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Different Diameters (different + diameter)
Selected AbstractsStudy on effects of damping in laminated rubber bearings on seismic responses for a , scale isolated test structureEARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 10 2002Bong Yoo Abstract The effects of damping in various laminated rubber bearings (LRB) on the seismic response of a ,-scale isolated test structure are investigated by shaking table tests and seismic response analyses. A series of shaking table tests of the structure were performed for a fixed base design and for a base isolation design. Two different types of LRB were used: natural rubber bearings (NRB) and lead rubber bearings (LLRB). Three different designs for the LLRB were tested; each design had a different diameter of lead plug, and thus, different damping values. Artificial time histories of peak ground acceleration 0.4g were used in both the tests and the analyses. In both shaking table tests and analyses, as expected, the acceleration responses of the seismically isolated test structure were considerably reduced. However, the shear displacement at the isolators was increased. To reduce the shear displacement in the isolators, the diameter of the lead plug in the LLRB had to be enlarged to increase isolator damping by more than 24%. This caused the isolator stiffness to increase, and resulted in amplifying the floor acceleration response spectra of the isolated test structure in the higher frequency ranges with a monotonic reduction of isolator shear displacement. Copyright © 2002 John Wiley & Sons, Ltd. [source] Effect of placement of calcium sulphate when used for the repair of furcation perforations on the seal produced by a resin-based materialINTERNATIONAL ENDODONTIC JOURNAL, Issue 2 2007L. Zou Abstract Aim, To evaluate the sealing ability of calcium sulphate when used under composite resin for the repair of furcation perforations having different diameters. Methodology, Perforations of different diameter were created in the floors of pulp chambers in 60 extracted human molar teeth with either a number 3 (1 mm diameter) or 5 (1.5 mm diameter) round bur. The specimens of each group were divided into four sub-groups which were repaired with composite resin either alone or in combination with calcium sulphate that created an artificial floor (15 teeth group -1). Eight teeth without furcation perforations served as negative controls. In the leakage detection device, 1 mol L,1 glucose solution was forced under a pressure of 1.5 KPa from the crown towards the pulp chamber floor. The concentration of leaked glucose was measured at 1, 2, 4, 7, 10, 15 and 20 days using a glucose oxidase method and the data evaluated using the rank sum test. Results, The specimens with larger perforations repaired with composite resin alone had significantly more leakage (P < 0.05). Using calcium sulphate as an artificial floor significantly decreased leakage of smaller perforations (P < 0.05). In groups repaired with calcium sulphate under composite resin, leakage in smaller perforations was markedly lower than that in larger ones (P < 0.05). No significant difference was found between the specimens with 1 or 1.5 mm perforations repaired with resin alone (P > 0.05). Conclusions, Calcium sulphate significantly improved the sealing ability of 1 mm perforations repaired with composite resin but not for 1.5 mm perforations. [source] Impact fracture toughness and morphology of diatomite-filled polypropylene compositesPOLYMER ENGINEERING & SCIENCE, Issue 8 2009Jizhao Liang Impact fracture strength is an important characterization for impact toughness of materials. A polypropylene (PP) filled with diatomite with different diameter (5, 7, and 13 ,m) was fabricated by means a twin-screw extruder. The impact fracture strength of these composites was measured at room temperature to identify the effects of diatomite content and diameter on impact fracture strength of filled polypropylene composites. The results showed that the influence of diatomite on the notched impact strength was significant. When the volume fraction of the diatomite (,f) was less than 10%, the notched impact strength (,I) increased quickly with an addition of ,f, and then the variation of ,I was slight. The notched impact strength of the composite with the diatomite diameter of 7 ,m is the highest when ,f was 10%. Furthermore, the impact fracture surface was observed by using a scanning electronic microscope (SEM) to study the toughening mechanisms. