Density functional theory of freezing for soft interactions in two dimensions

A density functional theory of two-dimensional freezing is presented for a soft interaction potential that scales as inverse cube of particle distance. This repulsive potential between parallel, induced dipoles is realized for paramagnetic colloids on an interface, which are additionally exposed to an external magnetic field. An extended modified weighted density approximation which includes correct triplet correlations in the liquid state is used. The theoretical prediction of the freezing transition is in good agreement with experimental and simulation data.Comment: 7 pages, 3 figures, submitted 200

Spin Precession and Oscillations in Mesoscopic Systems

We compare and contrast magneto-transport oscillations in the fully quantum (single-electron coherent) and classical limits for a simple but illustrative model. In particular, we study the induced magnetization and spin current in a two-terminal double-barrier structure with an applied Zeeman field between the barriers and spin disequilibrium in the contacts. Classically, the spin current shows strong tunneling resonances due to spin precession in the region between the two barriers. However, these oscillations are distinguishable from those in the fully coherent case, for which a proper treatment of the electron phase is required. We explain the differences in terms of the presence or absence of coherent multiple wave reflections.Comment: 9 pages, 5 figure

Field exposed water in a nanopore: liquid or vapour?

We study the behavior of ambient temperature water under the combined effects of nanoscale confinement and applied electric field. Using molecular simulations we analyze the thermodynamic causes of field-induced expansion at some, and contraction at other conditions. Repulsion among parallel water dipoles and mild weakening of interactions between partially aligned water molecules prove sufficient to destabilize the aqueous liquid phase in isobaric systems in which all water molecules are permanently exposed to a uniform electric field. At the same time, simulations reveal comparatively weak field-induced perturbations of water structure upheld by flexible hydrogen bonding. In open systems with fixed chemical potential, these perturbations do not suffice to offset attraction of water into the field; additional water is typically driven from unperturbed bulk phase to the field-exposed region. In contrast to recent theoretical predictions in the literature, our analysis and simulations confirm that classical electrostriction characterizes usual electrowetting behavior in nanoscale channels and nanoporous materials.Comment: 20 pages, 6 figures + T.O.C. figure, in press in PCC

Formation of a pedagogical worldview among future leaders of choreographic groups through the festival and competition movement

The article is devoted to the study of the formation of a pedagogical worldview among future leaders of choreographic groups by means of the festival and competition movement in the field of choreographic art. The relevance of the research is determined by the current state of socio-cultural reality and the state requirements for the qualifications of graduates of the University of culture. Based on a comparative analysis of foreign and domestic scientific literature, through generalization and concretization of research results, the authors consider the socio-cultural value of festivals and competitions of choreographic art, their importance in the preservation and development of cultural values, and highlight their pedagogical potential in the system of professional training of cultural professionals in higher education. With the help of a qualitative study of the individual stages of students' participation in festival and competitive events, the article defines how the pedagogical worldview of future leaders of choreographic groups is formed by means of the festival and competitive movement. In support of the author's position, the expert opinion of a specialist in the field of professional education, Professor of the Department of Choreography at the Oryol State Institute of Culture, is presented through the interviewing method. In order to establish the degree of festival and competitive activity of future leaders of choreographic groups, to determine their level of knowledge in the field under study and their emotional attitude to the festival and competitive movement, the authors conducted a sociological survey using the questionnaire method, the results of which are described through the prism of educational, emotional, value and creative activity components. Based on the results of the quantitative and qualitative analysis, the predominance of the average level of students' knowledge about the festival and competition movement and its impact on the formation of the pedagogical worldview of future leaders of choreographic groups was revealed. In conclusion, the article draws conclusions that are open to subsequent scientific discussion, and reveals the prospects for using the results obtained

Robustness of "cut and splice" genetic algorithms in the structural optimization of atomic clusters

We return to the geometry optimization problem of Lennard-Jones clusters to analyze the performance dependence of "cut and splice" genetic algorithms (GAs) on the employed population size. We generally find that admixing twinning mutation moves leads to an improved robustness of the algorithm efficiency with respect to this a priori unknown technical parameter. The resulting very stable performance of the corresponding mutation+mating GA implementation over a wide range of population sizes is an important feature when addressing unknown systems with computationally involved first-principles based GA sampling.Comment: 5 pages including 3 figures; related publications can be found at http://www.fhi-berlin.mpg.de/th/th.htm

Superparamagnetic colloids in viscous fluids

The influence of a magnetic field on the aggregation process of superparamagnetic colloids has been well known on short time for a few decades. However, the influence of important parameters, such as viscosity of the liquid, has received only little attention. Moreover, the equilibrium state reached after a long time is still challenging on some aspects. Indeed, recent experimental measurements show deviations from pure analytical models in extreme conditions. Furthermore, current simulations would require several years of computing time to reach equilibrium state under those conditions. In the present paper, we show how viscosity influences the characteristic time of the aggregation process, with experimental measurements in agreement with previous theories on transient behaviour. Afterwards, we performed numerical simulations on equivalent systems with lower viscosities. Below a critical value of viscosity, a transition to a new aggregation regime is observed and analysed. We noticed this result can be used to reduce the numerical simulation time from several orders of magnitude, without modifying the intrinsic physical behaviour of the particles. However, it also implies that, for high magnetic fields, granular gases could have a very different behaviour from colloidal liquids