Deactivation of copper-ion-exchanged hydrogen-mordenite-type zeolite catalyst by SO2 for no reduction by NH3

Deactivation of copper-ion-exchanged hydrogen-mordenite-type zeolite catalyst by SO₂ for NO reduction by NH₃ was examined in a fixed-bed flow reactor. The deactivation of the catalyst was strongly dependent on reaction temperature. At high reaction temperatures over 300°C, the catalyst did not lose its initial activity up to 50 h of operation, regardless of SO₂ feed concentration from 500 to 20,000 ppm. However, at low reaction temperatures near 250°C, apparent deactivation did occur. Changes in the physicochemical properties such as surface area and sulfur content of deactivated catalyst well correlated with catalyst activity, depending upon reaction temperatures. The deactivation was due to pore blocking and/or filling by deactivating agents, which plugged and/or filled the pores of catalyst. The deactivating agents deposited on the catalyst surface were presumed to be (NH₄)₂SO₄ and/or (NH₄)HSO₄ from the results of TGA and ion-chromatography measurement.     

Short-circuit power driven gate sizing technique for reducing powerdissipation

One major challenge in low-power technology is how to reduce overall power dissipation of a given subsystem without impacting its performance. In this paper we present a technique that can be applied to the nonspeed-critical nets in a circuit in order to reduce overall power dissipation. This technique involves a study of short-circuit power dissipation as a function of input signal slews and output load conditions, to aid in making a judicious choice of drive strengths for various gates in a circuit. The resulting low-power solution does not degrade the original performance and yields a circuit which occupies less silicon area. The technique described here can be incorporated into any power optimization or synthesis tool. Lastly, we present the savings in power and area for a 32-b carry lookahead adder which was designed using the technique described here     

K- and Q-bands CMOS frequency sources with X-band quadrature VCO

Fully integrated 10-, 20-, and 40-GHz frequency sources are presented, which are implemented with a 0.18-/spl mu/m CMOS process. A 10-GHz quadrature voltage-controlled oscillator (QVCO) is designed to have output with a low dc level, which can be effectively followed by a frequency multiplier. The proposed multipliers generate signals of 20 and 40 GHz using the harmonics of the QVCO. To have more harmonic power, a frequency doubler with pinchoff clipping is used without any buffers or dc-level shifters. The QVCO has a low phase noise of -118.67 dBc/Hz at a 1-MHz offset frequency with a 1.8-V power supply. The transistor size effect on phase noise is investigated. The frequency doubler has a low phase noise of -111.67 dBc/Hz at a 1-MHz offset frequency is measured, which is 7 dB higher than a phase noise of the QVCO. The doubler can be tuned between 19.8-22 GHz and the output is -6.83 dBm. A fourth-order frequency multiplier, which is used to obtain 40-GHz outputs, shows a phase noise of -102.0 dBc/Hz at 1-MHz offset frequency with the output power of -18.0 dBm. A large tuning range of 39.3-43.67 GHz (10%) is observed.     

Diagnosis of tapping operations using an AI approach

On-line diagnosis of the machining operations is essential because it can prevent potential problems caused by abnormal conditions. So far, little research has been done for the on-line diagnosis of tapping operations. However, tapping is a very important machining operation. And the on-line diagnosis is essential. In this work, an artificial neural network was utilized for the diagnosis of the tapping operation. The input vector for the neural network is obtained by processing the signals of the thrust, torque, and lateral forces during the tapping operations. A total of ten indices were used in the input layer of the network. The output of the artificial neural network provides the tapping states. Five different tapping states were investigated: normal operation, tap wear, misalignment, oversize hole, and undersize hole. The weights and thresholds of the artificial neural network can be modified by the generalized delta rule. Experimental results showed that diagnosis of tapping operations through an artificial neural network can reach a success rate of over 95%.     

Characterization of C-S-H from Highly Reactive β-Dicalcium Silicate Prepared from Hillebrandite

β-dicalcium silicate synthesized by thermal dissociation of hydrothermally prepared hillebrandite (Ca₂(SiO₃)(OH)₂) exhibits extremely high hydration activity. Characterization of the hydrates obtained and investigation of the hydration mechanism was carried out with the aid of trimethylsilylation analysis, ²⁹Si magic angle spinning nuclear magnetic resonance, transmission electron microscopy selected area electron diffraction, and XRD. The silicate anion structure of C-S-H consisted mainly of a dimer and a single-chain polymer. Polymerization advances with increasing curing temperature and curing time. The C-S-H has an oriented fibrous structure and exhibits a 0.73-nm dreierketten in the longitudinal direction. On heating, the C-S-H dissociates to form β-C₂S. The temperature at which βC₂S begins to form decreases with increasing chain length of the C-S-H or as the Ca/Si ratio becomes higher. The high activity of β-C₂S is due to its large specific surface area and the fact that the hydration is chemical-reaction-rate-controlled until its completion. As a result, the hydration progresses in situ and C-S-H with a high Ca/Si ratio is formed.     

Metabolic changes in blood and liver of dairy cows during either feed restriction or administration of 1,3-butanediol.

