• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 38
  • 7
  • 7
  • 6
  • 1
  • 1
  • Tagged with
  • 70
  • 24
  • 22
  • 12
  • 11
  • 11
  • 10
  • 8
  • 7
  • 7
  • 5
  • 5
  • 5
  • 5
  • 5
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
31

Local Structure and Molecular Dynamics of Supramolecules And Semicrystalline Polymers As Investigated By Solid State NMR

Chen, Wei 07 June 2016 (has links)
No description available.
32

Precession Electron Diffraction Assisted Characterization of Deformation in α and α+β Titanium Alloys

Liu, Yue (Focused ion beam microscope engineer) 08 1900 (has links)
Ultra-fine grained materials with sub-micrometer grain size exhibit superior mechanical properties when compared with conventional fine-grained material as well as coarse-grained materials. Severe plastic deformation (SPD) techniques have been shown to be an effective way to modify the microstructure in order to improve the mechanical properties of the material. Crystalline materials require dislocations to accommodate plastic strain gradients and maintain lattice continuity. The lattice curvature exists due to the net dislocation that left behind in material during deformation. The characterization of such defects is important to understand deformation accumulation and the resulting mechanical properties of such materials. However, traditional techniques are limited. For example, the spatial resolution of EBSD is insufficient to study materials processed via SPD, while high dislocation densities make interpretations difficult using conventional diffraction contrast techniques in the TEM. A new technique, precession electron diffraction (PED) has gained recognition in the TEM community to solve the local crystallography, including both phase and orientation, of nanocrystalline structures under quasi-kinematical conditions. With the assistant of precession electron diffraction coupled ASTARÔ, the structure evolution of equal channel angular pressing processed commercial pure titanium is studied; this technique is also extended to two-phase titanium alloy (Ti-5553) to investigate the existence of anisotropic deformation behavior of the constituent alpha and beta phases.
33

Ultra-large sheet formation by 1D to 2D hierarchical self-assembly of a “rod–coil” graft copolymer with a polyphenylene backbone

Huang, Yinjuan, Yuan, Rui, Xu, Fugui, Mai, Yiyong, Feng, Xinliang, Yan , Deyue 17 July 2017 (has links) (PDF)
This communication reports a unique ultra-large sheet formation through hierarchical self-assembly of a rod–coil graft copolymer containing a rigid polyphenylene backbone and flexible poly(ethylene oxide) (PEO) side chains. The hierarchical self-assembly process involved a distinctive morphological transition of 1D helical to 2D superstructures. The graft copolymer offers a new chance for the challenging bottom-up fabrication of ultra-large self-assembled nanosheets in solution, as well as a novel system for fundamental studies on 2D self-assembly of polymers.
34

Ultra-large sheet formation by 1D to 2D hierarchical self-assembly of a “rod–coil” graft copolymer with a polyphenylene backbone

Huang, Yinjuan, Yuan, Rui, Xu, Fugui, Mai, Yiyong, Feng, Xinliang, Yan, Deyue 17 July 2017 (has links)
This communication reports a unique ultra-large sheet formation through hierarchical self-assembly of a rod–coil graft copolymer containing a rigid polyphenylene backbone and flexible poly(ethylene oxide) (PEO) side chains. The hierarchical self-assembly process involved a distinctive morphological transition of 1D helical to 2D superstructures. The graft copolymer offers a new chance for the challenging bottom-up fabrication of ultra-large self-assembled nanosheets in solution, as well as a novel system for fundamental studies on 2D self-assembly of polymers.
35

[pt] DEGRADAÇÃO MECÂNICA DE SOLUÇÕES POLIMÉRICAS EM FLUXO LAMINAR EXTENSIONAL / [en] MECHANICAL DEGRADATION OF POLYMER SOLUTIONS IN EXTENSIONAL LAMINAR FLOW

