Cloud Size Research Articles

Urban Traffic Imaging Using Millimeter-Wave Radar

Imaging technology enhances radar environment awareness. Imaging radar can provide richer target information for traffic management systems than conventional traffic detection radar. However, there is still a lack of research on millimeter-wave radar imaging technology for urban traffic surveillance. To solve the above problem, we propose an improved three-dimensional FFT imaging algorithm architecture for radar roadside imaging in urban traffic scenarios, enabling the concurrence of dynamic and static targets imaging. Firstly, by analyzing the target characteristics and background noise in urban traffic scenes, the Monte-Carlo-based constant false alarm detection algorithm (MC-CFAR) and the improved MC-CFAR algorithm are proposed, respectively, for moving vehicles and static environmental targets detection. Then, for the velocity ambiguity solution problem with multiple targets and large velocity ambiguity cycles, an improved Hypothetical Phase Compensation algorithm (HPC-SNR) is proposed and complimented. Further, the Density-Based Spatial Clustering of Applications with Noise (DBSCAN) algorithm is used to remove outliers to obtain a clean radar point cloud image. Finally, traffic targets within the 50 m range are presented as two-dimensional (2D) point cloud imaging. In addition, we also try to estimate the vehicle type by target point cloud size, and its accuracy reaches more than 80% in the vehicle sparse condition. The proposed method is verified by actual traffic scenario data collected by a millimeter-wave radar system installed on the roadside. The work can support further intelligent transportation management and extend radar imaging applications.

Bubble-cloud characteristics and ablation efficiency in dual-frequency intrinsic threshold histotripsy

Intrinsic threshold histotripsy has been shown to nucleate bubble clouds and generate ablation closely matching the dimensions of the focal region above the intrinsic threshold (∼25–28MPa) with the ablation efficiency dependent upon the size and density of bubbles within the cloud. This work investigates the effects of dual-frequency histotripsy pulsing on bubble-cloud characteristics and ablation efficiency. Histotripsy was applied to agarose tissue phantoms (1%) using a dual-frequency 500kHz–3MHz array transducer with equal pressure delivered by each frequency. The arrival time of the 3 MHz pulse was varied relative to the 500 kHz pulse, and high-speed imaging was used to characterize the bubble-cloud dimensions, bubble density, and individual bubble size. Ablation was determined using red blood cell phantoms. Results indicated that dual-frequency pulsing generated bubble clouds with intermediate cloud size, bubble size, and bubble density compared to single-frequency (500 kHz and 3 MHz) pulsing, with these characteristics further modulated by the respective pulse arrival times. Additionally, dual-frequency pulsing increased ablation efficiency compared to previously published single frequencies (500 kHz and 3 MHz) with the most efficient ablation observed for cases where the 3 MHz pulse arrived at the leading edge of the 500 kHz pulse. Overall, this investigation demonstrates possible benefits of dual-frequency histotripsy pulsing, warranting further investigation.

Interactions between a propagating detonation wave and circular water cloud in hydrogen/air mixture

Interactions between a propagating hydrogen/air detonation wave and circular water cloud are studied. Eulerian-Lagrangian method involving two-way gas-droplet coupling is applied. Different droplet (diameter, concentration) and cloud (diameter) properties are considered. Results show that droplet size, concentration and cloud radius have significant effects on peak pressure trajectory of the detonation wave. Three propagation modes are identified: perturbed propagation, leeward re-detonation, and detonation extinction. Leeward re-detonation is analyzed from unsteady evolutions of gas and liquid droplet quantities. The detonation is re-initiated by a local hot spot from shock focusing of upper and lower diffracted detonations. Disintegration of water droplets proceeds when the detonation wave crosses the cloud. In addition, detonation extinction is featured by quickly fading peak pressure trajectories when the detonation wave passes the larger cloud, and no local autoignition occurs in the shock focusing area. Evolutions of thermochemical structures from the shocked area in an extinction process are also studied. The transfer rates of mass, energy and momentum of detonation success and failure are analyzed. Moreover, parametric studies demonstrate that the critical cloud size to quench a detonation decreases when the droplet concentration is increased. However, when the droplet concentration is beyond 0.84 kg/m3, the critical cloud size is negligibly influenced due to small droplets. Two-phase fluid interfacial instability is observed, and the mechanism of cloud evolution is studied with the distributions of droplet, vorticity, density / pressure gradient magnitudes, and gas velocity. Analysis confirms that velocity difference (due to two-phase momentum exchange) dominates the formation of large-scale vortices from the southern and northern poles, corresponding to Kelvin–Helmholtz instability. Moreover, the influences of effective Atwood number on the evolutions of cloud morphology, vorticity, and gas velocity are evaluated. Results show that higher droplet concentration results in wider droplet dispersion range due to larger vortices.

