Search results for "Spectral"
showing 10 items of 3116 documents
Nonresonant Spectral Hole Burning in the Slow Dielectric Response of Supercooled Liquids
1996
Large-amplitude, low-frequency electric fields can be used to burn spectral holes in the dielectric response of supercooled propylene carbonate and glycerol. This ability to selectively modify the dielectric response establishes that the non-Debye behavior results from a distribution of relaxation times. Refilling of the spectral hole was consistent with a single recovery time that coincided with the peak in the distribution. Moreover, refilling occurred without significant broadening, which indicates negligible direct exchange between the degrees of freedom that responded to the field. Nonresonant spectral hole burning facilitates direct investigation of the intrinsic response of systems t…
Spectral theory of a Neumann-Poincare-type operator and analysis of cloaking due to anomalous localized resonance
2011
The aim of this paper is to give a mathematical justification of cloaking due to anomalous localized resonance (CALR). We consider the dielectric problem with a source term in a structure with a layer of plasmonic material. Using layer potentials and symmetrization techniques, we give a necessary and sufficient condition on the fixed source term for electromagnetic power dissipation to blow up as the loss parameter of the plasmonic material goes to zero. This condition is written in terms of the Newtonian potential of the source term. In the case of concentric disks, we make the condition even more explicit. Using the condition, we are able to show that for any source supported outside a cr…
Dissymmetric calix[4]arenes: Optical resolution of some conformationally fixed derivatives
1993
Various possibilities to obtain intrinsically chiral calix[4]arenes are discussed. The enantiomers of three 1,3-dietheresters and one monoether compound derived from dissymmetric calix[4]arenes with C4 symmetry were separated by HPLC using chiral stationary phases and characterized by their CD spectra. © 1993 Wiley-Liss, Inc.
Diepoxyrollin and Diepomuricanin B: Two New Diepoxyacetogenins from Rollinia membranacea Seeds
1997
Diepoxyrollin (1) and diepomuricanin B (2), two new Annonaceous acetogenins were isolated from the cytotoxic MeOH extract of the seeds of Colombian Rollinia membranacea. Five others known acetogenins were also isolated, dieporeticanin 1, dieporeticanin 2, diepomuricanin A, rollinone, and sylvaticin. Their structures were elucidated on the basis of spectral data. Compounds 1 and 2 belong to the rare type of diepoxyacetogenins, which are probably precursors of the mono-tetrahydrofuran acetogenins.
Active locking and entanglement in type II optical parametric oscillators
2018
Type II optical parametric oscillators are amongst the highest-quality sources of quantum-correlated light. In particular, when pumped above threshold, such devices generate a pair of bright orthogonally-polarized beams with strong continuous-variable entanglement. However, these sources are of limited practical use, because the entangled beams emerge with different frequencies and a diffusing phase-difference. It has been proven that the use of an internal wave-plate coupling the modes with orthogonal polarization is capable of locking the frequencies of the emerging beams to half the pump frequency, as well as reducing the phase-difference diffusion, at the expense of reducing the entangl…
Relaxation of Polarization at the Broad Phase Transition in Modified PMN Ferroelectric Ceramics
2013
The reported study is focused on effects of relaxation of polarization within the range of the broad phase transition at strong sinusoidal measuring fields in modified lead magnesium niobate ceramics. The obtained results reveal an essential thermal broadening of the ϵ′(E) spectra specific to relaxor ferroelectrics. Temperature dependence of ϵ′ eff (T) at medium fields shows two broad maximums – at Tm and at 40°C. On the basis of analysis of the experimental data, admixture of lithium is suggested to promote formation of domains in lead magnesium niobate ceramics.
Pressure-induced phase transition in hydrothermally grown ZnO nanoflowers investigated by Raman and photoluminescence spectroscopy.
2015
This paper reports the pressure-dependent photoluminescence and Raman spectral investigation of hydrothermally synthesized ZnO nanoflowers at room temperature. Intrinsic near-band-edge UV emission from ZnO nanoflowers is monotonously blue-shifted under pressures up to 13.8 GPa with a pressure coefficient of 26 meV GPa(-1), and this pressure value is nearly 5 GPa above the transition pressure from the wurtzite to the rock salt phase for bulk ZnO. The Raman band corresponds to the wurtzite phase, the [Formula: see text] and [Formula: see text] modes were observed up to about 11 GPa from the spectra. The apparent discrepancy in the transition pressures as determined from photoluminescence and …
Spin- and phase transition in the spin crossover complex [Fe(ptz)6](BF4)2 studied by nuclear inelastic scattering of synchrotron radiation and by DFT…
2006
Abstract Nuclear inelastic scattering (NIS) spectra of [Fe(ptz) 6 ](BF 4 ) 2 (ptz = 1- n -propyl-tetrazole) have been measured for five phases differing in spin state and crystallographic structure. Different spectral patterns have been found for the low-spin and high-spin phases and are described in terms of normal coordinate analysis of the complex molecule. For both low-spin and high-spin phases the conversion from ordered to disordered phase results in splitting of the observed NIS bands. Packing becomes visible in the NIS spectra via coupling of the Fe–N stretching vibrations with those of the terminal n -propyl groups. The DFT-based normal coordinate analysis also reveals the characte…
Time-resolved coherent anti-Stokes Raman-scattering measurements of I2 in solid Kr: vibrational dephasing on the ground electronic state at 2.6-32 K.
2005
Time-resolved coherent anti-Stokes Raman-scattering (CARS) measurements are carried out for iodine (I2) in solid krypton matrices. The dependence of vibrational dephasing time on temperature and vibrational quantum number v is studied. The v dependence is approximately quadratic, while the temperature dependence of both vibrational dephasing and spectral shift, although weak, fits the exponential form characteristic of dephasing by pseudolocal phonons. The analysis of the data indicates that the frequency of the pseudolocal phonons is approximately 30 cm(-1). The longest dephasing times are observed for v = 2 being approximately 300 ps and limited by inhomogeneous broadening. An increase in…
A combined theoretical and experimental determination of the electronic spectrum of acetone
1996
A combined ab initio and experimental investigation has been performed of the main features of the electronic spectrum of acetone. Vertical transition energies have been calculated from the ground to the ny→π∗, π→π∗, σ→π∗, and the n=3 Rydberg states. In addition, the 1A1 energy surfaces have been studied as functions of the CO bond length. The 1A1 3p and 3d states were found to be heavily perturbed by the π→π∗ state. Resonant multiphoton ionization and polarization‐selected photoacoustic spectra of acetone have been measured and observed transitions were assigned on internal criteria. The calculated vertical transition energies to the ny→π∗ and all Rydberg states were found to be in agreeme…