SARS-CoV-2 in wastewater: From detection to evaluation.

SARS-CoV-2 presence in wastewater has been reported in several studies and has received widespread attention among the Wastewater-based epidemiology (WBE) community. Such studies can potentially be used as a proxy for early warning of potential COVID-19 outbreak, or as a mitigation measure for potential virus transmission via contaminated water. In this review, we summarized the latest understanding on the detection, concentration, and evaluation of SARS-CoV-2 in wastewater. Importantly, we discuss factors affecting the quality of wastewater surveillance ranging from temperature, pH, starting concentration, as well as the presence of chemical pollutants. These factors greatly affect the reliability and comparability of studies reported by various communities across the world. Overall, this review provides a broadly encompassing guidance for epidemiological study using wastewater surveillance.

Controlled Formation of Conduction Channels in Memristive Devices Observed by X-ray Multimodal Imaging.

Neuromorphic computing provides a means for achieving faster and more energy efficient computations than conventional digital computers for artificial intelligence (AI). However, its current accuracy is generally less than the dominant software-based AI. The key to improving accuracy is to reduce the intrinsic randomness of memristive devices, emulating synapses in the brain for neuromorphic computing. Here using a planar device as a model system, the controlled formation of conduction channels is achieved with high oxygen vacancy concentrations through the design of sharp protrusions in the electrode gap, as observed by X-ray multimodal imaging of both oxygen stoichiometry and crystallinity. Classical molecular dynamics simulations confirm that the controlled formation of conduction channels arises from confinement of the electric field, yielding a reproducible spatial distribution of oxygen vacancies across switching cycles. This work demonstrates an effective route to control the otherwise random electroforming process by electrode design, facilitating the development of more accurate memristive devices for neuromorphic computing.

Improved zT in Nb5Ge3-GeTe thermoelectric nanocomposite.

Robust electronic transport properties is a crucial in designing high performance thermoelectrics. A key similarity between superconductor and thermoelectric lies in their generally high electrical conductivity, even at above its superconducting temperature. In this work, we design a nanocomposite between Nb5Ge3 and GeTe-based thermoelectric to improve its thermoelectric figure of merit zT. Phase and microstructural characterization shows distinct Nb5Ge3 precipitates embed in Ge0.9Sb0.1Te matrix. In addition, experimental electronic and thermal transport analysis, together with density functional theory calculation were employed to show the synergistic effect of doping Sb and Nb5Ge3 nanocomposite approach. 10% Sb doping was found to optimize the electronic properties of the GeTe-based matrix. Further addition of 2 wt% Nb5Ge3 nanocomposite to the matrix enhances the phonon scattering, which consequently lowers the lattice thermal conductivity, which results in zT of up to 2.0 at 723 K. Such superconductor nanocomposite approach shown in this work can be employed to enhance the properties of other thermoelectric materials.

Upcycling Silicon Photovoltaic Waste into Thermoelectrics.

Two decades after the rapid expansion of photovoltaics, the number of solar panels reaching end-of-life is increasing. While precious metals such as silver and copper are usually recycled, silicon, which makes up the bulk of a solar cells, goes to landfills. This is due to the defect- and impurity-sensitive nature in most silicon-based technologies, rendering it uneconomical to purify waste silicon. Thermoelectrics represents a rare class of material in which defects and impurities can be engineered to enhance the performance. This is because of the majority-carrier nature, making it defect- and impurity-tolerant. Here, the upcycling of silicon from photovoltaic (PV) waste into thermoelectrics is enabled. This is done by doping 1% Ge and 4% P, which results in a figure of merit (zT) of 0.45 at 873 K, the highest among silicon-based thermoelectrics. The work represents an important piece of the puzzle in realizing a circular economy for photovoltaics and electronic waste.

Concave Array Ultrasonic Transducer From Multilayer Piezoelectric Ceramic for Photoacoustic Imaging.

Implementation of piezoelectric multilayer ceramic (MLC) is an effective way to reduce impedance and improve the performance of linear-array transducer for ultrasonic system applications. However, the ultrasonic image derived from a planar linear-array transducer generally suffers from degradation of lateral resolution and contrast. In this article, we designed and fabricated a focused 5-MHz 128-element linear-array ultrasonic transducer with concave structure using five-layered 0.1Pb (Ni1/3Nb2/3)O3 -0.35Pb(Zn1/3Nb2/3)O3 -0.15Pb(Mg1/3Nb2/3)O3-0.1PbZrO3-0.3PbTiO3 (PNN-PZN-PMN-PZ-PT) piezo- electric ceramic. The transducer showed a bandwidth of 63% at -6 dB and the lateral resolution up to 0.33 mm. An improved transmission signal of 90% higher than a commercial single-layer ceramic transducer was also achieved. We further demonstrated high-resolution photoacoustic imaging with the obtained concave linear-array transducer.

The Efficacy of Plant-Based Ionizers in Removing Aerosol for COVID-19 Mitigation.

Small-sized droplets/aerosol transmission is one of the factors responsible for the spread of COVID-19, in addition to large droplets and surface contamination (fomites). While large droplets and surface contamination can be relatively easier to deal with (i.e., using mask and proper hygiene measures), aerosol presents a different challenge due to their ability to remain airborne for a long time. This calls for mitigation solutions that can rapidly eliminate the airborne aerosol. Pre-COVID-19, air ionizers have been touted as effective tools to eliminate small particulates. In this work, we sought to evaluate the efficacy of a novel plant-based ionizer in eliminating aerosol. It was found that factors such as the ion concentration, humidity, and ventilation can drastically affect the efficacy of aerosol removal. The aerosol removal rate was quantified in terms of ACH (air changes per hour) and CADR- (clean air delivery rate-) equivalent unit, with ACH as high as 12 and CADR as high as 141 ft3/minute being achieved by a plant-based ionizer in a small isolated room. This work provides an important and timely guidance on the effective deployment of ionizers in minimizing the risk of COVID-19 spread via airborne aerosol, especially in a poorly-ventilated environment.

