Depth Of Surface Layer Research Articles

Zooplankton-Mediated Fluxes in the Eastern Tropical North Atlantic

Zooplankton organisms are a central part of pelagic ecosystems. They feed on all kinds of particulate matter and their egested fecal pellets contribute substantially to the passive sinking flux to depth. Some zooplankton species also conduct diel vertical migrations (DVMs) between the surface layer (where they feed at nighttime) and midwater depth (where they hide at daytime from predation). These DVMs cause the active export of organic and inorganic matter from the surface layer as zooplankton organisms excrete, defecate, respire, die and are preyed upon at depth. In the Eastern Tropical North Atlantic (ETNA), the daytime distribution depth of many migrators (300-600 m) coincides with an expanding and intensifying oxygen minimum zone (OMZ). We here assess the day and night-time biomass distribution of mesozooplankton with an equivalent spherical diameter of 0.39 to 20 mm in three regions of the ETNA, calculate the DVM-mediated fluxes and compare these to particulate matter fluxes and other biogeochemical processes. Integrated mesozooplankton biomass in the ETNA region is about twice as high at a central OMZ location (cOMZ; 11\si{\degree} N, 21\si{\degree} W) compared to the Cape Verde Ocean Observatory (CVOO; 17.6\si{\degree} N, 24.3\si{\degree} W) and an oligotrophic location at 5\si{\degree} N, 23\si{\degree} W (5N). At cOMZ, an in comparison to the other regions particularly strong Intermediate Particle Maximum (IPM) is found, which seems to be related to DVM activity. Zooplankton DVM is responsible for about 29 to 42\% of nitrogen loss from the upper 200m of the water column. Gut flux and mortality make up about \ivall{Perc_DVM_O2_flux_into_OMZ-cOMZ}\% of particulate matter supply to the 300 to 600 m depth layer at cOMZ, whereas it makes up about \ivall{Perc_DVM_O2_flux_into_OMZ-CVOO}\% and \ivall{Perc_DVM_O2_flux_into_OMZ-5N}\% at CVOO and 5N, respectively. Resident and migrant zooplankton are responsible for about 6 to 23\% of the total oxygen demand at 300 to 600 m depth. Changes in zooplankton abundance and migration behavior due to decreasing oxygen levels at midwater depth could therefore alter the elemental cycling of oxygen and carbon in the ETNA OMZ and impact the removal of nitrogen from the surface layer.

CFD-Based Metamodeling of the Propagation Distribution of Styrene Spilled from a Ship

The present study aimed to numerically establish a new metamodel for predicting the propagation distribution of styrene, which is one of the hazardous and noxious substances (HNSs) spilled from ships. Three-dimensional computational fluid dynamics (CFD) simulations were conducted for 80 different scenarios to gather large amounts of data on the spatial distribution of the change in concentration over time. We used the commercial code of ANSYS Fluent (V.17.2) to solve the Reynolds-averaged Navier–Stokes equations, together with the scalar transport equation. Based on the CFD results, we adopted the well-known kriging model to create a metamodel that estimated the propagation velocity and spatial distributions by considering the effect of the current surface velocity, deep current velocity, surface layer depth, and crack position. The results show that the metamodel accurately predicted the changes in the local distribution of styrene over time. This model was also evaluated using the hidden-point test.

Laser hardening of metallic materials

The surface microstructure of metallic materials formed under the effect of laser radiation is characterized by high degree of nonequilibrium, has layered structure consisting of the main three zones formed from the fused material, the heat-affected zone and the tempering zone. As the laser radiation energy increases, the size of the modified layer increases, and the coverage width of the melting zone and heat-affected zone is determined by the maximum penetration depth of the melting and polymorphic transformation isotherms. The distribution of microhardness over the depth depending on the laser radiation energy is exponential or extreme, and the microhardness is usually maximum in the heat-affected zone. As the laser energy increases, the microhardness of the hardened surfaces changes with extreme dependence. Laser hardening of metallic materials is the result of two competing hardening and softening processes. As result of mathematical processing of experimental results, empirical equations for the distribution of microhardness over the depth of laser-hardened surface layers of various steels and ARMCO-iron are obtained. Empirical equations consist of two terms, the first of which describes the processes of hardening, and the second — softening. The obtained equations allow optimizing the laser hardening modes and predicting the hardened layer depth.

