Nonlinear magnetoconductance of a classical ballistic system

We study nonlinear transport through a classical ballistic system accounting for the Coulomb interaction between electrons. The joint effect of the applied bias $V$ and magnetic field $H$ on the electron trajectories results in a component of the non-linear current $I(V,H)$ which lacks the $H\to -H$ symmetry: $\delta I=\alpha_{cl} V^2 H$. At zero temperature the magnitude of $\alpha_{cl}$ is of the same order as that arising from the quantum interference mechanism. At higher temperatures the classical mechanism is expected to dominate due to its relatively weak temperature dependence.Comment: 5 pages, 1 figur

Coherent current states in mesoscopic four-terminal Josephson junction

A theory is offered for the ballistic 4-terminal Josephson junction. The studied system consists of a mesoscopic two-dimensional normal rectangular layer which is attached in each side to the bulk superconducting banks (terminals). The relation between the currents through the different terminals, which is valid for arbitrary temperatures and junction sizes, is obtained. The nonlocal coupling of the supercurrents leads to a new effect, specific for the mesoscopic weak link between two superconducting rings; an applied magnetic flux through one of the rings produces a magnetic flux in the other ring even in the absence of an external flux through the other one. The phase dependent distributions of the local density of Andreev states, of the supercurrents and of the induced order parameter are obtained. The "interference pattern" for the anomalous average inside the two dimensional region can be regulated by the applied magnetic fluxes or the transport currents. For some values of the phase differences between the terminals, the current vortex state and the two dimensional phase slip center are appeared.Comment: 17 pages in Latex and 6 ps Figures. Will be published in Low Temp.Phy

Magnetic flux locking in two weakly coupled superconducting rings

We have analyzed the quantum interference effects in the macroscopic ''superconducting molecule''. The composite system consists of two massive superconducting rings, each interrupted by a Josephson junction, which are at the same time weakly coupled with one another. The special case of coupling via the Josephson four-terminal junction is considered. The structure of the macroscopic quantum states in an applied magnetic field is calculated. It is shown, that depending on the values of the magnetic fluxes through each ring, the system displays two groups of states, the ''orthostates'' with both induced currents going in the same direction, and the ''parastates'' with the opposite currents and with the total induced flux locked to zero value. The transition to the flux locked state with changing of the total applied flux is sudden and is preserved in a certain interval which is determined by the difference of the fluxes applied through each ring. It makes the system sensitive to small gradients of the external magnetic field.Comment: 8 pages in Latex, 3 figures (eps

Molecular mechanisms of vascular tissue patterning in <i>Arabidopsis thaliana</i> L. roots

A vascular system in plants is a product of aromorphosis that enabled them to colonize land because it delivers water, mineral and organic compounds to plant organs and provides effective communications between organs and mechanical support. Vascular system development is a common object of fundamental research in plant development biology. In the model plant Arabidopsis thaliana, early stages of vascular tissue formation in the root are a bright example of the self-organization of a bisymmetric (having two planes of symmetry) pattern of hormone distribution, which determines vascular cell fates. In the root, vascular tissue development comprises four stages: (1) specification of progenitor cells for the provascular meristem in early embryonic stages, (2) the growth and patterning of the embryo provascular meristem, (3) postembryonic maintenance of the cell identity in the vascular tissue initials within the root apical meristem, and (4) differentiation of their descendants. Although the anatomical details of A. thaliana root vasculature development have long been known and described in detail, our knowledge of the underlying molecular and genetic mechanisms remains limited. In recent years, several important advances have been made, shedding light on the regulation of the earliest events in provascular cells specification. In this review, we summarize the latest data on the molecular and genetic mechanisms of vascular tissue patterning in A. thaliana root. The first part of the review describes the root vasculature ontogeny, and the second reconstructs the sequence of regulatory events that underlie this histogenesis and determine the development of the progenitors of the vascular initials in the embryo and organization of vascular initials in the seedling root

Regulatory mechanisms tuning ethylen signaling in plants

Plant hormone ethylene regulates a wide range of physiological processes during plant development and coordinates different stress responses. Among others ethylene controls such practically significant characteristics of agricultural crops as fruit ripening rates and plant tolerance to stress conditions. That is why understanding molecular mechanisms underlying ethylene action is one of the basic questions in plant biology that is addressed in the context of both fundamental research and application in agriculture. Ethylene biosynthesis from methionine amino acid and the main points of its signaling pathway from membrane receptors to effector genes are studied in details and widely reviewed. Far less is known about genetic regulation of these two processes although it is the one that ensures accurate plant reaction to different endogenous and exogenous signals and causes the multiplicity of different physiological responses to ethylene. This review summarizes data about regulatory mechanisms of ethylene biosynthesis and signaling. It reports the key transcriptional and post-translational regulatory factors which control expression and stability of the main components of ethylene biosynthesis and signaling pathways, and describes multiple feed-backs supplementing the linear model of ethylene signaling. Particular attention is given to the role of hormonal crosstalk in the process. Different mechanisms of hormonal interaction are illustrated by synergy or antagonism of ethylene and auxin, jasmonates, cytokinins, brassinosteroids. Possible molecular basics of multiplicity of different physiological responses to ethylene is also discussed

