MAGNETIC RESONANCE IN MEDICINE, Issue 5 2008
Ethan K. Brodsky
Abstract Chemical-shift artifacts associated with non-Cartesian imaging are more complex to model and less clinically acceptable than the bulk fat shift that occurs with conventional spin-warp Cartesian imaging. A novel k -space based iterative decomposition of water and fat with echo asymmetry and least-squares estimation (IDEAL) approach is introduced that decomposes multiple species while simultaneously correcting distortion of off-resonant species. The new signal model accounts for the additional phase accumulated by off-resonant spins at each point in the k -space acquisition trajectory. This phase can then be corrected by adjusting the decomposition matrix for each k -space point during the final IDEAL processing step with little increase in reconstruction time. The technique is demonstrated with water-fat decomposition using projection reconstruction (PR)/radial, spiral, and Cartesian spin-warp imaging of phantoms and human subjects, in each case achieving substantial correction of chemical-shift artifacts. Simulations of the point-spread-function (PSF) for off-resonant spins are examined to show the nature of the chemical-shift distortion for each acquisition. Also introduced is an approach to improve the signal model for species which have multiple resonant peaks. Many chemical species, including fat, have multiple resonant peaks, although such species are often approximated as a single peak. The improved multipeak decomposition is demonstrated with water-fat imaging, showing a substantial improvement in water-fat separation. Magn Reson Med 59:1151,1164, 2008. © 2008 Wiley-Liss, Inc. [source]

STANDARDIZATION OF ENDOSCOPIC ULTRASONOGRAPHY PROCEDURES FOR THE PANCREAS USING RADIAL and CONVEX methods

DIGESTIVE ENDOSCOPY, Issue 2002
Yoshiki Hirooka
We describe the standard endoscopic ultrasonography (EUS) procedure of the pancreas used in our institute. Both radial scanning and convex (or linear) scanning methods have valid uses, so these two methods will coexist in the future. Physicians learning EUS need to master both types. It is important to standardize both types of EUS procedure. Generally, physicians persist in the method mastered first and don't make use of the other method. In order to plan the standardization of EUS procedures, it may be reasonable to standardize the procedures of both type EUS simultaneously, comparing radial scan mode and linear (convex) scan mode. Here we demonstrate our standard procedures for both EUS modes, mainly emphasizing the visualization maneuver of the pancreas. [source]

Single stimulation of the posterior cord is superior to dual nerve stimulation in a coracoid block

ACTA ANAESTHESIOLOGICA SCANDINAVICA, Issue 2 2010
J. RODRÍGUEZ
Background: Both multiple injection and single posterior cord injection techniques are associated with extensive anesthesia of the upper limb after an infraclavicular coracoid block (ICB). The main objective of this study was to directly compare the efficacy of both techniques in terms of the rates of completely anesthetizing cutaneous nerves below the elbow. Methods: Seventy patients undergoing surgery at or below the elbow were randomly assigned to receive an ICB after the elicitation of either a single radial nerve-type response (Radial group) or of two different main nerve-type responses of the upper limb, except for the radial nerve (Dual group). Forty milliliters of 1.5% mepivacaine was given in a single or a dual dose, according to group assignment. The sensory block was assessed in each of the cutaneous nerves at 10, 20 and 30 min. Block performance times and the rates of complete anesthesia below the elbow were also noted. Results: Higher rates of sensory block of the radial nerve were found in the Radial group at 10, 20 and 30 min (P<0.05). The rates of sensory block of the ulnar nerve at 30 min were 97% and 75% in the Radial and in the Dual groups, respectively (P<0.05). The rate of complete anesthesia below the elbow was also higher in the Radial group at 30 min (P<0.05). Conclusions: Injection of a local anesthetic after a single stimulation of the radial nerve fibers produced more extensive anesthesia than using a dual stimulation technique under the conditions of our study. [source]

Microscale Inhomogeneities in Aluminum Solution-Doping of Silica-Based Optical Fibers

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 1 2007
Feng Z. Tang
The microstructure of aluminum (Al) solution-doped soot layers in modified chemical vapor deposition fabrication of silica-based optical fibers has been studied. It is shown that such Al doping is predominantly determined by deposition temperature. Radial and longitudinal Al doping distributions have been investigated in soot layers, in fully sintered glass layers, and in collapsed preforms. Formation mechanisms are discussed. [source]

