Large Pitches Research Articles

Effects of Nozzle Pitch Adaptation in Micro-Scale Liquid Jet Impingement

With ever increasing integration density of electronic components, the demand for cooling solutions capable of removing the heat generated by such systems grows along with it. It has been shown that a viable answer to this demand is the use of direct liquid jet impingement. While this method can generally be scaled to the cooling of large areas, this is restricted by the necessity of coolant flow rate scaling. In this study, the benefits and restrictions of using increased nozzle pitch to remedy the increasing demand for overall flow rate are investigated. To this end, a model is validated against experimental findings and then used for computational fluid dynamics simulations, exploring effects of the pitch change for micro-scale nozzle diameters and nozzle-to-target spacings. It is found that while this method is efficient in adjusting the tradeoff between total coolant flow rate and pressure drop up to a certain pint, the occurrence of a hydraulic jump in the cavity causes a deterioration of its effect for large nozzle pitches.

Rotor performance enhancement by alternating current dielectric barrier discharge plasma actuation

An experimental system was established to explore the plasma flow control effect for helicopter rotors in hover mode. With the plasma actuator applied at the leading edge of the rotor blades, alternating current dielectric barrier discharge (AC-DBD) plasma actuation was generated by a sinusoidal AC high-voltage generator. By direct force measurement, the influence of actuation parameters on the aerodynamic performance of the rotor was investigated at a tip Reynolds number of 1.7 × 105. AC-DBD actuation can delay the blade stall to more than 3° with a 20% increase of about in the thrust coefficient at the post-stall pitch. At a constant motor power driving the rotor, AC-DBD actuation could reduce the rotor’s torque at the stalled pitch and increase the rotational speed of the rotor. Also, AC-DBD actuation could maintain a relatively high hover efficiency of the rotor at large collective pitches. In a wide range of actuation parameters, AC-DBD plasma actuation could improve the rotor’s aerodynamic performance at large blade pitches. High-speed photography of the tuft motion on the blade’s upper surface showed that AC-DBD plasma actuation could promote the reattachment of the blade’s separation flow.

MATHEMATICAL ESTIMATION OF ROUGHNESS Rz OF THREADED SURFACE OBTAINED BY MACHINING METHOD

The paper presents a mathematical model of the helical surface roughness Rz, obtained by the form-generating method with a to-size tool with a standard profile of cutting tool inserts. This machining method has maximum productivity with large pitches of the helix. The surface roughness of the auger flight is an important parameter since it works in a friction pair with an elastic element. The resulting dependence makes it possible to predict surface roughness in any of its sections, considering the helix curvature, depending on the feed and the cutting tool tip radius. The obtained dependence allows comparing the numerical solution with the linearized one obtained by finding the minimum distance from the intersection points of the tool edge circles at helical surface adjacent cutting points to the straight line connecting these adjacent points.

Experimental PIV investigation of the PZT fans array coupling effect at high Reynolds numbers

Piezoelectric fan arrays are being increasingly emphasized for heat dissipation in small-sized electronic devices. In this study, PIV experiments were conducted to investigate the flow fields induced by piezoelectric fan arrays with different vibration modes and pitches at high Reynolds numbers (324< Re <509) in a stationary air environment. As a result, when the PZT fan array is vibrating in-phase, the saddle points in the time averaged flow field are formed and separated gradually as the pitch increases, the remnant vortex and the induced vortex interact to form a jet with a periodic oscillation in the direction. Jet velocity reaches a maximum at P = 3A. In counter-phase vibration, saddle points are separated from one region under large pitches, the interaction of counter-rotating induced vortices forms a vertical upward jet. The morphology of induced and remnant vortices with different vibration modes and array pitches are responsible for the jet formation and flow field pattern. The interaction of counter-rotating vortices in counter-phase vibration leads the jet intensity higher than in-phase vibration induced jet, the optimal setting of the PZT fan under this study is determined as P = 2.5A with counter-phase vibration. The experimental results provide validation for the simulation study and give guidance to the application

Physical, Physiological, and Technical Demands in Ultimate Frisbee Small-Sided Games: Influence of Pitch Size.

