Curvature Method Research Articles

A decision-making model for light environment control of tomato seedlings aiming at the knee point of light-response curves

Light, the energy source for crop photosynthesis, is a key factor for plant growth. The present study proposes a decision-making model of light environment control. The photosynthesis rate of tomato seedlings under different light intensities, temperatures, and CO2 concentrations was determined in a nested experiment. These data were used to construct a predictive model of the photosynthesis rate using the support vector regression method, with an R2 of 0.9862, a root mean square error of 1.39 μmol·m−2·s−1, and a mean absolute error of 1.18 μmol·m−2·s−1. In total, 861 discrete light-response curves were obtained based on the predictive model, and their knee points were computed using the U-chord curvature method. These knee points were used to form a dataset for constructing a decision-making model for light environment control, with an R2 of 0.984 and a root mean square error of 9.55 μmol·m−2·s−1. The results of the validation experiment suggested that the average relative error of the model was 1.92%, indicating the robustness of the model. Compared with those of the light saturation control method, the average light demand for the decision-making model decreased by 60.49%, whereas the average photosynthesis rate reduced by 24.40%. Although the photosynthesis rate lost a bit, the rate of light saving is almost three times more than the rate of photosynthesis rate decreased slightly, which improved the production efficiency of tomato.

Determining the minimum size of experimental plot for evaluating field parameters for Arabica coffee

The coffee production chain has great socio-economic importance in Brazil, generating foreign exchange with great job-generating capacity. The Brazilian coffee production is circa 2.863 k tons and coffee research has contributed to the development of new technologies in order to increase yield. However, the size of plots used for coffee experiments has been variable and mostly based on the empirical researcher's experience. Therefore, this research was carried out aiming to determine the optimal size of experimental plots to evaluate field growing parameters of Arabica coffee. The modified maximum curvature model and the comparison of variances were the methods used. It is concluded that 2, 3, 3, and 6 plants per useful experimental plot of Arabica coffee are enough to evaluate the field growing parameters plant height, plant canopy diameter, vigor, and wet mass, respectively by the method of modified maximum curvature. Two plants per experimental plot were required when using the variance comparison method to the parameters plant height, and plant canopy diameter, and 4 plants were enough to the parameters vigor and wet mass. In general, four useful plants per experimental plot were enough using the variance comparison method and six useful plants when using the modified maximum curvature method.

Curve Fitting-Based Dynamic Path Planning and Tracking Control for Flexible Needle Insertion

Needle insertion is widely used in modern clinical practice, and flexible needles enable surgeons to adjust the needle insertion path to avoid obstacles and compensate for target drift. To increase the accuracy and safety of the needle insertion procedure, a path planning and tracking control method for flexible needle steering in dynamic environment is proposed in this paper. The path planning method is based on the artificial potential field algorithm and curve fitting algorithm, after several feasible paths with variant curvatures is obtained, they are furtherly optimized based on path length, obstacle clearance and control effort to select the best one. Simulations show that the proposed path planning method performs better than the current constant curvature method and the rapidly-exploring random tree (RRT) based method. By finely tuning the initial planned path, an intraoperative path replanning method is proposed, which are used to compensate for the drift of target and obstacles. Then to ensure the needle is inserted along the planned path, a tracking control method is adopted based on fuzzy logic algorithm. With the proposed intraoperative path planning and tracking control method, the robustness and accuracy of needle insertion in congested environment can be improved, and experiments also show that our proposed method achieves satisfactory insertion safety and targeting accuracy in dynamic environment. The obtained accuracy of 1.57 mm is sufficient for most clinical needle insertion applications.

