4,080 research outputs found
Viscoelasticity and metastability limit in supercooled liquids
A supercooled liquid is said to have a kinetic spinodal if a temperature Tsp
exists below which the liquid relaxation time exceeds the crystal nucleation
time. We revisit classical nucleation theory taking into account the
viscoelastic response of the liquid to the formation of crystal nuclei and find
that the kinetic spinodal is strongly influenced by elastic effects. We
introduce a dimensionless parameter \lambda, which is essentially the ratio
between the infinite frequency shear modulus and the enthalpy of fusion of the
crystal. In systems where \lambda is larger than a critical value \lambda_c the
metastability limit is totally suppressed, independently of the surface
tension. On the other hand, if \lambda < \lambda_c a kinetic spinodal is
present and the time needed to experimentally observe it scales as
exp[\omega/(\lambda_c-\lambda)^2], where \omega is roughly the ratio between
surface tension and enthalpy of fusion
Optical properties of a light-emitting polymer directly patterned by soft lithography
Copyright © 2002 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. The following article appeared in Applied Physics Letters 81 (2002) and may be found at http://link.aip.org/link/?APPLAB/81/1955/1We present the optical properties of a directly patterned light-emitting polymer. The patterned poly(2-methoxy-5-(3',7'-dimethyloctyloxy)-paraphenylenevinylene film is fabricated using hot embossing lithography. The effect of the embossed microstructure on the light emitted from the polymer is examined by measuring the angle-dependent photoluminescence and its photonic band structure. The imposed grating modifies the emitted light by Bragg scattering into free space light that would otherwise be trapped as waveguide modes. This simple patterning technique may find application in improving the performance of light-emitting polymer devices
Family Quality of Life Following Early Identification of Deafness
This is the published version, also available here: http://dx.doi.org/10.1044/0161-1461(2009/07-0093).Purpose: Family members’ perceptions of their
quality of life were examined following early identification of
deafness in children.
Method: A questionnaire was used to solicit ratings of satisfaction
from the family members of 207 children who were deaf and
younger than 6 years of age.
Results: Results indicated that families were generally satisfied
with the areas of family life surveyed. Descriptive analysis
suggested lower satisfaction ratings in the area of emotional wellbeing.
Families also reported that their child’s deafness had the
largest impact on their emotional well-being. Family members of
children using oral communication with a cochlear implant
reported higher satisfaction with their child’s speech production
and perception outcomes than family members of children using
hearing aids alone.
Implications: We recommend that service providers and early
hearing detection and intervention program coordinators consider
additional supports for family well-being following the early
identification of deafness in children
Quantum critical dynamics of a S = 1/2 antiferromagnetic Heisenberg chain studied by 13C-NMR spectroscopy
We present a 13C-NMR study of the magnetic field driven transition to
complete polarization of the S=1/2 antiferromagnetic Heisenberg chain system
copper pyrazine dinitrate Cu(C_4H_4N_2)(NO_3)_2 (CuPzN). The static local
magnetization as well as the low-frequency spin dynamics, probed via the
nuclear spin-lattice relaxation rate 1/T_1, were explored from the low to the
high field limit and at temperatures from the quantum regime (k_B T << J) up to
the classical regime (k_B T >> J). The experimental data show very good
agreement with quantum Monte Carlo calculations over the complete range of
parameters investigated. Close to the critical field, as derived from static
experiments, a pronounced maximum in 1/T_1 is found which we interpret as the
finite-temperature manifestation of a diverging density of zero-energy magnetic
excitations at the field-driven quantum critical point.Comment: 5 pages, 4 figure
Phase diagrams of correlated electrons: systematic corrections to the mean field theory
Perturbative corrections to the mean field theory for particle-hole
instabilities of interacting electron systems are computed within a scheme
which is equivalent to the recently developed variational approach to the
Kohn-Luttinger superconductivity. This enables an unbiased comparison of
particle-particle and particle-hole instabilities within the same approximation
scheme. A spin-rotation invariant formulation for the particle-hole
instabilities in the triplet channel is developed. The method is applied to the
phase diagram of the t-t' Hubbard model on the square lattice. At the Van Hove
density, antiferromagnetic and d-wave Pomeranchuk phases are found to be stable
close to half filling. However, the latter phase is confined to an extremely
narrow interval of densities and away from the singular filling, d-wave
superconducting instability dominates
Photonic band structure and emission characteristics of a metal-backed polymeric distributed feedback laser
Copyright © 2002 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. The following article appeared in Applied Physics Letters 81 (2002) and may be found at http://link.aip.org/link/?APPLAB/81/954/1Optical losses associated with the metallic contacts necessary for charge injection are an obstacle to the development of an electrically pumped polymer laser. We show that it may be possible to overcome these losses by demonstrating the operation of a distributed-feedback polymer laser fabricated upon a silver substrate. The device lasing threshold was ~150 times greater than that of an otherwise similar metal-free device, though similar to early polymer lasers. The device emission characteristics correlated well with the measured photonic band structure, allowing an explanation of the effect of the microstructure on device operation
Operating characteristics of a semiconducting polymer laser pumped by a microchip laser
Copyright © 2003 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. The following article appeared in Applied Physics Letters 82 (2003) and may be found at http://link.aip.org/link/?APPLAB/82/313/1We report the demonstration of a compact, all-solid-state polymer laser system featuring a microchip laser as the pump source. The laser was configured as a surface-emitting, two-dimensional distributed feedback laser, based on the conjugated polymer poly(2-methoxy-5-(2'-ethylhexyloxy)-1,4-phenylene vinylene). Pulsed, band-edge lasing was observed at 636 nm above a threshold pump energy of 4 nJ. The laser exhibited an energy slope efficiency of 6.8%, with a maximum output energy of 1.12 nJ at a pump energy of 20.4 nJ. The output beam had an azimuthally polarized annular profile with a beam quality factor (M2) of 2.2, close to the theoretical value of the lowest-order Laguerre–Gaussian and Bessel–Gaussian annular modes. We explain the origin of the azimuthal polarization as due to a coherent combination of the resonant fields supported by the two gratings
Low threshold edge emitting polymer distributed feedback laser based on a square lattice
Copyright © 2005 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. The following article appeared in Applied Physics Letters 86 (2005) and may be found at http://link.aip.org/link/?APPLAB/86/161102/1We report the demonstration of a low-threshold, edge-emitting polymer distributed feedback laser based on a square lattice. The lattice constant was 268 nm, which corresponds to a lattice line spacing in the ΓM symmetry direction of the Brillouin zone of 189 nm. The latter was employed to provide feedback at 630 nm via a first order diffraction process. The device operated on two longitudinal modes, which were situated on the band-edge near the M symmetry point. The two modes had thresholds of 0.66 nJ and 1.2 nJ—significantly lower than comparable surface-emitting DFB lasers. Angle dependent photoluminescence experiments were performed to investigate the effect of the square lattice on the laser operation and the origin of the low threshold
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