Detection of surge and stall in compression systems: an examplestudy

Issues concerning the detection of surge and rotating stall in a compression system are considered. It is observed that, when surge or rotating stall happens, the plenum pressure rise and mass flow rate of a compression system exhibit abrupt change while those of its linearized model do not. With this observation, it is shown that the surge and rotating stall can be successfully detected by employing a linear-based fault identification filter (FIDF) design technique. This is achieved by treating the difference between the output of the compression system and that of its linearized model at an unstalled operating point as a fault vector and then investigating the effect of the fault on the designed FIDE. Simulation results with regard to Moore and Greitzer's (1986) compression model are given to demonstrate the effectiveness of the proposed approach. The theoretical study presented in this note may provide a guideline of detecting the occurrence of unstable phenomena at the onset so that corrective responses can be made in the practical applications     

Users’ attitudes toward Web-based collaborative learning systems for knowledge management

The Web-based technology is a potential tool for supported collaborative learning that may enrich learning performance, such as individual knowledge construction or group knowledge sharing. Thus, understanding Web-based collaborative learning for knowledge management is a critical issue. The present study is to investigate learners’ attitudes toward Web-based collaborative learning systems. Based on this research, the results of factor analysis show that five attitude factors (system functions, system satisfaction, collaborative activities, learners’ characteristics, and system acceptance) should be examined at the same time when building a Web-based collaborative learning system. The results also provide an acceptance model for understanding users’ behavioral intention of facilitating Web-based collaborative systems.     

Nucleation and propagation of fatigue cracks in Al-304 stainless steel laminate composite

A study has been made of fatigue crack nucleation and propagation in Al-stainless steel (30 vol%) laminate composites. A Paris type power relationship between the crack growth rate, da/dN, and the alternating stress intensity, K, was obtained over the crack growth rates ranging from 10^–7 to 10^–4 mm/cycle, with an exponentm of 2.7. The cracks nucleated first in Al strips and then in stainless steel strips accompanied by some interface decohesion. The fatigue crack propagated in two stages. In the first stage, where the Al-steel interface was largely intact, the crack propagated in a plane strain mode (flat fracture surface with striations, each striation consisting of a cluster of interstriations). In the second stage, where there occurred extensive Al-steel interface delamination and the concomitant loss of mutual constraint, the crack propagated in the plane stress mode (slant fracture with voids). The crack growth was faster in Al than that in steel since the apparent striation spacing was larger in the former than in the latter. No one to one correspondence existed between the apparent striation spacing and the macroscopic crack growth rate.Thus, although, microscopically, the crack front was not planar; macroscopically, it could be regarded as planar, and a Paris type power relationship did characterize the macroscopic fatigue crack growth in this laminate system over the applied stress amplitude studied. Comparing the fatigue crack growth rates among Al-steel laminate, commercial or pure aluminium and 304 stainless steel, the Al-steel laminate has the lowest crack growth rate. This plus the weight and cost saving benefits make Al-steel laminate quite attractive.     

A simple recursive least square algorithm of space–temporal joint equalizer

The environment of the communication system will be more complicated in the future. Therefore, the adaptive array alone cannot cancel all the interferences in future communication system. Many space–temporal joint equalizers (STE) have been proposed to further enhance the capability of canceling the co-channel interferences (CCI) and the multi-path inter-symbol interferences (ISI). The recursive least square (RLS) algorithm of those joint methods will suffer the problems of system structure is complex, the convergent rate of performance is slow or number of calculations is large. In this paper, we propose a simple RLS algorithm (SRLS) of the STE to reduce the computation load, simplify the system structure and improve the system performance. The SRLS algorithm uses the output signal of STE to adjust the weights of adaptive array and equalizer simultaneously without using a transversal filter. Since there is no transversal filter required in the system, the system is simpler in comparison to the conventional STE. Besides, the RLS algorithm of conventional STE adjusts the weights of equalizer after the weights of adaptive array. The convergent rate of weights is slowly in those STE systems. The SRLS algorithm adjusts the weights of adaptive array and equalizer simultaneously. Therefore, the convergent rate of system will improve by the SRLS. Furthermore, the SRLS algorithm is found with input vectors of adaptive array and equalizer separately. Another STE method, which combines the input vectors of adaptive array and equalizer into a large dimension input vector, needs more number of calculations than the SRLS method. Thus, the SRLS of STE can simplify the complexity of system structure, reduce the computation load and improve the convergent performance of system effectively.     

A GA-based mobile RFID localization scheme for internet of things

In the current (Internet of Things) trend, the identification capability of RFID is integrated for the identification and applications of all objects, and this trend reveals the future demand for RFID wireless communication and localization. Therefore, this paper investigates the influences of RSSI and the distance to RFID and analyzes the common indoor localization algorithms, including range-based algorithms and range-free algorithms. However, there are too many interference factors in the indoor environment that easily lead to localization inaccuracy. To improve the RF-mapping technique in RFID that requires much time for initiation and lots of calculations, this paper proposes a GA-based (Genetic Algorithms, GA) localization algorithm to estimate the locations of unknown nodes and avoid the influence of environmental factors by pre-establishing the pattern. The designed scenarios and reference nodes in this paper are used to train our proposed algorithm and obtain the patents of the scenarios, which are adopted for RFID nodes to further compare and decrease errors. Therefore, as long as the algorithm is trained in advance with the scenarios and then include the patents in the new environment, the errors and the training time can be greatly reduced. Moreover, our proposed algorithm needs only little information about reference nodes to pre-establish the pattern.     

