Pulak Kumar Ghosh | Presidency University, Kolkata (original) (raw)
Uploads
Papers by Pulak Kumar Ghosh
1. Background and purpose Recently we have studied a model [1] of lightinduced proton and electro... more 1. Background and purpose Recently we have studied a model [1] of lightinduced proton and electron pump in artificial reaction centers. The model contains a molecular triad, which is inserted between two (either proton or electron) reservoirs. The molecular triad transports protons (mediated by a shuttle) and electrons energetically uphill: from the lower energy reservoir to the higher energy reservoir, using the energy of light. Applying the methods of quantum transport theory, we calculated the ranges of light intensity and potential energy of the electron/proton reservoir that maximize both the light-induced proton/electron current and the energy-transduction efficiency. We also have shown that under resonant tunneling conditions, and strong coupling of molecular triads with leads, the power conversion efficiency increases drastically. Thus, we obtained the optimalefficiency conditions. We also have extended our models presented in Ref [1] including additional four lightharvestin...
Physical Review E, 2021
We numerically investigated the transport of a passive colloidal particle in a one-dimensional pe... more We numerically investigated the transport of a passive colloidal particle in a one-dimensional periodic array of planar counter-rotating convection rolls at high Péclet numbers. We show that advection-enhanced diffusion is drastically suppressed by an external transverse bias but strongly reinforced by a longitudinal drive of appropriate intensity. Both effects are magnified by imposing free-slip flows at the array's edges. The dependence of the diffusion constant on an external forcing is interpreted as a measure of the fluid-mechanical robustness of the flow boundary layer mechanism governing diffusion in convection rolls.
Physical Review E, 2011
We analyze a theoretical model for energy and electron transfer in an artificial photosynthetic s... more We analyze a theoretical model for energy and electron transfer in an artificial photosynthetic system. The photosystem consists of a molecular triad (i.e., with a donor, a photosensitive unit, and an acceptor) coupled to four accessory light-harvesting antennas pigments. The resonant energy transfer from the antennas to the artificial reaction center (the molecular triad) is here described by the Förster mechanism. We consider two different kinds of arrangements of the accessory lightharvesting pigments around the reaction center. The first arrangement allows direct excitation transfer to the reaction center from all the surrounding pigments. The second configuration transmits energy via a cascade mechanism along a chain of light-harvesting chromophores, where only one chromophore is connected to the reaction center. We show that the artificial photosynthetic system using the cascade energy transfer absorbs photons in a broader wavelength range and converts their energy into electricity with a higher efficiency than the system based on direct couplings between all the antenna chromophores and the reaction center.
![Research paper thumbnail of Publisher's Note: Kinetics of self-induced aggregation of Brownian particles: Non-Markovian and non-Gaussian features [Phys. Rev. E 78, 051103 (2008)]](https://attachments.academia-assets.com/99302168/thumbnails/1.jpg)
](
The Journal of Chemical Physics, 2021
We numerically investigate the mean exit time of an inertial active Brownian particle from a circ... more We numerically investigate the mean exit time of an inertial active Brownian particle from a circular cavity with single or multiple exit windows. Our simulation results witness distinct escape mechanisms depending upon the relative amplitudes of the thermal length and self-propulsion length compared to the cavity and pore sizes. For exceedingly large self-propulsion lengths, overdamped active particles diffuse on the cavity surface, and rotational dynamics solely governs the exit process. On the other hand, the escape kinetics of a very weakly damped active particle is largely dictated by bouncing effects on the cavity walls irrespective of the amplitude of self-propulsion persistence lengths. We show that the exit rate can be maximized for an optimal self-propulsion persistence length, which depends on the damping strength, self-propulsion velocity, and cavity size. However, the optimal persistence length is insensitive to the opening windows' size, number, and arrangement. Numerical results have been interpreted analytically based on qualitative arguments. The present analysis aims to understand the transport controlling mechanism of active matter in confined structures.
