1,721,300 research outputs found
Towards a rational nomenclature of cultivated plants: proposal of taxonomic reassessment of Cicer reticulatum (Fabaceae) and Spinacia turkestanica (Chenopodiaceae)
No full textGuacchio, E. Del, Caputo, P. (2022): Towards a rational nomenclature of cultivated plants: proposal of taxonomic reassessment of Cicer reticulatum (Fabaceae) and Spinacia turkestanica (Chenopodiaceae). Phytotaxa 558 (3): 298-300, DOI: 10.11646/phytotaxa.558.3.
Materiali per lo Studio Storico Archeologico di Quarto Flegreo Carta archeologica dalla preistoria al tardo-antico
No full text
Biomass district heating system in Italy: A comprehensive model-based method for the assessment of energy, economic and environmental performance
Full text linkIn the framework of the energy strategy toward 2050, district heating systems (DHS) offers a great flexibility in terms of heat generation technologies and renewable resources integration, resulting, in case of proper management and supply conditions, in fossil primary energy and greenhouse gases savings compared to conventional technologies. In Italy, only the 2.5% of the thermal final uses are satisfied by DHS and, although widely available over the territory, those fuelled by wooden biomass represent less than the half of the total. Many studies in this framework have highlighted the need of methods and tools for a better understanding of the operative conditions, of the potentialities and of the optimal evolution of biomass DHS. To that end, a proper simulation model has been developed and calibrated on a real case study operating in cogeneration, in an urban area of Northern Italy. After investigating the current performance of the real case, some criticalities have been described and new operating scenarios have been defined and simulated. The achieved results represent a support for the stakeholders involved in BDHS and for future energy policies, providing hints on possible challenging evolutive scenarios and on measures to enhance the energy performance and the economic appeal
Block Factorization of the Relative Entropy via Spatial Mixing
No full textWe consider spin systems in the d-dimensional lattice Zd satisfying the so-called strong spatial mixing condition. We show that the relative entropy functional of the corresponding Gibbs measure satisfies a family of inequalities which control the entropy on a given region V⊂ Zd in terms of a weighted sum of the entropies on blocks A⊂ V when each A is given an arbitrary nonnegative weight αA. These inequalities generalize the well known logarithmic Sobolev inequality for the Glauber dynamics. Moreover, they provide a natural extension of the classical Shearer inequality satisfied by the Shannon entropy. Finally, they imply a family of modified logarithmic Sobolev inequalities which give quantitative control on the convergence to equilibrium of arbitrary weighted block dynamics of heat bath type
Mixing time of PageRank surfers on sparse random digraphs
No full textWe consider the generalized PageRank walk on a digraph G, with refresh probability (Formula presented.) and resampling distribution (Formula presented.). We analyze convergence to stationarity when G is a large sparse random digraph with given degree sequences, in the limit of vanishing (Formula presented.). We identify three scenarios: when (Formula presented.) is much smaller than the inverse of the mixing time of G the relaxation to equilibrium is dominated by the simple random walk and displays a cutoff behavior; when (Formula presented.) is much larger than the inverse of the mixing time of G on the contrary one has pure exponential decay with rate (Formula presented.); when (Formula presented.) is comparable to the inverse of the mixing time of G there is a mixed behavior interpolating between cutoff and exponential decay. This trichotomy is shown to hold uniformly in the starting point and uniformly in the resampling distribution (Formula presented.)
Stationary distribution and cover time of sparse directed configuration models
No full textWe consider sparse digraphs generated by the configuration model with given in-degree and out-degree sequences. We establish that with high probability the cover time is linear up to a poly-logarithmic correction. For a large class of degree sequences we determine the exponent γ≥ 1 of the logarithm and show that the cover time grows as nlog γ(n) , where n is the number of vertices. The results are obtained by analysing the extremal values of the stationary distribution of the digraph. In particular, we show that the stationary distribution π is uniform up to a poly-logarithmic factor, and that for a large class of degree sequences the minimal values of π have the form 1nlog1-γ(n), while the maximal values of π behave as 1nlog1-κ(n) for some other exponent κ∈ [0 , 1]. In passing, we prove tight bounds on the diameter of the digraphs and show that the latter coincides with the typical distance between two vertices
Mixing time trichotomy in regenerating dynamic digraphs
No full textWe study the convergence to stationarity for random walks on dynamic random digraphs with given degree sequences. The digraphs undergo full regeneration at independent geometrically distributed random time intervals with parameter α. Relaxation to stationarity is the result of an interplay of regeneration and mixing on the static digraph. When the number of vertices n tends to infinity and the parameter α tends to zero, we find three scenarios according to whether αlogn converges to zero, infinity or to some finite positive value: when the limit is zero, relaxation to stationarity occurs in two separate stages, the first due to mixing on the static digraph, and the second due to regeneration; when the limit is infinite, there is not enough time for the static digraph to mix and the relaxation to stationarity is dictated by the regeneration only; finally, when the limit is a finite positive value we find a mixed behavior interpolating between the two extremes. A crucial ingredient of our analysis is the control of suitable approximations for the unknown stationary distribution
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