Carbide phases synthesised from C/Mo powder compacts at specified sub-stoichiometric ratios by solar radiation heating to temperatures between 1600 C and 2500 C

There are a number of distinguishable carbide phases in the binary Mo-C system depending on C/Mo ratio as well as on temperature. In a preceding work published in this journal, carbide formation performance for graphite/molybdenum powder mixtures at specified levels of substoichiometric C/Mo atom ratio (C/Mo = 1/1, 3/4, 2/3 and 1/2) by exposure to concentrated solar radiation in a solar furnace at PROMESCNRS in Odeillo (France) was reported at a target temperature 1900 C. In the present work, the similar carbide synthesis experiments were carried out at 1600 C as well as at temperature exceeding 2500 C. The target temperature setting was adjusted by controlling the downward deviation of the test piece top surface position from the exact focal spot of the parabolic mirror concentrator located above. In this solar furnace at PROMES-CNRS, temperature of the test piece was raised from ambient temperature to the target temperature within fractions of a second. Reaction products detected were hexagonal -MoC1 x and -Mo2C (high temperature sub-carbide phase) depending on the C/Mo ratio in the starting material as well as on the processing temperature. No evidence of formation of cubic -MoC1 x was detected by X-ray diffraction analysis for any test piece examined

Thermal resistance of solar volumetric absorbers made of mullite, brown alumina and ceria foams under concentrated solar radiation

ABSTRACT: Three semi-closed open cell ceramic foams, namely mullite, brown alumina and ceria-based materials, were subjected to thermal cycles by direct concentrated solar irradiation to study their thermal resistance in view of their potential application as photothermal devices, such as volumetric solar absorbers. After cycling, the extent of the damage in the samples was determined by measuring the retained crushing (compressive) strength. The extent of the damage was found to depend on the composition, the applied surface temperature difference (Delta T) of thermal cycling and the temperature gradient across the foams. It was found that the retained crushing strength gradually decreased with an increase in Delta T and was independent of the number of thermal cycles in the range investigated. The ceria foams displayed the poorest thermal shock resistance. Experimental data fit the Gibson-Ashby model for the thermal shock resistance of ceramic foams, for a constant C = 0.65.info:eu-repo/semantics/publishedVersio

Bringing underused learning objects to the light: a multi-agent based approach

The digital learning transformation brings the extension of the traditional libraries to online repositories. Learning object repositories are employed to deliver several functionalities related to the learning object’s lifecycle. However, these educational resources usually are not described effectively, lacking, for example, educational metadata and learning goals. Then, metadata incompleteness limits the quality of the services, such as search and recommendation, resulting in educational objects that do not have a proper role in teaching/learning environments. This work proposes to bring an active role to all educational resources, acting on the analysis generated from the usage statistics. To achieve this goal, we created a multi-agent architecture that complements the common repository’s functionalities to improve learning and teaching experiences. We intend to use this architecture on a repository focused on ocean literacy learning objects. This paper presents some steps toward this goal by enhancing, when needed, the repository to adapt itself.info:eu-repo/semantics/publishedVersio

Nitriding VI-group metals (Cr, Mo and W) in stream of NH3 gas under concentrated solar irradiation in a solar furnace at PSA (Plataforma Solar de Almería)

Carbides and nitrides of d-group transition metals are classified as refractory hard material and their industrial importance has been recognized for long. In recent years, unique functionalities including catalytic function and superconductivity are discovered for this group of materials to raise serious attention of materials researchers and engineers to refractory carbides and nitrides as novel functional materials. Synthesis of refractory carbides and nitrides demands high temperature reaction route to consume considerable amount of electricity or gas in conventional industrial process. In view of saving cost of such conventional energy, feasibility of using concentrated solar beam as heat source for synthesizing carbide and nitride has been investigated by the authors since 1997. After verifying usefulness of concentrated solar beam as heat source for carbide forming reactions, similar attempts of employing concentrated solar beam as heat source for nitride synthesis were initiated recently. After brief experimental verification of nitride synthesis for IVa group metal, Ti, and Vg group metals, V, Nb and Ta, in N2 gas environment under irradiation with concentrated solar beam to 2000 °C, the authors decided to undertake nitride synthesis of VIa group metals, Cr, Mo and W, as well as of Fe in stream of ammonia (NH3) gas as a nitriding medium under irradiation of concentrated solar beam at temperatures not exceeding 1000 °C. NH3 gas with suppressed extent of dissociation by flowing is defined empirically as uncracked NH3 and it is proved to possess very high nitriding power to make synthesis of mono-nitride MoN of Mo coexisting with sub-nitride Mo and higher nitride Fe2N of Fe possible under normal pressure condition that are not possible when chemically stable N2 gas is used as a nitriding agent. VIa-group metals including Cr, Mo and W are known to be highly resistant against nitriding. In the present report, results of nitriding in flowing NH3 gas at a fixed flow rate 10 l/h (˜167 ml/min) under heating with concentrated solar beam for VIa-group metals, Cr, Mo and W, are summarized to demonstrate favorable effect of solar beam heating towards further enhancement of nitriding power of flowing NH3 gas compared with the situation in conventional electric furnace in which visible light components except infra-red (IR) heat wave component are absent in the reaction system.

