Energy and chemicals from rice husk

Rice husk is the only agro residue having maximum siliceous ash content and available in dry form. The present work on rice husk describes processes for producing controlled carbon-silica mixtures in amorphous form, electronic-grade potassium silicate and activated carbon.

Rice husk is first pyrolised in a reactor at less than 973 K to obtain the char which is subsequently heated and activated with steam at 1073–1173 K for about 1 h in another reactor. The char is leached with HCl. Analysis of the leached char indicates that it is amorphous in nature and contains mainly 40% carbon and 56% silica with small quantities of volatile matter. The utility of the material as filler for reinforcement of rubbers is tested. Test results show that a tenfold increase in tensile strength and modulus of elasticity can be achieved with 100 phr.

In another development, the leached char is digested with 10–15% KOH solution in the temperature range of 303–373 K for about 1–10 h. It is found that electronic-grade potassium silicate could be easily produced compared to the conventional method of fusion of sand with alkali at 1273–1473 K. The residue from this process is a good-quality activated carbon. A process flowsheet is presented for producing these chemicals with energy recovery aspects from rice husk.     

Influence of the dislocation density on the performance ofheteroepitaxial indium phosphide solar cells

The authors point out that heteroepitaxial indium phosphide solar cells developed to date have low efficiency due to misfit dislocations. Dislocations act as recombination centers and strongly influence the solar cell performance. Calculations have been made to study the dependence of heteroepitaxial InP solar cell efficiency on dislocation density. The effects of surface recombination velocity and cell emitter thickness are also considered. Calculated results are compared with the available experimental results on representative InP solar cells. It is shown that heteroepitaxial InP cells with over 20% AM0 efficiency could be fabricated if dislocation density can be reduced to <10⁵ cm^-2 and the surface recombination velocity reduced to <10⁵ cm/s     

Fiber-Optic Polarizer Using Resonant Tunneling through a Multilayer Overlay

We demonstrate an in-line fiber-optic polarizer using resonant tunneling through a leaky multilayer overlay for the first time. Polarization extinction ratio (PER) ? 27 dB with an insertion loss (IL) ? 3 dB has been demonstrated experimentally with scope of further improvement. A simple planar waveguide model is developed to analyze the device whose predictions match very well with the experimental results. It is further shown that by properly selecting the device parameters one can achieve PER ? 68 dB with IL ? 0.2 dB for λ = 0.6328 μm and PER ? 80 dB with IL ? 1.2 dB for λ = 1.3 μm.     

Network Protocol Development with nsclick

Ad hoc network protocols are often developed, tested and evaluated using simulators. However, when the time comes to deploy those protocols for use or testing on real systems the protocol must be reimplemented for the target platform. This usually results in two, completely separate code-bases that must be maintained. Bugs which are found and fixed under simulated conditions must also be fixed separately in the deployed implementation, and vice versa. There is ample opportunity for the two implementations to drift apart, possibly to the point where the deployed and simulated version have little actual resemblance to each other. Testing the deployed version may also require construction of a testbed, a potentially time-consuming and expensive endeavor. Even if constructing an actual testbed is feasible, simulators are very useful for running large, repeatable scenarios for tasks such as protocol evaluation and regression testing. Furthermore, since the implementation may require modification of the kernel network stack, there's a good chance that a particular implementation may only run on specific versions of specific operating systems. To address these issues, we constructed the nsclick simulation environment by embedding the Click Modular Router inside of the popular ns-2 network simulator. Routing protocols may be implemented as Click graphs and easily moved between simulation and any operating system supported by Click. This paper describes the design, use, validation and performance of nsclick.     

The effects of active layer thickness on Programmable Metallization Cell based on Ag–Ge–S

Programmable Metallization Cell (PMC) is a newly developed non-volatile memory device based on chalcogenide solid electrolytes. In this paper, we studied the PMC’s electrical properties as a function of its active layer thickness. The PMC devices are fabricated based on Ag-Ge-S materials using thermal evaporation method. The fabricated devices have their active layer thickness ranges from 8 nm to 30 nm. The I-V characteristics of the fabricated devices are studied as a function of their active layer thickness. It is observed that the ‘ON’ resistance of PMC displays a decreasing trend as we increase the active layer thickness. This is because less deposition nuclei can be formed on the cathode/electrolyte interface in thinner devices, which limits the number of conduction links that can be formed. The SET voltage also decreases slightly as increase of the active layer thickness. This is probably because thinner Ag-Ge-S layer localizes Ag ions’ movements due to the large size of Ag+ ion. On the other hand, the RESET voltage increases as we increase the active layer thickness, which is because there are more conduction links to be ionized in thicker devices.     

