Showing papers by "Southwest University of Science and Technology published in 2014"

Needle-like Co3O4 anchored on the graphene with enhanced electrochemical performance for aqueous supercapacitors.

Abstract: We synthesized the needle-like cobalt oxide/graphene composites with different mass ratios, which are composed of cobalt oxide (Co3O4 or CoO) needle homogeneously anchored on graphene nanosheets as the template, by a facile hydrothermal method. Without the graphene as the template, the cobalt precursor tends to group into urchin-like spheres formed by many fine needles. When used as electrode materials of aqueous supercapacitor, the composites of the needle-like Co3O4/graphene (the mass ratio of graphene oxide(GO) and Co(NO3)2·6H2O is 1:5) exhibit a high specific capacitance of 157.7 F g–1 at a current density of 0.1 A g–1 in 2 mol L–1 KOH aqueous solution as well as good rate capability. Meanwhile, the capacitance retention keeps about 70% of the initial value after 4000 cycles at a current density of 0.2 A g–1. The enhancement of excellent electrochemical performances may be attributed to the synergistic effect of graphene and cobalt oxide components in the unique multiscale structure of the composites.

A Hand Gesture Recognition Framework and Wearable Gesture-Based Interaction Prototype for Mobile Devices

Abstract: An algorithmic framework is proposed to process acceleration and surface electromyographic (SEMG) signals for gesture recognition. It includes a novel segmentation scheme, a score-based sensor fusion scheme, and two new features. A Bayes linear classifier and an improved dynamic time-warping algorithm are utilized in the framework. In addition, a prototype system, including a wearable gesture sensing device (embedded with a three-axis accelerometer and four SEMG sensors) and an application program with the proposed algorithmic framework for a mobile phone, is developed to realize gesture-based real-time interaction. With the device worn on the forearm, the user is able to manipulate a mobile phone using 19 predefined gestures or even personalized ones. Results suggest that the developed prototype responded to each gesture instruction within 300 ms on the mobile phone, with the average accuracy of 95.0% in user-dependent testing and 89.6% in user-independent testing. Such performance during the interaction testing, along with positive user experience questionnaire feedback, demonstrates the utility of the framework.

Silver Nanoparticles and Growth Factors Incorporated Hydroxyapatite Coatings on Metallic Implant Surfaces for Enhancement of Osteoinductivity and Antibacterial Properties

Abstract: Research on incorporation of both growth factors and silver (Ag) into hydroxyapatite (HA) coatings on metallic implant surfaces for enhancing osteoinductivity and antibacterial properties is a challenging work. Generally, Ag nanoparticles are easy to agglomerate and lead to a large increase in local Ag concentration, which could potentially affect cell activity. On the other hand, growth factors immobilization requires mild processing conditions so as to maintain their activities. In this study, bone morphology protein-2 (BMP-2) and Ag nanoparticle contained HA coatings were prepared on Ti surfaces by combining electrochemical deposition (ED) of Ag and electrostatic immobilization of BMP-2. During the ED process, chitosan (CS) was selected as the stabilizing agent to chelate Ag ions and generate Ag nanoparticles that are uniformly distributed in the coatings. CS also reduces Ag toxicity while retaining its antibacterial activity. Afterwards, a BMP/heparin solution was absorbed on the CS/Ag/HA coatings. Consequently, BMP-2 was immobilized on the coatings by the electrostatic attraction between CS, heparin, and BMP-2. Sustained release of BMP-2 and Ag ions from HA coatings was successfully demonstrated for a long period. Results of antibacterial tests indicate that the CS/Ag/HA coatings have high antibacterial properties against both Staphylococcus epidermidis and Escherichia coli. Osteoblasts (OB) culture reveals that the CS/Ag/HA coatings exhibit good biocompatibility. Bone marrow stromal cells (BMSCs) culture indicates that the BMP/CS/Ag/HA coatings have good osteoinductivity and promote the differentiation of BMSCs. Ti bars with BMP/CS/Ag/HA coatings were implanted into the femur of rabbits to evaluate the osteoinductivity of the coatings. Results indicate that BMP/CS/Ag/HA coatings favor bone formation in vivo. In summary, this study presents a convenient and effective method for the incorporation of growth factors and antibacterial agents into HA coatings. This method can be utilized to modify a variety of metallic implant surfaces.