Small-sided games (SSGs) are common drills used in various team sports, but the exercise intensity in ultimate Frisbee SSG has not yet been investigated. To clarify the physical, physiological, and technical demands of ultimate Frisbee SSG, we investigated the influence of pitch size on exercise intensity during SSG. Nine male college ultimate Frisbee players played (3 vs. 3) SSG on small (SSGS: 30 × 15 m) and large (SSGL: 40 × 20 m) pitches; both SSGs comprised of four 4 min periods, interspersed by 5 min of passive recovery. Players’ mean heart rate (170 ± 8 and 171 ± 7 bpm), peak heart rate (184 ± 7 and 184 ± 5 bpm), and blood lactate concentration (11.3 ± 4.7 and 11.8 ± 4.6 mmol/L) were similar in SSGS and SSGL, respectively. The total distance covered (1984 ± 166 m and 1702 ± 80 m) and the distance covered during quick (860 ± 112 m and 696 ± 69 m) and high-intensity running (439 ± 95 and 255 ± 44) in SSGL were significantly longer than those in SSGS (p < 0.05). Conversely, the number of accelerations (45 ± 3 and 41 ± 3) and decelerations (44 ± 3 and 40 ± 4), catching errors (2 ± 1 and 1 ± 1), and turnovers (8 ± 2 and 6 ± 2) in SSGS were significantly greater than those in SSGL (p < 0.05). This study suggests that ultimate Frisbee SSG provides high-intensity training, which stimulates the glycolytic pathway. Furthermore, manipulating SSG pitch size effectively modulates the physical demands of SSG.

Influence of pitch size and goalkeepers on external and internal load during small-sided games in amateur soccer players

PurposeTo analyse the influence of goalkeepers during 4-a-side small-sided games, played in pitches of two different sizes (small: 30 × 20 m, large: 40 × 30 m).MethodsTotal distance covered (TD), distance covered at low- (LSD), moderate- (MSD), high- (HSD) and very high-speed (VHSD), average and maximal speed, Edwards’ training load (Edw-TL), time spent above 90% of maximal heart rate (T90%) and rate of perceived exertion (RPE) were monitored, in 18 amateur soccer players.ResultsHigher TD (mean difference: + 181 m, Hedge’s g: 0.93 and + 400 m, 3.37), MSD (+ 85 m, 0.79 and + 146 m, 1.64), HSD (+ 101 m, 1.41 and + 179 m, 3.26), VHSD (+ 30 m, 1.89 and + 35 m, 1.26), average speed (+ 0.65 km h−1, 0.88 and + 1.47 km h−1, 3.31) and maximal speed (+ 3.60 km h−1, 1.40 and + 3.58 km h−1, 1.40) were found in large than small pitch, without and with goalkeepers, respectively. Goalkeeper’s presence increased Edw-TL (+ 8.4 AU, 0.70) and reduced TD (− 141 m, 0.75), HSD (− 54 m, 0.75) and average speed (− 0.54 km h−1, 0.76) in small pitch and maximal speed (1.59 km h−1, 0.60 and 1.61 km h−1, 0.66) in both small and large pitches, respectively. RPE was higher (+ 20, 1.52) in the large than small pitch when the goalkeepers were present.ConclusionImplementing small-sided games, coaches should be aware that lower external load with similar internal load could be provided using small pitch with goalkeeper rather than either small goals or larger pitch. Furthermore, large small-sided games without goalkeeper may be the best choice for eliciting high training load.

