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The interaction of oils with surfactant monolayers at the air-water surfaceCrichton, Donna January 1998 (has links)
No description available.
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Two-phase flow in straight pipe and 90° bendsBruce, James Masson January 1971 (has links)
A method of measuring the moan liquid velocity in an airwater two-phase flow has been successfully developed utilising an electrolyte tracer technique. Liquid holdup is derived from this velocity measurement and compared with existing correlation. Two new liquid holdup correlations are developed, one empirical the other theoretical. These are compared with the correlations and data of others over a wide range of experimental conditions with encouraging results Pressure drop has been measured for straight pipe and for six 90 degree bends, of relative radius, R/d = 1 to 6 inclusive, The straight pipe data is in agreement with the results of others, A theoretical analysis of straight pipe pressure drop is attempted and good agreement let demonstrated with the Lockhart-Martinelli correlation The data for the tends indicate that the Lockhart-Martinelli correlation will predict the predict the Pressure drop With acceptable accuracy. The applicability of a homogeneous model with a constant bend resistance coefficient is demonstrated. The total momentum flux has been measured at the pipe exit and a liquid entrainment factor is postulated in order to satisfy momentum and continuity constraints for a two-velocity flow model. Entrainment correlations are developed for slug flows and an existing correlation for annular flow is found satisfactory with modification.
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Effect of Group Delay Variations on Bit Error ProbabilityLaw, Eugene 10 1900 (has links)
International Telemetering Conference Proceedings / October 25-28, 1993 / Riviera Hotel and Convention Center, Las Vegas, Nevada / Group delay variations are a potential problem in many communication systems. This paper is slanted towards the effects of group delay variations in analog magnetic recorder/reproducer systems but the results are applicable in general. Because it is difficult to get an arbitrary group delay profile at the output of a recorder/reproducer, a method of generating arbitrary group delays for bit error probability (BEP) testing was developed. A 32-bit pattern in which all five-bit sequences appear with equal probability was selected as the test signal. The amplitude and phase of the discrete Fourier components were calculated for both non-return-to-zero-level (NRZ-L) and biphase-level (BI -L) waveforms. Filtering and group delay variations were computer generated by varying the amplitude and phase of the Fourier components. The modified signals were then programmed into an arbitrary waveform generator. Noise was added and the composite signal was applied to a bit synchronizer and bit error detector. BEPs were measured for various noise levels and group delay profiles.
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Caractérisation et commande des entraînements polyphasés en mode dégradé d’alimentation / Characterisation and control of multiphase drives under fault supply conditionsCrévits, Yvan 12 July 2010 (has links)
Le rétablissement d’un couple constant dans une machine polyphasée synchrone à aimants est décrit quand son alimentation statorique est dégradée par l’ouverture d’une ou plusieurs phases. Le chapitre un dresse un état de l’art des modélisations et des commandes des machines polyphasées dans un entraînement électromécanique, en mode normal et dégradé. Les outils de modélisation polyphasés du L2EP permettent une décomposition en machines fictives qui aboutit à une commande pour les deux modes de fonctionnement utilisant la Représentation Énergétique Macroscopique (REM). Il est enfin établi que ces méthodes de correction du couple sont inadaptées pour un grand nombre de phases. Le chapitre deux établit une modélisation causale de l’entraînement utilisable en fonctionnement normal et dégradé. La dégradation engendre des perturbations fréquentielles des courants dans les machines fictives. La correction du couple consiste alors à adapter les nombres de degrés de liberté de la commande et de l’entraînement dégradé, puis d’éliminer ces perturbations. À basse vitesse, les correcteurs PI réglés pour le fonctionnement normal sont suffisants, mais de meilleures performances à vitesse élevée utilisent des correcteurs résonants supplémentaires. Les courants perturbés non corrigés sont rejetés dans