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers [source] COMPARING BALLOON DIAMETER ON PERFORMING ENDOSCOPIC PAPILLARY BALLOON DILATATION WITH ISOSORBIDE DINITRATE DRIP INFUSION FOR REMOVAL OF BILE DUCT STONESDIGESTIVE ENDOSCOPY, Issue 4 2004Hiroshi Nakagawa Background:, Endoscopic papillary balloon dilatation (EPBD) is one of the methods to remove bile duct stones. EPBD might preserve the function of the sphincter of Oddi despite the potential risk of acute pancreatitis. There are only a few reports of EPBD reducing the risk of acute pancreatitis and, at same time, preserving the function of the sphincter of Oddi. Methods:, We performed EPBD for bile duct stone removal in 60 patients using two balloons with different diameters. Patients were randomized to EPBD with a 6 mm balloon (n = 30) or an 8 mm balloon (n = 30). In both groups, isosorbide dinitrate (ISDN) was infused in a rate of 5 mg/h while low pressure EPBD were being performed. The pressure of the sphincter of Oddi was observed before and after the EPBD procedures. Also, serum amylase level after EPBD was observed for both groups. Results:, Serum amylase level of the 6 mm group was signi,cantly higher than that of the 8 mm group (P < 0.05). Acute pancreatitis occurred in two patients ( 6.7%) in the 6 mm group whereas no case was observed for the 8 mm group. The rates of duct clearance were 93% in the 6 mm group and 100% in the 8 mm group. Stone removals were dif,cult in seven cases with 6 mm balloon dilatations due to the narrow ori,ces of the papilla. In the 6 mm group, there was no signi,cant difference between the basal sphincter of Oddi pressure (BSOP) and the phasic sphincter of Oddi pressure (PSOP) before and after EPBD. However in the 8 mm group, the BSOP observed after the EPBD procedure was signi,cantly higher than BSOP before the treatments. Within this group, BSOP values after EPBD were preserved by approximately 80% of the BSOP values before the treatments. In contrast, there was no signi,cant difference in PSOP before and after the treatments. Regarding the stone numbers, no signi,cant difference was observed in BSOP before and after the treatments for the 6 mm group with less than two stones. Also, as for stone size, no signi,cant difference was observed in BSOP before and after the treatments for the 6 mm group with stones of less than 6 mm in diameter. Conclusion:, We are now conducting EPBD with ISDN infusion using a 6 mm balloon for a patient who has less than two stones with size not exceeding 6 mm in diameter. An 8 mm balloon is used for a patient with more than two stones or a stone greater than 6 mm in size. [source] Comparison of the Electrochemical Reactivity of Carbon Nanotubes Paste Electrodes with Different Types of Multiwalled Carbon NanotubesELECTROANALYSIS, Issue 17 2008Xueling Li Abstract Carbon nanotubes (CNTs) are widely used in electrochemical studies. It is reported that CNTs with different source and dispersed in different agents [1] yield significant difference of electrochemical reactivity. Here we report on the electrochemical performance of CNTs paste electrodes (CNTPEs) prepared by multiwalled carbon nanotubes (MWNTs) with different diameters, lengths and functional groups. The resulting electrodes exhibit remarkable different electrochemical reactivity towards redox molecules such as NADH and K3[Fe(CN)6]. It is found that CNTPEs prepared by MWNTs with 20,30,nm diameter show highest catalysis to NADH oxidation, while CNTPEs prepared by MWNTs with carboxylate groups have best electron-transfer rate (The peak-peak separation (,Ep) is +0.108,V for MWNTs with carboxylate groups, +0.155,V for normal MWNTs, and +0.174,V for short MWNTs) but weak catalysis towards oxidation of NADH owing to the hydrophilicity of carboxylate groups. The electrochemical reactivity depends on the lengths of CNTs to some extent. The ,long' CNTs perform better in our study (The oxidation signals of NADH appear below +0.39,V for ,long' CNTs and above +0.46,V for the ,short' one totally). Readers may get some directions from this article while choose CNTs for electrochemical study. [source] A microfabricated hybrid device for DNA sequencingELECTROPHORESIS, Issue 21 2003Shaorong LiuArticle first published online: 6 NOV 200 Abstract We have created a hybrid device of a microfabricated round-channel twin-T injector incorporated with a separation capillary in order to extend the straight separation distance for high speed and long readlength DNA sequencing. Semicircular grooves on glass wafers are obtained using a photomask with a narrow line-width and a standard isotropic photolithographic etching process. Round channels are made when two etched wafers are face-to-face aligned and bonded. A two-mask fabrication process has been developed to make channels of two different diameters. The twin-T injector is formed by the smaller channels whose diameter matches the bore of the separation capillary, and the "usual" separation channel, now called the connection channel, is formed by the larger ones whose diameter matches the outer diameter of the separation capillary. The separation capillary is inserted through the connection channel all the way to the twin-T injector to allow the capillary bore flush with the twin-T injector channels. The total dead-volume of the connection is estimated to be , 5 pL. To demonstrate the efficiency of this hybrid device, we have performed four-color DNA sequencing on it. Using a 200 ,m twin-T injector coupled with a separation capillary of 20 cm