2,796 research outputs found
Light Assisted Collisional Loss in a Rb Ultracold Optical Trap
We have studied hetero- and homonuclear excited state/ground state collisions
by loading both Rb and Rb into a far off resonant trap (FORT).
Because of the relatively weak confinement of the FORT, we expect the hyperfine
structure of the different isotopes to play a crucial role in the collision
rates. This dependence on hyperfine structure allows us to measure collisions
associated with long range interatomic potentials of different structure: such
as long and short ranged; or such as purely attractive, purely repulsive, or
mixed attractive and repulsive. We observe significantly different loss rates
for different excited state potentials. Additionally, we observe that some
collisional channels' loss rates are saturated at our operating intensities
(~15 mW/cm). These losses are important limitations in loading dual
isotope optical traps.Comment: about 8 pages, 5 figure
Towards Understanding Photodegradation Pathways in Lignins:The Role of Intramolecular Hydrogen Bonding in Excited States
The photoinduced dynamics of the lignin building blocks syringol, guaiacol, and phenol were studied using time-resolved ion yield spectroscopy and velocity map ion imaging. Following irradiation of syringol and guaiacol with a broad-band femtosecond ultraviolet laser pulse, a coherent superposition of out-of-plane OH torsion and/or OMe torsion/flapping motions is created in the first excited 1ππ* (S1) state, resulting in a vibrational wavepacket, which is probed by virtue of a dramatic nonplanar → planar geometry change upon photoionization from S1 to the ground state of the cation (D0). Any similar quantum beat pattern is absent in phenol. In syringol, the nonplanar geometry in S1 is pronounced enough to reduce the degree of intramolecular H bonding (between OH and OMe groups), enabling H atom elimination from the OH group. For guaiacol, H bonding is preserved after excitation, despite the nonplanar geometry in S1, and prevents O–H bond fission. This behavior affects the propensities for forming undesired phenoxyl radical sites in these three lignin chromophores and provides important insight into their relative “photostabilities” within the larger biopolymer
Unraveling the molecular basis of subunit specificity in P pilus assembly by mass spectrometry
P pili are multisubunit fibers essential for the attachment of uropathogenic Escherichia coli to the kidney. These fibers are formed by the noncovalent assembly of six different homologous subunit types in an array that is strictly defined in terms of both the number and order of each subunit type. Assembly occurs through a mechanism termed “donor-strand exchange (DSE)” in which an N-terminal extension (Nte) of one subunit donates a β-strand to an adjacent subunit, completing its Ig fold. Despite structural determination of the different subunits, the mechanism determining specificity of subunit ordering in pilus assembly remained unclear. Here, we have used noncovalent mass spectrometry to monitor DSE between all 30 possible pairs of P pilus subunits and their Ntes. We demonstrate a striking correlation between the natural order of subunits in pili and their ability to undergo DSE in vitro. The results reveal insights into the molecular mechanism by which subunit ordering during the assembly of this complex is achieved
Space Mobile Network (SMN) User Demonstration Satellite (SUDS) for a Practical On-Orbit Demonstration of User Initiated Services (UIS)
This paper will discuss the various aspects of implementation of the Space Mobile Network (SMN) architecture framework within the context of operations of various nodes equipped with the User Initiated Services (UIS) protocol. These aspects include development of a Client-Server architecture in which space based Clients can create links with ground based Servers to negotiate passes with ground stations or contacts with the Tracking and Data Relay Satellite (TDRS) fleet. A key feature of this concept is that Users may require a mix of low data rate continuous contacts with one or more of the TDRS fleet and sporadic contacts with ground stations as passes become available. SUDS (SMN User Demonstration Satellite) will have the availability of TDRS contacts, the U.S. Naval Academy's ground station, NASA Near Earth Network ground sites and others. This mode of operations must be integrated within the traditional mode of scheduling contacts and passes. Thus, SUDS fits into a heterogeneous network operations concept of operations
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Problem gambling and suicidality in England: secondary analysis of a representative cross-sectional survey
Objectives: Problem gamblers in treatment are known to be at high risk for suicidality, but few studies have examined if this is evident in community samples. Evidence is mixed on the extent to which an association between problem gambling and suicidality may be explained by psychiatric comorbidity. We tested whether they are associated after adjustment for co-occurring mental disorders and other factors. Study design: Secondary analysis of the Adult Psychiatric Morbidity Survey 2007, a cross-sectional na- tional probability sample survey of 7403 adults living in households in England.
Methods: Rates of suicidality in problem gamblers and the rest of the population were compared. A series of logistic regression models assessed the impact of adjustment on the relationship between problem gambling and suicidality.
Results: Past year suicidality was reported in 19.2% of problem gamblers, compared with 4.4% in the rest of the population. Their unadjusted odds ratios (OR) of suicidality were 5.3 times higher. Odds attenuated but remained significant when depression and anxiety disorders, substance dependences, attention- deficit/hyperactivity disorder, and other factors were accounted for (adjusted OR 1⁄4 2.9, 95% confi- dence interval 1⁄4 1. 1, 8.1 P 1⁄4 0.023).
Conclusions: Problem gamblers are a high-risk group for suicidality. This should be recognised in indi- vidual suicide prevention plans and local and national suicide prevention strategies. While some of this relationship is explained by other factors, a significant and substantial association between problem gambling and suicidality remains
A Jitter Injection Signal Generation and Extraction System for Embedded Test of High-Speed Data I/O
Relativistic electron precipitation by EMIC waves: importance of nonlinear resonant effects
Relativistic electron losses in Earth's radiation belts are usually
attributed to electron resonant scattering by electromagnetic waves. One of the
most important wave mode for such scattering is the electromagnetic ion
cyclotron (EMIC) mode. Within the quasi-linear diffusion framework, the
cyclotron resonance of relativistic electrons with EMIC waves results in very
fast electron precipitation to the atmosphere. However, wave intensities often
exceed the threshold for nonlinear resonant interaction, and such intense EMIC
waves have been shown to transport electrons away from the loss cone due to the
force bunching effect. In this study we investigate if this transport can block
electron precipitation. We combine test particle simulations, low-altitude
ELFIN observations of EMIC-driven electron precipitation, and ground-based EMIC
observations. Comparing simulations and observations, we show that, despite of
the low pitch-angle electrons being transported away from the loss cone, the
scattering at higher pitch angles results in the loss cone filling and electron
precipitation
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