QoSatAr: a cross-layer architecture for E2E QoS provisioning over DVB-S2 broadband satellite systems

This article presents QoSatAr, a cross-layer architecture developed to provide end-to-end quality of service (QoS) guarantees for Internet protocol (IP) traffic over the Digital Video Broadcasting-Second generation (DVB-S2) satellite systems. The architecture design is based on a cross-layer optimization between the physical layer and the network layer to provide QoS provisioning based on the bandwidth availability present in the DVB-S2 satellite channel. Our design is developed at the satellite-independent layers, being in compliance with the ETSI-BSM-QoS standards. The architecture is set up inside the gateway, it includes a Re-Queuing Mechanism (RQM) to enhance the goodput of the EF and AF traffic classes and an adaptive IP scheduler to guarantee the high-priority traffic classes taking into account the channel conditions affected by rain events. One of the most important aspect of the architecture design is that QoSatAr is able to guarantee the QoS requirements for specific traffic flows considering a single parameter: the bandwidth availability which is set at the physical layer (considering adaptive code and modulation adaptation) and sent to the network layer by means of a cross-layer optimization. The architecture has been evaluated using the NS-2 simulator. In this article, we present evaluation metrics, extensive simulations results and conclusions about the performance of the proposed QoSatAr when it is evaluated over a DVB-S2 satellite scenario. The key results show that the implementation of this architecture enables to keep control of the satellite system load while guaranteeing the QoS levels for the high-priority traffic classes even when bandwidth variations due to rain events are experienced. Moreover, using the RQM mechanism the user’s quality of experience is improved while keeping lower delay and jitter values for the high-priority traffic classes. In particular, the AF goodput is enhanced around 33% over the drop tail scheme (on average)

Estudio de un efecto alcalinotérreo mixto sobre algunas propiedades de vidrios del sistema CaO-MgO-Al2O3-SiO2

[EN] In the present work, we studied a “Mixed Alkaline–Earth Effect”, i.e. the non-linear behaviour showed by the glass transition temperature as well as by the compressive strength of glasses of the CaO-MgO-Al2O3-SiO2 system, when a part of the CaO contained in them was substituted by a BaO/SrO mixture, in variable molar proportions. An important factor for the occurrence of this phenomenon was the difference in atomic weight, ionic radii and field strength of the Ba2+ and Sr2+ ions in comparison with those corresponding to the Ca2+ ion. Another factor considered was the likely occurrence of a microphase separation caused by the addition of BaO and/or SrO, together with the presence of F- and Mg2+ in the glasses. Other glass properties studied as a function of the CaO substitution level were density, glass molar volume, oxygen molar volume, packing fraction, and chemical resistance in neutral, basic and acidic aqueous media. In general, the structural reinforcement of the glass network caused by the partial substitution of CaO by a BaO/SrO mixture was accompanied by an improvement in the alkaline resistance of the materials, which were found to be suitable for applications in corrosive environments, especially in basic media.[ES] En el presente trabajo, se estudia el comportamiento no lineal mostrado por la temperatura de transición vítrea y por la resistencia a la compresión de vidrios del sistema CaO-MgO-Al2O3-SiO2, cuando una parte del CaO contenido en los mismos es sustituido por una mezcla de BaO/SrO, en relación molar variable. Factores importantes para que se de este comportamiento son la diferencia entre pesos atómicos, radios iónicos e intensidad de campo de los iones Ba2+ y Sr2+ y los del propio ión Ca2+. Otro factor considerado ha sido la probable existencia de una separación de microfases originada por la adición de BaO y/o SrO, junto con la presencia de flúor y magnesio en los vidrios. Otras propiedades estudiadas, en función del CaO sustituido, han sido la densidad, el volumen molar del vidrio, el volumen molar del oxígeno, la fracción de empaquetamiento, y la resistencia química en medios acuosos neutros, básicos y ácidos. En general, el refuerzo estructural del retículo vítreo causado por la sustitución parcial del CaO por una mezcla de BaO/SrO viene acompañada por una mejora en la resistencia alcalina, lo que hace que estos materiales sean adecuados para aplicaciones en ambientes corrosivos y especialmente en medios básicos.The authors acknowledge the financial support of the Mexican National Council of Science and Technology (CONACYT), through project number 31356-U, as well as through a scholarship granted to M.G.G. to carry out her Ph.D. studies at Cinvestav-Saltillo.Peer reviewe

