Abstract The influence of rotating and cross flow effect on local heat transfer coefficient and flow visualization for a single confined air/water jet with jet-to-wall spacing from 5 to 11.4, jet Reynolds number from 6500 to 26000, rotational Reynolds number from 0 to 112000, curvature ratio from 150 to , ratio of crossflow massflux to jet mass flux from 0 to 2, and the heat flux from 1430 to 12890W/m2 were reported. The local heat transfer coefficient for air/water along the surface is measured and the effect of the rotation, the jet-to-wall spacing, the surface curvature, local and average Nusselt number, are presented and discussed. Furthermore, flow visualization was made in the present study. Based on the experimental result, it is found that the rotation will induce the centrifugal and coriolis force. It also shows that the heat transfer response will be decreased when the impinging direction parallel to the rotating direction, and increased when impinging direction perpendicular to the rotating direction. Crossflow effect will make Nusselt number decrease to 48% when M=2. Moreover, the roughen surface will increase the heat transfer coefficient up to 22% due to the secondary flow. The flow visualization is used to observe the transition of laminar to turbulence flow and to calculate the boundary layer thickness.

<p>Denna avhandling presenterar experimentella studier av polyelektrolytadsorption på motsatt laddade ytor, där substrat av både kiseloxid och blekt barrsulfatmassa har använts. Ett huvudsakligt syfte med denna forskning var att karaktärisera konformationen hos adsorberade skikt av katjonisk polyakrylamid (CPAM) i jämförelse med katjonisk dextran (Cdextran) och relatera denna information till inbindningskapaciteten av kolloidal kiselsyra. Ett andra syfte i denna avhandling var att studera kinetiken för sekventiell adsorption av polyamidamin epiklorhydrin (PAE) och karboxymetyl cellulosa (CMC) på massafibrer och att bestämma adsorptionsisotermer för deponering av polyelektrolyter skikt för skikt på massafibrer.</p><p>Adsorptionen av CPAM på kiseloxidytor studeras med stagnationspunkts-reflektometri och kvartskristalls-mikrogravimetri för att bestämma adsorptionskinetiken och mättnadsadsorptionens beroende av polyelektrolytens laddningstäthet, pH och NaCl koncentration. Konformationen hos adsorberade skikt av CPAM och Cdextran bestämdes både före och efter sekundär tillsats av kolloidal kiselsyra (CS) och adsorptionen av CS kvantifierades också som funktion av yttäckningen av polyelektrolyt.</p><p>Resultaten indikerar att laddningstätheten hos CPAM kontrollerar den adsorberade mängden på kiseloxidytor vid låga NaCl koncentrationer. Både adsorptionen av CPAM och Cdextran på kiseloxid visades vara effektiv i NaCl koncentrationer upp till 1 M, vilket indikerar ett signifikant bidrag av icke-jonisk interaktion mellan polyelektrolyterna och kiseloxid. Adsorptionen av CS var högre på föradsorberad CPAM än Cdextran. Konformationen hos de adsorberade skikten efter tillsats av CS sågs expandera signifikant för skikt baserade på CPAM medan skikt av Cdextran vid låga salthalter verkade återta sin konformation efter en temporär expansion.</p><p>I den andra delen av avhandlingen studerades sekventiell adsorption av PAE och CMC på massafibrer. Adsorptionsisotermer skikt för skikt på avkryllad massa visade att PAE adsorberade i större mängd än CMC, både i hänseende av massa och laddning. Adsorptionen av PAE var signifikant långsammare än CMC och adsorptionstiden till 90% av mättnadsadsorptionen bestämdes till 3 respektive 1 minut. Zetapotentialen för kryll bestämdes för adsorption av de två första polyelektrolytskikten och resultaten tydde på att kryllmaterialet omladdade inom en minut efter tillsatserna av polyelektrolyt. Reflektometriförsök inom sekventiell adsorption av PAE och CMC på kiseloxid antydde att den låga molekylviktsfraktionen av PAE störde uppbyggnaden av polyelektrolyt-multiskikten.