Indentation Length Research Articles

Prevalence of Septate Uterus in a Large Population of Women of Reproductive Age: Comparison of ASRM 2016 and 2021, ESHRE/ESGE, and CUME Diagnostic Criteria: A Prospective Study.

In this study, we aimed to assess and compare the prevalence of septate uterus using the diagnostic criteria of the ESHRE-ESGE, ASRM 2016, ASRM 2021, and CUME classifications. This prospective observational study included 977 women of reproductive age. Each participant underwent a transvaginal ultrasound, and a 3D volume of the uterus was obtained for further analysis. Offline assessment of the uterine coronal plane was conducted to measure uterine wall thickness, fundal indentation length, and indentation angle. The diagnosis of a septate uterus was determined according to the criteria of the ESHRE-ESGE, ASRM, and CUME classifications. The prevalence of septate uterus was then calculated and compared across these classifications. The ESHRE-ESGE classification identified 132 women (13.5%) with a septate uterus. The 2016 ASRM classification identified nine women (0.9%), with an additional nine women falling into a grey zone. The 2021 ASRM classification identified fourteen women (1.4%), with eleven women in the grey zone. The CUME classification identified 23 women (2.4%). The prevalence of septate uterus was significantly higher when using the ESHRE-ESGE criteria compared to the 2016 ASRM [relative risk (RR): 7.33 (95% CI: 4.52-11.90)], the 2021 ASRM [RR: 5.28 (95% CI: 3.47-8.02)], and the CUME [RR: 5.94 (95% CI: 3.72-8.86)] (p < 0.001). Our findings indicate that the ESHRE-ESGE criteria result in a significantly higher prevalence of septate uterus compared to the ASRM and CUME criteria. The ASRM 2016 criteria may underdiagnose more than half of the cases.

Rebar indentation on performance of CFS columns strengthened by rebar at flange-lip

To facilitate easier construction when longitudinally reinforcing cold-formed thin-walled lipped channel steel columns with steel bars, here, both ends of the steel bars used for reinforcement were cut, and the impact on the reinforcement effect was studied through experimental and numerical simulation methods. Seven groups of reinforced column specimens with different indentation lengths and one group of unreinforced specimens were designed, and axial compression tests were conducted. Parametric analyses were performed using the numerical models calibrated by tests. These numerical models included three types of specimens with typical sections and several series of specimens with different steel plate thicknesses. Using these models, the effects of the steel bar indentation length Li, steel bar diameter D, and other factors on the ultimate bearing capacity and deformation of the reinforced specimens were studied. The experimental results indicated that when the steel bar is the same length as the specimen, the compressive bearing capacity of the cold-formed thin-walled lipped channel column can be significantly improved by bonding the steel bar. Additionally, the numerical analysis results indicated that the influence of changing the steel bar diameter D on the bearing capacity of the specimens is not significant when the steel bars are indented within a certain range. As the length of the steel bar indentation increases to a certain extent, the stress concentration at the end of the steel bar becomes more significant, causing local buckling of the specimen and ultimately leading to a sharp decrease in the bearing capacity of the specimen. To achieve reinforcement, facilitate construction, and ensure structural safety, the total indentation length Li of the steel bars should not be >2 cm in practical engineering projects. Considering the economy of reinforcement engineering, it is suggested that steel bars with smaller diameters, i.e., 6 mm, should be selected. Through a comparison between the FEA and the experimental process, it was confirmed that the failure model of the numerical model is basically consistent with the experimental phenomenon, and the bearing capacity deviation was <3.3%. This indicates that the FEM established in this study was reliable.

Numerical investigation of force and deflection of nanoneedle penetration into cell using finite element approach: Parameter study and experimental validation of results.

