• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 101
  • 35
  • 25
  • 25
  • 20
  • 18
  • 17
  • 8
  • 4
  • 2
  • 2
  • Tagged with
  • 288
  • 76
  • 67
  • 54
  • 51
  • 45
  • 43
  • 38
  • 37
  • 37
  • 36
  • 36
  • 33
  • 30
  • 30
  • 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.
251

Ordering in weakly bound molecular layers: organic-inorganic and organic-organic heteroepitaxy / Ordnungsprozesse in schwach gebundenen Molekülschichten: organisch-anorganische und organisch-organische Heteroepitaxie

Mannsfeld, Stefan 27 September 2004 (has links) (PDF)
It is an aim of this work to provide insight into the energetic influence on the ordering of molecular thin films on crystalline substrates. Here, the term substrate either refers to inorganic crystal surfaces or highly ordered layers of another organic molecular species. In order to calculate the total interface potential of extended molecular domains, a new calculation technique (GRID technique) is developed in the first part of this work. Compared to the standard approach, this method accelerates the potential calculation drastically (times 10000). The other parts of the thesis are dedicated to the comparison of experimental results (obtained by scanning tunneling microscopy and electron diffraction) to the optimal layer structure as predicted by optimization calculations. Potential calculations which are performed for the system perylenetetracarboxylicdianhydride (PTCDA) on graphite demonstrate that point-on-line coincident structures correspond to energetically favorable alignments of the molecular lattice with respect to the substrate lattice. The capability of the GRID technique to predict the optimal layer structure is demonstrated for the system peri-hexabenzocoronene (HBC) on graphite. The organic-organic heteroepitaxy system PTCDA on HBC on graphite is investigated in order to clarify to which extent the ordering mechanism there differs from that of the organic-inorganic heteroepitaxy system PTCDA on graphite. As a result of this investigation, a new type of epitaxy, i.e., substrate induced ordering is found. This new epitaxy type is governed by the inner structure of the substrate lattice unit cell. Here, the substrate surface is a layer of organic molecules itself, hence the substrate surface unit cell does indeed exhibit a complex inner structure. A generalized classification scheme for epitaxial growth incorporating this new type of epitaxy is proposed. In the last chapter, the structure of the first layers of titanylphthalocyanine (TiOPc) on Au(111) is investigated and compared to potential optimization calculations. The correspondence of experimental and theoretical results provides evidence that the GRID technique can, in principle, also be applied to molecular layers on metal surfaces. / Das Ziel der vorliegenden Arbeit ist es, Einblicke in die energetischen Einflüsse, die zur Ausbildung der Schichtstruktur organischer Moleküle auf kristallinen Substraten führen, zu geben. Diese Substrate sind entweder Oberflächen anorganische Kristalle oder selbst hochgeordnete Molekülschichten. Um das totale Grenzflächenpotential ausgedehnter Moleküldomänen berechnen zu können, wird im ersten Teil der Arbeit eine neue Berechnungsmethode (GRID Technik) vorgestellt. Im Vergleich mit herkömmlichen Berechnungsmethoden auf der Basis molekülmechanischer Kraftfelder ist diese neue Methode daher um ein Vielfaches schneller (Faktor 100000). Die folgenden Teile der Arbeit sind dem Vergleich experimenteller Ergebnisse (Rastertunnelmikroskopie und Elektronenbeugung) mit, durch Potentialoptimierungsrechnungen als energetisch günstig vorhergesagten, Schichtstrukturen gewidmet. So kann für das System Perylentetracarbonsäuredianhydrid (PTCDA) auf Graphit mittels Potentialberechnungen nachgewiesen werden, daß die experimentell gefundenen ?Point-on-line koinzidenten? Strukturen energetisch günstige Anordnungen des Molekülgitters bezüglich des Substratgitters darstellen. Die Eignung der neuen Berechnungsmethode zur Vorhersage der günstigsten Adsorbatgitterstruktur für ein gegebenes System aus Molekül und Substrat, wird anhand des Systems peri-Hexabenzocoronen (HBC) auf Graphit demonstriert. Das organisch-organische Heteroepitaxiesystem PTCDA auf HBC auf Graphit wird untersucht, um zu klären, inwieweit sich die dafür gültigen Ordnungsmechanismen von denen unterscheiden, die für das Wachstum des organisch-anorganischen Heteroepitaxiesystems PTCDA auf Graphit verantwortlich sind. Dabei gelingt es, eine bisher nicht klassifizierte Art von Epitaxie, d.h. substratinduzierter Ordnung, nachzuweisen. Dieser neue Epitaxietyp ist bedingt durch die innere Struktur einer Substrateinheitszelle - das Substrat ist ja hier selbst eine Schicht geordneter Moleküle, die natürlich eine innere Struktur aufweisen. Im folgenden wird ein verallgemeinertes Klassifizierungssystem für Epitaxietypen abgeleitet, welches den neuen Epitaxietyp beinhaltet. Im letzten Kapitel wird die Struktur von der ersten Lagen von Titanylphthalocyanin (TiOPc) auf Au(111) experimentell untersucht und mit entsprechenden Potentialoptimierungsrechnungen verglichen. Die Übereinstimmung von experimentellen und theoretischen Ergebnissen zeigt, daß die GRID Technik, zumindest prinzipiell, auch für Molekülschichten auf Metallsubstraten anwendbar ist.
252

