Slope Error Research Articles

Re-evaluating fetal scalp pH thresholds: An examination of fetal pH variations during labor.

Since the 1970s, fetal scalp blood sampling (FSBS) has been used as a second-line test of the acid-base status of the fetus to evaluate fetal well-being during labor. The commonly employed thresholds that delineate normal pH (>7.25), subnormal (7.20-7.25), and pathological pH (<7.20) guide clinical decisions. However, these experienced-based thresholds, based on observations and common sense, have yet to be confirmed. The aim of the study was to investigate if pH drop rate accelerates at the common thresholds (7.25 and 7.20) and to explore the possibility of identifying more accurate thresholds. A retrospective study was conducted at a tertiary maternity hospital between June 2017 and July 2021. Patients with at least one FSBS during labor for category II fetal heart rate and delivery of a singleton cephalic infant were included. The rate of change in pH value between consecutive samples for each patient was calculated and plotted as a function of pH value. Linear regression models were used to model the evolution of the pH drop rate estimating slope and standard errors across predefined pH intervals. Exploration of alternative pH action thresholds was conducted. To explore the independence of the association between pH value and pH drop rate, multiple linear regression adjusted on age, body mass index, parity, oxytocin stimulation and suspected small for gestational age was performed. We included 2047 patients with at least one FSBS (total FSBS 3467); with 2047 umbilical cord blood pH, and a total of 5514 pH samples. Median pH values were 7.29 1 h before delivery, 7.26 30 min before delivery. The pH drop was slow between 7.40 and 7.30, then became more pronounced, with median rates of 0.0005 units/min at 7.25 and 0.0013 units/min at 7.20. Out of the alternative pH thresholds, 7.26 and 7.20 demonstrated the best alignment with our dataset. Multiple linear regression revealed that only pH value was significantly associated to the rate of pH change. Our study confirms the validity and reliability of current guideline thresholds for fetal scalp pH in category II fetal heart rate.

The effects of diachronous surface uplift of the European Alps on regional climate and the oxygen isotopic composition of precipitation

Abstract. This study presents the simulated response of regional climate and the oxygen isotopic composition of precipitation (δ18Op) to different along-strike topographic evolution scenarios. These simulations are conducted to determine if the previously hypothesized diachronous surface uplift in the Western and Eastern Alps would produce δ18Op signals in the geologic record that are sufficiently large and distinct to be detected using stable isotope paleoaltimetry. We present a series of topographic sensitivity experiments conducted with the water-isotope-tracking atmospheric general circulation model (GCM) ECHAM5-wiso. The topographic scenarios are created from the variation of two free parameters, (1) the elevation of the Western–Central Alps and (2) the elevation of the Eastern Alps. The results indicate Δδ18Op values (i.e., the difference between δ18Op values at the low- and high-elevation sites) of up to −8 ‰ along the strike of the Alps for the diachronous uplift scenarios, primarily due to changes in orographic precipitation and adiabatic lapse rate driven localized changes in near-surface variables. These simulated magnitudes of Δδ18Op values suggest that the expected isotopic signal would be significant enough to be preserved and measured in geologic archives. Moreover, the simulated slight δ18Op differences of 1 ‰–2 ‰ across the low-elevation sites support the use of the δ–δ paleoaltimetry approach and highlight the importance of sampling far-field low-elevation sites to differentiate between the different surface uplift scenarios. The elevation-dependent rate of change in δ18Op (“isotopic lapse rate”) varies depending on the topographic configuration and the extent of the surface uplift. Most of the changes are significant (e.g., −1.04 ‰ km−1 change with slope error of ±0.09 ‰ km−1), while others were within the range of the statistical uncertainties (e.g., −0.15 ‰ km−1 change with slope error of ±0.13 ‰ km−1). The results also highlight the plausible changes in atmospheric circulation patterns and associated changes in moisture transport pathways in response to changes in the topography of the Alps. These large-scale atmospheric dynamics changes can complicate the underlying assumption of stable isotope paleoaltimetry and therefore require integration with paleoclimate modeling to ensure accurate reconstruction of the paleoelevation of the Alps.

