Geometric Bending Research Articles

Local Geometric Distortion to Stimulate Oxygen Reduction Activity of Atomically Dispersed Zn‐Nx Sites for Zn–Air Batteries

AbstractLocal geometric strain engineering is useful for modulating the performance of nitrogen‐coordinated transition metal‐carbon catalysts. However, realizing the nano‐level strain is technically challenging. Additionally, the structure‐property relationship between strain degree and performance remains poorly understood. Herein, it is conceptually predict that geometric bending induces more electron transfer from Zn to the coordinated N in Zn─N─C, leading to a positive shift of the d‐band center of the Zn atom, which promotes the adsorption reduction process of the O2 molecule and thus increases the intrinsic oxygen reduction reaction (ORR) activity. Moreover, a low‐temperature non‐saturated coordination strategy is proposed to prepare spherical porous carbon catalysts with surface‐enriched geometrically bent (20‐50°) Zn─N─C sites. Benefiting from the highly active Zn─N─C sites, large specific surface area and abundant pore structure, the optimized catalyst (S─Zn─N─C‐950) exhibited excellent intrinsic alkaline ORR activity (half‐wave potential E1/2 = 0.89 V) and high zinc‐air battery performance (peak power density of 229.2 mW cm−2), exceeding that of commercial Pt/C catalysts. Density functional theory (DFT) calculations show that when the geometrical bending angle is 30–45°, Zn centers with suitable charge transfer to the surrounding N can produce a moderate adsorption strength to the oxygen intermediate state, resulting in optimal ORR activity.

Synthesis of Defective Nanographenes Containing Joined Pentagons and Heptagons.

Defective nanographenes containing joined pentagons and heptagons exhibit striking physicochemical properties from both experimental and theoretical perspectives compared with their pure hexagonal counterparts. Thus, the synthesis and characterization of these unique polyarenes with well‐defined defective topologies have attracted increasing attention. Despite extensive research on nonalternant molecules since the last century, most studies focused on the corresponding mutagenic and carcinogenic activities. Recently, researchers have realized that the defective domain induces geometric bending and causes electronic perturbation, thus leading to significant alteration of the photophysical properties. This review discusses the synthesis and characterization of small nonalternant polycyclic hydrocarbons in the early stage and recent developments in embedding pentagon–heptagon (5–7) pairs into large carbon skeletons through in‐solution chemistry.

Experimental and Analytical Study of Geometric Nonlinear Bending of a Cantilever Beam under a Transverse Load

Experimental and Analytical Study of Geometric Nonlinear Bending of a Cantilever Beam under a Transverse Load

Fragmentation of star-forming filaments in the X-shaped nebula of the California molecular cloud

Context. Dense molecular filaments are central to the star formation process, but the detailed manner in which they fragment into prestellar cores is not well understood yet. Aims. Here, we investigate the fragmentation properties and dynamical state of several star-forming filaments in the X-shaped nebula region of the California molecular cloud in an effort to shed some light on this issue. Methods. We used multiwavelength far-infrared images from Herschel as well as the getsources and getfilaments extraction methods to identify dense cores and filaments in the region and derive their basic properties. We also used a map of 13CO(2−1) emission from the Arizona 10m Submillimeter Telescope (SMT) to constrain the dynamical state of the filaments. Results. We identified ten filaments with aspect ratios of AR > 4 and column density contrasts of C > 0.5, as well as 57 dense cores, including two protostellar cores, 20 robust prestellar cores, 11 candidate prestellar cores, and 24 unbound starless cores. All ten filaments have roughly the same deconvolved full width at half maximum (FWHM), with a median value of 0.12 ± 0.03 pc, which is independent of their column densities ranging from <1021 cm−2 to >1022 cm−2. Two star-forming filaments (# 8 and # 10) stand out since they harbor quasi-periodic chains of dense cores with a typical projected core spacing of ~0.15 pc. These two filaments have thermally supercritical line masses and are not static. Filament 8 exhibits a prominent transverse velocity gradient, suggesting that it is accreting gas from the parent cloud gas reservoir at an estimated rate of ~40 ± 10 M⊙ Myr−1 pc−1. Filament 10 includes two embedded protostars with outflows and it is likely at a somewhat later evolutionary stage than filament 8. In both cases, the observed (projected) core spacing is similar to the filament width and significantly shorter than the canonical separation of ~4 times the filament width predicted by classical cylinder fragmentation theory. It is unlikely that projection effects can explain this discrepancy. We suggest that the continuous accretion of gas onto the two star-forming filaments, as well as the geometrical bending of the filaments, may account for the observed core spacing. Conclusions. Our findings suggest that the characteristic fragmentation lengthscale of molecular filaments is quite sensitive to external perturbations from the parent cloud, such as the gravitational accretion of ambient material.

