HD 80606: Searching the chemical signature of planet formation

(Abridged) Binary systems with similar components are ideal laboratories which allow several physical processes to be tested, such as the possible chemical pattern imprinted by the planet formation process. Aims. We explore the probable chemical signature of planet formation in the remarkable binary system HD 80606 - HD 80607. The star HD 80606 hosts a giant planet with 4 MJup detected by both transit and radial velocity techniques, being one of the most eccentric planets detected to date. We study condensation temperature Tc trends of volatile and refractory element abundances to determine whether there is a depletion of refractories that could be related to the terrestrial planet formation. Methods. We carried out a high-precision abundance determination in both components of the binary system, using a line-by-line strictly differential approach, using the Sun as a reference and then using HD 80606 as reference. We used an updated version of the program FUNDPAR, together with ATLAS9 model atmospheres and the MOOG code. Conclusions. From the study of Tc trends, we concluded that the stars HD 80606 and HD 80607 do not seem to be depleted in refractory elements, which is different for the case of the Sun. Then, the terrestrial planet formation would have been less efficient in the components of this binary system than in the Sun. The lack of a trend for refractory elements with Tc between both stars implies that the presence of a giant planet do not neccesarily imprint a chemical signature in their host stars, similar to the recent result of Liu et al. (2014). This is also in agreement with Melendez et al. (2009), who suggest that the presence of close-in giant planets might prevent the formation of terrestrial planets. Finally, we speculate about a possible planet around the star HD 80607.Comment: 19 pages, 9 figures, A&A accepte

Kondo Resonance Decoherence by an External Potential

The Kondo problem, for a quantum dot (QD), subjected to an external bias, is analyzed in the limit of infinite Coulomb repulsion by using a consistent equations of motion method based on a slave-boson Hamiltonian. Utilizing a strict perturbative solution in the leads-dot coupling, T, to T^4 and T^6 orders, we calculate the QD spectral density and conductance, as well as the decoherent rate that drive the systemm from the strong to the weak coupling regime. Our results indicate thet the weak coupling regime is reached for voltages larger than a few units of the Kondo temperature.Comment: 5 figure

Fatigue failure analysis of vibrating screen spring by means of finite element simulation: a case study

Vibrating screens are often used in the mining industry to separate mineral particles by size. In many designs, spring arrays are used to provide the system with the necessary stiffness for screens to vibrate in a controlled manner. Naturally, these springs are subjected to varying loading cycles, which can cause their premature fatigue failure. This behavior has been studied by means of finite element analysis and compared with data obtained from a real case scenario, in which a helical spring failed. The 3D computational model was developed using the geometric characteristics and material properties of a fractured spring, as well as the loading characteristics of a specific vibrating screen. The meshing and the simulation tasks were performed in the general purpose software ANSYS Mechanical. Given the nature of the helical springs and the high-cycle loading conditions, for the fatigue analysis it was determined that a stress-life approach with constant amplitude and non-proportional loading best fit the investigated phenomenon. In solving the nonproportional loading case, stress values of two static scenarios were required to determine the upper and lower limits. Then, to perform the fatigue calculations a solution combination was used. In addition, in order to correct the effect of mean stress and calculate the stresses component respectively the Goodman and Von Mises theories were employed. Simulation results showed that spring would present failure below the second turn of the coil when working with the full nominal load during nearly forty million cycles. These results strongly agreed with the data extracted from a vibrating screen where fractured spring had been working. Fatigue analysis also predicted that the nominal load should be reduced to 90% in order for the spring to meet the minimum life requirements before failure occur

Anomalous optical absorption in a random system with scale-free disorder

We report on an anomalous behavior of the absorption spectrum in a one-dimensional lattice with long-range-correlated diagonal disorder with a power-like spectrum in the form S(k) ~ 1/k^A. These type of correlations give rise to a phase of extended states at the band center, provided A is larger than a critical value A_c. We show that for A < A_c the absorption spectrum is single-peaked, while an additional peak arises when A > A_c, signalling the occurrence of the Anderson transition. The peak is located slightly below the low-energy mobility edge, providing a unique spectroscopic tool to monitor the latter. We present qualitative arguments explaining this anomaly.Comment: 4 pages, 4 postscript figures, uses revtex

Estimating the Effects of Lenght of Exposure to Traning Program: The Case of Job Corps

Length of exposure to a training program is important in determining the labor market outcomes of participants. Employing methods to estimate the causal effects from continuous treatments, we provide insights regarding the effects of different lengths of enrollment to Job Corps (JC)— America’s largest and most comprehensive job training program for disadvantaged youth. We semiparametrically estimate average causal effects (on the treated) of different lengths of exposure to JC, using the “generalized propensity score” under the assumption that selection into different lengths is based on a rich set of observed covariates. “Placebo tests” are performed to gauge the plausibility of this assumption. We find that the estimated effects are increasing in the length of training, and that the marginal effects of additional training are decreasing with length of enrollment. We also document differences in the estimated effects of length of exposure across different demographic groups, which are particularly large between males and females. Finally, our results suggest an important “lock-in” effect in JC training.Training Programs, Continuous Treatments, Generalized Propensity Score, Dose-Response Function