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    A spectroscopic study of indigo dye in aqueous solution: A combined experimental and TD-DFT study
    (2018-12-01)
    Jiwalak, Naparat
    ;
    Daengngern, Rathawat
    ;
    Rungrotmongkol, Thanyada
    ;
    Jungsuttiwong, Siriporn
    ;
    Namuangruk, Supawadee
    This study reports UV–Visible spectra and electronic structures of indigo (IG) in aqueous solution using a combination of experimental and theoretical methods. In the visible region, the experimental absorption spectrum of the solution showed a broad peak with the longest wavelength of maximal absorption (λ<inf>max</inf>) value at 708 nm. For the theoretical method, a trans-IG monomer and a trans-IG bound with two water molecules (IG.2W) were optimized in the ground state using the B3LYP and B3LYP-D3 calculations with the 6-31 + G(d,p) basis set and the SCRF-CPCM model for taking solvent effect into account was also applied. Sequentially, the UV–Visible spectra and λ<inf>max</inf> of the optimized trans-IG and IG.2W models in the implicit water were simulated by the time-dependent density functional theory (TD-DFT) calculations. The TD-DFT methods including BLYP, B3LYP, PBE0, CAM-B3LYP, M06-2X, ωB97XD, LC-BLYP, and LC-ωPBE functionals without and with the D3 correction and the 6-31 + G(d,p) basis set were selected. The results pointed out that BLYP and BLYP-D3 were the best methods because they could reproduce the experimental λ<inf>max</inf> value of IG in aqueous solution. The predicted λ<inf>max</inf> values of IG.2W were almost equal to 708 nm (the experimental data), indicating that IG.2W could be responsible for optical properties of IG.
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    A numerical model for ultrasonic measurements of swelling and mechanical properties of a swollen PVA hydrogel
    (2010-08-01)
    Lohakan, M.
    ;
    Jamnongkan, T.
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    Pintavirooj, C.
    ;
    Kaewpirom, S.
    ;
    Boonsang, S.
    This paper presents a numerical model for the evaluation of mechanical properties of a relatively thin hydrogel. The model utilizes a system identification method to evaluate the acoustical parameters from ultrasonic measurement data. The model involves the calculation of the forward model based on an ultrasonic wave propagation incorporating diffraction effect. Ultrasonic measurements of a hydrogel are also performed in a reflection mode. A Nonlinear Least Square (NLS) algorithm is employed to minimize difference between the results from the model and the experimental data. The acoustical parameters associated with the model are effectively modified to achieve the minimum error. As a result, the parameters of PVA hydrogels namely thickness, density, an ultrasonic attenuation coefficient and dispersion velocity are effectively determined. In order to validate the model, the conventional density measurements of hydrogels were also performed. © 2010 Elsevier B.V. All rights reserved.
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    A mathematical model for pollution in a river and its remediation by aeration
    (2009-03-01)
    Pimpunchat, Busayamas
    ;
    Sweatman, Winston L.
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    Wake, Graeme C.
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    Triampo, Wannapong
    ;
    Parshotam, Aroon
    We present a simple mathematical model for river pollution and investigate the effect of aeration on the degradation of pollutant. The model consists of a pair of coupled reaction-diffusion-advection equations for the pollutant and dissolved oxygen concentrations, respectively. The coupling of these equations occurs because of reactions between oxygen and pollutant to produce harmless compounds. Here we consider the steady-state case in one spatial dimension. For simplified cases the model is solved analytically. We also present a numerical approach to the solution in the general case. The extension to the transient spatial model is relatively straightforward. The study is motivated by the crucial problem of water pollution in many countries and specifically within the Tha Chin River in Thailand. For such real situations, simple models can provide decision support for planning restrictions to be imposed on farming and urban practices. © 2008 Elsevier Ltd. All rights reserved.
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    Modelling river pollution and removal by aeration
    (2007-12-01)
    Pimpunchat, B.
    ;
    Sweatman, W. L.
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    Triampo, W.
    ;
    Wake, G. C.
    ;
    Parshotam, A.