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Acinetobacter baumannii is a nosocomial pathogen of serious healthcare concern that is becoming increasingly difficult to treat due to antibiotic treatment failure. Recent studies have revealed that clinically defined antibiotic-susceptible strains upregulate the expression of a repertoire of putative drug efflux pumps during their growth under biologically relevant conditions, e.g., in human serum, resulting in efflux-associated resistance to physiologically achievable antibiotic levels within a patient. This phenomenon, termed Adaptive Efflux Mediated Resistance (AEMR), has been hypothesized to account for one mechanism by which antibiotic-susceptible A. baumannii fails to respond to antibiotic treatment. In the current study, we sought to identify genetic determinants that contribute to A. baumannii serum-associated AEMR by screening a transposon mutant library for members that display a loss of the AEMR phenotype. Results revealed that mutation of a putative pirin-like protein, YhaK, results in a loss of AEMR, a phenotype that could be complemented by a wild-type copy of the yhaK gene and was verified in a second strain background. Ethidium bromide efflux assays confirmed that the loss of AEMR phenotype due to pirin-like protein mutation correlated with reduced overarching efflux capacity. Further, flow cytometry and confocal microscopy measures of a fluorophore 7-(dimethylamino)-coumarin-4-acetic acid (DMACA)-tagged levofloxacin isomer, ofloxacin, further verified that YhaK mutation reduces AEMR-mediated antibiotic efflux. RNA-sequencing studies revealed that YhaK may be required for the expression of multiple efflux-associated systems, including MATE and ABC families of efflux pumps. Collectively, the data indicate that the A. baumannii YhaK pirin-like protein plays a role in modulating the organism’s adaptive efflux-mediated resistance phenotype.

Ancylostoma caninumis the most common nematode parasite of dogs in the United States. This study aimed to describe the molecular epidemiology ofA. caninumisolates from the central and eastern states of the U.S. using the partial mitochondrialcox1gene and to compare them with those reported globally. We isolated eggs from fecal samples of dogs and characterized each isolate based oncox1sequences. A total of 60 samples originating from Kansas, Iowa, New York, Florida, and Massachusetts were included. 25 haplotypes were identified in the U.S. dataset with high haplotype diversity (0.904). Sequence data were compared to sequences from other world regions available in GenBank. Global haplotype analysis demonstrated 35 haplotypes with a haplotype diversity of 0.931. Phylogenetic and network analysis provide evidence for the existence of moderate geographical structuring of A.caninumhaplotypes. Our results provide an updated summary of A.caninumhaplotypes and data for neutral genetic markers with utility for tracking hookworm populations. Sequences have been deposited in GenBank (ON980650-ON980674). Further studies of isolates from other regions are essential to understand the genetic diversity of this parasite.

The glass transition is alternatively described as either a dynamic transition in which there is a dramatic slowing down of the kinetics, or as a thermodynamic phase transition. To examine the physical origin of the glass transition in fragile Cu-Ag liquids, we employed molecular dynamics (MD) simulations on systems in the range of 32,000 to 2,048,000 atoms. Surprisingly, we identified a 1st order freezing transition from liquid (L) to metastable heterogenous solid-like phase, denoted as the G-glass, when a supercooled liquid evolves isothermally below its melting temperature at deep undercooling. In contrast, a more homogenous liquid-like glass, denoted as the l -glass, is achieved when the liquid is quenched continuously to room temperature with a fast cooling rate of ~1011 K/sec. We report a thermodynamic description of the l -G transition and characterize the correlation length of the heterogenous structure in the G-glass. The shear modulus of the G-glass is significantly higher than the l -glass, suggesting that the first order l -G transition is linked fundamentally to long-range elasticity involving elementary configurational excitations in the G-glass.

