Internal friction of single polypeptide chains at high stretch.

PubMed

Khatri, Bhavin S; Byrne, Katherine; Kawakami, Masaru; Brockwell, David J; Smith, D Alastair; Radford, Sheena E; McLeish, Tom C B

2008-01-01

Experiments that measure the viscoelasticity of single molecules from the Brownian fluctuations of an atomic force microscope (AFM) have provided a new window onto their internal dynamics in an underlying conformational landscape. Here we develop and apply these methods to examine the internal friction of unfolded polypeptide chains at high stretch. The results reveal a power law dependence of internal friction with tension (exponent 1.3 +/- 0.5) and a relaxation time approximately independent of force. To explain these results we develop a frictional worm-like chain (FWLC) model based on the Rayleigh dissipation function of a stiff chain with dynamical resistance to local bending. We analyse the dissipation rate integrated over the chain length by its Fourier components to calculate an effective tension-dependent friction constant for the end-to-end vector of the chain. The result is an internal friction that increases as a power law with tension with an exponent 3/2, consistent with experiment. Extracting the intrinsic bending friction constant of the chain it is found to be approximately 7 orders of magnitude greater than expected from solvent friction alone; a possible explanation we offer is that the underlying energy landscape for bending amino acids and/or peptide bond is rough, consistent with recent results on both proteins and polysaccharides.

Local vibrational modes of the water dimer - Comparison of theory and experiment

NASA Astrophysics Data System (ADS)

Kalescky, R.; Zou, W.; Kraka, E.; Cremer, D.

2012-12-01

Local and normal vibrational modes of the water dimer are calculated at the CCSD(T)/CBS level of theory. The local H-bond stretching frequency is 528 cm-1 compared to a normal mode stretching frequency of just 143 cm-1. The adiabatic connection scheme between local and normal vibrational modes reveals that the lowering is due to mass coupling, a change in the anharmonicity, and coupling with the local HOH bending modes. The local mode stretching force constant is related to the strength of the H-bond whereas the normal mode stretching force constant and frequency lead to an erroneous underestimation of the H-bond strength.

Accurate calibration and uncertainty estimation of the normal spring constant of various AFM cantilevers.

PubMed

Song, Yunpeng; Wu, Sen; Xu, Linyan; Fu, Xing

2015-03-10

Measurement of force on a micro- or nano-Newton scale is important when exploring the mechanical properties of materials in the biophysics and nanomechanical fields. The atomic force microscope (AFM) is widely used in microforce measurement. The cantilever probe works as an AFM force sensor, and the spring constant of the cantilever is of great significance to the accuracy of the measurement results. This paper presents a normal spring constant calibration method with the combined use of an electromagnetic balance and a homemade AFM head. When the cantilever presses the balance, its deflection is detected through an optical lever integrated in the AFM head. Meanwhile, the corresponding bending force is recorded by the balance. Then the spring constant can be simply calculated using Hooke's law. During the calibration, a feedback loop is applied to control the deflection of the cantilever. Errors that may affect the stability of the cantilever could be compensated rapidly. Five types of commercial cantilevers with different shapes, stiffness, and operating modes were chosen to evaluate the performance of our system. Based on the uncertainty analysis, the expanded relative standard uncertainties of the normal spring constant of most measured cantilevers are believed to be better than 2%.

Metachronal Motion of Artificial Magnetic Cilia

NASA Astrophysics Data System (ADS)

Hanasoge, Srinivas; Hesketh, Peter; Alexeev, Alexander

2017-11-01

Most microorganisms use asymmetrically oscillating hair like cilia on their surface to achieve fluid transport. These cilia are often seen to beat in a metachronal fashion with a constant phase difference with the neighbors which generates a travelling wave. Although the origin of metachronal waves in such cilia is not well understood, mimicking such behavior in synthetic systems could prove useful in achieving similar advantages. In this work, we demonstrate metachronal waves in synthetic magnetic ciliary systems. The soft magnetic cilia are forced by a uniform rotating magnetic field. The cilia bend as the field rotates and tend to align along the direction of field to minimize the potential energy. Longer cilia bend to a larger degree, while the shorter cilia show less bending. This difference in the bending of cilia based on their length leads to a phase difference in their oscillation cycle. We exploit this phase differences to metachronally oscillate the synthetic cilia. We fabricate an array consisting of cilia with increasing lengths, in which the cilia beat with a constant phase difference with the neighboring cilia, producing a travelling wave. Such behavior could potentially be useful in enhanced fluid and particle transport as seen in natural systems. USDA.

Viscoelastic deformation of lipid bilayer vesicles.

PubMed

Wu, Shao-Hua; Sankhagowit, Shalene; Biswas, Roshni; Wu, Shuyang; Povinelli, Michelle L; Malmstadt, Noah

2015-10-07

Lipid bilayers form the boundaries of the cell and its organelles. Many physiological processes, such as cell movement and division, involve bending and folding of the bilayer at high curvatures. Currently, bending of the bilayer is treated as an elastic deformation, such that its stress-strain response is independent of the rate at which bending strain is applied. We present here the first direct measurement of viscoelastic response in a lipid bilayer vesicle. We used a dual-beam optical trap (DBOT) to stretch 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) giant unilamellar vesicles (GUVs). Upon application of a step optical force, the vesicle membrane deforms in two regimes: a fast, instantaneous area increase, followed by a much slower stretching to an eventual plateau deformation. From measurements of dozens of GUVs, the average time constant of the slower stretching response was 0.225 ± 0.033 s (standard deviation, SD). Increasing the fluid viscosity did not affect the observed time constant. We performed a set of experiments to rule out heating by laser absorption as a cause of the transient behavior. Thus, we demonstrate here that the bending deformation of lipid bilayer membranes should be treated as viscoelastic.

Viscoelastic deformation of lipid bilayer vesicles†

PubMed Central

Wu, Shao-Hua; Sankhagowit, Shalene; Biswas, Roshni; Wu, Shuyang; Povinelli, Michelle L.

2015-01-01

Lipid bilayers form the boundaries of the cell and its organelles. Many physiological processes, such as cell movement and division, involve bending and folding of the bilayer at high curvatures. Currently, bending of the bilayer is treated as an elastic deformation, such that its stress-strain response is independent of the rate at which bending strain is applied. We present here the first direct measurement of viscoelastic response in a lipid bilayer vesicle. We used a dual-beam optical trap (DBOT) to stretch 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) giant unilamellar vesicles (GUVs). Upon application of a step optical force, the vesicle membrane deforms in two regimes: a fast, instantaneous area increase, followed by a much slower stretching to an eventual plateau deformation. From measurements of dozens of GUVs, the average time constant of the slower stretching response was 0.225 ± 0.033 s (standard deviation, SD). Increasing the fluid viscosity did not affect the observed time constant. We performed a set of experiments to rule out heating by laser absorption as a cause of the transient behavior. Thus, we demonstrate here that the bending deformation of lipid bilayer membranes should be treated as viscoelastic. PMID:26268612

Theory of high-force DNA stretching and overstretching.

PubMed

Storm, C; Nelson, P C

2003-05-01

Single-molecule experiments on single- and double-stranded DNA have sparked a renewed interest in the force versus extension of polymers. The extensible freely jointed chain (FJC) model is frequently invoked to explain the observed behavior of single-stranded DNA, but this model does not satisfactorily describe recent high-force stretching data. We instead propose a model (the discrete persistent chain) that borrows features from both the FJC and the wormlike chain, and show that it resembles the data more closely. We find that most of the high-force behavior previously attributed to stretch elasticity is really a feature of the corrected entropic elasticity; the true stretch compliance of single-stranded DNA is several times smaller than that found by previous authors. Next we elaborate our model to allow coexistence of two conformational states of DNA, each with its own stretch and bend elastic constants. Our model is computationally simple and gives an excellent fit through the entire overstretching transition of nicked, double-stranded DNA. The fit gives the first value for the bend stiffness of the overstretched state. In particular, we find the effective bend stiffness for DNA in this state to be about 12 nm k(B)T, a value quite different from either the B-form or single-stranded DNA.

Accurate Calibration and Uncertainty Estimation of the Normal Spring Constant of Various AFM Cantilevers

PubMed Central

Song, Yunpeng; Wu, Sen; Xu, Linyan; Fu, Xing

2015-01-01

Measurement of force on a micro- or nano-Newton scale is important when exploring the mechanical properties of materials in the biophysics and nanomechanical fields. The atomic force microscope (AFM) is widely used in microforce measurement. The cantilever probe works as an AFM force sensor, and the spring constant of the cantilever is of great significance to the accuracy of the measurement results. This paper presents a normal spring constant calibration method with the combined use of an electromagnetic balance and a homemade AFM head. When the cantilever presses the balance, its deflection is detected through an optical lever integrated in the AFM head. Meanwhile, the corresponding bending force is recorded by the balance. Then the spring constant can be simply calculated using Hooke’s law. During the calibration, a feedback loop is applied to control the deflection of the cantilever. Errors that may affect the stability of the cantilever could be compensated rapidly. Five types of commercial cantilevers with different shapes, stiffness, and operating modes were chosen to evaluate the performance of our system. Based on the uncertainty analysis, the expanded relative standard uncertainties of the normal spring constant of most measured cantilevers are believed to be better than 2%. PMID:25763650

Creative wire bending--the force system from step and V bends.

PubMed

Burstone, C J; Koenig, H A

1988-01-01

The force system produced by wires with steps and V bends was studied analytically by means of a small deflection mathematic analysis. Characteristic force relationships were found in both the step and the V bend. Step bands centrally placed between adjacent brackets produce unidirectional couples that are equal in magnitude. Along with these couples, vertical or horizontal forces are produced depending upon the plane of activation. Mesiodistal placement of step bends is not critical because very little alteration in force system occurs if a step is centered or positioned off center. V bends, on the other hand, are very sensitive to the positioning mesiodistally of the apex of the V. If the apex of the V bend is placed on center, equal and opposite couples are produced. As the V-bend apex is moved off center, predictable combinations of moments and forces are created. A method for determination of the relative force system is described that allows for simple interpretation and prediction of the force system from a V bend. The clinical applications of these data and a rational basis for wire bending are presented based on the producing of a desired force system.

