The nature of dislocation motion in quasicrystals

Calculations in a hydrodynamic model of quasicrystal dynamics show that dislocation motion in these systems is impeded by a drag far greater than that in crystals.

Accelerometer-Based Force Balance for High Enthalpy Facilities

A single component accelerometer-based force balance is developed, calibrated, and used for high enthalpy applications. Functionality of this force balance, for such applications, is demonstrated for the first time during high enthalpy tests in a newly established free piston-driven shock tunnel, HST3, using a 60 degrees apex angle blunt cone model at 0 degrees angle of incidence. Usefulness of this force balance is also confirmed, for much complicated high enthalpy flow situations, during the drag reduction studies with counterflow supersonic jet from the stagnation point.

Gadamers hermeneutik och naturvetenskaplig experimentering

I detta arbete undersöks naturvetenskaplig kunskap ur ett filosofiskt perspektiv. Arbetets centrala ämne är det naturvetenskapliga experimenterandets praktiska aspekter och deras anknytningar till den teoretiska naturvetenskapliga kunskapen. Ämnet behandlas med hjälp av Hans-Georg Gadamers hermeneutiska filosofi i boken Wahrheit und Methode. Gadamers utgångspunkt i denna bok är att hermeneutiken beskriver vad som händer i texttolkning då en tolkare förstår en skriven text, men han antyder också att hermeneutiken har vidare tillämpningsområden, till och med att den universalt beskriver alla former av mänsklig förståelse. Syftet med detta arbete är att undersöka hur Gadamers hermeneutik kan tillämpas på naturvetenskaplig förståelse och vilka ändringar man då måste införliva i hermeneutiken samt att skissa grunddragen för en hermeneutisk modell av naturvetenskaplig kunskap. I arbetet presenteras först de centrala elementen i Gadamers hermeneutiska filosofi, speciellt föromdömens positiva inverkan på tolkandet och den verkningshistoriska effekten bakom varje tolkning. Sedan diskuteras bristerna i Gadamers argument för hermeneutikens universalitet, speciellt hans starka betoning av språket som grunden för all förståelse. Om Gadamers hermeneutik skall kunna tillämpas på naturvetenskapens område måste även observationer kunna vara föremål för tolkning. De dominanta trenderna i vetenskapsfilosofin då Gadamer skrev Wahrheit und Methode är en förklaring till att Gadamer starkt förbinder sig till textförståelsen och oftast diskuterar den naturvetenskapliga kunskapen endast som en negativ motpol till den humanvetenskapliga. Vetenskapsfilosofins utveckling efter Wahrheit und Methode, speciellt det faktum att fullständig objektivitet inte mera anses vara ett realistiskt ideal, höjer förväntningarna på hermeneutikens värde för naturvetenskapernas filosofi. Till följande diskuteras tre bidrag till naturvetenskapernas filosofi som är speciellt värdefulla för en hermeneutiken. Den första av dessa är Sylvain Brombergers analys av ovisshet i vetenskapliga undersökningar. Bromberger hävdar att vetenskaplig forskning riktas mot frågor vars svar forskaren inte kan föreställa sig på förhand. Brombergers analys tyder på att det finns en hermeneutisk dialektik av frågor och svar i naturvetenskapliga experiment där forskaren strävar till att göra observationer för att besvara sina frågor. Det andra bidraget är Michael Polanyis studie av den praktiska och personliga kunskapens betydelse för all vetenskaplig forskning. Här är speciellt det vetenskapliga språkets utveckling i samband med experimentering av intresse. Det tredje bidraget är Robert Creases studie av experimentella observationer som visar att observationstolkning innefattar många element som kan förknippas med hermeneutiken. Analysen av de tre ovannämnda studierna leder till följande slutsatser. Den naturvetenskapliga forskningens hermeneutiska element förväntas vara starkt framför allt i experimentell forskning där forskaren utreder nya frågor i en kontinuerlig dialog av tekniskt prövande, praktisk identifiering och språklig beskrivning av nya fenomen. Speciellt beaktansvärd är skillnaden mellan verifierande och upptäckande naturvetenskapliga undersökningar. Tidigare resultat kan verifieras med hjälp av mätningar som specificeras på förhand, men ingen kan på förhand specificera de tekniska och språkliga steg som krävs för ett framgångsrikt upptäckande experiment. Experimentella upptäckter kräver därför en praktisk kunskap som inte kan reduceras till ren teori eller metodologi. Denna praktiska kunskap kan beskrivas med hjälp av Gadamers hermeneutik. Till sist diskuteras vissa grundläggande drag som kan sägas vara karakteristiska för en hermeneutisk modell av naturvetenskaplig kunskap. Speciellt den naturvetenskapliga kunskapens historiska natur, fördomarnas betydelse i naturvetenskaplig forskning samt vikten av forskarens personliga perspektiv i den naturvetenskapliga observationen är viktiga stöttestenar som gör att den hermeneutiska naturvetenskapsmodellen skiljer sig betydligt från modeller som betonar naturvetenskapernas objektivitet. Men det hermeneutiska perspektivet utesluter inte nödvändigtvis andra perspektiv. Dess huvudsakliga nytta är att den tillåter oss att undersöka sidor av naturvetenskaplig kunskap som objektivitetsbetonande modeller lämnar alltför mycket i skymundan. Till dessa hör speciellt det praktiska arbetet i naturvetenskaplig experimentering.

