Optimal Pulse Frequency Research Articles

Mechanical and tribological properties of diamondlike carbon-coated polycarbonate

To improve the mechanical and tribological properties of polycarbonate, diamondlike carbon (DLC) coating was deposited on its surface by pulsed vacuum arc deposition with different pulse repetition rates at low substrate temperature (not more than 80 °C). The surface hardness increased by 20–33 times, the plasticity index increased by 1.6–2.5 times, the resistance to plastic deformation increased by 50–200 times, and the wear rate decreased by 170–600 times compared to untreated polycarbonate depending on the pulse frequency in the process of coating deposition. It has been shown that decreasing the pulse frequency during DLC deposition from 3 to 1 Hz increases the content of sp3-hybridized carbon atoms and level of internal stresses in the coating and increases its hardness. However, this is accompanied by an increase in the number of microcracks in the coating. Deposition with an optimal pulse frequency formed a polycarbonate/DLC system with high hardness and wear resistance as well as a low number of microcracks.

Pulse and pulsating supercharging phenomena in a semi-enclosed pipe

Considering the discontinuous square pulse wave and continuous sine pulsating wave, we report a distinctive supercharging phenomenon of fluid in a water-filled semi-enclosed pipe and reveal the supercharging regularity. We demonstrate that there can be significant supercharging phenomena at the pipe end-face if the water is periodically injected at the pipe inlet with certain frequency. Compared to the traditional pulsating injection method, the present injection strategy can remarkably enhance the peak pressure of the water at the end face of the pipe. We explained this phenomenon by numerical simulations based on the computational fluid dynamic method. It’s found that there is a quantitative relationship between the optimal pulse frequency, pipe length and wave speed. The proposed frequency model is suitable for the multi-waveform, such as sine wave, square wave and arcuate wave. The fluid pressure at the pipe end-face intermittently increases and the end-face peak pressure is largest when the inlet injection frequency equals to the optimal frequency.

The Optimal Sine Pulse Frequency of Pulse Hydraulic Fracturing for Reservoir Stimulation

Pulse hydraulic fracturing (PHF) is a key technique for reservoir stimulation. PHF can well accelerate the rupture of rock. However, the supercharging mechanism of PHF is not fully understood. The main reason is that the pressure distribution and its variation, especially the peak pressure characteristics, are unclear inside the pipe and fissure. The present research focuses on the sine pulse applied at the inlet of a pipe or fracture to reveal the variation regularity of peak pressure with the pulse frequency, amplitude, pipe length, diameter and wave speed. First, the weakly compressible Navier–Stokes equations were developed to simulate the variation of fluid pressure. The computation codes were developed using the MacCormack method validated by the existing experimental data. Then, the sine pulse effect was studied inside the pipe and fissure. Last, a new frequency model was built to describe the relationship between the optimal pulse frequency, wave speed and pipe length. The results show that there is a family of frequencies at which the peak pressure of the endpoint can be significantly enhanced and that these frequencies are the optimal pulse frequency. It is found that the optimal pulse frequency depends on the pipe or fissure length and wave speed. At the optimal pulse frequency, the peak pressure at the endpoint can be increased by 100% or more, and the cavitation phenomenon occurs. However, the peak pressure decreases when with the decrease in the pipe diameter and fissure departure due to the friction drag effect of the wall. These new landmark findings are very important for the PHF technique. In addition, a new universal frequency model is built to predict the optimal sine pulse frequency. The present research shows the variation regularity of the fluid pressure inside the pipe and develops a sine frequency-controlled method, providing a potential guide for reservoir stimulation.