We examine the stochastic energetics of directed quantum transport due to rectification of nonequ... more We examine the stochastic energetics of directed quantum transport due to rectification of nonequilibrium thermal fluctuations. We calculate the quantum efficiency of a ratchet device both in presence and absence of an external load to characterize two quantifiers of efficiency. It has been shown that the quantum current as well as efficiency in absence of load (Stokes efficiency) is higher as compared to classical current and efficiency, respectively, at low temperature. The conventional efficiency of the device in presence of load on the other hand is higher for a classical system in contrast to its classical counterpart. The maximum conventional efficiency being independent of the nature of the bath and the potential remains the same for classical and quantum systems.
Physical Chemistry Chemical Physics, 2021
Undesired advection effects are unavoidable in most nano-technological applications involving act... more Undesired advection effects are unavoidable in most nano-technological applications involving active matter.
The European Physical Journal Special Topics, 2014
We review recent advances in rectification control of artificial microswimmers, also known as Jan... more We review recent advances in rectification control of artificial microswimmers, also known as Janus particles, diffusing along narrow, periodically corrugated channels. The swimmer self-propulsion mechanism is modeled so as to incorporate a nonzero torque (propulsion chirality). We first summarize the effects of chirality on the autonomous current of microswimmers freely diffusing in channels of different geometries. In particular, left-right and upside-down asymmetric channels are shown to exhibit different transport properties. We then report new results on the dependence of the diffusivity of chiral microswimmers on the channel geometry and their own self-propulsion mechanism. The self-propulsion torque turns out to play a key role as a transport control parameter.
The Journal of chemical physics, Jan 28, 2017
We investigate both analytically and by numerical simulation the relaxation of an overdamped Brow... more We investigate both analytically and by numerical simulation the relaxation of an overdamped Brownian particle in a 1D multiwell potential. We show that the mean relaxation time from an injection point inside the well down to its bottom is dominated by statistically rare trajectories that sample the potential profile outside the well. As a consequence, also the hopping time between two degenerate wells can depend on the detailed multiwell structure of the entire potential. The nonlocal nature of the transitions between two states of a disordered landscape is important for the correct interpretation of the relaxation rates in complex chemical-physical systems, measured either through numerical simulations or experimental techniques.
The Journal of chemical physics, Jan 21, 2016
An active swimmer can tow a passive cargo by binding it to form a self-propelling dimer. The orie... more An active swimmer can tow a passive cargo by binding it to form a self-propelling dimer. The orientation of the cargo relative to the axis of the active dimer's head is determined by the hydrodynamic interactions associated with the propulsion mechanism of the latter. We show how the tower-cargo angular configuration greatly influences the dimer's diffusivity and, therefore, the efficiency of the active swimmer as a micro-towing motor.
Soft Matter, 2016
We model the two-dimensional diffusive dynamics of an eccentric artificial microswimmer in a high... more We model the two-dimensional diffusive dynamics of an eccentric artificial microswimmer in a highly viscous medium.
The Journal of Chemical Physics, 2015
A self-propelled artificial microswimmer is often modeled as a ballistic Brownian particle moving... more A self-propelled artificial microswimmer is often modeled as a ballistic Brownian particle moving with constant speed aligned along one of its axis, but changing direction due to random collisions with the environment. Similarly to thermal noise, its angular randomization is described as a memoryless stochastic process. Here, we speculate that finite-time correlations in the orientational dynamics can affect the swimmer's diffusivity. To this purpose, we propose and solve two alternative models. In the first one, we simply assume that the environmental fluctuations governing the swimmer's propulsion are exponentially correlated in time, whereas in the second one, we account for possible damped fluctuations of the propulsion velocity around the swimmer's axis. The corresponding swimmer's diffusion constants are predicted to get, respectively, enhanced or suppressed upon increasing the model memory time. Possible consequences of this effect on the interpretation of the experimental data are discussed.
