Location Of Inflection Point Research Articles

Subassemblage test and width-thickness design limit for steel built-up box columns subjected to axial load and cyclic lateral drift

This study investigates the behavior of first-story columns under reversed cyclic lateral loading and constant axial loading by using a full-scale, one-and-a-half story subassemblage testing scheme. Four subassemblages were designed with steel beams at the second floor and a moderately ductile built-up box column with a width-thickness ratio (b/t) of either 16.2 or 20.5, which are between the highly ductile (=12.9) and moderately ductile (=23.5) requirements in AISC 341 (2016). All built-up box columns were made by SM570MB steel with a nominal yield stress, Fy= 420 MPa. A high axial load (=4200–8000 kN, corresponding to 0.2–0.4 times the axial yield strength Py) was applied to the one-and-a-half story subassemblage column before cyclic lateral drifts. The second-floor beams and column provide rotational flexibility at the top end of first-story columns in the subassemblages, significantly changing column’s stiffness, moment distribution, and inflection point location observed from typical column testing. The subassemblage column and the isolated column had a similar maximum moment at the first cycle of 0.04 rad drift, but the later showed larger strength degradation in the following cycles due to larger fixity at the column top end. An experimental solution that relates the column width-thickness ratio to the moment strength deterioration was developed to obtain design b/t limits for highly and moderately ductile built-up box columns under combined high axial load (0.3–0.4Py) and cyclic lateral drift.

Absolute instability of plane incompressible jets

In this paper, the possibility of absolute instability in a plane unidirectional jet is analysed. We consider a parametrized family of velocity profiles with variable inflection point location and shear layer thickness. Using the inviscid saddle-point analysis, we show that absolute instability can occur in the case of a sufficiently low velocity at the inflection point or a sufficiently thin shear layer. Then we proceed to the viscous analysis and find the critical Reynolds numbers separating the zones of convective and absolute instability. We obtained a minimum value $Re = 315$ . As an independent verification of the theoretical results, we conduct a direct numerical simulation of the evolution of a localized pulse perturbation in the framework of the linearized Navier–Stokes equations. The calculated absolute/convective instability boundary is in a good agreement with theoretical results of the saddle-point analysis.

Quantifying the Spinal Lordosis Ratio Unique to the Type of Spinal Sagittal Alignment in a Normal Population.

Data collection of radiological parameters in non-pathological adult spines. Establishing a baseline database for measurements of the spinal lordosis ratio between upper and lower arcs of the lumbar spine unique to each type of spine described by Roussouly's classification. Illustrating the importance of correct rationing of the upper and lower arcs. Standardised standing true lateral plain radiographs of the spine (including base of skull and proximal femurs) from 373 adult volunteers were obtained. Exclusion criteria : any history of disease involving the spine, pelvis, hips or lower limbs. Incidental detection of any spinal deformity on radiography also excluded further participation in this study. Sacro-pelvic parameters data collected : Pelvic Incidence (PI), Pelvic Tilt (PT), Sacral Slope (SS), location of Inflection Point, number of vertebras in the spinal lordosis and type of Roussouly's spine. Values of upper arc, lower arc and spinal lordosis ratio (SLR) was determined. Bivariate analysis revealed statistically significant (P < .0001) correlation between the types of sagittal spinal alignments based on Roussouly's classification and the SLR. Type 1: SLR .76 ± .17, Type 2: SLR .60 ± .18, Type 3 with anteverted pelvis: SLR .53 ± .11, Type 3: SLR .49 ± .12, Type4: SLR .41 ± .11. With this data we are able to quantify the ratio of lumbar lordosis unique to each type of Roussouly's spine. It functions as a guide when planning lumbar spine surgeries in order to restore the SLR correctly and thus prevent post-op complications such as proximal junction kyphosis.

