Effect of Knotting on the Shape of Polymers

Momentary configurations of long polymers at thermal equilibrium usually deviate from spherical symmetry and can be better described, on average, by a prolate ellipsoid. The asphericity and nature of asphericity (or prolateness) that describe these momentary ellipsoidal shapes of a polymer are determined by specific expressions involving the three principal moments of inertia calculated for configurations of the polymer. Earlier theoretical studies and numerical simulations have established that as the length of the polymer increases, the average shape for the statistical ensemble of random configurations asymptotically approaches a characteristic universal shape that depends on the solvent quality. It has been established, however, that these universal shapes differ for linear, circular, and branched chains. We investigate here the effect of knotting on the shape of cyclic polymers modeled as random isosegmental polygons. We observe that random polygons forming different knot types reach asymptotic shapes that are distinct from the ensemble average shape. For the same chain length, more complex knots are, on average, more spherical than less complex knots.

Optimal coexistence of long-term and short-term contracts in labor Markets

We consider a market where firms hire workers to run their projects and such projects differ in profitability. At any period, each firm needs two workers to successfully run its project: a junior agent, with no specific skills, and a senior worker, whose effort is not verifiable. Senior workers differ in ability and their competence is revealed after they have worked as juniors in the market. We study the length of the contractual relationships between firms and workers in an environment where the matching between firms and workers is the result of market interaction. We show that, despite in a one-firm-one-worker set-up long-term contracts are the optimal choice for firms, market forces often induce firms to use short-term contracts. Unless the market only consists of firms with very profitable projects, firms operating highly profitable projects offer short-term contracts to ensure the service of high-ability workers and those with less lucrative projects also use short-term contracts to save on the junior workers' wage. Intermediate firms may (or may not) hire workers through long-term contracts.

Fission yeast: in shape to divide.

How are cell morphogenesis and cell cycle coordinated? The fission yeast is a rod-shaped unicellular organism widely used to study how a cell self-organizes in space and time. Here, we discuss recent advances in understanding how the cell acquires and maintains its regular rod shape and uses it to control cell division. The cellular body plan is established by microtubules, which mark antipodal growth zones and medial division. In turn, cellular dimensions are defined by the small GTPase Cdc42 and downstream regulators of vesicle trafficking. Yeast cells then repetitively use their simple rod shape to orchestrate the position and timing of cell division.

Effects of physiological self-crowding of DNA on shape and biological properties of DNA molecules with various levels of supercoiling.

DNA in bacterial chromosomes and bacterial plasmids is supercoiled. DNA supercoiling is essential for DNA replication and gene regulation. However, the density of supercoiling in vivo is circa twice smaller than in deproteinized DNA molecules isolated from bacteria. What are then the specific advantages of reduced supercoiling density that is maintained in vivo? Using Brownian dynamics simulations and atomic force microscopy we show here that thanks to physiological DNA-DNA crowding DNA molecules with reduced supercoiling density are still sufficiently supercoiled to stimulate interaction between cis-regulatory elements. On the other hand, weak supercoiling permits DNA molecules to modulate their overall shape in response to physiological changes in DNA crowding. This plasticity of DNA shapes may have regulatory role and be important for the postreplicative spontaneous segregation of bacterial chromosomes.

Opportunity to shape the prevention and management of obesity

Cooperation and Working Together (CAWT), the cross border health and social care partnership has been working with the Departments of Health to progress a three year cross border obesity prevention and management project aimed at families. They have been successful in securing funding from the EU INTERREG IVA programme. A planning workshop focussing on this will be held on Friday 26 June 2009.

Nature's shape.

Review of the book : "What shape is a snowflake?", by I.S. Weidenfeld & Nicholson, London, UK

Coexistence of antibodies to tick-borne agents of babesiosis and Lyme borreliosis in patients from Cotia county, State of São Paulo, Brazil

This paper reports a case of coinfection caused by pathogens of Lyme disease and babesiosis in brothers. This was the first case of borreliosis in Brazil, acquired in Cotia County, State of São Paulo, Brazil. Both children had tick bite history, presented erythema migrans, fever, arthralgia, mialgia, and developed positive serology (ELISA and Western-blotting) directed to Borrelia burgdorferi G 39/40 and Babesia bovis antigens, mainly of IgM class antibodies, suggestive of acute disease. Also, high frequencies of antibodies to B. bovis was observed in a group of 59 Brazilian patients with Lyme borreliosis (25.4%), when compared with that obtained in a normal control group (10.2%) (chi-square = 5.6; p < 0.05). Interestingly, both children presented the highest titers for IgM antibodies directed to both infective diseases, among all patients with Lyme borreliosis.

