389 research outputs found
Searching for tetraquarks on the lattice
We address the question whether the lightest scalar mesons sigma and kappa
are tetraquarks. We present a search for possible light tetraquark states with
J^PC=0^++ and I=0, 1/2, 3/2, 2 in the dynamical and the quenched lattice
simulations using tetraquark interpolators. In all the channels, we unavoidably
find lowest scattering states pi(k)pi(-k) or K(k)pi(-k) with back-to-back
momentum k=0,2*pi/L,.. . However, we find an additional light state in the I=0
and I=1/2 channels, which may be related to the observed resonances sigma and
kappa with a strong tetraquark component. In the exotic repulsive channels I=2
and I=3/2, where no resonance is observed, we find no light state in addition
to the scattering states.Comment: 3 pages, 1 figure, proceedings of Lepton-Photon 2009, Hambur
Chemical weathering and provenance evolution of Holocene–Recent sediments from the Western Indus Shelf, Northern Arabian Sea inferred from physical and mineralogical properties
We present a multi-proxy mineral record based on X-ray diffraction and diffuse reflectance spectrophotometry analysis for two cores from the western Indus Shelf in order to reconstruct changing weathering intensities, sediment transport, and provenance variations since 13 ka. Core Indus-10 is located northwest of the Indus Canyon and exhibits fluctuations in smectite/(illite + chlorite) ratios that correlate with monsoon intensity. Higher smectite/(illite + chlorite) and lower illite crystallinity, normally associated with stronger weathering, peaked during the Early–Mid Holocene, the period of maximum summer monsoon. Hematite/goethite and magnetic susceptibility do not show clear co-variation, although they both increase at Indus-10 after 10 ka, as the monsoon weakened. At Indus-23, located on a clinoform just west of the canyon, hematite/goethite increased during a period of monsoon strengthening from 10 to 8 ka, consistent with increased seasonality and/or reworking of sediment deposited prior to or during the glacial maximum. After 2 ka terrigenous sediment accumulation rates in both cores increased together with redness and hematite/goethite, which we attribute to widespread cultivation of the floodplain triggering reworking, especially after 200 years ago. Over Holocene timescales sediment composition and mineralogy in two localities on the high-energy shelf were controlled by varying degrees of reworking, as well as climatically modulated chemical weathering
Water exchange at a hydrated platinum electrode is rare and collective
We use molecular dynamics simulations to study the exchange kinetics of water
molecules at a model metal electrode surface -- exchange between water
molecules in the bulk liquid and water molecules bound to the metal. This
process is a rare event, with a mean residence time of a bound water of about
40 ns for the model we consider. With analysis borrowed from the techniques of
rare-event sampling, we show how this exchange or desorption is controlled by
(1) reorganization of the hydrogen bond network within the adlayer of bound
water molecules, and by (2) interfacial density fluctuations of the bulk liquid
adjacent to the adlayer. We define collective coordinates that describe the
desorption mechanism. Spatial and temporal correlations associated with a
single event extend over nanometers and tens of picoseconds.Comment: 10 pages, 9 figure
The Putative Liquid-Liquid Transition is a Liquid-Solid Transition in Atomistic Models of Water
We use numerical simulation to examine the possibility of a reversible
liquid-liquid transition in supercooled water and related systems. In
particular, for two atomistic models of water, we have computed free energies
as functions of multiple order parameters, where one is density and another
distinguishes crystal from liquid. For a range of temperatures and pressures,
separate free energy basins for liquid and crystal are found, conditions of
phase coexistence between these phases are demonstrated, and time scales for
equilibration are determined. We find that at no range of temperatures and
pressures is there more than a single liquid basin, even at conditions where
amorphous behavior is unstable with respect to the crystal. We find a similar
result for a related model of silicon. This result excludes the possibility of
the proposed liquid-liquid critical point for the models we have studied.
Further, we argue that behaviors others have attributed to a liquid-liquid
transition in water and related systems are in fact reflections of transitions
between liquid and crystal
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