Modeling and Optimization of the Effect of Sintering Parameters on the Hardness of Copper/Graphene Nanosheet Composites by Response Surface Methodology

Metal Science and Heat Treatment - Composites obtained by powder metallurgy from a mixture of copper powders and graphene nanosheets are studied. The response surface methodology is used to design...     

Effects of Post-Weld Heat Treatment on the Microstructure and Toughness of Flash Butt Welded High-Strength Low-Alloy Steel

Metallurgical and Materials Transactions A - Effect of post-weld heat treatment on the weld microstructure, texture, and its correlation to the toughness of flash butt welded joints were...     

Effect of succinonitrile and nano-hydroxyapatite on ionic conductivity and interfacial stability of polyether-based plasticized nanocomposite polymer electrolytes (PNCSPE)

A series of novel plasticized nanocomposite solid polymer electrolytes (PNCSPE) consisting of polyethylene oxide as polymer host, lithium bisoxalatoborate as salt with different weight ratios of succinonitrile and nano-hydroxyapatite was prepared by membrane hot-press technique. The electrical property of PNCSPE was investigated by AC impedance analysis. The migration of lithium ion in the polymer matrix was confirmed from cyclic voltammetry study. The incorporation of different compositions of filler and plasticizer in the polymer matrix significantly enhanced the amorphous nature resulted in increase in ionic conductivity of PNCSPE. The maximum ionic conductivity was found to be in the order of 10^?3.1 S/cm.     

Volumetric imaging with homogenised excitation and static field at 9.4 T

Objectives

To overcome the challenges of B₀ and RF excitation inhomogeneity at ultra-high field MRI, a workflow for volumetric B₀ and flip-angle homogenisation was implemented on a human 9.4 T scanner.

Materials and methods

Imaging was performed with a 9.4 T human MR scanner (Siemens Medical Solutions, Erlangen, Germany) using a 16-channel parallel transmission system. B₀- and B₁-mapping were done using a dual-echo GRE and transmit phase-encoded DREAM, respectively. B₀ shims and a small-tip-angle-approximation kT-points pulse were calculated with an off-line routine and applied to acquire T₁- and T ₂ ^* -weighted images with MPRAGE and 3D EPI, respectively.

Results

Over six in vivo acquisitions, the B₀-distribution in a region-of-interest defined by a brain mask was reduced down to a full-width-half-maximum of 0.10 ± 0.01 ppm (39 ± 2 Hz). Utilising the kT-points pulses, the normalised RMSE of the excitation was decreased from CP-mode’s 30.5 ± 0.9 to 9.2 ± 0.7 % with all B ₁ ⁺  voids eliminated. The SNR inhomogeneities and contrast variations in the T₁- and T ₂ ^* -weighted volumetric images were greatly reduced which led to successful tissue segmentation of the T₁-weighted image.

Conclusion

A 15-minute B₀- and flip-angle homogenisation workflow, including the B₀- and B₁-map acquisitions, was successfully implemented and enabled us to reduce intensity and contrast variations as well as echo-planar image distortions in 9.4 T images.

     

SARS-CoV-2, other respiratory viruses and bacteria in aerosols: Report from Kuwait's hospitals

The role of airborne particles in the spread of severe acute respiratory syndrome coronavirus type 2 (SARS-CoV-2) is well explored. The novel coronavirus can survive in aerosol for extended periods, and its interaction with other viral communities can cause additional virulence and infectivity. This baseline study reports concentrations of SARS-CoV-2, other respiratory viruses, and pathogenic bacteria in the indoor air from three major hospitals (Sheikh Jaber, Mubarak Al-Kabeer, and Al-Amiri) in Kuwait dealing with coronavirus disease 2019 (COVID-19) patients. The indoor aerosol samples showed 12–99 copies of SARS-CoV-2 per m³ of air. Two non-SARS-coronavirus (strain HKU1 and NL63), respiratory syncytial virus (RSV), and human bocavirus, human rhinoviruses, Influenza B (FluB), and human enteroviruses were also detected in COVID-positive areas of Mubarak Al Kabeer hospital (MKH). Pathogenic bacteria such as Mycoplasma pneumonia, Streptococcus pneumonia and, Haemophilus influenza were also found in the hospital aerosols. Our results suggest that the existing interventions such as social distancing, use of masks, hand hygiene, surface sanitization, and avoidance of crowded indoor spaces are adequate to prevent the spread of SARS-CoV-2 in enclosed areas. However, increased ventilation can significantly reduce the concentration of SARS-CoV-2 in indoor aerosols. The synergistic or inhibitory effects of other respiratory pathogens in the spread, severity, and complexity of SARS-CoV-2 need further investigation.     

