Offset Pattern Research Articles

Seizure onset and offset pattern determine the entrainment of the cortex and substantia nigra in the nonhuman primate model of focal temporal lobe seizures.

Temporal lobe epilepsy (TLE) is the most common form of drug-resistant epilepsy. A major focus of human and animal studies on TLE network has been the limbic circuit. However, there is also evidence suggesting an active role of the basal ganglia in the propagation and control of temporal lobe seizures. Here, we characterize the involvement of the substantia nigra (SN) and somatosensory cortex (SI) during temporal lobe (TL) seizures induced by penicillin injection in the hippocampus (HPC) of two nonhuman primates. The seizure onset and offset patterns were manually classified and spectral power and coherence were calculated. We then compared the 3-second segments recorded in pre-ictal, onset, offset and post-ictal periods based on the seizure onset and offset patterns. Our results demonstrated an involvement of the SN and SI dependent on the seizure onset and offset pattern. We found that low amplitude fast activity (LAF) and high amplitude slow activity (HAS) onset patterns were associated with an increase in activity of the SN while the change in activity was limited to LAF seizures in the SI. However, the increase in HPC/SN coherence was specific to the farther-spreading LAF onset pattern. As for the role of the SN in seizure cessation, we observed that the coherence between the HPC/SN was reduced during burst suppression (BS) compared to other termination phases. Additionally, we found that this coherence returned to normal levels after the seizure ended, with no significant difference in post-ictal periods among the three types of seizure offsets. This study constitutes the first demonstration of TL seizures entraining the SN in the primate brain. Moreover, these findings provide evidence that this entrainment is dependent on the onset and offset pattern and support the hypothesis that the SN might play a role in the maintenance and termination of some specific temporal lobe seizure.

A memristive chaotic system with two dimensional offset boosting and extreme multistability

Due to its unique nonlinearity and memory characteristics, memristor is considered one of the most promising partners for designing chaotic systems. In this paper, a memristor is introduced into a nonlinear system to produce complex dynamical behaviors. Symmetric extremely multistability induced by the initial condition of the memristor is observed in the asymmetric system. Attractors are arranged in the phase space by two independent offset boosters, strength cancellation gives birth to various offset boosting patterns. The effective action of the offset controller is reflected in the linear growth of the mean values and the linear shift of the signal diagrams. Moreover, the circuit implementation based on Multisim demonstrates consistency with numerical simulations and theoretical analyses. Finally, the Pseudorandom Number Generator (PRNG), tested through NIST, is developed to validate its high performance in engineering applications.

Static and dynamic responses of buried steel pipe under truck load: An experimental study

The behavior of a buried pipe under static and dynamic loading conditions has been investigated through full-scale field tests. A plain steel pipe with a diameter of 762 mm was gauged at the outer surface of two pipe sections. A dump truck was employed for the static and dynamic loading tests. Under static loading, the measured pipe strains increase with increasing axle load and decreasing cover depth. The measured strains under dynamic loading show three peaks, which correspond to the times at which the front, middle, and rear axles, respectively, reach the pipe centerline. The offset loading pattern produces greater strains than the non-offset one while keeping the axle load constant under both static and dynamic loads. It is discovered that the pipe strains caused by each truck axle vary with truck speed. Since the load transfer is influenced by a number of factors, including the truck load, road roughness, truck speed, and others, a moving truck load does not always result in higher pipe strains as compared to a static load. The complexity of dynamic pipe responses can be explained in part by a single-degree-of-freedom (SDOF) model.

Iterative Interferometric Denoising Filter for Traveltime Picking

Traveltime picking accuracy is frequently affected by incoherent or random data noise. Within this context, we put forth a new denoising method called iterative interferometric denoising filtering. This method leverages the pseudo-Wigner distribution function to capture the offset and time-symmetric patterns of source wavelets convolved in seismic signals. Incoherent or random noises without this characteristic are eliminated via this approach. The processed data have waveform information distortion and more frequency components. However, the traveltime information can be considered correct, and the improved signal-to-noise ratio makes traveltime picking much more convenient. Our method’s practical applications in a synthetic and in two field datasets show that this technology can increase the signal-to-noise ratio, and the picked traveltime information can be used in traveltime tomography. These two field datasets were collected near the Aqaba Gulf and the Qademah fault, located in King Abdullah Economic City.

