1,276 research outputs found
A direct primitive variable recovery scheme for hyperbolic conservative equations: the case of relativistic hydrodynamics
In this article we develop a Primitive Variable Recovery Scheme (PVRS) to
solve any system of coupled differential conservative equations. This method
obtains directly the primitive variables applying the chain rule to the time
term of the conservative equations. With this, a traditional finite volume
method for the flux is applied in order avoid violation of both, the entropy
and "Rankine-Hugoniot" jump conditions. The time evolution is then computed
using a forward finite difference scheme. This numerical technique evades the
recovery of the primitive vector by solving an algebraic system of equations as
it is often used and so, it generalises standard techniques to solve these kind
of coupled systems. The article is presented bearing in mind special
relativistic hydrodynamic numerical schemes with an added pedagogical view in
the appendix section in order to easily comprehend the PVRS. We present the
convergence of the method for standard shock-tube problems of special
relativistic hydrodynamics and a graphical visualisation of the errors using
the fluctuations of the numerical values with respect to exact analytic
solutions. The PVRS circumvents the sometimes arduous computation that arises
from standard numerical methods techniques, which obtain the desired primitive
vector solution through an algebraic polynomial of the charges.Comment: 19 pages, 6 figures, 2 tables. Accepted for publication in PLOS ON
An efficient protocol to perform genetic traceability of tissue and foods from Geoffroea decorticans
The quality of a DNA isolation method depends, among others, on the target tissue and the metabolites therein. Geoffroea decorticans Burkart (chanar) is a species that has nutritional and pharmacological potential. However, an effective method of DNA extraction capable of facilitating population studies and food genetic traceability has not been studied yet. The objective of the present work was to evaluate four methods of DNA extraction from leaves and chanar-based foods. The methods were evaluated based on yield, DNA purity, and molecular markers. The CCI-P (CTAB/Chloroform-Isoamylalcohol/pellet) method showed the highest yield of DNA obtained from leaves. However, the CPCI-SC (CTAB/Phenol-Chloroform-Isoamylalcohol/silica-column) method was the only one that resulted in acceptable DNA quality with both parameters (A260/A280 and A260/A230). The leaf DNA obtained with this method showed a greater amount of fragments with RAPD, and an acceptable amount of fragments with ISSR. On the other hand, the CCI-P method showed a higher yield of DNA from arrope de chanar (syrup). However, the CPCI-SC method was the only one that had relatively better DNA quality, which allowed the amplification of molecular markers. Regarding chanar flour, the CPCI-SC method showed the highest yield, DNA quality and good amplification with molecular markers. Therefore, the CPCI-SC extraction method is efficient for obtaining DNA from different matrices, and can support studies for a possible designation of origin of chanar-based foods
Revisiting the optical -symmetric dimer
Optics has proved a fertile ground for the experimental simulation of quantum
mechanics. Most recently, optical realizations of -symmetric
quantum mechanics have been shown, both theoretically and experimentally,
opening the door to international efforts aiming at the design of practical
optical devices exploiting this symmetry. Here, we focus on the optical
-symmetric dimer, a two-waveguide coupler were the materials show
symmetric effective gain and loss, and provide a review of the linear and
nonlinear optical realizations from a symmetry based point of view. We go
beyond a simple review of the literature and show that the dimer is just the
smallest of a class of planar -waveguide couplers that are the optical
realization of Lorentz group in 2+1 dimensions. Furthermore, we provide a
formulation to describe light propagation through waveguide couplers described
by non-Hermitian mode coupling matrices based on a non-Hermitian generalization
of Ehrenfest theorem.Comment: 25 pages, 12 figure
Why NiAl is an itinerant ferromagnet but NiGa is not
NiAl and NiGa are closely related materials on opposite sides of a
ferromagnetic quantum critical point. The Stoner factor of Ni is virtually the
same in both compounds and the density of states is larger in NiGa. So,
according to the Stoner theory, it should be more magnetic, and, in LDA
calculations, it is. However, experimentally, it is a paramagnet, while
NiAl is an itinerant ferromagnet. We show that the critical spin
fluctuations are stronger than in NiGa, due to a weaker q-dependence of the
susceptibility, and this effect is strong enough to reverse the trend. The
approach combines LDA calculations with the Landau theory and the
fluctuation-dissipation theorem using the same momentum cut-off for both
materials. The calculations provide evidence for strong, beyond LDA, spin
fluctuations associated with the critical point in both materials, but stronger
in NiGa than in NiAl.Comment: replaced (incorrect version submitted
Probing the nanoadhesion of Streptococcus sanguinis to titanium implant surfaces by atomic force microscopy
The authors would kindly like to thank the BecasChile PhD Scholarship Programme for funding this research
Microstructure-guided numerical simulations to predict the thermal performance of a hierarchical cement-based composite material
