Laser-excited electronic fluorescence: Self-quenching and quenching of CS2 vapour

Summary Using a laser-induced fluorescence technique, we have measured lifetimes of CS₂ as functions of pressure, collecting the emission at various wave-length regions. We have obtained quenching rate constants for pure CS₂ and CS₂ plus CH₃CN and CO₂ as collision partners. When the emission is collected at a very long wave-length, evidence is given of vibrational relaxation in the singlet state which leads to the existence of a low-energy pathway of intersystem crossing. Two different long-lived states are also detected in the wave-length region centred at 5860 ?, one in the low-pressure regime and the other at pressures above 0.2 Torr approximately. Quenching rate constants of triplet CS₂ by CO₂ are about the same for both long-lived states, suggesting that vibrational relaxation could occur in the triplet state as well.

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Riassunto Usando una tecnica a fluorescenza indotta da laser, sono state misurate le vite medie di CS₂ in funzione della pressione, raccogliendo le emissioni in varie regioni di lunghezza d'onda. Si sono ottenute costanti di spegnimento per CS₂ puro e CS₂ piú CH₃CN e CO₂ come associati nella collisione. Quando si registra emissione a lunghezza d'onda molto grande, si prova l'esistenza di rilassamento vibrazionale nello stato di singoletto che porta all'esistenza di un percorso a bassa energia dell'incrocio intersistemico. Sono anche determinati due differenti stati a lunga vita nella regione di lunghezza d'onda centrata a 5860 ?, uno nel regime di bassa pressione e l'altro approssimativamente a pressione sopra i 0.2 Torr. Le costanti di spegnimento del tripletto CS₂ mediante CO₂ sono quasi le stesse per entrambi gli stati a lunga vita, e ciò suggerisce che il rilassamento vibrazionale potrebbe verificarsi anche nello stato di tripletto.

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Резюме Используя технику лазера, возбужденного флуоресценцией, мы измеряем времена жизни CS₂, как функцию давления, собирая излучение в различных областях длин волн. Мы получаем постоянные скорости гашения для чистого CS₂ и для CS₂ плюс CH₃CN и CO₂, которые участвуют в соударениях. Когда излучение собирается для очень больших длин волн, то отмечается вибрационная релаксация в синглетном состоянии. Были обнаружены два различных долгоживущих состояния с длиной волны при 5860 ?, одно при низком давлении, а другое при давлениях около 0.2 тор. Постоянные скорости гашения триплетного CS₂, обусловленные CO₂, оказываются примерно одинаковыми для обоих долгоживущих состояний. Этот факт свидетельствует о том, что вибрационная релаксация может иметь место также в триплетном состоянии.

     

Dendronised block copolymers as potential vectors for gene transfection

A series of block copolymers containing a dendronised cationic block for efficient DNA binding and a poly(ethylene glycol) block for encapsulation of the complex were synthesised in a modular fashion using a combination of click chemistry and ring-opening metathesis polymerisation. DNA binding experiments, investigated using gel electrophoresis, dynamic light scattering and transmission electron microscopy, showed that all polymers prepared in this study strongly complex DNA and self-assemble into polyion complex micelles with apparent hydrodynamic radii ranging from 20-120 nm at physiological pH (7.4). The in vitro transfection efficiency and toxicity of these potential non-viral vectors were also evaluated in HeLadouble dagger cells using plasmid DNA encoding for green fluorescent protein as the reporter gene.     

Time-dependent scaling patterns in high frequency financial data

We measure the influence of different time-scales on the intraday dynamics of financial markets. This is obtained by decomposing financial time series into simple oscillations associated with distinct time-scales. We propose two new time-varying measures of complexity: 1) an amplitude scaling exponent and 2) an entropy-like measure. We apply these measures to intraday, 30-second sampled prices of various stock market indices. Our results reveal intraday trends where different time-horizons contribute with variable relative amplitudes over the course of the trading day. Our findings indicate that the time series we analysed have a non-stationary multifractal nature with predominantly persistent behaviour at the middle of the trading session and anti-persistent behaviour at the opening and at the closing of the session. We demonstrate that these patterns are statistically significant, robust, reproducible and characteristic of each stock market. We argue that any modelling, analytics or trading strategy must take into account these non-stationary intraday scaling patterns.     

