Periodic Pulse Train Research Articles

Quantum Resonances in Selective Rotational Excitation of Molecules with a Sequence of Ultrashort Laser Pulses

We experimentally investigate the effect of quantum resonance in the rotational excitation of the simplest quantum rotor--a diatomic molecule. Using the techniques of high-resolution femtosecond pulse shaping and rotational state-resolved detection, we measure directly the amount of energy absorbed by molecules interacting with a periodic train of laser pulses, and study their dependence on the train period. We show that the energy transfer is significantly enhanced at quantum resonance, and use this effect to demonstrate selective rotational excitation of two nitrogen isotopologs, (14)N(2) and (15)N(2). Moreover, by tuning the period of the pulse train in the vicinity of a fractional quantum resonance, we achieve selective rotational excitation of para- and ortho-isomers of (15)N(2).

Dynamical stabilization of the initial state in a periodically kicked three-dimensional Rydberg atom

We present the dynamical stabilization of the initial state of a three-dimensional Rydberg atom subjected to a periodic train of half-cycle pulses. It is shown as an existence of a broad maximum of the survival probability at train repetition frequencies close to the classical orbital frequency. Population of the initial state for train repetition frequencies from this plateau is almost constant, even for trains consisting of a large number of pulses. We find this phenomenon very well observable for the initial redshifted Stark states. It is shown that for initial states with high and intermediate values of the angular quantum number, the dynamical stabilization of the initial state occurs only partially. We show that for extreme members of the Stark manifold as the initial states, results are fully consistent with appropriate results for a one-dimensional Rydberg atom.

Neural ITD coding with bilateral cochlear implants: effect of binaurally coherent jitter

Poor sensitivity to the interaural time difference (ITD) constrains the ability of human bilateral cochlear implant users to listen in everyday noisy acoustic environments. ITD sensitivity to periodic pulse trains degrades sharply with increasing pulse rate but can be restored at high pulse rates by jittering the interpulse intervals in a binaurally coherent manner (Laback and Majdak. Binaural jitter improves interaural time-difference sensitivity of cochlear implantees at high pulse rates. Proc Natl Acad Sci USA 105: 814-817, 2008). We investigated the neural basis of the jitter effect by recording from single inferior colliculus (IC) neurons in bilaterally implanted, anesthetized cats. Neural responses to trains of biphasic pulses were measured as a function of pulse rate, jitter, and ITD. An effect of jitter on neural responses was most prominent for pulse rates above 300 pulses/s. High-rate periodic trains evoked only an onset response in most IC neurons, but introducing jitter increased ongoing firing rates in about half of these neurons. Neurons that had sustained responses to jittered high-rate pulse trains showed ITD tuning comparable with that produced by low-rate periodic pulse trains. Thus, jitter appears to improve neural ITD sensitivity by restoring sustained firing in many IC neurons. The effect of jitter on IC responses is qualitatively consistent with human psychophysics. Action potentials tended to occur reproducibly at sparse, preferred times across repeated presentations of high-rate jittered pulse trains. Spike triggered averaging of responses to jittered pulse trains revealed that firing was triggered by very short interpulse intervals. This suggests it may be possible to restore ITD sensitivity to periodic carriers by simply inserting short interpulse intervals at select times.

The effects of DBS patterns on basal ganglia activity and thalamic relay

Thalamic neurons receive inputs from cortex and their responses are modulated by the basal ganglia (BG). This modulation is necessary to properly relay cortical inputs back to cortex and downstream to the brain stem when movements are planned. In Parkinson's disease (PD), the BG input to thalamus becomes pathological and relay of motor-related cortical inputs is compromised, thereby impairing movements. However, high frequency (HF) deep brain stimulation (DBS) may be used to restore relay reliability, thereby restoring movements in PD patients. Although therapeutic, HF stimulation consumes significant power forcing surgical battery replacements, and may cause adverse side effects. Here, we used a biophysical-based model of the BG-Thalamus motor loop in both healthy and PD conditions to assess whether low frequency stimulation can suppress pathological activity in PD and enable the thalamus to reliably relay movement-related cortical inputs. We administered periodic pulse train DBS waveforms to the sub-thalamic nucleus (STN) with frequencies ranging from 0-140 Hz, and computed statistics that quantified pathological bursting, oscillations, and synchronization in the BG as well as thalamic relay of cortical inputs. We found that none of the frequencies suppressed all pathological activity in BG, though the HF waveforms recovered thalamic reliability. Our rigorous study, however, led us to a novel DBS strategy involving low frequency multi-input phase-shifted DBS, which successfully suppressed pathological symptoms in all BG nuclei and enabled reliable thalamic relay. The neural restoration remained robust to changes in the model parameters characterizing early to late PD stages.

