Modeling technique for honeycomb FRP deck bridges via finite elements

Honeycomb structures have been used in different engineering fields. In civil engineering, honeycomb fiber-reinforced polymer (FRP) structures have been used as bridge decks to rehabilitate highway bridges in the United States. In this work, a simplified finite-element modeling technique for honeycomb FRP bridge decks is presented. The motivation is the combination of the complex geometry of honeycomb FRP decks and computational limits, which may prevent modeling of these decks in detail. The results from static and modal analyses indicate that the proposed modeling technique provides a viable tool for modeling the complex geometry of honeycomb FRP bridge decks. The modeling of other bridge components (e.g., steel girders, steel guardrails, deck-to-girder connections, and pier supports) is also presented in this work.

Study of copper electrodeposition mechanism from a strike alkaline bath prepared with 1-hydroxyethane-1,1-diphosphonic acid through cyclic voltammetry technique

Copper strike baths are extensively used in metal plating industry as they present the ability to plate adherent copper layers on less-noble metal substrates such as steel and zinc die castings. However, in the last few years, due to environmental controls and safety policies for operators, the plating industry has been interested in replacing the toxic cyanide copper strike baths with environmentally friendly baths. A broad bibliographic review showed that the published papers, referring to the new nontoxic copper strike baths, are patents, having little or no emphasis focused on electrodeposition mechanisms. Therefore, it was decided to study the copper electrodeposition mechanism from a strike alkaline bath prepared with one of the most nontoxic chelating agents cited in many patents which is the 1-hydroxyethane-1,1-diphosphonic acid, known as HEDP. This acid forms very stable water soluble complexes with Cu(2+) ions, thus cupric sulfate was used for preparing the plating bath. The results obtained through a cyclic voltammetry technique showed that Cu(2+) ion reduction to Cu from an HEDP electrodeposition bath occurs via a direct reduction reaction without a formation of Cu(+) intermediates. (C) 2010 Elsevier Ltd. All rights reserved.

Animated solid model of the lung constructed from unsynchronized MR sequential images

This work discusses a 4D lung reconstruction method from unsynchronized MR sequential images. The lung, differently from the heart, does not have its own muscles, turning impossible to see its real movements. The visualization of the lung in motion is an actual topic of research in medicine. CT (Computerized Tomography) can obtain spatio-temporal images of the heart by synchronizing with electrocardiographic waves. The FOV of the heart is small when compared to the lung`s FOV. The lung`s movement is not periodic and is susceptible to variations in the degree of respiration. Compared to CT, MR (Magnetic Resonance) imaging involves longer acquisition times and it is not possible to obtain instantaneous 3D images of the lung. For each slice, only one temporal sequence of 2D images can be obtained. However, methods using MR are preferable because they do not involve radiation. In this paper, based on unsynchronized MR images of the lung an animated B-Repsolid model of the lung is created. The 3D animation represents the lung`s motion associated to one selected sequence of MR images. The proposed method can be divided in two parts. First, the lung`s silhouettes moving in time are extracted by detecting the presence of a respiratory pattern on 2D spatio-temporal MR images. This approach enables us to determine the lung`s silhouette for every frame, even on frames with obscure edges. The sequence of extracted lung`s silhouettes are unsynchronized sagittal and coronal silhouettes. Using our algorithm it is possible to reconstruct a 3D lung starting from a silhouette of any type (coronal or sagittal) selected from any instant in time. A wire-frame model of the lung is created by composing coronal and sagittal planar silhouettes representing cross-sections. The silhouette composition is severely underconstrained. Many wire-frame models can be created from the observed sequences of silhouettes in time. Finally, a B-Rep solid model is created using a meshing algorithm. Using the B-Rep solid model the volume in time for the right and left lungs were calculated. It was possible to recognize several characteristics of the 3D real right and left lungs in the shaded model. (C) 2007 Elsevier Ltd. All rights reserved.

Spectral characteristics of atrial electrograms in sinus rhythm correlates with sites of ganglionated plexuses in patients with paroxysmal atrial fibrillation

Aims To verify whether spectral components of atrial electrograms (AE) during sinus rhythm (SR) correlate with cardiac ganglionated plexus (GP) sites. Methods and results Thirteen patients undergoing atrial fibrillation (AF) ablation were prospectively enrolled. Prior to radio frequency application, endocardial AE were recorded with a sequential point-by-point approach. Electrical stimuli were delivered at 20 Hz, amplitude 100 V, and pulse width of 4 ms. A vagal response was defined as a high-frequency stimulation (HFS) evoked atrioventricular block or a prolongation of RR interval. Spectral analysis was performed on single AE during SR, sampling rate of 1000 Hz, Hanning window. Overall, 1488 SR electrograms were analysed from 186 different left atrium sites, 129 of them corresponding to negative vagal response sites, and 57 to positive response sites. The electrogram duration and the number of deflections were similar in positive and negative response sites. Spectral power density of sites with vagal response was lower between 26 and 83 Hz and higher between 107 and 200 Hz compared with negative response sites. The area between 120 and 170 Hz normalized to the total spectrum area was tested as a diagnostic parameter. Receiver operating characteristic curve analysis demonstrated that an area120-170/area(total) value >0.14 identified vagal sites with 70.9% sensitivity and 72.1% specificity. Conclusion Spectral analysis of AE during SR in sites that correspond to the anatomical location of the GP is feasible and may be a simpler method of mapping the cardiac autonomic nervous system, compared with the HFS technique.

