Search results for "DIPOLE"
showing 10 items of 982 documents
On the Theory of Domain Structure of Disordered Ferroelectrics
2009
We present a comprehensive analysis of domain structure formation in ferroelectric phase of incipient ferroelectrics with off-center dipole impurities like KTaO 3 :Li, Nb,Na. Our analysis is carried out on the base of effective free energy of disordered ferroelectrics, derived by us earlier. This free energy permits to apply the standard approach to domain structure calculation. Using coupled system of Maxwell equations with those obtained by minimization of above free energy, we calculate the physical characteristics of domain structure as functions of impurity dipoles concentration n. Our theory can be easily generalized for arbitrary temperature and crystal shape including thin films.
Entrapment of charged, nonwetting colloids near oil-water interfaces.
2007
Charged, nonwetting colloids with a contact angle $\ensuremath{\theta}=180\ifmmode^\circ\else\textdegree\fi{}$ are attracted to an oil-water interface due to image charge forces. Near the interface, the attractive image charge forces are balanced by repulsive van der Waals forces, and thus the colloids are trapped at a finite distance from the interface. Electrostatic and van der Waals pressure lead to a deformation of the interface in the equilibrium state. For parameters relevant to experiment, however, the effects of the deformed interface are negligible and thus the mutual interactions of such interfacially trapped colloids should be well characterized by electrostatic dipole repulsions.
Specific orientation of dipole moments in azocrown cetocyanine dyes determined by electrooptical absorption measurements (EOAM)
2019
Abstract From electrooptical absorption measurements (EOAM) follows that the dipole moments of azacrown ketocyanine dyes 2,5-di{(E)-1-[4-(4,7,10,13-tetraoxa-1-azacyclopentadecyl)phenyl]methylidene}-1-cyclopentanone (Compound 1) and (E)-1-(2-hydroxy-4methoxyphenyl)-3-[4-(4,7,10,13-tetraoxa-1-azacyclopentadecyl)phenyl]-2-propen-1-one (Compound 2) in the equilibrium ground state μg and the change of dipole moments upon transition to the excited Franck–Condon state Δaμ are large. This alteration causes a significant long-wavelength shift of the absorption and emission spectra, as well as large fluorescence Stokes shift with increasing polarity of the solvent. From the DFT calculations follows t…
Measurement of the transition dipole moment of silane 28SiH4 by diode laser spectroscopy
1992
Abstract A tunable diode laser IR spectrometer which is being used in various molecular spectroscopy experiments is described. Absorption spectra observed in the ( ν 1 , ν 3 ) dyad of silane 28 SiH 4 yield estimates of two parameters of the dipole moment operator responsible for absorbance in this region.
Negative capacitance caused by electron injection through interfacial states in organic light-emitting diodes
2006
The negative capacitance frequently observed at low frequencies in organic light-emitting diodes (LEDs) is explained as a signature of sequential electron injection at the organic/metal interface first to states in the bandgap in the dipole layer and then to bulk states. The negative capacitance occurs when the interfacial states depart from equilibrium with the metal Fermi level due to an increasing rate of hopping to the bulk states. A simple kinetic model compares well with the experimental results and provides a new tool to investigate interfacial properties for improving the performance of organic LEDs.
Radiation Defects in LiBaF3 Perovskites
2000
We investigated the electron paramagnetic resonance (EPR), recombination afterglow, thermostimulated luminescence (TSL) and absorption of LiBaF3 perovskites crystals X-irradiated at 80 K The self-trapped hole centre VK(F2-) oriented along the [110] axis and electron F type (FA) centres are identified. X-irradiation at temperatures below 200 K results in creation of a long-term temperature-independent afterglow-tunnelling luminescence (TL), with main emission bands at 300, 370 nm and 430 nm. The short wavelength TL bands are associated with the tunnelling recombination of the F type centre with the VK centre. The thermal stability of VK centre is estimated to be about 130 K.
A multi-sphere particle numerical model for non-invasive investigations of neuronal human brain activity
2013
In this paper, a multi-sphere particle method is built- up in order to estimate the solution of the Poisson's equation with Neumann boundary conditions describing the neuronal human brain activity. The partial difierential equations governing the relationships between neural current sources and the data produced by neuroimaging technique, are able to compute the scalp potential and magnetic fleld distributions generated by the neural activity. A numerical approach is proposed with current dipoles as current sources and going on in the computation by avoiding the mesh construction. The current dipoles are into an homogeneous spherical domain modeling the head and the computational approach i…
Orientational dynamics of fluctuating dipolar particles assembled in a mesoscopic colloidal ribbon
2017
We combine experiments and theory to investigate the dynamics and orientational fluctuations of ferromagnetic microellipsoids that form a ribbonlike structure due to attractive dipolar forces. When assembled in the ribbon, the ellipsoids display orientational thermal fluctuations with an amplitude that can be controlled via application of an in-plane magnetic field. We use video microscopy to investigate the orientational dynamics in real time and space. Theoretical arguments are used to derive an analytical expression that describes how the distribution of the different angular configurations depends on the strength of the applied field. The experimental data are in good agreement with the…
Theory of Near‐field Optical Imaging with a Single Molecule as Light Source
2002
Scanning near-field optical microscopes (SNOM) illuminate a sample in the very near-field using a nanometer sized tip. Ideally, the light source should be point-like and many efforts have been made to optimize tip efficiency (see, for example, the article of Heimel et al in this issue). Very recently, Sandoghdar et al have realized a molecular probe tip in which a terrylene molecule inserted in a paraterphenyl microcrystal is attached at the extremity of the probe tip [1]. The excited molecule behaves as a point-like light source which is raster scanned over an aluminium patterned structure. We propose here an analysis of this experiment based on the field-susceptibility formalism (also cal…
Conformational properties of N-acetyl-L-alanine N',N'-dimethylamide
2004
Ab initio/DFT analysis of the conformational properties of free Ac-Ala-NMe(2) (N-acetyl-L-alanine-N',N'-dimethylamide) in terms of the N-H.O, N-H.N, C-H.O hydrogen bonds and C(delta+) = O(delta-) dipole attractions was performed. The Ala residue combined with the C-terminal tertiary amide prefers an extended conformation and that characteristic of the (i + 1)th position of the betaVIb turn. These can be easily remodelled into a structure compatible with the (i + 1)th position of the betaII/betaVIa turn. The residue has also the potential to adopt the conformation accommodated at both central positions of the betaIII/betaIII' turn or the (i + 1)th position of the betaI/beta'I turn.