Semi-Supervised Radio Signal Identification

Radio emitter recognition in dense multi-user environments is an important tool for optimizing spectrum utilization, identifying and minimizing interference, and enforcing spectrum policy. Radio data is readily available and easy to obtain from an antenna, but labeled and curated data is often scarce making supervised learning strategies difficult and time consuming in practice. We demonstrate that semi-supervised learning techniques can be used to scale learning beyond supervised datasets, allowing for discerning and recalling new radio signals by using sparse signal representations based on both unsupervised and supervised methods for nonlinear feature learning and clustering methods

A Comparative Study of Physicochemical, Dielectric and Thermal Properties of Pressboard Insulation Impregnated with Natural Ester and Mineral Oil

Natural ester is considered to be a substitute of mineral oil in the future. To apply natural ester in large transformers safely, natural ester impregnated solid insulation should be proved to have comparable dielectric strength and thermal stability to mineral oil impregnated solid insulation. This paper mainly focuses on a comparative study of physicochemical, ac breakdown strength and thermal stability behavior of BIOTEMP natural ester/pressboard insulation and Karamay 25# naphthenic mineral oil/pressboard insulation after long term thermal ageing. The physicochemical and dielectric parameters including moisture, acids and the ac breakdown strength of these two oil/pressboard insulation systems at different ageing status were compared. The permittivity and ac breakdown strength of these two oil/pressboard insulation systems at different temperatures were also investigated. And a comparative result of the thermal stability behavior of these two oil/pressboard insulation systems with different ageing status was provided at last. Results show that though natural ester has higher absolute humidity and acidity during the long ageing period, the lower relative humidity of natural ester helps to keep its ac breakdown strength higher than mineral oil. The pressboard aged in natural ester also has higher ac breakdown strength than that aged in mineral oil. The lower relative permittivity ratio of natural ester impregnated paper to natural ester is beneficial to its dielectric strength. Using natural ester in transformer, the resistance to thermal decomposition of the oil/pressboard insulation system could be also effectively improved

Mechanical properties and chemical stability of pivalolactone-based poly(ether ester)s

The processing, mechanical and chemical properties of poly(ether ester)s, prepared from pivalolactone (PVL), 1,4-butanediol (4G) and dimethyl terephthalate (DMT), were studied. The poly(ether ester)s could easily be processed by injection moulding, owing to their favourable rheological and thermal properties. The tensile response of a poly(ether ester) with a butylene terephthalate (4GT) content of 72 mol%, which exhibited the phenomena of necking and strain-hardening, was related to the morphology of these copolymers. The influence of the short 4G-PVL segments was reflected in a high Young's modulus and yield stress, and resulted in a tough behaviour for the poly(ether ester), with an ultimate elongation of 500%. The poly(ether ester)s were stable towards treatment at room temperature with water or weakly acidic or alkaline solutions. Conditioning at 90°C in water for 264 h resulted in a water uptake of 1 wt%, whereas the rate of hydrolysis was 0.0003 (expressed in An rel h-1) for the poly(ether ester) with a 4GT content of 72 mol%. Although a decay in the mechanical properties for the PVL-based poly(ether ester) after exposure to water at 90°C was observed, these materials were assumed to have a higher hydrolytical stability than other poly(ether ester)

Ageing and Temperature Influence on Polarization/Depolarization Current Behaviour of Paper Immersed in Natural Ester

