Suitable Time Delay Research Articles

Third harmonic generation of a short pulse laser in a plasma density ripple created by a machining beam

An intense machining laser beam, impinged on a gas jet target, causes space periodic ionization of the gas and heats the electrons. The nonuniform plasma pressure leads to atomic density redistribution. When, after a suitable time delay, a second more intense laser pulse is launched along the periodicity wave vector q⃗, a plasma density ripple nq is instantly created, leading to resonant third harmonic generation when q=4ωp2∕(3ωcγ0), where ωp is the plasma frequency, ω is the laser frequency, and γ0 is the electron Lorentz factor. The third harmonic is produced through the beating of ponderomotive force induced second harmonic density oscillations and the quiver velocity of electrons at the fundamental. The relativistic mass nonlinearity plays no role in resonant coupling. The energy conversion efficiency scales as the square of plasma density and square of depth of density ripple, and is ∼0.2% for normalized laser amplitude ao∼1 in a plasma of 1% critical density with 20% density ripple. The theory explains several features of a recent experiment.

Determination of picloram in natural waters employing sequential injection square wave voltammetry using the hanging mercury drop electrode

This paper describes the development of a sequential injection analysis method to automate the determination of picloram by square wave voltammetry exploiting the concept of monosegmented flow analysis to perform in-line sample conditioning and standard addition. To perform these tasks, an 800 μL monosegment is formed, composed by 400 μL of sample and 400 μL of conditioning/standard solution, in medium of 0.10 mol L −1 H 2SO 4. Homogenization of the monosegment is achieved by three flow reversals. After homogenization the mixture zone is injected toward the flow cell, which is adapted to the capillary of a hanging drop mercury electrode, at a flow rate of 50 μL s −1. After a suitable delay time, the potential is scanned from −0.5 to −1.0 V versus Ag/AgCl at frequency of 300 Hz and pulse height of 25 mV. The linear dynamic range is observed for picloram concentrations between 0.10 and 2.50 mg L −1 fitting to the linear equation I p = (−2.19 ± 0.03) C picloram + (0.096 ± 0.039), with R 2 = 0.9996, for which the slope is given in μA L mg −1. The detection and quantification limits are 0.036 and 0.12 mg L −1, respectively. The sampling frequency is 37 h −1 when the standard addition protocol is followed, but can be increased to 41 h −1 if the protocol to obtain in-line external calibration curve is used for quantification. The method was applied for determination of picloram in spiked water samples and the accuracy was evaluated by comparison with high performance liquid chromatography using molecular absorption at 220 nm for detection. No evidences of statistically significant differences between the two methods were observed.

RLDDE: A novel reinforcement learning-based dimension and delay estimator for neural networks in time series prediction

Time series prediction is traditionally handled by linear models such as autoregressive and moving-average. However they are unable to adequately deal with the non-linearity in the data. Neural networks are non-linear models that are suitable to handle the non-linearity in time series. When designing a neural network for prediction, two critical factors that affect the performance of the neural network predictor should be considered; they are namely: (1) the input dimension, and (2) the time delay. The former is the number of delayed values for prediction, while the latter is the time interval between two data. Prediction accuracy can be improved using suitable input dimension and time delay. A novel method, called reinforcement learning-based dimension and delay estimator (RLDDE), is proposed in this paper to simultaneously determine the input dimension and time delay. RLDDE is a meta-learner that tries to learn the selection policy of the dimension and delay under different distribution of the data. Two benchmarked datasets with different noise levels and one stock price are used to show the effectiveness of the proposed RLDDE together with the benchmarking against other methods.

The Temperature Feature on the Step-Up Process of the Hydraulic Control Rod Driving System

As a new type of control rod driving system, the hydraulic control rod driving system (HCRDS) has long been applied in a 5-MW nuclear heating reactor, and the safety and the reliability of the system have been proven. The principle of the work and the step-up operation of the HCRDS have been introduced in this paper. Based on the theoretical model, the temperature influence on the static holding-flow rate, the dynamic holding-flow rate, and the working holding-flow rate has been studied. It indicates that with the increase of the temperature, the static and dynamic holding-flow rates will increase while the working holding-flow rate will decrease.A detailed analysis of the step-up process on various temperature conditions has been carried out. Considering the great temperature influence on the step-up operation of the system, the method of temperature compensation to select suitable delay time and working holding-flow rate in a certain temperature province is put forward to offset the influence. The analysis can be conducive to widespread availability of the HCRDS and establish a basis for further research and improvement.

