manuel morillo - Academia.edu (original) (raw)
Papers by manuel morillo
Journal of Surgical Oncology, 2006
Background and ObjectivesAdvanced ovarian cancer typically spreads in a diffuse intra-abdominal f... more Background and ObjectivesAdvanced ovarian cancer typically spreads in a diffuse intra-abdominal fashion. This characteristic suggests that combined radical surgery and intraperitoneal chemotherapy may be a useful treatment procedure. The purpose of this study was to review patients submitted to surgical debulking and hyperthermic intraoperative intraperitoneal chemotherapy (HIIC) and to evaluate the potential prognostic survival factors for advanced epithelial ovarian cancer in our center.Advanced ovarian cancer typically spreads in a diffuse intra-abdominal fashion. This characteristic suggests that combined radical surgery and intraperitoneal chemotherapy may be a useful treatment procedure. The purpose of this study was to review patients submitted to surgical debulking and hyperthermic intraoperative intraperitoneal chemotherapy (HIIC) and to evaluate the potential prognostic survival factors for advanced epithelial ovarian cancer in our center.MethodsA series of patients (N = 33) diagnosed of peritoneal carcinomatosis for epithelial ovarian cancer (stage III) from January 1997 to December 2004 submitted to radical surgery-peritonectomy and HIIC with paclitaxel was included in this study; 19 primary ovarian cancer and 14 recurrent ovarian cancer.A series of patients (N = 33) diagnosed of peritoneal carcinomatosis for epithelial ovarian cancer (stage III) from January 1997 to December 2004 submitted to radical surgery-peritonectomy and HIIC with paclitaxel was included in this study; 19 primary ovarian cancer and 14 recurrent ovarian cancer.ResultsCytoreduction R0 (P = 0.018) and negative lymph nodes (P = 0.005) were covariables for major prognostic survival. Patients with optimal cytoreduction R0 obtained survival rates of 63% at 5 years in recurrent ovarian cancer and 60% in primary ovarian cancer, 71% and 63%, respectively with associated subtotal infra-abdominal peritonectomy, and even better results if negative lymph nodes.Cytoreduction R0 (P = 0.018) and negative lymph nodes (P = 0.005) were covariables for major prognostic survival. Patients with optimal cytoreduction R0 obtained survival rates of 63% at 5 years in recurrent ovarian cancer and 60% in primary ovarian cancer, 71% and 63%, respectively with associated subtotal infra-abdominal peritonectomy, and even better results if negative lymph nodes.ConclusionsRadical surgery-peritonectomy with HIIQ has been shown to be a surgical procedure with high tolerability, low morbimortality, enhanced survival, and prolonged disease-free interval in patients with peritoneal carcinomatosis so much for recurrent or primary ovarian cancer. J. Surg. Oncol. 2006;94:316–324. © 2006 Wiley-Liss, Inc.Radical surgery-peritonectomy with HIIQ has been shown to be a surgical procedure with high tolerability, low morbimortality, enhanced survival, and prolonged disease-free interval in patients with peritoneal carcinomatosis so much for recurrent or primary ovarian cancer. J. Surg. Oncol. 2006;94:316–324. © 2006 Wiley-Liss, Inc.
Physical Review E, 1995
We study the long-time response of a stochastic system formed by very many interacting subsystems... more We study the long-time response of a stochastic system formed by very many interacting subsystems coupled by a mean-field interaction and subject to a time periodic external field. In the absence of a driving field; the system shows an order-disorder phase transition and its time evolution is well described by a Fokker-Planck equation which is nonlinear in the probability density.
Journal of Statistical Physics, 1987
A population of identical nonlinear oscillators, subject to random forces and coupled via a mean-... more A population of identical nonlinear oscillators, subject to random forces and coupled via a mean-field interaction, is studied in the thermodynamic limit. The model presents a nonequilibrium phase transition from a stationary to a time-periodic probability density. Below the transition line, the population of oscillators is in a quiescent state with order parameter equal to zero. Above the transition line, there is a state of collective rhythmicity characterized by a time-periodic behavior of the order parameter and all moments of the probability distribution. The information entropy of the ensemble is a constant both below and above the critical line. Analytical and numerical analyses of the model are provided.
