72 research outputs found
On orientational relief of inter-molecular potential and the structure of domain walls in fullerite C60
A simple planar model for an orientational ordering of threefold molecules on
a triangular lattice modelling a close-packed (111) plane of fullerite is
considered. The system has 3-sublattice ordered ground state which includes 3
different molecular orientations. There exist 6 kinds of orientational domains,
which are related with a permutation or a mirror symmetry. Interdomain walls
are found to be rather narrow.
The model molecules have two-well orientational potential profiles, which are
slightly effected by a presence of a straight domain wall. The reason is a
stronger correlation between neighbour molecules in triangular lattice versus
previously considered square lattice
A considerable reduction (up to one order) of orientational interwell
potential barrier is found in the core regions of essentially two-dimentional
potential defects, such as a three-domain boundary or a kink in the domain
wall. For ultimately uncorrelated nearest neighbours the height of the
interwell barrier can be reduced even by a factor of 100.Comment: 11 pages, 13 figures, LaTeX, to appear in Low Temperature Physic
Evolution of forest pedogenesis in the south of the forest-steppe of the Central Russian Upland in the Late Holocene
The Late Holocene stage of forest pedogenesis has been studied on the interfluves along river valleys in the forest-steppe zone of the Central Russian Upland. The development of gray forest soils from the former chernozems as a result of the Late Holocene advance of forest vegetation over steppes is discusse
Low temperature thermal expansion of pure and inert gas-doped Fullerite C60
The low temperature (2-24 K) thermal expansion of pure (single crystal and
polycrystalline) C60 and polycrystalline C60 intercalated with He, Ne, Ar, and
Kr has been investigated using high-resolution capacitance dilatometer. The
investigation of the time dependence of the sample length variations on heating
shows that the thermal expansion is determined by the sum of positive and
negative contributions, which have different relaxation times. The negative
thermal expansion usually prevails at helium temperatures. The positive
expansion is connected with the phonon thermalization of the system. The
negative expansion is caused by reorientation of the C60 molecules. It is
assumed that the reorientation is of quantum character. The inert gas
impurities affect very strongly the reorientation of the C60 molecules
especially at liquid helium temperatures. A temperature hysteresis of the
thermal expansion coefficient of Kr- and He- C60 solutions has been revealed.
The hysteresis is attributed to orientational polyamorphous transformation in
these systems.Comment: 18 pages, 12 figure
Thermal expansion of solid solutions Kr-CH4 at temperatures of liquid helium
A negative contribution of the CH4 impurity to the thermal expansion of the
solution has been revealed in dilatometric studies of solid Kr+0.76% CH4,
Kr+5.25% CH4 and Kr+10.5% CH4 solutions at 1-23 K. It is shown that the
negative contribution results from changes in the occupancy of the ground state
of the A-modifications of isolated CH4 molecules. Assuming that the CH4
impurity singles and clusters contribute to the thermal expansion
independently, we can estimate their contributions. The contribution of the
singles to the thermal expansion of the solid solution is negative. The
energies of the first excitational rotational states were determined for
singles and two-body and three-body clusters of CH4 molecules.Comment: 10 pages, 7 figure
On the polyamorphism of fullerite-based orientational glasses
The dilatometric investigation in the temperature range of 2-28K shows that a
first-order polyamorphous transition occurs in the orientational glasses based
on C60 doped with H2, D2 and Xe. A polyamorphous transition was also detected
in C60 doped with Kr and He. It is observed that the hysteresis of thermal
expansion caused by the polyamorphous transition (and, hence, the transition
temperature) is essentially dependent on the type of doping gas. Both positive
and negative contributions to the thermal expansion were observed in the low
temperature phase of the glasses. The relaxation time of the negative
contribution occurs to be much longer than that of the positive contribution.
