A multiple replica approach to simulate reactive trajectories

A method to generate reactive trajectories, namely equilibrium trajectories leaving a metastable state and ending in another one is proposed. The algorithm is based on simulating in parallel many copies of the system, and selecting the replicas which have reached the highest values along a chosen one-dimensional reaction coordinate. This reaction coordinate does not need to precisely describe all the metastabilities of the system for the method to give reliable results. An extension of the algorithm to compute transition times from one metastable state to another one is also presented. We demonstrate the interest of the method on two simple cases: a one-dimensional two-well potential and a two-dimensional potential exhibiting two channels to pass from one metastable state to another one

The biology of Cixius wagneri, the planthopper vector of ‘Candidatus Phlomobacter fragariae’ in strawberry production tunnels and its consequence for the epidemiology of strawberry marginal chlorosis

Abstract«Candidatus Phlomobacter fragariae» is the prevalent agent of strawberry marginal chlorosis (SMC) and is transmitted by the planthopper Cixius wagneri. Because the insect vector biology was unknown, a field experiment was set up to determine if it was able to reproduce on strawberry plants, to determine the number of insect generations per year and the ability of nymphs to transmit SMC. During spring 2004, 80 C. wagneri adults were delivered into 4 small insectproof tunnels containing 30 healthy plants. Fifteen percent of the delivered insect population were carrying the pathogen. In October 2004, only 3 young L1 instar nymphs were found in the first tunnel, demonstrating there were no new insect generations during the summer. In April 2005, 330 C. wagneri of early L1 to late L5 nymph instars were collected at the roots of the plants,clearly indicating that a single insect generation had overwintered as larvae andemerged at the following spring. All instars were shown to carry ‘Ca. P. fragariae’ (70 to 75 % of the larvae) and were able to transmit SMC as assessed by transmission assays. An insecticide treatment was applied in March 2005 in a third tunnel and a fourth tunnel was kept as a control. More than 120 C. wagneri adults were collected in the control tunnel 4 in June 2005 confirming that an insect generation arose in the tunnel, whereas no insects could be found in the treated tunnel 3. All plants were kept for two years, surveyed for symptom expression and tested for ‘Ca. P. fragariae’ infection by 16S-PCR. Results indicated a reduced mortality and SMC incidence in tunnel 3, and a higher mortality and SMC incidence in tunnel 2 than in tunnel 1, attesting that C. wagneri larvae had spread SMC and that an early insecticide treatment could control the disease.Keywords: Phloem-restricted bacteria, planthopper, insect vector, Fragaria x ananass

Detection of phloem restricted bacteria responsible for strawberry marginal chlorosis (SMC) by real-time PCR in a single assay

Two uncultured phloem restricted plant pathogens, the γ3 proteobacterium «Candidatus Phlomobacter fragariae » and the stolbur phytoplasma (group 16SrXII-A) are associated with strawberry marginal chlorosis (SMC) in France. As “Ca. P. fragariae” and stolbur phytoplasma induce identical symptoms, the only way to identify the pathogen infecting a given diseased plant is to perform conventional PCR assays. Because using two PCR techniques for detecting separately each of the two bacteria is time consuming and because specificity and sensitivity of the detection test needed to be improved, a new approach using triplex real time PCR was developed for the routine detection of “Ca. P. fragariae “ and stolbur phytoplasma. The real time PCR has the advantage of being faster reduces the risks of producing false positives. Furthermore, real-time PCR techniques provide the possibility of multiplexing by using probes with different compatible fluorescent dyes. Here, we present a new sensitive Taqman® method which permits the simultaneous amplification of three DNA targets in one test: the map gene of stolbur phytoplasma, the spoT gene of “Ca. P. fragariae” and the cox gene of strawberry chloroplast taken as an internal control. The specificity and the efficiency of this method were determined.Keywords: Strawberry Marginal Chlorosis, Triplex taqman® PCR ,Candidatus Phlomobacter fragariae, stolbur phytoplasma

Domain Dynamics of Magnetic Films with Perpendicular Anisotropy

We study the magnetic properties of nanoscale magnetic films with large perpendicular anisotropy comparing polarization microscopy measurements on Co_28Pt_72 alloy samples based on the magneto-optical Kerr effect with Monte Carlo simulations of a corresponding micromagnetic model. We focus on the understanding of the dynamics especially the temperature and field dependence of the magnetisation reversal process. The experimental and simulational results for hysteresis, the reversal mechanism, domain configurations during the reversal, and the time dependence of the magnetisation are in very good qualitative agreement. The results for the field and temperature dependence of the domain wall velocity suggest that for thin films the hysteresis can be described as a depinning transition of the domain walls rounded by thermal activation for finite temperatures.Comment: 7 pages Latex, Postscript figures included, accepted for publication in Phys.Rev.B, also availible at: http://www.thp.Uni-Duisburg.DE/Publikationen/Publist_Us_R.htm

Water Soluble Derivatives of Camptothecin/Homocamptothecin

Camptothecin and homocamptothecin analogs and derivatives are provided incorporating alkylamine and polyalkylamine moieties