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Constant Pressure (constant + pressure)
Selected AbstractsRotational and Vibrational Temperature Measurements in a High-Pressure Cylindrical Dielectric Barrier Discharge (C-DBD)CONTRIBUTIONS TO PLASMA PHYSICS, Issue 1 2005N. Masoud Abstract The rotational (TR) and vibrational (Tv) temperatures of N2 molecules were measured in a high-pressure cylindrical dielectric barrier discharge (C-DBD) source in Ne with trace amounts (0.02 %) of N2 and dry air excited by radio-frequency (rf) power. Both TR and Tv of the N2 molecules in the C 3,u state were determined from an emission spectroscopic analysis the 2nd positive system (C 3,u , B3,g). Gas temperatures were inferred from the measured rotational temperatures. As a function of pressure, the rotational temperature is essentially constant at about 360 K in the range from 200 Torr to 600 Torr (at 30W rf power) and increases slightly with increasing rf power at constant pressure. As one would expect, vibrational temperature measurements revealed significantly higher temperatures. The vibrational temperature decreases with pressure from 3030 K at 200 Torr to 2270 K at 600 Torr (at 30 W rf power). As a function of rf power, the vibrational temperature increases from 2520 K at 20 W to 2940 K at 60 W (at 400 Torr). Both TR and Tv also show a dependence on the excitation frequency at the two frequencies that we studied, 400 kHz and 13.56 MHz. Adding trace amounts of air instead of N2 to the Ne in the discharge resulted in higher TR and Tv values and in a different pressure dependence of the rotational and vibrational temperatures. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Responses of jawbone to pressure,GERODONTOLOGY, Issue 2 2004Gunnar E. Carlsson Objective:, To provide a literature review of bone resorption of edentulous jaws focusing on responses to pressure. Background:, After the extraction of all teeth in a jaw there is a continuous reduction of the residual ridge. The individual variation of bone resorption is great, and the aetiology is complex and not yet well understood. Materials and methods:, A search of the literature published up to May 2003 on bone resorption and pressure was performed using PubMed/Medline. Results:, Animal studies have demonstrated that excessive and constant pressure induces bone resorption. Recent experimental research has indicated that bone resorption is a pressure-regulated phenomenon with a lower threshold for continuous than for intermittent pressure. Clinical studies have suggested that residual ridge resorption is due more to the effects of denture wearing than to disuse atrophy. However, the results of leaving out dentures at night are not conclusive. Nor does the literature offer any strong evidence for the so-called combination syndrome, which has been described as a result of unfavourable loading. Clinical studies using multivariate analyses indicate that female gender and systemic factors may be of greater importance than oral and denture factors. Implant-supported prostheses have a bone preserving effect rather than the continuing resorption under complete dentures. Conclusions:, The best way to reduce bone resorption is to avoid total extraction, preserve a few teeth and fabricate overdentures. In edentulous jaws, placement of implant-supported prostheses will lead to less bone loss and may even promote bone growth. To increase our knowledge of residual ridge resorption extended experimental, clinical and statistical methods will be needed, preferably including collaboration between dental and medical researchers. [source] Semi-coupled air/water immersed boundary approach for curvilinear dynamic overset grids with application to ship hydrodynamicsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 6 2008Juntao Huang Abstract For many problems in ship hydrodynamics, the effects of air flow on the water flow are negligible (the frequently called free surface conditions), but the air flow around the ship is still of interest. A method is presented where the water flow is decoupled from the air solution, but the air flow uses the unsteady water flow as a boundary condition. The authors call this a semi-coupled air/water flow approach. The method can be divided into two steps. At each time step the free surface water flow is computed first with a single-phase method assuming constant pressure and zero stress on the interface. The second step is to compute the air flow assuming the free surface as a moving immersed boundary (IB). The IB method developed for Cartesian grids (Annu. Rev. Fluid Mech. 2005; 37:239,261) is extended to curvilinear grids, where no-slip and continuity conditions are used to enforce velocity and pressure boundary conditions for the air flow. The forcing points close to the IB can be computed and corrected under a sharp interface condition, which makes the computation very stable. The overset implementation is similar to that of the single-phase solver (Comput. Fluids 2007; 36:1415,1433), with the difference that points in water are set as IB points even if they are fringe points. Pressure,velocity coupling through pressure implicit with splitting of operators or projection methods is used for water computations, and a projection method is used for the air. The method on each fluid is a single-phase