Hz Pulsation Research Articles

Visualization of the frequency effect of pulsed electric field on enzymatic browning of peel ground tissue

The enzymatic browning behavior of a model ground tissue, banana peel, influenced by the frequency variable of pulsed electric field (PEF), has been visualized and studied. The tissue was PEF-treated with 15 µs pulse at 3.3 kV/cm using trains of 5, 15, and 30 pulses, each varying from 0.1 Hz to 10 Hz; images and electrical conductivity were recorded intermittently throughout the incubation. The degree of browning was quantified with a browning index (BI) term, and the uniformity of browning was visually assessed by inspecting the pattern of pigment distribution. Moreover, the degree of tissue disintegration was calculated using a conductivity-based tissue disintegration index (DI) and compared to the BI and specific energy input. Browning uniformity was found to be significantly affected and increased with decreasing frequency. The effect was most noticeable up to disintegration degree of about 63, DI, or when the frequency of 5 or 15 pulses was reduced from 1 Hz to 0.1 Hz. Remarkably, the decrease at 5 pulses resulted in a significant increase in BI without a substantial increase in DI. The observed effect has been attributed to increased electrophoretic mobility of browning agents along the extracellular path during 0.1 Hz pulsation. Furthermore, lowering the frequency to 0.1 Hz reduced the energy required for a browning level close to saturation by about 57% compared to 10 Hz.

Suppression of thermo-acoustic instabilities in horizontal Rijke tube using pulsating radial jets

Thermo-acoustic instability has been observed in gas turbines, rocket engines, and aero-engines. Acoustic perturbations grow and change the characteristics of the flow due to instability. The present work describes the use of pulsating air jets to suppress the thermo-acoustic instabilities. In present study pulsatile micro-jets are placed downstream of the burner radially which breaks the coupling between acoustic waves and unsteady heat release.A microphone connected to LIFA (LabVIEW Interface for Arduino) was used to detect the sound pressure levels. By controlling the airflow rate of the pulsatile jets, the sound pressure levels were suppressed down to the background noise level using minimum energy and time. A closed-loop control system is developed for this purpose, which works on the feedback signal acquired from microphone. To simulate the one dimensional combustion phenomenon, an experimental setup called Rijke tube was used. The suppression was most effective for the pulsatile jets of 27-33 Hz pulsation frequency range and at a flow rate of 6.8 LPM. This control strategy effectively controlled the combustion instability of around 35-42 dB.•The closed loop control method is built on DAQ and Arduino using the LabVIEW interface for Arduino (LIFA).•Developed closed loop active control method was observed to be effective for suppression of thermo-acoustic instability.•Optimum position of the radial planes of micro-jets with respect to the burner was decided to improve the efficacy of the pulsatile jets towards suppression of thermo-acoustic instability.

A COMMERCIAL-OFF-THE-SHELF FREQUENCY MODULATED CONTINUOUS WAVE RADAR FOR VITAL SIGN MONITORING

Objective: Radar systems are capable of retrieving remotely micro-movements with very high precision. Millimeter-wave radars are already used in several medical applications (e.g. sleep disorders, heart beat rate, patient monitoring) and have shown promising results towards a remote Doppler cardiogram or arterial pulse wave measurements techniques. In this work, we tested a 122 GHz commercial-off-the-shelf (COTS) Frequency Modulated Continuous Wave (FMCW) radar for vital (respiratory and cardiac) signals monitoring. This required the setting up of a very precise experimental bench and the investigation of a robust data processing procedure. Design and method: An experimental bench (see Figure 1-a) has been set up with a high precision Newport linear actuator: a small target can be then displaced with less than 3 μm accuracy. Such system can replicate the thorax displacements due to the respiratory and cardiac activity. Two different motions were simulated: a ‘large’ 8 mm displacement at 0.15 Hz (a.k.a. respiratory) and a ‘small’ 0.5 mm at 1 Hz (a.k.a. cardiac). Furthermore, a shaker system can be used to reproduce completely arbitrary movements, even from real acquired Electrocardiogram (ECG) data. In this case, however, a reference measurement system would be necessary to determine the accuracy. Results: A first measurement set was dedicated to evaluate the accuracy of the radar system: around 50 acquisitions for each type of displacements were carried out. The accuracy of the radar measurements results in the order of ∼10 μm (see Figure 2). A second measurement set tested the dynamic resolution: in this case, a 0.4 Hz sinusoidal signal and a 0.8 Hz pulsation mix were fed to the shaker system. The radar is capable of retrieving both signal signatures (see Figure 3), with errors due to the combination of sharp pulse rise and low radar sampling frequency Conclusions: We show that a COST radar is able to retrieve vital signs chest displacements with a good accuracy in both amplitude and dynamics, thus representing a valid option for a remotely continuous cardiovascular monitoring. Next objectives are In Vivo measurements with an in-house radar system and measurements of blood pulse waves.

