Adhesives bonded to erbium:yttrium-aluminum-garnet laser-irradiated dentin: transmission electron microscopy, scanning electron microscopy and tensile bond strength analyses

The aim of this in vitro study was to investigate the effect of erbium:yttrium-aluminum-garnet (Er:YAG) laser irradiation on dentinal collagen by transmission electron microscopy and to analyze the resin-dentin interface by scanning electron microscopy. A tensile bond strength test was also applied. Specimens from 69 sound human third molars were randomly divided into three groups: control (no laser), and two irradiated groups, laser 250 (250 mJ/2 Hz) and laser 400 (400 mJ/4 Hz). Then, specimens were restored with two adhesive systems, an etch-and-rinse or a self-etch system. Although ultrastructural examination showed a modified surface in the irradiated dentin, there was no statistical difference in bond strength values between the laser groups and controls (P < 0.05). In conclusion, the use of Er:YAG laser for ablating human dentin did not alter the main adhesion parameters when compared with those obtained by conventional methods, thus reinforcing its use in restorative dentistry.

Influence of the irradiation distance and the use of cooling to increase enamel-acid resistance with Er:YAG laser

Objectives: The aim of this study was to assess the influence of irradiation distance and the use of cooling in the Er:YAG laser efficacy in preventing enamel demineralization. Methods: 84 enamel blocks were randomly assigned to seven groups (n = 12): G1: control group - no treatment, G2-G7: experimental groups treated with Er:YAG laser (80 mJ/2 Hz) at different irradiation distances with or without cooling: G2: 4 mm/2 mL; G3: 4 mm/no cooling; G4: 8 mm/2 mL; G5: 8 mm/no cooling; G6: 16 mm/2 mL; G7: 16 mm/no cooling. The samples were submitted to an in vitro pH cycles for 14 days. Next, the specimens were sectioned in sections of 80-100 mu m in thickness and the demineralization patterns of prepared slices were assessed using a polarized light microscope. Three samples from each group were analyzed with scanning electronic microscopy. Analysis of variance and the Fisher test were performed for the statistical analysis of the data obtained from the caries-lesion-depth measurements (CLDM) (alpha = 5%). Results: The control group (CLDM = 0.67 mm) was statistically different from group 2 (CLDM = 0.42 mm), which presented a smaller lesion depth, and group 6 (0.91 mm), which presented a greater lesion depth. The results of groups 3 (CLDM = 0.74 mm), 4 (CLDM = 0.70 mm), 5 (CLDM = 0.67 mm) and 7 (CLDM = 0.89 mm) presented statistical similarity. The scanning electronic microscopy analysis showed ablation areas in the samples from groups 4, 5, 6 and 7, and a slightly demineralized area in group 2. Conclusions: It was possible to conclude that Er:YAG laser was efficient in preventing enamel demineralization at a 4-mm irradiation distance using cooling. (C) 2010 Elsevier Ltd. All rights reserved.

Ligand-field analysis of an Er(III) complex with a heptadentate tripodal N4O3 ligand

Polarized absorption and emission spectra of trigonal single crystals of an Er(III) complex coordinated to a heptadentate tripodal ligand are reported at temperatures between 8 and 298 K. The assigned energy levels below the onset of ligand absorption (< 25 000 cm(-1)) are fitted to a parametrized electronic Hamiltonian. The C-3 site symmetry of the Er(HI) ion requires eight parameters for a full description of the ligand field within a one-electron operator description. This compound shows unusually large splittings of the multiplets, and the fitted parameters imply that this heptadentate ligand imparts the largest ligand field reported for an Er(III) complex. The ligand field was also interpreted within the angular overlap model (AOM). We derive the AOM matrix to include both sigma and anisotropic pi bonding and show that a useful description of the C-3 ligand field can be made using only five parameters. The success of the AOM description is encouraging for applications on isomorphous complexes within the lanthanide series and in describing the ligand field of low-symmetry complexes with less parameters than in the usual spherical harmonic expansion.

