Ridge Depth Research Articles

Quantitative coarse graining of laminar fluid flow penetration in rough boundaries

The interaction between a fluid and a wall is described with a certain boundary condition for the fluid velocity at the wall. To understand how fluids behave near a rough wall in a completely laminar flow regime, the fluid velocity at every point on the rough surface may be provided. This approach requires detailed knowledge of, and likely depends strongly on the roughness. Another approach of modelling the boundary conditions of a rough wall is to coarse grain and extract a penetration depth over which on average the fluid penetrates into the roughness. In this work, we examine the impact of well-defined patterned surfaces on the fluid flow behaviour. We considered two extreme cases: one with horizontal ridges and another with vertical ridges on the wall and an intermediate case with ridges at an angle on the wall. We show that for a broad range of periodic roughness patterns and relative flow velocities, a universal penetration depth function can be obtained. We obtain these results with experiments and complementary numerical simulations. We evaluate how this penetration depth depends on the various roughness parameters such as ridge depth, ridge spacing and ridge angle. Our results present a novel approach to investigating wall roughness boundary conditions by considering the penetration depth δ that captures the spatially averaged behaviour of the decaying velocity profile between the asperities. We find that this penetration depth δ can be rescaled into a simple exponential master curve δ = δ∞(1 − e−kD/S) for horizontal ridges with varying depth D and spacing S. A similar variation of δ with D and S is observed for vertical ridges, but with a smaller magnitude δ∞, while for ridges at an angle, the penetration depth lies between the two extreme cases.

846 Bone Grafting as an Alternative Approach to Treating Severe Hypodontia in a Child

Abstract Background Severe hypodontia (developmental absence of teeth) can have significant functional and cosmetic impact, causing dietary restrictions, speech delay and bullying. Management in childhood is usually with removable dental prostheses, but retention and stability are often compromised by hypoplastic dento-alveolar bone ridges in the edentulous areas. Presenting problems A 3-year-old child was referred to Paediatric Dentistry with no erupted primary teeth. Radiographs revealed developmental absence of the entire primary dentition. Genetic investigation was negative for changes in genes known to be associated with hypodontia. In the permanent dentition only first molars were radiographically present. The child was struggling with bullying and self-confidence related to his dental appearance and speech. Investigations Plain films and cone beam computed tomography (CBCT) revealed agenesis of all canines and incisors in both jaws, an atrophic edentulous anterior maxilla, and soft tissue communication with the nasal fossa floor. Clinical management Despite provision of a retentive upper removable prosthesis was made impossible by a fleshy anterior maxillary ridge with severe atrophy of the dento-alveolar bone and inadequate sulcus depth. Multiple removable prostheses were fabricated, but retention and stability were poor. He was referred to maxillofacial surgery for excision of redundant fleshy tissue in the anterior maxilla and placement of corticocancellous block graft from the hip with Sonic Weld (KLS Martin) to augment and consolidate the ridge. A successfully retentive prosthesis was subsequently fabricated. Discussion This case presents an unusually invasive, but effective alternative approach to treating severe hypodontia in childhood, where hypoplastic dental ridge and sulcus depth can restrict treatment options.

Optimization of Cooling Channel Structure of Bipolar Plate for Proton Exchange Membrane Fuel Cells Based on CFD Analysis

The working temperature affects the performance of PEMFC, so a reasonable and efficient cooling channel is necessary to control the working temperature in an efficient area. In this study, the channel structure of the bipolar plate for PEMFC is analyzed using the FLUENT simulation calculation method. The influence of cell size and cooling water flow direction on cell temperature distribution is analyzed, including an examination of the channel ridge width, depth, and aspect ratio of the bipolar plate. After comparing and analyzing three ridge width sizes (0.5 mm, 1.5 mm and 2 mm) in the paper, it was found that a ridge width of 2 mm had the best heat transfer performance. And it was found that a groove depth of 0.5 mm had the best heat transfer performance when comparing three groove depth dimensions (0.5 mm, 1 mm and 1.5 mm). The aspect ratio size parameters had almost no effect on the maximum and average temperatures of the electric stacks, while the relative flow direction of cooling water had a great influence on the temperature distribution of the bipolar plate.

