Dissertations / Theses on the topic 'PBS'

Orientador: Gaston Eduardo Barberis
Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin
Made available in DSpace on 2018-07-19T12:09:06Z (GMT). No. of bitstreams: 1 ValdiviaLeon_JoseArturo_M.pdf: 1197413 bytes, checksum: 6e8b1e092f41a6caf14f26d982c90614 (MD5) Previous issue date: 1994
Resumo: Este trabalho apresenta a estrutura de bandas e a densidade de estados eletrônicos para os sais de chumbo PbTe, PbS e PbSe, usando o método de Combinação Linear de Orbitais Atômicos parametrizado de Slater e Koster com a base de Vogl sp3s*. O cálculo é feito considerando-se apenas primeiros vizinhos e o hamiltoniano relativista de Pauli. Os resultados mostram que com este simples modelo, que gera uma matriz 20 x 20 e treze parâmetros ajustáveis, é possível reproduzir aceitavelmente as bandas de valência e as primeiras bandas de condução obtidas por cálculos relativistas de Psudopotenciais Empírico local
Abstract: We present here the band structure and the density of states of the lead salts PbTe, PbS and PbSe, resulting from the parametrized Linear Combination of Atomic Orbitals method of Slater and Koster, with the Vogl base Sp3S.; by considering first neighbors and the Pauli's relativistic hamiltonian. Our results show that with this simple model, a 20 x 20 matrix and thirteen adjustable parameters, we can acceptly reproduce the valence and the first conduction bands ca1culated by relativistic local Empirical Pseudopotential Method
Mestrado
Física
Mestre em Física

Nanocrystal quantum dots (NQDs) show great promise in the advancement of the field of photovoltaics. While the maximum efficiency of conventional solar cell (SC) devices is limited to ∼ 31% (Shockley-Queisser limit), devices based on NQDs may attain a maximal thermodynamic efficiency of 42% through the exploitation of multiple exciton generation (MEG). In this process, several electron- hole pairs are created by the absorption of a single high energy photon, as opposed to the single excitons created in conventional solar cell devices. IV-VI semiconductor nanocrystals (PbS, PbSe) are of particular interest as candidates for the exploitation of MEG due to the narrow band gap, high confinement energies, and long radiative carrier lifetimes observed in these systems. In order to realise the full potential of MEG devices, full characterisation of the optoelectronic properties of the underlying nanoparticles is desirable. While the size-dependent properties of NQDs are well understood, the effects of NQD shape are less so. This thesis investigates the effect of ellipticity on the optoelectronic properties associated with spheroidal NQDs. To this end, a four-band, anisotropic, and radially variant k · p system Hamiltonian is expanded in a planewave basis in order to calculate single-particle eigenenergies and eigenfunctions of colloidal PbSe/PbS core/shell heterogeneous NQDs of varying ellipticity. Many-body effects are accounted for via a full configuration interaction (CI) Hamiltonian, the basis of which is comprised of the single-particle states. Exci- tonic and bi-excitonic corrections are then found by mixing of the basis states. In this manner, such diverse electronic and optical properties as quasi-particle binding energies, momentum matrix elements, and charge carrier lifetimes, both radiative and non-radiative, may be predicted.

Ce travail de recherche consiste à étudier les relations structure-propriétés de mélanges biopolymères à base de poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) et poly(butylène succinate) (PBS). Il est divisé en trois parties. La première partie est consacrée à l'étude des propriétés des mélanges PHBV/PBS préparés par voie fondue en fonction de la composition en termes de morphologie et de propriétés rhéologiques, mécaniques, thermiques et barrières. Les résultats obtenus ont été discutés par rapport aux polymères de base. La deuxième partie est consacrée à la compatibilisation des mélanges PHBV/PBS et l'amélioration des interactions à l'interface. Les effets de l'incorporation de la sépiolite à 5% en masse et du PHBV greffé par de l’anhydride maléique (PHBV-g-MA) à 5% en masse ont été étudiés en termes de changements morphologiques montrant un effet synergique entre le compatibilisant et la nanocharge sur les l’ensemble des propriétés des mélanges PHBV/PBS. Enfin, une étude sur le recyclage a été menée à travers une évaluation des effets du nombre de cycles d'extrusion sur les propriétés des matériaux. Elle révèle qu'après 6 cycles d'extrusion, la dégradation thermo-mécanique du PHBV est significativement réduite en présence du PBS
The main objective of this work was to study the structure-properties relationships of biopolymerblends based on poly (3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) and polybutylene succinate (PBS). The work was devised into three parts. The first part was devoted to the study of the properties of PHBV/PBS blends prepared by melt compounding at different weight ratio in terms of morphology and properties. The results obtained were discussed in terms of properties and compared with the neat polymers. The second part was devoted to the study of compatibility of PHBV/PBS blends aiming to improve the interactions at the interface between the two components. The effects of both sepiolite (5% wt.) and PHBV-g-MA (5% wt.) were studied in terms of properties. The results showed a synergistic effect between the compatibilizer PHBV-g-MA and the nanofiller sepiolite though an increase in thermal, mechanical and rheological properties. The last part dealing with the recyclability of PHBV/PBS through the study of the effects of repeated extrusion cycles on the properties of materials. The results showed that after 6 reprocessing cycles the thermo-mechanical degradation of PHBV is significantly reduced in the presence of PBS

Comprehensive evaluation of performance analysis of PBS INDUSTRY, a.s. When evaluating the performance of PBS INDUSTRY, a.s. the financial statements of the company for the period of 2005 -- 2008 are used. Performance evaluation is done through traditional methods of financial analysis and modern methods of economic added value. The interpretation of analytical results and recommendations was made.

Nanocrystal films may be used as detector material in sensors, as charge storage or conducting channels in devices. In this work lead sulphide (PbS) nanocrystals are generated in the gas-phase and deposited onto substrates forming nanocrystal films. A technology is developed for lateral structuring of these films on the substrate and to process them further by microelectronic standard processes. The pattern of the nanocrystal film is scaled down by several hundreds of nanometers compared to the used photoresist mask pattern. The responsible mechanism is found by consideration of physical mechanisms and usage of a trajectory simulation program. For basic electrical investigation a system is designed for production of nanocrystal films and electrical characterization under clean conditions. Noise measurements and I-V characterizations are performed. Both, single charge transport and charge transport through the interface of nanocrystal film and substrate have been found. The volume of the nanocrystal film is for the current transport not important. PbS nanocrystal films can be used in future devices for definition of high resolution current paths. Current designs can be used to downscale the device patterns without applying high resolution lithography. The parallel process technology with optical lithography still can be used to implement the films into microelectronic devices. With the trajectory simulation program the geometry can be predicted. The developed technology and the results can be transmitted to other material systems.

This thesis describes the optical and electrical properties of colloidal PbS nanocrystals synthesized in aqueous solution and comprising different capping ligands and/or matrices. Post-synthesis thermal annealing of thiol-capped PbS colloidal quantum dots (QDs) is discussed and shown to provide a novel means of tailoring the morphological and electronic properties of the QDs. Two different regimes are reported: at low annealing temperatures (< 80oC), the annealing provides a simple strategy for controlling and narrowing the QD size distribution and photoluminescence emission. At higher annealing temperatures, the displacement of the thiol-ligands promotes the fusion of nearby quantum dots thus leading to interconnected nanocrystals. A study of the circularly polarized magneto- photoluminescence of colloidal PbS nanocrystals under the influence of a magnetic field up to 30T is presented. A semiclassical model for the population of polarized excitons is used to account for the measured magnetic field and temperature dependence of the degree of circular polarization of the QD photoluminescence. The g-factor, gX, of the exciton and its dependence on the QD size is reported for the first time. The value of gX increases from 0.1 to 0.3 at low temperature with decreasing the nanocrystal diameter from 9 to 4 nm. The transport properties of a PbS QDs thin film deposited between two electrodes are investigated. This study reveals a non-linear dependence of the current on the applied bias. At low temperature (T<100 K), the conduction is limited by the charging energy (~20 meV) of the quantum dot. The fabrication of a solid-state device based on porous TiO2 impregnated with PbS QDs is discussed. The photovoltaic response of the device in the visible and near infrared wavelength range is obtained by exploiting the Schottky junction that forms at the interface between the PbS/TiO2 film and a metallic contact.