Ossification du ligament commun cervical postérieur : coexistence de spondylarthrite et d'une hyperostose idiopathique diffuse du squelette

Introduction: L'ossification du ligament commun vertébral postérieur (LCVP) est une hyperostose prédominant au rachis cervical, associée à différentes pathologies constructrices comme l'arthrose, la maladie de Forestier (ou DISH : Diffuse Idiopathic Squeletal Hyperostosis) ou les spondylarthrites (1). Nous rapportons le cas d'une patiente avec ossification cervicale du LCVP, avec coexistence de DISH et de spondylarthrite.Observation: Patiente de 55 ans, d'origine Irakienne, qui présente depuis l'âge de 40 ans des lombalgies et des talalgies attribuées initialement à un métier physique. En 2008, apparait une cervicobrachialgie C6 gauche. L'IRM cervicale retrouve plusieurs hernies discales (C5-C6 et C6-C7 gauches) avec un canal cervical étroit constitutionnel et une ossification du LCVP cervical. Cette ossification est attribuée à un DISH (Figure1). L'échec du traitement conservateur de la névralgie et la menace neurologique de l'ossification du LCVP conduisent en 2010 à une laminectomie C3-C6 avec fixation postérieure (figure 2). En 2011, la patiente consulte en raison de la persistance de cette névralgie, ainsi que pour des lombalgies inflammatoires. La coexistence de ces symptômes inflammatoires et de l'ossification du LCVP nous incite à réaliser une IRM des sacroiliaques qui retrouve une sacroiliite bilatérale (figure 3). Le diagnostic de spondylarthrite HLA B27 négative est retenu devant l'association des signes cliniques et radiologiques. L'étiologie précise quant à l'origine de l'ossification du LCVP reste incertaine, néanmoins un traitement spécifique de la spondylarthopathie est proposé.Discussion: L'ossification du ligament vertébral commun postérieur est une hyperostose dont les principales causes sont le DISH et les spondylarthrites. On retrouve une ossification du ligament commun vertébral, qu'il soit lombaire, cervical ou dorsal, dans 10 à 50 % des DISH, et 3.5 à 30% des spondylarthrites. 4 types d'ossification du LCVP sont décrites : continue, segmentaire, mixte ou circonscrite. Selon Resnick, le DISH se différencie de la spondylarthrite par la présence d'ossifications antérolatérales d'au moins 4 vertèbres contigües sans érosion des sacroiliaques. Cependant on retrouve dans la littérature quelques cas décrivant la coexistence des 2 pathologies. Récemment, Kim et al. Ont rapporté un cas similaire à notre patiente, avec ossification du LCVP cervical et coexistence de DISH et de spondylarthrite (2).Conclusion: Devant la présence d'une ossification du ligament vertébral commun postérieur cervical, il convient de rechercher des signes de DISH et de spondylarthrite, car leur coexistence est possible. La prévalence exacte de cette association reste encore à déterminer.

Shape complexity based on mutual information

Shape complexity has recently received attention from different fields, such as computer vision and psychology. In this paper, integral geometry and information theory tools are applied to quantify the shape complexity from two different perspectives: from the inside of the object, we evaluate its degree of structure or correlation between its surfaces (inner complexity), and from the outside, we compute its degree of interaction with the circumscribing sphere (outer complexity). Our shape complexity measures are based on the following two facts: uniformly distributed global lines crossing an object define a continuous information channel and the continuous mutual information of this channel is independent of the object discretisation and invariant to translations, rotations, and changes of scale. The measures introduced in this paper can be potentially used as shape descriptors for object recognition, image retrieval, object localisation, tumour analysis, and protein docking, among others

Do socioeconomic factors shape weight and obesity trajectories over the transition from midlife to old age? Results from the French GAZEL cohort study

BACKGROUND: Obesity is a contemporary epidemic that does not affect all age groups and sections of society equally. OBJECTIVE: The objective was to examine socioeconomic differences in trajectories of body mass index (BMI; in kg/m(2)) and obesity between the ages of 45 and 65 y. DESIGN: A total of 13,297 men and 4532 women from the French GAZEL (Gaz de France Electricité de France) cohort study reported their height in 1990 and their weight annually over the subsequent 18 y. Changes in BMI and obesity between ages 45 and 49 y, 50 and 54 y, 55 and 59 y, and 60 and 65 y as a function of education and occupational position (at age 35 y) were modeled by using linear mixed models and generalized estimating equations. RESULTS: BMI and obesity rates increased between the ages of 45 and 65 y. In men, BMI was higher in unskilled workers than in managers at age 45 y; this difference in BMI increased from 0.82 (95% CI: 0.66, 0.99) at 45 y to 1.06 (95% CI: 0.85, 1.27) at 65 y. Men with a primary school education compared with those with a high school degree at age 45 y had a 0.75 (95% CI: 0.51, 1.00) higher BMI, and this difference increased to 1.32 (95% CI: 1.03,1.62) at age 65 y. Obesity rates were 3.35% and 7.68% at age 45 y and 9.52% and 18.10% at age 65 y in managers and unskilled workers, respectively; the difference in obesity increased by 4.25% (95% CI: 1.87, 6.52). A similar trend was observed in women. Conclusions: Weight continues to increase in the transition between midlife and old age; this increase is greater in lower socioeconomic groups.

