Degrees Of Eccentricity Research Articles

Entrance Lengths for Fully Developed Laminar Flow in Eccentric Annulus

Abstract We study the entrance length in eccentric annular geometries, where the axes of the inner and outer pipes forming the annulus are offset from each other. Such geometries are considered relevant for several industrial applications, such as drilling of wells for hydrocarbon production or geothermal energy recovery, as well as biomedical research involving annular vessels. Previous studies have shown that eccentricity increases the entrance length in annular geometries, and this has been attributed to azimuthal redistribution of fluid between the wide and narrow sides of the annulus. The present computational study aims to increase the understanding of entrance lengths in eccentric annuli for laminar flow with Reynolds numbers spanning the range from the creep limit and up to intermediate laminar values, below the regime of annular gap instabilities. We find that the entrance lengths in eccentric annuli generally increase for narrower annular gaps (higher aspect ratios). Moreover, the entrance lengths in the annuli with higher aspect ratios are also more sensitive to the degree of eccentricity compared to wider annuli (lower aspect ratios). We report empirical correlations for the dimensionless entrance length using the same form as earlier studies (Le = [C0n + (C1 Re)n ]1/n ). We find that eccentricity, which breaks the axial symmetry of the annulus and causes azimuthal flow in the entrance region, impacts the value of the exponent n, which has been assigned the value of 1.6 in previous studies of axisymmetric conduits.

A parafoveal retinal cones analysis using adaptive-optics retinal camera in patients with primary open angle glaucoma

ObjectivesTo study the density, spacing, and regularity of retinal cone photoreceptors using an Adaptive Optics (AO) retinal camera (Rtx1TM, Imagine Eyes, Orsay, France) in patients with Primary Open Angle Glaucoma (POAG) and to compare the outcomes with those of healthy age-matched control subjects.MethodsThe study included 43 eyes with POAG and 31 eyes of normal subjects. POAG patients were divided into three groups according to the severity of the visual field defect. The AO Rtx1TM was used to obtain images of the parafoveal cone mosaic to calculate cone values. Analysis was performed at two and four degrees of eccentricity from the fovea along the four meridians (nasal, temporal, superior, inferior).ResultsIn POAG eyes, the mean ± standard deviation (SD) cone density at 2° considering all meridians was significantly lower than in normal controls (23,058.6 ± 3532.0 cones/mm2, and 25,511.7 ± 3157.5 cones/mm2, respectively; p = 0.003). Cone spacing was 7.3 ± 0.5 µm in POAG and 7.0 ± 0.4 µm in normal controls (p = 0.005), and cone regularity was 90.5 ± 4.9% and 93.5 ± 1.9% in POAG and normal controls, respectively (p < 0.001). At 4° similar trends were observed. However, no significant differences were found among patients with different severity of POAG (p > 0.05).ConclusionsUsing AO Rtx1TM, significant differences in retinal photoreceptors mosaic pattern were found between POAG eyes and age-matched controls, indicating a reduction in photoreceptors in POAG. No significant differences in retinal photoreceptor values were found among the three POAG groups.

Numerical Investigation of the Axial Load Capacity of Cold-Formed Steel Channel Sections: Effects of Eccentricity, Section Thickness, and Column Length

Cold-formed steel channel (CFSC) sections have gained widespread adoption in building construction due to their advantageous properties, including superior energy efficiency, expedited construction timelines, environmental sustainability, material efficiency, and ease of transportation. This study presents a numerical investigation into the axial compressive behavior of CFSC section columns. A rigorously developed finite element model for CFSC sections was validated against existing experimental data from the literature. Upon validation, the model was employed for an extensive parametric analysis encompassing a dataset of 208 CFSC members. Furthermore, the efficacy of the design methodologies outlined in the AISI Specification and AS/NZS Standard were evaluated by comparing the axial load capacities obtained from the numerically generated data with the results of four previously conducted experimental tests. The findings reveal that the codified design equations, based on nominal compressive resistances determined using the current direct strength method, exhibit a conservative bias. On average, these equations underestimate the actual load capacities of CFSC section columns by approximately 11.5%. Additionally, this investigation explores the influence of eccentricity, cross-sectional dimensions, and the point-of-load application on the axial load capacity of CFSC columns. The results demonstrate that a decrease in section thickness, an increase in column length, and a higher degree of eccentricity significantly reduce the axial capacity of CFSC columns.

