Study on flavour volatiles of γ-aminobutyric acid (GABA) green tea

The volatile components of γ-aminobutyric acid (GABA) tea produced by two different kinds of technological process separately namely: vacuum and water immersion were studied. It was shown by the sensory evaluation that the color of the soup and the extracted leaves of GABA tea were similar to that of the oolong tea, and the smell was similar to the aroma of cooked sweet red dates mixed with some of sour. In GABA tea, the contents of 2,6-bis(1,1-dimethylethyl)-4-methyl phenol, methyl myristate, methyl laurate and methyl palmitate were higher than that of the normal green tea. The characteristic aroma constituents of the GABA tea made by vacuum treatment concluded methyl myristate, hexadecane, methyl laurate and methyl palmitate, while to the GABA tea made by water immersion, they were 2,6-bis (1,1-dimethylethyl) -4-methylphenol and 1-octanol.Keywords: γ-Aminobutyric acid (GABA), GABA tea, volatile flavour compound

Compact Microwave Dual-band Bandpass Filter Design

The modern wireless communication systems require dual-band bandpass filters to support the standards that work at multiple frequency bands. This thesis demonstrates two design approaches for the development of compact microwave dual-band bandpass filters. The first approach is based on synthesising a dual-passband filter response utilising only one resonant frequency of the resonators. The second approach employs dual-band resonators that have tuneable the first and the second resonant frequencies to form the dual-passbands filter response. The dual-passband response synthesis method synthesises a response with dual passbands that is generated by a frequency transformation that places a finite frequency zero within the single- passband of a filter to split it into dual passbands. The transformed dual-passband response is characterised by the synthesised coupling matrix that consists of the coupling coefficients between coupled resonators. Two filters have been designed and fabricated using microstrip square open-loop and TE01δ mode quarter cylindrical dielectric resonators. The investigation based on simulation studies and measured results revealed that unloaded quality factor of the resonator is required to be ten times greater than the quality factor of each passband in order to realise the narrow passbands. The dual-band resonator methods employ multiple resonant modes of the resonator operating at different frequencies to implement the multiple passbands, respectively. Stepped impedance resonators in stripline and coaxial configurations have been presented and analysed for the realisation of dual-band bandpass filters. A second order dual-band bandpass filter formed by coaxial stepped impedance resonators has been designed, fabricated and tested. The measured frequency response agree well with the simulated response. The estimated breakdown power shows that the filter is capable of high power applications. Non-uniform pitch helical resonators are also proposed for the implementation of dual-band bandpass filters. Two non-uniform pitch helical resonator structures have been analytically modelled. The theoretical models of the non- uniform pitch helical resonators have been developed for accurate prediction of its dual-band characteristics. It is also employed in the general design process of the non-uniform pitch helical resonators. Resonator examples have been presented to show the applicability and validity of the analysis and simulation. Three dual-band bandpass filters have been designed and implemented using non-uniform pitch helical resonators. Their measured frequency responses agree reasonably with the ideal responses. Additionally, the simulation shows that the designed dual-band bandpass filters have relatively high power handling capability

Optimal Caching Policy of Stochastic Updating Information in Delay Tolerant Networks

To increase the speed of information retrieval, one message may have multiple replicas in Delay Tolerant Networks (DTN). In this paper, we adopt a discrete time model and focus on the caching policy of stochastic updating information. In particular, the source creates new version in every time slot with certain probability. New version is usually more useful than the older one. We use a utility function to denote the availability of different versions. To constrain the number of replicas, we propose a probabilistic management policy and nodes to discard information with certain probability determined by the version of the information. Our objective is to find the best value of the probability to maximize the total utility value. Because new version is created with certain probability, nodes other than the source may not know whether the information stored in them is the latest version. Therefore, they can make decisions only according to the local state and decisions based on the local state can be seen as local-policy. We also explore the global-policy, that is, nodes understand the real state. We prove that the optimal policies in both cases conform to the threshold form. Simulations based on both synthetic and real motion traces show the accuracy of our theoretical model. Surprisingly, numerical results show that local-policy is better than the global-policy in some cases

A vehicle stability control strategy with adaptive neural network sliding mode theory based on system uncertainty approximation

Modelling uncertainty, parameter variation and unknown external disturbance are the major concerns in the development of an advanced controller for vehicle stability at the limits of handling. Sliding mode control (SMC) method has proved to be robust against parameter variation and unknown external disturbance with satisfactory tracking performance. But modelling uncertainty, such as errors caused in model simplification, is inevitable in model-based controller design, resulting in lowered control quality. The adaptive radial basis function network (ARBFN) can effectively improve the control performance against large system uncertainty by learning to approximate arbitrary nonlinear functions and ensure the global asymptotic stability of the closed-loop system. In this paper, a novel vehicle dynamics stability control strategy is proposed using the adaptive radial basis function network sliding mode control (ARBFN-SMC) to learn system uncertainty and eliminate its adverse effects. This strategy adopts a hierarchical control structure which consists of reference model layer, yaw moment control layer, braking torque allocation layer and executive layer. Co-simulation using MATLAB/Simulink and AMESim is conducted on a verified 15-DOF nonlinear vehicle system model with the integrated-electro-hydraulic brake system (I-EHB) actuator in a Sine With Dwell manoeuvre. The simulation results show that ARBFN-SMC scheme exhibits superior stability and tracking performance in different running conditions compared with SMC scheme

