Lysozyme binding to poly(4-vinyl-N-alkylpyridinium bromide)

The adsorption behavior of polycations at ionic strengths (1) ranging from 0.001 to 0.1 onto silicon wafers was studied by means of ellipsometry, contact angle measurements and atomic force microscopy (AFM). Polycations chosen were bromide salts of poly(4-vinylpyridine) N-alkyl quaternized with linear aliphatic chains of 2 and 5 carbon atoms, QPVP-C2 and QPVP-C5, respectively. Under 1 0.001 the reduction of screening effects led to low adsorbed amounts of QPVP-C2 or QPVP-C5 (1.0 +/- 0.1 mg/m(2)), arising from the adsorption of extended chains. Upon increasing l to 0.1, screening effects led to conformational changes of polyelectrolyte chains ill Solution and to higher adsorbed amount values (1.9 +/- 0.2 mg/m(2)). Advancing contact angle theta(a) measurements performed with water drops onto QPVP-C2 and QPVP-C5 adsorbed layers varied from (45 +/- 2)degrees to (50 +/- 5)degrees, evidencing the exposure of both hydrophobic alkyl groups and charged moieties. The adsorption of lysozyme (LYZ) molecules to QPVP-C5 layers was more pronounced than to QPVP-C2 films. Antimicrobial effect of LYZ bound to QPVP-C2 or QPVP-C5 layers or to Si wafers was evaluated with enzymatic assays using Micrococcus luteus as Substrates. The adsorption behavior of QPVP-C2 and QPVP-C5 at the water-air interface was studied by means Of surface tension measurements. Only QPVP-C5 was able to reduce water Surface tension. Mixtures of LYZ and QPVP-C5 were more efficient in reducing Surface tension than pure LYZ solution, evidencing co-adsorption at liquid-air interface. Moreover, antimicrobial action observed for mixtures of LYZ and QPVP-C5 was more pronounced than that measured for pure LYZ. Hydrophobic interaction between LYZ and QPVP-C5 ill Solution seems to drive the binding and to preserve LYZ secondary structure. (c) 2008 Elsevier Inc. All rights reserved.

Cassava wastewater as a substrate for the simultaneous production of rhamnolipids and polyhydroxyalkanoates by Pseudomonas aeruginosa

Glycerol, cassava wastewater (CW), waste cooking oil and CW with waste frying oils were evaluated as alternative low-cost carbon substrates for the production of rhamnolipids and polyhydroxyalkanoates (PHAs) by various Pseudomonas aeruginosa strains. The polymers and surfactants produced were characterized by gas chromatography-mass spectrophotometry (MS) and by high-performance liquid chromatography-MS, and their composition was found to vary with the carbon source and the strain used in the fermentation. The best overall production of rhamnolipids and PHAs was obtained with CW with frying oil as the carbon source, with PHA production corresponding to 39% of the cell dry weight and rhamnolipid production being 660 mg l(-1). Under these conditions, the surface tension of the culture decreased to 30 mN m(-1), and the critical micelle concentration was 26.5 mg l(-1). It would appear that CW with frying oil has the highest potential as an alternative substrate, and its use may contribute to a reduction in the overall environmental impact generated by discarding such residues.

Unsaturated Infinite Slope Stability Considering Surface Flux Conditions

A slope stability model is derived for an infinite slope subjected to unsaturated infiltration flow above a phreatic surface. Closed form steady state solutions are derived for the matric suction and degree of saturation profiles. Soil unit weight, consistent with the degree of saturation profile, is also directly calculated and introduced into the analyzes, resulting in closed-form solutions for typical soil parameters and an infinite series solution for arbitrary soil parameters. The solutions are coupled with the infinite slope stability equations to establish a fully realized safety factor function. In general, consideration of soil suction results in higher factor of safety. The increase in shear strength due to the inclusion of soil suction is analogous to making an addition to the cohesion, which, of course, increases the factor of safety against sliding. However, for cohesive soils, the results show lower safety factors for slip surfaces approaching the phreatic surface compared to those produced by common safety factor calculations. The lower factor of safety is due to the increased soil unit weight considered in the matric suction model but not usually accounted for in practice wherein the soil is treated as dry above the phreatic surface. The developed model is verified with a published case study, correctly predicting stability under dry conditions and correctly predicting failure for a particular storm.