Minkowski vacuum stress tensor fluctuations

We study the fluctuations of the stress tensor for a massless scalar field in two- and four-dimensional Minkowski spacetime in the vacuum state. Covariant expressions for the stress tensor correlation function are obtained as sums of derivatives of a scalar function. These expressions allow one to express spacetime averages of the correlation function as finite integrals. We also study the correlation between measurements of the energy density along a world line. We find that these measurements may be either positively correlated or anticorrelated. The anticorrelated measurements can be interpreted as telling us that, if one measurement yields one sign for the averaged energy density, a successive measurement with a suitable time delay is likely to yield a result with the opposite sign.

The effect of oxygen and carbon dioxide concentration on soot formation in non-premixed flames

The influence of oxygen concentration and carbon dioxide as diluents in the oxidizer side on soot formation was studied by Time Resolved Laser Induced Incandescence (TIRE-LII) and TEM photography in non-premixed co-flowing flames. TIRE-LII method was used to measure the distribution of two-dimensional soot volume fraction and primary particle size. The soot was directly sampled by the thermophoretic method, and its diameter was examined by TEM photography. Two suitable delay times of the TIRE-LII method affecting measurable range and sensitivity were determined by comparing TEM photographs with the TIRE-LII signal. The effects of oxygen concentration and carbon dioxide as diluents in the oxidizer side on soot formation were investigated with these calibrated techniques. An O 2+(CO 2, N 2, and [Ar+CO 2]) mixtures in co-flow were used to isolate carbon dioxide effects systematically. The primary particle number concentration and soot volume fraction were abruptly decreased by the addition of carbon dioxide to co-flow. This suppression was resulted from the short residence time in inception region because of the late nucleation and the decrease of surface growth distance by the low flame temperature due to the higher thermal capacity and the chemical change of carbon dioxide. The increase of oxygen concentration in the co-flow caused an enhancement of soot nucleation and thus the residence time increase, but the specific growth rate showed almost the same value regardless of the co-flow mixture in the growth region. This result suggests that the specific growth rate has a weak dependence on the relative change of co-flow conditions in non-premixed co-flowing flames.

Suppression of pulse impairments due to cross-phase modulation by frequency domain phase conjugation

The use of optical frequency domain phase conjugation (FDPC) to suppress pulse impairments due to cross-phase modulation (XPM) in optical fiber systems is proposed. Evolution of Gaussian pulses in the system using midway FDPC is analyzed theoretically and simulated numerically. It is found that pulse waveform impairments induced by XPM can be suppressed effectively by FDPC. The impairments due to group-velocity dispersion and self-phase modulation can be suppressed simultaneously. Suitable initial time delay and pulse chirp of pulses can improve the suppression and compensation for the distortion.frequency domain phase conjugation, cross-phase modulation, group-velocity dispersion, self-phase modulation can be suppressed simultaneously. Suitable initial time delay and pulse chirp of pulses can improve the suppression and compensation for the distortion.

Ultrafast electronic dymamics during femtosecond laser-induced damage in omnidirectional reflector

The use of optical frequency domain phase conjugation (FDPC) to suppress pulse impairments due to cross-phase modulation (XPM) in optical fiber systems is propo sed. Evolution of Gaussian pulses in the system using midway FDPC is analyzed thoretically and simulated numerically. It is found that pulse waveform impairmen ts induced by XPM can be suppressed effectively by FDPC. The impairments due to group-velocity dispersion and self-phase modulation can be suppressed simultaneously. Suitable initial time delay and pulse chirp of pulses can improve the suppression and compensation for the distortion.

Developing a sequential injection-square wave voltammetry (SI-SWV) method for determination of atrazine using a hanging mercury drop electrode

This paper describes the development of a sequential injection analysis method to automate the determination of atrazine by square wave voltammetry exploiting the concept of monosegmented flow analysis to perform in-line sample conditioning and standard addition. To perform these tasks, an 800 μL monosegment is formed, composed by 400 μL of sample and 400 μL of buffer/standard solution. To obtain an efficient homogenization, the sample solution is divided in five zones intercalated by four zones of the Britton–Robinson buffer (pH 2.0) in presence of appropriate concentration of NaNO 3 and varying atrazine standard concentrations. This mixture zone is isolated from the carrier solution by two 100 μL air bubbles. After homogenization in an auxiliary reaction coil the mixture zone is injected toward the flow cell, which is adapted to the capillary of a hanging drop mercury electrode, at a flow rate of 50 μL s −1. After a suitable delay time, the potential is scanned from −0.5 to −1.2 V versus Ag/AgCl using a frequency of 300 Hz and pulse height of 25 mV. The linear dynamic range is observed for atrazine concentrations between 1.16 × 10 −7 and 2.32 × 10 −6 mol L −1, obeying the linear equation i p = (−6.91 ± 0.07) × 10 8[atrazine] + (4 ± 8), with r 2 = 0.9996, for which the slope is given in nA L mol −1. The detection and quantification limits of the method are 2.1 × 10 −8 and 7.0 × 10 −8 mol L −1, respectively. The sampling frequency is 37 h −1, when the standard addition protocol is followed. This frequency can be increased to 42 h −1 if the protocol to obtain in-line calibration curve is used for quantification. The method was applied for determination of atrazine in spiked river water samples and its accuracy was evaluated by comparison with the batch standard addition approach, which revealed that there is no evidence of statistically significant differences between the two methods.

