Sag Values Research Articles

Scleral contact lens for severe keratoconus with corneal hydrops: A case report

We describe a case of fitting a scleral contact lens for keratoconus management. A 37-year-old female has came for the keratoconus management opinion. She was using glasses for the last 20 years. She was presented with bilateral severe keratoconus with corneal hydrops, and it show high myopic. A standardized eye examination was thoroughly done in the hospital visual acuity, corneal oculyzer and slit lamp examination with IOP measurement. . The best spectacle corrected visual acuity was Right eye 6/60 with pinhole no improvement with the correction of -13.75/-2.00 x 35 and Left eye having best spectacle corrected visual acuity of counting finger- finger counting with pinhole no improvement with the correction of -14.00 dsph. Optimal fitting characteristics were found in terms of vault, centration and landing and coverage the final parameter that we selected base curve, diameter, power and sag value RE 7.34, 16.40 mm, -15.25/-1.00 X 40, 5.41; LE 6.75, 16.40, -19.25/-1.50 X 110, 5.68 respectively. With over refraction of this power visual acuity was 6/6p and 6/9 in right eye and left eye respectively. In this case we were fit the patient with miniscleral lens which are more comfortable, and the visual acuity was also improved and in the follow up of 3 months no ocular adverse effects were seen. This case report shows that in this patient a Maxim Scleral Lens could be fitted successfully for keratoconus management, providing good visual quality.

Simulation-Based Comparison of PID with Sliding Mode Controller for Matrix-Converter-Based Dynamic Voltage Restorer under Variation of System Parameters to Alleviate the Voltage Sag in Distribution System

A constant power supply is a basic need for each consumer due to the increase in sensitive equipment day by day. As per IEEE standards, a 10% reduction in voltage from the supply voltage is not acceptable and may cause the failure of equipment. Previously, different techniques have been used to alleviate the voltage sag, such as STATCOM, DSTATCOM, SVC, and shunt capacitors, but these devices are connected in parallel, which compensates for the low value of voltage sag, and they have high maintenance costs involved. Compensation for the low and high values of voltage sag is possible through a series-connected device such as a dynamic voltage restorer. In this paper, a matrix converter is presented for DVR to convert AC to AC voltage directly and free from batteries, capacitors, and multiple conversions as needed in a voltage source inverter, resulting in a reduced cost of DVR topology. The DVR is meaningless in the absence of a controller, so it is necessary to select a suitable controller for the satisfactory operation of the DVR under a variation of system parameters. In this paper, the performance of a linear PID controller is analyzed and compared with a nonlinear controller, such as a sliding-mode controller, under variation of power system parameters inorder to select a robust controller that performs satisfactorily for DVR. Earlier trial-and-error methods were used to obtain the parameters of PID gains, but they require a large time to obtain the parameters of the PID gains and there is a chance of inaccuracy. A genetic algorithm was used to obtain the gain parameters, but it has more convergence time and the particle swarm optimization technique has involves less reliability. In this research paper, the sliding surface coefficient parameters such as and Ki for the PI sliding surface of SMC and PID gains are taken through an ant colony algorithm to obtain the robustness of the controllers. The purpose of this paper is to introduce the best DVR topology with reduced cost. MATLAB simulation software was utilized to analyze the performance of the DVR with PID and SMC controllers under different fault conditions and also the THD% of proposed controllers was analyzed through FFT.

Dosimetric impact of mechanical movements of the Linac gantry during treatments with small fields.