G020013 培養骨芽細胞の増殖・分化に対するランダムパルス列電磁場の刺激効果

One of critical issues of bone tissue engineering is the establishment of technique to effectively promote the calcification of regenerative bone in culture. We have found that a random pulse tram electromagnetic fields (EMF) can promote more the calcification of osteoblasts than a periodic pulse train EMF in vitro. However, the mechanism behind this result is unknown. Cellular proliferation and alkaline phosphatase (ALP) activity are two of factors related to osteoblastic calcification. The purpose of this study is to investigate the effect of random pulse train EMF on the proliferation and ALP activity of osteoblasts in vitro MC3T3-E1 osteoblastic cells were seeded on a φ 35-mm culture dish at the density of 100 cells/mm^2. The cells on the central area within a radius of 9 mm were exposed to EMF for three minutes per day. The effect of random pulse train (RdPT) EMF was compared with those of periodic pulse tram (PrPT) EMF, continuous constant (CC) EMF, and no EMF stimulation control. The detection of ALP activity was conducted by using the lead citrate method on the culture dish. The cells proliferation did not show any difference among all the groups. On the other hand, in ALP activity, RdPT group showed the highest values among all the groups. These results suggest that the osteogenic effect of random pulse train EMF depends on the differentiation stage of osteoblasts, giving us useful information about the mechanism.

Virtual active touch using randomly patterned intracortical microstimulation.

Intracortical microstimulation (ICMS) has promise as a means for delivering somatosensory feedback in neuroprosthetic systems. Various tactile sensations could be encoded by temporal, spatial, or spatiotemporal patterns of ICMS. However, the applicability of temporal patterns of ICMS to artificial tactile sensation during active exploration is unknown, as is the minimum discriminable difference between temporally modulated ICMS patterns. We trained rhesus monkeys in an active exploration task in which they discriminated periodic pulse-trains of ICMS (200 Hz bursts at a 10 Hz secondary frequency) from pulse trains with the same average pulse rate, but distorted periodicity (200 Hz bursts at a variable instantaneous secondary frequency). The statistics of the aperiodic pulse trains were drawn from a gamma distribution with mean inter-burst intervals equal to those of the periodic pulse trains. The monkeys distinguished periodic pulse trains from aperiodic pulse trains with coefficients of variation 0.25 or greater. Reconstruction of movement kinematics, extracted from the activity of neuronal populations recorded in the sensorimotor cortex concurrent with the delivery of ICMS feedback, improved when the recording intervals affected by ICMS artifacts were removed from analysis. These results add to the growing evidence that temporally patterned ICMS can be used to simulate a tactile sense for neuroprosthetic devices.

Modeling and characteristic analysis of underwater acoustic signal of the accelerating propeller

The signal feature of propeller cavitation noise during acceleration or deceleration procedure can be used to passively detect and classify moving vessels and underwater vehicles in the port regions. By analyzing the chirp periodicity of the variation of propeller wake velocity under acceleration situation, this paper presents a time domain expression of the modulation envelope signal of the accelerating propeller noise, treating the signal as a Gaussian-shaped chirp periodic pulse train with increasing trend and fluctuating pulse amplitude. The paper investigates the characteristics of simplified fractional Fourier transform (SFRFT) spectrum of the chirp periodic signal, and thus obtains the relation between the chirp periodic signal and its chirp harmonics under the conditions of underwater passive detection. Furthermore, the experimental data of the cavitation tunnel satisfy the results obtained by simulation, which verifies the correctness of the proposed signal model.

Bistability and resonance in the periodically stimulated Hodgkin-Huxley model with noise

We describe general characteristics of the Hodgkin-Huxley neuron's response to a periodic train of short current pulses with Gaussian noise. The deterministic neuron is bistable for antiresonant frequencies. When the stimuli arrive at the resonant frequency the firing rate is a continuous function of the current amplitude I(0) and scales as (I(0)-I(th))(1/2), characteristic of a saddle-node bifurcation at the threshold I(th). Intervals of continuous irregular response alternate with integer mode-locked regions with bistable excitation edge. There is an even-all multimodal transition between the 2 : 1 and 3 : 1 states in the vicinity of the main resonance, which is analogous to the odd-all transition discovered earlier in the high-frequency regime. For I(0)<I(th) and small noise the firing rate has a maximum at the resonant frequency. For larger noise and subthreshold stimulation the maximum firing rate initially shifts toward lower frequencies, then returns to higher frequencies in the limit of large noise. The stochastic coherence antiresonance, defined as a simultaneous occurrence of (i) the maximum of the coefficient of variation and (ii) the minimum of the firing rate vs the noise intensity, occurs over a wide range of parameter values, including monostable regions. Results of this work can be verified experimentally.

