Different Levels Of Structure Research Articles

Genetic structure among 50 species of the northeastern Pacific rocky intertidal community.

Comparing many species' population genetic patterns across the same seascape can identify species with different levels of structure, and suggest hypotheses about the processes that cause such variation for species in the same ecosystem. This comparative approach helps focus on geographic barriers and selective or demographic processes that define genetic connectivity on an ecosystem scale, the understanding of which is particularly important for large-scale management efforts. Moreover, a multispecies dataset has great statistical advantages over single-species studies, lending explanatory power in an effort to uncover the mechanisms driving population structure. Here, we analyze a 50-species dataset of Pacific nearshore invertebrates with the aim of discovering the most influential structuring factors along the Pacific coast of North America. We collected cytochrome c oxidase I (COI) mtDNA data from populations of 34 species of marine invertebrates sampled coarsely at four coastal locations in California, Oregon, and Alaska, and added published data from 16 additional species. All nine species with non-pelagic development have strong genetic structure. For the 41 species with pelagic development, 13 show significant genetic differentiation, nine of which show striking FST levels of 0.1–0.6. Finer scale geographic investigations show unexpected regional patterns of genetic change near Cape Mendocino in northern California for five of the six species tested. The region between Oregon and Alaska is a second focus of intraspecific genetic change, showing differentiation in half the species tested. Across regions, strong genetic subdivision occurs more often than expected in mid-to-high intertidal species, a result that may reflect reduced gene flow due to natural selection along coastal environmental gradients. Finally, the results highlight the importance of making primary research accessible to policymakers, as unexpected barriers to marine dispersal break the coast into separate demographic zones that may require their own management plans.

Multiscale Mechanics of Fibrin Clots

Although we know a great deal about the structure, properties and many functions of fibrin(ogen), we still know very little about the microscopic and molecular origins of the clot's mechanical properties, even though they are necessary for its functions, since hemostasis is essentially a mechanical process. In addition, it has been shown that individuals who have myocardial infarction at an early age tend to form very stiff clots. We have carried out studies at different levels of structure and integrated the results through a model that demonstrates that fibrin clot mechanical properties are manifestations of the observed mechanical characteristics of fibrin(ogen) molecules. By stretching whole fibrin clots with an extensional rheometer, we observed fibrin's remarkable extensibility with a mechanical response that was initially linear with an increase in stiffness at larger elongation, above two-fold. These results are consistent with the large extensibility that has been observed in single fibrin fibers and may also play a role in the mechanics of blood clots at high strain, as in arterial blood flow. Furthermore, we found that protein structural transitions are required even at lower elongations. Some of the corresponding structural changes in the clots with stretching up to about four-fold were observed by electron microscopy. Scanning electron microscopy of the clots revealed extensive reorientation of the fibers making up the clots in the direction of applied stress. The orientational order was quantified from the scanning electron microscope images using a custom, automated image analysis algorithm that calculates a network order parameter, revealing a high degree of alignment for stretched, initially unoriented fibrin gels. Crosssections of stretched clots were examined by transmission electron microscopy. The most striking change observed was a huge (up to 10-fold) decrease in volume with stretching, with aggregation or bundling of fibers. Basic features of the mechanics of single fibrin fibers are known. These measurements have recently been extended to the level of single molecules using atomic force microscopy. When factor XIIIa-ligated fibrinogen oligomers were stretched by atomic force microscopy, the coiled-coils were found to unfold first under force. Until now, these observations at the molecular and fiber levels have not been correlated with the behavior of whole fibrin clots. These levels of structure were bridged through small angle X-ray fiber diffraction patterns obtained from fibrin clots, since the primary peaks in the X-ray diffraction pattern correspond to the characteristic 22.5 nm repeat distance in fibrin fibers arising from the molecular packing. In contrast to some earlier reported results, there was no change in periodicity with stretching. Instead, these peaks broadened as the sample was stretched, consistent with structural disruptions like protein unfolding while the position of the 22.5 nm peak corresponding to the fibrin repeat remained constant. Since all of these measurements are quantitative, we developed a constitutive model, including all of the features observed, that suggests that the whole clot and fiber mechanical properties are a consequence of coiled-coil unfolding. All together, this study has allowed us to develop a truly multiscale understanding of fibrin mechanics that reveals how clots or thrombi, even though they are made up of relatively stiff fibers, can still have large extensibility that allows them to withstand large strains and open and permeable structures such that they are readily lysed. Understanding how the network, fiber, and molecular properties give rise to fibrin mechanics could contribute to designs of tougher or more extensible clots or lead to new strategies for breaking up clots or making them less occlusive.

