Single Pulse Time Research Articles

Influence of pulsed gas injections on the stability of Townsend dielectric barrier discharges in nitrogen at atmospheric pressure

This work investigates the effects of pulsed nitrogen gas injections on the stability of Townsend dielectric barrier discharges operated in continuous nitrogen gas flows at atmospheric pressure. For single-pulse injections with pulse durations lower than the continuous gas residence time (∼50 ms), current–voltage characteristics reveal homogeneous discharges with a single current peak per half-cycle of the applied voltage. However, a sudden decrease of the discharge power over time combined with a temporary transition from homogeneous to filamentary discharge is observed for longer pulses at fixed pulsed gas flows and for higher pulsed gas flows at fixed pulse duration. In addition, for multiple pulsed gas injections with repetition frequencies between 0.1 and 10 Hz, discharge destabilisation increases with the number of pulses. Time-resolved optical emission spectroscopy reveals that, over the single pulse time scale, temporal variations of the emission intensities are longer than the expected residence times of the continuous and pulsed gas flows. Furthermore, a rise of oxygen impurities can be seen over both single and multiple-pulses time scales. Two-dimensional gas flow simulations reveal that pulsed injections introduce sharp and narrow temporal gas velocity profiles over the range of experimental conditions investigated, with no cumulative effects in the discharge cell from one pulse to the other. However, pulsed operation introduces significant changes in the neutral gas composition with time scales comparable to those revealed by electrical and optical diagnostics. In such conditions, the outgassing of impurities adsorbed on surfaces located upstream of the discharge cell plays a vital role in Townsend discharges’ physics and characteristics.

A Single Pulse Study of a Millisecond Pulsar PSR J0621+1002

Abstract We present radio observation of a millisecond pulsar PSR J0621+1002 using the Five-hundred-meter Aperture Spherical radio Telescope. The pulsar shows periodic pulse intensity modulations for both the first and the third pulse components. The fluctuation spectrum of the first pulse component has one peak of 3.0 ± 0.1 pulse periods, while that of the third pulse component has two diffused peaks of 3.0 ± 0.1 and 200 ± 1 pulse periods. The single pulse timing analysis is carried out for this pulsar and the single pulses can be divided into two classes based on the post-fit timing residuals. We examined the achievable timing precision using only the pulses in one class or bright pulses. However, the timing precision improvement is not achievable.

A novel timing and frequency offset estimation algorithm for filtered OFDM system

As a critical technology of 5G air interface waveform, filtered orthogonal frequency division multiplexing (F-OFDM) not only inherits the technical advantages of OFDM, but also has outstanding advantages in system flexibility and spectrum efficiency. However, as a multi-carrier technology, it is still extremely sensitive to sample timing offset (STO) and carrier frequency offset (CFO). In this letter, an improved Park frequency domain training sequence (FS-Park) is proposed to complete STO and CFO estimation of F-OFDM system. Firstly, a real-value pseudorandom number (PN) sequence is sent to each subcarrier as training sequence in frequency domain, the corresponding time domain training symbol has a conjugate symmetry structure. Secondly, the training symbol is utilized for timing synchronization, then the fractional frequency offset is estimated based on the cyclic prefix in time domain. Finally, the integer frequency offset is estimated in frequency domain based on the auto-correlation of PN sequence. The simulation results illustrate that the FS-Park algorithm not only has a single pulse timing metric curve and great STO estimation accuracy, but also has better performance of CFO estimation than classical Park algorithm and Liang Xiao’s method.

Study of Temperature Field in PECM Based on Multi-Physics Coupling Simulation about Titanium Alloys Blades

In order to study the temperature regularity of inter-electrode gap in PECM, the multi-physical coupling model based on COMSOL Multiphysics platform is established. The model of blades was used for this study, and the impact of some factors on the temperature is analyzed. The results show that the duty ratio is smaller or the inlet pressure is greater, the process of electrolyte convective and heat transfer is more sufficient. At the same time, the increase of the voltage and the decrease of the gaps will exacerbate the temperature fluctuations in a single pulse time. The lower voltage and duty ratio with larger inlet pressure should be selected in small gaps of PECM, so that we can effectively avoid the negative influence of high temperature in the processing zone.

