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Pseudo jahn-teller versus reconstrucao quimica : oxigenio em silicio.; Pseudo Jahn-Teller versus chemical reconstruction: oxygen in silicon.

Camargo, Francisco de Paula
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 03/09/1990 PT
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Estudamos neste trabalho o comportamento da impureza oxigênio em rede cristalina de silício, usando primeiramente o método INDO (lntermediate Neglect of Differential Overlap) com parametrização espectroscópica e incluímos os efeitos de muitos elétrons via Método CI-(Interacão de Configuração). Fazemos uma análise sobre as possíveis origens do posicionamento não-central (off-center) dessa impureza, - se decorrente de uma distorsão Pseudo Jahn-Teller: - se originária de um CR Reconstrução Química. Quando o átomo de Oxigênio é deslocado ao longo da direção [100] ocupa um sitio de mínimo absoluto. O oxigênio introduz no gap de banda um orbital anti-ligante de simetria a1 totalmente ocupado, situação semelhante à dos anti-sitios em materiais semi-condutores III-V. Estudamos também o comportamento dessa impureza quando a mesma é deslocada ao longo da direção [111], verificando que é criada uma posição de Instabilidade mas, os auto-valores têm comportamento não esperado para orbitais anti-ligantes.; In this work we studied the Oxygen impurity in Silicon. The calculations were performed using a semi-empirical method (INDO/S) with Configuration Interaction to account for many-electron effects. We analyse the origin of the off-center position for substitutional oxygen. Pseudo Jahn-Teller distortion or Chemical Rebonding effects. The oxygen introduces an a1 anti-bonding state in the forbidden band-gap similar to anti-site defects in III-V materials. To answer the question about distortion...

O bambu na arquitetura: desing de conexões estruturais

Padovan, Roberval Bráz
Fonte: Universidade Estadual Paulista (UNESP) Publicador: Universidade Estadual Paulista (UNESP)
Tipo: Dissertação de Mestrado Formato: 181 f. : il., gráfs., tabs. + anexo
POR
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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES); Pós-graduação em Design - FAAC; O bambu é considerado um dos mais antigos materiais para habitações, porém, o desenvolvimento de tecnologia própria, como material de construção de qualidade, vem acontecendo somente nas últimas três décadas, quando surgiu uma discussão mundial sobre sustentabilidade. A variável ambiental passou, então, a ser considerada em qualquer projeto de desenvolvimento, uma vez que influencia tanto na disponibilidade futura de matérias-primas e energia, quanto na qualidade de vida das populações. Uma das maiores dificuldades no pleno emprego do bambu na construção civil são as conexões estruturais entre seus elementos, que não permitem o uso da tecnologia de ligações aplicada a outros materiais, como o aço e a madeira maciça, para efetuar com eficiência a transferência de esforços, inviabilizando toda potencialidade estrutural oferecida pelo bambu. Este trabalho faz uma ampla revisão dos principais aspectos de arquitetura com bambu, bem como das técnicas de construção e conexões utilizadas. A partir de uma estratégia geral de inovação, baseada no processo de desenvolvimento de produtos, foi proposto o design de uma nova conexão estrutural...

Charge and the unexpected : solid state processes involving charged species

Stoneham, A. M.; Harker, A. H.; Ramos, Marta M. D.
Fonte: Societé Francaise du Vide Publicador: Societé Francaise du Vide
Tipo: Artigo de Revista Científica
Publicado em //2001 ENG
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We explore links between performance under electrical stress and the way in which charge is localised in two contrasted systems. Both systems are arnorphous. In one case inhomogeneity which plays a role; for the other, it is topology. For silicon dioxide, the gate dielectric of microelectronics, we show that the charge state of the oxidising species (mobile atomic or molecular oxygen) is critical for ultra-thin oxides. The surprises are firstly that the differences between crystalline and amorphous oxides are substantial, and secondly the way that the important charge states should vary systematically through the oxide thickness. We identify ways in which the oxide performance might be improved. For an amorphous polymer.. we establish that the mesostructure (spaghetti structure) of the polymer can have significant effects on its performance, both for insulating and conducting polymers. In the case of conducting polymers, the surprise is that modelling shows that, even for “trap-free” cases, electrons can be trapped for times long compared lo average transit times because the local configuration other carriers obstructs the direct routes lo the anode. In neither case is a simple continuum space charge description valid. We also present: results from self-consistent molecular dynamics which show that electronic excitation can cause local rebonding in ways which appear to resemble the initiation electrical breakdown.