Precipitation hardening of Cu-Fe-Cr alloys - Part I - Mechanical and electrical properties

This research is part of a project whose scope was to investigate the engineering properties of new non-commercial alloy formulations based on the Cu rich corner of the Cu-Fe-Cr ternary system with the primary aim of exploring the development of a new cost-effective high-strength, high-conductivity copper alloy. The literature indicated that Cu rich Cu-Cr and Cu-Fe alloys have been thoroughly investigated. A number of commercial alloys have been developed and these are used for a variety of applications requiring combinations of high-strength, high-conductivity and resistance to softening. Little evidence was found in the literature that the Cu rich corner of the Cu-Fe-Cr system had previously been investigated for the purpose of developing high-strength, high-conductivity copper alloys resistant to softening. The aim of these present investigations was to explore the possibility that new alloys could be developed that combined the properties of both sets of alloys, ie large precipitation hardening response combined with the ability to stabilise cold worked microstructures to high temperatures while at the same maintain high electrical conductivity. To assess the feasibility of this goal the following alloys were chosen for investigation: Cu-0.7wt%Cr-0.3wt%Fe, Cu-0.7wt%Cr-0.8wt%Fe, Cu-0.7wt%Cr-2.0wt%Fe. This paper reports on the mechanical property investigation which indicated that the Cu-0.7wt%Cr-0.3wt%Fe, and Cu-0.7wt%Cr-2.0wt%Fe alloys were worthy of further investigation. (C) 2001 Kluwer Academic Publishers.

Precipitation hardening of Cu-Fe-Cr alloys - Part II - Microstructural characterisation

This research is part of a project whose scope was to investigate the engineering properties of new non-commercial alloy formulations based on the Cu rich corner of the Cu-Fe-Cr ternary system with the primary aim of exploring the development of a new cost-effective high-strength, high-conductivity copper alloy. Promising properties have been measured for the following alloys: Cu-0.7wt%Cr-0.3wt%Fe and Cu-0.7wt%Cr-2.0wt%Fe. This paper reports on the microstructural characterisation of these alloys and discusses the mechanical and electrical properties of these alloys in terms of their microstructure, particularly the formation of precipitates. These alloys have evinced properties that warrant further investigation. Cost modelling has shown that Cu-0.7wt%Cr-0.3wt%Fe is approximately 25% cheaper to produce than commercial Cu-1%Cr. It has also been shown to be more cost efficient on a yield stress and % IACS per dollar basis. The reason for the cost saving is that the Cu-0.7%Cr-0.3%Fe alloy can be made with low carbon ferro-chrome additions as the source of chromium rather than the more expensive Cu-Cr master-alloy. For applications in which cost is one of the primary materials selection criteria, it is envisaged that there would be numerous applications in both cast and wrought form, where the Cu-0.7%Cr-0.3%Fe alloy would be more suitable than Cu-1%Cr. (C) 2001 Kluwer Academic Publishers.

Quaternary Cu-0.7%Cr-0.3%Fe-X alloys

This research is part of a project whose scope was to investigate the engineering properties of new non-commercial alloy formulations based on the Cu rich corner of the Cu-Fe-Cr ternary system with the primary aim of exploring the development of a new cost-effective high-strength, high-conductivity copper alloy. The aim of the present work was to increase the electrical conductivity and strength of the Cu-0.7wt%Cr-0.3wt%Fe alloy through selective minor additions (less than or equal to0.15 wt%) of elements expected to promote precipitation of dissolved Fe: Ti, B, P, Ni & Y. Such quaternary alloys with reduced Fe in solid solution would be expected to have properties equivalent to or better than those of the Cu-1%Cr reference alloy (Alloy Z). The investigation showed that none of the trace element additions significantly improved the size of the age hardening response or the peak aged electrical conductivity of Alloy A, although further work is required on the influence of Ti. Additions of P and B were detrimental. Other trace additions had little or no effect apart from causing some slight changes to the precipitation kinetics. The mechanical properties of the Cu-0.7%Cr-0.3%Fe alloy made with less expensive high carbon ferrochrome were found to be inferior to those of the equivalent alloy made with low carbon ferrochrome. (C) 2001 Kluwer Academic Publishers.

Cold worked Cu-Fe-Cr alloys

The aim of this project was to investigate the properties of copper rich Cu-Fe-Cr alloys for the purpose of developing a new cost effective, high-strength, high-conductivity copper alloy. This paper reports on the influence of cold work. The age hardening response of the Cu-0.7%Cr-2.0%Fe alloy was minimal, but the resistance to softening was superior to that reported for any commercial high-strength, high-conductivity (HSHC) copper alloy with comparable mechanical and electrical properties. For example, an excess of 85% of the original hardness of the 40% cold worked alloy is retained after holding at 700 degreesC for 1 hour, whereas commercial HSHC Cu-Fe-P alloys have been reported to soften significantly after 1 hours exposure at less than 500 degreesC. The Cu-0.7Cr-2.0Fe alloy would therefore be expected to be more suitable for applications with a significant risk of exposure to elevated temperatures. Optical microscope examination of cold worked and aged microstructures confirmed the high resistance to recrystallization for Cu-0.7%Cr-2.0%Fe. The Zener-Smith drag term, predicting the pinning effect of second phase particles on dislocations in cold worked microstructures, was calculated using the precipitate characteristics obtained from TEM, WDS and resistivity measurements. The pinning effect of the precipitate dispersions in the peak-aged condition was determined to be essentially equivalent for the Cu-0.7%Cr-0.3%Fe and Cu-0.7%Cr-2.0%Fe alloys. A lower recrystallisation temperature in the Cu-0.7%Cr-0.3%Fe alloy was therefore attributed to faster coarsening kinetics of the secondary precipitates resulting from a higher Cr concentration in the precipitates at lower iron content. (C) 2001 Kluwer Academic Publishers.

