Home About us Contact
|
Home About us Contact | ||
|
|
||
Sharp Edges (sharp + edge)
Selected AbstractsCatalyst-Free Efficient Growth, Orientation and Biosensing Properties of Multilayer Graphene Nanoflake Films with Sharp Edge Planes,ADVANCED FUNCTIONAL MATERIALS, Issue 21 2008Nai Gui Shang Abstract We report a novel microwave plasma enhanced chemical vapor deposition strategy for the efficient synthesis of multilayer graphene nanoflake films (MGNFs) on Si substrates. The constituent graphene nanoflakes have a highly graphitized knife-edge structure with a 2,3,nm thick sharp edge and show a preferred vertical orientation with respect to the Si substrate as established by near-edge X-ray absorption fine structure spectroscopy. The growth rate is approximately 1.6,µm min,1, which is 10 times faster than the previously reported best value. The MGNFs are shown to demonstrate fast electron-transfer (ET) kinetics for the Fe(CN)63,/4, redox system and excellent electrocatalytic activity for simultaneously determining dopamine (DA), ascorbic acid (AA) and uric acid (UA). Their biosensing DA performance in the presence of common interfering agents AA and UA is superior to other bare solid-state electrodes and is comparable only to that of edge plane pyrolytic graphite. Our work here, establishes that the abundance of graphitic edge planes/defects are essentially responsible for the fast ET kinetics, active electrocatalytic and biosensing properties. This novel edge-plane-based electrochemical platform with the high surface area and electrocatalytic activity offers great promise for creating a revolutionary new class of nanostructured electrodes for biosensing, biofuel cells and energy-conversion applications. [source] An N -bit digitally variable ultra-wideband pulse generator for GPR and UWB applicationsMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 7 2006Sertac Yilmaz Abstract This paper presents a low-cost ultra-wideband (UWB) pulse generator that can vary the pulse duration digitally by using a step-recovery diode (SRD), microstrip transmission lines, and PIN diodes. First, a sharp edge is generated by using SRD circuitry. Then a pulse is formed from the sharp edge through the use of transmission lines and the PIN diodes. Based on the number of transmission lines (N), the duration of the pulse can be varied in 2N steps. The UWB pulse generator circuits are implemented on an FR-4 substrate using microstrip-line technology and UWB pulses with durations of 550 to 2400 psec are measured. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 1334,1339, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21620 [source] Nanogold-Loaded Sharp-Edged Carbon Bullets as Plant-Gene CarriersADVANCED FUNCTIONAL MATERIALS, Issue 15 2010Periyasamy S. Vijayakumar Abstract The higher DNA delivery efficiency into plants by gold nanoparticles embedded in sharp carbonaceous carriers is demonstrated. These nanogold-embedded carbon matrices are prepared by heat treatment of biogenic intracellular gold nanoparticles. The DNA-delivery efficiency is tested on a model plant, Nicotiana tabacum, and is further extended to the monocot, Oryza sativa, and a hard dicot tree species, Leucaena leucocephala. These materials reveal good dispersion of the transport material, producing a greater number of GUS foci per unit area. The added advantages of the composite carrier are the lower plasmid and gold requirements. Plant-cell damage with the carbon-supported particles is very minimal and can be gauged from the increased plant regeneration and transformation efficiency compared with that of the commercial micrometer-sized gold particles. This is ascribed to the sharp edges that the carbon supports possess, which lead to better piercing capabilities with minimum damage. [source] A feature-preserving volumetric technique to merge surface triangulationsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 2 2002Juan R. Cebral Abstract Several extensions and improvements to surface merging procedures based on the extraction of iso-surfaces from a distance map defined on an adaptive background grid are presented. The main objective is to extend the application of these algorithms to surfaces with sharp edges and corners. In order to deal with objects of different length scales, the initial background grids are created using a Delaunay triangulation method and local voxelizations. A point enrichment technique that introduces points into the background grid along detected surface features such as ridges is used to ensure that these features are preserved in the final merged surface. The surface merging methodology is extended to include other Boolean operations between surface triangulations. The iso-surface extraction algorithms are modified to obtain the correct iso-surface for multi-component objects. The procedures are demonstrated with various examples, ranging from simple geometrical entities to complex engineering applications. The present algorithms allow realistic modelling of a large number of complex engineering geometries using overlapping components defined discretely, i.e. via surface triangulations. This capability is very useful for grid generation starting from data originated in measurements or images. Copyright © 2002 John Wiley & Sons, Ltd. [source] Practical techniques for a three-dimensional FEM analysis of incompressible fluid flow contained with slip walls and a downstream tube bundleINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 3 2001Yuzuru Eguchi Abstract Two practical techniques are proposed in this paper to simulate a flow contained in a plenum with a downstream tube bundle under a PC environment. First, a technique to impose slip wall conditions on smooth-faced planes and sharp edges is proposed to compensate for the mesh coarseness relative to boundary layer thickness. In particular, a new type of Poisson equation is formulated to simultaneously satisfy both such velocity boundary conditions on walls and the incompressibility constraint. Second, a numerical model for a downstream tube