method, thus avoiding ill-conditioned numerical systems caused by large differences of fluid properties between air and water. The computation is only slightly slower than the single-phase version, with complete absence of spurious velocity oscillations near the free surface, frequently present in fully coupled approaches. Validations are performed for laminar Couette flow over a wavy boundary by comparing with the analytical solution, and for the surface combatant model David Taylor Model Basin (DTMB) 5512 by comparing with Experimental Fluid Dynamics (EFD) and the results of two-phase level set computations. Complex flow computations are demonstrated for the ONR Tumblehome DTMB 5613 with superstructure subject to waves and wind, including 6DOF motions and broaching in SS7 irregular waves and wind. Copyright © 2008 John Wiley & Sons, Ltd. [source] Exergy analysis of a coal-based 210 MW thermal power plantINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 1 2007S. Sengupta Abstract In the present work, exergy analysis of a coal-based thermal power plant is done using the design data from a 210 MW thermal power plant under operation in India. The entire plant cycle is split up into three zones for the analysis: (1) only the turbo-generator with its inlets and outlets, (2) turbo-generator, condenser, feed pumps and the regenerative heaters, (3) the entire cycle with boiler, turbo-generator, condenser, feed pumps, regenerative heaters and the plant auxiliaries. It helps to find out the contributions of different parts of the plant towards exergy destruction. The exergy efficiency is calculated using the operating data from the plant at different conditions, viz. at different loads, different condenser pressures, with and without regenerative heaters and with different settings of the turbine governing. The load variation is studied with the data at 100, 75, 60 and 40% of full load. Effects of two different condenser pressures, i.e. 76 and 89 mmHg (abs.), are studied. Effect of regeneration on exergy efficiency is studied by successively removing the high pressure regenerative heaters out of operation. The turbine governing system has been kept at constant pressure and sliding pressure modes to study their effects. It is observed that the major source of irreversibility in the power cycle is the boiler, which contributes to an exergy destruction of the order of 60%. Part load operation increases the irreversibilities in the cycle and the effect is more pronounced with the reduction of the load. Increase in the condenser back pressure decreases the exergy efficiency. Successive withdrawal of the high pressure heaters show a gradual increment in the exergy efficiency for the control volume excluding the boiler, while a decrease in exergy efficiency when the whole plant including the boiler is considered. Keeping the main steam pressure before the turbine control valves in sliding mode improves the exergy efficiencies in case of part load operation. Copyright © 2006 John Wiley & Sons, Ltd. [source] Illegal Migration: What Can We Know And What Can We Explain?INTERNATIONAL MIGRATION REVIEW, Issue 3 2004The Case of Germany Methodological problems in the study of illegal migration as defined in this article relate to questions of indicators for illegal migration, with special reference to Germany. It is argued and demonstrated that illegal immigrants are traceable, to some degree, in official statistics and that these can be analyzed for trends. In present-day migration processes, illegal immigration frequently is undertaken with the support of human smugglers. The analysis of the social organization of different forms of smuggling is the other main focus of the article. From a methodological point of view, the literature and public discourse lack adequate concepts for describing and explaining the social organization of human smuggling. The theory of organized crime as a main actor in human smuggling is criticized. The study borrows concepts from market and networks theory and applies these to different forms of human smuggling and illegal migration. The social and technological organization of smuggling is under constant pressure to adapt to new conditions. The dynamism for this change results mainly from an "arms race" between smugglers and law enforcement. Since control over territory and population are central elements of state sovereignty, the state cannot simply withdraw from this race. [source] The Effect of Edible Coatings and Pressure Frying Using Nitrogen Gas on the Quality of Breaded Fried Chicken NuggetsJOURNAL OF FOOD SCIENCE, Issue 3 2006Tameshia S. Ballard ABSTRACT: The effects of 2 edible coatings, methylcellulose (MC) and whey protein isolate (WPI), and 2 pressure sources (nitrogen gas and steam) on the quality attributes (crispness, moisture and fat content, juiciness, color, and texture) of breaded fried chicken nuggets were evaluated. MC or WPI was incorporated into either the pre-dust or the batter before frying. Chicken nuggets were fried in a modified restaurant-type pressure fryer under a constant pressure of 163 kPa at 175°C for 240 s. Samples were held under a heat lamp at 60°C for 0-, 10-, 20-, and 30-min time intervals. Crispness was evaluated using a nondestructive ultrasonic technique. Coating type and pressure source had a significant effect (P < 0.05) on all quality attributes. Chicken nuggets fried using nitrogen gas were crispier (P < 0.05) than those fried with steam. The treatment combination of MC incorporated into the pre-dust and frying with nitrogen gas was the most effective at maintaining product crispness. [source] Continuous process for production of hydrogenated nitrile butadiene rubber using a Kenics® KMX static mixer reactorAICHE JOURNAL, Issue 11 2009Chandra Mouli R. Madhuranthakam Abstract A continuous process for hydrogenating nitrile butadiene rubber (NBR) was developed and its performance was experimentally investigated. A Kenics® KMX static mixer (SM) is used in the process as a gas,liquid reactor in which gaseous hydrogen reacts with NBR in an organic solution catalyzed by an organometallic complex such as an osmium complex catalyst. The Kenics® KMX SM was designed with 24 mixing elements with 3.81 cm diameter and arranged such that the angle between two neighboring elements is 90°. The internal structure of each element is open blade with the blades being convexly curved. The dimensions of the SM reactor are: 3.81 cm ID 80 S and 123 cm length and was operated cocurrently with vertical upflow. The NBR solutions of different concentrations (0.418 and 0.837 mol/L with respect to [CC]) were hydrogenated by using different concentrations of the osmium catalyst solution at various residence times. The reactions were conducted at a constant temperature of 138°C and at a constant pressure of 3.5 MPa. From the experimental results, it is observed that a conversion and/or degree of hydrogenation above 95% was achieved in a single pass from the designed continuous process. This is the first continuous process for HNBR production that gives conversions above 95% till date. Optimum catalyst concentration for a given mean residence time to achieve conversions above 95% were obtained. Finally, a mechanistic model for the SM reactor performance with respect to hydrogenation of NBR was proposed and validated with the obtained experimental results. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source] Hollow fiber membrane contactor for hydrogen sulfide odor controlAICHE JOURNAL, Issue 1 2008Noureddine Boucif Abstract Hollow fiber membrane modules are extensively used as gas,liquid contactors for acid gas removal from waste gas streams. Hydrogen sulfide is an important indoor and outdoor contaminant, but, given its toxicity, a limited number of experimental results have been reported for this compound. Moreover, chemical absorption has been exclusively investigated. In this study, hydrogen sulfide odor control by absorption in water thanks to a hollow fiber contactor has been studied both experimentally and theoretically. The scrubbing of hydrogen sulfide from air gas mixture is investigated in two porous polypropylene (PP) hollow fiber modules of different contact area and fiber packing fraction. The gas phase is circulated in the lumen of the fiber bore and the liquid phase in the shell in a nonwetted mode, i.e. the membrane pores being filled with gas. The gas phase was run in countercurrent contact with the liquid phase at constant pressure. A laminar parabolic velocity has been employed to describe the convective diffusive mass transport equation which has been solved analytically and numerically. The calculated extents of hydrogen sulfide depletion reasonably compare with the generated experimental results for both membrane modules. Up to 85% of acid gas could be removed at gaseous flowrates of 200 cm3/min for the large module and removals as high as 89% at 10 cm3/min have been observed for the smaller one. The overall mass transfer coefficients calculated from the experimental data, agree satisfactorily with those generated by the mathematical model. The relation of the dimensionless Sherwood number to the Graetz number is in a good agreement with the Levêque semianalytical solution. © 2007 American Institute of Chemical Engineers AIChE J, 54: 122,131, 2008 [source] Pressure generated on a simulated oral analog by impression materials in custom trays of different designsJOURNAL OF PROSTHODONTICS, Issue 3 2002Radi Masri BDS Purpose To measure the pressure exerted by maxillary edentulous impressions composed of 3 commonly used impression materials using four different impression tray configurations. Materials and Methods The study was performed using an oral analog that simulated an edentulous maxillary arch. Three pressure transducers were imbedded in the oral analog, 1 in the mid-palate area and the other 2 in the right and left ridge (maxillary first premolar areas). Custom trays of 4 different configurations were fabricated. The 3 impression materials tested were irreversible hydrocolloid, light-body and medium-body vinyl polysiloxane, and polysulfide. A total of 128 impressions were made. The custom tray and the oral analog were mounted using a reline jig. A Satec universal testing machine was used to apply a constant pressure of 2 kg/cm2 over a period of 5 minutes on the loaded custom tray. The pressure was recorded every 10 seconds. Factorial analysis of variance and Tukey's multiple comparison test were used to analyze the results. Results A significant difference in the pressure produced using different impression materials was found (p,0.001). Irreversible hydrocolloid and