In an attempt to reduce costs and improve customer satisfaction, manufacturers have been adopting strategies such as Delayed Product Differentiation (DPD) while managing broader product lines. In this study, first a general framework on DPD is formed in the light of basic articles in the literature. The vanilla box assembly process which is a special form of modular design type of DPD is modeled and analyzed. In the vanilla box assembly process, inventory is stored in a special form of semi-finished products, called vanilla boxes, that can serve more than one final product. We model the vanilla box assembly process considering the costs of inventory and unsatisfied demand under the capacity limitations, stochastic demand and bill of material requirements. We formulate the model as an extensive form of stochastic integer program in which stochastic demand is modeled using a set of demand scenarios each of which is assigned a probability of occurrence. The model is solved as a standard integer programming model that minimizes the expected value of the objective function. The impact of product demand scenarios, common component levels, shortage penalty cost to holding cost ratio levels and capacity restrictions on the total cost and fill rates is studied. We compare the performance of vanilla box assembly process to assemble-to-order process and provide insights on their performances. Computational results indicate that the vanilla box assembly process is a promising alternative to the assemble-to-order process in most of the problem instances.

Durante os últimos cinco anos, a nanotecnologia tem atingido avanços significativos em diversas áreas da ciência e tecnologia. Um dos assuntos que está sendo intensamente estudado pela comunidade científica é a intensificação de campo próximo (hot spot) que pode ser aplicada em dispositivos sensores com capacidade de detecção de apenas uma molécula e em nano-antenas ópticas aplicadas na fabricação de dispositivos plasmônicos. Neste sentido, as principais contribuições da presente tese são processos de fabricação de nanoestruturas metálicas e de silício e o estudo da intensificação de campo próximo denominada de pontos quentes (hot spots) nestas estruturas. As nanoestruturas metálicas de Au (ouro) foram obtidas a partir do processo de auto-organização de esferas de poliestireno. As esferas de poliestireno serviram como camada sacrificial (molde) para a obtenção de nanoestruturas metálicas organizadas. Sobre as estruturas de Au organizadas foram depositadas moléculas de cristal violeta para serem utilizadas como moléculas de prova (sondas) no monitoramento da existência dos pontos quentes com o auxílio do espalhamento Raman das moléculas. As nanoestruturas de Au possibilitaram uma intensificação do espalhamento Raman devido à intensificação do campo próximo na superfície metálica periódica de Au. As nanoestruturas e microestruturas de silício foram obtidas a partir da tecnologia de silício poroso. As propriedades do silício poroso foram moduladas através da implantação de íons de hidrogênio (H +) que possibilitou a formação de silício microporoso com forte emissão fotoluminescente (PL) e intensificação do espalhamento Raman superficial devido ao fenômeno de Raman ressonante. Sobre as estruturas macroporosas de silício foram adsorvidas moléculas de azul de metileno para serem utilizadas como moléculas de prova para monitoramento da intensificação do campo próximo e do efeito SERS no silício. A obtenção da intensificação de campo próximo em silício é uma contribuição completamente inédita, pois este fenômeno devia-se, até o momento, somente a materiais metálicos (nanoestruturas metálicas), mostrando sua existência também no silício. / During the last five years, nanotechnology has achieved significant progress in several areas of science and technology. One of the issues that are being intensively studied by the scientific community is the intensification of near-field (hot spot) that can be applied to devices with sensors capable of detecting a single molecule and nano-optical antennas used in the fabrication of plasmonic devices. In this sense, the main contributions of this thesis are processes for manufacture of metal and silicon nanostructures and the study of near-field intensification called hot spots in these structures. The metal nanostructures of Au (gold) were obtained from the process of self-assembling of polystyrene beads. The polystyrene beads were used as sacrificial layer (mold) for obtaining organized metallic nanostructures. On the structures of organized Au were deposited molecules of violet crystal to be used as proof of molecules (probes) to monitor the existence of hot spots with the help of Raman scattering of molecules. The Au nanostructures allowed an intensification of the Raman scattering due to the intensification of the near-field in the periodic Au surface. The microstructures and nanostructures of silicon were obtained using the porous silicon technology. The properties of porous silicon were modulated by the implantation of hydrogen ions (H +) that allowed the formation of microporous silicon which showed high photoluminescence emission (PL) and Raman scattering intensification of the surface due to the phenomenon of resonant Raman. Methylene blue molecules were adsorbed on the macroporous silicon structures to be used as probe molecule for the monitoring of near-field intensification and the SERS effect in silicon. The obtaining of near-field intensification in silicon is an entirely unprecedented contribution, because this phenomenon had been observed, so far, only on the metallic materials (metal nanostructures), showing its existence in the silicon too.

