Fast Densification of Ultra-High-Temperature Ceramics by Spark Plasma Sintering

This work investigated suitability and efficacy of the sintering technique known as spark plasma sintering to produce ultra-high-temperature-based Hf and Zr borides. Ceramic–matrix composites in the systems HfB₂–SiC, ZrB₂–MoSi₂, and ZrB₂–ZrC–SiC were processed by spark plasma sintering and hot pressing. The effects of processing were evaluated comparing the materials microstructure and properties. Compared with hot-pressing technique, spark plasma sintering offers the great advantage to fabricate successfully in short time (i.e., cuts in costs) poorly sinterable powder compositions without the help of any sintering activators.     

Influence of long term oxidation on the microstructure, mechanical and electrical properties of pressureless sintered AlN–SiC–MoSi2 ceramic composites

The effects of long term oxidation on the microstructural modification and on the electrical resistivity and mechanical strength of an AlN–SiC–MoSi₂ electroconductive ceramic composite are presented. The microstructure of the pressureless sintered composite is described and the oxidation behaviour is discussed. The formation of protective mullite layer at temperatures above 1000 °C provides good oxidation resistance for use at higher temperatures. At temperatures below 1000 °C, the AlN/SiC matrix disables the “pesting” phenomena and strength degradation, despite the fact that at these temperatures MoSi₂ oxidizes rapidly. The surface modification induced by oxidation on AlN–SiC–MoSi₂ composites does not affect the mechanical strength, while the electrical conductivity strongly decreases.     

Effect of the Sintering Additive on Microstructure and Mechanical Properties of Hi‐NicalonTM SiC Fibers in a HfB2 Matrix

This study is focused on the effect of the sintering additive on the microstructure and properties of HfB₂ composites reinforced with SiC Hi–Nicalon fibers. The materials were spark plasma sintered with addition of 5–10 vol% of Si₃N₄ or ZrSi₂. The fibers morphology was examined using scanning and transmission electron microscopy and remarkable differences were observed depending on the additive. Local hardness and Young's modulus were measured by nanoindentation to investigate the fiber mechanical behavior. The introduction of 20 vol% SiC short fibers into the HfB₂ matrix increased the fracture toughness up to 5.4 MPa m^1/2 for the material sintered with ZrSi₂. The room temperature flexural strength of the materials containing fibers slightly decreased when ZrSi₂ was used, but with the addition of Si₃N₄ an improvement of more than the 40%, as compared to the unreinforced material was observed.     

High-Density Pressureless-Sintered HfC-Based Composites

Hafnium carbide (HfC)-(5, 10, and 20 vol%) MoSi₂ ceramics were pressureless sintered at 1950°C in an argon flux. The materials had nearly full density (96%–98%), with mean grain sizes in the range of 3–4 μm. Depending on the MoSi₂ amount (5–20 vol%), the mechanical properties were in the following ranges: hardness 16–15 GPa, Young's modulus 434–385 GPa, fracture toughness 3.6–3.4 MPa·m^1/2, and room-temperature 4-point flexural strength 465–383 MPa.     

Linearity, Persistence and Testing Semantics in the Asynchronous Pi-Calculus

In [C. Palamidessi, V. Saraswat, F. Valencia and B. Victor. On the Expressiveness of Linearity vs Persistence in the Asynchronous Pi Calculus. LICS 2006:59–68, 2006] the authors studied the expressiveness of persistence in the asynchronous π-calculus (Aπ) wrt weak barbed congruence. The study is incomplete because it ignores the issue of divergence. In this paper, we present an expressiveness study of persistence in the asynchronous π-calculus (Aπ) wrt De Nicola and Hennessy's testing scenario which is sensitive to divergence. Following [C. Palamidessi, V. Saraswat, F. Valencia and B. Victor. On the Expressiveness of Linearity vs Persistence in the Asynchronous Pi Calculus. LICS 2006:59–68, 2006], we consider Aπ and three sub-languages of it, each capturing one source of persistence: the persistent-input calculus (PIAπ), the persistent-output calculus (POAπ) and persistent calculus (PAπ). In [C. Palamidessi, V. Saraswat, F. Valencia and B. Victor. On the Expressiveness of Linearity vs Persistence in the Asynchronous Pi Calculus. LICS 2006:59–68, 2006] the authors showed encodings from Aπ into the semi-persistent calculi (i.e., POAπ and PIAπ) correct wrt weak barbed congruence. In this paper we prove that, under some general conditions, there cannot be an encoding from Aπ into a (semi)-persistent calculus preserving the must testing semantics.     

TaB2-based ceramics: Microstructure, mechanical properties and oxidation resistance

TaB₂-based ceramics were hot pressed in low vacuum with addition of 5-10 vol% MoSi₂. Temperatures in the range of 1680-1780 °C led to relative density around 90-95%. The hardness was about 18 GPa, the fracture toughness 4.6 MPa m^1/2 and the room temperature flexural strength was around 630 MPa, but abruptly decreased above 1200 °C to 220 MPa. The composite containing 10 vol% of MoSi₂ was tested in a bottom-up furnace in the temperature range 1200-1700 °C for 30 min. The microstructure appeared covered by a SiO₂ layer, whose thickness increased with the temperature, but the bulk remained unaltered up to 1600 °C. At 1700 °C the specimen vaporized. Nanoindentation was employed on the oxidized cross sections in order to detect eventual mechanical properties modification associated to chemical/microstructural change, like formation of Ta-B-O solid solutions.     

Molecular Landscape and Therapeutic Strategies in Cholangiocarcinoma: An Integrated Translational Approach towards Precision Medicine

Cholangiocarcinomas (CCAs) are heterogeneous biliary tract malignancies with dismal prognosis, mainly due to tumor aggressiveness, late diagnosis, and poor response to current therapeutic options. High-throughput technologies have been used as a fundamental tool in unveiling CCA molecular landscape, and several molecular classifications have been proposed, leading to various targeted therapy trials. In this review, we aim to analyze the critical issues concerning the status of precision medicine in CCA, discussing molecular signatures and clusters, related to both anatomical classification and different etiopathogenesis, and the latest therapeutic strategies. Furthermore, we propose an integrated approach comprising the CCA molecular mechanism, pathobiology, clinical and histological findings, and treatment perspectives for the ultimate purpose of improving the methods of patient allocations in clinical trials and the response to personalized therapies.