Lateral Gradients Research Articles

Utilization of continental transforms in break-up: observations, models, and a potential link to magmatism

Abstract Reactivation of continental transform faults (hereafter transforms) is identified herein as a significant factor in continental break-up, based on a global review of divergent margins and numerical modelling. Divergent margins that have reactivated transforms are characterized by linear and abrupt terminations of thick continental crust. Transforms represent some of the largest structures on Earth, and these megastructures represent major lithospheric weaknesses and are therefore prone to reactivation upon changes in the stress field, which typically occur during plate break-up. The blunt termination of the margins is consistent with observations of very limited pre-break-up lithospheric thinning of such margins. This mode of break-up appears to occur abruptly, and contrasts notably with highly tapered and slowly extended divergent margins. Magma leakage along transforms is well-known worldwide where divergence occurs across such features. This leakage may evolve to dyke injections, further reducing the plate strength. We observe that many of the blunt margins we attribute to transform reactivation have been prone to above-normal magmatism and are marked by seaward-dipping reflectors underlain by high-velocity lower crustal intrusions. The magmatism may be directly related to the separation of abruptly terminated margins, whereby the large resulting lateral thermal gradients trigger edge-driven convection and melt addition.

Submesoscale Ageostrophic Motions Within and Below the Mixed Layer of the Northwestern Pacific Ocean

AbstractSubmesoscale dynamics below the mixed layer (ML) and their mechanisms are still unclear. By a series of nested simulations in the Pacific Northwest with high horizontal resolution of ∼500 m, this study reveals that there exist strong submesoscale ageostrophic motions in the upper pycnocline of the Kuroshio Extension region. These motions exhibit enhanced lateral buoyancy gradient and vigorous vertical velocity but with weak vertical vorticity distinct from the ML submesoscale activities. The vertical velocity in the high‐resolution simulation reaches tens of meters per day, consistent with recent observations (e.g., SubMESI and OSMOSIS). Our analysis shows that the enhanced vertical velocity is mostly attributed to the along‐isopycnal motions at the Kuroshio front, but in the region nearby the large vertical velocity mostly arises from the wave‐like vertical movement of isopycnals. To understand the mechanisms for the large vertical velocity, this paper further examined the instability of the flow and the frequency‐wavenumber spectra of vertical vorticity, lateral divergence, lateral buoyancy gradient, and vertical velocity. A criterion based on the ratio between divergence and vorticity variance in spectral space is used to roughly identify the upper bound of unbalanced submesoscales. The results suggest that the high‐frequency, high‐wavenumber processes dominate the vertical motions within and below the ML and significantly enhance the net vertical heat transport between the ML and the ocean interior. This study seeks to provide comprehension of the submesoscale ageostrophic motions below the ML and their impacts on the upper ocean.

Bubble vent localization for marine hydrocarbon seep surveys

Commercial success of marine seep hunting exploration campaigns involves acquisition of high-quality bathymetry and backscatter along with targeted coring of shallow geochemical sampling of seep sediments. The sharp lateral chemical gradient encompassing seafloor seeps requires accurate identification of seep sites from high-resolution acoustic data. Active seafloor seeps featuring plumes of gas bubbles and oil droplets rising into the water column can be imaged with modern multibeam echosounders providing an effective approach to remotely characterizing seafloor seeps. Interpreting the seafloor position of gas plume emissions in multibeam data using existing mapping methodology is hindered by slow processing due to large files sizes, a manual “by eye” qualitative assessment of each sonar ping searching for plume anomalies, skill and fatigue of the geoscientist, and environmental or acquisition artifacts that can mask the precise location of gas emission on the seafloor. These limitations of midwater backscatter mapping create a qualitative data set with varying inherent positional errors that can lead to missed or incorrect observations about seep-related seafloor features and processes. By vertically integrating midwater multibeam amplitude samples, a 2D midwater backscatter raster can be generated and draped over seafloor morphology, providing a quantitative synoptic overview of the spatial distribution of gas plume emission sites for more refined seafloor interpretation. We reprocess multibeam midwater data set from NOAA Cruise EX1402L2 in the northwestern Gulf of Mexico using a vertical amplitude stacking technique. Constructed midwater backscatter surfaces are compared with digitized plume positions collected during the survey for a comparison into assessing uncertainty in mapping approaches. Our results show that the accuracy of manually digitizing gas emission sites varies considerably when compared with the midwater backscatter amplitude maps. This quantitative plume mapping technique offers multiple advantages over traditional geopicking from cost effectiveness, offshore efficiency, repeatability, and higher accuracy, ultimately improving the detectability and sampling of active seafloor seeps through precisely located cores.

