Microscopic Irregularities Research Articles

Analysis of Cutting Capacity, Surface Finishing, and Mechanical Properties of NiTi Instruments 25/.04: ROTATE and LOGIC 2

IntroductionIn an effort to enhance the quality of mechanized endodontic instruments, various thermal treatment methods, and design modifications have been suggested. However, upon evaluation, these endodontic instruments may exhibit microscopic irregularities. The objective of this in vitro study was to analyze the cutting capacity, surface finish, and mechanical properties of Nickel-Titanium 25/.04 Rotate (VDW GmbH, Munich, Germany) and LOGIC 2 (Easy Equipamentos Odontológicos, Belo Horizonte, MG, Brazil) rotary instruments. MethodologyTwenty rotary instruments were divided into 2 groups: GR, the group with ROTATE instruments (n = 10); and GL2, the group with LOGIC 2 instruments (n = 10). They were evaluated for roughness, using a profilometer, for bending resistance, buckling resistance, and cutting capacity using a universal testing machine, as well as for torsional strength (torque and angular deflection) using a torquemeter. The instruments were visualized before and after the mechanical tests through scanning electron microscopy. ResultsGR showed better surface finish in terms of roughness, greater cutting capacity, and greater angular deflection than GL2 (P < .05). However, GL2 showed better flexibility than GR (P < .05). GL2 and GR did not show statistically significant differences in terms of buckling and torque (P > .05). ConclusionThe ROTATE and LOGIC 2 rotary instruments differed in their surface finish, cutting capacity, and mechanical properties, except for their buckling resistance and required fracture torque.

Shear bond strength of MDP-containing light-cured veneer adhesive system to zirconia with different surface preparations

This study aimed to evaluate the effects of different surface preparation techniques on the surface microstructure, the shear bond strength (SBS) between zirconia and an MDP-containing light-cured veneer adhesive system, and the adhesive failure mode. Sixty-four zirconia specimens were divided into four groups based on surface preparation methods (n = 16), including zirconia sandblasting (ZSB), zirconia vitrification or glaze-on (ZVG), zirconia surface architecture technique (ZSAT), and ZSAT-ZVG combined technique (ZSATVG) groups. Sixteen lithium disilicate specimens prepared by etching with hydrofluoric acid (HF) were used as a positive control group (LDE). Surface roughness measurement and scanning electron microscopy (SEM) evaluation were performed before and after surface preparation. All specimens were then bonded with an MDP-containing light-cured adhesive system, followed by SBS testing and adhesive failure mode analysis. The ZVG and ZSATVG groups showed the greatest differential roughness value and microscopic irregularities, while the ZSAT and LDE groups had the least surface change but the most micromechanical retentive structures for resin infiltration. SBS values were significantly different among groups (p < 0.001) with the highest SBS observed in the ZSAT group, followed by the ZSB group, LDE group, ZSATVG group, and lastly, the ZVG group. There was a statistically significant difference in failure types among the surface preparation groups (p < 0.001). The ZSAT group had the highest frequency of mixed failure, followed by the ZSB group, LDE group, and the ZSATVG and ZVG groups. Establishing direct micromechanical retention within zirconia itself yields a higher bond strength than indirect micromechanical retention within a glass ceramic layer.

Numerical Study of the Influence of the Geometrical Irregularities on Bodies of Revolution at High Angles of Attack

The flow at high angles of attack over axisymmetric configurations is not symmetric. The mechanism that triggers the asymmetry may be a combination of a global or hydrodynamic instability (temporal instability) combined with a convective instability (spatial instability) due to microscopic irregularities of the configuration. Poor repeatability of experiments and large differences in the global forces have been obtained with very small changes of the nose tip. In order to study theoretically this phenomenon, numerical simulations have been conducted for an ogive-cylinder configuration at subsonic flow and high angle of attack. For the numerical prediction of the flow about a missile type configuration, an assessment of the effect of structured and unstructured meshes is very important. How the body surface is modelled is very relevant; especially the tip zone of the body. Either configuration resembles a smooth or a rough model. The effect of the turbulence models is also decisive. The analysis has led to the conclusion that only Reynolds stress turbulence models (RSM) combined with Scale Adaptive Simulation (SAS), are the appropriate theoretical tools for the characterization of this flow. The geometrical similarity is very important. There is a roll or orientation angle effect for the unstructured grid, while the structured grid presents a bi-stable solution, one mirror of each other.

