3,006 research outputs found
Strain-Rate Frequency Superposition in Large-Amplitude Oscillatory Shear
In a recent work, Wyss, {\it et.al.} [Phys. Rev. Lett., {\bf 98}, 238303
(2007)] have noted a property of `soft solids' under oscillatory shear, the
so-called strain-rate frequency superposition (SRFS). We extend this study to
the case of soft solids under large-amplitude oscillatory shear (LAOS). We show
results from LAOS studies in a monodisperse hydrogel suspension, an aqueous
gel, and a biopolymer suspension, and show that constant strain-rate frequency
sweep measurements with soft solids can be superimposed onto master curves for
higher harmonic moduli, with the {\it same} shift factors as for the linear
viscoelastic moduli. We show that the behavior of higher harmonic moduli at low
frequencies in constant strain-rate frequency sweep measurements is similar to
that at large strain amplitudes in strain-amplitude sweep tests. We show
surface plots of the harmonic moduli and the energy dissipation rate per unit
volume in LAOS for soft solids, and show experimentally that the energy
dissipated per unit volume depends on the first harmonic loss modulus alone, in
both the linear and the nonlinear viscoelastic regime.Comment: 10 pages, 25 figures, accepted for publication in Physical Review E.
Incorporates referee comment
Coherent transport through graphene nanoribbons in the presence of edge disorder
We simulate electron transport through graphene nanoribbons of experimentally
realizable size (length L up to 2 micrometer, width W approximately 40 nm) in
the presence of scattering at rough edges. Our numerical approach is based on a
modular recursive Green's function technique that features sub-linear scaling
with L of the computational effort. We identify the influence of the broken A-B
sublattice (or chiral) symmetry and of K-K' scattering by Fourier spectroscopy
of individual scattering states. For long ribbons we find Anderson-localized
scattering states with a well-defined exponential decay over 10 orders of
magnitude in amplitude.Comment: 8 pages, 6 Figure
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
Magnitude of Magnetic Field Dependence of a Possible Selective Spin Filter in ZnSe/Zn_{1-x}Mn_{x}Se Multilayer Heterostructure
Spin-polarized transport through a band-gap-matched ZnSe/Zn_{1-x}Mn_{x}
Se/ZnSe/Zn_{1-x}Mn_{x}Se/ZnSe multilayer structure is investigated. The
resonant transport is shown to occur at different energies for different spins
owing to the split of spin subbands in the paramagnetic layers. It is found
that the polarization of current density can be reversed in a certain range of
magnetic field, with the peak of polarization moving towards a stronger
magnetic field for increasing the width of central ZnSe layer while shifting
towards an opposite direction for increasing the width of paramagnetic layer.
The reversal is limited in a small-size system. A strong suppression of the
spin up component of the current density is present at high magnetic field. It
is expected that such a reversal of the polarization could act as a possible
mechanism for a selective spin filter device
Direct conversion of rheological compliance measurements into storage and loss moduli
We remove the need for Laplace/inverse-Laplace transformations of
experimental data, by presenting a direct and straightforward mathematical
procedure for obtaining frequency-dependent storage and loss moduli
( and respectively), from time-dependent experimental
measurements. The procedure is applicable to ordinary rheological creep
(stress-step) measurements, as well as all microrheological techniques, whether
they access a Brownian mean-square displacement, or a forced compliance. Data
can be substituted directly into our simple formula, thus eliminating
traditional fitting and smoothing procedures that disguise relevant
experimental noise.Comment: 4 page
Anisotropic charge transport in non-polar GaN QW: polarization induced charge and interface roughness scattering
Charge transport in GaN quantum well (QW) devices grown in non-polar
direction has been theoretically investigated . Emergence of anisotropic line
charge scattering mechanism originating as a result of anisotropic rough
surface morphology in conjunction with in-plane built-in polarization has been
proposed. It has shown that in-plane growth anisotropy leads to large
anisotropic carrier transport at low temperatures. At high temperatures, this
anisotropy in charge transport is partially washed out by strong isotropic
optical phonon scattering in GaN QW.Comment: 4 pages, 4 figure
Antarctic polar stratospheric aerosols: The roles of nitrates, chlorides and sulfates
Nitric and hydrochloric acids have been postulated to condense in the winter polar stratosphere to become an important component of polar stratospheric clouds. One implication is that the removal of NO(y) from the gas phase by this mechanism allows high Cl(x) concentrations to react with O3, because the formation of ClNO3 is inhibited. Contributions of NO3 and Cl to the stratospheric aerosol were determined during the 1987 Airborne Antarctic Ozone Experiment by testing for the presence of nitrates and chlorides in the condensed phase. Aerosol particles were collected on four 500 micron diameter gold wires, each pretreated differently to give results that were specific to certain physical and chemical aerosol properties. One wire was carbon-coated for concentration and size analyses by scanning electron microscopy; X-ray energy dispersive analyses permitted the detection of S and Cl in individual particles. Three more wires were coated with Nitron, barium chloride and silver nitrate, respectively, to detect nitrate, sulfate and chloride in aerosol particles. All three ions, viz., sulfates, nitrates and chlorides were detected in the Antarctic stratospheric aerosol. In terms of number concentrations, the aerosol was dominated by sulfates, followed by chlorides and nitrates. An inverse linear regression can be established between nitrate concentrations and ozone mixing ratio, and between temperature and nitrates
Husimi Maps in Lattices
We build upon previous work that used coherent states as a measurement of the
local phase space and extended the flux operator by adapting the Husimi
projection to produce a vector field called the Husimi map. In this article, we
extend its definition from continuous systems to lattices. This requires making
several adjustments to incorporate effects such as group velocity and multiple
bands. Several phenomena which uniquely occur in lattice systems, like
group-velocity warping and internal Bragg diffraction, are explained and
demonstrated using Husimi maps. We also show that scattering points between
bands and valleys can be identified in the divergence of the Husimi map
A 12 GHz satellite video receiver: Low noise, low cost prototype model for TV reception from broadcast satellites
A 12-channel synchronous phase lock video receiver consisting of an outdoor downconverter unit and an indoor demodulator unit was developed to provide both low noise performance and low cost in production quantities of 1000 units. The prototype receiver can be mass produced at a cost under $1540 without sacrificing system performance. The receiver also has the capability of selecting any of the twelve assigned satellite broadcast channels in the frequency range 11.7 to 12.2 GHz
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