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To calibrate non-contact sensors with fast response and high scale factor, it is critical to develop step pulse generators capable of generating standard high voltage step pulses and accurately measuring the generated waveform. In this paper, two types of step pulse generators are designed with output voltages of 2 kV and 100 kV. The 2 kV step pulse generator can generate a step pulse with a rise time of ~300 ps and an adjustable pulse width. A step pulse with a rise time less than 5 ns and a pulse width over 1 s can be generated with the 100 kV step pulse generator. The uncertainty of 2 kV step pulse generator is then analyzed by simulations and experiments. Finally, a performance comparison with step pulse generators in previous studies is carried out. Bandwidth, linearity and repeatability of the sensors can be verified with the designed two step pulse generators.

This study numerically simulated and investigated the flow field characteristics of a typical dual-pulse solid rocket motor with a soft pulse separation device through thermal insulation ablation under high-temperature dual-pulse erosion. The ablation rate of ethylene -propylene-diene monomer (EPDM) insulator was measured after the experiment. Experimental results were analyzed through scanning electron microscopy and microcomputed tomography. The ablation mechanism of the EPDM insulator under the operation conditions of a dual-pulse solid rocket motor was evaluated by analyzing the results. The results reveal that the internal flow field of the motor with a soft pulse separation device is uniform. The original charred layer existing on the EPDM insulator surface in the first pulse combustor is the decisive factor affecting the final ablation rate of the dual-pulse motor during the second pulse operation, and the ablation characteristic region is easily formed with the exfoliation of the charred layer. The ablation rate difference of the insulator increases with gas velocity.

In this work, the influences of P-well design and turn-off gate-to-source bias on the surge robustness of SiC MOSFET’s body diode are studied. Devices with high and low P-well doping concentration designs are stressed with surge current pulses when gate-to-source is biased with 0V or -5 V. The gate-to-source bias is found to have effects on the surge capability of the low P-well doping designed device. In the case of 0 V bias, the channel is prone to turning on and acquires a higher surge capability than the devices under the -5 V. On the other hand, the surge capability of high P-well doping designed device is found less influenced by the gate-to-source bias. Furthermore, threshold voltage instability after repetitive surge pulses is also investigated. The device with low P-well doping shows better threshold stability due to its lower interface trap density. Based on the results above, a design methodology is proposed from the view of device mechanism and operation condition. Relatively low P-well doping design and negative gate bias are recommended for SiC MOSFET, as they can improve the single pulse surge robustness of body diode and minimize the threshold voltage instability in repetitive surge pulse events.

Selective harmonic elimination pulsewidth modulation (SHEPWM) is a modulation technique widely used to improve the efficiency and harmonic content in medium-voltage high-power converters. Among these converters, the three-level neutral-point-clamped (3L-NPC) converter is one of the most utilized topologies. However, the 3L-NPC converter requires a proper balancing of dc-link capacitor voltages. This paper presents a control technique, based on pulse shifting method, to regulate the neutral point voltage when SHE-PWM is utilized. The proposed technique performs well with any power factor and it can also be directly applied to T-type converters and easily extrapolated to other multilevel topologies. The proposed method is experimentally validated in a scaled-down power converter and a full-scale medium-voltage 3L-NPC converter.

We study the quantum interference between the excitation pathways in a three-level $\Lambda$-type atom interacting with two short laser pulse trains under the conditions of electromagnetically induced transparency. The probability amplitude equations which describe the interaction of a three-level $\Lambda$-type atom with two laser pulse trains are numerically solved. We derive analytical expressions for the population of the upper excited state for resonant laser pulse trains with a rectangular temporal profile. By varying the parameters of the laser pulse trains such as area of a single pulse, detuning, repetition period, and number of individual pulses, we analyze the quantum interference between the excitation pathways in terms of the upper excited state population.

Back-rotation and hinges were detected in in situ piles during lateral spreading, but they were not reported in model tests. This paper presents, for the first time, model tests on vertically loaded capped piles subjected to pulse-like soil movement. The study reveals (i) modes of pile–soil interaction, including sway at a sliding depth (SD) of 0.286l (l = pile embedment), back-rotation at SD = 0.57l and sliding of the piles at either SD; (ii) the evolution rule of yielding moments at the ground level (Moy) and maximum bending moment (Mm) of the pile body for each mode. Expressions are synthesised from the tests to estimate Mm, to define the ultimate state as a rotation angle exceeding 0.8–1.2 times that of free-head piles, to gain limiting soil movement wf* (that incurs hinges) and residual displacement of piles. The simple expressions offer a good estimation of limiting soil movement and permanent displacement for the piles underpinning bridges in Christchurch, New Zealand. They are useful to complement the three-layer modelling of the response of piles incurred by sliding, sway and back-rotation.