Triggering mechanism and brittle-ductile dynamics of active faults in the south-central Saurashtra horst, Gujarat, western India: A geospatial, geological, and geophysical approach

The seismically active Saurashtra horst is located within the intraplate volcanic continental margin of western India. The region is prone to moderate and low-magnitude earthquakes within the depth range of ∼ 3 to ∼ 24 km. We observed that the earthquakes in this region are associated with seismically active brittle and ductile crustal layers. To understand the dynamics of the earthquake generation process, we applied an integrated geological and geomorphological approach, supplemented by subsurface geophysical (magnetotelluric) studies. Additionally, the active surface deformation has been measured using the PSInSAR and GLA techniques. Based on the stream offset and geomorphic landform development pattern several NW-SE and NE-SW oriented strike-slip faults have been identified. The PSI-derived displacement analysis reveals that the area is deforming at the rate of ± 5 mm/yr. Furthermore, subsurface crustal heterogeneity with increasing depth has been identified using the magnetotelluric technique, which is reflected in the form of basaltic lava flows, plutonic emplacement within the granitic basement, and the presence of semi-crystallized magmatic bodies below the brittle-ductile level. Additionally, we proposed a model to depict the plutonic emplacement within the highly fractured/faulted granitic basement and their relationship to the earthquake generation process. Our model shows that crustal heterogeneity and the migration of hydrothermal fluid from the semi-crystallized magmatic body along the active fault cause earthquake nucleation processes within the brittle and ductile layers. We concluded that the upwelling magmatic fluid above the brittle-ductile transition (BDT) acted as a lubricant for the nucleation and triggering of the earthquake along the active faults. Similarly, the fractured ductile crust is weakened by fluid migration, which causes high fluid pressure in the ductile crust thereby decreasing the confining pressure and endorsing the velocity weakening in the aseismic layer, responsible for the shear instability that causes deep crustal earthquakes. More specifically, the lithological heterogeneity at brittle and ductile regimes is an important factor for the earthquake nucleation process in this part of the Indian plate.

PO48 Presentation Time: 10:00 AM: Clinical Implementation of an In-House Made Perineal Template for Low Dose Rate Prostate Brachytherapy Treatment

<h3>Purpose</h3> An in-house perineal needle-template device was developed to improve the interactive¹ low-dose-rate (LDR) brachytherapy treatment planning process for patients with small prostate volume size. One of the side effects of external beam radiation and androgen deprivation therapies is the significant reduction of the prostate gland volume (target) which can be challenging to plan with a standard 5mm hole spacing template. The new perineal needle template (new template) has additional rows with holes placed in a 2.5mm off-set grid pattern which provided more hole locations to place seeds inside the small prostate periphery region for a more conformal plan while meeting all dosimetric planning goals. <h3>Methods and Materials</h3> Thirty patients with different prostate gland volumes size were selected for this study. These thirty patients received either external beam radiation alone or external radiation combined with androgen deprivation therapy. Patients had LDR interactive planning performed using the new template, BARD I-125 seed model STM1251 (USA, IL), BARD QuickLink Delivery System for the seed train assembly, Oncentra - Prostate (Elekta, Sweden) for the treatment planning software (TPS) and the B-K Medical Ultrasound 3000 (USA, MA) for the internal organs imaging. On implant day (DAY 0), the radiation oncologist (physician) contoured target, urethra and rectum on TPS. The medical physicist proceeded to start the planning on the TPS using the inverse planning option to create plan and dose volume histogram (DVH) as the first iteration. Then, manually adjusted and customized the seeds locations with the MD input for a final DVH evaluation in order to proceed and deliver the implant. The AAPM TG-64² dosimetric guidelines were followed and reported. All patients had CT and MRI imaging studies performed approximately 30 days after the implant for a DAY 30 post implant evaluation. Using the Oncentra TPS, both imaging studies were fused, and the prostate, urethra and rectum were contoured. The implanted seeds were registered, and the DAY 0 prescription was used for the post-plan evaluation following the AAPM TG-64 dosimetric guidelines. <h3>Results</h3> Thirty patients were successfully treated using the new template. The new template was modeled in TPS and the ultrasound system. The new template did not affect the calculating time in the TPS and the increased amount of hole locations provided more options for an easier manual optimization "tweaking" to achieve a final plan, especially in the apex location where the target tapers down in size. Initially, physician adaptation to the new template was challenging for the first few cases but rapidly improved as the physician became more familiar with the new hole patterns. <h3>Conclusion</h3> We have successfully designed, built and implemented a new template for brachytherapy LDR treatments of small sizes targets (≤20 cc). The new template has provided a viable option to implant the seeds inside or closer to the target periphery thus improving the interactive planning process significantly.

