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Different Pressures (different + pressure)
Selected AbstractsCavitation 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] Contrasting Role Morality and Professional Morality: Implications for PracticeJOURNAL OF APPLIED PHILOSOPHY, Issue 1 2003Kevin Gibson Investigating role morality is important, since the mentality of role morality may allow agents to believe they can abdicate moral responsibility when acting in a role. This is particularly significant in the literature dealing with professional morality where professionals, because of their special status, may find themselves at odds with their best moral judgments. Here I tell four stories and draw out some distinctions. I conclude that role morality is a genuine and useful distinction. However, I suggest that the purported distinction between role morality and professional morality is over-determined. Therefore, alleged conflicts between the demands of role and profession (such as the different pressures on Pinto designers as employees and as engineers) are not conflicts between different kinds of demands, but rather conflicts arising from divergent roles that most workers will encounter regularly. Another analytical perspective is to look at moral choices at work in terms of power and the ability to bring about change. Finally, I draw the implication that we should stress moral awareness at a fairly abstract level for all employees and reinforce the moral primacy of individual choice. [source] Polymer-acid solutions: Their use for the enhancement of oil reservoir stimulationJOURNAL OF APPLIED POLYMER SCIENCE, Issue 3 2008Mohammed M. Amro Abstract A reduction in permeability occurring around the wellbore resulting from drilling, completion and/or workover fluids increases the flow resistance to the petroleum reservoir fluids and is defined as formation damage. Acidizing process removes near-wellbore damage and enhances hydrocarbon production from producing wells. This study investigates the effect of adding polymer as a retarding agent to acid solutions to slow and control the reaction in matrix acidizing treatment of carbonate rocks. Two different polymers, polyacrylamide (PAA) and polysaccharide (xanthan) and two different acids, acetic acid and formic acid, were used through this study. The results revealed that the presence of PAA did not change the viscosity of the acid solution significantly, while the viscosity of xanthan-acid solutions was decreased with increasing the acid concentration. Additionally, the reaction of polymer-acid solutions with the rock material was monitored under microscope. Original rock samples obtained from Saudi reservoirs containing mainly carbonate were used in the reaction. The PAA-acid solution did not show any decrease in the reaction rate compared to that of acid solution. Thus, the PAA solution applied in this study is not recommended as a retarder. However, xanthan-acid solutions showed a significant decrease in the reaction time. Therefore, xanthan was selected to perform further investigations in Rotating Disk Reactor at different pressures. Scanning electronic microscopy (SEM) was conducted on pretreated and posttreated rock samples. This provides the opportunity to perform a detailed description of the rock surface and facilitates the identification of the changes occurring due to polymer-acid treatment. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] Experimental and theoretical study of the influence of pressure on SCWOAICHE JOURNAL, Issue 11 2006M. D. Bermejo Abstract It is well known that pressure is an important parameter in the SCWO process, because it produces changes in the phase behavior and thermodynamics properties of the system. The influence of pressure on the oxidation efficiency of feeds containing isopropyl alcohol as fuel and acetic acid as waste was studied in an autothermal adiabatic transpiring wall reactor at pilot-plant scale, at pressures from 13 to 25 Mpa, and temperatures from 600 to 750°C. It was found that reaction temperature decreased between 40 and 100°C, when pressure was lowered, and, subsequently TOC removal decreased. At higher-temperatures, the decreasing of TOC removal due to pressure difference was reduced. The process was simulated at different pressures using a mathematical model previously developed for the reactor. The Anderko-Pitzer EoS, especially developed for aqueous systems at high-temperatures and pressures, was used to have accurate values of the heat capacities of the reaction mixture. It was found that having into account only the effect of pressure in the thermodynamical properties and in the concentration of the reagents, the experimental results could not be explained. Thus, the influence of the pressure in the reaction rate equation had to be considered. Results were qualitatively reproduced considering the reaction rate constant variable with pressure, using a constant volume of activation of ,1400 cm3/mol. © 2006 American Institute of Chemical Engineers AIChE J, 2006 [source] Adjustment and control of SERS activity of metal substrates by pressureJOURNAL OF RAMAN SPECTROSCOPY, Issue 4 2010Lixin Xia Abstract Metal