Vertical Bone Augmentation Using a Polytetrafluoroethylene Nonporous Barrier for Osseointegrated Implants Partially Inserted in Tibiae of Rabbits

Purpose: The aim of this study was to evaluate the possibility of obtaining guided bone regeneration using a poly-tetrafluoroethylene (PTFE) nonporous barrier for 2 endosseous implants, partially inserted in tibiae of rabbits.Materials and Methods: Histologic characteristics of the interface between titanium implants (one group with titanium plasma-coated implants and the other group with acid-treated surfaces) and of the regenerated bone were also studied. Twenty screw-vent implants were placed in tibiae of 5 male New Zealand rabbits, 2 at the right side and 2 at the left side, protruding 3 mm from the bone level, to create a horizontal bone defect. At the experimental group the implants were with a PTFE nonporous barrier, whereas no barriers were used in contralateral implants. Animals were sacrificed 3 months after surgery and biopsy specimens were evaluated histologically and histomorphometrically under light microscopy. Student's t test was used for statistical analysis.Results: The histologic measurements showed a mean gain in bone height of 2.15 and 2.42 mm for the barrier group and 1.95 and 0.43 mm for the control group, for the titanium plasma-spray and acid-treated implant surfaces, respectively.Conclusion: The results of the investigation revealed that the placement of implants protruding 3 nun from crestal bone defects may result in vertical bone augmentation using a nonporous PTFE barrier. (Implant Dent 2009;18:182-191)

The critical barrier to progress in dentine bonding with the etch-and-rinse technique

Objectives: The lack of durability in resin-dentine bonds led to the use of chlorhexidine as MMP-inhibitor to prevent the degradation of hybrid layers. Biomimetic remineralisation is a concept-proven approach in preventing the degradation of resin-dentine bonds. The purpose of this study is to examine the integrity of aged resin-dentine interfaces created with a nanofiller-containing etch-and-rinse adhesive after the application of these two approaches.Methods: The more established MMP-inhibition approach was examined using a parallel in vivo and in vitro ageing design to facilitate comparison with the biomimetic remineralisation approach using an in vitro ageing design. Specimens bonded without chlorhexidine exhibited extensive degradation of the hybrid layer after 12 months of in vivo ageing.Results: Dissolution of nanofillers could be seen within a water-rich zone within the adhesive layer. Although specimens bonded with chlorhexidine exhibited intact hybrid layers, water-rich regions remained in those hybrid layers and degradation of nanofillers occurred within the adhesive layer. Specimens subjected to in vitro biomimetic remineralisation followed by in vitro ageing demonstrated intrafibrillar collagen remineralisation within hybrid layers and deposition of mineral nanocrystals in nanovoids within the adhesive.Conclusions: The impact was realized by understanding the lack of an inherent mechanism to remove water from resin-dentine interfaces as the critical barrier to progress in bonding with the etch-and-rinse technique. The experimental biomimetic remineralisation strategy offers a creative solution for incorporating a progressive hydration mechanism to achieve this goal, which warrants its translation into a clinically applicable technique. (C) 2011 Elsevier Ltd. All rights reserved.

Tunneling time through a barrier using the local value of a time operator

A time for a quantum particle to traverse a barrier is obtained for stationary states by setting the local value of a time operator equal to a constant. This time operator, called the tempus operator because it is distinct from the time of evolution, is defined as the operator canonically conjugate to the energy operator. The local value of the tempus operator gives a complex time for a particle to traverse a barrier. The method is applied to a particle with a semiclassical wave function, which gives, in the classical limit, the correct classical traversal time. It is also applied to a quantum particle tunneling through a rectangular barrier. The resulting complex tunneling time is compared with complex tunneling times from other methods.

Dynamical localization of matter-wave solitons in managed barrier potentials

The bright matter-wave soliton propagation through a barrier with a rapidly oscillating position is investigated. The averaged-over rapid oscillations Gross-Pitaevskii equation is derived, where the effective potential has the form of a finite well. Dynamical trapping and quantum tunneling of the soliton in the effective finite well are investigated. The analytical predictions for the effective soliton dynamics is confirmed by numerical simulations of the full Gross-Pitaevskii equation.