Opposites Interact: Motivic Organization in Shapey's Clarinet Concerto

Ralph Shapey's Concerto for Clarinet and Chamber Group (1954) presents an intricately plotted narrative of two prominent musical ideas in apparent opposition. One, a [0,1,2,3] tetrachord realized as a motive in the shape of a wedge, saturates its confines chromatically. The other, a twelve-tone row generated solely through interval class 5, is a lyrical evocation of diatonicism. Evolving gradually from mere hints at the Concerto's opening, the two ideas achieve and retain distinctive identities that interact at different levels of structure and crystallize in a remarkable moment of equilibrium at the Concerto's approximate midpoint. Through his idiosyncratic serial techniques, Shapey transforms the row through interpolations, saving conventional serial operations for non-dodecaphonic, contrapuntal settings of the wedge motive.

Structure and mechanical response of sub-Apennine Blue Clays in relation to their geological and recent loading history

The paper discusses the intrinsic properties, geological history, natural structure and mechanical behaviour of stiff Italian clays, part of the sub-Apennine Blue Clay formation, which are located at different sites within the marine basin where the clay formation was deposited in the early Pleistocene. For all the clay deposits being considered, diagenesis, unloading due to erosion, and weathering of the top strata represent the main stages of the geological history. However, the clays have undergone different levels of unloading, and have developed different levels of structure due to their different locations in the basin. These differences are accounted for in the analysis of their current states and behaviour. Based upon a large experimental database, the structure and mechanical behaviour of the clay samples from the different sites are compared and related to the clay history. In particular, the soil structure is characterised based upon SEM analysis results and compression–swelling test results. The comparison of the response to compression–swelling cycles of the natural clay with that of the same clay when reconstituted leads to the evaluation of parameters such as the stress sensitivity Sσ and the swell sensitivity C*s/Cs, which are used to assess the structural strength of the natural clay with respect to that of the reconstituted clay. The stress–strain behaviour of the different clays along different constant stress-ratio compression paths and shear paths (from low to high pressures) is discussed in detail. The variations in stress–strain response of samples subjected to different pre-shear consolidation paths are outlined. The corresponding trends of the plastic strain increment ratios are investigated. As a result of the analysis, the features of the gross yield curves of the different clay horizons are also assessed. Finally, the study provides elements for the characterisation of the hardening properties of stiff clays, and therefore of the evolution of the material anisotropy during plastic deformation.

Organising R&D in Globalised Context: Convergence or Divergence? The Relative Influence of Dutch and Foreign Cultures on the Organisational Structure of R&D in Multinational Corporations

eBook: Organising R&D in Globalised Context: Convergence or Divergence? The Relative Influence of Dutch and Foreign Cultures on the Organisational Structure of R&D in Multinational Corporations (ISSN0935-9915) von aus dem Jahr 2006

A Service System Planning Model for Individuals With Serious Mental Illness

An institutional-based care system in mental health has been replaced by a network of community-based services with different levels of structure and support. This poses both an opportunity and a challenge to provide appropriate and effective care to persons with serious mental illnesses. This paper describes a simulation-based approach for mental health system planning, focused on hospital and residential service components that can be used as a decision support tool. A key feature of this approach is the ability to represent the current service configuration of psychiatric care and the client flow pattern within that framework. The strength of the simulation model is to help mental health service managers and planners visualize the interconnected nature of client flow in their mental health system and understand possible impacts of changes in arrival rates, service times, and bed capacity on overall system performance. The planning model will assist state mental health agencies to respond to requirements of the Olmstead decision to ensure that individuals with serious mental illness receive care in the least restrictive setting. Future plans for refining the model and its application to other service systems is discussed.

