Rough Topography Research Articles

Plant species diversity and composition in limestone forests of the Vietnamese Cat Ba National Park

Plant species diversity and composition play crucial roles in many ecosystem services and are largely influenced by environmental conditions, as well as natural and/or anthropogenic disturbances. However, our knowledge of the drivers of plant species diversity and composition in the limestone forests of Vietnam, a hotspot of biodiversity, is limited. To fill this knowledge gap, we surveyed plant species in the Cat Ba National Park (CBNP), located on a limestone archipelago. We hypothesised that: (1) topography, accessibility and spatial isolation drive the diversity and composition of plant communities in the CBNP and that (2) isolated areas contribute to high floristic regional diversity by supporting unique species assemblages. We expected high tree species diversity within the tropical limestone forests of the CBNP, but also that: (3) the abundance of non-tree species negatively affects tree regeneration diversity and abundance. Data were obtained from 90 random sample plots (500 m2) and 450 sub-sample plots (25 m2) in three areas of the CBNP. We differentiated four different plant species communities and found a total of 302 species belonging to 112 families. Tree species contributed 50% to total species richness. The distribution of different plant communities in the CBNP was driven mainly by topography; that is, the percentage of rock surface and slope and concomitant differences in soil depth. Contrary to our expectations, isolated areas did not contribute greatly to the CBNP’s plant species diversity. It seems that isolated areas and, as in our case, rough topography, may act as natural barriers to seed dispersal, creating an environmental filter for tree species. Across the CBNP, there was no effect of non-tree species on tree species regeneration, but regeneration patterns differed between communities. In species-rich communities growing under favourable site conditions (e.g. low rock surface and slope), greater coverage by non-tree species had an increasingly negative effect on tree species richness and abundance in the regeneration layer. The opposite was observed in communities growing under harsh site conditions. We conclude that plant species diversity in the CBNP is high, particularly in easily accessible lowland areas where tree species contribute greatly to biodiversity. However, here, non-tree species can even restrict tree regeneration.

Spectral element method for 3-D controlled-source electromagnetic forward modelling using unstructured hexahedral meshes

SUMMARYFor forward modelling of realistic 3-D land-based controlled-source electromagnetic (EM) problems, we develop a parallel spectral element approach, blending the flexibility and versatility of the finite element method in using unstructured grids with the accuracy of the spectral method. Complex-shaped structures and topography are accommodated by using unstructured hexahedral meshes, in which the elements can have curved edges and non-planar faces. Our code is the first spectral element algorithm in EM geophysics that uses the total field formulation (here that of the electric field). Combining unstructured grids and a total field formulation provides advantages in dealing with topography, in particular, when the transmitter is located on rough surface topography. As a further improvement over existing spectral element methods, our approach does not only allow for arbitrary distributions of conductivity, but also of magnetic permeability and dielectric permittivity. The total electric field on the elements is expanded in terms of high-order Lagrangian interpolants, and element-wise integration in the weak form of the boundary value problem is accomplished by Gauss–Legendre–Lobatto quadrature. The resulting complex-valued linear system of equations is solved using the direct solver MUMPS, and, subsequently, the magnetic field is computed at the points of interest by Faraday’s law. Five numerical examples comprehensively study the benefits of this algorithm. Comparisons to semi-analytical and finite element results confirm accurate representation of the EM responses and indicate low dependency on mesh discretization for the spectral element method. A convergence study illuminates the relation between high order polynomial approximation and mesh size and their effects on accuracy and computational cost revealing that high-order approximation yields accurate modelling results for very coarse meshes but is accompanied by high computational cost. The presented numerical experiments give evidence that 2nd and 3rd degree polynomials in combination with moderately discretized meshes provide better trade-offs in terms of computational resources and accuracy than lowest and higher order spectral element methods. To our knowledge, our final example that includes pronounced surface topography and two geometrically complicated conductive anomalies represents the first successful attempt at using 2nd order hexahedral elements supporting curved edges and non-planar faces in controlled-source EM geophysics.