Transformers play an important role in providing a reliable and efficient electricity supply and are one of the most critical equipments in electric power transmission and distribution systems. The most commonly used liquid in power transformers is mineral oil due to its low price and good properties. However the performance of mineral oil starts to be limited due to environmental consideration [1]. Natural ester insulating fluid offers fire safety, environment and insulation aging advantages over mineral oil and are found to be suitable for the use in transformer insulation system [1]. However, transformer owners require to assess the status of the cellulose insulation in transformer non-destructively. Polarization/depolarization Current (PDC) measurement [2] is one of the non-destructive techniques which have been used to achieve this aim. At the present, there are few publications about the PDC behaviour of natural ester-paper insulation, though the natural ester becomes more widely used in transformers. In this paper, the influence of ageing and temperature on the PDC behaviour of the paper immersed in natural ester and mineral oil were compared. Results show PDC technique can be used to assess the aging condition of the natural-ester paper insulation. The ageing and temperature have similar influence on the PDC behaviour of the paper immersed in natural ester and in mineral oil. The depolarization current of paper immersed in natural ester is lower than that immersed in mineral oil at the same test temperature. The depolarization current of the paper immersed in natural ester and mineral oil increase with the aging time increased. Therefore, the depolarization current can be used to indicate the aging status of natural ester-paper insulation

Effect of side chains on the dielectric properties of alkyl esters derived from palm kernel oil

Alkyl ester derivatives were synthesized from laboratory purified palm kernel oil. The steps in the synthesis involved transesterification of palm kernel oil to produce a methyl ester, followed by epoxidation and then the grafting of side chains by esterification with propionic and butyric anhydride. The dielectric and thermal properties of the ester derivatives were analyzed and compared with the methyl ester. The melting point of the ester derivatives were found to reduce with side chain attachment and antioxidant improved its thermal stability. The dielectric loss was dominated by mobile charged particles and the chemical modification appeared to increase the rate at which electric double layer was formed at the electrode-liquid interface. The esters possessed excellent breakdown strengths suggesting that the processing to optimize their physical properties did not have a negative influence on their electrical breakdown strength. This product may prove useful as an insulation fluid in Electrical Power Transformers

Asymptotic equivalence for inhomogeneous jump diffusion processes and white noise

We prove the global asymptotic equivalence between the experiments generated by the discrete (high frequency) or continuous observation of a path of a time inhomogeneous jump-diffusion process and a Gaussian white noise experiment. Here, the considered parameter is the drift function, and we suppose that the observation time $T$ tends to $\infty$. The approximation is given in the sense of the Le Cam $\Delta$-distance, under smoothness conditions on the unknown drift function. These asymptotic equivalences are established by constructing explicit Markov kernels that can be used to reproduce one experiment from the other.Comment: 20 pages; to appear on ESAIM: P\&S. In this version there are some improvements in the exposition following the reports suggestion

Credit risk transfers and the macroeconomy : [This Draft: September 2010]

The recent financial crisis has highlighted the limits of the “originate to distribute” model of banking, but its nexus with the macroeconomy and monetary policy remains unexplored. I build a DSGE model with banks (along the lines of Holmström and Tirole [28] and Parlour and Plantin [39] and examine its properties with and without active secondary markets for credit risk transfer. The possibility of transferring credit reduces the impact of liquidity shocks on bank balance sheets, but also reduces the bank incentive to monitor. As a result, secondary markets allow to release bank capital and exacerbate the effect of productivity and other macroeconomic shocks on output and inflation. By offering a possibility of capital recycling and by reducing bank monitoring, secondary credit markets in general equilibrium allow banks to take on more risk. Keywords: Credit Risk Transfer , Dual Moral Hazard , Monetary Policy , Liquidity , Welfare JEL Classification: E3, E5, G3 First Draft: December 2009, This Draft: September 201

Asymptotic equivalence for density estimation and gaussian white noise: An extension

The aim of this paper is to present an extension of the well-known as-ymptotic equivalence between density estimation experiments and a Gaussian white noise model. Our extension consists in enlarging the nonparametric class of the admissible densities. More precisely, we propose a way to allow densities defined on any subinterval of R, and also some discontinuous or unbounded densities are considered (so long as the discontinuity and unboundedness patterns are somehow known a priori). The concept of equivalence that we shall adopt is in the sense of the Le Cam distance between statistical models. The results are constructive: all the asymptotic equivalences are established by constructing explicit Markov kernels.Comment: 11 pages. arXiv admin note: text overlap with arXiv:1503.0453