The authors recently reported that undercooled liquid Ag and Ag–Cu alloys both exhibit a first order phase transition from the homogeneous liquid (L-phase) to a heterogeneous solid-like G-phase under isothermal evolution. Here, we report a similar L–G transition and heterogenous G-phase in simulations of liquid Cu–Zr bulk glass. The thermodynamic description and kinetic features (viscosity) of the L-G-phase transition in Cu–Zr simulations suggest it corresponds to experimentally reported liquid–liquid phase transitions in Vitreloy 1 (Vit1) and other Cu–Zr-bearing bulk glass forming alloys. The Cu–Zr G-phase has icosahedrally ordered cores versus fcc/hcp core structures in Ag and Ag–Cu with a notably smaller heterogeneity length scale Λ. We propose the L–G transition is a phenomenon in metallic liquids associated with the emergence of elastic rigidity. The heterogeneous core–shell nano-composite structure likely results from accommodating strain mismatch of stiff core regions by more compliant intervening liquid-like medium.

Bacterial keratitis (BK) severity in murine models has traditionally been measured by subjective clinical grading or quantification of ocular bacterial burden. This investigation explores an objective and repeatable quantification of slit lamp photography (SLP) images to measure BK severity.BALB/c strain mice underwent three parallel scratches of the right cornea with subsequent inoculation of 107Staphylococcus aureus cells. SLP imaging and clinical severity grading were performed at 48 hours post-infection. Stromal infiltrate (SI) area on SLP images were quantified. Bacterial burden was determined after enucleation and homogenization. Spearman rank correlations (rs) were used to estimate associations between SI area, clinical severity grades, and bacterial burden.BALB/c strain mice (n = 14) were evaluated with an average SI area of 0.92 mm2 (standard deviation, SD = 0.65) and average bacterial burden of 3.16 × 105 colony forming units per milliliter (CFU/mL) (SD = 8.3 × 105). Clinical severity grade positively correlated with SI area (rs = 0.59, p = 0.0276) and bacterial burden (rs = 0.66, p = 0.0106). There was a trend towards positive association between SI area and bacterial burden (rs = 0.51, p = 0.0543).SLP annotation of SI area is correlated with clinical severity and may provide an objective, quantitative, and repeatable assessment of BK disease severity.SLP annotation of SI area is a novel quantitative method to evaluate bacterial keratitis severity longitudinally in mouse models which may be a powerful tool to better understand BK pathogenesis and response to treatments.

An undercooled liquid-phase (L-phase) can undergo a first order configurational phase transition to either a crystal phase (X-phase) or a metastable, configurationally heterogeneous, rigid glassy phase (G-phase). To investigate the underlying mechanism of the L-G transition, we employ molecular dynamics simulations to study G-phase formation in a binary Cu-Ag system. We find that G-phase formation is driven by the reduction of local distortion energy arising from deviatoric strains in the liquid phase and demonstrate its local distribution. Reduction of distortion energy contributes over 80% of the latent heat of the L-G transition, suggesting that condensation of spatially varying random elastic fields in the liquid is primarily responsible for the first order L-G transition. By applying this analysis to crystallization and G-phase formation in elementary Ag, we show that deviatoric strain energy is the dominant driving force for the L-G and L-X transition also in the case of the pure metal.

A molten metal is an atomic liquid that lacks directional bonding and is free from chemical ordering effects. Experimentally, liquid metals can be undercooled by up to ∼20% of their melting temperature but crystallize rapidly in subnanosecond time scales at deeper undercooling. To address this limited metastability with respect to crystallization, we employed molecular dynamics simulations to study the thermodynamics and kinetics of the glass transition and crystallization in deeply undercooled liquid Ag. We present direct evidence that undercooled liquid Ag undergoes a first-order configurational freezing transition from the high-temperature homogeneous disordered liquid phase (L) to a metastable, heterogeneous, configurationally ordered state that displays elastic rigidity with a persistent and finite shear modulus, μ. We designate this ordered state as the G-phase and conclude it is a metastable non-crystalline phase. We show that the L–G transition occurs by nucleation of the G-phase from the L-phase. Both the L- and G-phases are metastable because both ultimately crystallize. The observed first-order transition is reversible: the G-phase displays a first-order melting transition to the L-phase at a coexistence temperature, T_(G,M). We develop a thermodynamic description of the two phases and their coexistence boundary.