Fiber-reinforced fixed partial dentures: a preliminary retrospective clinical study

Piovesan,Edno Moacir; Demarco,Flávio Fernando; Piva,Evandro
Fonte: Faculdade De Odontologia De Bauru - USP Publicador: Faculdade De Odontologia De Bauru - USP
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/04/2006 EN
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17.88%
The aim of this study was to evaluate the clinical performance (retention rate) of fiber-reinforced composite fixed partial dentures (FPDs). Polyethylene fiber (Ribbond®) was used combined with restorative composite during FPDs fabrication. FPDs were placed in thirteen patients in a private clinic. Nineteen FPDs were evaluated. The prosthetic space was filled with only one pontic using extracted teeth (2 cases), acrylic resin teeth (11 cases), or with composite resin (6 cases), combined with Polyethylene fiber. The clinical criterion used was based on retention rate of FPDs. If FPDs were in function in the mouth at the time of examination without previous repair they were classified as Complete Survival (CS) restorations. A classification of Survival with Rebonding (SR) was assigned in the event of an adhesive failure, but after rebonding the FPD still remained under evaluation. Treatment was classified as a Failure (F) if the FPD restoration was lost. The time of evaluation was 41.15 months (±15.13). The FPDs evaluated were retained (CS=94.75%), and no failure was found except for in one situation which required rebonding (SR=5.25%). According to the survival estimation method of Kaplan-Meyer the mean survival time was 42.3 months. At the time of evaluation investigated...

Optimal enamel conditioning strategy for rebonding orthodontic brackets: a laboratory study

Zhang, Qi-Feng; Yao, Hua; Li, Zhi-Yong; Jin, Li; Wang, Hui-Ming
Fonte: e-Century Publishing Corporation Publicador: e-Century Publishing Corporation
Tipo: Artigo de Revista Científica
Publicado em 15/09/2014 EN
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Objective: To compare the conventional etching and primer method (CEP) and the self-etching primer method (SEP) in rebonding brackets. Methods: Forty human maxillary second premolars extracted for orthodontic purpose were randomly divided into 4 equal groups. Group 1 and Group 2 were bonded using the CEP method; Group 3 and Group 4 using the SEP method. All the brackets were debonded and 40 new brackets were rebonded with four different protocols after surface cleaning: Group 1: CEP + adhesive; Group 2: CEP without etch step + adhesive; Group 3: SEP + adhesive; Group 4: non-acidic primer + adhesive. Then, the shear bond strength (SBS) of each group was tested and the measurements of adhesive remnant index scores (ARI) and SEM examination were performed. Results: The mean SBSs for Group 1, 2, 3 and 4 were 14.18, 6.57, 11.90, 5.91 MPa, respectively. Statistical differences of the SBS existed between Group 1 and 2 (P < 0.05) and between Group 3 and 4 (P < 0.05). No difference was found between Group 1 and 3, or Group 2 and 4. Conclusion: Omission of the acid-etching step in rebonding orthodontic brackets may be adequate for the clinical requirement. No differences in SBS and ARI of the rebonded brackets were showed between CEP and SEP methods.

