Modeling of transoceanic fiber-optic WDM communication systems

The rapid growth of long-haul wavelength-division multiplexing (WDM) fiber-optic telecommunications challenges lightwave system designers to increase the transmission capacity per fiber pair, while reducing the time to market. This makes it essential to have fast and accurate computer modeling tools to aid the systems design. There is a natural engineering tradeoff between simulation speed and accuracy; fast approximations tend to be inaccurate, while the exact treatment of the physical processes affecting transmission are nearly impossible to capture in a time-efficient algorithm. The proof of a successful tool development lies in the comparison of simulation results to transmission system measurements. In this paper, we discuss a new simulation technique based on careful evaluation of the key physical effects that produce system impairments. We show that this new approach can produce fast and accurate simulations of long-haul WDM transmission systems     

A Timing-Driven Approach to Synthesize Fast Barrel Shifters

In modern digital signal processing and graphics applications, the shifter is an important module, consuming a significant amount of delay. This brief presents an architectural optimization approach to synthesize a faster barrel shifter block, which can be useful to reduce the delay of the design without significantly increasing the area. We have divided the problem of generating the shifter into two steps: (i) timing-driven selection of multiple stages for merging, and (ii) the design of the merged stage. In our proposed method, we define the notion of dual merged stage, where two stages are merged and the triple merged stage, where three stages are merged into a single composite stage. These merged stages are identified by using a timing-driven algorithm and are used in conjunction with some single stages of the traditional barrel shifter. The use of these merged stages helps reduce the depth of the proposed barrel shifter architecture, thereby improving the delay. The timing-driven nature of our algorithm helps produce a faster implementation for the overall shifter block. We have evaluated the performance of our design by using a number of technology libraries, timing constraints and shifter bit-widths. Our experimental data shows that the shifter block generated by our algorithm is significantly faster (10.19% on average) than the shifter block generated by a commercially available datapath synthesis tool. These improvements were verified on placed-and-routed designs as well.     

On cone-invariant linear matrix inequalities

An exact solution for a special class of cone-preserving linear matrix inequalities (LMIs) is developed. By using a generalized version of the classical Perron-Frobenius theorem, the optimal value is shown to be equal to the spectral radius of an associated linear operator. This allows for a much more efficient computation of the optimal solution using, for instance, power iteration-type algorithms. This particular LMI class appears in the computation of upper bounds for some generalizations of the structured singular value μ (spherical μ) and in a class of rank minimization problems previously studied. Examples and comparisons with existing techniques are provided     

Carbon Nanotube Docking Stations: A New Concept in Catalysis

The mobility of surface-bound metallic nanoparticles (NPs) on catalyst supports results in agglomeration leading to a subsequent decrease in effectiveness of the catalytic behavior of the metal NPs over time. We report here the synthesis and characterization of a carbon nanotube (CNT) catalyst support system enhanced with ‘docking stations’ along the exterior which limit the surface mobility of ultra small iron catalyst particles on CNT surfaces during Fisher–Tropsch synthesis.     

Effect of H2, H2O,and CO2 on the deNOx characteristics of a combined passive NOx adsorber and NOx reduction catalyst

The effect of H₂, H₂O, and CO₂ on the NO_x removal characteristics of a non-PGM material (Ag/MgO/γ-Al₂O₃) is investigated, which is shown to be active for both NO_x adsorption and reduction. H₂O facilitates NO_x adsorption at early times but inhibits it at longer times. The inhibiting effect of CO₂ is observed at low temperatures and is proposed to be due to bicarbonates. However, the inhibiting effect of both H₂O and CO₂ decreases at higher temperatures. The formation of NO₂ at low temperatures is attributed to NO oxidation, and the contribution of stored NO_x to NO₂ formation increases with temperature. H₂O inhibits NH₃ oxidation at high temperatures as well as NO_x reduction by NH₃-SCR at low temperatures. However, the NO_x reduction activity is not affected by CO₂. H₂ significantly promotes the NH₃-SCR reactions, which is attributed to the facilitation of NO_x spillover from the reduced Ag sites to the support.     

