Respiratory bioaerosol deposition from a cough and recovery of viable viruses on nearby seats in a cabin environment

Respiratory bioaerosol deposition in public transport cabins is critical for risk analysis and control of contact transmission. In this work, we built a two-row four-seat setup and an air duct system to simulate a cabin environment. A thermal manikin on the rear left-hand seat was taken as the infected passenger (IP) and “coughed” three times through a cough generator. The deposited viruses and droplets on nearby seats were measured by a cultivation method and microscope, respectively. The effects of seat backrest and overhead gasper jet were studied. Results showed that the number of deposited virus on the front seat was one order of magnitude higher than that on other seats which only contained droplets smaller than 10 µm in diameter. When the backrest was 15 cm higher than the cough, the deposited number of viruses was reduced to 5% of that with the backrest at the same height with the cough. The gasper jet above the IP with a velocity of 1.5 m/s can reduce the deposited viruses to 4% of that with gasper off. It indicates that both the gasper jet and backrest can work as mitigation measures to block the cough jet and protect the nearby passengers.     

Identification of rockfall source areas using the seed cell concept and bivariate susceptibility modelling

The objective of this research was to prepare a rockfall susceptibility map. Explorations were conducted in the Dubra?ina River basin (Croatia). The input data included a geological map, an orthophoto and a 1-m digital terrain model (DTM). After a talus inventory was prepared, the seed cell concept was applied to define the rockfall source areas. The contributing factors (predictors) of rockfalls were evaluated by the chi-squared test. The analysis confirmed the following predictors: CORINE land cover, lithology, slope, aspect, distance from a spring, distance from a road, distance from a fault, distance from a stream, and distance from the rock-soil geological boundary. A matrix pairwise comparison of the predictor ratings was used to define the most significant contributing factors. The predictors that affected the susceptibility map in the share of 86.3% were the slope (61.6%), lithology (13.4%), CORINE land cover (6.2%), and distance from the rock-soil geological boundary (5.1%). Two susceptibility maps were prepared: one using all nine contributing factors and another using the four most significant factors. The analysis showed that both maps were good, with the same areas under the receiver operating characteristic (ROC) curves. The map prepared with only four contributing factors can be considered a better map due to its more precise spatial definition of critical areas. It can be concluded that geological map, 1-m DTM and orthophoto provide enough data to prepare reliable rockfall susceptibility map. The application of the bivariate statistical zonation method called the “frequency ratio method” was proven to be successful. This research demonstrates that the application of the seed cell concept can be useful to speed up the process of rockfall source area detections in large research regions.

     

Entropy‐Based Optimal Sensor Placement for Model Identification of Periodic Structures Endowed with Bolted Joints

The number of sensors and the corresponding locations are very important for the information content obtained from the measured data, which is a recognized challenging problem for large‐scale structural systems. This article pays special attention to the sensor placement issues on a large‐scale periodically articulated structure representing typical pipelines to extract the most information from measured data for the purpose of model identification. The minimal model parameter estimation uncertainties quantified by the information entropy (IE) measure is taken as the optimality criterion for sensors placement. By utilizing the inherent periodicity property of this type of structure together with the Bloch theorem, a novel tailor‐made modeling approach is proposed and the computational cost required for dynamic analysis to form the IE with respect to the entire periodic structure can be dramatically reduced regardless of the number of contained periodic units. In addition, to avoid the error of dynamic modeling induced by conventional finite element method based on static shape function, the spectral element method, a highly accurate dynamic modeling method, is employed for modeling the periodic unit. Moreover, a novel discrete optimization method is developed, which is very efficient in terms of the number of function evaluations. The proposed methodology is demonstrated by both numerical and laboratory experiments conducted for a bolt‐connected periodic beam model.     

Influence of Field Effects on the Performance of InGaAs-Based Terahertz Radiation Detectors

A detailed electrical characterization of high-performance bow-tie InGaAs-based terahertz detectors is presented along with simulation results. The local surface potential and tunnelling current were scanned over the surfaces of the detectors by means of Kelvin probe force microscopy (KPFM) and scanning tunnelling microscopy (STM), which also enabled the determination of the Fermi level. Current-voltage curves were measured and modelled using the Synopsys Sentaurus TCAD package to gain deeper insight into the processes involved in detector operation. In addition, we performed finite-difference time-domain (FDTD) simulations to reveal features related to changes in the electric field due to the metal detector contacts. The investigation revealed that field-effect-induced conductivity modulation is a possible mechanism contributing to the high sensitivity of the studied detectors.     