Engineering Refractive Index Contrast in Thin Film Barium Titanate-on-Insulator.

Barium titanate-on-insulator has demonstrated excellent vertical optical confinement, low loss, and strong electro-optic properties. To fabricate a waveguide-based device, a region of higher refractive index must be created to confine a propagating mode, one way of which is through dry etching to form a ridge. However, despite recent progress achieved in etching barium titanate and similar materials, the sidewall and surface roughness resulting from the physical etching typically used limit the achievable ridge depth. This motivates the exploration of etch-free methods to achieve the required index contrast. Here, we introduce three etch-free methods to create a refractive index contrast in barium titanate-on-insulator, including a metal diffusion method, proton beam irradiation method, and crystallinity control method. Notably, molybdenum-diffused barium titanate leads to a large index change of up to 0.17. The methods provided in this work can be further developed to fabricate various on-chip barium titanate optical waveguide-based devices.

Increase in inhibin beta A/Activin-A expression in the human epidermis and the suppression of epidermal stem/progenitor cell proliferation with aging

BackgroundAge-related thinning and reduced cell proliferation in the human epidermis are associated with the accumulation of senescent cells and decreases in the number and function of epidermal stem cells. ObjectiveThis study examined the expression of INHBA/Activin-A in human epidermis and expression differences with age, and the effect of Activin-A on epidermal stem/progenitor cells. MethodsImmunohistochemical staining was used to analyze age-related changes in the expression of INHBA/Activin-A in the epidermal tissue of young and old subjects. Epidermal INHBA/Activin-A expression levels, epidermal morphology, and the number of epidermal stem/progenitor cells or proliferating cells were investigated using older abdominal skin samples. The effects of Activin-A on the development of a three-dimensional (3D) reconstructed epidermis and cell proliferation were also assessed. ResultsINHBA/Activin-A expression levels in the human epidermis increased with age, although they varied among individuals. In the epidermis of older abdominal skin samples, INHBA/Activin-A expression levels negatively correlated with epidermal thickness, the rete ridge depth and the interdigitation index. The proportion of epidermal stem/progenitor cells and proliferating cells decreased with increases in INHBA/Activin-A expression levels. Activin-A had no effect on the differentiation of keratinocytes in the 3D-reconstructed epidermis; however, thinning of the 3D epidermis was noted. Moreover, the addition of Activin-A inhibited the proliferation of epidermal stem/progenitor cells in a concentration-dependent manner. ConclusionsAge-related increased in INHBA/Activin-A expression levels were observed in the human epidermis, and may contribute to epidermal thinning and decreases in the number of epidermal stem/progenitor cells and proliferative activity.

Controlling near-field focusing of a mesoscale binary phase plate in an optical radiation field with circular polarization

Binary Fresnel zone plates (ZP) are one of the most frequently used focusing elements of inplane optical schemes in micro- and nanophotonics. With a decrease in the diameter and focal distance of the ZP to meso-wavelength sizes, the parameters of the focusing region begin to be significantly influenced by features of the ZP design (material, thickness, relief depth). The spatial structure of the focal spot formed in the near-field is investigated by the numerical finite elements (FEM) simulations of the transmission of a plane optical wave through a mesoscale binary phase ZP. We show that there is a range of optimal etching depths of the ZP ridges and optimal thicknesses of the plate substrate, at which the best focusing of the incident optical wave is realized in terms of the maximum field intensity and the minimum size of the focal spot. In addition, a concept of a super-focusing binary phase ZP with an immersion layer in the form of a truncated cone fabricated of ZP material is proposed, which makes it possible to focus the circularly polarized light wave into a subdiffraction region with a half-width of about "lambda"/2n (n is the ZP refractive index).