FIBER-REINFORCED FIXED PARTIAL DENTURES: A PRELIMINARY RETROSPECTIVE CLINICAL STUDY

Piovesan, Edno Moacir; Demarco, Flávio Fernando; Piva, Evandro
Fonte: Faculdade de Odontologia de Bauru da Universidade de São Paulo Publicador: Faculdade de Odontologia de Bauru da Universidade de São Paulo
Tipo: Artigo de Revista Científica
Publicado em /04/2006 EN
Relevância na Pesquisa
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The aim of this study was to evaluate the clinical performance (retention rate) of fiber-reinforced composite fixed partial dentures (FPDs). Polyethylene fiber (Ribbond®) was used combined with restorative composite during FPDs fabrication. FPDs were placed in thirteen patients in a private clinic. Nineteen FPDS were evaluated. The prosthetic space was filled with only one pontic using extracted teeth (2 cases), acrylic resin teeth (11 cases), or with composite resin (6 cases), combined with Polyethylene fiber. The clinical criterion used was based on retention rate of FPDs. If FPDs were in function in the mouth at the time of examination without previous repair they were classified as Complete Survival (CS) restorations. A classification of Survival with Rebonding (SR) was assigned in the event of an adhesive failure, but after rebonding the FPD still remained under evaluation. Treatment was classified as a Failure (F) if the FPD restoration was lost. The time of evaluation was 41.15 months (±15.13). The FPDs evaluated were retained (CS=94.75%), and no failure was found except for in one situation which required rebonding (SR=5.25%). According to the survival estimation method of Kaplan-Meyer the mean survival time was 42.3 months. At the time of evaluation investigated...

Cleaning and retreatment protocol for a debonded ceramic restoration

Román-Rodríguez, Juan-Luis; Alonso-Pérez-Barquero, Jorge; Bruguera-Álvarez, August; Agustín-Panadero, Rubén; Fons-Font, Antonio
Fonte: Medicina Oral S.L. Publicador: Medicina Oral S.L.
Tipo: Artigo de Revista Científica
Publicado em 01/02/2015 EN
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Objectives: The aim of this article is to propose a resin cement cleaning protocol for use before recementing a debonded restoration. Study Design: Ceramic samples were fabricated from IPS d.sign® and IPS e.max Press® and were treated with hydrofluoric acid etching (HF), or HF+silane (S), or HF+S+adhesive or HF+S+A+resin cement. All samples were placed in a furnace at 650º for one minute in order to attempt to pyrolyze the composite. Each step was examined under scanning electron microscopy (SEM). Results: When the cleaning protocol had been performed, it left a clean and retentive surface. Conclusions: If the restoration is placed in a furnace at 650º for one minute, the composite cement will burn or pyrolyze and disappear, allowing conventional retreatment of the ceramic before rebonding.

Fiber reinforced fixed partial dentures a preliminary retrospective clinical study; Pr??teses parciais fixas refor??adas por fibras um estudo cl??nico retrospectivo preliminar

Piovesan, Edno Moacir; Demarco, Fl??vio Fernando; Piva, Evandro
Fonte: Universidade de S??o Paulo Publicador: Universidade de S??o Paulo
Tipo: Artigo de Revista Científica
EN_US
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The aim of this study was to evaluate the clinical performance (retention rate) of fiber-reinforced composite fixed partial dentures (FPDs). Polyethylene fiber(Ribbond??) was used combined with restorative composite during FPDs fabrication. FPDs were placed in thirteen patients in a private clinic. Nineteen FPDS were evaluated. The prosthetic space was filled with only one pontic using extracted teeth (2 cases), acrylic resin teeth (11 cases), or with composite resin (6 cases), combined with Polyethylene fiber. The clinical criterion used was based on retention rate of FPDs. If FPDs were in function in the mouth at the time of examination without previous repair they were classified as Complete Survival (CS) restorations. A classification of Survival with Rebonding (SR) was assigned in the event of an adhesive failure, but after rebonding the FPD still remained under evaluation. Treatment was classified as a Failure (F) if the FPD restoration was lost. The time of evaluation was 41.15 months(??15.13). The FPDs evaluated were retained (CS=94.75%), and no failure was found except for in one situation which required rebonding (SR=5.25%).According to the survival estimation method of Kaplan-Meyer the mean survival time was 42.3 months. At the time of evaluation investigated...

