Antimicrobial susceptibility and characterization of extended-spectrum β-lactamases in Escherichia coli isolated from bovine mastitic milk in South Korea from 2012 to 2015

In this study, we aimed to assess trends in antimicrobial resistance and to investigate the characteristics of extended-spectrum β-lactamase (ESBL)-producing isolates from bovine mastitic milk from 2012 to 2015. A total of 374 Escherichia coli isolates were analyzed (154 in 2012, 113 in 2013, 76 in 2014, and 31 in 2015). No consistent trends in antimicrobial resistance of E. coli isolates occurred during the 4-yr period. The most frequently observed resistance was tetracycline (23.3%), followed by streptomycin (17.1%), ampicillin (16.6%), neomycin (11.8%), and trimethoprim/sulfamethoxazole (11.2%). Multidrug resistance was observed in 15.5% of isolates. Among these isolates, 15 (4.0%) carried one or more bla_CTX-M and AmpC ESBL genes from 11 different farms, including bla_CTX-M-15 at 4 farms, bla_CTX-M-3 at 2 farms, bla_CTX-M-1 at 3 farms, and bla_CMY-2 at 3 farms. This study is the first report of bla_CTX-M-3-producing E. coli in dairy milk. Transfer of ESBL was observed in 3 bla_CTX-M-3-producing isolates, 1 bla_CTX-M-1-producing isolate, and all 3 bla_CMY-2-producing isolates. Almost all bla_CTX-M-15 and bla_CTX-M-1 genes possessed an insertion sequence, ISECP1, upstream of the bla_CTX-M gene. Identical pulsed-field gel electrophoresis profiles were also observed in bla_CTX-M-producing E. coli from the same farm. These results suggested that ESBL might spread by both clonal and horizontal spread in dairy farms in South Korea. Although no significant changes occurred in the antimicrobial resistance of E. coli during the 4-yr study period, the resistance rates and presence of ESBL were high compared with those in other countries. Thus, these findings suggest the importance of control measures for E. coli, particularly ESBL-producing bacteria, on dairy farms to reduce treatment failure and transmission to humans.     

Architecture and algorithm for ultra-high precision image rejectionmixer using digital compensation

A Weaver-type ultra-high precision image rejection RF mixer architecture composed of analogue RF and digital IF mixers is proposed, along with the error compensating algorithm for various gain and phase mismatches. A prototype 2.4 GHz image rejection mixer using this technique with an image rejection ratio >70 dB is demonstrated     

Sintering behavior of nanocrystalline γ-Ni-Fe powders

Solid state sintering behavior of nanocrystalline (35 nm) γ-Ni-Fe powders, which were sintered under hydrogen atmospheres at temperatures up to 1300 K, was investigated by laser-photo-dilatometry. The sinterability of the γ-Ni-Fe powders was found to depend crucially on the state of agglomeration and was generally limited to about 80 pct theoretical density. Metallographic observations revealed that the nanocrystalline powders showed a high degree of agglomeration which resulted in a difficult-to-sinter bimodal pore distribution. Although nanoscale intraagglomerate porosity was easily eliminated in the course of sintering, microscale interagglomerate porosity largely proved to resist densification. Experimentally observed shrinkage rates exhibit two densification maxima at the onset and the end of densification. No significant grain growth was observed during sintering.     

Application of bootstrap method in conservative estimation of reliability with limited samples

Accurate estimation of reliability of a system is a challenging task when only limited samples are available. This paper presents the use of the bootstrap method to safely estimate the reliability with the objective of obtaining a conservative but not overly conservative estimate. The performance of the bootstrap method is compared with alternative conservative estimation methods, based on biasing the distribution of system response. The relationship between accuracy and conservativeness of the estimates is explored for normal and lognormal distributions. In particular, detailed results are presented for the case when the goal has a 95% likelihood to be conservative. The bootstrap approach is found to be more accurate for this level of conservativeness. We explore the influence of sample size and target probability of failure on the quality of estimates, and show that for a given level of conservativeness, small sample sizes and low probabilities of failure can lead to a high likelihood of large overestimation. However, this likelihood can be reduced by increasing the sample size. Finally, the conservative approach is applied to the reliability-based optimization of a composite panel under thermal loading.     

