Hot carrier and hot phonon coupling during ultrafast relaxation of photoexcited electrons in graphene

We study, by means of a Monte Carlo simulator, the hot phonon effect on the relaxation dynamics in photoexcited graphene and its quantitative impact as compared to considering an equilibrium phonon distribution. Our multi-particle approach indicates that neglecting the hot phonon effect significantly underestimates the relaxation times in photoexcited graphene. The hot phonon effect is more important for a higher energy of the excitation pulse and photocarrier densities between $1$ and $3\times 10^{12} \mathrm{~cm}^{-2}$. Acoustic intervalley phonons play a non-negligible role, and emitted phonons with wavelengths limited up by a maximum (determined by the carrier concentration) induce a slower carrier cooling rate. Intrinsic phonon heating is damped in graphene on a substrate due to additional cooling pathways, with the hot phonon effect showing a strong inverse dependence with the carrier density.Comment: 12 pages, 5 figure

Einstein constraints on a characteristic cone

We analyse the Cauchy problem on a characteristic cone, including its vertex, for the Einstein equations in arbitrary dimensions. We use a wave map gauge, solve the obtained constraints and show gauge conservation.Comment: 10 pages, to be published in the Proceedings of the 15th International Conference on Waves and Stability in Continuous Media, held in Palermo, 28th June to 1st July 200

A complete gauge-invariant formalism for arbitrary second-order perturbations of a Schwarzschild black hole

Using recently developed efficient symbolic manipulations tools, we present a general gauge-invariant formalism to study arbitrary radiative $(l\geq 2)$ second-order perturbations of a Schwarzschild black hole. In particular, we construct the second order Zerilli and Regge-Wheeler equations under the presence of any two first-order modes, reconstruct the perturbed metric in terms of the master scalars, and compute the radiated energy at null infinity. The results of this paper enable systematic studies of generic second order perturbations of the Schwarzschild spacetime. In particular, studies of mode-mode coupling and non-linear effects in gravitational radiation, the second-order stability of the Schwarzschild spacetime, or the geometry of the black hole horizon.Comment: 14 page

Health status and retirement decisions for older European couples

In this paper we use data the European Community Household Panel (ECHP) to describe and analyse the dynamics of joint labour force behaviour of older couples for the EU12 countries. We focus on three main issues: the relevance of joint retirement across EU12 countries, the existence of complementarities in leisure and/or assortative matting and the effects of health variables. Concerning the evidence, we first find that a working spouse is more likely to retire the more recently the other spouse has retired; this effect is stronger if the wife is the working spouse. Second, there is evidence of assortative mating and/or complementarities in leisure; the effects of all relevant factors on the retirement decision of one spouse depend strongly on whether the other one is working, unemployed, or retired. Third, besides the standard evidence that poor health increases the retirement probability, we find that the husband's health affects the couple's retirement decisions much more strongly than the wife's health does. Additional asymmetric effects are detected with respect to income related variables.joint retirement decisions ; labour force transitions ; health variables ; asymmetric effects

An Empirical Analysis of the Demand for Physician Services Across the European Union

This paper presents parameter estimates for physician services equations using the European Community Household Panel for 12 countries covering the period 1994-1996. The focus is on two specific points: i) the identification of behavioural similarities and differences in the demand for health across the countries; ii) the variability of the demand for health captured through a joint model for all the countries. We find that there are significant differences across countries, although there are also similarities in the effect of variables such as the health stock, labour situation or family structure. An important fraction of the variability of the demand of health services across countries could be explained from differences in age, income, and the role of General Practitioners (GP) as a gatekeepers in the public health system. We also find some evidence of induced demand effects in both the decision to visit and the number of visits to specialists.count data; demand; physician services; latent class model; two-part model

A sequential model for older workers’ labor transitions after a health shock

In this work we study older workers’ (50—64) labor force transitions after a health/disability shock. We find that the probability of keeping working decreases with both age and severity of the shock. Moreover, we find strong interactions between age and severity in the 50—64 age range and none in the 30–49 age range. Regarding demographics we find that being female and married reduce the probability of keeping work. On the contrary, being main breadwinner, education and skill levels increase it. Interestingly, the effect of some demographics changes its sign when we look at transitions from inactivity to work. This is the case of being married or having a working spouse. Undoubtedly, leisure complementarities should play a role in the latter case. Since the data we use contains a very detailed information on disabilities, we are able to evaluate the marginal effect of each type of disability either in the probability of keeping working or in returning back to work. Some of these results may have strong policy implications.Health shocks, disability, labor force transitions, older workers, Spain