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Bubble Formation (bubble + formation)
Selected AbstractsFUTURES MARKETS AND BUBBLE FORMATION IN EXPERIMENTAL ASSET MARKETS*PACIFIC ECONOMIC REVIEW, Issue 2 2006Charles Noussair In addition to a spot market, there are futures markets in operation, one maturing at the beginning of each period of the life of the asset. We find that when futures markets are present, bubbles do not occur in the spot markets. The futures markets seem to reduce the speculation and the decision errors that appear to give rise to price bubbles in experimental asset markets. [source] Numerical Study on Bubble Formation of a Gas-Liquid Flow in a T-Junction MicrochannelCHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 12 2009L. Dai Abstract Bubble emergence in a gas-liquid flow in a T-junction microchannel of 100,,m diameter, operated under a squeezing regime, was simulated with the computational fluid dynamics method. In general, bubble formation in channels includes three stages: expansion, collapse and pinching off. After analyzing and comparing quantitatively the three forces of pressure, surface tension and shear stress acting on the gas thread in the whole process, their effects in the different stages were identified. The collapse stage was the most important for bubble formation and was investigated in detail. It was found that the collapse process was mostly influenced by the liquid superficial velocity, and the rate and time of collapse can be correlated with empirical equations including the liquid superficial velocity, the capillary number and the Reynolds number. [source] Cavitation versus Degassing: In Vitro Study of the Microbubble Phenomenon Observed During Echocardiography in Patients with Mechanical Prosthetic Cardiac ValvesECHOCARDIOGRAPHY, Issue 7 2002Grégoire Girod M.D. Background: With the advent of second harmonic imaging in echocardiography, microbubbles have been observed during opening and closure of mechanical prosthetic valves. The single phenomenon of cavitation, an extremely short event described in the literature, cannot explain the persistence of microbubbles during several hundred milliseconds. Therefore, in vitro we reproduced two distinct phenomena created by a local depression occurring during the closure and/or opening of prosthetic valves: Cavitation and degassing. Methods: We used a water circuit system enriched with CO2 that passes through a Venturi tube in order to create variable pressure gradients. Three types of observations were performed: (1) the dimensions of the bubbles as a function of pressure, (2) calibration of the echocardiograph, and (3) comparison and illustrations of the difference between bubble formation by cavitation (vaporization) and degassing (liberation of CO2). Results: According to the different pressures exerted, the dimensions of the bubbles only vary by several microns, not measurable in practice. Second, the calibration of the echocardiograph reveals that the dimensions of the bubbles measured by ultrasound are greater by a factor of 1.75. Finally, the observed cavitation is a short phenomenon (several milliseconds) and happens under a great local pressure gradient. The degassing produces microbubbles lasting up to as long as > 1 second under much lower pressure. Conclusion: This in vitro study suggests that microbubbles observed during several hundred milliseconds after the opening of prosthetic cardiac valves are the result of degassing of CO2 in blood rather than a cavitation phenomenon as suggested in the literature. [source] Separation of peptides by open-tubular capillary electrochromatography using Fe(III)-deuteroporphyrin as a covalently attached stationary phaseELECTROPHORESIS, Issue 13 2009Ángel Yone Abstract The separation of seven biologically active peptides was attempted by open-tubular capillary electrochromatography in fused-silica capillaries chemically modified with iron (III)-deuteroporphyrin using UV-absorption detection at 214,nm. The effect of BGE pH and content of organic solvent modifier was investigated. The best separations were obtained in 25,mM phosphate (BGE), pH 4.0, containing 5%,v/v ACN and 10,mM hydroquinone, which was added to prevent gas bubble formation. Considering the method sensitivity, lower concentration LODs were obtained for all peptides in their open-tubular capillary electrochromatography separation as compared with their CZE separation in bare fused-silica capillary. The iron (III)-deuteroporphyrin column proved to be highly stable over time and showed acceptable precision of migration times and corrected peak areas (RSD in the range 2,4%). [source] Micro freef-low IEF enhanced by active cooling and functionalized gelsELECTROPHORESIS, Issue 24 2006Jacob W. Albrecht Abstract Rapid