A novel point cloud simplification method using local conditional information

In three-dimensional measurement of large-scale parts, such as car bodies and aircraft wings, massive points (up to hundreds of millions) are collected. If all point cloud data is processed, a large amount of computing resources and storage space will be consumed. It is an important task to reduce the burden of processing while maintaining the feature of the point cloud as much as possible. This paper proposes a novel point cloud simplification method using local conditional information that is utilized to evaluate the features of each point in point clouds.The proposed method can reduce the size of point clouds while reserving significant features. Firstly, the original information of each point is evaluated by calculating the curvature of the original point cloud. Secondly, the point with the maximal information is selected and reserved in the target point cloud that will be updated as the alternative point cloud after simplification. The conditional information of each rest point is evaluated by the neighborhood and updated to the information of the current point, which attenuates with the distance from the other reserved points. Finally, the point with the maximal information is reserved iteratively until the number of points reserved satisfies the requirements of simplification according to enterprise needs. Experiments verify the effectiveness and performance of the proposed method. The experimental results indicate that the proposed method performs much better on feature retention than Voxel simplification and Curvature simplification.

Characterization of cavitation under ultrasonic horn tip – Proposition of an acoustic cavitation parameter

Acoustic cavitation, generated by a piezo-driven transducer, is a commonly used technique in a variety of processes, from homogenization, emulsification, and intensification of chemical reactions to surface cleaning and wastewater treatment. An ultrasonic horn, the most commonly used acoustic cavitation device, creates unique cavitation conditions under the horn tip that depend on various parameters such as the tip diameter, the driving frequency of the horn, its amplitude, and fluid properties. Unlike for hydrodynamic cavitation, the scaling laws for acoustic cavitation are poorly understood. Empirical relationships between cavitation dynamics, ultrasonic horn operating conditions, and fluid properties were found through systematic characterization of cavitation under the tip. Experiments were conducted in distilled water with various sodium chloride salt concentrations under different horn amplitudes, tip geometries, and ambient pressures. Cavitation characteristics were monitored by high-speed (200,000 fps) imaging, and numerous relations were found between operating conditions and cavitation dynamics. The compared results are discussed along with a proposal of a novel acoustic cavitation parameter and its relationship to the size of the cavitation cloud under the horn tip. Similar to the classical hydrodynamic cavitation number, the authors propose for the first time an acoustic cavitation parameter based on experimental results.

Экспериментально-аналитические исследования формирования пожаровзрывоопасных паровоздушных облаков в атмосфере при утечках и проливах жидкого водорода

Experimental and numerical studies of the process of formation of fire-explosive steam-air clouds in the atmosphere during leaks and spills of liquid hydrogen were carried out. Within their framework, the tasks were performed to determine the size and lifetime of a hydrogen-air cloud with a hazardous concentration of hydrogen from the point of view of explosion and fire hazard (including at the boundary of a visible cloud), and the relationship between the temperature and concentration of combustible gas in a gas-air cloud; studying the effect of cloud temperature on its parameters, the role of atmosphere involvement in the convective hydrogen jet; establishing the influence of moisture content in the atmospheric cloud and the mobility of the environment (wind exposure) on the dynamics of changes in the level of its fire and explosion hazard. It is shown that the humidity of the environment affects the concentration of hydrogen at the boundary of the visible cloud, and, consequently, its fire and explosion hazard. The assessment of the influence of humidity on the parameters of the studied turbulent convective jet indicates that the rate of change in the mass concentration of hydrogen on the axis of the low-temperature jet from the height of ascent depends on the humidity of the medium. The higher the humidity, the sharper the decrease in the mass concentration of hydrogen along the height of the convective jet becomes. In accordance with the calculations, the time for dissipation of a cloud to a fireproof hydrogen concentration in the presence of moisture condensate is reduced by 30 %, and the dissipation time to an explosive concentration of hydrogen is reduced by about 20 %. The coefficient of air involvement α in convective jets of hydrogen-air mixtures with positive buoyancy is 0.12 considering the real enthalpy and absolute humidity of the surrounding air of 15 g/m3 (90 % humidity at 20 °C). This coefficient can be used in the calculations of turbulent convective jets formed during stationary hydrogen evaporation. Wind at low speeds leads to an increase in the maximum transverse dimensions of the cloud, regardless of the concentration in the hydrogen jet, and at high speeds, to their decrease. For emergency hydrogen spills, the most dangerous case when a hydrogen-air cloud of large volumes is formed in the atmosphere, is the case with zero humidity and no wind (in a wide range of values of the initial mass flow of hydrogen: 0.1–100 kg/s).