A comprehensive experimental and numerical estimation of thermal contact conductance

Realizing perfect contact between any two surfaces is impossible due to the presence of microscopic irregularities in material surfaces. Therefore, for true thermal analysis of multiple components systems knowledge of thermal contact conductance (TCC) between two solid bodies is essential. Estimation of TCC for different applications has been carried out in this paper by inverse heat transfer technique. A novel stochastic Jaya algorithm has been developed for this purpose and its performance has been evaluated for different heat conduction problems like the estimation of TCC with two metals contact (case-1), periodically contacting surfaces (case-2), multilayer wall surfaces (case-3), and simultaneous estimation of TCC and boundary heat flux (case-4). The experiment has also been conducted to determine the efficacy of this new algorithm for real-life situations. Different parameters like population size, sensor location from the interface, and errors in measured temperature data are taken into consideration. The population size of 5 candidate solutions for case-1, 60 candidate solutions for case-2, and 50 candidate solutions for case-3 and case-4 is found to be suitable for estimation. The results are accurate with the root mean square (RMS) error of 12.62 W/m2K even when the sensors are located 50 mm far away from the interface. Although errors in measurements deteriorate the performance of the Jaya algorithm, it still gives stable results (RMS = 2.90 W/m2K at σ = 0.3). Jaya algorithm is found to be an accurate and promising algorithm for inverse problems.

Observation of fatigue microcracks and estimation of fatigue strength of a thin sheet arc welded part considering micro-ripples

Fatigue tests were conducted on a thin sheet arc welded part using two types of welding wires. Microscopic observations of specimens tested at the fatigue limit stress revealed that microcracks were initiated in the micro-ripples on the weld metal surface. Furthermore, a coarse ferrite structure often contains existing microcracks. A method for quantitatively evaluating the effects of microscopic irregularities on the weld metal surface and macroscopic toe shape on the fatigue strength is proposed. It was found that microscopic irregularities on weld metal have a significant impact on the fatigue limit, depending on their metallurgical structure.

Assessment of Surface Roughness Bounded by Concave Semicircles

For surface texture with microprojections bounded by concave semicircles in two-dimensional space, analytical formulas are derived for the probability of filling of the surface layer with material, both within cross sections and layers and over the volume as a whole. Comparison of probability estimates obtained by graphical and analytical methods permits judgments regarding their correspondence to the surface of parts machined by various methods. The probability characteristics provide quantitative assessment of the structure of the microscopic irregularities and take account of their shape, repetition frequency, and height in the case of identical geometric characteristics. An analytical expression for the shape of the profile in Fourier-series form is obtained and may be used in developing software for CNC machine tools.

Conjunctival Carcinomas Arising in the Anophthalmic Socket.

The aim of this study was to report management and outcomes of patients in which conjunctival carcinomas arose in the anophthalmic socket. The authors retrospectively analyzed the data of patients which presented the anophthalmic socket after surgery. The clinical records of 4 patients with histological diagnosis of conjunctival carcinoma in the anophthalmic socket, referred to our Department, between January 2014 and December 2019 was collected. The study included 4 men (median age 58 years). A previous enucleation surgery had been performed in all patients due to previous ocular trauma for three patients (Case 1, 3, and 4) and due to a retinoblastoma for 1 patient (Case 2). All patients underwent surgical excision of the lesion and only 1 patient (case 3) underwent orbital exenteration due to the high-grade of the cancer. The most common tumor was the squamous cell carcinoma (2 cases) followed by 1 case of high-grade mucoepidermoid carcinoma and 1 case of carcinoma in situ. Systemic work-up was performed for all the patients. Conjunctival TNM, according to the American Joint Committee on Cancer TNM staging system was used to stage the lesions. The median follow-up time was 15 months. Considering the severity and rarity of these tumors, a careful ophthalmological examination of the cavity and a correct revision of the prosthesis should be mandatory in order to ensure the elimination of any macro and microscopic irregularities that can then in the long-term cause chronic inflammation of the tissues and consequently promote the growth of carcinomas.