The intersecting cortical model (ICM), initially designed for image processing, is a special case of the biologically inspired pulse-coupled neural-network (PCNN) models. Although the ICM has been widely used, few studies concern the internal activities and firing conditions of the neuron, which may lead to an invalid model in the application. Furthermore, the lack of theoretical analysis has led to inappropriate parameter settings and consequent limitations on ICM applications. To address this deficiency, we first study the continuous firing condition of ICM neurons to determine the restrictions that exist between network parameters and the input signal. Second, we investigate the neuron pulse period to understand the neural firing mechanism. Third, we derive the relationship between the continuous firing condition and the neural pulse period, and the relationship can prove the validity of the continuous firing condition and the neural pulse period as well. A solid understanding of the neural firing mechanism is helpful in setting appropriate parameters and in providing a theoretical basis for widespread applications to use the ICM model effectively. Extensive experiments of numerical tests with a common image reveal the rationality of our theoretical results.

Wood poles are widely used to support overhead distribution and transmission power lines in North America and the world. These poles are vulnerable to internal deterioration due to extreme weather conditions, requiring a large number of poles to be inspected every year. This paper presents a comparative study of four stress wave-based nondestructive testing (NDT) methods commonly used for condition assessment of wood poles. These include the traditional approaches of sounding, sonic pulse velocity, and ultrasonic pulse velocity tests; and a new approach that considers the orthotropic characteristics of wood, uncertainties in the elastic properties, ultrasonic wave velocity and attenuation. Two poles with an internal hole of 4% of the cross-section are evaluated and compared by each method. Ultrasonic measurements of wave velocity and attenuation considering orthotropic characteristics of wood and uncertainties in the elastic properties provide a reliable wave-based NDT method for the detection of early decay in wood poles.

In this article, we propose a soft eel robot design using soft pneumatic actuators that mimic eel muscles. Four pairs of soft actuators are used to construct the eel robot body. Pulse signals with suitable shifting phases are utilized to control delivery of compressed air to the actuators in sequence to create a sinusoidal wave from head to tail of the robot body. A model of hydrodynamic forces acting on an anguilliform swimmer when moving in fluid was built to estimate the thrust force generated by the robot at different tail beat frequencies. Experimental data revealed that the generated thrust force was positively correlated with the beat frequency. Measured data showed that swimming efficiency depended on both generated thrust force and body posture

This article presents the spatial and temporal dynamics of high-power Gaussian laser pulse in relativistic plasma. At higher intensities, the self-focusing and self-compression of laser pulse take place due to the variation in the mass of plasma electrons moving with speed comparable to the speed of light. The two non-linear coupled differential equations for spatial and temporal pulsewidth parameters have been obtained using the moment theory approach. These equations have been solved numerically using the Runga-Kutta method. The variation in the spatial and temporal pulsewidth parameters with the distance of propagation is then used to calculate the energy gained by the electrons, which are trapped by the excited electron plasma wave during laser-plasma interaction. It is observed that spatio-temporal dynamics play an important role in electron acceleration in relativistic plasma.

Deinterleaving mixtures of radar pulse sequences is the first and the most vital step for modern electronic reconnaissance systems to intercept and analyze the intentions of non-cooperative radars. Currently, these systems are facing great challenges due to the emerging complexity of radar modulations. This paper proposes a novel method for deinterleaving mixtures of radar pulse sequences based on the time series characteristics of each source (component pulse sequences). Firstly, the mathematical representations are established to describe the structural characteristics of each source. Then, the deinterleaving problem is formulated as a minimization of a maximum-likelihood cost function that can be solved efficiently through a supervised neural machine translation (NMT) network, i.e. to translate each received pulse in the interleaved pulse sequence to the corresponding source label. A sequence-to-sequence NMT model is proposed to capture the structural relationships among the non-adjacent pulses originated from the same source in the mixtures and assign the corresponding label to each pulse. The proposed method does not require the exact knowledge of each component pulse sequence. The experimental results based on the time of arrival sequence of mixed pulse sequences show that the proposed method outperforms the state-of-the-art deinterleaving methods and achieves satisfactory performance under highly non-ideal situations with measuring noise and lost pulse conditions. The proposed method can be directly applied to other fields involving deinterleaving problems and multi-variate input conditions.