Tunneling time through a rectangular barrier

In this paper, we discuss the tunneling time of a quantum particle through a rectangular barrier. The reflection and transmission times associated with the wave packets representing the particle are discussed. By using an initial Gaussian momentum distribution, we carry out a comparative analysis of the stationary phases of the incident, reflected, and transmitted wave packets leading to the reflection and transmission times at, and Delta t(T), respectively. In the present treatment of this old and very known problem we take into account the deformations of the reflected and transmitted momentum distributions. These deformations produce a dependence of the reflection and transmission times on the location of the initial wave packet. In a parallel calculation, by numerically monitoring the time evolution of the system, we characterize a reflection and a transmission time. Such times agree with the ones obtained via the stationary phase method. [S1050-2947(98)07912-8].

CRITICAL EXPONENTS and SCALING PROPERTIES FOR THE CHAOTIC DYNAMICS of A PARTICLE IN A TIME-DEPENDENT POTENTIAL BARRIER

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Nature of potential barrier in (Ca-1/4,Cu-3/4)TiO3 polycrystalline perovskite

The nonohmic electrical features of (Ca-1/4,Cu-3/4)TiO3 perovskite ceramics, which have very strong gigantic dielectric is believed originate from potential barriers at the grain boundaries. In the present study, we used the admittance and impedance spectroscopy technique to investigate (Ca-1/4,Cu-3/4)TiO3 perovskite ceramics with low nonohmic electrical properties. The study was conducted under two different conditions: on as-sintered ceramics and on ceramics thermally treated in an oxygen-rich atmosphere. The results confirm that thermal treatment in oxygen-rich atmospheres influence the nonohmic properties. Annealing at oxygen-rich atmospheres improve the nonohmic behavior and annealing at oxygen-poor atmospheres decrease the nonohmic properties, a behavior already reported for common metal oxide nonohmic devices and here firstly evidenced for the (Ca-1/4,Cu-3/4)TiO3 perovskite related materials. The results show that oxygen also influences the capacitance values at low frequencies, a behavior that is indicative of the Schottky-type nature of the potential barrier. (c) 2006 Elsevier Ltd. All rights reserved.

Influence of cerium (IV) ions on the mechanism of organosilane polymerization and on the improvement of its barrier properties

In this work, the effect of cerium (IV) ammonium nitrate (CAN) addition on the polymerization of bis-[triethoxysilyl]ethane (BTSE) film applied on carbon steel was studied. The electrochemical characterization of the films was carried out in 0.1 mol L(-1) NaCl solution by open-circuit potential measurements, anodic and cathodic polarization curves and electrochemical impedance spectroscopy (EIS). Morphological and chemical characterization were performed by atomic force microscopy (AFM), contact angle measurements, infrared-spectroscopy, nuclear magnetic resonance and thermogravimetric analysis. The results have clearly shown the improvement on the protective properties of the Ce(4+) modified film as a consequence of the formation of a more uniform and densely reticulated silane film. A mechanism is proposed to explain the accelerating role of Ce(4+) ions on the cross-linking of the silane layer. (C) 2008 Elsevier Ltd. All rights reserved.

Breakdown of resistance in sweet pepper against Pepper yellow mosaic virus in Brazil

Plantas de Capsicum annuum cv. Magali R, resistentes ao Pepper yellow mosaic virus (PepYMV), exibindo sintomas severos de mosaico amarelo, malformação foliar e subdesenvolvimento foram encontradas em plantios na região de Lins, SP, Brasil, em 2003/04. Partículas semelhantes àquelas do gênero Potyvirus foram observadas em extrato foliar de planta infectada examinado em microscópio eletrônico de transmissão. O extrato foliar também reagiu com anti-soro contra o PepYMV em PTA-ELISA. Além de C. annuum cv. Magali R, esse potyvirus também infectou sistemicamente C. annuum cv. Rubia R, que é resistente ao PepYMV. A seqüência de nucleotídeos de parte do gene da proteína capsidial (CP) desse potyvirus apresentou 96-98% de identidade com a de outros isolados do PepYMV. A seqüência parcial de nucleotídeos da região 3' não traduzida (3' NTR) apresentou 94-96% de identidade com a do PepYMV. Esses resultados são indicativos de que o potyvirus que quebrou a resistência em pimentão é um isolado do PepYMV.

