896 research outputs found
Statistical mechanical systems on complete graphs, infinite exchangeability, finite extensions and a discrete finite moment problem
We show that a large collection of statistical mechanical systems with
quadratically represented Hamiltonians on the complete graph can be extended to
infinite exchangeable processes. This extends a known result for the
ferromagnetic Curie--Weiss Ising model and includes as well all ferromagnetic
Curie--Weiss Potts and Curie--Weiss Heisenberg models. By de Finetti's theorem,
this is equivalent to showing that these probability measures can be expressed
as averages of product measures. We provide examples showing that
``ferromagnetism'' is not however in itself sufficient and also study in some
detail the Curie--Weiss Ising model with an additional 3-body interaction.
Finally, we study the question of how much the antiferromagnetic Curie--Weiss
Ising model can be extended. In this direction, we obtain sharp asymptotic
results via a solution to a new moment problem. We also obtain a ``formula''
for the extension which is valid in many cases.Comment: Published at http://dx.doi.org/10.1214/009117906000001033 in the
Annals of Probability (http://www.imstat.org/aop/) by the Institute of
Mathematical Statistics (http://www.imstat.org
Synchronization versus stability of the invariant distribution for a class of globally coupled maps
We study a class of globally coupled maps in the continuum limit, where the
individual maps are expanding maps of the circle. The circle maps in question
are such that the uncoupled system admits a unique absolutely continuous
invariant measure (acim), which is furthermore mixing. Interaction arises in
the form of diffusive coupling, which involves a function that is discontinuous
on the circle. We show that for sufficiently small coupling strength the
coupled map system admits a unique absolutely continuous invariant
distribution, which depends on the coupling strength .
Furthermore, the invariant density exponentially attracts all initial
distributions considered in our framework. We also show that the dependence of
the invariant density on the coupling strength is Lipschitz
continuous in the BV norm.
When the coupling is sufficiently strong, the limit behavior of the system is
more complex. We prove that a wide class of initial measures approach a point
mass with support moving chaotically on the circle. This can be interpreted as
synchronization in a chaotic state
Alleviation of Extremely Power and Voltage Variations Caused by Wind Power and Load Demand Using SMES
Due to the high variations in wind speed and the continuing changes in load power demand (LPD), power and voltage at the point of common coupling (PCC) fluctuate according to the variations of injected wind power generation (WPG) and LPD simultaneously. Superconducting magnetic energy storage (SMES) plays a significant role in alleviating the power/voltage at PCC. This paper shows the impact of SMES in enhancing the performance of interconnected WPG system during high wind gust variations and the changes in LPD. WPG includes squirrel-cage induction generator (SCIG) type with a shunt-connected capacitor for improving the power factor. WPG, SMES and the load are located at PCC. Fuzzy logic control (FLC) is used with the DC-DC chopper to control the power exchange between AC system and SMES. FLC is designed where SMES can absorb/inject real power from/to the grid. On the other hand, reactive power is controlled to adjust the variation of PCC voltage. Two inputs are applied to the FLC; the summation of wind power variation and change of LPD as the first input and the variation of SMES current is the second one to control active power transferred between SMES and AC system. The suggested control approach of SMES is a fast response, as it successfully controlled the PCC voltage, line active and reactive powers during wind gusts and the variations of the load side
Validation of the Estimated Torques of an Open-chain Kinematic Model of the Human Body
The standing human body is frequently modeled as an inverted double pendulum restricted to a single plane. In order to capture the coordination efforts and interplay between spatial dimensions, the model has to capture motion and joint torques in all spatial dimensions. Our two-segment model covers two degrees of freedom (ML and AP revolutions) at the ankle and the hip level and utilizes the Denavit-Hartenberg convention. This work aimed to validate the model's torque estimation on a diverse group of participants (11 women, 22–56 years, 11 men, 22–61 years). The inverse dynamic calculations provide estimated joint torques for a motion capture recorded trial, while standing on a force platform enables the indirect measurement of ankle torques. A 60-second-long visually guided balancing task was recorded and repeated three times. The estimated and the indirectly measured torques were compared, and offset and variance type errors ( normalized RMSE and R2 ) were analyzed. The R2-values were excellent (R2 > 0.90) 64 out of the 66 cases (97%) for AP torques and 58 out of the 66 cases (88%) for ML torques. Normalized RMSE values were dominantly under the 0.35 value with some outliers. RMSE showed no evident connection with age, body height, body mass, or BMI. An open-chain kinematic model with two segments, following the Denavit-Hartenberg convention, is well suited to estimate the control torque traces of the human body during standing balancing and needs only three tracked positions
Erdőszegélyek fajösszetételét és szerkezetét meghatározó tényezők
Vizsgálatainkat
két eltérő termőhelyi viszonyok között kialakult e
rdőtársulás esetében
az
erdőállomány és a szomszédos nyílt terület átmeneti zónájában végeztük. A Budai-hegységben két cseres-
kocsánytalan tölgyes
(
Quercetum petraeae-cerris
S
oó
1963)
erdőállomány, illetve a szomszédos parlag
-
területek határán található,
különböző égtáji kitettségű (ÉK, ÉNY, DK, DNY) erdőszegélyeket
vizsgáltunk.