Physical review. E, Statistical, nonlinear, and soft matter physics, 2015
We numerically investigate the motion of active artificial microswimmers diffusing in a fuel conc... more We numerically investigate the motion of active artificial microswimmers diffusing in a fuel concentration gradient. We observe that, in the steady state, their probability density accumulates in the low-concentration regions, whereas a tagged swimmer drifts with velocity depending in modulus and orientation on how the concentration gradient affects the self-propulsion mechanism. Under most experimentally accessible conditions, the particle drifts toward the high-concentration regions (pseudochemotactic drift). A correct interpretation of experimental data must account for such an "anti-Fickian" behavior.
EPL (Europhysics Letters), 2015
We investigate the transport diffusivity of artificial microswimmers, a.k.a. Janus particles, mov... more We investigate the transport diffusivity of artificial microswimmers, a.k.a. Janus particles, moving in a sinusoidal channel in the absence of external biases. Their diffusion constant turns out to be quite sensitive to the self-propulsion mechanism and the geometry of the channel compartments. Our analysis thus suggests how to best control the diffusion of active Brownian motion in confined geometries.
Physical review. E, Statistical, nonlinear, and soft matter physics, 2014
We numerically simulate the diffusion of overdampd pointlike Janus particles along narrow two-dim... more We numerically simulate the diffusion of overdampd pointlike Janus particles along narrow two-dimensional periodically corrugated channels with reflecting walls. The self-propulsion velocity of the particle is assumed to rotate subject to an intrinsic bias modeled by a torque. Breaking the mirror symmetry of the channel with respect to its axis suffices to generate a directed particle flow with orientation and magnitude which depend on the channel geometry and the particle swimming properties. This means that chiral microswimmers drift autonomously along a narrow channel under more general asymmetry conditions than previously reported, a property of potential impact on their fabrication and technological applications.
Physical Review E, 2014
We numerically simulate the transport of elliptic Janus particles along narrow two-dimensional ch... more We numerically simulate the transport of elliptic Janus particles along narrow two-dimensional channels with reflecting walls. The self-propulsion velocity of the particle is oriented along either their major (prolate) or minor axis (oblate). In smooth channels, we observe long diffusion transients: ballistic for prolate particles and zero-diffusion for oblate particles. Placed in a rough channel, prolate particles tend to drift against an applied drive by tumbling over the wall protrusions; for appropriate aspect ratios, the modulus of their negative mobility grows exceedingly large (giant negative mobility). This suggests that a small external drive suffices to efficiently direct self-propulsion of rod-like Janus particles in rough channels.
The Journal of chemical physics, Jan 14, 2014
We numerically investigate the escape kinetics of elliptic Janus particles from narrow two-dimens... more We numerically investigate the escape kinetics of elliptic Janus particles from narrow two-dimensional cavities with reflecting walls. The self-propulsion velocity of the Janus particle is directed along either their major (prolate) or minor (oblate) axis. We show that the mean exit time is very sensitive to the cavity geometry, particle shape, and self-propulsion strength. The mean exit time is found to be a minimum when the self-propulsion length is equal to the cavity size. We also find the optimum mean escape time as a function of the self-propulsion velocity, translational diffusion, and particle shape. Thus, effective transport control mechanisms for Janus particles in a channel can be implemented.
The Journal of Physical Chemistry C, 2009
We theoretically examine the light-to-electricity energy conversion in a molecular triad coupled ... more We theoretically examine the light-to-electricity energy conversion in a molecular triad coupled to conducting leads. This coupling allows us to drive a current through the system. We derive the equations of motion for the electron density operators and determine the dependence of the current, quantum yield, and thermodynamic efficiency on temperature, the electrochemical potentials of the leads, as well as on the light intensity and frequency of the external electromagnetic field. For the molecular triad consisting of ferrocene, porphyrin, and fullerene molecules, we find that, in the case of relatively strong coupling to the leads, the powerconversion efficiency can exceed 40% and the quantum yield can be more than 90%, instead of the 25% quantum yield observed in experiments. Thus, this system is highly attractive for solar cell applications. The large predicted increase in the efficiency of this system is due to the stronger coupling to the contacts, which allows the triad to move more electrons through it, absorbing more photons per unit time, and doing more work.
