Anatole Kenfack

Freie Universität Berlin | FUB · Institute of Chemistry and Biochemistry

Metallic-based microcellular structures are widely used in heat and mass transfer processes owing to their unique combination of high porosity, high surface area, fixed pore morphology and high Young modulus, enabling their suitability as heat pipes in oil and gas processing equipment, biomedical materials for bone repair and bone substitution, sol...

A quantum resonance model is prepared by periodically kicking cold atoms exposed to an optical ratchet potential in the direction of the gravitational field. Within tailored parameters, intriguing phenomena emerge including absolute negative mobility, in which the atom surprisingly moves against the bias (gravity). In its upward motion, the particl...

This study presents a combined implementation of three‐dimensional (3D) advanced imaging and computational fluid dynamics (CFD) modeling and simulation techniques to interpret the effective transport properties of single and stacked samples of differential microcellular structures. 3D morphological analysis software (ScanIP) was used to create repr...

We investigate the dissociation dynamics of diatomic molecules subjected to both a femtosecond infrared (IR) laser pulse and a femtosecond pulse train (FPT) within the framework of the Morse potential model. When the IR and FPT are phase delayed, we observe well-resolved oscillations in dissociation probability, corresponding to multiple integers o...

We show in this Comment that the nonclassicality indicator proposed in Sadeghi et al. [Phys. Rev. A 82, 012102 (2010)] is controversial. Defined in terms of the interferences displayed by the quasidistribution function of at least two superposition states, this indicator may logically lead to zero for any single quantum state irrespective to its no...

We investigate the transport properties of a particle subjected to a deterministic inertial rocking system, under a constant bias, for which the phase of the symmetric spatial potential used is time modulated. We show that this modulated phase, assisted by a periodic driving force, can lead to the occurrence of the so-called absolute negative mobil...

We consider a deterministic chaotic ratchet model for which the driving force is designed to allow the rectification of current as well as the control of chaos of the system. Besides the amplitude of the symmetric driving force which is often used in this framework as control parameter, a phase has been newly included here. Exploring this phase, re...

We consider a particle in a spatial symmetric/asymmetric potential driven by time periodic bichromatic AC fields of ratchet type. The associated time-dependent Schrödinger equation is conveniently tackled with the Floquet theory. We next proceed to investigate the ratchet effect induced by the driver, comparing the symmetric with the asymmetric cas...

A molecule in the electronic ground state described in the Born-Oppenheimer approximation (BOA) by the wave function Ψ_BO = Φ_0 χ_0 (where Φ_0 is the time-independent electronic energy eigenfunction and χ_0 is a time-dependent nuclear wave packet) exhibits a non-zero nuclear flux density, whereas it always displays zero electronic flux density (EFD...

We present quantum simulations of a vibrating hydrogen molecule H2 and address the issue of electron correlation. After appropriately setting the frame and the observer plane, we were able to determine precisely the number of electrons and nuclei which actually flow by evaluating electronic and nuclear fluxes. This calculation is repeated for three...

Excited energy eigenstates and their superpositions typically exhibit a fine oscillatory structure near caustics. Semiclassical theory accesses these, but depends on detailed geometrical knowledge of the caustics. Here we show that a finite placement of coherent states on the classical region efficiently fits such extended states, reproducing struc...

This article presents the results of the first quantum simulations of the electronic flux density (j(e)) by the "coupled-channels" (CC) theory, the fundamentals of which are presented in the previous article [Diestler, D. J. J. Phys. Chem. A 2012, DOI: 10.1021/jp207843z]. The principal advantage of the CC scheme is that it employs exclusively stand...

A full quantum treatment shows that coupled electronic and nuclear fluxes exhibit a strong sensitivity to a small mass change in a vibrating molecule. This has been exemplified with the existing isotopes of H2+ as well as few fictitious ones. We find that the fluxes undergo a significant change as one goes from one isotope of reduced mass μ to anot...

Current reversal is an intriguing phenomenon that has been central to recent experimental and theoretical investigations of transport based on ratchet mechanism. By considering a system of two interacting ratchets, we demonstrate how the coupling can be used to control the reversals. In particular, we find that current reversal that exists in a sin...

We study onset and control of stochastic resonance (SR) phenomenon in two driven bistable systems, mutually coupled and subjected to independent noises, taking into account the influence of both the inertia and the coupling. In the absence of coupling, we found two critical damping parameters: one for the onset of SR and another for which SR is opt...

We demonstrate that coupled electronic and nuclear fluxes in molecules can strongly depend on the initial state preparation. Starting the dynamics of an aligned D2+ molecule at two different initial conditions, the inner and the outer turning points, we observe qualitatively different oscillation patterns of the nuclear fluxes developing after 30 f...

a b s t r a c t Common myth suggests synchronicity and unidirectionality of nuclear and electronic fluxes. Accurate quantum dynamics simulations of the vibrating model system, aligned H þ 2 , confirm this rule, but with exceptional opposite behaviours during short periods in the attosecond time domain. The ratio of elec-tronic versus nuclear fluxes...

For a laser driven molecule, we show that the ionization and the dissociation channels can be separated by preparing the molecule in a specific vibrational state. Specifically, we investigate the dynamics of the hydrogen molecular ion under a femtosecond infrared laser field aligned with the molecular axis. We find dissociation probabilities of mor...

We consider a system of two coupled bistable systems driven by both periodic and noise sources, focusing mainly on stochastic resonance (SR). In the absence of coupling, we found two critical damping parameters: one for the onset of resonances, and another for which theses resonances are optimum. We demonstrate that the absence of resonances in the...

A row of parallely ordered and coupled molecular nanoshafts is shown to develop a shuttling transport of charges at finite temperature. The appearance of a cu rrent without applying an external bias voltage is reported as well as a natura l diode effect allowing unidirectional charge transport along one field directi on while blocking the opposite...

