Magnitude Of Bending Research Articles

Electro-actuated hydrogel walkers with dual responsive legs

Stimuli responsive polyelectrolyte hydrogels may be useful for soft robotics because of their ability to transform chemical energy into mechanical motion without the use of external mechanical input. Composed of soft and biocompatible materials, gel robots can easily bend and fold, interface and manipulate biological components and transport cargo in aqueous solutions. Electrical fields in aqueous solutions offer repeatable and controllable stimuli, which induce actuation by the re-distribution of ions in the system. Electrical fields applied to polyelectrolyte-doped gels submerged in ionic solution distribute the mobile ions asymmetrically to create osmotic pressure differences that swell and deform the gels. The sign of the fixed charges on the polyelectrolyte network determines the direction of bending, which we harness to control the motion of the gel legs in opposing directions as a response to electrical fields. We present and analyze a walking gel actuator comprised of cationic and anionic gel legs made of copolymer networks of acrylamide (AAm)/sodium acrylate (NaAc) and acrylamide/quaternized dimethylaminoethyl methacrylate (DMAEMA Q), respectively. The anionic and cationic legs were attached by electric field-promoted polyion complexation. We characterize the electro-actuated response of the sodium acrylate hydrogel as a function of charge density and external salt concentration. We demonstrate that "osmotically passive" fixed charges play an important role in controlling the bending magnitude of the gel networks. The gel walkers achieve unidirectional motion on flat elastomer substrates and exemplify a simple way to move and manipulate soft matter devices and robots in aqueous solutions.

Mechanical behaviour of cross-country ski racing poles during double poling

The purpose of this study was to evaluate the behaviour of cross-country ski poles during double poling on a treadmill using three-dimensional kinematics. The results were compared with standard laboratory tests of the pole manufacturers. A total of 18 skiers were analysed at two speeds (85% and 95% of the maximal speed) at grades of 1.5% and 7%. Variables describing cycle characteristics, bending stiffness, bending behaviour, and trajectories of the pole markers were analysed. Triangular-shaped poles demonstrated the greatest stiffness and lowest variability in maximal bending. Softer poles demonstrated greater variability in bending behaviour and lost ground contact at high skiing speeds, which for some skiers resulted in failure to complete high-speed tests. Considerable variations in pole behaviour for similar poles between skiers were observed, which might be attributed to differences in technique, indicating that mechanical properties of the poles did not exclusively determine pole behaviour in the dynamic situation. The greatest magnitude of pole bending was in the middle part of the pole, which differed from the standard static pole analysis of the manufacturer. Increases in grade demonstrated the greatest effect on pole bending. Distinct differences from the pole manufacturers' laboratory measures were apparent, suggesting that basic pole testing might be adapted.

Origin of Rashba splitting in the quantized subbands at the Bi2Se3surface

We study the band structure of the $\text{Bi}_2\text{Se}_3$ topological insulator (111) surface using angle-resolved photoemission spectroscopy. We examine the situation where two sets of quantized subbands exhibiting different Rashba spin-splitting are created via bending of the conduction (CB) and the valence (VB) bands at the surface. While the CB subbands are strongly Rashba spin-split, the VB subbands do not exhibit clear spin-splitting. We find that CB and VB experience similar band bending magnitudes, which means, a spin-splitting discrepancy due to different surface potential gradients can be excluded. On the other hand, by comparing the experimental band structure to first principles LMTO band structure calculations, we find that the strongly spin-orbit coupled Bi 6$p$ orbitals dominate the orbital character of CB, whereas their admixture to VB is rather small. The spin-splitting discrepancy is, therefore, traced back to the difference in spin-orbit coupling between CB and VB in the respective subbands' regions.

