914 research outputs found
Temperature development of glassy alpha-relaxation dynamics determined by broadband dielectric spectroscopy
We present the temperature dependence of alpha-relaxation times of 13 glass
formers determined from broadband dielectric spectroscopy, also including data
from aging measurements. The data sets partly cover relaxation-time ranges of
up to 16 decades enabling a critical test of the validity of model predictions.
For this purpose, the data are provided for electronic download. Here we employ
these results to test the applicability of the Vogel-Fulcher-Tammann equation
and a recently proposed new approach that was demonstrated to provide superior
fits of a vast collection of viscosity data.Comment: 6 pages, 5 figures, final version with minor revisions according to
referee demands. The relaxation time data published in the present work can
be downloaded at http://link.aps.org/supplemental/10.1103/PhysRevE.81.05150
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
Nanometer Scale Dielectric Fluctuations at the Glass Transition
Using non-contact scanning probe microscopy (SPM) techniques, dielectric
properties were studied on 50 nanometer length scales in poly-vinyl-acetate
(PVAc) films in the vicinity of the glass transition. Low frequency (1/f) noise
observed in the measurements, was shown to arise from thermal fluctuations of
the electric polarization. Anomalous variations observed in the noise spectrum
provide direct evidence for cooperative nano-regions with heterogeneous
kinetics. The cooperative length scale was determined. Heterogeneity was
long-lived only well below the glass transition for faster than average
processes.Comment: 4 pages, 4 embedded PS figures, RevTeX - To appear in Phys. Rev. Let
Metastable liquid-liquid phase transition in a single-component system with only one crystal phase and no density anomaly
We investigate the phase behavior of a single-component system in 3
dimensions with spherically-symmetric, pairwise-additive, soft-core
interactions with an attractive well at a long distance, a repulsive soft-core
shoulder at an intermediate distance, and a hard-core repulsion at a short
distance, similar to potentials used to describe liquid systems such as
colloids, protein solutions, or liquid metals. We showed [Nature {\bf 409}, 692
(2001)] that, even with no evidences of the density anomaly, the phase diagram
has two first-order fluid-fluid phase transitions, one ending in a
gas--low-density liquid (LDL) critical point, and the other in a
gas--high-density liquid (HDL) critical point, with a LDL-HDL phase transition
at low temperatures. Here we use integral equation calculations to explore the
3-parameter space of the soft-core potential and we perform molecular dynamics
simulations in the interesting region of parameters. For the equilibrium phase
diagram we analyze the structure of the crystal phase and find that, within the
considered range of densities, the structure is independent of the density.
Then, we analyze in detail the fluid metastable phases and, by explicit
thermodynamic calculation in the supercooled phase, we show the absence of the
density anomaly. We suggest that this absence is related to the presence of
only one stable crystal structure.Comment: 15 pages, 21 figure
Thermodynamic Behavior of a Model Covalent Material Described by the Environment-Dependent Interatomic Potential
Using molecular dynamics simulations we study the thermodynamic behavior of a
single-component covalent material described by the recently proposed
Environment-Dependent Interatomic Potential (EDIP). The parameterization of
EDIP for silicon exhibits a range of unusual properties typically found in more
complex materials, such as the existence of two structurally distinct
disordered phases, a density decrease upon melting of the low-temperature
amorphous phase, and negative thermal expansion coefficients for both the
crystal (at high temperatures) and the amorphous phase (at all temperatures).
Structural differences between the two disordered phases also lead to a
first-order transition between them, which suggests the existence of a second
critical point, as is believed to exist for amorphous forms of frozen water.
For EDIP-Si, however, the unusual behavior is associated not only with the open
nature of tetrahedral bonding but also with a competition between four-fold
(covalent) and five-fold (metallic) coordination. The unusual behavior of the
model and its unique ability to simulation the liquid/amorphous transition on
molecular-dynamics time scales make it a suitable prototype for fundamental
studies of anomalous thermodynamics in disordeered systems.Comment: 48 pages (double-spaced), 13 figure
The Economic Resource Receipt of New Mothers
U.S. federal policies do not provide a universal social safety net of economic support for women during pregnancy or the immediate postpartum period but assume that employment and/or marriage will protect families from poverty. Yet even mothers with considerable human and marital capital may experience disruptions in employment, earnings, and family socioeconomic status postbirth. We use the National Survey of Families and Households to examine the economic resources that mothers with children ages 2 and younger receive postbirth, including employment, spouses, extended family and social network support, and public assistance. Results show that many new mothers receive resources postbirth. Marriage or postbirth employment does not protect new mothers and their families from poverty, but education, race, and the receipt of economic supports from social networks do
Highly Anisotropic Luminescence from Poly(9,9-dioctylfluorene) Nanowires Doped with Orientationally Ordered ÎČ-Phase Polymer Chains
Conventional methods fail to measure cp(omega) of glass-forming liquids
The specific heat is frequency dependent in highly viscous liquids. By
solving the full one-dimensional thermo-viscoelastic problem analytically it is
shown that, because of thermal expansion and the fact that mechanical stresses
relax on the same time scale as the enthalpy relaxes, the plane thermal-wave
method does not measure the isobaric frequency-dependent specific heat
c_p(omega). This method rather measures a "longitudinal" frequency-dependent
specific heat, a quantity defined and detailed here that is in-between
c_p(omega) and c_v(omega). This result means that no wide-frequency
measurements of c_p(omega) on liquids approaching the calorimetric glass
transition exist. We briefly discuss consequences for experiment
Proton Spin-Lattice Relaxation in Organic Molecular Solids: Polymorphism and the Dependence on Sample Preparation
We report solidâstate nuclear magnetic resonance 1H spinâlattice relaxation, singleâcrystal Xâray diffraction, powder Xâray diffraction, field emission scanning electron microscopy, and differential scanning calorimetry in solid samples of 2âethylanthracene (EA) and 2âethylanthraquinone (EAQ) that have been physically purified in different ways from the same commercial starting compounds. The solidâstate 1H spinâlattice relaxation is always nonâexponential at high temperatures as expected when CH3 rotation is responsible for the relaxation. The 1H spinâlattice relaxation experiments are very sensitive to the âseveralâmoleculeâ (clusters) structure of these van der Waals molecular solids. In the three differently prepared samples of EAQ, the relaxation also becomes very nonâexponential at low temperatures. This is very unusual and the decay of the nuclear magnetization can be fitted with both a stretched exponential and a double exponential. This unusual result correlates with the powder Xâray diffractometry results and suggests that the anomalous relaxation is due to crystallites of two (or more) different polymorphs (concomitant polymorphism)
Ejaculation in testicular cancer patients after post-chemotherapy retroperitoneal lymph node dissection
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