Prototype-Scale Physical Model of Wave Attenuation Through a Mangrove Forest of Moderate Cross-Shore Thickness: LiDAR-Based Characterization and Reynolds Scaling for Engineering With Nature

This study investigates the potential of a Rhizophora mangrove forest of moderate cross-shore thickness to attenuate wave heights using an idealized prototype-scale physical model constructed in a 104 m long wave flume. An 18 m long cross-shore transect of an idealized red mangrove forest based on the trunk-prop root system was constructed in the flume. Two cases with forest densities of 0.75 and 0.375 stems/m2 and a third baseline case with no mangroves were considered. LiDAR was used to quantify the projected area per unit height and to estimate the effective diameter of the system. The methodology was accurate to within 2% of the known stem diameters and 10% of the known prop root diameters. Random and regular wave conditions seaward, throughout, and inland of the forest were measured to determine wave height decay rates and drag coefficients for relative water depths ranging 0.36 to 1.44. Wave height decay rates ranged 0.008–0.021 m–1 for the high-density cases and 0.004–0.010 m–1 for the low-density cases and were found to be a function of water depth. Doubling the forest density increased the decay rate by a factor two, consistent with previous studies for other types of emergent vegetation. Drag coefficients ranged 0.4–3.8, and were found to be dependent on the Reynolds number. Uncertainty in the estimates of the drag coefficient due to the measured projected area and measured wave attenuation was quantified and found to have average combined standard deviations of 0.58 and 0.56 for random and regular waves, respectively. Two previous reduced-scale studies of wave attenuation by mangroves compared well with the present study when their Reynolds numbers were re-scaled by λ3/2 where λ is the prototype-to-model geometric scale ratio. Using the combined data sets, an equation is proposed to estimate the drag coefficient for a Rhizophora mangrove forest: CD = 0.6 + 3e04/ReDBH with an uncertainty of 0.69 over the range 5e03 < ReDBH < 1.9e05, where ReDBH is based on the tree diameter at breast height. These results may improve engineering guidance for the use of mangroves and other emergent vegetation in coastal wave attenuation.

Development of Single-Phase Microbial Cementation Method and to Investigate its Efficacy on Bearing Capacity, UCS, and Permeability of Sandy Soils

Microbially induced calcite precipitation (MICP) is a method based on collaborative knowledge of microbiology, chemistry and geotechnical engineering. The objective of this study was to investigate the increase of the bearing capacity and the unconfined compressive strength (UCS) as well as the reduction of the permeability of sandy soil using MICP. Experiments were carried out using Bacillus Pasteurii, on three different types of sand. The admixture of bacterial culture and cementation (BCC) solution all-in-one with sand by single-phase injection was applied to induce cementation. Three samples of the selected sand were treated with varied concentrations of BCC solution, ranging from 0.05 to 0.2 L/kg, with a curing period of 3, 7 and 14 days. The test results indicated an enhancement of 55% in UCS for sand treated with a BCC content of 0.05 to 0.2 L/Kg and a reduction of 40% in permeability for untreated sand with an effective diameter of 0.5 mm treated with 0.2 L/kg of BCC solution after 14 days of curing. The results of a plate load test (PLT) on MICP treated sand showed an increase in the ultimate bearing capacity (qu) by about 2.95 to 5.8 times and a 1.7 to 3.31-fold reduction in settlement corresponding to the same load applied on untreated footing. Further investigation of the size and shape of the bearing plate on bearing capacity and settlement was carried out through a plate load test. The higher and more favorable results shown by a rectangular plate compared to a circular plate indicate that the first is preferable.

Exponentially selective molecular sieving through angstrom pores

Two-dimensional crystals with angstrom-scale pores are widely considered as candidates for a next generation of molecular separation technologies aiming to provide extreme, exponentially large selectivity combined with high flow rates. No such pores have been demonstrated experimentally. Here we study gas transport through individual graphene pores created by low intensity exposure to low kV electrons. Helium and hydrogen permeate easily through these pores whereas larger species such as xenon and methane are practically blocked. Permeating gases experience activation barriers that increase quadratically with molecules’ kinetic diameter, and the effective diameter of the created pores is estimated as ∼2 angstroms, about one missing carbon ring. Our work reveals stringent conditions for achieving the long sought-after exponential selectivity using porous two-dimensional membranes and suggests limits on their possible performance.