Pseudo-Jahn-Teller origin of the low barrier hydrogen bond in N2H7+

García Fernández, Pablo (físico); García Canales, L.; García Lastra, J.M.; Junquera Quintana, Francisco Javier; Moreno Mas, Miguel; Aramburu-Zabala Higuera, José Antonio
Fonte: American Institute of Physics Publicador: American Institute of Physics
Tipo: info:eu-repo/semantics/article; publishedVersion
ENG
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The microscopic origin and quantum effects of the low barrier hydrogen bond (LBHB) in the proton-bound ammonia dimer cation N2H7+ were studied by means of ab initio and density-functional theory(DFT) methods. These results were analyzed in the framework of vibronic theory and compared to those obtained for the Zundel cation H5O2+. All geometry optimizations carried out using wavefunction-based methods [Hartree–Fock, second and fourth order Möller–Plesset theory (MP2 and MP4), and quadratic configuration interaction with singles and doubles excitations (QCISD)] lead to an asymmetrical H3N–H+⋯NH3 conformation (C3v symmetry) with a small energy barrier (1.26kcal/mol in MP4 and QCISD calculations) between both equivalent minima. The value of this barrier is underestimated in DFT calculations particularly at the local density approximation level where geometry optimization leads to a symmetric H3N⋯H+⋯NH3 structure (D3d point group). The instability of the symmetric D3d structure is shown to originate from the pseudo-Jahn–Teller mixing of the electronic A1g1ground state with five low lying excited states of A2u symmetry through the asymmetric α2u vibrational mode. A molecular orbital study of the pseudo-Jahn–Teller coupling has allowed us to discuss the origin of the proton displacement and the LBHB formation in terms of the polarization of the NH3 molecules and the transfer of electronic charge between the proton and the NH3 units (rebonding). The parallel study of the H5O2+ cation...

Analise in vitro da resistencia ao cisalhamento de braquetes metalicos submetidos a reciclagem repetida : fixados com diferentes materiais

Nadia Lunardi
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 09/12/2004 PT
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O objetivo desta pesquisa foi avaliar in vitro a resistência ao cisalhamento de braquetes ortodônticos metálicos submetidos a duas reciclagens consecutivas com jato de óxido de alumínio, em função de quatro tipos diferentes de materiais fixadores. A amostra consistiu de 40 incisivos bovinos para confecção dos corpos-de-prova. Quarenta braquetes metálicos edgewise, de incisivo central Ultraminitrim (Dentaurum), foram colados nos dentes bovinos com os seguintes materiais fixadores: Transbond XT, Concise, Smartbond e Fuji Orto, seguindo as instruções do fabricante. Após a colagem os corpos-de-prova foram armazenados em água destilada numa estufa a 37ºC por 24 horas e submetidos à 500 ciclos térmicos com 30 segundos em cada balho (5ºC e 55ºC). O ensaio de resistência ao cisalhamento foi realizado numa máquina Instron com velocidade de 0,5mm/min. Os braquetes removidos foram reciclados com jateamento de óxido de alumínio (50 micrômetro) e colados novamente no mesmo corpo-de-prova, utilizando os mesmos materiais fixadores. Após o segundo ensaio de resistência ao cisalhamento, os procedimentos de reciclagem, recolagem e ensaio de força foram repetidos. Os dados foram submetidos à análise de variância e ao teste de Tukey (p=0.05)...