Selenium and tellurium in Reykjanes Ridge and Icelandic basalts: Evidence for degassing-induced Se isotope fractionation

Selenium behaves as a chalcophile and moderately volatile element during planetary accretion and magmatic processes on Earth. Together with the geochemically similar S and Te, Se is more volatile than most other moderately volatile elements and thus potentially becomes a new tracer to constrain the mechanism of volatile depletion in the Earth’s mantle and other planetary bodies. As previously observed for several volatile elements, stable isotopes of Se are expected to fractionate upon eruptive outgassing of magmas. To understand the degassing behavior of Se and associated isotope fractionation, we report on Se and Te contents and Se isotope compositions (δ82Se) of submarine glasses across a range of distant ridge depth intervals along the Reykjanes Ridge and subglacial/subaerial basalts on Iceland (51–65°N; N = 22). Selenium (150–399 ng/g) and Te (2.61–14.5 ng/g) contents of the submarine glasses display progressive enrichment along the Reykjanes Ridge towards Iceland. This can be explained either by enhanced mantle melting towards Iceland or by enrichment of Se–Te contents in the mantle source due to the Icelandic plume–Reykjanes Ridge interaction. Both scenarios are equally plausible. The δ82Se values of submarine Reykjanes Ridge glasses range between −0.20 ± 0.08‰ and −0.08 ± 0.08‰ (on average −0.15 ± 0.07‰; 2SD, N = 15), which are unaffected by the Icelandic plume contribution and remain strictly within the previously reported average for depleted MORBs. These new data combined with literature δ82Se for depleted MORBs define a highly homogeneous depleted mantle composition δ82Se = −0.15 ± 0.11‰ (2SD, N = 44). On the other hand, we observed degassing of Se and Te to a variable extent (~40–95%) in submarine Reykjanes glasses at depths shallower than ~250 m and in subaerial/subglacial basalts on Iceland. Degassing-induced Se isotope fractionation shifted δ82Se of subaerial lavas towards heavier values (by up to ~0.44‰) well outside the range of submarine MORBs. However, when Se outgassing is associated with subglacial eruption, the outer glass rim of basalt preserves the primary/undegassed Se isotopic signature; whereas the pillow interior experiencing further Se loss (~50%) is enriched in heavier isotopes (−0.01 ± 0.12‰) relative to the outer glass rim (−0.22 ± 0.08‰). These observations are complemented by measurements of BHVO-2G from high-temperature heating experiments of the natural Hawaiian basalt BHVO-2, which show evaporation of 40% Se and 85% Te and resulting shift in δ82Se by ~+0.74‰. Degassing-induced Se isotope fractionation during volcanic eruption may be well explained by a simple Rayleigh distillation model with an empirical fractionation factor α of ~0.9998 (between volcanic gas and silicate melt). The results presented here show that Se isotope and Se–Te systematics can potentially contribute further constraints on degassing of chalcophile and volatile elements during terrestrial volcanism and large-scale planetary processes.

Correlations between oceanic crustal thickness, melt volume, and spreading rate from global gravity observation

Oceanic crustal accretion at mid-ocean ridges is a function of spreading rate, mantle temperature, and composition, which are intertwined in affecting melt production and oceanic crustal thickness. Sparse and irregular seismic and geochemical observations on a global scale showed no correlation between crustal thickness and spreading rate along slow to fast-spreading centers. Here, we compile a global oceanic crustal thickness model from gravity data to revisit this issue at a high resolution. Gravity-observed melt volume shows a positive correlation with spreading rate globally, implying that spreading rate is the dominant factor in melt production. However, oceanic crustal thickness is negatively correlated with spreading rate from slow to fast-spreading centers, and this trend is further consolidated by the increase in Curie point depth (a geothermal proxy) and ridge depth with increasing spreading rate. Thus, a decreasing near-ridge temperature probably contributes to crustal thinning from slow to fast-spreading centers. Inferred low melt volume anomalies beneath fast-spreading centers are consistent with a 20 °C temperature drop in the near-ridge mantle, likely caused by efficient hydrothermal cooling.

