16,957 research outputs found
Splashing of liquids: interplay of surface roughness with surrounding gas
We investigate the interplay between substrate roughness and surrounding gas
pressure in controlling the dynamics of splashing when a liquid drop hits a dry
solid surface. We associate two distinct forms of splashing with each of these
control parameters: prompt splashing is due to surface roughness and corona
splashing is due to instabilities produced by the surrounding gas. The size
distribution of ejected droplets reveals the length scales of the underlying
droplet-creation process in both cases.Comment: 6 pages, 6 figure
A blowup criterion for ideal viscoelastic flow
We establish an analog of the Beale-Kato-Majda criterion for singularities of
smooth solutions of the system of PDE arising in the Oldroyd model for ideal
viscoelastic flow
On 2D Viscoelasticity with Small Strain
An exact two-dimensional rotation-strain model describing the motion of
Hookean incompressible viscoelastic materials is constructed by the polar
decomposition of the deformation tensor. The global existence of classical
solutions is proved under the smallness assumptions only on the size of initial
strain tensor. The proof of global existence utilizes the weak dissipative
mechanism of motion, which is revealed by passing the partial dissipation to
the whole system.Comment: Different contributions of strain and rotation of the deformation are
studied for viscoelastic fluids of Oldroyd-B type in 2
Liquid drop splashing on smooth, rough and textured surfaces
Splashing occurs when a liquid drop hits a dry solid surface at high
velocity. This paper reports experimental studies of how the splash depends on
the roughness and the texture of the surfaces as well as the viscosity of the
liquid. For smooth surfaces, there is a "corona" splash caused by the presence
of air surrounding the drop. There are several regimes that occur as the
velocity and liquid viscosity are varied. There is also a "prompt" splash that
depends on the roughness and texture of the surfaces. A measurement of the size
distribution of the ejected droplets is sensitive to the surface roughness. For
a textured surface in which pillars are arranged in a square lattice,
experiment shows that the splashing has a four-fold symmetry. The splash occurs
predominantly along the diagonal directions. In this geometry, two factors
affect splashing the most: the pillar height and spacing between pillars.Comment: 9 pages, 11 figure
Gamma-Ray Polarimetry of Two X-Class Solar Flares
We have performed the first polarimetry of solar flare emission at gamma-ray
energies (0.2-1 MeV). These observations were performed with the Reuven Ramaty
High Energy Solar Spectroscopic Imager (RHESSI) for two large flares: the GOES
X4.8-class solar flare of 2002 July 23, and the X17-class flare of 2003 October
28. We have marginal polarization detections in both flares, at levels of 21%
+/- 9% and -11% +/- 5% respectively. These measurements significantly constrain
the levels and directions of solar flare gamma-ray polarization, and begin to
probe the underlying electron distributions.Comment: 33 pages, 12 figures, accepted for publication in Ap
Note on Global Regularity for 2D Oldroyd-B Fluids with Diffusive Stress
We prove global regularity of solutions of Oldroyd-B equations in 2 spatial
dimensions with spatial diffusion of the polymeric stresses
Predicting spring wheat yields based on water use-yield production function in a semi-arid climate
© 2019 INIA. Grain yield of spring wheat (Triticum aestivum L.) fluctuates greatly in Western Loess Plateau of China due to limited and highly variable precipitation. Farmers in this area need a simple tool to predict spring wheat grain yield and assess yield loss risk efficiently. The objectives of this study were to establish relations between water use and grain yield of spring wheat for predicting actual yield and attainable yield (water limited yield) under conventional management practice and mulching practices. Reference data during 1993-2013 and field experiment conducted from 1987 to 2011 were used to determine water use-yield production function and boundary function for spring wheat. Probability of achieving a given spring wheat grain yield threshold is determined based on available soil water content at sowing plus expected precipitation during growing season. Single linear equation was obtained with slope of 14.6 kg ha-1 mm-1 and x intercept at 126.3 mm for spring wheat water use-yield production function with different wheat varieties under varying climatic patterns. The slopes of the boundary function were 16.2 kg ha-1 mm-1 and 19.1 kg ha-1 mm-1 under conventional management practice and mulching practices, respectively. With increase of available soil water content at sowing, the probability of achieving at least 2000 and 4000 kg ha-1 of spring wheat for actual and attainable yield increased under different agricultural management practices
Dissipative Chaos in Semiconductor Superlattices
We consider the motion of ballistic electrons in a miniband of a
semiconductor superlattice (SSL) under the influence of an external,
time-periodic electric field. We use the semi-classical balance-equation
approach which incorporates elastic and inelastic scattering (as dissipation)
and the self-consistent field generated by the electron motion. The coupling of
electrons in the miniband to the self-consistent field produces a cooperative
nonlinear oscillatory mode which, when interacting with the oscillatory
external field and the intrinsic Bloch-type oscillatory mode, can lead to
complicated dynamics, including dissipative chaos. For a range of values of the
dissipation parameters we determine the regions in the amplitude-frequency
plane of the external field in which chaos can occur. Our results suggest that
for terahertz external fields of the amplitudes achieved by present-day free
electron lasers, chaos may be observable in SSLs. We clarify the nature of this
novel nonlinear dynamics in the superlattice-external field system by exploring
analogies to the Dicke model of an ensemble of two-level atoms coupled with a
resonant cavity field and to Josephson junctions.Comment: 33 pages, 8 figure
Mid-Infrared Spectra of Classical AGN Observed with the Spitzer Space Telescope
Full low resolution (65<R<130) and high resolution (R~600) spectra between 5
microns and 37 microns obtained with the Infrared Spectrograph (IRS) on the
Spitzer Space Telescope are presented for eight classical active galactic
nuclei (AGN) which have been extensively studied previously. Spectra of these
AGN are presented as comparison standards for the many objects, including
sources at high redshift, which are being observed spectroscopically in the
mid-infrared for the first time using the IRS. The AGN are NGC4151, Markarian
3, I Zwicky 1, NGC 1275, Centaurus A, NGC 7469, Markarian 231, and NGC 3079.
These sources are used to demonstrate the range of infrared spectra encountered
in objects which have widely different classification criteria at other
wavelengths but which unquestionably contain AGN. Overall spectral
characteristics - including continuum shape, nebular emission lines, silicate
absorption and emission features, and PAH emission features - are considered to
understand how spectral classifications based on mid-infrared spectra relate to
those previously derived from optical spectra. The AGN are also compared to the
same parameters for starburst galaxies such as NGC 7714 and the compact, low
metallicity starburst SBS 0335-052 previously observed with the IRS. Results
confirm the much lower strengths of PAH emission features in AGN, but there are
no spectral parameters in this sample which unambiguously distinguish AGN and
starbursts based only on the slopes of the continuous spectra.Comment: Accepted by Ap
- …