An experimental study of the configurational thermodynamics for a series of near-eutectic Pt(80-x)Cu(x)P(20) bulk metallic glass-forming alloys is reported where 14 < x < 27. The undercooled liquid alloys exhibit very high fragility that increases as x decreases, resulting in an increasingly sharp glass transition. With decreasing x, the extrapolated Kauzmann temperature of the liquid, T(K), becomes indistinguishable from the conventionally defined glass transition temperature, T(g). For x < 17, the observed liquid configurational enthalpy vs. T displays a marked discontinuous drop or latent heat at a well-defined freezing temperature, T(gm). The entropy drop for this first-order liquid/glass transition is approximately two-thirds of the entropy of fusion of the crystallized eutectic alloy. Below T(gm), the configurational entropy of the frozen glass continues to fall rapidly, approaching that of the crystallized eutectic solid in the low T limit. The so-called Kauzmann paradox, with negative liquid entropy (vs. the crystalline state), is averted and the liquid configurational entropy appears to comply with the third law of thermodynamics. Despite their ultrafragile character, the liquids at x = 14 and 16 are bulk glass formers, yielding fully glassy rods up to 2- and 3-mm diameter on water quenching in thin-wall silica tubes. The low Cu content alloys are definitive examples of glasses that exhibit first-order melting.

We identify a reduction reaction of boron oxide by Si during melt fluxing of the Fe-Co-Si-B-P system, which results in an unexpected and significant B enrichment and Si depletion in the alloy. Taking this reaction into account, an optimized Fe-Co-Si-B-P alloy free from oxide inclusions and demonstrating a global peak in glass forming ability is formed. Following a 22-h high temperature fluxing of the melt, alloy with composition Fe_(57.5)Co_(20.2)Si_(10.2)B_(2.1)P_(10) transforms to Fe_(57)Co_(19.2)Si_(6.8)B_(7.4)P_(9.6), and its critical rod diameter increases from 1 mm to 5 mm. The alloy also demonstrates excellent soft ferromagnetic performance characterized by a magnetic saturation of 1.53 T.

“Designing” metallic glasses to exhibit properties beyond those offered within the narrow composition ranges where glass formation is possible poses a formidable scientific challenge. This challenge may be tackled by forming composite structures comprising a metallic glass matrix and homogeneously precipitated dendrites, known as “metallic glass matrix composites” (MGMCs). In principle, MGMCs can be designed to exploit the attractive performance characteristics of the metallic glass while alleviating its negative undesirable attributes. In this work we introduce a MGMC development concept for designing color in metallic glass. MGMCs consisting of a white-gold metallic glass matrix with finely dispersed yellow-gold microdendrites are explored. A series of gold MGMCs is developed displaying uniform and visually-unresolved yellow colors over a broad range of chromaticity, along with high overall hardness. This design concept paves the way for the development of a new generation of metal alloys that combine advanced engineering performance with attractive cosmetic attributes.

Here we present measurements of surface tension and viscosity of the bulk glass-forming alloy Pd43Cu27Ni10P20 performed during containerless processing under reduced gravity. We applied the oscillating drop method in an electromagnetic levitation facility on board of parabolic flights. The measured viscosity exhibits a pronounced temperature dependence following an Arrhenius law over a temperature range from 1100 K to 1450 K. Together with literature values of viscosity at lower temperatures, the viscosity of Pd43Cu27Ni10P20 can be well described by a free volume model. X-ray diffraction analysis on the material retrieved after the parabolic flights confirm the glassy nature after vitrification of the bulk samples and thus the absence of crystallization during processing over a wide temperature range.