Analytic ray tracer on GPU for central receiver systems

An accurate ray tracer is essential to calculate the efficiency of central receiver systems. Furthermore, its runtime has a direct influence on the applicable optimization method for finding optimal layouts of heliostat fields. Developing a ray tracer that achieves both objectives is the main focus of this study. There exist several different ray tracing techniques, starting from the classical Monte Carlo method to analytical convolution methods. Within this work, we introduce a new analytical ray tracer with high accuracy at low runtime. This is achieved by integrating over the bivariate Gaussian distributions used in our convolution ray tracer. In such a way the raytracer is capable of including the effect of multiple solar rays without the need of simulating each ray. Besides the overall efficiency, the new ray tracer can also compute accurate flux maps with thousand times fewer rays than the Monte Carlo method. To further improve the overall model accuracy, a new equation to convolute the sun, slope and tracking error is derived. We show that it perfectly matches the results of a separate accounting for these errors. The newly integrated convolution ray tracer is developed on the same platform as a bidirectional Monte Carlo ray tracer and a convolution method. Besides a large cross-validation of the results, this allows for a reasonable direct run time comparison. With extensive case studies, the quality of the solution, the run time, and various other aspects are investigated. Furthermore, all ray tracers are also implemented on the GPU improving the run time compared to the CPU version by a factor of 50. We show that the integrated convolution ray tracer running on the GPU achieves an accuracy of 99.95% for an annual simulation in 0.7 s for the PS10 and in 1.8 s for the Gemasolar.

An improved algorithm for thermal compensation of synchrotron radiation optical mirrors based on Hessian matrix

The heaters-based thermal-compensated adaptive adjustment of a reflection mirror at Shanghai high repetition rate X-ray Free-Electron Laser and extreme light facility (SHINE) is presented here based on finite element analysis. The correction performance of different control algorithms [singular value decomposition and gradient descent (GD)] is analyzed and compared. This study has demonstrated that a significant control algorithm can further improve the surface shape accuracy of the mirror. After optimizing the mirror control algorithm, the calculated slope errors and height errors of the mirror are reduced to nearly less than 50 nrad rms and 0.5 nm rms, respectively. The optimization result indicates that the GD control algorithm based on the Hessian matrix exhibits superior performance and practicality compared to the control algorithm before optimization.

Characterized environmental influences on autocollimator measurement uncertainty using an extended Allan variance

Autocollimators play an important role in the high-precision testing of the slope errors of X-ray and large flat mirrors. However, the time-varying errors caused by environmental changes exhibit different characteristics over time, such as low-frequency drift errors and high-frequency random errors. Time-varying errors can seriously affect the accuracy of the autocollimator (AC) and the read repeatability. They have become important factors limiting the continued improvement of nano-optic-measuring machines and scanning pentaprism system accuracy. Considering the difficulty in quantitatively analyzing the influence of time-varying errors on the measurement uncertainties of the AC, this paper proposes the extended Allan variance to characterize environmental influences on the AC measurement uncertainty based on a point-wise scanning measurement mode. Taking advantage of the extended Allan variance's characteristics, which allow the identification of various errors and provide stability information about the AC measurement, the characteristic curves of the AC measurement uncertainty in a specific environment were obtained. Based on the characteristic curve parameters, the ultimate accuracy of AC in the current environment was obtained by optimizing the measurement strategy. Experimental results show that the measurement uncertainty of the AC can reach 2.3 nrad RMS in the measurement time-domain window.

