Effect of magnetic fluctuations on the normal state properties of Sr_2RuO_4

We investigate the normal state transport properties of Sr$_2$RuO$_4$ and we show that a consistent explanation of the experimental results can be obtained assuming that the system is near a quantum phase transition. Within the framework of a self-consistent spin fluctuation theory, we calculate the temperature variation of some relevant physical quantities and we discuss a possible microscopic origin of the quantum phase transition.Comment: 5 pages, 4 figures, to appear on Europhysics Letter

Anomalous metamagnetic-like transition in a FeRh/Fe3_3Pt interface occurring at T120 K in the field-cooled-cooling curves for low magnetic fields

We report on the magnetic properties of a special configuration of a FeRh thin film. An anomalous behavior on the magnetisation vs. temperature was observed when low magnetic fields are applied in the plane of a thin layer of FeRh deposited on ordered Fe$_3$Pt. The anomalous effect resembles a metamagnetic transition and occur only in the field-cooled-cooling magnetisation curve at temperatures near 120 K in samples without any heat treatment.Comment: 7 pages, 5 figures. arXiv admin note: text overlap with arXiv:1008.195

Does degradation from selective logging and illegal activities differently impact forest resources? A case study in Ghana

Degradation, a reduction of the ecosystem’s capacity to supply goods and services, is widespread in tropical forests and mainly caused by human disturbance. To maintain the full range of forest ecosystem services and support the development of effective conservation policies, we must understand the overall impact of degradation on different forest resources. This research investigates the response to disturbance of forest structure using several indicators: soil carbon content, arboreal richness and biodiversity, functional composition (guild and wood density), and productivity. We drew upon large field and remote sensing datasets from different forest types in Ghana, characterized by varied protection status, to investigate impacts of selective logging, and of illegal land use and resources extraction, which are the main disturbance causes in West Africa. Results indicate that functional composition and the overall number of species are less affected by degradation, while forest structure, soil carbon content and species abundance are seriously impacted, with resources distribution reflecting the protection level of the areas. Remote sensing analysis showed an increase in productivity in the last three decades, with higher resiliency to change in drier forest types, and stronger productivity correlation with solar radiation in the short dry season. The study region is affected by growing anthropogenic pressure on natural resources and by an increased climate variability: possible interactions of disturbance with climate are also discussed, together with the urgency to reduce degradation in order to preserve the full range of ecosystem functions

Principali patogeni e difesa

Olive as other woody perennial crops can be affected by several systemic pathogens, including bacteria, fungi and several vector-borne viruses. The most important olive diseases, caused by different pathogens, are described in this text. Pathogen biology, diagnostic technique and control strategies are reported for each disease. The main and widespread bacterial disease, caused by Pseudomonas savastanoi pv. savastanoi, is the olive knot. As concerns the most important and widespread fungal diseases, in this text are described the olive leaf spot, Verticillum wilt, cercosporiosis, anthracnose, fruit rot, parasitic brusca, root rot, sooty mold and wood rot. Infections caused by viruses are generally symptomless and do not result in diseased plants. Although, viruses do not cause detrimental disease on olive varieties, the infected olive trees represent a reservoir of virus inoculum for other crops, where these viruses are known to cause severe disease. Detection of these viruses represent an important critical step in the sanitary improvement of this crop. Recently, molecularbased assays have been effectively implemented to detect at least 8 of the 15 viruses known to infect this crop. Sanitation program using in vitro culture of shoot tip and thermotherapy have been recently described to recover virus-free plantlets.Realizzato nell'ambito del progetto "Ricerca ed Innovazione per l'Olivicoltura Meridionale", finanziato dal MiPAAFMiPAAF - Ministero delle politiche agricole alimentari e forestal

Plaquette operators used in the rigorous study of ground-states of the Periodic Anderson Model in D=2D = 2 dimensions

The derivation procedure of exact ground-states for the periodic Anderson model (PAM) in restricted regions of the parameter space and D=2 dimensions using plaquette operators is presented in detail. Using this procedure, we are reporting for the first time exact ground-states for PAM in 2D and finite value of the interaction, whose presence do not require the next to nearest neighbor extension terms in the Hamiltonian. In order to do this, a completely new type of plaquette operator is introduced for PAM, based on which a new localized phase is deduced whose physical properties are analyzed in detail. The obtained results provide exact theoretical data which can be used for the understanding of system properties leading to metal-insulator transitions, strongly debated in recent publications in the frame of PAM. In the described case, the lost of the localization character is connected to the break-down of the long-range density-density correlations rather than Kondo physics.Comment: 34 pages, 5 figure

Influência da palhada de gramíneas forrageiras sobre o desenvolvimento da planta de milho e das plantas daninhas.

Avaliou-se o efeito da palhada de gramíneas forrageiras (capim braquiarão, milheto e sorgo forrageiro) sobre o desenvolvimento da planta de milho e das plantas daninhas, em experimento realizado na Embrapa Milho e Sorgo, no período de março de 2006 a fevereiro de 2007. Os tratamentos foram constituídos pelas três plantas de cobertura, sofrendo ou não um corte após 60 dias de implantação das parcelas, mais um tratamento sem cobertura (pousio). A cobertura de capim braquiária interferiu negativamente no stand inicial, altura de plantas e de espigas. O diâmetro de colmo das plantas de milho na cobertura de milheto foi inferior. Não houve diferença significativa entre as coberturas e nem destas com relação ao pousio, para os demais parâmetros. Também não houve efeito significativo do corte sobre nenhuma das características agronômicas analisadas e nem para os dados de produção do milho. Nas três espécies de cobertura, os percentuais de redução na infestação de plantas daninhas em relação à testemunha sem palha (pousio) foram altos O efeito do corte não foi significativo na supressão de plantas daninhas. O capim braquiária foi superior no percentual de redução da infestação de plantas daninhas e na produção de palha, indicando provável correlação entre as duas variáveis

Does the 2D Hubbard Model Really Show d-Wave Superconductivity?

Some issues concerning the question if the two-dimensional Hubbard model really show d-wave superconductivity are briefly discussed.Comment: Revtex, no figure