Home About us Contact
|
Home About us Contact | ||
|
|
||
Different Shapes (different + shape)
Selected AbstractsTesting Nanomaterials of Unknown Toxicity: An Example Based on Platinum Nanoparticles of Different Shapes,ADVANCED MATERIALS, Issue 20 2007A. Elder Human endothelial and lung epithelial cells were exposed to nanosized Pt shapes following acellular analyses of their oxidant potential. Despite clear evidence of particle uptake by cells, the Pt nanoparticles were not found to induce cytotoxicity or oxidative stress in either cell type. Results from in vivo respiratory tract exposures suggest that the particles are retained by lung tissue and that minimal-mild lung inflammation results from exposure to the nanosized Pt particles. [source] Influence of particle shape and angularity on the behaviour of granular materials: a numerical analysisINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 14 2003C. Nouguier-Lehon Abstract This paper analyses the influence of grain shape and angularity on the behaviour of granular materials from a two-dimensional analysis by means of a discrete element method (Contact Dynamics). Different shapes of grains have been studied (circular, isotropic polygonal and elongated polygonal shapes) as well as different initial states (density) and directions of loading with respect to the initial fabric. Simulations of biaxial tests clearly show that the behaviour of samples with isotropic particles can be dissociated from that of samples with anisotropic particles. Indeed, for isotropic particles, angularity just tends to strengthen the behaviour of samples and slow down either local or global phenomena. One of the main results concerns the existence of a critical state for isotropic grains characterized by an angle of friction at the critical state, a critical void ratio and also a critical anisotropy. This critical state seems meaningless for elongated grains and the behaviour of samples generated with such particles is highly dependent on the direction of loading with respect to the initial fabric. The study of local variables related to fabric and particle orientation gives more information. In particular, the coincidence of the principal axes of the fabric tensor with those of the stress tensor is sudden for isotropic particles. On the contrary, this process is gradually initiated for elongated particles. Copyright © 2003 John Wiley & Sons, Ltd. [source] Cervical screening policies 2008 and beyondCYTOPATHOLOGY, Issue 2007R. Winder There are many developments in cytology and in the NHS that will impact on the NHS Cervical Screening Programme over the next few years. In the short term HPV is a major issue, whether triage, primary screening or vaccination with further evidence coming forward from NHS early implementers and from research trials. Cytology automation is also already being trialled for the UK. So far as NHS developments go, we already have the two Carter reports, one on pathology modernisation and one on commissioning are both likely to impact on our service, as is the forthcoming Cancer Reform Strategy which should be out in a few months time. This will set out a blue print for cancer services in 2012, by which time the cervical screening programme could have a very different shape. [source] Ultrastructure and functional features of midgut of an adult water mite Teutonia cometes (Koch, 1837) (Hydrachnidia: Teutoniidae)ACTA ZOOLOGICA, Issue 2 2010Andrew B. Shatrov Abstract Shatrov, A. B. 2010. Ultrastructure and functional features of midgut of an adult water mite Teutonia cometes (Koch 1837) (Hydrachnidia: Teutoniidae). ,Acta Zoologica (Stockholm) 91: 222,232 The midgut of the adult water mite Teutonia cometes (Koch 1837) (Hydrachnidia: Teutoniidae) was investigated by means of transmission electron microscopy and on semi-thin sections. The midgut is represented by a blind sac composed of the narrow ventriculus, two proventricular lateral diverticula and three pairs of postventricular caeca. A single-layered epithelium consists of one type of endodermal digestive cells of quite different shape and size, which may form protrusions into the midgut lumen. The large nuclei are frequently lobed and contain one to three nucleoli. The apical cell membrane forms short scarce microvilli, between their bases the pinocytotic vesicles of unspecific macropinocytosis as well as the narrow pinocytotic canals are formed and immersed into the cell. The intracellular digestion of the food ingested into the midgut after extraintestinal digestion is predominant. The pinocytotic vesicles fuse with small clear vesicles of proposed Golgi origin to form secondary lysosomes. The digestive cells also contain small amounts of rough endoplasmic reticulum, variously structured heterolysosomes, residual materials in the form of both the small electron-dense bodies and the large variously granulated substances, reserve nutritive materials such as lipid and glycogen, as well as clear vacuoles. Residual materials are obviously extruded from the cells into the gut lumen. [source] Notes on South American Valerianaceae IIFEDDES REPERTORIUM, Issue 5-6 2004F. Weberling Professor em. Entre ValerianapotopensisBriq., descripta para Bolivia, y Valeriana humahuacensisBorsini, descripta para Jujuy, la provincia contigua de la Argentina, no se han encontrado características morfológicas para distinguir ambas especies, por eso éstas estarían unidas bajo del nombre ValerianapotopensisBriq. Por otra parte Valeriana bolivianaBritton y Valeriana bangianaGraebn., serían según Graebner (1906) dos especies distintas, pero no dió caracteres seguros para diferen-ciarlas. En este trabajo se observa que la forma de los frutos de los materiales tomados como tipo y paratipos es diferente, frutos ovados, como descripto para V. boliviana, se observan en unos paratipos, también se ven frutos ancho-ovados con un margen grueso, pero los del lectotipo V. boliviana (Rusby 871 NY) tienen un contorno casi circular como una lenteja, con un margen tenue, casi membranoso como los del lectotipo de V. bangiana (Bang 2415 G). Ni los caracteres vegetativos ni los caracteres de los frutos serían suficientes para poder distinguir V. bangianaGraebn. 