Optical Conductivity Anisotropy in the Undoped Three-Orbital Hubbard Model for the Pnictides

The resistivity anisotropy unveiled in the study of detwinned single crystals of the undoped 122 pnictides is here studied using the two-dimensional three-orbital Hubbard model in the mean-field approximation. Calculating the Drude weight in the x and y directions at zero temperature for a Q=(\pi,0) magnetically ordered state, the conductance along the antiferromagnetic direction is shown to be larger than along the ferromagnetic direction. This effect is caused by the suppression of the d_{yz} orbital at the Fermi surface, but additional insight based on the momentum dependence of the transitions induced by the current operator is provided. It is shown that the effective suppression of the inter-orbital hopping d_{xy} and d_{yz} along the y direction is the main cause of the anisotropy.Comment: 5 pages, 4 figs, submitted to PRB(RC

Perceived Obstacles by ESL Instructors and Required Support for the Integration of Educational Technology

Nowadays, the use of technology has become a significant part of the language learning process inside and outside of the classroom. Many previous studies and surveys, most language educators hold a relatively positive attitude to the usage of technology in language teaching and learning. But many other studies also found that language teachers were not really using technology in their classrooms, or only for very low-level learning and teaching. The integration of technology in second language learning and teaching is still a problem that has not been fully researched.This descriptive study was designed to explore the obstacles that prevent ESL instructors from integrating technology into their teaching practice and gain a deep understanding of ESL instructors’ needs and expectations for technology use in the language classrooms in the community colleges. Findings suggest that most ESL instructors hold a relatively positive attitude toward integrating technology into language teaching, but at the same time they did encounter many obstacles and difficulties in the technology integration process. Lack of time, tools/technology not working as expected, and inadequate equipment were three main obstacles identified by the survey data. The qualitative interview data further confirms and explains the results of the survey, and at the same time brings new findings and a deeper understanding of the reasons behind the surface problems. Lack of necessary technology skills, generation gap, and neglect of ESL students’ perspectives were brought up in the interviews. At the same time, ESL instructors’ needs and expectations for technology in their classrooms were well addressed as well

