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Hierarchical Structure (hierarchical + structure)
Selected AbstractsTartatric Acid and L -Cysteine Synergistic-Assisted Synthesis of Antimony Trisulfide Hierarchical Structures in Aqueous SolutionEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 35 2009Jun Pan Abstract Alveolate amorphous Sb2S3 microspheres about 2 ,m in diameter were hydrothermally synthesized in aqueous solution without the use of a surfactant at 180 °C by using SbCl3, L -cysteine, and tartaric acid as starting materials. After annealing at 250 °C for 3 h under a nitrogen atmosphere, polycrystalline Sb2S3 hollow spheres were obtained. The morphology, structure, and phase composition of alveolate Sb2S3 microspheres were characterized by X-ray diffraction, field-emission scanning electron microscopy, energy dispersive X-ray analysis, and X-ray photoelectron spectroscopy. It was demonstrated that tartaric acid and L -cysteine play a key role in the formation of such hierarchical structures. In addition, the possible aggregation mechanism was proposed to illustrate the formation of Sb2S3 microspheres on the basis of the experimental results and analyses.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source] Hierarchical Structures in Tin(II) OxalatesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 9 2008Padmini Ramaswamy Abstract Six new SnII oxalates exhibiting a hierarchy of structures have been prepared employing hydrothermal methods. The compounds I [C10N2H10][Sn(C2O4)2], II [C10N2H10][Sn2(C2O4)3], and III [C8N4H26][Sn(C2O4)2]2·2H2O possess zero-dimensional molecular structures; IV [C10N2H8]2[Sn(C2O4)]2 and V [C12N2H8][SnC2O4] have one-dimensional chain structures; and compound VI [C5N2H14]2[Sn4(C2O4)6]·7H2O has a two-dimensional layer structure. The SnII ions have 4- and 6-coordination with square-pyramidal or pentagonal-bipyramidal geometry, in which the lone pair of electrons also occupies one of the vertices. Weak intermolecular forces such as hydrogen-bond interactions, ,···, interactions, and lone-pair,, interactions have been observed and appear to lendstructural stability. Theoretical studies indicate that the ,···, interaction energy between the bound 1,10-phenanthroline molecules is of the order of 5,6 kcal,mol,1 in V. Natural bond orbital (NBO) analysis on two model compounds, II and IV, indicates reasonable lone-pair,, interactions. The close structural relationship between all the compounds indicates that a building-up process from the zero-dimensional monomer can be considered. The present structures provide opportunities for evaluating the structure-directing role of the lone pair of electrons of SnII.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] Creating Hierarchical Structures in Renewable Composites by Attaching Bacterial Cellulose onto Sisal Fibers,ADVANCED MATERIALS, Issue 16 2008Julasak Juntaro The growth of bacterial-cellulose nanofibrils on the surfaces of micrometer-scale natural fibers provides a route to a new class of hierarchical, renewable, degradable composites. The nanofibrils improve the interaction between the primary fibers and the matrix, leading to improved mechanical properties and water resistance. [source] Hierarchical structure of niobate nanosheets in aqueous solutionJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 2007Satoshi Koizumi The hierarchical structure of an aqueous dispersion of niobate nanosheets was explored by using a combined method of ultra-small-angle and small-angle scattering of neutrons and X-rays. The concentration of the sheets studied was in the range where the dispersion exhibits a liquid-crystal phase as evidenced by observation between crossed polarizers in a previous report. The scattering data covered a wide q scale of more than four orders of magnitude [3 × 10,4,q, 10,nm,1, where q = (4,/,)sin(,/2), , and , being the wavelength of the incident beam and the scattering angle, respectively], corresponding to the length scale l = 2,/q from ~1,nm to ~20,µm. The scattering analyses provided information on the hierarchical structural elements including: (i) single nanosheets as a structure element (hierarchy I), (ii) parallel stacks of the sheets (hierarchy II), and (iii) spatial arrangements of the stacks (hierarchy III), in order of increasing length scale. Hierarchy II is closely related to the liquid-crystal nature of the dispersion in which the spacing and the persistence length, normal and parallel to the stack surface, respectively, were disclosed. Hierarchy III gives rise to the low- q upturn in the scattering profile, which may be characterized by mass-fractal-like power-law scattering behavior. This finding is a surprise from the viewpoint of the liquid-crystal nature of the dispersion, a possible model of which is proposed in the text. [source] Hierarchical structures of affect and psychopathology and their implications for the classification of emotional disorders,DEPRESSION AND ANXIETY, Issue 4 2008David Watson Abstract The Diagnostic and Statistical Manual of Mental Disorders,IV groups disorders into diagnostic classes on the basis of the subjective criterion of "shared phenomenological features." The current mood and anxiety disorders reflect the logic of older models emphasizing the existence of discrete emotions and, consequently, are based on a fundamental distinction between depressed mood (central to the mood disorders) and anxious mood (a