Hypersonic stagnation‐point boundary layers with massive blowing in the presence of a magnetic field

The effect of massive blowing rates on the steady laminar hypersonic boundary‐layer flow of an electrically conducting fluid in the stagnation region of an axisymmetric body with an applied magnetic field has been studied. The governing equations have been solved numerically by combining the implicit finite‐difference scheme with the quasi‐linearization technique. It is observed that the effect of massive blowing rates is to remove the viscous layer away from the boundary, whereas the effect of the magnetic field is just the opposite. It is also found that the velocity overshoot increases with blowing rates and also with magnetic field. The effect of the variation of the density‐viscosity product across the boundary layer is strong only when the blowing rate is small, but for the massive blowing rate the effect is negligible.

Field-tunable stochasticity in the magnetization reversal of a cylindrical nanomagnet

The nature of magnetization reversal in an isolated cylindrical nanomagnet has been studied employing time-resolved magnetoresistance measurement. We find that the reversal mode is highly stochastic, occurring either by multimode or single-step switching. Intriguingly, the stochasticity was found to depend on the alignment of the driving magnetic field to the long axis of the nanowires, where predominantly multimode switching gives way to single-step switching behavior as the field direction is rotated from parallel to transverse with respect to the nanowire axis.

Cross-field gas breakdown in a coaxial cylinder geometry

Sparking potentials in a coaxial cylinder geometry in oxygen and dry air were measured in crossed electric and magnetic fields. From the data effective collision frequencies were calculated using the equivalent pressure concept. It is shown that the equivalent pressure concept holds good for deriving the effective collision frequencies in non-uniform electric fields.

Solitons of Coupled Scalar Field Theories in Two Dimensions

This work offers a method for finding some exact soliton solutions to coupled relativistic scalar field theories in 1+1 dimensions. The method can yield static solutions as well as quasistatic "charged" solutions for a variety of Lagrangians. Explicit solutions are derived as examples. A particularly interesting class of solutions is nontopological without being either charged or time dependent.

Field intercomparison of four methane gas analysers suitable for eddy covariance flux measurements

Eddy covariance (EC)-flux measurement technique is based on measurement of turbulent motions of air with accurate and fast measurement devices. For instance, in order to measure methane flux a fast methane gas analyser is needed which measures methane concentration at least ten times in a second in addition to a sonic anemometer, which measures the three wind components with the same sampling interval. Previously measurement of methane flux was almost impossible to carry out with EC-technique due to lack of fast enough gas analysers. However during the last decade new instruments have been developed and thus methane EC-flux measurements have become more common. Performance of four methane gas analysers suitable for eddy covariance measurements are assessed in this thesis. The assessment and comparison was performed by analysing EC-data obtained during summer 2010 (1.4.-26.10.) at Siikaneva fen. The four participating methane gas analysers are TGA-100A (Campbell Scientific Inc., USA), RMT-200 (Los Gatos Research, USA), G1301-f (Picarro Inc., USA) and Prototype-7700 (LI-COR Biosciences, USA). RMT-200 functioned most reliably throughout the measurement campaign and the corresponding methane flux data had the smallest random error. In addition, methane fluxes calculated from data obtained from G1301-f and RMT-200 agree remarkably well throughout the measurement campaign. The calculated cospectra and power spectra agree well with corresponding temperature spectra. Prototype-7700 functioned only slightly over one month in the beginning of the measurement campaign and thus its accuracy and long-term performance is difficult to assess.

Estimation Of Charge Transport Parameters And Equivalent Circuit For Poly Alkyl Thiophene Field-Effect Transistors

The small signal ac response is measured across the source-drain terminals of organic field-effect transistors (OFET) under dc bias to obtain the equivalent circuit parameters of poly(2,5-bis(3-tetradecylthiophen-2-yl)thieno[3,2-b]thiophene) (PBTTT) and poly(3-hexyl thiophene) (P3HT) based devices. The numerically simulated response based on these parameters is in good agreement with the experimental data for PBTTT-FET except at low frequencies, while the P3HT-FET data show significant deviations. This indicates that the interface with the metal electrode is rather complex for the latter, involving additional circuit elements arising from contact impedance or charge injection processes. Such an investigation can help in identifying the operational bottlenecks and to improve the performance of OFETs.

A field-consistent and variationally correct representation of transverse shear strains in the nine-noded plate element

We present a biquadratic Lagrangian plate bending element with consistent fields for the constrained transverse shear strain functions. A technique involving expansion of the strain interpolations in terms of Legendre polynomials is used to redistribute the kinematically derived shear strain fields so that the field-consistent forms (i.e. avoiding locking) are also variationally correct (i.e. do not violate the variational norms). Also, a rational method of isoparametric Jacobian transformation is incorporated so that the constrained covariant shear strain fields are always consistent in whatever general quadrilateral form the element may take. Finally the element is compared with another formulation which was recently published. The element is subjected to several robust bench mark tests and is found to pass all the tests efficiently.