1906 de V. bolivianaBritton 1891 como especies separadas. Se observa también que Valeriana variabilisGraebn. sería una forma de Valeriana warburgiiGraebn. La primera especie solo se distinguiría por caracteres poco manifiestos como el indumento de los frutos y los pelos frecuentemente se pierden durante de la maduración de los mismos, estos caracteres no serían suficientes para separar las dos especies. Por lo tanto se considera una nueva combinación, Valeriana warburgiiGraebn. subsp. variabilis(Graebn.) Weberling stat. nov. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) ValerianapotopensisBriq., described from Bolivia, and Valeriana humahuacensisBorsini, described from Jujuy, the neighbouring province of Argentina, cannot be distinguished by reliable distinctive characters. This applies especially to the indument of the fruits, since the fruits of Valeriana often become increasingly glabrescent in advanced stages of development, with the mature fruits being completely bald. Therefore both species should be united under the older name ValerianapotopensisBriq. According to Graebner (1906) Valeriana bangianaGraebn., is to be regarded as separate species, differing from Valeriana bolivianaBritton by its vigorous densely foliated stem, a character cer-tainly insufficient for a reliable identification. The fruits of V. boliviana are described as "ovatis", which is confirmed by the para-type material of the Mandon collections. In the paratypes the fruits were found to be lanceolate-ovate (Rusby872) or broadly ovate with prominent nerves and a thickened solid margin (Rusby875). However, the fruits of the holotype Rusby 871 (Fig. 12a, b) present a different shape: compressed fruits of nearly circular outline, with a broad flattened some-what membraneous marginal ring. The same form of fruits, although considerably larger, was found in the type material of Valeriana bangiana. Because of the overlapping of the vegetative characters as well as the forms of the fruits V. bangianaGraebn. 1906 cannot be clearly separated from V. bolivianaBritton 1891, and is included into this species. Valeriana warburgiiGraebn. and V. variabilisGraebn. too cannot be separated at species level because of over-lapping characters. Again the indumentum of the fruits is apparently according to several authors the best key character, but is not at all reliable. However, the outline of the fruits shows some differences. Therefore V. variabilis is included into V. warburgii as follows: V. warburgiiGraebn. subsp. variabilis(Graebn.) Weberling stat. nov. [source] Biliary inorganic phosphate as a tool for assessing cold preservation-reperfusion injury: A study in the isolated perfused rat liver modelLIVER TRANSPLANTATION, Issue 2 2003Luciana L. Almada Ischemia-reperfusion injury is a major cause of early graft dysfunction after liver transplantation. The bile flow has been suggested as an index of ischemic damage, and severely impaired bile flow seems to be predictive of poor survival in experimental studies. Looking for injury markers, biliary inorganic phosphate has the potential of being a useful endogenous marker of diminished hepatobiliary function because this anion is excreted in the bile by a paracellular pathway and it can detect changes in permeability. The goal of this study was to evaluate the effects of cold preservation-reperfusion of the liver on bile flow and bile inorganic phosphate and their relationship with storage-related graft failure. The isolated and perfused rat liver was used to evaluate the injury for ischemia-reperfusion. The intrahepatic resistance, lactate dehydrogenase release, and potassium and biliary inorganic phosphate concentration were used to estimate viability and function of freshly isolated or cold-preserved livers. The intrahepatic resistance and the bile flow were consistent and significantly decreased throughout the perfusion time in relation to the increment in storage. Inorganic phosphate is more concentrated in bile from preserved livers, showing an alteration in paracellular pathway, confirmed by the biliary excretion of horseradish peroxidase. After preservation, concentration and excretion of the paracellular marker were increased during the first peak. The second peak appears earlier in preserved livers (10 minutes) with a different shape but without changes in concentration. In conclusion, inorganic phosphate in bile shows changes in paracellular permeability as occurs in livers after 48 hours of cold preservation. [source] Electromagnetic metamorphosis: Reshaping scatterers via conformal anisotropic metamaterial coatingsMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 10 2007Ozlem Ozgun Abstract We introduce a new technique (in the context of time-harmonic electromagnetic scattering), which renders an object (or scatterer) to be perceived as if it has a different shape, irrespective of the location of the observer. This is achieved through the usage of an anisotropic metamaterial layer, which is designed as conformal to the surface of the scatterer by employing the concept of coordinate transformation. We report some numerical results for finite element simulations of two-dimensional anisotropic metamaterial coatings. