1,751 research outputs found
Phase resolved PLIF and chemiluminescence for measuring combustion dynamics
Transient behavior of combustion systems has long been a subject of both fundamental and practical concerns. Extreme cases of very rapid changes include the ignition of reacting mixtures and detonation. At the other extreme is a wide range of quasi-steady changes of behavior, for example adjustments of the operating point of a combustion chamber. Between the limiting cases of 'infinitely fast' and 'infinitesimally slow' lie important fundamental problems of time-dependent behavior and a wide array
of practical applications. Among the latter are combustion instabilities and their active control, a primary motivation for the work reported in this paper. Owing to the
complicated chemistry, chemical kinetics and flow dynamics of actual combustion systems, numerical simulations of their behavior remains in a relatively primitive state.
Even as that situation continually improves, it is an essential part of the field that methods of measuring true dynamical behavior be developed to provide results having both fine spatial resolution and accuracy in time. This paper is a progress report of recent research
carried out in the Jet Propulsion Center of the California Institute of Technology
The Discovery of an X-ray/UV Stellar Flare from the Late-K/Early-M Dwarf LMC 335
We report the discovery of an X-ray/UV stellar flare from the source LMC 335,
captured by XMM-Newton in the field of the Large Magellanic Cloud. The flare
event was recorded continuously in X-ray for its first 10 hours from the
precursor to the late decay phases. The observed fluxes increased by more than
two orders of magnitude at its peak in X-ray and at least one in the UV as
compared to quiescence. The peak 0.1-7.0 keV X-ray flux is derived from the
two-temperature APEC model to be ~(8.4 +/- 0.6) x 10^-12 erg cm-2 s-1.
Combining astrometric information from multiple X-ray observations in the
quiescent and flare states, we identify the NIR counterpart of LMC 335 as the
2MASS source J05414534-6921512. The NIR color relations and spectroscopic
parallax characterize the source as a Galactic K7-M4 dwarf at a foreground
distance of (100 - 264) pc, implying a total energy output of the entire event
of ~(0.4 - 2.9) x 10^35 erg. This report comprises detailed analyses of this
late-K / early-M dwarf flare event that has the longest time coverage yet
reported in the literature. The flare decay can be modeled with two exponential
components with timescales of ~28 min and ~4 hours, with a single component
decay firmly ruled out. The X-ray spectra during flare can be described by two
components, a dominant high temperature component of ~40-60MK and a low
temperature component of ~10MK, with a flare loop length of about 1.1-1.3
stellar radius.Comment: 35 pages, 6 figures, 5 tables, accepted for publication in Ap
INJURY INCIDENCE, DISTRIBUTION, AND SEVERITY DURING A MARATHON TRAINING SEASON AND THE IMPLICATIONS
Marathon runners and their coaches are concerned about the potential for injury during an individual season. No published studies of running injuries address this training season as a meaningful entity. This study reports the incidence of injury and the distribution of injuries for runners (n=75) on two established marathon training teams during an individual season. An injury was defined as affecting seven consecutive days or three consecutive workouts. The incidence/risks of overuse injuries, for marathon runners in a single season were found to be: anterior knee pain (20%), iliotibial band syndrome (29%), plantar fasciitis (1%), Achilles tendonitis (9%) shin splints (16%) and stress fractures (4%). This risk, overall injury distribution, severity and length of longest run prior to presentation of injury are of interest to runners, coaches and biomechanists
A Chandra View of The Morphological And Spectral Evolution of Supernova Remnant 1987A
We present an update on the results of our monitoring observations of the
X-ray remnant of supernova (SN) 1987A with the {\it Chandra X-Ray Observatory}.
As of 2002 December, we have performed a total of seven observations of SN
1987A. The high angular resolution images from the latest data reveal
developments of new X-ray bright spots in the northwestern and the southwestern
portions of the remnant as well as changes on the eastern side. The latest
0.5-2 keV band flux ( 6 10 ergs cm
s) is four times brighter than three years earlier. The overall X-ray
emission is primarily from the blast wave shock with 2.4 keV. As
the blast wave approaches the dense circumstellar material, the contribution
from the decelerated slow shock ( 0.22 keV) to the observed X-ray
emission is becoming significant. The increase of this slow shock contribution
over the last two years is particularly noticeable in the western half of the
remnant. These results indicate that the shock front is now reaching the main
body of the inner circumstellar ring. Based on the best-fit two-shock spectral
model, we derive approximate densities of the X-ray-emitting regions (
235 cm for the fast shock and 7500 cm for the
slow shock). We obtain an upper limit on the observed X-ray luminosity of any
embedded point source ( 1.5 10 ergs s) in the
210 keV band. The X-ray remnant continues to expand linearly at a rate of
4167 km s.Comment: 22 pages (ApJ preprint style), 7 Figures, Accepted by ApJ (scheduled
on July 20, 2004), for high-quality Fig 1 and Fig 2, please contact
[email protected]
A Systematic Review of the Core Components of Language Learning Strategy Research in Taiwan
