Change In Radius Of Curvature Research Articles

An Active Compliance Adsorption Method for Climbing Machining Robot on Variable Curvature Surface

This article proposes an active compliance adsorption method for a negative pressure adsorption climbing robot with 3 active compliance suction units which integrate 3 degree of freedom active compliance actuators along with flexible adsorption chambers. This method enables the climbing robot to adsorb and move stably on the surface of large and complex components with variable curvature for machining purposes. The main contribution lies in two aspects. First, an adsorption performance indicator (API) depicting the stretch of the flexible sealing lip is proposed by analyzing the leaked airflow of the climbing robot's suction unit. Second, the pose control method of the suction chamber based on the real-time estimated adsorbed surface is proposed, where the API is used as the optimization target. The experiments have been performed and the results show that a 10 kg-weight climbing robot with three active compliance suction units can keep adsorption force over 1000 N when the surface's curvature radius changes continuously from 1.1 to 14.6 m, with a significant increase in the adsorption force up to 156% compared with only pure passive compliance adsorption method.

Tilting refractive x-ray lenses for fine-tuning of their focal length.

In this work, we measure and model tilted x-ray refractive lenses to investigate their effects on an x-ray beam. The modelling is benchmarked against at-wavelength metrology obtained with x-ray speckle vector tracking experiments (XSVT) at the BM05 beamline at the ESRF-EBS light source, showing very good agreement. This validation permits us to explore possible applications of tilted x-ray lenses in optical design. We conclude that while tilting 2D lenses does not seem interesting from the point of view of aberration-free focusing, tilting 1D lenses around their focusing direction can be used for smoothly fine-tuning their focal length. We demonstrate experimentally this continuous change in the apparent lens radius of curvature R: a reduction up to a factor of two and beyond is achieved and possible applications in beamline optical design are proposed.

Оптимизация решения фундамента путем проведения натурных экспериментальных исследований взаимодействия плиты с податливым основанием

Article considers the case of optimizing design solution for foundation of a 10-storey residential building on sandy soils. Optimization was achieved through experimental work with 2*2*0,2 m reinforced concrete slabs and 5000 cm2 stamps. During slabs testing slab settlements, in concrete and reinforcement, as well as contact pressure under slab were measured. During stamps testing displacements of the stamp and surrounding soil were measured at 21 points. As a result of the tests deflection slab mode, slab-soil contact stresses, changes in radius of curvature, relative deformation of concrete and reinforcement in upper and lower parts of the slab during loading were obtained. Results of experimental data made it possible to select a foundation model, which was later used for foundation design. Recommendations are given for determining soil deformation characteristics, modeling soil-plate interaction, as well as economic efficiency of foundation design solution.

Shape Loss of Autoclaved, Machine-Bent Cobalt-Chrome and Titanium Spine Surgery Rods.

Study Design:This was a biomechanical study.Objective:Shape loss of surgical spine rods has been implicated as a factor leading to postsurgical loss of alignment correction. Our objective was to compare the degree of shape loss in surgical spine rods of different compositions under physiological conditions that were bent before or after being autoclaved.Methods:10 CoCr and 10 commercially pure titanium (CPTi) surgical spine rods were contoured using a machine press. Five CoCr and 5 CPTi rods were bent before being autoclaved (preoperative bent group); 5 CoCr and 5 CPTi rods were bent after being autoclaved (intraoperative bent group). All rods were immersed in a phosphate-buffered saline bath at body temperature (37.2°C ± 2°C). Changes in radius of curvature were measured at different time intervals over an 8-week course using a high-definition scanner.Results:Each rod demonstrated shape loss in radius of curvature (range = 1.04-9.99 mm) over the duration of the study. Intraoperatively bent CPTi rods demonstrated the largest shape loss (range = 8.73-9.99 mm; median 9.33 mm; P < .01). Preoperatively bent CPTi (range = 1.04-1.71 mm; median = 1.39 mm; P < .01) and intraoperatively bent CoCr (range = 1.11-2.11 mm; median = 2.01 mm; P < .01) rods underwent the least amount of shape loss.Conclusion:CPTi spinal rods bent after autoclave may lead to considerable loss of alignment correction. In addition, our results suggest that preautoclave bent CPTi and CoCr spinal rods bent after autoclave may be a more ideal choice of implant because they may provide more resistance to shape loss over time.