När finanskrisen slog till i Finland

Avhandlingen kartlägger användandet av metaforer i ekonomijournalistik då den globala ekonomikrisen anlände till Finland under hösten 2008. Syftet med den här kvalitativa forskningen är inte bara att presentera olika metaforer utan också påvisa att metaforer bildar större helheter. Med hjälp av en metaforanalys redogör denna studie vilka metaforer förekom i ekonominyheter och hur de reflekterar ekonomikrisen och den verklighet vi lever i. Forskningen presenterar också deltagarna i ekonomikrisdiskussionen och diskuterar deras position i samhället i förhållande till maktfrågan. Den tredelning av metaforer som Lakoff och Johnson presenterar i sin bok Metaphors we live by (1980) ligger till grund för den här undersökningen. I den här forskningen delas metaforer enligt den kognitiva metaforteorin till tre större grupper; strukturella, ontologiska och orientationella metaforer. Användning av metaforer i undersökta artiklar var rikligt och den största gruppen utgjordes av strukturella metaforer. Mest förekom krigs-, spel-, sjukdoms- och naturmetaforer. Den största gruppen var krigsmetaforer vilka tillsammans med spelmetaforer användes mest i början av rapporteringen om den ekonomiska recessionen. Färg- och religionsmetaforer förekom också om än i ett mindre antal. Ontologiska metaforer förekom i form av personifiering. Bland annat var marknad och börs de fenomen som fick personliga drag då de var i panik, reagerade föll eller sov. Av de orientationella metaforer var horisontella upp-ner -metaforer vanligare än de vertikala fram-bak -metaforerna. Denna studie visar att de metaforer som journalisterna använde i sina artiklar bildade större helheter. Med hjälp av dessa metaforer ville man förtydliga att den ekonomiska recessionen ansågs vara en överraskning, speciellt för makthavare och ekonomiexperter. Krisen slog till i Finland överraskande och med en mycket stark volym och osäkerheten om framtiden förstärktes med metaforanvändandet. Avhandlingen har också ett samhälleligt perspektiv. I den undersöks deltagarna i ekonomikrisdiskussionen samt deras position i samhället. Forskningsresultatet är relaterat till maktfrågan med stöd av maktforskarna Michel Foucault och Ilkka Ruostetsaari. I dagens samhälle och globala värld har ekonomins makt bara ökat. Analysen av det empiriska materialet visar att näringslivet dominerade debatten och därmed hör det till makteliten. Alla diskussionsdeltagare använder metaforer, dock används de kraftigaste metaforerna av journalister.

Breakage and coalescence of drops in turbulent stirred dispersions

The various existing models for predicting the maximum stable drop diameterd max in turbulent stirred dispersions have been reviewed. Variations in the basic framework dictated by additional complexities such as the presence of drag reducing agents in the continuous phase, or viscoelasticity of the dispersed phase have been outlined. Drop breakage in the presence of surfactants in the continuous phase has also been analysed. Finally, the various approaches to obtaining expressions for the breakage and coalescence frequencies, needed to solve the population balance equation for the number density function of the dispersed phase droplets, have been discussed.

Blade manipulators in turbulent channel flow

We report here the results of a series of careful experiments in turbulent channel flow, using various configurations of blade manipulators suggested as optimal in earlier boundary layer studies. The mass flow in the channel could be held constant to better than 0.1%, and the uncertainties in pressure loss measurements were less than 0.1 mm of water; it was therefore possible to make accurate estimates of the global effects of blade manipulation of a kind that are difficult in boundary layer flows. The flow was fully developed at the station where the blades were mounted, and always relaxed to the same state sufficiently far downstream. It is found that, for a given mass flow, the pressure drop to any station downstream is always higher in the manipulated than in the unmanipulated flow, demonstrating that none of the blade manipulators tried reduces net duct losses. However the net increase in duct losses is less than the drag of the blade even in laminar flow, showing that there is a net reduction in the total skin friction drag experienced by the duct, but this relief is only about 20% of the manipulator drag at most.

