Theory of the unusual doping and temperature dependence of photoemission spectra in manganites

A recent, major, puzzle in the core-level photoemission spectra of doped manganites is the observation of a 1–2 eV wide shoulder with intensity varying with temperature T as the square of the magnetization over a T scale of order 200 K, an order of magnitude less than electronic energies. This is addressed and resolved here, by extending a recently proposed two-fluid polaron–mobile electron model for these systems to include core-hole effects. The position of the shoulder is found to be determined by Coulomb and Jahn-Teller energies, while its spectral weight is determined by the mobile electron energetics which is strongly T and doping dependent, due to annealed disorder scattering from the polarons and the t2g core spins. Our theory accounts quantitatively for the observed T dependence of the difference spectra, and furthermore, explains the observed correspondence between spectral changes due to increasing doping and decreasing T.

Simplified theory of optical nonlinearities in spin-polarized bulk GaAs

Apart from their intrinsic physical interest, spin-polarized many-body effects are expected to be important to the working of spintronic devices. A vast literature exists on the effects of a spin-unpolarized electron-hole plasma on the optical properties of a semiconductor. Here, we include the spin degree of freedom to model optical absorption of circularly polarized light by spin-polarized bulk GaAs. Our model is easy to implement and does not require elaborate numerics, since it is based on the closed-form analytical pair-equation formula that is valid in 3d. The efficacy of our approach is demonstrated by a comparison with recent experimental data.

Modified density matrix renormalization group algorithm for the zigzag spin-1/2 chain with frustrated antiferromagnetic exchange: Comparison with field theory at large J(2)/J(1)

A modified density matrix renormalization group (DMRG) algorithm is applied to the zigzag spin-1/2 chain with frustrated antiferromagnetic exchange J(1) and J(2) between first and second neighbors. The modified algorithm yields accurate results up to J(2)/J(1) approximate to 4 for the magnetic gap Delta to the lowest triplet state, the amplitude B of the bond order wave phase, the wavelength lambda of the spiral phase, and the spin correlation length xi. The J(2)/J(1) dependences of Delta, B, lambda, and xi provide multiple comparisons to field theories of the zigzag chain. The twist angle of the spiral phase and the spin structure factor yield additional comparisons between DMRG and field theory. Attention is given to the numerical accuracy required to obtain exponentially small gaps or exponentially long correlations near a quantum phase transition.

Hard Custom, Hard Dance : Social Organisation, (Un)Differentiation and Notions of Power in a Tabiteuean Community, Southern Kiribati