Seasonality of density currents induced by differential cooling

Abstract. When lakes experience surface cooling, the shallow littoral region cools faster than the deep pelagic waters. The lateral density gradient resulting from this differential cooling can trigger a cold downslope density current that intrudes at the base of the mixed layer during stratified conditions. This process is known as a thermal siphon (TS). TSs flush the littoral region and increase water exchange between nearshore and pelagic zones; thus, they may potentially impact the lake ecosystem. Past observations of TSs in lakes are limited to specific cooling events. Here, we focus on the seasonality of TS-induced lateral transport and investigate how seasonally varying forcing conditions control the occurrence and intensity of TSs. This research interprets 1-year-long TS observations from Rotsee (Switzerland), a small wind-sheltered temperate lake with an elongated shallow region. We demonstrate that TSs occur for more than 50 % of the days from late summer to winter and efficiently flush the littoral region within ∼10 h. We further quantify the occurrence, intensity, and timing of TSs over seasonal timescales. The conditions for TS formation become optimal in autumn when the duration of the cooling phase is longer than the time necessary to initiate a TS. The decrease in surface cooling by 1 order of magnitude from summer to winter reduces the lateral transport by a factor of 2. We interpret this transport seasonality with scaling relationships relating the daily averaged cross-shore velocity, unit-width discharge, and flushing timescale to the surface buoyancy flux, mixed-layer depth, and lake bathymetry. The timing and duration of diurnal flushing by TSs relate to daily heating and cooling phases. The longer cooling phase in autumn increases the flushing duration and delays the time of maximal flushing relative to the summer diurnal cycle. Given their scalability, the results reported here can be used to assess the relevance of TSs in other lakes and reservoirs.

Overview of the Processes Driving Exchange at Cape Hatteras Program

The Processes driving Exchange At Cape Hatteras (PEACH) program seeks to better understand seawater exchanges between the continental shelf and the open ocean near Cape Hatteras, North Carolina. This location is where the Gulf Stream transitions from a boundary-trapped current to a free jet, and where robust along-shelf convergence brings cool, relatively fresh Middle Atlantic Bight and warm, salty South Atlantic Bight shelf waters together, forming an important and dynamic biogeographic boundary. The magnitude of this convergence implies large export of shelf water to the open ocean here. Background on the oceanography of the region provides motivation for the study and gives context for the measurements that were made. Science questions focus on the roles that wind forcing, Gulf Stream forcing, and lateral density gradients play in driving exchange. PEACH observational efforts include a variety of fixed and mobile observing platforms, and PEACH modeling included two different resolutions and data assimilation schemes. Findings to date on mean circulation, the nature of export from the southern Middle Atlantic Bight shelf, Gulf Stream variability, and position variability of the Hatteras Front are summarized, together with a look ahead to forthcoming analyses.