Wind load and load-carrying optical performance of a large solar dish/stirling power system with 17.7 m diameter

Solar dish/Stirling power systems operating in open terrain, the optical performance is very sensitive to wind load because of their large windward area and poor wind permeability, so it is especially important to evaluate the optical performance under wind load. In this paper, a large 38 kW dish/Stirling system with 17.7 m diameter (named XEM-Dish system) is used, the wind loads are simulated and analyzed under 35 sets of wind conditions (17.1 m/s wind speed) with combination of wind direction angle θ∈[0°, 180°] and elevation angle β∈[0°, 90°], the correctness was verified by literature's results. Using an optical-mechanical integrated method, the effects of combined self-weight and wind load on its structural deformation, mirror slope error and flux distribution are evaluated, the main causes and manifestations of the optical deterioration of XEM-Dish system caused by wind load are found, which is similar to deviate-focusing problem affected by tracking errors. Only concentrator is deformed, the mirror slope error components SDx and SDy reach maximum value of 1.755 mrad and 1.828 mrad at worst 45°–0° condition, but optical efficiency still remains at 89.06%, which is excellent. When XEM-Dish system overall deformation, the SDx reached 7.702 mrad and flux distribution is extremely uneven at worst 45°–0° condition, but optical efficiency still reaches about 87.0%.

A 12-bit single slope ADC with multi-step structure and ramp calibration technique for image sensors

This paper presents a novel multi-step single slope analog to digital converter (MS SS ADC). The proposed ADC splits the 12-bit conversion into 3 steps, including 1-bit half section decision, 4-bit coarse conversion, and finally 8-bit fine conversion with 1-bit redundancy. The conversion step is substantially reduced from conventional 4096 to 276. The linearity of the ADC is guaranteed by a stable common mode voltage of the comparator varying only within 31.25 mV. Moreover, two high-accuracy ramp calibration techniques are utilized to correct the current variation in the fine ramp and the slope error between the coarse and fine ramps. A hybrid comparator is utilized in the ADC to save power while maintaining the performance. The ADC is designed and simulated in 0.18 μm CMOS process with 7.5 μm width. The differential nonlinearity and integral nonlinearity of the proposed ADC are reduced from +0.3/-1 LSB and +3.1/-2.55 LSB to +0.3/-0.3 LSB and +1/-0.45 LSB at 61.7 kS/s sample rate by the calibrations.

Analysis of space-based large light concentration reflective surfaces with errors

Space-based 100-m light condensing reflectors can undergo considerable structural deformations. The simple and accurate analysis of a concentrator system is important, especially when the system has large deformation errors. Further, slope error measurement of large reflectors is challenging. Gaussian distribution and other calculation models cannot accurately characterize the continuous changes of the actual model. Moreover, the analysis of fully fitted deformed surfaces is complicated. Therefore, this paper proposes a method for approximating surfaces by planers. The side lengths of the planes affect the speed and accuracy of modeling. Therefore, this paper analyzes the influence of the side length of the modeling plane and derives the allowable maximum side length of the plane. The model is also analyzed to ensure that its slope error does not change compared to the actual model during the modeling process. Spherical concentrators have great advantages in spatial concentrating owing to their rotational symmetry. Herein, the error model of a spherical low-ratio concentrator is calculated. Finally, an experiment is designed to verify the correctness of the calculations.

A nano-radian precision absolute local slope measurement method for X-ray reflectors.

Ultra-precise reflectors in the advanced light source facilities urgently call for local slope error measurements with nano-radian precision. However, the existing methods currently utilized in the long trace profiler systems struggle to meet the requirements. In this paper, we present a weak-value amplification enhanced absolute local slope measurement scheme, in which the surface height difference between two adjacent points can be measured directly with precision on the pico-meter level. As a result, the absolute local slope measurement reaches a record precision level of 9.7 nrad (RMS) with a small lateral separation of 0.5 mm. Comparing to the existing methods, our scheme is more disturbance-resistant, more compact and cost-effective. The local curvature measuring capability is also validated with two synchronously parallel local slope measurement paths, between which the separation is set as 2mm. A local curvature measurement is obtained with precision of 3.4 × 10-6m-1 (RMS) and its corresponding slope variation is 6.8 nrad. Our method exhibits important application prospects in the field of ultra-precise surface fabrication inspection.