Engineering thermal transport within Si thin films: The impact of nanoslot alignment and ion implantation

In recent years, nanoporous Si films have been intensively studied for their potential applications in thermoelectrics and the thermal management of devices. To minimize the thermal conductivity, ultrafine nanoporous patterns are required but the smallest structure size is largely limited by the spatial resolution of the employed nanofabrication techniques. Along this line, an effectively smaller characteristic length of a nanoporous film can be achieved with offset nanoslot patterns. Compared with periodic circular pores, the nanoslot pattern can achieve an even lower thermal conductivity, where a much smaller porosity is required using ultra-narrow nanoslots. The obtained low thermal conductivity can be understood from the thermally dead volume revealed by phonon Monte Carlo simulations. To further minimize the contribution from short-wavelength phonons, an additional 25% thermal conductivity reduction can be achieved with Ga ions implanted using a focused ion beam.

Meshless methods for magnetohydrodynamics with vector potential

We present a meshless method for magnetohydrodynamics by evolving the vector potential of magnetic fields. A novel scheme and numerical techniques are developed to restrict the divergence of magnetic field, based on the Meshless Finite Mass/Volume with HLLD Riemann solver for conservative flux calculation. We found the magnetic field could be stabilized by a proper smoothing process and so the long-term evolution becomes available. To verify the new scheme, we perform the Brio-Wu shock tube, 2D and 3D Orszag-Tang vortex and Magnetorotational Instability test problems. The results suggest that our method is robust and has better precision on central offset, amplitude and detailed pattern than an existing meshless code–GIZMO.

Study on parameter optimization of 3D bioprinting of hybrid bio-inks

Used mainly for manufacturing operative tissue structures to replace damaged ones, three-dimensional (3D) bioprinting is a burgeoning area of medical science with enormous potential. Since the technology is still relatively new, 3D bioprinting heavily relies on the trial-and-error approach for advancement, but the general process currently involves a mixture of various biomaterials in hydrogel form. The quality of the results is affected significantly by the parameters by which the print is made. Even the most seemingly minute details can drastically change the outcome of the print, including temperature, print time, print speed and nozzle diameter, and dispensing pressure. The biomaterial used is also of the utmost importance. Based on current results, an ideal biomaterial should include the same or similar chemical, biological, mechanical, and practical properties of the target end structure. It is critical to ascertain the closest parameters available to ensure a quality end resulting print. This study aims to determine and streamline process parameters to the nearest possible degree to optimize the bioprinting process of hybrid bio-inks. Using material made from unchanged alginate, alginate with gelatin and combined amino acids and derivatives with diphenylalanine, the medical properties of each biomaterial are examined, as well as their flow behavior, allowing a certain level of predictability on printing parameters. Printing parameters are the parameters by which we can predict how well a target structure can be accurately constructed using various bio-inks. Results for the study indicated that air pressure, nozzle speed, and diameter, as well as offset and angular pattern, all play significant roles in affecting printing quality. Ultimately, the results have also indicated that printing parameters primarily hinge on the composition of the hydrogels used. This study also presented a detailed frame of reference to assess amino acids and derivatives with diphenylalanine systematically, which can also be used in other areas of 3D bioprinting. The results of this study would be crucial in establishing 3D bioprinting as a one-stop manufacturing solution for biopharmaceutical industries.

