Pulsation Rate Research Articles

Implementation of a Sensorless Switched Reluctance Drive System for a Washing Machine with Reduced Vibration and Acoustic Noise

This article proposes a new method to reduce the vibration and acoustic noise in a sensorless reluctance drive system applied in a washing machine. By using the proposed fuzzy controller, the DC-bus voltage of the power converter can be suitably adjusted; then the rate of the current pulsations of the switched reluctance motor is obviously reduced. The vibration and acoustic noise of the washing machine, therefore, can be effectively reduced. In addition, some applications use a power factor correction stage to improve the input power factor. As a result, the washing machine has good performance, including a satisfactory power factor in the AC input side, reduced vibration, reduced acoustic noise, large torque, and good reliability. By using a 16-bit digital signal processor, a fully digital drive system, including a digital speed-loop controller and a digital current-loop controller, is implemented here. The hardware circuit of the drive system is very simple. The proposed system can start from a standstill. The adjustable speed range of the system is from 30 r/min to 1800 r/min. The details are discussed in this article, and several experimental results are presented to validate the theoretical analysis.

Development of a Hydraulic Actuator to Superimpose Oscillation in Metal-Forming Presses

A novel principle of a rotary piston valve and a high-frequency cylinder for a hydraulic actuation system are presented. This system will be utilized in metal-forming presses to superimpose a high-frequency oscillation on the movement of the ram. This technique was proven to enhance the forming parts quality, to extend the process limits and to reduce the forming force significantly. The key components of the valve are a stator and a rotary piston with radial drilled holes that is designed to provide a pulsating pressure and mass flow rate at a high frequency. A hydraulic cylinder is connected to the valve and converts the pulsating flow into a dynamic process force. The valve and the cylinder will be mounted on the bolster plate of a metal-forming press. In order to superimpose oscillation in the main forming direction, the cylinder is centered under the punch of the metal-forming tool. Three-dimensional computational fluid dynamics (CFD) simulations have been conducted to evaluate and to optimize the designs of the main components of the system. Hereby the commercial simulation code of ANSYS CFX was employed to determine the properties of the cylinder and the valve. Through its mesh motion technique, this simulation code allows the flow analysis between the rotary and the stationary part of the valve. Furthermore the dynamic characteristics of the system have been investigated under the influence of inertia and the compressibility of oil.

Evaluation of the Milking Machine Pulsator Characteristics by the Means of a Computer Controlled System

A computer-controlled system was developed in order to evaluate the working characteristics of the pulsator of a mechanical milking machine. The system contains a pulse generator, allowing the adjustment of both the pulsation rate (between 10 and 120 cycles/min) and extraction to massage ratio (between 10 and 90%), and a cyclic pressure indicator, which monitors the pressure applied to the teatcup short pulse tube. Two types of pulsators were tested in order to evaluate the precision and parameters of the developed system.

Response of Chrysaora quinquecirrha medusae to low temperature

Because of their high abundance in Chesapeake Bay, Chrysaora quinquecirrha medusae may be an important reservoir of organic matter. The timing and location of the decomposition of biomass from medusae may have implications for carbon cycling in the bay. Our objective was to identify the cause of C. quinquecirrha medusa disappearance to better understand when and where decomposition occurs. A time series of visual surface counts and vertical net hauls in the Choptank River, a tributary of Chesapeake Bay, showed that as temperatures approached 15°C, C. quinquecirrha medusae disappeared from the surface, but persisted in net hauls until temperatures reached 10°C. In order to test whether medusae sink upon cooling, we exposed C. quinquecirrha medusae to low temperatures in large static tanks and measured their depth and pulsation rates twice daily for at least 6 days. This procedure was repeated three times through the 2008 jellyfish season. On average, individuals exposed to temperatures below 15°C were found deeper and pulsed slower than those in the warmer control tank. This suggests that low temperatures cause the medusae to sink before cooling to the limit of their physiological tolerance and may have implications for the deposition of organic matter associated with the seasonal disappearance of medusae from Chesapeake Bay.