Intentional electromagnetic interference is a serious threat to the safety of electronic devices. Multiple electromagnetic pulses will be coupled and transmitted to electronic devices through the cables. Accumulative effects are generated, which make it easier for damage to occur in the electronic devices. In this article, the working principle of micro-silicon acceleration sensors is introduced. The accumulative effects of multiple pulses on acceleration sensors is studied by a large number of injection experiments. The accumulation trends of multiple pulses with different pulse numbers and intervals are analyzed. The damaged structures inside abnormal sensor amplifiers were observed via optical microscopy and scanning electron microscopy. The experimental results show that the accumulative effect is strengthened with increased pulse number or decreased pulse interval, and the threshold voltage for multiple pulses on the acceleration sensor decreases. The threshold voltage for a single pulse is 321.57 V. When the pulse interval is 1 μs and the pulse number is 5, the threshold voltage for multiple pulses is 163.42 V, which is reduced by 49.12% compared with a single pulse. These results provide a reference for the damage design of electromagnetic pulse weapons.

Comprehensive cancer therapy protocols are generally administered periodically (at discrete time points) and often determined by tumor size. In the literature, a class of mathematical models are proposed, including therapeutic protocols either with pulse therapy at fixed time points or with state-dependent therapy. However, it is clear in practice (in both clinical and experimental contexts) that the treatment process is much more complex combining pulse surveillance (pulse therapy) with a threshold policy (state-dependent implementation of therapy). Here, we propose a novel mathematical model describing tumor size-guided pulse therapies at fixed time points, which is more in line with the design of clinical protocols for cancer therapies. In studying the dynamics of the proposed model, we find a new kind of periodic solution for dynamical systems with pulse intervention, which we denote as a ( l + m ) T periodic solution. In more detail, the study of the existence and stability of semi-trivial periodic solutions uncovers very rich dynamics, including the existence of order-k effector-free periodic solutions. We obtain analytical expressions for these, and establish the existence of order-1 tumor-free periodic solutions. Furthermore, we discuss the existence and stability of positive periodic solutions. We initially establish the existence of stable order-1 periodic solutions through carefully considering the bifurcation near the effector cell-free periodic solution. Our numerical simulations confirm three possibilities: 1) that two different positive periodic solutions can be bi-stable, 2) that the positive equilibrium can be bi-stable with a positive periodic solution, or 3) that the solution is tri-stable with two different positive periodic solutions. Our main results show that no tumor-free periodic solution exists when the threshold policy is feasible, and this may be a reason why frequently a tumor can be only reduced to a certain low level and not eliminated completely. One of the key considerations in the threshold schedule is to determine an optimal threshold of tumor size to balance the therapy frequency (or the times of therapy) and the amplitude of the tumor size, furthermore the optimal therapy should also be individual-based (or personalized). We believe that our modelling approach can be widely applied into many other fields of life science, and provide critical guidance for the implementation of control strategies.

We firstly propose a roadmap for the design of high repetition rate (~100 MHz) Tm-doped ultrafast fiber laser with an emission wavelength above 2000 nm. This roadmap is confirmed by both theoretical simulation and experimental verification. The designed Tm-doped fiber oscillator not only operates in continuous wave regime with a broad tunable wavelength range of ~ 100 nm, but also in mode-locking regime with an emission wavelength > 2000 nm (up to 2020 nm). A 470-fs laser pulse with a pulse repetition rate of ~96 MHz and the maximum average power of 50 mW are achieved at the output wavelength of 2007 nm, matching well with the theoretical prediction. In a further step, the seed laser pulse is amplified to 3.3 W, accompanied by a Raman frequency shift of the output wavelength to 2346 nm. The homogeneous intense broadband spectrum with a bandwidth of 240-nm centered at 2200 nm is also observed.

