COMPRESSIVE BEHAVIOR OF BULK METALLIC GLASS UNDER DIFFERENT CONDITIONS —— COUPLED EFFECT OF TEMPERATURE AND STRAIN RATE

Metallic glass was first reported in 1960 by rapid quenching of Au-Si alloys. But, due to the size limitation, this material did not attract remarkable interest until the development of bulk metallic glasses (BMGs) with specimen sizes in excess of 1 mm. BMGs are considered to be promising engineering materials because of their ultrahigh strength, high elastic limit and wear resistance. However, they usually suffer from a strong tendency for localized plastic deformation with catastrophic failure. Many basic questions, such as the origin of shear softening and the strain rate effect remain unclear. In this thesis, the mechanical behavior of the Zr55Al10Ni5Cu30 bulk metallic glass and a metallic glass composite is investigated. The stress-strain relationship for Zr55Al10Ni5Cu30 over a wide range of strain rate (5 × 10-5 to 2 × 103s-1) was investigated in uniaxial compression loading using both MTS servo-hydraulic system (quasi-static) and compression Kolsky bar system (dy- namic). The effect of the strain rate on the fracture stress at room temperature was discussed. Based on the experimental results, the strain rate sensitivity of the bulk metallic glass changes from a positive value to a negative value at high strain rate, which is a consequence of the significant adiabatic temperature rise during the dynamic testing. In order to characterize the temperature effect on the mechanical behavior of the metallic glass, a synchronically assembled heating unit was designed to be attached onto the Kolsky bar system to perform high temperature and high strain rate mechanical testing. A transition from inhomogeneous deformation to homoge- neous deformation has been observed during the quasi-static compressive experiments at testing temperatures close to the glass transition temperature. However, no tran- sition has been observed at high strain rates at all the testing temperatures. A free volume based model is applied to analyze the stress-strain behavior of the homoge- neous deformation. To further examine the inelastic deformation of the Zr-based bulk metallic glasses, instrumented nanoindentation experiments were performed. A tran- sition from discrete plastic deformation to continuous plastic deformation was found when strain rate is increased but still within the quasi-static strain rate region. Moti- vated by the metal matrix composite material, a tungsten reinforced BMG composite was investigated at quasi-static and dynamic strain rates. The mechanical behavior of the metallic glass matrix was improved significantly by the addition of W particles

Isoglycyrrhizin protects mouse lungs against acute respiratory distress syndrome via regulation of AMPK/Nrf2/ARE pathway

Purpose: To study the effect of isoglycyrrhizin on LPS-mediated acute respiratory distress syndrome (ARDS) in a mouse model, as well as the associated mechanism of action.Methods: Ninety (90) wild-type C57BL/6 male mice were randomly assigned to 3 groups, viz, control, ARDS and isoglycyrrhizin groups. Pathological lesions in mice lungs were determined using H&E staining. The mRNA and protein expressions of inducible nitric oxide synthase (iNOS), heme oxygenase (HO-1), cyclooxygenase-2 (COX-2), AMP- dependent protein kinase (AMPK), serine/threonine proteinkinase (Akt), glycogen synthase kinase 3 (GSK3), nucleotide-binding domain-like receptor protein 3 (NLRP3), and Nrf2 were assayed using quantitative reverse transcription polymerase chain reaction (RT-PCR) and immunoblotting, respectively.Results: The levels of mRNA and protein expressions of INO) and COX-2 were significantly upregulated in ARDS, when compared to control, but were markedly down-regulated by isoglycyrrhizin (p < 0.05). Similarly, exposure of ARDS mice to isoglycyrrhizin led to upregulations of mRNA and proteinlevels of Nrf2, NQO1, HO-1, GCLM, GCLC, p-GSK3, GSK3, p-AMPK, AMPK, p-Akt and AKT (p < 0.05). Moreover, isoglycyrrhizin significantly downregulated p-IκB and Nucl-p65 with respect to protein and mRNA levels, but upregulated IκBα expression. Histopathological examination revealed that pretreatment of ARDS mice with isoglycyrrhizin significantly reduced the number of infiltrating inflammatory cells, edema and ARDS score (p < 0.05).Conclusion: Isoglycyrrhizin protects mouse lungs against ARDS via regulation of AMPK/Nrf2/ARE pathway. Thus, this compound has potential for use in the treatment of ARDS