Determination of The Site Amplification on Deep Soil Layer Using 1-D Site Response Analysis (Case study: Jakarta City, Indonesia)

The dynamic response of deep soil layers is used in the development of microzonation maps. The empirical correlation between standard penetratation blow count numbers and S-wave velocity was derived for practical purposes in site characterization based on local data in a case study in Jakarta, Indonesia. For estimating the intensity of potential earthquake shaking at the ground surface as a function of depth to the bedrock surface layer, 1-D site response analysis was carried out in 5745 simulations. The site amplification values were then evaluated by dividing the spectral acceleration (SA) at ground surface by the SA at rock outcrop. Plots of the SA amplification values at interested depth intervals of the bedrock surface layer were assigned. The results showed that the site amplification values estimated by considering the local depth of the bedrock surface layer were generally smaller than the SA amplification values from the Indonesian seismic building code SNI-1726-2012. Also, there appears to exist a tendency of lower levels of mean regression of amplification, in particular for the soft soil site class.

Gaseous surface hardening of Ti-6Al-4V fabricated by selective laser melting

The present work investigates the response of different gaseous thermochemical treatments on selective laser melted (SLM) Ti-6Al-4V. The resulting microstructures after thermochemical treatment were investigated with X-ray diffraction, light optical microscopy, scanning electron microscopy and Vickers-microhardness indentation. Nitriding, performed at 1000–1050 °C resulted in a diffusion zone of nitrogen in solid solution and surface compound layers consisting of TiN (and Ti2N at 1000 °C). Below the compound layer Al-enrichment of the α-zone was observed. Carbo-oxidising in a CO atmosphere at 1000–1050 °C resulted in deep diffusion zones and thick compound layers of the ternary compound TiC1-xOx. Both surface hardness and layer depth were found to increase with temperature and treatment time. Chemically controlled carbo-oxidising, applying the gas redox system CO-CO2, was performed at temperatures in the range 850–1050 °C, resulting in carbo-oxides and formation of oxides with increasing Ti:O ratio with increasing temperatures (rutile and Magnéli phases). Nitriding followed by (carbo-)oxidising treatment resulted in higher surface hardness owing to the formation of mixed interstitial compounds TiC1-x-yNxOy in the compound layer. The compound layer grew into the Al-rich zone as elongated structures.The improvement of wear by nitriding, carbo-oxidising and duplex nitriding/(carbo-)oxidising on SLM Ti-6Al-4V was evaluated by dry sliding wear testing. Lowering of the wear volume by up to a factor of 450 compared to an annealed reference sample was realised. Carbo-oxidising in CO at 1000 °C offered the best wear resistance and resulted in a lowering of the friction coefficient, averaging μ = 0.22, compared to μ = 0.45 for an annealed reference sample.

Analysis of Severe Elevated Thunderstorms over Frontal Surfaces Using DCIN and DCAPE

A 10-year study of elevated severe thunderstorms was performed using The National Centers for Environmental Information Storm Events Database. A total of 80 elevated thunderstorm cases were identified, verified, and divided into “Prolific” and “Marginal” classes. These severe cases occurred at least 80 km away from, and on the cold side of, a surface boundary. The downdraft convective available potential energy (DCAPE), downdraft convective inhibition (DCIN), and their ratio are tools to help estimate the potential for a downdraft to penetrate through the depth of a stable surface layer. The hypothesis is that as the DCIN/DCAPE ratio decreases, there exists enhanced possibility of severe surface winds. Using the initial fields from the Rapid Refresh numerical weather prediction model, datasets of DCIN, DCAPE, and their ratio were created. Mann-Whitney U tests on the Prolific versus Marginal case sets were undertaken to determine if the DCAPE and DCIN values come from different populations for the two different case sets. Results show that the Prolific cases have values of DCIN closer to zero, suggesting the downdraft is able to penetrate to the surface causing severe winds. Thus, comparing DCIN and DCAPE is a viable tool in determining if downdrafts will reach the surface from elevated thunderstorms.