Precisely controlling the surface roughness of silica nanoparticles for enhanced functionalities and applications

HypothesisColloids with rough topography demonstrate more complex interactions and tremendous potential in industrial applications. However, relevant studies suffer from a range of challenges, including cumbersome synthesis, complex characterization, and very limited functionalities. A comprehensive study of rough nanoparticles can not only broaden our understanding of rough colloids, but also help to avoid some of their detrimental impacts in real life (e.g., clogging and pumping failures in slurry processing). ExperimentsA facile route to precisely control the surface roughness of silica nanoparticles and a highly efficient method to characterize the surface roughness were developed respectively. The fabricated particles can be applied for the immobilization of metal nanostructures; their cytotoxic effects and the capability to be used as a drug-delivery vehicle were also evaluated. FindingsModifying the addition time of precursors (i.e., TEOS and MPTMS) can precisely control the surface roughness of silica nanoparticles. The developed characterization method based on TEM observations allows statistical analyses on a large number of particles, and therefore features very reasonable accuracy. These rough particles behave like microporous materials, where the loading strategy is closely related to their surface roughness. Medium rough particles are promising carriers of metal nanostructures, while the roughest ones are excellent candidate for doxorubicin delivery to cancer cells.

Extracting multiple surfaces from 3D microscopy images in complex biological tissues with the Zellige software tool

BackgroundEfficient tools allowing the extraction of 2D surfaces from 3D-microscopy data are essential for studies aiming to decipher the complex cellular choreography through which epithelium morphogenesis takes place during development. Most existing methods allow for the extraction of a single and smooth manifold of sufficiently high signal intensity and contrast, and usually fail when the surface of interest has a rough topography or when its localization is hampered by other surrounding structures of higher contrast. Multiple surface segmentation entails laborious manual annotations of the various surfaces separately.ResultsAs automating this task is critical in studies involving tissue-tissue or tissue-matrix interaction, we developed the Zellige software, which allows the extraction of a non-prescribed number of surfaces of varying inclination, contrast, and texture from a 3D image. The tool requires the adjustment of a small set of control parameters, for which we provide an intuitive interface implemented as a Fiji plugin.ConclusionsAs a proof of principle of the versatility of Zellige, we demonstrate its performance and robustness on synthetic images and on four different types of biological samples, covering a wide range of biological contexts.

Diapycnal displacement, diffusion, and distortion of tracers in the ocean

Abstract Small-scale mixing drives the diabatic upwelling that closes the abyssal ocean overturning circulation. Indirect microstructure measurements of in-situ turbulence suggest that mixing is bottom-enhanced over rough topography, implying downwelling in the interior and stronger upwelling in a sloping bottom boundary layer. Tracer Release Experiments (TREs), in which inert tracers are purposefully released and their dispersion is surveyed over time, have been used to independently infer turbulent diffusivities—but typically provide estimates in excess of microstructure ones. In an attempt to reconcile these differences, Ruan and Ferrari (2021) derived exact tracer-weighted buoyancy moment diagnostics, which we here apply to quasi-realistic simulations. A tracer’s diapycnal displacement rate is exactly twice the tracer-averaged buoyancy velocity, itself a convolution of an asymmetric upwelling/downwelling dipole. The tracer’s diapycnal spreading rate, however, involves both the expected positive contribution from the tracer-averaged in-situ diffusion as well as an additional non-linear diapycnal distortion term, which is caused by correlations between buoyancy and the buoyancy velocity, and can be of either sign. Distortion is generally positive (stretching) due to bottom-enhanced mixing in the stratified interior but negative (contraction) near the bottom. Our simulations suggest that these two effects coincidentally cancel for the Brazil Basin Tracer Release Experiment, resulting in negligible net distortion. By contrast, near-bottom tracers experience leading-order distortion that varies in time. Errors in tracer moments due to realistically sparse sampling are generally small (< 20%), especially compared to the O(1) structural errors due to the omission of distortion effects in inverse models. These results suggest that TREs, although indispensable, should not be treated as “unambiguous” constraints on diapycnal mixing.