An empirical study of attitudes towards green urban development

Chiang Hsieh, Lin-Han 13 January 2014 (has links)
This study focuses on how spatial circumstances affect property owners’ preference toward sustainable urban development, in the form of three-essays. In the first essay, property owners’ preference toward the concept of compact development is identified. Compact development is an increasingly popular concept that includes multiple aspects, such as mixed land use, high density, and pedestrian/transit-friendly options. Previous hedonic literature on the comprehensive effect of compact development is limited. Also, spatial dependence in the data, something likely endemic to compact development, has not yet been thoroughly addressed. This study uses a spatial fixed-effect model, a spatial-autoregressive model with auto-regressive disturbances (SARAR), and a spatial fixed-effect SARAR model to determine the price effect of “compactness” in a major U.S. metropolitan area. By analyzing of 47,000 sales records in Fulton County over a decade, this study indicates that home buyers prefer to have smaller, more diffuse greenspace nearby, rather than a large, concentrated greenspace at a longer walking distance. High parcel density and diverse land use is consistently disvalued, and the premium on accessing public transportation is not identified among all models. No specific trend over time has been observed, despite the recession starting in 2008. Finally, a comprehensive index of compactness shows relatively high willingness-to-pay for compact development. The second essay tests the spatial spillover of signaling within the pursuit of LEED certification. The benefit of pursuing green building certification mainly comes from two aspects: the cost-effectiveness from energy efficiency and the signaling consideration, including the premium on property values, benefits from a better reputation, morality values, or purely pride. By analyzing all new constructions that received LEED certification from 2000 to 2012 (LEED-NC v2.0 to v2.2) in the U.S., this study tries to identify the size of the signaling effects, and spillover of signaling, as building owners pursue LEED certification. The results show that the signaling effect affects decision making in pursuing LEED certification, especially at scores around thresholds. The size of signaling effects differs among different owner types and different certificate levels. For the Gold level or below, government and non-profit-organization owners value signaling more than do profit-seeking firms. At the Platinum level, there is no significant difference among owner types. This study also finds that the signaling effect clusters spatially for government and profit-seeking firms. Finally, the results show that the cluster of signaling is independent from the cluster of LEED buildings, indicating that mechanisms behind the cluster of signaling are different from those of LEED constructions. The third essay tests the distance effect on the support for Atlanta BeltLine. Atlanta BeltLine, a large urban redevelopment project currently underway in the center of Atlanta, transforms 22 miles of historical railroad corridors into parks, trails, pedestrian-friendly transit areas, and affordable housing. This study aims to determine the distance effect on the support of Atlanta BeltLine and whether the implement of Tax Increment Financing (TIF) affects the support. The contributions of this exercise are twofold. First, it demonstrates the risks and remedies to missing spatial data by solving the technical problem of missing precise spatial location values. Second, it tests underlying reasons why distance can help explain the level of support that Atlanta BeltLine has received, with striking implications for theories like the Homevoter hypothesis. Survey data used in this study was conducted in summer 2009, about three years after the declaration of the project. The support by both homeowners and renters significantly declines as distance from the BeltLine increases. However, when residents’ tendency to use BeltLine parks and transits is entered as a variable, the distance effect disappears. By indicating that the distance effect comes from homeowners’ and renters’ the accessibility to BeltLine amenities, the result rejects the homevoter hypothesis, which holds that property value increment is the main mechanism behind support. The results also show that whether or not a homeowner or renter is a parent in City of Atlanta affects a person’s support of the BeltLine. These results lead to the conclusion that the concern of TIF affecting future school quality hampers the support of the project.
253

