Investigation of Plasma Immersion Ion Implantation Process in Magnetic Mirror Geometry

Plasma immersion ion implantation (PIII) with low external magnetic field has been investigated both numerically and experimentally. The static magnetic field considered is essentially nonuniform and is generated by two magnetic coils installed outside the vacuum chamber. Experiments have been conducted to investigate the effect of two of the most important PIII parameters: target voltage and gas pressure. In that context, it was found that the current density increased when the external parameters were varied. Later, the PIII process was analyzed numerically using the 2.5-D computer code KARAT. The numerical results show that the system of crossed E x B fields enhances the PIII process. The simulation showed an increase of the plasma density around the target under the operating and design conditions considered. Consequently, an increase of the ion current density on the target was observed. All these results are explained through the mechanism of gas ionization by collisions with electrons drifting in crossed E x B fields.

Analysis of failed commercially pure titanium dental implants: A scanning electron microscopy and energy-dispersive spectrometer X-ray study

Background: the failure of osseointegration in oral rehabilitation has gained importance in current literature and in clinical practice. The integration of titanium dental implants in alveolar bone has been partly ascribed to the biocompatibility of the implant surface oxide layer. The aim of this investigation was to analyze the surface topography and composition of failed titanium dental implants in order to determine possible causes of failure.Methods: Twenty-one commercially pure titanium (cpTi) implants were retrieved from 16 patients (mean age of 50.33 +/- 11.81 years). Fourteen implants were retrieved before loading (early failures), six after loading (late failures), and one because of mandibular canal damage. The failure criterion was lack of osseointegration characterized as dental implant mobility. Two unused implants were used as a control group. All implant surfaces were examined by scanning electron microscopy (SEM) and energy-dispersive spectrometer x-ray (EDS) to element analysis. Evaluations were performed on several locations of the same implant.Results: SEM showed that the surface of all retrieved implants consisted of different degrees of organic residues, appearing mainly as dark stains. The surface topography presented as grooves and ridges along the machined surface similar to control group. Overall, foreign elements such as carbon, oxygen, sodium, calcium, silicon, and aluminum were detected in failed implants. The implants from control group presented no macroscopic contamination and clear signs of titanium.Conclusion: These preliminary results do not suggest any material-related cause for implant failures, although different element composition was assessed between failed implants and control implants.

Titanium surface topography after brushing with fluoride and fluoride-free toothpaste simulating 10 years of use

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Microbiological or Chemical Models of Enamel Secondary Caries Compared by Polarized-Light Microscopy and Energy Dispersive X-ray Spectroscopy

Different secondary caries models may present different results. The purpose of this study was to compare different in vitro secondary caries models, evaluating the obtained results by polarized-light microscopy (PLM), scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDS). Standardized human enamel specimens (n = 12) restored with different materials (Z250 conventional composite resin-CRZ, Freedom polyacid-modified composite resin-CRF, Vitremer resin-modified glass-ionomer-GIV, and Fuji IX conventional glass-ionomer cement-GIF) were submitted to microbiological (MM) or chemical caries models (CM). The control group was not submitted to any caries model. For MM, specimens were immersed firstly in sucrose broth inoculated with Streptococcus mutans ATCC 35688, incubated at 37 degrees C/5% CO(2) for 14 days and then in remineralizing solution for 14 days. For CM, specimens were submitted to chemical pH-cycling. Specimens were ground, submitted to PLM and then were dehydrated, gold-sputtered and submitted to SEM and EDS. Results were statistically analyzed by Kruskall-Wallis and Student-Newman-Keuls tests (alpha = 0.05). No differences between in vitro caries models were found. Morphological differences in enamel demineralization were found between composite resin and polyacid-modified composite resin (CRZ and CRF) and between the resin-modified glass-ionomer and the glass-ionomer cement (GIF and GIV). GIF showed higher calcium concentration and less demineralization, differing from the other materials. In conclusion, the glass-ionomer cement showed less caries formation under both in vitro caries models evaluated. (C) 2009 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 90B: 635-640, 2009

Analysis of Tooth Enamel After Excessive Bleaching: A Study Using Scanning Electron Microscopy and Energy Dispersive X-ray Spectroscopy

This study assessed alterations on bovine enamel after excessive bleaching. Coronal portions of bovine teeth (n = 30) were sectioned and divided into three groups (n = 10 per group). The coronal parts were further cut incisocervically into two halves. While one half received no bleaching (control), the other half was subjected to either one (group 1), three (group 2), or five bleaching sessions (group 3) with 35% hydrogen peroxide. The enamel surfaces were then analyzed using scanning electron microscopy and energy dispersive x-ray spectroscopy (EDS). Fxcessive bleaching affected the surface morphology and chemistry of the bovine enamel. EDS analysis showed the highest decrease in calcium ion percentages in groups 2 and 3 when compared to their nonbleached halves. Oxygen and phosphorus percentages were comparable on both the control and bleached enamel, regardless of the number of bleaching sessions. Consecutive bleaching sessions with 35% hydrogen peroxide may lead to morphologic and specific elemental changes when performed in a short period of time. Calcium ion percentages may decrease when this bleaching agent is used for more than one session. Int J Prosthodontics 2010;23:29-32.