Barium Titanate (BaTiO3 or BTO) has attracted an ever increasing research interest because of its wide range of potential applications. Nano-sized or nanostructured BTO has found applications in new, useful smart devices, such as sensors and piezoelectric devices. Not only limited to one material, multi-layers or multi-phases can lead to multifunctional applications; for example, nanocomposites can be fabricated with ferrite or metal phase with BTO. In this study, I synthesized various BTO-ferrites, ranging from nanoparticles, nanowires to thin films. BTO-ferrite coaxial nanotubes, BTO-ferrite self-assemble thin films, and BTO single phase films were prepared by pulsed laser deposition (PLD) and sol-gel process. BTO-ferrite nanocomposites were grown by solid state reaction. Furthermore, BTO-metal nanostructures were also synthesized by solid state reaction under hydrogen gas which gave us a great inspiration to fabricate metal-ceramic composites. To understand the relationship between metal and BTO ceramic phase, I also deposited BTO film on Au buffered substrates. A metal layer can affect the grain size and orientation in BTO film which can further help us to control the distribution of dielectric properties of BTO films. After obtaining different nanomaterials, I am interested in the applications of these materials. Recently, many interesting electric devices are developed based on nanotechnology, e.g.: memristor. Memristor is a resistor with memory, which is very important in the computer memory. I believe these newly-synthesized BTO based nanostructures are useful for development of memristor, sensors and other devices to fit increasing needs. / Ph. D.

Motorola在1980年代中期透過實施了六標準差方法，因而拉近了與日本企業的品質差距，同時也透過實施了六標準差方法，使得Motorola變得更有競爭優勢，之後奇異的其總裁傑克.威爾許更大幅地推動此套方法的普及，將六標準差全面的導入奇異的日常作業流程中，因此現在的六標準差，除了具備統計上的意義外，也代表著一套非常有系統的流程改善方法，甚至有些企業更以其作為企業策略與營運經營的方法，讓六標準差的應用範圍越來越廣。 本研究以六標準差改善手法的DMAIC步驟，來進行個案公司衛星廣播產品線UPA-ST組裝線的生產力提升。而在使用此方法之前，本研究則運用限制理論的思維來思考如何找出影響組裝線生產力的主要因素，因此本研究在界定的階段就發現了影響UPA-ST組裝線的生產力的關鍵因素主要有三項，第一項為瓶頸工站，第二項為工時變異大的工站，第三項則為組裝線未平衡的作業。針對各項關鍵因素，本研究透過數據的蒐集與分析來瞭解這三項關鍵因素如何影響組裝線的生產力，最後則透過了作業拆解與同步作業來提升了瓶頸工作站的生產力、透過了工站順序調動與合併來使組裝線能夠平衡、瞭解變異的來源與建立自主品檢流程來降低變異性大的工作站之變異，藉由減少這三項關鍵因素對組裝線生產力的影響，因此也使此條組裝線最後能增加產出與減少人力資源的投入，因而提升了生產力。 / Motorola used six-sigma way to shorten the quality difference in the middle of 1980s. Also, it became more competitive via six-sigma way. Then, the president of GE, Jack Welch, made much effort to popularize this way and implemented into this way to the daily process of GE. As a result, besides the meaning of statistics, current six-sigma also represents the set of systematic way to improve process. Further, some companies use it as strategies and operation ways. These cause the application of six-sigma way become more and more broad. This research use DMAIC steps of six-sigma way to increase the productivity of UPA-ST ‘s satellite broadcast product line. Before using this way, this research use limitation theory to think how to find the major factors which would influence the productivity of the assemble line. Consequently, this research finds there are three major factors to influence the productivity of UPA-ST’s assemble line: the first is the bottleneck station, the second is the station which exists big variance of working time, the third is the unbalance operation of the assemble line. For each major factors, this research uses data collection and analysis to understand how these three major factors affect the productivity of assemble line. Finally, it increases the productivity via taking apart the operation and synchronous way; it makes assemble line balance via adjust the order of work station and combination; it reduces the variance of the working station which exists big variance via understanding the source of variance and building the autonomous quality-control process. Through reducing the productivity influence of these three major factors, it consequently make the assemble line increase the output and reduce the input of manpower to increase the productivity.

