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Several Cycles (several + cycle)
Selected AbstractsFailure of masonry arches under impulse base motionEARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 14 2007Laura De Lorenzis Abstract Recent seismic events have caused damage or collapse of invaluable historical buildings, further proving the vulnerability of unreinforced masonry (URM) structures to earthquakes. This study aims to understand failure of masonry arches,typical components of URM historic structures,subjected to horizontal ground acceleration impulses. An analytical model is developed to describe the dynamic behaviour of the arch and is used to predict the combinations of impulse magnitudes and durations which lead to its collapse. The model considers impact of the rigid blocks through several cycles of motion, illustrating that failure can occur at lower ground accelerations than previously believed. The resulting failure domains are of potential use for design and assessment purposes. Predictions of the analytical model are compared with results of numerical modelling by the distinct element method, and the good agreement between results validates the analytical model and at the same time confirms the potential of the distinct element framework as a method of evaluating complex URM structures under dynamic loading. Copyright © 2007 John Wiley & Sons, Ltd. [source] Lyonization pattern of normal human nailsGENES TO CELLS, Issue 5 2008Mariko Okada To examine the X-inactivation patterns of normal human nails, we performed the human androgen receptor gene assay of DNA samples extracted separately from each finger and toe nail plates of nine female volunteers. The X-inactivation pattern of each nail was unique and constant for at least 2 years. The frequency of nails with one of the two X-chromosomes exclusively inactivated was 25.9%. In the nails composed of two types of cells with either one X-chromosome inactivated, the two cell types were distributed in patchy mosaics. These findings suggest that the composition of precursor cells of each nail is maintained at each site at least through several cycles of regeneration time, and that the nail plate has a longitudinal band pattern, each band consisting of cells with only one of the two X-chromosomes inactivated. Using the frequency of nails with one of two X-chromosomes exclusively inactivated, we estimated the number of progenitor cells that gave rise to the nail plate during development to be about 3, under the assumption that the process follows the binominal distribution model. A strong correlation observed among the big, index and little fingers, and among the corresponding toes suggests an interesting interpretation concerning their morphogenetic process. [source] Silicon Inverse-Opal-Based Macroporous Materials as Negative Electrodes for Lithium Ion BatteriesADVANCED FUNCTIONAL MATERIALS, Issue 12 2009Alexei Esmanski Abstract Several types of silicon-based inverse-opal films are synthesized, characterized by a range of experimental techniques, and studied in terms of electrochemical performance. Amorphous silicon inverse opals are fabricated via chemical vapor deposition. Galvanostatic cycling demonstrates that these materials possess high capacities and reasonable capacity retentions. Amorphous silicon inverse opals perform unsatisfactorily at high rates due to the low conductivity of silicon. The conductivity of silicon inverse opals can be improved by their crystallization. Nanocrystalline silicon inverse opals demonstrate much better rate capabilities but the capacities fade to zero after several cycles. Silicon,carbon composite inverse-opal materials are synthesized by depositing a thin layer of carbon via pyrolysis of a sucrose-based precursor onto the silicon inverse opals. The amount of carbon deposited proves to be insufficient to stabilize the structures and silicon,carbon composites demonstrate unsatisfactory electrochemical behavior. Carbon inverse opals are coated with amorphous silicon producing another type of macroporous composite. These electrodes demonstrate significant improvement both in capacity retentions and in rate capabilities. The inner carbon matrix not only increases the material conductivity but also results in lower silicon pulverization during cycling. [source] Increasing the vertical resolution of conventional sub-bottom profilers by parametric equalizationGEOPHYSICAL PROSPECTING, Issue 2 2002P. Cobo ABSTRACT