Polymer light emitting devices with Langmuir Blodgett (LB) films of a polyfluorene derivative

Polyfluorenes are promising materials for the emitting layer of polymer light emitting devices (PLEDs) with blue emission. In this work, we report on PLEDs fabricated with Langmuir-Blodgett (LB) films of a polyfluorene derivative, namely poly(9,9-di-hexylfluorenediyl vinylene-alt-1,4-phenylenevinylene) (PDHF-PV). Y-type LB films were transferred onto ITO substrates at a surface pressure of 35 mN m-1 and with dipping speed of 3 mm min -1. A thin aluminum layer was evaporated on top of the LB film, thus yielding a sandwich structure (ITO/PDHF-PV(LB)/Al). Current-voltage (I vs V) measurements indicate that the device displays a classical behavior of a rectifying diode. The threshold value is approximately 5 V, and the onset for visible light emission occurs at ca. 10 V. From the a.c. electrical responses we infer that the active layer has a typical behavior of PLEDs where the real component of ac conductivity obeys a power-law with the frequency. Cole-Cole plots (Im(Z) vs. Re(Z)) for the device exhibit a series of semicircles, the diameter of which decreases with increasing forward bias. This PLED structure is modeled by a parallel resistance and capacitance combination, representing the dominant mechanisms of charge transport and polarization in the organic layer, in series with a resistance representing the ITO contact. Overall, the results presented here demonstrate the feasibility of LEDs made with LB films of PDHF-PV.

Eucalyptus ESTs corresponding to the protoporphyrinogen IX oxidase enzyme related to the synthesis of heme, chlorophyll, and to the action of herbicides

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

The effect of adhesive systems on the pullout strength of a fiberglass-reinforced composite post system in bovine teeth

Purpose: To evaluate the pullout strength of a glass fiber-reinforced composite post (glass FRC) cemented with three different adhesive systems and one resin cement. The null hypothesis was that pullout strengths yielded by the adhesive systems are similar. Materials and Methods: Thirty bovine teeth were selected. The size of the specimens was standardized at 16 mm by sectioning off the coronal portion and part of the root. The specimens were divided into three groups, according to the adhesive system, which were applied following the manufacturers' instructions: G1, ScotchBond Multi-Purpose Plus; G2, Single Bond; G3, Tyrian SPE/One-Step Plus. The glass FRCs (Reforpost) were etched with 37% H3PO4 for 1 min and silanized (Porcelain Primer). Thereafter, they were cemented with the dual resin cement En-Force. The specimens were stored for 24 h, attached to an adapted device, and submitted to the pullout test in a universal testing machine (1 mm/min). The data were submitted to the one-way ANOVA and Tukey's test (α = 0.05). Results: G1 (30.2 ± 5.8 Kgf) displayed the highest pullout strength (p < 0.001) when compared to G2 (18.6 ± 5.8 Kgf) and G3 (14.3 ± 5.8 Kgf), which were statistically similar. Analysis of the specimens revealed that all failures occurred between the adhesive system and the root dentin (pullout of the post cement), regardless of group. Conclusion: The multiple-bottle, total-etch adhesive system provided higher pullout strength of the glass FRC when compared to the single-bottle, total-etch, and single-step self-etching adhesive systems. The null hypothesis was rejected (p < 0.001).

Fatigue resistance of the bond of a glass-infiltrated alumina ceramic to human dentin

