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Modification Process (modification + process)
Selected AbstractsBroad Beam Ion Sources for Electrostatic Space Propulsion and Surface Modification Processes: From Roots to Present ApplicationsCONTRIBUTIONS TO PLASMA PHYSICS, Issue 7 2007H. Neumann Abstract Ion thrusters or broad beam ion sources are widely used in electrostatic space propulsion and in high-end surface modification processes. A short historical review of the roots of electric space propulsion is given. In the following, we introduce the electrostatic ion thrusters and broad beam ion sources based on different plasma excitation principles and describe the similarities as well as the differences briefly. Furthermore, an overview on source plasma and ion beam characterisation methods is presented. Apart from that, a beam profile modelling strategy with the help of numerical trajectory codes as basis for a special grid system design is outlined. This modelling represents the basis for the adaptation of a grid system for required technological demands. Examples of model validation demonstrate their reliability. One of the main challenges in improvement of ion beam technologies is the customisation of the ion beam properties, e.g. the ion current density profile for specific demands. Methods of an ex-situ and in-situ beam profile control will be demonstrated. Examples for the use of ion beam technologies in space and on earth , the RIT-10 rescue mission of ESA's satellite Artemis, the RIT-22 for BepiColombo mission and the deposition of multilayer stacks for EUVL (Extreme Ultra Violet Lithography) mask blank application are provided in order to illustrate the potential of plasma-based ion beam sources. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Water-Miscible Liquid Multiwalled Carbon NanotubesADVANCED MATERIALS, Issue 17 2009Maurizio Fagnoni Viscous, water-miscible, liquid multiwalled carbon nanotubes with an extraordinarily high degree of functionalization (hf-MWCNTs) have been obtained by means of a deep-sidewall modification process. The hf-MWCNTs behave as an ionic liquid, with a conductivity of 1,mS,cm,1 at 100,°C. The unique properties of this material render it suitable in a wide spectrum of applications, ranging from nanomedicine to energetics. [source] Covalently-linked hyaluronan promotes bone formation around Ti implants in a rabbit modelJOURNAL OF ORTHOPAEDIC RESEARCH, Issue 5 2009Marco Morra Abstract The goal of this study was the in vivo evaluation of nanoporous titanium (Ti) implants bearing a covalently linked surface hyaluronan (HA) layer. Implant surface topography and surface chemistry were previously evaluated by scanning electron micorscopy and X-ray photoelectron spectroscopy. Results showed that the surface modification process did not affect surface topography, yielding a homogeneously HA-coated nanotextured implant surface. In vivo evaluation of implants in both cortical and trabecular bone of rabbit femurs showed a significant improvement of both bone-to-implant contact and bone ingrowth at HA-bearing implant interfaces at 4 weeks. The improvement in osteointegration rate was particularly evident in the marrow-rich trabecular bone (bone-to-implant contact: control 22.5%; HA-coated 69.0%, p,<,0.01). Mechanical testing (push-out test) and evaluation of interfacial bone microhardness confirmed a faster bone maturation around HA-coated implants (Bone Maturation Index: control 79.1%; HA-coated 90.6%, p,<,0.05). Suggestions based on the biochemical role of HA are presented to account for the observed behavior. Published by Wiley Periodicals, Inc. J Orthop Res 27: 657,663, 2009 [source] Photostabilizing effect of some thermal stabilizers for poly(vinyl chloride) in the presence of fillerJOURNAL OF VINYL & ADDITIVE TECHNOLOGY, Issue 4 2009D. Braun The commercial stabilizers Ca-Zn stearate and dibutyltin- S,S,-di(isooctyl thioglycolate) have been investigated as photostabilizers for rigid poly(vinyl chloride) (PVC) in the presence of two types of CaCO3 as filler (natural and modified). The results reveal the costabilizing efficiency of CaCO3, especially the natural type, when it is used in concentrations of 1,30% by weight. The stabilizing efficiency of CaCO3 is indicated by the longer induction period and the lower rate of dehydrochlorination. The stabilizing effect of CaCO3 may be attributed because of its opacity and action as a screening agent by reflecting ultraviolet light, thereby hindering the penetration of the light into the polymer matrix. In addition, CaCO3 has the ability