Structure

Distribution by Scientific Domains
Distribution within Chemistry

Kinds of Structure

  • GaA structure
  • abnormal structure
  • absolute structure
  • absorption fine structure
  • absorption near-edge structure
  • abundance structure
  • academic structure
  • acid structure
  • acoustic structure
  • actin structure
  • active site structure
  • active structure
  • actual structure
  • adjacent structure
  • administrative structure
  • adnexal structure
  • adsorption structure
  • age structure
  • aggregate structure
  • agricultural structure
  • airway structure
  • algebraic structure
  • amine structure
  • amorphous structure
  • amyloid structure
  • anatomic structure
  • anatomical structure
  • animal community structure
  • anisotropic structure
  • ant community structure
  • antenna structure
  • apo structure
  • architectural structure
  • artificial structure
  • assemblage structure
  • asymmetric structure
  • atomic resolution structure
  • atomic structure
  • attachment structure
  • autocorrelation structure
  • available structure
  • average structure
  • backbone structure
  • bacterial community structure
  • band structure
  • bank structure
  • bargaining structure
  • barrel structure
  • barrier structure
  • basic structure
  • beam structure
  • belief structure
  • bent structure
  • bilayer structure
  • bilayered structure
  • biofilm structure
  • biogeographical structure
  • biological structure
  • bipyramidal structure
  • block structure
  • board structure
  • body structure
  • bone structure
  • bony structure
  • boundary structure
  • brain structure
  • branched structure
  • branching structure
  • breeding structure
  • bridge structure
  • broad structure
  • brood structure
  • building structure
  • bulk structure
  • bundle structure
  • bureaucratic structure
  • buried structure
  • cage structure
  • call structure
  • candidate structure
  • canopy structure
  • capillary-like structure
  • capital structure
  • carbohydrate structure
  • carbon structure
  • cardiac structure
  • cardiovascular structure
  • career structure
  • cartilaginous structure
  • catalyst structure
  • causal structure
  • cavity structure
  • cell structure
  • cell wall structure
  • cellular structure
  • centrosymmetric structure
  • ceramic structure
  • cerebral structure
  • chain structure
  • chalcopyrite structure
  • changing structure
  • channel structure
  • characteristic structure
  • chemical structure
  • chiral structure
  • chromatin structure
  • chromosome structure
  • ciliary structure
  • circular structure
  • civil structure
  • class structure
  • clay structure
  • clonal structure
  • close-packed structure
  • cluster structure
  • co-crystal structure
  • coating structure
  • coding structure
  • cognitive structure
  • coherent structure
  • coil structure
  • coiled-coil structure
  • collagen structure
  • colloidal structure
  • colony genetic structure
  • columnar structure
  • combinatorial structure
  • committee structure
  • common structure
  • community structure
  • compact structure
  • compensation structure
  • complete structure
  • complex anatomical structure
  • complex crystal structure
  • complex structure
  • complex three-dimensional structure
  • complicated structure
  • component structure
  • composite structure
  • conceptual structure
  • concrete structure
  • conformational structure
  • conical structure
  • conjugated structure
  • constitutional structure
  • contact structure
  • continuous structure
  • control structure
  • controlled structure
  • controller structure
  • conventional structure
  • coordination structure
  • copolymer structure
  • core structure
  • core-shell structure
  • corporate structure
  • correlation structure
  • cortical structure
  • cost structure
  • covalent structure
  • covariance structure
  • cranial structure
  • craniofacial structure
  • critical structure
  • crosslink structure
  • crust structure
  • crustal structure
  • crystal structure
  • crystal x-ray structure
  • crystalline structure
  • crystallization structure
  • crystallographic structure
  • cubic perovskite structure
  • cubic structure
  • cultural structure
  • current structure
  • cyclic structure
  • cylindrical structure
  • cytoplasmic structure
  • cytoskeletal structure
  • damaged structure
  • data structure
  • decision structure
  • decision-making structure
  • deep structure
  • deeper structure
  • defect structure
  • defined structure
  • deformation structure
  • demographic structure
  • dendritic structure
  • dense structure
  • density structure
  • dental structure
  • dependence structure
  • designed structure
  • desired structure
  • detailed structure
  • detailed three-dimensional structure
  • determine crystal structure
  • determine structure
  • device structure
  • diamond structure
  • dielectric structure
  • different chemical structure
  • different community structure
  • different crystal structure
  • different secondary structure
  • different structure
  • diffraction structure
  • dimensional structure
  • dimer structure
  • dimeric structure
  • dinuclear structure
  • diode structure
  • disc structure
  • discourse structure
  • discrete structure
  • dislocation structure
  • disordered structure
  • distinct electronic structure
  • distinct structure
  • distinctive structure
  • diverse structure
  • dna structure
  • domain structure
  • domestic structure
  • dominant structure
  • dot structure
  • double layer structure
  • ductal structure
  • duplex structure
  • dynamic structure
  • dynamical structure
  • ecological structure
  • economic structure
  • ecosystem structure
  • edge structure
  • education structure
  • elastic structure
  • electrode structure
  • electron structure
  • electronic band structure
  • electronic structure
  • embryonic structure
  • employment structure
  • enamel structure
  • energy structure
  • engineering structure
  • entire structure
  • enzyme structure
  • epithelial structure
  • equilibrium structure
  • error structure
  • essential structure
  • exfoliated structure
  • existing structure
  • experimental crystal structure
  • experimental structure
  • extended x-ray absorption fine structure
  • fabricated structure
  • facial structure
  • factor structure
  • factorial structure
  • family structure
  • fascial structure
  • feed structure
  • feedback structure
  • feeding structure
  • female structure
  • fiber structure
  • fibril structure
  • fibrillar structure
  • fibrous structure
  • field structure
  • filament structure
  • filamentous structure
  • film structure
  • filter structure
  • final structure
  • financial structure
  • fine structure
  • fine-scale genetic structure
  • fine-scale population structure
  • fine-scale spatial genetic structure
  • firm capital structure
  • first crystal structure
  • first structure
  • first x-ray structure
  • fish assemblage structure
  • fish community structure
  • flexible structure
  • flow structure
  • flower structure
  • foam structure
  • fold structure
  • folded structure
  • food structure
  • food web structure
  • food-web structure
  • forest structure
  • foundation structure
  • fractal structure
  • frame structure
  • framework structure
  • frontal structure
  • functional structure
  • fundamental structure
  • fungal structure
  • g-quadruplex structure
  • gas-phase structure
  • gel structure
  • gene structure
  • general structure
  • genetic population structure
  • genetic structure
  • genital structure
  • genome structure
  • genomic structure
  • geographic structure
  • geographical structure
  • geological structure
  • geometric structure
  • geometrical structure
  • glandular structure
  • global structure
  • globular structure
  • glycan structure
  • governance structure
  • government structure
  • grain boundary structure
  • grain structure
  • grain-boundary structure
  • granular structure
  • granule structure
  • graph structure
  • grid structure
  • ground-state structure
  • group structure
  • growth structure
  • guild structure
  • habitat structure
  • hairpin structure
  • haplotype structure
  • hardware structure
  • hcp structure
  • head structure
  • heart structure
  • helical secondary structure
  • helical structure
  • helix structure
  • heterocyclic structure
  • heterogeneous structure
  • hexagonal structure
  • hexagonal wurtzite structure
  • hierarchical structure
  • high-resolution crystal structure
  • high-resolution structure
  • higher education structure
  • higher-order structure
  • highly ordered structure
  • highly porous structure
  • hippocampal structure
  • histological structure
  • hollow structure
  • homogeneous structure
  • homologous structure
  • honeycomb structure
  • horizontal structure
  • host structure
  • household structure
  • hybrid structure
  • hydraulic structure
  • hydrogen-bonded structure
  • hydrogen-bonded supramolecular structure
  • hyperbranched structure
  • hyperfine structure
  • ideal structure
  • identical structure
  • ii structure
  • impact structure
  • important structure
  • incentive structure
  • individual structure
  • industrial structure
  • industry structure
  • infection structure
  • information structure
  • initial structure
  • inner structure
  • inorganic structure
  • institutional structure
  • integrate structure
  • intellectual structure
  • intercalated structure
  • interesting structure
  • interface structure
  • interfacial structure
  • intergrowth structure
  • intermediate structure
  • internal structure
  • intracellular structure
  • inverse opal structure
  • ion structure
  • irregular structure
  • isomeric structure
  • its structure
  • jaw structure
  • joint structure
  • junction structure
  • kasper structure
  • key structure
  • kin structure
  • kinematic structure
  • knowledge structure
  • la structure
  • ladder structure
  • ladder-like structure
  • lamellar structure
  • laminar structure
  • laminated structure
  • large structure
  • large-scale structure
  • larger structure
  • laryngeal structure
  • laser structure
  • latent structure
  • lattice structure
  • layer structure
  • layered structure
  • lead structure
  • leadership structure
  • leaf structure
  • legal structure
  • level structure
  • liability structure
  • ligand structure
  • limbic structure
  • line structure
  • linear structure
  • lipid structure
  • lobe structure
  • local structure
  • logical structure
  • loop structure
  • low-energy structure
  • low-temperature structure
  • lowest energy structure
  • lung structure
  • lymphoid structure
