Modelling cytoskeletal traffic: an interplay between passive diffusion and active transport

We introduce the totally asymmetric exclusion process with Langmuir kinetics (TASEP-LK) on a network as a microscopic model for active motor protein transport on the cytoskeleton, immersed in the diffusive cytoplasm. We discuss how the interplay between active transport along a network and infinite diffusion in a bulk reservoir leads to a heterogeneous matter distribution on various scales. We find three regimes for steady state transport, corresponding to the scale of the network, of individual segments or local to sites. At low exchange rates strong density heterogeneities develop between different segments in the network. In this regime one has to consider the topological complexity of the whole network to describe transport. In contrast, at moderate exchange rates the transport through the network decouples, and the physics is determined by single segments and the local topology. At last, for very high exchange rates the homogeneous Langmuir process dominates the stationary state. We introduce effective rate diagrams for the network to identify these different regimes. Based on this method we develop an intuitive but generic picture of how the stationary state of excluded volume processes on complex networks can be understood in terms of the single-segment phase diagram.Comment: 5 pages, 7 figure

The midwife factor in obstetric procedures and neonatal outcome

Aims. In the face of major tendency towards midwiferyled-care it was our purpose to investigate the extent of the influence of the midwife on the rates of obstetric procedures and perinatal outcome. Methods. 5384 consecutive deliveries at the Department of Obstetrics and Gynecology. University of Graz, were enrolled in the study. The following data were collected: mode of delivery, pH of umbilical artery, Apgar score. Firstly, data were investigated for interindividual differences and, secondly, for relationship with age of the midwife as a measure of experience. Results. Interindividual differences were significant for episiotomy rates (minimum: 31.6%; maximum 76.9%; p<0.001), forceps rates (minimum: 1.7%; maximum 11.1%;p=0.002) and pH of umbilical arteries (minimum: 7.21:maxinium: 7.28 p=0.001) but not for cesarean section rates and Apgar scores. Linear regression analysis was significant between age of midwives and pH of umbilical arteries (p<0.001: r=0.055) and for one-minute Apgar score (p=0.009; r=0.050) but not for episiotomy rates, cesarean section rates, forceps rates and five-minutes Apgar score. Conclusions. There are large interindividual differences in obstetric intervention rates which cannot be explained by the midwives' age. Provision of health care should be primarily determined by need and not by the personal characteristics of the health care provider, thus interindividual differences should be reduced and more often taken into account when analyzing any kind of data

Quantum phase estimation algorithm in presence of static imperfections

We study numerically the effects of static imperfections and residual couplings between qubits for the quantum phase estimation algorithm with two qubits. We show that the success probability of the algorithm is affected significantly more by static imperfections than by random noise errors in quantum gates. An improvement of the algorithm accuracy can be reached by application of the Pauli-random-error-correction method (PAREC).Comment: 5 pages, 5 figures. Research avilable at http://www.quantware.ups-tlse.fr

Integrated optics for astronomical interferometry. I. Concept and astronomical applications

We propose a new instrumental concept for long-baseline optical single-mode interferometry using integrated optics which were developed for telecommunication. Visible and infrared multi-aperture interferometry requires many optical functions (spatial filtering, beam combination, photometric calibration, polarization control) to detect astronomical signals at very high angular resolution. Since the 80's, integrated optics on planar substrate have become available for telecommunication applications with multiple optical functions like power dividing, coupling, multiplexing, etc. We present the concept of an optical / infrared interferometric instrument based on this new technology. The main advantage is to provide an interferometric combination unit on a single optical chip. Integrated optics are compact, provide stability, low sensitivity to external constrains like temperature, pressure or mechanical stresses, no optical alignment except for coupling, simplicity and intrinsic polarization control. The integrated optics devices are inexpensive compared to devices that have the same functionalities in bulk optics. We think integrated optics will fundamentally change single-mode interferometry. Integrated optics devices are in particular well-suited for interferometric combination of numerous beams to achieve aperture synthesis imaging or for space-based interferometers where stability and a minimum of optical alignments are wished.Comment: 11 pages, 8 figures, accpeted by Astronomy and Astrophysics Supplement Serie

Exclusion processes on networks as models for cytoskeletal transport

We present a study of exclusion processes on networks as models for complex transport phenomena and in particular for active transport of motor proteins along the cytoskeleton. We argue that active transport processes on networks spontaneously develop density heterogeneities at various scales. These heterogeneities can be regulated through a variety of multi-scale factors, such as the interplay of exclusion interactions, the non-equilibrium nature of the transport process and the network topology. We show how an effective rate approach allows to develop an understanding of the stationary state of transport processes through complex networks from the phase diagram of one single segment. For exclusion processes we rationalize that the stationary state can be classified in three qualitatively different regimes: a homogeneous phase as well as inhomogeneous network and segment phases. In particular, we present here a study of the stationary state on networks of three paradigmatic models from non-equilibrium statistical physics: the totally asymmetric simple exclusion process, the partially asymmetric simple exclusion process and the totally asymmetric simple exclusion process with Langmuir kinetics. With these models we can interpolate between equilibrium (due to bi-directional motion along a network or infinite diffusion) and out-of-equilibrium active directed motion along a network. The study of these models sheds further light on the emergence of density heterogeneities in active phenomena.Comment: 55 pages, 26 figure

