697 research outputs found
Strongly nonlinear waves in capillary electrophoresis
In capillary electrophoresis, sample ions migrate along a micro-capillary
filled with a background electrolyte under the influence of an applied electric
field. If the sample concentration is sufficiently high, the electrical
conductivity in the sample zone could differ significantly from the
background.Under such conditions, the local migration velocity of sample ions
becomes concentration dependent resulting in a nonlinear wave that exhibits
shock like features. If the nonlinearity is weak, the sample concentration
profile, under certain simplifying assumptions, can be shown to obey Burgers'
equation (S. Ghosal and Z. Chen Bull. Math. Biol. 2010, 72(8), pg. 2047) which
has an exact analytical solution for arbitrary initial condition.In this paper,
we use a numerical method to study the problem in the more general case where
the sample concentration is not small in comparison to the concentration of
background ions. In the case of low concentrations, the numerical results agree
with the weakly nonlinear theory presented earlier, but at high concentrations,
the wave evolves in a way that is qualitatively different.Comment: 7 pages, 5 figures, 1 Appendix, 2 videos (supplementary material
Time dependence of the survival probability of an opinion in a closed community
The time dependence of the survival probability of an opinion in a closed
community has been investigated in accordance with social temperature by using
the Kawasaki-exchange dynamics based on previous study in Ref. [1]. It is shown
that the survival probability of opinion decays with stretched exponential law
consistent with previous static model. However, the crossover regime in the
decay of the survival probability has been observed in this dynamic model
unlike previous model. The decay characteristics of both two regimes obey to
stretched exponential.Comment: Revised version of the paper (9 page, 5 Figures). Submitted to Int.
J. Mod. Phys.
Non-exponential relaxation for anomalous diffusion
We study the relaxation process in normal and anomalous diffusion regimes for
systems described by a generalized Langevin equation (GLE). We demonstrate the
existence of a very general correlation function which describes the relaxation
phenomena. Such function is even; therefore, it cannot be an exponential or a
stretched exponential. However, for a proper choice of the parameters, those
functions can be reproduced within certain intervals with good precision. We
also show the passage from the non-Markovian to the Markovian behaviour in the
normal diffusion regime. For times longer than the relaxation time, the
correlation function for anomalous diffusion becomes a power law for broad-band
noise.Comment: 6 pages, 2 figure
An Experimental and Theoretical Investigation of the Skeletal Frequencies of the Paraffin Hydrocarbons and the Far InfraâRed Spectrum of Carbon Tetrachloride
The far infraâred spectra of the paraffin hydrocarbons and of carbon tetrachloride have been investigated. The following bands were located: propane at 370.6 cmâ1, nâbutane at 215 cmâ1, and carbon tetrachloride at 315 cmâ1, the latter showing isotope structure. The contours of the following near infraâred bands for nâbutane were surveyed, and some fine structure was revealed: 1342.9 cmâ1, 1295.6 cmâ1, 1135.6 cmâ1, 956.5 cmâ1, and 740.0 cmâ1. The assignment of the skeletal frequencies of vibration is made, and a theoretical analysis of the skeletal normal frequencies, assuming a valence potential for the molecules propane through pentane, is given.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/71089/2/JCPSA6-17-4-393-1.pd
Rotational Brownian motion on the sphere surface and rotational relaxation
The spatial components of the autocorrelation function of noninteracting
dipoles are analytically obtained in terms of rotational Brownian motion on the
surface of a unit sphere using multi-level jumping formalism based on Debye's
rotational relaxation model, and the rotational relaxation functions are
evaluated.Comment: RevTex, 4 pages, submitted to Chin. Phys. Let
Twist glass transition in regioregulated poly(3-alkylthiophenes)s
The molecular structure and dynamics of regioregulated poly(3-butylthiophene)
(P3BT), poly(3-hexylthiophene)(P3HT), and poly(3-dodecylthiophene) (P3DDT) were
investigated using Fourier transform infrared absorption (FTIR), solid state
C nuclear magnetic resonance (NMR), and differential scanning
calorimetry (DSC) measurements. In the DSC measurements, the endothermic peak
was obtained around 340 K in P3BT, and assigned to enthalpy relaxation that
originated from the glass transition of the thiophene ring twist in crystalline
phase from results of FTIR, C cross-polarization and magic-angle
spinning (CPMAS) NMR, C spin-lattice relaxation time measurements, and
centerband-only detection of exchange (CODEX) measurements. We defined this
transition as {\it twist-glass transition}, which is analogous to the plastic
crystal - glassy crystal transition.Comment: 9 pages, 10 figures, 2 tables. Phys.Rev.B, in pres
The InfraâRed Absorption Spectrum of Propane
Of the twentyâseven internal degrees of freedom of propane, all nondegenerate, twentyâtwo may appear as fundamental absorption bands. These bands fall into three symmetry classes, designated A1, B1 and B2, and distinguishable by their characteristic contours. Because of overlapping, however, it is impossible in many cases to determine their positions precisely. This is especially true in the regions of the CâH valence and deformation frequencies. Some ten or twelve fundamental bands may be identified with confidence as well as a number of combinations. An A1 band at 870 cmâ1 and a B2 band at 748 cmâ1 have been partially resolved, the line spacing being about 1.47 cmâ1 in agreement with predictions based upon electron diffraction measurements. The fine structure of the B1 bands has not been observed (the predicted spacing is 0.5 cmâ1) but the interval between maxima of the P and R branches is approximately 26 cmâ1 as expected. With 24 cmâatmospheres of gas no bands were observed between 15ÎŒ and 35ÎŒ, although the symmetrical CâC deformation might be expected to produce a band of appreciable intensity within these limits. This frequency has apparently been observed in Raman spectra at 375 cmâ1.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70815/2/JCPSA6-9-7-487-1.pd
A Hybrid model for the origin of photoluminescence from Ge nanocrystals in SiO matrix
In spite of several articles, the origin of visible luminescence from
germanium nanocrystals in SiO matrix is controversial even today. Some
authors attribute the luminescence to quantum confinement of charge carriers in
these nanocrystals. On the other hand, surface or defect states formed during
the growth process, have also been proposed as the source of luminescence in
this system. We have addressed this long standing query by simultaneous
photoluminescence and Raman measurements on germanium nanocrystals embedded in
SiO matrix, grown by two different techniques: (i) low energy
ion-implantation and (ii) atom beam sputtering. Along with our own experimental
observations, we have summarized relevant information available in the
literature and proposed a \emph{Hybrid Model} to explain the visible
photoluminescence from nanocrystalline germanium in SiO matrix.Comment: 23 pages, 8 figure
Anomalous Rotational Relaxation: A Fractional Fokker-Planck Equation Approach
In this study we obtained analytically relaxation function in terms of
rotational correlation functions based on Brownian motion for complex
disordered systems in a stochastic framework. We found out that rotational
relaxation function has a fractional form for complex disordered systems, which
indicates relaxation has non-exponential character obeys to
Kohlrausch-William-Watts law, following the Mittag-Leffler decay.Comment: Revtex4, 9 pages. Paper was revised. References adde
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