  • macroinvertebrate community structure
  • macromolecular crystal structure
  • macromolecular structure
  • magnetic structure
  • main-chain structure
  • major structure
  • man-made structure
  • management structure
  • mantle structure
  • many structure
  • market structure
  • masonry structure
  • material structure
  • mathematical structure
  • mating structure
  • matrix structure
  • matter structure
  • maturity structure
  • mdof structure
  • mechanical structure
  • mediating structure
  • membrane protein structure
  • membrane structure
  • membranous structure
  • mesoscale structure
  • mesoscopic structure
  • metal structure
  • metallic structure
  • metapopulation structure
  • micellar structure
  • microbial community structure
  • microbial structure
  • microcellular structure
  • microphase-separated structure
  • microporou structure
  • microscopic structure
  • microstrip structure
  • midline structure
  • minimum structure
  • minimum-energy structure
  • model structure
  • modeled structure
  • modified structure
  • modular structure
  • modulated crystal structure
  • modulated structure
  • molecular structure
  • monoclinic structure
  • monolayer structure
  • monomer structure
  • morphological structure
  • mosaic structure
  • multicellular structure
  • multilayer structure
  • multiple structure
  • multivariate structure
  • muscle structure
  • mutant structure
  • myocardial structure
  • n structure
  • nano structure
  • nanocomposite structure
  • nanoparticle structure
  • nanoporou structure
  • nanoscale structure
  • nanotubular structure
  • nanowire structure
  • narrative structure
  • native protein structure
  • native secondary structure
  • native structure
  • natural structure
  • near-edge structure
  • near-edge x-ray absorption fine structure
  • near-surface structure
  • nervous structure
  • nest structure
  • nested structure
  • network structure
  • network-like structure
  • neural network structure
  • neural structure
  • neuronal structure
  • neurovascular structure
  • neutron structure
  • new crystal structure
  • new lead structure
  • new structure
  • nmr solution structure
  • nmr structure
  • non-linear structure
  • nonlinear structure
  • nonplanar structure
  • normal structure
  • novel structure
  • nuclear structure
  • nucleic acid structure
  • observed structure
  • obtained structure
  • occupational structure
  • octahedral structure
  • ocular structure
  • of structure
  • olfactory structure
  • oligomeric structure
  • oligosaccharide structure
  • one-dimensional chain structure
  • one-dimensional structure
  • only structure
  • opal structure
  • open structure
  • operon structure
  • opportunity structure
  • optical structure
  • optimal capital structure
  • optimal structure
  • optimized structure
  • oral structure
  • ordered structure
  • organic structure
  • organisational structure
  • organization structure
  • organizational structure
  • original structure
  • orthorhombic structure
  • other crystal structure
  • other structure
  • ovarian structure
  • ownership structure
  • oxide structure
  • packaging structure
  • packing structure
  • papillary structure
  • partial structure
  • particle structure
  • particular structure
  • particulate structure
  • passive structure
  • pay structure
  • peak structure
  • peculiar structure
  • pedigree structure
  • peptide structure
  • periodic structure
  • periodontal structure
  • perovskite structure
  • personality structure
  • phase structure
  • photonic structure
  • phrase structure
  • phylogenetic structure
  • phylogeographic structure
  • phylogeographical structure
  • physical structure
  • placental structure
  • planar structure
  • plant community structure
  • plant structure
  • plate structure
  • polarized electronic structure
  • political opportunity structure
  • political structure
  • polycrystalline structure
  • polymer structure
  • polymeric structure
  • polymorphic structure
  • polysaccharide structure
  • population age structure
  • population genetic structure
  • population size structure
  • population structure
  • pore structure
  • porous structure
  • possible structure
  • potential structure
  • power structure
  • practical structure
  • precise structure
  • precursor structure
  • predicted structure
  • preference structure
  • present structure
  • previous crystal structure
  • previous structure
  • price structure
  • pricing structure
  • primary structure
  • probability structure
  • probable structure
  • production structure
  • program structure
  • proposed structure
  • protein crystal structure
  • protein secondary structure
  • protein structure
  • protein tertiary structure
  • prototype structure
  • psychological structure
  • published crystal structure
  • published structure
  • pure perovskite structure
  • pyrochlore structure
  • quadruplex structure
  • quality structure
  • quantitative structure
  • quantum dot structure
  • quantum structure
  • quaternary structure
  • rate structure
  • rc structure
  • real structure
  • recent structure
  • receptor structure
  • reference structure
  • refined structure
  • regional structure
  • regular structure
  • regulatory structure
  • relate structure
  • relational structure
  • relevant structure
  • repeat structure
  • reported structure
  • representative structure
  • reproductive structure
  • residual structure
  • resolution crystal structure
  • resolution structure
  • resonance structure
  • resonant structure
  • resonator structure
  • respiratory structure
  • resulting structure
  • retaining structure
  • reward structure
  • rhetorical structure
  • ribosomal structure
  • rigid structure
  • ring structure
  • ring-like structure
  • rna secondary structure
  • rna structure
  • rod structure
  • rod-like structure
  • room-temperature structure
  • root structure
  • rutile structure
  • same structure
  • sample structure
  • sandwich structure
  • scale structure
  • second structure
  • secondary structure
  • secretory structure
  • sedimentary structure
  • segment structure
  • self-assembled structure
  • semiconductor structure
  • sensory structure
  • service structure
  • several protein structure
  • several structure
  • sheet structure
  • sheet-like structure
  • shell structure
  • short-range structure
  • side-chain structure
  • significant spatial genetic structure
  • significant structure
  • silica structure
  • silicate structure
  • similar chemical structure
  • similar molecular structure
  • similar structure
  • simple structure
  • single crystal structure
  • single structure
  • single-crystal structure
  • single-crystal x-ray structure
  • site structure
  • size structure
  • skeletal structure
  • skin structure
  • sleep structure
  • small structure
  • small-scale structure
  • social structure
  • soft tissue structure
  • soft-tissue structure
  • soil structure
  • solid state structure
  • solid structure
  • solid-state structure
  • solution structure
  • solved structure
  • solvent structure
  • song structure
  • space structure
  • spatial genetic structure
  • spatial population structure
  • spatial structure
  • special structure
  • specialized structure
  • specific structure
  • spectral structure
  • sperm chromatin structure
  • sperm structure
  • spherical structure
  • spherulitic structure
  • spin structure
  • spinel structure
  • spiral structure
  • stable structure
  • stage structure
  • stand structure
  • state structure
  • static structure
  • statistical structure
  • steel structure
  • stem structure
  • stock structure
  • strong genetic structure
  • strong population structure
  • strong structure
  • subcellular structure
  • subcortical structure
  • substrate structure
  • subsurface structure
  • subunit structure
  • superlattice structure
  • support structure
  • supporting structure
  • supramolecular structure
  • surface structure
  • surrounding structure
  • sward structure
  • symmetric structure
  • symmetrical structure
  • synaptic structure
  • syntactic structure
  • system structure
  • target structure
  • tax structure
  • taxonomic structure
  • technical structure
  • telomere structure
  • temperature structure
  • template structure
  • temporal lobe structure
  • temporal structure
  • term structure
  • territorial structure
  • tertiary structure
  • test structure
  • tetragonal structure
  • tetrahedral structure
  • tetrameric structure
  • textile structure
  • their structure
  • theoretical structure
  • thermal structure
  • thin film structure
  • thin-walled structure
  • three-dimensional crystal structure
  • three-dimensional framework structure
  • three-dimensional network structure
  • three-dimensional protein structure
  • three-dimensional structure
  • three-factor structure
  • tight junction structure
  • timber structure
  • tio2 structure
  • tissue structure
  • tooth structure
  • topological structure
  • trabecular bone structure
  • trabecular structure
  • trade structure
  • traditional structure
  • transient structure
  • transition state structure
  • transition structure
  • tree structure
  • trial structure
  • triple-helical structure
  • trophic structure
  • true structure
  • truss structure
  • tube-like structure
  • tubular structure
  • tunnel structure
  • turbulent structure
  • turn structure
  • two-dimensional layer structure
  • two-dimensional structure
  • two-factor structure
  • two-phase structure
  • type structure
  • underground structure
  • underlying factor structure
  • underlying structure
  • uniform structure
  • unique structure
  • unknown structure
  • unusual structure
  • urban structure
  • variance structure
  • variety of structure
  • various structure
  • vascular structure
  • vegetation structure
  • velocity structure
  • vertical structure
  • very similar structure
  • vesicular structure
  • vessel-like structure
  • void structure
  • volatility structure
  • vortex structure
  • wage structure
  • wall structure
  • water structure
  • wave structure
  • waveguide structure
  • web structure
  • well-defined structure
  • white matter structure
  • whole structure
  • wick structure
  • wild-type structure
  • wood structure
  • wurtzite crystal structure
  • wurtzite structure
  • x-ray absorption fine structure
  • x-ray absorption near-edge structure
  • x-ray crystal structure
  • x-ray crystallographic structure
  • x-ray diffraction structure
  • x-ray structure
  • zeolite structure
  • zigzag chain structure
  • zincblende structure
  • zno structure
  • zooplankton community structure
  • zwitterionic structure

