Tip Shape Research Articles

Calibration of Paris law constants for crack propagation analysis of damaged steel plates strengthened with prestressed CFRP

Paris law constants, C and m, are two vital parameters of the Paris law for fatigue crack propagation of steel structures. Traditionally, the constants are determined through a linear regression of experimental crack growth curve under tension-to-tension cyclic loading. However, the direct linear regression would provide the value of C with larger error under negative stress ratios (tension-to-compression cyclic loading) probably caused by prestress. This study firstly proposed a reverse-reasoning methodology to obtain and calibrate Paris law constants based on the notched specimens with non– and prestressed CFRP (Carbon Fiber-reinforced Polymer) reinforcement under a wider range of stress ratios. Finite element (FE) modeling was then performed using a combination of the programs FRANC3D and ANSYS to compute the stress intensity factors (SIF) as well as crack tip shape evolution of the respective specimens. A sensitivity analysis was also made to investigate the variety of the constants affected by crucial factors. The comparison of experimental and theoretical results confirms excellent accuracy of the proposed method. The results indicated that the constant m is stable around 3.15 and prestress effect is significant not only on reduction of effective SIF range but also on change of the constant C. Moreover, the suggested value of m and C are 3.15 and 1.08E-12 for prestressed CFRP reinforced steel structures under negative stress ratio (R ≤ 0), and are 3.15 and 2.17E-13 for the positive stress ratio (R > 0) in the unit of mm and MPa, respectively.

Fabrication of probe tips via the FIB method for nanodiagnostics of the surface of solids by atomic force microscopy

In this work, we carried out an investigation of commercial atomic force microscope (AFM) probes for contact and semi-contact modes, which were modified by focused ion beam (FIB). This method was used to modify the original tip shape of silicon AFM probes, by ion-etching and ion-enhance gas deposition. we show a better performance of the FIB-modified probes in contrast with the non-modified commercial probes. These results were obtained after using both probes in semi-contact mode in a calibration grating sample.

Programming cell growth into different cluster shapes using diffusible signals.

Advances in genetic engineering technologies have allowed the construction of artificial genetic circuits, which have been used to generate spatial patterns of differential gene expression. However, the question of how cells can be programmed, and how complex the rules need to be, to achieve a desired tissue morphology has received less attention. Here, we address these questions by developing a mathematical model to study how cells can collectively grow into clusters with different structural morphologies by secreting diffusible signals that can influence cellular growth rates. We formulate how growth regulators can be used to control the formation of cellular protrusions and how the range of achievable structures scales with the number of distinct signals. We show that a single growth inhibitor is insufficient for the formation of multiple protrusions but may be achieved with multiple growth inhibitors, and that other types of signals can regulate the shape of protrusion tips. These examples illustrate how our approach could potentially be used to guide the design of regulatory circuits for achieving a desired target structure.

Segment tip geometry of sheet intrusions, I: Theory and numerical models for the role of tip shape in controlling propagation pathways

Inferences about sheet intrusion emplacement mechanisms have been built largely on field observations of intrusion tip zones: magmatic systems that did not grow beyond their observed state. Here we use finite element simulation of elliptical to superelliptical crack tips, representing observed natural sill segments, to show the effect of sill tip shape in controlling local stress concentrations, and the potential propagation pathways. Stress concentration magnitude and distribution is strongly affected by the position and magnitude of maximum tip curvature κmax. Elliptical tips concentrate stress in-plane with the sill, promoting coplanar growth. Superelliptical tips concentrate maximum tensile stress (σmax) and shear stress out-of-plane of the sill, which may promote non-coplanar growth, vertical thickening, or coplanar viscous indentation. We find that σmax = Pe(1+ 2(√[aκmax]), where Pe is magma excess pressure and a is sill half length. At short length-scales, blunted tips locally generate large tensile stresses; at longer length-scales, elliptical-tipped sills become more efficient at concentrating stress than blunt sills.