Validation of an Improved Method to Calculate the Orientation and Magnitude of Pedicle Screw Bending Moments

Previous methods of pedicle screw strain measurement have utilized complex, time consuming methods of strain gauge application, experience high failure rates, do not effectively measure resultant bending moments, and cannot predict moment orientation. The purpose of this biomechanical study was to validate an improved method of quantifying pedicle screw bending moment orientation and magnitude. Pedicle screws were instrumented to measure biplanar screw bending moments by positioning four strain gauges on flat, machined surfaces below the screw head. Screws were calibrated to measure bending moments by hanging certified weights a known distance from the strain gauges. Loads were applied in 30 deg increments at 12 different angles while recording data from two independent strain channels. The data were then analyzed to calculate the predicted orientation and magnitude of the resultant bending moment. Finally, flexibility tests were performed on a cadaveric motion segment implanted with the instrumented screws to demonstrate the implementation of this technique. The difference between the applied and calculated orientation of the bending moments averaged (±standard error of the mean (SEM)) 0.3 ± 0.1 deg across the four screws for all rotations and loading conditions. The calculated resultant bending moments deviated from the actual magnitudes by an average of 0.00 ± 0.00 Nm for all loading conditions. During cadaveric testing, the bending moment orientations were medial/lateral in flexion-extension, variable in lateral bending, and diagonal in axial torsion. The technique developed in this study provides an accurate method of calculating the orientation and magnitude of screw bending moments and can be utilized with any pedicle screw fixation system.

Computer Modeling and Parametric Study of Thermal Effects in Integral Abutment Bridge

Structural behavior of concrete integral abutment bridge subjected to temperature rise was investigated through a numerical modeling and parametric study. Long-term, field monitoring through the summer was performed on Industrial Park Bridge located in Heilongjiang province, China from June 13, 2010 until June 28, 2010. The collected data was used to validate the accuracy of a 3D-finite element model of the bridge which took into account soil-structure interaction. Based on the calibrated finite element model a parametric study considered two parameters, bridge length and abutment height, was carried out to investigate the effects of this parameters on structural behavior of integral abutment bridge subject to temperature rise. It was determined that Thermal load in the superstructure of the integral bridge develop significant magnitudes of bending and axial forces in the superstructure. The largest magnitude of thermally induced moment always occurs near the abutment, and axial force is constant across the length of each span. For bridge thermal expansion, longer bridges and taller abutments cause larger thermally induced superstructure axial force due to development of higher backfill pressure. Generally span length has a higher influence for thermally induced superstructure forces in terms of axial force and bending moment than the abutment height.

Detecting protein adsorption and binding using magnetic nanoparticle probes

Magnetic force induced microcantilever bending is used to enhance sensitivity of protein biomarker detection using magnetic nanoparticles. After modifying magnetic nanoparticles and microcantilever with antibodies, the existence of antigen in solution leads to immobilization of nanoparticles on microcantilever by forming antigen–antibody complexes. The microcantilever bends in the presence of magnetic field, and the magnitude of bending is dependent on strength of magnetic field and amount of immobilized magnetic nanoparticles. This method has been used to monitor protein adsorption, and detect protein biomarker in complex biological sample system, such as cell lysate. The magnetic induced bending offers high sensitivity, does not require an asymmetric surface modification on microcantilever, and can be used for the reliable detection of protein biomarkers in body biofluids.

How sequence directs bending in tropomyosin and other two-stranded alpha-helical coiled coils.

A quantitative analysis of the direction of bending of two-stranded alpha-helical coiled coils in crystal structures has been carried out to help determine how the amino acid sequence of the coiled coil influences its shape and function. Change in the axial staggering of the coiled coil, occurring at the boundaries of either clusters of core alanines in tropomyosin or of clusters of core bulky residues in the myosin rod, causes bending within the plane of the local dimer. The results also reveal that large gaps in the core of the coiled coil, which are seen for small core residues near large core residues or for unbranched core residues near canonical branched core residues, are correlated with bending out of the local dimeric plane. Comparison of tropomyosin structures determined in independent crystal environments provides further evidence for the concept that sequence directs the bending of the coiled coil, but that crystal environment is at least as important as sequence for determining the magnitude of bending. Tropomyosin thus appears to consist of more directionally restrained hinge-like joints rather than directionally variable universal joints, which helps account for and predicts the geometric and dynamic nature of its binding to F-actin.

