Depinning of a vortex chain in a disordered flow channel

We study depinning of vortex chains in channels formed by static, disordered vortex arrays. Depinning is governed either by the barrier for defect nucleation or for defect motion, depending on whether the chain periodicity is commensurate or incommensurate with the surrounding arrays. We analyze the reduction of the gap between these barriers as function of disorder. At large disorder, commensurability becomes irrelevant and the pinning force is reduced to a small fraction of the ideal shear strength of ordered channels. Implications for experiments on channel devices are discussed.Comment: 5 pages, 4 figures. Accepted for publication in Europhysics Letter

Depinning and dynamics of vortices confined in mesoscopic flow channels

We study the behavior of vortex matter in artificial flow channels confined by pinned vortices in the channel edges (CE's). The critical current $J_s$ is governed by the interaction with static vortices in the CE's. We study structural changes associated with (in)commensurability between the channel width $w$ and the natural row spacing $b_0$, and their effect on $J_s$. The behavior depends crucially on the presence of disorder in the CE arrays. For ordered CE's, maxima in $J_s$ occur at matching $w=nb_0$ ($n$ integer), while for $w\neq nb_0$ defects along the CE's cause a vanishing $J_s$. For weak CE disorder, the sharp peaks in $J_s$ at $w=nb_0$ become smeared via nucleation and pinning of defects. The corresponding quasi-1D $n$ row configurations can be described by a (disordered)sine-Gordon model. For larger disorder and $w\simeq nb_0$, $J_s$ levels at $\sim 30$ of the ideal lattice strength $J_s^0$. Around 'half filling' ($w/b_0 \simeq n\pm 1/2$), disorder causes new features, namely {\it misaligned} defects and coexistence of $n$ and $n \pm 1$ rows in the channel. This causes a {\it maximum} in $J_s$ around mismatch, while $J_s$ smoothly decreases towards matching due to annealing of the misaligned regions. We study the evolution of static and dynamic structures on changing $w/b_0$, the relation between modulations of $J_s$ and transverse fluctuations and dynamic ordering of the arrays. The numerical results at strong disorder show good qualitative agreement with recent mode-locking experiments.Comment: 29 pages, 32 figure

Coherent and Incoherent Vortex Flow States in Crossed Channels

We examine vortex flow states in periodic square pinning arrays with one row and one column of pinning sites removed to create an easy flow crossed channel geometry. When a drive is simultaneously applied along both major symmetry axes of the pinning array such that vortices move in both channels, a series of coherent flow states develop in the channel intersection at rational ratios of the drive components in each symmetry direction when the vortices can cross the intersection without local collisions. The coherent flow states are correlated with a series of anomalies in the velocity force curves, and in some cases can produce negative differential conductivity. The same general behavior could also be realized in other systems including colloids, particle traffic in microfluidic devices, or Wigner crystals in crossed one-dimensional channels.Comment: 5 pages, 4 postscript figure

Single File Diffusion enhancement in a fluctuating modulated 1D channel

We show that the diffusion of a single file of particles moving in a fluctuating modulated 1D channel is enhanced with respect to the one in a bald pipe. This effect, induced by the fluctuations of the modulation, is favored by the incommensurability between the channel potential modulation and the moving file periodicity. This phenomenon could be of importance in order to optimize the critical current in superconductors, in particular in the case where mobile vortices move in 1D channels designed by adapted patterns of pinning sites.Comment: 4 pages, 4 figure

Mode locking of vortex matter driven through mesoscopic channels

We investigated the driven dynamics of vortices confined to mesoscopic flow channels by means of a dc-rf interference technique. The observed mode-locking steps in the $IV$-curves provide detailed information on how the number of rows and lattice structure in the channel change with magnetic field. Minima in flow stress occur when an integer number of rows is moving coherently, while maxima appear when incoherent motion of mixed $n$ and $n\pm 1$ row configurations is predominant. Simulations show that the enhanced pinning at mismatch originates from quasi-static fault zones with misoriented edge dislocations induced by disorder in the channel edges.Comment: some minor changes were made, 4 pages, 4 figures, accepted for publication in Phys. Rev. Let

Пріоритети вдосконалення фінансової політики і структури зайнятості в бюджетному і промисловому секторах економіки

Обґрунтовано проблеми взаємозв’язку фінансування, зайнятості, віддачі праці та капіталу. Висвітлено засади формування фінансової політики, удосконалення структури зайнятості у бюджетному та промисловому секторах економіки України. Ключові слова: фінансова політика, зайнятість, проблеми, економіка України. -----Обосновываются проблемы взаимосвязи финансирования, занятости, отдачи труда и капитала. Освещаются принципы формирования финансовой политики, усовершенствования структуры занятости в бюджетном и промышленном секторах украинской экономики. Ключевые слова: финансовая политика, занятость, проблемы, украинская экономика. ------Problems concerning interrelations between financing, employment, return on labour and capital are grounded. Principles of forming the financial policy, improvements in the structure of employment in the budgetary and industrial sectors of the economy of Ukraine are described. Key words: financial policy, employment, problems, economy of Ukraine. ----

Potential biological sources of long chain alkyl diols in a lacustrine system

Long chain alkyl diols (LCDs) have been detected in a range of marine and lacustrine environments, as well as in several algal cultures. However, the identity of the producers, their preferred ecological niche and seasonality are uncertain. We applied a gene-based approach to determine the identity and abundance of Eustigmatophyceae 18S rRNA genes and compared the data with the distribution of LCDs in the water column of Lake Challa (East Africa). Gene-based analysis revealed three known and two novel Eustigmatophyceae groups. Maxima in the number of gene copies and LCD concentration coincided at 9 m water depth, signifying Eustigmatophyceae as important producers of LCDs. In addition, seasonal changes in LCD abundance in sedimenting particles revealed several blooms of LCD producers over the annual cycle