Design of a Small Centrifugal Blood Pump With Magnetic Bearings

ARTIFICIAL ORGANS, Issue 9 2009
Said Jahanmir
Abstract Design of a blood pump with a magnetically levitated rotor requires rigorous evaluation of the magnetic bearing and motor requirements and analysis of rotor dynamics and hydraulic performance with attention to hemolysis and thrombosis potential. Given the desired geometric dimensions, the required operating speed, flow in both the main and wash flow regions, and magnetic bearing performance, one of several design approaches was selected for a new prototype. Based on the estimated operating speed and clearance between the rotor and stator, the motor characteristics and dimensions were estimated. The motor stiffness values were calculated and used along with the hydraulic loading due to the fluid motion to determine the best design for the axial and radial magnetic bearings. Radial and axial stability of the left ventricular assist device prototype was verified using finite element rotor dynamic analysis. The analysis indicated that the rotor could be completely levitated and spun to the desired operating speed with low power loss and no mechanical contact. In vitro experiments with a mock loop test setup were performed to evaluate the performance of the new blood pump prototype. [source]

Folding of the tectal cortex by local remodeling of neural differentiation

DEVELOPMENTAL DYNAMICS, Issue 3 2004
Tatsuo Mima
Abstract The folding pattern of the brain cortex is a precisely regulated process, but the mechanism involved during development remains unclear. A proposed theory predicts that the initiation of cortical folding depends, at least partly, on nonuniform distribution of neuronal differentiation and neurite growth. We tested this theory experimentally, by remodeling the normal pattern of neuronal cell differentiation within the embryonic optic tectum. Multiple foci of activated fibroblast growth factor signaling were created in the tectal cortex to locally change the neural differentiation and axonal growth patterns. At these foci, tectal cells remained undifferentiated and their radial and tangential migration was suppressed. These local changes in the neuronal cell differentiation resulted in a conversion of the tectal cortex from smoothly extended into precociously folded. The results provide in vivo experimental evidence that microscopic changes in the neuronal cell differentiation pattern can induce or remodel the folding pattern of the brain cortex. Developmental Dynamics 229:475,479, 2004. © 2004 Wiley-Liss, Inc. [source]

CLINICAL USE OF THE NEWLY DEVELOPED ELECTRONIC RADIAL ULTRASOUND ENDOSCOPE

DIGESTIVE ENDOSCOPY, Issue 1 2006
Masami Ogawa
Background:, Endoscopic ultrasonography (EUS) is widely accepted as a diagnostic tool for bilio-pancreatic and gastrointestinal tract diseases. Recently, an ultrasound endoscope with an electronic radial scan transducer has been developed. To evaluate the clinical usefulness of this system, its image quality, advantages and disadvantages were evaluated. Materials and methods:, Ultrasound endoscope with electronic radial scan transducer and its monitor unit were used. The direction of the imaging plane was similar to that of the mechanical radial models. Color Doppler function and tissue harmonic imaging were feasible by this system. To evaluate this endoscope, we investigated the image quality and distance resolution by in-vitro study using thin papers, and 50 patients were examined by this system. Results:, Comparison with the mechanical radial endoscope GF-UM2000 revealed that the image quality was almost equivalent. However, the ultrasound penetration of the electronic radial scanner was better and more satisfactory with less echoic reduction. In addition, the blood-flow signal could be obtained by using the color Doppler function. In contrast, the diameter of the new endoscope was bigger than the advanced mechanical radial models, the monitor unit was bigger than that of the mechanical radial system, and the operation of this unit was complicated. Conclusion:, A prototype of the ultrasound endoscope with electronic radial scan showed satisfactory results regarding the image quality, ultrasound penetration, and clinical diagnosis. The blood flow could be investigated by using the color Doppler function, which is useful to diagnose lesions and detect involvement of the blood vessels in cancers. [source]

STANDARDIZATION OF ENDOSCOPIC ULTRASONOGRAPHY PROCEDURES FOR THE PANCREAS USING RADIAL and CONVEX methods

Phylogenetic comparison of spicule networks in cryptobranchiate dorid nudibranchs (Gastropoda, Euthyneura, Nudibranchia, Doridina)

ACTA ZOOLOGICA, Issue 4 2008
Brian K. Penney
Abstract Many dorid nudibranchs possess large numbers of calcareous spicules in their mantle, gill, rhinophores and foot. However, the arrangements of these structures and their differences among taxa are poorly known. Spicule networks were stained with Alizarin red and compared among 12 species of cryptobranchiate dorid nudibranchs and four outgroups. Three general types of networks were found: a cobweb-like, unbraced framework of one or few spicules per side; a ramifying system of thick, spiculated tracts; and a lattice-like arrangement of distinct radial and circumferential tracts. The Discodorididae species investigated shared a cobweb-like network and papillae supported by a ring of spicules, while the Porostomata showed consistent characters leading to a lattice-like network with larger spicules in the central notum. The Dorididae studied were not cohesive, but each species shared characters with the aforementioned groups. Therefore, spicule network form may provide new characters to help resolve the phylogeny of Doridina. [source]