Effect of wing bend on the experimental force and moment characteristics of an oblique wing

NASA Technical Reports Server (NTRS)

Hopkins, E. J.; Nelson, E. R.

1976-01-01

Static longitudinal and lateral/directional force and moment characteristics are presented for an elliptical oblique wing mounted on top of a Sears-Haack body of revolution. The wing had an aspect ratio of 6 (based on the unswept span) and was tested at various sweep angles relative to the body axis ranging from 0 to 60 deg. In an attempt to create more symmetrical spanwise wing stalling characteristics, both wing panels were bent upward to produce washout on the trailing wing panel and washing on the leading wing panel. Small fluorescent tufts were attached to the wing surface to indicate the stall progression on the wing. The tests were conducted throughout a Mach number range from 0.6 to 1.4 at a constant unit Reynolds number of 8.2 x 10 per meter. The test results indicate that upward bending of the wing panels had only a small effect on the linearity of the moment curves and would require an impractical wing-pivot location at low lift to eliminate the rolling moment resulting from this bending.

Torsion and Antero-Posterior Bending in the In Vivo Human Tibia Loading Regimes during Walking and Running

PubMed Central

Yang, Peng-Fei; Sanno, Maximilian; Ganse, Bergita; Koy, Timmo; Brüggemann, Gert-Peter; Müller, Lars Peter; Rittweger, Jörn

2014-01-01

Bending, in addition to compression, is recognized to be a common loading pattern in long bones in animals. However, due to the technical difficulty of measuring bone deformation in humans, our current understanding of bone loading patterns in humans is very limited. In the present study, we hypothesized that bending and torsion are important loading regimes in the human tibia. In vivo tibia segment deformation in humans was assessed during walking and running utilizing a novel optical approach. Results suggest that the proximal tibia primarily bends to the posterior (bending angle: 0.15°–1.30°) and medial aspect (bending angle: 0.38°–0.90°) and that it twists externally (torsion angle: 0.67°–1.66°) in relation to the distal tibia during the stance phase of overground walking at a speed between 2.5 and 6.1 km/h. Peak posterior bending and peak torsion occurred during the first and second half of stance phase, respectively. The peak-to-peak antero-posterior (AP) bending angles increased linearly with vertical ground reaction force and speed. Similarly, peak-to-peak torsion angles increased with the vertical free moment in four of the five test subjects and with the speed in three of the test subjects. There was no correlation between peak-to-peak medio-lateral (ML) bending angles and ground reaction force or speed. On the treadmill, peak-to-peak AP bending angles increased with walking and running speed, but peak-to-peak torsion angles and peak-to-peak ML bending angles remained constant during walking. Peak-to-peak AP bending angle during treadmill running was speed-dependent and larger than that observed during walking. In contrast, peak-to-peak tibia torsion angle was smaller during treadmill running than during walking. To conclude, bending and torsion of substantial magnitude were observed in the human tibia during walking and running. A systematic distribution of peak amplitude was found during the first and second parts of the stance phase. PMID:24732724

Torsion and antero-posterior bending in the in vivo human tibia loading regimes during walking and running.

PubMed

Yang, Peng-Fei; Sanno, Maximilian; Ganse, Bergita; Koy, Timmo; Brüggemann, Gert-Peter; Müller, Lars Peter; Rittweger, Jörn

2014-01-01

Bending, in addition to compression, is recognized to be a common loading pattern in long bones in animals. However, due to the technical difficulty of measuring bone deformation in humans, our current understanding of bone loading patterns in humans is very limited. In the present study, we hypothesized that bending and torsion are important loading regimes in the human tibia. In vivo tibia segment deformation in humans was assessed during walking and running utilizing a novel optical approach. Results suggest that the proximal tibia primarily bends to the posterior (bending angle: 0.15°-1.30°) and medial aspect (bending angle: 0.38°-0.90°) and that it twists externally (torsion angle: 0.67°-1.66°) in relation to the distal tibia during the stance phase of overground walking at a speed between 2.5 and 6.1 km/h. Peak posterior bending and peak torsion occurred during the first and second half of stance phase, respectively. The peak-to-peak antero-posterior (AP) bending angles increased linearly with vertical ground reaction force and speed. Similarly, peak-to-peak torsion angles increased with the vertical free moment in four of the five test subjects and with the speed in three of the test subjects. There was no correlation between peak-to-peak medio-lateral (ML) bending angles and ground reaction force or speed. On the treadmill, peak-to-peak AP bending angles increased with walking and running speed, but peak-to-peak torsion angles and peak-to-peak ML bending angles remained constant during walking. Peak-to-peak AP bending angle during treadmill running was speed-dependent and larger than that observed during walking. In contrast, peak-to-peak tibia torsion angle was smaller during treadmill running than during walking. To conclude, bending and torsion of substantial magnitude were observed in the human tibia during walking and running. A systematic distribution of peak amplitude was found during the first and second parts of the stance phase.

Moving Force Identification: a Time Domain Method

NASA Astrophysics Data System (ADS)

Law, S. S.; Chan, T. H. T.; Zeng, Q. H.

1997-03-01

The solution for the vertical dynamic interaction forces between a moving vehicle and the bridge deck is analytically derived and experimentally verified. The deck is modelled as a simply supported beam with viscous damping, and the vehicle/bridge interaction force is modelled as one-point or two-point loads with fixed axle spacing, moving at constant speed. The method is based on modal superposition and is developed to identify the forces in the time domain. Both cases of one-point and two-point forces moving on a simply supported beam are simulated. Results of laboratory tests on the identification of the vehicle/bridge interaction forces are presented. Computation simulations and laboratory tests show that the method is effective, and acceptable results can be obtained by combining the use of bending moment and acceleration measurements.

Fringe Field Effects on Bending Magnets, Derived for TRANSPORT/TURTLE

DOE Office of Scientific and Technical Information (OSTI.GOV)

Molloy, Riley; Blitz, Sam

2013-08-05

A realistic magnetic dipole has complex effects on a charged particle near the entrance and exit of the magnet, even with a constant and uniform magnetic field deep within the interior of the magnet. To satisfy Maxwell's equations, the field lines near either end of a realistic magnet are significantly more complicated, yielding non-trivial forces. The effects of this fringe field are calculated to first order, applying both the paraxial and thin lens approximations. We find that, in addition to zeroth order effects, the position of a particle directly impacts the forces in the horizontal and vertical directions.

Mechanical behavior of a novel non-fusion scoliosis correction device.

PubMed

Wessels, M; Hekman, E E G; Verkerke, G J

2013-11-01

We developed an innovative non-fusion correction system (XS LATOR) consisting of two individual implants that are extendable and extremely flexible. One implant, the XS LAT, generates a lateral, bending moment and one implant, the XS TOR, generates a torsion moment. Two 'inverse' implants were developed for generating torsion and lateral bending in a porcine model was tested for force delivery. An in vitro experiment was set up to describe the mechanical behavior of both implants. Narrow and wide ('inverse') versions of the XS TOR and XS LAT were mounted on an apparatus that was able to simulate different spinal geometries. The implants were anchored to three artificial vertebrae with integrated 6D force sensors, after which the vertebrae were rotated and translated towards the demanded position. The reaction forces and moments were recorded in all configurations. The maximal (lateral) bending moment, which occurred at the middle vertebra, was determined and, similarly, torque applied at the center of rotation of the middle vertebra was calculated. As expected, the wide and the small versions of the XS TOR generate a torque that increases during the growth of the system. Similarly, the XS LAT generates a bending moment that slightly increases during the growth of the system. The produced moments approximate the theoretically predicted ones. The contribution to the spinal stiffness ranges between 0.01Nm/° and 0.04Nm/° in bending and between 0.03Nm/° and 0.08Nm/° in torsion. The XS TOR and the XS LAT are able to generate a torque and a bending moment that remain (fairly) constant during spinal growth when a shape change due to the generated moment/torque is achieved. The stiffness of the implants is extremely low, being only a fraction of the stiffness of conventional, spinal fusion constructs. Current fusion systems, such as non-segmental spinal constructs generally, have 11 times higher stiffness in torsion and 6 times higher stiffness in lateral bending. Implantation of the XS LATOR adds 9% stiffness in axial rotation and 17% stiffness in lateral bending (to the original spinal stiffness). By preserving the flexibility of the spine after implantation, fusion of the vertebrae in the instrumented region is likely to be prevented. © 2013 Elsevier Ltd. All rights reserved.

[Experimental study of recovery force of surface-modified TiNi memory alloy rod].

PubMed

Wang, Aiyuan; Peng, Jiang; Zhang, Xian; Xu, Wenjin; Wang, Xing; Sun, Minxue; Lu, Shibi

2006-08-01

The recovery force of Ti-Nb coated and uncoated TiNi shape memory alloy rods was investigated. The rods were 6.0 mm, 6.5 mm and 7.0 mm in diameter respectively. The mean transition temperature was 33.0 degrees C. The rods were stored at -18 degrees C and pre-bent with a three-point bending fixture, the span was 20. 0 centimeters and the deflections were 5.0 mm, 10.0 mm, 15.0 mm and 20.0 mm, respectively. The rods were then heated in a constant temperature saline solution chamber. The experimental temperature was 37.0 C and 50.0 C respectively. The recovery force was measured in a constant displacement mode on biomaterial test machine. The results showed that the recovery force of the memory alloy rod increased with increasing recovery temperature, rod diameter and deformation of both Ti-Nb coated and uncoated surface. The recovery force of Ti-Nb coated rods of 6.0 and 6.5 millimeter in diameter was lower than the uncoated rods in the same diameter. However, the recovery force of 7.0-mm-diameter rods showed no significant difference between coated and uncoated surface.

New method for evaluation of bendability based on three-point-bending and the evolution of the cross-section moment

NASA Astrophysics Data System (ADS)

Troive, L.

