents, and a more thoroughly cured film was obtained upon irradiation. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 70: 897–906, 1998     

Network structure and reaction mechanisms in high pressure and peroxide vulcanization of polybutadiene: Microstructural changes studied by 13C solid-state NMR

This article is concerned with the microstructural changes during peroxide and high pressure vulcanization of polybutadiene that is unfilled and filled with carbon black. The main tool is ¹³C solid-state NMR; it shows that vinyl unsaturations are consumed in both filled and unfilled samples under peroxide and high pressure vulcanization. Chemical shift calculations of unvulcanized polybutadiene show good agreement with the observed peaks. Calculations of proposed structures, based on a possible reaction mechanism, suggest that a large number of peaks will appear, each at very low intensity. Nevertheless, some changes can be seen as a result of the crosslinking reaction, and the results provide support for the suggested reaction mechanism. Thus, the proposed addition crosslinking mechanism over vinyl unsaturations seems to be a reasonable explanation of the crosslink formation in high pressure vulcanization. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 2799–2806, 1999