Unified Dark Matter scalar field models with fast transition

We investigate the general properties of Unified Dark Matter (UDM) scalar field models with Lagrangians with a non-canonical kinetic term, looking specifically for models that can produce a fast transition between an early Einstein-de Sitter CDM-like era and a later Dark Energy like phase, similarly to the barotropic fluid UDM models in JCAP1001(2010)014. However, while the background evolution can be very similar in the two cases, the perturbations are naturally adiabatic in fluid models, while in the scalar field case they are necessarily non-adiabatic. The new approach to building UDM Lagrangians proposed here allows to escape the common problem of the fine-tuning of the parameters which plague many UDM models. We analyse the properties of perturbations in our model, focusing on the the evolution of the effective speed of sound and that of the Jeans length. With this insight, we can set theoretical constraints on the parameters of the model, predicting sufficient conditions for the model to be viable. An interesting feature of our models is that what can be interpreted as w_{DE} can be <-1 without violating the null energy conditions.Comment: Slightly revised version accepted for publication in JCAP, with a few added references; 27 pages, 13 figure

Affine parameterization of the dark sector: costraints from WMAP5 and SDSS

We study a set of universe models where the dark sector is described by a perfect fluid with an affine equation of state $P=P_0+\alpha \rho$, focusing specifically on cosmological perturbations in a flat universe. We perform a Monte Carlo Markov Chain analysis spanning the full parameter space of the model using the WMAP 5 years data and the SDSS LRG4 survey. The affine fluid can either play the role of a unified dark matter (UDM), accounting for both dark matter and a cosmological constant, or work alongside cold dark matter (CDM), as a form of dark energy. A key ingredient is the sound speed, that depends on the nature of the fluid and that, for any given background model, adds a degree of freedom to the perturbations: in the barotropic case the square of the sound speed is simply equal to the affine parameter $\alpha$; if entropic perturbations are present the effective sound speed has to be specified as an additional parameter. In addition to the barotropic case, we consider the two limiting cases of effective sound speed equal to 0 or 1. For $\alpha=c_s^2=0$ our UDM model is equivalent to the standard $\Lambda$CDM with adiabatic perturbations. Apart of a trivial subcase, all models considered satisfy the data constraints, with quite standard values for the usual cosmological parameters. In general our analysis confirms that cosmological datasets require both a collisionless massive and cold component to form the potential wells that lead to structure formation, and an effective cosmological constant that drives the late accelerated expansion.Comment: 10 pages, 9 figure

A Zero Energy Concept Building for the Mediterranean Climate

open4siThe Mediterranean climate distinguishes for a mild heating season and a hot (and usually dry) cooling season. All along the year solar radiation is plentiful and the daily range of temperature during the summer is large, due to dry and clear conditions. This environment allowed to design and build a zero energy concept building (a detached single family house) on the basis of passive heating and cooling technologies, supported, when required, by short time active conditioning. The design process was optimized by extensive energy simulations, resulting in an optimal energy balance and favorable thermal comfort conditions along the year. The building is instrumented with an accurate building automation control system, and a number of sensors for a detailed energy and environmental monitoring. The monitoring equipment and framework, have been devised to support further detailed studies to improve the design concept and to provide accurate and comprehensive data to the scientific community.Causone, Francesco; Carlucci, Salvatore; Pagliano, Lorenzo; Pietrobon, MarcoCausone, Francesco; Carlucci, Salvatore; Pagliano, Lorenzo; Pietrobon, Marc

A high performance home in the Mediterranean climate: From the design principle to actual measurements

Experience developed in the northern European countries led, in the last decades, to standard and shared procedures for the design and construction of passive houses and similar high performance buildings. These approaches are specifically developed for cold climates, therefore cannot be directly applied to the Mediterranean climate, where substantially different climatic conditions must be challenged. The design and early monitoring of a customized zero energy house, located in Sicily, is proposed as an exemplary case study for the future generation of high performance and nearly-zero energy buildings in the Mediterranean area. The key role played by the control of heat gains, and the correct use of thermal mass is highlighted, showing similarities and differences with passive houses built in the North Europe. The measurements of energy and environmental performance of the building show the effectiveness of the response of the adopted design approach to the specific climatic conditions

Analysis of ventilation strategies for the nearly zero energy retrofit of a day care center

The scientific literature often reports examples of educational buildings with extremely poor ventilation performance. An in-field investigation for the environmental and energy assessment of a day care center in Italy in Milano, confirmed that operable windows were not opened on days when the average daily outdoor temperature was below 15°C, seriously affecting indoor air quality and potentially affecting the wellbeing and learning process of the children. A numerical model for the dynamic energy simulation of the school building was developed to optimize the thermal insulation of opaque and transparent envelope, the solar control strategy, reducing energy needs and uses to implement a nearly zero-energy approach to the retrofit. Different ventilation strategies were therefore simulated, in order to evaluate the one(s) that best fit the deep energy retrofit of the building, including building envelope and systems. A control logic for hybrid ventilation was simulated and analyzed, with the aim to develop a strategy suited for replication and effective in ameliorating both energy performance and indoor environmental quality. Daytime and nighttime natural ventilation showed to be extremely effective in improving thermal comfort conditions, during the cooling season, performing better than mechanical ventilation

