1,721,130 research outputs found
Multi-objective Models and Methods for Design and Management of Sustainable Logistic Systems
Full text linkLogistics is typically defined as the design and operation of the physical, managerial and informational systems needed to allow goods to overcome space and time. Traditional models and methods for logistic system design and management focus on the optimization of the techno-economic performances. However, logistic activities are distinguished by a huge environmental impact. For instance, the final energy consumption for freight transportation reached in recent years the alarming value of 13% of the total end-use energy worldwide, equal to 40 EJ per year. Thus, innovative techniques for logistic system design and management have to guarantee these system overall sustainability not only from a technical and economic perspective but also from an environmental viewpoint. To this end, multi-objective optimization is of strong help. This is a mathematical programming technique to systematically and simultaneously optimize a collection of objective functions, often conflicting among them.
Considering this scenario, aim of this Ph.D. thesis is to develop, propose and validate innovative multi-objective models and methods for design and management of sustainable logistic systems simultaneously optimizing the system technical performance, economic profitability and environmental impact.
The developed models fully manage the material flow from suppliers to assembly or manufacturing areas and from these to final customers through the distribution, storage and retrieving activities among and within the logistic actors. An original decision support system is proposed to jointly minimize the operating cost, carbon footprint and delivery time in the design of multi-modal multi-level distribution networks considering the most relevant features of the delivered products. Concerning warehousing systems, both design and operation problems are tackled. A multi-objective optimization model is developed to determine the warehouse building configuration, namely length, width and height, which simultaneously minimizes travel time, total cost and carbon footprint objective functions. These two latter are estimated through a lifecycle approach. All the activities related to warehouse building installation and operating phases are evaluated both from an economic and an environmental perspective. Warehousing system operation is analyzed by means of storage assignment strategy. A time and energy based strategy is proposed to jointly minimize the travel time and the energy required by the material handling vehicles to store and retrieve the unit loads. Proper vehicle motion configuration and unit load features are considered to accurately model the objective functions. Finally, the presented models and methods are tested and validated against case studies from the food and beverage industry. The results demonstrate that a tremendous environmental impact reduction is possible at negligible technical and economic performance worsening
Kinetic Aspects of SSP of polyesters, Chapt. 3 in Solid-State Polymerization, D. Papaspyrides and S. VouyioukaEd., 2009 –
No full textThe book deals with the solid state polymerizazion of various polimeres and the chapter written by the italian authors deals in particular with the kinetic aspects of the solid state polymerization of polyesters
Qualification of pipe-grade HDPEs: Part I, development of a suitable accelerated ageing method
No full textSeveral techniques of polymer characterization and different aging methods have been used with the aim of developing a simple, fast and reliable method to qualify com. pipe-grade polyethylene samples, and possibly to evidence the presence of recycled PE within PE pipes. The results of the different techniques used have been compared with respect to their capability to evidence differences in the degrdn. rate of different HDPE samples (including virgin HDPE, HDPE pipes obtained from virgin HDPE and HDPE pipes that probably contain recycled HDPE)
Smooth surface polypyrrole-silica core-shell nanoparticles: preparation, characterization and properties
No full textPolypyrrole-silica nanoparticles were prepd. by in-situ polymn. of pyrrole monomer in the presence of specially modified silica nanoparticles having vinyl functional groups on the surface. The presence of polypyrrole (PPy) on the surface of silica nanoparticles was confirmed using FT-IR spectroscopy. The core-shell morphol. was analyzed by TEM. A uniform and smooth shell of PPy on the silica nanoparticles and absence of free PPy homopolymer were the main features of the proposed method that employs modified silica nanoparticles for the synthesis of the PPy-coated silica nanoparticles. SEM investigation of the particles deposited on a glass surface showed a narrow size distribution with an av. diam. of 240 nm for the particles. The wt. percentage of PPy was estd. using TGA and DSC to be approx. 10 wt.-%. Further investigations a by two-probe cond. method of glass slides coated with the nanoparticles showed an elec. cond. of 7 S • cm-1. The static water contact angle was as high as 169°
Polypyrrole grafting onto the surface of pyrrole-modified silica nanoparticles prepared by one-step synthesis
No full textThe grafting of polypyrrole onto the surface of modified silica nanoparticles has been investigated. These silica nanoparticles were modified with pyrrole moieties prepared by the well-known Stober method in one-step starting from TEOS and a pyrrole-bearing trialkoxysilane compound. The effects of various reaction conditions, including reaction time, solvent, and molar ratio of water to alkoxy groups, have been investigated in order to obtain pyrrole-modified silica nanoparticles with the optimal coreshell structure and the smallest possible particle size. The grafting was carried out in aqueous FeCl3 solution containing the modified silica nanoparticles, with pyrrole monomers already adsorbed on the surface of the particles by soaking. Several analytical tools have been employed to characterize the particles and to assess the degree of grafting, namely TEM, SEM, TGA, FTIR, and XPS. The final polypyrrole-grafted silica nanoparticles obtained had a mean diameter of about 220 nm and 50 wt.% of grafted polypyrrole with respect to the total weight of polypyrrole formed around the surface of the cores