</p> / <p>This thesis presents experimental studies of polyelectrolyte adsorption on oppositely charged surfaces, where substrates of both silica and bleached softwood kraft pulp were used. A major aim of this research was to characterise the conformation of adsorbed layers of cationic polyacrylamide (CPAM), in comparison to cationic dextran (Cdextran), and relate this information to the binding capacity of colloidal silica. A second aim in this thesis was to study the kinetics of the sequential adsorption of polyamide epichlorohydrine (PAE) and carboxymethyl cellulose (CMC) on pulp fibres, and to determine the adsorption isotherms for the layer-by-layer deposition of polyelectrolytes on pulp fibres.</p><p>The adsorption of CPAM on silica surfaces was studied using stagnation point adsorption reflectometry and quartz crystal microgravimetry to determine its adsorption kinetics as well as the dependencies of polyelectrolyte charge densities, pH, and NaCl concentration on saturation adsorption. The conformation of adsorbed layers of CPAM and Cdextran, analysed in terms of amount of water and layer thickness, was determined both before and after the secondary adsorption of colloidal silica (CS), and the adsorption of CS was also quantified as a function of the surface coverage of the polyelectrolyte.</p><p>Results indicate that the charge density of CPAM controlled the amount of the polyelectrolyte adsorbed on silica surfaces at low NaCl concentrations. The adsorption of both CPAM and Cdextran on silica was shown to be effective at up to 1 M NaCl concentrations, which indicates that non-ionic interactions between the polyelectrolytes and silica contribute significantly. CS adsorption was higher on pre-adsorbed CPAM than on Cdextran. The conformation of the adsorbed layer after CS addition was seen to expand significantly in CPAM-based layers, while the Cdextran layer appeared to restore its conformation after a temporary expansion at low salt concentrations.</p><p>In the second part of the thesis, the sequential adsorption of PAE and CMC on pulp fibres was determined using the polyelectrolyte titration technique. Layer-by-layer adsorption isotherms derived on fractionated pulp showed that PAE adsorbed in higher amounts than CMC did, both in terms of adsorbed mass and adsorbed charge. The adsorption of PAE was significantly slower compared to CMC, and the adsorption times required to reach 90% of the saturation adsorption were 3 and 1 min, respectively. The zeta potential of pulp fines was determined for the adsorption of the two first polyelectrolyte layers, and data indicated that the fines recharge within one minute after the polyelectrolyte additions. Reflectometry experiments regarding the sequential adsorption of PAE and CMC on silica indicated that the low-molecular-weight fraction of PAE disturbed the formation of polyelectrolyte multilayers.</p>

