761 research outputs found
Structural and ultrametric properties of twenty(L-alanine)
We study local energy minima of twenty(L-alanine). The minima are generated
using high-temperature Molecular Dynamics and Chain-Growth Monte Carlo
simulations, with subsequent minimization. We find that the lower-energy
configurations are -helices for a wide range of dielectric constant
values and that there is no noticeable difference
between the distribution of energy minima in space for different
values of Ultrametricity tests show that lower-energy -helical) configurations form a set which is ultrametric to a
certain degree, providing evidence for the presence of fine structure among
those minima. We put forward a heuristic argument for this fine structure. We
also find evidence for ultrametricity of a different kind among and energy minima. We analyze the distribution of lengths of
-helical portions among the minimized configurations and find a
persistence phenomenon for the ones, in qualitative agreement
with previous studies of critical lengths. Email contact:
[email protected]: Saclay-T93/025 Email: [email protected]
From the Quantum Link Model on the Honeycomb Lattice to the Quantum Dimer Model on the Kagom\'e Lattice: Phase Transition and Fractionalized Flux Strings
We consider the -d quantum link model on the honeycomb lattice
and show that it is equivalent to a quantum dimer model on the Kagom\'e
lattice. The model has crystalline confined phases with spontaneously broken
translation invariance associated with pinwheel order, which is investigated
with either a Metropolis or an efficient cluster algorithm. External
half-integer non-Abelian charges (which transform non-trivially under the
center of the gauge group) are confined to each other
by fractionalized strings with a delocalized flux. The strands
of the fractionalized flux strings are domain walls that separate distinct
pinwheel phases. A second-order phase transition in the 3-d Ising universality
class separates two confining phases; one with correlated pinwheel
orientations, and the other with uncorrelated pinwheel orientations.Comment: 16 pages, 20 figures, 2 tables, two more relevant references and one
short paragraph are adde
From the Quantum Link Model on the Honeycomb Lattice to the Quantum Dimer Model on the Kagom\'e Lattice: Phase Transition and Fractionalized Flux Strings
We consider the -d quantum link model on the honeycomb lattice
and show that it is equivalent to a quantum dimer model on the Kagom\'e
lattice. The model has crystalline confined phases with spontaneously broken
translation invariance associated with pinwheel order, which is investigated
with either a Metropolis or an efficient cluster algorithm. External
half-integer non-Abelian charges (which transform non-trivially under the
center of the gauge group) are confined to each other
by fractionalized strings with a delocalized flux. The strands
of the fractionalized flux strings are domain walls that separate distinct
pinwheel phases. A second-order phase transition in the 3-d Ising universality
class separates two confining phases; one with correlated pinwheel
orientations, and the other with uncorrelated pinwheel orientations.Comment: 16 pages, 20 figures, 2 tables, two more relevant references and one
short paragraph are adde
Manning condensation in two dimensions
We consider a macroion confined to a cylindrical cell and neutralized by
oppositely charged counterions. Exact results are obtained for the
two-dimensional version of this problem, in which ion-ion and ion-macroion
interactions are logarithmic. In particular, the threshold for counterion
condensation is found to be the same as predicted by mean-field theory. With
further increase of the macroion charge, a series of single-ion condensation
transitions takes place. Our analytical results are expected to be exact in the
vicinity of these transitions and are in very good agreement with recent
Monte-Carlo simulation data.Comment: 4 pages, 4 figure
Status of the tiger beetle Cicindela hirticollis Say (Coleoptera: Cicindelidae) in New York City and on Long Island, New York, USA
Coastal species are under considerable threat from recreational activities and climate change. The tiger beetle Cicindela hirticollis Say (Coleoptera: Cicindelidae) was recorded historically from 30 locations along the shores of New York City and Long Island, New York. We conducted surveys for extant populations of this species at 40 sites from 1989 to 2010. Adults of C. hirticollis were found at 13 beaches. Only four sites had 40 or more adults of C. hirticollis active at the time the beach was surveyed. No beetles were detected on the large coastal beaches that were formerly occupied by this species. Many coastal beaches of New York receive heavy human foot and vehicle traffic and are therefore unlikely to provide suitable habitat for C. hirticollis without a shift in beach management that recognizes the potential of some beaches as wilderness systems capable of supporting the full array of beach-dependent species
Dominant Reaction Pathways in High Dimensional Systems
This paper is devoted to the development of a theoretical and computational
framework to efficiently sample the statistically significant thermally
activated reaction pathways, in multi-dimensional systems obeying Langevin
dynamics. We show how to obtain the set of most probable reaction pathways and
compute the corrections due to quadratic thermal fluctuations around such
trajectories. We discuss how to obtain predictions for the evolution of
arbitrary observables and how to generate conformations which are
representative of the transition state ensemble. We present an illustrative
implementation of our method by studying the diffusion of a point particle in a
2-dimensional funneled external potential.Comment: 18 pages, 7 figures. Improvement in the text and in the figures.
