Preparation of porous PLLA/PCL blend by a combination of PEO phase and NaCl particulate leaching in PLLA/PCL/PEO/NaCl blend

In this study, the ternary blends containing microporosity based on poly(l-lactic acid) (PLLA), poly(ε-caprolactone) (PCL) and polyethylene oxide (PEO) were prepared using an internal mixer via a polymer leaching technique. The particulate leaching is the most widely used technique to create porosity. To introduce macroporosity besides micropores, NaCl particulates were incorporated into the ternary blends at 40–80 wt % and macropores were formed by particulate leaching. Samples porosity were evaluated by calculating the ratio of porous scaffold density (ρ*) to the non-porous material density (ρ _s). The results showed that with an increase in NaCl particulate content, the amount of porosity increased and the distribution of pore size was gradually transformed from monomodal into bimodal form. The porosity plays a key role in governing the compression properties. Mechanical properties are presented by Gibson–Ashby model. Compressive modulus decreased with an increase in NaCl particulate concentration due to the increase in porosity and thinning of pore wall that caused rupture at these weaker spots. Blending and forming of the bio-scaffold can be made using conventional polymer processing equipment. This process seems promising for a large-scale production of porous bio-scaffold of many sizes through an economic method.     

Synthesis of imidazo[2,1-b]thiazoles through the reaction of thiohydantoins and α-bromoketones

Imidazo-fused heterocycles are used as anticancer agents. In this study, some novel imidazo[2,1-b]thiazoles were synthesized from thiohydantoins and α-bromoketones in good yields. This method has the advantages of simple operation, high yields, and mild reaction conditions and uses less toxic and low-cost chemical reagents.     

Carbon nanotubes: properties,synthesis, purification,and medical applications

Current discoveries of different forms of carbon nanostructures have motivated research on their applications in various fields. They hold promise for applications in medicine, gene, and drug delivery areas. Many different production methods for carbon nanotubes (CNTs) have been introduced; functionalization, filling, doping, and chemical modification have been achieved, and characterization, separation, and manipulation of individual CNTs are now possible. Parameters such as structure, surface area, surface charge, size distribution, surface chemistry, and agglomeration state as well as purity of the samples have considerable impact on the reactivity of carbon nanotubes. Otherwise, the strength and flexibility of carbon nanotubes make them of potential use in controlling other nanoscale structures, which suggests they will have a significant role in nanotechnology engineering.     

3D experimental and numerical analysis of wind flow around domed-roof buildings with open and closed apertures

This paper presents experimental and numerical study of airflow distribution around a reduced-scale model of a common type of domed-roof building. Measurements are performed in an open loop wind tunnel. A new modified Counihan scheme is developed for constructing a part-depth atmospheric boundary layer (ABL). Measured quantities include: wind velocity profile, turbulence intensity and airflow pattern around the building. To conduct the experiments, a 1:54 scale model of a real domed-roof building with six windows and an aperture on the roof is fabricated and placed in the test section of the wind tunnel. In addition, using a numerical modeling, turbulent airflow around such scale model in the wind tunnel is simulated and airflow field inside and outside the model as well as ventilating discharge coefficient are computed. It is illustrated that, airflow around this type of building contains complex adjacent recirculation flows. The building with open apertures has acceptable discharge coefficient for ventilation, which can be a factor to ensure comfort condition for residents as well as complying with energy-saving considerations.     

A time-domain noise-coupling technique for continuous-time sigma-delta modulators

In this paper, a time-domain noise-coupling technique based on the pulse width modulation is proposed. The time-domain quantization error is digitally extracted and shaped by an asynchronous digital filter. This digitally filtered quantization error is applied to the quantizer input to increase the modulator’s noise-shaping order. By using this technique in continuous-time sigma-delta modulators, the modulator’s shaping property is significantly enhanced. Comparative analytical calculations and simulation results are presented to estimate the performance of modulators employing the proposed quantizer. System-level simulation results reveal a (L + 2)th order noise-shaping capability of the proposed modulator while it employs only L analog integrators. The effects of main circuit non-idealities in the modulator’s performance are analytically investigated and confirmed by the simulation results.     

Design of CMOS three-stage amplifiers for fast-settling switched-capacitor circuits

In this paper, a time-domain design procedure for fast-settling three-stage amplifiers is presented. In the proposed design approach, the amplifier is designed to settle within a specific time with a given settling accuracy and circuit noise budget by optimizing both the power consumption and silicon die area. Both linear and nonlinear settling regions of three-stage amplifiers are considered and optimal values of the amplifier stages transconductance and compensation capacitors are obtained using the genetic algorithm optimization. Detailed design equations are provided and circuit level simulation results using a 90 nm CMOS technology are presented to evaluate the usefulness of the proposed design scheme respected to the previously reported design approaches.     

