24,909 research outputs found
Temperature dependence of the solvation dynamics in alkylcyanobiphenyls
No full textEarlier investigations of the solvation dynamics of the cationic dye rhodamine 700 in the isotropic phase of the nematogenic substance: octylcyanobiphenyl (Rau, J., Ferrante, C., Deeg, F. W., Brauchle, C. J. Phys. Chem. B 1999, 103, 931) have shown that in this liquid two different contributions to the solvation dynamics exist. The slower one can-be explained in terms of polar solvation, while the second one Is not yet fully understood. The latter one is temperature independent from the nematic-isotropic phase transition temperature. up to 20 K above the transition temperature. We present in this paper two different approaches to a better understanding of the solvation dynamics of the alkylcyanobiphenyls. First, it was investigated if a different member of the family of the alkylcyanobiphenyls, butylcyanobiphenyl, exhibits similar dynamic behavior. To check the possible influence of the probe chromophore, the neutral dye coumarin 153 was dissolved in octylcyanobiphenyl for a second set of measurements. The time-resolved dynamic Stokes shift S(t) was measured above the nematic-isotropic phase transition. Butylcyanobiphenyl with the probe chromophore rhodamine 700 -and octylcyanobiphenyl with coumarin 153 show qualitatively the same contributions as found in the solution of rhodamine 700 in octylcyanobiphenyl. From this, we conclude that the peculiar dynamics observed is characteristic for the whole family of the alkylcyanobiphenyls and not only for a special system of probe molecule and Liquid. In addition to the solvation dynamics the temperature dependence of the rotational relaxation times of the dye molecules was recorded
Characteristics of Solvation Dynamics of Rhodamine 700 in Cyanobypheyls
No full textThe results of solvation dynamics measurements of rhodamine 700 in the isotropic phase of two different liquid crystalline substances, 8CB and 4CB, are presented. It is shown that solvation takes place on a length scale shorter than the orientational correlation length of the pseudonematic domains. Two processes contribute to the solvation: The slower process can be described by dielectric relaxation. The faster component is interpreted in terms of intermolecular interactions specific to liquid crystalline sample
Solvation dynamics of Rhodamine 700 in the nematogenic liquid octylcyanobiphenyl
No full textAn investigation of the solvation dynamics of rhodamine 700 in the isotropic phase of the nematogenic substance octylcyanobiphenyl is presented. The time-resolved dynamic Stokes shift S(t) was measured above the nematic-isotropic phase transition and at two temperatures below it. At all temperatures S(t) is characterized by a fast and a slow component on a 10 and 100 ps time scale, respectively. The slow component shows an exponentially activated temperature dependence analogous to the one observed in polar liquids. The fast component exhibits a distinctly different temperature dependence. It is temperature independent from the nematic-isotropic phase transition temperature to 20 K above the transition temperature. Only at higher temperatures does this decay becomes faster. These fast dynamics are associated with the specific anisotropic potential in the locally ordered nematogenic liquid. Additional measurements of the reorientational dynamics of the chromophore are compared with the solvation dynamics investigations
W. F. Mitchell
No full textEarlier this year, an article was published in the News Bulletin
(February 2012) on the background of Captain Boyns Hedley
Hocking, a dentist who became one of the first casualties in the
bombing of Darwin in 1942. The author, W F Mitchell, has kindly
provided a summary of the 70th anniversary activities held in
Darwin in February 2012 to commemorate this significant event in
the Northern Territory?s historyDate:2012-09News Bulletin no. 413, p. 36 - 37
Solvation dynamics of Nile Blue in ethanol confined in porous sol-gel glasses
No full textWe report on solvation dynamics measurements of the chromophore nile blue in ethanol confined to sol-gel glasses with 50 Angstrom and 75 Angstrom average pore size and compare them with the dynamics of the respective bulk solution. Both the amplitude of the dynamic Stokes shift as well as the dynamics of the solvation process are drastically changed upon confinement. In both confined solutions the dynamic Stokes shift is reduced by a factor of about 2. As the large majority of the chromophores is adsorbed at the inner pore surfaces the solute molecules interact with only a "half-space" of solvent molecules. In a first approximation this decreases the stabilization energy by a factor of 2. The solvation dynamics in the confined solutions show nonexponential behavior comparable to the bulk. However, the whole solvation process slows down and the single decay time constants characterizing it increase with decreasing pore size of the sol-gel glass. We have introduced two phenomenological models to rationalize this behavior. The enhanced polarization field model takes into account the confinement and predicts a strengthening of the solvent's polarization field in an extended solvation cage induced by the electrical field of the chromophore. The steric hindrance model focuses on the interaction of the liquid with the surface reducing molecular mobility resulting in longer relaxation times. Probably both effects are of relevance in the confined solutions investigated. Confinement affects the steady-state spectra as well leading to a redshift of the absorption and a blueshift of the fluorescence. Additional data on the reorientational dynamics of the chromophore are consistent with the fact that the molecules are predominantly adsorbed at the pore surfaces