Physical Review E, 2006
We explore stochastic resonance effects in the response of a complex stochastic system formed by ... more We explore stochastic resonance effects in the response of a complex stochastic system formed by a finite number of interacting, identical subunits driven by a time-periodic force. The driving force alone cannot induce sustained oscillations between the different attractors of the dynamics in the absence of noise. We focus on a global stochastic variable defined as the arithmetic mean of the relevant stochastic variable of each subunit. We construct numerical approximations to its first two long time cumulant moments and its long time correlation function. We also compute the output signal-to-noise ratio and the stochastic resonance gain, for a wide range of parameter values and several types of driving forces. The coupling between the subsystems leads, within adequate ranges of the parameter values, to global outputs with very large signal-to-noise ratios. We have also observed gains larger than unity in the global response to subthreshold sinusoidal driving forces.
Physical Review E, 1995
The response of a symmetric bistable system driven by a time periodic rectangular input signal an... more The response of a symmetric bistable system driven by a time periodic rectangular input signal and subject to a white noise is studied. The analysis shows that the stochastic resonant enhancement of a weak amplitude signal implies a distortion of the input shape for intermediate frequencies, due to the dispersivity of the response. On the other hand, the shape can
Physical Review E, 2008
We analyze the stochastic response of a finite set of globally coupled noisy bistable units drive... more We analyze the stochastic response of a finite set of globally coupled noisy bistable units driven by rather weak time-periodic forces. We focus on the stochastic resonance and phase frequency synchronization of the collective variable, defined as the arithmetic mean of the variable characterizing each element of the array. For single-unit systems, stochastic resonance can be understood with the powerful tools of linear response theory. Proper noise-induced phase frequency synchronization for a single-unit system in this linear response regime does not exist. For coupled arrays, our numerical simulations indicate an enhancement of the stochastic resonance effects leading to gains larger than unity as well as genuine phase frequency synchronization. The nonmonotonicity of the response with the strength of the coupling strength is investigated. Comparison with simplifying schemes proposed in the literature to describe the random response of the collective variable is carried out.
Physical Review E, 2003
The main objective of this work is to explore aspects of stochastic resonance (SR) in noisy bista... more The main objective of this work is to explore aspects of stochastic resonance (SR) in noisy bistable, symmetric systems driven by subthreshold periodic rectangular external signals possessing a large duty cycle of unity. Using a precise numerical solution of the Langevin equation, we carry out a detailed analysis of the behavior of the first two cumulant averages, the correlation function and its coherent and incoherent parts. We also depict the non-monotonic behavior versus the noise strength of several SR quantifiers such as the average output amplitude, i.e. the spectral amplification (SPA), the signal-to-noise ratio (SNR) and the SR-gain. In particular, we find that with subthreshold amplitudes and for an appropriate duration of the pulses of the driving force the phenomenon of stochastic resonance (SR), is accompanied by SR-gains exceeding unity. This analysis thus sheds new light onto the interplay between nonlinearity and the nonlinear response which in turn yields nontrivial, unexpected SR-gains above unity.
Physical Review E, 2004
We analyze the phenomenon of nonlinear stochastic resonance (SR) in noisy bistable systems driven... more We analyze the phenomenon of nonlinear stochastic resonance (SR) in noisy bistable systems driven by pulsed time periodic forces. The driving force contains, within each period, two pulses of equal constant amplitude and duration but opposite signs. Each pulse starts every half-period and its duration is varied. For subthreshold amplitudes, we study the dependence of the output signal-to-noise ratio (SNR) and the SR gain on the noise strength and the relative duration of the pulses. We find that the SR gains can reach values larger than unity, with maximum values showing a nonmonotonic dependence on the duration of the pulses.
Physical Review Letters, 2003
An amenable, analytical two-state description of the nonlinear population dynamics of a noisy bis... more An amenable, analytical two-state description of the nonlinear population dynamics of a noisy bistable system driven by a rectangular subthreshold signal is put forward. Explicit expressions for the driven population dynamics, the correlation function (its coherent and incoherent part), the signal-to-noise ratio (SNR) and the Stochastic Resonance (SR) gain are obtained. Within a suitably chosen range of parameter values this reduced description yields anomalous SR-gains exceeding unity and, simultaneously, gives rise to a non-monotonic behavior of the SNR vs. the noise strength. The analytical results agree well with those obtained from numerical solutions of the Langevin equation.