Geological Structure and Tectonic Reconstruction of Botutonuo and Surrounding Areas, Gorontalo

The research aimed to reconstruct the geological structure and tectonics based on fault, shear fracture and veins data of the Botutonuo and surrounding areas. This research was conducted with DEM interpretation method to determine the lineament pattern of rock offsets and the geological structure mapping method. Geological structure analysis was carried out by using kinematic analysis method of fault, fracture and veins data using the Win Tensor program to obtain the direction and type of stress forming it. Based on the results of the analysis, extensive stress and transtensive stress trendingN-S resulted direction of Normal Fault and Slip Fault (NE-SW). Extensional stress trending (NE-SW) is the result of reorientation stress trending (N-S) in the North Sulawesi arm which is accommodated by the Gorontalo Fault regime. Normal fault and slip fault are the 2nd order faults of the 1st order faults of Gorontalo faults.

“Microfluidics Studies of the Regulation of Myoblast Migration and Differentiation Behaviour – Possible Application in Wound Healing”

Natural extracellular matrices made from cultured cells or tissues, are tissue and cell specific, and critical in tissue engineering and cellular applications. This study focused on the effects of a more naturally produced substrate, made by myotubes differentiated within a device channel, on migration and proliferation (haptotaxis) of a second set of cells (set2) loaded into the device. First, four different microfluidic devices were designed with pillars in either an offset pattern or aligned rows along the channel to investigate the myotube formation. C2C12 cells preloaded with Hoechst stain to label DNA (set1 cells), were loaded into device channels in medium with 2% serum to induce differentiation. Results showed that in devices with aligned rows, cells were more concentrated toward pillars, and their distance from a pillar was smaller than for cells in devices with offset rows of pillars. An average of 20-30 set2 cells was tracked over 10 hours, by image capture every 2 hours in the 3 or 4 channels of each device. Results were compiled in Excel and analyzed by multi-way ANOVAs using Jamovi software. Minimum distance to a pillar occurred rapidly, at day 0 for all four devices and increased over time. After allowing set1 cells to differentiate for 5 days, prestained set2 cells were loaded. The nucleus position of set2 cells was categorized as located nearest to one of four places in the migration channel: the nucleus of a set1 cell, an extension of a set1 cell, a pillar, or the device-channel wall. Results showed that a 3-channel device with offset rows of pillars was best able to lead set1 cells to form and align myotubes in the channel and then attract the most set2 cells to nuclei of those set1 cells. Since cellular proximity is critical to myotube formation and set 2 cells were closer to the set1 nuclei than to device pillars over 10 hours imaging. Differences in flow rate among the four devices suggest that the pillars’ orientation, channel dimensions, and initial velocity are factors that influenced behavioural variations among set1 cells from the time of loading to the end of the 5-day differentiation period. Experiments in devices that were precoated with a fibronectin substrate showed that fibronectin shortened the time to confluency of set1 cells by about 2 days. Perfusion of set1 cells after 5 days of differentiation with an RGD inhibitor ((Arg-Gly-Asp) peptide) of fibronectin binding to integrins, induced a significant shift in the behavior of set2 cells toward proximity to set1 nuclei, whereas without RGD, set2 cells moved toward a device pillar. Additional experiments targeting processes during the fibronectin signaling in migration are in progress to further explore mechanism targeted by variations in device design that affect cell behavior or movement. Further study of cellular taxis should provide clues to identifying a device that would best create a muscle by promoting muscle fiber growth (by fusion of set2 to set1 cells) or in the longer term, induce set2 cells to become quiescent satellite (stem) cells.