Interfaces in the prosodic hierarchy: New structures and the phonological parser

In this paper I investigate the assignation of syllabic structure to segments in second language learners invoking principles of parsing and learnability. Drawing on the model of Phillips (1996) in parsing, and the work of Fodor (1999) and Dresher (1999) in learnability, I discuss the implications for second language learning. I also look at the question of whether new phonological structure can be triggered if that structure is lacking in the first language. Drawing on evidence from the acquisition of (1) phonological features in Japanese, Chinese and French learners of English, as well as English learners of Czech, and (2) moraic structure by an English speaker learning Japanese consonant and vowel length contrasts, I argue that second language learners can trigger new prosodic structure. The process of acquisition is a combination of acquiring new structures, and mapping the interfaces of different levels of structure via a phonological parser.

La dualidad y la agregación de categorías sociales

Duality is a conception of micro-macro linkage that implies that elements at each of two different levels of structure (such as persons and groups, or—as in the data we analyze—identities and practices) co-constitute one another. We present an algorithm for the aggregation of social categories that are dual to each other. Our algorithm is applicable to the study of data in contingency tables. We apply our algorithm in a study of the joint construction of social identities (including racial and ethnic labels) and educational practices in a university context.

Simulation of Wave Processes under Conditions of Friction of Rough Surfaces (Review)

We show that, under conditions of friction, there arise heat, deformation, and acoustic waves. We also describe the nature of their onset and analyze the statistical distribution of regular and irregular roughness on an actual discrete contact surface for different levels of structure and dimensions. We substantiate the possibility of development of new heat-dynamic models of temperature flashes with regard for the periodic discreteness of actual friction surfaces.

Sequence Specific Liquid Crystallinity in Thick Films of Model Collagen-like Polyhexapeptides

To study hierarchical self-assembly of fibrous proteins, methods need to be developed to elucidate the nature of information flow between different levels of structure. The collagens present an interesting example. Sequence-dependent conformational effects are well-known in the collagen triple helix, forming a repetitive sequence (Gly-X-Y; X or Y often hydroxyproline or proline). It should thus be possible to “travel up” the structural hierarchy, and examine the features of long-range ordered structure in light of what is known about sequence and conformational relationships. The next step along this path of structural complexity is an examination of the packing of the collagen triple helices in a condensed phase and the corresponding effect of this organization on any larger domains formed. Studies of crystal structures and solid free surfaces formed by collagen peptides, slowly dried to form glassy solids with very small embedded crystallites, have been used to compare the molecular scale packing behavior of the triple helices within the longer length scale structure of the solid phase. In this instance the peptides go through a state where they are very concentrated viscous, syrupy liquids and where they form solid cholesteric-analogue phases as they dry. A qualitative correlation between the molecular packing geometry of the triple helix and the apparent chirality of the dried cholesteric phase is observed.

PH and urea dependence of amide hydrogen-deuterium exchange rates in the beta-trefoil protein hisactophilin.