Solvation dynamics of ionic dyes in the isotropic phase of liquid crystals
No full textWe present a solvation dynamics study of Rhodamine 700 in the isotropic phase of octylcyanobiphenyl approaching the nematic-isotropic phase transition. From our experiments we detect two kinds of processes. A fast process, with decay time constants of tens of ps, shows no clear temperature dependence and is attributed to local reorientational motion of the solvent in the proximity of the chromophore. A slow process, with time constants in the hundreds of ps, shows a temperature activated behavior. This process does not seem to be influenced by the molecular order displayed by nematogenic substances and resembles the solvation dynamics behavior observed in simple polar liquids and predicted by dielectric theories
Assessing the George W. Bush Presidency: A Tale of Two Terms
No full textIn one of the first volumes assessing the full two terms of the George W. Bush presidency, Wroe and Herbert have gathered the work of leading American and European scholars. In fifteen succinct and incisive chapters, authorities such as Jim Pfiffner, John Maltese, Graham Wilson and Alan Gitelson offer assessments of the Bush administration's successes and failures. Extensive attention is paid to Bush's foreign policy, including 'The War on Terror' but the focus is broadened to absorb not only the Bush Doctrine and its repercussions, but also his trade and homeland security policies. The president's domestic leadership in economics and social policy is investigated, as are his dealings as president with the other institutions of the U.S. political system. The result is a comprehensive guide to the Bush presidency and its legacy
Barbara W. [F...] to Sir (2 October 1962)
No full textSigned by Barbara W. [F...]https://egrove.olemiss.edu/mercorr_pro/1499/thumbnail.jp
Influence of confinement on the solvation and rotational dynamics of coumarin 153 in ethanol
No full textThe solvation and rotational dynamics of the chromophore coumarin 153 in ethanol confined in sol-gel glasses with average pore sizes of 50 and 25 Angstrom have been investigated and compared with the dynamics of the respective bulk solution. The measurements show that no adsorption of the chromophore at the inner pore surface occurs. Nevertheless, the amplitude and the dynamics of the Stokes shift as well as the time-resolved anisotropy are drastically changed upon confinement. The solvation dynamics in the confined solutions show nonexponential behavior comparable to that in the bulk. However, the whole solvation process slows down, and the single decay-time constants characterizing it increase with decreasing pore size of the sol-gel glass. However, an increase of the mean rotational diffusion time constant sets in until the pore diameter decreases to less than 50 Angstrom. Two phenomenological models are put forward to rationalize this behavior. The model of a surface solvent layer with changed physical properties such as the viscosity and dielectric constant focuses on the interaction of the liquid with the inner pore surface reducing the molecular mobility and resulting in longer relaxation times. The modified polarization field model takes into account the confinement and predicts a variation of the solvent's reaction field induced by a preferential alignment along the pore walls. Probably both effects are of relevance in the confined solutions investigated. Confinement affects the steady-state spectra and leads to a red shift of the absorption and a blue shift of the fluorescence
Ekstremalne dobowe sumy opadów w Północno-Zachodniej Polsce
No full textThe paper presents an analysis of the extreme precipitation recorded in north-western Poland between
1951 and 1995. The author of the present paper selected a day with a maximal twenty-fourhour
precipitation sum out of each month. The author also selected intervals characterized by specific
twenty-four-hour values: 0.1-9.9 mm, 10.0-19.9 mm, 20.0-29.9 mm, 30.0-49.9 mm, 50.0-99.9
mm and ≥100 mm. The author selected frequencies of their occurrence and a monthly average and
annual maximums’ sum of precipitation. A concept of an extreme precipitation relates to twentyfour-
hour sums 50.0-99.9 mm and ≥100 mm. Moreover the author selected the days with extreme
twenty-four-hour sums ≥100 mm and specified the atmospheric circulation types, distinguished by