Recycled arc mantle recovered from the Mid-Atlantic Ridge

Plate tectonics and mantle dynamics necessitate mantle recycling throughout Earth’s history, yet direct geochemical evidence for mantle reprocessing remains elusive. Here we present evidence of recycled supra-subduction zone mantle wedge peridotite dredged from the Mid-Atlantic Ridge near 16°30′N. Peridotite trace-element characteristics are inconsistent with fractional anhydrous melting typically associated with a mid-ocean ridge setting. Instead, the samples are best explained by hydrous flux melting which changed the melting reactions such that clinopyroxene was not exhausted at high degrees of melting and was retained in the residuum. Based on along-axis ridge depth variations, this buoyant refractory arc mantle is likely compensated at depth by denser, likely garnet-rich, lithologies within the mantle column. Our results suggest that highly refractory arc mantle relicts are entrained in the upper mantle and may constitute >60% of the upper mantle by volume. These highly refractory mantle domains, which contribute little to mantle melting, are under-represented in compilations of mantle composition that rely on inverted basalt compositions alone.

Evidence for dehydration-modulated small-scale convection in the oceanic upper mantle from seafloor bathymetry and Rayleigh wave phase velocity

It is well established that the evolution of oceanic lithosphere departs from the predictions of the half-space cooling model (HSC). Understanding the magnitude, spatial distribution and physical origin of this departure is fundamental to our understanding of plate tectonics and the Earth's thermal evolution. Here we analyze Rayleigh wave phase velocities and seafloor topography separately along spreading-history trajectories, which track each piece of seafloor since its formation at the mid-ocean ridge, in the Pacific and the Atlantic basins. We identify the age along each trajectory at which HSC fails to satisfy the observations. Bathymetry and seismic velocity yield consistent results on whether or not HSC gives a statistically better fit to the observations than the plate cooling model at 80% of the locations we examine. Locations of HSC failure identified by velocity but not topography overlap with SS precursor detections in the Pacific, suggesting partial melting at these places. For the locations where the two data sets agree, in the Atlantic the probability of HSC failure is correlated with the axial depth of the present-day ridge. Along trajectories for which the present-day ridge is shallow (deep), HSC failure occurs later (earlier). A similar dependence in the Pacific is difficult to observe since both ridge depth and HSC failure age vary little. We show that the patterns of HSC failure are best explained by small-scale convection in the oceanic upper mantle for which the onset time is governed by rheological stratification created by partial melting at the ridge.

Oceanic axial depth and age-depth distribution of oceanic lithosphere: Comparison of magnetic anomaly picks versus age-grid models

