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High Velocity (high + velocity)
Selected AbstractsThree-dimensional seismic structure beneath the Australasian region from refracted wave observationsGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 3 2000Y. Kaiho The earthquakes in the seismicity belt extending through Indonesia, New Guinea, Vanuatu and Fiji to the Tonga,Kermadec subduction zone recorded at the 65 portable broad-band stations deployed during the Skippy experiment from 1993,1996 provide good coverage of the lithosphere and mantle under the Australian continent, Coral Sea and Tasman Sea. The variation in structure in the upper part of the mantle is characterized by deter-mining a suite of 1-D structures from stacked record sections utilizing clear P and S arrivals, prepared for all propagation paths lying within a 10° azimuth band. The azimuth of these bands is rotated by 20° steps with four parallel corridors for each azimuth. This gives 26 separate azimuthal corridors for which 15 independent 1-D seismic velocity structures have been derived, which show significant variation in P and S structure. The set of 1-D structures is combined to produce a 3-D representation by projecting the velocity values along the ray path using a turning point approximation and stacking into 3-D cells (5° by 50 km in depth). Even though this procedure will tend to underestimate wave-speed perturbations, S -velocity deviations from the ak135 reference model exceed 6 per cent in the lithosphere. In the uppermost mantle the results display complex features and very high S -wave speeds beneath the Precambrian shields with a significant low-velocity zone beneath. High velocities are also found towards the base of the transition zone, with highS -wave speeds beneath the continent and high P -wave speeds beneath the ocean. The wave-speed patterns agree well with independent surface wave studies and delay time tomography studies in the zones of common coverage. [source] Opiate-induced oesophageal dysmotilityALIMENTARY PHARMACOLOGY & THERAPEUTICS, Issue 5 2010R. E. KRAICHELY Aliment Pharmacol Ther,31, 601,606 Summary Background, Opiates have well characterized (troublesome) untoward effects on the gastrointestinal tract. Opioid bowel dysfunction has been a subject of research and even drug design, but surprisingly little is known with regard to clinical effects of opiates on the oesophagus. Aim, To characterize opiate effects on motor function of the oesophagus in patients presenting with dysphagia. Methods, Retrospective review of 15 patients with dysphagia referred for oesophageal manometry while on chronic opiates. Manometry was completed during opiate use and in three cases, after opiates were discontinued. Results, All patients demonstrated motility abnormalities. Incomplete lower oesophageal sphincter (LOS) relaxation (11.5 ± 1.6 mmHg) was seen in most cases. Ten patients demonstrated nonperistaltic contractions in ,3 of 10 swallows. Additional abnormalities included high amplitude contractions; triple peaked contractions; and increased velocity. The average resting lower oesophageal sphincter (LOSP) met criteria for hypertensive LOS in three patients. These features were suggestive of spasm or achalasia. Repeat manometry off opiates was performed in three cases. LOS relaxation was noted to be complete upon repeat manometry in these cases. There was also improved peristalsis and normal velocity. Conclusions, A range of manometric abnormalities were seen in patients with dysphagia in the setting of opiate use: impaired LOS relaxation, high amplitude/velocity and simultaneous oesophageal waves. These data suggest that the oesophagus is susceptible to the effects of opiates and care must be taken before ascribing dysphagia to a primary oesophageal motility disorder in patients taking opiates. [source] The lowermost mantle beneath northern Asia,II.GEOPHYSICAL JOURNAL INTERNATIONAL, Issue 1 2002Evidence 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] Internal structure of an alpine rock glacier based on crosshole georadar traveltimes and amplitudesGEOPHYSICAL PROSPECTING, Issue 3 2006Martin Musil ABSTRACT Rapid melting of permafrost in many alpine areas has increased the probability of catastrophic rock slides. In an attempt to provide critical structural information needed for the design and implementation of suitable mitigation procedures, we have acquired low frequency (22 MHz) cross-hole radar data from within a fast-moving rock glacier, an important form of alpine permafrost. Since the ice, rock and pockets of water and air found in the underground of high alpine areas have very different dielectric permittivities and