Numerical simulation of the wall shear stress distribution in a carotid artery bifurcation

Journal of Mechanical Science and Technology - The effect of stenosis for a carotid artery bifurcation with elastic and rigid walls is investigated numerically. In the present study, the blood flow...     

Energy provisioning in wireless rechargeable sensor networks with limited knowledge

Internet of Things in many applications depends on Wireless Sensor Networks where the sensors are battery powered. Recent advances in wireless energy transfer and rechargeable batteries provide a new chance for Wireless Rechargeable Sensor Networks when the mobile chargers (MCs) patrol the network field and replenish the power of sensors. We consider multiple MCs and a few charging stations (CSs) in the network. The MCs lose their power too, so they move toward CSs to replenish the energy of themselves. We propose an approach named Limited Knowledge Charging (LKC) where each CS makes a virtual area by using grid cells. Based on the cell’s information, CSs coordinate among themselves to direct MCs in the network. The main design goal of LKC is to prolong the network lifetime, by using many techniques such as balancing the energy of network areas. LKC reduces movements of MCs too as a second goal. LKC is an online approach that adapts itself with situation changes of the network. Many related studies use global knowledge, which is not always satisfied in practice. Instead, LKC is a local knowledge approach. Using exhaustive simulation, the satisfaction of the design goals of LKC is demonstrated.

     

Nisin‐loaded alginate‐high methoxy pectin microparticles: preparation and physicochemical characterisation

The bacteriocin nisin has been extensively used as potential natural preservative in the food industry. However, antimicrobial activity of nisin due to its binding with food components and inactivation by enzymatic degradation is reduced when it is applied in food. Encapsulation of nisin is an efficient approach to overcome the problems related to the direct application of this antimicrobial peptide in foods. In this study, nisin was encapsulated in alginate‐high methoxy pectin (HMP) microparticles, and its release studies were performed in water to determine the diffusion and the kinetic behaviour of the matrix. Results showed that the nisin content had a significant influence on encapsulation efficiency (EE), loading capacity (LC) and microparticles size. The values of EE, LC and particle mean diameter were about 47–54%, 16–21% and 57–131 μm, respectively. The nisin‐loaded microparticles showed nearly spherical structure with fold on the surface, as displayed by scanning electron micrograph. Interaction between alginate and HMP was confirmed by the changes in the intensity and wave number of the stretching vibrations of the hydroxyl and carboxyl groups in alginate‐HMP microparticles FTIR spectra. Furthermore, the addition of nisin resulted in a markedly increase in intensity of carboxylic peak at 1620 cm^?1, indicating the presence of nisin inside of the microparticles. The in vitro nisin release from these microparticles followed a sustained release profile consistent with a Fickian diffusion mechanism.     

Hydroxymethylfurfural in fruit puree and juice: preconcentration and determination using microextraction method coupled with high-performance liquid chromatography and optimization by Box–Behnken design

In the present study, a sensitive and rapid method for separation and determination of hydroxymethylfurfural (HMF) in fruit puree and juices was proposed. Dispersive liquid–liquid microextraction (DLLME) coupled with high-performance liquid chromatography (HPLC) was used for extraction and quantitative determination of HMF in fruit puree and juices. The effective parameters such as the type and volume of extraction and dispersive solvents, pH and salt amount (NaCl) were studied and optimized with the aid of response surface methodology based on Box–Behnken design to obtain the best condition for HMF extraction. At the optimized conditions, parameter values were 60 µL extracting solvent, 600 µL dispersive solvent, 2 g NaCl and pH 5. Repeatability of the method, described as the relative standard deviation, was 3.1% (n?=?6) and the recovery was 98.4%. The limit of detection and limit of quantitation were 1.47 and 5.28 µg L^?1, respectively. The merit figures of DLLME–HPLC–UV method showed that the proposed method can be noticed as a new, fast and good alternative method for investigation of HMF in various fruit puree and juice samples.     

