Non-Linear Sigma Models on a Half Plane

In the context of integrable field theory with boundary, the integrable non-linear sigma models in two dimensions, for example, the $O(N)$, the principal chiral, the ${\rm CP}^{N-1}$ and the complex Grassmannian sigma models are discussed on a half plane. In contrast to the well known cases of sine-Gordon, non-linear Schr\"odinger and affine Toda field theories, these non-linear sigma models in two dimensions are not classically integrable if restricted on a half plane. It is shown that the infinite set of non-local charges characterising the integrability on the whole plane is not conserved for the free (Neumann) boundary condition. If we require that these non-local charges to be conserved, then the solutions become trivial.Comment: 25 pages, latex, no figure

Metastable Vacua in Brane Worlds

We analyze vacuum decay in brane world setups, where a free scalar field in five dimensions has a localized potential admitting metastable vacua. We study in particular the bounce solution and its properties in flat and warped spaces. In the latter case, placing into a deeply warped region the term in the potential that lifts the vacuum degeneracy, can increase indefinitely the lifetime of the false vacuum. We discuss the application to metastable vacua in supersymmetric brane-world constructions.Comment: LaTeX, 24 page

Automated image processing for quantification of blue-stain discolouration of Norway spruce wood

Bioincising is a promising method for enhancing liquid uptake (e.g. preservatives or wood-modification agents) in refractory wood. Incubation with the white-rot fungus, Physisporinus vitreus, which selectively degrades pit membranes, results in deeper and more homogeneous penetration of liquids. Conventional methods of assessing the degree of fungal discolouration of wood after treatment with preservatives (e.g. European standard EN 152) are partly based on a subjective rating scale, which gives a rough value of the surface colonisation by blue-stain fungi. Hence, an automated image processing (AIP) procedure was developed for standardised quantification of the segmentation thresholds of discolouration and tested against manual segmentation analysis. Using the red filter in the AIP method revealed high correlation (R 2 0.95) and allowed for more user friendly and objective determination of blue staining of woo

Language influences on tweeter geolocation

We investigate the influence of language on the accuracy of geolocating Twitter users. Our analysis, using a large corpus of tweets written in thirteen languages, provides a new understanding of the reasons behind reported performance disparities between languages. The results show that data imbalance has a greater impact on accuracy than geographical coverage. A comparison between micro and macro averaging demonstrates that existing evaluation approaches are less appropriate than previously thought. Our results suggest both averaging approaches should be used to effectively evaluate geolocation

DIRDOP: a directivity approach to determining the seismic rupture velocity vector

Directivity effects are a characteristic of seismic source finiteness and are a consequence of the rupture spread in preferential directions. These effects are manifested through seismic spectral deviations as a function of the observation location. The directivity by Doppler effect method permits estimation of the directions and rupture velocities, beginning from the duration of common pulses, which are identified in waveforms or relative source time functions. The general model of directivity that supports the method presented here is a Doppler analysis based on a kinematic source model of rupture (Haskell, Bull Seismol Soc Am 54:1811–1841, 1964) and a structural medium with spherical symmetry. To evaluate its performance, we subjected the method to a series of tests with synthetic data obtained from ten typical seismic ruptures. The experimental conditions studied correspond with scenarios of simple and complex, unilaterally and bilaterally extended ruptures with different mechanisms and datasets with different levels of azimuthal coverage. The obtained results generally agree with the expected values. We also present four real case studies, applying the method to the following earthquakes: Arequipa, Peru (Mw = 8.4, June 23, 2001); Denali, AK, USA (Mw = 7.8; November 3, 2002); Zemmouri– Boumerdes, Algeria (Mw = 6.8, May 21, 2003); and Sumatra, Indonesia (Mw = 9.3, December 26, 2004). The results obtained from the dataset of the four earthquakes agreed, in general, with the values presented by other authors using different methods and data

Satellite applications to marine geodesy

Potential use of satellites for enhancing positioning capabilities and for marine geodetic contro

Processo de rotura do sismo Mw 7.0 de 2006 em Moçambique inferido através de dados sísmicos e de SAR.

This work is about the rupture process of the 2006 earthquake in Mozambique inferred from different types of data (seismic and SAR). We used 38 body waves from tele-seismic stations, two SAR images acquired by ENVISAT satellite and the map of surface faulting along the Machaze fault (Feton and Bommer, 2006), to study this earthquake. The model of rupture was determined by the body waves inversion and were used this parameters: strike = 165º, dip =76 º and rake = -90º; The model showed good results for a fault plane with 40.6km long and 29 km wide. The model of the displacement was obtained from the Okada equations and it revealed a displacement consistent with the maximum displacement of 86.8 cm observed in the interferogram and the vertical displacements measurements by Fenton and Bommer (2006)

Modelling the impact of climate change on cereal yield in Morocco

To assess the impact of climate change different studies were conducted in several regions of Morocco. The assessment of climate change and its impacts involves the simulation of a range of different socio-economic and physical processes. Some of these processes are well known such temperature, rainfall, storms, etc.., others not. Hence for each modeling step researchers need to consider what is known, what is not known, and how climate change can be expressed.This paper is a contribution to research on climate change impact on cereal yield in the last 50 years. The application of the multiple linear regression model to a set of time series of yield, rainfall, temperature and storm has generated significant coefficients that can explain the relation between yield and the three climate variables. The model output confirms the results of the previous studies of yield variability. The positive effect of rainfall and the negative one of storm and temperature ware recorded. Above the three factors, temperature and storms have a negative effect on cereal yield. So more efforts on germplasm, crop management and agricultural policy measures are needed to alleviate the impact of climate change. An estimate coefficient of -4.943 for temperature is very indicating the high impact of temperature on yield. The R² is around 0.45indicates that more than 55% of total yield variability is explained by other factors than rain, temperature and storm

Estudo da fonte do sismo do Haiti de 12 de janeiro de 2010 a partir de combinação de dados sísmicos e geodésicos

Neste trabalho é apresentada uma metodologia baseada no cruzamento de técnicas e dados sísmicos (ondas de volume com registo telessísmico por estações de banda larga) e geodésicos (SAR - Radar de Abertura Sintética) com o intuito de estudar o complexo processo de ruptura do sismo do Haiti de 12 de Janeiro de 2010. Esta metodologia baseia-se: 1) na análise da diretividade para estimar a direção e a velocidade média de ruptura; b) inversão de ondas de volume para reconstituição do modelo cinemático de ruptura (distribuição espaço-temporal de deslizamentos); 3) modelação da deformação cossísmica, a partir dos resultados do modelo de fonte obtido por inversão de dados sísmicos, e comparação com a correspondente deformação medida com dados SAR, para aferição do modelo de fonte obtido. A aplicação desta metodologia ao sismo do Haiti revela uma ruptura complexa que se propaga de ENE para OSO sobre um plano de falha inclinado para norte, com uma velocidade média de 2.5km/s, durante aproximadamente 12s. A ruptura é composta basicamente por duas asperidades: a primeira (e mais significativa) ocorre durante os primeiros 5s de ruptura e ocupa uma área aproximadamente circular com cerca de 6km de raio, centrada no hipocentro; a segunda ocorre nos últimos 6s de ruptura, cobre uma superfície rectangular com cerca de 10km de comprimento (ao longo da direção da ruptura) por 3km de largura (na direção da inclinação). Os vetores deslizamento mostram que a primeira asperidade tem mecanismo compatível com desligamento esquerdo com uma pequena componente inversa e o mecanismo da segunda asperidade é semelhante ao mecanismo da primeira asperidade