A comparative study of duty cycle and argon / methane flow ratio effect on the tribological behavior of DLC coatings over nitrided Astaloy Mo-based steel

Surface properties of Astaloy Mo-based steel were enhanced by using DLC deposition. The specimens were formed by double-sided compaction and heated for 30 min at 1393 K, in the NH₃ atmosphere. Following this, the plasma nitriding process was applied to improve the adhesion of the DLC coating. Afterward, the DLC coating was performed by Pulsed DC PACVD. Surface characteristics were studied by changing the duty cycle and the Argon/Methane flow ratio. The reciprocating method was carried out to evaluate wear behavior. Field emission scanning electron microscopy equipped with EDS and Raman spectroscopy, hardness tester, nanoindentation test and surface roughness tester were used to evaluate the chemical structure, wear mechanisms of DLC coatings. This study proved that hardness reached up to 12.2 ± 1.11 GPa and the wear behavior was enhanced significantly by the DLC coating deposition. The mass loss increased with a rise in the duty cycle. Increasing the Argon/Methane ratio from 4:1 to 6:1 caused a decrease in the mass loss of DLC coatings. Burnishing, pulling out and adhesive wear were the dominant mechanisms.     

The energy minimization algorithm for elastic optical networks

Photonic Network Communications - In this paper, a novel energy-aware grooming-based algorithm, named energy minimization algorithm (EMA), is proposed that aims at providing the quality of service...     

Comparative Study of Elastic Buckling of Plates Stiffened with Angle Bar Stiffeners

Interactions of different buckling modes in stiffened plates reduce Euler stress. In lieu of detailed analysis, in classification societies rule and in the literature, each buckling mode is treated independently and restraining effect of the adjacent elements is considered as rotational spring. It is the main aim of the present work to compare different rule-based and literature-based expressions proposed for the stiffness of these rotational springs and to determine the accuracy and applicability of them using energy method. Different buckling modes including, plate, torsional, and web buckling and interaction of them are investigated. Upon comparison with given expressions and finite element method, it is found that some of the proposed expressions for stiffness of rotational spring are not applicable in certain conditions.

     

CFD simulation of gas-solid bubbling fluidized bed containing FCC particles

The hydrodynamics of a bubbling gas-solid fluidized bed of 57.4 μm FCC particles was simulated by using a state-of-the-art two-fluid model integrating the kinetic theory of granular flow for particulate phase stresses. The overestimation of the bed expansion was resolved by using a suitable scale factor in the drag model as suggested by McKeen and Pugsley (T.R. McKeen, T.S. Pugsley, Powder Technol., 129, 139 (2003)). This study showed that the method was appropriate in simulation of a gas-solid fluidized bed of Geldart A particles at high gas velocities (0.3 to 0.61 m/s). The reduction of computational time especially for simulation of large-scale systems was achieved. The time-averaged local voidage was compared with the experimental data and the trend of varying several parameters on the hydrodynamic of the bed was investigated. The simulation results showed both qualitative and quantitative agreement with the literature.     

One-Step Synthesis of Zirconia and Magnetite Nanocomposite Immobilized Chitosan for Micro-Solid-Phase Extraction of Organophosphorous Pesticides from Juice and Water Samples Prior to Gas Chromatography/Mass Spectroscopy

In this research, a magnetic sorbent was prepared by immobilizing zirconia and magnetite (Fe₃O₄) nanoparticles in chitosan, which is characterized and used as an effective nanosorbent in magnetic dispersive micro-solid-phase extraction (MDMSPE) of organophosphorous pesticides (OPPs) from juice and water samples prior to gas chromatography-mass detection (GC-MS). The properties and morphology of synthesized sorbent were characterized by scanning electron microscopy (SEM), Fourier transform-infrared spectroscopy (FT-IR), vibrating sample magnetometry (VSM), and differential scanning calorimetric (DSC) analysis. The main experimental parameters including pH level, extraction time, sorbent mass, salt concentration, and desorption conditions were investigated and optimized to maximize extraction efficiency. Under optimized conditions, the calibration curves were obtained in the concentration range of 0.1–500 ng mL^?1 with correlation coefficients between 0.9993 and 0.9999. The limits of detection (signal-to-noise ratio (S/N) = 3) and limits of quantification (S/N = 10) of the method ranged from 0.031 to 0.034 ng mL^?1 and 0.105–0.112 ng mL^?1, respectively. The intra-day and inter-day RSDs were 2.2–5.7 and 2.5–7.5%, respectively. The method was successfully applied to the analysis of OPPs in fruit juices (apple, peach, and cherry) and water (mineral, tap, and river) real samples, with recoveries in the range of 86.0–106.0% for the spiked juice and water samples. The results showed that with combination of high selectivity of zirconia and magnetic property of magnetite as well as immobilizing ability of chitosan, the fabricated sorbent exhibited exceptional extraction ability toward the OPPs.     

