Multi-instanton and string loop corrections in toroidal orbifold models

We analyze N=2 (perturbative and non-perturbative) corrections to the effective theory in type I orbifold models where a dual heterotic description is available. These corrections may play an important role in phenomenological scenarios. More precisely, we consider two particular compactifications: the Bianchi-Sagnotti-Gimon-Polchinski orbifold and a freely-acting Z_2 x Z_2 orbifold with N=1 supersymmetry and gauge group SO(q) x SO(32-q). By exploiting perturbative calculations of the physical gauge couplings on the heterotic side, we obtain multi-instanton and one-loop string corrections to the K\"ahler potential and the gauge kinetic function for these models. The non-perturbative corrections appear as sums over relevant Hecke operators, whereas the one-loop correction to the K\"ahler potential matches the expression proposed in [1,2]. We argue that these corrections are universal in a given class of models where target-space modular invariance (or a subgroup of it) holds.Comment: 37 pages, 3 figure

Differential Effects of Buffer pH On Ca\u3csup\u3e2+\u3c/sup\u3e-Induced ROS Emission with Inhibited Mitochondrial Complexes I and III

Excessive mitochondrial reactive oxygen species (ROS) emission is a critical component in the etiology of ischemic injury. Complex I and complex III of the electron transport chain are considered the primary sources of ROS emission during cardiac ischemia and reperfusion (IR) injury. Several factors modulate ischemic ROS emission, such as an increase in extra-matrix Ca2+, a decrease in extra-matrix pH, and a change in substrate utilization. Here we examined the combined effects of these factors on ROS emission from respiratory complexes I and III under conditions of simulated IR injury. Guinea pig heart mitochondria were suspended in experimental buffer at a given pH and incubated with or without CaCl2. Mitochondria were then treated with either pyruvate, a complex I substrate, followed by rotenone, a complex I inhibitor, or succinate, a complex II substrate, followed by antimycin A, a complex III inhibitor. H2O2 release rate and matrix volume were compared with and without adding CaCl2 and at pH 7.15, 6.9, or 6.5 with pyruvate + rotenone or succinate + antimycin A to simulate conditions that may occur during in vivo cardiac IR injury. We found a large increase in H2O2 release with high [CaCl2] and pyruvate + rotenone at pH 6.9, but not at pHs 7.15 or 6.5. Large increases in H2O2 release rate also occurred at each pH with high [CaCl2] and succinate + antimycin A, with the highest levels observed at pH 7.15. The increases in H2O2 release were associated with significant mitochondrial swelling, and both H2O2 release and swelling were abolished by cyclosporine A, a desensitizer of the mitochondrial permeability transition pore (mPTP). These results indicate that ROS production by complex I and by complex III is differently affected by buffer pH and Ca2+ loading with mPTP opening. The study suggests that changes in the levels of cytosolic Ca2+ and pH during IR alter the relative amounts of ROS produced at mitochondrial respiratory complex I and complex III

The crystal structure of sacrofanite, the 74 Å phase of the cancrinite–sodalite supergroup

Sacrofanite, a = 12.903(2) Å, c = 74.284(8) Å, space group View the MathML source, belongs to the cancrinite–sodalite supergroup of minerals, and displays a 28-layer stacking sequence along the c axis. Its stacking sequence is ABCABACACABACBACBACABABACABC…, where A, B and C stand for the positions of six-member rings of tetrahedra in each layer. It corresponds to the Zhdanov symbol |12(8)21|12(8)21|, and gives rise to a framework with topological symmetry P63/mmc. The ordering of Si and Al in the tetrahedral sites reduces the symmetry to View the MathML source. The members of this supergroup of minerals belong to the wider ABC-6 family, where also double rings of tetrahedra may occur. They share many structural features with zeolites, showing structural cages hosting extra-framework ions as well as H2O molecules. The crystal structure of sacrofanite has been modelled on the basis of High Resolution Transmission Electron Microscopy (HRTEM) images. The resulting model has been successfully refined by using both single-crystal synchrotron radiation and laboratory data. The refinements converged to R = 0.083 for 4228 unique reflections, and to R = 0.096 for 15,795 unique reflections, respectively. The resulting framework is formed by eight cancrinite and four sodalite cages superimposed along [0, 0, z], whereas one cancrinite, four sodalite, two losod, and one liottite cages occur along [1/3, 2/3, z] and [2/3, 1/3, z]. The structural formula of sacrofanite, as obtained from the refinement and by crystal chemical considerations, is (Na61K19Ca32)∑=112(Si84Al84O336)(SO4)26Cl2F6·2H2O

ENSINANDO GEOMETRIA SEM O USO DE CALCULADORES: UM CASO EXPERIMENTAL EM APRENDIZES TAILANDESES DA 9ª SÉRIE

Should we solve geometry problems using calculators? This study identified the effect of using (and not using) calculators during calculations on geometry problems sets, as well as the perceived impact on the use of calculators based on students’, parents’ and school administrators’ perception in a school in Bangkok, Thailand. This study combined both qualitative (survey and interview) and quantitative techniques (experiment) to address the research problem. Findings revealed that the performance of students who used calculators in the experiment did not significantly differ with those who did not which suggests that non-usage of calculators will not affect solving geometry problems, at least in the context of Thai Math education. Further, survey showed that students only used calculators ‘sometimes’ outside class and gave diverse responses when asked why. Interview with parents, students and administrators showed transcript extracts mostly on their agreement to use calculators in geometry class citing the convenience and speed of doing problems but implied a negative impact on their academic performance in math problems in the real world. This study could provide a baseline information on the use of calculators in the teaching of Math lessons for other nationalities.Devemos resolver problemas de geometria usando calculadoras? Este estudo identificou o efeito do uso (ou não) de calculadoras durante cálculos em conjuntos de problemas de geometria, bem como o impacto percebido no uso de calculadoras com base na percepção de alunos, pais e administradores de escolas em uma escola em Bangkok, Tailândia . Este estudo combinou técnicas qualitativas (pesquisa e entrevista) e quantitativas (experimento) para abordar o problema de pesquisa. Os resultados revelaram que o desempenho dos alunos que usaram calculadoras no experimento não diferiu significativamente daqueles que não o fizeram, o que sugere que o não uso de calculadoras não afetará a resolução de problemas de geometria, pelo menos no contexto do ensino de matemática tailandês. Além disso, a pesquisa mostrou que os alunos só usavam calculadoras "às vezes" fora da classe e deram diversas respostas quando questionados sobre o motivo. Entrevistas com pais, alunos e administradores mostraram trechos de transcrição principalmente sobre sua concordância em usar calculadoras nas aulas de geometria, citando a conveniência e a velocidade de resolver os problemas, mas implicando um impacto negativo em seu desempenho acadêmico em problemas matemáticos no mundo real. Este estudo pode fornecer informações básicas sobre o uso de calculadoras no ensino de aulas de matemática para outras nacionalidades

Selective epitaxial growth of graphene on SiC

We present an innovative method of selective epitaxial growth of few layers graphene (FLG) on a pre-patterned SiC substrate. The methods involves, successively, the sputtering of a thin AlN layer on top of a mono-crystalline SiC substrate and, then, patterning it with e-beam lithography (EBL) and wet etching. The sublimation of few atomic layers of Si from the SiC substrate occurs only through the selectively etched AlN layer. The presence of the Raman G-band at ~1582 cm-1 in the AlN-free areas is used to validate the concept, it gives absolute evidence of the selective FLG growth.Comment: comments: 3 pages, reference 3 replace