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 2386,2392, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22784 [source] Macroanatomical Investigation of the Aorticorenal Ganglion in 1-Day-Old Infant SheepANATOMIA, HISTOLOGIA, EMBRYOLOGIA, Issue 3 2009J. Kle, kowska-Nawrot Summary The aorticorenal gland belongs to the paired splanchnic ganglion, which is the main component of the coeliac plexus. It lies near the renal artery and suprarenal gland. The research was conducted on 13 1-day-old infant sheep , eight males and five females. Based on the conducted studies, it was concluded that the aorticorenal ganglion is characterized by the variable location in relation to the abdominal aorta, renal artery, caudal vena cava and suprarenal gland (holotopy), the thoracic and lumbar segment of the vertebral column (skeletotopy) (between L1 and L3) and also a different shape (elongated, round, triangular, oval) as well as variable length (the aorticorenal ganglion is longer on the left side of the body; 2.72 mm) and distance from the caudal end of the suprarenal gland (longer on the left side of the body; 8.34 mm). With regard to the sex of the animal, the ganglion is the longest on the left side in ewes (3.02 mm), while in rams it is the longest on the right side (2.68 mm). Regarding the division according to sex, the longest segment was observed on the right side in ewes (9.27 mm), and the shortest segment in rams was also on the right side (6.84 mm). [source] Self-Organisation in the Assembly of Gels from Mixtures of Different Dendritic Peptide Building BlocksCHEMISTRY - A EUROPEAN JOURNAL, Issue 8 2007Andrew Abstract This paper investigates dendritic peptides capable of assembling into nanostructured gels, and explores the effect on self-assembly of mixing different molecular building blocks. Thermal measurements, small angle X-ray scattering (SAXS) and circular dichroism (CD) spectroscopy are used to probe these materials on macroscopic, nanoscopic and molecular length scales. The results from these investigations demonstrate that in this case, systems with different "size" and "chirality" factors can self-organise, whilst systems with different "shape" factors cannot. The "size" and "chirality" factors are directly connected with the molecular information programmed into the dendritic peptides, whilst the shape factor depends on the group linking these peptides together,this is consistent with molecular recognition hydrogen bond pathways between the peptidic building blocks controlling the ability of these systems to self-recognise. These results demonstrate that mixtures of relatively complex peptides, with only subtle differences on the molecular scale, can self-organise into nanoscale structures, an important step in the spontaneous assembly of ordered systems from complex mixtures. [source] Response of SDOF system to non-stationary earthquake excitationEARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 15 2004R. S. Jangid Abstract Earthquake excitation is often modelled by non-stationary random process (i.e. uniformly modulated broad-band excitation) for analysis of structural safety subjected to seismic hazards. In this paper, the non-stationary response of a single-degree-of-freedom (SDOF) system to non-stationary earthquake motion is investigated for different shapes of modulating functions. The evolutionary power-spectral density function (PSDF) of the displacement of the SDOF system is obtained using the time-varying frequency response function and the PSDF of the earthquake excitation. The close form expressions for time-varying frequency response function are derived for different shapes of the modulating functions. In order to study the effects of the shape of the modulating function, a comparison of the non-stationary earthquake response of the SDOF system is also made for different modulating functions having the same energy content. Copyright © 2004 John Wiley & Sons, Ltd. [source] A Study of the Determination of Cu(II) by Anodic Stripping Voltammetry on a Novel Nylon/Carbon Fiber ElectrodeELECTROANALYSIS, Issue 7 2004A. Mylonakis Abstract In this work we report a new electrode material formed by injection-moulding of a conducting polymer consisting of carbon fibers in a Nylon matrix. This material is highly conductive, inexpensive, easy to mould in different shapes and requires minimal pretreatment. The electrode was tested as a mercury-free sensor for the trace determination of Cu(II) by anodic stripping voltammetry (ASV). The deposition and stripping behavior of copper on the conducting material was initially studied by cyclic voltammetry and the chemical and instrumental parameters of the determination were investigated. The electrode has been shown to be suitable for the determination of Cu(II) in the range 8,,g L,1 to 30,mg,L,1 (with deposition times ranging from 30,s to 10,min) with a relative standard deviation of 2.2% (at the 0.5,mg,L,1 level) and a limit of detection of 8,,g L,1 Cu(II) for 10,min of accumulation (at a S/N ratio of 5). The electrode was, finally, applied to the determination of copper in tap-water, pharmaceutical tablets and bovine serum with recoveries of 97.4, 94.9 and 93.4%, respectively [source] Seed morphology of some species of Convolvulaceae from Egypt (Identification of species and systematic significance)FEDDES REPERTORIUM, Issue 1-2 2007K. Abdel Khalik Seed morphology of 31 taxa belong to six genera of Convolvulaceae from Egypt were examined by using light and scanning electron microscopy. Macro- and micromorphological characters, including seed shape, colour, size, surface, epidermal cell shape, anticlinal boundaries, outer periclinal cell wall and relief of outer cell walls, are presented. Three types of basic anticlinal cell wall boundaries and three types of relief outer cell walls are recognized and four different shapes of the outer periclinal cell wall are described. A key for the identification of the investigated taxa based on seed characters is provided. