Performance Evolution in Satellite Communication Networks Along with Markovian Channel Prediction

Abstract Augmenting accurate predict ion of channel attenuations can be of immense value in improving the quality of signals athigh frequency for satellite co mmunication networks. Such prediction of weather related attenuation factors for the impendingweather conditions based on the weather data and the Markovian theory are the main object of this paper. The paper also describes anintelligent weather aware control system (IWACS) that is used to emp loy the predict ions made fro m Markov model to maintainthe quality of service (QoS) in channels that are impacted by rain, gaseous, cloud, fog, and scintillat ion attenuations. Based onthat, a three dimensional relationship is proposed among estimated at mospheric attenuations, propagation angle, and predictedrainfall rate (RR pr ) at a given location and operational frequency. This novel method of pred icting weather characteristicssupplies valuable data for mit igation planning, and subsequently for developing an algorithm to iteratively tune the IWACS byadaptively selecting appropriate channel frequency, modulation, coding, propagation angle, transmission power level, and datatransmission rate to imp rove the satellite's system performance. So me simulat ion results are presented to show the effectiveness of the proposedscheme

Energy Efficient Resource and Topology Management for Heterogeneous Cellular Networks

This thesis investigates how resource and topology management techniques can be applied to achieve energy efficiency while maintaining acceptable quality of service (QoS) in heterogeneous cellular networks comprising high power macrocells and dense deployment of low power small cells. Partially centralised resource and topology management algorithms involving the sharing of decision making responsibilities regarding resource utilization and activation or deactivation of small cells among macrocells, small cells and a central node are developed. Resource management techniques are proposed to enable mobile users to be served by resources of a few small cells. A topology management scheme is applied to switch off idle small cells and switch on sleeping cells in accordance with traffic load and QoS. Resource management techniques, when combined with the topology management technique, achieve significant energy efficiency. A choice restriction technique that restricts users to resources from only a subset of suitable small cells is proposed to mitigate interference and improve QoS. A good balance between energy efficiency and QoS is achieved through this approach. Furthermore, energy saving under different generations of small cell base stations is investigated to provide insights to guide the design of energy saving strategies and the enhancement of existing ones. Also, an online, adaptive energy efficient joint resource and topology management technique is developed to correct deteriorating QoS conditions automatically by using a novel confidence level strategy to estimate QoS and regulate decision making epochs at the central node. Finally, a novel linear search scheme is applied together with database records of performance metrics to select appropriate resource and topology management policies for different traffic loads. This approach achieves better balance between QoS and energy efficiency than previous schemes proposed in the literature

At the Interface of Isomorphous Behavior in a 3 × 3 Isomer Grid of Monochlorobenzamides: Analyses of the Interaction Landscapes via Contact Enrichment Studies

International audienceThe physicochemical properties of a 33 isomer grid of mono-chlorobenzamides (Clxx) are reported with comprehensive studies of their crystal structures and interaction environments (Clx = para-/meta-/ortho-chlorobenzoyl and x = para-/meta-/ortho-aminopyridine substitutions). The nine compound Clxx series was synthesised from the three p-/m-/o-chlorobenzoyl chlorides and three p-/m-/o-aminopyridine isomers using standard synthetic procedures. Clxx exhibits some similarities to the related Fxx and Brxx congeners e.g. the isomorphous behaviour of Clpp (para-Chloro-N'-(para-pyridyl)benzamide) with several close relatives, and there are five isomorphous pairs of Clxx and Brxx crystal structures. Notably Clmp and Clpm both crystallise with Z'=4 in space group P but show important differences. The overall lack of isomers crystallising with solvate molecules is noteworthy, except for Clmm(H 2 O). In all Clxx crystal structures, strong N-H…N hydrogen bonds form, however, Clpo also crystallises as the unexpected Clpo_O polymorph with N-H…O=C intermolecular hydrogen bonding. The Clxo triad (with ortho-pyridines) exhibits the expected cyclic N-H…N dimer formation with R 2 2 (8) hydrogen bonded rings. The H C atom type, forming weak C-H…Cl hydrogen bonds, is the only favoured interaction partner of chlorine in Clxx. Conformational analyses (gas phase) together with crystal contact enrichment studies place Clxx in context and at the interface of hydrogen and halogen bonding interactions, though strong hydrogen bonding dominates. In Clxx the interaction energies with nearest neighbours are shown to contribute to most of the lattice electrostatic energies. The melting temperatures T m show correlation with both molecular symmetry (Carnelley's rule) and total electrostatic energy of the weak interactions; in addition, these T m values can be well predicted from a linear fit combining both descriptors. In Clxx, N-H…N hydrogen bonds dominate, largely in the absence of solvates, and with five Clxx forming isomorphous pairs with Brxx analogues; Clpp being isomorphous with several close benzamide relatives. Analysis of T m reveals correlations involving both symmetry and electrostatic energies