Physics Letters A, 2005
We examine the noise-induced transition in a fluctuating bistable potential of a driven quantum s... more 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 cooperative effect among the noise processes and the weak periodic signal.
Physics Letters A, 2006
We consider the quantum stochastic dynamics of a system whose interaction with the reservoir is c... more We consider the quantum stochastic dynamics of a system whose interaction with the reservoir is considered to be linear in bath coordinates but nonlinear in system coordinates. The role of the space-dependent friction and diffusion has been examined in the decay rate of a particle from a meta-stable well. We show how the decay rate can be hindered by inhomogeneous dissipation due nonlinear system-bath coupling strength.
1. Background and purpose Recently we have studied a model [1] of lightinduced proton and electro... more 1. Background and purpose Recently we have studied a model [1] of lightinduced proton and electron pump in artificial reaction centers. The model contains a molecular triad, which is inserted between two (either proton or electron) reservoirs. The molecular triad transports protons (mediated by a shuttle) and electrons energetically uphill: from the lower energy reservoir to the higher energy reservoir, using the energy of light. Applying the methods of quantum transport theory, we calculated the ranges of light intensity and potential energy of the electron/proton reservoir that maximize both the light-induced proton/electron current and the energy-transduction efficiency. We also have shown that under resonant tunneling conditions, and strong coupling of molecular triads with leads, the power conversion efficiency increases drastically. Thus, we obtained the optimalefficiency conditions. We also have extended our models presented in Ref [1] including additional four lightharvestin...
Physical Review E, 2021
We numerically investigated the transport of a passive colloidal particle in a one-dimensional pe... more We numerically investigated the transport of a passive colloidal particle in a one-dimensional periodic array of planar counter-rotating convection rolls at high Péclet numbers. We show that advection-enhanced diffusion is drastically suppressed by an external transverse bias but strongly reinforced by a longitudinal drive of appropriate intensity. Both effects are magnified by imposing free-slip flows at the array's edges. The dependence of the diffusion constant on an external forcing is interpreted as a measure of the fluid-mechanical robustness of the flow boundary layer mechanism governing diffusion in convection rolls.
Physical Review E, 2011
We analyze a theoretical model for energy and electron transfer in an artificial photosynthetic s... more We analyze a theoretical model for energy and electron transfer in an artificial photosynthetic system. The photosystem consists of a molecular triad (i.e., with a donor, a photosensitive unit, and an acceptor) coupled to four accessory light-harvesting antennas pigments. The resonant energy transfer from the antennas to the artificial reaction center (the molecular triad) is here described by the Förster mechanism. We consider two different kinds of arrangements of the accessory lightharvesting pigments around the reaction center. The first arrangement allows direct excitation transfer to the reaction center from all the surrounding pigments. The second configuration transmits energy via a cascade mechanism along a chain of light-harvesting chromophores, where only one chromophore is connected to the reaction center. We show that the artificial photosynthetic system using the cascade energy transfer absorbs photons in a broader wavelength range and converts their energy into electricity with a higher efficiency than the system based on direct couplings between all the antenna chromophores and the reaction center.
The Journal of Chemical Physics, 2021
We numerically investigate the mean exit time of an inertial active Brownian particle from a circ... more We numerically investigate the mean exit time of an inertial active Brownian particle from a circular cavity with single or multiple exit windows. Our simulation results witness distinct escape mechanisms depending upon the relative amplitudes of the thermal length and self-propulsion length compared to the cavity and pore sizes. For exceedingly large self-propulsion lengths, overdamped active particles diffuse on the cavity surface, and rotational dynamics solely governs the exit process. On the other hand, the escape kinetics of a very weakly damped active particle is largely dictated by bouncing effects on the cavity walls irrespective of the amplitude of self-propulsion persistence lengths. We show that the exit rate can be maximized for an optimal self-propulsion persistence length, which depends on the damping strength, self-propulsion velocity, and cavity size. However, the optimal persistence length is insensitive to the opening windows' size, number, and arrangement. Numerical results have been interpreted analytically based on qualitative arguments. The present analysis aims to understand the transport controlling mechanism of active matter in confined structures.