Theoretical Insight into the Structural Nonplanarity in Aromatic Fused-Ring Metallabenzenes.

Metalla-aromatics have attracted considerable attention due to their fascinating structural and reactive properties as well as their potential as prospective functional materials. Metallabenzenes and their fused-ring counterparts are significant members of metalla-aromatics, while their crystal structures often display seemly counterintuitive nonplanar geometry. The geometric bending of metallabenzenes has been attributed to the unfavorable antibonding interactions in the σ-space orbitals rather than the general opinion regarding the π-space orbitals of an aromatic compound. However, the origin of the geometric bending in fused-ring metallabenzenes remains elusive. In this work, we elucidated that such a "σ-control mechanism" still holds for fused-ring metallabenzenes by performing systematic calculations for a plethora of metallabenzenes and fused-ring metallabenzenes. Furthermore, we found that a more bent geometry can be achieved for fused-ring metallabenzenes than their corresponding metallabenzenes by fusing the aromatic rings at the ortho-position of a metal center to induce extra repulsion. The more significant bending in fused-ring metallabenzenes also favors the aromaticity enhancement. These findings not only provide mechanistic insight into the unexpected geometric distortion in both metallabenzenes and fused-ring metallabenzenes but also pave the way to design and develop bent metalla-aromatics with enhanced metalla-aromaticity, which hold great potential as aromatic functional materials.

CALIBRATION AND VALIDATION OF CORONA KH-4B TO GENERATE HEIGHT MODELS AND ORTHOIMAGES

Abstract. At 48 years of age CORONA-KH-4B images are important for actual urban planning in Bangladesh, where no old maps or aerial images exist, indicating locations of former water courses that are no longer visible, but causing problems for the stability of building ground.CORONA KH-4B images are available for very low cost or even free of charge. A forward and a backward-looking panoramic camera with a nadir angle of approximately 15° enabled a stereoscopic coverage. Taken from a height of 154km, an image covers approximately 220km × 14km up to 17km with a height to base relation of 1:1.85. The ground sampling distance (GSD) varies with the incidence angle from 1.77m in the centre of the image up to 2.18m in Y-direction and 2.69m in the X-direction at the ends of the images. These nice conditions of the old images are affected by geometric problems of the panoramic images. A geometric bending can be improved by a correction based on the available sidelines, nevertheless deformations dominantly in the longitudinal direction only can be determined based on ground control points. A group of neighboured images have similar deformations, allowing the determination of a correction grid, describing the systematic image errors. This improved the geometry strongly, but could not eliminate all individual and local geometric problems. The high morphologic quality of the CORONA images, but limited absolute height accuracy has been improved by merging with the highly accurate TDM90 height model. For ortho images a fitting of neighboured images was required.

Plastic instability and spheroidization in a nanolayered Au-20Sn alloy during the hot rolling process

Au-20Sn eutectic alloys are an important lead-free solder applied in the welding temperature range from 280 to 350 °C. However, the poor formability originating from the brittle eutectic structure (AuSn + Au5Sn) restricts its applications because it is difficult to deform this alloy to the specifications required for industrial applications. In this study, the hot rolling process was carried out on an as-cast Au-20Sn alloy, and the deformation behaviour as well as the spheroidization evolution of the nanolayered structure was investigated in detail because the goal was to evaluate and optimize the thermoforming process of the Au-20Sn alloy. The results indicated that plastic instability occurred across the multilayers during hot rolling, which showed a gradual transition from geometric bending to the “S” type shear mode as the rolling strain increased. As a result, nanostructure spheroidization in a lamellar colony could take place preferentially based on these shear instability regions owing to a high strain accumulation in these places. Even so, the formation of high-angle grain boundaries in the AuSn lamellae occurred faster than that in the Au5Sn lamellae, resulting in a higher spheroidizing velocity in the AuSn phase. After spheroidization, a (0001)//transverse direction deformation texture formed in the AuSn phase, while a (0001)//normal direction deformation texture was introduced in the Au5Sn phase. Such differences in texture formation were primarily due to the different deformation mechanisms activated in these two phases due to their very different c/a ratios. This study can provide insights to improve the formability of Au-20Sn alloys during thermoforming.

