22,917 research outputs found
Aerodynamics on a transport aircraft type wing-body model
The DFLR-F4 wing-body combination is studied. The 1/38 model is formed by a 9.5 aspect ratio transonic wing and an Airbus A 310 fuselage. The F4 wing geometrical characteristics are described and the main experimental results obtained in the S2MA wind tunnel are discussed. Both wing-fuselage interferences and viscous effects, which are important on the wing due to a high rear loading, are investigated by performing 3D calculations. An attempt is made to find their limitations
Vortex pattern development on the upper surface of a swept wing at high angle of attack
An experimental study, based on a swept wing, was undertaken in the water tunnel and the wind tunnel at low speeds, with a view to improving the understanding of the intervening phenomena and to make easier their modelling. The vortex flow effects on the wing are first illustrated from global effort measurements and static pressure distributions. The domain of existence of this type of flow is deduced as a function of both sweep angle and angle of attack. By a phenomenological study in the water tunnel, an attempt is made to describe the physical pattern of the vortex flow, from its formation near the apex to its breakdown at the trailing edge. Lastly, by means of a clinometric probe, the flow field over the wing is determined
Canonical Transformation Approach to the Ultrafast Non-linear Optical Dynamics of Semiconductors
We develop a theory describing the effects of many-particle Coulomb
correlations on the coherent ultrafast nonlinear optical response of
semiconductors and metals. Our approach is based on a mapping of the nonlinear
optical response of the ``bare'' system onto the linear response of a
``dressed'' system. The latter is characterized by effective time-dependent
optical transition matrix elements, electron/hole dispersions, and interaction
potentials, which in undoped semiconductors are determined by the
single-exciton and two-exciton Green functions in the absence of optical
fields. This mapping is achieved by eliminating the optically-induced charge
fluctuations from the Hamiltonian using a Van Vleck canonical transformation.
It takes into account all many-body contributions up to a given order in the
optical fields as well as important Coulomb-induced quantum dynamics to all
orders in the optical field. Our approach allows us to distinguish between
optical nonlinearities of different origins and provides a physically-intuitive
interpretation of their manifestations in ultrafast coherent nonlinear optical
spectroscopy.Comment: 24 page
High-gain weakly nonlinear flux-modulated Josephson parametric amplifier using a SQUID-array
We have developed and measured a high-gain quantum-limited microwave
parametric amplifier based on a superconducting lumped LC resonator with the
inductor L including an array of 8 superconducting quantum interference devices
(SQUIDs). This amplifier is parametrically pumped by modulating the flux
threading the SQUIDs at twice the resonator frequency. Around 5 GHz, a maximum
gain of 31 dB, a product amplitude-gain x bandwidth above 60 MHz, and a 1 dB
compression point of -123 dBm at 20 dB gain are obtained in the non-degenerate
mode of operation. Phase sensitive amplification-deamplification is also
measured in the degenerate mode and yields a maximum gain of 37 dB. The
compression point obtained is 18 dB above what would be obtained with a single
SQUID of the same inductance, due to the smaller nonlinearity of the SQUID
array.Comment: 7 pages, 4 figures, 23 reference
Entropy concepts and DNA investigations
Topological and metric entropies of the DNA sequences from different
organisms were calculated. Obtained results were compared each other and with
ones of corresponding artificial sequences. For all envisaged DNA sequences
there is a maximum of heterogeneity. It falls in the block length interval
[5,7].
Maximum distinction between natural and artificial sequences is shifted on
1-3 position from the maximum of heterogeneity to the right as for metric as
for topological entropy. This point on the specificity of real DNA sequences in
the interval.Comment: 10 pages 7 figures submitted to PL
Long May They Run
Long May They Run, an article in Maine Boats, Homes & Harbors Magazine about the history and culture of the Maine sardine industry. In 2010, the Year of the Sardine and the closure of the Stinson sardine plant, the last in the United States, prompted an exploration of why writers, painters, and other artists are so drawn to this humble fish that once supported so many of Maine\u27s coastal communities.
In 2010, the Stinson Sardine Cannery in Prospect Harbor, Maine, the last sardine cannery in the United States, closed. As historians and photographers rushed in to document the loss, poets and artists celebrated the Year of Sardine with events along the coast of Maine. In addition to supporting an industry and providing food, sardines (Atlantic herring) once played a major part of Maine communities, culture, and art
- …