Photonic crystal-based permutation switch for optical networks

We present, for the first time, the design of a low-cross talk scalable permutation switch employing photonic crystal ring resonators in an optical network. Through this novel approach, the transition between different states of the \(2 \times 2\) optical switch, as the basic element, is achieved by applying different operating wavelengths. Subsequently, the shuffling mechanisms in \(3 \times 3\) and \(4 \times 4\) optical networks are realized by controlling the position of photonics crystal ring resonators. Lowest cross talk levels of 6 and 5% are obtained for “bar” and “cross” switching states, respectively.     

Outage Performance of Energy Harvesting DF Relaying NOMA Networks

In this paper, we investigate energy harvesting decode-and-forward relaying non-orthogonal multiple access (NOMA) networks. We study two cases of single relay and multiple relays with partial relay selection strategy. Specifically, one source node wishes to transmit two symbols to two respective destinations directly and via the help of one selected intermediate energy constraint relay node, and the NOMA technique is applied in the transmission of both hops (from source to relay and from relay to destinations). For performance evaluation, we derive the closed-form expressions for the outage probability (OP) at D ₁ and D ₂ with both cases of single and multiple relays. Our analysis is substantiated via Monte Carlo simulation. The effect of several parameters, such as power allocation factors in both transmissions in two hops, power splitting ratio, energy harvesting efficiency, and the location of relay nodes to the outage performances at the two destinations is investigated.     

A reversible data hiding scheme for VQ indices using locally adaptive coding

Data hiding is designed to solve the problem of secure information exchange through public networks such as Internet. In this paper, we present an improved reversible data hiding scheme that can recover original VQ indices after data extraction. As with Chang et al.’s scheme, our proposed scheme also depends on the locally adaptive coding scheme. However, experimental results confirm that the hiding capacity of our proposed scheme is around 1.36 bpi in most digital images, which is typically higher than that of Chang et al.’s [17]. Moreover, the average compression rate that can be achieved with our proposed scheme is 0.49 bpp, which outperforms both Lin and Chang’s scheme (0.50 bpp), Tsai (0.50 bpp), Chang et al.’s scheme (0.53 bpp), and Yang and Lin’s scheme (0.53 bpp).     

Linear phase paraunitary filter bank with filters of differentlengths and its application in image compression

In this paper, the theory, structure, design, and implementation of a new class of linear-phase paraunitary filter banks (LPPUFBs) are investigated. The novel filter banks with filters of different lengths can be viewed as the generalized lapped orthogonal transforms (GenLOTs) with variable-length basis functions. Our main motivation is the application in block-transform-based image coding. Besides having all of the attractive properties of other lapped orthogonal transforms, the new transform takes advantage of its long, overlapping basis functions to represent smooth signals in order to reduce blocking artifacts, whereas it reserves short basis functions for high-frequency signal components like edges and texture, thereby limiting ringing artifacts. Two design methods are presented, each with its own set of advantages: the first is based on a direct lattice factorization, and the second enforces certain relationships between the lattice coefficients to obtain variable length filters. Various necessary conditions for the existence of meaningful solutions are derived and discussed in both cases. Finally, several design and image coding examples are presented to confirm the validity of the theory     

Modulation Transfer Noise Effects from a Continuous Digital Carrier to FDM/FM Carriers in Memoryless Nonlinear Devices

An analysis of the modulation transfer noise effects from a continuous (nonbursty) digital carrier to multiple FDM/FM carriers in a common memoryless nonlinear amplifier (e.g., satellite transponder TWTA) is presented. It is shown that the modulation transfer noise, which is caused by the random envelope variations of the digital carrier due to the random data patterns and filtering of the PSK pulses, consists of both discrete and continuous spectral components in the baseband of the FDM/FM carriers. Numerical examples in terms of the noise power ratio as well as a comparison between measured and computed results are given. In general, the discrete or tonal interference component at the symbol rate of the digital carrier is quite significant. Results of this paper should be useful in the planning of FDMA satellite transponders employing the mixed PSK-FM mode of operation.     

Simulation of the High-Frequency Response of a Heterogeneous Ground through the Finite Difference Technique

To simulate the propagation of an electromagnetic plane wave in an inhomogeneous ground, the finite difference approach can be used. One of the main problems in using this method is imposing the boundary conditions near the ground surface, especially at high frequency. Indeed, for the E polarization, the upper top of the numerical grid must be sufficiently far away from the air-ground interface in order to neglect the field due to the heterogeneities and the discretization of the atmosphere is necessary. For magneto-telluric modeling, improved boundary conditions have already been proposed. This paper deals with a new condition, valid everywhere in air and which can be applied for E and H polarization. Thus even at high frequency, as for radar applications, only one line is added to the grid discretizing the ground.     