Spatiotemporal analysis of sheet and cloud cavitation and its damage potential

The cavitation regime has a substantial influence on the damage potential, thus it has to be considered in any specific investigation. For this purpose, we set up a test rig at the Technische Universität Darmstadt using a Circular Leading Edge hydrofoil (CLE) to analyse the damage potential of sheet and cloud cavitation. Exceeding a critical Reynolds number Re c, the cavitation regime transitions from harmless sheet cavitation to aggressive cloud cavitation. High-speed recordings of the cavitation regime are correlated with high frequency pressure data from a wall-mounted piezoelectric pressure transducer. Spatial and temporal content of the cavitating flow are captured applying proper orthogonal decomposition (POD) to the high-speed recordings. In order to determine the damage potential of the cavitation regime we apply a copper foil on the hydrofoil surface, on which plastic, crater-shaped deformations due to bubble collapses occur. Images of the surface are recorded before and after each run via two-dimensional Pit-Count microscopy. We correlate spatial modes from the cavitating flow field with the eroded surface rate from pitting tests leading to the result that cloud cavitation associated with increasing cloud size is more aggressive. A power law is identified where pitting rate increases with fourteenth power of the Reynolds number.

BFS 10: a nascent bipolar H ii region in a filamentary molecular cloud

ABSTRACT We present a study of the compact blister H ii region BFS 10 and its highly filamentary molecular cloud. We utilize 12CO observations from the Five College Radio Astronomy Observatory to determine the distance, size, mass, and velocity structure of the molecular cloud. Infrared observations obtained from the UKIRT Infrared Deep Sky Survey and the Spitzer Infrared Array Camera, as well as radio continuum observations from the Canadian Galactic Plane Survey, are used to extract information about the central H ii region. This includes properties such as the ionizing photon rate and infrared luminosity, as well as identifying a rich embedded star cluster associated with the central O9 V star. Time-scales regarding the expansion rate of the H ii region and lifetime of the ionizing star reveal a high likelihood that BFS 10 will develop into a bipolar H ii region. Although the region is expected to become bipolar, we conclude from the cloud’s velocity structure that there is no evidence to support the idea that star formation at the location of BFS 10 was triggered by two colliding clouds. A search for embedded young stellar objects (YSOs) within the molecular cloud was performed. Two distinct regions of YSOs were identified: one region associated with the rich embedded cluster and another sparse group associated with an intermediate-mass YSO.

A Data-Driven Reduced-Order Model for Estimating the Stimulated Reservoir Volume (SRV)

The main goal of hydraulic fracturing stimulation in unconventional and tight reservoirs is to maximize hydrocarbon production by creating an efficient stimulated reservoir volume (SRV) around the horizontal wells. To zreach this goal, a physics-based model is typically used to design and optimize the hydraulic fracturing process before executing the job. However, two critical issues make this approach insufficient for achieving the mentioned goal. First, the physics-based models are based on several simplified assumptions and do not correctly represent the physics of unconventional reservoirs; hence, they often fail to match the observed SRVs in the field. Second, the success of the executed stimulation job is evaluated after it is completed in the field, leaving no room to modify some parameters such as proppant concentration in the middle of the job. To this end, this paper proposes data-driven and global sensitivity approaches to address these two issues. It introduces a novel workflow for estimating SRV in near real-time using some hydraulic fracturing parameters that can be inferred before or during the stimulation process. It also utilizes a robust global sensitivity framework known as the Sobol Method to rank the input parameters and create a reduced-order (mathematically simple) model for near real-time estimation of SRV (referred to as DSRV). The proposed framework in this paper has two main advantages and novelties. First, it is based on a pure data-based approach, with no simplified assumptions due to the use of a simulator for generating the training and test dataset, which is often the case in similar studies. Second, it treats SRV generation as a rock mechanics problem (rather than a reservoir engineering problem with fixed fracture lengths), accounting for changes in hydraulic fracture topology and SRV changes with time. A dataset from the Marcellus Shale Energy and Environment Laboratory (MSEEL) project is used. The model’s input parameters include stimulation variables of 58 stages of two wells. These parameters are stage number, step, pump rate and duration, proppant concentration and mass, and treating pressure. The model output consists of the corresponding microseismic (MS) cloud size at each step (i.e., time window) during the job. Based on the model, guidelines are provided to help operators design more efficient fracturing jobs for maximum recovery and to monitor the effectiveness of the hydraulic fracturing process. A few future improvements to this approach are also provided.