Preparation and characterization of low‐density polyethylene/thermoplastic starch composites reinforced by cellulose nanofibers

In the current study, the effect of extracted cellulose nanofibers (CNFs) on rheological and mechanical properties and biodegradability of polyethylene/starch blend was investigated. The CNFs were extracted from wheat straws using a chemo‐mechanical method. Polyethylene/starch blend was reinforced by different amounts of CNF (6–14 wt%) using an internal mixer followed by a single screw extruder. The flow properties of nanocomposites were investigated by determining Melt Flow Index (MFI) and viscosity. Due to the weak interaction of cellulosic nanofibers and polymers, the flow behavior of nanocomposites was undesirable. Tensile tests were performed to evaluate the mechanical performance of nanocomposites. By increasing the CNF content, the tensile strength and elongation at break declined; whereas, the Young's modulus was improved. The biodegradation of cellulose nanocomposites was investigated by water absorption and degradability tests. Both experiments confirmed the progressive effect of cellulose nanofibers on the degradation of the composites. POLYM. COMPOS., 36:2309–2316, 2015. © 2014 Society of Plastics Engineers     

Synthesis,characterization, and optimization of α‐Fe2O3/silica nanocomposites using homogenous precipitation method

The purpose of this study was to systematically synthesize and characterize the high surface area 10 wt% nanocomposites of α‐Fe₂O₃ (hematite)/silica using a simple and economically effective homogenous precipitation (HP) route via Response Surface Method combined with Central Composite Design (CCD). Accordingly, the RSM‐CCD approach including 20 experiments was designed to investigate the effects of three factors including concentration of iron chloride solution, pH and calcinations temperature on the final surface area of α‐Fe₂O₃/silica nanocomposites. The optimum surface area was 373 m²/g at the condition including iron chloride concentration of 0.018 mol/L, pH=8.95, and calcination temperature of 573°C.     

The effect of nano sized SrFe<Subscript>12</Subscript>O<Subscript>19</Subscript> additions on the magnetic properties of chromium-doped strontium-hexaferrite ceramics

Strontium hexaferrite (SrFe₁₂O₁₉) which crystallizes in the hexagonal system and has a uniaxial magnetoplumbite structure, displays distinctive magnetic characteristics, good chemical stability, good tribological properties and a weak temperature dependent coercivity at about room temperature. In the present work the synthesis conditions for the solid-state preparation of the chromium-doped hexaferrite SrCr_0.3Fe_11.7O₁₉ were optimised and the effect on the magnetic properties of this compound of additions of nanosized SrFe₁₂O₁₉ was studied. The nanosized SrFe₁₂O₁₉ additive, synthesized by the citrate–nitrate reaction, was substituted in varying amounts for a commercial calcium silicate borate sintering additive mixture. A combination of 0.75 wt% of nano-sized SrFe₁₂O₁₉ with 0.75 wt% of the commercial additive increases the intrinsic coercivity, remanence magnetization and rectangularity ratio and results in superior magnetic properties than obtained with 1.5 wt% of nanosized SrFe₁₂O₁₉ or the commercial sintering additive alone.     

Design of X‐band Moreno cross‐guide coupler based on superformula curves

This article deals with the design of Moreno cross‐guide couplers based on supershapes for X‐band applications. Crossed‐waveguide couplers are mainly used due to their compact structures. In these couplers, cross‐aperture structures are usually employed to offer flat coupling and high isolation. In the present article, the possible shapes for apertures and metal inserts that can be derived by the superfomula curves are explored and the effects of variations of superformula parameters are investigated on the performance of Moreno coupler. Finally, the proposed Moreno coupler is validated through fabrication and measurement. The experimental validation shows an excellent agreement with the simulated results. In the frequency range from 8 to 12.5 GHz, the measured coupling value changes from 18.8 to 20.8 dB and the directivity is better than 38 dB and 29 dB from 8 to 11 GHz and 11 to 12.5 GHz, respectively. The results are valuable for the design and evaluation of broadband high directive waveguide couplers.     

Ultra-low power inductorless differential LNA for WSN application

Analog Integrated Circuits and Signal Processing - In this paper, a wide band inductorless differential low noise amplifier (LNA) is designed and analyzed. To attain ultra-low power consumption,...     

The influence of different preparation methods on the aggregation status of pyrogenic nanosilicas used in concrete

Investigation of the effects of nanosilica materials in cementitious mixtures has attracted considerable research attention due to the very high specific surfaces of these materials. However, high surface area leads to aggregation of these materials due to high surface attraction forces, which could seriously reduce their nano filler effect. In this research the dispersion of pyrogenic nanosilicas in water and parameters influencing it were investigated. The results show that serious aggregation of pyrogenic nanosilicas in water occurs. Increasing the amount of applied forces, particularly the use of ultrasonic waves, has considerable effect in breaking aggregates into smaller aggregates with maximum size up to 0.9 μm. Increasing the pH was found to be very effective in improving dispersion of nanosilicas and through combined use of high pH and applying high levels of energy such as ultrasonic method it is possible to break all the aggregates into primary aggregates with maximum size of about 0.06 μm.