Effective interaction between helical bio-molecules

The effective interaction between two parallel strands of helical bio-molecules, such as deoxyribose nucleic acids (DNA), is calculated using computer simulations of the "primitive" model of electrolytes. In particular we study a simple model for B-DNA incorporating explicitly its charge pattern as a double-helix structure. The effective force and the effective torque exerted onto the molecules depend on the central distance and on the relative orientation. The contributions of nonlinear screening by monovalent counterions to these forces and torques are analyzed and calculated for different salt concentrations. As a result, we find that the sign of the force depends sensitively on the relative orientation. For intermolecular distances smaller than $6\AA$ it can be both attractive and repulsive. Furthermore we report a nonmonotonic behaviour of the effective force for increasing salt concentration. Both features cannot be described within linear screening theories. For large distances, on the other hand, the results agree with linear screening theories provided the charge of the bio-molecules is suitably renormalized.Comment: 18 pages, 18 figures included in text, 100 bibliog

How patients understand depression associated with chronic physical disease - A systematic review

Background: Clinicians are encouraged to screen people with chronic physical illness for depression. Screening alone may not improve outcomes, especially if the process is incompatible with patient beliefs. The aim of this research is to understand peoples beliefs about depression, particularly in the presence of chronic physical disease. Methods: A mixed method systematic review involving a thematic analysis of qualitative studies and quantitative studies of beliefs held by people with current depressive symptoms. MEDLINE, EMBASE, PSYCHINFO, CINAHL, BIOSIS, Web of Science, The Cochrane Library, UKCRN portfolio, National Research Register Archive, Clinicaltrials.gov and OpenSIGLE were searched from database inception to 31st December 2010. A narrative synthesis of qualitative and quantitative data, based initially upon illness representations and extended to include other themes not compatible with that framework. Results: A range of clinically relevant beliefs was identified from 65 studies including the difficulty in labeling depression, complex causal factors instead of the biological model, the roles of different treatments and negative views about the consequences of depression. We found other important themes less related to ideas about illness: the existence of a self-sustaining depression spiral; depression as an existential state; the ambiguous status of suicidal thinking; and the role of stigma and blame in depression. Conclusions: Approaches to detection of depression in physical illness need to be receptive to the range of beliefs held by patients. Patient beliefs have implications for engagement with depression screening

A new Late Agenian (MN2a, Early Miocene) fossil assemblage from Wallenried (Molasse Basin, Canton Fribourg, Switzerland)

Excavations of two fossiliferous layers in the Wallenried sand- and marl pit produced a very diversified vertebrate fauna. New material allows the reassessment of the taxonomic position of the ruminant taxa Andegameryx andegaviensis and endemic Friburgomeryx wallenriedensis. An emended diagnosis for the second species is provided and additional material of large and small mammals, as well as ectothermic vertebrates, is described. The recorded Lagomorpha show interesting morphological deviations from other Central European material, and probably represent a unique transitional assemblage with a co-occurrence of Titanomys, Lagopsis and Prolagus. Rodentia and Eulipotyphla belong to typical and well-known species of the Agenian of the Swiss Molasse Basin. Abundant small mammal teeth have allowed us to pinpoint the biostratigraphic age of Wallenried to late MN2a. The biostratigraphic age conforms to data derived from the charophyte assemblages and confirms the oldest occurrence of venomous snake fangs. The palaeoenvironmental context is quite complex. Sedimentary structures and fauna (fishes, frogs, salamanders, ostracods) are characteristic for a humid, lacustrine environment within a flood plain system

Scaling theory and enthalpy of mixing for binary fluids

According to a classical result for binary mixtures one can, from the existence of lower and upper critical solution temperatures, draw resonable conclusions concerning the signs of the enthalpy of mixing. A crucial assumption in the various derivations of this result is the possibility of an expansion of the free energy in a Taylor series at the critical point. We give an alternative derivation based on the modern theory of critical phenomena

Interpenetration of interacting coils in polymer monolayers

Monte Carlo simulations demonstrate that in two-dimensional binary systems of interacting chains, such as in miscible polymer blends, interpenetration of the chains and expansion occurs. Both these observations differ from available results for single component melts in two dimensions

Polymer Miscibility in Capillaries

A thermodynamic analysis predicts an increase in miscibility, relative to that in the bulkstate, for a polymer mixture confined in a capillary with a diameter of the order of the sizeof the polymer coils. This is derived by using both the concepts of growing domains and aconsideration of the thickness of polymer-polymer interfaces. The analysis is combinedwith a Monte Carlo lattice simulation that provides results on such confined systems.Intermixing, described in terms of the number of heterocontacts and the dimensions ofthe polymer chains in the capillary parallel and perpendicular to the tubular axis, is investigated.The results confirm that demixing in homogeneous mixtures is hindered, whereasintermixing is enhanced, in the capillary relative to that in the unconfined mixture

Surface Segregation in Polymer Blends: A Monte Carlo Simulation

A Monte Carlo (MC) simulation of surface enrichment in polymer blends is presented. The algorithm introduced by Madden is used in this simulation, in which a compressible blend is condensed against a solid wall, with the surface of the blend forming an interface with holes (or solvent) that is parallel to the wall. Three regimes in the mixture are thus recognized: the interface at the wall, the bulk regime, and the interface with the vacuum (or solvent) at the surface of the mixture. Under certain conditions, enrichment of one of the components is observed, both at the surface and close to the wall. We find that the surface enrichment even in systems with the same cohesive energy in both components is driven byintermacromolecular interaction and asymmetric composition effects. A smaller part of the driving force arises from the difference in coil sizes between components, with the surface layer of the blend containing an excess of the component with the smaller coil size. A difference in coil sizes in a mixture containing polymers of equal chain length occurs in systems of asymmetric composition and with favorable interaction between components: in this case the majority chains act as a favorable solvent for the minority chains. In such asymmetric compositions, the minority chains move from the surface layers into the more favorable bulk regime. The results are compared with recent mean-field (MF) theory predictions and with those of available experiments. An important finding is that this type of segregation in miscible blends can occur well within the one-phase region of the phase diagram aswell asat its more expected location close to the binodal region