Clusters identification and characterization in a gas–solid fluidized bed by the wavelet analysis

The local solid flow structure of the bubbling fluidized bed of sand particles was investigated in order to identify and characterize the clusters. Extensive experiments were carried out using an optical fibre probe, measuring the velocity and the diameter of clusters. Under all operating conditions, ascending and descending clusters co‐existed at all measurement locations. The locus of the inversion point at which the directions of cluster motion changed was determined. The velocity of the ascending clusters was a function of both superficial gas velocity and the radial and axial position. With increasing superficial gas velocity, both the velocity and the diameter of ascending clusters decreased near the wall. However, the velocity of descending clusters depended mainly on superficial gas velocity and the largest clusters existed closer to the wall. The results of this study help to explain cluster hydrodynamics in fluidized beds.     

Optimized Catalytic Bleaching Sequences for Eucalyptus Kraft Pulp

Contemporary multi-stage bleaching processes partially remove residual lignin and hexenuronic acid from cellulosic pulps. The reactions in the steps could be faster and consume smaller amounts of chemicals. Catalytic bleaching (H_cat), utilizing hypochlorite (H), triethylenediamine (DABCO) and its derivative N-carboxymethyl triethylenediamine (CM-DABCO), is a new discovery that has the potential to improve the chemical and energetic efficiency of bleaching processes in chemical pulp mills, e.g. through reducing the reaction time of the bleaching processes. The objective of this study was to clarify if new kraft pulp bleaching sequences with initial stage of chlorine dioxide (ClO₂; D) and an intermediate stage of H_cat could provide fully bleached pulps. The bleaching sequences of the studied eucalyptus pulps include D₀E_(OP)H_cat(Q)P and H_catZ/DP, which attained a final brightness of 88 and 89% ISO, respectively. H_catZ/DP showed to be the best sequence for the catalytic bleaching of eucalyptus kraft pulps. This study may open new doors to future bleaching of cellulose pulps with fewer towers and decreased use of chemicals.     

A Speculative and Adaptive MPI Rendezvous Protocol Over RDMA-enabled Interconnects

Overlapping computation with communication is a key technique to conceal the effect of communication latency on the performance of parallel applications. Message Passing Interface (MPI) is a widely used message passing standard for high performance computing. One of the most important factors in achieving a good level of overlap is the MPI ability to make progress on outstanding communication operations. In this paper, we propose a novel speculative MPI Rendezvous protocol that uses RDMA Read and RDMA Write to effectively improve communication progress and consequently the overlap ability. Performance results based on a modified MPICH2 implementation over 10-Gigabit iWARP Ethernet reveal a significant (80–100%) improvement in receiver side overlap and progress ability. We have also observed up to 30% improvement in application wait time for some NPB applications as well as the RADIX application. For applications that do not benefit from this protocol, an adaptation mechanism is used to stop the speculation to effectively reduce the protocol overhead.     

Investigation of in-flight reduction of magnetite concentrate by hydrogen

In this study, hydrogen reduction of in-flight fine particles of magnetite ore concentrate at constant heat flux condition has been investigated, experimentally and numerically. A 3D turbulent mathematical model was developed to simulate the dynamic motion of these particles and also progress of the reaction. An experimental set-up was made up to evaluate the simulation. The fabricated set-up contains a vertical furnace, a ceramic tube and a handmade powder feeder. There was an excellent agreement between the prediction results and the experimental data. Our simulation and also the experimental data showed a large fraction of the inlet particles traps in the reactor. This is an important issue, should be solved in an industrial scale of the process.     

Improving energy efficiency of asymmetric chip multithreaded multiprocessors through reduced OS noise scheduling

The performance of the emerging chip multithreaded symmetric multiprocessors (SMPs) is of great importance to the high performance computing community. However, the growing power consumption of such systems is of increasing concern, and techniques that can be used to increase the overall system power efficiency while sustaining the performance are very desirable. Operating system (OS) noise can have a dramatic effect on the system performance. Effectively handling the smaller OS tasks while simultaneously preserving application thread synchronicity leads to gains in the overall system efficiency. Recently, under a fixed power budget, asymmetric multiprocessors (AMP) have been proposed to improve the performance of multithreaded applications. An AMP in this context is a multiprocessor system in which its processors are not operating at the same frequency. This paper proposes two simple scheduling methods that reduce the impact of OS noise, while simultaneously taking advantage of an opportunity to increase the overall machine energy efficiency on AMP servers. Prototyping AMPs on a commercial 2‐way dual‐core Hyper‐Threaded (HT) Intel Xeon SMP server, using real power measurements across six SPEC OpenMP applications, indicates that the first proposed scheduler performs better on average for HT‐enabled systems, whereas the second scheduler is superior on average for HT‐disabled systems. Copyright © 2009 John Wiley & Sons, Ltd.     

