A SURVEY ON PUBLISHED PAPERS ON OPTIMIZATION IN THE ASSEMBLY LINE BALANCING PROBLEMS IN A HEAVY ENGINEERING INDUSTRY

This paper gives a survey report on different optimization techniques used by different authors on assembly line balancing problems . The author gives a new technique which is different from them on minimization of number of work stations of a ALBP-1

Sviluppo di un algoritmo genetico per il bilanciamento multiobiettivo di una linea di montaggio manuale

Nella presente tesi si implementa un algoritmo genetico che ha come obiettivo l'ottimizzazione dei problemi di assemblaggio nelle linee di montaggio manuali. Nella prima parte del lavoro si cerca di definire lo stato dell’arte e gli elementi che costituiscono e influenzano i sistemi di assemblaggio, con particolare riferimento alle linee di produzione manuali. Dopodiché, con il fine di provare ad individuare la miglior soluzione di montaggio, si introduce uno dei tanti strumenti in grado di risolvere i problemi di ottimizzazione: l’algoritmo genetico. Questo ha ricevuto negli ultimi anni molta attenzione da parte dei ricercatori, in quanto considerato metodo in grado di trovare soluzioni ottime in tempi ragionevolmente brevi. Si passa perciò alla parte centrale del lavoro nella quale si implementa l'algoritmo tenendo conto di obiettivi che, sulla base di valide giustificazioni, si ritengono fondamentali per una gestione più completa possibile di ogni tipo di risorsa necessaria alla fase di assemblaggio. Si applica quindi tale algoritmo a due casi di studio e se ne variano i parametri per giudicarne il comportamento. L’ultima parte della tesi discute i risultati raggiunti sulla base degli obiettivi proposti e trae le conclusioni. L’implementazione dello strumento è stata realizzata in ambiente MATLAB, programmando prima l’esecuzione dell’intero algoritmo, e poi una serie di interfacce grafiche che facilitano in input l’inserimento di dati sia del prodotto che dell’algoritmo, e in output la visualizzazione dei risultati ottenuti

Validazione e miglioramento di un algoritmo genetico per il bilanciamento delle linee di assemblaggio manuali

Il presente lavoro di tesi si focalizza sulla validazione e il miglioramento di un algoritmo genetico utilizzato per il bilanciamento delle linee di assemblaggio manuali. Il lavoro si suddivide in due sezioni distinte, la validazione dell’algoritmo per problemi mono-obiettivo e la validazione per problemi multi-obiettivo. La prima fase concerne la definizione della tipologia di validazione utilizzata per testare la bontà dell’algoritmo. Si sono quindi trascritti i dati necessari su Matlab, ambiente su cui è stato implementato l’algoritmo, e si è fatto girare per comprenderne il comportamento. I risultati ottenuti sono stati analizzati e discusse le problematiche scaturite. Sono state proposte alcune modifiche per risolvere i problemi mono-obiettivo, trascritte su Matlab e si è fatto rigirare l’algoritmo. I risultati ottenuti sono stati confrontati con quelli che l’algoritmo aveva ottenuto precedentemente. La stessa cosa è stata svolta per risolvere le difficoltà inerenti i problemi multi-obiettivo. I risultati che si sono riscontrati in entrambe le tipologie di problemi riguardano un miglioramento evidente delle soluzioni che l’algoritmo è in grado di trovare rispetto ai risultati precedenti. The following thesis is focused on the validation and improvement of a genetic algorithm for the assembly manual line balancing problem. The work is divided into two distinct sections, the validation of the algorithm for mono-objective and validation for multi-objective problems. The first stage concerns the definition of the type of validation used to test the algorithm's goodness. Then, the necessary data are transcribed on Matlab, on which th algorithm has been implemented. The algorithm had been turn in order to understand the behavior. The results obtained were analyzed and the issues arising were discussed. Have been proposed some changes to address the mono-objective problems, they have been recorded in Matlab and was made reshoot the algorithm. The results obtained were compared with those that the algorithm had obtained previously. The same thing has been done to resolve the difficulties in the multi-objective problems. The results that were found in both types of problems relate a clear improvement of the solutions that the algorithm is able to find compared to previous results

Advances in Evolutionary Algorithms

With the recent trends towards massive data sets and significant computational power, combined with evolutionary algorithmic advances evolutionary computation is becoming much more relevant to practice. Aim of the book is to present recent improvements, innovative ideas and concepts in a part of a huge EA field