Purpose: To evaluate the fatigue resistance of the bond between dentin and glass-infiltrated alumina ceramic, using different luting protocols. Materials and Methods: The null hypothesis is that the fatigue resistance varies with the luting strategy. Forty blocks of In-Ceram Alumina were prepared, and one surface of each block was abraded with 110-μm aluminum oxide particles. Then, the blocks were luted to flat dentin surfaces of 40 human third molars, using 4 different luting strategies (luting system [LS]/ceramic surface conditioning [CSC]) (n=10): (G1) [LS] RelyX-Unicem/[CSC] airborne abrasion with 110-μm Al2O3 particles; (G2) [LS] One-Step + Duo-Link (bis-GMA-based resin)/[CSC] etching with 4% hydrofluoric acid + silane agent; (G3) [LS] ED-Primer + Panavia F (MDP-based resin)/[CSC] Al2O 3; (G4) [LS] Scotchbond1+RelyX-ARC (bis-GMA-based resin)/[CSC] chairside tribochemical silica coating (air abrasion with 30-μm SiO x particles + silane). After 24 h of water storage at 37°C, the specimens were subjected to 106 fatigue cycles in shear with a sinusoidal load (0 to 21 N, 8 Hz frequency, 37°C water). A fatigue survivor score was given, considering the number of the fatigue cycles until fracture. The failure modes of failed specimens were observed in a SEM. Results: G3 (score = 5.9, 1 failure) and G4 (score = 6, no failures) were statistically similar (p = 0.33) and had significantly higher fatigue resistance than G1 (score = 3.9, 5 failures) and G2 (score = 3.7, 6 failures) (p < 0.03). SEM analysis of fractured specimens of G1 and G2 showed that almost all the failures were between ceramic and cement. Conclusion: The MDP-based resin cement + sandblasting with Al2O3 particles (G3) and bis-GMA-based resin cement + tribochemical silica coating (G4), both using the respective dentin bonding systems, were the best luting protocols for the alumina ceramic. The null hypothesis was confirmed.

Dispersed lipid liquid crystalline phases stabilized by a hydrophobically modified cellulose

Aqueous dispersions of monoolein (MO) with a commercial hydrophobically modified ethyl hydroxyethyl cellulose ether (HMEHEC) have been investigated with respect to the morphologies of the liquid crystalline nanoparticles. Only very low proportions of HMEHEC are accepted in the cubic and lamellar phases of the monoolein-water system. Due to the broad variation of composition and size of the commercial polymer, no other single-phase regions were found in the quasi-ternary system. Interactions of MO with different fractions of the HMEHEC sample induced the formation of lamellar and reversed hexagonal phases, identified from SAXD, polarization microscopy, and cryogenic TEM examinations. In excess water (more than 90 wt %) coarse dispersions are formed more or less spontaneously, containing particles of cubic phase from a size visible by the naked eye to small particles observed by cryoTEM. At high polymer/MO ratios, vesicles were frequently observed, often oligo-lamellar with inter-lamellar connections. After homogenization of the coarse dispersions in a microfluidizer, the large particles disappeared, apparently replaced by smaller cubic particles, often with vesicular attachments on the surfaces, and by vesicles or vesicular particles with a disordered interior. At the largest polymer contents no proper cubic particles were found directly after homogenization but mainly single-walled defected vesicles with a peculiar edgy appearance. During storage for 2 weeks, the dispersed particles changed toward more well-shaped cubic particles, even in dispersions with the highest polymer contents. In some of the samples with low polymer/MO ratio, dispersed particles of the reversed hexagonal type were found. A few of the homogenized samples were freeze-dried and rehydrated. Particles of essentially the same types, but with a less well-developed cubic character, were found after this treatment. © 2007 American Chemical Society.

Microtensile bond strength of a repair composite to leucite-reinforced feldspathic ceramic

The purpose of this study was to evaluate the microtensile bond strength of a repair composite resin to a leucite-reinforced feldspathic ceramic (Omega 900, VITA) submitted to two surface conditionings methods: 1) etching with hydrofluoric acid + silane application or 2) tribochemical silica coating. The null hypothesis is that both surface treatments can generate similar bond strengths. Ten ceramic blocks (6x6x6 mm) were fabricated and randomly assigned to 2 groups (n=5), according to the conditioning method: G1- 10% hydrofluoric acid application for 2 min plus rinsing and drying, followed by silane application for 30 s; G2- airborne particle abrasion with 30 μm silica oxide particles (CoJet-Sand) for 20 s using a chairside air-abrasion device (CoJet System), followed by silane application for 5 min. Single Bond adhesive system was applied to the surfaces and light cured (40 s). Z-250 composite resin was placed incrementally on the treated ceramic surface to build a 6x6x6 mm block. Bar specimens with an adhesive area of approximately 1 ± 0.1 mm2 were obtained from the composite-ceramic blocks (6 per block and 30 per group) for microtensile testing. No statistically significant difference was observed between G1 (10.19 ± 3.1 MPa) and G2 (10.17 ± 3.1 MPa) (p=0.982) (Student's t test; á = 0.05). The null hypothesis was, therefore, accepted. In conclusion, both surface conditioning methods provided similar microtensile bond strengths between the repair composite resin and the ceramic. Further studies using long-term aging procedures should be conducted.