Static and dynamic effects of train-track-bridge system subject to environment-induced deformation of long-span railway bridge

Laying ballastless tracks on a long-span railway bridge with a main span greater than 300 m is a challenge in engineering practice and has aroused significant concerns. Influenced by complicated environmental factors, long-span railway bridges in service deform with large amplitudes and complex shapes, which may result in damage to the track structure and threaten the running safety and ride comfort of trains. In this study, we investigate some typical statics and dynamics problems under the actual conditions of a long-span cable-stayed high-speed railway bridge with a main span of 400 m and laying ballastless track. The track-bridge finite element model and dynamic interaction model of the train-track-bridge system are first established. Furthermore, the influences of the complicated environment-induced bridge deformations are comprehensively investigated using the curvature method that reveals the deformation compatibility of the bridge-track system and indicates the dynamic interaction behavior of the train-track-bridge system subject to train running speeds and bridge deformations. Results indicate that excellent dynamic performance of the train-track-bridge system can be achieved by setting an elastic cushion of 0.1 N/mm3 under the track bed. Interface damage between track layers will not occur directly because of the complex deformations of the bridge decks. The bridge deformations induced by the environmental temperature and the concrete creep are qualified. The dynamic responses of the train-track-bridge system are also excellent under the excitations of bridge deformations. Dynamic simulations of the train-track-bridge system are proposed to evaluate long-span bridge deformations subject to complicated service situations in comparison with an oversimplified statics evaluation.

Effect of coating architecture on stress and energy relief efficiency of TiZrN coating on Si substrate

This study aims to investigate the extent of stress relief achieved by employing different types of coating architectures, and evaluate the energy relief efficiency in the coating architectures by an energy-balance physical model. TiZrN, TiZrN/Ti, TiZrN/TiN and TiZrN/TiN/Ti coatings with various thickness of TiN were deposited by unbalanced magnetron sputtering. Laser curvature method and the average X-ray strain method combined with nanoindentation were used to measure the residual stress of the entire coating and individual layers, respectively. Experimental results showed that higher stress relief in TiZrN coating could be attained by introducing an interlayer with TiN/Ti architecture than by adding a single Ti interlayer. The tri-layer specimen with a 300-nm TiN layer showed the largest stress relief among all specimens, where the TiZrN coating had the lowest residual stress, -2.01 GPa. The energy-balance model postulated that the release of stored elastic energy in the top coating and in the Si substrate were both converted into the plastic work of the Ti interlayer. The model analysis indicated that the TiN transitional layer served as a channel that effectively transferred the stored elastic energy in TiZrN to the Ti interlayer, by which the distinct stress gradient at the original TiZrN/Ti interface could be reduced, thereby increasing the plastic deformation capacity of the underlying Ti interlayer, and therefore a larger fraction of the residual stress in TiZrN was relieved compared to the TiZrN/Ti bilayer coating. Adding a TiN transitional layer into the TiZrN/Ti coating system only slightly changed the overall energy relief efficiency, while it increased the energy relief fraction in the TiZrN coating. The stress relief in an architectured coating, including transitional layer and metal interlayer, should be evaluated based on the measurements of overall stress and the stress in the major hard coating. The energy balance model could be employed to differentiate the fraction of energy relief in hard coating and in Si substrate, by which the efficiency of stress relief, or energy relief, could be correctly revealed.

Seismic Drill-Bit Tracking for Improved Well Positioning

Summary The lateral well position uncertainty of magnetic/gyro measurement-while-drilling (MWD) measurements can often exceed the requirements regarding anticollision, for optimal placement of infill wells between existing producers, or for hitting targets with limited geological extent. The positional uncertainty can be significantly reduced by implementing high-precision drill-bit localization using passive seismic data. Consequently, not only drilling risks can be reduced, but optimal reservoir drainage is ensured as well. By using passive seismic recordings from the seafloor, we can “listen” to the noise generated by the bottomhole assembly (BHA) while drilling. Despite various noise sources in the vicinity (e.g., vessels and rigs), advanced data processing and the combination of hundreds of seafloor receivers spread above the ongoing drilling enable us to detect the drilling signal and locate the drill bit. Whereas the magnetic and gyro MWD tools have errors that accumulate with measured depth (MD), each bit position derived from seismic (usually every 90 seconds) is completely independent. For horizontal sections, the error does not increase with MD and hence can provide improved lateral accuracy. No additional BHA tool is required, and the measurements are neither dependent on the magnetic nor gravitational field. Moreover, the passive seismic measurements can be used to obtain an improved lateral well position estimate. This is done by optimizing the azimuth information of the well trajectory in the minimum curvature method. A lateral uncertainty measure can be derived from the residuals between the passive measurements and the updated well path. Since 2018, we have used the continuous stream of passive data from permanent seafloor sensors at the Grane Field, with its reservoir depth of around 1800 m true vertical depth subsea (TVDSS) to follow all wells with this drill-bit tracking scheme. Lateral deviations from the official well path based on magnetic/gyro measurements are mostly within ±30 m. The lateral position uncertainty can be as low as a couple of meters under optimal conditions.

