Uniform Cross-sectional Area Research Articles

American English schwa characteristics in the context of vowel reduction

The mid-central unrounded vowel schwa has been understood as a vocalic produced with a uniform cross-sectional area of the vocal tract that is correlated with formant frequencies occupying the center of the acoustic vowel space. As such, schwas have also been associated with reduced vowels. Vowel reduction occurs in a variety of contexts and factors, and it is commonly described as centralization toward the middle of the vowel space or a migration of formant frequencies toward those associated with a tube of uniform cross-sectional areas. Nonetheless, little is known regarding the extent to which reduced vowels approximate schwa values. The purpose of this study was to establish a within-speaker reference of schwa in the context of vowel reduction. Two questions were addressed. First, do the acoustic characteristics of schwa correspond to the centroid of vowel space? Second, how do schwa values compare to those of reduced vowels? Formant frequencies of vowels in citation and connected speech tasks were compared to schwa productions for the same speaker. It was hypothesized that schwa can be characterized as a centroid region defined within individual speakers’ vowel spaces. It was further hypothesized that reduced vowels in connected speech would closely approximate this centroid region.

Investigation of the Elastic Modulus Effect on Free Vibration Characteristics of Fiber Reinforced Polymer Composite Beams Made of Various Fundamental Shapes

Woven fiber reinforced polymer composites plays major role in structural applications. Structures subjected to dynamic situations, this leads to increased attention in finding characteristic behaviour/performance of FRP composites beams under vibrating conditions. The objective of this work is to understand and investigate the influence of cross sectional shapes of beams on successive vibration resonance frequencies and its damping performance under cantilever end conditions. The beams were fabricated by hand lay-up method in two different modulus material and cross sections like I and channel; maintaining uniform cross sectional area and moment of inertia apart from length of the beams using woven carbon fibre. The investigation was performed by impulse frequency response method using standard test procedure on low modulus Glass/epoxy composite beams and compared with high modulus Carbon/epoxy beams. Frequency response curve of I and channel shaped beams were compared for their damping performance. The modal frequencies of all fabricated beams were obtained using MEScopeVES® software and modal resonant frequencies, loss factor were compared against shapes.

Design of Pocket Dies for Metal Extrusion Using the Finite Element Method

Metal extrusion is currently very beneficial for producing workpieces with long dimensions or when a uniform cross section area is required. Design of extrusion dies, which results to the shape, geometry and size of the workpiece, is the main factor for quality, productivity and durability of the products. Besides improving the bearing length, a die pocket is a good solution to effectively control the velocity of material flow into the die hole. Therefore, this study aimed to evaluate the structures of die pockets that influence the material flow in the extrusion process. Thus, the finite element method (FEM) was used to determine the parameters that affect the strength of the extrusion die due to the maximum stresses which occurred on the die and pocket. From this study, it was found that the circular shaped pocket with 31degrees pocket angle, 22 mm pocket die thickness and made of titanium alloy provided the maximum strengths and safety factors. This result from the simulations can sufficiently predict the risk of damages on the extrusion die and pocket for further extension of the tool’s life cycle.

Hot Spline Forming of Ultra-High Strength Steel Gear Drum Using Resistance Heating

A hot spline forming process of die-quenched gear drums using resistance heating of a side wall of a cup formed by cold deep drawing and ironing was developed. The side wall having uniform cross-sectional area is resistance-heated by passage of the current in the axial direction, the heated side wall of the drawn cup is ironed and is finally die-quenched. The gear drum was successfully formed and the hardness was between 400 and 500 HV. Not only the formability was improved but also the formed dram was hardly oxidised because of rapid resistance heating.

