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Structural Forms (structural + form)
Selected AbstractsA method to determine direct- and quadrature-axis inductances of permanent magnet synchronous motorsELECTRICAL ENGINEERING IN JAPAN, Issue 3 2010Shu Yamamoto Abstract The equivalent circuit constants of permanent magnet synchronous motors are needed in the calculation of operation characteristics, construction of a control system, etc. These constants can be computed from the data on structural form and materials. However, measurements are necessary to obtain highly precise values. Methods for measurement of the d- and q-axis inductances can be roughly divided into rotational and standstill methods. The standstill methods have the advantage that they are easy to carry out. However, it is difficult to consider magnetic saturation and distortion of the change in the armature winding inductance. The accuracy of the standstill method can be improved if these effects can be readily taken into account. This paper describes a standstill method for measuring accurate d- and q-axis synchronous inductances of permanent magnet synchronous motors. By utilizing the fact that the EMF interference terms in the motor voltage equation considering the distortion of the inductance change are equal to zero when the rotor is in a specific position, the proposed method determines the inductances considering both magnetic saturation and inductance distortion effects from simple off-line standstill testing. In addition, this method is capable of taking cross-magnetic saturation into account when used with the necessary testing equipment. The proposed method was implemented on a 0.4-kW interior permanent magnet synchronous motor with concentrated stator winding. The validity of the proposed method was demonstrated by comparing the measured and calculated results of the no-load and on-load characteristics. © 2010 Wiley Periodicals, Inc. Electr Eng Jpn, 171(3): 41,50, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20969 [source] Soil-aggregate formation as influenced by clay content and organic-matter amendmentJOURNAL OF PLANT NUTRITION AND SOIL SCIENCE, Issue 1 2007Stephen Wagner Abstract Naturally occurring wetting-and-drying cycles often enhance aggregation and give rise to a stable soil structure. In comparatively dry regions, such as large areas of Australia, organic-matter (OM) contents in topsoils of arable land are usually small. Therefore, the effects of wetting and drying are almost solely reliant on the clay content. To investigate the relations between wetting-and-drying cycles, aggregation, clay content, and OM in the Australian environment, an experiment was set up to determine the relative influence of both clay content (23%, 31%, 34%, and 38%) and OM amendments of barley straw (equivalent to 3.1,t,ha,1, 6.2,t,ha,1, and 12.4,t,ha,1) on the development of water-stable aggregates in agricultural soil. The aggregate stability of each of the sixteen composite soils was determined after one, three, and six wet/dry cycles and subsequent fast and slow prewetting and was then compared to the aggregate stabilities of all other composite soils. While a single wet/dry cycle initiated soil structural evolution in all composite soils, enhancing macroaggregation, the incorporation of barley straw was most effective for the development of water-stable aggregates in those soils with 34% and 38% clay. Repeated wetting-and-drying events revealed that soil aggregation is primarily based on the clay content of the soil, but that large straw additions also tend to enhance soil aggregation. Relative to untreated soil, straw additions equivalent to 3.1,t,ha,1 and 12.4,t,ha,1 increased soil aggregation by about 100% and 250%, respectively, after three wet/dry cycles and fast prewetting, but were of less influence with subsequent wet/dry cycles. Straw additions were even more effective in aggregating soil when combined with slow prewetting; after three wet/dry cycles, the mean weight diameters of aggregates were increased by 70% and 140% with the same OM additions and by 160% and 290% after six wet/dry cycles, compared to samples without organic amendments. We suggest that in arable soils poor in OM and with a field texture grade of clay loam or