Systems biology analysis of the WOX5 gene and its functions in the root stem cell niche

WUSCHEL RELATED HOMEOBOX 5 (WOX5) gene encodes the transcription factor, which is one of the key regulators, maintaining structure and functioning of the stem cell niche in plant root tips. Protein WOX5 is expressed in the quiescent center of the root apical meristem, preventing differentiation of columella initials and altogether with SCR, SHR, PLT1 and PLT2 participating in the control of differentiation of other root meristem initials. However, the details of WOX5 functioning are unclear. The WOX5 protein belongs to WUSCHEL related homeobox (WOX) family, the founder of which is the transcription factor WUSCHEL (WUS) providing maintenance of the stem cell niche in the shoot apical meristem. WOX5 and WUS diverged from a common ancestor at the base of angiosperms, which resulted in a specialization of shoot and root stem cell niches. However, the problem of WOX5 structural and functional divergence during angiosperm evolution was poorly addressed. In this review we present a systems biology analysis of the WOX5 gene to reveal specific features of its evolution and functioning. To this end, we performed a phylogenetic analysis on 62 publicly available WOX5 amino acid sequences, generalized published data about WOX5 expression domain in Arabidopsis and other species and its role in development, integrated the results of experiments on identification of primary and secondary targets for this transcription factor. Data on possible mechanisms of direct and indirect regulation of WOX5 expression were discussed. Particularly, we performed the analysis of WOX5 promoter regions from 30 species. Possible direct regulators of the WOX5 gene expression were proposed based on the presence of putative binding sites for the candidate transcription factors in conserved WOX5 promoter regions

State owned enterprises as bribe payers: the role of institutional environment

Our paper draws attention to a neglected channel of corruption—the bribe payments by state-owned enterprises (SOEs). This is an important phenomenon as bribe payments by SOEs fruitlessly waste national resources, compromising public welfare and national prosperity. Using a large dataset of 30,249 firms from 50 countries, we show that, in general, SOEs are less likely to pay bribes for achieving organizational objectives owing to their political connectivity. However, in deteriorated institutional environments, SOEs may be subjected to potential managerial rent-seeking behaviors, which disproportionately increase SOE bribe propensity relative to privately owned enterprises. Specifically, our findings highlight the importance of fostering democracy and rule of law, reducing prevalence of corruption and shortening power distance in reducing the incidence of SOE bribery

MATHEMATICAL MODEL OF PHYTOHORMONE REGULATION OF ROOT MERISTEMATIC ZONE FORMATION

The apical meristem located at the root tip of a plant is one of the most convenient objects to study the organization of the stem cell niche. In the root apical meristem, mitotically inactive cells of the quiescent center coexist with intensely dividing cells, which lose this ability at a certain distance from the quiescent center. It is known that plant hormones auxin and cytokinin play an important role in the regulation of this structure formation, but the mechanisms maintaining the dynamics of this structure remain unknown. We propose a mathematical model that summarizes experimental data on the distribution of auxin and cytokinin along the root longitudinal axis and their role in cell cycle regulation

THE KEY ROLE OF PIN PROTEINS IN AUXIN TRANSPORT IN ARABIDOPSIS THALIANA ROOTS

The phytohormone auxin is the key factor in plant morphogenesis. Being unevenly distributed in plant tissues, it forms gradients and concentration maxim а, according to which cells grow, divide, and differentiate. The family of PIN-FORMED (PIN) proteins, transmembrane transporters of auxin, play the key role in the formation of auxin gradients. The plant root is the most appropriate model for studying the regulation of morphogenesis, because of its relatively simple cellular organization. This review concerns the expression patterns of PIN transporters and their contribution to auxin distribution in the root of Arabidopsis. Mathematical models that prove the relationship between the expression pattern of PIN proteins and auxin distribution in the root meristem are discussed

COMPUTATIONAL ANALYSIS AND FUNCTIONAL ANNOTATION OF AP2/ERF TRANSCRIPTION FACTOR BINDING SITES IN ARABIDOPSIS THALIANA L. GENOME

The plant hormone ethylene regulates both developmental processes and various stress responses in plants. Ethylene perception in plants is followed by activation of some transcription factors from the large family of APETALA2/ETHYLENE response factors (ERFs). ERF TF binding sites contain a specific GCCGCC motif, called GCC-box. In this study, we applied TF binding site recognition tools oPWM and SiteGA for sequence analysis of experimentally proven GCC-boxes. We carried out GCC box recognition and tested its distribution in the Arabidopsis thaliana L. genome. Functional annotation and microarray data analysis of the genes possessing predicted GCC-boxes elucidated their role in ethylene response