O muco protege o corpo humano de partículas externas, mas também representa uma barreira para a entrega de controlada de medicamentos através de nanocarregadores. Para ultrapassar a barreira do muco e impedir mucoadesão, nanopartículas sólidas são normalmente revestidas com polímeros inertes, tais como o polietileno glicol (PEG). No entanto, trata-se de um procedimento relativamente complexa. Nesta tese, estudamos métodos para fabricar nanocarreadores com uma excepcional combinação de propriedades, incluindo uma boa capacidade de mucopenetração e uma grande capacidade de carga. Ao contrário dos métodos convencionais de revestimento, usamos um copolímero dibloco, que consiste em dois blocos hidrofóbicos e hidrofílicos, que se auto-organiza em polimerosomos sob hidratação. Devido à inércia do bloco hidrofílico, estes polimerosomos devem ser, por natureza, muco penetradores. Além disso, sua estrutura oca fornece os polimersomos para serem carregados com carga hidrofílica, enquanto a carga hidrofóbica pode ser transportada através da membrana. Por conta da utilização de um polímero hidrolisável na presença de ácido, ácido poli láctico (PLA) como a espinha dorsal copolímero, demonstramos que estes polimerosomos podem liberar o conteúdo, após aplicação do estímulos externo relacionado ao pH. Os experimentos de rastreamento de partículas demonstraram que os polimersomos se difundem mais rápido do que as partículas não revestidas, em muco de intestino de porco, e testes de biodistribuição apresentaram resultados encorajadores para a entrega localizada de fármacos de maneira mais homogênea, melhorando a biodisponibilidade e efeitos terapeuticos. Mais estudos relacionados ao aumento da eficiência de encapsulação e testes de efetividade in vivo no tratamento de doenças devem ser promovidos. Acreditarmos que combinação das vantagens relacionadas à estrutura vesicular dos polimerossomas, estabilidade, e muco penetração possibilitam o desenvolvimento de uma nova plataforma para a entrega controlada de medicamentos na mucosa. / Mucus protects the human body by trapping foreign particulates but also poses a barrier for drug delivery by slowing down the mobility of drug carriers. To design mucus penetrating carriers, solid particles are typically coated with inert polymers such as polyethylene glycol (PEG) to prevent mucoadhesion. However, the solid structure of these particles limits their loading capabilities and the process to coat them requires a complex synthesis. In this thesis we studied methods to fabricate nanocarriers with an exceptional combination of properties including a good mucus-penetration capability and loading capacity of hydrophilic and hydrophobic cargos. Unlike conventional coating methods, we use a diblock copolymer, consisting of both hydrophobic and hydrophilic blocks, which self-assembles into polymersomes under hydration. Because of the inertness of the hydrophilic block, these polymersomes should be mucus-penetrating by nature. Moreover, their hollow structure provides the polymersomes to be loaded with hydrophilic cargo, whereas hydrophobic cargo can be carried through the membrane. Importantly, by using a hydrolysable acid-catalyzed polymer (poly lactic acid, PLA) as the copolymer backbone, we demonstrate that these polymersomes can release contents upon application of external pH stimuli. Particle Tracking experiments demonstrated that polymersomes diffuse faster than uncoated particles in porcine intestine mucus, and biodistribution tests displayed encouraging results towards more homogeneous local drug-delivery, helping bioavailability as well as therapeutic efects. More studies related to the increase of encapsulation efficiency, and in vivo disease treatment tests should be promoted. Although we believe that combining the advantages of polymersome carrier, and tunning the membrane composition, this mucus-penetrating carrier we propose may provide as a new platform for mucosal drug delivery.