Změny elektronické struktury bimetalických systémů při interakci s molekulami plynu / Electronic structure of bimetallic systems - study of gas molecule interaction

Píš, Igor January 2013 (has links)
Bimetallic Rh-V system was studied by means of surface science experimental methods. Properties of ultra-thin Rh-V layers supported by γ-Al2O3 were compared with model systems prepared by vacuum V deposition on Rh(111), Rh(110) and polycrystalline rhodium. Formation of ordered V- Rh(111)-(2×2), V-Rh(110)-(2×1) and V-Rh(110)-(1×2) subsurface alloys and their electronic and atomic structure were investigated and models of the surface reconstructions were proposed. Influence of the subsurface alloy formation on interaction with CO and O2 molecules as well as the influence of the molecule adsorption on this alloy was investigated. The bond between CO molecules and Rh-V alloy surface was weakened due to pronounced changes in surface valence band structure. Oxygen which adsorbed on the alloy surface reacted with the subsurface vanadium at elevated temperature and blocked the interaction of the metal substrate with CO molecules.
254

Certificações ambientais para edifícios: um estudo sobre apropriação de valor

Assumpção, Thaís Malheiros 25 April 2017 (has links)
Submitted by Thaís Malheiros Assumpção (thaismalheiros1983@gmail.com) on 2017-05-18T17:53:46Z No. of bitstreams: 1 2017-05-15 Diss Thais.pdf: 2818930 bytes, checksum: 90a535e19962c8866c9749b2bd1f0597 (MD5) / Approved for entry into archive by Pamela Beltran Tonsa (pamela.tonsa@fgv.br) on 2017-05-18T17:58:57Z (GMT) No. of bitstreams: 1 2017-05-15 Diss Thais.pdf: 2818930 bytes, checksum: 90a535e19962c8866c9749b2bd1f0597 (MD5) / Made available in DSpace on 2017-05-18T19:58:13Z (GMT). No. of bitstreams: 1 2017-05-15 Diss Thais.pdf: 2818930 bytes, checksum: 90a535e19962c8866c9749b2bd1f0597 (MD5) Previous issue date: 2017-04-25 / O propósito desta pesquisa foi examinar a apropriação de valor gerado por certificações ambientais para edifícios de escritórios. Para responder a essa pergunta, primeiramente examinou-se o universo brasileiro desse tipo de selo por meio de pesquisa documental, que mostrou que o selo LEED é o mais utilizado em edificações de escritórios. Em seguida, entrevistas semi-estruturadas foram conduzidas com três grupos de stakeholders desse mercado: empresas usuárias, incorporadoras e gestores de fundos de investimentos imobiliário. Como ferramenta para triangular os dados primários, entrevistou-se um consultor especializado no processo de certificação de empreendimentos. Os resultados sugeriram que os três grupos apropriam o valor gerado pelo LEED por meio de menores despesas operacionais; empresas usuárias e incorporadoras identificaram que essa apropriação também se dá por meio de ganhos reputacionais; e incorporadores e gestores de fundos de investimentos apontaram o acesso a locatários que exigem essa certificação. Além disso, as incorporadoras citaram maior taxa de ocupação dos empreendimentos; e as empresas usuárias mencionaram acesso a novos conhecimentos, vantagens advindas de uma melhor qualidade ambiental interna e gestão mais profissional do edifício. Esse último fator, não identificado na literatura, constitui uma contribuição relevante dessa pesquisa, já que acrescenta à literatura de green buildings um novo aspecto a ser investigado. / The purpose of this research was to examine the appropriation of value generated by environmental certifications for office buildings. To answer this question, we first examined the Brazilian universe of this type of certification through documentary research, which showed that LEED is the most used certification in office buildings. Then, semi-structured interviews were conducted with three groups of stakeholders: user companies, real estate investment fund managers and developers. As a tool to triangulate the primary data, a consultant specialized in the process of this type of certification was interviewed. The results suggested that the three groups appropriated the value generated by LEED through lower operating expenses; User and incorporating companies have identified that this appropriation also takes place through reputational gains; And developers and fund managers pointed out access to renters who require this certification. In addition, the developers cited a higher rate of occupation of the projects; And the user companies mentioned access to new knowledge, advantages resulting from a better internal environmental quality and more professional management of the building. This last factor, not identified in the literature, constitutes a relevant contribution of this research, since it adds to the green buildings literature a new aspect to be investigated.
255

