Pulse Packet Research Articles

Photocatalytic titanium dioxide thin films prepared by reactive pulse magnetron sputtering at low temperature

An innovative reactive pulse magnetron sputtering (PMS) system allowing to change the pulse mode (unipolar, bipolar or pulse packet) has been used to deposit TiO2 films at dynamic deposition rates of 8…50 nm m/min. Photo-induced hydrophilicity and photocatalytic degradation by UV-A illumination were investigated by measuring the decrease of the water contact angle and the decomposition of methylene blue organic dye, respectively.It was observed that using the PMS technology the TiO2 layers can be deposited in situ crystalline at temperatures much lower than the necessary annealing temperature for amorphous deposited layers. Moreover, these in situ crystalline deposited layers have superior photocatalytic properties to that of amorphous deposited post-annealed TiO2 layers. Thin TiO2 films (<50 nm) deposited at substrate temperatures as low as 130 °C exhibit sufficient photocatalytic activity for many applications.

Excitability in a model with a saddle-node homoclinic bifurcation

In order to describe excitable reaction-diffusion systems, we derive a two-dimensional model with a Hopf and a semilocal saddle-node homoclinic bifurcation. This model gives the theoretical framework for the analysis of the saddle-node homoclinic bifurcation as observed in chemical experiments, and for the concepts of excitability and excitability threshold. We show that if diffusion drives an extended system across the excitability threshold then, depending on the initial conditions, wave trains, propagating solitary pulses and propagating pulse packets can exist in the same extended system. The extended model shows chemical turbulence for equal diffusion coefficients and presents all the known types of topologically distinct activity waves observed in chemical experiments. In particular, the approach presented here enables to design experiments in order to decide between excitable systems with sharp and finite width thresholds.

High rate deposition of insulating TiO2 and conducting ITO films for optical and display applications

An innovative reactive pulse magnetron sputtering (PMS-) system allowing to change the pulse mode (unipolar, bipolar or pulse packet) and the pulse parameters (duty cycle, frequency) of the discharge has been used to deposit different materials at high deposition rates. The new pulse packet mode combines the two fundamental pulse modes of unipolar and bipolar by applying ‘packets’ of unidirectional pulses between the two targets and changing the polarity of the discharge after each packet. As a new pulse parameter, the number of pulses of each packet can be varied. The advantages of the PMS-system were demonstrated by the reactive deposition of insulating titanium oxide (TiO 2 ) and conducting indium tin oxide (ITO) films. The TiO 2 layers sputtered on unheated substrates at deposition rates of up to 50 nm*m/min exhibited amorphous, mixed anatase/rutile or rutile structure in dependence of the pulse mode and the pulse parameters that were applied. Hardness, Young's modulus, roughness and refractive index varied in dependence of the structure of the layers. Although the sputtering from ceramic target is the most common coating technique for ITO, another economical way is the use of metallic InSn-targets. The effect of various pulse modes on the optical and electrical properties of reactively sputtered ITO layers on float glass was investigated. The specific resistivity of ITO was minimized by process parameter optimisation.

High rate deposition of insulating TiO 2 and conducting ITO films for optical and display applications

An innovative reactive pulse magnetron sputtering (PMS-) system allowing to change the pulse mode (unipolar, bipolar or pulse packet) and the pulse parameters (duty cycle, frequency) of the discharge has been used to deposit different materials at high deposition rates. The new pulse packet mode combines the two fundamental pulse modes of unipolar and bipolar by applying ‘packets’ of unidirectional pulses between the two targets and changing the polarity of the discharge after each packet. As a new pulse parameter, the number of pulses of each packet can be varied. The advantages of the PMS-system were demonstrated by the reactive deposition of insulating titanium oxide (TiO 2) and conducting indium tin oxide (ITO) films. The TiO 2 layers sputtered on unheated substrates at deposition rates of up to 50 nm*m/min exhibited amorphous, mixed anatase/rutile or rutile structure in dependence of the pulse mode and the pulse parameters that were applied. Hardness, Young's modulus, roughness and refractive index varied in dependence of the structure of the layers. Although the sputtering from ceramic target is the most common coating technique for ITO, another economical way is the use of metallic InSn-targets. The effect of various pulse modes on the optical and electrical properties of reactively sputtered ITO layers on float glass was investigated. The specific resistivity of ITO was minimized by process parameter optimisation.

