4,129 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
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
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
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
The charmonium and bottomonium mass spectroscopy with a simple approximaton of the kinetic term
In this paper we propose a particular description of meson spectroscopy, with
emphasis in heavy bound states like charmonia and bottomonia, after working on
the main aspects of the construction of an effective potential model. We use
the prerogatives from ``soft QCD'' to determine the effective potential terms,
establishing the asymptotic Coulomb term from one gluon exchange approximation.
At the same time, a linear confinement term is introduced in agreement with QCD
and phenomenological prescription. The main aspect of this work is the
simplification in the calculation, consequence of a precise and simplified
description of the kinetic term of the Hamiltonian. With this proposition we
perform the calculations of mass spectroscopy for charmonium and bottomonium
mesons and we discuss the real physical possibilities of developing a
generalized potential model, its possible advantages relative to experimental
parameterization and complexity in numerical calculations
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
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
Monitoring the CMS strip tracker readout system
The CMS Silicon Strip Tracker at the LHC comprises a sensitive area of approximately 200 m2 and 10 million readout channels. Its data acquisition system is based around a custom analogue front-end chip. Both the control and the readout of the front-end electronics are performed by off-detector VME boards in the counting room, which digitise the raw event data and perform zero-suppression and formatting. The data acquisition system uses the CMS online software framework to configure, control and monitor the hardware components and steer the data acquisition. The first data analysis is performed online within the official CMS reconstruction framework, which provides many services, such as distributed analysis, access to geometry and conditions data, and a Data Quality Monitoring tool based on the online physics reconstruction. The data acquisition monitoring of the Strip Tracker uses both the data acquisition and the reconstruction software frameworks in order to provide real-time feedback to shifters on the operational state of the detector, archiving for later analysis and possibly trigger automatic recovery actions in case of errors. Here we review the proposed architecture of the monitoring system and we describe its software components, which are already in place, the various monitoring streams available, and our experiences of operating and monitoring a large-scale system
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
Fine structure splittings of excited P and D states in charmonium
It is shown that the fine structure splittings of the and
excited states in charmonium are as large as those of the state if the
same is used. The predicted mass
GeV appears to be 120 MeV lower that the center of gravity of the
multiplet and lies below the threshold. Our value of
is approximately 80 MeV lower than that from the paper by Godfrey and Isgur
while the differences in the other masses are \la 20 MeV. Relativistic
kinematics plays an important role in our analysis.Comment: 12 page
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