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71.
There is a perceived need within the database community to extend the traditional relational database systems so as to accommodate applications which are deductive in nature. One major problem involved in such an extension is the efficient processing of recursive queries. To this end, parallel processing is expected to play an important role. While substantial work has been done in devising strategies for processing recursive queries in parallel, it is perhaps surprising that little has been reported on the implementation and the run-time performance of these strategies. In the paper we report our experience of implementing a pipelined evaluation strategy on transputers. A wide range of queries, database structures and architectural configurations are considered as benchmarks in this study. The performance is studied in terms of both speed-up factors and communication costs. The experimental results show the potential of processing recursive queries in parallel, and provide insight into the usefulness of using transputers for such applications. 相似文献
72.
John C. Bell 《Lubrication Science》1990,2(3):195-217
There are numerous wear problems associated with the use of pivoted cam follower valve train systems in modern high-speed automotive engines. These problems have led to the introduction of an increasing number of engines of this type as specification tests to assess the antiwear performance of lubricants. Critical conditions for wear in these systems have been identified by the application of a steady-wear process model to the kinematic analysis of the cam/follower contact cycle. The positions of maximum wear identified by this technique showed better agreement with worn engine components than the more commonly used criteria of maximum contact pressure and oil film thickness. 相似文献
73.
Angel S. Wimolkiatisak James P. Bell Daniel A. Scola Jemei Chang 《Polymer Composites》1990,11(5):274-279
The overall objective of this research was to correlate the processing—fiber arrangement—properties relationships of composites. In order to do this, an experimental technique to quantitatively characterize the fiber arrangement was developed. Using this technique, the compression molded graphite/epoxy composites, CMC, were found to have a standard deviation of fiber spacing of about twice the value of those from the simulated random composites, SRC. The standard deviation of fiber volume fraction for CMC was about 4 times the value of SRC. In other words, the fibers in this laboratory CMC were poorly distributed relative to SRC. 相似文献
74.
Richard M. Gunner Rory P. Wilson Mark D. Holton Phil Hopkins Stephen H. Bell Nikki J. Marks Nigel C. Bennett Sam Ferreira Danny Govender Pauli Viljoen Angela Bruns O. Louis van Schalkwyk Mads F. Bertelsen Carlos M. Duarte Martin C. van Rooyen Craig J. Tambling Aoife Gppert Delmar Diesel D. Michael Scantlebury 《Journal of the Royal Society Interface》2022,19(186)
The combined use of global positioning system (GPS) technology and motion sensors within the discipline of movement ecology has increased over recent years. This is particularly the case for instrumented wildlife, with many studies now opting to record parameters at high (infra-second) sampling frequencies. However, the detail with which GPS loggers can elucidate fine-scale movement depends on the precision and accuracy of fixes, with accuracy being affected by signal reception. We hypothesized that animal behaviour was the main factor affecting fix inaccuracy, with inherent GPS positional noise (jitter) being most apparent during GPS fixes for non-moving locations, thereby producing disproportionate error during rest periods. A movement-verified filtering (MVF) protocol was constructed to compare GPS-derived speed data with dynamic body acceleration, to provide a computationally quick method for identifying genuine travelling movement. This method was tested on 11 free-ranging lions (Panthera leo) fitted with collar-mounted GPS units and tri-axial motion sensors recording at 1 and 40 Hz, respectively. The findings support the hypothesis and show that distance moved estimates were, on average, overestimated by greater than 80% prior to GPS screening. We present the conceptual and mathematical protocols for screening fix inaccuracy within high-resolution GPS datasets and demonstrate the importance that MVF has for avoiding inaccurate and biased estimates of movement. 相似文献
75.
The disinfection activity of a new multipurpose disinfection solution (OPTI-FREE Express with ALDOX) was compared to several other contact lens disinfecting solutions. The new solution is preserved with polyquaternium-1 and myristamidopropyl dimethylamine. The other solutions included 3% hydrogen peroxide systems and multipurpose solutions (MPS) preserved with polyhexamethylene biguanide. The products were tested for antimicrobial activity against Staphylococcus spp., Pseudomonas aeruginosa, Serratia marcescens, Candida albicans, Fusarium solani, and Aspergillus fumigatus. OPTI-FREE Express provided a broader range of antimicrobial activity than the MPS. It provided activity similar to that demonstrated by 3% hydrogen peroxide systems, but unlike the hydrogen peroxide system tested, it also prevented re growth of the organisms during extended storage. 相似文献
76.