free-flow IEF is achieved in a microfluidic device by separating the electrodes from the focusing region with porous buffer regions. Moving the electrodes outside enables the use of large electric fields without the detrimental effects of bubble formation in the active region. The anode and cathode porous buffer regions, which are formed by acrylamide functionalized with immobilized pH groups, allow ion transport while providing buffering capacity. Thermoelectric cooling mitigates the effects of Joule heating on sample focusing at high field strengths (,500,V/cm). This localized cooling was observed to increase device performance. Rapid focusing of low-molecular-weight pI markers and Protein G,mouse IgG complexes demonstrate the versatility of the technique. Simulations provide insight into and predict device performance based on a well-defined sample composition. [source] Capillary electrochromatography with monolithic silica column:,I.ELECTROPHORESIS, Issue 3 2003Preparation of silica monoliths having surface-bound octadecyl moieties, applications to the separation of neutral, charged species, their chromatographic characterization Abstract Monolithic silica columns with surface-bound octadecyl (C18) moieties have been prepared by a sol-gel process in 100 ,m ID fused-silica capillaries for reversed-phase capillary electrochromatography of neutral and charged species. The reaction conditions for the preparation of the C18-silica monoliths were optimized for maximum surface coverage with octadecyl moieties in order to maximize retention and selectivity toward neutral and charged solutes with a sufficiently strong electroosmotic flow (>,2 mm/s) to yield rapid analysis time. Furthermore, the effect of the pore-tailoring process on the silica monoliths was performed over a wide range of treatment time with 0.010 M ammonium hydroxide solution in order to determine the optimum time and conditions that yield mesopores of narrow pore size distribution that result in high separation efficiency. Under optimum column fabrication conditions and optimum mobile phase composition and flow velocity, the average separation efficiency reached 160,000 plates/m, a value comparable to that obtained on columns packed with 3 ,m C18-silica particles with the advantages of high permeability and virtually no bubble formation. The optimized monolithic C18-silica columns were evaluated for their retention properties toward neutral and charged analytes over a wide range of mobile phase compositions. A series of dimensionless retention parameters were evaluated and correlated to solute polarity and electromigration property. A dimensionless mobility modulus was introduced to describe charged solute migration and interaction behavior with the monolithic C18-silica in a counterflow regime during capillary electrochromatography (CEC )separations. The mobility moduli correlated well with the solute hydrophobic character and its charge-to-mass ratio. [source] Low-voltage electroosmosis pump for stand-alone microfluidics devicesELECTROPHORESIS, Issue 1-2 2003Yuzuru Takamura Abstract Two types of low-voltage electroosmosis pumps were developed using microfabrication technology for usage in handy or stand-alone applications of the micrototal analysis systems (,-TAS) and the lab-on-a-chip. This was done by making a thin (<,1 ,m) region in the flow path and by only applying voltages near this thin region using electrodes inserted into the flow path. The inserted electrodes must be free from bubble formation and be gas-tight in order to avoid pressure leakage. For these electrodes, Ag/AgCl or a gel salt bridge was used. For patterning the gel on the chip, a hydrophilic photopolymerization gel and a photolithographic technique were optimized for producing a gel with higher electric conductivity and higher mechanical strength. For high flow rate application, wide (33.2 mm) and thin (400 nm) pumping channels were compacted into a 1 mm×6 mm area by folding. This pump achieves an 800 Pa static pressure and a flow of 415 nL/min at 10 V. For high-pressure application, a pump was designed with the thin and thick regions in series and positive and negative electrodes were inserted between them alternatively. This pump could increase the pumping pressure without increasing the supply voltage. A pump with 10-stage connections generated a pressure of 25 kPa at 10 V. [source] Small-angle X-ray scattering measurements of helium-bubble formation in borosilicate glassJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 5 2006Alexander Y. Terekhov Small-angle X-ray scattering (SAXS) measurements have been performed to study helium-bubble formation in borosilicate glass. Helium was introduced by He+ implantation over an energy range of 1 to 2,MeV to give a uniform distribution