LUA SELENE DA SILVA ALMEIDA 28 June 2021 (has links)
[pt] Devido ao seu comportamento físico-químico, os polímeros solúveis em água são utilizados em várias fases de perfuração, completação, e produção de poços de petróleo. Portanto, é fundamental prever e controlar o comportamento em meio poroso para entender o desempenho do polímero. Experimentos foram conduzidos para estudar a degradação de uma solução aquosa semi-diluída de PEO, usando dois capilares com diâmetros de entrada diferentes (100 micrômetros e 200 micrômetros) ambos com constrição de 50 micrômetros, criando fluxos transientes rápidos em seu centro. Diferentes vazões foram impostas a fim de observar diferentes taxas de cisalhamento e de alongamento no sistema. O efluente do fluxo foi coletado e reinjetado, e suas propriedades reológicas foram utilizadas como proxies para a degradação. Observamos que, para a contração mais abrupta, a vazão mínima necessária para degradar a solução é menor. Este resultado, analisado apenas sob a perspectiva da taxa de cisalhamento, não é razoável, já que a taxa de cisalhamento na constrição a que o polímero é submetido é igual em ambos os capilares. Portanto, inferimos que a brusquidão da contração desempenha um papel na degradação, o que significa que a taxa de alongamento pode ser responsável pela menor taxa de fluxo crítico. Também foi observado um padrão de como ocorre a degradação com as injeções subsequentes. Podemos inferir que injeções subsequentes causam degradação incremental antes de se aproximar de um patamar de estabilização e que vazões mais altas geram patamares de degradação mais baixos. / [en] Due to their physical-chemical behavior, water-soluble polymers are used extensively in various phases of drilling, completion, workover, and production of oil and gas wells. Therefore, it is fundamental to predict and to control in-situ porous medium behavior in order to understand polymer performance. Experiments were conducted to study the degradation of a semi diluted (2000 ppm) aqueous solution of PEO, using two capillaries with different entrance diameter (100 micrometers and 200 micrometers) both with 50 micrometers radius constriction, creating Fast-Transient Flows in their center. Different injection rates were imposed in order to observe different shear and extensional rates in the system. The effluent of the flow was collected, and reinjected, and rheological properties of the fluids were used as proxies for the degradation of the solution. We observed that for the more abrupt contraction, the minimum flow rate needed for degrading the polymer solution is lower. This result, when analyzed purely under shear rate perspective, is not reasonable, since the constriction shear rates to which the polymer is subjected are equal at both capillaries. Therefore, we inferred that the abruptness of the contraction plays a role in the degradation, which means elongational rate may be responsible for the lower critical flow rate. It was also observed a pattern for how the degradation occurs with subsequent injections. We could infer that subsequent injections cause incremental degradation before approaching a stabilization plateau and that higher flow rates generated lower degradation plateaus.
36