effective separation distance, we have obtained readlengths of 800 plus bases at an accuracy of 98.5% in 56 min, compared to about 650 bases in 100 min on a conventional 40 cm long capillary sequencing machine under similar conditions. At an increased separation field strength and using a diluted sieving matrix, the separation time has been reduced to 20 min with a readlength of 700 bases at 98.5% base-calling accuracy. [source] Direction of cross-modal information transfer affects human brain activation: a PET studyEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 1 2002Ryuta Kawashima Abstract The purpose of this study was to determine the functional organization of the human brain involved in cross-modal discrimination between tactile and visual information. Regional cerebral blood flow was measured by positron emission tomography in nine right-handed volunteers during four discrimination tasks; tactile,tactile (TT), tactile,visual (TV), visual,tactile (VT), and visual,visual (VV). The subjects were asked either to look at digital cylinders of different diameters or to grasp the digital cylinders with the thumb and index finger of the right hand using haptic interfaces. Compared with the motor control task in which the subjects looked at and grasped cylinders of the same diameter, the right lateral prefrontal cortex and the right inferior parietal lobule were activated in all the four discrimination tasks. In addition, the dorsal premotor cortex, the ventral premotor cortex, and the inferior temporal cortex of the right hemisphere were activated during VT but not during TV. Our results suggest that the human brain mechanisms underlying cross-modal discrimination have two different pathways depending on the temporal order in which stimuli are presented. [source] The effects of morphology and substrate diameter on climbing and locomotor performance in male spidersFUNCTIONAL ECOLOGY, Issue 2 2010John Prenter Summary 1.,Spiders are the most sexually size dimorphic terrestrial animals and the evolution of this dimorphism is controversial. Patterns of sexual size dimorphism (SSD) in spiders have been related to individual performance and size. In 2002 Moya-Laraño, Halaj & Wise proposed the ,gravity hypothesis' to explain patterns of sexual size dimorphism in spiders whereby species building webs high in the vegetation are predicted to show greater SSD than those that build lower down. They advocated an advantage in climbing speed in smaller males searching for females in high places. The gravity hypothesis predicts a negative relationship between male size and climbing speed. In 2007 Brandt & Andrade questioned this interpretation and proposed that the pattern of SSD in spiders is better explained by an advantage for larger males of low-dwelling species to run faster along the ground. 2.,We induced male spiders to run a standard distance up vertical poles of different diameters to examine the predicted relationship between size and climbing speed. We tested two species of extremely size-dimorphic orb-web spiders, Argiope keyserlingi and Nephila plumipes, that differ in the height at which females tend to build webs, and one species of jumping spider, Jacksonoides queenslandica, with low levels of size dimorphism. We also examined morphological determinants of horizontal motility by inducing males to run along a raceway. 3.,Substrate diameter was consistently found to influence climbing performance. In N. plumipes, climbing speed was slowest on the widest diameter substrate. In A. keyserlingi, size-adjusted leg length and substrate diameter interacted to determine climbing speed, while in J. queenslandica, there was an interaction between body size and substrate diameter on climbing speed. In the effect of substrate diameter, we have identified a potential bias in previous tests of the gravity hypothesis. 4.,Our results do not support the prediction of the gravity hypothesis. There was no evidence of a negative relationship between body size and climbing speed in the two orb-web species with high levels of SSD. Our results are also not consistent with a recent modification of the gravity hypothesis that suggests a curvilinear relationship between climbing speed and size. 5.,Body size was positively associated with maximum running speed only in the cursorial hunter J. queenslandica. For this spider, results are more consistent with Brandt & Andrade's explanation for variation in SSD in spiders, that larger males are selected for superior running ability in low-dwelling species, rather than selection for smaller size for climbing to females in high-dwelling species. [source] Structural and Magnetic Properties of Various Ferromagnetic NanotubesADVANCED MATERIALS, Issue 45 2009Xiu-Feng Han Abstract The structural and magnetic properties of ferromagnetic nanotubes fabricated by a low cost electrodeposition method are investigated. The fabrication of various elemental ferromagnetic materials are described, such as Fe, Co, and Ni, and ferromagnetic alloys, such as