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Symmetry
Kinds of Symmetry Terms modified by Symmetry Selected AbstractsClosed-form Blending of Local SymmetriesCOMPUTER GRAPHICS FORUM, Issue 5 2010Deboshmita Ghosh Abstract We present a closed-form solution for the symmetrization problem, solving for the optimal deformation that reconciles a set of local bilateral symmetries. Given as input a set of point-pairs which should be symmetric, we first compute for each local neighborhood a transformation which would produce an approximate bilateral symmetry. We then solve for a single global symmetry which includes all of these local symmetries, while minimizing the deformation within each local neighborhood. Our main motivation is the symmetrization of digitized fossils, which are often deformed by a combination of compression and bending. In addition, we use the technique to symmetrize articulated models. [source] Symmetries and anisotropies of the electronic states within full spin,orbit couplingPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 9 2005G. E. Marques Abstract We have analyzed how the symmetries and the anisotropies of energy dispersions and of the spinor states, within full spin,orbit interaction, form the two independent circular spin polarizations. We also compare how the effects produced by Rashba and Dresselhauss interaction terms act on the structure of the Hilbert space. These aspects are used to envisage a voltage controlled multichannel spin-filtering regime in nonmagnetic diode structures. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] ChemInform Abstract: Theoretical Investigation of Clusters of Phosphorus and Arsenic: Fascination and Temptation of High Symmetries.CHEMINFORM, Issue 30 2008Paola Nava Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] The costs and benefits of fast livingECOLOGY LETTERS, Issue 12 2009Karen E. Rose Abstract Growth rates play a fundamental role in many areas of biology (Q. Rev. Biol., 67, 1992, 283; Life History Invariants. Some Explorations of Symmetry in Evolutionary Biology, 1993; Philos. Trans. R. Soc. Lond. B Biol. Sci., 351, 1996, 1341; Plant Strategies, Vegetation Processes, and Ecosystem Properties, 2002; Trends Ecol. Evol., 18, 2003, 471; Q. Rev. Biol., 78, 2003, 23; J. Ecol., 95, 2007, 926.) but the cost and benefits of different growth rates are notoriously difficult to quantify (Q. Rev. Biol., 72, 1997, 149; Funct. Ecol., 17, 2003, 328). This is because (1) growth rate typically declines with size and yet the most widely used growth measure , relative growth rate or RGR (conventionally measured as the log of the ratio of successive sizes divided by the time interval) , is not size-corrected and so confounds growth and size, (2) organisms have access to different amounts of resource and (3) it is essential to allow for the long-term benefits of larger size. Here we experimentally demonstrate delayed costs and benefits of rapid growth in seven plant species using a novel method to calculate size-corrected RGR. In control treatments, fast-growing plants benefited from increased reproduction the following year; however, fast-growing plants subjected to an experimental stress treatment (defoliation) showed strongly reduced survival and reproduction the following year. Importantly, when growth was estimated using the classical RGR measure, no costs or benefits were found. These results support the idea that life-history trade-offs have a dominant role in life-history and ecological theory and that the widespread failure to detect them is partly due to methodological shortcomings. Ecology Letters (2009) 12: 1379,1384 [source] Experience Plays a Role in Female Preference for Symmetry in the Swordtail Fish Xiphophorus malincheETHOLOGY, Issue 9 2009M. Scarlett Tudor Variation in female mating preferences was previously detected in wild-caught Xiphophorus cortezi and Xiphophorus malinche females: smaller (presumed younger) females preferred symmetrical males, while larger (presumed older) females preferred asymmetrical males. We examined the influence of experience on this variation in female preference by determining if X. malinche females would express a preference for symmetry as virgins, shift their preferences for bar symmetry as they got larger (older) and if experience with males of different bar number symmetry could explain the variation in female preference previously detected. Virgin females exhibited no preference for vertical bar number symmetry when tested in the young- or old-age classes. However, young virgins spent more time with the opposite treatment in the second when compared with first test, indicating an ability to detect the difference between symmetry and asymmetry, and potentially a preference to mate with multiple males. When females were reared in one of three treatments, housed with symmetrical, barless or both symmetrical and asymmetrical males, we detected both a treatment and tank