Information processing with spiking neurons in a cortical architecture framework under the control of an oscillatory signal

In this work we analyze information processing in spiking neurons in the cortex by investigating how short (10 ms) pulse packets of spikes are processed in cortical neurons. These signals are compliant with constraints of rapid feedforward recognition in the visual cortex. We add an oscillatory membrane potential modulation that simulates the effect of 40 Hz (evoked) gamma oscillations. We find that depending on the oscillation signal different input features are decoded, processed and encoded in a single output spike. We demonstrate that a latency-coding of information is possible.

Integrable models for the dynamics of a longitudinal-transverse acoustic wave in a crystal with paramagnetic impurities

We theoretically study the evolution of longitudinal-transverse acoustic pulses propagating parallel to an external magnetic field in a system of resonant paramagnetic impurities with an effective spin S=1/2. For equal group velocities of the longitudinal and transverse waves, the pulse dynamics is shown to be described by evolution equations. In limiting cases, these equations reduce to equations integrable in terms of the inverse scattering transform method (ISTM). For the most general integrable system of equations that describes the dynamics of acoustic pulses outside the scope of the slow-envelope approximation, we derive the corresponding ISTM equations. These equations are used to find a soliton solution and a self-similar solution. The latter describes the leading edge of the packet of acoustic pulses generated when the initial unstable state of a spin system decays. Analysis of our solutions and models indicates that the presence of a longitudinal acoustic wave leads not only to a change in the amplitude and phase of the transverse wave but also to a qualitatively new dynamics of sound in such a medium.

A synfire chain in layered coincidence detectors with random synaptic delays

In this paper we analyze a synfire chain in a spiking neuron network. We also employ a coincidence-detector model showing the characteristics of temporal information processing more directly than the integrate-and-fire (I&F) model often discussed in the literature. There are two sources of randomness in a feed-forward network, however, only randomness in input spikes has attracted the attention of researchers and the randomness in synaptic delays has largely been ignored. Theoretical analyses of the synfire chain in I&F neurons without randomness in synaptic delays have shown that the dynamics of pulse packets can be viewed as a shift of the membrane potential distribution made by random noise input spikes. We introduce jittered synaptic delays instead of random noise inputs in a network of coincidence detectors and show that the network has almost the same dynamics as that of the I&F neurons. The distribution of the output spikes can be approximately described by an ordinary differential equation useful in understanding the dynamics of the pulse packets.

Cyclic jerky opening of magma sheet and caldera formation during the 2000 Miyakejima volcano eruption

NIED volcanic observation network at Miyakejima volcano, central Japan, repeatedly detected extraordinary step‐like tilt changes during the 2000 Miyakejima eruption. Associated with these tilt steps, broadband seismometers recorded very long pulse waves with a duration of about 50‐s. During this stage, the summit of the volcano collapsed and sank, forming a caldera with a depth of about 400 m and a diameter of about 1.6 km in total. Prior to the tilt steps, long‐period earthquakes were acceleratingly generated in the shallow part of the volcano, and the ground tilt changes suggested inflation of the volcanic body. The analysis of these data from the tiltmeters and broadband seismometers suggests that the tilt steps and the 50‐s pulse packets were caused by the opening of sill(sheet)‐like tensile cracks oriented in a SE‐NW direction beneath the volcano with a depth of about 6–8 km and a volumetric change of about 106–107 m3.

