Spark-Plasma Sintering of Silicon Carbide Whiskers (SiCw) Reinforced Nanocrystalline Alumina

The combined effect of rapid sintering by spark-plasma-sintering (SPS) technique and mechanical milling of γ-Al₂O₃ nanopowder via high-energy ball milling (HEBM) on the microstructural development and mechanical properties of nanocrystalline alumina matrix composites toughened by 20 vol% silicon carbide whiskers was investigated. SiC_w/γ-Al₂O₃ nanopowders processed by HEBM can be successfully consolidated to full density by SPS at a temperature as low as 1125°C and still retain a near-nanocrystalline matrix grain size (∼118 nm). However, to densify the same nanopowder mixture to full density without the benefit of HEBM procedure, the required temperature for sintering was higher than 1200°C, where one encountered excessive grain growth. X-ray diffraction (XRD) and scanning electron microscopy (SEM) results indicated that HEBM did not lead to the transformation of γ-Al₂O₃ to α-Al₂O₃ of the starting powder but rather induced possible residual stress that enhances the densification at lower temperatures. The SiC_w/HEBMγ-Al₂O₃ nanocomposite with grain size of 118 nm has attractive mechanical properties, i.e., Vickers hardness of 26.1 GPa and fracture toughness of 6.2 MPa·m^1/2.     

Extreme multielectron ionization of elemental clusters in ultraintense laser fields

In this paper we present computational and theoretical studies of extreme multielectron ionization in Xe_n clusters (n = 55-2171, initial cluster radii R₀ = 8.7-31.0 Å) driven by ultraintense Gaussian infrared laser fields (peak intensity I_M = 10 ¹⁵ -10 ²⁰ W cm⁻², temporal pulse length τ = 10-100 fs, and frequency v = 0.35fs⁻¹). The microscopic approach, which rests on three sequential-parallel processes of inner ionization, nanoplasma formation, and outer ionization, properly describes the high ionization levels (with the formation of {Xe^q+}_n with q = 5-36), the inner/outer cluster ionization mechanisms, and the nanoplasma response. The cluster size and laser intensity dependence of the inner ionization levels are determined by a complex superposition of laser-induced barrier suppression ionization (BSI), with the contributions of the inner field BSI manifesting ignition enhancement and screening retardation effects, together with electron impact ionization. The positively charged nanoplasma produced by inner ionization reveals intensity-dependent spatial inhomogeneity and spatial anisotropy, and can be either persistent (at lower intensities) or transient (at higher intensities). The nanoplasma is depleted by outer ionization that was semiquantitatively described by the cluster barrier suppression electrostatic model, which accounts for the cluster size, laser intensity, and pulse length dependence of the outer ionization yield.     

Reactive blending of functionalized polypropylene and polyamide 6: In situ polymerization and in situ compatibilization

Compatibilized polypropylene/polyamide 6 blends were prepared with polypropylene, ε‐caprolactam and maleic anhydride grafted polypropylene via in situ polymerization and in situ compatibilization in a batch mixer. Scanning electron microscopy and differential scanning calorimetric analysis showed that the compatibilizing effect was significantly enhanced through use of this method compared to the classic method of blending premade polymers. The optimum processing parameters were obtained for the reactive blends and the effect of maleic anhydride grafted polypropylene content, and the effect of relative weight fraction of maleic anhydride grafted polypropylene to ε‐caprolactam on the overall morphology of the blend system was investigated. It was found that the domain sizes of the polypropylene and polyamide components in the blends could be easily controlled through proper management of the polymerization and compatibilizing reactions during processing. Polym. Eng. Sci. 44:648–659, 2004. © 2004 Society of Plastics Engineers.     

Esterified Trehalose Analogues Protect Mammalian Cells from Heat Shock

Trehalose is a disaccharide produced by many organisms to better enable them to survive environmental stresses, including heat, cold, desiccation, and reactive oxygen species. Mammalian cells do not naturally biosynthesize trehalose; however, when introduced into mammalian cells, trehalose provides protection from damage associated with freezing and drying. One of the major difficulties in using trehalose as a cellular protectant for mammalian cells is the delivery of this disaccharide into the intracellular environment; mammalian cell membranes are impermeable to the hydrophilic sugar trehalose. A panel of cell‐permeable trehalose analogues, in which the hydrophilic hydroxyl groups of trehalose are masked as esters, have been synthesized and the ability of these analogues to load trehalose into mammalian cells has been evaluated. Two of these analogues deliver millimolar concentrations of free trehalose into a variety of mammalian cells. Critically, Jurkat cells incubated with these analogues show improved survival after heat shock, relative to untreated Jurkat cells. The method reported herein thus paves the way for the use of esterified analogues of trehalose as a facile means to deliver high concentrations of trehalose into mammalian cells for use as a cellular protectant.     

Truly Electroforming‐Free and Low‐Energy Memristors with Preconditioned Conductive Tunneling Paths

1S1R (1 selector and 1 memristor) is a laterally scalable and vertically stackable scheme that can lead to the ultimate memristor density for either memory or neural network applications. In such a scheme, the memristor device needs to be truly electroforming‐free and operated at both low currents and low voltages in order to be compatible with a two‐terminal selector. In this work, a new type of memristor with a preconditioned tunneling conductive path is developed to achieve the required performance characteristics, including truly electroforming‐free, low current below 30 µA (potentially <1 µA), and simultaneously low voltage ≈±0.7 V in switching operations. Such memristors are further integrated with two types of recently developed selectors to demonstrate the feasibility of 1S1R integration.     