Gender and weight shape brain dynamics during food viewing.

Hemodynamic imaging results have associated both gender and body weight to variation in brain responses to food-related information. However, the spatio-temporal brain dynamics of gender-related and weight-wise modulations in food discrimination still remain to be elucidated. We analyzed visual evoked potentials (VEPs) while normal-weighted men (n = 12) and women (n = 12) categorized photographs of energy-dense foods and non-food kitchen utensils. VEP analyses showed that food categorization is influenced by gender as early as 170 ms after image onset. Moreover, the female VEP pattern to food categorization co-varied with participants' body weight. Estimations of the neural generator activity over the time interval of VEP modulations (i.e. by means of a distributed linear inverse solution [LAURA]) revealed alterations in prefrontal and temporo-parietal source activity as a function of image category and participants' gender. However, only neural source activity for female responses during food viewing was negatively correlated with body-mass index (BMI) over the respective time interval. Women showed decreased neural source activity particularly in ventral prefrontal brain regions when viewing food, but not non-food objects, while no such associations were apparent in male responses to food and non-food viewing. Our study thus indicates that gender influences are already apparent during initial stages of food-related object categorization, with small variations in body weight modulating electrophysiological responses especially in women and in brain areas implicated in food reward valuation and intake control. These findings extend recent reports on prefrontal reward and control circuit responsiveness to food cues and the potential role of this reactivity pattern in the susceptibility to weight gain.

Different arbuscular mycorrhizal fungi alter coexistence and resource distribution between co-occurring plants

It is often thought that the coexistence of plants and plant diversity is determined by resource heterogeneity of the abiotic environment. However, the presence and heterogeneity of biotic plant resources, such as arbuscular mycorrhizal fungi (AMF), could also affect plant species coexistence. In this study, Brachypodium pinnatum and Prunella vulgaris were grown together in pots and biotic resource heterogeneity was simulated by inoculating these pots with one of three different AMF taxa, with a mixture of these three taxa, or pots remained uninoculated. The AMF acted as biotic plant resources since the biomass of plants in pots inoculated with AMF was on average 11.8 times higher than uninoculated pots. The way in which the two plant species coexisted, and the distribution of phosphorus and nitrogen between the plant species, varied strongly depending on which AMF were present. The results showed that the composition of AMF communities determines how plant species coexist and to which plant species nutrients are allocated. Biotic plant resources such as AMF should therefore be considered as one of the factors that determine how plant species coexist and how soil resources are distributed among co-occurring plant species.

Mass detection on mammograms: influence of signal shape uncertainty on human and model observers.

We studied the influence of signal variability on human and model observers for detection tasks with realistic simulated masses superimposed on real patient mammographic backgrounds and synthesized mammographic backgrounds (clustered lumpy backgrounds, CLB). Results under the signal-known-exactly (SKE) paradigm were compared with signal-known-statistically (SKS) tasks for which the observers did not have prior knowledge of the shape or size of the signal. Human observers' performance did not vary significantly when benign masses were superimposed on real images or on CLB. Uncertainty and variability in signal shape did not degrade human performance significantly compared with the SKE task, while variability in signal size did. Implementation of appropriate internal noise components allowed the fit of model observers to human performance.

Weighted Shape-based Averaging with Neighborhood Prior Model for Multiple Atlas Fusion-based Medical Image Segmentation

In medical imaging, merging automated segmentations obtained from multiple atlases has become a standard practice for improving the accuracy. In this letter, we propose two new fusion methods: "Global Weighted Shape-Based Averaging" (GWSBA) and "Local Weighted Shape-Based Averaging" (LWSBA). These methods extend the well known Shape-Based Averaging (SBA) by additionally incorporating the similarity information between the reference (i.e., atlas) images and the target image to be segmented. We also propose a new spatially-varying similarity-weighted neighborhood prior model, and an edge-preserving smoothness term that can be used with many of the existing fusion methods. We first present our new Markov Random Field (MRF) based fusion framework that models the above mentioned information. The proposed methods are evaluated in the context of segmentation of lymph nodes in the head and neck 3D CT images, and they resulted in more accurate segmentations compared to the existing SBA.