Theory and simulation of short-range models of globular protein solutions

We report theoretical and simulation studies of phase coexistence in model globular protein solutions, based on short-range, central, pair potential representations of the interaction among macro-particles. After reviewing our previous investigations of hard-core Yukawa and generalised Lennard-Jones potentials, we report more recent results obtained within a DLVO-like description of lysozyme solutions in water and added salt. We show that a one-parameter fit of this model based on Static Light Scattering and Self-Interaction Chromatography data in the dilute protein regime, yields demixing and crystallization curves in good agreement with experimental protein-rich/protein-poor and solubility envelopes. The dependence of cloud and solubility points temperature of the model on the ionic strength is also investigated. Our findings highlight the minimal assumptions on the properties of the microscopic interaction sufficient for a satisfactory reproduction of the phase diagram topology of globular protein solutions.Comment: 17 pages, 8 figures, Proc. of Conference "Structural Arrest Transitions in Colloidal Systems with Short-Range Attractions", Messina (ITALY) 17-20 December 200

Attraction between DNA molecules mediated by multivalent ions

The effective force between two parallel DNA molecules is calculated as a function of their mutual separation for different valencies of counter- and salt ions and different salt concentrations. Computer simulations of the primitive model are used and the shape of the DNA molecules is accurately modelled using different geometrical shapes. We find that multivalent ions induce a significant attraction between the DNA molecules whose strength can be tuned by the averaged valency of the ions. The physical origin of the attraction is traced back either to electrostatics or to entropic contributions. For multivalent counter- and monovalent salt ions, we find a salt-induced stabilization effect: the force is first attractive but gets repulsive for increasing salt concentration. Furthermore, we show that the multivalent-ion-induced attraction does not necessarily correlate with DNA overcharging.Comment: 51 pages and 13 figure

Thermal and Cold Neutron Computed Tomography at the Los Alamos Neutron Scattering Center Using an Amorphous Silicon Detector Array

The use of the EG&G-Heimann RTM 128 [1] or dpiX FS20 [2] amorphous silicon (a-Si) detector array for thermal neutron radiography/computed tomography has proven to be a quick and efficient means of producing high quality digital radiographic images. The resolution, although not as good as film, is about 750 μm with the RTM and 127 μm with the dpiX array with a dynamic range in excess of 2800. In many respects using an amorphous silicon detector is an improvement over other techniques such as imaging with a CCD camera, using a storage phosphor plate or film radiography. Unlike a CCD camera, which is highly susceptible to radiation damage, a-Si detectors can be placed in the beam directly behind the object under examination and do not require any special optics or turning mirrors. The amorphous silicon detector also allows enough data to be acquired to construct a digital image in just a few seconds (minimum gate time 40 ms) whereas film or storage plate exposures can take many minutes and need to be digitized with a scanner. The flat panel can, therefore, acquire a complete 3D computed tomography data set in just a few tens of minutes. While a-Si detectors have been proposed for use in imaging neutron beams [3], this is the first reported implementation of such a detector for neutron imaging [4]

DIAGNÓSTICO DE LAS ACTIVIDADES EXTRACTIVAS EN EL ÁREA PROTEGIDA DE LOS MANGLARES DE LA BAHÍA DE CHAME, PANAMÁ, AÑO 2010

This work considers the study of settlement evaluated by ANAM and OIMT in 1994 during the Project Mangrove (ANAM, 2009; CONFOREC, 2007), as part of the Investigation of Management, Conservation and Development of the Mangrove (Diagnostic Social and Economical of Benefits from Mangrove in Chame). With this background, the data is compiled from National Census to determinate socioeconomic basis of the selected communities. Additionally, 43 surveys were conducted and over 30 interviews with users of the mangrove (woodcutters, colliers, fishermen and crabbers) of the communities of: Sajalices, El Espavé, y La Cresta, ANAM’s staff, CEDESAN’s members and mangrove product’s dealers. There are multiple benefits of mangroves ((Lugo and Snedaker, 1974), that this   work aims to know the extractive human activities of the Chame Mangrove, for this it is carried out through a survey in 2011 in three (3) villages of the district of Chame. Where it was found that the communities make extractive activities of the Chame Mangrove as a complement to their income and do not depend directly as an economic means.Este trabajo considera el estudio de las comunidades estudiadas por Autoridad Nacional del Ambiente (ANAM) y la Organización Internacional de Maderas Tropicales (OIMT) en 1994 durante la ejecución del Proyecto Manglares (ANAM, 2009; CONFOREC, 2007), como parte del Proyecto de Investigación de Manejo, Conservación y Desarrollo de los Manglares (Diagnóstico Socioeconómico de los Beneficiarios del Manglar del Área de Chame). Con este antecedente se recaba información proveniente de los censos nacionales, para determinar la base socioeconómica de las comunidades elegidas. Adicionalmente, se realizaron 43 encuestas y más de 30 entrevistas a los usuarios del manglar (leñadoras, carboneros, pescadores, concheros y cangrejeros) de las comunidades de Sajalices, El Espavé, y La Cresta, funcionarios de ANAM y CEDESAN, S.A, e intermediarios de productos del manglar. Son múltiples los beneficios de los manglares (Lugo y Snedaker, 1974), que este trabajo tiene como objetivo conocer las actividades humanas extractivas del Manglar de Chame, para ello se realiza por medio de una encuesta en el año 2011 en tres (3) poblados del distrito de Chame. Donde se encontró que las comunidades hacen actividades extractivas del Manglar de Chame como complemento a sus ingresos y no dependen directamente como medio económico

