On improving the iterative convergence properties of an implicit approximate-factorization finite difference algorithm

The iterative convergence properties of an approximate-factorization implicit finite-difference algorithm are analyzed both theoretically and numerically. Modifications to the base algorithm were made to remove the inconsistency in the original implementation of artificial dissipation. In this way, the steady-state solution became independent of the time-step, and much larger time-steps can be used stably. To accelerate the iterative convergence, large time-steps and a cyclic sequence of time-steps were used. For a model transonic flow problem governed by the Euler equations, convergence was achieved with 10 times fewer time-steps using the modified differencing scheme. A particular form of instability due to variable coefficients is also analyzed

Mitochondrial Stress Signalling: HTRA2 and Parkinson's Disease

Mitochondria are cellular energy generators whose activity requires a continuous supply of oxygen. Recent genetic analysis has suggested that defects in mitochondrial quality control may be key factors in the development of Parkinson's disease (PD). Mitochondria have a crucial role in supplying energy to the brain, and their deterioration can affect the function and viability of neurons, contributing to neurodegeneration. These organelles can sow the seeds of their own demise because they generate damaging oxygen-free radicals as a byproduct of their intrinsic physiological functions. Mitochondria have therefore evolved specific molecular quality control mechanisms to compensate for the action of damaging agents such as oxygen-free radicals. PTEN-induced putative kinase 1 (PINK1) and high-temperature-regulated A2 (HTRA2), a mitochondrial protease, have recently been proposed to be key modulators of mitochondrial molecular quality control. Here, we review some of the most recent advances in our understanding of mitochondria stress-control pathways, focusing on how signalling by the p38 stress kinase pathway may regulate mitochondrial stress by modulating the activity of HTRA2 via PINK1 and cyclin-dependent kinase 5 (CDK5). We also propose how defects in this pathway may contribute to PD

Challenges in load balance due to renewable energy sources penetration: The possible role of energy storage technologies relative to the Italian case

With the rapid growth of the electricity produced by RES (renewable energy sources), especially those highly variable and unprogrammable (e.g. wind and solar power), the need of energy system flexibility increases significantly. Since RES currently represent a significant fraction of the power supply, their variable nature poses challenges to power grid operation, such as RES curtail and loss in global efficiency of thermoelectric plants, since they are often operated at part-load as fluctuating back-up power. In particular, thermoelectric plants recently moved their role from base-load power to fluctuating back-up power. Such a cycling operation represents a less obvious effect of grid flexibility requirement due to RES penetration. Main effect is the increment of both energetic costs, due to reduced efficiency operation, and wear-and-tear costs. This aspect is deeply analysed in reference to the Italian electricity generation mix in the period 2008-2012. Moreover, the possible coupling of energy storage systems with thermoelectric plants is highlighted as an alternative solution respect to retrofitting of existing plants

Analysis of different typologies of natural insulation materials with economic and performances evaluation of the same in building

Considering the significant impact that the residential sector has on energy consumption, it is particularly important to implement policies aimed at improving energy efficiency in buildings for saving primary energy, and also to spread the concept of sustainable development through the use of appropriate technology and proper project criteria both for new constructions and for the rehabilitation of existing ones. It is in this context and in an attempt to reduce as much as possible the consumption of resources that fits the possibility of utilizing "natural" materials for the insulation of buildings. In this work they have been analyzed the natural insulation materials present on the Italian building market, where for "natural" it is meant the ones that are derived from renewable materials, which emit no pollutants and that are recyclable or biodegradable. Then it has been created a database which highlights the physical and thermohygrometrical characteristics (density, conductivity, specific heat, vapor permeability, etc.), as well as the possible applications (ceiling, wall, roof). Then it has been carried out a performing and economic comparison related to the replacement of the traditional insulation of a residential building located in Perugia (Central Italy) with the majority of the insulating materials identified in relation to its type of use. The synthetic insulating materials have been replaced in order to reach, for the analysed building, the same thermal performances obtained with the application of traditional insulators. From the analysis of dynamic thermal parameters has been deduced that the building envelope insulated with natural products has better thermal summer performances compared to the same insulated with traditional materials such as XPS, with the same thermal winter performances. This improvement is mainly due to the high value of the specific heat characteristic of the natural insulators. Finally, it has been carried out an economic comparison between the two types of insulation from which it has been possible to deduce that the utilize of natural insulation products have meant an increase in the costs which is widely variable depending on the type of natural insulator used

Multi-criteria investigation of a pumped thermal electricity storage (PTES) system with thermal integration and sensible heat storage

