Peak Flow Speeds Research Articles

Solar Wind Entry Into Midtail Current Sheet via Low‐Latitude Mantle Under Dominant IMF By: ARTEMIS Observation

AbstractIt is expected from global simulations that the low‐latitude mantle may be an important pathway for the solar wind entry into the tail current sheet when interplanetary magnetic field (IMF) By is dominant, which is different from the pathways for northward or southward IMF dominant conditions. To evaluate this pathway and the predicted plasma asymmetries between the southern and northern lobes resulting from the low‐latitude mantle, we analyze 222 current sheet crossing events observed in the midtail. Each of the events is selected to have the spacecraft observe both lobes within 20 min. For the majority of the events, the different north‐south asymmetries of the lobe density observed on the dawnside and duskside corresponding to different IMF By directions are consistent with the appearance of the low‐latitude mantle plasma. No significant north‐south asymmetry in the lobe magnetic field strength is found so that the density asymmetry also results in north‐south asymmetric lobe Alfvén speed. Within the tail current sheet, the cross‐tail profiles show that density can be higher, but temperatures and peak flow speed lower, near the flanks than near midnight. Magnitudes of these current sheet plasma parameters are found to positively correlate with the values of the asymmetric lobe parameters concurrently observed, indicating that the low‐latitude mantle can be a particle source for the current sheet. Also, the asymmetric lobe parameters are positively correlated with some solar wind parameters. These good correlations support the expectation that the pathway through the low‐latitude mantle becomes more important as the IMF By becomes more dominant.

Strong Transient Flows Generated by Thermoplasmonic Bubble Nucleation.

The challenge of inducing and controlling localized fluid flows for generic force actuation and for achieving efficient mass transport in microfluidics is key to the development of next-generation miniaturized systems for chemistry and life sciences. Here we demonstrate a methodology for the robust generation and precise quantification of extremely strong flow transients driven by vapor bubble nucleation on spatially isolated plasmonic nanoantennas excited by light. The system is capable of producing peak flow speeds of the order mm/s at modulation rates up to ∼100 Hz in water, thus allowing for a variety of high-throughput applications. Analysis of flow dynamics and fluid viscosity dependence indicates that the transient originates in the rapid bubble expansion that follows nucleation rather than being strictly thermocapillary in nature.

Flow field impact assessment of a tidal farm in the Putuo-Hulu Channel

Waters surrounding Zhoushan Archipelago have the most abundant tidal current energy in China, which makes it a promising site for tidal farm construction in the future. Before deploying tidal current turbines, the potential environmental impacts on surrounding waters must be evaluated. In this work, we focus on the flow field impact assessment of an assumed tidal farm installed in Zhoushan Putuo-Hulu Channel. First, in order to evaluate the tidal characteristics there, a 2-month ADCP campaign is carried out, and a 3-D hydrodynamic model is established and validated with the in-situ measurements. Additionally, tidal current velocity and water depth as well as flow heading asymmetry information are used to evaluate the tidal stream exploitability within this channel. Second, a tidal farm consisting of 115 turbines is planned and assumed to be deployed throughout this channel. Blade element momentum method is used to numerically characterize the flow-turbine interactions, and then the spatial-temporal flow field variations caused by the assumed tidal farm are evaluated. It can be seen from the results that the peak flow speed reduction produced by the tidal farm could be over 0.5 m/s within the wake zones, while the flow velocity increment along two islands could reach 0.6 m/s. In particular, a flow speed phase shift phenomenon can be observed. Besides, the water level experiences a small overall rise, and the difference compared with the reference is within ±3.0 cm. Moreover, the seabed shear stress within the wake zones could drop by 65%, while the areas along the two islands might see over 100% increase, indicating the risk of sediment deposition and coastal erosion.

