1,102 research outputs found
Structural modeling of aircraft tires
A theoretical and experimental investigation of the feasibility of determining the mechanical properties of aircraft tires from small-scale model tires was accomplished. The theoretical results indicate that the macroscopic static and dynamic mechanical properties of aircraft tires can be accurately determined from the scale model tires although the microscopic and thermal properties of aircraft tires can not. The experimental investigation was conducted on a scale model of a 40 x 12, 14 ply rated, type 7 aircraft tire with a scaling factor of 8.65. The experimental results indicate that the scale model tire exhibited the same static mechanical properties as the prototype tire when compared on a dimensionless basis. The structural modeling concept discussed in this report is believed to be exact for mechanical properties of aircraft tires under static, rolling, and transient conditions
Assertion, Uniqueness and Epistemic Hypocrisy
Pascal Engel (2008) has insisted that a number of notable strategies for rejecting the knowledge norm of assertion are put forward on the basis of the wrong kinds of reasons. A central aim of this paper will be to establish the contrast point: I argue that one very familiar strategy for defending the knowledge norm of assertionâviz., that it is claimed to do better in various respects than its competitors (e.g. the justification and the truth norms)â relies on a presupposition that is shown to be ultimately under motivated. That presupposition is the uniqueness thesisâthat there is a unique epistemic rule for assertion, and that such a rule
will govern assertions uniformly. In particular, the strategy I shall take here will be to challenge the sufficiency leg of the knowledge norm in a way that at the same time counts against Williamsonâs (2000) own rationale for the uniqueness thesis. However, rather than to challenge the sufficiency leg of the knowledge norm via the familiar style of âexpert opinionâ and, more generally, âsecond-hand knowledgeâ cases (e.g. Lackey (2008)), a strategy that has recently been called into question by Benton (2014), Iâll instead advance a very different line of argument against the sufficiency thesis, one which turns on a phenomenon I call epistemic hypocrisy
High-Energy Gamma-Ray Observations of Two Young, Energetic Radio Pulsars
We present results of Compton Gamma-Ray Observatory EGRET observations of the
unidentified high-energy gamma-ray sources 2EG J1049-5847 (GEV J1047-5840, 3EG
J1048-5840) and 2EG J1103-6106 (3EG J1102-6103). These sources are spatially
coincident with the young, energetic radio pulsars PSRs B1046-58 and
J1105-6107, respectively. We find evidence for an association between PSR
B1046-58 and 2EG J1049-5847. The gamma-ray pulse profile, obtained by folding
time-tagged photons having energies above 400 MeV using contemporaneous radio
ephemerides, has probability of arising by chance of 1.2E-4 according to the
binning-independent H-test. A spatial analysis of the on-pulse photons reveals
a point source of equivalent significance 10.2 sigma. Off-pulse, the
significance drops to 5.8 sigma. Archival ASCA data show that the only hard
X-ray point source in the 95% confidence error box of the gamma-ray source is
spatially coincident with the pulsar within the 1' uncertainty (Pivovaroff,
Kaspi & Gotthelf 1999). The double peaked gamma-ray pulse morphology and
leading radio pulse are similar to those seen for other gamma-ray pulsars and
are well-explained in models in which the gamma-ray emission is produced in
charge-depleted gaps in the outer magnetosphere. The inferred pulsed gamma-ray
flux above 400 MeV, (2.5 +/- 0.6) x 10E-10 erg/cm^2/s, represents 0.011 +/-
0.003 of the pulsar's spin-down luminosity, for a distance of 3 kpc and 1 sr
beaming. For PSR J1105-6107, light curves obtained by folding EGRET photons
using contemporaneous radio ephemerides show no significant features. We
conclude that this pulsar converts less than 0.014 of its spin-down luminosity
into E > 100 MeV gamma-rays beaming in our direction (99% confidence), assuming
a distance of 7 kpc, 1 sr beaming and a duty cycle of 0.5.Comment: Accepted for publication in the Astrophysical Journa
RXTE Monitoring of the Anomalous X-ray Pulsar 1E 1048.1-5937
We report on long-term monitoring of the anomalous X-ray pulsar 1E
1048.1-5937 using the Rossi X-ray Timing Explorer. This pulsar's timing
behavior is different from that of other AXPs. In particular, the pulsar shows
significant deviations from simple spin-down such that phase-coherent timing
has not been possible over time spans longer than a few months. We show that in
spite of the rotational irregularities, the pulsar exhibits neither pulse
profile changes nor large pulsed flux variations. We discuss the implications
of our results for AXP models. We suggest that 1E 1048.1-5937 may be a
transition object between the soft gamma-ray repeater and AXP populations, and
the AXP most likely to one day undergo an outburst.Comment: 6 pages, to appear in Proceedings of the 20th Texas Symposium on
Relativistic Astrophysics, AIP pres
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