Triangular Tip Research Articles

Investigation of nanoscratch anisotropy of C-plane sapphire wafer using friction force microscope

In this study, nanoscratch experiments using side-forward multiple scans by friction force microscope with triangular pyramidal monocrystalline diamond tip were conducted on a (0001) plane sapphire wafer substrate to clarify the ductile-regime machining mechanism including its anisotropy. Various characteristics, such as scratch force, depth and specific energy for each scratch direction on C-plane of sapphire, were manifested by a friction force microscope, and the specific scratch energy showed a trend of three-fold symmetry. Subsequently, cutting chips which adhere to the diamond tip exhibited plastic deformations features were testified by a scanning election microscope. Based on slip/twinning systems of sapphire, Schmid factor was calculated for each scratch direction using the resultant force, and the calculated Schmid factors on the rhombohedral planes became the highest. Following the results, the resolved shear stresses along the twinning directions on the rhombohedral planes were calculated using a simple chip formation model, and they were several times larger than the critical resolved shear stress for rhombohedral twinning. As a result, it was found that when the scratch direction is set so that one of the three faces of the diamond tip is close to parallel to one of the rhombohedral planes, the rhombohedral plane acts as the chip shear plane and the specific scratch/cutting energy can be minimized. The cross-sectional transmission electron microscope images of scratched sub-surface also distinctly displayed the existence of subsurface damages consisting of twins and stacking faults relating rhombohedral planes.

<strong><em>Impatiens bullatisepala</em> (Balsaminaceae), a new species from Guizhou, China</strong>

Impatiens bullatisepala (Balsaminaceae), a new species supported by morphological and phylogenetic evidence from Fanjing Mountain, Guizhou province in China, is described here. It is morphologically similar to I. davidii but can be distinguished by its dorsally ridged lateral sepals with sunk reticulate veins and bullate projections on abaxial surface, 2–2.5 cm deep saccate lower sepal with ca. 0.8 cm long narrowly triangular tip at the mouth, and broadly ovate dorsal petal. Phylogenetic analyses of a combined dataset of nuclear ITS and plastid atpB-rbcL intergenic spacer DNA sequences furtherly confirmed its novelty.

Description of Paraxiopsis/ kensleyi/ n. sp., a new axiid lobster from the Gulf of Mexico (Crustacea: Decapoda: Axiidea).

A new species of axiid was discovered during sampling offshore deep banks on the middle continental shelf off Louisiana. Paraxiopsis kensleyi n. sp. appears to inhabit interstices and cavities of coralline algal rubble, rhodoliths, coral rubble, and other eroded calcareous substrates. Weakly separated from Eutrichocheles Wood-Mason, 1876 on the basis of morphology, present assignments of western Atlantic species to Paraxiopsis de Man, 1905 are regarded as provisional. The new species is described morphologically, and the coloration of freshly captured specimens is documented and compared to related species where possible. Coloration readily distinguishes mature specimens of the new species from Paraxiopsis spinipleura Kensley, 1996, with which it was initially confused. The diagnosis includes GenBank accession numbers for COI sequences to allow future molecular phylogenetic comparisons. Compared to regional species that share a similar dentation or spination on the submedian carina, the pleon of the new species is distinctive in the truncate ventral margin on pleura 2-4, as opposed to being broadly rounded or directed ventrally in an acutely triangular tip. The new species is the eighteenth species of Paraxiopsis worldwide and the ninth from western Atlantic waters, seven of which are now known to range into the Gulf of Mexico. An updated key to western Atlantic members of the genus is provided.