Effects of upper respiratory tract anatomy and head movement on the buoyant flow and particle dispersion generated in a violent expiratory event

In the wake of the COVID-19 pandemic, interest in understanding the turbulent dispersion of airborne pathogen-laden particles has significantly increased. The ability of infectious particles to stay afloat and disperse in indoor environments depends on their size, the environmental conditions and the hydrodynamics of the flow generated by the exhalation. In this work we analyze the impact of three different aspects, namely, the buoyancy force, the upper airways geometry and the head rotation during the exhalation on the short-term dispersion. Large-Eddy Simulations have been used to assess the impact of each separate effect on the thermal puff and particle cloud evolution over the first 2 s after the onset of the exhalation. Results obtained during this short-term period suggest that due to the rapid mixing of the turbulent puff, buoyancy forces play a moderate role on the ability of the particles to disperse. Because of the enhanced mixing, buoyancy reduces the range and increases the vertical size of the small particle clouds. In comparison to the fixed frame case, head rotation has been found to notably affect the size and shape of the cloud by enhancing the vertical transport as the exhalation axial direction sweeps vertically during the exhalation. The impact of the upper airway geometry, in comparison to an idealized mouth consisting in a pipe of circular section, has been found to be the largest when it is considered along with the head rotation.

Predicting HCN, HCO+, multi-transition CO, and dust emission of star-forming galaxies

The interstellar medium is a turbulent, multiphase, and multi-scale medium that follows scaling relations that link the surface density, volume density, and velocity dispersion with the cloud size. Galactic clouds range from below 1 pc to about 100 pc in size. Extragalactic clouds appear to follow the same range, although they are only now becoming observable in atomic and molecular lines. Analytical models of galactic gaseous disks need to take the multi-scale and multiphase nature of the interstellar medium into account. They can be described as clumpy star-forming accretion disks in vertical hydrostatic equilibrium, with the mid-plane pressure balancing the gravity of the gaseous and stellar disk. Interstellar medium turbulence is taken into account by applying Galactic scaling relations to the cold atomic and molecular gas phases. Turbulence is maintained through energy injection by supernovae. With the determination of the gas mass fraction at a given spatial scale, the equilibrium gas temperature between turbulent heating and line cooling, the molecular abundances, and the molecular line emission can be calculated. The resulting model radial profiles of infrared, HI, CO, HCN, and HCO+ emission are compared to THINGS, HERACLES, EMPIRE, SINGS, and GALEX observations of 17 local spiral galaxies. The model free parameters were constrained for each galactic radius independently. The Toomre parameter, which measures the stability against star formation (cloud collapse), exceeds unity in the inner disk of a significant number of galaxies. In two galaxies it also exceeds unity in the outer disk. Therefore, in spiral galaxies Qtot = 1 is not ubiquitous. The model gas velocity dispersion is consistent with the observed HI velocity dispersion where available. Within our model, HCN and HCO+ is already detectable in relatively low-density gas (∼1000 cm−3). We derive CO and HCN conversion factors and molecular gas depletion times. Both conversion factors are consistent with values found in the literature. Whereas in the massive galaxies the viscous timescale greatly exceeds the star-formation timescale, the viscous timescale is smaller than the star-formation timescale within R ∼ 2 Rd, the disk scale length, in the low-mass galaxies. We suggest that massive spiral galaxies undergo starvation in the absence of gas accretion from the halo, whereas in low-mass galaxies the fuel for star formation reaches R ∼ 2 Rd from outside via a thick gas disk component with a high radial infall velocity observable in the HI line.