Introducing Some Correlations to Calculate Entropy Generation in Extended Surfaces with Uniform Cross Sectional Area

The optimum length of extended surfaces with uniform cross sectional area has been analyzed numerically, based on the concept of entropy generation minimization. The extended surface studied is a pin fin. The rate of entropy generation is investigated for different boundary conditions. First, some correlations are introduced to calculate this rate, and then a model is offered to find optimum length of the fin for adiabatic and convection heat transfer boundary conditions. The accuracy of the model presented is compared with experimental data. Although Bejan introduced a correlation to calculate optimal Reynolds number and consequently the optimum length of a pin fin, but the results showed the new method has high accuracy compared with the Bejan method. Also, it is found that there is a strong relation between optimum length (based on the entropy generation minimization concept) in one side, and temperature distribution in the other side.

Experimental investigation of natural circulation in a symmetrical loop under large scale rolling motion conditions

In ocean environment, the ship motion significantly affects the natural circulation behavior in ship-based integrated-type reactor. This paper theoretically and experimentally investigated natural circulation characteristics in symmetrical loops under rolling condition. Experiments were carried out on a test loop with a symmetrical configuration by simulating the structure of an accrual reactor. The theoretical results revealed that only angular acceleration contributes to the resultant force under zero power rolling condition. In a closed circuit with a uniform cross-section area, the angular acceleration force integral is proportional to the angular acceleration and the area enclosed by the circuit. The integral value varies over time and causes flow oscillations. However, the angular acceleration force does not influence the flow status in the shared part of the two symmetrical neighbor circuits due to force interactions. Rolling experiments with a zero power load confirmed these results. Full power experiments under rolling condition exhibited observable flow rate and temperature oscillations in each branch of the flow channel. The oscillations in the side flow channels had the same values for both the period and the phase with the variation of rolling angle. The angular acceleration force was the main cause of this. The oscillations in the middle channel had a period half the value of the rolling period. The periodical variation of the vertical component of gravity caused this. The horizontal component of gravity was out-phasing with angular acceleration. Therefore, it alleviated oscillation in the side channels. The experimental results showed that for the same rolling period, as the rolling angle increased, the average flow rate decreased and oscillation amplitudes increased. Also, as the power load increased, the oscillations in the middle channel increased and the oscillation in the side channel decreased.

THE IMPORTANCE OF GEOMETRIC EFFECTS IN CORONAL LOOP MODELS

We systematically investigate the effects of geometrical assumptions in one-dimensional (1D) models of coronal loops. Many investigations of coronal loops have been based on restrictive assumptions, including symmetry in the loop shape and heating profile, and a uniform cross-sectional area. Starting with a solution for a symmetric uniform-area loop with uniform heating, we gradually relax these restrictive assumptions to consider the effects of nonuniform area, nonuniform heating, a nonsymmetric loop shape, and nonsymmetric heating, to show that the character of the solutions can change in important ways. We find that loops with nonuniform cross-sectional area are more likely to experience thermal nonequilibrium, and that they produce significantly enhanced coronal emission, compared with their uniform-area counterparts. We identify a process of incomplete condensation in loops experiencing thermal nonequilibrium during which the coronal parts of loops never fully cool to chromospheric temperatures. These solutions are characterized by persistent siphon flows. Their properties agree with observations (Lionello et al.) and may not suffer from the drawbacks that led Klimchuk et al. to conclude that thermal nonequilibrium is not consistent with observations. We show that our 1D results are qualitatively similar to those seen in a three-dimensional model of an active region. Our results suggest that thermal nonequilibrium may play an important role in the behavior of coronal loops, and that its dismissal by Klimchuk et al., whose model suffered from some of the restrictive assumptions we described, may have been premature.

Spline forming of ultra-high strength gear drum using resistance heating of side wall of cup

A spline forming process of an ultra-high strength steel gear drum using resistance heating of a side wall of a cup formed by cold deep drawing and ironing was developed. The side wall having uniform cross-sectional area was heated by the electrification in the axial direction. The uniformity of the temperature was improved by inserting copper foils between the electrode and the side wall, and by decreasing the area of contact. Although the high strength steel cup was fractured by cold spline forming, the gear drum was successfully formed by the heating.

