Conical Tip Research Articles

Universality in freezing of an asymmetric drop

We present the evidence of universality in conical tip formation during the freezing of arbitrary-shaped sessile droplets. The focus is to demonstrate the relationship between this universality and the liquid drop shape. We observe that, in the case of asymmetric drops, this universal shape is achieved when the tip reconfigures by changing its location, which subsequently alters the frozen drop shape. The proposed “two-triangle” model quantifies the change in the tip configuration as a function of the asymmetry of the drop that shows a good agreement with the experimental evidence. Finally, based on the experimental and theoretical exercise, we propose the scaling dependence between the variations in the tip configuration and the asymmetry of the drop.

Effects of Te additions and stirring in the In segregation in Ga1-xInxSb alloys

The influence of tellurium in the indium segregation of Ga1-xInxSb:Te ingots obtained by the conventional vertical Bridgman method (CVBM), under stirred and non-stirred conditions, was investigated. Three Te-doped ingots and three no-doped ingots were unidirectionally solidified at a constant speed of 2.0 mm/hour, inside quartz ampoules, closed under argon, and with a conical tip. The furnace temperature was set for overheating between 73.5 - 93oC, and temperature gradients between 3.0 - 3.3oC/mm. The tellurium doped ingots showed a smaller number of grains and no cracks in the middle region of the ingots, right after the tip, in comparison with the no-doped ingots. Moreover, when comparing the stirred with the non-stirred ingots, the EDS experimental profile of indium in Te-doped synthetized without melt stirring ingot showed a better agreement with the Scheil-Gulliver equation than the stirred Te-doped ingots. The Te-doped ingots when stirring the melt during synthesis showed a more constant axial indium distribution, up to 85% of their lengths. The constant lattice estimated from TEM diffraction images are respectively 6.29 A for the non-doped sample and 6.17 A for the Te-doped sample. A qualitative account for the increase of the lattice parameter and the Hall measurements results is that the tellurium compensates for the native acceptor defects, contributing to the microstructural quality in the Ga1-xInxSb ingots.

The effect of craniokinesis on the middle ear of domestic chickens (Gallus gallus domesticus).

The avian middle ear differs from that of mammalians and contains a tympanic membrane, one ossicle (bony columella and cartilaginous extra-columella), some ligaments and one muscle. The rim of the eardrum (closing the middle ear cavity) is connected to the neurocranium and, by means of a broad ligament, to the otic process of the quadrate. Due to the limited number of components in the avian middle ear, the possibilities of attenuating the conduction of sound seem to be limited to activity of the stapedius muscle. We investigate to what extent craniokinesis may impact the components of the middle ear because of the connection of the eardrum to the movable quadrate. The quadrate is a part of the beak suspension and plays an important role in craniokinesis. Micro-computed tomography was used to visualize morphology and the effect of craniokinesis on the middle ear in the domestic chicken (Gallus gallus domesticus). Both hens and roosters are considered because of their difference in vocalization capacity. It is hypothesized that effects, if present, of craniokinesis on the middle ear will be greater in roosters because of their louder vocalization. Maximal lower jaw depression was comparable for hens and roosters (respectively 34.1±2.6° and 32.7±2.5°). There is no overlap in ranges of maximal upper jaw elevation between the sexes (respectively 12.7±2.5° and 18.5±3.8°). Frontal rotation about the transversal quadrato-squamosal, and inward rotation about the squamosal-mandibular axes of the quadrate were both considered to be greater in roosters (respectively 15.4±2.8° and 11.1±2.5°). These quadrate rotations did not affect the columellar position or orientation. In hens, an influence of the quadrate movements on the shape of the eardrum could not be detected either; however, craniokinesis caused slight stretching of the eardrum towards the caudal rim of the otic process of the quadrate. In roosters, an inward displacement of the conical tip of the tympanic membrane of 0.378±0.21mm, as a result of craniokinesis, was observed. This is linked to a flattening and slackening of the eardrum. These changes most likely go along with a deformation of the extra-columella. Generally, in birds, larger beak opening is related to the intensity of vocalization. The coupling between larger maximal upper jaw lifting in roosters and the slackening of the eardrum suggest the presence of a passive sound attenuation mechanism during self-vocalization.

