1,603 research outputs found
Current reversals in a rocking ratchet: the frequency domain
Motivated by recent work [D. Cubero et al., Phys. Rev. E 82, 041116 (2010)],
we examine the mechanisms which determine current reversals in rocking ratchets
as observed by varying the frequency of the drive. We found that a class of
these current reversals in the frequency domain are precisely determined by
dissipation-induced symmetry breaking. Our experimental and theoretical work
thus extends and generalizes the previously identified relationship between
dynamical and symmetry-breaking mechanisms in the generation of current
reversals
Current reversals in a rocking ratchet: dynamical vs symmetry-breaking mechanisms
Directed transport in ratchets is determined by symmetry-breaking in a system
out of equilibrium. A hallmark of rocking ratchets is current reversals: an
increase in the rocking force changes the direction of the current. In this
work for a bi-harmonically driven spatially symmetric rocking ratchet we show
that a class of current reversal is precisely determined by symmetry-breaking,
thus creating a link between dynamical and symmetry-breaking mechanisms
Vibrational mechanics in an optical lattice: controlling transport via potential renormalization
We demonstrate theoretically and experimentally the phenomenon of vibrational
resonance in a periodic potential, using cold atoms in an optical lattice as a
model system. A high-frequency (HF) drive, with frequency much larger than any
characteristic frequency of the system, is applied by phase-modulating one of
the lattice beams. We show that the HF drive leads to the renormalization of
the potential. We used transport measurements as a probe of the potential
renormalization. The very same experiments also demonstrate that transport can
be controlled by the HF drive via potential renormalization.Comment: Phys. Rev. Lett., in pres
Isospin effect on nuclear stopping in intermediate energy Heavy Ion Collisions
By using the Isospin Dependent Quantum Molecular Dynamics Model (IQMD), we
study the dependence of nuclear stopping Q_{ZZ}/A and R in intermediate energy
heavy ion collisions on system size, initial N/Z, isospin symmetry potential
and the medium correction of two-body cross sections. We find the effect of
initial N/Z ratio, isospin symmetry potential on stopping is weak. The
excitation function of Q_{ZZ}/A and R depends on the form of medium correction
of two-body cross sections, the equation of state of nuclear matter (EOS). Our
results show the behavior of the excitation function of Q_{ZZ}/A and R can
provide clearer information of the isospin dependence of the medium correction
of two-body cross sections.Comment: 3 pages including 4 figure
High-frequency effects in the FitzHugh-Nagumo neuron model
The effect of a high-frequency signal on the FitzHugh-Nagumo excitable model
is analyzed. We show that the firing rate is diminished as the ratio of the
high-frequency amplitude to its frequency is increased. Moreover, it is
demonstrated that the excitable character of the system, and consequently the
firing activity, is suppressed for ratios above a given threshold value. In
addition, we show that the vibrational resonance phenomenon turns up for
sufficiently large noise strength values.Comment: 4 pages, 4 figures (to appear in Physical Review E
Electronic transport in disordered n-alkanes: From fluid methane to amorphous polyethylene
We use a fast Fourier transform block Lanczos diagonalization algorithm to study the electronic states of excess electrons in fluid alkanes (methane, ethane, and propane) and in a molecular model of amorphous polyethylene (PE) relevant to studies of space charge in insulating polymers. We obtain a new pseudopotential for electron–PE interactions by fitting to the electronic properties of fluid alkanes and use this to obtain new results for electron transport in amorphous PE. From our simulations, while the electronic states in fluid methane are extended throughout the whole sample, in amorphous PE there is a transition between localized and delocalized states slightly above the vacuum level (∼+0.06 eV). The localized states in our amorphous PE model extend to −0.33 eV below this level. Using the Kubo–Greenwood equation we compute the zero-field electron mobility in pure amorphous PE to be μ≈2×10−3 cm2/V s. Our results highlight the importance of electron transport through extended states in amorphous regions to an understanding of electron transport in PE.EPSRC through Grants No.GR/R18222 and No. GR/M9442
South American perspective of the International Charter "Space and Major Disasters"
International audienceThe International Charter "Space and Major Disasters" is about joint operations and tasking of imaging satellites and other space resources of the member space agencies and operators in the delivery of information products to assist in responding to disasters of natural and technological causes. Authorized Users, who are the civil protection, emergency response or similar organizations of a state that is member of the Charter, can request the data and products. A specialist, called the Project Manager (PM), manages the overall data acquisition and delivery process. Regional initiatives, as for the Latin American countries, are under way to involve PMs from non-member states to have access to satellite data and apply these to disaster coverage in their respective regions. Volcanic eruptions are typical examples of disasters that affect the Latin American countries. A few Charter activations on this disaster type are described to highlight the information products provided under the Charter
Exploring the Counterion Atmosphere around DNA: What Can Be Learned from Molecular Dynamics Simulations?
AbstractThe counterion distribution around a DNA dodecamer (5′-CGCGAATTCGCG-3′) is analyzed using both standard and novel techniques based on state of the art molecular dynamics simulations. Specifically, we have explored the population of Na+ in the minor groove of DNA duplex, and whether or not a string of Na+ can replace the spine of hydration in the narrow AATT minor groove. The results suggest that the insertion of Na+ in the minor groove is a very rare event, but that when once the ion finds specific sites deep inside the groove it can reside there for very long periods of time. According to our simulation the presence of Na+ inside the groove does not have a dramatic influence in the structure or dynamics of the duplex DNA. The ability of current MD simulations to obtain equilibrated pictures of the counterion atmosphere around DNA is critically discussed
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