Pulse supercharging phenomena in a water-filled pipe and a universal prediction model of optimal pulse frequency

A water hammer is an important natural phenomenon that can be used to fracture rock with enhanced local water pressure. The oscillatory injection of a column of water can be used to make a pipe water hammer. However, the optimal injection frequency to create a water hammer has not yet been found. The main reason for this is that the distribution of fluid pressure and its variation are unclear inside a pipe. In this study, we demonstrate for the first time that there can be significant supercharging phenomena and a law governing their appearance in a water-filled pipe. We first find the optimal pulse frequency to reproduce the supercharging process. We also clarify the supercharging mechanism at an optimal frequency. First, a simplified pipe model is adopted, and weakly compressible Navier–Stokes equations are developed to simulate the flow of water in pulse hydraulic fracturing (PHF). The computation code is developed using the MacCormack method, which has second-order accuracy in time and space. The computation codes and program are validated using experimental data of weakly compressible flows. Then, the square pulse effects are studied inside a pipe, including the effects of pulse frequency, amplitude, pipe length, diameter, and wave speed. Finally, a new universal frequency model is built to describe the relationship among optimal pulse frequency, wave speed, and pipe length. The results show that in square PHF, there is a family of frequencies for which the fluid peak pressure can be significantly enhanced, and these frequencies include the optimal pulse frequency. The optimal frequency of a square pulse depends on the pipe length and wave speed. At the optimal pulse frequency, the maximum peak pressure of the fluid can be increased by 100% or more, and cavitation occurs. These new landmark findings are very valuable for understanding pulse supercharging in an internal water wave. In addition, a new universal frequency model is built to predict optimal pulse frequency. This study identifies an evolution law of peak pressure inside a pipe and proposes a practical frequency-control model for the first time, which can provide a theoretical guide for PHF design.

An Approach to Recover Energy From Discarded Primary Batteries Before Being Disassembled

This article demonstrates the feasibility of recovering energy from discarded primary batteries (e.g., alkaline or zinc-carbon) that would be disposed of as normal household waste based on self-adaptive pulse discharge (SAPD) method. The SAPD approach is utilized to search the optimal pulse frequency and duty cycle for different types of used batteries with the maximum allowed discharge current. To assess the performance of the proposed approach, a prototype including improved passive cell balancing circuit, SAPD control circuit, and series–parallel switching circuit of supercapacitor banks was designed and implemented to drain a battery bank that consisted of at least 6 but at most 10 used cells of different brands in series. Discharging experiments show that the energy recovery with six to ten used batteries ranges from 798 to 1455 J, and the corresponding recovery efficiency is about 33.49%–46.43%. Although outcomes are still far from being satisfactory in the efficiency with the proposed approach, the rate of energy recovery may depend on the remaining capacity of discarded batteries and so may be advantageous if the battery has a high remaining capacity. Therefore, authors conclude that there is possibly a direct link between the recovery efficiency and the remaining capacity of discarded batteries.

Numerical investigation on fluidization characteristics of binary particles in supercritical water fluidized bed reactor under pulsed conditions

The fluidization properties of binary particles in a supercritical water fluidized bed reactor (SCWFBR) are numerically investigated based on coupled Computational Fluid Dynamics-Discrete Element Method (CFD-DEM) simulations. The accuracy and effectiveness of the CFD-DEM model is firstly validated via previously published experimental data. Then, the model is adopted to study the effect of flow velocities and sinusoidal pulse on the mixing of the binary particles. Numerical results show that it is effective to promote mixing of binary particles in SCWFBR by introducing external energy pulses, which cannot be achieved by simply increasing the flow velocities without pulses. Compared to high frequency pulses, low frequency pulses are more effective in promoting mixing. Within the parameters considered here, it is also found that the pulse amplitude is almost positively correlated with the effect on the promotion of particle mixing when it is smaller than the fixed flow velocity. In addition, an efficient and economical method based on Fast Fourier Transform (FFT) on the bed pressure drop is given to determine the optimal pulse frequency, which can prevent the waste of manpower and the physical resources from happening. This study can provide technical guidance to achieve optimal mixing of binary particles in SCWFBR and offer theoretical support for the design and optimization.

Maximum Isometric Tetanic Force Measurement of the Tibialis Anterior Muscle in the Rat.

