805 research outputs found
Partner selection in indoor-to-outdoor cooperative networks: an experimental study
In this paper, we develop a partner selection protocol for enhancing the
network lifetime in cooperative wireless networks. The case-study is the
cooperative relayed transmission from fixed indoor nodes to a common outdoor
access point. A stochastic bivariate model for the spatial distribution of the
fading parameters that govern the link performance, namely the Rician K-factor
and the path-loss, is proposed and validated by means of real channel
measurements. The partner selection protocol is based on the real-time
estimation of a function of these fading parameters, i.e., the coding gain. To
reduce the complexity of the link quality assessment, a Bayesian approach is
proposed that uses the site-specific bivariate model as a-priori information
for the coding gain estimation. This link quality estimator allows network
lifetime gains almost as if all K-factor values were known. Furthermore, it
suits IEEE 802.15.4 compliant networks as it efficiently exploits the
information acquired from the receiver signal strength indicator. Extensive
numerical results highlight the trade-off between complexity, robustness to
model mismatches and network lifetime performance. We show for instance that
infrequent updates of the site-specific model through K-factor estimation over
a subset of links are sufficient to at least double the network lifetime with
respect to existing algorithms based on path loss information only.Comment: This work has been submitted to IEEE Journal on Selected Areas in
Communications in August 201
Ballistic charge transport in a triple-gate silicon nanowire transistor
In this paper we investigate the electrostatics and charge transport in a triplegate
Silicon Nanowire transistor. The quantum confinement in the transversal dimension
of the wire have been tackled using the Schr¨odinger equation in the Effective Mass Approximation
coupled to the Poisson equation. This system have been solved efficiently
using a Variational Method. The charge transport along the longitudinal dimension of the
wire has been considered using the semiclassical approximation, in the ballistic regime
Cation composition effects on oxide conductivity in the Zr_2Y_2O_7-Y_3NbO_7 system
Realistic, first-principles-based interatomic potentials have been used in
molecular dynamics simulations to study the effect of cation composition on the
ionic conductivity in the Zr2Y2O7-Y3NbO7 system and to link the dynamical
properties to the degree of lattice disorder. Across the composition range,
this system retains a disordered fluorite crystal structure and the vacancy
concentration is constant. The observed trends of decreasing conductivity and
increasing disorder with increasing Nb5+ content were reproduced in simulations
with the cations randomly assigned to positions on the cation sublattice. The
trends were traced to the influences of the cation charges and relative sizes
and their effect on vacancy ordering by carrying out additional calculations in
which, for example, the charges of the cations were equalised. The simulations
did not, however, reproduce all the observed properties, particularly for
Y3NbO7. Its conductivity was significantly overestimated and prominent diffuse
scattering features observed in small area electron diffraction studies were
not always reproduced. Consideration of these deficiencies led to a preliminary
attempt to characterise the consequence of partially ordering the cations on
their lattice, which significantly affects the propensity for vacancy ordering.
The extent and consequences of cation ordering seem to be much less pronounced
on the Zr2Y2O7 side of the composition range.Comment: 22 pages, 8 figures, submitted to Journal of Physics: Condensed
Matte
Cooperative Regions For Coded Cooperation Over Time-Varying Fading Channels
The performance analysis of coded cooperation has been mainly focused on two extreme cases of channel variability, i.e. the block-fading (BF) and the fast-fading (FF) model. In more practical propagation environments the fading correlation across time depends on the level of user mobility. This paper analyzes the effects of time-selective fading on the performance of coded cooperation by providing an analytical framework for the error rate evaluation as a function of the mobility degree of the mobile station (MS) and of the quality of the inter-MS channel. The purpose is to evaluate the conditions on the propagation settings where the additional exploitation of spatial diversity (when time-diversity is available) provided by cooperative transmission is able to enhance substantially the performance of the non-cooperative transmission. We show that coded cooperation can outperform the non-cooperative (coded and bit-interleaved) transmission only up to a certain degree of mobility. The cooperative region is defined as the collection of mobility settings for which coded cooperation can be regarded as a competitive strategy compared to non-cooperative transmission. Contrary to what has been previously shown for BF channels, we demonstrate that the inter-MS channel quality plays a key role in the definition of the cooperative region
investigation of integrated organic rankine cycles and wind turbines for micro scale applications
Abstract The aim of this work is the investigation of the performance of an innovative biomass/wind energy integrated system for Combined Heat and Power (CHP) generation in small-scale applications. The system is based on an Organic Rankine Cycle (ORC) fed with biomass and a wind turbine (WT). The ORC and WT sub-systems operate in parallel to produce the required electrical energy and an auxiliary boiler provides thermal energy if the CHP output is low. A preliminary investigation is performed to define the proper size of the wind turbine. Afterwards, the analysis is focused on the integrated system. In particular, the application to the Italian residential sector is analysed. Results illustrate that hybridisation improves the global conversion efficiency, by reducing the biomass consumption and overcoming the intermittency of the wind source. When the wind source is significant, the ORC system can be switched off or operated at partial load
