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Nanosize thermoelectric powder can exhibit improved performance index owing to reduction of lattice thermal conductivity. Currently, chemical or physical processes such as polyol synthesis, gas atomization, and mechanical milling are employed to prepare such powders. In this study, Te nanopowders of 5N purity were prepared using an evaporation–condensation process. The formation mechanisms for Te nanopowders and coarse crystals are discussed and correlated with condensation temperature gradient and Ar flow rate. Prepared Te powders exhibited particle sizes ranging from tens to hundreds of micrometers upon high-temperature processing to as low as tens of nanometers at low-temperature processing (room temperature). In addition, these nanopowders began to oxidize at 225 °C, and subsequently, began to evaporate at 733 °C, as observed through thermogravimetric analysis. The procedure presented here has been found to be an economical method for preparing high-purity Te nanopowders from low-purity Te feedstock.

Numerical analysis was performed on a vacuum distillation process for Te purification. The effects of temperature gradient and Ar gas flow rate and vacuum level on the evaporation behavior of Te were investigated through a series of simulations with a diffusion-coupled convection model. An overall yield of up to 95% of 4 N pure Te was achieved at an average distillation rate of ∼5.6 × 10−4 g · cm−2 · s−1 from 2 N pure indigenous Te. The diffusion and condensation factors of impurities were investigated under different distillation conditions such as vacuum degree, temperature and argon flow rate. It was found that the numerical model could be used to predict impurity level during vacuum distillation process of Te and designing and optimization of a larger-scale distillation process also could be possible with a sufficient reliability.

To increase the spectral efficiency of HFC network, the standard of digital video broadcasting for cable systems (DVB-C2) was completed in 2010 and products that support the DVB-C2 is expected to be released within years. Before making products for DVB-C2 receiver, the performance of them should be investigated under various channel conditions first. Thus, we show the performance of the proposed structure for a pre-FEC in DVB-C2 receiver considering the channel model including additive white Gaussian noise (AWGN), a frequency offset, and echo channels to provide information about the implementation of DVB-C2 receiver. Based on the simulation results, we implement the pre-FEC using two field programmable gate arrays (FPGAs) and show the measured symbol error rate (SER) between the transmitted and received quadrature amplitude modulation (QAM) symbols with respect to various symbol timing estimations (STEs) of synchronization (SYNC) and powers of analog-to-digital converter (ADC) input. Because the STE makes the received pilot symbols in preamble rotated and these rotated pilot symbols are used in channel estimation, it affects the channel estimation and SER of pre-FEC. In addition, the channel estimation impaired by the STE causes the received QAM symbols to have biased mean values compared with the transmitted 4096QAM symbols. Since this degrades the performance of pre-FEC, the automatic gain control (AGC) is added after zero-forcing linear equalizer (ZF-LE) to improve the performance of pre-FEC. As the power of ADC input decreases, the SER increases due to the noise enhancement of ZF-LE.

A passive infrared or pyroelectric infrared (PIR) sensor is mainly used to sense the existence of moving objects in an indoor environment. However, in an outdoor environment, there are often outbreaks of false alarms from environmental changes and other sources. Therefore, it is difficult to provide reliable detection outdoors. In this paper, two algorithms are proposed to reduce false alarms and provide trustworthy quality to surveillance systems. We gather PIR signals outdoors, analyze the collected data, and extract the target features defined as window energy and alarm duration. Using these features, we model target and false alarms, from which we propose two target decision algorithms: window energy detection and alarm duration detection. Simulation results using real PIR signals show the performance of the proposed algorithms.

We propose a flow admission control (FAC) for setting up a wire-speed connection for new flows based on their negotiated bandwidth. It also terminates a flow that does not have a packet transmitted within a certain period determined by the users. The FAC can be used to provide a reliable transmission of user datagram and transmission control protocol applications. If the period of flows can be set to a short time period, we can monitor active flows that carry a packet over networks during the flow period. Such powerful flow management can also be applied to security systems to detect a denial-of-service attack. We implement a network processor called a flow management network processor (FMNP), which is the second generation of the device that supports FAC. It has forty reduced instruction set computer core processors optimized for packet processing. It is fabricated in 65-nm CMOS technology and has a 40-Gbps process performance. We prove that a flow router equipped with an FMNP is better than legacy systems in terms of throughput and packet loss.

The MPEG-D unified speech and audio coding (USAC) standardization process was initiated by MPEG to develop an audio codec that is able to provide consistent quality for mixed speech and music contents. The current USAC reference model structure consists of frequency domain (FD) and linear prediction domain (LPD) core modules and is controlled using a signal classifier tool. In this letter, we propose an LPD singlemode USAC structure using an adaptive widowing-based transform-coded excitation module. We tested our system using official test items for all mono-evaluation modes. The results of the experiment show that the objective and subjective performances of the proposed single-mode USAC system are better than those of the FD/LPD dual-mode USAC system.

A receiver of upstream cable modem (CM) for data over cable service interface specifications (DOCSIS) 3.0 is proposed and implemented in field programmable gate arrays (FPGAs). The receiver, which can demodulate four upstream channels simultaneously, consists of a digital down converter (DDC), a pre-forward error correction (FEC) and a FEC decoder. In DDC, fixed decimation and variable decimation with respect to symbol rate are used to remove adjacent channel images. An automatic gain control (AGC) uses a power calculation in a packet detection (PD) to reduce hardware complexity. Coefficients of symbol timing estimation (STE) use the sign of preamble symbols for eliminating multipliers. In addition, STE operates only for some parts of preamble to save power consumption. We simulate estimated AGC values, success probability of STE, estimated frequency offsets. In addition, it is found that when the bit error rate (BER) of the pre-FEC of 64QAM is 10-5, the required Eb/N0 is 19.5 dB under the conditions of additive white Gaussian noise (AWGN), a frequency offset, and echo channel. We measure the spectrum of DDC output, an estimated AGC value, and an estimated frequency offset, and experiment on FEC decoder. Measured results show the maximum transmitted error vector magnitude (EVM) of 1.54 % and the maximum received EVM of 2.67%.

When the product of contrast and size of an object, which is to be reconstructed by using the ultrasound inverse scattering tomography algorithm, is large, it is well known that those algorithms fail to converge to a unique global minimum. In order to solve this well known and difficult convergence problem, in this paper we present a new method, which converges to the true solution, for obtaining the scattering potential without using the Born or Rytov approximation. This method converts the nonlinear nature of the problem into a linear one. Through computer simulations we will show the validity of the new approach for high contrast two-dimensional scattering objects which are insonified by an incident ultrasound plane wave. Numerical results show that the reconstruction error is very small for circularly symmetric two-dimensional cylindrical objects whose refractive indices range from small to even sufficiently large values for which the previous inverse scattering algorithms fail to converge.

In an uplink cable modem, it is crucial to employ a preamble pattern suitable for frame acquisition, channel estimation and coarse timing/frequency acquisition. Proposed is an oversampled constant envelope zero autocorrelation code (CAZAC) for an uplink cable modem compliant with the data over cable service interface specification. The false alarm and missing probability of the proposed preamble pattern are investigated and compared to those of the existing preamble pattern based on the extended CAZAC sequence.