The diploma thesis is focused on cost control management in a manufacturing company. The diploma thesis deals with the calculation of product. It describes existing system of calculations and on the basis of theoretical knowledge suggest effective solutions. This solution should help to find hidden costs.

The purpose of this analysis is used PBS Turbo turbochargers like a steam-air turbine in the Flexible Energy System. The System is analogy of Brayton cycle with high efficiency, but heat is transferred to the cycle through a heat exchanger. Main parts of this work are the literature search, the thermodynamic model of the steam-air cycle, and solution for other possibilities. The goal is to find maximum available electrical output and efficiency. The thermodynamic model is used to: - check computation of the standard turbocharger - computation of the steam-air turbine contain one turbocharger - computation of the steam-air turbine contain two turbochargers. The steam-air turbine is different from the turbocharger. They are compared and than there is found some new design of the new steam-air turbine. The one-turbocharger steam-air turbine is used to test steam-air cycle. The double-turbocharger steam-air turbine is suitable for Flexible Energy System. This solution has a lot of advantages.

Magneto optical studies of colloidal PbS nanocrystals (NCs) have been undertaken to determine their fundamental properties. Measurements including absorption, photoluminescence (PL) and PL lifetime decay are presented along with their dependence upon temperature, magnetic field, and magnetic dopant concentration for undoped and doped PbS NCs. Temperature dependence of undoped PbS NCs, recorded from 300 K down to 3 K, displays a Stoke shift increasing from ~7 5 meV to ~125 meV which is fitted using a three-level rate equation model, supported by PL lifetime decay measurements, that indicate energy separation of ~ 6.0 ± 0.3 meV between the two optically active levels within PbS NCs. Magneto optical studies of undoped PbS NCs at low temperature using a field sweep from -7 Tesla to 7 Tesla are presented. Analysis of the magneto-PL data yields a degree of circular polarization (DCP) of 33% at 7 T and 2 K. Further analysis predicts an excitonic g-factor, gu for the -4 nm diameter PbS NCs of ....().54 by taking account of random orientation of PbS NCs. Using this value of g~x the expected Zeeman splitting at 7T ,ΔEzeeman , is calculated to be ~0.22 meV. Optical studies of PbS NCs with TIFffCNQ molecule showed modification of the PL spectra and PL lifetime. It is proposed that the quenching effect on the PL of PbS-TTF in the range of 900 nm to 1300 nm is due to a charge transfer mechanism . The PL obtained from PbS-TCNQ solutions display a second emission peak centred at ~700 nm which is directly related to the TCNQ concentration. A study of the optical properties of Mn-implanted PbS NCs was undertaken and compared with that of undoped PbS NCs. The PL spectra of all Mn-implanted PbS NCs showed a significant red shift of the PL peak compared to undoped PbS NCs. Based on fitting of a Brillouin function to the difference in the temperature dependent Stokes shift between the Mn-implanted and undoped PbS NCs an effective exchange field of ~81 T is predicted.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Physics, 2015.
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 149-159).
In this thesis, we study charge transport in nanopatterned arrays of PbS colloidal quantum dots using conventional two-probe measurements and an integrated charge sensor. PbS dots are synthesized in solution with an organic ligand or cap that serves to passivate the surface of the dot, provide a tunnel barrier as well as colloidal stability. These dots can self assemble into an array as the solvent evaporates from a drop of solution on a surface. The self-assembled arrays can be thought of as tunable artificial solids, where the coupling between the dots can be tuned by changing the ligand. Using electron beam lithography followed by a lift-off process, we develop a novel technique to nanopattern these arrays and present the first colloidal quantum dot arrays of nanoscale dimensions. Nanopatterning makes it possible to study the electrical properties intrinsic to the dots unimpeded by macroscopic defects, such as cracking and clustering that typically exist in larger-scale arrays. We find that the electrical conductivity of the nanoscale films is higher than that of drop-cast, microscopic films made of the same type of dot. We achieve unprecedented versatility in integrating the patterned films into device structures, which will be valuable both for studying the intrinsic electrical properties of the dots and for nanoscale optoelectronic applications. From two-probe measurements on the nanopatterned arrays that are approximately 15 dots wide, we observe large noise in the current as a function of time. The noise is proportional to the current when the latter is varied by applying source-drain or gate voltage in a field-effect structure or when changing temperature. Owing to the small number of current paths in the system, we often observe telegraph switching, and find that the off times follow non-poissonian statistics. We show that the results can be understood in terms of a model in which a quasi-one-dimensional percolation path is turned on and off, by charging of a dot along the path. Long organic ligands lead to highly resistive colloidal quantum dot arrays, making the low bias regime inaccessible with conventional two-probe measurements. We use an integrated charge sensor to study transport in the low bias regime as a function of the coupling between the dots. We present transport measurements on butylamine and oleic acid capped PbS dots. The resistances measured are the highest measured for colloidal quantum dots. For the native oleic acid ligand, and weak coupling between the dots, the conduction mechanism is nearest neighbor hopping, and the conductance is simply activated. At low source-drain bias voltages, the activation energy is given by the energy required to release a carrier from a trap state plus the activation over barriers resulting from site disorder. The barriers from site disorder are eliminated with a sufficiently high source-drain bias. For the shorter ligand, which gives stronger coupling, the data are consistent with Mott's variable range hopping as the conduction mechanism.
by Nirat Ray.
Ph. D.

Grazie ai continui progressi dell’ingegneria tissutale, branca dell’ingegneria che si occupa della ricostruzione in vitro di tessuti, sta diventando sempre più concreta la possibilità di superare i principali limiti della medicina tradizionale, fino ad ora limitata al trapianto di organi provenienti da donatori e a trattamenti farmacologici diretti non solo al sito di destinazione ma a tutto l’organismo (con possibili effetti collaterali). Tramite lo studio dei biomateriali e delle loro proprietà è possibile realizzare soluzioni ad hoc per l’ingegneria tissutale di diversi tessuti. Nel presente studio, è stato realizzato mediante elettrofilatura uno scaffold in P(BSBTDTP), un copolimero a base di PBS contenente co-unità ditiodipropioniche, caratterizzate dalla presenza del legame -S-S-, potenzialmente capace di migliorare la biocompatibilità e biodegradabilità dell’omopolimero. Il PBS è infatti un polimero sintetico biocompatibile già approvato dalla Food and Drug Administration, ma caratterizzato da un alto grado di cristallinità, che porta a lunghi i tempi di degradazione e a proprietà meccaniche spesso non adatte ad applicazioni nell’ingegneria dei tessuti molli. Il tappetino elettrofilato ottenuto tramite electrospinning è stato sottoposto inizialmente a caratterizzazione molecolare, termica e meccanica. Inoltre, in vista delle possibili applicazioni nell’ambito dell’ingegneria tissutale, il materiale è stato sottoposto anche a test di biodegradazione in ambiente enzimatico e prove di biocompatibilità in vitro. In conclusione, dalle indagini fatte, seppur preliminari, è risultato che lo scaffold realizzato in P(BSBTDTP), porta ad una migliore adesione e proliferazione cellulare e ad una velocità di degradazione in ambiente biologico leggermente superiore al suo corrispondente in PBS.

