Spontaneous Momentum Dissipation and Coexistence of Phases in Holographic Horndeski Theory

We discuss the possible phases dual to the AdS hairy black holes in Horndeski theory. In the probe limit breaking the translational invariance, we study the conductivity and we find a non-trivial structure indicating a collective excitation of the charge carriers as a competing effect of momentum dissipation and the coupling of the scalar field to Einstein tensor. Going beyond the probe limit, we investigate the spontaneous breaking of translational invariance near the critical temperature and discuss the stability of the theory. We consider the backreaction of the charged scalar field to the metric and we construct numerically the hairy black hole solution. To determine the dual phases of a hairy black hole, we compute the conductivity. When the wave number of the scalar field is zero, the DC conductivity is divergent due to the conservation of translational invariance. For nonzero wave parameter with finite DC conductivity, we find two phases in the dual theory. For low temperatures and for positive couplings, as the temperature is lower, the DC conductivity increases therefore the dual theory is in metal phase, while if the coupling is negative we have the opposite behavior and it is dual to an insulating phase. We argue that this behavior of the coupling of the scalar field to Einstein tensor can be attributed to its role as an impurity parameter in the dual theory.Comment: 21 pages,15 figures. Published versio

A Service Based Architecture for Multidisciplinary IoT Experiments with Crowdsourced Resources

Research on emerging networking paradigms, such as Mobile Crowdsensing Systems, requires new types of experiments to be conducted and an increasing spectrum of devices to be supported by experimenting facilities. In this work, we present a service based architecture for IoT testbeds which (a) exposes the operations of a testbed as services by following the Testbed as a Service (TBaaS) paradigm; (b) enables diverse facilities to be federated in a scalable and standardized way and (c) enables the seamless integration of crowdsourced resources (e.g. smartphones and wearables) and their abstraction as regular IoT resources. The architecture enables an experimenter to access a diverse set of resources and orchestrate experiments via a common interface by hiding the underlying heterogeneity and complexity. This way, the field of IoT experimentation with real resources is further promoted and broadened to also address researchers from other fields and discipline

Sizing a hybrid wind-diesel stand-alone system on the basis of minimum long-term electricity production cost

Hybrid wind-diesel systems are an interesting solution for the electrification of isolated consumers. The proposed system, including a properly sized battery, leads to a significant reduction of the fuel consumption, in comparison with a diesel-only installation, also protecting the diesel generator from excessive wear. On the other hand, a properly designed wind-diesel installation remarkably reduces the required battery capacity, in relation to a wind-only based stand-alone system, especially in medium-low wind potential areas. In this context, a complete sizing model, based on a long-term energy production cost analysis is developed, able to predict the optimum configuration of a hybrid wind-diesel stand-alone system on the basis of minimum long-term cost. According to the application results obtained for representative wind potential cases, the proposed hybrid system guarantees one year's long energy autonomy of a typical remote consumer, presenting a significant cost advantage in relation either to a diesel-only or to a wind-based stand-alone system.Hybrid wind-diesel system Stand-alone Optimum system sizing Energy cost Long-term operational cost

Optical Properties and Applications of Nanoscale Silicon

This paper, from Adam Filios, Yeong S. Ryu, and Kamal Shahrabi, of Farmingdale State College, covers optical properties and application of nanoscale silicon. Topics covered include the importance of silicon, silicon optoelectronics and nanotechnology, light emissions from nanoscale silicon, and characterization of silicon nanoparticles by raman spectroscopy, among others.Â

Income loss due to wind energy rejected by the Crete island electrical network - the present situation

