17 research outputs found
Fluctuation Theorems for Entropy Production and Heat Dissipation in Periodically Driven Markov Chains
Asymptotic fluctuation theorems are statements of a Gallavotti-Cohen symmetry
in the rate function of either the time-averaged entropy production or heat
dissipation of a process. Such theorems have been proved for various general
classes of continuous-time deterministic and stochastic processes, but always
under the assumption that the forces driving the system are time independent,
and often relying on the existence of a limiting ergodic distribution. In this
paper we extend the asymptotic fluctuation theorem for the first time to
inhomogeneous continuous-time processes without a stationary distribution,
considering specifically a finite state Markov chain driven by periodic
transition rates. We find that for both entropy production and heat
dissipation, the usual Gallavotti-Cohen symmetry of the rate function is
generalized to an analogous relation between the rate functions of the original
process and its corresponding backward process, in which the trajectory and the
driving protocol have been time-reversed. The effect is that spontaneous
positive fluctuations in the long time average of each quantity in the forward
process are exponentially more likely than spontaneous negative fluctuations in
the backward process, and vice-versa, revealing that the distributions of
fluctuations in universes in which time moves forward and backward are related.
As an additional result, the asymptotic time-averaged entropy production is
obtained as the integral of a periodic entropy production rate that generalizes
the constant rate pertaining to homogeneous dynamics
Genotoxic effect induced by hydrogen peroxide in human hepatoma cells using comet assay
Background: Hydrogen peroxide is a common reactive oxygen intermediate generated by variousforms of oxidative stress. Aims: The aim of this study was to investigate the DNA damage capacity ofH2O2 in HepG2 cells. Methods: Cells were treated with H2O2 at concentrations of 25 μM or 50 μM for5 min, 30 min, 40 min, 1 h or 24 h in parallel. The extent of DNA damage was assessed by the cometassay. Results: Compared to the control, DNA damage by 25 μM and 50 μM H2O2 increasedsignificantly with increasing incubation time up to 1 h, but it was not increased at 24 h. Conclusions:Our Findings confirm that H2O2 is a typical DNA damage inducing agent and thus is a good modelsystem to study the effects of oxidative stress. DNA damage in HepG2 cells increased significantlywith H2O2 concentration and time of incubation but later decreased likely due to DNA repairmechanisms and antioxidant enzyme
Effects of lattice disorder in the UCu
The UCu(5-x)Pd(x) system exhibits non-Fermi liquid (NFL) in the thermodynamic
and transport properties at low temperatures for Pd concentrations 0.9 <~ x <~
1.5. The local structure around the U, Cu, and Pd atoms has been measured for 0
<= x <= 1.5 using the X-ray Absorption Fine Structure (XAFS) technique in order
to quantify the effects of lattice disorder on the NFL properties. A model
which allows a percentage of the Pd atoms to occupy nominal Cu (16e) sites, s,
was used to fit the Pd and Cu K edge and U L(III) edge data. Pd/Cu site
interchange was found to occur in all samples (x != 0), reaching a minimum
value of s ~0.17 at x = 0.7 and increasing monotonically to s ~ 0.4 at x=1.5.
These data also determine the static disorder the nearest neighbor U--Cu pairs.
The results indicate that the measured U--Cu static disorder is not sufficient
to explain the NFL behavior of the magnetic susceptibility within the
single-ion Kondo disorder model and casts doubt on the applicability of this
model to UCu(5-x)Pd(x).Comment: 14 pages, 12 EPS figures, Phys. Rev. B, in pres