Initial Assessments of a Handheld Indentation Probe's Correlation With Cancellous Bone Density, Stiffness, and Strength: An Objective Alternative to “Thumb Testing”

Abstract Objective: During shoulder arthroplasty, surgeons must select the optimal implant for each patient. The metaphyseal bone properties affect this decision; however, the typical resection “thumb test” lacks objectivity. This investigation's purposes were to determine the correlation strength between the indentation depth of a handheld mechanism and the density, compressive strength, and modulus of a bone surrogate; as well as to assess how changing the indenter tip shape and impact energy may affect the correlation strengths. Methods: A spring-loaded indenter was developed. Four tip shapes (needle, tapered, flat, and radiused cylinders) and four spring energies (0.13 J–0.76J) were assessed by indenting five cellular foam bone surrogates of varying density, every five times. After each indentation, the indentation depth was measured with a separate probe and correlated with manufacturer specifications of the apparent density, compressive strength, and modulus. Results: indentation depth plateaued as the bone surrogate's material properties increased, particularly for indentation tips with larger footprints and the 0.13 J spring. All tip shapes produced strong (R2≥0.7) power-law relationships between the indentation depth metric and the bone surrogate's material properties (density: 0.70 ≤ R2 ≤ 0.95, strength: 0.75 ≤ R2 ≤ 0.97, modulus: 0.70 ≤ R2 ≤ 0.93); though the use of the needle tip yielded the widest indentation depth scale. Interpretation: these strong correlations suggest that a handheld indenter may provide objective intra-operative evidence of cancellous material properties. Further investigations are warranted to study indenter tip shape and spring energy in human tissue; though the needle tip with spring energy between 0.30 J and 0.76 J seems the most promising.

Wind tunnel testing of a swept tip shape and comparison with multi-fidelity aerodynamic simulations

Abstract. One promising design solution for increasing the efficiency of modern horizontal axis wind turbines is the installation of curved tip extensions. However, introducing such complex geometries may move traditional aerodynamic models based on blade element momentum (BEM) theory out of their range of applicability. This motivated the present work, where a swept tip shape is investigated by means of both experimental and numerical tests. The latter group accounted for a wide variety of aerodynamic models, allowing us to highlight the capabilities and limitations of each of them in a relative manner. The considered swept tip shape is the result of a design optimization, focusing on locally maximizing power performance within load constraints. For the experimental tests, the tip model is instrumented with spanwise bands of pressure sensors and is tested in the Poul la Cour wind tunnel at the Technical University of Denmark (DTU). The methods used for the numerical tests consisted of a blade element model, a near-wake model, lifting-line free-wake models, and a fully resolved Navier–Stokes solver. The comparison of the numerical and the experimental test results is performed for a given range of angles of attack and wind speeds, which is representative of the expected conditions in operation. Results show that the blade element model cannot predict the measured normal force coefficients, but the other methods are generally in good agreement with the measurements in attached flow. Flow visualization and pressure distribution compare well with computational fluid dynamics (CFD) simulations. The agreement in the clean case is better than in the tripped case at the inboard sections. Some uncertainties regarding the effect of the boundary layer at the inboard tunnel wall and the post-stall behavior remain.

Atomic Force Microscopy and Infrared Nanospectroscopy of COVID-19 Spike Protein for the Quantification of Adhesion to Common Surfaces.

The COVID-19 pandemic has claimed millions of lives worldwide, sickened many more, and has resulted in severe socioeconomic consequences. As society returns to normal, understanding the spread and persistence of SARS CoV-2 on commonplace surfaces can help to mitigate future outbreaks of coronaviruses and other pathogens. We hypothesize that such an understanding can be aided by studying the binding and interaction of viral proteins with nonbiological surfaces. Here, we propose a methodology for investigating the adhesion of the SARS CoV-2 spike glycoprotein on common inorganic surfaces such as aluminum, copper, iron, silica, and ceria oxides as well as metallic gold. Quantitative adhesion was obtained from the analysis of measured forces at the nanoscale using an atomic force microscope operated under ambient conditions. Without imposing further constraints on the measurement conditions, our preliminary findings suggest that spike glycoproteins interact with similar adhesion forces across the majority of the metal oxides tested with the exception to gold, for which attraction forces ∼10 times stronger than all other materials studied were observed. Ferritin, which was used as a reference protein, was found to exhibit similar adhesion forces as SARS CoV-2 spike protein. This study results show that glycoprotein adhesion forces for similar ambient humidity, tip shape, and contact surface are nonspecific to the properties of metal oxide surfaces, which are expected to be covered by a thin water film. The findings suggest that under ambient conditions, glycoprotein adhesion to metal oxides is primarily controlled by the water capillary forces, and they depend on the surface tension of the liquid water. We discuss further strategies warranted to decipher the intricate nanoscale forces for improved quantification of the adhesion.