Modeling the Self-Capacitance of an Irregular Solenoid

Irregular solenoids, i.e., sparse solenoids, varied-pitch solenoids, and noncylindrical solenoids, has started to appear recently for specific applications, and an accurate and fast modeling of their self-capacitance is necessary to accelerate the design and optimization process of such coils. Conventional capacitance modeling methods only work for coils, which are standard tightly wound cylindrical solenoids, but fail for irregular solenoids. Full-wave electromagnetic (EM) simulators provide good accuracy, but the computation time is usually long. In this article, a fast and accurate model to calculate the self-capacitance of an irregular solenoid is proposed. A modified turn-to-turn capacitance model, which considers the capacitance in the insulation layer of a wire as well as the air capacitance between the nearest neighbouring loops and the second nearest neighbouring loops is adopted. It works for solenoids of different types (e.g., sparse, varied-pitched, and noncylindrical ones). The accuracy of the proposed model is validated by comparing the calculation results to both those obtained by using commercial full-wave simulators and experimental results. For sparse solenoids, the proposed model is always accurate for coils with either small or large pitches. For varied-pitch solenoid and noncylindrical solenoid, the error rate of the proposed model is around 10%. Computational time wise, the computation time of the proposed model is reduced by over $10^4$ times compared to that of a commercial EM simulator whereas the accuracy is comparable.

An experimental study on the air side heat transfer performance of the perforated fin-tube heat exchangers under the frosting conditions

In this paper, perforated fins were applied to enhance the air side heat transfer performance under frosting conditions for fin-tube heat exchangers with large fin pitches. The frost mass, frost thickness, heat transfer rate and heat transfer coefficient of the perforated fin-tube heat exchangers were measured and analyzed. Although, the frost mass for the perforated fin-tube heat exchangers was 46.7% more than that for the plain fin. The total heat transfer rate and the heat transfer coefficient of the perforated fin was increased by 38.9% and 31.8%. Moreover, under the same heat transfer rate, the heat exchangers with the perforated fins generated less frost mass compared with the plain fin. Two empirical correlations for predicting the j-factor and frost mass of the perforated fin-tube heat exchangers were developed respectively. The correlations were functions of the Reynold number, dimensionless fin pitch, dimensionless temperature, and humidity and Fourier number. The deviations between these predictions and the corresponding measured experimental data fell within ±15.0%.

An Accurate Model for Fast Calculating the Resonant Frequency of an Irregular Solenoid

A fast and accurate calculation of the resonant frequency of a solenoid coil is needed in many applications, e.g., wireless power transfer and magnetic resonance imaging. It helps to accelerate the design and optimization of a coil. However, the existing calculation models for the key equivalent parameters, the inductance ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$L$ </tex-math></inline-formula> ) and the capacitance ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$C$ </tex-math></inline-formula> ), of the solenoid coils can only provide estimations for standard tightly wound cylindrical coils, and the accuracy is not high. There are no accurate models available for calculating <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$L$ </tex-math></inline-formula> , <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$C$ </tex-math></inline-formula> , and the resonant frequency when a solenoid becomes irregular, e.g., when it is sparse (with a large pitch), when it has nonuniform pitches, or when it is noncylindrical. In this paper, we propose a fast and accurate model for such an irregular solenoid coil to calculate its inductance, capacitance, and, thus, the resonant frequency. The accuracy of the proposed model is tested on the solenoid coils (with large pitches, nonuniform pitches, or noncylindrical shape) by comparing the calculated results to those using commercial simulation software and the measurement results. For a sparsely wound solenoid, the proposed model provides an accurate calculation of the inductance with a maximal pitch-to-wire-diameter ratio of 40 (an error rate of 8.33% at this ratio). For a varied-pitch solenoid and a noncylindrical one, an error rate of less than 5% can be achieved for a calculation of the inductance.