Strong pulses detected from rotating radio transient J1819 − 1458

We analyze individual pulses detected from RRAT J1819$-$1458. From April 2007 to April 2010, we carried out observations using the Nanshan 25-m radio telescope of Urumqi Observatory at a central frequency of 1541.25 MHz. We obtain a dispersion measure $DM=195.7\pm0.3$ pc cm^{-3} by analyzing all the 423 detected bursts. The tri-band pattern of arrival time residuals is confirmed by a single pulse timing analysis. Twenty-seven bimodal bursts located in the middle residual band are detected, and, profiles of two typical bimodal bursts and two individual single-peak pulses are presented. We determine the statistical properties of SNR and W$_{50}$ of bursts in different residual bands. The W$_{50}$ variation with SNR shows that the shapes of bursts are quite different from each other. The cumulative probability distribution of intensity for a possible power law with index $\alpha=1.6\pm0.2$ is inferred from the number of those bursts with $SNR\ge6$ and high intensities.

Single pulse time resolved studies on the characteristics of a transverse pumped HMP–GIG dye laser and the role of pump beam divergence

Single pulse time resolved studies on the development of dye laser characteristics are conspicuous by their absence. In this paper we report, for the first time, studies on the temporal variation of bandwidth and divergence of a transverse pumped, prism beam expander grazing incidence grating dye laser within a single pulse. It is shown that the characteristics of the dye laser pulse depend on the divergence of the pump beam and its temporal variation.

Single-pulse time- and fluence-resolved optical measurements at femtosecond excited surfaces

We describe a new technique for optical pump–probe measurements at femtosecond excited surfaces. By combining time-resolved microscopy with cylindrical focusing of the pump, complete mapping of the time and fluence dependence of laser-induced optical changes becomes possible in a single-pulse experiment.

Multi‐trace deconvolution with unknown trace scale factors: Omnilinear inversion of P and S waves for source time functions

Seismic source and wave propagation theories allow seismologists to compute long period synthetic seismograms that commonly match even subtle details of observed waveshapes, but the overall trace amplitudes must be scaled by arbitrary factors to emphasize the excellent waveshape correspondence. This unexplained amplitude scatter causes considerable difficulties when formally inverting observed waveforms for seismic source parameters. Omnilinear inversion simultaneously determines the linear model parameters and trace scaling factors to minimize the mismatch between observed and synthetic seismograms. Omnilinear inversion is applied to source time function deconvolution from long period P and SH waves. A simulation with synthetic data shows that omnilinear inversion finds the proper scaling factors, and the source time function and focal depth are better determined than for “standard” linear inversion. Omnilinear inversion is then applied to a data set of seven P waves and one SH wave from the underthrusting earthquake of July 5, 1968 (Ms 6.6) in northern Honshu, Japan. Omnilinear inversion produces a best‐fit focal depth of 36 km with a single pulse time function of 6 s duration and seismic moment of 4×1018 N m (Mw 6.4). This focal depth supports the notion that the seismically coupled plate interface extends no deeper than 40 km in northern Honshu.

The breakdown of superfluidity in liquid 4 He: an experimental test of Landau’s theory

A single pulse time of flight technique has been used to determine the drift velocity F of the negative ions injected into liquid 4 He from a field emission source. Measurements of v as a function of temperature T , pressure P and electric field E are presented within the range: 0.29 ≤ T ≤ 0.5 K; 21 x 10 5 ≤ P ≤ 25 x 10 5 Pa; 1 ≤ E ≤ 300kV m -1 . The experimental results are in good agreement with Landau’s theory of superfluidity. The data are used to demonstrate the inapplicability of two theories of supercritical dissipation: by Takken, based on an assumption of coherent roton emission; and by Bowley & Sheard, based on the assumption of incoherent single-roton emission. The results are, however, shown to be in excellent agreement with Bowley & Sheard’s incoherent two-roton theory, and the data are used to derive a numerical value of the matrix element characterizing two-roton emission. The surprising absence of the single-roton emission process is discussed, and an upper bound is placed on the relevant matrix element.