Cosmic Sculpture: A new way to visualise the Cosmic Microwave Background

3D printing presents an attractive alternative to visual representation of physical datasets such as astronomical images that can be used for research, outreach or teaching purposes, and is especially relevant to people with a visual disability. We here report the use of 3D printing technology to produce a representation of the all-sky Cosmic Microwave Background (CMB) intensity anisotropy maps produced by the Planck mission. The success of this work in representing key features of the CMB is discussed as is the potential of this approach for representing other astrophysical data sets. 3D printing such datasets represents a highly complementary approach to the usual 2D projections used in teaching and outreach work, and can also form the basis of undergraduate projects. The CAD files used to produce the models discussed in this paper are made available.Comment: Accepted for publication in the European Journal of Physic

Chaotic Explosions

We investigate chaotic dynamical systems for which the intensity of trajectories might grow unlimited in time. We show that (i) the intensity grows exponentially in time and is distributed spatially according to a fractal measure with an information dimension smaller than that of the phase space,(ii) such exploding cases can be described by an operator formalism similar to the one applied to chaotic systems with absorption (decaying intensities), but (iii) the invariant quantities characterizing explosion and absorption are typically not directly related to each other, e.g., the decay rate and fractal dimensions of absorbing maps typically differ from the ones computed in the corresponding inverse (exploding) maps. We illustrate our general results through numerical simulation in the cardioid billiard mimicking a lasing optical cavity, and through analytical calculations in the baker map.Comment: 7 pages, 5 figure

Success determinants of small and medium enterprises: The case of Portugal

The success determinants of Portuguese small and medium enterprises (SMEs) are examined using a sample of 207 Portuguese firms from several industries listed in the Dun & Bradstreet database that are at least five years old and with ten or more employees. The empirical study is based on the Lussier (1995) success versus failure prediction model. Our results do not fully support the international research on the determinants of SMEs’ success. The determinants of Portuguese SMEs’ success are: capital, record-keeping and financial control, planning, professional advice, age of owner, and marketing skills. Using logistic regression, the model adequately fits the data, and accurately predicts 43.4 percent of the failed businesses and 87.0 percent of the successful businesses for an overall accuracy rate of 73.2 percent.info:eu-repo/semantics/acceptedVersio

Recreational, Cultural and Aesthetic Services from Estuarine and Coastal Ecosystems

The role of economic analysis in guiding the sustainable development of estuarine and coastal ecosystems is investigated based on a comprehensive review of the literature on the valuation of the recreation, cultural and aesthetic services. The implications of the findings for the sustainable management of coral reefs, Marine Protected Areas, and Small Island Developing States are discussed. Finally, the potential of meta-analytical benefit transfer and scaling up of values at various aggregation levels is demonstrated in the context of coastal tourism and recreation in Europe. The results of the study support the conclusion that the non-material values provided by coastal and estuarine ecosystems in terms of recreational, cultural and aesthetic services represent a substantial component of human well-being.Aesthetic Values, Coastal Recreation, Coral Reefs, Cultural Values, Ecosystem Services Valuation, Ecosystem Services, Estuarine Ecosystems, Marine Protected Areas, Non-market Valuation, Non-use Values, Passive Values, Recreational Fishing, Small Island Developing States, Spiritual and Religious Values.

Detecting customer defections: an application of continuous duration models

The considerable increase of business competition in the Portuguese fixed telecommunications industry for the last decades has given rise to a phenomenon of customer defection, which has serious consequences for the business financial performance and, therefore, for the economy. As such, researchers have recognised the importance of an in-depth study of customer defection in different industries and geographic locations. This study aims to understand and predict customer lifetime in a contractual setting in order to improve the practice of customer portfolio management. A duration model is developed to understand and predict the residential customer defection in the fixed telecommunications industry in Portugal. The models are developed by using large-scale data from an internal database of a Portuguese company which presents bundled offers of ADSL, fixed line telephone, pay-TV and home-video. The model is estimated with a large number of covariates, which includes customer’s basic information, demographics, churn flag, customer historical information about usage, billing, subscription, credit, and other. The results of this study are very useful to the computation of the customer lifetime value

Estimating a customer churn model in the ADSL industry in Portugal: The use of a Semi-Markov model

Customer churn has been stated as one of the main reasons of profitability losses in the telecommunications industry. As such, it seems critical to have an a priori knowledge about the risk of a given customer to churn at any moment, in order to take preventive measures to avoid the defection of potentially profitable customers. This study intends to develop a duration model of the residential customer churn in this industry in Portugal. We found empirical evidence that the variables that influence customer churn are the total number of overdue bills since ever, average monthly spending, average value of additional internet traffic, payment method, equipment renting, and the subscription of a flat plan. We also found that the probability of a customer to churn is neither constant over time nor across customers.info:eu-repo/semantics/publishedVersio

On the use of discounted cash flow method on the customer valuation

The Discounted Cash Flow Method has been widely argued as the best method to asset valuation. This article is about the valuation of customers. The use of historic customer profitability and the Discounted Cash Flow Method to customer valuation are discussed. Moreover, the components of customer lifetime value is presented and described

Performance assessment of portuguese secondary schools: the society and educational authorities perspectives

This paper describes a performance assessment of Portuguese secondary schools using data envelopment analysis (DEA). The assessment adopts two perspectives: a society perspective where schools are viewed as promoting students achievement given student characteristics in terms of academic abilities and socio-economic background; and an educational authorities perspective where schools are viewed as transforming a set of resources (including student academic abilities, socio-economic background, and also school resources, such as teachers) into students' achievement. Two types of DEA analysis are performed for each perspective: one using an output oriented model allowing factor weights to vary freely from school to school and another using a model that restricts factor weights to be equal for all schools. The first model is well suited for identifying inefficient schools, whereas the latter is best suited for improving discrimination between efficient schools when pursuing the identification of benchmarks. Our sample comprised a small number of schools and therefore the results obtained are mainly illustrative of the potential of the method. Future research will explore the use of this method for the assessment of schools at a national leve