Математическое моделирование огибающей реверберационного процесса с помощью алгоритма Шредера

Стаття присвячена дослідженню алгоритму оберненого інтегрування (метод Шредера) який використовується при побудові огинаючої ревербераційного процесу. Ґрунтуючись на різні методи вимірювання була розроблена програма для моделювання процесу реверберації в закритому приміщенні та проведений модельний експеримент. Аналіз отриманих результатів показав, що огинаюча ревербераційного процесу, побудованого за методом зворотного інтегрування, має мінімальне середньоквадратичне відхилення від заданого експериментального спадання, а це означає, що використовуючи його можна отримати більш точне значення часу реверберації.The article is devoted to research of reverse integration algorithm (Schroder’s method) which is used for the construction of reverberation prosess circumflex. Based on the different methods of measuring, the program for reverberation process design in the closed room was developed and a model experiment was carried out. The analysis of the results showed that reverberation process circumflex built by reverse integration method has minimum standard deviation from the set experimental downturn, and it means that it is possible to get more exact meaning of reverberation time using this program.Статья посвящена исследованию алгоритма обратного интегрирования (метод Шредера) который используется при построении огибающей реверберационного процесса. Основываясь на различные методы измерения была разработана программа для моделирования процесса реверберации в закрытом помещении и проведен модельный эксперимент. Анализ полученных результатов показал, что огибающая реверберационного процесса, построенного за методом обратного интегрирования, имеет минимальное среднеквадратическое отклонение от заданного экспериментального спада, а это значит, что используя его можно получить более точное значение времени реверберации

Fluorescence Probing of Thiol-Functionalized Gold Nanoparticles: Is Alkylthiol Coating of a Nanoparticle as Hydrophobic as Expected?

Understanding the interaction of fluorescent dyes with monolayer-protected gold nanoparticles (AuNPs) is of fundamental importance in designing new fluorescent nanomaterials. Among a variety of molecular sensors and reporters, fluorescent probes based on a 3-hydroxychromone (3HC) skeleton appear to be very promising. They exhibit the phenomenon of dual band emission, resulting from excited-state intramolecular proton transfer (ESIPT), known to be highly sensitive to a nature of microenvironment surrounding a fluorophore. In this study, dodecanethiol-protected gold nanoparticles were synthesized, and, owing to the transmission electron micrograph imaging, their average diameter was found to be ∼1.4 nm. Fluorescence titrations of the 3HC ESIPT probes with AuNPs in toluene solutions demonstrate significant changes in the intensity ratio of their normal and tautomeric emission bands, suggesting that the probe molecules become noncovalently bound to a dodecanethiol layer of AuNPs. Despite expected fluorescence quenching induced by close proximity to the metal surface, no fluorescence lifetime decrease was observed, indicating that a bound-fluorophore is shielded from a nanoparticle core. Further spectral analysis revealed that the ratiometric fluorescence changes could be interpreted as a consequence of intermolecular hydrogen bonding between a probe and residual ethanol molecules, trapped into the dodecanethiol shell of AuNPs during the synthesis. Evidences for residual traces of ethanol in the ligand shell of the nanoparticles were also observed in NMR spectra, suggesting that alkylthiol-coated gold nanoparticles may not be as hydrophobic as one could expect. To elucidate structural features of dodecanethiol-stabilized gold nanoparticles at the supramolecular level, a molecular dynamics (MD) model of AuNP was developed. The model was based on the all-atom CHARMM27 force field parameters and parametrized according to available experimental data of the synthesized AuNPs. Our MD simulations show that in bulk toluene the 3HC probe molecule becomes weakly bound to a dodecanethiol monolayer, so that a fluorophore favors residence in an outer shell of AuNP. In addition, MD simulations of transfer of AuNP from bulk ethanol to toluene demonstrate that a small population of ethanol molecules are able to penetrate deeply into the dodecanethiol layer and may indeed be trapped into the ligand shell of alkylthiol-functionalized gold nanoparticles. The results of our fluorescence experiments and molecular dynamics simulation suggest that 3-hydroxychromones can be used as a noncovalent fluorescent labeling agent for alkylthiol-stabilized noble metal nanoparticles

Fluorescence Probing of Thiol-Functionalized Gold Nanoparticles: Is Alkylthiol Coating of a Nanoparticle as Hydrophobic as Expected?

Understanding the interaction of fluorescent dyes with monolayer-protected gold nanoparticles (AuNPs) is of fundamental importance in designing new fluorescent nanomaterials. Among a variety of molecular sensors and reporters, fluorescent probes based on a 3-hydroxychromone (3HC) skeleton appear to be very promising. They exhibit the phenomenon of dual band emission, resulting from excited-state intramolecular proton transfer (ESIPT), known to be highly sensitive to a nature of microenvironment surrounding a fluorophore. In this study, dodecanethiol-protected gold nanoparticles were synthesized, and, owing to the transmission electron micrograph imaging, their average diameter was found to be ∼1.4 nm. Fluorescence titrations of the 3HC ESIPT probes with AuNPs in toluene solutions demonstrate significant changes in the intensity ratio of their normal and tautomeric emission bands, suggesting that the probe molecules become noncovalently bound to a dodecanethiol layer of AuNPs. Despite expected fluorescence quenching induced by close proximity to the metal surface, no fluorescence lifetime decrease was observed, indicating that a bound-fluorophore is shielded from a nanoparticle core. Further spectral analysis revealed that the ratiometric fluorescence changes could be interpreted as a consequence of intermolecular hydrogen bonding between a probe and residual ethanol molecules, trapped into the dodecanethiol shell of AuNPs during the synthesis. Evidences for residual traces of ethanol in the ligand shell of the nanoparticles were also observed in NMR spectra, suggesting that alkylthiol-coated gold nanoparticles may not be as hydrophobic as one could expect. To elucidate structural features of dodecanethiol-stabilized gold nanoparticles at the supramolecular level, a molecular dynamics (MD) model of AuNP was developed. The model was based on the all-atom CHARMM27 force field parameters and parametrized according to available experimental data of the synthesized AuNPs. Our MD simulations show that in bulk toluene the 3HC probe molecule becomes weakly bound to a dodecanethiol monolayer, so that a fluorophore favors residence in an outer shell of AuNP. In addition, MD simulations of transfer of AuNP from bulk ethanol to toluene demonstrate that a small population of ethanol molecules are able to penetrate deeply into the dodecanethiol layer and may indeed be trapped into the ligand shell of alkylthiol-functionalized gold nanoparticles. The results of our fluorescence experiments and molecular dynamics simulation suggest that 3-hydroxychromones can be used as a noncovalent fluorescent labeling agent for alkylthiol-stabilized noble metal nanoparticles