90,803 research outputs found
The Star Formation Histories and Efficiencies of Two Giant HII Regions in M33
photometry is used to re-identify the OB associations which power the
two most luminous HII regions in M33, NGC 604 and NGC 595. There is a
significant difference (2-3 Myr) in the ages of the most recent star formation
episode in these two regions, while NGC 595 also has undergone a prior episode
of star formation (10-15 Myr ago). These data, combined with the presence of
molecular clouds in the heart of NGC 604, suggest that molecular clouds may
survive at least one intense episode of massive star formation. The star
formation efficiencies (mass of stars per mass of gas) of these two HII regions
are up to a factor of 3 larger than the average efficiency in the inner disk of
M33 or in Galactic molecular clouds, but are still only 2-5\%.Comment: 26 pages including 2 figures, uuencoded compressed postscript file
(Figure 1 not available electronically). Accepted to Ap
The electrical response matrix of a regular 2n-gon
Consider a unit-resistive plate in the shape of a regular polygon with 2n
sides, in which even-numbered sides are wired to electrodes and odd-numbered
sides are insulated. The response matrix, or Dirichlet-to-Neumann map, allows
one to compute the currents flowing through the electrodes when they are held
at specified voltages. We show that the entries of the response matrix of the
regular 2n-gon are given by the differences of cotangents of evenly spaced
angles, and we describe some connections with the limiting distributions of
certain random spanning forests.Comment: 10 pages, 4 figures; v2 adds more background informatio
Behavior of composite bolted joints at elevated temperature
Experimental results from an investigation which examines the combined effects of temperature, joint geometry and out-of-plane constraint upon the response of mechanically fastened composite joints are presented. Data are presented for simulated mechanically fastened joint conditions in two laminate configurations fabricated from Hercules AS/3501-6 graphite-epoxy. Strength and failure mode results are presented for the test temperatures of 21 C, 121 C and 177 C and for a range of the geometric parameters W/D and e/D from 3.71 to 7.43 and 1.85 to 3.69, respectively. A hole diameter, D of 5.16 mm was utilized for all tests. Pin bearing tests with out-of-plane constraint were conducted at room temperature only. All elevated temperature data were generated for pin bearing conditions. Ultrasonic C scan inspection of the failed specimens was employed to assess the damage region and to determine failure mode. Comparative data are presented for pin bearing and out-of-plane constraint conditions for the above mentioned joint configurations. The joint under pin loading was modeled by two dimensional finite element methods. Predicted net section strain concentrations were compared with experimental results
Influence of constituent properties and geometric form on behavior of woven fabric reinforced composites
Th potential for woven fabric composite forms to increase the interlaminar strength and toughness properties of laminated composite septems is studied. Experimental and analytical studies were performed on a z-axis fabric
Methods of resistance estimation in permanent magnet synchronous motors for real-time thermal management
Real-time thermal management of electrical ma- chines relies on sufficiently accurate indicators of internal tem- perature. One indicator of temperature in a permanent-magnet synchronous motor (PMSM) is the stator winding resistance. Detection of PMSM winding resistance in the literature has been made on machines with relatively high resistances, where the resistive voltage vector is significant under load. This paper describes two techniques which can be applied to detect the winding resistance, through ‘Fixed Angle’ and ‘Fixed Mag- nitude’ current injection. Two further methods are described which discriminate injected current and voltages from motoring currents and voltages: ‘Unipolar’ and ‘Bipolar’ separation. These enable the resistance to be determined, and hence the winding temperature in permanent-magnet machines. These methods can be applied under load, and in a manner that does not disturb motor torque or speed. The method distinguishes between changes in the electro-motive force (EMF) constant and the resistive voltage. This paper introduces the techniques, whilst a companion paper covers the application of one of the methods to a PMSM drive system
Induced scattering of short radio pulses
Effect of the induced Compton and Raman scattering on short, bright radio
pulses is investigated. It is shown that when a single pulse propagates through
the scattering medium, the effective optical depth is determined by the
duration of the pulse but not by the scale of the medium. The induced
scattering could hinder propagation of the radio pulse only if close enough to
the source a dense enough plasma is presented. The induced scattering within
the relativistically moving source places lower limits on the Lorentz factor of
the source. The results are applied to the recently discovered short
extragalactic radio pulse.Comment: submitted to Ap
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