core feature of the anxiety disorders). This distinction, however, ignores subsequent work that has established the existence of a general negative affect dimension that (a) produces strong correlations between anxious and depressed mood and (b) is largely responsible for the substantial comorbidity between the mood and anxiety disorders. More generally, there are now sufficient data to eliminate the current rational system and replace it with an empirically based taxonomy that reflects the actual,not the assumed,similarities among disorders. The existing structural evidence establishes that the mood and anxiety disorders should be collapsed together into an overarching superclass of emotional disorders, which can be decomposed into three subclasses: the distress disorders (major depression, dysthymic disorder, generalized anxiety disorder, posttraumatic stress disorder), the fear disorders (panic disorder, agoraphobia, social phobia, specific phobia), and the bipolar disorders (bipolar I, bipolar II, cyclothymia). An empirically based system of this type will facilitate differential diagnosis and encourage the ultimate development of an etiologically based taxonomy. Depression and Anxiety 25:282,288, 2008. Published 2008 Wiley-Liss, Inc. [source] Hierarchical structures formed by partially crystalline polymers in solution: from fundamentals to applications , a combined conventional, focusing and ultra-small-angle neutron scattering studyJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 2007Dietmar Schwahn Multilevel aggregates with characteristic sizes covering four orders of magnitude, from 1,nm to 10,µm, are formed upon cooling decane solutions of poly(ethylene-butene) random copolymers (designated as PEB- n, where n is the number of ethyl side branches per 100 backbone C atoms) and wax-containing mixed solutions. The partially crystalline PEB-7.5 copolymers form two distinct morphologies that evolve on a range of length scales. When these polymers are mixed with wax molecules having a crystallization point lower than the polymer aggregation temperature, a hierarchy of morphologies evolves on decreasing the temperature. The multilevel structures were elucidated by combining conventional small-angle neutron scattering, focusing small-angle neutron scattering and ultra-small-angle neutron scattering investigations with microscopy. Contrast-matching analysis of the wax and copolymer components within the common morphologies revealed the wax-crystal modification capacity of the PEB-7.5 copolymers. Since the copolymers limit the growth of wax crystals, they are potential pour-point depressants for the fuel industry. [source] Hierarchical structures of dendritic polymersPOLYMER INTERNATIONAL, Issue 2 2010Masaki Ujihara Abstract Dendritic polymers' highly specific and three-dimensional architectures set them apart from linear and slightly branched polymers. Their unique properties also allow them to form hierarchical organizations, which can be classified as planar or non-planar. The preparation of a planar hierarchy consisting of dendritic polymers can be achieved by conventional techniques of adsorption or Langmuir monolayer and Langmuir,Blodgett accumulation, and the resultant hierarchy is well ordered. Non-planar hierarchies are built on non-planar scaffolds, for example by self-assembly. In this mini-review, the practical/potential applications of dendritic polymers such as for electrical or optical devices, sensing systems, or medical diagnosis are also reviewed in association with their structures. Copyright © 2009 Society of Chemical Industry [source] Tunneling enhanced by web page content block partition for focused crawlingCONCURRENCY AND COMPUTATION: PRACTICE & EXPERIENCE, Issue 1 2008Tao Peng Abstract The complexity of web information environments and multiple-topic web pages are negative factors significantly affecting the performance of focused crawling. A highly relevant region in a web page may be obscured because of low overall relevance of that page. Segmenting the web pages into smaller units will significantly improve the performance. Conquering and traversing irrelevant page to reach a relevant one (tunneling) can improve the effectiveness of focused crawling by expanding its reach. This paper presents a heuristic-based method to enhance focused crawling performance. The method uses a Document Object Model (DOM)-based page partition algorithm to segment a web page into content blocks with a hierarchical structure and investigates how to take advantage of block-level evidence to enhance focused crawling by tunneling. Page segmentation can transform an uninteresting multi-topic web page into several single topic context blocks and some of which may be interesting. Accordingly, focused crawler can pursue the interesting content blocks to retrieve the relevant pages. Experimental results indicate that this approach outperforms Breadth-First, Best-First and Link-context algorithm both in harvest rate, target recall and target length. Copyright © 2007 John Wiley & Sons, Ltd. [source] Compiling data-parallel programs for clusters of SMPsCONCURRENCY AND COMPUTATION: PRACTICE & EXPERIENCE, Issue 2-3 2004Siegfried Benkner Abstract Clusters of shared-memory multiprocessors (SMPs) have become the most promising parallel computing platforms for scientific computing. However, SMP clusters significantly increase the complexity of user application development when