183 research outputs found
Efficiency at maximum power of minimally nonlinear irreversible heat engines
We propose the minimally nonlinear irreversible heat engine as a new general
theoretical model to study the efficiency at the maximum power of heat
engines operating between the hot heat reservoir at the temperature and
the cold one at (). Our model is based on the extended
Onsager relations with a new nonlinear term meaning the power dissipation. In
this model, we show that is bounded from the upper side by a function
of the Carnot efficiency as . We demonstrate the validity of our theory by showing that
the low-dissipation Carnot engine can easily be described by our theory.Comment: 6 pages, 1 figur
Molecular kinetic analysis of a finite-time Carnot cycle
We study the efficiency at the maximal power of a
finite-time Carnot cycle of a weakly interacting gas which we can reagard as a
nearly ideal gas. In several systems interacting with the hot and cold
reservoirs of the temperatures and , respectively,
it is known that which
is often called the Curzon-Ahlborn (CA) efficiency . For the
first time numerical experiments to verify the validity of
are performed by means of molecular dynamics simulations and reveal that our
does not always agree with , but
approaches in the limit of .
Our molecular kinetic analysis explains the above facts theoretically by using
only elementary arithmetic.Comment: 6 pages, 4 figure
Onsager coefficients of a Brownian Carnot cycle
We study a Brownian Carnot cycle introduced by T. Schmiedl and U. Seifert
[Europhys. Lett. \textbf{81}, 20003 (2008)] from a viewpoint of the linear
irreversible thermodynamics. By considering the entropy production rate of this
cycle, we can determine thermodynamic forces and fluxes of the cycle and
calculate the Onsager coefficients for general protocols, that is, arbitrary
schedules to change the potential confining the Brownian particle. We show that
these Onsager coefficients contain the information of the protocol shape and
they satisfy the tight-coupling condition irrespective of whatever protocol
shape we choose. These properties may give an explanation why the
Curzon-Ahlborn efficiency often appears in the finite-time heat engines
Detection of topological transitions by transport through molecules and nanodevices
We analyze the phase transitions of an interacting electronic system weakly
coupled to free-electron leads by considering its zero-bias conductance. This
is expressed in terms of two effective impurity models for the cases with and
without spin degeneracy. We demonstrate using the half-filled ionic Hubbard
ring that the weight of the first conductance peak as a function of external
flux or of the difference in gate voltages between even and odd sites allows
one to identify the topological charge transition between a correlated
insulator and a band insulator.Comment: 4 pages, 5 figures, to appear in Phys. Rev. Let
Electronic transport properties of Cs-encapsulated single-walled carbon nanotubes created by plasma ion irradiation
Bounds of Efficiency at Maximum Power for Normal-, Sub- and Super-Dissipative Carnot-Like Heat Engines
The Carnot-like heat engines are classified into three types (normal-, sub-
and super-dissipative) according to relations between the minimum irreversible
entropy production in the "isothermal" processes and the time for completing
those processes. The efficiencies at maximum power of normal-, sub- and
super-dissipative Carnot-like heat engines are proved to be bounded between
and , and , 0 and
, respectively. These bounds are also shared by linear, sub-
and super-linear irreversible Carnot-like engines [Tu and Wang, Europhys. Lett.
98, 40001 (2012)] although the dissipative engines and the irreversible ones
are inequivalent to each other.Comment: 1 figur
Thermopower of Kondo Effect in Single Quantum Dot Systems with Orbital at Finite Temperatures
We investigate the thermopower due to the orbital Kondo effect in a single
quantum dot system by means of the noncrossing approximation. It is elucidated
how the asymmetry of tunneling resonance due to the orbital Kondo effect
affects the thermopower under gate-voltage and magnetic-field control.Comment: 4 pages, 4 figures, proceeding of Second International Symposium on
Nanometer-Scale Quantum Physic
Interference and interaction effects in multi-level quantum dots
Using renormalization group techniques, we study spectral and transport
properties of a spinless interacting quantum dot consisting of two levels
coupled to metallic reservoirs. For strong Coulomb repulsion and an applied
Aharonov-Bohm phase , we find a large direct tunnel splitting
between the levels of
the order of the level broadening . As a consequence we discover a
many-body resonance in the spectral density that can be measured via the
absorption power. Furthermore, for , we show that the system can be
tuned into an effective Anderson model with spin-dependent tunneling.Comment: 5 pages, 4 figures included, typos correcte
- …