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Two-step Process (two-step + process)
Selected AbstractsVibration Causes Acute Vascular Injury in a Two-Step Process: Vasoconstriction and Vacuole DisruptionTHE ANATOMICAL RECORD : ADVANCES IN INTEGRATIVE ANATOMY AND EVOLUTIONARY BIOLOGY, Issue 8 2008Sandya R. Govindaraju Abstract Hand,arm vibration syndrome is a vasospastic and neurodegenerative occupational disease. In the current study, the mechanism of vibration-induced vascular smooth muscle cell (SMC) injury was examined in a rat-tail vibration model. Tails of male Sprague Dawley rats were vibrated continuously for 4 hr at 60 Hz, 49 m/s2 with or without general anesthesia. Ventral tail arteries were aldehyde fixed and embedded in epoxy resin to enable morphological analysis. Vibration without anesthesia caused vasoconstriction and vacuoles in the SMC. Anesthetizing rats during vibration prevented vasoconstriction and vacuole formation. Exposing tail arteries in situ to 1 mM norepinephrine (NE) for 15 min induced the greatest vasoconstriction and vacuolation. NE induced vacuoles were twice as large as those formed during vibration. When vibrated 4 hr under anesthesia after pretreatment with NE for 15 min, the SMC lacked vacuoles and exhibited a longitudinal banding pattern of dark and light staining. The extracellular matrix was filled with particulates, which were confirmed by electron microscopy to be cellular debris. The present findings demonstrate that vibration-induced vasoconstriction (SMC contraction) requires functioning central nervous system reflexes, and the physical stress of vibration damages the contracted SMC by dislodging and fragmenting SMC vacuoles. Anat Rec, 291:999,1006, 2008. © 2008 Wiley-Liss, Inc. [source] ChemInform Abstract: Mild Two-Step Process for the Transition-Metal-Free Synthesis of Carbon,Carbon Bonds from Allylic Alcohols/Ethers and Grignard Reagents.CHEMINFORM, Issue 33 2010Xinping Han Abstract The method involves the photochemically promoted allylic substitution reaction of allylic alcohols or ethers with phosphorothioic acid ester (II) followed by sp3,sp3 or sp2,sp3 bond formation of the resulting allylic phosphorothioate esters with various Grignard reagents. [source] Teaching image processing: A two-step processCOMPUTER APPLICATIONS IN ENGINEERING EDUCATION, Issue 3 2008Clarence Han-Wei Yapp Abstract An interactive program for teaching digital image processing techniques is presented in this article. Instead of heavy programming tasks and mathematical functions, students are led step by step through the exercises and then allowed to experiment. This article evaluates the proposed program and compares it with existing techniques. © 2008 Wiley Periodicals, Inc. Comput Appl Eng Educ 16: 211,222, 2008; Published online in Wiley InterScience (www.interscience.wiley.com); DOI 10.1002/cae.20149 [source] Gel immobilization of acrylamide-modified single-stranded DNA template for pyrosequencingELECTROPHORESIS, Issue 12 2007Pengfeng Xiao Dr. Abstract A novel two-step process was developed to prepare ssDNA templates for pyrosequencing. First, PCR-amplified DNA templates modified with an acrylamide group and acrylamide monomers were copolymerized in 0.1,M NaOH solution to form polyacrylamide gel spots. Second, ssDNA templates for pyrosequencing were prepared by removing electrophoretically unbound complementary strands, unmodified PCR primers, inorganic pyrophosphate (PPi), and excess deoxyribonucleotides under alkali conditions. The results show that the 3-D polyacrylamide gel network has a high immobilization capacity and the modified PCR fragments are efficiently captured. After electrophoresis, gel spots copolymerized from 10,,L of the crude PCR products and the acrylamide monomers contain template molecules on the order of pmol, which generate enough light to be detected by a regular photomultiplier tube. The porous structure of gel spots facilitated the fast transportation of the enzyme, dNTPs and other reagents, and the solution-mimicking microenvironment guaranteed polymerase efficiency for pyrosequencing. Successful genotyping from the crude PCR products was demonstrated. This method can be applied in any laboratory; it is cheap, fast, simple, and has the potential to be incorporated into a DNA-chip format for high-throughput pyrosequencing analysis. [source] Open-tubular capillary columns with a porous layer of monolithic polymer for highly efficient and fast separations in electrochromatographyELECTROPHORESIS, Issue 21 2006Sebastiaan Eeltink Abstract Open-tubular columns for CEC separations having inner-wall coated with a thin layer of porous monolithic polymer have been studied. A two-step process including (i),UV-initiated polymerization leading to a layer of porous poly(butyl methacrylate- co -ethylene dimethacrylate), and (ii),UV-initiated grafting of ionizable monomers appear to be well suited for the preparation of these columns. The thickness of the porous polymer layer is controlled by the percentage of monomers in the polymerization mixture and/or length of the irradiation time. The layer thickness significantly affects retention, efficiency, and