Physiology of heartbeat reversal in adult Drosophila melanogaster (Diptera: Drosophilidae)

Heartbeat patterns were monitored in the living bodies of decapitated adult flies using several electrocardiographic methods (pulse-light optocardiography, thermocardiography, strain-gauge cardiography). Unlike other insect species, in which there is a peristaltic segmental propagation of cardiac contractions, Drosophila uses extremely efficient synchronic cardiac contractions. The rate of synchronic cardiac pulsation, which is characterized by simultaneous propagation of anterograde systolic contractions along all the segments of the heart, is relatively fast (~ 4 Hz at room temperature). This pulsation is used mainly for the vigorous pumping of haemolymph into the head and thorax through a narrow elastic tube, the aorta (anterograde I heartbeat). In addition, this synchronic pulsation is also used to enhance the circulation of haemolymph throughout the abdominal body cavity (anterograde II heartbeat). The switch between thoracic (anterograde I) and abdominal (anterograde II) haemolymph circulation is regulated by peri- odically alternating, tetanic contractions and relaxations of the conical heart chamber (ventricle). In the latter there is a pair of slit- like apertures, which are closed or opened by contraction or relaxation of the organ, respectively. During contraction of the conical chamber, the apertures are tightly constricted for several seconds and haemolymph is pumped forwards into the aorta (anterograde I heartbeat). Conversely, during relaxation of the conical chamber, the apertures are wide open for a few seconds, haemolymph leaves the heart and leaks out through open apertures and circulates from the tail to the base of the abdomen. The backward oriented, retro- grade heartbeat recorded in other insects, has a lower frequency (1 to 2 Hz), occurs in Drosophila only sporadically and usually in the form of individual or twinned systolic peaks of large amplitude. Unlike the synchronic nature of the anterograde I and II cardiac contractions, propagation of the relatively slow retrograde heartbeat is by peristalsis. The newly discovered, compact ventricle with atrium and synchronic functioning of the insect heart shows structural and functional analogies with the functioning of the human heart.

Effect of a PEGylated Lipid on the Dispersion Stability and Dynamic Surface Tension of Aqueous DPPC and on the Interactions with Albumin

Dispersions of dipalmitoylphosphatidylcholine (DPPC) vesicles at 0.1 wt % (1000 ppm) in aqueous isotonic buffer solutions produced by extensive sonication were found to be colloidally stable for hours and days. They also had very low (<10 mN/m) dynamic surface tension minima (DSTM) under pulsating area conditions at 37 degrees C at 20 rpm area pulsation rate. When a 1000 ppm DPPC dispersion was mixed with a stable solution of 1000 ppm bovine serum albumin (BSA), it became colloidally unstable, aggregating within minutes, implying that heterocoagulation between lipid vesicles and albumin takes place. The heterocoagulated dispersion produced high DSTM because the lipid transport rate to the interface became slower. Moreover, the protein may have been transported to the surface faster and adsorbed more than the lipid at the surface. DPPC lipid vesicles were modified for reducing aggregation with other vesicles or with the protein with the addition of a small weight fraction of a neutral "PEGylated" lipid, with a covalently bonded poly(ethylene glycol) (PEG) group. The mixed vesicles were found to be quite more stable than the DPPC vesicles, remaining stable for months, apparently stabilized by steric forces. The colloidal stability at the initial stages of coagulation was evaluated quantitatively from the Fuchs-Smoluchowski stability ratio W. When the modified lipid vesicle dispersion was mixed with the albumin, the vesicles showed no tendency to aggregate with the albumin molecules for days, also probably because of steric repulsion between the PEGylated lipid and the protein. Finally, the mixed lipid dispersions maintained their low DSTM as did the DPPC vesicles without the albumin, and also in the presence of albumin. The results have implications on the use of DPPC or DPPC-based lipids in treating alveolar respiratory diseases without albumin inhibition of their surface tension lowering ability.

