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Large Structures (large + structure)
Selected AbstractsHeart inflow tract of the African lungfish Protopterus dolloiJOURNAL OF MORPHOLOGY, Issue 1 2005José M. Icardo Abstract We report a morphologic study of the heart inflow tract of the African lungfish Protopterus dolloi. Attention was paid to the atrium, the sinus venosus, the pulmonary vein, and the atrioventricular (AV) plug, and to the relationships between all these structures. The atrium is divided caudally into two lobes, has a common part above the sinus venosus, and appears attached to the dorsal wall of the ventricle and outflow tract through connective tissue covered by the visceral pericardium. The pulmonary vein enters the sinus venosus and runs longitudinally toward the AV plug. Then it fuses with the pulmonalis fold and disappears as an anatomic entity. However, the oxygenated blood is directly conveyed into the left atrium by the formation of a pulmonary channel. This channel is formed cranially by the pulmonalis fold, ventrally by the AV plug, and caudally and dorsally by the atrial wall. The pulmonalis fold appears as a wide membranous fold which arises from the left side of the AV plug and extends dorsally to form the roof of the pulmonary channel. The pulmonalis fold also forms the right side of the pulmonary channel and sequesters the upper left corner of the sinus venosus from the main circulatory return. The AV plug is a large structure, firmly attached to the ventricular septum, which contains a hyaline cartilaginous core surrounded by connective tissue. The atrium is partially divided into two chambers by the presence of numerous pectinate muscles extended between the dorsal wall of the atrium and the roof of the pulmonary channel. Thus, partial atrial division is both internal and external, precluding the more complete division seen in amphibians. The present report, our own unpublished observations on other Protopterus, and a survey of the literature indicate that not only the Protopterus, but also other lungfish share many morphologic traits. J. Morphol. 263:30,38, 2005. © 2004 Wiley-Liss, Inc. [source] An experimental investigation of water level effects on the dynamic behaviour of a large arch damEARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 8 2001Jean Proulx Abstract The need for full-scale dynamic tests, which are recognized as the most reliable method to evaluate a structure's vibration properties, is increasing as new analysis techniques are developed that take into account the complex interaction phenomenons that occur in dam,reservoir,foundation systems. They are extremely useful to obtain reliable data for the calibration of newly developed numerical methods. The Earthquake Engineering and Structural Dynamics Research Center (CRGP) at the University of Sherbrooke has been developing and applying dynamic testing methods for large structures in the past 10 years. This paper presents the experimental evaluation of the effects of the varying water level on the dynamic response of the 180 m Emosson arch dam in Switzerland. Repeated forced-vibration tests were carried out on the dam during four different periods of the reservoir's filling cycle during a one-year span. Acceleration and hydrodynamic pressure frequency responses were obtained at several locations while the dam was subjected to horizontal harmonic loading. The variation of the resonant frequencies as a function of the reservoir level is investigated. A summary of the ongoing numerical correlation phase with a three-dimensional finite element model for the dam,reservoir,foundation system is also presented. Copyright © 2001 John Wiley & Sons, Ltd. [source] The aerodynamics and efficiency of wind pollination in grassesFUNCTIONAL ECOLOGY, Issue 4 2010James E. Cresswell Summary 1.,Under natural selection for sexual success, the reproductive organs of plants should evolve to become highly effective pollen receptors. Among wind-pollinated plants, larger reproductive structures appear counter-adapted to accumulate pollen by impaction on their windward surfaces, because airborne particles are less able to penetrate the thicker boundary layer of larger targets. Therefore, it has been proposed that wind-pollinated plants with pollen receptors on relatively large structures, like some grasses (family Poaceae), are architecturally adapted to create downstream vortices in which airborne pollen recirculates before accumulating on leeward surfaces. From this basis, the striking diversity among the grasses in the architecture of their flowering stems has been attributed in part to the existence of these contrasting mechanisms for effecting pollen receipt, namely impact collection and recirculatory collection. 2.,We investigated the relative importance of impact and recirculatory collection in grasses by analysing a model system in silico using Computational Fluid Dynamics and by conducting in vivo experiments, both in a wind tunnel and outdoors, using two grass species with compact inflorescences, Alopecurus pratensis and Anthoxanthum odoratum. 