Hard Custom, Hard Dance: Social Organisation, (Un)Differentiation and Notions of Power in a Tabiteuean Community, Southern Kiribati is an ethnographic study of a village community. This work analyses social organisation on the island of Tabiteuea in the Micronesian state of Kiribati, examining the intertwining of hierarchical and egalitarian traits, meanwhile bringing a new perspective to scholarly discussions of social differentiation by introducing the concept of undifferentiation to describe non-hierarchical social forms and practices. Particular attention is paid to local ideas concerning symbolic power, abstractly understood as the potency for social reproduction, but also examined in one of its forms; authority understood as the right to speak. The workings of social differentiation and undifferentiation in the village are specifically studied in two contexts connected by local notions of power: the meetinghouse institution (te maneaba) and traditional dancing (te mwaie). This dissertation is based on 11 months of anthropological fieldwork in 1999‒2000 in Kiribati and Fiji, with an emphasis on participant observation and the collection of oral tradition (narratives and songs). The questions are approached through three distinct but interrelated topics: (i) A key narrative of the community ‒ the story of an ancestor without descendants ‒ is presented and discussed, along with other narratives. (ii) The Kiribati meetinghouse institution, te maneaba, is considered in terms of oral tradition as well as present-day practices and customs. (iii) Kiribati dancing (te mwaie) is examined through a discussion of competing dance groups, followed by an extended case study of four dance events. In the course of this work the community of close to four hundred inhabitants is depicted as constructed primarily of clans and households, but also of churches, work co-operatives and dance groups, but also as a significant and valued social unit in itself, and a part of the wider island district. In these partly cross-cutting and overlapping social matrices, people are alternatingly organised by the distinct values and logic of differentiation and undifferentiation. At different levels of social integration and in different modes of social and discursive practice, there are heightened moments of differentiation, followed by active undifferentiation. The central notions concerning power and authority to emerge are, firstly, that in order to be valued and utilised, power needs to be controlled. Secondly, power is not allowed to centralize in the hands of one person or group for any long period of time. Thirdly, out of the permanent reach of people, power/authority is always, on the one hand, left outside the factual community and, on the other, vested in community, the social whole. Several forms of differentiation and undifferentiation emerge, but these appear to be systematically related. Social differentiation building on typically Austronesian complementary differences (such as male:female, elder:younger, autochtonous:allotochtonous) is valued, even if eventually restricted, whereas differentiation based on non-complementary differences (such as monetary wealth or level of education) is generally resisted, and/or is subsumed by the complementary distinctions. The concomitant forms of undifferentiation are likewise hierarchically organised. On the level of the society as a whole, undifferentiation means circumscribing and ultimately withholding social hierarchy. Potential hierarchy is both based on a combination of valued complementary differences between social groups and individuals, but also limited by virtue of the undoing of these differences; for example, in the dissolution of seniority (elder-younger) and gender (male-female) into sameness. Like the suspension of hierarchy, undifferentiation as transformation requires the recognition of pre-existing difference and does not mean devaluing the difference. This form of undifferentiation is ultimately encompassed by the first one, as the processes of the differentiation, whether transformed or not, are always halted. Finally, undifferentiation can mean the prevention of non-complementary differences between social groups or individuals. This form of undifferentiation, like the differentiation it works on, takes place on a lower level of societal ideology, as both the differences and their prevention are always encompassed by the complementary differences and their undoing. It is concluded that Southern Kiribati society be seen as a combination of a severely limited and decentralised hierarchy (differentiation) and of a tightly conditional and contextual (intra-category) equality (undifferentiation), and that it is distinctly characterised by an enduring tension between these contradicting social forms and cultural notions. With reference to the local notion of hardness used to characterise custom on this particular island as well as dance in general, it is argued in this work that in this Tabiteuean community some forms of differentiation are valued though strictly delimited or even undone, whereas other forms of differentiation are a perceived as a threat to community, necessitating pre-emptive imposition of undifferentiation. Power, though sought after and displayed - particularly in dancing - must always remain controlled.

Joseph A. Schumpeter's Theory of Social and Economic Evolution : a Reconstruction and Critique

The book presents a reconstruction, interpretation and critical evaluation of the Schumpeterian theoretical approach to socio-economic change. The analysis focuses on the problem of social evolution, on the interpretation of the innovation process and business cycles and, finally, on Schumpeter s optimistic neglect of ecological-environmental conditions as possible factors influencing social-economic change. The author investigates how the Schumpeterian approach describes the process of social and economic evolution, and how the logic of transformations is described, explained and understood in the Schumpeterian theory. The material of the study includes Schumpeter s works written after 1925, a related part of the commentary literature on these works, and a selected part of the related literature on the innovation process, technological transformations and the problem of long waves. Concerning the period after 1925, the Schumpeterian oeuvre is conceived and analysed as a more or less homogenous corpus of texts. The book is divided into 9 chapters. Chapters 1-2 describe the research problems and methods. Chapter 3 is an effort to provide a systematic reconstruction of Schumpeter's ideas concerning social and economic evolution. Chapters 4 and 5 focus their analysis on the innovation process. In Chapters 6 and 7 Schumpeter's theory of business cycles is examined. Chapter 8 evaluates Schumpeter's views concerning his relative neglect of ecological-environmental conditions as possible factors influencing social-economic change. Finally, chapter 9 draws the main conclusions.