Physical Review E, 2005
We investigate the role of noise in the phenomenon of stochastic synchronization of switching eve... more We investigate the role of noise in the phenomenon of stochastic synchronization of switching events in a rocked, overdamped bistable potential driven by white Gaussian noise, the archetype description of Stochastic Resonance. We present a new approach to the stochastic counting process of noise-induced switching events: starting from the Markovian dynamics of the nonstationary, continuous particle dynamics one finds upon contraction onto two states a non-Markovian renewal dynamics. The output frequency is determined as the velocity of the underlying discrete phase dynamics. The phenomenon of noise-assisted phase synchronization is investigated in terms of an effective, instantaneous phase diffusion. The theory is applied to rectangular-shaped rocking signals versus increasing input-noise strengths. Precise numerical simulations corroborate very favorably our analytical results. The novel theoretical findings are also compared with prior findings.
European Physical Journal B, 2009
In this article, we investigate the stochastic resonance (SR) effect in a finite array of noisy b... more In this article, we investigate the stochastic resonance (SR) effect in a finite array of noisy bistable systems with nearest-neighbor coupling driven by a weak time-periodic driving force. The array is characterized by a collective variable. By means of numerical simulations, the signal-to-noise ratio (SNR) and the gain are estimated as functions of the noise and the interaction coupling strength. A strong enhancement of the SR phenomenon for this collective variable in comparison with SR in single unit bistable systems is observed. Gains larger than unity are obtained for some parameter values and multi-frequency driving forces, indicating that the system is operating in a non-linear regime albeit the smallness of the driving amplitude. The large SNR values observed are basically due to the fact that the output fluctuations are small and short lived, in comparison with their typical values in a linear regime. A non-monotonic behavior of the SNR with the coupling strength is also obtained.
The main objective of this work is to explore aspects of stochastic resonance (SR) in noisy bista... more The main objective of this work is to explore aspects of stochastic resonance (SR) in noisy bistable, symmetric systems driven by subthreshold periodic rectangular external signals possessing a large duty cycle of unity. Using a precise numerical solution of the Langevin equation, we carry out a detailed analysis of the behavior of the first two cumulant averages, the correlation function and its coherent and incoherent parts. We also depict the non-monotonic behavior versus the noise strength of several SR quantifiers such as the average output amplitude, i.e. the spectral amplification (SPA), the signal-to-noise ratio (SNR) and the SR-gain. In particular, we find that with subthreshold amplitudes and for an appropriate duration of the pulses of the driving force the phenomenon of stochastic resonance (SR), is accompanied by SR-gains exceeding unity. This analysis thus sheds new light onto the interplay between nonlinearity and the nonlinear response which in turn yields nontrivial, unexpected SR-gains above unity.
We investigate the role of noise in the phenomenon of stochastic synchronization of switching eve... more We investigate the role of noise in the phenomenon of stochastic synchronization of switching events in a rocked, overdamped bistable potential driven by white Gaussian noise, the archetype description of Stochastic Resonance. We present a new approach to the stochastic counting process of noise-induced switching events: starting from the Markovian dynamics of the nonstationary, continuous particle dynamics one finds upon contraction onto two states a non-Markovian renewal dynamics. The output frequency is determined as the velocity of the underlying discrete phase dynamics. The phenomenon of noise-assisted phase synchronization is investigated in terms of an effective, instantaneous phase diffusion. The theory is applied to rectangular-shaped rocking signals versus increasing input-noise strengths. Precise numerical simulations corroborate very favorably our analytical results. The novel theoretical findings are also compared with prior findings. * jcasado@us.es; http://numerix.us.es † Present address:
Physical Review E, 2007
We study the phenomenon of nonlinear stochastic resonance (SR) in a complex noisy system formed b... more We study the phenomenon of nonlinear stochastic resonance (SR) in a complex noisy system formed by a finite number of interacting subunits driven by rectangular pulsed time periodic forces. We find that very large SR gains are obtained for subthreshold driving forces with frequencies much larger than the values observed in simpler one-dimensional systems. These effects are explained using simple considerations.
Physical Review E, 2008
Previously derived expressions for the characteristic function of work performed on a quantum sys... more Previously derived expressions for the characteristic function of work performed on a quantum system by a classical external force are generalized to arbitrary initial states of the considered system and to Hamiltonians with degenerate spectra. In the particular case of microcanonical initial states explicit expressions for the characteristic function and the corresponding probability density of work are formulated. Their classical limit as well as their relations to the respective canonical expressions are discussed. A fluctuation theorem is derived that expresses the ratio of probabilities of work for a process and its time reversal to the ratio of densities of states of the microcanonical equilibrium systems with corresponding initial and final Hamiltonians.From this Crooks-type fluctuation theorem a relation between entropies of different systems can be derived which does not involve the time reversed process. This entropy-from-work theorem provides an experimentally accessible way to measure entropies.