Automatic recognition of whole-spine sagittal alignment and curvature analysis through a deep learning technique

PurposeArtificial intelligence based on deep learning (DL) approaches enables the automatic recognition of anatomic landmarks and subsequent estimation of various spinopelvic parameters. The locations of inflection points (IPs) and apices (APs) in whole-spine lateral radiographs could be mathematically determined by a fully automatic spinal sagittal curvature analysis system.MethodsWe developed a DL model for automatic spinal curvature analysis of whole-spine lateral plain radiographs by using 1800 annotated images of various spinal disease etiologies. The DL model comprised a landmark localizer to detect 25 vertebral landmarks and a numerical algorithm for the generation of an individualized spinal sagittal curvature. The characteristics of the spinal curvature, including the IPs, APs, and curvature angle, could thus be analyzed using mathematical definitions. The localization error of each landmark was calculated from the predictions of 300 test images to evaluate the performance of the landmark localizer. The interrater reliability among a senior orthopedic surgeon, a radiologist, and the DL model was assessed using the intraclass correlation coefficient (ICC).ResultsThe accuracy of the landmark localizer was within an acceptable range (median error: 1.7–4.1 mm), and the interrater reliabilities between the proposed DL model and each expert were good to excellent (all ICCs > 0.85) for the measurement of spinal curvature characteristics.ConclusionThe interrater reliability between the proposed DL model and human experts was good to excellent in predicting the locations of IPs, APs, and curvature angles. Future applications should be explored to validate this system and improve its clinical efficiency.

Air quality model of Anhui Province based on the EKC fitting

Under the background of carbon neutrality, this paper selects the economic development and air quality panel data of 16 prefecture-level cities in Anhui Province from 2005 to 2017 to verify the existence of the characteristics of EKC curve and the location of inflection point by establishing econometric model and using Eviews8.0 software, to explore the internal mechanism of action between economy and the environment, improve the economic development model of prefecture-level cities according to local conditions and realize the concept of coordinated and sustainable development of economy and environment. The results showed that the PM10 concentration and GDP per capita showed an inverse “N” type, and SO2, NO2 concentration and GDP per capita showed an “N” type, and did not show the characteristics of EKC curve. Secondly, on the internal effect mechanism between economic system and environmental system, the paper explores the influence of five control variables on the shape of EKC curve by introducing industrial structure, urbanization rate, the number of private cars, science and technology expenditure and greenery coverage of urban area. The shape of the curve changes by adding control variables. The results implied that why pollution levels vary between cities.

Using Social Network Analysis to Identify Spatiotemporal Spread Patterns of COVID-19 around the World: Online Dashboard Development.

The COVID-19 pandemic has spread widely around the world. Many mathematical models have been proposed to investigate the inflection point (IP) and the spread pattern of COVID-19. However, no researchers have applied social network analysis (SNA) to cluster their characteristics. We aimed to illustrate the use of SNA to identify the spread clusters of COVID-19. Cumulative numbers of infected cases (CNICs) in countries/regions were downloaded from GitHub. The CNIC patterns were extracted from SNA based on CNICs between countries/regions. The item response model (IRT) was applied to create a general predictive model for each country/region. The IP days were obtained from the IRT model. The location parameters in continents, China, and the United States were compared. The results showed that (1) three clusters (255, n = 51, 130, and 74 in patterns from Eastern Asia and Europe to America) were separated using SNA, (2) China had a shorter mean IP and smaller mean location parameter than other counterparts, and (3) an online dashboard was used to display the clusters along with IP days for each country/region. Spatiotemporal spread patterns can be clustered using SNA and correlation coefficients (CCs). A dashboard with spread clusters and IP days is recommended to epidemiologists and researchers and is not limited to the COVID-19 pandemic.

A waveform decomposition technique based on wavelet function and differential cuckoo search algorithm

Waveform decomposition is widely used for the separation of echoes from full-waveform LiDAR (FWL) signal, and some previous studies employed Gaussian function for laser pulse modeling and waveform decomposition. However, it was difficult to guarantee the waveform parameters on the neighbor of optimal solution, because of the limited amplitude range. In addition, waveform parameters were usually set by the amplitude and location of inflection points, which may enlarge the difference between decomposed and original waveforms. Hence, a novel waveform decomposition technique based on wavelet function and differential cuckoo search algorithm is proposed, where wavelet function has a high-order vanishing moment, cuckoo search algorithm has a strong optimization ability, and differential operator avoids trapping into the local optima. The proposed technique is tested on airborne FWL point cloud and compared with other corresponding approaches, experimental results demonstrate that the decomposed waveforms are obtained with a reasonable convergence rate and feature characterization, as the rRMSE is lower than 7% for all of waveforms, the whole process of waveform decomposition only takes 0.3s, and waveform parameters are used as the features to recognize different objects from point cloud.