Flow regimes identification of air water counter current flow in vertical annulus using differential pressure signals and machine learning

This study investigates the gas–liquid two-phase counter-current flow through a vertical annulus, a phenomenon prevalent across numerous industrial fields. The presence of an inner pipe and varying degrees of eccentricity between the inner and outer pipes often blur the clear demarcation of flow regime boundaries. To address this, we designed a vertical annulus with adjustable eccentricity (outer and inner diameters of 125 mm and 75 mm, respectively). We conducted gas–liquid counter-current flow experiments under specific conditions: gas superficial velocity ranging from 0.06 to 5.04 m/s, liquid superficial velocity from 0.01 to 0.25 m/s, and five levels of eccentricity (e = 0, 0.25, 0.5, 0.75, 1). We collected differential pressure data at two distinct height distances (DP1: 50 mm and DP2: 1000 mm). We used vectors, composed of both the probability density functions (PDFs) of the differential pressure signals and the power spectral density (PSD) reduced via Principal Component Analysis, as features. Using the CFDP clustering algorithm—based on local density—we clustered the flow regimes of the experimental data, thereby achieving an objective and consistent identification of the flow regime of gas–liquid two-phase counter-current flow in a vertical annulus. Our analysis reveals that for DP1, the main differences in the PSD of various flow regimes occur within the 0.5–1 Hz range. Among the three flow regimes involved, the slug flow exhibits the highest power intensity, followed by the bubbly flow, with the churn flow having the least. In terms of differential pressure distribution, the bubbly and churn flows have a concentrated distribution, while the slug flow is more dispersed. For DP2, the PSD differences primarily exist within the 0.5–2 Hz range. The churn flow has the highest power intensity, followed by the slug flow, with the bubbly flow being the weakest. Here, the bubbly flow's differential pressure distribution is concentrated, while the slug and churn flows are more dispersed. Based on the results of the flow regime classification, we generated a flow regime map and analyzed the influence of annulus eccentricity on the flow regime. We found that in most cases, pipe eccentricity does not significantly affect the flow regime. However, in the transition region—such as the bubbly to slug flow transition zone—flows with medium eccentricity values (e = 0.5, 0.75) are more likely to transition to slug flow. We compared the visual recognition results of flow regimes with the clustering results. 4.04% of the total samples showed different results from visual recognition and clustering, primarily located in the flow regime transition area. Since visually distinguishing flow regimes in these areas is typically challenging, our methodology offers an objective classification approach for gas–liquid two-phase counter-current flow in a vertical annulus.

Adaptive optics retinal imaging in patients with usher syndrome.

To determine the structure of the cone photoreceptor mosaic in the macula in eyes with retinitis pigmentosa related to Usher syndrome using adaptive optics fundus (AO) imaging and to correlate these findings with those of the standard clinical diagnostics. Ten patients with a genetically confirmed retinitis pigmentosa in Usher syndrome due to biallelic variants in MYO7A or USH2A were enrolled in the study. All patients underwent a complete ophthalmological examination including best corrected visual acuity (BCVA), spectral-domain optical coherence tomography (SD-OCT) with fundus autofluorescence photography (FAF), full-field (ffERG) and multifocal electroretinography (mfERG) and Adaptive Optics Flood Illuminated Ophthalmoscopy (AO, rtx1™, Imagine Eyes, Orsay, France). The cone density was assessed centrally and at each 0.5 degree horizontally and vertically from 1-4 degree of eccentricity. In the AO images, photoreceptor cell death was visualized as a disruption of the cone mosaic and low cone density. In the early stage of the disease, cones were still visible in the fovea, whereas outside the fovea a loss of cones was recognizable by blurry, dark patches. The blurry patches corresponded to the parafoveal hypofluorescent ring in the FAF images and the beginning loss of the IS/OS line and external limiting membrane in the SD-OCT images. FfERGs were non-recordable in 7 patients and reduced in 3. The mfERG was reduced in all patients and correlated significantly (p <0.001) with the cone density. The kinetic visual field area, measured with III4e and I4e, did not correlate with the cone density. The structure of the photoreceptors in Usher syndrome patients were detectable by AO fundus imaging. The approach of using high-resolution technique to assess the photoreceptor structure complements the established clinical examinations and allows a more sensitive monitoring of early stages of retinitis pigmentosa in Usher syndrome.