effect on strength of preference for symmetry, suggesting that barring pattern and some other aspect of the social environment influenced the development of this mating preference. Finally, we detected no effect of age class on mean strength of preference for symmetry; however, there was a statistically different relationship between female size and strength of preference for symmetry across the two age classes, suggesting that the preference function for symmetry may not be linear in relation to female size. [source] Fluctuating Asymmetry of Responders Affects Offers in the Ultimatum Game Oppositely According to Attractiveness or Need as Perceived by ProposersETHOLOGY, Issue 7 2009Darine Zaatari The Ultimatum Game (UG) measures cooperative tendencies in humans. A proposer offers to split a given sum of money between self and a responder, who may accept or reject the offer. If accepted, each receives the proposed split; if rejected, nobody receives anything. We studied the effect of the putative responder's degree of facial symmetry (fluctuating asymmetry, FA) on the offer he/she received in opposite-sexed UGs. Symmetry is an important measure of biological quality so subjects were expected to receive higher offers when symmetrical than asymmetrical. In a sample of Jamaicans, individuals played two UGs with opposite-sexed responders, a symmetrical photo of a Lebanese and an asymmetrical one. Individuals do indeed give more to symmetrical responders (p = 0.032). When subjects are asked their motivation, a striking dichotomy emerges: those who cite ,attractiveness' as a motive, give strongly to symmetrical responders while those citing ,need' invariably give more to asymmetrical ones (p < 0.0001). Females also show a nearly significant tendency to cite need as a motive more often than do males. [source] Extended Hartree,Fock theory of chemical reactions.INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 15 2009Abstract Symmetry and broken symmetry (BS) in molecular orbital description of transition structures and intermediates in oxygenation reactions have been revisited to elucidate states correlation diagrams and mechanisms for addition reactions of molecular oxygen and metal-oxo MO (M = Mn(II) and Fe(II)) species to CC double bonds. Relative stabilities between diradical (DR) and perepoxide (PE) intermediates were thoroughly investigated by several BS hybrid DFT (HDFT) methods and BS CCSD(T) method with and without spin projection. It has been found that recovery of spin symmetry, namely eliminating spin contamination error from the BS solutions, is crucial for the elucidation of reasonable state correlation diagrams and energy differences of the key structures in the oxygenation reactions because the singlet-triplet energy gap for molecular oxygen is large (22 kcal/mol). The BS HDFT followed by spin correction reproduced activation barriers for transition structures along both PE and DR reaction pathways by the use of the CASPT2 method. Basis set dependence on the relative stability between PE and DR intermediates were also examined thoroughly. Solvation effect for DR and PE intermediates was further examined with self-consistent reaction field (SCRF) and SCIPCM methods. Both BS HDFT and CASPT2 have concluded that the DR mechanism is favorable for the addition reaction of singlet oxygen to ethylene, supporting our previous conclusions. The BS HDFT with spin correction was concluded to be useful enough for theoretical investigations of mechanisms of oxygenation reactions. Implications of the computational results were discussed in relation to the theoretical framework (four configuration model) for elucidation of possible mechanisms of epoxidation reactions with Fe(IV)O cores in metalloenzymes on the basis of isolobal analogies among O, OO, and Fe(IV)O. Correspondence between magnetic coupling mode and radical pathway in oxygenations with these species was clarified based on the BS MO interaction diagrams, leading to local singlet and triplet diradical mechanisms for epoxidations. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2009 [source] Synchronization patterns in spaghetti-like nanoclustersINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 15 2008Acep Purqon Abstract Spaghetti-like nanoclusters concern disordered shapes and irregular shape fluctuations in few correlated biological lipids. We evaluate the shape fluctuations by introducing Symmetry- S as a physical parameter for measuring symmetry degrees and detecting shape transitions. From numerical simulation of few correlated lipids of POPC and POPE at 300 K and 340 K by using molecular dynamics, we investigate the symmetry dynamics for each individual cluster by analyzing both spatiotemporal and frequency. From spatiotemporal analysis, we find several jump motions in S -dynamics and non-Gaussian distributions in S -distribution. Interestingly, the jump motions likely contribute on the existence of transitions