2017-09-01

Friction-free 3-point bending has become a common test-method since the VDA 238-100 plate-bending test [1] was introduced. According to this test the criterion for failure is when the force suddenly drops. It was found by the author that the evolution of the cross-section moment is a more preferable measure regarding the real material response instead of the force. Beneficially, the cross-section moment gets more or less a constant maximum steady-state level when the cross-section becomes fully plastified. An expression for the moment M is presented that fulfils the criteria for energy of conservation at bending. Also an expression calculating the unit-free moment, M/Me, i.e. current moment to elastic-moment ratio, is demonstrated specifically proposed for detection of failures. The mathematical expressions are simple making it easy to transpose measured force F and stroke position S to the corresponding cross-section moment M. From that point of view it’s even possible to implement, e.g. into a conventional measurement system software, studying the cross-section moment in real-time during a test. It’s even possible to calculate other parameters such as flow-stress and shape of curvature at every stage. It has been tested on different thicknesses and grades within the range from 1.0 to 10 mm with very good results. In this paper the present model is applied on a 6.1 mm hot-rolled high strength steel from the same batch at three different conditions, i.e. directly quenched, quenched and tempered, and a third variant quench and tempered with levelling. It will be shown that very small differences in material-response can be predicted by this method.

A parabolic mirror x-ray collimator

NASA Astrophysics Data System (ADS)

Franks, A.; Jackson, K.; Yacoot, A.

2000-05-01

A robust and stable x-ray collimator has been developed to produce a parallel beam of x-rays by total external reflection from a parabolic mirror. The width of the gold-coated silica mirror varies along its length, which allows it to be bent from a plane surface into a parabolic form by application of unequal bending forces at its ends. A family of parabolas of near constant focal length can be formed by changing the screw-applied bending force, thus allowing the collimator to cater for a range of wavelengths by the turning of a screw. Even with radiation with a wavelength as short as that as Mo Kicons/Journals/Common/alpha" ALT="alpha" ALIGN="TOP"/> 1 (icons/Journals/Common/lambda" ALT="lambda" ALIGN="TOP"/> = 0.07 nm), a gain in flux by a factor of 5.5 was achieved. The potential gain increases with wavelength, e.g. for Cu Kicons/Journals/Common/alpha" ALT="alpha" ALIGN="TOP"/> 1 radiation this amounts to over a factor of ten.

Nonharmonic oscillations of nanosized cantilevers due to quantum-size effects

NASA Astrophysics Data System (ADS)

Olsen, Martin; Gradin, Per; Lindefelt, Ulf; Olin, Håkan

2010-02-01

Using a one-dimensional jellium model and standard beam theory we calculate the spring constant of a vibrating nanowire cantilever. By using the asymptotic energy eigenvalues of the standing electron waves over the nanometer-sized cross-section area, the change in the grand canonical potential is calculated and hence the force and the spring constant. As the wire is bent more electron states fits in its cross section. This has an impact on the spring “constant” which oscillates slightly with the bending of the wire. In this way we obtain an amplitude-dependent resonance frequency of the oscillations that should be detectable.

Backed Bending Actuator

NASA Technical Reports Server (NTRS)

Costen, Robert C.; Su, Ji

2004-01-01

Bending actuators of a proposed type would partly resemble ordinary bending actuators, but would include simple additional components that would render them capable of exerting large forces at small displacements. Like an ordinary bending actuator, an actuator according to the proposal would include a thin rectangular strip that would comprise two bonded layers (possibly made of electroactive polymers with surface electrodes) and would be clamped at one end in the manner of a cantilever beam. Unlike an ordinary bending actuator, the proposed device would include a rigid flat backplate that would support part of the bending strip against backward displacement; because of this feature, the proposed device is called a backed bending actuator. When an ordinary bending actuator is inactive, the strip typically lies flat, the tip displacement is zero, and the force exerted by the tip is zero. During activation, the tip exerts a transverse force and undergoes a bending displacement that results from the expansion or contraction of one or more of the bonded layers. The tip force of an ordinary bending actuator is inversely proportional to its length; hence, a long actuator tends to be weak. The figure depicts an ordinary bending actuator and the corresponding backed bending actuator. The bending, the tip displacement (d(sub t)), and the tip force (F) exerted by the ordinary bending actuator are well approximated by the conventional equations for the loading and deflection of a cantilever beam subject to a bending moment which, in this case, is applied by the differential expansion or contraction of the bonded layers. The bending, displacement, and tip force of the backed bending actuator are calculated similarly, except that it is necessary to account for the fact that the force F(sub b) that resists the displacement of the tip could be sufficient to push part of the strip against the backplate; in such a condition, the cantilever beam would be effectively shortened (length L*) and thereby stiffened and, hence, made capable of exerting a greater tip force for a given degree of differential expansion or contraction of the bonded layers. Taking all of these effects into account, the cantilever-beam equations show that F(sub b) would be approximately inversely proportional to d(sup 1/2) for d less than a calculable amount, denoted the transition displacement (dt). For d less than d(sub t), part of the strip would be pressed against the backplate. Therefore, the force F(sub b) would be very large for d at or near zero and would decrease as d increases toward d(sub t). At d greater than d(sub t), none of the strip would be pressed against the backplate and F(sub b) would equal the tip force F of the corresponding ordinary bending actuator. The advantage of the proposal is that a backed bending actuator could be made long to obtain large displacement when it encountered little resistance but it could also exert a large zero-displacement force, so that it could more easily start the movement of a large mass, throw a mechanical switch, or release a stuck mechanism.

Influence of sliding friction on leveling force of superelastic NiTi arch wire: A computational analysis

NASA Astrophysics Data System (ADS)

Razali, M. F.; Mahmud, A. S.; Mokhtar, N.; Abdullah, J.

2017-10-01

This study investigated the influence of sliding friction toward the effective force of superelastic NiTi arch wire applied in orthodontic bracing for tooth leveling. A three-dimensional finite-element model integrated with superelastic subroutine and contact interaction was used to predict the contribution of friction on force-deflection curve of NiTi wire in three brackets bending configuration. It was found that the friction between the wire and the bracket increased proportionally as a function of wire deflection, thus transforming the constant force characteristic of NiTi material into a slope. The highest magnitude of sliding friction was measured to be 3.1 N and 2.2 N with respect to the activation and deactivation of the arch wire.

Analytic description of the frictionally engaged in-plane bending process incremental swivel bending (ISB)

NASA Astrophysics Data System (ADS)

Frohn, Peter; Engel, Bernd; Groth, Sebastian

2018-05-01

Kinematic forming processes shape geometries by the process parameters to achieve a more universal process utilizations regarding geometric configurations. The kinematic forming process Incremental Swivel Bending (ISB) bends sheet metal strips or profiles in plane. The sequence for bending an arc increment is composed of the steps clamping, bending, force release and feed. The bending moment is frictionally engaged by two clamping units in a laterally adjustable bending pivot. A minimum clamping force hindering the material from slipping through the clamping units is a crucial criterion to achieve a well-defined incremental arc. Therefore, an analytic description of a singular bent increment is developed in this paper. The bending moment is calculated by the uniaxial stress distribution over the profiles' width depending on the bending pivot's position. By a Coulomb' based friction model, necessary clamping force is described in dependence of friction, offset, dimensions of the clamping tools and strip thickness as well as material parameters. Boundaries for the uniaxial stress calculation are given in dependence of friction, tools' dimensions and strip thickness. The results indicate that changing the bending pivot to an eccentric position significantly affects the process' bending moment and, hence, clamping force, which is given in dependence of yield stress and hardening exponent. FE simulations validate the model with satisfactory accordance.

Control of Superelastic Behavior of NiTi Wires Aided by Thermomechanical Treatment with Reference to Three-Point Bending

NASA Astrophysics Data System (ADS)

Shahmir, Hamed; Nili-Ahmadabadi, Mahmoud; Naghdi, Fariba; Habibi-Parsa, Mohammad; Haririan, Ismaeil

2014-04-01

The aim of this study is to investigate the effect of thermomechanical treatment on the superelastic behavior of a Ti-50.5 at.%Ni wire in terms of loading/unloading plateau, mechanical hysteresis, and permanent set to optimize these parameters for orthodontic applications. A new three-point bending fixture, oral cavity configuration three-point bending (OCTPB) test, was utilized to determine the superelastic property in clinical condition, and therefore, the tests were carried out at 37 °C. The results indicate that the thermomechanical treatment is crucial for thermal transformation and mechanically induced transformation characteristics of the wire. Annealing of thermomechanically treated specimens at 300 and 400 °C for 1/2 and 1 h leads to good superelasticity for orthodontic applications. However, the best superelasticity at body temperature is obtained after annealing at 300 °C for 1/2 h with regard to low and constant unloading force and minimum permanent set.

Dynamics of a Pipeline under the Action of Internal Shock Pressure

NASA Astrophysics Data System (ADS)

Il'gamov, M. A.

2017-11-01

The static and dynamic bending of a pipeline in the vertical plane under the action of its own weight is considered with regard to the interaction of the internal pressure with the curvature of the axial line and the axisymmetric deformation. The pressure consists of a constant and timevarying parts and is assumed to be uniformly distributed over the entire span between the supports. The pipeline reaction to the stepwise increase in the pressure is analyzed in the case where it is possible to determine the exact solution of the problem. The initial stage of bending determined by the smallness of elastic forces as compared to the inertial forces is introduced into the consideration. At this stage, the solution is sought in the form of power series and the law of pressure variation can be arbitrary. This solution provides initial conditions for determining the further process. The duration of the inertial stage is compared with the times of sharp changes of the pressure and the shock waves in fluids. The structure parameters are determined in the case where the shock pressure is accepted only by the inertial forces in the pipeline.

Internal vibrations of a molecule consisting of rigid segments. I - Non-interacting internal vibrations

NASA Technical Reports Server (NTRS)

He, X. M.; Craven, B. M.