Experimental study on mechanical properties of corroded grouted sleeve splice

Grouted sleeve splices are widely used in precast-concrete (PC) structures. Although extensive tensile tests have been conducted on grouted sleeves, the force mechanism and changing rules of grouted sleeve connections as influenced by environmental corrosion have rarely been investigated. Accelerated corrosion and monotonic tensile tests were conducted on twenty-five grouted sleeves. The investigated variables of the sleeve splices were the degree of corrosion, rebar eccentricity, and geometrical sizes of the rebar and sleeve. Based on the test results, the three-dimensional corrosion characteristics of the sleeve were analyzed, and the influences of the corrosion distribution, rebar eccentricity, and sleeve size on the failure mode, force–displacement curve, and strain distribution of the sleeves were discussed. The results indicated that the surface roughness parameters Sz, Sa, and Sq of the sleeve increased with an increase in corrosion. As a result of sleeve corrosion, the failure mode of the grouted sleeve connection changed from rebar fracture to sleeve fracture, accompanied by an increase in the longitudinal and circumferential strains of the sleeve, and reductions in strength, deformation capacity, and energy dissipation ability. In addition, the rebar eccentricity led to an uneven strain distribution in the circumferential direction.

Investigation of Taylor bubble dynamics in annular conduits with counter-current flow

This study numerically investigates counter-current slug flow by considering the motion of a Taylor bubble in annular conduits with downward-flowing liquids using the Volume-of-Fluid method implemented in the commercial computational fluid dynamics software ANSYS Fluent (Release 19.2). The translational velocity of a counter-current ascending or co-current descending Taylor bubble in vertical concentric annuli and the corresponding distribution parameter (C0) are analyzed. The latter is correlated in terms of Eötvös number (Eo) and inverse viscosity number (Nf) within the range of Eo between 40 and 400 and Nf between 40 and 320. The proposed correlation provides an accurate fit to the numerical data with an average error of 2.64%, and is successfully compared with published numerical findings. In general, the smooth and stable shape of the bubble is disrupted as the counter-current flow velocity (Frl) increases above a critical value, leading to the formation of surface waves and the displacement of the bubble tip away from the annular gap center and towards the outer pipe. C0 increases with Eo and Nf, plateauing at high values of Eo. The effects of annulus inclination (θ) and eccentricity (ε) on bubble rise velocity are examined within the common range of θ and ε encountered during the drilling of oil, gas, or geothermal wells, i.e. 0° ≤ θ ≤ 60° and 0 ≤ ε ≤ 0.7, and their impact on the C0. The increasing Frl and θ lead to a streamlined bubble with pointed nose and thus a reduction in the wrap angle (θwrap), ultimately leading to reduced drag compared to the vertical annulus case and a decrease in C0. As the ε increases, which is accompanied by an increase in the degree of bubble eccentricity, the corresponding C0 decreases. For a constant Eo = 100 and Nf = 160 with inclination angle of θ = 40°and eccentricity of ε = 0.5, the C0 < 1 is observed.

A Novel Data Generation and Quantitative Characterization Method of Motor Static Eccentricity With Adversarial Network

Eccentricity can cause motor damage. It is necessary to obtain the degree of motor eccentricity for health management or eccentricity suppression. Due to the complex electromagnetic mechanism, it is hard to obtain the degree of motor eccentricity in traditional way. The neural network is suitable for obtaining the degree of eccentricity, but the eccentricity data are too few to train network. In this paper, a data generation and quantitative characterization method for motor eccentricity based on improved generative adversarial network is proposed. The mathematical model is improved for pre-training, and the network and objective function are improved for data generation and eccentricity characterization. The results show the validity of proposed method.