Development of a Lateral Topographic Weathering Gradient in Forested Podzols

Development of a Lateral Topographic Weathering Gradient in Forested Podzols

A comparative study of low-cost coating processes for green & sustainable organic solar cell active layer manufacturing

Owing to their facile integration into existing commercial products, high volume manufacturing of organic solar cells (OSCs) can be expected in the upcoming years. Therefore, it is important to evaluate the performance and sustainability of various active layer coating methods for OSCs. Herein, we compare four active layer coating processes: spin-coating, blade-coating, spray-coating and push-coating for poly(2,7-carbazole-alt-dithienylbenzothiadiazole):[6,6]-Phenyl-C71-butyric acid methyl ester (PCDTBT:PC71BM) active layers deposition. The optical, morphological and photovoltaic parameters of the active layers are studied. The suitability of each coating method for industrial manufacturing of PCDTBT:PC71BM OSCs is discussed in terms of environmental impact, necessary investments and running costs. Our results confirm that, despite producing high quality and high performance OSCs, spin-coating is unsuitable for high volume manufacturing due to the large amounts of materials and hazardous solvents wasted in the process. Blade-coating provides a good balance between low running costs, low environmental impact and decent performances but the process introduces lateral compositional gradients which could be detrimental for large area OSC processing. Spray-coating requires minimal initial investments but has relatively low performance and low manufacturing sustainability. Push-coating yields OSCs which perform as well as spin-coated ones, with a much lower environmental impact and cost. We should thus look forward to seeing whether this green and sustainable technology can develop into a large area coating process in the future.

Bipolar electrodeposition of gradient polypyrrole films as a catalyst matrix for anodic ethanol oxidation

Lateral gradient coatings displaying various compositions and microstructures along a single surface are desirable for material screening. Here we report a successful application of bipolar electrochemistry to deposit lateral gradient polypyrrole films on a graphite strip substrate. The gradient film shows varying morphologies and a wettability gradient along the length of the bipolar electrode, with superabsorbent property in the middle portion of the film. The film was use as a catalyst matrix for ethanol oxidation in alkaline electrolyte. Aqueous Ni(NO3)2 solution as the catalyst precursor was absorbed into the film. Area-step cyclic voltammetry was used to evaluate the electrocatalytic activity of various local parts along the gradient film to ethanol oxidation. The local surface with the highest catalytic activity was screened out and the excellent catalytic activity is attributed to the outstanding properties of this zone in both water absorption and electrical conductivity. The nickel oxide catalyst can be highly dispersed in the nanoporous network polymer matrix, due to the uniform penetration of the aqueous precursor solution into the superabsorbent film. XPS and EIS analyses support the catalytic mechanism based on the redox transition between NiOOH and Ni(OH)2. This work indicates that loading aqueous catalyst precursors into superabsorbent conducting polymer films may be a promising method for the preparation of electrocatalysts.

Observations of Nutrient Supply by Mesoscale Eddy Stirring and Small‐Scale Turbulence in the Oligotrophic North Atlantic

AbstractSustaining biological export over the open ocean requires a physical supply of nutrients to the mixed layer and thermocline. The relative importance of diapycnal mixing, diapycnal advection, and isopycnal stirring by mesoscale eddies in providing this nutrient supply is explored using a field campaign in oligotrophic waters in the subtropical North Atlantic, consisting of transects over and off the mid‐Atlantic ridge. Eddy stirring rates are estimated from the excess temperature variance dissipation relative to the turbulent kinetic energy dissipation, and using eddy statistics from satellite observations combined with 9‐month‐long mooring data. The vertical nutrient fluxes by diapycnal mixing, diapycnal advection, and isopycnal mesoscale eddy stirring are assessed using nitrate measurements from observations or a climatology. Diapycnal mixing and advection provide a nutrient supply within the euphotic zone, but a loss of nutrients within the upper thermocline. Eddy stirring augments, and is comparable to, the diapycnal transfer of nutrients within the summertime upper thermocline, while also acting to replenish nutrients within the deeper parts of the thermocline. The eddy supply of nitrate is relatively small in the center of the subtropical gyre, reaching up to 0.06 mol N m−2yr−1, but is likely to be enhanced on the flanks of the gyre due to larger isopycnal slopes and lateral nitrate gradients. The nutrient supply to the euphotic zone is achieved via a multistage mechanism: a diapycnal transfer of nutrients by small‐scale turbulence to the euphotic zone, and an isopycnal stirring of nutrients by mesoscale eddies replenishing nutrients in the upper thermocline.