We examine the stochastic energetics of directed quantum transport due to rectification of nonequ... more We examine the stochastic energetics of directed quantum transport due to rectification of nonequilibrium thermal fluctuations. We calculate the quantum efficiency of a ratchet device both in presence and absence of an external load to characterize two quantifiers of efficiency. It has been shown that the quantum current as well as efficiency in absence of load (Stokes efficiency) is higher as compared to classical current and efficiency, respectively, at low temperature. The conventional efficiency of the device in presence of load on the other hand is higher for a classical system in contrast to its classical counterpart. The maximum conventional efficiency being independent of the nature of the bath and the potential remains the same for classical and quantum systems.
Physical Chemistry Chemical Physics, 2021
Undesired advection effects are unavoidable in most nano-technological applications involving act... more Undesired advection effects are unavoidable in most nano-technological applications involving active matter.
The European Physical Journal Special Topics, 2014
We review recent advances in rectification control of artificial microswimmers, also known as Jan... more We review recent advances in rectification control of artificial microswimmers, also known as Janus particles, diffusing along narrow, periodically corrugated channels. The swimmer self-propulsion mechanism is modeled so as to incorporate a nonzero torque (propulsion chirality). We first summarize the effects of chirality on the autonomous current of microswimmers freely diffusing in channels of different geometries. In particular, left-right and upside-down asymmetric channels are shown to exhibit different transport properties. We then report new results on the dependence of the diffusivity of chiral microswimmers on the channel geometry and their own self-propulsion mechanism. The self-propulsion torque turns out to play a key role as a transport control parameter.
The Journal of chemical physics, Jan 28, 2017
We investigate both analytically and by numerical simulation the relaxation of an overdamped Brow... more We investigate both analytically and by numerical simulation the relaxation of an overdamped Brownian particle in a 1D multiwell potential. We show that the mean relaxation time from an injection point inside the well down to its bottom is dominated by statistically rare trajectories that sample the potential profile outside the well. As a consequence, also the hopping time between two degenerate wells can depend on the detailed multiwell structure of the entire potential. The nonlocal nature of the transitions between two states of a disordered landscape is important for the correct interpretation of the relaxation rates in complex chemical-physical systems, measured either through numerical simulations or experimental techniques.
The Journal of chemical physics, Jan 21, 2016
An active swimmer can tow a passive cargo by binding it to form a self-propelling dimer. The orie... more An active swimmer can tow a passive cargo by binding it to form a self-propelling dimer. The orientation of the cargo relative to the axis of the active dimer's head is determined by the hydrodynamic interactions associated with the propulsion mechanism of the latter. We show how the tower-cargo angular configuration greatly influences the dimer's diffusivity and, therefore, the efficiency of the active swimmer as a micro-towing motor.
Soft Matter, 2016
We model the two-dimensional diffusive dynamics of an eccentric artificial microswimmer in a high... more We model the two-dimensional diffusive dynamics of an eccentric artificial microswimmer in a highly viscous medium.
The Journal of Chemical Physics, 2015
A self-propelled artificial microswimmer is often modeled as a ballistic Brownian particle moving... more A self-propelled artificial microswimmer is often modeled as a ballistic Brownian particle moving with constant speed aligned along one of its axis, but changing direction due to random collisions with the environment. Similarly to thermal noise, its angular randomization is described as a memoryless stochastic process. Here, we speculate that finite-time correlations in the orientational dynamics can affect the swimmer's diffusivity. To this purpose, we propose and solve two alternative models. In the first one, we simply assume that the environmental fluctuations governing the swimmer's propulsion are exponentially correlated in time, whereas in the second one, we account for possible damped fluctuations of the propulsion velocity around the swimmer's axis. The corresponding swimmer's diffusion constants are predicted to get, respectively, enhanced or suppressed upon increasing the model memory time. Possible consequences of this effect on the interpretation of the experimental data are discussed.