Shear bond strength of new and recycled brackets to enamel

Tavares,Stenyo Wanderley; Consani,Simonides; Nouer,Darcy Flávio; Magnani,Maria Beatriz Borges de Araújo; Nouer,Paulo Roberto Aranha; Martins,Laura Moura
Fonte: Fundação Odontológica de Ribeirão Preto Publicador: Fundação Odontológica de Ribeirão Preto
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/01/2006 EN
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The purpose of this study was to evaluate in vitro the shear bond strength of recycled orthodontic brackets. S2C-03Z brackets (Dental Morelli, Brazil) were bonded to the buccal surfaces of 50 extracted human premolars using Concise Orthodontic chemically cured composite resin (3M, USA). The teeth were randomly assigned to 5 groups (n=10), as follows. In group I (control), the bonded brackets remained attached until shear testing (i.e., no debonding/rebonding). In groups II, III and IV, the bonded brackets were detached and rebonded after recycling by 90-mum particle aluminum oxide blasting, silicon carbide stone grinding or an industrial process at a specialized contractor company (Abzil-Lancer, Brazil), respectively. In group V, the bonded brackets were removed and new brackets were bonded to the enamel surface. Shear bond strength was tested in an Instron machine at a crosshead speed of 0.5 mm/min. Data were analyzed statistically by ANOVA and Tukey's test at 5% significance level. There was no statistically significant difference (p>0.05) between the control brackets (0.52 kgf/mm²), brackets recycled by aluminum oxide blasting (0.34 kgf/mm²) and new brackets attached to previously bonded teeth (0.43 kgf/mm²). Brackets recycled by the specialized company (0.28 kgf/mm²) and those recycled by silicon carbide stone grinding (0.14 kgf/mm²) showed the lowest shear strength means and differed statistically from control brackets (0.52 kgf/mm²) (p<0.05). In conclusion...

Rebonding of unused brackets with different orthodontic adhesives

Jimenez,Emigdio Enrique Orellana; Hilgenberg,Sérgio Paulo; Rastelli,Márcia Cristina; Pilatti,Gibson Luiz; Orellana,Bruno; Coelho,Ulisses
Fonte: Dental Press International Publicador: Dental Press International
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/04/2012 EN
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OBJECTIVE: To compare in vitro shear bond strength (SBS) of different orthodontic adhesives in bonding and repeatedly rebonding metal brackets, and to evaluate the bond failure site with the adhesive remnant index (ARI). METHODS: Specimens consisted of 90 extracted human first premolars, randomly divided into three groups (n=30). The adhesives Alpha Plast (AP), ConciseTM (CO) and TransbondTM XT (TB) were used in each group. Three SBS tests were performed, i.e., one at T0 (initial) and the other two at T1 and T2 (first and second rebondings, respectively), observing a 24-hour interval. The tests were performed in a Shimadzu AG-I (10kN) SBS testing machine, at a speed of 0.5 mm/min. RESULTS: SBS data were subjected to ANOVA, Tukey's test and Bonferroni test (p<0.05). For the ARI, the Kruskal Wallis test was performed, followed by the Dunn test. The results revealed that at T0 groups AP and CO showed SBS values that were near, but above TB values; and at T1 and T2, the highest SBS values were observed for the AP group, followed by the CO and TB groups. CONCLUSION: Statistically significant differences were found in SBS between groups AP, CO and TB during bonding and repeated rebondings of unused metal brackets, with group AP achieving the highest SBS value. Regarding ARI...

Schwoebel barriers on Si(111) steps and kinks

Kodiyalam, S.; Khor, K. E.; Sarma, S. Das
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 05/03/1996
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Motivated by our previous work using the Stillinger-Weber potential, which shows that the [$\overline{2}11$] step on 1$\times$1 reconstructed Si(111) has a Schwoebel barrier of 0.61$\pm$0.07 eV, we calculate here the same barrier corresponding to two types of kinks on this step - one with rebonding between upper and lower terrace atoms (type B) and the other without (type A). From the binding energy of an adatom, without additional relaxation of other atoms, we find that the Schwoebel barrier must be less than 0.39 eV (0.62 eV) for the kink of type A (type B). From the true adatom binding energy we determine the Schwoebel barrier to be 0.15$\pm$0.07eV (0.50$\pm$0.07 eV). The reduction of the Schwoebel barrier due to the presence of rebonding along the step edge or kink site is argued to be a robust feature. However, as the true binding energy plots show discontinuities due to significant movement of atoms at the kink site, we speculate on the possibility of multi-atom processes having smaller Schwoebel barriers.; Comment: Manuscript in revtex twocolumn format (7pgs - which includes 14 postscript files). Submitted to the The Journal of Vacuum Science and Technology (Proceedings of the Physics and Chemistry of Semi- conductor Interfaces - 23 (1996))