Chemical and thermal performance analysis of a solar thermochemical reactor for hydrogen production via two-step WS cycle

Ceria-based H2O/CO2-splitting solar-driven thermochemical cycle produces hydrogen or syngas. Thermal optimization of solar thermochemical reactor (STCR) improves the solar-to-fuel conversion efficiency. This research presents two conceptual designs and thermal modelling of RPC-ceria-based STCR cavities to attain the optimal operating conditions for CeO2 reduction step. Presented hybrid geometries consisting of cylindrical–hemispherical and conical frustum–hemispherical structures. The focal point was positioned at x = 0, -10 mm, and -20 mm from the aperture to examine the flux distribution in both solar reactor configurations. Case-1 with 2 milliradian S.E (slope error) yields a 27% greater solar flux than case-1 with 4 milliradians S.E, despite the 4 milliradian S.E produces an elevated temperature in the reactor cavity. The mean temperature in the reactive porous region was most significant for case-2 (x = -10 mm) with 4 mrad S.E for model-2, reaching 1966 K and 2008 K radially and axially, respectively. In case-2 (x = -10 mm) for 4 mrad S.E, model-1 attained 1720 K. The efficiency analysis shows that the highest conversion efficiency value was obtained to be 7.95% for case-1 with 4 milliradian S.E.

Shape optimization design of the offset mirror in FEL-1 beamline at S3FEL

Nowadays, due to the advantages of high peak power, high average power, ultra-short pulse, and fully coherent characteristics, the high-repetition-rate free-electron laser (FEL) is thriving in many countries around the world. The thermal load caused by high-repetition-rate FEL poses a great challenge to the mirror surface shape. Especially in the case of high average power, how to perfectly control the mirror shape to maintain the coherence of the beam has become a difficult problem in beamline design. In addition to multi-segment PZT, when multiple resistive heaters are used to compensate for the mirror shape, the heat flux (or power) generated by each heater must be optimized to obtain sub-nanometer height error. This article establishes MHCKF model for the mirror surface deformation under the combined effect of the mirror initial deformation, the thermal deformation caused by X-rays, and the deformation compensated by multiple heaters. By searching the perturbation term in the mathematical model, the least squares solution of the heat fluxes generated by all heaters can be obtained. This method can not only set multiple constraints on the heat fluxes but also quickly obtain their values when minimizing the mirror shape error. It overcomes the problem of time-consuming optimization processes encountered by traditional finite element analysis software, especially in the context of multi-parameter optimization. This article focuses on the offset mirror in the FEL-1 beamline at S3FEL. Using this method, the optimization of 25 heat fluxes generated by all resistive heaters was accomplished within a few seconds utilizing an ordinary laptop. The results indicate that the height error RMS decreased from 40 nm to 0.009 nm, and the slope error RMS reduced from 192.7nrad to 0.4nrad. Wave-optics simulations show that the wavefront quality has been significantly improved. In addition, some factors affecting mirror shape error, such as the number of heaters, higher repetition rate, film coefficient, and the length of copper tube, were analyzed. The results show that the MHCKF model and optimization algorithm can effectively solve the optimization problem of compensating for the mirror shape with multiple heaters.

Ion Beam Figuring System for Synchrotron X-Ray Mirrors Achieving Sub-0.2-µrad and Sub-0.5-nm Root Mean Square

Optics with high-precision height and slope are increasingly desired in numerous industrial fields. For instance, Kirkpatrick–Baez (KB) mirrors play an important role in synchrotron X-ray applications. A KB system is composed of two aspherical, grazing-incidence mirrors used to focus an X-ray beam. The fabrication of KB mirrors is challenging due to the aspherical departure of the mirror surfaces from base geometries and the high-quality requirements for slope and height residuals. In this paper, we present the process of manufacturing an elliptical cylinder KB mirror using our in-house-developed ion beam figuring (IBF) and metrology technologies. First, the key aspects of figuring and finishing processes with IBF are illustrated in detail. The effect of positioning error on the convergence of the residual slope error is highlighted and compensated. Finally, inspection and cross-validation using different metrology instruments are performed and used as the final validation of the mirror. Results confirm that relative to the requested off-axis ellipse, the mirror has achieved 0.15-µrad root mean square (RMS) and 0.36-nm RMS residual slope and height errors, respectively, while maintaining the initial 0.3-nm RMS microroughness.