Impact of Ionomer Content on Proton Exchange Membrane Fuel Cell Performance

The effect of Nafion ionomer content on performance of a proton exchange membrane (PEM) fuel cell operated with home‐made anodic and cathodic electrodes fabricated from a novel metal organic framework (MOF) derived Pt‐based electrocatalyst was investigated via numerical simulation and experimental measurement. First, the parameter sensitivity analysis was performed to identify the most influential parameters of the model. Then, these parameters were calibrated for different fuel cell designs investigated in the current study by employing the corresponding experimental data. Afterwards, the calibrated model was used to examine the impact of Nafion content in the catalyst layer of home‐made electrodes. Finally, the qualitative trend predicted by this model was experimentally surveyed by varying the Nafion content between 10–50 wt.% in the catalyst layer of home‐made electrodes. At the anode side, the performance of home‐made electrode in a PEM fuel cell demonstrated small dependency on Nafion content. For the cathodic home‐made electrode, Nafion content was found to affect the PEM fuel cell performance more strongly. Although the model could correctly capture the impact of Nafion content on calculated polarization curves, the model predicted optimum values significantly deviate from the experimental results. This was related to the several simplifications made during model development.     

Efficient communication using message prediction for clusters of multiprocessors

With the increasing uniprocessor and symmetric multiprocessor computational power available today, interprocessor communication has become an important factor that limits the performance of clusters of workstations/multiprocessors. Many factors including communication hardware overhead, communication software overhead, and the user environment overhead (multithreading, multiuser) affect the performance of the communication subsystems in such systems. A significant portion of the software communication overhead belongs to a number of message copying operations. Ideally, it is desirable to have a true zero‐copy protocol where the message is moved directly from the send buffer in its user space to the receive buffer in the destination without any intermediate buffering. However, due to the fact that message‐passing applications at the send side do not know the final receive buffer addresses, early arrival messages have to be buffered at a temporary area. In this paper, we show that there is a message reception communication locality in message‐passing applications. We have utilized this communication locality and devised different message predictors at the receiver sides of communications. In essence, these message predictors can be efficiently used to drain the network and cache the incoming messages even if the corresponding receive calls have not yet been posted. The performance of these predictors, in terms of hit ratio, on some parallel applications are quite promising and suggest that prediction has the potential to eliminate most of the remaining message copies. We also show that the proposed predictors do not have sensitivity to the starting message reception call, and that they perform better than (or at least equal to) our previously proposed predictors. Copyright © 2002 John Wiley & Sons, Ltd.     

A Low-Power Single-Weight-Combiner 802.11abg SoC in 0.13 µm CMOS for Embedded Applications Utilizing An Area and Power Efficient Cartesian Phase Shifter and Mixer Circuit

A low-power 802.11abg SoC which achieves the best reported sensitivity as well as lowest reported power consumption and utilizes an extensive array of auto calibrations is reported. This SoC utilizes a two-antenna array receiver to build a single weight combiner (SWC) system. A new signal-path Cartesian phase generation and combination technique is proposed that shifts the RF signal in 22.5deg phase steps. A 3 dB improvement in received SNR is achieved in comparison to the single path receiver. The radio and AFE occupy 10 mm² of area in a digital 0.13 mum CMOS process of which 0.29 mm² is occupied by the SWC RF receiver. The radio+AFE consume 85 mW of power in active Rx mode of which 30 mW is utilized by the SWC RF front-end.     

Novel synthesis formulas to design square patch frequency selective surface absorber based on equivalent circuit model

A new procedure is presented to design electromagnetic absorbers based on resistive square patch frequency selective surface (FSS) over grounded dielectric. The periodicity (p) and the distance between two adjacent squares in the lattice (w) are two unknowns to be solved, given the thickness and permittivity of the substrate, surface impedance of the square patches and the desired reflectivity in some specified frequency. Equivalent circuit model and transmission line method are employed here. Previously reported analysis formulas to calculate the square patch FSS admittance are exploited and novel synthesis formulas are extracted based of them. The final synthesis equations to calculate p and w are presented in term of polynomials. Usually an absorber is supposed to have a maximum reflectivity r in a frequency band [f₁, f₂]. The (p, w) pairs for reflectivity less than r in f₁, define an area in p‐w plane. The intersection of the so‐called area with the similar one defined by f₂ specifies all possible (p, w) pairs. Finally the results are tested and verified by the commercial full wave simulator Ansys‐HFSS as well as some experimental design. There is a good agreement between the expected results with the full wave analysis and practical test.     

Process Arrival Pattern Aware Alltoall and Allgather on InfiniBand Clusters

Recent studies show that MPI processes in real applications could arrive at an MPI collective operation at different times. This imbalanced process arrival pattern can significantly affect the performance of the collective operation. MPI_Alltoall() and MPI_Allgather() are communication-intensive collective operations that are used in many scientific applications. Therefore, their efficient implementations under different process arrival patterns are critical to the performance of scientific applications running on modern clusters. In this paper, we propose novel RDMA-based process arrival pattern aware MPI_Alltoall() and MPI_Allgather() for different message sizes over InfiniBand clusters. We also extend the algorithms to be shared memory aware for small to medium size messages under process arrival patterns. The performance results indicate that the proposed algorithms outperform the native MVAPICH implementations as well as other non-process arrival pattern aware algorithms when processes arrive at different times. Specifically, the RDMA-based process arrival pattern aware MPI_Alltoall() and MPI_Allgather() are 3.1 times faster than MVAPICH for 8 KB messages. On average, the applications studied in this paper (FT, RADIX, and N-BODY) achieve a speedup of 1.44 using the proposed algorithms.