in the non-Gaussian distributions. Additionally, even number of lipids show more symmetric than the odd number of lipids and the symmetry distributions shift at higher temperature, while, from three dimension of actual position of symmetry dynamics, they are not easy to configure high symmetry as well as showing certain patterns. From power spectra density analysis, each individual cluster shows nearly random fluctuation. Besides individual clusters, we also investigate mutual clusters. Surprisingly, although individual clusters show fluctuations randomly, mutual clusters show certain direction correlations. Moreover, they show certain patterns in delayed time analysis such as mutual fluctuations periodically occur for same number of lipids. It indicates that an existence of synchronization patterns occur in shape fluctuations of spaghetti-like nanoclusters. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2008 [source] A Symmetry-Based Synthesis of the Heterobicyclic Core of the Zaragozic Acids/SqualestatinsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 13 2009Yuzhou Wang Abstract The pseudo C2 -symmetrical diketone 22 was efficiently constructed from furan-3,4-dimethanol (7) using a two-directional route featuring a double asymmetric dihydroxylation. Acidic hydrolysis of the cyclopentylidene acetals of 22 triggered a selective cyclization of the resulting hexaol diketone to generate the 2,8-dioxabicyclo[3.2.1]octane core of the zaragozic acids/squalestatins. Chemoselective oxidative cleavage of a superfluous two-carbon appendage and further functional group manipulations yielded the enantiomerically pure triester 30, which offers itself as a general heterobicyclic building block for naturally occurring zaragozic acids/squalestatins and unnatural analogues. [source] A path from Ih to C1 symmetry for C20 cage moleculeJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 12 2005Zhigang Wang Abstract The symmetry of the C20 cage is studied based on the intrinsical relationship among point groups (Bradley, C. J.; Cracknell, A. P. The Mathematical Theory of Symmetry in Solids; Claredon Press: Oxford, 1972). The structure of the C20 cage with Ih symmetry is constructed, as are eight other structures with subgroup symmetry. A path from Ih symmetry to C1 symmetry is obtained for the closed-shell electronic state, and the structure with D2h symmetry is the most stable on this path. Using the D2h structure the correlation energy correction is studied on the condition of restricted excitation space at the CCSD(T) level. We obtain curves on the relation between the orbital numbers and the total energy at the CCSD(T), CCSD, and MP2 level, respectively. The results of these curves obtained from MP2 and CCSD(T) methods have the same tendency, while the results of CCSD gradually diverge with an increase in orbital numbers. When the orbitals used in the calculation reach 460, the total energy is ,759.644 hartree at MP2 level and is ,759.721 hartree by the CCSD(T) method. From the calculation results, we find that a large basis set can improve the reliability of the MP2 method, and to restrict excitation space is necessary when using the CCSD(T) method. © 2005 Wiley Periodicals, Inc. J Comput Chem 12: 1279,1283, 2005 [source] Concurrence Between the Maxillary Midline and Bisector to the Interpupillary LineJOURNAL OF ESTHETIC AND RESTORATIVE DENTISTRY, Issue 1 2009EVANIA ESKELSEN DDS ABSTRACT Purpose:, Symmetry is one of the factors that contributes to facial harmony, and in oral rehabilitation it determines the success of esthetic treatment. Therefore, the aim of the present study was to analyze the axial symmetry between the bipupillar midline and maxillary central incisors midline of 102 dental students (both genders) distributed across five Brazilian dental schools. Materials and Methods:, Students with no teeth missing and who had never been subjected to any dental treatment were selected. Photographs were taken with a Dental Eye III camera with a 100-mm macro objective and ratio of 1 : 10 from natural size, recorded on an Ektachrome ASA/ISO 100 film. The images were developed and applied to Microsoft Office Power Point 2007 software. The results were analyzed by analysis of variance and Student's t -test (, = 0.05). Results:, There was no significant correlation between bipupillar midline and the maxillary dental midline, irrespective of gender. Conclusion:, No significant coincidence was observed between the interpupillary and dental midline. However, the interpupillar distance and its relationship with other anatomic structures may be used as a reference in treatment, but measurements must be assessed individually. CLINICAL SIGNIFICANCE Anatomic measurements and facial proportions can be helpful during the planning of esthetic oral rehabilitation. [source] Dentition and tooth replacement pattern in Chalcides (Squamata; Scincidae)JOURNAL OF MORPHOLOGY, Issue 2 2003Sidney Delgado