  • Terms modified by Structure

  • structure activity relationship
  • structure activity relationships
  • structure alignment
  • structure alone
  • structure alteration
  • structure analysis
  • structure analysis.
  • structure assignment
  • structure available
  • structure calculation
  • structure change
  • structure characteristic
  • structure characterization
  • structure choice
  • structure clinical examination
  • structure comparable
  • structure comparison
  • structure confirmation
  • structure consistent
  • structure consisting
  • structure constant
  • structure containing
  • structure content
  • structure control
  • structure controller
  • structure data
  • structure database
  • structure decision
  • structure description
  • structure descriptor
  • structure design
  • structure determination
  • structure determine
  • structure development
  • structure difference
  • structure different
  • structure effect
  • structure element
  • structure elucidation
  • structure embedded
  • structure evolution
  • structure factor
  • structure feature
  • structure formation
  • structure generation
  • structure increase
  • structure information
  • structure interaction
  • structure interaction problem
  • structure interaction simulation
  • structure interview
  • structure investigation
  • structure lead
  • structure leading
  • structure map
  • structure measurement
  • structure model
  • structure modeling
  • structure models
  • structure modification
  • structure motif
  • structure necessary
  • structure optimization
  • structure parameter
  • structure prediction
  • structure present
  • structure propensity
  • structure property
  • structure quality
  • structure refinement
  • structure regulation
  • structure relationships
  • structure result
  • structure reveal
  • structure set
  • structure shows
  • structure similar
  • structure solution
  • structure spectroscopy
  • structure studies
  • structure study
  • structure suitable
  • structure system
  • structure theorem
  • structure theory
  • structure type
  • structure unit
  • structure used
  • structure validation
  • structure variable
  • structure variation

  • Selected Abstracts


    An alignment-free methodology for modelling field-based 3D-structure activity relationships using inductive logic programming

    JOURNAL OF CHEMOMETRICS, Issue 12 2007
    Bård Buttingsrud
    Abstract Traditional 3D-quantitative structure,activity relationship (QSAR)/structure,activity relationship (SAR) methodologies are sensitive to the quality of an alignment step which is required to make molecular structures comparable. Even though many methods have been proposed to solve this problem, they often result in a loss of model interpretability. The requirement of alignment is a restriction imposed by traditional regression methods due to their failure to represent relations between data objects directly. Inductive logic programming (ILP) is a class of machine-learning methods able to describe relational data directly. We propose a new methodology which is aimed at using the richness in molecular interaction fields (MIFs) without being restricted by any alignment procedure. A set of MIFs is computed and further compressed by finding their minima corresponding to the sites of strongest interaction between a molecule and the applied test probe. ILP uses these minima to build easily interpretable rules about activity expressed as pharmacophore rules in the powerful language of first-order logic. We use a set of previously published inhibitors of factor Xa of the benzamidine family to discuss the problems, requirements and advantages of the new methodology. Copyright © 2007 John Wiley & Sons, Ltd. [source]


    LEARNING PRECONDITIONS FOR PLANNING FROM PLAN TRACES AND HTN STRUCTURE

    COMPUTATIONAL INTELLIGENCE, Issue 4 2005
    Okhtay Ilghami
    A great challenge in developing planning systems for practical applications is the difficulty of acquiring the domain information needed to guide such systems. This paper describes a way to learn some of that knowledge. More specifically, the following points are discussed. (1) We introduce a theoretical basis for formally defining algorithms that learn preconditions for Hierarchical Task Network (HTN) methods. (2) We describe Candidate Elimination Method Learner (CaMeL), a supervised, eager, and incremental learning process for preconditions of HTN methods. We state and prove theorems about CaMeL's soundness, completeness, and convergence properties. (3) We present empirical results about CaMeL's convergence under various conditions. Among other things, CaMeL converges the fastest on the preconditions of the HTN methods that are needed the most often. Thus CaMeL's output can be useful even before it has fully converged. [source]


    ON THE RELATIONSHIP BETWEEN FAMILY STRUCTURE AND ANTISOCIAL BEHAVIOR: PARENTAL COHABITATION AND BLENDED HOUSEHOLDS,

    CRIMINOLOGY, Issue 1 2008
    ROBERT APEL
    In the last several decades, the American family has undergone considerable change, with less than half of all adolescents residing with two married biological parents. Using the National Longitudinal Survey of Youth 1997, we construct an elaborate measure of family structure and find considerable heterogeneity in the risk of antisocial and delinquent behavior among groups of youth who reside in what are traditionally dichotomized as intact and nonintact families. In particular, we find that youth in "intact" families differ in important ways depending on whether the two biological parents are married or cohabiting and on whether they have children from a previous relationship. In addition, we find that youth who reside with a single biological parent who cohabits with a nonbiological partner exhibit an unusually high rate of antisocial behavior, especially if the custodial parent is the biological father. [source]


    Representing genetic variation as continuous surfaces: an approach for identifying spatial dependency in landscape genetic studies