Experimental study of oil shale separation using binary medium by pulsed fluidized bed

ABSTRACT A large amount of the<6 mm fine particle oil shale created during mining and processing is frequently discarded, creating waste and an environmental hazard. A suitable fluidized dry separation technology would allow that fine particle to be de-ashed and improve the oil shale quality for effective utilization. This paper studies pulsed fluidized beds to determine the effectiveness of pulsation frequency, fines content and operating gas velocity on fluidization and separation of the fine oil shale. It was found that the introduction of fine particles could significantly improve the fluidization quality. When the content of fine particles is 5%, the average density of the bed is~2.3 g/cm3. The effective separation of the 6–3 mm oil shale was achieved using a mixed medium, with optimal separation conditions of 5% fine particle content, 4 Hz pulsation frequency, and 1.5U mf gas velocity. Finally, high efficiency dry beneficiation of 6-3 mm oil shale in pulsed fluidized bed was achieved, which is of great significance for future industrial applications.

Pulsed Fluidization of Nanosilica: Rigorous Evaluation of the Efficacy of Pulsation Frequency.

Assisted fluidization techniques can significantly improve the hydrodynamics of difficult- to-fluidize solids. Among these techniques, the pulsed flow strategy is highly promising owing to its cost-effectiveness and amenability to implementation for largescale processing. Using commercial-grade, highly porous nanosilica that shows strong agglomeration behavior, we implemented the pulsed flow with square-wave pulsation schemes of 0.05, 0.10, and 0.25 Hz frequencies, and compared their effectiveness in each case. Besides the conventional approach of assessing their efficacy using the pressure drop data, we have proposed a new approach in this work that consists of computing the power of the overall pressure drop transient signals. Using the theoretical value, i.e., the effective bed weight per unit area as a reference, the percentage increase in the power was 27 ± 4, 71 ± 5, and 128 ± 4, respectively, for 0.05, 0.10, and 0.25 Hz pulsation frequencies. In fact, the average pressure drop values were substantially higher when the partial bed collapse occurred between successive pulsations when compared with the case of low-frequency pulsations. The pulsation frequency also affected the evolution of local bed dynamics in various bed regions during the expansion and collapse of the bed. Moreover, the local and global pressure transients have shown interesting mutual correlations which were otherwise not evident from their individual transient profiles.

ВЛИЯНИЕ ПУЛЬСАЦИИ ОСВЕЩЕННОСТИ В ПТИЧНИКЕ НА ПРОДУКТИВНЫЕ КАЧЕСТВА КУР ПРИ ИСПОЛЬЗОВАНИИ СВЕТОДИОДНЫХ СИСТЕМ ОСВЕЩЕНИЯ

Effect of light pulsation frequency in poultry house has been studied on industrial herd layers livability and production in LED lighting system usage. LED light lamps usage with less than 488 Hz pulsation frequency has been deter- mined to lead to livability and production decreasing and efficiency of feed usage decreasing too.

