1,485 research outputs found
Johari-Goldstein relaxation far below Tg: Experimental evidence for the Gardner transition in structural glasses?
Experimental evidence for the Gardner transition, theoretically predicted to
arise deep in the glassy state of matter, is scarce. At this transition, the
energy landscape sensed by the particles forming the glass is expected to
become more complex. In the present work, we report the dielectric response of
two typical glass formers with well-pronounced Johari-Goldstein beta relaxation
following this response down to unprecedented low temperatures, far below the
glass transition. As the Johari-Goldstein process is believed to arise from the
local structure of the energy landscape, its investigation seems an ideal tool
to seek evidence for the Gardner transition. Indeed, we find an unusual
broadening of the beta relaxation below TG ~ 110 K for sorbitol and TG ~ 100 K
for xylitol, in excess of the expected broadening arising from a distribution
of energy barriers. Thus, these results provide hints at the presence of the
Gardner transition in canonical structural glass formers.Comment: 6 pages, 3 figures + 2 pages, 3 figures in Supplemental Materia
Meiotic recombination proteins localize to linear elements in Schizosaccharomyces pombe
Peer reviewedPostprin
- and - Relaxation Dynamics of a fragile plastic crystal
We present a thorough dielectric investigation of the relaxation dynamics of
plastic crystalline Freon112, which exhibits freezing of the orientational
degrees of freedom into a glassy crystal below 90 K. Among other plastic
crystals, Freon112 stands out by being relatively fragile within Angell's
classification scheme and by showing an unusually strong -relaxation.
Comparing the results to those on Freon112a, having only a single molecular
conformation, points to the importance of the presence of two molecular
conformations in Freon112 for the explanation of its unusual properties.Comment: 17 pages, 6 figure
The influence of dust properties on the mass loss in pulsating AGB stars
We are currently studying carbon based dust types of relevance for
carbon-rich AGB stars, to obtain a better understanding of the influence of the
optical and chemical properties of the grains on the mass loss of the star. An
investigation of the complex interplay between hydrodynamics,radiative transfer
and chemistry has to be based on a better knowledge of the micro-physics of the
relevant dust species.Comment: 4 pages, 2 figures. Proceedings for IAU Colloquium 185 "Radial and
Nonradial Pulsations as Probes of Stellar Physics
Negative Refraction in Ferromagnet/Superconductor Superlattices
Negative refraction, which reverses many fundamental aspects of classical
optics, can be obtained in systems with negative magnetic permeability and
negative dielectric permittivity. This Letter documents an experimental
realization of negative refraction at millimeter waves, finite magnetic fields
and cryogenic temperatures utilizing a multilayer stack of ferromagnetic and
superconducting thin films. In the present case the superconducting
YBa_2Cu_3O_7 layers provide negative permittivity while negative permeability
is achieved via ferromagnetic (La:Sr)MnO_3 layers for frequencies and magnetic
fields close to the ferromagnetic resonance. In these superlattices the
refractive index can be switched between positive and negative regions using
external magnetic field as tuning parameter.Comment: 4 Pages, 3 Figures, Phys. Rev. Lett., accepte
Ions in glass forming glycerol: Close correlation of alpha and fast beta relaxation
We provide broadband dielectric loss spectra of glass-forming glycerol with
varying additions of LiCl. The measurements covering frequencies up to 10 THz
extend well into the region of the fast beta process, commonly ascribed to
caged molecule dynamics. Aside of the known variation of the structural alpha
relaxation time and a modification of the excess wing with ion content, we also
find a clear influence on the shallow loss minimum arising from the fast beta
relaxation. Within the framework of mode-coupling theory, the detected
significant broadening of this minimum is in reasonable accord with the found
variation of the alpha-relaxation dynamics. A correlation between
alpha-relaxation rate and minimum position holds for all ion concentrations and
temperatures, even below the critical temperature defined by mode-coupling
theory.Comment: 5 pages, 5 figure
Low temperature dielectric relaxation study of aqueous solutions of diethylsulfoxide
In the present work, dielectric spectra of mixtures of diethylsulfoxide
(DESO) and water are presented, covering a concentration range of 0.2 - 0.3
molar fraction of DESO. The measurements were performed at frequencies between
1 Hz and 10 MHz and for temperatures between 150 and 300 K. It is shown that
DESO/water mixtures have strong glass-forming abilities. The permittivity
spectra in these mixtures reveal a single relaxation process. It can be
described by the Havriliak-Negami relaxation function and its relaxation times
follow the Vogel-Fulcher-Tammann law, thus showing the typical signatures of
glassy dynamics. The concentration dependence of the relaxation parameters,
like fragility, broadening, and glass temperature, are discussed in detail.Comment: 20 pages, 5 figure
Magnetic susceptibility of the frustrated spinels ZnCr2O4, MgCr2O4 and CdCr2O4
We analyzed the magnetic susceptibilities of several Cr spinels using two
recent models for the geometrically frustrated pyrochlore lattice, the Quantum
Tetrahedral Mean Field model and a Generalized Constant Coupling model. Both
models can describe the experimental data for ACr2 O4 (with A = Zn, Mg, and Cd)
satisfactorily, with the former yielding a somewhat better agreement with
experiment for A = Zn, Mg. The obtained exchange constants for nearest and
next-nearest neighbors are discussed.Comment: 4 pages, 1 figure, 1 table, conferenc
Dust grain properties in atmospheres of AGB stars
We present self-consistent dynamical models for dust driven winds of
carbon-rich AGB stars. The models are based on the coupled system of
frequency-dependent radiation hydrodynamics and time-dependent dust formation.
We investigate in detail how the wind properties of the models are influenced
by the micro-physical properties of the dust grains that enter as parameters.
The models are now at a level where it is necessary to be quantitatively
consistent when choosing the dust properties that enters as input into the
models. At our current level of sophistication the choice of dust parameters is
significant for the derived outflow velocity, the degree of condensation and
the estimated mass loss rates of the models. In the transition between models
with and without mass-loss the choice ofmicro-physical parameters turns out to
be very significant for whether a particular set of stellar parameters will
give rise to a dust-driven mass loss or not.Comment: 10 pages, 3 figures. To appear in: Modelling of Stellar Atmospheres,
N.E. Piskunov, W.W. Weiss, D.F. Gray (eds.), IAU Symposium Vol. xxx.
Proceedings for the IAU Symposium 210, Uppsala, June 200
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