Compatibility of Neoseiulus paspalivorus and Proctolaelaps bickleyi, candidate biocontrol agents of the coconut mite Aceria guerreronis: spatial niche use and intraguild predation

The eriophyid mite Aceria guerreronis occurs in most coconut growing regions of the world and causes enormous damage to coconut fruits. The concealed environment of the fruit perianth under which the mite resides renders its control extremely difficult. Recent studies suggest that biological control could mitigate the problems caused by this pest. Neoseiulus paspalivorus and Proctolaelaps bickleyi are two of the most frequently found predatory mites associated with A. guerreronis on coconut fruits. Regarding biological control, the former has an advantage in invading the tight areas under the coconut fruit perianth while the latter is more voracious on the pest mites and has a higher reproductive capacity. Based on the idea of the combined use/release of both predators on coconut fruits, we studied their compatibility in spatial niche use and intraguild predation (IGP). Spatial niche use on coconut fruits was examined on artificial arenas mimicking the area under the coconut fruit perianth and the open fruit surface. Both N. paspalivorus and P. bickleyi preferentially resided and oviposited inside the tight artificial chamber. Oviposition rate of P. bickleyi and residence time of N. paspalivorus inside the chamber were reduced in the presence of a conspecific female. Residence of N. paspalivorus inside the chamber was also influenced by the presence of P. bickleyi. Both N. paspalivorus and P. bickleyi preyed upon each other with relatively moderate IGP rates of adult females on larvae but neither species yielded nutritional benefits from IGP in terms of adult survival and oviposition. We discuss the relevance of our findings for a hypothetic combined use of both predators in biological control of A. guerreronis.

Does using stepwise variable selection to build sequential path analysis models make sense?

Causal inference methods - mainly path analysis and structural equation modeling - offer plant physiologists information about cause-and-effect relationships among plant traits. Recently, an unusual approach to causal inference through stepwise variable selection has been proposed and used in various works on plant physiology. The approach should not be considered correct from a biological point of view. Here, it is explained why stepwise variable selection should not be used for causal inference, and shown what strange conclusions can be drawn based upon the former analysis when one aims to interpret cause-and-effect relationships among plant traits.

Cu and Fe metallic ions-mediated oxidation of low-density lipoproteins studied by NMR, TEM and Z-scan technique

In this work we report on a study of the morphological changes of LDL induced in vitro by metallic ions (Cu(2+) and Fe(3+)). These modifications were characterized by transmission electron microscopy, nuclear magnetic resonance and the Z-scan technique. The degree of oxidative modification of LDL was determined by the TBARS and lipid hydroperoxides assays. It is shown that distinct pathways for modifying lipoproteins lead to different morphological transformations of the particles characterized by changes in size and/or shape of the resulting particles, and by the tendency to induce aggregation of the particles. There were no evidence of melting of particles promoted by oxidative processes with Cu and Fe. (C) 2010 Elsevier Ireland Ltd. All rights reserved.

Application of hydrophobic resin adhesives to acid-etched dentin with an alternative wet bonding technique

Hydrophilic dentin adhesives are prone to water sorption that adversely affects the durability of resin-dentin bonds. This study examined the feasibility of bonding to dentin with hydrophobic resins via the adaptation of electron microscopy tissue processing techniques. Hydrophobic primers were prepared by diluting 2,2-bis[4(2-hydroxy-3-methacryloyloxy-propyloxy)-phenyl] propane/triethyleneglycol dimethacrylate resins with known ethanol concentrations. They were applied to acid-etched moist dentin using an ethanol wet bonding technique that involved: (1) stepwise replacement of water with a series of increasing ethanol concentrations to prevent the demineralized collagen matrix from collapsing; (2) stepwise replacement of the ethanol with different concentrations of hydrophobic primers and subsequently with neat hydrophobic resin. Using the ethanol wet bonding technique, the experimental primer versions with 40, 50, and 75% resin exhibited tensile strengths which were not significantly different from commercially available hydrophilic three-step adhesives that were bonded with water wet bonding technique. The concept of ethanol wet bonding may be explained in terms of solubility parameter theory. This technique is sensitive to water contamination, as depicted by the lower tensile strength results from partial dehydration protocols. The technique has to be further improved by incorporating elements of dentin permeability reduction to avoid water from dentinal tubules contaminating water-free resin blends during bonding. (c) 2007 Wiley Periodicals, Inc. J Biomed Mater Res 84A: 19-29, 2008.

