Factors Affecting the Stability of CdTe/CdS Solar Cells Deduced from Stress Tests at Elevated Temperature

CdTe/CdS solar cells were subjected to heat stress at 200 °C in the dark under different environments (in N₂ and in air), and under illumination (in N₂). We postulate that two independent mechanisms can explain degradation phenomena in these cells: i) Excessive Cu doping of CdS: Accumulation of Cu in the CdS with stress, in the presence of Cl, will increase the photoconductivity of CdS. With limited amounts of Cu in CdS, this does NOT affect the photovoltaic behavior, but explains the crossover of light/dark current–voltage (J–V) curves. Overdoping of CdS with Cu can be detrimental to cell performance by creating deep acceptor states, acting as recombination centers, and compensating donor states. Under illumination, the barrier to Cu cations at the cell junction is reduced, and, therefore, Cu accumulation in the CdS is enhanced. Recovery of light‐stress induced degradation in CdTe/CdS cells in the dark is explained by dissociation of the acceptor defects. ii) Back contact barrier: Oxidation of the CdTe back surface in O₂/H₂O‐containing environment to form an insulating oxide results in a back‐contact barrier. This barrier is expressed by a rollover in the J–V curve. Humidity is an important factor in air‐induced degradation, as it accelerates the oxide formation. Heat treatment in the dark in inert atmosphere can stabilize the cells against certain causes of degradation, by completing the back contact anneal.     

Novel A-sandwich radome design for airborne applications

A novel A-sandwich hybrid variable thickness radome design, based on optimised power reflection, is presented. The radome performance parameters are evaluated accurately by a 3D ray-tracing procedure in conjunction with the aperture integration method. This design is demonstrated to be a better choice when multiple performance parameters need to be satisfied simultaneously.     

Radar Absorbing Structures Using Frequency Selective Surfaces: Trends and Perspectives

Journal of Electronic Materials - Microwave radar absorbers are widely used in the strategic sector and wireless communication systems to reduce the radar cross-section of a target and...     

A reliability test-plan for series systems with components havingstochastic failure rates

This paper proposes a reliability test plan for a series system, by considering the parameter λ_j of the exponential distribution to be a random variable having uniform distribution over [0, &thetas;_j], j = 1, 2,..., n. Explicit expressions are obtained for the optimal values of the t_j, when the number of components in the system is 2. The general solution, albeit implicit, has also been obtained when the number of components in a given system is ⩾3. Mathematical programming is used to find the optimal solution and to illustrate it with numerical results     

Steganalysis of Network Packet Length Based Data Hiding

Recently, data hiding by modifying network parameters like packet header, payload, and packet length has become popular among researchers. Different algorithms have been proposed during the last few years which have altered the network packets in different ways to embed the data bits. Some of these algorithms modify the network packet length for embedding. Although most of the packet length based embedding schemes try to imitate the normal network traffic distribution, they have altered the statistical distribution of network packet lengths during embedding. These statistical anomalies can be exploited to detect such schemes. In this paper, a second order detection scheme for packet length based steganography has been proposed. A comprehensive set of experiments have been carried out to show that the proposed detection scheme can detect network packet length based steganography with a considerably high accuracy.     

Explanation of P/E cycling impact on drain disturb in flash EEPROMs under CHE and CHISEL programming operation

The impact of program/erase (P/E) cycling on drain disturb in NOR Flash EEPROM cells under channel hot electron (CHE) and channel-initiated secondary electron (CHISEL) programming operation is studied. Charge gain disturb increases and charge loss disturb decreases after cycling under CHE and CHISEL operation. Carefully designed experiments and fullband Monte Carlo simulations were used to explain this behavior. P/E cycling induced degradation in gate coupling coefficient and the resulting increase in source/drain leakage, reduction in band-to-band tunneling and change in carrier injection area seems to explain well the behavior of CHE and CHISEL drain disturb after cycling.     

Improving the photocatalytic performance of TiO2 via hybridizing with graphene

In this paper an improvement in the photocatalytic performance of TiO₂ was carried out via hybridizing with graphene. Graphene-TiO₂ (GR-TiO₂)nanocomposites with different weight addition ratios of graphene oxide (GO) have been prepared via a facile microwave irradiation of GO and tetrabutyl titanate in isopropyl alcohol. Raman spectroscopy (RS), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV-visible spectroscopy (UV-vis), Fourier transform infrared spectra (FTIR), energy dispersive X-ray spectroscopy (EDX) and photoluminescence spectra (PL) are employed to determine the properties of the samples. Microwave irradiation can heat the reactant to a higher temperature in a short time, simultaneously GO is reduced to graphene and TiO₂ nanoparticles grown on the surface of GR. GR-TiO₂ nanocomposites synthesized via this approach have efficient electron conductivity in GR, resulting in a reduced electron-hole recombination rate. Among the synthesized nanocomposites, GT-8wt% exhibited the best photocatalytic activity toward photocatalytic degradation of MB. Our current work provides a new insight for the fabrication of GR-TiO₂ nanocomposites within a short reaction time and also explains the mechanism of photocatalysis employing radical and hole scavengers.     

Individualized interactive home-based haptic telerehabilitation

We present a haptic telerehabilitation framework for patients with upper-limb dysfunction that is well-suited for deployment in patients' homes. Specifically, a commercial-off-the-shelf (COTS) haptic force-feedback driving wheel interfaces with a PC to create a haptic Virtual Driving Environment (hVDE). Coupling this framework with parametric exercise/ movement protocols-structured as driving exercises along paths of varying complexity-is the key to the creation of an inexpensive, immersive, and yet individualized personal-movement trainer.     

Dual frequency miniature microstrip antenna

A single-feed dual frequency compact microstrip antenna with a shorting pin is described. This new antenna configuration gives a large variation in frequency ratio of the two operating frequencies, without increasing the overall size of the antenna