The semi-automated classification of acoustic imagery for characterizing coral reef ecosystems

Coral reef habitat maps describe the spatial distribution and abundance of tropical marine resources, making them essential for ecosystem-based approaches to planning and management. Typically, these habitat maps have been created from optical and acoustic remotely sensed imagery using manual, pixel- and object-based classification methods. However, past studies have shown that none of these classification methods alone are optimal for characterizing coral reef habitats for multiple management applications because the maps they produce (1) are not synoptic, (2) are time consuming to develop, (3) have low thematic resolutions (i.e. number of classes), or (4) have low overall thematic accuracies. To address these deficiencies, a novel, semi-automated object- and pixel-based technique was applied to multibeam echo sounder imagery to determine its utility for characterizing coral reef ecosystems. This study is not a direct comparison of these different methods but rather, a first attempt at applying a new classification technique to acoustic imagery. This technique used a combination of principal components analysis, edge-based segmentation, and Quick, Unbiased, and Efficient Statistical Trees (QUEST) to successfully partition the acoustic imagery into 35 distinct combinations of (1) major and (2) detailed geomorphological structure, (3) major and (4) detailed biological cover, and (5) live coral cover types. Thematic accuracies for these classes (corrected for proportional bias) were as follows: (1) 95.7%, (2) 88.7%, (3) 95.0%, (4) 74.0%, and (5) 88.3%, respectively. Approximately half of the habitat polygons were manually edited (hence the name ‘semi-automated’) due to a combination of mis-classifications by QUEST and noise in the acoustic data. While this method did not generate a map that was entirely reproducible, it does show promise for increasing the amount of automation with which thematically accurate benthic habitat maps can be generated from acoustic imagery.     

Geometric invariance and reference conditioning ideas for control of overflow metabolism

In many biotechnological processes, the optimal productivity corresponds to operating at critical substrate concentration. The problem, then, consists in finding the feeding rate compatible with the critical constraint which gives a specific growth rate as close as possible to the desired one, so as to avoid overflow metabolism. This value may be unknown and may change from experiment to experiment and from strain to strain, and even in the same experiment due to changing environmental and/or process conditions. Particularly, in the fed-batch fermentation of the industrial strain Saccharomyces cerevisiae a small amount of ethanol is allowed to be present in the culture, and the control problem is one of regulating the ethanol concentration at a given low reference value. In this paper, an approach based on geometric invariance via sliding mode reference conditioning is proposed to achieve the closest specific growth rate to the desired reference which is compatible with system constraints (e.g. ethanol concentration lower than a given threshold). It is shown how this approach is robust with respect to uncertainties in the process dynamics and with respect to unknown perturbations affecting the critical point.     

Development of a Liquid Rocket Ground Demonstrator Through Thermal Analyses

Abstract

CIRA, the Italian Aerospace Research Center, manages the HYPROB (HYdrocarbon PROpulsion test Bench) Program, supported by the Italian Ministry of University and Research, with the aim of improving the national capabilities to develop rocket engines for future applications. A system line, named HYPROB-BREAD, focusing on liquid oxygen/liquid Methane (LOX/LCH₄) technology and relative breadboards, is included. A step-by-step approach has been adopted to validate critical design aspects by simplified technological breadboards. The reliable operation of an engine is ensured by thermally efficient cooling jackets, which require the in-depth comprehension of the coolant behavior. For this purpose, a specific breadboard has been designed and tested. Another important issue is the evaluation of the thermal loads, transferred by the combustion hot gases to the thrust chamber walls. In this view, a Subscale Calorimetric Breadboard has been designed; 13 disks surround the chamber: they are fed up by water and provide the cooling and the measurement of the exchanged thermal power. The final article is a 3-ton-class LOX/LCH₄ regenerative demonstrator, whose coolant is liquid methane, flowing in a cooling system, made by several axial channels. This paper aims at describing the thermal investigations, conducted in the design and the verification phase for the aforementioned breadboards and demonstrator cooling jacket.     

Deductive entity relationship modeling

An entity relationship oriented model, that includes the notion of class, together with different types of assertions on classes, is presented. The assertions are used to model IS-A and disjointness relations both between entities and between relationships, part-of relations between entities and relationships, mandatory participation of an entity in a relationship, and interdependencies between the projections of relationships. The semantics of the model are defined in terms of first-order logic, and a sound and complete inference algorithm for such a model is presented. The algorithm is shown to have polynomial time complexity in the case where interdependencies on the projections of relationships are not taken into account. It is suggested that the model and the associated inference capabilities provide a suitable formal basis for designing an effective environment supporting conceptual modeling     

Bridge dynamics and aerodynamics: design and practical requirements for high structural performance and safety

Abstract

Bridge dynamics and aerodynamics have been in many cases overlooked in the design stages and consequent low behaviour performance and safety margin have been not rarely observed and detected by means of structural monitoring of the bridge soon after it is brought into full service. In this paper, a selection of important issues regarding design and practical requirements for a high structural performance of main components of conventional and cable-stayed bridges are pointed out and discussed briefly. The paper encompasses sections describing some relevant aspects regarding the numerical and physical modelling of the structural system and the mathematical modelling of the dynamic and aerodynamic loads. Special attention is given to the dynamic interaction between vehicles and structures of roadways and railway bridges and also to the aeroelastic analyses of bridges′ behaviour and their consequent implications on the structural performance of a bridge during its service life. Case examples of actual bridges subjected to dynamic forces produced by the traffic of heavy vehicles and by the wind action are explored to depict the main sources of problems which in some cases caused structural misbehaviour. Some practical measures to improve the behaviour and performance of bridge structures are outlined.     