This paper aims to develop a numerical methodology to investigate the penetration process of nanoneedles into cells and the corresponding force and indentation length. The finite element approach via the explicit dynamic method handles convergence difficulties in the nonlinear phenomenon. The cell is modeled as an isotropic elastic hemiellipsoidal shell with a thickness of 200 nm, which represents the lipid membrane and actin cortex, encapsulating cytoplasm that is regarded as an Eulerian body because of its fluid-type behavior. Nanoneedles with diameters 400, 200, and 50 nm are considered for model development based on available experimental data. The Von Mises strain failure criterion is used for rupture detection. A parameter study using 1, 2.5, 5, 7.5, and 10 kPa shows that Young's modulus of the HeLa cell membrane is about 5 kPa. Moreover, a failure strain of 1.2 chosen among 0.2, 0.4, 0.6, 0.8, 1, and 1.2 matches best the experimental data. In addition, a diameter study shows that the relations between force-diameter and indentation length-diameter are linear and polynomial, respectively. Furthermore, regarding the experimental data and by using contour of minimum principal stress around needle and an analytical equation for calculation of buckling force of a woven fabric, we proposed that for a given cell, membrane structural stability-a function of the coupled effect of Young's modulus and actin meshwork size-contributes directly to needle insertion success rate for that type of cell.

3D transvaginal ultrasound diagnosis of uterine septa according to different classifications: are there other measurements that correlate to reproductive outcome in small indentation length?

High discrepancy between current classifications was observed in the definition of uterine septa, especially for indentation lengths >5 <10mm. To assess the discrepancy between current classifications in the diagnoses of septate uterus and to correlate them with reproductive outcomes; to detect 3D transvaginal ultrasound (TVS) additional measurements, which can better correlate small indentation lengths >5 <10mm to reproductive failures. Observational study enrolling 664 women of reproductive age with 3D ultrasound diagnosis of an indentation length ≥3mm. For each patient a detailed reproductive history was taken before performing 3D transvaginal examination. Patients with previous uterine surgery or metroplasty were excluded. Indentation lengths >5 <10mm showed high discrepancy in the diagnosis of uterine septum between different classifications. For these small indentations additional 3D measurements (indentation angle, septal width and septal length/ fundal myometrial thickness (L/M) ratio) were correlated to infertility and recurrent miscarriage. Among the cohort, 215 patients showed an indentation length >5 <10mm; 136 tried to conceive: 69 (51%) were infertile, 38 (28%) had recurrent miscarriages (≥2) and 5 (4%) had at least one delivery. Recurrent miscarriage significantly correlated to an indentation angle >134°; whereas infertility to an indentation width <32mm and a L/M ratio >75%. Wide discrepancies between different classifications are more evident in indentation lengths >5 <10mm. Additional measurements on 3D coronal section may help to evaluate the risk of infertility or recurrent miscarriage. Additional 3D TVS measurements, beyond septal lengths, in particular for small fundal indentation, may help in predicting the risk of developing adverse reproductive outcomes.

Validation of a Cost-effective Cast Saw Simulation-based Educational Module to Improve Cast Removal Safety.

Inexperience in cast removal in the pediatric population can lead to a range of cast saw-related injuries. The purpose of this study is to validate a simple simulation-based wax model that is both reproducible and economical while providing a valuable tool that can be used to grade cast saw use performance in trainees. Cylindrical wax models were used as an analog for a pediatric upper extremity. The wax models were casted in a proscribed reproducible fashion for consistency. Two groups, the first consisting of 15 experienced cast saw users and the second consisting of 15 inexperienced individuals, completed 4 sequential longitudinal cuts in the casted wax models. After removal of the cast material, marks left by the cast saw in the wax were counted and measured. Indentation length, maximum depth, and maximum width were measured on each wax model. The total length of the cast saw indentations per cast saw user was also calculated. For the inexperienced cast saw users, the average total length of the cast saw indentations was 526.56 mm, average maximum depth was 1.91 mm, and average maximum width was 3.24 mm. For experienced cast saw users, the average total length of the cast saw indentations was 156.57 mm with an average maximum depth of 1.06 mm and average maximum width of 2.19 mm. Receiver operating characteristic curves of the total number of errors, total error length, maximum error depth, and maximum error width show effective discrimination of experienced from inexperienced trainees. This study provides valid evidence supporting a cost-effective, time-efficient, and easily reproducible educational simulation module that can objectively measure cast saw the performance in trainees. This model demonstrates construct validity and can distinguish novice from experienced cast saw users. It is sensitive enough to identify mistakes even in the most experienced cast saw users, creating a platform that can provide performance-based feedback to cast saw users of all experience levels. Level III-diagnostic test.