As the broader field of individual differences in second/foreign language learning has grown tremendously over the past few decades, its subfields have expanded with a similar intensity. Language learning strategies (LLS) is one such area. Developments have been made regarding the scope and methodology of LLS research, especially. While there have been a number of reviews of the field’s output, few have targeted research in a specific context. With this in mind, the current study offers a situated view of LLS research in Taiwan. It focuses on three core components that are essential to empirical research: (a) contexts and participant characteristics; (b) theoretical-conceptual aspects; and (c) methodological characteristics. Drawing on journal articles systematically collected from major databases and reviews conducted by multiple researchers to ensure reliability and to minimize bias, we provide an overview of the field as it has manifested in Taiwan. Findings from select studies are also discussed. In doing so, this article makes connections between LLS research in Taiwan and the larger, global context, with implications for "the road ahead." We hope it will be a valuable resource for anyone interested in reading about and/or conducting LLS research in this setting and others
The Ultraluminous X-ray Sources near the Center of M82
We report the identification of a recurrent ultraluminous X-ray source (ULX),
a highly absorbed X-ray source (possibly a background AGN), and a young
supernova remnant near the center of the starburst galaxy M82. From a series of
Chandra observations taken from 1999 to 2005, we found that the transient ULX
first appeared in 1999 October. The source turned off in 2000 January, but
later reappeared and has been active since then. The X-ray luminosity of this
source varies from below the detection level (~2.5e38 erg/s) to its active
state in between ~7e39 erg/s and 1.3e40 erg/s (in the 0.5-10 keV energy band)
and shows unusual spectral changes. The X-ray spectra of some Chandra
observations are best fitted with an absorbed power-law model with photon index
ranging from 1.3 to 1.7. These spectra are similar to those of Galactic black
hole binary candidates seen in the low/hard state except that a very hard
spectrum was seen in one of the observations. By comparing with near infrared
images taken with the Hubble Space Telescope, the ULX is found to be located
within a young star cluster. Radio imaging indicates that it is associated with
a H II region. We suggest that the ULX is likely to be a > 100 solar mass
intermediate-mass black hole in the low/hard state. In addition to the
transient ULX, we also found a highly absorbed hard X-ray source which is
likely to be an AGN and an ultraluminous X-ray emitting young supernova remnant
which may be related to a 100-year old gamma-ray burst event, within 2 arcsec
of the transient ULX.Comment: 9 pages, 8 figures. Accepted for publication in Ap
Adaptive algorithm for increasing image rejection ratio in Low-IF receivers
An adaptive method for compensating mismatch effect on an I/Q demodulation is presented. It is based on the correlation between the desired and image band that appears when there is a mismatch in any branch. The proposed algorithm is specially intended for narrowband low-IF receivers. No calibration source is neccesary. Up to 91 dB of image rejection ratio is achieved with narrow-bandwidth signals (up to 6.25% of the sampling frequency)
Helping to distinguish primary from secondary transfer events for trace DNA.
DNA is routinely recovered in criminal investigations. The sensitivity of laboratory equipment and DNA profiling kits means that it is possible to generate DNA profiles from very small amounts of cellular material. As a consequence, it has been shown that DNA we detect may not have arisen from a direct contact with an item, but rather through one or more intermediaries. Naturally the questions arising in court, particularly when considering trace DNA, are of how DNA may have come to be on an item. While scientists cannot directly answer this question, forensic biological results can help in discriminating between alleged activities. Much experimental research has been published showing the transfer and persistence of DNA under varying conditions, but as of yet the results of these studies have not been combined to deal with broad questions about transfer mechanisms. In this work we use published data and Bayesian networks to develop a statistical logical framework by which questions of transfer mechanism can be approached probabilistically. We also identify a number of areas where further work could be carried out in order to improve our knowledge base when helping to address questions about transfer mechanisms. Finally, we apply the constructed Bayesian network to ground truth known data to determine if, with current knowledge, there is any power in DNA quantities to distinguish primary and secondary transfer events
High Resolution X-Ray Imaging of the Center of IC342
We presented the result of a high resolution (FWHM~0.5'') 12 ks Chandra HRC-I
observation of the starburst galaxy IC342 taken on 2 April 2006. We identified
23 X-ray sources within the central 30' x 30' region of IC342. Our HRC-I
observation resolved the historical Ultraluminous X-ray sources (ULX), X3, near
the nucleus into 2 sources, namely C12 and C13, for the first time. The
brighter source C12, with L(0.08-10keV)=(6.66\pm0.45)\times10^{38}ergs^-1, was
spatially extended (~82 pc x 127 pc). From the astrometric registration of the
X-ray image, C12 was at R.A.=03h:46m:48.43s, decl.=+68d05m47.45s, and was
closer to the nucleus than C13. Thus we concluded that source was not an ULX
and must instead be associated with the nucleus. The fainter source C13, with
L(0.08-10keV)=(5.1\pm1.4) x 10^{37}ergs^-1 was consistent with a point source
and located $6.51'' at P.A. 240 degree of C12.
We also analyzed astrometrically corrected optical Hubble Space Telescope and
radio Very Large Array images, a comparison with the X-ray image showed
similarities in their morphologies. Regions of star formation within the
central region of IC342 were clearly visible in HST H alpha image and this was
the region where 3 optical star clusters and correspondingly our detected X-ray
source C12 were observed. We found that a predicted X-ray emission from
starburst was very close to the observed X-ray luminosity of C12, suggesting
that nuclear X-ray emission in IC342 was dominated by starburst. Furthermore,
we discussed the possibility of AGN in the nucleus of IC342. Although our data
was not enough to give a firm existence of an AGN, it could not be discarded.Comment: 29 page, 8 figures, accepted by Ap
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