WGM Micro-Fluidic-Channel Based on Reflection Type Fiber-Tip-Coupled Hollow-Core PCFs

A micro-fluidic-channel is proposed based on a fiber-tip-excited hollow-core photonic crystal fiber microresonator. The reflection conical fiber tip is fabricated based on electric arc fusion technique. A quality factor up to $8.65 \times 10^{\mathrm { {4}}}$ has been experimentally acquired at $\sim 1557.75$ nm. Theoretical simulation results indicate that the refractive index sensitivity of the whispering-gallery-mode resonance wavelength reaches 1259.9211 nm/RIU for biocompatible low refractive index range. The proposed microfluidic detection platform has a few desirable merits, such as ease of fabrication, low-cost, and structure robustness, which ensures its applicability for practical use in chemical as well as biological sensing applications.

Detection of individual nanoparticle impacts using etched carbon nanoelectrodes

A rapid and reliable nanofabrication route produces electrodes with beneficial properties for electrochemistry based on stochastic nanoparticle collision events. Carbon nanoelectrodes are etched to expose conical carbon tips which present an increased surface area for the detection of nanoparticle impacts. The tuneable electrode size as well as the conical geometry allow to increase the observed particle impact frequency while maintaining low background noise. Moreover, anodic particle coulometry for the sizing of silver nanoparticles shows that the detected impacts are representative of the polydisperse particle population.

Traceable measurement and imaging of the complex permittivity of a multiphase mineral specimen at micron scales using a microwave microscope

This paper describes traceable measurements of the dielectric permittivity and loss tangent of a multiphase material (particulate rock set in epoxy) at micron scales using a resonant Near-Field Scanning Microwave Microscope (NSMM) at 1.2GHz. Calibration and extraction of the permittivity and loss tangent is via an image charge analysis which has been modified by the use of the complex frequency to make it applicable for high loss materials. The results presented are obtained using a spherical probe tip, 0.1mm in diameter, and also a conical probe tip with a rounded end 0.01mm in diameter, which allows imaging with higher resolution (≈10µm). The microscope is calibrated using approach-curve data over a restricted range of gaps (typically between 1% and 10% of tip diameter) as this is found to give the best measurement accuracy. For both tips the uncertainty of scanned measurements of permittivity is estimated to be±10% (at coverage factor k=2) for permittivity ⪝10. Loss tangent can be resolved to approximately 0.001. Subject to this limit, the uncertainty of loss tangent measurements is estimated to be±20% (at k=2). The reported measurements inform studies of how microwave energy interacts with multiphase materials containing microwave absorbent phases.

Generation of Microwave Capillary Argon Plasmas at Atmospheric Pressure

A technique has been developed to generate stable Ar plasmas at atmospheric pressure inside of a quartz capillary tube. The microwave plasma in the capillary tube is produced by utilizing a single mode resonant circular cavity applicator with 2.45 GHz frequency excitation. The plasma can be confined or fully exposed outside the cavity as plasma jets depending on the operating conditions. The profile of the plasma front has been characterized as a conical tip or split branching jet plume. The measured discharge length and the power density of the plasma range from 6 to 10 cm and 35 to 75 W $\cdot $ cm $^{-3}$ , respectively. Addition of CH4 into the Ar plasma results in an increase in the abundances of excited CN and C2 carbon radicals and a concomitant decrease in the intensity of the Ar emission.