CFCC fatigue: A literature review

In this article, the current understanding of cyclic fatigue in continuous-fiber-rein-forced ceramic-matric composites is reviewed, with particular emphasis on the stress-number of cycles (S-N) approach to experimentally characterize and theoretically predict fatigue life. N. Miryala earned his M. Tech. in metallurgical engineering from the Indian Institute of Technology at Bombay, India, in 1990. He is a Ph.D. candidate at the University of Tennessee. Mr. Miriyala is a member of TMS. P.K. Liaw is a professor and Ivan Racheff Chair of Excellence in the Department of Materials Science and Engineering at the University of Tennessee. Dr. Liaw is a member of TMS.     

Synthesis and properties of novel aromatic polyimides derived from bis(p-aminophenoxy)methylphenylsilane

A novel siloxane-containing diamine, bis(p-aminophenoxy)methylphenylsilane (BAMPS), was synthesized from the condensation of dichloromethylphenylsilane with p-aminophenol in the presence of triethylamine. A series of BAMPS-based aromatic polyimides were prepared from BAMPS and various aromatic tetracarboxylic dianhydrides by the usual two-step procedure including ring-opening polyaddition to poly(amic acid)s and subsequent cyclodehydration to polyimides. The inherent viscosities of poly(amic acid)s III_a - III_f ranged from 0.09 to 0.36 dL g⁻¹ in N,N-dimethylacetamide at a concentration of 0.5 g dL⁻¹ at 30°C. The inherent viscosities of polyimides were between 0.06 and 0.32 dL g⁻¹ in various solvents at 30°C. Polyimides, especially IV_c and IV_f , were soluble in a wide range of organic solvents such as N-methyl-2-pyrrolidinone, concentrated H₂SO₄, N,N-dimethylacetamide, N,N-dimethylformamide, and dimethyl sulfoxide. The polyimides were characterized by elementary analysis, IR spectra, TGA, and DSC. They also had glass transition temperatures ranging from 128 to 181°C. The 10% mass loss temperature was recorded in the range of 404–443°C in nitrogen and of 315–339°C in oxygen. © 1997 John Wiley & Sons, Inc.     

The QseEF Two-Component System-GlmY Small RNA Regulatory Pathway Controls Swarming in Uropathogenic Proteus mirabilis

Bacterial sensing of environmental signals through the two-component system (TCS) plays a key role in modulating virulence. In the search for the host hormone-sensing TCS, we identified a conserved qseEGF locus following glmY, a small RNA (sRNA) gene in uropathogenic Proteus mirabilis. Genes of glmY-qseE-qseG-qseF constitute an operon, and QseF binding sites were found in the glmY promoter region. Deletion of glmY or qseF resulted in reduced swarming motility and swarming-related phenotypes relative to the wild-type and the respective complemented strains. The qseF mutant had decreased glmYqseEGF promoter activity. Both glmY and qseF mutants exhibited decreased flhDC promoter activity and mRNA level, while increased rcsB mRNA level was observed in both mutants. Prediction by TargetRNA2 revealed cheA as the target of GlmY. Then, construction of the translational fusions containing various lengths of cheA 5′UTR for reporter assay and site-directed mutagenesis were performed to investigate the cheA-GlmY interaction in cheA activation. Notably, loss of glmY reduced the cheA mRNA level, and urea could inhibit swarming in a QseF-dependent manner. Altogether, this is the first report elucidating the underlying mechanisms for modulation of swarming motility by a QseEF-regulated sRNA GlmY, involving expression of cheA, rcsB and flhDC in uropathogenic P. mirabilis.     

Synthesis of novel thermally stable electrochromic polynorbornenes containing symmetrical diarylamine and unsymmetrical triarylamine chromophores via ring-opening metathesis polymerisation

A new electrochromic norbornene derivative (NB) containing symmetrical diphenylamine and unsymmetrical triphenylamine groups, was synthesised from norbornene amine and unsymmetrical triphenylamine-substituted bromide. NB was used to obtain unsaturated PNB via ring-opening metathesis polymerization using different Grubbs' catalysts, followed by hydrogen reduction to obtain saturated HPNB. PNB and HPNB were highly soluble in common organic solvents such as toluene, xylene, benzene, chlorobenzene, 1,2-dichlorobenzene, and tetrahydrofuran at room temperature. The glass transition temperatures (T_g) of PNB and hydrogenated HPNB were 162 °C and 117 °C, respectively. The 10% weight-loss temperatures of PNB and hydrogenated HPNB were 410 °C and 450 °C, respectively. Cyclic voltammogram of HPNB film cast onto an indium-tin oxide (ITO)-coated glass substrate exhibited three reversible oxidation redox couples at 0.52, 0.85 and 1.30 V versus Ag/Ag⁺ in acetonitrile solution. The electrochromic characteristics of HPNB showed excellent stability and reversibility, with multi-staged colour changes from light yellow to green, dark-blue and purple as the potential changed from 0 to 1.35 V. The colour switching time and the bleaching time of the HPNB were 8.7 s and 4.3 s, respectively, at 1084 nm and 7.9 s and 3.8 s at 879 nm.