Background Suppression in Frequency-Domain Fluorometry

Gated detection is often used in time-domain measurements of long-lived fluorophores for suppression of interfering short-lived autofluorescence. However, no direct method has been available for gated detection and background suppression when using frequency-domain fluorometry. We describe a direct method for real-time suppression of autofluorescence in frequency-domain fluorometry. The method uses a gated detector and the sample is excited by a pulsed train. The detector is gated on following each excitation pulse after a suitable time delay for decay of the prompt autofluorescence. Under the same experimental conditions a detectable reference signal is obtained by using a long lifetime standard with a known decay time. Because the sample and reference signals are measured under identical excitation, gating and instrumental conditions, the data can be analyzed as usual for frequency-domain data without further processing. We show by simulations that this method can be used to resolve single and multiexponential decays in the presence of short lifetime autofluorescence.

Design of dynamic-floating-gate technique for output ESD protection in deep-submicron CMOS technology

A novel dynamic-floating-gate technique is proposed to improve ESD robustness of the CMOS output buffers with small driving/sinking currents. This dynamic-floating-gate design can effectively solve the ESD protection issue which is due to the different circuit connections on the output devices. By adding suitable time delay to dynamically float the gates of the output NMOS/PMOS devices which are originally unused in the output buffer, the human-body-model (machine-model) ESD failure threshold of a 2-mA output buffer can be practically improved from the original 1.0 kV (100 V) up to greater than 8 kV (1500 V) in a 0.35-μm bulk CMOS process.

Earth‐average temperature: A time delay approach

Earth‐average temperature is investigated using a simple energy balance model of the Budyko‐Sellers‐Ghil type expressed as a delay‐differential equation describing the absorption and reflection of incoming solar radiation and surface‐reflected infrared radiation. Cloud albedos for both radiations and the surface albedo as affected by ice coverage are assumed to depend upon the temperature that existed some time ago, introducing a time delay into the model. A variety of steady and oscillatory states are possible for Earth‐average temperature, assuming plausible functions for the albedos, blackbody cooling, and suitable delay times. Multiple true steady states and multiple transient pseudo steady states as well as periodic, chaotic, and square‐wave relaxation‐oscillations result, The bifurcation structure relating the appearance of these phenomena to system parameters is explored. This very simple climate model exhibits complex behavior in global temperature without solar variation or environmental perturbation. Bifurcations exist at which small changes in parameters lead to destabilization of steady states and dramatic changes in qualitative behavior.

Lamb wave generation in composite plates with a thin linear array of piezoelectric elements

Since Lamb waves are very efficient in the nondestructive testing of composite plates, new transducers are developed nowadays. They may be movable, stuck onto the surface, or integrated into the plates (‘‘smart structures’’). In order to detect defaults with few transducers, a multi-element linear array transducer has been developed to generate single-mode Lamb waves able to propagate over long distances. Movable prototypes were designed in order to evaluate their ability to generate the appropriate waves. Then, composite plates have been equipped with the same kind of transducers consisting of several thin PZT plates. High response levels have been obtained using a unidirectional composite with propagation along the fiber direction. Results for cross-ply laminates were inferior but still acceptable. The main result obtained during this experimental work was the understanding of the generation process for this kind of transducer. Unlike comb transducers, each element generates a separate wave and suitable time delays or spacing between the elements can improve the global response in accordance with linear rules. Furthermore, the delays are easily determined from the responses of each element. This behavior is very interesting as default detection is possible using the properties of the generation process.

98/02301 A study on final volatile yield of pulverized coal pyrolysis with thermobalance

The influence of oxygen concentration and carbon dioxide as diluents in the oxidizer side on soot formation was studied by Time Resolved Laser Induced Incandescence (TIRE-LII) and TEM photography in non-premixed co-flowing flames. TIRE-LII method was used to measure the distribution of two-dimensional soot volume fraction and primary particle size. The soot was directly sampled by the thermophoretic method, and its diameter was examined by TEM photography. Two suitable delay times of the TIRE-LII method affecting measurable range and sensitivity were determined by comparing TEM photographs with the TIRE-LII signal. The effects of oxygen concentration and carbon dioxide as diluents in the oxidizer side on soot formation were investigated with these calibrated techniques. An O2+(CO2, N2, and [Ar+CO2]) mixtures in co-flow were used to isolate carbon dioxide effects systematically. The primary particle number concentration and soot volume fraction were abruptly decreased by the addition of carbon dioxide to co-flow. This suppression was resulted from the short residence time in inception region because of the late nucleation and the decrease of surface growth distance by the low flame temperature due to the higher thermal capacity and the chemical change of carbon dioxide. The increase of oxygen concentration in the co-flow caused an enhancement of soot nucleation and thus the residence time increase, but the specific growth rate showed almost the same value regardless of the co-flow mixture in the growth region. This result suggests that the specific growth rate has a weak dependence on the relative change of co-flow conditions in non-premixed co-flowing flames.