Influence of Al on Microstructure and Mechanical Behavior of Cr-Containing Transformation-Induced Plasticity Steel

Chromium in transformation-induced plasticity (TRIP) steel is known to have a detrimental effect on the mechanical properties by increasing the hardenability of austenite introduced during intercritical heat treatment. In this study, it is suggested that an Al addition can counterbalance the effect of Cr by encouraging ferrite formation during fast cooling and austempering. This contributes to securing the thermal stability of austenite and to retrieving the excellent mechanical properties of TRIP steel even with the addition of Cr.     

Bioprocessing aspects of fuels and chemicals from biomass

This review deals with a recent development of biofuels and chemicals from biomass. Some of the grainbased biofuels and chemicals have already been in commercial operation, including fuel ethanol, biodiesel, 1.3-propanediol, polylactic acid (PLA) and polyhydroxy butyric acid/alkanoates (PHB/PHA). The next generation bioproducts will be based on lignocellulosics due to their abundance and to stabilize rising food prices. However, the technologies of handling biomass are yet in their infancy and suffer from low yield, low product titer, and low productivity. This review focuses on bioprocessing technologies for biofuels production: organic raw biomaterials available in Korea; volatile fatty acids platform, multi-stage continuous high cell density culture (MSC-HCDC), enrichment of fermentation broth by forward osmosis; various purification methods of pervaporation of ethanol, solvent extraction on succinic, lactic acids and reactive separation methods.     

Design optimization framework for tiltrotor composite wings considering whirl flutter stability

This paper constructs the design optimization framework for the composite wing of a tiltrotor aircraft based on the Korea Aerospace Research Institute (KARI) Smart Unmanned Aerial Vehicle (SUAV) TRS4 model. The present optimal design attempts to find the cross-section layout that minimizes the structural weight of a composite wing, while satisfying a series of design constraints. The framework consists of various analysis and design tools that include a 2-D beam cross-section analysis, a whirl flutter analysis, and a 3-D strain/stress analysis under the worst wing-loading case. The variation of wing sectional properties of tiltrotor aircrafts in the course of design optimization greatly affects the whirl flutter stability and shows considerable influence on the structural integrity of the wing. In the design framework, the whirl flutter stability is analysed by the nonlinear flexible multibody analysis code DYMORE and the structural integrity is investigated using a MATLAB-based 3-D strain analysis module along with the previous load analysis result. The MATLAB is used to conduct the optimization with a gradient-based optimizer and integrate all of the design and analysis tools. The nonlinear constraints associated with the aeroelastic stability and the structural integrity are also considered. For optimal design examples using the developed framework, a simplified cross-section model based on the KARI SUAV TRS4 composite wing is considered as an initial model. Design optimization examples are investigated to show the validity of the proposed framework and to illustrate the reduction of the structural weight of the composite wing. It is observed that weight reductions of wing structures by 26% and 40% are achieved, while maintaining the whirl flutter stability margins.     

Internal stress analysis of a stepped rounded D-ring under a uniform squeeze rate and internal pressure using a photoelastic experimental hybrid method

Internal stresses occurring in a stepped rounded D-ring compressed to 20% squeeze and pressurized with internal pressures of 0, 0.98, 1.96, 2.94, 3.92 and 4.9 MPa are analyzed using a photoelastic experimental hybrid method. At a pressure of 0 MPa and 20% squeeze, the photoelastic isochromatic fringes of the stepped rounded D-ring were almost symmetrical. As the internal pressure increased, the isochromatics shifted and curved towards the extrusion gap. By supplying a radius of 0.33 mm at the corners of the stepped D-ring, the high stresses at the sharp corners were reduced by up to 25%. These results further indicate that extrusion of the stepped rounded D-ring occurred at an internal pressure of 4.9 MPa which was about 25% higher than the pressure at which the extrusion of the stepped unrounded D-ring occurred.     

Electrochemical capacitors of flower-like and nanowire structured MnO2 by a sonochemical method

Nanostructured manganese dioxide, MnO₂, was synthesized by a sonochemical method. Nanostructured MnO₂ had the shapes of flower-like and nanowires by changing the pH in the aqueous solution, as observed via scanning electron microscopy and transmission electron microscopy. The electrochemical capacitance was studied by cyclic voltammetry. A maximum specific capacitance of 300 Fg⁻¹ was obtained for the nanowires in a potential range from 0.1 to 0.9 V vs. SCE in 1 M sodium sulfate solution at a scan rate of 5 mV s⁻¹. These materials can be useful to increase the specific capacitance by wetting behavior of electrolytes from their structural properties.