An innovative information fusion method with adaptive Kalman filter for integrated INS/GPS navigation of autonomous vehicles

Information fusion method of INS/GPS navigation system based on filtering technology is a research focus at present. In order to improve the precision of navigation information, a navigation technology based on Adaptive Kalman Filter with attenuation factor is proposed to restrain noise in this paper. The algorithm continuously updates the measurement noise variance and processes noise variance of the system by collecting the estimated and measured values, and this method can suppress white noise. Because a measured value closer to the current time would more accurately reflect the characteristics of the noise, an attenuation factor is introduced to increase the weight of the current value, in order to deal with the noise variance caused by environment disturbance. To validate the effectiveness of the proposed algorithm, a series of road tests are carried out in urban environment. The GPS and IMU data of the experiments were collected and processed by dSPACE and MATLAB/Simulink. Based on the test results, the accuracy of the proposed algorithm is 20% higher than that of a traditional Adaptive Kalman Filter. It also shows that the precision of the integrated navigation can be improved due to the reduction of the influence of environment noise

Effects of thermal process conditions on crystallinity and mechanical properties in material extrusion additive manufacturing of discontinuous carbon fibre reinforced polyphenylene sulphide composites

This study investigates the thermal behaviour of discontinuous carbon fibre reinforced polyphenylene sulphide (CF/PPS), additively manufactured by material extrusion, with a focus on the effects of thermal process conditions on the degree of crystallinity, oxidation crosslinking and mechanical properties of CF/PPS from filament fabrication, material extrusion to annealing treatment. The screw extrusion parameters are optimised by performing a thermal analysis of the fabricated filaments. The effect of crosslinking reactions on the crystallinity process in determining the mechanical properties of the printed samples is illustrated by investigating the influence of the printing conditions. Furthermore, the effect of annealing treatment on the semi-crystalline polyphenylene sulphide (PPS) is studied by measuring the degree of crystallinity and viscoelasticity behaviours. Results demonstrate that the flexural properties of the printed CF/PPS composites at elevated processing temperatures are determined by the oxidation crosslinking between PPS chains. These enhance the crystallisation process of semi-crystalline polymers by acting as the nucleating agent first but negatively affect the mechanical properties at higher temperatures because of the detrimental effects of the polymer inter-chain bonding. The maximum flexural strength of printed CF/PPS reached 164.65 MPa when processing at an extrusion temperature of 280°C, a printing temperature of 320°C, and an annealing temperature of 130°C for 6 h. By adjusting the thermal treatment conditions, the degree of the crystallinity and the mechanical properties of the printed CF/PPS composites can be designed, controlled and tailored

Research in nonlinearity of surface acoustic wave devices

Surface acoustic wave (SAW) devices are one of the indispensable components in the radio frequency (RF) front-end of mobile phones. With the development of mobile communication technology, the requirements for linear specification of devices are more and more strict. Nonlinear distortions of SAW devices have a serious influence on the application of mobile RF modules. To satisfy the strict requirement of linearity of communication system, it is necessary to understand the generation mechanism of nonlinearity and study the accurate modeling, appropriate measurement methods, and nonlinear response elimination technology. In this paper, we summarize the research progress on the nonlinearity of SAW devices in recent years from four aspects: the generation mechanism, simulation methods, measurement system, and suppression technology. The nonlinear harmonics with the nonlinear Mason equivalent circuit model are simulated. Furthermore, harmonics and intermodulation signals of SAW filters are tested by the authors. Thanks to these research studies, it is of great significance to the development of future RF front-end modules with high linear SAW devices

Aero-Engine Fault Diagnosis Using Improved Local Discriminant Bases and Support Vector Machine

This paper presents an effective approach for aero-engine fault diagnosis with focus on rub-impact, through combination of improved local discriminant bases (LDB) with support vector machine (SVM). The improved LDB algorithm, using both the normalized energy difference and the relative entropy as quantification measures, is applied to choose the optimal set of orthogonal subspaces for wavelet packet transform- (WPT-) based signal decomposition. Then two optimal sets of orthogonal subspaces have been obtained and the energy features extracted from those subspaces appearing in both sets will be selected as input to a SVM classifier to diagnose aero-engine faults. Experiment studies conducted on an aero-engine rub-impact test system have verified the effectiveness of the proposed approach for classifying working conditions of aero-engines