NiFe, CoPt, CoFeB, and CoCrPt nanotube arrays, in aluminum oxide templates and polycarbonate membranes with different diameters, wall thicknesses, and lengths. The structural, magnetic, and magnetization reversal properties of these nanotubes are investigated as a function of the geometrical parameters. The angular dependence of the coercivity indicates a transition from the curling to the coherent mode for the ferromagnetic nanotubes. The results show that nanotube fabrication allows the outer and inner diameter, length, and thickness of the nanotubes to be tuned systematically. The magnetization processes of ferromagnetic nanotubes are influenced by the wall thickness. [source] Effect of placement of calcium sulphate when used for the repair of furcation perforations on the seal produced by a resin-based materialINTERNATIONAL ENDODONTIC JOURNAL, Issue 2 2007L. Zou Abstract Aim, To evaluate the sealing ability of calcium sulphate when used under composite resin for the repair of furcation perforations having different diameters. Methodology, Perforations of different diameter were created in the floors of pulp chambers in 60 extracted human molar teeth with either a number 3 (1 mm diameter) or 5 (1.5 mm diameter) round bur. The specimens of each group were divided into four sub-groups which were repaired with composite resin either alone or in combination with calcium sulphate that created an artificial floor (15 teeth group -1). Eight teeth without furcation perforations served as negative controls. In the leakage detection device, 1 mol L,1 glucose solution was forced under a pressure of 1.5 KPa from the crown towards the pulp chamber floor. The concentration of leaked glucose was measured at 1, 2, 4, 7, 10, 15 and 20 days using a glucose oxidase method and the data evaluated using the rank sum test. Results, The specimens with larger perforations repaired with composite resin alone had significantly more leakage (P < 0.05). Using calcium sulphate as an artificial floor significantly decreased leakage of smaller perforations (P < 0.05). In groups repaired with calcium sulphate under composite resin, leakage in smaller perforations was markedly lower than that in larger ones (P < 0.05). No significant difference was found between the specimens with 1 or 1.5 mm perforations repaired with resin alone (P > 0.05). Conclusions, Calcium sulphate significantly improved the sealing ability of 1 mm perforations repaired with composite resin but not for 1.5 mm perforations. [source] Electrospinning pH-Responsive Block Copolymer Nanofibers,ADVANCED MATERIALS, Issue 21 2007L. Wang Ultrafine fibers of a pH-responsive triblock copolymer with different diameters, alignment, and microdomain order are prepared via electrospinning and solvent-vapor annealing. Fibrous samples display much quicker response times than the corresponding films owing to the increase in external surface area. The fibrils of annealed, aligned, electrospun fibers show a dramatic apparent "1D" pH-induced size-change during the experiment. [source] Morphology and function of the forelimb in arboreal frogs: specializations for grasping ability?JOURNAL OF ANATOMY, Issue 3 2008Adriana S. Manzano Abstract Frogs are characterized by a unique morphology associated with their saltatory lifestyle. Although variation in the form and function of the pelvic girdle and associated appendicular system related to specialized locomotor modes such as swimming or burrowing has been documented, the forelimbs have typically been viewed as relatively unspecialized. Yet, previous authors have noted versatility in forelimb function among arboreal frogs associated with feeding. Here we study the morphology and function of the forelimb and hand during locomotion in two species of arboreal frogs (Litoria caerulea and Phyllomedusa bicolor). Our data show a complex arrangement of the distal forelimb and hand musculature with some notable differences between species. Analyses of high-speed video and video fluoroscopy recordings show that forelimbs are used in alternating fashion in a diagonal sequence footfall pattern and that the position of the hand is adjusted when walking on substrates of different diameters. Electromyographic recordings show that the flexors of the hand are active during substrate contact, suggesting the use of gripping to generate a stabilizing torque. Measurements of grasping forces in vivo and during stimulation experiments show that both species, are capable of executing a so-called power grip but also indicates marked differences between species, in the magnitude of forces generated. Stimulation experiments showed an increased control of digit flexion in the more specialized of the two species, allowing it to execute a precision grip paralleled only by that seen in primates. [source] Heat conduction from two spheresAICHE JOURNAL, Issue 9 2010R. S. Alassar Abstract An exact solution of heat conduction from two spheres is obtained using the bispherical coordinates system. The two spheres may be of different diameters and