Barite in the Ediacaran Doushantuo Formation and its implications for marine carbon cycling during the largest negative carbon isotope excursion in Earth’s history

The Ediacaran Period (∼635–539 Ma) witnessed the largest negative inorganic carbon isotope (δ13Ccarb) excursion in Earth’s history (i.e., the Shuram Excursion), which is characterized by decoupling from the organic carbon isotope (δ13Corg) record. The cause(s) of this event remains highly debated. Here, we report a major (∼8–9-Myr-long) episode of strong barium (Ba) accumulation during the Shuram Excursion in the form of barite, as recorded in the Ediacaran Doushantuo Formation (∼635–551 Ma) of South China. The inner-shelf Zhangcunping section exhibits minimal Ba enrichment, while the slope Siduping section shows maximal Ba enrichment with the intrashelf basinal Jiulongwan section in the middle. The Siduping section contains ∼5 μm-diameter, ellipsoidal barite crystals of marine origin; and the Jiulongwan section contains large (>50 μm), euhedral barite crystals and cements that are partly replaced by pyrite, pointing to a diagenetic origin with barite formation within the sulfate-methane transition zone. The barite δ34S is ∼10‰ higher than δ34S of carbonate-associated sulfate at Jiulongwan in contrast to similar values of these two components at Siduping, suggesting a limited influence of methane oxidation, if any, on the formation of Shuram Excursion at Jiulongwan. The Ce/Ce* exhibits a lateral gradient among study sections which is reverse to the Ba enrichment, supporting the hypothesis that local surface-water productivity controlled dissolved oxygen levels in the Ediacaran surface ocean. Based on these findings, we attribute the highest Ba enrichment at Siduping to oceanic upwelling which enhanced local marine productivity. Furthermore, we propose that episodic oceanic upwelling in the Ediacaran shelf regions likely transported phosphorus and dissolved organic carbon (DOC) to shallow waters, increasing their productivity and facilitating the oxidation of DOC, contributing to the largest negative carbon isotope excursion in Earth’s history.

Constructing lateral sulfur-gradient Sb2(SxSe1-x)3 heterostructures for Sb2Se3 nanorod photocathodes with enhanced photoelectrochemical properties

Antimony selenide (Sb2Se3) has recently gathered intense attention as a light-harvesting material due to its unique optoelectronic properties. The identical crystal structure of Sb2Se3 and Sb2S3 allows the novel heterostructure to be designed for efficient photoelectrochemical water splitting. Here, we first report the Sb2(SxSe1-x)3 photocathode with lateral heterojunctions within nanorod and sulfur-gradient band structure via vapor transport deposition process followed by postsulfurization, which is beneficial for the charge carrier spatial migration. The lateral Sb2(SxSe1-x)3 nanorod photocathode with [101] preferred orientation achieves a higher photocurrent density (0.8 mA cm−2), which is 30 times higher than that of pure Sb2Se3 nanorod photocathode (0.025 mA cm−2). The high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) images clearly demonstrates that the Sb2(SxSe1-x)3 photocathode is a novel sulfur-gradient nanorod structure with the gradient composition of the S/Se ratio, which is a cascaded band alignment. The Sb2(SxSe1-x)3 photoelectrode has superior H2 generation activity (13.04 μmol cm−2 h−1) without any noble metal as a cocatalyst and shows favorable stability after a continuous test for 1 h under neutral conditions. This novel lateral gradient nanorod structure provides a new insight into the design of efficient optoelectronic devices for antimony chalcogenides.

