Circular Cross-sectional Shape Research Articles

Wet spinning of silk polymer: I. Effect of coagulation conditions on the morphological feature of filament

Regenerated silk fibroin (SF) filaments were prepared by the wet spinning technique. The effect of coagulation conditions, such as coagulant type and coagulation temperature, was investigated on the morphological feature of SF filaments and a theoretical approach was also performed to understand the coagulation phenomena. SEM observation revealed that as the R group size of alcoholic coagulant (ROH) increased, the cross-sectional shape deviated more from a circular form. This is attributed to the fact that as the R group size increased, the mass transfer rate difference increased, but the coagulation rate decreased due to a reduced diffusion rate. Most non-alcoholic coagulants exhibited this circular cross-sectional shape, except dioxane, which showed a clover shape. As the coagulation bath temperature increased, the cross-section deviated less from a circular form, with the reduction of fiber diameter. When methanol/water mixture was used as a coagulant, an ellipse or a dog-bone shape was obtained with higher water content in methanol, which was attributed to the decrease of coagulation rate. Although methanol exhibited a positive value of mass transfer rate difference, a circular shape of cross-section was obtained due to the density difference of the coagulated and uncoagulated parts in the coagulating SF filament.

Zeta potential determination by streaming current modelization and measurement in electrophoretic microfluidic systems.

Electrophoresis in capillary and microfluidic systems, used in analytical chemistry to separate charged species, are quite sensitive to surface phenomena in terms of separation performances. In order to improve theses performances, new surface functionalization techniques are required. There is a need for methods to provide fast and accurate quantification about surface charges at liquid/solid interfaces. We present a fast, simple, and low-cost technique for the measurement of the zeta-potential, via the modelization and the measurement of streaming currents. Due to the small channel cross section in microfluidic devices, the streaming current modelization is easier than the streaming potential measurement. The modelization combines microfluidic simulations based on the Navier-Stokes equation and charge repartition simulations based on the Poisson-Boltzmann equation. This method has been validated with square and circular cross section shape fused-silica capillaries and can be easily transposed to any lab-on-chip microsystems.

Parametric Investigation of Viscous Dissipation Effects on Optimized Air Cooling Microchanneled Heat Sinks

The effects of viscous dissipation of working fluid on the optimum heat sink parameters are investigated for the case of air cooling with a micro-/narrow-channeled compact heat sink. For this purpose, an optimization method is introduced first on the basis of dimensionless groups while employing several assumptions. This method yields minimum pumping work or pressure drop with a set of optimized geometric/hydrodynamic parameters when outer dimension of a heat sink and imposed thermal load are specified. Especially for the case of laminar flow, the procedure presents an explicit existence of cooling limit by the viscous heat generation, giving an analytical expression of the maximum removable heat Q max . The relationships between thermal load and each parameter are calculated for both laminar and turbulent regimes under the conditions of compact heat sink dimension (20 mm 2 20 mm 2 2 mm) and circular cross-sectional shape of channels. The results show that the cooling capability under such conditions is largely limited by the salient manifestation of viscous dissipation, when compared with our previous investigation on water cooling presented in [1]. From the discussion, it was concluded that when a micro-/narrow-channeled heat sink is to be designed with air, the effect of viscous dissipation should be taken into account in order to avoid falling on wrong optimum solutions.

D02 流線形断面の細線を編んで得る再生器メッシュの研究

A regenerator wire mesh obtained by knitting, lengthwise and crosswise, whose wires' cross sectional shape are streamline to the flow, is considered to become smaller flow resistance than usual wire mesh of circular cross-sectional shape. Although, Nusselt number may be decrease a little bit than usual mesh, wire mesh having streamline cross-sectional shape is probably superior to that having circular shape cross section because the effect of decrease of flow resistance is larger than that of Nusselt number. In order to confirm this idea, comparison between parallel thin flat plates' flow and cross flow over banks of circular cylinders is carried out. Also simple numerical calculation was carried out.

The effects of torsion on the initial geometry of bars having non-circular cross-sections

The most important effect of torsion on bars twisted with large angles of twist is represented by the change of their initial geometry. Concerning this aspect, previous experimental investigations have presented many and different results obtained in the study of bars having circular cross-sectional shapes. The present paper analyses the effects of torsion on the geometry of bars having square and rectangular cross-sectional shapes.

Structure and Properties of Cotton Sirospun® Yarn

Cotton Sirospun® yarn has a circular cross-sectional shape, with the two strands segregated and consolidated into an adjacent array. When it is untwisted, the strand twists in an alternate direction. When compared to single yam with the same linear density and twist multiplier, cotton Sirospun yam is superior in tenacity, evenness, hairiness, and abrasion resistance. Although cotton Sirospun yam is less hairy and more extensible than two-plied yarn, it is inferior to two-plied yam in evenness and imperfections.