une machine fictive qui ne produit aucun couple grâce à un profil de f.e.m. approprié. La validation du modèle de la dégradation et de la méthode sur une machine heptaphasée répondant aux hypothèses sont satisfaisantes. Le bilan de la méthode de rétablissement du couple est enfin dressé pour une machine conçue pour un fonctionnement en dégradé et évoque le cas de machines moins spécifiques. / This work describes a constant torque control method in a multiphase permanent magnet synchronous machine under open-circuited fault supply conditions. The chapter one draws up a state of the art of the modellings and the controls of the multiphase machines used in electromechanical drive, in normal mode as degraded supply mode. The multiphase modelling methodologies of the L2EP laboratory applied to multiphase machines reveals the decomposition in several fictitious machines and their control are deduced from the Energetic Macroscopic Representation (EMR) for the two supply modes. It is finally established that these methods of torque correction are unsuited for a large number of phases. The chapter two establishes a causal modelling of the drive usable in normal and fault mode. Degradation generates frequency disturbances of the currents in the fictitious machines. The torque correction then consists in adapting the numbers of degrees of freedom of the command and the degraded drive, then to eliminate these disturbances. At low speed, pi-controllers tuned for the normal operating are sufficient, but better performances at high speed use additional resonant controllers. The not corrected disturbed currents are rejected into a fictitious machine that does not produce any torque thanks to a suitable emf profile. The validation of the degradation model and the methodology on a seven-phase machine answering the assumptions are satisfactory. The method assessment of torque re-establishment is finally drawn up for a machine designed for fault-mode operating and evokes the less specific case of machines.
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A long-term record of sudden phase anomalies at CollmKürschner, Dierk, Jacobi, Christoph 31 January 2017 (has links) (PDF)
Sudden phase anomalies (SPA) of low-frequency radio waves reflected from the D-region of the lower ionosphere exclusively occur during the daylight hours when rapid changes in the ionospheric reflection height take place. They lead to abrupt changes in the linear superposition of the ground wave and the sky wave and consequently in the total field strength of the received signal. Such sudden rapid reflection height changes are usually connected with shortperiod (minutes to hours) enhancements of electron density in the lower ionosphere following solar flares, which sometimes are associated with a dramatically increase of solar X-ray radiation. This additional wave radiation can penetrate into the lower ionosphere and intensify the D region ionisation. The mean level and the number of solar X-ray bursts varies with the 11-year sunspot cycle, so that statistically investigations of number and intensity of observed SPAs can give insight into solar-terrestrial connections concerning the upper atmosphere. At Collm Observatory, SPAs are recorded since several decades. These records are combined to an index characterising the monthly mean disturbance state of the ionosphere 1983-2002. / Plötzliche Phasenanomalien (engl. sudden phase anomalies, SPA) von Langwellen, die in den Tageslichtstunden von der ionosphärischen D- Region reflektiert werden, treten auf, wenn schnelle Änderungen in der Reflexionshöhe stattfinden. Sie führen zu einer abrupten Änderung der linearen Superposition von Raum- und Bodenwelle am Beobachtungspunkt und in der Folge im Feldstärkebetrag der empfangenen Signale. Solche plötzlichen schnellen Reflexionshöhenänderungen sind gewöhnlich mit einer kurzen (Minuten bis Stunden) Zunahme der Elektronendichte in der unteren Ionosphäre verbunden und nach Sonneneruptionseffekten zu beobachten, die mit einer erheblichen Erhöhung der emittierten kurzwelligen Röntgenstrahlung einhergehen. Das mittlere Strahlungsniveau und die Anzahl von Bursts variiert mit dem 11-jährigen Sonnenfleckenzyklus, so dass statistische Untersuchungen von Anzahl und Intensität der SPA- Effekte spezielle Hinweise auf solar-terrestrische, die obere Atmosphäre betreffende Verbindungen geben können. An der Außenstelle Observatorium Collm der Universität Leipzig werden SPAs seit mehreren Jahrzehnten registriert. Sie stellen eine Datenbasis für die Jahre 1983-2002 zur Untersuchung solar-terrestrischer Beziehungen dar.
