4,962 research outputs found
Glass transition and alpha-relaxation dynamics of thin films of labeled polystyrene
The glass transition temperature and relaxation dynamics of the segmental
motions of thin films of polystyrene labeled with a dye,
4-[N-ethyl-N-(hydroxyethyl)]amino-4-nitraozobenzene (Disperse Red 1, DR1) are
investigated using dielectric measurements. The dielectric relaxation strength
of the DR1-labeled polystyrene is approximately 65 times larger than that of
the unlabeled polystyrene above the glass transition, while there is almost no
difference between them below the glass transition. The glass transition
temperature of the DR1-labeled polystyrene can be determined as a crossover
temperature at which the temperature coefficient of the electric capacitance
changes from the value of the glassy state to that of the liquid state. The
glass transition temperature of the DR1-labeled polystyrene decreases with
decreasing film thickness in a reasonably similar manner to that of the
unlabeled polystyrene thin films. The dielectric relaxation spectrum of the
DR1-labeled polystyrene is also investigated. As thickness decreases, the
-relaxation time becomes smaller and the distribution of the
-relaxation times becomes broader. These results show that thin films
of DR1-labeled polystyrene are a suitable system for investigating confinement
effects of the glass transition dynamics using dielectric relaxation
spectroscopy.Comment: 10 pages, 11 figures, 2 Table
The Stokes-Einstein Relation in Supercooled Aqueous Solutions of Glycerol
The diffusion of glycerol molecules decreases with decreasing temperature as
its viscosity increases in a manner simply described by the Stokes-Einstein(SE)
relation. Approaching the glass transition, this relation breaks down as it
does with a number of other pure liquid glass formers. We have measured the
diffusion coefficient for binary mixtures of glycerol and water and find that
the Stokes-Einstein relation is restored with increasing water concentration.
Our comparison with theory suggests that addition of water postpones the
formation of frustration domainsComment: 4 Pages and 3 Figure
Preliminary Evaluation of Lectins as Fluorescent Probes of Seed Structure and Composition
Several commercially available fluoresceinisothiocyanate and rhodamine isothiocyanateconjugated plant lectins have been applied to cereal and oilseed tissues to permit identification and localization of specific structures and carbohydrates by fluorescence microscopy . Ulex europeaus Agglutinin I (UEAl) and Ricinis communis Agglutinin I (RCA I) showed specificity for the amyloids in rapeseed cotyledonary cell walls . Wheat Germ Agglutinin (WGA) bound to rapeseed coat mucilage, as well as fungal hyphae in infected wheat . Lens culinaris Agglutinin (LCA) bound only to starch in cereal sections, and at higher magnifications of isolated starch granules , the annular structure was clearly visible
Thermal Time Scales in a Color Glass Condensate
In a model of relativistic heavy ion collisions wherein the unconfined
quark-gluon plasma is condensed into glass, we derive the Vogel-Fulcher-Tammann
cooling law. This law is well known to hold true in condensed matter glasses.
The high energy plasma is initially created in a very hot negative temperature
state and cools down to the Hagedorn glass temperature at an ever decreasing
rate. The cooling rate is largely determined by the QCD string tension derived
from hadronic Regge trajectories. The ultimately slow relaxation time is a
defining characteristic of a color glass condensate.Comment: 5 pages, ReVTeX format, nofigure
Spacings of Quarkonium Levels with the Same Principal Quantum Number
The spacings between bound-state levels of the Schr\"odinger equation with
the same principal quantum number but orbital angular momenta
differing by unity are found to be nearly equal for a wide range of power
potentials , with . Semiclassical approximations are in accord with this behavior. The
result is applied to estimates of masses for quarkonium levels which have not
yet been observed, including the 2P states and the 1D
states.Comment: 20 pages, latex, 3 uuencoded figures submitted separately (process
using psfig.sty
Relation between positional specific heat and static relaxation length: Application to supercooled liquids
A general identification of the {\em positional specific heat} as the
thermodynamic response function associated with the {\em static relaxation
length} is proposed, and a phenomenological description for the thermal
dependence of the static relaxation length in supercooled liquids is presented.
Accordingly, through a phenomenological determination of positional specific
heat of supercooled liquids, we arrive at the thermal variation of the static
relaxation length , which is found to vary in accordance with in the quasi-equilibrium supercooled temperature regime, where
is the Vogel-Fulcher temperature and exponent equals unity. This
result to a certain degree agrees with that obtained from mean field theory of
random-first-order transition, which suggests a power law temperature variation
for with an apparent divergence at . However, the phenomenological
exponent , is higher than the corresponding mean field estimate
(becoming exact in infinite dimensions), and in perfect agreement with the
relaxation length exponent as obtained from the numerical simulations of the
same models of structural glass in three spatial dimensions.Comment: Revised version, 7 pages, no figures, submitted to IOP Publishin
Entropic Origin of the Growth of Relaxation Times in Simple Glassy Liquids
Transitions between ``glassy'' local minima of a model free-energy functional
for a dense hard-sphere system are studied numerically using a
``microcanonical'' Monte Carlo method that enables us to obtain the transition
probability as a function of the free energy and the Monte Carlo ``time''. The
growth of the height of the effective free energy barrier with density is found
to be consistent with a Vogel-Fulcher law. The dependence of the transition
probability on time indicates that this growth is primarily due to entropic
effects arising from the difficulty of finding low-free-energy saddle points
connecting glassy minima.Comment: Four pages, plus three postscript figure
Inherent Structures in models for fragile and strong glass
An analysis of the dynamics is performed, of exactly solvable models for
fragile and strong glasses, exploiting the partitioning of the free energy
landscape in inherent structures. The results are compared with the exact
solution of the dynamics, by employing the formulation of an effective
temperature used in literature. Also a new formulation is introduced, based
upon general statistical considerations, that performs better. Though the
considered models are conceptually simple there is no limit in which the
inherent structure approach is exact.Comment: 19 pages, 4 figure
Glassiness in a model without energy barriers
We propose a microscopic model without energy barriers in order to explain
some generic features observed in structural glasses. The statics can be
exactly solved while the dynamics has been clarified using Monte Carlo
calculations. Although the model has no thermodynamic transition it captures
some of the essential features of real glasses, i.e., extremely slow
relaxation, time dependent hysteresis effects, anomalous increase of the
relaxation time and aging. This suggests that the effect of entropy barriers
can be an important ingredient to account for the behavior observed in real
glasses.Comment: 11 Pages + 3 Figures, Revtex, uufiles have been replaced since figure
2 was corrupted in the previous submissio
Free Energy Landscape Of Simple Liquids Near The Glass Transition
Properties of the free energy landscape in phase space of a dense hard sphere
system characterized by a discretized free energy functional of the
Ramakrishnan-Yussouff form are investigated numerically. A considerable number
of glassy local minima of the free energy are located and the distribution of
an appropriately defined ``overlap'' between minima is calculated. The process
of transition from the basin of attraction of a minimum to that of another one
is studied using a new ``microcanonical'' Monte Carlo procedure, leading to a
determination of the effective height of free energy barriers that separate
different glassy minima. The general appearance of the free energy landscape
resembles that of a putting green: deep minima separated by a fairly flat
structure. The growth of the effective free-energy barriers with increasing
density is consistent with the Vogel-Fulcher law, and this growth is primarily
driven by an entropic mechanism.Comment: 10 pages, 6 postscript figures, uses iopart.cls and iopart10.clo
(included). Invited talk at the ICTP Trieste Conference on "Unifying Concepts
in Glass Physics", September 1999. To be published in J. Phys. Cond. Ma
- …