Conformal Field Theory Methods for Variants of Schramm-Loewner Evolutions

This thesis consists of an introduction, four research articles and an appendix. The thesis studies relations between two different approaches to continuum limit of models of two dimensional statistical mechanics at criticality. The approach of conformal field theory (CFT) could be thought of as the algebraic classification of some basic objects in these models. It has been succesfully used by physicists since 1980's. The other approach, Schramm-Loewner evolutions (SLEs), is a recently introduced set of mathematical methods to study random curves or interfaces occurring in the continuum limit of the models. The first and second included articles argue on basis of statistical mechanics what would be a plausible relation between SLEs and conformal field theory. The first article studies multiple SLEs, several random curves simultaneously in a domain. The proposed definition is compatible with a natural commutation requirement suggested by Dubédat. The curves of multiple SLE may form different topological configurations, ``pure geometries''. We conjecture a relation between the topological configurations and CFT concepts of conformal blocks and operator product expansions. Example applications of multiple SLEs include crossing probabilities for percolation and Ising model. The second article studies SLE variants that represent models with boundary conditions implemented by primary fields. The most well known of these, SLE(kappa, rho), is shown to be simple in terms of the Coulomb gas formalism of CFT. In the third article the space of local martingales for variants of SLE is shown to carry a representation of Virasoro algebra. Finding this structure is guided by the relation of SLEs and CFTs in general, but the result is established in a straightforward fashion. This article, too, emphasizes multiple SLEs and proposes a possible way of treating pure geometries in terms of Coulomb gas. The fourth article states results of applications of the Virasoro structure to the open questions of SLE reversibility and duality. Proofs of the stated results are provided in the appendix. The objective is an indirect computation of certain polynomial expected values. Provided that these expected values exist, in generic cases they are shown to possess the desired properties, thus giving support for both reversibility and duality.

Simplified theory of optical nonlinearities in spin-polarized bulk GaAs

Apart from their intrinsic physical interest, spin-polarized many-body effects are expected to be important to the working of spintronic devices. A vast literature exists on the effects of a spin-unpolarized electron-hole plasma on the optical properties of a semiconductor. Here, we include the spin degree of freedom to model optical absorption of circularly polarized light by spin-polarized bulk GaAs. Our model is easy to implement and does not require elaborate numerics, since it is based on the closed-form analytical pair-equation formula that is valid in 3d. The efficacy of our approach is demonstrated by a comparison with recent experimental data.

Non-Fermi liquid theory of quantum hall effects

Within the Grassmannian U(2N)/U(N) x U(N) nonlinear sigma-model representation of localization, one can study the low-energy dynamics of both a free and interacting electron gas. We study the crossover between these two fundamentally different physical problems. We show how the topological arguments for the exact quantization of the Hall conductance are extended to include the Coulomb interaction problem. We discuss dynamical scaling and make contact with the theory of variable range hopping. (C) 2005 Pleiades Publishing, Inc.

Surface instability of confined elastic bilayers: Theory and simulations

The surface of a soft elastic film becomes unstable and forms a self-organized undulating pattern because of adhesive interactions when it comes in contact proximity with a rigid surface. For a single film, the pattern length scale lambda, which is governed by the minimization of the elastic stored energy, gives lambda similar to 3h, where h is the film thickness. Based on a linear stability analysis and simulations of adhesion and debonding, we consider the contact instability of an elastic bilayer, which provides greater flexibility in the morphological control of interfacial instability. Unlike the case of a single film, the morphology of the contact instability patterns, debonding distance, and debonding force in a bilayer can be controlled in a nonlinear way by varying the thicknesses and shear moduli of the films. Interestingly, the pattern wavelength in a bilayer can be greatly increased or decreased compared to a single film when the adhesive contact is formed by the stiffer or the softer of the two films, respectively. In particular, lambda as small as 0.5h can be obtained. This indicates a new strategy for pattern miniaturization in elastic contact lithography.