FAILURE MODES OF PEO BASED ABUSE DETERRENT OPIOIDS AND PROMETHAZINE HYDROCHLORIDE TABLETS

Salma Salem (7042751) 15 August 2019 (has links)
<p>Opioid addiction has become a global epidemic and a national health crisis in recent years. In 2016, approximately 64,000 Americans under 50 years old were killed because of opioid overdoses. The aim of developing an abuse deterrent opioid is to render any form of manipulation that encourages abuse challenging and therefore, non-profitable. With this goal, the Food and Drug Administration (FDA) is extensively supporting research into the development of abuse deterrent technologies and prioritizing their production as a public health necessity. Abuse deterrent approaches include but are not limited to the following: (1) using a physical barrier (e.g., Polyethylene oxide PEO) that basically limit the release of the drugs in the blood or the digestive tract and prevent mechanical alteration of the drugs by crushing, grating, grinding, chewing etc, (2) using chemical barriers that employ gelling agents that prevent the aqueous or organic extraction of the drugs, and (3) combining the drug with an antagonist that blocks the post-abuse euphoria.</p> <p>PEO is a popular polymer used as a matrix in these complex opioid products. The polymer is responsible for the abuse deterrent properties as well as extended release behavior of opioid drugs. PEO hinders the extraction of Opioid drugs from Abuse Deterrent Formulations (ADF), makes it challenging to be injected, and resists mechanical stress and pulverization when crushed. PEO can be subjected to thermal processing such as thermal curing, compression molding, melt extrusion, and injection molding owing to its thermoplasticity.</p> <p>Assessment of the impact of using various manufacturing processes to develop ADFs and the effect of using various grades of this polymer is essential to improve upon the next generation of ADFs. There are three main categories of premarket studies: Category 1 – laboratory based (in-vitro manipulations and drug extractions), category 2 – pharmacokinetic and category 3 –clinical. These studies are required by the FDA to demonstrate that a given formulation exhibit abuse deterrent properties before a drug product is released to the market. In vitro laboratory based manipulation and extraction studies which are used to assess AD properties of these products are challenging, but essential for product development and generic abuse deterrent product approvals. It is important to realize that there is a great correlation between the laboratory based in vitro manipulation and extraction studies and the expectations of potential abuse and misuse of opioid drugs. The ability of these studies to mimic the manipulation techniques applied by abusers to defeat the abuse deterrent properties of a given formulation optimizes predictions on post-market abuse and misuse potential of ADFs. These studies should also correlate well with <i>in-vivo</i> studies since there is a direct correlation with the concentration (mg/mL in water) and the “high” obtained by an abuser. </p> <p>This research aimed to conduct laboratory based in vitro manipulation and extraction studies to investigate failure modes of PEO-based prescription opioids and Promethazine Hydrochloride PMZ HCl tablets. It highlighted the formulation components and the manufacturing parameters that might affect the dose dumping of Active Pharmaceutical Ingredients (APIs). Furthermore, this research identified model compounds that can be used as surrogates for Oxycodone and the best experimental setup that can be used to conduct smoking simulation experiments. Moreover, it provided an overview of the societal impacts of the opioid crisis in the state of Indiana.</p> <p>Investigations of the failure modes of the PEO-based prescription opioids and PMZ HCL tablets showed that physical manipulation techniques via chopping or grinding are much more effective in the destruction of the PEO matrix than thermal manipulation via the application of heat thus promoting the fast release. The factor with the most significant effect on the failure modes of PMZ HCL tablets was the application of physical manipulation, while the one with the lowest impact was the polymer grade. Moreover, producing PEO-based matrix tablets via Direct Compression DC significantly affected dose dumping behavior of the API from the drug products. The production of the PEO-based matrix tablets via DC was found to be favored over the usage of the melt extrusion method and molding techniques. It was clear that DC kept the integrity of the polymer, allowed for slow and controlled release fashion of the API, and rendered the extraction process relatively hard compared to the Hot Melt Extrusion HME and Molding techniques.</p> <p>Furthermore, the release profile of the investigated PMZ HCL products consisted of various phases of polymer swelling and API release. Thermal manipulations via the application of heat were found to accelerate the dose dumping behavior (90% release) of the APIs from the compressed, extruded, and molded PEO-based matrix formulations similarly. On the other hand, heating was much more effective in the extraction of APIs than chopping or grinding thus promoting the ability to<b> </b>draw a solution containing the API into a syringe for injection relatively easy and facilitate higher % API recovery.</p> <p>Among the formulation components that might have an impact on the AD properties of the PEO-based drug products are; the choice of the antioxidant, the use of complexing agents, chelating agents, and plasticizers. On the other hand, manufacturing process variables that might have a critical impact on AD properties of the PEO-based drug products include but are not limited to; processing temperature compared to the melting point of the polymer and time of exposure</p> <p>PMZ HCl was used as a model drug for Oxycodone in dissolution and extractability studies, while Caffeine and L-Nicotine were used as model drugs in smoking simulation experiments. The combination of the propane torch and Kugelrohr apparatus mimic the real-world scenario for smoking Opioids; however, this experimental setup caused thermal degradation rather than vaporization of some model drugs.</p> <p>According to the National Center for Health Statistics; a statistically significant increase in drug overdose death rates was reported in 2016 in the state of Indiana among other states. The number of deaths related to opioid pain relievers increased by 3732 folds in 2017 compared to the number of deaths in 2014. Moreover, Males were more affected by the opioid crisis than females. On the other hand, the age group 25-44 years, and white people were the most affected by the opioid crisis in Indiana. </p>
37