Mechanical contributions to astrocyte adhesion using a novel in vitro model of catheter obstruction

Drainage and diversion of cerebrospinal fluid (CSF) through shunt systems is the most common treatment for hydrocephalus, but complications due to tissue obstruction of the catheter occur in up to 61% of patients. Although shunt systems have undergone limited technological advancements to resist mammalian cell adhesion, there is a need to further reduce adhesion that can exacerbate obstruction. The high intrinsic variability in clinical studies and an inability to predict chronic adhesion of host cells in vitro while maintaining the environmental conditions observed in hydrocephalus have impeded progress. We designed the hydrocephalus shunt catheter bioreactor (HSCB) to measure inflammatory cell adhesion under experimentally manipulated conditions of CSF pressure, pulsation rate, and flow rates. For a 20-h period, astrocytes were perfused through the pulsatile flow system, and adhesion on silicone catheters was recorded. These results were compared with those obtained under static cell culture conditions. Astrocyte adhesion was significantly increased under conditions of increased flow rate (0.25 and 0.30 mL/min), and a trend toward increased adhesion was observed under conditions of elevated pressure and pulsation rate. Because the HSCB represents physiologic conditions more accurately than static cell culture, our results suggest that standard static cell culturing techniques are insufficient to model inflammatory cell adhesion on catheters used in the treatment of hydrocephalus and that changes to the ventricular microenvironment can alter the mechanisms of cellular adhesion. The HSCB represents a relevant test system and is an effective model system for the analysis of cellular adhesion and occlusion of shunt catheters.

Impact of location and flow rate oscillation of the pilot jet on the flow structures in swirling premixed flames

The paper investigates the swirling flow structures in an unconfined coannular swirl burner under different conditions, namely, with or without heat release, two locations of the pilot jet, and constant or pulsating mass flow rate in the pilot jet. Six turbulent premixed swirling flames as well as two isothermal turbulent swirling flow cases for reference are studied with the aid of large-eddy simulation. Detailed comparisons with experimental data are performed for velocity statistics, and generally good agreement is achieved. Furthermore, coherent structures are analyzed, and local power spectra are computed. In the nonreactive case with retracted pilot jet, a very strong precessing vortex core (PVC) is observed in both the numerical result and the experiment. The PVC is weak in the nonretracted case. In the reactive cases in which the whole central recirculation zone is enclosed in the high-temperature postflame region, the PVC is almost completely suppressed. In pulsating reactive jets, the vortex str...

Advancement of high power ultrasound technology for the destruction of surface active waterborne contaminants

The current paper explores recent advances in sonochemical techniques to improve the ultrasound-mediated degradation efficiency of surface active, waterborne contaminants. Sonochemical degradation efficiency of surface active contaminants generally has a strong dependence on the concentration of contaminant at the gas/solution surface of cavitation bubbles. This in turn depends on the thermodynamic and diffusion/kinetic-controlled adsorption properties of the surfactant at the rapidly pulsating gas/solution surface of acoustic cavitation bubbles. The adsorption properties of surfactants can be exploited to enhance their sonochemical decomposition by varying ultrasound exposure parameters such that changes in the nature of the bubble population (especially the bubble life-time and rate of pulsations) cause changes in the amount of surfactant that adsorbs to the gas/solution interface of cavitation bubbles. Herein we describe recent results on the effect of ultrasound frequency and pulsing mode on sonochemical degradation of surfactants in aqueous solutions and show how the exposure parameters can be adjusted in ways to produce more efficient decomposition of contaminants, even under exposure conditions where seemingly poor sonochemical activity is detected in the bulk solution. The relevance of these results to scale-up of ultrasound decontamination processes is discussed.