Risco Biológico e/ou Químico eventualmente associado ao uso de adereços pelo Trabalhador (como anéis, alianças, relógios, pulseiras)

Introduction/ background/ objectives There are some manuals of Good Practices, in some professional sectors, that highlight the need to stop use jewelry at work (such as finger rings, watches, bracelets and/ or equivalent), relating to the potentialization of contact with biological agents and/ or chemical. The studies dedicated to this theme are very scarce and all related to health professionals; although, in many other sectors, it is a relevant topic, like in food production, tattooing, preparation of equipment that needs to be sterile and any sector that deals with chemical agents, for example. Methodology It is an Scoping Review, initiated through a research conducted in December 2019 in the databases “CINALH plus with full text, Medline with full text, Database of Effects Review Abstracts, Cochrane Central Register of Controlled Trials, Cochrane Database of Systematic Reviews, Cochrane Methodology Record, Nursing and Allied Health Collection: comprehensive, MedicLatina, Scopus and RCAAP ”. Content The use of finger rings decreases efficacy of hand washing, since some bacteria can remain in microscopic irregularities under the ring. In addition, they can tear the protective gloves; even so, the use of this individual protective equipment attenuates the microbial load of the rings. However, some investigators argue that there is no statistical evidence that the use of rings will alter postoperative infraction rates. Those with smooth surfaces, like classic wedding rings, do not appear to be so problematic. As for watches and bracelets, it appears that they do not contribute to a significant increase in the rate of infringement; yet some researchers recommend that they be removed, before hand washing. The use of nail varnish decreases efficacy of hand washing, since some bacteria can remain in the microscopic irregularities of the varnish; however, there is no robust statistical evidence that the use of varnishes alters the rate of postoperative infection. Long nails have a higher microbial load, especially if recovered by irregular varnish (with a few days). In addition, big nails can also increase the likelihood of tearing the glove, whether natural or artificial. So it makes sense that some professionals use them short. Since scientific evidence that correlates hospital infection to the use of artificial jewelry or nails among healthcare professionals is not very robust, the norms at some institutions are in the format of recommendations only. Conclusions Studies are scarce and do not appear to be concordant or robust on several occasions, so it would be useful that Occupational Health teams, from companies with biological and/ or chemical risk, design and carry out studies and, subsequently, publish it to specialty magazines. In doubt, until clear evidence appears, objects such as finger rings, rings, watches and bracelets should be removed before work and hand washing and the size of long/ artificial nails or varnish must be carefully pondered.

An Update on Corneal Imaging Techniques: from Macroscale to Nanostructure

The structural integrity of the cornea and transparency are critical for normal vision. Corneal evaluation in ophthalmology and clinical research requires fast and user-friendly techniques allowing accurate diagnoses and follow-up of pathologies, injuries or surgery. Macroscopic irregularities in the anterior corneal surface are the main cause of irregular refractive vision problems. The microscopic and nanoscopic irregularities within the three-dimensional architecture of cornea are the cause of loss of optical transparency and scattering. In this review, the state of the art of the different corneal imaging techniques with three-dimensional capabilities will be detailed and discussed according to the descriptive level of analysis: macroscopic, microscopic and nanoscopic scales.