Particle suspension reactors and materials for solar-driven water splitting

Reactors based on particle suspensions for the capture, conversion, storage, and use of solar energy as H_2 are projected to be cost-competitive with fossil fuels. In light of this, this review paper summarizes state-of-the-art particle light absorbers and cocatalysts as suspensions (photocatalysts) that demonstrate visible-light-driven water splitting on the laboratory scale. Also presented are reactor descriptions, theoretical considerations particular to particle suspension reactors, and efficiency and performance characterization metrics. Opportunities for targeted research, analysis, and development of reactor designs are highlighted

Time-gated energy-selected cold neutron radiography

A technique is under development at the Los Alamos Neutron Science Center (LANSCE), Manuel Lujan Jr. Neutron Scattering Center (Lujan Center) for producing neutron radiography using only a narrow energy range of cold neutrons. The technique, referred to as Time-Gated Energy-Selected (TGES) neutron radiography, employs the pulsed neutron source at the Lujan Center with time of flight to obtain a neutron pulse having an energy distribution that is a function of the arrival time at the imager. The radiograph is formed on a short persistence scintillator and a gated, intensified, cooled CCD camera is employed to record the images, which are produced at the specific neutron energy range determined by the camera gate. The technique has been used to achieve a degree of material discrimination in radiographic images. For some materials, such as beryllium and carbon, at energies above the Bragg cutoff the neutron scattering cross section is relatively high while at energies below the Bragg cutoff the scattering cross section drops significantly. This difference in scattering characteristics can be recorded in the TGES radiography and, because the Bragg cutoff occurs at different energy levels for various materials, the approach can be used to differentiate among these materials. This paper outlines the TGES radiography technique and shows an example of radiography using the approach

Site-Selective Passivation of Defects in NiO Solar Photocathodes by Targeted Atomic Deposition

For nanomaterials, surface chemistry can dictate fundamental material properties, including charge-carrier lifetimes, doping levels, and electrical mobilities. In devices, surface defects are usually the key limiting factor for performance, particularly in solar-energy applications. Here, we develop a strategy to uniformly and selectively passivate defect sites in semiconductor nanomaterials using a vapor-phase process termed targeted atomic deposition (TAD). Because defects often consist of atomic vacancies and dangling bonds with heightened reactivity, we observe-for the widely used p-type cathode nickel oxide-that a volatile precursor such as trimethylaluminum can undergo a kinetically limited selective reaction with these sites. The TAD process eliminates all measurable defects in NiO, leading to a nearly 3-fold improvement in the performance of dye-sensitized solar cells. Our results suggest that TAD could be implemented with a range of vapor-phase precursors and be developed into a general strategy to passivate defects in zero-, one-, and two-dimensional nanomaterials

Comparing multiple competing interventions in the absence of randomized trials using clinical risk-benefit analysis

<p>Abstract</p> <p>Background</p> <p>To demonstrate the use of risk-benefit analysis for comparing multiple competing interventions in the absence of randomized trials, we applied this approach to the evaluation of five anticoagulants to prevent thrombosis in patients undergoing orthopedic surgery.</p> <p>Methods</p> <p>Using a cost-effectiveness approach from a clinical perspective (i.e. risk benefit analysis) we compared thromboprophylaxis with warfarin, low molecular weight heparin, unfractionated heparin, fondaparinux or ximelagatran in patients undergoing major orthopedic surgery, with sub-analyses according to surgery type. Proportions and variances of events defining risk (major bleeding) and benefit (thrombosis averted) were obtained through a meta-analysis and used to define beta distributions. Monte Carlo simulations were conducted and used to calculate incremental risks, benefits, and risk-benefit ratios. Finally, net clinical benefit was calculated for all replications across a range of risk-benefit acceptability thresholds, with a reference range obtained by estimating the case fatality rate - ratio of thrombosis to bleeding.</p> <p>Results</p> <p>The analysis showed that compared to placebo ximelagatran was superior to other options but final results were influenced by type of surgery, since ximelagatran was superior in total knee replacement but not in total hip replacement.</p> <p>Conclusions</p> <p>Using simulation and economic techniques we demonstrate a method that allows comparing multiple competing interventions in the absence of randomized trials with multiple arms by determining the option with the best risk-benefit profile. It can be helpful in clinical decision making since it incorporates risk, benefit, and personal risk acceptance.</p

The primary cilium as a dual sensor of mechanochemical signals in chondrocytes

The primary cilium is an immotile, solitary, and microtubule-based structure that projects from cell surfaces into the extracellular environment. The primary cilium functions as a dual sensor, as mechanosensors and chemosensors. The primary cilia coordinate several essential cell signaling pathways that are mainly involved in cell division and differentiation. A primary cilium malfunction can result in several human diseases. Mechanical loading is sense by mechanosensitive cells in nearly all tissues and organs. With this sensation, the mechanical signal is further transduced into biochemical signals involving pathways such as Akt, PKA, FAK, ERK, and MAPK. In this review, we focus on the fundamental functional and structural features of primary cilia in chondrocytes and chondrogenic cells