Yliopisto-opetuksen yhteistoiminnallinen kehittäminen

The main aim of this work is to study the possibility of applying the cooperative learning approach to develop academic learning and teaching culture. In this work cooperative learning refers to a pedagogical approach that applies social psychological knowledge of group dynamics and small group teaching. Furthermore, theories of collaborative learning and organization development have been applied. Based on these theories a model of developing learning and teaching culture was developed. The model was tested in the development project that was carried out in the Faculty of Agriculture and Forestry of Helsinki University. The research questions were: How were the theories of cooperative and collaborative learning and organization development applied in the project? What kind of effects did the development project have on the learning and teaching culture? Through which kind of mechanisms did the project influence this culture? How should the development model be revised after the empirical test? The project lasted five years and the major part of the project consisted of a one-year pedagogical training course. Altogether 145 people (teachers, researchers, library staff, and students) participated in the training, two to three departments at a time. In the pedagogical training cooperative learning methods were widely used. A questionnaire was used to study effects of the development project. The questionnaire was sent to 87 people and 65.5 % answered it. Both the answers to the questionnaire and a sample of learning diaries (n=61) were used to study the mechanism of the project. A sample of the learning diaries consisted of two pedagogical training group members diaries. The frequency distributions were calculated as extrapolations from the answers to the structured questions. Furthermore the answers were classified by the main background variables. The analysis of the open answers to the questionnaire and the learning diaries were data-based. According to the answers to the questionnaire, the effects of the pedagogical training were as follows: The participants consider learning more as an active process of constructing knowledge. Furthermore they considered the individual learning styles and strategies, cooperation and motivation as more important part of the learning process than before the pedagogical training. The role of the teacher was viewed more challenging than before. Additionally the cooperation between teachers, other staff members and students had projected to increase. After the project had ended the teaching methods in the whole faculty were viewed to become varied and the teaching was considered to be more valued than before. According to the answers to the questionnaire, the project influenced through the following ways: the project stimulated the change process, provided new methods for learning and teaching, had an effect on conceptions of learning and teaching and facilitated meaningful communication with others (staff and students). The analysis of the learning diaries supported these findings. In addition, the analysis of the learning diaries deepened the understanding of how the cooperative learning methods supported positive learning atmosphere and reduced the negative effect of the status differences between the members of the group. The critical comments in the learning diaries could be interpreted as collision between cooperative and traditional teaching culture. Cooperative learning gives theory-based methods to develop academic learning and teaching culture. The approach helps the developer to create positive collaborative learning environment and gives ways to support learning in small groups, which can promote cultural change. On the other hand, to understand the whole process of organization development and promote change the theories of organizations and more sosioconstructivist theory of learning are needed. Cooperative learning, collaborative learning, higher education, group dynamics, social constructionism, organisational culture, organisation development

Theory of laminar flame propagation with non-normal diffusion.

A study has been made of the problem of steady, one-dimensional, laminar flame propagation in premixed gases, with the Lewis number differing from (and equal to) unity. Analytical solutions, using the method of matched asymptotic expansions, have been obtained for large activation energies. Numerical solutions have been obtained for a wide range of the reduced activation temperature parameter (n {geometrically equal to} E/RTb), and the Lewis number δ. The studies reveal that the flame speed eigenvalue is linear in Lewis number for first order and quadratic in Lewis number for second order reactions. For a quick determination of flame speeds, with reasonable accuracy, a simple rule, expressing the flame speed eigenvalue as a function of the Lewis number and the centroid of the reaction rate function, is proposed. Comparisons have been made with some of the earlier works, for both first and second order reactions.

Interculturality in Theory and Practice in the Master's Programme of Intercultural Bilingual Education in Bolivia

