189 research outputs found
Nonlinear dynamics of two coupled nano-electromechanical resonators
As a model of coupled nano-electromechanical resonantors we study two
nonlinear driven oscillators with an arbitrary coupling strength between them.
Analytical expressions are derived for the oscillation amplitudes as a function
of the driving frequency and for the energy transfer rate between the two
oscillators. The nonlinear restoring forces induce the expected nonlinear
resonance structures in the amplitude-frequency characteristics with asymmetric
resonance peaks. The corresponding multistable behavior is shown to be an
efficient tool to control the energy transfer arising from the sensitive
response to small changes in the driving frequency. Our results imply that the
nonlinear response can be exploited to design precise sensors for mass or force
detection experiments based on nano-electromechanical resonators.Comment: 19 pages, 2 figure
POLAR, an instrument to measure GRB polarization. Design and laboratory tests.
International audienceReliable polarization measurements of photons from Gamma Ray Bursts (GRB) would make the understanding of the GRB phenomenon progress enormously. POLAR is a concept for an instrument that would enable such a measurement. We report about performances predicted by of Monte-Carlo and on laboratory tests to validate some critical aspects of the desig
Kinetochore alignment within the metaphase plate is regulated by centromere stiffness and microtubule depolymerases
During mitosis in most eukaryotic cells, chromosomes align and form a metaphase plate halfway between the spindle poles, about which they exhibit oscillatory movement. These movements are accompanied by changes in the distance between sister kinetochores, commonly referred to as breathing. We developed a live cell imaging assay combined with computational image analysis to quantify the properties and dynamics of sister kinetochores in three dimensions. We show that baseline oscillation and breathing speeds in late prometaphase and metaphase are set by microtubule depolymerases, whereas oscillation and breathing periods depend on the stiffness of the mechanical linkage between sisters. Metaphase plates become thinner as cells progress toward anaphase as a result of reduced oscillation speed at a relatively constant oscillation period. The progressive slowdown of oscillation speed and its coupling to plate thickness depend nonlinearly on the stiffness of the mechanical linkage between sisters. We propose that metaphase plate formation and thinning require tight control of the state of the mechanical linkage between sisters mediated by centromeric chromatin and cohesion
Chaotic Phenomenon in Nonlinear Gyrotropic Medium
Nonlinear gyrotropic medium is a medium, whose natural optical activity
depends on the intensity of the incident light wave. The Kuhn's model is used
to study nonlinear gyrotropic medium with great success. The Kuhn's model
presents itself a model of nonlinear coupled oscillators. This article is
devoted to the study of the Kuhn's nonlinear model. In the first paragraph of
the paper we study classical dynamics in case of weak as well as strong
nonlinearity. In case of week nonlinearity we have obtained the analytical
solutions, which are in good agreement with the numerical solutions. In case of
strong nonlinearity we have determined the values of those parameters for which
chaos is formed in the system under study. The second paragraph of the paper
refers to the question of the Kuhn's model integrability. It is shown, that at
the certain values of the interaction potential this model is exactly
integrable and under certain conditions it is reduced to so-called universal
Hamiltonian. The third paragraph of the paper is devoted to quantum-mechanical
consideration. It shows the possibility of stochastic absorption of external
field energy by nonlinear gyrotropic medium. The last forth paragraph of the
paper is devoted to generalization of the Kuhn's model for infinite chain of
interacting oscillators
Measurement of the analyzing powers in pd elastic and pn quasi-elastic scattering at small angles
The analyzing powers in proton-deuteron elastic and proton-neutron
quasi-elastic scattering have been measured at small angles using a polarized
proton beam at the COSY storage ring incident on an unpolarized deuterium
target. The data were taken at 796MeV and five higher energies from 1600MeV to
2400MeV. The analyzing power in pd elastic scattering was studied by detecting