Large Eddy Simulation of Film Cooling Involving Compound Angle Hole with Bulk Flow Pulsation

The effects of pulsations in the main flow on film cooling from a cylindrical hole with a spanwise injection angle (orientation angle) are analyzed using numerical methods. The hole is located on a flat plate with a 35° inclined injection angle, and the compound angle denotes the orientation and inclination angles. The film cooling flow fields for the sinusoidal flow pulsation of 36 Hz from a cylindrical hole with 0° and 30° orientation angles at the time-averaged blowing ratio of M = 0.5 are simulated via large eddy simulation (LES). The CFD results are validated using the experimental data and compared to the Reynolds-averaged Navier–Stokes (RANS) and URANS results. The results reveal that if the pulsation frequency goes from 0 to 36 Hz, the adiabatic film cooling effectiveness decreases regardless of the compound angle; however, the film cooling for the 30° orientation angle exhibits better performance than that for a simple angle (0°). Moreover, if 36 Hz pulsation is applied, the film cooling effectiveness obtained by unsteady RANS exhibits a large deviation from the experimental data, unlike the LES results. The credibility of the LES results relative to the experimental data is demonstrated by comparing the time-averaged η and the phase-averaged temperature contours. The LES results demonstrate that LES can more accurately predict η than the experimental data; in contrast, URANS results are highly overpredicted around the centerline of the coolant spreading. Thus, LES results are more consistent with the experimental results for the time- and phase-averaged temperature contours than the URANS results.

Pulsating Air Pollinator for Greenhouse Cultivation

Greenhouses has been accepted worldwide for round the year cultivation of quality produce. Greenhouse provides a desired climatic condition for crops but, at the same time, has obstacles for natural pollination. A pollinator was designed on the principle of pulsating air jet for pollination. The pollinator was developed with 3D printed three pulsation units with a provision for varied air pulsation frequency and angular movement to cover the complete flower bed. This can be easily moved by an operator in the greenhouse alleys. The developed pollinator was compared with hand pollination and pollination by a blower in tomato crops. The effects of Airflow rates, Pulsation frequencies of air and Exposure times on pollination efficiency and yield were studied. Experiments were performed in tomato plants cultivated in greenhouse. The highest pollination efficiency (83.66%) was achieved at 1.99 m 3 /min airflow rate, 23.50 Hz pulsation frequency and exposure time of 19.40 seconds; Average yield of 19.52 kg was observed at 1.99 m 3 /min of airflow rate, 22.25 Hz of pulsation frequency and exposure time of 15.78 seconds in flowers of 5 m length sections. The yield was also higher with developed pollinator compared to pollination by a blower (36.6%) and controlled plot (95.7%).

Large Eddy Simulation of Film Cooling with Bulk Flow Pulsation: Comparative Study of LES and RANS

The effects of bulk flow pulsations on film cooling in gas turbine blades were investigated by conducting large eddy simulation (LES) and Reynolds-averaged Navier–Stokes simulation (RANS). The film cooling flow fields under 32 Hz pulsation in the mainstream from a cylindrical hole inclined 35° to a flat plate at the average blowing ratio of M = 0.5 were numerically simulated. The LES results were compared to the experimental data of Seo, Lee, and Ligrani (1998) and Jung, Lee, and Ligrani (2001). The credibility of the LES results relative to the experimental data was demonstrated through a comparison of the time-averaged adiabatic film cooling effectiveness, time- and phase-averaged temperature contours, Q-criterion contours, time-averaged velocity profiles, and time- and phase-averaged Urms profiles with the corresponding RANS results. The adiabatic film cooling effectiveness predicted using LES agreed well with the experimental data, whereas RANS highly overpredicted the centerline effectiveness. RANS could not properly predict the injectant topology change in the streamwise normal plane, but LES reproduced it properly. In the case of the injectant trajectory, which greatly influences film cooling effectiveness, RANS could not properly predict the changes in the streamwise velocity peak due to flow pulsation, but they were predicted well with LES. RANS greatly underpredicted the streamwise velocity fluctuations, which determine the mixing of main flow and injectant, whereas LES prediction was close to the experimental data.