On improving ballistic limit of bi-layer ceramic–metal armor

This paper investigates experimentally and numerically methods to enhance the ballistic performance of ceramic armor. Initially we demonstrate an experimental set-up to impose pre-stress to ceramic-metal bi-layer armor and study the depth of penetration to measure the ballistic efficiency as a function of pre-stress intensity validating our previous numerical studies on effect of pre-stress on the ballistic limit of ceramic armor (Int. Journal of Impact Engineering, 2015(84)159-170). Secondly, a module is designed and tested to achieve interface defeat in ceramic armor with multiple interface layers. Finally, influence of thickness of the steel cover plate (CP) on ballistic performance of SiC ceramic is studied through AUTODYN® finite element simulations for normal and oblique (NATO 60°) against long rod projectile (LRP) with a conical tip. The LRP and CP are modeled using smooth particle hydrodynamic (SPH) particles and rest of the component is modeled using Lagrangian domain. The numerical analyses of armor modules are compared via depth of penetration (DOP) and LRP residual length for varying cover plate thicknesses.

Engineering Gold Nanoparticles in Compass Shape with Broadly Tunable Plasmon Resonances and High-Performance SERS.

We present the uniform and high-yield synthesis of a novel gold nanostructure of compass shape composed of a Au sphere at the central and two gradually thinning conical tips at the opposed poles. The Au compass shapes were synthesized through a seed-mediated growth approach employing a binary mixture of cetyltrimethylammonium bromide (CTAB) and sodium oleate (NaOL) as the structure-directing agents. Under the condition of single surfactant (CTAB), the spherical seeds tend to grow into larger spherical Au nanoparticles (NPs); while the spherical seeds favor the formation of Au compass shaped NPs using two mixed surfactants (CTAB/NaOL). The reaction kinetics clearly shows a growth mechanism of Au compass shaped NPs. Interestingly, due to their anisotropic structure, Au compass shaped NPs show two distinctive plasmonic resonances, similar to those from Au nanorods. Particularly, the longitudinal surface plasmon resonances of Au compass shaped NPs exhibit a broadly tunable range from 600 to 865 nm. In addition, the obtained Au compass shaped NPs can be self-assembled into a two-dimensional monolayer with closely packed and highly aligned NPs, which results in periodic arrays of overlapped Au tips, generating hot spots for high-performance surface-enhanced Raman scattering.

Influence of the surface chemistry-structure relationship on the nanoscale friction of nitrided and post-oxidized iron

The relationship between the friction behavior and surface properties such as surface chemistry, morphology and phase distribution is not fully understood. In the case of surface treatments involving steels, the alloying elements introduce non-controllable variables in tribological experiments. We further advance this discussion by designing experiments where the friction behavior of a conical diamond tip sliding on different plasma nitrided and post-oxidized pure iron substrates was determined. Also, a detailed chemical and microstructural surface characterization using discharge optical emission spectroscopy, X-ray diffraction, and atom probe tomography was performed. Implementing composition profiling and localized elemental distribution analysis throughout the outermost layer, the formation of iron oxide with non-homogenous morphology was detected. Although the coefficient of friction decreases as a function of the post-oxidation time, the friction force is under a relative great dispersion at intermediate post-oxidation times. The dispersion of the friction force obtained from the sliding analyses can be understood as a combination of surface chemistry and different phases (structure) at the surface.

Etchant-based design of gold tip apexes for plasmon-enhanced Raman spectromicroscopy

In this paper, we gain insight into the design and optimization of plasmonic (metallic) tips prepared with dc-pulsed voltage electrochemical etching gold wires, provided that, a duty cycle is self-tuned. Physically, it means that etching electrolyte attacks the gold wire equally for all pulse lengths, regardless of its surface shape. Etchant effect on the reproducibility of a curvature radius of the tip apex is demonstrated. It means that the gold conical tips can be designed chemically with a choice of proper etchant electrolyte. It is suggested to use a microtomed binary polymer blend consisting of polyamide and low density polyethylene, as a calibration grating, for optimizing and standardizing tip-enhanced Raman scattering performance.

Influence of corona on strike probability of grounded electrodes by high voltage discharges

This paper presents the results of an investigation into the influence of corona formation processes at the tips of grounded rod electrodes on the probability of those rods being “struck” by high-voltage discharges. Experiments simulating the final stage of the attachment process were carried out with a composite voltage comprising a simultaneously applied impulse and DC potential of different levels to grounded rod electrodes simulating lightning rods, featuring either a spherical or pointed (conical) tip. The experiments show that corona does not influence the probability of the electrode being struck until a critical electric field (EF) strength is reached.