Spontaneous Mutations in HIV-1 Gag,Protease, RT p66 in the First Replication Cycle and How They Appear: Insights from an In Vitro Assay on Mutation Rates and Types

While drug resistant mutations in HIV-1 are largely credited to its error prone HIV-1 RT, the time point in the infection cycle that these mutations can arise and if they appear spontaneously without selection pressures both remained enigmatic. Many HIV-1 RT mutational in vitro studies utilized reporter genes (LacZ) as a template to investigate these questions, thereby not accounting for the possible contribution of viral codon usage. To address this gap, we investigated HIV-1 RT mutation rates and biases on its own Gag, protease, and RT p66 genes in an in vitro selection pressure free system. We found rare clinical mutations with a general avoidance of crucial functional sites in the background mutations rates for Gag, protease, and RT p66 at 4.71 × 10⁻⁵, 6.03 × 10⁻⁵, and 7.09 × 10⁻⁵ mutations/bp, respectively. Gag and p66 genes showed a large number of ‘A to G’ mutations. Comparisons with silently mutated p66 sequences showed an increase in mutation rates (1.88 × 10⁻⁴ mutations/bp) and that ‘A to G’ mutations occurred in regions reminiscent of ADAR neighbor sequence preferences. Mutational free energies of the ‘A to G’ mutations revealed an avoidance of destabilizing effects, with the natural p66 gene codon usage providing barriers to disruptive amino acid changes. Our study demonstrates the importance of studying mutation emergence in HIV genes in a RT-PCR in vitro selection pressure free system to understand how fast drug resistance can emerge, providing transferable applications to how new viral diseases and drug resistances can emerge.     

A comparison of cognitive and organizational classification of publications in the social sciences and humanities

Scientometrics - We study the discrepancy between two ways of classifying publications in the social sciences and humanities (SSH): on the basis of the contents of publications and publication...     

Injectable Granular Hydrogels with Multifunctional Properties for Biomedical Applications

Injectable hydrogels are useful for numerous biomedical applications, such as to introduce therapeutics into tissues or for 3D printing. To expand the complexity of available injectable hydrogels, shear‐thinning and self‐healing granular hydrogels are developed from microgels that interact via guest–host chemistry. The microgel properties (e.g., degradation, molecule release) are tailored through their crosslinking chemistry, including degradation in response to proteases. When microgels of varied formulations are mixed, complex release and degradation behaviors are observed, including after injection to permit cellular invasion.     

The Crystallinity and Aspect Ratio of Cellulose Nanomaterials Determine Their Pro‐Inflammatory and Immune Adjuvant Effects In Vitro and In Vivo

Nanocellulose is increasingly considered for applications; however, the fibrillar nature, crystalline phase, and surface reactivity of these high aspect ratio nanomaterials need to be considered for safe biomedical use. Here a comprehensive analysis of the impact of cellulose nanofibrils (CNF) and nanocrystals (CNC) is performed using materials provided by the Nanomaterial Health Implications Research Consortium of the National Institute of Environmental Health Sciences. An intermediary length of nanocrystals is also derived by acid hydrolysis. While all CNFs and CNCs are devoid of cytotoxicity, 210 and 280 nm fluorescein isothiocyanate (FITC)‐labeled CNCs show higher cellular uptake than longer and shorter CNCs or CNFs. Moreover, CNCs in the 200–300 nm length scale are more likely to induce lysosomal damage, NLRP3 inflammasome activation, and IL‐1β production than CNFs. The pro‐inflammatory effects of CNCs are correlated with higher crystallinity index, surface hydroxyl density, and reactive oxygen species generation. In addition, CNFs and CNCs can induce maturation of bone marrow–derived dendritic cells and CNCs (and to a lesser extent CNFs) are found to exert adjuvant effects in ovalbumin (OVA)‐injected mice, particularly for 210 and 280 nm CNCs. All considered, the data demonstrate the importance of length scale, crystallinity, and surface reactivity in shaping the innate immune response to nanocellulose.     

A large-scale study of architectural evolution in open-source software systems

From its very inception, the study of software architecture has recognized architectural decay as a regularly occurring phenomenon in long-lived systems. Architectural decay is caused by repeated, sometimes careless changes to a system during its lifespan. Despite decay’s prevalence, there is a relative dearth of empirical data regarding the nature of architectural changes that may lead to decay, and of developers’ understanding of those changes. In this paper, we take a step toward addressing that scarcity by introducing an architecture recovery framework, ARCADE, for conducting large-scale replicable empirical studies of architectural change across different versions of a software system. ARCADE includes two novel architectural change metrics, which are the key to enabling large-scale empirical studies of architectural change. We utilize ARCADE to conduct an empirical study of changes found in software architectures spanning several hundred versions of 23 open-source systems. Our study reveals several new findings regarding the frequency of architectural changes in software systems, the common points of departure in a system’s architecture during the system’s maintenance and evolution, the difference between system-level and component-level architectural change, and the suitability of a system’s implementation-level structure as a proxy for its architecture.