Determination of inflection points of CyberKnife dose profiles within acceptability criteria of deviations in measurements.

The aim of this study was to determine the Inflection Points (IPs) of flattening filter free (FFF) CyberKnife dose profiles for cone-based streotactic radiotherapy. In addition, dosimetric field sizes were determined. The increased need for treatment in the early stages of cancer necessitated the treatment of smaller tumors. However, efforts in that direction required the modeling accuracy of the beam. Removal of the flattening filter (FF) from the path of x-ray beam has provided the solution to those efforts, but required a different normalization approach for the beam to ensure the delivery of the dose accurately. As a solution, researchers proposed a normalization factor based on IPs. Measurements using microDiamond (PTW 60019), Diode SRS (PTW 60018) and Monte Carlo (MC) calculations of dose profiles were completed at SAD 80cm and 5cm depth for 15-60mm cones. Performance analysis of detectors with respect to MC calculation was carried out. Gamma evaluation method was used to determine achievable acceptability criteria for FFF CyberKnife beams. Acceptability within (3%-0.5mm) was found to be anachievable criterion for all dose profile measurements of the cone beams used in this study. To determine the IP, the first and second derivatives of the dose profile were determined via the cubic spline interpolation technique. Derivatives of the interpolated profiles showed that locations of IPs and 50% isodose points coincide.

Reflectance Properties of Hemiboreal Mixed Forest Canopies with Focus on Red Edge and Near Infrared Spectral Regions

This study present the results of airborne top-of-canopy measurements of reflectance spectra in the spectral domain of 350–1050 nm over the hemiboreal mixed forest. We investigated spectral transformations that were originally designed for utilization at very different spectral resolutions. We found that the estimates of red edge inflection point by two methods—the linear four-point interpolation approach (S2REP) and searching the maximum of the first derivative spectrum ( D m a x ) according to the mathematical definition of red edge inflection point—were well related to each other but S2REP produced a continuously shifting location of red edge inflection point while D m a x resulted in a discrete variable with peak jumps between fixed locations around 717 nm and 727 nm for forest canopy (the third maximum at 700 nm appeared only in clearcut areas). We found that, with medium high spectral resolution (bandwidth 10 nm, spectral step 3.3 nm), the in-filling of the O 2 -A Fraunhofer line ( F a r e a ) was very strongly related to single band reflectance factor in NIR spectral region ( ρ = 0.91, p &lt; 0.001) and not related to Photochemical Reflectance Index (PRI). Stemwood volume, basal area and tree height of dominant layer were negatively correlated with reflectance factors at both visible and NIR spectral region due to the increase in roughness of canopy surface and the amount of shade. Forest age was best related to single band reflectance at NIR region ( ρ = −0.48, p &lt; 0.001) and the best predictor for allometric LAI was the single band reflectance at red spectral region ( ρ = −0.52, p &lt; 0.001) outperforming all studied vegetation indices. It suggests that Sentinel-2 MSI bands with higher spatial resolution (10 m pixel size) could be more beneficial than increased spectral resolution for monitoring forest LAI and age. The new index R 751 /R 736 originally developed for leaf chlorophyll content estimation, also performed well at the canopy level and was mainly influenced by the location of red edge inflection point ( ρ = 0.99, p &lt; 0.001) providing similar info in a simpler mathematical form and using a narrow spectral region very close to the O 2 -A Fraunhofer line.

New insights into the physics of inertial microfluidics in curved microchannels. I. Relaxing the fixed inflection point assumption.