On Resonant Values of Parameters in the Problem on the Stability of Lagrangian Solutions in the Near-Circular Restricted Three-Body Problem

The restricted problem of three bodies (material points) moving under the action of gravitational attraction according to Newton’s law is considered. The orbits of the main attracting bodies are considered to be ellipses with a small eccentricity, and a passively gravitating body can perform arbitrary spatial motion near the triangular libration point. For the Hamiltonian function corresponding to such a motion, the structure of the normal form is pointed in the cases of third-order resonances. In the planar restricted three-body problem, the equations up to the second degree of eccentricity for resonance curves for all resonances up to the sixth order inclusive are obtained.

Performance assessment of partially corrosion-damaged RC segment incorporating the spatial variability of steel corrosion

Steel corrosion is a dominant source of structural performance deterioration for reinforced concrete (RC) shield tunnels, which is always spatially nonuniform and discretely distributed in RC segmental linings. To accurately estimate the deteriorated performance of RC segmental linings under coupling actions of flexural and axial loads, the research on the mechanical behavior of RC segments has to be integrated with the effects of nonuniform steel corrosion and loading eccentricity. In this paper, the failure modes of corroded RC segmental specimens and their damaging evolution under ultimate loading were experimentally investigated, and the effects of spatial variability of steel corrosion and level of sustained load were discussed. A probabilistic model for simulating the spatial variability of steel corrosion within a partial length of longitudinal reinforcement was proposed. Finally, Monte Carlo simulation (MCS) incorporated with finite element (FE) analysis was performed to investigate the strength loss of corroded RC segmental specimens, emphasizing on the effects of spatial distribution of steel cross-section area loss, degree of steel corrosion and eccentricity of loading.

Взаимная гравитационная энергия сфероидальных тел

The problem of mutual gravitational energy Wmut for a system of two homogeneous prolated spheroids whose symmetry axes are on the same line is set and solved. The method of equigravitating elements is applied, where the external potentials of three-dimensional spheroids are represented by the potentials of one-dimensional inhomogeneous focal rods. The solution of the problem is reduced to the integration of the potential of one rod over the segment of the second rod. As a result, the expression Wmut for two prolated spheroids can be obtained in a finite analytic form through elementary functions. The force of attraction between the spheroids is found. The function Wmut is also represented by a series of degrees of eccentricity of the spheroids. Possible applications of the obtained results are discussed.

Study on the stability of oil-water annular flow under different amplitude

Compared with the traditional transportation of high-viscosity crude oil, water annular transportation has the advantages of low energy consumption and no change in crude oil composition. With the continuous development of marine heavy oil transportation, submarine oil pipelines are inevitably subjected to vibration and impact, affecting the annular flow in the pipeline. In this paper, the VOF model in Fluent software is used to simulate the stability of oil-water annular flow in a horizontal pipeline under different amplitudes and the interface characteristic parameters of annular flow. In addition, the influence of vibration on oil-water annular flow in the horizontal pipeline under different marine environments is studied. The results showed that the vibration parameters have an influence on the flow of oil-water annular flow in the horizontal pipeline. Under the condition of constant inlet velocity, the eccentricity degree of oil core is analyzed to reveal the law that the stability of annular flow decreases with the increase of amplitude. The relationship between the eccentricity of oil core and the vibrational parameters of pipes are explored in this paper. At the same time, the unit pressure drop under the condition of pipe vibration and its mechanism are studied. These results could provide references for parameters optimization of heavy oil-water annular flow transportation under vibration conditions.

Achromatic and chromatic perceived contrast are reduced in the visual periphery.

The loss of contrast sensitivity with eccentricity is well documented, and is steeper for higher spatial frequencies, and for L/M cone-opponent stimuli compared to achromatic or S-cone-opponent. Here, we ask how perceived contrast depends on eccentricity when stimuli are presented at suprathreshold contrasts, and test two opposing predictions. Contrast constancy predicts no loss in perceived contrast across the visual field regardless of changes in detection threshold - appearance depends only on physical contrast. Conversely, perceived contrast may be scaled in the same way as detection threshold, reflecting the proportional increase in stimulus contrast above threshold. We measured perceived contrast for L/M cone-opponent, S-cone opponent, and Ach stimuli up to 18 degrees of eccentricity using a 2AFC contrast matching method between fovea and periphery. We tested a range of reference contrasts from low (close to detection threshold) to high suprathreshold contrasts and we relate suprathreshold perceived contrast to measured detection thresholds. We find evidence for a hybrid model in which apparent contrast is reduced with eccentricity for stimuli in the low and mid contrast range, with contrast constancy only attained at the highest contrasts. When equated for similar sensitivity losses, we find no difference between chromatic and Ach contrast responses.

