Microwave and terahertz dielectric properties of MgTiO3–CaTiO3 ceramics

The THz dielectric properties of MgTiO3–CaTiO3 ceramics are reported. The ceramics were prepared via a solid-state reaction route and the sintering conditions were optimized to obtain ceramics with high permittivity and low loss in the terahertz frequency domain. The amount of impurities (MgTi2O5) and grain size increased with increasing sintering temperature. The dielectric properties improved with increasing density, and the best terahertz dielectric performance was obtained at 1260 °C, with a permittivity of 17.73 and loss of 3.07×10−3. Ceramics sintered above 1260 °C showed a sharp increase in loss, which is ascribed to an increase in the impurity content

Anomalous Heat Conduction and Anomalous Diffusion in Low Dimensional Nanoscale Systems

Thermal transport is an important energy transfer process in nature. Phonon is the major energy carrier for heat in semiconductor and dielectric materials. In analogy to Ohm's law for electrical conductivity, Fourier's law is a fundamental rule of heat transfer in solids. It states that the thermal conductivity is independent of sample scale and geometry. Although Fourier's law has received great success in describing macroscopic thermal transport in the past two hundreds years, its validity in low dimensional systems is still an open question. Here we give a brief review of the recent developments in experimental, theoretical and numerical studies of heat transport in low dimensional systems, include lattice models, nanowires, nanotubes and graphenes. We will demonstrate that the phonon transports in low dimensional systems super-diffusively, which leads to a size dependent thermal conductivity. In other words, Fourier's law is breakdown in low dimensional structures

Magnetotransport in the Normal State of La1.85Sr0.15Cu(1-y)Zn(y)O4 Films

We have studied the magnetotransport properties in the normal state for a series of La1.85Sr0.15Cu(1-y)Zn(y)O4 films with values of y, between 0 and 0.12. A variable degree of compressive or tensile strain results from the lattice mismatch between the substrate and the film, and affects the transport properties differently from the influence of the zinc impurities. In particular, the orbital magnetoresistance (OMR) varies with y but is strain-independent. The relations for the resistivity and the Hall angle and the proportionality between the OMR and tan^2 theta are followed about 70 K. We have been able to separate the strain and impurity effects by rewriting the above relations, where each term is strain-independent and depends on y only. We also find that changes in the lattice constants give rise to closely the same fractional changes in other terms of the equation.The OMR is more strongly supressed by the addition of impurities than tan^2 theta. We conclude that the relaxation ratethat governs Hall effect is not the same as for the magnetoresistance. We also suggest a correspondence between the transport properties and the opening of the pseudogap at a temperature which changes when the La-sr ratio changes, but does not change with the addition of the zinc impurities

Precision Measurement of the Proton Flux in Primary Cosmic Rays from Rigidity 1 GV to 1.8 TV with the Alpha Magnetic Spectrometer on the International Space Station

A precise measurement of the proton flux in primary cosmic rays with rigidity (momentum/charge) from 1 GV to 1.8 TV is presented based on 300 million events. Knowledge of the rigidity dependence of the proton flux is important in understanding the origin, acceleration, and propagation of cosmic rays. We present the detailed variation with rigidity of the flux spectral index for the first time. The spectral index progressively hardens at high rigidities.</p

Wyner-Ziv coding for the half-duplex relay channel

Cover and El Gamal derived the tightest bounds on the capacity of the relay channel using random coding and proposed two coding strategies, namely decode-and-forward (DF) and compress-and-forward (CF), to provide the best known lower bounds of the achievable rate region. Depending on transmission parameters, either DF or CF could be superior. Several practical code designs based on DF have appeared recently. We present the first practical CF design for the half-duplex Gaussian relay channel based on Wyner-Ziv coding of the received source signal at the relay. Assuming ideal source and channel coding, our design achieves the lower bound of CF. It thus realizes the performance gain of CF over DF promised by the theory when the relay is close to the destination. Our practical implementation based on LDPC codes for error protection at the source and nested scalar quantization and IRA codes for Wyner-Ziv coding at the relay comes as close as 0.76 dB to the theoretical limit of CF