Dc electrokinetic transport of cylindrical cells in straight microchannels.

Electrokinetic transport of cylindrical cells under dc electric fields in a straight microfluidic channel is experimentally and numerically investigated with emphasis on the dielectrophoretic (DEP) effect on their orientation variations. A two-dimensional multiphysics model, composed of the Navier-Stokes equations for the fluid flow and the Laplace equation for the electric potential defined in an arbitrary Lagrangian-Eulerian framework, is employed to capture the transient electrokinetic motion of cylindrical cells. The numerical predictions of the particle transport are in quantitative agreement with the obtained experimental results, suggesting that the DEP effect should be taken into account to study the electrokinetic transport of cylindrical particles even in a straight microchannel with uniform cross-sectional area. A comprehensive parametric study indicates that cylindrical particles would experience an oscillatory motion under low electric fields. However, they are aligned with their longest axis parallel to the imposed electric field under high electric fields due to the induced DEP effect.

A study of PZT valveless micropump with asymmetric obstacles

The results of a study on a new type of PZT valveless micropump with asymmetric obstacles are presented in this paper. The valveless micropump was made through a MEMS fabrication process by using simply only one photo mask. Asymmetric obstacles are used for the flow directing device instead of the diffuser/nozzle elements used in previous studies. In this study, numerical simulations were also carried out to evaluate the design and the performance of the new micropump. The main feature of the present micropump is that it has a uniform cross-section area across the micro-channel, which gives many advantages. The differential pressure head and the pumping flow rate can be adjusted easily by using obstacles of different shapes and changing the PZT operating frequency without changing the dimensions of the micro-channel. In this experiment, the performance of the micropump was evaluated by measuring the pressure head difference and the flow rate as the input voltage ranged from 20 to 40 V, a range much lower than those in previous studies. The pumping pressure can reach a maximum of 1.2 kPa, and the maximum net volume flow rate is 156 μl/min. These test data indicate that this micropump fulfills the demands for most micro-fluidic systems. Moreover, the present device can be easily applied to complex systems with combinations of several pumps and microchannels in the future.

Analysis of Turbulent Flow in 180 deg Turning Ducts With and Without Guide Vanes

This paper presents a numerical study of the turbulent flows through a number of 2D and 3D 180 deg U-ducts, with and without guide vanes, using the Reynolds-averaged Navier–Stokes method. Computations have been first carried out for a 2D U-duct flow (W/H=1.0) with four turbulence models (V2F, k-ε, shear stress transport (SST), and Reynolds stress). The models’ capability for predicting streamline curvature effects on turbulence and separation has been assessed, using flow and turbulence data. The effects of adding a guide vane inside the bend have been analyzed to reduce/avoid flow separation. Three vanes with different radial locations have been studied, and the mechanism for pressure loss reduction has been examined. Analyses have been performed for turbulent flows in 3D U-ducts with square cross section and sharp 180 deg turning (W/D=0.2), similar to the U-bends in typical turbine blade cooling passages. The predictions are compared with the data of outer-wall pressure. The effects of the guide vane and outer-wall shape on the flow separation, secondary-flow vortices, and pressure loss have been evaluated. The combined vane and uniform cross section area are found to improve the flow distribution and reduce the pressure loss significantly.

Efficiency and Optimization of a Straight Rectangular Fin with Combined Heat and Mass Transfer

An analysis was carried out to study the efficiency of a straight rectangular fin with a uniform cross-section area when subjected to simultaneous heat and mass transfer mechanisms. The temperature and humidity ratio differences are the driving forces for the heat and mass transfer, respectively. Numerical solutions are obtained for the temperature distribution over the fin surface when the fin surface is dry, fully wet, and partially wet. The psychrometric correlation of an air-water vapor mixture was used to simulate the relation between the temperature and humidity ratio instead of the linear approximate correlations used in the literature. The effect of atmospheric pressure on the fin efficiency was also studied, in addition to fin optimum thickness for specific operating conditions. The numerical solution was compared with those of previous studies in order to find if the linear model in the published analytical results are near to the real situation. It is found that the linear model for the relation between the humidity ratio and the temperature used by Wu and Bong is a reasonable engineering approximation for small values of the fin parameter and at low relative humidities.

