265 research outputs found
The OH-streamer in Sgr A revisited: analysis of hydroxyl absorption within 10 pc from the Galactic centre
We study the structure and kinematics of the OH-streamer and the +80 km/s
cloud and their interactions with the circumnuclear disk (CND) and with other
molecular clouds in the vicinity of the Galactic centre (GC), and we map OH
absorption at about 6" resolution at R 10 pc from the GC, with about 9
km/s velocity resolution. The VLA was used to map OH line absorption at the
1665 and 1667 MHz lambda doublet main lines towards the Sagittarius A complex.
Strong OH absorption was found in the OH-streamer, the southern streamer (SS),
the +20, +50, and +80 km/s molecular clouds, the molecular belt, the CND, the
expanding molecular ring (EMR), and the high negative velocity gas (HNVG). The
OH-streamer was found to comprise three parts, head, middle, and tail, and to
interact with the SS/+20, +80 km/s clouds and the CND. Optical depths and
column densities have been calculated for the OH-streamer and the +80 km/s
cloud. The OH-streamer, the SS, the +20 and +80 km/s clouds, and the CND are
intimately related in position and velocity space. The OH-streamer was found to
be a clumpy object stretching in projection from the inner radius of the CND at
about 1.8 pc from Sgr A* towards and partly engulfing Sgr A*. As a side result
of our data, a possible link between the near side of the EMR and the CND's
southwest lobe was found. Additionally, we found OH absorption against all four
of the previously known Compact HII Regions A-D, located east of Sgr A East,
indicating their close association with the +50 km/s cloud.Comment: Accepted for publication in Astronomy & Astrophsyics and including
maps of the 1665 and 1667 MHz data cubes. These data cubes are available in
electronic form at the CDS at http://vizier.u-strasbg.fr/viz-bin/Vizie
Dynamical Insights into the Decomposition of 1,2-Dioxetane
Chemiluminescence in 1,2-dioxetane occurs through a thermally activated
decomposition reaction into two formaldehyde molecules. Both ground-state and
nonadiabatic dynamics (including singlet excited states) of the decomposition
reaction have been simulated, starting from the first O-O bond-breaking
transition structure. The ground-state dissociation occurs between t = 30 fs
and t = 140 fs. The so-called entropic trap leads to frustrated dissociations,
postponing the decomposition reaction. Specific geometrical conditions are
necessary for the trajectories to escape from the entropic trap and for
dissociation to be possible. The singlet excited states participate as well in
the trapping of the molecule: dissociation including the nonadiabatic
transitions to singlet excited states now occurs from t = 30 fs to t = 250 fs
and later. Specific regions of the seam of the S0/S1 conical intersections that
would "retain" the molecule for longer on the excited state have been
identified
The Muse approach to OR-parallel Prolog
Muse (Multi-sequential Prolog engines) is a simple and efficient approach to Or-parallel execution of Prolog programs. It is based on having several sequential Prolog engines, each with its local address space, and some shared memory space. It is currently implemented on a
7-processors machine with local/shared memory constructed at SICS, a 16-processors Sequent Symmetry, a 96-processors BBN Butterfly I, and a 45-processors BBN Butterfly II. The sequential SICStus Prolog system has been adapted to Or-parallel implementation. Extra overhead associated
with this adaptation is very low in comparison with the other approaches. The speed-up factor is very close to the number of processors in the system for a large class of problems. The goal of this paper is to present the Muse execution model, some of its implementation issues, a
variant of Prolog suitable for multiprocessor implementations, and some experimental results obtained from two different multiprocessor systems
Hydroxyl, water, ammonia, carbon monoxide and neutral carbon towards the Sgr A complex
We observed OH, HO, HN, CO, and C towards the +50 km/s
cloud (M-0.02-0.07), the CND and the +20 km/s (M-0.13-0.08) cloud in the Sgr A
complex with the VLA, Odin and SEST. Strong OH absorption, HO emission and
absorption lines were seen at all three positions. Strong CO emissions
were seen towards the +50 and +20 km/s clouds. The CND is rich in HO and
OH, and these abundances are considerably higher than in the surrounding
clouds, indicating that shocks, star formation and clump collisions prevail in
those objects. A comparison with the literature reveals that it is likely that
PDR chemistry including grain surface reactions, and perhaps also the
influences of shocks has led to the observed abundances of the observed
molecular species studied here. In the redward high-velocity line wings of both
the +50 and +20 km/s clouds and the CND, the very high HO abundances are
suggested to be caused by the combined action of shock desorption from icy
grain mantles and high-temperature, gas-phase shock chemistry. Only three of
the molecules are briefly discussed here. For OH and HO three of the nine
observed positions are shown, while a map of the CO emission is
provided. An extensive paper was recently published with Open Access (Karlsson
et al. 2013; http://www.aanda.org/articles/aa/pdf/2013/06/aa20471-12.pdf ).Comment: Proc. of a Conf. on IAU Symposium No.303: The Galactic Center:
Feeding and Feedback in a Normal Galactic Nucleus 2013, Santa Fe, NM (USA
How Do Methyl Groups Enhance the Triplet Chemiexcitation Yield of Dioxetane?