1993-01-01

For molecular crystals, a procedure is proposed for interpreting experimentally determined atomic mean square anisotropic displacement parameters (ADPs) in terms of the overall molecular vibration together with internal vibrations with the assumption that the molecule consists of a set of linked rigid segments. The internal librations (molecular torsional or bending modes) are described using the variable internal coordinates of the segmented body. With this procedure, the experimental ADPs obtained from crystal structure determinations involving six small molecules (sym-trinitrobenzene, adenosine, tetra-cyanoquinodimethane, benzamide, alpha-cyanoacetic acid hydrazide and N-acetyl-L-tryptophan methylamide) have been analyzed. As a consequence, vibrational corrections to the bond lengths and angles of the molecule are calculated as well as the frequencies and force constants for each internal torsional or bending vibration.

Structural mechanics of DNA wrapping in the nucleosome.

PubMed

Battistini, Federica; Hunter, Christopher A; Gardiner, Eleanor J; Packer, Martin J

2010-02-19

Experimental X-ray crystal structures and a database of calculated structural parameters of DNA octamers were used in combination to analyse the mechanics of DNA bending in the nucleosome core complex. The 1kx5 X-ray crystal structure of the nucleosome core complex was used to determine the relationship between local structure at the base-step level and the global superhelical conformation observed for nucleosome-bound DNA. The superhelix is characterised by a large curvature (597 degrees) in one plane and very little curvature (10 degrees) in the orthogonal plane. Analysis of the curvature at the level of 10-step segments shows that there is a uniform curvature of 30 degrees per helical turn throughout most of the structure but that there are two sharper kinks of 50 degrees at +/-2 helical turns from the central dyad base pair. The curvature is due almost entirely to the base-step parameter roll. There are large periodic variations in roll, which are in phase with the helical twist and account for 500 degrees of the total curvature. Although variations in the other base-step parameters perturb the local path of the DNA, they make minimal contributions to the total curvature. This implies that DNA bending in the nucleosome is achieved using the roll-slide-twist degree of freedom previously identified as the major degree of freedom in naked DNA oligomers. The energetics of bending into a nucleosome-bound conformation were therefore analysed using a database of structural parameters that we have previously developed for naked DNA oligomers. The minimum energy roll, the roll flexibility force constant and the maximum and minimum accessible roll values were obtained for each base step in the relevant octanucleotide context to account for the effects of conformational coupling that vary with sequence context. The distribution of base-step roll values and corresponding strain energy required to bend DNA into the nucleosome-bound conformation defined by the 1kx5 structure were obtained by applying a constant bending moment. When a single bending moment was applied to the entire sequence, the local details of the calculated structure did not match the experiment. However, when local 10-step bending moments were applied separately, the calculated structure showed excellent agreement with experiment. This implies that the protein applies variable bending forces along the DNA to maintain the superhelical path required for nucleosome wrapping. In particular, the 50 degrees kinks are constraints imposed by the protein rather than a feature of the 1kx5 DNA sequence. The kinks coincide with a relatively flexible region of the sequence, and this is probably a prerequisite for high-affinity nucleosome binding, but the bending strain energy is significantly higher at these points than for the rest of the sequence. In the most rigid regions of the sequence, a higher strain energy is also required to achieve the standard 30 degrees curvature per helical turn. We conclude that matching of the DNA sequence to the local roll periodicity required to achieve bending, together with the increased flexibility required at the kinks, determines the sequence selectivity of DNA wrapping in the nucleosome. 2009 Elsevier Ltd. All rights reserved.

Low-energy vibrations of the group 10 metal monocarbonyl MCO (M = Ni, Pd, and Pt): rotational spectroscopy and force field analysis.

PubMed

Okabayashi, Toshiaki; Yamamoto, Takuya; Okabayashi, Emi Y; Tanimoto, Mitsutoshi

2011-03-17

The rotational spectra of NiCO and PdCO in the ground and ν(2) excited vibrational states were observed by employing a source-modulated microwave spectrometer. The NiCO and PdCO molecules were generated in a free space cell by the sputtering reaction of nickel and palladium sheets, respectively, lining the inner surface of a stainless steel cathode with a dc glow plasma of CO and Ar. The molecular constants of NiCO and PdCO were determined by least-squares analysis. By force field analysis for the molecular constants of not only NiCO and PdCO but also of PtCO as previously reported, the harmonic force constants were determined for these three group 10 metal monocarbonyls. The vibrational wavenumbers derived for the lower M-C stretching vibrations were in good agreement with those obtained from the IR spectra in noble gas matrices and those predicted by several quantum chemical calculations published in the past. The bending vibrational wavenumbers derived by the force field analysis were also consistent with most quantum chemical calculations previously reported, but showed systematic discrepancies from the matrix IR values by about 40 cm(-1), even after reassignment (ν(2) band → 2ν(2) band) of the matrix IR spectra of PdCO and PtCO.

Bending stiffness of catheters and guide wires.

PubMed

Wünsche, P; Werner, C; Bloss, P

2002-01-01

An important property of catheters and guide wires to assess their pushability behavior is their bending stiffness. To measure bending stiffness, a new bending module with a new clamping device was developed. This module can easily be mounted in commercially available tensile testing equipment, where bending force and deflection due to the bending force can be measured. To achieve high accuracy for the bending stiffness, the bending distance has to be measured with even higher accuracy by using a laser-scan micrometer. Measurement results of angiographic catheters and guide wires were presented and discussed. The bending stiffness shows a significant dependence on the angle of the test specimen's rotation around its length axis.

Curvature versus v-bends in a group B titanium T-loop spring.

PubMed

Martins, Renato Parsekian; Buschang, Peter H; Viecilli, Rodrigo; dos Santos-Pinto, Ary

2008-05-01

To compare the system of forces acting on curvature and preactivated V-bends in titanium T-loop springs (TTLSs) made of 0.017- x 0.025-inch TMA (titanium molibdenium alloy) wire. Pictures of TTLSs preactivated by curvature and V-bends were inserted in the LOOP software program to design both TTLSs. Symmetry was assured using the program. Both TTLSs used the same amount (length) of wire and had the same angulation between their anterior and posterior extremities when passive. The loops were activated 7 mm, and forces and moments were registered after each 0.5 mm of deactivation. The brackets were at the same height, separated by 23 mm and angulated 0 degrees . The preactivated curvature TTLS delivered horizontal forces ranging from 34 gF to 456 gF, while the TTLS preactivated by V-bends delivered forces ranging from 54 gF to 517 gF. The forces decreased more (30 gF vs 33 gF) with every 0.5 mm of activation on the preactivated V-bend TTLS than on the preactivated curvature TTLS. Vertical forces were low and clinically insignificant for both TTLSs. The moment to force (MF) ratios were systematically higher on the preactivated curvature than on the preactivated V-bend TTLS (from 5.8 mm to 38.8 mm vs 4.7 mm to 28.3 mm). Although both loops show symmetrical moments in their anterior and posterior extremities and can be used for group B anchorage, the curvature preactivated TTLS delivers lower horizontal forces and higher MF ratios than the acute preactivated V-bend TTLS.

Computer-assisted image analysis of plant growth, thigmomorphogenesis and gravitropism

NASA Technical Reports Server (NTRS)

Jaffe, M. J.; Wakefield, A. H.; Telewski, F.; Gulley, E.; Biro, R.

1985-01-01

A nonintrusive auxonometric system, based on the DARWIN image processor (Telewski et al. 1983 Plant Physiol 72: 177-181), is described and demonstrated in the analysis of gravitropism and thigmomorphogenesis in corn seedlings (Zea mays). Using this system, growth and bending of regularly shaped plants or organs can be quickly and accurately measured without, in any way, interfering with the plant. Furthermore, the growth and bending curves are automatically plotted. Thigmomorphogenesis in the aerial part of corn seedlings involves growth promotion at a low force load and growth retardation at higher force loads. The time courses of the two kinds of response are somewhat different, with retardation occurring immediately after mechanical perturbation and growth promotion taking somewhat longer to begin. Gravitropic experiments show that when dark-grown corn seedlings are placed on their side in the light, the resulting curvature is due to two consecutive morphological mechanisms. In the first instance, lasting for about 15 minutes, the elongation of the bottom edge of the plant accelerates, while the elongation of the top edge remains constant. After that, for the next 1.75 hours, the elongation of the top edge decelerates and stops while that of the bottom edge remains constant at the increased rate for most of the period. The measurements taken from both experiments at relatively high resolution (0.08-0.1 millimeter) show that the growth curves are not smooth but show many small irregularities which may or may not involve micronutations.

A correlation between extensional displacement and architecture of ionic polymer transducers

NASA Astrophysics Data System (ADS)

Akle, Barbar J.; Duncan, Andrew; Leo, Donald J.

2008-03-01

Ionic polymer transducers (IPT), sometimes referred to as artificial muscles, are known to generate a large bending strain and a moderate stress at low applied voltages (<5V). Bending actuators have limited engineering applications due to the low forcing capabilities and the need for complicated external devices to convert the bending action into rotating or linear motion desired in most devices. Recently Akle and Leo reported extensional actuation in ionic polymer transducers. In this study, extensional IPTs are characterized as a function of transducer architecture. In this study 2 actuators are built and there extensional displacement response is characterized. The transducers have similar electrodes while the middle membrane in the first is a Nafion / ionic liquid and an aluminum oxide - ionic liquid in the second. The first transducer is characterized for constant current input, voltage step input, and sweep voltage input. The model prediction is in agreement in both shape and magnitude for the constant current experiment. The values of α and β used are within the range of values reported in Akle and Leo. Both experiments and model demonstrate that there is a preferred direction of applying the potential so that the transducer will exhibit large deformations. In step response the model well predicted the negative potential and the early part of the step in the positive potential and failed to predict the displacement after approximately 180s has elapsed. The model well predicted the sweep response, and the observed 1st harmonic in the displacement further confirmed the existence of a quadratic in the charge response. Finally the aluminum oxide based transducer is characterized for a step response and compared to the Nafion based transducer. The second actuator demonstrated electromechanical extensional response faster than that in the Nafion based transducer. The Aluminum oxide based transducer is expected to provide larger forces and hence larger energy density.