using the low-level application programming interfaces MPI and OpenMP, forcing users to deal with both distributed-memory and shared-memory parallelization details. In this paper we present extensions of High Performance Fortran (HPF) for SMP clusters which enable the compiler to adopt a hybrid parallelization strategy, efficiently combining distributed-memory with shared-memory parallelism. By means of a small set of new language features, the hierarchical structure of SMP clusters may be specified. This information is utilized by the compiler to derive inter-node data mappings for controlling distributed-memory parallelization across the nodes of a cluster and intra-node data mappings for extracting shared-memory parallelism within nodes. Additional mechanisms are proposed for specifying inter- and intra-node data mappings explicitly, for controlling specific shared-memory parallelization issues and for integrating OpenMP routines in HPF applications. The proposed features have been realized within the ADAPTOR and VFC compilers. The parallelization strategy for clusters of SMPs adopted by these compilers is discussed as well as a hybrid-parallel execution model based on a combination of MPI and OpenMP. Experimental results indicate the effectiveness of the proposed features. Copyright © 2004 John Wiley & Sons, Ltd. [source] Parsing the general and specific components of depression and anxiety with bifactor modeling,DEPRESSION AND ANXIETY, Issue 7 2008Leonard J. Simms Ph.D. Abstract Recent hierarchical models suggest that both general and specific components are needed to fully represent the variation observed among mood and anxiety disorders. However, little is known about the relative size, severity, and psychological meaning of these components. We studied these features through bifactor modeling of the symptoms from the Inventory of Depression and Anxiety Symptoms [IDAS; Watson et al., 2007] in 362 community adults, 353 psychiatric patients, and 673 undergraduates. Results revealed that although all IDAS symptom types loaded prominently both on a general factor as well as specific factors, some symptom groups,such as dysphoria, generalized anxiety, and irritability,were influenced more strongly by the general factor, whereas others,e.g., appetite gain, appetite loss, and low well-being,contained a larger specific component. Second, certain symptom groups,e.g., Suicidality, Panic, Appetite Loss, and Ill Temper,reflected higher severity than other symptom groups. Finally, general factor scores correlated strongly with markers of general distress and negative emotionality. These findings support a hierarchical structure among mood and anxiety symptoms and have important implications for how such disorders are described, assessed, and studied. Depression and Anxiety 0:1,13, 2007. Published 2007 Wiley-Liss, Inc. [source] Coordinated voltage control of transformer taps with provision for hierarchical structure in power systemELECTRICAL ENGINEERING IN JAPAN, Issue 4 2009Yoshiki Nakachi Abstract Participation of distributed generators (DGs), such as wind turbines, cogeneration systems, etc., is a natural trend from an ecological point of view and will continue to increase. The outputs of these DGs mainly depend on weather conditions but do not correspond to the changes of electrical load demand necessarily. On the other hand, due to deregulation of the electric power market, the power flow in a power system will uncertainly vary with several power transactions. Thus, complex power flow by DGs or transactions will cause voltage deviation. It will be difficult to sustain the voltage quality by using conventional voltage/reactive power control in the near future. In this paper, in order to avoid such voltage deviation and to decrease the frequency of transformer tap operations, the coordinated voltage control scheme of transformer taps on account of hierarchical structure in the power system is proposed. In the proposed scheme, integral of voltage deviation at each layer bus is applied to decide the timing of each transformer tap operation. Numerical simulations confirm that the proposed scheme is able to respond to every condition on voltage deviation. © 2008 Wiley Periodicals, Inc. Electr Eng Jpn, 166(4): 48,55, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20531 [source] Comparative population genetic structures of the fruit fly Urophora cardui and its primary parasitoid Eurytoma robustaENTOMOLOGIA EXPERIMENTALIS ET APPLICATA, Issue 3 2003Jes Johannesen Abstract The interaction between two species may depend on geographic scale and this in turn can affect co-evolution among them. The present study comparatively examines population genetic structures of the tephritid gall fly Urophora cardui and its primary ectoparasitoid Eurytoma robusta for inference of relative dispersal patterns and host-parasitoid specificity. Genetic differentiation patterns indicated two levels of hierarchical structure in both species: locally similar distance-dependencies but globally differences. Locally, both species showed isolation by distance and a high correlation between host and parasitoid FST for the same population-pairs was found. At the local level, E. robusta populations were most structured. These findings suggest that locally E. robusta is tracking behind its host, U. cardui, and that colonisation of new patches by both species underlie a stepping-stone dispersal process. The