Geomorphology of the onset area of a paleo-ice stream, Marguerite Bay, Antarctic Peninsula

EARTH SURFACE PROCESSES AND LANDFORMS, Issue 4 2008
John B. Anderson
Abstract Geomorphic features indicate that both glacial and melt-water erosion characterize the onset area of the ancestral Marguerite Ice Stream. The large size of these features indicates that they formed over repeated glacial cycles, most recently during the Last Glacial Maximum. Ice drainage within the bay and on the inner continental shelf was strongly influenced by tectonic fabric. Deep, isolated basins surrounded by rugged bedrock bathymetry characterize the innermost part of the bay. Drumlins and other streamlined features occur in the floors of these basins at depths of up to 900 m. The outer bay has three large interconnected basins. Drumlins and megaflutings within these basins indicate ice was grounded at water depths up to 1000 m. The orientations of these features show convergence of drainage from the northeast, east and south into the Marguerite paleo-ice stream. On the inner continental shelf, the ice converged into a single, wide trough dominated by mega-scale glacial lineations. This transition in geomorphic features from drumlins and megaflutings to mega-scale glacial lineations occurs at the location on the continental shelf where sedimentary strata blanket bedrock, and marks a zone of acceleration of the ice stream. The glacially sculptured geomorphic features within Marguerite Bay co-exist with anastomosing, radial and relatively straight channels, which become increasingly focused in a seaward direction. This implies that a well organized subglacial drainage system existed within the bay at some point in the past. Copyright © 2008 John Wiley & Sons, Ltd. [source]

Neuromast formation in the prehatching embryos of the Japanese flounder (Paralichthys olivaceus)

ACTA ZOOLOGICA, Issue 2 2003
Machiko Otsuka
Abstract The present paper clarifies the initial development of the lateral line organs in the embryonic Japanese flounder, Paralichthys olivaceus. The first appearances of lateral line primordia, and the proliferation, distribution and morphological development of the free neuromasts, including nerve ending formation: establishment of hair cell innervations via the formation of synapses, were examined by light microscopy, scanning and transmission electron microscopy. The first pair of neuromast primordia appeared in the otic region , 30 h prior to hatching and subsequently differentiated into free neuromasts, otic neuromasts, after , 8 h. At hatching, a pair of free neuromasts and three pairs of neuromast primordia were present on the head, and three pairs of neuromast primordia were present on the trunk. The hair cell polarity of the otic neuromast until just prior to hatching was radial, but not bi-directional. The typical afferent and efferent nerve endings in the otic neuromasts had formed by the time of hatching, suggesting that the otic neuromasts are functional prior to hatching. The three neuromast primordia located on each side of the trunk were derived from a long, narrow ectodermal cell cluster and erupted through the epidermis after hatching. [source]

Proposal and development of radial air-gap coreless generator suitable for small wind turbine used in urban area

ELECTRICAL ENGINEERING IN JAPAN, Issue 1 2009
Toshiyuki Takahashi
Abstract Independent distributed power generation using small wind turbines is becoming more widespread as wind power generation increases. Installation of small wind turbines in densely populated urban areas is not only useful from the viewpoint of extracting wind power sources in weak-wind areas but also for making renewable energy easier to access when power supplies are closer to consumers. It is from this point of view that the authors proposed "urban wind power generation" using a collective system with a number of small vertical wind turbines, and have developed a suitable generator for low-speed vertical wind turbines such as a Savonius windmill. Based on a standard coreless generator, the proposed generator is designed to make the direction of the magnetic flux radial in order to install the magnets and coils on the outer end of the generator. The change of magnet composition and flux direction maximizes the speed of the flux change and output voltage within a limited space. With the above configuration, the power of the proposed generator is independent of the diameter. In this report, the authors describe and evaluate the fundamental performance of a prototype of the proposed generator. Based on the experiments, a maximum output power of 283 W was obtained. The obtained starting torque is small enough to begin rotation under weak wind conditions of no more than 1 m/s. Therefore, it is clear that the proposed "radial" coreless generator is suitable for self-starting and producing high power at low wind speed. © 2009 Wiley Periodicals, Inc. Electr Eng Jpn, 167(1): 26, 34, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20695 [source]

Electrophysiological sensory demyelination in typical chronic inflammatory demyelinating polyneuropathy

