1,441 research outputs found
Density minimum and liquid-liquid phase transition
We present a high-resolution computer simulation study of the equation of
state of ST2 water, evaluating the liquid-state properties at 2718 state
points, and precisely locating the liquid-liquid critical point (LLCP)
occurring in this model. We are thereby able to reveal the interconnected set
of density anomalies, spinodal instabilities and response function extrema that
occur in the vicinity of a LLCP for the case of a realistic, off-lattice model
of a liquid with local tetrahedral order. In particular, we unambiguously
identify a density minimum in the liquid state, define its relationship to
other anomalies, and show that it arises due to the approach of the liquid
structure to a defect-free random tetrahedral network of hydrogen bonds.Comment: 5 pages, 4 figure
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
Instability of Myelin Tubes under Dehydration: deswelling of layered cylindrical structures
We report experimental observations of an undulational instability of myelin
figures. Motivated by this, we examine theoretically the deformation and
possible instability of concentric, cylindrical, multi-lamellar membrane
structures. Under conditions of osmotic stress (swelling or dehydration), we
find a stable, deformed state in which the layer deformation is given by \delta
R ~ r^{\sqrt{B_A/(hB)}}, where B_A is the area compression modulus, B is the
inter-layer compression modulus, and h is the repeat distance of layers. Also,
above a finite threshold of dehydration (or osmotic stress), we find that the
system becomes unstable to undulations, first with a characteristic wavelength
of order \sqrt{xi d_0}, where xi is the standard smectic penetration depth and
d_0 is the thickness of dehydrated region.Comment: 5 pages + 3 figures [revtex 4
Liquid-liquid equilibrium for monodisperse spherical particles
A system of identical particles interacting through an isotropic potential
that allows for two preferred interparticle distances is numerically studied.
When the parameters of the interaction potential are adequately chosen, the
system exhibits coexistence between two different liquid phases (in addition to
the usual liquid-gas coexistence). It is shown that this coexistence can occur
at equilibrium, namely, in the region where the liquid is thermodynamically
stable.Comment: 6 pages, 8 figures. Published versio
Pressure-induced amorphization and polyamorphism in one-dimensional single crystal TiO2 nanomaterials
The structural phase transitions of single crystal TiO2-B nanoribbons were
investigated in-situ at high-pressure using the synchrotron X-ray diffraction
and the Raman scattering. Our results have shown a pressure-induced
amorphization (PIA) occurred in TiO2-B nanoribbons upon compression, resulting
in a high density amorphous (HDA) form related to the baddeleyite structure.
Upon decompression, the HDA form transforms to a low density amorphous (LDA)
form while the samples still maintain their pristine nanoribbon shape. HRTEM
imaging reveals that the LDA phase has an {\alpha}-PbO2 structure with short
range order. We propose a homogeneous nucleation mechanism to explain the
pressure-induced amorphous phase transitions in the TiO2-B nanoribbons. Our
study demonstrates for the first time that PIA and polyamorphism occurred in
the one-dimensional (1D) TiO2 nanomaterials and provides a new method for
preparing 1D amorphous nanomaterials from crystalline nanomaterials.Comment: 4 figure
Charging axisymmetric space-times with cosmological constant
Ernst's solution generating technique for adding electromagnetic charge to
axisymmetric space-times in general relativity is generalised in presence of
the cosmological constant. Ernst equations for complex potentials are found and
they are traced back to an affective dual complex dynamical system, whose
symmetries are studied. In particular this method is able to generate charged,
asymptotically (A)dS black holes from their uncharged version: as an example,
it is shown explicitly how to pass from the Kerr-(A)dS to the Kerr-Newman-(A)dS
metric. A new solution describing a magnetic universe in presence of the
cosmological constant is also generated.Comment: 15 pages, v2: typos correcte
Physics of the liquid-liquid critical point
Within the inherent structure (IS) thermodynamic formalism introduced by
Stillinger and Weber [F. H. Stillinger and T. A. Weber, Phys. Rev. A {\bf 25},
978 (1982)] we address the basic question of the physics of the liquid-liquid
transition and of density maxima observed in some complex liquids such as water
by identifying, for the first time, the statistical properties of the potential
energy landscape (PEL) responsible for these anomalies.
We also provide evidence of the connection between density anomalies and the
liquid-liquid critical point. Within the simple (and physically transparent)
model discussed, density anomalies do imply the existence of a liquid-liquid
transition.Comment: Physical Review Letters, in publicatio
Ernst equation and spheroidal coordinates with a cosmological constant term
We discuss solution generating techniques treating stationary and axially
symmetric metrics in the presence of a cosmological constant. Using the
recently found extended form of Ernst's complex equation, which takes into
account the cosmological constant term, we propose an extension of spheroidal
coordinates adapted to asymptotically de-Sitter and anti de-Sitter static
spacetimes. In the absence of a cosmological constant we show in addition that
any higher dimensional metric parametrised by a single angular momentum can be
given by a 4 dimensional solution and Weyl potentials parametrising the extra
Killing directions. We explicitly show how a stationary, and a static axially
symmetric spacetime solution in 4 dimensions, can be {\it added} together to
give a 5 dimensional stationary and axisymmetric solution.Comment: 9 pages, no figures, some additional results to gr-qc/0610091.
Prepared for 12th Conference on Recent Developments in Gravity (NEB XII),
Nafplio, Greece, 29 Jun - 2 Jul 200
Chargino Contributions in Asymmetry
CP asymmetry in decay is studied in a special context of
supersymmetry theories, in which the charginos play an important role. We find
that in addition to the gluino, chargino can also make large contributions to
CP asymmetry in decay. After considering the constraints from
decay, we study three special scenarios: (a). Large mixing on
left-handed charm and top squarks (LL mixing); (b). Large mixing on
right-handed charm and top squarks (RR mixing); (c). Large mixing on
left-handed charm and top squarks plus right-handed charm and top squarks (LL +
RR mixing). We show quantitatively that because of large squark mixing within
second and third generations, an (1) effect on CP violation in is possible
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