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Assembly Process (assembly + process)
Selected AbstractsA Nanoparticle Convective Directed Assembly Process for the Fabrication of Periodic Surface Enhanced Raman Spectroscopy SubstratesADVANCED MATERIALS, Issue 38 2010V. Liberman A highly scalable approach for producing surface-enhanced Raman spectroscopy substrates is introduced. The novel method involves assembling individual nanoparticles in pre-defined templates, one particle per template, forming a high denisity of nanogaps over large areas, while decoupling nanostructure synthesis from placement. [source] A Novel In situ Recognition of Misalignment between Mating Parts in Robotic Assembly ProcessesJOURNAL OF FIELD ROBOTICS (FORMERLY JOURNAL OF ROBOTIC SYSTEMS), Issue 11 2002W. S. Kim A visual sensing system is utilized mainly to estimate the misalignment between mating parts, the recognition of which is the integral part of any assembly process. The recognition, however, requires the information on the state of the misalignment that includes the shapes of parts in mating motion and instantaneous relative position and angular orientation between mating parts. Normally, this information has been given in advance by an operator to facilitate assembly action. Therefore, in order to recognize the assembly state in sequence without intervention of an operator, it requires an effective sensing system and algorithm capable of working well even without a priori information on part shape and location. In this paper, we propose a novel system that can assemble parts under such uncertain environments. The system, composed of an omnidirectional sensing module and a recognition module, is capable of acquiring information on the sequential state of parts assembly motion from which instantaneous, relative location and orientation between the mating parts can be determined. Since the system does not utilize a priori knowledge on the shape of mating parts, it greatly reduces the degree of human intervention, thus increasing autonomy and flexibility. To evaluate the performance of the proposed system, a series of assembly experiments are performed. The results show that the proposed system, indeed, demonstrates effectiveness of vision guided assembly action. © 2002 Wiley Periodicals, Inc. [source] Flow-Guided Assembly ProcessesCHEMPHYSCHEM, Issue 7 2008Shengnian Wang Dr. Abstract This Concept article focuses on capillary, hydrodynamics and electrokinetic flow-guided assembly processes that can produce patterned or gradient functional surfaces either on solid surfaces or in deep micro- and nanoscale channels. This concept has the potential to produce low-cost nanostructures, internal surface modifications, and devices in nanomedicine. [source] Titelbild: Dynamers at the Solid,Liquid Interface: Controlling the Reversible Assembly/Reassembly Process between Two Highly Ordered Supramolecular Guanine Motifs (Angew. Chem.ANGEWANDTE CHEMIE, Issue 11 201011/2010) Dynamere in Aktion können mit geeigneten supramolekularen Architekturen an Grenzflächen beobachtet werden. In der Zuschrift auf S.,2007,ff. beschreiben G.,P. Spada, P. Samorì et,al. den Einsatz der Rastertunnelmikroskopie, um die metallvermittelte reversible Anordnung/Neuanordnung von N9 -Alkylguaninmonoschichten auf der submolekularen Ebene zu visualisieren. Durch pH-Wert-Änderung werden an der Graphit-Lösungs-Grenzfläche hoch geordnete Quartett- in bandartige Architekturen überführt. [source] Dynamers at the Solid,Liquid Interface: Controlling the Reversible Assembly/Reassembly Process between Two Highly Ordered Supramolecular Guanine Motifs,ANGEWANDTE CHEMIE, Issue 11 2010Artur Ciesielski Band oder Quartett: Die Zugabe von [2.2.2]Cryptand, Kaliumpicrat (K+(pic),) und Trifluormethansulfonsäure löst eine dynamische Neuanordnung in Octadecylguanin(G)-Monoschichten aus. Die gebildeten Strukturen, die zwischen einem H-Brücken-gebundenen G-Band und einem G-Quartett alternieren, wurden an einer Graphit-flüssig-Grenzfläche mit STM verfolgt (siehe Bild). [source] Automatic Palletizing of Concrete Pavement Blocks: An Algorithm for Near-Optimal AssemblyCOMPUTER-AIDED CIVIL AND INFRASTRUCTURE ENGINEERING, Issue 3 2001Shraga Shoval Palletizing concrete pavement blocks is a labor-intensive task that requires high levels of workmanship, skill, and concentration. This article proposes an automatic system in which palettes with required design patterns are assembled automatically off-site and then shipped to the construction site. The efficiency of the assembly process can be improved by incorporating automatic equipment consisting of assembly heads and feeders. An algorithm was developed to determine the optimal layout of the feeders (of different blocks) around the palette and the exact assembly sequence of each layer of blocks. Experimental results show that the algorithm is near optimal and that the solutions provided by it reduce palletizing cycle time for various patterns and sizes of concrete block by 20 