3.,Irrespective of the experimental approach, we found that although pollen recirculated in the leeward eddies of inflorescences, over 95% of the accumulated pollen was collected by windward surfaces. 4.,In A. pratensis, the collection efficiency (proportion of oncoming pollen collected) was between 5% and 20%, depending on wind speed in the range 0·5,1·9 m s,1 and these levels conform to those predicted by a mechanistic model of impact collection. 5.,Our results demonstrate that grass species with larger inflorescences are, like those with smaller inflorescences, primarily impact collectors of airborne pollen, which suggests that dissimilar reproductive morphology among species cannot be attributed to differentiation in the mode of pollen capture and, instead, requires reference to other factors, such as the need to produce, protect and disperse seeds of different sizes in different environments. [source] Sensor architecture for the robotic control of large flexible space structuresJOURNAL OF FIELD ROBOTICS (FORMERLY JOURNAL OF ROBOTIC SYSTEMS), Issue 4 2007Amy Bilton The future construction and maintenance of very large space structures such as orbital solar power stations and telescopes will require teams of free-flying space robots. For robots to effectively perform these tasks, they will require knowledge of the structure's vibrations. Here, a robotic based sensor architecture for the vibration estimation of very large structures is presented. It is shown that this information can be effectively estimated by combining data provided by free-flying remote robot "observers" equipped with range sensors with structure-mounted acceleration sensors. A modified Kalman filter fuses low-bandwidth vision data from the remote sensing robots with the high bandwidth, but spatially sparse structure-mounted acceleration sensors. Results from experimental studies are presented that confirm the effectiveness of this approach. 2007 Wiley Periodicals, Inc. [source] A combinatorial approach to studying protein complex composition by employing size-exclusion chromatography and proteome analysisJOURNAL OF SEPARATION SCIENCE, JSS, Issue 10 2007Shi-Sheng Li Abstract The genome sequences of numerous organisms are available now, but gene sequences alone do not provide sufficient information to accurately deduce protein functions. Protein function is largely dependent on the association of multiple polypeptide chains into large structures with interacting subunits that regulate and support each other. Therefore, the mapping of protein interaction networks in a physiological context is conducive to deciphering protein functions, including those of hypothetical proteins. Although several high-throughput methods to globally identify protein interactions have been reported in recent years, these approaches often have a high rate of nonspecific or artificial interactions detected. For instance, the fraction of false positives of the protein interactions identified by yeast two-hybrid assay has been predicted to be of the order of 50%. We have developed a strategy to globally map Bacillus subtilis protein,protein interactions in a physiological context by fractionating the cell lysates using size-exclusion chromatography (SEC), followed by proteome analysis. Components of both known and unknown protein complexes, multisubunits and multiproteins, have been identified using this strategy. In one case, the partners of the B. subtilis protein complex have been coexpressed in Escherichia coli, and the formation of the overexpressed protein complex has been further confirmed by a pull-down assay. [source] A model of cloud fragmentationMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2008George B. Field ABSTRACT We present a model in which the supersonic motions observed in molecular clouds are driven by gravitational energy released as large structures fragment into smaller ones. The fragmentation process begins in large molecular clouds, and continues down to fragments of a critical mass defined as the mass at which gravitational confinement may be replaced by pressure confinement. The power laws that describe the scaling of density, mass, and number spectra of the fragments are given in terms of the observed velocity dispersion of the fragments. The results agree with observations over the range from several to about a third of a million solar masses. [source] Spatial distribution of galaxies in the Puppis regionMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2004Pierre Chamaraux ABSTRACT We determine the spatial distribution of the galaxies located behind the part of the zone of avoidance of the Milky Way defined by 220° < l < 260°, |b| < 20°, ,, 0°, up to a distance of 8000 km s,1. We use a sample of 369 galaxies with measured redshifts, of which 97 have been detected with the Nançay radio telescope. We show that our sample can be considered to be complete in apparent diameter down to 1.9 arcmin, a property that allows us to correct the