Understanding resolution limit of displacement Talbot lithography

Displacement Talbot lithography (DTL) is a new technique for patterning large areas with sub-micron periodic features with low cost. It has applications in fields that cannot justify the cost of deep-UV photolithography, such as plasmonics, photonic crystals, and metamaterials and competes with techniques, such as nanoimprint and laser interference lithography. It is based on the interference of coherent light through a periodically patterned photomask. However, the factors affecting the technique's resolution limit are unknown. Through computer simulations, we show the mask parameter's impact on the features' size that can be achieved and describe the separate figures of merit that should be optimized for successful patterning. Both amplitude and phase masks are considered for hexagonal and square arrays of mask openings. For large pitches, amplitude masks are shown to give the best resolution; whereas, for small pitches, phase masks are superior because the required exposure time is shorter. We also show how small changes in the mask pitch can dramatically affect the resolution achievable. As a result, this study provides important information for choosing new masks for DTL for targeted applications.

A Numerical Study on Determination of the Optimal Hole Diameter and Pitch Value for the Unglazed Transpired Solar Collectors

This investigation is concerned with the unglazed transpired solar collector (solar wall) type. With this purpose, the optimum hole arrangement has been determined by investigating the effect of hole diameter and pitch on the thermal efficiency of the system for different environmental condition. A thermodynamic model is used to simulate the heating process within the system. As a result, for extremely small hole diameters or extremely large hole pitches, the system works as a Trombe wall (glazed thermal storage wall) rather than an unglazed transpired solar collector because of the fact that there is not enough air flow through the absorber.

Tube-side heat transfer and friction characteristics of titanium corrugated tubes used for steam condensers

Usage of enhanced tubes in electric utility steam condensers have many advantages including smaller condenser size, additional electricity generation by lowered condenser back pressure, etc. In the present study, titanium corrugated tubes were tested for application to electric utility steam condensers. The tubes have relatively small corrugation heights and large corrugation pitches. In addition, the lowest helix angle is 18o, which is much lower than those of existing studies. The friction factor increased as corrugation pitch decreased and corrugation height increased. The penalty factor ranged from 1.09 to 1.89. The heat transfer coefficients showed similar trend with that of the friction factor. The enhancement factor ranged from 1.05 to 1.46. Exiting correlations did not adequately predict the present friction factors and heat transfer coefficients. The reason was attributed to the geometric difference of the present corrugated tubes (large p/e and small e/Di). New correlations were developed, which predicted the present data within ±20 %.

Asymmetric integral imaging system for a see-through three-dimensional display with background imaging function.

A see-through three-dimensional display with variable background imaging function is proposed. The proposed display system is based on integral imaging and consists of three lens arrays and a transparent flat-panel display. An asymmetric alignment of the three lens arrays enables variable background imaging. The background scene situated at any distance from the display system can be imaged at an intended distance from the display system. The possible imaging regions are shown. The proposed technique was experimentally verified using two optical systems that consisted of lens arrays with large and small lens pitches.

The Influence of Pitch Size on Running Performance and Physiological Responses During Hurling-Specific Small-Sided Games.

The current study examined how the impact of pitch dimensions influences physiological and running performance during 4-minute small-sided games (SSGs). Twenty-four (n = 24) hurling players were monitored with global positioning system and heart rate monitors during the in-season training period. Total distance (in meters), high-speed running distance (in meters) (≥17 km·h), very high-speed running distance (≥22 km·h) (in meters), total accelerations (n), acceleration distance (in meters), and peak and mean velocity (in kilometers per hour) were calculated. Additionally, SSGs rate of perceived exertion (RPESSG; AU), % maximum heart rate, and individualized training impulse (iTRIMP; AU) were collected. The current results show that the manipulation of SSGs pitch size has an impact on the running performance and physiological responses. The data showed that SSGs played on large pitches (SSG80 × 20 m) had greater running demands than medium (SSG60 × 20 m) or small (SSG40 × 20 m) pitches, with significantly more distance covered in all movement categories. Total distance covered at high speed was 354 ± 111 m on a large pitch, 254 ± 72 m on a medium pitch, and 198 ± 62 m on a small pitch. Large pitch dimensions resulted in greater physiological and perceptual demands on players (higher %HRmax, iTRIMP [AU], and RPESSG [AU]) compared with medium and small pitches. The current data help applied practitioners to understand further how modifying different aspects of SSGs can alter the running and physiological responses of players. Moreover, applied practitioners now have consistent information to design and optimize their training time in mixing the physical, technical, and tactical elements within specific SSGs pitch dimensions.