Critical phenomena in periodic stratified media due to time-varying dielectric permittivity functions

The critical phenomena in a one-dimensional periodic stratified medium with time-varying dielectric permittivity functions are theoretically investigated for both TM and TE waves by solving the time-dependent electric displacement equation and the magnetic field equation, respectively. It is found that there exists a critical value of the varying amplitude when the dielectric permittivity function is changing with time. When the varying amplitude is below or at the critical value, the periodic structure can reflect an incident plane wave into a periodic femtosecond pulse train with respect to time. On the other hand, when the varying amplitude is much above the critical value, the reflectivity is descending more rapidly with time, which means that, at one moment, the incident light is transmitted thoroughly and the periodic structure is becoming transparent. The effect of the layer number on the reflectivity is also presented. Especially at the critical value, the pulse train generated is periodic with almost 100% peaks and zero troughs for both TM and TE waves when the layer number is up to 11. These interesting conclusions could find potential realistic applications in the future.

加速螺旋桨水声信号建模及其特性分析

The signal feature of propeller cavitation noise during acceleration or deceleration procedure can be used to passively detect and classify moving vessels and underwater vehicles in the port regions. By analyzing the chirp periodicity of the variation of propeller wake velocity under acceleration situation, this paper presents the time domain expression of the modulation envelope signal of the accelerating propeller noise, treating the signal as a Gaussian-shaped chirp periodic pulse train with increasing trend and fluctuating pulse amplitude. The paper investigates the characteristics of simplified fractional Fourier transform (SFRFT) spectrum of the chirp periodic signal, and thus obtains the relation between the chirp periodic signal and its chirp harmonics under the conditions of underwater passive detection. Furthermore, the experimental data of the cavitation tunnel satisfy the results obtained by simulation, which verifies the correctness of the proposed signal model.

Spectral self-imaging effect by time-domain multilevel phase modulation of a periodic pulse train

We propose and analyze a novel (to our knowledge) approach to implement the spectral self-imaging effect of optical frequency combs. The technique is based on time-domain multilevel phase-only modulation of a periodic optical pulse train. The method admits both infinite- and finite-duration periodic pulse sequences. We show that the fractional spectral self-imaging effect allows one to reduce by an integer factor the comb frequency spacing. Numerical simulation results support our theoretical analysis.

Cooperation and competition between lateral and medial perforant path synapses in the dentate gyrus

It has been suggested that non-spatial and spatial pieces of information are transmitted to the dentate gyrus from entorhinal cortex layer II through the lateral and medial perforant paths (LPP and MPP), which establish synapses on granule cell dendrites in the outer and middle one-thirds of the dentate molecular layer, respectively. In the present paper, we first investigated cooperation and competition between MPP and LPP synapses being subject to STDP rules, using a four-compartmental granule cell model. MPP and LPP were stimulated simultaneously by periodic and random pulse trains, respectively. Both synapses were gradually enhanced by cooperation between those synapses in the early stage, and then either the MPP or the LPP synapse was rapidly enhanced through synaptic competition in the following stage, depending on their initial synaptic conductances. The dominant cause of synaptic competition is that the distance between the MPP synapse and the soma is shorter than that between the LPP synapse and the soma. These results suggest that the LPP and MPP synapses tend to be enhanced in the dentate supra- and infrapyramidal blades, respectively, taking account of the thickness of each of the LPP and MPP fiber laminae in the blades. The dentate gyrus may select spatial and non-spatial pieces of information through synaptic cooperation, and may open a gate for each piece of information through synaptic competition. Then we investigated the role of inhibitory local circuits in synaptic competition in the dentate gyrus. The feed-forward GABA(B) inhibition suppressed unusual high-frequency firing of the granule cell, and consequently prevented excessive synaptic depression due to synaptic competition through STDP. The feed-forward and feedback GABA(A) inhibitions tend to reduce synaptic conductance fluctuations resulting from large increments and decrements due to very small spike-timings happening occasionally.

Radio frequency pulsed-gate charge spectroscopy on coupled quantum dots

Time-resolved electron dynamics in coupled quantum dots is directly observed by a pulsed-gate technique. While individual gate voltages are modulated with periodic pulse trains, average charge occupations are measured with a nearby quantum point contact as detector. A key component of our setup is a sample holder optimized for broadband radio frequency applications. Our setup can detect displacements of single electrons on time scales well below a nanosecond. Tunneling rates through individual barriers and relaxation times are obtained by using a rate equation model. We demonstrate the full characterization of a tunable double quantum dot using this technique, which could also be used for coherent charge qubit control.

Generation of chaotic microwave pulses with the help of passive synchronization of spin wave self-modulation frequencies in self-oscillatory ring systems

Passive synchronization (PS) of spin wave self-modulation frequencies of a chaotic microwave signal has been observed for the first time in a self-oscillatory ring system involving a nonlinear passive element with saturable absorption. The development of PS led to the generation of a periodic train of chaotic microwave pulses with an off/duty ratio exceeding 20. It is established that the repetition period of chaotic microwave pulses can be controlled by changing gain in the ring system.