During the last 4 years, a substantial wind energy penetration was encountered mainly in the Greek mainland. At the same time, limited size new wind-parks were built in the numerous Greek islands, although their wind potential is clearly higher than the one for the mainland and their wind energy generation could be used to replace electricity produced by diesel engines and gas turbines at moderate and high cost, respectively. This negative conclusion for the Greek island communities underlines the inability of the local weak autonomous electrical networks to entirely absorb the gradually increased wind-energy production. Thus, in the present work, special attention is paid to correctly estimate the annual income loss of existing wind-parks, due to the wind energy rejection by the autonomous island electrical grids. For this purpose a complete and reliable method is developed, able to realistically calculate the instantaneous wind-power production rejected by the local electricity-generation system, according to the information provided by the system operator and the wind-park owners. The present analysis is based on extensive time series of real data and measurements. Applying the proposed method to the Crete-island network situation, a remarkable amount of wind produced electric-energy rejection is predicted for the last 3 years, which is definitely rising in the course of time. Calculation results are well in agreement with the official monthly data provided by the local power-utility, in view of the existing power-purchase agreement between the private wind-power investors and the local network management.Wind power Autonomous electrical-generation systems Energy rejection Financial loss Wind park Power-purchase agreement

Riconnettere il tessuto di Atene Piranesi Prix de Rome et d’Athènes – 2022-23 Call internazionale di Progettazione per l’Acropoli di Atene e le adiacenze comprese nella buffer zone UNESCO

Reconnecting the Fabric of Athens Introduction, objectives, method Dimitris Pikionis, the architect who redesigned the paths of the Acropolis and the Philopappus, inspired us for a sentimental topography project. On its path, our urban graft introduces an ephemeral and light architecture, capable of transforming itself over time. Its pavements convey a strong message: use a collage of materials from different cultures and eras to create a timeless result. He works according to the concept of 'hiding and framing', showcasing monuments and connecting the visitor with nature and landscape. Following these principles, our routes evoke the original itineraries of the area. A paving, inspired by the work of Paul Klee, a master for Pikionis himself, makes way for citizens and visitors by dressing the colours that once adorned the monuments of ancient Greece. Intervention in the archaeological space of the Plateau is minimal. The restoration site here is intertwined with the sightseeing tour, instructing the visitor in the work in progress. Scope 1 We acted on several fronts using recurring components, 'objects' in natural materials, repeatable, adaptable, variably modular; these are pergolas, fences and pavings. Accessibility and multi-sensory enjoyment are objectives pursued here for both fenced archaeological sites and new and existing free access areas. We redefine the perimeters of some of the existing archaeological sites and extend the free ones by integrating them into the existing green system. We reopen the Panathenaic Way, now almost forgotten, rehabilitating its daily use, guiding the visitor towards the Acropolis starting from the Kerameikos and passing through the Agora. We cover the stretch connecting the Panathenaic Street with Monastiraki Square and the Kerameikos site. Between the Ancient Agora and the Pnice we envisage an intervention that extends the public spaces, particularly in the natural hollow that separates the hill of the Areopagos from the Pnice. At the esplanade on the Pnice hill, we envisage a pavement that promotes the organisation of outdoor events. At the main entrance to the site of the Acropolis we envisage two large pergolas under which new ticket booths manage the incoming flows, while a new entrance to the archaeological area of the Agora punctually widens the pedestrian street Apostolou Pavlou. In the area to the east of the Theatre of Dionysus, we propose to complement our general reconnection proposal with new pedestrian routes. Scope 2 Pursuing the general idea of 'reconnection' we redesign the main access to the Acropolis, improving the use of these spaces by adding new paving and shading elements. The entrance to the caves on the north side of the Acropolis is redesigned so that they are open and usable to the public. We revitalise the Peripatos by upgrading its paths, including by reopening the Via Panatenaica. In addition, we enhance elements such as the boundary stone of the fountain-house, the Koranic monument Thrasyllos and the adjacent Christian church. Scope 3 Regarding the plateau of the Acropolis, we want to improve the visitor experience by remaining almost 'invisible' as with the Pikionis project. We introduce vegetal elements, in particular on the Persian trench, which without occluding the views allow new shading. We rethink the organisation of the site areas, rationalising and optimising them, moving containers, screening them with vegetation and moving the most impactful ones to the old museum. The existing building thus becomes a place to support the construction site and the restoration workshop. Its roof becomes practicable, paved and with elements of potted greenery, without impairing existing views and panoramic cones, but rather creating new ones. Imagine, therefore, a continuous building site, able to fascinate and educate visitors to understand the place where the classical world originated, as well as the very idea of architecture