Force system generated by elastic archwires with vertical V bends: a three-dimensional analysis.

PubMed

Upadhyay, Madhur; Shah, Raja; Peterson, Donald; Asaki, Takafumi; Yadav, Sumit; Agarwal, Sachin

2017-04-01

Our previous understanding of V-bend mechanics is primarily from two-dimensional (2D) analysis of archwire bracket interactions in the second order. These analyses do not take into consideration the three-dimensional (3D) nature of orthodontic appliances involving the third order. To quantify the force system generated in a 3D two bracket set up involving the molar and incisors with vertical V-bends. Maxillary molar and incisor brackets were arranged in a dental arch form and attached to load cells capable of measuring forces and moments in all three planes (x, y, and z) of space. Symmetrical V-bends (right and left sides) were placed at 11 different locations along rectangular beta-titanium archwires of various sizes at an angle of 150degrees. Each wire was evaluated for the 11 bend positions. Specifically, the vertical forces (Fz) and anterio-posterior moments (Mx) were analysed. Descriptive statistics were used to interpret the results. With increasing archwire size, Fz and Mx increased at the two brackets (P < 0.05). The vertical forces were linear and symmetric in nature, increasing in magnitude as the bends moved closer to either bracket. The Mx curves were asymmetric and non-linear displaying higher magnitudes for molar bracket. As the bends were moved closer to either bracket a distinct flattening of the incisor Mx curve was noted, implying no change in its magnitude. This article provides critical information on V-bend mechanics involving second order and third order archwire-bracket interactions. A model for determining this force system is described that might allow for easier translation to actual clinical practice. © The Author 2016. Published by Oxford University Press on behalf of the European Orthodontic Society. All rights reserved. For permissions, please email: journals.permissions@oup.com

Wire and Cable Cold Bending Test

NASA Technical Reports Server (NTRS)

Colozza, Anthony

2010-01-01

One of the factors in assessing the applicability of wire or cable on the lunar surface is its flexibility under extreme cold conditions. Existing wire specifications did not address their mechanical behavior under cold, cryogenic temperature conditions. Therefore tests were performed to provide this information. To assess this characteristic 35 different insulated wire and cable pieces were cold soaked in liquid nitrogen. The segments were then subjected to bending and the force was recorded. Any failure of the insulation or jacketing was also documented for each sample tested. The bending force tests were performed at room temperature to provide a comparison to the change in force needed to bend the samples due to the low temperature conditions. The results from the bending tests were plotted and showed how various types of insulated wire and cable responded to bending under cold conditions. These results were then used to estimate the torque needed to unroll the wire under these low temperature conditions.

Theory of nanoscale friction on chemically modified graphene

NASA Astrophysics Data System (ADS)

Ko, Jae-Hyeon; Kim, Yong-Hyun

2013-03-01

Recently, it is known from FFM experiments that friction force on graphene is significantly increased by chemical modification such as hydrogenation, oxidization, and fluorination, whereas adhesion properties are altered marginally. A novel nanotribological theory on two-dimensional materials is proposed on the basis of experimental results and first-principles density-functional theory (DFT) calculations. The proposed theory indicates that the total lateral stiffness that is the proportional constant of friction force is mostly associated with the out-of-plane bending stiffness of two-dimensional materials. This contrasts to the case of three-dimensional materials, in which the shear strength of materials determines nanoscale friction. We will discuss details of DFT calculations and how to generalize the current theory to three dimensional materials.

Bending stiffness, torsional stability, and insertion force of cementless femoral stems.

PubMed

Incavo, S J; Johnson, C C; Churchill, D L; Beynnon, B D

2001-04-01

In cementless total hip arthroplasty, increased femoral stem flexibility and decreased fracture propensity are desirable characteristics. The slotting and tapering of the stem have been introduced to achieve this. These features should not, however, be allowed to interfere with the ability of the distal stem to provide initial mechanical stability, especially under rotation. This study was done to investigate the ability of slotted and tapered stem designs to reduce stiffness and insertion force while still maintaining adequate torsional strength. The torsional strength, maximum insertion force, and insertional work of straight, slotted, and taper stems were measured by inserting each type into rigid polyurethane foam and torque testing to failure. Bending stiffness of each stem design was calculated using numerical methods. When compared to a straight stem, a unislot stem has similar torsional strength, maximum insertional force, and work of insertion. The bending stiffness is decreased by 19% to 82% depending on the bending direction. A trislot design decreased torque strength by 29%, maximal insertion force by 36%, and work by 11%. Bending stiffness was decreased by 74% and was not dependent on bending direction. A 0.5-mm taper decreased torque strength by 11% and insertional work by 14%. No difference was seen in maximum insertional force. We conclude that the design features studied (slots and taper) are effective in decreasing stem stiffness and reducing fracture propensity.

Distributed force probe bending model of critical dimension atomic force microscopy bias

NASA Astrophysics Data System (ADS)

Ukraintsev, Vladimir A.; Orji, Ndubuisi G.; Vorburger, Theodore V.; Dixson, Ronald G.; Fu, Joseph; Silver, Rick M.

2013-04-01

Critical dimension atomic force microscopy (CD-AFM) is a widely used reference metrology technique. To characterize modern semiconductor devices, small and flexible probes, often 15 to 20 nm in diameter, are used. Recent studies have reported uncontrolled and significant probe-to-probe bias variation during linewidth and sidewall angle measurements. To understand the source of these variations, tip-sample interactions between high aspect ratio features and small flexible probes, and their influence on measurement bias, should be carefully studied. Using theoretical and experimental procedures, one-dimensional (1-D) and two-dimensional (2-D) models of cylindrical probe bending relevant to carbon nanotube (CNT) AFM probes were developed and tested. An earlier 1-D bending model was refined, and a new 2-D distributed force (DF) model was developed. Contributions from several factors were considered, including: probe misalignment, CNT tip apex diameter variation, probe bending before snapping, and distributed van der Waals-London force. A method for extracting Hamaker probe-surface interaction energy from experimental probe-bending data was developed. Comparison of the new 2-D model with 1-D single point force (SPF) model revealed a difference of about 28% in probe bending. A simple linear relation between biases predicted by the 1-D SPF and 2-D DF models was found. The results suggest that probe bending can be on the order of several nanometers and can partially explain the observed CD-AFM probe-to-probe variation. New 2-D and three-dimensional CD-AFM data analysis software is needed to take full advantage of the new bias correction modeling capabilities.

A wave-bending structure at Ka-band using 3D-printed metamaterial

NASA Astrophysics Data System (ADS)

Wu, Junqiang; Liang, Min; Xin, Hao

2018-03-01

Three-dimensional printing technologies enable metamaterials of complex structures with arbitrary inhomogeneity. In this work, a 90° wave-bending structure at the Ka-band (26.5-40 GHz) based on 3D-printed metamaterials is designed, fabricated, and measured. The wave-bending effect is realized through a spatial distribution of varied effective dielectric constants. Based on the effective medium theory, different effective dielectric constants are accomplished by special, 3D-printable unit cells, which allow different ratios of dielectric to air at the unit cell level. In contrast to traditional, metallic-structure-included metamaterial designs, the reported wave-bending structure here is all dielectric and implemented by the polymer-jetting technique, which features rapid, low-cost, and convenient prototyping. Both simulation and experiment results demonstrate the effectiveness of the wave-bending structure.

Vibrational analysis of vertical axis wind turbine blades

NASA Astrophysics Data System (ADS)

Kapucu, Onur

The goal of this research is to derive a vibration model for a vertical axis wind turbine blade. This model accommodates the affects of varying relative flow angle caused by rotating the blade in the flow field, uses a simple aerodynamic model that assumes constant wind speed and constant rotation rate, and neglects the disturbance of wind due to upstream blade or post. The blade is modeled as elastic Euler-Bernoulli beam under transverse bending and twist deflections. Kinetic and potential energy equations for a rotating blade under deflections are obtained, expressed in terms of assumed modal coordinates and then plugged into Lagrangian equations where the non-conservative forces are the lift and drag forces and moments. An aeroelastic model for lift and drag forces, approximated with third degree polynomials, on the blade are obtained assuming an airfoil under variable angle of attack and airflow magnitudes. A simplified quasi-static airfoil theory is used, in which the lift and drag coefficients are not dependent on the history of the changing angle of attack. Linear terms on the resulting equations of motion will be used to conduct a numerical analysis and simulation, where numeric specifications are modified from the Sandia-17m Darrieus wind turbine by Sandia Laboratories.

Numerical analysis and experimental verification of elastomer bending process with different material models

NASA Astrophysics Data System (ADS)

Kut, Stanislaw; Ryzinska, Grazyna; Niedzialek, Bernadetta

2016-01-01

The article presents the results of tests in order to verifying the effectiveness of the nine selected elastomeric material models (Neo-Hookean, Mooney with two and three constants, Signorini, Yeoh, Ogden, Arruda-Boyce, Gent and Marlow), which the material constants were determined in one material test - the uniaxial tension testing. The convergence assessment of nine analyzed models were made on the basis of their performance from an experimental bending test of the elastomer samples from the results of numerical calculations FEM for each material models. To calculate the material constants for the analyzed materials, a model has been generated by the stressstrain characteristics created as a result of experimental uniaxial tensile test with elastomeric dumbbell samples, taking into account the parameters received in its 18th cycle. Using such a calculated material constants numerical simulation of the bending process of a elastomeric, parallelepipedic sampleswere carried out using MARC / Mentat program.