Enhancement of rolling contact fatigue performance of ferrite–pearlite steel with laser shock peening

The laser shock peening effect and its influence on rolling contact fatigue of ferrite–pearlite steel were investigated experimentally. Microhardness on the steel surface is increased after laser shock treatment. The depth of surface layer affected by laser shock hardening is above 1 mm. The maximum residual compressive stress generated on the specimen surface is around 1 GPa. The twin-disk test showed that laser shock-treated steel disk presents better rolling contact fatigue resistance than untreated one. Laser shock-induced strain hardening and compressive residual stress alter crack inclination angle and propagation behavior, which results in a longer fatigue life.

Formation and assessment of enamel subsurface lesions in vitro.

The present study compared two pH-cycling models designed to induce subsurface lesions (SLs) with a less demineralized surface layer on teeth, with the aim of developing new technologies for assessment of such lesions by examining the performance of confocal Raman microscopy for detection of white spot lesions (WSLs). Twelve sound premolars were exposed to two sets of model conditions (A, B) designed to induce SLs. Teeth on which white lesions had formed in vivo were used as positive controls. All specimens were inspected using an intraoral camera and Raman microscopy to detect small changes in the appearance and structure of the enamel. Changes in the natural color of the teeth during the treatment were recorded via the camera. Phosphate maps with their spectra were constructed from the phosphate peak at 960 cm-1. The depth of lesions was measured on the basis of variations in phosphate peak intensity. Protocol B was reliable for reproducing SLs in a relatively short period. Both protocols had intrinsic limitations in not completely simulating the complex intraoral conditions leading to WSL formation with respect to lesion depth and preservation of an intact surface layer. Raman microscopy can be considered the gold standard for analysis of hard tissue mineralization.

A mixing‐length‐scale‐based analytical model for predicting velocity profiles of open‐channel flows with submerged rigid vegetation

AbstractIn open‐channel flows with submerged vegetation, the vertical velocity profile can often be described by two layers: the vegetation layer in the lower region and the surface layer in the upper non‐vegetated region. In this paper, a new mixing‐length scale of eddy is proposed for predicting the vertical velocity profile of flow in an open‐channel with submerged rigid vegetation. The analytical model of velocity profile is based on the momentum equation of flow where the turbulent eddy viscosity is assumed to have a linear relationship with the local velocity. The proposed model was tested against different datasets from the literature. The 22 datasets used cover a range of submergence [flow depth (H)/vegetation height (h) = 1.25 ~ 3.38], different vegetation densities of ah = 0.11 ~ 1.85 (a defined as the frontal area of the vegetation per unit volume) and bed slopes (So = 1.8 × 10−6 ~4.0 × 10−3). This study showed that the proposed model can predict the velocity profiles well against all datasets, and that the mixing length scale of eddies (λ) is well related with both vegetation height (h) and flow depth of surface layer (i.e. the height of non‐vegetation layer, H–h). Close examination of λ in the proposed model showed that when λ = 0.03, the model predicts vertical velocity profiles well for all datasets used except for very shallow submergence (i.e. H/h < 1.5).