Previous research has shown that a combination of feed restriction and dietary 1,3-butanediol starting at 14 d post-partum resulted in fatty liver and ketosis. Sixteen multiparous Holstein cows were used to determine effects of feed restriction or 1,3-butanediol as separate treatments. Treatments during d 14 to 42 postpartum were 1) control (ad libitum intake), 2) 20% feed restriction, or 3) control plus dietary 1,3-butanediol (5.5% of DM). From d 43 to 56, cows assigned to treatments 2 and 3 received a combination of feed restriction and butanediol. One cow on treatment 2 developed ketosis, but not fatty liver, after only 4 d of feed restriction. No other cows developed fatty liver or ketosis. Both treatments decreased milk production compared with controls. Feed restriction increased the extent of negative energy balance and caused transient increases in concentrations of NEFA, acetate, and beta-hydroxybutyrate in plasma. Concentrations of beta-hydroxybutyrate and insulin in plasma were increased by butanediol, which is a potent ketone body precursor. Concentration of glycogen in liver was less in feed-restricted cows, whereas glycogen and total lipid were greater in cows given butanediol separately. Gluconeogenic capacity of liver slices was not different among groups. Addition of 1,3-butanediol to in vitro incubation media decreased oxidation of propionate to CO2. Neither feed restriction nor dietary 1,3-butanediol as separate treatments induced the fatty liver and ketosis observed in earlier experiments in which the two treatments were given together.     

Monolithically integrated four-channel receiver array using diffused InGaAs (JFET technology)

Four-channel receiver arrays have been fabricated by monolithically integrating diffused InGaAs JFET-based electronics with InGaAs pin photodiodes. Cascode and simple inverter transimpedance amplifier circuits have been produced, both of which use a micro-FET as a tunable feedback element to vary bandwidth between 20 and 800 MHz. A sensitivity of -28.2 dBm was achieved at 1.25 Gbit/s with crosstalk between adjacent channels of -50 dB (electrical).<>     

Heparin Use in Daily Hemodialysis

More frequent dialysis is thought to be associated with increased heparin requirements; however, limited data are available which compare heparin requirements of conventional to daily dialysis. Objectives: To determine differences in heparin dose during conventional thrice‐weekly dialysis (CHD) compared to daily hemodialysis (DHD). Methods: All patients within the daily home hemodialysis at the Northwest Kidney Centers were evaluated for heparin dose both pre‐ and post initiation of daily hemodialysis. Patients on DHD received an initial bolus of heparin, without a continuous heparin drip, and supplemental heparin midway through the dialysis run as needed to maintain adequate activated clotting times (ACTs). CHD patients received a heparin bolus, followed by initiation of heparin drip as needed to maintain adequate ACTs. Results: Of the 1117 patients who dialyze at the NKC, 55% were Caucasian, 21% African‐American, 20% Asian/Pacific Islander, and 35% were of other ethnicity. The majority of patients were greater than 60 years (56%), while 36% ranged from 40–60 years and 13% ranged from 20–40 years. Male patients constituted 54% of patients. Diabetes was the primary cause of renal disease (36%), followed by hypertension (21%) and glomerular disease (18%). Of those patients in the home hemodialysis program (n = 45), 10 patients started daily home hemodialysis using the Aksys daily home hemodialysis system. Of those, the majority was male (100%), Caucasian (78.8%) with an average age of 46.7 ± 18 years. Glomerulonephritis was the primary cause of end‐stage renal disease (40%), while the percentages of other diseases were similar [Alport's syndrome (20%), hypertension (20%) and diabetes (10%)]. Compared to initial DHD heparin requirements (10,111 ± 2219 units), CHD heparin dose requirements (6833 ± 2715 units) were significantly lower (p = 0.045); however, total heparin needs were similar between groups (10,166 ± 4380 units vs. 10,778 ± 2959 units) (p = 0.324). Conclusion: Although patients initiating DHD have greater initial heparin requirements than when on CHD, total heparin doses remain similar to those required on conventional thrice‐weekly hemodialysis. Greater initial heparin doses required during short daily dialysis appear safe compared to those of conventional dialysis.     

Distributed Multirobot Exploration and Mapping

Efficient exploration of unknown environments is a fundamental problem in mobile robotics. We present an approach to distributed multirobot mapping and exploration. Our system enables teams of robots to efficiently explore environments from different, unknown locations. In order to ensure consistency when combining their data into shared maps, the robots actively seek to verify their relative locations. Using shared maps, they coordinate their exploration strategies to maximize the efficiency of exploration. This system was evaluated under extremely realistic real-world conditions. An outside evaluation team found the system to be highly efficient and robust. The maps generated by our approach are consistently more accurate than those generated by manually measuring the locations and extensions of rooms and objects.     

Performance of a turbo‐coded CDMA system in a mobile satellite channel

The bit error rate (BER) performance of a turbo‐coded code‐division multiple‐access (CDMA) system operating in a satellite channel is analysed and simulated. The system performance is compared for various constituent decoders, including maximum a posteriori probability (MAP) and Max‐Log‐MAP algorithms, and the soft‐output Viterbi algorithm. The simulation results indicate that the Max‐Log‐MAP algorithm is the most promising among these three algorithms in overall terms of performance and complexity. It is also shown that, for fixed code rate, the BER performance is improved substantially by increasing the number of iterations in the turbo decoder, or by increasing the interleaver length in the turbo encoder. The results in this paper are of interest in CDMA‐based satellite communications applications. Copyright © 2005 John Wiley & Sons, Ltd.