Cellular Automata

Modelling and simulation are disciplines of major importance for science and engineering. There is no science without models, and simulation has nowadays become a very useful tool, sometimes unavoidable, for development of both science and engineering. The main attractive feature of cellular automata is that, in spite of their conceptual simplicity which allows an easiness of implementation for computer simulation, as a detailed and complete mathematical analysis in principle, they are able to exhibit a wide variety of amazingly complex behaviour. This feature of cellular automata has attracted the researchers' attention from a wide variety of divergent fields of the exact disciplines of science and engineering, but also of the social sciences, and sometimes beyond. The collective complex behaviour of numerous systems, which emerge from the interaction of a multitude of simple individuals, is being conveniently modelled and simulated with cellular automata for very different purposes. In this book, a number of innovative applications of cellular automata models in the fields of Quantum Computing, Materials Science, Cryptography and Coding, and Robotics and Image Processing are presented

Structural study and thermoelectric properties of some group 9 ternary metal chalcogenides

The crystal structure and thermoelectric properties of the anion-substituted ternary skutterudites MQ1.5Y1.5 (M = Co, Rh, Ir; Q = Ge, Sn; Y = S, Te) have been investigated. A group theoretical analysis based on powder neutron diffraction data of CoGe1.5Te1.5 is presented, revealing new symmetry elements overlooked in previous studies of similar compounds. The new model obtained was applied in a subsequent neutron diffraction study of the sulphides MGe1.5S1.5 (M = Co, Rh, Ir). A resonant scattering synchrotron experiment has also been performed on the tellurides MQ1.5Te1.5 (M = Co, Rh, Ir; Q = Ge, Sn) in order to assess the extent of anion disorder. The thermoelectric properties of all the compounds under study were measured and put into context with both state-of-the-art and new thermoelectric materials. The synthesis of the fully filled skutterudite LaFe3CoGe6Te6 has also been attempted. The results as well as the theoretical background have been presented in a separate results chapter. An attempted synthesis of the ternary skutterudite RhGe1.5Te1.5 led to the unexpected preparation of the equiatomic RhGeTe phase. Replacement of the transition metal atom by other group 9 elements resulted in the synthesis of the phase CoGeTe. The crystal structure of these materials has been investigated using single-crystal and powder X-ray diffraction. These results have been complemented with a study of both their magnetic and electrical properties. Finally, a thermal conductivity measurement provides an assessment of these materials in terms of their thermoelectric properties up to 350 K. During the course of a study of the Co-Sn-S ternary phase diagram, the ternary phase Co3Sn2S2 was synthesized, instead of the sought CoSn1.5S1.5 phase. It had been reported that such compound presented a break in the resistivity vs. temperature plot around 150 K and was ascribed to a likely phase transition, possibly magnetic. As a result of that, a powder neutron diffraction experiment was undertaken in order to shed some light on the origin of such anomaly. Moreover, transport property and magnetic measurements were carried out to obtain a further insight into the electronic nature of Co3Sn2S2. The results obtained support those of the diffraction experiment and form the last results chapter within this thesis

Towards new generation of neuro-implantable devices : engineering neuron/carbon nanotubes integrated functional units