to 30 percent. [source] NMR of peptides and proteins in oriented membranesCONCEPTS IN MAGNETIC RESONANCE, Issue 3 2002Francesca M. Marassi Abstract Solid-state NMR spectroscopy is used to determine the structures of membrane peptides and proteins in lipid bilayers. The methodology for membrane protein structure determination using solid-state NMR of oriented lipid bilayer samples is outlined. Recent developments in recombinant bacterial expression systems for the preparation of isotopically labeled membrane proteins, pulse sequences for high-resolution spectroscopy, and structural indices that guide the structure assembly process greatly extend the capabilities of the technique. © 2002 Wiley Periodicals, Inc. Concepts in Magn Reson 14, 212,224, 2002. [source] A FAK/Src chimera with gain-of-function properties promotes formation of large peripheral adhesions associated with dynamic actin assemblyCYTOSKELETON, Issue 1 2008Priscila M. F. Siesser Abstract Formation of a complex between the tyrosine kinases FAK and Src is a key integrin-mediated signaling event implicated in cell motility, survival, and proliferation. Past studies indicate that FAK functions in the complex primarily as a "scaffold," acting to recruit and activate Src within cell/matrix adhesions. To study the cellular impact of FAK-associated Src signaling we developed a novel gain-of-function approach that involves expressing a chimeric protein with the FAK kinase domain replaced by the Src kinase domain. This FAK/Src chimera is subject to adhesion-dependent activation and promotes tyrosine phosphorylation of p130Cas and paxillin to higher steady-state levels than is achieved by wild-type FAK. When expressed in FAK ,/, mouse embryo fibroblasts, the FAK/Src chimera resulted in a striking cellular phenotype characterized by unusual large peripheral adhesions, enhanced adhesive strength, and greatly reduced motility. Live cell imaging of the chimera-expressing FAK ,/, cells provided evidence that the large peripheral adhesions are associated with a dynamic actin assembly process that is sensitive to a Src-selective inhibitor. These findings suggest that FAK-associated Src kinase activity has the capacity to promote adhesion integrity and actin assembly. Cell Motil. Cytoskeleton 2008. © 2007 Wiley-Liss, Inc. [source] The merging of community ecology and phylogenetic biologyECOLOGY LETTERS, Issue 7 2009Jeannine Cavender-Bares Abstract The increasing availability of phylogenetic data, computing power and informatics tools has facilitated a rapid expansion of studies that apply phylogenetic data and methods to community ecology. Several key areas are reviewed in which phylogenetic information helps to resolve long-standing controversies in community ecology, challenges previous assumptions, and opens new areas of investigation. In particular, studies in phylogenetic community ecology have helped to reveal the multitude of processes driving community assembly and have demonstrated the importance of evolution in the assembly process. Phylogenetic approaches have also increased understanding of the consequences of community interactions for speciation, adaptation and extinction. Finally, phylogenetic community structure and composition holds promise for predicting ecosystem processes and impacts of global change. Major challenges to advancing these areas remain. In particular, determining the extent to which ecologically relevant traits are phylogenetically conserved or convergent, and over what temporal scale, is critical to understanding the causes of community phylogenetic structure and its evolutionary and ecosystem consequences. Harnessing phylogenetic information to understand and forecast changes in diversity and dynamics of communities is a critical step in managing and restoring the Earth's biota in a time of rapid global change. [source] Species loss leads to community closureECOLOGY LETTERS, Issue 6 2000P. Lundberg Global extinction of a species is sadly irreversible. At a local scale, however, extinctions may be followed by re-invasion. We here show that this is not necessarily the case and that an ecological community may close its doors for re-invasion of species lost from it. Previous studies of how communities are assembled have shown that there may be rules for that process and that limitations are set to the order by which species are introduced and put together. Instead of focusing on the assembly process we randomly generated simple competitive model communities that were stable and allowed for two to 10 coexisting species. When a randomly selected single species was removed from the community, the cascading species loss was recorded and frequently the resulting community was more than halved. Cascading extinctions have previously been recorded, but we here show that the relative magnitude of the cascade is dependent on community size (and not only trophic structure) and that the reintroduction of the original species lost often is impossible. Hence, species loss does