Traumatic nerve injuries result in substantial functional loss and segmental nerve defects often necessitate the use of autologous interposition nerve grafts. Due to their limited availability and associated donor side morbidity, many studies in the field of nerve regeneration focus on alternative techniques to bridge a segmental nerve gap. In order to investigate the outcomes of surgical or pharmacological experimental treatment options, the rat sciatic nerve model is often used as a bioassay. There are a variety of outcome measurements used in rat models to determine the extent of nerve regeneration. The maximum output force of the target muscle remains the most relevant outcome for clinical translation of experimental therapies. Isometric force measurement of tetanic muscle contraction has previously been described as a reproducible and valid technique for evaluating motor recovery after nerve injury or repair in both rat and rabbit models. In this video, we will provide a step-by-step instruction of this invaluable procedure for assessment of functional recovery of the tibialis anterior muscle in a rat sciatic nerve defect model using optimized parameters. We will describe the necessary pre-surgical preparations in addition to the surgical approach and dissection of the common peroneal nerve and tibialis anterior muscle tendon. The isometric tetanic force measurement technique will be detailed. Determining the optimal muscle length and stimulus pulse frequency is explained and measuring the maximum tetanic muscle contraction is demonstrated.

Valley polarization in biased bilayer graphene using circularly polarized light

Achieving a population imbalance between the two inequivalent valleys is a critical first step for any valleytronic device. A valley polarization can be induced in biased bilayer graphene using circularly polarized light. In this paper, we present a detailed theoretical study of valley polarization in biased bilayer graphene. We show that a nearly perfect valley polarization can be achieved with the proper choices of external bias and pulse frequency. We find that the optimal pulse frequency $\ensuremath{\omega}$ is given by $\ensuremath{\hbar}\ensuremath{\omega}=2a,$ where $2a$ is the potential energy difference between the graphene layers. We also find that the valley polarization originates not from the Dirac points themselves, but rather from a ring of states surrounding each. Intervalley scattering is found to greatly reduce the valley polarization for high-frequency pulses. Thermal populations are found to significantly reduce the valley polarization for small biases. This work provides insight into the origin of valley polarization in bilayer graphene and will aid experimentalists seeking to study valley polarization in the laboratory.

Fast in vivo multiphoton light-sheet microscopy with optimal pulse frequency.

Improving the imaging speed of multiphoton microscopy is an active research field. Among recent strategies, light-sheet illumination holds distinctive advantages for achieving fast imaging in vivo. However, photoperturbation in multiphoton light-sheet microscopy remains poorly investigated. We show here that the heart beat rate of zebrafish embryos is a sensitive probe of linear and nonlinear photoperturbations. By analyzing its behavior with respect to laser power, pulse frequency and wavelength, we derive guidelines to find the best balance between signal and photoperturbation. We then demonstrate one order-of-magnitude signal enhancement over previous implementations by optimizing the laser pulse frequency. These results open new opportunities for fast live tissue imaging.

Wind tunnel and flight tests of glider flow separation control by microsecond dielectric barrier discharge

As a new kind of active flow control technology, plasma flow control has a bright future, for its simple structure, fast response, and wide frequency band. The wind tunnel and flight tests were conducted with microsecond dielectric barrier discharge on a glider. For the tests, the microsecond pulse power supply and remote control system were designed and built. In the wind tunnel test, the flow separation on the glider wing surface can be controlled effectively, and static pressure at the leading edge pressure is decreases by 177%. The flow control effects under different pulse frequencies are compared, and the optimal pulse frequency for actuation is found to be 100 Hz. A significant hysteresis effect was observed with microsecond dielectric barrier discharge at small angle of attack (α ≤ 18°), which means the flow control effect can last more than 300 s after turning off the plasma actuation. In the flight test, the maximum roll angle decreases by 7.0°, and the maximum aileron deflection angle decreases by 9.4° with plasma actuation at both sides of the wing, which means the glider becomes more stable with microsecond dielectric barrier discharge. With unilateral actuation, the rolling moment generated by the plasma actuation is larger than that produced by the ailerons with the angle of attack within 12.94° ≤ α ≤ 29.77°, which shows strong rolling control ability of microsecond dielectric barrier discharge. The wind tunnel and flight tests results verified the flow control effect of microsecond dielectric barrier discharge, and paved the way for the plasma flow control technology to practical applications.

