51 research outputs found
Anharmonic quantum contribution to vibrational dephasing
Based on a quantum Langevin equation and its corresponding Hamiltonian within
a c-number formalism we calculate the vibrational dephasing rate of a cubic
oscillator. It is shown that leading order quantum correction due to
anharmonicity of the potential makes a significant contribution to the rate and
the frequency shift. We compare our theoretical estimates with those obtained
from experiments for small diatomics , and .Comment: 21 pages, 1 figure and 1 tabl
Scaling of intrinsic noise in an autocratic reaction network
Biochemical reactions in living cells often produce stochastic trajectories due to the fluctuations of the finite number of the macromolecular species present inside the cell. A significant number of computational and theoretical studies have previously investigated stochasticity in small regulatory networks to understand its origin and regulation. At the systems level regulatory networks have been determined to be hierarchical resembling social networks. In order to determine the stochasticity in networks with hierarchical architecture, here we computationally investigated intrinsic noise in an autocratic reaction network in which only the upstream regulators regulate the downstream regulators. We studied the effects of the qualitative and quantitative nature of regulatory interactions on the stochasticity in the network. We established an unconventional scaling of noise with average abundance in which the noise passes through a minimum indicating that the network can be noisy both in the low and high abundance regimes. We determined that the bursty kinetics of the trajectories are responsible for such scaling. The scaling of noise remains intact for a mixed network that includes democratic subnetworks within the autocratic network
Noise-induced transition in a quantum system
We examine the noise-induced transition in a fluctuating bistable potential
of a driven quantum system in thermal equilibrium. Making use of a Wigner
canonical thermal distribution for description of the statistical properties of
the thermal bath, we explore the generic effects of quantization like vacuum
field fluctuation and tunneling in the characteristic stationary probability
distribution functions undergoing transition from unimodal to bimodal nature
and in signal-to-noise ratio characterizing the co-operative effect among the
noise processes and the weak periodic signal.Comment: To appear on Physics Letters
Numerical simulation of transmission coefficient using c-number Langevin equation
We numerically implement the reactive flux formalism on the basis of a
recently proposed c-number Langevin equation [Barik \textit{et al}, J. Chem.
Phys. {\bf 119}, 680 (2003); Banerjee \textit{et al}, Phys. Rev. E {\bf 65},
021109 (2002)] to calculate transmission coefficient. The Kramers' turnover,
the enhancement of the rate at low temperatures and other related
features of temporal behaviour of the transmission coefficient over a range of
temperature down to absolute zero, noise correlation and friction are examined
for a double well potential and compared with other known results. This simple
method is based on canonical quantization and Wigner quasiclassical phase space
function and takes care of quantum effects due to the system order by order
Investigation of chemical noise in multisite phosphorylation chain using linear noise approximation
Quantitative and qualitative nature of chemical noise propagation in biochemical reaction networks depend crucially on the topology of the networks. Multisite reversible phosphorylation-dephosphorylation of target proteins is one such recurrently found topology that regulates host of key functions in living cells. Here we analytically calculated the stochasticity in multistep reversible chemical reactions by determining variance of phosphorylated species at the steady state using linear noise approximation to investigate the effect of mass action and Michaelis-Menten kinetics on the noise of phosphorylated species. We probed the dependence of noise on the number of phosphorylation sites and the equilibrium constants of the reaction equilibria to investigate the chemical noise propagation in the multisite phosphorylation chain
Noise-induced quantum transport
We analyze the problem of directed quantum transport induced by external
exponentially correlated telegraphic noise. In addition to quantum nature of
the heat bath, nonlinearity of the periodic system potential brings in quantum
contribution. We observe that quantization, in general, enhances classical
current at low temperature, while the differences become insignificant at
higher temperature. Interplay of quantum diffusion and quantum correction to
system potential is analyzed for various ranges of temperature, correlation
time and strength of external noise and asymmetry parameters. A possible
experimental realization of the observed quantum effects in a superionic
conductor placed in a random asymmetric dichotomous electric field has been
suggested.Comment: 23 pages and 5 figures. To be published in Physical Review
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