Αντικείμενο της παρούσας διδακτορικής διατριβής αποτελεί η θεωρητική και υπολογιστική προσομοίωση της πτήσης ατμοσφαιρικής καθόδου υψηλών ταχυτήτων, με ιδιαίτερη έμφαση στις υπερυπερηχητικές ταχύτητες και την αεροδυναμική και θερμοδυναμική ανάλυσή της. Η μεθοδολογία που ακολουθείται έχει ως κύριο σκοπό την πρόβλεψη του ίχνους επιστροφής υπερυπερηχητικών οχημάτων στη Γη, με δεδομένο οι ταχύτητες πτήσης να φτάνουν τα 15000 m/s (αριθμός Mach ~ 40) και οι θερμοκρασίες ανακοπής τους 15000 Κ. Στην εργασία αυτή ακολουθείται μεθοδολογική προσέγγιση και συστηματική βιβλιογραφική έρευνα στον επιστημονικοτεχνικό τομέα της αεροδυναμικής υπερθέρμανσης, που υφίστανται Υπερυπερηχητικά Οχήματα (Υ/Ο), κατά την πτήση τους στην ατμόσφαιρα. Η ανάλυση της υπερυπερηχητικής ροής, των θερμικών φορτίων και οι μέθοδοι θερμοθωράκισης των Υ/Ο αναπτύσσονται τις τελευταίες δεκαετίες και εξελίσσονται συνεχώς, αλλά μέχρι και σήμερα (2008), προκύπτουν αστοχίες, κυρίως κατά την επανείσοδό τους στην ατμόσφαιρα από το διάστημα. Για την προσομοίωση της υπερυπερηχητικής πτήσης καθόδου στην ατμόσφαιρα γίνεται μελέτη και ανάλυση των θερμοχημικών ιδιοτήτων και παραμέτρων, οι οποίες χαρακτηρίζουν τα ροϊκά πεδία στις υψηλές ταχύτητες και υψηλές θερμοκρασίες. Ο προσδιορισμός των μεταβαλλόμενων ροϊκών συνθηκών, των θερμοδυναμικών ιδιοτήτων και μεγεθών μεταφοράς θα συμβάλλει στις θεωρίες μοντελοποίησης και υπολογισμού της υψηλής θερμικής καταπόνησης, της σύστασης του υπέρθερμου αέρα και της υψηλής θερμοκρασίας του στην εξωτερική επιφάνεια του θερμομονωτικού τοιχώματος οχημάτων υψηλών ταχυτήτων, κατά την πτήση τους στην ατμόσφαιρα της Γης. Στα πλαίσια αυτά αναπτύσσονται υπολογιστικοί αλγόριθμοι προσομοίωσης και επιτυχούς πρόβλεψης του ατμοσφαιρικού ίχνους καθόδου οχημάτων υπερυπερηχητικής μεταφοράς. Τα βασικά αεροδυναμικά χαρακτηριστικά των ανωστικών οχημάτων στις υψηλές ταχύτητες υπολογίζονται με κατάλληλη προσαρμογή της κλασσικής Νευτώνειας Ροής στις υψηλές ταχύτητες και επιβεβαιώνονται με πειραματικά δεδομένα αεροδυναμικών μετρήσεων σε αεροσήραγγες υψηλών ταχυτήτων της NASA. Επιπλέον στη διατριβή ενσωματώνονται μοντέλα προσομοίωσης των ιδιοτήτων συμπεριφοράς του υπέρθερμου αέρα ως πραγματικού αερίου σε συνθήκες θερμοδυναμικής ισορροπίας σε ακραίες ροϊκές συνθήκες (υψηλές ταχύτητες, υψηλές πιέσεις και χαμηλές πυκνότητες). Πιο συγκεκριμένα γίνεται ανάλυση της μεταβαλλόμενης σύστασης και των ιδιοτήτων του αέρα (θερμοδυναμικά μεγέθη και μεγέθη μεταφοράς) στις πολύ υψηλές θερμοκρασίες του υπέρθερμου ροϊκού πεδίου. Η μελέτη αυτή θα οδηγήσει στην εξαγωγή ενός νέου μοντέλου υπολογισμού της μεταφερόμενης θερμικής ροής στην περιοχή ανακοπής υπερυπερηχητικών οχημάτων, το οποίο επιβεβαιώνεται τόσο με διεθνώς αναγνωρισμένα θερμικά μοντέλα (όπως αυτό των Fay-Riddell) όσο και με υπολογιστικές προσομοιώσεις άλλων ερευνητών. Η μεθοδολογία που ακολουθείται θα αποτελέσει τη βάση για την εξαγωγή ενός νέου θεωρητικού μοντέλου υπολογισμού της θερμοκρασίας του αέρα στην επιφάνεια του θερμοθώρακα του υπερυπερηχητικού οχήματος. Η αποτελεσματικότητα της προτεινόμενης μεθοδολογίας, με το συνδυασμό κινηματικής και αεροθερμοδυναμικής ανάλυσης σε ενιαίο υπολογιστικό αλγόριθμο, αποδεικνύεται και ενισχύεται μέσω της εφαρμογής των ανωτέρω μοντέλων προσομοίωσης σε βαλλιστικό (διαστημικός θαλαμίσκος Απόλλων) και ανωστικό (Σύστημα Διαστημικής Μεταφοράς, γνωστό ως Διαστημικό Λεωφορείο Space Shuttle) υπερυπερηχητικό όχημα. Τα αποτελέσματα της προτεινόμενης μεθόδου συγκρίνονται, αξιολογούνται και πιστοποιούνται με παρόμοια από διεθνώς αναγνωρισμένα υπολογιστικά συστήματα και πειραματικά δεδομένα μετρήσεων σε υπερυπερηχητικές αεροσήραγγες οχημάτων υψηλών ταχυτήτων. Μέσα στις επόμενες δεκαετίες, η εξέλιξη των υπερυπερηχητικών συστημάτων μεταφοράς θα είναι ραγδαία και ιδιαίτερα ελκυστική από τεχνολογικής πλευράς με ελπιδοφόρα μηνύματα για "γήϊνες" μετακινήσεις με υψηλές ταχύτητες σε σύντομους χρόνους, αλλά και πιθανές μετοικήσεις ανθρώπων-αστροναυτών σε άλλους πλανήτες του ηλιακού συστήματος. Έτσι η παρούσα διδακτορική διατριβή, αξιοποιώντας τις προόδους που έχουν συντελεστεί τα τελευταία χρόνια, εκτιμάται ότι συμβάλλει ουσιαστικά στο ακόμα υπό εξέλιξη – για τα ελληνικά δεδομένα πρωτόγνωρο – επιστημονικό πεδίο της Υπερυπερηχητικής Αεροθερμοδυναμικής, και στην