Optimizing Brownian escape rates by potential shaping.

Brownian escape is key to a wealth of physico-chemical processes, including polymer folding and information storage. The frequency of thermally activated energy barrier crossings is assumed to generally decrease exponentially with increasing barrier height. Here, we show experimentally that higher, fine-tuned barrier profiles result in significantly enhanced escape rates, in breach of the intuition relying on the above scaling law, and address in theory the corresponding conditions for maximum speed-up.

Thermal bath engineering for swift equilibration.

We provide a theoretical and experimental protocol that dynamically controls the effective temperature of a thermal bath, through a well-designed noise engineering. We use this powerful technique to shortcut the relaxation of an overdamped Brownian particle in a quadratic potential by a joint time engineering of the confinement strength and of the noise. For an optically trapped colloid, we report an equilibrium recovery time reduced by about two orders of magnitude compared to the natural relaxation time.

Search in patchy media: Exploitation-exploration tradeoff.

How to best exploit patchy resources? We introduce a minimal exploitation-migration model that incorporates the coupling between a searcher's trajectory, modeled by a random walk, and ensuing depletion of the environment by the searcher's consumption of resources. The searcher also migrates to a new patch when it takes S consecutive steps without finding resources. We compute the distribution of consumed resources F_{t} at time t for this non-Markovian searcher and show that consumption is maximized by exploring multiple patches.

Universality classes of foraging with resource renewal.

We determine the impact of resource renewal on the lifetime of a forager that depletes its environment and starves if it wanders too long without eating. In the framework of a minimal starving random-walk model with resource renewal, there are three universal classes of behavior as a function of the renewal time. For sufficiently rapid renewal, foragers are immortal, while foragers have a finite lifetime otherwise.

Mean perimeter of the convex hull of a random walk in a semi-infinite medium.

We study various properties of the convex hull of a planar Brownian motion, defined as the minimum convex polygon enclosing the trajectory, in the presence of an infinite reflecting wall. Recently [Phys. Rev.

Convex hull of a Brownian motion in confinement.

We study the effect of confinement on the mean perimeter of the convex hull of a planar Brownian motion, defined as the minimum convex polygon enclosing the trajectory. We use a minimal model where an infinite reflecting wall confines the walk to one side. We show that the mean perimeter displays a surprising minimum with respect to the starting distance to the wall and exhibits a nonanalyticity for small distances.

Survival probability of a Brownian motion in a planar wedge of arbitrary angle.

We study the survival probability and the first-passage time distribution for a Brownian motion in a planar wedge with infinite absorbing edges. We generalize existing results obtained for wedge angles of the form π/n with n a positive integer to arbitrary angles, which in particular cover the case of obtuse angles. We give explicit and simple expressions of the survival probability and the first-passage time distribution in which the difference between an arbitrary angle and a submultiple of π is contained in three additional terms.

Mean cover time of one-dimensional persistent random walks.

The cover time is defined as the time needed for a random walker to visit every site of a confined domain. Here, we focus on persistent random walks, which provide a minimal model of random walks with short-range memory. We derive the exact expression of the mean cover time of a one-dimensional lattice by such a persistent random walk, both for periodic and reflecting boundary conditions.

Characterization of the early events leading to totipotency in an Arabidopsis protoplast liquid culture by temporal transcript profiling.

The molecular mechanisms underlying plant cell totipotency are largely unknown. Here, we present a protocol for the efficient regeneration of plants from Arabidopsis thaliana protoplasts. The specific liquid medium used in our study leads to a high rate of reentry into the cell cycle of most cell types, providing a powerful system to study dedifferentiation/regeneration processes in independent somatic cells.

Large-scale dissociation and sequential reassembly of pericentric heterochromatin in dedifferentiated Arabidopsis cells.

Chromocenters in Arabidopsis thaliana are discrete nuclear domains of mainly pericentric heterochromatin. They are characterized by the presence of repetitive sequences, methylated DNA and dimethylated histone H3K9. Here we show that dedifferentiation of specialized mesophyll cells into undifferentiated protoplasts is accompanied by the disruption of chromocenter structures.

Successful gene tagging in lettuce using the Tnt1 retrotransposon from tobacco.

The tobacco (Nicotiana tabacum) element Tnt1 is one of the few identified active retrotransposons in plants. These elements possess unique properties that make them ideal genetic tools for gene tagging. Here, we demonstrate the feasibility of gene tagging using the retrotransposon Tnt1 in lettuce (Lactuca sativa), which is the largest genome tested for retrotransposon mutagenesis so far.

Molecular and functional characterization of Slide, an Ac-like autonomous transposable element from tobacco.

A new transposable element of tobacco, Slide, was isolated from the tl mutant line, which shows somatic instability, after its transposition into a locus encoding nitrate reductase (NR). The Slide-124 element is 3733 bp long and its coding sequences show similarities with conserved domains of the transposases of Ac, Tam3 and hobo. Excision from the NR locus is detectable in somatic leaf tissues and Slide mobility is triggered by in vitro tissue culture.

Regeneration and characterization of plants produced from mature tobacco pollen protoplasts via gametosomatic hybridization.

Mature pollen protoplasts (n) isolated from kanamycin resistant plants of Nicotiana tabacum (2n = 4x = 48) were fused with somatic mesophyll protoplasts (2n) of Nicotiana plumbaginifolia (2n = 20) to produce plants. A total of 3.6·10(6) mature pollen protoplasts were fused with 7·10(6) mesophyll protoplasts using a PEG/Ca(2+) method.

Improved flax regeneration from hypocotyls using thidiazuron as a cytokinin source.

The effects of thidiazuron, benzyladenine and zeatin were tested with respect to bud regeneration of different flax explants from hypocotyls, cotyledons and apices of two fibre varieties (Ariane, Viking) and one linseed variety (Antarès). These three cytokinins were tested either alone or in combination with naphthalene acetic acid, indole acetic acid or 2,4-dichlorophenoxyacetic acid.Hypocotyls were the most responsive explants.

A Lactuca universal hybridizer, and its use in creation of fertile interspecific somatic hybrids.

A Lactuca sativa cv. Ardente line heterozygous for a gene encoding resistance to kanamycin, a positive and dominant trait, was crossed with cv. Girelle, which is heterozygous for a recessive albinism marker.