Under what conditions can non‐uniformly spaced stimulation enhance auditory sensitivity? An investigation using time‐resetting maps.

Most cochlear implants excite auditory nerve fibers with electric current pulses that are uniformly spaced in time. Yet, studies of the vesicle release properties of the ribbon synapses present at the inner hair cell show that temporal spacing of vesicular release is not uniform in time. It is possible that this non‐uniform excitation contributes to the high sensitivity and temporal responsiveness of the healthy auditory system and that restoring this feature to the deafened nerve via electrical stimulation would be beneficial. This study uses time‐resetting maps, computed from Hodgkin–Huxley‐type models, to analyze the conditions under which a non‐uniform periodic pulse train, consisting of an alternating sequence of short and long intervals, produces higher modulation sensitivity than a uniform pulse train of the same average rate.

Acousto-optic modulation by pulsed optical excitation: implications to imaging in turbid media

We show that the transient response of acoustically modulated optical flux in a turbid medium irradiated by a pulsed point source of light is delayed in time relative to the light-alone flux obtained in the absence of acoustic modulation. The time delay is shown to result from an initial phase of flux reversal, as determined by the time point of the input pulse onset with reference to the ultrasound cycle. Both the time delay and amplitude of modulation are shown to be dependent on the effective attenuation coefficient of the medium. Application of a periodic train of excitation pulses spaced at equal intervals at, or in multiples of, the ultrasound period enables a time-locked detection of the modulated light, without the deleterious effects caused by speckle artifacts.

Electrostatic structures associated with dusty electronegative magnetoplasmas

By using the hydrodynamic equations of positive and negative ions, the Boltzmann electron density distribution and the Poisson equation with stationary dust, a three-dimensional (3D) Zakharov–Kuznetsov (ZK) equation is derived for small but finite amplitude ion-acoustic waves. However, the ZK equation is not appropriate to describe the system either at critical plasma compositions or in the vicinity of the critical plasma compositions. Therefore, the modified ZK (MZK) and extended ZK (EZK) equations are derived. The generalized expansion method is used to analytically solve the ZK, MZK and EZK equations. A new class of solutions that admits a train of well-separated bell-shaped periodic pulses is obtained. In certain conditions, the latter degenerates to either solitary or shock wave solutions. The effects of the physical parameters on the nonlinear structures are examined in many plasma environments having different negative ion species, such as D- and F-regions of the Earth's ionosphere, as well as in laboratory plasma experiments. Numerical analysis of the solutions revealed that the profile of the nonlinear pulses suffers amplitude and width modifications due to enhancement of the dust practices, negative ions, positive-to-negative ion mass ratio and positive/negative ion cyclotron frequency. Furthermore, the necessary conditions for both solitons and shocks propagation as well as their polarity are examined.

Advertisement Call and Geographic Distribution ofElachistocleis piauiensisCaramaschi &amp; Jim, 1983 (Amphibia, Microhylidae), with Notes on the Presence of Post-Commissural Gland in the Genus

New records of Elachistocleis piauiensis, a poorly known species of microhylid, from São Luís, State of Maranhão, allowed us to record the advertisement call. The advertisement call consists of a single periodic pulse train with harmonic structure. The new geographic record extends the known distribution by about 290 km West of Parnaíba, State of Piauí. We also comment on the post-commissural gland distribution in the genus Elachistocleis.

Broadband Chaos Generated by an Optoelectronic Oscillator

We study an optoelectronic time-delay oscillator that displays high-speed chaotic behavior with a flat, broad power spectrum. The chaotic state coexists with a linearly stable fixed point, which, when subjected to a finite-amplitude perturbation, loses stability initially via a periodic train of ultrafast pulses. We derive approximate mappings that do an excellent job of capturing the observed instability. The oscillator provides a simple device for fundamental studies of time-delay dynamical systems and can be used as a building block for ultrawide-band sensor networks.

Three dimensional cylindrical Kadomtsev–Petviashvili equation in a very dense electron-positron-ion plasma

By using the hydrodynamic equations of ions, Thomas–Fermi electron/positron density distribution, and Poisson equation, a three-dimensional cylindrical Kadomtsev–Petviashvili (CKP) equation is derived for small but finite amplitude ion-acoustic waves. The generalized expansion method is used to analytically solve the CKP equation. New class of solutions admits a train of well-separated bell-shaped periodic pulses is obtained. At certain condition, the latter degenerates to solitary wave solution. The effects of physical parameters on the solitary pulse structures are examined. Furthermore, the energy integral equation is used to study the existence regions of the localized pulses. The present study might be helpful to understand the excitation of nonlinear ion-acoustic waves in a very dense astrophysical objects such as white dwarfs.