EUROPEAN JOURNAL OF NEUROLOGY, Issue 7 2010
Y. A. Rajabally
Background:, The presence of electrophysiological demyelination of sensory nerves is not routinely assessed in the evaluation of suspected chronic inflammatory demyelinating polyneuropathy (CIDP). Whether this can be useful is unknown. Methods:, We compared, using surface recording techniques, in 19 patients with typical CIDP and 26 controls with distal large fibre sensory axonal neuropathy, the forearm median sensory conductions, sensory nerve action potential (SNAP) amplitudes and durations and sensory nerve conduction velocities (SNCVs) of median, radial and sural nerves. Results:, Median nerve sensory conduction block (SCB) across the forearm was greater in CIDP patients than in controls (P = 0.005). SNAP durations were longer in CIDP patients for median (P = 0.001) and sural nerves (P = 0.004). Receiver operating characteristic (ROC) curves provided sensitive (>40%) and specific (>95%) cut-offs for median nerve SCB as well as median and sural SNAP durations. SNCVs were significantly slower for median and sural nerves in CIDP patients, but ROC curves did not demonstrate cut-offs with useful sensitivities/specificities. Median SCB or prolonged median SNAP duration or prolonged sural SNAP duration offered a sensitivity of 73.7% for CIDP and specificity of 96.2%. Used as additional parameters, they improved diagnostic sensitivity of the American Academy of Neurology (AAN) criteria for CIDP of 1991, from 42.1% to 78.9% in this population, with preserved specificity of 100%. Discussion:, Sensory electrophysiological demyelination is present and may be diagnostically useful in typical CIDP. SCB detection and SNAP duration prolongation appear to represent more useful markers of demyelination than SNCV reduction. [source]

Rapid functional plasticity in the primary somatomotor cortex and perceptual changes after nerve block

EUROPEAN JOURNAL OF NEUROSCIENCE, Issue 12 2004
Thomas Weiss
Abstract The mature human primary somatosensory cortex displays a striking plastic capacity to reorganize itself in response to changes in sensory input. Following the elimination of afferent return, produced by either amputation, deafferentation by dorsal rhizotomy, or nerve block, there is a well-known but little-understood ,invasion' of the deafferented region of the brain by the cortical representation zones of still-intact portions of the brain adjacent to it. We report here that within an hour of abolishing sensation from the radial and medial three-quarters of the hand by pharmacological blockade of the radial and median nerves, magnetic source imaging showed that the cortical representation of the little finger and the skin beneath the lower lip, whose intact cortical representation zones are adjacent to the deafferented region, had moved closer together, presumably because of their expansion across the deafferented area. A paired-pulse transcranial magnetic stimulation procedure revealed a motor cortex disinhibition for two muscles supplied by the unaffected ulnar nerve. In addition, two notable perceptual changes were observed: increased two-point discrimination ability near the lip and mislocalization of touch of the intact ulnar portion of the fourth finger to the neighbouring third finger whose nerve supply was blocked. We suggest that disinhibition within the somatosensory system as a functional correlate for the known enlargement of cortical representation zones might account for not only the ,invasion' phenomenon, but also for the observed behavioural correlates of the nerve block. [source]

Optimal allocation of distributed generation and reactive sources considering tap positions of voltage regulators as control variables

EUROPEAN TRANSACTIONS ON ELECTRICAL POWER, Issue 3 2007
Mohamad Esmail Hamedani Golshan
Abstract In this paper, by defining and solving an optimization problem, amount of distributed generators (DGs) and reactive power sources (RSs) in selected buses of a distribution system are computed to make up a given total of distributed generation for minimizing losses, line loadings, and total required reactive power capacity. The formulated problem is a combinatorial problem, therefore Tabu search algorithm is applied for solving the optimization problem. Results of solving the optimization problem for a radial 33-bus distribution system and a meshed 6-bus system are presented. When using less amount of reactive capacity, regarding tap positions of voltage regulators as control variables has considerable role in loss reduction and improvement of voltage profile. In the case of meshed systems, including line loadings in the cost function can significantly change results of solving the optimization problem such as amount of the required reactive capacity and how to assign DGs and RSs to the selected buses. Copyright © 2006 John Wiley & Sons, Ltd. [source]

Time to ignition, heat release rate and fire endurance time of wood in cone calorimeter test

FIRE AND MATERIALS, Issue 4 2001
Toshiro HaradaArticle first published online: 15 MAR 200
The combustibility of wood specimens was tested by cone calorimeter. A total of nine wood species (four softwood and five hardwood) were used. The thicknesses of the specimens were 10, 20 and 40 mm. The heated surfaces were radial, tangential, and cross-sections of wood. The irradiance levels were 20, 25, 30, 40 and 50 kWm,2. The effects of wood species, density, specimen thickness, heated surface (radial, tangential or cross-section), and irradiance level on time to ignition, mass loss rate, heat release rate and fire endurance time were studied. Simple formulae were proposed to forecast those indices and their validity was examined. Copyright © 2002 John Wiley & Sons, Ltd. [source]