Internatsionaliseerumise protsessid Hiina firmades: teadmuse roll

Väitekirja elektrooniline versioon ei sisalda empiirilisi uuringuid.Kasutades nii kvantitatiivseid kui ka kvalitatiivseid meetodeid ühendades võrdlevaid uuringuid ja pikaajalisi analüüse, on doktoritöö eesmärgiks välja selgitada teadmuse roll Hiina ettevõtete internatsionaliseerumise protsessides. Töös töödeldakse süstemaatiliselt, Hiina kontekstist lähtuvalt, rahvusvahelistumise uuringuid, otse allikast saadud ettevõttetasandil olevaid andmeid ning viie originaal väljaande tulemusi, mis on ühendatud vastavalt teenima sama eemärki, ent neil on eri teadusuuringulised eesmärgid, mis keskenduvad erinevatele aspektidele, kasutades erinevaid meetodeid. Doktoritöö teoreetiline osa põhineb rahvusvahelistumise teemalisel kirjandusel, eriti Uppsala mudelil ja Born Global mudelil. Samuti keskendub töö kirjandus ettevõtete välismaiste kogemuslikule teadmusele ja selle omandamisele. Autor leiab, et välisturu teadmus on oluline ettevõtete rahvusvahelistumise seisukohast. Selle puudumise korral võib aeglustuda rahvusvahelistumise protsess ja põhjustada ettevõtete esialgset sisenemist lähiriikidesse, kasutades selleks kõige lihtsamaid sisenemise mudeleid. Ettevõtted võivad omandada välisturule sisenemise teadmisi, mitte üksnes otsesest turukogemusest, vaid ka palgates teatud liiki uut personali, tehes koostööd jne. Välisturu tundmine võib positiivselt mõjutada ettevõtete rahvusvahelistumise protsessi, kuid ei pruugi tagada edu. Ettevõtete rahvusvaheliseerumine ei pruugi olla sujuv, vaid pigem lainekujuline protsess, mis hõlmab endas oodatud ja radikaalseid muututusi. Kasutades esmaallikatasandist pärinevaid ettevõtte andmeid ning analüüsides neid kombineeritud meetodite abil, selgus, et nii Hiina BG ja NBG ettevõtted rahvusvahelistusid esilagu edukalt, vaatamata puuduvale teadmusele. Madal teadmuse tase ei mõjuta nende rahvusvahelistumise kiirust, kuid kõik ettevõtted kasutasid eksportimist kui välismaist töörežiimi. Mõlemad BG-d ja NBG-d valivad kultuuriliselt ja geograafiliselt kaugemad riigid, mis on suurema elanikkonna ja arenenuma majandusega. Pärast sisenemist oma kolme esimesele välisturule, ettevõtted hakkavad omandama teadmisi, mis hakkavad mõjutama nende edasisi välisturgudele laienemise strateegiaid. Muutuste ja kriisiperioodil määrab teadmuse tase, kas ettevõtted lahkuvad välisturgudelt ning kui edukas on nende taassisenemine välisturule.teadmisedettevõttedrahvusvahelistuminekvantitatiivsed uurimismeetodidkvalitatiivsed uurimismeetodidvõrdlevuuringudHiinaUsing both quantitative and qualitative methods, and combining comparative studies and longitudinal analysis, the aim of this dissertation is to identify the role of knowledge in internationalization processes of Chinese firms. By systematically reviewing the literature on internationalization studies in the Chinese context, and by using firsthand firm-level data, five original publications result, which are united under the same goal yet have separate research tasks that focus on different aspects using various methodologies.The theoretical part of this thesis is based on the internationalization literature, particular on streams of Uppsala model and Born global model. It also focuses on the literature regarding firms’ foreign experiential knowledge and its acquisition. Author concludes that foreign market knowledge is important to firms’ internationalization. A lack of it may slow down the internationalization process and cause firms to initially enter the closest countries, using the simplest entry modes. Firms may acquire foreign market knowledge not only through direct market experience, but also by hiring certain types of personnel, cooperation, and so on. Foreign market knowledge may positively affect firms’ internationalization processes, but does not guarantee success. Firms’ internationalization is not necessarily a smooth path, but rather a wave- shaped process that involves expected and radical changes.Through the mixed-methods, by using first-hand firm level data, this research discovers that both Chinese BGs and NBGs initially internationalize successfully, despite lacking knowledge. Low knowledge levels do not affect their internationalization speed, but firms all use exporting as their foreign operation mode. Both BGs and NBGs select culturally and geographically more distant countries that have a higher population and more advanced economic development. After entering their first three foreign markets, firms start to gain knowledge, which affects their foreign expansion strategy going forward. During periods of radical change and crisis, knowledge level determines decisions relating to the firms’ foreign market exit, and the success of reentry.knowledgefirmsinternationalisationquantitative research methodsqualitative research methodscomparative researchChin

Theoretical Study on Spontaneous Symmetry Breaking in Strongly Correlated Electrons

In the early days of condensed matter physics, the single electron approximation was considered to be a very good approach in order to explore the properties of many systems. However, as time goes on, a variety of new systems have been discovered and many of them, such as high temperature superconductors and manganites, show phenomenas that evidently can not be explained by single electron theories. Spontaneous symmetry breaking is a very important and famous concept in physics, from the Higgs mechanism in particle physics to the spin density wave in condensed matter physics. The present text describes the detailed studies that the author has done, in order to explore the role of electron-electron interaction induced spontaneous symmetry breaking in two different systems: the iron-pnictides and perovskite [111] bilayers. For the iron-pnictides, we firstly derived the t − J model from the two- orbital Hubbard model in the strong coupling limit. The result is totally different from the famous single-orbital t−J model. Following this model, our group calculated the phase diagram of the iron-pnictides via the Lanczos method.[1] Secondly, we calculated the optical conductivity of the iron-pnictides using the three-orbital Hubbard model under the mean-field approximation and obtained the anisotropy of the optical conductivity which agrees with experiments well. We explained this phenomenon by an effective shift of the Fermi surface induced by electron-electron interaction. For the perovskite [111] bilayers, we used the two-orbital Hubbard model under the mean-field approximation to explore how will the electron-electron interaction produce a Chern-insulator when a flat band is present, and also how can domain structures be formed by applying doping to a quantum Hall ferromagnet