investigation as a whole showed that U. cardui populations were hierarchically structured across a genetic-geographical cline. There was no sign of a comparable cline in E. robusta where populations globally became independent of one another and of the host. The different degree of hierarchical genetic structure of the two species suggests that dispersal processes or interactions differ relative to geographical scale and population history. [source] Bayesian hierarchical models in ecological studies of health,environment effectsENVIRONMETRICS, Issue 2 2003Sylvia Richardson Abstract We describe Bayesian hierarchical models and illustrate their use in epidemiological studies of the effects of environment on health. The framework of Bayesian hierarchical models refers to a generic model building strategy in which unobserved quantities (e.g. statistical parameters, missing or mismeasured data, random effects, etc.) are organized into a small number of discrete levels with logically distinct and scientifically interpretable functions, and probabilistic relationships between them that capture inherent features of the data. It has proved to be successful for analysing many types of complex epidemiological and biomedical data. The general applicability of Bayesian hierarchical models has been enhanced by advances in computational algorithms, notably those belonging to the family of stochastic algorithms based on Markov chain Monte Carlo techniques. In this article, we review different types of design commonly used in studies of environment and health, give details on how to incorporate the hierarchical structure into the different components of the model (baseline risk, exposure) and discuss the model specification at the different levels of the hierarchy with particular attention to the problem of aggregation (ecological) bias. Copyright © 2003 John Wiley & Sons, Ltd. [source] EuIII -Doping of Lamellar Bilayer and Amorphous Mono-Amide Cross-Linked Alkyl/Siloxane HybridsEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 18 2010Silvia C. Nunes Abstract Two structurally different but chemically similar families of alkyl/siloxane mono-amidosil hosts, represented by m-A(x) [where x = 14 or 8 represents the number of CH2 groups of the pendant alkyl chains directly bonded to the carbonyl group of the amide cross-link] have been doped with a wide range of concentrations of Eu(CF3SO3)3. Mono-amidosils m-A(x)nEu(CF3SO3)3 with n,,,10 (where n is the molar ratio of carbonyl groups per Eu3+ ion) have been analyzed. The m-A(8)nEu(CF3SO3)3 mono-amidosils are transparent and amorphous films, in which the alkyl chains adopt gauche conformations. In contrast, the m-A(14)nEu(CF3SO3)3 mono-amidosils are solid powders; here the lamellar bilayer hierarchical structure of m-A(14) coexists with a new lamellar phase in which the Eu3+ ions are bonded to carbonyl oxygen atoms of the amide groups. At n = 10 the hydrogen-bonded associations formed are highly ordered and considerably stronger than those found in the less concentrated hybrids and in the nondoped matrices. "Free" and weakly coordinated triflate ions occur in all the mono-amidosil samples. The hybrids are white light emitters (maximum quantum yield: 0.08,±,0.01), presenting a broad emission band in the blue/purplish-blue spectral region (ascribed to the hybrid host) superimposed on the 5D0,7F0,4 Eu3+ intra-4f6 transitions. Two Eu3+ local coordination sites (named A and B) have been discerned in both systems. Site A is attributed to weakly coordinated Eu3+/CF3SO3, ion pairs, whereas site B involves Eu3+ coordination to the oxygen atoms of the C=O groups, of the CF3SO3, ions and of the water molecules. For site B, the long-range order of the hybrid host induces distinct features in the energy of the 5D0,7F0,4 transitions, the 5D0 lifetime and the degree of covalency of the Eu3+,first-ligand bonds. [source] Fracture Properties of Wood and Wood CompositesADVANCED ENGINEERING MATERIALS, Issue 7 2009Stefanie E. Stanzl-Tschegg Wood has a complex hierarchical structure and is a kind of polymeric composite with elongated cells in an amorphous matrix. Therefore, fracturing is a complicated process that is influenced by loading mode and direction, humidity, etc. Standard linear-elastic fracture mechanics methods mostly cannot sufficiently quantify fracturing, and combining fracture mechanical with structural investigations at different levels of magnification (centimeter to nanometer levels) helps obtaining insight into the fracture mechanisms. [source] EXHAUSTION OF MORPHOLOGIC CHARACTER STATES AMONG FOSSIL TAXAEVOLUTION, Issue 2 2000Peter J. Wagner Abstract., Frequencies of new character state derivations are analyzed for 56 fossil taxa. The hypothesis that new character states are added continuously throughout clade history can be rejected for 48 of theses clades. Two alternative explanations are considered: finite states and ordered states. The former hypothesizes a limited number of states available to each character and is tested using rarefaction equations. The latter hypothesizes that there are limited possible descendant morphologies for any state, even if the character has infinite potential states. This is tested using power functions. The finite states hypothesis explains states: steps relationships significantly better than does the ordered states hypothesis in 14 cases; the converse is true for 14 other cases. Under either hypothesis, trilobite