Vertical resolution, i.e. the ability to resolve two close reflectors, is a crucial aspect of pulses used in geo-acoustic exploration of sea sub-bottoms. This paper deals with the problem of exploring the shallowest unconsolidated layers of the seafloor with conventional piezo-electric sonar pulses. Such transducers do not have a sufficiently broad transmission response to enable them to radiate short high-resolution pulses. Therefore, some kind of equalization process must be applied to broaden the transmission response. Here, inverse filtering is used to calculate the transducer driving waveform so that the subsequent acoustic pulse has a zero-phase cosine-magnitude nature. Within a specified bandwidth, this pulse has minimum length, i.e. maximum resolution. The method has been applied to compress the acoustic pulses radiated by two piezo-electric transducers. In conventional performance, these transducers radiate narrowband pulses which contain several cycles at the natural resonance frequency. Under equalized driving, both transducers emit broadband pulses, with resolving power greatly increased, at the cost of some amplitude loss. That is, the pulses radiated by both transducers have been shortened from 1 ms (low-frequency transducer) and 0.274 ms (high-frequency transducer) in conventional performance to 0.13 ms and 0.038 ms in equalized mode, with amplitude losses of 33% and 56%, respectively. The great improvement in the resolution of this technique is demonstrated by comparing the synthetic echograms that should be obtained when exploring a wedge model using zero-phase cosine-magnitude pulses with conventional ping pulses. [source] Synthesis of Some Novel Thioxanthenone-Fused Azacrown Ethers, and Their Use as New Catalysts in the Efficient, Mild, and Regioselective Conversion of Epoxides to , -Hydroxy Thiocyanates with Ammonium ThiocyanateHELVETICA CHIMICA ACTA, Issue 7 2007Hashem Sharghi Abstract The regioselective ring-opening reactions of some epoxides with ammonium thiocyanate in the presence of a series of new 9H -thioxanthen-9-one-fused azacrown ethers, i.e., 7,11 (Scheme,1), and also of dibenzo[18]crown-6 (12), Kryptofix®22 (13), and benzo[15]crown-5 (14) were studied (Tables 1 and 2). The epoxides were subjected to cleavage by NH4SCN in the presence of these catalysts under mild conditions in various aprotic solvents. Reagents and conditions were identified for the synthesis of individual , -hydroxy thiocyanates in high yield and with more than 90% regioselectivity. The results can be discussed in terms of a four-step mechanism (Scheme,2): 1) formation of a complex between catalyst and NH4SCN, 2) release of SCN, from the complex, 3) reaction of the released SCN, at the sterically less hindered site of the epoxide, and 4) regeneration of the catalyst. The major advantages of this method are the high regioselectivity, the simple regeneration of the catalyst, the reuse of it through several cycles without a decrease of activity, and the ease of workup of the reaction mixtures. [source] Thermodynamic analysis of two-step solar water splitting with mixed iron oxidesINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 10 2009Martin Roeb Abstract A two-step thermochemical cycle for solar production of hydrogen from water has been developed and investigated. It is based on metal oxide redox pair systems, which can split water molecules by abstracting oxygen atoms and reversibly incorporating them into their lattice. After successful experimental demonstration of several cycles of alternating hydrogen and oxygen production, the present work describes a thermodynamic study aiming at the improvement of process conditions and at the evaluation of the theoretical potential of the process. In order to evaluate the maximum hydrogen production potential of a coating material, theoretical considerations based on thermodynamic laws and properties are useful and faster than actual tests. Through thermodynamic calculations it is possible to predict the theoretical maximum output of H2 from a specific redox-material under certain conditions. Calculations were focussed on the two mixed iron oxides nickel,iron-oxide and zinc,iron-oxide. In the simulation the amount of oxygen in the redox-material is calculated before and after the water-splitting step on the basis of laws of thermodynamics and available material properties for the chosen mixed iron oxides. For the simulation the commercial Software FactSage and