electrical conductivities, the radar method was well-suited for investigating the structure and state of the rock glacier. Our interpretation of the radar velocities and attenuations was constrained by geomorphological observations, borehole lithological logs and the results of a surface seismic survey. The radar data revealed the existence of a discontinuous 7,11 m thick ice-rich zone distinguished by high velocities (0.14,0.17 m/ns) and low attenuations (0.04,0.09 m,1) and a thin underlying ice-free zone characterized by moderate velocities (0.11,0.12 m/ns) and low attenuations (0.04,0.09 m,1). Beneath these two zones, we observed a prominent band of high velocities (0.14,0.17 m/ns) and moderately high attenuations (0.10,0.20 m,1) associated with unconsolidated glacial sediments and numerous large air-filled voids, which in the past were probably filled with ice. At greater depths, the variably dry to water-saturated sediments were represented by generally lower velocities (0.08,0.10 m/ns) and higher attenuations (0.16,0.24 m,1). The bedrock surface was represented by an abrupt ,0.03 m/ns velocity increase. We speculate that the disappearance of ice, both laterally and with depth, occurred during the past one to two decades. [source] Indentation of a free-falling lance penetrometer into a poroelastic seabedINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 2 2005Derek Elsworth Abstract A solution is developed for the build-up, steady and post-arrest dissipative pore fluid pressure fields that develop around a blunt penetrometer that self-embeds from freefall into the seabed. Arrest from freefall considers deceleration under undrained conditions in a purely cohesive soil, with constant shear strength with depth. The resulting decelerating velocity field is controlled by soil strength, geometric bearing capacity factors, and inertial components. At low impact velocities the embedment process is controlled by soil strength, and at high velocities by inertia. With the deceleration defined, a solution is evaluated for a point normal dislocation penetrating in a poroelastic medium with a prescribed decelerating velocity. Dynamic steady pressures, PD, develop relative to the penetrating tip geometry with their distribution conditioned by the non-dimensional penetration rate, UD, incorporating impacting penetration rate, consolidation coefficient and penetrometer radius, and the non-dimensional strength, ND, additionally incorporating undrained shear strength of the sediment. Pore pressures develop to a steady peak magnitude at the penetrometer tip, and drop as PD=1/xD with distance xD behind the tip and along the shaft. Peak induced pressure magnitudes may be correlated with sediment permeabilities, post-arrest dissipation rates may be correlated with consolidation coefficients, and depths of penetration may be correlated with shear strengths. Together, these records enable strength and transport parameters to be recovered from lance penetrometer data. Penetrometer data recorded off La Palma in the Canary Islands (J. Volcanol. Geotherm. Res. 2000; 101:253) are used to recover permeabilities and consolidation coefficients from peak pressure and dissipation response, respectively. Copyright © 2004 John Wiley & Sons, Ltd. [source] Single Particle Detection and Size Analysis with Statistical Methods from Particle Imaging DataPARTICLE & PARTICLE SYSTEMS CHARACTERIZATION, Issue 2 2006Benno Wessely Abstract The application of imaging techniques for particle characterization in the micrometer range is often advantageous under process conditions. Particle imaging analysis of disperse systems not only allows the evaluation of the particle size, but also the concentration of particles and particle shape. Under process conditions online imaging techniques have to deal with high particle concentrations and sometimes with high velocities. Two general principles for the evaluation of particle images are discussed in this paper: particle analysis by means of object identification and a statistical method to analyze overlapping clusters of particles. [source] Excitation of millimeter-wave oscillations in InAlAs/InGaAs heterostructuresPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 1 2008S. Pérez Abstract We study the origin of strong Terahertz (THz) oscillations taking place in InAlAs/InGaAs slot diodes - base of High Electron Mobility Transistor (HEMT) devices - when bias surpasses 0.5 V. To this end we perform a microscopic analysis of current fluctuations, calculated by means of an ensemble Monte Carlo (MC) simulator. The millimeter and submillimeter waves are caused by the presence of Gunn-like oscillations whose dynamics is controlled by ballistic , valley electrons in the channel. These carriers are capable to reach extremely high velocities due to the influence of degeneracy effects (preventing scattering mechanisms) and the presence of a recessed geometry. The dependence of this process on the recess and recess-drain lengths is analyzed in order to improve the frequency and magnitude of the oscillations. