On the explicit analytic solution of Cheng-Chang equation

An analytic technique is applied to solve the free convection over a heated horizontal flat surface embedded in a porous medium. An explicit, totally analytic and uniformly valid solution is given to the so-called Cheng-Chang equation, which agrees well with numerical results.     

The influence of short time heat treatment on the structural and magnetic behaviour of Nd2Fe14B/α-Fe nanocomposite obtained by mechanical milling

The structure, microstructure and magnetic properties of Nd₂Fe₁₄B/α-Fe nanocomposite obtained after 8 h of high energy milling and different heat treatments are investigated. Two types of annealing have been performed: a conventional heat treatment at 550 °C for 1.5 h is used for comparison with rapid annealing for maximum 3 min at 700, 750 or 800 °C. It is found that these rapid annealing are much more efficient to promote the recrystallisation of the hard phase with a limited grain growth of the soft magnetic phase thus leading to better magnetic properties. Indeed, the best coercive field of 0.55 T was obtained for samples annealed at 700, 750 and 800 °C for 2.5, 1.5 and 1 min respectively. This behaviour is explained by both, a good recovery of crystallinity for the hard phase and relatively small size Fe nanocrystallites. The different heat treatments do not result in significant changes for remanent magnetization, which is between 93 and 107 A m²/kg. X-ray diffraction patterns were used to follow the evolution of the structure and the microstructure. The magnetic behaviour was checked from hysteresis curves and dM/dH vs. H plots.     

Effects of buoyancy assisting and opposing flows on mixed convection boundary layer flow over a permeable vertical surface

The present study deals with new similarity solution of steady mixed convection boundary layer flow over a permeable surface for convective boundary condition. It has been shown that a self similar solution is possible when the mass transfer velocity at the surface of the plate varies like x^−1/2, where x is the distance from the leading edge of the solid surface. Two point boundary value problem governed by non-linear coupled ordinary differential equations have been solved numerically using implicit finite difference scheme in combination with the quasi-linearization technique. It is interesting to note that dual solutions exist for buoyancy assisting flow, besides that usually reported in literature for buoyancy opposing flow. Further, the buoyancy assisting force causes considerable overshoot in the velocity profile and the Prandtl number strongly affects the thermal boundary layer thickness including the surface heat transfer rate.     

Effect of precursor concentration on structural,morphological and opto-electric properties of ZnO thin films prepared by spray pyrolysis

Sprayed ZnO films were grown on glass substrate at 400 °C using zinc chloride as precursor with different molar concentrations varying from 0.05 to 0.2 M. X-ray diffraction patterns reveal that ZnO films are polycrystalline with hexagonal wurtzite structure with preferred orientation in (002) plane. Optical measurements show that transmittance reaches a maximum value of 95% in the visible region for ZnO films prepared from precursor with 0.05 M concentration. The films obtained from the precursor with 0.1 M concentration have the highest electrical conductivity and photocurrent values.     

Vitamin D Supplementation: Oxidative Stress Modulation in a Mouse Model of Ovalbumin-Induced Acute Asthmatic Airway Inflammation

Asthma oxidative stress disturbances seem to enable supplementary proinflammatory pathways, thus contributing to disease development and severity. The current study analyzed the impact of two types of oral vitamin D (VD) supplementation regimens on the redox balance using a murine model of acute ovalbumin-induced (OVA-induced) asthmatic inflammation. The experimental prevention group received a long-term daily dose of 50 µg/kg (total dose of 1300 µg/kg), whereas the rescue group underwent a short-term daily dose of 100 µg/kg (total dose of 400 µg/kg). The following oxidative stress parameters were analyzed in serum, bronchoalveolar lavage fluid (BALF) and lung tissue homogenate (LTH): total oxidative status, total antioxidant response, oxidative stress index, malondialdehyde and total thiols. Results showed that VD significantly reduced oxidative forces and increased the antioxidant capacity in the serum and LTH of treated mice. There was no statistically significant difference between the two types of VD supplementation. VD also exhibited an anti-inflammatory effect in all treated mice, reducing nitric oxide formation in serum and the expression of nuclear factor kappa B p65 in the lung. In conclusion, VD supplementation seems to exhibit a protective role in oxidative stress processes related to OVA-induced acute airway inflammation.     

