Ontogeny of a subtidal point bar in the microtidal Venice Lagoon (Italy) revealed by three-dimensional architectural analyses

Sedimentological and architectural features of meandering subtidal channels are relatively unexplored, and their deposits are commonly investigated based on facies models set up for intertidal meandering channels. The Venice Lagoon (northern Adriatic Sea, Italy) is affected by a micro-tidal regime and hosts a dense network of active and buried tidal channels. It represents an excellent natural laboratory to improve the current knowledge on subtidal meander morphodynamics and related deposits. In this study, the integration of high-resolution geophysical images and core data allows reconstruction of the architectural three-dimensional model of a meandering subtidal palaeochannel, which is buried below a modern subtidal flat. The study palaeochannel was 35 m wide and 3 m deep, and formed three adjacent meander bends and related point bars. A detailed three-dimensional architectural reconstruction was carried out for deposits associated with one of these meander bends, that was crossed by a minor, low-sinuosity channel with two minor bank-attached bars. This reconstruction highlights that the study point bar has a horseshoe shape, which arose from the onset of bar accretion from an already-sinuous channel. Reconstructed growth stages of the studied bends show that point-bar accretion can follow different styles of planform transformation, also experiencing simultaneously landward (or seaward) deposition according to the dominant flow direction (i.e. local tidal asymmetry). The analyses show that planform transformations occurred in parallel with elevation changes of the related channel thalweg, which shaped pools with geometry varying with the radius of curvature of the bend. The present study highlights the relevance of high-resolution three-dimensional reconstructions to link palaeomorphodynamic processes with related sedimentary products

Fermion Mixing Renormalization and Gauge Invariance

We study the renormalization of the fermion mixing matrix in the Standard Model and derive the constraints that must be satisfied to respect gauge invariance to all orders. We demonstrate that the prescription based on the {\it on-shell} renormalization conditions is not consistent with the Ward-Takahashi Identities and leads to gauge dependent physical amplitudes. A simple scheme is proposed that satisfies all theoretical requirements and is very convenient for practical calculations.Comment: 10 pages, LaTex; Revised version accepted for publication in Phys. Lett.

Spatial and Temporal Changes of Tidal Inlet Using Object-Based Image Analysis of Multibeam Echosounder Measurements: A Case from the Lagoon of Venice, Italy

Scientific exploration of seabed substrata has significantly progressed in the last few years. Hydroacoustic methods of seafloor investigation, including multibeam echosounder measurements, allow us to map large areas of the seabed with unprecedented precision. Through time-series of hydroacoustic measurements, it was possible to determine areas with distinct characteristics in the inlets of the Lagoon of Venice, Italy. Their temporal variability was investigated. Monitoring the changes was particularly relevant, considering the presence at the channel inlets of mobile barriers of the Experimental Electromechanical Module (MoSE) project installed to protect the historical city of Venice from flooding. The detection of temporal and spatial changes was performed by comparing seafloor maps created using object-based image analysis and supervised classifiers. The analysis included extraction of 25 multibeam echosounder bathymetry and backscatter features. Their importance was estimated using an objective approach with two feature selection methods. Moreover, the study investigated how the accuracy of classification could be affected by the scale of object-based segmentation. The application of the classification method at the proper scale allowed us to observe habitat changes in the tidal inlet of the Venice Lagoon, showing that the sediment substrates located in the Chioggia inlet were subjected to very dynamic changes. In general, during the study period, the area was enriched in mixed and muddy sediments and was depleted in sandy deposits. This study presents a unique methodological approach to predictive seabed sediment composition mapping and change detection in a very shallow marine environment. A consistent, repeatable, logical site-specific workflow was designed, whose main assumptions could be applied to other seabed mapping case studies in both shallow and deep marine environments, all over the world

Gauge-Independent W-Boson Partial Decay Widths

We calculate the partial decay widths of the W boson at one loop in the standard model using the on-shell renormalization scheme endowed with a gauge-independent definition of the Cabibbo-Kobayashi-Maskawa (CKM) mixing matrix. We work in $R_\xi$ gauge and explicitly verify that the final expressions are independent of the gauge parameters. Furthermore, we establish the relationship between the on-shell and $\bar{\mathrm{MS}}$ definitions of the CKM matrix, both in its generic form and in the Wolfenstein parameterization. As a by-product of our analysis, we recover the beta function of the CKM matrix.Comment: 15 pages; reference added; input parameters updated according to 2000 PDG report; accepted for publication in Phys. Rev.