Fabrication of Polycaprolactone/Nano Hydroxyapatite (PCL/nHA) 3D Scaffold with Enhanced In Vitro Cell Response via Design for Additive Manufacturing (DfAM).

In this study, we investigated the dual-pore kagome-structure design of a 3D-printed scaffold with enhanced in vitro cell response and compared the mechanical properties with 3D-printed scaffolds with conventional or offset patterns. The compressive modulus of the 3D-printed scaffold with the proposed design was found to resemble that of the 3D-printed scaffold with a conventional pattern at similar pore sizes despite higher porosity. Furthermore, the compressive modulus of the proposed scaffold surpassed that of the 3D-printed scaffold with conventional and offset patterns at similar porosities owing to the structural characteristics of the kagome structure. Regarding the in vitro cell response, cell adhesion, cell growth, and ALP concentration of the proposed scaffold for 14 days was superior to those of the control group scaffolds. Consequently, we found that the mechanical properties and in vitro cell response of the 3D-printed scaffold could be improved by kagome and dual-pore structures through DfAM. Moreover, we revealed that the dual-pore structure is effective for the in vitro cell response compared to the structures possessing conventional and offset patterns.

Rock Physical Model and AVO Patterns for the Mud-Rich Source Rock

Rock physical model and amplitude variation with offset (AVO) patterns considering the content of organic matter and the composition of minerals have a wider significance for guiding the identification and prediction of the mud-rich source rock. A rock physical model is proposed for describing the elastic properties of kerogen in different maturity stages. The proposed rock physical model builds an intrinsic connection between the elastic properties and physical parameters of the mud-rich source rock, thereby providing a theoretical basis for a seismic inversion and a seismic forward modeling. To overcome the limitations of laboratory measurement, a combination-four-parameter regression (CFPR) method is further proposed to estimate the continuous total organic carbon (TOC) values for the verification and analysis of the rock physical model. The modeling results reveal that the P-wave velocity and P-wave impedance will decrease with an increase in TOC, and the Poisson ratio and Poisson impedance will increase as the mud content increases, which are consistent with the conclusions of the cross plot using the actual well data. Based on the proposed rock physical model, the seismic responses of the mud-rich source rock are further modeled. The synthetic seismic records are consistent with the well-side seismic records, the top reflection of the mud-rich source rock behaves as a stronger negative event dimming with an incident angle corresponding to a class IV AVO pattern, and the bottom reflection exhibits a class I AVO anomaly. In addition, a two-layer model is constructed to analyze an effect of the TOC content and mud content on the AVO characteristics. The results indicate that increasing the TOC content and mud content will significantly increase the interceptions and slightly change the gradients of the P-P reflection coefficients. These results help to guide the identification and evaluation of the mud-rich source rock.

Nanoslot Patterns for Enhanced Thermal Anisotropy of Si Thin Films

Materials with a large thermal anisotropy can be widely used to guide the heat flow for various energy-related applications. Other than the well-known thermal conductivity contrast along the in-plane and cross-plane directions of a thin film, the in-plane thermal anisotropy within a thin film is less emphasized. However, such a thermal anisotropy can be easily adopted for the thermal management of thin-film-based electronic devices in practice. In this work, two-dimensional Si thin films patterned with through-film nanoslots are studied for their enhanced in-plane thermal anisotropy. Specifically, the anisotropy of the nanoslot pattern can be further increased if rows of nanoslot patterns have an offset. Within the limitation of nanofabrication techniques, offset nanoslot patterns can provide more scopes for tailoring the transport properties. These nanoslot-patterned thin films can be widely used for applications such as heat guide, thermal insulation, and thermoelectrics.

