2,812 research outputs found
On the non-linear vibration of rotor-squeeze film damper assemblies
No full textSqueeze film dampers (SFDs) have long been used to attenuate the vibration of high-speed rotating machines such as gas turbine engines, turbo-chargers, etc. Due to their highly non-linear behaviour, it is often difficult to calculate the steady state vibration response of rotor-SFD systems. Over the years, methods such as the Runge-Kutta-Merson Method (RKMM) have been applied to solve the non-linear equations of motion for the system. However such a method requires huge amounts of computational time especially when a flexible shaft system is involved. In order to accelerate the calculations of the rotor-SFD system vibration response, the Modified Harmonic Balance Method and the Modified Iteration Method are introduced in this work. It is shown that their results agree very well with the RKMM predictions and the experimental measurements.The circumferential oil-feeding groove within the SFD radial clearance is designed to prevent oil starvation in the squeeze film. The pressure generated by the groove is traditionally neglected. To date, many experiments are designed to test SFDs with groove-depth to clearance ratios (cg/c) between 3 to 10 but no attempts have been made to assess the merits and weaknesses of various existing squeeze film force models under a wider range of parameters. In this work, the vibration responses of the SFDs tested with various groove depths (i.e. 3<Cg/c<41) are investigated experimentally and theoretically. Highly non-linear fluid stiffness, damping and inertia are observed and the fluid damping is sensitively related to oil viscosity and unbalance. It is found that none of the theoretical models assessed is able to provide a good correlation with all the studied experimental responses. However, it is shown that the special groove-two land model is able to predict the vibration behaviour of a very shallow grooved SFD (c^c <3) and the conventional two-land theory is applicable to SFD with a very deep groove (Cg/c >40). These observations should be sufficient to provide useful guidelines for engineers to design a shallow or deep grooved SFD-rotor assembly.The SFD can be sealed to increase its damping. Empirical methods are commonly used to predict the vibration response but deeper understanding of the oil flow within the damper is not achieved. In this work, the flow balance principle is used to find the boundary conditions of the end-sealed SFD. With the assumption of a short bearing, averaging the one-land and two-land pressure distributions within the damper clearance, the current research shows that a good estimation of the end-sealed SFD vibration can be achieved. Such a model would be useful for the development of a comprehensive analytical end-sealed SFD model
Evaluation of various fluid-film models for use in the analysis of squeeze film dampers with a central groove
No full textExperimental vibration responses of squeeze film dampers (SFDs) are obtained with four different central groove depths, two types of lubricant and various unbalance levels. Highly non-linear fluid stiffness and damping are observed, the damping being sensitively related to oil viscosity and unbalance. Existing oil film models are applied to predict the SFD behaviour. A special groove-two land model is able to predict the vibration behaviour of a very shallow grooved SFD and the conventional two-land theory is applicable to a SFD with a very deep groove. These observations provide useful guidelines for designing a shallow or deep grooved SFD-rotor assembly
A template-based approach to inhibitors of calpain 2, 20S proteasome, and HIV-1 protease
No full textArticle first published online: 15 OCT 2013Specificity counts: A template-based approach to protease inhibitors is presented using a core macrocycle that presents a generic β-strand template for binding to protease active sites. This is then specifically functionalized at P2 , and the C and N termini to give inhibitors of calpain 2, 20S proteasome, and HIV-1 protease.Seth A. Jones, Paul M. Neilsen, Limei Siew, David F. Callen, Nathan E. Goldfarb, Ben M. Dunn, and Andrew D. Abel
A C++ standard template library intelligent tutoring system with Bayesian and fuzzy logic student model / Christine Lee Siew Ken
No full textEarlier work on Intelligent Tutoring Systems (ITSs) for programming focused more on teaching programming syntax than its application. The main tutoring approach is to present a problem specification for the student to solve, followed by intelligent analysis of the solution with various feedback. It is also observed that existing ITSs suffer from static domain knowledge and are restricted to the tutoring session. Therefore, this research proposes the development of a web-based ITS for both curriculum planners and implementer-tutors to teach students the application of the C++ Standard Template Library (STL) to problem solving.
From experience, it is discovered that students find the C++ STL difficult due to their weaknesses in understanding various object-oriented concepts. This ITS overcomes the learning and teaching challenges by modelling the program specification based on prerequisite concepts. Bayesian Theorem is applied to model the student’s knowledge and direct the tutoring intelligently. Bayesian probability reasoning is a well-known Artificial Intelligence technique for uncertainties management. The development of the C++ STL ITS applies practices from the eXtreme Programming methodology and J2EE technologies. The 3-tier architecture ITS constitutes three main components – Student Modelling Module, Tutoring Module and Users Administration Module providing the authoring of the domain knowledge dynamically. Hence, tutors can then fully participate in the design of the curriculum and tutoring sessions as well as in the implementation of the tutorials for their students for effective teaching and learning.