Scoping review of facilitative aspects of occupational, personal and environmental factors of caregivers occupational performance when caring for a person with major neurocognitive disorder (NCD)

Tuomi, Paula January 2019 (has links)
People with neurocognitive disorders (NCD) condition called dementia are mainly taken care by family members. The number of people suffering from neurocognitive disorders is estimated to increase. Providing care for the person with NCD can be stressful and demanding which is why effective interventions to support caregivers are needed. Occupational therapy practitioners have unique knowledge of the person, environment and occupation and how those factors influence on individuals occupational performance. Occupational therapy ́s interventions to support caregivers with NCD have mainly concentrated on problems in the behaviour of person with NCD. The aim of this scoping review was to identify why some caregivers are managing better as a caregiver before any interventions have been done. What are those aspects of Person (P), Occupation (O) and Environment (E) that facilitate occupational performance (OP) when taking care for a person with NCD. PEO-model by Law et. al (Law et al., 1996) was utilized to formulate research question, in search words and in summarizing the results. The search from Ageline, Cinahl, Psycinfo and PubMed databases was done in January 2018 and went back 10 years. Results found 23 relevant articles for inclusion in the scoping review. Facilitating factors emphasized the supports of relationship seen as an overlap of caregivers and individuals with NCD on occupational performance. Facilitating personal factors of resilience, finding gains in caregiving, self -efficacy and religiosity were found to have an impact on care that the caregiver provides. Facilitative aspects of occupations highlighted importance of daily occupations as a source of well-being for both caregiver and person with NCD. In conclusion, facilitating aspects of relationships, personal factors and engagement in activities and hobbies supported occupational performance of both the caregiver and a person with NCD. Taking these factors into consideration could help target interventions more precisely to meet caregivers needs.
38

Flocculation Behavior Of Two Different Clay Samples From Kirka Tincal Deposit

Cirak, Mustafa 01 September 2010 (has links) (PDF)
Kirka Boron Plant in Eski
39

Příprava tenkých vrstev plazmovou polymerací jako stabilních podložek pro biolékařské aplikace / Thin films of plasma polymers as stable supports for biomedical applications

Gordeev, Ivan January 2012 (has links)
Title: Thin films of plasma polymers as stable supports for biomedical applications Author: Ivan Gordeev Institute: Charles University in Prague, Department of Macromolecular Physics Supervisor of the doctoral thesis: Doc. Ing. Andrey Shukurov, Ph.D, Charles University in Prague, Department of Macromolecular Physics. Abstract: Plasma polymers have been widely considered for use as bio-active coatings. In biomedicine, the surfaces that withstand accumulation of biofilms are of particular importance. This thesis is focused on development of new plasma-based methods for deposition of bio-resistant (non-fouling) plasma polymers. Poly(ethylene oxide) was the subject material. R.f. magnetron sputtering, plasma-assisted thermal vapour deposition and amplitude modulated atmospheric pressure surface dielectric barrier discharge were the methods adapted to fabricate thin films with tunable chemical composition, cross-link density and biological response. A new insight was gained into the processes of plasma polymerization as well as into composition/structure relationship and its effect on biological properties of resultant films. Keywords: plasma polymerization, PEO, 'non-fouling' properties, protein adsorption, cell adhesion
40

Fotocatálise heterogênea em substratos de titânio tratados por oxidação eletrolítica assistida a plasma / Heterogeneous photocatalysis in titanium substrates treated by plasma electrolytic oxidation