Detecting Cochlear Synaptopathy Through Curvature Quantification of the Auditory Brainstem Response.

The sound-evoked electrical compound potential known as auditory brainstem response (ABR) represents the firing of a heterogenous population of auditory neurons in response to sound stimuli, and is often used for clinical diagnosis based on wave amplitude and latency. However, recent ABR applications to detect human cochlear synaptopathy have led to inconsistent results, mainly due to the high variability of ABR wave-1 amplitude. Here, rather than focusing on the amplitude of ABR wave 1, we evaluated the use of ABR wave curvature to detect cochlear synaptic loss. We first compared four curvature quantification methods using simulated ABR waves, and identified that the cubic spline method using five data points produced the most accurate quantification. We next evaluated this quantification method with ABR data from an established mouse model with cochlear synaptopathy. The data clearly demonstrated that curvature measurement is more sensitive and consistent in identifying cochlear synaptic loss in mice compared to the amplitude and latency measurements. We further tested this curvature method in a different mouse model presenting with otitis media. The change in curvature profile due to middle ear infection in otitis media is different from the profile of mice with cochlear synaptopathy. Thus, our study suggests that curvature quantification can be used to address the current ABR variability issue, and may lead to additional applications in the clinic diagnosis of hearing disorders.

Residual stress tuned magnetic properties of thick CoMnP/Cu multilayers

Electrodeposited hard magnetic thick films have vast applications in the microelectromechanical systems (MEMS). Yet the very large residual stresses (σr) built-up in monolayered thick magnetic films leads to cracks, dimensional changes and deteriorated magnetic properties. Here, we explored quantitatively magnetic properties of CoMnP/Cu multilayers tuned by σr, which in turn are varied by the inserted soft Cu interlayer and thickness of single CoMnP magnetic layers. The configuration of the multilayers is an alternating CoMnP/Cu on Cu-substrate. The thickness of Cu interlayer was 1.4 μm. We kept a sum of all magnetic layers in the multilayers at ∼20 μm to benchmark with a 19.4 μm monolayered CoMnP. The magnetic layers are 94 wt.% Co and possess highly textured (002) hexagonal close packed microstructures. We characterized the apparent crystallite stresses through sin2ψ method by X-ray diffractometer (XRD) and residual film stress by curvature method. The insertion of Cu interlayers effectively reduces σr by 23% through stacking with six single-layered CoMnP. The out-of-plane (OP) anisotropy is slightly reduced. While the maximum energy product in the in-plane (IP) direction can be significantly enhanced by 430% ∼ 690% with increasing the number of the CoMnP single layer in the multilayers. The magneto-elastic behaviors well explain the evolution of the total anisotropy energy of the mono- and multi-layers. By CoMnP/Cu configurations we successfully worked out a strategy to preserve prestigious OP performance while to enhance IP properties by 4 to 6 times to meet ever increasing challenges in MEMS applications.

Directional wavelet modal curvature method for damage detection in plates

Abstract Vibration-based damage detection using the 2D modal curvature has become a research focus. However, the traditional methods based on modal curvature lack the sensitivity to direction of the damage. To address this problem, a directional 2D Morlet wavelet modal curvature is proposed in this paper. The directional wavelet modal curvatures show the following merits: robust to noise interference and sensitive to direction of damage. By the numerical simulation, the efficiency of the proposed method is demonstrated in the plate-like structure.