Finding Shortest Non-Separating and Non-Contractible Cycles for Topologically Embedded Graphs

We present an algorithm for finding shortest surface non-separating cycles in graphs embedded on surfaces in time, where V is the number of vertices in the graph and g is the genus of the surface. If , this represents an improvement over previous results by Thomassen, and Erickson and Har-Peled. We also give algorithms to find a shortest non-contractible cycle in time, which improves previous results for fixed genus. This result can be applied for computing the face-width and the non-separating face-width of embedded graphs. Using similar ideas we provide the first near-linear running time algorithm for computing the face-width of a graph embedded on the projective plane, and an algorithm to find the face-width of embedded toroidal graphs in time.     

Mechanistic Studies on the Salicylate-Catalyzed Peroxyoxalate Chemiluminescence in Aqueous Medium

The peroxyoxalate reaction is one of the most efficient chemiluminescence transformations known and the only system occurring by an intermolecular chemically initiated electron exchange luminescence (CIEEL) mechanism with confirmed high quantum yields. The peroxyoxalate chemiluminescence (PO-CL) is mainly studied in anhydrous organic medium; however, for bioanalytical application, it should be performed in aqueous media. In the present work, we study the peroxyoxalate system in a binary 1,2-dimethoxyethane/water mixture with bis(2,4,6-trichlorophenyl) oxalate (TCPO), bis(4-methylphenyl) oxalate (BMePO) and bis[2-(methoxycarbonyl)phenyl] oxalate (DMO), catalyzed by sodium salicylate, in the presence of rhodamine 6G as activator. Reproducible kinetic results are obtained for all systems; emission decay rate constants depend on the salicylate as well as hydrogen peroxide concentration, and the occurrence of a specific base catalysis is verified. Although singlet quantum yields determined are lower than in anhydrous media in comparable conditions, they are still considerably high and adequate for analytical applications. The highest singlet quantum yields are obtained for the “ecologically friendly” derivative DMO indicating that this derivative might be the most adequate substrate for the use of the peroxyoxalate system in bioanalytical applications.     

Vocal Nodules and Laryngeal Morphology

Our purpose was to study the occurrence of vocal fold nodules under conditions of habitual vocal abuse associated with increased laryngeal muscle tension, to identify the existence of a relationship between vocal nodules and laryngeal morphology. We studied one group of 30 subjects with vocal nodules, 18 to 50 years old, who were compared with two control groups, one of females and one of males, consisting of 30 subjects each. The parameters evaluated were: type of vocal folds coaptation, glottic proportion (GP) and abduction angle (AA), obtained by videotelelaryngoscopy. In the nodules group, the larynges presented a mean value of GP similar to that of the female group, both of which were lower than the mean GP value of the male group. On the other hand, the mean AA was lower than the one in the female group, and closer to the one in the male group. We concluded that vocal nodules were present only in larynges with a predominantly young female morphology, with functional limitations of abduction.     

NMR depth profiles as a non-invasive analytical tool to probe the penetration depth of hydrophobic treatments and inhomogeneities in treated porous stones

Hydrophobic treatment is one of the most important interventions usually carried out in the conservation of stone artifacts and monuments. The analytical study reported in this paper was aimed at answering general questions such as the penetration depth of a hydrophobic treatment into a porous material, its capability to impair the water absorption, how the presence of a treatment may change the open porosity available to the water, and how a treatment may affect the diffusion of water inside a porous structure. Also, inhomogeneities in treated stones due to sharp variations of the amount of the absorbed product in the porous material were evidenced and scaled. The results of this fully non-invasive analytical study were rationalized in terms of new parameters obtained by a suitable process of nuclear magnetic resonance data. These analytical parameters reported here for the first time, namely the hydrophobic efficiency, the penetration depth, and angles describing changes in slope in depth profiles, gave important information in assessing the performance of a treatment.