Although pulse charging strategy has many advantages, it is still controversial. The paradox is that it prolongs the charging time to eliminate the polarization voltage by the pulse interval, and the AC component in pulse current will increase the ohmic losses. In this paper, an optimal charging strategy with complementary pulse current of Lithium-ion is proposed to address and alleviate these issues. For the pulse frequency, the optimization can be achieved through the electrochemical impedance spectroscopy (EIS) analysis to reduce the battery’s AC impedance. For the pulse amplitude, based on the battery’s internal resistance characteristics, minimize the ohmic losses to obtain the optimal amplitude. For the pulse duty cycle, it is adjusted to achieve state of charge (SOC) balancing in the early charging stage, and battery’s terminal voltage balancing in the later stage. Based on the optimized charging strategy, a pulse charger concept is proposed, which can flexibly control the pulse charging currents and use complementary pulses to completely eliminate the prolonged charging time caused by the pulse interval. In the end, an experimental platform for pulse charger of lithium-ion batteries is designed, and the theoretical analysis is verified by the comparative experiments.

Bifurcation amplifiers are two-state systems that behave as flip-flops. We propose a two-bit shift register with coupled bidirectional bifurcation amplifiers. We consider a model of the amplifier that is based on a driven nonlinear vibrational system with Duffing nonlinearity. A discussed physical implementation is a nano-mechanical system. The analysis of bifurcation points provides a design framework for driving forces. We use a modulated two-level pulse at the first amplifier and a periodic three-level pulse at the second. We numerically demonstrate that these driving forces allow for the transfer of digital data between each amplifier. Our investigation provides an alternative approach for developing digital shift registers using nonlinear dynamics at the nanoscale.

KHNP had licensed Dynamic Control rod Reactivity Measurement (DCRM) method using detector current signals of PWRs in 2006. The method has been applied to all PWRs in Korea for about 15 years successfully. However, the original method was inapplicable to PWRs using low-sensitivity integral fission chamber as ex-core detectors because of their pulse pile-up and the nonlinearity of the mean-square voltage at low power region. Therefore, to overcome this disadvantage, a modified method, DCRM-EK, was developed using kinetics behavior after equilibrium condition where the pulse counts maintain the maximum value before pulse pile-up. Overall measurement, analysis procedure, and related computer codes were changed slightly to reflect the site test condition. The new method was applied to a total of 15 control rods of 1000 MWe and 1400 MWe PWRs in Korea with worths in the range of 200 pcm–1200 pcm. The results show the average difference of -0.4% and the maximum difference of 7.1% compared to the design values. Therefore, the new DCRM-EK will be applied to PWRs using low sensitivity integral fission chambers, and also can replace the original DCRM when the evaluation fails by big noises present in current or voltage signals of uncompensated/compensated ion chambers.

A theoretical novel model of generalized photo-thermoelasticity and hyperbolic two-temperature theory is studied in this paper. The elastic medium is excited by an external magnetic field and pulsed laser based. The model is established in the context of memory-depended derivative (MDD) when the material is time-dependent. The governing equations describe the interaction processes for isotropic homogeneous hyperbolic thermoelastic medium in one-dimensional (1D) space when the non-Gaussian laser pulse model is applied with time delay. Moreover, The Laplace transforms is used to obtain analytical solutions of the main fields. As such, the medium is loaded when traction is free and shocked thermally with time-dependent. The complete solutions are obtained in Laplace time domain when the invers of Laplace transform are used numerically. Numerical results of the main quantities are discussed graphically with the effect of hyperbolic two-temperature when time-delay parameter is taken into account.

International audience; In high dose per pulse charged particle beams, all online detectors saturate due to ion recombination. It is therefore impossible to count detector pulses separately. Silicon carbide due to its high band gap, high thermal conductivity and high displacement energy, is seen as an alternative. Analyzing waveforms in real time is challenging in terms of bandwidth, measurable energy range, sensor size, data rate. In this contexte, an Analog Front-End (AFE) was designed for radiation signal processing. It is based on a TransImpedance Amplifier (TIA) and Charge Sentitive Amplifier (CSA) to analyze the shape of generated signal. The methodology used to characterize AFE for high detector capacitance is described. The results extracted from simulations, experimental and measurements in radiative environment are also presented.

Acoustic levitation is considered one of the most effective noncontact particle manipulation methods, along with aerodynamic, ferromagnetic, and optical levitation techniques. It is not restricted by the material properties of the target. However, existing acoustic levitation techniques have some drawbacks that limit their potential applications. Therefore, in this article, an innovative approach is proposed to manipulate objects more intuitively and freely. By taking advantage of the transition periods between the acoustic pulse trains and electrical driving signals, acoustic traps can be created by switching the acoustic focal spots rapidly. Since the high-energy-density points are not formed simultaneously, the computation of the acoustic field distribution with complicated mutual interference can be eliminated. Therefore, compared to the existing approaches that created acoustic traps by solving pressure distributions using iterative methods, the proposed method simplifies the computation of time delay and makes it possible to be solved even with a microcontroller. In this work, three experiments have been demonstrated successfully to prove the capability of the proposed method including lifting a Styrofoam sphere, transportation of a single target, and suspending two objects. Besides, simulations of the distributions of acoustic pressure, radiation force, and Gor'kov potential were conducted to confirm the presence of acoustic traps in the scenarios of lifting one and two objects. The proposed tactic should be considered effective since the results of the practical experiments and simulations support each other.

