Fibration models and localisation of categories

AbstractWe define a fibration model on the basis of a Thomason model and use it to analyse the localisation of a category. We show that the model suffices to prove existence of the localisation and to develop the basic homological tools, including derived functors, homotopy pullbacks and the unstable triangulated structure. The corresponding constructions in the case of Quillen, Baues and Thomason models can be recovered as special cases

Feasibility Analysis of Retrofit Strategies for the Achievement of NZEB Target on a Historic Building for Tertiary Use

Abstract According to directive 2010/31/EU, a NZEB (nearly zero energy building) is defined as a high performance building whose very low or almost zero energy needs should be mostly provided by renewable sources. The study reported in this work has the objective to establish criteria and design solutions to improve buildings energy performances in order to reach NZEB targets for those buildings characterized by historical constraints. For this purpose, a comparative numerical analysis on the space cooling and heating of a historical building sited in Agrigento (Sicily, Italy) was performed by means of two energy tools: Termo and Trnsys. The first one is a stationary energy certification software based on the algorithms and mathematical methods listed in the UNI TS 11300 standard reference. The second one is a well calibrated dynamic tool based on hourly climate data and able to take into account the thermal inertia phenomena of structures. In order to obtain reliable results, measured climate data extracted from a weather station located near the reference building were used as input for the simulations. Starting from the simulation results, several retrofit scenarios were hypothesized, in order to achieve NZEB target, and then followed by a cost analysis carried out to reach optimal economic solutions and energy savings. The study can constitute a contribution to policy formulation and adoption of measures to facilitate design choices for the energy improving of historical buildings

A new tri-generation system: thermodynamical analysis of a micro compressed air energy storage

There is a growing interest in the electrical energy storage system, especially for matching intermittent sources of renewable energy with customers’ demand. Furthermore, it is possible, with these system, to level the absorption peak of the electric network (peak shaving) and the advantage of separating the production phase from the exertion phase (time shift). CAES (compressed air energy storage systems) are one of the most promising technologies of this field, because they are characterized by a high reliability, low environmental impact and a remarkable energy density. The main disadvantage of big systems is that they depend on geological formations which are necessary to the storage. The micro-CAES system, with a rigid storage vessel, guarantees a high portability of the system and a higher adaptability even with distributed or stand-alone energy productions. This article carries out a thermodynamical and energy analysis of the micro-CAES system, as a result of the mathematical model created in a Matlab/Simulink® environment. New ideas will be discussed, as the one concerning the quasi-isothermal compression/expansion, through the exertion of a biphasic mixture, that will increase the total system efficiency and enable a combined production of electric, thermal and refrigeration energies. The exergy analysis of the results provided by the simulation of the model reports that more than one third of the exergy input to the system is lost. This is something promising for the development of an experimental device

Probing Wilson loops in N=4{\cal N}=4 Chern-Simons-matter theories at weak coupling

For three-dimensional ${\cal N}=4$ super Chern-Simons-matter theories associated to necklace quivers $U(N_0) \times U(N_1) \times \cdots U(N_{2r-1})$, we study at quantum level the two kinds of 1/2 BPS Wilson loop operators recently introduced in arXiv:1506.07614. We perform a two-loop evaluation and find the same result for the two kinds of operators, so moving to higher loops a possible quantum uplift of the classical degeneracy. We also compute the 1/4 BPS bosonic Wilson loop and discuss the quantum version of the cohomological equivalence between fermionic and bosonic Wilson loops. We compare the perturbative result with the Matrix Model prediction and find perfect matching, after identification and remotion of a suitable framing factor. Finally, we discuss the potential appearance of three-loop contributions that might break the classical degeneracy and briefly analyse possible implications on the BPS nature of these operators.Comment: 7 pages, 2 figure

opaque construction materials solar loads calculation dependence on directional reflectance