Designing arm cavities free of parametric instability for gravitational wave detectors

Parametric instability is an intrinsic problem in high power laser interferometer gravitational wave detectors. Optical cavity modes interact with acoustic modes of the test masses, leading to laser power dependent exponential growth of acoustic vibration of the test masses. Future detectors are being planned with designed optical power as high as 5 MW. This increases the requirements for suppressing of parametric instability through various currently available methods. Parametric instabilities could also be alleviated through careful design of the acoustic mode structure and optical mode spacing. Here we study parametric instabilities in future gravitational wave detectors with arm lengths between 6 and 10 km. We show that by careful choice of test mass radii of curvature, dimensions and arm lengths it is possible to design detectors that are free of parametric instability up to 3 MW of intra-cavity power with large enough tolerance on mirror radii of curvature change. We present several case studies and give an example of a design with 6335 m arm cavities and test mass diameter of 52 cm that is parametric instability free. This design is relatively tolerant, staying free of instabilities for a 45 m change in test mass radius of curvature. Maintaining this radius of curvature could easily be done with good design and thermal compensation.

The shear stiffness criterion for rock joints considering rock wear behaviour

Rock is a material that is affected by wear, and the curvature of the asperities on a rock joint surface increases with the degree of wear after shearing. Based on the Greenwood and Williamson (GW) model, a new model considering the change of asperity curvature is proposed to explain the wear behaviour of rock joints. First, the shear stiffness formula for a joint surface is derived when the asperity curvature is constant, which shows that the shear stiffness increases with increase of asperity curvature. According to the Mohr–Coulomb criterion, the yield position of a single asperity under normal force and tangential friction force is discussed. Then, the critical normal force for a single asperity at a specific friction coefficient is obtained, which shows that the normal force corresponds to the curvature radius of the asperity. A rough surface model with multi-level curvature radius is proposed. With increase of normal force, the higher-order asperities gradually fail and the curvature radius become larger. A specific pressure value excites a specific radius of curvature, and the larger the pressure, the larger the radius of curvature. The relation between the normal force and the curvature radius is proposed and a shear stiffness formula considering the change of curvature radius of the asperity is derived. The proposed model is verified on the basis of the published experimental results. The calculation results of the proposed model can reflect the test results well: for a given joint surface, with increase in normal force the joint surface gradually becomes smooth; for different joint surfaces, with increase in roughness, the joint surface is more easily smoothed.

Cone beam computed tomography assessment of canal transportation, centering ability, and radius change of two single file systems in curved root canals

Objective: assessment the canal transportation and centering ability of two single file systems (Reciproc and Neoniti) in curved mesiobuccal (MB) root canal of natural lower first molars, by cone beam computed tomography (CBCT) scanning. Methods: Forty non-calcified Mesio-buccal root canals with complete formed root and apical curvature of 20-45o and Radius ≤ 15mm were chosen from extracted human lower first molars. The samples were divided based on the instrument (n=20) into two main groups group I (Reciproc R 25/08) and group II (Neoniti R 25/08). Each group has another subdivided based on the motion into (n=10) Subgroup A: reciprocation motion Subgroup B: full rotation motion. The apical transportation, centering ability and radius change were measured by pre- and post-instrumentation CBCT scans by superimposing in four section (2, 4, 6 and 8 mm from apical foramen). Values were recorded, tabulated for each group and statistically analyzed. Results: The ability of instruments to remain centered in prepared canals at 2and 4 mm levels was higher in Neoniti reciprocation in MD dimension. The centering ratio at 6 and 8 mm level and in BL dimension were not significantly different between the tested subgroups. The change of the radius values and percentage produced no significant difference. Conclusion: Both Neoniti and Reciproc systems haven’t significant difference in canal transportation, centering ability and change in curvature radius expect when using reciprocation motion Neoniti produced significantly better results than Reciproc especially in the apical third.

Two-year changes in corneal stiffness parameters after accelerated corneal cross-linking