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Characterization of the Vestibulo-Ocular Reflex Evoked by High-Velocity MovementsTHE LARYNGOSCOPE, Issue 7 2004François D. Roy HBSc Abstract Objectives/Hypothesis: The horizontal angular vestibulo-ocular reflex (VOR) plays an important role in stabilizing images on the retina throughout head rotations. Current evidence suggests that the VOR behaves linearly at low velocities and nonlinearly at high velocities. The aim of the research was to evaluate and characterize the normal behavior of the reflex evoked by high-velocity head rotations. Study Design: Case control study. Methods: Manually applied head-thrust movements with peak velocities in the range of 100° to 500°/s and peak accelerations up to 7,000°/s 2 were performed on normal volunteers. These head thrusts were comparable with those described in detail by Halmagi and coworkers. Eye and head movements were recorded using the magnetic search coil method. Results: The gain of the VOR is linear at low velocities and saturates at head velocities greater than 350°/s. The values for the normal gain of the reflex were approximated by means of the area between two nonlinear functions. The directional difference parameter, exploring the symmetry of the reflex, indicated that the VOR in normal subjects is symmetric. Conclusion: The gain of the VOR in individuals with intact vestibular function is nonlinear at high angular head velocities. We propose a quantitative means using two nonlinear functions to characterize the normal range of values for the gain of the VOR in individuals with normal vestibular function. A directional difference parameter used in conjunction with the normal range of gains can detect small differences in the symmetry of the VOR and, consequently, reveal unilateral vestibular loss. [source] Combined seismic tomographic and ultrashallow seismic reflection study of an Early Dynastic mastaba, Saqqara, EgyptARCHAEOLOGICAL PROSPECTION, Issue 4 2005Mohamed Metwaly Abstract Mastabas were large rectangular structures built for the funerals and burials of the earliest Pharaohs. One such mastaba was the basic building block that led to the first known stone pyramid, the,>4600-year old Step Pyramid within the Saqqara necropolis of Egypt. We have tested a number of shallow geophysical techniques for investigating in a non-invasive manner the subsurface beneath a large Early Dynastic mastaba located close to the Step Pyramid. After discovering that near-surface sedimentary rocks with unusually high electrical conductivities precluded the use of the ground-penetrating radar method, a very high-resolution seismic data set was collected along a profile that extended the 42.5,m length of the mastaba. A sledgehammer source was used every 0.2,m and the data were recorded using a 48-channel array of single geophones spaced at 0.2,m intervals. Inversions of the direct- and refracted-wave travel times provided P-wave velocity tomograms of the shallow subsurface, whereas relatively standard processing techniques yielded a high-fold (50,80) ultrashallow seismic reflection section. The tomographic and reflection images were jointly interpreted in terms of loose sand and friable limestone layers with low P-wave velocities of 150,650,m,s,1 overlying consolidated limestone and shale with velocities,>,1500,m,s,1. The sharp contact between the low- and high-velocity regimes was approximately horizontal at a depth of ca. 2,m. This contact was the source of a strong seismic reflection. Above this contact, the velocity tomogram revealed moderately high velocities at the surface location of a friable limestone outcrop and two low-velocity blocks that probably outlined sand-filled shafts. Below the contact, three regularly spaced low velocity blocks probably represented tunnels and/or subsurface chambers. Copyright © 2005 John Wiley & Sons, Ltd. [source] Kinematics and metallicity analysis for nearby F, G and K starsASTRONOMISCHE NACHRICHTEN, Issue 1 2009S. Vidojevi Abstract A sample containing 1 026 stars of spectral types F, G, and K, mainly dwarfs, from the solar neighbourhood with available space velocities and metallicities is treated. The treatment comprises a statistical analysis of the metallicity and velocity data and calculation of galactocentric orbits. Sample