Landau Level Crossings and Extended-State Mapping in Magnetic Two-dimensional Electron Gases

We present longitudinal and Hall magneto-resistance measurements of a ``magnetic'' two-dimensional electron gas (2DEG) formed in modulation-doped Zn$_{1-x-y}$Cd$_{x}$Mn$_{y}$Se quantum wells. The electron spin splitting is temperature and magnetic field dependent, resulting in striking features as Landau levels of opposite spin cross near the Fermi level. Magnetization measurements on the same sample probe the total density of states and Fermi energy, allowing us to fit the transport data using a model involving extended states centered at each Landau level and two-channel conduction for spin-up and spin-down electrons. A mapping of the extended states over the whole quantum Hall effect regime shows no floating of extended states as Landau levels cross near the Fermi level.Comment: 10 pages, 4 figures, submitted to Phys. Rev.

The Hagedorn transition in non-commutative open string theory

The Hagedorn transition in non-commutative open string theory (NCOS) is relatively simple because gravity decouples. For NCOS theories in no more than five spacetime dimensions, the Hagedorn transition is second order, and the high temperature phase involves long, nearly straight fundamental strings separating from the D-brane on which the NCOS theory is defined. Above five spacetime dimensions interaction effects become important below the Hagedorn temperature. Although this complicates studies of the transition, we believe that the high temperature phase again involves long strings liberated from the bound state.Comment: 22 pages, latex, one figure. v2: references added. v3: more references adde

ФОРМИРОВАНИЕ ТУАЛЕТНЫХ НАВЫКОВ У ДЕТЕЙ ИЗ СЕМЕЙ ОБЩЕЙ ПОПУЛЯЦИИ И СЕМЕЙ С ВЫСОКИМ СОЦИАЛЬНО-ЭКОНОМИЧЕСКИМ СТАТУСОМ. СРАВНИТЕЛЬНОЕ ИССЛЕДОВАНИЕ

Goal: to compare the main parameters of toilet skills formation in between children of the common population and those from families with a high social and economic status. Methods: 1068 parents with children 2–5 years of age were questioned using a specially developed questionnaire. Results: 1012 children from the common population (CP) and 56 children from families with a relatively high economic and social status (RHESS) were studied. The average age at the beginning of toilet training appeared to be the same 15,17 ± 0,23 months (CP) and 15,6 ± 0,8 months (RHESS). In the CP group 29.5% of parents started toilet training before their children reached the age of 1 year — which is twice more often than in the RHESS group. The RHESS children finish toilet training approx. 1.9 months earlier. The overall training turned out to be shorter in the RHESS group by more than 2 months: 10,5 ± 0,6 against 12,88 ± 0,41 months (р < 0,05). Serious differences were discovered in the teaching methods: parents from the CP group are more inclined towards forced placement of the child onto the pot and to more active actions demonstrating at the same time more variety in methodology, while in the RHESS group the methodology is more homogeneous with techniques oriented at the child’s choice and a moderate parental activity are dominating. Conclusion. The methods of child toilet training in families with a high economic and social status is different from those most popular in the general population. The training in the RHESS group is slightly faster and is concluded earlier.  Цель исследования: сравнение основных параметров формирования навыков туалета у детей из семей общей популяции и детей из семей с высоким социально-экономическим статусом. Методы. Проведено анкетирование 1068 родителей детей в возрасте от 2 до 5 лет с помощью специально разработанного опросника. Результаты. Всего обследовано 1012 детей общей популяции (ОП) и 56 детей из семей с относительно высоким социально-экономическим статусом (ВСЭС). Средний возраст детей к моменту начала обучения навыкам туалета в группах оказался одинаковым: 15,17 ± 0,23 мес (группа ОП) и 15,6 ± 0,8 мес (группа ВСЭС). В группе ОП обучение в возрасте ребенка до 1 года жизни начинало 29,5% родителей ― в два раза чаще, чем в группе ВСЭС. Дети из группы высокого социально-экономического статуса завершают обучение примерно на 1,9 мес раньше. Средняя продолжительность обучения туалетным навыкам от самых первых попыток обучения до полного освоения туалетных навыков в группе ВСЭС оказалась более чем на 2 мес короче, чем в группе ОП: 10,5 ± 0,6 против 12,88 ± 0,41 мес (р < 0,05). Выявлены существенные различия в методологии обучения: родители группы ОП более привержены к принудительным высаживаниям ребенка на горшок и более активным действиям при большей вариабельности методологии, тогда как в группе ВСЭС методология более однородна и доминируют техники, ориентированные на выбор ребенка и умеренную активность родительских действий в основной стадии обучения. Заключение. Методология обучения детей навыкам туалета в семьях с высоким социально-экономическим статусом отличается от наиболее популярных в общей популяции. Обучение туалетным навыкам в группе ВСЭС несколько быстрее и завершается также несколько ранее.

Toilet Training of Children from the General Population and From Families with a High Social and Economic Status. Comparative Research

Goal: to compare the main parameters of toilet skills formation in between children of the common population and those from families with a high social and economic status. Methods: 1068 parents with children 2–5 years of age were questioned using a specially developed questionnaire. Results: 1012 children from the common population (CP) and 56 children from families with a relatively high economic and social status (RHESS) were studied. The average age at the beginning of toilet training appeared to be the same 15,17 ± 0,23 months (CP) and 15,6 ± 0,8 months (RHESS). In the CP group 29.5% of parents started toilet training before their children reached the age of 1 year — which is twice more often than in the RHESS group. The RHESS children finish toilet training approx. 1.9 months earlier. The overall training turned out to be shorter in the RHESS group by more than 2 months: 10,5 ± 0,6 against 12,88 ± 0,41 months (р < 0,05). Serious differences were discovered in the teaching methods: parents from the CP group are more inclined towards forced placement of the child onto the pot and to more active actions demonstrating at the same time more variety in methodology, while in the RHESS group the methodology is more homogeneous with techniques oriented at the child’s choice and a moderate parental activity are dominating. Conclusion. The methods of child toilet training in families with a high economic and social status is different from those most popular in the general population. The training in the RHESS group is slightly faster and is concluded earlier

The strength–grain size relationship in ultrafine-grained metals

Metals processed by severe plastic deformation (SPD) techniques, such as equal-channel angular pressing (ECAP) and high-pressure torsion (HPT), generally have submicrometer grain sizes. Consequently, they exhibit high strength as expected on the basis of the Hall–Petch (H–P) relationship. Examples of this behavior are discussed using experimental data for Ti, Al, and Ni. These materials typically have grain sizes greater than ~50 nm where softening is not expected. An increase in strength is usually accompanied by a decrease in ductility. However, both high strength and high ductility may be achieved simultaneously by imposing high strain to obtain ultrafine-grain sizes and high fractions of high-angle grain boundaries. This facilitates grain boundary sliding, and an example is presented for a cast Al-7 pct Si alloy processed by HPT. In some materials, SPD may result in a weakening even with a very fine grain size, and this is due to microstructural changes during processing. Examples are presented for an Al-7034 alloy processed by ECAP and a Zn-22 pct Al alloy processed by HPT. In some SPD-processed materials, it is possible that grain boundary segregation and other features are present leading to higher strengths than predicted by the H–P relationshi