may be located at any distance from each other. The solution is given in terms of the temperature distribution and the local and average Nusselt numbers. © 2010 American Institute of Chemical Engineers AIChE J, 2010 [source] Cagelike polymer microspheres with hollow core/porous shell structuresJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 5 2007Xiaodong He Abstract Submicron-scaled cagelike polymer microspheres with hollow core/porous shell were synthesized by self-assembling of sulfonated polystyrene (PS) latex particles at monomer droplets interface. The swelling of the PS latex particles by the oil phase provided a driving force to develop the hollow core. The latex particles also served as porogen that would disengage automatically during polymerization. Influential factors that control the morphology of the microspheres, including the reserving time of emulsions, polymerization rate, and the Hildebrand solubility parameter and polarity of the oil phase, were studied. A variety of monomers were polymerized into microspheres with hollow core/porous shell structure and microspheres with different diameters and pore sizes were obtained. The polymer microspheres were characterized by scanning electron microscopy, transmission electron microscopy, optical microscopy, and Fourier transform infrared spectroscopy. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 933,941, 2007 [source] Prediction of gas chromatographic retention times of capillary columns of different inside diametersJOURNAL OF SEPARATION SCIENCE, JSS, Issue 18 2003Kornkanok Aryusuk Abstract The retention times (t R) of n -alkanes (C16,C22) eluted from capillary columns of different diameters are accurately predicted by using the equation proposed by Krisnangkura et al. (J. Chromatogr. Sci.1997, 35, 329,332). The numerical values of four thermodynamically related constants (a, b, c, and d) of the BP-1 (100% dimethylpolysiloxane) capillary column (0.32 mm ID×25 m, film thickness, 0.25 ,m) are ,6.169, ,0.512, 226.98, and 410.30, respectively. For columns of the same stationary phase but of different inside diameters and film thickness, accurate tR values can be predicted by using the same numerical values of the last three constants but the first constant (a) is changed by the difference in the natural logarithm of the column phase ratios (,). All the derived numerical values of each column were tested with FAMEs and with n -alkanes in temperature-programmed GC (TPGC). All the predicted tR values agree well with the experimental values. About 77% of the TPGC data have errors lower than 0.5% and the largest value is ,1.04%. [source] Orientation of Syndiotactic Polystyrene Crystallized in Cylindrical NanoporesMACROMOLECULAR RAPID COMMUNICATIONS, Issue 3 2009Hui Wu Abstract Syndiotactic polystyrene (sPS) nanorods with different diameters have been prepared by using anodic aluminum oxide templates, and the orientation of the sPS crystals in the nanorods has been investigated by FT-IR spectroscopy. It is found that the c axis of the ,, crystals preferentially oriented perpendicular to the axis of the nanorod, and the degree of orientation is lower as the diameter of the nanorod decreases. This unexpected result is attributed to nuclei formed at the surface of the nanopores and their subsequent growth, in addition to the preferential growth compatible with the pore direction by the nuclei formed in the bulk film and in the nanorods. [source] G-mode behaviour of closed ended single wall carbon nanotubes under pressurePHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 3 2009Ahmad J. Ghandour Abstract We have performed high pressure Raman experiments on closed-ended single wall carbon nanotubes using two different excitation wavelengths: 632.8 nm and 514 nm. We found that the shape of the G-mode spectrum changes while changing the excitation wavelength at lower pressures, while it becomes similar at 3.5 GPa. In addition we record that the value of the transition pressure, associated with the structural transitions in the tubes, has also changed with changing the excitation wavelength even though we are examining tubes from the same produced sample. We attribute these results to the tubes having different electronic nature (metallic; semi-conducting) and different diameters in resonance with each excitation wavelength. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] High pressure Raman study of the second-order vibrational modes of single- and double-walled carbon nanotubesPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 11 2007K. Papagelis Abstract The pressure response of the second-order Raman G, band of bundled double- (DWCNTs) and single-wall carbon nanotubes (SWCNTs) has been investigated by means of Raman spectroscopy using the 632.8 nm excitation. The different pressure responses of the G, peak in SWCNTs and its corresponding components associated with the inner and the outer tubes in DWCNTs can be attributed to the different diameters of the resonantly probed tubes and the strength of the inner-outer tube interaction. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Multifocal mesenchymal hamartoma of the chest wallRESPIROLOGY, Issue 3 2006Semsi ALTANER Abstract: Chest wall hamartomas are extremely rare. Frequently mesenchymal hamartomas are presented as a single mass and contain some primitive mesenchymal elements such as chondroid and trabecular bone structures. A 60-year-old man presented to hospital with chest pain. Thirteen years earlier, his CXR and thoracic CT showed three masses on the right and two masses on the left, but he had not received any treatment thereafter. His CT showed the same masses present 13 years earlier, but they were bigger and right thoracotomy was undertaken. At thoracotomy, two sections of the mass in the right posterior mediastinum and one section of the mass in the right apex were excised. They had an occasional bloody appearance and contained small cystic areas, and some areas were extremely hard. Microscopic examination showed that the lesions consisted of mature adipose tissue, a large number of veins of different diameters and collagen tissue. Besides, primitive mesenchymal elements, lymphoid cell accumulations and trabecular bone structures were seen focally. Bilateral chest wall hamartomas are extremely rare and may be confused with malignancy. [source] Three-dimensional architecture of the left ventricular myocardiumTHE ANATOMICAL RECORD : ADVANCES IN INTEGRATIVE ANATOMY AND EVOLUTIONARY BIOLOGY, Issue 6 2006Paul P. Lunkenheimer Abstract Concepts for ventricular function tend to assume that the majority of the myocardial cells are aligned with their long axes parallel to the epicardial ventricular surface. We aimed to validate the existence of aggregates of myocardial cells orientated with their long axis intruding obliquely between the ventricular epicardial and endocardial surfaces and to quantitate their amount and angulation. To compensate for the changing angle of the long axis of the myocytes relative to the equatorial plane of the ventricles with varying depths within the ventricular walls, the so-called helical angle, we used pairs of cylindrical knives of different diameters to punch semicircular slices from the left ventricular wall of pigs, the slices extending from the epicardium to the endocardium. The slices were pinned flat, fixed in formaldehyde, embedded in paraffin, sectioned, stained with azan or hematoxilin and eosin, and analyzed by a new semiautomatic procedure. We made use of new techniques in informatics to determine the number and angulation of the aggregates of myocardial cells cut in their long axis. The alignment of the myocytes cut longitudinally varied markedly between the epicardium and the endocardium. Populations of myocytes, arranged in strands, diverge by varying angles from the epicardial surface. When paired knives of decreasing diameter were used to cut the slices, the inclination of the diagonal created by the arrays increases, while the lengths of the array of cells cut axially decreases. The visualization of the size, shape, and alignment of the myocytic arrays at any side of the ventricular wall is determined by the radius of the knives used, the range of helical angles subtended by the alignment of the myocytes throughout the thickness of the wall, and their angulation relative to the epicardial surface. Far from the majority of the ventricular myocytes being aligned at angles more or less tangential to the epicardial lining, we found that three-fifths of the myocardial cells had their long axes diverging at angles between 7.5 and 37.5° from an alignment parallel to the epicardium. This arrangement, with the individual myocytes supported by connective tissue, might control the cyclic rearrangement of the myocardial fibers. This could serve as an important control of both ventricular mural thickening and intracavitary shape. Anat Rec Part A 288A:565,578, 2006. © 2006 Wiley-Liss, Inc. [source] Local Bubble Dynamics and Macroscopic Flow Structure in Bubble Columns with Different ScalesTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 6 2003Wei Chen Abstract Local bubble behaviours were investigated in three bubble columns with different diameters of 200, 400 and 800 mm. By means of a novel single-tip optical fibre probe employing laser Doppler technique, the local gas holdup, bubble frequency, bubble size and velocity were measured simultaneously at different locations of the columns. Measurements were performed in air-water system at superficial gas velocities up to 90 mm/s. The averaged profiles and instantaneous measurements were analyzed and compared for different columns. The presence of a coherent gross circulation structure spanning the entire column diameter in the larger column rather than a pair of symmetrical circulation cells observed in the smaller columns has been confirmed. Les comportements locaux des bulles ont été étudiés dans trois colonnes à bulles de diamètres différents, soient 200, 400 et 800 mm. Au moyen d'une nouvelle sonde à