Physical Review E, 2003
In the context of the phenomenon of Stochastic Resonance (SR) we study the correlation function, ... more In the context of the phenomenon of Stochastic Resonance (SR) we study the correlation function, the signal-to-noise ratio (SNR) and the ratio of output over input SNR, i.e. the gain, which is associated to the nonlinear response of a bistable system driven by time-periodic forces and white Gaussian noise. These quantifiers for SR are evaluated using the techniques of Linear Response Theory (LRT) beyond the usually employed two-mode approximation scheme. We analytically demonstrate within such an extended LRT description that the gain can indeed not exceed unity. We implement an efficient algorithm, based on work by Greenside and Helfand (detailed in the Appendix), to integrate the driven Langevin equation over a wide range of parameter values. The predictions of LRT are carefully tested against the results obtained from numerical solutions of the corresponding Langevin equation over a wide range of parameter values. We further present an accurate procedure to evaluate the distinct contributions of the coherent and incoherent parts of the correlation function to the SNR and the gain. As a main result we show for subthreshold driving that both, the correlation function and the SNR can deviate substantially from the predictions of LRT and yet, the gain can be either larger or smaller than unity. In particular, we find that the gain can exceed unity in the strongly nonlinear regime which is characterized by weak noise and very slow multifrequency subthreshold input signals with a small duty cycle. This latter result is in agreement with recent analogue simulation results by Gingl et al. in Refs. [18, 19].
Physical Chemistry Chemical Physics, 2001
Phys. Chem. Chem. Phys., 2001, 3, 1271-1276 DOI:10.1039/B009004M (Paper). Experimental and simula... more Phys. Chem. Chem. Phys., 2001, 3, 1271-1276 DOI:10.1039/B009004M (Paper). Experimental and simulation studies of the electron transfer reaction between [Ru(NH 3 ) 5 pz] 2+ and [Co(C 2 O 4 ) 3 ] 3− . Pilar Pérez-Tejeda ...
Journal of Surgical Oncology, 2006
Background and ObjectivesAdvanced ovarian cancer typically spreads in a diffuse intra-abdominal f... more Background and ObjectivesAdvanced ovarian cancer typically spreads in a diffuse intra-abdominal fashion. This characteristic suggests that combined radical surgery and intraperitoneal chemotherapy may be a useful treatment procedure. The purpose of this study was to review patients submitted to surgical debulking and hyperthermic intraoperative intraperitoneal chemotherapy (HIIC) and to evaluate the potential prognostic survival factors for advanced epithelial ovarian cancer in our center.Advanced ovarian cancer typically spreads in a diffuse intra-abdominal fashion. This characteristic suggests that combined radical surgery and intraperitoneal chemotherapy may be a useful treatment procedure. The purpose of this study was to review patients submitted to surgical debulking and hyperthermic intraoperative intraperitoneal chemotherapy (HIIC) and to evaluate the potential prognostic survival factors for advanced epithelial ovarian cancer in our center.MethodsA series of patients (N = 33) diagnosed of peritoneal carcinomatosis for epithelial ovarian cancer (stage III) from January 1997 to December 2004 submitted to radical surgery-peritonectomy and HIIC with paclitaxel was included in this study; 19 primary ovarian cancer and 14 recurrent ovarian cancer.A series of patients (N = 33) diagnosed of peritoneal carcinomatosis for epithelial ovarian cancer (stage III) from January 1997 to December 2004 submitted to radical surgery-peritonectomy and HIIC with paclitaxel was included in this study; 19 primary ovarian cancer and 14 recurrent ovarian cancer.ResultsCytoreduction R0 (P = 0.018) and negative lymph nodes (P = 0.005) were covariables for major prognostic survival. Patients with optimal cytoreduction R0 obtained survival rates of 63% at 5 years in recurrent ovarian cancer and 60% in primary ovarian cancer, 71% and 63%, respectively with associated subtotal infra-abdominal peritonectomy, and even better results if negative lymph nodes.Cytoreduction R0 (P = 0.018) and negative lymph nodes (P = 0.005) were covariables for major prognostic survival. Patients with optimal cytoreduction R0 obtained survival rates of 63% at 5 years in recurrent ovarian cancer and 60% in primary ovarian cancer, 71% and 63%, respectively with associated subtotal infra-abdominal peritonectomy, and even better results if negative lymph nodes.ConclusionsRadical surgery-peritonectomy with HIIQ has been shown to be a surgical procedure with high tolerability, low morbimortality, enhanced survival, and prolonged disease-free interval in patients with peritoneal carcinomatosis so much for recurrent or primary ovarian cancer. J. Surg. Oncol. 2006;94:316–324. © 2006 Wiley-Liss, Inc.Radical surgery-peritonectomy with HIIQ has been shown to be a surgical procedure with high tolerability, low morbimortality, enhanced survival, and prolonged disease-free interval in patients with peritoneal carcinomatosis so much for recurrent or primary ovarian cancer. J. Surg. Oncol. 2006;94:316–324. © 2006 Wiley-Liss, Inc.
