Mechanism of phase transitions and the electronic density of states in (La,Sm)FeAsO1−x_{1-x}Fx_x from ab initio calculations

The structure and electronic density of states in layered LnFeAsO$_{1-x}$F$_x$ (Ln=La,Sm; $x$=0.0, 0.125, 0.25) are investigated using density functional theory. For the $x$=0.0 system we predict a complex potential energy surface, formed by close-lying single-well and double-well potentials, which gives rise to the tetragonal-to-orthorhombic structural transition, appearance of the magnetic order, and an anomaly in the specific heat capacity observed experimentally at temperatures below $\sim$140--160 K. We propose a mechanism for these transitions and suggest that these phenomena are generic to all compounds containing FeAs layers. For $x>$0.0 we demonstrate that transition temperatures to the superconducting state and their dependence on $x$ correlate well with the calculated magnitude of the electronic density of states at the Fermi energy.Comment: 4 pages, 3 figures, 1 tabl

Quality of life of school and university students with acne

Acne may have severe negative impact on different aspects of patient health-related quality of life (HRQoL). Prevalence of acne in university and school students is high, and the HRQoL of students with acne from different countries was studied. There is a lack of studies on direct comparison of HRQoL impairment of university and school students with acne. The Cardiff Acne Disability Index (CADI) was used to assess the HRQOL in university and school students with self-assessed acne. The CADI results from 159 university and 99 school students with self-reported acne were obtained. Mean age of university and school students was 20.99±1.47 (mean ± Standard Deviation) and 14.10±0.51 years, respectively. Reported impact on QoL of university students was significantly higher (3.33±2.26 and 2.76±2.42, P&lt;0.05). Total CADI scores negatively correlated with the age of university students (r=-0.16; P&lt;0.05). Analysis of gender differences of university students showed that negative correlation of HRQoL with age was present in women (r=-0.22; P&lt;0.05) but absent in male students (r=0.05; P=0.77). Female university students reported more severe impact of acne on their life (2.55±2.31 in male and 3.59±2.20 in female students, P&lt;0.01). Our results showed that university students experience higher impact of acne on their life than school students. The highest is the impact on young female university students. We recommend paying more attention to the psychological aspects of young female students with acne during consultations. </p

Quality of life of school and university students with acne

Acne may have severe negative impact on different aspects of patient health-related quality of life (HRQoL). Prevalence of acne in university and school students is high, and the HRQoL of students with acne from different countries was studied. There is a lack of studies on direct comparison of HRQoL impairment of university and school students with acne. The Cardiff Acne Disability Index (CADI) was used to assess the HRQOL in university and school students with self-assessed acne. The CADI results from 159 university and 99 school students with self-reported acne were obtained. Mean age of university and school students was 20.99±1.47 (mean ± Standard Deviation) and 14.10±0.51 years, respectively. Reported impact on QoL of university students was significantly higher (3.33±2.26 and 2.76±2.42, P&lt;0.05). Total CADI scores negatively correlated with the age of university students (r=-0.16; P&lt;0.05). Analysis of gender differences of university students showed that negative correlation of HRQoL with age was present in women (r=-0.22; P&lt;0.05) but absent in male students (r=0.05; P=0.77). Female university students reported more severe impact of acne on their life (2.55±2.31 in male and 3.59±2.20 in female students, P&lt;0.01). Our results showed that university students experience higher impact of acne on their life than school students. The highest is the impact on young female university students. We recommend paying more attention to the psychological aspects of young female students with acne during consultations. </p

First order transition and phase separation in pyrochlores with colossal-magnetoresistance

Tl$_{2}$Mn$_{2}$O$_{7}$ pyrochlores present colossal magnetoresistance (CMR) around the long range ferromagnetic ordering temperature (T$_{C}$). The character of this magnetic phase transition has been determined to be first order, by purely magnetic methods, in contrast to the second order character previously reported by Zhao et al. (Phys. Rev. Lett. 83, 219 (1999)). The highest CMR effect, as in Tl$_{1.8}$Cd$_{0.2}$Mn$_{2}$O$_{7}$, corresponds to a stronger first order character. This character implies a second type of magnetic interaction, besides the direct superexchange between the Mn$^{4+}$ ions, as well as a phase coexistence. A model is proposed, with a complete Hamiltonian (including superexchange and an indirect interaction), which reproduce the observed phenomenology.Comment: 6 pages. Figures include