Both summative and formative evaluations were conducted on the C++ STL ITS. The evaluation results revealed that the Bayesian Theorem has the capability of modelling the student’s prerequisite and directing the student during the tutorial session. The Fuzzy Stereotyping of Students Expert System works well in categorizing the students according to four stereotypes – novice, beginner, intermediate and advanced.
Short term future enhancements include extending the tutorial questions, domain knowledge, accommodating more feedback on the programming syntax, and incorporating the fuzzy expert system into the C++ STL ITS. Three areas of research proposed for long term are application of alternative knowledge acquisition techniques, integration of learning styles into the student model, and representation of domain knowledge using ontologies
A novel multiplex PCR-RFLP method for simultaneous detection of the <it>MTHFR 677 C > T</it>, <it>eNOS +894 G > T</it> and <it>- eNOS -786 T > C</it> variants among Malaysian Malays
No full textAbstract Background Hyperhomocysteinemia as a consequence of the MTHFR 677 C > T variant is associated with cardiovascular disease and stroke. Another factor that can potentially contribute to these disorders is a depleted nitric oxide level, which can be due to the presence of eNOS +894 G > T and eNOS −786 T > C variants that make an individual more susceptible to endothelial dysfunction. A number of genotyping methods have been developed to investigate these variants. However, simultaneous detection methods using polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) analysis are still lacking. In this study, a novel multiplex PCR-RFLP method for the simultaneous detection of MTHFR 677 C > T and eNOS +894 G > T and eNOS −786 T > C variants was developed. A total of 114 healthy Malay subjects were recruited. The MTHFR 677 C > T and eNOS +894 G > T and eNOS −786 T > C variants were genotyped using the novel multiplex PCR-RFLP and confirmed by DNA sequencing as well as snpBLAST. Allele frequencies of MTHFR 677 C > T and eNOS +894 G > T and eNOS −786 T > C were calculated using the Hardy Weinberg equation. Methods The 114 healthy volunteers were recruited for this study, and their DNA was extracted. Primer pair was designed using Primer 3 Software version 0.4.0 and validated against the BLAST database. The primer specificity, functionality and annealing temperature were tested using uniplex PCR methods that were later combined into a single multiplex PCR. Restriction Fragment Length Polymorphism (RFLP) was performed in three separate tubes followed by agarose gel electrophoresis. PCR product residual was purified and sent for DNA sequencing. Results The allele frequencies for MTHFR 677 C > T were 0.89 (C allele) and 0.11 (T allele); for eNOS +894 G > T, the allele frequencies were 0.58 (G allele) and 0.43 (T allele); and for eNOS −786 T > C, the allele frequencies were 0.87 (T allele) and 0.13 (C allele). Conclusions Our PCR-RFLP method is a simple, cost-effective and time-saving method. It can be used to successfully genotype subjects for the MTHFR 677 C > T and eNOS +894 G > T and eNOS −786 T > C variants simultaneously with 100% concordance from DNA sequencing data. This method can be routinely used for rapid investigation of the MTHFR 677 C > T and eNOS +894 G > T and eNOS −786 T > C variants.</p
Cross sections of 8 to 9 mixed assets after hypothesis testing
No full textSet 1 = (A) gold, (B) silver, (C) palladium, (D) S\&P 500, (E) Hang Seng, (F) platinum, (G) Dow Jones, (H) Nikkei, and (I) NASDAQ, prices between Apr 2, 1990 and Jan 28, 2018.
Set 2 = (A) 5-year US bond, (B) 10-year US bond, (C) 2-year US bond, (D) 6-month US bond, (E) wheat, (F) coffee, (G) corn, (H) soybean, and (I) sugar, prices between Mar 21, 1994 and Mar 18, 2007.
Set 3 = (A) AUD-USD, (B) CAD-USD, (C) EUR-USD, (D) GBP-USD, (E) JPY-USD, (F) coal, (G) gasoline, (H) kerosene, prices between Mar 28, 1994 and Mar 4, 2018
Hidden-State Modelling of a Cross-section of Geoelectric Time Series Data Can Provide Reliable Intermediate-term Probabilistic Earthquake Forecasting in Taiwan
No full text(C, V, S, K) index time series data generated using 0.5-Hz GEMS time series data from Taiwan. In this data set, C is a modified autocorrelation function, V is the variance, S the skewness, and K the kurtosis of the GEMS geo-electric field time series
Cross section of 5 DJI component stocks
No full text['A', 'B', 'C', 'D', 'E', 'STC', 'STC5', 'TC5', 'fTC5', 'fTC5null', 'lmax', 'lmin', 'nSTCempty', 'setTC5', 'sigseqp001', 'sigseqp005', 'sigseqp005n5'
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