261 research outputs found
Quantum Chemical Analysis of the Excited State Dynamics of Hydrated Electrons
Quantum calculations are performed for an anion water cluster representing
the first hydration shell of the solvated electron in solution. The absorption
spectra from the ground state, the instant excited states and the relaxed
excited states are calculated including CI-SD interactions. Analytic
expressions for the nonadiabatic relaxation are presented. It is shown that the
50fs dynamics recently observed after s->p excitation is best accounted for if
it is identified with the internal conversion, preceded by an adiabatic
relaxation within the excited p state. In addition, transient absorptions found
in the infrared are qualitatively reproduced by these calculations
An Expanding HI Photodissociated Region Associated with the Compact HII Region G213.880-11.837 in the GGD 14 Complex
We present high angular and spectral resolution HI 21~cm line observations
toward the cometary-shaped compact HII region G213.880-11.837 in the GGD~14
complex.The kinematics and morphology of the photodissociated region, traced by
the HI line emission, reveal that the neutral gas is part of an expanding flow.
The kinematics of the HI gas along the major axis of G213.880-11.837 shows that
the emission is very extended toward the SE direction, reaching LSR radial
velocities in the tail of about 14 km/s. The ambient LSR radial velocity of the
molecular gas is 11.5 km/s, which suggests a champagne flow of the HI gas. This
is the second (after G111.61+0.37) cometary HII/HI region known.Comment: Accepted for publication in the Astronomical Journal (10 pages, 4
figures, 1 table
Relationship between quantum decoherence times and solvation dynamics in condensed phase chemical systems
A relationship between the time scales of quantum coherence loss and
short-time solvent response for a solute/bath system is derived for a Gaussian
wave packet approximation for the bath. Decoherence and solvent response times
are shown to be directly proportional to each other, with the proportionality
coefficient given by the ratio of the thermal energy fluctuations to the
fluctuations in the system-bath coupling. The relationship allows the
prediction of decoherence times for condensed phase chemical systems from well
developed experimental methods.Comment: 10 pages, no figures, late
The non-thermal, time-variable radio emission from Cyg OB2 # 5: A wind-collision region
The radio emission from the well-studied massive stellar system Cyg OB2 #5 is
known to fluctuate with a period of 6.7 years between a low-flux state when the
emission is entirely of free-free origin, and a high-flux state when an
additional non-thermal component (of hitherto unknown nature) appears. In this
paper, we demonstrate that the radio flux of that non-thermal component is
steady on timescales of hours, and that its morphology is arc-like. This shows
that the non-thermal emission results from the collision between the strong
wind driven by the known contact binary in the system, and that of an unseen
companion on a somewhat eccentric orbit with a 6.7-yr period and a 5 to 10 mas
semi-major axis. Together with the previously reported wind-collision region
located about 0.8 arcsec to the north-east of the contact binary, Cyg OB2 #5
appears to be the only multiple system known so far to harbor two radio-imaged
wind-collision regions.Comment: Accepted for publication in The Astrophysical Journa
Tide and skew surge independence: new insights for flood risk
Storm surges are a significant hazard to coastal communities around the world, putting lives at risk and costing billions of dollars in damage. Understanding how storm surges and high tides interact is crucial for estimating extreme water levels so that we can protect coastal communities. We demonstrate that in a tidal regime the best measure of a storm surge is the skew surge, the difference between the observed and predicted high water within a tidal cycle.
Based on tide gauge records spanning decades from the UK, US, Netherlands and Ireland we show that the magnitude of high water exerts no influence on the size of the most extreme skew surges. This is the first systematic proof that any storm surge can occur on any tide, which is essential for understanding worst case scenarios. The lack of surge generation dependency on water depth emphasises the dominant natural variability of weather systems in an observations-based analysis. Weak seasonal relationships between skew surges and high waters were identified at a minority of locations where long period changes to the tidal cycle interact with the storm season. Our results allow advances to be made in methods for estimating the joint probabilities of storm surges and tides
Local Alignment Refinement Using Structural Assessment
Homology modeling is the most commonly used technique to build a three-dimensional model for a protein sequence. It heavily relies on the quality of the sequence alignment between the protein to model and related proteins with a known three dimensional structure. Alignment quality can be assessed according to the physico-chemical properties of the three dimensional models it produces
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