Thermal welding of polymeric biomaterials: Development of a novel device for temperature controlled local application

Abstract We present a thermal processing device, equipped for local heating and welding of biomaterials, e.g. electrospun nonwovens or polymer films. Depending on the application and choice of materials, we aim to determine appropriate processing parameters for permanent and non-permanent welds. Due to the modular device structure, applicationspecific heating tools can be used. Process temperature up to 250 °C is feasible. In this concept study, a welding tool with interchangeable small-size heating tips of different geometric shapes were investigated regarding their suitability for welding of polycarbonate urethane based silicone elastomer nonwovens. Generated welds were examined by imaging techniques and tensile testing. Regardless of the tip shape, welds were generated withstanding forces up to 3.0 N and 4.3 N for tensile and shear loading, respectively.

Experimental study on the influence of cutter shape on cutter wear for hard rocks

Cutter shape is an important factor on cutter wear for hard rock TBMs. In this paper, the influence of cutter shape on the cutter wear was investigated by the wear tests on small-size cutters with the scale of 1/10 of the actual size, and the related rock fragmentation characteristics induced by different cutters was studied as well. In the tests, 6 types of small-size cutters, considering the design parameters of cutter diameter, cutter tip width and cutter tip shape, were selected. The granite samples were collected from the Beishan site, Gansu province of China. For each test, the cutting distance of the single cutter was 100m, and then the cutter wear could be obtained by weighing method. The tests shown that, 1) the cutter wear was basically proportional to the cutter tip width when the same penetration was reached, while the cutter force was not reduced remarkably for the narrow cutter when compared with that of wide-tip cutter; 2) the wear of 17-inch cutter was much higher when compared with that of 19-in and 20-in cutters; 3) the wear of round-edged cutter was obviously lower than that of flat-edged cutter, due to the former hardly presented curling behaviour after cutting while the latter had obviously curled. The test results facilitated better understanding of wear mechanism of TBM cutters and provided the references for cutter selection for TBM tunnelling in hard rock.

Morphological characterization of Gossypium arboreum germplasm using qualitative descriptors

The study was undertaken to determine the Distinctness, Uniformity and Stability characteristics of fifty-seven germplasm accessions of Asiatic cotton. The experiment was carried out using Augmented Block Design during summer 2021. Based on dissimilarity matrix scores, the genotypes were divided into five distinct clusters. Cluster V had the most genotypes (29), while Cluster II had only one genotype (PDB 4). Seven principal components were defined through Principal Component Analysis (PCA), accounting for 84.43 per cent of the total variation. The first principal component (PC 1) was associated with boll tip (0.62) and boll shape (0.56). The second principal component (PC 2) was associated with boll color (0.43) and stem pigmentation (0.38). The trait boll colour had the highest diversity index (4.04). Petiole pigmentation (3.532) had the lowest diversity index, followed by leaf nectaries (3.640) and leaf pubescence (3.742). Genotypes namely PDB 4, CNA 1054, PDB 29, DWDA 1602, NDLA 3086 and MDL 2663 occupied convex of the hull and had the highest point among the variables. Key words: DUS characters, Asiatic cotton, clusters, principal component analysis

