The Influence of high pressure on the bending rigidity of model membranes

Curvature is a fundamental lipid membrane property that influences many membrane-mediated biological processes and dynamic soft materials. One of the key parameters that determines the energetics of curvature change is the membrane bending rigidity. Understanding the intrinsic effect of pressure on membrane bending is critical to understanding the adaptation and structural behavior of biomembranes in deep-sea organisms as well as soft material processing. However, it has not previously been possible to measure the influence of high hydrostatic pressure on membrane bending energetics, and this bottleneck has primarily been due to a lack of technology platforms for performing such measurements. We have developed a new high-pressure microscopy cell which, combined with vesicle fluctuation analysis, has allowed us to make the first measurements of membrane bending rigidity as a function of pressure. Our results show a significant increase in bending rigidity at pressures up to 40 MPa. Above 40 MPa, the membrane mechanics become more complex. Corresponding small and wide-angle X-ray diffraction shows an increase in density and thickness of the bilayer with increasing pressure which correlates with the micromechanical measurements. These results are consistent with recent theoretical predictions of the bending rigidity as a function of hydrocarbon chain density. This technology has the potential to transform our quantitative understanding of the role of pressure in soft material processing, the structural behavior of biomembranes, and the adaptation mechanisms employed by deep-sea organisms

A case study of asthma care in school age children using nurse-coordinated multidisciplinary collaborative practices

Aim: To describe the role of school nursing in leading and coordinating a multidisciplinary networked system of support for children with asthma, and to analyze the strengths and challenges of undertaking and supporting multiagency interprofessional practice. Background: The growth of networked and interprofessional collaborations arises from the recognition that a number of the most pressing public health problems cannot be addressed by single-discipline or -agency interventions. This paper identifies the potential of school nursing to provide the vision and multiagency leadership required to coordinate multidisciplinary collaboration. Method: A mixed-method single-case study design using Yin’s approach, including focus groups, interviews, and analysis of policy documents and public health reports. Results: A model that explains the integrated population approach to managing school-age asthma is described; the role of the lead school nurse coordinator was seen as critical to the development and sustainability of the model. Conclusion: School nurses can provide strategic multidisciplinary leadership to address pressing public health issues. Health service managers and commissioners need to understand how to support clinicians working across multiagency boundaries and to identify how to develop leadership skills for collaborative interprofessional practice so that the capacity for nursing and other health care professionals to address public health issues does not rely on individual motivation. In England, this will be of particular importance to the commissioning of public health services by local authorities from 2015

Re-entrant magnetic field induced charge and spin gaps in the coupled dual-chain quasi-one dimensional organic conductor Perylene2_2[Pt(mnt)2_2]

An inductive method is used to follow the magnetic field-dependent susceptibility of the coupled charge density wave (CDW) and spin-Peierls (SP) ordered state behavior in the dual chain organic conductor Perylene$_2$[Pt(mnt)$_2$]. In addition to the coexisting SP-CDW state phase below 8 K and 20 T, the measurements show that a second spin-gapped phase appears above 20 T that coincides with a field-induced insulating phase. The results support a strong coupling of the CDW and SP order parameters even in high magnetic fields, and provide new insight into the nature of the magnetic susceptibility of dual-chain spin and charge systems.Comment: 6 pages, 6 figure

Debye relaxation in high magnetic fields

Dielectric relaxation is universal in characterizing polar liquids and solids, insulators, and semiconductors, and the theoretical models are well developed. However, in high magnetic fields, previously unknown aspects of dielectric relaxation can be revealed and exploited. Here, we report low temperature dielectric relaxation measurements in lightly doped silicon in high dc magnetic fields B both parallel and perpendicular to the applied ac electric field E. For B//E, we observe a temperature and magnetic field dependent dielectric dispersion e(w)characteristic of conventional Debye relaxation where the free carrier concentration is dependent on thermal dopant ionization, magnetic freeze-out, and/or magnetic localization effects. However, for BperpE, anomalous dispersion emerges in e(w) with increasing magnetic field. It is shown that the Debye formalism can be simply extended by adding the Lorentz force to describe the general response of a dielectric in crossed magnetic and electric fields. Moreover, we predict and observe a new transverse dielectric response EH perp B perp E not previously described in magneto-dielectric measurements. The new formalism allows the determination of the mobility and the ability to discriminate between magnetic localization/freeze out and Lorentz force effects in the magneto-dielectric response.Comment: 19 pages, 6 figure