not simply leave a void potentially refilled, but permanently alters the entire community structure and consequently the adaptive landscape for potential re-invaders. [source] Intra- and inter-allelic ordering of T cell receptor , chain gene assemblyEUROPEAN JOURNAL OF IMMUNOLOGY, Issue 3 2005Bernard Khor Abstract Allelic exclusion at the TCR, locus mandates that gene assembly be regulated in a manner that permits feedback inhibition of further complete TCR, rearrangements upon pre-TCR expression. Here we show that assembly of TCR, chain genes from V,, D, and J, gene segments is intra-allelically ordered, proceeding primarily through DJ,, and not VD,, intermediates. This ensures that V, to DJ, rearrangement, which can be feedback inhibited, is the final step in the assembly process. A newly assembled VDJ, rearrangement must be tested to determine if it is in-frame before V, to DJ, rearrangement is permitted on the alternate allele. This inter-allelic ordering may occur through a general inefficiency of V, to DJ, rearrangement and/or through static differences in accessibility of the two TCR, alleles. However, we find that within the regulatory context of allelic exclusion, V, to DJ, rearrangement proceeds to completion on both alleles. Furthermore, all possible VDJ, rearrangements are not completed on one allele before V, to DJ, rearrangement is initiated on the alternate allele. Together, these data support a dynamic model of inter-allelic accessibility that permits the ordered and efficient assembly of complete variable region genes on both TCR, alleles during T cell development. [source] Biomimetic Self-Assembly of Tetrapeptides into Fibrillar Networks and OrganogelsEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 27 2008Sajid Iqbal Abstract The self-assembly features of a family of tetrapeptides with a silk-inspired structure are presented. An exhaustive study of the influence of the terminal alkyl chain length in this process is undertaken. Scanning electron microscopy (SEM), wide-angle X-ray diffraction (WAXD), FTIR spectroscopy, and circular dichroism were used for structural analysis. These compounds, as in the natural model, self-assemble into antiparallel ,-sheet structures that further organize to form fibrillar aggregates. Furthermore, some of them arecapable of forming a crowded network that entraps thesolvent leading to physical gels with different microscopic morphologies. A model for the assembly process is proposed.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] Full-length prion protein aggregates to amyloid fibrils and spherical particles by distinct pathwaysFEBS JOURNAL, Issue 9 2008Driss El Moustaine As limited structural information is available on prion protein (PrP) misfolding and aggregation, a causative link between the specific (supra)molecular structure of PrP and transmissible spongiform encephalopathies remains to be elucidated. In this study, high pressure was utilized, as an approach to perturb protein structure, to characterize different morphological and structural PrP aggregates. It was shown that full-length recombinant PrP undergoes ,-sheet aggregation on high-pressure-induced destabilization. By tuning the physicochemical conditions, the assembly process evolves through two distinct pathways leading to the irreversible formation of spherical particles or amyloid fibrils, respectively. When the PrP aggregation propensity is enhanced, high pressure induces the formation of a partially unfolded aggregated protein, AggHP, which relaxes at ambient pressure to form amorphous aggregates. The latter largely retain the native secondary structure. On prolonged incubation at high pressure, followed by depressurization, AggHP transforms to a monodisperse population of spherical particles of about 20 nm in diameter, characterized by an essentially ,-sheet secondary structure. When the PrP aggregation propensity is decreased, an oligomeric reaction intermediate, IHP, is formed under high pressure. After pressure release, IHP relaxes to the original native structure. However, on prolonged incubation at high pressure and subsequent depressurization, it transforms to amyloid fibrils. Structural evaluation, using optical spectroscopic methods, demonstrates that the conformation adopted by the subfibrillar oligomeric intermediate, IHP, constitutes a necessary prerequisite for the formation of amyloids. The use of high-pressure perturbation thus provides an insight into the molecular mechanism of the first stages of PrP misfolding into amyloids. [source] Identification and characterization of cytochrome bc1 subcomplexes in mitochondria from yeast with single and double deletions of genes encoding cytochrome bc1 subunitsFEBS JOURNAL, Issue 17 2007Vincenzo Zara We have examined the status of the cytochrome bc1 complex in mitochondrial membranes from yeast mutants in which genes for one or more of the cytochrome bc1 complex subunits were deleted. When membranes from wild-type yeast were resolved by native gel