A complete analysis of the effects of transfer phenomenons and reaction heats on sono-hydrogen production from reacting bubbles: Impact of ambient bubble size

Several experimental and computational works have been focused on the production of hydrogen by using ultrasonic irradiation. However, the effects of the different ultrasonic conditions have been analyzed by considering a single value for the ambient bubble radius R₀ (mean value), which is not the true case as the size of active bubbles in sonicating medium is an interval rather than a sole value. In the present paper, the impacts of mass transport, heat exchange and chemical reactions heat on the sono-production of hydrogen are examined over a range of ambient bubble radii. These effects are shown for various ultrasonic frequencies of 355, 500 and 1000 kHz and under a range of acoustic amplitudes, from 1.5 to 3 atm. The numerical simulations results demonstrated that the increase of the production rate of hydrogen (around R₀ of the maximal production rate) is amortized (for all models) for the wave frequencies of 355 and 500 kHz at higher amplitude (i.e. 3 atm). On the other hand, the total production rate (around R₀ of the maximal response) is increased proportionally with the reduction of ultrasonic frequency or if the acoustic amplitude is increased. The effect of heat exchange mechanism (on H₂ and the total production rate) was found to be dominant whatever the acoustic amplitude or the wave frequency (on all the range of R₀). It has been demonstrated that at the acoustic amplitudes >1.5 atm (for f = 355 and 500 kHz) and >2 atm (for f = 1000 kHz), the impacts of chemical reactions heat and mass transport are clear compared to the normal model throughout a range of bubble sizes. The ambient bubble size (R₀) of the maximal response (maximal production rate) is shifted toward lower values when the ultrasound frequency or the acoustic amplitude is raised. In addition, it is observed that the increase in the wave frequency or the decrease in acoustic amplitude cause a narrowing in the range of active bubbles.     

Design of an autonomous solar desalination plant using vacuum membrane distillation,the MEDINA project

The unit presented in this paper is designed to provide a high quality of potable water in remote coastal areas with bad infrastructure and without a network connection. The installation is designed completely autonomous; indeed the only source of energy is the sun.     

Reactive compatibilization of poly(l‐lactide)/poly(butylene succinate) blends through polyester maleation: from materials to properties

The melt blending of poly(l ‐lactide) (PLLA) with biodegradable poly(butylene succinate) (PBS) is considered with a view to fine‐tuning its mechanical properties and its degradability. For this purpose, both maleic‐anhydride‐grafted PLLA (PLLA‐g‐MA) and maleic‐anhydride‐grafted PBS (PBS‐g‐MA) were prepared and used as reactive compatibilizers. The influence of PBS melt viscosity on the morphology and mechanical properties of PLLA/PBS blends was studied. Interestingly, the blending of low viscosity PBS with PLLA allows PLLA to be toughened while the use of high viscosity PBS led to PLLA/PBS blends exhibiting co‐continuous morphology. The nanostructure of the co‐continuous blends may be tuned through the joint action of organo‐modified clays and reactive compatibilizers. The effect of PBS on PLLA degradability was also investigated. The accelerated weathering testing of blends reveals that such combination of biodegradable polymers allows their degradability rate to be tailored. It is found that the addition of 20 wt% PBS to PLLA allows the molar mass loss fraction to be doubled after 425 h of testing. © 2014 Society of Chemical Industry     

Improving CSMA/CA network performance under hidden collision

Dynamic spectrum access policy allows a secondary user (SU) to access a primary user (PU) channel when it is idle. However, the idle state may result from the PU's silent activities, which can be wrongly perceived as an opportunity for the SU to access the channel and lead to “hidden collision” when it effectively tries to access the channel under this condition. At best of our knowledge, this issue has yet to be addressed in the literature. In this paper, we will first define a three‐state model that describes hidden collision conditions, then propose a probabilistic model in which a transient state is added to force the SU to wait a certain period of time before accessing the channel, thereby translating into better protection for the PU. Based on this model and using Carrier Sense Multiple Access/Collision Avoidance protocol, we will evaluate the PU's and SU's throughput and delay with and without transient state as well as the gain in using our approach. Our computation results show a substantial improvement of the PU's throughput from 19.6 to 61.1%.     