Effect of "Tongdu Tiaoshen" needling combined with swallowing training on dysphagia, cerebral blood flow and serum BDNF and NGF levels in ischemic stroke patients

To observe the efficacy of Tongdu Tiaoshen (dredging Governor Vessel and regulating mind) needling combined with swallowing training in the treatment of ischemic stroke (IS) with dysphagia, and to investigate its effect on cerebral blood flow and serum levels of brain-derived neurotrophic factor (BDNF) and nerve growth factor (NGF). A total of 100 IS inpatients with dysphagia were enrolled in the present study, and randomly and equally divided into control group and treatment group by using a random number table. The patients of the control group received routine swallowing training including tongue extending and retracting, cheek-muscle training, breathing exercise, and laryngopharyngeal exercise, beginning from the 2nd day after hospitalization. The patients of the treatment group received manual acupuncture stimulation of Dazhui (GV14), Fengfu (GV16), Shenting (GV24), Shendao (GV11), Baihui (GV20), Shuigou (GV26), etc., on the basic treatment as those mentioned in the control group. The treatment was conducted once daily, 5 times per week and for 4 successive weeks. The swallowing ability was tested by using video fluoroscopic swallowing study (VFSS), Kubota water swallowing test, and the standard swallowing function assessment (SSA) scale, separately, and patients' daily life quality was assessed by using swallowing related quality of life questionnaire (SWAL-QOL). The cerebral hemodynamics including mean blood flow velocity (Vm), maximum peak flow speed (Vs), and vascular resistance index (RI) of the bilateral cerebral arteries was detected by transcranial color Doppler ultrasound tests, and serum BDNF and NGF contents were assayed by enzyme linked immunosorbent assay. The therapeutic effect of swallowing ability was evaluated after the treatment. After 4 weeks' treatment, the scores of Kubata water swallowing test, SSA, and SWAL-QOL and RI were considerably decreased (P<0.01), and the VFSS scores, Vs and Vm levels as well as serum BDNF and NGF contents were significantly increased (P<0.01) in both groups compared with their own pre-treatment. Of the 48 and 49 cases in the control and treatment groups, 4 (8.33%) and 8(16.33%) were cured, 26 (54.17%) and 33 (67.35%) effective, 18 (37.50%) and 8 (16.33%) failed, with the effective rate being 62.50% and 83.67%, respectively. The therapeutic effect of the treatment group was significantly superior to that of the control group in the effective rate (P<0.05), and in lowering the scores of Kubota water swallowing test, SWAL-QOL, SSA, RI, and in up-regulating the scores of VFSS, Vs and Vm, and serum BDNF and NGF levels (P<0.01). Tongdu Tiaoshen needling combined with swallowing training is effective in improving swallowing ability, promoting cerebral blood flow and in up-regulating serum neurotrophic factor levels in patients with dysphagia after ischemic stroke.

Predictable changes in fish school characteristics due to a tidal turbine support structure

There is uncertainty on the ecological effects of tidal stream turbines. Concerns include animal collision with turbine blades, disruption of migratory and foraging behaviour, attraction of animals to prey aggregating around turbines, or conversely displacement of animals from preferred habitat.This study used concurrent ecological and physical measurements to show the predictability of fish school characteristics (presence, school area and height above seabed) in a high energy tidal site across spring/neap, ebb/flood and daily cycles, and how this changed around a turbine structure.The rate of schools and school area per hour increased by 1.74 and 1.75 times respectively around a turbine structure compared to observations under similar conditions without a turbine structure. The largest schools occurred at peak flow speeds and the vertical distribution of schools over the diel cycle was altered around the turbine structure.While predictable attraction or aggregation of prey may increase prey availability and predator foraging efficiency, attraction of predators has the potential to increase animal collision risk. Predictable changes from the installation of turbine structures can be used to estimate cumulative effects on predators at a population level. This study can guide a strategic approach to the monitoring and management of turbines and arrays.