Ultrasound-based vessel wall tracking: an auto-correlation technique with RF center frequency estimation

Vessel diameter is related to the distending blood pressure, and is used in estimations of vessel stiffness parameters. The vessel walls can be tracked by integrating wall velocities estimated by ultrasound (US) Doppler techniques. The purpose of this work was to evaluate the performance of the modified autocorrelation estimator when applied on vessel wall motion. As opposed to the conventional autocorrelation method that only estimates the mean Doppler frequency, the modified autocorrelation method estimates both the mean Doppler frequency and the radiofrequency (RF) center frequency. To make a systematic evaluation of the estimator, we performed computer simulations of vessel wall motion, where pulse bandwidth, signal-to-noise ratio (SNR), signal-to-reverberation ratio, packet size and sample volume were varied. As reference, we also analyzed the conventional autocorrelation method and the cross-correlation method with parabolic interpolation. Under the simulation conditions considered here, the modified autocorrelation method had the lowest bias and variance of the estimators. When integrating velocity estimates over several cardiac cycles, the resulting tissue displacement curves might drift. This drift is directly related to the magnitude of the estimator bias and variance. Hence, the modified autocorrelation method should be the preferred choice of method. (E-mail: s.i.rabben@klinmed.uio.no)

Algorithms Using a Coherent Pulse Packet: Estimation Accuracy and Measure of Resolution for a Carrier Frequency and Its Rate of Change

Algorithms Using a Coherent Pulse Packet: Estimation Accuracy and Measure of Resolution for a Carrier Frequency and Its Rate of Change

Fokker–Planck approach to the pulse packet propagation in synfire chain

We applied the Fokker–Planck method to the so-called ‘synfire chain’ network model and showed how a synchronous population spike (pulse packet) evolves to a narrow pulse packet (width <1 ms) or fades away, depending on its initial size and width. The results of numerical integration of the Fokker–Planck equation are in good agreement with those of simulations on a network of leaky integrate-and-fire neurons. For a narrow input pulse packet, the integration of the Fokker–Planck equation requires careful numerical treatment. However, we can construct a precise analytical waveform of an output packet, which proves valid for narrow input pulse packets, from the stationary solution to the Fokker–Planck equation and a previously proposed approximate input–output relationship. Our methods enable us also to understand an essential role of the synaptic noise in the evolution, the peculiar temporal evolution of a broader pulse packets, and the irrelevance of the refractory period in determining the waveform of a pulse packet. Furthermore, we elucidate possible functional roles of multiple interactive pulse packets in spatiotemporal information processing, i.e. the association of information and the temporal competition.

Propagation of cortical synfire activity: survival probability in single trials and stability in the mean

The synfire hypothesis states that under appropriate conditions volleys of synchronized spikes ( pulse packets) can propagate through the cortical network by traveling along chains of groups of cortical neurons. Here, we present results from network simulations, taking full account of the variability in pulse packet realizations. We repeatedly stimulated a synfire chain of model neurons and estimated activity ( a) and temporal jitter ( σ) of the spike response for each neuron group in the chain in many trials. The survival probability of the activity was assessed for each point in ( a, σ)-space. The results confirm and extend our earlier predictions based on single neuron properties and a deterministic state-space analysis [Diesmann, M., Gewaltig, M.-O., & Aertsen, A. (1999). Stable propagation of synchronous spiking in cortical neural networks. Nature, 402, 529–533].

Cortical synfire-activity: Configuration space and survival probability

The synfire hypothesis states that under appropriate conditions volleys of synchronized spikes ( pulse packets) can propagate through chains of groups of neurons. Here, we present results from network simulations, taking full account of the variability in pulse packet realizations. We repeatedly stimulated a synfire-chain of model neurons and estimated the activity ( a) and response–jitter ( σ) for each group in the chain over many trials. The survival probability of the activity was assessed for each point in the (a, σ) –space. The results agree well with our earlier predictions based on single neuron properties and a deterministic state-space analysis.

The analysis of structural defects in piezo and ferroelectric materials by the “heat pulse” method

We consider the “heat pulse” technique for the analysis of structural imperfections. This method is based on the propagation of a pulse or packet of pulses of non-equilibrium acoustic phonons with 1011–1012 Hz frequencies. Analyse des défauts structuraux dans les matériaux piézo-ferroélectriques par la méthode “heat pulse”. Cette méthode, basée sur la propagation pulsée de phonons acoustiques hors équilibre vers 1011–1012 Hz, permet l'étude des défauts structuraux et autres imperfections présents dans les cristaux piézo-ferroélectriques.