pellets of silver and copper for surface-enhanced Raman scattering (SERS) spectroscopy were prepared by compression with different pressures. It was found that the SERS activity of the pellet could be controlled by pressure. Enhanced Raman scattering properties of the metal pellets in the presence of adsorbed 4-mercaptobenzoic acid (4-MBA) with excitation at 632.8 or 514 nm could be obtained by choosing proper pressure of pellatization. The SERS peak intensity of the band at ,1584 cm,1 of 4-MBA adsorbed on the metal pellets varies as a function of applied pressure, and which is about 1.2,32 times greater than when it is adsorbed on silver and copper particles. The calculated results of three-dimensional finite-difference time-domain method (3D-FDTD) are in good agreement with the experimental data. Moreover, no spurious peaks appear in the SERS spectra of the samples because no other chemicals are involved in the simple preparation process of the metal pellets, which will facilitate its use as an SERS-active substrate for analytical purposes. In summary, SERS-active metal pellets can be produced simply and cost effectively by the method reported here, and this method is expected to be utilized in the development of SERS-based analytical devices. Copyright © 2009 John Wiley & Sons, Ltd. [source] Absolute measurement of internal volume changes inside the pulse damper: Discrepancy between delay and dwell volumesJOURNAL OF SEPARATION SCIENCE, JSS, Issue 10 2010Eduard Rogatsky Abstract We have developed a novel technique for the absolute determination of the mobile phase volume stored inside of a variable volume pulse damper at different pressures. Using an Agilent HPLC pulse damper we found a linear volume increase of ,1,,L/bar. We found that pump pressurization is a relatively slow process and takes ,1,min to reach 90% and takes ,2,min to reach 99% equilibration at flow rates below 1,mL/min. During pump pressurization, column flow rate will be less than the pre-set, since part of the mobile phase is retained inside of the pulse damper. During our experiments we observed a discrepancy between data obtained by UV techniques and direct absolute measurements. This difference can be explained by a fundamental difference between the gradient delay volume and dead (dwell) volume. [source] Cultural Constructions of Childhood and Early LiteracyLITERACY, Issue 2 2001Tricia David This paper is based on the findings of two research teams, working collaboratively, between 1998 and 2000 in four countries: Australia, Singapore, France and England (see David et al 2000). Taking an ecological stance (Bronfenbrenner 1979), both teams adopted a cross-cultural approach in order to gain a better understanding of the contexts in which young children become familiar with literacy. The team led by Bridie Raban worked in Singapore and Australia, that led by Tricia David in France and England. Early years practitioners in all four countries responded to questionnaires, were observed in action and interviewed. (Information about their training and about entry to primary school in each of the countries is given in the endnote.) In addition, the research teams carried out document analyses on Governmental, research and training literature and teachers' plans, and discussed their findings with others in positions to be able to ,authenticate', or refute , findings. Further data were obtained through group interviews with parents of children attending selected settings involved in the research. Here we provide some of the evidence about the different views expressed by practitioners, our observational findings and analysis of the different pressures relating to literacy experienced in early childhood education and care settings. In each case the learning experiences practitioners provided for children were influenced by a range of factors, such as the contested role of preschools as preparation for schooling. In some settings this preparation was not explicit and practitioners often emphasised the importance of the ,here and now' nature of young children's experiences. Rosenthal's (2000) framework for exploring ,collectivist' and ,individualist' cultures in relation to their valued educational practices was applied to our findings, in order to identify how the cultural assumptions about literacy, learning and young children influenced the teaching approaches selected. [source] Protease-activated receptor-4 (PAR4): a role as inhibitor of visceral pain and hypersensitivityNEUROGASTROENTEROLOGY & MOTILITY, Issue 11 2009C. Augé Abstract, Protease-activated receptor-4 (PAR4) belongs to the family of receptors activated by the proteolytic cleavage of their extracellular N-terminal domain and the subsequent binding of the newly released N-terminus. While largely expressed in the colon, the role of PAR4 in gut functions has not been defined. We have investigated the effects of PAR4 agonist on colonic sensations and sensory neuron signalling, and its role in visceral pain. We observed that a single administration of the PAR4 agonist peptide (AYPGKF-NH2), but not the control peptide (YAPGKF-NH2) into the colon lumen of mice significantly reduced the visceromotor response to