Surgical needles in orthopedics and trauma surgery

Für Chirurgen in der Klinik und Praxis ist der Umgang mit Nahtmaterial das „tägliche Brot“. Daher könnte man annehmen, dass die Kenntnisse dieses Materials kompetent und umfassend sind. Die tägliche Erfahrung zeigt indes ein anderes Bild. Oft sind die Kenntnisse bezüglich Nadelform, Nadelbeschaffenheit sowie Nadelgröße nur marginal und der Chirurg muss sich auf die Kenntnisse seiner OP-Pflegefachkraft verlassen. Die Wahl der Nadel ist für jeden Operationsschritt und jedes Gewebe ausschlaggebend. Die Verwendung des korrekten Nahtmaterials in Bezug auf das zu nähende Gewebe ist jedoch essenziell, einerseits hinsichtlich der Qualität der Naht, aber auch hinsichtlich der Traumatisierung des Gewebes andererseits. Je nach Gewebe sind an Nadel wie auch an Fäden verschiedene Anforderungen zu stellen respektive zu berücksichtigen. Mit diesem Beitrag sollen die wesentlichsten und grundlegendsten Kenntnisse vermittelt werden wie Einfluss der Nadelform und Dimension, Auswirkung von atraumatischen respektive traumatischen (sog. scharfe) Nadeln auf das Gewebe, die Form der Nadelspitze. Das Zusammenspiel zwischen Nadelhalter und Nadel und der Hand des Operateurs bei verschiedenen Anwendungen wird dargestellt. In diesem Beitrag wird das Hauptaugenmerk auf Nadel und Nadelhalter gelegt. In Planung ist ein Nachfolgebeitrag, der sich speziell dem Nahtmaterial widmet. Der Beitrag erhebt nicht den Anspruch auf 100 %ige Vollständigkeit, es sollen jedoch die wesentlichsten, alltäglich vorkommenden Fragen geklärt werden.Zusatzmaterial onlineDie Online-Version dieses Beitrags (10.1007/s00064-021-00734-7) enthält eine Vergleichstabelle der chirurgischen Nadeln verschiedener Hersteller (ESM2) inklusive Erläuterungen (ESM1) sowie 2 Videos zu den Nadelhaltergriffen: Video 1 Nadelhaltergriff: Daumen-Ringfinger-Griff (ESM3) und Video 2 Nadelhaltergriff: Daumenballengriff (ESM4) (Videos: Mit freundl. Genehmigung von © Dr. Theddy Slongo [Autor der Videos], Inselspital Bern, Paediatric Trauma and Orthopaedics, University Children’s Hospital, Dept. of Paediatric Surgery. Alle Rechte vorbehalten).

A NEW SPECIES OF ALLINTOSHIUS (NEMATODA: HELIGMOSOMOIDEA) FROM TWO SPECIES OF BATS IN BRAZIL.

Allintoshius Chitwood, 1937 is the only genus of the family Ornithostrongylidae (Travassos, 1937) Durette-Desset and Chabaud, 1981 that parasitizes bats. Currently, there are 10 valid species in the genus, of which 3 were described from Brazil. This study describes a new species of Allintoshius and records the first occurrence of a nematode of this genus parasitizing Artibeus lituratus (Olfers). Allintoshius gomesae n. sp. is characterized by having anterior region coiled, cephalic vesicle with cuticular dilation striated transversely, and claviform esophagus. Synlophe in females consists of 16 cuticular ridges at the mid-body. Males have large caudal bursa, and conic and small spicules, and the gubernaculum is absent. Females have uterus didelphic, amphidelphic, tail tip tapered, and ovijector divided into 2 divergent branches, subequal in length. The new species differs from its congeners especially by the shape of the tail tip, vulvar opening, and size of spicules. Allintoshius gomesae is the fourth species of Allintoshius from Brazil and the first report in Ar. lituratus, increasing the number of species recognized of the genus.

Analysis of Mechanical Behavior of Different Needle Tip Shapes During Puncture of Carbon Fiber Fabric

Abstract In the present study, the fiber-bending around the needle during the piercing process of the carbon fabric is investigated. In this regard, a mathematical model is established to investigate the bending elongation of the carbon fiber around the needle and the interaction between the carbon fiber and the needle tip. Then the mechanical behavior of the carbon fabric when moving down the tip of the steel needle is analyzed. Based on the performed analysis, a shape curve equation that satisfies the puncture needle tip is established. Furthermore, the influence of different needle tip shapes on the mechanical behavior of the carbon fiber is analyzed. The performance of the needle tip is subjected to different loads, including the puncture template, horizontal tension of the fiber to the needle tip, frictional resistance between the fiber and the needle tip, sliding force, and the bending moment. The performed analysis shows that when the shape of the needle tip assumes the form of curve 10, the downward force, horizontal tension, friction resistance, sliding force, and bending moment are minimized. Accordingly, curve 10 is proposed as the optimal shape for the needle tip. The present study is expected to provide theoretical guidance for selecting overall puncture process parameters.

