Optimal control of particle size distribution in semi-batch emulsion polymerisation

Imperial Users onl

Modelling the distribution of health related quality of life of advancedmelanoma patients in a longitudinal multi-centre clinical trial using M-quantile random effects regression

Health-related quality of life assessment is important in the clinical evaluation of patients with metastatic disease that may offer useful information in understanding the clinical effectiveness of a treatment. To assess if a set of explicative variables impacts on the health-related quality of life, regression models are routinely adopted. However, the interest of researchers may be focussed on modelling other parts (e.g. quantiles) of this conditional distribution. In this paper, we present an approach based on quantile and M-quantile regression to achieve this goal. We applied the methodologies to a prospective, randomized, multi-centre clinical trial. In order to take into account the hierarchical nature of the data we extended the M-quantile regression model to a three-level random effects specification and estimated it by maximum likelihood

Predicting the Impact of Climate Change on Thermal Comfort in A Building Category: The Case of Linear-type Social Housing Stock in Southern Spain

The Climate Change scenario projected by the IPCC for the year 2050 predicts noticeable increases in temperature. In severe summer climates, such as the Mediterranean area, this would have very negative e ects on thermal comfort in the existing housing stock, given the current high percentage of dwellings which are obsolete in energy terms and house a population at serious risk of energy poverty. The main aim of this paper is to generate a predictive model in order to assess the impact of this future climate scenario on thermal comfort conditions in an entire building category. To do so, calibrated models representing linear-type social multi-family buildings, dating from the post-war period and located in southern Spain, will be simulated extensively using transient energy analyses performed by EnergyPlus. In addition, a sensitivity analysis will be performed to identify the most influential parameters on thermal discomfort. The main results predict a generalized deterioration in indoor thermal comfort conditions due to global warming, increasing the average percentage of discomfort hours during the summer by more than 35%. This characterization of the future thermal behaviour of the residential stock in southern Spain could be a trustworthy tool for decision-making in energy retrofitting projects which are so badly needed. To do so, further work is required on some limitations of this model so that di erent user profiles and typologies can be represented in detail and an economic assessment can be included

Environmental and Economic Impact of the Antifreeze Agents in Geothermal Heat Exchangers

Borehole heat exchangers (BHEs) generally employ water-antifreeze solutions to allow working fluid temperatures to fall below 0 °C. However, some local regulations have forbidden antifreeze additives (even non-toxic ones) to avoid groundwater pollution in case of pipe leakage. This paper presents a techno-economic and environmental analysis of four different fluids: propylene glycol at 25% and 33% weight concentrations, calcium chloride at 20% weight concentration (CaCl2 20%), and pure water. Thermal loads from 36 case studies in six different climate zones are used to perform BHE sizing and compare the abovementioned fluids from the economic, operational, and environmental points of view. The economic analysis and the carbon footprint assessment are performed on a life cycle of 25 years considering the installation (BHE drilling, fluid) and operation (heat pump and ground-side circulation pump energy demand, fluid replacement) of the simulated GSHPs. Results highlight that using pure water as a heat carrier fluid is convenient for cooling-dominated buildings but, for heating-dominated buildings, this choice leads to a noticeable increase of the BHE needed length which is not compensated by the lower operational costs. On the other hand, avoiding the use of antifreeze additives generally leads to a reduction of the lifetime carbon footprint, with a few exceptions in very cold climates. CaCl2 20% proves to be a good choice in most cases, both from the economic and the environmental points of view, as it allows a strong reduction of the installed BHE length in cold climates with a low additional cost and carbon footprint

a new approach for the dimensioning of an air conditioning system with cold thermal energy storage

Abstract In this work, a new approach for the design of air conditioning systems with cold thermal energy storage is described and tested, considering the case study represented by a vapor-compression chiller, coupled with a chilled water storage system, producing cooling for a small multi-apartment building situated in Italy. In the present approach, at the aim of limiting shut-downs and start-ups of the chiller, which involve inefficiencies during transients, and can lead to a drastic reduction of the equipment lifetime, the nominal power of the chiller, and the amount of cooling to be stored are first estimated in a pre-design phase. Successively, the outputs of the pre-design are used to fix the size of the cold storage tank, and to set up the numerical simulation of the cold thermal energy storage system. Finally, the results of the numerical simulation of the cold storage system are used to evaluate the effective size of the chiller. Both the pre-design and the numerical simulations of the cold storage systems have been done by means of home-made numerical tool realized with Simulink. In the paper, the specifications relative to the operational strategy are explored, and the analytical models used for the numerical simulation of the cold storage system relative to the Italian case study are reported in detail. Finally, the results of the pre-design, and of the cold storage system simulations relative to the case study are presented and discussed. The results relative to the Italian case study demonstrates the effectiveness of the present approach in limiting the number of shut-downs and start-ups of the chiller. The present approach can represent a useful tool for the economic optimization of the design of air conditioning systems

Periodic Structural Defects in Graphene Sheets Engineered via Electron Irradiation