stars identified as members of the galactic halo are detached from the rest of the sample based on the values of their metallicities, velocity components and galactocentric orbits. In identifying halo stars a new, kinematical, criterion is proposed. Except one, these halo stars are the metal-poorest ones in the sample. Besides, they have very high velocities with respect to LSR. On the other hand, the separation between the thin disc and thick one is done statistically based on LSR space velocities, membership probability (Schwarzschild distribution with assumed parameters) and galactocentric orbits. In the metallicity these two groups are not much different. For each of the three subsamples the mean motion and velocity ellipsoid are calculated. The elements of the velocity ellipsoids agree well with the values found in the literature, especially for the thin disc. The fractions of the subsystems found for the present sample are: thin disc 93%, thick disc 6%, halo 1%. The sample stars established to be members of the thin disc are examined for existence of star streams. Traces of both, known and unknown, star streams are not found (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] SiO Maser Sources within 30 pc of the Galactic CenterASTRONOMISCHE NACHRICHTEN, Issue S1 2003Shuji Deguchi Abstract Using the Nobeyama 45-m radio telescope, we have observed 314 large amplitude variables within 30 pc of the Galactic center in SiO maser lines. Resulting detections give the radial velocities of 174 stars; light-variation periods have been known for all of these stars. The SiO detection rate increases sharply with the period and it is about twice of the OH maser detection rate. The radial-velocity data show slow and rapid rotations of the outer and inner circumnuclear-disk stars, respectively. Five high-velocity stars were found only at the negative-longitude side of the Galactic center. Estimation of the ages of high velocity stars suggests that these stars must be be accelerated to high velocities within 108 years. [source] Dental squash injuries , a survey among players and coaches in Switzerland, Germany and FranceDENTAL TRAUMATOLOGY, Issue 5 2006Robert Persic Abstract,,, Squash belongs to sporting activities with medium risk of causing dental trauma. Because of high velocity, close body contact and the use of rackets the injury potential in squash has increased. The aim of this work was to conduct a comparative study between Switzerland, Germany and France on a number of issues: the frequency of dental and facial injuries in squash, athletes' habits of wearing mouthguards, as well as the general level of information about emergency measures after a dental trauma and the resulting consequences. Using a standardized questionnaire a total of 653 individuals, 600 squash players and their 53 coaches, were interviewed. In each of the three countries 200 players belonging to four different divisions (juniors, amateurs, semi-professionals and professionals) were surveyed. Of these 653 interviewees 133 (20.4%) have already observed a dental injury; 27 (4.5%) have experienced a dental trauma themselves. Less than half of all interviewed players and coaches (47.6%) were aware of the possibility of replanting avulsed teeth. Just 5.1% were familiar with the tooth rescue kit. Only one individual wore a mouthguard. The results show that the area of squash requires more information about prevention through sports associations, coaches and dentists. [source] An attenuation model for distant earthquakesEARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 2 2004Adrian Chandler Abstract Large magnitude earthquakes generated at source,site distances exceeding 100km are typified by low-frequency (long-period) seismic waves. Such induced ground shaking can be disproportionately destructive due to its high displacement, and possibly high velocity, shaking characteristics. Distant earthquakes represent a potentially significant safety hazard in certain low and moderate seismic regions where seismic activity is governed by major distant sources as opposed to nearby (regional) background sources. Examples are parts of the Indian sub-continent, Eastern China and Indo-China. The majority of ground motion attenuation relationships currently available for applications in active seismic regions may not be suitable for handling long-distance attenuation, since the significance of distant earthquakes is mainly confined to certain low to moderate seismicity regions. Thus, the effects of distant earthquakes are often not accurately represented by conventional empirical models which were typically developed from curve-fitting earthquake strong-motion data from