Surface conditioning of a composite used for inlay/onlay restorations: Effect on μTBS to resin cement

Purpose: To assess the effect of the composite surface conditioning on the microtensile bond strength of a resin cement to a composite used for inlay/onlay restorations. Materials and Methods: Forty-two blocks (6 × 6 × 4 mm) of a microfilled composite (Vita VMLC) were produced and divided into 3 groups (N = 14) by composite surface conditioning methods: Gr1 - etching with 37% phosphoric acid, washing, drying, silanization; Gr2 - air abrasion with 50-l̀m Al2O3 particles, silanization; Gr3 - chairside tribochemical silica coating (CoJet System), silanization. Single-Bond (one-step adhesive) was applied on the conditioned surfaces and the two resin blocks treated with the same method were cemented using RelyX ARC (dual-curing resin cement). The specimens were stored for 7 days in water at 37°C and then sectioned to produce nontrimmed beam samples, which were submitted to microtensile bond strength testing (μTBS). For statistical analysis (one-way ANOVA and Tukey's test, · = 0.05), the means of the beam samples from each luted specimen were calculated (n = 7). Results: μTBS values (MPa) of Gr2 (62.0 ± 3.9a) and Gr3 (60.5 ± 7.9a) were statistically similar to each other and higher than Gr1 (38.2 ± 8.9b). The analysis of the fractured surfaces revealed that all failures occurred at the adhesive zone. Conclusion: Conditioning methods with 50-l̀m Al2O3 or tribochemical silica coating allowed bonding between resin and composite that was statistically similar and stronger than conditioning with acid etching.

A new antifungal phenolic glycoside derivative and iridoids and lignans from Alibertia sessilis (Vell.) K. Schum. (Rubiaceae)

A new antifungal phenolic glycoside, 3,4,5-trimethoxyphenyl-1-O-β-D- (5-O-syringoyl)-apiofuranosyl-(1→6)-β-D-glucopyranoside (1), together with four known iridoids, geniposidic acid (2), geniposide (3), 6α-hydroxygeniposide (4) and 6β-hydroxygeniposide (5); two lignans, (+)-lyoniresinol-3α-O-β-D-glucopyranoside (6), (-)-lyoniresinol- 3α-O-β-D-glucopyranoside (7); and two phenolic acids, chlorogenic (8) and salicylic acids (9) and D-manitol (10), were isolated from the ethanolic extract of the stems of Alibertia sessilis. Structures of 1 and of the known compounds were determined by spectroscopic analysis. All compounds isolated were evaluated for their antifungal activities against two phytopathogenic fungi strains Cladosporium cladosporioides and C. sphaerospermum by direct bioautography. ©2007 Sociedade Brasileira de Química.

Gravitational field of a straight cosmic string in the framework of higher-derivative gravity

The gravitational properties of a straight cosmic string are studied in the linear approximation of higher-derivative gravity. These properties are shown to be very different from those found using linearized Einstein gravity: there exists a short range gravitational (anti-gravitational) force in the nonrelativistic limit; in addition, the deflection angle of a light ray moving in a plane orthogonal to the string depends on the impact parameter. © 2008 World Scientific Publishing Company.

Longitudinal bond strength evaluation using the deproteinized dentin technique

This study evaluated bond strength to dentin as a result of storage time for conventional adhesive systems (with or without collagen) that had been deproteinized with 10% sodium hypochlorite (NaOCl). For this study, 72 human molars were sectioned in a mesiodistal axial plane and embedded in acrylic resin; at that point, the vestibular and lingual surfaces were worn down with abrasive paper. Acid etching was performed for 15 seconds (using 37% phosphoric acid) and the specimens were divided into 12 groups (n = 6), depending on the adhesive system used, the dentin treatment performed, and the length of evaluation (24 hours or six months). A resin composite was inserted over the prepared area with the aid of a metal matrix. Following a mechanical shear test, fractured surfaces were analyzed by stereomicroscope and the data were submitted to ANOVA and Tukey's test. It was concluded that the dentin deproteinization treatment with 10% NaOCI improved the bond strength in five of the six groups. The bond strength after 24 hours was significantly higher than the bond strength measured after six months. Of the three adhesive systems tested in this study, DenTASTIC UNO demonstrated the lowest bond strength.