Study on mat-surface fabrication utilizing fixed-abrasive tool (Application to brittle material)

Mat-surface is a surface with microscopic irregularities whose dimensions are close to the wavelengths of visible light (400-700 nanometers).The new method that utilizes fixed-abrasive tool to fabricate mat-surface without pre-masking and large scale back up facility, is proposed in our last report. The report clarifies that, mat-surface must be produced with fixed-abrasive process, If the relative motion between tool and work in grinding process can be realized as that in blasting,In the reports, however, materials of workpieces which are ductile, such as steel and aluminium alloy, were selected. These materials are relatively easy to be indented. Therefore, in order to develop a new application of the proposed method, the method is applied to brittle material such as glass, it is investigated whether mat-surface can be obtained.

Development of feedback-speed-control system of fixed-abrasive tool for mat-surface fabrication

This study deals with the new method to fabricate a mat-surface by using fixed-abrasive tool. Mat-surface is a surface with microscopic irregularities whose dimensions are close to the wavelengths of visible light (400-700 nanometers). In order to develop the new method to fabricate mat-surface without pre-masking and large scale back up facility, utilization of fixed-abrasive tool is discussed. The discussion clarifies that abrasives in shot blasting are given kinetic energy along to only plunge-direction while excluding traverse-direction. If the relative motion between tool and work in fixed-abrasive process can be realized as that in blasting, mat-surface will be accomplished with fixed-abrasive process. To realize the proposed idea, new surface-fabrication system to which is adopted feedback-speed-control of abrasive wheel has been designed. The system consists of micro-computer unit (MPU), work-speed sensor, fixed-abrasive wheel, and wheel driving unit. The system can control relative speed between work and wheel in optimum range to produce mat-surface. Finally experiment to verify the developed system is carried out. The results of experiments show that the developed system is effective and it can produce the surface from grinding to mat-surface seamlessly.

Adsorption on Nanopores of Different Cross Sections Made by Electron Beam Nanolithography.

Adsorption on nanoporous matrices is characterized by a pronounced hysteresis loop in the adsorption isotherm, when the substrate is loaded and unloaded with adsorbate, the origin of which is a matter of immense debate in the literature. In this work, we report a study of argon adsorption at 85 K on nonconnecting nanopores with one end closed to the surrounding where the effects of different pore cross sections fabricated by electron beam lithography (EBL) are investigated. A polymethylmethacrylate (PMMA) resist is deposited on the electrodes of a sensitive quartz crystal microbalance without degradation of the resonance quality factor or the long-term and short-term stabilities of the device even at cryogenic temperatures. Four different pores' cross sections: circular, square, rectangular, and triangular, are produced from EBL, and the isotherms for these pore shapes exhibit pronounced hysteresis loops whose adsorption and desorption branches are nearly vertical and have almost the same slopes. No difference is observed in the hysteresis loops of the isotherms for the pores with triangular and square cross sections, whereas the hysteresis loop for the pore with circular cross sections is much narrower, suggesting that they are more regular than the other pores. All of these observations suggest that the hysteresis behavior resulted mainly from microscopic geometric irregularities present in these porous matrices.

Mapping microscale wetting variations on biological and synthetic water-repellent surfaces

Droplets slip and bounce on superhydrophobic surfaces, enabling remarkable functions in biology and technology. These surfaces often contain microscopic irregularities in surface texture and chemical composition, which may affect or even govern macroscopic wetting phenomena. However, effective ways to quantify and map microscopic variations of wettability are still missing, because existing contact angle and force-based methods lack sensitivity and spatial resolution. Here, we introduce wetting maps that visualize local variations in wetting through droplet adhesion forces, which correlate with wettability. We develop scanning droplet adhesion microscopy, a technique to obtain wetting maps with spatial resolution down to 10 µm and three orders of magnitude better force sensitivity than current tensiometers. The microscope allows characterization of challenging non-flat surfaces, like the butterfly wing, previously difficult to characterize by contact angle method due to obscured view. Furthermore, the technique reveals wetting heterogeneity of micropillared model surfaces previously assumed to be uniform.