finer, the addition of straw, which is often available from preceding crops, may be useful for improving aggregation. For a satisfactory degree of aggregate stability and an improved soil structural form, we found that straw additions of at least 6.2,t,ha,1 were required. However, rapid wetting of straw-amended soil will disrupt newly formed aggregates, and straw has only a limited ability to sustain structural improvement. [source] Double-helix structure in multiwall boron nitride nanotubesACTA CRYSTALLOGRAPHICA SECTION A, Issue 6 2005Ayten Celik-Aktas A new nanotube structural form is reported that resembles a double helix in multiwall boron nitride nanotubes (MW-BNNT) grown by a carbon-free chemical-vapor-deposition process as documented by evidence obtained by transmission electron diffraction and microscopy. The double-helix structure is found in MW-BNNTs exhibiting the same chirality in its different walls. The MW-BNNTs deviate from the structure of ideal nested coaxial cylindrical tubes. Most significantly, bright- and dark-field electron imaging reveals regular zigzag dark and bright spots on the side walls of the nanotubes. The repeating distance between the bright, or dark, spots is related to the chiral angle of the nanotube. Electron diffraction patterns recorded from individual nanotubes show additional diffraction spots belonging to the ,201, zone axes, which are not allowed in a perfectly cylindrical nanotube. These additional diffraction spots become asymmetrical as smaller sections of the nanotube are probed. A series of diffraction patterns recorded along the tube axis showed that the imperfections giving rise to these spots move in a regular fashion around the circumference of the tube. It is shown that all experimental evidence supports the structure model of two helices; one is polygonal in cross section and highly crystalline and the other is circular and less ordered. It is further suggested that the double-helix structure is a result of stronger wall,wall interactions associated with the ionic bonding in boron nitride. [source] Enhancing the natural defences and barrier protection of aquaculture speciesAQUACULTURE RESEARCH, Issue 3 2010John W Sweetman Abstract The promotion of nutritional strategies that optimize natural defence mechanisms in fish is of critical importance in producing robust juveniles and adult fish. These animals are more capable of minimizing the impact of opportunistic pathogen attack, thus improving liveability and performance characteristics. The importance of the piscine gastrointestinal tract as a major endocrine and osmoregulatory organ is well reported as is its function as a defensive barrier to pathogen attack. Investigations using the inclusion of a specific structural form of mannan oligosaccharide have been shown to improve the performance parameters, immune status, and gut morphology and improve an important aspect of barrier protection through the enhancement of mucal production in a number of aquaculture species. The selenium status of an animal is pivotal in determining the success of the innate and adaptive immune response of the animal, and the use of an organic selenium source, in the form of a selenoyeast, has been shown to improve enzyme function and tissue uptake. The antioxidant role of many of the selenoptroteins and the role of selenium in the glutathione peroxidase enzyme pathways involved in the control of oxidative stress is critical if oxidative damage and cell membrane lipid peroxidation are to be prevented. The use of these compounds as feed additives has important implications for health management in commercial aquaculture facilities. Further research is needed to evaluate the benefits offered by a range of commercial products. [source] A high-efficiency preparation, properties and structure of (R, S)-and (S, S)-pyrrolidine-2-carboxylic acid 3,5-dioxa-4-boracyclohepta [2,1- a; 3,4- a,] dinaphthalen-4-yl estersCHINESE JOURNAL OF CHEMISTRY, Issue 10 2003Zi-Xing Shan Abstract A highly-efficient preparative procedure for (R, S) and (S, S)-pyrrolidine-2-carboxylic acid 3,5-dioxa-4-boracyclohepta[2, 1- a; 3, 4- a] dinaphthalen-4-yl esters [namely (R, S)-BNBAP and (S, S)-BNBAP] is described and the crystal structure of (R, S)-BNBAP was obtained. The data indicate