available databases for the required material properties were used. The analysis showed that a maximum hydrogen yield is achieved if the reduction temperature is raised to the limits of the operation range, if the temperature for the water splitting is lowered below 800°C and if the partial pressure of oxygen during reduction is decreased to the lower limits of the operational range. The predicted effects of reduction temperature and partial pressure of oxygen could be confirmed in experimental studies. The increased hydrogen yield at lower splitting temperatures of about 800°C could not be confirmed in experimental results, where a higher splitting temperature led to a higher hydrogen yield. As a consequence it can be stated that kinetics must play an important role especially in the splitting step. Copyright © 2009 John Wiley & Sons, Ltd. [source] One-Pot Suzuki/Heck Sequence for the Synthesis of (E)-Stilbenes Featuring a Recyclable Silica-Supported Palladium Catalyst via a Multi-Component Reaction in 1,3-PropanediolADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 11-12 2010Lionel Joucla Abstract The synthesis of (E)-stilbenes was performed following a one-pot Suzuki/Heck sequence through the use of potassium vinyltrifluoroborate. The combination of heterogeneous palladium/silica (Pd/SiO2) catalyst with potassium phosphate monohydrate (K3PO4,H2O) as base resulted in useful to good isolated yields regardless of the ortho- , meta- or para- substitution of the aryl halides employed. In a sustainable approach, we found that bio-sourced 1,3-propanediol could advantageously replace N -methylpyrrolidone (NMP) as similar yields were obtained. Moreover, the reactivity gap between aryl iodides and bromides resulting from the use of 1,3-propanediol allowed an efficient multi-component approach toward the synthesis of (E)-stilbenes. Furthermore, this heterogeneous catalyst was found to be extremely robust despite the use of aerobic conditions and was successfully re-used over several cycles. [source] Reusable Copper-Aluminum Hydrotalcite/rac -BINOL System for Room Temperature Selective Aerobic Oxidation of AlcoholsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 16 2009M. Lakshmi Kantam Abstract An efficient catalyst system consisting of copper-aluminum hydrotalcite/rac- BINOL ligand has been developed for the oxidation of alcohols using air as a green oxidant at room temperature. Various alcohols could be transformed into their corresponding aldehydes or ketones in good to excellent yields using the set of optimal conditions. This composite catalytic system can also be recovered and reused for several cycles without a significant loss of catalytic activity. [source] Sorption of tannic acid on zirconium pillared clayJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 1 2002P Vinod Abstract Zirconium pillared clay (PILC) was prepared using montmorillonite as the base clay. Adsorption of tannic acid (tannin) was studied by a batch equilibrium technique, as a function of adsorbate concentration, temperature, pH, agitation speed, particle size of the adsorbent and ionic strength. The process of uptake is governed by diffusion controlled first-order reversible rate kinetics. The higher uptake for the pH range 4.0,6.0 was attributed to external hydrogen bonding between phenolic-OH groups of tannin molecules and the hydrogen bonding sites on the clay. The removal of tannin by adsorption was found to be >99.0% depending on the initial concentration in the pH range of 4.0,6.0. The process involves both film and pore diffusion to different extents. The effects of solute concentration, temperature, agitation speed and particle size on the diffusion rate were investigated. Tannin uptake was found to increase with ionic strength due to the compression of diffuse double layers. The applicability of Langmuir and Freundlich isotherm models has been tested. The maximum adsorption capacity of PILC was found to be 45.8,µmol,g,1 of clay and the affinity constant is 2.9,×,10,2,dm3,µmol,1 at 30,°C. Thermodynamic parameters such as ,G,°,,H,° and ,S,° were calculated to predict the nature of adsorption. The isosteric enthalpies of adsorption were also determined and found to decrease with increasing surface coverage. Regeneration with hot water (60,°C) has been investigated for several cycles with a view to recovering the adsorbed tannin and also restoring the sorbent to its original state. Copyright © 2001 Society of Chemical Industry [source] Complete replication of human cytomegalovirus in explants of first trimester human placentaJOURNAL OF MEDICAL VIROLOGY, Issue 4 2001Liliana Gabrielli Abstract Tissue integrity and viability of first trimester placenta explants were obtained in culture for 3 weeks. Explants were infected with human cytomegalovirus (HCMV), several cycles of HCMV replication were obtained and the progression of the infection was observed within a tissue that maintains its normal cellular organization. In agreement with recent clinical data, 3 weeks were necessary for the virus to colonize the placenta fully. Complete HCMV replication was observed in trophoblasts, followed by subsequent transmission of the infection to the stromal fibroblasts and fetal endothelial capillary cells. Viral DNA replication was monitored and the production of infectious viral progeny documented. J. Med. Virol. 64:499,504, 2001. © 2001 Wiley-Liss, Inc. [source] Perpetuation of subgingival biofilms in an in vitro modelMOLECULAR ORAL MICROBIOLOGY, Issue 1 2010L.M. Shaddox Summary This study evaluated the reproducibility of in-vitro -grown biofilms, initiated with subgingival plaque from patients with periodontal disease, and continued through several cycles by re-inoculating new biofilms from previously grown biofilms. Subgingival plaque samples from bleeding pockets along with saliva samples were collected from three patients with chronic periodontitis and perpetuated through seven cycles. Calcium hydroxyapatite disks were coated with sterilized saliva inoculated with dispersed subgingival plaque. The biofilms were grown anaerobically at 37°C for 10 days, and at specific intervals total viable bacteria were enumerated and the species present were analysed by DNA,DNA checkerboard hybridization. All cycles of biofilm growth occurred at similar rates and reached steady-state at day 7. No statistically or microbially significant differences were found for viable counts or species present, at the same period of maturation, among the different cycles. This study demonstrated that growth of certain target subgingival periodontal species in this biofilm model was reproducible and could be perpetuated in vitro through several cycles. The model could be useful in future studies to characterize different periodontopathogenic properties and biofilm interactions, especially in recolonization studies. [source] Development of the Insect Pathogenic Alga HelicosporidiumTHE JOURNAL OF EUKARYOTIC MICROBIOLOGY, Issue 3 2006VERENA-ULRIKE BLÄSKE-LIETZE ABSTRACT. This study examined the morphogenesis and replication dynamics of the different life stages (cysts, filamentous cells, vegetative cells) of Helicosporidium sp., a non-photosynthetic, entomopathogenic alga. The isolate (SjHe) used originated from an infected black fly larva. Filamentous cell transformation into vegetative cells and autosporulation during vegetative cell replication were observed under controlled in vitro conditions. The transformation process was initiated by a partial swelling of the filamentous cell along with the reorganization of the nuclear material. Two subsequent nuclear and cell divisions resulted in the release of 4 rod-shaped daughter cells, which divided into oval to spherical vegetative cells. These underwent several cycles of autosporogenic cell division. Multiple-passaged vegetative cell cultures formed non-motile, adherent cell clusters (palmelloid colonies). Vegetative replication dynamics were also observed in 2 experimental noctuid hosts, Spodoptera exigua and Helicoverpa zea. The average density of helicosporidial cells produced per microliter hemolymph exceeded cell concentrations obtained in vitro by 15- and 46-fold in S. exigua and H. zea, respectively. Cyst morphogenesis was only observed in the hemolymph, whereas no cysts differentiated at various in vitro conditions. [source] Performance of phased rotation, conformation and translation function: accurate protein model building with tripeptidic and tetrapeptidic fragmentsACTA CRYSTALLOGRAPHICA SECTION D, Issue 9 2010Franti, ek Pavel The automatic building of protein structures with tripeptidic and tetrapeptidic fragments was investigated. The oligopeptidic conformers were positioned in the electron-density map by a phased rotation, conformation and translation function and refined by a real-space refinement. The number of successfully located fragments lay within the interval 75,95% depending on the resolution and phase