Physical review. E, Statistical, nonlinear, and soft matter physics, 2015
We numerically investigate the motion of active artificial microswimmers diffusing in a fuel conc... more We numerically investigate the motion of active artificial microswimmers diffusing in a fuel concentration gradient. We observe that, in the steady state, their probability density accumulates in the low-concentration regions, whereas a tagged swimmer drifts with velocity depending in modulus and orientation on how the concentration gradient affects the self-propulsion mechanism. Under most experimentally accessible conditions, the particle drifts toward the high-concentration regions (pseudochemotactic drift). A correct interpretation of experimental data must account for such an "anti-Fickian" behavior.
EPL (Europhysics Letters), 2015
We investigate the transport diffusivity of artificial microswimmers, a.k.a. Janus particles, mov... more We investigate the transport diffusivity of artificial microswimmers, a.k.a. Janus particles, moving in a sinusoidal channel in the absence of external biases. Their diffusion constant turns out to be quite sensitive to the self-propulsion mechanism and the geometry of the channel compartments. Our analysis thus suggests how to best control the diffusion of active Brownian motion in confined geometries.
Physical review. E, Statistical, nonlinear, and soft matter physics, 2014
We numerically simulate the diffusion of overdampd pointlike Janus particles along narrow two-dim... more We numerically simulate the diffusion of overdampd pointlike Janus particles along narrow two-dimensional periodically corrugated channels with reflecting walls. The self-propulsion velocity of the particle is assumed to rotate subject to an intrinsic bias modeled by a torque. Breaking the mirror symmetry of the channel with respect to its axis suffices to generate a directed particle flow with orientation and magnitude which depend on the channel geometry and the particle swimming properties. This means that chiral microswimmers drift autonomously along a narrow channel under more general asymmetry conditions than previously reported, a property of potential impact on their fabrication and technological applications.
Physical Review E, 2014
We numerically simulate the transport of elliptic Janus particles along narrow two-dimensional ch... more We numerically simulate the transport of elliptic Janus particles along narrow two-dimensional channels with reflecting walls. The self-propulsion velocity of the particle is oriented along either their major (prolate) or minor axis (oblate). In smooth channels, we observe long diffusion transients: ballistic for prolate particles and zero-diffusion for oblate particles. Placed in a rough channel, prolate particles tend to drift against an applied drive by tumbling over the wall protrusions; for appropriate aspect ratios, the modulus of their negative mobility grows exceedingly large (giant negative mobility). This suggests that a small external drive suffices to efficiently direct self-propulsion of rod-like Janus particles in rough channels.
The Journal of chemical physics, Jan 14, 2014
We numerically investigate the escape kinetics of elliptic Janus particles from narrow two-dimens... more We numerically investigate the escape kinetics of elliptic Janus particles from narrow two-dimensional cavities with reflecting walls. The self-propulsion velocity of the Janus particle is directed along either their major (prolate) or minor (oblate) axis. We show that the mean exit time is very sensitive to the cavity geometry, particle shape, and self-propulsion strength. The mean exit time is found to be a minimum when the self-propulsion length is equal to the cavity size. We also find the optimum mean escape time as a function of the self-propulsion velocity, translational diffusion, and particle shape. Thus, effective transport control mechanisms for Janus particles in a channel can be implemented.
