On the Maximum Skidding Output of the "Timberjack 380" Forest Tractor

An analysis has been carried out of the skidding operations performed by the "Timberjack 380" forest tractor for an initial thinning of a Pinusradiata D. Don plantation. Knowing the maximum tractive force exerted by the tractor and allowing for the different resistances to forward movement (rolling friction, slope and load resistance), it has been calculated that the tractor can skid 10.1 m3 of material on a dry, compacted earth track, and 5.2 m3 on a wet track. An examination of the various phases of the operations shows that total time per trip to be expressed by the following relation: s„ su -aV where su (speed of tractor without load) = 151.45 m/ min a = 13.4352 V = volume transported d = skidding distance. On the basis of this relation and of the more general one expressing the output (P = 60 V/T), the maximum output was calculated for the "trip without load" phase and for the whole log removal phase. For the "trip with load" phase the maximum output, whatever the skidding distance, is obtained by transporting 5.636 m3, while, for the whole cycle, to achieve the maximum output the load should be 6.970 m3 over a distance of 800 m, and 8.180 m3 over a distance of 100 m. From the analysis carried out and the results obtained, it is clear that the tractor, to ensure maximum performance, should transport material having a high unit volume, such as that obtained from clearcut-ting operations

A numerical investigation on the use of the virtual element method for topology optimization on polygonal meshes

A classical formulation of topology optimization addresses the problem of finding the best distribution of an assigned amount of isotropic material that minimizes the work of the external forces at equilibrium. In general, the discretization of the volume-constrained minimum compliance problem resorts to the adoption of four node displacement-based finite elements, coupled with element-wise density unknowns. When regular meshes made of square elements are used, well-known numerical instabilities arise, see in particular the so-called checkerboarded patterns. On the other hand, when unstructured meshes are needed to cope with geometry of any shape, additional instabilities can steer the optimizer towards local minima instead of the expected global one. Unstructured meshes approximate the strain energy of the members of the arising optimal design with an accuracy that is strictly related to the geometrical features of the discretization, thus remarkably affecting the achieved layouts. In light of the above remarks, in this contribution we consider polygonal meshes and implement the virtual element method (VEM) to solve two classes of topology optimization problems. The robustness of the adopted discretization is exploited to address problems governed by (nearly incompressible and compressible) linear elasticity and problems governed by Stokes equations. Numerical results show the capabilities of the proposed polygonal VEM-based approach with respect to more conventional discretizations

Anisotropic a posteriori error estimate for the virtual element method

We derive an anisotropic a posteriori error estimate for the adaptive conforming virtual element approximation of a paradigmatic two-dimensional elliptic problem. In particular, we introduce a quasi-interpolant operator and exploit its approximation results to prove the reliability of the error indicator. We design and implement the corresponding adaptive polygonal anisotropic algorithm. Several numerical tests assess the superiority of the proposed algorithm in comparison with standard polygonal isotropic mesh refinement schemes

Cleaning activity among Labridae in the Azores: the rainbow wrasse Coris julis and the Azorean blue wrasse Centrolabrus caeruleus

Copyright © Cambridge University Press 2009.Cleaning interactions among the rainbow wrasse Coris julis and the azorean blue wrasse Centrolabrus caeruleus are presented with photographic registers, as well as the first record of the latter cleaning conspecifics from Azorean shallow rocky reefs

Rocky reef fish community structure in two Azorean islands (Portugal) central North Atlantic

Copyright © Cambridge University Press 2010.The community structure of shallow rocky reef fish fauna of the Azores Archipelago is described from underwater visual censuses carried out at eight areas (Terceira and Corvo Islands). A total of 52 fish species from 26 different families was observed, and the ten most abundant fish corresponded to 82.7% of all fish. Trophic categories are given for observed species with comments on distribution and densities along sampled depth strata. Mean densities along sampled strata were tested for significant differences. Sparidae, Labridae and Carangidae were the most speciose families being Diplodus sargus, Pagellus acarne, Coris julis, Thalassoma pavo and Tripterygion delaisi the most abundant species that consequently also accounted for the highest densities

Global occurrence of Torque teno virus in water systems

Bacterial indicator organisms are used globally to assess the microbiological safety of waters. However, waterborne viral outbreaks have occurred in drinking water systems despite negative bacterial results. Using viral markers may therefore provide more accurate health risk assessment data. In this study, fecal, wastewater, stormwater, surface water (fresh and salt), groundwater, and drinking water samples were analyzed for the presence or concentration of traditional indicators, innovative indicators and viral markers. Samples were obtained in the United States, Italy, and Australia and results compared to those reported for studies conducted in Asia and South America as well. Indicators included total coliforms, Escherichia coli, enterococci, male-specific coliphages, somatic coliphages and microviradae. Viral markers included adenovirus, polyomavirus, and a potential new surrogate, Torque teno virus (TTV). TTV was more frequently found in wastewaters (38-100%) and waters influenced by waste discharges (25%) than in surface waters used as drinking water sources (5%). TTV was also specific to human rather than animal feces. While TTV numbers were strongly correlated to other viral markers in wastewaters, suggesting its utility as a fecal contamination marker, data limitations and TTV presence in treated drinking waters demonstrates that additional research is needed on this potential viral indicator