13,441 research outputs found
Shock waves and drag in the numerical calculation of isentropic transonic flow
Properties of the shock relations for steady, irrotational, transonic flow are discussed and compared for the full and approximate governing potential in common use. Results from numerical experiments are presented to show that the use of proper finite difference schemes provide realistic solutions and do not introduce spurious shock waves. Analysis also shows that realistic drags can be computed from shock waves that occur in isentropic flow. In analogy to the Oswatitsch drag equation, which relates the drag to entropy production in shock waves, a formula is derived for isentropic flow that relates drag to the momentum gain through an isentropic shock. A more accurate formula for drag, based on entropy production, is also derived, and examples of wave drag evaluation based on these formulas are given and comparisons are made with experimental results
Symbolic computation of exact solutions expressible in hyperbolic and elliptic functions for nonlinear PDEs
Algorithms are presented for the tanh- and sech-methods, which lead to
closed-form solutions of nonlinear ordinary and partial differential equations
(ODEs and PDEs). New algorithms are given to find exact polynomial solutions of
ODEs and PDEs in terms of Jacobi's elliptic functions.
For systems with parameters, the algorithms determine the conditions on the
parameters so that the differential equations admit polynomial solutions in
tanh, sech, combinations thereof, Jacobi's sn or cn functions. Examples
illustrate key steps of the algorithms.
The new algorithms are implemented in Mathematica. The package
DDESpecialSolutions.m can be used to automatically compute new special
solutions of nonlinear PDEs. Use of the package, implementation issues, scope,
limitations, and future extensions of the software are addressed.
A survey is given of related algorithms and symbolic software to compute
exact solutions of nonlinear differential equations.Comment: 39 pages. Software available from Willy Hereman's home page at
http://www.mines.edu/fs_home/whereman
Evidence for a Fractional Quantum Hall Nematic State in Parallel Magnetic Fields
We report magneto-transport measurements for the fractional quantum Hall
state at filling factor 5/2 as a function of applied parallel magnetic
field (). As is increased, the 5/2 state becomes increasingly
anisotropic, with the in-plane resistance along the direction of
becoming more than 30 times larger than in the perpendicular direction.
Remarkably, the resistance anisotropy ratio remains constant over a relatively
large temperature range, yielding an energy gap which is the same for both
directions. Our data are qualitatively consistent with a fractional quantum
Hall \textit{nematic} phase
Observation of An Anisotropic Wigner Crystal
We report a new correlated phase of two-dimensional charged carriers in high
magnetic fields, manifested by an anisotropic insulating behavior at low
temperatures. It appears near Landau level filling factor in hole
systems confined to wide GaAs quantum wells when the sample is tilted in
magnetic field to an intermediate angle. The parallel field component
() leads to a crossing of the lowest two Landau levels, and an
elongated hole wavefunction in the direction of . Under these
conditions, the in-plane resistance exhibits an insulating behavior, with the
resistance along more than 10 times smaller than the resistance
perpendicular to . We interpret this anisotropic insulating phase as a
two-component, striped Wigner crystal
A site-specific standard for comparing dynamic solar ultraviolet protection characteristics of established tree canopies
A standardised procedure for making fair and comparable assessments of the ultraviolet protection of an established tree canopy that takes into account canopy movement and the changing position of the sun is presented for use by government, planning, and environmental health authorities. The technique utilises video image capture and replaces the need for measurement by ultraviolet radiometers for surveying shade quality characteristics of trees growing in public parks, playgrounds and urban settings. The technique improves upon tree shade assessments that may be based upon single measurements of the ultraviolet irradiance observed from a fixed point of view. The presented technique demonstrates how intelligent shade audits can be conducted without the need for specialist equipment, enabling the calculation of the Shade Protection Index (SPI) and Ultraviolet Protection Factor (UPF) for any discreet time interval and over a full calendar year
Inheritance of Black Hair Patterns in Cattle Lacking the Extension Factor for Black (E.). IV, Partitioning Phenotypes by Castration
Author Institution: Department of Dairy Science, Ohio Agricultural Experiment Station, Wooste
Multicomponent fractional quantum Hall states with subband and spin degrees of freedom
In wide GaAs quantum wells where two electric subbands are occupied we apply
a parallel magnetic field or increase the electron density to cause a crossing
of the two Landau levels of these subbands and with opposite spins. Near
the crossing, the fractional quantum Hall states in the filling factor range
exhibit a remarkable sequence of pseudospin polarization transitions
resulting from the interplay between the spin and subband degrees of freedom.
The field positions of the transitions yield a new and quantitative measure of
the composite Fermions' discrete energy level separations. Surprisingly, the
separations are smaller when the electrons have higher spin-polarization
Even-denominator Fractional Quantum Hall Effect at a Landau Level Crossing
The fractional quantum Hall effect (FQHE), observed in two-dimensional (2D)
charged particles at high magnetic fields, is one of the most fascinating,
macroscopic manifestations of a many-body state stabilized by the strong
Coulomb interaction. It occurs when the filling factor () of the quantized
Landau levels (LLs) is a fraction which, with very few exceptions, has an odd
denominator. In 2D systems with additional degrees of freedom it is possible to
cause a crossing of the LLs at the Fermi level. At and near these crossings,
the FQHE states are often weakened or destroyed. Here we report the observation
of an unusual crossing of the two \emph{lowest-energy} LLs in high-mobility
GaAs 2D systems which brings to life a new \emph{even-denominator} FQHE
at
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