Sinterización reactiva de mezclas de dolomita mexicana – circón

[EN] The present work has been conducted aiming to develop additional phase [Ca3SiO5, Ca2SiO4 and/or Ca3Mg(SiO4)2]-bonded magnesia refractory materials via reaction sintering of dolomite-zircon mixtures, employing a Mexican dolomite containing an excess of 3 wt% of CaCO3. The study was based on phase equilibrium data extracted from the quaternary system CaO – MgO – SiO2 – ZrO2, to put it more precisely, base on the projection from the MgO-apex of the liquidus surface of the primary crystallization volume of MgO onto the opposite face of the above mentioned quaternary system. The refractory materials designed within this system were obtained by attrition milling, followed by cold isostatic pressing and high temperature reaction sintering. All initial and produced materials were characterized by ICP-AES, XRF, XRD, SEM-EDX, DTA and TG analyses. The results obtained indicated that reaction sintering of dolomite-zircon mixtures is an interesting route to produce MgO-CaZrO3-additional phase refractory materials.[ES] El propósito de este trabajo ha sido obtener materiales refractarios de magnesia, aglomerados con una fase adicional [Ca3SiO5, Ca2SiO4 y/o Ca3Mg(SiO4)2], mediante la sinterización reactiva de mezclas de dolomita-circón, empleando para ello una dolomita mexicana que contiene un exceso de 3% en peso de CaCO3. El estudio se basa en la información relativa al equilibrio de fases del sistema CaO – MgO – SiO2 – ZrO2. En concreto se usa la proyección, desde el vértice del MgO, de la superficie de liquidus del volumen de cristalización primaria de este, hacia la cara opuesta de sistema cuaternario. Los materiales refractarios diseñados se han obtenido por molienda de atrición, seguida de un prensado isostático en frío y sinterización reactiva a alta temperatura. Todos los materiales, iniciales y finales, han sido caracterizados mediante ICPAES, FRX, DRX, MEB-EDX, ATD y TG. Los resultados obtenidos indican que la sinterización reactiva de las mezclas de dolomita-circón es una ruta interesante para la producción de materiales refractarios de MgO-CaZrO3-fase adicional.The authors acknowledge the financial support of CINVESTAV and CONACYT (project number 39557-Y), both from México. Berenice Fernández-Arguijo thanks Eng. Felipe de Jesús Márquez-Torres of CINVESTAV-Saltillo for his assistance in the preparation of samples for SEM observations, as well as Eng. Carlos Palacios of Química del Rey, MET – MEX Peñoles, who supplied the dolomite used in this work.Peer reviewe

Synthesis of Ba_0.75Sr_0.25Al₂Si₂O₈ - ZrO₂ Ceramic Composites by Solid State Reaction of Mechanically Activated Precursor Mixtures

Precursor mixtures composed of fly ash, BaCO3, SrCO3, Al2O3 and ZrO2, were subjected to attrition milling for 0-8 h and then uniaxially pressed and sintered at 900-1500 °C/5 h, for the in situ solid state synthesis of composites with nominal Ba0.75Sr0.25Al2Si2O8 (SBAS)/ZrO2 mass ratios of: 1) 90/10, 2) 70/30, and 3) 50/50. Mechanical activation, combined with the likely generation of a considerable amount of transient liquid during sintering of the composites, notably enhanced the reactivity of the precursor mixtures. ZrO2 decreased the conversion from the hexagonal (Hexacelsian) into the monoclinic (Celsian) phases of SBAS in the composites, which became more pronounced when the content of ZrO2 was increased in the materials. Nearly full conversions could be achieved at temperatures as low as 1100 °C, by mechanically activating the precursor mixtures for times that increased with increasing content of ZrO2 in the materials. An increment in the time of mechanical activation of the precursor mixtures, as well as in their ZrO2 content and in the sintering temperature, increased the mechanical properties of the synthesized materials. Thus, the best mechanical properties were obtained for composition 3 milled for 8 h and sintered at 1500 °C.Mezclas precursoras de cenizas volantes, BaCO3, SrCO3, Al2O3 y ZrO2, fueron activadas mecánicamente en un molino de atrición por 0-8 h y luego prensadas uniaxialmente y sinterizadas a 900-1500 °C/5 h, para la síntesis in situ por reacción en el estado sólido de compósitos con relaciones nominales Ba0.75Sr0.25Al2Si2O8 (SBAS)/ZrO2 en masa de: 1) 90/10, 2) 70/30, y 3) 50/50. La activación mecánica, combinada con la probable generación de una cantidad considerable de líquido transitorio, incrementó notablemente la reactividad de las mezclas precursoras. La ZrO2 disminuyó la conversión de la fase hexagonal (Hexacelsiana) a la monoclínica (Celsiana) del SBAS, lo cual fue más pronunciado cuando el contenido de ZrO2 se incrementó en los compósitos. Fue posible obtener conversiones casi completas a temperaturas tan bajas como 1100 °C, activando mecánicamente las mezclas precursoras por tiempos que se incrementaron con el incremento en el contenido de ZrO2 en los materiales. El incremento en el tiempo de activación mecánica de las mezclas precursoras, así como en su contenido de ZrO2 y en la temperatura de sinterización, incrementó las propiedades mecánicas de los materiales sintetizados. Así, las mejores propiedades mecánicas correspondieron a la composición 3 molida por 8 h y sinterizada a 1500 °C