Investigation of electrical conductivity as a function of dopant-ion radius in the systems Zr0.75Ce0.08M0.17O1.92 (M=Nd, Sm, Gd, Dy, Ho, Y, Er, Yb, Sc)

Electrical conductivity versus dopant ionic radius studies in zirconia- and ceria-based, solid oxide fuel cell (SOFC) electrolyte systems have shown that oxygen-ion conductivity is highest when the host and dopant ions are similar in size [J. Am. Ceram. Soc. 48 (1965) 286; Solid State Ionics 37 (1989) 67; Solid State Ionics 5 (1981) 547]. Under these conditions, it is thought that the conduction paths within the crystal lattice become less distorted [Solid State Ionics 8 (1983) 201]. In this study, binary ZrO2-M2O3 unit cells were expanded, via the partial substitution of Ce+4 for Zr+4 into the lattice, in an attempt to identify new, ternary, zirconia/ceria-based electrolyte systems with enhanced electrical conductivity. The compositions Zr0.75Ce0.08M0.17O1.92 (M = Nd, Sm, Gd, Dy, Ho, Y, Yb, Sc) were prepared using traditional solid state techniques. Bulk phase characterisation and precise lattice parameter measurements were performed with X-ray diffraction techniques. Four-probe DC conductivity measurements between 400 and 900 degreesC showed that the dopant-ion radius influenced electrical conductivity. The conductivity versus dopant-ion radius trends previously observed in zirconia-based, binary systems are clearly apparent in the ternary systems investigated in this study. The addition of ceria was found to have a negative influence on the electrical conductivity over the temperature range 400-900 degreesC. It is suggested that distortion of the oxygen-ion conduction path by the presence of the larger M+3 and Ce+4 species (relative to Zr+4) is the reason for the decreasing electrical conductivity as a function of increasing dopant size and ceria addition, respectively. (C) 2002 Elsevier Science B.V. All rights reserved.

Programa caminho da escola

O Fundo Nacional de Desenvolvimento da Educa????o (FNDE) concebeu o modelo do Programa Caminho da Escola almejando uma solu????o aos problemas enfrentados no ??mbito do transporte escolar. Desde o princ??pio, o programa procurou alcan??ar resultados concretos e eficientes para transpor as conhecidas dificuldades de ve??culos que trafegam na zona rural e enfrentam condi????es severas de opera????o como vias sem asfaltamento, com poeira, lama, buracos, pontes prec??rias e mata-burros, assim como as embarca????es, que navegam com estiagens e enchentes por rios caudalosos e com grande incid??ncia de troncos e galhos, sem p??er para atraca????o. A fim de facilitar esse processo de melhoria da gest??o de transporte escolar, foi disponibilizada aos munic??pios, estados e Distrito Federal uma linha de cr??dito do Banco Nacional de Desenvolvimento Econ??mico Social (BNDES) com menores juros de mercado e extenso prazo para quita????o, facultando-lhes um modelo de compras que -reduziu expressivamente os custos e lhes isentou do processo licitat??rio para a aquisi????o de ve??culos que atendem rigidamente a especifica????es pr??prias e que contam com chancela de qualidade e conformidade

Programa de cr??dito produtivo popular Crediamigo: central de microcr??dito do Nordeste