The impact of Sirococcus shoot blight on radial and height growth of Norway spruce (Picea abies) in young plantations

FOREST PATHOLOGY, Issue 3 2000
E. Halmschlager
Summary The impact of Sirococcus shoot blight on the radial and height growth of Norway spruce in a young plantation (approximately 20 years old) was investigated by examining the increment losses for four infection intensities (classes). The average diameter at breast height of trees in the lightly damaged class was 72% when compared with the average diameter of the healthy trees, whereas moderately and severely damaged tree classes were 67 and 57%, respectively. Using tree ring analysis, the development of radial growth over time due to intensity of infection was studied. Height growth of affected trees was also significantly reduced (up to 43%) compared with the healthy trees, thus indicating a dramatic impact of Sirococcus conigenus on the growth of young Norway spruce. [source]

Parablastoid holdfasts from the Lower Ordovician of South Wales

GEOLOGICAL JOURNAL, Issue 3 2005
John C. W. Cope
Abstract Problematical discoid fossils from the Lower Arenig (Moridunian Stage) of the Llangynog Inlier, South Wales, are interpreted as parablastoid holdfasts. They constitute the first record of holdfasts in this rare echinoderm class. The lower surface has a radial ribbed structure, in contrast to the concentric, reticulate structure of the upper surface. The substrate for attachment was not lithified and may instead have been sediment stabilized by microbial mats. An associated pluricolumnal indicates that the parablastoid column was homeomorphic. Copyright © 2005 John Wiley & Sons, Ltd. [source]

Surface deformation due to loading of a layered elastic half-space: a rapid numerical kernel based on a circular loading element

GEOPHYSICAL JOURNAL INTERNATIONAL, Issue 1 2007
E. Pan
SUMMARY This study is motivated by a desire to develop a fast numerical algorithm for computing the surface deformation field induced by surface pressure loading on a layered, isotropic, elastic half-space. The approach that we pursue here is based on a circular loading element. That is, an arbitrary surface pressure field applied within a finite surface domain will be represented by a large number of circular loading elements, all with the same radius, in which the applied downwards pressure (normal stress) is piecewise uniform: that is, the load within each individual circle is laterally uniform. The key practical requirement associated with this approach is that we need to be able to solve for the displacement field due to a single circular load, at very large numbers of points (or ,stations'), at very low computational cost. This elemental problem is axisymmetric, and so the displacement vector field consists of radial and vertical components both of which are functions only of the radial coordinate r. We achieve high computational speeds using a novel two-stage approach that we call the sparse evaluation and massive interpolation (SEMI) method. First, we use a high accuracy but computationally expensive method to compute the displacement vectors at a limited number of r values (called control points or knots), and then we use a variety of fast interpolation methods to determine the displacements at much larger numbers of intervening points. The accurate solutions achieved at the control points are framed in terms of cylindrical vector functions, Hankel transforms and propagator matrices. Adaptive Gauss quadrature is used to handle the oscillatory nature of the integrands in an optimal manner. To extend these exact solutions via interpolation we divide the r -axis into three zones, and employ a different interpolation algorithm in each zone. The magnitude of the errors associated with the interpolation is controlled by the number, M, of control points. For M= 54, the maximum RMS relative error associated with the SEMI method is less than 0.2 per cent, and it is possible to evaluate the displacement field at 100 000 stations about 1200 times faster than if the direct (exact) solution was evaluated at each station; for M= 99 which corresponds to a maximum RMS relative error less than 0.03 per cent, the SEMI method is about 700 times faster than the direct solution. [source]

A preliminary study of crustal structure in Taiwan region using receiver function analysis

GEOPHYSICAL JOURNAL INTERNATIONAL, Issue 1 2004
Kwang-Hee Kim
SUMMARY Selected teleseismic data observed at temporary and permanent broad-band stations have been analysed using the receiver function method in order to investigate the very complex crustal structure in Taiwan region. Very significant azimuthal variations of radial and transverse receiver function responses from broad-band stations could be attributed to, among other things, the sampling of incoming seismic waves across the nearby subduction zone, a subsurface dipping interface, or a localized anisotropic region. A mid-crust discontinuity, interpreted as the Conrad discontinuity, can be identified at 18,20 km depth beneath TATO and TPUB stations in the Western Foothills, but is absent beneath the two nearby stations SSLB and TDCB in the Central Mountain Range. The separation of upper and lower crust beneath the Western Foothills and the steady increase in crustal velocity as a function of depth across the entire thicker crust beneath the Central Mountain Range suggest that the tectonic evolution of the crust may be significantly different for these two adjacent regions. Although a ,thin-skinned' model may be associated with the tectonic evolution of the upper crust of the Western Foothills and Western Coastal Plain, a ,thick-skinned' or ,lithospheric deformation' model can probably be applied to explain the crustal evolution of the Central Mountain Range. A trend of crustal thinning from east (50,52 km) to west (28,32 km) is in very good agreement with the results from two east,west-trending deep seismic profiles obtained using airgun sources. The thinner crust (20,30 km) beneath TWB1 station in northeastern Taiwan can be associated with the high-heat-flow backarc opening at the western terminus of the Okinawa trough behind the subduction of the Philippine Sea plate. The relatively simple crustal structure beneath KMNB station, offshore southeastern China, depicts typical continental crust, with the Moho depth at 28,32 km. An apparent offset of the thickest Moho beneath NACB station from the topographic high in the central Central Mountain Range suggests that the Taiwan orogeny has probably not reached its isostatic status. [source]