    ECOGRAPHY, Issue 6 2008
    Melanie A. Murphy
    Landscape genetics, an emerging field integrating landscape ecology and population genetics, has great potential to influence our understanding of habitat connectivity and distribution of organisms. Whereas typical population genetics studies summarize gene flow as pairwise measures between sampling localities, landscape characteristics that influence population genetic connectivity are often continuously distributed in space. Thus, there are currently gaps in both the ability to analyze genotypic data in a continuous spatial context and our knowledge of expected of landscape genetic structure under varying conditions. We present a framework for generating continuous "genetic surfaces", evaluate their statistical properties, and quantify statistical behavior of landscape genetic structure in a simple landscape. We simulated microsatellite genotypes under varying parameters (time since vicariance, migration, effective population size) and used ancestry (q) values from STRUCTURE to interpolate a genetic surface. Using a spatially adjusted Pearson's correlation coefficient to test the significance of landscape variable(s) on genetic structure we were able to detect landscape genetic structure on a contemporary time scale (,5 generations post vicariance, migration probability ,0.10) even when population differentiation was minimal (FST,0.00015). We show that genetic variation can be significantly correlated with geographic distance even when genetic structure is due to landscape variable(s), demonstrating the importance of testing landscape influence on genetic structure. Finally, we apply genetic surfacing to analyze an empirical dataset of black bears from northern Idaho USA. We find black bear genetic variation is a function of distance (autocorrelation) and habitat patch (spatial dependency), consistent with previous results indicating genetic variation was influenced by landscape by resistance. These results suggest genetic surfaces can be used to test competing hypotheses of the influence of landscape characteristics on genetic structure without delineation of categorical groups. [source]


    DYNAMICS OF POLYPLOID FORMATION IN TRAGOPOGON (ASTERACEAE): RECURRENT FORMATION, GENE FLOW, AND POPULATION STRUCTURE

    EVOLUTION, Issue 7 2010
    V. Vaughan Symonds
    Polyploidy is a major feature of angiosperm evolution and diversification. Most polyploid species have formed multiple times, yet we know little about the genetic consequences of recurrent formations. Among the clearest examples of recurrent polyploidy are Tragopogon mirus and T. miscellus (Asteraceae), each of which has formed repeatedly in the last ,80 years from known diploid progenitors in western North America. Here, we apply progenitor-specific microsatellite markers to examine the genetic contributions to each tetraploid species and to assess gene flow among populations of independent formation. These data provide fine-scale resolution of independent origins for both polyploid species. Importantly, multiple origins have resulted in considerable genetic variation within both polyploid species; however, the patterns of variation detected in the polyploids contrast with those observed in extant populations of the diploid progenitors. The genotypes detected in the two polyploid species appear to represent a snapshot of historical population structure in the diploid progenitors, rather than modern diploid genotypes. Our data also indicate a lack of gene flow among polyploid plants of independent origin, even when they co-occur, suggesting potential reproductive barriers among separate lineages in both polyploid species. [source]


    EVOLUTION ON A LOCAL SCALE: DEVELOPMENTAL, FUNCTIONAL, AND GENETIC BASES OF DIVERGENCE IN BILL FORM AND ASSOCIATED CHANGES IN SONG STRUCTURE BETWEEN ADJACENT HABITATS

    EVOLUTION, Issue 8 2008
    Alexander V. Badyaev
    Divergent selection on traits involved in both local adaptation and the production of mating signals can strongly facilitate population differentiation. Because of its links to foraging morphologies and cultural inheritance song of birds can contribute particularly strongly to maintenance of local adaptations. In two adjacent habitats,native Sonoran desert and urban areas,house finches (Carpodacus mexicanus) forage on seeds that are highly distinct in size and shell hardness and require different bite forces and bill morphologies. Here, we first document strong and habitat-specific natural selection on bill traits linked to bite force and find adaptive modifications of bite force and bill morphology and associated divergence in courtship song between the two habitats. Second, we investigate the developmental basis of this divergence and find that early ontogenetic tissue transformation in bill, but not skeletal traits, is accelerated in the urban population and that the mandibular primordia of the large-beaked urban finches express bone morphogenetic proteins (BMP) earlier and at higher level than those of the desert finches. Further, we show that despite being geographically adjacent, urban and desert populations are nevertheless genetically distinct corroborating findings of early developmental divergence between them. Taken together, these results suggest that divergent selection on function and development of traits involved in production of mating signals, in combination with localized learning of such signals, can be very effective at maintaining local adaptations, even at small spatial scales and in highly mobile animals. [source]


    MINIMAL SELFING, FEW CLONES, AND NO AMONG-HOST GENETIC STRUCTURE IN A HERMAPHRODITIC PARASITE WITH ASEXUAL LARVAL PROPAGATION

    EVOLUTION, Issue 3 2006
    Charles D. Criscione
    Abstract Little is known about actual mating systems in natural populations of parasites or about what constitutes the limits of a parasite deme. These parameters are interesting because they affect levels of genetic diversity, opportunities for local adaptation, and other evolutionary processes. We expect that transmission dynamics and the distribution of parasites among hosts should have a large effect on mating systems and demic structure, but currently we have mostly speculation and very few data. For example, infrapopulations (all the parasites in a single host) should behave as demes if parasite offspring are transmitted as a clump from host to host over several generations. However, if offspring are well mixed, then the parasite component population (all the parasites among a host population) would function as the deme. Similarly, low mean intensities or a high proportion of worms in single infections should increase the selfing rate. For species having an asexual amplification stage, transmission between intermediate and definitive (final) hosts will control the variance in clonal reproductive success, which in turn could have a large influence on effective sizes and rates of inbreeding. We examined demic structure, selfing rates, and the variance in clonal reproductive success in natural populations of Plagioporus shawi, a hermaphroditic trematode that parasitizes salmon. Overall levels of genetic diversity were very high. An a posteriori inference of population structure overwhelmingly supports the component population as the deme, rather than individual infrapopulations. Only a single pair of 597 adult individuals was identified as clones. Thus, the variance in clonal reproductive success was almost zero. Despite being hermaphroditic, P. shawi appears to be almost entirely outcrossing. Genetic estimates of selfing (<5%) were in accordance with the proportion of parasites from single infections. Thus, it appears that individual flukes outcross whenever possible and only resort to selfing when alone. Finally, our data support the hypothesis that aquatic transmission and the use of several intermediate hosts promotes high genetic diversity and well-mixed infrapopulations. [source]


    PHYLOGENETIC ANALYSIS OF ECOMORPHOLOGICAL DIVERGENCE, COMMUNITY STRUCTURE, AND DIVERSIFICATION RATES IN DUSKY SALAMANDERS (PLETHODONTIDAE: DESMOGNATHUS)

    EVOLUTION, Issue 9 2005
    Kenneth H. Kozak
    Abstract An important dimension of adaptive radiation is the degree to which diversification rates fluctuate or remain constant through time. Focusing on plethodontid salamanders of the genus Desmognathus, we present a novel synthetic analysis of phylogeographic history, rates of ecomorphological evolution and species accumulation, and community assembly in an adaptive radiation. Dusky salamanders are highly variable in life history, body size, and ecology, with many endemic lineages in the southern Appalachian Highlands of eastern North America. Our results show that lifehistory evolution had important consequences for the buildup of plethodontid-salamander species richness and phenotypic disparity in eastern North America, a global hot spot of salamander biodiversity. The origin of Desmognathus species with aquatic larvae was followed by a high rate of lineage accumulation, which then gradually decreased toward the present time. The peak period of lineage accumulation in the group coincides with evolutionary partitioning of lineages with aquatic larvae into seepage, stream-edge, and stream microhabitats. Phylogenetic simulations demonstrate a strong correlation between morphology and microhabitat ecology independent of phylogenetic effects and suggest that ecomorphological changes are concentrated early in the radiation of Desmognathus. Deep phylogeographic fragmentation within many codistributed ecomorph clades suggests long-term persistence of ecomorphological features and stability of endemic lineages and communities through multiple climatic cycles. Phylogenetic analyses of community structure show that ecomorphological divergence promotes the coexistence of lineages and that repeated, independent evolution of microhabitat-associated ecomorphs has a limited role in the evolutionary assembly of Desmognathus communities. Comparing and contrasting our results to other adaptive radiations having different biogeographic histories, our results suggest that rates of diversification during adaptive radiation are intimately linked to the degree to which community structure persists over evolutionary time. [source]