Most school based initiatives are not implemented long-term and do not reach sustainability (McDermott, 2000; Mirel, 1994; Rice & Malen, 2003). Schools are implementing School-Wide Positive Behavior Support (SWPBS) as an initiative to target social emotional development and behavior. Schools that have implemented SWPBS have experienced decreases in rate of Office Discipline Referrals (ODR), In-School Suspension (ISS) and Out-of-School Suspension (OSS) (e.g. Bohanon et al., 2006; Childs et al., 2009; Lassen et al., 2006). Research has also shown that schools that implement with a higher degree of fidelity have better outcomes (Childs et al., 2009; Florida's Positive Behavior Support Project, 2009). However, it is not known what mediating factor(s) assist with schools with implementation of Tier 1 PBS at a higher degree of fidelity. This study examined action plans that schools developed during their initial training of Tier 1 PBS, to determine if the action plans are one of the possible mediating factor(s). There are differences between the quality of action plans developed by schools implementing with a higher degree of fidelity compared to schools implementing with a lower degree of fidelity. Based on a path analysis, the action plans are not a mediating factor between fidelity of implementation and student outcomes (i.e. office discipline referrals, In-School Suspension, and Out-of-School Suspension).

xx, 134 p. : ill. (some col.)
Solar energy is a green alternative to fossil fuels but solar technologies to date have been plagued by low conversion efficiencies and high input costs making solar power inaccessible to much of the developing world. Semiconductor nanoparticles (NPs) may provide a route to efficient, economical solar devices through a phenomenon called multiple exciton generation (MEG). Through MEG, semiconductor NPs use a high-energy input photon to create more than one exciton (electron-hole pair) per photon absorbed, thereby exhibiting large photoconversion efficiencies. While MEG has been studied in many NP systems, and we understand some of the factors that affect MEG, a rigorous analysis of the NP-ligand interface with respect to MEG is missing. This dissertation describes how the NP ligand shell directly affects MEG and subsequent charge carrier recombination. Chapter I describes the motivation for studying MEG with respect to NP surface chemistry. Chapter II provides an in-depth overview of the transient absorption experiment used to measure MEG in the NP samples. Chapter III highlights the effect of oleic acid and sodium 2, 3-dimercaptopropane sulfonate on MEG in PbS NPs. The differences in carrier recombination were accounted for by two differences between these ligands: the coordinating atom and/or the secondary structure of the ligand. Because of these hypotheses, experiments were designed to elucidate the origin of these effects by controlling the NP ligand shell. Chapter IV details a viable synthetic route to thiol and amine-capped PbS NPs using sodium 3-mercaptopropane sulfonate as an intermediate ligand. With the versatile ligand exchange described in Chapter IV, the MEG yield and carrier recombination was investigated for ligands with varying headgroups but the same secondary structure. The correlation of ligand donor atom to MEG is outlined in Chapter V. Finally, Chapter VI discusses the conclusions and future outlook of the research reported in this dissertation. This dissertation includes previously published and unpublished co-authored material.
Committee in charge: Dr. Geraldine L. Richmond, Chairperson; Dr. David R. Tyler, Advisor; Dr. Mark C. Lonergan, Member; Dr. Catherine J. Page, Member; Dr. Hailin Wang, Outside Member

L’objectif premier de ce travail de thèse concerne la réalisation et la caractérisation de différents films multicouches afin d’étudier l’impact du phénomène de confinement des couches de polymères sur les propriétés barrières du polymère confiné et du film multicouche. Des films multicouches constitué de polycarbonate (PC) et de poly(m-xylène adipamide) (MXD6), polymères actuellement utilisés par les industries de l’emballage, ont tout d’abord été étudiés. Puis, dans un second temps, des films multicouches composés de polyesters biodégradables, à savoir des films multicouches d’acide polylactique (PLA) avec comme polymère confiné soit du poly(butylène succinate-co-butylène adipate) (PBSA) ou du poly(butylène succinate) (PBS), ont été élaborés.Une fois la structure multicouche obtenue et avoir confirmé l’amélioration de l’effet barrière grâce au phénomène de confinement, le deuxième objectif a été d’incorporer des charges lamellaires de type montmorillonite (Cloisite® 30B) dans la couche de polymère confiné dans le but d’accroitre davantage l’effet barrière du film multicouche sélectionné.Pour comprendre l’amélioration des propriétés barrières aux gaz et à l’eau des films multicouches élaborés, une analyse de la microstructure par DSC et DRX ainsi qu’une analyse des propriétés mécaniques ont été menées conjointement avec une observation par microscopie
The objective of the work was the elaboration and the characterization of different multilayer films in order to study the impact of the confinement effect of the polymer layers on the barrier properties. Multilayer films of polycarbonate (PC) and poly(m-xylene adipamide) (MXD6), which are usual polymers for packaging industries, have been studied. Then, multilayer films composed of biodegradable polyesters, such as polylactic acid (PLA) with poly(butylene succinate-co-butylene adipate) (PBSA) or poly(butylene succinate) (PBS) as the confined layers, have been prepared and characterized.For the multilayer structure presenting improved barrier performances due to the confinement effect, the second objective was to insert lamellar clays (Cloisite® 30B) into the confined polymer layers to again improve the barrier properties of the multilayer film. To understand the gas and water barrier improvement of the multilayer films, a microscopic observation of the films and an analysis of the microstructure by DSC and XRD have been performed with mechanical properties measurements

The purpose of this thesis is to outline the research undertaken into the synthesis of metal chalcogenide nanomaterials followed by their behavior of in diverse thermodynamic conditions. This thesis will focus on the research of novel routes to metal chalcogenides, especially CdS, PbS and PbSe. An effort was made in order to improve existing techniques by combining knowledge from diverse fields. Instabilities in nanoparticles and related behaviors, e.g. tendency to grow in specific shapes, aggregate and coalesce, were the other focusing point of this thesis. This thesis is divided into five main chapters. The first chapter introduces nanomaterials and their potential applications. An emphasis is made on the synthetic techniques to nanomaterials and their properties. Chapter two describes the synthetic approaches that were investigated during this work. Soft-hydrothermal and microwave-assisted hydrothermal routes to nanoparticles will be described. Chapter three focuses on the formation of stable nano-shapes different than the bulk-shape for PbS and PbSe nanocrystals. Their ability to self-organise on an amorphous substrate is also presented. Chapter four describes the research undertaken by transmission electron microscopy, on the coalescence of nanocrystals. Chapter five contains detailed descriptions of the experiments that were involved during this work. A general conclusion is then followed by appendixes that contain extra-information related to this thesis.

This thesis presents a study on different school actors’ narratives about how they have experienced a participation in a school development collaboration called PBS, problem based school development. A school development and research project based at Karlstad University. The analysis is inspired by a narrative approach and a critical perspective on policy, were policy is understood as both text and discourse. The aim of the study is to show how the carrying through of this new policy (PBS) is received and reconstructed in three Swedish municipal settings. In the analysis the participant’s narratives are also related to the reconstructions of the field of education politics that has been carried out the last decades, here in Sweden as well as in other countries around the world. In this study 46 interviews were carried out. Official texts from each of the three school organizations have also been studied. As analytical tools parts of a model called the zoom-model and three different concepts, taken from the field of organization studies have been used. The overall result shows that those who work in schools today are engaged in a large amount of development works, claims and ways of working that they themselves choose to enact. The results also show how the interviewees receive and charge these ideas with their own previous experiences and how this is done in discursive contexts that shape what is considered normal and evident. One conclusion is that further attention ought to be made to the significance of the local context when it comes to carry through a new idea on development and change. A conclusion drawn from how interpretations and reconstructions of both development models prior to PBS and of the national steering model came to play important roles in how PBS was received and reconstructed in the studied municipalities. But different interpretations of the PBS model also led to tensions within and between the different areas of the organizations. Tensions that can be described as dilemmas, implicated by an ongoing cacophony of policy voices, whose prescriptions pull on different directions. When the PBS-policy arrives in this discursive room the results show how this policy can become a tool in line with new discursive narratives of education, regardless the intensions formulated in the context of policy text construction.
PBS-Problembaserad skolutveckling

Undersökningen som redovisas i den här uppsatsen har haft som syfte att undersöka om det finns någon koppling mellan lärares inställning och förståelse av PBS och den betydelse de upplever att PBS har haft för deras arbete.

Sex lärare har deltagit i undersökningen och för att synliggöra deras förståelse av PBS har föreställningskarta med intervju använts som metod. De olika föreställningskartorna har sedan funnits som underlag för att beskriva lärarnas förståelse av PBS. De mönster likheter och skillnader som fanns mellan föreställningskartorna har sedan lett fram till resultatet.