Inertial microfluidics represents a powerful new tool for accurately positioning cells and microparticles within fluids for a variety of biomedical, clinical, and industrial applications. In spite of enormous advancements in the science and design of these devices, particularly in curved microfluidic channels, contradictory experimental results have confounded researchers and limited progress. Thus, at present, a complete theory which describes the underlying physics is lacking. We propose that this bottleneck is due to one simple mistaken assumption-the locations of inflection points of the Dean velocity profile in curved microchannels are not fixed, but can actually shift with the flow rate. Herein, we propose that the dynamic distance (δ) between the real equilibrium positions and their nearest inflection points can clearly explain several (previously) unexplained phenomena in inertial microfluidic systems. More interestingly, we found that this parameter, δ, is a function of several geometric and operational parameters, all of which are investigated (in detail) here with a series of experiments and simulations of different spiral microchannels. This key piece of understanding is expected to open the door for researchers to develop new and more effective inertial microfluidic designs.

Visibility distance estimation in foggy situations and single image dehazing based on transmission computation model

The existing visibility distance estimation algorithms in foggy situations use the region growing method to extract the vertical position of inflection point of image intensity changing. These algorithms have lower inflection point location accuracy for an image with a non-homogeneous road surface. To deal with these problems, this study presents a novel visibility distance measuring technique under foggy weather conditions. This method combines two major models: inflection point estimation (IPE) model and transmission refining (TR) model. The proposed IPE model based on transmission computation model derives a very useful relation between the transmission value of inflection points and the constant ${\rm e}^{ - 2}$e -2 . In order to acquire the more accurate transmission map and vertical position of each inflection point, this study establishes an effective TR model. This model exploits the edge information of input images, in order to significantly reduce the effects of artefact. The proposed algorithm provides more accurate visibility distance estimation of an image with a non-homogeneous road surface than the well-known algorithm through qualitative evaluations in experiments. The experimental results also show that the TR model has better outcomes than the guided filter approach through qualitative and quantitative evaluations.

Preliminary experience with SpineEOS, a new software for 3D planning in AIS surgery.

Preoperative planning of scoliosis surgery is essential in the effective treatment of spine pathology. Thus, precontoured rods have been recently developed to avoid iatrogenic sagittal misalignment and rod breakage. Some specific issues exist in adolescent idiopathic scoliosis (AIS), such as a less distal lower instrumented level, a great variability in the location of inflection point (transition from lumbar lordosis to thoracic kyphosis), and sagittal correction is limited by both bone-implant interface. Since 2007, stereoradiographic imaging system is used and allows for 3D reconstructions. Therefore, a software was developed to perform preoperative 3D surgical planning and to provide rod's shape and length. The goal of this preliminary study was to assess the feasibility, reliability, and the clinical relevance of this new software. Retrospective study on 47 AIS patients operated with the same surgical technique: posteromedial translation through posterior approach with lumbar screws and thoracic sublaminar bands. Pre- and postoperatively, 3D reconstructions were performed on stereoradiographic images (EOS system, Paris, France) and compared. Then, the software was used to plan the surgical correction and determine rod's shape and length. Simulated spine and rods were compared to postoperative real 3D reconstructions. 3D reconstructions and planning were performed by an independent observer. 3D simulations were performed on the 47 patients. No difference was found between the simulated model and the postoperative 3D reconstructions in terms of sagittal parameters. Postoperatively, 21% of LL were not within reference values. Postoperative SVA was 20mm anterior in 2/3 of the cases. Postoperative rods were significantly longer than precontoured rods planned with the software (mean 10mm). Inflection points were different on the rods used and the planned rods (2.3 levels on average). In this preliminary study, the software based on 3D stereoradiography low-dose system used to plan AIS surgery seems reliable for preoperative planning and precontoured rods. It is an interesting tool to improve surgeons' practice, since 3D planning is expected to reduce complications such as iatrogenic malalignment and to help for a better understanding of the complications, choosing the location of the transitional vertebra. However, further work is needed to improve thoracic kyphosis planning. These slides can be retrieved under Electronic Supplementary Material.