A Backprojection-Based Autofocus Imaging Method for Circular Synthetic Aperture Radar

Circular synthetic aperture radar (CSAR) can obtain higher image resolution and more target information through 360° observation of the target. However, CSAR is often subject to motion errors due to the sensor’s accuracy limitations and the unique trajectory of the system. The autofocusing back projection algorithm based on the optimization of image sharpness compensates for motion errors through phase-error estimation. This method can attain relatively good performance while assuming the same error for all pixels; it ignores the spatial variance of motion errors. In order to solve this problem, this paper proposes an autofocusing method based on the Prewitt operator and particle swarm optimization (PSO), which first extracts the subaperture image feature points as a new dataset using the Prewitt operator, estimates the radar slope error on the new dataset using PSO, and subsequently compensates the subaperture image. Finally, the subaperture images are synthesized using an image-alignment method. The results of both the simulated experiments and the measured data validate the effectiveness of this method.

Spurious Dianeutral Advection and Methods for Its Minimization

Abstract An existing approximately neutral surface, the ω surface, minimizes the neutrality error and hence also exhibits very small fictitious dianeutral diffusivity Df that arises when lateral diffusion is applied along the surface, in nonneutral directions. However, there is also a spurious dianeutral advection that arises when lateral advection is applied nonneutrally along the surface; equivalently, lateral advection applied along the neutral tangent planes creates a vertical velocity esp through the ω surface. Mathematically, esp = u ⋅ s, where u is the lateral velocity and s is the slope error of the surface. We find that esp produces a leading-order term in the evolution equations of temperature and salinity, being similar in magnitude to the influence of cabbeling and thermobaricity. We introduce a new method to form an approximately neutral surface, called an ωu·s surface, that minimizes esp by adjusting its depth so that the slope error is nearly perpendicular to the lateral velocity. The esp on a surface cannot be reduced to zero when closed streamlines contain nonzero neutral helicity. While esp on the ωu·s surface is over 100 times smaller than that on the ω surface, the fictitious dianeutral diffusivity on the ωu·s surface is larger, nearly equal to the canonical 10−5 m2 s−1 background diffusivity. Thus, we also develop a method to minimize a combination of esp and Df, yielding the surface, which is recommended for inverse models since it has low Df and it significantly decreases esp through the surface, which otherwise would be a leading term that cannot be ignored in the conservation equations.

PREDICTING PREECLAMPSIA DURING PREGNANCY: THE VALUE OF BLOOD PRESSURE MEASUREMENT TRENDS TO IDENTIFY WOMEN AT HIGHEST RISK