The oceanic age-depth relationship is a fundamental consequence of Earth’s convective system. The new analysis presented here integrates four major data sets to assess the global age-depth distribution of the oceanic lithosphere. First, the distribution of depths along the modern mid-oceanic-ridge axis was obtained using an updated digitized divergent plate-boundary data set for the main ocean basins. Mid-ocean ridges vary in depth by ∼8 km, from −6453 m to +1998 m, with a median depth of −3000 m, modal depth of −2670 m (with a second mode at −2770 m), and area-weighted mean depth of −3044 m. Ridge depth has some correlation with spreading rate up to about 50 mm/yr if the hotspot-impacted North Atlantic and Sheba Ridges are excluded. Second, zero-age crustal thickness, based on a compilation of ∼1000 estimates, was used to test the relationship of oceanic crustal thickness with axial depth. There is some correlation, but it is not a compact correlation, implying that other processes are contributing to both axial depth and crustal thickness variations. Third, a revised sediment-load correction is presented based on assessment of 9,260,185 records from 1263 deep-sea drilling sites with wet bulk density measurements. This can be extrapolated to thicknesses in excess of 8000 m, with an exponential porosity-depth relationship with an initial porosity of ϕ0 = 0.61. Dispersion of integrated wet bulk density measurement-derived sediment-load corrections for the 1263 sites implies ∼±100 m uncertainty in the sediment-load correction at 1300 m sediment thickness. Fourth, the age-depth relationship of oceanic lithosphere was derived based on sediment-load corrected depths of ∼90,000 explicitly dated, globally distributed magnetic reversal picks restricted to the main ocean basins and filtered to exclude large igneous provinces and trench-impacted locations. A best-fit global age-median sediment-corrected depth relationship was derived using a plate model with zero-age ridge depth of −2309 m, temperature difference of 1304 °C, and asymptotic plate thickness of 122 km. The dispersion of sediment-load corrected depths as a function of age is comparable to that observed along the mid-oceanic-ridge system, suggesting that zero-age depths contribute to dispersion at all ages. This is borne out for oceanic lithosphere at relatively young ages (ca. <70 Ma), but the dispersion at older ages appears to be dominated by superposition of hotspots and other large-scale perturbations. In addition, a comparison was made with various vintages of age-grid–derived age-depth distributions, as well as previous age-depth models. The implied age-depth relationship using older versions of the age grid deviates significantly from the age-depth relationship obtained using the magnetic reversal picks alone. There is considerable disparity between pick ages and corresponding grid cell ages for these data sets. In contrast, the most recent age grid (2016) more closely matches the age-depth relationship derived here and shows significantly less disparity with magnetic reversal pick ages. A qualitative suggestion is made that the deviation of the age-depth relationship from a half-space cooling to exponential model reflects the advective contribution of asthenospheric flow associated with asthenospheric tractions contributing to plate-driving forces.

Reassessing the Thermal Structure of Oceanic Lithosphere With Revised Global Inventories of Basement Depths and Heat Flow Measurements

AbstractHalf‐space cooling and plate models of varying complexity have been proposed to account for changes in basement depth and heat flow as a function of lithospheric age in the oceanic realm. Here, we revisit this well‐known problem by exploiting a revised and augmented database of 2,028 measurements of depth to oceanic basement, corrected for sedimentary loading and variable crustal thickness, and 3,597 corrected heat flow measurements. Joint inverse modeling of both databases shows that the half‐space cooling model yields a mid‐oceanic axial temperature that is &gt;100°C hotter than permitted by petrologic constraints. It also fails to produce the observed flattening at old ages. Then, we investigate a suite of increasingly complex plate models and conclude that the optimal model requires incorporation of experimentally determined temperature‐ and pressure‐dependent conductivity, expansivity, and specific heat capacity, as well as a low‐conductivity crustal layer. This revised model has a mantle potential temperature of 1300 ± 50°C, which honors independent geochemical constraints and has an initial ridge depth of 2.6 ± 0.3 km with a plate thickness of 135 ± 30 km. It predicts that the maximum depth of intraplate earthquakes is bounded by the 700°C isothermal contour, consistent with laboratory creep experiments on olivine aggregates. Estimates of the lithosphere‐asthenosphere boundary derived from studies of azimuthal anisotropy coincide with the 1175 ± 50°C isotherm. The model can be used to isolate residual depth and gravity anomalies generated by flexural and sub‐plate convective processes.

A Near-Infrared Perfect Absorber Assisted by Tungsten-Covered Ridges

A periodic tungsten-covered dielectric ridge on substrate assembly is proposed in this article to investigate the perfect absorption in the near-infrared regime. The localized dipolar resonance and the propagating surface plasmon mode significantly restrict the reflectance thus forming two discrete absorption peaks. In the process of discovering perfect absorption, the geometrical parameters such as the tungsten layer thickness, ridge depth and width, substrate spacer thickness and the lateral period are correspondingly numerically explored and a rather high absorption rate of 99.9% can be achieved. Furthermore, the absorption peak is sensitive to the ground substrate index which makes it a potential candidate for compactly integrated on chip sensing applications. The polarization direction of the incident light modulates the absorption to a wider bandwidth and the oblique incidence splits the propagating mode along with a rather weak Fano-type absorption peak. The research may pave way for transition metal integrated on chip absorption system.