Second-order slope–deflection equations for imperfect beam–column structures with semi-rigid connections

A new set of second-order slope–deflection equations for Euler–Bernoulli beam–columns of symmetric cross-section including the effects of initial imperfections (i.e., initial curvature, out-of-plumbness and axial load eccentricities) and semi-rigid connections is developed in a classical manner. The proposed method has the following advantages: (1) it can be utilized in the stability and second-order analysis of framed structures made of Euler–Bernoulli imperfect beam–columns with rigid, semi-rigid, and simple connections subject to axial and transverse loads; (2) the effects of semi-rigid connections and member imperfections are condensed into the slope–deflection equations for tension and compression axial loads; (3) it is more accurate than any other method available in the technical literature and capable of capturing not only the first-order and second-order elastic responses of frames made of imperfect beam–columns but also the phenomenon of reversals of deflections along the members as the axial loads are increased; and (4) it is powerful, practical, versatile and easy to apply. Analytical studies indicate that the initial imperfections (a) act as if they were additional transverse loads proportional to the bending stiffness and magnitudes of the imperfections of the corresponding beam–column; and (b) are detrimental to structures, increasing the lateral deflections, moments, and shears, and also reducing the critical axial loads of beam–columns and framed structures. This is particularly critical in structures made of beam–columns with initial crookedness and low stiffness connections subjected to high compressive axial loads. In addition, the effects of initial curvature are amplified by the compressive axial loads applied at the ends of the member. Four comprehensive examples are included that show the effectiveness of the proposed method.

Evolution of electron states at an n-type InSb surface in a depletion-layer formation process: Effect of nonparabolicity of the conduction-band dispersion

Advancing adsorption on an n-type InSb(110) surface induces gradual formation of a carrier-depletion layer at the surface. Incorporating a highly nonparabolic (NP) dispersion of the conduction band into the local-density-functional formalism in a complete manner, we investigate evolution of electron states at the n-type InSb surface in the depletion-layer formation process. By comparing the calculated results for the NP dispersion with those for the parabolic (P) dispersion corresponding to the band-edge effective mass, we evaluate the effects of the nonparabolicity on surface electron states. The nonparabolicity is found to make significant differences in the effective one-electron potential and the carrier-density distribution at the surface. The band bending occurs in the closer vicinity of the surface and with a smaller bending magnitude in the NP dispersion than in the P dispersion. This can be explained by the fact that carrier electrons operate to screen positive charges of ionized donors in the depletion layer more effectively in the NP dispersion than in the P dispersion. Accurate treatment of the nonparabolicity is indispensable in evaluating the surface electron states at each stage of the formation process.

A measure of bending in nucleic acids structures applied to A-tract DNA.

A method is proposed to measure global bending in DNA and RNA structures. It relies on a properly defined averaging of base-fixed coordinate frames, computes mean frames of suitably chosen groups of bases and uses these mean frames to evaluate bending. The method is applied to DNA A-tracts, known to induce considerable bend to the double helix. We performed atomistic molecular dynamics simulations of sequences containing the A4T4 and T4A4 tracts, in a single copy and in two copies phased with the helical repeat. Various temperature and salt conditions were investigated. Our simulations indicate bending by roughly 10° per A4T4 tract into the minor groove, and an essentially straight structure containing T4A4, in agreement with electrophoretic mobility data. In contrast, we show that the published NMR structures of analogous sequences containing A4T4 and T4A4 tracts are significantly bent into the minor groove for both sequences, although bending is less pronounced for the T4A4 containing sequence. The bending magnitudes obtained by frame averaging are confirmed by the analysis of superhelices composed of repeated tract monomers.