An evaluation of the liquid cloud droplet effective radius derived from MODIS, airborne remote sensing, and in situ measurements from CAMP<sup>2</sup>Ex

Abstract. The cloud drop effective radius (Re) of the drop size distribution derived from passive satellite sensors is a key variable used in climate research. Validation of these satellite products has often taken place under stratiform cloud conditions that favor the assumption of cloud horizontal homogeneity used by the retrieval techniques. However, many studies have noted concerns with respect to significant biases in retrieved Re arising from cloud heterogeneity, for example, in cumulus cloud fields. Here, we examine data collected during the 2019 “Cloud, Aerosol and Monsoon Processes Philippines Experiment” (CAMP2Ex), which, in part, targeted the objective of providing the first detailed evaluation of Re retrieved across multiple platforms and techniques in a cumulus and congestus cloud region. Our evaluation consists of cross-comparisons of Re between the Moderate Resolution Imaging Spectroradiometer (MODIS) onboard the Terra satellite, the Research Scanning Polarimeter (RSP) onboard the NASA P-3 aircraft, and in situ measurements from both the NASA P-3 and Learjet aircraft that are all taken in close spatiotemporal proximity to the same cloud fields. A particular advantage of our approach lies in the capability of the RSP to retrieve Re using a bi-spectral MODIS approach and a polarimetric approach, which allows for the evaluation of bi-spectral and polarimetric Re retrievals from an airborne perspective using the same samples. Averaged over all P-3 flight segments examined here for warm clouds, the RSP polarimetric method, the in situ method, and the bias-adjusted MODIS method of Fu et al. (2019) show a comparable median (mean ± standard deviation) for the Re samples of 9.6 (10.2 ± 4.0) µm, 11.0 (13.6 ± 11.3) µm, and 10.4 (10.8 ± 3.8) µm, respectively. These values are far lower than the values of 15.1 (16.2 ± 5.5) µm and 17.2 (17.7 ± 5.7) µm from the bi-spectral retrievals of RSP and MODIS, respectively. Similar results are observed when Re is segregated by cloud-top height and in detailed case studies. The clouds sampled during CAMP2Ex consist of mostly small (mean transect length ∼ 1.4 km) and low clouds (mean cloud-top height ∼ 1 km), which had more numerous small clouds than the trade wind cumuli sampled in past field campaigns such as Rain in Shallow Cumulus over the Ocean (RICO) and the Indian Ocean Experiment (INDOEX). The overestimates of Re from the RSP bi-spectral technique compared with the polarimetric technique increased as cloud size and cloud optical depth decreased. Drizzle, cloud-top bumpiness, and solar zenith angle, however, are not closely correlated with the overestimate of bi-spectral Re. For shallow clouds that dominated the liquid cloud cover for the CAMP2Ex region and period, we show that 3-D radiative transfer and cloud heterogeneity, particularly for the optically thin and small clouds, appear to be the leading cause of the large positive biases in bi-spectral retrievals. Because this bias varies with the underlying structure of the cloud field, caution continues to be warranted in studies that use bi-spectral Re retrievals in cumulus cloud fields.

PointpartNet: 3D point-cloud registration via deep part-based feature extraction

This paper proposes a deep learning model for point cloud registrations of different sizes. 3D point clouds play a very important role in various fields. They have been widely studied, and recently deep learning has also started to deal with point clouds. PointNet was the first deep learning model for point cloud classification and semantic segmentation. Since then, methods based on PointNet for tasks like point cloud registration have also been proposed. However, these methods are only suitable for identical or nearly identical point clouds. However, in practice, the sizes of point clouds vary depending on the capture distance, sensor type, the environment, and many other factors. Therefore, it is often the case that point clouds that need to be registered are of very different sizes. For example, point clouds captured in the same environment by an omnidirectional LiDAR and an RGB-D camera will have very different sizes. Conventional methods cannot cope with such situations. In this paper, we propose ‘PointpartNet', a new deep neural network based on partial feature extraction. This network enables feature extraction of partial point clouds by partitioning the point clouds. It uses the features of partial point clouds to search for matching regions between point clouds of different sizes. This makes it capable of registering point clouds of different sizes. In qualitative experiments, we demonstrate its high robustness and accuracy for point cloud registration of different sizes in comparison to previous research.

