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

Investment and Growth in Rich and Poor Countries

This paper revisits the association between investment and growth. The empirical findings highlight substantial heterogeneity for the effect of investment on growth and suggest a possible negative association. Results based on a battery of cross-sectional and time-series regressions show that the link between investment and growth has weakened over time and that investment in high-income countries is more likely to have a negative effect on growth. The adverse effect for high-income countries appears to have increased over time. An implication is that uphill capital flows could be associated with negative or zero returns. The result is robust to the presence of control variables that are commonly included in growth studies.

Rural youth in search of social lift: opportunities and risks

В докладе представлены результаты социологического исследования современной сельской молодежи Краснодарского при помощи глубинного интервью. Анализируются особенности социальных перемещений молодых сельчан в условиях социально-экономической стагнации сельской местности.This report presents the results of the survey of contemporary rural youth Krasnodar using in-depth interviews. Analyzes the characteristics of the social movements of young villagers in terms of socio-economic stagnation countryside

Моделирование авиапассажирских перевозок России

The use of economic and mathematical methods of forecasting the results of activities of civil aviation organisations, and in particular assessment of the volume of air passenger traffic is quite relevant due to the importance of operational planning of air transport processes, development of strategic directions, technological and technical renewal of air enterprises.The objective of the study is to plan the traffic flow of air passengers using a regression model, considering the results of multifactorial selection of determinants, particularly distinguishing fundamental macro indicators are distinguished, as well as significant indicators of the aviation market.The study of passenger air transportation was carried out using methods of system analysis, methods of mathematical statistics and econometrics. Modelling of the process of passenger transportation has identified the main determinants that positively or negatively affect the dynamics of air passenger traffic. The multiple regression of the study of the processes of connectivity and synchronicity of changes in development of passenger traffic and selected macro indicators in a generalised form is the sum of vectors of influencing variables adjusted for the calculated coefficients.Six-, four- and three-factor regression models were developed. The three-factor model turned to be more reliable with values most close to actual data. Nevertheless, while applying regression model for forecasting air traffic it is necessary to consider not only theoretical aspects, data of official forecasts of macro indicators but expert opinions as well.Применение экономико-математических методов прогнозирования результатов деятельности организаций гражданской авиации и, в частности, объёмов авиапассажирских перевозок в силу важности оперативного планирования процессов авиатранспорта, разработки стратегических направлений его развития, технологического и технического обновления авиапредприятий достаточно актуально.Цель исследования состоит в планировании авиапотока пассажиров по регрессионной модели с учётом результатов многофакторного отбора детерминант, среди которых выделяют фундаментальные макропоказатели, а также значимые показатели авиарынка.Исследование пассажирских авиаперевозок проводилось с использованием методов системного анализа, методов математической статистики и эконометрики. При моделировании процесса пассажирских перевозок выделены основные детерминанты, положительно или отрицательно влияющие на динамику авиапассажиропотока. Множественная регрессия исследования процессов связанности и синхронности изменений развития пассажиропотока и отобранных макропоказателей в обобщённом виде является суммой векторов влияющих переменных с поправкой на рассчитанные коэффициенты.В результате разработаны шести-, четырёх- и трёх- факторные регрессионные модели, из которых последняя обладает наибольшей достоверностью с достаточно близкими к фактическим значениям данными. При прогнозировании пассажиропотока по регрессионной модели необходимо учитывать не только теоретические аспекты, данные официальных прогнозов макропоказателей, но и мнение экспертов

Моделирование цен авиаперевозок пассажиров

The pricing policy of airlines is developed based on a retrospective analysis of the price dynamics of air transportation and forecasting the market situation of supply and demand. The price dynamics of passenger air transportation has a certain structure and patterns, the identification of which helps to develop a competitive price offer for consumers.The objective of the work is to determine the structure of price dynamics and identify patterns of price fluctuations in passenger air transportation from 2008 to 2022, which is important to consider when developing the pricing policy of airlines and the range of tariffs. Studies of the price dynamics of airline tickets by econometric methods allowed to identify the structure of the time series of prices and develop several models.The study of the price dynamics structure, first, identified and analysed the seasonal component of the dynamics of airline ticket prices. Its calculation was carried out using additive and multiplicative models. The range of seasonal changes was -8,5% to +12,5%. The autocorrelation function of the dynamics of average monthly prices showed that the time series of airline ticket prices contained a trend. In addition to trend and seasonal components, cyclical fluctuations were identified in the price dynamics, the modelling of which was carried out based on regression analysis. Cyclical changes in the dynamics of air ticket prices, identified from 2008 to the present, are not sustainable.Analysed dynamics revealed several medium-term cycles with a duration of 4–6 years. The cyclical dynamics of air transportation prices largely coincides with the general economic medium-term cycles, but there are time lags or lagging growth and decline rates.Thus, the change in prices for civil air transportation has a natural trend-cyclical character shaped under the influence of fundamental macroeconomic factors and new determinants, the effect of which may result in a stronger change but with shorter impact or lag effect. Additive and multiplicative models will help predict average annual prices.Ценовая политика авиакомпаний разрабатывается на основании ретроспективного анализа ценовой динамики авиаперевозок и прогнозирования рыночной ситуации спроса и предложения. Ценовая динамика пассажирских авиаперевозок имеет определённую структуру и закономерности, выявление которых помогает формировать конкурентоспособное ценовое предложение для пассажиров.Цель работы заключается в исследовании структуры ценовой динамики с 2008 года по 2022 год и выявлении закономерностей движения цен на пассажирские авиаперевозки, что важно учитывать при определении ценового курса и диапазона цен тарифов. Исследования ценовой динамики авиабилетов эконометрическими методами позволили выявить структуру временного ряда цен и разработать ряд моделей.При исследовании структуры ценовой динамики в первую очередь была выделена и проанализирована сезонная компонента, расчёт которой проводился по аддитивным и мультипликативным моделям. Диапазон сезонных изменений составляет -8,5 % до +12,5 %. Автокорреляционная функция динамики среднемесячных цен показала, что временной ряд цен на авиабилеты содержит тренд. Кроме трендовых и сезонных компонент в динамике цен выделены циклические колебания, моделирование которых проводилось на основе регрессионного анализа. Циклические изменения динамики цен на авиабилеты, выявленных с 2008 года по настоящее время, не имеют устойчивого характера.В анализируемой динамике выделено несколько среднесрочных циклов продолжительностью 4–6 лет. Цикличность динамики цен на авиаперевозки во многом совпадает с общеэкономическими среднесрочными циклами, но присутствуют временные лаги запаздывания или отставание темпов роста или снижения.Таким образом, изменение цен на гражданские авиаперевозки имеет закономерный трендциклический характер, формирующийся под действием фундаментальных макроэкономических факторов и новых детерминант, действие которых может вызывать более сильное изменение, но с кратким периодом воздействия, или лаговое влияние. Аддитивные и мультипликативные модели помогут спрогнозировать среднегодовые цены авиатарифов

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

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