B. Osuchowska-Klein (1975).W pracy przybliżono problematykę ekstremalnych opadów w północno-zachodniej Polsce.
Badanie ekstremalnych wartości elementów meteorologicznych to jedno z najważniejszych
zagadnień klimatologii. Występowanie tych elementów może spowodować straty ekonomiczne,
społeczne czy środowiskowe. W analizie uwzględniono dobowe sumy opadów
z 14 stacji, obejmujące lata 1951-1995. Dla obszaru północno-zachodniej Polski za opad
ekstremalny przyjęto sumy dobowe 50,0-99,9 mm i ³100 mm, następnie przeprowadzono
analizę wybranych dni, w których wystąpiły ekstremalne dobowe sumy opadów ≥100 mm
i określono typy cyrkulacji atmosferycznej, wyróżnione przez B. Osuchowską-Klein (1975).
Z przeprowadzonych analiz wynika, że na obszarze północno-zachodniej Polski występują
opady ekstremalne, które przekraczają granice bezpieczeństwa, powodując zagrożenia
społeczno-gospodarcze i środowiskowe. Sumy dobowe 50,0-99,9 mm pojawiały się od maja
do października oraz w lutym, natomiast sumy ≥100 mm występowały tylko w letnich miesiącach. W badanym wieloleciu 1951-1995, przy uwzględnieniu 14 stacji z obszaru północno-
zachodniej Polski ekstremalne opady 50,0-99,9 mm wystąpiły 102 razy (6%), natomiast
opady ≥100 mm – 3 razy: w Łebie (24.07.1988 r.), Koszalinie (18.08.1991 r.) i Toruniu
(15.06.1980 r.). Jednakże, przy uwzględnieniu większej liczby stacji (185 stacji dla okresu
1961-1980) sumy ≥100 mm wystąpiły w 14 innych stacjach. Dla tych dni wykonano mapy
i określono typ cyrkulacji atmosferycznej. Otrzymano, że ekstremalne opady występowały
przy typach cyrkulacji cyklonalnej – Eo (północno-wschodnia i wschodnia), F (południowo-
-wschodnia) i CB (północno-zachodnia) oraz antycyklonalnej – E1 (południowo-wschodnia
i wschodnia) i C2D (zachodnia). W wybranych 8 dniach opady ekstremalne wystąpiły: w czerwcu
(2 razy) – przy typach F i E1; w lipcu (3 razy) – przy typach Eo (2 razy) i C2D i w sierpniu
(3 razy) – przy typach Eo, F i CB. W 6 dniach przyczyną opadów ekstremalnych były typy
cyklonalne.
W ciepłym okresie roku, przy typach cyrkulacji ze składową północną na obszar północno-
zachodniej Polski napływa chłodne powietrze, natomiast przy typach południowo-wschodnich
i wschodnich napływa bardzo ciepłe powietrze, często o dużej wilgotności względnej.
W obu przypadkach adwekcja powietrza może prowadzić do rozwoju konwekcji i w rezultacie
powstają opady o ekstremalnej sumie
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