25,272 research outputs found
Adaptive optics in coherent lidar wind measurements: A feasibility study
Laser Doppler radar (lidar) is widely used for remote sensing of wind velocities. Usable wavelengths for the laser are limited by the effects of atmospheric turbulence. An adaptive optical system is proposed to compensate for turbulence effects on signal power. The feasibility of an adaptive system is considered in light of the effects of speckle from the aerosol target. It is concluded that adaptive optics is a promising technique for improving the performance of a 2 micron lidar wind measurement system. The chief technical challenges are a laser that will give the required output and pulse repetition rate, a combined Hartmann sensor and heterodyne detector, and a suitable reconstruction algorithm
Bounds on the attractor dimension for magnetohydrodynamic channel flow with parallel magnetic field at low magnetic Reynolds number
We investigate aspects of low-magnetic-Reynolds-number flow between two
parallel, perfectly insulating walls, in the presence of an imposed magnetic
field parallel to the bounding walls. We find a functional basis to describe
the flow, well adapted to the problem of finding the attractor dimension, and
which is also used in subsequent direct numerical simulation of these flows.
For given Reynolds and Hartmann numbers, we obtain an upper bound for the
dimension of the attractor by means of known bounds on the nonlinear inertial
term and this functional basis for the flow. Three distinct flow regimes
emerge: a quasi-isotropic 3D flow, a non-isotropic three-dimensional (3D) flow,
and a 2D flow. We find the transition curves between these regimes in the space
parameterized by Hartmann number Ha and attractor dimension . We
find how the attractor dimension scales as a function of Reynolds and Hartmann
numbers (Re and Ha) in each regime. We also investigate the thickness of the
boundary layer along the bounding wall, and find that in all regimes this
scales as 1/Re, independently of the value of Ha, unlike Hartmann boundary
layers found when the field is normal to the channel. The structure of the set
of least dissipative modes is indeed quite different between these two cases
but the properties of turbulence far from the walls (smallest scales and number
of degrees of freedom) are found to be very similar
Die längsten Titel der Filmgeschichte : eine Liste
Eine Suche nach den längsten Titeln der Filmgeschichte erweist sich als recht mühsame Sammeltätigkeit. Ohne Hinweise von Freunden wäre vieles hier nicht genannt worden. Dank gilt Caroline Amann, Britta Hartmann, Tobias Sunderdiek, Bodo Traber und Hans J. Wulff. Es sei an alle Leser die Bitte ausgesprochen, fehlende Titel an uns weiterzumelden
[Review of] Elwyn T. Ashton. The Welsh in the United States
Ashton\u27s mid-sized volume about the Welsh in America joins the first, and very short account by David Williams, Wales and America (published in Wales in 1946 as part of a bilingual pamphlet series), and Edward George Hartmann\u27s Americans from Wales (nearly three hundred pages, published in 1967 and reprinted in America in 1978)
An Overview of Transience Bounds in Max-Plus Algebra
We survey and discuss upper bounds on the length of the transient phase of
max-plus linear systems and sequences of max-plus matrix powers. In particular,
we explain how to extend a result by Nachtigall to yield a new approach for
proving such bounds and we state an asymptotic tightness result by using an
example given by Hartmann and Arguelles.Comment: 13 pages, 2 figure
Validation of a magneto- and ferro-hydrodynamic model for non-isothermal flows in conjunction with Newtonian and non-Newtonian fluids
This work focuses on the validation of a magnetohydrodynamic (MHD) and ferrohydrodynamic
(FHD) model for non-isothermal flows in conjunction with Newtonian and non-
Newtonian fluids. The importance of this research field is to gain insight into the interaction of
non-linear viscous behaviour of blood flow in the presence of MHD and FHD effects, because
its biomedical application such as magneto resonance imaging (MRI) is in the centre of research
interest. For incompressible flows coupled with MHD and FHD models, the Lorentz force and
a Joule heating term appear due to the MHD effects and the magnetization and magnetocaloric
terms appear due to the FHD effects in the non-linear momentum and temperature equations,
respectively. Tzirtzilakis and Loukopoulos [1] investigated the effects of MHD and FHD for
incompressible non-isothermal flows in conjunction with Newtonian fluids in a small rectangular
channel. Their model excluded the non-linear viscous behaviour of blood flows considering
blood as a Newtonian biofluid. Tzirakis et al. [2, 3] modelled the effects of MHD and FHD for
incompressible isothermal flows in a circular duct and through a stenosis in conjunction with
both Newtonian and non-Newtonian fluids, although their approach neglects the non-isothermal
magnetocaloric FHD effects. Due to the fact that there is a lack of experimental data available
for non-isothermal and non-Newtonian blood flows in the presence of MHD and FHD effects,
therefore the objective of this study is to establish adequate validation test cases in order to assess
the reliability of the implemented non-isothermal and non-Newtonian MHD-FHD models.
The non-isothermal Hartmann flow has been chosen as a benchmark physical problem to study
velocity and temperature distributions for Newtonian fluids and non-Newtonian blood flows in
a planar microfluidic channel. In addition to this, the numerical behaviour of an incompressible
and non-isothermal non-Newtonian blood flow has been investigated from computational
aspects when a dipole-like rotational magnetic field generated by infinite conducting wires. The
numerical results are compared to available computational data taken from literature
Antiproton-nucleus potentials from global fits to antiprotonic X-rays and radiochemical data
We report on global fits of optical-model parameters to 90 data points for
X-rays and 17 data points of radiochemical data put together. With the
help of separate fits to the two kinds of data it is possible to determine
phenomenologically the radial region where the absorption of antiprotons takes
place and to obtain neutron densities which represent the average behaviour
over the periodic table. A finite-range attractive and absorptive -nuclear isoscalar potential fits the data well. Self-consistent dynamical
calculations within the RMF model demonstrate that the polarization of the
nucleus by the {\it atomic} antiproton is negligible.Comment: 18 pages, 6 figures, one table. Extended discussion, to appear in
Nucl. Phys.
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