Wrinkling prediction for GPa-grade steels in sheet metal forming process

This paper newly proposes a phenomenological wrinkling criterion to predict the formation of severe wrinkling in GPa-grade steels by adopting a critical amount of compressive strain with respect to the specific triaxiality and the geometrical bending strain, which were updated incrementally. To enhance the accuracy of the wrinkling criterion during the sheet metal forming process, the non-flange and flange wrinkling criteria were separately applied to the adapted region, which was distinguished from the entire domain by checking the blank holding pressure (BHP) caused by the contact pressure between the sheet and binder, systematically. The proposed wrinkling criterion exhibits superior performance in the prediction of experimental wrinkles that occur in the B-pillar and crash forming with a TRIP1180 sheet when compared with conventional criteria such as geometrical bending strain, thickness strain, and potential wrinkling.

Analysis of the influence of the pipe’s wall thickness on the corrugation of the surface during inductive bending of pipes

The paper presents a calculation model for simulation the technological process of inductive bending of pipes. In the case of an incorrect combination of geometric bending parameters (pipe diameter, bend radius and pipe wall thickness) occurs the corrugation of the inner part in the pipe bend. The proposed calculation model for the ADINA FE software allows for a relatively short time and at low cost to predict the emergence of corrugation.

Impact and Implementation of Higher‐Order Ionospheric Effects on Precise GNSS Applications

AbstractHigh precision Global Navigation Satellite Systems (GNSS) positioning and time transfer require correcting signal delays, in particular higher‐order ionospheric (I2+) terms. We present a consolidated model to correct second‐ and third‐order terms, geometric bending and differential STEC bending effects in GNSS data. The model has been implemented in an online service correcting observations from submitted RINEX files for I2+ effects. We performed GNSS data processing with and without including I2+ corrections, in order to investigate the impact of I2+ corrections on GNSS products. We selected three time periods representing different ionospheric conditions. We used GPS and GLONASS observations from a global network and two regional networks in Poland and Brazil. We estimated satellite orbits, satellite clock corrections, Earth rotation parameters, troposphere delays, horizontal gradients, and receiver positions using global GNSS solution, Real‐Time Kinematic (RTK), and Precise Point Positioning (PPP) techniques. The satellite‐related products captured most of the impact of I2+ corrections, with the magnitude up to 2 cm for clock corrections, 1 cm for the along‐ and cross‐track orbit components, and below 5 mm for the radial component. The impact of I2+ on troposphere products turned out to be insignificant in general. I2+ corrections had limited influence on the performance of ambiguity resolution and the reliability of RTK positioning. Finally, we found that I2+ corrections caused a systematic shift in the coordinate domain that was time‐ and region‐dependent and reached up to −11 mm for the north component of the Brazilian stations during the most active ionospheric conditions.

Remote leveling of tide gauges using GNSS reflectometry: case study at Spring Bay, Australia

We further developed a new approach using GNSS reflectometry to determine the leveling connection between a tide gauge and a GNSS antenna. This approach includes the optimization of the unknown receiver bandwidth and the estimation of frequency changes in the signal-to-noise ratio (SNR) oscillation through an extended Kalman filter/smoother algorithm. We also corrected the geometric bending of the GNSS signals due to tropospheric refraction using local meteorological observations. Using 3 weeks of SNR data in Spring Bay, Australia, from a GNSS antenna placed sideways (i.e., ground plane orientated vertically and directed in azimuth toward the sea surface) to improve the SNR interference near the horizon, we obtained mean leveling differences of approximately 5 mm, with an RMS of approximately 3 cm level with respect to the nominal leveling from classical surveying techniques. SNR data from three different receiver manufacturers, coupled to the same antenna, provided similar leveling results. With a second antenna in the usual upright configuration, we obtained mean leveling differences of 1---2 cm and a RMS of about 10 cm. In the upright configuration, the leveling differences may include errors in the GNSS antenna phase center calibration, which are avoided in our technique but not in the classical surveying techniques. These results demonstrate the usefulness of the reflectometry technique to obtain precisely and remotely the leveling between a GNSS antenna and a tide gauge. In addition, this technique can be applied continuously, providing an independent and economical means to monitor the stability of the tide gauge zero.

