5,031 research outputs found
Prion degradation pathways: Potential for therapeutic intervention
Prion diseases are fatal neurodegenerative disorders. Pathology is closely linked to the misfolding of native cellular PrP(C) into the disease-associated form PrP(Sc) that accumulates in the brain as disease progresses. Although treatments have yet to be developed, strategies aimed at stimulating the degradation of PrP(Sc) have shown efficacy in experimental models of prion disease. Here, we describe the cellular pathways that mediate PrP(Sc) degradation and review possible targets for therapeutic intervention. This article is part of a Special Issue entitled 'Neuronal Protein'
Triton's surface age and impactor population revisited in light of Kuiper Belt fluxes: Evidence for small Kuiper Belt objects and recent geological activity
Neptune's largest satellite, Triton, is one of the most fascinating and
enigmatic bodies in the solar system. Among its numerous interesting traits,
Triton appears to have far fewer craters than would be expected if its surface
was primordial. Here we combine the best available crater count data for Triton
with improved estimates of impact rates by including the Kuiper Belt as a
source of impactors. We find that the population of impactors creating the
smallest observed craters on Triton must be sub-km in scale, and that this
small-impactor population can be best fit by a differential power-law size
index near -3. Such results provide interesting, indirect probes of the unseen
small body population of the Kuiper Belt. Based on the modern, Kuiper Belt and
Oort Cloud impactor flux estimates, we also recalculate estimated ages for
several regions of Triton's surface imaged by Voyager 2, and find that Triton
was probably active on a time scale no greater than 0.1-0.3 Gyr ago (indicating
Triton was still active after some 90% to 98% of the age of the solar system),
and perhaps even more recently. The time-averaged volumetric resurfacing rate
on Triton implied by these results, 0.01 km yr or more, is likely
second only to Io and Europa in the outer solar system, and is within an order
of magnitude of estimates for Venus and for the Earth's intraplate zones. This
finding indicates that Triton likely remains a highly geologically active world
at present, some 4.5 Gyr after its formation. We briefly speculate on how such
a situation might obtain.Comment: 14 pages (TeX), plus 2 postscript figures Stern & McKinnon, 2000, AJ,
in pres
External liquid-spray cooling of turbine blades Patent
External device for liquid spray cooling of gas turbine blade
Flight and tunnel test results of the MDC mechanical jet noise suppressor nozzle
The flight and wind tunnel tests to determine the acoustic and performance effects of a mechanical jet noise suppressor nozzle mounted on a Viper engine of an HS-125 airplane are discussed. Flyover noise measurements were made with microphones mounted on top of a 137.5 m bridge tower. Seven nozzle configurations including two references nozzles, two suppressors, and three ejector inlets were tested. The suppressor nozzle of interest for an advanced supersonic transport, the suppressor/treated ejector, achieved a measured noise reduction of 14 EPNdB relative to a conventional conical reference nozzle at the highest pressure ratio tested (approximately 2.5). The unique engine nacelle, flight hardware, and nacelles from the HS-125 flight test program, combined with a simulated HS-125 fuselage were windtunnel tested. Both propulsion and acoustic data were recorded. Preliminary thrust data results from the wind tunnel tests are summarized and compared to other mechanical suppressor test results. The test results indicate that a noise reduction of at least 16 EPNdB would be possible for the suppressor/ejector nozzle scaled to typical AST engine size with a 5% thrust loss at a typical takeoff climb speed
The Transition between Nonorthogonal Polarization Modes in PSR B2016+28 at 1404 MHz
Polarization observations of the radio emission from PSR B2016+28 at 1404 MHz
reveal properties that are consistent with two, very different, interpretations
of the pulsar's viewing geometry. The pulsar's average polarization properties
show a rapid change in position angle (PA) near the pulse center, suggesting
that the observer's sightline nearly intersects the star's magnetic pole. But
single pulse, polarization observations of the pulsar show nearly orthogonal
modes of polarization following relatively flat and parallel PA trajectories
across the pulse, suggesting that the sightline is far from the pole.
Additionally, PA histograms reveal a "modal connecting bridge", of unknown
origin, joining the modal PA trajectories over much of the pulse and following
the rapid PA change shown in the average data. The nonorthogonality of
polarization modes is incorporated in a statistical model of radio polarization
to account for the deviations from mode orthogonality that are observed in the
pulsar. The model is used to interpret the rapid PA change and modal connecting
bridge as a longitudinally-resolved transition between modes of nonorthogonal
polarization. Thus, the modal PA trajectories are argued to reflect the
pulsar's true viewing geometry. This interpretation is consistent with the
pulsar's morphological classification, preserves the Radhakrishnan & Cooke
model of pulsar radio emission, and avoids the complication that the modal
connecting bridge might be produced by some other emission mechanism. The
statistical model's ability to simulate the rich variety of polarization
properties observed in the emission lends additional support to the model's
applicability and its underlying assumption that the polarization modes occur
simultaneously.Comment: Accepted for publication in Ap
Ellipticity and Deviations from Orthogonality in the Polarization Modes of PSR B0329+54
We report on an analysis of the polarization of single pulses of PSR B0329+54
at 328 MHz. We find that the distribution of polarization orientations in the
central component diverges strongly from the standard picture of orthogonal
polarization modes (OPMs), making a remarkable partial annulus on the Poincare
sphere. A second, tightly clustered region of density appears in the opposite
hemisphere, at a point antipodal to the centre of the annulus. We argue that
this can be understood in terms of birefringent alterations in the relative
phase of two elliptically polarized propagation modes in the pulsar
magnetosphere (i.e. generalised Faraday rotation). The ellipticity of the modes
implies a significant charge density in the plasma, while the presence of both
senses of circular polarization, and the fact that only one mode shows the
effect, supports the view that refracted ordinary-mode rays are involved in the
production of the annulus. At other pulse longitudes the polarization
(including the circular component) is broadly consistent with an origin in
elliptical OPMs, shown here quantitatively for the first time, however
considerable non-orthogonal contributions serve to broaden the orientation
distribution in an isotropic manner.Comment: 13 pages, 5 figures, to appear in A&
Control of airplanes at low speeds
Loss of control over the orientation of an airplane as the incidence approaches and enters the region of stalled flight is a prolific cause of serious accidents. This report discusses methods of landing at slow speeds approaching stall
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