In Situ Separation and Analysis of Lipids by Paper Spray Ionization Mass Spectrometry

Paper spray ionization (PSI) is an extractive ambient ionization technique for mass spectrometry (MS), whereby a triangular paper tip serves as the sampling base and the electrospray tip. During PSI, analytes are extracted and transported to the edge of the paper tip by the applied spraying solvent. Analytes can be purified from a sample matrix and separated from each other by this transportation process. In this study, we investigated and utilized the analyte transportation process of PSI for the in situ separation and analysis of lipid mixtures. We found that differential transport of phosphatidylcholine (PC) and triacylglycerol (TAG), the two most abundant lipid classes in animals, occurred during PSI. We also found that the order in which these lipids moved strongly depended on how the spraying solvent was applied to the paper base. The more polar PC moved faster than the less polar TAG during PSI, when a polar solvent was slowly fed into a paper tip, whereas TAG was transported faster than PC when excess solvent was applied to the tip at once. In addition, we achieved a complete separation and detection of PC and TAG by slowly supplying a nonpolar solvent to a PSI tip.

Mechanism behind the paper spray chemical ionization phenomenon and the choice of solvent.

Paper spray chemical ionization (PSCI) combined with mass spectrometry has been proposed as a sensitive method for the analysis of nonpolar aromatic compounds; however, the mechanism behind PSCI is not well understood. In the present study, the evidence for the occurrence of corona discharge is provided and its mechanism is proposed. Photographs taken with a highly sensitive camera evidently demonstrate the occurrence of corona discharge at the end of the triangular shape tip when a nonpolar solvent such as hexane was used at an applied potential of 6-7 kV. Nevertheless, corona discharge was not observed in the presence of a polar solvent. The occurrence of the corona discharge was attributed to charge accumulation in the dielectric layer generated by the nonpolar solvent on the fibers of the paper tip. Specifically, corona discharge was generated at the tip end when the charge approached a critical threshold. In the presence of a polar solvent, however, the dielectric layer was not generated and, hence, corona discharge was not observed. Based on this information, three nonpolar solvents were selected and their sensitivity for analyzing the phenanthrene and maltene fractions of crude oil was evaluated. Chlorobenzene provided the highest signal abundance; therefore, it was suggested as the optimum solvent for PSCI. Notably, the fundamental understanding of corona discharge in PSCI acquired in this study provides a basis for further improvement of this technique by way of surface modification.

On the uniqueness of intrinsic viscoelastic properties of materials extracted from nanoindentation using FEMU

Instrumented nanoindentation is widely used to extract the material properties from the measured force-displacement curves. In this work, the uniqueness/non-uniqueness of the intrinsic viscoelastic properties of materials determined by nanoindentation during load-unload tests is investigated. A four-parameter viscoelastic law with constant Poisson's ratio is used to model the mechanical behavior of a polymer material and a 2D-axisymmetric Finite Element Model (FEM) is used to simulate the nanoindentation test. Firstly, a nanoindentation experimental triangular load-unload test is performed on a bulk sample of polypropylene (PP) with a Berkovich indenter tip at a depth rate of 1000 nm/min. The values of the four material parameters are estimated by the Finite Element Model Updating (FEMU). The numerical results can accurately fit the experimental data. However, several quasi-solutions are shown to exist. These load-unload data allow to identify only three viscoelastic parameters if the Poisson's ratio is known. Secondly, the effect of nanoindentation depth rate, loading type (triangular, trapezoidal, exponential, sinusoidal) and apex angle is numerically investigated using an identifiability index based on the conditioning of the inverse problem. We show a correlation between the identifiability index and the energy dissipated by the material during the tests. The extraction of all material parameters remains impossible using a single test. Finally, some combinations of several nanoindentation triangular tests and indenter tip angles are also investigated. We show that a dual nanoindentation technique (cube corner and Berkovich tips) with triangular load-unload tests is an interesting combination to reliably extract all the viscoelastic parameters, provided that plasticity is taken into account. This result illustrates the interest of using this numerical identifiability index to design nanoindentation experiments to ensure the robustness of the intrinsic viscoelastic properties extraction.