Electrical and microstructural properties of microwave sintered SnO2-based varistors

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

BARRIER VOLTAGE DEFORMATION OF ZNO VARISTORS BY CURRENT PULSE

The phenomenon of electrical degradation in ZnO varistors was studied by application of high-intensity current pulses. A wave shape of 8 X 20-mu-s and rectangular waves of 1 and 2 ms were used. The degradation was estimated by reference electric-field variation and by Schottky voltage barrier deformation. The results showed that current pulses reduce both the height and the width of the barrier voltage. It was also observed that the donor density N(d) did not change but the surface states density N(s) decreased with degradation.

Effect of La2O3 doping on the microstructure and electrical properties of a SnO2-based varistor

The effect of La2O3 addition on the densification and electrical properties of the (0.9895 - x) SnO2 + 0.01 CoO + 0.0005 Nb2O5 + x La2O5 system, where x = 0.0005 or 0.00075, was considered in this study. The samples were sintered at 1300 degreesC for 2 and 4 h and a single SnO2 phase was identified by X-ray diffraction. Microstructure analysis by scanning electron microscopy showed that the affect of La2O3 addition is to decrease the SnO2 grain size. J versus E curves indicated that the system exhibits a varistor behavior and the effect of La2O3 is to increase both the non-linear coefficient (alpha) and the breakdown voltage (E-2). Considering the Schottky thermionic emission model the potential height and the width were estimated. The addition of small amounts of La2O3 to the basic system increases the potential barrier height and decreases both grain size and potential barrier width. (C) 2001 Kluwer Academic Publishers.

Electrical and micro structural properties of (Zn, Nb, Fe)-doped SnO2 varistor systems

The electrical and microstructural properties of SnO2-based varistors with the addition of 0.025 and 0.050 mol% of Fe2O3 have been characterised. Electric field (E) versus current density (J) curves showed that the effect of Fe2O3 addition is to increase both the non-linear coefficient and the breakdown voltage. Variations in the potential barrier height were inferred from impedance spectroscopy (IS) analysis. Through transmission electron microscopy (TEM), the presence of precipitates of secondary phases was confirmed. Samples with precipitates displayed poor electrical properties. (c) 2004 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

THE ENERGY BARRIER FOR ELECTRON TRAPPING IN ALXGA1-XAS

Transient decay of persistent photoconductivity measurements are carried out in samples of different compositions. The capture barrier for electron trapping by DX centers is obtained using a method which employs the Brooks-Herring equation for the electronic mobility. The effect of polarization of the screening cloud is analysed using Takimoto's potential and specifies the limits of applicability of the Brooks-Herring equation in AlxGa1-xAs.

Characterization of BaTi1-xZrxO3 thin films obtained by a soft chemical spin-coating technique

Single-phase perovskite structure BaZrxTi1-xO3 (BZT) (0.05less than or equal toxless than or equal to0.25) thin films were deposited on Pt-Ti-SiO2-Si substrates by the spin-coating technique. The structural modifications in the thin films were studied using x-ray diffraction and micro-Raman scattering techniques. Lattice parameters calculated from x-ray data indicate an increase in lattice (a axis) with the increasing content of zirconium in these films. Such Zr substitution also result in variations of the phonon mode wave numbers, especially those of lower wave numbers, for BaZrxTi1-xO3 thin films, corroborate to the structural change caused by the zirconium doping. on the other hand, Raman modes persist above structural phase transition, although all optical modes should be Raman inactive in the cubic phase. The origin of these modes must be interpreted as a function of a local breakdown of the cubic symmetry, which could be a result of some kind of disorder. The BZT thin films exhibited a satisfactory dielectric constant close to 181-138, and low dielectric loss tan delta<0.03 at the frequency of 1 kHz. The leakage current density of the BZT thin films was studied at elevated temperatures and the data obey the Schottky emission model. Through this analysis the Schottky barrier height values 0.68, 1.39, and 1.24 eV were estimated to the BZT5, BZT15, and BZT25 thin films, respectively. (C) 2004 American Institute of Physics.