Graphene edge structures: Folding, scrolling, tubing, rippling and twisting

Ivanovskaya, Viktoria V.; Wagner, Philipp; Zobelli, Alberto; Suarez-Martinez, Irene; Yaya, Abu; Ewels, Christopher P.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 20/07/2012
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Conventional three-dimensional crystal lattices are terminated by surfaces, which can demonstrate complex rebonding and rehybridisation, localised strain and dislocation formation. Two dimensional crystal lattices, of which graphene is the archetype, are terminated by lines. The additional available dimension at such interfaces opens up a range of new topological interface possibilities. We show that graphene sheet edges can adopt a range of topological distortions depending on their nature. Rehybridisation, local bond reordering, chemical functionalisation with bulky, charged, or multi-functional groups can lead to edge buckling to relieve strain, folding, rolling and even tube formation. We discuss the topological possibilities at a 2D graphene edge, and under what circumstances we expect different edge topologies to occur. Density functional calculations are used to explore in more depth different graphene edge types.; Comment: Additional figure in published version

Pb chains on reconstructed Si(335) surface

Krawiec, Mariusz
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 02/04/2009
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The structural and electronic properties of Si(335)-Au surface decorated with Pb atoms are studied by means of density-functional theory. The resulting structural model features Pb atoms bonded to neighboring Si and Au surface atoms, forming monoatomic chain located 0.2 nm above the surface. The presence of Pb chain leads to a strong rebonding of Si atoms at the step edge. The fact that Pb atoms occupy positions in the middle of terrace is consistent with STM data, and also confirmed by simulated STM images. The calculated band structure clearly shows one-dimensional metallic character. The calculated electronic bands remain in very good agreement with photoemission data.; Comment: 8 pages, 8 figures

Electronic structure and rebonding in the onion-like As@Ni12@As20 cluster

Baruah, Tunna; Zope, Rajendra R.; Richardson, Steven L.; Pederson, Mark R.; ;
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
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We present the first ab initio study of the geometry, electronic structure, charged states, bonding and vibrational modes of the recently synthesized fullerene-like As@Ni12@As20 cluster which has icosahedral point symmetry [Science, 300, 778 (2003)]. We show that the molecule is vibrationally stable and will be electronically most stable in its -3 oxidation state in the condensed phase and in -2 state in the gas phase. We examine the bonding in this unusually structured molecule from charge transfer between atoms, infrared and Raman spectra, and charge density isosurfaces.; Comment: 5 pages, revised version to appear in Physical Review B Rapid Communication

Self healing of vacancy defects in single layer graphene and silicene

Özçelik, V. Ongun; Gurel, H. Hakan; Ciraci, S.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 01/08/2013
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Self healing mechanisms of vacancy defects in graphene and silicene are studied using first principles calculations. We investigated host adatom adsorption, diffusion, vacancy formation and revealed atomistic mechanisms in the healing of single, double and triple vacancies of single layer graphene and silicene. Silicon adatom, which is adsorbed to silicene at the top site forms a dumbbell like structure by pushing one Si atom underneath. The asymmetric reconstruction of the single vacancy in graphene is induced by the magnetization through the rebonding of two dangling bonds and acquiring a significant magnetic moment through remaining unsaturated dangling bond. In silicene, three two-fold coordinated atoms surrounding the single vacancy become four-fold coordinated and nonmagnetic through rebonding. The energy gained through new bond formation becomes the driving force for the reconstruction. Under the external supply of host atoms, while the vacancy defects of graphene heal perfectly, Stone-Wales defect can form in the course of healing of silicene vacancy. The electronic and magnetic properties of suspended, single layer graphene and silicene are modified by reconstructed vacancy defects.; Comment: Published in PRB: http://prb.aps.org/abstract/PRB/v88/i4/e045440

Photoelectron spectroscopy investigation of the temperature-induced deprotonation and substrate-mediated hydrogen transfer in a hydroxyphenyl-substituted porphyrin