As pol??ticas de desenvolvimento consideram que um dos principais obst??culos para o crescimento dos microeempreendimentos ?? a falta de acesso ??s fontes de financiamento, principalmente ??queles emergidos como formas alternativas de ocupa????o e renda. Esses pequenos neg??cios, em sua maioria informais, vem apresentando n??veis de alto crescimento em todo o Pa??s, em especial na regi??o Nordeste, principalmente nos grandes centros urbanos, comprovada por pesquisas cient??ficas realizadas. Considerando que o acesso dessa camada da popula????o ao sistema banc??rio ?? dif??cil, devido ao baixo n??vel operacional, ao tamanho dos neg??cios e ?? qualidade ou inexist??ncia de garantias, o Banco do Nordeste lan??a o Programa CrediAmigo com o objetivo de contribuir para o crescimento de microempresas, mediante a oferta de cr??dito para atividades produtivas e servi??os de capacita????o, de forma a garantir ao agente produtivo condi????es para ele gerir bem seus neg??cios, atrav??s da melhoria da competitividade e integra????o ao mercado globalizado. Dessa forma, o CrediAmigo permite f??cil acesso a esse segmento da popula????o marginalizada do sistema financeiro formal e que recorrem e dependem de agiotas e fornecedores que lhes cobram taxas de juros bem acima do mercado. Para atender esses agentes produtivos o CrediAmigo utiliza uma metodologia inovadora de concess??o de cr??dito que permite a libera????o dos recursos de forma ??gil, desburocratizada e sem as garantias tradicionais exigidas, funcionando com grupos solid??rios, proporcionando uma maior democratiza????o do cr??dito. At?? jul/99 o CrediAmigo j?? atendeu a 121.444 cidad??os com financiamento na ordem de R$ 74,2 milh??es

Redesenho do processo de concess??o de cr??dito

As muta????es verificadas no cen??rio mundial passaram a exigir das organiza????es posicionamento proativo voltado para a percep????o do cliente. Tornou-se imperativo a ado????o de medidas que induzissem ?? descentraliza????o, ?? desregulamenta????o e ?? desburocratiza????o, tornando-as din??micas, ??geis, descomplicadas e voltadas para o enfoque do mercado e, acima de tudo, buscando a satisfa????o do cliente. Referido Processo, considerado o mais cr??tico da Institui????o, inaugurou um conjunto de medidas reformuladoras, de ordem processual, atitudinal e comportamental, buscando como premissa b??sica o foco no cliente. Esse redesenho resultou na elimina????o de atividades redundantes, retrabalhos e mudan??as desnecess??rias de interlocutores, permitindo o atendimento tempestivo e oportuno com a conseq??ente satisfa????o do cliente, o agente produtivo, capacitando-o, oferecendo-lhe produtos e servi??os que viabilizem os seus empreendimentos produtivos, tornando-os competitivos via integra????o nas cadeias produtivas e inser????o nas pol??ticas de desenvolvimento regional e nacional. A mensura????o dos resultados pode ser expressa, em princ??pio, com a observa????o de alguns indicadores: Em 1994, o prazo m??dio de atendimento de uma proposta de cr??dito era de 217 dias. Ap??s implementadas as mudan??as situou-se em 21 dias. A quantidade de projetos/ano atendidos evoluiu de 27 mil, em 1994, para 286 mil, em 1997

Introdu????o ?? cr??tica da raz??o desestatizante

O artigo compreende uma vis??o cr??tica sobre os processos de reestrutura????o do Estado baseados na l??gica neoliberal, que caracterizam as reformas minimalistas da d??cada de 80. O tema da reforma do Estado ?? visto como um dos grandes desafios intelectuais e pol??ticos deste fim de s??culo, devendo necessariamente ser contextualizado historicamente, uma vez que n??o existe uma ??nica crise do Estado, mas v??rias crises dos Estados espec??ficas e particulares, cujas solu????es n??o s??o ??nicas nem universais, mas dependentes do diagn??stico de cada caso. Entende-se que a raz??o desestatizante apresenta limita????es, reconhecidas at?? mesmo pelas institui????es financeiras internacionais que antes a defendiam. O cen??rio de um novo modo de atua????o estatal ?? apresentado como mais prov??vel, sendo o conceito de reestatiza????o mais adequado para as mudan??as que se fazem necess??rias.

Transformando burocracias para financiar os mais pobres: a evolu????o do Pronaf Cr??dito Grupo B

Institui????es banc??rias tradicionalmente n??o oferecem servi??os financeiros, principalmente cr??dito produtivo, aos grupos de mais baixa renda. Considerando-se a rigidez do sistema financeiro em trabalhar com os mais pobres, o presente artigo descreve o processo de cria????o e aperfei??oamento de uma pol??tica p??blica de microcr??dito rural dentro do Programa Nacional de Fortalecimento da Agricultura Familiar (Pronaf). S??o apresentadas as motiva????es para altera????es no desenho da linha de cr??dito, assim como as mudan??as normativas, de fontes e de agentes operadores, efetuadas em cada ano-safra para tornar poss??vel superar os desafios apresentados pela burocracia do Sistema Nacional de Cr??dito Rural ??? SNCR. O texto apresenta ainda o impacto no n??mero de contrata????es resultante das diversas medidas tomadas. Finalmente, ?? feito um balan??o das principais li????es aprendidas assim como dos desafios atuais de maior qualifica????o do microcr??dito e integra????o com outras pol??ticas p??blicas.