Amide hydrogen/deuterium exchange rates were measured as a function of pH and urea for 37 slowly exchanging amides in the beta-trefoil protein hisactophilin. The rank order of exchange rates is generally maintained under different solution conditions, and trends in the pH and urea dependence of exchange rates are correlated with the rank order of exchange rates. The observed trends are consistent with the expected behavior for exchange of different amides via global and/or local unfolding. Analysis of the pH dependence of exchange in terms of rate constants for structural opening and closing reveals a wide range of rates in different parts of the hisactophilin structure. The slowest exchanging amides have the slowest opening and closing rates. Many of the slowest exchanging amides are located in trefoil 2, but there are also some slow exchanging amides in trefoils 1 and 3. Slow exchangers tend to be near the interface between the beta-barrel and the beta-hairpin triplet portions of this single-domain structure. The pattern of exchange behaviour in hisactophilin is similar to that observed previously in interleukin-1 beta, indicating that exchange properties may be conserved among beta-trefoil proteins. Comparisons of opening and closing rates in hisactophilin with rates obtained for other proteins reveal clear trends for opening rates; however, trends in closing rates are less apparent, perhaps due to inaccuracies in the values used for intrinsic exchange rates in the data fitting. On the basis of the pH and urea dependence of exchange rates and optical measurements of stability and folding, EX2 is the main exchange mechanism in hisactophilin, but there is also evidence for varying levels of EX1 exchange at low and high pH and high urea concentrations. Equilibrium intermediates in which subglobal portions of structure are cooperatively disrupted are not apparent from analysis of the urea dependence of exchange rates. There is, however, a strong correlation between the Gibbs free energy of opening and the denaturant dependence of opening for all amides, which suggests exchange from a continuum of states with different levels of structure. Intermediates are not very prominent either in equilibrium exchange experiments or in quenched-flow kinetic studies; hence, hisactophilin may not form partially folded states as readily as IL-1 beta and other beta-trefoil proteins.

Identifying key structural indicators of mechanical strength in networks of fat crystals

The mechanical properties of edible fats can be influenced by a series of factors, including the amount of solids, the polymorphism of the solid-state, as well as the microstructure of networks of polycrystalline particles created upon crystallization. This work demonstrates that for binary mixtures of the high-melting fraction of milk fat (HMF) with cocoa butter as well as for mixtures of HMF with the middle-melting fraction of milk fat, changes in the storage shear modulus ( G′) are mostly controlled by the solid fat content (SFC), and the material’s microstructure. The SFC, in turn is a function of the phase behavior of the mixtures in the solid state. Experimental techniques used in the characterization of the different levels of structure are presented in this work. A model developed to explain mechanical properties of these materials taking into account all levels of structure is proposed. The polymorphism of the solid state did not seem to influence the mechanical properties of the fats, indicative of this material being structured as a network of weakly-attractive polycrystalline particles. Moreover, the mass fractal dimension of the network was closely related to the polymorphism of the solid state.

Knowledge of language and the multilingual mind

Contrary to the conclusions suggested by Magnetic Resonance Imaging (MRI) and Positron Emission Tomography (PET) and other techniques in electronic imaging of mind, it seems that knowledge of language may not be the property of a particular part of mind. How is the knowledge of language organized by a multilingual mind then? Are different languages stored in different and isolated cells? We do not know for certain yet, but instances of reading, writing, listening and speaking errors by multilingual people suggest that knowledge of any number of languages is organized together, though at different levels of structure.

Spatial frequency and attention: effects of level-, target-, and location-repetition on the processing of global and local forms.

Is attentional selection between local and global forms based on spatial frequency? This question was examined by having subjects identify local or global forms of stimuli that had been "contrast balanced," a technique that eliminates low spatial frequencies. Response times (RTs) to global (but not local) forms were slowed for contrast-balanced stimuli, suggesting that low spatial frequencies mediate the global RT advantage typically reported. In contrast, the beneficial effect of having targets appear at the same, as opposed to a different, level as that on the immediately preceding trial was unaffected by contrast balancing. This suggests that attentional selection between different levels of structure is not based on spatial frequency. The data favor an explanation in terms of "priming," rather than in terms of adjustments in the diameter of an attentional "spotlight."

The role of spatial frequency in the processing of hierarchically organized stimuli.

Can spatial frequency differences between local and global forms account for differences in the way different levels of structure are analyzed? We examined this question by having subjects identify local or global forms of hierarchical stimuli that had been contrast balanced. Contrast balancing eliminates low spatial frequencies, so that both local and global forms must be identified on the basis of high spatial frequency information. Response times (RTs) to global (but not local) forms were slowed for contrast-balanced stimuli, suggesting that low spatial frequencies mediate the global RT advantage typically found. In contrast, interference between local and global forms was little affected by contrast balancing or by shifts of attention between local and global forms, suggesting that it does not result from inhibitory interactions between spatial frequency channels or from temporal precedence of low versus high spatial frequency information. Finally, shifts of attention between local and global forms were also little affected by contrast balancing, suggesting that they were not based on spatial frequency.