Abstract This study was undertaken as a prerequisite to investigations on tooth differentiation in a squamate, the Canarian scincid Chalcides. Our main goal was to determine whether the pattern of tooth replacement, known to be regular in lizards, could be helpful to predict accurately any stage of tooth development. A growth series of 20 laboratory-reared specimens, aged from 0.5 month after birth to about 6 years, was used. The dentition (functional and replacement teeth) was studied from radiographs of jaw quadrants. The number of tooth positions, the tooth number in relation to age and to seasons, and the size of the replacement teeth were recorded. In Chalcides, a single row of pleurodont functional teeth lies at the labial margin of the dentary, premaxillary, and maxillary. Whatever the age of the specimens, 16 tooth positions were recorded, on average, in each quadrant, suggesting that positions are maintained throughout life. Replacement teeth were numerous whatever the age and season, while the number of functional teeth was subject to variation. Symmetry of tooth development was evaluated by comparing teeth two by two from the opposite side in the four jaw quadrants of several specimens. Although the relative size of some replacement teeth fitted perfectly, the symmetry criterion was not reliable to predict the developmental stage of the opposite tooth, whether the pair of teeth compared was left,right or upper,lower. The best fit was found when comparing the size of successive replacement teeth from the front to the back of the jaw. Every replacement tooth that is 40,80% of its definitive size is followed, in the next position on the arcade, by a tooth that is, on average, 20% less developed. Considering teeth in alternate positions (even and odd series), each replacement tooth was a little more developed than the previous, more anterior, one (0.5,20% when the teeth are from 10,40% of their final size). The latter pattern showed that tooth replacement occurred in alternate positions from back to front, forming more or less regular rows (i.e., "Zahnreihen"). In Chalcides, the developmental stage of a replacement tooth in a position p can be accurately predicted provided the developmental stage of the replacement tooth in position p-1 or, to a lesser degree, in position p-2 is known. This finding will be particularly helpful when starting our structural and ultrastructural studies of tooth differentiation in this lizard. J. Morphol. 256:146,159, 2003. © 2003 Wiley-Liss, Inc. [source] Laser scanner analysis in reconstruction of traumatic laceration of the facial nerveLASER PHYSICS LETTERS, Issue 6 2007D.F. Kalbermatten Abstract To present a new concept of outcome analysis after immediate reconstruction of traumatic lesions of the frontal branch of the facial nerve. With the aid of laser surface scanning, changes induced by frontal muscle contraction, i.e. frowning, in skin surface area on the forehead were measured in nine patients after repair of traumatic transection of the frontal branch of the facial nerve and in 10 healthy volunteers. With laser surface scanning analysis, consistent changes in surface area on the forehead were measured in both patients and healthy volunteers. Symmetry of 74 ± 15% in forehead wrinkling was obtained 12 months after coaptation of the transected nerve. Laser surface scanning is a promising tool to assess outcome after repair of facial nerve laceration. It is easy to use, yields reproducible results and might be used in the future for other procedures. (© 2007 by Astro Ltd., Published exclusively by WILEY-VCH Verlag GmbH & Co. KGaA) [source] Ontological Symmetry in Language: A Brief ManifestoMIND & LANGUAGE, Issue 4 2006PHILIPPE SCHLENKER Various results from recent research in formal semantics suggest that this is not so, and that there is in fact a pervasive symmetry between the linguistic means with which we refer to these three domains. Reference to individuals, times and worlds is uniformly effected through generalized quantifiers, definite descriptions, and pronouns, and in each domain grammatical features situate the reference of terms as near, far or ,further' from the actual or from a reported speech act. We outline various directions in which a program of ontological symmetry could be developed, and we offer in the Appendix a symmetric fragment developed in a logic that can be seen as a compromise between an extensional and an intensional system. [source] Symmetry Comes of Age: The Role of Pattern in Culture by Dorothy K. Washburn and Donald W. Crowe, edsMUSEUM ANTHROPOLOGY, Issue 1 2009SCARLETT CHIU [source] Symmetry-based analysis of the electron,phonon interaction in graphenePHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 11-12 2009I. Milo Abstract Symmetry-based analysis of the electron,phonon interaction in graphene is performed. Some nontrivial physical properties of graphene are shown to be direct consequence of