Current accepted linac Quality Assurance (QA) guidelines used for Volumetric Modulated Arc Therapy (VMAT) suggest a mechanical isocentre tolerance level of 1mm. However, this tolerance level has not been well-established for the specific case of small field stereotactic VMAT. This study aims to evaluate the clinical impact of mechanical uncertainty on this treatment modality by modelling systematic gantry sag derived isocentre variance in the Treatment Planning System (TPS). A previously reported dataset of gantry sag values in the literature served as a starting point for this study. Using an in-house developed VMAT arc splitting algorithm, isocentre shifts were applied at a Control Point (CP) level to DICOM-RT treatment plans. Dose distributions for varying isocentre shift magnitudes were calculated for a set of 29 stereotactic VMAT plans using the Eclipse Acuros XB dose algorithm. These plans had a range of Planning Target Volume (PTV) sizes. A quantitative comparison of each plan was conducted by evaluating five Dose Volume Histogram (DVH)-derived plan quality metrics. All metrics exhibited a deterioration in plan quality with increasing magnitudes of isocentre shift. At small PTV sizes, these effects were amplified, exhibiting significant changes at 1mm of average shift when typical targets and tolerances were considered. For plans with PTVs between 0 and 5 cm3, a 1mm shift reduced PTV coverage by 6.6 ± 2.2% and caused a 12.1 ± 3.8% deterioration in the conformity index. Based on the results of this study, the prevalent tolerance of 1mm may not be suitable for treatments of small PTVs with small fields. In contrast to commonly accepted values, an absolute mechanical isocentre of 0.5mm with action level at 0.75mm is recommended for stereotactic VMAT of PTV sizes below 10 cm3.

On Real-Time Detection of Line Sags in Overhead Power Grids Using an IoT-Based Monitoring System: Theoretical Basis, System Implementation, and Long-Term Field Verification

For overhead power grids, unexpected serious line sagging of extra-high voltage transmission lines would easily lead to major blackouts. Different direct and indirect sag measuring methods have been proposed, but they all have their own limitations. In this study, an Internet of Things (IoT)-based sag-monitoring system is proposed, which is able to perform real-time detection of line sags. The whole system has been deployed on two 161-kV lines for long-term field testing. The effectiveness of the proposed sag-monitoring system is verified through both theoretical calculation and field measurements. In this sag-monitoring system, a sag-sensing module is equipped with an embedded triaxial accelerometer to detect line sags at different spans of a single circuit. A catenary equation that takes temperature dependency into consideration is derived, so the measured accelerometer parameters can be converted to accurate line sag values. The long-term testing results show that the proposed sag-monitoring system yields an average error of 2.09%. The average differences between the sag values coming from the proposed system and a commercial sag measuring device are relatively small (between 0.57% and 4.14%), which proves that the sag values provided by the proposed system are reliable and accurate in the long-term testing. In addition, compared to the other existing sag measuring methods, the advantages of employing the proposed system are high measurement accuracy, and enabling wide field implementation, online monitoring, long-term field operation, and real-time transmission.

Numerical Analysis of the Effect of Heterogeneity on Underground Roadway Stability under Dynamic Loads

With the increasing depth of coal mining and expanding mining scale, the rocks surrounding deep roadways are in a complex mechanical condition of frequent dynamic disturbance. The heterogeneity has an important influence on rock mass failure under dynamic loads. Therefore, it is necessary to study the deformation and failure of heterogeneous roadway under dynamic load. In this paper, the effect of heterogeneity on stability of roadway under static and different dynamic loads is studied. According to the results, the effect of rock mass heterogeneity on the deformation and failure of surrounding rock varies with different degrees of heterogeneity. Under static loading conditions, the stability of roadway is negatively correlated with the degree of heterogeneity of the rock mass. Under dynamic loading conditions, the change of heterogeneity degree has significant influence on the stability of surrounding rock. With the increase in dynamic load strength, the change in variation difference in the average value of roof sag, stress distribution, and plastic zone caused by variations in heterogeneity will increase. This study contributes to understanding the deformation and failure characteristics of heterogeneous roadways under dynamic loads and can be used to analyze heterogeneous roadways under dynamic loads.

Fitting Pearls for Scleral Lenses

Scleral lenses are the large diameter rigid gas permeable lenses which have a large number of potential benefits, the dispensing of this lenses are increased exponentially over the last decade. Scleral lenses now-a-days are designed with the use of software and advanced manufacturing machines. This not only allow the eye care practitioner to design the lens on micro level but also increase the optical quality and comfort of the lens on eye. In the past, one major disadvantage of fitting scleral is chair time, skills and expense required to fit them. Scleral lenses are available in different diameters and sag values which helps ECP to fit lens accordingly. Scleral lens fitting philosophy differs from that of corneal GP lenses. Different scleral lenses may use different fitting methods.