Design of S-Graded Buffer Layers for Metamorphic ZnS y Se1−y /GaAs (001) Semiconductor Devices

We present design equations for error function (or “S-graded”) graded buffers for use in accommodating lattice mismatch of heteroepitaxial semiconductor devices. In an S-graded metamorphic buffer layer the composition and lattice mismatch profiles follow a normal cumulative distribution function. Minimum-energy calculations suggest that the S-graded profile may be beneficial for control of defect densities in lattice-mismatched devices because they have several characteristics which enhance the mobility and glide velocities of dislocations, thereby promoting long misfit segments with relatively few threading arms. First, there is a misfit-dislocation-free zone (MDFZ) adjacent to the interface, which avoids dislocation pinning defects associated with substrate defects. Second, there is another MDFZ near the surface, which reduces pinning interactions near the device layer which will be grown on top. Third, there is a large built-in strain in the top MDFZ, which enhances the glide of dislocations to sweep out threading arms. In this paper we present approximate design equations for the widths of the MDFZs, the built-in strain, and the peak misfit dislocation density for a general S-graded semiconductor with diamond or zincblende crystal structure and (001) orientation, and show that these design equations are in fair agreement with detailed numerical energy-minimization calculations for ZnS _y Se_1?y /GaAs (001) heterostructures.     

Predicting Spam Messages Using Back Propagation Neural Network

Wireless Personal Communications - With the increase in popularity of smartphones, text-based communication has also gained popularity. Availability of messaging services at low cost has resulted...     

Rigid-motion-invariant classification of 3-D textures

This paper studies the problem of 3-D rigid-motion-invariant texture discrimination for discrete 3-D textures that are spatially homogeneous by modeling them as stationary Gaussian random fields. The latter property and our formulation of a 3-D rigid motion of a texture reduce the problem to the study of 3-D rotations of discrete textures. We formally develop the concept of 3-D texture rotations in the 3-D digital domain. We use this novel concept to define a "distance" between 3-D textures that remains invariant under all 3-D rigid motions of the texture. This concept of "distance" can be used for a monoscale or a multiscale 3-D rigid-motion-invariant testing of the statistical similarity of the 3-D textures. To compute the "distance" between any two rotations R(1) and R(2) of two given 3-D textures, we use the Kullback-Leibler divergence between 3-D Gaussian Markov random fields fitted to the rotated texture data. Then, the 3-D rigid-motion-invariant texture distance is the integral average, with respect to the Haar measure of the group SO(3), of all of these divergences when rotations R(1) and R(2) vary throughout SO(3). We also present an algorithm enabling the computation of the proposed 3-D rigid-motion-invariant texture distance as well as rules for 3-D rigid-motion-invariant texture discrimination/classification and experimental results demonstrating the capabilities of the proposed 3-D rigid-motion texture discrimination rules when applied in a multiscale setting, even on very general 3-D texture models.     

HSCA: a novel harmony search based efficient clustering in heterogeneous WSNs

Clustering objective reasons scalability, fault tolerance, data aggregation or fusion, load balancing of cluster heads, stabilized network topology, maximal network lifetime, increased connectivity, reduced routing delay, collision avoidance and utilizing sleeping schemes in wireless sensor networks. Load balanced clustering effectively organize the network into a connected hierarchy. Clustering is a discrete problem that can have more than one solution under different operating constraints. In this scenario, meta-heuristic algorithms are found suitable because they give set of solutions in acceptable time constraints. In the literature, several analytical and meta-heuristic approaches have been developed for load balanced clustering. In this paper, a novel harmony search based energy efficient load balanced clustering algorithm is presented and it is tested on a large sample network. Results demonstrated that the proposed approach has faster convergence and gives reliable and efficient load balanced clustering as compared to conventional harmony search algorithm (HSA) and several other methods in the literature. Moreover, the robustness of the proposed approach is also verified for different cases of fixed and variable parameters of HSA.     

Nonvolatile Silicon Memory Using GeO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>-Cladded Ge Quantum Dots Self-Assembled on SiO<Subscript>2</Subscript> and Lattice-Matched II–VI Tunnel Insulator

This paper presents fabrication and characterization of a quantum dot-based floating gate nonvolatile memory device with site-specific self-assembly of germanium oxide-cladded germanium (GeO _x -Ge) quantum dots on SiO₂ and ZnS/ZnMgS/ZnS (II–VI lattice-matched high-κ dielectric) tunnel insulator material. These monodispersed and individually cladded quantum dots have the potential to store charge uniformly in the floating gate and are well suited for nonvolatile memory applications.