1,655 research outputs found
Nondestructive assessment of penetration of electron-beam welds
Empirical method correlates penetration of an electron-beam weld with external measurements of the weld. Empirical polygon accurately confirms full-penetration welds while a second, larger polygon provides for penetration of welds near the tip
Liquid-immersible electrostatic ultrasonic transducer
A broadband megahertz range electrostatic acoustic transducer for use in a liquid environment is described. A liquid tight enclosure includes a metallic conducting membrane as part of its outside surface and has a means inside the liquid tight enclosure for applying a tension to the membrane and for mounting an electrode such that the flat end of the electrode is aproximately parallel to the membrane. The invention includes structure and a method for ensuring that the membrane and the flat end of the electrode are exactly parallel and a fixed predetermined distance from each other
COLD-SAT feasibility study safety analysis
The Cryogenic On-orbit Liquid Depot-Storage, Acquisition, and Transfer (COLD-SAT) satellite presents some unique safety issues. The feasibility study conducted at NASA-Lewis desired a systems safety program that would be involved from the initial design in order to eliminate and/or control the inherent hazards. Because of this, a hazards analysis method was needed that: (1) identified issues that needed to be addressed for a feasibility assessment; and (2) identified all potential hazards that would need to be controlled and/or eliminated during the detailed design phases. The developed analysis method is presented as well as the results generated for the COLD-SAT system
The Raman Spectra of Carbon and Silicon Tetrafluorides
We have photographed the Raman spectra for the tetrafluorides of carbon and silicon in both the liquid and gaseous states. The results are presented in Table I together with the Raman frequencies for CCl4 for purposes of comparison
XUV Frequency Combs via Femtosecond Enhancement Cavities
We review the current state of tabletop extreme ultraviolet (XUV) sources
based on high harmonic generation (HHG) in femtosecond enhancement cavities
(fsEC). Recent developments have enabled generation of high photon flux (1014
photons/sec) in the XUV, at high repetition rates (>50 MHz) and spanning the
spectral region from 40 nm - 120 nm. This level of performance has enabled
precision spectroscopy with XUV frequency combs and promises further
applications in XUV spectroscopic and photoemission studies. We discuss the
theory of operation and experimental details of the fsEC and XUV generation
based on HHG, including current technical challenges to increasing the photon
flux and maximum photon energy produced by this type of system. Current and
future applications for these sources are also discussed.Comment: invited review article, 38 page
VUV frequency combs from below-threshold harmonics
Recent demonstrations of high-harmonic generation (HHG) at very high
repetition frequencies (~100 MHz) may allow for the revolutionary transfer of
frequency combs to the vacuum ultraviolet (VUV). This advance necessitates
unifying optical frequency comb technology with strong-field atomic physics.
While strong-field studies of HHG have often focused on above-threshold
harmonic generation (photon energy above the ionization potential), for VUV
frequency combs an understanding of below-threshold harmonic orders and their
generation process is crucial. Here we present a new and quantitative study of
the harmonics 7-13 generated below and near the ionization threshold in xenon
gas. We show multiple generation pathways for these harmonics that are
manifested as on-axis interference in the harmonic yield. This discovery
provides a new understanding of the strong-field, below-threshold dynamics
under the influence of an atomic potential and allows us to quantitatively
assess the achievable coherence of a VUV frequency comb generated through below
threshold harmonics. We find that under reasonable experimental conditions
temporal coherence is maintained. As evidence we present the first explicit VUV
frequency comb structure beyond the 3rd harmonic.Comment: 16 pages, 4 figures, 1 tabl
Optical Behavior of GRB 061121 around its X-Ray Shallow Decay Phase
Aims. We report on a detailed study of the optical afterglow of GRB 061121
with our original time-series photometric data. In conjunction with X-ray
observations, we discuss the origin of its optical and X-ray afterglows.
Methods. We observed the optical afterglow of Swift burst GRB 061121 with the
Kanata 1.5-m telescope at Higashi-Hiroshima Observatory. Our observation covers
a period just after an X-ray plateau phase. We also performed deep imaging with
the Subaru telescope in 2010 in order to estimate the contamination of the host
galaxy. Results. In the light curve, we find that the optical afterglow also
exhibited a break as in the X-ray afterglow. However, our observation suggests
a possible hump structure or a flattening period before the optical break in
the light curve. There is no sign of such a hump in the X-ray light curve.
Conclusions. This implies that the emitting region of optical was distinct from
that of X-rays. The hump in the optical light curve was possibly caused by the
passage of the typical frequency of synchrotron emission from another forward
shock distinct from the early afterglow. The observed decay and spectral
indices are inconsistent with the standard synchrotron-shock model. Hence, the
observation requires a change in microphysical parameters in the shock region
or a prior activity of the central engine. Alternatively, the emission during
the shallow decay phase may be a composition of two forward shock emissions, as
indicated by the hump structure in the light curve.Comment: 8 pages, including 4 figures and 2 tables. Accepted to A&
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