IGBDD: Intelligent Grid Based Data Dissemination Protocol for Mobile Sink in Wireless Sensor Networks

Lifetime and energy efficiency are important factors in the design of wireless sensor network. A critical issue during data collection is the formation of energy holes near the sink. Sensors which are located near the sink have to participate in relaying data on behalf of other sensors and thus their energy will be depleted very quickly. Mobile sink movement yields the significant performance gained by decreasing the amount of energy consumption. In this paper, we propose an Intelligent Grid Based Data Disseminating protocol for mobile sink in wireless sensor networks. We have utilized a virtual grid as the protocol’s substructure. In our proposed method, cell heads (CHs) will be selected based on the locations of virtual cross points (CPs) and CPs selection is needless to transfer any required data between neighbor nodes. We have optimized CPs selection using linear programming technique in order to increase network lifetime. By selecting the CHs based on our proposed algorithm, data will be disseminated toward the sink. Our data dissemination protocol is simple and has low overhead to construct and maintain. Also, we have presented a new method for sink location update which leads to the least cost in data transfer. Simulation results illustrate that by utilizing hierarchical functionality and selecting appropriate CPs and consequently selecting CHs, energy consumption will be decreased in comparison with other presented methods which directly lead to network lifetime increment. Also by determining an optimal cell size, packet delivery rate will be improved noticeably.     

Energy Detector in Ultra Wideband Systems Using Phase Compensation Technique

Energy detectors have the advantage of simple structure and inexpensive price. Due to the low signal to noise ratio (SNR) of the received signal in ultra-wideBand (UWB) system, these desirable advantages can be achieved at the expense of non-trivial performance degradation. This paper presents a phase compensation (PC) technique to improve the performance of energy detector in UWB systems. In PC-UWB, the frequency dependent phase of the system response at the transmitter is extracted and its opposite spectral phase is used as prefilter. Because of Low complexity, cost and energy consumption of energy detectors, PC techniques has extensive potential for future of UWB communication systems. Measurement results show that the use of PC-UWB leads to signal power concentration at the receiver, which reduces the number of RAKE fingers required in coherent detection as well as achieves a higher data rate with less intersymbol interference. However time reversal UWB can achieve secure data transmission, but its performance is worse than PC-UWB. Simulation results show that phase compensation reduces the inter symbol interference impacts. Therefore it is possible to use a simple receiver with insignificant performance degradation. It is also shown that PC-UWB considerably outperforms TR-UWB and has satisfying performance in SNR greater than 13 dB.     

Low-Power Symmetrical Rectifier for Passive UHF RFID Transponder

Rectifier design is one of the challenging issues in passive radio-frequency identification (RFID) systems. Differential structures are good candidates as rectifiers to their high conversion efficiencies. In this paper, a novel structure is proposed to produce symmetrical power-supply utilizing differential circuit configuration simulated in 130nm CMOS technology. The proposed rectifier can provide 1.34 V DC power with 382% voltage conversion efficiency, thus demonstrated its higher performance over existing designs.     

A Novel Evolutionary-Based Cooperative Spectrum Sensing Mechanism for Cognitive Radio Networks

Cognitive radio (CR) is considered as a feasible intelligent technology for 4G wireless networks or self-organization networks and envisioned as a promising paradigm of exploiting intelligence for enhancing efficiency of underutilized spectrum bands. In CR, one of the main concerns is to reliably sense the presence of primary users, to attain protection against harmful interference caused by the potential spectrum access of secondary users (SUs). In this paper, evolutionary algorithms, namely, genetic algorithm (GA) and particle swarm optimization (PSO) are investigated. An imperialistic competitive algorithm (ICA) is proposed to minimize error detection at the common soft data fusion (SDF) center for structurally centralized cognitive radio network (CRN). By using these techniques, evolutionary operations are invoked to optimize the weighting coefficients applied on the sensing measurement components received from multiple cooperative SUs. The proposed method is compared with other evolutionary algorithms, as well as other conventional deterministic, such as maximal ratio combining- (MRC-), modified deflection coefficient- (MDC-), normal deflection coefficient- (NDC-) based SDF schemes and OR-rule HDF based. MATLAB simulations confirm the superiority of the ICA-based scheme over the PSO-, GA-based and other conventional schemes in terms of detection performance. In addition, the ICA-based scheme also shows promising convergence and time running performance as compared to other iterative-based schemes. This makes ICA an adequate solution to meet real-time requirements.