to absorb the HCl evolved during processing. The slight difference in the stabilizing effect of natural CaCO3 compared to that of the modified one can be attributed to the modification process, that may decrease the number of active sites on the surface of CaCO3, that in turn are responsible for the absorption of the evolved HCl. VINYL ADDIT. TECHNOL., 2009. © 2009 Society of Plastics Engineers [source] Continuous surface modification process with ultraviolet/ozone for improving interfacial adhesion of poly(ethylene terephthalate)/epoxy compositesPOLYMER COMPOSITES, Issue 5 2006Paisan Khanchaitit This study proposed a continuous UV/ozone surface modification process for the production of polymeric fiber-reinforced polymer composite. A gas phase photoreactor using the conventional low-pressure mercury UV lamps and the economically made ozone generators were designed and constructed. Poly(ethylene terephthalate) (PET) fibers and epoxy resin were chosen as a reinforcement and a matrix, respectively. The synergistic effects of UV and various gas species (nitrogen, air, oxygen, air/ozone, and oxygen/ozone) exposure as well as the effects of exposure time, i.e., 2, 5, and 10 min, on the morphology and chemistry of PET-fiber surfaces were investigated by using a scanning electron microscope coupled with energy dispersive x-ray analysis (SEM/EDX). The tensile testing and analysis of fractography of the resulted composites were performed to evaluate the effectiveness of the process. The SEM/EDX results showed that the effects of the treatment were dependent on both the concentration of reactive species present in the gases and the exposure time. The PET fibers treated under UV/O2 + O3 exposure for 5 min yielded the resulting composite with the highest tensile strength value. Under this condition, the tensile strength of the composite can be increased up to 63% in comparison with that of the untreated PET fiber/epoxy composite. The results are of interest for application as an in-line surface modification for composite productions. POLYM. COMPOS., 27:484,490, 2006. © 2006 Society of Plastics Engineers [source] Crystallization and preliminary X-ray diffraction analysis of the tRNA-modification enzyme GidA from Aquifex aeolicusACTA CRYSTALLOGRAPHICA SECTION F (ELECTRONIC), Issue 5 2009Takuo Osawa The 5-carboxymethylaminomethyl modification of uridine at the first position of the tRNA anticodon is crucial for accurate protein synthesis by stabilizing the correct codon,anticodon pairing on the ribosome. Two conserved enzymes, GidA and MnmE, are involved in this modification process. Aquifex aeolicus GidA was crystallized in two different crystal forms: forms I and II. These crystals diffracted to 3.2 and 2.3,Å resolution, respectively, using synchrotron radiation at the Photon Factory. These crystals belonged to space groups I212121 and P21 with unit-cell parameters a = 101.6, b = 213.3, c = 231.7,Å and a = 119.4, b = 98.0, c = 129.6,Å, , = 90.002°, respectively. The asymmetric units of these crystals are expected to contain two and four molecules, respectively. [source] Effects of citraconylation on enzymatic modification of human proinsulin using trypsin and carboxypeptidase BBIOTECHNOLOGY PROGRESS, Issue 4 2009Young-Jin Son Abstract Insulin is a polypeptide hormone which is produced by the ,-cell of pancreas and controls the blood glucose level in the human body. Enzymatic modification of human proinsulin using trypsin and carboxypeptidase B generally causes high accumulation of insulin derivatives, leading to more complicated purification processes. A simple method including citraconylation and decitraconylation in the enzymatic modification process was developed for the reduction of a major derivative, des-threonine human insulin. Addition of 3.0 g citraconic anhydride per g protein into the reaction solution led to the citraconylation of lysine residues in human proinsulin and reduction of relative des-threonine insulin content from 13.5 to 1.0%. After the enzymatic hydrolysis of the citraconylated proinsulin, 100% of lysine residues can be decitraconylated and restored by adjusting pH to 2,3 at 25 °C. Combination of hydrogen peroxide addition and citraconylation of proinsulin expressed in recombinant Escherichia coli remarkably improved the conversion yield of insulin from 52.7 to 77.7%. Consequently, citraconylation of lysine residues blocked the unexpected cleavage of human proinsulin by trypsin, minimized the formation of des-threonine insulin and hence increased the production yield of active insulin. © 2009 American Institute