Physical Review E, 1995
We study the long-time response of a stochastic system formed by very many interacting subsystems... more We study the long-time response of a stochastic system formed by very many interacting subsystems coupled by a mean-field interaction and subject to a time periodic external field. In the absence of a driving field; the system shows an order-disorder phase transition and its time evolution is well described by a Fokker-Planck equation which is nonlinear in the probability density.
Journal of Statistical Physics, 1987
A population of identical nonlinear oscillators, subject to random forces and coupled via a mean-... more A population of identical nonlinear oscillators, subject to random forces and coupled via a mean-field interaction, is studied in the thermodynamic limit. The model presents a nonequilibrium phase transition from a stationary to a time-periodic probability density. Below the transition line, the population of oscillators is in a quiescent state with order parameter equal to zero. Above the transition line, there is a state of collective rhythmicity characterized by a time-periodic behavior of the order parameter and all moments of the probability distribution. The information entropy of the ensemble is a constant both below and above the critical line. Analytical and numerical analyses of the model are provided.
Physical Review E, 2006
We explore stochastic resonance effects in the response of a complex stochastic system formed by ... more We explore stochastic resonance effects in the response of a complex stochastic system formed by a finite number of interacting, identical subunits driven by a time-periodic force. The driving force alone cannot induce sustained oscillations between the different attractors of the dynamics in the absence of noise. We focus on a global stochastic variable defined as the arithmetic mean of the relevant stochastic variable of each subunit. We construct numerical approximations to its first two long time cumulant moments and its long time correlation function. We also compute the output signal-to-noise ratio and the stochastic resonance gain, for a wide range of parameter values and several types of driving forces. The coupling between the subsystems leads, within adequate ranges of the parameter values, to global outputs with very large signal-to-noise ratios. We have also observed gains larger than unity in the global response to subthreshold sinusoidal driving forces.
Physical Review E, 1995
The response of a symmetric bistable system driven by a time periodic rectangular input signal an... more The response of a symmetric bistable system driven by a time periodic rectangular input signal and subject to a white noise is studied. The analysis shows that the stochastic resonant enhancement of a weak amplitude signal implies a distortion of the input shape for intermediate frequencies, due to the dispersivity of the response. On the other hand, the shape can
Physical Review E, 2008
We analyze the stochastic response of a finite set of globally coupled noisy bistable units drive... more We analyze the stochastic response of a finite set of globally coupled noisy bistable units driven by rather weak time-periodic forces. We focus on the stochastic resonance and phase frequency synchronization of the collective variable, defined as the arithmetic mean of the variable characterizing each element of the array. For single-unit systems, stochastic resonance can be understood with the powerful tools of linear response theory. Proper noise-induced phase frequency synchronization for a single-unit system in this linear response regime does not exist. For coupled arrays, our numerical simulations indicate an enhancement of the stochastic resonance effects leading to gains larger than unity as well as genuine phase frequency synchronization. The nonmonotonicity of the response with the strength of the coupling strength is investigated. Comparison with simplifying schemes proposed in the literature to describe the random response of the collective variable is carried out.