Novel piezoelectric structures for sensor and actuator applications

The piezoelectric behaviour of ferroelectric ceramics is commonly utilised for sensors and actuators. Simple shapes (bimorph beams, moonies and rainbows), thin films, composite and layered structures have been used thus far. Processing technologies developed at the University of Birmingham allow the production of novel complex shapes which, as well as improving the mechanical strength of the ceramic, may well allow the application of piezoelectric elements into areas previously unexplored. This paper concentrates on circular cross-sectional shapes in the form of helical springs, and describes the preliminary investigation carried out to characterise the response of springs to both dynamic and static impulses. The application of such geometries to sensor and actuator devices is discussed and possible areas of further work to realise the potential of the processing technology are also outlined.

Impact energy absorption of 6061 aluminum extruded tubes with different cross-sectional shapes

The present article aims at evaluating experimentally impact absorption energies of an extruded 6061 aluminum tube for space frame and at investigating the effect of cross-sectional shape on the compressive deformation behavior under dynamic loading. The dynamic compressive test was conducted on extruded aluminum tube specimens, whose shape and thickness/width (or diameter) ratio are different, using a high performance servo-hydraulic machine. Asymmetric folds were formed mainly in the rectangular tube specimens, whereas symmetric folds were formed in the circular tube specimens. However, the fold shape tended to become symmetric as the thickness/width ratio increased, and absorption energy increased linearly within the scope of the present study. To improve impact absorption energy and maximum resistive force against compressive load of extruded aluminum tube for space frame, it is recommended to make the thickness/width ratio large enough and to design the circular cross-sectional shape in a way to promote the formation of symmetric folds instead of asymmetric ones.

Determination of spectral dispersion curves of polypropylene fibres

A new mathematical formula is derived to determine the spectral dispersion curve of a fibre having a circular cross sectional shape. This formula depends on the principle of a variable wavelength interferometric technique taking into consideration the area under the fringe shift instead of the fringe shift itself. This method overcomes the difficulty of the presence of any irregularity of the transverse circular cross sectional shape of the fibre. Analysis of the new mathematical formula is given and applied experimentally for polypropylene fibres with draw ratio 3.5 and 4.0. Optical microscopy and optical diffraction methods are used to determine the cross sectional area of the fibres. Also, conventional VAWI and two-beam methods are applied for these fibres to confirm the results of the new analysis. Microinterferograms are given for illustration.

Restoration of Hydrophilicity of Field-Opened Cotton Fibers by Cyanoethylation Treatment.

Field-opened American cotton fibers were treated with acrylonitrile after impregnation with aqueous sodium hydroxide. By this treatment the water absorbency and the amount of bound water as determined by DSC were increased and approached those of never-dried cotton. As for tensile strength, the increase in dry strength was higher than that of wet strength. On DSC cooling curves peak II, ascribable to freezable bound water, was observed as a small shoulder for field-opened and mercerized cotton fibers. However, this peak disappeared after the acrylonitrile treatment. Those treated fibers showed a nearly circular cross-sectional shape. Lumen and convolution could hardly be observed.

The compliance of three-point bend round beam specimens calculated with the slice synthesis method

The compliance of two kinds of three-point bend (3PB) round beam specimens is calculated with the slice synthesis method. In this method, the round beam is divided into a number of slices, and every slice is considered as a 3PB beam with a rectangular cross-section for which the compliance is known, then these slices are combined together to give the compliance of the round beam. The calculated results have shown good accuracy. It is postulated that the slice synthesis method can be used to obtain the compliance of bend specimens with a circular cross-section and various crack front shapes.

Left ventricular mechanics in the preterm infant and their effect on the measurement of cardiac performance

The effects of the transition from fetal to postnatal circulation on left ventricular geometry, wall motion, and echocardiographic measurements of function in the human preterm infant are largely unknown. To determine whether abnormalities in left ventricular geometry are present in the normal preterm infant after birth and, if so, for how long, and to examine possible contributing factors and their effect on the measurement of cardiac performance, we obtained serial echocardiograms of 14 healthy preterm infants (gestational age, 33 +/- 2 weeks; birth weight, 1940 +/- 470 gm) at 9.5 +/- 3.5 days of age (time 1) and again at 51 +/- 16 days (time 2). Left ventricular shape and wall motion were measured and estimates of wall stress and mass were made. Performance was assessed by standard M-mode shortening fraction and by transverse two-dimensional area shortening. At time 1 septal flattening caused distortion of left ventricular shape. As the patients grew older, septal flattening resolved and the left ventricle tended to assume a circular cross-sectional shape. Wall-motion analysis demonstrated poor motion of the midseptum and anterior free wall at time 1, which improved at time 2 (p = 0.06). Left ventricular mass increased from 24 +/- 5 to 41 +/- 7 gm/m2 (p = 0.0001) and wall stress decreased from 49 +/- 21 to 38 +/- 13 gm/cm2 (p = 0.005) between time 1 and time 2. Shortening fraction was lower at time 1 than at time 2 (18% +/- 7% vs 28% +/- 8%; p = 0.001; normal limit = 28% to 45%); however, there was no significant difference in area shortening between time 1 and time 2 (49% +/- 10% vs 53% +/- 8%; normal limit = 45% to 65%). We conclude that the preterm newborn infant has distorted left ventricular shape and abnormal wall motion, which alter measurements of shortening fraction and persist for the first weeks of life. Area shortening may be necessary to assess left ventricular performance during the first weeks of life in the premature infant.

