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Spectral Width (spectral + width)
Selected AbstractsUV Spectra and Excitation Delocalization in DNA: Influence of the Spectral WidthCHEMPHYSCHEM, Issue 7 2005Emanuela Emanuele Abstract The singlet excited states of the model DNA duplex (dA)10.(dT)10 are studied. Calculations are performed in the exciton theory framework. Molecular dynamics calculations provide the duplex geometry. The dipolar coupling is determined using atomic transition charges. The monomer transition energies are simulated by Gaussian functions resembling the absorption bands of nucleosides in aqueous solutions. Most of the excited states are found to be delocalized over at least two bases and result from the mixing of different monomer states. Their properties are only weakly affected by conformational changes of the double helix. On average, the highest oscillator strength is carried by the upper eigenstates. The duplex absorption spectra are shifted a few nanometers to higher energies with respect to the spectra of noninteracting monomers. The states with larger spatial extent are located close to the maximum of the absorption spectrum. [source] Convective mixing in a tropopause foldTHE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 599 2004H. J. Reid Abstract We present a case study of the passage of a tropopause fold over the UK behind a cold front, with emphasis on the mixing caused by convection extending into the fold. The event took place on 15,16 January 1999, and was the subject of intensive observations using the Met Office C130 aircraft and the mesosphere,stratosphere,troposphere (MST) radar at Aberystwyth. Here we concentrate on radar and satellite observations during the afternoon of 16 January, when the surface cold front had passed over the UK. A tongue of moist air moved north-eastwards over Wales at 700 hPa at this time, which, because of the very dry air in the fold above, resulted in potential instability. The resulting convection was clearly observed in NOAA satellite images. The MST radar depicted the passage of the cold front and tropopause fold as a layer of high-echo power and vertical wind shear ascending with time. Spectral widths showed the fold to be free of turbulence until 1200 UTC on 16 January, when convection was observed reaching into the frontal zone and generating turbulence. Eddy dissipation and diffusivity rates of 8.6 mW kg,1 and 8.5 m2s,1, respectively, were derived for this event. To place these figures in context, they are compared with corresponding rates derived for sixteen other passages of tropopause folds over the radar, each resulting from shear rather than convective instability. The convective event is found to be comparable to the strongest shear events, and to correspond to moderate turbulence as experienced by an aircraft. This process is of potential importance for atmospheric chemistry because it mixes boundary layer air directly with stratospheric air over a timescale of 1,2 hours. Copyright © 2004 Royal Meteorological Society [source] Retrieval of spectral and dynamic properties from two-dimensional infrared pump-probe experimentsJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 9 2008Riccardo Chelli Abstract We have developed a fitting algorithm able to extract spectral and dynamic properties of a three level oscillator from a two-dimensional infrared spectrum (2D-IR) detected in time resolved nonlinear experiments. Such properties go from the frequencies of the ground-to-first and first-to-second vibrational transitions (and hence anharmonicity) to the frequency-fluctuation correlation function. This last is represented through a general expression that allows one to approach the various strategies of modeling proposed in the literature. The model is based on the Kubo picture of stochastic fluctuations of the transition frequency as a result of perturbations by a fluctuating surrounding. To account for the line-shape broadening due to pump pulse spectral width in double-resonance measurements, we supply the fitting algorithm with the option to perform the convolution of the spectral signal with a Lorentzian function in the pump-frequency dimension. The algorithm is tested here on 2D-IR pump-probe spectra of a Gly-Ala dipeptide recorded at various pump-probe delay times. Speedup benchmarks have been performed on a small Beowulf cluster. The program is written in FORTRAN language for both serial and parallel architectures and is available free of charge to the interested reader. © 2008 Wiley Periodicals, Inc. J Comput Chem, 2008 [source] Generation of 1.2-nJ pulses with 19.4-nm rectangle-shaped spectrum from erbium fiber laser without using dispersion compensationMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 3 2005Deshuang Zhao Abstract By combining a lumped amplifier and a coupler with high output ratio, we present a passively mode-locked Er3+ -doped fiber laser with ring cavity, which directly produces 1.2-nJ pulses with a rectangle-shaped spectrum of 19.4 nm. To our knowledge, they are the highest pulse-energy and broadest spectral width obtained directly from Er3+ -doped fiber lasers without using the dispersion-compensation technique. © 2005 Wiley Periodicals, Inc. Microwave Opt Technol Lett 47: 254,256, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21139 [source] A novel approach for the growth of InGaN quantum dotsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 11 2006T. Yamaguchi Abstract A novel two-step growth method for creating InGaN quantum dots (QDs) was developed by using a combination of an InxGa1,xN nucleation layer with a platelet structure and an InyGa1,yN formation layer with an indium content lower than that of the InxGa1,xN nucleation layer. The realized QDs were investigated by micro-photoluminescence measurements. We observed sharp emission lines at 4 K with a spectral width down to the spectral resolution limit of the experimental setup of 0.17 meV. This growth concept is discussed in comparison with conventional growth methods. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Do transient gravity waves in a shear flow break?THE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 634 2008M. Pulido Abstract The propagation of transient gravity waves in a shear flow towards their critical levels is examined using a ray tracing approximation and a higher-degree (quasi-optic) approximation. Because of its transient forcing, the amplitude of transient waves decays to zero in the neighbourhood of the critical region so that it is not clear whether transient gravity waves will reach the convective instability threshold or not. The analysis shows that the horizontal perturbation decays asymptotically as the inverse of the square root of time, while the vertical wavenumber depends linearly on time, thus transient gravity waves attain convective instability for long times. The theoretical results are compared with numerical simulations. The ray path approximation is not able to reproduce the maximum amplitude, but the quasi-optic approximation gives a reasonable agreement at short and long times. There are three breaking regimes for transient gravity waves. For wave packets with a narrow frequency spectrum (quasi-steady waves) and large enough initial wave amplitude, the wave breaking is similar to the abrupt monochromatic wave overturning. On the other hand, highly transient wave packets will dissipate near the critical region for very long times with small wave amplitudes and high vertical wavenumber. The third regime is a transition between the two extremes; in this case both wave amplitude and vertical wavenumber are important to produce the convective threshold. The dependencies of the convective instability height (a quantity that may be useful for gravity wave parametrizations) on the Richardson number and the frequency spectral width are obtained. Copyright © 2008 Royal Meteorological Society [source] Size-Tunable Highly Luminescent SiO2 Particles Impregnated with Number-Adjusted CdTe NanocrystalsCHEMPHYSCHEM, Issue 4 2010Ping Yang Dr. Abstract Highly luminescent SiO2 particles impregnated with CdTe nanocrystals (NCs) are prepared by a sol,gel procedure. Partial ligand exchange from thioglycolic acid to 3-mercaptopropyltrimethoxysilane (MPS) on the NCs enables retention of the initial photoluminescence (PL) efficiency of the NCs in water, while the simultaneous addition of a poor solvent (ethanol) results in regulated assembly of the NCs through condensation of hydrolyzed MPS. The SiO2 particles thus prepared have, for example, a diameter of 16 nm and contain three NCs each. The PL efficiency of these particles is 40,%, while the initial efficiency is 46,% in a colloidal solution. The redshift and narrowed spectral width in PL observed after impregnation indicate that the concentration of NCs in these nearly reaches the ultimate value (on the order of 1021 particles per liter). The porosity of these particles is investigated by means of N2 adsorption,desorption isotherms. Due to the SiO2 shell, these particles have higher stability in phosphate-buffered saline buffer solution than the initial NCs. Their potential use for labeling in bio-applications is investigated by conjugating biotinylated immunoglobulin G to them by using streptavidin maleimide as linker. Successful conjugation is confirmed by electrophoresis in agarose gel. This preparation method is an important step towards fabricating intensely emitting biocompatible SiO2 particles impregnated with semiconductor NCs. [source] HSQC pulse sequences for 19FMAGNETIC RESONANCE IN CHEMISTRY, Issue 4 2008Bruce Adams Abstract Heteronuclear single quantum coherence (HSQC) sequences using adiabatic (or composite) 180° pulses, suitable for applications requiring wide spectral widths in F2, are described. The sequences can be used with or without multiplicity editing. One variant will work even in the presence of homonuclear couplings that are equal to the heteronuclear 1-bond coupling. Copyright © 2008 John Wiley & Sons, Ltd. [source] High resolution in heteronuclear 1H,13C NMR experiments by optimizing spectral aliasing with one-dimensional carbon dataMAGNETIC RESONANCE IN CHEMISTRY, Issue 1 2003Damien Jeannerat Abstract In the chemistry literature it is common to provide NMR data on both proton and carbon spectra based on one-dimensional experiments, but often only proton spectra are assigned. The absence of a complete attribution of the carbons is in good part due to the difficulty in reaching the necessary resolution in the carbon dimension of two-dimensional experiments. It has already been shown that high-resolution heteronuclear spectra can be acquired within nearly the same acquisition time using a violation of the Nyquist condition. For a spectral width reduction by a given factor k, the resolution increases by the same factor as long as it is not limited by relaxation. The price to pay for such an improvement is a k -fold ambiguity in the chemical shift of the signal along the folded or aliased dimension. The computer algorithm presented in this paper takes advantage of the peak list stemming from one-dimensional spectra in order to calculate spectral widths for which the ambiguities in the aliased dimension of heteronuclear experiments are eliminated or at least minimized. The resolution improvement factor is only limited by the natural lineshape and reaches a typical value higher than 100. The program may be set to run automatically on spectrometers equipped with automatic sample changers. Applications to short-range HSQC experiments and long-range HMBC spectra of steroids, carbohydrates, a peptide and a mixture of isomers are shown as examples. Copyright © 2002 John Wiley & Sons, Ltd. [source] | ||||||||||