Ability of different restorative materials to prevent in situ secondary caries: analysis by polarized light-microscopy and energy-dispersive X-ray

Secondary caries is the main cause of direct restoration replacement. The purpose of this study was to analyze enamel adjacent to different restorative materials after in situ cariogenic challenge using polarized-light microscopy (PLM), scanning electron microscopy (SEM) and energy-dispersive X-ray analysis (EDS). Twelve volunteers, with a low level of dental plaque, a low level of mutans streptococci, and normal salivary flow, wore removable palatal acrylic appliances containing enamel specimens restored with Z250 composite, Freedom composite, Fuji IX glass-ionomer cement, or Vitremer resin-modified glass-ionomer for 14 days. Volunteers dripped one drop of 20% sucrose solution (n = 10) or distilled water (control group) onto each specimen 8 times per day. Specimens were removed from the appliances and submitted to PLM for examination of the lesion area (in mm(2)), followed by dehydration, gold-sputtering, and submission to SEM and EDS. The calcium (Ca) and phosphorus (P) contents were evaluated in weight per cent (%wt). Differences were found between Z250 and Vitremer, and between Z250 and FujiIX, when analyzed using PLM. Energy-dispersive X-ray analysis results showed differences between the studied materials regarding Ca %wt. In conclusion, enamel adjacent to glass-ionomer cement presented a higher Ca %wt, but this material did not completely prevent enamel secondary caries under in situ cariogenic challenge.

Whitham method for the Benjamin-Ono-Burgers equation and dispersive shocks

The Whitham modulation equations for the parameters of a periodic solution are derived using the generalized Lagrangian approach for the case of the damped Benjamin-Ono equation. The structure of the dispersive shock is considered in this method.

Theory of optical dispersive shock waves in photorefractive media

The theory of optical dispersive shocks generated in the propagation of light beams through photorefractive media is developed. A full one-dimensional analytical theory based on the Whitham modulation approach is given for the simplest case of a sharp steplike initial discontinuity in a beam with one-dimensional striplike geometry. This approach is confirmed by numerical simulations, which are extended also to beams with cylindrical symmetry. The theory explains recent experiments where such dispersive shock waves have been observed.

Blood glucose responses in humans mirror lactate responses for individual anaerobic threshold and for lactate minimum in track tests

The equilibrium point between blood lactate production and removal (La-min(-)) and the individual anaerobic threshold (IAT) protocols have been used to evaluate exercise. During progressive exercise, blood lactate [La-](b), catecholamine and cortisol concentrations, show exponential increases at upper anaerobic threshold intensities. Since these hormones enhance blood glucose concentrations [Glc](b), this study investigated the [Glc] and [La-](b) responses during incremental tests and the possibility of considering the individual glucose threshold (IGT) and glucose minimum;(Glc(min)) in addition to IAT and La-min(-) in evaluating exercise. A group of 15 male endurance runners ran in four tests on the track 3000 m run (v(3km)); IAT and IGT- 8 x 800 m runs at velocities between 84% and 102% of v(3km); La-min(-) and Glc(min) - after lactic acidosis induced by a 500-m sprint, the subjects ran 8 x 800 m at intensities between 87% and 97% of v(3km); endurance test (ET)- 30 min at the velocity of IAT. Capillary blood (25 mu l) was collected for [La-](b) and [Glc](b) measurements. The TAT and IGT were determined by [La-](b) and [Glc](b) kinetics during the second test. The La-min(-) and Glc(min) were determined considering the lowest [La-] and [Glc](b) during the third test. No differences were observed (P < 0.05) and high correlations were obtained between the velocities at IAT [283 (SD 19) and IGT 281 (SD 21)m. min(-1); r = 0.096; P < 0.001] and between La,, [285 (SD 21)] and Glc(min) [287 (SD 20) m. min(-1) = 0.77; P < 0.05]. During ET, the [La-](b) reached 5.0 (SD 1.1) and 5.3 (SD 1.0) mmol 1(-1) at 20 and 30 min, respectively (P > 0.05). We concluded that for these subjects it was possible to evaluate the aerobic capacity by IGT and Glc(min), as well as by IAT and La-min(-).

