Convective stability of a weakly conducting liquid in an electric field

In an inhomogeneously heated weakly conductive liquid (electrical conductivity 10^–12–1 cm^–1) located in a constant electric field a volume charge is induced because of thermal inhomogeneity of electrical conductivity and dielectric permittivity. The ponderomotive forces which develop set the liquid into intense motion [1–6]. However, under certain conditions equilibrium proves possible, and in that case the question of its stability may be considered. A theoretical analysis of liquid equilibrium stability in a planar horizontal condenser was performed in [2, 4]. Critical problem parameters were found for the case where Archimedean forces are absent [2]. Charge perturbation relaxation was considered instantaneous. It was shown that instability is of an oscillatory character. In [4] only heating from above was considered. Basic results were obtained in the limiting case of disappearingly small thermal diffusivity in the liquid (infinitely high Prandtl numbers). In the present study a more general formulation will be used to examine convective stability of equilibrium of a vertical liquid layer heated from above or below and located in an electric field. For the case of a layer with free thermally insulated boundaries, an exact solution is obtained. Values of critical Rayleigh number and neutral oscillation frequency for heating from above and below are found Neutral curves are constructed. It is demonstrated that with heating from below instability of both the oscillatory and monotonic types is possible, while with heating from above the instability has an oscillatory character. Values are found for the dimensionless field parameter at which the form of instability changes for heating from below and at which instability becomes possible for heating from above.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 5, pp. 16–23, September–October, 1976.In conclusion, the author thanks E. M. Zhukhovitskii for this interest in the study and valuable advice.     

Possibility of the levitation of droplets in the atmosphere when they are charged by induction in an electric field under nonuniform evaporation conditions

The behavior of droplets in the atmosphere in an electric field has important bearing on the theory of thunderstorms. One of the possible mechanisms by which droplets become charged—the induction mechanism in the presence of nonuniform evaporation—is investigated in greater detail on the basis of recent experimental results (V. A. Saranin, Zh. Tekh. Fiz. 65(6), 21 (1995) [Tech. Phys. 40, 332 (1995)]). Zh. Tekh. Fiz. 68, 16–21 (February 1998)     

Spin squeezing and quantum correlations

We discuss the notion of spin squeezing considering two mutually exclusive classes of spin-s states, namely, oriented and non-oriented states. Our analysis shows that the oriented states are not squeezed while non-oriented states exhibit squeezing. We also present a new scheme for construction of spin-s states using 2s spinors oriented along different axes. Taking the case of s=1, we show that the ‘non-oriented’ nature and hence squeezing arise from the intrinsic quantum correlations that exist among the spinors in the coupled state.     

Atomic and electronic structures of Ag/Si(100)-c(6 × 2) surface: A first-principles study

Using the experimental data obtained mainly with the scanning tunneling microscopy observations, density functional theory calculations have been applied to examine an atomic structure of the Ag/Si(100)-c(6 × 2) reconstruction. A set of structural models has been proposed having a similar Si(100) substrate reconstruction which incorporates rows of top Si atom dimers and troughs in between the rows. Stability of about twenty models with various Ag coverage ranging from 1/6 to 1 ML has been tested, that allows reducing the number of plausible models to four. Two of these four models have been attributed to the “regular” intrinsic Ag/Si(100)-c(6 × 2) reconstruction, while the other two to its defect-induced modification. The latter is observed in the local areas near defects and domain boundaries and exhibits 3 × 2 periodicity. Comparing the results of calculations with the experimental STM images, it has been concluded that while the Si(100) substrate reconstruction is solid, the Ag subsystem is flexible due to the presence of the lightly bonded mobile Ag atoms.     

Structural properties of Cu clusters on Si(1 1 1):Cu2Si magic family

Basing on the results of the scanning tunneling microscopy (STM) observations and density functional theory (DFT) calculations, the structural model for the Cu magic clusters formed on Si(1 1 1)7 × 7 surface has been proposed. Using STM, composition of the Cu magic clusters has been evaluated from the quantitative analysis of the Cu and Si mass transport occurring during magic cluster converting into the Si(1 1 1)‘5.5 × 5.5’-Cu reconstruction upon annealing. Evaluation yields that Cu magic cluster accommodates 20 Cu atoms with 20 Si atoms being expelled from the corresponding 7 × 7 half unit cell (HUC). In order to fit these values, it has been suggested that the Cu magic clusters resemble fragments of the Cu₂Si-silicide monolayer incorporated into the rest-atom layer of the Si(1 1 1)7 × 7 HUCs. Using DFT calculations, stability of the nineteen models has been tested of which five models appeared to have formation energies lower than that of the original Si(1 1 1)7 × 7 surface. The three of five models having the lowest formation energies have been concluded to be the most plausible ones. They resemble well the evaluated composition and their counterparts are found in the experimental STM images.     

Diverse magic nanoclustering in submonolayer Tl/Si(1 1 1) system

Using scanning tunneling microscopy, ordered magic nanoclustering in the submonolayer Tl/Si(1 1 1)7 × 7 system has been studied. In contrast to the other known metal/silicon systems where ordered magic nanoclustering takes place, the Tl/Si(1 1 1) system has been found to be the only one to exhibit the diverse magic clustering. In the present study, occurrence of, at least, three distinct types of the well-defined Tl/Si(1 1 1) magic clusters has been detected.     

Peculiarities of Al magic cluster self-assembly on Si(1 0 0) surface

Using scanning tunneling microscopy observations and density functional theory calculations, regularities of the Al magic cluster array self-assembly on Si(1 0 0) surface has been elucidated. While a single Al cluster occupies an area of 4a × 3a, an ordered Al-cluster array exhibits a 4 × 5 periodicity, as the clusters in the array are separated by the 4a × 2a “spacers”. The plausible structural model for the “spacer” was proposed in which the “spacer” is arranged as an ordinary 4a × 3a-Al cluster in which the central atomic row with the topmost Si atom is missing. Appearance of the “spacers” in the Al-cluster array was found to reduce formation energy of the array. Ability to incorporate the rows of Al-“spacers” into the completed 4 × 3 In-cluster array was demonstrated.