Alumina-zircon filler based ceramic shell moulds for directionally solidified cast shrouded low pressure turbine blades

Ceramic shell moulds for investment casting of shrouded low-pressure turbine (LPT) blades were prepared by using colloidal silica binder and partial substitution of the zircon filler with fine alumina. Among the two ceramic slurry systems designed, the first slurry system comprised of polymer-free colloidal silica binder, and the second slurry system comprised of polymer-containing colloidal silica binder. The samples prepared from the first slurry system showed higher fired residual strength and self-load sag values (lesser sag resistance). The casting of shrouded LPT blades was carried out at 1525 °C and 1550 °C using CM247LC superalloy. Ceramic shell moulds prepared from the second slurry system, containing 30 wt% of fine alumina filler, yielded aeronautical grade casting (at 1550 °C) of blades with required dimensional accuracy and average surface roughness. Microstructural analysis of the cut surfaces of self-load sag tested samples was carried out to understand the effect of fine alumina substitution on shell characteristics.

Advanced Power Line Diagnostics Using Point Cloud Data—Possible Applications and Limits

The advance in remote sensing techniques, especially the development of LiDAR scanning systems, allowed the development of new methods for power line corridor surveys using a digital model of the powerline and its surroundings. The advanced diagnostic techniques based on the acquired conductor geometry recalculation to extreme operating and climatic conditions were proposed using this digital model. Although the recalculation process is relatively easy and straightforward, the uncertainties of input parameters used for the recalculation can significantly compromise such recalculation accuracy. This paper presents a systematic analysis of the accuracy of the recalculation affected by the inaccuracies of the conductor state equation input variables. The sensitivity of the recalculation to the inaccuracy of five basic input parameters was tested (initial temperature and mechanical tension, elasticity modulus, specific gravity load and tower span) by comparing the conductor sag values when input parameters were affected by a specific inaccuracy with an ideal sag-tension table. The presented tests clearly showed that the sag recalculation inaccuracy must be taken into account during the safety assessment process, as the sag deviation can, in some cases, reach values comparable to the minimal clearance distances specified in the technical standards.

Variation in sag values in daily disposable, reusable and toric soft contact lenses

PurposeWhile knowledge of the ocular surface sagittal height (OC-SAG) is increasing with newer instrumentation, understanding of soft lens sag values (CL-SAG) in daily clinical practice is limited. This study aimed to report the differences in CL-SAG of a large collection of daily disposable (DD), reusable (2-week and 4-week replacement) and toric lens designs. Methods12 different spherical DD and 15 reusable lens types were analysed (labelled power −3.00D); 17 different toric lens types analysed (6 DD and 11 reusable) in −3.00D =C 0.75 × 180. Posterior CL-SAG was measured directly using a spectral domain OCT-based instrument (Optimec is830). ResultsThe range in CL-SAG for DDs was 3,398-3,912 microns, for reusable lenses 3,372-4,004 microns and for toric lenses 3,536-4,157 microns. Lens diameter and BC together influence CL-SAG values. For lenses with the same labelled base curve (BC), the maximum difference in the DD group was 264 microns, in the reusable group 418 microns and in the toric group 345 microns. Three lens designs within the DD group and five in the reusable group offer two BCs, with an average variation (±SD) in CL-SAG of 276 ± 39 microns; one toric lens with two BCs showed a 377-micron difference. ConclusionsMarked differences in CL-SAG values were found in this study, also between lenses of the same BC. While ECPs should be aware that diameter and BC together influence CL-SAG, this also indicates that lens substitution based on BC alone could result in substantial differences in CL-SAG, with a potential impact on lens fit. Lens designs offering two BCs showed a somewhat narrow band in absolute terms in CL-SAG, and switching from a spherical to a toric lens of the same lens manufacturer could result in a significant change in CL-SAG.

