839 research outputs found
Grand canonical ensemble of a -dimensional Reissner-Nordstr\"om black hole in a cavity
The grand canonical ensemble of a -dimensional Reissner-Nordstr\"om black
hole space in a cavity is analyzed. The realization of this ensemble is made
through the Euclidean path integral approach by giving the Euclidean action for
the black hole with the correct topology, and boundary conditions corresponding
to a cavity, where the fixed quantities are the temperature and the electric
potential. One performs a zero loop approximation to find and analyze the
stationary points of the reduced action. This yields two solutions for the
electrically charged black hole, , which is the smaller and unstable,
and , which is the larger and stable. One also analyzes the most
probable configurations, which are either a stable charged black hole or hot
flat space, mimicked by a nongravitating charged shell. Making the
correspondence between the action and the grand potential, one can get the
black hole thermodynamic quantities, such as the entropy, the mean charge, the
mean energy, and the thermodynamic pressure, as well as the Smarr formula,
shown to be valid only for the unstable black hole. We find that thermodynamic
stability is related to the positivity of the heat capacity at constant
electric potential and area of the cavity. We also comment on the most
favorable thermodynamic phases and phase transitions. We then choose ,
which is singled out naturally from the other higher dimensions as it provides
an exact solution for the problem, and apply all the results previously found.
The case is mentioned. We compare thermodynamic radii with the photonic
orbit radius and the Buchdahl-Andr\'easson-Wright bound radius in
-dimensional Reissner-Nordstr\"om spacetimes and find they are unconnected,
showing that the connections displayed in the Schwarzschild case are not
generic, rather they are very restricted holding only in the pure gravitational
situation.Comment: 28 pages, 5 figure
Normal modes of Proca fields in AdS spacetime
A normal mode analysis for Proca fields in the anti-de Sitter (AdS) spacetime
is given. It is found that the equations for the Proca field can be decoupled
analytically. This is performed by changing the basis of the vector spherical
harmonics (VSH) decomposition. The normal modes and the normal mode frequencies
of the Proca equation in the AdS spacetime are then analytically determined. It
is also shown that the Maxwell field can be recovered by taking the massless
limit of the Proca field with care so that the nonphysical gauge modes are
eliminated.Comment: 6 page
Chitosan microparticles loaded with essential oils having in view leather applications
Chitosan is a biopolymer attracting considerable attention for diverse applications due to its unique properties like biodegradability, biocompability, non-toxicity and antimicrobial activity. It is obtained by the partial N-deacetylation of chitin, which is the second most abundant polysaccharide in nature, next to cellulose. Chitosan is a viable base material for functional coatings development, namely due to its antimicrobial activity. This characteristic is especially useful for footwear applications that constitute products prone to microbial attack. In this context, developing antimicrobial coatings to be used in footwear components in direct contact with the feet are of great interest, both at industrial level (reducing possibility of material deterioration and quality loss), as well as, from the consumer’s point of view (decrease of skin infections and minor unpleasant odours). Following our previous work, where leather impregnation with chitosan was studied at laboratorial level with quite promising results, and having in view the final application (footwear leather components), where the antimicrobial effect must need to be enhanced, we have developed the idea of microencapsulate different essential oils, with recognized antimicrobial activity like lemon, oregano, eucalyptus and pine. These chitosan-based microparticles, loaded with the chosen essential oil are intended to be applied conjunctly with the chitosan coating process previously studied. Microencapsulation will ensure that the loaded core material will be progressively released, reinforcing the antimicrobial durability and effectiveness of the final product.COMPETE, QREN and EU within the project QREN-ADI-1585-ADVANCEDSHO
Chitosan-based leather functional coatings with improved antimicrobial properties
Among the interesting biological activities that have been
ascribed to chitosan, the antimicrobial activity is probably the one
that generates the higher number of applications. Developing
antimicrobial coatings for footwear components to be used in
direct contact with the feet is of great interest; both at industrial
level (reducing the possibility of material deterioration and quality
loss) and from the consumer’s point of view (decreasing skin
infections and minimizing unpleasant odours). One weakness of
this application is addressed to the durability and efficiency of the
product antimicrobial activity, since it is directly associated with
the availability of the positively charged R–NH3
+ groups that are
depleted during use
EBSD Analysis of Metal Matrix Nanocomposite Microstructure Produced by Powder Metallurgy
The development of metal nanocomposites reinforced by carbon nanotubes (CNTs) remains a focus of the scientific community due to the growing need to produce lightweight advanced materials with unique mechanical properties. However, for the successful production of these nanocomposites, there is a need to consolidate knowledge about how reinforcement influences the matrix microstructure and which are the strengthening mechanisms promoting the best properties. In this context, this investigation focuses on the study of the reinforcement effect on the microstructure of an Ni-CNT nanocomposites produced by powder metallurgy. The microstructural evolution was analysed by electron backscattered diffraction (EBSD). The EBSD results revealed that the dispersion/mixing and pressing processes induce plastic deformation in the as-received powders. The dislocation structures produced in those initial steps are partially eliminated in the sintering process due to the activation of recovery and recrystallization mechanisms. However, the presence of CNTs in the matrix has a significant effect on the dislocation annihilation, thus reducing the recovery of the dislocation structures
Additive manufacturing of bioactive glass in a biodegradable matrix
Bioactive glass can induce a specific and fast response in the human body that supports tissue regeneration. It is possible to control the design of customized bioapplications with advanced technologies. Although currently used in research, only a few of these technologies have been approved by the FDA to be applied in Tissue Engineering. There is dedicated additive manufacturing equipment to manufacture biomaterials. Since they are emerging technologies in emerging fields of application it is necessary to study and develop formulations with suitable processing characteristics [1].
