10,900 research outputs found
N-expansive homeomorphisms on surfaces
We exploit the techniques developed in [Le] to study N-expansive
homeomorphisms on surfaces. We prove that when f is a 2-expansive homeomorphism
defined on a compact boundaryless surface M without wandering points then f is
expansive. This condition on the wandering set cannot be relaxed: we present an
example of a 2-expansive homeomorphisms on the bitorus with wandering points
that is not expansive
New cw-expansive homeomorphisms of surfaces
In this article we characterize monotone extensions of cw-expansive
homeomorphisms of compact metric spaces. We study the topology of its quotient
space in the case of a compact surface. These results are applied to prove that
there are cw-expansive homeomorphisms of compact surfaces with infinitely many
fixed points and empty wandering set. The examples are quotients of topological
perturbations of pseudo-Anosov diffeomorphisms. We also show that there is a
cw-expansive homeomorphism with the shadowing property of the 2-sphere.Comment: 22 pages, 2 figure
Optimization of a low weight electronic differential for LEVs
It is presented a performance analysis of an Electronic Differential (ED) system designed for Light Electric Vehicles (LEVs). We have developed a test tricycle vehicle with one front steering wheel and two rear fixed units is a same axis with a brushless DC integrated in each of them. Each motor has an independent controller unit and a common Arduino electronic CPU based that can plan specific speeds for each wheels as curves are being traced.
Different implementations of sensors (input current/torque, steering angle and speed of the wheels) are discussed related to hardware complexity, and performance obtained based on speed level requirements and slipping on the traction wheels.Universidad de Málaga. Campus de Excelencia Internacional AndalucĂa Tech
Unemployment duration, unemployment benefits and recalls
We use administrative micro-data to investigate exits from unemployment of benefit recipients in Spain. Because the data allow us to distinguish between transitions to a new job and recall to the same employer, we apply a competing risks model with
observed and unobserved heterogeneity. We are also able to control for the type of
benefit received by the worker: insurance benefit or assistance benefit. We find
significant differences between the new job hazard and the recall hazard. Both hazard
rates increase around the time that insurance benefit elapses. We also find that when
larger firms recall unemployed workers they tend to do so faster than smaller firms. In
general, our results are consistent with predictions derived from search and implicit
contract models. They highlight the importance of taking into account the possibility of recall in the analysis of unemployment duration among unemployment benefit recipients
Three-Dimensional Wave Packet Approach for the Quantum Transport of Atoms through Nanoporous Membranes
Quantum phenomena are relevant to the transport of light atoms and molecules
through nanoporous two-dimensional (2D) membranes. Indeed, confinement provided
by (sub-)nanometer pores enhances quantum effects such as tunneling and zero
point energy (ZPE), even leading to quantum sieving of different isotopes of a
given element. However, these features are not always taken into account in
approaches where classical theories or approximate quantum models are
preferred. In this work we present an exact three-dimensional wave packet
propagation treatment for simulating the passage of atoms through periodic 2D
membranes. Calculations are reported for the transmission of He and He
through graphdiyne as well as through a holey graphene model. For
He-graphdiyne, estimations based on tunneling-corrected transition state theory
are correct: both tunneling and ZPE effects are very important but competition
between each other leads to a moderately small He/He selectivity. Thus,
formulations that neglect one or another quantum effect are inappropriate. For
the transport of He isotopes through leaky graphene, the computed transmission
probabilities are highly structured suggesting widespread selective adsorption
resonances and the resulting rate coefficients and selectivity ratios are not
in agreement with predictions from transition state theory. Present approach
serves as a benchmark for studies of the range of validity of more approximate
methods.Comment: 4 figure
Applying stress-testing on value at risk (VaR) methodologies
In recent years, Value at Risk (VaR) methodologies, i. e., Parametric VaR, Historical
Simulation and the Monte Carlo Simulation have experienced spectacular growth within the new
regulatory framework which is Basle II. Moreover, complementary analyses such a Stress-testing
and Back-testing have also demonstrated their usefulness for financial risk managers.
In this paper, we develop an empirical Stress-Testing exercise by using two historical scenarios
of crisis. In particular, we analyze the impact of the 11-S attacks (2001) and the Latin
America crisis (2002) on the level of risk, previously calculated by different statistical methods.
Consequently, we have selected a Spanish stock portfolio in order to focus on market risk
Exits from unemployment : recall or new job
This paper studies transitions out of unemployment in Spain distinguishing between recall to the same employer and reemployment in a new job. We use a large sample of newly unemployed workers obtained from Social Security records for Spain. These data contain information about each individual's employer identy before and after the unemployment spell. A discrete-time duration model with competing risks of exits serves us to investigate the factors that influence the probabilities of leaving unemployment to return to the same employer or to find a new job with a different employer. We find that the route to exit unemployment is determinant to understand the influence of individual an job characteristics on the hazard rate, as well as the latter dependence on unemployment duration. The recall hazard rate exhibits positive duration dependence during the first months and negative duration dependence thereafter (it is larger for females), while the new-job hazard presents positive duration dependence (it is larger for males
Social security and the search behaviour of workers approaching retirement
This paper explores the links between unemployment, retirement and their associated public insurance programs. It is a contribution to a growing body of literature focused on a better understanding of the labor behavior of advanced—age workers, which has gained importance as the pension crisis looms. The analysis combines the development of a new theoretical model and a detailed exploration of the empirical regularities using the Spanish Muestra Continua de Vidas Laborales (MCVL) dataset. The model is a extension of the standard search model, designed to reproduce the non—stationary environment faced by workers approaching retirement and to explore the interaction of unemployment benefits and retirement pensions. Via calibrated simulations we show that the basic empirical reemployment and retirement patterns can be rationalized as the optimal responses to both the labor market conditions and the institutional incentives. Generous Unemployment Benefits (for durations of up to two years) together with very significant early retirement penalties, make optimal to stay unemployed without searching for large groups of unemployed workers. This moral hazard problem can he substantially alleviated through institutional reform. Setting the early retirement penalties according to the age when the individual withdraws from the labor force (rather than when he/she claims the pension for the first time) seems particularly beneficial. It increases the labor supply, reduces the financial cost for the social security system and generate enough extra resources to compensate for the welfare loss of those unemployed directly hit by the reform.Unemployment search, job benefit, retirement
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