17,741 research outputs found
Scintillation Caustics in Planetary Occultation Light Curves
We revisit the GSC5249-01240 light curve obtained during its occultation by
Saturn's North polar region. In addition to refractive scintillations, the
power spectrum of intensity fluctuations shows an enhancement of power between
refractive and diffractive regimes. We identify this excess power as due to
high amplitude spikes in the light curve and suggest that these spikes are due
to caustics associated with ray crossing situations. The flux variation in
individual spikes follows the expected caustic behavior, including diffraction
fringes which we have observed for the first time in a planetary occultation
light curve. The presence of caustics in scintillation light curves require an
inner scale cut off to the power spectrum of underlying density fluctuations
associated with turbulence. Another possibility is the presence of gravity
waves in the atmosphere. While occultation light curves previously showed the
existence of refractive scintillations, a combination of small projected
stellar size and a low relative velocity during the event have allowed us to
identify caustics in this occultation. This has led us to re-examine previous
data sets, in which we have also found likely examples of caustics.Comment: 4 pages, 3 figures; ApJL submitte
Linear and non-linear theory of a parametric instability of hydrodynamic warps in Keplerian discs
We consider the stability of warping modes in Keplerian discs. We find them
to be parametrically unstable using two lines of attack, one based on
three-mode couplings and the other on Floquet theory. We confirm the existence
of the instability, and investigate its nonlinear development in three
dimensions, via numerical experiment. The most rapidly growing non-axisymmetric
disturbances are the most nearly axisymmetric (low m) ones. Finally, we offer a
simple, somewhat speculative model for the interaction of the parametric
instability with the warp. We apply this model to the masing disc in NGC 4258
and show that, provided the warp is not forced too strongly, parametric
instability can fix the amplitude of the warp.Comment: 14 pages, 6 figures, revised version with appendix added, to be
published in MNRA
Time to publication for NIHR HTA programme-funded research: a cohort study
ObjectiveTo assess the time to publication of primary research and evidence syntheses funded by the National Institute for Health Research (NIHR) Health Technology Assessment (HTA) Programme published as a monograph in Health Technology Assessment and as a journal article in the wider biomedical literature.Study designRetrospective cohort study.SettingPrimary research and evidence synthesis projects funded by the HTA Programme were included in the cohort if they were registered in the NIHR research programmes database and was planned to submit the draft final report for publication in Health Technology Assessment on or before 9 December 2011.Main outcome measuresThe median time to publication and publication at 30?months in Health Technology Assessment and in an external journal were determined by searching the NIHR research programmes database and HTA Programme website.ResultsOf 458 included projects, 184 (40.2%) were primary research projects and 274 (59.8%) were evidence syntheses. A total of 155 primary research projects had a completion date; the median time to publication was 23?months (26.5 and 35.5?months to publish a monograph and to publish in an external journal, respectively) and 69% were published within 30?months. The median time to publication of HTA-funded trials (n=126) was 24?months and 67.5% were published within 30?months. Among the evidence syntheses with a protocol online date (n=223), the median time to publication was 25.5?months (28?months to publication as a monograph), but only 44.4% of evidence synthesis projects were published in an external journal. 65% of evidence synthesis studies had been published within 30.0?months.ConclusionsResearch funded by the HTA Programme publishes promptly. The importance of Health Technology Assessment was highlighted as the median time to publication was 9?months shorter for a monograph than an external journal article
The development of thermally stable adhesives for titanium alloy and boron composite structures
Developing thermally stable adhesives for bonding titanium alloy and boron composite substrate
Delayed phlegmon with gallstone fragments masquerading as soft tissue sarcoma.
Complications from lost gallstones after cholecystectomy are rare but varied from simple perihepatic abscess to empyema and expectoration of gallstones. Gallstone complications have been reported in nearly every organ system, although reports of malignant masquerade of retained gallstones are few. We present the case of an 87-year-old woman with a flank soft tissue tumor 4 years after laparoscopic cholecystectomy. The initial clinical, radiographic and biopsy findings were consistent with soft tissue sarcoma (STS), but careful review of her case in multidisciplinary conference raised the suspicion for retained gallstones rather than STS. The patient was treated with incisional biopsy/drainage of the mass, and gallstones were retrieved. The patient recovered completely without an extensive resectional procedure, emphasizing the importance of multidisciplinary sarcoma care to optimize outcomes for potential sarcoma patients
Reconnection in Marginally Collisionless Accretion Disk Coronae
We point out that a conventional construction placed upon observations of
accreting black holes, in which their nonthermal X-ray spectra are produced by
inverse comptonization in a coronal plasma, suggests that the plasma is
marginally collisionless. Recent developments in plasma physics indicate that
fast reconnection takes place only in collisionless plasmas. As has recently
been suggested for the Sun's corona, such marginal states may result from a
combination of energy balance and the requirements of fast magnetic
reconnection.Comment: Revised in response to referee. Accepted ApJ. 11 pp., no figures.
Uses aastex 5.0
Experimental evidence of high-resolution ghost imaging and ghost diffraction with classical thermal light
High-resolution ghost image and ghost diffraction experiments are performed
by using a single source of thermal-like speckle light divided by a beam
splitter. Passing from the image to the diffraction result solely relies on
changing the optical setup in the reference arm, while leaving untouched the
object arm. The product of spatial resolutions of the ghost image and ghost
diffraction experiments is shown to overcome a limit which was formerly thought
to be achievable only with entangled photons.Comment: 5 pages, 4 figure
Model-independent measurements of the sodium magneto-optical trap's excited-state population
We present model-independent measurements of the excited-state population of
atoms in a sodium (Na) magneto-optical trap (MOT) using a hybrid ion-neutral
trap composed of a MOT and a linear Paul trap (LPT). We photoionize excited Na
atoms trapped in the MOT and use two independent methods to measure the
resulting ions: directly by trapping them in our LPT, and indirectly by
monitoring changes in MOT fluorescence. By measuring the ionization rate via
these two independent methods, we have enough information to directly determine
the population of MOT atoms in the excited-state. The resulting measurement
reveals that there is a range of trapping-laser intensities where the
excited-state population of atoms in our MOT follows the standard two-level
model intensity-dependence. However, an experimentally determined effective
saturation intensity must be used instead of the theoretically predicted value
from the two-level model. We measured the effective saturation intensity to be
for the type-I Na MOT and
for the type-II Na MOT,
approximately 1.7 and 3.6 times the theoretical estimate, respectively. Lastly,
at large trapping-laser intensities, our experiment reveals a clear departure
from the two-level model at a critical intensity that we believe is due to a
state-mixing effect, whose critical intensity can be determined by a simple
power broadening model.Comment: 10 pages, 8 figure
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