Efficient mining of intertransaction association rules

Most of the previous studies on mining association rules are on mining intratransaction associations, i.e., the associations among items within the same transaction. We extend the scope to include multidimensional, intertransaction associations. In a database of stock price information, an example of such an association is "if (company) A's stock goes up on day one, B's stock will go down on day two but go up on day four:" whether we treat company or day as the unit of transaction, the items belong to different transactions. Moreover, such an intertransaction association can be extended to associate multiple properties in the same rule, so that multidimensional intertransaction associations can also be defined and discovered. Mining intertransaction associations pose more challenges on efficient processing than mining intratransaction associations because the number of potential association rules is extremely large. We introduce the notion of intertransaction association rule and develop an efficient algorithm, FITI (first intra then inter), for mining intertransaction associations, which adopts two major ideas: 1) an intertransaction frequent itemset contains only the frequent itemsets of its corresponding intratransaction counterpart; and 2) a special data structure is built among intratransaction frequent itemsets for efficient mining of intertransaction frequent itemsets.     

Density-controllable growth of SnO2 nanowire junction-bridging across electrode for low-temperature NO2 gas detection

The junction-bridging structure of metal oxide nanowires (NWs) improves gas-sensing properties. In this study, an on-chip growth method was used to fabricate gas sensors, it easily and effectively controls NW junctions. SnO₂ NWs were synthesized by thermal evaporation at 800 °C with tin powder as the source. The density of the NW junctions was controlled by changing the mass of the source material. A source material with large mass yielded high-density NW junctions. With electrode spacing of 20 μm, NW junctions were formed from the source material of larger than 2 mg. Gas sensing results revealed that the junction sensors exhibited a good response to NO₂ gas at a concentration of 1–10 ppm. The sensors exhibited a good response to NO₂ gas at low temperature of up to 100 °C and short response–recovery time (~20 s). The sensors also had good selectivity to NO₂ gas. The response (R _gas /R _air) to 1 ppm NO₂ was as high as 22 at 100 °C, whereas the cross gas responses (R _air /R _gas) to 10 ppm CO, 10 ppm H₂S, 100 ppm C₂H₅OH, and 100 ppm NH₃ were negligible (1.1–1.3).     

A stabilized discrete shear gap extended finite element for the analysis of cracked Reissner–Mindlin plate vibration problems involving distorted meshes

In this work, a new approach in the framework of the local partition of unity finite element method (XFEM) to significantly improve the accuracy of natural frequency in free vibration analysis of cracked Reissner–Mindlin plates is presented. Different from previous approaches, the present formulation is expected to be more accurate and effective in modeling cracked plates by integrating the stabilized discrete shear gap (DSG) into the XFEM setting. Intensive numerical results at low frequency demonstrated that the novel DSG-based XFEM approach possesses the following desirable properties: (1) the awkwardness of transverse shear-locking phenomenon can be overcome easily; (2) the DSG-based XFEM can be applicable to both moderately thick and thin plates straightforwardly; (3) the representation of cracks is independent of finite element mesh; (4) mesh distortion is insensitive and controllable; (5) the accuracy of natural frequency obtained by the present method is high and (6) the present method uses three-node triangular elements that can be much easily generated automatically for problems even with complicated geometry. These properties of the DSG-based XFEM are confirmed through several numerical examples of cracked plates with different boundary conditions.     

Alumina‐Supported CoFe Alloy Catalysts Derived from Layered‐Double‐Hydroxide Nanosheets for Efficient Photothermal CO2 Hydrogenation to Hydrocarbons

A series of novel CoFe‐based catalysts are successfully fabricated by hydrogen reduction of CoFeAl layered‐double‐hydroxide (LDH) nanosheets at 300–700 °C. The chemical composition and morphology of the reaction products (denoted herein as CoFe‐x) are highly dependent on the reduction temperature (x). CO₂ hydrogenation experiments are conducted on the CoFe‐x catalysts under UV–vis excitation. With increasing LDH‐nanosheet reduction temperature, the CoFe‐x catalysts show a progressive selectivity shift from CO to CH₄, and eventually to high‐value hydrocarbons (C₂₊). CoFe‐650 shows remarkable selectivity toward hydrocarbons (60% CH₄, 35% C₂₊). X‐ray absorption fine structure, high‐resolution transmission electron microscopy, Mössbauer spectroscopy, and density functional theory calculations demonstrate that alumina‐supported CoFe‐alloy nanoparticles are responsible for the high selectivity of CoFe‐650 for C₂₊ hydrocarbons, also allowing exploitation of photothermal effects. This study demonstrates a vibrant new catalyst platform for harnessing clean, abundant solar‐energy to produce valuable chemicals and fuels from CO₂.     