that (R, S)- BNBAP is a spirocyclic inner borate salt with almost normal tetrahedral configuration. This structural form may be the basic reason for their high chemical, optical and thermodynamic stability. [source] Sources for sedimentary bacteriohopanepolyols as revealed by 16S rDNA stratigraphyENVIRONMENTAL MICROBIOLOGY, Issue 7 2008Marco J. L. Coolen Summary Bacteriohopanoids are widespread lipid biomarkers in the sedimentary record. Many aerobic and anaerobic bacteria are potential sources of these lipids which sometimes complicates the use of these biomarkers as proxies for ecological and environmental changes. Therefore, we applied preserved 16S ribosomal RNA genes to identify likely Holocene biological sources of bacteriohopanepolyols (BHPs) in the sulfidic sediments of the permanently stratified postglacial Ace Lake, Antarctica. A suite of intact BHPs were identified, which revealed a variety of structural forms whose composition differed through the sediment core reflecting changes in bacterial populations induced by large changes in lake salinity. Stable isotopic compositions of the hopanols formed from periodic acid-cleaved BHPs, showed that some were substantially depleted in 13C, indicative of their methanotrophic origin. Using sensitive molecular tools, we found that Type I and II methanotrophic bacteria (respectively Methylomonas and Methylocystis) were unique to the oldest lacustrine sediments (> 9400 years BP), but quantification of fossil DNA revealed that the Type I methanotrophs, including methanotrophs related to methanotrophic gill symbionts of deep-sea cold-seep mussels, were the main precursors of the 35-amino BHPs (i.e. aminopentol, -tetrol and -triols). After isolation of the lake ,3000 years ago, one Type I methanotroph of the ,methanotrophic gill symbionts cluster' remained the most obvious source of aminotetrol and -triol. We, furthermore, identified a Synechococcus phylotype related to pelagic freshwater strains in the oldest lacustrine sediments as a putative source of 2-methylbacteriohopanetetrol (2-Me BHT). This combined application of advanced geochemical and paleogenomical tools further refined our knowledge about Holocene biogeochemical processes in Ace Lake. [source] (4-Acyl-5-pyrazolonato)titanium Derivatives: Oligomerization, Hydrolysis, Voltammetry, and DFT StudyEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 17 2003Francesco Caruso Abstract Twenty 4-acyl-5-pyrazolonato (Q) titanium derivatives of varied nuclearity have been synthesized from Ti(OR)4 or TiCl4 and characterized with spectroscopic methods (IR, NMR, ESI-MS). While Ti,(,-diketonato) cleavage is not seen in isolated solids, Ti,O(alkoxy) (or Ti,Cl) bonds cleave upon hydrolysis, leading to several structural forms, including oligomers. Ionic Q species with no Ti, i.e., obtained after Ti,Q cleavage, are seen for some Ti,Q derivatives by ESI-MS, which also indicates a varied nuclearity for a given species, e.g., the isolated polynuclear [Q2Ti-,-O]n has several "n" values. Mononuclear Ti complexes are obtained under rigorous anhydrous conditions. The cis structures of the mononuclear species (QT)2Ti(OCH3)2, QT = 3-methyl-4-(neopentylcarbonyl)-1-phenylpyrazol-5-onato have been analyzed with DFT methods. A trans influence is a major driving force that accounts for several sets of Ti,O bonds. One of the cis stereoisomers is 56 kcal/mol higher in energy than the other two. In contrast, all (QT)2TiCl2cis isomers show similar energies. Voltammetry of the mononuclear species (QT)2Ti(OnPr)2 and the antitumor tetranuclear compound [(QB)2Ti-,-O]4, (QB = 4-benzoyl-3-methyl-1-phenylpyrazol-5-onato) indicate that the TiIV is less prone to reduction to TiIII in the latter (Epc for the TiIV/TiIII couple is ,1.71 V and ,1.46 V versus Fc+/Fc, respectively). Potential antitumor compounds having a Ti/Q ratio of 1:1 do not disproportionate, unlike the equivalent acetylacetonato derivatives, and are water-soluble. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source] Computational form-finding of tension membrane structures,Non-finite element approaches: Part 1.INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 5 2003Use of cubic splines in finding minimal surface membranes Abstract This paper, presented in three parts, discusses a computational methodology for form-finding of tension membrane structures (TMS), or fabric structures, used as roofing forms. The term ,form-finding' describes a process of finding the shape of a TMS under its initial tension. Such a shape is neither known a priori, nor can it be described by a simple mathematical function. The work is motivated by the need to provide an efficient numerical tool, which will allow a better integration of the design/analysis/manufacture of TMS. A particular category of structural forms is considered, known as minimal surface membranes (such as can be reproduced by soap films). The numerical method adopted throughout is dynamic relaxation (DR) with kinetic damping. Part 1 describes a new form-finding approach, based on the Laplace,Young equation and cubic spline fitting to give a full, piecewise, analytical description of a minimal surface. The advantages arising from the approach, particularly with regard to manufacture of cutting patterns for a membrane, are highlighted. Part 2 describes an alternative and novel form-finding approach, based on a constant tension field and faceted (triangular mesh) representation of the minimal surface. It presents techniques for controlling mesh distortion and discusses effects of mesh control on the accuracy and computational efficiency of the solution, as well as on the subsequent stages in design. Part 3 gives a comparison of the performance of the initial method (Part 1) and the faceted approximations (Part 2). Functional relations, which encapsulate the numerical efficiency of each method, are presented. Copyright © 2002 John Wiley & Sons, Ltd. [source] Computational form-finding of tension membrane structures,Non-finite element approaches: Part 2.INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 5 2003Triangular mesh discretization, control of mesh distortion in modelling minimal surface membranes Abstract This paper, presented in three parts, discusses a computational methodology for form-finding of tension membrane structures (TMS), or fabric structures, used as roofing forms. The term ,form-finding' describes a process of finding the shape of a TMS under its initial tension. Such a shape is neither known a priori, nor can it be described by a simple mathematical function. The work is motivated by the need to provide an efficient numerical tool, which will allow a better integration of the design/analysis/manufacture of TMS. A particular category of structural forms is considered, known as minimal surface membranes (such as can be reproduced by soap films). The numerical method adopted throughout is dynamic relaxation (DR) with kinetic damping. Part 1 gave a background to the problem of TMS design, described the DR method, and presented a new form-finding methodology, based on the Laplace,Young equation and cubic spline fitting to give a full, piecewise, analytical description of the surface. Part 2 describes an alternative and novel form-finding method, based on a constant tension field and faceted (triangular mesh) representation of the minimal surface. Techniques for controlling mesh distortion are presented, and their effects on the accuracy and computational efficiency of the solution, as well as on the subsequent stages in design, are examined. Part 3 gives a comparison of the performance of the initial method (Part 1) and the faceted approximations (Part 2). Functional relations, which encapsulate the numerical efficiency of each method, are presented. Copyright © 2002 John Wiley & Sons, Ltd. [source] An ab initio theoretical study of electronic structure and properties of 2,-deoxyguanosine in gas phase and aqueous mediaJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 5 2002S. K. Mishra Abstract Molecular geometries of two structural forms of 2,-deoxyguanosine (keto-N9R and keto-N7R, R = the sugar moiety) considering both the C2,-endo and C3,-endo conformations of the sugar ring and those of the complexes of these species with two water molecules each were optimized employing the ab initio RHF procedure. A mixed basis set consisting of the 6-311+G* basis set for the nitrogen atom of the amino group and the 4-31G basis set for all the other atoms was used. The RHF calculations were followed by correlation correction of the total energy