Inference for mixtures of symmetric distributions

This article discusses the problem of estimation of parameters in finite mixtures when the mixture components are assumed to be symmetric and to come from the same location family. We refer to these mixtures as semi-parametric because no additional assumptions other than symmetry are made regarding the parametric form of the component distributions. Because the class of symmetric distributions is so broad, identifiability of parameters is a major issue in these mixtures. We develop a notion of identifiability of finite mixture models, which we call k-identifiability, where k denotes the number of components in the mixture. We give sufficient conditions for k-identifiability of location mixtures of symmetric components when k=2 or 3. We propose a novel distance-based method for estimating the (location and mixing) parameters from a k-identifiable model and establish the strong consistency and asymptotic normality of the estimator. In the specific case of L_2-distance, we show that our estimator generalizes the Hodges--Lehmann estimator. We discuss the numerical implementation of these procedures, along with an empirical estimate of the component distribution, in the two-component case. In comparisons with maximum likelihood estimation assuming normal components, our method produces somewhat higher standard error estimates in the case where the components are truly normal, but dramatically outperforms the normal method when the components are heavy-tailed.Comment: Published at http://dx.doi.org/10.1214/009053606000001118 in the Annals of Statistics (http://www.imstat.org/aos/) by the Institute of Mathematical Statistics (http://www.imstat.org

An XPS Study of the Radiation-induced Effect on the Thermal Degradation and Charring of Butadiene and its Copolymers

A pseudo-in-situ XPS approach shows that cross-linking induced by irradiation may lead to char formation even though it shows only a small or no effect on the onset temperature of degradation

To what extent can a future public transport system be designed to cater for private travel preferences? - The role of individuals’ attitude in two suburban neighbourhoods - Kangjian, Shanghai and Bull Creek, Perth

This thesis researches the role of individual factors, such as travel attitudes, in choice of transport mode and analyses the extent to which public transport planning practice caters such passenger factors. Consideration is given to the potential for combining the policy aspirations of government with the individual needs of residents

Pattern Division Multiple Access with Large-scale Antenna Array

In this paper, pattern division multiple access with large-scale antenna array (LSA-PDMA) is proposed as a novel non-orthogonal multiple access (NOMA) scheme. In the proposed scheme, pattern is designed in both beam domain and power domain in a joint manner. At the transmitter, pattern mapping utilizes power allocation to improve the system sum rate and beam allocation to enhance the access connectivity and realize the integration of LSA into multiple access spontaneously. At the receiver, hybrid detection of spatial filter (SF) and successive interference cancellation (SIC) is employed to separate the superposed multiple-domain signals. Furthermore, we formulate the sum rate maximization problem to obtain the optimal pattern mapping policy, and the optimization problem is proved to be convex through proper mathematical manipulations. Simulation results show that the proposed LSA-PDMA scheme achieves significant performance gain on system sum rate compared to both the orthogonal multiple access scheme and the power-domain NOMA scheme.Comment: 6 pages, 5 figures, this paper has been accepted by IEEE VTC 2017-Sprin

Phyto-gene therapy using antisense oligonucleotides to control cereal fungal disease by silencing virulence factors and their regulators

With increasing concerns regarding food security, alternative solutions are required for disease control in crops, including those caused by fungal pathogens. Antisense single stranded short oligodeoxynucleotides (ASO) based gene therapy is widely used in medicine but is still emerging in plant sciences. The ASO gene silencing approach using phosphorothioate modified oligodeoxynucleotides (asPTOs) delivered to excised barley leaves was first devised as a tool for in planta transient host induced gene silencing (HIGS) to query the virulence role of genes from the biotrophic fungal pathogen, Blumeria graminis f.sp. hordei (Bgh), the causal agent of barley powdery mildew. Following this, our project aimed at exploiting the HIGS approach for discovering new key players for virulence of Bgh and some of the major wheat pathogens, B. graminis f.sp. tritici (Bgt) and Fusarium graminearum, the causal agent of Fusarium head blight. The ASO gene silencing approach was also evaluated for its suitability to protect wheat against fungi by targeting host susceptibility genes. AsPTOs to silence vital Bgh genes (actin, GAPDH, 2-Glycosyl transferase) successfully reduced powdery mildew infection in several barley cultivars. Similarly, silencing the metallo-protease-like effector BEC1019 impacted on Bgh and Bgt virulence in barley and wheat respectively. Following promoter sequence analysis of Bgh effectors expressed in haustoria, the HIGS approach allowed to confirm the implication of ZAP1 and PacC transcription factors in regulating BEC1019 and BEC1011 effector expression, while affecting Bgh virulence. To adapt ASO based gene silencing for disease control, in planta gene silencing of F. graminearum known virulence genes was attempted but with no convincing impact. However, asPTOs to silence BEC1011 were delivered into whole barley seedlings by root uptake resulting in reduced powdery mildew infection. This suggests that asPTOs based HIGS could be further investigated as a strategy to control fungal diseases in crops. <br/

Hybridization of localized surface plasmon resonance-based Au-Ag nanoparticles

The hybrid Au - Ag triangular nanoparticles were proposed for the purpose of biosensing. To construct the nanoparticles, an Au thin film was deposited on top of the Ag nanoparticles supported with glass substrate. The hybrid nanoparticles can prevent oxidation of the pure Ag nanoparticles due to the Au protective layer caped on the Ag nanoparticles. The hybrid nanoparticles were designed using finite-difference and time-domain algorithm. Extinction spectra of the hybrid nanoparticles excited by visible light beam with plane wave were calculated, and the corresponding electric fields at peak position of the extinction spectra were expressed also. It is clear that the hybrid nanoparticles can excite the localized surface plasmon resonance wave which can be used to detect biomolecules. As an application example, we presented relevant detection results by means of using protein A to covalently link surface of the hybrid nanoparticles. Refractive index sensitivity of the hybrid nanoparticles was derived through both computational numerical calculation and experimental detection. Both the calculated and the experimental extinction spectra show that the hybrid Au - Ag nanoparticles are useful for detecting the biomolecules. © Springer Science+Business Media, LLC 2008