bundle is proposed, where hydraulic resistance in a tube is imposed as a traction boundary condition on a fluid surface contacting the tube bundle end. The effectiveness of the techniques is numerically demonstrated in the application to a flow in a condenser water box. Copyright © 2001 John Wiley & Sons, Ltd. [source] Riga,Fede disease: association with microcephalyINTERNATIONAL JOURNAL OF PAEDIATRIC DENTISTRY, Issue 6 2002Z. D. Baghdadi Summary. A case of microcephaly associated with traumatic ulceration to the ventral surface of the tongue (Riga-Fede disease) in a 12-month-old female is presented. To the best of our knowledge, such association has not been described previously. A conservative treatment regime was used, involving medical management, elimination of the sharp edges of the teeth and use of topical triamcinolone, and the ulceration healed over a period of 4 weeks. [source] Supershells in deformed harmonic oscillators and atomic clustersINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 4 2002Dennis Bonatsos Abstract From the mathematical point of view, the appearance of supershells is a general feature of potentials having relatively sharp edges. In physics, supershells have been observed in systems of metal clusters, which are also known to exhibit an underlying shell structure with magic numbers intermediate between the magic numbers of the 3-D isotropic harmonic oscillator and those of the 3-D square well. In the present study, Nilsson's modified harmonic oscillator (without any spin,orbit interaction), as well as the 3-D q -deformed harmonic oscillator with uq(3) , soq(3) symmetry, are considered. The former model has been used for an early schematic description of shell structure in metal clusters, while the latter has been found to successfully reproduce the magic numbers of metal clusters up to 1500 atoms, the expected limit of validity for theories based on the filling of electronic shells. The systematics of the appearance of supershells in the two models will be considered, putting emphasis on the differences between the spectra of the two oscillators. While the validity of Nilsson's modified harmonic oscillator framework is limited to relatively low particle numbers, the 3-D q -deformed harmonic oscillator gives reliable descriptions of the first supershell in metal clusters, which lies within its region of validity. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002 [source] Mixing immiscible blends in an intermeshing counter-rotating twin screw extruderADVANCES IN POLYMER TECHNOLOGY, Issue 2 2006Ramesh Potluri Abstract Domain size of 10% dispersed polystyrene in polyethylene was followed in a 34-mm intermeshing counter-rotating twin screw extruder. Variables studied included the effects of barrel temperature, screw speed, viscosity ratio of dispersed-to-continuous phase, and parallel melt versus preblended solids feeds. After steady state was achieved, die samples were quenched for later photomicrographing. The extruder was then stopped and quenched, with subsequent pulling of the screws. From 7 to 12 additional samples were taken along the 18/1 L/D extruder for determination of the mechanism of dispersion and dispersed phase domain size by optical microscopy. At low temperatures, the polystyrene tended to fracture with sharp edges. The fine particles formed in the initial breakup underwent no further size reduction. At higher temperatures, fractured segments had rounder edges, but the size of the small domains remained constant throughout the axial length. There was some evidence of flocculation and coalescence prior to exit through the die. © 2006 Wiley Periodicals, Inc. Adv Polym Techn 25: 81,89, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.20065 [source] A study of sulfamerazine single crystals using atomic force microscopy, transmission light microscopy, and Raman spectroscopyJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 9 2005Xiaoping Cao Abstract Sulfamerazine (SMZ) Form I and II single crystals were prepared from aqueous dispersions of SMZ bulk samples and studied using several microscopic and spectroscopic techniques. Transmission light microscopy and Raman spectroscopy were used to observe and identify single crystals. The results indicated that Form I single crystals tended to be rectangular laths while Form II ones tended to be hexagonal laths. Surface morphology of individual single crystals was further investigated by atomic force microscopy (AFM). AFM images revealed a smooth top surface, a uniform height, and sharp edges for both forms of single crystals. Both height and phase images showed crystalline terraces with different step heights for the top surface of Form I. Surface properties of single crystals were evaluated using AFM force measurements. Experimental results indicated that the top surface of Form I single crystals was more hydrophilic than that of Form II. Theoretical calculations predicted a dominant crystal face of (020) for the Form I single crystals and (002) for the Form II ones. The correlations between calculation predictions and experimental results were discussed. © 2005 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 94:1881,1892, 2005 [source] Arctic roars , laryngeal anatomy and vocalization of the muskox (Ovibos moschatus Zimmermann, 1780, Bovidae)JOURNAL OF ZOOLOGY, Issue 4 2006R. Frey Abstract The impressive roaring of adult male muskoxen most often occurs during rutting contests. Roaring in adult females is primarily relevant to mother,infant communication. Loud roars are produced by taking up a specific roaring posture. Acoustic recordings were made in a small herd of zoo muskoxen during three successive rutting seasons. Earlier recordings of a different herd were used for comparison. Head-and-neck specimens were subjected to vascular injection, macroscopic anatomical dissection, computer tomographic analysis and skeletonization. Isolated preserved larynges of young animals were dissected for ontogenetic comparison. Despite a pronounced sexual dimorphism of head mass, larynx size