Nonlinear Bending Response and Buckling of Channel Section Beams of Finite Length under Minor-Axis Pure Bending

In this paper, the geometric nonlinear bending response of channel-section beams of finite length is investigated by using energy methods. The basic assumptions used in the present study are that the total strain energy of a channel-section beam subjected to pure bending can be simplified into a two-stage analysis process. One is the local bending response of the web behaving as the plate; the other is the overall bending response as a beam with flattened section. Analytical solutions for both static and dynamic instabilities of channel section beams of finite length subjected to pure bending about its minor axis are derived by applying the minimum potential energy principle. To validate the analytical solution developed, geometric nonlinear finite element analyses are also conducted. Good agreement between the present solution and the FEA results is demonstrated. The effect of beam's length on the critical load is also discussed.

Nonlinear bending analysis of laminated composite stiffened plates

This paper deals with the geometric nonlinear bending analysis of laminated composite stiffened plates subjected to uniform transverse loading. The eight-noded degenerated shell element and three-noded degenerated curved beam element with five degrees of freedom per node are adopted in the present analysis to model the plate and stiffeners respectively. The Green-Lagrange strain displacement relationship is adopted and the total Lagrangian approach is taken in the formulation. The convergence study of the present formulation is carried out first and the results are compared with the results published in the literature. The stiffener element is reformulated taking the torsional rigidity in an efficient manner. The effects of lamination angle, depth of stiffener and number of layers, on the bending response of the composite stiffened plates are considered and the results are discussed.

Distribution and mitigation of higher‐order ionospheric effects on precise GNSS processing

Higher‐order ionospheric effects (I2+) are one of the main limiting factors in very precise Global Navigation Satellite Systems (GNSS) processing, for applications where millimeter accuracy is demanded. This paper summarizes a comprehensive study of the I2+ effects in range and in GNSS precise products such as receiver position and clock, tropospheric delay, geocenter offset, and GNSS satellite position and clock. All the relevant higher‐order contributions are considered: second and third orders, geometric bending, and slant total electron content (dSTEC) bending (i.e., the difference between the STEC for straight and bent paths). Using a realistic simulation with representative solar maximum conditions on GPS signals, both the effects and mitigation errors are analyzed. The usage of the combination of multifrequency L band observations has to be rejected due to its increased noise level. The results of the study show that the main two effects in range are the second‐order ionospheric and dSTEC terms, with peak values up to 2 cm. Their combined impacts on the precise GNSS satellite products affects the satellite Z coordinates (up to +1 cm) and satellite clocks (more than ±20 ps). Other precise products are affected at the millimeter level. After correction the impact on all the precise GNSS products is reduced below 5 mm. We finally show that the I2+ impact on a Precise Point Positioning (PPP) user is lower than the current uncertainties of the PPP solutions, after applying consistently the precise products (satellite orbits and clocks) obtained under I2+ correction.

Analysis of polarisation conversion in cascaded bent photonic crystal fibre

A rigorous analysis of polarisation conversion in a novel design of cascaded bent silica photonic crystal fibre is proposed using full vectorial finite difference method as well as full vectorial finite difference beam propagation method. The influence of different structural geometrical parameters on the polarisation rotator performance is investigated. The numerical results reveal that by a careful adjustment of the structural geometrical parameters and bending radius, nearly a 100% polarisation conversion ratio with nine sections only and low bending losses can be achieved.