Cell penetration efficiency analysis of different atomic force microscopy nanoneedles into living cells

Over the last decade, nanoneedle-based systems have demonstrated to be extremely useful in cell biology. They can be used as nanotools for drug delivery, biosensing or biomolecular recognition inside cells; or they can be employed to select and sort in parallel a large number of living cells. When using these nanoprobes, the most important requirement is to minimize the cell damage, reducing the forces and indentation lengths needed to penetrate the cell membrane. This is normally achieved by reducing the diameter of the nanoneedles. However, several studies have shown that nanoneedles with a flat tip display lower penetration forces and indentation lengths. In this work, we have tested different nanoneedle shapes and diameters to reduce the force and the indentation length needed to penetrate the cell membrane, demonstrating that ultra-thin and sharp nanoprobes can further reduce them, consequently minimizing the cell damage.

The value of three-dimensional ultrasound in identifying Mullerian anomalies at risk of adverse pregnancy outcomes

Objective To examine the reliability of three-dimensional ultrasound (3 D-US) in the differentiation between subseptate and arcuate uteri, due to the different associated pregnancy outcomes; refine the existing 3 D-US parameters and evaluate the concordance between 3 D-US and MRI in diagnosing these anomalies. Study design This was a prospective cohort study of 455 women suspected of having a Mullerian anomaly. The diagnosis of subseptate, bicornuate or arcuate uterus was made by 3 D-US in 55 women. Two independent examiners manipulated the 3 D-US volume datasets and recorded the internal intercornual distance, indentation length, indentation tip angle, and myometrial wall thickness in the coronal plane of the uterus. Subsequently, 48 women underwent MRI which was used as the reference test for diagnosis. We calculated the degree of correlation between the two ultrasound assessors’ 3 D-US measurements using interclass correlation coefficient and as well as a Bland-Altman plot. The mean values of the four parameters were used to create receiver operating characteristic curves for determining the best cutoff values for differentiation between subseptate and arcuate uterui. We used the Cohen’s Kappa test to measure the level of agreement between 3 D-US and MRI. Results There was good interobserver agreement between the two 3 D-US assessors for all four parameters. There was a substantial level of agreement between 3 D-US and MRI in differentiating between bicornuate, subseptate and arcuate uteri with a kappa value of 0.727 (95% CI 0.443–0.856). Distinction between subseptate and arcuate uterus was improved when using an indentation length ≥12.5 mm (AUC 0.99) and indentation tip angle ≤89.25 degrees (AUC 0.97) as cutoffs for diagnosis but not the internal intercornual distance or myometrial wall thickness. Conclusion 3 D-US evaluation of the coronal view of the uterus can be relied upon to make a noninvasive, accurate differentiation between subseptate and arcuate uteri. The fundal indentation length and indentation tip angle cut offs of ≥12.5 mm and ≤88 mm, respectively were found to be most accurate for distinction. Thus, allowing for individualizing pre-pregnancy management plans and patient-informed healthcare choices. Highlights There are no agreed upon criteria for differentiating arcuate from subseptate uteri. Such differentiation is critical for counseling and management due to the substantial difference in pregnancy outcome. We aimed to propose cut off values for ultrasound measurements standardized against MRI diagnostic criteria for accurate differentiation between arcuate and subseptate uteri. We demonstrated substantial agreement between 3D-US and MRI in differentiating between bicornuate, subseptate and arcuate uteri. 3D-US evaluation of the coronal view of the uterus is reliable to make an accurate differentiation between subseptate and arcuate uteri. Using the indentation length ≥12.5 mm and indentation tip angle ≤89.25 degrees as parameters to be measured on the coronal view by 3D-US increases its diagnostic accuracy for distinction between arcuate and subseptate uteri.