Shape optimization of tapered I-beams with lateral-torsional buckling, deflection and stress constraints

Built-up tapered I-beams, which are mostly loaded so as to be under bending about their strong axis for the economical use of the structural material, are commonly used in wide span steel structures. Lateral-torsional buckling, excessive deflection and partial or complete yielding of the material are the important failure modes, which should be considered in design of these members. However, today's “modern design” concept not only requires the satisfaction of certain constraints but also a lightweight structure. This study presents the shape optimization of flange and/or web tapered doubly-symmetric I-beams and discusses the contribution of flange and/or web tapering and inflection point location to the economical design. The optimization procedure is constructed by slightly modifying the Big Bang - Big Crunch algorithm, which is a simple and effective population-based metaheuristic, and installing the Deb's constraint handling method. Four beam configurations with various loading and restraint conditions are optimized and final designs are validated by finite element analysis software. It is shown that tapering, and therefore the inflection point location may not have a significant effect on the material economy in certain conditions.

A Seismic Design Procedure for Moment-Frame Structures

ABSTRACTA procedure for the performance-based seismic design of moment-resistant frames is presented. The design procedure utilizes an estimate of the yield displacement of the roof in conjunction with yield point spectra to determine the required lateral strength. Beam strengths are established using a plastic mechanism approach, while a modified Portal Frame method is used to establish the strengths of critical sections of columns, considering the locations of inflection points and the desire to avoid weak-story mechanisms. An example illustrates the application to reinforced concrete frames. Due to the stability of the yield displacement, few (if any) iterations are needed.

State of health estimation of battery modules via differential voltage analysis with local data symmetry method

Cyclic voltammogram (CV) and differential voltage analysis (DVA) are two effective techniques to analyze the aging mechanism and estimate the aging state of a battery. However, the effectiveness of the two methods reported previously is based on single battery cells. In this paper, a comparison of the two methods is stated, and the equivalent relation is further derived. Besides, a local data symmetry method is introduced to calculate the differential voltage (DV) curve. The DV curves calculated by the proposed method are much smoother than that by the numerical-derivative method. Based on the location interval of two inflection points in the DV curve, a new method is inferred for lithium iron phosphate (LiFePO4) battery cells, and is applied to estimate the state of health (SOH) of battery modules. The applicability of the method is further verified via battery module simulation and experimental data. The results show that the DV curves fluctuate and do not overlap in the voltage plateau region due to the uneven currents flowing through each in-parallel battery cells. There is also a good linear regression of the two inflection point location interval versus battery module capacity within 2% error bounds, suggesting that the DVA method inferred from battery cells can be directly applied to battery modules.

Investigating the Transition Region in Scanned Probe Images of the Cyclotron Orbit in Graphene

A cooled scanning probe microscope (SPM) has been used to image cyclotron orbits of electrons through high-mobility graphene in a magnetic field.1-5 In a hBN-graphene-hBN device patterned into a hall bar geometry, the magnetic field focuses a current Ii injected from one narrow contact into another narrow contact located an integer number of cyclotron diameters away, creating a voltage Vc. The degree of focusing is measured by the transresistance Rm = Vc/Ii. In SPM, the tip can either enhance or decrease conductance in the sample by deflecting electrons into or away from the second contact, respectively.3,4 Our SPM images of magnetic focusing feature a region in which the tip transitions from enhancing to decreasing the conductance in the sample where the change in transresistance caused by the tip is equal to zero. In this paper, we investigate how the location of this region in the graphene sample changes as we modulate the electron density n and magnetic field B. By plotting line-cuts of the change in trans-resistance for different electron densities and magnetic fields, we identify trends in the inflection point where the tip changes from enhancing to decreasing the conductance in the sample. From the location of each transition region, we show that the cyclotron diameter of the electron trajectories can be obtained, and explain the trends in inflection point location for different electron densities and magnetic fields.

On-board state of health estimation of LiFePO4 battery pack through differential voltage analysis

Battery state of health (SOH) estimation is a crucial challenge for electric vehicles due to the complicated aging mechanism of a battery. In this paper, a new method for battery SOH estimation is proposed using the location interval between two inflection points or the transformation parameter of the differential voltage (DV) curve. And a new algorithm to obtain the DV curve according to the center least squares method is presented. Four LiFePO4 battery cells in different aging states are tested to validate the proposed method. Results show that the linear regression of the location interval between two inflection points versus the battery capacity from one single battery cell is able to evaluate the SOH of other three battery cells within 2% error bound. Transforming the measured DV curve to be congruent with the initial DV curve provided by the manufacturer, battery cell SOH can be estimated according to the transformation parameter with the error being within 2.5%. Furthermore, a battery pack SOH monitoring framework is inferred from the inflection point location and the transformation parameter of the DV curve to realize battery pack SOH estimation.