Effect of Turbulence on Emerging Magnetic Flux Tubes in the Convection Zone

Working under the hypothesis that magnetic flux in the sun is generated at the bottom of the convection zone, Choudhuri and Gilman (1987; Astrophys. J. 316, 788) found that a magnetic flux tube symmetric around the rotation axis, when released at the bottom of the convection zone, gets deflected by the Coriolis force and tends to move parallel to the rotation axis as it rises in the convection zone. As a result, all the flux emerges at rather high latitudes and the flux observed at the typical sunspot latitudes remains unexplained. Choudhuri (1989; Solar Physics, in press) finds that non-axisymmetric perturbations too cannot subdue the Coriolis force. In this paper, we no longer treat the convection zone to be passive as in the previous papers, but we consider the role of turbulence in the convection zone in inhibiting the Coriolis force. The interaction of the flux tubes with the turbulence is treated in a phenomenological way as follows: (1) Large scale turbulence on the scale of giant cells can physically drag the tubes outwards, thus pulling the flux towards lower latitudes by dominating over the Coriolis force. (2) Small scale turbulence of the size of the tubes can exchange angular momentum with the tube, thus suppressing the growth of the Coriolis force and making the tubes emerge at lower latitudes. Numerical simulations show that the giant cells can drag the tubes and make them emerge at lower latitufes only if the velocities within the giant cells are unrealistically large of if the radii of the flux tubes are as small as 10 km. However, small scale turbulence can successfully suppress the growth of the Coriolis force if the tubes have radii smaller than about 300 km which may not be unreasonable. Such flux tubes can then emerge at low latitudes where sunspots are seen.

Out-of-equilibrium microrheology using optical tweezers to probe directional viscoelastic properties under shear

Many wormlike micellar systems exhibit appreciable shear thinning due to shear-induced alignment. As the micelles get aligned introducing directionality in the system, the viscoelastic properties are no longer expected to be isotropic. An optical-tweezers-based active microrheology technique enables us to probe the out-of-equilibrium rheological properties of a wormlike micellar system simultaneously along two orthogonal directions-parallel to the applied shear, as well as perpendicular to it. While the displacements of a trapped bead in response to active drag force carry signature of conventional shear thinning, its spontaneous position fluctuations along the perpendicular direction manifest an orthogonal shear thickening, an effect hitherto unobserved. Copyright (C) EPLA, 2010

Can equipartition fields produce the tilts of bipolar magnetic regions?

The effect of turbulence on the nonaxisymmetric flux rings of equipartition field strength in bipolar magnetic regions is studied on the basis of the small-scale momentum exchange mechanism and the giant cell drag combined with the Kelvin-Helmholtz drag mechanism. It is shown that the giant cell drag and small-scale momentum exchange mechanism can make equipartition flux loops emerge at low latitudes, in addition to making them exhibit the observed tilts. However, the sizes of the flux tubes have to be restricted to a couple of hundred kilometers. An ad hoc constraint on the footpoints of the flux loops is introduced by not letting them move in the phi direction, and it is found that equipartition fields of any size can be made to emerge at sunspot latitudes with the observed tilts by suitably adjusting the footpoint separations.

Flap‐Lag Damping in Hover and Forward Flight with a Three‐Dimensional Wake

Prediction of lag damping is difficult owing to the delicate balance of drag, induced drag and Coriolis forces in the in‐plane direction. Moreover, induced drag” is sensitive to dynamic wake, bath shed and trailing components, and thus its prediction requires adequate unsteady‐wake representation. Accordingly, rigid‐blade flap‐lag equations are coupled with a three‐dimensional finite‐state wake model; three isolatcd rotor canfigurations with three, four and five blades are treated over a range of thrust levels, tack numbers, lag frequencies and advance ratios. The investigation includes convergence characteristics of damping with respect to the number of radial shape functions and harmonics of the wake model for multiblade modes of low frequency (< 1/ rev.) to high frequency (> 1/rev.). Predicted flap and lag damping levels are then compared with similar predictions with 1) rigid wake (no unsteady induced now), 2) Loewy lift deficiency and 3) dynamic inflow. The coverage also includes correlations with the measured lag regressive‐mode damping in hover and forward flight and comparisons with similar correlations with dynamic inflow. Lag‐damping predictions with the dynamic wake model are consistently higher than the predictions with the dynamic inflow model; even for the low frequency lag regressive mode, the number of wake harmonics should at least be equal to twice the number of blades.