Multi-agent Collision Avoidance Using Interval Analysis and Symbolic Modelling with its Application to the Novel Polycopter

Coordination is fundamental component of autonomy when a system is defined by multiple mobile agents. For unmanned aerial systems (UAS), challenges originate from their low-level systems, such as their flight dynamics, which are often complex. The thesis begins by examining these low-level dynamics in an analysis of several well known UAS using a novel symbolic component-based framework. It is shown how this approach is used effectively to define key model and performance properties necessary of UAS trajectory control. This is demonstrated initially under the context of linear quadratic regulation (LQR) and model predictive control (MPC) of a quadcopter. The symbolic framework is later extended in the proposal of a novel UAS platform, referred to as the ``Polycopter" for its morphing nature. This dual-tilt axis system has unique authority over is thrust vector, in addition to an ability to actively augment its stability and aerodynamic characteristics. This presents several opportunities in exploitative control design. With an approach to low-level UAS modelling and control proposed, the focus of the thesis shifts to investigate the challenges associated with local trajectory generation for the purpose of multi-agent collision avoidance. This begins with a novel survey of the state-of-the-art geometric approaches with respect to performance, scalability and tolerance to uncertainty. From this survey, the interval avoidance (IA) method is proposed, to incorporate trajectory uncertainty in the geometric derivation of escape trajectories. The method is shown to be more effective in ensuring safe separation in several of the presented conditions, however performance is shown to deteriorate in denser conflicts. Finally, it is shown how by re-framing the IA problem, three dimensional (3D) collision avoidance is achieved. The novel 3D IA method is shown to out perform the original method in three conflict cases by maintaining separation under the effects of uncertainty and in scenarios with multiple obstacles. The performance, scalability and uncertainty tolerance of each presented method is then examined in a set of scenarios resembling typical coordinated UAS operations in an exhaustive Monte-Carlo analysis

Enhanced heavy oil recovery by hybrid thermal-chemical processes

textDeveloping hybrid processes for heavy oil recovery is a major area of interest in recent years. The need for such processes originates from the challenges of heavy oil recovery relating to fluid injectivity, reservoir heating, and oil displacement and production. These challenges are particularly profound in shaley thin oil deposits where steam injection is not feasible and other recovery methods should be employed. In this work, we aim to develop and optimize a hybrid process that involves moderate reservoir heating and chemical enhanced oil recovery (EOR). This process, in its basic form, is a three-stage scheme. The first stage is a short electrical heating, in which the reservoir temperature is raised just enough to create fluid injectivity. After electrical heating has created sufficient fluid injectivity, high-rate high-pressure hot water injection accelerates the raise in temperature of the reservoir and assists oil production. At the end of hot waterflooding the oil viscosities are low enough for an Alkali-Co-solvent-Polymer (ACP) chemical flood to be performed where oil can efficiently be mobilized and displaced at low pressure gradients. A key aspect of ultra-low IFT chemical flood, such as ACP, is the rheology of the microemulsions that form in the reservoir. Undesirable rheology impedes the displacement of the chemical slug in the reservoir and results in poor process performance or even failure. The viscosity of microemulsions can be altered by the addition of co-solvents and branched or twin-tailed co-surfactants and by an increase in temperature. To reveal the underlying mechanisms, a consistent theoretical framework was developed. Employing the membrane theory and electrostatics, the significance of charge and/or composition heterogeneity in the interface membrane and the relevance of each to the above-mentioned alteration methods was demonstrated. It was observed that branched co-surfactants (in mixed surfactant formulations) and temperature only modify the saddle-splay modulus (k ̅) and bending modulus (k) respectively, whereas co-solvent changes both moduli. The observed rheological behavior agrees with our findings. To describe the behavior of microemulsions in flow simulations, a rheological model was developed. A key feature of this model is the treatment of the microemulsion as a bi-network. This provides accuracy and consistency in the calculation of the zero-shear viscosity of a microemulsion regardless of its type and microstructure. Once model parameters are set, the model can be used at any concentration and shear rate. A link between the microemulsion rheological behavior and its microstructure was demonstrated. The bending modulus determines the magnitude of the viscous dissipations and the steady-shear behavior. The new model, additionally, includes components describing the effects of rheology alteration methods. Experimental viscosity data were used to validate the new microemulsion viscosity model. Several ACP corefloods showing the large impact of microemulsion viscosity on process performance were matched using the UTCHEM simulator with the new microemulsion rheology model added to the code. Finally, numerical simulations based on Peace River field data were performed to investigate the performance of the proposed hybrid thermal-chemical process. Key design parameters were identified to be the method of heating, duration of the heating, ACP slug size and composition, polymer drive size, and polymer concentration in the polymer drive. An optimization study was done to demonstrate the economic feasibility of the process. The optimization revealed that short electrical heating and high-rate high-pressure waterflooding are necessary to minimize the energy use and operational expenses. The optimum slug and polymer drive sizes were found to be ~0.25 PV and ~1 PV, respectively. It was shown that the well costs dominate the expenditure and the overall cost of the optimized process is in the range of 20-30 $⁄bbl of incremental oil production.Petroleum and Geosystems Engineerin