A numerical study on the air-side heat transfer of perforated finned-tube heat exchangers with large fin pitches

For a finned-tube heat exchangers (FHEXs) with large fin pitches, the enhancement of air-side heat transfer performance by using perforated fins has been numerically investigated in this paper. The effects of the perforation size and number on the air-side j factor and heat transfer rates of the FHEX are analyzed in detail at different large fin pitches. Numerical simulation results indicate that an optimal perforation design can be obtained to realize maximum increase in the j factor for the perforated FHEX compared with those of the plate FHEX without perforations. It is also found that the enhancement of the j factor increases with the rising air-side Reynolds number from 750 to 2350. For the perforated FHEX with fin pitch of 10.0mm, the j factor increases by 0.3% at Re=750 and 8.1% at Re=2350, respectively, with the optimal perforation design. In addition, the results present that the j factor increase of the perforated FHEX compared with that of the plain FHEX is more obvious at smaller fin pitches. When the fin pitch varies from 20.0mm to 7.5mm, the increase in the j factor varies from 2.7% to 9.2% at Re=2350. However, the total heat transfer surfaces of the perforated FHEX are reduced by perforations, its heat transfer rates may be decreased. The results show that the air-side heat transfer rate is reduced by 6.3% at Re=750 when the fin pitch is 7.5mm. For this case, two methods are further proposed to compensate total surfaces for the perforated FHEX in order to obtain higher air-side j factor while ensuring identical heat transfer rate.

The Influence of pitch size on running performance during Gaelic football small sided games

The current study examined the impact of small sided game (SSG) pitch dimensions on running performance during 4 min SSG. Twenty four elite Gaelic football players were monitored with GPS (4-Hz, VX Sport, New Zealand) over an in-season training period. Total distance (m) high speed running distance (m) (≥17 km·h-1), very high speed running distance (≥22 km·h-1) (m), total accelerations (n), acceleration distance (m) peak and mean velocity (km·h-1) were calculated. The current results show that the manipulation of SSG pitch size has an impact on the running performance responses. The data showed that SSG played on large pitches (SSG80x20m) had greater running demands than medium (SSG60x20m) or small (SSG40x20m) pitches, with significantly more distance covered in all movement categories. During SSGs the total distance covered were 515 ± 89 [426 – 594] m, 719 ± 145 [564 - 854] m and 1029 ± 189 [810 - 1128] m corresponding to a relative distance of 128 ± 22 [57 - 101] m·min-1, 179 ± 36 [91 - 163] m·min-1 and 257 ± 46 [139 - 231] m·min-1 for small, medium and large pitch dimensions respectively The current data may help applied practitioners to understand further how modifying different aspects of SSG can alter the running performance responses of players. Moreover, applied practitioners now have consistent information to design and optimise their training time in mixing the physical, technical and tactical elements within specific SSG pitch dimensions.

Airside performances of finned eight-tube heat exchangers

For applications in the relatively low temperature refrigeration systems with large constant temperature bath, the present work performed the experimental studies on the airside performances of the staggered finned eight-tube heat exchangers with large fin pitches. The airside heat transfer coefficients and pressure drops for three fin types and two fin pitches are obtained and analyzed. The heat transfer enhancement with louver fins is 11–16 % higher than the flat fins and that with sinusoidal corrugated fins is 1.1–3.4 % higher than the flat fins. Higher Re brings larger enhancement for various fins. Fin pitches show weak influence on heat transfer for eight tube rows. However, effects of fin pitch on heat transfer for both the sinusoidal corrugation and the louvered fin are larger than the flat fins and they are different from those for N ≤ 6. Airside Colburn j factor are compared with previous and it could be concluded that the airside j factor is almost constant for finned tube heat exchangers with eight tubes and large fin pitches, when Re is from 250 to 2500. The results are different from previous studies for fewer tube rows.