fibre optique à embout unique employant la technique laser Doppler, des mesures locales de la rétention de gaz, de la fréquence des bulles, de la taille des bulles et de la vitesse ont été effectuées simultanément à différents endroits dans les colonnes. Ces mesures ont été effectuées pour un système air-eau à des vitesses de gaz superficielles atteignant 90 mm/s. Les profils moyennés et les mesures instantanées ont été analysés puis comparés pour différentes colonnes. La présence d'une structure de circulation unique cohérente occupant tout le diamètre de la colonne dans la colonne la plus large plutôt qu'une paire de cellules de circulation symétriques observées dans les colonnes plus petites est confirmée. [source] Gas hold-up in bubble columns: Operation with concentrated slurries versus high viscosity liquidTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 3 2000Rajamani Krishna Abstract The hydrodynamics of bubble columns with concentrated slurries of paraffin oil (density, ,L = 790 kg/m3; viscosity, ,L = 0.0029 Pa·s; surface tension, , = 0.028 N·m1) containing silica particles (mean particle diameter dp = 38 ,m) has been studied in columns of three different diameters, 0.1, 0.19 and 0.38 m. With increasing particle concentration, the total gas hold-up decreases significantly. This decrease is primarily caused by the destruction of the small bubble population. The hold-up of large bubbles is practically independent of the slurry concentration. The measured gas hold-up with the 36% v paraffin oil slurry shows remarkable agreement with the corresponding data obtained with Tellus oil (,L = 862 kg/m3; ,L = 0.075 Pa·s; , = 0.028 N·m,1) as the liquid phase. Dynamic gas disengagement experiments confirm that the gas dispersion in Tellus oil also consists predominantly of large bubbles. The large bubble hold-up is found to decrease significantly with increasing column diameter. A model is developed for estimation of the large bubble gas hold-up by introduction of an wake-acceleration factor into the Davies-Taylor-Collins relation (Collins, 1967), describing the influence of the column diameter on the rise velocity of an isolated spherical cap bubble. On a étudié dans des colonnes de trois diamètres différents, soient 0,1, 0,19 et 0,38 m, l'hydrodynamique de colonnes à bulles avec des suspensions concentrées d'huile de paraffine (masse volumique, ,L = 790 kg/m3; viscosité, ,L = 0,0029 Pa·s; tension de surface, , = 0,028 N·m,1) contenant des particules de silice (diamètre moyen des particules dp = 38 ,m). Lorsque la concentration de particules augmente, la rétention de gaz totale diminue considérablement. Cette diminution est principalement due à la destruction de la population de petites bulles. La rétention de grosses bulles est pratiquement indépendante de la concentration des suspensions. La rétention de gaz mesurée avec la suspension d'huile paraffine à 36% volumique concorde remarquablement bien avec les données correspondantes obtenues avec de l'huile de Tellus (,L = 86 kg/m,3; ,L = 0,075 Pa·s; , = 0,028 N·m,1) comme phase liquide. Des expériences de dégagement de gaz dynamiques confirment que la dispersion dans l'huile de Tellus se compose essentiellement de grosses bulles. On a trouvé que la rétention de grosses bulles diminuait de manière significative avec l'augmentation du diamètre de la colonne. On a mis au point un modèle pour l'estimation de la rétention de grosses bulles de gaz par l'introduction d'un facteur d'accélération dans le sillage dans la relation de Davies-Taylor-Collins (Collins, 1967), décrivant l'influence du diamètre de colonne sur la vitesse de montée d'une bulle à t,te sphérique isolée. [source] Do physical forces contribute to cryodamage?BIOTECHNOLOGY & BIOENGINEERING, Issue 4 2009Joseph Saragusty Abstract To achieve the ultimate goal of both cryosurgery and cryopreservation, a thorough understanding of the processes responsible for cell and tissue damage is desired. The general belief is that cells are damaged primarily due to osmotic effects at slow cooling rates and intracellular ice formation at high cooling rates, together termed the "two factor theory." The present study deals with a third, largely ignored component,mechanical damage. Using pooled bull sperm cells as a model and directional freezing in large volumes, samples were frozen in the presence or absence of glass balls of three different diameters: 70,110, 250,500, and 1,000,1,250,µm, as a means of altering the surface area with which the cells come in contact. Post-thaw evaluation included motility at 0,h and after 3,h at 37°C, viability, acrosome integrity, and hypoosmotic swelling test. Interactions among glass balls, sperm cells, and ice crystals were observed by directional freezing cryomicroscopy. Intra-container pressure in relation to volume was also evaluated. The series of studies presented here indicate that the higher the surface area with which the cells come in contact, the greater the damage, possibly because the cells are squeezed between the ice crystals and the surface. We further demonstrate that with a decrease in volume, and thus increase in surface area-to-volume ratio, the intra-container pressure during freezing increases. It is suggested that large volume freezing, given that heat dissipation is solved, will inflict less cryodamage to the cells than the current practice of small volume freezing. Biotechnol. Bioeng. 