Improvement of the Identification Rate using Finger Veins based on the Enhanced Maximum Curvature Method using Morphological Operators

All human biological traits are unique as biometrics, such as fingerprint, palm, iris, palm veins, finger veins and other biometrics. Using these biometrics has always been challenging. One of the challenges in biometrics is physical injuries. Finger vein biometrics is one of the characteristics that is most resistant to physical injuries. Numerous algorithms for authentication have been proposed with the help of this biometrics, which have weaknesses such as high computational complexity and low identification accuracy. In this paper, a new method in identification based on maximum curvature algorithm and morphological operators is proposed. The maximum curvature algorithm extracts image properties using a set of operations based on image returns. This process has been enhanced in the proposed method with morphological operators. What distinguishes the proposed method from other methods is that this algorithm is very accurate in distinguishing images which are similar but belonging to different classes. The proposed method, in addition to having a reasonable computational complexity, has been able to record very good identification accuracy in the challenge of low image quality. The identification accuracy of the proposed method is 97.5%, which compared to other methods has been able to improve more than 3%. Also, the identification speed of the proposed method is 0.84 seconds, which is very fast in its kind.

An analytical framework of the kinematic geometry for general point-contact gears from contact path

Based on the idea that the relative curvature relationships along total contact path will better reflect the contact characteristics of gears, this study attempts to develop an analytical framework for the kinematic geometry of point-contact gears from the contact paths. First, a general method for obtaining the contact path of a gear from a pinion is proposed. Second, a normal curvature and geodesic torsion calculation method in the contact path direction is developed. Then, based on the linearly dependent condition of the tangent vectors of the two contact paths, two relative normal curvature analysis methods are proposed by applying the fundamental form theory. Finally, a sample case is presented to show the application and complete the verification of the kinematic geometry methods. The sample case agrees with the analytical model.

Compressive Stress and Charge Redistribution during CO Adsorption onto Pt.

The change in surface stress associated with the adsorption and oxidative stripping of carbon monoxide (CO) on (111)-textured Pt is examined using the wafer curvature method in 0.1 mol/L KHCO3 electrolyte. The curvature of the Pt cantilever electrode was monitored as a function of potential in both CO-free and CO-saturated electrolytes. Although CO adsorbs as a neutral molecule, significant compressive stress, up to -1.3 N/m, is induced in the Pt. The magnitude of the stress change correlates directly with the CO coverage and, within the detection limits of the stress measurement, is elastically reversible. Density functional theory calculations of a CO-bound Pt surface indicate that charge redistribution from the first atomic layer of Pt to subsurface layers accounts for the observed compressive stress induced by the charge neutral adsorption of CO. A better understanding of adsorbate-induced surface stress is critical for the development of material platforms for sensing and catalysis.

A unified comparative study on the classical lamination theory, hole drilling, slitting, and curvature measurement methods for assessment of residual stress in laminated polymeric composites

Residual stresses are balanced, non-uniform, undesirable, and often harmful in laminated polymer composite materials. Different methods are developed to measure these stresses in composites. In this manuscript, three experimental measurement methods, namely ‘hole drilling’, ‘slitting’, and ‘curvature’ methods, are considered, and the results are compared with those of classical lamination theory (CLT). It is demonstrated that the hole drilling technique can be used to measure residual stress in the near-surface areas of the structures, while the slitting method is often employed to assess residual stresses through the depth of specimens. Moreover, the curvature method shows great potential for estimating the overall residual stress quality in laminated composites with un-symmetrical configurations.

A reconstruction method to determine crack length based on virtual extensometers

The laboratory measurement accuracy of crack length has an influence on the study of material properties and behaviors. There are some defects in the existing methods for determining crack length, such as strong subjectivity, complex experimental process and difficult data processing. To solve the above problems, based on the surface deformation data recorded by DIC, a method of reconstructing the virtual extensometers and measuring the crack length is proposed by fixing the virtual extensometers along the crack growth path. The fracture process is analyzed based on the plastic hinge hypothesis, and the whole deformation data of the specimen is obtained by analyzing the length change of the virtual extensometers. The rigid components of virtual extensometers deformation along the crack growth path are reconstructed and compared with the original elongation curve to determine the crack length. It shows that the reconstruction method has a high reliability to compare the prediction results with those of the curvature method, the direct-reading method and the Martinelli-Venzi model method. The characteristic of virtual extensometers fixed after experiment and programming design of analysis process are applied to simplify the experiment and data processing. On the basis, the influence of the initial length of the virtual extensometer and the decomposition process on the results is discussed. The results show that reconstruction method has good adaptability to tunneling effect, and it is expected to realize automatic data collection and processing based on this method.

