Temperature effects on electrical double layer at solid-aqueous solution interface

Despite the significant influence of solution temperature on the structure of electrical double layer, the lack of theoretical model intercepts us to explain and predict the interesting experimental observations. In this work, we study the structure of electrical double layer as a function of thermochemical properties of the solution by proposing a phenomenological temperature dependent surface complexation model. We found that by introducing a buffer layer between the diffuse layer and stern layer, one can explain the sensitivity of zeta potential to temperature for different bulk ion concentrations. Calculation of the electrical conductance as function of thermochemical properties of solution reveals the electrical conductance not only is a function of bulk ion concentration and channel height but also the solution temperature. The present work model can provide deep understanding of micro- and nanofluidic devices functionality at different temperatures.     

Ammonia fiber expansion pretreatment and enzymatic hydrolysis on two different growth stages of reed canarygrass

Plant materials from the vegetative growth stage of reed canarygrass and the seed stage of reed canarygrass are pretreated by ammonia fiber expansion (AFEX) and enzymatically hydrolyzed using 15 filter paper units (FPU) cellulase/g glucan to evaluate glucose and xylose yields. Percent conversions of glucose and xylose, effects of temperature and ammonia loading, and hydrolysis profiles are analyzed to determine the most effective AFEX treatment condition for each of the selected materials. The controls used in this study were untreated samples of each biomass material. All pretreatment conditions tested enhanced enzyme digestibility and improved sugar conversions for reed canarygrass compared with their untreated counterparts. Based on 168 h hydrolysis results using 15 FPU Spezyme CP cellulase/g glucan the most effective AFEX treatment conditions were determined as: vegetative growth stage of reed canarygrass--100 degrees C, 60% moisture content, 1.2:1 kg ammonia/kg of dry matter (86% glucose and 78% xylose) and seed stage of reed canarygrass--100 degrees C, 60% moisture content, 0.8:1 kg ammonia/kg of dry matter (89% glucose and 81% xylose). Supplementation by commercial Multifect 720 xylanase along with cellulase further increased both glucose and xylose yields by 10-12% at the most effective AFEX conditions.     

Effect of notch depth and radius on the critical fracture load of bainitic functionally graded steels under mixed mode I + II loading

Functionally graded steels are produced from austenitic stainless steel and carbon steel by controlling the chemical distribution of chromium, nickel and carbon atoms at the remelting stage through electroslag remelting process. In the present paper, the strain-energy density criterion is employed to assess the critical load of rounded V-notched components made of functionally graded bainitic steel. A crack arrester configuration under mixed mode loading is considered. The flow (yield/ultimate) strength and fracture toughness are assumed to vary exponentially along the notch depth direction while the Young’s modulus and the Poisson’s ratio are assumed to be constant. The control volume, which is a reminiscent of Neuber’s elementary structural volume, depends on the ultimate tensile strength σ_ut and the fracture toughness K _IC in the case of brittle or quasi-brittle materials subjected to static loadings. Since, σ_ut and K _IC are not constant along the notch depth, the control volume which can be obtained numerically as a function of the variation of these material properties through the specimen width. Different values of the notch root radius (from 0.2 to 2.0 mm) and notch depth (from 5 to 7 mm) are considered. The assessed critical fracture loads are in sound agreement with the experimental results.     

A modified (S − 1, S) inventory system for deteriorating items with Poisson demand and non-zero lead time

An inventory system is considered for continuous decaying items with non-zero lead time and stochastic demand when shortages are allowed and all unsatisfied demands are backlogged. In this research we consider orders as separate packages where replenishment is one-for-one and a modified base stock policy is applied. In this paper, a penalty cost is introduced for stochastic inventory models with decaying items when less than one unit of the product is delivered to the customers. The objective of the warehouse is to maximize his average profit. Since the concavity analysis of the model is extremely complicated, an upper bound is introduced and an algorithm is presented for finding the optimal solution. Finally, a numerical example is presented and sensitivity analysis is carried out for a number of important parameters.     

Plasma-assisted hot filament chemical vapor deposition of AlN thin films on ZnO buffer layer: toward highly c-axis-oriented,uniform, insulative films

c-Axis-oriented aluminum nitride (AlN) thin film with improved quality was deposited on Si(111) substrate using ZnO buffer layer by plasma-assisted hot filament chemical vapor deposition. The optical and electrical properties and surface morphology as well as elemental composition of the AlN films deposited with and without ZnO buffer layer were investigated using a host of measurement techniques: X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, field emission scanning electron microscopy (FESEM), and current–voltage (I–V) characteristic measurement. The XRD and XPS results reveal that the AlN/ZnO/Si films are free of metallic Al particles. Also, cross-sectional FESEM observations suggest formation of a well-aligned, uniform, continuous, and highly (002) oriented structure for a bi-layered AlN film when Si(111) is covered with ZnO buffer. Moreover, a decrease in full width at half maximum of the E₂ (high)-mode peak in Raman spectrum indicates a better crystallinity for the AlN films formed on ZnO/Si substrate. Finally, I–V curves obtained indicate that the electrical behavior of the AlN thin films switches from conductive to insulative when film is grown on a ZnO-buffered Si substrate.     