The evolution and determination of plasmid transfer rate and subsequent effect on competition

Horizontal gene transfer by conjugation is one of the processes that determines the persistence, prevalence and transmission of antibiotic resistance genes that can be found on bacterial plasmids. In order to appropriately tackle the spread of antibiotic resistance we must therefore understand how plasmid dynamics function in complex microbial communities. Various aspects of plasmid dynamics and how they contribute to the spread of antibiotic resistance are unclear and require attention. For example, plasmid transfer rates vary widely, but the ways in which environmental, plasmid and host factors explain this variation and the relative importance of each factor is unclear. In addition, the evolutionary forces that differentially affect plasmids and hosts to determine specific transfer rates have not been fully explored; in particular, the effects of host-plasmid conflicts in non-selective conditions and the impact of the relationship between plasmid cost on host growth and plasmid transfer rate. A theoretical understanding of transfer rates must then be placed within the context of the other parameters that affect plasmid dynamics (e.g. plasmid cost, loss etc.) to make assertions on plasmid persistence and prevalence, and theoretical results must be compared with experimental data in increasing microbial complexity. Experiments are rarely conducted using multiple species and the impacts and interactions of plasmid presence on a community have yet to be explored fully in the lab. The first data chapter of this thesis (chapter 2) seeks to address the question of how transfer rate variation can be attributed to various environmental variables in addition to the effects of plasmid, donor and recipient identities. A meta-analysis of published transfer rates was therefore conducted and the variation assessed by applying series of multivariate linear models to the data. Over three quarters of the variation from the meta-analysis could be explained, with plasmid repression and media type explaining the most variation. The results also identify the recipient identity as an important variable that explains up to 34\% of the variation. Given the variation in transfer rates, the next chapter (chapter 3) asks how the various selection pressures on host and plasmid may interact to determine specific rates of transfer. In particular, it asks how the costs of plasmid transfer impact transfer rates, and how host-plasmid conflicts in transfer rate may subsequently affect plasmid prevalence. Adaptive dynamics and invasion analyses were applied to simple conjugation models under selective and non-selective conditions, and using different plasmid transfer-cost relationships. The findings were then combined to model the effects that host-plasmid conflicts in non-selective conditions may have on transfer rates and plasmid prevalence. The results of separate analyses demonstrate the role of the recipient in controlling transfer rates, and show that plasmid-controlled transfer rate can be predicted with only three parameters (host growth rate, plasmid loss rate and the cost of plasmid transfer on growth). Low frequency genetic variation in transfer rate is predicted to accumulate, which can facilitate rapid adaptation to changing conditions. Further modelling showed that in order to substantially affect plasmid prevalence (and corresponding cumulative costs a plasmid has on a population in non-selective conditions) a host may need to decrease the transfer rate by several orders of magnitude, indicating that hosts must have strong control mechanisms to be valuable. In the final data chapter (chapter 4) I ask if and how plasmid dynamics focusing on the interaction of plasmid presence and inter-species competition in simple microbial communities can be predicted using independently measured parameters. In particular, how does the rate of plasmid transfer impact species competitive advantage and the outcomes of competition? A series of experiments were conducted to estimate parameters for two plasmids and two bacterial species for use in a simplified two-species bacterial conjugation model to make predictions of competitive advantage. These predictions were then compared with a series of corresponding competition assays. The effects of the plasmid distribution on competition and the presence of multiple species on plasmid stability in the community were also noted and described. The model accurately predicted many of the experimental results, but deviated from those results where specific parameters were over or underestimated. The results emphasise the importance of appropriate parameter measurement. Plasmid presence reduced the competitive ability of each host and incurred higher costs from the plasmid with a higher transfer rate. These effects were limited or exacerbated dependent on whether the plasmid was able to successfully invade the other species where it incurred similar costs. These results demonstrate the complex effects of plasmid transfer, cost and host interactions on plasmid dynamics in a microbial community and the competitive dynamics of that community. These results show that transfer rates are highly variable according to environmental conditions and that, while the majority of the variation can be assigned to some variables, additional work is required to evaluate the effects of particular variables, such as temperature and the effects of plasmid-host coevolution. While this work demonstrates how selective pressures act on transfer rates, more work is also required to link particular observed transfer rates to the conditions in which they evolve. The results highlight the importance of the variable and potentially conflicting selection pressures on host and plasmid that combine to determine the rate of transfer, emphasising the sometimes neglected role of the recipient. The relationship between plasmid cost and plasmid transfer rate is identified as a key part of transfer rate evolution and also requires future attention to describe this relationship in order to fully understand how plasmid transfer rates are constructed. These results increase our understanding of the factors that affect plasmid dynamics, have implications for the way we consider and handle the spread of antibiotic resistance, and provide direction for future research opportunities.Open Acces