electrophoresis and analyzed by immunodecoration, the cytochrome bc1 complex was detected as a mixed population of enzymes, consisting of cytochrome bc1 dimers, and ternary complexes of cytochrome bc1 dimers associated with one and two copies of the cytochrome c oxidase complex. When membranes from the deletion mutants were resolved and analyzed, the cytochrome bc1 dimer was not associated with the cytochrome c oxidase complex in many of the mutant membranes, and membranes from some of the mutants contained a common set of cytochrome bc1 subcomplexes. When these subcomplexes were fractionated by SDS/PAGE and analyzed with subunit-specific antibodies, it was possible to recognize a subcomplex consisting of cytochrome b, subunit 7 and subunit 8 that is apparently associated with cytochrome c oxidase early in the assembly process, prior to acquisition of the remaining cytochrome bc1 subunits. It was also possible to identify a subcomplex consisting of subunit 9 and the Rieske protein, and two subcomplexes containing cytochrome c1 associated with core protein 1 and core protein 2, respectively. The analysis of all the cytochrome bc1 subcomplexes with monospecific antibodies directed against Bcs1p revealed that this chaperone protein is involved in a late stage of cytochrome bc1 complex assembly. [source] Identification of phospholipids as new components that assist in the in vitro trimerization of a bacterial pore proteinFEBS JOURNAL, Issue 3 2001Hans De Cock The in vitro trimerization of folded monomers of the bacterial pore protein PhoE, into its native-like, heat- and SDS-stable form requires incubations with isolated cell envelopes and Triton X-100. The possibility that membranes could be isolated that are enriched in assembly factors required for assembly of the pore protein was now investigated. Fractionation of total cell envelopes of Escherichia coli via various techniques indeed revealed the existence of membrane fractions with different capacities to support assembly in vitro. Fractions containing mainly inner membrane vesicles supported the formation of trimers that were associated with these membrane vesicles. However, only a proportion of these trimers were heat- and SDS-stable and these were formed with slow kinetics. In contrast, fractions containing mainly outer membrane vesicles supported formation of high amounts of heat-stable trimers with fast kinetics. We identified phospholipids as active assembly components in these membranes that support trimerization of folded monomers in a process with similar characteristics as observed with inner membrane vesicles. Furthermore, phospholipids strongly stimulate the kinetics of trimerization and increase the final yield of heat-stable trimers in the context of outer membranes. We propose that lipopolysaccharides stabilize the assembly competent state of folded monomers as a lipochaperone. Phospholipids are involved in converting the folded monomer into new assembly competent intermediate with a short half-life that will form heat-stable trimers most efficiently in the context of outer membrane vesicles. These results provide biochemical evidence for the involvement of different lipidic components at distinct stages of the porin assembly process. [source] Assembly of Gold Nanoparticles in a Rod-Like Fashion Using Proteins as Templates,ADVANCED FUNCTIONAL MATERIALS, Issue 3 2006R. Bhattacharya Abstract An area of considerable current interest is the development of a practical approach for assembling inorganic nanoparticles into well-defined arrays because such a technique would offer immense opportunities leading to applications in microimaging, optoelectronics, therapeutics, etc. This paper illustrates a new, simple one-step process in which proteins act as templates to assemble gold nanoparticles in a shape-selective fashion. We show, for the first time, that antibodies to vascular endothelial growth factor 165 isoform, 2C3, and epidermal growth factor receptor can act as templates when present in solution during the synthesis of gold nanoparticles. These proteins direct the assembly of the gold nanoparticles into rod-like shapes when cooled to ,20,°C followed by thawing at room temperature. Immunoglobulin,G and bovine serum albumin can also direct the assembly process in a similar fashion; however, small molecules, such as poly(L -lysine) and lysine, cannot. The formation of a self-assembled structure in the form of a continuous rod, or the assembly of discrete nanoparticles in a rod-like fashion, can be tailored by controlling the ratio of the precursor gold salt, HAuCl4, to the antibody/protein used as the template. The nanoconjugates are characterized using UV-vis spectroscopy, transmission electron microscopy, and infrared spectroscopy. The nano-bioconjugates obtained via this process may find wide application in areas ranging from optoelectronics and biosensors to therapeutics in neoplastic disorders. [source] pH-Dependent Assembly of DNA,Gold Nanoparticles Based on the i-Motif: A