Effects of methotrexate on the viscoelastic properties of single cells probed by atomic force microscopy.

Methotrexate is a commonly used anti-cancer chemotherapy drug. Cellular mechanical properties are fundamental parameters that reflect the physiological state of a cell. However, so far the role of cellular mechanical properties in the actions of methotrexate is still unclear. In recent years, probing the behaviors of single cells with the use of atomic force microscopy (AFM) has contributed much to the field of cell biomechanics. In this work, with the use of AFM, the effects of methotrexate on the viscoelastic properties of four types of cells were quantitatively investigated. The inhibitory and cytotoxic effects of methotrexate on the proliferation of cells were observed by optical and fluorescence microscopy. AFM indenting was used to measure the changes of cellular viscoelastic properties (Young's modulus and relaxation time) by using both conical tip and spherical tip, quantitatively showing that the stimulation of methotrexate resulted in a significant decrease of both cellular Young's modulus and relaxation times. The morphological changes of cells induced by methotrexate were visualized by AFM imaging. The study improves our understanding of methotrexate action and offers a novel way to quantify drug actions at the single-cell level by measuring cellular viscoelastic properties, which may have potential impacts on developing label-free methods for drug evaluation.

Identification of molecules through the fluorescence enhancement by a metal tip

A fluorescence enhancement phenomenon, which is realized as a result of a sharp increase in the radiative decay rate of a quantum dipole emitter (QDE) is investigated theoretically in the vicinity of a conical metal tip. The QDE relaxation process is considered as a self-stimulated transition from an excited state into the ground state due to the feedback field formation from the tip. The dynamics of the system shows a stepped relaxation behavior that differs significantly from the conventional exponential decay. This effect can be observed in a small region of the resonance frequency, which is defined by an angle of conical tip. The increase of fluorescence when approaching of molecule to the metal tip on the surface enables one to determine its location.

Length scale dependence in elastomers – comparison of indentation experiments with numerical simulations

Abstract Probing depth dependent deformation at nano- and micrometer length scales has been observed in indentation experiments of polymers. Unlike in metals, where size effects are observed in plastic deformation and are attributed to geometrically necessary dislocations, the origin of size dependence in polymers is not well understood. As classical continuum theories are unable to describe such phenomena, higher order gradient theories have been developed to capture such size dependent deformation behavior. The present study adopts the penalty finite element approach for a couple stress elasticity theory under axisymmetric conditions to numerically simulate and analyze the probing depth dependent deformation. Polydimethylsiloxane (PDMS) and natural rubber have been used as model materials to analyze the depth dependent deformation at different probing depths. Simulations were performed on PDMS using spherical indenter tips of different radii to show the influence of strain/rotation gradients on elastic modulus. To capture the experimentally observed increase in hardness with decreasing probing depth, simulations applying a conical indenter tip were performed and compared with experimental data.

Simulation of torpedo anchor set-up

Torpedo anchors are used for station keeping of floating offshore platforms and fixing risers to the seabed in deep water. Their main benefit over other anchors is reduction in anchor installation cost via free falling in the water. A torpedo anchor has a steel cylindrical shaft with a conical tip and is ballasted in order to deepen the soil penetration and increase the anchor holding capacity. In order to address the installation effects on the soil strength and consequently the anchor pull-out capacity, first reconsolidation (set-up) of soil next to the anchor after installation is studied by a finite-element (FE) analysis of coupled deformation and fluid flow in porous media. The results of the set-up analysis indicate the rate of dissipation of excess pore-water pressure and soil-strength recovery. These are important considerations in predicting the anchor pull-out capacity at different times after installation. In the absence of a documented complete set of installation and set-up tests, the results are validated qualitatively using available albeit limited field test data.