Data Descriptor: high resolution multibeam and hydrodynamic datasets of tidal channels and inlets of the Venice Lagoon

Tidal channels are crucial for the functioning of wetlands, though their morphological properties, which are relevant for seafloor habitats and flow, have been understudied so far. Here, we release a dataset composed of Digital Terrain Models (DTMs) extracted from a total of 2,500 linear kilometres of high-resolution multibeam echosounder (MBES) data collected in 2013 covering the entire network of tidal channels and inlets of the Venice Lagoon, Italy. The dataset comprises also the backscatter (BS) data, which reflect the acoustic properties of the seafloor, and the tidal current fields simulated by means of a high-resolution three-dimensional unstructured hydrodynamic model. The DTMs and the current fields help define how morphological and benthic properties of tidal channels are affected by the action of currents. These data are of potential broad interest not only to geomorphologists, oceanographers and ecologists studying the morphology, hydrodynamics, sediment transport and benthic habitats of tidal environments, but also to coastal engineers and stakeholders for cost-effective monitoring and sustainable management of this peculiar shallow coastal system

Single Higgs boson production at future linear colliders

In this work, we present the order #alpha#_s corrections of the process e"+e"- #-># t anti bH"- and its charge conjugate counterpart within the minimal supersymmetric extension of the standard model. Large logarithmic corrections that arise in the on-mass-shell renormalization scheme for the quark mass in the t anti bH"- Yukawa coupling are resummed by adopting the modified minimal-subtraction scheme. The inclusion of the order #alpha#_s corrections leads to a significant reduction of the theoretical uncertainties due to scheme and scale dependence. We consider moreover the standard model process e"+e"-#-># tth and compute the order #alpha#_s corrections. We investigate the effect of electron and positron beam polarization and show that the cross sections of the considered processes can be largely enhanced by a suitable choice of the polarization. (orig.)SIGLEAvailable from TIB Hannover: RA 8913(2002-053) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Using historical data to examine the accuracy of sand transport field measurements in two nearshore marine settings

A re-Analysis of historical data from two field campaigns was undertaken to examine the accuracy of measurements of bed load (Qb) and total transport (Qtot) of sand in (1) a wave-dominant shoreface off western Newfoundland, Canada, and (2) a tide-dominant inlet of Venice Lagoon, Italy. Video tapes recorded within Sea Carousel (a benthic annular flume) deployed off Newfoundland were used to determine the transport of medium to coarse sand under controlled unidirectional flow conditions. These results were compared with Helley-Smith sand trap measurements of bed load of fine to medium sand in a tidal inlet of Venice Lagoon, Italy. Ripple migration rates in Sea Carousel were similar to those measured in rivers and shallow marine settings at similar flows. Accuracy of sand transport rate (derived from ripple motion) was assessed by comparison to fundamental methods presented in the literature. Some of the scatter in correlations with earlier methods was removed by using a nondimensional form of total sand transport and correlating it to excess stream power (i.e. above a traction threshold). Better correlations were found between immersed (bed load) transport rate and excess stream power by applying a published adjustment to the observations for flow depth and grain diameter. Total immersed (normalized) sand transport in Sea Carousel correlated with excess stream power in a fashion similar to results reported in the literature: = 0.288(ω-ωcr)1.65 kg m-1 s-1, where the immersed total sand transport is normalized with respect to flow depth and grain diameter. The sand trap data also followed this fit in part (2006 data only) but demonstrated greater scatter. The data herein thus fell in line with those reported in the literature from a wide variety of flume and field settings and for a wide variety of grain sizes. It is concluded that annular benthic flumes offer a reasonable and reliable method of assessing sand transport under controlled conditions of flow. The results from Sea Carousel and the Helley-Smith traps appear to follow the same relationships and so appear compatible. However, benthic sand traps show a higher degree of scatter, perhaps due to the uncertainties in how they sit on the seabed, and due to the arbitrary conditions of flow to which they are subjected when deployed.</p