80,181 research outputs found
Nondestructive testing of brazed rocket engine components
Report details study made of nondestructive radiographic, ultrasonic, thermographic, and leak test methods used to inspect and evaluate the quality of the various brazed joints in liquid-propellant rocket engine components and assemblies. Descriptions of some of the unique equipment and methods developed are included
From Point Defects in Graphene to Two-Dimensional Amorphous Carbon
While crystalline two-dimensional materials have become an experimental
reality during the past few years, an amorphous 2-D material has not been
reported before. Here, using electron irradiation we create an sp2-hybridized
one-atom-thick flat carbon membrane with a random arrangement of polygons,
including four-membered carbon rings. We show how the transformation occurs
step-by-step by nucleation and growth of low-energy multi-vacancy structures
constructed of rotated hexagons and other polygons. Our observations, along
with first-principles calculations, provide new insights to the bonding
behavior of carbon and dynamics of defects in graphene. The created domains
possess a band gap, which may open new possibilities for engineering
graphene-based electronic devices.Comment: 10 pages, 10 figures including supplementary informatio
Performance of transducers with segmented piezoelectric stacks using materials with high electromechanical coupling coefficient
Underwater acoustic transducers often include a stack of thickness polarized
piezoelectric material pieces of alternating polarity interspersed with
electrodes, bonded together and electrically connected in parallel. The stack
is normally much shorter than a quarter wavelength at the fundamental resonance
frequency, so that the mechanical behavior of the transducer is not affected by
the segmentation. When the transducer bandwidth is less than a half octave, as
has conventionally been the case, stack segmentation has no significant effect
on the mechanical behavior of the device. However, when a high coupling
coefficient material such as PMN-PT is used to achieve a wider bandwidth, the
difference between a segmented stack and a similar piezoelectric section with
electrodes only at the two ends can be significant. This paper investigates the
effects of stack segmentation on the performance of wideband underwater
acoustic transducers, particularly tonpilz transducer elements. Included is
discussion of transducer designs using single crystal piezoelectric material
with high coupling coefficient compared with more traditional PZT ceramics.Comment: 26 pages including 14 figures, one table and one appendi
Public Release of 2dF data from the Fornax Cluster Spectroscopic Survey
Thanks to the 2dF spectrograph on the Anglo-Australian Telescope, we have
recently completed the first stage of a complete spectroscopic survey more than
one order of magnitude larger than any previous study, measuring 7000 spectra
in a 6 sq.deg. area as part of our study of the Fornax Cluster. In this article
we describe the public release of 3600 spectra from our first field. We hope
that this public release will encourage colleagues making surveys for rare
objects to choose these fields, as much of the follow-up spectroscopy that
might be required is available from our data.Comment: To appear in the AAO Newsletter. Data online at
http://astro.ph.unimelb.edu.au/data
Fast ignition of inertial fusion targets by laser-driven carbon beams
Two-dimensional simulations of ion beam driven fast ignition are presented.
Ignition energies of protons with Maxwellian spectrum and carbon ions with
quasimonoenergetic and Maxwellian energy distributions are evaluated. The
effect of the coronal plasma surrounding the compressed deuterium-tritium is
studied for three different fuel density distributions. It is found that quasi-
monoenergetic ions have better coupling with the compressed deuterium-tritium
and substantially lower ignition energies. Comparison of quasimonoenergetic
carbon ions and relativistic electrons as ignitor beams shows similar laser
energy requirements, provided that a laser to quasimonoenergetic carbon ion
conversion efficiency around 10% can be achieved.Comment: 8 pages, 10 figures, published in Physics of Plasma
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