active seismic regions. Numerous well-known existing attenuation relationships are evaluated in this paper, to highlight their limitations in long-distance applications. In contrast, basic seismological parameters such as the Quality factor (Q -factor) could provide a far more accurate representation for the distant attenuation behaviour of a region, but such information is seldom used by engineers in any direct manner. The aim of this paper is to develop a set of relationships that provide a convenient link between the seismological Q -factor (amongst other factors) and response spectrum attenuation. The use of Q as an input parameter to the proposed model enables valuable local seismological information to be incorporated directly into response spectrum predictions. The application of this new modelling approach is demonstrated by examples based on the Chi-Chi earthquake (Taiwan and South China), Gujarat earthquake (Northwest India), Nisqually earthquake (region surrounding Seattle) and Sumatran-fault earthquake (recorded in Singapore). Field recordings have been obtained from these events for comparison with the proposed model. The accuracy of the stochastic simulations and the regression analysis have been confirmed by comparisons between the model calculations and the actual field observations. It is emphasized that obtaining representative estimates for Q for input into the model is equally important.Thus, this paper forms part of the long-term objective of the authors to develop more effective communications across the engineering and seismological disciplines. Copyright © 2003 John Wiley & Sons, Ltd. [source] Geophysical investigation and dynamic modelling of unstable slopes: case-study of Kainama (Kyrgyzstan)GEOPHYSICAL JOURNAL INTERNATIONAL, Issue 1 2008G. Danneels SUMMARY The presence of massive Quaternary loess units at the eastern border of the Fergana Basin (Kyrgyzstan, Central Asia) makes this area particularly prone to the development of catastrophic loess earthflows, causing damages and injuries almost every year. Efficient disaster management requires a good understanding of the main causes of these mass movements, that is, increased groundwater pressure and seismic shaking. This paper focuses on the Kainama earthflow, mainly composed of loess, which occurred in 2004 April. Its high velocity and the long run-out zone caused the destruction of 12 houses and the death of 33 people. In summer 2005, a field survey consisting of geophysical and seismological measurements was carried out along the adjacent slope. By combination and geostatistical analysis of these data, a reliable 3-D model of the geometry and properties of the subsurface layers, as shown in the first part of the paper, was created. The analysis of the seismological data allowed us to point out a correlation between the thickness of the loess cover and the measured resonance frequencies and associated amplification potential. The second part of this paper is focused on the study of the seismic response of the slope by numerical simulations, using a 2-D finite difference code named FLAC. Modelling of the seismic amplification potential along the slope confirmed the results obtained from the seismological survey,strong amplifications at the crest and bottom of the slope where there is a thick loess cover and almost no amplification in the middle part of the slope. Furthermore, dynamic slope stability analyses were conducted to assess the influence of local amplifications and increased groundwater pressures on the slope failure. The results of the dynamic modelling, although preliminary, show that a combination of seismic and hydrologic origin (pore pressure build-up during the seismic shaking) is the most probable scenario responsible for the 2004 failure. [source] Geographical history of the central-western Pacific black fly subgenus Inseliellum (Diptera: Simuliidae: Simulium) based on a reconstructed phylogeny of the species, hot-spot archipelagoes and hydrological considerationsJOURNAL OF BIOGEOGRAPHY, Issue 9 2001Douglas A. Craig Aim With six new species of subgenus Inseliellum Rubtsov recently described, a revised reconstructed phylogeny based on morphology is required. Geological history of islands where Inseliellum occurs, plus a cladistic analysis and hydrological considerations, provide the basis for a reconstructed geographical history of the species. Location Inseliellum is widely distributed and occurs in Micronesia, Cook Islands and Polynesia. A single specimen is known from Tonga Islands. Methods Maximum parsimony criteria using PAUP*, plus cytological information, were used to arrive at a preferred phylogenic reconstruction. Island ages of