Seiche modes in multi‐armed lakes

AbstractThe effect of multiple arms on standing wave patterns, or seiches, present within a lake is not easy to predict. This study examines free seiche modes in fjord‐type multi‐armed lakes in order to generalize features of the response of those lakes. To do so, the study develops a simplified analytical model that predicts modal frequencies and associated mode‐shapes based on idealized lake geometries. The model demonstrates that multi‐armed lakes are subject to two different types of behavior: a full‐lake response, in which all arms are active for all modes; and a decoupled response, in which seiching is constrained to only two arms of the lake for each mode. Which of the two behaviors is expressed depends on relative values of the travel time of a progressive shallow‐water wave in each arm. In general, a decoupled response will exist if the mode‐shape along a two‐armed extent of the lake contains a node exactly at the confluence point between those two arms. We show that the period and associated mode‐shape structure of the fundamental mode in multi‐armed lakes conforms to that of a simple elongated lake as predicted by Merian's formula, but higher modes are highly impacted by lake geometry. Depth and width variation within the arms can lead to localization of mode‐shapes, but this effect is distinct from the possible decoupled behavior. In some instances, it may be possible to apply the model to baroclinic modes which would then act as having a constant bottom depth equal to the surface layer depth.

Multilevel Tower Observations of Vertical Eddy Diffusivity and Mixing Length in the Tropical Cyclone Boundary Layer during Landfalls

Abstract This study analyzes the fast-response (20 Hz) wind data collected by a multilevel tower during the landfalls of Tropical Storm Lionrock (1006), Typhoon Fanapi (1011), and Typhoon Megi (1015) in 2010. Turbulent momentum fluxes are calculated using the standard eddy-correlation method. Vertical eddy diffusivity Km and mixing length are estimated using the directly measured momentum fluxes and mean-wind profiles. It is found that the momentum flux increases with wind speed at all four levels. The eddy diffusivity calculated using the direct-flux method is compared to that using a theoretical method in which the vertical eddy diffusivity is formulated as a linear function of the friction velocity and height. It is found that below ~60 m, Km can be approximately parameterized using this theoretical method, though this method overestimates Km for higher altitude, indicating that the surface-layer depth is close to 60 m in the tropical cyclones studied here. It is also found that Km at each level varies with wind direction during landfalls: Km estimated based on observations with landward fetch is significantly larger than that estimated using data with seaward fetch. This result suggests that different parameterizations of Km should be used in the boundary layer schemes of numerical models forecasting tropical cyclones over land versus over the ocean.

Modeling optical and UV polarization of AGNs

Context. Optical observations cannot resolve the structure of active galactic nuclei (AGN), and a unified model for AGN was inferred mostly from indirect methods, such as spectroscopy and variability studies. Optical reverberation mapping allowed us to constrain the spatial dimension of the broad emission line region and thereby to measure the mass of supermassive black holes. Recently, reverberation was also applied to the polarized signal emerging from different AGN components. In principle, this should allow us to measure the spatial dimensions of the sub-parsec reprocessing media.Aim. We conduct numerical modeling of polarization reverberation and provide theoretical predictions for the polarization time lag induced by different AGN components. The model parameters are adjusted to the observational appearance of the Seyfert 1 galaxy NGC 4151.Methods. We modeled scattering-induced polarization and tested different geometries for the circumnuclear dust component. Our tests included the effects of clumpiness and different dust prescriptions. To further extend the model, we also explored the effects of additional ionized winds stretched along the polar direction, and of an equatorial scattering ring that is responsible for the polarization angle observed in pole-on AGN. The simulations were run using a time-dependent version of the STOKES code.Results. Our modeling confirms the previously found polarization characteristics as a function of the observer‘s viewing angle. When the dust adopts a flared-disk geometry, the lags reveal a clear difference between type 1 and type 2 AGN. This distinction is less clear for a torus geometry where the time lag is more sensitive to the geometry and optical depth of the inner surface layers of the funnel. The presence of a scattering equatorial ring and ionized outflows increased the recorded polarization time lags, and the polar outflows smooths out dependence on viewing angle, especially for the higher optical depth of the wind (τ = 0.3).Conclusions. Together with other AGN observables, the polarization time lag places new, independent “seismological” constraints on the inner geometry of AGN. If we conduct time-dependent spectropolarimetric observing campaigns of AGN, this method has a high potential for a census of supermassive black holes.