Abstract 5655: Autoantibodies Against Endothelin-1 Receptors Are Involved in the Pathogenesis of Pulmonary Arterial Hypertension

Background In patients with pulmonary arterial hypertension (PAH) production of endothelin-1 (ET-1) is increased and elevated ET-1 plasma levels correlate with PAH severity. After repeated detection of agonistic antibodies against the ET-1 A receptor (ETA) in PAH patients’ sera we assessed their prevalence and properties. Methods Using spontaneously beating rat neonatal cardiomyocytes as bioassay we analyzed sera of PAH patients for the presence of autoantibodies (AABs) against ETA receptors. AABs were purified by affinity chromatography. Results At the time of AAB testing, the pulmonary vascular resistance (PVR) in the 58 evaluated PAH patients varied between 500 and 1920 dyn • sec • cm −5 (median 1088 dyn • sec • cm −5 ) and 45 (77.6%) were in functional NYHA/WHO class ≥ III. Of these 58 patients 44 (78.7%) tested positive for AABs against ETA receptors. ET-1 and the AABs against ETA exerted agonistic negative chronotropic effects on the neonatal cardiomyocytes (decrease in pulsation rate), which were blocked by the ETA antagonist BQ610, but not by the ET-1 B receptor blocker BQ788. The AABs induced permanent stimulation without desensitization of the receptor mediated signal cascade and the effect increases with higher AAB concentrations. First attempts to eliminate by immunoadsorption these AABs (which appeared to belong to the IgG2 subclass) in 5 PAH patients showed encouraging results. After AAB removal, which was well tolerated by all patients, at the first controls performed 3 and 6 weeks later all 5 patients showed reduction in right ventricular diameters, lower pulmonary arterial pressure, higher cardiac index and improved exercise tolerance (increase in both VO 2 max and 6 minute walk distance). In one patient the AABs reappeared after 2 months and this AAB reappearance was associated with clinical worsening and PVR increase. Conclusions The majority of patients with advanced PAH tested positive for functional serum AABs against ETA These AABs activate the receptors, like ET-1, but prevent the desensitization of the receptor-mediated signal cascade normally seen with ongoing receptor stimulation. Our results suggest that these AABs could be involved in PAH pathogenesis. AAB removal by immunoadsorption might be a possible new therapeutic approach.

Sources of functional magnetic resonance imaging signal fluctuations in the human brain at rest: a 7 T study

Signal fluctuations in functional magnetic resonance imaging (fMRI) can result from a number of sources that may have a neuronal, physiologic or instrumental origin. To determine the relative contribution of these sources, we recorded physiological (respiration and cardiac) signals simultaneously with fMRI in human volunteers at rest with their eyes closed. State-of-the-art technology was used including high magnetic field (7 T), a multichannel detector array and high-resolution (3 mm(3)) echo-planar imaging. We investigated the relative contribution of thermal noise and other sources of variance to the observed fMRI signal fluctuations both in the visual cortex and in the whole brain gray matter. The following sources of variance were evaluated separately: low-frequency drifts due to scanner instability, effects correlated with respiratory and cardiac cycles, effects due to variability in the respiratory flow rate and cardiac rate, and other sources, tentatively attributed to spontaneous neuronal activity. We found that low-frequency drifts are the most significant source of fMRI signal fluctuations (3.0% signal change in the visual cortex, TE=32 ms), followed by spontaneous neuronal activity (2.9%), thermal noise (2.1%), effects due to variability in physiological rates (respiration 0.9%, heartbeat 0.9%), and correlated with physiological cycles (0.6%). We suggest the selection and use of four lagged physiological noise regressors as an effective model to explain the variance related to fluctuations in the rates of respiration volume change and cardiac pulsation. Our results also indicate that, compared to the whole brain gray matter, the visual cortex has higher sensitivity to changes in both the rate of respiration and the spontaneous resting-state activity. Under the conditions of this study, spontaneous neuronal activity is one of the major contributors to the measured fMRI signal fluctuations, increasing almost twofold relative to earlier experiments under similar conditions at 3 T.