resolution in open-tubular CEC. Under optimized conditions, column efficiencies up to 400,000 plates/m can be achieved. Use of higher temperature and application of pressure enables a significant acceleration of the open-tubular CEC separations. [source] Variation in Individual Investment Strategies among Social AnimalsETHOLOGY, Issue 8 2006Jan Komdeur Invited Review Abstract Cooperation and conflict are ubiquitous features of life in the vast majority of animals and can occur over a wide range of functional contents and at various levels. In this review I describe known and less well-known proximate aspects of cooperation and conflict over reproductive behaviour in social animals, where individuals other than the genetic parents contribute to the provisioning of care (,alloparental care'). Traditionally the evolution of alloparental care is viewed as a two-step process: the decision to delay dispersal and independent breeding, usually as a consequence of the existence of constraints on independent breeding, and the decision to behave as alloparents by which individuals that have delayed dispersal gain a net fitness benefit. Behavioural ecological theory generally assumes that all individuals are similar in ,make-up' and that life history and behavioural decisions are facultative. However, there is probably more individual variation in the amount and type of social behaviour than originally anticipated. Here, I demonstrate that some of these differences in behaviours are because of environmental factors, which may be associated with ,reaction norms' or the genotype's quantitative phenotypic variation, or which may yield polyethisms. Most evolutionary models of animal cooperation are based on optimality approaches that do not consider individual genetic variation and maternal effects on the variation in the expression of social behaviour. Further research on the genetic basis of cooperations and subordinate,breeder interactions may be crucial for understanding the evolution of social behaviour. If we take individual differences into account our conclusions and explanations of social behaviour may change. Given the conceptual similarities between the various research disciplines addressing different types of cooperation and conflict over investment, the issues described here should lead to more mutual attraction between the different disciplines and stimulate further development in our understanding of cooperation strategies in general. [source] Sterically Demanding Iminopyridine LigandsEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 26 2007Torsten Irrgang Abstract Two sterically demanding iminopyridine ligands, (2,6-diisopropylphenyl)[6-(2,4,6-triisopropylphenyl)pyridin-2-ylmethylene]amine and (2,6-diisopropylphenyl)[6-(2,6-dimethylphenyl)pyridin-2-ylmethylene]amine, were prepared by a two-step process: first, condensation of 6-bromopyridine-2-carbaldehyde with an equimolecular amount of 2,6-diisopropylaniline, and second, Kumada-type coupling of in-situ-formed Grignard compounds of 1-bromo-2,6-dimethylphenyl and 1-bromo-2,4,6-triisopropylphenyl. Dichlorido complexes of the ligands were synthesized starting from FeCl2, [PdCl2(cod)], [NiCl2(dme)], and CoCl2 (cod = 1,5-cyclooctadiene, dme = dimethoxyethane). X-ray crystal structure analyses of a Fe, Pd, and Co complex were determined. Ethylene polymerization/oligomerization behavior of the dichlorido complexes after activation with methylaluminoxane or triethylaluminum was studied. Ethylene dimerization selectivity greater than 95,% was observed.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] Enzymatic fatty acid exchange in glycero-phospholipids,EUROPEAN JOURNAL OF LIPID SCIENCE AND TECHNOLOGY, Issue 10 2003Patrick Adlercreutz Abstract Lipases can be used to exchange fatty acids in the sn -1 position of glycerophospholipids and phospholipase A2 is useful for the corresponding exchange reaction in the sn -2 position. In both cases, the exchange can be done in a one-step acidolysis process or in a two-step process. In the latter case, the original fatty acid in the desired position is removed by enzymatic hydrolysis or alcoholysis and after isolation of the resulting lysophospholipid, the new fatty acid is introduced, using the same enzyme, in an esterification reaction. Several synthesis examples from the literature are reviewed. Incorporation of a new fatty acid into the sn -1 position is more favourable than incorporation into the sn -2 position because of the magnitudes of the equilibrium constants of the reactions and because lipases can be used at much lower water activity than phospholipase A2. With the consecutive use of both enzymes highly pure products with defined fatty acids in both positions can be obtained. [source] The Mechanism of the Stetter Reaction , A DFT StudyEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 33 2008Kirsty J. Hawkes Abstract On the basis of Breslow's mechanism for benzoin condensation, a model asymmetric Stetter reaction has been investigated using DFT methods. In contrast to the concerted benzoin condensation, after formation of the Breslow intermediate the Stetter reaction is found to be a two-step process in which the rate-determining C,C coupling of the Breslow intermediate and the Michael acceptor precedes final proton transfer. In addition, the enolamine is found to play a significant role in the stereochemistry of the product, with the energy difference between stereoisomers of this intermediate reflected throughout the remainder of the reaction sequence. Consequently, electronic and steric control of the stereochemistry of this intermediate should directly enhance the ee values of the product. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] Enantioselective One-Pot Two-Step Synthesis of Hydrophobic Allylic Alcohols in Aqueous Medium through the Combination of a Wittig Reaction and an Enzymatic Ketone ReductionEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 31 2007Marina Kraußer Abstract A one-pot two-step process for the enantioselective synthesis of hydrophobic allylic alcohols was developed, which comprises ketone formation by the Wittig reaction and their enzymatic in situ biotransformation into the desired target products. By means of this combined Wittig reaction and bioreduction, the allylic alcohols were prepared with conversions of up to 90,%, and with excellent enantioselectivities of >99,% ee. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] Near IR Sensitization of Organic Bulk Heterojunction Solar Cells: Towards Optimization of the Spectral Response of Organic Solar CellsADVANCED FUNCTIONAL MATERIALS, Issue 2 2010Markus Koppe Abstract The spectroscopic response of a poly(3-hexylthiophene)/[6,6]-phenyl-C61 -butyric acid methyl ester (P3HT/PCBM)-based bulk heterojunction solar cell is extended into the near infrared region (NIR) of the spectrum by adding the low bandgap polymer poly[2,6-(4,4-bis-(2-ethylhexyl)-4H -cyclopenta[2,1- b;3,4- b´]-dithiophene)- alt -4,7-(2,1,3-benzothiadiazole)] [PCPDTBT] to the blend. The dominant mechanism behind the enhanced photosensitivity of the ternary blend is found to be a two-step process: first, an ultrafast and efficient photoinduced charge transfer generates positive charges on P3HT and PCPDTBT and a negative charge on PCBM. In a second step, the positive charge on PCPDTBT is transferred to P3HT. Thus, P3HT serves two purposes. On the one hand it is involved in the generation of charge carriers by the photoinduced electron transfer to PCBM, and, on the other hand, it forms the charge transport matrix for the positive carriers transferred from PCPDTBT. Other mechanisms, such as energy transfer or photoinduced charge transfer directly between the two polymers, are found to be absent or negligible. [source] Fire history and the global carbon budget: a 1°× 1° fire history reconstruction for the 20th centuryGLOBAL CHANGE BIOLOGY, Issue 3 2005Florent Mouillot Abstract A yearly global fire history is a prerequisite for quantifying the contribution of previous fires to the past and present global carbon budget. Vegetation fires can have both direct (combustion) and long-term indirect effects on the carbon cycle. Every fire influences the ecosystem carbon budget for many years, as a consequence of internal reorganization, decomposition of dead biomass, and regrowth. We used a two-step process to estimate these effects. First we synthesized the available data available for the 1980s or 1990s to produce a global fire map. For regions with no data, we developed estimates based on vegetation type and history. Second, we then worked backwards to reconstruct the fire history. This reconstruction was based on published data when available. Where it was not, we extrapolated from land use practices, qualitative reports and local studies, such as tree ring analysis. The resulting product is intended as a first approximation for questions about consequences of historical changes in fire for the global carbon budget. We estimate that an average of 608 Mha yr,1 burned (not including agricultural fires) at the end of the 20th century. 86% of this occurred in tropical savannas. Fires in forests with higher carbon stocks consumed 70.7 Mha yr,1 at the beginning of the century, mostly in the boreal and temperate forests of the Northern Hemisphere. This decreased to 15.2 Mha yr,1 in the 1960s as a consequence of fire suppression policies and the development of efficient fire fighting equipment. Since then, fires in temperate and boreal forests have decreased to 11.2 Mha yr,1. At the same time, burned areas increased exponentially in tropical forests, reaching 54 Mha yr,1 in the 1990s, reflecting the use of fire in deforestation for expansion of agriculture. There is some evidence for an increase in area burned in temperate and boreal forests in the closing years of the 20th century. [source] Sphingosine kinase 1 inhibition sensitizes hormone-resistant prostate cancer to docetaxelINTERNATIONAL JOURNAL OF CANCER, Issue 11 2009Lysann Sauer Abstract It has recently been shown that docetaxel chemotherapy is effective in prolonging life in patients with prostate cancer (PCa). We have investigated potential ways of increasing the effectiveness of chemotherapy in this disease. We have previously reported that sphingosine kinase 1 (SphK1) inhibition is a key step in docetaxel-induced apoptosis in the PC-3 PCa cell line and that pharmacologicalSphK1 inhibition is chemosensitizing in the docetaxel-resistant PCa LNCaP cell line. In this study we have addressed the mechanism of docetaxel-induced apoptosis of PC-3 cells and identified SphK1-dependent and -independent components. We have shown that SphK1 inhibition by docetaxel is a two-step process involving an initial loss of enzyme activity followed by a decrease in SphK1 gene expression. Using hormoneresistant PC-3 and DU145 PCa cells we have demonstrated that both pharmacological and siRNA-mediated SphK1 inhibition leads to a four-fold decrease in the docetaxel IC50 dose. This work points out to potential ways of increasing the effectiveness of chemotherapy for PCa by SphK1 inhibition. © 2009 UICC [source] Thermal dehydration kinetics of a rare earth hydroxide, Gd(OH)3INTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 2 2007Chengkang Chang This paper reports the synthesis, characterization, and dehydration kinetics of a rare earth hydroxide, Gd(OH)3. Uniform rod-like Gd(OH)3 powder was prepared by a colloidal hydrothermal method. The powder thus obtained dehydrated into its oxide form in a two-step process, where crystalline GdOOH was obtained as the intermediate phase. Crystal structure study revealed a monoclinic structure for GdOOH, with space group P2/1m and lattice parameters a = 6.0633, b = 3.7107, c = 4.3266, and , = 108.669. The first-step dehydration follows the F2 mechanism, while the second step follows the F1 model, indicating that both the steps are controlled by nucleation/growth mechanism. The activation energy Ea and frequency factor A are 231±12 kJ/mol and 2.08 × 1018 s,1 for the first step and 496 ± 32 kJ/mol and 7.88 × 1033 s,1 for the second step, respectively. Such high activation energy calculated from the experimental data can be ascribed to the high bonding energy of GdO bond, and the difference in activation energy for the two steps is due to the change in the bond length of hexagonal Gd(OH)3 and monoclinic GdOOH. © 2006 Wiley Periodicals, Inc. Int J Chem Kinet 39: 75,81, 2007 [source] Efficient Solvent-Free Robinson Annulation Protocols for the Highly Enantioselective Synthesis of the Wieland,Miescher Ketone and AnaloguesADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 14-15 2009Ben Bradshaw Abstract A highly efficient (93% overall yield) and enantioselective (94% ee) synthesis of the Wieland,Miescher ketone (10-g scale) through a solvent-free Robinson annulation procedure is reported. The process involves only 1,mol% triethylamine as the base in the initial Michael process and the organocatalyst N -tosyl-(Sa)-binam- L -prolinamide (2,mol%) and benzoic acid (0.5,mol%) for the intramolecular aldol process. This green protocol is applied to a wide range of valuable building block analogues of the Wieland,Miescher ketone (10 examples). Among these, a noteworthy compound for terpene synthesis is the 8a-allyl derivative, which is prepared in 93% yield and 97% ee in a process allowing the recovery and reutilization of the organocatalyst. Furthermore, a one-pot, two-step process has also been developed. [source] Structure and properties of cross-linked polyurethane copolymersADVANCES IN POLYMER TECHNOLOGY, Issue 3 2009S. Oprea Abstract Polyurethane elastomers based on polyester diols and aromatic or aliphatic diisocyanates can be used as vibration dampers and isolation materials. Two series of cross-linked polyurethanes with various hard segment structures and different amounts were prepared and thermomechanical properties of these materials were studied. Cross-linked polyurethane copolymers composed of poly(ethylene adipate)diol as soft segment and 4,4,-methylenebis(phenylisocyanate), 1,6-hexamethylene diisocyanate, and diols glycerin, 1,4-butanediol, and 1,6-hexanediol as hard segments were synthesized by a two-step process. The networks have been prepared by end-linking a mixture of the bifunctional precursor chains with trifunctional cross-linkers at off-stoichiometric ratios. The results show that the cross-link and the polyurethane hard segment interaction play a special role in the interconnected chain density and its magnitude is revealed by the mechanical properties. Of most importance, maximum stress, tensile modulus, and elongation at break increased significantly at the 22 wt % composition of hard segment content. Interchain cross-linking improves thermal stability, which was measured by thermogravimetric analysis and differential scanning calorimetry. Cross-linked polyurethane behaves as an elastomer and is useful for shock, noise, and vibration control. © 2009 Wiley Periodicals, Inc. Adv Polym Techn 28:165,172, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.20155 [source] Estimating survival and movements using both live and dead recoveries: a case study of oystercatchers confronted with habitat changeJOURNAL OF APPLIED ECOLOGY, Issue 1 2009Olivier Duriez Summary 1Animals facing partial habitat loss can try to survive in the remaining habitat or emigrate. Effects on survival and movements should be studied simultaneously since survival rates may be underestimated if emigrants are not considered, and since emigrants may experience reduced survival. 