3,449 research outputs found
Polyamorphism of ice at low temperatures from constant-pressure simulations
We report results of MD simulations of amorphous ice in the pressure range 0
- 22.5 kbar. The high-density amorphous ice (HDA) prepared by compression of Ih
ice at T = 80 K is annealed to T = 170 K at intermediate pressures in order to
generate relaxed states. We confirm the existence of recently observed
phenomena, the very high-density amorphous ice and a continuum of HDA forms. We
suggest that both phenomena have their origin in the evolution of the network
topology of the annealed HDA phase with decreasing volume, resulting at low
temperatures in the metastability of a range of densities.Comment: 11 pages, 5 postscript figures. To be published in Physical Review
Letter
Implication of the B -> rho rho data on the B -> pi pi puzzle
We point out that the B -> rho rho data have seriously constrained the
possibility of resolving the B -> pi pi puzzle from the large observed B^0 ->
pi^0 pi^0 branching ratio in the available theoretical approaches. The
next-to-leading-order (NLO) contributions from the vertex corrections, the
quark loops, and the magnetic penguin evaluated in the perturbative QCD (PQCD)
approach have saturated the experimental upper bound of the B^0 -> rho^0 rho^0
branching ratio, and do not help. The NLO PQCD predictions for the B^0 ->
rho^\mp rho^\pm and B^\pm -> rho^\pm rho^0 branching ratios are consistent with
the data. The inclusion of the NLO jet function from the soft-collinear
effective theory into the QCD-improved factorization approach, though enhancing
the B^0 -> pi^0 pi^0 branching ratio sufficiently, overshoots the bound of the
B^0 -> rho^0 rho^0 branching ratio, and deteriorates the predictions for the
B^\pm -> pi^0 K^\pm and B^0 -> pi^\mp K^\pm direct CP asymmetries.Comment: 15 pages, 1 figure, REVTeX4; title changed, version to appear in
Phys. Rev.
A Potential Energy Landscape Study of the Amorphous-Amorphous Transformation in HO
We study the potential energy landscape explored during a
compression-decompression cycle for the SPC/E (extended simple point charge)
model of water. During the cycle, the system changes from low density amorphous
ice (LDA) to high density amorphous ice (HDA). After the cycle, the system does
not return to the same region of the landscape, supporting the interesting
possibility that more than one significantly different configuration
corresponds to LDA. We find that the regions of the landscape explored during
this transition have properties remarkably different from those explored in
thermal equilibrium in the liquid phase
Influence of deflocculant on the isoelectric point of refractory powders: Considerations on the action of deflocculant
Isoelectric point changes in suspensions of refractory materials vis-a-vis the role of deflocculants used in monolithic refractories were investigated by considering the mineral compositions and adsorbed ions in four kinds of clay. Three types of curves represented the relation between the isoelectric point and the deflocculant. The surface charge of clay particles in the suspensions became negative as a result of the deflocculant, since the isoelectric point of suspensions decreased as the deflocculant was added. The isoelectric point changes of calcined alumina were also compared with those of the clays, and a similar phenomenon was observed, except that the deflocculant dispersed the calcined alumina better than it did the clays. A simple model was used to analyze the results
Ice XII in its second regime of metastability
We present neutron powder diffraction results which give unambiguous evidence
for the formation of the recently identified new crystalline ice phase[Lobban
et al.,Nature, 391, 268, (1998)], labeled ice XII, at completely different
conditions. Ice XII is produced here by compressing hexagonal ice I_h at T =
77, 100, 140 and 160 K up to 1.8 GPa. It can be maintained at ambient pressure
in the temperature range 1.5 < T < 135 K. High resolution diffraction is
carried out at T = 1.5 K and ambient pressure on ice XII and accurate
structural properties are obtained from Rietveld refinement. At T = 140 and 160
K additionally ice III/IX is formed. The increasing amount of ice III/IX with
increasing temperature gives an upper limit of T ~ 150 K for the successful
formation of ice XII with the presented procedure.Comment: 3 Pages of RevTeX, 3 tables, 3 figures (submitted to Physical Review
Letters
Interplay Between Time-Temperature-Transformation and the Liquid-Liquid Phase Transition in Water
We study the TIP5P water model proposed by Mahoney and Jorgensen, which is
closer to real water than previously-proposed classical pairwise additive
potentials. We simulate the model in a wide range of deeply supercooled states
and find (i) the existence of a non-monotonic ``nose-shaped'' temperature of
maximum density line and a non-reentrant spinodal, (ii) the presence of a low
temperature phase transition, (iii) the free evolution of bulk water to ice,
and (iv) the time-temperature-transformation curves at different densities.Comment: RevTeX4, 4 pages, 4 eps figure
Large electroweak penguin contribution in B -> K pi and pi pi decay modes
We discuss about a possibility of large electroweak penguin contribution in B
-> K pi and pi pi from recent experimental data. The experimental data may be
suggesting that there are some discrepancies between the data and theoretical
estimation in the branching ratios of them. In B -> K pi decays, to explain it,
a large electroweak penguin contribution and large strong phase differences
seem to be needed. The contributions should appear also in B -> pi pi. We show,
as an example, a solution to solve the discrepancies in both B -> K pi and B ->
pi pi. However the magnitude of the parameters and the strong phase estimated
from experimental data are quite large compared with the theoretical
estimations. It may be suggesting some new physics effects are including in
these processes. We will have to discuss about the dependence of the new
physics. To explain both modes at once, we may need large electroweak penguin
contribution with new weak phases and some SU(3) breaking effects by new
physics in both QCD and electroweak penguin type processes.Comment: 23 pages, 9 figure
- …