The lowermost mantle beneath northern Asia,II.

GEOPHYSICAL JOURNAL INTERNATIONAL, Issue 1 2002
Evidence for lower-mantle anisotropy
Summary We have analysed prediffracted S -waves with turning points beneath northern Siberia in a study of anisotropy in the lowermost mantle. Deep-focus earthquakes beneath the Marianas, Izu Bonin and the Sea of Japan recorded at stations in western Europe are used. A correction for upper-mantle anisotropy is applied to the data. Comparisons of the data with synthetic data for models with and without a high velocity D, layer suggest that there is a velocity discontinuity at the top of the D, region and that the style of anisotropy is transversely isotropic in this region. Time separations between S -waves on the radial and transverse component show a weak trend where the separation increases with epicentral distance. A normalization of this separation with the travel distance within D, (300 km thick in this region) suggests that the anisotropy is uniformly distributed within this layer and has an average value of 0.5 per cent. A combination of different studies which investigate the structure of the lowermost mantle beneath Europe and northern Siberia reveals a complicated picture. Tomographic models from this area and evidence of D, anisotropy, lower mantle scatterers, reflections from a D, discontinuity and ultra-low-velocity zones suggest two distinct regions. One exhibits high velocities, D, anisotropy, a D, discontinuity and no evidence of scatterers or ultra-low-velocity zones. These features are likely associated with the palaeosubduction of the Izanagi plate well into the lowermost mantle. The other region has a lower overall velocity and shows evidence of scatterers and ultra-low-velocity zones, perhaps suggesting the presence of partial melt. These results suggest dramatic lateral variations in the nature of the lowermost mantle beneath northern Asia over a length scale of roughly 30 degrees. [source]

A Maslov-propagator seismogram for weakly anisotropic media

GEOPHYSICAL JOURNAL INTERNATIONAL, Issue 1 2002
Georg Rümpker
Summary We introduce a formalism to calculate shear-wave seismograms for weakly-anisotropic and inhomogeneous media. The method is based on the combination of the forward-propagator method, which accounts for shear-wave interaction along a single reference ray, and the Maslov ray-summation, which incorporates amplitude and phase information from neighbouring rays to account for waveform and diffraction effects at caustics and in shadow regions. The approach is based on the assumption that the multiply split shear waves, on the way to a given receiver, travel along a common ray path that can by obtained from ray tracing in an isotropic reference medium (i.e. the common-ray approximation). The forward propagator and the Maslov amplitude are expressed with respect to radial and transverse coordinates (perpendicular to the ray propagation direction) that are defined uniquely by the initial conditions. Local polarizations and slownesses of the fast and slow shear-waves in the direction of propagation are obtained from the eikonal equation. The Maslov-propagator phase is given by the average shear-wave traveltime along the reference ray. Phase advances and delays of individual shear wave components are accounted for by the propagator. The geometrical-spreading information required for the Maslov integration is supplied by dynamic ray tracing in the isotropic reference medium. In the high-frequency limit effective phase functions are defined to assess the validity of the Maslov propagator phase information. For a homogeneous isotropic reference medium, we find good agreement with exact Maslov phase functions for anisotropic perturbations of up to 20 per cent. As a numerical application we consider effects of inhomogeneous anisotropy in a shear-wave cross-hole survey. The variations of the transversely-isotropic medium require 2-D slowness integrals. The method can handle discontinuities of the fast polarization along the ray path and also for neighbouring rays which is important for the slowness integration. Smooth transitions between isotropic and anisotropic regions along the ray path can be accounted for without the need to switch between numerical formulations. [source]

Enhancement of heat transfer in hydrogen storage tank with hydrogen absorbing alloy (optimum fin layout)

HEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 3 2008
Yuichi Mitsutake
Abstract Optimization of the fin layout in a metal hydride (MH) bed has been sought to enhance poor heat transmission in a hydrogen storage tank, and to obtain a maximum hydrogen absorption rate with a smaller volume of fins. Two different fin configurations, radial and circular fins, in a vertical cylindrical reactor vessel were tested with a La-Ni-based AB5 type hydrogen storage alloy. A two-dimensional transient heat conduction analysis, coupled with predicted temperature and concentration of absorbed hydrogen in the bed for the exothermic hydride reaction, was used to evaluate enhancement of the hydrogen absorption time. The estimated temperature and concentration agreed within 6 K and 8.5%, respectively, with our experimental results. The effect of thickness and the spacing and shape of fins on the hydrogen absorption time were analytically evaluated, so that the optimum range of the each fin layout was obtained by the trade off between absorption time and reduction in the MH volume due to the volume occupied by fins. The hydrogen absorption time for the recommended layout of circular fins was reduced to approximately one-third of that without fins. © 2008 Wiley Periodicals, Inc. Heat Trans Asian Res, 37(3): 165,183, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.20195 [source]

Nonuniform Nanowire Doping Profiles Revealed by Quantitative Scanning Photocurrent Microscopy

ADVANCED MATERIALS, Issue 30 2009
Jonathan E. Allen
Scanning photocurrent microscopy (SPCM) is used in semiconductor nanowire devices to establish quantitative potential profiles correlated with nonuniformities in electrical resistivity. Surface doping leads to a nonuniform axial photocurrent (a). Surface etching improves the uniformity of the local photocurrent (b) and reduces the radial and axial carrier concentration gradients (c, blue curve after etching). [source]

Influence of liquid bridges on the mechanical behaviour of polydisperse granular materials

INTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 3 2006
F. Soulié
Abstract We investigate a polydisperse granular material in which the particle interactions are governed by a capillary force law. The cohesion force for a grain-pair with unequal diameters is expressed as an explicit function of the inter-particle distance and the volume of the liquid bridge. This analytical relation is validated by experiments on a reference material. Then, it is completed by a rupture criterion and cast in the form of a force law that accounts for solid contact, capillary force and rupture characteristics of a grain-pair. Finally, in order to evaluate the influence of capillary cohesion on the macroscopic behaviour, radial and axial compression tests on cylindrical assemblies of wet particles are simulated using a 3D distinct element method. Copyright © 2005 John Wiley & Sons, Ltd. [source]

Coupling of mapped wave infinite elements and plane wave basis finite elements for the Helmholtz equation in exterior domains

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING, Issue 10 2003
Rie Sugimoto
Abstract The theory for coupling of mapped wave infinite elements and special wave finite elements for the solution of the Helmholtz equation in unbounded domains is presented. Mapped wave infinite elements can be applied to boundaries of arbitrary shape for exterior wave problems without truncation of the domain. Special wave finite elements allow an element to contain many wavelengths rather than having many finite elements per wavelength like conventional finite elements. Both types of elements include trigonometric functions to describe wave behaviour in their shape functions. However the wave directions between nodes on the finite element/infinite element interface can be incompatible. This is because the directions are normally globally constant within a special finite element but are usually radial from the ,pole' within a mapped wave infinite element. Therefore forcing the waves associated with nodes on the interface to be strictly radial is necessary to eliminate this internode incompatibility. The coupling of these elements was tested for a Hankel source problem and plane wave scattering by a cylinder and good accuracy was achieved. This paper deals with unconjugated infinite elements and is restricted to two-dimensional problems. Copyright © 2003 John Wiley & Sons, Ltd. [source]

Free vibration analysis of arches using curved beam elements

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 13 2003
Jong-Shyong Wu
Abstract The natural frequencies and mode shapes for the radial (in-plane) bending vibrations of the uniform circular arches were investigated by means of the finite arch (curved beam) elements. Instead of the complicated explicit shape functions of the arch element given by the existing literature, the simple implicit shape functions associated with the tangential, radial (or normal) and rotational displacements of the arch element were derived and presented in matrix form. Based on the relationship between the nodal forces and the nodal displacements of a two-node six-degree-of-freedom arch element, the elemental stiffness matrix was derived, and based on the equation of kinetic energy and the implicit shape functions of an arch element the elemental consistent mass matrix with rotary inertia effect considered was obtained. Assembly of the foregoing elemental property matrices yields the overall stiffness and mass matrices of the complete curved beam. The standard techniques were used to determine the natural frequencies and mode shapes for the curved beam with various boundary conditions and subtended angles. In addition to the typical circular arches with constant curvatures, a hybrid beam constructed by using an arch segment connected with a straight beam segment at each of its two ends was also studied. For simplicity, a lumped mass model for the arch element was also presented. All numerical results were compared with the existing literature or those obtained from the finite element method based on the conventional straight beam element and good agreements were achieved. Copyright © 2003 John Wiley & Sons, Ltd. [source]