Stark Physical and Biogeochemical Differences and Implications for Ecosystem Stressors in the Northeast Pacific Coastal Ocean

AbstractRegional differences in water properties and responses to stressors are key to understanding ecosystem vulnerabilities in coastal regions globally. Our study focuses on Canada's British Columbia coastal waters, from Queen Charlotte Strait to the Strait of Georgia. This area is bisected by shallow, narrow, tidally mixed channels with some of the strongest tidal currents in the world. We examine differences between regions on either side of this constriction, focusing on physical water properties and responses to three potential physical and biogeochemical stressors: nutrient levels, marine heatwaves, and ocean acidification. Our results quantify a spatially abrupt and temporally persistent lateral gradient in temperature, salinity, and density co‐located with a previously documented strong mixing zone. The distributions of density on either side of this front remain largely distinct throughout the tidal cycle, for all seasons, and for over 70 individual years for which data are available. Additionally, nutrient concentrations and molar ratios north of the front are statistically distinct from those to the south, and regions north of the front responded more strongly to the arrival of the marine heatwave known as “The Blob”. Lastly, regional differences in sensitivity to ocean acidification are identified, with high values at the surface in the Discovery Islands making that area very sensitive to ocean acidification. These results demonstrate the degree to which dramatic water property differences in adjacent coastal regions can persist over a wide range of time scales, with important connections to their responses to environmental stressors and implications for present and future ecosystem vulnerability.

Thermomechanical fatigue damage modeling and material parameter calibration for thin film metallizations

Numerical fatigue damage models can help to save cost and time when studying fatigue damage in the copper metallization layers of power semiconductor devices. However, their predictive capabilities strongly depend on the parameters associated with these models. This paper presents a strategy for calibrating parameters of a numerical fatigue damage model using experimental results from thermomechanical fatigue experiments. Fatigue damage is predicted by the Fatemi–Socie critical plane method in combination with a Coffin–Manson law. Experimentally, test devices are utilized which can reproduce loading conditions that approximate those occurring in real semiconductor devices. Damage is measured in form of visible surface cracks by the means of surface imagery. Experimental results from devices with pronounced lateral thermal gradients are used for calibrating the fatigue parameters of the Coffin–Manson law. Eventually, the model with the calibrated fatigue parameters is used to predict fatigue damage for a second experiment with different loading conditions. For all investigated test devices the numerical predictions are in good agreement with experimental results. The simulations show that significantly more damage occurs in regions with higher temperatures and that the surface topology has a strong influence on local fatigue damage.

The Root-Cause Analysis on Failed Patient-Specific Measurements of Pencil-Beam-Scanning Protons

The purpose of this study is to present the root-cause analysis on failed patient-specific quality assurance (QA) measurements of pencil-beam-scanning (PBS) protons; referred to as PBS-QA measurement.A criterion to fail a PBS-QA measurement is having a < 95% passing-rate in a 3.0%-3.0mm Gamma-index analysis. The 2D Gamma-index analysis toolkit was clinically used to obtain the passing-rate. A 2D detection array with finite-size ionization-chamber was utilized.A total 2488 PBS-QA measurements were catalogued. The percentage of measurements for the sites of Head/Neck, Breast, Prostate, and Other are 53.3%, 22.7%, 10.5%, and 13.5% respectively. The percentage of measurements with a passing rate of 100%-to-95%, 94%-to-89%, and < 89% were 93.6%, 5.6%, and 0.8% respectively. The percentage of failed measurements with a < 95% passing rate was 10.9%. 8.1% became acceptable by either re-measurement or re-analysis to remove the setup or user errors. A feature of > 3% per-mm dose gradient along depth of beam path was observed on the failed measurements. To study the effect of depth dose gradient, a 3D Gamma-index analysis toolkit was used. 43.1% of measurements improved using this 3D toolkit. A feature among measurements that remained sub-optimal was a sharp > 3% per-mm lateral dose gradient that may not be well handled by using the detector size of 5.0mm in-diameter. An analysis of the sampling of finite-size detectors using 1D error function showed a large dose deviation at locations of low doses in a valley between two plateaus. User error, large depth dose gradient, and the effect of detector-size are identified.With an understanding and mitigation of these root causes, the goals of patient-specific QA, specifically detecting actual deviation of beam delivery or identifying limitations of dose calculation algorithm in used treatment planning system, can be directly related to the failure of PBS-QA measurements.