Characteristics of the conjugative transfer system of the IncM plasmid pCTX-M3 and identification of its putative regulators

Plasmid conjugative transfer systems comprise type IV secretion systems (T4SS) coupled to DNA processing and replication. The T4SSs are divided into two phylogenetic subfamilies, namely, IVA and IVB or based on the phylogeny of the VirB4 ATPase into eight groups. The conjugation system of the IncM group plasmid pCTX-M3, from Citrobacter freundii, is classified in the IVB subfamily and in the MPFI group, as are the conjugation systems of IncI1 group plasmids. Although the majority of the conjugative genes of the IncM and IncI1 plasmids display conserved synteny, there are several differences. Here, we present a deletion analysis of 27 genes in the conjugative transfer regions of pCTX-M3. Notably, the deletion of either of two genes dispensable for conjugative transfer, namely, orf35 and orf36, resulted in an increased plasmid mobilization efficiency. Transcriptional analysis of the orf35 and orf36 deletion mutants suggested an involvement of these genes in regulating the expression of conjugative transfer genes. We also revised the host range of the pCTX-M3 replicon by finding that this replicon is unable to support replication in Agrobacterium tumefaciens, Ralstonia eutropha and Pseudomonas putida although its conjugation system is capable of introducing plasmids bearing oriTpCTX-M3 into these bacteria, which are representatives of Alpha-, Beta- and Gammaproteobacteria, respectively. Thus, the conjugative transfer system of pCTX-M3 has a much broader host range than does its replicon. Importance Horizontal gene transfer is responsible for rapid changes in bacterial genomes, and the conjugative transfer of plasmids has a great impact on the plasticity of bacteria. Here, we present a deletion analysis of the conjugative transfer system genes of the pCTX-M3 plasmid of the IncM group, which is responsible for the dissemination of antibiotic resistance genes in Enterobacteriaceae. We found that deletion of the orf35 or orf36 genes, which are dispensable for conjugative transfer, increased the plasmid mobilization efficiency. RT-qPCR analysis suggested the involvement of orf35 and orf36 in regulating the expression of transfer genes. We also revised the host range of pCTX-M3 by showing that its conjugative transfer system has a much broader host range than does its replicon

Microsurgical Technique of Simultaneous Pancreas/Kidney Transplantation in the Rat: Clinical Experience and Review of the Literature

Background: For experimental basic research, standardized transplantation models reflecting technical and immunologic aspects are necessary. This article describes an experimental model of combined pancreas/kidney transplantation (PKTx) in detail. Materials and Methods: Donor rats underwent en bloc pancreatectomy and nephrectomy. Revascularization was performed using the aorta with the superior mesenteric artery and the inferior vena cava with the portal vein. Exocrine drainage of the pancreas took place over a segment of the duodenum which was transplanted side-to-side to the jejunum. The kidney vessels were transplanted end-to-side. The ureter was anastomosed by patch technique. Postoperatively, serum parameters were monitored daily. Biopsies for histopathology were taken on days 5, 8 and 12. Results: All 12 recipients survived the combined PKTx without serious surgical complications. One thrombosis of the portal vein led to organ failure. Blood glucose levels were normal by the 3rd postoperative day. The transplanted duodenal segment showed slight villous atrophy, and the kidneys were well perfused without vascular complications. The anastomosis between ureter and bladder was leakproof. Conclusions: Excellent graft function and survival rates can be achieved due to simplified operation technique and short operation time. It may thus have high clinical relevance to immunologic issues within the scope of basic research. Copyright (C) 2009 S. Karger AG, Base

Role of pseudospin in quasiparticle interferences in epitaxial graphene probed by high-resolution scanning tunneling microscopy

Pseudospin, an additional degree of freedom related to the honeycomb structure of graphene, is responsible of many of the outstanding electronic properties found in this material. This article provides a clear understanding of how such pseudospin impacts the quasiparticle interferences of monolayer (ML) and bilayer (BL) graphene measured by low temperature scanning tunneling microscopy and spectroscopy. We have used this technique to map, with very high energy and space resolution, the spatial modulations of the local density of states of ML and BL graphene epitaxialy grown on SiC(0001), in presence of native disorder. We perform a Fourier transform analysis of such modulations including wavevectors up to unit-vectors of the reciprocal lattice. Our data demonstrate that the quasiparticle interferences associated to some particular scattering processes are suppressed in ML graphene, but not in BL graphene. Most importantly, interferences with 2qF wavevector associated to intravalley backscattering are not measured in ML graphene, even on the images with highest resolution. In order to clarify the role of the pseudospin on the quasiparticle interferences, we use a simple model which nicely captures the main features observed on our data. The model unambiguously shows that graphene's pseudospin is responsible for such suppression of quasiparticle interferences features in ML graphene, in particular for those with 2qF wavevector. It also confirms scanning tunneling microscopy as a unique technique to probe the pseudospin in graphene samples in real space with nanometer precision. Finally, we show that such observations are robust with energy and obtain with great accuracy the dispersion of the \pi-bands for both ML and BL graphene in the vicinity of the Fermi level, extracting their main tight binding parameters