Characteristics of the radiation of an Nd:YAG laser with an intracavity spatiotemporal modulator based on a PLZT electro-optical ceramic

The characteristics of the radiation of a laser with intracavity scanning with the aid of electrically controlled spatiotemporal modulators based on a transparent electro-optical PLZT ceramic were investigated. The possibility of the generation of packets of single pulses of scanning laser radiation with a repetition frequency up to 100 kHz, and up to 10 kHz under the conditions of continuous flashlamp pumping with an intracavity spatiotemporal modulator is demonstrated. Possible applications of the laser are discussed.

Synthesis of spectrum of packet of radio pulsesby phase-only control

An iterative fast-convergent phase-only method for shaping the amplitude spectrum of a packet of radio pulses is developed. Its efficiency is verified by a numerical experiment.

Chain‐length‐dependent termination rate constant: Effect on molecular weight distributions formed by pulsed laser radical polymerization

AbstractFor polymerization initiated by an arbitrary sequence of laser pulses a numerical technique for calculating molecular weight distributions (MWDs) is developed, which takes into consideration the chain length dependence of the termination rate constant kt. The MWDs for methyl methacrylate and styrene are calculated by use of α and k0 values (for the law k = k0(i)−α of termination of radicals with chain length i) and averages \documentclass{article}\pagestyle{empty}\begin{document}$ \overline {(i,{\rm }j)} $\end{document} (for rate constants k = k0\documentclass{article}\pagestyle{empty}\begin{document}$ \overline {(i,{\rm }j)} $\end{document} of termination of radicals with different degrees of polymerization) taken from the literature. The dependences of the overall termination constant 〈kt〉 on initiation parameters (pulse repetition rate (v) and pulse intensity for initiation by periodic laser pulses) are presented. Two methods are proposed for α and k0 determination: (a) by experiments on polymerization with periodic laser pulses where monomer‐to‐polymer conversions per pulse are determined for different v; (b) by experiments on polymerization with packets of pulses where the constant kp (the rate constant of propagation), α and k0 can be determined simultaneously from MWD. For both methods simple analytical equations are derived for evaluation of the constants. The limits of application of the methods are determined by use of the numerical technique for MWD calculation.

Postpolymerization effect on molecular weight distribution generated by pulsed laser radical polymerization

AbstractThe postpolymerization effect on molecular weight distribution (MWDs) and on the Pulsed Laser Polymerization (PLP) technique for evaluation of kinetic constants is investigated. General expressions for moments are derived for a polymerization scheme that contains the reactions of chain initiation, propagation, and termination by recombination or disproportionation, under polymerization initiation by an arbitrary sequence of radiation pulses. The results of calculation of MWDs and of the weight‐average degree of polymerization (Pw) for methyl methacrylate are presented. It is shown that the Pw value strongly depends on postpolymerization. A new method for determining the rate constants of chain propagation and chain termination from a single experiment by polymerization with packets of laser pulses is presented.

Propagation of synchronous spiking activity in feedforward neural networks

‘Synfire’ activity has been proposed as a model for the experimentally observed accurate spike patterns in cortical activity. We investigated the structural and dynamical aspects of this theory. To quantify the degree of synchrony in neural activity, we introduced the concept of ‘pulse packets’. This enabled us to derive a novel neural transmission function which was used to assess the role of the single neuron dynamics and to characterize the stability conditions for propagating synfire activity. Thus, we could demonstrate that the cortical network is able to sustain synchronous spiking activity using local feedforward (synfire) connections. This new approach opens the way for a quantitative description of neural network dynamics, and enables us to test the synfire hypothesis on physiological data.

Partial discharge pulse distribution pattern analysis

Statistical data analysis has been recently requisite for partial discharge (PD) study. This has been enabled by the recent development of microprocessors or the downsizing of computers. It is important to pay more attention to profiles of a packet of PD pulses on the voltage phase angle. Statistical parameters such as skewness and kurtosis have been intensively investigated for PD analysis. More recently, the neural network algorithm has been utilised especially to discriminate PD signals from noise signals for insulation diagnosis.