Concave Tips Research Articles

Diffraction and thermal effect of a Bessel-Gaussian laser for Ag nanoparticle deposition

Nanoparticles are known to sinter at much lower temperatures than the corresponding bulk or micro size particles. A laser-assisted sintering process is considered in this study to sinter Ag nanoparticles by dispensing Ag paste onto an indium tin oxide-coated Si substrate. The Gaussian beam of a CO2 laser source is propagated through axicon and biconvex lenses, and the resulting hollow beam is focused on the Ag paste with a hollow parabolic mirror. A Bessel-Gaussian irradiance distribution is obtained at the focal plane of the parabolic mirror due to the interference of the hollow laser cone. The Fresnel diffraction approximation is considered to determine the phasor of the laser and an analytical approach is implemented to calculate the irradiance distribution of the Bessel-Gaussian beam. This irradiance distribution is utilized as a heat source in a heat conduction model and the temperature distribution is analyzed for thin Ag films formed during the laser sintering of Ag nanoparticles. An analytical expression is obtained for the temperature distribution by solving the heat conduction equation using Fourier transform for finite media. The widths of the deposited Ag lines are predicted from the temperature profiles and the model predictions compare well with the experimental results. The isotherms are found to be geometrically noncongruent with convex and concave tips depending on the locally maximum and minimum irradiances of the Bessel-Gaussian beam, respectively. The convex and concave tips, however, appear in the same isotherm for sufficiently high substrate speed relative to the laser beam.

Digital image processing method for estimating leaf length and width tested using kiwifruit leaves (Actinidia chinensis Planch).

In this study, an image-analysis-based method is proposed to estimate the length and width of plant leaves, some of which have concave tips and petiole insertions. Here, kiwifruit leaves are used. Using the proposed method, orthophotographs of the leaves were obtained through image segmentation and image correction. The coordinates of the pixels along the edge of the kiwifruit leaf were then extracted. Finally, the leaf length was determined based on the sum of the number of pixels between the leaf tip and petiole insertion, and the leaf width was calculated based on the sum of the number of pixels for the widest region of the leaf. The experimental results were evaluated by analyzing the mean absolute error (MAE), root mean square error (RMSE), and accuracy. The maximum MAE and RMSE for the three examined cultivars are 0.281 and 0.366 cm, respectively. The analysis also showed that the proposed method outperforms other prevalent approaches, achieving high accuracy rates of 98.88% and 98.83% for the length and width of kiwifruit leaves, respectively. The low MAE and RMSE and high accuracy prove the capability of the proposed method with regard to calculating the length and width of such leaves. In addition, the proposed method can be extended to other plants whose leaf shape is comparable to that of a kiwifruit leaf.

A Study on the Radius of Curvature of Concave Optical Fiber Tips fabricated by Laser-Induced Photothermal Effect

A Study on the Radius of Curvature of Concave Optical Fiber Tips fabricated by Laser-Induced Photothermal Effect

A Study on the Radiation Characteristics of Concave Optical Fiber Tips

A Study on the Radiation Characteristics of Concave Optical Fiber Tips

Fractal analysis of the role of the rough interface between Bi2Sr2CaCu2Ox filaments and the Ag matrix in the mechanical behavior of composite round wires

Multifilamentary round wires (RWs) of Bi2Sr2CaCu2Ox (Bi2212) superconductor in a Ag/AgMg matrix have complex microstructures that strongly influence their electrical and mechanical behavior. The Bi2212/Ag interfaces, which in some locations are characterized by Bi2212 growths into the Ag matrix that result in rough, jagged interfaces, and in other locations are characterized by Bi2212 growths that bridge and connect to neighboring Bi2212 filaments, are believed to be amongst the most important microstructural features; yet their role is not well understood. In this work, a fractal-based framework is created in an effort to understand the role of the structure of individual filaments and the Bi2212/Ag interfaces in determining the macroscopic electromechanical behavior of Bi2212 RW. Scanning electron micrographs of an individual Bi2212 filament extracted from a Bi2212 RW are used to analyze the rough Bi2212/Ag interface and develop a fractal model using the Weierstrass–Mandelbrot (W–M) fractal function. The W–M fractal function is then used to generate simulated Bi2212/Ag microstructures. Finally, the mechanical behavior of the microstructures is investigated. It is found that the interfilamentary bridges which play a significant role in Bi2212 transport are not likely to be the cause of electromechanical degradation and failure. Instead, large stress concentrations are identified at the concave tips that occur along the jagged Bi2212/Ag interface. In particular, locations where the concave tips are within the Bi2212 filament are the likely initiation points of failure in Bi2212 RWs.