Ceramic shell moulds with zircon filler and colloidal silica binder for investment casting of shrouded low-pressure turbine blades

Zircon (ZrO2·SiO2) powder filler and colloidal silica binder were used to prepare the ceramic shell moulds for investment casting of shrouded low-pressure turbine blades (LPTB). Ceramic slurries were prepared by using two types of colloidal silica binders (polymer-free binder A and polymer-containing binder B). The samples prepared from binder B showed lesser self-load sag values than those developed from binder A. Ceramic shell moulds made from an optimized slurry composition (having binder A) yielded aeronautical grade casting of blades at 1500 °C with required dimensional accuracy and average surface roughness (Ra). The blades cast from shell moulds (having binder B) showed dimensional accuracy at 1500 °C as well as at 1525 °C. The Ra values of blades cast at 1500 °C and 1525 °C by using shell system with binder B were observed to be higher than those cast from shell system having binder A.

Sag and Tension of 275 kV Transmission Line using Catenary

This research will develop a catenary method to determine the sag and tension analysis on the 275 kV transmission line conductors. The catenary method is dependent on the equation of the weight of the conductor, the maximum tensile stress of the conducting wire, the length of the span, and the maximum sag of the conductor. The method will be used in determining the value of sag and tension with the design of the model using software AutoCAD. The results of research for the same tower sag height of 6.86 m, with a tension of 4610.83 kg and a conductor length of 401.06 m, while sag for the tower is not the same height of 8.14 m, with a tension of 4612.84 kg, and changes in conductor length 401.06 m. The increase in current causes the sag value to increase, when the minimum current sag value is 6.9828 m, and the maximum current sag value increases to 8.44 m. While the tension will decrease along so that temperature is increased the current minimum pressure of 4531.27kg, and at the time of maximum tension of 3749.728kg. Sag and tension are also affected by ambient temperature when the minimum temperature is 20 ℃ sags are 6.8621 m and when the maximum temperature is 40 ℃ sag increases to 7.793492 m. Tension will decrease with each increase in temperature when the minimum temperature is 20 ℃ tension 4610.538 kg when the maximum temperature is 40 ℃ the tension is reduced to 4062.345 kg.

Correlation of Corneal and Scleral Topography in Cases with Ectasias and Normal Corneas

Background and Objective
 To determine the relationships between corneal and scleral elevation topography in subjects with corneal ectasias and normal corneas.
 
 Material and Methods
 This is a multi-site retrospective study. Ocular surface topography (sMap3D, Precision Ocular Metrology, US) was collected on 115 eyes with prolate cornea profile (Group A) and 227 eyes showing corneal ectasia (Group B). Sagittal height (SAG 1) was measured in the axis of the highest elevated point of the cornea (apex), defined by the meridian joining this apex to the geometrical center of the cornea at an 16 mm chord diameter (8-mm radius). Another sag value was evaluated 180° away (SAG 2) at the same diameter/radius. The difference in height between SAG 1 and SAG 2 represents a quadrant specific effect (QSE). Conjunctival toricity is estimated by comparing the best fit of the conjunctival/scleral shape data to a toric (Sin2) curve; the root- mean-squared error (RMSE) of this curve, a measure of irregularity, was also calculated.
 
 Results
 The ectasia subjects demonstrated greater QSE, (p<0.001), standard toricity (p<0.001) and RMSE (p<0.001) on the sclera compared to normal cornea cases. If the apex of the ectasia was ≥1.25mm from the corneal center, the asymmetry was greater. Within the Group A, standard toricity was significantly higher than QSE (p<0.001) suggesting a more regular conjunctival pattern. As a proof, a significantly greater proportion of cases in Group B vs. Group A (57% vs. 26%, p<0.001) were found with conjunctival irregular shape, as previously defined. In both groups, subjects graded as having spherical/toric scleral shape had significantly lower RMSE values than those graded as having irregular shapes (p<0.001).
 