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No. of bitstreams: 2 Tese - Lucileide Vilela Resende - 2013.pdf: 3679172 bytes, checksum: 19c64d2dca0756ea4259ae775b9de738 (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) Previous issue date: 2013-03-15 / Fundação de Amparo à Pesquisa do Estado de Goiás - FAPEG / This study aimed to estimate the genetic diversity and inbreeding, perform genetic relationships analysis, and estimate heritability for morphometric variables in quails using microsatellite markers. We used the following morphometric measurements: weight (PO), length (CO), and width (LO) of eggs, weight (P), body length (CC), length (CB), height (AB), and width (LB) of beak, wing length (CA), tarsus length (CT), and toe length (CD). We verified the genetic association for the morphometric variables in the progenies. Also, we checked whether features P, CC, CB, AB, LB, CA, CT, and CD were related to the amount of offspring (QF) from adults in quail families from a commercial flock. We used seven cages containing six females and two males each, which resulted in a progeny of 672 individuals. The genotypes of the individuals were obtained in an automated DNA sequencer. Genotypes were used for genetic diversity, inbreeding, and genetic link analyzes of two generations, and to perform analyzes of variance components, descriptive statistics, Pearson correlations, heritability, t-test, and Utest of Mann-Whitney. In the parental generation we found high probability of combined paternity exclusion (PE = 0.999956), low probability of combined identity (PI = 1.47 x 10-13), and that null alleles frequency was near zero. The values of expected (He) and observed (Ho) heterozygosity, and polymorphism information content (PIC) were equal to 0.768, 0.766 and 0.734, respectively, indicating a high genetic diversity. When we assessed only the progenies, the genetic diversity was maintained (He = 0.760, Ho = 0.757 and PIC = 0.725). The inbreeding coefficient (f) was low and not significant. The genetic link analysis was efficient to assign paternity and maternity for 97% of the progeny. The weight of the offspring at birth and the variables analyzed in eggs are highly correlated. There is also a significant correlation between most measures analyzed. Estimates of heritability values were considered moderate to high. The average number of offspring was 15.93 per female, and 44.6 for males. Females were, on average, heavier than males. The QF was only correlated with the CC in females. We found significant difference between the weight of heavier males when compared to lighter males, but the comparison between QF and weight category was not significant. These results indicated that the 12 microsatellite markers used in the study were robust for the genetic relationships and genetic variability analysis in this species. We also found that the egg’s variables and progeny’s weight were highly correlated, and heritability estimates ranged from moderate to high in the variables analyzed. Females were heavier than males, QF was correlated only with CC in females, and there was no significant difference between heavier males and lighter males. All these information may be useful in future breeding programs for Coturnix japonica. / O objetivo deste estudo foi utilizar marcadores microssatélites para estimar diversidade genética e endogamia, realizar análises de vínculo genético, estimar a herdabilidade para as variáveis morfométricas: peso (PO), comprimento (CO) e largura do ovo (LO), peso (P), comprimento do corpo (CC), comprimento do bico (CB), altura do bico (AB), largura do bico (LB), comprimento da asa (CA), comprimento do tarso (CT) e comprimento do dedo (CD) e verificar a associação genética para estas variáveis nas progênies e verificar quais características: P, CC, CB, AB, LB, CA, CT e CD estão relacionadas com quantidade de filhos (QF) nos adultos em famílias oriundas de um plantel comercial de codornas. Para o desenvolvimento do trabalho foi instalado um experimento com sete gaiolas contendo seis fêmeas e dois machos, resultando em uma progênie de 672 indivíduos. O genótipo dos indivíduos foi obtido em sequenciador automático de DNA. Os genótipos foram utilizados para realização das análises de diversidade genética, endogamia e vínculo genético nas duas gerações e para realizar análises de componentes de variância, estatísticas descritivas, correlações de Pearson, herdabilidade, teste t e teste U de Mann-Whitney. Considerando a geração parental foi encontrada alta probabilidade de exclusão de paternidade combinada (PE = 