Smykalla, Lars; Shukrynau, Pavel; Mende, Carola; Lang, Heinrich; Knupfer, Martin; Hietschold, Michael
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 25/02/2015
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The temperature dependent stepwise deprotonation of 5,10,15,20-tetra(p-hydroxyphenyl)porphyrin is investigated using photoelectron spectroscopy. An abundance of pyrrolic relative to iminic nitrogen and a decrease in the ratio of the amount of -NH- to -N= with increasing annealing temperature is found. In contrast to the molecules adsorbed on Au(111), on the more reactive Ag(110) surface, partial dissociation of the hydroxyl groups and subsequent diffusion and rebonding of hydrogen to the central nitrogen atoms resulting in a zwitterionic molecule was clearly observed. Moreover, partial C-H bond cleavage and the formation of new covalent bonds with adjacent molecules or the surface starts at a relatively high annealing temperature of 300{\deg}C. This reaction is identified to occur at the carbon atoms of the pyrrole rings, which leads also to a shift in the N 1s signal and changes in the valence band of the molecules. Our results show that annealing can significantly alter the molecules which were deposited depending on the maximum temperature and the catalytic properties of the specific substrate. The thermal stability should be considered if a molecular monolayer is prepared from a multilayer by desorption, or if annealing is applied to enhance the self-assembly of molecular structures.; Comment: 10 pages...

Próteses parciais fixas reforçadas por fibras: um estudo clínico retrospectivo preliminar; Fiber-reinforced fixed partial dentures: a preliminary retrospective clinical study

Piovesan, Edno Moacir; Demarco, Flávio Fernando; Piva, Evandro
Fonte: Universidade de São Paulo. Faculdade de Odontologia de Bauru Publicador: Universidade de São Paulo. Faculdade de Odontologia de Bauru
Tipo: info:eu-repo/semantics/article; info:eu-repo/semantics/publishedVersion; Formato: application/pdf
Publicado em 01/04/2006 ENG
Relevância na Pesquisa
17.88%
O objetivo deste estudo foi avaliar a performance clínica (percentagem de retenção) de próteses parciais fixas reforçadas por fibras. Fibras de polietileno (Ribbond®) foram usadas em combinação com resina composta durante a confecção das próteses. Os tratamentos foram realizadas em 13 pacientes, em uma clínica privada., sendo que 19 próteses foram reavaliadas. O espaço protético era preenchido com um pôntico usando o próprio dente extraído (2 casos), dentes de acrílico (11 casos) ou confeccionados com resina composta (6 casos), em todas as situações eram empregadas fibras de polietileno. Os critérios clínicos usados foram baseados na percentagem de retenção das próteses parciais fixas. As próteses que estavam em função no momento da avaliação, sem nunca necessitar de qualquer reparo prévio, foram classificadas como sobrevivência completa (SC). A classificação de sobrevivência com nova colagem (SR) foi utilizada para os casos de falha adesiva, com posterior cimentação da peça, a qual permanecia em função. O tratamento era classificado como falha (F) quando a restauração era perdida. O tempo médio de avaliação foi de 41,15 meses (±15,13). Nenhum caso de falha foi detectado, em apenas um caso houve falha adesiva com posterior colagem da peça (SR=5...

Harnessing entropy to direct the bonding/debonding of polymer systems based on reversible chemistry

Guimard, Nathalie; Ho, Junming; Brandt, Josef; Lin, Ching-Yeh; Namazian, Mansoor; Mueller, Jan O.; Oehlenschlaeger, Kim; Hilf, Stefan; Lederer, Albena; Schmidt, Friedrich Georg; Coote, Michelle; Barner-Kowollik, Christopher
Fonte: Royal Society of Chemistry Publicador: Royal Society of Chemistry
Tipo: Artigo de Revista Científica
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The widely accepted approach for controlling polymer debonding/rebonding properties in responsive materials has been to purposefully engineer the functional end-groups responsible for monomer dynamic bonding. Here, however, we evidence that the debonding