Behavior of API 5L X56 submarine pipes under transverse impact

The performance of API 5L X56 submarine pipes subjected to transverse impact is investigated through both drop weight impact tests and finite element simulations. To study the improvement of resistance to transverse impact for pipe-in-pipe specimens, corresponding single-layer pipe specimens under impacting load were also tested for comparison. From the experimental tests, the failure mode, the impact force-time history curve, the displacement-time history curve, the strain-time history curve and the impact force - displacement curve of all specimens were obtained. The pipe-in-pipe specimens are found to have superior performance to resist impacting loading compared to single-layer specimens because smaller global bending deformation and local indentation were observed in them. In addition, the cross-section deformation rate, R, was proposed, and the local indentation length of the specimen was divided into three zones based on experimental observation and numerical simulation. A comprehensive comparison of the length and the depth of local indentation in the pipe-in-pipe specimens shows that the local indentation decreases and the impact resistance increases due to the presence of the inner tube. Finally, the post-peak mean force (Pm) and the energy absorption capacity (EAC) were used to evaluate the energy dissipation mechanism of different specimens. The results also indicate that the pipe-in-pipe specimens have better energy absorption performance.

Twinning in CoCrFeNiMn high entropy alloy induced by nanoindentation

The nanoindentation tests of CoCrFeNiMn high entropy alloy prepared by mechanical alloying route have been performed. Pop-ins on loading curves have been characterized by their indentation load, depth and length. Locations of indents within the grains, grain sizes and their orientation were obtained by the Scanning Electron Microscope/Electron Back Scattered Diffraction analysis. The stress state under the indenter was analyzed by Finite Element Method simulations using von Mises plasticity. The analysis has shown that pop-in events can be attributed to twin initiation as the pop-in length can be correlated with the twin thickness. The estimated critical twin shear stress corresponds to the one measured by the tensile test when the indentation size effect is taken into account. Fine grained HEA has very close Critical Resolved Shear Stress values for slip and twinning.

Shear localization and its dependence on microstructural length scales in metallic glass composites

Extrinsic approaches for the pursuit of ductility in metallic glasses have involved the introduction of a ductile crystalline phase to inhibit the propagation of a dominant shear front through the amorphous matrix material. Using nanoindentation, we explore the role of crystalline inclusions in metallic glass matrix composites with a focus on the onset of shear banding in the amorphous matrix and the nature of shear band propagation using the propensity for localization and its dependence on indentation strain rate. When indentation length scales are favorable to distribute strain to both the crystalline dendrites and amorphous matrix, we reveal a reduction in the number of detectable displacement bursts and an accompanying decrease in the magnitude of individual depth excursions from shear banding. A decrease in the stress at the onset of shear banding is also correlated with shear band trajectories interacting with the amorphous-crystalline interfaces (ACIs). Our results thus demonstrate that ACIs reducing the activation barrier for shear banding combined with dendrites arresting propagating shear fronts act to enhance the nucleation rate and in turn, promote a more homogeneous plastic response.

The role of diagnostic hysteroscopy in diagnosis of incomplete uterine septum/significant arcuate uterine anomaly in infertile patients in the era of transvaginal 3D ultrasound scan

BackgroundTo determine the accuracy of measurement of internal indentation length on transvaginal 3D ultrasound scan (TV 3D US) in detecting patients with an incomplete uterine septum (IUS) or a significant arcuate uterine anomaly (AUA) based on the actual length as measured on diagnostic hysteroscopy. We compared the mean internal indentation length on TV 3D US and on diagnostic hysteroscopy in patients with IUS or a significant AUA.ResultsThis is a retrospective study of 546 patients who were found to have IUS (134) or significant AUA (412) on diagnostic hysteroscopy and who had TV 3D US prior to surgery. The mean internal indentation length measured in millimeter on hysteroscopy was significantly higher than the mean internal indentation length measured on TV 3D US in patients with IUS (16.7 + 5.5 vs 5.5 + 4.2; P < 0.001), in patients with significant AUA (12.9 + 2.8 vs 3.9 + 4.6; P < 0.001), and in the overall population (13.8 + 4.0 vs 4.3 + 4.5; P < 0.001). The same findings were obtained when the comparison was limited to patients who had moderate significant internal indentation length (10–14 mm) and those with significant internal indentation length (15–25 mm).ConclusionData in this study suggests that the mean internal indentation length in patients with IUS or AUA can be underestimated on TV 3D US. A diagnostic hysteroscopy is the only gold standard to make the correct diagnosis in these patients.

