Faraday Instability in a Surface-Frozen Liquid

Faraday surface instability measurements of the critical acceleration, a_c, and wavenumber, k_c, for standing surface waves on a tetracosanol (C_24H_50) melt exhibit abrupt changes at T_s=54degC above the bulk freezing temperature. The measured variations of a_c and k_c vs. temperature and driving frequency are accounted for quantitatively by a hydrodynamic model, revealing a change from a free-slip surface flow, generic for a free liquid surface (T>T_s), to a surface-pinned, no-slip flow, characteristic of a flow near a wetted solid wall (T < T_s). The change at T_s is traced to the onset of surface freezing, where the steep velocity gradient in the surface-pinned flow significantly increases the viscous dissipation near the surface.Comment: 4 pages, 3 figures. Physical Review Letters (in press

МОДЕЛЮВАННЯ ТА ЕЛЕМЕНТИ ПРОГНОЗУВАННЯ ЗМІН ЕКОЛОГІЧНОГО СТАНУ ОЗЕРА

The mathematical model of ecological system of lake is offered including a complex index of quality for characterizing nature protective and economic activity. The procedures of change prediction of parameters of the ecological conditions of lake are systematized considering the elements of theory of risks. Key words: ecology, system of lakes, complex index of quality, risk, prognostication. &nbsp;Подано математичну модель екосистеми озера, в основі якої комплексний показник якості, що характеризує природоохоронну та господарську діяльність. Систематизовано процедуру прогнозування змін параметрів екологічного стану озера з урахуванням елементів теорії ризиків. Ключові слова: екологія, озерні системи, комплексний показник якості, ризики, прогнозування

Segmental front line dynamics of randomly pinned ferroelastic domain walls

Dynamic mechanical analysis (DMA) measurements as a function of temperature, frequency, and dynamic force amplitude are used to perform a detailed study of the domain wall motion in LaAlO3. In previous DMA measurements Harrison et al. [Phys. Rev. B 69, 144101 (2004)] found evidence for dynamic phase transitions of ferroelastic domain walls in LaAlO3. In the present work we focus on the creep-to-relaxation region of domain wall motion using two complementary methods. We determine, in addition to dynamic susceptibility data, waiting time distributions of strain jerks during slowly increasing stress. These strain jerks, which result from self-similar avalanches close to the depinning threshold, follow a power-law behavior with an energy exponent ɛ=1.7±0.1. Also, the distribution of waiting times between events follows a power law N(tw)∝t−(n+1)w with an exponent n=0.9, which transforms to a power law of susceptibility S(ω)∝ω−n. The present dynamic susceptibility data can be well fitted with a power law, with the same exponent (n=0.9) up to a characteristic frequency ω≈ω∗, where a crossover from stochastic DW motion to the pinned regime is well described using the scaling function of Fedorenko et al

Are solidified fillings of mesopores basically bulk-like except for the geometric confinement?

A short review of our thermodynamic and structural work on Ar, N2, CO, O2, and the n-alkane C19H40 in mesoporous glasses is presented. The experimental information comes from X-ray diffraction, vapour pressure isotherms, optical transmission, heat capacity, and dielectric measurements. The filling in the pore centre formed by capillary condensation is distinguished from the adsorbed layers on the pore walls and is compared to the bulk state. Special attention is paid to metastable states and to the rearrangement of partial fillings that show up as a consequence of phase transitions