Relationship between Corporate Social Responsibility and Financial Performance in the Mineral Industry: Evidence from Chinese Mineral Firms

Abstract: This paper examines the relationship between Corporate Social Responsibility (CSR) and Corporate Financial Performance (CFP) using panel data for 228 Chinese mineral listed firms from 2010 to 2013 with Pooled Least Squares regression analysis. Our study considers five different sublevel CSR issues—shareholder responsibility, employee responsibility, environmental responsibility, public responsibility, and supplier, customer and consumer responsibility—in capturing the effects of CSR elements on CFP. The estimation results show the different effects of each sublevel CSR issue on CFP. Overall, shareholder, employee responsibility, environmental responsibility, supplier, customer and consumer responsibility have significant relationships with CFP, which are the stakeholders who have the closest linkage with firm operations. Meanwhile, public responsibility outside the firm does not show significant interaction with CFP, which is why many mineral firms ignore the public interest and this leads to conflicts. Shareholder responsibility has the most significant positive effect on CFP. Supplier, customer and consumer responsibility and environmental responsibility usually have negative effects on CFP as costs increase. Moreover, all 228 listed mineral firms that were selected in this paper have been classified into five sub-sectors: the extractive industry, metal fabrication industry, oil and gas industry, gas and water-related industry, and oil-producing equipment industry, based on the Industry Classification Benchmark (ICB). Our study shows that the differences in the relationship between CSR and CFP for five sublevel industries are due to industry characteristics. If the government wants to solve these conflicts and positively encourage firms to adopt CSR, it is necessary to create a mining development environment whereby firm profits are closely tied to CSR.

Facile, continuous and large-scale synthesis of CL-20/HMX nano co-crystals with high-performance by ultrasonic spray-assisted electrostatic adsorption method

Abstract: High-performance of CL-20/HMX nano co-crystals is readily synthesized by ultrasonic spray-assisted electrostatic adsorption method. This facile and continuous approach reduces handling time, minimizes the potential of aggregation via the electrostatic repulsive force among nano co-crystal particles and opens up new perspectives in fabricating various organic nano-sized co-crystals on a large-scale.

Improved piezoelectricity of PVDF-HFP/carbon black composite films

Abstract: We report a substantial improvement of piezoelectricity for poly(vinylidene fluoride-hexafluoropropylene) (PVDF-HFP) copolymer films by introducing carbon black (CB) into the PVDF-HFP to form PVDF-HFP/CB composite films. The optimized output voltage of the composite film at an optimal CB content of 0.5 wt% is found to be 204% of the pristine PVDF-HFP film. Its harvested electrical power density is 464% and 561% of the pristine PVDF-HFP film by using ac and dc circuits, respectively. Through Fourier transform infrared spectroscopy analysis, differential scanning calorimetry analysis, and polarized optical microscopy observations, we clarify the enhancement mechanism of piezoelectricity for the PVDF-HFP/CB composite films. We find that the added CB acts as nucleating agent during the initial formation of crystals, but imposes an insignificant effect on the α–β phase transformation during stretching. We also demonstrate that the addition of optimal CB reduces crystal size yet increases the number of crystals in the composite films. This is beneficial for the formation of elongated, oriented and fibrillar crystalline morphology during stretching and consequently results in a highly efficient poling process. The addition of overdosed CB leads to the formation of undersized crystals, lowered crystallinity, and hence reduced piezoelectric performance of the PVDF-HFP/CB composite films.

Preparation and characterization of sulfonated polyimide/TiO2 composite membrane for vanadium redox flow battery

Abstract: A sulfonated polyimide (SPI)/TiO2 composite membrane was fabricated by a blend way to improve its performance in vanadium redox flow battery (VRB). Both EDS and XRD results verify the successful preparation of the SPI/TiO2 composite membrane. The surface SEM image shows its homogeneous structure. TG analysis identifies its thermal stability. The SPI/TiO2 composite membrane possesses much lower permeability of VO2+ ions (2.02 × 10−7 cm2 min−1) and favorable proton conductivity (3.12 × 10−2 S cm−1). The VRB single cell with SPI/TiO2 composite membrane shows higher coulombic efficiency (93.80–98.00 %) and energy efficiency (83.20–67.61 %) at the current density ranged from 20 to 80 mA cm−2 compared with that with Nafion 117 membrane. And the operational stability of the as-prepared composite membrane is good after 50 times of cycling tests. Therefore, the low-cost SPI/TiO2 composite membrane with excellent battery performance exhibits a great potential for application in VRB.

H∞ filtering for a class of discrete-time singular Markovian jump systems with time-varying delays.

Abstract: The problem of H∞ filtering for a class of discrete-time singular Markovian jump systems with time-varying delays is investigated in this paper. The transition probabilities under consideration are time-varying, i.e., Markovian chain is nonhomogeneous. By using the Lyapunov functional approach and reciprocally convex technique, a less conservative delay-dependent bounded real lemma is developed in terms of linear matrix inequalities. Moreover, a sufficient condition for the existence of the desired filter which guarantees the stochastic admissibility and the H∞ performance index of the resulting filtering error system is presented. Numerical examples are employed to show the usefulness of the proposed results.