Kinetics of Si and Ge nanowires growth through electron beam evaporation

Si and Ge have the same crystalline structure, and although Si-Au and Ge-Au binary alloys are thermodynamically similar (same phase diagram, with the eutectic temperature of about 360°C), in this study, it is proved that Si and Ge nanowires (NWs) growth by electron beam evaporation occurs in very different temperature ranges and fluence regimes. In particular, it is demonstrated that Ge growth occurs just above the eutectic temperature, while Si NWs growth occurs at temperature higher than the eutectic temperature, at about 450°C. Moreover, Si NWs growth requires a higher evaporated fluence before the NWs become to be visible. These differences arise in the different kinetics behaviors of these systems. The authors investigate the microscopic growth mechanisms elucidating the contribution of the adatoms diffusion as a function of the evaporated atoms direct impingement, demonstrating that adatoms play a key role in physical vapor deposition (PVD) NWs growth. The concept of incubation fluence, which is necessary for an interpretation of NWs growth in PVD growth conditions, is highlighted

Symmetries, Cluster Synchronization, and Isolated Desynchronization in Complex Networks

Synchronization is of central importance in power distribution, telecommunication, neuronal, and biological networks. Many networks are observed to produce patterns of synchronized clusters, but it has been difficult to predict these clusters or understand the conditions under which they form, except for in the simplest of networks. In this article, we shed light on the intimate connection between network symmetry and cluster synchronization. We introduce general techniques that use network symmetries to reveal the patterns of synchronized clusters and determine the conditions under which they persist. The connection between symmetry and cluster synchronization is experimentally explored using an electro-optic network. We experimentally observe and theoretically predict a surprising phenomenon in which some clusters lose synchrony while leaving others synchronized. The results could guide the design of new power grid systems or lead to new understanding of the dynamical behavior of networks ranging from neural to social

Complete Characterization of Stability of Cluster Synchronization in Complex Dynamical Networks

Synchronization is an important and prevalent phenomenon in natural and engineered systems. In many dynamical networks, the coupling is balanced or adjusted in order to admit global synchronization, a condition called Laplacian coupling. Many networks exhibit incomplete synchronization, where two or more clusters of synchronization persist, and computational group theory has recently proved to be valuable in discovering these cluster states based upon the topology of the network. In the important case of Laplacian coupling, additional synchronization patterns can exist that would not be predicted from the group theory analysis alone. The understanding of how and when clusters form, merge, and persist is essential for understanding collective dynamics, synchronization, and failure mechanisms of complex networks such as electric power grids, distributed control networks, and autonomous swarming vehicles. We describe here a method to find and analyze all of the possible cluster synchronization patterns in a Laplacian-coupled network, by applying methods of computational group theory to dynamically-equivalent networks. We present a general technique to evaluate the stability of each of the dynamically valid cluster synchronization patterns. Our results are validated in an electro-optic experiment on a 5 node network that confirms the synchronization patterns predicted by the theory.Comment: 6 figure

Heteroepitaxial Growth of Ge Nanowires on Si Substrates

Electron beam evaporation has been used to prepare Ge nanowires (NWs) on top of (111) Si substrates. Despite the non-UHV growth conditions, scanning and transmission electron microscopies demonstrate that NWs are single crystal with specific crystallographic growth directions ([111], [110], and [112]). NWs are faceted, exhibiting the lower energy plans on the surface. The faceting depends on the growth direction. Moreover, the detrimental effects for Ge NWs growth of O atoms contamination are discussed. Finally, we describe how a proper preparation of the Au catalyst is able to increase the Ge NW density by a factor of 4, while heteroepitaxy and faceting features are maintained

Morphing Technologies: Adaptive Ailerons

European Union is involving increasing amount of resources on research projects that will dramatically change the costs of building and operating aircraft in the near future. Morphing structures are a key to turn current airplanes to more efficient and versatile means of transport, operating into a wider range of flight conditions

GIS system and livestock field survey as tools to manage the potential reducing of fuel load for fire prevention

This study would mark the potential role of grazing by Podolian cattle for reducing fuel load of fire prevention and propagation. The interconnection of Geographic Information System (GIS) and livestock field survey allowed to monitor different grazing and nograzing areas in Basilicata region. Fifteen grazing areas were monitored for five years during the summer pasture, when the Podolian cattle graze on green grazing areas. These areas were monitored by using GIS system and GPS application. The potential impact of Podolian cattle was monitored for the same time period. The cattle consistency allowed to calculate different parameters: livestock unit, dry matter intake and stocking estimation of potential amount of dry matter intake to understand the removal biomass in order to reduce the fuel load for fire prevention. The spatial analysis (GIS) showed that there were only four grazing areas burned during the time sampling, compared to the surrounding areas used as control (no-grazing area). Therefore an efficient management of grazing by Podolian cattle could be an important tool to prevent the fire propagation

A multiscale approach for BTJ-VCSEL electro-optical analysis

This paper presents a theoretical comparison of the electro-optical characteristics of 850nm GaAs/AlGaAs pin-and BTJ-based VCSELs. The calculations are based on a drift-diffusion model coupled with a NEGF formalism, able to model accurately the tunneling across the TJ. The resulting LIV characteristics demonstrate promising improvements, at both 25 and 80°C, enabled by TJ confinement scheme