A novel intelligent microcatheter-shaping method for embolization of intracranial aneurysm

Objective:This study proposed and validated an intelligent microcatheter-shaping algorithm for interventional embolization of intracranial aneurysms.Methods:A stepwise microcatheter simulation algorithm constrained by a vessel center line was developed based on the geometry of aneurysms and parent arteries, and a collision correction factor of vessel walls was introduced to automatically calculate the optimal microcatheter path and tip shape. The efficacy of this intelligent shaping method was verified in an in vitro aneurysm model experiment.Results:The microcatheter path can be automatically generated using the intelligent microcatheter-shaping algorithm. Furthermore, the experiment verified that the delivery performance of an intelligently shaped microcatheter was excellent with 100% placement accuracy, superior to that of three pre-shaped microcatheters: straight (0°), 45°, and 90°. In three typical cases, the microcatheter could not be placed in the aneurysms successfully within 5 min with the aid of a microwire using a manual shaping scheme; however, it can be placed in the aneurysms successfully within 5 min using an intelligent microcatheter- shaping scheme, and the time of microcatheter placement in aneurysms was short.Conclusion:This intelligent microcatheter-shaping algorithm based on three-dimensional image data is effective and reasonable. This approach has advantages over standard pre-shaped microcatheters, with a potential clinical application value.

Laboratory study on negative spark inception direction and breakdown characteristics in rod–rod air gaps

To better understand the inception direction and breakdown characteristics of negative sparks in rod–rod air gaps, experiments have been carried out with negative 250/2500μs voltage impulses in 0.4m-1.2m air gaps. Three types of air gaps were used including rod-double rods air gaps and two kinds of rod–rod air gaps. Initial angle of spark channel defined as the angle between tangential directions of the initial spark channel to vertical was found to follow Normal distribution in rod–rod air gaps. The average initial angle of negative sparks in rod–rod air gaps is 14°-62° which is larger than that of positive sparks in 0.5m rod-plane air gaps and close to those in 7m-8m rod-plane air gaps. The inception direction and breakdown characteristics of 0.4m-1.2m rod–rod air gaps are influenced by gap distance, grounded rod tip shape and applied voltage amplitude. The negative 50% breakdown voltage increases linearly with gap distance, which is also influenced by gap configuration. As gap distance was elongated, longer upward streamer occurred at conical grounded rod tip resulting in larger attraction and higher striking probability of grounded rod with conical tip; with higher voltage amplitude, the initial angle and striking selectivity of grounded rods become more random.

Morphometrics and Redescription of Aphyllon fasciculatum and Aphyllon franciscanum, Two Widespread but Previously Conflated Species in Western North America

Abstract— We continue the taxonomic reevaluation of Aphyllon sect. Aphyllon by describing a widespread species throughout western North America previously recognized within a polyphyletic A. fasciculatum. To support our description and revised key, we analyzed fifteen continuous and discrete characters sampled from 186 herbarium specimens and iNaturalist observations representing the geographic and host ranges. Principal component and multiple correspondence analyses reveal clear variation in floral characters. Discriminant analyses show that three aspects of floral color, corolla lobe tip shape, the calyx cup to calyx lobe ratio, calyx lobe length, and degree of bend in the corolla tube are useful distinguishing features, but not diagnostic in every case.

Effects of Nozzle and Roll on Surface Condition of Al-1%Si Strip Cast Using Vertical type High Speed Twin Roll Caster

When a strip of Al-Si alloy with an Si content of 1% was cast using a vertical-type high-speed twin-roll caster, cracks form in its surface. The effects of the pouring method, the shape and position of the nozzle, and the roll surface texture on surface crack formation were evaluated with a roll caster. The rolls were made of a copper alloy, and the roll speed was 30 m/min. The as-cast strips were bent to investigate the degree of crack formation, and the outer surface of the strips was observed without magnification and with a stereomicroscope to determine the influence of the pouring method, the shape and position of the nozzle, and the roll surface. A roll machined to form V-shaped grooves 0.4 mm deep on the surface of the strips was most useful for reducing surface cracking. Changing the shape of the nozzle tip was second-most effective. There was a clear correlation between the roll surface condition and surface cracking in the Al-Si strip.

