A QUARTZ CRYSTAL MICROBALANCE STUDY OF THIOL:ENE POLY(IONIC LIQUID) POLYMERIZATION AND GAS ABSORPTION

ABSTRACT The polymerization process of, and gas absorption by, imidazolium-containing thiol:ene poly (ionic liquid)s (PILs), prepared from bisallylimidazolium bis(trifluoromethyl sulfonyl)imide [NTf2-] and pentaerythritoltetrakis(3 mercaptopropionate), was studied. The thiol:ene PILs examined were recently reported by groups at Murray State University. The advantage of thiol:ene PILs over other reported PILs is that thiol:ene polymers are made rapidly by UV exposure and exhibit high mechanical and thermal stability due to high cross-linking. The properties of interest for the thiol:ene PILs were studied using a quartz crystal microbalance (QCM). QCM techniques are based on the piezoelectric effect, where certain crystals (e.g., quartz) will oscillate mechanically (vibrate) under an oscillating electrical potential. The frequency of crystal vibration has been shown to depend on the properties of the environment of the crystal surface, including adsorbed mass, and both the density and viscosity of the surrounding fluid. The frequency of vibration can be measured with such high sensitivity that QCM has picogram detection limits. There are three major models which were applied to the data obtained in this project: Sauerbrey’s equation, Kanazawa’s equation, and an equation combining Henry’s Law and Sauerbrey’s equation. Sauerbrey’s equation is the simplest model used to evaluate mass changes in thin, rigid films. Many cases do not fulfill the requirement for Sauerbrey to be valid (e.g. thick, viscoelastic films). Therefore, other models have been employed. For example, in liquid contact measurements Kanazawa’s equation is used to measure density and viscosity changes. In some measurements of gas absorption by ionic liquids, an equation derived from Sauerbrey and Henry’s Law has been used to determine gas solubilities. The polymerization process for five thiol:ene ratios was studied. Bisallylimidazolium was mixed in various ratios pentaerythritol tetrakis(3-mercaptopropionate) (PTMP), along with ~1 wt% of the photoinitiator 2,2-dimethoxy-2-phenyl-acetophenone (DMPA). The mixture was shaken until homogeneous and spin coated onto a QCM crystal. After the chip was loaded into the QCM, instrument frequency was monitored until an equilibrium response was obtained. The crystal then was exposed to UV light until re-equilibration. From the measured data, both the rate of frequency change/polymerization, and change in ρL (density) and ηL (viscosity) could be obtained. Gas absorption by PILs was also studied. Monomers were prepared and spin coated onto the crystal as before. Then, before loading into the QCM instrument, photopolymerization was performed. In these experiments, the instrument was placed inside an airtight chamber that could be evacuated and filled with the desired gas. After crystal vibration achieved equilibrium the chamber was subjected to vacuum then filled with either CO2 or N2. Based on change of quartz oscillation frequency (Δf) between vacuum and CO2/N2 filled, the various models mentioned earlier could be applied. Then, the relative absorption/solubility of the gases by the various thiol:ene polymers could be determined

Modelling and Linear Control of a Buoyancy-Driven Airship

International audienceWe describe the modelling and control of a newkind airship which is propelled by buoyancy. Based on the Newton-Euler equations and Kirchhoff equations, and referred to the models of underwater gliders and aircraft, a 6DOF nonlinear mathematical model of a buoyancy-driven airship is derived, with features distributed internal mass, and no thrust, elevators and rudders. The attitudes are controlled by the motion of internal mass. The performances of the airship are studied in the vertical plane. A linear feedback controller is derived for the nonlinear model. The results of simulation display robustness properties of the controllers to disturbances

Gitor: Scalable Code Clone Detection by Building Global Sample Graph

Code clone detection is about finding out similar code fragments, which has drawn much attention in software engineering since it is important for software maintenance and evolution. Researchers have proposed many techniques and tools for source code clone detection, but current detection methods concentrate on analyzing or processing code samples individually without exploring the underlying connections among code samples. In this paper, we propose Gitor to capture the underlying connections among different code samples. Specifically, given a source code database, we first tokenize all code samples to extract the pre-defined individual information. After obtaining all samples individual information, we leverage them to build a large global sample graph where each node is a code sample or a type of individual information. Then we apply a node embedding technique on the global sample graph to extract all the samples vector representations. After collecting all code samples vectors, we can simply compare the similarity between any two samples to detect possible clone pairs. More importantly, since the obtained vector of a sample is from a global sample graph, we can combine it with its own code features to improve the code clone detection performance. To demonstrate the effectiveness of Gitor, we evaluate it on a widely used dataset namely BigCloneBench. Our experimental results show that Gitor has higher accuracy in terms of code clone detection and excellent execution time for inputs of various sizes compared to existing state-of-the-art tools. Moreover, we also evaluate the combination of Gitor with other traditional vector-based clone detection methods, the results show that the use of Gitor enables them detect more code clones with higher F1.Comment: 12 pages, 5 figure