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) Morphologie der Samen einiger Arten der Convolvulaceae aus Ägypten (Bestimmung von Arten und systematische Bedeutung) Unter Anwendung von Licht- und Elektronenmikroskopie wurde die Morphologie der Samen von 31 Arten aus sechs Gattungen der Convolvulaceae untersucht. Berücksichtigt wurden die makro- und mikromorphologischen Merkmale der Samen umfassend äußere Form, Farbe, Größe, Oberfläche, Form der Epidermiszellen, antiklinale und periklinale Zellwände und Relief der äußeren Zellwände. Drei Typen basaler antiklinaler Zellwände und drei Typen des Reliefs der äußeren Zellwände wurden nachgewiesen; ferner werden vier Formen der äußeren periklinalen Zellwände beschrieben. Ein Schlüssel zur Bestimmung der untersuchten Taxa auf der Basis der Merkmale der Samen wird vorgelegt. [source] Seed morphology of Cuscuta L. (Convolvulaceae) in Egypt and its systematic significanceFEDDES REPERTORIUM, Issue 3-4 2006K. N. Abdel Khalik The seed morphology of eight taxa of Cuscuta from Egypt has been studied using light and scanning electron microscopy, to determine the significance of seed coat features as taxonomic characters. Macro- and micromorphological characters, including seed shape, colour, size, epidermal cell shape, anticlinal boundaries, outer periclinal cell wall and relief of outer cell walls are presented. Three types of anticlinal cell wall boundaries are recognized and two different shapes of outer periclinal cell wall are described. The secondary sculpture of the cell wall varies from striate to micro-reticulate, and smooth to fine folds. A key for the identification of the investigated taxa based on seed characters is provided. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) Samenmorphologie von Cuscuta L. (Convolvulaceae) in Ägypten und ihre systematische Bedeutung Die Morphologie des Samens von acht ägyptischen Cuscuta -Taxa wurde mittels Licht- und Elektronenmikroskopie untersucht, um die Bedeutung der Merkmale der Samenschale für die Taxonomie zu ermitteln. Makro- und mikromorphologische Merkmale einschließlich Samengestalt, Farbe, Größe, Form der Epidermiszellen, antiklinale Zellwände, äußere Periklinal-Zellwände und Relief der äußeren Zellwände umfassend, wurden untersucht. Drei Typen antiklinaler Zellwand-Umrisse und zwei unterschiedliche Formen der äußeren Periklinal-Zellwände werden beschrieben. Die sekundäre Skulptur der Zellwände variiert von striat bis mikro-reticulat, und von glatt zu leicht gefaltet. Ein Bestimmungsschlüssel basierend auf den Samenmerkmalen der untersuchten Sippen wird vorgelegt. [source] What determines the relationship between plant diversity and habitat productivity?GLOBAL ECOLOGY, Issue 6 2008Martin Zobel ABSTRACT The relationship between biodiversity and habitat productivity has been a fundamental topic in ecology. Although the relationship between these parameters may exhibit different shapes, the unimodal shape has been frequently encountered. The decrease in diversity at high productivity has usually been attributed to competitive exclusion. We suggest that evolutionary history and dispersal limitation may be even more important in shaping the diversity,productivity relationship. On a global scale, unimodal diversity,productivity relationships dominate in temperate regions, whereas positive relationships are more common in the tropics. This difference can be accounted for by contrasting evolutionary history. Temperate regions have smaller species pools for productive habitats since these habitats have been scarce historically for speciation, while the opposite is true for the tropics. In addition, dispersal within a region may limit diversity either due to the lack of dispersal syndromes at low productivity or the low number of diaspores at high productivity. Thereafter, biotic interactions (competition and facilitation) can shape the relationship. All these processes can act independently or concurrently. We recommend that the common approach to examining empirical diversity,environmental relationships should start with the role of large-scale processes such as evolutionary history and dispersal limitation, followed by influences associated with ecological interactions. [source] Magnetic-Field-Induced Phase-Selective Synthesis of Ferrosulfide Microrods by a Hydrothermal Process: Microstructure Control and Magnetic Properties,ADVANCED FUNCTIONAL MATERIALS, Issue 8 2006Z. He Abstract Microrods of the ferrosulfide minerals greigite (Fe3S4) and marcasite (FeS2) are selectively synthesized by an in,situ magnetic-field-assisted hydrothermal route. Each complex microrod is composed of fine building blocks with different shapes. The unique magnetic properties of the microrods and electrical performance of a single microrod are studied. The results demonstrate that the magnetic properties of the ferrosulfide minerals are strongly related to their corresponding microstructures. The value of the low-temperature transition increases as the greigite component in the product decreases. The combination of small-molecule sulfur precursors and an applied magnetic field makes possible the selective synthesis of ferrosulfide minerals with different phases and distinct microstructures, underlining the fact that the magnetic field can be a useful tool as well as an independent parameter for the phase-selective synthesis and self-assembly of inorganic building blocks in solution chemistry. [source] Canal shapes produced sequentially during instrumentation with Quantec SC rotary nickel,titanium instruments: a study in simulated canalsINTERNATIONAL ENDODONTIC JOURNAL, Issue 2 2001I. T. Griffiths Abstract Aim The aim of this study was to determine the shaping ability of Quantec SC nickel,titanium rotary instruments in simulated root canals. Methodology Forty simulated canals consisting of four different shapes in terms of angle and position of curvature were prepared with Quantec SC instruments. Sequential still images were taken of the canals using a video camera attached to a computer with image analysis software. Images were taken preoperatively, and then after instrument 7 (Size 25, 0.05 taper), instrument 8 (size 25, 0.06 taper), and instrument 10 (size 45, 0.02 taper) were taken to length. Each sequential postoperative image was superimposed individually over the preoperative image in order to highlight the amount and position of material removed during preparation. Results Overall, the mean preparation time to size 10 was 3.6 min with 12 mm canals taking on average less time than 8 mm canals. There was a highly significant difference between the canal types (P < 0.0001). No instruments fractured within the canal or deformed, although one instrument separated from the latch grip. All canals remained patent. Following preparation to size 10, 19 canals (48%) retained their length, eight (20%) lost length, and 13 (32%) gained length; the magnitude of the change in length was always 0.5 mm or below. Following preparation to size 7 instruments all canals showed aberrant shapes. Excess removal of material along the outer aspect of the curve between the beginning of the curve and the end-point (outer widening) was found in 26 canals (65%) after instrument 7. At the same stage of preparation six canals (15%) had zips, three (8%) had ledges and five (13%) had perforations. Following preparation to size 10, 27 (68%) canals were perforated. Conclusions Under the conditions of the study, Quantec SC instruments consistently produced aberrations when canals were enlarged to size 7 (size 25, 0.05 taper) or above. Care should be exercised when using these instruments in real teeth. [source] Shaping ability of Hero 642 rotary nickel,titanium instruments in simulated root canals: Part 2INTERNATIONAL ENDODONTIC JOURNAL, Issue 3 2000S. A. Thompson Abstract Aim To determine the shaping ability of Hero 642 nickel,titanium rotary instruments during the preparation of simulated canals. Methodology A total of 40 simulated root canals made up of four different shapes, in terms of angle and position of curvature, were prepared by Hero 642 instruments using a crown-down preparation sequence. Pre- and postoperative images of the canals were taken using a video camera attached to a computer with image analysis software. The pre- and postoperative views were superimposed to highlight the amount and position of material removed during preparation. This report describes the efficacy of the instruments in terms of prevalence of canal aberrations, the amount and direction of canal transportation and overall postoperative shape. Results Four zips and four elbows were created during preparation, all in canals with 40°, 12 mm curves. No perforations or danger zones were created. Highly significant differences (P < 0.001) were apparent between the canal shapes in total canal width at the apex and beginning of the curve, and in the amount of resin removed from the inner and outer aspects of the curve at the orifice. Canal transportation was most frequently directed toward the outer aspect of the curve at specific points along the canal, except at the orifice, where it was apparent that canals with 20° curves transported toward the inner. Overall, mean absolute transportation was always less than 0.15 mm; however, significant differences occurred between canal shapes at the end-point (P < 0.01), apex of the curve (P < 0.01) and at the orifice (P < 0.01). Conclusions Under the conditions of this study, Hero 642 rotary nickel,titanium instruments created canals with few aberrations and no perforations. The relatively high proportion of aberrations in canals with short, acute curves may indicate that instruments with increased taper should be used with caution at or near the full working distance. Further research in real teeth is necessary to elucidate the full potential of these new rotary instruments for use in root canal preparation. [source] Computation of the J -integral for large strainsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING, Issue 12 2008Ágnes Horváth Abstract The phenomenon of failure by catastrophic crack propagation in structural materials poses problems of design and analysis in many fields of engineering. Cracks are present to some degree in all structures. They may exist as basic defects in the constituent materials or they may be induced in construction or during service life. Using the finite element method, a lot of papers deal with the calculation of stress intensity factors for two- and three-dimensional geometries containing cracks of different shapes under various loadings to elastic bodies. In order to increase the accuracy of the results, special elements have been used. They are described together with methods for calculating the stress intensity factors from the computed results. At the vicinity of a crack tip, the strains are not always small, but they may also be large. In this case, the J -integral can also be applied to characterize the cracks in elastic or elastic,plastic bodies. This paper describes the computation of the two-dimensional J -integral for large strains to elastic and elastic,plastic bodies and represents some numerical examples. Copyright © 2007 John Wiley & Sons, Ltd. [source] An a posteriori error estimator for the mimetic finite difference