The role of diagnostic hysteroscopy in diagnosis of incomplete uterine septum in patients with recurrent pregnancy loss in the era of transvaginal 3D ultrasound scan

PurposeTo determine the accuracy of transvaginal 3D ultrasound scan (TV 3D US) in detecting partial septate uterus (PSU) in patients with recurrent pregnancy loss (RPL).MethodsThis retrospective study included 113 patients with an initial diagnosis of unexplained RPL, who were subsequently found to have PSU on diagnostic hysteroscopy and who had TV 3D US prior to surgery. The diagnosis of PSU was made at the time of a diagnostic hysteroscopy based on ESHRE-ESGE classification of Müllerian anomalies. Based on hysteroscopic findings, patients were divided into two groups: those with PSU and a central point of indentation at an acute angle < 90° (PSUAA) [30.1%], and those who had PSU and a central point of indentation at an obtuse angle (PSUOA) [69.9%]. We compared the mean internal indentation length at the fundal midline (IILFM) in millimeters on TV 3D US and on diagnostic hysteroscopy. For the purpose of this study, a diagnosis of PSU on hysteroscopy was made if IILFM measured ≥ 10 mm.ResultsThe mean IILFM (mm) on hysteroscopy was significantly higher than the mean IILFM (mm) measured on TV 3D US in patients with PSUAA (18.5 ± 6.5 vs 4.9 ± 4.4; P < 0.001), in patients with PSUOA (14.1 ± 3.8 vs 4.3 ± 3.4; P < 0.001), and in the overall population (15.3 ± 5.1 vs 4.1 ± 4.4; P < 0.001).ConclusionsThe data suggest that mean IILFM in patients with RPL and PSU can be underestimated on TV 3D US. Therefore, its diagnostic accuracy in such patients may need further evaluation.

A Simulation of Non-Simultaneous Ice Crushing Force for Wind Turbine Towers with Large Slopes

When the offshore wind energy industry attempts to develop in cold regions, ice load becomes the main technological challenge for offshore wind turbine foundation design. Dynamic ice loads acting on wind turbine foundations should be calculated in a reasonable way. The scope of this study is to present a numerical model that considers the non-simultaneous ice crushing failure acting on the vertical structure of a wind turbine’s foundation. The local ice crushing force at the contact surface between the ice sheet and structure is calculated. The boundary of the ice sheet is updated at each time step based on the indentation length of the ice sheet according to its structure. Ice loads are validated against two model tests with three different structure models developed by other researchers. The time series of the ice forces derived from the simulation and model tests are compared. The proposed numerical model can capture the main trends of ice–wind turbine foundation interaction. The simulation results agree well with measured data from the model tests in terms of maximum ice force, which is a key factor for wind turbine design. The proposed model will be helpful for assisting the initial design of wind turbine foundations in cold regions.

Strain rate dependence of the indentation size effect in Ti–10V–2Fe–3Al alloy

ABSTRACTThe influence of strain rates on the indentation size effect (ISE) was explored experimentally. A strong ISE phenomenon on the hardness of Ti–10V–2Fe–3Al (Ti-1023) alloy was found when the peak-load was less than 3500 mN, regardless of the variation of loading rates. However, as indenter strain rates increased, the degree of ISE reduced considerably, which was related to the decrease of the internal indentation length scale ranging from 23.08 to 6.80 µm. Furthermore, a positive strain rate sensitivity of the hardness in the whole peak-load range was found in Ti-1023 alloy, which showed a linear function of indenter load. The underlying mechanism was well explained by the variation of geometrically necessary dislocation and statistically stored dislocations in Ti-1023 alloy.

