The present investigation is primarily focused on the study of effect of nanosized clay and TiO_2 on the structure and thermal properties of electrically conducting poly (aniline-co-o-toluidine)/nanocomposite system. These nanocomposites are synthesized by the in situ oxidative polymerization method with peroxy disulphate as a lone chemical initiator, HCl as an external dopant and clay and TiO_2 as a host material. The nanocomposites are characterized by analytical tools like Fourier transform infrared, Keithley instrument, thermal gravimetric analysis, and high resolution transmission electron microscopy.
The ultraviolet (1, 0) B ^{2}Σ_{u}^{+} - X ^{2}Σ_{g}^{+} transition in the N_{2}^{+} cation was measured with the absorption cavity ring down technique. The N_{2}^{+} cations were produced in a stationary DC discharge in nitrogen under reduced ( ≈ 0.5 Tr) pressure. The weak band due to the (4, 0) A ^{2}Π_{u} - X ^{2}Σ_{g}^{+} transition in the red part of the spectrum was also recorded. Several of the observed transitions correspond to absorptions from the vibrationally excited (ν'=1) states of N_{2}^{+} and to absorptions from the neutral N_{2} molecules in the triplet state.
Developments of three new time-resolved vibrational spectroscopies and their applications to electronically excited states are reviewed. Transformlimited picosecond time-resolved Raman spectroscopy has been used to study the vibrational dynamics of trans-stilbene in the lowest excited singlet state. Picosecond time-frequency two-dimensional multiplex Coherent Antistokes Raman Scattering spectroscopy has been used to probe the structure of diphenylacetylene in the lowest and the second lowest excited singlet states. Nanosecond time-resolved dispersive infrared spectroscopy has detected the singlet and triplet intramolecular charge transfer states of 4-(di-methylamino)benzonitrile. Strong evidence for a charge transfer structure has been obtained.
A critical analysis of available experimental and theoretical data on transition probabilities for spectral lines of singly ionized nitrogen was performed. J-file sum rule tests for the 3s-3p triplet supermultiplet in NII were performed on the basis of recently calculated and measured line strengths. It is shown that the inclusion of intersystem transitions in the analysis leads to a better agreement of the data with the J-file sum rule prediction.
Influence of the buffer gas on the multiphoton absorption and dissociation in different mixtures was investigated. Simple method based on the empirical and theoretical vibrational energy distribution is applied for high fluence regime. Collisional effects of buffer gas (Ar) are introduced to enhance the absorption and relaxation of irradiated molecules (SF_6 and C_2H_4). Functional dependences of mean number of absorbed photons per molecule (ீ nு_{total}) on the molecular excitation level are presented, enabling us to confirm or predict the level of excitation, number of molecules directly involved in the absorption process and dissociated during the laser pulse.
Generalized coupled two-level model is applied in different gas mixtures and investigated for high fluence regime. Functional dependences of mean number of absorbed photons per molecule 〈 nு_{total} on buffer-gas pressure (p_{buff}) are presented, used to confirm or predict some possible physical and chemical processes, like enhanced absorption and/or dissociation. Limitations of proposed models are analyzed depending on both gas pressure and laser fluence. Results are compared with other previously obtained by the same experimental technique, but for different absorbing molecule.
The polycrystals of 2,4 diaminotoluene were produced by slow evaporation of solvent. The polycrystalline samples were exposed to ⁶⁰Co gamma rays with dose rate of 0.950 kGy/h, at room temperature, for 12, 24, 48, and 72 hours. The electron paramagnetic resonance measurements were carried out on these samples in the temperature range between 298 K and 400 K. No electron paramagnetic resonance signal was observed in the samples irradiated for 12, 24, 48 hours. Two types of radicals were detected using ESR spectrometer in the sample irradiated for 72 h. These radiation damage centers were called RI and RII. The average values of g and the hyperfine coupling constant were calculated. This study also investigates the potential usage of machine learning methods and aims to test the success of these methods and to select the best method.
For the assessment of irradiation influence on 2-(piperidin-1-ylmethyl)phenol single crystals (C₁₂H₁₇NO), electron paramagnetic resonance measurements were carried out on the samples exposed to ⁶⁰Co radiation at dose values of 22.8, 45.6 and 68.4 kGy at room temperature. Electron paramagnetic resonance signals were not observed in non-irradiated sample and in samples irradiated at dose values of 22.8 and 45.6 kGy. The electron paramagnetic resonance measurements were performed on the single crystals. This irradiated single crystal was rotated in steps of 10°. One type of radical center was found. The average values of g and hyperfine constant of the detected radiation damage center were calculated from experimental spectra as follows: g=2.0052, A_{H} = 0.74 mT.
In the present study, calix[4]arene and its derivate 25,27-di(4-nitrobenzyl)-26,28-dihydroxycalix[4]arene were irradiated for 72 hours by ⁶⁰Co gamma rays at dose rate of 0.720 kGy/h. These irradiated samples were analyzed by EPR method and it was found that one type of radical was produced in calix[4]arene, and two type of radicals were produced in 25,27-di(4-nitrobenzyl)-26,28-dihydroxycalix[4]arene. The measurements were performed in the temperature range of 273-400 K using x-band EPR spectrometer. It was observed that the spectra, obtained from two samples, have very weak temperature dependence. Hyperfine and g parameters were calculated for two samples.
The free radicals and their concentration in resin materials may impact biocompatibility and polymerization properties of dental materials. The aim of this study was to determine whether there are free radicals and to obtain useful information about thermal stability of materials using electron spin resonance (ESR) spectroscopy, TGA (Thermogravimetry Analysis) and DTA (Differential Thermal Analysis) methods. Epoxy resin-based sealers AHPlus and MM-Seal samples, freshly mixed and set, were prepared to be analysed with ESR and thermal methods. The free radicals were found in dental materials. As radical concentration in AHPlus have changed very slowly, the concentration in MM-Seal have decreased dramatically. Also, MM-Seal was found to decompose in three steps with the increasing temperature, while decomposition of the AHPlus occurred in two steps.
The antioxidant activity of phytochemicals and of the methanolic extract of Lavandula stoechas was evaluated by β-carotene-linoleate bleaching, DPPH radical scavenging, ferric reducing/antioxidant power (FRAP). The obtained results were compared with antioxidant activities of synthetic antioxidants, such as BHT and BHA. The highest antioxidant activity of the extract was observed by DPPH radical scavenging assay, which was 84.45±5.1% at 1 mg ml¯¹. Rutin, rosmarinic acid, and caffeic acid were main phenolics in the extract. The total phenolic content of the methanolic extract of Lavandula stoechas was found to be 105.5±2.7 mg gallic acid equivalent (GAE). Electron spin resonance (ESR) measurements were also performed on the samples. Free radicals were determined by ESR method. g value was found to be 2.0034 for the Lavandula stoechas; 2.0052 for quercetin.
Poly(2-hydroxyethyl methacrylate)-co-poly(4-vinyl pyridine) and poly(HEMA)-co-poly-(4-VP) copolymers were synthesized by free radical polymerization. K₂S₂O₈ was used as an initiator. Chain lengths of the copolymer was changed by varying the monomer/initiator ratio. These polymers have molarites of 2.6 and 2.1 respectively and are called COP2 and COP4. The samples were exposed to gamma rays at room temperature. After irradiation, the EPR spectra of COP2 and COP4 were recorded between 120 K and 450 K. From the temperature dependence of the line intensity, it was concluded that unpaired spin concentration in the irradiated samples has been changing with temperature. A theoretical study, presented in this report, was aimed to test success of the machine learning methods and to select the best learning method.
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