Applicability of The Equivalent Diameter Approach to Estimate Vortex Shedding Frequency and Acoustic Resonance Excitation From Different Finned Cylinders In Cross-Flow

This article explores the applicability of utilizing different equivalent diameter (Deq) equations to estimate the vortex shedding frequency and onset of self-excited acoustic resonance for various types of finned cylinders. The focus is on three finned cylinder types that are commonly used in industrial heat exchangers: straight, twist-serrated, and crimped spirally finned cylinders. Within each type of fins, at least three different finned cylinders are investigated. The results indicate that at off-resonance conditions, utilizing the appropriate equivalent diameter collapses the Strouhal number data within the typical Strouhal number variations of an equivalent diameter circular, bare cylinder. However, when acoustic resonance is initiated, the onset and the peak of resonance excitation in all of the finned cylinder cases generally occurred at a reduced flow velocity earlier than that observed from their equivalent diameter bare cylinders. This suggests that although utilizing the appropriate equivalent diameter can reasonably estimate the vortex shedding frequency away from acoustic resonance excitation, it cannot be used to predict the onset of acoustic resonance in finned tubes. The findings of this study indicate that the effective diameter approach is not sufficient to capture the intrinsic changes in the flow-sound interaction mechanism as a result of adding fins to a bare cylinder. Thus, a revision of the acoustic Strouhal number charts is required for finned tubes of different types and arrangements.

Position-dependent mechanical characterization of the PBF-EB-manufactured Ti6Al4V alloy

By means of additive manufacturing, the production of components with nearly unlimited geometrical design complexity is feasible. Especially, powder bed fusion techniques such as electron beam powder bed fusion (PBF-EB) are currently focused. However, equal material properties are mandatory to be able to transfer this technique to a wide scope of industrial applications. Within the scope of this work, the mechanical properties of the PBF-EB-manufactured Ti6Al4V alloy are investigated as a function of the position on the building platform. It can be stated that as-built surface roughness changes within building platform whereby highest surface roughness detected by computed tomography (Ra = 46.0 ± 5.3 µm) was found for specimens located in the front of the building platform. In contrast, no significant differences in relative density could be determined and specimens can be assumed as nearly fully dense (> 99.9%). Furthermore, all specimens are affected by an undersized effective diameter compared to the CAD data. Fatigue tests revealed that specimens in the front of the building platform show slightly lower performance at higher stress amplitudes as compared to specimens in the back of the building platform. However, process-induced notch-like defects based on the surface roughness were found to be the preferred location for early crack initiation.

Comparison of methods for calculating effective doses for children during CT examinations of the chest organs

Computed tomography is associated with high patient doses. CT is actively used for pediatric, however, currently there is no reliable data on the pediatric patient doses in the Russian Federation. The current study presents the data on the anthropometric characteristics of 5, 10 and 15-year-old pediatric patients, as well as the results of a comparative assessment of the effective doses of these patients during CT-examinations of chest, considering their anthropometric data. The effective doses were calculated using three methods: based on the actual guidelines (MU 2.6.1.3584-19) using the age specific conversion coefficients; using the conversion coefficients considered patient body mass and effective diameter; using a specialized software NCICT 3.0. The difference between effective doses according to actual guidelines and considering patient body mass and effective diameter was about 7.1 % (max-65 %). High deviations were observed in patients with abnormally large or abnormally low body mass. Effective doses calculated using NCICT 3.0 were higher compared to doses calculated according to actual guidelines on average by 18 % (max — 53 %). Such differences are explained by the fact that in MU 2.6.1.3584-19 conversion coefficients are presented for the most common CT-scan parameters of protocols, and in NCICT 3.0 the calculation considers individual scan parameters for each patient. The difference between effective doses according to NCICT 3.0 and considering patient body mass and effective diameter was about 32 % (max-70 %). This difference can be explained by the differences in the anthropometric data of some patients, and by the use of different types of phantoms: a stylized phantom (Golikov et al) and a voxel phantom in NCICT 3.0.