Specially designed long period grating with internal geometric bending for enhanced refractive index sensitivity

We propose a long period grating (LPG) characterized by specially designed refractive index (RI) profile in which each grating plane is tilted at increasing angles, as moving away from the center of symmetry of the structure towards its both edges. This internally manufactured geometric structure, which basically simulates the bending of an optical fiber, increases the RI sensitivity of an LPG to the external medium. We experimentally demonstrate a three-fold improvement in the RI sensitivity, thus providing the basis for another step forward in the field of RI sensors based on optical fiber gratings.

Rupture segmentation and slip partitioning of the mid-eastern part of the Kunlun Fault, north Tibetan Plateau

The Kunlun Fault, an active fault on the border between the Bayan Har and Kunlun-Qaidam blocks, is one of the major left lateral strike-slip faults in the Tibetan Plateau. Previous research has not reached a consensus on agreeable slip rates along much of its length and the slip rate gradient along the eastern part, both of which play critical roles in a range of models for the eastward extrusion and thickened crust of the Tibetan Plateau. New slip rates have been determined at sites along the eastern part of the Kunlun Fault by dating deposits and measuring atop displaced fluvial terrace risers. Field investigations and interpretation of satellite images reveal geometrical features of the fault and the late Quaternary offset, new earthquake ruptures and surface-rupturing segmentation, from which long-term slip rates and earthquake recurrence intervals on the fault are estimated. The tectonic geomorphology method has determined that the long-term horizontal slip rates on the Tuosuohu, Maqin and Maqu segments from west to east are 11.2±1, 9.3±2, and 4.9±1.3 mm/a while their vertical slip rates are 1.2±0.2, 0.7±0.1, and 0.3 mm/a in the late Quaternary. Results indicate that the slip rates regularly decrease along the eastern ∼300 km of the fault from >10 to <5 mm/a. This is consistent with the decrease in the gradient such that at the slip rate break point is at the triple point intersection with the transverse fault, which in turn is transformed to the Awancang Fault. The vector decomposition for this tectonic transformation shows that the western and eastern branches of the Awancang Fault fit the slip-partitioning mode. The slip rate of the southwestern wall is 4.6 mm/a relative to the northeastern wall and the slip direction is 112.1°. The mid-eastern part of the Kunlun Fault can be divided into three independent segments by the A’nyemaqen double restraining bend and the Xigongzhou intersection zone, which compose the surface rupture segmentation indicators for themselves as well as the ending point of the 1937 M7.5 Tuosuohu earthquake. The average recurrence interval of the characteristic earthquakes are estimated to be 500–1000 a, respectively. The latest earthquake ruptures occurred in AD 1937 on the western Tuosuohu segment, as compared to ∼514–534 a BP on the Maqin segment, and ∼1055 to 1524 a BP on the Maqu segment. This may indicate a unidirectional migration for surface rupturing earthquakes along the mid-eastern Kunlun Fault related to stress triggered between these segments. Meanwhile, the long-term slip rate is obtained through the single event offset and the recurrence interval, which turn out to be the same results as those determined by the offset tectonic geomorphology method, i.e., the decreasing gradient corresponds to the geometrical bending and the fault’s intersection with the transverse fault. Therefore, the falling slip rate gradient of the mid-eastern Kunlun Fault is mainly caused by eastward extension of the fault and its intersection with the transverse fault.

A Review of Higher Order Ionospheric Refraction Effects on Dual Frequency GPS

Higher order ionospheric effects are increasingly relevant as precision requirements on GPS data and products increase. The refractive index of the ionosphere is affected by its electron content and the magnetic field of the Earth, so the carrier phase of the GPS L1 and L2 signals is advanced and the modulated code delayed. Due to system design the polarisation is unaffected. Most of the effect is removed by expanding the refractive index as a series and eliminating the first term with a linear combination of the two signals. However, the higher order terms remain. Furthermore, transiting gradients in refractive index at a non-perpendicular angle causes signal bending. In addition to the initial geometric bending term, another term allows for the difference that the curvature makes in electron content along each signal. Varying approximations have been made for practical implementation, mainly to avoid the need for a vertical profile of electron density. The magnetic field may be modelled as a tilted co-centric dipole, or using more realistic models such as the International Geomagnetic Reference Field. The largest effect is from the second term in the expansion of the refractive index. Up to several cm on L2, it particularly affects z-translation, and satellite orbits and clocks in a global network of GPS stations. The third term is at the level of the errors in modelling the second order term, while the bending terms appear to be absorbed by tropospheric parameters. Modelling improvements are possible, and three frequency transmissions will allow new possibilities.

