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(1) The aliasing of radial velocities from weather radars is a known challenge in meteorology. It may also occur during bird migration if the unambiguous velocity threshold is below the birds' ground speed. High variability in birds' radial velocities and high flight speeds lead to multiple aliasing (folding) and challenge meteorological dealiasing approaches. Unfolded radial velocities are essential for calculating flight directions and speed and derived migration traffic rates for aeroecological applications. (2) We study the occurrence of aliasing in measurements of different pulse repetition frequencies (PRF) in C-band weather radars in bird and insect cases and test the efficiency of a dealiasing algorithm widely used in biological weather radar software. We use dual-PRF measurements as a reference to avoid the folding of radial velocities in quantitative and qualitative bird migration outputs. (3) The dealiasing algorithm performed poorly in single-PRF measurements during bird migration, though not in insect and precipitation cases. In contrast, dual-PRF velocities yielded proper flight speeds, flight directions and migration traffic rates. (4) The study unveils severe biases in aeroecological analyses of C-band weather radars from imperfectly dealiased single-PRF radial velocities. Dual-PRF measurements with appropriate dealiasing postprocessing offer a valid alternative to single PRF and should be preferred whenever available. [ABSTRACT FROM AUTHOR]

Purpose: Extracellular vesicles (EVs) serve as carriers of intracellular factors with therapeutic effects, including tissue regeneration and attenuation of inflammatory responses. The majority of EVs in vivo are derived from skeletal muscle, which is reported to have anti-inflammatory effects. While high-intensity pulsed ultrasound (US) irradiation has been shown to promote EV secretion from myotubes, the impact of pulse repetition frequency, a US parameter affecting pulse length, on EV release remains unclear. This study aimed to investigate the impact of pulse repetition frequency of US on the release of EVs from myotubes. Methods: C2C12 myoblasts were used in this study. After differentiation into C2C12 myotubes, US was performed for 5 min at an intensity of 3.0 W/cm2, duty cycle of 20%, acoustic frequency of 1 MHz, and different pulse repetition frequencies (100 Hz, 10 Hz, or 1 Hz). After 12 h, EVs and cells were collected for subsequent analyses. Results: US did not cause a reduction in cell viability across all US groups compared to the control. The concentration of EVs was significantly higher in all US groups compared to the control group. In particular, the highest increase was observed in the 1-Hz group on EV concentration as well as intracellular Ca2+ level. Conclusion: This study investigated the effect of three different pulse repetition frequencies of US on the release of EVs from cultured myotubes. It is concluded that a low-pulse repetition frequency of 1 Hz is the most effective for enhancing EV release from cultured myotubes with pulsed ultrasound. [ABSTRACT FROM AUTHOR]

Background: Non-invasive brain stimulation techniques such as transcranial magnetic stimulation and transcranial direct current stimulation hold promise for inducing brain plasticity. However, their limited precision may hamper certain applications. In contrast, Transcranial Ultrasound Stimulation (TUS), known for its precision and deep brain targeting capabilities, requires further investigation to establish its efficacy in producing enduring effects for treating neurological and psychiatric disorders. Objective: To investigate the enduring effects of different pulse repetition frequencies (PRF) of TUS on motor corticospinal excitability. Methods: T1-, T2-weighted, and zero echo time magnetic resonance imaging scans were acquired from 21 neurologically healthy participants for neuronavigation, skull reconstruction, and the performance of transcranial ultrasound and thermal modelling. The effects of three different TUS PRFs (10, 100, and 1000 Hz) with a constant duty cycle of 10 % on corticospinal excitability in the primary motor cortex were assessed using TMS-induced motor evoked potentials (MEPs). Each PRF and sham condition was evaluated on separate days, with measurements taken 5-, 30-, and 60-min post-TUS. Results: A significant decrease in MEP amplitude was observed with a PRF of 10 Hz (p = 0.007), which persisted for at least 30 min, and with a PRF of 100 Hz (p = 0.001), lasting over 60 min. However, no significant changes were found for the PRF of 1000 Hz and the sham conditions. Conclusion: This study highlights the significance of PRF selection in TUS and underscores its potential as a non-invasive approach to reduce corticospinal excitability, offering valuable insights for future clinical applications.