clades show appreciably more homoplasy after the same numbers of steps than do molluscs, echinoderms, or vertebrates. The prevalence of the exhaustion pattern among different taxonomic groups implies that worker biases are not to blame and instead implicates biological explanations such as intrinsic constraints or persistent selective trends. Regardless of the source of increased homoplasy, clades appear to exhaust their available character spaces. Nearly all examined taxa show significant increases in proportions of incompatible character pairs (i.e., those necessarily implying homoplasy) as progressively younger taxa are added to character matrices. Thus, a deterioration of hierarchical structure accompanies character state exhaustion. Exhaustion has several implications: (1) the basic premise of cladistic analyses (i.e., that maximum congruence reflects homology rather than homoplasy) becomes increasingly less sound as clades age; (2) sampling high proportions of taxa probably is needed for congruence to discern homoplasy from homology; (3) stratigraphic data might be necessary to discern congruent homoplasy from congruent homology; and (4) in many cases, character states appear to have evolved in ordered patterns. [source] Soft ontologies, spatial representations and multi-perspective explorabilityEXPERT SYSTEMS, Issue 5 2008Mauri Kaipainen Abstract: It is against the dynamically evolving nature of many contemporary media applications to be analysed in terms of conventional rigid ontologies that rely on expertise-based fixed categories and hierarchical structure. Many of these rely on sharing ,folksonomies', personal descriptions of information and objects for one's own retrieval. Such applications involve many feedback mechanisms via the community, and have been shown to have emergent properties of complex dynamic systems. We propose that such dynamically evolving information domains can be more usefully described by means of a soft ontology, a dynamically flexible and inherently spatial metadata approach for ill-defined domains. Our contribution is (1) the elaboration of the so far intuitive concept of soft ontology in a way that supports conceptualizing dynamically evolving domains. Further, our approach proposes (2) a whole new mode of interaction with information domains by means of recurring exploration of an information domain from multiple perspectives in search of more comprehensive understanding of it, i.e. multi-perspective exploration. We demonstrate this concept with an example of collaborative tagging in an educational context. [source] Fabrication and Characterization of Superhydrophobic Surfaces with Dynamic StabilityADVANCED FUNCTIONAL MATERIALS, Issue 19 2010Xi Yao Abstract Superhydrophobic surfaces of dynamic stability are crucial for applications in water-repellent materials. In this work, a hierarchical structure composed of a dendritic microporous surface with nanostructured porosity is demonstrated that shows robust superhydrophobicity with dynamic stability. The hierarchical structures are obtained on both copper foils and wires by a dynamic gas-bubble template-assisted electrochemical deposition method. The substrates can then be modified with alkyl thiols to obtain the surface superhydrophobicity. A new kind of testing, mechanical monitor-assisted continuous water surface strokes, is developed to reveal the dynamic stability of the as-prepared superhydrophobic copper wires. The as-prepared superhydrophobic copper wires can exert a high propulsive force, and particularly, show little adhesive force in the process of continuous strokes on the water surface, exhibiting robust superhydrophobicity with dynamic stability. The approach allows a strategy for the fabrication of superhydrophobic surfaces with dynamic stability, and suggests a new method to evaluate the dynamic stability of superhydrophobic surfaces. [source] Biomimetic Composites: Protein Localization in Silica Nanospheres Derived via Biomimetic Mineralization (Adv. Funct.ADVANCED FUNCTIONAL MATERIALS, Issue 18 2010Mater. Abstract Lysozyme-templated precipitation of silica synthesized by sol-gel chemistry produces a composite material with antimicrobial properties. This study investigates the structural properties of the composite material that allow for retention of the antimicrobial activity of lysozyme. Scanning (SEM) and transmission (TEM) electron microscopy reveal that the composite has a hierarchical structure composed of quasi-spherical structures (,450 nm diameter), which are in turn composed of closely packed spherical structures of ,8,10 nm in diameter. Using small-angle neutron scattering (SANS) with contrast variation, the scattering signatures of the lysozyme and silica within the composite were separated. It was determined that the lysozyme molecules are spatially correlated in the material and form clusters with colloidal silica particles. The size of the clusters determined by SANS agrees well with the structural architecture observed by TEM. BET analysis revealed that the surface area of the composite is relatively low (4.73 m2/g). However, after removal of the protein by heating to 200 °C, the surface area is increased by ,20%. In addition to demonstrating a well organized sol-gel synthesis which generates a functional material with antimicrobial applications, the analysis and modeling approaches described herein can be used for characterizing a wide range of