Influence of template strut morphology on the mechanical performance of SiC reticulated porous ceramics

SiC reticulated porous ceramics (RPCs), as the key functional components, are widely applied in field of molten-metal filtration. However, the hollow struts with triangular tips caused by burnt out of polymer foam reduced the strength of SiC RPCs, which limited their engineering application. Aiming to reveal the effects of template strut morphology on the mechanical performance of SiC RPCs, templates with triangular, square and circular cross sections were designed by additive manufacturing. Subsequently, SiC RPCs with varied strut structures were prepared by slurry immersion, followed by sintering at elevated temperature. The blunt of template strut improved the mechanical property of SiC RPCs, samples with circular hollow struts showed the highest crushing strength and strain than that of triangular and square hollow struts. From the results of simulation calculation, triangular hollow struts led to the significant stress concentration in the connection of struts and their middle parts, while the smaller stress uniformly distributed in the whole SiC skeleton as hollow struts became circle, thereby the improved mechanical properties were obtained in SiC RPCs.

Miniaturization optimized weapon killing power during the social stress of late pre-contact North America (AD 600-1600).

Before Europeans arrived to Eastern North America, prehistoric, indigenous peoples experienced a number of changes that culminated in the development of sedentary, maize agricultural lifeways of varying complexity. Inherent to these lifeways were several triggers of social stress including population nucleation and increase, intergroup conflict (warfare), and increased territoriality. Here, we examine whether this period of social stress co-varied with deadlier weaponry, specifically, the design of the most commonly found prehistoric archery component in late pre-contact North America: triangular stone arrow tips (TSAT). The examination of modern metal or carbon projectiles, arrows, and arrowheads has demonstrated that smaller arrow tips penetrate deeper into a target than do larger ones. We first experimentally confirm that this relationship applies to arrow tips made from stone hafted onto shafts made from wood. We then statistically assess a large sample (n = 742) of late pre-contact TSAT and show that these specimens are extraordinarily small. Thus, by miniaturizing their arrow tips, prehistoric people in Eastern North America optimized their projectile weaponry for maximum penetration and killing power in warfare and hunting. Finally, we verify that these functional advantages were selected across environmental and cultural boundaries. Thus, while we cannot and should not rule out stochastic, production economizing, or non-adaptive cultural processes as an explanation for TSAT, overall our results are consistent with the hypothesis that broad, socially stressful demographic changes in late pre-contact Eastern North America resulted in the miniaturization–and augmented lethality–of stone tools across the region.

Stall Control by Plasma Actuators: Characterization along the Airfoil Span

A dielectric barrier discharge actuator (DBD) is considered and studied as a stall recovery device. The DBD is installed on the nose of a NACA0015 airfoil with chord × span 300 × 930 mm. The geometry of the exposed electrode has periodic triangular tips purposely designed for the case under study. Wind tunnel tests have been carried out over a range of airspeeds up to 35 m/s with a Reynolds number of 700 k. The flow morphology has been characterized by means of the particle image velocimetry technique, obtaining velocity fields and pressure coefficients. By exploring different planes along the model span, the three-dimensional effect of the DBD has been reconstructed, identifying the flow region mainly sensitive to the plasma actuation. Finally, the actuator effectiveness has been quantified accounting for the power consumption data, leading to defining further design improvements in view of a better efficiency.

Configurations of triangular prism and slit electrode pairs to enhance the performance of electro-conjugate fluid micropumps

Previously, electro-conjugate fluid (ECF) micropumps with triangular prism and slit electrode pairs (TPSEs) have been developed and utilized for various mechanical, optical, chemical, and biomedical applications. However, the structural parameters of TPSEs have been determined by trial-and-error rather than systematical analysis. To this end, we select four structural parameters (i.e. hole width of a slit electrode: w, hole depth of a slit electrode: t, tip angle of a triangular prism electrode: , and gap between the triangular prism electrode and slit one: d) and implement the optimization to investigate their effects on the characteristic performance of ECF micropumps mainly depending on the combination of MEMS fabrication and experimental validation. Firstly, as a supplementary means, the simulation analysis is conducted with just consideration of the electric field intensity generated by TPSEs. After MEMS fabrication, the characteristic performance is experimentally characterized by comprehensively considering the generated electric field intensity, the flow dynamics, and the defect of microfabrication. The results show that the designed ECF micropump can attain the maximal output power under an applied DC voltage of 2 kV at the conditions of the slit hole width w = 200 µm, the slit hole depth t = 200 µm, the triangular tip angle = 60°, and the electrode gap d =200 µm. This optimization of TPSEs offers the helpful design guidance of ECF micropumps with higher output performance and promotes their further widespread use.