Mechanical properties of dense cordierite discs sintered by solar radiation heating

Consolidation of cordierite disc specimens was undertaken under concentrated solar beam in a solar furnace at PSA (Plataforma Solar de Almerıá). Satisfactory extent of densification was achieved by the present solar-sintering experiment. The mechanical properties measured for the solar-sintered cordierite test pieces were; density ¼ 2:45 0:02 g/cm3, Vickers microhardness HV ¼ 7:31 0:29 GPa, Young’s modulus E ¼ 97 5 GPa, shear modulus G ¼ 38 2 GPa, Poisson ratio ¼ 0:27 0:01, fracture toughness KIC ¼ 1:50 0:15 MPa m1=2 and modulus of rupture evaluated by ring-on-ring test MORROR ¼ 57:8 13:7 MPa which were comparable to those of the counterparts sintered by conventional industrial gas furnace

Influence of linear flow velocity of uncracked ammonia (NH3) gas on formation of higher nitrides, -MoN and -Fe2N, under concentrated solar irradiation in the SF40 solar furnace at PSA

ABSTRACT: Nitriding experiments for powder specimens of Mo and Fe were carried out using a solar furnace SF40 at PSA (Plataforma Solar de Almería) in Tabernas (Spain) in uncracked ammonia NH3 gas (NH3 gas with suppressed extent of dissociation by flowing) aiming at determining the range of linear velocity v of NH3 gas flow to yield higher nitride phases, δ-MoN for Mo and ε-Fe2N for Fe. Standard solar exposure duration at a specified reaction temperature T was set to be 60 min over range of v between 1.14 mm·s-1 and 11.4 mm·s-1. By X-ray diffraction (XRD) analysis, presence of δ-MoN was detected besides γ-Mo2N and metallic Mo for Mo powder specimen heated to 900 ºC in NH3 gas flow at v = 1.14 mm·s-1 but XRD peaks identifiable as δ-MoN became indiscernible when v was increased to 11.4 mm·s-1. On the other hand, for Fe powder specimen exposed to NH3 gas flow at v = 1.14 mm·s-1 at T = 500 ºC, remnant metallic α-Fe was detectable by XRD at the down-stream side of the specimen holder but no metallic α-Fe was detected at the up-stream side of the specimen holder suggesting that chemical activity a(N) of N atom in uncracked NH3 gas tended to decrease along the NH3 gas flow path on going from the up-stream side to the down-stream side.info:eu-repo/semantics/publishedVersio

Nano-meter size WC whiskers grown over a compacted pellet of praphite: tungsten powder mixture heated with an ultra-fast heating rate by a concentrated solar beam

In equilibrium binary W-C system, mono-carbide WC is acknowledged as the stable phase under presence of excess free carbon up to temperature 2700 C whereas sub-carbideW2C would form between 1250 C and 2700 C under the carbon-deficiency condition. In unique setup of solar furnace at PROMES-CNRS in Odeillo (France), temperature of specimen is raised from the ambient temperature to target temperature up to 2000 C within fractions of a second. In the recent experimental attempts of W2C phase synthesis using this unique experimental facility starting from compacted pellet consisted of graphite and tungsten powders at ratios smaller than 0.50, we detected growth of nano-meter size WC whisker at the top surface directly exposed to the concentrated solar beam. The presence of WC was confirmed also by X-ray diffraction (XRD) of the top surface but, when the specimen as a whole was subjected to powder XRD analysis, WC became indiscernible being masked by principal W2C phase. Mechanism of formation of the detected WC nano-whisker over sub-stoichiometric C/W pellet during ultra-fast heating by concentrated solar beam is discussed

Caracterización de ejercicios terapéuticos tradicionales en la atención físico-terapéutica en pacientes con enfermedad de Parkinson.(Original)