mesoporous and ultrastructural materials. [source] Protein Localization in Silica Nanospheres Derived via Biomimetic MineralizationADVANCED FUNCTIONAL MATERIALS, Issue 18 2010Mateus B. Cardoso Abstract Lysozyme-templated precipitation of silica synthesized by sol-gel chemistry produces a composite material with antimicrobial properties. This study investigates the structural properties of the composite material that allow for retention of the antimicrobial activity of lysozyme. Scanning (SEM) and transmission (TEM) electron microscopy reveal that the composite has a hierarchical structure composed of quasi-spherical structures (,450 nm diameter), which are in turn composed of closely packed spherical structures of ,8,10 nm in diameter. Using small-angle neutron scattering (SANS) with contrast variation, the scattering signatures of the lysozyme and silica within the composite were separated. It was determined that the lysozyme molecules are spatially correlated in the material and form clusters with colloidal silica particles. The size of the clusters determined by SANS agrees well with the structural architecture observed by TEM. BET analysis revealed that the surface area of the composite is relatively low (4.73 m2/g). However, after removal of the protein by heating to 200 °C, the surface area is increased by ,20%. In addition to demonstrating a well organized sol-gel synthesis which generates a functional material with antimicrobial applications, the analysis and modeling approaches described herein can be used for characterizing a wide range of mesoporous and ultrastructural materials. [source] Population genetic structure reveals terrestrial affinities for a headwater stream insectFRESHWATER BIOLOGY, Issue 10 2007DEBRA S. FINN Summary 1. The spatial distribution of stream-dwelling organisms is often considered to be limited primarily according to the hierarchical structure of the hydrologic network, and previous conceptual models of population genetic structure have reflected this generality. Headwater specialists, however, are confined to short upstream sections of the network, and therefore are unlikely to respond in the same way as species with a broader range of habitat tolerance. 2. Here, we propose a model to describe spatial patterns of genetic diversity in headwater specialists with a limited ability for among-stream dispersal. The headwater model predicts a partitioning of genetic variance according to higher-elevation ,islands' of terrestrial habitat that provide required headwater stream conditions. The model therefore expects a geographic pattern of genetic variance similar to that expected for low-dispersal terrestrial species occupying the adjacent habitat. 3. Using a 1032-bp mitochondrial DNA fragment encompassing parts of the COI and COII genes, we demonstrate that Madrean Sky Islands populations of the giant water bug Abedus herberti conform to the proposed headwater model. Furthermore, they exhibit phylogeographic patterns broadly concordant with those shown for several terrestrial species in the region, including a major zone of discontinuity in the Chiricahua mountain range. 4. Overall, populations are highly isolated from one another, and a nested clade analysis suggested that A. herberti population structure, similarly to terrestrial Sky Islands species studied previously, has been influenced by Pleistocene climatic cycles causing expansion and contraction of temperate woodland habitat. 5. Because they have no ability to disperse among present-day mountaintop habitat islands, A. herberti and other headwater species with limited dispersal ability are vulnerable to the projected increasing rate of climatic warming in this region. [source] Morphological clines in dendritic landscapesFRESHWATER BIOLOGY, Issue 9 2007A. CHAPUT-BARDY Summary 1. In complex landscapes such as river networks, organisms usually face spatio-temporal heterogeneity and gradients in geomorphological, water, ecological or landscape characteristics are often observed at the catchment scale. These environmental variables determine developmental conditions for larval stages of freshwater insects and influence adult phenotypic characteristics. Environmental clines are therefore expected to generate morphological clines. Such a process has the potential to drive gradual geographical change in morphology-dependent life history traits, such as dispersal. 2. We studied the influence of aquatic and terrestrial environmental factors on morphological variations in Calopteryx splendens across the Loire drainage. To investigate these effects we took explicitly into account the hierarchical structure of the river network. 3. We analysed eight morphological traits. Results showed significant body size variation between tributaries and the presence of a morphological cline at the drainage scale. We observed an effect of pH and water temperature on body size. Individuals in downstream sites were larger than individuals in upstream sites, and adults whose larval stages were exposed to alkaline pH and high temperatures during summer were larger. 