Hydrodynamic characteristics of sawdust in a pulsed slot-rectangular spouted bed

The effects of the pulsation frequency and slot dimensions on the hydrodynamic characteristics and the particle motion of sawdust of mean diameter 1.29 mm were investigated in a pulsed slot-rectangular spouted bed. Pulsation frequencies ranged from 1 to 5 Hz. The pulsed gas flow helped to mobilize the sawdust particles, regardless of the slot dimensions and initial bed height. The fountain height depended more on the slot dimensions than on the pulsation frequency. The time-average bed pressure drop increased with increasing pulsation frequency, while the maximum bed pressure drop was higher for low pulsation frequencies than for high frequency. A slot fully spanning the column thickness and a 3 Hz pulsation frequency were optimal conditions for spouting of sawdust particles without inert particles.

Investigation of the flow characteristics in a main nuclear power plant pump with eccentric impeller

The main pump is a key component in nuclear power plants. The operating stability and security of the main pump is crucial to the power plant operation. In this study, CFD simulations based on the detached eddy simulation method were used to study the flow characteristics in the pump. The overall performance, the pressure pulsations and the forces on the impeller are studied in detail. The predicted pump head and efficiency agree well with experimental data around the design flow condition even though undesirable flow is found in the guide vanes and circular volute. However, the CFD simulations did not correctly predict the pressure pulsation frequency even for the design flow condition. The experiments showed pressure pulsations at 50 Hz and at multiples of 50 Hz that were not predicted in the CFD simulation. After a small eccentricity was added to the impeller in the simulation, the 50 Hz pulsation was then captured with each impeller revolution in the CFD simulations at multiple pressure pulsation monitoring points. The amplitudes of the 50 Hz frequency and its multiples increase with the impeller eccentricity. Thus, the impeller eccentricity influences the pressure pulsations and the axial and radial forces. The impeller eccentricity has an important effect on the operating stability and security of the main pump. In addition, simulations must consider the impeller eccentricity for accurate analyses of the main pump in nuclear power plants.

Experimental study on hydrodynamic characteristics of gas–solid pulsed fluidized bed

Abstract The purpose of this study is to investigate the hydrodynamic characteristics of pulsed fluidized bed experimentally. Three different particles, silica with 196 μm mean diameter, alumina with 95 μm mean diameter and alumina with 10 μm mean diameter were introduced into the fluidized bed. Experiments were performed in 0.11 m ID and 0.5 m height fluidized bed. Pulsed airflow was introduced using square waves at 1 to 10 Hz pulsation frequency, which were generated using a solenoid valve connected to an electronic circuit. A high speed camera recorded the bed behavior to measure the bubble size and velocity. Results indicate that for alumina 95 μm the bed surface oscillation increases with decrease of pulsation frequency. Increasing the pulsation frequency decreases the bed expansion ratio and the bubble's diameter and velocity. In addition, the mean bed pressure drop becomes closer to the continuous airflow by increasing the pulsation frequency. This study indicates that the pulsating airflow decreases the minimum fluidization velocity and enhances fluidization of fine cohesive particles.

Radar detection of a localized 1.4 Hz pulsation in auroral plasma, simultaneous with pulsating optical emissions, during a substorm

Abstract. Many pulsating phenomena are associated with the auroral substorm. It has been considered that some of these phenomena involve kilometer-scale Alfvén waves coupling the magnetosphere and ionosphere. Electric field oscillations at the altitude of the ionosphere are a signature of such wave activity that could distinguish it from other sources of auroral particle precipitation, which may be simply tracers of magnetospheric activity. Therefore, a ground based diagnostic of kilometer-scale oscillating electric fields would be a valuable tool in the study of pulsations and the auroral substorm. In this study we attempt to develop such a tool in the Poker Flat incoherent scatter radar (PFISR). The central result is a statistically significant detection of a 1.4 Hz electric field oscillation associated with a similar oscillating optical emission, during the recovery phase of a substorm. The optical emissions also contain a bright, lower frequency (0.2 Hz) pulsation that does not show up in the radar backscatter. The fact that higher frequency oscillations are detected by the radar, whereas the bright, lower frequency optical pulsation is not detected by the radar, serves to strengthen a theoretical argument that the radar is sensitive to oscillating electric fields, but not to oscillating particle precipitation. Although it is difficult to make conclusions as to the physical mechanism, we do not find evidence for a plane-wave-like Alfvén wave; the detected structure is evident in only two of five adjacent beams. We emphasize that this is a new application for ISR, and that corroborating results are needed.