An Analog Integrated-Circuit Vocal Tract

We present the first experimental integrated-circuit vocal tract by mapping fluid volume velocity to current, fluid pressure to voltage, and linear and nonlinear mechanical impedances to linear and nonlinear electrical impedances. The 275 muW analog vocal tract chip includes a 16-stage cascade of two-port pi-elements that forms a tunable transmission line, electronically variable impedances, and a current source as the glottal source. A nonlinear resistor models laminar and turbulent flow in the vocal tract. The measured SNR at the output of the analog vocal tract is 64, 66, and 63 dB for the first three formant resonances of a vocal tract with uniform cross-sectional area. The analog vocal tract can be used with auditory processors in a feedback speech locked loop-analogous to a phase locked loop-to implement speech recognition that is potentially robust in noise. Our use of a physiological model of the human vocal tract enables the analog vocal tract chip to synthesize speech signals of interest, using articulatory parameters that are intrinsically compact and linearly interpolatable.

Jet screech reduction with perforated flat reflector

In the present experimental study, investigations have been carried out to evaluate the performance of the new control technique of jet screech with different perforated flat reflectors. Mainly two types of porous flat reflectors had been used in the experiment. One reflector (reflector-V) designed for placing the reflector surface vertical to the jet axis, when, another type of reflector (reflector-H) designed for placing the reflecting surface horizontal to the jet axis. In both cases the reflectors had been placed at the nozzle (base tube with uniform cross-sectional area) exit. The diameter of the reflector-V was 15D when the diameter of the reflector-H was 10D. The porous area of the reflector-V was 6D and 4.5D for reflector-H where D indicated the diameter of the nozzle exit. The placement of the reflector at the exit of the nozzle reduces the sound pressure at the nozzle exit. Thus the muted sound can not excite the unstable disturbance at the nozzle exit and the loop of the feedback mechanism disappeared, finally, the generation of jet screech be cancelled. The suction space located at the back side of the porous surface of the reflector-V improves the efficiency of the screech control technique. However, in the case of reflector-H, the receptivity process of feedback loop had been controlled by reducing the disturbances at the effective shock fronts as well as at the nozzle exit. The performance of the proposed method was verified with a flat reflector concept and good performance in jet screech suppression has been confirmed in the case of porous reflector.

Determination of the Temperature Distribution The Perforated Fins Under Natural Convection

This work treats the problem of heat transfer for perforated fins under natural convection. The temperature distribution is examined for an array of rectangular fins (15 fins) with uniform cross-sectional area (100×270 mm) embedded with various vertical body perforations that extend through the fin thickness. The patterns of perforations include 18 circular perforations (holes). Experiments were carried out in an experimental facility that was specifically design and constructed for this purpose. The heat transfer rate and the coefficient of heat transfer increases with perforation diameter increased.

DETERMINATION OF THE TEMPERATURE DISTRIBUTION THE PERFORATED FINS UNDER

This work treats the problem of heat transfer for perforated fins under natural convection. The temperature distribution is examined for an array of rectangular fins (15 fins) with uniform cross-sectional area (100x270 mm) embedded with various vertical body perforations that extend through the fin thickness. The patterns of perforations include 18 circular perforations (holes). Experiments were carried out in an experimental facility that was specifically design and constructed for this purpose. The heat transfer rate and the coefficient of heat transfer increases with perforation diameter increased.