Design,Synthesis, In Silico and In Vitro Studies for New Nitric Oxide-Releasing Indomethacin Derivatives with 1,3,4-Oxadiazole-2-thiol Scaffold

Starting from indomethacin (IND), one of the most prescribed non-steroidal anti-inflammatory drugs (NSAIDs), new nitric oxide-releasing indomethacin derivatives with 1,3,4-oxadiazole-2-thiol scaffold (NO-IND-OXDs, 8a–p) have been developed as a safer and more efficient multitarget therapeutic strategy. The successful synthesis of designed compounds (intermediaries and finals) was proved by complete spectroscopic analyses. In order to study the in silico interaction of NO-IND-OXDs with cyclooxygenase isoenzymes, a molecular docking study, using AutoDock 4.2.6 software, was performed. Moreover, their biological characterization, based on in vitro assays, in terms of thermal denaturation of serum proteins, antioxidant effects and the NO releasing capacity, was also performed. Based on docking results, 8k, 8l and 8m proved to be the best interaction for the COX-2 (cyclooxygense-2) target site, with an improved docking score compared with celecoxib. Referring to the thermal denaturation of serum proteins and antioxidant effects, all the tested compounds were more active than IND and aspirin, used as references. In addition, the compounds 8c, 8h, 8i, 8m, 8n and 8o showed increased capacity to release NO, which means they are safer in terms of gastrointestinal side effects.     

Method for early detection of the regenerative instability in turning

Nowadays, approaches in chatter detection and control are based on chatter prediction, by using a machining system dynamic model, or on chatter detection by different techniques, but after chatter onset. They are not efficient because the models are complicated and specific (in the first case) respectively because of chatter unwanted consequences occurrence (in the second case). This paper presents a method for early detection of the process regenerative instability state (as a specific process current dynamical state), based on cutting force monitoring. Using the cutting force records, the process current dynamical state is assessed. Appropriate cutting force signal features are defined, based on signal statistic processing, signal chaotic modeling or signal harmonic analysis, and used on this purpose. The process dynamical state evolution is modeled aiming the features values prediction. Two types of models were used in this purpose: linear and neural. The instability regenerative mechanism is identified by using either dedicated features or input variable selection. The method was conceived and experimentally implemented in the case of turning process. The results show the method reliability and the possibility of using it in developing an intelligent system for stability control.     

The role of electrical and thermal contact resistance for Joule breakdown of single-wall carbon nanotubes

Several data sets for the electrical breakdown in air of single-wall carbon nanotubes (SWNTs) on insulating substrates are collected and analyzed. A universal scaling of the Joule breakdown power with nanotube length is found, which appears to be independent of the substrate thermal properties of their thickness. This suggests that the thermal resistances at SWNT-insulator and at SWNT-electrode interfaces govern heat sinking from the nanotube. Analytical models for the breakdown power scaling are presented, providing an intuitive, physical understanding of the breakdown process. The electrical and thermal resistances at the electrode contacts limit the breakdown behavior for sub-micron SWNTs; the breakdown power scales linearly with length for tubes that are microns long, and a minimum breakdown power (～0.05?mW) is observed for the intermediate (～0.5?μm) length range.     

Basestock Oils for Lubricants from Mixtures of Corn Oil and Synthetic Diesters

Environmentally friendly vegetable oils and their derivatives represent alternatives to mineral-based lubricants. Vegetable oils have high biodegradability and low production costs. Their poor thermo-oxidative stability and poor low temperature properties are disadvantages in their use as lubricant basestocks. In our study we used corn oil and diester mixtures, which become lubricants when additives are introduced. These mixtures of corn oil and di-2-ethylhexyl-adipate (DOA) and di-2-ethylhexyl-sebacate (DOS) offer a wide range of kinematic viscosities, pour points lower than −39 °C and flash points over 218 °C. The diameters of wear scars measured under four-ball testing (40 daN) are less than 0.90 mm and the copper strip corrosion test result is 1a. The differential scanning calorimetry study and thermogravimetric study under nitrogen atmosphere and in synthetic air are reported. From these studies a higher thermal stability was observed for corn oil than for diester oils. The thermo-oxidative instability occurred at temperatures higher than 350 °C. The low production cost of corn oil and its mixtures with diesters makes them an attractive alternative to mineral oil lubricants.     

Opto-electronic properties of SnO2 layers obtained by SPD and ECD techniques

The paper presents a comparative approach concerning the properties of SnO₂ thin layers obtained via spray pyrolysis deposition (SPD) and electro-chemical deposition (ECD). The influences of crystalline structure (X-ray diffraction), morphology (atomic force microscopy, contact angle) on the electric (electrical conductivity) properties of the layers were studied. The SPD samples present a porous morphology with high surface energy compared with ECD samples characterized by a dense morphology. The photocatalytic efficiency of the samples was tested in the photodegradation of methylene blue and the higher values (57%) correspond to SPD samples.