14,316 research outputs found
Femtosecond pulses and dynamics of molecular photoexcitation: RbCs example
We investigate the dynamics of molecular photoexcitation by unchirped
femtosecond laser pulses using RbCs as a model system. This study is motivated
by a goal of optimizing a two-color scheme of transferring
vibrationally-excited ultracold molecules to their absolute ground state. In
this scheme the molecules are initially produced by photoassociation or
magnetoassociation in bound vibrational levels close to the first dissociation
threshold. We analyze here the first step of the two-color path as a function
of pulse intensity from the low-field to the high-field regime. We use two
different approaches, a global one, the 'Wavepacket' method, and a restricted
one, the 'Level by Level' method where the number of vibrational levels is
limited to a small subset. The comparison between the results of the two
approaches allows one to gain qualitative insights into the complex dynamics of
the high-field regime. In particular, we emphasize the non-trivial and
important role of far-from-resonance levels which are adiabatically excited
through 'vertical' transitions with a large Franck-Condon factor. We also point
out spectacular excitation blockade due to the presence of a quasi-degenerate
level in the lower electronic state. We conclude that selective transfer with
femtosecond pulses is possible in the low-field regime only. Finally, we extend
our single-pulse analysis and examine population transfer induced by coherent
trains of low-intensity femtosecond pulses.Comment: 25 pages, 12 figure
Prevalence of X-ray variability in the Chandra Deep Field South
We studied the X-ray variability of sources detected in the Chandra Deep
Field South (Giacconi et al. 2002), nearly all of which are low to moderate z
AGN (Tozzi et al. 2001). We find that 45% of the sources with >100 counts
exhibit significant variability on timescales ranging from a day up to a year.
The fraction of sources found to be variable increases with observed flux,
suggesting that >90% of all AGNs possess intrinsic variability. We also find
that the fraction of variable sources appears to decrease with increasing
intrinsic absorption; a lack of variability in hard, absorbed AGNs could be due
to an increased contribution of reflected X-rays to the total flux. We do not
detect significant spectral variability in the majority (~70%) of our sources.
In half of the remaining 30%, the hardness ratio is anti-correlated with flux,
mimicking the high/soft-low/hard states of galactic sources. The X-ray
variability appears anti-correlated with the luminosity of the sources, in
agreement with previous studies. High redshift sources, however, have larger
variability amplitudes than expected from extrapolations of their low-z
counterparts, suggesting a possible evolution in the accretion rate and/or size
of the X-ray emitting region. Finally, we discuss some effects that may produce
the observed decrease in the fraction of variable sources from z=0.5 out to
z=2.Comment: 24 pages, including 15 figures and 1 table. In press on Ap
The Language Archiving Technology domain
The Max Planck Institute for Psycholinguistics (MPI) manages an archive of linguistic research data with a current size of almost 20 Terabytes. Apart from in-house researchers other projects also store their data in the archive, most notably the Documentation of Endangered Languages (DoBeS) projects. The archive is available online and can be accessed by anybody with Internet access. To be able to manage this large amount of data the MPI's technical group has developed a software suite called Language Archiving Technology (LAT) that on the one hand helps researchers and archive managers to manage the data and on the other hand helps users in enriching their primary data with additional layers. All the MPI software is Java-based and developed according to open source principles (GNU, 2007). All three major operating systems (Windows, Linux, MacOS) are supported and the software works similarly on all of them. As the archive is online, many of the tools, especially the ones for accessing the data, are browser based. Some of these browser-based tools make use of Adobe Flex to create nice-looking GUIs. The LAT suite is a complete set of management and enrichment tools, and given the interaction between the tools the result is a complete LAT software domain. Over the last 10 years, this domain has proven its functionality and use, and is being deployed to servers in other institutions. This deployment is an important step in getting the archived resources back to the members of the speech communities whose languages are documented. In the paper we give an overview of the tools of the LAT suite and we describe their functionality and role in the integrated process of archiving, management and enrichment of linguistic data
Evidence for RNA transport in rat optic nerve
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/66066/1/j.1471-4159.1969.tb08995.x.pd
Dimensional Changes of Upper Airway after Rapid Maxillary Expansion: A Prospective Cone-beam Computed Tomography Study
Introduction: The aim of this prospective study was to use cone-beam computed tomography to assess the dimensional changes of the upper airway in orthodontic patients with maxillary constriction treated by rapid maxillary expansion.
Methods: Fourteen orthodontic patients (mean age, 12.9 years; range, 9.7-16 years) were recruited. The patients with posterior crossbite and constricted maxilla were treated with rapid maxillary expansion as the initial part of their comprehensive orthodontic treatments. Before and after rapid maxillary expansion conebeam computed tomography scans were taken to measure the retropalatal and retroglossal airway changes in terms of volume, and sagittal and cross-sectional areas. The transverse expansions by rapid maxillary expansion were assessed between the midlingual alveolar bone plates at the maxillary first molar and first premolar levels. The measurements of the before and after rapid maxillary expansion scans were compared by using paired t tests with the Bonferroni adjustment for multiple comparisons.
Results: After rapid maxillary expansion, significant and equal amounts of 4.8 mm of expansion were observed at the first molar (P 5 0.0000) and the first premolar (P 5 0.0000) levels. The width increase at the first premolar level (20.0%) was significantly greater than that at the first molar level (15.0%) (P 5 0.035). As the primary outcome variable, the cross-sectional airway measured from the posterior nasal spine to basion level was the only parameter showing a significant increase of 99.4 mm2 (59.6%) after rapid maxillary expansion (P 5 0.0004).
Conclusions: These results confirm the findings of previous studies of the effect of rapid maxillary expansion on the maxilla. Additionally, we found that only the cross-sectional area of the upper airway at the posterior nasal spine to basion level significantly gains a moderate increase after rapid maxillary expansion
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