On the growth of calcium tartrate tetrahydrate single crystals

Calcium tartrate single crystals were grown using silica gel as the growth medium. Calcium formate mixed with formic acid was taken as the supernatant solution. It was observed that the nucleation density was reduced and the size of the crystals was improved to a large extent compared to the conventional way of growing calcium tartrate crystals with calcium chloride. The role played by formate-formic acid on the growth of crystals is discussed. The grown crystals were characterized by atomic absorption spectroscopy (AAS), X-ray diffraction analysis (XRD), microhardness measurement, Fourier transform infrared spectroscopy (FTIR), thermogravimetry (TG) and differential thermal analysis (DTA). The results obtained are compared with the previous work.     

Numerical and experimental evaluation of RF shimming in the human brain at 9.4 T using a dual-row transmit array

Objective

To provide a numerical and experimental investigation of the static RF shimming capabilities in the human brain at 9.4 T using a dual-row transmit array.

Materials and methods

A detailed numerical model of an existing 16-channel, inductively decoupled dual-row array was constructed using time-domain software together with circuit co-simulation. Experiments were conducted on a 9.4 T scanner. Investigation of RF shimming focused on B₁ ⁺ homogeneity, efficiency and local specific absorption rate (SAR) when applied to large brain volumes and on a slice-by-slice basis.

Results

Numerical results were consistent with experiments regarding component values, S-parameters and B₁ ⁺ pattern, though the B₁ ⁺ field was about 25 % weaker in measurements than simulations. Global shim settings were able to prevent B₁ ⁺ field voids across the entire brain but the capability to simultaneously reduce inhomogeneities was limited. On a slice-by-slice basis, B₁ ⁺ standard deviations of below 10 % without field dropouts could be achieved in axial, sagittal and coronal orientations across the brain, even with phase-only shimming, but decreased B₁ ⁺ efficiency and SAR limitations must be considered.

Conclusion

Dual-row transmit arrays facilitate flexible 3D RF management across the entire brain at 9.4 T in order to trade off B₁ ⁺ homogeneity against power-efficiency and local SAR.     

Characterization of semipurified enterocins produced by Enterococcus faecium strains isolated from raw camel milk

Food safety has become an issue of great interest worldwide. Listeria monocytogenes is a food-borne pathogen that causes listeriosis and is difficult to control in the dairy industry. The use of lactic acid bacteria (LAB) and their antimicrobial substances against Listeria is promising in food applications. Here, we report the isolation from raw camel milk of LAB displaying antilisterial activity. Two isolates were selected for their secretion of bacteriocin(s) and identified by 16S rRNA sequencing as Enterococcus faecium S6 and R9. The produced bacteriocins were partially purified by ammonium sulfate precipitation and then biochemically characterized. Antimicrobial activity was estimated to be 6,400 and 400 AU (arbitrary units)/mL for E. faecium S6 and R9, respectively. The proteinaceous nature of the bacteriocins was confirmed via enzymatic reactions. Moreover, lipolytic and glycolytic enzymes completely inactivated the antimicrobial effect of the bacteriocins. These bacteriocins were heat-resistant and stable over a wide range of pH (2.0 to 10.0). To confirm its inactivation by lipolytic and glycolytic enzymes, the bacteriocin of E. faecium S6 was further purified by gel filtration, which suggested the existence of carbohydrate and lipid moieties. In addition, enterocin-coding genes were identified by PCR, showing DNA fragments corresponding in size to enterocins A, B, and P for E. faecium S6 and to enterocins B and P for E. faecium R9. In conclusion, these results indicate that partially purified bacteriocins from E. faecium S6 and R9 may be beneficial in controlling Listeria in the dairy industry.