A Method for Avoiding Bias from Feature Selection with Application to Naive Bayes Classification Models

For many classification and regression problems, a large number of features are available for possible use - this is typical of DNA microarray data on gene expression, for example. Often, for computational or other reasons, only a small subset of these features are selected for use in a model, based on some simple measure such as correlation with the response variable. This procedure may introduce an optimistic bias, however, in which the response variable appears to be more predictable than it actually is, because the high correlation of the selected features with the response may be partly or wholely due to chance. We show how this bias can be avoided when using a Bayesian model for the joint distribution of features and response. The crucial insight is that even if we forget the exact values of the unselected features, we should retain, and condition on, the knowledge that their correlation with the response was too small for them to be selected. In this paper we describe how this idea can be implemented for ``naive Bayes'' models of binary data. Experiments with simulated data confirm that this method avoids bias due to feature selection. We also apply the naive Bayes model to subsets of data relating gene expression to colon cancer, and find that correcting for bias from feature selection does improve predictive performance

Research and development of nickel based catalysts for carbon dioxide reforming of methane

Consuming two major greenhouse gases, carbon dioxide (CO2) and methane (CH4), to produce synthesis gas, which is a mixture of carbon monoxide (CO) and hydrogen (H2), CO2 reforming of CH4 shows significant environmental and economic benefits. However, the process has not found wide industrial application due to severe catalyst deactivation, basically caused by carbon formation. Therefore, it is of great interest to develop stable catalysts without severe deactivation. This work is primarily focused on the development of novel nickel-based catalysts to achieve stable operation for CO2 reforming of CH4. Following Dowden’s strategy of catalyst design, a series of nickel-based catalysts are designed with a general formula: Ni-Me/AlMgOx (Me = Co, Cu, Fe, or Mn). The designed catalysts are prepared using co-precipitation method and tested for CO2 reforming of CH4. Catalyst screening showed that the Ni-Co/AlMgOx catalyst has superior performance in terms of activity and stability to other Ni-Me/AlMgOx (Me = Cu, Fe, or Mn) catalysts. A 2000 h long-term deactivation test has shown that the Ni-Co/AlMgOx has high activity and excellent stability for CO2 reforming of CH4. Further investigation on the Ni-Co/AlMgOx catalysts shows that adjusting Ni/Co ratio and Ni-Co loading can significantly affect the catalyst performance. Carbon free operation for CO2 reforming of CH4 can be achieved on the catalysts with a Ni/Co close to 1 and Ni-Co overall loading between 4-10 %. In addition, calcination temperature shows important impacts on the performance of Ni-Co/AlMgOx catalysts. A calcination temperature range of 700-900 oC is recommended. The Ni-Co/AlMgOx catalysts are characterized using various techniques such as ICP-MS, BET, CO-chemiosorption, XRD, TPR, TG/DTA, TEM, and XPS. It has been found that the high activity and excellent stability of Ni-Co/AlMgOx catalysts can be ascribed to its high surface area, high metal disperation, small particle size, strong metal-support interaction, and synergy between Ni and Co. Kinetic studies have shown that the CH4 decomposition and CO2 activation could be the rate-determining steps. Both Power-Law and Langmuir-Hinshelwood kinetic models can fit the experiment data with satisfactory results

Research and Field Application of Top Screen Cementing Technology with the Salvaging Type Plug-Drilling-Free Tool

Top screen pipe cementing technology of casing in horizontal well has been one of the main completion, especially for developing reservoirs with bottom and edge water and heavy oil reservoirs. Main drawbacks of screen top cementing completion technology in horizontal wells are casing wear in the process of drilling plug and burrs in the inner surface after drilling plug which are obstacles of well intervention. The salvaging type Non-plug-drilling tool eliminates the disadvantages of plug-drilling. By optimizing tool structure, improving technology, the reliability of salvaging type plug-drilling-free tool has been increased. More than 133 wells in 2012 had adopted the salvaging type plug-drilling-free tool with high reliability in Pai 601 Block of Xinjiang with 100% success rate.  Key words: Horizontal well; The salvaging type plug-drilling-free technology; Completion; Top screen cementing technology; Field applicatio