Embers are a potent mechanism for wildfire propagation because the particles can carry farther than the flame front and nullify defensible zones. PyroSim, a Fire Dynamics Simulator (FDS) tool that visually processes text editor inputs for simulating fire-driven fluid flow, is leveraged to model ember transport and accumulation patterns on buildings during a wildfire. This research begins with benchmark analysis against existing findings in literature for validating its usage. It focuses particularly on the transport and accumulation patterns of non-combusting particles with realistic ember parameters which are carried via wind over sample buildings. This study tested various ember sizes, ember densities, wind speed in the horizontal and vertical direction, rooftop styles, and fire effects to examine how each factor impacted ember behavior. Results indicate that roofs with a ridge line perpendicular to wind direction are more likely to accumulate embers. Additionally, horizontal and vertical wind speeds must be strong to facilitate ember transport but not so great that embers are unable to deposit and settle onto buildings. Regardless of building design, a plurality of embers come to rest against the front-facing walls of the structure, posing the biggest risk to fire spread. Surface fires impact flow behavior, so a ground fire was introduced to the model to examine how results change. Ultimately, it is theorized that fire-driven turbulence may facilitate ember transport but negate accumulation in unstable regions, such as rooftops.

The authors describe Taiwan's successful strategy in achieving control of coronavirus disease (COVID-19) without economic shutdown, despite the prediction that millions of infections would be imported from travelers returning from Chinese New Year celebrations in Mainland China in early 2020. As of September 2, 2020, Taiwan reports 489 cases, 7 deaths, and no locally acquired COVID-19 cases for the last 135 days (greater than 4 months) in its population of over 23.8 million people. Taiwan created quasi population immunity through the application of established public health principles. These non-pharmaceutical interventions, including public masking and social distancing, coupled with early and aggressive identification, isolation, and contact tracing to inhibit local transmission, represent a model for optimal public health management of COVID-19 and future emerging infectious diseases.

This research examines changes in the ion current and the release of carbon monoxide (CO) from surface-impinging coflow diffusion flames when subjecting those flames to high DC electric fields. Carbon monoxide results from the incomplete oxidation of hydrocarbon fuels and, while CO can be desirable in some syngas processes, it is usually a dangerous emission from forest fires, gas heaters, stoves, or furnaces where the core reaction insufficiently oxidizes the fuel to carbon dioxide and water. Electrical aspects of flames, specifically, the production of chemi-ions in hydrocarbon flames and the convective flows driven by these ions, have been investigated in ranges of application, and this research examines the use of electric fields as one mechanism for governing combustion as flames are partially extinguished when impinging on nearby surfaces. We evaluate the ion current and study the flame behavior at saturation current in response to the impinging plate location. We also measure the changes in CO emission, as correlated with variations in flame structure observed using OH chemiluminescence and OH planar laser induced fluorescence (PLIF), as a function of burner-to-plate distance and electrical potential applied to the flame. Three major saturation current impact regions in plate distance is observed, and it uses chemiluminescence with PLIF to illuminate the relative locations of the peak heat release zone and the extended oxidative zone changing by external electric fields. The results show that CO release correlates strongly with changes in location and extent of high concentration regions of OH in the surface-impinging diffusion flames.  The results also show that electric fields affect the CO emission but that the burner-to-plate distance has the dominant influence.  The detailed findings indicate that a continuous monitor of ion current from the flame to the impinging surface can be an effective sensing index of flame behavior and CO emission.

The COVID-19 pandemic has strained health care system resources and reduced the availability of life-sustaining and medical-grade personal protective equipment (PPE) though the combination of increased demand and disrupted manufacturing supply chains. As a result of these shortages, many health care providers have temporarily used largely untested, improvised PPE (iPPE). Lack of quality control for makeshift PPE and frequent repurposing of used items to conserve supplies increase both the risk of provider infection and nosocomial spread to uninfected patients. One strategy to reduce risk of infection and preserve existing equipment is the implementation of secondary barrier devices placed directly over patients or providers. The authors describe an inexpensive, disposable, positive-pressure head isolation unit that can be rapidly constructed from materials readily available in nearly all health care settings for under five US dollars. The unit was successfully deployed in Taiwan during the 2003 Severe Acute Respiratory Syndrome (SARS) outbreak, and again during the COVID-19 pandemic. The iPPE worn directly by the health care workers (HCWs) can be donned prior to patient contact in the presence of an air source. This strategy may be more protective than a covering placed over the patient in an aerosol-generating environment, which requires the HCW to be in close contact with the patient prior to securing the protective device.

Carbon monoxide (CO) results from the incomplete oxidation of hydrocarbon fuels. While CO can be desirable in some syngas processes, it is a dangerous emission from fires, gas heaters, gas stoves, or furnaces where insufficient oxygen in the core reaction prevents complete oxidation of fuel to carbon dioxide and water, particularly when the reaction is interrupted by interaction with relatively cool solid boundaries. This research examines the physico-thermo-chemical processes responsible for carbon monoxide release from a small laminar non-premixed methane/air flame impinging on a nearby surface. We measure the changes in CO emission as correlated with variations in flame structure observed using planar laser induced fluorescence (PLIF of OH and 2-photon CO), and two-line OH PLIF thermometry, as a function of burner-to-plate distance. In particular, this work combines the use of OH and CO PLIF, and PLIF thermometry to describe the relative locations of the CO rich region, the peak heat release zone as indicated by chemiluminescence and OH gradients, and the extended oxidative zone in the impinging flames. The results show that CO release correlates strongly with stagnating flow-driven changes in the location and extent of high concentration regions of OH in surface-impinging diffusion flames.

Methane hydrates are crystalline solids of water that contain methane molecules trapped inside their molecular cavities. Gas hydrates with methane as a guest molecule form structure I hydrates with two small dodecahedral cages and six tetra decahedral large cages. This study assesses the influence of occupation and the behavior of methane release from the molecular perspective during the dissociation process, particularly for the purpose of testing a series of molecular dynamics simulations. The dissociation cases conducted include an ideal 4 × 4 × 4 and 2 × 2 × 2 supercell methane hydrate system while inducing dissociation with two different types of temperature-rising functions for understanding the limitation and capability. These temperature-rising functions are temperature ramping and a single temperature step simulating in 5-7 various conditions. Temperature step results showed the earliest dissociation starting 50 ps into the simulation at an ΔT of 100 K, while at an ΔT of 80 K, dissociation was not observed. There was not a distinct dissociation preference observed between large and small cages, so it appears that the dissociation affects the entire structure uniformly when temperature increases are applied throughout the system rather than transport from a boundary. Temperature ramping simulations showed that the dissociation temperature increased with a higher heating rate. The mean-squared displacement results for the oxygen atoms in the water molecules at a high heating rate of 400 TK/s showed behavior similar to that for methane gas. As in the temperature step simulation, there were no clear differences in dissociation between large and small cages, which suggested homogeneous dissociation in all cases. Finally, a coordination analysis was performed on a 3 × 4 × 4 structure I methane hydrate with two free surfaces to demonstrate clear free surface boundaries and its location.

The influence of probe laser chirp on hybrid femtosecond/picosecond pure-rotational coherent anti-Stokes Raman scattering is studied theoretically and experimentally. Experiments of N2(hybrid fs/ps pure-rotational coherent anti-Stokes Raman scattering) are carried out using an in-house built second harmonic bandwidth compressor, results with different probe chirps of are reported. The experimental spectra are fitted with and without considering probe chirp. Including the chirp improves the fit to experimental spectra at all probe delays. The effect of probe pulse chirp is evaluated through a quantitative analysis of matching residuals.