approximation of elliptic problemsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 11 2008Lourenço Beirão da Veiga Abstract We present an a posteriori error indicator for the mimetic finite difference approximation of elliptic problems in the mixed form. We show that this estimator is reliable and efficient with respect to an energy-type error comprising both flux and pressure. Its performance is investigated by numerically solving the diffusion equation on computational domains with different shapes, different permeability tensors, and different types of computational meshes. Copyright © 2008 John Wiley & Sons, Ltd. [source] Physics-based preconditioner for iterative algorithms in multi-scatterer and multi-boundary method of moments formulationsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 3 2002Jürgen v. Hagen Abstract An efficient method to solve electromagnetic scattering problems involving several metallic scatterers or bodies composed of dielectric and metallic regions is proposed. So far, the method of moments has successfully been applied to large arrays of identical scatterers when it was combined with preconditioned iterative algorithms to solve for the linear system of equations. Here, the method is generalized to geometries that are composed of several metallic elements of different shapes and sizes, and also to scatterers that are composed of metallic and dielectric regions. The method uses in its core an iterative algorithm, preferably the transpose-free quasi-minimum residual (TFQMR) algorithm, and a block diagonal Jacobi preconditioner. For best performance, the blocks for the preconditioner are chosen according to individual scatterers or groups of scatterers for the array case, and according to the electric and magnetic current basis functions for dielectric/metallic scatterers. The iterative procedure converges quickly for an optimally chosen preconditioner, and is robust even for a non-optimal preconditioner. Reported run times are compared to run times of an efficiently programmed LU factorization, and are shown to be significantly lower. Copyright © 2002 John Wiley & Sons, Ltd. [source] A volume-of-fluid method for incompressible free surface flowsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 12 2009I. R. Park Abstract This paper proposes a hybrid volume-of-fluid (VOF) level-set method for simulating incompressible two-phase flows. Motion of the free surface is represented by a VOF algorithm that uses high resolution differencing schemes to algebraically preserve both the sharpness of interface and the boundedness of volume fraction. The VOF method is specifically based on a simple order high resolution scheme lower than that of a comparable method, but still leading to a nearly equivalent order of accuracy. Retaining the mass conservation property, the hybrid algorithm couples the proposed VOF method with a level-set distancing algorithm in an implicit manner when the normal and the curvature of the interface need to be accurate for consideration of surface tension. For practical purposes, it is developed to be efficiently and easily extensible to three-dimensional applications with a minor implementation complexity. The accuracy and convergence properties of the method are verified through a wide range of tests: advection of rigid interfaces of different shapes, a three-dimensional air bubble's rising in viscous liquids, a two-dimensional dam-break, and a three-dimensional dam-break over an obstacle mounted on the bottom of a tank. The standard advection tests show that the volume advection algorithm is comparable in accuracy with geometric interface reconstruction algorithms of higher accuracy than other interface capturing-based methods found in the literature. The numerical results for the remainder of tests show a good agreement with other numerical solutions or available experimental data. Copyright © 2009 John Wiley & Sons, Ltd. [source] Assemblies of Metal Nanoparticles and Self-Assembled Peptide Fibrils,Formation of Double Helical and Single-Chain Arrays of Metal Nanoparticles,ADVANCED MATERIALS, Issue 11 2003X. Fu Double helical and single-chain arrays of Au and Pd metal nanoclusters have been achieved by assembling the corresponding metal nanoparticles on peptide nanofibril templates at different pH values. The assembled metal nanoparticles are useful for studying the superstructures of the peptide nanofibrils. Pd nanowires of different shapes have also been prepared by varying the amount of metal deposition. [source] Support vector machines-based generalized predictive controlINTERNATIONAL JOURNAL OF ROBUST AND NONLINEAR CONTROL, Issue 17 2006S. Iplikci Abstract In this study, we propose a novel control methodology that introduces the use of support vector machines (SVMs) in the generalized predictive control (GPC) scheme. The SVM regression algorithms have extensively been used for modelling nonlinear systems due to their assurance of global solution, which is achieved by transforming the regression problem into a convex optimization problem in dual space, and also their higher generalization potential. These key features of the SVM structures lead us to the idea of employing a SVM model of an unknown plant within the GPC context. In particular, the SVM model can be employed to obtain gradient information and also it can predict future trajectory of the plant output, which are needed in the cost function minimization block. Simulations have confirmed that proposed SVM-based GPC scheme can provide a noticeably high control performance, in other words, an unknown nonlinear plant controlled by SVM-based GPC can accurately track the reference inputs with different shapes. Moreover, the proposed SVM-based GPC scheme