2We analysed movements and survival of adult wintering oystercatcher Haematopus ostralegus in response to the 1986,1987 partial closure of the Oosterschelde in the Dutch Delta. This reduced by one-third the tidal area of this major European wintering area for waders. 3We developed a novel variant of a multistate capture,recapture model allowing simultaneous estimation of survival and movement between sites using a mixture of data (live recaptures and dead recoveries). We used a two-step process, first estimating movements between sites followed by site-specific survival rates. 4Most birds were faithful to their ringing site. Winter survival was negatively affected by winter severity and was lowest among birds changing wintering site (i.e. moving outside of the Oosterschelde). 5During mild winters, survival rates were very high, and similar to before the closure in both changed and unchanged sectors of the Oosterschelde. However, the combined effect of habitat loss with severe winters decreased the survival of birds from changed sectors and induced emigration. 6The coastal engineering project coincided with three severe winters and high food stock, making assessment of its effects difficult. However, the habitat loss seems to have had less impact on adult survival and movements than did winter severity. 7 Synthesis and applications. Human-induced habitat change may result in population decline through costly emigration or reduced survival or reproduction of individuals that stay. Long-term monitoring of marked individuals helps to understand how populations respond to environmental change, but site-specific survival and movement rates should be integrated in the same model in order to maximize the information yield. Our modelling approach facilitates this because it allows the inclusion of recoveries from outside the study area. [source] Bioactive and mechanically strong Bioglass®-poly(D,L -lactic acid) composite coatings on surgical suturesJOURNAL OF BIOMEDICAL MATERIALS RESEARCH, Issue 2 2006Q. Z. Chen Abstract New coating processes have been investigated for degradable (Vicryl®) and nondegradable (Mersilk®) sutures with the aim to develop Bioglass® coated polymer fibers for wound healing and tissue engineering scaffold applications. First, the aqueous phase of a Bioglass® particle slurry was replaced with a poly(D,L -lactic acid) (PDLLA) polymer dissolved in solvent dimethyle carbonate (DMC) to act as third phase. SEM observations indicated that this alteration significantly improved the homogeneity of the coatings. Second, a new coating strategy involving two steps was developed: the sutures were first coated with a Bioglass®,PDLLA composite film followed by a second PDLLA coating. This two-step process of coating has addressed the problem of poor adherence of Bioglass® particles on suture surfaces. The coated sutures were knotted to determine qualitatively the mechanical integrity of the coatings. The results indicated that adhesion strength of coatings obtained by the two-step method was remarkably enhanced. A comparative assessment of the bioactivity of one-step and two-step produced coatings was carried out in vitro using acellular simulated body fluid (SBF) for up to 28 days. Coatings produced by the two-step process were found to have similar bioactivity as the one-step produced coatings. The novel Bioglass®/PDLLA/Vicryl® and Bioglass®/PDLLA/Mersilk® composite sutures are promising bioactive materials for wound healing and tissue engineering applications. © 2005 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2006 [source] Indicators of leadership development in undergraduate military educationJOURNAL OF LEADERSHIP STUDIES, Issue 2 2010Rebecca S. Shepherd Despite the reputation of service academies and military colleges for producing leaders of character who serve as commissioned officers in America's armed forces, little is known about the actual effects these institutions have on the leadership development of their students. A two-step process, this cross-sectional study sought to investigate leadership development through the lens of the leadership identity development model as measured by the aptitude for commission grade. From a review of the military leadership curriculum at American service academies and military colleges, the initial phase of research established that leadership development occurred. The second phase used quantitative methods and a cross-sectional design to investigate the effects of peer ranking, cumulative grade point average, leadership grades, and varsity athletic participation on leadership development throughout four years of undergraduate education. Findings indicated that company ranking by peers was significant regardless of gender or ethnicity. Mixed significant findings resulted for grade point average, leadership grades, and varsity athletic participation when based on gender and self-identified minority status. [source] Latices of poly(fluoroalkyl mathacrylate)- b -poly(butyl methacrylate) copolymers prepared via reversible