Horizontal geometry of trade wind cumuli – aircraft observations from a shortwave infrared imager versus a radar profiler

Abstract. This study elaborates on how aircraft-based horizontal geometries of trade wind cumulus clouds differ whether a one-dimensional (1D) profiler or a two-dimensional (2D) imager is used. While nadir profiling devices are limited to a 1D realization of the cloud transect size, with limited representativeness of horizontal cloud extension, 2D imagers enhance our perspectives by mapping the horizontal cloud field. Both require high resolutions to detect the lower end of the cloud size spectrum. In this regard, the payload aboard the HALO (High Altitude and LOng Range Research Aircraft) achieves a comparison and also a synergy of both measurement systems. Using the NARVAL II (Next-Generation Aircraft Remote-Sensing for Validation Studies) campaign, we combine HALO observations from a 35.2 GHz cloud and precipitation radar (1D) and from the hyperspectral 2D imager specMACS (Munich Aerosol Cloud Scanner), with a 30 times higher along-track resolution, and compare their cloud masks. We examine cloud size distributions in terms of sensitivity to sample size, resolution and the considered field of view (2D or 1D). This specifies impacts on horizontal cloud sizes derived from the across-track perspective of the high-resolution imager in comparison to the radar curtain. We assess whether and how the trade wind field amplifies uncertainties in cloud geometry observations along 1D transects through directional cloud elongation. Our findings reveal that each additional dimension, no matter of the device, causes a significant increase in observed clouds. The across-track field yields the highest increase in the cloud sample. The radar encounters difficulties in characterizing the trade wind cumuli size distribution. More than 60 % of clouds are subgrid scale for the radar. The radar has issues in the representation of clouds shorter than 200 m, as they are either unresolved or are incorrectly displayed as single grid points. Very shallow clouds can also remain unresolved due to too low radar sensitivity. Both facts deteriorate the cloud size distribution significantly at this scale. Double power law characteristics in the imager-based cloud size distribution do not occur in radar observations. Along-track measurements do not necessarily cover the predominant cloud extent and inferred geometries' lack of representativeness. Trade wind cumuli show horizontal patterns similar to ellipses, with a mean aspect ratio of 3:2 and having tendencies of stronger elongation with increasing cloud size. Instead of circular cloud shape estimations based on the 1D transect, elliptic fits maintain the cloud area size distribution. Increasing wind speed tends to stretch clouds more and tilts them into the wind field, which makes transect measurements more representative along this axis.

Amplification of high-intensity pressure waves and cavitation in water using a multi-pulsed laser excitation and black-TiOx optoacoustic lens.

A method for amplification of high-intensity pressure waves generated with a multi-pulsed Nd:YAG laser coupled with a black-TiOx optoacoustic lens in the water is presented and characterized. The investigation was focused on determining how the multi-pulsed laser excitation with delays between 50 µs and 400 µs influences the dynamics of the bubbles formed by a laser-induced breakdown on the upper surface of the lens, the acoustic cavitation in the focal region of the lens, and the high-intensity pressure waves generation. A needle hydrophone and a high-speed camera were used to analyze the spatial distribution and time-dependent development of the above-mentioned phenomena. Our results show how different delays (td ) of the laser pulses influence optoacoustic dynamics. When td is equal to or greater than the bubble oscillation time, acoustic cavitation cloud size increases 10-fold after the fourth laser pulse, while the pressure amplitude increases by more than 75%. A quasi-deterministic creation of cavitation due to consecutive transient pressure waves is also discussed. This is relevant for localized ablative laser therapy.

General and Device-Specific Reasons for ENDS Use: A Qualitative Study with Adult ENDS Users.

Background: A scientific consensus on the public health impact of electronic nicotine delivery systems (ENDS) remains elusive. This is partly due to the wide variation in product characteristics often lumped together under one category. Research is needed to better understand what ENDS device type characteristics motivate their use by adults. Methods: Nine focus groups of 32 current ENDS users who were 18+ years old, had used ENDS in the previous 30 days, and had been using ENDS for more than two months were held either in person or online between February and June 2020. Results: Participants’ reasons for their choice of ENDS characteristics included both general, applying to all ENDS products, and specific, relating to particular ENDS devices. Health benefits and the lack of offensive odor were commonly identified as important reasons for using ENDS in general. Flavor and product discreteness were both general and device-specific determinants of ENDS use. Conversely, nicotine delivery, cloud size, battery properties, aesthetics, ease of use, and cost were device-specific drivers of participants’ choice. Conclusions: The reasons that adults choose to use ENDS are complex and sometimes related to both ENDS as a category and as specific ENDS product types. Regulations and public communication campaigns should reflect their ultimate objective and consider both general and specific motivations when attempting to achieve public health objectives.