colorectal distension at different pressures of distension. Further, intracolonic administration of the PAR4 agonist, but not the control peptide, was able to significantly inhibit PAR2 agonist- and transcient receptor potential vanilloid-4 (TRPV4) agonist-induced allodynia and hyperalgesia in response to colorectal distension. Protease-activated receptor-4 was detected in sensory neurons projecting from the colon, and isolated from the dorsal root ganglia, where it co-expressed with PAR2 and TRPV4. In total sensory neurons, PAR4 agonist exposure inhibited free intracellular calcium mobilization induced by the pro-nociceptive agonists of PAR2 and TRPV4. Finally, PAR4 -deficient mice experienced increased pain behaviour in response to intracolonic administration of mustard oil, compared with wild-type littermates. These results show that PAR4 agonists modulate colonic nociceptive response, inhibit colonic hypersensitivity and primary afferent responses to pro-nociceptive mediators. Endogenous activation of PAR4 also plays a major role in controlling visceral pain. These results identify PAR4 as a previously unknown modulator of visceral nociception. [source] Theoretical and visual study of bubble dynamics in foam injection moldingPOLYMER ENGINEERING & SCIENCE, Issue 3 2010Mehdi Mahmoodi This article presents an experimental observation and a theoretical prediction of bubble dynamics in foam injection molding process with a main focus on the cell collapse phenomenon under pressure. Using a visualizing setup, cell growth behavior under a nonisothermal condition was monitored. In conjunction with the growth behavior, dynamics of cell collapse under different pressures and the effect of growing time on collapse behavior and final cell size were studied. Theoretical simulation of bubble behavior included power law model, which predicted bubble dynamics during foaming process. The results show that collapse phenomenon strongly depends on both exerted holding pressure and growth time. The presented model can also give a reasonable prediction of growth and collapse of cells and could give insight to control of cell size in injection foaming process. POLYM. ENG. SCI., 2010. © 2009 Society of Plastics Engineers [source] Life history and locomotion in Cebus capucinus and Alouatta palliataAMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY, Issue 3 2009Michelle Bezanson Abstract As an individual matures from birth to adulthood, many factors may influence the positional repertoire. The biological and behavioral changes that accompany a growing individual are expected to influence foraging strategy, social status and interaction, diet, predator avoidance strategies, and ultimately positional behavior as a behavioral link between anatomy and the environment. In this work, positional behavior is considered as an important feature of life history in juvenile and adult white-faced capuchins (Cebus capucinus) and mantled howling monkeys (Alouatta palliata) inhabiting the same tropical forest in Costa Rica. During growth and development ontogenetic changes in body size, limb proportions, and motor skills are likely to influence locomotion and posture through the arboreal canopy. I collected data on positional behavior, activity, branch size, branch angle, and crown location during a 12-month period at Estación Biológica La Suerte in northeastern Costa Rica. Life history timing and differences in rates of growth did not predictably influence the development of adultlike positional behaviors in Cebus and Alouatta. Young Cebus resembled the adult pattern of positional behavior by 6 months of age while howlers exhibited significant differences in several positional behavior categories through 24 months of age. The positional repertoire of both species revealed similarities in the types of modes used during feed/forage and travel in juveniles and adults. Data presented here suggest that the environment exerts different pressures on growing Cebus and Alouatta that may relate to diet, energy expenditure, foraging skill, and/or social learning. Am J Phys Anthropol, 2009 © 2009 Wiley-Liss, Inc. [source] Regular and inverted batch process structures for pressure swing distillation: a case studyASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 6 2009Andreas Klein Abstract The main focus of this paper is on the comparison of the inverted and the regular pressure swing batch distillation processes for the separation of a homogenous azeotropic mixture. On the basis of a successful, experimentally validated rigorous model, a simulation study to identify the differences between the two processes and the influences of different structures on them is carried out. This identification of influences helps in finding out a heuristic base of the most suitable batch structure for a given separation problem. Especially the influence of the feed flow rate on the processes and the differences between the results on operation with different pressures will be addressed. Furthermore advantages, disadvantages and the limitations of both processes will be shown. In the end the best way of operating the pressure swing batch distillation will be presented depending on the