16,809 research outputs found
Energy management of three-dimensional minimum-time intercept
A real-time computer algorithm to control and optimize aircraft flight profiles is described and applied to a three-dimensional minimum-time intercept mission
An on-board near-optimal climb-dash energy management
On-board real time flight control is studied in order to develop algorithms which are simple enough to be used in practice, for a variety of missions involving three dimensional flight. The intercept mission in symmetric flight is emphasized. Extensive computation is required on the ground prior to the mission but the ensuing on-board exploitation is extremely simple. The scheme takes advantage of the boundary layer structure common in singular perturbations, arising with the multiple time scales appropriate to aircraft dynamics. Energy modelling of aircraft is used as the starting point for the analysis. In the symmetric case, a nominal path is generated which fairs into the dash or cruise state. Feedback coefficients are found as functions of the remaining energy to go (dash energy less current energy) along the nominal path
Implementing Quantum Gates by Optimal Control with Doubly Exponential Convergence
We introduce a novel algorithm for the task of coherently controlling a
quantum mechanical system to implement any chosen unitary dynamics. It performs
faster than existing state of the art methods by one to three orders of
magnitude (depending on which one we compare to), particularly for quantum
information processing purposes. This substantially enhances the ability to
both study the control capabilities of physical systems within their coherence
times, and constrain solutions for control tasks to lie within experimentally
feasible regions. Natural extensions of the algorithm are also discussed.Comment: 4+2 figures; to appear in PR
Optimal symmetric flight with an intermediate vehicle model
Optimal flight in the vertical plane with a vehicle model intermediate in complexity between the point-mass and energy models is studied. Flight-path angle takes on the role of a control variable. Range-open problems feature subarcs of vertical flight and singular subarcs. The class of altitude-speed-range-time optimization problems with fuel expenditure unspecified is investigated and some interesting phenomena uncovered. The maximum-lift-to-drag glide appears as part of the family, final-time-open, with appropriate initial and terminal transient exceeding level-flight drag, some members exhibiting oscillations. Oscillatory paths generally fail the Jacobi test for durations exceeding a period and furnish a minimum only for short-duration problems
Quantifying stretching and rearrangement in epithelial sheet migration
Although understanding the collective migration of cells, such as that seen
in epithelial sheets, is essential for understanding diseases such as
metastatic cancer, this motion is not yet as well characterized as individual
cell migration. Here we adapt quantitative metrics used to characterize the
flow and deformation of soft matter to contrast different types of motion
within a migrating sheet of cells. Using a Finite-Time Lyapunov Exponent (FTLE)
analysis, we find that - in spite of large fluctuations - the flow field of an
epithelial cell sheet is not chaotic. Stretching of a sheet of cells (i.e.,
positive FTLE) is localized at the leading edge of migration. By decomposing
the motion of the cells into affine and non-affine components using the metric
D, we quantify local plastic rearrangements and describe the motion
of a group of cells in a novel way. We find an increase in plastic
rearrangements with increasing cell densities, whereas inanimate systems tend
to exhibit less non-affine rearrangements with increasing density.Comment: 21 pages, 7 figures This is an author-created, un-copyedited version
of an article accepted for publication in the New Journal of Physics. IOP
Publishing Ltd is not responsible for any errors or omissions in this version
of the manuscript or any version derived from it. The Version of Record is
available online at doi:10.1088/1367-2630/15/2/02503
Spitzer Observations of Spacecraft Target 162173 (1999 JU3)
Near-Earth asteroid 162173 (1999 JU3) is the primary target of the Hayabusa-2
sample return mission, and a potential target of the Marco Polo sample return
mission. Earth-based studies of this object are fundamental to these missions.