Sliding discharge plasma actuation for forebody vortex control on a slender body at high angles of attack

Two innovative kinds of sliding discharge plasma actuators based on different formation hypotheses of forebody asymmetric vortices are designed using a slender body model. Particle image velocimetry and surface pressure measurements are synchronously used to compare the control effect of antiflow and along-flow sliding discharge actuators for a forebody asymmetric vortex at high angles of attack. The experimental results show that the two kinds of sliding discharge plasma actuators can effectively change the random lateral force caused by the asymmetric vortices, and a better control effect is manifested using the along-flow sliding discharge plasma actuator, which contributes to the approximately linear proportional control of the lateral force. This finding suggests that the convective instability of the forebody vortex system in the leeward region of the slender body has a significant influence on the random lateral forces and moments. Through improving the spatial stability of forebody vortices, the flow control efficiency can be effectively improved. An optimal pulse frequency exists in each of the three actuation modes, but it may vary due to the different geometry configuration of the plasma actuator. In this regard, the research findings will potentially provide technical guidance for improving the efficiency of plasma actuators and understanding the formation mechanism of asymmetric vortices.

Pulsed-Current Electrochemical Codeposition and Heat Treatment of Ti-Dispersed Ni-Matrix Layers

An electrochemical deposition is a fast and cost-efficient process to produce film or coating. In this research, Ni-Ti electrodeposition is developed by codepositing a Ti-dispersed Ni-matrix layer from a Ni-plating solution suspended with Ti particles. To enhance the coating uniformity and control the atomic composition, the pulsed current was applied to codeposit Ni-Ti layers with varying pulse duty cycles (10 to 100 pct) and frequencies (10 to 100 Hz). The microstructures and compositions of the codeposited layers were analyzed by scanning electron microscopy, X-ray diffraction, and X-ray fluorescent techniques. The pulsed current significantly improved the quality of the Ni-Ti layer as compared to a direct current. The Ni-Ti layers could be electroplated with a controlled composition within 48 to 51 at. pct of Ti. The optimal pulse duty cycle and frequency are 50 pct and 10 Hz, respectively. The standalone Ni-49Ti layers were removed from copper substrates by selective etching method and subsequently heat-treated under Ar-fed atmosphere at 1423 K (1150 °C) for 5 hours. The phase and microstructures of the post-annealed samples exhibit different Ni-Ti intermetallic compounds, including NiTi, Ni3Ti, and NiTi2. Yet, the contamination of TiN and TiO2 was also present in the post-annealed samples.

Comparison of sterilization efficiency of pulsed and continuous UV light using tunable frequency UV system

Abstract Whether or not pulsed UV light was more bactericidal than continuous UV was still debated. The aim of this work was to compare the disinfection efficiency of continuous and pulsed UV light at different frequencies. A tunable frequency UV system was designed to allow indicator bacteria to be exposed to continuous or pulsed UV light with a same low pressure mercury lamp, which can emit UV light with a wavelength of 253.7 nm, and the pulse frequency was adjustable. The germicidal ability against Escherichia coli and Salmonella spp. of pulsed UV light at frequencies 0 (represented continuous irradiation), 2, 4, 6, 8, 10 Hz was compared. The results showed that pulse frequency is a factor influencing the ultimate inactivation ability of pulsed UV light and at specific frequencies pulsed UV light was more bactericidal than continuous UV. Industrial relevance Pulsed UV light for microbial inactivation has been applied for more than 30 years. As a very important factor, pulse frequency has been ignored for a long time. We have demonstrated that at some specific frequencies, pulsed UV light was more bactericidal than continuous UV using low pressure mercury lamp. And if further studies could come to the similar results in inert-gas flash lamps and/or medium-pressure UV lamps and figure out the optimal pulse frequency, it might improve the sterilization efficiency of the existing pulsed UV system.

