Boson localization and universality in YBa2Cu(3-x)M(x)O(7-delta)

We consider a two component mixture of charged fermions on neutralizing background with all sign combinations and arbitrarily small mass ratios. In the two impurity limit for the heavier component we show that the pair forms a bound state for all charge combinations. In the lowest order approximation we derive a closed form expression Veff(r) for the binding potential which has short-range repulsion followed by attraction. In the classical limit, when the mass of embedded particles is large m2 much greater than m, we can calculate from Veff(r) also the cohesive energy E and the bond length R of a metallic crystal such as lithium. The lowest order result is R = 3.1 A, E = -0.9 eV, not entirely different from the experimental result for lithium metal. The same interaction for two holes on a parabolic band with m2 greater than m gives the quantum mechanical bound state which one may interpret as a boson or local pair in the case of high-Te and heavy fermion superconductors. We also show that for compounds of the type YBa2Cu(3 - x)M(x)O(7 - delta) one can understand most of the experimental results for the superconducting and normal states with a single temperature dependent boson breaking function f(T) for each impurity content x governing the decay of bosons into pairing fermions. In the normal state f(T) turns out to be a linear, universal function, independent of the impurity content I and the oxygen content delta. We predict with universality a depression in Tc(x) with slight down bending in agreement with experiment. As a natural consequence of the model the bosons become localized slightly above Tc due to the Wigner crystallization, enhanced with lattice local field minima. The holes remain delocalized with a linearly increasing concentration in the normal state, thus explaining the rising Hall density. The boson localization temperature T(sub BL) shows up as a minimum in the Hall density R(sub ab)(exp -1). We also give explanation for very recently observed scaling of temperature dependent Hall effect in La(2 - x)Sr(x)CuO4

Heavy fermion behavior explained by bosons

Conventional heavy fermion (HF) theories require existence of massive fermions. We show that heavy fermion phenomena can also be simply explained by existence of bosons with moderate mass but temperature dependent concentration below the formation temperature T(sub B), which in turn is close to room temperature. The bosons B(++) are proposed to be in chemical equilibrium with a system of holes h(+): B(++) = h(+) + h(+). This equilibrium is governed by a boson breaking function f(T), which determines the decreasing boson density and the increasing fermion density with increasing temperature. Since HF-compounds are hybridized from minimum two elements, we assume in addition existence of another fermion component h(sub s)(+) with temperature independent density. This spectator component is thought to be the main agent in binding the bosons in analogy with electronic or muonic molecules. Using a linear boson breaking function we can explain temperature dependence of the giant linear specific heat coefficient gamma(T) coming essentially from bosons. The maxima in resistivity, Hall coefficient, and susceptibility are explained by boson localization effects due to the Wigner crystallization. The antiferromagnetic transitions in turn are explained by similar localization of the pairing fermion system when their density n(sub h)(T(sub FL)) becomes lower than n(sub WC), the critical density of Wigner crystallization. The model applies irrespective whether a compound is superconducting or not. The same model explains the occurrence of low temperature antiferromagnetism also in high-T(sub c) superconductors. The double transition in UPt3 is proposed to be due to the transition of the pairing fermion liquid from spin polarized to unpolarized state

Business Models for Electronic Commerce - Analysis of Grocery Retailing Industry

Electronic commerce can dramatically alter the current delivery and sales channels, as well as value chains in many industries. Accordingly, consumers will change or supplement their channel preferences with increasing amount of electronic services available. This study focuses on the different types of business models used in the grocery retailing industry, to serve consumers. The empirical part of he analysis is based on a longitudinal analysis of existing EGS’ in 1998 and 1999 in Europe, North America and Pacific Asia. The analysis shows that the majority of the electronic grocery shops are extensions of existing physical stores. There are, however, some signs of interesting new business strategies. These strategies are compared to the theoretical alternatives proposed by the model of Customer Channels and conclusions are drawn regarding the development of electronic commerce in grocery industry

Miten sukupuoli ja sukupuolistereotypiat näkyvät musiikkikasvatuksen koulutuksessa?:musiikkikasvatuksen opiskelijoiden kokemuksia