Spatial heterogeneity in boundary layer dynamism and PM2.5 surface concentration over the complex terrain of Brahmaputra valley

Despite its importance, comprehensive investigation of the variation of particulate matter ≤2.5 μm (PM2.5), Aerosol Optical Depth at 550 nm (AOD 550 nm) and Planetary Boundary Layer Height (PBLH) for diurnal, seasonal and valley scales is virtually non-existent in the Brahmaputra Valley (BV). PBLH data obtained from MERRA-2 and ERA5 ECMWF were validated with reference to collocated radiosonde PBLH estimates of the Dibrugarh station in BV. MERRA-2 PBLH showed good agreement with radiosonde PBLH estimates with R2 = 0.48 and RMSE = 1.08 m. Remarkable diurnal synergism between PBLH and PM2.5 was demonstrated; deep daytime PBLH (1199–2100 m) coincident with lowered PM2.5 concentration (12.39–93.06 μg/m3); while shallow night-time PBLH (328–1233 m) co-existed with heightened PM2.5 concentration (46–142 μg/m3). Pre-monsoon PBLH was deepest (1414.07 m–939.40 m), declined in the monsoon (817 m–487 m) and post-monsoon (818 m–622 m), and increased in winter (1180 m–588 m). Turbulence and valley wind breezes generated in the PBLH, are effective in reducing PM2.5 surface concentration. Changes in spatial and seasonal PBLH reflected changes in PM2.5 and AOD 550 nm. Further, results of PBLH-PM2.5 relationship revealed an unusual weak to strong positive pan-seasonal correlation (r = 0.52 to 0.91). The rough eastern BV topography evinced a relatively strong correlation than western and central parts. To our best knowledge, this is the first report on diurnal and seasonal variability of PBLH, AOD 550 nm and PM2.5-PBLH relationship at the valley-site scale for BV.

The use of gravity data to determine orthometric heights at the Hong Kong territories

Abstract The Hong Kong Principal Datum (HKPD) is the currently adopted official geodetic vertical datum at the Hong Kong territories. The HKPD is practically realized by heights of levelling benchmarks. The HKPD heights are, however, neither normal nor orthometric. The reason is that heights of levelling benchmarks were determined from precise levelling measurements, but without involving gravity observations along levelling lines. To reduce systematic errors due to disregarding the gravity information along levelling lines, we used terrestrial and marine gravity data to interpolate gravity values at levelling benchmarks in order to compute and apply the orthometric correction to measured levelling height differences. Our results demonstrate the importance of incorporating the gravity information even for a relatively small region but characterized by a rough topography with heights of levelling benchmarks exceeding several hundreds of meters. According to our estimates, the orthometric correction reaches (and even slightly exceeds) ±2 cm, with maxima along levelling lines crossing mountain chains.

Turbulent Mixing Variability in an Energetic Standing Meander of the Southern Ocean

Abstract This study presents novel observational estimates of turbulent dissipation and mixing in a standing meander between the Southeast Indian Ridge and the Macquarie Ridge in the Southern Ocean. By applying a finescale parameterization on the temperature, salinity, and velocity profiles collected from Electromagnetic Autonomous Profiling Explorer (EM-APEX) floats in the upper 1600 m, we estimated the intensity and spatial distribution of dissipation rate and diapycnal mixing along the float tracks and investigated the sources. The indirect estimates indicate strong spatial and temporal variability of turbulent mixing varying from O(10−6) to O(10−3) m2 s−1 in the upper 1600 m. Elevated turbulent mixing is mostly associated with the Subantarctic Front (SAF) and mesoscale eddies. In the upper 500 m, enhanced mixing is associated with downward-propagating wind-generated near-inertial waves as well as the interaction between cyclonic eddies and upward-propagating internal waves. In the study region, the local topography does not play a role in turbulent mixing in the upper part of the water column, which has similar values in profiles over rough and smooth topography. However, both remotely generated internal tides and lee waves could contribute to the upward-propagating energy. Our results point strongly to the generation of turbulent mixing through the interaction of internal waves and the intense mesoscale eddy field.