Separation Control by Plasma Actuators: Effects of Direct Momentum Injection and Vortex Generation

In this work, Dielectric Barrier Discharge actuators with triangular tips on their exposed electrodes are applied on a NACA 0015 airfoil and tested in the wind tunnel at an airspeed of 20 m/s (Re = 330k); the actuator set has been defined after previous laboratory studies. Steady and pulsed actuation are tested on all devices, including a straight DBD as reference. Force coefficients and electrical power are measured for every actuator, evaluating their performance in terms of aerodynamic coefficients changes with respect to the smooth airfoil and to the unpowered case, which is also characterized by means of surface visualizations. The influence of discharge length and tip spacing is studied by image processing techniques. The local field of motion is characterized by means of boundary layer velocity profiles, acquired with plasma off and on. Boundary layer thickness and momentum coefficients are determined at different spanwise locations for all the devices. The results are discussed evaluating the different impacts of streamwise momentum injection and vortex generation on the actuators performance, assuming these mechanisms as proper models for the data interpretation. In turn, this leads to outline possible design rules for this kind of DBD.

Fracture Behavior of Mullite Reticulated Porous Ceramics for Porous Media Combustion.

Mullite reticulated porous ceramics (RPC) are one of the key components for porous media burner, the mechanical properties of mullite RPC decided the service life of the burner. However, the irregularities of cellular structure made it difficult to reveal the fracture behavior of mullite RPCs. In this study, the three-dimensional (3-D) structures of mullite RPCs were analyzed by X-ray computed tomography. The strength and damage behavior of mullite RPCs were respectively investigated via the compression tests and finite element modeling based on the actual 3-D model, also the corresponding strengthening mechanism was proposed. The results indicated that the reconstructed 3-D model exhibited the real microstructure of mullite RPCs, containing the hollow struts and strut defects. The Young's modulus calculated from actual 3-D structures was lower than that from Gibson-Ashby theory. In addition, the surface defects preceded triangular tips to generate the area of stress concentration, leading to the fracture behavior first occurred at the strut defects. With the formation of dense strut in mullite RPCs, the stress uniformly distributed in the whole solid skeleton, thus significantly improving the damage resistance of mullite RPCs.

Ice-sheet scale distribution and morphometry of triangular-shaped hummocks (murtoos): a subglacial landform produced during rapid retreat of the Scandinavian Ice Sheet

AbstractHigh-resolution digital elevation models of Finland and Sweden based on LiDAR (Light Detection and Ranging) reveal subglacial landforms in great detail. We describe the ice-sheet scale distribution and morphometric characteristics of a glacial landform that is distinctive in morphology and occurs commonly in the central parts of the former Scandinavian Ice Sheet, especially up-ice of the Younger Dryas end moraine zone. We refer to these triangular or V-shaped landforms as murtoos (singular, ‘murtoo’). Murtoos are typically 30–200 m in length and 30–200 m in width with a relief of commonly <5 m. Murtoos have straight and steep edges, a triangular tip oriented parallel to ice-flow direction, and an asymmetric longitudinal profile with a shorter, but steeper down-ice slope. The spatial distribution of murtoos and their geomorphic relation to other landforms indicate that they formed subglacially during times of climate warming and rapid retreat of the Scandinavian Ice Sheet when large amounts of meltwater were delivered to the bed. Murtoos are formed under warm-based ice and may be associated with a non-channelized subglacial hydraulic system that evacuated large discharges of subglacial water.