0,999956), baixa probabilidade de identidade combinada (PI = 1,47x10-13) e frequência de alelos nulos próximas a zero. Os valores de heterozigosidade esperada (He) e observada (Ho) e conteúdo de informação polimórfica (PIC) foram iguais a 0,768, 0,766 e 0,734 respectivamente, indicando uma elevada diversidade genética. A diversidade genética foi mantida quando se avaliou apenas as progênies (He = 0,760, Ho = 0,757 e PIC = 0,725). O coeficiente de endogamia (f) foi baixo e não significativo. A análise de vínculo genético foi eficiente para atribuir a paternidade e maternidade para 97% das progênies. O peso das progênies ao nascimento e as variáveis analisadas nos ovos estão altamente correlacionadas e também existe correlação significativa entre a maioria das medidas. As estimativas de herdabilidade encontradas são consideradas de moderada a alta. A média de filhotes por fêmea foi 15,93 e de machos 44,6, com fêmeas, em média, mais pesadas que os machos. A QF só foi correlacionada com o CC das fêmeas. Houve diferença significativa entre o peso dos machos mais pesados em relação aos mais leves, mas a comparação da QF por categoria de peso não foi significativa. Esses resultados permitem concluir que este painel de 12 marcadores microssatélites é robusto para a realização de análises de vínculo genético e para estudos de variabilidade genética nesta espécie, com as variáveis analisadas nos ovos e peso das progênies altamente correlacionadas, estimativas de herdabilidades moderadas a altas para as variáveis analisadas. As fêmeas são mais pesadas que os machos, QF só está correlacionada com o CC das fêmeas, não apresentando diferença significativa entre o peso dos machos mais pesados em relação aos mais leves. Essas informações podem ser úteis em futuros programas de melhoramento genético para Coturnix japonica.

O muco protege o corpo humano de partículas externas, mas também representa uma barreira para a entrega de controlada de medicamentos através de nanocarregadores. Para ultrapassar a barreira do muco e impedir mucoadesão, nanopartículas sólidas são normalmente revestidas com polímeros inertes, tais como o polietileno glicol (PEG). No entanto, trata-se de um procedimento relativamente complexa. Nesta tese, estudamos métodos para fabricar nanocarreadores com uma excepcional combinação de propriedades, incluindo uma boa capacidade de mucopenetração e uma grande capacidade de carga. Ao contrário dos métodos convencionais de revestimento, usamos um copolímero dibloco, que consiste em dois blocos hidrofóbicos e hidrofílicos, que se auto-organiza em polimerosomos sob hidratação. Devido à inércia do bloco hidrofílico, estes polimerosomos devem ser, por natureza, muco penetradores. Além disso, sua estrutura oca fornece os polimersomos para serem carregados com carga hidrofílica, enquanto a carga hidrofóbica pode ser transportada através da membrana. Por conta da utilização de um polímero hidrolisável na presença de ácido, ácido poli láctico (PLA) como a espinha dorsal copolímero, demonstramos que estes polimerosomos podem liberar o conteúdo, após aplicação do estímulos externo relacionado ao pH. Os experimentos de rastreamento de partículas demonstraram que os polimersomos se difundem mais rápido do que as partículas não revestidas, em muco de intestino de porco, e testes de biodistribuição apresentaram resultados encorajadores para a entrega localizada de fármacos de maneira mais homogênea, melhorando a biodisponibilidade e efeitos terapeuticos. Mais estudos relacionados ao aumento da eficiência de encapsulação e testes de efetividade in vivo no tratamento de doenças devem ser promovidos. Acreditarmos que combinação das vantagens relacionadas à estrutura vesicular dos polimerossomas, estabilidade, e muco penetração possibilitam o desenvolvimento de uma nova plataforma para a entrega controlada de medicamentos na mucosa. / Mucus protects the human body by trapping foreign particulates but also poses a barrier for drug delivery by slowing down the mobility of drug carriers. To design mucus penetrating carriers, solid particles are typically coated with inert polymers such as polyethylene glycol (PEG) to prevent mucoadhesion. However, the solid structure of these particles limits their loading capabilities and the process to coat them requires a complex synthesis. In this thesis we studied methods to fabricate nanocarriers with an exceptional combination of properties including a good mucus-penetration capability and loading capacity of hydrophilic and hydrophobic cargos. Unlike conventional coating methods, we use a diblock