Study on sterol fraction of commercial brands of milk,yoghurt and butter sold in Iranian market and chemometric data analysis

A gas chromatographic procedure for analysis of sterols was developed to detect possible addition of vegetable oils to milk, yoghurt and butter samples. The method involved fat extraction, saponification, hexane extraction, silylation of sterols and then analysis by gas chromatography. The sterol content of 102 samples of milk, yoghurt and butter was determined. Phytosterol content higher than 5% of total sterol was observed in four samples of milk and yoghurt. Principal component analysis showed that there was a direct relationship between the level of phytosterols and fat percentage in yoghurt samples. The described method is accurate and reliable enough to be employed regularly in food quality laboratories.     

OCGRR: A New Scheduling Algorithm for Differentiated Services Networks

We propose a new fair scheduling technique, called OCGRR (Output Controlled Grant-based Round Robin), for the support of DiffServ traffic in a core router. We define a stream to be the same-class packets from a given immediate upstream router destined to an output port of the core router. At each output port, streams may be isolated in separate buffers before being scheduled in a frame. The sequence of traffic transmission in a frame starts from higher-priority traffic and goes down to lower-priority traffic. A frame may have a number of small rounds for each class. Each stream within a class can transmit a number of packets in the frame based on its available grant, but only one packet per small round, thus reducing the intertransmission time from the same stream and achieving a smaller jitter and startup latency. The grant can be adjusted in a way to prevent the starvation of lower priority classes. We also verify and demonstrate the good performance of our scheduler by simulation and comparison with other algorithms in terms of queuing delay, jitter, and start-up latency.     

Comparative and competitive adsorption of Cu(II), Cd(II) and Pb(II) onto Sepia pharaonis endoskeleton biomass from aqueous solutions

In this research, the possibility of simultaneous removal of lead, cadmium and copper divalent ions from water samples through the use of Sepia pharaonis endoskeleton powder (SPEB) as bio‐material, was investigated. The bio‐sorbent was characterised by Fourier transform infrared spectrum (FT‐IR), atomic force microscopy (AFM) and X‐ray fluorescence (XRF). The different factors affecting the bio‐sorption process were studied. Langmuir and Freundlich isotherm models were applied to analyse the experimental data. The kinetic studies showed that the pseudo‐second order model kinetics were compatible with the investigated systems. It was found that under optimal conditions, this bio‐sorbent was efficient in the uptake of these heavy metal ions from both mono and multi‐metal solutions, and high removal percentages were achieved. This study verified the potential ability of SPEB as an efficient natural adsorbent for removal of Pb(II), Cd(II) and Cu(II) ions from river, tap and mineral water samples.     

Quantitative evaluation of arterial pulsatile flow and pressure, applying impedance plethysmography to a human arterial model incorporating anatomical branching and scale

This paper presents the theoretical basis of a new noninvasive method for obtaining arterial pulsatile flow and pressure. The proposed technique uses a model of the human arterial system based on the anatomical branching structure of the arterial tree. Arteries are divided into segments represented by uniform thin-walled elastic tubes with realistic arterial dimensions and wall properties. A simple mathematical model equivalent to electrical transmission lines is developed which is able to fit the electrical impedance plethysmograph waveform produced by the subjects throughout the complete cardiac cycle. Ensemble averaging is suggested as an option for processing of the impedance data. This technique provides artifact-free impedance data which enables the model to be used during exercise as well as quiet breathing. The proposed model provides an enhanced capability for measuring pulsatile blood flow and pressure in both clinical and research applications.     

Biocompatible graphene-embedded PCL/PGS-based nanofibrous scaffolds: A potential application for cardiac tissue regeneration

Research in the field of tissue engineering, especially heart tissue engineering, is growing rapidly. Herein, the morphological, chemical, mechanical and biological properties of poly (caprolactone) (PCL)/poly (glycerol sebacate) (PGS) and PCL/PGS/graphene nanofibrous scaffolds are investigated. Initially, PGS pre-polymer is synthesized and characterized by nuclear magnetic resonance and Fourier transform infrared spectroscopies. Then, in order to use the benefits of PGS, this polymer is mixed with PCL. Blending PGS with PCL resulted in the enhancement of ultimate elongation and reduction in the elastic modulus due to the intrinsic properties of PGS. The hydrophobicity of PCL nanofibers is reduced by adding PGS as hydrophilic polymer (105 ± 3° vs. 44 ± 2°). Also, the addition of graphene to the blend nanofibers is balanced the hydrophilicity. Degradation rate of pure PCL nanofibers is very slow but it is increased in the presence of PGS. All nanofibrous scaffolds are biocompatible and non-toxic. The highest cell adhesion (covered area = 0.916 ± 0.032) and biocompatibility (98.79 ± 1%) are related to PCL/PGS loaded with 1% wt of graphene (PCL/PGS/graphene ₁). Thus, this sample can be a good candidate for further examinations of cardiac tissue engineering.