Evolution and Mutations Predisposing to Daptomycin Resistance in Vancomycin-Resistant Enterococcus faecium ST736 Strains

We recently identified a novel vancomycin-resistant Enterococcus faecium (VREfm) clone ST736 with reduced daptomycin susceptibility. The objectives of this study were to assess the population dynamics of local VREfm strains and genetic alterations predisposing to daptomycin resistance in VREfm ST736 strains. Multilocus sequence typing and single nucleotide variant data were derived from whole-genome sequencing of 250 E. faecium isolates from 1994-1995 (n = 43), 2009-2012 (n = 115) and 2013 (n = 92). A remarkable change was noticed in the clonality and antimicrobial resistance profiles of E. faecium strains between 1994-1995 and 2013. VREfm sequence type 17 (ST17), the prototype strain of clade A1, was the dominant clone (76.7%) recognized in 1994-1995. By contrast, clone ST736 accounted for 46.7% of VREfm isolates, followed by ST18 (26.1%) and ST412 (20.7%) in 2013. Bayesian evolutionary analysis suggested that clone ST736 emerged between 1996 and 2009. Co-mutations (liaR.W73C and liaS.T120A) of the liaFSR system were identified in all ST736 isolates (n = 111, 100%) examined. Thirty-eight (34.2%) ST736 isolates exhibited daptomycin-resistant phenotype, of which 13 isolates had mutations in both the liaFSR and cardiolipin synthase (cls) genes and showed high level of resistance with a daptomycin MIC50 of 32 mug/mL. The emergence of ST736 strains with mutations predisposing to daptomycin resistance and subsequent clonal spread among inpatients contributed to the observed high occurrence of daptomycin resistance in VREfm at our institution. The expanding geographic distribution of ST736 strains in other states and countries raises concerns about its global dissemination

Enterovirus D68 subclade B3 Strain Circulating and Causing an Outbreak in the United States in 2016

In 2014 the United States experienced a nationwide outbreak of Enterovirus D68 (EV-D68) infection. There were no confirmed cases of EV-D68 in 2015 and CDC was only aware of limited sporadic EV-D68 detection in the US in 2016. In this report, we analyzed 749 nasopharyngeal (NP) specimens collected in 2015 and 2016 from patients in the Lower Hudson Valley, New York using a previously validated EV-D68-specific rRT-PCR assay. EV-D68 was detected in none of 199 NP specimens collected in 2015, and in one of 108 (0.9%) samples from January to May and 159 of 442 (36.0%) samples from July to October 2016. Complete EV-D68 genome sequences from 22 patients in 2016 were obtained using a metagenomic next-generation sequencing assay. Comparative genome analysis confirmed that a new EV-D68 strain belonging to subclade B3, with 3.2-4.8% divergence in nucleotide from subclade B1 strains identified during the 2014 US outbreak, was circulating in the US in 2016 and caused an outbreak in the Lower Hudson Valley, New York with 160 laboratory-confirmed cases. Our data highlight the genetic variability and capacity in causing outbreak by diverse EV-D68 strains, and the necessity of awareness and more surveillance on their active circulation worldwide

Complete Genome Sequences of Four Toxigenic ;Clostridium difficile Clinical Isolates from Patients of the Lower Hudson Valley, New York, USA

Complete genome sequences of four toxigenic Clostridium difficile isolates from patients in the lower Hudson Valley, New York, USA, were achieved. These isolates represent four common sequence types (ST1, ST2, ST8, and ST42) belonging to two distinct phylogenetic clades. All isolates have a 4.0- to 4.2-Mb circular chromosome, and one carries a phage

A Survey on Approximate Multiplier Designs for Energy Efficiency: From Algorithms to Circuits

Given the stringent requirements of energy efficiency for Internet-of-Things edge devices, approximate multipliers, as a basic component of many processors and accelerators, have been constantly proposed and studied for decades, especially in error-resilient applications. The computation error and energy efficiency largely depend on how and where the approximation is introduced into a design. Thus, this article aims to provide a comprehensive review of the approximation techniques in multiplier designs ranging from algorithms and architectures to circuits. We have implemented representative approximate multiplier designs in each category to understand the impact of the design techniques on accuracy and efficiency. The designs can then be effectively deployed in high-level applications, such as machine learning, to gain energy efficiency at the cost of slight accuracy loss.Comment: 38 pages, 37 figure