of Chemical Engineers Biotechnol. Prog., 2009 [source] Investigation of the Substrate Specificity of Lacticin 481 Synthetase by Using Nonproteinogenic Amino AcidsCHEMBIOCHEM, Issue 5 2009Matthew R. Levengood Abstract One enzyme, many substrates. The substrate specificity of a lantibiotic biosynthetic enzyme, lacticin 481 synthetase, was probed by using synthetic prepeptides containing a variety of nonproteinogenic amino acids, including unnatural ,-amino acids, ,-amino acids, D -amino acids, and peptoids. Lantibiotics are peptide antimicrobial compounds that are characterized by the thioether-bridged amino acids lanthionine and methyllanthionine. For lacticin 481, these structures are installed in a two-step post-translational modification process by a bifunctional enzyme, lacticin 481 synthetase (LctM). LctM catalyzes the dehydration of Ser and Thr residues to generate dehydroalanine or dehydrobutyrine, respectively, and the subsequent intramolecular regio- and stereospecific Michael-type addition of cysteines onto the dehydroamino acids. In this study, semisynthetic substrates containing nonproteinogenic amino acids were prepared by expressed protein ligation and [3+2]-cycloaddition of azide and alkyne-functionalized peptides. LctM demonstrated broad substrate specificity toward substrates containing ,-amino acids, D -amino acids, and N -alkyl amino acids (peptoids) in certain regions of its peptide substrate. These findings showcase its promise for use in lantibiotic and peptide-engineering applications, whereby nonproteinogenic amino acids might impart improved stability or modulated biological activities. Furthermore, LctM permitted the incorporation of an alkyne-containing amino acid that can be utilized for the site-selective modification of mature lantibiotics and used in target identification. [source] Study on Lead Dioxide Modified Electrode and Its Application in Detection of PhenolsCHINESE JOURNAL OF CHEMISTRY, Issue 2 2003Ai Shi-Yun Abstract The conditions for the preparation of PbO2 modified Pt rotation disc electrode in solutions containing HC104 and Pb(II) were studied, and the morphology and composition of the obtained PbO2 film were characterized by SEM and XRD techniques, respectively. The results show that the modification process of PbO is dependent on the rotation velocity of the electrode and the concentrations of HCIO4 and Pb(II). And it was observed that the obtained PbO2 film was rutile ,-PDO2 structure. At a certain positive potential, HO· and HO2· radicals can be generated on the surface of the modified PbO2/Pt electrode and then oxidize phenols. According to the change of the responding anodic current, the determination of phenols was realizable and good results were obtained. [source] Phylogeny and the modalities of acoustic diversification in extant Eneopterinae (Insecta, Orthoptera, Grylloidea, Eneopteridae)CLADISTICS, Issue 3 2004Tony Robillard Calling with a tegminal stridulatory apparatus is widespread in crickets. However, the evolution of cricket stridulums has been poorly studied and then only on the basis of prephylogenetic models, which are unable to account for the huge diversity recently documented for acoustic features in crickets. The present paper focuses on the evolution of acoustic devices in the subfamily Eneopterinae. This is the first attempt to reconstruct the phylogeny of a large and diverse cricket clade in order to analyze the evolution of emitting structures using precise homology statements. In the first step, we reconstruct the phylogeny of this clade using a morphological data set of 193 characters and 45 taxa. The resultant phylogeny supports the monophyly of the subfamily and that of the 13 genera represented by at least two species in our taxonomic sample. Phylogenetic relationships within the subfamily also support the definition of five tribes: Eurepini, Eneopterini, Nisitrini, Xenogryllini and Lebinthini. In the second step, the evolution of acoustic devices is studied by optimization of venation characters defined on precise homology statements. As hypothesized by previous authors, losses of acoustic communication occur independently in the course of eneopterine evolution; however, they happen abruptly with no intermediate state. Our results also document for the first time the modalities of forewing evolution: the diversification of male forewing venation originates from two processes, a continuous and regular modification process, responsible for slight venation change; and an irregular, more intense punctuated process, allowing the emergence of different