11,553 research outputs found
Particle-size characteristics of the vertical dust profiles of two contrasting dust events in the Channel Country of western Queensland, Australia
Spatial and temporal variations in vegetation and soil surface conditions of rangelands add a level of complexity to wind erosion processes which is often difficult to model or measure. Butler and colleagues have developed a methodology which combines computer simulation and experimental measurement to analyse how spatial and temporal changes in dust source area emission rates and atmospheric conditions affect vertical dust concentration profiles during wind erosion events in the Queensland Channel Country. This methodology has not, however, taken into account how variations in dust source area particle-size can affect vertical dust concentration profiles.
The present paper examines how the particle-size characteristics of dust source soils affect both vertical dust concentration profiles and the vertical distribution of particle-sizes in two contrasting wind erosion events in the Queensland Channel Country. Comparisons are made between computer simulations of these events and the results of field measurements (of vertical dust concentration profiles) and laboratory measurements (of dust particle-size). Computer simulations of the particle-size emissions from the different dust source areas during the two events produce vertical distributions of dust particle-sizes which are similar to the measured dust particle-sizes for these events. These results indicate that erodibility-induced spatial and temporal variations in particle-size emissions of dust source areas have important influences upon: dust fluxes, vertical dust concentration profiles and the vertical distribution of dust particle-sizes within these profile
Study of orientation effect on nanoscale polarization in BaTiO3 thin films using piezoresponse force microscopy
We have investigated the effect of texture on in-plane (IPP) and out- of plane (OPP) polarizations of pulsed-laser-deposited BaTiO3 thin films grown on Pt and La0.5Sr0.5CoO3 (LSCO) buffered Pt electrodes. The OPP and IPP polarizations were observed by piezoresponse force microscopy (PFM) for three-dimensional polarization analyses in conjunction with conventional diffraction methods using x-ray diffraction and reflection high energy electron diffraction measurements. BaTiO3 films grown on Pt electrodes exhibited highly (101) preferred orientation with higher IPP component whereas BaTiO3 film grown on LSCO/Pt electrodes showed (001) and (101) orientations with higher OPP component. Measured effective d(33) values of BaTiO3 films deposited on Pt and LSCO/ Pt electrodes were 14.3 and 54.0 pm/ V, respectively. Local piezoelectric strain loops obtained by OPP and IPP-PFM showed that piezoelectric properties were strongly related to film orientation
Cracks in rubber under tension exceed the shear wave speed
The shear wave speed is an upper limit for the speed of cracks loaded in
tension in linear elastic solids. We have discovered that in a non-linear
material, cracks in tension (Mode I) exceed this sound speed, and travel in an
intersonic range between shear and longitudinal wave speeds. The experiments
are conducted in highly stretched sheets of rubber; intersonic cracks can be
produced simply by popping a balloon.Comment: 4 pages, 5 eps figure
Electroweak phase transition in technicolor
Several phenomenologically viable walking technicolor models have been
proposed recently. I demonstrate that these models can have first order
electroweak phase transitions, which are sufficiently strong for electroweak
baryogenesis. Strong dynamics can also lead to several separate transitions at
the electroweak scale, with the possibility of a temporary restoration and an
extra breaking of the electroweak symmetry. First order phase transitions will
produce gravitational waves, which may be detectable at future experiments.Comment: 6 pages, 4 figures. Talk at PASCOS 2010 conference, Valencia, 19-23
July 201
A Unifying Framework for Strong Structural Controllability
This paper deals with strong structural controllability of linear systems. In
contrast to existing work, the structured systems studied in this paper have a
so-called zero/nonzero/arbitrary structure, which means that some of the
entries are equal to zero, some of the entries are arbitrary but nonzero, and
the remaining entries are arbitrary (zero or nonzero). We formalize this in
terms of pattern matrices whose entries are either fixed zero, arbitrary
nonzero, or arbitrary. We establish necessary and sufficient algebraic
conditions for strong structural controllability in terms of full rank tests of
certain pattern matrices. We also give a necessary and sufficient graph
theoretic condition for the full rank property of a given pattern matrix. This
graph theoretic condition makes use of a new color change rule that is
introduced in this paper. Based on these two results, we then establish a
necessary and sufficient graph theoretic condition for strong structural
controllability. Moreover, we relate our results to those that exists in the
literature, and explain how our results generalize previous work.Comment: 11 pages, 6 Figure
Internal wave pressure, velocity, and energy flux from density perturbations
Determination of energy transport is crucial for understanding the energy
budget and fluid circulation in density varying fluids such as the ocean and
the atmosphere. However, it is rarely possible to determine the energy flux
field , which requires simultaneous measurements of
the pressure and velocity perturbation fields, and . We present
a method for obtaining the instantaneous from density
perturbations alone: a Green's function-based calculation yields , and
is obtained by integrating the continuity equation and the
incompressibility condition. We validate our method with results from
Navier-Stokes simulations: the Green's function method is applied to the
density perturbation field from the simulations, and the result for
is found to agree typically to within with
computed directly using and from the Navier-Stokes
simulation. We also apply the Green's function method to density perturbation
data from laboratory schlieren measurements of internal waves in a stratified
fluid, and the result for agrees to within with results from
Navier-Stokes simulations. Our method for determining the instantaneous
velocity, pressure, and energy flux fields applies to any system described by a
linear approximation of the density perturbation field, e.g., to small
amplitude lee waves and propagating vertical modes. The method can be applied
using our Matlab graphical user interface EnergyFlux
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