1,584 research outputs found
Heterogeneous critical nucleation on a completely-wettable substrate
Heterogeneous nucleation of a new bulk phase on a flat substrate can be
associated with the surface phase transition called wetting transition. When
this bulk heterogeneous nucleation occurs on a completely-wettable flat
substrate with a zero contact angle, the classical nucleation theory predicts
that the free energy barrier of nucleation vanishes. In fact, there always
exist a critical nucleus and a free energy barrier as the first-order
pre-wetting transition will occur even when the contact angle is zero.
Furthermore, the critical nucleus changes its character from the critical
nucleus of surface phase transition below bulk coexistence (undersaturation) to
the critical nucleus of bulk heterogeneous nucleation above the coexistence
(oversaturation) when it crosses the coexistence. Recently, Sear [J.Chem.Phys
{\bf 129}, 164510 (2008)] has shown by a direct numerical calculation of
nucleation rate that the nucleus does not notice this change when it crosses
the coexistence. In our work the morphology and the work of formation of
critical nucleus on a completely-wettable substrate are re-examined across the
coexistence using the interface-displacement model. Indeed, the morphology and
the work of formation changes continuously at the coexistence. Our results
support the prediction of Sear and will rekindle the interest on heterogeneous
nucleation on a completely-wettable substrate.Comment: 11pages, 9 figures, Journal of Chemical Physics to be publishe
Scaling properties of critical bubble of homogeneous nucleation in stretched fluid of square-gradient density-functional model with triple-parabolic free energy
The square-gradient density-functional model with triple-parabolic free
energy is used to study homogeneous bubble nucleation in a stretched liquid to
check the scaling rule for the work of formation of the critical bubble as a
function of scaled undersaturation , the
difference in chemical potential between the bulk undersaturated
and saturated liquid divided by between the liquid
spinodal and saturated liquid. In contrast to our study, a similar
density-functional study for a Lennard-Jones liquid by Shen and Debenedetti [J.
Chem. Phys. {\bf 114}, 4149 (2001)] found that not only the work of formation
but other various quantities related to the critical bubble show the scaling
rule, however, we found virtually no scaling relationships in our model near
the coexistence. Although some quantities show almost perfect scaling relations
near the spinodal, the work of formation divided by the value deduced from the
classical nucleation theory shows no scaling in this model even though it
correctly vanishes at the spinodal. Furthermore, the critical bubble does not
show any anomaly near the spinodal as predicted many years ago. In particular,
our model does not show diverging interfacial width at the spinodal, which is
due to the fact that compressibility remains finite until the spinodal is
reached in our parabolic models.Comment: 10 pages, 10 figures, Journal of Chemical Physics accepted for
publicatio
Millimeter- and Submillimeter-Wave Observations of the OMC-2/3 Region; I. Dispersing and Rotating Core around an Intermediate-mass Protostar MMS 7
We report the results of H13CO+(1-0), CO(1-0), and 3.3 mm dust continuum
observations toward one of the strongest mm-wave sources in OMC-3, MMS 7, with
the Nobeyama Millimeter Array (NMA) and the Nobeyama 45 m telescope. With the
NMA, we detected centrally-condensed 3.3 mm dust-continuum emission which
coincides with the MIR source and the free-free jet. Our combined H13CO+
observations have revealed a disk-like envelope. The size and the mass of the
disk-like envelope are 0.15 times 0.11 pc and 5.1 - 9.1 M_sun, respectively.
The combined map also shows that the outer portion of the disk-like envelope
has a fan-shaped structure which delineates the rim of the CO(1-0) outflow
observed with the NMA. The position-velocity (P-V) diagrams in the H13CO+ (1-0)
emission show that the velocity field in the disk-like envelope is composed of
a dispersing gas motion and a possible rigid-like rotation. The mass dispersing
rate is estimated to be (3.4 - 6.0) times 10^-5 M_sun/yr, which implies that
MMS 7 has an ability to disperse ~10 M_sun during the protostellar evolutional
time of a few times 10^5 yr. The specific angular momentum of the possible
rotation in the disk-like envelope is nearly two orders of magnitude larger
than that in low-mass cores. The turn-over point of the power law of the
angular momentum distribution in the disk-like envelope (< 0.007 pc), which is
likely to be related to the outer radius of the central mass accretion, is
similar to the size of the 3.3 mm dust condensation. The intermediate-mass
protostar MMS 7 is in the last stage of the main accretion phase and that the
substantial portion of the outer gas has already been dispersed, while the mass
accretion may still be on-going at the innermost region traced by the dusty
condensation.Comment: 19 pages, 9 figures, ApJ accepted pape
New possibility of the ground state of quarter-filled one-dimensional strongly correlated electronic system interacting with localized spins
We study numerically the ground state properties of the one-dimensional
quarter-filled strongly correlated electronic system interacting
antiferromagnetically with localized spins. It is shown that the
charge-ordered state is significantly stabilized by the introduction of
relatively small coupling with the localized spins. When the coupling becomes
large the spin and charge degrees of freedom behave quite independently and the
ferromagnetism is realized. Moreover, the coexistence of ferromagnetism with
charge order is seen under strong electronic interaction. Our results suggest
that such charge order can be easily controlled by the magnetic field, which
possibly give rise to the giant negative magnetoresistance, and its relation to
phthalocyanine compounds is discussed.Comment: 5pages, 4figure
Quantum Melting of Charge Order due to Frustration in Two-Dimensional Quarter-Filled Systems
The effect of geometrical frustration in a two-dimensional 1/4-filled
strongly correlated electron system is studied theoretically, motivated by
layered organic molecular crystals. An extended Hubbard model on the square
lattice is considered, with competing nearest neighbor Coulomb interaction, V,
and that of next-nearest neighbor along one of the diagonals, V', which favor
different charge ordered states. Based on exact diagonalization calculations,
we find a metallic phase stabilized over a broad window at V' ~ V even for
large Coulomb repulsion strengths as a result of frustrating the charge ordered
states. Slightly modifying the lattice geometry relevant to the actual organic
compounds does not alter the results, suggesting that this `quantum melting' of
charge order is a robust feature of frustrated strongly correlated 1/4-filled
systems.Comment: 5 pages, 4 figures, to be published in Phys. Rev.