Automatic assessment of the ergonomic risk for manual manufacturing and assembly activities through optical motion capture technology
No full textSafeguard the operator health is nowadays a hot topic for most of the companies whose production process relies on manual manufacturing and assembly activities. European legislations, national regulations and international standards force the companies to assess the risk of musculoskeletal disorders of operators while they are performing manual tasks. Furthermore, international corporates typically require their partners to adopt and implement particular indices and procedures to assess the ergonomic risks specific of their industrial sector. The expertise and time required by the ergonomic assessment activity compels the companies to huge financial, human and technological investments. An original Motion Analysis System (MAS) is developed to facilitate the evaluation of most of the ergonomic indices traditionally adopted by manufacturing firms. The MAS exploits a network of marker-less depth cameras to track and record the operator movements and postures during the performed tasks. The big volume of data provided by this motion capture technology is employed by the MAS to automatically and quantitatively assesses the risk of musculoskeletal disorders over the entire task duration and for each body part. The developed hardware/software architecture is tested and validated with a real industrial case study of a car manufacturer which adopts the European Assembly Worksheet (EAWS) to assess the ergonomic risk of its assembly line operators. The results suggest how the MAS is a powerful architecture compared to other motion capture solutions. Indeed, this technology accurately assesses the operator movements and his joint absolute position in the assembly station 3D layout. Finally, the MAS automatically and quantitatively fill out the different EAWS sections, traditionally evaluated through time- and resource-consuming activities
Poly(epsilon-caprolactone)-poly(fluoroalkylene oxide)-poly(epsilon-caprolactone) block copolymers as surface modifiers of poly(vinyl chloride)
No full textBlends of poly(epsilon-caprolactone)-poly(fluoroalkylene oxide)-poly(epsilon-caprolactone) (PCL-PFPE-PCL) triblock copolymers (with different length of PFPE and PCL segments) and poly(vinyl chloride) (PVC) were prepared by casting from tetrahydrofuran solution. DSC analysis revealed a complex morphology deriving from miscibility between PCL and PVC segments. XPS analysis showed strong surface enrichment of PFPE segments for all films prepared. Treatment with a PFPE selective solvent showed that the fraction of PCL-PFPE-PCL removed from surface decreased with increasing length of PCL blocks, indicating an anchorage effect by PCL segments with respect to PVC matrix
Improvement of thermo-oxidative stability of electrically insulating polymeric materials by organic-inorganic hybrid coating
No full textThe thermooxidative stability of poly(ethylene terephthalate) (PET) and low-d. polyethylene (LDPE) films, coated with org.-inorg. hybrid coatings of various compns., was investigated after accelerated ageing tests, in order to ascertain a possible beneficial effect of these coatings on the elec. performances of these insulating materials. The results have shown that the coating affects degrdn. mechanisms for both LDPE and PET. Thermooxidn. is slow in LDPE, leading to significantly better insulating characteristics after ageing: a strong redn. of the embrittlement time was also obsd. The strong increase of crystallinity upon ageing, obsd. for both coated and uncoated PET samples, probably dominates the effect of ageing on the elec. properties. As a consequence, only slight beneficial effects on PET elec. performances was obsd. (both on cond. and elec. strength). On the other hand, the coating has a strong effect on mol. wt. changes leading to a significant increase of mol. wt. for coated PET, while uncoated PET undergoes a significant decrease. This suggests that coated PET should present significantly better properties upon very long times of ageing
Economic and environmental bi-objective design of an off-grid photovoltaic-battery-diesel generator hybrid energy system
No full textGenerally, off-grid fossil fuel generators provide energy supply to remote regions. The integration of photovoltaic (PV) plants to battery energy storage (BES) systems potentially increases reliability, the system autonomy and lifetime, reducing the generator working hours and the system environmental impact. PV-BES-Diesel generator hybrid energy systems (HESs) offer technical, economic and environmental benefits compared to traditional off-grid systems. This paper proposes a bi-objective design model for off-grid PV-BES-Diesel generator HESs. The aim is to identify the PV plant rated power, the BES system capacity and the technical configuration able to jointly reduce the levelised cost of the electricity (LCOE) and the carbon footprint of energy (CFOE). Furthermore, the comparison of the LCOE and CFOE values of the HES against a traditional diesel generator allows determining the economic and environmental advantages coming from the described system. Despite the proposed model is general and suitable for any installation site and HES configuration, this paper exemplifies its application designing a HES to be installed in a remote village in Yakutsk, Russia. The model takes into account the hourly energy demand, the irradiation and temperature profiles of the installation location calculating the hourly PV plant yield, the battery charge-discharge processes and the required generator energy. Results highlight the technical, economic and environmental feasibility of the system for a context with a medium irradiation level, i.e. ∼1400 kW h/(m2 year), and relatively low fuel cost, i.e. 0.7 €/l. For the best economic scenario LCOE and CFOE reductions are of about 8% and 28%, respectively. Finally, the most effective trade-off between economic and environmental performances leads to a CFOE decrease of about 48% and a slight decrease of the economic performances (-2%)
- …
