Width and extremal height distributions of fluctuating interfaces with window boundary conditions

We present a detailed study of squared local roughness (SLRDs) and local extremal height distributions (LEHDs), calculated in windows of lateral size $l$, for interfaces in several universality classes, in substrate dimensions $d_s = 1$ and $d_s = 2$. We show that their cumulants follow a Family-Vicsek type scaling, and, at early times, when $\xi \ll l$ ($\xi$ is the correlation length), the rescaled SLRDs are given by log-normal distributions, with their $n$th cumulant scaling as $(\xi/l)^{(n-1)d_s}$. This give rise to an interesting temporal scaling for such cumulants $\left\langle w_n \right\rangle_c \sim t^{\gamma_n}$, with $\gamma_n = 2 n \beta + {(n-1)d_s}/{z} = \left[ 2 n + {(n-1)d_s}/{\alpha} \right] \beta$. This scaling is analytically proved for the Edwards-Wilkinson (EW) and Random Deposition interfaces, and numerically confirmed for other classes. In general, it is featured by small corrections and, thus, it yields exponents $\gamma_n$'s (and, consequently, $\alpha$, $\beta$ and $z$) in nice agreement with their respective universality class. Thus, it is an useful framework for numerical and experimental investigations, where it is, usually, hard to estimate the dynamic $z$ and mainly the (global) roughness $\alpha$ exponents. The stationary (for $\xi \gg l$) SLRDs and LEHDs of Kardar-Parisi-Zhang (KPZ) class are also investigated and, for some models, strong finite-size corrections are found. However, we demonstrate that good evidences of their universality can be obtained through successive extrapolations of their cumulant ratios for long times and large $l$'s. We also show that SLRDs and LEHDs are the same for flat and curved KPZ interfaces.Comment: 11 pages, 10 figures, 4 table

Modeling field evaporation degradation of metallic surfaces by first principles calculations: A case study for Al, Au, Ag, and Pd

Indexación: Scopus.Under the effects of an extreme electric field, the atoms on a metallic surface evaporate by breaking their bonds with the surface. In this work, we present the effects of a high electric field, by the use of computational simulations, for different metallic surface chemistries: Al, Au, Ag, and Pd. To model this bond breaking procedrure (i.e. field evaporation), we use density functional theory through the Quantum-Espresso (QE) simulation package, which incorporates the electric fields by adding a saw-like funcion into the Hamiltonian. This approach, known as dipole correction, was applied to all simulations as is implemented in the QE package. In this work, we calculate the evaporation field (Fe ) for all metallic species, which corresponds to the mean field at which atoms can break their bonds from the surface and evaporate. This result is compared with experimantal data from Atom Probe Tomography (APT) and computational data from prior simulations. © Published under licence by IOP Publishing Ltd.This work was supported by the Proyecto FONDECYT Iniciación 11130501. JP Also acknowledges partial support from Proyecto FONDECYT Regular 1140514 and Proyecto UAB-775. CL acknowledges support from Proyecto FONDECYT Iniciación 11150279, Proyecto PAI-79140025, and Proyecto DI-1350-16/R.https://iopscience.iop.org/article/10.1088/1742-6596/1043/1/01203

Haffner 16: A Young Moving Group in the Making

The photometric properties of main sequence (MS) and pre-main sequence (PMS) stars in the young cluster Haffner 16 are examined using images recorded with the Gemini South Adaptive Optics Imager (GSAOI) and corrected for atmospheric blurring by the Gemini Multi-Conjugate Adapative Optics System (GeMS). A rich population of PMS stars is identified, and comparisons with isochrones suggest an age < 10 Myr assuming a distance modulus of 13.5 (D = 5 kpc). When compared with the solar neighborhood, Haffner 16 is roughly a factor of two deficient in objects with sub-solar masses. PMS objects in the cluster are also more uniformly distributed on the sky than bright MS stars. It is suggested that Haffner 16 is dynamically evolved, and that it is shedding protostars with sub-solar masses. Young low mass clusters like Haffner 16 are one possible source of PMS stars in the field. The cluster will probably evolve on time scales of ~ 100 - 1000 Myr into a diffuse moving group with a mass function that is very different from that which prevailed early in its life.Comment: To appear in the Publications of the Astronomical Society of the Pacifi

Mixed-mode impedance and reflection coefficient of two-port devices

From the point of view of mixed-mode scattering parameters, Smm, a two-port device can be excited using different driving conditions. Each condition leads to a particular set of input reflection and input impedance coefficient definitions that should be carefully applied depending on the type of excitation and symmetry of the two-port device. Therefore, the aim of this paper is to explain the general analytic procedure for the evaluation of such reflection and impedance coefficients in terms of mixed-mode scattering parameters. Moreover, the driving of a two-port device as a one-port device is explained as a particular case of a two-port mixed-mode excitation using a given set of mixed-mode loads. The theory is applied to the evaluation of the quality factor, Q, of symmetrical and non- symmetrical inductors.Ministerio de Innovación y Ciencia TEC2010-14825/MIC, TEC2010-21484Junta de Andalucía TIC-253

Three-nucleon mechanisms in photoreactions

The $^{12}$C$(\gamma,ppn)$ reaction has been measured for E$_{\gamma}$=150-800 MeV in the first study of this reaction in a target heavier than $^3$He. The experimental data are compared to a microscopic many body calculation. The model, which predicts that the largest contribution to the reaction arises from final state interactions following an initial pion production process, overestimates the measured cross sections and there are strong indications that the overestimate arises in this two-step process. The selection of suitable kinematic conditions strongly suppresses this two-step contribution leaving cross sections in which up to half the yield is predicted to arise from the absorption of the photon on three interacting nucleons and which agree with the model. The results indicate $(\gamma,3N)$ measurements on nuclei may be a valuable tool for obtaining information on the nuclear three-body interaction.Comment: 5 pages, 3 figure

On the monitoring of surface displacement in connection with volcano reactivation in Tenerife, Canary Islands, using space techniques

Geodetic volcano monitoring in Tenerife has mainly focused on the Las Cañadas Caldera, where a geodetic micronetwork and a levelling profile are located. A sensitivity test of this geodetic network showed that it should be extended to cover the whole island for volcano monitoring purposes. Furthermore, InSAR allowed detecting two unexpected movements that were beyond the scope of the traditional geodetic network. These two facts prompted us to design and observe a GPS network covering the whole of Tenerife that was monitored in August 2000. The results obtained were accurate to one centimetre, and confirm one of the deformations, although they were not definitive enough to confirm the second one. Furthermore, new cases of possible subsidence have been detected in areas where InSAR could not be used to measure deformation due to low coherence. A first modelling attempt has been made using a very simple model and its results seem to indicate that the deformation observed and the groundwater level variation in the island may be related. Future observations will be necessary for further validation and to study the time evolution of the displacements, carry out interpretation work using different types of data (gravity, gases, etc) and develop models that represent the island more closely. The results obtained are important because they might affect the geodetic volcano monitoring on the island, which will only be really useful if it is capable of distinguishing between displacements that might be linked to volcanic activity and those produced by other causes. One important result in this work is that a new geodetic monitoring system based on two complementary techniques, InSAR and GPS, has been set up on Tenerife island. This the first time that the whole surface of any of the volcanic Canary Islands has been covered with a single network for this purpose. This research has displayed the need for further similar studies in the Canary Islands, at least on the islands which pose a greater risk of volcanic reactivation, such as Lanzarote and La Palma, where InSAR techniques have been used already