5,828 research outputs found
Molecular wires acting as quantum heat ratchets
We explore heat transfer in molecular junctions between two leads in the
absence of a finite net thermal bias. The application of an unbiased,
time-periodic temperature modulation of the leads entails a dynamical breaking
of reflection symmetry, such that a directed heat current may emerge (ratchet
effect). In particular, we consider two cases of adiabatically slow driving,
namely (i) periodic temperature modulation of only one lead and (ii)
temperature modulation of both leads with an ac driving that contains a second
harmonic, thus generating harmonic mixing. Both scenarios yield sizeable
directed heat currents which should be detectable with present techniques.
Adding a static thermal bias, allows one to compute the heat current-thermal
load characteristics which includes the ratchet effect of negative thermal bias
with positive-valued heat flow against the thermal bias, up to the thermal
stop-load. The ratchet heat flow in turn generates also an electric current. An
applied electric stop-voltage, yielding effective zero electric current flow,
then mimics a solely heat-ratchet-induced thermopower (``ratchet Seebeck
effect''), although no net thermal bias is acting. Moreover, we find that the
relative phase between the two harmonics in scenario (ii) enables steering the
net heat current into a direction of choice.Comment: 9 pages, 8 figure
Epoch Dependent Dark Energy
We present a model in which the equation of state parameter w approaches -1
near a particular value of z, and has significant negative values in a
restricted range of z. For example, one can have w ~ -1 near z = 1, and w >
-0.2 from z = 0 to z = 0.3, and for z > 9. The ingredients of the model are
neutral fermions (which may be neutrinos, neutralinos, etc) which are very
weakly coupled to a light scalar field. This model emphasises the importance of
the proposed studies of the properties of dark energy into the region z > 1.Comment: 7pp., 2 figs. Invited talk at the 5th Int'l. Wkshp. on the Dark Side
of the Universe, 1-5 June 2009 Melbourne, DSU09; to appear in the proceeding
Further results on exponential estimates of markovian jump systems with mode-dependent time-varying delays
This technical note studies the problem of exponential estimates for Markovian jump systems with mode-dependent interval time-varying delays. A novel LyapunovKrasovskii functional (LKF) is constructed with the idea of delay partitioning, and a less conservative exponential estimate criterion is obtained based on the new LKF. Illustrative examples are provided to show the effectiveness of the proposed results. © 2010 IEEE.published_or_final_versio
Tourism demand modelling and forecasting : how should demand be measured?
2009-2010 > Academic research: refereed > Publication in refereed journalVersion of RecordPublishe
Controlling Excitations Inversion of a Cooper Pair Box Interacting with a Nanomechanical Resonator
We investigate the action of time dependent detunings upon the excitation
inversion of a Cooper pair box interacting with a nanomechanical resonator. The
method employs the Jaynes-Cummings model with damping, assuming different decay
rates of the Cooper pair box and various fixed and t-dependent detunings. It is
shown that while the presence of damping plus constant detunings destroy the
collapse/revival effects, convenient choices of time dependent detunings allow
one to reconstruct such events in a perfect way. It is also shown that the mean
excitation of the nanomechanical resonator is more robust against damping of
the Cooper pair box for convenient values of t-dependent detunings.Comment: 11 pages, 5 figure
Force Modulating Dynamic Disorder: Physical Theory of Catch-slip bond Transitions in Receptor-Ligand Forced Dissociation Experiments
Recently experiments showed that some adhesive receptor-ligand complexes
increase their lifetimes when they are stretched by mechanical force, while the
force increase beyond some thresholds their lifetimes decrease. Several
specific chemical kinetic models have been developed to explain the intriguing
transitions from the "catch-bonds" to the "slip-bonds". In this work we suggest
that the counterintuitive forced dissociation of the complexes is a typical
rate process with dynamic disorder. An uniform one-dimension force modulating
Agmon-Hopfield model is used to quantitatively describe the transitions
observed in the single bond P-selctin glycoprotein ligand
1(PSGL-1)P-selectin forced dissociation experiments, which were respectively
carried out on the constant force [Marshall, {\it et al.}, (2003) Nature {\bf
423}, 190-193] and the force steady- or jump-ramp [Evans {\it et al.}, (2004)
Proc. Natl. Acad. Sci. USA {\bf 98}, 11281-11286] modes. Our calculation shows
that the novel catch-slip bond transition arises from a competition of the two
components of external applied force along the dissociation reaction coordinate
and the complex conformational coordinate: the former accelerates the
dissociation by lowering the height of the energy barrier between the bound and
free states (slip), while the later stabilizes the complex by dragging the
system to the higher barrier height (catch).Comment: 8 pages, 3 figures, submitte
Full Quantum Analysis of Two-Photon Absorption Using Two-Photon Wavefunction: Comparison with One-Photon Absorption
For dissipation-free photon-photon interaction at the single photon level, we
analyze one-photon transition and two-photon transition induced by photon pairs
in three-level atoms using two-photon wavefunctions. We show that the
two-photon absorption can be substantially enhanced by adjusting the time
correlation of photon pairs. We study two typical cases: Gaussian wavefunction
and rectangular wavefunction. In the latter, we find that under special
conditions one-photon transition is completely suppressed while the high
probability of two-photon transition is maintained.Comment: 6 pages, 4 figure
Generalized - Model
By parameterizing the t-j model we present a new electron correlation model
with one free parameter for high-temperature superconductivity. This model is
of symmetry. The energy spectrums are shown to be modulated by
the free parameter in the model. The solution and symmetric structures of the
Hilbert space, as well as the Bethe ansatz approach are discussed for special
cases.Comment: 13 page, Latex, to appear in J. Phys.
Real Scalar Field Scattering with Polynomial Approximation around Schwarzschild-de Sitter Black-hole
As one of the fitting methods, the polynomial approximation is effective to
process sophisticated problem. In this paper, we employ this approach to handle
the scattering of scalar field around the Schwarzschild-de Sitter black-hole.
The complex relationship between tortoise coordinate and radial coordinate is
replaced by the approximate polynomial. The Schrdinger-like equation,
the real boundary conditions and the polynomial approximation construct a full
Sturm-Liouville type problem. Then this boundary value problem can be solved
numerically according to two limiting cases: the first one is the Nariai
black-hole whose horizons are close to each other, the second one is when the
horizons are widely separated. Compared with previous results (Brevik and
Tian), the field near the event horizon and cosmological horizon can have a
better description.Comment: revtex4 source file, 11 pages, 8 figure
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