2008/2009Le nanotecnologie sono un campo delle scienze che utilizza materiali e dispositivi ingegnerizzati aventi la più piccola organizzazione funzionale a livello di dimensioni nanometriche. Questo implica che nanodispositivi e nanomateriali possano interagire con i sistemi biologici a livello molecolare con un elevato grado di specificità. É largamente accettato che l’applicazione delle nanotecnologie nell’ambito delle neuroscienze abbia un forte potenziale (Silva, 2006). In questo contesto, i nanotubi di carbonio (CNT), un’innovativa forma di carbonio composta da strutture tubulari di grafite dalle dimensioni nanometriche dotate di buone proprietà di conduzione elettrica, si sono dimostrati promettenti candidati per sviluppare la tecnologia di dispositivi impiantabili in ambito biomedico. Diversi studi hanno dimostrato la biocompatibilità dei substrati di CNT per i neuroni in termini di adesione, crescita e differenziamento cellulare (riassunti in Sucapane et al., 2009). Al fine di aumentare la nostra conoscenza riguardo alle interazioni presenti in sistemi ibridi formati da CNT e neuroni, abbiamo caratterizzato l’attività di reti neuronali cresciuti su supporti di CNT attraverso la tecnica del patch clamp. Il nostro gruppo ha riportato che circuti neuronali cresciuti in vitro su substrati di CNT presentano un’aumentata attività sinaptica spontanea rispetto al controllo a fronte di comparabili proprietà base (proprietà passive di membrana, morfologia e densità dei neuroni) delle colture nelle due condizioni di crescita (Lovat et al., 2005). Si è quindi ipotizzato che tale aumentata attività spontanea potesse originare da una modificazione nel modo in cui i singoli neuroni generano il segnale elettrico. A tal fine, si sono monitorate variazioni nelle proprietà elettrogeniche di singoli neuroni, utilizzando un protocollo standard per caratterizzare l’integrazione di potenziali d’azione retropropaganti nei dendriti (Larkum et al., 1999). In configurazione current clamp, attraverso brevi iniezioni di corrente nel soma della cellula, abbiamo indotto una serie di regolari potenziali d’azione (PA) a varie frequenze nel neurone sotto registrazione, quindi abbiamo studiato la presenza di un’addizionale depolarizzazione somatica dopo l’ultimo PA del treno. Abbiamo osservato che neuroni di controllo mostrano nella maggioranza dei casi una iperpolarizzazione (AHP) del potenziale di membrana dopo l’ultimo PA del treno, mentre una depolarizzazione (ADP) è presente solo in una piccola quota di casi. In presenza di CNT, invece, l’ADP risulta essere l’evento predominante. L’ADP è inoltre abolita dall’applicazione di CoCl2, un bloccante non specifico dei canali calcio voltaggio dipendenti. Per di più, l’area dell’ADP può essere diminuita dall’applicazione di nifedipina (10 μM) e l’ulteriore coapplicazione di NiCl2 (50 μM) elimina totalmente l’ADP, suggerendo che sia i canali calcio voltaggio dipendenti ad alta soglia di attivazione, sia quelli a bassa soglia, siano coinvolti in questo processo (Cellot et al., 2009). Attraverso la microscopia elettronica a trasmissione (TEM) e, più recentemente, mediante quella a scansione (SEM) è stata messa in evidenza la presenza di discontinui punti di stretto contatto tra CNT e membrane neuronali: la nostra ipotesi è che tali strutture ibride siano in grado di favorire la retropropagazione dei PA nei dendriti distali. La maggiore eccitabilità a livello del singolo neurone, inoltre, potrebbe essere responsabile dell’incremento di attività spontanea della rete neuronale. Abbiamo quindi ulteriormente caratterizzato l’attività della rete neuronale attraverso registrazioni da coppie di neuroni, dove il neurone presinaptico veniva stimolato ad avere treni di potenziali d’azione a 20 Hz in configurazione current clamp e simultaneamente il neurone postsinaptico era monitorato in configurazione voltage clamp per vedere la presenza o l’assenza di una risposta sinaptica. I nostri esperimenti indicano che la probabilità di trovare connessioni monosinaptiche gabaergiche tra neuroni è aumentata in presenza di CNT (56% vs 40% in controllo). Inoltre, è stato rilevato un ulteriore effetto dei CNT sulla plasticità a breve termine delle sinapsi: nelle condizioni di controllo, treni di potenziali d’azione nella cellula presinaptica evocano nella cellula postsinaptica nel 90% dei casi una chiara depressione nell’ampiezza di consecutivi ePSCs, mentre solo in meno del 10% è possibile rilevare una facilitazione. Al contrario, in presenza di CNT, nel 39% delle coppie, il neurone postsinaptico risponde in modo chiaramente facilitativo. Nelle più recenti serie di esperimenti, abbiamo voluto indagare più approfonditamente l’origine di questa modificazione in termini di plasticità sinaptica; a tal fine, abbiamo trattato neuroni in controllo e su CNT con tetrodotossina 1 µM per 5 giorni, al fine di bloccare completamente l’attività elettrica della rete neuronale, e abbiamo compiuto delle registrazioni da coppie di neuroni. Mentre la risposta prevalentemente di depressione dei controlli non è modificata da tale trattamento, neuroni cresciuti su substrati di cnt in condizioni di blocco dell’attività elettrica non presentano più sinapsi con caratteristiche di facilitazione, ma hanno un comportamento simile ai contolli. Questi risultati indicano che la facilitazione è una proprietà tipica di sinapsi attive sviluppatesi in presenza di CNT.XXII Ciclo198

Localised electronic states in model systems and semiconductors

Accurately modelling charge trapping phenomena is a vital part of understanding and improving the behaviour of semiconductors in both current and future devices. While charge traps are frequently observed in doped crystals, the formation of socalled self-trapped polarons means that charges can trap even in defect-free bulk crystals. This in turn reduces charge carrier mobility in materials, sometimes to the detriment of the underlying device. More effective methods of modelling self-trapping typically introduce a few free parameters, each of which can significantly influence results obtained by the model. The focus of this thesis is on developing parameterfree, computationally inexpensive and accurate approaches to modelling charge trapping, with a focus on titanium dioxide, a material used in promising new photovoltaics. Through comparison to both experimental data and solutions to the exact many-electron Schr¨odinger equation, this thesis demonstrates that use of the generalised Koopmans’ theorem in conjunction with hybrid functionals can yield strikingly accurate results. This technique is subsequently used to predict the formation of selftrapped charges in a number of titania phases, including the well-studied rutile and anatase, and less-known brookite, TiO2(H), TiO2(R) and TiO2(B). Intrinsic point defects are also investigated in rutile and anatase, where it is found that several interesting and unique electronic phenomena occur in their vicinity