Patterns of microcracking in apple fruit skin reflect those of the cuticular ridges and of the epidermal cell walls.

Microcracks in the cuticle of developing apples are aligned with ridges on the inner cuticle surface and are indicative of stress-strain concentrations above the anticlinal cell walls. Microcracks occur in cuticles of most fruits. Growth strains are considered causal. In apples (Malus × domestica), microcracks usually form a mesh pattern similar to that formed by cuticular ridges. Ridge patterns are similar to those of the epidermal cells' anticlinal walls. Our aim was to identify the mechanistic bases for these pattern similarities. By quantifying ridge depth, ridge width, and the areas enclosed by ridges, we reveal the presence of major and minor ridges. Major ridges enclose two-to-four epidermal cells, minor ridges only one cell. There are similar and overlying patterns of microcracking on the cuticle's outer surface and of ridges on its inner surface-microcracks generally follow the outlines of the major ridges. In biaxial tensile tests at 20kPa, strains were low and microcracks shallow, but at > 40kPa, strains were higher and microcracks deeper. Microcracks traversing the cuticle are usually aligned with the anticlinal walls of the underlying epidermal cells. In general, increased skin strain is associated with increased skin transpiration. Transpiration increases are reversible for low strains but irreversible for high strains. The alignment of cuticular microcracks with the major ridges, and these with the anticlinal cell walls, indicates associated stress/strain concentrations.

Vanadium isotope compositions of mid-ocean ridge lavas and altered oceanic crust

Vanadium isotope compositions of igneous rocks have the potential to constrain variations of physico-chemical conditions such as oxidation states during magmatism. Here, we present V isotope data for 27 fresh lavas (ranging from basaltic to dacitic compositions) from mid-ocean ridges, 31 altered basalts and gabbros from IODP site 1256 near the East Pacific Rise (EPR), and 2 back arc basin basalts (BABB). Our analyses of fresh mid-ocean ridge basalt (MORB) provide new constraints on the V isotope composition of MORBs, i.e. δ51V=−0.84±0.02‰ (2SE, n=22). In addition, the mean δ51V of MORBs from individual segments is correlated with the mean ridge depth and Na8.0 of the segment, which might reflect the effect of melting extent on V isotope fractionation during mantle melting.The mafic profile of intact altered oceanic crust (AOC) from the IODP site 1256 has δ51V ranging from −1.01 to −0.77‰, similar to that of fresh MORBs, suggesting that V isotope fractionation is limited during alteration of oceanic crust. These results also indicate the V isotopic homogeneity of the bulk oceanic crust with average δ51V of −0.85±0.02‰ (2SE, n=53), which is unaffected by ocean water and hydrothermal fluid alteration. Our results provide a guideline for application of V isotopes into studies of low and high temperature geochemical processes.The evolved lavas (basaltic andesites, andesites, and dacites) from the East Pacific Rise (EPR) show apparent shifts towards heavy δ51V values with increasing degree of differentiation, which can be explained by the crystal–liquid fractionation during crystallization with an inferred isotope fractionation factor of Δ51Vmineral-melt=−0.15×106/T2. The enrichment of 51V with increasing differentiation degree for the 9°N Overlapping Spreading Center (OSC) lavas is consistent with direction of the isotope shift observed in lavas from Anatahan Island (Northern Mariana Arc) and Hekla Volcano (Iceland), but the magnitude (0.3‰) is much smaller than that (2‰) reported in Prytulak et al. (2017). Modeling of V isotope fractionation between mineral and melt shows that variations in redox condition are important for controlling V isotope fractionation, but insufficient to explain the dramatically different Δ51Vmineral-melt between 9°N OSC lavas and Anatahan/Hekla suites. More studies are necessary for better understanding of mechanisms of V isotope fractionation during magmatism.