Non-invasive brain stimulation techniques such as transcranial magnetic stimulation and transcranial direct current stimulation hold promise for inducing brain plasticity. However, their limited precision may hamper certain applications. In contrast, Transcranial Ultrasound Stimulation (TUS), known for its precision and deep brain targeting capabilities, requires further investigation to establish its efficacy in producing enduring effects for treating neurological and psychiatric disorders. To investigate the enduring effects of different pulse repetition frequencies (PRF) of TUS on motor corticospinal excitability. T1-, T2-weighted, and zero echo time magnetic resonance imaging scans were acquired from 21 neurologically healthy participants for neuronavigation, skull reconstruction, and the performance of transcranial ultrasound and thermal modelling. The effects of three different TUS PRFs (10, 100, and 1000 Hz) with a constant duty cycle of 10 % on corticospinal excitability in the primary motor cortex were assessed using TMS-induced motor evoked potentials (MEPs). Each PRF and sham condition was evaluated on separate days, with measurements taken 5-, 30-, and 60-min post-TUS. A significant decrease in MEP amplitude was observed with a PRF of 10 Hz (p = 0.007), which persisted for at least 30 min, and with a PRF of 100 Hz (p = 0.001), lasting over 60 min. However, no significant changes were found for the PRF of 1000 Hz and the sham conditions. This study highlights the significance of PRF selection in TUS and underscores its potential as a non-invasive approach to reduce corticospinal excitability, offering valuable insights for future clinical applications. • TUS holds potential for LTD-like plasticity induction. • TUS with 10 Hz PRF and 10 % DC induces MEP inhibition for at least 30 min. • TUS with 100 Hz PRF and 10 % DC induces MEP inhibition lasting over 60 min. • TUS with 1000 Hz PRF and 10 % DC does not change corticospinal excitability. [ABSTRACT FROM AUTHOR]

Copyright of Bearing is the property of Bearing Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Objectives: To investigate the appropriate combination of pulse length (PL) and pulse repetition frequency (PRF) when performing ultrasound stimulated microbubble (USMB) to enhance doxorubicin (DOX) delivery to tumors. Methods: A total of 48 tumor‐bearing mice were divided into four groups, namely groups A–D. The mice in groups B–D were treated with chemotherapy and USMB treatment with different combinations of PL and PRF, and group A was control. Contrast‐enhanced ultrasound imaging was conducted to analyze tumor blood perfusion. Fluorescence microscopy and high‐performance liquid chromatography were used to qualitatively and quantitatively analyse DOX release. The structural changes of tumors were observed under light microscope and transmission electron microscope. Furthermore, another 24 tumor‐bearing mice were treated with sonochemotherapy and some related inflammatory factors were measured to explore the underlying mechanism. Results: With PL of three cycles and PRF of 2 kHz, the tumor perfusion area ratio increased by 26.67%, and the DOX concentration was 4.69 times higher than the control (P <.001). With PL of 34.5 cycles and PRF of 200 Hz, the tumor perfusion area ratio decreased by 12.7% and DOX did not exhibit increased extravasation compared with the control. Microvascular rupture and hemorrhage were observed after long PL and low PRF treatment. While vasodilation and higher levels of some vasodilator inflammatory factors were found after treatment with short PL and high PRF. Conclusions: USMB treatment using short PL and high PRF could enhance tumor blood perfusion and increase DOX delivery, whereas long PL and low PRF could not serve the same purpose. [ABSTRACT FROM AUTHOR]

The corona-stabilized switch has the potential to be a high repetition rate pulsed-power switching device, but there has been limited investigation into its repetitive breakdown stability and insulation recovery characteristics. Repetitive breakdowns of gas are characterized by a memory effect, where the subsequent breakdown process is inevitably influenced by the preceding one. However, there are still some issues that require further exploration in the current research on the mechanism of memory effect on repetitive breakdown characteristics. To clarify the factors and mechanisms that affect the repetitive breakdowns of corona-stabilized switches, this paper introduced optical observation methods into the experimental investigation. Through optical–electrical coupled diagnosis, the repetitive breakdown stability and insulation recovery performance of corona-stabilized switches under different working conditions and repetition frequencies were analyzed. The monotonic promoting effect of corona stabilization on switch insulation strength recovery is proposed as well as the non-monotonic and complex regulatory mechanism of corona stabilization on repetitive breakdown stability. The research results provide a theoretical and practical basis for clarifying the mechanism of repetitive corona-stabilized breakdowns and optimizing the design of corona-stabilized switches. [ABSTRACT FROM AUTHOR]