    EFFECTIVE POPULATION SIZES AND TEMPORAL STABILITY OF GENETIC STRUCTURE IN RANA PIPIENS, THE NORTHERN LEOPARD FROG

    EVOLUTION, Issue 11 2004
    Eric A. Hoffman
    Abstract Although studies of population genetic structure are very common, whether genetic structure is stable over time has been assessed for very few taxa. The question of stability over time is particularly interesting for frogs because it is not clear to what extent frogs exist in dynamic metapopulations with frequent extinction and recolonization, or in stable patches at equilibrium between drift and gene flow. In this study we collected tissue samples from the same five populations of leopard frogs, Rana pipens, over a 22,30 year time interval (11,15 generations). Genetic structure among the populations was very stable, suggesting that these population were not undergoing frequent extinction and colonization. We also estimated the effective size of each population from the change in allele frequencies over time. There exist few estimates of effective size for frog populations, but the data available suggest that ranid frogs may have much larger ratios of effective size (Ne) to census size (Nc) that toads (bufonidae). Our results indicate that R. pipiens populations have effective sizes on the order of hundreds to at most a few thousand frogs, and Nee/Nc ratios in the range of 0.1,1.0. These estimates of Ne/Nc are consistent with those estimated for other Rana species. Finally, we compared the results of three temporal methods for estimating Ne. Moment and pseudolikelihood methods that assume a closed population gave the most similar point estimates, although the moment estimates were consistently two to four times larger. Wang and Whitlock's new method that jointly estimates Ne and the rate of immigration into a population (m) gave much smaller estimates of Ne and implausibly large estimates of m. This method requires knowing allele frequencies in the source of immigrants, but was thought to be insensitive to inexact estimates. In our case the method may have failed because we did not know the true source of immigrants for each population. The method may be more sensitive to choice of source frequencies than was previously appreciated, and so should be used with caution if the most likely source of immigrants cannot be identified clearly. [source]


    PHYLOGEOGRAPHIC STRUCTURE AND CRYPTIC SPECIATION IN THE TRANS-ANTARCTIC MOSS PYRRHOBRYUM MNIOIDES

    EVOLUTION, Issue 2 2003
    Stuart F. McDaniel
    Abstract Many bryophyte species have distributions that span multiple continents. The hypotheses historically advanced to explain such distributions rely on either long-distance spore dispersal or slow rates of morphological evolution following ancient continental vicariance events. We use phylogenetic analyses of DNA sequence variation at three chloroplast loci (atpB-rbcL spacer, rps4 gene, and trnL intron and 3,spacer) to examine these two hypotheses in the trans-Antarctic moss Pyrrhobryum mnioides. We find: (1) reciprocal monophyly of Australasian and South American populations, indicating a lack of intercontinental dispersal; (2) shared haplotypes between Australia and New Zealand, suggesting recent or ongoing migration across the Tasman Sea; and (3) reciprocal monophyly among Patagonian and neotropical populations, suggesting no recent migration along the Andes. These results corroborate experimental work suggesting that spore features may be critical determinants of species range. We use the mid-Miocene development of the Atacama Desert, 14 million years ago, to calibrate a molecular clock for the tree. The age of the trans-Antarctic disjunction is estimated to be 80 million years ago, consistent with Gondwanan vicariance, making it among the most ancient documented cases of cryptic speciation. These data are in accord with niche conservatism, but whether the morphological stasis is a product of stabilizing selection or phylogenetic constraint is unknown. [source]


    PLASTICITY IN QUEEN NUMBER AND SOCIAL STRUCTURE IN THE INVASIVE ARGENTINE ANT (LINEPITHEMA HUMILE)

    EVOLUTION, Issue 10 2002
    Krista K. Ingram
    Abstract., In many polygynous social insect societies, ecological factors such as habitat saturation promote high queen numbers by increasing the cost of solitary breeding. If polygyny is associated with constrained environments, queen number in colonies of invasive social insects should increase as saturation of their new habitat increases. Here I describe the variation in queen number, nestmate relatedness, and nest size along a gradient of time since colonization in an invading population of Argentine ants (Linepithema humile) in Haleakala, Hawaii. Nest densities in this population increase with distance from the leading edge of the invasion, reaching a stable density plateau approximately 80 m from the edge (> 2 years after colonization). Although the number of queens per nest in Haleakala is generally lower than previously reported for Argentine ants, there is significant variation in queen number across this population. Both the observed and effective queen numbers increase across the density gradient, and nests in the center of the population contain queen numbers three to nine times higher than those on the edge of the invasion. The number of workers per nest is correlated with queen number, and nests in the center are six times larger than nests at the edge. Microsatellite analysis of relatedness among nestmates reveals that all nests in the Haleakala population are characterized by low relatedness and have evidence of multiple reproducing queens. Relatedness values are significantly lower in nests in the center of the population, indicating that the number of reproducing queens is greater in areas of high nest density. The variation in queen number and nestmate relatedness in this study is consistent with expectations based on changes in ecological constraints during the invasion of a new habitat, suggesting that the social structure of Argentine ant populations is strongly influenced by ecological factors. Flexibility in social structure may facilitate persistence in variable environments and may also confer significant advantages to a species when introduced into new areas. [source]


    CREATIVE INDUSTRIES IN THE NETHERLANDS: STRUCTURE, DEVELOPMENT, INNOVATIVENESS AND EFFECTS ON URBAN GROWTH

    GEOGRAFISKA ANNALER SERIES B: HUMAN GEOGRAPHY, Issue 2 2008
    Erik Stam
    ABSTRACT. Creativity is central in stimulating economic growth in cities, regions and advanced capitalist economies in general. There is, of course, no one-to-one relation of the number of firms in creative industries to economic growth. Innovation is a key mechanism explaining the relationship of creative industries with economic performance. Based on an empirical study in the Netherlands we explore the effect of creative industries on innovation, and ultimately on employment growth in cities. In the Netherlands the three specific domains of creative industries - arts, media and publishing, and creative business services - make up 9 per cent of the business population. Drawing on survey data we find that firms in creative industries are indeed relatively innovative. Yet substantial differences are found across the three domains: firms in the arts domain are clearly less innovative, most likely due to a different (less market-oriented) dominant ideology. In addition, firms in creative industries located in urban areas are more innovative than their rural counterparts. We go on to analyse how the concentration of creative industries across cities is connected with employment growth. With the exception of the metropolitan city of Amsterdam, we find no measurable spill-over effect from creative industries. The presence of the creative class (in all kinds of industries other than creative ones) appears to be a much stronger driver of employment growth than creative industries. [source]


    THE CHANGING STRUCTURE OF THE CENTRAL PLACE SYSTEM IN TRØNDELAG, NORWAY, OVER THE PAST 40 YEARS , VIEWED IN THE LIGHT OF OLD AND RECENT THEORIES AND TRENDS

    GEOGRAFISKA ANNALER SERIES B: HUMAN GEOGRAPHY, Issue 2007
    Britt Dale
    ABSTRACT. The IGU Symposium on Urban Geography in Lund in 1960 was a path-breaking event towards new nomothetic thinking within the discipline. In nearly half of the papers, the state of the art in central place research was presented and debated. The symposium was the main source of inspiration for a study of the central place system in Midt-Norge in the 1960s, a research project that has been followed up in stages over a 40-year period. The result is a unique collection of data, covering all central places in the region and the location of approximately 200 service functions of different categories in the 1960s, 1980s and c. 2000. Despite the profound changes that have taken place on the part of the consumer, as well as the supplier, the main structure of the central place hierarchy has been surprisingly stable. However, when looking at the growth and decline of each of the different service functions, considerable dynamics have been found. There are tendencies of centralization/concentration as well as decentralization/dispersion. Furthermore, the functional division of labour by vertical steps and tiers in the 1960s has been supplemented by horizontal specialization between places, and also in the lower levels of the central place hierarchy. In this paper, we present and discuss some of the main changes that have taken place in the system in the light of older and newer theories and trends. [source]


