Hydroxyapatite/alumina nanocrystalline composite powders synthesized by sol-gel process for biomedical applications

Hydroxyapatite/alumina nanocrystalline composite powders needed for various biomedical applications were successfully synthe- sized by sol-gel process. Structural and morphological investigations of the prepared composite powders were performed using X-ray dif- fractometer （XRD）, scanning electron microscopy （SEM）, X＇Pert HighScore software, and Clemex Vision image analysis software. The re- suits show that the crystallite size of the obtained composite powders is in the range of 25 to 90 nm. SEM evaluation shows that the obtained composite powders have a porous structure, which is very useful for biomedical applications. The spherical nanoparticles in the range of 60 to 800 nm are embedded in the agglomerated clusters of the prepared composite powders.     

Bulk and rheological properties of polyacrylamide hydrogels for water shutoff treatment

Presenting an optimal hydrogel for water shutoff, based on the bulk and rheological properties, was the main purpose of this research. To determine gelation time, a bottle test was conducted using central composite design method with two factors, AN125VLM and Cr(OAc)₃, as copolymer and crosslinker, respectively. To select hydrogel with high strength network, crosslinking density and consistency modulus were also measured. Hence, a hydrogel with 26,340 ppm concentration of copolymer, 0.12 ratio of crosslinker/copolymer, maximum value of crosslinking density (1,950) and consistency modulus (31,900 Pa) was selected as the optimal one. To study the gelation time among different factors in porous media, rheological experiments were carried out by Plackett-Burman design to screen the eight factors (NaCl, CaCl₂, KCl and MgCl₂ concentrations, temperature, pH, sodium lactate and nanoclay). Accordingly, temperature was the most effective factor controlling the gelation time, while pH and other factors had negligible effect on the gelation time of the optimal hydrogel.     

Starve fed emulsion copolymerization of vinyl acetate and 1‐hexene at ambient pressure

A novel emulsion copolymer of vinyl acetate (VAc) and 1‐hexene was synthesized at ambient pressure. The feeding technique, initiation system and reaction time of the copolymerization were optimized based on molecular characteristics such as the weight contribution of 1‐hexene in the copolymer chains and glass transition temperature (T_g) as well as on bulk properties like minimum film‐formation temperature (MFFT) and solid content. According to nuclear magnetic resonance spectroscopy and differential scanning calorimetry results, the combination of starve feeding and redox initiation, within a reaction time of 4 h, effectively led to the copolymerization at ambient pressure between highly reactive polar VAc monomers and non‐polar 1‐hexene monomers of low reactivity. The copolymer showed a lower T_g and MFFT, and a reasonable solid content compared to the poly(vinyl acetate) (PVAc) homopolymer. The consumption rate, hydrolysis of acetate groups and chain transfer reactions during the polymerization were followed using infrared spectroscopy. Based on the results, the undesirable reactions between the VAc blocks were hindered by the neighbouring 1‐hexene molecules. Tensile testing revealed an improvement in the toughness and elongation at break of VAc–1‐hexene films compared to PVAc films. © 2014 Society of Chemical Industry     

Y2O3–Nd2O3 double stabilized ZrO2–TiCN nanocomposites

Yttria-neodymia double stabilized ZrO₂-based nanocomposites with 40 vol% electrical conductive TiCN were fully densified by means of pulsed electric current sintering (PECS) in the 1400–1500 °C range. The Y₂O₃ stabilizer content was fixed at 1 mol% whereas the Nd₂O₃ co-stabilizer content was varied between 0.75 and 2 mol% in order to optimise the mechanical properties. The mechanical (Vickers hardness, fracture toughness and bending strength), electrical (electrical resistivity) and microstructural properties were investigated and the hydrothermal stability in steam at 200 °C was assessed.The nanocomposites with 1–1.75 mol% Nd₂O₃, PECS at 1400 or 1450 °C, have an excellent fracture toughness of 8 MPa m^1/2, although the grain size of both ZrO₂ and TiCN phases after densification is in the 100 ± 30 nm range. Moreover, the composites combine a hardness of about 13 GPa, a bending strength of 1.1–1.3 GPa with a low electrical resistivity (1.6–2.2 × 10^?5 Ω m) allowing electrical discharge machining. The hydrothermal stability of the double stabilizer nanocomposites was higher than for yttria-stabilized ZrO₂-based composites with the same overall stabilizer content.     