Objective To determine the effects of ultrasound stimulated microbubble (USMB) by different ultrasound combinations of pulse length (PL) and pulse repetition frequency (PRF) under fixed mechanical index and duty cycle on tumor perfusion and drug delivery in C57BL/6 mice. Methods Twenty-four female C57BL/6 mice (6~8 weeks old, average body weight 17.74±0.43 g) were randomly divided into 3 groups (n=8): control group (group A), DOX+PL3.0+PRF2000 group (group B) and DOX+PL30.5+PRF200 group (group C) after being carried with MC38 xenograft tumor. Contrast-enhanced ultrasound (CEUS) was performed before and after USMB treatment to compare the peak intensity (PI), area under the curve (AUC) and tumor perfusion percentage. Doxorubicin (DOX) was injected slowly after USMB treatment, and then the concentration of DOX in the tumor was detected with high-performance liquid chromatography (HPLC). Microstructure of the tumor was observed pathologically. Results The values of PI and AUC after treatment had no significant differences when compared with those before treatment in group A (P>0.05), the values were increased by 19.3% and 18.0%, respectively in group B (P0.05), and the area increased by 21.0% in group B (P0.05). The pathological results showed that the tumor microvessels in group A and B were slightly and moderately dilated, while those in group C were ruptured and bleeding. Conclusion Under the fixed mechanical index and duty cycle, USMB with higher PRF and lower PL can enhance tumor blood perfusion and promote drug delivery. However, higher PL and lower PRF can block tumor blood perfusion.

The corona-stabilized switch has the potential to be a high repetition rate pulsed-power switching device, but there has been limited investigation into its repetitive breakdown stability and insulation recovery characteristics. Repetitive breakdowns of gas are characterized by a memory effect, where the subsequent breakdown process is inevitably influenced by the preceding one. However, there are still some issues that require further exploration in the current research on the mechanism of memory effect on repetitive breakdown characteristics. To clarify the factors and mechanisms that affect the repetitive breakdowns of corona-stabilized switches, this paper introduced optical observation methods into the experimental investigation. Through optical–electrical coupled diagnosis, the repetitive breakdown stability and insulation recovery performance of corona-stabilized switches under different working conditions and repetition frequencies were analyzed. The monotonic promoting effect of corona stabilization on switch insulation strength recovery is proposed as well as the non-monotonic and complex regulatory mechanism of corona stabilization on repetitive breakdown stability. The research results provide a theoretical and practical basis for clarifying the mechanism of repetitive corona-stabilized breakdowns and optimizing the design of corona-stabilized switches.

In this paper, the design, performance and characterization of a low temperature argon plasma jet with a Surface Dielectric Barrier Discharge (SDBD)-like structure are presented. Based on this structure, the argon plasma jet is generated in a SDBD-like structure with a mixed electric field. SDBD-like structure, refers to the plasma jet generated by the surface dielectric barrier discharge. The effects of high frequency electric pulse as the main igniter for plasma jet generation and low frequency sinusoidal electric field in order to modify the dynamic behavior of plasma jet are investigated in this paper. The effect of these variations on the plasma jet along with the decrease in pulse repetition frequency were recorded by Schlieren imaging method. This study revealed the important role of decreasing the pulse repetition frequency in the mixed electric field in the SDBD-like plasma jet structure. Increasing the cross-sectional area of the plasma colliding with the target surface is the most important advantage of this structure for the generation of plasma jets. Also, the trend of decreasing plasma column continuity with increasing pulse repetition frequency is another result of this study. Under these conditions, the diameter of the cross section of the plasma jet increases to 9 mm without increasing the consumption of more electrical power and with equal jet length. Finally, the surface hydrophilicity was measured after treatment by plasma jet and the operation resulted in a super-hydrophilic surface. [ABSTRACT FROM AUTHOR]

Purpose: Tissue elasticity can be measured and mapped using color Doppler elastography. In a previous study, a binary pattern of shear waves was observed using a color flow imaging (CFI) system with matched pulse Doppler packet size as well as shear wave frequency and displacement condition. In the present study, we demonstrate the possibility of mapping shear wave velocity and resolving phantom elasticity using any commercial ultrasound machine without fulfilling that condition. Methods: We derive a relation between Doppler autocorrelator integration time and the estimated flow velocity. The underlying principles behind the shear wave shadows captured by a typical modern ultrasound machine are investigated. The ultrasound machine measurement preset is calibrated to remove the effect of transducer array scanning delay in modifying the appearing wavenumber and thus correct the measurement error. Results: The method was used to successfully measure the elasticity of a biological tissue-mimicking phantom and distinguish a stiff phantom from a soft phantom. Conclusion: Using this method, the elasticity of a biological tissue-mimicking phantom can be recovered with less strict constraint. As a result, it provides more flexibility to be implemented in common ultrasound machines. This method may be practically used to help identify tissue stiffness-related disease. [ABSTRACT FROM AUTHOR]