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Management of the Potential Challenges in the Consolidation Phase : A Case Study of a Scandinavian CompanyAbrahamsson, Louise, Dufva, Malin January 2013 (has links)
Purpose: The purpose of this thesis is to explore how to manage the potential challenges organizations may face in the consolidation phase, and in order to achieve this, potential challenges need to be identified. Methodology: The research has been performed through an abductive case study method to the subject of change management. The empirical data was gathered from semistructured interviews conducted at an international company, Company X, primarily from the electronic commerce department. The authors used a thematic analysis inspired by Boyatzis (1998) when analyzing the data. Research Limitation: Due to the limited amount of time, the research is limited to only embrace the consolidation phase of an organizational change process. The case study includes 10 interviews from one organization, which will limit the research. The authors apply anonymity due to the company's desire; however, it is also done in order to protect the respondents from any possible harm that might derive from this study (Waldorf,2006). Theoretical Perspective: Literature covering different but highly related areas of change management, and its relation to the consolidation phase constitutes the theoretical foundation of the thesis. Results: The authors identified four potential challenges when consolidating change; communication, prioritize consolidation, policies and employee involvement. Conclusion: In order for organizations to successfully manage the four identified challenges they have to increase the flow of communication, prioritize the consolidation phase, and thereby also allocate resources, which enables the employees to consolidate changes, set up clear policies for the consolidation phase and involve the employees within all levels, in order to increase the employee motivation.
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Discharging two-phase flow through single and multiple branches: experiments and CFD modellingGuyot, Meghan 17 November 2016 (has links)
The main objectives of this study were to obtain new experimental data for conditions not previously tested for discharging two-phase flow through two 6.35 mm diameter branches with centrelines falling in an inclined plane and to assess the applicability of ANSYS CFX in modelling discharging two-phase flow through various single and multiple branch geometries. The present results are relevant to many industrial applications including headers and manifolds, multichannel heat exchangers and small breaks in horizontal pipes.
In the experimental investigation, onsets of liquid and gas entrainment data were obtained, analyzed and correlated for two different branch spacings and two different angles between the branches. For each combination of branch spacing and angle between the branches, a wide range of Froude numbers was used. Two-phase mass flow rate and quality results were also obtained and analyzed for a range of interface heights for 16 different combinations of branch spacing, inclination angle, test section pressure and pressure drop across each branch. New correlations were developed to predict the dimensionless mass flow rate and the quality. The new correlations show good agreement with the present data and with previous correlations.
Using ANSYS CFX, the inhomogeneous, free surface model was used to model discharging two-phase flow through horizontal branches with the following configurations: a single short branch of square cross-section (G1), a single long branch of square cross-section (G2), a single long branch of round cross section (G3), two round branches located one on top of the other (G4), and two round branches with their centreplane angled 30° from the horizontal. For these five geometries, results were compared with previous and present results and showed good agreement for Geometries G1, G2, G3 and G5. For Geometry G4, CFX was unable to predict results when the interface was located such that the two phases flowed through both branches simultaneously. Under these conditions, the flow phenomena were too complicated and further investigations are necessary. / February 2017
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Phase-change and carbon based materials for advanced memory and computing devicesHosseini, Peiman January 2013 (has links)
The aggressive scaling of CMOS technology, to reduce device size while also increasing device performance, has reached a point where continuing improvement is becoming increasingly problematic and alternative routes for the development of future memory and processing devices may be necessary; in this thesis the use of phase-change and carbon based materials as one such alternative route is investigated. As pointed out by Ovshinsky [1, 2] some phase-change material should be capable of non-binary arithmetic processing, multi-value logic and biological (neuromorphic) type processing. In this thesis, generic, nanometre-sized, phase-change pseudodevices were fabricated and utilised to perform various types of computational operations for the first time, including addition, subtraction, division, parallel factorization and logic using a novel resistive switching accumulator-type regime in the electrical domain. The same accumulator response is also shown to provide an electronic mimic of an integrate-and-fire type neuron. The accumulator-type regime uses fast electrical pulses to gradually crystallize a phase-change device in a finite number of steps and does not require a multilevel detection scheme. The phase-change materials used in this study were protected by a capping layer of sputtered amorphous carbon. It was found that this amorphous carbon layer also underwent a form of resistive switching when subjected to electrical pulses. In particular, sputtered amorphous carbon layers were found to switch from an initially high resistivity state to a low resistivity state when a voltage pulse was locally applied using a Conductive Atomic Force Microscope (CAFM) tip. Further experiments on amorphous carbon vertical pseudo-devices and lithographically defined planar devices showed that it has potential as a new material for Resistive Random Access Memory (ReRam) applications. The switching mechanism was identified as clustering of the sp2 hybridized carbon sites induced by Joule heating. It was not possible to reset the devices back to their initial high resistivity state presumably due to the highly conductive nature of sputtered amorphous carbon.