Sinterización por plasma de particulas ultrafinas de cromita de lantano dopado con clacio obtenidas por síntesis hidrotermal

[EN] Lanthanum chromite nano-particles, with a composition of La0.9Ca0.1CrO3 and La0.8Ca0.2CrO3, were produced by 1 h of hydrothermal reaction at 400 and 425°C respectively. The sintering of the powders was conducted using a spark plasma apparatus over the temperature range 1300-1550ºC for 1 min with a constant loading pressure of 45 MPa. Additional sintering experiments using conventional firing were carried out for comparison. Fully densified (98 % r.d.) lanthanum chromite pellets with fine equiaxial grains 2.3 μm in size were obtained using the SPS (spark plasma sintering) method. In contrast, a maximum relative density of 97 % was produced using La0.8Ca0.2CrO3 sintered conventionally at 1400ºC for 300 min, and the average grain size of the resulting sintered sample was 6 μm.[ES] Partículas ultrafinas de cromita de lantano, con una composición de La0.9Ca0.1CrO3 y La0.8Ca0.2CrO3, se obtuvieron después de 1 hora de síntesis hidrotermal a las temperaturas de 400 y 425°C respectivamente. Los compuestos obtenidos, con un tamaño de partícula de ~ 200 nm, se caracterizaron utilizando las técnicas de DRX, MEB y MET. La sinterización de estos polvos se efectuó en un equipo de chispa de plasma en el rango de temperatura de 1300-1500°C durante 1 min, y a una presión de compactación de 45 MPa. Ambos polvos también se sinterizaron siguiendo un tratamiento térmico convencional, en aire, con el propósito de comparar ambos métodos de sinterización. Las muestras de cromita de lantano sinterizadas por plasma presentaban una densidad relativa del 98 % (ρ/ρt); y una microestructura monofásica con granos equaxiales con un tamaño medio de grano menor de 2.3 μm. En contraste, la composición La0.8Ca0.2CrO3, sinterizada a 1400°C/300 min, por métodos convencionales alcanzó una densidad relativa máxima del 97 % y su microestructura estaba formada por una sola fase con un tamaño medio de grano de 6 μm.The authors acknowledge the support of CONACyT through the research grant (Project 34830-U) and CINVESTAV (Mexico). L.P.R.V. is indebted to the CONACyT for financial support in the form of a PhD scholarship.Peer reviewe

The Mechanism of corrosion of MgO CaZrO3–calcium silicate materials by cement clinker

The chemical reactions involved in the corrosion of MgO CaZrO3–calcium silicate materials by cement clinker were studied using a hot-stage microscope up to 1600 ◦C. The phases formed at 1500 ◦C were characterized by RLOM and SEM–EDS of the crystalline phases conducted near the reaction front and on unreacted refractory area. The general corrosion mechanism of attack on MgO CaZrO3–calcium silicate materials involves a mechanism of matter diffusion of the liquid clinker phase through the grain boundaries and pores into the refractory substrate. The liquid phases in the clinker mainly enriched in calcium, iron and aluminium are rapidly diffused and preferentially react with magnesium spinel, calcium zirconate and magnesia, which are the major constituents in the refractory substrates. The dissolution of the CaZrO3 refractory phase produces the enrichment with zirconium of the liquid phase increasing its viscosity and hindering the liquid phase diffusion. © 2006 Elsevier Ltd. All rights reserved.Peer reviewe