A failed subarachnoid block due to prolonged surgical duration continues to be a challenging problem for anesthesia providers. This evidence-based review updates a 2013 systematic review describing the use of intravenous dexmedetomidine as an extrathecal spinal adjunct capable of extending the duration of a subarachnoid block. Eight randomized controlled trials published after the 2013 systematic review met the inclusion criteria. The evidence continues to support the use of intravenous dexmedetomidine as an effective method for prolonging the duration of motor and sensory blockade and postoperative analgesia in a subarachnoid block, with minimal side effects. This updated review reported a more consistent use of assessment tools measuring motor and sensory recovery, expanded the volume of evidence related to postoperative analgesia, and further validated the safe and efficacious use of intravenous dexmedetomidine in extending the duration of a subarachnoid block. Future studies are needed to evaluate the rescue benefit of intravenous dexmedetomidine in failed subarachnoid blocks converted to general anesthesia resulting from prolonged surgical times.

Owing to their glassy nature, metallic glasses demonstrate a toughness that is extremely sensitive to the frozen-in configurational state. This sensitivity gives rise to the so-called “annealing embrittlement”, which is often severe and in many respects limits the technological advancement of these materials. Here, equilibrium configurations (i.e. “inherent states”) of a metallic glass are established around the glass transition, and the configurational properties along with the plane-strain fracture toughness are evaluated. An association between the intrinsic toughness and the inherent state properties is attempted in an effort to identify the fundamental origin of embrittlement of metallic glasses. The established correlations reveal a one-to-one correspondence between a decreasing toughness and an increasing shear modulus, which is robust and continuous over a broad range of inherent states. This annealing embrittlement sensitivity is shown to vary substantially between metallic glass compositions, and appears to correlate well with the fragility of the metallic glass.

This work presents a novel focal plane module architecture based on kilo-pixel arrays able to image from UV to far-infrared scenes. The focal plane arrays are integrated with custom-made, chopper-stabilized read-out integrated circuits into sub-assembly modules to be mounted on the optical telescope of the instrument.

There have been a number of attempts to commercialize bulk metallic glass over the past 20 years. William L. Johnson, the Mettler Professor of Materials Science at California Institute of Technology, has been a prominent figure in these efforts and gives Nature Materials his perspective on the topic.

The material properties of bulk metallic glass matrix composites (BMGMCs) depend strongly on the morphology and elastic constants of the included crystalline phase. Transformation induced plasticity (TRIP) BMGMCs based on the Cu–Zr system are alternatives to traditional dendrite-reinforced BMGMCs. Samples of a representative alloy, Zr_(48)Cu_(47.5)Al_4Co_(0.5), are fabricated in various dimensions and characterized using DSC, SEM, and ultrasonic measurement of elastic constants. It is shown that the Cu–Zr system uniquely softens during crystallization, and the microstructure of the alloy depends strongly on the rate of cooling. We conclude by discussing how combinations of part design and alloy development could be used to utilize these alloys in applications.

A quantitative description of the millisecond capacitive discharge heating and forming process built on a finite-element simulation platform is introduced. The platform incorporates thermodynamic and rheological models that extend beyond the supercooled liquid regime accessible by conventional calorimetry and rheology, accessing the regime that has just recently been uncovered via millisecond Ohmic heating. For the first time, a description of the dynamic glass transition is introduced and incorporated into the platform. The platform accurately simulates the process evolution and the thermodynamic and rheological response of the metallic glass, providing excellent agreement with experiments. Features such as the rapid temperature response, a dynamic glass-transition accommodated by a broad enthalpy recovery, a remarkable temperature and deformational uniformity, and an enthalpy trend that validates the adiabatic constraint, are accurately simulated. The platform is considered a useful tool for modeling the dynamic response and process evolution of metallic glasses under rapid uniform heating.