SNARC meets SPARC in fMRI—Interdependence of compatibility effects depends on semantic content

BackgroundStimulus-response compatibility (SRC) plays a major role in choice-reaction tasks. In specific cases, SRC leads to phenomena like the Spatial Numerical Association of Response Codes (SNARC) or the Spatial Pitch Association of Response Codes (SPARC) effect: small numbers or low pitches lead to faster responses when answered with the left hand, whereas large numbers or high pitches lead to faster responses when answered with the right hand. The previous study, investigating the combination of SNARC and SPARC with numbers spoken in different pitch heights, points towards an interdependency of both SNARC and SPARC compatibility effects, suggesting an automatic process. MethodsIn the present event-related functional magnetic resonance imaging (fMRI) study, we investigated the underlying neural activity when SNARC and SPARC are combined within the same auditory stimulus (numerical condition). Additionally, we included a categorical condition (the words “small” and “large”) as variation of the stimulus type. ResultsWe found neither an effect for SNARC nor for SPARC Compatibility in the neuronal data, whereas SNARC Compatibility was found in the behavioral data. According to the behavioral as well as the neuronal data, in the bilateral auditory cortex, SNARC and SPARC Compatibility interacts with Stimulus Type, i.e., whether numerical or categorical stimuli were presented. ConclusionsWe concluded that both effects are interdependent and that this interaction strongly depends on the semantic information.

Simulation of the cytoskeletal response of cells on grooved or patterned substrates.

We analyse the response of osteoblasts on grooved substrates via a model that accounts for the cooperative feedback between intracellular signalling, focal adhesion development and stress fibre contractility. The grooved substrate is modelled as a pattern of alternating strips on which the cell can adhere and strips on which adhesion is inhibited. The coupled modelling scheme is shown to capture some key experimental observations including (i) the observation that osteoblasts orient themselves randomly on substrates with groove pitches less than about 150 nm but they align themselves with the direction of the grooves on substrates with larger pitches and (ii) actin fibres bridge over the grooves on substrates with groove pitches less than about 150 nm but form a network of fibres aligned with the ridges, with nearly no fibres across the grooves, for substrates with groove pitches greater than about 300 nm. Using the model, we demonstrate that the degree of bridging of the stress fibres across the grooves, and consequently the cell orientation, is governed by the diffusion of signalling proteins activated at the focal adhesion sites on the ridges. For large groove pitches, the signalling proteins are dephosphorylated before they can reach the regions of the cell above the grooves and hence stress fibres cannot form in those parts of the cell. On the other hand, the stress fibre activation signal diffuses to a reasonably spatially homogeneous level on substrates with small groove pitches and hence stable stress fibres develop across the grooves in these cases. The model thus rationalizes the responsiveness of osteoblasts to the topography of substrates based on the complex feedback involving focal adhesion formation on the ridges, the triggering of signalling pathways by these adhesions and the activation of stress fibre networks by these signals.

Temperature dependency of the emission properties from positioned In(Ga)As/GaAs quantum dots

In this letter we study the influence of temperature and excitation power on the emission linewidth from site-controlled InGaAs/GaAs quantum dots grown on nanoholes defined by electron beam lithography and wet chemical etching. We identify thermal electron activation as well as direct exciton loss as the dominant intensity quenching channels. Additionally, we carefully analyze the effects of optical and acoustic phonons as well as close-by defects on the emission linewidth by means of temperature and power dependent micro-photoluminescence on single quantum dots with large pitches.