Surface properties of bionic micro-pillar arrays with various shapes of tips

Gecko-inspired micro-pillar arrays with various tip structures including spatular, spherical and concave tips were fabricated by a facile soft-molding method. The tip structures of micro-pillar arrays strongly depend on different curing processes in soft-molding using the same template. The adhesion and the wetting properties of these micro-pillar arrays are investigated by means of triboindenter and optical contact angle measurement. The results suggest that the surface properties are determined by different tip structures of micro-pillars. The spatular tip and concave tip are helpful for the adhesion enhancement and the shape of tip can control the contact angles and stabilities of water droplets on the micro-pillar arrays. In addition, the procedures demonstrate that the present route to fabricate gecko-inspired micro-pillar arrays with various tip structures is reliable and convenient. We believe that this research may pave the road to further understanding the gecko-inspired attachment systems and designing new artificial structures for dry adhesives.

Tailoring Gaussian Laser Beam Shape Through Controlled Etching of Single-Mode and Multimode Fibers: Simulation and Experimental Studies

A new class of all-fiber beam shaping devices has been realized by inverse etching the end face of single-mode and multimode fibers to form a concave cone tip. Concave tip fiber can convert a Gaussian beam profile to a flat top beam profile with a uniform intensity distribution. A flat top beam with intensity variation of approximately 5% and flat top diameter to spot diameter ratio of 67% has been achieved. This device can also change the beam shape from a Gaussian to a donut by moving the observation plane. A flat top multimode fiber beam delivery is attractive for applications which require high power and uniform intensity distribution. In single-mode fiber, concave tips could be used to reduce the beam spot size diameter, enabling efficient light coupling from a single-mode fiber to an integrated optical waveguide.

Laser beam shaping and mode conversion in optical fibers

A new class of all-fiber beam shaping devices has been realized by inverse etching the end face of single mode and multimode fibers to form a concave cone tip. Concave tip fiber can convert a Gaussian beam profile to a flat top beam profile with a uniform intensity distribution. A flat top beam with intensity variation of approx. 5% and flat top diameter to spot diameter ratio of 67% has been achieved. This device can also change the beam shape from a Gaussian to a donut by moving the observation plane. A flat top multimode fiber beam delivery is attractive for applications which require high power and uniform intensity distribution. In single mode fiber, concave tips could be used to reduce the beam spot size diameter, enabling efficient light coupling from a single mode fiber to an integrated optical waveguide.

Tip Geometry Controls Adhesive States of Superhydrophobic Surfaces

Inspired by biological attachment systems, aligned polystyrene (PS) nanopillars terminating in flat, concave tips and nanotubes were fabricated by a simple and reproducible method. All the obtained surfaces show both the contact angles larger than 150 degrees (superhydrophobicity) and high adhesion of water to it. The tip geometry plays an important role in determining the adhesive property. Surface with the concave tips has the highest adhesion, and then the surface with flat tips, whereas aligned nanotube surface has a relatively lower adhesion. Besides different van der Waals forces between the PS surfaces and water, another important factor, i.e., different negative pressures produced by the different volumes of sealed air, may be the crucial factor for their different adhesions. These findings provide the experimental evidence of the influence of the tip geometry on the adhesion of structured superhydrophobic surfaces, which is helpful for us to further understand the biological attachment systems and to optimum design of artificial analogues.

Fabrication of a fiber-based microcavity with spherical concave fiber tips

A straightforward method for manufacturing concave fiber ends with optical quality surfaces is presented. This method allows for the indention of bare cleaved fiber ends of single-mode Bi2O3 fibers by way of conventional heating and subsequent contact with ultra-smooth sinter metal spheres. The resulting high quality surfaces show promise for microcavity experiments. Results for a simple plano-concave cavity composed of a single indented fiber and a plane mirror are presented.

