2,830 research outputs found
Note on the physical basis of spatially resolved thermodynamic functions
The spatial resolution of thermodynamic functions, exemplified by the
entropy, is discussed. A physical definition of the spatial resolution based on
a spatial analogy of the partial molar entropy is advocated. It is shown that
neither the grid cell theory (Gerogiokas et al., J. Chem. Theory Comput., 10,
35 [2014]), nor the first-order grid inhomogeneous solvation theory (Nguyen et
al. J. Chem. Phys., 137, 044101 [2012]), of spatially resolved hydration
entropies satisfies the definition.Comment: Essentially 2 double-column pages, no figure
Modification of the Gay-Berne potential for improved accuracy and speed
A modification of the Gay-Berne potential is proposed which is about 10% to
20% more speed efficient (that is, the original potential runs 15% to 25%
slower, depending on architecture) and statistically more accurate in
reproducing the energy of interaction of two linear Lennard-Jones tetratomics
when averaged over all orientations. For the special cases of end-to-end and
side-by-side configurations, the new potential is equivalent to the Gay-Berne
one.Comment: 5 pages (incl. title page), [preprint,aip,jcp]{RevTEX-4.1}, 1 figure,
1 table. Revised version fixes mathematical typos and adds short paragraph on
a natural generalization to dissimilar particle
Natural selection reduced diversity on human Y chromosomes
The human Y chromosome exhibits surprisingly low levels of genetic diversity.
This could result from neutral processes if the effective population size of
males is reduced relative to females due to a higher variance in the number of
offspring from males than from females. Alternatively, selection acting on new
mutations, and affecting linked neutral sites, could reduce variability on the
Y chromosome. Here, using genome-wide analyses of X, Y, autosomal and
mitochondrial DNA, in combination with extensive population genetic
simulations, we show that low observed Y chromosome variability is not
consistent with a purely neutral model. Instead, we show that models of
purifying selection are consistent with observed Y diversity. Further, the
number of sites estimated to be under purifying selection greatly exceeds the
number of Y-linked coding sites, suggesting the importance of the highly
repetitive ampliconic regions. While we show that purifying selection removing
deleterious mutations can explain the low diversity on the Y chromosome, we
cannot exclude the possibility that positive selection acting on beneficial
mutations could have also reduced diversity in linked neutral regions, and may
have contributed to lowering human Y chromosome diversity. Because the
functional significance of the ampliconic regions is poorly understood, our
findings should motivate future research in this area.Comment: 43 pages, 11 figure
Edit Distance for Pushdown Automata
The edit distance between two words is the minimal number of word
operations (letter insertions, deletions, and substitutions) necessary to
transform to . The edit distance generalizes to languages
, where the edit distance from to
is the minimal number such that for every word from
there exists a word in with edit distance at
most . We study the edit distance computation problem between pushdown
automata and their subclasses. The problem of computing edit distance to a
pushdown automaton is undecidable, and in practice, the interesting question is
to compute the edit distance from a pushdown automaton (the implementation, a
standard model for programs with recursion) to a regular language (the
specification). In this work, we present a complete picture of decidability and
complexity for the following problems: (1)~deciding whether, for a given
threshold , the edit distance from a pushdown automaton to a finite
automaton is at most , and (2)~deciding whether the edit distance from a
pushdown automaton to a finite automaton is finite.Comment: An extended version of a paper accepted to ICALP 2015 with the same
title. The paper has been accepted to the LMCS journa
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