The objective of this non-randomized trial was comparison of two-year changes in dynamic corneal response (DCR) between 18 mW/cm2 (5- min) and 9 mW/cm2 (10-min) cross-linking (CXL) protocols, using novel stiffness parameters and correlating them to clinical indices. The two groups were evaluated before and 2 years after the procedure using Corvis ST (Oculus Optikgeräte GmbH, Germany) and DCR parameters such as deformation amplitude ratio at 1 mm and 2 mm (DA ratio-1 mm and DA ratio-2 mm) and integrated radius and stiffness parameters at A1 (SP-A1). Two-year follow-up was completed for 16 of the 30 eyes in the 5-min group and 21 of the 25 eyes in the 10-min group; data from those who were lost to follow-up was not included in the analyses. Mean age at baseline was 21.7 ± 4.9 and 21.5 ± 5.2 years in the 5- and 10-min groups, respectively (P = 0.895). At 2 years after CXL, in the 5-min group, the reduction in integrated radius (−1.12 ± 1.27 mm, P = 0.003) was significant, and the increase in SP-A1 (7.11 ± 14.86 mmHg/mm, P = 0.075) was borderline, while in the 10-min group, the decrease in DA ratio-2 mm (−0.43 ± 0.58, P = 0.003) and integrated radius (−1.89 ± 1.72 mm, P < 0.001), and increase in SP-A1 (7.67 ± 10.92 mmHg/mm, P = 0.004) were significant. In both groups, the strongest and significant correlation was observed between DCR parameters and changes in radius of curvature. In conclusion, results indicated corneal strengthening with both protocols especially with the 9 mW/cm2. Corvis ST indices can provide “in vivo” biomechanical evidence on the efficacy of CXL that may occur prior to clinical indices.

Effect of Physical Aging on the Bending Recovery of PEEK and PI Films

The relationship between the viscoelasticity and bending recovery responses of PI and PEEK films were studied as well as the effect of physical aging treatment on these properties. The residual elastic modulus (Er) and degree of aging of the films were measured from the stress relaxation-recovery experiment using DMA and the enthalpy relaxation endotherms near glass transition temperature using DSC, respectively. The instantaneous bending recovery ratio (BR+) of the films was measured from the change in radius of curvature before and after the bending under the condition of 85 °C/85%RH/24 hr. The DMA test was also performed at 85 °C in order to evaluate the progression of the stress relaxation during bending. The Er and BR+ values showed good correlation, and higher contributions of elastic response or longer delay of the stress relaxation led to improved bending recovery. Films with BR+ values close to zero can be obtained if the conditions of Er <0.05 are satisfied. A physical aging method was proven to be effective for controlling the viscoelastic response of the films; it contributes to the retardation of stress relaxation. The optimum physical aging temperatures were 200 °C for PI and 130 °C for PEEK, respectively. Both films achieved a sufficient aging effect with the treatment time of 24 hours.

14‐4: Optical Characteristics of Flexible Display Light Sources with Arbitrary Curvatures

New emerging flexible light sources (FLS) have a variety of features that boost their usage. The issues of FLSs with small radii are resolved for arbitrary curvatures and the differences between flat and curved light sources are explained. We found that the change in curvature radius of a FLS, either convex or concave, results a defocus issue, a change in emission surface, a variation of luminous intensity distribution and a change in etendue of the FLS. The effect of curvature on the optical properties of curved OLEDs as FLSs are verified in experiments.

Split-ring resonator-based sensors on flexible substrates for glaucoma monitoring

Glaucoma is an eye disease that may cause blindness by damaging the optic nerve due to elevation of the intraocular pressure. Patients with glaucoma require monitoring of intraocular pressure. This paper presents split-ring resonator-based strain sensors designed and characterized for glaucoma detection application. The geometry of the sensor is optimized such that it can be embedded in a conventional contact lens. Silver conductive paint is used to form the sensors realized on flexible substrates made of cellulose acetate and latex rubber. The devices are excited and interrogated using a pair of monopole antennas. Scattering parameters are measured between the ports of the antennas, and the characteristics of devices with different curvature profiles are obtained. Finite-element based models are developed to analyse the operation of the devices and to optimize the sensor structure. The sensitivity of the device, i.e. the change in resonant frequency for a unit change in radius of curvature, on acetate film is experimentally characterized as −4.73MHz/mm and the sensitivity of the device on latex is 33.2MHz/mm. The experimental results supported by finite-element based models indicate that the demonstrated device is suitable for glaucoma diagnosis and monitoring.

Parametric Study of Single Cell Box Girder Bridge under Different Radii of Curvature

Box girders are now prominently used in freeway and bridge systems because of its structural efficiency, better stability, serviceability, economy of construction and pleasing aesthetics. Due to its high torsional rigidity box girders are most suited for curved bridges. In the present investigation, a comparative study of straight and curved box girder bridges with trapezoidal cross section has been carried out. The analysis is carried under the dead load, super imposed dead load, live load of IRC Class A tracked vehicle and prestressed load .This paper focus on the parametric study of box girders with different radius of curvature by keeping the span, cross sectional shape and material properties constant. The parametric investigations performed on curved box girders helps to evaluate the effects of change in radius of curvature on the behaviour of the box girders. This study would help the bridge engineers to better understand the behaviour of straight and curved box girder bridges. The results obtained from this study will be a valuable guidance to the bridge designers.