Low substrate temperature synthesis of carbon nanowalls by ultrasonic spray pyrolysis

In this paper, we report the synthesis of two-dimensional wall like carbon nanostructures (i.e. carbon nanowalls) by ultrasonic spray pyrolysis of ethanol and fullerene mixture. At higher temperature carbon nanofibers were formed on the substrate placed at the center of the reactor tube, whereas carbon nanowalls were observed on the substrate placed downstream of the tube below 100 °C. Spaces between the nanowalls changed with distance of the substrates from the furnace. Qualitative analysis of materials was performed using scanning electron microscopy, transmission electron microscopy and Raman spectroscopy.     

Iminodiacetic acid functionalized cation exchange resin for adsorptive removal of Cr(VI), Cd(II), Ni(II) and Pb(II) from their aqueous solutions

Iminodiacetic acid functionality has been introduced on styrene-divinyl benzene co-polymeric beads and characterized by FT-IR in order to develop weak acid based cation exchange resin. This resin was evaluated for the removal of different heavy metal ions namely Cd(II), Cr(VI), Ni(II) and Pb(II) from their aqueous solutions. The results showed greater affinity of resin towards Cr(VI) for which 99.7% removal achieved in optimal conditions following the order Ni(II)>Pb(II)>Cd(II) with 65%, 59% and 28% removal. Experiments were also directed towards kinetic studies of adsorption and found to follow first order reversible kinetic model with the overall rate constants 0.3250, 0.2393, 0.4290 and 0.2968 for Cr(VI), Ni(II), Pb(II) and Cd(II) removal respectively. Detailed studies of Cr(VI) removal has been carried out to see the effect of pH, resin dose and metal ion concentration on adsorption and concluded that complexation enhanced the chromium removal efficacy of resin drastically, which is strongly pH dependent. The findings were also supported by the comparison of FT-IR spectra of neat resin with the chromium-adsorbed resin.     

An ADC BIST with on-chip ramp generator

This work presents built-in self-test (BIST) techniques for the production testing of mixed signal circuits. The special test strategy for the typical mixed-signal component analog-to-digital converter (ADC) is discussed. The traditional test for such mixed-signal components can be completed through a DSP-based mixed-signal tester with an arbitrary waveform generator and a signal digitizer, but such a test is very costly and time consuming. Hence, a BIST strategy based on an on chip ramp generator (OCRG) is proposed in this work for testing ADC. This BIST method has an advantage testing ADC without DAC to overcome area overhead. This BIST method realizes the test controller, test pattern generation and output response analyser at the aspect of the on-chip circuitry. The demonstration of the proposed BIST is given through various simulation results in the last parts of this work.     

Uplift Capacity of Axially Loaded Piles in Clays

The present study aims at determining the uplift capacity of axially loaded piles in clays whose undrained cohesion increases linearly with depth. With the application of the axisymmetric static limit analysis approach, proposed recently by the writers, the variation of the nondimensional uplift factors with respect to changes in the embedment ratio (H/B) has been obtained for several rates of increase of soil cohesion with depth defined in terms of a nondimensional factor m for given values of soil cohesion (c0) along the ground surface and diameter (B) of pile. The uplift resistance has been evaluated in the form of the uplift factors, Fcb and Fct due to the components of the shaft resistance and the total resistance, respectively. For the given values of c0 and B, the magnitude of the uplift resistance increases continuously with an increase in the value of m. Furthermore, the Fcb values are found to remain unaffected with the variation in the shaft adhesion, whereas, the Fct values increase continuously with an increase in the adhesion factor of the pile shaft.     

Performance of RS-BCH Concatenated Codes and BCH Single-Stage Codes on an Interference Satellite Channel

In this correspondence, a model is analyzed that was designed to study interference on satellite channels. We developed this model to obtain performance results for a coherent phase-shift keyed (CPSK) system in which RS-BCH concatenated codes and BCH singlestage codes are applied to a satellite channel corrupted by cochannel interference. These results make use of earlier work on performance analysis of anm-phase CPSK system operating in the presence of random Gaussian noise and non-Gaussian interference. Earlier work on performance evaluation of concatenated codes on an equierror channel is also used. Our model incorporates features that account for the burst behavior of the interference sources. Results indicate that the use of RS-BCH concatenated coding provides significant performance improvement over no coding as well as single-stage BCH coding.