    TOWARD A MORE COMPLETE MODEL OF OPTIMAL CAPITAL STRUCTURE

    JOURNAL OF APPLIED CORPORATE FINANCE, Issue 1 2002
    Roger Heine
    Most corporate finance practitioners understand the trade-off involved in making effective use of debt capacity while safeguarding the firm's ability to execute its business strategy without disruption. But quantifying that trade-off to arrive at an optimal level of debt can be a complicated and challenging task. This paper develops a simulation model of capital structure that starts by generating multiple estimates of market rates (LIBOR, currency rates) and corresponding company operating cash flows. To arrive at an optimal capital structure, the model then incorporates the shareholder value effects of alternative financing decisions by directly measuring the costs of financial distress, including the costs of missed investment opportunities and higher working capital requirements. The model generates both a target credit rating and a lower fallback rating that permits a higher level of debt to maintain investments and dividends when operating cash flows are weak. As the model shows, companies with volatile cash flows and significant investment opportunities can add substantial shareholder value by establishing a fallback credit rating that is one or two notches below the target rating. The model also optimizes the mix of fixed versus floating debt, the maturity structure, and the currency composition. Another distinctive feature of the model is its ability to estimate the expected cost of alternative liability structures that can provide the liquidity insurance necessary to sustain the firm through periods of severe stress. This cost turns out to be quite small relative to the total market capitalization of the average firm. [source]


    ADHESION TO LASER-PREPARED TOOTH STRUCTURE

    JOURNAL OF ESTHETIC AND RESTORATIVE DENTISTRY, Issue 6 2006
    MS Author, Thomas J. Hilton DMD
    The use of Er:YAG (erbium : yttrium aluminum garnet and Er,Cr:YAG (erbium, chromium : yttrium scandium gallium garnet) lasers for tooth preparation has received much attention in recent years. Several advantages have been attributed to these devices, including a reduced need for local anesthesia for tooth preparation, less vibration to the patient, and more conservative cavity preparation. Another purported advantage has been the contention that adhesion to tooth structure is enhanced compared with other means of cavity preparation, even to the point of eliminating the need for conditioning and/or etching prior to adhesive system application. As the use of bonded, esthetic restorations has increased, it is important to know if this purported bonding advantage is valid. This Critical Appraisal examines evidence in the peer-reviewed scientific literature that contradicts this contention, and discusses concerns regarding the use of lasers in cavity preparation. [source]


    CYLINDRICAL AND CONICAL FOLD GEOMETRIES IN THE CANTARELL STRUCTURE, SOUTHERN GULF OF MEXICO: IMPLICATIONS FOR HYDROCARBON EXPLORATION

    JOURNAL OF PETROLEUM GEOLOGY, Issue 3 2006
    J. J. Mandujano V.
    The NW-SE trending Cantarell structure in the Gulf of Campeche hosts the largest oilfield in Mexico. The oil occurs predominantly in latest Cretaceous , earliest Tertiary breccias with subsidiary reserves in Upper Jurassic (Oxfordian and Kimmeridgian) and Lower Cretaceous oolitic and partially dolomitized limestones, dolomites and shaly limestones. Cantarell has been interpreted both as a fold-and-thrust zone and as a dextral transpressional structure. Analysis of structure contours at 100m intervals, on the tops of the Tertiary breccia and the Kimmeridgian (Upper Jurassic) dolomite, indicates that the structure is an upright cylindrical fold with gently plunging conical terminations; there is also a conical portion in the central part of the structure. The axes of the central, NW and SE cones are subvertical. This geometry indicates that the two fold terminations and the central cone are aprons rather than points, with the NW and central cone axes intersecting the cylindrical fold axis at the point where the geometry switches from conical to cylindrical. The apical angle (i.e. the angle between the fold and cone axes) varies as follows: (i) in the NW cone, it is ,70° in the breccia and ,76° in the Kimmeridgian dolomite; (ii) in the central cone, it is ,77° in the breccia and ,73° in the Kimmeridgian dolomite; and (iii) in the SE cone, it is ,64° in the breccia and ,57° in the Kimmeridgian dolomite. This indicates that whereas the fold opens with depth in the NW cone, it tightens with depth in the central and SE cones. Assuming a parallel fold geometry, these apical angles indicate an increase in volume in the NW cone (i.e. larger hydrocarbon reservoirs), compared to the central and SE cones. Theoretical considerations indicate that the curvature increases dramatically towards the point of the cone. In the case of the Cantarell structure, the apices of the cones are located at the conical-cylindrical fold junctions, where the highest curvature may have resulted in a higher degree of fracturing. The coincidence of maximum curvature and the intersection of the conical and cylindrical fold axes in the fold culminations with porous and permeable reservoir rocks may have made these locations favourable for the accumulation of hydrocarbons. [source]


    A REVIEW OF EOCENE NUMMULITE ACCUMULATIONS: STRUCTURE, FORMATION AND RESERVOIR POTENTIAL

    JOURNAL OF PETROLEUM GEOLOGY, Issue 1 2001
    A. Racey
    Eocene nummulite accumulations, also referred to as nummullte "banks", form Important hydrocarbon reservoirs in Tunisia and Libya and may constitute exploration targets in other parts of North Africa, the Mediterranean and the Middle East. Porosities commonly average 10,20% and permeabilities 10,50md. Foraminifera of the genus Nummulites may comprise up to 98% of the bioclasts in these carbonate reservoirs, although only one or two species may be present. The absence of associated fauna is generally taken to indicate an oligotrophic depositional environment. In this paper, the palaeoecology of the genus Nummulites is discussed together with depositional models for two nummulitic carbonate reservoirs , the Middle Eocene Seeb Limestone of Oman and the Early Eocene El Garia/Jdeir Formation of Tunisia and Libya. The El Garia and Seeb Limestone Formations were deposited in ramp settings, and comprise a series of amalgamated sheets or low-relief banks. In the Hasdrubal field offshore Tunisia, where the El Garia Formation constitutes the reservoir rock, most of the nummulites have been redeposited from shallow into deeper waters whilst in the Bourri field (offshore Libya) they occur as an in situ "bank". Nummulite accumulations often show evidence that both physical reworking (scouring, winnowing and imbrication) and biological processes (reproduction strategies and bioturbation) have influenced their formation. A general model is outlined for discriminating between physically and ecologically produced biofabrics, and the implications for reservoir quality are discussed. [source]


    DIFFERENCES IN POLYSACCHARIDE STRUCTURE BETWEEN CALCIFIED AND UNCALCIFIED SEGMENTS IN THE CORALLINE CALLIARTHRON CHEILOSPORIOIDES (CORALLINALES, RHODOPHYTA),