Attending to different levels of structure in a visual image.

Two experiments are reported in which observers had to utilize information from one of two structural levels of visual stimulus patterns (large letters composed of smaller ones). They could utilize information more rapidly form one level only at the cost of slower utilization from the other. This trade off defines an empirical attention operating characteristic (AOC) which is consistent with a simple mathematical model of the perceptual process: when viewing a stimulus, the observer selects one of two alternative “attentional” strategies, where each strategy is optimal for utilizing information from one structural level, but less than optimal for the other.

Global precedence in attention and decision.

This article examines the order in which people recognize and respond to different levels of structure within a visual display. Certain previous experiments have been interpreted as showing that information about global characteristics of an array is extracted by the visual system before information about local characteristics. Results from a task in which the observer must attend to both global and local information demonstrate that local information has a large influence on reaction time even when information at the global level is sufficient to determine the response. This finding implies that local information becomes available to decision processes with a time course similar to that of global information. Effects previously attributed to the order in which different levels of structure are recognized may result from differential ease of directing attention to these different levels and selecting responses based on them.

The evolution of protein sequences by repetitious gene duplication: clostridial flavodoxin.

Internal regularities of amino acid sequences of flavodoxins, FMN-containing, low molecular weight flavoproteins, were statistically examined using the minimum mutation method. The sequence of Clostridium pasteurianum flavodoxin shows statistically significant evidence of repetitious internal gene duplications at different levels of structure. Peptide pairs with a low chance probabilitiy of occurrence were frequently observed at a shift of 5 residues. The pairs with the lowest chance probabilities are a pair of heptapeptides at positions39--45 vs. 44--50, a 5 residue shift (p = 9 x 10(-6)). Most of the related pairs are consistent and could best be explained by the repeating pentapeptide sequence: (Lys-Gly-Ala-Asp-Val-)n and appropriate gaps. Internal repetitions with longer shifts were also suggested for other flavodoxins. Repetitious gene duplication is proposed for the early stages of flavodoxin evolution.

A Task Contingent Model of Work-Unit Structure

The authors are grateful for support of this research from the Wisconsin Employment Security Division, Department of Industry, Labor, and Human Relations, and the Center for Business and Economic Research, Graduate School of Business Administration, Kent State University. Appreciation is also extended to Elmer Burack, Anant Negandhi, Johannes Pennings, Richard Schoenherr, and Joseph Schwitter for helpful comments on previous drafts of this paper. A model for explaining structural variations between work units within the complex organization is presented. Based upon an analysis of the impact of task difficulty and task variability on intraorganizational structure, a taxonomy of alternative work-unit structures is derived. The taxonomy suggests that work units within a complex organization can be classified into three basic structural modes: (1 ) a systematized mode, (2) a service mode, and (3) a group mode; with variations in each mode. However, the structural distinction between modes is one of kind or type, while the distinctions within modes is one of degree. Data on 120 work units within a large government employment-security agency are presented. Empirical support was found for the taxonomy. The work units sampled at six different levels of structure did discriminate empirically on the bases of task difficulty and variability using a fixed-effects model, and were shown to fit in different cells of the taxonomy as predicted.

External inversion, internal inversion, and reflection invariance

Having in mind that physical systems have different levels of structure we develop the concept of external, internal and total improper Lorentz transformation (space inversion and time reversal). A particle obtained from the ordinary one by the application of internal space inversion or time reversal is generally a different particle. From this point of view the intrinsic parity of a nuclear particle (`elementary particle') is in fact the external intrinsic parity, if we take into account the internal structure of a particle. We show that non-conservation of the external parity does not necessarily imply non-invariance of nature under space inversion. The conventional theory of beta-decay can be corrected by including the internal degrees of freedom to become invariant under total space inversion, though not under the external one.