Preparation and Dielectric Properties of Nonstoichiometric β-SiC Powder by Combustion Synthesis

The nonstoichiometric β-SIC powders were synthesized via combustion reaction of Si and C system in a 0.1 MPa nitrogen atmosphere, using Teflon as the chemical activator. The prepared powders were invistigated by XRD and Raman spectra. The results indicates that the cell parameters of all the prepared β-SIC powder are smaller than the standard value of β-SIC because of generation of CSi defects. The complex permittivity of prepared products was carried out in the frequency range of 8.2-12.4 GHz. It shows that the dielectric property of prepared β-SiC powder decrease with increasing PTFE content. The effect of CSi defects on dielectric property of β-SiC powder has been discussed.

A NOVEL SVM ENSEMBLE APPROACH USING CLUSTERING ANALYSIS

A novel Support Vector Machine(SVM) ensemble approach using clustering analysis is proposed. Firstly,the positive and negative training examples are clustered through subtractive clus-tering algorithm respectively. Then some representative examples are chosen from each of them to construct SVM components. At last,the outputs of the individual classifiers are fused through ma-jority voting method to obtain the final decision. Comparisons of performance between the proposed method and other popular ensemble approaches,such as Bagging,Adaboost and k.-fold cross valida-tion,are carried out on synthetic and UCI datasets. The experimental results show that our method has higher classification accuracy since the example distribution information is considered during en-semble through clustering analysis. It further indicates that our method needs a much smaller size of training subsets than Bagging and Adaboost to obtain satisfactory classification accuracy.

2D-HIDDEN MARKOV MODEL FEATURE EXTRACTION STRATEGY OF ROTATING MACHINERY FAULT DIAGNOSIS

A new feature extraction method based on 2D-hidden Markov model（HMM） is proposed. Meanwhile the time index and frequency index are introduced to represent the new features. The new feature extraction strategy is tested by the experimental data that collected from Bently rotor experiment system. The results show that this methodology is very effective to extract the feature of vibration signals in the rotor speed-up course and can be extended to other non-stationary signal analysis fields in the future.

Effects of different mixing ratios on emissions from passenger cars fueled with methanol/gasoline blends

Regulated and unregulated emissions from four passenger cars fueled with methanol/gasoline blends at different mixing ratios （M15,M20,M30,M50,M85 and M100） were tested over the New European Driving Cycle （NEDC）.Volatile organic compounds （VOCs） were sampled by Tenax TA and analyzed by thermal desorption-gas chromatograph/mass spectrometer （TD-GC/MS）.Carbonyls were trapped on dinitrophenylhydrazine （DNPH） cartridges and analyzed by high performance liquid chromatography （HPLC）.The results showed that total emissions of VOCs and BTEX （benzene,toluene,ethylbenzene,p,m,o-xylene） from all vehicles fueled with methanol/gasoline blends were lower than those from vehicles fueled with only gasoline.Compared to the baseline,the use of M85 decreased BTEX emissions by 97.4%,while the use of M15 decreased it by 19.7%.At low-to-middle mixing ratios （M15,M20,M30 and M50）,formaldehyde emissions showed a slight increase while those of high mixing ratios （M85 and M100） were three times compared with the baseline gasoline only.When the vehicles were retrofitted with new three-way catalytic converters （TWC）,emissions of carbon monoxide （CO）,total hydrocarbon （THC）,and nitrogen oxides （NOx） were decreased by 24%–50%,10%–35%,and 24%–58% respectively,compared with the cars using the original equipment manufacture （OEM） TWC.Using the new TWC,emissions of formaldehyde and BTEX were decreased,while those of other carbonyl increased.It is necessary that vehicles fueled with methanol/gasoline blends be retrofitted with a new TWC.In addition,the specific reactivity of emissions of vehicles fueled with M15 and retrofitted with the new TWC was reduced from 4.51 to 4.08 compared to the baseline vehicle.This indicates that the use of methanol/gasoline blend at a low mixing ratio may have lower effect on environment than gasoline.

Theory and experimental verification of valveless piezoelectric pump with rotatable unsymmetrical slopes

A valveless piezoelectric pump with rotatable unsymmetrical slopes is developed in this research.It has the following features:The pump integrates driving and transporting,and it can mix different fluids while transporting them.In this paper,firstly,the design of the valveless piezoelectric pump with rotatable unsymmetrical slopes was proposed,and the single-direction flow principle was explained.Then,the fluid mechanics model of the valveless piezoelectric pump with rotatable unsymmetrical slopes was established.Meanwhile,the numerical simulation of the pump was performed.Finally,the experiments on relationship between the rotation angles of the slope and the flow rates were conducted.The experimental results showed that the maximum flow was 32.32 mL min 1.The maximum relative error between the theoretical results and the experimental ones was 14.59%.For the relationship between rotation angles and flow ratio of two inlets,the relative error between the experimental and theoretical maxima was 3.75%.Thus,the experiments proved the feasibility of the pump design and verified the theory.