Numerical simulation of the blood flow through the coronary artery stenosis: Effects of varying eccentricity

Blockages within arteries, called stenoses, are a common cause of coronary artery disease (CAD). Stenosis is a result of atherosclerotic plaque build-up limits blood flow and hence oxygen and nutrient supplies. Past studies on stenosed arterial flows often assumed stenosis to be axisymmetric in shape. However, medical imaging modalities have shown that stenoses in the coronary arteries are often asymmetric. To address it, an asymmetric stenosis is considered in the model which is based on common dimensions of the left anterior descending artery (LAD). The hemodynamic impacts are studied over a range of degrees of eccentricity (DoE) and degree of stenosis (DoS). Blood flow within the artery is analyzed by solving the incompressible Navier-Stokes equations with both resting and hyperemic flow rates. The wall shear stress (WSS), oscillatory shear index (OSI) and fractional flow reserve (FFR) are calculated.The eccentricity makes the flow deflect away from the model's centerline. Behavior of the deflected flow is significantly altered downstream of the stenosis. Transverse dimension of the recirculation zone grows with increasing DoE, while its longitudinal dimension mainly depends on DoS. Eccentricity also contributes to the development of secondary flow distal to the stenosis. Such complex flow behavior contributes to a further pressure loss and hence a significant change in FFR (<0.8). Calculated WSS and OSI indicate that in actual eccentric stenotic LAD the asymmetric remodeling is anticipated. Thus, consideration of the DoE, along with the DoS, could lead to better patient stratification.

The effect of varying degrees of stenosis on transition to turbulence in oscillatory flows

Many complications in physiology are associated with a deviation in flow in arteries due to a stenosis. The presence of stenosis may transition the flow to weak turbulence. The degree of stenosis as well as its configuration whether symmetric or non-symmetric to the parent artery influences whether the flow would stay laminar or transition to turbulence. Plenty of research efforts focus on investigating the role of varying degrees of stenosis in the onset of turbulence under steady and pulsatile flow conditions. None of the studies, however, have focused on investigating this under oscillatory flow conditions as flow reversal is a major occurrence in a number of physiologic flows, and is of particular relevance in cerebrospinal fluid flow research. Following up on the previous work in which a 75% stenosis was studied, this contribution is a detailed investigation of the role of degrees of stenosis on transition in an oscillatory flow. A cylindrical pipe with 25%, 50% and 60% reductions in area in axisymmetric and eccentric configurations is studied for transition with 3 different pulsation frequencies of a purely oscillatory flow. Cycle averaged Reynolds numbers between 1800 and 2100 in steps of 100 are studied for each configuration resulting in 72 simulations each conducted on 76,800 CPU cores of a modern supercomputer. It is found that a higher degree of stenosis and eccentricity causes earlier transition to turbulence in oscillatory flow. The results further demonstrate that a higher frequency of oscillation results in larger hydrodynamic instability in the flow, which is more prominent in smaller degrees of stenosis.

Spatiokinematic models of five nova remnants: correlations between nova shell axial ratio, expansion velocity, and speed class

ABSTRACT We present long-slit intermediate-dispersion spectroscopic observations and narrow-band direct imaging of four classical nova shells, namely T Aur, HR Del, DQ Her, and QU Vul, and the nova-like source CK Vul. These are used to construct models of their nebular remnants using the morphokinematic modelling tool shape to reveal their 3D shape. All these nova remnants but CK Vul can be described by prolate ellipsoidal shells with different eccentricity degree, from the spherical QU Vul to the highly elongated shell with an equatorial component HR Del. On the other hand, CK Vul shows a more complex structure, with two pairs of nested bipolar lobes. The spatiokinematic properties of the ellipsoidal nova shells derived from our models include their true axial ratios. This parameter is expected to correlate with the expansion velocity and decline time t3 (i.e. their speed class) of a nova as the result the interaction of the ejecta with the circumstellar material and rotation speed and magnetic field of the white dwarf. We have compared these three parameters including data available in the literature for another two nova shells, V533 Her and FH Ser. There is an anticorrelation between the expansion velocity and the axial ratio and decline time t3 for nova remnants with ellipsoidal morphology, and a correlation between their axial ratios and decline times t3, confirming theoretical expectations that the fastest expanding novae have the smallest axial ratios. We note that the high expansion velocity of the nova shell HR Del of 615 km s−1 is inconsistent with its long decline time t3 of 250 d.