Risk assessment of airborne COVID-19 exposure in social settings.

The COVID-19 pandemic has led to many countries oscillating between various states of lock-down as they seek to balance keeping the economy and essential services running and minimizing the risk of further transmission. Decisions are made about which activities to keep open across a range of social settings and venues guided only by ad hoc heuristics regarding social distancing and personal hygiene. Hence, we propose the dual use of computational fluid dynamic simulations and surrogate aerosol measurements for location-specific assessment of risk of infection across different real-world settings. We propose a 3-tiered risk assessment scheme to facilitate classification of scenarios into risk levels based on simulations and experiments. Threshold values of <54 and >840 viral copies and <5% and >40% of original aerosol concentration are chosen to stratify low, medium, and high risk. This can help prioritize allowable activities and guide implementation of phased lockdowns or re-opening. Using a public bus in Singapore as a case study, we evaluate the relative risk of infection across scenarios such as different activities and passenger positions and demonstrate the effectiveness of our risk assessment methodology as a simple and easily interpretable framework. For example, this study revealed that the bus's air-conditioning greatly influences dispersion and increases the risk of certain seats and that talking can result in similar relative risk to coughing for passengers around an infected person. Both numerical and experimental approaches show similar relative risk levels with a Spearman's correlation coefficient of 0.74 despite differing observables, demonstrating applicability of this risk assessment methodology to other scenarios.

Broadband Ultrasonic Array Transducer From Multilayer Piezoelectric Ceramic With Lowered Co-Firing Temperature.

Increasing array transducer bandwidth (BW) and signal-to-noise ratio (SNR) is a critical issue for producing a high-quality medical ultrasound image. However, array elements with small size tend to have poor sensitivity due to a much higher impedance compared with the electrical impedance of the transmitter and receiver circuit. Implementation of multilayer ceramic (MLC) is an effective way of reducing impedance, and thus, with a potential for improving SNR for an ultrasonic probe. In this work, we fabricated multilayer piezoelectric ceramic with a composition of 0.1Pb(Ni1/3Nb2/3)O3-0.35Pb(Zn1/3Nb2/3)O3-0.15Pb(Mg1/3Nb2/3)O3-0.1PbZrO3-0.3PbTiO3-4mol% excess NiO (PNN-PZN-PMN-PZ-PT), by a roll to roll tape casting process and co-fired with 90Ag/10Pd electrode at a low temperature of 950 °C. Using five-layer MLC (5L-MLC) as obtained, we designed and demonstrated a 5 MHz 32-element array transducer for ultrasonic and photoacoustic imaging. The five-layer transducer element exhibited a BW of 87% at -6 dB, substantially higher than 62% for single-layer ceramic (SLC) element. In addition, the insertion loss was improved by 16.2 dB over the SLC element with an external impedance of 50 Ω . Both the experimental results and theoretical analysis showed that our array transducer made of the PNN-PZN-PMN-PZ-PT MLC is promising for acquiring high-quality ultrasonic and photoacoustic images.

Giant piezoelectricity in oxide thin films with nanopillar structure.

High-performance piezoelectric materials are critical components for electromechanical sensors and actuators. For more than 60 years, the main strategy for obtaining large piezoelectric response has been to construct multiphase boundaries, where nanoscale domains with local structural and polar heterogeneity are formed, by tuning complex chemical compositions. We used a different strategy to emulate such local heterogeneity by forming nanopillar regions in perovskite oxide thin films. We obtained a giant effective piezoelectric coefficient [Formula: see text] of ~1098 picometers per volt with a high Curie temperature of ~450°C. Our lead-free composition of sodium-deficient sodium niobate contains only three elements (Na, Nb, and O). The formation of local heterogeneity with nanopillars in the perovskite structure could be the basis for a general approach to designing and optimizing various functional materials.

Lead-Free Piezoelectric Ceramic Coatings Fabricated by Thermal Spray Process.

This paper starts from a review on the progress in fabrication of piezoelectric ceramic coatings by thermal spray method. For our experimental work, two types of lead-free piezoelectric ceramic coatings, including potassium-sodium niobate-based and bismuth sodium titanate-based, are fabricated by thermal spray process, and their structure, morphology, and piezoelectric properties are characterized. Our obtained lead-free ceramic coatings exhibit single phase of perovskite structure, relatively dense morphology, and competitive piezoelectric coefficients. The mechanism of forming the piezoelectric perovskite crystalline phase by thermal spray involving melting-recrystallization process is analyzed in comparison to that of ceramic synthesis through solid-state reaction. Suppression of volatile loss and decomposition at high temperature due to the extremely high melting and cooling rate in the thermal spray process, and the impact on the resulting structure are discussed. Significant advantages of the thermal spray method over alternative processing methods for forming piezoelectric ceramic coatings are summarized. The combination of environmentally friendly lead-free compositions and the scalable thermal spray processing method will promote more applications of piezoelectric ceramic coatings for producing distributive sensors and transducers, and forming advanced smart structures and systems.