16,231 research outputs found
Macroeconomics of the New and the Used Car Markets
The new cars of today are used cars of tomorrow and some people assume a competition between new and used markets. There are numerous, preconceived ideas and academic theories regarding the interactions between primary and secondary markets. To investigate the relations, we provide a macroeconomic analysis of the French, the British and the US car markets. We aim at answering the following questions. What are the interactions between the new and the second-hand car markets? Can we use the interactions to estimate the car prices of tomorrow? Our results indicate that the relations appear limited for France and the UK, whereas the US market faces a Scitovscky mechanism, defined by constant disequilibrium and multiple interactions between primary and secondary markets. Furthermore, they illustrate that the interrelations are not strong enough to fully explain and forecast market patterns.second-hand market, automotive market, prices, causality, cyclical correlations, VAR.
Moss and liverwort epiphytes on trunks of Cyathea delgadii in a fragment of tropical rain forest, São Paulo State, Brazil
This study is a survey of the bryophyte species that occur on the trunks of Cyathea delgadii Sternb. (Cyatheaceae), a native tree fern, encountered in a fragment of Atlantic forest located in the area of the „Parque Estadual das Fontes do Ipiranga (PEFI)“, São Paulo State, Brazil. Specimens of bryophytes were collected from March 2001 to October 2003. We found 35 bryophyte species (12 spp. of mosses and 23 of liverworts). Ceratolejeuenea dentacornuta Steph. is presented as a new record for Brazil. A brief discussion about previous records of bryophyte species growing on trunks of tree ferns in Brazil is also presented
A Generalized Sznajd Model
In the last decade the Sznajd Model has been successfully employed in
modeling some properties and scale features of both proportional and majority
elections. We propose a new version of the Sznajd model with a generalized
bounded confidence rule - a rule that limits the convincing capability of
agents and that is essential to allow coexistence of opinions in the stationary
state. With an appropriate choice of parameters it can be reduced to previous
models. We solved this new model both in a mean-field approach (for an
arbitrary number of opinions) and numerically in a Barabasi-Albert network (for
three and four opinions), studying the transient and the possible stationary
states. We built the phase portrait for the special cases of three and four
opinions, defining the attractors and their basins of attraction. Through this
analysis, we were able to understand and explain discrepancies between
mean-field and simulation results obtained in previous works for the usual
Sznajd Model with bounded confidence and three opinions. Both the dynamical
system approach and our generalized bounded confidence rule are quite general
and we think it can be useful to the understanding of other similar models.Comment: 19 pages with 8 figures. Submitted to Physical Review
Connections between the Sznajd Model with General Confidence Rules and graph theory
The Sznajd model is a sociophysics model, that is used to model opinion
propagation and consensus formation in societies. Its main feature is that its
rules favour bigger groups of agreeing people. In a previous work, we
generalized the bounded confidence rule in order to model biases and prejudices
in discrete opinion models. In that work, we applied this modification to the
Sznajd model and presented some preliminary results. The present work extends
what we did in that paper. We present results linking many of the properties of
the mean-field fixed points, with only a few qualitative aspects of the
confidence rule (the biases and prejudices modelled), finding an interesting
connection with graph theory problems. More precisely, we link the existence of
fixed points with the notion of strongly connected graphs and the stability of
fixed points with the problem of finding the maximal independent sets of a
graph. We present some graph theory concepts, together with examples, and
comparisons between the mean-field and simulations in Barab\'asi-Albert
networks, followed by the main mathematical ideas and appendices with the
rigorous proofs of our claims. We also show that there is no qualitative
difference in the mean-field results if we require that a group of size q>2,
instead of a pair, of agreeing agents be formed before they attempt to convince
other sites (for the mean-field, this would coincide with the q-voter model).Comment: 15 pages, 18 figures. To be submitted to Physical Revie
Numerical Simulation of III-V Solar Cells Using D-AMPS
Numerical simulation of devices plays a crucial role in their design, performance prediction, and comprehension of the fundamental phenomena ruling their operation. Here, we present results obtained using the code D-AMPS-1D, that was conveniently modified to consider the particularities of III-V solar cell devices. This work, that is a continuation of a previous paper regarding solar cells for space applications, is focused on solar cells structures than find application for terrestrial use under concentrated solar illumination. The devices were fabricated at the Solar Energy Institute of the Technical University of Madrid (UPM). The first simulations results on InGaP cells are presented. The influence of band offsets and band bending at the window-emitter interface on the quantum efficiency was studied. A remarkable match of the experimental quantum efficiency was obtained. Finally, numerical simulation of single junction n-p InGaP-Ge solar cells was performed
Empowering Rural Citizen Journalism Via Web 2.0 Technologies
Once acquainted with the modern information and communication tools made available with the advent of the Internet, five Brazilian rural communities participating in a pilot project to develop a self-sustaining telecenter model, engaged in citizen journalism using inexpensive digital video cameras. Community members used Web 2.0 collaborative tools to post short videos on the telecenter portal. The 95 video blogs published between September 2006 and May 2008 recorded various aspects of community life,including religious celebrations,oral history arts and crafts traditions,folklore,and envirnmental concerns. This study evaluates the impact of video blogging in these communities
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