Dual responsive physical networks from asymmetric biosynthetic triblock copolymers

The aim of the project is to develop biosynthetically produced amino acid polymers which are composed of three distinct blocks A-C-B, each with a separate function. A is a first self-assembling block capable of ‘recognizing’ (upon a trigger) other A blocks; C is an inert, random coil-like connector, and B is a second self-assembling block. A and B have to be chosen such that they do not cross-assemble. With these molecules it should be possible to fabricate hydrogels in which direct ‘loops’ are excluded. We exploited genetic engineering to design proper genes encoding asymmetric triblock protein polymer and fermentation to produce monodisperse protein polymers. There different asymmetric triblock protein polymers were produced and characterized. The first molecule, silk-elastin hybrid molecule (SCE), was inspired by natural silk and elastin. The silk-like block (S) forms a pH-sensitive beta-roll (beta-sheet like) structure that further stacks into long fibrils. The elastin-like block(E) has thermo-responsive properties; above the lower critical solution temperature (LCST), it forms aggregates. We find that polymers that have both silk and elastin-like domains show temperature dependent fibril formation. At high temperature, the elastin blocks irreversibly induce bundling and aggregation of fibrils. The presence of the elastin-like block also changes the kinetics of fibril formation. Whereas silk-like protein without elastin forms monodisperse fibrils, the presence of elastin results in polydisperse fibrils due to homogenous nucleation. The self-assembly of silk-elastin hybrid molecule is further analysed in the presence of NaCl. We find that the thermo-responsive behaviors of elastin-like block are strongly dependent on salt concentration. At high salt concentration, the aggregation transition is much more pronounced. At high pH, where the S block does not self-assemble, the polymer forms micellar aggregates upon heating in the presence of NaCl. At low temperature, lowering the pH leads to fibril formation. When both blocks are induced to self-assemble, the final structure reveals a pathway-dependence. Heating the solution of fibrils formed at low temperature results in fibril aggregates which do not dissociate upon cooling. The pH-triggered fibril formation of preheated protein solutions leads to the formation of large objects, which likely cause sedimentation. The structural difference is also demonstrated clearly in the morphology of gels formed at high protein concentration: whereas the gel formed in the first pathway (first lower the pH, then increase the temperature) is transparent, the gel formed in the latter pathway (first increase the temperature, then lower the pH) is milky and has a higher elastic modulus. The second type of asymmetric triblock copolymer (TR4H or TR4K) has a collagen-like, triple-helix-forming motif at one end, and a poly cationic block at the other. The collagen-like end-block T consists of 9 (PGP) repeats and forms thermo-responsive triple helices upon cooling. Such helices are reversibly disrupted when the temperature is raised above the melting temperature. The other end-block has 6 positively charged amino acids (histidine-H or lysine-K) and forms micelles when a negatively charged polymer is added. The charge-driven complexation of this block depends on its degree of deprotonation, which is determined by the pKa and the pH. The additives used in this study are a flexible polyanion (polystyrene sulfonate, PSS) and a semi-flexible polyanion (xanthan). We find micelle-to-network transition of the triblock TR4H in complexation with PSS. First, the self-assembly of each end-block is studied separately. As expected, the collagen-like block reversibly forms triple helices upon cooling. The cationic H block forms charge-driven complexes upon adding PSS, leading to micelles with an aggregation number that depends on ionic strength. At high concentration, the micellar TR4H/PSS solutions form a viscoelastic gel upon cooling, which melts at high temperature, indicating the formation of helical junctions between the micelles. Liquid-liquid phase separation is observed when the concentration is below the gelation point (around 90 g/L). This leads to a dilute phase on top of a concentrated gel phase. The phase separation is driven by the attraction between charge-driven micelles caused by the triple helices. It disappears when the solution is heated or when the ionic strength is increased. The charge-driven complexation of TR4K with xanthan, a negatively charged polysaccharide is also studied. At