Pulse tube is one of the main parts of the pulse tube cryocooler. Ideally, the pulse tube works under adiabatic environment without heat transfer loss. But in real case, entropy is generated in the pulse tube itself from heat exchanged with the walls, turbulent mixing of the hot and cold gas segments, circulation of the gas within the tube, and end effect losses from the adiabatic to isothermal transition in the cycle. All these processes reduce the enthalpy flow in the pulse tube from the ideal acoustic power. However, no 1D model can sufficiently simulate these effects in the past. Also, most of the 1D models about the pulse tube part with a heat transfer coefficient is far from accurate, especially for micro pulse tube in which the heat transfer is more obvious. This work revealed that the basic heat transfer changes instantaneously and shows different tendencies in different time of one cycle, and no suitable law or explanation could fare well the phenomenon eventually. The phase angle changes from negative to positive that results in the relatively heat flux along the pulse tube becomes smaller, that could help the pulse tube to make a good performance.

Quantum cascade lasers are highly stable against optical feedback, where the reflection mirror is well aligned with the optical path. Therefore, it is challenging to produce pulse oscillations in quantum cascade lasers through normal optical feedback. In this work, we show that tilted optical feedback with a misaligned reflection mirror triggers quantum cascade lasers to generate low-frequency oscillations, including irregular pulse oscillations and square wave oscillations. The oscillation period is in the microsecond range, and generally decreases with increasing tilt angle. In addition, the duty cycle of the square waves is tunable through varying the tilt angle. It is also found that a weak feedback strength or a low pump current yields rare occurrence of the pulse oscillations.

A multistage signal estimation scheme is proposed for phase-and-amplitude modulated soliton communication systems. The estimator provides a significant mean-squared-error reduction in soliton amplitude estimation, which, in conjunction with detection of encoded phase information, results in spectral-efficiency improvements. A low-complexity version of the multistage estimation scheme is also proposed, whose performance is studied via numerical simulations under the distributed Raman amplification strategy. The achievable information rate is increased by about 1 bit/symbol for pulse bandwidth of 30 GHz, 40 GHz, and 50 GHz.

In current exploration, a die-sinking EDM technique on two various Ni based alloy materials (Alloy 625, Alloy 718) were planned to optimize numerous performance attributes depends on Taguchi method. Nickel based Super alloy like Alloy 625 and Alloy 718 are mostly used in aerospace, marine, nuclear industries due to its remarkable chemical and mechanical properties. Experimentation have been proposed by Taguchi’s design to see impact of four input process machining factors like pulse on time, off time, current and tool rotation on material removal rate, electrode wear rate, average surface roughness and overcut. A combined route of optimization of satisfaction function with Taguchi method was used for the multiple performances optimization. The optimum and most cogent parametric setting for machining was obtained at: [pulse on time = 100 µs, pulse off time = 50 µs, current = 17A, tool rotation = 825 rpm] for alloy 625; [pulse on time = 300 µs, pulse off time = 75 µs, current = 14A, tool rotation = 925 rpm] for alloy 718.

Under the frequency modulated continuous wave (FMCW) system, the “stop-and-go” echo model of traditional pulse synthetic aperture radar (SAR) is no longer applicable. The range-azimuth coupling term introduced by fast time going term cannot be ignored, or otherwise it will cause degradation in the quality of generated image. This paper proposes a Sliding Spotlight SAR imaging algorithm based on improved two-step method. To address the problems of big interval of FMCW SAR and difference from the pulse SAR echo model triggered by dechirp reception, the proposed algorithm has improved the ωk algorithm and realized great focusing of FMCW signal. Furthermore, this algorithm adopts the method of focusing azimuth deramp in frequency domain to prevent the aliasing problem in image domain encountered by the classic two-step method. The simulation and real data results prove that this method can realize good focusing of FMCW SAR Sliding Spotlight mode.