We study the bifurcations and the chaotic behaviour of a periodically forced double-well Duffing oscillator coupled to a single-well Duffing oscillator. Using the amplitude and the frequency of the driving force as control parameters, we show that our model presents phenomena which were not observed in coupled periodically forced Duffing oscillator...

Low-order quantum resonances manifested by directed currents have been realized with cold atoms. Here we show that by increasing the strength of an experimentally achievable delta-kicking ratchet potential, quantum resonances of a very high order may naturally emerge and can induce larger ratchet currents than low-order resonances, with the underly...

Just as a coherent state may be considered as a quantum point, its restriction to a factor space of the full Hilbert space can be interpreted as a quantum plane. The overlap of such a factor coherent state with a full pure state is akin to a quantum section. It defines a reduced pure state in the cofactor Hilbert space. Physically, this factorizati...

We show that ionization and dissociation can be influenced separately in a molecule with appropriate external noise. Specifically we investigate the hydrogen molecular ion under a stochastic force quantum mechanically beyond the Born-Oppenheimer approximation. We find that up to 30% of dissociation without ionization can be achieved by suitably tun...

We investigate the dynamics of diatomic molecules subjected to both a femtosecond mid-infrared laser pulse and Gaussian white noise. The stochastic Schr\"odinger equation with a Morse potential is used to describe the molecular vibrations under noise and the laser pulse. For weak laser intensity, well below the dissociation threshold, it is shown t...

Low-order quantum resonances manifested by directed currents have been realized with cold atoms. Here we show that by increasing the strength of an experimentally achievable delta-kicking ratchet potential, quantum resonances of a very high order may naturally emerge and can induce larger ratchet currents than low-order resonances, with the underly...

Mateos [Phys. Rev. Lett. 84, 258 (2000)] conjectured that current reversal in a classical deterministic ratchet is associated with bifurcations from chaotic to periodic regimes. This is based on the comparison of the current and the bifurcation diagram as a function of a given parameter for a periodic asymmetric potential. Barbi and Salerno [Phys....

A parametrically modified sine-Gordon model subject to an applied spatial periodic field is considered. It is shown by analyzing the phase plane that the deformable parameter R plays an important role since it can induce a new configuration of the system. The Melnikov's method is used to derive the bifurcation curves. We find threshold theoretical...

The bifurcation and chaotic behavior of unidirectionally coupled deterministic ratchets is studied as a function of the driving force amplitude and frequency . A classification of the various types of bifurcations likely to be encountered in this system was done by examining the stability of the steady state in linear response as well as constructi...

The fragmentation of diatomic molecules under a stochastic force is investigated both classically and quantum mechanically, focusing on their dissociation probabilities. It is found that the quantum system is more robust than the classical one in the limit of a large number of kicks. The opposite behavior emerges for a small number of kicks. Quantu...

The fragmentation of diatomic molecules under a stochastic force is investigated both classically and quantum mechanically, focussing on their dissociation probabilities. It is found that the quantum system is more robust than the classical one in the limit of a large number of kicks. The opposite behavior emerges for a small number of kicks. Quant...

The bifurcation and chaotic behaviour of unidirectionally coupled deterministic ratchets is studied as a function of the driving force amplitude ($a$) and frequency ($\omega$). A classification of the various types of bifurcations likely to be encountered in this system was done by examining the stability of the steady state in linear response as w...

A measure of non-classicality of quantum states based on the volume of the negative part of the Wigner function is proposed. We analyse this quantity for Fock states, squeezed displaced Fock states and cat-like states defined as coherent superposition of two Gaussian wavepackets.

A measure of nonclassicality of quantum states based on the volume of the negative part of the Wigner function is proposed. We analyze this quantity for Fock states, squeezed displaced Fock states and cat-like states defined as coherent superposition of two Gaussian wave packets. Comment: 10 pages, 7 figures

The bifurcation structure of coupled periodically driven double-well Duffing oscillators is investigated as a function of the strength of the driving force $f$ and its frequency $\Omega$. We first examine the stability of the steady state in linear response, and classify the different types of bifurcation likely to occur in this model. We then expl...

A two-step optimization is proposed to represent an arbitrary quantum state to a desired accuracy with the least number of gaussians in phase space. The Husimi distribution of the quantum state provides the information to determine the modulus of the weight for the gaussians. Then, the phase information contained in the Wigner distribution is used...

Chaotic responses induced by an applied rf signal on the long Josephson junction influenced by a constant dc-driven field are investigated by means of a model based on the sine-Gordon equation. We assume that the localized nonlinear excitations present in the system as initial data are the breatherlike mode. Thus, in order to analyze in detail the...

Breathers excitations in a driven long Josephson junction influenced by a localized impurity due to a spatial variation of the inductance are discussed. By use of the perturbation method, it is shown that, in the absence of the bias current, the breather can break into a fluxon-antifluxon pair , for values of the inductance greater than a threshold...

structures of molecular p-channel organic semiconductors Semiconductor (cm2/Vs) Ion/Ioff Rubrene (air, PMMA) 1.5-20 1.5-20 P5 1.5 10 8 P5 (PVP-CP) 2.9-3.0 10 5 P5 (Al2O3) 0.06-0.1 ∼ 10 6 P5 (SiNx) 0.2-0.4 ∼ 10 8 P5 (Ta2O5) 0.24 10 4 P5 (Gd2O3) 0.1 10 3 P5 TiO2+PMS 0.8 10 4 P5 (BZT or BST) 0.32-0.60 ∼ 10 5 P5-precursor 0.01-0.2 ∼ 10 5 P5-precursor 0...