This article shows development and performance evaluation of a MicroX-SAR demonstration satellite, scheduled to be launched in 2020 for synthetic aperture radar (SAR) application. This compact SAR system and its instruments are briefly described. The SAR antenna consists of deployable seven panels with a slot array and the antenna size is 4.9 × 0.7 m. This article proposes a simple evaluation method of the SAR antenna. The seven-panel antenna array performance is estimated from isolated single-panel antenna measurement results and synthesized scattering matrix. It is validated by comparing with near-field measurement of a seven-panel antenna array. The on-board SAR system is combined with a single-point source simulator and the point source SAR image is evaluated. The ambiguity to the signal ratio is computed for the bandwidth-integrated seven-panel antenna radiation patterns, and finally the pulse repetition frequency selection is computed along with noise equivalent sigma zero to estimate the SAR image quality based on various requirements of swath-width and ground-range resolution as per the application of interest. The prototype system is capable of 1-m ground-range resolution SAR image acquisition for 28-km swath-width within acceptable limits of signal-to-noise ratio and ambiguity levels.

Conventional noninvasive electroencephalogram (EEG) is limited to poor spatial resolution due to volume conduction effect. To overcome this limitation, the acoustoelectric effect (AE) based acoustoelectric brain imaging (ABI) is proposed for mapping brain electrical activity in a high temporal and spatial resolution. Through phantom and vivo rat brain experiments, this study investigated a biological current source coding mechanism with pulse focused ultrasound (PFU) at pulse repetition frequency (PRF). First, the current source coding mechanism is deduced in theory. Then, with phantom experiment, the coding relationship between AE signal and PRF is investigated in details. With different PRFs, including 100 Hz, 200 Hz, 500 Hz and 1 kHz, amplitude spectrum analysis results indicate that obvious high amplitude response of AE signal appear at each PRF and corresponding harmonic frequencies. And for different current sources of 10 Hz and 30 Hz, the AE signal oscillate at the the same frequency as corresponding PRF. Additionally, for each PRF, the decoded AE signal is of the same frequency and phase with the current source. Finally, coding mechanism is further validated in vivo rat experiment with different PRFs, including 500 Hz, 1 kHz and 2 kHz. The AE signal envelope and decoded AE signal both have significant correlation with low frequency EEG with ultrasound not only in the low frequency band but also in specific frequency. Also, the mean amplitude of delta rhythm respectively calculated from envelope of AE signal and decoded AE signal are obviously higher than the other rhythms which reflects the brain state of anesthesia or lethargy. These theory and experiment results validate that PFU has a coding effect on current source at PRF and demonstrate the feasibility of restoring current source from the coded AE signal which are critical for making ABI a clinical neuroimaging technique.

Objective: The aim of the study was to evaluate the characteristics of dentin ablation with a high pulse repetition rate Q-switching 2.79 lm laser. Materials and methods: Dentin was ablated using a homemade Q-switching Er:YSGG laser with a high pulse repetition rate. Er:YSGG radiation was applied with a pulse energy of 1 or 10mJ for 100 or 3Hz pulse repetition rate, respectively. A scanning electron microscope (SEM) was used to observe the microstructures of dentin samples after ablation. Teeth were irradiated in vitro with a 100 Hz pulse repetition rate under two different modes: free running and Q-switching. A thermocouple was applied to measure the temperature in the pulp cavity during ablation. Results: A 100 or 3Hz Q-switching laser was used to irradiate dentin for 30 and 100 sec, respectively. There was no significant difference in ablation mass loss between the two conditions. The SEM photographs showed more dentinal tubules and no damage in the ablation area when using the 100 Hz Q-switching laser. The temperature of the pulp cavity was maintained below 41°C when using a Q-switching laser. Conclusions: The Q-switching Er:YSGG laser with a high pulse repetition rate exhibited greater ablation efficiency and better morphology than the low pulse repetition rate Q-switching laser. The experimental results also demonstrate the significant advantage of the Q-switching laser over free-running lasers for protecting dental pulp tissue. The Q-switching Er:YSGG laser with a high pulse repetition rate is expected to become an efficient new dental tool. [ABSTRACT FROM AUTHOR]