Ventilation strategies for the deep energy retrofit of a kindergarten

The scientific literature often reports example of educational buildings with extremely poor ventilation performance. An in-field investigation for the environmental and energy assessment of a kindergarten in Milano, confirmed that operable windows were not operated when the average daily temperature dropped below 14 °C, jeopardizing indoor air quality and kids learning performance. Seven different ventilation strategies were therefore simulated, in order to evaluate the one that better fitted a general project of deep energy retrofit of the building, including building envelope and systems. The best scenario resulted to be the one using hybrid ventilation at nighttime and mechanical ventilation at daytime. Both energy and thermal comfort conditions were evaluated and a tradeoff between them was established. Nighttime ventilation showed to be extremely effective in improving thermal comfort conditions, during the cooling season. It resulted much better than mechanical ventilation in the simulated case study. Simulations show that under moderate weather conditions and if the building is properly operated (ventilation, lighting and solar screening systems) the retrofitted building may perform well also without additional active cooling

Seven- and eight-coordinate lanthanide(III) amidophosphate complexes: synthesis, characterization and photoluminescence

Diphenyl N-dimethylamidophosphate, O=P(OPh)2(NMe2), was introduced in the coordination sphere of trivalent lanthanide ions in combination with ß-diketonates, to obtain seven- and eight-coordinated complexes having general formula [Ln(ß-dike)3{O=P(OPh)2(NMe2)}n] (Ln = Eu, ß-dike = dibenzoylmethanate, n = 1; Ln = Eu, ß-dike = tenoyltrifluoroacetonate, n = 2; Ln = Tb, ß-dike = acetylacetonate, n = 2). The compounds were characterized spectroscopically and, in the case of the dibenzoylmethanate derivative, by means of single-crystal X-ray diffraction. The Eu(III) complexes exhibited bright red emission associated to the 5D0→7FJ transitions of the metal centre, with noticeable antenna-effect from the coordinated ligands and lifetimes strongly dependent upon the coordination number. The Tb(III) derivative showed intense green photoluminescence, related to the 5D4→7FJ transitions of the metal io

Light harvesting indolyl-substituted phosphoramide ligand for the enhancement of Mn(ii) luminescence

The reaction of N,N,N',N'‐tetramethyl‐P‐indol‐1‐ylphosphonic diamide (L) with Mn(II) halides under mild conditions allowed the isolation of tetrahedral neutral complexes having general formula [MnX2L2] (X = Cl, Br, I). The structures of the new coordination compounds were ascertained by single‐crystal X‐ray diffraction. The three species exhibited noticeable luminescence in the green region upon excitation with UV light, with emissions related to the Mn(II) 4T1(4G)→6A1(6S) transition, without appreciable luminescence from the coordinated ligands. Luminescence was caused by both metal and ligand excitations. The good light harvesting features of the indol‐1‐yl fragment allowed the luminescence enhancement with respect to comparable phenyl‐substituted derivatives

Identification of cost-optimal and NZEB refurbishment levels for representative climates and building typologies across Europe

The energy consumptions of the building stock are playing a central role in the energy policy of the European Union. While the Member States are applying the Directives in force, the European Commission is working to update the regulatory framework. Specifically, it is necessary to achieve the great unrealized potential for energy savings in existing buildings. With this aim, the nearly zero-energy building (NZEB) target was introduced, and a comparative methodology framework to calculate cost-optimal levels of minimum energy performance requirements was proposed. This study focuses on the issue of building renovation, and it presents the results obtained with the application of a cost-optimal calculation method for identifying proper retrofit measures to reach cost-optimal levels and NZEB levels. The assessment takes into account an exhaustive set of passive and active renovation options and it was extended to various building types of 60s-70s (residential and non-residential) in a wide range of representative European climatic conditions. A very relevant energy-saving potential was found for all cost-optimal benchmarks, and in many cases, the obtained NZEB refurbishments have resulted interesting also from an economic point of view

Affine equation of state from quintessence and k-essence fields

We explore the possibility that a scalar field with appropriate Lagrangian can mimic a perfect fluid with an affine barotropic equation of state. The latter can be thought of as a generic cosmological dark component evolving as an effective cosmological constant plus a generalized dark matter. As such, it can be used as a simple, phenomenological model for either dark energy or unified dark matter. Furthermore, it can approximate (up to first order in the energy density) any barotropic dark fluid with arbitrary equation of state. We find that two kinds of Lagrangian for the scalar field can reproduce the desired behaviour: a quintessence-like with a hyperbolic potential, or a purely kinetic k-essence one. We discuss the behaviour of these two classes of models from the point of view of the cosmological background, and we give some hints on their possible clustering properties.Comment: 9 pages, 6 figures. Minor updates, accepted by CQ