In-situ synthesis of WC–X% Co composite in the WO3–Co3O4–C system by carbothermal reduction method

The main aim of this study is to show the fabrication of WC–Co composite with different content of cobalt (13–33% wt) from WO3 and Co3O4 by in-situ carbothermic reduction method while using activated carbon as a reducing agent. Cobalt and tungsten oxide powders with different ratio and 17% carbon (30% more than stoichiometric value) were mixed by ball milling under atmosphere of argon for 20 h. The homogenized powder mixture followed the process of pressing and heat treatment (carbothermic reduction + sintering) under different protective layer or atmosphere at 1500 °C for 2 h. To evaluate the appropriate temperature for carbothermic reduction, the differential thermal analyses (DTA) were conducted on mixture sample of WO3, Co3O4, and C. Hardness (Vickers), toughness (Vickers indentation and crack length measurement), density (Archimedes), phase composition (XRD), and micro structure (scanning electron and optical microscopic) of sintered sample were evaluated. DTA results show the complete reduction of oxides at 1050 °C and the formation of tungsten carbide and the metallic phase of cobalt. The XRD results showed that in the milling stage even up to 20 h no reduction reaction occurred and only powder activation took place; therefore, the reduced compacted samples show the presence of unreduced oxides and extra phases protective foil of steel in comparison with alumina and carbon mixture as a layer protective. From investigated composites, the composites with 25% cobalt showed the highest density and strength while the composite with 36 and 14% cobalt showed the highest toughness and hardness, respectively.

The effects of fluoride, strontium, theobromine and their combinations on caries lesion rehardening and fluoridation

ObjectiveThe aim was to investigate the effects of fluoride, strontium, theobromine and their combinations on caries lesion rehardening and fluoridation (EFU) under pH cycling conditions. DesignHuman enamel specimens were demineralized at 37°C for 24h using a pH 5.0 solution containing 50mM lactic acid and 0.2% Carbopol 907 which was 50% saturated with respect to hydroxyapatite. Lesions were assigned to nine treatment groups (n=16) based on Knoop surface microhardness indentation length. Treatmentaqueous solutions were: placebo, 11.9mM sodium fluoride (F), 23.8mM sodium fluoride (2×F), 1.1mM strontium chloride hexahydrate (Sr), 1.1mM F theobromine, Sr+theobromine, F+Sr, F+theobromine, F+Sr+theobromine. Lesions were pH cycled for 5d (daily protocol: 3×1min-treatment; 2×60min-demineralization; 4×60min & overnight-artificial saliva). Knoop indentation length was measured again and%surface microhardness recovery (%SMHr) calculated. EFU was determined using the acid-etch technique. Data were analysed using ANOVA. ResultsModel showed fluoride dose-response for both variables (2×F>F>placebo). For%SMHr, F+Sr+/−theobromine resulted in more rehardening than F, however less than 2×F. F+theobromine was similar to F. For EFU, F+Sr was inferior to F, F+theobromine and F+Sr+theobromine which were similar and inferior to 2×F. In absence of fluoride, Sr, theobromine or Sr+theobromine were virtually indistinguishable from placebo and inferior to F. ConclusionsIt can be concluded that a) strontium aids rehardening but not EFU and only in presence of fluoride; b) theobromine does not appear to offer any anti-caries benefits in this model; c) there are no synergistic effects between strontium and theobromine in the presence or absence of fluoride.

Deformation behavior of micro-indentation defects under uniaxial and biaxial loads

The microdefects of structure frequently act as the source to generate initial cracks and lead to the fracture failure. Study on the deformation behaviors of embedded defects would be conducive to better understand the failure mechanisms of structural materials. Micro-indentation technique was applied to prepare the initial indentations as embedded surface defects at the gauge length section and central section of a cross-shaped AZ31B magnesium alloy specimen. A novel in situ biaxial tensile device was developed to apply the synchronous biaxial loads. Via the observation by an optical microscope with three-dimensional imaging and measurement functions, the changing laws of the indentation topographies under uniaxial and biaxial tensile loads were discussed. Compared with the gauge length section, the increasing trend of the indentation length of the central section was relatively flat, and the decreasing trend of the indentation depth was more significant. The changes of indentation topographies were explained by the Poisson effect, and the significant plastic tensile stress has led to the releasing of the residual stress around the indentation location and also promoted the planarization of the pileup.