Structural studies and physical properties of novel Sm-doped Sb2Se3 nanorods

Sm³⁺ doped Sb₂Se₃ nanorods were synthesized by the co-reduction method at 180 °C and pH=12 for 48 h. Powder XRD patterns indicate that the Sm_xSb_2−xSe₃ crystals (x=0.00-0.05) are isostructural with Sb₂Se₃. The cell parameters increase for Sm³⁺ upon increasing the dopant content (x). SEM images show that doping of Sm³⁺ ions in the lattice of Sb₂Se₃ results in nanorods. High-resolution transmission electron microscopic (HRTEM) studies reveal that the Sm_0.05Sb_1.95Se₃ is oriented in the [1 0 −1] growth direction. UV-vis absorption reveals mainly electronic transitions of the Sm³⁺ ions in doped nanomaterials. Emission spectra of doped materials, in addition to the characteristic red emission peaks of Sb₂Se₃, show other emission bands originating from f-f transitions of the Sm³⁺ ions. The electrical conductance of Sm-doped Sb₂Se₃ is higher than undoped Sb₂Se₃ and increase with temperature.     

Electrochemical Investigation of Cytochrome c Immobilized onto Self‐Assembled Monolayer of Captopril

The electrochemical behavior of cytochrome c (cyt‐c) that was electrostatically immobilized onto a self‐assembled monolayer (SAM) of captopril (capt) on a gold electrode has been investigated. Cyclic voltammetry, scanning electrochemical microscopy (SECM) and electrochemical impedance spectroscopy were employed to evaluate the blocking property of the capt SAM. SECM was used to measure the bimolecular electron transfer (ET) kinetics (k_BI) between a solution‐based redox probe and the immobilized protein. In addition, the tunneling ET between the immobilized protein and the underlying gold electrode was calculated. A k_BI value of (5.0±0.6)×10⁸ mol^?1 cm³ s^?1 for the bimolecular ET and a standard tunneling rate constant (k⁰) of 46.4±0.2 s^?1 for the tunneling ET have been obtained.     

Gas Sensing Ability of a Nanostructured Conducting Polypyrrole Film Prepared by Catalytic Electropolymerization on Cu/Au Interdigital Electrodes

Nanostructured conductive polypyrrole has been prepared electrochemically on the surfaces of Cu/Au interdigital electrodes in the presence of Fe(II) as catalyst and ClO₄^? as anion dopant by using constant potential amperometry and cyclic voltammetry. The morphology of the conducting films was examined by field emission scanning electron microscopy, indicating a dependence from the processing technique. The synthesized polymer was used to investigate the properties of the gas sensing ability. The effect of the catalyst concentration on the oxidation mechanism of pyrrole was discussed. The PPy‐ClO₄ gas sensors had demonstrated fast response time and high sensitivity to VOCs.     

Synthesis of Cu-mediated nano-sized salbutamol-imprinted polymer and its use for indirect recognition of ultra-trace levels of salbutamol

Cu²⁺-mediated salbutamol-imprinted polymer nanoparticles, synthesized by precipitation polymerization, were mixed with graphite powder and n-eicosane in order to fabricate a modified carbon paste electrode. This electrode was then applied for indirect differential pulse voltammetry determination of salbutamol. In the presence of Cu²⁺ ions, the formed Cu²⁺–salbutamol complex was adsorbed in to the pre-designed cavities of the MIP particles, situated on the electrode surface. Since the electrochemical signal of salbutamol was intrinsically small, the oxidation peak of the participant Cu²⁺, after reduction step, was recorded and used as an indication of salbutamol amount, adsorbed in the electrode. Different variables influencing the sensor performance were studied and the best conditions were chosen for the determination purpose. Correlation between the sensor response to salbutamol and its concentration was linear in the range of 1.0 × 10⁻⁹–5.5 × 10⁻⁸ M. Detection limit was calculated equal to 6.0 × 10⁻¹⁰ M (S/N). Five replicated determination of salbutamol (1 × 10⁻⁸ M) resulted in standard error of 3.28%, meaning a satisfactory precision of the determination method. The prepared sensor was applied for real sample analysis. In order to minimize the interference effect, the synthesized polymer was successfully used as a solid phase sorbent for salbutamol extraction, before analysis of real samples by the developed sensor.