The natural force density method for the shape finding of taut structures

This work presents, with the aid of the natural approach, an extension of the force density method for the initial shape finding of cable and membrane structures, which leads to the solution of a system of linear equations. This method, here called the natural force density method, preserves the linearity which characterizes the original force density method. At the same time, it overcomes the difficulties that the original procedure presents to cope with irregular triangular finite element meshes. Furthermore, if this method is applied iteratively in the lines prescribed herewith, it leads to a viable initial configuration with a uniform, isotropic plane Cauchy stress state. This means that a minimal surface for the membrane can be achieved through a succession of equilibrated configurations. Several numerical examples illustrate the simplicity and robustness of the method. (C) 2008 Elsevier B.V. All rights reserved.

Quantification of MgO surface excess on the SnO(2) nanoparticles and relationship with nanostability and growth

In this work, we experimentally showed that the spontaneous segregation of MgO as surface excess in MgO doped SnO(2) nanoparticles plays an important role in the system`s energetics and stability. Using Xray fluorescence in specially treated samples, we quantitatively determined the fraction of MgO forming surface excess when doping SnO(2) with several different concentrations and established a relationship between this amount and the surface energy of the nanoparticles using the Gibbs approach. We concluded that the amount of Mg ions on the surface was directly related to the nanoparticles total free energy, in a sense that the dopant will always spontaneously distribute itself to minimize it if enough diffusion is provided. Because we were dealing with nanosized particles, the effect of MgO on the surface was particularly important and has a direct effect on the equilibrium particle size (nanoparticle stability), such that the lower the surface energy is, the smaller the particle sizes are, evidencing and quantifying the thermodynamic basis of using additives to control SnO(2) nanoparticles stability. (C) 2010 Elsevier B.V. All rights reserved.

Acidity and Aluminum Speciation as Affected by Surface Liming in Tropical No-Till Soils

Aluminum toxicity is one of the major soil factors limiting root growth in acidic soils. Because of the increase in organic matter content in the upper few centimeters of soils under no-till systems (NTS), most Al in soil solution may be complexed to dissolved organic C (DOC), thus decreasing its bioavailability. The aim of this study was to evaluate the effects of surface liming on Al speciation in soil solution in Brazilian sites under NTS. Field experiments were performed in two regions with contrasting climates and levels of soil acidity: Rondonopolis, Mato Grosso State, on a Rhodic Haplustox, and Ponta Grossa, Parana State, on a Typic Hapludox. The treatments consisted of a control and three lime rates, surface applied to raise the base saturation to 50, 70, and 90%. Soil solution was obtained at soil water equilibrium (1:1 w/w soil/water ratio). The effects of surface liming on soil chemical attributes and on the composition of the soil solution were dependent on weather conditions, time under NTS, and soil weathering. Most Al in soil solution was complexed to DOC, representing about 70 to 80% of the total Al at pH <5.0, and about 30 to 4096 at pH >5.0. Under pH 5.5, the results were closely correlated with the solubility line for amorphous Al. Organic complexes may control Al(3+) release into soil solution at pH <5.5. Results suggest that in areas under NTS for a long period of time, Al toxicity might decrease due to its complexation to high-molecular-weight organic compounds.