Switchable Device with the Potential of a NanomachineHELVETICA CHIMICA ACTA, Issue 9 2006Frank Seela Abstract The pH-dependent self-assembling of gold nanoparticles is described. Oligonucleotides containing four or six consecutive dC residues are immobilized on 15-nm gold nanoparticles. Their assembly is based on the formation of a DNA i-motif as determined by the color change from red to blue between pH,5.5 and 6.5. The process occurs within a narrow pH range and is reversible. The i-motif is formed by the antiparallel intercalation of two parallel duplexes provided by two different gold nanoparticles. This assembly process can be utilized to generate novel systems for colorimetric sensing, applications in medical imaging and therapy, and for the construction of a proton-driven nanomachine. [source] Curving Nanostructures Using Extrinsic StressADVANCED MATERIALS, Issue 21 2010Jeong-Hyun Cho We demonstrate the concept of inducing stresses in thin films post-deposition (extrinsic stress) to curve nanostructures on demand. The remarkably high extrinsic stress, induced by triggering grain coalescence in Sn thin films, was used to self]assemble 3D nanostructures with radii of curvature as small as 20,nm. The fabrication methodology required only simple processing steps and the self]assembly process was highly parallel. Curved nanostructures with any desired pattern and both homogeneous (rings, tubes) and variable radii of curvature (spirals, talons) could be constructed. [source] Soft Langmuir,Blodgett Technique for Hard NanomaterialsADVANCED MATERIALS, Issue 29 2009Somobrata Acharya Abstract Materials and their assemblies of dimensions down to a few nanometers have attracted considerable scientific interest in physical, chemical, and biological sciences because of unique properties not available in their bulk counterparts. The Langmuir,Blodgett (LB) technique allows rigid nanomaterials to be aligned in particular structures through a flexible assembly process at liquid interfaces. In this review, we summarize the development of assembly of hard nanomaterials using soft LB techniques. An initial summary of the basic features of nanomaterials will include dimension-related effects, synthesis, characterization, and analysis, and will be followed by examples of LB assemblies of nanomaterials described according to their morphology: nanoparticles, nanorods, nanowires, nanotubes, and nanosheets. Some of the nanomaterials have been fabricated in orientation-controlled morphologies, and have been incorporated into prototype devices for gas sensing and photocurrent transport. In the final part of this review, the challenges remaining for LB techniques of hard nanomaterials will be overviewed, and will include a comparison with the widely-used LB technique involving soft materials. [source] Analysis of a late gene, orf101 from Helicoverpa armigera single nucleocapsid nucleopolyhedrovirusINSECT SCIENCE, Issue 5 2005SHI-HENG AN Abstract Helicoverpa armigera single nucleocapsid nucleopolyhedrovirus open reading frame 101 (ha101) is 762 nts in length and encodes a 254 amino acid peptide with predicted 29 kDa molecular weight. The homologues of ha101 were explored using BLASTP searching tool in the updated GenBank/EMBL and SWISS-PROT databases. The results showed that the homologues of ha101 were present in all the completely sequenced lepidopteran nucleopolyhedroviruses and granuloviruses, suggesting that ha101 might be a functional gene associated with their lepidopteran hosts. Sequence alignment of ha101 and its homologues revealed that 10 amino acids were completely conserved. RT-PCR analysis of ha101 manifested that the transcript of ha101 was first detected at 24 hpi and remained detectable at up to 122 hpi, suggesting that ha101 was transcribed during late stages of infection. Ha101 was expressed using Bac to Bac system in Tn5B-1-4 cells. The product of ha101 expressed in Tn5B-1-4 cells was approximately 29 kDa, consistent with the predicted molecular weight, and the results were confirmed by western blot analysis. The subcellular localization indicated that ha101 was aggregated along nuclear envelope during the early stages of infection and spread out to the entire nucleus including virogenic stroma in late stages of infection, suggesting that ha101 may play a specific role in virion assembly process or virogenic stroma arrangement. [source] Molecular mechanics in the context of the finite element methodINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 7 2009Jens Wackerfuß Abstract In molecular mechanics, the formalism of the finite element method can be exploited in order to analyze the behavior of atomic structures in a computationally efficient way. Based on the atom-related consideration of the atomic interactions, a direct correlation between the type of the underlying interatomic potential and the design of the related finite element is established. Each type of potential is represented by a specific finite element. A general formulation that