The use of bulk metallic glasses (BMGs) as the flexspline in strain wave gears (SWGs), also known as harmonic drives, is presented. SWGs are unique, ultra-precision gearboxes that function through the elastic flexing of a thin-walled cup, called a flexspline. The current research demonstrates that BMGs can be cast at extremely low cost relative to machining and can be implemented into SWGs as an alternative to steel. This approach may significantly reduce the cost of SWGs, enabling lower-cost robotics. The attractive properties of BMGs, such as hardness, elastic limit and yield strength, may also be suitable for extreme environment applications in spacecraft.

Owing to their glassy nature, metallic glasses demonstrate a toughness that is extremely sensitive to the frozen-in configurational state. This sensitivity gives rise to “annealing embrittlement,” which is often severe and in many respects limits the technological advancement of these materials. Here, equilibrium configurations (i.e., “inherent states”) of a metallic glass are established around the glass transition, and the configurational properties along with the plane-strain fracture toughness are evaluated to associate the intrinsic glass toughness with the inherent state properties and identify the fundamental origin of embrittlement. The established correlations reveal a one-to-one correspondence between toughness and shear modulus continuous over a broad range of inherent states, suggesting that annealing embrittlement is controlled almost solely by an increasing resistance to shear flow. This annealing embrittlement sensitivity is shown to vary substantially between metallic glass compositions, and appears to correlate well with the fragility of the metallic glass.

To gain insight into the large toughness variability observed between metallic glasses (MGs), we examine the origin of fracture toughness through bending experiments and molecular dynamics (MD) simulations for two binary MGs: Pd_(82)Si_(18) and Cu_(46)Zr_(54). The bending experiments show that Pd_(82)Si_(18) is considerably tougher than Cu_(46)Zr_(54), and the higher toughness of Pd_(82)Si_(18) is attributed to an ability to deform plastically in the absence of crack nucleation through cavitation. The MD simulations study the initial stages of cavitation in both materials and extract the critical factors controlling cavitation. We find that for the tougher Pd_(82)Si_(18), cavitation is governed by chemical inhomogeneity in addition to topological structures. In contrast, no such chemical correlations are observed in the more brittle Cu_(46)Zr_(54), where topological low coordination number polyhedra are still observed around the critical cavity. As such, chemical inhomogeneity leads to more difficult cavitation initiation in Pd_(82)Si_(18) than in Cu_(46)Zr_(54), leading to a higher toughness. The absence of chemical separation during cavitation initiation in Cu_(46)Zr_(54) decreases the energy barrier for a cavitation event, leading to lower toughness.

The microstructure and tension ductility of a series of Ti-based bulk metallic glass matrix composite (BMGMC) is investigated by changing content of the β stabilizing element vanadium while holding the volume fraction of dendritic phase constant. The ability to change only one variable in these novel composites has previously been difficult, leading to uninvestigated areas regarding how composition affects properties. It is shown that the tension ductility can range from near zero percent to over ten percent simply by changing the amount of vanadium in the dendritic phase. This approach may prove useful for the future development of these alloys, which have largely been developed experimentally using trial and error.

With damage tolerance rivalling advanced engineering alloys and thermoplastic forming capabilities analogous to conventional plastics, metallic glasses are emerging as a modern engineering material. Here, we take advantage of their unique electrical and rheological properties along with the classic Lorentz force concept to demonstrate that electromagnetic coupling of electric current and a magnetic field can thermoplastically shape a metallic glass without conventional heating sources or applied mechanical forces. Specifically, we identify a process window where application of an electric current pulse in the presence of a normally directed magnetic field can ohmically heat a metallic glass to a softened state, while simultaneously inducing a large enough magnetic body force to plastically shape it. The heating and shaping is performed on millisecond timescales, effectively bypassing crystallization producing fully amorphous-shaped parts. This electromagnetic forming approach lays the groundwork for a versatile, time- and energy-efficient manufacturing platform for ultrastrong metals., Metallic glasses can be softened to different shapes whilst maintaining mechanical properties, and the related thermoplastic processing requires a heating source and an applied force. Here, the authors show an effective thermoplastic approach by a coupling between electric pulses and a magnetic field.