product purity and the feed concentration for a given example. Copyright © 2009 Curtin University of Technology and John Wiley & Sons, Ltd. [source] Deep Fractionation of Clinopyroxene in the East Pacific Rise 13°N: Evidence from High MgO MORB and Melt InclusionsACTA GEOLOGICA SINICA (ENGLISH EDITION), Issue 2 2009Guoliang ZHANG Abstract: Mid-ocean ridge basalts (MORBs) from East Pacific Rise (EPR) 13°N are analysed for major and trace elements, both of which show a continuous evolving trend. Positive MgO,Al2O3 and negative MgO,Sc relationships manifest the cotectic crystallization of plagioclase and olivine, which exist with the presence of plagioclase and olivine phenocrysts and the absence of clinopyroxene phenocrysts. However, the fractionation of clinopyroxene is proven by the positive correlation of MgO and CaO. Thus, MORB samples are believed to show a "clinopyroxene paradox". The highest magnesium-bearing MORB sample E13,3B (MgO = 9.52%) is modelled for isobaric crystallization with COMAGMAT at different pressures. Observed CaO/Al2O3 ratios can be derived from E13,3B only by fractional crystallization at pressure >4 ±1 kbar, which necessitates clinopyroxene crystallization and is not consistent with cotectic crystallization of olivine plus plagioclase in the magma chamber (at pressure ,1 kbar). The initial compositions of the melt inclusions, which could represent potential parental magmas, are reconstructed by correcting for post-entrapment crystallization (PEC). The simulated crystallization of initial melt inclusions also produce observed CaO/Al2O3 ratios only at >4±1 kbar, in which clinopyroxene takes part in crystallization. It is suggested that MORB magmas have experienced clinopyroxene fractionation in the lower crust, in and below the Moho transition zone. The MORB magmas have experienced transition from clinopyroxene+plagioclase+olivine crystallization at >4±1 kbar to mainly olivine+plagioclase crystallization at <1 kbar, which contributes to the explanation of the "clinopyroxene paradox". [source] Study of the Kinetics and Morphology of Gas Hydrate FormationCHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 8 2006Abstract The kinetics and morphology of ethane hydrate formation were studied in a batch type reactor at a temperature of ca. 270,280,K, over a pressure range of 8.83,16.67,bar. The results of the experiments revealed that the formation kinetics were dependant on pressure, temperature, degree of supercooling, and stirring rate. Regardless of the saturation state, the primary nucleation always took place in the bulk of the water and the phase transition was always initiated at the surface of the vortex (gas-water interface). The rate of hydrate formation was observed to increase with an increase in pressure. The effect of stirring rate on nucleation and growth was emphasized in great detail. The experiments were performed at various stirring rates of 110,190,rpm. Higher rates of formation of gas hydrate were recorded at faster stirring rates. The appearance of nuclei and their subsequent growth at the interface, for different stirring rates, was explained by the proposed conceptual model of mass transfer resistances. The patterns of gas consumption rates, with changing rpm, have been visualized as due to a critical level of gas molecules in the immediate vicinity of the growing hydrate particle. Nucleation and decomposition gave a cyclic hysteresis-like phenomena. It was also observed that a change in pressure had a much greater effect on the rate of decomposition than it did on the formation rate. Morphological studies revealed that the ethane hydrate resembles thread or is cotton-like in appearance. The rate of gas consumption during nucleation, with different rpm and pressures, and the percentage decomposition at different pressures, were explained precisely for ethane hydrate. [source] Pressure-Induced Emission Enhancement of a Series of Dicyanovinyl-Substituted Aromatics: Pressure Tuning of the Molecular Population with Different ConformationsCHEMPHYSCHEM, Issue 8 2008Qian Wang Dr. Abstract A series of dicyanovinyl-substituted aromatic compounds (Ar-DCV; Ar=9-anthracenyl, 1-naphthyl, 1-pyrenyl) with dual fluorescence are prepared, and their emission properties,when molecularly dispersed in a polymer medium,are investigated under pressure perturbation. The total emission intensity is enhanced drastically from ambient pressure up to 70 kbar. Emission 30,107 times more intense than that at ambient pressure is observed at higher pressure. In dual emission, the enhancement of the local excited state (LE state) is significantly different from that of the intramolecular charge-transfer state (ICT state). The intensity of the ICT emission increases faster (30,370 times) than that of the LE emission (less than 20 times). In accordance with spectroscopic data, emission dynamics at different pressures, and computational studies on the molecular conformations of these compounds, a kinetic model is proposed to explain the effect of pressure on the emissive properties of the Ar-DCV compounds from the point of view of pressure-dependent populations of the species in the ground state. [source] | ||||||||||||||||