Quasi-Love wave scattering reveals tectonic history of Australia and its margins reflected by mantle anisotropy

The Australian continental crust preserves a rich geological history, but it is unclear to what extent this history is expressed deeper within the mantle. Here an investigation of Quasi-Love waves is performed to detect scattering of seismic surface waves at mantle depths (between 100–200 km) by lateral gradients in seismic anisotropy. Across Australasia 275 new observations of Quasi-Love waves are presented. The inferred scattering source and lateral anisotropic gradients are preferentially located either near the passive continental margins, or near the boundaries of major geological provinces within Australia. Pervasive fossilized lithospheric anisotropy within the continental interior is implied, on a scale that mirrors the crustal geology at the surface, and a strong lithosphere that has preserved this signal over billions of years. Along the continental margins, lateral anisotropic gradients may indicate either the edge of the thick continental lithosphere, or small-scale dynamic processes in the asthenosphere below.

Effect of particle deposition on film cooling from fan-shaped holes

Film cooling from fan-shaped holes is an essential cooling technology in modern gas turbines. The cooling performance degradation and life reduction of high-temperature components caused by calcium-magnesium-alumino-silicates (CMAS) blockage in film cooling holes have received little attention in the public literature. The emphasis of this study lies in using the large eddy simulation (LES) method to reveal the effects of blockage on the flow, mixing, and heat transfer physics of fan-shaped hole film cooling. Blockages were predicted by the improved composite deposition model. The blowing ratio of 0≤M≤3 and the blockage level of 0≤H/D≤0.75 represent the typical practice in gas turbines. The conjugate heat transfer analysis shows that the particle deposition was closely related to the blowing ratio and the film cooling effectiveness, and the fan-shaped holes were blocked for more than 0.5D after 500 hours of service under the studied conditions. LES results indicate that blockages significantly change the organization of turbulent coherent structures and the mixing between coolant and hot gas. Spiral and lateral reorient structures and pressure gradients play important roles in coolant streamwise extension, lateral coverage, and vortex evolution. At the low blowing ratio, small blockages induced the differentiation of “hairpin vortex forest” and the formation of anti-counter-rotating vortex pairs (Anti-CRVP), and the downwash effect of coolant improved the film cooling effectiveness. At the high blowing ratio, the blockage promoted the fusion of hairpin vortices to the midspan, resulting in the dominance of large-scale CRVP and the attenuation or even complete dissipation of Anti-CRVP. The strong hot gas entrainment effect of CRVP leads to the intensification of vertical mixing and the weakening of lateral dispersion of coolant, and the dramatic decrease of film cooling effect. It was found that the maximum degradation rate of the area-averaged effectiveness caused by blockages can reach more than 90%. The discharge coefficient and aerodynamic loss increase significantly under large blockage and blowing ratios. Whether blocked or not, operating near the optimal effective momentum flux ratio (0.2 ∼ 0.32) is helpful to achieve efficient cooling.

Sound speed, submesoscale, and spice: The role of rapidly evolving instabilities in setting upper ocean properties

Sound speed characteristics in the upper ocean are sometimes thought to be set by a combination of mostly one-dimensional vertical mixing processes and (slow) mesoscale advection and stirring. However, a series of recent projects have showcased the role of small-scale (tens of meters to tens of km horizontally), rapidly evolving (hours to days) submesoscale instabilities in setting both stratification and sound speed properties. The observations also reveal that sound speed structure set by such processes is fundamentally three dimensional, with significant lateral gradients at a broad range of scales. Some relevant processes are frontogenetic and create sometimes rapid secondary circulations near lateral density gradients. Some are associated with wind-driven near-inertial oscillations or internal waves. Some of the more interesting recent observations concern the intersection of submesoscale and internal wave processes. Here, I will review a few highlights from the last decade of observations on unbalanced, nonlinear processes that conspire to set density, spice, and sound speed profiles in several contrasting oceans.