copolymer, consisting of both hydrophobic and hydrophilic blocks, which self-assembles into polymersomes under hydration. Because of the inertness of the hydrophilic block, these polymersomes should be mucus-penetrating by nature. Moreover, their hollow structure provides the polymersomes to be loaded with hydrophilic cargo, whereas hydrophobic cargo can be carried through the membrane. Importantly, by using a hydrolysable acid-catalyzed polymer (poly lactic acid, PLA) as the copolymer backbone, we demonstrate that these polymersomes can release contents upon application of external pH stimuli. Particle Tracking experiments demonstrated that polymersomes diffuse faster than uncoated particles in porcine intestine mucus, and biodistribution tests displayed encouraging results towards more homogeneous local drug-delivery, helping bioavailability as well as therapeutic efects. More studies related to the increase of encapsulation efficiency, and in vivo disease treatment tests should be promoted. Although we believe that combining the advantages of polymersome carrier, and tunning the membrane composition, this mucus-penetrating carrier we propose may provide as a new platform for mucosal drug delivery.

This report is the result of a 20-points project at the University of Jönköping. The project was carried out in form of a case study with the object of analysing the value flow at DIAB AB’s confection department in Laholm. The aim of this project is to submit proposals to the production management on how to increase the efficiency of the production flow at the confection department and reduce the capital accumulation in form of products in work. The information in this report is gathered from interviews, observations and measurements. Furthermore, a literature study was carried out in view to find suitable theories when analysing present as well as future suggested production conditions. This report is based on four main questions: • What does the existing process of the value flow for the most produced product family look like? • How does the process of the value flow for GS perform considering the through-put-time? o How long through-put-time does a representative product of the GS-family have? o How long is the value- and no value adding time for that product along its production flow? • Which production related disturbances and cost prompters exist in the present value flow process? • How could the process of the value flow for GS be made more efficient, less persistent to disturbances and more competitive? The existing process of the value flow for the most producing product family has been mapped and is illustrated in appendix 3. For now, the process includes nine working stations along the production chain. The through-put-time of a representative GS-product is according to my survey 18,5 days. The value adding time is only 16,1 minutes, that is 0,061 % of the entire through-put-time. The remaining time, in other words the no value adding time, is 440 hours and it represents mainly storage and transport of products. The representative production disturbances and cost prompters that characterise the process of the value flow contain material related disturbances, a high number of long shifts, long storage time prior to the customer order point and with that, high capital accumulation and finally unnecessary transports. Improvement proposals aim to increase the efficacy of the process of the value flow and reduce the capital amounts by shifting from the present production strategy involving manufacturing towards order (TMO) to assembling towards order (MMO). In order to make this possible a semi-manufactured storage will be introduced after the standard confection which will represent the new decoupling point. The production at the standard confection will then occur according to the semi-manufactured storage. The standard confection should produce in larger aggregated order quantities based on prognosis in order to benefit from the advantages of economy of scale and the production must proceed in a continuous flow according to the FIFU-system (First In First Out). In addition to that, the special confection must produce according to a pull-system and only when the customer makes a request. The tact-time of the GS products should constitute a limit for all the cycle times along the production chain, both on the standard- and special confection. This is partly due to creating a constant and balanced production flow which enables short through-put-time and partly due to avoiding in-between-storage as a result of various bottlenecks.

