295 research outputs found
Vibrational origin of the fast relaxation processes in molecular glass-formers
We study the interaction of the relaxation processes with the density
fluctuations by molecular dynamics simulation of a flexible molecule model for
o-terphenyl (oTP) in the liquid and supercooled phases. We find evidence,
besides the structural relaxation, of a secondary vibrational relaxation whose
characteristic time, few ps, is slightly temperature dependent. This i)
confirms the result by Monaco et al. [Phys. Rev, E 62, 7595 (2000)] of the
vibrational nature of the fast relaxation observed in Brillouin Light
Scattering (BLS) experiments in oTP; and ii) poses a caveat on the
interpretation of the BLS spectra of molecular systems in terms of a purely
center of mass dynamics.Comment: RevTeX, 5 pages, 4 eps figure
Effective temperature of active matter
We follow the dynamics of an ensemble of interacting self-propelled motorized
particles in contact with an equilibrated thermal bath. We find that the
fluctuation-dissipation relation allows for the definition of an effective
temperature that is compatible with the results obtained using a tracer
particle as a thermometer. The effective temperature takes a value which is
higher than the temperature of the bath and it is continuously controlled by
the motor intensity
Optimizing the Dynamic Performance of a Wind Driven Standalone DFIG Using an Advanced Control Algorithm
The article seeks to improve the dynamic performance of a standalone doubly fed induction generator (DFIG) which driven by a wind turbine, with the help of an effective control approach. The superiority of the designed predictive controller can be confirmed through evaluating the performance of the DFIG under other control algorithm, which is the model predictive direct torque control (MPDTC), model predictive current control (MPCC) as classic types of control. Firstly, the operating principles of the two controllers are described in details. After that, a comprehensive comparison is performed among the dynamic performances of the designed MPDTC, MPCC techniques and the predictive control strategy, so we can easily present the merits and deficiencies of each control scheme to be able to easily select the most appropriate algorithm to be utilized with the DFIG. The comparison is carried out in terms of system simplicity, dynamic response, ripples’ content, number of performed commutations and total harmonic distortion (THD). The results of the comparison prove the effectiveness and validation of our proposed predictive controller; as it achieves the system simplicity, its dynamic response is faster than that of MPDTC and MPCC, it presents a lower content of ripples compared to MPDTC and MPCC. Moreover, it can minimize the computational burden, remarkably. Furthermore, the numerical results are showing a marked reduction in the THD with a percentage of 2.23 % compared to MPDTC and 1.8 % compared to MPCC. For these reasons, it can be said that the formulated controller is the most convenient to be used with the DFIG to achieve the best dynamic performance
Balanced metrics on homogeneous vector bundles
Let be a holomorphic vector bundle over a compact Kaehler
manifold and let be its
decomposition into irreducible factors. Suppose that each admits a
-balanced metric in Donaldson-Wang terminology. In this paper we prove
that admits a unique -balanced metric if and only if
for all , where denotes
the rank of and . We apply our result to the case
of homogeneous vector bundles over a rational homogeneous variety
and we show the existence and rigidity of balanced Kaehler embedding from into Grassmannians.Comment: 5 page
On the Refractive Index of Ageing Dispersions of Laponite
Aqueous dispersion of Laponite at low ionic concentration is of interest
since it undergoes structural evolution with respect to time, which is usually
termed as ageing. In this work we study the refractive index behavior as a
function of ageing time, concentration and temperature. We observed that the
extended Lorenz-Lorentz equation fitted the refractive index dependence on
concentration and temperature very well. The refractive index did not show any
dependence on ageing time. However, the dependence of refractive index on
concentration showed a marked change as the system underwent transition from an
isotropic to a biphasic state. The slope of the refractive index-density data
is remarkably close to that of water at all Laponite concentrations. In the
context of transport phenomena, optical measurements such as interferometry can
exploit the water-like behavior of Laponite dispersions.Comment: 13 pages, 3 figures, to appear in Applied Clay Scienc
Finite-Size Effects in a Supercooled Liquid
We study the influence of the system size on various static and dynamic
properties of a supercooled binary Lennard-Jones liquid via computer
simulations. In this way, we demonstrate that the treatment of systems as small
as N=65 particles yields relevant results for the understanding of bulk
properties. Especially, we find that a system of N=130 particles behaves