Reaction Sintering of Mexican Dolomite – Zircon Mixtures

The present work has been conducted aiming to develop additional phase [Ca3SiO5, Ca2SiO4 and/or Ca3Mg(SiO4)2]-bonded magnesia refractory materials via reaction sintering of dolomite-zircon mixtures, employing a Mexican dolomite containing an excess of 3 wt% of CaCO3. The study was based on phase equilibrium data extracted from the quaternary system CaO – MgO – SiO2 – ZrO2, to put it more precisely, base on the projection from the MgO-apex of the liquidus surface of the primary crystallization volume of MgO onto the opposite face of the above mentioned quaternary system. The refractory materials designed within this system were obtained by attrition milling, followed by cold isostatic pressing and high temperature reaction sintering. All initial and produced materials were characterized by ICP-AES, XRF, XRD, SEM-EDX, DTA and TG analyses. The results obtained indicated that reaction sintering of dolomite-zircon mixtures is an interesting route to produce MgO-CaZrO3-additional phase refractory materials.<br><br>El propósito de este trabajo ha sido obtener materiales refractarios de magnesia, aglomerados con una fase adicional [Ca3SiO5, Ca2SiO4 y/o Ca3Mg(SiO4)2], mediante la sinterización reactiva de mezclas de dolomita-circón, empleando para ello una dolomita mexicana que contiene un exceso de 3% en peso de CaCO3. El estudio se basa en la información relativa al equilibrio de fases del sistema CaO – MgO – SiO2 – ZrO2. En concreto se usa la proyección, desde el vértice del MgO, de la superficie de liquidus del volumen de cristalización primaria de este, hacia la cara opuesta de sistema cuaternario. Los materiales refractarios diseñados se han obtenido por molienda de atrición, seguida de un prensado isostático en frío y sinterización reactiva a alta temperatura. Todos los materiales, iniciales y finales, han sido caracterizados mediante ICPAES, FRX, DRX, MEB-EDX, ATD y TG. Los resultados obtenidos indican que la sinterización reactiva de las mezclas de dolomita-circón es una ruta interesante para la producción de materiales refractarios de MgO-CaZrO3-fase adicional

Spark plasma sintering of hydrothermally derived ultrafine Ca doped lanthanum chromite powders

Lanthanum chromite nano-particles, with a composition of La0.9Ca0.1CrO3 and La0.8Ca0.2CrO3, were produced by 1 h of hydrothermal reaction at 400 and 425°C respectively. The sintering of the powders was conducted using a spark plasma apparatus over the temperature range 1300-1550ºC for 1 min with a constant loading pressure of 45 MPa. Additional sintering experiments using conventional firing were carried out for comparison. Fully densified (98 % r.d.) lanthanum chromite pellets with fine equiaxial grains 2.3 μm in size were obtained using the SPS (spark plasma sintering) method. In contrast, a maximum relative density of 97 % was produced using La0.8Ca0.2CrO3 sintered conventionally at 1400ºC for 300 min, and the average grain size of the resulting sintered sample was 6 μm.<br><br>Partículas ultrafinas de cromita de lantano, con una composición de La0.9Ca0.1CrO3 y La0.8Ca0.2CrO3, se obtuvieron después de 1 hora de síntesis hidrotermal a las temperaturas de 400 y 425°C respectivamente. Los compuestos obtenidos, con un tamaño de partícula de ~ 200 nm, se caracterizaron utilizando las técnicas de DRX, MEB y MET. La sinterización de estos polvos se efectuó en un equipo de chispa de plasma en el rango de temperatura de 1300-1500°C durante 1 min, y a una presión de compactación de 45 MPa. Ambos polvos también se sinterizaron siguiendo un tratamiento térmico convencional, en aire, con el propósito de comparar ambos métodos de sinterización. Las muestras de cromita de lantano sinterizadas por plasma presentaban una densidad relativa del 98 % (/t); y una microestructura monofásica con granos equaxiales con un tamaño medio de grano menor de 2.3 μm. En contraste, la composición La0.8Ca0.2CrO3, sinterizada a 1400°C/300 min, por métodos convencionales alcanzó una densidad relativa máxima del 97 % y su microestructura estaba formada por una sola fase con un tamaño medio de grano de 6 μm

Facile Synthesis of Perovskite-Structured Powders Using Barite–Celestite Ore under Hydrothermal Alkaline Conditions

Barite–celestite (BC) crystals were treated in highly concentrated alkaline hydrothermal fluid (5 M KOH) coexisting with a Ti(OH)₄·4.5H₂O gel to produce SrTiO₃ particles between 150 and 250 °C for several intervals between 6 h and 96 h. The BC transformation was initiated at a lower temperature (150 °C) and the total precursors consumption was completed at 250 °C for 96 h, resulting only in the crystallization of SrTiO₃ particles. Different temperatures of reaction (≤200 °C) lead to variations in morphology and particle size of the SrTiO₃ . The crystal growth of faceted cubic agglomerates was achieved at 250 °C, and it is provoked by the Oswald ripening mechanism. The release of barium to the hydrothermal fluid from the precursor occurred simultaneously with the transformation process. A low value of activation energy required for the single-step transformation of the BC plates into SrTiO₃ particles was observed (26.33 kJ mol‾¹), under static hydrothermal conditions