Study Subject The research concerns attempts to computerize the foundations of pulse diagnostics of Tibetan medicine. An expert in Tibetan pulse diagnostics can evaluate the functioning of an organism (twelve internal organs and three psychophysiological systems) by feeling the pulse in six palpation points on the radial arteries of both wrists of a patient. Nowadays many physicists make attempts to computerize this method. The paper shows a few tests that are intended to «teach» a pulse diagnostics device to identify the diagnostically relevant characteristics of pulse waves. Objective of the Research This investigation is an attempt to objectify basic characteristics of pulse diagnostics. Though pulse diagnostics has always been a subjective art of an experienced doctor, it may also become part of an objective science due to the physical basis that underlies it. Method The paper presents tests of pulse measurements by a pulse diagnostics device in conditions that create certain predictable responses of an organism to outer stimuli. A group of volunteers were exposed to certain stimuli that can bring about predictable responses of the organism to be detected, processed and analyzed by the pulse diagnostics equipment. Conclusion Experiments of this kind give practical material for the analysis of the pulse waves obtained under special conditions, which provides the development of the software for the pulse diagnostic equipment and confirms that objectifying basic characteristics of pulse diagnostics of Tibetan medicine is possible, though in a limited scope.

Efficient and cost effective utilization of WEDM process is a challenge for leading edge era of manufacturing because of the complex and non-linear behavior of the process. The current study focuses on an experimental inquiry carried out for WEDM of Nitronic-30 to obtain optimum process parameters for improved surface roughness (SR) and material removal rate (MRR), Nitronic-30 is austenitic stainless steel offers high strength with good corrosion resistant property which high potential in applications such as automotive parts, aqueous applications, solid handling equipment. Therefore, multi-response optimization of Nitronic-30 on WEDM is very essential. Experiments were carried out with Taguchi's DoE and a L9 orthogonal series, with machining parameters like pulse on time (Ton), pulse off time (Toff), and peak current (IP). Minitab-17 software was used to evaluate response variables such as material removal rate and surface roughness. Analysis of variance (ANOVA) and SN Ratio plot of GRG indicates that peak current is the most important parameter. Grey Relational Analysis (GRA) provides optimal process parameters like pulse on time 124 machine units, pulse off time 40 machine units and peak current 230A for optimal response variables as 4.019 µm SR and 8.683 mm3/min MRR.

A method of reconstructing the original partial discharge (PD) signal to improve the accuracy of PD localization in cross‐linked polyethylene (XLPE) cables is presented here. XLPE cables, extremely sensitive to PDs, are the most popular underground cables in urban grids. The conventional PD localization methods, based on evaluation of the arrival times of PD pulses in the time domain, are negatively affected by the dispersion and attenuation of PD signals propagating in the power cable. A method for the accurate localization of PDs realized through inverse frequency domain modelling (IFDM) is presented here. The method, eliminating the systematic localization error caused by the dispersion and attenuation, significantly improves the localization accuracy. The locations of the PD are identified by comparing peak values of the initial PD signals reconstructed from different extracted pulses. A method for evaluating the propagation constant of the cable is also presented. The efficiency of the accurate localization method was verified by laboratory experiments. Besides, the inherent limitations of the conventional PD localization method for longer cable tests are discussed. The inevitable location error in the conventional methods does not exist in the new method.

In order to improve the gas energy conversion efficiency at the outlet of the pulse detonation combustor, numerical calculation methods were used to study the influence of three different cross-section obstacle structures of square, circle and trapezoid on the distribution characteristics of gas pressure potential energy, kinetic energy and internal energy in a single cycle at the outlet of pulse detonation combustor. The results show that: the expansion of pulse detonation gas mainly includes three stages: primary expansion, secondary expansion, and over-expansion. Gas pressure potential energy, kinetic energy and internal energy increase during the primary and secondary expansion stages, and decrease during the over-expansion stage; Pulse detonation combustor with trapezoidal cross-section obstacle structure has the smallest proportion of gas energy at the outlet of the combustor during the over-expansion stage and the highest proportion during the secondary expansion stage; compared with square and circle cross-section obstacle structures, the gas energy distribution at the outlet of the pulse detonation combustor with trapezoidal cross-section obstacle structure is the easiest for turbomachinery to convert the gas energy.