Computer-Assisted Image Analysis of Plant Growth, Thigmomorphogenesis, and Gravitropism 1

PubMed Central

Jaffe, Mordecai J.; Wakefield, Andrew H.; Telewski, Frank; Gulley, Edward; Biro, Ronald

1985-01-01

A nonintrusive auxonometric system, based on the DARWIN image processor (Telewski et al. 1983 Plant Physiol 72: 177-181), is described and demonstrated in the analysis of gravitropism and thigmomorphogenesis in corn seedlings (Zea mays). Using this system, growth and bending of regularly shaped plants or organs can be quickly and accurately measured without, in any way, interfering with the plant. Furthermore, the growth and bending curves are automatically plotted. Thigmomorphogenesis in the aerial part of corn seedlings involves growth promotion at a low force load and growth retardation at higher force loads. The time courses of the two kinds of response are somewhat different, with retardation occurring immeditely after mechanical perturbation and growth promotion taking somewhat longer to begin. Gravitropic experiments show that when dark-grown corn seedlings are placed on their side in the light, the resulting curvature is due to two consecutive morphological mechanisms. In the first instance, lasting for about 15 minutes, the elongation of the bottom edge of the plant accelerates, while the elongation of the top edge remains constant. After that, for the next 1.75 hours, the elongation of the top edge decelerates and stops while that of the bottom edge remains constant at the increased rate for most of the period. The measurements taken from both experiments at relatively high resolution (0.08-0.1 millimeter) show that the growth curves are not smooth but show many small irregularities which may or may not involve micronutations. Images Fig. 1 Fig. 2 Fig. 3 PMID:11539042

Localized states in an arbitrarily bent quantum wire (bend-imitating approach)

NASA Astrophysics Data System (ADS)

Vakhnenko, Oleksity O.

1996-02-01

The bend-imitating matching technique is proposed to simplify the quantum mechanical treatment of singly and multiply bent 2D quantum wires of constant width, arbitrary bending angles, arbitrary bending radii and arbitrary distances between the bends. The spectrum of one-electron localized states and its dependence on the bending angle and the bending radius in a singly bent wire is explicitly calculated. Doubly bent wires are shown to possess doubly split localized states. The splitting energies as a function of the distance between the bends and the bending angles and bending radii have also been obtained. A similar description of bent 3D quantum wires and bent optical fibers is expected to be possible.

The value of radiographs obtained during forced traction under general anaesthesia in predicting flexibility in idiopathic scoliosis with Cobb angles exceeding 60 degree.

PubMed

Ibrahim, T; Gabbar, O A; El-Abed, K; Hutchinson, M J; Nelson, I W

2008-11-01

Our aim in this prospective radiological study was to determine whether the flexibility rate calculated from radiographs obtained during forced traction under general anaesthesia, was better than that of fulcrum-bending radiographs before corrective surgery in predicting the extent of the available correction in patients with idiopathic scoliosis. We evaluated 33 patients with a Cobb angle > 60 degrees on a standing posteroanterior radiograph, who had been treated by posterior correction. Pre-operative standing fulcrum-bending radiographs and those with forced-traction under general anaesthesia were obtained. Post-operative standing radiographs were taken after surgical correction. The mean forced-traction flexibility rate was 55% (SD 11.3) which was significantly higher than the mean fulcrum-bending flexibility rate of 32% (SD 16.1) (p < 0.001). We found no correlation between either the forced-traction or fulcrum-bending flexibility rates and the correction rate post-operatively (p = 0.24 and p = 0.44, respectively). Radiographs obtained during forced traction under general anaesthesia were better at predicting the flexibility of the curve than fulcrum-bending radiographs in curves with a Cobb angle > 60 degrees in the standing position and may identify those patients for whom supplementary anterior surgery can be avoided.

Grip and limb force limits to turning performance in competition horses

PubMed Central

Tan, Huiling; Wilson, Alan M.

2011-01-01

Manoeuverability is a key requirement for successful terrestrial locomotion, especially on variable terrain, and is a deciding factor in predator–prey interaction. Compared with straight-line running, bend running requires additional leg force to generate centripetal acceleration. In humans, this results in a reduction in maximum speed during bend running and a published model assuming maximum limb force as a constraint accurately predicts how much a sprinter must slow down on a bend given his maximum straight-line speed. In contrast, greyhounds do not slow down or change stride parameters during bend running, which suggests that their limbs can apply the additional force for this manoeuvre. We collected horizontal speed and angular velocity of heading of horses while they turned in different scenarios during competitive polo and horse racing. The data were used to evaluate the limits of turning performance. During high-speed turns of large radius horizontal speed was lower on the bend, as would be predicted from a model assuming a limb force limit to running speed. During small radius turns the angular velocity of heading decreased with increasing speed in a manner consistent with the coefficient of friction of the hoof–surface interaction setting the limit to centripetal force to avoid slipping. PMID:21147799

Grip and limb force limits to turning performance in competition horses.

PubMed

Tan, Huiling; Wilson, Alan M

2011-07-22

Manoeuverability is a key requirement for successful terrestrial locomotion, especially on variable terrain, and is a deciding factor in predator-prey interaction. Compared with straight-line running, bend running requires additional leg force to generate centripetal acceleration. In humans, this results in a reduction in maximum speed during bend running and a published model assuming maximum limb force as a constraint accurately predicts how much a sprinter must slow down on a bend given his maximum straight-line speed. In contrast, greyhounds do not slow down or change stride parameters during bend running, which suggests that their limbs can apply the additional force for this manoeuvre. We collected horizontal speed and angular velocity of heading of horses while they turned in different scenarios during competitive polo and horse racing. The data were used to evaluate the limits of turning performance. During high-speed turns of large radius horizontal speed was lower on the bend, as would be predicted from a model assuming a limb force limit to running speed. During small radius turns the angular velocity of heading decreased with increasing speed in a manner consistent with the coefficient of friction of the hoof-surface interaction setting the limit to centripetal force to avoid slipping.

Hydrophilic guidewires: evaluation and comparison of their properties and safety.

PubMed

Torricelli, Fabio Cesar Miranda; De, Shubha; Sarkissian, Carl; Monga, Manoj

2013-11-01

To compare physical and mechanical properties of 10 commercially available hydrophilic guidewires. In vitro testing was performed to evaluate 10 different straight hydrophilic guidewires (5 regular and 5 stiff wires): Glidewire, NiCore, EZ Glider, Hiwire, and Zipwire. The forces required for tip perforation, tip bending, shaft bending, and friction during movement were measured for all 10 wires. The tip contour was measured using high power light microscopy. The Glidewire required the greatest force to perforate our model (P = .01). The EZ Glider, Zipwire, and Glidewire had the lowest tip bending forces (P <.001). The Glidewire had the stiffest shaft (P <.001). The EZ Glider and Glidewire required the greatest forces in the friction test (P <.001). Regarding the stiff guidewires, the GlidewireS required the greatest force in the perforation test (P ≤.05). The GlidewireS and EZ GliderS required the lowest tip bending force (P ≤.004). The ZipwireS and NiCoreS had the stiffest shafts (P ≤.01). The GlidewireS required the greatest force in the friction test (P <.001). Measurement of the tip contour showed the Zipwire, HiwireS, and EZ GliderS had the roundest tips. Each wire has unique properties with advantages and disadvantages. The Glidewires (both stiff and regular) have the lowest potential for perforation, although they are less slippery. The Glidewire and EZ Glider required the least tip force to bend around a point of obstruction. Copyright © 2013 Elsevier Inc. All rights reserved.

Curvature effect on hemodynamic conditions at the inner bend of the carotid siphon and its relation to aneurysm formation.

PubMed

Lauric, Alexandra; Hippelheuser, James; Safain, Mina G; Malek, Adel M

2014-09-22

Although high-impact hemodynamic forces are thought to lead to cerebral aneurysmal change, little is known about the aneurysm formation on the inner aspect of vascular bends such as the internal carotid artery (ICA) siphon where wall shear stress (WSS) is expected to be low. This study evaluates the effect of vessel curvature and hemodynamics on aneurysm formation along the inner carotid siphon. Catheter 3D-rotational angiographic volumes of 35 ICA (10 aneurysms, 25 controls) were evaluated in 3D for radius of curvature and peak curvature of the siphon bend, followed by univariate statistical analysis. Computational fluid dynamic (CFD) simulations were performed on patient-derived models after aneurysm removal and on synthetic variants of increasing curvature. Peak focal siphon curvature was significantly higher in aneurysm bearing ICAs (0.36 ± 0.045 vs. 0.30 ± 0.048 mm(-1), p=0.003), with no difference in global radius of curvature (p=0.36). In CFD simulations, increasing parametric curvature tightness (from 5 to 3mm radius) resulted in dramatic increase of WSS and WSS gradient magnitude (WSSG) on the inner wall of the bend. In patient-derived data, the location of aneurysms coincided with regions of low WSS (<4 Pa) flanked by high WSS and WSSG peaks. WSS peaks correlated with the aneurysm neck. In contrast, control siphon bends displayed low, almost constant, WSS and WSSG profiles with little spatial variation. High bend curvature induces dynamically fluctuating high proximal WSS and WSSG followed by regions of flow stasis and recirculation, leading to local conditions known to induce destructive vessel wall remodeling and aneurysmal initiation. Copyright © 2014 Elsevier Ltd. All rights reserved.

Asymmetry-symmetry transition of double-sided adhesive tapes

NASA Astrophysics Data System (ADS)

Yamaguchi, Tetsuo; Muroo, Hiroyuki; Sumino, Yutaka; Doi, Masao

2012-06-01

We report on the debonding process of a double-sided adhesive tape sandwiched between two glass plates. When the glass plates are separated from each other at a constant rate, a highly asymmetric extension of top and bottom adhesive layers and bending of the inner film are observed first. As the separation proceeds, the elongation of both layers becomes symmetric, and the inner film becomes flat again. When this happens, there appears a local maximum in the force-displacement curve. We explain this asymmetry-symmetry transition and discuss the role of the bimodal force-displacement relation of each adhesive layer. We also discuss the effect of the inner film thickness and the separation rate on the debonding behavior, which causes undesirable early detachment of the double-sided adhesive tape in a certain condition.