Warm and Cold Denaturation in the Phase Diagram of a Protein Lattice Model

Studying the properties of the solvent around proteins, we propose a much more sophisticated model of solvation than temperature-independent pairwise interactions between monomers, as is used commonly in lattice representations. We applied our model of solvation to a 16-monomer chain constrained on a two-dimensional lattice. We compute a phase diagram function of the temperature and a solvent parameter which is related to the pH of the solution. It exhibits a native state in which the chain coalesces into a unique compact conformation as well as a denatured state. Under certain solvation conditions, both warm and cold denaturations occur between the native and the denatured states. A good agreement is found with the data obtained from calorimetric experiments, thereby validating the proposed model.Comment: 7 pages, 2 figure

Dependencia de la densidad en los ánades norteamericanos

The existence or otherwise of density dependence within a population can have important implications for the management of that population. Here, we use estimates of abundance obtained from annual aerial counts on the major breeding grounds of a variety of North American duck species and use a state space model to separate the observation and ecological system processes. This state space approach allows us to impose a density dependence structure upon the true underlying population rather than on the estimates and we emonstrate the improved robustness of this procedure for detecting density dependence in the population. We adopt a Bayesian approach to model fitting, using Markov chain Monte Carlo (MCMC) methods and use a reversible jump MCMC scheme to calculate posterior model probabilities which assign probabilities to the presence of density dependence within the population, for example. We show how these probabilities can be used either to discriminate between models or to provide model–averaged predictions which fully account for both parameter and model uncertainty.La existencia o ausencia de efectos dependientes de la densidad en una población puede acarrear importantes repercusiones para la gestión de la misma. En este artículo empleamos estimaciones de abundancia obtenidas a partir de recuentos aéreos anuales de las principales áreas de reproducción de diversas especies de ánades norteamericanos, utilizando un modelo de estados espaciales para separar los procesos de observación y los procesos del sistema ecológico. Este enfoque basado en estados espaciales nos permite imponer una estructura que depende de la densidad de la población subyacente real, más que de las estimaciones, además de demostrar la robustez mejorada de este procedimiento para detectar la dependencia de la densidad en la población. Para el ajuste de modelos adoptamos un planteamiento bayesiano, utilizando los métodos de Monte Carlo basados en cadenas de Markov (MCMC), así como un programa MCMC de salto reversible para calcular, por ejemplo, las probabilidades posteriores de los modelos que asignan probabilidades a la presencia de una dependencia de la densidad en la población. También demostramos cómo pueden emplearse estas probabilidades para discriminar entre modelos o para proporcionar predicciones promediadas entre modelos que tengan totalmente en cuenta tanto la incertidumbre referente a parámetros como a modelos

Medium Modifications of Hadron Properties and Partonic Processes

Chiral symmetry is one of the most fundamental symmetries in QCD. It is closely connected to hadron properties in the nuclear medium via the reduction of the quark condensate , manifesting the partial restoration of chiral symmetry. To better understand this important issue, a number of Jefferson Lab experiments over the past decade have focused on understanding properties of mesons and nucleons in the nuclear medium, often benefiting from the high polarization and luminosity of the CEBAF accelerator. In particular, a novel, accurate, polarization transfer measurement technique revealed for the first time a strong indication that the bound proton electromagnetic form factors in 4He may be modified compared to those in the vacuum. Second, the photoproduction of vector mesons on various nuclei has been measured via their decay to e+e- to study possible in-medium effects on the properties of the rho meson. In this experiment, no significant mass shift and some broadening consistent with expected collisional broadening for the rho meson has been observed, providing tight constraints on model calculations. Finally, processes involving in-medium parton propagation have been studied. The medium modifications of the quark fragmentation functions have been extracted with much higher statistical accuracy than previously possible.Comment: to appear in J. Phys.: Conf. Proc. "New Insights into the Structure of Matter: The First Decade of Science at Jefferson Lab", eds. D. Higinbotham, W. Melnitchouk, A. Thomas; added reference

Density dependence in North American ducks

The existence or otherwise of density dependence within a population can have important implications for the management of that population. Here, we use estimates of abundance obtained from annual aerial counts on the major breeding grounds of a variety of North American duck species and use a state space model to separate the observation and ecological system processes. This state space approach allows us to impose a density dependence structure upon the true underlying population rather than on the estimates and we demonstrate the improved robustness of this procedure for detecting density dependence in the population. We adopt a Bayesian approach to model fitting, using Markov chain Monte Carlo (MCMC) methods and use a reversible jump MCMC scheme to calculate posterior model probabilities which assign probabilities to the presence of density dependence within the population, for example. We show how these probabilities can be used either to discriminate between models or to provide model-averaged predictions which fully account for both parameter and model uncertainty