OPTICAL SENSOR SYSTEM FOR THE NON-INVASIVE ASSESSMENT OF ARTERIAL STIFFNESS QUANTIFIED BY FOURTH DERIVATIVE OF PHOTOPLETHYSMOGRAM

Arterial stiffness, resulting in loss of the elastic properties of arteries walls, is an indicator of cardiovascular risk, though the presence of disease is not clinically evident. Augmentation index is an important biomarker of arterial stiffness by which the cardiac risk of the patient can be diagnosed. The current paper outlines the non-invasive assessment of arterial stiffness by analyzing the morphology or contour of PhotoPlethysmoGraph (PPG) signal. PPG pulse was optically acquired with the developed photometric measurement device and the desired features were extracted to determine PPG augmentation Index (PAI) through advanced signal processing implemented in MATLAB. PAI was quantified by the fourth derivative of the signal by enhancing the location of inflection point (augmentation point) after conditioning the signal by efficient pre-processing and filtering techniques. The results reveal that the statistical distribution of PAI for healthy subjects presents a very low value and a very tight distribution. On the contrary, patients have a higher value of PAI and a wide asymmetrical shape of distribution. This work also establishes the usefulness of PPG contour analysis in the investigation of changes in the elastic properties of the vascular system. In conclusion, PAI has revealed to be a non-invasive indicator for arterial stiffness assessments.

Generation of a Patient-Specific Model of Normal Sagittal Alignment of the Spine

Study DesignMathematical modeling of normal sagittal spinal alignment. ObjectiveTo create a patient specific 3-dimensional (3D) model of normal adolescent spinal shape and alignment. Summary of Background DataRecreating normal sagittal balance is a key goal in spinal deformity surgery. Because of the variation in normal sagittal alignment based on inherent pelvic parameters, it is difficult to know what is normal for a given patient who presents with spinal deformity. MethodsSimultaneous biplanar 2-dimensional digital radiographs were taken for pediatric patients with no known spinal disease using the EOS system. Three-dimensional reconstructions were produced using sterEOS and imported into custom MATLAB software. The researchers defined relationships to approximate orientations and positions of the vertebral bodies from patients' pelvic incidence (PI). The predicted spinal contour was then calculated to optimize congruence to patients' sagittal T1–sacrum offset, sagittal curve inflection point location, and predicted vertebral body orientations and positions. ResultsA total of 75 patients (26 male and 49 female) were included, mean age 14.5 ± 2.6 years. Baseline measurements were PI 46.7° ± 10.2°, sacral lope 40.2° ± 8.9°, T1–T12 kyphosis 39.8° ± 8.8°, and L1–L5 lordosis −37.1° ± 11.2°. Average difference in vertebral position in the anteroposterior direction between actual spines and their predicted models was 1.2 ± 1.2 mm and varied from an absolute minimum of 0.2 mm (T3) to an absolute maximum of 3.7 mm (L2). ConclusionsThis model uses an adolescent patient's PI to predict the normal sagittal alignment that best matches that patient's native sagittal curve. The model was validated on patients with no spinal deformity; average difference between actual sagittal positions of each vertebra and those predicted by the model was less than 5 mm at each vertebral level. This model may be useful in adolescent scoliotic patients with altered sagittal alignment to determine the magnitude of 3D deformity (compared with predicted normal values) and the completeness of 3D correction.

Qualitative trend analysis for process monitoring and supervision based on likelihood optimization: state-of-the-art and current limitations

In this study, two recently developed methods for qualitative trend analysis are applied and compared on the basis of two different data sets. One of the methods is globally optimal in the maximum likelihood sense but is computationally expensive. This method is based on shape constrained spline function. The second method is based on kernel regression and a Hidden Markov Model. This is more efficient but cannot be guaranteed to be optimal. Nevertheless, both methods deliver satisfying results with respect to the estimation of the location of inflection points as well as the corresponding tangent slopes. In contrast, only the globally optimal method appears useful to identify time series which do not satisfy a presupposed shape.