4. Body size affects flight abilities in insects. Thus, our results suggest that morphological clines may generate an asymmetric dispersal pattern along the downstream,upstream axis, downstream populations dispersing farther than upstream ones. Such a process is expected to influence population genetic structure at the drainage scale if larval drift and floods do not balance an asymmetrical dispersal pattern of adults along the downstream,upstream gradient. To assess the influence of environmental gradients on the variation of life history traits it is important to understand the population biology of freshwater insects, and more generally of riverine organisms. It is also essential to integrate such data in conservation or restoration programmes. [source] High-Performance Multifunctional TiO2 Nanowire Ultrafiltration Membrane with a Hierarchical Layer Structure for Water TreatmentADVANCED FUNCTIONAL MATERIALS, Issue 23 2009Xiwang Zhang Abstract A novel, multifunctional TiO2 nanowire ultrafiltration (UF) membrane with a layered hierarchical structure is made via alkaline hydrothermal synthesis, followed by a filtration and hot-press process. The TiO2 UF membrane has high surface porosity (21.3%) and pore size values around 20,nm. The membrane possesses multifunctional capabilities under UV irradiation, such as anti-fouling, anti-bacterial, concurrent separation, and photocatalytic oxidation. The unique properties of the membrane indicate its potential in applications for environmental purification. [source] Inside Front Cover: A Unique Microcracking Process Associated with the Inelastic Deformation of Haversian Bone (Adv. Funct.ADVANCED FUNCTIONAL MATERIALS, Issue 1 2009Mater. Human cortical bone is capable of adapting to the mechanical environment through dynamic remodeling of the Haversian systems. The presence of Haversian canals, however, also introduces stress concentration and could have detrimental effects on the fracture resistance of bone. How is the hierarchical structure in bone designed to alleviate such stress concentrations? On page 57, Vincent Ebacher and Rizhi Wang report a unique and stable microcracking process accompanying the inelastic deformation of Haversian bone. The results lead to the critical role of the well-organized bone lamellae surrounding each Haversian canal. [source] Using multilevel models for assessing the variability of multinational resource use and cost dataHEALTH ECONOMICS, Issue 2 2005Richard Grieve Abstract Multinational economic evaluations often calculate a single measure of cost-effectiveness using cost data pooled across several countries. To assess the validity of pooling international cost data the reasons for cost variation across countries need to be assessed. Previously, ordinary least-squares (OLS) regression models have been used to identify factors associated with variability in resource use and total costs. However, multilevel models (MLMs), which accommodate the hierarchical structure of the data, may be more appropriate. This paper compares these different techniques using a multinational dataset comprising case-mix, resource use and cost data on 1300 stroke admissions from 13 centres in 11 European countries. OLS and MLMs were used to estimate the effect of patient and centre-level covariates on the total length of hospital stay (LOS) and total cost. MLMs with normal and gamma distributions for the data within centres were compared. The results from the OLS model showed that both patient and centre-level covariates were associated with LOS and total cost. The estimates from the MLMs showed that none of the centre-level characteristics were associated with LOS, and the level of spending on health was the centre-level variable most highly associated with total cost. We conclude that using OLS models for assessing international variation can lead to incorrect inferences, and that MLMs are more appropriate for assessing why resource use and costs vary across centres. Copyright © 2004 John Wiley & Sons, Ltd. [source] A randomisation program to compare species-richness valuesINSECT CONSERVATION AND DIVERSITY, Issue 3 2008JEAN M. L. RICHARDSON Abstract., 1Comparisons of biodiversity estimates among sites or through time are hampered by a focus on using mean and variance estimates for diversity measures. These estimators depend on both sampling effort and on the abundances of organisms in communities, which makes comparison of communities possible only through the use of rarefaction curves that reduce all samples to the lowest sample size. However, comparing species richness among communities does not demand absolute estimates of species richness and statistical tests of similarity among communities are potentially more straightforward. 2This paper presents a program that uses randomisation methods to robustly test for differences in species richness among samples. Simulated data are used to show that the analysis has acceptable type I error rates and sufficient power to detect violations of the null hypothesis. An analysis of published bee data collected in 4 years shows how both sample size and hierarchical structure in sample type are incorporated into the analysis. 