Fe-Pt Alloy Nanowire Arrays Prepared by Pulse DC Electrodeposition

Highly ordered Fe-Pt nanowire arrays were fabricated using anodic aluminum oxide templates by pulse DC electrodeposition. The influences of pulse ratio and frequency on the microstructural and magnetical properties of Fe-Pt nanowire arrays have been studied. The composition of Fe-Pt nanowires can be adjusted by pulse ratio and the crystallization of wires can be modified by pulse frequency. By choosing an optimal pulse ratio and pulse frequency, the Fe-Pt nanowire arrays with out-of plane coercivity up to 1620 Oe can be achieved. Annealing of Fe-Pt nanowire arrays could improve the crystallinity of wires and accordingly enhance the coercivity.

Combined optimal pulse width modulation and pulse frequency modulation strategy for controlling switched mode DC–DC converters over a wide range of loads

This paper develops a combined optimal pulse width modulation (PWM) and pulse frequency modulation (PFM) strategy for controlling switched mode DC-DC converters. The peak ripple magnitudes of both the output-voltages and -currents during all operating modes over a wide range of loads are minimised subject to specifications on the minimum efficiency bounds of the converters. This problem is posed as a multi-objective functional inequality constrained optimal control problem. By expressing the initial state of each operating mode at the steady state as a function of the switched time instants, as well as applying the time scaling transform method and the constraint transcription method, the multi-objective functional inequality constrained optimal control problem is converted to a conventional optimal control problem. Finally, a control parameterisation technique is applied to solve the problem. Computer numerical simulations show that the combined control strategy could achieve low peak ripple magnitudes of both the output-voltages and -currents for all operating modes over a wide range of loads and guarantees the satisfaction of the specifications on the minimum efficiency bounds of the converter over a wide range of loads. © 2012 The Institution of Engineering and Technology.

Adhesive-based liquid metal radio-frequency microcoil for magnetic resonance relaxometry measurement

This paper reports the fabrication and characterization of an adhesive-based liquid-metal microcoil for magnetic resonance relaxometry (MRR). Conventionally, microcoils are fabricated by various techniques such as electroplating, microcontact printing and focused ion beam milling. These techniques require considerable fabrication efforts and incur high cost. In this paper, we demonstrate a novel technique to fabricate three-dimensional multilayer liquid-metal microcoils together with the microfluidic network by lamination of dry adhesive sheets. One of the unique features of the adhesive-based technique is that the detachable sample chamber can be disposed after each experiment and the microcoil can be reused without cross-contamination multiple times. The integrated microcoil has a low direct-current (DC) resistance of 0.3 Ω and a relatively high inductance of 67.5 nH leading to a high quality factor of approximately 30 at 21.65 MHz. The microcoil was characterized for ∼0.5 T proton MRR measurements. The optimal pulse duration, amplitude, and frequency for the 90° pulse were 131 μs, -30 dB (1.56 W) and 21.6553 MHz, respectively. In addition, we used the liquid-metal microcoil to perform a parametric study on the transverse relaxation rate of human red blood cells at different hematocrit levels. The transverse relaxation rate increases quadratically with the hematocrit level. The results from the liquid-metal microcoil were verified by measurements with a conventional solenoid coil.

Decoding GnRH neurohormone pulse frequency by convergent signalling modules

Gonadotropin-releasing hormone (GnRH) mediates control of reproduction. It is secreted in pulses and acts via intracellular effectors to activate gonadotrophin secretion and gene expression. Sub-maximal GnRH pulse frequency can elicit maximal responses, yielding bell-shaped frequency-response curves characteristic of genuine frequency decoders. GnRH frequency decoding is therapeutically important (pulsatile GnRH can drive ovulation in assisted reproduction whereas sustained activation can treat breast and prostate cancers), but the mechanisms are unknown. Here, we consider the possibility that it is due to convergence of distinct pulsatile signals at the transcriptome. We develop a model that mirrors wet-laboratory data for activation and nuclear translocation of GnRH effectors (extracellular signal regulated kinase and nuclear factors of activated T-cells) and incorporates transcription. The model predicts genuine frequency decoding when two transcription factors (TFs) converge at a cooperative gate, and shows how optimal pulse frequency could reflect TF activation kinetics and affinities. Importantly, this behaviour is revealed as an emergent feature of the network, rather than an intrinsic feature of a given protein or pathway, and since such network topology is extremely common, may well be widespread in biological systems.