Resultatet visade att lärarna hade olika förståelse av PBS och att de hade gjort olika lärdomar. En slutsats är att förståelsen inte har något samband med inställningen till PBS. Det finns en koppling att de som har förstått  PBS som en lärprocess i vardagsarbetet har gjort lärdomar som de anser att de har kunnat omsätta i praktiken.

The survey that is presented in this essay has had as aim to examine about there be some link average teachers' attitude and understanding of PBS and that importance they experience that PBS has had for their work.

Six teachers have participated in the survey and in order to make visible their understanding of PBS has attitude map with interview been used as method. The the different attitude maps has afterwards been as bases in order to describe the teachers' understanding of PBS. Those standards resemblances and differences that were the average attitude maps have since lett until the result.

The result showed that the teachers had various understanding of PBS and that they had done various lessons. A conclusion is that the understanding does not have any connection with the attitude to PBS. There is a link that they that has understood PBS as a faith process in the everyday existence work has done lessons that they consider that they have can have a turnover of in practice.

PBS - problembaserad lärdomsbaserad skolutveckling

Quantum dots offer a number of advantages over standard fluorescent dyes for monitoring biological systems including high luminescence, stability against photobleaching, and a wide range of fluorescence wavelengths from blue to infrared depending on the particle size. In this work, we investigated in using the protein cage apoferritin as a template for the synthesis of colloidal quantum dots. We obtained apoferritin after reductive dissolution of the ferritin iron core and showed that the protein structure was left intact during this process. We further studied the solubility of ferritin, apoferritin and cationized ferritin in organic and fluorinated solvents by hydrophobic ion pairing methodology in order to expand the possibility of using an apoferritin template for the synthesis of quantum dots in organic media. We then focused on the synthesis and fluorescence properties of PbS quantum dots in aqueous solution. PbS dots are thermally stable and emit in the range 1,100 to 1,300 nm depending on their size. We demonstrated the encapsulation of these PbS quantum dots within the cavity of the iron storage protein apoferritin using two routes: 1) the disassembly/reassembly of apoferritin subunits trapping previously synthesised PbS quantum dots; and 2) use of the channels present in the protein shell to allow the entrance of Pb2+ and S2- ions leading to formation of quantum dots in the apoferritin cavity. We show that PbS-apoferritin composites emit in the near infrared region which make them promising labels for biological applications. Furthermore, we demonstrated that PbS QDs can be excited via a bioluminescence resonance energy transfer (BRET) using luciferin from Luciola mingrelica which could be developed into a self-illuminating labelling system. Finally, in order to make PbS-apoferritin composites selectively attachable to biomolecules during labelling experiments, the apoferritin was modified by the incorporation of analogues of methionine introducing azido groups absent in the proteins. The azido groups can then be selectively modified in complex mixtures e.g. cell lysates using `bio-orthogonal' reactions such as the Cu(I) catalysed Staudinger ligation and Huisgen cycloaddition. This would allow highly selective addition of receptor targeting or cellular permeation of peptides to the outer surface of the apoferritin shell.