the hot spot archipelagoes involved are well known. The phylogeny was then compared with the palaeogeology. Information on evolution of running water habitats as islands age was incorporated into the biogeography. Results Cladistic analysis of forty of the forty-eight known Inseliellum species with Simulium (Nevermannia) neornatipes Dumbleton from New Caledonia and S. (Hebridosimulium) laciniatum Edwards from Fiji as outgroups, shows basal species and clades to be on widely separated older islands. In the Society Islands basal species are widely spread. Derived species, with morphological adaptations to deal with specialized habitats, are on younger islands (e.g. Tahiti), where a major species radiation has taken place. The reconstructed phylogeny indicates dispersal back to older islands, with minor subsequent species radiation. Main conclusions Palaeogeological evidence provides a basis for postulating that Inseliellum entered the western Pacific area some 20 Ma, with the possibility that it rafted eastwards on proto-Tonga Islands to the edge of southern-central Pacific. Older Cook Islands were present at that time. Movement into the Marquesas Islands was not earlier than 6 Ma and into the Society Islands perhaps 8,10 Ma. Basal species with generalized habitat requirements would have found suitable habitats (inferred from hydrological postulates) on leaves in the original, small shaded streams. With erosion and valley development, in particular on Tahiti, species radiated into specialized habitats such as cascades. Rich seston and high velocity probably drove reduction of filtering fans in some clades. With collapse of the caldera and formation of large rivers at c. 0.9 Ma, S. exasperans Craig and S. tahitiense Edwards adapted to deep, swiftly flowing water, all indicative that specialized habitat availability drove species radiation in Inseliellum. In the Society Islands, dispersal of derived species back to the oldest western islands was not possible because erosion has removed suitable habitats. [source] Investigation of impinging-jet crystallization with a calcium oxalate model systemAICHE JOURNAL, Issue 9 2003Jean M. Hacherl An impinging-jet crystallizer was investigated in this work to assess its operational sensitivity and reproducibility for the production of small, monodisperse crystals using calcium oxalate, a model system capable of forming multiple hydrates. The impinging-jet mixer provides rapid mixing of the reactant solutions through the impingement of two narrow reactant streams at high velocity. Impinging jet linear velocity and postjetting conditions were studied, with the jet operated in nonsubmerged mode. Hydrate form and crystal-size distribution (CSD) were determined using optical microscopy and image analysis techniques. The impinging jet consistently produced small, monodisperse crystals. However, at a high level of supersaturation, slight variations in the CSD were observed for apparently identical conditions, suggesting a degree of sensitivity in the system that could lead to difficulty in its application. An apparent trend between impinging-jet linear velocity and crystal size and number was observed, with more small crystals produced at higher linear velocity. [source] Transient fluidization and segregation of binary mixtures of particlesAICHE JOURNAL, Issue 11 2000A. Marzocchella Fluidization of binary mixtures of particles belonging to group B of the Geldart classification of powders was studied. Beds tested were prepared by mixing in different proportions particles with almost equal density (,2,500 kg/m3) and dissimilar size (125 ,m silica sand and 500 ,m glass beads). Experiments were carried out using a segmented fluidization column equipped with multiple pressure transducers. Experimental procedures included continuous monitoring of pressure drop at different locations along the bed during quasi-steady or stepwise changes of gas superficial velocity, and characterization of particle-size distributions in each segment of the fluidization column after fluidization of the bed for given times. Three ranges of gas superficial velocity were recognized for each solids mixture. At low velocity the bed behaves as a fixed bed. At high velocity, it is fully and steadily fluidized. In an intermediate velocity range, transient fluidization takes place: an initially uniform fluidized bed eventually undergoes segregation, giving rise to a defluidized bottom layer rich in the coarser solids and to a "supernatant" fluidized layer where finer particles prevail. The thresholds between these velocity ranges are rather sharp and were characterized as functions of initial bed composition. Rates at which the defluidized