A comparative study of slab deformation under heavy width reduction by sizing press and vertical rolling using FE analysis

A detailed comparison between the quality of slabs formed by sizing press and vertical rolling mill is presented. ABAQUS/explicit commercial finite element software with elasto-viscoplastic constitutive model for material is used to study the geometric characteristics and deformation pattern during width reduction in these processes. Finite element models developed for both sizing press and vertical rolling processes are validated by comparing their results with experimental data available in literature. Parametric studies are performed using validated finite element models for sizing press mill to determine the effect of input process parameters such as initial slab width and thickness, width reduction and transfer pitch on the process outputs such as dogbone formation, head and end fishtail profiles, width necking at the leading end of the slab and slab edge quality. Similarly, developed finite element models for vertical rolling are used to investigate the effects of different input parameters on the slab deformation after passing through a vertical rolling stand with the aim of comparing the two width reduction processes. According to the results, benefits and drawbacks of each width reduction method are discussed. The enhancing effect of subsequent horizontal rolling after sizing press and vertical rolling processes on the final slab thickness is also presented.     

Novel probabilistic bounds on power level profile of spectrally-encoded spread-time CDMA signals

In this letter we introduce an effective tool to demonstrate signal power behavior of a typical spectrallyencoded spread-time (SE/ST) CDMA system using probabilistic approach. By defining power level profile (PLP), as the probability of stretching instantaneous power from a pre-specified threshold, we can find novel upper bounds on the signal power profile. We discuss various properties owing to PLP and elaborate on the main parameters affecting the PLP value. We present three theorems, propose some simple upper bounds on the PLP, and give an insight on the main contributions of the results. We introduce a fundamental parameter, namely β, as a key design parameter which relates the most important quantities affecting the PLP behavior. Finally, we propose a corollary demonstrating an approach to guarantee that the PLP value is set at zero. It is shown that using suitable distributions, we can also obtain some distribution gain, thereby enhancing the overall system performance.     

Schultz Index of Armchair Polyhex Nanotubes

The study of topological indices – graph invariants that can be used for describing and predicting physicochemical or pharmacological properties of organic compounds – is currently one of the most active research fields in chemical graph theory. In this paper we study the Schultz index and find a relation with the Wiener index of the armchair polyhex nanotubes TUV C₆[2p; q]. An exact expression for Schultz index of this molecule is also found.     

Velocity-based Formation Damage Characterization Method for Produced Water Re-injection: Application on Masila Block Core Flood Tests

With increasing environmental regulations, more and more produced water is being re-injected; however, water injection programs may have low efficiency due to formation damage around the injected wellbore. Traditionally, formation damage was treated as a deep bed filtration (DBF) type of process characterized by laboratory-based damage parameters. These parameters inquire expensive concentration measurement, and lab-scaled results are not usually applicable for field cases. Recent studies on formation damage are more attracted to history-based approaches using an empirical damage equation to capture the uniqueness of each case study. In our previous work, such empirical (velocity based) model was studied and shown to be more practical than (and equivalent to) the DBF model. A robust characterization method was developed to calculate the damage parameters explicitly, and it was successfully tested against offshore field data. In this work, the method has been applied for analysis of a series of core flood tests on cores from the Masila Block field in Yemen and compared with measured damage parameters. Good agreement with lab-measured values validates the characterization method. The accuracy of the method is comparable to the DBF approach, while it is simpler and more suitable for implementing in reservoir simulators.