Tiivistelmä. Pro gradu -tutkielmani tavoitteena on selvittää, miten sukupuoliroolit ja -stereotypiat ilmenevät opiskelijoiden kokemusten ja käsitysten mukaan musiikkikasvatuksen opinnoissa. Aineistoni on kerätty sähköisellä kyselyllä Oulun yliopiston musiikkikasvatuksen opiskelijoilta helmikuussa 2021. Vastauksia kertyi 13 kappaletta. Otos edusti eri-ikäisiä, eri sukupuolten edustajia sekä eri vuosikurssien opiskelijoita. Kaikkien oppilaitosten tulee laatia tasa-arvosuunnitelma ja pyrkiä sukupuolten väliseen tasa-arvoon. Musiikissa sukupuoliroolit näkyvät edelleen vahvasti muun muassa sukupuolittuneissa toimijuuksissa, musiikinhistorian kertomuksissa sekä laulujen sanoituksissa. Maskuliinisuus hallitsee musiikissa esimerkiksi populaarimusiikin kentällä ja länsimaisessa taidemusiikissa. Säveltäjien, kapellimestarien ja festivaalien esiintyjien joukossa naiset ovat vähemmistössä. Näiden ilmiöiden pohjalta halusin selvittää, missä määrin nämä ilmiöt näkyvät musiikkikasvatuksen opinnoissa. Musiikkikasvattajat uudistavat ja ylläpitävät musiikkikulttuuria, joten heillä on tärkeä rooli sukupuolten tasa-arvon edistäjinä musiikin kentällä. Tutkimukseni käsittelee sukupuolten tasa-arvoa ja sen näkökulma on feministinen. Tutkimukseni on laadullinen ja tutkimuksellinen lähestymistapa on fenomenografinen. Fenomenografisen menetelmän mukaisesti tutkielmani keskiössä ovat opiskelijoiden käsitykset ja kokemukset tutkittavasta ilmiöstä. Teoreettinen viitekehykseni pohjautuu aiempiin tutkimuksiin ja aiheesta kirjoitettuihin kotimaisiin sekä kansainvälisiin julkaisuihin. Monipuolinen aineisto lisää tutkimukseni luotettavuutta. Luotettavuutta lisää myös aineiston analyysivaiheiden tarkka kuvaaminen fenomenografisen analyysimenetelmän mukaisesti. Aineistosta nousi esiin kolme kuvauskategoriaa, jotka kuvaavat tutkielmani tuloksia. Nämä ovat tehtävien jakautuminen, tasa-arvo ei toteudu ja sukupuoli ei juurikaan näy. Tulokset osoittavat, että sukupuoliroolit ovat edelleen näkyvissä musiikkikasvatuksen opinnoissa. Soittimet jakautuvat vahvasti sukupuolen mukaan: miehet soittavat bändisoittimia ja naiset soittavat pianoa tai laulavat. Musiikkiteknologian osaaminen painottuu miesten vahvuudeksi. Osa vastaajista koki, että koulutuksessa ei pyritä aktiivisesti purkamaan sukupuolistereotypioita. Naisvastaajista jotkut kokivat joutuneensa ponnistelemaan opinnoissaan enemmän kuin miesopiskelijat. Kolmas kuvauskategoria osoittaa, että kaikki eivät kokeneet sukupuolen näkyvän opinnoissa tai eivät olleet ainakaan kiinnittäneet asiaan huomiota. Tutkielman tulokset ovat samassa linjassa aiempien tutkimusten kanssa ja osoittavat, että sukupuolten tasa-arvon saavuttamiseksi on vielä tehtävä töitä

Leaded tin bronzes: the effects of casting method on dry sliding behaviour

In metal-to-metal sliding bearing applications, leaded tin bronzes are widely known as materials with excellent seizure resistance. In conditions of boundary or dry lubrication, lead may smear across the sliding surface, preventing surface contact and catastrophic seizure. The aim of this study was to determine the effects of casting method on the dry sliding behaviour of leaded tin bronzes. Continuous cast, centrifugally cast, and sand cast leaded tin bronze samples with varying lead contents were subjected to pin-on-disk- testing. It was found that casting method has a significant effect on the wear behaviour of leaded tin bronzes in dry sliding conditions. With continuous cast samples, the dominant wear mode was rapid, stable microcracking along copper/lead interfacial boundaries. With centrifugally and sand cast samples, wear occurred more slowly and erratically through the formation of transfer layers. The dominant wear mode was found to be connected to the coarseness of the distribution of lead particles in the copper matrix

On the modeling of planetary plasma environments by a fully kinetic electromagnetic global model HYB-em

Peer reviewe

Development of a test device for the evaluation of journal bearings

Journal and thrust bearings are widely used in heavy industry. Today, there is a growing need for studying different kinds of new bearing material and coating solutions in operating conditions where full film lubrication cannot be achieved or sustained. A test device for the evaluation of journal bearings was developed. The device consists of a rotating shaft and four stationary test bearings. This scheme eliminates the need for support bearings, allowing an accurate measurement of friction. The initial tests were carried out with a variety of loads and sliding speeds in mixed and full film regimes. The friction results in the form of a Stribeck curve were obtained and found to be in line with general trends. The results also indicate that the bearing lift-off speed occurs when the value of the non-dimensional ηen / ppro - parameter is in the range of 0.5·10-8 - 1.0·10-8

Four decades of global surface albedo estimates in the third edition of the CM SAF cLoud, Albedo and surface Radiation (CLARA) climate data record

We present the surface albedo data in the third edition of the CM SAF cLoud, Albedo and surface Radiation (CLARA) data record family. The temporal coverage of this edition is extended from 1979 until the near-present day. The core algorithms and data format remain unchanged from previous editions, but now white- and blue-sky albedo estimates are also available for the first time in CLARA data. We present an overview of the retrieval, followed by an assessment of the accuracy and stability of the data record, based on collocated comparisons with reference surface albedo measurements and intercomparisons with preceding satellite-based albedo data records. Specific attention is paid to addressing the spatial representativeness problem inherent in the “point-to-pixel” validation of satellite-based coarse surface albedo estimates against in situ measurements. We find the CLARA-A3 albedo data to match or improve upon the accuracy and robustness of the predecessor record (CLARA-A2), with good agreement found when compared to in situ measurements. In cases of a large bias, the spatial representativeness of the measurement site typically explains most of the increase. We conclude with a summarizing discussion on the observed strengths and weaknesses of the new data record, including guidance for potential users. The data are available at https://doi.org/10.5676/EUM_SAF_CM/CLARA_AVHRR/V003 (Karlsson et al., 2023b).</p