Milk flow-controlled changes of pulsation ratio and pulsation rate affect milking characteristics in dairy cows

To test a system with milk flow-controlled pulsation, milk flow was recorded in 29 Holstein cows during machine milking. The three different treatments were routine milking (including a pre-stimulation of 50-70 s), milking with a minimum of teat preparation and milking with milk flow-controlled b-phase, i.e. with a gradually elongated b-phase of the pulsation cycle with increasing milk flow rate and shortening again during decreasing milk flow. For data evaluation the herd was divided into three groups based on the peak flow rate at routine milking (group 1: <3.2 kg/min; group 2: 3.2-4.5 kg/min; group 3: >4.5 kg/min). Compared with routine milking, milking with milk flow-controlled b-phase caused a significant elevation of the peak flow rate and the duration of incline lasted longer especially in cows with a peak flow rate of >3.2 kg/min in routine milking. In milking with a minimum of teat preparation the duration of incline lasted longer compared with the two other treatments. Bimodality of milk flow, i.e. delayed milk ejection at the start of milking, was most frequent at milking with a minimum of teat preparation. No significant differences between routine milking and milking with milk flow-controlled b-phase were detected for all other milking characteristics. In summary, milking with milk flow-controlled b-phase changes the course of milk removal, however mainly in cows with high peak flow rates.

Effects of a Low Vacuum Level on Vacuum Stability and Milking Parlor Performance for Sheep

In line with the current interest in animal welfare in animal husbandry, this study of two groups of 24 sheep compares milking performances at a low vacuum level (28 kPa) and at a standard level (42 kPa) that is normally used for sheep. The two working vacuum levels were tested with three different combinations of pulsator rate and pulsator ratio. Each of the experiments lasted 21 days, of which 11 were for adaptation and 10 were for collecting data. The milking machine used was a low line with 24 stalls, 12 milking units controlled by two operators, a milk line 74 mm in diameter, and a cluster with a total mass of 490 g. The measurements performed were the dynamics of the vacuum level in the short milk tube and the milk line during milking, and the time duration for each individual milking. There were no significant differences in fluctuations in vacuum in either the short tube or the milk line at the two vacuum levels used. By contrast, there was a significant increase in vacuum fluctuations in the short milk tube when the pulsator ratio changed from 50% to 60%. The milk flow time for each sheep increased on average by 17% with low vacuum, while the throughput of the system was reduced by some 4%, from 333 to 321 sheep/h.

Exact Navier-Stokes Solution for the Pulsatory Viscous Channel Flow with Arbitrary Pressure Gradient

In this article, an exact solution of the Navier–Stokes equations is presented for the motion of an incompressible viscous fluidinachannelwitharbitrarypressuredistribution.Ageneralizationispursuedbyexpressingthepressure signal in terms of Fourier coefficients. The flow is characterized by two principal parameters: the pulsation parameter based on the periodic pressure gradient, and the kinetic Reynolds number based on the pulsation frequency. By way of verification, it is shown that for large kinetic Reynolds numbers, the Poiseuille flow may be recovered. Conversely, the purely oscillatory solution by Rott is regained for large pulsation parameters. For sinusoidalpulsations,the flowrateisdeterminedandcomparedwiththesteady flowanalogobtainedunderthesame pressure gradient. The amount of flow amplification or attenuation is determined as a function of frequency and pulsation parameters. For large frequencies, the maximum flow rate is evaluated and related to the pulsation parameter. By characterizing the velocity, vorticity, and shear stress distributions, cases of flow reversal are identified. Conditions leading to flow reversal are delineated for small and large kinetic Reynolds numbers in both planar and axisymmetric chambers. For an appreciable pulsation rate, we find that the flow reverses when the pulsation parameter is increased to the point of exceeding the Stokes number. By evaluating the skin friction coefficient and its limiting value, design criteria for minimizing viscous losses are realized. The optimal frequency that maximizes the flow rate during pulsing is also determined. Finally, to elucidate the effect of curvature, comparisons between planar and axisymmetric flow results are undertaken. The family of exact solutions presented here can thus be useful in verifying and validating computational models of complex unsteady motions in both propulsiveandnonpropulsive applications. Theycan alsobeused toguide the designoffuel injectors andcontrolled experiments aimed at investigating the transitional behavior of periodic flows.