LMI-based digital redesign of linear time-invariant systems with state-derivative feedback

A simple method for designing a digital state-derivative feedback gain and a feedforward gain such that the control law is equivalent to a known and adequate state feedback and feedforward control law of a digital redesigned system is presented. It is assumed that the plant is a linear controllable, time-invariant, Single-Input (SI) or Multiple-Input (MI) system. This procedure allows the use of well-known continuous-time state feedback design methods to directly design discrete-time state-derivative feedback control systems. The state-derivative feedback can be useful, for instance, in the vibration control of mechanical systems, where the main sensors are accelerometers. One example considering the digital redesign with state-derivative feedback of a helicopter illustrates the proposed method. © 2009 IEEE.

Effect of light energy density on conversion degree and hardness of dual-cured resin cement

This study evaluated the effect of different light energy densities on conversion degree (CD) and Knoop hardness number (KHN) of RelyX ARC (RLX) resin cement. After manipulation according to the manufacturer's instructions, RLX was inserted into a rubber mold (0.8 mm X 5 mm) and covered with a Mylar strip. The tip of the lightcuring unit (LCU) was positioned in contact with the Mylar surface. Quartz-tungsten-halogen (QTH) and light-emitting diode (LED) LCUs with light densities of 10, 20 and 30 J/cm2 were used to light-cure the specimens. After light curing, the specimens were stored dry in lightproof containers at 37°C. After 24 hours, the CD was analyzed by FT-Raman and, after an additional 24-hours, samples were submitted to Knoop hardness testing. The data of the CD (%) and KHN were submitted to two-way ANOVA and the Tukey's test (α=0.05). QTH and LED were effective light curing units. For QTH, there were no differences among the light energy densities for CD or KHN. For LED, there was a significant reduction in CD with the light energy density set at 10 J/cm2. KHN was not influenced by the lightcuring unit and by its light energy density. © Operative Dentistry.

Hypercomplex geometric derivative from a Cauchy-like integral formula

The derivation and integration of hipercomplex functions have been investigated along the years, see [7], [11], [14]. The main purpose of this brief article is to give a geometrical interpretation for quaternionic derivatives, based on a recent determination of a Cauchy-like formula for quaternions, see [3]. © 2011 Academic Publications.

Absence of genotoxic effects of the coumarin derivative 4-methylesculetin in vivo and its potential chemoprevention against doxorubicin-induced DNA damage

4-Methylesculetin (4-ME) is a synthetic derivative of coumarin that displays a potent reactive oxygen species (ROS) scavenger and metal chelating agent and therefore has been produced to help reduce the risk of human disease. The main objective of this study was to investigate the in vivo genotoxicity of 4-ME and initially to verify its potential antigenotoxicity on doxorubicin (DXR)-induced DNA damage. Different doses of 4-ME (500, 1000 and 2000mgkg -1 body weight) were administered by gavage only or with a simultaneous intraperitoneal (i.p.) injection of DXR (80mgkg -1). The following endpoints were analyzed: DNA damage in peripheral blood, liver, bone marrow, brain and testicle cells according to an alkaline (pH>13) comet assay and micronucleus induction in bone marrow cells. Cytotoxicity was assessed by scoring polychromatic (PCE) and normochromatic (NCE) erythrocytes (PCE/NCE ratio). No differences were observed between the negative control and the groups treated with a 4-ME dose for any of the endpoints analyzed, indicating that it lacks genotoxic and cytotoxic effects. Moreover, 4-ME demonstrated protective effects against DXR-induced DNA damage at all tested doses and in all analyzed cell types, which ranged from 34.1% to 93.3% in the comet assay and 54.4% to 65.9% in the micronucleus test.

Degree of conversion of polymer-matrix composite assessed by FTIR analysis

Aims and objectives: The behavior of polymer-matrix composite is dependent on the degree of conversion. The aim of this study was to evaluate the degree of conversion of two resin cements following storage at 37°C immediately, 24 and 48 hours, and 7 days after light-curing by FTIR analysis. Materials and methods: The specimens were made in a metallic mold and cured with blue LED with power density of 500 mW/cm2 for 30 seconds. The specimens were pulverized, pressed with KBr and analyzed with FTIR following storage times. Statistical analysis used: ANOVA (two-way) and Tukey's post hoc. Results: To the polymer-matrix composites between 24 and 48 hours does not show a significant increase (p > 0.05), however, the highest values were found after 7 days. Conclusion: The polymer-matrix composites used in this study showed similarity on the degree of conversion and increased of according to the time of storage.