2,351 research outputs found
Rhythmic Motion of a Droplet under a DC Electric Field
The effect of a stationary electric field on a water droplet with a diameter
of several tens micrometers in oil was examined. Such a droplet exhibits
repetitive translational motion between the electrodes in a spontaneous manner.
The state diagram of this oscillatory motion was deduced; at 0-20 V the droplet
is fixed at the surface of the electrode, at 20-70 V the droplet exhibits
small-amplitude oscillatory motion between the electrodes, and at 70-100 V the
droplet shows large-amplitude periodic motion between the electrodes. The
observed rhythmic motion is explained in a semi-quantitative manner by using
differential equations, which includes the effect of charging the droplet under
an electric field. We also found that twin droplets exhibit synchronized
rhythmic motion between the electrodes
Spin-Peierls and Antiferromagnetic Phases in Cu{1-x}Zn{x}GeO{3}: A Neutron Scattering Study
Comprehensive neutron scattering studies were carried out on a series of
high-quality single crystals of Cu_{1-x}Zn_xGeO_3. The Zn concentration, x, was
determined for each sample using Electron Probe Micro-Analysis. The measured Zn
concentrations were found to be 40-80% lower than the nominal values.
Nevertheless the measured concentrations cover a wide range which enables a
systematic study of the effects due to Zn-doping. We have confirmed the
coexistence of spin-Peierls (SP) and antiferromagnetic (AF) orderings at low
temperatures and the measured phase diagram is presented. Most surprisingly,
long-range AF ordering occurs even in the lowest available Zn concentration,
x=0.42%, which places important constraints on theoretical models of the AF-SP
coexistence. Magnetic excitations are also examined in detail. The AF
excitations are sharp at low energies and show no considerable broadening as x
increases indicating that the AF ordering remains long ranged for x up to 4.7%.
On the other hand, the SP phase exhibits increasing disorder as x increases, as
shown from the broadening of the SP excitations as well as the dimer reflection
peaks.Comment: 17 preprint style pages, 9 postscript files included. Submitted to
Phys. Rev. B. Also available from
http://insti.physics.sunysb.edu/~mmartin/pubs.htm
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
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.
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
The first-order phase transition between dimerized-antiferromagnetic and uniform-antiferromagnetic phases in Cu_(1-x)M_xGeO_3
We have performed detailed magnetic susceptibility measurements as well as
synchrotron x-ray diffraction studies to determine the temperature vs
concentration ( - ) phase diagram of CuMgGeO. We
observe clear double peaks in the magnetic susceptibility implying two
antiferromagnetic (AF) transition temperatures in samples with Mg
concentrations in the range 0.0237 0.0271. We also observe a
drastic change in the inverse correlation length in this concentration range by
x-ray diffraction. The drastic change of the AF transition temperature as well
as the disappearance of the spin-Peierls (SP) phase have been clarified; these
results are consistent with a first-order phase transition between dimerized AF
(D-AF) and uniform AF (U-AF) phases as reported by T. Masuda {\it et al.}
\lbrack Phys. Rev. Lett. {\bf 80}, 4566 (1998)\rbrack. The - phase
diagram of CuZnGeO is similar to that of
CuMgGeO, which suggests that the present phase transition
is universal for CuGeO.Comment: 7 pages, 5 figures. submitted to PR
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
Bimodal Size-distribution of Bainite Plates
There are two well-known phenomena associated with the bainite reaction, which have been exploited in the present work to enhance the mechanical behaviour of steel. Firstly, the bainite plate size decreases as the transformation temperature is reduced. Secondly, it is bad to have large regions of untransformed austenite in the microstructure; this is because they can transform, under the influence of external stress, into corresponding large regions of untempered, brittle martensite.
By adopting a two stage heat treatment in which coarse bainite is produced by isothermal transformation at a high temperature, followed by isothermal transformation at a lower temperature, it has been possible to eliminate blocks of austenite. This leads to a microstructure containing an organized dispersion of fine plates of bainitic ferrite in the regions between the coarse plates. The mechanical properties of this mixture are shown to be better than those of bainite obtained by transformation at any single temperature.
The experiments have been conducted in the context of very strong steels, where the strength and hardness can exceed 2.5GPa and 650 HV respectively.Peer reviewe
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