A QM/MM approach for the study of monolayer-protected gold clusters

We report the development and implementation of hybrid methods that combine quantum mechanics (QM) with molecular mechanics (MM) to theoretically characterize thiolated gold clusters. We use, as training systems, structures such as Au25(SCH2-R)18 and Au38(SCH2-R)24, which can be readily compared with recent crystallographic data. We envision that such an approach will lead to an accurate description of key structural and electronic signatures at a fraction of the cost of a full quantum chemical treatment. As an example, we demonstrate that calculations of the 1H and 13C NMR shielding constants with our proposed QM/MM model maintain the qualitative features of a full DFT calculation, with an order-of-magnitude increase in computational efficiency.Comment: Journal of Materials Science, 201

Effects of metal-contaminated soils on the accumulation of heavy metals in gotu kola (Centella asiatica) and the potential health risks: a study in Peninsular Malaysia

Centella asiatica is a commonly used medicinal plant in Malaysia. As heavy metal accumulation in medicinal plants which are highly consumed by human is a serious issue, thus the assessment of heavy metals in C. asiatica is important for the safety of consumers. In this study, the heavy metal accumulation in C. asiatica and the potential health risks were investigated. Samples of C. asiatica and surface soils were collected from nine different sites around Peninsular Malaysia. The concentration of six heavy metals namely Cd, Cu, Ni, Fe, Pb and Zn were determined by air-acetylene flame atomic absorption spectrophotometer (AAS). The degree of anthropogenic influence was assessed by calculating the enrichment factor (EF) and index of geoaccumulation (Igeo). The heavy metal uptake into the plant was estimated through the calculation of translocation factor (TF), bioconcentration factor (BCF) and correlation study. Estimated daily intakes (EDI) and target hazard quotients (THQ) were used to determine the potential health risk of consuming C. asiatica. The results showed that the overall surface soil was polluted by Cd, Cu and Pb, while the uptake of Zn and Ni by the plants was high. The value of EDI and THQ showed that the potential of Pb toxicity in C. asiatica was high as well. As heavy metal accumulation was confirmed in C. asiatica, daily consumption of the plant derived from polluted sites in Malaysia was not recommended

Development of a quality indicator set to measure and improve quality of ICU care in low- and middle-income countries

PURPOSE: To develop a set of actionable quality indicators for critical care suitable for use in low- or middle-income countries (LMICs). METHODS: A list of 84 candidate indicators compiled from a previous literature review and stakeholder recommendations were categorised into three domains (foundation, process, and quality impact). An expert panel (EP) representing stakeholders from critical care and allied specialties in multiple low-, middle-, and high-income countries was convened. In rounds one and two of the Delphi exercise, the EP appraised (Likert scale 1–5) each indicator for validity, feasibility; in round three sensitivity to change, and reliability were additionally appraised. Potential barriers and facilitators to implementation of the quality indicators were also reported in this round. Median score and interquartile range (IQR) were used to determine consensus; indicators with consensus disagreement (median < 4, IQR ≤ 1) were removed, and indicators with consensus agreement (median ≥ 4, IQR ≤ 1) or no consensus were retained. In round four, indicators were prioritised based on their ability to impact cost of care to the provider and recipient, staff well-being, patient safety, and patient-centred outcomes. RESULTS: Seventy-one experts from 30 countries (n = 45, 63%, representing critical care) selected 57 indicators to assess quality of care in intensive care unit (ICU) in LMICs: 16 foundation, 27 process, and 14 quality impact indicators after round three. Round 4 resulted in 14 prioritised indicators. Fifty-seven respondents reported barriers and facilitators, of which electronic registry-embedded data collection was the biggest perceived facilitator to implementation (n = 54/57, 95%) Concerns over burden of data collection (n = 53/57, 93%) and variations in definition (n = 45/57, 79%) were perceived as the greatest barrier to implementation. CONCLUSION: This consensus exercise provides a common set of indicators to support benchmarking and quality improvement programs for critical care populations in LMICs

A Low-profile and Efficient Front-End Antenna for Point-to-Point Wireless Communication Links

This paper investigates the design and performance of an efficient, medium-gain, front-end antenna of the type of radial line slot array (RLSA), for wireless communication systems. The antenna consists of two conducting metal plates forming a radial waveguide. The top plate is composed of six rings of radiating slots in a spiral pattern. A single coaxial connector is used to feed the electromagnetic energy from the bottom of the radial waveguide. The antenna has a radius of 0.15 m and operating at a frequency of 12 GHz. It was simulated using Computer Simulation Technology (CST) Microwave Studio 2019 and the results show that the antenna has an acceptable level of impedance matching in the frequency range from 11 GHz to 13 GHz, with a peak directivity of 25.6 dBi and a peak realized gain of 25 dBic at 12 GHz. Its radiation efficiency is 96% and a total efficiency is 85.3% at 12 GHz

A Beam Squinted Linearly Polarised Radial Line Slot Array Antenna with Improved Return Loss Bandwidth

This paper presents an investigation to improve the poor return loss performance of linearly polarised radial line slot array (RLSA) antenna. The problem was tackled by applying the beam squinting technique. The antenna consists of radiating surface with a circular cavity and supports outward-travelling electromagnetic waves. The antenna is excited via a rear mounted modified disk-ended dielectric coated SMA connector. The simulation results show that the return loss performance has improved significantly over the entire frequency band with a return loss bandwidth of 52.5%. The far-field result indicates that the antenna has achieved a peak directivity of 24.7 dBi at 17 GHz with a beam squinted angle of 18° and a side lobe level of -10 dB

A Double Layer Circularly Polarised Radial Line Slot Array Antenna with Uniform Aperture Illumination

In this paper, we have designed and investigated a double layer circularly polarised radial line slot array (RLSA) antenna for satellite communication. The antenna is composed of twofold radial waveguide with slots acting as radiating elements on its surface. The radiating slots are arranged in a spiral pattern on the antenna aperture. Every slot has a particular length and position. The slots are oriented in a way to intercept the radial currents on the upper waveguide. The slot lengths were varied to achieve a uniform aperture distribution. The electromagnetic power is fed from center of the lower waveguide. Numerical results show that the antenna is well matched within the operating frequency range. The far-field results indicate a peak directivity of 27 dBi at 20 GHz with a good pattern quality and lower side lobe level of -27.2 dB