Podzolization as a deferralitization process: dynamics and chemistry of ground and surface waters in an Acrisol-Podzol sequence of the upper Amazon Basin

Hydrochemical processes involved in the development of hydromorphic Podzols are a major concern for the upper Amazon Basin because of the extent of the areas affected by such processes and the large amounts of organic carbon and associated metals exported to the rivers. The dynamics and chemical composition of ground and surface waters were studied along an Acrisol-Podzol sequence lying in an open depression of a plateau. Water levels were monitored along the sequence over a period of 2 years by means of piezometers. Water was sampled in zero-tension lysimeters for groundwater and for surface water in the drainage network of the depression. The pH and concentrations of organic carbon and major elements (Si, Fe and Al) were determined. The contrasted changes reported for concentrations of Si, organic carbon and metals (Fe, Al) mainly reflect the dynamics of the groundwater and the weathering conditions that prevail in the soils. Iron is released by the reductive dissolution of Fe oxides, mostly in the Bg horizons of the upslope Acrisols. It moves laterally under the control of hydraulic gradients and migrates through the iron-depleted Podzols where it is exported to the river network. Aluminium is released from the dissolution of Al-bearing minerals (gibbsite and kaolinite) at the margin of the podzolic area but is immobilized as organo-Al complexes in spodic horizons. In downslope positions, the quick recharge of the groundwater and large release of organic compounds lead to acidification and a loss of metals (mainly Al), previously stored in the Podzols.

Tension band wire fixation for valgus osteotomies of the proximal femur: A biomechanical study of three configurations of fixation

Background. A variety of techniques can be used to achieve stabilization of femoral valgus osteotomies in children, but what is lacking is a versatile fixation system that associates stability and versatility at different ages and for different degrees of deformity. Methods. Mechanical tests of three configurations used to fix femoral valgus osteotomies, based oil the tension band wire principle, were carried out. A 30 degrees wedge valgus osteotomy was performed at the subtrochanteric level in 60 swine femurs and fixed with three different systems. In Group 1, two Kirschner wires (K wire) were introduced from the tip of the greater trochanter to the medial cortex, crossing the osteotomy. A flexible steel wire was anchored to the K wires into holes in the lateral cortex and tightened to form a tension band. The same setup was used in Group 2, but two additional smooth K wires were inserted into the lateral surface of the greater trochanter and driven to the femoral head with the distal extremities bent and tied around tile bone shaft. In Group 3, the fixation was similar to that in Group 2, but tile ascending K wires were introduced below the osteotomy level, crossing the osteotonly. Mechanical tests in bending-compression and torsion were used to access the stability. Findings. The torsional relative stiffness was 116% greater for Group 3 (0.27 N m/degree) and no significant difference was found between Group 1 (0.10 N m/degree) and Group 2 (0.12 N m/degree). The average torque was 103% higher for Group 3 (1.86 N m). Stiffness in bending-compression was significantly higher in Group 3 (508 x 10(3) N/m) than in Group 1 (211 x 10(3) N/m) and Group 2 (219 x 10(3) N/m). Interpretation. Fixation as used in Group 3 was significantly more stable, both in torsion and bending-compression tests, than tile other two techniques. (c) 2007 Elsevier Ltd. All rights reserved.

Coupling of composite resin cements to quartz fiber posts: A comparison of industrial and ""chairside"" treatments of the post surface

Purpose: To evaluate the influence of surface treatments on microtensile bond strength of luting resin cements to fiber posts. Materials and Methods: Forty-two quartz fiber posts (Light Post, RTD) were divided into 7 groups (n = 6) according to the surface treatment. I and 11: experimental patented industrial treatment consisting of zirconium oxide coating and silanization (RTD); III: industrial treatment followed by adhesive application (XPBond, Dentsply Caulk); IV: adhesive (XPBond); V: adhesive (Prime&Bond NT, Dentsply Caulk); VI: silane (Calibra Silane, Dentsply Caulk); VII: no treatment. Adhesives were used in the self-curing mode. Two cements (Sealbond, RTD - group 1, and Calibra, Dentsply Caulk - groups 11 to VII) were applied on the posts to produce cylindrical specimens. Post/cement interfaces were evaluated under SEM. The surface of the industrially coated posts was examined using energy dispersive analysis by x-ray. Cylinders were cut to obtain microtensile sticks that were loaded in tension at a crosshead speed of 0.5 mm/min until failure. Statistical analysis was performed using Kruskal-Wallis analysis of variance followed by Dunn`s multiple range test for post-hoc comparisons (p < 0.05). Weibull analysis was also performed. Results: The post/cement bond strength was significantly higher on fiber posts treated industrially (I: 23.14 +/- 8.05 MPa; II: 21.56 +/- 7.07 MPa; III: 22.37 +/- 7.00 MPa) or treated with XPBond adhesive (IV: 21.03 +/- 5.34 MPa) when compared to Prime&Bond NT application (V: 14.05 +/- 5.06 MPa), silanization (VI: 6.31 +/- 4.60 MPa) or no treatment (VII: 4.62 +/- 4.31) of conventional fiber posts (p < 0.001). Conclusion: The experimental industrial surface treatment and the adhesive application enhanced fiber post to resin cement interfacial strength. Industrial pretreatment may simplify the clinical luting procedure.