maintains its control performance under noisy conditions. Copyright © 2006 John Wiley & Sons, Ltd. [source] Synthesis and characterization of polypyrrole rod doped with p -toluenesulfonic acid via micelle formationJOURNAL OF APPLIED POLYMER SCIENCE, Issue 6 2008Duk Ki Kim Abstract Rod-type polypyrrole (PPY) doped with p -toluenesulfonic acid (TSA) was synthesized by chemical oxidative polymerization via a self-assembly process. The shape of the PPY particles is mainly determined by the ratio of TSA/pyrrole (PY) and feed rate of the oxidant. Particle of different shapes (rod, grain, and partially rod) exhibit differences in morphology, electrical properties, dispersity, and thermal properties. Wide-angle X-ray diffraction patterning analysis was used to investigate the mechanism of rod formation. The effect of the TSA concentration on the PPY structure was investigated using Fourier transform infrared spectroscopy. The PPY rods doped with TSA exhibited better electrical conductivity than granular PPY doped with TSA, and their dispersity and thermal stability were also higher. Self-orientation of PPY in the micelles of TSA and high crystallinity of the rod particles led to improved thermal stability. Hence, the decomposition temperature of the polymer chain was considerably increased. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2008 [source] The importance of nest cleaning in egg rejection behaviour of great reed warblers Acrocephalus arandinaceasJOURNAL OF AVIAN BIOLOGY, Issue 1 2003Csaba Moskát We tested the importance of nest cleaning in egg rejection behaviour of the great reed warbler Acrocephalus arundinaceus in a highly parasitised population in which about 64% of nests are parasitised by the common cuckoo Cuculus canorus. Three types of objects of the same weight, texture and colour but with different shapes (dummy cuckoo eggs, sticks and disks) were placed into great reed warbler nests. We investigated the response of hosts in two stages of breeding: pre-incubation when the risk of brood parasitism is high, and during incubation when the risk of parasitism is low. The dummy cuckoo eggs were rejected less often than the other objects in both breeding stages, although we did not find any difference in the frequency of rejection between pre-incubation and incubation. We integrate these results into current views on the evolution of host,parasite interactions, and propose a hierarchical concept to understand egg rejection behaviour: (1) hosts reject all non-egg shaped objects as a general cleaning mechanism; (2) adaptations for the hosts' ability to recognise their own eggs allows them to distinguish these eggs from similar objects and parasitic eggs. [source] Sorption of copper by a highly mineralized peat in batch and packed-bed systemsJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 2 2010Marta Izquierdo Abstract BACKGROUND: The performance of peat for copper sorption was investigated in batch and fixed-bed experiments. The effect of pH was evaluated in batch experiments and the experimental data were fitted to an equilibrium model including pH dependence. Hydrodynamic axial dispersion was estimated by tracing experiments using LiCl as a tracer. Six fixed-bed experiments were carried out at copper concentrations between 1 and 60 mg dm,3 and the adsorption isotherm in dynamic mode was obtained. A mass transport model including convection,dispersion and sorption processes was applied for breakthrough curve modelling. RESULTS: Maximum uptake capacities in batch mode were 22.0, 36.4, and 43.7 mg g,1 for pH values of 4.0, 5.0, and 6.0, respectively. Uptake capacities in continuous flow systems varied from 36.5 to 43.4 mg g,1 for copper concentrations between 1 and 60 mg dm,3. Dynamic and batch isotherms showed different shapes but a similar maximum uptake capacity. Sorbent regeneration was successfully performed with HCl. A potential relationship between dispersion coefficient and velocity was obtained with dispersion coefficients between 5.00 × 10,8 and 2.95 × 10,6 m2 s,1 for water velocities ranging between 0.56 × 10,4 and 5.03 × 10,4 m s,1. The mass transport model predicted both the breakpoints and the shape of the breakthrough curves. CONCLUSIONS: High retention capacities indicate that peat can be used as an effective sorbent for the treatment of wastewater containing copper ions. Copyright © 2009 Society of Chemical Industry [source] Plasticity of death rates in stationary phase in Saccharomyces cerevisiaeAGING CELL, Issue 1 2009Nadège Minois Summary For the species that have been most carefully studied, mortality rises with age and then plateaus or declines at advanced ages, except for yeast. Remarkably, mortality for yeast can rise, fall and rise again. In the present study we investigated (i) if this complicated shape could be modulated by environmental conditions by measuring mortality with different food media and temperature; (ii) if it is triggered by biological heterogeneity by measuring mortality in stationary phase in populations fractionated into subpopulations of young, virgin cells, and replicatively older, non-virgin cells. We also discussed the results of a staining method to measure viability instead of measuring the number of cells able to exit stationary phase and form a colony. We showed that different shapes of age-specific death rates were observed and that their appearance depended on the environmental conditions. Furthermore, biological heterogeneity explained the shapes of mortality with homogeneous populations of young, virgin cells exhibiting a simple shape of mortality in conditions under which more heterogeneous populations of older cells or unfractionated populations displayed complicated death rates. Finally, the staining