quality. The overlaps of partially located fragments were analyzed. The correctly positioned fragments were connected into chains. Chains formed in this way were extended directly into the electron density and a sequence was assigned. In the initial stage of the model building the number of located fragments was between 60% and 95%, but this number could be increased by several cycles of reciprocal-space refinement and automatic model rebuilding. A nearly complete structure can be obtained on the condition that the resolution is reasonable. Computer graphics will only be needed for a final check and small corrections. [source] Monopilegründungen von Offshore-Windenergieanlagen , Zum Ansatz der BettungBAUTECHNIK, Issue 1 2005Jürgen Grabe Univ.-Prof. Bei der Gründung von Offshore-Windenergieanlagen mit Monopiles stellt die große Momenten- und Horizontalkraftbelastung und deren zyklisches Auftreten eine besondere Herausforderung an die Prognose der Pfahlverformungen dar. Für ein System mit beispielhaften Abmessungen, Baugrundverhältnissen und Belastungen werden die konventionellen Verfahren zur Berechnung der horizontalen Pfahltragfähigkeit und -verformung, Bettungsmodulverfahren und API-Verfahren, mit den Ergebnissen einer 3D-FE-Analyse verglichen. Es zeigt sich, daß die konventionellen Verfahren für die Prognose der Verformungen im Gebrauchszustand, also deutlich unterhalb der Grenzlast, für dieses Beispiel unzureichend sind. Die Verteilung des Bettungsmoduls über die Tiefe wird mit keinem der Verfahren zutreffend abgebildet. Des weiteren wird die Veränderung des Bettungsmoduls über mehrere Zyklen für Schwell- und Wechselbelastungen untersucht. Vor allem bei einer Schwellast wird der auf den Ausgangszustand bezogene Bettungsmodul mit jedem Zyklus verändert. Die Verschiebung des Pfahlkopfs steigt auch nach 20 Belastungszyklen noch an. Der aus der ödometrischen Steifigkeit des Bodens abgeleitete Bettungsmodul ist zur Prognose der Pfahlverformungen insbesondere bei zyklischer Last fragwürdig. Hierfür besteht insbesondere in Anbetracht der geplanten Investitionen erheblicher Forschungsbedarf. Monopile foundations for Offshore-Wind Power Plants , approach of subgrade reaction. The large moments and horizontal forces and their cyclic occurrence represent a special challenge to the prognosis of the deformations of Monopiles as a foundation of offshore wind energy plants. The conventional procedures for the computation of the horizontal pile bearing capacity and deformation, subgrade reaction procedure and API procedure, are compared with the results of a 3D-FE analysis for a system with exemplary dimensions, soil conditions and loads. It is shown that the conventional procedures for the prognosis of the deformations in the serviceability limit state, thus clearly underneath the maximum load, for this example are insufficient. The distribution of the subgrade reaction modulus over the depth is sufficiently approximated with none of these procedures. Moreover the change of the subgrade reaction modulus is investigated for several cycles swelling and alternated loads. The modulus of subgrade reaction, referred to the initial pile position, changes especially under swelling loads for each loading cycle. The displacement of the pilehead still increases after 20 cycles. The modulus of subgrade reaction derived from the oedometric soil stiffness does not produce an accurate prognosis of the pile deformation particularly for cyclic loads. For this purpose further investigations are necessary. [source] Preparation of Bismuth Oxide Quantum Dots and their Photocatalytic Activity in a Homogeneous SystemCHEMCATCHEM, Issue 9 2010Prof. Hua Zhang Abstract Colloidal oil-soluble Bi2O3 quantum dots (QDs) are synthesized through an alcoholysis route in organic media. Water-soluble Bi2O3 QDs are then obtained from the initial oil-soluble QDs through phase transfer by surface modification with mercaptopropionic acid. X-ray diffraction and transmission electron microscopy studies show that the crystallinity is enhanced and particles grow larger after phase transfer. The water-soluble Bi2O3 QDs exhibit excellent photocatalytic activity for the degradation of methyl orange at a wide range of pH values. After several cycles, the Bi2O3 QDs retain high degradation efficiency. Simulation according to the first-order reaction dynamics indicates that the degradation reaction may follow complicated quasi-homogeneous photocatalysis. [source] | ||||||||||||||||