Objective: Hypertensive disorders of pregnancy, including preeclampsia are serious complications increasing the risk of morbidity and mortality for both mother and baby. We hypothesise that blood pressure (BP) trends during pregnancy are a useful, accessible and practical predictor of preeclampsia onset. In this study we aimed to determine: (i) the association between mean arterial pressure (MAP), Systolic BP (SBP) and Diastolic BP (DBP) at time of pregnancy booking with subsequent preeclampsia development, and (ii) whether repeated measures of BP thought pregnancy can improve prediction of preeclampsia. Design and method: Data were from 11,008 women with a singleton pregnancy who received antenatal care and gave birth across three metropolitan Sydney hospitals 2017-2020. BP measurements were represented as MAP, SBP and DBP. Three sets of logistic regression models were used to yield odds ratios (ORs) with 95% confidence intervals (CIs) for the association of preeclampsia with: (1) booking BP, (2) summary BP measurements (mean, maximum, standard deviation (SD)) and (3) growth curve parameters (mean BP, slope and standard error of slope) derived from mixed effects models, representing each women's BP trajectory. Akaike's information criterion was used to determine the ‘best fitting’ model. Results: Booking BP was taken between 5 and 15 weeks of pregnancy (median 14 weeks). There were 80,624 BP measurements taken throughout pregnancy, the number and timing varied between women: median (min, max): 8(3,17) measurements. There were 191 cases of preeclampsia. Booking MAP before 16 weeks’ gestation (OR (95%CI) (per SD higher) (1.78 (1.53, 2.06) yielded a better model fit than SBP (1.67 (1.44, 1.94) or DBP (1.66 1.43, 1.96)) for preeclampsia. Of the summary measures, maximum MAP yielded the best fitting model (OR (95%CI) (per SD higher): 4.37 (3.76, 5.11). Growth curve parameters were significant predictors of preeclampsia, and substantially improved model fit in comparison to booking BP alone. Conclusions: Booking visit MAP was more strongly associated with preeclampsia than SBP or DBP. Using repeated BP measures, in the form of summary MAP measures and BP trajectories, improved the prediction of preeclampsia.

A multi-terrain feature-based deep convolutional neural network for constructing super-resolution DEMs

Scale conversion between DEMs is an important issue in geomorphometry. There are many mature studies on the generation of low-resolution(LR) DEMs from high-resolution(HR) DEMs. However, as an important and convenient means of obtaining HR DEMs, traditional super resolution (SR) methods have shown insufficient consideration of the terrain features embedded in DEMs. Therefore, this article investigates the combination of terrain features and the use of convolutional neural networks (CNN) to reconstruct HR DEMs, and proposes a multi-terrain feature-based deep CNN for super-resolution(SR) DEMs (MTF-SR). In the experiments, from the perspective of vector and raster terrain features, we fuse raster terrain features in the input and loss functions, and fuse vector terrain features in the optimization of the output of the model. The results show that the MTF-SR model has a 30–50 % reduction in mean absolute error (MAE) compared with interpolation methods, has the lowest slope and aspect error and has a 10 to 30 % improvement in streamline matching rate (SMR). These results point to the advantages of the method in overall elevation accuracy and the preservation of terrain features.

Distributed focusing reduces mirror error sensitivity on x-ray beamlines.

The appearance of very low emittance, high-power synchrotron sources has resulted in ever longer beamlines, often requiring a very weak curvature on the mirrors that transport the beam to the experiment, where the radius of curvature is on the order of kilometers. Manufacturing weakly curved, low figure error grazing incidence mirrors is difficult as the mirrors must be manufactured to an accuracy comparable to the wavelength of the transmitted light. Often the delivered mirrors have figure errors at various length scales (general shape, slope errors, roughness), which compromise image quality. An error in general shape, like the radii of a toroidal mirror, results in long-sighted or short-sighted imaging that is not so simply corrected by changing the distances and incidence angles as the mirror controls the beam focus in both vertical and horizontal directions; for a toroidal mirror, the tangential and sagittal radii need to match correctly for the desired focusing effect. Adaptive downstream optics can compensate for this. In this paper, an alternative method to reduce the sensitivity to a large radius error outside the specified tolerance range in the first mirror of a plane grating monochromator beamline at MAX IV is presented. It is found that distributed focusing by two passive, fixed radius mirrors reduces greatly the sensitivity to the radius errors in both mirrors. The radius tolerance of a mirror initially found to be unacceptable for single stage focusing is easily accommodated on both mirrors in distributed focusing, without compromising the imaging capability.