symmetry, independent on the applied dynamical model. Namely, it is found that there are vibronically uncoupled non symmetric modes which thus might be responsible for the stability of the honeycomb lattice. Symmetry also predicts vanishing of the electron,phonon interaction for quite a number of the normal displacements. Consequently, lattice dynamics along these degrees of freedom is governed by the ion repulsion which leads to the anharmonic terms, being linear in absolute elongation. In particular, this effect is attributed to the K and , points of the Brillouin zone, giving insight into origin of the Kohn anomaly. The results are further numerically confirmed within full and tight-binding density functional calculations and force constants model. [source] Symmetry of electron states and optical transitions in GaN/AlN hexagonal quantum dotsPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 13 2004P. Tronc Abstract The exact symmetry of hexagonal quantum dots (QDs) made of materials with the wurtzite structure such as GaN/AlN QDs for example, is described by the C3v point group and does not depend on the existence of a wetting layer. We have determined the possible exact symmetries of electron states and vibration modes in the dots and derived the optical selection rules. The vibration modes involved in the Frölich interaction are totally symmetric with respect to the C3v group and can induce transitions only between states with the same symmetry. The not totally symmetric modes provide other channels for lowering the energy of excited carriers and excitons by connecting states with symmetries different one from another. The rapid decay of created polarons, due to the short lifetime of vibration modes, releases the carriers and excitons into ground levels. In the envelope function approximation (EFA), the symmetry of the dots is represented by the C6v point group. Interband transitions are allowed only between states whose envelope functions have the same symmetry. EFA artificially increases the number of dark exciton symmetries. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Photoluminescence excitation spectroscopy of Er3+ ions in cubic GaN:ErPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7 2007V. Glukhanyuk Abstract In this paper we report the results of study of cubic GaN implanted with erbium by means of photoluminescence (PL) and photoluminescence excitation (PLE) spectroscopy. Only one optical emission center is observable at resonant excitation of Er3+ ions to 4I9/2 state. The positions of erbium energy levels were determined from the results of PL and PLE measurements for 4I15/2 and 4I9/2 state. Symmetry of energy levels has been assign according to group theory. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Symmetry and bifurcation in vestibular systemPROCEEDINGS IN APPLIED MATHEMATICS & MECHANICS, Issue 1 2007Marty Golubitsky The vestibular system in almost all vertebrates, humans included, controls balance by employing a set of six semicircular canals, three in each inner ear, to detect angular accelerations of the head. Signals from the canals are transmitted to neck motoneurons and activate eight corresponding muscle groups. These signals may be either excitatory or inhibitory, depending on the direction of acceleration. McCollum and Boyle have observed that in the cat the network of neurons concerned possesses octahedral symmetry, a structure deduced from the known innervation patterns (connections) from canals to muscles. We re-derive the octahedral symmetry from mathematical features of the probable network architecture, and model the movement of the head in response to the activation patterns of the muscles concerned. We assume that connections among neck muscles can be modeled by a ,coupled cell network', a system of coupled ODEs whose variables correspond to the eight muscles, and that network also has octahedral symmetry. The network and its symmetries imply that these ODEs must be equivariant under a suitable action of the octahedral group. Using results of Ashwin and Podvigina, we show that with the appropriate group actions, there are six possible spatiotemporal patterns of time-periodic states that can arise by Hopf bifurcation from an equilibrium corresponding to natural head motions. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Breaking symmetry in protein dimers: Designs and functionsPROTEIN SCIENCE, Issue 1 2006Jerry H. Brown Abstract Symmetry, and in particular point group symmetry, is generally the rule for the global arrangement between subunits in homodimeric and other oligomeric proteins. The structures of fragments of tropomyosin and bovine fibrinogen are recently published examples, however, of asymmetric interactions between chemically identical chains. Their departures from strict twofold symmetry are based on simple and generalizable chemical designs, but were not anticipated prior to their structure determinations. The current review aims to improve our understanding of the structural principles and functional consequences of asymmetric interactions in proteins. Here, a survey of >100 diverse homodimers has focused on the structures immediately adjacent to the twofold axis. Five regular frameworks in ,-helical coiled coils and antiparallel ,-sheets accommodate many of the twofold symmetric axes. On the basis of these frameworks, certain sequence motifs can break symmetry in geometrically defined manners. In antiparallel ,-sheets, these asymmetries include register slips between strands of repeating residues and the adoption of different side-chain rotamers to avoid steric clashes of bulky residues. In parallel coiled coils, an axial stagger between the ,-helices is produced by clusters of core alanines. Such simple designs lead to a basic understanding of the functions of diverse proteins. These functions include regulation of muscle contraction by tropomyosin, blood clot formation by fibrin, half-of-site reactivity of caspase-9, and adaptive protein recognition in the matrix metalloproteinase MMP9. Moreover, asymmetry between chemically identical subunits, by producing multiple equally stable conformations, leads to unique dynamic and self-assembly properties. [source] Crystallography and the World of Symmetry.ACTA CRYSTALLOGRAPHICA SECTION A, Issue 2 2009By Sanat K. Chatterjee. First page of article [source] A systematic approach to the derivation of standard orientation-location parts of symmetry-operation symbolsACTA CRYSTALLOGRAPHICA SECTION A, Issue 6 2007Kazimierz Stró Automatically generated orientation-location parts, or coordinate triplets describing the geometric elements, differ frequently from the corresponding parts of the symmetry-operation symbols listed in International Tables for Crystallography [(1983), Vol. A, Space-Group Symmetry, edited by Th. Hahn. Dordrecht: Reidel]. An effective algorithm enabling the derivation of standard orientation-location parts from any symmetry matrix is described and illustrated. The algorithm is based on a new concept alternative to the `invariant points of reduced operation'. First, the geometric element that corresponds to a given symmetry operation is oriented and located in a nearly convention free manner. The application of the direction indices [uvw] or Miller indices (hkl) gives a unique orientation provided the convention about the positive direction is defined. The location is fixed by the specification of a unique point on the geometric element, i.e. the point closest to the origin. Next, both results are converted into the standard orientation-location form. The standardization step can be incorporated into other existing methods of derivation of the symmetry-operation symbols. A number of standardization examples are given. [source] Polarization anisotropy of X-ray atomic factors and `forbidden' resonant reflectionsACTA CRYSTALLOGRAPHICA SECTION A, Issue 5 2005Vladimir E. Dmitrienko Symmetry and physical aspects of `forbidden' reflections excited by a local polarization anisotropy of the X-ray susceptibility are surveyed. Such reflections are observed near absorption edges where the anisotropy is caused by distortions of the atomic electronic states owing to interaction with neighbouring atoms. As a consequence, they allow for extracting nontrivial information about the resonant atom's local environment and their physical conditions. The unusual polarization properties of the considered reflections are helpful to distinguish them from other types of `forbidden' reflections. When such reflections are excited, it is, for example, possible to determine not only the intrinsic anisotropy of an atomic form factor but also additional anisotropy induced by thermal motion, point defects and/or incommensurate modulations. Even the local `chirality' of atoms in centrosymmetric crystals is accessible. Unsolved key problems and possible future developments are addressed. [source] Symmetry of platelet defects in diamond: new insights with synchrotron lightACTA CRYSTALLOGRAPHICA SECTION B, Issue 5 2010Alexei Bosak Mapping of reciprocal space for Ia -type diamond single crystals with synchrotron radiation has uncovered a variety of diffuse scattering features, some of them have not been observed before. The main component of diffuse scattering in the form of diffuse rods corresponds to a set of platelets which join together blocks of diamond structure. The platelets are ordered structural entities with lattice periodicity , where is a unit-cell dimension of diamond. Intensity distribution along the rods has been measured and used for recognition of symmetry elements of the platelet structure. These findings, together with previously reported transmission electron microscopy (TEM) observations, provide strong constraints for atomistic modelling of the platelet structure. [source] Synthesis of a DNA,Silica Complex with Rare Two-Dimensional Square p4mm