Length-weight relationships of coral reef fishes from the Alacran Reef, Yucatan, Mexico

Length-weight relationships were computed for 42 species of coral reef fishes from 14 families from the Alacran Reef (Yucatan, Mexico). A total of 1 892 individuals was used for this purpose. The fish species were caught by different fishing techniques such as fishhooks, harpoons, gill and trawl nets. The sampling period was from March 1998 to January 2000

Abundance and diversity of soil arthropods in olive grove ecosystem (Portugal): effect of pitfall trap type

Soil arthropod biodiversity is an indicator of soil quality and can be studied using pitfall trapping. In this research, olive grove edaphic fauna was assessed at different sampling dates by comparing two different diameters (7 and 9 cm) and three different contents (empty, water and preservative) of pitfall traps in order to determine which type of pitfall trap is more efficient. Considering all pitfall trap types and sampling times, a total of 12,937 individual edaphic arthropods belonging to 11 taxa were recovered. Smaller traps with preservative collected significantly more individuals than the other pitfalls tested. Larger and empty traps collected significantly more spiders and traps with preservative collected more beetles. Smaller and empty traps collected fewer individuals than the other trap types. Both Shannon’s diversity and Pielou’s evenness indexes were higher in the larger and empty traps and richness was higher in the smaller traps filled with water. The study of myrmecocenosis was emphasised because olive grove soil fauna was numerically dominated by Formicidae (56.6% of all organisms captured) belonging to 12 genera and 24 species; Tapinoma nigerrimum, Messor barbarus, Cataglyphis hispanicus, Tetramorium semilaeve, Cataglyphis ibericus, Messor bouvieri and Camponotus cruentatus were the most abundant ant species. Traps with preservative reached the highest accumulation of species for a small number of pitfalls when compared with the other pitfalls studied and a sampling effort of 20 samples is apparently sufficient to sample the greater part of the ant species of the olive grove. From this study, it seems that traps with preservative are the best choice to use in further studies concerning the epiedaphic fauna of the olive grove

Charge-density waves in the Hubbard chain: evidence for 4k_F instability

Charge density waves in the Hubbard chain are studied by means of finite-temperature Quantum Monte Carlo simulations and Lanczos diagonalizations for the ground state. We present results both for the charge susceptibilities and for the charge structure factor at densities \rho=1/6 and 1/3; for \rho=1/2 (quarter filled) we only present results for the charge structure factor. The data are consistent with a 4k_F instability dominating over the 2k_F one, at least for sufficiently large values of the Coulomb repulsion, U. This can only be reconciled with the Luttinger liquid analyses if the amplitude of the 2k_F contribution vanishes above some U^*(\rho).Comment: RevTeX, 4 two-column pages with 7 colour figures embedded in tex

Localization of damage in beams using interferometric techniques

Two interferometric techniques and their applications in structural damage identification are presented in this paper. Out-of-plane displacement fields of modal response are measured with a pulsed electronic speckle pattern interferometric system(ESPI). The modal rotation fields, defined as the spatial derivative of the displacement field, are measured with a pulsed speckle shearography system. The measurements using these two interferometric systems are compared with measurements from experimental modal analysis and results from finite element analysis. This comparison shows that these two interferometric techniques, which allow non-contact, full-field measurements, are well suited to the measurement of modal response. A damaged beam with free-free boundary conditions is analyzed. The damages studied are small cuts perpendicular to the beams longitudinal axis. The bending moments and shear forces, which are related to the second and third order spatial derivatives of the modal displacement field, in the undamaged and damaged states are computed using numerical differentiation techniques. The damage is localized by looking for maximum values and/or perturbations of damage indicators based on bending moments and shear forces along the beam. The pulsed speckle shearography system leads to a significant improvement in the computation of bending moments and shear forces and, therefore, better damage localizations than the ones obtained with the pulsed ESPI system.The authors greatly appreciate the financial support of FCOMP -01-0124-FEDER-010236 through Project Ref. FCT PTDC/EME-PME/102095/2008

Improvements in damage detection using modal strain fields measured by digital shearography

In this paper we present a novel approach for damage detection based on discontinuities analysis of experimental modal strain fields. These fields are extracted from the combination of two rotation fields and they are measured using digital shearography with stroboscopic double illumination. The rotation fields of a damaged laminated plate are frozen by the synchronization between the LASER illumination and the modal vibration of the object. The quantitative evaluation is performed for each digital shearogram using a time modulation technique. The evaluation of a delamination damage on composite plates is performed by using dedicate image processing techniques. Finally, a comparative analysis of damage detections using the experimental measurement of rotation and deformation fields and their spatial derivatives is presented