Etude des propriétés structurales et spectroscopiques des couches ultra-minces d'alcalins déposées sur Si(111) - B / Investigation of structural and spectroscopic properties of alkali ultra-thin films deposited on Si(111) - B

Cardenas Arellano, Luis Alfonso 08 January 2010 (has links)
Les propriétés structurales et électroniques de films ultra-minces d'alcalins (K,Cs) déposés sur un substrat de Si(111)-v3´v3R30:B ont été étudiés par diffraction d'électrons lents (LEED), spectroscopie Auger, microscopie à effet tunnel (STM) et photoemission (ARPES, XPS). Un état de surface de symétrie s-pz a été mis en évidence par photoémission résolue en angle celui-ci présentant un maximum au taux optimal. Le site d'adsorption H3 a été identifié par IV-LEED en accord avec les prédictions théoriques. Nos mesures ARPES mettent en évidence un repliement de la bande de surface, son caractère fortement isolant ainsi qu'une largeur de bande très étroite. Dans le cas des dépôts de Césium, le gap est cependant réduit et il apparaît du poids spectral au niveau de Fermi. Ces résultats sont a priori en accord avec le caractère corrélé de ces états, ceux-ci ayant été définis initialement comme des isolants de Mott. Cependant, nous mettons en évidence dans ce travail une nouvelle reconstruction 2v3´2v3 caractérisée par un quadruplement de la maille de surface et associée à un gain d'énergie des électrons participant à l'état de surface. De plus, la dépendance en température des spectres de photoémission suggèrent un fort élargissement Franck-Condon associé à un fort couplage électron-phonon. L'étude des raies de cœur par photoémission haute résolution sur la ligne CASSIOPEE (synchrotron SOLEIL) nous a permis de mettre en évidence un ordre de charge à la surface pour les deux types de reconstruction observées en LEED. Tous nos résultats expérimentaux indiquent un fort couplage avec le réseau des électrons de l'état de surface induit par les alcalins ce qui n'a jamais été reporté auparavant ni fait l'objet de prédictions. Un scénario basé sur l'établissement d'une onde de densité de charge à la surface dans la limite d'un fort couplage électron-phonon est proposé. IL est proposé que la limite de l'isolant bi-polaronique soit atteinte dans le cas des couches ultra-minces d'alcalins/Si(111) offrant ainsi la possibilité d'étudier le comportement des électrons fortement couplés au réseau en présence de corrélations électroniques sur un réseau triangulaire. / Low energy electron diffraction (LEED), Auger spectroscopy, scanning tunneling microscopy (STM) and angle-resolved photoemission (ARPES) have been used to study ultrathin films of alkali atoms deposited on Si(111)-v3´v3R30:B surface. An alkali-induced surface state of s-pz symmetry has been evidenced by photoemission being maximum close to the saturation coverage of 1/3 monolayer. A quantitative IV-LEED study evidences the H3 alkali adsorption site as predicted by ab initio calculations. High resolution ARPES data presented in this work evidence a band-folding, a large alkali-dependent semi-conducting gap and a narrow bandwidth. The Cs- induced surface band is shown to present a smaller gap together with a non-zero spectral weight at the Fermi level. These results are a priori consistent with the correlated nature of these materials, the Harrison criterion U/W>>1 being fulfilled for these half-filled surface bands. Moreover, a novel 2v3´2v3 lattice and charge ordering has been discovered below 300 K characterized by a quadrupling of the unit cell and a net energy gain for the surface band. In addition, the temperature dependence of the ARPES spectra suggests these materials are characterized by a strong electron-phonon coupling. High resolution core-levels photoemission spectroscopy recorded at the CASSIOPEE beamline (synchrotron SOLEIL) evidence a local charge ordering at surface in both phases. The corresponding band mapping agree well with the 2(v3´v3) symmetry also for both phases. All these experimental results sign a strong interplay between the charge and lattice degrees of freedom which have never been predicted for these semiconducting surfaces. Therefore, a scenario assuming a charge density wave at surface in the strong electron-phonon coupling limit is proposed. As a striking point, the bi-polaronic insulating ground state is proposed to be reached making these alkali/Si(111) semi-conducting surfaces model systems to study polaronic signatures on the physical properties of low dimensional strongly correlated materials.
256