Optimized nanosecond pulsed electric field therapy can cause murine malignant melanomas to self‐destruct with a single treatment

We have identified a new, nanosecond pulsed electric field (nsPEF) therapy capable of eliminating murine melanomas located in the skin with a single treatment. When these optimized parameters are used, nsPEFs initiate apoptosis without hyperthermia. We have developed new suction electrodes that are compatible with human skin and have applied them to a xenograft nude mouse melanoma model system to identify the optimal field strength, pulse frequency and pulse number for the treatment of murine melanomas. A single treatment using the optimal pulse parameters (2,000 pulses, 100 ns in duration, 30 kV/cm in amplitude at a pulse frequency of 5-7 pulses/sec) eliminated all 17 melanomas treated with those parameters in 4 mice. This was the highest pulse frequency that we could use without raising the treated skin tumor temperature above 40 degrees C. We also demonstrate that the effects of nsPEF therapy are highly localized to only cells located between electrodes and results in very little scarring of the nsPEF-treated skin.

Electrically-evoked Neural Activities of rd1 Mice Retinal Ganglion Cells by Repetitive Pulse Stimulation

For successful visual perception by visual prosthesis using electrical stimulation, it is essential to develop an effective stimulation strategy based on understanding of retinal ganglion cell (RGC) responses to electrical stimulation. We studied RGC responses to repetitive electrical stimulation pulses to develop a stimulation strategy using stimulation pulse frequency modulation. Retinal patches of photoreceptor-degenerated retinas from rd1 mice were attached to a planar multi-electrode array (MEA) and RGC spike trains responding to electrical stimulation pulse trains with various pulse frequencies were observed. RGC responses were strongly dependent on inter-pulse interval when it was varied from 500 to 10 ms. Although the evoked spikes were suppressed with increasing pulse rate, the number of evoked spikes were >60% of the maximal responses when the inter-pulse intervals exceeded 100 ms. Based on this, we investigated the modulation of evoked RGC firing rates while increasing the pulse frequency from 1 to 10 pulses per second (or Hz) to deduce the optimal pulse frequency range for modulation of RGC response strength. RGC response strength monotonically and linearly increased within the stimulation frequency of 1~9 Hz. The results suggest that the evoked neural activities of RGCs in degenerated retina can be reliably controlled by pulse frequency modulation, and may be used as a stimulation strategy for visual neural prosthesis.

Parameters influencing augmentation of cerebral blood flow by cervical spinal cord stimulation

Cervical spinal cord stimulation (SCS) has been shown to augment cerebral blood flow (CBF) and protect the brain from focal ischemia. However, the application of SCS in the treatment of cerebral ischemia requires a better understanding of the limits of the cerebrovascular effect and the optimal stimulation parameters. In the present study, we investigated the effects of various stimulation parameters on CBF augmentation, as well as the issue of tachyphylaxis of the CBF response. SCS was performed in adult Sprague Dawley rats, and CBF was assessed using cortical laser Doppler flowmetry (LDF). In separate experimental series, stimulation amplitude, frequency, and pulse width were varied, and the effect on the LDF response was recorded. Finally, using the stimulation parameters found to elicit the strongest LDF response, we examined the effect of lengthening the period of SCS. SCS elicited a robust increase in cortical LDF values as previously demonstrated. The magnitude of the response varied in a dose-dependent fashion with the stimulation amplitude. LDF values increased by more than 80% over baseline with an amplitude of 1.5 mA. The optimal pulse width and frequency of the stimulation were 0.25 ms and 50 Hz, respectively. Lengthening the stimulation period up to 20 minutes resulted in a persistent increase in cerebral LDF values during the entire stimulation period, although the magnitude of this effect diminished to approximately 50% over the baseline after 10 minutes. SCS elicits a robust augmentation in CBF, which lasts the entire stimulation duration. Stimulation parameters required for optimal cerebrovascular response are within normally used therapeutic ranges in the clinical settings. These results provide further evidence that SCS may provide a novel therapeutic strategy for the treatment of cerebral ischemia.