Abstract Generally the solar reflectance associated to construction material surfaces is considered perfectly diffuse, namely they reflect in every direction the incident irradiance. Therefore reflectance and absorptance are assumed to be constant and independent on the incidence angles. This assumption, generally used in the most of energy analysis simulation tools, has to be considered not valid for materials characterized by a regular reflection, like glass or polished surfaces, where an angular dependence of their optical–radiative properties is observed. However, many opaque construction materials often show a mixed behavior, which includes regular and diffuse (or scattering) reflectance components. Moreover, the apparent roughness of the materials surface changes according to the angle of incidence of the solar irradiance. This issue is relevant for some cool materials, which are polished or treated with other methods to offer a very smooth surface, to increase the solar reflectance. In this work the dependence of opaque materials on the directional properties of their surfaces are investigated to assess the impact on solar loads and energy performances of the building envelope. The reflectance shape and the hemispherical values of two materials used for roofing are measured by means of a goniophotometer to characterize the directional reflectance. A numerical analysis was carried out to compute the differences in solar loads during cold and hot seasons between a reflectance angular dependent model and a constant reflectance model. Sensible discrepancies between the two models put in evidence that solar reflectance angular dependence should be included in the calculation tools to achieve more accurate results

A matrix model for the latitude Wilson loop in ABJM theory

In ABJ(M) theory, we propose a matrix model for the exact evaluation of BPS Wilson loops on a latitude circular contour, so providing a new weak-strong interpolation tool. Intriguingly, the matrix model turns out to be a particular case of that computing torus knot invariants in $U(N_1|N_2)$ Chern-Simons theory. At weak coupling we check our proposal against a three-loop computation, performed for generic framing, winding number and representation. The matrix model is amenable of a Fermi gas formulation, which we use to systematically compute the strong coupling and genus expansions. For the fermionic Wilson loop the leading planar behavior agrees with a previous string theory prediction. For the bosonic operator our result provides a clue for finding the corresponding string dual configuration. Our matrix model is consistent with recent proposals for computing Bremsstrahlung functions exactly in terms of latitude Wilson loops. As a by-product, we extend the conjecture for the exact $B^{\theta}_{1/6}$ Bremsstrahlung function to generic representations and test it with a four-loop perturbative computation. Finally, we propose an exact prediction for $B_{1/2}$ at unequal gauge group ranks.Comment: 73 pages; v2: several improvements, JHEP published versio

Characterizing PSPACE with Shallow Non-Confluent P Systems

In P systems with active membranes, the question of understanding the power of non-confluence within a polynomial time bound is still an open problem. It is known that, for shallow P systems, that is, with only one level of nesting, non-con uence allows them to solve conjecturally harder problems than con uent P systems, thus reaching PSPACE. Here we show that PSPACE is not only a bound, but actually an exact characterization. Therefore, the power endowed by non-con uence to shallow P systems is equal to the power gained by con uent P systems when non-elementary membrane division and polynomial depth are allowed, thus suggesting a connection between the roles of non-confluence and nesting depth

Characterizing PSPACE with Shallow Non-Confluent P Systems

In P systems with active membranes, the question of understanding the power of non-confluence within a polynomial time bound is still an open problem. It is known that, for shallow P systems, that is, with only one level of nesting, non-con uence allows them to solve conjecturally harder problems than con uent P systems, thus reaching PSPACE. Here we show that PSPACE is not only a bound, but actually an exact characterization. Therefore, the power endowed by non-con uence to shallow P systems is equal to the power gained by con uent P systems when non-elementary membrane division and polynomial depth are allowed, thus suggesting a connection between the roles of non-confluence and nesting depth

Percutaneous ablation holds the potential to substitute for surgery as first choice treatment for symptomatic benign thyroid nodules.

Sir,We read with interest the letter by Tez M. regarding our article recently published in International Journal of Hyperthermia entitled "Benign thyroid nodules treatment using percutaneous laser ..

Is operators' experience more important than the ablation technique in image-guided thermal ablations?

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