Artificially-induced defects in the lattice of graphene are a powerful tool for engineering the properties of the crystal, especially if organized in highly-ordered structures such as periodic arrays. A method to deterministically induce defects in graphene is to irradiate the crystal with low-energy (<20 keV) electrons delivered by a scanning electron microscope. However, the nanometric precision granted by the focused beam can be hindered by the pattern irradiation itself due to the small lateral separation among the elements, which can prevent the generation of sharp features. An accurate analysis of the achievable resolution is thus essential for practical applications. To this end, we investigated patterns generated by low-energy electron irradiation combining atomic force microscopy and micro-Raman spectroscopy measurements. We proved that it is possible to create well-defined periodic patterns with precision of a few tens of nanometers. We found that the defected lines are influenced by electrons back-scattered by the substrate, which limit the achievable resolution. We provided a model that takes into account such substrate effects. The findings of our study allow the design and easily accessible fabrication of graphene devices featuring complex defect engineering, with a remarkable impact on technologies exploiting the increased surface reactivity

analysis of a biomass fired cchp system considering different design configurations

Abstract This work aims to present the results of an energetic and economic analysis of a biomass fueled CCHP system operating according to different design configurations. The investigated system consists of a biomass-fueled cogeneration unit, an absorption chiller, a thermal energy storage system and a cold one, providing electricity, heat and cooling to an Italian cluster of buildings. For each simulated configuration, the feasible investment cost of the CHP unit is evaluated considering the economic savings obtained with respect to separate generation of electricity, heat and cooling. The best configuration from the economic point of view is indicated, and the incidence of the variation of the absorption chiller and storage systems sizes on the feasible investment cost of the CHP unit is evaluated and discussed as well. Results indicate that the most influencing parameter is represented by the absorption chiller power

Operability timescale of defect-engineered graphene

Defects in the lattice are of primal importance to tune graphene chemical, thermal and electronic properties. Electron-beam irradiation is an easy method to induce defects in graphene following pre-designed patterns, but no systematic study of the time evolution of the resulting defects is available. In this paper, the change over time of defected sites created in graphene with low-energy ($\leq 20$ keV) electron irradiation is studied both experimentally via micro-Raman spectroscopy for a period of $6\times 10^3$ hours and through molecular dynamics simulations. During the first 10 h, the structural defects are stable at the highest density value. Subsequently, the crystal partially reconstructs, eventually reaching a stable, less defected condition after more than one month. The simulations allow the rationalization of the processes at the atomic level and confirm that the irradiation induces composite clusters of defects of different nature rather than well-defined nanoholes as in the case of high-energy electrons. The presented results identify the timescale of the defects stability, thus establishing the operability timespan of engineerable defect-rich graphene devices with applications in nanoelectronics. Moreover, long-lasting chemical reactivity of the defective graphene is pointed out. This property can be exploited to functionalize graphene for sensing and energy storage applications.Comment: 21 pages, 5 figure

Optimal control of road vehicles: theory and applications

In this thesis Optimal Control (OC) of road vehicles is studied especially focusing on minimum lap time simulations. The theory underlying the most used optimal control solving techniques is described, including both the Pontryagin Maximum Principle and the reduction to Nonlinear Programming. Direct and indirect methods for optimal control problems are presented and compared against minimum lap time simulations (LTS). Modelling of vehicles for OC-LTSs is studied in order to understand how different design choices can affect simulation outcomes. Novel multibody models of four wheeled vehicles - a GP2 car and a go-kart - for OC-LTSs are developed and validated thorough comparison with experimental data. Particular attention is dedicated to the simulation of tyre load dynamics, that is achieved by a proper modelling of the chassis and suspension motions and of the aerodynamic forces. OC-LTSs are applied to electric vehicles too, specifically to optimise the design of an electric motorbike taking part at the Tourist Trophy Zero competition. A concise yet effective model is proposed in order to perform reliable simulations on a 60km long road in a reasonable amount of time. Experimental data is used to validate the model. A direct full collocation transcription method for OCPs dealing with implicit differential equations and control derivatives is presented, moreover the structure of the resulting NLP problem is accurately described. The relationship between the first order necessary conditions and the Lagrange multipliers of the NLP and OC problems are derived under the adopted discretisation scheme. The presented transcription method is implemented into a software which is currently in use at the University of Padova to solve OC-LTSs

Comparison of direct and indirect methods for minimum lap time optimal control problems

Minimum lap time simulations are especially important in the design, optimisation and setup of race vehicles. Such problems usually come in different flavours, e.g. quasi-steady state models vs full dynamic models and pre-defined (fixed) trajectory problems vs free trajectory problems. This work is focused on full dynamic models with free trajectory. Practical solution techniques include direct methods (i.e. solution of an NLP problem, widespread approach) and indirect method (i.e. based on Pontryagins principle, less common, yet quite efficient in some cases). In this contribution the performance of the direct and indirect methods are compared in a number of vehicle related problems