venations. This diversification process with sudden changes could be related to the occurrence of acoustic novelties in advertisement calls. [source] Broad Beam Ion Sources for Electrostatic Space Propulsion and Surface Modification Processes: From Roots to Present ApplicationsCONTRIBUTIONS TO PLASMA PHYSICS, Issue 7 2007H. Neumann Abstract Ion thrusters or broad beam ion sources are widely used in electrostatic space propulsion and in high-end surface modification processes. A short historical review of the roots of electric space propulsion is given. In the following, we introduce the electrostatic ion thrusters and broad beam ion sources based on different plasma excitation principles and describe the similarities as well as the differences briefly. Furthermore, an overview on source plasma and ion beam characterisation methods is presented. Apart from that, a beam profile modelling strategy with the help of numerical trajectory codes as basis for a special grid system design is outlined. This modelling represents the basis for the adaptation of a grid system for required technological demands. Examples of model validation demonstrate their reliability. One of the main challenges in improvement of ion beam technologies is the customisation of the ion beam properties, e.g. the ion current density profile for specific demands. Methods of an ex-situ and in-situ beam profile control will be demonstrated. Examples for the use of ion beam technologies in space and on earth , the RIT-10 rescue mission of ESA's satellite Artemis, the RIT-22 for BepiColombo mission and the deposition of multilayer stacks for EUVL (Extreme Ultra Violet Lithography) mask blank application are provided in order to illustrate the potential of plasma-based ion beam sources. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Chemical modification of polyethersulfone nanofiltration membranes: A reviewJOURNAL OF APPLIED POLYMER SCIENCE, Issue 1 2009B. Van der Bruggen Abstract Polysulfone (PS) and poly(ether)sulfone (PES) are often used for synthesis of nanofiltration membranes, due to their chemical, thermal, and mechanical stability. The disadvantage for applying PS/PES is their high hydrophobicity, which increases membrane fouling. To optimize the performance of PS/PES nanofiltration membranes, membranes can be modified. An increase in membrane hydrophilicity is a good method to improve membrane performance. This article reviews chemical (and physicochemical) modification methods applied to increase the hydrophilicity of PS/PES nanofiltration membranes. Modification of poly(ether)sulfone membranes in view of increasing hydrophilicity can be carried out in several ways. Physical or chemical membrane modification processes after formation of the membrane create more hydrophilic surfaces. Such modification processes are (1) graft polymerization that chemically attaches hydrophilic monomers to the membrane surface; (2) plasma treatment, that introduces different functional groups to the membrane surface; and (3) physical preadsorption of hydrophilic components to the membrane surface. Surfactant modification, self-assembly of hydrophilic nanoparticles and membrane nitrification are also such membrane modification processes. Another approach is based on modification of polymers before membrane formation. This bulk modification implies the modification of membrane materials before membrane synthesis of the incorporation of hydrophilic additives in the membrane matrix during membrane synthesis. Sulfonation, carboxylation, and nitration are such techniques. To conclude, polymer blending also results in membranes with improved surface characteristics. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009 [source] Plasmabromination , the Selective Way to Monotype Functionalized Polymer SurfacesPLASMA PROCESSES AND POLYMERS, Issue 9 2007Sascha Wettmarshausen Abstract In contrast to other plasma modification processes of polymer surfaces, the bromination is very selective and shows a high yield in CBr groups. The most convenient bromination process was found using bromoform, which was thus preferred to elemental bromine, allyl bromide, vinyl bromide or tert -butylbromide. The bromoform process give yields in CBr up to 40 CBr or more, with only 2,3% co-introduction of O-functionalities whereas allyl bromide results in yields of about 20 CBr and more, but in more than 10% oxygen-containing by-products. CBr groups serve as anchoring points for grafting of molecules, oligomers and pre-polymers of diole or diamine character. [source] | ||||||||||||||||||||||||||||