1,336 research outputs found
Topological derivation of shape exponents for stretched exponential relaxation
In homogeneous glasses, values of the important dimensionless
stretched-exponential shape parameter beta are shown to be determined by magic
(not adjusted) simple fractions derived from fractal configuration spaces of
effective dimension d* by applying different topological axioms (rules) in the
presence (absence) of a forcing electric field. The rules are based on a new
central principle for defining glassy states: equal a priori distributions of
fractal residual configurational entropy. Our approach and its beta estimates
are fully supported by the results of relaxation measurements involving many
different glassy materials and probe methods. The present unique topological
predictions for beta typically agree with observed values to ~ 1% and indicate
that for field-forced conditions beta should be constant for appreciable ranges
of such exogenous variables as temperature and ionic concentration, as indeed
observed using appropriate data analysis. The present approach can also be
inverted and used to test sample homogeneity and quality.Comment: Original 13 pages lengthened to 21 pages (longer introduction, added
references and discussion of new experimental data published since original
submission
Determination of solid mass fraction in partially frozen hydrocarbon fuels
Filtration procedures alone are insufficient to determine the amounts of crystalline solid in a partially frozen hydrocarbon distillate fraction. This is due to the nature of the solidification process by which a large amount of liquid becomes entrapped within an interconnected crystalline structure. A technique has been developed to supplement filtration methods with an independent determination of the amount of liquid in the precipitate thereby revealing the actual value of mass percent crystalline solid, %S. A non-crystallizing dye is injected into the fuel and used as a tracer during the filtration. The relative concentrations of the dye in the filtrate and precipitate fractions is subsequently detected by a spectrophotometric comparison. The filtration apparatus was assembled so that the temperature of the sample is recorded immediately above the filter. Also, a second method of calculation has been established which allows significant reduction in test time while retaining acceptable accuracy of results. Data have been obtained for eight different kerosene range hydrocarbon fuels
Temperature in nonequilibrium systems with conserved energy
We study a class of nonequilibrium lattice models which describe local
redistributions of a globally conserved energy. A particular subclass can be
solved analytically, allowing to define a temperature T_{th} along the same
lines as in the equilibrium microcanonical ensemble. The
fluctuation-dissipation relation is explicitely found to be linear, but its
slope differs from the inverse temperature T_{th}^{-1}. A numerical
renormalization group procedure suggests that, at a coarse-grained level, all
models behave similarly, leading to a two-parameter description of their
macroscopic properties.Comment: 4 pages, 1 figure, final versio
Heat capacity at the glass transition
A fundamental problem of glass transition is to explain the jump of heat
capacity at the glass transition temperature without asserting the
existence of a distinct solid glass phase. This problem is also common to other
disordered systems, including spin glasses. We propose that if is defined
as the temperature at which the liquid stops relaxing at the experimental time
scale, the jump of heat capacity at follows as a necessary consequence
due to the change of system's elastic, vibrational and thermal properties. In
this picture, we discuss time-dependent effects of glass transition, and
identify three distinct regimes of relaxation. Our approach explains widely
observed logarithmic increase of with the quench rate and the correlation
of heat capacity jump with liquid fragility
New evidence shows that letting people vote early benefits Republicans while Election-Day Registration helps Democrats
While Republicans tend to make it harder for people to vote through initiatives such as Voter ID requirements, Democrats tend to be in favor of measures which make voting easier, such as early and Election-Day registration. But do both measures advocated by Democrats actually have an impact on turnout? Barry Burden, David Canon, Ken Mayer and Donald Moynihan have examined vote returns across three presidential elections and find that while Election-Day registration laws are better at stimulating those who are on the fence to turn out – usually Democrats, early voting measures tend to encourage those who have already decided to vote – usually Republicans
The Glass Transition Temperature of Water: A Simulation Study
We report a computer simulation study of the glass transition for water. To
mimic the difference between standard and hyperquenched glass, we generate
glassy configurations with different cooling rates and calculate the
dependence of the specific heat on heating. The absence of crystallization
phenomena allows us, for properly annealed samples, to detect in the specific
heat the simultaneous presence of a weak pre-peak (``shadow transition''), and
an intense glass transition peak at higher temperature.
We discuss the implications for the currently debated value of the glass
transition temperature of water. We also compare our simulation results with
the Tool-Narayanaswamy-Moynihan phenomenological model.Comment: submitted to Phys. Re
Internal Friction and Vulnerability of Mixed Alkali Glasses
Based on a hopping model we show how the mixed alkali effect in glasses can
be understood if only a small fraction c_V ofthe available sites for the mobile
ions is vacant. In particular, we reproduce the peculiar behavior of the
internal friction and the steep fall (''vulnerability'') of the mobility of the
majority ion upon small replacements by the minority ion. The single and mixed
alkali internal friction peaks are caused by ion-vacancy and ion-ion exchange
processes. If c_V is small, they can become comparable in height even at small
mixing ratios. The large vulnerability is explained by a trapping of vacancies
induced by the minority ions. Reasonable choices of model parameters yield
typical behaviors found in experiments.Comment: 4 pages, 4 figure
Challenges Encountered Using Ophthalmic Anesthetics in Space Medicine
On orbit, ophthalmic anesthetics are used for tonometry and off-nominal corneal examinations. Proparacaine has been flown traditionally. However, the manufacturers recently changed its storage requirements from room temperature storage to refrigerated storage to preserve stability and prolong the shelf-life. Since refrigeration on orbit is not readily available and there were stability concerns about flying proparacaine unrefrigerated, tetracaine was selected as an alternative ophthalmic anesthetic in 2013. We will discuss the challenges encountered flying and using these anesthetics on the International Space Station
Feasibility of single-order parameter description of equilibrium viscous liquid dynamics
Molecular dynamics results for the dynamic Prigogine-Defay ratio are
presented for two glass-forming liquids, thus evaluating the experimentally
relevant quantity for testing whether metastable-equilibrium liquid dynamics to
a good approximation are described by a single parameter. For the Kob-Andersen
binary Lennard-Jones mixture as well as for an asymmetric dumbbell model liquid
a single-parameter description works quite well. This is confirmed by
time-domain results where it is found that energy and pressure fluctuations are
strongly correlated on the alpha-time scale in the NVT ensemble; in the NpT
ensemble energy and volume fluctuations similarly correlate strongly.Comment: Phys. Rev. E, in pres
Solidity of Viscous Liquids
Recent NMR experiments on supercooled toluene and glycerol by Hinze and
Bohmer show that small rotation angles dominate with only few large molecular
rotations. These results are here interpreted by assuming that viscous liquids
are solid-like on short length scales. A characteristic length, the "solidity
length", separates solid-like behavior from liquid-like behavior.Comment: Plain RevTex file, no figure
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