Orsetti, Fábio Rodrigues [UNESP] 16 August 2017 (has links)
Submitted by FABIO RODRIGUES ORSETTI null (faorsetti@yahoo.com.br) on 2017-10-10T13:37:14Z No. of bitstreams: 1 Dissertação Orsetti, F. 10.0 .pdf: 3909374 bytes, checksum: bec785688b506e52ae3168e3e40bbb30 (MD5) / Approved for entry into archive by Luiz Galeffi (luizgaleffi@gmail.com) on 2017-10-11T16:51:31Z (GMT) No. of bitstreams: 1 cruz_nc_me_bauru.pdf: 3909374 bytes, checksum: bec785688b506e52ae3168e3e40bbb30 (MD5) / Made available in DSpace on 2017-10-11T16:51:31Z (GMT). No. of bitstreams: 1 cruz_nc_me_bauru.pdf: 3909374 bytes, checksum: bec785688b506e52ae3168e3e40bbb30 (MD5) Previous issue date: 2017-08-16 / A fotocatálise heterogênea utilizando óxido de titânio tem se mostrado promissora na degradação de poluentes orgânicos. Neste contexto, a oxidação eletrolítica assistida por plasma (do inglês, Plasma electrolytic oxidation – PEO) é um método bastante compatível por possibilitar a formação de superfícies fotocatalíticas com porosidade e com composição química controladas. Neste trabalho, a oxidação por PEO foi utilizada na geração de superfícies porosas em um substrato de titânio, usando uma solução eletrolítica contendo 5 ou 10 g/L de oxalato amoniacal de nióbio, com a finalidade de incorporar nióbio às superfícies de óxido de titânio, visando de aumentar sua atividade fotocatalítica sob luz visível. No processo de PEO foram utilizadas as tensões de 500 e 600 V, com frequência fixada em 60 Hz e tempo de tratamento variando de 60 a 600 s. As morfologias, topografias superficiais e estruturas cristalinas das amostras foram analisadas por microscopia eletrônica de varredura (MEV), microscopia de força atômica (AFM) e difração de raios X (DRX), respectivamente. Energia dispersiva de raios X (EDS) foram empregadas para determinação de estrutura cristalina e composição química, respectivamente. O gap óptico das amostras foi determinado a partir de espectros de reflexão na região do ultravioleta visível (UV-Vis). Rugosidade foi determinada por perfilometria e um goniômetro automatizado foi usado para determinação do ângulo de contato e energia de superfície. A atividade fotocatalítica foi avaliada a partir da degradação de azul de metileno. A amostra que apresentou a melhor atividade fotocatalítica foi a produzida usando 500 V, 600 s e 10 g/L, a qual resultou na degradação de 70% de azul de metileno após 120 min sob irradiação com uma lâmpada de luz ultravioleta. / Heterogeneous photocatalysis using titanium oxide has shown to be promising in degradation of organic pollutants, reducing their toxicity and allowing them to be degraded by the environment. In this context, Plasma Electrolytic Oxidation (PEO) is a very interesting method because it allows the formation of photocatalytic surfaces with controlled porosity and chemical composition. In this work, PEO oxidation was used for the generation of porous surfaces of titanium substrates, using an electrolytic solution containing 5 or 10 g / L of niobium ammonium oxalate, with the purpose of incorporating niobium to titanium oxides, aiming the enhance of its photocatalytic activity under visible light. In the PEO process, voltages of 500 and 600 V were used, with a frequency set at 60 Hz and treatment time ranging from 60 to 600 s. The samples surface morphologies; topography and crystallographic structure were analyzed by scanning electron microscopy (SEM), atomic force microscopy (AFM) and X-ray diffraction (XRD), respectively. X-ray dispersive energy spectroscopy (EDS) have been employed for crystallographic structure and chemical composition evaluations, respectively. The optical gap of the samples was determined from reflection spectra in the visible ultraviolet region (UV-Vis). Roughness was determined by profilometry and an automated goniometer was used for contact angle and surface energy measurements. The photocatalytic activity was evaluated from the degradation of methylene blue. The sample with best photocatalytic activity was produced using 500 V, 600 s and 10 g / L, which resulted in the degradation of 70% methylene blue after 120 min under irradiation with ultraviolet light.

Page generated in 0.0331 seconds