addition,fragmentation chain transfer polymerizationJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 3 2007Xiaodong Zhou Abstract Poly(fluoroalkyl mathacrylate)- block -poly(butyl methacrylate) diblock copolymer latices were synthesized by a two-step process. In the first step, a homopolymer end-capped with a dithiobenzoyl group [poly(fluoroalkyl mathacrylate) (PFAMA) or poly(butyl methacrylate) (PBMA)] was prepared in bulk via reversible addition,fragmentation chain transfer (RAFT) polymerization with 2-cyanoprop-2-yl dithiobenzoate as a RAFT agent. In the second step, the homopolymer chain-transfer agent (macro-CTA) was dissolved in the second monomer, mixed with a water phase containing a surfactant, and then ultrasonicated to form a miniemulsion. Subsequently, the RAFT-mediated miniemulsion polymerization of the second monomer (butyl methacrylate or fluoroalkyl mathacrylate) was carried out in the presence of the first block macro-CTA. The influence of the polymerization sequence of the two kinds of monomers on the colloidal stability and molecular weight distribution was investigated. Gel permeation chromatography analyses and particle size results indicated that using the PFAMA macro-CTA as the first block was better than using the PBMA RAFT agent with respect to the colloidal stability and the narrow molecular weight distribution of the F-copolymer latices. The F-copolymers were characterized with 1H NMR, 19F NMR, and Fourier transform infrared spectroscopy. Comparing the contact angle of a water droplet on a thin film formed by the fluorinated copolymer with that of PBMA, we found that for the diblock copolymers containing a fluorinated block, the surface energy decreased greatly, and the hydrophobicity increased. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 471,484, 2007 [source] Synthesis and properties of novel polyimides derived from 2,2,,3,3,-benzophenonetetracarboxylic dianhydrideJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 9 2004Xing-Zhong Fang Abstract A new synthetic route to 2,2,,3,3,-BTDA (where BTDA is benzophenonetetracarboxylic dianhydride), an isomer of 2,3,,3,,4,-BTDA and 3,3,,4,4,-BTDA, is described. Single-crystal X-ray diffraction analysis of 2,2,,3,3,-BTDA has shown that this dianhydride has a bent and noncoplanar structure. The polymerizations of 2,2,,3,3,-BTDA with 4,4,-oxydianiline (ODA) and 4,4,-bis(4-aminophenoxy)benzene (TPEQ) have been investigated with a conventional two-step process. A trend of cyclic oligomers forming in the reaction of 2,2,,3,3,-BTDA and ODA has been found and characterized with IR, NMR, matrix-assisted laser desorption/ionization time-of-flight mass spectrometry, and elemental analyses. Films based on 2,2,,3,3,-BTDA/TPEQ can only be obtained from corresponding polyimide (PI) solutions prepared by chemical imidization because those from their polyamic acids by thermal imidization are brittle. PIs from 2,2,,3,3,-BTDA have lower inherent viscosities and worse thermal and mechanical properties than the corresponding 2,3,,3,,4,-BTDA- and 3,3,,4,4,-BTDA-based PIs. PIs from 2,2,,3,3,-BTDA and 2,3,,3,,4,-BTDA are amorphous, whereas those from 3,3,,4,4,-BTDA have some crystallinity, according to wide-angle X-ray diffraction. Furthermore, PIs from 2,2,,3,3,-BTDA have better solubility, higher glass-transition temperatures, and higher melt viscosity than those from 2,3,,3,,4,-BTDA and 3,3,,4,4,-BTDA. Model compounds have been prepared to explain the order of the glass-transition temperatures found in the isomeric PI series. The isomer effects on the PI properties are discussed. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2130,2144, 2004 [source] Copper-mediated radical polymerization on a microcellular monolith surfaceJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 5 2004Laurence Moine Abstract High-capacity microcellular monoliths were prepared by a two-step process, including the synthesis of a bromoester-functionalized scaffold by the copolymerization of a highly concentrated emulsion and an in situ surface polymerization of methyl methacrylate with atom transfer radical polymerization. The influence of various parameters, such as the feed ratio, the concentration of immobilized bromoester groups, and the presence of a spacer group on the poly(methyl methacrylate) loading, was studied. Monoliths with capacities of up to 7 mmol g,1 were obtained. Thermogravimetric analyses, scanning electron microscopy experiments, and mercury intrusion porosimetry measurements were used for the characterization of the final materials. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1216,1226, 2004 [source] Synthesis and thermal behavior of poly(ethylene oxide) poly(N-substituted urethane)JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 23 2001Jung-Ohk Kweon Abstract Poly(N-substituted urethane)s with an alkyl or ligo(ethylene oxide) monomethyl ether side chain were synthesized by the reaction operating in the following two-step process: first, by metalation of the starting polymer with potassium tertiary butoxide (t -BuOK) and then by treatment of the obtained urethane polyanion with tosylate in dimethyl sulfoxide. The thermal properties of poly(ethylene oxide) poly(N-substituted urethane) (N-sub PEOPU) were investigated in view of the N-substitution degree and properties of the substituent. The chemical structures were characterized by Fourier transform infrared, 1H NMR, and 13C NMR spectroscopies. DSC and thermogravimetric analysis (TGA) were used to investigate the thermal properties of N-sub PEOPUs. As the degree of N-methylation increased, the glass-transition temperature (Tg) of the N-sub PEOPUs linearly decreased from 6 to ,29 °C, and the weight-loss temperature of 5% (T) from TGA in air increased from 278 to 360 °C. In the fully N-substituted PEOPUs, the behavior of the thermal decomposition of the PEOPU that was processed in two stages was changed to one-step decomposition in the temperature range of 360,440 °C. The Tg was shifted to a lower temperature with an increasing length of the substituent in N-sub PEOPU. Improvement of the thermal stability by N-substitution was more significant in N-alkyl PEOPU than in N-ethoxylate PEOPU. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 4129,4138, 2001 [source] Synthesis and Characterization of Magnetic NanocontainersJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 4 2008Christos Tapeinos Magnetic hollow spheres were synthesized through a two-step process and were evaluated by Fourier transform infrared spectroscopy, scanning electron microscopy, super quantum interference device, vibrating sample magnetometry and Mössbauer spectroscopy methods. First, polystyrene spheres (PS) were produced using emulsion polymerization. Second, the PS spheres were coated via the sol,gel method to form an iron oxide layer. The size of the PS spheres was controlled by the concentration of the monomer (styrene), the initiator (potassium persulfate), and the emulsifier (sodium dodecylsulfate). The sol,gel coatings were prepared by controlled hydrolysis of aqueous solutions of FeCl3 in the presence of PS latex, polyvinylpyrrolidone, and hydrochloric acid. The composite was treated in air to burn off the PS latex. Temperature treatments were optimized after extensive differential thermal analysis and thermo gravimetric analysis characterization of the samples. Treatments under hydrogen atmosphere at various temperatures gave control over the formation and extend of magnetic phases in the nanocontainers such as a Fe, hematite (Fe2O3), and magnetite (Fe3O4). The size of the containers ranged between 300 and 400 nm. [source] Transformation Mechanism of the Dehydration of DiasporeJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 4 2003Lars Löffler The dehydration of diaspore to corundum was investigated by means of X-ray powder diffraction at reaction temperatures (400° and 600°C) as well as by transmission electron microscopy (TEM). The TEM studies were performed at the reaction interface of partially dehydrated natural diaspore crystals. The corundum produced consisted of thin dense regions which were separated by nanometer-sized pores forming lamellae with a periodicity of 3.7 nm. At the reaction front a transition phase (D,) could be detected in electron diffraction patterns. The phase D, is isotypic to diaspore, but with a larger spacing of the close-packed (100) oxygen planes (aD, from 0.475 to 0.480 nm). The expansion with respect to diaspore is explained by breaking of the hydrogen bonds of diaspore, considered to be the initial step of the transformation. The spacing of the lamellar pore system in corundum is explained by the misfit of the (100) planes of D, and the (0003) planes of corundum. We conclude that at well-fitting regions of the closed-packed planes at the D,/C interface, dense corundum is formed, while at misfitting regions, the formation of corundum is not favored and the pores are produced. Hence, the transformation of the solid phases takes place as a two-step process, i.e., D , D,, C. [source] Processability and characterization of poly(vinyl chloride)- b -poly(n -butyl acrylate)- b -poly(vinyl chloride) prepared by living radical polymerization of vinyl chloride.JOURNAL OF VINYL & ADDITIVE TECHNOLOGY, Issue 4 2006Comparison with a flexible commercial resin formulation prepared with PVC, dioctyl phthalate This work reports the synthesis and processing of a new flexible material based on PVC produced by living radical polymerization. The synthesis was carried out in a two-step process. In the first step the macroinitiator ,, ,-di(iodo)poly(butyl acrylate) [,, ,-di(iodo)PBA] was synthesized in water by single electron transfer/degenerative chain transfer mediated living radical polymerization (SET-DTLRP) catalyzed by Na2S2O4. In the second step this macroinitiator was reinitiated by SET-DTLRP of vinyl chloride (VC), thereby leading to the formation of the block copolymer poly(vinyl chloride)- b -poly(butyl acrylate)- b -poly(vinyl chloride) [PVC- b -PBA- b -PVC]. This new material was processed on a laboratory scale. The DMTA traces showed only a single glass transition temperature, thus indicating that no phase segregation was present. The copolymers were studied with regard to their processing, miscibility, and mechanical properties. The first comparison with commercial formulations made with PVC and dioctyl phthalate (DOP) is presented. J. VINYL ADDIT. TECHNOL., 12:156,165, 2006. © 2006 Society of Plastics Engineers [source] Influence of Reactice Processing on the Properties of PP/Glass Fiber Composites Compatibilized with SilaneMACROMOLECULAR MATERIALS & ENGINEERING, Issue 4 2006Afonso H. O. Felix Abstract Summary: Composites of PP reinforced with 20 wt.