Split-Ring Resonator-Based Strain Sensor on Flexible Substrates for Glaucoma Detection

This paper presents split-ring resonator-based strain sensors designed and characterized for glaucoma detection application. The geometry of the sensor is optimized such that it can be embedded in a contact lens. Silver conductive paint is to form the sensors realized on flexible substrates made of cellulose acetate and latex rubber. The devices are excited and interrogated using a pair of monopole antennas and the characteristics of devices with different curvature profiles are obtained. The sensitivity of the device, i.e. the change in resonant frequency for a unit change in radius of curvature, on acetate film is calculated as -4.73 MHz/mm and the sensitivity of the device on latex is 33.2 MHz/mm. The results indicate that the demonstrated device is suitable for glaucoma diagnosis.

Steel plate curvatures of soil-steel structures during construction and exploitation

The paper analyses the deformation of cir- cumferential bands of shells made of corrugated metal sheets in soil-steel structures. A change of curvature in the crown of a shell is assumed as a measure of deformation. In the upper part of analysed objects, regardless of their cross-sectional geometry, e.g. arched or elliptical shaped, a section of shell with a constant radius of curvature R is nowadays designed. As a result of earth pressure, moving loads and the self-weight of metal sheets, the shape of this part is subjected to deformation with a noticeable deviation from the circular shape. The change of curvature radius is determined in the paper on the basis of three coordinates of measuring points that form a triangle inscribed in a circle. Every (asymmetrical) position of the measuring points is taken into account. A system of three such points is transformed into a form of an equilateral triangle, and thus the radius of curvature is determined. Based on the change of curvature formulated during the construction and exploitation of soil-steel structures, the bending moments and normal stresses in the shell crown can be estimated and therefore a safety evaluation of the objects is possible.

Relationship between retinal distance and object field angles for finite schematic eyes.

Retinal anatomical studies have used the Drasdo & Fowler three-refracting surface schematic eye to convert between retinal distances and object field angles. We compared its performance at this task with those of more sophisticated four-refracting surface schematic eyes. Raytracing was performed for Drasdo & Fowler, Lotmar, Navarro, Liou & Brennan, Kooijman and Atchison schematic eyes, and some of their variants. The Drasdo & Fowler eye gives a greater rate of change of object field angle with retinal distance at the retinal centre of about 5% than the other schematic eyes. This rate of change also increases much more quickly into the peripheral retina for the Drasdo & Fowler eye than for the other eyes. The reason for these differences is only that the Drasdo & Fowler eye is shorter than the other eyes. The relationship between retinal distance and visual field angle appears robust to changes in retinal radius of curvature when the retina is spherical. The retinal asphericity of Kooijman and Atchison eyes appears to play a role beyond 14 mm (~50°). Changing the length of the Drasdo & Fowler eye, to match those of the four-refracting surface schematic eyes, gives similar relationships between retinal distance and object field angle up to a retinal distance of approximately 14 mm (~50°). The relationship will change with refractive error as this is related to axial length and to retinal shape, and this should be taken into consideration for accurate conversions. For distances and angles beyond 14 mm and ~50°, retinal shape should be taken into account.

Mixed lubrication analysis of modified cycloidal gear used in the RV reducer

Based on the actual working condition of the cycloidal gear on the RV reducer, the maximum normal contact load of gear tooth and mesh tooth pair for varied quantity of plus equidistant modification and minus radial-moving modification were analyzed. By considering the macroscopic geometry, the contact load, and the real tooth surface roughness and transient effect of the contact area between pinwheel and cycloidal gear, a mixed lubrication model was established. The effects of normal load, curvature radius at the meshing point, fillet radius, as well as the speed on the lubrication condition were discussed. The results suggest that load, fillet radius, and speed have different degrees of influence on the lubricating conditions while the change of curvature radius in a small range has no significant effect on the lubrication, which also helps in the optimization of cycloidal gear tooth profile modification, therefore, to obtain better comprehensive performance of RV reducer.