medium-body vinyl polysiloxane produced a significantly higher pressure than light-body vinyl polysiloxane and polysulfide impression materials. The presence of holes and/or relief did not significantly alter the magnitude of pressure. Conclusions All impression materials produced pressure during maxillary edentulous impression making. Tray modification was not important in changing the amount of pressure produced. The impression materials used had more effect on the pressure produced during impression making on the simulated oral analog. [source] A reappraisal of sovereignty in the light of global environmental concernsLEGAL STUDIES, Issue 3 2001Duncan A French The concept of the sovereignty of the nation state is at the very core of our understanding of public international law. Nevertheless, the concept is under constant pressure to adapt to the changing global situation. This is particularly true when sovereignty is examined in the light of environmental concerns. Is the traditional paradigm still relevant in an age when so many transboundary and global environmental issues confront the international legal order? This paper suggests that whilst sovereignty remains a central pillar of international law, it is one that increasingly must be responsive to the needs and concerns of an interdependent international community. It must not be treated as a static, immovable fact, but rather as a flexible tool through which states can more effectively act in an increasingly interdependent global society. [source] Polymer Chain Collapse in Supercritical Fluids.MACROMOLECULAR SYMPOSIA, Issue 1 2009Abstract A few years ago we reported the first observation, by computer simulations, of polymer chain collapse near the lower critical solution temperature (LCST).1 In the present work, we extended the above study to understand the underlying physics of a single polymer chain collapse near LCST and its relationship to phase boundaries in the T-x plane. Effects of solvent and monomer sizes, and solvent and monomer energetic interactions are studied. Using Monte Carlo simulations, the mean end-to-end distance (R) and gyration radius (Rg) are calculated for a single chain in a supercritical fluid solvent over a broad range of densities, pressures and temperatures. In general, the chain collapses as temperature increases at constant pressure. Upon a further temperature increase, the chain expands again to approach the athermal limit provided that the temperature is sufficiently high. The collapse is related to an LCST phase boundary while the expansion represents the signature of an upper-critical solution temperature (UCST) suggesting the existence of a closed-immiscibility loop. By manipulating the strength of the energetic interactions as well as the solvent-to-monomer size ratio, the size of the size of the immiscibility loop can be fine-tuned. The relationship among size and the segment-solvent energetic interaction are correlated by a conformational parameter (,) for the first time. By monitoring the , behavior, it is possible to predict solution's phase behavior, transition zone from LCST-UCST in a closed-loop miscibility behavior. The above relationship between chain conformation to phase boundaries may be useful in understanding phase stability in compressible polymer-solvent mixtures. [source] A Roche model for uniformly rotating ringsMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 3 2009Stefan Horatschek ABSTRACT A Roche model for describing uniformly rotating rings is presented, and the results are compared with the numerical solutions to the full problem for polytropic rings. In the thin ring limit, the surfaces of constant pressure including the surface of the ring itself are given in analytical terms, even in the mass-shedding case. [source] Isotactic polypropylene solidification under pressure and high cooling rates.POLYMER ENGINEERING & SCIENCE, Issue 11 2000A master curve approach Solidification in industrial processes very often involves flow fields, high thermal gradients and high pressures: the development of a model able to describe the polymer behavior becomes complex. Recently a new equipment has been developed and improved to study the crystallization of polymers when quenched under pressure. An experimental apparatus based on a modified, special injection moulding machine has been employed. Polymer samples can be cooled at a known cooling rate up to 100°C/s and under a constant pressure up to 40 MPa. Density, Micro Hardness (MH), Wide angle X-ray diffraction (WAXD), and annealing measurements were then used to characterize the obtained sample morphology. Results on one iPP sample display a lower density and a lower density dependence on cooling rate for increasing pressure. Micro hardness confirms the same trend. A deconvolution technique of WAXD patterns is used to evaluate the final phase content of samples and to assess a crystallization kinetics behavior. A master curve approach to explain iPP behavior under pressure and high cooling rates was successfully applied on density results. On the basis of this simple model it is possible to predict the final polymer density by superposition of the effect of cooling rate and the effect of pressure in a wide range of experimental conditions. [source] Cation Leaching from the Basalt JB,1a by 2M NaCl Hydrothermal