ανάπτυξη μεθοδολογίας για τον αεροθερμοδυναμικό σχεδιασμό υπερυπερηχητικών οχημάτων. Το προτεινόμενο σύνθετο μοντέλο κινηματικής και θερμοδυναμικής υπολογιστικής ανάλυσης και η μεθοδολογία που ακολουθείται έχει ισχύ και εφαρμογή στην πλειονότητα των περιπτώσεων των υπερυπερηχητικών πτήσεων στη γήινη και, με κατάλληλες προσαρμογές, σε οποιαδήποτε πλανητική ατμόσφαιρα. Βεβαίως, η προτεινόμενη μεθοδολογία έχει περιθώρια εξέλιξης και ανάπτυξης, προκειμένου να βελτιωθεί η απόδοσή της με την εισαγωγή και νέων στοιχείων, αλλά και να διευρυνθεί το φάσμα των δυνατών εφαρμογών της. / The object of the present doctoral thesis constitutes the theoretical and calculating simulation of high-speed atmospheric flightmotion, with particular emphasis in hypersonic speeds and aerodynamic and thermodynamic analysis. The methodology that is followed has as main aim the prediction of return flight trace of hypersonic vehicles in Earth’s ground, assuming the speeds of flight to reach the 15000 m/s (Mach number ~ 40) and stagnation temperatures the 15000 K. In this work are followed methodological approach and systematic bibliographic research in the scientific field of aerodynamic overheating that suffers Hypersonic Vehicles(H/V) at their flight in Earth’s atmosphere. The analysis of hypersonic flow, thermal loads and new methods for thermal protection systems of H/V are developed the last decades and are evolved continuously, but until today (2008) resulting failures mainly at their reentry in atmosphere from the interval. For the simulation of the atmospheric hypersonic flight motion become study and analysis of thermodynamic properties and parameters, that characterize the flow fields in high speeds and high temperatures. The determination of altered flow conditions, thermodynamic properties and transport magnitudes will contribute in the theories of modelling and high thermal strain calculations, in the constitution of overheating air and it’s high temperature determination in the external surface of heat insulation wall of high-speed vehicles at their flight in Earth’s atmosphere. In this work are developed calculating algorithms of simulation for the successful prediction of atmospheric flight motion of hypersonic transport vehicles. The basic aerodynamic characteristics of lifting vehicles in high speeds are calculated with suitable adaptation of classic Newtonian Flow in high speeds and are confirmed with experimental data of aerodynamic measurements in high speed wind-tunnels of NASA. Moreover in this thesis are incorporated models for the simulation of properties of overheating air behaviour as real gas in thermodynamic balance in extreme flow conditions (high speeds, high pressures and low densities). Particularly becomes analysis of the altered constitution and properties of air (thermodynamic magnitudes and transport magnitudes) in very high temperatures on hypersonic flow field. This study will lead to the export of a new model for the transported thermal stagnation region calculations of hypersonic vehicles, which is confirmed so much with internationally recognized thermal models (as that of Fay-Riddell) and with calculating simulations of other researchers. The methodology that is followed will constitute the base for the export of a new theoretical model for high temperature air calculations in thermal protection systems surface of hypersonic vehicles. The effectiveness of proposed methodology, with the combination kinematic and aerothermodynamics analysis in united calculating algorithm, is proved and confirmed via the application of above simulation models on ballistic (Apollo Command Module) and lifting (Space Transportation System, known as Space