The waiting time to form a crystal in a unit volume of homogeneous undercooled liquid exhibits a pronounced minimum τX* at a ‘nose temperature' T* located between the glass transition temperature Tg, and the crystal melting temperature, TL. Turnbull argued that τX* should increase rapidly with the dimensionless ratio trg=Tg/TL. Angell introduced a dimensionless ‘fragility parameter', m, to characterize the fall of atomic mobility with temperature above Tg. Both trg and m are widely thought to play a significant role in determining τX*. Here we survey and assess reported data for TL, Tg, trg, m and τX* for a broad range of metallic glasses with widely varying τX*. By analysing this database, we derive a simple empirical expression for τX*(trg, m) that depends exponentially on trg and m, and two fitting parameters. A statistical analysis shows that knowledge of trg and m alone is therefore sufficient to predict τX* within estimated experimental errors. Surprisingly, the liquid/crystal interfacial free energy does not appear in this expression for τX*., The crystal formation waiting time of a homogeneous supercooled liquid exhibits a pronounced minimum depending on temperature, and this minimum is a measure of glass forming ability. Here, the authors propose an expression for this minimum for all metallic glasses that depends only on two fitting parameters.

The threat of micro-meteoroid and orbital debris (MMOD) collisions with spacecraft and satellites has been increasing with the increasing worldwide use of low earth orbit. Providing low-areal-density shielding for the mitigation of these high velocity impacts is essential for ensuring successful and cost effective missions. Here, we report results obtained from hypervelocity impact testing on bulk metallic glass (BMG) matrix composites. Their carbide-like hardness, low melting temperatures, ultra-high strength-to-weight ratio and the ability to be processed like polymers are material attributes ideally suited for spacecraft shielding, particularly as an outer wall bumper shield.

A 2 wt.% Ag/γ-Al 2 O 3 catalyst was studied for the ethanol selective catalytic reduction of NO x from 200 to 550 °C and space velocities between 30,000 h −1 and 140,000 h −1 . Peak NO x conversions reached 85% at 400 °C, and an activation energy was determined to be 57 kJ/mol with a feed of ethanol to NO x or HC 1 /NO x = 3. Up to 80% of the NO is oxidized to NO 2 at 250 °C, but overall NO x conversion is only 15%. Interestingly, ethanol oxidation occurs at much lower temperatures than NO x reduction; at 250 °C, ethanol oxidation is 80% when flowing ethanol + NO + O 2 . This increased reactivity, compared to only 15% when flowing only ethanol + O 2 , combined with the observation that NO is not oxidized to NO 2 in the absence of ethanol illustrates a synergistic relationship between the reactants. To further investigate this chemistry, a series of DRIFTS experiments were performed. To form nitrates/nitrites on the catalysts it was necessary to include ethanol in the feed with NO. These nitrates/nitrites were readily formed when flowing NO 2 over the catalyst. It is proposed that ethanol adsorbs through an ethoxy-intermediate that results in atomic hydrogen on the surface. This hydrogen aids the release of NO 2 from Ag to the gas-phase which, can be subsequently adsorbed at γ-Al 2 O 3 sites away from Ag. The disappearance of these nitrates/nitrites at higher temperatures proceeds in parallel with the increase in NO x reduction reactivity between 300 and 350 °C observed in the kinetic study. It is therefore proposed that the consumption of nitrates is involved in the rate determining step for this reaction.

Compact Charpy impact testing was employed to investigate the effect of low temperatures on the impact toughness of bulk metallic glass matrix composites (BMGMCs). Samples were fabricated via suction casting and impacted from room temperature down to liquid nitrogen temperature. Unlike monolithic glasses, BMGMCs do exhibit a steep decrease in toughness as the temperature is reduced from the ambient, caused by embrittlement in the ductile reinforcing phase. However, at cryogenic temperatures, BMGMCs have a toughness equivalent to their glassy matrix.