7,429 research outputs found
The Strauss conjecture on asymptotically flat space-times
By assuming a certain localized energy estimate, we prove the existence
portion of the Strauss conjecture on asymptotically flat manifolds, possibly
exterior to a compact domain, when the spatial dimension is 3 or 4. In
particular, this result applies to the 3 and 4-dimensional Schwarzschild and
Kerr (with small angular momentum) black hole backgrounds, long range
asymptotically Euclidean spaces, and small time-dependent asymptotically flat
perturbations of Minkowski space-time. We also permit lower order perturbations
of the wave operator. The key estimates are a class of weighted Strichartz
estimates, which are used near infinity where the metrics can be viewed as
small perturbations of the Minkowski metric, and the assumed localized energy
estimate, which is used in the remaining compact set.Comment: Final version, to appear in SIAM Journal on Mathematical Analysis. 17
page
Pressure Sensitive Skin for Prosthetic Hands:2D Contact Location Determination Using Output Connections from a Single Side
The human hand is a vital component of our interaction with the environment, containing a large number of sensory receptors. The loss of a hand is, therefore, a serious and debilitating injury. Surveys have shown that 98% of users of upper limb prostheses desire to feel the level of force they apply through their prosthetic hands. Developments in tactile sensors have yielded many functional electronic skins. However, their complexity remains a barrier to their use in commercial prosthetic hands. This paper introduces a new design of a simple, flexible pressure sensor using carbon fibre tows as both the sensor and the electrodes. The design results in a dynamic pressure range of 0.35 to 280 kPa in a 25-by-25 mm prototype.</p
Testing White Dwarf Crystallization Theory with Asteroseismology of the Massive Pulsating DA Star BPM 37093
It was predicted more than 40 years ago that the cores of the coolest white
dwarf stars should eventually crystallize. This effect is one of the largest
sources of uncertainty in white dwarf cooling models, which are now routinely
used to estimate the ages of stellar populations in both the Galactic disk and
the halo. We are attempting to minimize this source of uncertainty by
calibrating the models, using observations of pulsating white dwarfs. In a
typical mass white dwarf model, crystallization does not begin until the
surface temperature reaches 6000-8000 K. In more massive white dwarf models the
effect begins at higher surface temperatures, where pulsations are observed in
the ZZ Ceti (DAV) stars. We use the observed pulsation periods of BPM 37093,
the most massive DAV white dwarf presently known, to probe the interior and
determine the size of the crystallized core empirically. Our initial
exploration of the models strongly suggests the presence of a solid core
containing about 90% of the stellar mass, which is consistent with our
theoretical expectations.Comment: minor changes for length, accepted for ApJ Letter
A web-based resource for radiation safety courses
CQU runs regular courses for intending Radiation Safety Officers from a variety of industry sectors. Participants have varying levels of prior knowledge to bring to the intensive three day program. To cater for those students whose prior knowledge of radiation physics is weak the print-based media for the course have been converted into a CD-ROM incorporating animations, worked examples, progress checks and self-assessment items. This allows the students who need extra study time on the basic physics concepts to cover as much as possible of the material before commencement of the course. The first course sessions can then concentrate on students’ individual problems and the required program content. This approach also allows the student with strong prior learning to submit an assessment test and be awarded a partial course exemption.
Although the material selection is specifically for Radiation Safety training the CD-ROM has also been used in bridging courses, as reinforcement for first year students, and within our Engineering Technology Instrumentation program. The number of students who have used the CD-ROM is not statistically significant but student feedback on the material is very positive
A maximum-likelihood method for improving faint source flux and color estimates
Flux estimates for faint sources or transients are systematically biased high
because there are far more truly faint sources than bright. Corrections which
account for this effect are presented as a function of signal-to-noise ratio
and the (true) slope of the faint-source number-flux relation. The corrections
depend on the source being originally identified in the image in which it is
being photometered. If a source has been identified in other data, the
corrections are different; a prescription for calculating the corrections is
presented. Implications of these corrections for analyses of surveys are
discussed; the most important is that sources identified at signal-to-noise
ratios of four or less are practically useless.Comment: 9 pp., accepted for publication in PAS
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