The positive contribution is found to be due to phonon and libron modes, whilst
the negative contribution is attributed to tunneling states of the C60
molecules. The characteristic time of the phase transformation from the low-T
phase to the high-T phase has been found for the C60-H2 system at 12K. A
theoretical model is proposed to interpret these observed phenomena. The
theoretical model proposed, includes a consideration of the nature of
polyamorphism in glasses, as well as the thermodynamics and kinetics of the
transition. A model of non-interacting tunneling states is used to explain the
negative contribution to the thermal expansion. The experimental data obtained
is considered within the framework of the theoretical model. From the
theoretical model the order of magnitude of the polyamorphous transition
temperature has been estimated. It is found that the late stage of the
polyamorphous transformation is described well by the Kolmogorov law with an
exponent of n=1. At this stage of the transformation, the two-dimensional phase
boundary moves along the normal, and the nucleation is not important.Comment: 29 pages, 14 figures, added references, corrected typo
Le pluralisme politique à l’épreuve de la vie privée : entre normes et pratiques
L’espace des relations interpersonnelles et privées, en tant qu’espace de politisation et d’expression des choix politiques, est peu connu. C’est à une meilleure connaissance du « citoyen privé » et de la « politisation intime » que cet article veut contribuer, en étudiant les ressemblances et les divergences idéologiques au sein du cercle des proches. Présentant les résultats d’une enquête quantitative et représentative de la population française inédite, « Famille, amour et politique », réalisée par le CEVIPOF, il examine la filiation, la conjugalité, et l’amitié et montre les interactions et les transactions qui opèrent entre le système des normes et le système des affects des individus. La famille apparaît plus hétérogame politiquement tandis que le couple et le cercle des amis sont plus homogames. Toutefois, c’est le niveau de politisation des individus qui est en dernière instance le plus déterminant. Une affiliation politique affirmée, et tout particulièrement à gauche, ainsi qu’un intérêt marqué pour la politique, renforcent toujours l’homogamie politique au sein du cercle des proches, dans les principes comme dans les faits. Plus largement, l’article ouvre une réflexion sur l’espace de la vie privée en tant que terrain d’expérience des conditions de la pluralité démocratique.Little is known of the role played by private interpersonal relationships in politicization and the expression of political choices. This article aims to improve our understanding of “private citizens” and “personal politicization” through a study of ideological similarities and divergences within family and friendship circles. The analysis, based on findings from an unprecedented quantitative representative French population survey by the CEVIPOF (Center for the study of French political life) entitled “Famille, amour et politique” [Family, love and politics], examines filiation, conjugality and friendship, showing the interactions and transactions that take place between the system of norms and the system of individual feelings. Families appear more heterogamous politically, while couples and friendship circles are more homogamous. However, individuals’ level of politicization is ultimately the most determinant factor. Having a strong political affiliation, particularly on the left of the political spectrum, and a strong interest in politics always strengthens intra-circle political homogamy in terms of both principles and actions. At a more general level, the article reflects on the sphere of private life as a field for the development of conditions of democratic pluralism
Mapping of periodically poled crystals via spontaneous parametric down-conversion
A new method for characterization of periodically poled crystals is developed
based on spontaneous parametric down-conversion. The method is demonstrated on
crystals of Y:LiNbO3, Mg:Y:LiNbO3 with non-uniform periodically poled
structures, obtained directly under Czochralski growth procedure and designed
for application of OPO in the mid infrared range. Infrared dispersion of
refractive index, effective working periods and wavelengths of OPO were
determined by special treatment of frequency-angular spectra of spontaneous
parametric down-conversion in the visible range. Two-dimensional mapping via
spontaneous parametric down-conversion is proposed for characterizing spatial
distribution of bulk quasi-phase matching efficiency across the input window of
a periodically poled sample.Comment: 19 pages, 6 figure
Specific features of thermal expansion and polyamorphism in CH4–C60 solutions at low temperatures
The temperature dependence of the linear thermal expansion coefficient α(T) has been investigated in the temperature range of 2.5 to 23 K for two different CH4–C60 solutions in which CH4 molecules occupied 24 and 50% of the octahedral interstitial sites of the C60 lattice. In both cases, α(T) exhibits hysteresis, suggesting the existence of two types of orientational glass associated with these solutions. The temperature of the first-order phase transition between these two glasses was estimated and the behavior of these two glasses compared. The characteristic times of thermalization τ1, reorientation of the C60 molecules τ2, and of the phase transformation between the glasses τ', have been estimated for these solutions. Both the temperature dependence of α(T) and the characteristic thermalization time τ1are found to have features near the phase transition temperature and an explanation has been put forward to explain these observed features
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