98/02295 Soot microstructure in steady and flickering laminar methane/air diffusion flames

The influence of oxygen concentration and carbon dioxide as diluents in the oxidizer side on soot formation was studied by Time Resolved Laser Induced Incandescence (TIRE-LII) and TEM photography in non-premixed co-flowing flames. TIRE-LII method was used to measure the distribution of two-dimensional soot volume fraction and primary particle size. The soot was directly sampled by the thermophoretic method, and its diameter was examined by TEM photography. Two suitable delay times of the TIRE-LII method affecting measurable range and sensitivity were determined by comparing TEM photographs with the TIRE-LII signal. The effects of oxygen concentration and carbon dioxide as diluents in the oxidizer side on soot formation were investigated with these calibrated techniques. An O2+(CO2, N2, and [Ar+CO2]) mixtures in co-flow were used to isolate carbon dioxide effects systematically. The primary particle number concentration and soot volume fraction were abruptly decreased by the addition of carbon dioxide to co-flow. This suppression was resulted from the short residence time in inception region because of the late nucleation and the decrease of surface growth distance by the low flame temperature due to the higher thermal capacity and the chemical change of carbon dioxide. The increase of oxygen concentration in the co-flow caused an enhancement of soot nucleation and thus the residence time increase, but the specific growth rate showed almost the same value regardless of the co-flow mixture in the growth region. This result suggests that the specific growth rate has a weak dependence on the relative change of co-flow conditions in non-premixed co-flowing flames.

Use of solid state protonic conductors for oxygen potentiometric sensor at room temperature

The use of oxygen sensors based on oxygen conductors such as stabilized zirconia is restricted at temperatures 300°C. Oxygen sensors operating at room temperature are however required for many purposes, especially in environmental and biological analyses. We have therefore studied the realization of a simple solid state sensor for oxygen at room temperature, which utilizes a thin film of pellicular zirconium phosphate or NAFION as protonic conductor, a titanium hydride plate as solid state reference electrode and a sensing catalytic electrode of Pt. Such a sensor is based on the H 2-O 2 mixed potential which is produced at the sensing electrode when short pulses of current are applied. Potential measurements are periodically performed after a suitable delay time forms the end of each pulse. The potential is a linear function over a large range of log P o 2 , while, in the most favourable conditions, the sensitivity limit is of a few parts per millions.

Biasing Circuit for Microwave GaAs MESFET Power Amplifier

GaAs MESFET is a sensitive device and a proper dc biasing bas to be given to gate and drain terminals. In this paper a dc biasing circuit for driving GaAs MESFET in power amplifier applications is presented. Separate circuits are used for gate and drain supply which are connected by a suitable time delay for switching the two circuits.

Theory of Ultrashort Pulse Generation and Amplification by Gain‐Switched Semiconductor Lasers

AbstractA theory of the nonlinear ultrashort dynamic response of unbiased gain‐switched semiconductor laser amplifiers is presented. For suitable time delays between the incident laser pulse and the injection current pulse driving the laser amplifier, optical pulse compression due to self‐induced gain depletion is found. The finestructure of the emitted pulse resulting from multiple reflections is shown to depend crucially upon the detuning off cavity resonances and upon the ratio of input signal width to cavity round‐trip time.

Dynamic theory of picosecond optical pulse shaping by gain-switched semiconductor laser amplifiers

A dynamic theory of semiconductor laser amplifiers is developed that takes into account the coherent time-dependent amplification of an incident optical pulse as well as the nonlinear dynamics of the semiconductor laser when driven be an unbiased injection-current pulse. For suitable time delays between the optical and the electrical pulse, a strongly nonlinear self-induced shortening of the emitted laser pulse is predicted.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

The Delay Controller: An Improvement Over PID Regulator

If the derivative term in a proportional-integral-derivative (PID) controller is replaced by a suitable time delay, the noise contamination in the output is smoothed out while the other good effects of PID action are preserved. Sufficient conditions for the choice of time delay are established. Optimization of such a system with a prescribed degree of stability is worked out and compared with the response of a system with PID controller. The output is substantially noise free.