In the latter half of the 20th century the first active environmentalist movements such as Greenpeace and the International Energy Agency were born and initiated a gradual rethinking of environmental awareness. Against all expectations the sole agency under international law for climate protection policy, called the United Nations Framework Convention on Climate Change, was formed 20 years later. Today the awareness of sustained, regenerative and environmental policies permeates throughout all areas of life, science and industry. But energy provision is the most decisive topic, especially since the discussions concerning the phase out of nuclear power where the voices calling for alternative energy sources have become much more vociferous. In addition the depletion of fossil fuels is expected to occur in the not too distant future. All new energy generation methods are required to meet the present and future energy demands, need to be ecological and need to exhibit the same or significantly lower cost expenditure than current energy sources. Unfortunately mankind is confronted with the problem that current commercial alternative energies are more expensive and not yet remotely as efficient as the present energy sources. Although energy provision based on water, wind, sun and geothermal sources have a huge potential because of their continuous presence, unfortunately, they are plagued by inefficient energy conversion caused by the state of technology i.e. the conversion of sun light into electricity loses energy through heat emission, reflection of the sun light, the inability of the material to absorb the entire sun spectrum and the ohmic losses in the transmission of electric current. The sun power is the most exhaustless resource and moreover through photovoltaic action, one of the most direct and cleanest source for use in energy conversion. Presently incoming sun light is not transformed in its entirely, as much degradation occurs during photon absorption and electron transfer processes. A number of other innovative possibilities have also been researched. With respect to cost and efficiency one of the most promising devices is injection solar cells (ISC). By dint of the dye sensitised solar cell (DSSC) Grätzels findings provided the foundations for much research into this type of solar cell where the light absorbing molecule employed in is a dye.[1] The current is obtained through charge separation in the dye, which is initiated through the connection between the dye and a metal oxide on the one hand and a matched redox couple on the other. In a variant of the DSSC the charge separation processes can also occur between a nanoporous metal oxide and nanoparticles giving rise to a quantum dot sensitised solar cell (QDSSC).[2] The use of nanoparticle (NP) properties can be utilized for the harvesting of solar energy, as demonstrated by Kamat and coworkers[3] who were able to exploit these findings subsequently and prepare a number of nanoparticle based solar cells. Nanoparticle research has comprised a wide field of science and nanotechnology for a number of years. As the size of a material approaches dimensions on the nm scale the surface properties contribute proportionally more to the sum of the properties than the volume due to the increase in the surface to volume ratio. These dimensions also constitute a threshold in which quantum physical effects need to be taken into account. Hence the properties of devices or materials in this size regime are inevitably size dependent. The basic principles can be described by two different theories, one of which is based on molecular orbital theory in which the particle is treated as a molecule. For this reason n atomic orbitals with the same symmetry and energy can build up n molecular orbitals through their linear combination based on the LCAO method (Linear Combination of Atomic Orbitals).[4] In the case of solids the orbitals build up energy bands, where the unoccupied states form the quasi continous conduction band (CB) and the occuppied states form the quasi continous valence band (VB). The energy \"forbidden\" area in between these two bands is called the band gap. The band gap is a fixed material property for bulk solids but depends on size in the case of the nanoparticles. In contrast to the LCAO method, simplified solid state theory will be used throughout the present work, the theoretical background of which is provided by the effective mass approximation.[5] When an absorption of a photon occurs, an exciton (electron-hole pair) can be generated. By promoting an electron (e-) from the valence band into the conduction band a hole (h+) may be said to remain in the valence band. By comparison to bulk solids, in a small particle the free charges can sense the potential barrier i.e. the edges of the nanoparticle. Analogous to the particle in a box model this potential barrier interaction results in an increase in the band gap as the particle size decreases. In a solar cell NPs with a particle size which possess a band gap energy in the near infrared (NIR) may be utilised and therefore the NPs will be able to absorb in this spectral region. However NPs also have the ability to absorb higher energy photons due to the continuum present in their band structure, so that almost the entire sun spectral range from the NIR up to UV wavelengths may be absorbed just by using the appropriate NP material and size. Suitable NPs are metal chalcogenides e.g. MX (where M = cadmium, zinc or lead and X = sulfur, selenium or tellurium) because of their bandgap size[6–10] and their relative band positions compared to those of the semiconductor oxide states. Both the TiO2/CdSe[11–14] and TiO2/CdTe[15–18] systems have already been successfully fabricated and many of the anomalies reported.[3] Much interest in the lead chalcogenides has been generated by reports that they may feature the possibility to exhibit multiple exciton generation (MEG) where the absorption of one high energy photon can result in more than one electron-hole pairs.[19–25] Currently electrochemical impedance spectroscopy (EIS) is being used more and more to clarify processes at polarisable surfaces and materials such as nanoparticles. Likewise this method has been rediscovered in photovoltaic research and its use in the characterisation of DSSCs has been discussed in the literature.[26–31] In a number of publications the evaluation of nanoporous and porous structures has been quite extensively explored.[28,29,32–34] Since the mid-20th century Jaffé’s[35] theoretical work concerning the steady- state ac response of solid and liquid systems lead to the formation of the basics of EIS. Further developments in the measurement technology have lead to a broader range of analysis becoming possible. Nevertheless the most challenging part still remains the interpretation of the results and especially to merge the measured data with the theoretical model. EIS quantifies the changes in a small ac current response at electrode electrolyte interfaces i.e. the rate at which the polarized domain will respond, when an ac potential is applied. In this way dielectric properties of materials or composites, such as charge transfers, polarization effects, charge recombination and limitations can be measured as a function of frequency and mechanistic information may be unveiled. Hence EIS allows one to draw a conclusion concerning chemical reactions, surface properties as well as interactions between the electrodes and the electrolyte. Other very useful tools that may be employed for quantifying electron transfer processes and their time domains are intensity modulated photocurrent spectroscopy (IMPS) and intensity modulated photovoltage spectroscopy (IMVS). IMPS permits the generation of time-resolved plots of particular photo-processes in the system, each of which may be specifically addressed through varying the excitation wavelength. For the IMPS technique a sinusoidal wave with a small amplitude is applied, analogous to that of electrochemical impedance spectroscopy, but in this case the modulation is applied to a light source and not to the electrochemical cell as in EIS.[35] The current response is associated with the photogenerated charge carriers which flow through the system and finally discharge into the circuit. The amount of generated and discharged charge carriers is often different due to the presence of recombination and capture processes in surface or trap states. Ultimately the phase shift and magnitude of these currents reveal the kinetics of such processes. The only processes that will be addressed will be those that occur in the same frequency domain or on the same time scale as that of the modulated frequency of the illuminated light. In the literature some explanation of the kinetics of simple systems can be found and basic theories and introductive disquisitions may be found elsewhere.[36–38] Furthermore in solar cell research a multiplicity of studies are available which give an account of IMPS measurements on TiO2 nanoporous structures. Such studies permitted proof for the electron trapping and detrapping mechanism in TiO2 surface states.[39,40] An analysis of TiO2 electrodes combined with a dye sensitization step was established in the work of Peter and Ponomarev.[41–43] Hickey et.al.[44,45] have previously published kinetic studies on CdS nanoparticle (NP) modified electrodes. A theory was presented which allows for the IMPS data to be the interpreted in the case of CdS NP based electrodes. The back transfer, recombination and surface states have been demonstrated to be important as was determined from their inclusion in the theory. Similar attempts to explain the kinetics of CdS quantum dots are described by Bakkers et.al.[46]. In the present work the most important questions concern the behaviour of the photovoltaic assembly. Such assemblies can be equated with an electrode in contact with an electrolyte. Preliminary remarks about such electrodes as components of an electrochemical cell will be introduced in the first part of chapter 2. Thereafter the properties of electrodes in contact with the electrolyte and under illuminated conditions are illustrated. This is followed by a description of the important electrochemical and opto-electrochemical methods which have been employed in these studies. In particular, two separate subsections are dedicated to the methods of EIS and IMPS and the experimental section which are then linked to the theoretical section. The synthesis of all substances used and the preparation of the solar cell substrates are also dealt with in this section as will the equipment used and the instrument settings employed. The optical response of the working photoactive electrode is not only dependent on the substances used but also on their arrangement and linkage. The substrate which was employed in chapter 3 consists of a nanoporous ZnO gel layer upon which an organic linker has been placed in order to connect the oxide layer with the light absorbing component, the PbS NPs. Chapter 3 deals with the linker dependence on the ZnO layer and reports the typical optical characteristics and assembly arrangements of six different linkers on the ZnO layer which is an important intermediate stage in the fabrication of an ISC. The questions concerning how the type of linking affects the photo response and other electrochemical interactions of the complete solar cell substrate will be outlined in chapter 4. Further an examination of the electrochemical and opto-electrochemical behaviours of the samples will be presented similar to that presented in chapter 3. The most interesting substrate resulting from the investigations as described in chapter 3 and 4 will be used for a more in-depth characterisation by EIS in chapter 5. A suitable model and the results of the calculation of the ISC and the intermediate stages will be presented. The potential dependence, the dependence on the illuminated wavelength and also the size dependence of the PbS nanoparticles will be discussed. It will be revealed that ZnO is chemically unstable in contact with some of the linkers. For that reason the same linker study has been repeated with the more stable TiO2 employed as the wide band metal oxide. Comparisons between the different semiconductor metal oxides are made in chapter 6. In addition a number of open questions which previously had remained unanswered due to the instability of the ZnO can now be answered. In chapter 7 another highly porous structure different from that of the ZnO gel structure has been studied to determine its suitability as an ISC substrate. The structure arises from the electrodeposition of a ZnO reactant in the presence of eosin Y dye molecules. In the end the desorption of the dye provides a substrate with a high degree of porosity. Compared to the ZnO gel which was prepared and used for measurements in chapter 3 and 4, the electrodeposited ZnO is of a higher crystallinity and possesses a more preferential orientation. This results in a lower amount of grain boundaries which in turn results in fewer trap processes and subsequently yields a higher effective diffusion of the electron through the layer.[47,48] Optical and (opto-)electrochemical methods have been used for the basic characterisation of the untreated ZnO/Eosin Y and all other materials used in the fabrication of the ISC and a comparison with the ZnO gel used in chapter 3 and 4 will be made. Finally in chapter 8 an alternative metal oxide structure will be discussed. The background to this last chapter is to examine the influence of the ISC where the oxidic layer is present as a highly periodic arrangement, known as a photonic crystal. The TiO2 metal oxide which was also used in chapter 6 has been structured to form an inverse opal. First preparative findings and the first illustration of the (opto-)electrochemical results are presented. Consequently suggestions for improvements will be made. It is envisaged that the information gathered and presented here will help to achieve a deeper understanding of solar cells and help to improve the device efficiency and the interplay of the materials. Elementary understanding paves the way for further developments which can also contribute to providing devices for more efficient energy conversion.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2015.
This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (pages 131-139).
Photovoltaic (PV) solar cells that constitute semiconducting sunlight absorber and metallic electrical contacts convert solar energy to electricity. Even though silicon represents roughly 90% of installed solar PV capacity as the clear current leader among PV technology, another class of solid-state solar cells, referred to as quantum dot (QD) solar cells, have gained much attentions from both academia and industry with the ability to provide further substantial enhancement of PV efficiency, together with the low possible manufacturing/installation cost. The power conversion efficiencies (P.C.E.) of QD-PVs based on lead sulfide (PbS) have been enhanced dramatically in only several years: current leading groups are able to fabricate reliably QD-PVs with 7-10% P.C.E. owing to favorable optical properties of PbS QDs including facile tunability of bandgaps with the variation in dot sizes or shapes, wide spectral responses, and multiple exciton generation. To date, the efficiency advances of QD solar cells have been carried out almost exclusively through tremendous numbers of trial and error experiments. Examples include materials set variations, donor and acceptor layer thickness optimization, and device structure modification. The core of the work described in this thesis deals with the theoretical understanding and design of PbS QDs with the goal of achieving a deeper and more fundamental understanding of the wide range of material's properties at the atomic scale in these devices. To this end, we employ a technique of computational electronic structure calculation methods, namely density functional theory (DFT) calculations. In this thesis, we select and investigate, using DFT calculations, three important electronic or optical properties: 1) band-edge energy (Chapter 2), 2) trap states (Chapter 3), and 3) Stokes shift (Chapter 4), all of which can contribute to PV performance improvements only if appropriately tailored. It is worth emphasizing that ligands which are used during QD synthesis for prevention of QD agglomeration plays a key role in tuning each property of interest in this thesis. Our theoretical work of band-edge energy shifts presented in Chapter 2 identifies ligand-induced surface dipoles as a hitherto-underutilized means of control over the absolute energy levels in PVs, complementary to well known bandgap tuning. This work have guided our experimental collaborators to build up a device architecture with a novel interfacial band alignment where a surplus loss of current collection can be minimized, leading to "certified" efficiency of 8.6% in 2014. Improvements of JSC presented in Chapter 2 led us to pay much attention to another figure of merit, open-circuit voltage (VOC): maximum Voc of 0.5-0.6 (V) has been achieved in single-junction PVs using PbS QDs with the bandgap of 1.1-1.3 (eV). Such large deficit of Voc in QD-PVs is attributed to the following sources: (1) high density of mid-gap trap states, (2) large Stokes shift, each of which is investigated and elaborated on in Chapters 3 and 4. Based on the fundamental understanding on the origin of these properties obtained from DFT calculations, we together with our experimental collaborators are actively working to develop PbS QD films with improved properties and to incorporate them into PV devices for further performance enhancements. This thesis document is organized as follows: Chapter 1 introduces PbS QDs and PVs, Chapters 2,3, and 4 illustrates theoretical investigations of key electronic and optical properties of PbS QDs (i.e. band-edge energy, trap states, and Stokes shift, respectively) supported by relevant experimental results from collaborators for better understanding of the this thesis. Lastly Chapter 5 closes the thesis with brief summary of works and future impacts to PVs and other optoelectronic applications.
by Donghun Kim.
Ph. D.

