Dislocation-mediated growth of bacterial cell walls

Recent experiments have illuminated a remarkable growth mechanism of rod-shaped bacteria: proteins associated with cell wall extension move at constant velocity in circles oriented approximately along the cell circumference (Garner et al., Science (2011), Dominguez-Escobar et al. Science (2011), van Teeffelen et al. PNAS (2011). We view these as dislocations in the partially ordered peptidoglycan structure, activated by glycan strand extension machinery, and study theoretically the dynamics of these interacting defects on the surface of a cylinder. Generation and motion of these interacting defects lead to surprising effects arising from the cylindrical geometry, with important implications for growth. We also discuss how long range elastic interactions and turgor pressure affect the dynamics of the fraction of actively moving dislocations in the bacterial cell wall.Comment: to appear in PNA

A model of membrane contraction predicting initiation and completion of bacterial cell division

Bacterial cell division involves a complex and dynamic sequence of events whereby polymers of the protein FtsZ assemble at the division plane and rearrange to achieve the goal of contracting the cell membrane at the site of cell division, thus dividing the parent cell into two daughter cells. We present a mathematical model (which we refer to as CAM-FF: Critical Accumulation of Membrane-bound FtsZ Fibres) of the assembly of the contractile ring in terms of the accumulation of short linear polymers of FtsZ that associate and dissociate from the cell membrane. In prokaryotes, the biochemical function of FtsZ is thought to underpin the assembly and at least the initial kinetic force of ring contraction. Our model extends earlier work of Surovtsev et al. [PLoS Comput. Biol., 2008, 4, e1000102] by adding (i) the kinetics of FtsZ accumulation on cell membrane anchor proteins and (ii) the physical forces required to deform the cell against its surface tension. Moreover, we provide a more rigorous treatment of intracellular diffusion and we revise some of the model parameter values in light of the experimental evidence now available. We derive a critical contraction parameter which links the chemical population dynamics of membrane-bound FtsZ molecules to the force of contraction. Using this parameter as a tool to predict the ability of the cell to initiate division, we are able to predict the division outcome in cells depleted of key FtsZ-binding proteins

Quantum-classical transition in Scale Relativity

The theory of scale relativity provides a new insight into the origin of fundamental laws in physics. Its application to microphysics allows us to recover quantum mechanics as mechanics on a non-differentiable (fractal) spacetime. The Schrodinger and Klein-Gordon equations are demonstrated as geodesic equations in this framework. A development of the intrinsic properties of this theory, using the mathematical tool of Hamilton's bi-quaternions, leads us to a derivation of the Dirac equation within the scale-relativity paradigm. The complex form of the wavefunction in the Schrodinger and Klein-Gordon equations follows from the non-differentiability of the geometry, since it involves a breaking of the invariance under the reflection symmetry on the (proper) time differential element (ds - ds). This mechanism is generalized for obtaining the bi-quaternionic nature of the Dirac spinor by adding a further symmetry breaking due to non-differentiability, namely the differential coordinate reflection symmetry (dx^mu - dx^mu) and by requiring invariance under parity and time inversion. The Pauli equation is recovered as a non-relativistic-motion approximation of the Dirac equation.Comment: 28 pages, no figur

Australian Sphingidae – DNA Barcodes Challenge Current Species Boundaries and Distributions

© 2014 Rougerie et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. The attached file is the published version of the article

The protocol for positive body experience (PBE); introducing a psychomotor therapy intervention based on positive body exposure targeting negative body image in eating disorders

Negative body experience is a core characteristic of eating disorders, and poses a serious risk factor for its development, maintenance and relapse. This underlines the importance of specific therapeutic attention to body experience. In the past ten years a body-oriented treatment protocol with the focus on positive body exposure, called 'Protocol Positive body experience' has been developed. The aim of this paper is to describe the scientific basis of the protocol and to give an impression of its content and structure, illustrated by clinical case vignettes. An important and innovative aspect of the protocol is to enhance not only aesthetic, but also functional and tactile body experience. The protocol enables body-oriented therapists and psychomotor therapists to treat negative body experience in an evidence-based way and facilitates further research to validate the effect of positive body exposure