We present a mid-infrared spectrum (5-38 microns) of 1999 JU3 obtained with
NASA's Spitzer Space Telescope in May 2008. These observations place new
constraints on the surface properties of this asteroid. To fit our spectrum we
used the near-Earth asteroid thermal model (NEATM) and the more complex
thermophysical model (TPM). However, the position of the spin-pole, which is
uncertain, is a crucial input parameter for constraining the thermal inertia
with the TPM; hence, we consider two pole orientations. In the extreme case of
an equatorial retrograde geometry we derive a lower limit to the thermal
inertia of 150 J/m^2/K/s^0.5. If we adopt the pole orientation of Abe et al.
(2008a) our best-fit thermal model yields a value for the thermal inertia of
700+/-200 J/m^2/K/s^0.5 and even higher values are allowed by the uncertainty
in the spectral shape due to the absolute flux calibration. The lower limit to
the thermal inertia, which is unlikely but possible, would be consistent with a
fine regolith similar to wthat is found for asteroid 433 Eros. However, the
thermal inertia is expected to be higher, possibly similar to or greater than
that on asteroid 25143 Itokawa. Accurately determining the spin-pole of
asteroid 162173 will narrow the range of possible values for its thermal
inertia.Comment: 4 pages, 2 figures; to be published as a Letter in Astronomy and
Astrophysic
Temperature dependence of the superconducting gap anisotropy in BiSrCaCuO
We present the first detailed data of the momentum-resolved, temperature
dependence of the superconducting gap of ,
complemented by similar data on the intensity of the photoemission
superconducting condensate spectral area. The gap anisotropy between the
and directions increases markedly with increasing
temperature, contrary to what happens for conventional anisotropic-gap
superconductors such as lead. Specifically, the size of the superconducting gap
along the direction decreases to values indistinguishable from zero
at temperatures for which the gap retains virtually full value along the
direction.Comment: APS_REVTEX. 19 pages, including 8 figures, available upon request.
UW-Madison preprin
Consumer Interest in Gardening Topics and Preferred Information Sources
A survey was conducted to quantify what gardening topics consumers were interested in learning and what sources they used to learn about these topics. Approximately half of the participants (48.2%) responded that they were currently interested in a topic. Friend/neighbor/family members (53.4%), garden center staff (51.0%), and gardening books (48.2%) were the most popular sources for this information. University Web sites, Extension offices, and Master Gardener programs were among the least five sources used. Survey results can help Extension personnel with consumer horticulture responsibilities provide appropriate information to consumers. Results can also help provide a measure of Extension impact
Localization Effects in Bi2Sr2Ca(Cu,Co)2O8+y High Temperature Superconductors
Doping Bi2Sr2Ca1Cu2O8+y with Co causes a superconductor-insulator transition.
We study correlations between changes in the electrical resistivity RHOab(T)
and the electronic bandstructure using identical single crystalline samples.
For undoped samples the resistivity is linear in temperature and has a
vanishing residual resistivity. In angle resolved photoemission these samples
show dispersing band-like states. Co-doping decreases TC and causes and
increase in the residual resistivity. Above a threshold Co-concentration the
resistivity is metallic (drab/dT >0) at room temperature, turns insulating
below a characteristic temperature Tmin and becomes super- conducting at even
lower temperature. These changes in the resistivity correlate with the
disappearance of the dispersing band-like states in angle resolved
photoemission. We show that Anderson localization caused by the impurity
potential of the doped Co-atoms provides a consistent explanation of all
experimental features. Therefore the TC reduction in 3d-metal doped high-
temperature superconductors is not caused by Abrikosov Gor'kov pair- breaking
but by spatial localization of the carriers. The observed suppression of TC
indicates that the system is in the homogenous limit of the
superconductor-insulator transition. The coexistance of insulating (dRHOab/dT
<0) normal state behavior and super- conductivity indicates that the
superconducting ground state is formed out of spatially almost localized
carriers.Comment: Postscript file 11 pages plus 4 figures available on reques
Climb-dash real-time calculations
On-board rear-optimal climb-dash energy management, optimal symmetric flight with an intermediate vehicle model, and energy states are presented
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