Evaluation of the Normal Cochlear Second Interscalar Ridge Angle and Depth on 3D T2-Weighted Images: A Tool for the Diagnosis of Scala Communis and Incomplete Partition Type II.

Cochlear malformations may be be subtle on imaging studies. The purpose of this study was to evaluate the angle and depth of the lateral second interscalar ridge or notch in ears without sensorineural hearing loss (normal ears) and compare them with ears that have a documented incomplete type II partition malformation. The second interscalar ridge notch angle and depth were measured on MR imaging in normal ears by a single experienced neuroradiologist. The images of normal and incomplete partition II malformation ears were then randomly mixed for 2 novice evaluators to measure both the second interscalar ridge notch angle and depth in a blinded manner. For the mixed group, interobserver agreement was calculated, normal and abnormal ear measurements were compared, and receiver operating characteristic curves were generated. The 94 normal ears had a mean second interscalar ridge angle of 80.86° ± 11.4° and depth of 0.54 ± 0.14 mm with the 98th percentile for an angle of 101° and a depth of 0.3 mm. In the mixed group, agreement between the 2 readers was excellent, with significant differences for angle and depth found between normal and incomplete partition type II ears for angle and depth on average (P < .001). Receiver operating characteristic cutoffs for delineating normal from abnormal ears were similar for both readers (depth, 0.31/0.34 mm; angle, 114°/104°). A measured angle of >114° and a depth of the second interscalar ridge notch of ≤0.31 mm suggest the diagnosis of incomplete partition type II malformation and scala communis. These measurements can be accurately made by novice readers.

Earth’s Constant Mean Elevation: Implication for Long-Term Sea Level Controlled by Oceanic Lithosphere Dynamics in a Pitman World

AbstractOn a spherical Earth, the mean elevation (approximately −2440 m) would be everywhere at a mean Earth radius from the center. This directly links an elevation at the surface to physical dimensions of Earth, including surface area and volume, which are at most very slowly evolving components of the Earth system. Earth’s mean elevation thus provides a framework within which to consider changes in height of Earth’s solid surface as a function of time. In this article, the focus will be on long-term, nonglacially controlled sea level. Long-term sea level has long been argued to be largely controlled by changes in ocean basin volume related to changes in the area-age distribution of oceanic lithosphere. As generally modeled by Walter Pitman and subsequent workers, the age-depth relationship of oceanic lithosphere, including both the ridge depth and the coefficients describing the age-depth relationship, are assumed constant. This article examines the consequences of adhering to these assumptions when pl...

