4,303 research outputs found
The effect of the lateral interactions on the critical behavior of long straight rigid rods on two-dimensional lattices
Using Monte Carlo simulations and finite-size scaling analysis, the critical
behavior of attractive rigid rods of length k (k-mers) on square lattices at
intermediate density has been studied. A nematic phase, characterized by a big
domain of parallel k-mers, was found. This ordered phase is separated from the
isotropic state by a continuous transition occurring at a intermediate density
\theta_c, which increases linearly with the magnitude of the lateral
interactions.Comment: 7 pages, 6 figure
Cloud services, interoperability and analytics within a ROLE-enabled personal learning environment
The ROLE project (Responsive Open Learning Environments, EU 7th Framework Programme, grant agreement no.: 231396, 2009-2013) was focused on the next generation of Personal Learning Environments (PLEs). A ROLE PLE is a bundle of interoperating widgets - often realised as cloud services - used for teaching and learning. In this paper, we first describe the creation of new ROLE widgets and widget bundles at Galileo University, Guatemala, within a cloud-based infrastructure. We introduce an initial architecture for cloud interoperability services including the means for collecting interaction data as needed for learning analytics. Furthermore, we describe the newly implemented widgets, namely a social networking tool, a mind-mapping tool and an online document editor, as well as the modification of existing widgets. The newly created and modified widgets have been combined in two different bundles that have been evaluated in two web-based courses at Galileo University, with participants from three different Latin-American countries. We measured emotional aspects, motivation, usability and attitudes towards the environment. The results demonstrated the readiness of cloud-based education solutions, and how ROLE can bring together such an environment from a PLE perspective
Critical behavior of self-assembled rigid rods on triangular and honeycomb lattices
Using Monte Carlo simulations and finite-size scaling analysis, the critical
behavior of self-assembled rigid rods on triangular and honeycomb lattices at
intermediate density has been studied. The system is composed of monomers with
two attractive (sticky) poles that, by decreasing temperature or increasing
density, polymerize reversibly into chains with three allowed directions and,
at the same time, undergo a continuous isotropic-nematic (IN) transition. The
determination of the critical exponents, along with the behavior of Binder
cumulants, indicate that the IN transition belongs to the q=1 Potts
universality class.Comment: 6 pages, 5 figure
Scheme to measure squeezing and phase properties of a harmonic oscillator
We propose a simple scheme to measure squeezing and phase properties of a
harmonic oscillator. We treat in particular the case of a the field, but the
scheme may be easily realized in ion traps. It is based on integral transforms
of measured atomic properties as atoms exit a cavity. We show that by measuring
atomic polarizations it is possible, after a given integration, to measure
several properties of the field.Comment: Presented at XI Central European Workshop on Quantum Optics, Trieste,
Italy, 18-20 July, 200
Critical behavior of long straight rigid rods on two-dimensional lattices: Theory and Monte Carlo simulations
The critical behavior of long straight rigid rods of length (-mers) on
square and triangular lattices at intermediate density has been studied. A
nematic phase, characterized by a big domain of parallel -mers, was found.
This ordered phase is separated from the isotropic state by a continuous
transition occurring at a intermediate density . Two analytical
techniques were combined with Monte Carlo simulations to predict the dependence
of on , being . The first involves
simple geometrical arguments, while the second is based on entropy
considerations. Our analysis allowed us also to determine the minimum value of
(), which allows the formation of a nematic phase on a
triangular lattice.Comment: 23 pages, 5 figures, to appear in The Journal of Chemical Physic
Entropy-driven phase transition in a system of long rods on a square lattice
The isotropic-nematic (I-N) phase transition in a system of long straight
rigid rods of length k on square lattices is studied by combining Monte Carlo
simulations and theoretical analysis. The process is analyzed by comparing the
configurational entropy of the system with the corresponding to a fully aligned
system, whose calculation reduces to the 1D case. The results obtained (1)
allow to estimate the minimum value of k which leads to the formation of a
nematic phase and provide an interesting interpretation of this critical value;
(2) provide numerical evidence on the existence of a second phase transition
(from a nematic to a non-nematic state) occurring at density close to 1 and (3)
allow to test the predictions of the main theoretical models developed to treat
the polymers adsorption problem.Comment: 14 pages, 6 figures. Accepted for publication in JSTA
A Diabatic Three-State Representation of Photoisomerization in the Green Fluorescent Protein Chromophore
We give a quantum chemical description of bridge photoisomerization reaction
of green fluorescent protein (GFP) chromophores using a representation over
three diabatic states. Bridge photoisomerization leads to non-radiative decay,
and competes with fluorescence in these systems. In the protein, this pathway
is suppressed, leading to fluorescence. Understanding the electronic structure
of the photoisomerization is a prerequisite to understanding how the protein
suppresses this pathway and preserves the emitting state of the chromophore. We
present a solution to the state-averaged complete active space problem, which
is spanned at convergence by three fragment-localized orbitals. We generate the
diabatic-state representation by applying a block diagonalization
transformation to the Hamiltonian calculated for the anionic chromophore model
HBDI with multi-reference, multi-state perturbation theory. The diabatic states
that emerge are charge-localized structures with a natural valence-bond
interpretation. At planar geometries, the diabatic picture recaptures the
charge transfer resonance of the anion. The strong S0-S1 excitation at these
geometries is reasonably described within a two-state model, but extension to a
three-state model is necessary to describe decay via two possible pathways
associated with photoisomerization of the (methine) bridge. Parametric
Hamiltonians based on the three-state ansatz can be fit directly to data
generated using the underlying active space. We provide an illustrative example
of such a parametric Hamiltonian
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