Shuttle) hypersonic vehicles. The results of proposed method are compared, evaluated and certified with similarly by internationally recognized calculating systems and experimental data of measurements in hypersonic wind-tunnels for high speed vehicles. In the next decades, the development of hypersonic transportation systems will be rapid and particularly attractive from technological side with hopeful messages for “earthy” transfers with high speeds in short times, but also likely persons-astronaut missions in other planets of solar system. Thus the present doctoral thesis, developing the progress that has taken place in the past few years, is appreciated that it contributes substantially in still under development - for the Greek data unusual - scientific field of Hypersonic Aerothermodynamics, and in the growth of methodology for the aerothermodynamic construction of hypersonic vehicles. The proposed complex model of kinematic and thermodynamic calculating analysis and it’s methodology that is followed have influence and application in the majority of cases of hypersonic flights in earthy and, with properly adaptations, in anyone planetary atmosphere. Of course, the proposed methodology has margins of development and growth in order to improve her efficiency with the import of also new elements and also extended the spectrum of her possible applications.

A novel combustor design, referred to as the Stagnation Point Reverse-Flow (SPRF) combustor, was recently developed that is able to operate stably at very lean fuel-air mixtures and with low NOx emissions even when the fuel and air are not premixed before entering the combustor. The primary objective of this work is to elucidate the underlying physics behind the excellent stability and emissions performance of the SPRF combustor. The approach is to experimentally characterize velocities, species mixing, heat release and flame structure in an atmospheric pressure SPRF combustor with the help of various optical diagnostic techniques: OH PLIF, chemiluminescence imaging, PIV and Spontaneous Raman Scattering. Results indicate that the combustor is primarily stabilized in a region downstream of the injector that is characterized by low average velocities and high turbulence levels; this is also the region where most of the heat release occurs. High turbulence levels in the shear layer lead to increased product entrainment levels, elevating the reaction rates and thereby enhancing the combustor stability. The effect of product entrainment on chemical timescales and the flame structure is illustrated with simple reactor models. Although reactants are found to burn in a highly preheated (1300 K) and turbulent environment due to mixing with hot product gases, the residence times are sufficiently long compared to the ignition timescales such that the reactants do not autoignite. Turbulent flame structure analysis indicates that the flame is primarily in the thin reaction zones regime throughout the combustor, and it tends to become more flamelet like with increasing distance from the injector. Fuel-air mixing measurements in case of non-premixed operation indicate that the fuel is shielded from hot products until it is fully mixed with air, providing nearly premixed performance without the safety issues associated with premixing. The reduction in NOx emissions in the SPRF combustor are primarily due to its ability to stably operate under ultra lean (and nearly premixed) condition within the combustor. Further, to extend the usefulness of this combustor configuration to various applications, combustor geometry scaling rules were developed with the help of simplified coaxial and opposed jet models.