Les systèmes assemble-to-order (ATO) peuvent être considérés comme une affectation de ressources multiples qui induit planification de production, satisfaction des contraintes et affectation des stocks. Les systèmes ATO représentent une stratégie de logistique populaire utilisée en gestion de fabrication. En raison de la complexité croissante des systèmes de fabrication d'aujourd'hui, le défi pour les systèmes ATO est de gérer efficacement les stocks de composants et de trouver les décisions optimales de production et d'affectation.Nous étudions un système ATO avec un produit unique qui est assemblé à partir de plusieurs composants. Le système doit répondre à une demande non seulement du produit assemblé, mais aussi des composants individuels. Nous considérons le cas avec seulement des lost sales puis le cas mixte lost sales et backorders avec des temps de production suivant des lois de type exponentiel et une demande sous forme de loi de Poisson. Nous formulons le problème comme un Processus de décision markovien (MDP), et nous considérons deux critères d'optimalité qui sont le coût actualisé et le coût moyen par période. Nous caractérisons la structure de la politique optimale et étudions l'impact des différents paramètres du système sur cette politique. Nous présentons également plusieurs heuristiques pour le cas lost sales et le cas mixte lost sales et backorders. Ces heuristiques fournissent des méthodes simples, mais efficaces pour contrôler la production et l'affectation des stocks du système ATO

Vikram Sarabhai Space Centre,Trivandrum / In the space surrounding the earth there are two major regions where orbital debris causes concern. They are the Low Earth Orbits (LEO) up to about 2000 km, and Geosynchronous Orbits (GEO) at an altitude of around 36000 km. The impact of the debris accumulations are in principle the same in the two regions; nevertheless they require different approaches and solutions, due to the fact that the perturbations in the orbital decay due to atmospheric drag effects predominates in LEO, gravitational forces including earth’s oblateness and luni solar effects dominating in GEO are different in these two regions. In LEO it is generally known that the debris population dominates even the natural meteoroid population for object sizes 1 mm and larger. This thesis focuses the study mainly in the LEO region. Since the first satellite breakup in 1961 up to 01 January 2003 more than 180 spacecraft and rocket bodies have been known to fragment in orbit. The resulting debris fragments constitute nearly 40% of the 9000 or more of the presently tracked and catalogued objects by USSPACECOM. The catalogued fragment count does not include the much more numerous fragments, which are too small to be detected from ground. Hence in order to describe the trackable orbital debris environment, it is important to develop mathematical models to simulate the trackable fragments and later expand it to untrackable objects. Apart from the need to better characterize the orbital debris environment down to sub millimeter particles, there is also a pressing necessity of simulation tools able to model in a realistic way the long term evolution of space debris, to highlight areas, which require further investigations, and to study the actual mitigation effects of space policy measures. The present thesis has provided newer perspectives for five major issues in space debris modeling studies. The issues are (i) breakup modeling, (ii) environment modeling, (iii) evolution of the debris environment, (iv) collision probability analysis and (v) reentry prediction. The Chapter 1 briefly describes an overview of space debris environment and the issues associated with the growing space debris populations. A literature survey of important earlier work carried out regarding the above mentioned five issues are provided in the Chapter 2. The new contributions of the thesis commence from Chapter 3. The Chapter 3 proposes a new breakup model to simulate the creation of debris objects by explosion in LEO named “A Semi Stochastic Environment Modeling for Breakup in LEO” (ASSEMBLE). This model is based on a study of the characteristics of the fragments from on orbit breakups as provided in the TLE sets for the INDIAN PSLV-TES mission spent upper stage breakup. It turned out that based on the physical mechanisms in the breakup process the apogee, perigee heights (limited by the breakup altitude) closely fit suitable Laplace distributions and the eccentricity follows a lognormal distribution. The location parameters of these depend on the orbit of the parent body at the time of breakup and their scale parameters on the intensity of explosion. The distribution of the ballistic coefficient in the catalogue was also found to follow a lognormal distribution. These observations were used to arrive at the proper physical, aerodynamic, and orbital characteristics of the fragments. Subsequently it has been applied as an inverse problem to simulate and further validate it based on some more typical well known historical on orbit fragmentation events. All the simulated results compare quite well with the observations both at the time of breakup and at a later epoch. This model is called semi stochastic in nature since the size and mass characteristics have to be obtained from empirical relations and is capable of simulating the complete scenario of the breakup. A new stochastic environment model of the debris scenario in LEO that is simple and impressionistic in nature named SIMPLE is proposed in