Steady-state nucleation rate and flux of composite nucleus at saddle point
The steady-state nucleation rate and flux of composite nucleus at the saddle
point is studied by extending the theory of binary nucleation. The
Fokker-Planck equation that describes the nucleation flux is derived using the
Master equation for the growth of the composite nucleus, which consists of the
core of the final stable phase surrounded by a wetting layer of the
intermediate metastable phase nucleated from a metastable parent phase recently
evaluated by the author [J. Chem. Phys. {\bf 134}, 164508 (2011)]. The
Fokker-Planck equation is similar to that used in the theory of binary
nucleation, but the non-diagonal elements exist in the reaction rate matrix.
First, the general solution for the steady-state nucleation rate and the
direction of nucleation flux is derived. Next, this information is then used to
study the nucleation of composite nucleus at the saddle point. The dependence
of steady-state nucleation rate as well as the direction of nucleation flux on
the reaction rate in addition to the free-energy surface is studied using a
model free-energy surface. The direction of nucleation current deviates from
the steepest-descent direction of the free-energy surface. The results show the
importance of two reaction rate constants: one from the metastable environment
to the intermediate metastable phase and the other from the metastable
intermediate phase to the stable new phase. On the other hand, the gradient of
the potential or the Kramers crossover function (the commitment or
splitting probability) is relatively insensitive to reaction rates or
free-energy surface.Comment: 12 pages, 6 figures, to be published in Journal of Chemical Physic
Effects of Fermi surface and superconducting gap structure in the field-rotational experiments: A possible explanation of the cusp-like singularity in YNiBC
We have studied the field-orientational dependence of zero-energy density of
states (FODOS) for a series of systems with different Fermi surface and
superconducting gap structures. Instead of phenomenological Doppler-shift
method, we use an approximate analytical solution of Eilenberger equation
together with self-consistent determination of order parameter and a
variational treatment of vortex lattice. First, we compare zero-energy density
of states (ZEDOS) when a magnetic field is applied in the nodal direction
() and in the antinodal direction (), by taking
account of the field-angle dependence of order parameter. As a result, we found
that there exists a crossover magnetic field so that for for , consistent with our previous analyses. Next, we showed that and the
shape of FODOS are determined by contribution from the small part of Fermi
surface where Fermi velocity is parallel to field-rotational plane. In
particular, we found that is lowered and FODOS has broader minima, when a
superconducting gap has point nodes, in contrast to the result of the
Doppler-shift method. We also studied the effects of in-plane anisotropy of
Fermi surface. We found that in-plane anisotropy of quasi-two dimensional Fermi
surface sometimes becomes larger than the effects of Doppler-shift and can
destroy the Doppler-shift predominant region. In particular, this tendency is
strong in a multi-band system where superconducting coherence lengths are
isotropic. Finally, we addressed the problem of cusp-like singularity in
YNiBC and present a possible explanation of this phenomenon.Comment: 13pages, 23figure
Isochronous explicit time integration framework: illustration to thermal stress problems involving both first- and second-order transient systems
In this article, an isochronous explicit time integration framework (or the explicit iIntegrator) for solving thermal stress problems is illustrated. Similar to the implicit case, the same adaptation process of the isochronous integration is valid for the explicit case. That is, the adaptation process endows the explicit version of the generalized single step family of algorithms for second-order systems (explicit GS4-2 family of algorithms) with the applicability to first-order systems, and the explicit version of the GS4 family of algorithms for first-order systems (explicit GS4-1 family of algorithms) is automatically generated. Two illustrative thermal stress dynamic applications are shown to demonstrate the practicality and convenience of the explicit iIntegrator
- …