Analysis of multi-source energy system for small-scale domestic applications. Integration of biodiesel, solar and wind energy
The paper aims at analysing the energy performance of an innovative multi-source energy system for residential small-scale combined heat and power (CHP) applications. The integrated system is based on an Organic Rankine Cycle (ORC) fuelled by biodiesel, a wind turbine, and a photovoltaic unit. The application refers to the Italian residential sector. The ORC system operates in order to satisfy the thermal demand of domestic users while wind and solar based sub-systems work in parallel to increase the electric self-consumption rate. An auxiliary boiler provides thermal energy when the CHP thermal output is low. Furthermore, when the solar and/or wind sources are significant, the ORC can be switched-off or operated at partial load.A preliminary investigation is performed to define the proper size of the ORC unit. Afterwards, the analysis is focused on a multi-variable optimisation of the integrated system. In particular, the nominal power of the wind turbine and photovoltaic units have been found in order to guarantee a proper trade-off between electric self-consumed and surplus energy. Keywords: Biodiesel, Combined heat and power, Multi-source generation, Organic Rankine cycle, Solar, Win
Phylogenetic analysis of grapevine cv. Ansonica growing on the island of Giglio, Italy, by AFLP and SSR markers
The geographic origin of the grapevine cultivar Ansonica (Vitis vinifera L.) grown on the island of Giglio, Tuscany, Italy, was investigated with molecular tools, i.e. AFLP and SSR (microsatellite) analysis. The scored polymorphic DNA bands were statistically analysed and the results were expressed in dendrograms showing the degree of genomic similarity among the tested cultivars: three Ansonica vines sampled in some of the oldest vineyards of the island, one Ansonica specimen grown in Tuscany, one Inzolia specimen grown in Sicily, 23 cultivars grown in different Mediterranean regions and 40 Greek cultivars. The results obtained from AFLP or SSR approaches led to equivalent conclusions: the three grapevines sampled in Giglio were indistinguishable and showed genetic similarity with cv. Ansonica grown in the Tuscan mainland and with cv. Inzolia from Sicily, Airen from Spain, Clairette from France and Roditis from Greece. The SSR analysis showed that Sideritis and Roditis have the highest genomic similarity with Ansonica among the 40 tested Greek cultivars. The molecular analysis gives conclusive evidence for the Greek origin of Ansonica grown on the island, as previously proposed on the basis of morphological and historical studies
Phylogenetic analysis of grapevine cv. Ansonica growing on the island of Giglio, Italy, by AFLP and SSR markers
The geographic origin of the grapevine cultivar Ansonica (Vitis vinifera L.) grown on the island of Giglio, Tuscany, Italy, was investigated with molecular tools, i.e. AFLP and SSR (microsatellite) analysis. The scored polymorphic DNA bands were statistically analysed and the results were expressed in dendrograms showing the degree of genomic similarity among the tested cultivars: three Ansonica vines sampled in some of the oldest vineyards of the island one Ansonica specimen grown in Tuscany, one Inzolia specimen grown in Sicily, 23 cultivars grown in different Mediterranean regions and 40 Greek cultivars. The results obtained from AFLP or SSR approaches led to equivalent conclusions: the three grapevines sampled in Giglio were indistinguishable and showed genetic similarity with cv. Ansonica grown in the Tuscan mainland and with cv. Inzolia from Sicily, Airen from Spain, Clairette from France and Roditis from Greece. The SSR analysis showed that Sideritis and Roditis have the highest genomic similarity with Ansonica among the 40 tested Greek cultivars. The molecular analysis gives conclusive evidence for the Greek origin of Ansonica grown on the island, as previously proposed on the basis of morphological and historical studies
Immune control of HIV-1 infection after therapy interruption: immediate versus deferred antiretroviral therapy
Abstract Background The optimal stage for initiating antiretroviral therapies in HIV-1 bearing patients is still a matter of debate. Methods We present computer simulations of HIV-1 infection aimed at identifying the pro et contra of immediate as compared to deferred Highly Active Antiretroviral Therapy (HAART). Results Our simulations highlight that a prompt specific CD8+ cytotoxic T lymphocytes response is detected when therapy is delayed. Compared to very early initiation of HAART, in deferred treated patients CD8+ T cells manage to mediate the decline of viremia in a shorter time and, at interruption of therapy, the virus experiences a stronger immune pressure. We also observe, however, that the immunological effects of the therapy fade with time in both therapeutic regimens. Thus, within one year from discontinuation, viral burden recovers to the value at which it would level off in the absence of therapy. In summary, simulations show that immediate therapy does not prolong the disease-free period and does not confer a survival benefit when compared to treatment started during the chronic infection phase. Conclusion Our conclusion is that, since there is no therapy to date that guarantees life-long protection, deferral of therapy should be preferred in order to minimize the risk of adverse effects, the occurrence of drug resistances and the costs of treatment.</p
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