Tämän tutkielman aiheena on kulttuurienvälisyys kulttuurienvälisessä kaksikielisessä opetuksessa (Educación Intercultural Bilingüe, EIB) Boliviassa ja erityisesti kulttuurienvälisen kaksikielisen koulutuksen maisteriohjelmassa (Maestría en Educación Intercultural Bilingüe), jota koordinoi PROEIB Andes -järjestö yhteistyössä Cochabamban Universidad Mayor de San Simónin kanssa. Tutkielman tarkoituksena on selvittää, miten kulttuurienvälisyys määritellään ja mitä se käytännössä merkitsee opetuksen eri osa-alueilla: sisällöissä, opetusmetodeissa ja -materiaaleissa sekä arvioinnissa. Koska kulttuurienvälisen kaksikielisen opetuksen toteutus ja tutkiminen eri Latinalaisen Amerikan maissa on tähän asti painottunut lähes yksinomaan perusopetukseen, pyrin työssäni keskittymään kulttuurienvälisyyden ilmentymiin nimenomaan bolivialaisessa korkeakoulukontekstissa. Tutkielman aineistona on käytetty kahdeksaa EIB -asiantuntijoiden teemahaastattelua, jotka FM Eila Isotalus on tehnyt Boliviassa vuonna 2004. Haastatteluaineisto analysoitiin teoriasidonnaista eli abduktiivista sisällönanalyysiä käyttäen. Tutkielman teoriatausta koostuu yhtäältä kulttuurienvälisyyteen ja monikulttuurisuuteen liittyvien käsitteiden määrittelystä, ja toisaalta kulttuurienväliseen opetukseen liittyvien mallien esittelystä. Aineiston analyysissä avuksi on ollut etenkin James A. Banksin teoria monikulttuurisen opetuksen viidestä ulottuvuudesta, joiden kautta on voitu pohtia kulttuurienvälisyyden toteutumista opetuksen eri osa-alueilla ja nostaa esille bolivialaisen kulttuurienvälisen opetuksen erityispiirteitä. Aineiston analyysissä ilmenee, että kulttuurienvälisyyden käsitteen määrittely on vahvasti kontekstisidonnainen ja jatkuva prosessi, johon vaikuttavat eri toimijoiden näkemykset ja vaatimukset. EIB -asiantuntijoiden esittämät määrittelyt voidaan jakaa makro- ja mikrososiaaliseen kategoriaan sen mukaan, nähdäänkö kulttuurienvälisyys ensisijaisesti yhteiskunnallisena vai yksilötason käsitteenä. Aineistossa korostuu ajatus latinalaisamerikkalaisesta kulttuurienvälisyydestä poliittisena käsitteenä, jonka keskiössä on vaatimus yhteiskunnallisten valtasuhteiden muutoksesta. Yksi suurimmista haasteista kulttuurienvälisyyden toteuttamisessa bolivialaisessa korkeakouluopetuksessa ovat akateemiseen kulttuuriin liittyvät perinteet, jotka vaikeuttavat uusien toimintatapojen omaksumista. Kulttuurienvälisyys opetuksessa on toistaiseksi tarkoittanut etupäässä sisältöjen monipuolistamista lisäämällä opetusohjelmiin elementtejä paikallisista kulttuureista. Tärkeänä askeleena EIB:n kehityksessä voidaan pitää painopisteen siirtymistä sisältökysymyksistä kulttuurienvälisten opetusmetodien luomiseen. Näiden opetusmenetelmien tulisi pohjautua ymmärrykseen oppimisesta kokonaisvaltaisena, yhteisöllisenä prosessina ja siten kuroa umpeen kuilua koulun ja yhteisöjen arkielämän välillä. Opetusmenetelmien ja -materiaalien suhteen keskeinen kulttuurienvälisyyteen liittyvä kysymys on intiaanikansojen suullisen kulttuurin ja tiedon jakamisen perinteiden hyödyntäminen opetuksessa. Maisteriohjelman opiskelijoiden arvioinnissa pyritään huomioimaan yksilön kokonaisvaltainen kehitys pelkkien opintosuoritusten sijasta, mutta arvosanoihin pohjautuvasta arvostelukäytännöstä ei ole toistaiseksi voitu luopua yliopiston vaatimusten vuoksi. Kaiken kaikkiaan kulttuurienvälisyyden toteuttaminen EIB:ssä ja maisteriohjelmassa on pitkän tähtäimen prosessi, joka vaatii perinteisten opetuskäytäntöjen kyseenalaistamista ja korkeakouluopetuksessa myös akateemisen kulttuurin haastamista. On oleellisen tärkeää, että prosessiin osallistuvat asiantuntijoiden ohella myös esimerkiksi opiskelijat, intiaaniyhteisöt ja -järjestöaktiivit.

A generalized mathematical theory and experimental verification of proportional notches

A theory and generalized synthesis procedure is advocated for the design of weir notches and orifice-notches having a base in any given shape, to a depth a, such that the discharge through it is proportional to any singular monotonically-increasing function of the depth of flow measured above a certain datum. The problem is reduced to finding an exact solution of a Volterra integral equation in Abel form. The maximization of the depth of the datum below the crest of the notch is investigated. Proof is given that for a weir notch made out of one continuous curve, and for a flow proportional to the mth power of the head, it is impossible to bring the datum lower than (2m − 1)a below the crest of the notch. A new concept of an orifice-notch, having discontinuity in the curve and a division of flow into two distinct portions, is presented. The division of flow is shown to have a beneficial effect in reducing the datum below (2m − 1)a from the crest of the weir and still maintaining the proportionality of the flow. Experimental proof with one such orifice-notch is found to have a constant coefficient of discharge of 0.625. The importance of this analysis in the design of grit chambers is emphasized.