Transition metal nanoparticles doped carbon paper as a cost-effective anode in a microbial fuel cell powered by pure and mixed biocatalyst cultures

The poor wettability and high cost of the carbonaceous electrodes materials prohibited the practical applications of microbial fuel cells (MFCs) on large scale. Here, a novel nanoparticles of metal sheathed with metal oxide is electrodeposited on carbon paper (CP) to introduce as high-performance anodes of microbial fuel cell (MFC). This thin layer of metal/metal oxide significantly enhance the microbial adhesion, the wettability of the anode surface and decrease the electron transfer resistance. The investigation of the modified CP anodes in an air-cathode MFCs fed by various biocatalyst cultures shows a significant improving in the MFC performance. Where, the generated power and current density was 140% and 210% higher as compared to the pristine CP. Mixed culture of exoelectrogenic microorganism in wastewater exhibited good performance and generated higher power and current density compared to yeast as pure culture. The excellent capacitance with a distinctive nanostructure morphology of the modified-CP open an avenues for practical applications of MFCs.     

Scalable and fault‐tolerant key agreement protocol for dynamic groups

With the widespread use of the Internet, the popularity of group communication‐based applications has grown considerably. Since most communications over the Internet involve the traversal of insecure networks, basic security services are necessary for these collaborative applications. These security services can be facilitated if the authorized group members share a common secret. In such distributed applications, key agreement protocols are preferred to key distribution protocols. In the past two decades, there have been many proposals for key agreement protocols. Most of these protocols are not efficient and limit the size of the underlying group. In this paper, we consider the scalability problem in group key agreement protocols. We propose a novel framework based on extension of the Diffie–Hellman key exchange protocol. The efficiency of our protocol comes from the clustering of the group members, where the common session key is established collaboratively by all participants. We present the auxiliary protocols needed when the membership changes. We show that our protocol is superior in complexity in both communication and computation overheads required to generate the session key. Copyright © 2006 John Wiley & Sons, Ltd.     

Experimental evaluation of space/frequency/polarization diversityin the indoor wireless channel

A series of experiments that were conducted to evaluate the relative merits of frequency, space, and polarization diversities in indoor portable radio channels at 900 MHz are described. Unmodulated tones were used to probe the channel in a typical university work environment. The statistics of the signal envelopes were analyzed to determine the correlation of the field strengths when the signals are separated in space, frequency or polarization. According to the results presented here, the performance of a narrowband system (<200 kHz) at 900 MHz could greatly benefit from a frequency diversity scheme provided that the separation between the two frequencies is greater than approximately 5 MHz. Similarly, the advantage of space diversity is found significant when the two antennas are spaced by 3/4 wavelength or more. Co-polarized and cross-polarized signals are nearly uncorrelated and their relative field strengths differ by less than 2 dB in most locations     

Scheduling schemes for multimedia service in wireless OFDM systems

Scheduling schemes play a key role in the system performance of broadband wireless systems such as WLANs/WMANs. Maximal SNR and round robin are two conventional scheduling strategies that emphasize efficiency and fairness, respectively. The proportional fair scheme provides a trade-off between efficiency and fairness, and has been well studied in TDMA and CDMA systems. In this article we extended the PF scheduling scheme to OFDM-based BWSs (OPF). In addition, we propose three variations: adaptive OPF (AOPF), multimedia AOPF (MAOPF), and normalized MAOPF (NMAOPF) in order to meet the QoS requirements for multirate services in multimedia systems. The adaptive modulation and coding schemes in time varying and frequency selective fading are considered. The system performances of the algorithms are compared in terms of efficiency (throughput and mean packet delay) and fairness (user satisfaction rate and average user rate). Joint physical and media access control layer simulation results show that AOPF and MAOPF can improve throughput at the cost of fairness, and NMAOPF can provide the highest throughput without losing fairness.     

Generation of trajectory sensitivities: minimal-order realization

The problem of obtaining a minimal-order realization of a trajectory sensitivity model is investigated for a linear multi-input multi-output system. The dimension of the minimal realization is a function of some structural parameters of the system model and can be computed in a closed form. Several examples are given to illustrate the results.     

Wake capturing in potential flow calculations

Summary In this paper, we present a formulation for irrotational, isentropic flows in terms of velocity components which is equivalent to the classical potential equation, except the wake is not fixed and it is captured as part of the solution with no special treatment. Preliminary numerical results are presented to validate this new approach.     

Comparison studies between cement and cement-kaolinite properties for incorporation of low-level radioactive wastes

Comparison between the properties of cement and cement mixed with 7.5% kaolinite was performed to choose the most suitable matrix to incorporate radio-active wastes. The cement-kaolinite mixtures were prepared as uncured, cured, and heated specimens. The physical properties of the cement-kaolinite mixture, namely density, porosity, and water absorption percent, were determined. Compressive strength, infrared spectra, thermal analysis, and the effect of gamma rays on the samples were studied. The studies were extended to the cement-kaolinite mixture in the presence of some chemical additives at different concentrations. Leachability of radioactive isotopes from the cement-kaolinite mixture was measured as a function of time. The physical and mechanical properties of cement were decreased in the presence of 7.5% kaolinite, whereas ¹³⁷Cs and ⁶⁰Co were less leached from the cement-kaolinite mixture.     

Pulpal response to a resin-modified glass-ionomer material on nonexposed and exposed monkey pulps

OBJECTIVE: This study evaluated the biocompatibility of a resin-modified glass-ionomer material on monkey pulps. METHOD AND MATERIALS: Standardized Class V cavities were prepared in 112 teeth distributed in six healthy adult monkeys. The resin-modified glass-ionomer cement was placed in 24 nonexposed and 36 exposed pulps according to manufacturer's instructions. ZOE was used as a control in nonexposed pulps, while calcium hydroxide was used as a control for exposed pulps. Tissues were collected at 6 to 7, 21 to 27, and 90 to 97 days. After demineralization, the teeth were serially sectioned, stained, and observed by light microscopy. RESULTS: Except for one resin-modified glass-ionomer pulp at 6 days, there were no differences between the responses of nonexposed pulps to resin-modified glass-ionomer specimens and ZOE controls. In exposed pulps, eight of 36 resin-modified glass-ionomer pulps showed various grades of inflammatory response, all associated with stained bacteria. Pulpal healing was similar in both resin-modified glass-ionomer and calcium hydroxide direct-capped exposures. Twenty-two of 26 exposed pulps restored with the resin-modified glass-ionomer cement showed dentin bridge formation at 21 and 97 days. CONCLUSION: The resin-modified glass-ionomer material exhibited acceptable biologic compatibility in exposed and nonexposed cavities.