Symmetry,ANGEWANDTE CHEMIE, Issue 49 2009Chenyu Jin Verzahnt: Das Titelsystem wurde mit einem quartären Ammoniumsilan als DNA-kondensierendem Agens und Cokondensierer mit der Siliciumquelle hergestellt. Der kleine Achsenabstand in elektrostatischen DNA-DNA-,Reißverschlüsssen" und die zwischen diagonal angeordneten DNA-Strängen gebildeten Siliciumwände sind für die Bildung der p4mm -Struktur optimal. [source] Science, engineering, and statisticsAPPLIED STOCHASTIC MODELS IN BUSINESS AND INDUSTRY, Issue 5-6 2006T. P. Davis Abstract Symmetry and parsimony, together with unification through synthesis are important principles that govern the character of physical law. We show how these principles can be applied to engineering to develop an approach to reliability, and engineering in general, that centres on the identification, detection, and avoidance of failure modes through design. A definition of reliability, not presented in terms of probability, but rather based on physics, geometry, and the properties of materials, will be emphasized to support this approach. We will also show how the nature of the inductive,deductive learning cycle provides the framework for statistical science to be embedded into engineering practice, with particular regard to improving reliability through failure mode avoidance. Copyright © 2006 John Wiley & Sons, Ltd. [source] Trade taxes and international investmentCANADIAN JOURNAL OF ECONOMICS, Issue 3 2009Emily J. Blanchard Abstract This paper demonstrates that international investment disturbs the conventionally understood equivalence between import tariffs and export taxes. Fundamentally, remittances to foreigners introduce an additional pecuniary channel between countries so that two-good Lerner Symmetry generally will not hold. Moreover, because tariffs subsidize investors in the local import competing sector while export taxes can extract rent from foreign investors in the export sector, the pattern of international investment will influence government preferences over trade policy,instruments,as well as levels. Notably, trade tax symmetry is restored by introducing a third policy tool in the form of a direct a tax on international remittances. Ce mémoire montre que l'investissement international bouscule l'équivalence canonique présumée entre tarifs à l'importation et taxe à l'exportation. Fondamentalement, des versements aux étrangers ouvrent un canal additionnel entre pays qui fait que la Symétrie de Lerner ne tient plus. De plus, parce que les tarifs subventionnent les investisseurs dans le secteur national protégé, alors que la taxe à l'exportation peut extraire une rente des investisseurs étrangers dans le secteur d'exportation, le pattern d'investissement international va influencer les préférences du gouvernement quant à l'usage d'un instrument de politique commerciale ou un autre et quant à la vigueur avec laquelle il sera utilisé. La symétrie des taxes sur le commerce international est restaurée en introduisant un troisième intrument de politique sous la forme d'une taxe directe sur les versements internationaux. [source] Early ostial saphenous vein graft stenosis associated with the use of Symmetry sutureless aortic proximal anastomosis device: Successful percutaneous revascularizationCATHETERIZATION AND CARDIOVASCULAR INTERVENTIONS, Issue 2 2004Sharon L. Cline MD Abstract A recent advance in technology permits the creation of sutureless proximal aortic anastomosis during coronary artery bypass graft surgery. This new tool has significant potential benefit by minimizing aortic manipulation with subsequent reduction in neuroembolization. Implantation of a nitinol-based proximal aortic connector (Symmetry) has a potential to elicit intimal hyperplastic reaction analogous to restenosis after coronary stent placement. We report cases of early vein graft stenosis in association with the use of the Symmetry device. Three patients suffered from severe ostial stenosis within 6 months of bypass surgery with symptomatic presentation. Of these three patients, two underwent successful percutaneous revascularization. Fluoroscopic star-shaped appearance of the metallic Symmetry allows device recognition during angiography. We review current data regarding graft patency with the use of Symmetry device and discuss technical issues to address specific problems during percutaneous revascularization. Catheter Cardiovasc Interv 2004;62:203,208. © 2004 Wiley-Liss, Inc. [source] In Pursuit of Conceptual Change: the Case of Legendre and SymmetryCENTAURUS, Issue 4 2009Giora Hon First page of article [source] ChemInform Abstract: GeB4O9×H2en: An Organically Templated Borogermanate with Large 12-Ring Channels Built by B4O9 Polyanions and GeO4 Units: Host,Guest Symmetry and Charge Matching in Triangular-Tetrahedral Frameworks.CHEMINFORM, Issue 36 2008Chun-Yang Pan Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. 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