5-Nitro-1,2,4-triazole-3-one: A review of recent advances（英）

The 3-Nitro-1,2,4-triazole-5-one (NTO) is a high energydensity materials of keen interest for both commercial and scientific worlds owing to its reduced sensitivity, better thermal stability and high performances. It plays a significant role to replace the current energetic ingredients. In this review, we summarize various strategies involved in the synthesis of NTO as well as the existing approaches to tailor its particle morphology and sizes. The most prominent properties of NTO, such as insensitivity and performance, which are usually required to produce efficient formulations,have been concisely discussed. In addition, this overview reports on some newer forms of NTO including derivatives and co-crystals available inthe literature, which can enhance the NTO features and extend its applications. The advantages and shortcomings of various NTO forms for specific and potential use are also highlighted together with the attempts made to overcome these issues. Therefore, efforts will certainly continue to improve characteristics and performances of NTO either by chemical modification or by co-crystallization in order to produce promisingformulations for widespread applications in the near future.     

Local Coverage Probability Estimation in Single Frequency Networks

In OFDM based Single Frequency Networks (SFNs) such as Digital AudioBroadcasting (DAB) and Digital Video Broadcasting (DVB), the mobilereceiver is provided by the same signal from several synchronoustransmitters at the same carrier frequency.This transmitter diversity structure makes SFNs very efficientin fading channels with an excellent spectrum saving, and very goodpower utilization over the service area.However, depending on the position of the mobile within the servicearea, these signals arrive with different delays causing possibleechoes at the receiver.These echoes contribute to both the useful and the interferingparts of the signal.As the average received power in radio channels is a stochasticprocess, such contribution creates correlation between the differentcomponents of the Signal-to-Interference Ratio (SIR).In broadcasting practice, correlation was not taken into accountwhen estimating the distribution of the SIR and the local coverageprobability.This paper considers the effect of correlation on the estimation ofthe SIR and the coverage probability in OFDM based SFNs.Analyses are provided to show that in some situations the estimationerror can be considerable when neglecting this correlation.To obtain a better estimation, the correlation coefficient between thetotal useful and total interfering parts of the received signal isfirst evaluated and then used as a correction factor in estimating themean and standard deviation of the SIR.The obtained results show that such method can significantly reducethe estimation error of local coverage probability without increasingthe computation complexity.     

A multicarrier allocation (MCA) scheme for variable-rate 3Gwirelesssystems

High spectral efficiency and flexible data rate access are the main focus of future wireless networks. Multiple channel allocation schemes have the potential of achieving this goal. By assigning multiple slots and/or multiple carriers to one user, it is possible to provide a flexible data rate with quite low complexity. In this article we propose a simple allocation scheme where each user is assigned a fixed group of carriers. These carriers are adaptively used depending on the interference situation within the system. The system performance in terms of average throughput is investigated for two different types of allocation schemes: a fully centralized scheme and a distributed one that uses frequency diversity as a mean of improving the user link quality. The obtained results show that both schemes improve the system throughput over single carrier allocation without affecting the capacity of the system in terms of number of users per cell     

A discontinuous Galerkin method for the wave equation

We present a new discontinuous Galerkin method for solving the second-order wave equation using the standard continuous finite element method in space and a discontinuous method in time directly applied to second-order ode systems. We prove several optimal a priori error estimates in space–time norms for this new method and show that it can be more efficient than existing methods. We also write the leading term of the local discretization error in terms of Lobatto polynomials in space and Jacobi polynomials in time which leads to superconvergence points on each space–time cell. We discuss how to apply our results to construct efficient and asymptotically exact a posteriori estimates for space–time discretization errors. Numerical results are in agreement with theory.     

Ni-olivine catalysts prepared by thermal impregnation: Structure, steam reforming activity, and stability

Ni-olivine catalysts prepared by thermal impregnation are candidate materials for in-bed catalytic tar removal during fluidized bed biomass gasification. The present work examined the structure and surface properties of the Ni-olivine catalysts prepared by thermal impregnation following preparation, during reduction by in-situ techniques, and following naphthalene-steam reforming in simulated biomass derived syngas. Catalysts were characterized by BET surface area, laser Raman spectroscopy (LRS), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). During the preparation, secondary phases containing Mg (i.e., (Mg,Fe)₃Si₂O₅(OH)₄ and MgFe₂O₄) reacted to form an olivine phase enriched in Mg and either MgO or Mg-enriched (Mg,Ni)O. The presence of excess steam in the naphthalene-steam reforming appeared to limit coking and also caused behavior to be different than was observed under reducing conditions. Post-reaction characterization indicated the loss of a metallic phase through a possible alloying process and the exchange of Fe for Mg in the olivine structure. Either can potentially explain the high coke resistance of the Ni-olivine catalysts prepared by thermal impregnation compared to Ni-olivine catalysts prepared by incipient wetness impregnation or the olivine support. Finally, the properties of the olivine catalysts with and without Ni were compared through activity for methanol- and ethylene-steam reforming.