PIV characterization of a separated flow controlled by a DBD actuator

This work investigates the three-dimensional effects of a dielectric barrier discharge actuator as a stall recovery device. The actuator is installed on a NACA0015 airfoil with a 930 mm span and a 300 mm chord and the exposed electrode has periodic triangular tips specifically designed for the case under study. It was tested at progressively increasing velocities, up to 35 m/s corresponding to a Reynolds number of 7×105. The PIV technique has been used to characterize the flow morphology along the model span, identifying the flow region mainly sensitive to the plasma effect and suggesting possible design improvements to achieve a better efficiency.

Effects of diamond tip orientation on the dynamic ploughing lithography of single crystal copper

In the present study, molecular dynamics (MD) simulation and experimental tests are employed to investigate the influence of the probe orientation on the machined depth, generation of the material pile-up, and average cutting force when implementing dynamic ploughing process on a single crystal copper surface. A typical triangular pyramid diamond AFM tip is selected, and three probe orientations are studied. The energy dissipation per oscillation of the AFM cantilever is utilized to describe the interaction between the probe and sample surface experimentally. Results show that the probe orientation has a significant effect on the machined depth and material pile-up on the sides of the groove. The MD simulations mainly agree well with the experimental results. Based on the MD simulations, the difference of the machined depth results from the various material flow directions during the ploughing process. The average cutting force is also studied by the MD simulations, which shows good consistency with the variation of probe-sample contact area during the dynamic ploughing along each machined groove. These results indicate the tip orientation is also an important factor in the dynamic ploughing process, which can be used as a reference to improve the machining accuracy and optimize machining parameters in the dynamic ploughing lithography to broaden its practical application.

Flow separation control by pulsed corona actuators

In this experimental work, corona actuators with triangular tips on their anodes are applied on a symmetric airfoil and tested in the wind tunnel at a freestream velocity of 20 m/s (Re = 330k). The actuators are driven by a periodic waveform that improves remarkably their operability with respect to DC driving, increasing also their efficiency. The basic waveform or carrier wave can be modulated introducing a pulsed actuation as usually done for other kinds of plasma actuators. Steady (carrier only) and pulsed (modulated) operation are tested for two actuators, selected out of a larger set previously studied in the laboratory, and compared here with a standard wire-plate corona as reference. The diagnostics include measurements of aerodynamic forces, electrical parameters and local velocities, completed by surface visualizations. Force coefficients and electrical power are used to evaluate the actuators performance in terms of coefficients changes with respect to the smooth airfoil and to the unpowered case, determining also effectiveness parameters in N/W. At the same time, the control mechanism is studied by acquiring boundary layer velocity profiles with plasma off and on, and determining the momentum coefficient of the devices. The passive effects of the unpowered actuators are measured separately and also described by means of surface visualizations. The results confirm the streamwise momentum injection as main mechanism for these actuators, and lead to determine the best flow control achievable by this technique.

Influence of Disc Tip Geometry on the Aerodynamic Performance and Flow Characteristics of Multichannel Tesla Turbines

As a competitive small-scale turbomachinery option, Tesla turbines have wide potential in various fields, such as renewable energy generation systems and small power equipment. This paper investigates the influence of disc tip geometry, including its profile and relative height, on the aerodynamic performance and flow characteristics of one-to-one and one-to-many multichannel Tesla turbines. The results indicate that compared to the turbine with blunt tips, the isentropic efficiency of the one-to-one turbine with sharp tips has a little decrease, which is because the relative tangential velocity gradient near the rotational disc walls decreases a little and additional vortices are generated at the rotor inlet, while that of the one-to-many turbine with sharp tips increases significantly, resulting from an increase in the relative tangential velocity in the disc channels and a decrease in the low Mach number and vortex area; for instance the turbine efficiency for the former relatively decreases by 3.6% and that for the latter increases by 13.5% at 30,000 r/min. In addition, the isentropic efficiency of the one-to-many turbine with sharp tips goes up with increasing relative height due to increasing improvement of flow status, and its increment rate slows down. A circular or elliptic tip performs better with lower relative height and a triangular tip behaves better with higher relative height. To sum up, a blunt disc tip is recommended for the one-to-one turbine, and a sharp disc tip is for the one-to-many turbine. The relative height and tip profile of the one-to-many turbine should be determined according to their effects on turbine performance, manufacturing difficulty and mechanical deformation.