over ,1,µm depth. The implanted dose was varied from 9 × 1013 to 2.8 × 1016,ions,cm,2, corresponding to a local concentration range of 40 to 11200 atomic parts per million (a.p.p.m.) averaged over the implantation depth. The SAXS response was fit with the Percus,Yevick hard-sphere interaction potential to account for interparticle interference. The fits yield helium-bubble radii and helium-bubble volume fractions that vary from 5 to 15,Å and from 10,3 to 10,1, respectively, as the dose increased from 9 × 1013 to 2.8 × 1016,cm,2. The SAXS data are also consistent with maximum helium solubility with respect to bubble formation between 40 and 200 a.p.p.m. in the borosilicate glass matrix. [source] Experimental investigation on evaporation of urea-water-solution droplet for SCR applicationsAICHE JOURNAL, Issue 12 2009Tae Joong Wang Abstract The evaporation behavior of urea-water-solution (UWS) droplet was investigated for application to urea-selective catalytic reduction (SCR) systems. A number of experiments were performed with single UWS droplet suspended on the tip of a fine quartz fiber. To cover the temperature range of real-world diesel exhausts, droplet ambient temperature was regulated from 373 to 873 K using an electrical furnace. As a result of this study, UWS droplet revealed different evaporation characteristics depending on its ambient temperature. At high temperatures, it showed quite complicated behaviors such as bubble formation, distortion, and partial rupture after a linear D2 -law period. However, as temperature decreases, these phenomena became weak and finally disappeared. Also, droplet diminishment coefficients were extracted from transient evaporation histories for various ambient temperatures, which yields a quantitative evaluation on evaporation characteristics of UWS droplet as well as provides valuable empirical data required for modeling or simulation works on urea-SCR systems. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source] Photothermal antimicrobial nanotherapy and nanodiagnostics with self-assembling carbon nanotube clustersLASERS IN SURGERY AND MEDICINE, Issue 7 2007Jin-Woo Kim PhD Abstract Background and Objectives Unique properties of carbon nanotubes (CNTs) would open new avenues for addressing challenges to realize rapid and sensitive antimicrobial diagnostics and therapy for human pathogens. In this study, new CNTs' capabilities for photothermal (PT) antimicrobial nanotherapy were explored in vitro using Escherichia coli as a model bacterium. Study Design/Materials and Methods Single-walled carbon nanotubes (SWNTs) and multi-walled carbon nanotubes (MWNTs) were incubated with E. coli K12 strain. CNTs' locations in bacteria and laser-induced thermal and accompanied effects around CNTs were estimated with TEM and PT microscopy, respectively. Multi-pulse lasers at 532 and 1064 nm with 12-ns pulse duration were used for irradiating sample mixtures at different laser fluences. Cell viability was evaluated using a bacterial viability test kit and epi-fluorescence microscopy. Results This study revealed CNTs' high binding affinity to bacteria, their capability to self-assemble as clusters at bacteria surfaces, and their inherent near-infrared (NIR) laser responsiveness. Cell viability was affected neither by CNTs alone nor by NIR irradiations alone. Notable changes in bacteria viability, caused by local thermal and accompanied bubble-formation phenomena, were observed starting at laser fluences of 0.1,0.5 J/cm2 with complete bacteria disintegration at 2,3 J/cm2 at both wavelengths. Furthermore, ethanol in reaction mixtures significantly (more than one order) enhanced bubble formation phenomena. Conclusion This first application of laser-activated CNTs as PT contrast antimicrobial agents demonstrated its great potential to cause irreparable damages to disease-causing pathogens as well as to detect the pathogens at single bacterium level. This unique integration of laser and nanotechnology may also be used for drinking water treatment, food processing, disinfection of medical instrumentation, and purification of grafts and implants. Furthermore, the significant ethanol-induced enhancement of bubble formation provides another unique possibility to improve the efficiency of selective nanophotothermolysis for treating cancers, wounds, and vascular legions. Lesers Surg. Med. 39:622,634, 2007. © 2007 Wiley-Liss, Inc. [source] Incipient stable bubble formation during bulk polymerization of methyl methacrylate under near-isothermal conditions.POLYMER ENGINEERING & SCIENCE, Issue 12 2009Methyl methacrylate is polymerized under near-isothermal conditions in a 1-l stainless steel batch reactor having a glass bottom and stirred with an anchor agitator. A camcorder is used to obtain images