Chapter 4. Firstly among the orbital debris, the distribution of the orbital elements namely altitude, perigee height, eccentricity and the ballistic coefficient values for TLE sets of data in each of the years were analyzed to arrive at their characteristic probability distributions. It is observed that the altitude distribution for the number of fragments exhibits peaks and it turned out that such a feature can be best modeled with a tertiary mixture of Laplace distributions with eight parameters. It was noticed that no statistically significant variations could be observed for the parameters across the years. Hence it is concluded that the probability density function of the altitude distribution of the debris objects has some kind of equilibrium and it follows a three component mixture of Laplace distributions. For the eccentricity ‘e’ and the ballistic parameter ‘B’ values the present analysis showed that they could be acceptably quite well fitted by Lognormal distributions with two parameters. In the case of eccentricity also the describing parameter values do not vary much across the years. But for the parameters of the B distribution there is some trend across the years which perhaps may be attributed to causes such as decay effect, miniaturization of space systems and even the uncertainty in the measurement data of B. However in the absence of definitive cause that can be attributed for the variation across the years, it turns out to be best to have the most recent value as the model value. Lastly the same kind of analysis has also been carried out with respect to the various inclination bands. Here the orbital parameters are analyzed with respect to the inclination bands as is done in ORDEM (Kessler et al 1997, Liou et al 2001) for near circular orbits in LEO. The five inclination bands considered here are 0-36 deg (in ORDEM they consider 19-36 deg, and did not consider 0-19 deg), 36-61 deg, 61-73 deg, 73-91 deg and 91- 180 deg, and corresponding to each band, the altitude, eccentricity and B values were modeled. It is found that the third band shows the models with single Laplace distribution for altitude and Lognormal for eccentricity and B fit quite well. The altitude of other bands is modeled using tertiary mixture of Laplace distributions, with the ‘e’ and ‘B’ following once again a Lognormal distribution. The number of parameter values in SIMPLE is, in general, just 8 for each description of altitude or perigee distributions whereas in ORDEM96 it is more. The present SIMPLE model captures closely all the peak densities without losing the accuracy at other altitudes. The Chapter 5 treats the evolution of the debris objects generated by on orbit breakup. A novel innovative approach based on the propagation of an equivalent fragment in a three dimensional bin of semi major axis, eccentricity, and the ballistic coefficient (a, e, B) together with a constant gain Kalman filter technique is described in this chapter. This new approach propagates the number density in a bin of ‘a’ and ‘e’ rapidly and accurately without propagating each and every of the space debris objects in the above bin. It is able to assimilate the information from other breakups as well with the passage of time. Further this approach expands the scenario to provide suitable equivalent ballistic coefficient values for the conglomeration of the fragments in the various bins. The heart of the technique is to use a constant Kalman gain filter, which is optimal to track the dynamically evolving fragment scenario and further expand the scenario to provide time varying equivalent ballistic coefficients for the various bins. In the next chapter 6 a new approach for the collision probability assessment utilizing the closed form solution of Wiesel (1989) by the way of a three dimensional look up table, which takes only air drag effect and an exponential model of the atmosphere, is presented. This approach can serve as a reference collision probability assessment tool for LEO debris cloud environment. This approach takes into account the dynamical behavior of the debris objects propagation and the model utilizes a simple propagation for quick assessment of collision probability. This chapter also brings out a comparison of presently available collision probability assessment algorithms based on their complexities, application areas and sample space on which they operate. Further the quantitative assessment of the collision probability estimates between different presently available methods is carried out and the obtained collision probabilities are match qualitatively. The Chapter 7 utilizes once again the efficient and robust constant Kalman gain filter approach that is able to handle the many uncertain, variable, and complex features existing in the scenario to predict the reentry time of the risk objects. The constant gain obtained by using only a simple orbit propagator by considering drag alone is capable of handling the other modeling errors in a real life situation. A detailed validation of the approach was carried out based on a few recently reentered objects and comparison of the results with the predictions of other agencies during IADC reentry campaigns are also presented. The final Chapter 8 provides the conclusions based on the present work carried together with suggestions for future efforts needed in the study of space debris. Also the application of the techniques evolved in the present work to other areas such as atmospheric data assimilation and forecasting have also been suggested.