Deposition of polycrystalline Lead sulfide nano thin films onto Si and glass substrates at temperatures (200- 300 °C) was carried out by chemical spraying route using optimized preparative conditions. The XRD pattern confirmed the formation of PbS semiconducting films with orthorhombic structure. The electrical and optical properties of the nano crystalline thin films were studied aiming to better understanding for the electrical and opto-electrical properties of a hetrojunction with p-type Si. It was found that, the average grain size of PbS in the films was between 4 nm and 7 nm. The band gap was also calculated from the absorption co-efficient curves and showed a blue shift due to the grain size of the nano PbS in the films. The current-voltage (I-V) and photoresponse characteristics were obtained with different illumination intensities. The detector exhibits an evident wide-range spectral responsivity.

Tese (Doutorado) - Universidade Federal de Santa Catarina, Centro Tecnológico.
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Semiconductor colloidal quantum dots have an interesting potential to increase solar cell efficiency, with strong absorption in the infrared region and a tunable band gap. In this work an attempt was made to adopt a manufacturing process for PbS quantum dot solar cells, proven successful at Uppsala University. Two optimizations were investigated and the stability of the quantum dot films was analyzed with regards to three storage conditions, varying oxygen accessibility and light exposure, and measured with UV-Vis spectroscopy and X-ray photoelectron spectroscopy. Functioning solar cells were obtained but with lower performance than the results from Uppsala. Optimizations were partly successful with regards to improved spreading of the EDT solution on the PbS quantum dot film using ethanol and methanol as solvents. No improved cell performance was observed by applying both QD films inside argon atmosphere, as opposed to only the first one. Clear differences in oxidization of the films and loss of iodine ligand could be identified for the different storage conditions, with best stability exhibited by films stored under argon atmosphere.
Kvantprickar av halvledande material har en intressant potential att förbättra solcellers verkningsgrad genom en stark absorption inom de infraröda spektrat och ett justerbart bandgap. I detta arbete gjordes ett försök att återskapa en tillverkningsprocess av kvantprickssolceller av PbS, som visat sig framgångsrik vid Uppsala universitet. Två optimeringar undersöktes och stabiliteten av kvantpricksfilmerna analyserades med avseende på tre förvaringsmiljöer med olika exponering för ljus och syre, och mättes med UV-visspektroskopi samt röntgenfotoelektronspektroskopi. Fullt fungerande solceller framställdes men med en lägre prestanda jämfört med resultaten i Uppsala. Optimeringarna var delvis lyckade gällande spridning av EDTlösningen på kvantpricksfilmen av PbS genom att använda etanol och metanol som lösningsmedel. Ingen förbättrad prestanda observerades hos cellerna genom att applicera båda kvantpricksfilmerna i argonatmosfär, jämfört med endast den första. Tydliga skillnader i oxidation för filmerna samt förluster av jodligand kunde identifieras för de olika förvaringsmiljöerna, med bäst stabilitet uppvisad av filmerna som förvarades i argonatmosfär.

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This work describes studies on the underpotential deposition (UPD) of selenium, zinc, as well for Zn/Se systems deposited on polycrystalline Pt electrodes in acid solutions. The effects of Zn presence in the Se dissolution process were also investigated in the UPD and bulk potential range, 0.6 and 0.03 V respectively. The measurements were carried out using cyclic voltammetry and electrochemical quartz crystal microbalance (EQCM). Furthermore Lead sulfide (PbS) multilayers were grown on a single crystal Ag(111) substrate by Electrochemical Atomic Layer Epitaxy (ECALE) method. For Zn UPD in sulfuric acid, two different processes were observed, which are attributed to the dissolution of submonolayer of Znads and H-atoms adsorbed on the electrode surface. For Se UPD was observed that hydrogen desorption were completely inhibited indicating that Se film recovered the Pt surface. The deposition of UPD Se in perchloric acid solution showed the transference of 4 electrons with 1.4 and 1.12 active sites of Pt occupied by 1 Se ad-atom in the UPD and bulk potential range, respectively. In the evaluation of the Se monolayers dissolution process formed at 0.03 V during 2000 s a process not mentioned in the literature it was observed which was evaluated by the technique MECQ. The experimental results obtained by this technique allowed to end that the dissolution process occurred by two stages, and the first involved the participation of 6e-. The dissolution mechanism with 6e- happens with the participation of water in the dissolution process of Se, leading to the formation of an oxygenated selenium compound which in next step undergo slow oxidation and is dissolved as soluble Se(VI) species. Then the total dissolution process of Se occurs in a six-electron transfer reaction. For Se deposition in the Zn presence the dissolution charges associated with Se UPD increase, indicating that the presence of Zn favors the deposition of UPD Se. In the case of PbS multilayers on Ag (111) the voltammetric analysis of the first PbUPD and SUPD peaks indicates a mechanism of two-dimensional growth, which is consistent with epitaxial growth. Electrochemical stripping measurements indicate that the amount of Pb and S deposited in a given number of cycles is a function of the number of cycles employed, again suggesting a layer-by-layer growth. This result indicates that the amount of Pb and S in these films corresponds to the stoichiometric 1:1 ratio, indicating the formation of a compound.
Este trabalho descreve os estudos da deposicao em regime de subtensao (DRS) de Se, Zn, assim como para sistemas Zn/Se depositados sobre eletrodos policristalinos de Pt em solucoes acidas. Os efeitos da presenca de Zn no processo de dissolucao de Se tambem foram investigados em uma regiao de potenciais de DRS e deposicao massiva 0,6 V e 0,03 V, respectivamente. As medidas foram realizadas usando voltametria ciclica e microbalanca eletroquimica de cristal de quartzo (MECQ). Alem disso, multicamadas de sulfeto de chumbo (PbS) foram crescidas sobre substrato de Ag(111) utilizando o metodo de deposicao eletroquimica de camadas atomicas epitaxiais (ECALE). Para a DRS de Zn em meio de acido sulfurico dois processos distintos foram observados os quais foram atribuidos a submonocamadas de Znads e atomos de H adsorvidos sobre a superficie do eletrodo. Para a DRS do Se observou-se a inibicao completa da dessorcao de hidrogenio o que indicou recobrimento total da superficie de Pt por ad-atomo de Se. A deposicao de Se em meio de acido perclorico mostrou a transferencia de 4 eletrons com 1,4 e 1,12 sitios da Pt ocupados por cada ad-atomo de Se, em potenciais de deposicao em DRS e sobretensao, respectivamente. Na avaliacao do processo de dissolucao das monocamadas de Se formadas a 0,03 V e por um tempo de deposicao de 2000 s um processo nao mencionado na literatura foi observado o qual foi avaliado pela tecnica MECQ. Os resultados experimentais obtidos por esta tecnica permitiram concluir que o processo de dissolucao do Se ocorria por duas etapas, sendo que a primeira envolvia a participacao de uma 6 eletrons e a segunda de 4 eletrons. O mecanismo de dissolucao com 6 eletrons ocorre com a participacao de agua no processo de dissolucao do Se, levando a formacao de compostos de Se oxigenados, os quais em uma etapa posterior sofrem uma oxidacao lenta e se dissolvem como especies soluveis de Se(VI). Entao o processo total de dissolucao de Se ocorre em uma reacao de transferencia de 6 eletrons. Ja para a deposicao de Se na presenca de Zn pode-se concluir, devido ao aumento da carga de dissolucao da DRS de Se, que a presenca de Zn favorece o processo de deposicao do Se. No caso das multicamadas de PbS o estudo voltametrico das primeiras camadas de Pb DRS e S DRS indicam um mecanismo de crescimento bidimensional, que e consistente com o crescimento epitaxial. As cargas medidas no processo de dissolucao das camadas indicaram que a quantidade de Pb e S depositados para um dado numero de ciclos e uma funcao do numero de ciclos realizados, sugerindo novamente um crescimento camada por camada Este resultado sugere que a quantidade de Pb e S nos filmes possuem uma relacao estequiometrica de 1:1, indicando a formacao de um composto.