is almost identical in adult male and female muskoxen, as is the fundamental frequency of their roars. Remarkably, the larynges of both sexes of muskoxen are provided with an unpaired ventrorostral ventricle. Probably, this ventricle is inflated during the initial phase of a roar. The ventricle may have two functions: to increase the amplitude of roaring and to darken the timbre of the roars by acting as an additional resonance space. The vocal fold of adult female and young individuals has a sharp rostral edge and a vocal ligament is still present. During male ontogeny the vocal ligament becomes transformed into a large fat pad extending into the wall of the laryngeal vestibulum. Accordingly, the glottic region in the adult male lacks any sharp edges of the mucosa. In both sexes the thyroarytenoid muscle is divided into three portions. A single roar may comprise phases of different sound volume. The roars of both muskox sexes are characterized by a pulsed structure. We suggest that two oscillating systems are involved in the production of roars: one comprising only the medial portion of the vocal fold and one including its lateral portion. [source] Snow metamorphism as revealed by scanning electron microscopyMICROSCOPY RESEARCH AND TECHNIQUE, Issue 1 2003Florent Dominé Abstract Current theories of snow metamorphism indicate that sublimating snow crystals have rounded shapes, while growing crystals have shapes that depend on growth rates. At slow growth rates, crystals are rounded. At moderate rates, they have flat faces with rounded edges. At fast growth rates, crystals have flat faces with sharp edges, and they have hollow faces at very fast growth rates. The main growth/sublimation mechanism is thought to be by the homogeneous nucleation of new layers at or near crystal edges. It was also suggested that the equilibrium shape of snow crystals would be temperature dependent: rounded above ,10.5°C, and faceted below. To test these paradigms, we have performed SEM investigations of snow samples having undergone metamorphism under natural conditions, and of snow samples subjected to isothermal metamorphism at ,4° and ,15°C in the laboratory. In general, current theories predicting crystal shapes as a function of growth rates, and of whether crystals are growing or sublimating, are verified. However, the transition in equilibrium shapes from rounded to faceted at ,10.5°C is not observed in our isothermal experiments that reveal a predominance of rounded shapes after more than a month of metamorphism at ,4 and ,15°C. Some small crystals with flat faces that also have sharp angles at ,15°C, are observed in our isothermal experiments. These faces are newly formed, and contradict current theory. Several hypotheses are proposed to explain their occurrence. One is that they are due to sublimation at emerging dislocations. Microsc. Res. Tech. 62:33,48, 2003. © 2003 Wiley-Liss, Inc. [source] Perceived blur in amblyopiaOPHTHALMIC AND PHYSIOLOGICAL OPTICS, Issue 6 2002A. J. Simmers Purpose:, It is well documented that visual acuity and contrast sensitivity in amblyopia are attenuated at high spatial frequencies: this would predict that amblyopes should perceive objects as blurred because they lack high spatial frequency information necessary to adequately represent sharp edges. In a series of experiments, we explored the representation of blur in amblyopia with blur discrimination and blur matching tasks. Methods:, Monocular blur discrimination thresholds were measured in a spatial 2-Alternative Force Choice procedure. The luminance profiles of the blurred edge were cumulative Gaussians with the standard deviation of the reference blurred edge being fixed at 1.88, 3.75, 7.5, 15, 30, or 60 min arc. Observers were required to discriminate which edge (right or left) appeared to be the less blurred. Observers also interocularly matched edges which were identical to those employed in the blur discrimination tasks, with the exception that they were viewed dichoptically at all times. Results:, Blur discriminination thresholds were elevated in both the amblyopic and fellow fixing eye but were within the normal range for interocular matching thresholds. Our results suggest that blur is veridically represented in the amblyopic visual system. Conclusions:, The surprising result here is that all amblyopes, even those with the most severe visual loss, veridically matched all blurred edges, including the sharpest ones. This implies that amblyopes are able to represent levels of blur that are defined by spatial structure beyond their resolution limit. These results also raise interesting questions about the mechanism by which blur is represented in the visual system. [source] Heterogeneous nucleation of three-dimensional protein nanocrystalsACTA CRYSTALLOGRAPHICA SECTION D, Issue 5 2007Dilyana G. Georgieva Nucleation is the rate-limiting step in protein crystallization. Introducing heterogeneous substrates may in some cases lower the energy barrier for nucleation and thereby facilitate crystal growth. To date, the mechanism of heterogeneous protein nucleation remains poorly understood. In this study, the nucleating properties of fragments of human hair in crystallization experiments have been investigated. The four proteins that were tested, lysozyme, glucose isomerase, a polysaccharide-specific Fab fragment and potato serine protease inhibitor, nucleated preferentially on the hair surface. Macrocrystals and showers of tiny crystals of a few hundred nanometres thickness were obtained also under conditions that did not produce crystals in the absence of the nucleating agent. Cryo-electron diffraction showed that the nanocrystals diffracted to at least 4,Å resolution. The mechanism of heterogeneous nucleation was studied using confocal fluorescent microscopy which demonstrated that the protein is concentrated on the nucleating surface. A substantial accumulation of protein was observed on the sharp edges of the hair's cuticles, explaining the strong nucleating activity of the surface. [source] | ||||||||||||||||