3The randomisation program is shown to be very robust to the presence of a dominant species, many rare species, and decreased sample size, giving quantitatively similar conclusions under all conditions. This method of testing for differences in biodiversity provides an important tool for researchers working on questions in community ecology and conservation biology. [source] Influence of Structural Principles on the Mechanics of a Biological Fiber-Based Composite Material with Hierarchical Organization: The Exoskeleton of the Lobster Homarus americanusADVANCED MATERIALS, Issue 4 2009Helge-Otto Fabritius Abstract The cuticle of the lobster Homarus americanus is a nanocomposite, such as most structural biological materials. It consists of a matrix of chitin-protein fibers associated with various amounts of crystalline and amorphous calcium carbonate in the rigid parts of the body, and is organized hierarchically at all length scales. One prominent design principle found in the hierarchical structure of such biological fibrous composite materials is the twisted plywood structure. In the lobster cuticle, it is formed by superimposing and gradually rotating planes of parallel aligned chitin-protein fibers. To adjust the mechanical properties to the requirements on the macroscopic level, the spatial arrangement and the grade of mineralization of the fibers can be modified. A second design principle of lobster cuticle is its honeycomb-like structure, generated by the well-developed pore canal system, whose twisted ribbon-shaped canals penetrate the cuticle perpendicular to its surface. Due to the hierarchical structure, the mechanical properties of the lobster cuticle have to be investigated at different length scales, which is essential for the understanding of the structure,mechanical function relations of mineralized tissues (e.g., potentially also bone and teeth). In order to investigate the influence of the structural principles on the mechanical properties on the macroscopic scale miniaturized tensile, compression, and shear tests were carried out to obtain integral mechanical data. Characterization of the microstructure included scanning electron microscopy (SEM) combined with energy dispersive X-ray (EDX) measurements. [source] Template Synthesis of Hierarchically Structured Composites,ADVANCED MATERIALS, Issue 15 2008Wei Wei Abstract The subtle performance of a virus is closely related to its specific hierarchical structure, which is composed of a rigid shell and transverse, responsive, nanometer-sized channels. Virus-like structured colloids are of great interest for their potential applications, for example in drug delivery. Adequate knowledge of the structure and composition control of both colloids and mesoporous materials is significant in the design and synthesis of hierarchically structured colloids to mimic viruses. Some recent developments in the synthesis of composite colloids and mesoporous materials are summarized. Template synthesis is a major tool to control both the macroscopic morphology and microstructures of these composites, in which gel colloids and supramolecular structures from amphiphilic species are used as templates. [source] Experts, dialects, and discourseINTERNATIONAL JOURNAL OF APPLIED LINGUISTICS, Issue 1 2002Rakesh Mohan Bhatt This paper examines "expert" discourse , complexes of signs and practices that organize and legitimize social existence and social reproduction , to demonstrate the ideological processes involved in the manufacture of Standard English ideology and its continual duplication as necessitated by the three axiomatic conceptions of the English-sacred imagined community (cf. Anderson 1991). It is argued that the hierarchical structure needed to sustain the sacred imagined community can only be guaranteed if Standard English is accepted by all members as inevitable and the speakers of this standard accepted as uncontested authorities of English language use. How is this ideological manipulation and indoctrination in fact accomplished? This paper focuses on two sites of ideological manipulation , the learning and teaching of English in post-colonial contexts , and argues that expert promulgations enable what Foucault has called régimes of truth to be organized around the language. Expert discourse establishes a habit of thought which makes the standard variety of English (British/American) desirable, necessary, normal, natural, universal, and essential, and all other varieties instances of deficit and deviation. The key ideological process is a naturalizing move that drains the conceptual of its historical content, making it seem universal and timelessly true (Woolard & Schieffelin 1994). [source] Capacity analysis for underlaying CDMA microcell/macrocell systemsINTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 4 2001Jen-Kung Chung Abstract The CDMA system can provide more capacity than the conventional AMPS system and the hierarchical layer of cells is required for system design in the future. However, the problem is whether the same RF channels used in a CDMA underlaying macrocell/microcell structure also obtain high capacity as in the homogeneous structure. This paper investigates the interference of uplink and downlink from both the microcell and macrocell in a hierarchical structure. Downlink power control is also considered. The results show that the capacity of microcell in a hierarchical structure is 23 per cent less than in homogeneous cells. The capacity of macrocell in a hierarchical structure decreases dramatically in proportion to the number of microcells. The capacities of the microcell and macrocell are limited in downlink, and uplink, respectively. In addition, more efforts for microcell should be made, such as more power is transmitted by microcell basestation if the same RF channel is used in a hierarchical structure. The results suggest that different RF channels are used in a two-tier cellular environment. Copyright © 2001 John Wiley & Sons, Ltd. [source] | |||||||||||||||||||||||||||||||||||||||||||