We propose an all-fiber passively mode-locked laser for high-purity high-order mode generation by combining a two-mode long period fiber grating (TM-LPFG) and a two-mode fiber Bragg grating (TM-FBG). The grating combination fully plays respective advantages: highly efficient mode conversion of the LPFG, mode selection and spectrum filtering of the TM-FBG. A semiconductor saturable absorber (SESAM) is used to achieve passively mode-locking. As a result, the mode-locked cylindrical vector beam (CVB) pulse with a 3-dB spectral width of 0.08 nm at a repetition rate of 12.88 MHz has been obtained, and the signal to noise ratio (SNR) is as high as 68 dB. Moreover, the azimuthally and radially polarized CVBs obtained after degeneracy elimination have high purity of 95.6% and 98.3%, respectively. This laser may have the potential for generation of high-purity CVB pulse.

The general performance of diffractometers at the first long pulse spallation source ESS, is compared with their counterparts at J-PARC, a short pulse spallation source. The difference in the inherent pulse structure of these neutron sources presents opportunities for new concepts for instrumentation, where performance does not scale simply with source power. The article describes advantages and disadvantages of those diffractometers, adapting to the very different source characteristics. We find that the two sources offer comparable performance in flux and resolution when operating in high-resolution mode. ESS offers significant advantages in tunability and flexibility, notably in the ability to relax resolution in order to increase flux for a given experiment. The slow repetition rate of ESS favors long instruments. On the other hand, J-PARC instruments perform very well in spite of the lower source power and allow better access to epithermal neutrons, of particular interest for PDF analysis of diffraction data.

In multi-sensor data based partial discharge (PD) source location in high voltage (HV) cable, poor reliability of detection of pulse arrival time against noises, waveform distortion, amplitude attenuation is the major barriers to practical application. In this paper, an improved Allen-Bear PD pulse detection algorithm, which combines the advantage of the characteristic functions of the two time-window energy ratio based detection algorithms, is proposed for robust PD location. The most critical contribution of proposed method is the extension of frequency domain component compared to the characteristic functions of the original algorithm. Simulation and physical experiment results demonstrate that the proposed method not only ensures the detection accuracy of the PD pulse arrival time, but also improves the reliability under harsh practical scenarios. It performs significantly better than the existing detection algorithm in terms of anti-noise, anti-waveform distortion, time window length variation, etc. It has significant value for practical applications.

A new type series inertance tube pulse tube refrigerator is introduced. It includes series cold heads. Each cold head's pulse tube connects an inertance tube as phase shifter. The acoustic power of the first pulse tube is partially used by the first inertance tube for phase shifting, while the remaining is used for generating additional cooling power. It is high efficiency with multi refrigeration temperature. A two-dimensional axisymmetric model was introduced for simulation by the commercial CFD software ANSYS Fluent. The numerical results show that it has high potential for getting higher efficiency. A protype series inertance tube pulse tube refrigerator was made and tested. Its efficiency is higher than the ordinary inertance tube pulse tube refrigerator at higher temperature range. At 232K, the efficiency is increased by 10%. The results show that it is valuable for further development.

In this work, a numerical study of the solutions of the parabolic and hyperbolic equations of heat conduction with the same physical parameters is carried out and a comparative analysis of the results obtained is carried out. The mathematical formulation of the problem is discussed. The action of the laser is taken into account through the source function, which was chosen as a double femtosecond laser pulse. In the hyperbolic equation, in contrast to the parabolic one, there is an additional parameter that characterizes the relaxation time of the heat flux. In addition, the source of the hyperbolic equation contains an additional term - the derivative of the power density of the source of the parabolic equation. This means that the temperature of the sample is influenced not only by the power density of the source, but also by the rate of its change. The profiles of the sample temperature at different times and its dynamics at different target depths are shown. The calculations were carried out for different time delays between pulses and for different relaxation parameters.

We describe an ultrafast optics laboratory comprising a mode-locked erbium fiber laser, autocorrelation measurements, and a free-space parallel grating dispersion compensation apparatus. The gain spectrum of Er fiber provides a broad bandwidth capable of supporting sub-100 fs pulses centered near a wavelength of 1550 nm. The fiber laser design used here produces a train of pulses at a repetition rate of 55 MHz with pulse duration as short as 108 fs. The pulse duration is measured with a homebuilt autocorrelator using a simple Michelson interferometer that takes advantage of the two-photon nonlinear response of a common silicon photodiode. To compensate for temporal stretching of the short pulse due to group velocity dispersion in the fiber, an apparatus based on a pair of parallel gratings is used for pulse compression. A detailed part that lists in the supplementary material includes previously owned and common parts used by the telecommunications industry, which helps decrease costs of the laboratory. This provides a cost-effective way to introduce the principles of ultrafast optics to undergraduate laboratories.