Living in a trash can: turbulent convective flows impairDrosophilaflight performance

Turbulent flows associated with thermal convection are common in areas where the ground is heated by solar radiation, fermentation or other processes. However, it is unknown how these flow instabilities affect the locomotion of small insects, like fruit flies, that inhabit deserts and urban landscapes where surface temperatures can reach extreme values. We quantified flight performance of fruit flies (Drosophila melanogaster) traversing a chamber through still air and turbulent Rayleigh-Bénard convection cells produced by a vertical temperature gradient. A total of 34% of individuals were unable to reach the end of the chamber in convection, although peak flow speeds were modest relative to typical outdoor airflow. Individuals that were successful in convection were faster fliers and had larger wing areas than those that failed. All flies displayed higher pitch angles and lower mean flight speeds in convection. Successful individuals took longer to cross the chamber in convection, due to lower flight speeds and greater path sinuosity. All individuals displayed higher flapping frequencies in convection, and successful individuals also reduced stroke amplitude. Our results suggest that thermal convection poses a significant challenge for small fliers, resulting in increased travel times and energetic costs, or in some cases precluding insects from traversing these environments entirely.

Evershed and Counter-Evershed Flows in Sunspot MHD Simulations

Abstract There have been a few reports in the literature of counter-Evershed flows observed in well-developed sunspot penumbrae, i.e., flows directed toward the umbra along penumbral filaments. Here, we investigate the driving forces of such counter-Evershed flows in a radiative magnetohydrodynamic simulation of a sunspot, and compare them to the forces acting on the normal Evershed flow. The simulation covers a timespan of 100 solar hours and generates an Evershed outflow exceeding 8 km s−1 in the penumbra along radially aligned filaments where the magnetic field is almost horizontal. Additionally, the simulation produces a fast counter-Evershed flow (i.e., an inflow near ) in some regions within the penumbra, reaching peak flow speeds of ∼12 km s−1. The counter-Evershed flows are transient and typically last a few hours before they turn into outflows again. By using the kinetic energy equation and evaluating its various terms in the simulation box, we found that the Evershed flow occurs due to overturning convection in a strongly inclined magnetic field, while the counter-Evershed flows can be well-described as siphon flows.

Ultrasound for the assessment of distal shunt malfunction in adults with internal ventricular shunts

Shunts that are used for the treatment of hydrocephalus have a propensity towards malfunction, however, diagnosing a shunt malfunction can sometimes be a challenge. The purpose of this study was to investigate whether ultrasound technology can be safely and effectively used to assess for distal shunt malfunction. This was a prospective cohort study at a single institution. Eighteen adult patients that received a radionuclide shunt patency study also underwent an ultrasound shunt patency study. Ultrasound with Doppler technology was used to visualize flow through the shunt tubing following manual compression of the shunt reservoir. A peak flow speed was recorded and the results were compared to the results of the radionuclide shunt patency study. A Receiver Operating Characteristic (ROC) curve comparing the ultrasound to the radionuclide shunt patency study was generated, revealing an Area Under the Curve (AUC) of 0.95 (95% CI: 0.84–1.00). The ultrasound test performed maximally with a cutoff speed of ≤10cm/s as the criteria for malfunction, with a sensitivity of 100.00%, specificity of 90.91%, accuracy of 94.44%, positive likelihood ratio of 11.000 and negative likelihood ratio of 0.000 using the radionuclide study results as criteria for comparison. Overall, ultrasound has the potential to be a safe, quick, available and cost-effective screening test for patients with suspected distal shunt malfunction. The high sensitivity of the test makes it an attractive option for use as a screening method that could potentially reduce the number of cases requiring radionuclide shunt patency study.

Premixed methane/air gas deflagration simulations in closed-end and open-end tubes

The overpressures, flame velocities and flow speeds were investigated in closed-end and open-end tubes via numerical simulations. Our results suggest that the tube geometry influences the evolution of these parameters. The peak overpressure initially decreased and eventually increased with the aspect ratio in both types of tubes. The flow speed initially increased and then decreased with the propagation distance in the closed-end tube, but it increased with increasing distance in the open-end tube. Empirical equations relating the peak overpressure and the peak flow speed are presented. The flame velocities in the open-end tubes were always greater than those in the closed-end tubes, especially the maximum flame velocity. The open end promoted flame acceleration, while the closed end resulted in near-wall deceleration. The results provide a reference for future limited-space gas explosion studies.