Influence of Pin Offset and Weave Pattern on the Performance of Al-Cu Joints Reinforced with Graphene Particles

The friction stir welding technique is currently employed for different alloy combinations like magnesium, titanium, copper, nickel-based composites. Dissimilar materials may be efficiently joined by the process and this has been used in several structural applications such as automotive components, aircraft structure, shipbuilding, and space shuttle external tank and train bodies. Even though improvement in the joint strength was achieved, problems such as voids, tunnels, cracks persisted in the weldments. The objective is to achieve defect-free joints. Tool pin offset for joining of aluminum alloy enables better stirring action and an easy flow of plasticised material in the weld nugget. Hence, to overcome the above-mentioned problem, a technique of combined effect of weaving, tool pin offset, and reinforcement of self-lubricated graphene nanoplatelets was attempted. The tensile strength obtained with the effect of tool rotational speed under weave weld with pin offset condition with reinforcement was 13.82 % higher than the weld obtained under the same condition without reinforcement. IMCs such as AlCu, Al2Cu, and Al4Cu9 large size band layers were observed with the linear welding condition, whereas weave welding conditions resulted in the formation of the thin uniform layer.

MRMkit: Automated Data Processing for Large-Scale Targeted Metabolomics Analysis.

MRMkit is an open-source software package designed for automated processing of large-scale targeted mass spectrometry-based metabolomics data. With improvements in the automation of sample preparation for LC-MS analysis, a challenging next step is to fully automate the workflow to process raw data and ensure the quality of measurements in large-scale analysis settings. MRMkit capitalizes on the richness of large-sample data in capturing peak shapes and interference patterns of transitions across many samples and delivers fully automated, reproducible peak integration results in a scalable and time-efficient manner. In addition to fast and accurate peak integration, the tool also provides reliable data normalization functions and quality metrics along with visualizations for fast data quality evaluation. In addition, MRMkit learns retention time offset patterns by user-specified compound classes and makes recommendations for peak picking in multimodal ion chromatograms. In summary, MRMkit offers highly consistent and scalable data processing capacity for targeted metabolomics, substantially curtailing the time required to produce the final quantification results after LC-MS analysis.

A double peak in the seasonality of California's photosynthesis as observed from space

Abstract. Solar-induced chlorophyll fluorescence (SIF) has been shown to be a powerful proxy for photosynthesis and gross primary productivity (GPP). The recently launched TROPOspheric Monitoring Instrument (TROPOMI) features the required spectral resolution and signal-to-noise ratio to retrieve SIF from space. Here, we present a downscaling method to obtain 500 m spatial resolution SIF over California. We report daily values based on a 14 d window. TROPOMI SIF data show a strong correspondence with daily GPP estimates at AmeriFlux sites across multiple ecosystems in California. We find a linear relationship between SIF and GPP that is largely invariant across ecosystems with an intercept that is not significantly different from zero. Measurements of SIF from TROPOMI agree with MODerate Resolution Imaging Spectroradiometer (MODIS) vegetation indices – the normalized difference vegetation index (NDVI), enhanced vegetation index (EVI), and near-infrared reflectance of vegetation index (NIRv) – at annual timescales but indicate different temporal dynamics at monthly and daily timescales. TROPOMI SIF data show a double peak in the seasonality of photosynthesis, a feature that is not present in the MODIS vegetation indices. The different seasonality in the vegetation indices may be due to a clear-sky bias in the vegetation indices, whereas previous work has shown SIF to have a low sensitivity to clouds and to detect the downregulation of photosynthesis even when plants appear green. We further decompose the spatiotemporal patterns in the SIF data based on land cover. The double peak in the seasonality of California's photosynthesis is due to two processes that are out of phase: grasses, chaparral, and oak savanna ecosystems show an April maximum, while evergreen forests peak in June. An empirical orthogonal function (EOF) analysis corroborates the phase offset and spatial patterns driving the double peak. The EOF analysis further indicates that two spatiotemporal patterns explain 84 % of the variability in the SIF data. Results shown here are promising for obtaining global GPP at sub-kilometer spatial scales and identifying the processes driving carbon uptake.