Physical Review E, 2003
The main objective of this work is to explore aspects of stochastic resonance (SR) in noisy bista... more The main objective of this work is to explore aspects of stochastic resonance (SR) in noisy bistable, symmetric systems driven by subthreshold periodic rectangular external signals possessing a large duty cycle of unity. Using a precise numerical solution of the Langevin equation, we carry out a detailed analysis of the behavior of the first two cumulant averages, the correlation function and its coherent and incoherent parts. We also depict the non-monotonic behavior versus the noise strength of several SR quantifiers such as the average output amplitude, i.e. the spectral amplification (SPA), the signal-to-noise ratio (SNR) and the SR-gain. In particular, we find that with subthreshold amplitudes and for an appropriate duration of the pulses of the driving force the phenomenon of stochastic resonance (SR), is accompanied by SR-gains exceeding unity. This analysis thus sheds new light onto the interplay between nonlinearity and the nonlinear response which in turn yields nontrivial, unexpected SR-gains above unity.
Physical Review E, 2004
We analyze the phenomenon of nonlinear stochastic resonance (SR) in noisy bistable systems driven... more We analyze the phenomenon of nonlinear stochastic resonance (SR) in noisy bistable systems driven by pulsed time periodic forces. The driving force contains, within each period, two pulses of equal constant amplitude and duration but opposite signs. Each pulse starts every half-period and its duration is varied. For subthreshold amplitudes, we study the dependence of the output signal-to-noise ratio (SNR) and the SR gain on the noise strength and the relative duration of the pulses. We find that the SR gains can reach values larger than unity, with maximum values showing a nonmonotonic dependence on the duration of the pulses.
Physical Review Letters, 2003
An amenable, analytical two-state description of the nonlinear population dynamics of a noisy bis... more An amenable, analytical two-state description of the nonlinear population dynamics of a noisy bistable system driven by a rectangular subthreshold signal is put forward. Explicit expressions for the driven population dynamics, the correlation function (its coherent and incoherent part), the signal-to-noise ratio (SNR) and the Stochastic Resonance (SR) gain are obtained. Within a suitably chosen range of parameter values this reduced description yields anomalous SR-gains exceeding unity and, simultaneously, gives rise to a non-monotonic behavior of the SNR vs. the noise strength. The analytical results agree well with those obtained from numerical solutions of the Langevin equation.
Physical Review E, 2005
We investigate the role of noise in the phenomenon of stochastic synchronization of switching eve... more We investigate the role of noise in the phenomenon of stochastic synchronization of switching events in a rocked, overdamped bistable potential driven by white Gaussian noise, the archetype description of Stochastic Resonance. We present a new approach to the stochastic counting process of noise-induced switching events: starting from the Markovian dynamics of the nonstationary, continuous particle dynamics one finds upon contraction onto two states a non-Markovian renewal dynamics. The output frequency is determined as the velocity of the underlying discrete phase dynamics. The phenomenon of noise-assisted phase synchronization is investigated in terms of an effective, instantaneous phase diffusion. The theory is applied to rectangular-shaped rocking signals versus increasing input-noise strengths. Precise numerical simulations corroborate very favorably our analytical results. The novel theoretical findings are also compared with prior findings.
European Physical Journal B, 2009
In this article, we investigate the stochastic resonance (SR) effect in a finite array of noisy b... more In this article, we investigate the stochastic resonance (SR) effect in a finite array of noisy bistable systems with nearest-neighbor coupling driven by a weak time-periodic driving force. The array is characterized by a collective variable. By means of numerical simulations, the signal-to-noise ratio (SNR) and the gain are estimated as functions of the noise and the interaction coupling strength. A strong enhancement of the SR phenomenon for this collective variable in comparison with SR in single unit bistable systems is observed. Gains larger than unity are obtained for some parameter values and multi-frequency driving forces, indicating that the system is operating in a non-linear regime albeit the smallness of the driving amplitude. The large SNR values observed are basically due to the fact that the output fluctuations are small and short lived, in comparison with their typical values in a linear regime. A non-monotonic behavior of the SNR with the coupling strength is also obtained.
The main objective of this work is to explore aspects of stochastic resonance (SR) in noisy bista... more The main objective of this work is to explore aspects of stochastic resonance (SR) in noisy bistable, symmetric systems driven by subthreshold periodic rectangular external signals possessing a large duty cycle of unity. Using a precise numerical solution of the Langevin equation, we carry out a detailed analysis of the behavior of the first two cumulant averages, the correlation function and its coherent and incoherent parts. We also depict the non-monotonic behavior versus the noise strength of several SR quantifiers such as the average output amplitude, i.e. the spectral amplification (SPA), the signal-to-noise ratio (SNR) and the SR-gain. In particular, we find that with subthreshold amplitudes and for an appropriate duration of the pulses of the driving force the phenomenon of stochastic resonance (SR), is accompanied by SR-gains exceeding unity. This analysis thus sheds new light onto the interplay between nonlinearity and the nonlinear response which in turn yields nontrivial, unexpected SR-gains above unity.
