Search results for "transition [photon]"
showing 10 items of 273 documents
Phase transition in NaSn2(PO4)3 and thermal expansion of NaMIV2 (PO43; MIV = Ti, Sn, Zr
1991
Abstract NaSn2(PO4)3 presents a fast and reversible second order phase transition about 575°C. Both phases above and below the transition point are rhombohedral. The high temperature phase is isostructural with NaTi2(PO4)3 and NaZr2(PO4)3, NZP structure. The lattice thermal expansion of these three compounds has been determined from x-ray diffraction data at different temperatures ranging from room temperature up to 1000°C. Differences in behaviour are discussed in relation to the structure.
Chirality effects on 2D phase transitions
1996
Monolayers of the racemate and pure enantiomers of 1-hexadecyl-glycerol were investigated by grazing incidence X-ray diffraction (GID) at 5 and 20 °C on compression from 0 mN m−1 to pressures greater than 30 mN m−1. The racemate lattice is centred-rectangular for both temperatures at all investigated pressures. However, at both temperatures, there is a sharp phase transition from a low-pressure phase, in which the molecules are tilted towards nearest neighbours (NN) and the distortion azimuth also points towards NN, to a high-pressure phase, in which the molecules are tilted towards next-nearest neighbours (NNN) and an NNN-distorted lattice is observed. At 5 °C, the transition pressure is 1…
Mechanisms at structural phase transitions
2007
Abstract Structural phase transitions in crystalline solids are accompanied with the change of symmetry. After EHRENFEST [Ehrenfest, P., Phasenumwandlungen im ublichen und erweiterten Sinn, klassifiziert nach den entsprechenden Singularitaten des thermodynamischen Potentials. Proc. Kon., Amsterdam Acad., 1933, 36(Suppl 75b), 153–157] they can be distinguished between first and second order transitions. Two examples for first and second order transitions will be discussed in order two elaborate the characteristic features. The statements are verified by diffraction experiments; the second order transitions will be discussed on the basis of the LANDAU [Landau, L. and Lifshitz, E.M., Lehrbuch …
Preparation of superconducting thin films of UNiAl
2005
Abstract Epitaxial thin films of the unconventional heavy fermion superconductor UNi 2 Al 3 we prepared by coevaporation of the elementary components in a molecular beam epitaxy system (MBE). The phase purity and structural quality of the films deposited on (0 1 0)- or (1 1 2)-oriented YAlO 3 substrates were studied by X-ray diffraction and RHEED. The observed R ( T ) behavior is consistent with data obtained from bulk samples and proves the purity of the films. Superconductivity was found with transition temperature T c =0.97 K.
Polarization and suburbanisation in Warsaw
2001
The economic transition in Poland leads to a restructuration of economic activities which affects spatial patterns of cities, especially in Warsaw. Analyzing the location and re-location of population and employment in Poland’s capital allows to enlarge the debate on the suburbanization forms to the Central and Oriental European Countries. The results support the fact that the city center is still largely the most important district in terms of population andemployment, so that in 1999 the city keeps a strong monocentric character. However, from 1994 to 1999, population and employment move towards the Warsaw’s suburbs. Two significant observations, namely the suburbanization of retailing an…
Choices and Enrollments in French Secondary and Higher Education: Repercussions for Second-Generation Immigrants
2013
En ligne sur http://www.jstor.org/discover/10.1086/670729?uid=16804784&uid=3738016&uid=2129&uid=2134&uid=2&uid=70&uid=3&uid=67&uid=16735408&uid=62&uid=5909928&sid=21102655856551; International audience; In France, the proportion of second-generation immigrants enrolling in tertiary education has increased as education has undergone a process of "democratization." This article analyzes their postsecondary choices, access to tertiary programs, dropout, and transition to the labor market, compared to those of students of French origin. Youths of Portuguese origin are more likely to enter vocational higher programs concordant with their preferences and have better chances of completing a tertia…
The Oblivion of Demography in Sustainability’s Studies
2017
[RESUMEN] A lo largo de la historia del Homo sapiens, su número se ha mantenido muy reducido y hubo que esperar a principios del siglo XIX para que alcanzara los mil millones. Se inició entonces un rápido crecimiento y durante el siglo XX la población mundial casi se cuadriplicó, superando los 6000 millones, lo que llevó a estudiar, con lógica preocupación, los posibles efectos de esta explosión demográfica sobre el conjunto de la biosfera y sobre la propia especie humana. Hoy, sin embargo, cuando se han sobrepasado los 7500 millones y la población mundial sigue aumentando en unos 80 millones cada año, la problemática demográfica ha dejado de tener una presencia relevante en los estudios y …
La transición a la sostenibilidad como objetivo urgente para la superación de la crisis sistémica actual
2016
Este trabajo pretende contribuir a cuestionar la creencia, ampliamente extendida entre la ciudadanía, los responsables políticos, e incluso entre los educadores, de que la transición a la Sostenibilidad es un objetivo para el futuro, que puede esperar ante las necesidades urgentes del presente. Se intenta mostrar que, por el contrario, dicha transición es necesaria ahora para dar solución a graves problemas interconectados, que amenazan ya seriamente a la presente generación, como el cambio climático, la pérdida de biodiversidad, el agotamiento de recursos fundamentales, o la pobreza y el desempleo masivo que destruyen la cohesión social. Se puede de este modo dar respuesta hoy a las necesi…
Molecular origin and hydration dependence of protein anharmonicity: an elastic neutron scattering study.
2010
Two main onsets of anharmonicity are present in protein dynamics. Neutron scattering on protein hydrated powders revealed a first onset at about 150 K and a second one at about 230 K (the so called dynamical transition). In order to assess the molecular origin of protein anharmonicity, we study different homomeric polypeptides by incoherent elastic neutron scattering, thus disentangling the contribution of different molecular groups in proteins. We show that methyl group rotations are the main contributors to the low temperature onset. Concerning the dynamical transition, we show that it also occurs in absence of side chains; however, the presence and mobility of side chains substantially i…
Marchés du travail et disparités régionales en Pologne
2001
This article evaluates empirically the effect o f market introduction on the level o f regional inequalities and on the polarisation o f economic activities in Poland. We note an increase o f the disparities between regions over the relevant period. The re-polarisation process cannot been explained by a spatial re-allocation of labour force but rather results o f the differentiation of sectoral restructuring between regions the regional diversity o f sectoral adaptation. The search for agglomeration economies explains the spatial concentration o f services and o f added value in the regions where the biggest cities are located. A cumulative process o f agglomeration is observed. Therefore, …