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191.
Jianghua Wei Martin C. Hawley John D. Delong Mark Demeuse 《Polymer Engineering and Science》1993,33(17):1132-1140
Stoichiometric mixtures of DGEBA (diglycidyl ether of bisphenol A)/DDS (diaminodiphenyl sulfone) and DGEBA/mPDA (meta phenylene diamine) have been isothermally cured by electromagnetic radiation and conventional heating using thin film sample configurations. Fourier transform infrared spectroscopy (FTIR) was used to measure the extent of cure. Thermal mechanical analysis (TMA) was used to determine the glass transition temperatures directly from the cured thin film samples. Well-defined glass transitions were observed in the TMA thermograph for both thermal and microwave cured samples. Significant increases in the reaction rates have been observed in the microwave cured DGEBA/DDS samples. Only slight increases in the reaction rates have been observed in the microwave cured DGEBA/mPDA samples. Higher glass transition temperatures were obtained in microwave cured samples compared to those of thermally cured ones after gelation. The magnitude of increases of glass transition temperature is much larger for the DGEBA/DDS system than DGEBA/mPDA system. The microwave radiation effect was much more significant in DGEBA/DDS system than in DGEBA/mPDA system. DiBenedetto's model was used to fit the experimental Tg data of both thermal and microwave cured epoxy resins. 相似文献
192.
The use of colorimetry within industry has grown extensively in the last few decades. Central to many of today's instruments is the CIE system, established in 1931. Many have questioned the validity of the assumptions made by Wright1 and Guild,2 some suggesting that the 1931 color‐matching functions are not the best representation of the human visual system's cone responses. A computational analysis was performed using metameric data to evaluate the CIE 1931 color‐matching functions as compared to with other responsivity functions. The underlying assumption was that an optimal set of responsivity functions would yield minimal color‐difference error between pairs of visually matched metamers. The difference of average color differences found in the six chosen sets of responsivity functions was small. The CIE 1931 2° color‐matching functions on average yielded the largest color difference, 4.56 ΔE. The best performance came from the CIE 1964 10° color‐matching functions, which yielded an average color difference of 4.02 ΔE. An optimization was then performed to derive a new set of color‐matching functions that were visually matched using metameric pairs of spectral data. If all pairs were to be optimized to globally minimize the average color difference, it is expected that this would produce an optimal set of responsivity functions. The optimum solution was to use a weighted combination of each set of responsivity functions. The optimized set, called the Shaw and Fairchild responsivity functions, was able to reduce the average color difference to 3.92 ΔE. In the final part of this study a computer‐based simulation of the color differences between the sets of responsivity functions was built. This simulation allowed a user to load a spectral radiance or a spectral reflectance data file and display the tristimulus match predicted by each of the seven sets of responsivity functions. © 2002 Wiley Periodicals, Inc. Col Res Appl, 27, 316–329, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/col.10077 相似文献
193.
Marina Fridin Mark Belokopytov 《International journal of human-computer interaction》2014,30(6):459-469
Embodied robots are known to be preferable in most cases to their virtual agents for interaction with and performance by human subjects. This study compared the efficacy of an embodied robot-coacher and its virtual agent in involving preschool children in the performance of playlike motor tasks. The robot or its virtual agent demonstrated movements, asked the children to repeat them, and provided positive feedback on their performance. The difficulty of the motor tasks was increased over the course of the session. Two groups of children were studied, one of them with and the other without previous experience of interaction with the embodied robot. In the experienced group, involvement in motor tasks was successfully induced by both the embodied robot and its virtual agent, but the children interacted less well with the virtual agent than with the embodied robot. Children in the inexperienced group did not interact at all during the experiment with the virtual agent. Because participants in the experiment were preschool children in their natural environment, this study proposes the combined use of an embodied robot and its virtual agent for motor involvement. 相似文献
194.
This work investigates two different melt‐blending strategies for preparing compatibilized polypropylene‐clay nanocomposites, specifically: (1) conventional twin‐screw extrusion, and (2) single‐screw extrusion capable of direct supercritical carbon dioxide (scCO2) feed to the extruder barrel. Proportional amounts (3 : 1) of maleic anhydride functionalized polypropylene compatibilizer and organically modified montmorillonite clay at clay loadings of 1, 3, and 5 wt % are melt‐blended with a polypropylene homopolymer using the two approaches. The basal spacing, degree of exfoliation, and dispersion of organoclay is assessed using X‐ray diffraction, transmission electron microscopy, and rheology. In terms of the latter, both steady shear and small‐amplitude oscillatory shear provide information about the apparent yield stress and solid‐like terminal behavior respectively. Finally, nanoindentation is performed to determine the room temperature modulus of each melt‐blended nanocomposite. The results reveal unequivocally that the high shear of the twin‐screw process is vastly superior to the single‐screw with in‐line scCO2 addition in generating well‐exfoliated, percolated polypropylene‐clay nanocomposites. It is likely that increased contact time between clay and scCO2 is necessary for scCO2 to positively affect exfoliation. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 884–892, 2007 相似文献
195.