Investigation of k-ε Turbulent Models and Their Effects on Offset Jet Flow Simulation

In the case in which relatively low thickness and high-velocity flow enter into the lower velocity fluid, the resulting interference field of these two flows is called the jet. This phenomenon is the dominant output of power plants and some of the dams. The jets can be divided into two categories of free jets and confined jets, caused by the distance from the discharge to limited boundaries points. The offset jet is a type of confined jet in which both free surface and wall boundaries are near the diffusion location. The jet flow due to the extreme curvature in the main flow path and the proximal portion of this flow with solid boundaries have characteristics that make it difficult to solve with simple turbulence models.In this research, the offset jet phenomenon and related issues have been investigated. For this purpose, the offset jet flow pattern and probable factors in the complexity of this model have been simulated using Fluent software which analyses fluid flow in a two dimensional and three dimensional finite volume method. The simulation of offset jet flow pattern has been performed with a focus on investigating different models of turbulence k-ε, also boundary conditions, various wall functions and other effective coefficients in the numerical model and the model results compared with test case data findings and validating results, the necessary approaches in numerical simulation of this phenomenon for using in the next stages had been taken.

Fluctuating radiocarbon offsets observed in the southern Levant and implications for archaeological chronology debates

Considerable work has gone into developing high-precision radiocarbon (14C) chronologies for the southern Levant region during the Late Bronze to Iron Age/early Biblical periods (∼1200-600 BC), but there has been little consideration whether the current standard Northern Hemisphere 14C calibration curve (IntCal13) is appropriate for this region. We measured 14C ages of calendar-dated tree rings from AD 1610 to 1940 from southern Jordan to investigate contemporary 14C levels and to compare these with IntCal13. Our data reveal an average offset of ∼19 14C years, but, more interestingly, this offset seems to vary in importance through time. While relatively small, such an offset has substantial relevance to high-resolution 14C chronologies for the southern Levant, both archaeological and paleoenvironmental. For example, reconsidering two published studies, we find differences, on average, of 60% between the 95.4% probability ranges determined from IntCal13 versus those approximately allowing for the observed offset pattern. Such differences affect, and even potentially undermine, several current archaeological and historical positions and controversies.

Morphodynamic evolution and stratal architecture of translating tidal point bars: Inferences from the northern Venice Lagoon (Italy)

AbstractThe widespread distribution of tidal creeks and channels that undertake meandering behaviour in modern coasts contrasts with their limited documentation in the fossil record, where point‐bar elements arising from the interaction between a mix of both fluvial and tidal currents are mainly documented. The sedimentary products of tidal channel‐bend evolution are relatively poorly known, and few studies have focused previously on specific facies models for tidal point bars present in modern settings. This study improves understanding of tidal channel meander bends through a multi‐disciplinary approach that combines analyses of historical aerial photographs, measurements of in‐channel flow velocity, high‐resolution facies analyses of sedimentary cores and three‐dimensional architectural modelling. The studied channel bend (12 to 15 m wide and 2 to 3 m deep) drains a salt marsh area located in the north‐eastern sector of the microtidal Venice Lagoon, Italy. Historical photographs show that, during the past 77 years, the bend has translated seaward ca 15 m. Results show that the channel bend formed on a non‐vegetated mud flat that was progressively colonized by vegetation. Seaward translation occurred under aggradational conditions, with an overall migration rate of 0·2 to 0·3 m year−1, and was promoted by the occurrence of cohesive, poorly erodible outer bank deposits. Ebb currents are dominant, and translation of the channel bend promotes erosion and deposition along the landward and seaward side of the bar, respectively. Tidal currents show a clear asymmetry in terms of velocity distribution, and their offset pattern provides a peculiar grain‐size distribution within the bar. During the flood stage, sand sedimentation occurs in the upper part of the bar, where the maximum flow velocity occurs. During the ebb stage, the bar experiences the secondary helical flow that accumulates sand at the toe of the bar. Lateral stacking of flood and ebb deposits has caused the formation of localized coarsening‐upward and fining‐upward sedimentary packages, respectively.