Lanthanum doped octacalcium phosphate/polylactic acid scaffold fabricated by 3D printing for bone tissue engineering

Lanthanum (La) has tremendous potential in the treatment and prevention of bone diseases especially osteoporosis and metabolic disorders. However, controlling its distribution and keeping the release of La3+ ions sustained and steady in the body is still a big challenge. In this study, we prepared La-OCP powders via co-precipitation method, and further prepared La-OCP/PLA porous scaffolds by 3D printing. La3+ was successfully introduced into the OCP crystal structure and substituted Ca2+ at the Ca-5 and Ca-8 sites. In particular, some La3+ ions were deposited on the crystal surface in the form of nanoparticles. Both octacalcium phosphate (OCP, Ca8H2(PO4)6·5H2O) crystals and nanoparticles played as the carriers for La3+ ions. The La-OCP/PLA scaffolds displayed obvious mineralization effects and sustained release of La3+. The scaffolds contained a uniform structure with rough micro surface topography which acted as a suitable pathway for BMSCs cells to adhere, grow and proliferation. At a certain La3+ concentration, the extracts from La-OCP/PLA scaffolds increased the expression of osteogenesis-related genes, thus promoting the osteogenic differentiation of BMSCs. Moreover, the extracts regulated the immune responses. The experiment in vivo proved that La-OCP/PLA porous scaffolds were safe and could enhance bone defect regeneration in vivo. These findings suggest that 3D printed La-OCP/PLA porous scaffolds have promising potentials in bone tissue engineering.

3D printed zirconia dental implants with integrated directional surface pores combine mechanical strength with favorable osteoblast response

Dental implants need to combine mechanical strength with promoted osseointegration. Currently used subtractive manufacturing techniques require a multi-step process to obtain a rough surface topography that stimulates osseointegration. Advantageously, additive manufacturing (AM) enables direct implant shaping with unique geometries and surface topographies. In this study, zirconia implants with integrated lamellar surface topography were additively manufactured by nano-particle ink-jetting. The ISO-14801 fracture load of as-sintered implants (516±39 N) resisted fatigue in 5–55 °C water thermo-cycling (631±134 N). Remarkably, simultaneous mechanical fatigue and hydrothermal aging at 90 °C significantly increased the implant strength to 909±280 N due to compressive stress generated at the seamless transition of the 30–40 µm thick, rough and porous surface layer to the dense implant core. This unique surface structure induced an elongated osteoblast morphology with uniform cell orientation and allowed for osteoblast proliferation, long-term attachment and matrix mineralization. In conclusion, the developed AM zirconia implants not only provided high long-term mechanical resistance thanks to the dense core along with compressive stress induced at the transition zone, but also generated a favorable osteoblast response owing to the integrated directional surface pores. Statement of significanceZirconia ceramics are becoming the material of choice for metal-free dental implants, however significant efforts are required to obtain a rough/porous surface for enhanced osseointegration, along with the risk of surface delamination and/or microstructure variation. In this study, we addressed the challenge by additively manufacturing implants that seamlessly combine dense core with a porous surface layer. For the first time, a unique surface with a directional lamellar pore morphology was additively obtained. This AM implant also provided strength as strong as conventionally manufactured zirconia implants before and after long-term fatigue. Favorable osteoblast response was proved by in-vitro cell investigation. This work demonstrated the opportunity to AM fabricate novel ceramic implants that can simultaneously meet the mechanical and biological functionality requirements.