The Long‐Term Evolution of the Spin, Pulse Shape, and Orbit of the Accretion‐powered Millisecond Pulsar SAX J1808.4−3658

We present a 7 yr timing study of the 2.5 ms X-ray pulsar SAX J1808.4-3658, an X-ray transient with a recurrence time of ~2 yr, using data from the Rossi X-ray Timing Explorer covering 4 transient outbursts (1998-2005). We verify that the 401 Hz pulsation traces the spin frequency fundamental and not a harmonic. Substantial pulse shape variability, both stochastic and systematic, was observed during each outburst. Analysis of the systematic pulse shape changes suggests that, as an outburst dims, the X-ray "hot spot" on the pulsar surface drifts longitudinally and a second hot spot may appear. The overall pulse shape variability limits the ability to measure spin frequency evolution within a given X-ray outburst (and calls previous nudot measurements of this source into question), with typical upper limits of |nudot| < 2.5x10^{-14} Hz/s (2 sigma). However, combining data from all the outbursts shows with high (6 sigma) significance that the pulsar is undergoing long-term spin down at a rate nudot = (-5.6+/-2.0)x10^{-16} Hz/s, with most of the spin evolution occurring during X-ray quiescence. We discuss the possible contributions of magnetic propeller torques, magnetic dipole radiation, and gravitational radiation to the measured spin down, setting an upper limit of B < 1.5x10^8 G for the pulsar's surface dipole magnetic field and and Q/I < 5x10^{-9} for the fractional mass quadrupole moment. We also measured an orbital period derivative of Pdot = (3.5+/-0.2)x10^{-12} s/s. This surprising large Pdot is reminiscent of the large and quasi-cyclic orbital period variation observed in the so-called "black widow" millisecond radio pulsars, supporting speculation that SAX J1808.4-3658 may turn on as a radio pulsar during quiescence. In an appendix we derive an improved (0.15 arcsec) source position from optical data.

Heat transfer in a pulsed bubbling fluidized bed

Surface-to-bed heat transfer and pressure measurements were carried out in a 0.17 m ID pulsed bubbling fluidized bed with glass bead and silica sand particles having mean diameters ranging from 37 μm to 700 μm to investigate the effects of flow pulsation on heat transfer and bed hydrodynamics. A solenoid valve was used to supply pulsed air to the bed at 1 to 10 Hz. The bed surface was found to oscillate with the frequency of pulsation, the oscillation's amplitude decreasing with frequency. The standard deviation of the bed pressure drop in the pulsed bed was found to be larger than that in the conventional bed due to the acceleration force imposed by pulsation. For both Geldart B and A particles, high frequency pulsation (7, 10 Hz) enhances the heat transfer compared to continuous flow, the enhancement diminishing with superficial gas velocity and particle size. For Geldart B particles, the effect of pulsation on heat transfer ceases around U o/ U mf = 3.5, whereas 24% improvement in heat transfer coefficient was obtained for 60 μm glass bead particles (Group A) at superficial gas velocities as high as U o/ U mf = 27. Furthermore, in the fixed bed ( U o/ U mf < 1) for Geldart B particles, 1 Hz pulsation was found to be very effective resulting in two- to three-fold increase in heat transfer coefficient compared to continuous flow at the same superficial gas velocity. The flow pulsation loses its effect on heat transfer with increasing static bed height, i.e., when H bed/ D > 0.85.