at the MP2 level. Both the structural forms of 2,-deoxyguanosine were solvated using the polarized continuum model (PCM) of the self-consistent reaction field (SCRF) theory and the corresponding RHF optimized geometries at the RHF and MP2 levels. Geometry optimization was also performed in aqueous media using the Onsager model at the RHF level using the above-mentioned mixed basis set, and subsequently, using the reoptimized geometries, single-point MP2 calculations were performed. It is found that both the keto-N9R and keto-N7R forms of 2,-deoxyguanosine as well as their complexes with two water molecules each would occur, particularly at the water,air interface. Though the normal Watson,Crick-type base pairing would not be possible with the keto-N7R form of 2,-deoxyguanosine(G*), two other (G*-C and G*-T) base pairing schemes may occur with this form of the nucleoside, which may cause mutation. The present calculated geometry of the keto-N9R form of the anti -conformation of 2,-deoxyguanosine including the dihedral angle ,CN agree satisfactorily with the available crystallographic results. The present results also agree satisfactorily with those obtained by other authors earlier for the keto-N9R form of 2,-deoxyguanosine using B3LYP and MP2 methods employing the 6-31G* basis set. Using transition state calculations, it is shown that tautomerism of guanine and other similar molecules where the tautomers would coexist would be facilitated by the occurrence of the H+ and OH, fragments of water molecules. Further, this coexistence of the two tautomers appears to make the C8 carbon atom located between the N7 and N9 nitrogen atoms susceptible to attack by the OH, group. Thus, an explanation is obtained for the efficient formation of the reaction product 8-hydroxy-2,-deoxyguanosine, which serves as a biomarker for oxidative damage to DNA in biological systems. © 2002 Wiley Periodicals, Inc. J Comput Chem 23: 530,540, 2002; DOI 10.1002/jcc.10046 [source] Molten Salt Synthesis and Characterization of Potassium Polytitanate Ceramic Precursors with Varied TiO2/K2O Molar RatiosJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 9 2008Tomas Sanchez-Monjaras Semi-crystalline potassium titanates, useful as precursors to produce composite materials and coatings, were synthesized by thermal treatment of powdered TiO2 in molten mixtures of KNO3 and KOH at 450°,550°C. The products obtained had similar structures of laminar crystals, aggregated in particles of about 3 ,m of n=TiO2/K2O molar ratio in the range 2.8,6.0. The value of n could be regulated by the temperature of synthesis, the weight ratio of [KOH]/[KNO3] in the molten salt mixture, and the number of water washing operations. The reduction of the TiO2/K2O molar ratio increased the contents of H2O in the composition of potassium polytitanate, from 5.3 to 11.4 and from 0.2 to 8.6 (wt%) in the adsorbed and structural forms. The thermal treatment of the potassium polytitanate precursors obtained resulted in dehydration and chemical interaction with unreacted TiO2 at 500°,750°C, amorphization at 750°,850°C, crystallization of K2Ti4O9 (in some cases K3Ti8O17) at 850°,1090°C, and crystallization of K2Ti6O13 at temperatures >1090°C. The mechanisms of the structural transformation and phase evolution were considered as a function of the TiO2/K2O molar ratio in the potassium polytitanate. [source] Reactivity with dichotomous determinants of Ro 60 stratifies autoantibody responses in lupus and primary Sjögren's syndromeARTHRITIS & RHEUMATISM, Issue 5 2010Joanne H. Reed Objective Analysis of B cell determinants of Ro 60 exposed on the surface of apoptotic cells (apotopes) or intracellular epitopes provides insight into the structural forms of the autoantigen that break immune tolerance. This study was initiated to compare anti,Ro 60 responses in systemic lupus erythematosus (SLE) and primary Sjögren's syndrome (SS) against membrane-bound and intracellular forms of Ro 60. Methods The reactivity of autoantibodies from patients with SLE and primary SS to Ro 60 apotopes and epitopes was assessed by multiparameter flow cytometry and solid-phase immunoassay. Anti,Ro 60 IgG was eluted from early apoptotic cells or recombinant Ro 60 immobilized on nitrocellulose, and binding to membrane-bound and