Dopad ekonomické krize na stavební trh a aktuální trendy ve stavebnictví / Impact of the economic crisis on the construction market and the current trends in the construction sector

Nováková, Barbora January 2015 (has links)
The diploma thesis Impact of the economic crisis on the construction market and the current trends in the construction sector focuses mainly on the development of the Czech construction market in relation to the economic crisis of 2008-2009, while looking for conjunctions with macroeconomic indicators. It also describes the following period of development of the construction sector with an emphasis on current trends. Exemplifying how this is implemented into practice, the diploma thesis includes a description of the activities of a group of companies called EBM Group.
257

Závislost povrchové struktury Fe2O3(012) na prostředí / Environment-Dependent Surface Structure of Fe2O3(012)

Komora, Mojmír January 2018 (has links)
Táto diplomová práca sa zaoberá štúdiom alfa-Fe2O3(012) vystaveného vodnému prostrediu. Súčasný stav poznania ohľadom oxidov železa s pozornosťou vkladanou do popisu alfa-Fe2O3 a jeho (012) povrchu je stručne zhrnutá. Experimentálná časť tejto práce začína s popisom unikátného zariadenia na depozíciu kvapalnej vody na povrchy monokryštalických vzoriek compatibilného s podmienkami ultra vysokého vákuua. Jednotlivé konštrukčné časti a detaily sú diskutované. Navrhnutý systém bol testovaný na vzorkách striebornej fólie a monokryštálu Fe3O4 s povrchovom v rovine [100]. Chemické zloženie a morfológia povrchu po experimente s kvapalnou vodou je diskutovaná. Navrhnuté zariadenie bolo použité na štúdium interakcie vody so známymi (1x1) a (2x1) povrchovými alfa-Fe2O3(012). Experimentálne dáta ukazujú, že voda sa viaže na obe reconštrukcie disociatívne s určitým množstvom molekulárnej vody naviazanej na adsorbované hydroxydi. (1x1) sa zdá javý stabilná po expozícii rôznym tlakom vodnej pary, zatial čo (2x1) vykazuje zmenu na (1x1) pri expozíciach vyšším tlakom vodnej pary alebo po niekolo minútovej expozíci electrónovému zväzku. Ďalej sú v tejto práci prezentované prvé výsledky z štúdie prechodu (1x1) rekonštrukcie na (2x1) pomocou mikroskpie nízkoenergiových elektrónov. Výsledky ukazujú, že táto premena na nižších teplotách je inciovaná na hranách atomárnych vrstiev a defektov na povrchu, ktorá potom postupuje smerom k stredu atomárnych terás. Meranie na vyšších teplotách vykazuje postupnú premenu povrchu naznačúju viaceru nukleačných centrech z ktorých sa (2x1) povrch širi ďalej.
258

Site selection for small retail stores using sustainable and location-driven indicators : Case study: Starbucks coffee shops in Los Angeles