Evaluation of a novel, ultrathin, tip-bending endoscope in a synthetic force-sensing pancreas with comparison to medical guide wires

PubMed Central

Chandler, John E; Lee, Cameron M; Babchanik, Alexander P; Melville, C David; Saunders, Michael D; Seibel, Eric J

2012-01-01

Purpose Direct visualization of pancreatic ductal tissue is critical for early diagnosis of pancreatic diseases and for guiding therapeutic interventions. A novel, ultrathin (5 Fr) scanning fiber endoscope (SFE) with tip-bending capability has been developed specifically to achieve high resolution imaging as a pancreatoscope during endoscopic retrograde cholangiopancreatography (ERCP). This device has potential to dramatically improve both diagnostic and therapeutic capabilities during ERCP by providing direct video feedback and tool guidance to clinicians. Methods Invasiveness of the new tip-bending SFE was evaluated by a performance comparison to ERCP guide wires, which are routinely inserted into the pancreatic duct during ERCP. An in vitro test model with four force sensors embedded in a synthetic pancreas was designed to detect and compare the insertion forces for 0.89 mm and 0.53 mm diameter guide wires as well as the 1.7 mm diameter SFE. Insertions were performed through the working channel of a therapeutic duodenoscope for the two types of guide wires and using a statistically similar direct insertion method for comparison to the SFE. Results Analysis of the forces detected by the sensors showed the smaller diameter 0.53 mm wire produced significantly less average and maximum forces during insertion than the larger diameter 0.89 mm wire. With the use of tip-bending and optical visualization, the 1.7 mm diameter SFE produced significantly less average force during insertion than the 0.89 mm wire at every sensor, despite its larger size. It was further shown that the use of tip-bending with the SFE significantly reduced the forces at all sensors, compared to insertions when tip-bending was not used. Conclusion Combining high quality video imaging with two-axis tip-bending allows a larger diameter guide wire-style device to be inserted into the pancreatic duct during ERCP with improved capacity to perform diagnostics and therapy. PMID:23166452

Dynamic curvature regulation accounts for the symmetric and asymmetric beats of Chlamydomonas flagella

PubMed Central

Sartori, Pablo; Geyer, Veikko F; Scholich, Andre; Jülicher, Frank; Howard, Jonathon

2016-01-01

Cilia and flagella are model systems for studying how mechanical forces control morphology. The periodic bending motion of cilia and flagella is thought to arise from mechanical feedback: dynein motors generate sliding forces that bend the flagellum, and bending leads to deformations and stresses, which feed back and regulate the motors. Three alternative feedback mechanisms have been proposed: regulation by the sliding forces, regulation by the curvature of the flagellum, and regulation by the normal forces that deform the cross-section of the flagellum. In this work, we combined theoretical and experimental approaches to show that the curvature control mechanism is the one that accords best with the bending waveforms of Chlamydomonas flagella. We make the surprising prediction that the motors respond to the time derivative of curvature, rather than curvature itself, hinting at an adaptation mechanism controlling the flagellar beat. DOI: http://dx.doi.org/10.7554/eLife.13258.001 PMID:27166516

Strain Distribution in REBCO-Coated Conductors Bent With the Constant-Perimeter Geometry

DOE PAGES

Wang, Xiaorong; Arbelaez, Diego; Caspi, Shlomo; ...

2017-10-24

Here, cable and magnet applications require bending REBa 2Cu 3O 7-δ (REBCO, RE = rare earth) tapes around a former to carry high current or generate specific magnetic fields. With a high aspect ratio, REBCO tapes favor the bending along their broad surfaces (easy way) than their thin edges (hard way). The easy-way bending forms can be effectively determined by the constant-perimeter method that was developed in the 1970s to fabricate accelerator magnets with flat thin conductors. The method, however, does not consider the strain distribution in the REBCO layer that can result from bending. Therefore, the REBCO layer canmore » be overstrained and damaged even if it is bent in an easy way as determined by the constant-perimeter method. To address this issue, we developed a numerical approach to determine the strain in the REBCO layer using the local curvatures of the tape neutral plane. Two orthogonal strain components are determined: the axial component along the tape length and the transverse component along the tape width. These two components can be used to determine the conductor critical current after bending. The approach is demonstrated with four examples relevant for applications: a helical form for cables, forms for canted cos θ dipole and quadrupole magnets, and a form for the coil end design. The approach allows us to optimize the design of REBCO cables and magnets based on the constant-perimeter geometry and to reduce the strain-induced critical current degradation.« less

Strain Distribution in REBCO-Coated Conductors Bent With the Constant-Perimeter Geometry

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Xiaorong; Arbelaez, Diego; Caspi, Shlomo

Here, cable and magnet applications require bending REBa 2Cu 3O 7-δ (REBCO, RE = rare earth) tapes around a former to carry high current or generate specific magnetic fields. With a high aspect ratio, REBCO tapes favor the bending along their broad surfaces (easy way) than their thin edges (hard way). The easy-way bending forms can be effectively determined by the constant-perimeter method that was developed in the 1970s to fabricate accelerator magnets with flat thin conductors. The method, however, does not consider the strain distribution in the REBCO layer that can result from bending. Therefore, the REBCO layer canmore » be overstrained and damaged even if it is bent in an easy way as determined by the constant-perimeter method. To address this issue, we developed a numerical approach to determine the strain in the REBCO layer using the local curvatures of the tape neutral plane. Two orthogonal strain components are determined: the axial component along the tape length and the transverse component along the tape width. These two components can be used to determine the conductor critical current after bending. The approach is demonstrated with four examples relevant for applications: a helical form for cables, forms for canted cos θ dipole and quadrupole magnets, and a form for the coil end design. The approach allows us to optimize the design of REBCO cables and magnets based on the constant-perimeter geometry and to reduce the strain-induced critical current degradation.« less

Evolution of flexural rigidity according to the cross-sectional dimension of a superelastic nickel titanium orthodontic wire.

PubMed

Garrec, Pascal; Tavernier, Bruno; Jordan, Laurence

2005-08-01

The choice of the most suitable orthodontic wire for each stage of treatment requires estimation of the forces generated. In theory, the selection of wire sequences should initially utilize a lower flexural rigidity; thus clinicians use smaller round cross-sectional dimension wires to generate lighter forces during the preliminary alignment stage. This assessment is true for conventional alloys, but not necessarily for superelastic nickel titanium (NiTi). In this case, the flexural rigidity dependence on cross-sectional dimension differs from the linear elasticity prediction because of the martensitic transformation process. It decreases with increasing deflection and this phenomenon is accentuated in the unloading process. This behaviour should lead us to consider differently the biomechanical approach to orthodontic treatment. The present study compared bending in 10 archwires made from NiTi orthodontics alloy of two cross-sectional dimensions. The results were based on microstructural and mechanical investigations. With conventional alloys, the flexural rigidity was constant for each wire and increased largely with the cross-sectional dimension for the same strain. With NiTi alloys, the flexural rigidity is not constant and the influence of size was not as important as it should be. This result can be explained by the non-constant elastic modulus during the martensite transformation process. Thus, in some cases, treatment can begin with full-size (rectangular) wires that nearly fill the bracket slot with a force application deemed to be physiologically desirable for tooth movement and compatible with patient comfort.

Ionic and viscoelastic mechanisms of a bucky-gel actuator

NASA Astrophysics Data System (ADS)

Kruusamäe, Karl; Sugino, Takushi; Asaka, Kinji

2015-07-01

Ionic electromechanically active polymers (IEAPs) are considered attractive candidates for soft, miniature, and lightweight actuators. The bucky-gel actuator is a carbonaceous subtype of IEAP that due to its structure (i.e. two highly porous electrodes sandwiching a thin ion-permeable electrolyte layer) and composition (i.e. being composed of soft porous polymer, carbon nanotubes, and ionic liquid) is very similar to an electric double-layer capacitor. In response to the voltage applied between the electrodes of a bucky-gel actuator, the laminar structure bends. The time domain behavior exhibits, however, a phenomenon called the back-relaxation, i.e., after some time the direction of bending is reversed even though voltage remains constant. In spite of the working mechanism of IEAP actuators being generally attributed to the transport of ions within the soft multilayer system, the specific details remain unclear. A so-called two-carrier model proposes that the bending and subsequent back-relaxation are caused by the relocation of two ionic species having different mobilities as they enter and exit the electrode layers. By adopting the two-carrier model for bucky-gel actuators, we see very good agreement between the mathematical representation and the experimental data of the electromechanical behavior. Furthermore, since the bucky-gel actuator is viscoelastic, we propose to use the time domain response of a blocking force as the key parameter related to the inner ionic mechanism. We also introduce a method to estimate the viscoelastic creep compliance function from the time domain responses for curvature and blocking force. This analysis includes four types of bucky-gel actuators of varying composition and structure.

Vibrational and elastic properties of silicate spinels A2SiO4 (A = Mg, Fe, Ni, and Co)

NASA Astrophysics Data System (ADS)

Kushwaha, A. K.; Ma, C.-G.; Brik, M. G.; Akbudak, S.

2018-06-01

A six-parameter bond-bending force constant model is used to calculate the zone-center (Γ = 0) Raman and infrared phonon mode frequencies, elastic constants and related properties, the Debye temperatures, and sound velocities along high-symmetry directions for A2SiO4 (A = Mg, Fe, Ni, and Co) spinels. The main outcomes of the calculations are that the interactions between Si and O atoms (first-neighbor interaction) are stronger than those between A and Oatoms (A = Mg, Fe, Ni, and Co) (second-neighbor interaction). The elastic constants C11, C12, and C44 decrease in the order Mg > Fe > Ni > Co. The calculated bulk modulus, Poisson's ratio, and anisotropy decrease in the sequence Fe2SiO4 → Ni2SiO4 → Co2SiO4 → Mg2SiO4. On comparison, we find overall good agreement with the available experimental and previously calculated data.

Piezoelectric Pre-Stressed Bending Mechanism for Impact-Driven Energy Harvester

NASA Astrophysics Data System (ADS)

Abdal, A. M.; Leong, K. S.