Chemiluminescence is the emission of light as a result of a nonadiabatic
chemical reaction. The present work is concerned with understanding the yield
of chemiluminescence, in particular how it dramatically increases upon
methylation of 1,2-dioxetane. Both ground-state and nonadiabatic dynamics
(including singlet excited states) of the decomposition reaction of various
methyl-substituted dioxetanes have been simulated. Methyl-substitution leads to
a significant increase in the dissociation time scale. The rotation around the
O-C-C-O dihedral angle is slowed; thus, the molecular system stays longer in
the "entropic trap" region. A simple kinetic model is proposed to explain how
this leads to a higher chemiluminescence yield. These results have important
implications for the design of efficient chemiluminescent systems in medical,
environmental, and industrial applications
Совершенствование маркетинговой деятельности промышленного предприятия (на примере ОАО «БМЗ – управляющая компания холдинга-БМК»)
Phase contrast MRI is a powerful tool for the assessment of blood flow. However, especially in the highly complex and turbulent flow that accompanies many cardiovascular diseases, phase contrast MRI may suffer from artifacts. Simulation of phase contrast MRI of turbulent flow could increase our understanding of phase contrast MRI artifacts in turbulent flows and facilitate the development of phase contrast MRI methods for the assessment of turbulent blood flow. We present a method for the simulation of phase contrast MRI measurements of turbulent flow. The method uses an Eulerian-Lagrangian approach, in which spin particle trajectories are computed from time-resolved large eddy simulations. The Bloch equations are solved for each spin for a frame of reference moving along the spins trajectory. The method was validated by comparison with phase contrast MRI measurements of velocity and intravoxel velocity standard deviation (IVSD) on a flow phantom consisting of a straight rigid pipe with a stenosis. Turbulence related artifacts, such as signal drop and ghosting, could be recognized in the measurements as well as in the simulations. The velocity and the IVSD obtained from the magnitude of the phase contrast MRI simulations agreed well with the measurements
Nanocomposites and polyethylene blends: two potentially synergistic strategies for HVDC insulation materials with ultra-low electrical conductivity
Among the various requirements that high voltage direct current (HVDC) insulation materials need to satisfy, sufficiently low electrical conductivity is one of the most important. The leading commercial HVDC insulation material is currently an exceptionally clean cross-linked low-density polyethylene (XLPE). Previous studies have reported that the DC-conductivity of low-density polyethylene (LDPE) can be markedly reduced either by including a fraction of high-density polyethylene (HDPE) or by adding a small amount of a well dispersed, semiconducting nanofiller such as Al2O3 coated with a silane. This study demonstrates that by combining these two strategies a synergistic effect can be achieved, resulting in an insulation material with an ultra-low electrical conductivity. The addition of both HDPE and C8–Al2O3 nanoparticles to LDPE resulted in ultra-insulating nanocomposites with a conductivity around 500 times lower than of the neat LDPE at an electric field of 32 kV/mm and 60–90 \ub0C. The new nanocomposite is thus a promising material regarding the electrical conductivity and it can be further optimized since the polyethylene blend and the nanoparticles can be improved independently
Meropenem/colistin synergy testing for multidrug-resistant Acinetobacter baumannii strains by a two-dimensional gradient technique applicable in routine microbiology
Objectives Precise assessment of potential therapeutic synergy, antagonism or indifference between antimicrobial agents currently depends on time-consuming and hard-to-standardize in vitro chequerboard titration methods. We here present a method based on a novel two-dimensional antibiotic gradient technique named Xact™. Methods We used a test comprising a combination of perpendicular gradients of meropenem and colistin in a single quadrant. We compared test outcomes with those obtained with classical chequerboard microbroth dilution testing in a study involving 27 unique strains of multidrug-resistant Acinetobacter baumannii from diverse origins. Results We were able to demonstrate 92% concordance between the new technology and classical chequerboard titration using the A. baumannii collection. Two strains could not be analysed by Xact™ due to their out-of-range MIC of meropenem (>128 mg/L). Conclusions The new test was shown to be diagnostically useful, easy to implement and less labour intensive than the classical metho
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