This paper presents a microstructure-guided numerical homogenization technique to predict the effective thermal conductivity of a hierarchical cement-based material containing phase change material (PCM)-impregnated lightweight aggregates (LWA). Porous inclusions such as LWAs embedded in a cementitious matrix are filled with multiple fluid phases including PCM to obtain desirable thermal properties for building and infrastructure applications. Simulations are carried out on realistic three-dimensional microstructures generated using pore structure information. An inverse analysis procedure is used to extract the intrinsic thermal properties of those microstructural components for which data is not available. The homogenized heat flux is predicted for an imposed temperature gradient from which the effective composite thermal conductivity is computed. The simulated effective composite thermal conductivities are found to correlate very well with experimental measurements for a family of LWA-PCM composites considered in the paper. Comparisons with commonly used analytical homogenization models show that the microstructure-guided simulation approach provides superior results for composites exhibiting large property contrast between phases. By linking the microstructure and thermal properties of hierarchical materials, an efficient framework is available for optimizing the material design to improve thermal efficiency of a wide variety of heterogeneous materials
A Multi-scale Biophysical Approach to Develop Structure-Property Relationships in Oral Biofilms
Over the last 5-10 years, optical coherence tomography (OCT) and atomic force microscopy (AFM) have been individually applied to monitor the morphological and mechanical properties of various single-species biofilms respectively. This investigation looked to combine OCT and AFM as a multi-scale approach to understand the role sucrose concentration and age play in the morphological and mechanical properties of oral, microcosm biofilms, in-vitro. Biofilms with low (0.1% w/v) and high (5% w/v) sucrose concentrations were grown on hydroxyapatite (HAP) discs from pooled human saliva and incubated for 3 and 5 days. Distinct mesoscale features of biofilms such as regions of low and high extracellular polymeric substances (EPS) were identified through observations made by OCT. Mechanical analysis revealed increasing sucrose concentration decreased Young's modulus and increased cantilever adhesion (p < 0.0001), relative to the biofilm. Increasing age was found to decrease adhesion only (p < 0.0001). This was due to mechanical interactions between the indenter and the biofilm increasing as a function of increased EPS content, due to increasing sucrose. An expected decrease in EPS cantilever contact decreased adhesion due to bacteria proliferation with biofilm age. The application OCT and AFM revealed new structure-property relationships in oral biofilms, unattainable if the techniques were used independently
A simple and robust method for pre-wetting poly (lactic-co-glycolic) acid microspheres
Poly (lactic-co-glycolic) acid microspheres are amenable to a number of biomedical procedures that support delivery of cells, drugs, peptides or genes. Hydrophilisation or wetting of poly (lactic-co-glycolic) acid are an important pre-requisites for attachment of cells and can be achieved via exposure to plasma oxygen or nitrogen, surface hydrolysis with NaOH or chloric acid, immersion in ethanol and water, or prolonged incubation in phosphate buffered saline or cell culture medium. The aim of this study is to develop a simple method for wetting poly (lactic-co-glycolic) acid microspheres for cell delivery applications. A one-step ethanol immersion process that involved addition of serum-supplemented medium and ethanol to PLGA microspheres over 30 min–24 h is described in the present study. This protocol presents a more efficient methodology than conventional two-step wetting procedures. Attachment of human skeletal myoblasts to poly (lactic-co-glycolic) acid microspheres was dependent on extent of wetting, changes in surface topography mediated by ethanol pre-wetting and serum protein adsorption. Ethanol, at 70% (v/v) and 100%, facilitated similar levels of wetting. Wetting with 35% (v/v) ethanol was only achieved after 24 h. Pre-wetting (over 3 h) with 70% (v/v) ethanol allowed significantly greater (p ≤ 0.01) serum protein adsorption to microspheres than wetting with 35% (v/v) ethanol. On serum protein-loaded microspheres, greater numbers of myoblasts attached to constructs wetted with 70% ethanol than those partially wetted with 35% (v/v) ethanol. Microspheres treated with 70% (v/v) ethanol presented a more rugose surface than those treated with 35% (v/v) ethanol, indicating that more efficient myoblast adhesion to the former may be at least partially attributed to differences in surface structure. We conclude that our novel protocol for pre-wetting poly (lactic-co-glycolic) acid microspheres that incorporates biochemical and structural features into this biomaterial can facilitate myoblast delivery for use in clinical settings.This project was supported by grants from the UK Medical Research Council (MR/L002752/1) and Sir Halley Stewart Trust. The research was undertaken at UCL/UCLH which receives funding from the Department of Health’s NIHR as a Comprehensive Biomedical Research Centre.Published versio
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