high temperature and at very low xanthan concentration, the TR4K binds to the xanthan backbone via the charged block K, leading to charge-driven bottle brushes, as indicated by a significant increase in light scattering intensity due to the increased mass. This interaction is dependent on the pH, due to protonation of the cationic K block. The xanthan/TR4K complex shows thermo-sensitivity due to the helical interaction of the collagen-like blocks. At a xanthan concentration around the overlap concentration (~7 g/L), the presence of the triblock results in an increase in elastic modulus of xanthan gels. At high temperature, the elastic modulus increases by 3 times after adding the triblock. As triple helices do not form, this must be due to changes in the entanglement of the bottle brushes. Also the non-linear rheology of the xanthan/TR4K gels differs significantly from that of xanthan alone. At low temperatures when the helical junctions are formed, the elastic modulus increases even further approximately two times compared with the corresponding value at high temperature. This is ascribed to the formation of crosslinks induced by the proteins between the xanthan molecules. The triblock protein modifies the properties of the xanthan hydrogels in three ways: (1) a significant increase in storage modulus, (2) thermo-sensitivity and (3) a two-step strain softening, where the first step is probably due to unbinding of the proteins from the xanthan backbones. The third molecule is an asymmetric triblock copolymer (TR4T-Cys), which has two triple helix forming end-blocks (T), with a cysteine residue (Cys) added to one of these. Under oxidizing conditions, the cysteine residues can form disulfide bonds between two polymers whereas reducing conditions restore the thiol groups. Since cysteine can form only one S-S bridge, intramolecular loops are prevented. The presence of S-S bonds significantly enhances the thermal stability of the triple helical network. This results in the appearance of two melting temperatures, of which the higher one is due to the S-S stabilized triple helices. The elastic modulus of the physical gels in the presence of S-S bonds is almost 2 times higher than that of the physical gels in the absence of S-S bonds. The relaxation time also triples under oxidizing conditions, which indicates that triple helical knots are also kinetically stabilized by S-S bonds. In summary, the design of S-C-S (S: functional end-block, C: connector) network-forming components might meet the increasing demands of high performance biomaterials that must be able to build a physical gel under narrowly defined conditions. Such class of telechelic polymer might display various interesting dynamic behaviors including shear banding, self-assembly, rheochaos, and phase-separation. Another aspect is the functionality of the end-block which self-assembles upon triggering. However, connectors often return to the same nodes, resulting in loop formation. Loop formation is a structural imperfection that weakens network connectivity and lowers the material’s elasticity. The asymmetric triblock with two different end-blocks is designed in order to: (1) prevent unimolecular loops and improve mechanical properties (2) achieve multi-responsiveness: this allows us to observe different assembling pathways. In this work, with respect to (1), we indeed observed the decrease in loop formation in physical gels formed by TR4T-Cys due to the formation of S-S bridges. With respect to (2), we indeed obtained multi-responsive hydrogels with all three asymmetric triblock proteins. However, we have only scratched the surface as understanding kinetics of self-assembly and pathway dependent processes. Further investigations are needed to get more insights into how to manipulate various parameters in controlling the final structures. </p

Climate-Smart Forestry in Mountain Regions

This open access book offers a cross-sectoral reference for both managers and scientists interested in climate-smart forestry, focusing on mountain regions. It provides a comprehensive analysis on forest issues, facilitating the implementation of climate objectives. This book includes structured summaries of each chapter. Funded by the EU’s Horizon 2020 programme, CLIMO has brought together scientists and experts in continental and regional focus assessments through a cross-sectoral approach, facilitating the implementation of climate objectives. CLIMO has provided scientific analysis on issues including criteria and indicators, growth dynamics, management prescriptions, long-term perspectives, monitoring technologies, economic impacts, and governance tools