Holographic recording in [Sb(Po-3)(3)](n)-Sb2O3 glassy films by photoinduced volume and refraction index changes

Glassy films of 0.2[Sb(PO3)(3)]-0,8Sb(2)O(3) with 0.8 mum-thickness were deposited on quartz substrates by electron beam evaporation. A contraction in the film thickness (photoinduced decrease in volume) and photobleaching effect associated with a decrease of up to 25% in the index of refraction has been observed in the films after irradiation near the bandgap (3.89 eV), using the 350.7 nm (3.54 eV) Kr+ ion laser line with 2.5 W/cm(2) for 30 min. A loss of 30% in the phosphorus concentration was measured by wavelength dispersive X-ray microanalysis in the film after laser irradiation with 5.0 W/cm(2) for 1.0 h. These photoinduced changes in the samples are dependent on the power density and intensity profile of the laser beam. Using a Lloyd's mirror setup for continuous wave holography it was possible to record holographic gratings with period from 500 nm up to 20 mum and depth profile of similar to50 nm in the films after laser irradiation with 5.0 W/cm(2) for 1 h. Real-time diffraction efficiency measurements have shown that ultraviolet irradiation induces first a refractive index grating formation, and after this, the photocon traction effect takes place generating an irreversible relief grating. Diffraction efficiency up to 10% was achieved for the recorded gratings. 3D-refraction index measurements and atomic force microscopy images are presented. (C) 2004 Elsevier B.V. All rights reserved.

Relativistic deformed mean-field calculation of binding energy differences of mirror nuclei

Binding energy differences of mirror nuclei for A = 15, 17, 27, 29, 31, 33, 39 and 41 are calculated in the framework of relativistic deformed mean-field theory. To fully include the effects of the polarization of the nuclear core due to the extra particle or hole, the spatial components of the vector meson fields and the photon are taken into account in a self-consistent manner. The calculated binding energy differences are systematically smaller than the experimental values and lend support to the existency of the Okamoto-Nolen-Schiffer anomaly found decades ago in nonrelativistic calculations, For the majority of the nuclei studied, however, the results are such that the anomaly is significantly smaller than the one obtained within state-of-the-art nonrelativistic calculations.

Photoinduced effect in Ga-Ge-S based thin films

Glassy films of Ga10Ge25S65 with 4 mu m thickness were deposited on quartz substrates by electron beam evaporation. Photoexpansion (PE) (photoinduced increase in volume) and photobleaching (PB) (blue shift of the bandgap) effects have been examined. The exposed areas have been analyzed using perfilometer and an expansion of 1.7 mu m (Delta V/V approximate to 30%) is observed for composition Ga10Ge25S65 exposed during 180 min and 3 mW/cm(2) power density. The optical absorption edge measured for the film Ge25Ga10S65 above and below the bandgap show that the blue shift of the gap by below bandgap photon illumination is considerable higher (Delta E-g = 440 meV) than Delta E-g induced by above bandgap illumination (Delta E-g = 190 meV). The distribution of the refraction index profile showed a negative change of the refraction index in the irradiated samples (Delta n = -0.6). The morphology was examined using a scanning electron microscopy (SEM). The chemical compositions measured using an energy dispersive analyzer (EDX) indicate an increase of the oxygen atoms into the irradiated area. Using a Lloyd's mirror setup for continuous wave holography it was possible to record holographic gratings using the photoinduced effects that occur in them. Diffraction efficiency up to 25% was achieved for the recorded gratings and atomic force microscopy images are presented. (c) 2005 Elsevier B.V. All rights reserved.

Paper-based diffusive gradients in thin films technique coupled to energy dispersive X-ray fluorescence spectrometry for the determination of labile Mn, Co, Ni, Cu, Zn and Pb in river water

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

Study of plasma immersion ion implantation into silicon substrate using magnetic mirror geometry

The effect of magnetic field enhanced plasma immersion ion implantation (PIII) in silicon substrate has been investigated at low and high pulsed bias voltages. The magnetic field in magnetic bottle configuration was generated by two magnetic coils installed outside the vacuum chamber. The presence of both, electric and magnetic field in PIII creates a system of crossed E x B fields, promoting plasma rotation around the target. The magnetized electrons drifting in crossed E x B fields provide electron-neutral collision. Consequently, the efficient background gas ionization augments the plasma density around the target where a magnetic confinement is achieved. As a result, the ion current density increases, promoting changes in the samples surface properties, especially in the surface roughness and wettability and also an increase of implantation dose and depth. (C) 2012 Elsevier B. V. All rights reserved.

Long-wave and short-wave asymptotics in nonlinear dispersive systems

In this paper we study the interplay between short- and long-space scales in the context of conservative dispersive systems. We consider model systems in (1 + 1) dimensions that admit both long- and short-wavelength solutions in the linear regime. A nonlinear analysis of these systems is constructed, making use of multiscale expansions. We show that the equations governing the lowest order involve only short-wave properties and that the long-wave effects to leading order are determined by a secularity elimination procedure. © 1999 The American Physical Society.