Limitations of Separate Cloud and Rain Categories in Parameterizing Collision‐Coalescence for Bulk Microphysics Schemes

AbstractWarm rain collision‐coalescence has been persistently difficult to parameterize in bulk microphysics schemes. We use a flexible bulk microphysics scheme with bin scheme process parameterizations, called AMP, to investigate reasons for the difficulty. AMP is configured in a variety of ways to mimic bulk schemes and is compared to simulations with the bin scheme upon which AMP is built. We find that an important limitation in traditional bulk schemes is the use of separate cloud and rain categories. When the drop size distribution is instead represented by a continuous distribution, the simulation of cloud‐to‐rain conversion is substantially improved. We also find large sensitivity to the threshold size to distinguish cloud and rain in traditional schemes; substantial improvement is found by decreasing the threshold from 40 to 25 μm. Neither the use of an assumed functional form for the size distribution nor the choice of predicted distribution moments has a large impact on the ability of AMP to simulate rain production. When predicting four total moments of the liquid drop size distribution, either with a traditional two‐category, two‐moment scheme with a reduced size threshold, or a four‐moment single‐category scheme, errors in the evolution of mass and the cloud size distribution are similar, but the single‐category scheme has a substantially better representation of the rain size distribution. Optimal moment combinations for the single‐category approach are investigated and appear to be linked more to the information content they provide for constraining the size distributions than to their correlation with collision‐coalescence rates.

Combined effects of soil moisture and microphysical perturbations on convective clouds and precipitation for a locally forced case over Central Europe

AbstractTo study the combined impact of soil moisture and microphysical perturbations on convective clouds and precipitation over Central Europe, an ensemble of five dozen real‐world weather prediction forecasts was conducted with the COnsortium for Small‐scale MOdeling (COSMO) model at convection‐permitting resolution for a case with weak large‐scale forcing (6 June 2016). We find a large sensitivity of precipitation, ranging from +10% to 23% in 12‐hr precipitation totals. While the homogeneous soil‐moisture bias of 25% primarily controls the timing of convection initiation and the amount of surface rainfall, the number of cloud condensation nuclei and width of the cloud droplet size distribution mainly control the number, size, and lifetime of convective clouds. In moisture‐limited conditions, mainly positive couplings are acting. Drier soils, cleaner air, and a broader cloud droplet size distribution result in less rainfall. Wetter soils and more polluted conditions lead to fewer, but larger, cloud clusters. Since microphysical process rates depend systematically on the sign of the perturbations, but rainfall does not, there are compensating effects at work that buffer microphysical perturbations directly and impact the cloud condensate amount and the rainfall at the ground.

A mathematical response curve for probabilistic explosion analysis

Accurate calculation of flammable cloud sizes is important for area classification and risk analysis. Numerical models, such as response surfaces, are at the heart of Monte Carlo simulations for probabilistic explosion risk analysis. In the current work, we developed a mathematical model that can be used to calculate flammable cloud sizes in the context of probabilistic explosion analysis. The model considers the released fluid, the wind speed, the wind direction, the leak rate, the leak direction, and the geometry. The model is based on two non-dimensional groups that were developed using dimensional analysis. We applied the Π theorem of Buckingham, and we show that the two non-dimensional groups correlate in a unique way. Resorting the Kinetic Theory of Gases, the model shows that the flammable cloud volume in the process area increases up to a maximum value and then it decays exponentially. The two constants in the model that consider the gas dilution and the mixing are tuned using a minimum number of computational fluid dynamics (CFD) simulations. The model is then compared with numerical data (not used in the development), and good agreement is observed. Moreover, the model is straightforward to implement, and it can be used for risk analysis calculation and probabilistic explosion analysis.

Transition radiation in the THz range generated in the relativistic laser—tape target interaction

Generation of terahertz (THz) radiation in the interaction of laser pulse with intensity ∼5 × 1018 W cm−2 with a controlled preplasma, created by an additional laser pulse interacting with a 16 μm film target, was studied. The mechanism of generation of THz radiation in the frequency range 1–5 THz was found to be coherent transition radiation of accelerated electrons transversing the rear plasma-vacuum boundary. Angular distribution of the THz radiation changes with the delay between main pulse and prepulse due to different regimes of electron acceleration, while THz radiation spectrum reflects the spatial size of the preplasma cloud and may be used for diagnostics purposes. THz radiation energy reaches ∼0.1 mJ in 1–5 THz spectral range, corresponding to 0.2% conversion efficiency, and increases linearly with laser pulse energy.