Summary Elastomeric networks of polydimethylsiloxane prepared by end-linking chains having molecular weights in the range 18,500 to
220 g mol-1 were studied from -128 to 50°C using a Rheovibron DDV III Viscoelastometer. In the case of the unimodal networks, the glass
transition temperature Tg was generally insensitive to degree of cross-linking. The intensity of the tan δ relaxation, however, increased by over an
order of magnitude over the range of cross-link densities investigated. Bimodal networks prepared from mixtures of relatively
long and very short PDMS chains also had values of Tg which were insensitive to degree of cross-linking. Finally, as expected, the intensities of the tan δ peak for the bimodal
networks could not be explained on the basis of simple additivity of contributions from the relatively long and the very short
network chains. 相似文献
196.
Cleland LG Proudman SM Hall C Stamp LK McWilliams L Wylie N Neumann M Gibson RA James MJ 《Lipids》2003,38(4):419-424
Dietary fish oil supplements have been shown to have benefits in rheumatoid arthritis (RA), other inflammatory diseases, and
in cardiovascular disease. As with any medical advice, variability will exist with regard to adherence and consequent biochemical
or pharmacophysiologic effects. The aim was to explore the utility of plasma phospholipid EPA as a measure of n−3 PUFA intake
and response to standardized therapeutic advice given in an outpatient or office practice setting, to increase dietary n−3
PUFA, including a fish oil supplement. Patients with early RA were given verbal and written advice to alter their dietary
n−3 PUFA intake, including ingestion of 20 mL of bottled fish oil on juice daily. The advice included instructions to increase
n−3 PUFA and to avoid foods rich in n−6 PUFA. Every 3 mon, blood samples were obtained for analysis of plasma phospholipid
FA. Plasma phospholipid EPA was used as the primary index of n−3 PUFA intake. A diverse response was seen, with about one-third
of patients achieving a substantial elevation of plasma phospholipid EPA over the 12-mon study period. A third had little
change, with the remainder achieving intermediate levels. Data obtained longitudinally from individual patients indicated
that substantial elevations of EPA (>5% total plasma phospholipid FA) could be maintained for more than 3 yr. Plasma phospholipid
EPA is a convenient measure of adherence to advice to take a dietary n−3 PUFA-rich fish oil supplement. This measure may prove
a useful adjunct to intention to treat analyses in determining the effect of dietary fish oil supplements on long-term outcomes
in arthritis and other chronic inflammatory diseases. It may also provide a guide to the effectiveness of therapeutic and
preventive messages designed to increase n−3 PUFA intake. 相似文献
197.
Oyster tissue contained 2.4% lipid, 0.14 μmole aldehyde per milligram lipid and at least 10 μg phosphorous per milligram lipid.
The neutral lipid represented 58%, the glycolipid 6%, and the polar lipid 36% of the total lipid recovered after silicic acid
column chromatography. Aldehydes were found in all fractions, but the presence of plasmalogen was verified in only the neutral
and polar lipid fractions. At least 68% of the plasmalogen in oyster lipid was found in the polar lipid fraction. At least
13% of the phosphorous in oyster lipids was present as phosphonolipid. The distribution of phosphate and phosphonate lipids
was: diacyl phospholipid 38.1%, plasmalogen phospholipid 21.8%, sphingophosphonolipid 13.5%, glyceryl ether phospholipid 8.3%,
sphingophospholipid 6.9%, plasmalogen phosphonolipid 6.4%, diacyl phosphonolipid 2.6%, and glyceryl ether phosphonolipid 2.4%.
When the per cent of phosphorous as phosphonolipid within the plasmalogen and glyceryl ether classes was calculated, similar
values were obtained. These results support the hypothesis that there is a product precursor relationship between these two
classes of lipids.
Some of the data taken from a thesis to be submitted to the Graduate School, University of Maryland, by Leslye Johnson in
partial fulfillment of the requirements for the M.S. degree in biochemistry. 相似文献
198.