2009; 104: 719,728 © 2009 Wiley Periodicals, Inc. [source] Age-Dependent Radial Increases in Wood Specific Gravity of Tropical Pioneers in Costa RicaBIOTROPICA, Issue 5 2010G. Bruce Williamson ABSTRACT Wood specific gravity is the single best descriptor of wood functional properties and tree life-history traits, and it is the most important variable in estimating carbon stocks in forests. Tropical pioneer trees produce wood of increasing specific gravity across the trunk radius as they grow in stature. Here, we tested whether radial increases in wood specific gravity were dependent on a tree's diameter or its age by comparing trees of different diameters within cohorts. We cored trunks of four pioneer species in naturally regenerating, even-aged stands in the lowland, wet forests of Costa Rica. For each core, specific gravity was determined for 1-cm radial wood segments, pith to bark. Increases across the radius were evident in all four species studied, and in four different stands for one species. For any given species in a given stand, the rate of radial increase in specific gravity as a function of radial distance from the pith was greater in smaller diameter trees. As the trees in a stand represent a colonizing cohort, these results strongly suggest that the radial increases in specific gravity in lowland pioneers are associated with tree age, not with tree diameter. Furthermore, the specific gravity of the outermost wood was not associated with tree radius, further negating size dependence. One consequence of these results is that species-specific biomass estimates for trees in secondary forests are likely to be confounded by age, as diameter alone may be a poor indicator of specific gravity in individual trees for pioneers of tropical wet forests. Abstract in Spanish is available at http://www.blackwell-synergy.com/loi/btp [source] Interspecific Competition and Niche Separation in Primates: A Global AnalysisBIOTROPICA, Issue 3 2009Brian M. Schreier ABSTRACT Primates are an extraordinarily well-known tropical forest, mammalian taxon. We investigated potential modes of niche separation in primates by identifying sympatric species with putatively similar niche characteristics and assessing potential competition using data gleaned from an extensive literature review. We defined competing species-pairs as (a) sympatric species in which (b) the body mass of the larger species was within 30 percent of the smaller species' mass and (c) the species had the same category of diet. A sample of 43 well-studied forests (7,20 per continent) provided 673 pairs of sympatric primate species. Of these, 45 pairs (7%) are potential competitors by our definition. Africa has the largest number of competing pairs (17 pairs), while Asia might have the highest percentage of competitors in each forest site (17%). Niche separation was investigated for each pair by examining them for each of eight possible modes of separation: detailed differences in diets (28% of potential competitors), use of different heights in the forest (25%), use of different types of forest (14%), use of different locations within the forest (11%), use of support branches of different diameters (7%), different ranging behavior (6%), different techniques of prey capture (4%), and differential timing of activity (4%). The use of different heights in the forest is the dominant form of potential separation in Africa (31% of competing species-pairs) and Asia (38%), while detailed differences in diet appears to be the primary mode of niche separation in the Americas (26%) and Madagascar (32%). [source] The Structure-Controlling Solventless Synthesis and Optical Properties of Uniform Cu2S NanodisksCHEMISTRY - A EUROPEAN JOURNAL, Issue 35 2008Yu-Biao Chen Dr. Abstract Uniform Cu2S nanodisks have been synthesized from a well-characterized layered copper thiolate precursor by structure-controlling solventless thermolysis at 200,220,°C under a N2 atmosphere. The development from small Cu2S nanoparticles (diameter ,3,nm) to nanodisks (diameter 8.3,nm) and then to faceted nanodisks (diameter 27.5,nm, thickness 12.7,nm) is accompanied by a continuous phase transition from metastable orthorhombic to monoclinic Cu2S, the ripening of small particles by aggregation, and finally the crystallization process. The growth of the nanoproduct is constrained by the crystal structure of the precursor and the in situ-generated thiol molecules. Such controlled anisotropic growth leads to a nearly constant thickness of faceted nanodisks with different diameters, which has been confirmed by TEM observations and optical absorption measurements. [source] | |||||||||||||||||||