Pseudospectral versus finite-differences schemes in the numerical integration of stochastic models of surface growth

We present a comparison between finite differences schemes and a pseudospectral method applied to the numerical integration of stochastic partial differential equations that model surface growth. We have studied, in 1+1 dimensions, the Kardar, Parisi and Zhang model (KPZ) and the Lai, Das Sarma and Villain model (LDV). The pseudospectral method appears to be the most stable for a given time step for both models. This means that the time up to which we can follow the temporal evolution of a given system is larger for the pseudospectral method. Moreover, for the KPZ model, a pseudospectral scheme gives results closer to the predictions of the continuum model than those obtained through finite difference methods. On the other hand, some numerical instabilities appearing with finite difference methods for the LDV model are absent when a pseudospectral integration is performed. These numerical instabilities give rise to an approximate multiscaling observed in the numerical simulations. With the pseudospectral approach no multiscaling is seen in agreement with the continuum model.Comment: 13 single column pages, RevTeX, 6 eps fig

Trajectory-Based, Probabilistic Risk Model for UAS Operations

To enable the safe integration of Unmanned Aircraft System (UAS) into the civil airspace, the European Aviation Safety Agency (EASA) has elaborated a new regulatory framework that is operation-centric and risk-based. Based on this principle, gaining authorization to conduct certain types of operations depends on a safety risk assessment. To harmonize this process, the Joint Authorities for Rulemaking on Unmanned Systems (JARUS) released a qualitative methodology called Specific Operation Risk Assessment (SORA). However, SORA is not a complete safety assessment tool since, in some cases, a quantitative risk analysis is still required. This work develops a probabilistic risk model that extends SORA to evaluate the ground risk and the air risk components along a specified UAS trajectory quantitatively. The proposed model is supplied with illustrative data and is validated in a representative UAS mission. In the future, the risk model will be exploited to develop a decision tool for determining the minimum-risk trajectory when multiple, alternative routes are available

Scaling of Local Slopes, Conservation Laws and Anomalous Roughening in Surface Growth

We argue that symmetries and conservation laws greatly restrict the form of the terms entering the long wavelength description of growth models exhibiting anomalous roughening. This is exploited to show by dynamic renormalization group arguments that intrinsic anomalous roughening cannot occur in local growth models. However some conserved dynamics may display super-roughening if a given type of terms are present.Comment: To appear in Phys. Rev. Lett., 4 pages in RevTeX style, no fig

Catálogo actualizado de los briófitos de la Región de Murcia (Sureste de España)

An updated checklist of the bryophytes of the Region of Murcia is provided. Bryophyte diversity in Murcia consists of 200 especies and 15 infraespecific taxa (77 genera) of mosses and 32 species (20 genera) of liverworts. Grimmia tergestina is confirmed in the territory. Aschisma cuynetii, Brachytheciastrum dieckii, Brachythecium albicans, Brachythecium rutabulum, Brachythecium salebrosum, Bryum alpinum, Bryum elegans, Campyliadelphus chrysophyllus, Campylopus pilifer and Didymodon eckeliae are new reported for Murcia. Bryum tenuisetum, Entosthodon attenuatus and Fissidens bryoides are excluded from the check-list.Se actualiza el catálogo de los briófitos de la Región de Murcia. Para este territorio se aceptan 200 especies y 15 taxones infraespecíficos (77 géneros) de musgos y 32 especies de hepáticas (20 géneros). Grimmia tergestina se confirma en el territorio. Aschisma cuynetii, Brachytheciastrum dieckii, Brachythecium albicans, Brachythecium rutabulum, Brachythecium salebrosum, Bryum alpinum, Bryum elegans, Campyliadelphus chrysophyllus, Campylopus pilifer y Didymodon eckeliae son nuevas citas para Murcia. Bryum tenuisetum, Entosthodon attenuatus y Fissidens bryoides se excluyen del catálogo