Technological Parameters Forming the Surface Texture in Hyper Productive Surface Plastic Deformation Processing

The hyper productive surface plastic deformation processing technology called as wide burnishing (WB) was developed in Russian Federation. The mechanics of new WB technology is different from the classic SPD technologies (rolling or burnishing). For example applied force during processing of burnishing is 150-300 N, of WB is 2500-5000 N due to condition of process implementation in mass production with limited processing time (3-4 turnovers of workpiece). WB also has a high degree of deformation due to a multiple deformation passes. To determine the optimal WB processing parameters single and double instrumental devices were implemented and tested. Specimens made of steel 40 and high-strength cast iron 75-50-03 were tested. Initial roughness of steel 40 specimen’s surface was Ra = 0.5 microns and high-strength cast iron was Ra = 0.85 microns. Results of surface texture parameters of processed parts such as surface roughness Ra of steel 40 and high-strength cast iron 75-50-03 under varying load values P and number of cycles (the number of workpieces revolutions during the period of burnishing) were acquired. It was established that the minimum Ra value of the processed surface correspond with values of P = 210 N/mm2 for steel 40 and P = 410 N/mm2 for high-strength cast iron 75-50-03 regardless of number of burnishing cycles. Plastic deformation mechanism (processing time and pressure on the surface) influences on the processed surface roughness formation. It is possible to assume that straining state forms at the optimal values of P in terms of achieving a minimum value of Ra in which the reached degree of hardening allows to minimize the height of the microscopic irregularities of the previous grinding processing. In this case there is no plastic flow of the metal surface layer.

Development of Designs of Damping Cutting Tools

Different designs of damping cutting tools intended to assure the stability of the cutting process and high quality of surface treatment are proposed. Theoretical and experimental studies of models of a cutting tool together with a determination of the microscopic irregularities of the worked surface are performed.

Influence of tool surface topography on the material transfer tendency and tool wear in the turning of 316L stainless steel

The influence of tool surface topography on the initiation and build-up of transfer layers in the orthogonal turning of 316L austenitic stainless steel have been studied under well controlled conditions. Tool materials include CVD Ti(C,N)-Al2O3-TiN and PVD (Ti, Al)N-(Al,Cr)2O3 coated cemented carbide inserts prepared using different grinding and polishing treatments. Post-test characterization of the inserts was performed using high resolution scanning electron microscopy and energy dispersive X-ray spectroscopy.The results show that the transfer tendency of work material is strongly affected by the surface topography of the rake face. For both types of inserts, the initial transfer and the build-up of transfer layers are localised to microscopic surface irregularities on the rake face. Consequently, an appropriate surface treatment of the cemented carbide substrate before coating deposition and the as-deposited CVD and PVD coating can be used in order to reduce the transfer tendency and the mechanical interaction between the mating surfaces. Also, an improved surface finish was found to reduce coating wear and consequently the crater wear rate of the inserts investigated. This can most likely be explained by the reduced tendency to discrete chipping of coating fragments in the contact zone and the formation of a thin transfer layer composed of Al, Si, Ca, O with beneficial friction properties which are promoted by a smooth coating surface.

Finite Element Simulation of Temperature and Current Distribution in a Superconductor, and a Cell Model for Flux Flow Resistivity—Interim Results