A low threshold single transverse mode 852 nm semiconductor laser diode

A 852 nm ridge waveguide edge emitting laser has important applications. But lateral mode instability leads to its poor beam quality because of its ridge structure. Such a structure gives rise to two guidance mechanisms (gain-guide and index-guide), whose change leads to kink effect. So, the control of the single fundamental lateral mode is more difficult. There is no well-informed study in these aspects for ridge waveguide edge emitting lasers. In this paper we study how to improve the beam quality for achieving a stable fundamental lateral mode output experimentally. We are to investigate the influence of lateral mode characteristics of the laser with different ridge depth-to-width ratios in detail by waveguide theory and equivalent refractive index method. Depth and width of the ridge are two key parameters influencing lateral mode. The depth can control lateral guidance mechanism, and the width can control lateral mode order. We find that the ratio must be in a limited range to ensure the single fundamental lateral mode steady. Through theoretical analysis of waveguide theory and equivalent refractive index method, we obtain a limited range of depth-to-width ratio. Then we conduct an experimental comparison, where we adjust the ridge depth, with the width fixed, to control the ratio. Meanwhile we improve the fabrication technology to ensure the accuracy of the structure. We design and fabricate an asymmetric waveguide ridge waveguide edge emitting laser with isolation grooves, whose active region is the core of asymmetric waveguide epitaxy structure. The key structural parameters are 5 m in ridge width, 500 nm in ridge depth, 2 m in isolation grooves depth, 10 m in width, 30 m in spacing between the grooves, and 1 mm in cavity length. Isolation grooves are very useful for improving the performance of the laser: threshold decreased by 50%, output power raised by 44%, and slop efficiency increased by 17%. And the equally crucial role of grooves is to avoid being damaged at packaging process to maintain laser structure. Finally we achieve a stable single fundamental lateral mode output and an accurate tuning wavelength at 852 nm of ridge waveguide edge emitting laser without cavity surface coated at working current 150 mA, working temperature 30 ℃ (working conditions can be changed in a small range). The slope efficiency is on average 0.7 mW/mA (its maximum value is 0.89 mW/mA), and the full wave at half maximum is less than 1 nm. Although we improve the performance of ridge waveguide edge emitting laser and beam quality for stable output, there is still a need to further study the stable output over a wide range. The results in this paper will provide a useful reference for realizing the stable output ridge waveguide edge emitting lasers and the ultra-narrow line-width lasers.

Effect of implant placement depth on the peri-implant bone defect configurations in ligature-induced peri-implantitis: An experimental study in dogs.

BackgroundThe subcrestal placement of implant platform has been considered a key factor in the preservation of crestal bone, but the influence of implant placement depth on bone remodeling combined with peri-implantitis is not fully understood. The aim of this study was to assess the effect of the crestal or subcrestal placement of implants on peri-implant bone defects of ligature-induced peri-implantitis in dogs.Material and MethodsEight weeks after tooth extraction in six beagle dogs, two different types of implants (A: OsseoSpeed™, Astra, Mölndal, Sweden; B: Integra-CP™, Bicon, Boston, USA) were placed at either crestal or subcrestal (-1.5 mm) positions on one side of the mandible. Ligature-induced peri-implantitis was initiated four weeks after the installation of the healing abutment connections. After 12 weeks, tissue biopsies were processed for histological analyses.ResultsSupra-alveolar bone loss combined with a shallow infrabony defect was observed in crestal level implants while deep and wide infrabony defects were present in subcrestal level groups. Subcrestal groups showed significantly greater ridge loss, depths and widths of infrabony defects when compared to crestal groups (P<0.001).ConclusionsWithin the limitations of the animal study, it can be stated that the implants at subcrestal position displayed greater infra-osseous defect than implants at crestal position under an experimental ligature-induced peri-implantitis. Key words:Subcrestal, peri-implantitis, histology.

Influence of continental growth on mid‐ocean ridge depth

AbstractThe interconnectedness of life, water, and plate tectonics is strikingly apparent along mid‐ocean ridges (MOR) where communities of organisms flourish off the disequilibrium of chemical potentials created by circulation of hydrothermal fluids driven by Earth's heat. Moreover, submarine hydrothermal environments may be critical for the emergence of life on Earth. Oceans were likely present in the Hadean but questions remain about early Earth's global tectonics, including when seafloor spreading began and whether mid‐oceanic ridges were deep enough for maximum hydrothermal activities. For example, plate tectonics influences global sea level by driving secular variations in the volume of ocean basins due to continental growth. Similarly, variations in the distribution of seafloor age and associated subsidence, due to assembly and dispersal of supercontinents, explain the largest sea level variation over the past 140 Myr. Using synthetic plate configurations derived from numerical models of mantle convection appropriate for early Earth, we show that MOR have remained submerged and their depths potentially constant over geologic time. Thus, conditions in the early Earth existed for hydrothermal vents at similar depths as today, providing environments conducive for the development of life and allowing for processes such as hydrothermal alteration of oceanic crust to influence the mantle's geochemical evolution.