Modelling charge self-trapping in wide-gap dielectrics: Localization problem in local density functionals

We discuss the adiabatic self-trapping of small polarons within the density functional theory (DFT). In particular, we carried out plane-wave pseudo-potential calculations of the triplet exciton in NaCl and found no energy minimum corresponding to the self-trapped exciton (STE) contrary to the experimental evidence and previous calculations. To explore the origin of this problem we modelled the self-trapped hole in NaCl using hybrid density functionals and an embedded cluster method. Calculations show that the stability of the self-trapped state of the hole drastically depends on the amount of the exact exchange in the density functional: at less than 30% of the Hartree-Fock exchange, only delocalized hole is stable, at 50% - both delocalized and self-trapped states are stable, while further increase of exact exchange results in only the self-trapped state being stable. We argue that the main contributions to the self-trapping energy such as the kinetic energy of the localizing charge, the chemical bond formation of the di-halogen quasi molecule, and the lattice polarization, are represented incorrectly within the Kohn-Sham (KS) based approaches.Comment: 6 figures, 1 tabl

Spin Fluctuation-Induced Superconductivity in Organic Compounds

Spin fluctuation-induced superconductivity in two-dimensional organic compounds such as \kappa-(ET)_2-X is investigated by using a simplified dimer Hubbard model with right-angled isosceles triangular lattice (transfer matrices -\tau, -\tau^\prime). The dynamical susceptiblity and the self-energy are calculated self-consistently within the fluctuation exchange approximation and the value for T_c as obtained by solving the linearized Eliashberg-type equations is in good agreement with experiment. The pairing symmetry is of d_{x^2-y^2} type. The calculated (U/\tau)-dependence of T_c compares qualitatively well with the observed pressure dependence of T_c. Varying the value for \tau^\prime/\tau from 0 to 1 we interpolate between the square lattice and the regular triangular lattice and find firstly that values of T_c for \kappa-(ET)_2-X and cuprates scale well and secondly that T_c tends to decrease with increasing \tau^\prime/\tau and no superconductivity is found for \tau^\prime/\tau=1, the regular triangular lattice.Comment: 4 pages, 6 eps figures, uses jpsj.st

Ценности и электоральное поведение российских граждан на президентских выборах (2012, 2018 гг.): постоянство и изменчивость

