Ultrahigh-Temperature Ceramics

Ultrahigh temperature ceramics (UHTCs) are a class of materials that include the diborides of metals such as hafnium and zirconium. The materials are of interest to NASA for their potential utility as sharp leading edges for hypersonic vehicles. Such an application requires that the materials be capable of operating at temperatures, often in excess of 2,000 C. UHTCs are highly refractory and have high thermal conductivity, an advantage for this application. UHTCs are potentially applicable for other high-temperature processing applications, such as crucibles for molten-metal processing and high-temperature electrodes. UHTCs were first studied in the 1960 s by the U.S. Air Force. NASA s Ames Research Center concentrated on developing materials in the HfB2/SiC family for a leading-edge application. The work focused on developing a process to make uniform monolithic (2-phase) materials, and on the testing and design of these materials. Figure 1 shows arc-jet models made from UHTC materials fabricated at Ames. Figure 2 shows a cone being tested in the arc-jet. Other variations of these materials being investigated elsewhere include zirconium based materials and fiber-reinforced composites. Current UHTC work at Ames covers four broad topics: monoliths, coatings, composites, and processing. The goals include improving the fracture toughness, thermal conductivity and oxidation resistance of monolithic UHTCs and developing oxidation-resistant UHTC coatings for thermal-protection-system substrates through novel coating methods. As part of this effort, researchers are exploring compositions and processing changes that have yielded improvements in properties. Computational materials science and nanotechnology are being explored as approaches to reduce materials development time and improve and tailor properties

Economic poverty and inequality at regional level in malta: focus on the situation of children

This paper performs an economic poverty and inequality mapping of three children age categories in Malta; it consists in the first attempt based on income from the EU-SILC survey and Census data. From a policy-making point of view, the availability of such key economic indicators at locality level certainly provides a valuable tool in assessing the effectiveness of national strategies and in identifying areas that need to be targeted by new policies; in fact sample surveys alone cannot provide reliable information at such a fine level of detail, while national censuses are not designed to and cannot be extended to cover specific topics such as economic poverty and inequality. Thus, the merging of the two sources provides policy-makers with a new insight into the differences between localities. There are also benefits of a technical nature, particularly in terms of sampling strategies, that can be derived from this study. Through such an exercise it is possible to identify economic homogeneity and/or heterogeneity among households with children in different localities: this is useful when defining strata for sampling design for surveys aiming at studying other economic phenomena relating to children

Sintering Behavior of Diboride Based Materials

A brief history of diboride research, an overview of processing, and sintering studies are covered in this viewgraph presentation. UHTCs are a family of ceramic materials, including diborides of Hf and Zr, with extremely high melting temperatures. Spark Plasma Sintering (SPS) is a novel processing technique useful in consolidating difficult materials. The presentation also contains microphotographs of the microstructure of HfB2 and ZrB2 processed in different ways

Processing and Properties of HfB2 Based Materials

Contents include the following: Modified hot pressing schedule has significantly improved UHTC billet processing: density and microstructure uniformity have improved. 2 in. dia. x 2 in. tall UHTC billets have been successfully hot pressed: scaled up billets have slightly higher density gradients axially than 1 in. billets. Hot press schedule has not been optimized for scaled up billets. Strengths and strength distributions are improving with experience: need to evaluate strength uniformity in the center of the billets. CTE or ARC materials compares favorably with heritage materials. Thermal conductivity of ARC materials considerably different than that of heritage materials

Processing, Properties and Arc Jet Testing of HfB2/SiC

Contents include the following: Background on Ultra High Temperature Ceramics - UHTCs. Summary UNTC processing: power processing, scale-up. Preliminary material properties: mechanical, thermal. Arc jet testing: flat face models, cone models. Summary

Geoeconomic variations in epidemiology, ventilation management, and outcomes in invasively ventilated intensive care unit patients without acute respiratory distress syndrome: a pooled analysis of four observational studies

Background: Geoeconomic variations in epidemiology, the practice of ventilation, and outcome in invasively ventilated intensive care unit (ICU) patients without acute respiratory distress syndrome (ARDS) remain unexplored. In this analysis we aim to address these gaps using individual patient data of four large observational studies. Methods: In this pooled analysis we harmonised individual patient data from the ERICC, LUNG SAFE, PRoVENT, and PRoVENT-iMiC prospective observational studies, which were conducted from June, 2011, to December, 2018, in 534 ICUs in 54 countries. We used the 2016 World Bank classification to define two geoeconomic regions: middle-income countries (MICs) and high-income countries (HICs). ARDS was defined according to the Berlin criteria. Descriptive statistics were used to compare patients in MICs versus HICs. The primary outcome was the use of low tidal volume ventilation (LTVV) for the first 3 days of mechanical ventilation. Secondary outcomes were key ventilation parameters (tidal volume size, positive end-expiratory pressure, fraction of inspired oxygen, peak pressure, plateau pressure, driving pressure, and respiratory rate), patient characteristics, the risk for and actual development of acute respiratory distress syndrome after the first day of ventilation, duration of ventilation, ICU length of stay, and ICU mortality. Findings: Of the 7608 patients included in the original studies, this analysis included 3852 patients without ARDS, of whom 2345 were from MICs and 1507 were from HICs. Patients in MICs were younger, shorter and with a slightly lower body-mass index, more often had diabetes and active cancer, but less often chronic obstructive pulmonary disease and heart failure than patients from HICs. Sequential organ failure assessment scores were similar in MICs and HICs. Use of LTVV in MICs and HICs was comparable (42·4% vs 44·2%; absolute difference -1·69 [-9·58 to 6·11] p=0·67; data available in 3174 [82%] of 3852 patients). The median applied positive end expiratory pressure was lower in MICs than in HICs (5 [IQR 5-8] vs 6 [5-8] cm H2O; p=0·0011). ICU mortality was higher in MICs than in HICs (30·5% vs 19·9%; p=0·0004; adjusted effect 16·41% [95% CI 9·52-23·52]; p<0·0001) and was inversely associated with gross domestic product (adjusted odds ratio for a US$10 000 increase per capita 0·80 [95% CI 0·75-0·86]; p<0·0001). Interpretation: Despite similar disease severity and ventilation management, ICU mortality in patients without ARDS is higher in MICs than in HICs, with a strong association with country-level economic status