Objective. Pulsed focused ultrasound (FUS) can deliver therapeutics to the brain by using intravenous microbubbles (MBs) to open the blood-brain barrier (BBB). MB emissions indicate treatment outcomes, like BBB opening (harmonics) and damage (broadband). Typically, a pulse repetition frequency (PRF) of 1 Hz is used, but the effect of PRF on MBs is not fully understood. We investigated the effect of PRF on MB activity and tracer delivery. Approach. The effect of PRF (0.125, 0.25, 0.5, 1, and 2 Hz) on MB activity was monitored through harmonic and wideband emissions during FUS sonications of the rat brain at 274.3 kHz. BBB opening was quantified through fluorescence imaging to estimate the concentration of Trypan Blue (TB) dye following a 75-pulse FUS exposure for PRFs of 1 and 0.25 Hz. Main results. At a fixed acoustic pressure, the percentage change in maximum harmonic amplitude compared to the control (PRF = 1 Hz) decreased with increasing PRF, with a median change of 73.8% at 0.125 Hz and -38.3% at 2 Hz. There was no difference in the pressure threshold for broadband emissions between PRFs of 0.25 and 1 Hz. PRF = 0.25 Hz, led to a 68.2% increase in the mean concentration of TB measured after FUS, with a 53.9% increase in the mean harmonic sum, compared with PRF = 1 Hz. Harmonic emissions-based control at PRF = 0.25 Hz yielded similar TB delivery, with less damage at histology, compared with 1 Hz. Significance. For a fixed number of FUS pulses, reducing the PRF was shown to increase the magnitude of harmonic emissions and TB delivery, but not the threshold for broadband emissions. While further research is necessary to understand the mechanisms involved, these results may be useful to improve clinical safety margins and sensitivity to detecting small harmonic signals from cavitating MBs., (© 2024 Institute of Physics and Engineering in Medicine.)

Objective: The aim of this study is to determine the effect of scale/pulse repetition frequency (PRF) on the appearance of color Doppler twinkling artifact. Materials and Methods: We commenced this cross-sectional study for 20 months from November 2014 to July 2016. During routine ultrasound examination, we observed multiple case of twinkling artifact produced by renal stones, calcifications in the thyroid nodules, bony fragments and intestinal gases, etc., We observed twinkling artifact with low- and high-PRF settings in 500 different structures. A total of 500 other structures were included wherein there was no Doppler twinkling artifact produced by them, with usual optimum PRF settings. These structures were also evaluated with low- and high-PRF to determine the effect of PRF on twinkling artifact effectively. All the patients were examined according to the AIUM guideline for appropriate examination protocol. Data were collected from the observation of twinkling artifact with low- and high-PRF/scale and evaluated with the help of IBM SPSS 24 package, the results were summarized as follow. Results: Change in scale/PRF could not affect the twinkling artifact. The twinkling artifact observed with low-PRF was the same as seen with high-PRF. There was a significant agreement between low- and high-PRF in the production of color twinkling artifact. The kappa value of agreement was estimated as 0.96, whereas the Pearson's correlation was significant with the value of 0.001. Same twinkling artifact was created with low- and high-PRF, with no significant variation. Conclusion: Twinkling artifact is independent of PRF/Scale.

In tropical forests, the penetration ability of airborne laser scanning (ALS) may be limited because of highly dense vegetation cover. However, in the typical planning of ALS surveys, the ability of laser pulses to penetrate forests is not considered. Nine round-trip flight lines covering the area of a tropical forest on the northeast side of the Tsengwen Reservoir in Taiwan were designed in this study. Five flight lines flew at altitudes of 1.525, 1.830, 2.135, 2.440, and 2.745 km, and the other four had pulse repetition frequencies (PRFs) of 100, 150, 200, and 250 kHz. The laser penetration index (LPI) is a quantitative index measuring the penetration ability of the ALS and consists of the ratio of the number of laser pulses reaching the forest floor to the total number of laser pulses. The LPI was used to represent the laser penetration rate and investigate the influence of flying altitude and PRF on the LPI. The results showed that as the flying altitude decreased by 1 km, the average LPI increased by 10%, and as the PRF decreased by 50 kHz, the average LPI increased by 2%. The effect of the LPI on digital elevation models (DEMs) was confirmed by visual images obtained by DEMs at five altitudes. The DEM obtained at an altitude of 2.745 km was coarsely textured, whereas that obtained at an altitude of 1.525 km was finely textured. The in-situ height data obtained from the electronic Global Navigation Satellite System (eGNSS) were compared with the data of the ALS-generated DEMs. The results indicated that when the LPI ≥60%, the height difference between the in situ data and DEM data was not prominent. However, when the LPI