X-ray elastic constants determined by the combination of sin2 ψ and substrate-curvature methods

Abstract A new methodology is presented that allows the quantification of experimental X-ray elastic constants of polycrystalline thin films without use of special diffractometer attachments. The approach is based on the combination of sin2 ψ and curvature methods. The elastic strains in the polycrystalline films are characterized by the measurement of lattice spacings at different sample tilt angles, while the macroscopic stress in the film is calculated from the substrate curvature applying the Stoney formula. The radius of the curvature is determined from a sequence of rocking curves measured at different sample positions. The method is demonstrated on Al thin films deposited on Si(100) substrates. The X-ray diffraction measurements were performed at the synchrotron source BESSY in Berlin.

Evaluation of stress and energy relief efficiency of ZrN/Ti and ZrN/Zr

The purpose of this study was to investigate the extent of stress relief (Δσ%) and energy relief efficiency (ξtot) of metal interlayers in bilayer ZrN/Zr and ZrN/Ti thin films using an energy balance model based on the concept that the stored elastic energy in the ZrN coating could be partly relieved by the plastic deformation of metal interlayer. ZrN/Zr and ZrN/Ti specimens with different thicknesses of metal interlayers ranging from 100 to 300 nm were deposited on Si substrate using unbalanced magnetron sputtering. ZrN/Ti specimens were also deposited at different substrate bias voltages for investigating the energy relief efficiency by Ti interlayer under different stress levels in ZrN. The metal interlayers, Zr and Ti, were selected due to their different strain hardening behavior. Laser curvature method (LCM) and average X-ray strain combined with nanoindentation technique were employed to accurately measure the residual stresses in the entire specimen and the ZrN coating, respectively. Experimental results showed that Δσ% was more significant by Ti interlayer than by Zr interlayer. Δσ% of the entire specimen increased with interlayer thickness, while decreased with increasing stress of the top ZrN layer. The energy balance model was employed to evaluate ξtot by the interlayers. The contributions of energy relief from the ZrN coatings (ηZrN) and bending curvature relaxation of Si substrate (ηSi) could be separately assessed by the model. The results revealed that ξtot decreased by increasing Zr or Ti interlayer thickness, where the energy relief was mainly contributed from ηSi for ZrN/Zr specimens, while ηZrN was substantial for ZrN/Ti specimens, and there was an optimum interlayer thickness close to 100 nm, by which ξtot could reach up to 79.0 and 83.1% for Zr and Ti interlayers, respectively. For the ZrN coatings with different stress level ranging from −2.87 to −3.94 GPa, the variation of ξtot was less distinct, ranging from 39.1 to 48.8%, and the energy relief was mostly from ηZrN, except for σZrN close to −4 GPa, where the energy relief was mostly from ηSi. Although ξtot could serve as a better measure than Δσ% in evaluating the effectiveness of a metal interlayer, ηZrN and ηSi are the critical indexes that could reveal the actual energy relief in the hard coating. It is found that ηZrN and ηSi are related to the strength coefficient (k) of the interlayer. Therefore, in selecting a metal interlayer, it should be considered not only the capacity of energy absorption (Wp,max) but also the malleability (k) of the metal.

Size effects in the plastic deformation of NiAl thin films

Abstract This paper presents the first study of the plastic behavior of NiAl thin films with thicknesses in the micron and sub-micron range. The influence of geometrical and microstructural constraints was studied for different Al contents (45 to 50 at.% Al) and film thicknesses (0.2 to 3.1 μm) in the temperature range from 20 to 700 °C. The films were deposited on Si substrates and subjected to temperature changes resulting in thermal strains of up to 0.84%. The stress evolution in the films was measured by the substrate curvature method. The residual stress at room temperature of nearstoichiometric NiAl films significantly increased with decreasing film thickness indicating an increase of the film strength. At temperatures above 400 °C strong stress relaxation was found, which was more pronounced in thinner films suggesting the contribution of diffusional creep processes. The existence of a critical film thickness is suggested at which a transition from diffusion-controlled to dislocation-controlled plasticity occurs. The results have potential implications for the reliability of NiAl films as protective coatings in thermal engines.