of the entrapped vapor bubbles at different times so as to identify the point, Bi, where stable clusters of vapor bubbles first (incipient) get formed. This is being referred to as the transition point. Data on the monomer conversion, xm,Bi, the weight average molecular weight, Mw,Bi, and the viscosity, ,Bi, of the reaction mass at this point have been generated for a variety of experimental conditions. It is observed that the pressure above the liquid reaction mixture and the RPM of the stirrer have little effect on the results in the ranges studied. Correlations have been developed for xm,Bi, Mw,Bi, and ,Bi, relating these to the initiator loading, Io, and the constant set-point temperature, T. Results are compared with those obtained earlier for reactors stirred with ribbon agitators. The transition point is useful for the design of the first stage of polymerization reactors. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers [source] Incipient bubble formation during bulk polymerization of methyl methacrylate under near-isothermal conditions using a ribbon agitatorPOLYMER ENGINEERING & SCIENCE, Issue 5 2009Gurpreet J. Singh The polymerization of methyl methacrylate (MMA) is carried out under near-isothermal conditions in a 1-liter stainless steel stirred batch reactor with a glass bottom. A ribbon agitator is used to study the incipient stable-bubble formation point, Bi, during the bulk polymerization of MMA. A camcorder has been used to get images of the bubbles from the beginning of the polymerization till just beyond the incipient stable-bubble formation point. Experimental data on the monomer conversion, xm,Bi, the weight average molecular weight, Mw,Bi, and the viscosity, ,Bi, of the reaction mass have been generated at this important point. Data have been taken at several values of the (near-isothermal) temperature, initiator loading, reactor pressure, and the RPM of the ribbon stirrer. No significant effect of pressure and the RPM of the stirrer were observed over the ranges of these variables studied. Correlations have been developed for xm,Bi, Mw,Bi, and ,Bi, relating these to the initiator loading and the temperature. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers [source] Studies on Liquid,Gas and Three-Phase Fluidized Beds with Pulsating Air FlowsTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 1 2003Christopher G. J. Baker Abstract The effects of air-flow pulsation and water and air flowrates on the hydrodynamics of liquid,gas and three-phase fluidized beds containing 3-mm glass beads have been studied in a 90-mm i.d. column. Under steady-flow conditions, both types of bed contained a relatively large number of small bubbles. With a pulsing air flow, however, a smaller number of much larger bubbles or slugs were formed. This was attributed to different mechanisms of bubble formation at the distributor. Variations in phase holdup were explained in terms of the effects of the operating parameters on the bubble characteristics. On a étudié dans une colonne de 90 mm de diamètre intérieur les effets de la pulsation air-écoulement et des débits d'eau et d'air sur l' hydrodynamique de lits fluidisés gaz,liquide et triphasiques contenant des billes de verre de 3 mm. Dans des conditions d'écoulement en régime permanent, les deux types de lit contenaient un nombre relativement important de petites bulles. Toutefois, avec un écoulement à air pulsé, il s 'est formé un moins grand nombre de bulles de très grande dimension ou de bouchons. Ceci est imputable aux différents mécanismes de formation des bulles au niveau du distributeur. Les variations dans la rétention des phases sont expliquées par les effets des paramètres opératoires sur les caractéristiques des bulles. [source] Numerical Study on Bubble Formation of a Gas-Liquid Flow in a T-Junction MicrochannelCHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 12 2009L. Dai Abstract Bubble emergence in a gas-liquid flow in a T-junction microchannel of 100,,m diameter, operated under a squeezing regime, was simulated with the computational fluid dynamics method. In general, bubble formation in channels includes three stages: expansion, collapse and pinching off. After analyzing and comparing quantitatively the three forces of pressure, surface tension and shear stress acting on the gas thread in the whole process, their effects in the different stages were identified. The collapse stage was the most important for bubble formation and was investigated in detail. It was found that the collapse process was mostly influenced by the liquid superficial velocity, and the rate and time of collapse can be correlated with empirical equations including the liquid superficial velocity, the capillary number and the Reynolds number. [source] | |||||||||||||