Concave biological surfaces for strong wet adhesion

Plant leaves, insects and geckos are masters of adhesion or anti-adhesion by smartly designed refined surface structures with micro- and nano- ‘technologies’. Understanding the basic principles in the design of the unique surface structures is of great importance in the manufacture or synthesis of micro- and nano- devices in MEMS or NEMS. This study is right inspired by this effort, focusing on the mechanics of wet adhesion between fibers having concave tips and a at substrate via capillary forces. We show that the concave surface can effectively enhance the wet adhesion by reducing the effective contact angle of the fiber, firmly pinning the liquid bridge at its circumferential edge. A critical contact angle is identified below which the adhesion strength can achieve its maximum, being insensitive to the contact angle between the fiber and liquid. The analytical expression for the critical angle is derived. Then a tentative design for the profile of concave surfaces is proposed, considering the effects of chamfering size, deformation and buckling, etc. The effect of liquid volume on the wet adhesion of multiple-fiber system is also discussed.

Capillary force with a concave probe-tip for micromanipulation

This letter describes the measurement of capillary force with a concave probe-tip for micromanipulation. Using an electric balance, we measure the capillary force for a given gap distance between a spherical object and a concave surface coaxially fabricated on a cylinder. We used three different materials (glass, stainless steel, and polytetrafluoroethylene) to check the influence of contact angles. The results are in good agreement with the theoretical prediction expressed in the normalized form; these indicate that a concave tip can generate a much larger capillary force than a flat one, provided the tip is designed to fit the convex surface of the object; moreover the results clarify that the more wettable a material is, the greater capillary force it can generate. This suggests micromanipulation by capillary force should be more practical by using probes with concave tips specifically designed for the object.

A POSSIBLE NEW SENSILLUM ON THE ANTENNAE OF ITOPLECTIS CONQUISITOR (HYMENOPTERA: ICHNEUMONIDAE)

AbstractA sensillum in the shape of a truncate cylindrical peg is present on the apex of the antenna in both sexes of Itoplectis conquisitor (Say). The sensilla occur in distinct fields of 19 to 38 pegs per antenna in males , and 26 to 35 pegs per antenna in females (x = 30.6). The pegs measure 1 to 15 μ, in height in males and 4 to 13 μ in females, and 2 to 6 μ in diameter in males and 2 to 5 μ in females. Pegs in the inside ranks at the very tip of the antenna are shorter than those in outside ranks which are more subterminal in position. This height variation results in the flat to slightly concave tips of the pegs being aligned on approximately the same plane. Innervation was confirmed by light microscope observations of sectioned material. The placement of the pegs at the antennal apex suggests that they perceive stimuli in the act of antennal tapping.

Milking ability in relation to size and shape of teats

SUMMARYLength and diameter of teats were measured on first-lactation cows at Danish progeny testing stations. The cows were also classified into four groups according to shape of teat and teat tip. All traits were corrected for yield level and interval after calving and correlated with milking characteristics. The conclusions drawn were:1. Teat length influences both average rate of milk flow and yield on hand stripping. The most satisfactory milking is obtained in cows with short teats. In Red Danish, Black and White Danish and Jersey cows, respectively, desirable length of fore teat is ≤ 6, ≤ 6, and ≤ 5 cm, and of rear teat about 1 cm shorter.2. Teat diameter is of no significant importance to average rate of milk flow, but yield on hand stripping is most satisfactory when the diameter is ≤ 2·4 cm.3. Teat shape must be very extreme before an adverse influence is recorded on average rate of milk flow and yield on hand stripping.4. The milking characteristics of cows are correlated with shape of the teat tip. The highest rate of milk flow and the lowest yield on hand stripping is found in cows with flat and concave teat tips.5. A relationship exists between teat length and the shape of the teat tip, and partial correlation coefficients show that of the teat traits investigated the most important factor affecting average rate of milk flow is the shape of the teat tip whilst teat length—similar to the effect of teat diameter—is of greater importance to the yield on hand stripping. Investigations into the possible consequences for udder health must, however, be conducted before selection for a special shape of the teat tips is introduced.