Simulation and Field Campaign Evaluation of an Optical Particle Counter on a Fixed-Wing UAV

Unmanned aerial vehicles (UAVs) have great potential to be utilised as an airborne platform for measurement of atmospheric particulates and droplets. In particular, the spatio-temporal resolution of UAV measurements could be of use for the characterisation of aerosol, cloud, and radiation (ACR) interactions, which contribute to the largest uncertainty in the radiative forcing of climate change throughout the industrial era (Zelinka et al., 2014). Due to the infancy of the technique however, UAV-instrument combinations must be extensively validated to ensure the data is of high accuracy and reliability. This paper presents an evaluation of a particular UAV-instrument combination: the FMI-Talon fixed-wing UAV and the UCASS open-path optical particle counter. The performance of the UCASS was previously evaluated on a multi-rotor airframe by Girdwood et al. (2020). However, fixed-wing measurements present certain advantages—namely endurance, platform stability, and maximum altitude. Airflow simulations were utilised to define limiting parameters on UAV sampling—that is, an angle of attack limit of 10° and a minimum airspeed of 20 ms−1—which were then applied retroactively to field campaign data as rejection criteria. The field campaign involved an inter-comparison with reference instrumentation mounted on a research station, which the UAV flew past through stratus cloud. The effective diameter measured by the UAV largely agreed within 2 μm. The droplet number concentration agreed within 15 % on all but 5 profiles. It was concluded that UCASS would benefit from a mechanical redesign to avoid calibration drifts, and UAV attitude variations during measurement should be kept to a minimum.

Influence of Cavitation in Common-Rail Diesel Nozzles on the Soot Formation Process through Measuring Soot Emissions

The influence of cavitation in common-rail diesel nozzles on the soot formation process has been analysed experimentally. The soot formation process was characterized by measuring soot emissions in a single-cylinder engine, which was mounted on a test bench equipped with an opacimeter. In order to do this, operating conditions where the soot oxidation process was equivalent were chosen, whereby differences in the soot formation process were possible to be analysed. The results achieved confirm that cavitation provokes a soot formation process reduction. This reduction can be attributed by combining results of three effects: a reduction of the effective diameter, an increase in effective injection velocity, and an increase in turbulence level inside the nozzle orifice leading to a longer lift-off length. The three effects lead to a decrease in relative fuel/air ratio at the lift-off, therefore explaining the soot formation reduction.

Correlation Between Anterior–Posterior and Lateral Dimensions with the Effective and Water-Equivalent Diameters in Axial Images From Head Computed Tomography Examinations

The study aims to correlate the effective diameter (Deff) and water-equivalent diameter (Dw) parameters with anterior–posterior (AP), lateral (LAT) and AP + LAT dimensions in order to estimate the patient dose in head CT examinations. Seventy-four patient datasets from head CT examinations were retrospectively collected. The patient’s sizes were calculated from the middle slice using a software of IndoseCT. Dw and Deff were plotted as functions of AP, LAT and AP + LAT dimensions. The best trendline fit for LAT and AP functions was a second order polynomial, which resulted in R2 of 0.89 for Deff vs LAT, 0.88 for Dw vs LAT, 0.92 for Deff vs AP and 0.91 for Dw vs AP. A linear correlation was found for Deff vs AP + LAT, Dw vs AP + LAT and Dw vs Deff with R2 of 0.97, 0.96 and 0.98, respectively.

Prediction for cloud spacing confirmed using stereo cameras

Using three years of the Clouds Optically Gridded by Stereo (COGS) product, the mean cloud base, cloud top, cloud width, and cloud spacing are described with respect to their seasonal and/or diurnal evolution at the Atmospheric Radiation Measurement (ARM) Southern Great Plains (SGP) site. In addition to confirming and extending prior results, the data show that the effective diameter of shallow cumuli are approximately equal to the height above ground of the lifting condensation level (LCL). Furthermore, the cloud spacing is found to closely match a prediction by Thuburn and Efstathiou for the horizontal scale of the largest unstable eddies in an unsheared convective boundary layer.