Robert M. Boddey Mark B. Peoples Brian Palmer Peter J. Dart 《Nutrient Cycling in Agroecosystems》2000,57(3):235-270
Biological nitrogen fixation (BNF) associated with trees and shrubs plays a major role in the functioning of many ecosystems, from natural woodlands to plantations and agroforestry systems, but it is surprisingly difficult to quantify the amounts of N2 fixed. Some of the problems involved in measuring N2 fixation by woody perennials include: (a) diversity in occurrence, and large plant-to-plant variation in growth and nodulation status of N2-fixing species, especially in natural ecosystems; (b) long-term, perennial nature of growth and the seasonal or year-to-year changes in patterns of N assimilation; and (c) logistical limitations of working with mature trees which are generally impossible to harvest in their entirety. The methodology which holds most promise to quantify the contributions of N2 fixation to trees is the so-called `15N natural abundance' technique which exploits naturally occurring differences in 15N composition between plant-available N sources in the soil and that of atmospheric N2. In this review we discuss probable explanations for the origin of the small differences in 15N abundance found in different N pools in both natural and man-made ecosystems and utilise previously published information and unpublished data to examine the potential advantages and limitations inherent in the application of the technique to study N2 fixation by woody perennials. Calculation of the proportion of the plant N derived from atmospheric N2 (%Ndfa) using the natural abundance procedure requires that both the 15N natural abundance of the N derived from BNF and that derived from the soil by the target N2-fixing species be determined. It is then assumed that the 15N abundance of the N2-fixing species reflects the relative contributions of the N derived from these two sources. The 15N abundance of the N derived from BNF (B) can vary with micro-symbiont, plant species/provenance and growth stage, all of which create considerable difficulties for its precise evaluation. If the%Ndfa is large and the 15N abundance of the N acquired from other sources is not several 15N units higher or lower than B, then this can be a major source of error. Further difficulties can arise in determining the 15N abundance of the N derived from soil (and plant litter, etc.) by the target plant as it is usually impossible to predict which, if any, non-N2-fixing reference species will obtain N from the same N sources in the same proportions with the same temporal and spatial patterns as the N2-fixing perennial. The compromise solution is to evaluate the 15N abundance of a diverse range of neighbouring non-N2-fixing plants and to compare these values with that of the N2-fixing species and the estimate of B. Only then can it be determined whether the contribution of BNF to the target species can be quantified with any degree of confidence. This review of the literature suggests that while the natural abundance technique appears to provide quantitative measures of BNF in tree plantation and agroforestry systems, particular difficulties may arise which can often limit its application in natural ecosystems. 相似文献
199.
Garrett BC Dixon DA Camaioni DM Chipman DM Johnson MA Jonah CD Kimmel GA Miller JH Rescigno TN Rossky PJ Xantheas SS Colson SD Laufer AH Ray D Barbara PF Bartels DM Becker KH Bowen KH Bradforth SE Carmichael I Coe JV Corrales LR Cowin JP Dupuis M Eisenthal KB Franz JA Gutowski MS Jordan KD Kay BD Laverne JA Lymar SV Madey TE McCurdy CW Meisel D Mukamel S Nilsson AR Orlando TM Petrik NG Pimblott SM Rustad JR Schenter GK Singer SJ Tokmakoff A Wang LS Wettig C Zwier TS 《Chemical reviews》2005,105(1):355-390
200.
Metallo-Supramolecular Polymerization: A Route to Easy-To-Process Organic/Inorganic Hybrid Materials
Mark Burnworth Daniel Knapton Stuart J. Rowan Christoph Weder 《Journal of Inorganic and Organometallic Polymers and Materials》2007,17(1):91-103
The self-assembly polymerization of ditopic macromolecules via metal–ligand binding is a facile route for the preparation
of metallo-supramolecular polymers (MSPs). We herein review our recent work focused on the synthesis and investigation of
metallo-supramolecular polymers based on 2,6-bis(1′-methylbenzimidazolyl)pyridine endcapped poly(p-phenylene ethynylene) and poly(p-xylene) macromonomers. These materials are readily solution-processable and display appreciable mechanical properties as
well as other attractive properties such as specific opto/electrical functions or high thermal stability. Our work illustrates
that metallosupramolecular polymerization offers an attractive approach to assemble high-molecular-weight macromolecules from
well-defined, easy to process precursors. Variation of the ditopic ligands and metal ions allows one to easily tailor the
desired properties.
This paper is dedicated to Professor Ian Manners and his scientific accomplishments. 相似文献