Mechanical properties of PLA specimens obtained by additive manufacturing process reinforced with flax fibers

Abstract Although polylactic acid (PLA) is one of the most used materials in additive manufacturing, its mechanical properties are quite limiting for its practical application, therefore, to improve these properties it is frequent to add fibers and, in this way, create a more resistant composite material. In this paper, the authors developed PLA composites reinforced with flax fibers to evaluate the improvement of tensile and flexural strength. The experimental design of experiments was based on the L18 Taguchi array where the control factors were the extruder temperature (three levels), number of strands (three levels), infill percentage of the specimens (three levels), and whether the flax fiber had surface chemical treatment. The tensile and flexural specimens were made on a 3D printing machine and was a mold was developed to fix and align the fiber strands during the printing process. The tensile and flexural experimental tests were performed in agreement with ASTM D638.14 and ISO 14125 standards, respectively. Analyzing the results, it was verified that the surface chemical treatment (NaOH) of the fiber did not show any influence in the mechanical properties of the composites; in contrast, the infill density demonstrated a huge influence for the improvement of mechanical strength. The maximum values of tensile and bending stress were 50 MPa and 73 MPa, respectively. The natural fiber reinforcement can improve the mechanical properties of the PLA composites.info:eu-repo/semantics/publishedVersio

Avaliação de diferentes substâncias activas contra a geração antófaga da traça da oliveira, Prays oleae (Bern.).

Com o objectivo de avaliar as possibilidades de três substâncias activas – o dimetoato, a azadiractina e a metoxifenozida – na protecção contra a geração antófaga da traça da oliveira, Prays oleae Bern., quer na sua eficácia, quer nos efeitos secundários sobre as taxas de parasitismo e predação, em 2002, fez-se um ensaio num olival localizado em Paradela (Mirandela). Os tratamentos realizaram-se a 29 de Maio, quando 10 % das flores se encontravam abertas e 18 a 28,8 % dos cachos florais estavam atacados. A avaliação dos resultados foi feita 6, 9 e 14 dias após o tratamento (T6, T9, T14), através da recolha de quatro fragmentos de ramo em cada uma de 10 árvores de cada modalidade ensaiada, registando-se o número de lagartas vivas, mortas e parasitadas. Para além disso, na geração carpófaga e em duas datas distintas colheram-se 25 frutos em cada uma de 10 árvores por modalidade, para registo do número de posturas e do seu estado (eclodidas, não eclodidas, predadas e parasitadas). O dimetoato foi o insecticida que apresentou melhor eficácia contra a praga, originando 82,1 % de redução da população em T6, 100,0 % em T9 e 85,9 % em T14, seguido da metoxifenozida com 82,1 % em T6, 85,9 % em T9 e 78,6 % em T14 e, em último lugar, da azadiractina com 17,9 % em T6, 57,8 % em T9 e 0,0 % em T14. A parcela tratada com dimetoato também foi a que apresentou menor número de frutos atacados. No entanto, a parcela tratada com azadiractina apresentou maior número de ovos predados, e, em geral, também maior percentagem de lagartas parasitadas, sugerindo menor toxidade para a fauna auxiliar

Automatização de processos de soldadura de estruturas hiperestáticas em ligas de alumínio

Este projeto tem como objetivo a promoção da tecnologia de soldadura robotizada, avançada, e com carácter de significativo grau de transversalidade à indústria, tendo em vista o desenvolvimento de processos mais eficientes, em termos de utilização de recursos de produção, em processo de soldadura.info:eu-repo/semantics/publishedVersio

Charge-density waves in one-dimensional Hubbard superlattices

We study the formation of charge density waves (CDW's) in one-dimensional Hubbard superlattices, modeled by a repeated pattern of repulsive (U>0) and free (U=0) sites. By means of Lanczos diagonalizations for the ground state, we calculate the charge structure factor. Our results show that while the superlattice structure affects the modulation of the charge density waves, the periodicity can still be predicted through an effective density. We also show that, for a fixed repulsive layer thickness, the periodicity of the CDW is an oscillatory function of the free layer thickness.Comment: 4 pages, 4 figure