Hydrogels Containing Gradients in Vascular Density Reveal Dose-Dependent Role of Angiocrine Cues on Stem Cell Behavior.

Biomaterials that replicate patterns of microenvironmental signals from the stem cell niche offer the potential to refine platforms to regulate stem cell behavior. While significant emphasis has been placed on understanding the effects of biophysical and biochemical cues on stem cell fate, vascular-derived or angiocrine cues offer an important alternative signaling axis for biomaterial-based stem cell platforms. Elucidating dose-dependent relationships between angiocrine cues and stem cell fate are largely intractable in animal models and 2D cell cultures. In this study, microfluidic mixing devices are leveraged to generate 3D hydrogels containing lateral gradients in vascular density alongside murine hematopoietic stem cells (HSCs). Regional differences in vascular density can be generated via embossed gradients in cell, matrix, or growth factor density. HSCs co-cultured alongside vascular gradients reveal spatial patterns of HSC phenotype in response to angiocrine signals. Notably, decreased Akt signaling in high vessel density regions led to increased expansion of lineage-positive hematopoietic cells. This approach offers a combinatorial tool to rapidly screen a continuum of microenvironments with varying vascular, biophysical, and biochemical cues to reveal the influence of local angiocrine signals on HSC fate.

Multidirectional Anisotropic Total Variation and Its Application in the Tomography of the Surrounding Rock of Coal Mining Faces

The computed tomography (CT) reconstruction algorithm is one of the crucial components of the CT system. To date, total variation (TV) has been widely used in CT reconstruction algorithms. Although TV utilizes the a priori information of the longitudinal and lateral gradient sparsity of an image, it introduces some staircase artifacts. To overcome the current limitations of TV and improve imaging quality, we propose a multidirectional anisotropic total variation (MATV) that uses multidirectional gradient information. The surrounding rock of coal mining faces uses principles of tomography similar to those of medical X-rays. The velocity distribution for the surrounding rock can be obtained by the first-arrival traveltime tomography of the transmitted waves in the coal mining face. Combined with the geological data, we can interpret the geological hazards in the coal mining face. To perform traveltime tomography, we first established the objective function of the first-arrival traveltime tomography of the transmitted waves based on the MATV regularization and then used the split Bregman method to solve the objective function. The simulated data and real data show that the MATV regularization method proposed in this paper can better maintain the boundaries of geological anomalies and reduce the artifacts compared with the isotropic total variation regularization method and the anisotropic total variation regularization method. Furthermore, this approach describes the distribution of geological anomalies more accurately and effectively and improves imaging accuracy.

Full Poincaré beam delineation based on the Stokes vortex ring

Axial and lateral polarization gradients in optical beams that can be created by counter/co-propagating fields have many applications including atom optics and optical lattices. One such beam studied in recent years is a Poincaré beam with interesting topological polarization structures such as Möbius strips, lemon, monstar, and star singularities. Though topological constructs such as linear and circular-basis hybrid-order Poincaré spheres are used to represent these beams as points on these spheres, there is no study on the spatial extent of these beams to qualify them as full Poincaré beams. In this article, we adopt the Stokes vortex ring approach to characterize Poincaré beams and their spatial extent. This ring separates the polarization states present in the beam into two parts that can be mapped onto two hemispherical regions on the fundamental Poincaré sphere. In general, a Poincaré beam containing C-points with its neighborhood of all sizes are treated on equal footing. Experimental and theoretical results are also presented to show that in finite-sized beams, the Stokes vortex ring can be tuned wisely to realize full Poincaré beams.