Improving the energy distribution uniformity of solar dish collector system under tracking error using a cavity receiver position adjustment method

The tracking error of solar dish collector (SDC) system will cause extremely non-uniform energy distribution and local high flux in circumference surface of the cavity receiver, which brings serious challenges to safe and efficient operation of SDC system. Improve tracking accuracy is a conventional but costly solution, while this paper proposes a receiver position adjustment method to improve or eliminate the adverse effects of tracking errors, including translational adjustment and rotation adjustment methods. Taking cylindrical and conical cavity receivers as examples, the improved effect of position adjustment methods on circumferential energy distribution of cavity receivers under the tracking error was studied in detail using ray-tracing method and outdoor experiment. The influence of concentrator size, tracking error, mirror slope error, cavity receiver shape and size are fully considered, the evaluation indexes such as peak LCR and energy distribution uniformity before and after the receiver position adjustment are comparative analysis. The results amply demonstrate that the translational adjustment method is very effective to improve the receiver's energy distribution uniformity and significantly reduce the peak LCR, but rotational adjustment method has not significantly. This work provides a new solution to eliminate the adverse effects of tracking errors in SDC system, which has the advantage of low-cost and easy to implement.

Comparison of Various Annual Land Cover Datasets in the Yellow River Basin

Accurate land cover (LC) datasets are the basis for global environmental and climate change studies. Recently, numerous open-source annual LC datasets have been created due to advances in remote sensing technology. However, the agreements and sources of error that affect the accuracy of current annual LC datasets are not well understood, which limits the widespread use of these datasets. We compared four annual LC datasets, namely the CLCD, MCD12Q1, CCI-LC, and GLASS-LC, in the Yellow River Basin (YRB) to identify their spatial and temporal agreement for nine LC classes and to analyze their sources of error. The Mann–Kendall test, Sen’s slope analysis, Taylor diagram, and error decomposition analysis were used in this study. Our results showed that the main LC classes in the four datasets were grassland and cropland (total area percentage &gt; 80%), but their trends in area of change were different. For the main LC classes, the temporal agreement was the highest between the CCI-LC and CLCD (0.85), followed by the MCD12Q1 (0.21), while the lowest was between the GLASS-LC and CLCD (−0.11). The spatial distribution of area for the main LC classes was largely similar between the four datasets, but the spatial agreement in their trends in area of change varied considerably. The spatial variation in the trends in area of change for the cropland, forest, grassland, barren, and impervious LC classes were mainly located in the upstream area region (UA) and the midstream area region (MA) of the YRB, where the percentage of systematic error was high (&gt;68.55%). This indicated that the spatial variation between the four datasets was mainly caused by systematic errors. Between the four datasets, the total error increased along with landscape heterogeneity. These results not only improve our understanding of the spatial and temporal agreement and sources of error between the various current annual LC datasets, but also provide support for land policy making in the YRB.

Thermal-mechanical performance analysis of parabolic trough receivers under various optical errors based on coupled optical-thermal-stress model

As green and sustainable technology, the parabolic trough receiver's thermal-mechanical performance is widely concerned because of the optical errors in all practical systems. The coupled MCRT-FVM-FEM approach was employed to construct the receiver's optical-thermal-stress model. The receiver's safety and thermal-mechanical performance is thoroughly analyzed using the model to illustrate the coupling effects of tracking error (σt), slope error (σs), and installation error (σx and σy). Bellows and Kovar ring's deformation and thermal stresses under multi-error are investigated for the first time. Bellows and Kovar rings' variable expansion and uneven axial stresses are brought on by the uneven heat flux distribution and absorber's heat transfer. While bellows and Kovar ring enhance absorber's deformation and stress. Optical errors mainly affect the bellow's axial tensile stress and the Kovar ring's axial compressive stress. Tracking and installation errors have less impact on receiver safety when σs exceeds 4 mrad. However, they enhance the risk of receiver failure when σs is sufficiently small (<4 mrad). Positive σy leads to receiver's maximum deformation (23.57 mm), significantly increasing the Kovar ring's maximum compressive stress and threatening the receiver's safety. Therefore, the impact of bellows and Kovar ring on receiver safety should be considered when simulating actual operation.