Length scale effects in epoxy: The dependence of elastic moduli measurements on spherical indenter tip radius

Significant increases in the measured elastic moduli with decreasing indentation depth have been previously found in various polymers by indentation tests with a Berkovich tip at micro-to nanometer length scales. These increases in the determined elastic moduli were related to second order displacement gradients which increase with decreasing depth when a conical tip is applied. When a spherical tip is applied, such depth dependence should not be present as the second order displacement gradients remain essentially unchanged with indentation depth. However, these gradients should be proportional to the radius of the spherical tip. To examine the notion of second order displacement gradient dependence in measurements of elastic moduli, indentation experiments are conducted on epoxy with spherical tips of different nominal radii. Accounting for tip imperfections, an increase in the determined elastic moduli is found with decreasing tip radius, which corroborates the notion of second order displacement gradient dependence.

Experimental Investigation of the Supersonic Flow over an Axisymmetric Ring Cavity

This paper presents the results of the experimental investigation of the supersonic flow over a ring cavity of rectangular cross-section on a cylindrical body with a conical tip. The evolution of the flow over a cavity with its continuously changing extent has been investigated. The transition zone boundaries within which both an open and a closed schemes of flow are possible have been determined by the parameter of the relative extent of the cavity. It has been shown that the flow conditions in the transition zone depend on the prehistory of the flow. The main stages of cavity flow restricuting at the transition zone boundaries have been described.

Detection of structure in asteroid analogue materials and Titan’s regolith by a landing spacecraft

We compare measurements made by two impact penetrometers of different sizes and with different tip shapes to further understand penetrometer design for performing penetrometry on an asteroid. To this end we re-visit the interpretation of data from the Huygens’ penetrometer, ACC-E, that impacted Titan’s surface. In addition we investigate the potential of a spacecraft fitted with a penetrometer to bounce using a test rig, built at The Open University (UK).Analysis of ACC-E laboratory data, obtained from impacts into ∼4mm diameter gravel, was found to produce an unusual decrease in resistance with depth (force–depth gradient) which was also seen in the Huygens’ ACC-E data from Titan and originally interpreted as a wet or moist sand. The downward trend could also be reproduced in a hybrid Discrete Element Model (DEM) if it was assumed that the near surface particles are more readily mobilised than those deeper in the target.With regard to penetrometer design penetration resistance was found to be sensitive to the ratio of particle to tip diameter. A clear trend was observed with a conical tip penetrometer, X-PEN, of decreasing force–depth gradients with increasing particle sizes most likely due to a transformation from a bulk displacement of material by the penetrating tip to more local interactions. ACC-E, which has a hemispherical tip, was found to produce a wider range of force–depth gradients than X-PEN, which had a conical tip, possibly due to difficulties dislodging jammed particles. Both penetrometers were able to determine particle diameter and mass after post-processing of the data.Laboratory simulations of landings with the test rig suggest that a large impact penetrometer under certain circumstances could absorb a significant amount of the elastic energy of the spacecraft possibly aiding landing. Alternatively a small impact penetrometer would allow the spacecraft to bounce freely off the surface to make a measurement at another location.

Status of Apostolepis borellii Peracca 1904 (Serpentes, Xenodontinae), with restriction of the A. nigroterminata concept

Apostolepis borellii has been considered a junior synonym of A. nigroterminata . However, examination of the holotypes showed significant differences between the species, such as head narrow (vs. wide, stocky), slandering snout (vs. wide and rounded), background color brown (vs. red), black nuchal collar wide, reaching the gular region (vs. short, not reaching gular region), tail extremity slandering with conic tip (vs. stocky, rounded tip), tail blotch complete reaching dorsals and subcaudals (vs. only dorsal, with white ring anteriorly). Apostolepis borellii occurs in the Cerrado, while A. nigroterminata , in the Amazonian Forest, two diverse biomes. The former may constitute a new group of small sized species, own from central-western Brazil to Bolivia; the latter is allocated in the nigrolineata group, both presented herein. Keywords: Brazil, Peru, Cerrado, Amazonian Forest, revalidation.