Strain hardening equation and the prediction of tensile strength of rolled polymers

A number of thermoplastic polymers were tested in tension to investigate their strain hardening behavior. A strain hardening equation has been proposed in terms of the true stress, true strain and two constants σ_o and m. The three material constants, viz. σ_o m and the true fracture strain, are shown to be adequate to describe completely the material's nonlinear viscoelastic or the so-called “plastic” behavior. The true stress-strain data for the polymers rolled to varying amounts of cold-work fits the strain hardening plot of the unrolled material. The same strain hardening equation, therefore, applies to rolled materials as well. The procedure for predicting the tensile strength of rolled materials is given.     

Multiple Antenna Enhancements for a High Rate CDMA Packet Data System

A High Data Rate (HDR) system has been proposed for providing downlink wireless packet service by using a channel-aware scheduling algorithm to transmit to users in a time-division multiplexed manner. In this paper, we propose using multiple antennas at the transmitter and/or at the receiver to improve performance of an HDR system. We consider the design tradeoffs between scheduling and multi-antenna transmission/detection strategies and investigate the average Shannon capacity throughput as a function of the number of antennas assuming ideal channel estimates and rate feedback. The highest capacities are achieved using multiple antennas at both the transmitter and receiver. For such systems, the best performance is achieved using a multi-input multi-output capacity-achieving transmission scheme such as BLAST (Bell Labs Layered Space-Time) in which the transmitted signal is coded in space and time, and the receive antennas are used to resolve the spatial interference. In the second part of the paper, we discuss practical transmitter and receiver architectures using BLAST for approaching the theoretical gains promised by the capacity analysis. Because the terminal receivers will be portable devices with limited computational and battery power, we perform a computational complexity analysis of the receiver and make high-level assessments on its feasibility. We conclude that the overall computational requirements are within the reach of current hardware technology.     

Electron transport in non-crystalline garnet films

Thin films of yttrium iron garnet (yig) and Gd-substitutedyig of different thickness have been prepared by flash evaporation. The surfacedc andac electrical resistivity and thermopower in these films have been studied. The results are explained on the basis of Mott and Davis model in which narrow tails of localised states exist at the extreme valence and conduction bands and a band of localised levels near the middle of the gap. For the temperature range studied, the main conduction mechanism is on account of excitation of carriers into localised states at the band edges and hopping at energies close to the band tails.     

Studies on viscosity of calcium soaps in aqueous methanol

Viscosity measurements of calcium soaps show that two kinds of micelles are formed in aqueous methanol mixtures. The change in the nature of micelles from hydrophilic oleomicelles to lipophilic hydromicelles occurs in solvents containing 40–50% (v/v) of methanol. The equations of Vand and Moulik are applicable only above the critical micelle concentration of the soaps. The parameters of the equations have been evaluated. These may be used to calculate the viscosity of soap solutions in the concentration range in which the equations hold good.     

Mössbauer spectroscopy of titanium-substituted iron garnets

The Mössbauer spectroscopy of polycrystalline Y_3?x Ca _x Fe_5?x Ti _x O₁₂ (x=0·2, 0·5, 0·7) garnets has been studied at room temperature. The hyperfine fields both at the octahedral and tetrahedral sites decrease with increasing titanium content. The hyperfine fields both ata andd-sites are linearly proportional to magnetization. The quadrupole splitting fora-site shows no dependence on Ti content while the quadrupole splitting ford-site increases slightly withx. The results are explained on the basis of lattice distortion due to Ti substitution ona-site.     

城域网和接入网发展需要的低水峰单模光纤

密集波分复用(DWDM)的出现扩大了长途传输网的容量,但是DWDM技术的复杂性和使用了昂贵的器件,限制了DWDM在城域网的应用.最新研制的光纤,其在整个宽工作带,包括在(1 380±3) nm上都具有低水峰.低水峰光纤与粗波分复用(CWDM)系统比用标准单模光纤(SMF)的同一系统所用的信道间隔宽33%.经过恶劣的环境试验证明,低水峰光纤具有稳定的抗氢气引起的衰减性能,可确保现场安装的低水峰光纤光缆长期可靠地工作.由于低水峰光纤具有优异的弯曲敏感性,使其与最近研制的宽带接入技术,即所谓的光纤到驻地(FTTP)完全相适应.     

Perfect reconstruction of uniform samples from K-th order nonuniform samples

In this paper, we propose a new discrete-time model which relates uniform samples and K-th order nonuniform (KONU) samples. Typically, such situations may occur in practice where the sampling rates of analog-to-digital converters (ADCs) in a cluster of sensors may be different. This paper also outlines a digital signal processing approach to reconstructing uniform samples from the nonuniform samples produced by time interleaving analog-to-digital converters (TI-ADCs) with different sampling rates and time-mismatches.     

RF channelizer architectures using 3-way iterative down conversion for concurrent or fast-switching spectrum analysis

A wide-band RF channelizer architecture using the concept of 3-way iterative down-conversion is introduced. An example RF channelizer implementation splits the input spectrum of 0.6–9 GHz into 7 channels each with a 1.2 GHz bandwidth. This RF channelizer implementation has the ability of concurrently down-converting 3 channels enabling multi-Gbps aggregate data reception. It further demonstrates the ability to rapidly switch from receiving one channel to another which is crucial for rapid spectrum analysis. A prototype of the RF channelizer has been fabricated in a 65 nm standard CMOS process. A 400 Mbps (BPSK) data reception has been demonstrated by down-converting two channels concurrently. Channel switching can be as fast as 8 ns and is always faster than \(1\,\upmu s\). The chip occupies an area of 2 mm \(\times\) 1 mm and consumes an average power of 435 mW while offering a dynamic range between 58 and 63 dB.