Response surface methodology applied to the analysis of rice bran oil extraction process with ethanol

P>Vegetable oils can be extracted using ethanol as solvent. The main goal of this work was to evaluate the ethanol performance on the extraction process of rice bran oil. The influence of process variables, solvent hydration and temperature was evaluated using the response surface methodology, aiming to maximise the soluble substances and gamma-oryzanol transfer and minimise the free fatty acids extraction and the liquid content in the underflow solid. It can be noted that oil solubility in ethanol was highly affected by the water content. The free fatty acids extraction is improved by increasing the moisture content in the solvent. Regarding the gamma-oryzanol, it can be observed that its extraction is affected by temperature when low level of water is added to ethanol. On the other hand, the influence of temperature is minimised with high levels of water in the ethanol.

Temperature (over) compensation in an oscillatory surface reaction

Biological rhythms are regulated by homeostatic mechanisms that assure that physiological clocks function reliably independent of temperature changes in the environment. Temperature compensation, the independence of the oscillatory period on temperature, is known to play a central role in many biological rhythms, but it is rather rare in chemical oscillators. We study the influence of temperature on the oscillatory dynamics during the catalytic oxidation of formic acid on a polycrystalline platinum electrode. The experiments are performed at five temperatures from 5 to 25 degrees C, and the oscillations are studied under galvanostatic control. Under oscillatory conditions, only non-Arrhenius behavior is observed. Overcompensation with temperature coefficient (q(10), defined as the ratio between the rate constants at temperature T + 10 degrees C and at T) < I is found in most cases, except that temperature compensation with q(10) approximate to I predominates at high applied currents. The behavior of the period and the amplitude result from a complex interplay between temperature and applied current or, equivalently, the distance from thermodynamic equilibrium. High, positive apparent activation energies were obtained under voltammetric, nonoscillatory conditions, which implies that the non-Arrhenius behavior observed under oscillatory conditions results from the interplay among reaction steps rather than, from a weak temperature dependence of the individual steps.

Validation of an experimental polyurethane model for biomechanical studies on implant supported prosthesis - tension tests

OBJECTIVES: The complexity and heterogeneity of human bone, as well as ethical issues, frequently hinder the development of clinical trials. The purpose of this in vitro study was to determine the modulus of elasticity of a polyurethane isotropic experimental model via tension tests, comparing the results to those reported in the literature for mandibular bone, in order to validate the use of such a model in lieu of mandibular bone in biomechanical studies. MATERIAL AND METHODS: Forty-five polyurethane test specimens were divided into 3 groups of 15 specimens each, according to the ratio (A/B) of polyurethane reagents (PU-1: 1/0.5, PU-2: 1/1, PU-3: 1/1.5). RESULTS: Tension tests were performed in each experimental group and the modulus of elasticity values found were 192.98 MPa (SD=57.20) for PU-1, 347.90 MPa (SD=109.54) for PU-2 and 304.64 MPa (SD=25.48) for PU-3. CONCLUSION: The concentration of choice for building the experimental model was 1/1.