Evident glass relaxation at room temperature induced by size effect

Probing the relaxation dynamics of glasses at temperatures far below the glass transition remains challenging owing to the extremely slow relaxation characteristic and the lack of appropriate experimental techniques. We utilized a sensitive laser reflection curvature method to probe the slow relaxation dynamics of metallic glassy (MG) films of different thicknesses at room temperature. It was found that the relaxation dynamics of MG films can be dramatically accelerated by the thickness reduction, similar to the role of temperature. We also compared the size-induced relaxation of MG films to the relaxation of MG ribbons at varying temperatures. Similar effects of size and temperature on the relaxation dynamics are revealed. We show that a MG film with a thickness of $\ensuremath{\sim}10$ nm at room temperature has a fast relaxation dynamics equivalent to that of a bulk MG near the glass transition temperature within an observation time scale of 1 s, indicating that the liquidlike behavior in glass can be induced by size reduction. Our observation for MGs, similar to that of polymer glasses reported previously, suggests that the size-induced enhanced relaxation dynamics and glass transition is universal in glassy materials.

Residual stress analysis of electrodeposited thick CoMnP monolayers and CoMnP/Cu multilayers

Residual stress in electroplated hard magnetic layers is crucial to the stability and durability in end applications. We electrodeposited highly HCP (002) textured CoMnP hard magnetic layers on copper substrate. We characterized and compared the residual stresses of mono- and multi-layered configurations using sin2ψ X-ray diffraction (XRD) for the apparent crystallite stress (σXRD), and curvature measurement methods for the macro-stress (σf). Intermediate Cu layer having a fixed thickness of 1.4 μm was introduced as a stress reliever for the multilayered CoMnP/Cu through sequential electrodeposition. In multilayers, thickness of all single magnetic layers was added to around ~20 μm similar to that of a monolayer. The surface morphology, layer composition and microstructure remain the same regardless of individual CoMnP single layer thickness. XRD results of ϕ-scan and ψ-scan depict the transversely isotropic CoMnP layers are under an equi-biaxial stress status, making a simplified analytical solution of sin2ψ method. The residual stresses measured by XRD sin2ψ method have been correlated with those acquired by curvature method. Increasing the number of layers from 2, 3 to 6 in the CoMnP/Cu multilayers reduces the σXRD by 8.3%, 25%, 33%, respectively; while the σf by 7.7%, 15% and 23%, respectively, as compared to those of the CoMnP mono-layer. These reductions are attributed to the released strain energy due to soft interlayer confinement and stacking fault formation. Elaborated includes unambiguous understandings of residual stress and microstructures for the electrodeposited CoMnP layers.

Potential field data interpolation by Taylor series expansion

Data interpolation is critical in the analysis of geophysical data when some data are missing or inaccessible. We interpolate irregular or missing potential field data using the relation between adjacent data points inspired by the Taylor series expansion (TSE). The TSE method first finds the derivatives of a given point near the query point using data from neighboring points and then uses the Taylor series to obtain the value at the query point. The TSE method works by extracting local features represented as derivatives from the original data for interpolation in the area of data vacancy. Compared with other interpolation methods, the TSE provides a complete description of potential field data. Specifically, the remainder in TSE can measure local fitting errors and help obtain accurate results. Implementation of the TSE method involves two critical parameters — the order of the Taylor series and the number of neighbors used in the calculation of derivatives. We find that the first parameter must be carefully chosen to balance between the accuracy and numerical stability when data contain noise. The second parameter can help us build an over-determined system for improved robustness against noise. Methods of selecting neighbors around the given point using an azimuthally uniform distribution or the nearest-distance principle are also presented. Our approach is first illustrated by a synthetic gravity data set from a single survey line, and then it is generalized to the case over a survey grid. In both numerical experiments, the TSE method demonstrates an improved interpolation accuracy in comparison with the minimum curvature method. Finally, we apply the TSE method to a ground gravity data set from the Abitibi Greenstone Belt, Canada, and an airborne gravity gradient data set from the Vinton Dome, Louisiana, USA.