In the present paper a multicriteria analysis of a Rankine Pumped Thermal Electricity Storage (PTES) system with low-grade thermal energy integration is performed. The system is composed by an ORC for the discharging phase and a high-temperature heat pump for the charging phase. As previously demonstrated, the low-grade thermal energy can be provided at the heat pump evaporator to boost the PTES performances. As it regards the multi-criteria analysis, a tradeoff is required when electric-to-electric energy ratio ηrt, total exergy exploitation efficiency ψut and energy density ρen, are maximized concurrently. By means of multi-objective optimization, theoretical performances of the system are derived in two different layouts, which are differentiated by the presence, or not, of internal regeneration in charge and discharge subsystems. Results showed that regeneration can be very effective, as it relaxes the tradeoff between the objectives, thus yielding better global performances. Pareto fronts are built and explored to characterize the PTES system. Configurations of interest are proposed, and PTES performances are compared with other storage technologies. Theoretical results showed that, by exploiting thermal energy at temperature lower than 80 °C, ηrt ≈ 0.55 and ρen ≈ 15 kWh/m3 can be concurrently achieved. This can be done at the cost of an inefficient exploitation of the thermal source, as ψut ≈ 0.05. If higher total exergy utilization efficiency is required, storage density can still be maintained high, but ηrt must drop down to 0.4

Rankine carnot batteries with the integration of thermal energy sources: A review

This paper provides an overview of a novel electric energy storage technology. The Thermally Integrated Pumped Thermal Electricity Storage (TI-PTES) stores electric energy as thermal exergy. Compared to standard PTES, TI-PTES takes advantage of both electric and low-temperature heat inputs. Therefore, TI-PTES is a hybrid technology between storage and electric production from low-temperature heat. TI-PTES belongs to a technology group informally referred to as Carnot Batteries (CBs). As the TI-PTES grows in popularity, several configurations have been proposed, with different claimed performances, but no standard has emerged to date. The study provides an overview of the component and operating fluid selection, and it describes the configurations proposed in the literature. Some issues regarding the performance, the ratio between thermal and electrical inputs, and the actual TI-PTES utilisation in realistic scenarios are discussed. As a result, some guidelines are defined. The configurations that utilise high-temperature thermal reservoirs are more extensively studied, due to their superior thermodynamic performance. However, low-temperature TI-PTES may achieve similar performance and have easier access to latent heat storage in the form of water ice. Finally, to achieve satisfactory performance, TI-PTES must absorb a thermal input several times larger than the electric one. This limits TI-PTES to small-scale applications

Adequacy of hospitals in Rome to an unconventional event (CBRNe). TTX simulation and HTA

Background Rome hosts thousands of sensible targets. Healthcare reaction has been guaranteed by 6 advanced Emergency Departments (EDs) and 7 basic ones. Everyday Rome hosts 6 millions of people/die, ± 2 million in particular occasions. About National Stockpile Antidotes (SNA), Rome hosts 3 warehouses. In case of events, stockpiles are activated with a long-time call; then stockpiles are charged in delivering trucks. Methods Study analyzes PEIMAF (State of emergency plans for massive influx of injures) of advanced EDs in Rome and their adequacy in a possible CBRNe attack. Hypothesis of C/N attack on Saint Peter's Square during Angelus on Wednesday (at 12.00 AM) or E attack in Trastevere on Saturday (at 9.00 PM). Analysis of activation of SNA and travel times between SNA warehouse and EDs. Comparison with French EDs during Paris attacks. Results EDs are chronically undermanned in ordinary conditions already, and would have issues in hosting a very large number of critical patients all at once. Some hospitals do not inform their workers about PEIMAF or they do not consider CBRNe emergencies in their PEIMAF, and even if it has been considered, hardly any simulation/exercitation is ever performed. Moreover, news of the CBRNe attack may not reach immediately the healthcare personal already at work in EDs; this is extremely problematic since they could be at major risk of contamination in case of CBRNe attacks. Furthermore, without a standardize protocol active in the whole city, no cross-hospital organization can be performed. Conclusions All data point towards the weakness and fragmentation of actual organizative system. Time of activation and charging are crucials for first aid efficacy and efficiency; a smart call system can reduce the activation time of SNA. A better organization of SNA in major Rome hospitals can reduce delivering time and help save more lives

Choroidal thickness changes measured by enhanced depth imaging optical coherence tomography in third trimester pregnant women

The aim of this article is to underline the effect of pregnancy on the variations of choroidal thickness caused by hormonal and haemodynamic changes

impact of consumption profile discontinuities on the feasibility of a pv plant

Abstract The revenues of a grid-connected photovoltaic plant are strongly related to the local climatic conditions. In addition, since self-consumed electricity is much more valuable than that traded with the main power grid, also consumption profile plays a key role in the profitability of a PV system. Self-consumption to total PV production ratio depends on the temporal mismatch between energy generation and demand. The amount of energy that is not self-consumed may be very high in the case of a consumption profile with several discontinuities. This study is focused on the analysis of a grid-connected PV system serving a compressed natural gas (CNG) fueling station. These facilities are energy-intensive users, characterized by high variability of electricity demand due to intermittent operation of gas compressors: in a few seconds the total load may change from 100% to 5% and vice versa very frequently during the day. The analysis was based on data acquired on the field for the compression station and those already present in the literature for solar irradiation. The influence on plant design of the time step used for the analysis was studied in detail. The outcomes showed that the typical and well-assessed design approaches of a PV pant may lead to errors when used for the design of systems with several consumption profile discontinuities