Lappi VR Thimothe J Walker J Bell J Gall K Moody MW Wiedmann M 《Journal of food protection》2004,67(6):1163-1169
Two ready-to-eat crawfish processing plants were monitored for 2 years to study the impact of Listeria control strategies, including employee training and targeted sanitation procedures, on Listeria contamination. Environmental, raw material, and finished product samples were collected weekly during the main processing months (April to June) and tested for Listeria spp. and Listeria monocytogenes. Before implementation of control strategies (year 1), the two processing plants showed Listeria spp. prevalences of 29.5% (n = 78) in raw, whole crawfish, 5.2% (n = 155) in the processing plant environment, and 0% (n = 78) in finished products. In year 2, after plant-specific Listeria control strategies were implemented, Listeria spp. prevalence increased in raw crawfish (57.5%, n = 101), in the processing plant environment (10.8%, n = 204), and in the finished product (1.0%, n = 102). Statistical analysis showed a significant increase in Listeria spp. prevalence (P < 0.0001) and a borderline nonsignificant increase in L. monocytogenes prevalence (P = 0.097) on raw material in year 2. Borderline nonsignificant increases were also observed for Listeria spp. prevalence in environmental samples (P = 0.082). Our data showed that Listeria spp. prevalence in raw crawfish can vary significantly among seasons. However, the increased contamination prevalence for raw materials only resulted in a limited Listeria prevalence increase for the processing plant environment with extremely low levels of finished product contamination. Heat treatment of raw materials combined with Listeria control strategies to prevent cross-contamination thus appears to be effective in achieving low levels of finished product contamination, even with Listeria spp. prevalences for raw crawfish of more than 50%. 相似文献
77.
The effects of adding mixtures of titania and zirconia on the methanol synthesis activity and selectivity of Cu/SiO2 were investigated. The synthesis of methanol from both CO/H2 and CO2/H2 mixtures was examined at 0.65 MPa and temperatures between 448 and 573 K. For CO hydrogenation, the addition of ZrO2 alone increased the methanol synthesis activity of Cu/SiO2 by up to three-fold. Substitution of a portion of the ZrO2 by TiO2 decreased the methanol synthesis activity of the catalyst relative to that observed when only ZrO2 is added. ZrO2 addition also enhanced the methane synthesis activity by as much as seven fold. In the case of CO2 hydrogenation, the maximum methanol synthesis activity is achieved when a 50/50 wt% mixture of ZrO2 and TiO2 is added to Cu/SiO2. Neither the presence of the oxide additive nor its composition had any effect on the activity of the reverse water–gas-shift reaction, which suggests that this reaction proceeds only on Cu. The observed effects of ZrO2 and TiO2 on the catalytic activity of methanol synthesis from CO and CO2, and methane synthesis from CO, are interpreted in terms of the strength and concentration of acidic and basic groups on the surface of the dispersed oxide. 相似文献
78.
Lisa J. Lobree In‐Chul Hwang Jeffrey A. Reimer Alexis T. Bell 《Catalysis Letters》1999,63(3-4):233-240
The interactions of NO, O2 and NO2 with Fe‐ZSM‐5, as well as the reduction of NO by C3H8 in the presence of O2, have been investigated using in situ infrared spectroscopy. The sample of Fe‐ZSM‐5 (Fe/Al =0.56) was prepared by solid‐state
ion exchange. NO adsorption in the absence of O2 produces only mono‐ and dinitrosyl species associated with Fe2+ cations. Adsorbed NO2/NO3 species are formed via the reaction of adsorbed O2 with gas‐phase NO or by the adsorption of gas‐phase NO2. The reduction of NO in the presence of O2 begins with the reaction of gas‐phase C3H8 with adsorbed NO2/NO3 species to form a nitrogen‐containing polymeric species. A reaction pathway is proposed for the catalyzed reduction of NO
by C3H8 in the presence of O2.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
79.
The results of an investigation of the porous structure of the Al2O3-SnO2 system and its properties after hydrogen treatment are presented. Pore size distribution was determined on the basis of low temperature nitrogen adsorption measurements. Reduction of the system by H2 leads to a decrease of the parameters defining porous structure. We conclude that this is due to the reduction of Sn(IV) species to oxidation state II. 相似文献
80.
Polyethylene multiwalled carbon nanotube composites 总被引:4,自引:0,他引:4
Tony McNally Petra Pötschke Michael Murphy Steven E.J. Bell Daniel Bein John Paul Quinn 《Polymer》2005,46(19):8222-8232
Polyethylene (PE) multiwalled carbon nanotubes (MWCNTs) with weight fractions ranging from 0.1 to 10 wt% were prepared by melt blending using a mini-twin screw extruder. The morphology and degree of dispersion of the MWCNTs in the PE matrix at different length scales was investigated using scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM) and wide-angle X-ray diffraction (WAXD). Both individual and agglomerations of MWCNTs were evident. An up-shift of 17 cm−1 for the G band and the evolution of a shoulder to this peak were obtained in the Raman spectra of the nanocomposites, probably due to compressive forces exerted on the MWCNTs by PE chains and indicating intercalation of PE into the MWCNT bundles. The electrical conductivity and linear viscoelastic behaviour of these nanocomposites were investigated. A percolation threshold of about 7.5 wt% was obtained and the electrical conductivity of PE was increased significantly, by 16 orders of magnitude, from 10−20 to 10−4 S/cm. The storage modulus (G′) versus frequency curves approached a plateau above the percolation threshold with the formation of an interconnected nanotube structure, indicative of ‘pseudo-solid-like’ behaviour. The ultimate tensile strength and elongation at break of the nanocomposites decreased with addition of MWCNTs. The diminution of mechanical properties of the nanocomposites, though concomitant with a significant increase in electrical conductivity, implies the mechanism for mechanical reinforcement for PE/MWCNT composites is filler-matrix interfacial interactions and not filler percolation. The temperature of crystallisation (Tc) and fraction of PE that was crystalline (Fc) were modified by incorporating MWCNTs. The thermal decomposition temperature of PE was enhanced by 20 K on addition of 10 wt% MWCNT. 相似文献