method suggested that cells lost the capacity to exit stationary phase and to divide long before they died in stationary phase. These results explain a phenomenon that was puzzling because it appeared to reflect a radical departure from mortality patterns observed for other species. [source] COMPLEX METHOD FOR NONLINEAR CONSTRAINED MULTI-CRITERIA (MULTI-OBJECTIVE FUNCTION) OPTIMIZATION of THERMAL PROCESSINGJOURNAL OF FOOD PROCESS ENGINEERING, Issue 4 2003FERRUH ERDO ABSTRACT The goal in a multi-objective function optimization problem is to optimize the several objective functions simultaneously. the complex method is a powerful algorithm to find the optimum of a general nonlinear function within a constrained region. the objective of this study was to apply the complex method to two different shapes (a sphere and a finite cylinder) subjected to the same thermal processing boundary conditions to find a variable process temperature profile (decision variable) to maximize the volume-average retention of thiamine. A process temperature range of 5 to 150C was used as an explicit constraint. Implicit constraints were center temperature and accumulated center lethality of the sphere and the finite cylinder. the objective functions for both shapes were combined into a single one using a weighting method. Then, the previously developed complex algorithm was applied using Lexicographic Ordering to order the objective functions with respect to their significance. the results were reported as optimum variable process temperature profiles using the given geometries and objective functions. the thiamine retentions were also compared with a constant process temperature process, and 3.0% increase was obtained in the combined objective function. the results showed that the complex method can be successfully used to predict the optimum variable process temperature profiles in multi-criteria thermal processing problems. [source] Origin of the conformation dependence of protein charge-state distributions in electrospray ionization mass spectrometryJOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 1 2003Rita Grandori Abstract The influence of tertiary structure on the electrospray ionization mass spectra of proteins is a well known and broadly exploited phenomenon. However, the underlying mechanism is not well understood. This paper discusses the bases and the implications of the two current hypotheses (solvent accessibility and Coulombic repulsions), pointing out the remaining open questions. Evidence reported here supports a third hypothesis, i.e. that intramolecular interactions in folded proteins play a key role in determining the observed charge-state distributions. It is proposed that native protein structures stabilize to a large extent pre-existing charges of the opposite polarity to the net charge of the ion, preventing their neutralization during the electrospray process. Thus, the higher charge states of unfolded conformations, relative to the folded structure, would not derive from a more extensive ionization of the former, but rather from a higher content of neutralizing charges in the latter. This interpretation allows several other problematic observations to be explained, including the different shapes of the spectra of folded and unfolded proteins, the discrepancies between observed and predicted gas-phase reactivity of protein ions and the apparent inconsistency of positive- and negative-ion mode results. Copyright © 2003 John Wiley & Sons, Ltd. [source] Structural basis for preferential binding of non- ortho -substituted polychlorinated biphenyls by the monoclonal antibody S2B1JOURNAL OF MOLECULAR RECOGNITION, Issue 4 2005Jean-Luc Pellequer Abstract Polychlorinated biphenyls (PCBs) are a family of 209 isomers (congeners) with a wide range of toxic effects. In structural terms, they are of two types: those with and those without chlorines at the ortho positions (2, 2,, 6 and 6,). Only 20 congeners have no ortho chlorines. Three of these are bound by the aryl hydrocarbon receptor and are one to four orders of magnitude more toxic than all others. A monoclonal antibody, S2B1, and its recombinant Fab have high selectivity and nanomolar binding affinities for two of the most toxic non- ortho -chlorinated PCBs, 3,4,3,,4,-tetrachlorobiphenyl and 3,4,3,,4,,5,-pentachlorobiphenyl. To investigate the basis for these properties, we built a three-dimensional structure model of the S2B1 variable fragment (Fv) based on the high-resolution crystallographic structures of antibodies 48G7 and N1G9. Two plausible conformations for the complementarity-determining region (CDR) H3 loop led to two putative PCB-binding pockets with very different shapes (models A and B). Docking studies using molecular mechanics and potentials of mean force (PMF) indicated that model B was most consistent with the selectivity observed for S2B1 in competition ELISAs. The binding site in model B had a deep, narrow pocket between VL and VH, with a slight constriction at the top that opened into a wider pocket between CDRs H1 and H3 on the antibody surface. This binding site resembles those of esterolytic antibodies that bind haptens with phenyl rings. One phenyl ring of the PCB fits into the deep pocket, and the other ring is bound in the shallower one. The bound PCB is surrounded by the side chains of TyrL91, TyrL96 and TrpH98, and it has a ,-cation interaction with ArgL46. The tight fit of the binding pocket around the ortho positions of the bound PCBs indicates that steric hindrance of ortho chlorines in the binding site, rather than induced conformational change of the PCBs, is responsible for the selectivity of S2B1. Copyright © 2005 John Wiley & Sons, Ltd. [source] | ||||||||||||||||||||||||||||||||||