Broadband monolithic passive baluns and monolithic double-balancedmixer

The design and fabrication of four broadband monolithic passive baluns including CPW Marchand, multilayer MS Marchand, planar-transformer and broadside-coupled line baluns are presented. Operational frequencies range from 1.5 GHz to 24 GHz. Maximum relative bandwidths in excess of 3:1 are achieved. Simulated performances using full wave electromagnetic analysis are shown to agree with the measured results. Two accurate equivalent circuit models constructed from either electromagnetic simulated or measured S-parameters are developed for the MS Marchand and transformer baluns making the optimization of baluns and circuit design using the baluns much more efficient. The design of monolithic double-balanced diode mixer using two planar-transformer baluns is also presented. Without DC bias, the mixer shows a minimum conversion loss of 6 dB with the RF at 5 GHz and a LO drive of 15 dBm at 4 GHz. The measured input IP₃ of this mixer is better than 15 dBm over the 4 to 5.75 GHz frequency band     

CdS Quantum Dots Encapsulated in Chiral Nematic Mesoporous Silica: New Iridescent and Luminescent Materials

Simultaneous integration of light emission and iridescence into a semiconducting photonic material is attractive for the design of new optical devices. Here, a straightforward, one‐pot approach for liquid crystal self‐assembly of semiconductor quantum dots into cellulose nanocrystal‐templated silica is developed. Through a careful balance of the intermolecular interactions between a lyotropic tetraalkoxysilane/cellulose nanocrystal dispersion and water‐soluble polyacrylic acid/mercaptopropionic acid‐stabilized CdS quantum dots, CdS/silica/nanocellulose composites that retain both chiral nematic order of the cellulose nanocrystals and emission of the quantum dots are successfully co‐assembled. Subsequent removal of the cellulose template and organic stabilizers in the composites by controlled calcination generates new freestanding iridescent, luminescent chiral nematic mesoporous silica‐encapsulated CdS films. The pores of these materials are accessible to analytes and, consequently, the CdS quantum dots undergo strong luminescence quenching when exposed to TNT solutions or vapor.     

Association of Ligamentum Flavum Hypertrophy with Adolescent Idiopathic Scoliosis Progression—Comparative Microarray Gene Expression Analysis

The role of the ligamentum flavum (LF) in the pathogenesis of adolescent idiopathic scoliosis (AIS) is not well understood. Using magnetic resonance imaging (MRI), we investigated the degrees of LF hypertrophy in 18 patients without scoliosis and on the convex and concave sides of the apex of the curvature in 22 patients with AIS. Next, gene expression was compared among neutral vertebral LF and LF on the convex and concave sides of the apex of the curvature in patients with AIS. Histological and microarray analyses of the LF were compared among neutral vertebrae (control) and the LF on the apex of the curvatures. The mean area of LF in the without scoliosis, apical concave, and convex with scoliosis groups was 10.5, 13.5, and 20.3 mm², respectively. There were significant differences among the three groups (p < 0.05). Histological analysis showed that the ratio of fibers (Collagen/Elastic) was significantly increased on the convex side compared to the concave side (p < 0.05). Microarray analysis showed that ERC2 and MAFB showed significantly increased gene expression on the convex side compared with those of the concave side and the neutral vertebral LF cells. These genes were significantly associated with increased expression of collagen by LF cells (p < 0.05). LF hypertrophy was identified in scoliosis patients, and the convex side was significantly more hypertrophic than that of the concave side. ERC2 and MAFB genes were associated with LF hypertrophy in patients with AIS. These phenomena are likely to be associated with the progression of scoliosis.     

Modeling of microstructure effects on the mechanical behavior of ultrafine-grained nickels processed by hot isostatic pressing

Bulk ultrafine-grained nickel specimens having grain sizes in the range of 0.25-5 μm were consolidated by hot isostatic pressing technique. The resulting microstructures were characterized by transmission electron microscopy and X-ray diffraction analysis. Compression tests were carried out at room temperature and at strain rate of 1.6×10⁻⁴ s⁻¹. It was found that the measured yield strength does not follow the Hall-Petch law as a consequence of the presence of oxide phase. Therefore, the use of micromechanics based model, which takes into account only the Hall-Petch relationship at grain level for predicting the grain sized effects on mechanical behavior of this kind of materials, is not accurate yet. In this study, a modification made to the generalized self-consistent model was proposed for studying both grain size and oxide phase dependence of ultrafine-grained materials behavior. Because of the novel modification, an optimization procedure with two steps was required to identify the parameters of micromechanical model. An acceptable agreement between experimental and numerical results was achieved. Moreover, the influence of texture on the yield strength and the application of the proposed model to the spark plasma sintering processed materials were also discussed.