A critical problem arises when current distribution in a high-temperature superconductor and its stability against quench shall be predicted: is it correct to assume homogeneous temperature distribution in superconductors, in general or only in LHe-cooled devices? The finite element analysis presented in this paper shows that during the very first instants following a disturbance, like single Dirac or periodic heat pulses, or large fault currents, temperature distribution in a BSCCO 2223 conductor is highly inhomogeneous. This is because disturbances, of transient or continuous, isolated or extended types in conductor volumes, create hot spots of comparatively long life cycle. As a consequence, separation between Ohmic and flux flow current limiter types, or decisions on the mechanism that initialises current sharing, cannot be made definitely. A semi-empirical cell model is presented in this paper to estimate flux flow resistivity in multi-filamentary superconductors in a successive approximation approach. Weak links are modelled, as nano- and microscopic surface irregularities and corresponding resistances, in analogy to thermal transport. Though the model requests input of a large amount of data (dimensions, porosities, field-dependent quantities) that still have to be verified experimentally, it is by its flexibility superior to ideas relying on, for example, imagination of separate, non-interacting chains of strong and weak links switched in parallel. In particular, and in contrast to the standard expression to calculate flux flow resistivity, the cell model suggests to replace solid conduction by an effective resistivity, a method that is more appropriate for multi-filamentary conductors. The paper also discusses integration time steps in numerical simulations that have to be selected in conformity with several characteristic times of current and thermal transport.

Influence of mechanical damage generated by small space debris on electrostatic discharge

Recent studies have indicated that hypervelocity impacts by meteoroids and space debris can induce spacecraft anomalies. However, the basic physical process through which space debris impacts cause anomalies is not entirely clear. Currently, impact-generated plasma is thought to be the primary cause of electrical spacecraft anomalies, while the effects of impact- generated mechanical damage have rarely been researched. This paper presents new evidence showing that impact- generated mechanical damage strongly influences electrostatic discharge. Hypervelocity impact experiments were conducted in a plasma drag particle accelerator, using particles with diameters of 200–500 µm and velocities of 2–7 km/s. The impact-generated mechanical damage on a specimen surface was measured by a stereoscopic microscope and 3D Profilometer and it indicated that microscopic irregularities around the impact crater could be responsible for local electric field enhancement. Furthermore, the influence of impact-generated mechanical damage on electrostatic discharge was simulated in an inverted potential gradient situation. The experimental results show that the electrostatic discharge voltage threshold was significantly reduced after the specimen was impacted by particles.

The influence of surface roughness and surface dynamics on the attachment of Methicillin-Resistant Staphylococcus aureus onto orthodontic retainer materials.

Staphylococci species have been isolated from removable orthodontic retainers. The aims of this study were to determine the most suitable device to analyze surface roughness of autopolymerized acrylic and thermoplastic materials and whether the surface dynamics of these materials influences the attachment of Methicillin-Resistant Staphylococcus aureus (MRSA). Clinically simulated samples of autopolymerized acrylic and thermoplastic material were first evaluated using laser non-contact, stylus mechanical profilometries and atomic force microscopy (AFM) followed by contact angle measurement to characterize their surface dynamics. Finally, an in vitro biofilm assay was carried out using a constant depth film fermentor to assess biofilm attachment. The results showed a significant difference between the roughness values obtained from the tested profilometers with the AFM exhibiting the most consistent roughness values. MRSA tended to accumulate initially within the microscopic irregularities of autopolymerized acrylic samples whereas acid-base and electron donor interactions influenced the bacterial attachment onto the thermoplastic samples.

Effective slip law for general viscous flows over an oscillating surface

We consider the non‐stationary three‐dimensional viscous flow in a bounded domain, with the lateral surface containing microscopic surface irregularities. Under the assumption of a smooth flow in the domain without roughness, we prove that there is a smooth solution to a problem with the rough boundary. In the papers by Jäger and Mikelić, the friction law was obtained as a perturbation of the Poiseuille flows. Here, the situation is more complicated. Nevertheless, after studying the corresponding boundary layers and using the results on solenoidal vector fields in domains with rough boundaries, we obtain rigorously the Navier friction condition. It is valid when the size and amplitude of the imperfections tend to zero. Furthermore, the friction matrix in the law is determined through a family of auxiliary boundary‐layer type problems. Effective equations approximate velocity at order O (ε) in the H1‐norm, uniformly in time, and O(ε3 ∕ 2) in the L2‐norm, also uniformly in time. Approximation for the pressure is O(ε3 ∕ 2) in the ‐norm. Copyright © 2013 John Wiley &amp; Sons, Ltd.