A first look at the effects of ionospheric signal bending on a globally processed GPS network

This study provides a first attempt at quantifying potential signal bending effects on the GPS reference frame, coordinates and zenith tropospheric delays (ZTDs). To do this, we homogeneously reanalysed data from a global network of GPS sites spanning 14 years (1995.0–2009.0). Satellite, Earth orientation, tropospheric and ground station coordinate parameters were all estimated. We tested the effect of geometric bending and dTEC bending corrections, which were modelled at the observation level based, in part, on parameters from the International Reference Ionosphere 2007 model. Combined, the two bending corrections appear to have a minimal effect on site coordinates and ZTDs except for low latitude sites. Considering five days (DOY 301–305, 28 October–1 November 2001) near ionospheric maximum in detail, they affect mean ZTDs by up to ~1.7 mm at low latitudes, reducing to negligible levels at high latitudes. Examining the effect on coordinates in terms of power-spectra revealed the difference to be almost entirely white noise, with noise amplitude ranging from 0.3 mm (high latitudes) to 2.4 mm (low latitudes). The limited effect on station coordinates is probably due to the similarity in the elevation dependence of the bending term with that of tropospheric mapping functions. The smoothed z-translation from the GPS reference frame to ITRF2005 changes by less than 2 mm, though the effect combines positively with that from the second order ionospheric refractive index term. We conclude that, at the present time, and for most practical purposes, the geometric and dTEC bending corrections are probably negligible at current GPS/reference frame precisions.

Model of bending of a hydrostatically compressed shell near its stability threshold

A circular cylindrical shell compressed from the outer side of the surface by a high-pressure fluid loses stability of its form at a certain value of the external pressure (“collapse” or nonlinear buckling occurs). As a result, bumps and dents extended along the shell generatrix appear on the shell surface; in the shell cross section, these structures alternate [1]. Deformations of the thin shell remain elastic and, as a whole, are consistent with its geometric bending [2]. Therefore, the initial stage of changes in the shell form can be described within the framework of the nonlinear theory of elasticity [3–5]. Equations of the nonlinear theory of elasticity take into account not only the geometric nonlinearity of the problem caused by nonlinearity of the strain tensor, but also the physical nonlinearity characterizing the material properties and described by the highest invariants of the strain tensor in the expansion of the expression for nonlinearly elastic energy of the medium. Correct allowance of the highest invariants is of principal importance, because the emergence of nonlinearity effects leads to localization of shell bendings. In the final analysis, formation of spatially localized patterns from dents on the shell surface at the initial stage of changes in its form is the result of interaction of nonlinearity and dispersion effects. One important feature of the problem is the absence of dispersion terms in the original equations of the nonlinear theory of elasticity. In simplified models of shells, dispersion terms appear owing to elimination of the “fast” variable characterizing the nonuniformity of strains along the normal to the shell surface. There are some novel methods [6] that allow obtaining simplified models, based on proven equations of the nonlinear theory of elasticity without using ap riorihypotheses and with controlled accuracy in terms of small parameters characterizing the shell size, magnitude of external stress, space and time scales of deformations, and geometric and physical nonlinearity of the problem. Such methods reveal latent dynamic symmetry of the problem; therefore, the simplified equations are universal and close to integrated models, which allows their solutions to be analyzed in detail by methods of the advanced theory of solitons. Nevertheless, the nonlinearly elastic dynamics of shells near their stability thresholds and the possibilities of its approximation by integrated models have not been studied yet. A variant of the reductive perturbation theory suitable for solving nonlinear boundary-value problems, where the final surface of the deformed shell is not known in advance and is found in the course of solving the problem, is proposed in the present paper. The expression for the initial nonlinearly elastic energy of the material is presented in the form of an expansion over all strain-tensor invariants admitted by medium symmetry. The method proposed allows automatic selection of invariants from equations of the nonlinear theory of elasticity and contributions of