unifies the various finite elements is proposed. Arbitrary diagonal- and cross-terms dependent on bond length, valence angle, dihedral angle, improper dihedral angle and inversion angle can also be considered. The finite elements are formulated in a geometrically exact setting; the related formulas are stated in detail. The mesh generation can be performed using well-known procedures typically used in molecular dynamics. Although adjacent elements overlap, a double counting of the element contributions (as a result of the assembly process) cannot occur a priori. As a consequence, the assembly process can be performed efficiently line by line. The presented formulation can easily be implemented in standard finite element codes; thus, already existing features (e.g. equation solver, visualization of the numerical results) can be employed. The formulation is applied to various interatomic potentials that are frequently used to describe the mechanical behavior of carbon nanotubes. The effectiveness and robustness of this method are demonstrated by means of several numerical examples. Copyright © 2008 John Wiley & Sons, Ltd. [source] Directed Deposition of Nanoparticles Using Diblock Copolymer Templates,ADVANCED MATERIALS, Issue 3 2003M.J. Misner Nanoporous film generation from diblock copolymers has been used to direct the assembly of ligand-stabilized CdSe nanoparticles (see Figure). The number of particles forced into each pore is dependent on the concentration of the nanoparticles in solution. Further, the photoluminescence of the particles is maintained in the assembly process. [source] A Novel In situ Recognition of Misalignment between Mating Parts in Robotic Assembly ProcessesJOURNAL OF FIELD ROBOTICS (FORMERLY JOURNAL OF ROBOTIC SYSTEMS), Issue 11 2002W. S. Kim A visual sensing system is utilized mainly to estimate the misalignment between mating parts, the recognition of which is the integral part of any assembly process. The recognition, however, requires the information on the state of the misalignment that includes the shapes of parts in mating motion and instantaneous relative position and angular orientation between mating parts. Normally, this information has been given in advance by an operator to facilitate assembly action. Therefore, in order to recognize the assembly state in sequence without intervention of an operator, it requires an effective sensing system and algorithm capable of working well even without a priori information on part shape and location. In this paper, we propose a novel system that can assemble parts under such uncertain environments. The system, composed of an omnidirectional sensing module and a recognition module, is capable of acquiring information on the sequential state of parts assembly motion from which instantaneous, relative location and orientation between the mating parts can be determined. Since the system does not utilize a priori knowledge on the shape of mating parts, it greatly reduces the degree of human intervention, thus increasing autonomy and flexibility. To evaluate the performance of the proposed system, a series of assembly experiments are performed. The results show that the proposed system, indeed, demonstrates effectiveness of vision guided assembly action. © 2002 Wiley Periodicals, Inc. [source] High-pressure granulites in the Sanggan area, North China craton: metamorphic evolution, P,T paths and geotectonic significanceJOURNAL OF METAMORPHIC GEOLOGY, Issue 8 2002J. H. Guo Abstract High-pressure basic granulites are widely distributed as enclaves and sheet-like blocks in the Huaian TTG gneiss terrane in the Sanggan area of the Central Zone of the North China craton. Four stages of the metamorphic history have been recognised in mineral assemblages based on inclusion, exsolution and reaction textures integrated with garnet zonation patterns as revealed by compositional maps and compositional profiles. The P,T conditions for each metamorphic stage were obtained using thermodynamically and experimentally calibrated geothermobarometers. The low-Ca core of growth-zoned garnet, along with inclusion minerals, defines a prograde assemblage (M1) of garnet + clinopyroxene + plagioclase + quartz, yielding 700 °C and 10 kbar. The peak of metamorphism at about 750,870 °C and 11,14.5 kbar (M2) is defined by high-Ca domains in garnet interiors and inclusion minerals of clinopyroxene, plagioclase and quartz. Kelyphites or coronas of orthopyroxene + plagioclase ± magnetite around garnet porphyroblasts indicate garnet breakdown reactions (M3) at conditions around 770,830 °C and 8.5,10.5 kbar. Garnet exsolution lamellae in clinopyroxene and kelyphites of amphibole + plagioclase around garnet formed during the cooling process at about 500,650 °C and 5.5,8 kbar (M4). These results help define a sequential P,T path containing prograde, near-isothermal decompression (ITD) and near-isobaric cooling (IBC) stages. The clockwise hybrid ITD and IBC P,T paths of the HP granulites in the Sanggan area