Based on the empirical data of two sociological studies conducted in accordance with the uniform methodology using the personal questionnaire method in April 2012 and May 2018 (almost immediately after the election of the President of the Russian Federation), the article analyzes the structure of values of Russian urban voters, influencing their attitude to participation in the presidential elections and to the competing candidates. The socio-economic and socio-political conditions in Russia and their influence on the structure of values of urban voters are considered in the article. The article reveals the reasons why the fewer urban voters participated in the elections and a much larger number of them voted for Vladimir Putin when the economic situation of voters deteriorated in 2012 compared to 2018.The article shows that the structure of values of urban voters remains predominantly “materialistic” (according to Ronald Inglehart). The influence of the value structure of voters on their participation in voting at the presidential election and on the support of a certain candidate is revealed. On the basis of comparing the results of the presidential elections in 2012 and 2018, it is shown that during 6 years the ideological spectrum of candidates has expanded and began to express a wider range of political views on the further development of Russian society and state — from extremely liberal, democratic to extremely conservative, totalitarian, which is essential feature of the modern Russian party and political system. The middle of this spectrum was represented by liberal conservatism of Vladimir Putin, and his support in 2018 reflects a shift in the values of urban voters from the extreme right and the extreme left to the middle, toward liberal conservatism that is becoming inherent in an increasing number of urban voters.It is revealed that within the framework of the “materialistic” value structure of urban voters, the value of material wealth does not play a significant role when voters choose the future development of Russia. The value of unselfish patriotism and family is in the first place. The difficult political conditions in Russia in 2018 gave the voters patriotism a militant character that was absent in 2012. It united Russian society around Vladimir Putin even more and was the cause of a significant increase in his support from voters. Liberal component of conservatism in the program of Vladimir Putin (the expansion of economic, political, and spiritual freedoms) led to his support from moderately liberal voters. All these factors together predetermined the great success of Vladimir Putin in the presidential elections in Russia in 2018.На протяжении многих лет кафедра методологии социологических исследований разрабатывает проблему ценностного измерения российского общества и связь его ценностной структуры с политическим поведением граждан. Результаты проведенных исследований опубликованы в ряде статей в научных журналах. Результаты последнего исследования данной проблемы представлены в данной статье.На основе эмпирических данных двух социологических исследований, проведенных по единой методике с использованием метода личного анкетирования, в апреле 2012 г. и мае 2018 г. — почти сразу после выборов Президента РФ, в статье анализируется структура ценностей городских избирателей России, оказывающая влияние на их отношение к участию в президентских выборах, к выдвинувшимся на них кандидатам. Рассматриваются социально-экономические и социально-политические условия в России и их влияние на структуру ценностей городских избирателей. Выявляются причины того, почему при ухудшении экономического положения избирателей в 2018 г. по сравнению с 2012 г., меньшее количество городских избирателей участвовало в выборах и существенно большее их количество проголосовало за В. Путина.В статье показано, что структура ценностей городских избирателей остается преимущественно “материалистической” (по Р. Инглхарту), при этом в ней усиливается роль “постматериалистических” ценностей. Раскрыто влияние ценностной структуры избирателей на их участие в голосовании на президентских выборах и на поддержку того или иного кандидата. На основе сравнения результатов президентских выборов в 2012 и 2018 г. показано, что за 6 лет идеологический спектр кандидатов расширился и стал выражать более широкий диапазон политических взглядов на дальнейшее развитие российского общества и государства — от крайне либеральных, демократических, до крайне консервативных, тоталитарных, что является существенной особенностью современной российской партийно-политической системы. Середину этого спектра представлял либеральный консерватизм В. Путина и его поддержка в 2018 г. отражает сдвиг ценностей городских избирателей от крайне правых и крайне левых к середине — к либеральному консерватизму.Выявлено, что в рамках “материалистической” структуры ценностей городских избирателей, ценность материального достатка не играет существенной роли при выборе избирателями будущего развития России. На первом месте находится ценность бескорыстного патриотизма и семьи. Сложные политические условия, в которых оказалась Россия в 2018 г., придали патриотизму избирателей воинственный характер, который отсутствовал в 2012 г., что в еще большей степени объединило российское общество вокруг В. Путина и стало причиной существенного роста его поддержки со стороны избирателей. Либеральная составляющая консерватизма в программе В. Путина — расширение экономических, политических и духовных свобод — привела к его поддержке со стороны умеренно либеральных избирателей. Все это вместе предопределило самый большой успех В. Путина на выборах Президента РФ в 2018 г

Perturbation Theory on the Transition Temperature and Electronic Properties of Organic Superconductor

We study the superconducting transition temperature and the electronic properties of the metallic phase of $\kappa$-type (BEDT-TTF)$_2$X which shows unconventional properties in experiments, on the basis of the third order perturbation theory for a simple effective Hubbard model of a nearly triangular lattice. Appropriate transition temperatures and $d_{x^2-y^2}$ symmetry of the gap function are obtained in good agreement with experimental results. We also calculate the transition temperature by the fluctuation-exchange approximation(FLEX) in order to compare the two approaches; FLEX gives higher transition temperatures rather than the perturbation approach. However, it is also found that the vertex corrections, which are ignored in FLEX, have a crucial effect on $T_{\rm c}$ for strongly frustrated systems. The density of states and the normal self-energy calculated in this perturbation scheme show the nature of the conventional Fermi liquid near the Mott-insulator. Thus, our perturbation approach is applicable to the conventional metallic phase of this compound, while it cannot explain the (pseudo-)spin gap phenomenon which signals the non-Fermi liquid