Version submitted for publicatio
Asymptotic Freedom of Elastic Strings and Barriers
We study the problem of a quantized elastic string in the presence of an
impenetrable wall. This is a two-dimensional field theory of an N-component
real scalar field which becomes interacting through the restriction that
the magnitude of is less than , for a spherical wall of
radius . The N=1 case is a string vibrating in a plane between
two straight walls. We review a simple nonperturbative argument that there is a
gap in the spectrum, with asymptotically-free behavior in the coupling (which
is the reciprocal of ) for N greater than or equal to one. This
scaling behavior of the mass gap has been disputed in some of the recent
literature. We find, however, that perturbation theory and the 1/N expansion
each confirms that these theories are asymptotically free. The large N limit
coincides with that of the O(N) nonlinear sigma model. A theta parameter exists
for the N=2 model, which describes a string confined to the interior of a
cylinder of radius .Comment: Text slightly improved, bibilography corrected, more typos corrected,
still Latex 7 page
Bridge Hopping on Conducting Polymers in Solution
Configurational fluctuations of conducting polymers in solution can bring
into proximity monomers which are distant from each other along the backbone.
Electrons can hop between these monomers across the "bridges" so formed. We
show how this can lead to (i) a collapse transition for metallic polymers, and
(ii) to the observed dramatic efficiency of acceptor molecules for quenching
fluorescence in semiconducting polymers.Comment: RevTeX 12 pages + 2 Postscript figure
Analisis Keputusan Pembelian Konsumen melalui Media Online (E-Marketing)
Tujuan dari penelitian ini adalah untuk mengidentifikasi dan menentukan variabel yang dominan dalam mempengaruhi keputusan pembelian konsumen serta mengetahui variabel Manfaat atau Hambatan dalam bertransaksi yang secara dominan merupakan variabel yang dipertimbangkan dalam keputusan pembelian konsumen melalui media online (e-Marketing) dan juga mengetahui kecenderungan perilaku konsumen dimasa yang akan datang jika dilihat dari Zscore yang terbentuk. Metode Penelitian yang digunakan adalah metode deskriptif kuantitatif. Teknik pengumpulan data yang dilakukan dengan survey terhadap 100 responden melalui penyebaran kuesioner. Sampel dalam penelitian ini diambil dengan menggunakan teknik quota dan purposive sampling. Berdasarkan fungsi diskriminan dapat disimpulkan bahwa ternyata dari kedua variabel tersebut ternyata variabel manfaat dalam bertransaksi yang paling dominan dalam mempengaruhi keputusan pembelian konsumen melalui media online (e-Marketing). Berdasarkan hasil perhitungan Zscore, didapatkan kecenderungan perilaku konsumen dimasa yang akan datang dalam keputusan pembelian ( jarang atau sering) yaitu lebih banyak konsumen yang sering membeli dibandingkan dengan konsumen yang jarang membeli
- …