Effect of biofunctionalized implant surface on osseointegration: a histomorphometric study in dogs

Among the different properties that influence bone apposition around implants, the chemical or biochemical composition of implant surface may interfere on its acceptance by the surrounding bone. The aim of this study was to investigate if a biofunctionalization of implant surface influences the bone apposition in a dog model and to compare it with other surfaces, such as a microstructured created by the grit-blasting/acid-etching process. Eight young adult male mongrel dogs had the bilateral mandibular premolars extracted and each one received 6 implants after 12 weeks, totaling 48 implants in the experiment. Four groups of implants were formed with the same microrough topography with or without some kind of biofunctionalization treatment. After histomorphometric analysis, it was observed that the modified microstructured surface with a "low concentration of the bioactive peptide" provided a higher adjacent bone density (54.6%) when compared to the other groups (microstructured + HA coating = 46.0%, microstructured only = 45.3% and microstructured + "high concentration of the bioactive peptide" = 40.7%), but this difference was not statistically significant. In conclusion, biofunctionalization of the implant surface might interfere in the bone apposition around implants, especially in terms of bone density. Different concentrations of bioactive peptide lead to different results.

Assessment in vitro of brushing on dental surface roughness alteration by laser interferometry

Noncarious cervical lesions (NCCLs) are considered to be of multifactorial origin, normally associated with inadequate brushing. This study assessed the influence in vitro of simulated brushing on NCCL formation. Fifteen human premolars were submitted to brushing in the cementoenamel junction region, using hard-, medium- and soft-bristled brushes associated with a toothpaste of medium abrasiveness under a 200 g load, at a speed of 356 rpm for 100 minutes. The surface topography of the region was analyzed before and after brushing, by means of a laser interferometer, using "cut-off" values of 0.25 and considering roughness values in mm. The initial roughness (mm) results for dentin (D / bristle consistency: 1 - soft, 2 - medium and 3 - hard) were as follows: (D1) 1.25 ± 0.45; (D2) 1.12 ± 0.44; (D3) 1.05 ± 0.41. For enamel (E / bristle consistency: 1 - soft, 2 - medium and 3 - hard), the initial results were: (E1) 1.18 ± 0.35; (E2) 1.32 ± 0.25; (E3) 1.50 ± 0.38. After brushing, the following were the values for dentin: (D1) 2.32 ± 1.99; (D2) 3.30 ± 0.96; (D3) Over 500. For enamel, the values after brushing were: (E1) 1.37 ± 0.31; (E2) 2.15 ± 0.90; (E3) 1.22 ± 0.47. Based on the results of the ANOVA and Tukey statistical analyses (a = .05) it was concluded that soft, medium and hard brushes are not capable of abrading enamel, whereas dentin showed changes in surface roughness by the action of medium- and hard-bristled brushes.

Effect of different cleansers on the surface of removable partial denture

Removable partial dentures (RPD) demand specific hygienic cleaning and the combination of brushing with immersion in chemical solutions has been the most recommended method for control of biofilm. However, the effect of the cleansers on metallic components has not been widely investigated. This study evaluated the effect of different cleansers on the surface of RPD. Five disc specimens (12 mm x 3 mm metallic disc centered in a 38 x 18 x 4 mm mould filled with resin) were obtained for each experimental situation: 6 solutions [Periogard (PE), Cepacol (CE), Corega Tabs (CT), Medical Interporous (MI), Polident (PO), 0.05% sodium hypochlorite (NaOCl), and distilled water (DW) control] and 2 Co-Cr alloys [DeguDent (DD) and VeraPDI (VPDI)] were used for each experimental situation. A 180-day immersion was simulated and the measurements of roughness (Ra, µm) of metal and resin were analyzed using 2-way ANOVA and Tukey’s test. The surface changes and tarnishes were examined with a scanning electronic microscopy (SEM). In addition, energy dispersive x-ray spectrometry (EDS) analysis was carried out at representative areas. Visually, NaOCl and MI specimens presented surface tarnishes. The roughness of materials was not affected by the solutions (p>0.05). SEM images showed that NaOCl and MI provided surface changes. EDS analysis revealed the presence of oxygen for specimens in contact with both MI and NaOCl solutions, which might suggest that the two solutions promoted the oxidation of the surfaces, thus leading to spot corrosion. Within the limitations of this study, it may be concluded that the NaOCl and MI may not be suitable for cleaning of RPD.