Size‐dependent vibration of double‐bonded carbon nanotube‐reinforced composite microtubes conveying fluid under longitudinal magnetic field

In the present research, vibration and instability of visco‐elastically coupled carbon nanotube reinforced composite (CNTRC) microtubes conveying fluid is investigated. Single‐walled carbon nanotubes are arranged in a longitudinal direction inside poly methyl methacrylate matrix. The longitudinal magnetic field is applied on coupled system. The surrounding medium is simulated by visco‐Pasternak model due to considerable damping and shearing effects. Based on Mori–Tanaka theory, the properties of composite microtubes are obtained. In order to achieve more accurate results, strain gradient theory is developed in Timoshenko beam model. The motion equations are derived utilizing Hamilton's principle and solved by means of differential quadrature method. Considering slip flow regime, the influences of various parameters such as magnetic intensity, elastic medium, Knudsen number, and volume fraction of CNTs on the vibration characteristics of coupled system are studied in details. Results demonstrated that the stability of coupled system can be significantly improved by applying magnetic field. The result of this study can be useful to control and improve the performance of micro‐mechanical systems conveying fluid. POLYM. COMPOS., 37:1375–1383, 2016. © 2014 Society of Plastics Engineers     

High dynamic range pseudo–two-level digital pulse-width modulation for power-efficient RF transmitters

Radio frequency (RF) power amplification based on pulse-width modulation (PWM) has been widely discussed as a potential solution to achieve higher efficiency in RF transmitters. A digitally implemented PWM introduces a large amount of in-band distortion due to spectral aliasing. In this paper, a novel memoryless PWM modulator with a built-in anti-aliasing filter is proposed that effectively reduces the in-band distortion in digital implementation. The spectral characteristics of the proposed PWM modulator as well as the statistical properties of its output PWM signal are analytically studied. The pseudo–two-level output of the proposed modulator provides the capability to compromise between the efficiency, linearity, and complexity of transmitter, based on the given design targets. The proposed PWM method benefits from a simple circuit implementation in both digital and RF sections of the transmitter. Moreover, it preserves the low distortion property at low oversampling ratios of digital baseband. Simulations, as well as measurements, verify the performance of the proposed method.     

Implementation of ISO 14001:2004 (environmental management system standard) for reverse osmosis desalination plants for the first time in Iran

Implementation of ISO 14001:2004 (environmental management system) has been executed for reverse osmosis desalination plants for the first time in Iran at Noor Vijeh Company (N.V. Co), a water and wastewater firm based in Tehran. The scope of work was the activities and product of company's BWRO desalination plant in the city of Qom (3000 m³ per day) and SWRO desalination plant in Assaluyeh, Pars Special Economic and Energy Zone, Iran. The aims of this project were in line with company’s approach to sustainable development and its direction towards conducting environmental friendly activities and production characteristics.

Initially the famous PDCA (Plan, Do, Check, Act) was used to identify the aspects and evaluate their effects. The significant aspects of each plant affecting the environment are then identified and preventive control measures and reducing their probabilities of loss are anticipated. These cover the normal activities within each plant and those aspects arising from emergency conditions such as earthquakes, fire, etc.

Elements of this system are

• Environmental policy and its targets and programmes

• Practical methods for environmental management system processes

• Executive manuals for implementing special activities

• Tables and indexes for environmental aspects for each plant

• Organizational charts, positions, qualifications, and necessary trainings for the involved personnel.

Environmental aspects are evaluated through their interaction with and effects over, releases to water, emissions to air, land contamination, waste management, energy use, and use of natural resources and raw material.     

Pasternak foundation effect on the axial and torsional waves propagation in embedded DWCNTs using nonlocal elasticity cylindrical shell theory

The axial and torsional wave propagation in a double-walled carbon nanotube (DWCNT) embedded on elastic foundations are investigated using nonlocal continuum shell theory. The effects of the surrounding elastic medium are considered using the spring constant of the Winkler-type and the shear constant of the Pasternak-type. The van der Waals (vdW) forces between the inner and the outer nanotubes are taken into account. The dynamic response of the carbon nanotube is formulated on the basis of nonlocal elasticity shell theory. The cut-off frequencies are obtained and it has been concluded that the cut-off frequencies are independent of small scale coefficient and shear modulus of the elastic medium. It has been found that the phase velocity sharply decreases by increasing the axial half wave number and approaches a constant value. It has also been concluded that the maximum phase velocity predicted by nonlocal theory is located between 5 and 10 nanometers while for local theories the phase velocity sharply decreases in this interval and approaches a constant value. Results show that the effect of Pasternak-type on phase velocity is significant but the effect of Winkler-type is not really considerable.     