Neurodegenerative diseases are the main cause of physical-motor limitations, such as Parkinson's disease. In spite of the advances in the field of health this disease does not have a definitive cure, within the main treatments physical rehabilitation constitutes one of the fundamental pillars supported by the concept of neuroplasticity, however, there is a tendency to use conventional physical exercises to the detriment of the traditional ones, wasting their potentialities. In accordance with the above, the authors questioned the current situation of traditional therapeutic exercises (TTE) in the physical-therapeutic attention to motor manifestations in patients with Parkinson's disease (PD) and proposed as an objective to diagnose the current situation of traditional therapeutic exercises in the physical-therapeutic care to motor manifestations in patients with Parkinson's disease. The research is descriptive and cross-sectional. A population-based study was carried out among 45 physical culture teachers working in the public health areas of Holguin municipality, determining the poor application of TTE and its interrelation with the requirements for the application of therapeutic physical culture with a tendency to use conventional physical exercises and agents, scarce knowledge about the manifestations of PD on the part of physical culture professionals. In addition to the lack of guidelines and methodological indications for the implementation of TTE in the programs and protocols for the treatment of patients with Parkinson's disease.Las enfermedades neurodegenerativas son la principal causa de limitaciones físico-motoras, tal como la enfermedad de Parkinson. A pesar de los adelantos en el campo de la salud esta enfermedad no posee una cura definitiva, dentro de los principales tratamientos la rehabilitación física constituye uno de los pilares fundamentales respaldado por el concepto de neuroplasticidad, sin embargo, existe una tendencia al empleo de ejercicios físicos convencionales en detrimento de los tradicionales desaprovechando sus potencialidades. En concordancia con lo anterior, los autores se cuestionaron cual es la situación actual de los ejercicios terapéuticos tradicionales (ETT) en la atención físico-terapéutica a las manifestaciones motoras en pacientes con enfermedad de Parkinson (EP) y se propusieron como objetivo diagnosticar la situación actual de los ejercicios terapéuticos tradicionales en la atención físico-terapéutica a las manifestaciones motoras en pacientes con enfermedad de Parkinson. La investigación posee un carácter descriptivo y transversal. Se realizó un estudio poblacional a los 45 profesores de Cultura física que laboran en las áreas de salud pública del municipio Holguín, determinando la pobre aplicación de los ETT y su interrelación con los requisitos para la aplicación de la cultura física terapéutica con una tendencia al empleo de ejercicios y agentes físico convencionales, escasos conocimientos sobre las manifestaciones de la EP por parte de los profesionales de Cultura física. Además de la carencia de orientaciones e indicaciones metodológicas para la implementación de ETT en los programas y protocolos para el tratamiento de pacientes con enfermedad de Parkinson

Heterogeneity along the Height in Disc Specimens of Graphite/Tungsten Powder Mixtures with Sub-Stoichiometric Carbon Atom Ratios Heated by Concentrated Solar Beam to 1600 C

Compositional heterogeneity along the thickness of compacted disc specimens of graphite/tungsten powder mixtures with substoichiometric carbon atom ratios (0.35, 0.50 and 1.00) heated by concentrated solar beam to 1600 C was characterised by X-ray diffraction. Top surface of any examined test piece was consisted purely of mono-carbide WC while the bottom surface showed different constitution depending on the net initial C/W ratio of the test piece; almost pure metallicWfor the C/W ¼ 0:35 specimen, dominant metallicWassociated with small proportion ofW2C for the C/W ¼ 0:50 and dominantW2C with trivial proportion of WC for the C/W ¼ 1:0. In the intermediate zone between the top and the bottom layers, the constitution held virtually constant depending on the nominal C/W ratio of the starting material: co-existing metallicWandW2C for the C/W ¼ 0:35, pureW2C for the C/W ¼ 0:50 and predominant WC with traceW2C for the C/W ¼ 1:00. Unlike for the top surface of the C/W ¼ 0:35 test piece heated in a solar furnace to 1900 C reported earlier, no evidence of formation of nano-meter scale WC whisker was detected for the top surface in any sample heated to 1600 C in the present work

Portland cement clinker production using concentrated solar energy : a proof-of-concept approach

ABSTRACT: The aim of this work was to demonstrate the feasibility of producing Portland cement clinker upon direct exposure of the raw materials under concentrated solar radiation using the PSA high concentration solar furnace SF40. For this purpose, a short thermal cycle ( < 40 min) was devised including 5 min dwell times at temperatures in the range 900-950 degrees C and 1250-1300 degrees C, followed by 10-15 min at 1500-1550 degrees C. The chemical and mineralogical data of the grey clinker produced are encouraging since values of 51.0 +/- 6.9% C3S, 22.7 +/- 5.3% C2S, 8.6 +/- 0.4% C(3)A and 10.8 +/- 0.7% C(4)AF are similar to those observed for conventional clinker used for the production of Portland cement in accordance to EN 197-1 standard. White clinker, in turn, could not be produced by direct irradiation in this setup conditions because of its low absorptance of solar energy.info:eu-repo/semantics/publishedVersio