Parmi les biopolymères, le poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV) fait l’objet d’un grand intérêt de la part des chercheurs et des industriels. Cependant, sa sensibilité thermique et son comportement mécanique fragile restreint son utilisation dans certaines applications. Ainsi pour améliorer ses propriétés, deux grandes stratégies ont été suivies au cours de cette thèse. La première consiste à incorporer une argile de type halloysite (HNT), issue du gisement de Djebel Debbagh à Guelma (Algérie). À cet effet, des nanocomposites PHBV/HNT ont été élaborés par voie fondue. Les résultats de la microscopie électronique à balayage (MEB) et STEM ont montré une distribution relativement homogène de l’HNT avec la présence de larges agrégats. En conséquence et dans le but, d’améliorer la dispersion de ces nanotubes, il a été nécessaire de procéder à la modification des interfaces polymère-argile, soit par la modification chimique de l’halloysite, soit par l’incorporation d’un compatibilisant de type PHBV-g-MA dans le système binaire. Les résultats obtenus mettent en évidence la coexistence d’agrégats et de nanotubes individualisés. La seconde approche consiste à mélanger le PHBV avec un autre biopolymère comme le polybutylène succinate (PBS). Celui-ci a été choisi pour sa bonne stabilité thermique et ses bonnes propriétés mécaniques. Des systèmes hybrides ont été préparés par voie "fondue" en incorporant l’HNT et le PHBV-g-MA comme compatibilisant. L’étude révèle à travers le MEB que l’ajout de 5% en masse de PHBV-g-MA améliore la morphologie du mélange PHBV/PBS 80/20 qui se traduit par une diminution de la taille des nodules de PBS. L’ajout de 5% en masse de l’HNT dans le mélange favorise aussi la diminution de la taille des nodules de PBS. Cependant, la combinaison du PHBV-g-MA et de l’HNT limite l’effet émulsifiant de l’agent compatibilisant dû à l’agrégation de l’HNT. Les résultats de DSC et d’ATG montrent que le PHBV-g-MA n’a aucun effet sur les propriétés et la stabilité thermiques du mélange PHBV/PBS. Toutefois, la présence de l’HNT joue un rôle positif dans la diminution du pic de dégagement de chaleur (HRR). Les propriétés mécaniques du mélange ternaire PHBV/PBS/HNT avec ou sans compatibilisant sont comparables à celles du mélange pur PHBV/PBS 80/20.Une dernière partie des travaux a été menée sur le recyclage thermomécanique à travers une évaluation des effets du nombre de cycles d'excursion répétés sur le PHBV, le PBS, les nanocomposites PHBV/HNT et PBS/HNT, le mélange binaire PHBV/PBS 80/20 et ternaire PHBV/PBS 80/20+HNT avec et sans compatibilisant. Les résultats de cette étude ont montré que la recyclabilité de ces systèmes est possible du fait que la nanostructure du matériau recyclé soit améliorée et que les propriétés thermiques et mécaniques ne sont pas affectées après 5 cycles d’extrusion
Among biopolymers, the poly (hydroxybutyrate-Co-hydroxyvalerate) (PHBV) has attracted the attention of researchers and industry. However, its thermal sensitivity and its fragility limited its use for some applications. Thus, to improve its properties, two great strategies were considering during this thesis. The first consists in incorporating halloysite (HNT), type of clay, collected from Djebel Debbagh in Guelma (Algeria). For this purpose, nanocomposites PHBV/HNT were prepared by melt compounding. The results of scanning electron microscopy (SEM) and STEM showed a relatively homogeneous distribution of the HNT with the presence of large aggregates. Consequently and in the aim to improve the dispersion of these nanotubes, it was necessary to carry out the modification of interfaces polymer-clay, either by the chemical modification of halloysite, or by the incorporation of compatibilizer like PHBV-g -MA in the binary system. The results obtained highlight the coexistence of individualized and aggregated nanotubes.The second approach consists in mixing the PHBV with another biopolymère like polybutylene succinate (PBS). This one was selected for its good thermal stability and its good mechanical properties. Hybrid systems were prepared by melt compounding by incorporating HNT and PHBV-g-MA as compatibilizers. The SEM analysis reveals that the addition of 5wt.% of PHBV-g-MA improves morphology of PHBV/PBS 80/20 blend inducing a reduction in the size of PBS nodules. The addition of 5wt.% of the HNT in the blend favorites also the reduction in the size of PBS nodules. However, the combination of PHBV-g-MA and the HNT limits the emulsifying effect of the compatibilizer due to the aggregation of the HNT. DSC analysis and TGA show that PHBV-g-MA has no effect on the thermal properties and the thermal stability PHBV/PBS blend. However, the presence of the HNT plays a positive role in the reduction in the peak of heat release rate (HRR). The mechanical properties of ternary mixture PHBV/PBS/HNT with or without compatibilisant are comparable with those of PHBV/PBS 80/20 pure blend.Another study came supplemented this work from thesis while being focused on the thermomechanical recycling of the PHBV, the PBS, nanocomposites PHBV/HNT and PBS/HNT, the PHBV/PBS 80/20 binary blend and PHBV/PBS 80/20+ HNT ternary blend with and without compatibilization. The results of this study showed that the recyclability of these systems is possible owing to the fact that the nanostructure of recycled material is improved and that the thermal and mechanical properties are not affected after 5 cycles of extrusion

Ce travail concerne le développement de polymères alvéolaires biosourcés adaptés à l’injection microcellulaire physique (Mucell®) ainsi que l’identification des leviers (procédé et/ou matériau) permettant de contrôler la structure cellulaire.Les paramètres directeurs du procédé ont été optimisés à l’aide d’un plan d’expérience de type Taguchi permettant d’atteindre un allégement de 15% tout en conservant un niveau de performance mécanique acceptable. Par ailleurs, des modifications structurales du PBS ont été menées dans le but de contrôler le processus de formation de la structure cellulaire (dissolution du gaz, nucléation, croissance cellulaire et stabilisation de la structure). La morphologie cellulaire a été améliorée en modifiant la conformation moléculaire des chaînes, en favorisant la nucléation hétérogène ou en modifiant les propriétés élongationnelles et la tension de surface du matériau. La formulation résultante a permis une diminution de plus de 80% de la taille des cellules et une densité cellulaire multipliée par 450.Enfin, une technique de mesure du comportement rhéologique du système monophasé polymère/gaz a été développée à l’aide d’une buse instrumentée en ligne permettant d’évaluer l’effet de la dissolution du gaz sur la viscosité du matériau en fonction des conditions expérimentales de l’étude
This work focused on the development of biobased polymer foams adapted to the microcellular injection molding (Mucell®) and the identification of the key parameters (process and/or material) controlling the cell structure.The process parameters were optimized using a Taguchi design of experiment which achieves 15% lightweighting while maintaining acceptable mechanical performances. In addition, structural modifications of PBS were carried out in order to control the foaming mechanism (gas dissolution, cell nucleation, cell growth and cell stabilization). Cell morphology has been improved by modifying the molecular conformation, promoting heterogeneous nucleation, or by adjusting the extensional viscosity and surface tension of the material. The resulting formulation exhibit a decrease of more than 80% in cell size and a cell density multiplied by 450.Finally, a measurement technique for the rheological behavior of the single phase polymer/gas mixture was developed using an instrumented on-line nozzle to evaluate the effect of gas dissolution on the viscosity under experimental conditions

