Synthesis of PANI nanostructures with various morphologies from fibers to micromats to disks doped with salicylic acid

Shape-controllable polyaniline (PANI) nanostructures varying from fibers to micromats and disks were synthesized via a self-assembly process with salicylic acid (SA) as dopant. It has been achieved just by tuning the concentration of aniline, the mole ratio of SA to aniline, and the mole ratio of APS to aniline in the same reaction. The diameters of the fibers could be controlled from 30 to 400 nm by adjusting the concentration of aniline. Micromats of fibers would be formed by changing the mole ratio of SA to aniline. Disk-like PANI nanostructures were synthesized when decreasing the mole ratio of APS to aniline. Scanning electron microscopy and transmission electron microscopy were applied to investigate various kinds of morphologies. The mechanism of forming these morphologies was proposed to be adjusted by the pH value during polymerization. Ultraviolet–visible (UV–vis) absorption spectra and Raman spectra suggested that these as-prepared PANI were in conductive emeraldine state and featured obviously different molecular structures, which aroused from different reaction conditions.     

Clinical biomechanics of spinal fixation-anterior, posterior, andlateral

The three primary systems of spinal fracture-fixation may be categorized as follows: (a) Posterior fixation of the fractured spine by means of devices attached to posterior structures of the spinal column. These devices apply flexion-resisting forces to the deformed spinal column but cannot correct the spinal deformity nor decompress the spinal cord; (b) Lateral fixation of the fractured spine by means of devices that are attached parallel to the intact vertebral bodies above and below the fractured body, and bypass the loading on the spine across its fractured segment; (c) Anterior fixation of the fractured spine by means of a device that replaces the fractured vertebral body segment and transmits the load through it from the intact vertebral body above the fractured body to the intact spinal fracture below it. Here the authors provide biomechanical analyses of the function and efficacy of each of these systems, supported by some case histories     

Nonlinear adaptive filtering using kernel‐based algorithms with dictionary adaptation

Nonlinear adaptive filtering has been extensively studied in the literature, using, for example, Volterra filters or neural networks. Recently, kernel methods have been offering an interesting alternative because they provide a simple extension of linear algorithms to the nonlinear case. The main drawback of online system identification with kernel methods is that the filter complexity increases with time, a limitation resulting from the representer theorem, which states that all past input vectors are required. To overcome this drawback, a particular subset of these input vectors (called dictionary) must be selected to ensure complexity control and good performance. Up to now, all authors considered that, after being introduced into the dictionary, elements stay unchanged even if, because of nonstationarity, they become useless to predict the system output. The objective of this paper is to present an adaptation scheme of dictionary elements, which are considered here as adjustable model parameters, by deriving a gradient‐based method under collinearity constraints. The main interest is to ensure a better tracking performance. To evaluate our approach, dictionary adaptation is introduced into three well‐known kernel‐based adaptive algorithms: kernel recursive least squares, kernel normalized least mean squares, and kernel affine projection. The performance is evaluated on nonlinear adaptive filtering of simulated and real data sets. As confirmed by experiments, our dictionary adaptation scheme allows either complexity reduction or a decrease of the instantaneous quadratic error, or both simultaneously. Copyright © 2015 John Wiley & Sons, Ltd.     

Reversible tuning of plasmon coupling in gold nanoparticle chains using ultrathin responsive polymer film

We demonstrate large and reversible tuning of plasmonic properties of gold nanoparticles mediated by the reversible breaking and making of linear and branched chains of gold nanoparticles adsorbed on an ultrathin (1 nm) responsive polymer film. Atomic force microscopy revealed that at pH below the isoelectric point of the polybase (extended state of the polymer chains), gold nanoparticles adsorbed on the polymer layer existed primarily as individual nanoparticles. On the other hand, at higher pH, the polymer chains transition from coil to globule (collapsed) state, resulting in the formation of linear and branched chains with strong interparticle plasmon coupling. Reversible aggregation of the nanoparticles resulted in large and reversible change in the optical properties of the metal nanostructure assemblies. In particular, we observed a large redistribution of the intensity between the individual and coupled plasmon bands and a large shift (nearly 95 nm) in the coupled plasmon band with change in pH. Large tunability of plasmonic properties of the metal nanostructure chains reported here is believed to be caused by the chain aggregates of nanoparticles and un-cross-linked state of the adsorbed polymer enabling large changes in polymer chain conformation.     

Modeling Formation Damage Due to Flocculated Asphaltene Deposition

Abstract

In this article, a hybrid model of an analytical and artificial neural network simulation and corresponding analytical method are applied using laboratory data obtained by performing various dynamic displacement experiments with preseparated oil asphaltene content that resulted a close agreement, so it could predict the trend of permeability reduction due to deposition of asphaltene using the hybrid model described. The procedure of matching is described here.

The main conclusion is the ability to predict the deposition of asphaltene in the reservoir without the need to generate data from expensive downhole samples and/or laboratory tests.     

The Investigation of Vertical Wells' Optimum Two-phase Flow Empirical Correlation for the Ab-Teymour Reservoir

Abstract

There are different procedures for predicting pressure drop in two-phase flow pipelines. However, for each reservoir one or two correlations or mechanistic models give more accurate results. The authors investigated various correlations and mechanistic models in order to match fluid pressure losses considering all parameters such as friction, liquid holdup, superficial velocities, densities, viscosities, and interfacial tension. Commercial software, Pipesim, was used to simulate the fluid pressure losses. Drift flux modeling for predicting pressure profile was also investigated. A program for calculating pressure drops and average deviation of calculated pressures using this drift flux model was developed and the results were compared with other correlations.     

The biomechanics of back pain

Low back pain with sciatica due to lumbar-disc stress-deformation and herniation is a major health problem. The myriad of data on precautions, safeguards, and management of the back have failed to reduce back-pain incidence. In addition, surgical treatment often fails to eliminate pain and complications. This article attempts to address both the preventative and treatment aspects of back pain. For prevention, the authors discuss the biomechanics of back postures that are effective in maintaining a healthy spine. In the area of treatment, a biomechanical analysis of a procedure called percutaneous discectomy is presented     

Interfacial polarization and layer thickness effect on electrical insulation in multilayered polysulfone/poly(vinylidene fluoride) films

In this study, we report layer thickness effect on the electrical insulation property of polysulfone (PSF)/poly(vinylidene fluoride) (PVDF) multilayer films having a fixed composition of PSF/PVDF = 30/70 (vol./vol.). Breakdown strength, dielectric lifetime, and electrical conductivity were studied for 32- and 256-layer films having various total film thicknesses. Among these films, those having thinner PVDF and PSF layers exhibited lower breakdown strength, shorter lifetime, and higher electrical conductivity than those having thicker layers. These experimental results were explained by Maxwell–Wagner–Sillars interfacial polarization due to contrasts in dielectric constant and electronic conductivity for PVDF and PSF, respectively. When both PVDF and PSF layers were thick (ca. > 100–200 nm), more space charges were available in PVDF and no electronic conduction was allowed for PSF. These accumulated interfacial charges could serve as effective traps for injected electrons from metal electrodes under high electric fields. As a result, reduced electrical conductivity and enhanced breakdown strength/dielectric lifetime properties were obtained. When both layers were thin (ca. < 100 nm), fewer space charges were available in PVDF and significant electronic conduction through PSF resulted in low interfacial polarization. Consequently, higher electrical conductivity, lower breakdown strength, and shorter lifetime were observed. These results provide us insights into potential physics to enhance electrical insulation property of polymer films using a multilayered structure having large dielectric constant contrast.