Nonequilibrium plastic roughening of metallic glasses yields self-affine topographies with strain-rate and temperature-dependent scaling exponents

We study nonequilibrium roughening during compressive plastic flow of initially flat Cu$_{50}$Zr$_{50}$ metallic glass using large-scale molecular dynamics simulations. Roughness emerges at atomically flat interfaces beyond the yield point of the glass. A self-affine rough topography is imprinted at yield and is reinforced during subsequent deformation. The imprinted topographies have Hurst exponents that decrease with increasing strain-rate and temperature. After yield, the root-mean-square roughness amplitude grows as the square-root of the applied strain with a prefactor that also drops with increasing strain-rate and temperature. Our calculations reveal the emergence of spatial power-law correlations from homogeneous samples during plastic flow with exponents that depend on the rate of deformation and the temperature. The results have implications for interpreting and engineering roughness profiles.

Dynamics of eddying abyssal mixing layers over sloping rough topography

Abstract ABSTRACT: The abyssal overturning circulation is thought to be primarily driven by small-scale turbulent mixing. Diagnosed watermass transformations are dominated by rough topography “hotspots”, where the bottom-enhancement of mixing causes the diffusive buoyancy flux to diverge, driving widespread downwelling in the interior—only to be overwhelmed by an even stronger up-welling in a thin Bottom Boundary Layer (BBL). These watermass transformations are significantly underestimated by one-dimensional (1D) sloping boundary layer solutions, suggesting the importance of three-dimensional physics. Here, we use a hierarchy of models to generalize this 1D boundary layer approach to three-dimensional eddying flows over realistically rough topography. When applied to the Mid-Atlantic Ridge in the Brazil Basin, the idealized simulation results are roughly consistent with available observations. Integral buoyancy budgets isolate the physical processes that contribute to realistically strong BBL upwelling. The downwards diffusion of buoyancy is primarily balanced by upwelling along the sloping canyon sidewalls and the surrounding abyssal hills. These flows are strengthened by the restratifying effects of submesoscale baroclinic eddies and by the blocking of along-ridge thermal wind within the canyon. Major topographic sills block along-thalweg flows from restratifying the canyon trough, resulting in the continual erosion of the trough’s stratification. We propose simple modifications to the 1D boundary layer model which approximate each of these three-dimensional effects. These results provide local dynamical insights into mixing-driven abyssal overturning, but a complete theory will also require the non-local coupling to the basin-scale circulation.

Interaction of rough ellipsoidal particles with random surface asperities in colloidal systems

Currently, information on the interaction of ellipsoidal particles with rough topography is limited. In this work, a mathematical model was developed based on the extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory and surface element integral (SEI) to simulate the total interaction energy created between ellipsoidal particles with rough surfaces, which were constructed by the modified two-variable Weierstrass-Mandelbrot (WM) function. The simulated results revealed that an increase in the fractal roughness and relative fractal roughness of particle surface would increase the surface roughness of particles and weaken the total interaction energy between ellipsoidal particles. Compared with spherical shape particles, the ellipsoidal particles provided greater interaction energy because an ellipsoidal shape would generate a greater interaction area than a spherical shape between particles. Amplifying the aspect ratio diminished the interaction energy between particles but enlarging particles would strengthen the interaction energy. In addition, the orientation angle of ellipsoidal particles would affect their interaction.

Hikurangi megathrust slip behavior influenced by lateral variability in sediment subduction

AbstractSubduction megathrusts exhibit a range of slip behaviors spanning from large earthquakes to aseismic creep, yet what controls spatial variations in the dominant slip mechanism remains unresolved. We present multichannel seismic images that reveal a correlation between the lithologic homogeneity of the megathrust and its slip behavior at a subduction zone that is world renowned for its lateral slip behavior transition, the Hikurangi margin. Where the megathrust exhibits shallow slow-slip in the central Hikurangi margin, the protolith of the megathrust changes ~10 km downdip of the deformation front, transitioning from pelagic carbonates to compositionally heterogeneous volcaniclastics. At the locked southern Hikurangi segment, the megathrust forms consistently within pelagic carbonates above thickened nonvolcanic siliciclastic sediments (unit MES), which subduct beyond 75 km horizontally. The presence of the MES layer plays a key role in smoothing over rough volcanic topography and establishing a uniform spatial distribution of lithologies and frictional properties that may enable large earthquake ruptures.