The Journal of Physical Chemistry C, 2009
We theoretically examine the light-to-electricity energy conversion in a molecular triad coupled ... more We theoretically examine the light-to-electricity energy conversion in a molecular triad coupled to conducting leads. This coupling allows us to drive a current through the system. We derive the equations of motion for the electron density operators and determine the dependence of the current, quantum yield, and thermodynamic efficiency on temperature, the electrochemical potentials of the leads, as well as on the light intensity and frequency of the external electromagnetic field. For the molecular triad consisting of ferrocene, porphyrin, and fullerene molecules, we find that, in the case of relatively strong coupling to the leads, the powerconversion efficiency can exceed 40% and the quantum yield can be more than 90%, instead of the 25% quantum yield observed in experiments. Thus, this system is highly attractive for solar cell applications. The large predicted increase in the efficiency of this system is due to the stronger coupling to the contacts, which allows the triad to move more electrons through it, absorbing more photons per unit time, and doing more work.
Physics Letters A, 2005
We examine the noise-induced transition in a fluctuating bistable potential of a driven quantum s... more 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 cooperative effect among the noise processes and the weak periodic signal.
Physics Letters A, 2006
We consider the quantum stochastic dynamics of a system whose interaction with the reservoir is c... more We consider the quantum stochastic dynamics of a system whose interaction with the reservoir is considered to be linear in bath coordinates but nonlinear in system coordinates. The role of the space-dependent friction and diffusion has been examined in the decay rate of a particle from a meta-stable well. We show how the decay rate can be hindered by inhomogeneous dissipation due nonlinear system-bath coupling strength.
Our daily life experience says that noise is a disturbing element and enemy of order. But in ce... more Our daily life experience says that noise is a disturbing element and enemy of order. But in certain nonlinear system, including electronic circuit, biological sensory organs, presence of noise play a constructive role in the dynamics. Stochastic resonance (SR), Resonant activation (RA),Brownian Ratchet are some typical noise induced phenomena where noise can play such role. Aim Stochastic Resonance, underlying mechanism and applications in physics and biology. Resonant Activation, underlying mechanism, application in chemical systems. Interference effect of Stochastic Resonance and resonant activation and its implication in stochastic localization and product distribution in a parallel reaction.
We study a model of light-induced proton and electron pump in artificial reaction centers. The mo... more We study a model of light-induced proton and electron pump in artificial reaction centers. The model contains a molecular triad, which is inserted between two (either proton or electron) reservoirs. The molecular triad transports protons (mediated by a shuttle) and electrons energetically uphill: from the lower energy reservoir to the higher energy reservoir, using the energy of light. Applying the methods of quantum transport theory, we calculated the ranges of light intensity and potential energy of the electron/proton reservoir that maximize both the light-induced proton/electron current and the energy-transduction efficiency. We also studied the effect of temperature on energy transduction efficiency. Our results explain previous experiments on artificial photosynthetic reaction centers. We also show that under resonant tunneling conditions, and strong coupling of molecular triads with leads, the power conversion efficiency increases drastically. Thus, we obtained the optimal-efficiency conditions. These results could be useful for further experiments, e.g., for choosing donors, acceptors and conducting leads (on the basis of reorganization energies and reduction potentials) to achieve higher energy-conversion efficiency.
We investigate the quantum dynamics of electronic energy and charge transfer in a wheel-shaped ar... more We investigate the quantum dynamics of electronic energy and charge transfer in a wheel-shaped artificial photosynthetic antenna-reaction center complex. To describe quantum effects on a femtosecond time scale, we derive a set of non-Markovian equations taking into account the time evolution of the off-diagonal elements of the density matrix. We show that the energy of the initially-excited antenna chromophores is efficiently funneled to the porphyrin-fullerene reaction center, where a charge-separated state is set up in a few picoseconds, with a quantum yield of the order of 95 %. In the single-exciton regime, we observe quantum beatings of energy between two resonant antenna pigments with a decoherence time of ~ 100 fs. We also analyze the double-exciton regime, when two porphyrin molecules are initially-excited. In this regime we obtain pronounced quantum oscillations of the charge on the fullerene molecule with a decoherence time of about 20 fs (at liquid nitrogen temperatures).