Commentary: Renewed interest in off-axis retinoscopy and peripheral refraction for it's role in control of myopia progression.

We all know that vision is a combination of optical input and neural processing. Traditionally, retinoscopy has remained the benchmark for the assessment of refractive errors for the optical input that is perceived by the eye and then processed by the brain. Conventionally, it has always been known that “on the visual axis” (on-axis) retinoscopy gives a more accurate estimate of refractive error compared to retinoscopy that is done off the visual axis (off-axis). However, in practical terms, retinoscopy is frequently performed slightly off the visual axis and there are situations in which on the visual axis retinoscopy is difficult or even impossible. These include retinoscopy in uncooperative children or when the subject has been anesthetized. Chaurasiya et al.[1] in their current study on “refractive changes during off-the-axis retinoscopy in myopia” and many other researchers, over the years have tried to quantify the error in the quantum of refractive error when this is measured with “off-axis” retinoscopy in routine clinical practice. Ferree et al.[2] in 1931 measured peripheral refraction with the Zeiss parallax refractometer (Carl Zeiss, Jena, Germany). Rempt et al.[3] was the first to perform eccentric retinoscopy and introduced the skiagram to categorize different peripheral refractive error patterns. Jackson et al.[4] examined off the visual axis retinoscopy in eight adults (spherical equivalent <±2.5 D) who had undergone cycloplegia. The degrees of the eccentricity of up to 20° along the temporal horizontal field were examined and they found a myopic shift of 5% in spherical equivalent and an increase in cylindrical power of 3% for every degree of eccentricity. In the present study, the authors have noted an increase in myopic shift with approximately 7 and 18% for 10 and 20° of eccentricity, respectively, in the mean spherical equivalent refraction of 10° myopic patients. What is traditionally believed and agreed upon is that the error in refraction, which is noted in off-axis retinoscopy, is generally small and clinically insignificant when the deviation of axis and the quantum of refractive error is small, and more often than not, this error is eliminated in the process of subjective refraction which follows retinoscopy. However, this error in retinoscopy can become significant if the deviation of the axis of retinoscopy from the visual axis is large or if the quantum of refraction being measured is large, for example, as in high myopia.[5] Of late, there has been renewed interest in the measurement of peripheral refraction as it is increasingly believed that peripheral refractive defocus plays a role in myopia progression by inducing axial growth of the eye. Animal studies have shown that depending on the location of the image relative to the retina, axial elongation can be stopped or triggered. Experiments in chickens and monkeys whose vision were defocused either with negative spectacle lenses (hyperopic defocus) or positive lenses (myopic defocus), showed that their visual system was altering their refractive state by accelerating or slowing axial elongation in order to compensate for the imposed defocus.[6] This applies both in the fovea and in the periphery of the retina. Originally, it was believed that only foveal optical errors could regulate eye growth, but it is now believed that peripheral image quality can also modify ocular growth even in the presence of a sharp foveal image. This is the reason that many researchers have advocated the use of bifocal or progressive addition lenses (PAL) for children as a strategy to retard the progression of myopia, but as of now, there is no consensus regarding their clinical efficacy.[7] Studies with PAL have typically shown a small but clinically insignificant effect on slowing myopia progression as noted in Cochrane review 2020.[8] A meta-analysis noted small reductions in myopia progression (0.25 D) and axial elongation (−0.12 mm).[9] So, there is indeed a value in studying the variation of refractive error assessment between the on-axis and off-axis retinoscopy but more work needs to be done to have more clarity regarding the clinical application of this work, especially in control of myopia progression.

Refractive changes during off-the-axis retinoscopy in myopia.