Formulations of bioactive glass (CaO·P2O5·MgO·SiO2 system) in two different biodegradable matrices (polylactide (PLA) and polycaprolactone (PCL)) were prepared and processed by material extrusion process, namely by Fused Filament Fabrication technique.. The polymer (PLA or PCL) involves bioactive particles in biocompatible media and allows to acquire extrudable skills. The formulations with different solid contents (20–50 wt.%) were prepared using a brabender mixer type and were characterized by different techniques (e.g., X-ray diffraction (XRD), differential scanning calorimetry (DSC), melt flow index (MFI)).
The inorganic particles influence the rheological and thermal properties of bioactive glass composites. The viscosity decreases with the increase of bioactive glass content in the polymer matrix. Mechanical standard samples and scaffolds were printed and characterized. Bioactive glass composites until 40 wt.% of solid content can be printed. The bioactive glass improves the mechanical resistance of composites compared to a neat polymer matrix. However, formulations with high bioactive glass solid content (50 wt.%) showed printing limitations by their brittleness and clogging tendency.publishe
Estudio histolĂłgico, inmuno-histoquĂmico y de cultivo celular de mamas humana y canina normal y cancerosa
Objetivo. Comparar las caracterĂsticas morfolĂłgicas de cĂ©lulas normales y cancerosas derivadas de glándulas mamarias de las especies humana y canina. Materiales y mĂ©todos. Fueron colectadas 10 muestras de parĂ©nquima mamario normal y 14 de parĂ©nquima tumoral de la especie canina, asĂ como seis muestras de parĂ©nquima mamario normal y tres de parĂ©nquima tumoral de la especie humana. Para el cultivo de cĂ©lulas fue utilizada la tĂ©cnica de cultivo de cĂ©lulas de mamĂferos y para la histoquĂmica la tĂ©cnica de la avidina- biotina- peroxidasa, con utilizaciĂłn del anticuerpo monoclonal 32-2B (anti-desmoglĂ©ina-1). Resultados. A los estudios histolĂłgicos y morfolĂłgicos las cĂ©lulas de la glándula mamaria normal humana demostraron semejanzas con las cĂ©lulas de la glándula mamaria normal canina. Se observĂł adhesiĂłn y proliferaciĂłn de cĂ©lulas normales en ambas especies por aproximadamente tres meses de cultivo. Las cĂ©lulas normales de las especies humana y canina mostraron baja actividad de proliferaciĂłn cuando se compararon con las cancerosas de las especies en estudio. Los grupos de cĂ©lulas epiteloides que se adhirieron al sustrato de los dos cultivos tuvieron dependencia de las cĂ©lulas estromales, porque en la medida que las cĂ©lulas fibroblastoides se retiraron, las cĂ©lulas epiteloides detuvieron su crecimiento. Conclusiones. Comparando los resultados obtenidos por medio de análisis inmuno-histoquĂmico de cĂ©lulas normales de mujeres y perras fue posible observar cambios en el patrĂłn de coloraciĂłn en cĂ©lulas cancerosas en ambas especies, demostrando que las estructuras relacionadas con la adhesiĂłn celular (desmosomas) pueden estar alteradas
Chitosan as an antimicrobial agent for footwear leather components
In the footwear industry, microorganisms’ growth can pose problems of material deterioration with associated unpleasant smell and generate possible infections in susceptible individuals. Generally, footwear presents high relative humidity conditions that enable the growth of bacteria and fungi. Additionally, leather itself and some tannery agents such as oils and greases, provide a substrate where microorganisms can grow. In the foot, microtraumas caused by ingrown nails, abrasions and lacerations can allow microbial invasion through epidermis, resulting in skin infection.
In this work, the applicability of chitosan functional coatings to leather was tested, with the purpose to develop new base materials to produce footwear components. The leather treated with chitosan was then studied for its antibacterial properties against 3 different bacteria.COMPETE, QREN and EU (project QREN-ADI-1585-ADVANCEDSHOE)
Spectrophotometric flow injection determination of total phosphorus in beer using on-line UV/thermal induced digestion
A flow injection system for the automatic determination
of total phosphorus in beer is described. The
developed manifold uses a two-stage photooxidation/thermal
digestion procedure together with oxidizing and hydrolyzing
reagents to convert all forms of phosphorus
compounds to orthophosphate. Polyphosphates are hydrolyzed
by acid and heat, and organo-phosphates are digested
by UV-catalyzed peroxodisulfate oxidation. The
orthophosphate formed is then spectrophotometrically determined
by the phosphomolybdenum blue reaction, using
stannous chloride as reducing agent. The results obtained
for a set of 19 beer samples (with concentrations from 120
to 735 mg P/L) were in good agreement with the reference
method, the maximum relative deviation found being
4.7%. Relative standard deviations for ten consecutive determinations
were lower than 1.5%, and a detection limit
of 1 mg P/L was achieved
Development of a prototype to access biodegradability of TPU shoe soles under controlled conditions
In the last years, the increasing problems posed by waste
management have stimulated the interest in developing more
sustainable and bio-based solutions for the footwear industry,
including the use of biodegradable materials. As part of the
NEWALK project, the objective of this work consisted in
optimizing and implementing a respirometry system prototype.
Besides evaluating different variables, two different approaches
for measuring the evolved CO2 were assayed. Compared to
manual titration, the use of conductivity offers the advantage of
an automatic continuous monitoring.info:eu-repo/semantics/publishedVersio
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