We study the existence and stability of standing pulse solutions to a singularly perturbed three-component reaction–diffusion system with one activator and two inhibitors. We apply the MAE (matched asymptotic expansion) method to construct solutions and the SLEP (singular limit eigenvalue problem) method to evaluate their stability. This approach is not just an alternative approach to geometric singular perturbation and the associated Evans function, it also yields two advantages: one is extendability to higher dimensional cases, and the other is that it allows us to obtain more precise information about the behaviors of critical eigenvalues. This implies the existence of codimension-two singularities of drift and Hopf bifurcations for the standing pulse solution. Moreover, it is numerically confirmed that stable standing and traveling breathers emerge around the singularity in a physically acceptable region.

Permeability and porosity are the two most important parameters of rocks for the evaluation and exploitation of oil/gas reservoirs. In this study, a modified pulse‐decay method has been developed to measure both permeability and porosity simultaneously. In the present method, the gas pressure in one chamber is changed (increased or decreased) instantaneously and then maintained constant, while the pressure response changing with time in the other one is monitored. A mathematical model of this procedure has been formulated, and a general analytical solution, including the early‐time and late‐time evolutions, has been obtained. The late‐time solution is presented for postprocessing of experimental data, which leads to the simultaneous measurement of permeability and porosity values of tight rocks. Our measurements agree well with those from the classical pulse‐decay and gas expansion methods. Compared with measuring the permeability and porosity separately, the proposed method can reduce the total test time and ensure the permeability and porosity are measured under the same effective stress condition.

The time of flight of a plane wavefront generated from an acoustic pulse is expected to decrease when the medium length between the wave emitter and receiver is shortened. This simple idea is extrapolated to the case of reservoir compaction in order to obtain a geophysical parameter R (dilation factor) that relates the rock deformation to the variation of time of flight (also called time-lapse time shift in 4D seismics) or acoustic velocity of a plane wave propagating in the same direction of deformation. Interpretation of a few laboratory compressive tests with simultaneous ultrasonic acquisition, performed on oil-saturated calcarenite samples, are presented and discussed. The samples were subjected to several stress regimes and simultaneous ultrasonic acquisitions. Despite the formerly ultrasonic acquisition rate limitations, it was possible to obtain R values for various lateral-vertical stress ratios for each sample's linear and nonlinear stress-strain trends.

International audience; Many-particle time domain methods are rising alternatives to particle-in-cell (PIC) or frequency methods to simulate the wave–beam interactions in traveling wave tubes (TWTs). We focus on two of those: our Hamiltonian discrete model DIMOHA is compared analytically against the pseudospectral method RUBEUS. Although based on two completely different approaches—the Gel’fand transform for DIMOHA and the telegraphist circuit for RUBEUS—we surprisingly find out that they share perfectly parallel sets of equations and variables. However, we conclude that DIMOHA is more flexible than RUBEUS in terms of pitch tapering and absorbing boundary conditions. It also shows excellent stability for steady-state simulation, allowing us to explain some discrepancies of RUBEUS with experimental results. These come from a standing wave pattern which is detectable in the vicinity of the sever. Finally, DIMOHA is tested for the first time with ultra-short pulses and exhibits excellent agreement with RUBEUS.

Reducing the occurrence of pipe bursts, reducing leakage, and reducing energy consumption are the three main goals in implementing pressure control programs in water distribution networks. Service pressure regulation strategy is an evolved approach that encompasses all goals of pressure management. This paper has investigated this approach in a rural network with hydraulic complexities as a case study so that some parts of the network have excess pressure and other low pressure. A computer code based on the method of characteristics (MOC) has been developed for network hydraulic analysis. The generated code analyzes unsteady flow, pressure-driven demand analysis, and dynamic adjustment of pressure control valves based on the target node. Also, the experimental results of a laboratory network have been applied to validate and calibrate the numerical simulation. In addition, by measuring the flow rate and pressure of the network and the results of the minimum night flow method, three consumption patterns were used to generate pulsed nodal demands. Studies show that creating pressure-management areas by hydraulic analysis by MOC will determine the best control strategies. The mean pressure decreased 54% by applying this strategy. Furthermore, the average fluctuations of pressure reduced from 9.7 meters to 3.5 meters.