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Surface, Aggregation, and Phase Characterization of Microbially-Produced & Chemically-Synthesized MonorhamnolipidsEismin, Ryan J., Eismin, Ryan J. January 2017 (has links)
The purpose of this research has been to explore the native monorhamnolipid (mRL) mixture produced by Pseudomonas aeruginosa ATCC 9027, as well as newly- synthesized monorhamnolipid diastereomers (R,R)-Rha-C10-C10, (R,S)-Rha-C10-C10, (S,S)-Rha-C10-C10 and (S,R)-Rha-C10-C10, to understand their aggregation and phase behavior in aqueous solution. This work is in response to the consideration that biosurfactants offer a "greener" alternative to conventional surfactants. Relationships between chemical structure of the diastereomers and surface activity were studied using surface tension measurements. It was found that the critical aggregation concentration (CAC) values are lower for deprotonated (R,S)-Rha-C10-C10 and higher for protonated (R,S)-Rha-C10-C10 compared to the other diastereomers or the native mRL mixture. Furthermore, the 1:1:1:1 diastereomeric mixture has the overall lowest cross-sectional area for deprotonated rhamnolipids. Dynamic light scattering (DLS) was used to study the hydrodynamic radii (Rh) of the mRL aggregates and the four diastereomers in aqueous solution. In all five surfactants studied, each observed at pH 8.0 and 4.0, three aggregate populations were observed. For all deprotonated rhamnolipids the micelle, at a hydrodynamic radius of ~2 nm, was found to be in the highest abundance where the two lower abundant other population take on a lamellar aggregate structure. Data to support this were collected using fluorescence probing techniques. For the surfactants in the protonated state, pH 4.0, it was found that all form primarily lamellar structures, also confirmed using fluorescence probing. The average aggregation numbers (Nagg) of the micelles for the deprotonated native mRL mixture and the four diastereomers were studied using steady-state and time-resolved fluorescence quenching measurements. Somewhat unexpectedly, the Nagg values were observed to be a strong function of the rhamnolipid concentration for all systems. At low concentrations, pre-micellar aggregates with aggregation numbers too small for micelles were observed. A critical concentration is identified at which a critical aggregation number is defined; this is proposed to be the smallest fully-formed micelle in solution with values of ~25-30 molecules/micelle for the native mRL mixture and all four diastereomers. Thus, the aggregation properties of the native mRL mixture and the four diastereomers are generally similar at this critical concentration. However, the increase in aggregation number above this critical point varies for all the surfactants, where the (R,R)-Rha-C10-C10 diastereomer has the greatest increase in monomers with concentration and the (S,S) and (R,S) diastereomers have the lowest. The increased observed aggregation number is consistent with the computational work showing increased growth with concentration for the deprotonated rhamnolipid micelles. Furthermore, these computations have confirmed the ability of protonated rhamnolipids to form lamellar structures in solution. Fluorescence probing work was also used to study rhamnolipid phase behavior as a function of varying solution conditions, such as ionic strength, solution pH, surfactant concentration, and temperature. Steady-state fluorescence methods are utilized to probe the surfactant microenvironment using the polarity-sensitive dyes prodan and laurdan. By dissolving the dye within the rhamnolipid aggregates and observing their solvatochromic behavior, all surfactants studied are known to form more micellar aggregates at high pH and low surfactant concentration, whereas elongation of the micelle is observed at low pH and moderate to high surfactant concentration.
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Phase Shift Determination for Elastic Potential Scattering, Using the IBM 360-50 ComputerPsencik, James A. 05 1900 (has links)
The primary objective of this paper is to present a computerized method for the extraction of phase shifts from an angular distribution. This was accomplished using a least squares curve fitting routine.
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