Расчетное прогнозирование влияния технологических условий обработки на эксплуатационные свойства деталей машин

The paper reports theoretical dependences defining a correlation of technological processing conditions (cutting modes, tool tip geometry, properties of worked and tool materials), quality parameters of a surface layer (surface roughness, degree and depth of cold work, residual stresses) and performance properties of machinery (fatigue resistance, wear-resistance, contact rigidity, press-fit connection strength) which can be used in a team-work of a designer and a technologist at simultaneous technological pre-production.

Influence of cutting edge asymmetry on grain refinement of Ti6Al4V

Asymmetrical cutting edges have been proven to influence the resulting surface layer states of machined metal parts. As machining of Ti6Al4V alloy is subject to rather high tool wear, tool geometry changes during machining can influence the resulting surface layer states like residual stresses and nanocrystalline surface layer depth. In this paper, the influence of asymmetric cutting edge microgeometries (characterized by form-factor) and different process parameters on the resulting surface layer microstructure of Ti6Al4V is investigated through face turning experiments and focused ion beam analyses. 2D-FE simulations are conducted using the software Simufact Forming, and a Johnson-Cook model with triaxiality based damage criterion. According to the known mechanisms of grain refinement, mechanical and thermal states are analyzed and related to the experimental data. Relative roundness higher than one, and form-factors smaller than one lead to severe surface layer deformation and increased recrystallization depths, with the effect of form-factor clearly dominating compared to relative roundness.

Present status of 137Cs in seawaters of the Lombok Strait and the Flores Sea at the Indonesia Through Flow (ITF) following the Fukushima accident

Due to thermocline and surface water from the western equatorial Pacific Ocean, which are transported to the Indian Ocean, Indonesian marine waters play an important role in the global ocean circulation. The objective of this study was to assess the spatial distribution of 137Cs in the Lombok Strait as part of a national monitoring program concerning the possible impacts of radionuclides released as a result of the Fukushima accident. Sampling was conducted in the Flores sea and Lombok Strait on 15 to 24 November 2013. Measurements for the Lombok strait showed that 137Cs concentrations at surface layer, thermocline layer and 1000m depth were 0.27Bqm−3; 0.42Bqm−3 and <MDA (0.01Bqm−3), respectively. The water concentration of 134Cs at all monitoring stations were under MDA (0.01Bqm−3). The results the study indicate that the radiocesium input was from global fallout.

Release of free-volume bubbles by cooperative-rearrangement regions during the deposition growth of a colloidal glass

Vapor deposition can directly produce ultrastable glasses which are similar to conventional glasses aged over thousands of years. The highly mobile surface layer is believed to accelerate the ageing process of vapor-deposited glasses, but its microscopic kinetics have not been experimentally observed. Here we study the deposition growth kinetics of a two-dimensional colloidal glass at the single-particle level using video microscopy. We observe that newly deposited particles in the surface layer (depth, d < 14 particles) relax via out-of-cage diffusions of individual particles, while particles in the deeper middle layer (14 < d ≲ 100 particles) relax via activation of cooperative-rearrangement regions. These cooperative-rearrangement regions are much larger, more anisotropic and occur more frequently than cooperative-rearrangement regions in the bulk (d ≳ 100 particles) or after deposition. Cooperative-rearrangement regions move towards the surface and released free-volume bubbles at the surface, while the particles within cooperative-rearrangement regions move towards the bulk, resulting in a more compact bulk glass.