Discovery of the Accretion-powered Millisecond X-Ray Pulsar IGR J00291+5934

We report on observations of the sixth accretion-powered millisecond pulsar, IGR J00291+5934, with the Rossi X-Ray Timing Explorer. The source is a faint recurrent X-ray transient initially identified by the International Gamma-Ray Astrophysics Laboratory. The 599 Hz (1.67 ms) pulsation had a fractional rms amplitude of 8% in the 2-20 keV range, and its shape was approximately sinusoidal. The pulses show an energy-dependent phase delay, with the 6-9 keV pulses arriving up to 85 μs earlier than those at lower energies. No X-ray bursts, dips, or eclipses were detected. The neutron star is in a circular 2.46 hr orbit with a very low-mass donor, most likely a brown dwarf. The binary parameters of the system are similar to those of the first known accreting millisecond pulsar, SAX J1808.4-3658. Assuming that the mass transfer is driven by gravitational radiation and that the 2004 outburst fluence is typical, the 3 yr recurrence time implies a distance of at least 4 kpc.

SAX J1808.4--3658 and the origin of X-ray variability in X-ray binaries and active galactic nuclei

The aperiodic X-ray variability in neutron star and black hole X-ray binaries (XRBs), and active galactic nuclei (AGN) shows a characteristic linear relationship between rms amplitude and flux, implying a multiplying-together or `coupling' of variability on different time-scales. Such a coupling may result from avalanches of flares, due to magnetic reconnection in an X-ray emitting corona. Alternatively this coupling may arise directly from the coupling of perturbations in the accretion flow, which propagate to the inner emitting regions and so modulate the X-ray emission. Here, we demonstrate explicitly that the component of aperiodic variability which carries the rms-flux relation in the accreting millisecond pulsar SAX J1808.4-3658 is also coupled to the 401 Hz pulsation in this source. This result implies that the rms-flux relation in SAX J1808.4-3658 is produced in the accretion flow on to the magnetic caps of the neutron star, and not in a corona. By extension we infer that propagating perturbations in the accretion flow, and not coronal flares, are the source of the rms-flux relations and hence the aperiodic variability in other XRBs and AGN.

Discovery of a High-Latitude Accreting Millisecond Pulsar in an Ultracompact Binary

We have identified the third known accretion-powered millisecond pulsar, XTE J0929-314, with the Rossi X-Ray Timing Explorer. The source is a faint, high Galactic latitude X-ray transient (d ≳ 5 kpc) that was in outburst during 2002 April-June. The 185 Hz (5.4 ms) pulsation had a fractional rms amplitude of 3%-7% and was generally broad and sinusoidal, although occasionally double-peaked. The hard X-ray pulses arrived up to 770 μs earlier than the soft X-ray pulses. The pulsar was spinning down at an average rate of = (-9.2 ± 0.4) × 10-14 Hz s-1; the spin-down torque may arise from magnetic coupling to the accretion disk, a magnetohydrodynamic wind, or gravitational radiation from the rapidly spinning pulsar. The pulsations were modulated by a 43.6 minute ultracompact binary orbit, yielding the smallest measured mass function (2.7 × 10-7 M☉) of any stellar binary. The binary parameters imply an ≃0.01 M☉ white dwarf donor and a moderately high inclination. We note that all three known accreting millisecond pulsars are X-ray transients in very close binaries with extremely low mass transfer rates. This is an important clue to the physics governing whether or not persistent millisecond pulsations are detected in low-mass X-ray binaries.

Dynamics of a pulsating monodisperse mixture

Dynamics equations for a monodisperse two-phase mixture are derived with regard to interphase forces due to a difference in velocity, the associated mass effect, and changes in the velocity field near particles. Numerical solutions are given for low-frequency (10-1-102 Hz) pulsation of the carrier phase. It was found that the residence time of the disperse phase in a column depends primarily on its retention capacity and pulsation frequency.