SolutionsRESOURCE GEOLOGY, Issue 2 2000Etsuo UCHIDA The experiments were carried out using standard cold-seal pressure vessels in the temperature range from 300 to 800C under the constant pressure of 1000 bars and also in the pressure range from 500 to 1000 bars at 600°C. The concentrations of Fe, Mn, Zn and Co in the hydrothermal solutions increased significantly with increasing temperature and with decreasing pressure. The thermodynamic analysis of the experimental results suggests that this is due to the formation of trichloro-complexes and also partly due to the temperature dependence of ion exchange between augite and aqueous chloride solution. The Na concentration in the aqueous solution decreases with increasing temperature and with decreasing pressure. On the other hand, the behavior of K, Ca and Mg is complex and their concentrations seem to be controlled by the coexisting minerals. Judging from the experimental results, it is concluded that the transition elements are effectively leached from the basalt under higher temperatures and lower pressures. This means that higher temperature and lower pressure conditions are preferable for the production of ore-forming hydrothermal solutions. [source] The Future of Freedom of Information in the United KingdomTHE POLITICAL QUARTERLY, Issue 1 2008BENJAMIN WORTHY This article investigates the future of Britain's Freedom of Information Act [FOIA]. It argues that the UK FOI regime faces a set of unique opportunities and challenges that may decisively impact upon the shape of FOI policy in Britain. On the one hand, the increasingly assertive FOIA appeal bodies, constant pressure from requesters, alongside the more open habits practised within the Civil Service, may serve together to ,open up' government information access. This in turn may widen and strengthen the British FOI regime. On the other hand, a series of potential obstacles may inhibit or undermine the new FOI regime. Delay and inconsistency, potential record management problems and ,gaps' within the scope of the Act, all present possible barriers to further openness. Most of all, following the two recent attempts to limit the scope of the legislation, the intentions and actions of the government will be crucial in shaping the future of FOI policy. [source] Mouse isolated perfused heart: Characteristics and cautionsCLINICAL AND EXPERIMENTAL PHARMACOLOGY AND PHYSIOLOGY, Issue 11 2003Fiona J Sutherland Summary 1.,Owing to the considerable potential for manipulating the murine genome and, as a consequence, the increasing availability of genetically modified models of cardiovascular diseases, the mouse is fast becoming a cornerstone of animal research. However, progress in the use of various murine preparations is hampered by the lack of facilities and skills for the adequate physiological assessment of genetically modified mice. 2.,We have attempted to address this problem by refining and characterizing a mouse isolated heart preparation that was originally developed for use with larger hearts. 3.,We used the isolated buffer-perfused Langendorff preparation (perfused at constant flow or constant pressure) to characterize: (i) the frequency,response characteristics; (ii) heart isolation conditions; (iii) perfusion chamber conditions; (iv) temperature,function relationships; (v) stability over extended periods of perfusion; (vi) perfusate calcium,function relationships; (vii) pressure,volume relationships; (viii) pressure,rate relationships; and (ix) flow,function relationships. [source] An approximate projection method for incompressible flowINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 10 2002David E. Stevens This paper presents an approximate projection method for incompressible flows. This method is derived from Galerkin orthogonality conditions using equal-order piecewise linear elements for both velocity and pressure, hereafter Q1Q1. By combining an approximate projection for the velocities with a variational discretization of the continuum pressure Poisson equation, one eliminates the need to filter either the velocity or pressure fields as is often needed with equal-order element formulations. This variational approach extends to multiple types of elements; examples and results for triangular and quadrilateral elements are provided. This method is related to the method of Almgren et al. (SIAM J. Sci. Comput. 2000; 22: 1139,1159) and the PISO method of Issa (J. Comput. Phys. 1985; 62: 40,65). These methods use a combination of two elliptic solves, one to reduce the divergence of the velocities and another to approximate the pressure Poisson equation. Both Q1Q1 and the method of Almgren et al. solve the second Poisson equation with a weak error tolerance to achieve more computational efficiency. A Fourier analysis of Q1Q1 shows that a consistent mass matrix has a positive effect on both accuracy and mass conservation. A numerical comparison with the widely used Q1Q0 (piecewise linear velocities, piecewise constant pressures) on a periodic test case with an analytic solution verifies this analysis. Q1Q1 is shown to have comparable accuracy as Q1Q0 and good agreement with experiment for flow over an isolated cubic obstacle and dispersion of a point source in its wake. Copyright © 2002 John Wiley & Sons, Ltd. [source] | |||||||||||||||||||||||||