intracellular forms of Ro 60 was quantitated by flow cytometry. Results An immunodominant apotope, which was recognized by IgG from a subset of SLE patients with anti-Ro, but not anti-La, autoantibodies, was mapped to a region forming a helix-loop-helix at the apical tip of the Ro 60 molecule. Immobilization of this region to the solid phase exposed an epitope that was recognized by IgG from primary SS and SLE patients whose sera had both anti-Ro and anti-La autoantibodies. Autoantibodies eluted from either the surface of apoptotic cells or the Ro 60 epitope on the solid phase were non,cross-reactive and specifically recognized membrane-bound or cytoplasmic forms of Ro 60. Conclusion This is the first example of a dichotomy of human autoantibody responses against mutually exclusive determinants linked to a single domain of a systemic autoantigen and supports a model in which tolerance is broken by different immunogenic forms of Ro 60. [source] Hierarchical gene expression profiles of HUVEC stimulated by different lipid A structures obtained from Porphyromonas gingivalis and Escherichia coliCELLULAR MICROBIOLOGY, Issue 4 2007Casey Chen Summary The ability of lipid A structural variants to elicit unique endothelial cell gene expression was examined by measuring global gene expression profiles in human umbilical cord vein endothelial cells (HUVEC) using Affymetrix full genome chips. Two lipid A structural variants obtained from Porphyromonas gingivalis designated PgLPS1435/1449 and PgLPS1690 as well as LPS obtained from Escherichia coli wild type and an E. coli msbB mutant (missing myristic acid in the lipid A) were examined. Each of these lipid A structures has been shown to interact with TLR4; however, PgLPS1435/1449 and E. coli msbB LPS have been shown to be TLR4 antagonists while PgLPS1690 and wild-type E. coli LPS are TLR4 agonists. It was found that PgLPS1435/1449 and PgLPS1690 as well as E. coli msbB LPS activated a subset of those genes significantly transcribed in response to E. coli wild-type LPS. Furthermore, the subset of genes expressed in response to the different lipid A structural forms were those most significantly activated by wild-type E. coli LPS demonstrating a hierarchy in TLR4-dependent endothelial cell gene activation. A unique gene expression profile for the weak TLR4 agonist PgLPS1690 was observed and represents a TLR4 hierarchy in endothelial cell gene activation. [source] Encapsulation of Cyanometalates by a Tris-macrocyclic Ligand Tricopper(II) Complex: Syntheses, Structural Variation, and Magnetic Exchange Coupling PathwaysCHEMISTRY - A EUROPEAN JOURNAL, Issue 3 2006Mihail Atanasov Prof. Dr. Abstract The reaction of [M(CN)6]3, (M=Cr3+, Mn3+, Fe3+, Co3+) and [M(CN)8]4,/3, (M=Mo4+/5+, W4+/5+) with the trinuclear copper(II) complex of 1,3,5-triazine-2,4,6-triyltris[3-(1,3,5,8,12-pentaazacyclotetradecane)] ([Cu3(L)]6+) leads to partially encapsulated cyanometalates. With hexacyanometalate(III) complexes, [Cu3(L)]6+ forms the isostructural host,guest complexes [{[Cu3(L)(OH2)2][M(CN)6]2}{M(CN)6}],[M(CN)6],30,H2O with one bridging, two partially encapsulated, and one isolated [M(CN)6]3, unit. The octacyanometalates of Mo4+/5+ and W4+/5+ are encapsulated by two tris-macrocyclic host units. Due to the stability of the +IV oxidation state of Mo and W, only assemblies with [M(CN)8]4, were obtained. The Mo4+ and W4+ complexes were crystallized in two different structural forms: [{Cu3(L)(OH2)}2{Mo(CN)8}](NO3)8,15,H2O with a structural motif that involves isolated spherical [{Cu3(L)(OH2)}2{M(CN)8}]8+ ions and a "string-of-pearls" type of structure [{[Cu3(L)]2[M(CN)8]}{M(CN)8}](NO3)4, 20,H2O, with [M(CN)8]4, ions that bridge the encapsulated octacyanometalates in a two-dimensional network. The magnetic exchange coupling between the various paramagnetic centers is characterized by temperature-dependent magnetic susceptibility and field-dependent magnetization data. Exchange between the Cu,,,Cu pairs in the [Cu3(L)]6+ "ligand" is weakly antiferromagnetic. Ferromagnetic interactions are observed in the cyanometalate assemblies with Cr3+, exchange coupling of Mn3+ and Fe3+ is very small, and the octacoordinate Mo4+ and W4+ systems have a closed-shell ground state. 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