Preliminary Observations on the Response ofChironex fleckeri(Cnidaria: Cubozoa: Chirodropida) to Different Colors of Light

Cubozoans are well known for their attraction to light and light-colored objects. Two highly venomous types are a public safety concern in Australian waters and elsewhere: Chironex fleckeri, long considered the world's deadliest animal and colloquially called the box jellyfish; and the irukandjis, a group of at least 10 species that cause various degrees of debilitating illness. We were asked by the tourism industry whether there might be a color of light that box jellyfish and irukandjis are not attracted to, such that nighttime diving activities might pose less risk of being stung. Our preliminary trials with Chironex fleckeri indicated a marked positive response to lights of white, red, yellow, green, orange, and blue. All colors elicited a strong and directed attraction to light; however, medusae slowed down their pulsation rate, streamed out their tentacles, and performed a series of figure-eight patterns back and forth through the lighted area when exposed to blue light, which we interpreted as feeding behavior. This compares curiously with a report subsequent to our testing, in which the small, mangrove-inhabiting cubomedusa Tripedalia cystophora and the beach-dwelling Chiropsella bronzie demonstrate a peak sensitivity to blue-green light in the region of 500 nm, and that the former is behaviorally attracted to blue and green light, but ignores red. This leaves open the possibility that Irukandji species, which are more closely related to Tripedalia than to Chironex, may be blind to red.

An experimental study of pulsating turbulent flow in a pipe

An experimental study of pulsating turbulent flow in a pipe is reported in which measurements of instantaneous velocity were made using a two-component Laser Doppler Anemometer system. Local values of ensemble-averaged axial velocity, and radial and axial components of root-mean-square turbulent velocity fluctuation were obtained from the measurements. The frequency of the imposed pulsation of flow rate was varied systematically over a wide range covering inner scale dimensionless frequency ω ν / u τ 2 from 0.004 to 0.04. In terms of outer scale frequency ω D / u τ the corresponding values varied from 1.8 to 18. In addition, effects of changing the mean flow rate and the amplitude of flow rate pulsation were studied. Radial distributions of the amplitude of the modulation of ensemble-averaged axial velocity and the axial and radial components of RMS turbulent fluctuation, and their phase shifts relative to the imposed flow pulsation, are presented for conditions which include the low, intermediate and high frequency ranges. These add to and reinforce the body of information available from earlier experimental work and have enabled useful progress to be made in evaluating and validating approaches used for correlating such data. By relating observed behaviour to the fundamental processes of turbulence production, redistribution of turbulence energy between its components and radial propagation of turbulence, a good understanding of the results has been obtained.

Relaxation-diffusion processes in natural porous media: sedimentary rocks

Carr-Purcell-Meiboom-Gill (CPMG) experiments were made upon sedimentary rock samples at different RF pulsation rates. A dispersion of the transversal relaxation rate was observed. The experiments revealed that due to the diffusional processes there is a diminution of the second moment of the absorption line with the delay time between the RF pulses and the echo time, with a complex evolution characterized either as a stretched exponential or a power-law behavior as a function of the echo time, with parameters dependent on the characteristic time of the experiment, i.e., the delay between RF pulses. Results show that the observed behavior is dependent on permeability and geometrical properties of the sedimentary rock.