Potential flow around obstacles using the scaled boundary finite-element method

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 7 2003
Andrew J. Deeks
Abstract The scaled boundary finite-element method is a novel semi-analytical technique, combining the advantages of the finite element and the boundary element methods with unique properties of its own. The method works by weakening the governing differential equations in one co-ordinate direction through the introduction of shape functions, then solving the weakened equations analytically in the other (radial) co-ordinate direction. These co-ordinate directions are defined by the geometry of the domain and a scaling centre. The method can be employed for both bounded and unbounded domains. This paper applies the method to problems of potential flow around streamlined and bluff obstacles in an infinite domain. The method is derived using a weighted residual approach and extended to include the necessary velocity boundary conditions at infinity. The ability of the method to model unbounded problems is demonstrated, together with its ability to model singular points in the near field in the case of bluff obstacles. Flow fields around circular and square cylinders are computed, graphically illustrating the accuracy of the technique, and two further practical examples are also presented. Comparisons are made with boundary element and finite difference solutions. Copyright © 2003 John Wiley & Sons, Ltd. [source]

Evolution of histoid leprosy (de novo) in lepromatous (multibacillary) leprosy

INTERNATIONAL JOURNAL OF DERMATOLOGY, Issue 7 2005
Virendra N. Sehgal MD
A 26-year-old man presented with persistent redness of the face over the past 2 years and thickening of the ears for a year. The current state was preceded by three to four episodes of epistaxis, 2,3 months previously. The patient had not received any treatment. Cutaneous examination revealed indurated (infiltrated) plaques on the face and ears over an apparently normal-looking skin, and numerous, small, ill-defined, slightly hypopigmented, shiny macules all over the body. They were bilateral and symmetric (Fig. 1a,b). There was no variation in the cutaneous sensations of temperature, touch, and pain. The patient showed loss of the lateral eyebrows and conjunctival congestion. Examination of the nerves revealed enlargement of the ulnar, radial, posterior tibial, and right common peroneal nerves; however, there was no tenderness of the nerves. Systemic examination was within normal limits. Examination of a slit-skin smear (under oil immersion), prepared from a representative lesion (plaque), demonstrated an abundance of solid and uniform-staining acid-fast bacilli, occurring either singly or in parallel clumps/globii, in an average field (6+). Furthermore, a scraping mount (10% KOH) prepared from the lesion on the back was negative. Figure 1. (a, b) Histoid leprosy Hematoxylin and eosin-stained sections prepared from a biopsy taken from a plaque revealed a conspicuous granuloma composed of peculiar spindle-shaped histiocytes. Several of the granulomas were present in the mid and lower dermis. They were characterized by whorled, criss-cross, or parallel patterns. Solid and uniform-staining, slender, rod-like (length three times that of the breadth) acid-fast bacilli were found scattered throughout the section. A few histiocytes closely packed with acid-fast bacilli, together with lymphocytic infiltrates, were also seen. There was a prominent eosinophilic stained clear zone just below the epidermis. It was free from acid-fast bacilli as well as the inflammatory infiltrate (Fig. 2a,b). A definitive diagnosis of untreated lepromatous leprosy (LL) changing to histoid leprosy (de novo) was made. Figure 2. (a, b) Histoid leprosy depicting granuloma formed by histiocytes displaying whorl-wind, criss-cross or interlacing pattern, and a clear zone beneath the epidermis (H&E ×40) Solid and uniform staining acid fast bacilli, , slender, rod-like, length 3 times that of breadth found scattered throughout the granuloma (H&E ×100) [source]

Renewed focus on the developing human neocortex

JOURNAL OF ANATOMY, Issue 4 2010
Gavin Clowry
Abstract Many specifically human psychiatric and neurological conditions have developmental origins. Rodent models are extremely valuable for the investigation of brain development, but cannot provide insight into aspects that are specifically human. The human brain, and particularly the cerebral cortex, has some unique genetic, molecular, cellular and anatomical features, and these need to be further explored. Cortical expansion in human is not just quantitative; there are some novel types of neurons and cytoarchitectonic areas identified by their gene expression, connectivity and functions that do not exist in rodents. Recent research into human brain development has revealed more elaborated neurogenetic compartments, radial and tangential migration, transient cell layers in the subplate, and a greater diversity of early-generated neurons, including predecessor neurons. Recently there has been a renaissance of the study of human brain development because of these unique differences, made possible by the availability of new techniques. This review gives a flavour of the recent studies stemming from this renewed focus on the developing human brain. [source]