 Conclusion
 Subjects with corneal ectasia have a different scleral shape compared to those with normal corneal profiles, largely presenting as a quadrant specific effect along the same axis. This difference is higher if the apex of the ectasia is ≥1.25 mm from the corneal center. RMSE seems to correlate with scleral shape classification in both groups.

A hybrid fabrication approach and profile error compensation for silicon aspheric optics

Aspheric optics is widely used for many optical applications due to their advantages, that is, light weight, cost-effectiveness and efficiency. There are many fabrication challenges which affect the quality of aspheric optics used for infrared-based applications. Diamond turning is one of the most suitable techniques for fabrication of infrared aspheric lens with high profile accuracies, due to its deterministic approach. However, for optics with large sag value, multiple machining cycles are required to make the best fit surface. Repeated machining cycles result in generation of inherent stresses leading to subsurface deformation and poor quality. In this study, hybrid approach of grinding and machining is proposed for fabrication of silicon infrared optics in large volume. The proposed approach results in reduced fabrication time and subsurface deformation with improved surface quality and tool life. The profile accuracy after compensation of profile error ( Pt) is 0.21 µm and surface roughness ( Ra) 10.5 nm is achieved.

Estimation of Current and Sag in Overhead Power Transmission Lines With Optimized Magnetic Field Sensor Array Placement

Power distribution mechanism in smart grid necessitates the development of an easy-to-install and contactless sensing system to monitor the operational state of overhead high-voltage transmission lines. Here, we propose a robust phase current and sag estimation method at support structures. Novelty in our work is the use of dual-axis magnetic field (MF) sensors equal to the number of phase conductors. This is realized by installing an array of sensors optimally placed in the same vertical plane as of conductors on the tower. The optimal position of sensor array was found while minimizing the condition number of governing linear system close to unity. For any circuit configuration, our method processes the sensed MF vector projections through a linear system, which is based on the Biot–Savart law. It considers the practical factors, such as sag, span length, and sensor-to-conductor distance. An algorithm is then designed to estimate the electric current and sag by iterative comparison between the measured and calculated MF. The method is first tested by numerical simulations for a typical one-circuit configuration, which involves three scenarios of symmetrical and unsymmetrical sag in conductors. The algorithm converges to a maximum error of $\le 1$ % within 300 iterations. We then experimentally verify our scheme on a scaled laboratory setup. Retrieved current and sag values were verified with the readings from ammeter and vernier caliper, respectively. The results prove the viability of our approach within $\le 2.6$ % deviation for current and $\le 1$ % for sag in all conductors.

New Gen Algorithm for Detecting Sag and Swell Voltages in Single Phase Inverter System for Micro grid

In this manuscript, a novel sag and peak detector by means of a delta square operation for a single-phase is suggested. The established sag detector is from a single phase digital phase-locked loop (DPLL) that is founded on a d-q transformation employing an all-pass filter (APF). The d-q transformation is typically employed in the three-phase coordinate system. The APF produces a virtual phase with a 90° phase delay, but the virtual phase can not reproduce an abrupt variation of the grid voltage, at the moment in which the voltage sag transpires. As a consequence, the peak value is severely garbled, and settles down gradually. A modified APF produces the virtual q-axis voltage factor from the difference between the current and the former value of the d-axis voltage component in the stationary reference frame. Nevertheless, the amended APF cannot sense the voltage sag and peak value when the sag transpires around the zero crossing points such as 0° and 180° since the difference voltage is not adequate to sense the voltage sag. The suggested algorithm is proficient to sense the sag voltage through all regions as well as the zero crossing voltage. Furthermore, the precise voltage drop can be obtained by computing the q-axis component, which is relational to the d-axis component. To authenticate the legitimacy of the suggested scheme, the orthodox and suggested approaches are contrasted by means of the simulations and investigational results.