    JOURNAL OF PHYCOLOGY, Issue 3 2010
    Patrick T. Martone
    The articulated coralline Calliarthron cheilosporioides Manza produces segmented fronds composed of calcified segments (intergenicula) separated by uncalcified joints (genicula), which allow fronds to bend and reorient under breaking waves in the wave-swept intertidal zone. Genicula are formed when calcified cells decalcify and restructure to create flexible tissue. The present study has identified important differences in the main agaran disaccharidic repeating units [,3)-,- d -Galp (1, 4)-,- l -Galp(1,] synthesized by genicular and intergenicular segments. Based on chemical and spectroscopical analyses, we report that genicular cells from C. cheilosporioides biosynthesize a highly methoxylated galactan at C-6 position with low levels of branching with xylose side stubs on C-6 of the [,3)-,- d -Galp (1,] units, whereas intergenicular segments produce xylogalactans with high levels of xylose and low levels of 6- O -methyl ,- d -Gal units. These data suggest that, during genicular development, xylosyl branched, 3-linked ,- d -Galp units present in the xylogalactan backbones from intergenicular walls are mostly replaced by 6- O -methyl -d- galactose units. We speculate that this structural shift is a consequence of a putative and specific methoxyl transferase that blocks the xylosylation on C-6 of the 3-linked ,- d -Galp units. Changes in galactan substitutions may contribute to the distinct mechanical properties of genicula and may lend insight into the calcification process in coralline algae. [source]


    BENTHIC AND PLANKTONIC ALGAL COMMUNITIES IN A HIGH ARCTIC LAKE: PIGMENT STRUCTURE AND CONTRASTING RESPONSES TO NUTRIENT ENRICHMENT,

    JOURNAL OF PHYCOLOGY, Issue 6 2005
    Sylvia Bonilla
    We investigated the fine pigment structure and composition of phytoplankton and benthic cyanobacterial mats in Ward Hunt Lake at the northern limit of High Arctic Canada and the responses of these two communities to in situ nutrient enrichment. The HPLC analyses showed that more than 98% of the total pigment stocks occurred in the benthos. The phytoplankton contained Chrysophyceae, low concentrations of other protists and Cyanobacteria (notably picocyanobacteria), and the accessory pigments chl c2, fucoxanthin, diadinoxanthin, violaxanthin, and zeaxanthin. The benthic community contained the accessory pigments chl b, chl c2, and a set of carotenoids dominated by glycosidic xanthophylls, characteristic of filamentous cyanobacteria. The black surface layer of the mats was rich in the UV-screening compounds scytonemin, red scytonemin-like, and mycosporine-like amino acids, and the blue-green basal stratum contained high concentrations of light-harvesting pigments. In a first bioassay of the benthic mats, there was no significant photosynthetic or growth response to inorganic carbon or full nutrient enrichment over 15 days. This bioassay was repeated with increased replication and HPLC analysis in a subsequent season, and the results confirmed the lack of significant response to added nutrients. In contrast, the phytoplankton in samples from the overlying water column responded strongly to enrichment, and chl a biomass increased by a factor of 19.2 over 2 weeks. These results underscore the divergent ecophysiology of benthic versus planktonic communities in extreme latitudes and show that cold lake ecosystems can be dominated by benthic phototrophs that are nutrient sufficient despite their ultraoligotrophic overlying waters. [source]


    THE STRUCTURE AND NANOMECHANICAL PROPERTIES OF THE ADHESIVE MUCILAGE THAT MEDIATES DIATOM-SUBSTRATUM ADHESION AND MOTILITY,

    JOURNAL OF PHYCOLOGY, Issue 6 2003
    Michael J. Higgins
    We investigated the adhesive mucilage and mechanism of cell-substratum adhesion of two benthic raphid diatoms, the marine species Craspedostauros australis E. J. Cox and the freshwater species Pinnularia viridis (Nitzsch) Ehrenberg. SEM images of P. viridis and C. australis cells revealed the presence of multistranded tethers that appear to arise along the raphe openings and extend for a considerable distance from the cell before forming a "holdfast-like" attachment with the substratum. We propose that the tethers result from the elongation/stretching of composite adhesive mucilage strands secreted from raphes during the onset of cell adhesion and reorientation. Atomic force microscopy (AFM) force measurements reveal that the adhesive strands originating from the nondriving raphe of live C. australis and P. viridis are highly extensible and accumulate to form tethers. During force measurements tethers can be chemically stained and are seen to extend between the cantilever tip and a cell during elongation and relaxation. In most cases, AFM force measurements recorded an interaction with a number of adhesive strands that are secreted from the raphe. The force curves of C. australis and P. viridis revealed a sawtooth pattern, suggesting the successive unbinding of modular domains when the adhesive strands were placed under stress. In addition, we applied the "fly-fishing" technique that allowed the cantilever, suspended a distance above the cell, to interact with single adhesive strands protruding from the raphe. These force curves revealed sawtooth patterns, although the binding forces recorded were in the range for single molecule interactions. [source]


    USING INCIDENT LIGHT TO MAXIMIZE RESOLUTION OF STRUCTURE ON DIATOM VALVES WITH A LIGHT MICROSCOPE

    JOURNAL OF PHYCOLOGY, Issue 2001
    Article first published online: 24 SEP 200
    Siver, P. A. Botany Department, Connecticut College, New London, CT 06320 Because of their abundance in a diverse array of aquatic habitats and chemical conditions, and the fact that their species-specific siliceous outer coverings remain for millennia in sediments, diatoms have become one of the most powerful organismal groups used in the reconstruction of historical environmental conditions. Although SEM is now needed to identify some species, the bulk of the identifications and data collection is still accomplished with a light microscope. In this paper I will demonstrate the use of interference reflection contrast (incident light) for the examination of diatoms that significantly improves the resolution of structural detail. Using incident light one can routinely distinguish between structures close to the theoretical limit of resolution for visible light, and about 70 nm closer together than resolvable with standard transmitted light optics. Examples of how the incident light technique can improve data collection with light microscopy will be given. Most research light microscopes could be easily and inexpensively outfitted to use this technique. [source]


    ENDOMEMBRANE STRUCTURE AND THE CHLOROPLAST PROTEIN TARGETING PATHWAY IN HETEROSIGMA AKASHIWO (RAPHIDOPHYCEAE, CHROMISTA)

    JOURNAL OF PHYCOLOGY, Issue 6 2000
    Ken-ichiro Ishida
    Chloroplasts in heterokont algae are surrounded by four membranes and probably originated from a red algal endosymbiont that was engulfed and retained by eukaryotic host. Understanding how nuclear-encoded chloroplast proteins are translocated from the cytoplasm into the chloroplast across these membranes could give us some insights about how the endosymbiont was integrated into the host cell in the process of secondary symbiogenesis. In multiplastid heterokont algae such as raphidophytes, it has been unclear if the outermost of the four membranes surrounding the chloroplast (the chloroplast endoplasmic reticulum [CER] membrane) is continuous with the nuclear envelope and rough endoplasmic reticulum (ER). Here, we report detailed ultrastructural observations of the raphidophyte Heterosigma akashiwo (Hada) Hada ex Y. Hara et Chihara that show that the CER membranes were continuous with ER membranes that had attached ribosomes, implying that the chloroplast with three envelope membranes is located within the ER lumen, that is, topologically the same structure as that of monoplastid heterokont algae. However, the CER membrane of H. akashiwo had very few, if any, ribosomes attached, unlike the CER membranes in other heterokont algae. To verify that proteins are first targeted to the ER, we assayed protein import into canine microsomes using a precursor for a nuclear-encoded chloroplast protein, the fucoxanthin-chlorophyll a/c protein of H. akashiwo. This demonstrated that the precursor has a functional signal sequence for ER targeting and is cotranslationally translocated into the ER, where a signal sequence of about 17 amino acids is removed. Based on these data, we hypothesize that in H. akashiwo, nuclear-encoded chloroplast protein precursors that have been cotranslationally transported into the ER lumen are sorted in the ER and transported to the chloroplasts through the ER lumen. [source]


    STRUCTURE, COMPOSITION AND BIOGENESIS OF PRASINOPHYTE SCALES

    JOURNAL OF PHYCOLOGY, Issue 2000
    B. Becker
    The cell body and flagellar surfaces of prasinophytes are covered by non-mineralyzed scales. Scales consist mainly of acidic polysaccharides containing large amounts of 2-keto sugar acids. Glycoproteins are minor components and probably mainly involved in mediating scale-subunit and scale-membrane interactions. In thecate prasinophytes the cell body scales coalesce to form a rigid cell wall, generally known as a theca. We have studied the polysaccharides and glycoproteins of the thecate prasinophytes Tetraselmis striata and Scherffelia dubia over the last years. New results regarding the structure of carbohydrates and proteins will be presented. [source]


