2,546 research outputs found
Aging and fluctuation-dissipation ratio in a nonequilibrium -state lattice model
A generalized version of the nonequilibrium linear Glauber model with
states in dimensions is introduced and analyzed. The model is fully
symmetric, its dynamics being invariant under all permutations of the
states. Exact expressions for the two-time autocorrelation and response
functions on a -dimensional lattice are obtained. In the stationary regime,
the fluctuation-dissipation theorem holds, while in the transient the aging is
observed with the fluctuation-dissipation ratio leading to the value predicted
for the linear Glauber model
A Novel Photonic Material for Designing Arbitrarily Shaped Waveguides in Two Dimensions
We investigate numerically optical properties of novel two-dimensional
photonic materials where parallel dielectric rods are randomly placed with the
restriction that the distance between rods is larger than a certain value. A
large complete photonic gap (PG) is found when rods have sufficient density and
dielectric contrast. Our result shows that neither long-range nor short-range
order is an essential prerequisite to the formation of PGs. A universal
principle is proposed for designing arbitrarily shaped waveguides, where
waveguides are fenced with side walls of periodic rods and surrounded by the
novel photonic materials. We observe highly efficient transmission of light for
various waveguides. Due to structural uniformity, the novel photonic materials
are best suited for filling up the outer region of waveguides of arbitrary
shape and dimension comparable with the wavelength.Comment: 4 figure
VLBI2010 - The TWIN radio telescope project at Wettzell, Germany
The Twin Telescope Wettzell (TTW) Project is funded to be exec
uted during the period of 2008-2011. The design of the TTW was based on the VLBI2010 vision of the corresponding IVS Working Group. In the first two project years the design passed the simulations with respect to its specifications and was approved for production. At the Geodetic Observatory Wettzell a thorough soil analysis was made in order to define the sites for the towers of the new radio telescopes. Meanwhile the construction work has begun and acceptance tests of several telescope parts, e.g. azimuth bearings, took place. The full assembly of the radio telescopes is scheduled for the next two years. In parallel to the construction work at the Wettzell site, the design work for the different feed options progressed
Reentrant Spin-Peierls Transition in Mg-Doped CuGeO_3
We report a synchrotron x-ray scattering study of the diluted spin-Peierls
(SP) material Cu_{1-x}Mg_xGeO_3. In a recent paper we have shown that the SP
dimerization attains long-range order only for x < x_c = 0.022(0.001). Here we
report that the SP transition is reentrant in the vicinity of the critical
concentration x_c. This is manifested by broadening of the SP dimerization
superlattice peaks below the reentrance temperature, T_r, which may mean either
the complete loss of the long-range SP order or the development of a
short-range ordered component within the long-range ordered SP state. Marked
hysteresis and very large relaxation times are found in the samples with Mg
concentrations in the vicinity of x_c. The reentrant transition is likely
related to the competing Neel transition which occurs at a temperature similar
to T_r. We argue that impurity-induced competing interchain interactions play
an essential role in these phenomena.Comment: 5 pages, 4 embedded eps figure
The fluctuation-dissipation theorem and the linear Glauber model
We obtain exact expressions for the two-time autocorrelation and response
functions of the -dimensional linear Glauber model. Although this linear
model does not obey detailed balance in dimensions , we show that the
usual form of the fluctuation-dissipation ratio still holds in the stationary
regime. In the transient regime, we show the occurence of aging, with a special
limit of the fluctuation-dissipation ratio, , for a quench at
the critical point.Comment: Accepted for publication (Physical Review E
Separation of the magnetic phases at the N\'{e}el point in the diluted spin-Peierls magnet CuGeO3
The impurity induced antiferromagnetic ordering of the doped spin-Peierls
magnet Cu(1-x)Mg(x)GeO(3) was studied by ESR technique. Crystals with the Mg
concentration x<4% demonstrate a coexistence of paramagnetic and
antiferromagnetic ESR modes. This coexistence indicates the separation of a
macroscopically uniform sample in the paramagnetic and antiferromagnetic
phases. In the presence of the long-range spin-Peierls order (in a sample with
x=1.71%) the volume of the antiferromagnetic phase immediately below the
N\'{e}el point T_N is much smaller than the volume of the paramagnetic phase.
In the presence of the short-range spin-Peierls order (in samples with x=2.88%,
x= 3.2%) there are comparable volumes of paramagnetic and antiferromagnetic
phases at T=T_N. The fraction of the antiferromagnetic phase increases with
lowering temperature. In the absence of the spin-Peierls dimerization (at
x=4.57%)the whole sample exhibits the transition into the antiferromagnetic
state and there is no phase separation. The phase separation is explained by
the consideration of clusters of staggered magnetization located near impurity
atoms. In this model the areas occupied by coherently correlated spins expand
with decreasing temperature and the percolation of the ordered area through a
macroscopic distance occurs.Comment: 7pages, 10 figure
Lifetime Adherence to Physical Activity Recommendations and Fall Occurrence in Community-dwelling Older Adults: a Retrospective Cohort Study
Falling is a major health concern for community-dwelling older adults. Regular physical activity has been proposed to prevent falls. The aim of this study was to assess whether the achievement of the 2004 UK Department of Health physical activity recommendations over a lifetime had a protective effect against falling in older people. 313 community-dwelling older adults completed a questionnaire about lifetime physical activity and fall occurrence. There were significantly fewer falls in those who had led an active lifestyle compared to those who had not (Ï2Yates=4.568, p=0.033), with a lower relative risk of fall occurrence for the active respondents (RR=0.671) compared to the inactive (RR=1.210). Of those who were sufficiently active in their early adulthood, the decade where there was the biggest decrease in remaining active enough was in the 60s. It is concluded that an active lifestyle may have decreased the likelihood of having a fall in older ag
Spin-phonon coupled modes in the incommensurate phases of doped CuGeO
The doping effect of the folded phonon mode at 98 cm was investigated
on the Si-doped CuGeO by magneto-optical measurements in far-infrared (FIR)
region under high magnetic field. The folded phonon mode at 98 cm
appears not only in the dimerized (D) phase but also in the
dimerized-anitiferromagnetic (DAF) phase on the doped CuGeO. The splitting
was observed in the incommensurate (IC) phase and the antiferromagnetically
ordered incommensurate (IAF) phase above . The split-off branches exhibit
different field dependence from that of the pure CuGeO in the vicinity of
, and the discrepancy in the IAF phase is larger than that in the IC
phase. It is caused by the interaction between the solitons and the impurities.Comment: 7 pages, 4 figures, resubmitted to Phys. Rev.
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