Csáfordjánosfa határában egy síkvidéki üde tölgy-kőris-szil ligeterdő (
Fraxino pannonicae-Ulmetum
S
oó
in
A
S
zód
1935 corr. 1963), illetve a szomszédos dunántúli mocsárrét (
Deschampsietum caespitosae
)
határán ki
-
alakult, az előbbiekkel
megegyező égtáji kitettségű erdőszegélyeket
vizsgáltuk.
Célunk volt annak megállapítása, hogy van-e határozott különbség az átmeneti zóna egyes szerkezeti ele
-
meinek (nyílt terület, lágyszárú szegély, cserjés szegély, erdőköpeny, erdőbelső) fajösszetétele között, az egyes
erdőtársulások, illetve a különböző égtáji kitettségű szegélyek esetében.
Eredményeink alapján a cseres-kocsánytalan tölgyes és a tölgy-kőris-szil ligeterdő állományok szegélyei
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nek fajösszetétele teljes mértékben eltér egymástól. Az erdőszegélyek fajösszetétele és szerkezete minden eset
-
ben az
égtáji kitettségtől függően alakul
Synthesis of Homogeneous Manganese-Doped Titanium Oxide Nanotubes from Titanate Precursors
We report a novel synthesis route of homogeneously manganese-doped titanium
dioxide nanotubes in a broad concentration range. The scroll-type trititanate
(H(2)Ti(3)O(7)) nanotubes prepared by hydrothermal synthesis were used as
precursors. Mn2+ ions were introduced by an ion exchange method resulting
Mn(x)H(2-x)Ti(3)O(7). In a subsequent heat-treatment they were transformed into
Mn(y)Ti(1-y)O(2) where y=x/(3+x). The state and the local environment of the
Mn2+ ions in the precursor and final products were studied by Electron Spin
Resonance (ESR) technique. It was found that the Mn2+ ions occupy two
positions: the first having an almost perfect cubic symmetry while the other is
in a strongly distorted octahedral site. The ratio of the two Mn2+ sites is
independent of the doping level and amounts to 15:85 in Mn(x)H(2-x)Ti(3)O(7)
and to 5:95 in Mn(y)Ti(1-y)O(2). SQUID magnetometry does not show long-range
magnetic order in the homogeneously Mn2+-doped nanotubes.Comment: 7 pages, 6 figure
Calm Multi-Baryon Operators
Outstanding problems in nuclear physics require input and guidance from
lattice QCD calculations of few baryons systems. However, these calculations
suffer from an exponentially bad signal-to-noise problem which has prevented a
controlled extrapolation to the physical point. The variational method has been
applied very successfully to two-meson systems, allowing for the extraction of
the two-meson states very early in Euclidean time through the use of improved
single hadron operators. The sheer numerical cost of using the same techniques
in two-baryon systems has been prohibitive. We present an alternate strategy
which offers some of the same advantages as the variational method while being
significantly less numerically expensive. We first use the Matrix Prony method
to form an optimal linear combination of single baryon interpolating fields
generated from the same source and different sink interpolators. Very early in
Euclidean time this linear combination is numerically free of excited state
contamination, so we coin it a calm baryon. This calm baryon operator is then
used in the construction of the two-baryon correlation functions.
To test this method, we perform calculations on the WM/JLab iso-clover gauge
configurations at the SU(3) flavor symmetric point with m{\pi} 800 MeV
--- the same configurations we have previously used for the calculation of
two-nucleon correlation functions. We observe the calm baryon removes the
excited state contamination from the two-nucleon correlation function to as
early a time as the single-nucleon is improved, provided non-local (displaced
nucleon) sources are used. For the local two-nucleon correlation function
(where both nucleons are created from the same space-time location) there is
still improvement, but there is significant excited state contamination in the
region the single calm baryon displays no excited state contamination.Comment: 8 pages, 3 figures, proceedings for LATTICE 201
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