Microwave Assisted Spark Ignition (MAI) is a potential technology to improve lean combustion characteristics in spark ignition engines. This paper investigates the MAI performance with C 2 H 2 -Air spherical expanding flames in a Constant Volume Combustion Chamber (CVCC) system under ambient pressures from 0.1 to 0.6 MPa and equivalence ratios (φ) from 0.5 to 1.9. Results show that MAI greatly increases early flame kernel radius compared with SI mode particularly in the cases close to lean or rich limit under 0.1 MPa. The enhancement decreases obviously as equivalence ratio approaches stoichiometric ratio. With ambient pressure increasing, the MAI enhancement gets weakened. Normalized Reduced Electric Field (REF) is found to correlate well with the decreasing trend of normalized flame radius enhancement with increasing ambient pressure, indicating that REF is probably one of the key factors affecting MAI performance. The influence of microwave Pulse Repetition Frequency (PRF) on MAI under PRF from 1 to 80 kHz are studied and discussed for both non-combustion discharge and ignition tests. Increasing PRF, the enhancement of MAI is strengthened as more microwave energy is injected in high-absorption-efficiency period which is dominated by electron density. At last, the formation mechanism for "fluorescence spot" and its dependence on pressure are offered to explain the observed increasing light intensity in the flame kernel with ambient pressure. [ABSTRACT FROM AUTHOR]

Electrical discharge machining (EDM) is a non‐conventional machining technique that requires pulse generators to create sparks between the tool and the workpiece. Classical texts describe only two types of EDM pulse generators (EPGs), although there are several different types. This work presents a classification and detailed comparative study of 13 important EPG topologies from the power electronics perspective. The operation of each topology is explained using simulation studies for EDM load with spark current of 10 A and pulse repetition frequency of 1 kHz. Control schemes of each topology are explained from the viewpoint of mechanical performance parameters, viz. material removal rate, surface finish, and tool electrode wear ratio. A general analytical methodology to compute efficiency based on machining duty is illustrated considering the existence of two distinct switching frequencies. Overall comparison between EPG topologies is presented considering control aspects, size, efficiency, voltage stresses and suitability for any required application. As an example, a case of investigation of cutting silicon ingots with wire EDM is considered and experimental results are provided for the same. This work can be used as a guideline to understand and develop EPG based on particular target specifications. [ABSTRACT FROM AUTHOR]

Cognitive radars have the capability of using the prior environmental information to improve the radar performance. In this study, a cost function for fully adaptive waveform parameters design for cognitive tracking radars is proposed. These parameters include – but not limited to – pulse length, pulse repetition frequency, number of transmitted pulses, and target revisit rate. Thus, the proposed cost function is capable of reducing the tracking error, using adaptive waveform parameters, along the time resource management, with adaptive coherent processing interval and target revisit time. The purpose of the proposed cost function is balancing the different radar measurement errors (which depend on radar transmitted waveform in contrary directions), with respect to the target manoeuvre scenario, to reach the radar tolerable tracking error. Simulation results show that using the proposed waveform parameter design cost function, tracking error is reduced, and an optimised radar time resource usage is obtained. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Soil Sciences & Agricultural Engineering is the property of Egyptian National Agricultural Library (ENAL) and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Compared with the conventional single-channel sampling or azimuth multichannel sampling of SAR system, the multiple-input multiple-output (MIMO) sampling has the potential to realise the high-resolution wide swath (HRWS) imaging and the ground moving target indication (GMTI) simultaneously. As a key parameter in the design of SAR system, the pulse repetition frequency (PRF) has important impacts on the performances of HRWS and GMTI. From this perspective, the impacts of PRF design on GMTI performance of MIMO-SAR for hypersonic platform with curved trajectory have been analysed here. Specifically, the steering vectors of the ambiguous clutter and moving target are derived first under the curved trajectory model. Furthermore, according to MIMO-SAR system parameters, the optimum PRF design is simulated from the aspects of the blind velocity, the spatial ambiguity, and the detection probability. Finally, the real clutter data are further used to verify the effectiveness of PRF design on GMTI performance optimisation.