Effects of Downstream Structures on Aero Elastic Energy Harvesters From Wake-Induced Vibration

An upstream cylindrical bluff body connected to a tip body via an aluminum cantilever beam was tested as energy harvester in a wind tunnel. The characteristics and behavior of the different tip body configurations and lengths of aluminum cantilever beam were studied to optimize design to extract wind energy. Particular attention was paid to measure vibration amplitude and frequency response as a function of reduced velocity. Dynamic response showed that the device's behavior was dependent on both tip body shape and cantilever beam length. Flow visualization tests showed that high amplitude vibration was obtainable when a vortex was fully formed on each side of the downstream tip body. This was exemplified in a symmetrical triangular prism tip body at L/D1 = 5, where its structure's vibration frequency was close to its natural frequency. At such configuration, electrical energy was captured using a polyvinylidene fluoride (PVDF) piezoelectric beam of different load resistances, where an optimized load resistance could be found for each Reynolds number. Although power output and efficiency obtained were considerably weak when compared to those of traditional wind turbine, the design merits further research to improve its performance under various circumstances.

Simple interface for scanning chemical compounds on developed thin layer chromatography plates using electrospray ionization mass spectrometry

A simple and cheap design for interfacing thin layer chromatography (TLC) with electrospray ionization mass spectrometry (ESI/MS) was developed to scan and characterize compounds on TLC plate. The developed TLC plate was rapidly and easily modified into two sawtooth-edged pieces that were positioned on an XYZ stage so that one of the triangular tips was pointed toward the MS inlet. A drop of methanol and high DC voltage was applied at the tip to induce ESI. After the analytes in the first tip were analyzed, the TLC piece was moved so that the second triangular tip was pointed toward the MS inlet for analysis. The process was repeated until all the triangular tips on the piece were analyzed. In this manner, the analytes, no matter visible or non-visible bands, were scanned and characterized. Since a 4.8 cm long TLC track were cut to 32 triangles on two sawtooth pieces for analysis, the spatial resolution of using the sawtooth TLC-ESI/MS for analysis is 1.5 mm/band. A mixture of dye standards and Datura metel flower extract was analyzed to demonstrate the capability of sawtooth TLC-ESI/MS on scanning and characterizing chemical compounds on the TLC plates. The limits of detection of the dye standards were between 0.25 and 2.5 ng/band. TLC bands containing alkaloids such as scopolamine and norscopolamine from the Datura metel flower extract were not visualized on the developed TLC track, but were successfully detected at different triangular tips using sawtooth TLC-ESI/MS. Based on these results, the Rf values of scopolamine and norscopolamine were determined.

Size and shape effects on the field enhancement induced at a silver triangular tip

A computational study is conducted on the near field enhancement induced by localized surface plasmon resonance (LSPR) around a silver nanotape of various sizes and shapes. The results show the consistent dominance of the dipole field generated at the rectangular Ag nanotape surfaces of various lengths by a normal incident electromagnetic plane wave of polarization along the long edge. The dipole field is further shown to exhibit monotonous spectral redshifts and increased magnitudes with increased length (ℓ) of the rectangular nanotape. In contrary, the spectral peak and the field magnitude do not show the simple consistent variations with varied apex angle (θ) of the triangular nanotape. The calculated result for the triangular tape does exhibit the largely concentrated near field magnitude at the tip. It is found that a remarkable enhancement factor of 107 is attained at θ = 45° and ℓ = 50 nm.