Measuring body satisfaction in women with eating disorders and healthy women:appearance-related and functional components in the Body Cathexis Scale (Dutch version)

Purpose Differentiating the concept of body satisfaction, especially the functional component, is important in clinical and research context. The aim of the present study is to contribute to further refinement of the concept by evaluating the psychometric properties of the Dutch version of the Body Cathexis Scale (BCS). Differences in body satisfaction between clinical and non-clinical respondents are also explored. Method Exploratory factor analysis (EFA) and confirmatory factor analysis (CFA) were used to investigate whether functional body satisfaction can be distinguished as a separate factor, using data from 238 adult female patients from a clinical sample and 1060 women from two non-clinical samples in the Netherlands. Univariate tests were used to identify differences between non-clinical and clinical samples. Results EFA identified functionality as one of three factors, which was confirmed by CFA. CFA showed the best fit for a three-factor model, where functionality, non-weight, and weight were identified as separate factors in both populations. Internal consistency was good and correlations between factors were low. Women in the non-clinical sample scored significantly higher on the BCS than women with eating disorders on all three subscales, with high effect sizes. Conclusions The three factors of the BCS may be used as subscales, enabling researchers and practitioners to use one scale to measure different aspects of body satisfaction, including body functionality. Use of the BCS may help to achieve a more complete understanding of how people evaluate body satisfaction and contribute to further research on the effectiveness of interventions focussing on body functionality

Shifting the Focus:A Pilot Study on the Effects of Positive Body Exposure on Body Satisfaction, Body Attitude, Eating Pathology and Depressive Symptoms in Female Patients with Eating Disorders

One of the most commonly used techniques for the treatment of body image problems in eating disorders (ED) is body exposure (BE). However, evidence of its effectiveness in clinical populations is scarce. In the Positive Body Experience (PBE) protocol, the focus of positive BE is on aesthetic, functional and tactile aspects of the body. The current study evaluates the outcomes of positive BE with regard to changes in attitudinal body image and eating pathology, as well as the factors that influence these changes, in a sample of 84 adult female patients with different EDs who did not receive any other treatment for their EDs during the period in which BE treatment occurred. The results show significant positive changes in attitudinal body image, ED behaviors and depressive symptoms, with depressive symptoms at baseline mediating the changes in attitudinal body image. This study indicates that the PBE protocol is a suitable intervention for reducing negative attitudinal body image in anorexia and bulimia nervosa patients, as well as those with binge eating disorder. Furthermore, the results suggest that positive non-weight-related and functional body satisfaction are strong catalysts for change and that depressive symptoms play an important role in the ability to change. Additional RCTs are needed to gain more insight into the effects of PBE

Performance breakdown effects dissociate from error detection effects in typing

Mistakes in skilled performance are often observed to be slower than correct actions. This error slowing has been associated with cognitive control processes involved in performance monitoring and error detection. A limited literature on skilled actions, however, suggests that preerror actions may also be slower than accurate actions. This contrasts with findings from unskilled, discrete trial tasks, where preerror performance is usually faster than accurate performance. We tested 3 predictions about error-related behavioural changes in continuous typing performance. We asked participants to type 100 sentences without visual feedback. We found that (a) performance before errors was no different in speed than that before correct key-presses, (b) error and posterror key-presses were slower than matched correct key-presses, and (c) errors were preceded by greater variability in speed than were matched correct key-presses. Our results suggest that errors are preceded by a behavioural signature, which may indicate breakdown of fluid cognition, and that the effects of error detection on performance (error and posterror slowing) can be dissociated from breakdown effects (preerror increase in variability). © 2013 © 2013 The Experimental Psychology Society