Time Domain Simulation of the 3D Bending Hysteresis Behavior of an Unbonded Flexible Riser

This paper presents a “state-of-the-art” development in time domain dynamic simulation of 3D bending hysteresis behavior of a flexible riser under offshore environment loading. The main technical challenge is to understand and model the riser tensile armor behavior under continuous changes in both the magnitude and direction of bending, and its subsequent impact on the riser’s bending hysteresis characteristics. On account of this technical obstacle, the current industry practice is to model the riser as a linear structure, with certain conservatism enforced, and then to extract the global dynamic loads to a detailed local model for stress and life assessment. Two 3D flexible riser bending hysteresis models developed by Wellstream and Orcina are introduced in this paper, with their calibrations against the bending hysteresis loops measured in full scale tests. Both models are implemented using the analysis program ORCAFLEX. The Wellstream model is a detailed model that calculates both the total bending moment and the stresses in the tensile armor, whereas the Orcina model is a simpler model that only calculates the total bending moment. The study presented illustrates the difference in riser dynamic responses with and without consideration of the bending hysteresis behavior and assesses the difference in dynamic responses between the Wellstream and Orcina 3D bending hysteresis models. This development permits the modeling of more realistic riser structural properties in the dynamic simulation and reports detailed time history stress or strain results for strength components of the riser, and so expands the current practice of riser fatigue analysis, which uses the regular wave approach only, to using an irregular wave approach employing the rainflow counting method.

Performance of composite members subjected to axial load and bi-axial bending

This study focuses on the experimental evaluation of steel-concrete composite member seismic performance. Relationships between the members’ seismic performance and structural parameters, such as the sectional steel strength ratios and bi-axial bending magnitudes were defined. Test results show that the strength deterioration rates increased when the members’ steel strength ratios in the weak-axis were increased. The test results also suggested that steel strength ratios in the strong and weak sectional directions be adequately adjusted so that high member performance could be achieved. It is proposed in this study that the ratio between the strong and weak-axes steel strength ratios be set to approximately 2.2 to optimize the member’s seismic performance.

Magnitude and direction of DNA bending induced by screw-axis orientation: influence of sequence, mismatches and abasic sites

DNA-bending flexibility is central for its many biological functions. A new bending restraining method for use in molecular mechanics calculations and molecular dynamics simulations was developed. It is based on an average screw rotation axis definition for DNA segments and allows inducing continuous and smooth bending deformations of a DNA oligonucleotide. In addition to controlling the magnitude of induced bending it is also possible to control the bending direction so that the calculation of a complete (2-dimensional) directional DNA-bending map is now possible. The method was applied to several DNA oligonucleotides including A(adenine)-tract containing sequences known to form stable bent structures and to DNA containing mismatches or an abasic site. In case of G:A and C:C mismatches a greater variety of conformations bent in various directions compared to regular B-DNA was found. For comparison, a molecular dynamics implementation of the approach was also applied to calculate the free energy change associated with bending of A-tract containing DNA, including deformations significantly beyond the optimal curvature. Good agreement with available experimental data was obtained offering an atomic level explanation for stable bending of A-tract containing DNA molecules. The DNA-bending persistence length estimated from the explicit solvent simulations is also in good agreement with experiment whereas the adiabatic mapping calculations with a GB solvent model predict a bending rigidity roughly two times larger.

角度分解光電子分光による金属／酸化物界面の研究―Ｃｕ吸着ＺｎＯ極性表面の価電子バンド構造―

Angle-resolved photoemission measurements are carried out to investigate the valence electronic structures of two different ZnO surfaces that are (0001) Zn-terminated (ZnO-Zn) and (000-1) O-terminated (ZnO-O) surfaces, and also of Cu clusters supported on these surfaces. On the clean ZnO surfaces, two valence bands are observed at ∼4 and 5−8 eV with a clear dispersion feature. Although these bands are associated with the bulk bands, it is found that the dispersion widths of the bands exhibit the termination dependence of the polar ZnO surfaces. Deposition of Cu on the polar ZnO surfaces induces downward bending of the ZnO band. Magnitude of Cu-induced bending is larger on ZnO-O than on ZnO-Zn. This indicates that the Cu—ZnO interface interaction is greater for the Cu/ZnO-O system than for the Cu/ZnO-Zn system. The analysis of the Cu 3d band structure implies that coupling between the Cu 3d band and the ZnO band is operative at the Cu—ZnO-O interface, whereas such coupling seems to be missing at the Cu—ZnO-Zn interface. We propose that the effect of electronic coupling is one of the factors that determine the interface interaction between the Cu cluster and polar ZnO surfaces.

