Handling sequential pattern decay: Developing a two-stage collaborative recommender system

This study proposes a sequential pattern based collaborative recommender system that predicts the customer’s time-variant purchase behavior in an e-commerce environment where the customer’s purchase patterns may change gradually. A new two-stage recommendation process is developed to predict customer purchase behavior for the product categories, as well as for product items. The time window weight is introduced to produce sequential patterns closer to the current time period that possess a larger impact on the prediction than patterns relatively far from the current time period. This study is the first to propose time-decaying sequential patterns within a collaborative recommender system. The experimental results show that the proposed system outperforms the traditional collaborative system using a public food mart dataset and a synthetic dataset.     

Multilevel reversible data hiding based on histogram modification of difference images

Reversible data hiding has drawn considerable attention in recent years. Reversibility allows original media to be completely recovered from marked media without distortion after embedded message has been extracted. In this paper we propose a multilevel reversible data hiding scheme based on the difference image histogram modification that uses the peak point to hide messages. Through a joint imperceptibility and hiding capacity evaluation, we show that our proposed scheme uses a multilevel hiding strategy to achieve large hiding capacity and keep distortion low. Performance comparisons with other existing reversible hiding schemes are provided to demonstrate the validity of our proposed scheme.     

一个基于“恶意对抗”的公平交互机制的研究

由于多代理交互环境中检测机制、仲裁机制的有限性,合法代理将注定要遭受损失。针对上述现象,该文提出了一个恶意对抗机制（Malice-Antagonized Interaction Mechanism,MAIM),即在该机制下,交互代理双方都允许表现出恶意行为,以期实现交互的公平性,为了分析MAIM机制的可行性,文中应用游戏理论对MAIM在几种典型的游戏中实现交互公平性的情况进行了分析和证明。最终得出结论：在完善信息的纯策略游戏中,MAIM无法实现交互的公平性,而在完美信息的混合策略游戏、不完美信息的顺序游戏和同时决策游戏中,能实现交互的公平性。从而从理论上证明了恶意对抗机制的可行性。     

Catalytic oxidation of methane over novel Ce–Ni–O mixed oxide catalysts prepared by oxalate gel-coprecipitation

A novel approach for the synthesis of a new type of binary Ce–Ni–O mixed oxide catalysts is reported. The synthesis method involves the homogeneous gel-coprecipitation of oxalate precursor in alcoholic solution followed by calcinations in air. The results show that the as-prepared samples have high specific surface area and high component dispersion, exhibiting remarkably high activity in the catalytic combustion of methane as compared to the catalysts prepared by conventional coprecipitation techniques. It is suggested that the superior catalytic performance of the oxalate gel-coprecipitated Ce–Ni–O mixed oxide catalysts could be attributed to the generation of highly dispersed NiO_x species and the creation of highly active oxygen vacancies as a consequence of an easier incorporation of Ni²⁺ ions into ceria lattice by the formation of solid solution in the mixed oxide samples.     

Imaging tissue engineering scaffolds using multiphoton microscopy

In this study, we combined two-photon autofluorescence and second harmonic generation imaging to investigate the three-dimensional microstructure and nonlinear optical properties of tissue engineering scaffolds. We focused on five different types of scaffold materials commonly used in tissue engineering, including: open-cell polylactic acid, polyglycolic acid, collagen composite scaffold, collagraft bone graft matrix strip, and nylon. By the use of multiphoton microscopy and a motorized stage, we obtained high resolution, spectrally resolved structural information of the scaffolds over large areas or in three-dimensions. Our results show that the nonlinear optical properties of the scaffolds will enable us to spectrally and morphologically distinguish the different types of scaffold materials investigated. We envision multiphoton microscopy to be a useful technique in tissue engineering applications in understanding the interplay between cultured cells and the scaffold materials.     