IPv6-in-IPv4 Tunnel Discovery: Methods and Experimental Results

Tunnels are widely used to improve security and to expand networks without having to deploy native infrastructure. They play an important role in the migration to IPv6, which relies on IPv6-in-IPv4 tunnels where native connectivity is not available. However, tunnels offer lower performance and are less than native links. In this paper we introduce a number of techniques to detect, and collect information about, IPv6-in-IPv4 tunnels, and show how a known tunnel can be used as a ?vantage point? to launch third-party tunnel-discovery explorations, scaling up the discovery process. We describe our Tunneltrace tool, which implements the proposed techniques, and validate them by means of a wide experimentation on the 6bone tunneled network, on native networks in Italy, the Netherlands, and Japan, and through the test boxes deployed worldwide by the RIPE NCC as part of the Test Traffic Measurements Service. We assess to what extent 6bone registry information is coherent with the actual network topology, and we provide the first experimental results on the current distribution of IPv6-in-IPv4 tunnels in the Internet, showing that even ?native? networks reach more than 60 percent of all IPv6 prefixes through tunnels. Furthermore, we provide historical data on the migration to native IPv6, showing that the impact of tunnels in the IPv6 Internet did not significantly decrease over a six-month period. Finally, we briefly touch on the security issues posed by IPv6-in-IPv4 tunnels, discussing possible threats and countermeasures.     

A new mthod for determining oven aging stability of polypropylene monofilament

A precise method of oven-aging polypropylene monofilament has been developed employing a tubular oven in which temperature and air velocity within each tube are accurately controlled. The monofilaments are suspended within each tube by means of specially construced heat stabilized polypropylene holders (no metal contact), which facilitate handling and record keeping. Each filament is held in an attitude perpendicular to the air flow. Failures almost invariably occur in the middle of each filament. Oxidative stabilities of filaments aged in the tubular oven at a constant temperature and air flow were found to be dependent upon (a) distance of the filaments from the incoming air side and (b) whether the exposure was continuous or intermittent. If these parameters are kept constant, relatively good precision can be obtained. The 95% confidence level for a single observed value was found to be on the order of ±10% of the average oven stability within the whole oven and ±7% within a single tube. Precisions of about ±2.5% can be obtained by employing averages of 10 replicates exposed on the same specimen holder.     

Mass Transfer In Trickle‐Bed Reactors With Structured Packing

An experimental investigation was carried out to examine the fluid dynamic and mass transfer behavior of structured packing, with the liquid and gas phase flowing co‐currently downwards in the column. Liquid to packing mass transfer coefficients for three positions within the pack were measured by an electrochemical method, varying both the liquid and gas loads as well as the physical properties of the liquid phase. Due to the high void fraction of structured packing, much higher liquid flow rates can be used than in traditional particle trickle‐beds. It was found that in the range studied, the gas superficial velocity has no effect on the mass transfer rate and thus, a general mass transfer correlation in terms of liquid Reynolds number only, was developed. Wetted areas and the radial distribution of liquid through the packing element were determined by a colorimetric method. Within the range of liquid flow rates investigated, complete wetting is not achieved, even with the low viscosity solutions. The measured ratios of hydraulic to geometric area, agree reasonably well with values predicted by existing relationships.     

Upward drawings of triconnected digraphs

A polynomial-time algorithm for testing if a triconnected directed graph has an upward drkwing is presented. An upward drkwing is a planar drkwing such that all the edges flow in a common direction (e.g., from bottom to top). The problem arises in the fields of automatic graph drkwing and ordered sets, and has been open for several years. The proposed algorithm is based on a new combinatorial characterization that maps the problem into a max-flow problem on a sparse network; the time complexity isO(n+r ²⁾ , wheren is the number of vertices andr is the number of sources and sinks of the directed graph. If the directed graph has an upward drkwing, the algorithm allows us to construct one easily.This work was partially supported by the Progetto Finalizzato Sistemi Informatici e Calcolo Parallelo of the Italian National Research Council (CNR) Sottoprogetto 6, Infokit and by the ESPRIT II Basic Research Actions Program of the EC (project ALgorithms and COMplexity). An extended abstract of this paper has been presented in P. Bertolazzi and G. Di Battista, On Upward Drkwing Testing of Triconnected Digraphs,Proc. 7th ACM Symposium on Computational Geometry, pp. 272–280, 1991.