L'ingegneria tissutale è una branca delle scienze biomediche che negli ultimi anni si sta sviluppando come mezzo risolutivo per numerose problematiche mediche. Un'applicazione di particolare importanza è il trattamento di patologie cardiovascolari, le quali sono una delle principali cause di morte nel mondo. La mancanza di tessuto autologo e i problemi legati alle terapie cardiache, hanno incentivato numerosi studi basati sulla ricerca di biomateriali adeguati alla realizzazione di tessuti sintetici sostitutivi. In questo ambito, il polibutilene succinato (PBS) riveste sicuramente un ruolo importante. La sua biocompatibilità insieme alla biodegradabilità, non sono però sufficienti a renderlo idoneo ad applicazioni miocardiche, a causa dell’elevata rigidità. Allo scopo di migliorare le proprietà meccaniche del PBS nell’ottica di un’applicazione nel campo della rigenerazione del tessuto cardiaco, ma senza andare a detrimento delle proprietà già buone, il presente lavoro di Tesi propone un nuovo copolimero a base di PBS. Tale materiale è stato ottenuto tramite reazione di estensione di catena di un blocco hard (PBS) e un blocco soft (costituito da un copolimero statistico P(BSNS)). Il materiale ottenuto è stato analizzato sia sottoforma di film che di scaffold. Dopo una prima caratterizzazione molecolare (1H-NMR e GPC), il copolimero multiblocco è stato sottoposto anche ad analisi termica (DSC e TGA), diffrattometrica (WAXS) e meccanica. Si è evidenziato un miglioramento della stabilità termica e soprattutto una diminuzione del modulo elastico unitamente all’aumento dell’allungamento a rottura, in particolare nello scaffold. E’ stata inoltre valutata la velocità di degradazione idrolitica, evidenziandone una riduzione rispetto all’omopolimero. I risultati ottenuti confermano il miglioramento delle proprietà non soddisfacenti del PBS, indicando il copolimero multiblocco, oggetto della presenti Tesi, come materiale più idoneo alle applicazioni sopracitate.

Grazie all’ingegneria tissutale, branca dell’ingegneria che si occupa della ricostruzione in vitro di tessuti, sta diventando sempre più concreta la possibilità di superare i principali limiti della medicina tradizionale, basata essenzialmente sul trapianto e sui trattamenti farmacologici, soluzioni non sempre praticabili e/o efficaci. Tramite lo studio dei biomateriali e delle loro proprietà è possibile realizzare soluzioni ad hoc per l’ingegneria tissutale di diversi tessuti. Nel caso particolare di questo studio, è stato realizzato mediante elettrofilatura uno scaffold a partire da una blend fisica di poli(butilene succinato) (PBS) e cheratina. Il primo è un polimero sintetico biocompatibile e approvato dalla Food and Drug Administration, con buone resistenza meccanica e lavorabilità, ma tempi di degradazione piuttosto lenti, a differenza della cheratina, polimero naturale, che risulta troppo rigido e difficile da processare, ma con buoni tempi di degradazione ed un’ottima biocompatibilità. Il tappetino elettrofilato così ottenuto è stato sottoposto a caratterizzazione molecolare, termica e meccanica. Inoltre, in vista di possibili applicazioni nell’ambito dell’ingegneria tissutale, il materiale è stato sottoposto anche a test di biodegradazione in ambiente enzimatico e prove di biocompatibilità in vitro. In conclusione, ogni tipo di indagine, seppur preliminare, ha comprovato che l’unione tra il PBS e la cheratina ha dato vita ad un nuovo biomateriale di supporto facilmente processabile e in grado di promuovere l’accrescimento, la migrazione e il differenziamento cellulare.

The control over the immigration of labour has become one of the most important and hotly debated policy issues in recent times and this culminated, on November 27th 2008, in what has been described as the biggest shake up in the UK's immigration system for 45 years, with the introduction of a new points based scheme (PBS). For the hospitality sector, it was predicted that the consequences of the PBS would be seriously detrimental and exacerbate the skills and labour shortages that already characterise the sector. Little empirical research has been conducted to discover employers' views of the consequences of the new legislation and their opinions on the different segments of the labour market that are available to them. To address the lack of research, this thesis investigates employers' attitudes towards employability and what key factors determine who secures employment in hotels. Theoretical development is offered via presentation of a theory of demand-led employability within the industry for customer-facing job roles. In developing this theory, the researcher draws upon empirical data from fifteen hotels in which he conducted twenty-nine semi-structured interviews. The research is underpinned by a grounded theoretical approach which the researcher believes to be important in allowing the respondents to direct the path of enquiry, and in so doing, demonstrate that the PBS has had little or no impact, then going on to develop a theory which is both pertinent and relevant when looking at employability. The theory presented shows that employment within hotels is dependent on a range of interconnected factors including stereo-typical assumptions about gender, age, class, criteria of the job offered and a range of competencies including attitude, flexibility, aesthetics and skills. Central to the theory and influencing alI areas the researcher argues, are the manager's preconceived notions of what constitutes the "ideal" person to work in a hotel and serve customers and also how they view different segments of the labour market that are available to them such as migrants or the long-term unemployed. The researcher, therefore, argues that the findings presented in this thesis make a valuable contribution to extending perspectives on employability within the sector.

Thesis (Ph. D.)--Ohio State University, 2004.
Title from first page of PDF file. Document formatted into pages; contains xviii, 167 p.; also includes graphics (some col.) Includes bibliographical references (p. 115-121). Available online via OhioLINK's ETD Center

Förändringar som berör arbetslivet kan innebära stor påverkan på

individerna, där vissa drabbas av konsekvenser för hälsan och andra

drabbas inte. Studier har funnit samband mellan personer som

drabbats av utmattningssyndrom och personer vars självkänsla

baseras på egna prestationer, prestationsbaserad självkänsla (pbs).

Studiens syfte var att undersöka om intervjusvaren från personer som

diagnostiserats med utmattningssyndrom, kunde beskriva beteenden

som stämmer med teorin om pbs. Sex semistrukturerade kvalitativa

intervjuer genomfördes och analyserades, främst med deduktiv

tematisk analysmetod. Resultatets teman utgjordes av begrepp som

kunde hittas i teorin om prestationsbaserad självkänsla och den skala

som mäter detta, pbs-skalan. Studiens resultat ger förståelse för vad

prestationsbaserad självkänsla innebär, samt att det kan vara

användbar kunskap för personer med personalansvar ute i arbetslivet.

The purpose of the study was to further examine the potential efficacy of the Bully Prevention in Positive Behavior Support (BP-PBS) program in addressing bullying in an urban public elementary school with a large and diverse student population, implementing school-wide positive behavior support with relatively low fidelity. Specifically, the study examined the extent to which BP-PBS could decrease target students’ bullying behavior across settings and increase appropriate active response to bullying of students being bullied. Changes in the students’ perceptions and attitudes on school safety were also examined. This study involved a multiple probe design across participants targeting multiple settings for six students (three bullies and three victims) to assess the impact of the BP-PBS intervention and to examine its generalization effects to a non-targeted setting. The results indicated that the BP-PBS intervention was effective in reducing the target students’ bullying maintained by peer and adult attention and increasing active response to bullying. The intervention also increased positive perceptions and attitudes on school safety in students being bullied and the bullies. Changes in student bullying and appropriate and inappropriate responses to bullying were generalized to non-training settings and remained at intervention levels for all participants. Social validity surveys indicated high acceptability of the BP-PBS intervention by teachers.