Sokol, Vadym, Jordanov, Kristijan January 2020 (has links)
Site selection decisions remains a complex yet crucial process for strong business performance. Despite the extensive number of publications in this field, the emergence of new data collection technique, improved location analytics, and changes in consumers’ preferences call for testing of new models and hypothesis. This study compares traditional site selection indicators (e.g. property size, proximities, competition, and demographic profiles) with novel site-selection indicators (e.g. environmental sustainability performance and socio-demographic characteristics from Tapestry data). By investigating a case study of Starbucks coffee stores in Los Angeles, we argue that environmental sustainability performance and socio-demographic Tapestry segments correlate with business performance indicators of small retail shops in two ways. First, higher sustainability scores result in increased foot traffic, and by extension increased business performance. Second, Tapestry segmentation stands as significant indicator of business performance in site selection modeling – specifically, by demonstrating the significant correlation between socio-demographic consumers’ segments and the number of visitors per location. The output of this study offers an alternative location-driven site selection method, important for businesses and key industry-players in sharpening location-allocation decision-making processes.
259

Diffraction studies on ordering of quasi-one-dimensional structures and nanowires on silicon surfaces induced by metals

Timmer, Frederic Yaw 20 November 2017 (has links)
In this thesis the morphology and the atomic structure of quasi-one-dimensional structures grown on Si were determined by means of diffraction experiments in combination with kinematic diffraction theory calculations. In the first and the second study a formerly unknown superstructure of Dy/Tb on Si(111) was characterized by means of STM, DFT, SPA-LEED experiments and kinematic diffraction calculations. Here, a structure model could be proposed which contains half as many subsurface Si vacancies as compared to the well-known superstructure of Dy/Tb on Si(111) it was derived from. Due to the decreased number of subsurface Si vacancies the reconstruction is subject to an uni-axial strain which is mitigated by the formation of domains separated by anti-phase domain boundaries. It could be shown that two different types of domains alternate across the surface forming quasi-one-dimensional domains. Additionally, the distribution of the domains could be derived by comparison with kinematic diffraction calculations. In the third study a deeper insight into the complex system of bundled rare-earth silicide nanowires on Si(001) was given. Here, the distributions of the NW width, the bundle width and the bundle distance were deduced from the diffraction patterns collected by SPA-LEED and the subsequent comparison to kinematic diffraction theory calculations. Additionally, it was shown that the (2 x 1) reconstruction sometimes observed on top of the NWs by STM cannot exist over larger parts of the sample and instead a (1 x 1) reconstruction needs to be assumed to explain the experimentally observed diffraction data. In the fourth study the atomic structure of the gold induced atomic wires of the Si(111)-(5 x 2)-Au system was analyzed. The Patterson function of the in-plane SXRD data was compared to the Patterson functions derived from the atomic structure models proposed in literature (AN, EBH, KK) ruling out the AN-model. By comparison of the experimental out-of-plane SXRD data to the corresponding (calculated) SXRD data for the EBH- and the KK-model the KK-model could be identified as the most probable model. Additionally, a refined atomic structure model was derived for the KK-model. In conclusion, the results presented in this thesis clearly display the power of diffraction experiments especially in conjunction with the comparison to kinematic diffraction theory calculations and prove that they are applicable even to low dimensional (e.g., quasi-one-dimensional) structures. Furthermore, it was shown that diffraction experiments can deliver complementary information (e.g., information on deeper atomic layers) as compared to local probing methods (e.g. STM or Atomic Force Microscopy) and especially the combination of local probing methods, DFT calculations and diffraction experiments allows for the explanation of even very complicated material systems.
260

Phase transitions of rare earth oxide films grown on Si(111)

Wilkens, Henrik 21 March 2014 (has links)
In this work the structural transitions of the rare earth oxides praseodymia and ceria grown on Si(111) are investigated. It is demonstrated that several of the rare earth intermediate phases can be stabilizied by post deposition annealing in ultra high vacuum. However, in most cases no single phased but coexisting species are observed. In addition, the surface structure and morphology of hex-Pr2O3(0001) as well as reduced ceria films are investigated.

Page generated in 0.0607 seconds