Navier-Stokes computations of vortex asymmetries controlled by smallsurface imperfections

Navier-Stokes analyses are employed to explore the driving mechanisms controlling asymmetric vortical flows with Re(D) = 0.8 million (Reynolds number based on maximum diameter) over a 3.5 caliber tangent-ogive cylinder at large angles of attack (alpha = 20, 30, and 40 degrees). All flowfield results are steady-state solutions to the three-dimensional, incompressible Navier-Stokes equations in the thin-layer approximation. The numerical results are temporally and spatially fully converged, and are in good agreement with experimental data. The major findings are: (1) for alpha not less than 30 degrees, the vortex flows are genuinely asymmetric yet recurrent; (2) asymmetric vortex patterns are highly sensitive toward such parameters as machine accuracy, grid topology, etc., unless triggered by a slight deformation (similar to an out-of-round nose tip) in the neighborhood of the apex; and (3) for alpha = 20 degrees, the flow is symmetric for both circular and elliptic cross-sectional shapes of the nose tip.

Measurement of refractive indices of homogeneous fibers with regular or irregular transverse sections

Seven fibers of different cross-sectional shape are studied interferometrically using multiple-beam Fizeau fringes. These fibers are of circular, rectangular, triangular, trilobal, elliptical, kidney, and dog-bone cross-sectional shapes. The areas enclosed under the interference fringe shift is considered to represent the optical path difference integrated across the fiber. This principal is applied to nylon 6 fibers of trilobal cross-sectional shape. The described method is suitable for the measurement of refractive indices of any fiber with regular or irregular transverse sections. Microinterferograms are given for illustration.

The trachea and esophagus after repair of esophageal atresia and distal fistula: Computed tomographic observations

Five patients, whose esophageal atresia and distal tracheoesophageal fistula had been repaired in infancy, were examined by computed tomography at age 2 to 21 because of recurrent or persistent tracheal or esophageal problems. Their tracheas generally failed to have the roughly circular cross-sectional shape found in controls. The pars membranacea was often unusually broad, with much more section-to-section variation in area than in controls. Change in cross-sectional area with respiratory phase, in the one patient assessed, was much greater than in a control. These tracheal abnormalities help to explain the tracheal symptoms found in these and similar patients. Their esophagi contained much air and fluid.

Structural changes in the femur with the transition to agriculture on the Georgia coast.

Structural characteristics of the femur are compared in preagricultural (2200 B.C.-A.D. 1150) and agricultural (A.D. 1150-1550) subsistence strategy groups from the Georgia coast. Using an automated technique, cross-sectional geometric properties used in structural analyses (areas, second moments of area) were determined at midshaft and distal to the lesser trochanter in 20 adults from each group. A significant decline in magnitude of almost every geometric property occurs in the agricultural group. The differences between groups are reduced but still significant for many properties after standardizing for bone length differences. In addition, a remodeling of the femoral cortex to one of relatively smaller medullary and subperiosteal diameter, as well as a more circular cross-sectional shape, is characteristic of agricultural femora. Thus, while the relative cross-sectional area of bone remains the same, the spatial distribution of bone area is different in the two groups. The results strongly suggest a relative reduction in mechanical loadings of the femur in the agricultural group, implying different levels and possibly types of activity involving the lower limb in the two groups. The data are also compared with similar data available for the Pecos Pueblo (agricultural) sample. The comparison indicates that types of activity may have been more similar in the two agricultural samples, but that general levels of activity were more similar in the Pecos Pueblo and Georgia coast preagricultural samples.

Slender streams with gravity: Outer asymptotic expansions. II

Higher order terms in the outer asymptotic expansions for flows of slender streams in the presence of gravity are computed. In particular, for the case of jet flow, higher order terms corresponding to a basic flow with either a circular or elliptical cross-sectional shape are discussed in detail and an inherent spatial instability (due to the effects of gravity) in the jet is discussed. Higher order terms for pipe flow and channel flow are also calculated and an example is presented. The pressure distribution within the flow is also computed and the effects of the pressure on the flow when a free surface is present is discussed.