Electrically Active States of Charge Capture and Transfer Causing Slow Recombination in Thallium-Bromide Crystals at Low Temperatures

TlBr single crystals grown by the Bridgman–Stockbarger method are studied. It is established that frozen-conductivity effects manifest themselves under interband excitation by light at temperatures below 200 K. Herewith, clearly pronounced superlinear dependences of the induced photoconductivity on the strength of the applied electric field manifest themselves. The results of studying thermally stimulated conductivity evidence that these phenomena can be associated with the filling of trap states with thermal activation energies of 0.08–0.12 eV. This state can be removed due to thermal quenching at temperatures of ?180 K because of the emptying of energy states with an activation energy of 0.63–0.65 eV filled after optical generation.     

Peak Ground Acceleration Estimation by Linear and Nonlinear Models with Reduced Order Monte Carlo Simulation

Abstract: Estimation of the peak ground acceleration (PGA) is one of the main tasks in civil and earthquake engineering practice since it is an important factor for the design spectrum. The Boore–Joyner–Fumal (BJF) and the Crouse–McGuire formula are well‐known empirical models by estimating the PGA with the magnitude of earthquake, the fault‐to‐site distance, and the site foundation properties. It is obvious that a predictive model class with more effective free parameters often fit the data better. However, this does not imply that the complicated formula is more realistic since overfitting may happen when the formula has too many free parameters. In this article, 32 linear and 16 nonlinear predictive model classes are constructed and investigated. The Bayesian model class selection approach is utilized to obtain the most suitable predictive model class for the seismic attenuation formula. In this approach, each predictive model class is evaluated by the plausibility conditional on the data and it is proportional to the evidence which involves a high‐dimensional integral. This integral has closed‐form solution for the linear model classes. Analytic work was done to improve the original asymptotic expansion in this study. For the nonlinear model classes, the evidence integral can be reduced to two‐dimensional and then Monte Carlo simulation is utilized to evaluate the double integral. The most plausible model class is robust in the sense that it balances between the data‐fitting capability and the sensitivity to noise. A database of 266 strong‐motion records, obtained from the China Earthquake Data Center, is utilized for the analysis. The most plausible predictive model class and its updated model parameters are determined. It turns out that the most plausible model class is generally simpler than the full BJF empirical formula. In the case where no single model class has dominant plausibility, one can utilize the multi‐model predictive formula that is a plausibility‐weighted average of the prediction of different predictive models.     

A slip model for micro/nano gas flows induced by body forces

A slip model for gas flows in micro/nano-channels induced by external body forces is derived based on Maxwell’s collision theory between gas molecules and the wall. The model modifies the relationship between slip velocity and velocity gradient at the walls by introducing a new parameter in addition to the classic Tangential Momentum Accommodation Coefficient. Three-dimensional Molecular Dynamics simulations of helium gas flows under uniform body force field between copper flat walls with different channel height are used to validate the model and to determine this new parameter.     

Enhancement of detecting defects in pipes with focusing techniques

Ultrasonic guided waves have been widely utilized for long range inspection of structures such as oil and petrochemical pipes. However, weldments, support, insulation, and attenuation make it difficult to examine pipe-like structures. In order to overcome such difficulties, it is desired to focus ultrasonic guided wave at the area under interrogation. In this paper, we discuss two focusing techniques: angular profile tuning and signal based focusing. The angular profile tuning approach relies on a theoretical prediction of pressure field of ultrasonic guided wave produced by an ultrasonic transducer mounted on the pipe. And, the signal based focusing is focusing ultrasonic guided waves using cross-correlation analysis. To compare the performance of these two techniques, non-axisymmetric guided waves are focused to abnormalities such as a through-wall hole and a circumferential notch, using an ultrasonic guided wave array system that has been specially fabricated for this purpose. The advantages and limitations of these two focusing techniques are addressed.