imply a model of thickening followed by extension in a collisional environment. Furthermore, the relatively high-pressures (6,14.5 kbar) of the four metamorphic stages and the geometry of the P,T paths suggest that the HP granulites, together with their host Huaian TTG gneisses, represent the lower plate in a crust thickened during collision. The corresponding upper-plate might be the tectonically overlying Khondalite series, which was subjected to medium- to low-pressure (MP/LP: 7,4 kbar) granulite facies metamorphism with a clockwise P,T path including an ITD segment. Both the HP and the MP/LP granulite facies events occurred contemporaneously at c. 1.90,1.85 Ga in a collisional environment created by the assembly process of the North China craton. [source] Disc formation and the origin of clumpy galaxies at high redshiftMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY: LETTERS (ELECTRONIC), Issue 1 2009Oscar Agertz ABSTRACT Observations of high-redshift galaxies have revealed a multitude of large clumpy rapidly star-forming galaxies. Their formation scenario and their link to present-day spirals are still unknown. In this Letter, we perform adaptive mesh refinement simulations of disc formation in a cosmological context that are unrivalled in terms of mass and spatial resolution. We find that the so-called ,chain-galaxies' and ,clump-clusters' are a natural outcome of early epochs of enhanced gas accretion from cold dense streams as well as tidally and ram-pressured stripped material from minor mergers and satellites. Through interaction with the hot halo gas, this freshly accreted cold gas settles into a large disc-like system, not necessarily aligned to an older stellar component, that undergoes fragmentation and subsequent star formation, forming large clumps in the mass range 107,109 M,. Galaxy formation is a complex process at this important epoch when most of the central baryons are being acquired through a range of different mechanisms , we highlight that a rapid mass loading epoch is required to fuel the fragmentation taking place in the massive arms in the outskirts of extended discs, an accretion mode that occurs naturally in the hierarchical assembly process at early epochs. [source] Stepwise disassembly and apparent nonstepwise reassembly for the oligomeric RbsD proteinPROTEIN SCIENCE, Issue 6 2006Yongjun Feng Abstract Many cellular proteins exist as homo-oligomers. The mechanism of the assembly process of such proteins is still poorly understood. We have previously observed that Hsp16.3, a protein exhibiting chaperone-like activity, undergoes stepwise disassembly and nonstepwise reassembly. Here, the disassembly and reassembly of a nonchaperone protein RbsD, from Escherichia coli, was studied in vitro. The protein was found to mainly exist as decamers with a small portion of apparently larger oligomeric forms, both of which are able to refold/reassemble effectively in a spontaneous way after being completely unfolded. Disassembly RbsD intermediates including pentamers, tetramers, trimers, dimers, and monomers were detected by using urea-containing pore gradient polyacrylamide gel electrophoresis, while only pentamers were detected for its reassembly. The observation of stepwise disassembly and apparent nonstepwise reassembly for both a chaperone protein (Hsp16.3) and a nonchaperone protein (RbsD) strongly suggests that such a feature is most likely general for homo-oligomeric proteins. [source] Stellar archaeology: Exploring the Universe with metal-poor starsASTRONOMISCHE NACHRICHTEN, Issue 5 2010A. Frebel Abstract The abundance patterns of the most metal-poor stars in the Galactic halo and small dwarf galaxies provide us with a wealth of information about the early Universe. In particular, these old survivors allow us to study the nature of the first stars and supernovae, the relevant nucleosynthesis processes responsible for the formation and evolution of the elements, early star- and galaxy formation processes, as well as the assembly process of the stellar halo from dwarf galaxies a long time ago. This review presents the current state of the field of "stellar archaeology" , the diverse use of metal-poor stars to explore the high-redshift Universe and its constituents. In particular, the conditions for early star formation are discussed, how these ultimately led to a chemical evolution, and what the role of the most iron-poor stars is for learning about Population III supernovae yields. Rapid neutron-capture signatures found in metal-poor stars can be used to obtain stellar ages, but also to constrain this complex nucleosynthesis process with observational measurements. Moreover, chemical abundances of extremely metal-poor stars in different types of dwarf galaxies can be used to infer details on the formation scenario of the halo and the role of dwarf galaxies as Galactic building blocks. I conclude with an outlook as to where this field may be heading within the next decade. A table of ~ 1000 metal-poor stars and