A 10-bit 50-MS/s redundant SAR ADC with split capacitive-array DAC

A new architecture for successive-approximation register analog-to-digital converters (SAR ADC) using generalized non-binary search algorithm is proposed to reduce the complexity and power consumption of the digital circuitry. The proposed architecture is based on the split capacitive-array DAC with a simple switching logic as compared to the conventional non-binary SAR ADC architecture. A 10-bit 50-MS/s SAR ADC is designed based on the proposed architecture in a 0.18 μm CMOS technology. Simulation results show that at a supply voltage of 1.2 V, the SAR ADC achieves a peak signal-to-noise-and-distortion ratio of 59.5 dB, and a power consumption of 1.3 mW, resulting in a figure of merit of 33 fJ/conversion-step.     

Surrogate-based multi-objective optimization of a composite laminate with curvilinear fibers

A variable stiffness design can increase the structural performance of a composite plate and provides flexibility for trade-offs between structural properties. In this paper, we examine the simultaneous optimization of stiffness and buckling load of a composite laminate plate with curvilinear fiber paths. The problem, which falls in the area of multi-objective optimization, is formulated and solved through a surrogate-based optimization algorithm capable of finding the set of optimum Pareto solutions. We integrate surrogate modeling into an evolutionary algorithm to reduce the high computational cost required to solve the optimization process. The results show that a curvilinear fiber path can increase both buckling load and stiffness simultaneously over the quasi-isotropic laminate. Furthermore, the optimum direction for varying the fiber angle is dependent on the loading direction and boundary conditions. The results for a plate under uniform compression with free transverse edges shows that varying the fiber orientation perpendicular to the loading direction can increase the buckling load by 116% with respect to that of a quasi-isotropic laminate.     

Nonlinear vibration and instability analysis of functionally graded CNT-reinforced cylindrical shells conveying viscous fluid resting on orthotropic Pasternak medium

In this study, nonlinear vibration and instability of embedded temperature-dependent cylindrical shell conveying viscous fluid resting on temperature-dependent orthotropic Pasternak medium are investigated. The equivalent material properties of nanocomposites are estimated using rule of mixture. Both cases of uniform distribution and functionally graded distribution patterns of reinforcements are considered. Based on orthotropic Mindlin shell theory, the governing equations are derived. Generalized differential quadrature method is applied for obtaining the frequency and critical fluid velocity of a system. The effects of different parameters, such as distribution type of single-walled carbon nanotubes (SWCNTs), volume fractions of SWCNTs, and Pasternak medium are discussed.     

Tetracycline hydrochloride-containing poly (ε-caprolactone)/poly lactic acid scaffold for bone tissue engineering application: in vitro and in vivo study

In the current study, tetracycline hydrochloride (TCH), an antibiotic against most of the medically relevant bacteria, was incorporated into poly (ε-caprolactone)/poly lactic acid solution in order to develop a composite scaffold with both antibacterial and osteoinductive properties for the repair of infected bone defects. The composite scaffolds were produced from poly (ε-caprolactone) (PCL) and poly lactic acid (PLA) solution (1:1 (w/w)) incorporated with 3, 5, and 10% (w/w) of TCH by thermally induced phase separation technique. The scaffolds were evaluated regarding their morphology, wettability, porosity, degradation, mechanical properties, and cellular response. The scaffold containing 10% of TCH (PCL/PLA/TCH10%) was chosen as the optimum scaffold for further investigation in a rat femoral defect model. The study showed that after eight weeks, the bone formation was relatively higher in PCL/PLA/TCH10%-treated group with completely filled defect when compared with control (PCL/PLA scaffold without TCH). Histopathological evaluation showed that the defect in PCL/PLA/TCH10%-treated group was fully replaced by new bone and connective tissue. Our results provide evidence supporting the possible applicability of TCH-containing scaffolds for successful bone regeneration.     

Novel Movable Typing for Personalized Vein-Chips in Large Scale: Recapitulate Patient-Specific Virchow's Triad and its Contribution to Cerebral Venous Sinus Thrombosis

The Vein-Chip recapitulates CVST Virchow's triad and enables systematic characterization of venous thrombogenesis with respect to fibrin formation and platelet aggregation. Distinct from the arterial setting, platelets universally adhere across the entire CVS Vein-Chip independent of stenotic geometry and flow disturbance. Intriguingly, fibrin propagates along with the flow direction, but exclusively deposits to the inner vessel wall. Upon inflammatory endothelial injury, fibrin deposition mirrors to the outer vessel wall, but still not in the lumen. Together, the Vein-Chip promises future applications for personalized thrombotic assessment and monitoring.