Water-level controls on macro-tidal rip currents

Field measurements and numerical modelling have been used to investigate the water-level control of rip current dynamics on a macro-tidal beach. Field data collected over 32 complete tidal cycles, spanning a range of wave and tide conditions, demonstrate that rip current strength and behaviour is modulated at the semi-diurnal frequency by tide-induced changes in the water-level over bar/rip morphology. Peak flow speeds in the rip neck 〈uv〉 correspond to the time of maximum wave breaking 1.5h before and after low water.Alongshore-directed water surface gradients ∂η/∂y were measured along the feeder channel and around the ends of the inter-tidal bar, with head differences O(0.1m). The numerical model reproduced ∂η/∂y with a good level of skill and showed that ∂η/∂y and 〈uv〉 increase with the proportion of breaking waves Qb over the inter-tidal bar; but 〈uv〉 was maximised during peak Qb, maximum ∂η/∂y occurred when wave breaking moved offshore to the sub-tidal bar and Qb was reduced. Around low water, the forcing of the rip current by the alongshore pressure-driven feeder current was reduced by the decrease in Qb over the bar and feeder regions, but an offshore flow through the rip channel was maintained by a localised intensification of ∂η/∂y around the ends of the inter-tidal bar.

Independently evolved upper jaw protrusion mechanisms show convergent hydrodynamic function in teleost fishes

A protrusible upper jaw has independently evolved multiple times within teleosts and has been implicated in the success of two groups in particular: Acanthomorpha and Cypriniformes. We use digital particle image velocimetry (DPIV) to compare suction feeding flow dynamics in a representative of each of these clades: goldfish and bluegill. Using DPIV, we contrast the spatial pattern of flow, the temporal relationship between flow and head kinematics, and the contribution of jaw protrusion to the forces exerted on prey. As expected, the spatial patterns of flow were similar in the two species. However, goldfish were slower to reach maximal kinematic excursions, and were more flexible in the relative timing of jaw protrusion, other jaw movements and suction flows. Goldfish were also able to sustain flow speeds for a prolonged period of time as compared with bluegill, in part because goldfish generate lower peak flow speeds. In both species, jaw protrusion increased the force exerted on the prey. However, slower jaw protrusion in goldfish resulted in less augmentation of suction forces. This difference in force exerted on prey corresponds with differences in trophic niches and feeding behavior of the two species. The bluegill uses powerful suction to capture insect larvae whereas the goldfish uses winnowing to sort through detritus and sediment. The kinethmoid of goldfish may permit jaw protrusion that is independent of lower jaw movement, which could explain the ability of goldfish to decouple suction flows (due to buccal expansion) from upper jaw protrusion. Nevertheless, our results show that jaw protrusion allows both species to augment the force exerted on prey, suggesting that this is a fundamental benefit of jaw protrusion to suction feeders.

Scaling of suction-induced flows in bluegill: morphological and kinematic predictors for the ontogeny of feeding performance

During ontogeny, animals undergo changes in size and shape that result in shifts in performance, behavior and resource use. These ontogenetic changes provide an opportunity to test hypotheses about how the growth of structures affects biological functions. In the present study, we ask how ontogenetic changes in skull biomechanics affect the ability of bluegill sunfish, a high-performance suction feeder, to produce flow speeds and accelerations during suction feeding. The flow of water in front of the mouth was measured directly for fish ranging from young-of-year to large adults, using digital particle imaging velocimetry (DPIV). As bluegill size increased, the magnitude of peak flow speed they produced increased, and the effective suction distance increased because of increasing mouth size. However, throughout the size range, the timing of peak fluid speed remained unchanged, and flow was constrained to approximately one gape distance from the mouth. The observed scaling relationships between standard length and peak flow speed conformed to expectations derived from two biomechanical models, one based on morphological potential to produce suction pressure (the Suction Index model) and the other derived from a combination of morphological and kinematic variables (the Expanding Cone model). The success of these models in qualitatively predicting the observed allometry of induced flow speed reveals that the scaling of cranial morphology underlies the scaling of suction performance in bluegill.