PC4. Comparative Geometric Analysis of Renal Artery Anatomy Before and After Fenestrated or Snorkel/Chimney EVAR

Values in mean 6 standard deviation. D, Change from pre-op to post-op; NS, no Positive end-stent angle indicates vessel angulation with respect to the stent end Significant changes from pre-op to post-op (P < .05). Significant difference between LRA and RRA (P < .05). underwent computed tomography angiography before and after F-EVAR (n 1⁄4 21) or Sn-EVAR (n 1⁄4 20), which involved a total of 74 renal artery stents. Renal artery geometry was quantified using three-dimensional modelbased centerline extraction. Stented length was computed from vessel origin to stent end. Branch angle was computed relative to orthogonal configuration with respect to the aorta at vessel origin. End-stent angle was computed relative to distal native renal artery. The radius of curvature was defined by the circumscribed circle at the highest curvature within the proximal portion from the origin to the stent end, and distal portion from the stent end to first renal artery bifurcation. Results: Stented renal artery length, branch angle, end-stent angle, and maximum change in radius of curvature from preoperative to postoperative are presented in the Table. Sn-renals had greater stented length compared with F-renals (P < .02). From preoperative to postoperative, origins of the Sn-renals angled increasingly downward (P < .002), whereas F-renals angled increasingly upward (P < .002). End-stent angle of SnRRA increased from preoperative to postoperative (P < .00001), and Sn-RRA exhibited a greater magnitude change in end-stent angle compared with Sn-LRA (P < .05) and F-RRA (P < .0005). Radius of curvature decreased in distal Sn-RRAs (P < .02). Acute renal failure occurred in 9.8% of patients, and none required dialysis. Renal stent patency was 98.6% at mean follow-up of 13.7 months. Five type IA endoleaks were identified, prompting one secondary procedure. One renal artery reintervention was performed due to an asymptomatic kinked left renal stent. Conclusions: Stented renal arteries were angled more inferiorly after Sn-EVAR and superiorly after F-EVAR due to stent configuration. Sn-EVAR induced significantly greater angle change at the stent end and curvature change distal to the stent compared to F-EVAR due to greater angle change of the Sn-renals, although no difference in patency was noted. Sn-RRA exhibited larger endstent angle change from preoperatively to postoperatively compared to the Sn-LRA, likely because the presence of the IVC on the right side restricts motion of the proximal RRA. The occurrence of the kinked left renal stent is consistent with the proximal right renal artery being more mechanically supported by the IVC. Additional

Helical buckling of a thin rod with connectors constrained in a torus

Kinds of tubular strings are widely applied to oil exploration & development. In the preceding studies, theses tubular strings are usually taken as homogeneous thin rods without connectors constrained in a straight cylinder or torus. Recent studies have indicated that the effect of connectors on the tubular strings is ignorable. On the basis of the previous studies, the paper provides an analytical model describing the helical buckling behaviors of a rod with connectors constrained in a torus. The new model is solved based on beam-column model and minimum potential energy theory. There are three contact cases between the rod and the torus, namely no contact, point contact and wrap contact. The deflections of the rod and critical conditions between different contact cases are calculated. The results show that the deflections and critical conditions are quite different when the equivalent torus curvature radius changes. The effects of equivalent torus curvature radius, rod buckling and connectors on bending moment and contact force are analyzed. The results show that connector is an important factor which should not be neglected.

Study of insertion force and deformation for suturing with precurved NiTi guidewire.

This research presents an experimental study evaluating stomach suturing using a precurved nickel-titanium (NiTi) guidewire for an endoscopic minimally invasive obesity treatment. Precise path planning is critical for accurate and effective suturing. A position measurement system utilizing a hand-held magnetic sensor was used to measure the shape of a precurved guidewire and to determine the radius of curvature before and after suturing. Ex vivo stomach suturing experiments using four different guidewire tip designs varying the radius of curvature and bevel angles were conducted. The changes in radius of curvature and suturing force during suturing were measured. A model was developed to predict the guidewire radius of curvature based on the measured suturing force. Results show that a small bevel angle and a large radius of curvature reduce the suturing force and the combination of small bevel angle and small radius of curvature can maintain the shape of guidewire for accurate suturing.

Curvature Characterization of Flex Sensors for Human Posture Recognition

Resistive flex sensors have been increasingly used in different areas for their interesting property to change their resistance when bent. They can be employed in those systems where a joint rotation has to be measured, in particular biomedical systems, to measure human joint static and dynamic postures. In spite of their interesting properties, such as robustness, low price and long life, to date commercial flex sensors have been only characterized against the variation of the bend angle with small fixed curvature radius mostly around the device center, so limiting the application to the measure of human joints. Here we aimed to investigate the flex sensor's response when there is a change in curvature radius as it is, for instance, for the measure of the postures of the human torso. So, we designed a novel automated test process to obtain resistances vs. curvature radius pairs. Results demonstrated the usability of flex sensors to other parts of the human body rather than simply joints, differently as it is currently done.