basically as two non-interacting systems of half the size.Comment: Proceedings of the III Workshop on Non Equilibrium Phenomena in
Supercooled Fluids, Glasses and Amorphous Materials, Sep 2002, Pis
Improving signal-to-noise resolution in single molecule experiments using molecular constructs with short handles
We investigate unfolding/folding force kinetics in DNA hairpins exhibiting
two and three states with newly designed short dsDNA handles (29 bp) using
optical tweezers. We show how the higher stiffness of the molecular setup
moderately enhances the signal-to-noise ratio (SNR) in hopping experiments as
compared to conventional long handles constructs (approximately 700 bp). The
shorter construct results in a signal of higher SNR and slower
folding/unfolding kinetics, thereby facilitating the detection of otherwise
fast structural transitions. A novel analysis of the elastic properties of the
molecular setup, based on high-bandwidth measurements of force fluctuations
along the folded branch, reveals that the highest SNR that can be achieved with
short handles is potentially limited by the marked reduction of the effective
persistence length and stretch modulus of the short linker complex.Comment: Main paper: 20 pages and 6 figures. Supplementary Material: 25 page
Sub-sampling a large physical soil archive for additional analyses to support spatial mapping; a pre-registered experiment in the Southern Nations, Nationalities, and Peoples Region (SNNPR) of Ethiopia
The value of physical archives of soil material from field sampling activities has been widely recognized. If we want to use archive material for new destructive analyses to support a task, such as spatial mapping, then an efficient sub-sampling strategy is needed, both to manage analytical costs and to conserve the archive material. In this paper we present an approach to this problem when the objective is spatial mapping by ordinary kriging. Our objective was to subsample the physical archive from the Ethiopia Soil Information System (EthioSIS) survey of the Southern Nations, Nationalities and Peoples Region (SNNPR) for spatial mapping of two variables, concentrations of particular fractions of selenium and iodine in the soil, which had not been measured there. We used data from cognate parts of surrounding regions of Ethiopia to estimate variograms of these properties, and then computed prediction error variances for maps in SNNPR based on proposed subsets of the archive of different size, selected to optimize a spatial coverage criterion (with some close sample pairs included). On this basis a subsample was selected. This is a preregistered experiment in that we have proposed criteria for evaluating the success of our approach, and are publishing that in advance of receiving analytical data on the subsampled material from the laboratories where they are being processed. A subsequent short report will publish the outcome. The use of preregistered trials is widely recommended and used in areas of science including public health, and we believe that it is a sound strategy to promote reproducible research in soil science
The Glassy Potts Model
We introduce a Potts model with quenched, frustrated disorder, that enjoys of
a gauge symmetry that forbids spontaneous magnetization, and allows the glassy
phase to extend from down to T=0. We study numerical the 4 dimensional
model with states. We show the existence of a glassy phase, and we
characterize it by studying the probability distributions of an order
parameter, the binder cumulant and the divergence of the overlap
susceptibility. We show that the dynamical behavior of the system is
characterized by aging.Comment: 4 pages including 4 (color) ps figures (all on page 4
Large Scale Cross-Correlations in Internet Traffic
The Internet is a complex network of interconnected routers and the existence
of collective behavior such as congestion suggests that the correlations
between different connections play a crucial role. It is thus critical to
measure and quantify these correlations. We use methods of random matrix theory
(RMT) to analyze the cross-correlation matrix C of information flow changes of
650 connections between 26 routers of the French scientific network `Renater'.
We find that C has the universal properties of the Gaussian orthogonal ensemble
of random matrices: The distribution of eigenvalues--up to a rescaling which
exhibits a typical correlation time of the order 10 minutes--and the spacing
distribution follow the predictions of RMT. There are some deviations for large
eigenvalues which contain network-specific information and which identify
genuine correlations between connections. The study of the most correlated
connections reveals the existence of `active centers' which are exchanging
information with a large number of routers thereby inducing correlations
between the corresponding connections. These strong correlations could be a
reason for the observed self-similarity in the WWW traffic.Comment: 7 pages, 6 figures, final versio
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