Photoelastic stress analysis of mode I fracture toughness tests using PMMA samples

Rocks are usually inhomogeneous and anisotropic materials. The presence of foliation planes, grain boundaries or even microcracks may alter the stress distribution. In order to identify whether unusual behaviours in rocks are due to these imperfections or result from other factors (e.g. experimental configuration), the analyses of homogenous and isotropic materials is an useful approach. We have performed a series of mode I fracture toughness (KIC ) tests using polymethyl methacrylate (PMMA) samples, which has the advantage of allowing photoelastic stress analysis based on its birefringent nature. Three different testing configurations were considered in the study: S\\ emi-circular bend (SCB) test, the pseudo-compact tension (pCT) test, and a new alternative configuration based on the previous two that we have called pseudo-SCB (pSCB) test. To perform the photoelastic analysis, all the experiments were complemented with a specially-designed experimental setup consisting in two orthogonally arranged circular polarizers placed on both sides of the tested specimens. Using a source of white (polychromatic) light on one end it is possible to record the stress distribution using a digital camera aligned with the samples on the other end. As the load increases, a distinct evolving pattern of colour fringes can be visualized in the samples illustrating the spatially distributed stress levels. Based on this analysis we observe in some of the tests performed non-symmetrical stress fields. Although this behaviour could be related with the testing configuration, results suggest that other features, such as the shape of the notch tip, imperfections in sample preparation, or the misalignment of the samples in the testing device may also have an influence in stress distribution.

Recognition and differentiation of dural puncture click sensation: A subjective and objective prospective study of dural puncture forces using fine-gauge spinal needles.

We hypothesized that the click perceived when puncturing the dura-arachnoid with fine-gauge spinal needles can be subjectively identified, and investigated whether it may be distinguishable among different needle types. Subjective and objective evaluations were performed. First, physicians punctured the polyamide film or porcine dura mater (n = 70 and n = 20, respectively) with seven types of spinal needles and numerically evaluated the perceived click sensations. Using an 11-point numerical rating scale (from "0" for "no click sensation" to "10" for "the strongest click perceived") data, subjective differentiation among needle types was assessed. Second, in the objective part of the study, total forces elicited by polyamide film or porcine dura mater punctures with each needle were measured using a biomechanical testing device, and load-displacement curves evaluated. Third, the results of subjective and objective evaluations were compared. All participants recognized the click and could discriminate among needles of different tip shape. The load-displacement curves for polyamide film and porcine dura mater were similar and needle-specific. The subjective numerical rating scale values corresponded well with the objectively measured changes in total forces (R2 = 0.862 and R2 = 0.881 for polyamide film and porcine dura mater, respectively), indicating that an increase in the largest drop in total force value of 0.30 N or 0.21 N would produce an increase of numerical rating scale value of 1 for polyamide film and porcine dura mater, respectively. We provide an objective proof of the click sensation felt upon dural puncture using different fine-gauge spinal needles. Click recognition could be used as an additional indicator of successful spinal puncture.

Creation and Characterization of an Atomically Sharp Single/Trimer Atom Ir/W(111) Tip by Thermal Field-Assisted Faceting

Atomically sharpened tips have attracted much interest in the imaging and manufacturing fields due to their high spatial resolutions. Typically, tungsten (W) is mainly used as the material of such a tip, but when the W tip is used in an oxygen environment, a limit is revealed due to corrosiveness stemming from a reaction with the oxygen gas. To solve this problem, methods of depositing a metal on W that does not react with oxygen have been studied. In this study, we introduce a method of depositing iridium (Ir) directly onto an insulating layer without an additional pretreatment to remove the insulating layer remaining on the W surface, forming an Ir-nanopyramid structure at the apex of the W tip by field evaporation and faceting. Field ion microscopy and atom probe tomography were used to analyze the crystal structure and composition at the apex during the faceting process, and the overall tip shape change after faceting was compared and analyzed with transmission electron microscopy. The proposed method does not have a tip heating step when creating an atomically sharp tip such that it can be made easily with a simpler equipment configuration than in the existing method.