Purpose:To analyze the refractive shift during off-the-axis retinoscopy under cycloplegic drugs in myopic patients during ocular examination.Methods:Prospective cross-sectional study was carried out among 10 myopic patients having refractive errors of −3.00 D or less. All the subjects underwent cycloplegic refraction by a single examiner at 0°, 10°, and 20°. Descriptive data were analyzed as mean and standard deviation. Paired t-test was used to compare the mean differences between on-axis (0°) and off-axis (10° and 20°) retinoscopy.Result:The mean spherical equivalent refraction of 10 myopic patients showed an increase in myopic shift with approximately 7% and 18% for 10° and 20° of eccentricity, respectively. Similarly, the mean spherical equivalent measure on axis (0°) and off axis (10° and 20°) were -2.5495, −2.737, and −3.0265, respectively. The mean spherical equivalent differences between on-axis (0°) and off-axis (10° and 20°) showed statistically significant differences with P < 0.05.Conclusion:This study concluded that a greater degree of eccentricity will induce a greater amount of errors in retinoscopy.

Effect of eccentricity of overnight lenses on 2-year axial growth and visual quality

AIM: To explore the effect of eccentricity of overnight orthokeratology (OK) lenses on 2-year eye axial growth and visual quality. METHODS: Based on the degree of eccentricity of OK lenses, patients were divided into three groups: a low degree of eccentricity group (degree of eccentricity ≤0.5 mm), a group of moderate eccentricity (eccentric degree &gt;0.5-1.0 mm) and a group with a high degree of eccentricity (eccentric degree &gt;1-1.5 mm). The degree of eccentricity of the OK lens, spherical equivalent (SE), the uncorrected visual acuity (UCVA) after wearing OK lenses, axial length (AL) before and after wearing OK lenses, total higher-order aberrations (HOA), comas, and spherical aberrations (SA) for 3 mm pupils were analyzed. The difference among the three groups for all parameters was compared using the Kruskal-Wallis H Rank-Sum test. RESULTS: The study retrospectively analyzed 75 cases (139 eyes). In the low eccentricity group (53 eyes), the mean age was 11.4±2.4y, SE was -3.24±1.48 D, and AL was 24.85±1.01 mm. In the moderate eccentricity group (53 eyes), the mean age was 11.4±2.2y, SE was -3.22±1.29 D, and AL was 25.15±0.92 mm. In the high eccentricity group (31 eyes), the mean age was 11.5±1.9y, SE was -3.54±1.43 D, and AL was 24.95±0.84mm. After two years, there was no significant difference in the changes of the axis among the three groups (P=0.089). The HOA, SA, and coma in the high eccentric group were significantly higher than in the middle eccentric group (P&lt;0.05). The HOA, SA, and coma in the high eccentric group were also significantly higher than those in the low eccentric group (P&lt;0.05). CONCLUSION: For OK lenses, it is unnecessary to strictly require the absolute centralization of the lens position. An unnecessary change of the lenses may delay the eye-axis control. However, the balance between axial control and visual quality should be assessed.

Experimental study on resin-anchored bolt concentricity including a device for more consistent bolt centering

The bolts not being coaxial with the boreholes they are installed in is a common problem during roof bolting in tunnels and underground roadways. This paper uses theoretical analysis and laboratory experiments to analyze the influence of noncoaxial bolt on resin-anchored and to find an effective solution for eccentric bolt. After analyzing the stress distributions along the resin–rock interface (the R-R interface), we found that when the bolt is eccentric, the shear stress distribution at the interface is not uniform. The shear stress at the R-R interface closer the bolt is higher and this causes the bond at the R-R interface to fail more easily, which reduces the anchoring performance. The strength of bolts anchored with different degrees of eccentricity was analyzed using pullout tests. The test results show that bolt concentricity is positively correlated with both the anchoring strength and the energy absorption capacity. This indicates that an eccentric bolt will weaken the anchoring quality of bolt. To solve the eccentric bolt problem while taking the mechanics of bolt installation into account, a bolt radial limiting device (BRLD) has been designed. Laboratory experimental results show that the BRLD can effectively ensure the concentricity of a bolt. This research has explained why bolts that are not centered decrease the anchoring strength of resin. It also provides an economical and convenient method for ensuring that bolts are installed concentricity to improve anchoring system performance.