We investigate the role of noise in the phenomenon of stochastic synchronization of switching eve... more We investigate the role of noise in the phenomenon of stochastic synchronization of switching events in a rocked, overdamped bistable potential driven by white Gaussian noise, the archetype description of Stochastic Resonance. We present a new approach to the stochastic counting process of noise-induced switching events: starting from the Markovian dynamics of the nonstationary, continuous particle dynamics one finds upon contraction onto two states a non-Markovian renewal dynamics. The output frequency is determined as the velocity of the underlying discrete phase dynamics. The phenomenon of noise-assisted phase synchronization is investigated in terms of an effective, instantaneous phase diffusion. The theory is applied to rectangular-shaped rocking signals versus increasing input-noise strengths. Precise numerical simulations corroborate very favorably our analytical results. The novel theoretical findings are also compared with prior findings. * jcasado@us.es; http://numerix.us.es † Present address:
Physical Review E, 2007
We study the phenomenon of nonlinear stochastic resonance (SR) in a complex noisy system formed b... more We study the phenomenon of nonlinear stochastic resonance (SR) in a complex noisy system formed by a finite number of interacting subunits driven by rectangular pulsed time periodic forces. We find that very large SR gains are obtained for subthreshold driving forces with frequencies much larger than the values observed in simpler one-dimensional systems. These effects are explained using simple considerations.
Physical Review E, 2008
Previously derived expressions for the characteristic function of work performed on a quantum sys... more Previously derived expressions for the characteristic function of work performed on a quantum system by a classical external force are generalized to arbitrary initial states of the considered system and to Hamiltonians with degenerate spectra. In the particular case of microcanonical initial states explicit expressions for the characteristic function and the corresponding probability density of work are formulated. Their classical limit as well as their relations to the respective canonical expressions are discussed. A fluctuation theorem is derived that expresses the ratio of probabilities of work for a process and its time reversal to the ratio of densities of states of the microcanonical equilibrium systems with corresponding initial and final Hamiltonians.From this Crooks-type fluctuation theorem a relation between entropies of different systems can be derived which does not involve the time reversed process. This entropy-from-work theorem provides an experimentally accessible way to measure entropies.
Physical Review E, 2003
In the context of the phenomenon of Stochastic Resonance (SR) we study the correlation function, ... more In the context of the phenomenon of Stochastic Resonance (SR) we study the correlation function, the signal-to-noise ratio (SNR) and the ratio of output over input SNR, i.e. the gain, which is associated to the nonlinear response of a bistable system driven by time-periodic forces and white Gaussian noise. These quantifiers for SR are evaluated using the techniques of Linear Response Theory (LRT) beyond the usually employed two-mode approximation scheme. We analytically demonstrate within such an extended LRT description that the gain can indeed not exceed unity. We implement an efficient algorithm, based on work by Greenside and Helfand (detailed in the Appendix), to integrate the driven Langevin equation over a wide range of parameter values. The predictions of LRT are carefully tested against the results obtained from numerical solutions of the corresponding Langevin equation over a wide range of parameter values. We further present an accurate procedure to evaluate the distinct contributions of the coherent and incoherent parts of the correlation function to the SNR and the gain. As a main result we show for subthreshold driving that both, the correlation function and the SNR can deviate substantially from the predictions of LRT and yet, the gain can be either larger or smaller than unity. In particular, we find that the gain can exceed unity in the strongly nonlinear regime which is characterized by weak noise and very slow multifrequency subthreshold input signals with a small duty cycle. This latter result is in agreement with recent analogue simulation results by Gingl et al. in Refs. [18, 19].
Physical Chemistry Chemical Physics, 2001
Phys. Chem. Chem. Phys., 2001, 3, 1271-1276 DOI:10.1039/B009004M (Paper). Experimental and simula... more Phys. Chem. Chem. Phys., 2001, 3, 1271-1276 DOI:10.1039/B009004M (Paper). Experimental and simulation studies of the electron transfer reaction between [Ru(NH 3 ) 5 pz] 2+ and [Co(C 2 O 4 ) 3 ] 3− . Pilar Pérez-Tejeda ...