Improved Graphitic Structure of Continuous Carbon Nanofibers via Graphene Oxide Templating

Continuous carbon nanofibers (CNF) present an attractive building block for a variety of multifunctional materials and devices. However, the carbonization of poly(acrylonitrile) (PAN) precursors usually results in CNFs with poor graphitic structure and, consequently, modest/non‐optimized properties. This paper reports that the graphitic structure of CNFs can be improved with an addition of a small amount of graphene oxide into PAN prior to processing. Continuous CNFs with 1.4 wt% of graphene oxide nanoparticles are prepared from PAN solutions by electrospinning, stabilized, and carbonized at 800 °C, 1200 °C, and 1850 °C. While the as‐prepared graphene oxide‐filled PAN nanofibers exhibit a considerable reduction in polymer crystallinity, Raman analysis of the carbonized nanofibers shows that both templating with graphene oxide and increasing the carbonization temperature significantly improve the graphitic order in CNFs. The effect of graphene oxide is more significant at higher carbonization temperatures. Selected area electron diffraction analysis of individual nanofibers reveals increased graphitic order and preferred orientation both in the vicinity of visible graphene oxide nanoparticles and in the regions where nanoparticles were not visible. These results indicate a possibility of global templating in CNFs, where the addition of a small amount of graphene oxide nanoparticles can template the formation of good, preferentially oriented graphitic crystallites in CNFs, leading to improved structure and mechanical and transport properties.     

Stereo Video Retargeting with Representative Seams in a Group of Stereoscopic Frames

The important requirements for stereo video retargeting are threefold: keeping temporal coherence, preventing depth distortion, and minimizing shape distortions of the retargeted video. To meet these requirements, the left and right video sequences are divided into groups of frames (GoFs), where the GoF is a basic unit for the seam carving and we assign a set of fixed seams for all frames within the GoF. To determine the fixed seams for each GoF, we need to find the GoF boundary in the video first. Then, the representative frame for each GoF is generated by considering the spatial saliency and temporal coherence. Also, the confidence of the stereoscopic correspondence between the left and right frames is considered to prevent depth distortion.     

Image superresolution using support vector regression.

A thorough investigation of the application of support vector regression (SVR) to the superresolution problem is conducted through various frameworks. Prior to the study, the SVR problem is enhanced by finding the optimal kernel. This is done by formulating the kernel learning problem in SVR form as a convex optimization problem, specifically a semi-definite programming (SDP) problem. An additional constraint is added to reduce the SDP to a quadratically constrained quadratic programming (QCQP) problem. After this optimization, investigation of the relevancy of SVR to superresolution proceeds with the possibility of using a single and general support vector regression for all image content, and the results are impressive for small training sets. This idea is improved upon by observing structural properties in the discrete cosine transform (DCT) domain to aid in learning the regression. Further improvement involves a combination of classification and SVR-based techniques, extending works in resolution synthesis. This method, termed kernel resolution synthesis, uses specific regressors for isolated image content to describe the domain through a partitioned look of the vector space, thereby yielding good results.     

Fabricating Strong and Stiff Bioplastics from Whole Spirulina Cells

Since the 1950s, 8.3 billion tonnes (Bt) of virgin plastics have been produced, of which around 5 Bt have accumulated as waste in oceans and other natural environments, posing severe threats to entire ecosystems. The need for sustainable bio-based alternatives to traditional petroleum-derived plastics is evident. Bioplastics produced from unprocessed biological materials have thus far suffered from heterogeneous and non-cohesive morphologies, which lead to weak mechanical properties and lack of processability, hindering their industrial integration. Here, a fast, simple, and scalable process is presented to transform raw microalgae into a self-bonded, recyclable, and backyard-compostable bioplastic with attractive mechanical properties surpassing those of other biobased plastics such as thermoplastic starch. Upon hot-pressing, the abundant and photosynthetic algae spirulina forms cohesive bioplastics with flexural modulus and strength in the range 3–5 GPa and 25.5–57 MPa, respectively, depending on pre-processing conditions and the addition of nanofillers. The machinability of these bioplastics, along with self-extinguishing properties, make them promising candidates for consumer plastics. Mechanical recycling and fast biodegradation in soil are demonstrated as end-of-life options. Finally, the environmental impacts are discussed in terms of global warming potential, highlighting the benefits of using a carbon-negative feedstock such as spirulina to fabricate plastics.