Effect of uncertainty on helicopter performance predictions

The effect of uncertainties on performance predictions of a helicopter is studied in this article. The aeroelastic parameters such as the air density, blade profile drag coefficient, main rotor angular velocity, main rotor radius, and blade chord are considered as uncertain variables. The propagation of these uncertainties in the performance parameters such as thrust coefficient, figure of merit, induced velocity, and power required are studied using Monte Carlo simulation and the first-order reliability method. The Rankine-Froude momentum theory is used for performance prediction in hover, axial climb, and forward flight. The propagation of uncertainty causes large deviations from the baseline deterministic predictions, which undoubtedly affect both the achievable performance and the safety of the helicopter. The numerical results in this article provide useful bounds on helicopter power requirements.

Wind loading over the top portions of tall stacks with and without external landing platforms

The variation of the drag force near the top portions of tall stacks with and without external landing platforms, and with the exit open and closed, has been examined by model studies in a wind tunnel at Reynolds numbers of about 10(5). Pressure measurements on three models of different height to diameter ratios have been supplemented by flow visualisation studies. Observations confirm that when there is no platform, significant load enhancement over the top three to four diameters occurs, due to the high suction caused by the sharp separation of the flow over the top from the rim, in the aft regions of the stack. The enhanced loading is found to be greater if the exit is closed. A platform at the top, of less than twice the exit diameter, further increases the drag force near the top, but a still larger platform at the top, of about three times the exit diameter, decreases the drag force to values less than those much further below, effectively nullifying the enhanced drag force. It was found that such a reduction of the enhanced drag force in the top regions can also be achieved by a smaller platform of 1.1 to 1.3 times the local diameter, located at about three to five diameters below the top.

Tunable Brownian vortex at the interface

A general kind of Brownian vortices is demonstrated by applying an external nonconservative force field to a colloidal particle bound by a conservative optical trapping force at a liquid-air interface. As the liquid medium is translated at a constant velocity with the bead trapped at the interface, the drag force near the surface provides enough rotational component to bias the particle's thermal fluctuations in a circulatory motion. The interplay between the thermal fluctuations and the advection of the bead in constituting the vortex motions is studied, and we infer that the angular velocity of the circulatory motion offers a comparative measure of the interface fluctuations.

Suboptimal Midcourse Guidance of Interceptors for High-Speed Targets with Alignment Angle Constraint

Using the recently developed computationally efficient model predictive static programming and a closely related model predictive spread control concept, two nonlinear suboptimal midcourse guidance laws are presented in this paper for interceptors engaging against incoming high-speed ballistic missiles. The guidance laws are primarily based on nonlinear optimal control theory, and hence imbed effective trajectory optimization concepts into the guidance laws. Apart from being energy efficient by minimizing the control usage throughout the trajectory (minimum control usage leads to minimum turning, and hence leads to minimum induced drag), both of these laws enforce desired alignment constraints in both elevation and azimuth in a hard-constraint sense. This good alignment during midcourse is expected to enhance the effectiveness of the terminal guidance substantially. Both point mass as well as six-degree-of-freedom simulation results (with a realistic inner-loop autopilot based on dynamic inversion) are presented in this paper, which clearly shows the effectiveness of the proposed guidance laws. It has also been observed that, even with different perturbations of missile parameters, the performance of guidance is satisfactory. A comparison study, with the vector explicit guidance scheme proposed earlier in the literature, also shows that the newly proposed model-predictive-static-programming-based and model-predictive-spread-control-based guidance schemes lead to lesser lateral acceleration demand and lesser velocity loss during engagement.

Nonequilibrium stationary states of a particle in a gravitational field driven by a vibrating surface

Stationary velocity distribution functions are determined for a particle in a gravitational field driven by a vibrating surface in the limit of small dissipation. It is found that the form of the distribution function is sensitive to the mechanism of energy dissipation, inelastic collisions or viscous drag, and also to the form of the amplitude function of the vibrating surface. The velocity distributions obtained analytically are found to be in excellent agreement with the results of computer simulations in the limit of low dissipation. [S0031-9007(99)08898-5].