    A SEARCH FOR MULTIPLE EQUILIBRIA IN URBAN INDUSTRIAL STRUCTURE,

    JOURNAL OF REGIONAL SCIENCE, Issue 1 2008
    Donald R. Davis
    ABSTRACT Theories featuring multiple equilibria are widespread across economics. Yet little empirical work has asked if multiple equilibria are features of real economies. We examine this in the context of the Allied bombing of Japanese cities and industries in World War II. We develop a new empirical test for multiple equilibria and apply it to data for 114 Japanese cities in eight manufacturing industries. The data provide no support for the existence of multiple equilibria. In the aftermath even of immense shocks, a city typically recovers not only its population and its share of aggregate manufacturing, but even the industries it had before. [source]


    CONSTRUCTION COSTS AND THE SUPPLY OF HOUSING STRUCTURE,

    JOURNAL OF REGIONAL SCIENCE, Issue 4 2006
    Joseph Gyourko
    ABSTRACT Construction costs account for the bulk of the price of new houses in most markets, but their study has been relatively neglected. We document that there are economically large differences in construction costs across U.S. housing markets. We also estimate a very elastic supply for physical structure; hence, differences in construction activity across markets do not explain the variation in costs. Supply shifters that collectively do account for differences in building costs include the extent of unionization within the construction sector, local wages, local topography in terms of the presence of high hills and mountains, and the local regulatory environment. [source]


    THE SOCIAL STRUCTURE OF BOTTLENOSE DOLPHINS, TURSIOPS TRUNCATUS, IN THE BAHAMAS

    MARINE MAMMAL SCIENCE, Issue 4 2004
    Cindy A. Rogers
    Abstract The social structure of coastal ecotype bottlenose dolphins, Tursiops truncatus, is largely unknown as they inhabit regions far from shore. This study reports on a community of bottlenose dolphins , 27 km from Grand Bahama Island (May-September, 1993,2002). Resident and non-resident dolphins occurred in the area. Some dolphins traveled over 320 km between communities; others showed long- term site fidelity up to 17 yr. Average group size was 3,5, and was significantly larger with calves present and significantly smaller when traveling. The half-weight index was used to determine coefficients of association (COA) for individuals of known sex annually and for pooled years. Permutation tests revealed non-random associations and presence of preferred/avoided companions in all data sets. Annual COAs were low: female-female ,= 0.31, male-male ,= 0.30, and mixed-sex ,= 0.26. Mother-calf associations showed the highest values. Some males formed strong, long-term bonds. Female COAs fluctuated with reproductive status. Using pooled data, COAs were lower and the same basic trends were evident. However, strong associations seen in the annual data were not evident in pooled data. Bottlenose dolphins that inhabit offshore, shallow water show many of the same social structure characteristics as in well-studied coastal populations. [source]


    GEOGRAPHIC GENETIC STRUCTURE IN THE FRANCISCANA DOLPHIN (PONTOPORIA BLAINVILLEI)

    MARINE MAMMAL SCIENCE, Issue 2 2004
    Marila Lázaro
    Abstract The franciscana, Pontoporia blainvillei, is endemic to the South Atlantic coast of South America. The species is of conservation concern because it suffers elevated mortality rates due to incidental captures in fishing nets, and perhaps it is one of the most threatened small cetaceans in this region. Previous morphological and genetic studies have suggested the existence of at least two distinct stocks to the north and south of Santa Catarina Island in Brazil. Fixed differences were found between a sample from Rio de Janeiro and one from Rio Grande do Sul, in southern Brazil. Using 94 sequences of the control region of mitochondrial DNA, we examined the genetic structure of the species. We found no shared haplotypes between Rio de Janeiro and samples from the southern range of the species distribution. However, a phylogenetic analysis suggests that the former population is diphyletic with respect to the southern samples. This suggests that the populations have not been isolated long enough to reach reciprocal monophyly. Furthermore, genetic differentiation is broadly consistent with a simple model of isolation by distance, that therefore appears as an alternative to a model of strict isolation of two stocks. The estimated levels of gene flow are higher among neighboring populations, and decrease as more distant localities are compared. Finally, the molecular data suggest that franciscanas have expanded in Rio de Janeiro. [source]


    POPULATION GENETIC STRUCTURE OF FINLESS PORPOISES, NEOPHOCAENA PHOCAENOIDES, IN CHINESE WATERS, INFERRED FROM MITOCHONDRIAL CONTROL REGION SEQUENCES

    MARINE MAMMAL SCIENCE, Issue 2 2002
    Guang Yang
    Abstract Seven hundred and twenty base pairs (bp) of the mitochondrial control region from 73 finless porpoises, Neophocaena phocaenoides, in Chinese waters were sequenced. Thirteen variable sites were determined and 17 haplotypes were defined. Of these, 5 and 7 were found only in the Yellow Sea population and the South China Sea population, respectively, whereas no specific haplo-type was found in the Yangtze River population. Phylogenetic analyses using NJ and ML algorithm did not divide the haplotypes into monophyletic clades representing recognized geographic populations of finless porpoises in Chinese waters, suggesting the existence of migration and gene flow among populations. Analysis of molecular variance showed the obvious population genetic structure (,st= 0.41, P < 0.05); however, the structure was mainly between either the Yangtze River population or the Yellow Sea population and the South China Sea population. The genetic diversity (nucleotide diversity and haplotypic diversity) of the Yellow Sea population was significantly higher than those of the Yangtze River population and the South China Sea population, suggesting the relatively later divergence of the latter two populations and supporting the Yellow Sea population as the original center of Neophocaena. [source]


    THE DEPENDENCE STRUCTURE OF RUNNING MAXIMA AND MINIMA: RESULTS AND OPTION PRICING APPLICATIONS

    MATHEMATICAL FINANCE, Issue 1 2010
    Umberto Cherubini
    We provide general results for the dependence structure of running maxima (minima) of sets of variables in a model based on (i) Markov dynamics; (ii) no Granger causality; (iii) cross-section dependence. At the time series level, we derive recursive formulas for running minima and maxima. These formulas enable to use a "bootstrapping" technique to recursively recover the pricing kernels of barrier options from those of the corresponding European options. We also show that the dependence formulas for running maxima (minima) are completely defined from the copula function representing dependence among levels at the terminal date. The result is applied to multivariate discrete barrier digital products. Barrier Altiplanos are simply priced by (i) bootstrapping the price of univariate barrier products; (ii) evaluating a European Altiplano with these values. [source]


    PRICING IN AN INCOMPLETE MARKET WITH AN AFFINE TERM STRUCTURE

    MATHEMATICAL FINANCE, Issue 3 2004
    Virginia R. Young
    We apply the principle of equivalent utility to calculate the indifference price of the writer of a contingent claim in an incomplete market. To recognize the long-term nature of many such claims, we allow the short rate to be random in such a way that the term structure is affine. We also consider a general diffusion process for the risky stock (index) in our market. In a complete market setting, the resulting indifference price is the same as the one obtained by no-arbitrage arguments. We also show how to compute indifference prices for two types of contingent claims in an incomplete market, in the case for which the utility function is exponential. The first is a catastrophe risk bond that pays a fixed amount at a given time if a catastrophe does not occur before that time. The second is equity-indexed term life insurance which pays a death benefit that is a function of the short rate and stock price at the random time of the death of the insured. Because we assume that the occurrence of the catastrophe or the death of the insured is independent of the financial market, the markets for the catastrophe risk bond and the equity-indexed life insurance are incomplete. [source]