20,472 research outputs found
Becoming the Expert - Interactive Multi-Class Machine Teaching
Compared to machines, humans are extremely good at classifying images into
categories, especially when they possess prior knowledge of the categories at
hand. If this prior information is not available, supervision in the form of
teaching images is required. To learn categories more quickly, people should
see important and representative images first, followed by less important
images later - or not at all. However, image-importance is individual-specific,
i.e. a teaching image is important to a student if it changes their overall
ability to discriminate between classes. Further, students keep learning, so
while image-importance depends on their current knowledge, it also varies with
time.
In this work we propose an Interactive Machine Teaching algorithm that
enables a computer to teach challenging visual concepts to a human. Our
adaptive algorithm chooses, online, which labeled images from a teaching set
should be shown to the student as they learn. We show that a teaching strategy
that probabilistically models the student's ability and progress, based on
their correct and incorrect answers, produces better 'experts'. We present
results using real human participants across several varied and challenging
real-world datasets.Comment: CVPR 201
How Hot is the Wind from TW Hydrae?
It has recently been suggested that the winds from Classical T Tauri stars in
general, and the wind from TW Hya in particular, reaches temperatures of at
least 300,000 K while maintaing a mass loss rate of \Msol
yr or larger. If confirmed, this would place strong new requirements on
wind launching and heating models. We therefore re-examine spectra from the
Space Telescope Imaging Spectrograph aboard the Hubble Space Telescope and
spectra from the Far Ultraviolet Spectroscopic Explorer satellite in an effort
to better constrain the maximum temperature in the wind of TW Hya. We find
clear evidence for a wind in the \ion{C}{2} doublet at 1037 \AA and in the
\ion{C}{2} multiplet at 1335 \AA. We find no wind absorption in the \ion{C}{4}
1550 \AA doublet observed at the same time as the \ion{C}{2} 1335 \AA line or
in observations of \ion{O}{6} observed simultaneously with the \ion{C}{2} 1037
\AA line. The presence or absence of \ion{C}{3} wind absorption is ambiguous.
The clear lack of a wind in the \ion{C}{4} line argues that the wind from TW
Hya does not reach the 100,000 K characteristic formation temperature of this
line. We therefore argue that the available evidence suggests that the wind
from TW Hya, and probably all classical T Tauri stars, reaches a maximum
temperature in the range of 10,000 -- 30,000 K.Comment: 17 pages, 3 figures, Figure 1 in 2nd version fixes a small velocity
scaling error and new revision adds a reference to an additional paper
recently foun
Theoretical Spectra and Light Curves of Close-in Extrasolar Giant Planets and Comparison with Data
We present theoretical atmosphere, spectral, and light-curve models for
extrasolar giant planets (EGPs) undergoing strong irradiation for which {\it
Spitzer} planet/star contrast ratios or light curves have been published (circa
June 2007). These include HD 209458b, HD 189733b, TrES-1, HD 149026b, HD
179949b, and And b. By comparing models with data, we find that a
number of EGP atmospheres experience thermal inversions and have stratospheres.
This is particularly true for HD 209458b, HD 149026b, and And b.
This finding translates into qualitative changes in the planet/star contrast
ratios at secondary eclipse and in close-in EGP orbital light curves. Moreover,
the presence of atmospheric water in abundance is fully consistent with all the
{\it Spitzer} data for the measured planets. For planets with stratospheres,
water absorption features invert into emission features and mid-infrared fluxes
can be enhanced by a factor of two. In addition, the character of near-infrared
planetary spectra can be radically altered. We derive a correlation between the
importance of such stratospheres and the stellar flux on the planet, suggesting
that close-in EGPs bifurcate into two groups: those with and without
stratospheres. From the finding that TrES-1 shows no signs of a stratosphere,
while HD 209458b does, we estimate the magnitude of this stellar flux
breakpoint. We find that the heat redistribution parameter, P, for the
family of close-in EGPs assumes values from 0.1 to 0.4. This paper
provides a broad theoretical context for the future direct characterization of
EGPs in tight orbits around their illuminating stars.Comment: Accepted to Ap. J., provided here in emulateapj format: 28 pages, 8
figures, many with multiple panel
Prediction of flow in diesel engine cylinders
Imperial Users onl
Supersonic flutter of cylindrical shells
The general theories of thin elastic cylindrical shells as derived
by Love and Novozhilov are compared and then used in a simple binary
flutter analysis which permits the existence of both axial and circumferential
waves of deformation. Linear piston theory has been used
and the results obtained indicate that the axi-symmetric mode of
deformation is the most critical. Comparisons are then made with
other published results and apparent inconsistencies in those papers
are found to arise from certain assumptions made in the deformation
equations used. In a further axisymmetric mode analysis the use of a
travelling wave form of radial deflection is shown to give similar results
as standing wave forms when applied to a shell of finite length
The flutter of thin, plane, elliptic panels
The effect of various parameters on the flutter of elliptic panels is studied by
simple theoretical analyses. For clamped edge panels, compressive membrane
stresses are shown to have destabilising effects. Structural damping is, in general,
destabilising, except for very low values of the ratio of structural and aerodynamic
damping coefficients.
The addition of a concentrated mass may also have a destabilising effect,
depending upon the position of the added mass. The effect of sweepback is stabilising
or destabilising, depending on whether the panel aspect ratio is less than, or
greater than, unity. The effect of variations in the edge conditions is shown for the
case of circular panels where the difference between simply supported and fully
clamped edges corresponds to a difference of 20% in critical panel thickness
Thermal stresses in thin cylindrical shells, stiffened by plane bulkheads, for arbitrary temperature distributions
A study has been made of the thermal stresses reulting near the
joint of a cylinder and internal bulkhead due to arbitrary temperature
distributions in the configuration and to the consequent compatability
forces and moments at the joint. The method is general enough to permit
the inclusion of joint thermal resistance but certain limitations are placed
on the form of the axial temperature distribution in the cylinder.
An approximate method to determine the transient temperatures for
completely general heating programmes is also proposed
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