198 research outputs found
Adsorption from Solution
A major problem of the thermodynamic theory of adsorption
at the solid/liquid interface is concerned with the definition of
the heterogeneous surface in terms of mathematically treatable
model. The paper gives a review of the theoretical approaches
applied to studies of adsorption from concentrated and diluted
binary mixtures.
Experimental work has enjoyed much success since the
uniform surface, graphitized carbon blacks became available.
Results are described and discussed of measurements of heats
of immersion on such surfaces
Gas-Liquid Nucleation in Two Dimensional System
We study the nucleation of the liquid phase from a supersaturated vapor in
two dimensions (2D). Using different Monte Carlo simulation methods, we
calculate the free energy barrier for nucleation, the line tension and also
investigate the size and shape of the critical nucleus. The study is carried
out at an intermediate level of supersaturation(away from the spinodal limit).
In 2D, a large cut-off in the truncation of the Lennard-Jones (LJ) potential is
required to obtain converged results, whereas low cut-off (say, is
generally sufficient in three dimensional studies, where is the LJ
diameter) leads to a substantial error in the values of line tension,
nucleation barrier and characteristics of the critical cluster. It is found
that in 2D, the classical nucleation theory (CNT) fails to provide a reliable
estimate of the free energy barrier. It underestimates the barrier by as much
as 70% at the saturation-ratio S=1.1 (defined as S=P/PC, where PC is the
coexistence pressure at reduced temperature ). Interestingly,
CNT has been found to overestimate the nucleation free energy barrier in three
dimensional (3D)systems near the triple point. In fact, the agreement with CNT
is worse in 2D than in 3D. Moreover, the existing theoretical estimate of the
line tension overestimates the value significantly.Comment: 24 pages, 8 figure
Sorption of Water and Polar-Nonpolar Organic Vapors on Microporous Chromia
High surface area, narrow particle size distribution chromic;t
was investigated for its microporosity. Adsorption studies with
argon, water vapor, methanol, isopropanol, butane, isobutane, neopentane,
and heptane indicated alternative approaches to the
determination of micropore volume
Improving Policy Learning via Language Dynamics Distillation
Recent work has shown that augmenting environments with language descriptions improves policy learning. However, for environments with complex language abstractions, learning how to ground language to observations is difficult due to sparse, delayed rewards. We propose Language Dynamics Distillation (LDD), which pretrains a model to predict environment dynamics given demonstrations with language descriptions, and then fine-tunes these language-aware pretrained representations via reinforcement learning (RL). In this way, the model is trained to both maximize expected reward and retain knowledge about how language relates to environment dynamics. On SILG, a benchmark of five tasks with language descriptions that evaluate distinct generalization challenges on unseen environments (NetHack, ALFWorld, RTFM, Messenger, and Touchdown), LDD outperforms tabula-rasa RL, VAE pretraining, and methods that learn from unlabeled demonstrations in inverse RL and reward shaping with pretrained experts. In our analyses, we show that language descriptions in demonstrations improve sample-efficiency and generalization across environments, and that dynamics modeling with expert demonstrations is more effective than with non-experts
Curvature Dependence of Surface Free Energy of Liquid Drops and Bubbles: A Simulation Study
We study the excess free energy due to phase coexistence of fluids by Monte
Carlo simulations using successive umbrella sampling in finite LxLxL boxes with
periodic boundary conditions. Both the vapor-liquid phase coexistence of a
simple Lennard-Jones fluid and the coexistence between A-rich and B-rich phases
of a symmetric binary (AB) Lennard-Jones mixture are studied, varying the
density rho in the simple fluid or the relative concentration x_A of A in the
binary mixture, respectively. The character of phase coexistence changes from a
spherical droplet (or bubble) of the minority phase (near the coexistence
curve) to a cylindrical droplet (or bubble) and finally (in the center of the
miscibility gap) to a slab-like configuration of two parallel flat interfaces.
Extending the analysis of M. Schrader, P. Virnau, and K. Binder [Phys. Rev. E
79, 061104 (2009)], we extract the surface free energy gamma (R) of both
spherical and cylindrical droplets and bubbles in the vapor-liquid case, and
present evidence that for R -> Infinity the leading order (Tolman) correction
for droplets has sign opposite to the case of bubbles, consistent with the
Tolman length being independent on the sign of curvature. For the symmetric
binary mixture the expected non-existence of the Tolman length is confirmed. In
all cases {and for a range of radii} R relevant for nucleation theory, gamma(R)
deviates strongly from gamma (Infinity) which can be accounted for by a term of
order gamma(Infinity)/gamma(R)-1 ~ 1/R^2. Our results for the simple
Lennard-Jones fluid are also compared to results from density functional theory
and we find qualitative agreement in the behavior of gamma(R) as well as in the
sign and magnitude of the Tolman length.Comment: 25 pages, submitted to J. Chem. Phy
A Study of the Mechanism of Micropore Filling. I. Molecular Sieve Effects
The adsorptive properties of two microporous carbons and a
microporous silica have been investigated and compared using
argon and benzene. The micropore volumes determined using the
Theory for Volume filling of Micropores (TVFM) agreed to within
40/o of the total micropore volumes determined from the a8 method
of pore analysis. Adsorption data of argon at 77 °K and benzene
at 298 °K on the microporous carbons were interpreted in terms
of the Dubinin-Astakhov and Dubinin-Radushkevich equations,
and Weibull and Gaussian distributions of the adsorption free
energy with pore volume, respectively. The Weibull distribution
was found to apply better than the Gaussian distribution, although
variations from linear D-A plots occurred. The adsorption data on
the silica sample were best interpreted as a two-term D-R equation.
Plots of the distribution of adsorption energy with pore volume of
the silica sample for each term of the D-R equation and their
effective contribution to the cumulative distribution curve gave
conclusive evidence of the ordering of the adsorption process
within micropores of varying dimensions
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