Compared with the conventional single-channel sampling or azimuth multichannel sampling of SAR system, the multiple-input multiple-output (MIMO) sampling has the potential to realise the high-resolution wide swath (HRWS) imaging and the ground moving target indication (GMTI) simultaneously. As a key parameter in the design of SAR system, the pulse repetition frequency (PRF) has important impacts on the performances of HRWS and GMTI. From this perspective, the impacts of PRF design on GMTI performance of MIMO-SAR for hypersonic platform with curved trajectory have been analysed here. Specifically, the steering vectors of the ambiguous clutter and moving target are derived first under the curved trajectory model. Furthermore, according to MIMO-SAR system parameters, the optimum PRF design is simulated from the aspects of the blind velocity, the spatial ambiguity, and the detection probability. Finally, the real clutter data are further used to verify the effectiveness of PRF design on GMTI performance optimisation. [ABSTRACT FROM AUTHOR]

Color Doppler ultrasound is the diagnostic cornerstone of vascular assessment. Almost all arteries and veins of the human body are accessible to this diagnostic imaging, which as a result is very often used as first-line diagnostic test. Recent technological developments in high-end ultrasound machines enable us to optimize image quality in color-coded duplex ultrasound of arteries and veins. To obtain an optimal instrument setting, all relevant adjustments of imaging must be considered. In B-Mode ultrasound, the basic vascular imaging method, the most important settings to optimize are ultrasound frequency, gain, dynamic range, and focus, whereas color Doppler depends on angle supersonic sounding and its application in clinical practice. Most mistakes in measuring blood flow velocities, a frequent cause of misinterpretation, result from insufficient angle correction. Cardiac pathologies may result in typical changes of arterial and venous Doppler curves. [ABSTRACT FROM AUTHOR]

Among the recently prevailing flame stabilization enhancement by electric field and plasma, repetitive DC electric pulse discharge is applied to a turbulent lifted diffusion jet flame to improve the reattachment in this study. The main objectove of this study is to characterize experimentally the stability and the reattachment behaviors of lifted flames under the electric pulse effect with a proposed electrode configuration. The effects of pulse repetition frequency (PRF) and voltage polarity on flame are investigated. The reattachment velocity increases by increasing PRF. The time history of flame base trace and absolute flame speed with positive-voltage-pulse are illustrated. The electric corona discharge is observed during upstream propagation process, and its role in flame acceleration is discussed. In addition, 2D-PIV measurement conditioned by high speed sequence images is conducted. Finally, the conditionally instantaneous flame propagation speed is enhanced and exceeds 3 times that of stoichiometric laminar flame speed, which leads to lifted flame reattachment. [ABSTRACT FROM AUTHOR]

Purpose. Purpose of the article is to show the possibility of joint efficient operation of semiconductor switches and spark arresters in high-powerful high-voltage generators for obtaining nanosecond and shorter pulse fronts on a high-voltage load. Methodology. The variants of generators of power high-voltage pulses with semiconductor switches in the form of IGBT-transistors, SOS-diodes and spark dischargers as pulse front peaking spark gaps are considered. A scheme is proposed for such a generator of high-voltage pulses with nanosecond front on the basis of a linear pulsed transformer in the Tesla scheme. Results. On the complex load of the generator in the form of a serial connection of a gas bubble in water with a discharge in it and a layer of water under the bubble, voltage pulses with an amplitude of 23 kV and current pulses with an amplitude of 15 A were obtained. In this case, the pulse front, both voltage and current, on the levels 0.1-0.9, was approximately 10 ns, and the repetition rate of pulses in the load ranged from 1200 to 5000 pulses per second. Originality. A scheme is proposed for a generator of high-voltage pulses with a nanosecond front. The difference of the proposed generator with a nanosecond front, high pulse repetition rate, using its high-voltage and low-voltage circuits in the discharge circuit, is the presence in its composition of a linear pulse transformer and a system of peaking of pulse front using SOS diodes and spark gaps. Practical value. These generators considered in this work can find wide application in high-voltage technologies, including decontaminating water treatment, water purification by electric discharges.