Mixing in the Philippine Sea: Geography variability and parameterization

The Philippine Sea Mixing Experiment (PhiMix) was carried out in 2021 concurrently from two research vessels, obtaining microstructure measurements and fine structure-based estimates of turbulence and diffusivity covering nearly the whole Philippine basin for the first time. The inhomogeneous spatial distribution and weak magnitudes of turbulent mixing in the Philippine Sea basin were revealed, according to the upper-ocean turbulence measurements and full-depth CTD datasets. The averaged diffusivities in the Philippine Basin were ∼10−2 m2s−1 in the surface mixed layer and ∼10−5.5 m2s−1 in the ocean interior. Below the thermocline, the diffusivities generally increased and reached 10−4 m2s−1 above rough topography. Centered on the Palau Ridge, a significant east-west asymmetry was noted, with stronger mixing on the east side of the ridge. Additionally, the diapycnal diffusivity's spatial variability coincided with that inferred from tidal mixing between 500 and 3000 m. Typical dissipation rate and diapycnal diffusivity profiles in the Philippine Sea differed from the global averaged profiles, which form the basis of most existing mixing parameterizations. Here we proposed an improved parameterization scheme based on these new direct microstructure observations in the Philippine Sea. The new mixing parameterization scheme (PhiMixPar-PMP) performed well for the Northwest Pacific Ocean in ocean simulations. This regional study on mixing properties in the Philippine Sea can fill a knowledge gap in the big picture of global mixing geography and improve turbulence parameterizations in the ocean models.

Diurnal Coastal Trapped Waves and Associated Deep‐Ocean Mixing Near the Head of Suruga Trough

AbstractCoastal submarine canyons are expected to be sites of enhanced turbulent mixing which create productive fishing areas in coastal waters. Recent studies suggested the potential role of diurnal coastal trapped waves (CTWs) in inducing significant turbulent mixing in coastal submarine canyons poleward of 30° where the diurnal tide becomes subinertial. Nevertheless, the detailed physical processes responsible for the generation and dissipation of CTWs in such submarine canyons have hardly been investigated so far. In the present study, to investigate the turbulent mixing processes associated with diurnal CTWs in submarine canyons, we carry out high‐resolution (Δx, Δy = 1/240°) non‐hydrostatic three‐dimensional numerical experiments focusing on Suruga Bay located at the north end of Suruga Trough, Japan. The numerical experiments show that diurnal (subinertial) tidal currents over the Izu Ridge generate CTWs which propagate cyclonically along the coast of Suruga Bay. In the middle of Suruga Bay, bottom‐intensified flow due to the diurnal CTWs interacts with rough seafloor topography to excite upward propagating internal lee waves, which create mixing hotspots extending high above the seafloor. The resulting diurnal (subinertial) tidal energy dissipation in Suruga Bay is found to be much larger than that associated with semidiurnal (superinertial) internal tides. Furthermore, it is found that baroclinic energy flux based on a simple barotropic‐baroclinic decomposition severely underestimates the wave energy flux in areas with high CTW activity. These results strongly indicate that the existence of CTWs might be a key factor to clarify the dissipation/mixing processes in submarine canyons.

Updated parameterization of internal tidal mixing in the deep ocean based on laboratory rotating tank experiments

The Coriolis effect plays an important role in the generation and dissipation of internal tides. In this study, the effects of the Coriolis parameter on internal tides generated by tidal current flowing over rough subsurface topography were investigated in the laboratory. The results show that the variation in the internal tidal local dissipation rate with variation in the Coriolis parameter in the deep layer follows a Gaussian distribution. The strongest dissipation occurs near the critical latitude where the local Coriolis parameter is half of the tidal frequency. A modified internal tidal mixing parameterization was developed by introducing a correction function related to the Coriolis effect on internal tidal local dissipation in the deep ocean, based on the original version developed by St. Laurent et al. (2002). The new parameterization was then implemented in a parallel ocean model. The results indicate that the deep global meridional overturning circulation (GMOC) is strengthened in the low and middle latitudes and the Southern Ocean by the change, compared with the original parameterization.

