Mohamed N.A. Nasr

Thermoelectric power factor performance of Bi85Sb15/graphene composite

Composite materials based on Bi85Sb15 with commercial graphene (Gr) nanoparticles have been synthesized by mechanical alloying and hot isostatic pressing. The effect of different amount of Gr nanoparticles (x = 0.02, 0.04, 0.06, and 0.08 wt %) on the thermoelectric properties of (Bi85Sb15)1− x Gr x composite was investigated. X-ray diffraction and scanning electron microscopy were carried out for the structure characterization of the composites. Transport properties, including electrical resistivity, Seebeck coefficient, and calculated power factor, were investigated and their variations were discussed with regard to microstructures in the temperature range of 173–373 K. Resistivity significantly declines in the sample with x = 0.04 wt % Gr, and the enhancement was 7% at 230 K and reached about 7.6% at room temperature. With 0.08 wt % Gr, a high absolute value of the Seebeck coefficient was observed. The power factor reaches its maximum of 3.7 × 10−3 Wm−1K−2 with x = 0.08 wt % at 173 K. The results reflect that this synthesis process can be a powerful method of obtaining homogeneous Bi–Sb thermoelectric composite materials rapidly and at low cost. In addition, the demand for uniform coherent composites was significant because of their high-performance transport properties.

Error Source Identification in Measuring Soft Tissue Stiffness and Self Compensating This Error Using Three Probes Configuration

One of the biggest challenges for measuring soft tissue stiffness using tactile sensors is to have an output independent of the contact conditions. Although the approach of using two springs with different stiffness is used, the output of sensor is usually unstable because of the soft tissue surface irregularity. This irregularity creates an inclination angle between the sensor tips and the tissue. By scanning some real organs of a chicken using laser microscope, it is found that the angle value does not exceed 3 degrees. A modification on the original sensor is proposed to compensate that error. A finite element analysis for the two sensors is carried out to compare their behavior. The error of the original approach is about 55% and 103% with an inclination angle 3 degrees on the left and right direction, respectively. However, the modified sensor output is stable up to 8 degrees with an error not exceeding 4%. Furthermore, it could differentiate between different soft tissues stiffness within the specified range.

Auto Inter-Carrier Frequency Offset Rectification Using Conjugate Cancellation in Multi-carrier CDMA Broadband Communications

—Self cancellation schemes confirmed its effectiveness for mitigating the intercarrier interference (ICI) in orthogonal frequency multiplexing (OFDM) system. The main source of ICI is the carrier frequency offsets (CFO) in mobile radio channel which destroys the carriers orthogonality. In this paper, we employ a self cancellation scheme known as the conjugate self cancellation scheme to reduce the impact the ICI in Multicarrier CDMA systems that use Time-Frequency domain (TF or Hybrid) spreading and are used in broadband wireless communications. We show with proof that TF-domain spreading Multicarrier CDMA system with conjugate cancellation (CC) works significantly better than conventional MC-CDMA system if the normalized frequency offset is less than 0.3 in the fading channels and in additive white Gaussian channel. The CC algorithm provides a high carrier to interference power ratio (CIR) in the small frequency offset compared with other self cancellation schemes and uses low cost receiver without increase in the system complexity. The drawback of this algorithm is the reduction in bandwidth efficiency, which can be compensated by using larger signal alphabet sizes. Simulation results show good agreement with the numerical results.