14,021 research outputs found
Pendulum Integration and Elliptic Functions
Revisiting canonical integration of the classical pendulum around its
unstable equilibrium, normal hyperbolic canonical coordinates are constructe
Classical Analog of Electromagnetically Induced Transparency
We present a classical analog for Electromagnetically Induced Transparency
(EIT). In a system of just two coupled harmonic oscillators subject to a
harmonic driving force we can reproduce the phenomenology observed in EIT. We
describe a simple experiment performed with two linearly coupled RLC circuits
which can be taught in an undergraduate laboratory class.Comment: 6 pages, two-column, 6 figures, submitted to the Am. J. Phy
Bistable forespore engulfment in Bacillus subtilis by a zipper mechanism in absence of the cell wall
To survive starvation, the bacterium Bacillus subtilis forms durable spores.
The initial step of sporulation is asymmetric cell division, leading to a large
mother-cell and a small forespore compartment. After division is completed and
the dividing septum is thinned, the mother cell engulfs the forespore in a slow
process based on cell-wall degradation and synthesis. However, recently a new
cell-wall independent mechanism was shown to significantly contribute, which
can even lead to fast engulfment in 60 of the cases when the cell
wall is completely removed. In this backup mechanism, strong ligand-receptor
binding between mother-cell protein SpoIIIAH and forespore-protein SpoIIQ leads
to zipper-like engulfment, but quantitative understanding is missing. In our
work, we combined fluorescence image analysis and stochastic Langevin
simulations of the fluctuating membrane to investigate the origin of fast
bistable engulfment in absence of the cell wall. Our cell morphologies compare
favorably with experimental time-lapse microscopy, with engulfment sensitive to
the number of SpoIIQ-SpoIIIAH bonds in a threshold-like manner. By systematic
exploration of model parameters, we predict regions of osmotic pressure and
membrane-surface tension that produce successful engulfment. Indeed, decreasing
the medium osmolarity in experiments prevents engulfment in line with our
predictions. Forespore engulfment may thus not only be an ideal model system to
study decision-making in single cells, but its biophysical principles are
likely applicable to engulfment in other cell types, e.g. during phagocytosis
in eukaryotes
Boundary Dissipation in a Driven Hard Disk System
A simulation is performed aiming at checking the existence of a well defined
stationary state for a two dimensional system of driven hard disks when energy
dissipation takes place at the system boundaries and no bulk impurities are
presentComment: 5 pages, 7 figure
Three-body properties of low-lying Be resonances
We compute the three-body structure of the lowest resonances of Be
considered as two neutrons around an inert Be core. This is an extension
of the bound state calculations of Be into the continuum spectrum. We
investigate the lowest resonances of angular momenta and parities, ,
and . Surprisingly enough, they all are naturally occurring in
the three-body model. We calculate bulk structure dominated by small distance
properties as well as decays determined by the asymptotic large-distance
structure. Both and have two-body Be-neutron d-wave
structure, while has an even mixture of and d-waves. The
corresponding relative neutron-neutron partial waves are distributed among ,
, and d-waves. The branching ratios show different mixtures of one-neutron
emission, three-body direct, and sequential decays. We argue for spin and
parities, , and , to the resonances at 0.89, 2.03, 5.13,
respectively. The computed structures are in agreement with existing reaction
measurements.Comment: To be published in Physical Review
Trademark cancellation for non use in EU
The report focuses on the peculiarities of trademark cancellation i
Phasing of gravitational waves from inspiralling eccentric binaries
We provide a method for analytically constructing high-accuracy templates for
the gravitational wave signals emitted by compact binaries moving in
inspiralling eccentric orbits. By contrast to the simpler problem of modeling
the gravitational wave signals emitted by inspiralling {\it circular} orbits,
which contain only two different time scales, namely those associated with the
orbital motion and the radiation reaction, the case of {\it inspiralling
eccentric} orbits involves {\it three different time scales}: orbital period,
periastron precession and radiation-reaction time scales. By using an improved
`method of variation of constants', we show how to combine these three time
scales, without making the usual approximation of treating the radiative time
scale as an adiabatic process. We explicitly implement our method at the 2.5PN
post-Newtonian accuracy. Our final results can be viewed as computing new
`post-adiabatic' short period contributions to the orbital phasing, or
equivalently, new short-period contributions to the gravitational wave
polarizations, , that should be explicitly added to the
`post-Newtonian' expansion for , if one treats radiative effects
on the orbital phasing of the latter in the usual adiabatic approximation. Our
results should be of importance both for the LIGO/VIRGO/GEO network of ground
based interferometric gravitational wave detectors (especially if Kozai
oscillations turn out to be significant in globular cluster triplets), and for
the future space-based interferometer LISA.Comment: 49 pages, 6 figures, high quality figures upon reques
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