Timing is everything: coordination of strike kinematics affects the force exerted by suction feeding fish on attached prey

During aquatic suction feeding, the predator opens its mouth and rapidly expands its buccal cavity, generating a flow field external to the mouth. The rapid expansion of the buccal cavity produces high fluid velocities and accelerations that extend only a short distance from the mouth (about half of one mouth diameter), and only persist for several milliseconds. Therefore, the predator must precisely time its strike to locate the prey within the narrow region of high flow, during the brief period when flow is at its peak. With flow being the agent for transferring force to the prey, the predator may enhance these forces by producing higher water velocities and faster acceleration at the mouth, but also through increasing the strike's accuracy, i.e. locating the prey closer to the mouth at the instant of peak flow speed. The objectives of this study were to directly measure forces exerted by bluegill Lepomis macrochirus on their prey and to determine how bluegill modify force output. Bluegill were offered ghost shrimp tethered to a load cell that recorded force at 5000 Hz, and feeding sequences were synchronously recorded using 500 Hz video. Peak forces exerted on attached 20 mm shrimp ranged from 0.005 N to 0.506 N. In accordance with the short duration of the strikes (average time to peak gape of approximately 13 ms), the forces recorded were brief (approximately 12 ms from initiation to peak force), and force magnitude declined rapidly after peak force. Statistical analysis indicated that rate of buccal expansion, and prey size, but not strike initiation distance, significantly affected peak force. These observed variables were used with results from flow visualization studies to estimate the flow at the prey's location, which allowed the calculation of drag, pressure gradient force and acceleration reaction force. The relationship between these calculated forces and the measured forces was strong, indicating that the model can be used to estimate forces from strike kinematics. This model was then used to study the effects of strike initiation distance on peak force and on the rate of increasing force. Comparisons of model output to empirical results indicated that bluegill time their strike so as to exert an average of approximately 70% of the peak possible force on the prey, and that the observed strike initiation distance corresponded to the distance that maximized modeled force on an attached prey. Our results highlight the ability of bluegill to produce high forces on their prey, and indicate that precision and visual acuity play important roles in prey acquisition, beyond their recognized role in prey detection.

Quantum swirling of superfluid helium films.

Circularly polarized third-sound resonances are used to drive up and drive down persistent flow states in the superfluid $^{4}\mathrm{He}$ film inside the resonator, analogous to swirling a classical fluid by agitation. The induced flow states involve vortex densities pinned by the roughness of the substrate which can include left and right circulating vortices present simultaneously within the resonator. Densities are measured to be on the order of ${10}^{5}$/${\mathrm{cm}}^{2}$. The peak flow speed of the wave oscillations necessary to swirl the film are near the critical velocity for dc flow dissipation.

The concentration of the large-scale solar magnetic field by a meridional surface flow

We calculate analytical and numerical solutions to the magnetic flux transport equation in the absence of new bipolar sources of flux, for several meridional flow profiles and a range of peak flow speeds. We find that a poleward flow with a broad profile and a nominal 10 m s−1 maximum speed concentrates the large-scale field into very small caps of less than 15° half-angle, with average field strengths of several tens of gauss, contrary to observations. A flow which reaches its peak speed at a relatively low latitude and then decreases rapidly to zero at higher latitudes leads to a large-scale field pattern which is consistent with observations. For such a flow, only lower latitude sunspot groups can contribute to interhemispheric flux annihilation and the resulting decay and reversal of the polar magnetic fields.