Characteristics of two types of stabilized nano zero-valent iron and transport in porous media

Nano-scale zero-valent iron (NZVI) has been shown to be suitable for remediating contaminated aquifers. However, they usually aggregate rapidly and result in a very limited migration distance that inhibits their usefulness. This study employed poly acrylic acid (PAA) and carboxymethyl cellulose (CMC) to synthesize two types of stabilized styles of NZVI with finer sizes (namely PNZVI and CNZVI). The mobility of stabilized NZVI was also demonstrated on the basis of transport in porous media. The results show that the PNZVI has a uniform particle size of 12 nm. However, tens of CNZVI particles with diameters of 1-3 nm were packed into secondary particles. Both the PNZVI and the CNZVI exhibited amorphous structures, and the stabilizer was bound to particle surfaces in the form of bidentate bridging via the carboxylic group, which could provide both electrostatic and steric repulsion to prevent particle aggregation. This study also proposes presumed stabilized configurations of PNZVI and CNZVI to reasonably illustrate their different dispersed suspension types. On the basis of the breakthrough curves and mass recovery, this study observed that the mobility of PNZVI in classic Ca²⁺ concentration of groundwater was superior to CNZVI. Nonetheless, the mobility of CNZVI would be decreased less significantly than PNZVI when encountering high Ca²⁺ concentrations (40 mM). Presumably, increasing the pore flow velocity would enhance the mobility of stabilized NZVI. Overall, the results of this study indicate that PNZVI has the potential to become an effective reactive material for in situ groundwater remediation.     

Structure-controlled mesoporous SBA-15-derived mixed matrix membranes for H2 purification and CO2 capture

The composite mixed matrix membranes (MMMs) were prepared by incorporating mesopore SBA-15 as a filler to discuss the effects of its particle shape, particle size, and loadings on the organic–inorganic interfacial morphology. The SBA-15 was synthesized by template method and it's particle shape and size was adjusted by adding electrolyte. The results indicated that the spherical SBA-15 can improve the dispersion and have better adhesion with organic phase, which showed better permselectivity than the rod-like one. The SBA-15 filler also could increase the diffusion selectivity of MMMs by the addition of different particle sizes. The permeabilities of H₂ and CO₂ were 1207.9 and 552.86 Barrer, respectively, with selectivities of H₂/CH₄ and CO₂/CH₄ reached 247.0 and 112.8, respectively, when 1.6 μm spherical SBA-15 was added at 3 wt. %. The dissimilarity occurring in the perm-selectivity values with changes made in the particle shape and size are much more pronounced at the lower SBA-15 loading, which exceeded the 2008 Robeson's upper bound limited.     

Implementation and management of a mobile phone filtering system

This paper presents the system design and network management of a mobile phone filtering system (MOFIS) for filtering clones of cellular international calls by an IN‐based service node approach. Copyright © 2000 John Wiley & Sons, Ltd.     

Integration of voice/data services over PACS systems using a movable boundary slot allocation scheme

The integration of voice and data services over PACS systems using a movable boundary scheme is studied. First, we use the theory of discrete‐time Markov chain to analyse the system; then, an approximate analysis using the continuous‐time Markov chain model is conducted. For the initial access of voice calls we consider two distinct schemes: at most one idle slot being marked available, and all the idle slots being marked available. Numerical results show that the performance difference for voice calls between both schemes is trivial, but the former scheme offers a performance advantage for data calls over the latter scheme. Besides, the performance obtained by the continuous‐time Markov model is very close to that obtained by the discrete‐time Markov model. This finding suggests the effectiveness of the usage of the continuous‐time Markov model, which can dramatically simplify the analysis. Copyright © 2000 John Wiley & Sons, Ltd.     

A fully differential current copier for performance improvement

This paper presents a new current copier which uses a differential‐pair as its storage cell. The differential‐pair storage unit (DPSU) significantly reduces clock‐feedthrough errors and achieves high linearity, large dynamic range, and less cross‐talk noise. Therefore, the proposed high‐performance DPSU can be used to improve the speed performance of analog‐to‐digital converters which implement the proposed fully differential switched‐current technique. Copyright © 2000 John Wiley & Sons, Ltd.     

Simple yet accurate current copiers for low-voltage current-mode signal-processing applications

As pressures increase on VLSI designers to use a lower supply voltage of 3.3 V rather than the present 5 V, currentmode signal-processing techniques will surely become increasingly important and attractive. Numerous current copiers have been proposed. Among them, the copier with a negative feedback approach is the best candidate for low-voltage current-mode signal-processing applications. However, the copier using a positive-gain feedback amplifier achieves better accuracy at the cost of increasing circuit complexity and settling time. This paper presents an alternative circuit implementation of the negative feedback approach. the proposed current copier uses a negative-gain feedback amplifier which can be easily realized by a simple circuitry with high accuracy and faster settling time. Simulation results show that with the simple digital CMOS process the proposed copier can be realized with only three transistors, achieves a dynamic range from 300 to 550 μA with an accuracy of 0.1% and can be settled within 3 ns with a power supply of 3.3 V. Thus the copier is well suited to our low-voltage current-mode sensor array applications.     

High speed InGaAs/InP p-i-n photodiodes fabricated on asemi-insulating substrate

High speed, mass-produced InGaAs-InP p-i-n photodiodes have been fabricated on a semi-insulating substrate. The FWHM (full width at half maximum) impulse response of a 25-μm² device has been measured to be under 16 ps, entirely limited by the measurement system. The high speed of this structure was achieved by scaling the area down to 25 μm² and the intrinsic layer thickness down to 0.3 μm. Further scaling of this structure is possible, and bandwidths in excess of 200 GHz should be achievable. This structure is also useful for integration with bias tees, matching networks, and optical and electronic preamplifiers     

Built-in self-test (BIST) design of high-speed carry-free dividers

This paper presents the built-in self-test (BIST) design of a C-testable high-speed carry-free divider which can be fully tested by 72 test patterns irrespective of the divider size. Using a graph labeling scheme, the test patterns, expected outputs, and control signals can be represented by sets of labels and generated by a simple circuitry. As a result, test patterns can be easily generated inside chips, responses to test patterns need not to be stored, and use of expensive test equipment is not necessary. Results show that the hardware cost for generating such labels is virtually constant irrespective of the circuit size. For the BIST design of a 64 b C-testable divider, its hardware overhead is less than 5%     

Performance characterization of a harmonically mode-locked erbiumfiber ring laser

We describe the performance of a harmonically mode-locked, erbium fiber ring laser. Transform-limited pulses with durations of 20-50 ps at 5.044 GHz repetition rate are obtained. The modulation frequency can be detuned by up to ±70 kHz and the lasing wavelength can be varied over the entire erbium gain bandwidth. Pulsewidths and pulse bandwidths are measured as a function of modulation power and frequency detuning. The laser is actively stabilized by locking intra-cavity Fabry-Perot etalon passbands to the laser modes