Experimental studies of translation-rotational motions of rolling bodies under elastic-frictional interaction with the bases

Experimental studies and their results are described for the translation-rotational motion of rolling bodies subjected to forces and elastic deformations of the contact tribological conjunction regions between such bodies and the bases. Most attention is paid to the motion of such bodies outside the contact surfaces in the regions of preliminary displacements and behind these regions. In several experiments, the processes are recorded and analyzed from the very beginning to the termination of the rolling body finite displacements. All displacement stages exhibit oscillations due to variations in the character of motions of the rolling bodies. In the case where the body is only under the action of its weight, the regions of normal strains symmetric with respect to the axis of the weight action are shown as surface indentations outside the region of direct contact between the base and the rolling body. The photographs of the base nonsymmetric deformations due to the additional action of the tangential force on the rolling body are presented. One can see that the indentation slope in the motion or the force action direction is steeper and the indentation depth and length are smaller than those on the opposite side. This suggests that, on the side where the rolling body surface enters the base, the volumes of their deformations and hence the elastic force are greater than on the opposite side. The graphs are constructed for the variation in the values of preliminary and kinematic (in motion) displacements and the arm of rolling friction force for two motor cars, for a solid steel roller, and for a steel roller with two foam rubber wheels. The graphs show that, quantitatively, the displacement values are by one and more orders of magnitude greater than the values of these arms of force. Qualitatively, the arms of rolling friction force, just as the displacements, are characterized by the presence of proportionality and saturation segments of their characteristics. The motion processes of the considered rolling bodies in the directions opposite to those in which each of the bodies moved under the action of the tangential external force are also shown.

Comparison of Knoop and Vickers surface microhardness and transverse microradiography for the study of early caries lesion formation in human and bovine enamel

ObjectiveThe aims of the present laboratory study were twofold: a) to investigate the suitability of Knoop and Vickers surface microhardness (SMH) in comparison to transverse microradiography (TMR) to investigate early enamel caries lesion formation; b) to compare the kinetics of caries lesion initiation and progression between human and bovine enamel. DesignSpecimens (90×bovine and 90×human enamel) were divided into six groups (demineralization times of 8/16/24/32/40/48h) of 15 per enamel type and demineralized using a partially saturated lactic acid solution. SMH was measured before and after demineralization and changes in indentation length (ΔIL) calculated. Lesions were characterized using TMR. Data were analyzed (two-way ANOVA) and Pearson correlation coefficients calculated. ResultsΔIL increased with increasing demineralization times but plateaued after 40h, whereas lesion depth (L) and integrated mineral loss (ΔZ) increased almost linearly throughout. No differences between Knoop and Vickers SMH in their ability to measure enamel demineralization were observed as both correlated strongly. Overall, ΔIL correlated strongly with ΔZ and L but only moderately with the degree of surface zone mineralization, whereas ΔZ and L correlated strongly. Bovine demineralized faster than human enamel (all techniques). ConclusionsLesions in bovine formed faster than in human enamel, although the resulting lesions were almost indistinguishable in their mineral distribution characteristics. Early caries lesion demineralization can be sufficiently studied by SMH, but its limitations on the assessment of the mineral status of more demineralized lesions must be considered. Ideally, complementary techniques to assess changes in both physical and chemical lesion characteristics would be employed.

Strengthening mechanism of aluminum nitride ceramics from 293 to 77 K

In this study, the flexural strength of aluminum nitride (AlN) ceramics at cryogenic temperatures was reported for the first time. The flexural strength increased from 364.6±29.2MPa to 415.3±21.7MPa with temperature decreasing from 293 to 77K. The strengthening mechanism was explored based on the Griffith equation for a brittle solid and was rationalized by the analysis of lattice constants of AlN and the Vickers indentation length at ambient and cryogenic temperatures. The increase of elastic modulus and fracture surface energy could contribute to the strengthening of AlN ceramics at cryogenic temperatures. The above results showed that AlN ceramics could be a promising candidate for cryogenic engineering.