Päivikin sadusta Metsolan lapsiin : Aili Somersalon lastenkirjojen nimistö 1910-luvulta 1950-luvulle

Tutkielmassa selvitetään, millaiset piirteet ovat tyypillisiä Aili Somersalon kirjoittamien satuteosten nimistölle. Tarkasteltavana on 274 nimeä, jotka on poimittu kymmenestä Somersalon vuosina 1918 1951 julkaistusta lastenkirjasta. Nimiaineisto on jaettu kuuteen eri kategoriaan: ihmisten nimiin, eläinten nimiin, kuvitteellisiin nimiin, fantastisten satuolentojen nimiin, paikannimiin ja lainanimiin. Tutkielmassa keskitytään nimien rakenteellisten piirteiden ja funktioiden erittelyyn. Tämän lisäksi pohditaan, kuinka nimet ovat motivoituneet ja muuttuuko kirjailijan nimenanto vuosikymmenten aikana. Tutkielmassa sivutaan myös nimen ja nimityksen välistä rajaa sekä kyseenalaistetaan iso alkukirjain proprin tunnusmerkkinä kaunokirjallisessa kontekstissa. Aineiston nimille tyypillisiä rakenteellisia piirteitä ovat yksinimisyys, yhdysnimirakenne ja nimien kaksiosaisuus, appellatiivisuus ja adjektiivien esiintyminen nimenä tai nimenosana, johtimien käyttö sekä erilaiset äänteelliset piirteet. Nimen perustehtävän, identifioinnin, lisäksi aineiston nimet pyrkivät kuvailemaan, luokittelemaan ja lokalisoimaan tarkoitteitaan. Vuosikymmenten aikana teosten nimimäärä kasvaa maltillisesti. Teosten sisältämissä konventionaalisissa nimissä näkyy kulloisenkin vuosikymmenen nimimuoti. Merkillepantavaa on myös teoksissa esiintyvä hahmojen samanimisyys. Mielenkiintoisen lisän analyysiin tuovat aineiston lainanimet, jotka ovat peräisin paitsi universaalista satuperinteestä, myös suomalaisesta kansanmytologiasta ja Kalevalasta. Kansallisromanttisuus näkyy myös teoksiin valikoituneissa konventionaalisissa nimissä, joista suuri osa on omakielisiä. Kirjailija on lainannut teoksiinsa nimiä myös omasta elämänpiiristään. Somersalon nimenmuodostus nojaa vahvasti leksikkoon. Aineiston nimien ja nimitysten välinen raja ei ole yksiselitteinen, ja aineiston voikin luonnehtia koostuvan nimityksen kaltaisista nimistä ja nimen kaltaisista nimityksistä. Kaiken kaikkiaan aineiston nimet ovat hyvin informatiivisia, tarkoitteen fyysisiä tai mentaalisia ominaisuuksia kuvailevia, ja toimivat olennaisena osana tarinankerrontaa. Nimet kielivät kirjailijan kannattamasta ideologiasta, ja kytkeytyvät siten myös reaalimaailmaan. Vaikka kirjailijan nimenanto on osin huolimatonta, on se silti selvästi harkittua. Aili Somersalon luoma nimimaisema on omalakinen ja tunnistettava.

Path integral quantisation of topological field theories

Conditions for quantum topological invariance of classically topological field theories in the path integral formulation are discussed. Both the three-dimensional Chern-Simons system and a Witten-type topological field theory are shown to satisfy these conditions.

Mean-field theories of Hubbard and t-J models

We report novel results obtained for the Hubbard and t-J models by various mean-field approximations.

Electrostatic Field Analysis of Electrooptic Devices

We describe a Finite Difference Method for the determination of the electrostatic field in a multilayered electrooptic device. The Laplace equation is solved, assuming a suitable closed area, by taking into account the different permittivities of the various layers. The effect of a higher permittivity in the guiding layer has been explicitly considered. As a practical example, we calculate the phase shift of a guided optical wave within an electrooptic modulator. A review of the various methods in use for the field analysis is given. Some criteria for the selection of the appropriate method are also mentioned.

Analysis of the evanescent field coupling between a fiber and a planar waveguide using the explicit finite difference method with a nonuniform mesh (Journal Paper)

We investigate an optical waveguide system consisting of an unclad fiber core suspended at a constant distance parallel to the surface of a planar waveguide. The coupling and propagation of light in the combined system is studied using the three-dimensional explicit finite difference beam propagation method with a nonuniform mesh configuration. The power loss in the fiber and the field distribution in the waveguide are studied as a function of various parameters, such as index changes, index profile, and propagation distance, for the combined system.