A Novel Method for Single and Simultaneous Fault Location in Distribution Networks

This paper introduces a novel method for single and simultaneous fault location in distribution networks by means of a sparse representation (SR) vector, Fuzzy-clustering, and machine-learning. The method requires few smart meters along the primary feeders to measure the pre- and during-fault voltages. The voltage sag values for the measured buses produce a vector whose dimension is less than the number of buses in the system. By concatenating the corresponding rows of the bus impedance matrix, an underdetermined set of equation is formed and is used to recover the fault current vector. Since the current vector ideally contains few nonzero values corresponding to fault currents at the faulted points, it is a sparse vector which can be determined by $\ell^{{{1}}}$ -norm minimization. Because the number of nonzero values in the estimated current vector often exceeds the number of fault points, we analyze the nonzero values by Fuzzy-c mean to estimate four possible faults. Furthermore, the nonzero values are processed by a new machine learning method based on the k-nearest neighborhood technique to estimate a single fault location. The performance of our algorithms is validated by their implementation on a real distribution network with noisy and noise-free measurement.

Impact of Data Errors on Sag Calculation Accuracy for Overhead Transmission Line

The difference between a designed and actual transmission-line conductor sag value due to conductor properties' dispersion and measurement errors is estimated. Total error of sag calculation is presented as a weighted sum of partial errors of six measured/specified parameters involved in the state equation. The resulting formula for weighting factors for partial error is obtained by differentiating the state equation and enables analysis of the contribution of each error. It is shown that the factors for error in elasticity modulus or in creep values are small, so these errors have a weak effect on final result error. In contrast, weights for errors in sag and temperature measurements during stringing operation are large, and these errors contribute significantly to final sag error. Derived formula for weighting factors provides the tool to evaluate the total error of sag calculation and enables establishment of the possible limits for transmission-line thermal rating. Absolute error of sag calculation for the ACSR conductor is about 1.5 m for a 350-m span and about 2 m for a 500-600 m span. Absolute sag error for the AAAC Al59 conductor is 25% less.

Impact of Unified Power-Quality Conditioner Allocation on Line Loading, Losses, and Voltage Stability of Radial Distribution Systems

This paper presents an investigative study on the impact of unified power-quality conditioner (UPQC) allocation on radial distribution systems. A design approach for UPQC, called sag-based design for phase-angle control for UPQC (UPQC-SPAC) is proposed. The phase-angle shifting of the load voltage required to mitigate a given value of voltage sag is determined and the same is used during a healthy operating condition in order to provide the reactive power compensation of a distribution network. To study the impact of the UPQC-SPAC allocation on distribution systems, it is placed at each node, except the substation node, one at a time. The load-flow algorithm for radial distribution systems is suitably modified to incorporate the UPQC-SPAC model. The simulation results show that a significant amount of power-loss reduction, under voltage mitigation, and the enhancement of voltage stability margin can be obtained with an appropriate placement of the UPQC-SPAC in a distribution network. The performance comparison of the UPQC-SPAC with one previously reported design approach shows that it is more efficient in undervoltage mitigation. An appropriate allocation of the UPQC-SPAC is also found to be beneficial for the networks with distributed-generation units.

Rogowski Coil for Current and On-Temperature Monitoring Overhead Transmission Lines

This letter describes the development of a rogowski coil current and on-chip temperature sensor for evaluating the sag of conductors in high voltage transmission line. A rogowski coil has a air core instead of an iron core. The measurement show excellent linearity with practical no saturation problems. In addition, the rogowski rate highly for electrical isolation from the bus bar, and is light weight with low material cost. The uses reliably proven universal serial bus technology to energize the electronic circuitry. The data collected together with sag information will provide support for the development of an algorithm for estimation conductor sag values.

A Real-Time Conductor Sag Measurement System Using a Differential GPS

A real-time and “direct” method of measuring the absolute value of sag on a transmission-line conductor using a differential global positioning system (DGPS) is presented. The method includes a real-time data-processing module integrated into the DGPS system. The GPS signals corresponding to physical movement of the midspan of a transmission-line conductor were obtained so that conductor-to-ground clearance could be recorded in real time. Several field tests were designed and implemented to test the DGPS method under varying conditions of the transmission-line current. A comparison of results obtained from the DGPS method with those from a laser-range finder indicates an accuracy of 1 in.