Development of an antibiotics delivery system for topical treatment of the neglected tropical disease Buruli ulcer

Skin infection by Mycobacterium ulcerans causes Buruli ulcer (BU) disease, a serious condition that significantly impact patient’ health and quality of life and can be very difficult to treat. Treatment of BU is based on daily systemic administration of antibiotics for at least 8 weeks and presents drawbacks associated with the mode and duration of drug administration and potential side effects. Thus, new therapeutic strategies are needed to improve the efficacy and modality of BU therapeutics, resulting in a more convenient and safer antibiotic regimen. Hence, we developed a dual delivery system based on poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV) microparticles and a gellan gum (GG) hydrogel for delivery of rifampicin (RIF) and streptomycin (STR), two antibiotics used for BU treatment. RIF was successfully loaded into PHBV microparticles, with an encapsulation efficiency of 43%, that also revealed a mean size of 10 µm, spherical form and rough topography. These microparticles were further embedded in a GG hydrogel containing STR. The resultant hydrogel showed a porous microstructure that conferred a high water retention capability (superior to 2000%) and a controlled release of both antibiotics. Also, biological studies revealed antibacterial activity against M. ulcerans, and a good cytocompatibility in a fibroblast cell line. Thus, the proposed drug delivery system can constitute a potential topical approach for treatment of skin ulcers caused by BU disease.

Superhydrophobic Modification of Biomass Cuttlebone Applied to Oil Spill Remediation.

The spills of crude oil and other organic chemicals are common around the world, resulting in severe damage to the environment and ecosystem. Therefore, developing low-cost and eco-friendly absorption material is in urgent need. In this study, we report a superhydrophobic and oleophilic porous material using biomass cuttlebone as the scaffold. A layer of polydopamine is grafted on the cuttlebone as the adhesion layer between the cuttlebone and the superhydrophobic coating. The in situ grown silica micro/nanoparticles on top of the adhesion layer provide the anchoring spots for grafting the fluorinated hydrocarbon and a rough topography for realizing superhydrophobicity. The static water contact angle of the superhydrophobic cuttlebone reaches 152°, and its oil contact angle is ~0°. The excellent oil–water separation efficiency of the prepared superhydrophobic cuttlebone is demonstrated using high-density oil/water mixtures and low-density oil/water mixtures.

Energetics and Mixing of Stratified, Rotating Flow over Abyssal Hills

Abstract One of the proposed mechanisms for energy loss in the ocean is through dissipation of internal waves, in particular above rough topography where internal lee waves are generated. Rates of dissipation and diapycnal mixing are often estimated using linear internal wave generation theory and a constant value for mixing efficiency. However, previous oceanographic measurements found that nonlinear dynamics may be important close to topography. To investigate the role of nonlinear interactions, we conduct idealized 3D direct numerical simulations (DNS) of steady flow over 1D topography and vary the topographic height, which correlates to the degree of flow nonlinearity. We analyze the spatial distribution of energy transfer rates between internal waves and the nongeostrophic portion of the time-mean flow, and of dissipation and diapycnal mixing rates. In our simulations with taller, more nonlinear topographies, energy transfer rates are similar to previously unexplained oceanographic observations near topography: internal waves gain energy from time-mean flow through horizontal straining and lose energy through vertical shearing. In the tall topography simulations, buoyancy fluxes also play a significant role, consistent with observations but contrary to linear wave theory, suggesting that quasigeostrophy-based approximations and linear theory may not hold in some regions above rough topography. Both dissipation and mixing rates increase with topographic height, but their vertical distributions differ between topographic regimes. As such, the vertical profile of mixing efficiency is different for linear and nonlinear topographic regimes, which may need to be incorporated into parameterizations of small-scale processes in models and estimates of ocean energy loss.