Comment on "Cooling Fin Design"

N A recent paper, Bertola and Cafaro [1] posed a design problem for cooling fins whereby the temperature boundary condition at bothends(Tb atthebaseand Tt atthetip)andtheheat fluxatthebase qb were specified, and it was desired to determine the corresponding fin length L. Their analysis appeared to assume a free-ended tip, as indicatedbyFig.1intheirpaper,andtherateofheattransferatthetip was not considered. Their mathematical analysis based on onedimensional, steady-state heat conduction led them to conclude that for fixedvaluesof Tb and Tt,thereisarangeof qb forwhichthereare two possible solutions for L. Bertola and Cafaro attributed the existenceoftwopossible solutionstotheuseofthreeconditions(Tb, Tt, and qb) in solving the pertaining second-order differential equation. It is demonstrated in this Comment that the two solutions, while mathematically possible, correspond to two completely different physical arrangements and thus, they cannot be considered in design as alternative solutions to the same set of conditions. It is also shown that fins with prescribed tip temperature are typically connected to another body at the tip, except for a certain restrictive condition. Consider a fin of uniform cross-sectional area Ac, perimeter P, length L, thermal conductivity k, base temperature Tb, and tip temperature Tt immersed in a medium at a temperature Ta with a uniform convection heat transfer coefficient h (as shown in Fig. 1). The governing energy-balance equation is given by [2–4]

Architecture of optimal transport networks

We analyze the structure of networks minimizing the global resistance to flow (or dissipative energy) with respect to two different constraints: fixed total channel volume and fixed total channel surface area. First, we show that channels must be straight and have uniform cross-sectional areas in such optimal networks. We then establish a relation between the cross-sectional areas of adjoining channels at each junction. Indeed, this relation is a generalization of Murray's law, originally established in the context of local optimization. We establish a relation too between angles and cross-sectional areas of adjoining channels at each junction, which can be represented as a vectorial force balance equation, where the force weight depends on the channel cross-sectional area. A scaling law between the minimal resistance value and the total volume or surface area value is also derived from the analysis. Furthermore, we show that no more than three or four channels meet at each junction of optimal bidimensional networks, depending on the flow profile (e.g., Poiseuille-like or pluglike) and the considered constraint (fixed volume or surface area). In particular, we show that sources are directly connected to wells, without intermediate junctions, for minimal resistance networks preserving the total channel volume in case of plug flow regime. Finally, all these results are compared with the structure of natural networks.

Prominence Formation by Thermal Nonequilibrium in the Sheared‐Arcade Model

The existence of solar prominences—cool, dense, filamented plasma suspended in the corona above magnetic neutral lines—has long been an outstanding problem in solar physics. In earlier numerical studies we identified a mechanism, thermal nonequilibrium, by which cool condensations can form in long coronal flux tubes heated locally above their footpoints. To understand the physics of this process, we began by modeling idealized symmetric flux tubes with uniform cross-sectional area and a simplified radiative-loss function. The present work demonstrates that condensations also form under more realistic conditions, in a typical flux tube taken from our three-dimensional MHD simulation of prominence magnetic structure produced by the sheared arcade mechanism. We compare these results with simulations of an otherwise identical flux tube with uniform cross-sectional area, to determine the influence of the overall three-dimensional magnetic configuration on the condensation process. We also show that updating the optically thin radiative loss function yields more rapidly varying, dynamic behavior in better agreement with the latest prominence observations than our earlier studies. These developments bring us substantially closer to a fully self-consistent, three-dimensional model of both magnetic field and plasma in prominences.

Hold Time Calculations for Non-Standard Enclosures

Current methods of calculating hold time for a fire fighting gas assume that the enclosure is of uniform horizontal cross-sectional area and has horizontal upper and lower boundaries (a standard enclosure). The paper shows that the hold time equation for continuous mixing in standard enclosures may also be used for non-standard enclosures, presents exact and simplified equations for descending interfaces in non-standard enclosures, and discusses the accuracy of the simplified equation. Considering the error when the simplified equation is applied to standard enclosures, and that it is always conservative for an enclosure of any shape, it is suggested that it may be used as an approximation for non-standard enclosures. The paper also presents a hold time equation for a descending interface in a standard enclosure with laminar flow in the leaks.