Bend sensing with long-period fiber gratings in capillaries embedded in structures

Bend responses of an LPG inscribed with a CO 2 laser in a conventional single-mode fiber are investigated in an arrangement, where the LPG is inserted into a thin silica capillary bonded to a steel strip. The curvature of the strip, laid on two supports and bent with a micrometer driver in the middle between the supports, decreases linearly with distance from the center of bending to the supports. Experiments are done for a very large range of bend deflections with the LPG in three positions shifted with respect to the center of bending, and two distinct opposite rotational orientations with respect to the plane of bending. Responses obtained for the above positions and orientations are greatly different and some of them show features which have not been reported for LPGs bent with a constant curvature and smaller deflections. They are, particularly, maxima and minima of the central wavelength's shift along with reversals of its direction, or the reappearance of a previously vanished attenuation band with increasing magnitude of bending. Also, it is found that the responses depend not only on the average curvature of the bent LPG, but also on the particular dependence of the curvature along the LPG's length. Some of the results obtained cannot be satisfactorily explained at the present level of knowledge, and a more thorough theoretical analysis is needed.

High-resolution numerical modeling of stress distribution in visco-elasto-plastic subducting slabs

We employ high-resolution 2D thermomechanical modelling with complex elasto-visco-plastic rheology to analyse stresses in subducting and overriding plates. The model contains a dynamic subduction channel, defined as a few km thick zone of specific (weak) visco-plastic rheology between the slab and the overriding plate. Our high-resolution model corresponds to the zoom-in of the large-scale thermomechanical model of the Central Andes, with the 4-fold resolution increase. Initial model configuration (material, temperature and stress distributions) was interpolated from the parent model. Boundary conditions including slab pull and push velocities as well as velocity of the overriding plate, were also re-mapped from the large scale model. We demonstrate that, for shallow-dipping overridden slabs, the dominant stress is unbending stress at 50–100 km depth. This stress reaches 1–1.5 GPa and strongly prevails over the slab bending stress near the trench, which is limited by the frictional plastic yield. Unbending creates double (5–10 km distance between maximums) compression zone in the upper part of the slab and a zone of extension some 20–30 km below. Pressure in these zones differs from the lithostatic pressure to as much as plus/minus 0.8 GPa. Details of the distribution and magnitude of bending and unbending stresses in the slab are mainly controlled by the overriding velocity and direction of the slab-pull force. Overpressure in the subduction channel in all models does not exceed 100 MPa. Large over- and under-pressures in the slab, do not, however, lead to significant (more than 10 km) offsets of main dehydration reactions in crust and mantle of the slab.

Stainless steel stub columns subject to combined bending and axial loading

This paper examines the behaviour of cold-formed stainless steel stub columns where the material follows a Ramberg–Osgood stress–strain law. The stub column length is varied to examine the effects on the failure capacity when the stub columns are subjected to varying magnitudes of combined bending and axial compression loading. The paper follows the work reported by the same authors in 2003 [Macdonald, M, Rhodes J. and Kotelko M. Behaviour of stainless steel columns under combined bending and axial compression loading. Proceedings of the 10th Symposium on Stability of Structures, Zakopane, Poland. 2003], but here, three different methods of analysis are employed: (i) the Eurocode 3, Part 1.4 design code using an enhanced 0.2% proof stress combined with a full section moment capacity within the interaction formula with nominal levels of loading eccentricity, (ii) the same approach using the Polish cold formed carbon steel code PN-90/B-03200 to ascertain its applicability and (iii), the same approaches but using the true eccentricity with reference to the unsupported length of the columns. The results are compared with those obtained from a series of compression tests performed on cold-formed stainless steel Type 304 stub columns of lipped channel cross-section for the same conditions.