Va., George Mason Univ., Dep. of Economics, Diss.--Fairfax, 2003. / Kopie, ersch. im Verl. UMI, Ann Arbor, Mich. - Enth. 3 Beitr.

This study explores the possibility that cheep credit, provided to firms when profit opportunities on real investments are low, and when opportunities of financial investments are present, will loose some of it’s stimulus effect due to a crowding out effect of financial investments on real investments. Analyzing the changes in debt, and it’s channels of use during the recession of the covid19 pandemic, between firms with a history of stock buybacks, and firms without such a history, the study finds a significantly higher increase in debt for firms with a history of doing stock buybacks. The study concludes that this effect is due to firms finding financial uses of more cheap credit, which does crowd out real investments.

No description available.

This dissertation of limited scope traces the attempts by Gorbachev (1985-1991) to reform an economic, political and social system which was in a state of terminal decline. The origins of its demise, it is argued, lay in the ossified command economy inherited from Stalin. The enormous damage inflicted on Soviet agriculture during collectivisation in the 1930s~ when millions of productive peasants died, proved to be a fatal blow to that sector. Tlms, Gorbachev followed a two-fold strategy ofrefonn. Glasnost (openness) was introduced to allow constructive debate on economic and social matters. Despite a hesitant beginning, the right to criticise allowed the emergence of more radical campaigners, such as Yeltsin who demanded greater democracy. Significantly, the revival of ethnic nationalist demands in the republics led to disintegration. Perestroika (restructuring) was intended to modernise and boost living standards. The economy faltered but the market was not yet in place / History / M.A. (History)

The treatment of owner-occupied housing (OOH) is probably the most important unresolved issue in inflation measurement. How -- and whether -- it is included in the Consumer Price Index (CPI) affects inflation expectations, the measured level of real interest rates, and the behavior of governments, central banks and market participants. We show that none of the existing treatments of OOH are fit for purpose. Hence we propose a new simplified user cost method with better properties. Using a micro-level dataset, we then compare the empirical behavior of eight different treatments of OOH. Our preferred user cost approach pushes up the CPI during housing booms (by 2 percentage points or more). Our findings relate to the following important debates in macroeconomics: the behavior of the Phillips curve in the US during the global financial crisis, and the response of monetary policy to housing booms, secular stagnation, and globalization. / Series: Department of Economics Working Paper Series

O trabalho procura compreender o processo de estagnação urbana do distrito do Pari, um fenômeno que ocorre em determinadas áreas da metrópole como uma forma de criarem fronteiras de expansão ao capital imobiliário. Para compreender como esse processo ocorreu no distrito do Pari foi analisada a história da formação geográfica do bairro, a história social e demográfica, a história da atividade imobiliária e econômica e a história da Política pública do espaço. O processo ocorrido no Pari mostrou que o distrito concentra diversas atividades, usos, estrutura e população que, na verdade, podem ser considerados estagnados. Mas, mais importante do que a estagnação, é o fato que a sociedade considera essas atividades, usos, estrutura e população com desprezo e isso é uma forma ideológica que traz este conceito, uma vez que é associado com as classes mais pobres. / This thesis seeks the understanding the process of urban stagnation that took place in the District of Pari, São Paulo, Brazil. Urban stagnation is understood as a process which occurs in certain areas of a metropolis as a means of establishing barriers for the expansion of real estate capital. For the purpose of understanding how this process has occurred in that district it is analyzed its demographic, geographic, urban-spatial, economic, social and governmental history. Similarities and differences between different central districts of São Paulo are studied in order to understand the process Pari has undergone. It was shown that the district concentrates several activities, land uses, structures and population which, in fact, may be considered stagnant, but more important than that is the fact that society as a whole looks upon such activities, population, structures and land uses, with scorn and that stagnation is an ideological way of conveying that contempt, since they are associated with lower social classes.