Nuclear Quadrupole Resonance: A Technique to Control Hydration Processes in the Pharmaceutical Industry

Pharmaceuticals can exist in many solid forms, which can have different physical and chemical properties. These solid forms include polymorphs, solvates, amorphous, and hydrates. Particularly, hydration process can be quite common since pharmaceutical solids can be in contact with water during manufacturing process and can also be exposed to water during storage. In the present work, it is proved that NQR technique is capable of detecting different hydrated forms not only in the pure raw material but also in the final product (tablets), being in this way a useful technique for quality control. This technique was also used to study the dehydration process from pentahydrate to trihydrate.

Biomarkers of selenium status in the amazonian context: Blood, urine and sequential hair segments

Selenium (Se) is an essential element and deficit or excess of dietary Se is associated with health disorders. Relatively elevated Se levels have been reported in the Brazilian Amazon, where there are also important annual variations in the availability of different foods. The present study was conducted among six riparian communities of the Tapajos River to evaluate seasonal variations in blood and sequential hair cm Se concentrations, and to examine the relationships between Se in blood and hair, and blood and urine. Two cross-sectional studies were conducted, at the descending water (DWS, n = 259) and the rising water (RWS, n = 137) seasons, with repeated measures for a subgroup (n = 112). Blood Se (B-Se), hair Se (H-Se) and urine Se (U-Se) were determined. Match-paired analyses were used for seasonal comparisons and the method of best fit was used to describe the relationships between biomarkers. B-Se levels presented a very large range (142-2447 mu g/l) with no overall seasonal variation (median 284 and 292 mu g/l, respectively). Sequential analysis of 13 cm hair strands showed significant variations over time: Se concentrations at the DWS were significantly lower compared with the rising water season (medians: 0.7 and 0.9 mu g/g; ranges: 0.2-4.3 mu g/g and 0.2-5.4 mu g/g, respectively). At both seasons, the relationships between B-Se and H-Se were linear and highly significant (r(2) = 67.9 and 63.6, respectively), while the relationship between B-Se and U-Se was best described by a sigmoid curve. Gender, age, education and smoking did not influence Se status or biomarker relationships. Variations in H-Se suggest that there may be seasonal availability of Se sources in local food. For populations presenting a large range and/or elevated Se exposure, sequential analyses of H-Se may provide a good reflection of variations in Se status.

A wavelet-based adaptive technique for adsorption problems involving steep gradients

A general, fast wavelet-based adaptive collocation method is formulated for heat and mass transfer problems involving a steep moving profile of the dependent variable. The technique of grid adaptation is based on sparse point representation (SPR). The method is applied and tested for the case of a gas–solid non-catalytic reaction in a porous solid at high Thiele modulus. Accurate and convergent steep profiles are obtained for Thiele modulus as large as 100 for the case of slab and found to match the analytical solution.

A finite integral transform technique for solving the diffusion-reaction equation with Michaelis-Menten kinetics

An approximate analytical technique employing a finite integral transform is developed to solve the reaction diffusion problem with Michaelis-Menten kinetics in a solid of general shape. A simple infinite series solution for the substrate concentration is obtained as a function of the Thiele modulus, modified Sherwood number, and Michaelis constant. An iteration scheme is developed to bring the approximate solution closer to the exact solution. Comparison with the known exact solutions for slab geometry (quadrature) and numerically exact solutions for spherical geometry (orthogonal collocation) shows excellent agreement for all values of the Thiele modulus and Michaelis constant.

New calibration technique for multiple-component stress wave force balances

Force measurement in hypervelocity expansion tubes is not possible using conventional techniques. The stress wave force balance technique can be applied in expansion tubes to measure forces despite the short test times involved. This paper presents a new calibration technique for multiple-component stress wave force balances where an impulse response created using a load distribution is required and no orthogonal surfaces on the model exist.. This new technique relies on the tensorial superposition of single-component impulse responses analogous to the vectorial superposition of the calibration loads. The example presented here is that of a scale model of the Mars Pathfinder, but the technique is applicable to any geometry and may be useful for cases where orthogonal loads cannot be applied.

CO2 reforming of methane on Ni catalysts: Effects of the support phase and preparation technique

The effects of the support phase and catalyst preparation methods on catalytic activity and carbon deposition were systematically investigated over nickel catalysts supported on Al2O3, SiO2 and MgO for the reforming reaction of methane with carbon dioxide. It is found that the pore structure of the support and metal-support interaction significantly affected the catalytic activity and coking resistance. Catalyst with well-developed porosity exhibited higher catalytic activity. Strong interaction between metal and the support made the catalyst more resistant to sintering and coking, thus resulting in a longer time of catalyst stability. (C) 1998 Elsevier Science B.V.