solids layer builds up from initially uniform beds, and the ultimate compositions of the defluidized bottom and fluidized top layers are characterized for beds with different compositions at variable gas superficial velocity. [source] Characterization of downflowing high velocity fluidized bedsAICHE JOURNAL, Issue 3 2000Chunshe Cao A downer-riser circulating high velocity fluidization apparatus was developed to study the fundamentals of downflowing gas-solid particle mixtures. The acceleration and deceleration of solids due to the influences of the entrance and exit sections result in a relatively uniform axial solids distribution. Radial solid density profiles detected with an X-ray imaging system in the downer show the existence of a core-annulus flow with a dilute core surrounded by a denser wall region. Local solids flux profiles were obtained with an aspirating probe device and the solid velocity profile obtained from the two measured quantities. These confirm that the majority of solids segregates in a wall region that flows faster than the dilute core region. Thus, the shorter residence time in the high-speed downer wall region is coupled with faster reaction rates due to the accompanying high concentration of catalyst, while the dilute core has slower reaction rates with longer residence time due to the lower catalyst concentration and flow velocity. This results in much more uniform reaction extent over the cross-sectional area of the downer and, therefore, should improve the product selectivity. [source] Gas dispersion in downflowing high velocity fluidized bedsAICHE JOURNAL, Issue 3 2000Chunshe Cao Measurements are presented of gas mixing in a downflowing high-velocity fluidized bed using helium tracer detected by an on-line analyzer. It was found that gas backmixing is very limited in the downer, and the lateral mixing is comparable with that in the riser. A dispersion model is applied to characterize the behavior of the gas mixing in the two-phase downflowing mixture. [source] Wet scrubbing intensification applied to hydrogen sulphide removal in waste water treatment plantTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 4 2010Pierre-François Biard Abstract Hydrogen sulphide removal in a waste water treatment plant at semi-industrial scale in a compact wet scrubber has been investigated. The gas residence time in the scrubber was reduced to 30,ms using a NaOCl caustic scrubbing solution. The contactor is composed of a wire mesh packing structure where liquid and gas flow co-currently at high velocity (>12,m,s,1). H2S removal percentages higher than 95% could be achieved whereas a moderate pressure drop was measured (<4000,Pa). Both the hydrodynamic and chemical conditions can influence the efficiency of the process. Correlations were developed to predict both the pressure drop and the H2S removal efficiency at given operating conditions. Le traitement du sulfure d'hydrogène dans un laveur de gaz compact a été étudié à l'échelle semi-industrielle en station d'épuration. Le temps de contact dans le laveur est réduit à une trentaine de ms en utilisant une solution d'hypochlorite de sodium à pH basique. Le contacteur se compose d'une structure tissée métallique dans laquelle le gaz et le liquide circulent à co-courant et grande vitesse (>12,m,s,1). Un abattement de l'H2S de plus de 95% peut être obtenu avec une perte de charge modérée (<4000,Pa). A la fois les conditions chimiques et hydrodynamiques influencent les performances de traitement. Des corrélations ont été développées pour prédire la perte de charge mais aussi l'abattement dans des conditions opératoires données. [source] The iron emission line complex of MCG-5-23-16: the long XMMNewton lookASTRONOMISCHE NACHRICHTEN, Issue 10 2006V. Braito Abstract We present the results of the simultaneous XMM- Newton and Chandra observations of the bright Seyfert 1.9 galaxy MCG,5-23-16, which is one of the best known examples of a relativistically broadened iron K, line. We find that: a) the soft X-ray emission is likely to be dominated by photoionized gas, b) the complex iron emission line is best modelled with a narrow and a broad component with a FWHM ,44000 km/s. This latter component has an EW ,50 eV and its profile is well described with an emission line mainly originating from the accretion disk a few tens of gravitational radii from the central black hole and viewed with an inclination angle ,40°. We found evidence of a possible sporadic absorption line at ,7.7 keV which, if associated with Fe XXVI K, resonance absorption, is indicative of a possible high velocity (v , 0.1c) outflow. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | ||||||||||||||||||||||