their abundances as collected from the literature is provided in electronic format (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Impact of physicochemical parameters on in vitro assembly and disassembly kinetics of recombinant triple-layered rotavirus-like particlesBIOTECHNOLOGY & BIOENGINEERING, Issue 4 2009Maria Candida M. Mellado Abstract Virus-like particles constitute potentially relevant vaccine candidates. Nevertheless, their behavior in vitro and assembly process needs to be understood in order to improve their yield and quality. In this study we aimed at addressing these issues and for that purpose triple- and double-layered rotavirus-like particles (TLP 2/6/7 and DLP 2/6, respectively) size and zeta potential were measured using dynamic light scattering at different physicochemical conditions, namely pH, ionic strength, and temperature. Both TLP and DLP were stable within a pH range of 3,7 and at 5,25°C. Aggregation occurred at 35,45°C and their disassembly became evident at 65°C. The isoelectric points of TLP and DLP were 3.0 and 3.8, respectively. In vitro kinetics of TLP disassembly was monitored. Ionic strength, temperature, and the chelating agent employed determined disassembly kinetics. Glycerol (10%) stabilized TLP by preventing its disassembly. Disassembled TLP was able to reassemble by dialysis at high calcium conditions. VP7 monomers were added to DLP in the presence of calcium to follow in vitro TLP assembly kinetics; its assembly rate being mostly affected by pH. Finally, DLP and TLP were found to coexist under certain conditions as determined from all reaction products analyzed by capillary electrophoresis. Overall, these results contribute to the design of new strategies for the improvement of TLP yield and quality by reducing the VP7 detachment from TLP. Biotechnol. Bioeng. 2009; 104: 674,686 © 2009 Wiley Periodicals, Inc. [source] A General Method for Constructing Optically Active Supramolecular Assemblies from Intrinsically Achiral Water-Insoluble Free-Base PorphyrinsCHEMISTRY - A EUROPEAN JOURNAL, Issue 6 2008Yiqun Zhang Abstract We have developed a general method to construct optically active porphyrin supramolecular assemblies by using a simple air,water interfacial assembly process. The method involved the in situ diprotonation of the free-base porphyrins at the air,water interface and subsequent assembly under compression. We showed that two intrinsically achiral water-insoluble free-base porphyrin derivatives, 2,3,7,8,12,13,17,18-octaethyl-21H,23H -porphine (H2OEP) and 5,10,15,20-tetra- p -tolyl-21H,23H -porphine (H2TPPMe), could be diprotonated when spread onto a 2.4,M hydrochloric acid solution surface, and the Langmuir,Schaefer (LS) films fabricated from the subphase exhibited strong circular dichroism (CD) absorption, whereas those fabricated from pure Milli-Q water subphase did not. The experimental data suggested that the helical stacking of the achiral porphyrin building blocks was responsible for the supramolecular chirality of the assemblies. Interestingly, such a method was successfully applied to a series of other intrinsically achiral free-base porphyrins such as 5,10,15,20-tetrakis(4-methoxyphenyl)-21H,23H -porphine (H2TPPOMe), 5,10,15,20-tetraphenyl-21H,23H -porphine (H2TPP), 5,10,15,20-tetrakis(4-(allyloxy)phenyl)-21H,23H -porphine (H2TPPOA), and 5,10,15,20-tetrakis(3,5-dimethoxyphenyl)-21H,23H -porphine (H2TPPDOMe). A possible mechanism has been proposed. The method provides a facile way to obtain optically active porphyrin supramolecular assemblies by using intrinsically achiral water-insoluble free-base porphyrin derivatives. [source] Two-Dimensional Self-Assembly of a Porphyrin,Polypyridyl Ruthenium(II) Hybrid on HOPG Surface through Metal,Ligand InteractionsCHEMPHYSCHEM, Issue 9 2010Aimei Gao Dr. Abstract The synthesis and self-assembly behavior of porphyrin,polypyridyl ruthenium(II) hybrid, which consists of a flexible alkyl chain attached with two conjugated moieties is described. The electronic absorption spectrum and emission spectra show that the [C8 -TPP-(ip)Ru(phen)2](ClO4)2, abbreviated as (C8ip)TPPC has optical properties. Scanning tunneling microscopy (STM) studies found that the ,,, interaction and metal,ligand interaction allow (C8ip)TPPC to form self-assembled structure and have an edge-on orientation on the highly oriented pyrolytic graphite (HOPG) surface. The multidentate structure in (C8ip)TPPC molecules act as linkers between the molecules and form metal,ligand coordination, which forces the assembly process in the direction of stable columnar arrays. In addition, although the sample was stored for two months in ambient conditions, STM experiments showed that the order of (C8ip)TPPC self-assembly only slightly decreased which indicates that the self-assembled monolayer is stable. This work demonstrates that introducing a metal-ligand in the porphyrin-polypyridyl compound is a useful strategy to obtain novel surface assemblies. [source] | |||||||||||||||||||||||||