the low energy recoil deuteron in telescopes placed symmetrically in the COSY
plane to the left and right of the beam whereas for pn quasi-elastic scattering
a low energy proton was registered in one of the telescopes in coincidence with
a fast scattered proton measured in the ANKE magnetic spectrometer. Though the
experiment explores new domains, the results are consistent with the limited
published information.Comment: 10 pages with 8 figure
First measurements of spin correlations in the np -> d pi^0 reaction
The transverse spin correlations Axx and Ayy in the np-> d pi^0 reaction have
been measured for the first time in quasi-free kinematics at the COSY-ANKE
facility using a polarised deuteron beam incident on a polarised hydrogen cell
target. The results obtained for neutron energies close to 353 MeV and 600 MeV
are in good agreement with the partial wave analysis of data on the
isospin-related pp-> d pi^+ reaction, though the present results cover also the
small-angle region, which was largely absent from these data
Absence of spin dependence in the final state interaction of the d(pol) p --> 3He eta reaction
The deuteron tensor analysing power t_{20} of the d(pol) p --> 3He eta
reaction has been measured at the COSY-ANKE facility in small steps in excess
energy Q up to Q = 11 MeV. Despite the square of the production amplitude
varying by over a factor of five through this range, t_{20} shows little or no
energy dependence. This is evidence that the final state interaction causing
the energy variation is not influenced by the spin configuration in the
entrance channel. The weak angular dependence observed for t_{20} provides
useful insight into the amplitude structure near threshold.Comment: 5 pages, 4 figure
Measuring the Polarization of a Rapidly Precessing Deuteron Beam
This paper describes a time-marking system that enables a measurement of the
in-plane (horizontal) polarization of a 0.97-GeV/c deuteron beam circulating in
the Cooler Synchrotron (COSY) at the Forschungszentrum J\"ulich. The clock time
of each polarimeter event is used to unfold the 120-kHz spin precession and
assign events to bins according to the direction of the horizontal
polarization. After accumulation for one or more seconds, the down-up
scattering asymmetry can be calculated for each direction and matched to a
sinusoidal function whose magnitude is proportional to the horizontal
polarization. This requires prior knowledge of the spin tune or polarization
precession rate. An initial estimate is refined by re-sorting the events as the
spin tune is adjusted across a narrow range and searching for the maximum
polarization magnitude. The result is biased toward polarization values that
are too large, in part because of statistical fluctuations but also because
sinusoidal fits to even random data will produce sizeable magnitudes when the
phase is left free to vary. An analysis procedure is described that matches the
time dependence of the horizontal polarization to templates based on
emittance-driven polarization loss while correcting for the positive bias. This
information will be used to study ways to extend the horizontal polarization
lifetime by correcting spin tune spread using ring sextupole fields and thereby
to support the feasibility of searching for an intrinsic electric dipole moment
using polarized beams in a storage ring. This paper is a combined effort of the
Storage Ring EDM Collaboration and the JEDI Collaboration.Comment: 28 pages, 15 figures, prepared for Physical Review ST - Accelerators
and Beam
Resonance-like coherent production of a pion pair in the reaction in the GeV region
The reaction was studied at 0.8-2.0 GeV proton
beam energies with the ANKE magnetic spectrometer at the COSY synchrotron
storage ring. The proton-deuteron pairs emerging with high momenta, 0.6-1.8
GeV/, were detected at small angles with respect to the proton beam.
Distribution over the reaction missing mass reveals a local enhancement
near the threshold of the pion pair production specific for the so-called ABC
effect. The enhancement has a structure of a narrow bump placed above a smooth
continuum. The invariant mass of the system in this enhancement
region exhibits a resonance-like peak at GeV/
with the width GeV/. A possible interpretation of
these features is discussed.Comment: 14 pages, 16 figures, submitted to Eur. Phys. J. A. v2: Added
references [42,43] in section IV.A. v3: revised version according to referee
remarks v4: revised version according to referee remark
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