-% of short glass fibers were prepared by extrusion using VTES as a coupling agent. The addition of VTES was performed via in-situ functionalization of PP and by a two-step process in which PP was functionalized before the composite preparation. The obtained samples were characterized using rheometry, mechanical tests and microscopy. Both processes allowed the fiber/matrix interaction to increase. It was found that the VTES content affected the viscosity of the system by means of three different mechanisms: reduction of , -scission reactions, decrease of fiber sliding and plasticizing effect on the matrix. Whereas the first two mechanisms increased the viscosity of the final composite after unreacted VTES removal, the third one reduced the viscosity during the process and contributed to fiber-length preservation. The effects of VTES and peroxide contents on the Young's modulus were closely related to their effects on the final fiber length, indicating the effectiveness of using VTES as a coupling agent. Comparison between in-situ functionalization and the two-step process with prefunctionalization showed that in-situ functionalization led to a lower degree of chain breakage, even when it was performed in the presence of peroxide. Scanning electron micrographs of PP/glass fiber composite prepared without coupling agent. [source] Agrobacterium type IV secretion is a two-step process in which export substrates associate with the virulence protein VirJ in the periplasmMOLECULAR MICROBIOLOGY, Issue 5 2002Mario Pantoja Summary Type IV secretion systems are virulence determinants in many bacteria and share extensive homology with many conjugal transfer systems. Although type IV systems and their homologues have been studied widely, the mechanism by which substrates are secreted remains unclear. In Agrobacterium, we show that type IV secretion substrates that lack signal peptides form a soluble complex in the periplasm with the virulence protein VirJ. Additionally, these proteins co-precipitate with constituents of the type IV transporter: the VirB pilus and the VirD4 protein. Our findings suggest that the substrate proteins localized to the periplasm may associate with the pilus in a manner that is mediated by VirJ, and suggest a two-step process for type IV secretion in Agrobacterium. Our analyses of protein,protein interactions in a variety of mutant backgrounds indicate that substrates are probably secreted independently of one another. [source] Premotor Parkinson's disease: Clinical features and detection strategies,MOVEMENT DISORDERS, Issue S2 2009Randolph Stephenson MD Abstract In many areas of medicine, the focus has shifted from treating existing disease to screening and prevention. The technology to screen for Parkinson's disease (PD) already exists. The current challenge is to define the appropriate use of predictive testing for PD. Imaging technologies currently offer the highest degree of accuracy for identifying premotor PD, but they are expensive as screening tools. Efficiency is greatly enhanced by combining imaging with a prescreening test, such as olfactory testing. This two-step process has the potential to greatly reduce costs while retaining diagnostic accuracy. Ultimately, the role of preclinical detection of PD will be determined by the ability of emerging therapies to influence clinical outcomes. As such, implementation of large-scale screening strategies awaits the arrival of clearly safe and effective therapies that address the underlying pathogenesis of PD. Current research to evaluate efficient screening methods and to understand the clinical and physiological features of "premotor" PD will lay the foundation for the screening and prevention strategies of the future. © 2008 Movement Disorder Society [source] TEM characterization of VLS-grown ZnTe nanowiresPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 12 2008H. Kirmse Abstract ZnTe nanowires were grown via a vapour-liquid-solid pro- cess. Nano-sized droplets of a gold-based eutectic act as catalysts. The comprehensive transmission electron microscopy studies reveal that the nanowires are single crystals with numerous stacking faults and twins. The dimension of the wires is several micrometers in length and a few tens of nanometers in diameter. At the sidewall of the nanowires additional nanocrystals of ZnO embedded in an amorphous layer are identified. The formation process of the nanowires can be understood as a two-step process. The first step is the one-dimensional growth along the wire axis by consuming all the material deposited near the droplet. In a second step, facets are formed due to lateral growth of the nanowire. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | ||||||||||||||||||||||