Effects of different immersion media in multiphoton imaging of the epithelium and dermis of human skin

In this work, we compared the performance of objectives with similar numerical aperture of 0.75 but different immersion media of air, water, glycerin, and oil in the imaging of human skin epithelium and dermis. In general, we found that the oil immersion objective recorded the strongest intensity at the same mechanical depth. We also characterized the focal shifts and found that with decreasing refractive index, the focal shift becomes increasingly more negative (for both the epithelium and dermis). In imaging the dermis, we estimated the image resolution at the depths of 18.8 and 30.2 microm, and found that the image resolution were comparable at these depths under the four types of immersion conditions. Our results demonstrate that by changing the immersion media, the main microscopic imaging effects are the recorded axial intensities and the focal shifts. The effects on the image resolution are negligible.     

Preservation of Acidithiobacillus caldus: A moderately thermophilic bacterium and the effect on subsequent bioleaching of chalcopyrite

Four bacterial preservation methods: passage culture, sterile sand tube preservation, freezing preservation and freeze-drying preservation, were used to store Acidithiobacillus caldus strain S2, a moderately thermophilic bacterium. Among the four methods, the second is shown to be the best for short term preservation (6 months), and the fourth is the best for long term preservation (15 months). Specifically, the results show that using the second method, 32% cell viability was obtained after 6 months, and the cell survival rate reaches 17% using the fourth method after 15 months. In the bioleaching experiments, A. caldus strain S2 preserved via the second and the fourth methods, along with Leptospirillum ferriphilum strain YSK, were applied to bioleach chalcopyrite. Under the two preservation methods for A. caldus strain S2, the results show that 3.72 g/L and 1.68 g/L copper are extracted in the first 20 days and the maximum biomass delays to the 15th day and to the 18th day, respectively. When the bioleaching time was extended to the 40th day, copper extraction increased significantly to 5.02 g/L and 4.88 g/L, respectively. However, A. caldus strain S2 under no preservation, along with L. ferriphilum strain YSK, extract only 0.54 g/L Cu from the 20th day to the 40th day and finally release 5.14 g/L Cu. Therefore, the preserved culture shows almost the same total copper extraction as the unpreserved one in 40 days. As a result, sterile sand tube preservation and freeze-drying preservation greatly prolong the lag phase of cell growth without much decrease in the bioleaching ability of A. caldus strain S2.     

华法林负荷量法抗凝治疗短暂性脑缺血发作的研究

目的 观察华法林抗凝治疗短暂性脑缺血发作(TIA) 的安全性和疗效。 方法 2003 年1 月至2004 年1 月入院的TIA 病人, 适合抗凝治疗者, 按Roberts 依年龄调整华法林负荷量指南用药, 对照组为2002 年1 月至2003 年1 月住院的TIA 病人, 并剔除用肝素治疗的病人。 结果 华法林组10 d 内无脑卒中发生, 仅有4 人次再次TIA, 未发现有出血者;对照组10 d 内脑梗死6 例, 再次TIA 12 人次, 华法林组于TIA 发作后10 d 内发生脑梗死及再次TIA较对照组低(P <0.05)。 结论 按Roberts 华法林负荷量指南抗凝治疗TIA 优于非抗凝治疗, 而且安全。     

丰富煤炭企业文化内涵造就优秀营销人员

企业文化的内涵长期以来备受国内理论界和煤炭企业界的关注。通过对煤炭企业文化进行深入的了解和剖析,不断丰富其内涵;重新认识营销岗位的重要性,为营销人员塑造过硬的心理素质和成熟的心态,树立优秀营销人员应具备的能力;经过匹配有效的绩效考核,经过掌握一些营销技巧和沟通能力,为煤炭企业造就优秀的营销人员,为煤炭企业创造佳绩。     

正交独立边带制调幅立体声广播的探讨

本文提出的正交调幅独立边带制(QUAM-ISB),综合了目前世界上存在的调幅立体声制式的优点。它利用了正交调制技术,主副频道的音频信号分别调制在一对互相正交的载频上,发射信号的调幅分量与MOTOROLA制一样进行修正,因而获得了综合性能较好的优点;另一特点是主副信道的音频信号在调制之前已移相90°,因此发射信号的频谱具有独立边带特性。它与正交特性相比具有与KAHN制相同的特性。本文详细地讨论了正交独立边带制的构成及发射机与接收机的方框图,然后利用CAA技术分析与计算了发射信号的频谱,最后研究了它的一些基本特性。