Forces in stainless steel, TiMolium® and TMA® intrusion arches, with different bending magnitudes

The present study compared forces in stainless steel, TiMolium and TMA, V-bend intrusion arches with different magnitudes of flexion. The sample consisted of rectangular-section wires, caliber .017" x .025", with ten arches of each alloy. All V-bends were made 48 mm from the midline, using the same phantom upper jaw, maintaining the same distance between the tubes fixed to the molars and the midline. Loads necessary to deflect the arches by 5, 10, 15 and 20 mm were measured by means of an Instron dynamometer with a 1 kgf load cell. Calculations for sample size confirmed the suitability of using 10 arches of each alloy. Variance tests (ANOVA) of one factor and three levels, complemented by the Tukey test for multiple comparisons, identified that TMA(R) intrusion arches required a smaller quantity of load in relation to conventional steel and TiMolium at all levels of flexion. Furthermore, TiMolium presented intermediary characteristics between steel and TMA, and in all alloys increase in distance entailed a significant increase in force between all registered values, and that the increase in load necessary to deflect the arches at the intervals tended to decrease from first to last interval, these differences being more significant in steel, less in TiMolium and practically non-existent in TMA.

Young's Diagnostics of Phase Singularities into Polychromatic Light Fields

Two original approaches for the diagnostics of phase singularities (such as optical vortices, screw dislocations of a wave front) based on the Young-Rubinowicz mOdel of diffraction phenomena are represented. Both techniques are implemented without using a separate reference wave, as in common interference techniques. That is why they are very convenient for analysis of spatially coherent polychromatic fields. The first technique is based on the use of an opaque strip as the diffraction device. Bending Young's interference fringes produced by the edge diffraction waves from two rims of the strip within the geometrical shadow region reflect helicity of a wave front, so that the direction and magnitude of bending correspond directly to the sign and the modulus of topological charge of the optical vortex, respectively. This technique is practicable for diagnostics of isolated polychromatic vortices, such as rainbow Laguerre-Gaussian mode, where the condition of mutual spectral purity is satisfied. Another technique is based on the use of knife-edge diffraction. The edge of an opaque screen serves as the source of a reference wave, which interferes with the tested field within the directly illuminated region. One observes typical interference forklets near the geometrical shadow boundary, which detect optical vortices. This technique is more applicable to diagnostics of phase singularities in polychromatic speckle fields due to the condition of mutual spectral purity is satisfied automatically.

Structural Basis for p53 Binding-induced DNA Bending

Specific p53 binding-induced DNA bending has important biological implications such as transcription activation. However, the detailed structures of the bent DNA and the p53-DNA complex are still unavailable, hampering our understanding of the mechanism for p53-induced DNA bending and its consequent biological significance. To gain insight into the p53 binding-induced DNA bending, we performed molecular dynamics simulations on DNA segments with the consensus sequence for p53-specific binding, half site DNA-p53 complexes, and full site DNA-p53 complexes. We show that each DNA-bound p53 core domain caused a local DNA conformational change within the quarter site; upon the binding of the p53 dimer, there was an apparent DNA bending at the center of the half site; when bound with two p53 dimers, the full site DNAs with two different sequences bent 20 and 35 degrees, respectively. These results are in agreement with experimental observations. Our simulations demonstrate that the two p53 dimers favored a staggered conformation in which they make favorable interactions at the interface. This dimer-dimer interface organization necessitated conformational changes in the DNA, leading to the bending at the center of the full site, which in turn is dependent on the DNA sequence. Overall, our results provide the detailed atomic model for the DNA-p53 tetramer complex and delineate the roles of DNA-p53, p53 dimer-dimer interactions, and DNA sequence in specific p53 binding-induced DNA conformational changes.