A Study of the Effects on Transmission Loss of Modelled Water Column Variations within an Area off the East Australian Coast

The present accuracy of ocean and atmospheric models permits the description of water column features, and sea surface wind stress, at a resolution which enables employment in underwater acoustic transmission applications. In an investigation of aspects of linking modelled ocean data with range-dependent acoustic transmission models, a Parabolic Equation (PE) transmission code was used with data generated by the BLUElink suite of ocean and atmospheric models for a deep-water region off the east Australian coast for a particular summer period. A typical presence of warm and cold core eddies was observed to accompany a highly variable acoustic environment. Variations in expected range to particular levels of Transmission Loss were found to be mainly related to changes in the depth of the mixed surface layer, but also due to changes in the sound speed gradient in the thermocline. The study also made a brief consideration of the likely impact of wind speed variation over the region, and the effects of modelled ocean currents on acoustic transmission.

Wire electrical discharge machining of E110 zirconium alloy

The paper deals with the results of experimental research carried out by scanning electron microscopy (SEM) and X–ray diffraction analysis (XRD) to define, how the modes of wire electrical discharge machining (WEDM) influence on the elemental and the phase composition of E110 zirconium alloy’s surface layer.Investigation of the phase composition allowed us to determine the main α and δ phase’s distribution through the depth of zirconium surface layer, in common with phases of oxygen, copper, zirconium, and niobium specific compounds. It was also established the maximum depth of the defect level containing amorphous phase for all of WEDM modes, and proposed the grinding and polishing as potential mechanical methods of its removal.

An analytical model of a typhoon wind field based on spiral trajectory

In typhoon risk assessment and warning, a critical component is a good representation of the typhoon wind field model. In this study, a new analytical model based on the logarithmic spiral trajectory model is developed to simulate the surface wind speed distribution of a typhoon. The logarithmic spiral trajectory model could overcome the limitation of the parametric gradient wind model. A slab surface layer of constant depth is used to solving the tangential equilibrium equation, and the frictional drag at the upper boundary of the surface layer is considered correctly. Consequently, the theoretical method for determining the Holland β parameter is derived from the logarithmic spiral trajectory model. It is concluded that β increases with the surface layer depth or decreases with the radius to maximum winds. By analyzing the change in kinetic energy of the air particle, the interpretation of the relationship between β and the influencing factors is provided. The models are applied to the 17th typhoon NESAT and the 19th typhoon NALGAE of 2011. Through comparisons between the observed wind records and the simulation results, the logarithmic spiral trajectory model proposed in this study could accurately simulate the wind speeds.

Influence of volcanic activity on vegetation succession and growth environment on the hillslope of Sakurajima Volcano in southern Kyushu, Japan

This study was conducted in order to examine the influence of long-term volcanic activity on vegetative succession and growth on the slope of Sakurajima in southern Kyushu, Japan. We investigated the vegetation, depth of the volcanic ash layer, and dry density and pH of the surface soil at six places on the north-northwestern slope, 2.3–3.4 km from the Minami-dake crater, where a layer of pumice stone was deposited by the Taisho eruption in 1914. The height and diameter at breast height (DBH) of the trees increased with increasing distance from the Minami-dake crater, as did the number of individuals and species, and basal area. The Shannon–Wiener diversity index (H′) demonstrates that vegetative succession is significantly affected by distance from the Minami-dake crater, as areas farther from the crater exhibited later seral stages. Comparison of the diversity index and species number of the crater region with that of the climax forest in Kagoshima indicates that vegetative growth alone cannot advance succession in the study area, as the local vegetative community is heavily influenced by the harsh environmental conditions associated with continual exposure to long-term volcanic activity. Seral stage, ash layer depth, dry density, and pH of the soil surface layer are governed by distance from the Minami-dake crater. The results of this study indicate that conditions for vegetative growth and succession improve with increasing distance from the source of constant volcanic activity. Thus, soil development is promoted by the acidification of the soil, which decreases the dry density and pH of the soil surface layer. The introduction of plant species resistant to volcanic ash and gas is recommended to promote soil development and improve the infiltration capacity of the soil.