density of galaxies for the loss of objects with distance. We then search for groups of galaxies using a companionship method and find 12 groups with at least five members, of which five are new. The members of one group are H i deficient by a factor of 1.6 on average. The method is then used to search for large structures and allows us to characterize the Puppis wall at 1400 < V0 < 2600 km s,1; it is 30 Mpc long, with the main axis being parallel to the sky plane, and it connects the Antlia cluster to the Fornax cluster through the zone of avoidance. The density of galaxies in the wall is approximately 20 times the general density of galaxies, i.e. half that observed in the densest part of the Pisces,Perseus supercluster. No internal motions are found along the line of sight, indicating that the Puppis wall has not yet collapsed. [source] Flow modeling and simulation for vacuum assisted resin transfer molding process with the equivalent permeability methodPOLYMER COMPOSITES, Issue 2 2004Renliang Chen Vacuum assisted resin transfer molding (VARTM) offers numerous advantages over traditional resin transfer molding, such as lower tooling costs, shorter mold filling time and better scalability for large structures. In the VARTM process, complete filling of the mold with adequate wet-out of the fibrous preform has a critical impact on the process efficiency and product quality. Simulation is a powerful tool for understanding the resin flow in the VARTM process. However, conventional three-dimensional Control Volume/Finite Element Method (CV/FEM) based simulation models often require extensive computations, and their application to process modeling of large part fabrication is limited. This paper introduces a new approach to model the flow in the VARTM process based on the concept of equivalent permeability to significantly reduce computation time for VARTM flow simulation of large parts. The equivalent permeability model of high permeable medium (HPM) proposed in the study can significantly increase convergence efficiency of simulation by properly adjusting the aspect ratio of HPM elements. The equivalent permeability model of flow channel can simplify the computational model of the CV/FEM simulation for VARTM processes. This new modeling technique was validated by the results from conventional 3D computational methods and experiments. The model was further validated with a case study of an automobile hood component fabrication. The flow simulation results of the equivalent permeability models were in agreement with those from experiments. The results indicate that the computational time required by this new approach was greatly reduced compared to that by the conventional 3D CV/FEM simulation model, while maintaining the accuracy, of filling time and flow pattern. This approach makes the flow simulation of large VARTM parts with 3D CV/FEM method computationally feasible and may help broaden the application base of the process simulation. Polym. Compos. 25:146,164, 2004. © 2004 Society of Plastics Engineers. [source] Upgrading the twin variables algorithm for large structuresACTA CRYSTALLOGRAPHICA SECTION A, Issue 2 2000K. Bethanis Phase extension from lower to higher resolution by using an upgraded TWIN variables algorithm [Hountas & Tsoucaris (1995). Acta Cryst. A51, 754,763] in protein molecules with close to 1000 non-H atoms is presented. Three points of this procedure are of particular interest. (i) The use of a set of auxiliary variables providing a satisfactory fit for many kinds of constraints: the new algorithm works efficiently despite the extreme `dilution' of very limited initial phase information into a much larger set of auxiliary variables. (ii) The extension of this auxiliary variables set beyond the resolution of the observed data, which enhances the phase extension in a so-called `super-resolution' sphere. (iii) The use of the crystallographic symmetry as a new figure of merit and as a reliable test for the correctness of the phase-extension process allows an efficient screening. [source] Ill-conditioned Shake-and-Bake: the trap of the false minimumACTA CRYSTALLOGRAPHICA SECTION A, Issue 2 2000Hongliang Xu The alternation of phase refinement with the imposition of real-space constraints is the essence of the Shake-and-Bake procedure. Typically, these constraints prevent trial structures from falling into local minima. Nevertheless, structures appear to migrate to false minima with significant frequency. These false minima are characterized by the presence of a large `uranium' peak on the corresponding Fourier map. Fortunately, they can be recognized and avoided by considering the values of the minimal function both before and after the application of constraints. However, it appears that finding solutions for large structures is likely also to require parameter-shift conditions different from those that have been found to work well in other space groups. In fact, these conditions often yield an unusually high percentage of solutions. [source] | ||||||||||||||||