Vacuum level for opening the teat sphincter and the change in the teat end wall thickness in response to the machine milking of indigenous Greek goats

The aim of this paper was to study some of the teat characteristics involved in the milking ability of indigenous Greek goats such as the vacuum level of the milking machine that is required for the opening of the teat canal sphincter and the changes in the teat end wall thickness induced by milking. Thirty-six dams (12 of the first, 12 of the second and 12 of the third and subsequent lactations) were used after weaning (60 ± 5 days). Dams were milked twice a day (8:00 and 18:00 h) for 12 weeks in a milking parlour 1 × 12 side by side of Casse type with 6 milking units and a low milk line and air pipeline. The main functional characteristics of milking machine were: vacuum level 44 kPa, pulsation rate 90 pulsations/min and pulsation ratio 50:50. Every 14 days, during morning and evening milking the vacuum level that was required for the opening of the teat sphincter (VOTS) was measured. The measurement of teat end wall thickness (TEWT) was performed before and after milking. The results of this study showed that during the experimental period the mean VOTS was 23.57 ± 0.36 kPa and decreased significantly as the stage of lactation progressed (&lt;I&gt;P&lt;/I&gt;&lt; 0.001). The post-milking TEWT was 3.55% higher in comparison with that before milking (&lt;I&gt;P&lt;/I&gt; &lt; 0.01). A continuous and significant decrease in teat thickness was observed during the lactation stage (&lt;I&gt;P&lt;/I&gt; &lt; 0.001), which suggests a reaction to intramammary pressure and milk quantity in the udder. The TEWT was affected significantly by the parity (&lt;I&gt;P&lt;/I&gt; &lt; 0.01). A positive correlation was found between VOTS and TEWT before and after milking (0.4 and 0.36, respectively). It could be said that a lower vacuum level is required for the opening of the teat sphincter of the udder in goats of the indigenous Greek breed. The thicker teat end wall and more resistant sphincter could be less favourable in the machine milking of goats.

A membrane-based serpentine-shape pneumatic micropump with pumping performance modulated by fluidic resistance

This paper reports a new membrane-based pneumatic micropump with new serpentine-shape (S-shape) pneumatic channels intended for achieving high-throughput pumping in a microfluidic system at a relatively low pumping rate and a board flow rate range. The key feature of this design is the ability to modulate the pumping rates by fine-tuning the fluidic resistance of injected compressed air in the designed pneumatic microchannels and the chambers of the micropump. In the study, several S-shape pneumatic micropumps with various layouts were designed and fabricated based on thick-film photoresist lithography and polydimethylsiloxane (PDMS) replication processes. To investigate designs with a suitable pumping performance, S-shape pneumatic micropumps with varied lengths (1000, 5000 and 10 000 µm), varied widths (20, 40 and 200 µm) of the pneumatic microchannel bridging two rectangular pneumatic chambers, and different numbers of pneumatic channel bends (two and four U-shape bends) were designed and evaluated experimentally by using high-speed CCD-coupled microscopic observation of the movement of PDMS membrane pulsation and pumping rate measurements. The results revealed that under the experimental conditions studied, the layout of the S-shape pneumatic micropump with three rectangular pneumatic chambers, 5000 µm long and 40 µm wide pneumatic microchannel and four U-shape bends in the pneumatic microchannel was found to be capable of providing a broader pumping rate range from 0 to 539 µl h−1 compared to the other designs. As a whole, the experimental results demonstrate the use of fluidic resistance of injected air in a pneumatic micropump with S-shape layout to control its pumping performance, which largely expands the flexibility of its pumping application in a microfluidic system.

Three‐dimensional radar observation of a submillimeter meteoroid fragmentation

We present and discuss two examples of pulsating meteor events observed with the tristatic 930 MHz EISCAT UHF radar system. One of them provides the first strong observational evidence of a submillimeter‐sized meteoroid breaking apart into two distinct fragments. The received power fluctuates regularly in the time profiles of all three receivers, but the fluctuation frequencies are different. The pulsations are interpreted as being due to interference from two distinct scattering centers and the three detected pulsation rates are utilized to calculate the differential velocity of the fragments. The result is consistent with interference from two fragments of unequal cross‐sectional area over mass ratio, separating from each other due to different deceleration along the trajectory of their parent meteoroid. The other meteor event is an example of a meteoroid undergoing quasi‐continuous disintegration. This manifests itself as simultaneous pulsations at all three receivers. Both observations indicate a head echo target upper size limit of the order of half the 32 cm radar wavelength.