Packet erasure protection for multicasting

Priority encoding transmission is an efficient forward error correction system for the robust transmission of scalable image and video data over packet erasure networks. For a memoryless packet erasure channel we first study the sensitivity of an optimal protection solution to a change in the packet erasure rate and in the number of packets. We then propose a practical error protection algorithm for multicasting and broadcasting applications. Instead of computing an optimal solution for each client independently, we show that comparable results can be obtained much faster by refining protections already computed for other clients. We also consider the situation where clients share a bottleneck link and develop layered multiple description codes that provide a better quality trade-off among all clients than previous solutions

Fast forward error protection of packetized multimedia bitstreams for transmission over varying channels

We propose a real-time optimization algorithm that selects an appropriate channel code for hybrid systems that combine packetization of an embedded wavelet bitstream into independently decodable packets and forward error correction using a family of channel codes with error detection and error correction capability. Such systems are very powerful for the transmission of audio, images, and video over fading and erasure channels with varying statistics. We also give an implementation that uses an optimal packetization technique and a concatenated cyclic redundancy check/rate-compatible punctured convolutional coder. Experimental results show that the peak signal-to-noise ratio of the average mean square error of our system is up to 1.74 dB higher than that of the previous best hybrid system for a Rayleigh fading channel and a transmission rate of 0.25 bits per pixel. Finally, we compare the hybrid approach to a state-of-the-art approach that uses a product code to protect the information bitstream

Rate-based versus distortion-based optimal joint source-channel coding

We consider a joint source-channel coding system that protects an embedded wavelet bitstream against noise using a finite family of channel codes with error detection and error correction capability. The performance of this system may be measured by the expected distortion or by the expected number of correctly received source bits subject to a target total transmission rate. Whereas a rate-based optimal solution can be found in linear time, the computation of a distortion-based optimal solution is prohibitive. Under the assumption of the convexity of the operational distortion-rate function of the source coder, we give a lower bound on the expected distortion of a distortion-based optimal solution that depends only on a rate-based optimal solution. Then we show that a distortion-based optimal solution provides a stronger error protection than a rate-based optimal solution and exploit this result to reduce the time complexity of the distortion-based optimization. Finally, we propose a fast iterative improvement algorithm that starts from a rate-based optimal solution and converges to a local minimum of the expected distortion. Experimental results for a binary symmetric channel with the SPIHT coder and JPEG 2000 show that our lower bound is close to optimal. Moreover, the solution given by our local search algorithm has about the same quality as a distortion-based optimal solution, whereas its complexity is much lower than that of the previous best solution

Joint product code optimization for scalable multimedia transmission over wireless channels

State-of-the-art systems for the transmission of images over wireless channels generate an embedded bitstream and protect it with a product code where the row code is a concatenation of an outer cyclic redundancy check (CRC) code and an inner rate-compatible punctured convolutional (RCPC) code, and the column code is a Reed-Solomon (RS) code. In previous works, the product code was optimized by searching for the best RS protection for each RCPC code rate. We present a local search algorithm that jointly optimizes the RS and the RCPC codes. Experimental results show that our algorithm provides an approximately optimal solution, while its time complexity is much lower than that of the previous works

Product code error protection of packetized multimedia bitstreams

Sherwood and Zeger proposed a source-channel coding system where the source code is all embedded bitstream and the channel code is a product code such that each row code is a concatenation of a cyclic redundancy: check (CRC) and rate-compatible punctured convolutional codes (RCPC) and the column codes are Reed-Solomon (RS) codes. Re improve this system for wireless applications by efficiently reorganizing the source code into a set of independently decodable packets, which makes it more robust ill varying channels. We also give a linear-time algorithm for finding all optimal equal error protection for the resulting system. Experimental results show that the performance of our system significantly! outperforms that of the current slate-of-the-art in fading channels with varying statistics