2017-06-01

This paper experimentally demonstrates and evaluates a piezoelectric power generator bending mechanism based on pre-stressed condition whereby the piezoelectric transducer being bended and remained in the stressed condition before applying a force on the piezoelectric bending structure, which increase the stress on the piezoelectric surface and hence increase the generated electrical charges. An impact force is being exerted onto bending the piezoelectric beam and hence generating electrical power across an external resistive load. The proposed bending mechanism prototype has been manufactured by employing 3D printer technology in order to conduct the evaluation. A free fall test has been conducted as the evaluation method with varying force using a series of different masses and different fall heights. A rectangular piezoelectric harvester beam with the size of 32mm in width, 70mm in length, and 0.55mm in thickness is used to demonstrate the experiment. It can be seen from the experiment that the instantaneous peak to peak AC volt output measured at open-circuit is increasing and saturated at about of 70V when an impact force of about 80N is being applied. It is also found that a maximum power of about 53mW is generated at an impact force of 50N when it is connected to an external resistive load of 0.7KΩ. The reported mechanism is a promising candidate in the application of energy harvesting for powering various wireless sensor nodes (WSN) which is the core of Internet of Things (IoT).

Active damping using a control structure interaction approach

NASA Astrophysics Data System (ADS)

Umland, Jeffrey W.

1991-12-01

The vibration control of flexible structures using electromagnetic actuators is investigated. A model of an electromagnetic voice coil actuator is developed from elementary theory, and the required parameters are measured. Given a constant magnetic field, the force output of the voice coil varies linearly with the current flowing through the coil. The primary damping mechanism of the actuator used is found to be Coulomb friction. It is seen that Coulomb friction inhibits the response of the actuator to low levels of excitation. It is also seen that the actuator displayed a nonlinear relationship between force and current indicating that the applied magnetic field was not constant. This nonlinearity leads to a closed loop instability. Several design improvements are considered. Four different feedback control laws are developed to add active damping to a structure. The actuator is used as both a point force source and as a link in a mechanism that applies bending moments at two places on the structure. The actuator is used as both a point force source and as a link in a mechanism that applies bending moments at two places on the structure. The first control law uses the actuator as a traditional passive vibration absorber. The second control law is direct structural velocity feedback plus direct proof mass position feedback. The third control strategy is also direct structural velocity feedback but using compensated feedback of the proof mass position. The compensator is designed according to an H infinity optimization technique. The fourth control law uses the actuator as an equivalent mechanical viscous damper connected to two points on the structure. The results show that using direct structural velocity feedback provides improved vibration suppression in comparison to a traditional vibration absorber. Furthermore, the tuning criteria is only restricted to maintaining the actuator's single degree of freedom natural frequency below those of the structure to which it is attached.

A numerical simulation of tooth movement by wire bending.

PubMed

Kojima, Yukio; Fukui, Hisao

2006-10-01

In orthodontic treatment, wires are bent and attached to teeth to move them via elastic recovery. To predict how a tooth will move, the initial force system produced from the wire is calculated. However, the initial force system changes as the tooth moves and may not be used to predict the final tooth position. The purpose of this study was to develop a comprehensive mechanical, 3-dimensional, numerical model for predicting tooth movement. Tooth movements produced by wire bending were simulated numerically. The teeth moved as a result of bone remodeling, which occurs in proportion to stress in the periodontal ligament. With an off-center bend, a tooth near the bending position was subjected to a large moment and tipped more noticeably than the other teeth. Also, a tooth far from the bending position moved slightly in the mesial or the distal direction. With the center V-bend, when the second molar was added as an anchor tooth, the tipping angle and the intrusion of the canine increased, and movement of the first molar was prevented. When a wire with an inverse curve of Spee was placed in the mandibular arch, the calculated tendency of vertical tooth movements was the same as the measured result. In these tooth movements, the initial force system changed as the teeth moved. Tooth movement was influenced by the size of the root surface area. Tooth movements produced by wire bending could be estimated. It was difficult to predict final tooth positions from the initial force system.

Formulas for the elastic constants of plates with integral waffle-like stiffening

NASA Technical Reports Server (NTRS)

Dow, Norris R; Libove, Charles; Hubka, Ralph E

1954-01-01

Formulas are derived for the fifteen elastic constants associated with bending, stretching, twisting, and shearing of plates with closely spaced integral ribbing in a variety of configurations and proportions. In the derivation the plates are considered, conceptually, as more uniform orthotropic plates somewhat on the order of plywood. The constants, which include the effectiveness of the ribs for resisting deformations other than bending and stretching in their longitudinal directions, are defined in terms of four coefficients, and theoretical and experimental methods for the evaluation of these coefficients are discussed. Four of the more important elastic constants are predicted by these formulas and are compared with test results. Good correlation is obtained. (author)

In Silico Measurements of Twist and Bend Moduli for β-Solenoid Protein Self-Assembly Units.

PubMed

Heinz, Leonard P; Ravikumar, Krishnakumar M; Cox, Daniel L

2015-05-13

We compute potentials of mean force for bend and twist deformations via force pulling and umbrella sampling experiments for four β-solenoid proteins (BSPs) that show promise in nanotechnology applications. In all cases, we find quasi-Hooke's law behavior until the point of rupture. Bending moduli show modest anisotropy for two-sided and three-sided BSPs, and little anisotropy for a four-sided BSP. There is a slight clockwise/counterclockwise asymmetry in the twist potential of mean force, showing greater stiffness when the applied twist follows the intrinsic twist. When we extrapolate to beam theory appropriate for amyloid fibrils of the BSPs, we find bend/twist moduli which are somewhat smaller than those in the literature for other amyloid fibrils. Twist persistence lengths are on the order of a micron, and bend persistence lengths are several microns. Provided the intrinsic twist can be reversed, these results support the usage of BSPs in biomaterials applications.

Theory and algorithms to compute Helfrich bending forces: a review.

PubMed

Guckenberger, Achim; Gekle, Stephan

2017-05-24

Cell membranes are vital to shield a cell's interior from the environment. At the same time they determine to a large extent the cell's mechanical resistance to external forces. In recent years there has been considerable interest in the accurate computational modeling of such membranes, driven mainly by the amazing variety of shapes that red blood cells and model systems such as vesicles can assume in external flows. Given that the typical height of a membrane is only a few nanometers while the surface of the cell extends over many micrometers, physical modeling approaches mostly consider the interface as a two-dimensional elastic continuum. Here we review recent modeling efforts focusing on one of the computationally most intricate components, namely the membrane's bending resistance. We start with a short background on the most widely used bending model due to Helfrich. While the Helfrich bending energy by itself is an extremely simple model equation, the computation of the resulting forces is far from trivial. At the heart of these difficulties lies the fact that the forces involve second order derivatives of the local surface curvature which by itself is the second derivative of the membrane geometry. We systematically derive and compare the different routes to obtain bending forces from the Helfrich energy, namely the variational approach and the thin-shell theory. While both routes lead to mathematically identical expressions, so-called linear bending models are shown to reproduce only the leading order term while higher orders differ. The main part of the review contains a description of various computational strategies which we classify into three categories: the force, the strong and the weak formulation. We finally give some examples for the application of these strategies in actual simulations.

Bending creep and load duration of Douglas-fir 2 by 4s under constant load for up to 12-plus years

Treesearch

Charles C. Gerhards

2000-01-01

This paper finalizes research on graded Douglas-fir 2 by 4 beams subjected to constant bending loads of various levels and durations. Compared to results for testing in a controlled environment, results confirm that load duration did not appear to be shortened by tests in an uncontrolled environment, at least extending out to 12-plus years. By the same comparison,...

Modeling and Experimental Evaluation of Bending Behavior of Soft Pneumatic Actuators Made of Discrete Actuation Chambers.

PubMed

Alici, Gursel; Canty, Taylor; Mutlu, Rahim; Hu, Weiping; Sencadas, Vitor

2018-02-01

In this article, we have established an analytical model to estimate the quasi-static bending displacement (i.e., angle) of the pneumatic actuators made of two different elastomeric silicones (Elastosil M4601 with a bulk modulus of elasticity of 262 kPa and Translucent Soft silicone with a bulk modulus of elasticity of 48 kPa-both experimentally determined) and of discrete chambers, partially separated from each other with a gap in between the chambers to increase the magnitude of their bending angle. The numerical bending angle results from the proposed gray-box model, and the corresponding experimental results match well that the model is accurate enough to predict the bending behavior of this class of pneumatic soft actuators. Further, by using the experimental bending angle results and blocking force results, the effective modulus of elasticity of the actuators is estimated from a blocking force model. The numerical and experimental results presented show that the bending angle and blocking force models are valid for this class of pneumatic actuators. Another contribution of this study is to incorporate a bistable flexible thin metal typified by a tape measure into the topology of the actuators to prevent the deflection of the actuators under their own weight when operating in the vertical plane.

Infrared laser absorption spectroscopy of the nu4 (sigma u) fundamental and associated nu11(pi u) hot band of C7 - Evidence for alternating rigidity in linear carbon clusters

NASA Technical Reports Server (NTRS)

Heath, J. R.; Saykally, R. J.

1991-01-01

The first characterization of the bending potential of the C7 cluster is reported via the observation of the v = 1(1) and v = 2 deg levels of the nu11 (pi u) bend as hot bands associated with the nu4 (sigma u) antisymmetric stretch fundamental. The lower state hot band rotational constants are measured to be 1004.4(1.3) and 1123.6(9.0) MHz, constituting a 9.3 and 22 percent increase over the ground state rotational constant, 918.89 (41) MHz. These large increases are strong quartic and sextic centrifugal distortion constants determined for the ground and nu 4 = 1 states are found to be anomalously large and negative, evidencing strong perturbations between stretching and bending modes.

Bending and Torsion Load Alleviator With Automatic Reset

NASA Technical Reports Server (NTRS)

delaFuente, Horacio M. (Inventor); Eubanks, Michael C. (Inventor); Dao, Anthony X. (Inventor)

1996-01-01

A force transmitting load alleviator apparatus and method are provided for rotatably and pivotally driving a member to be protected against overload torsional and bending (moment) forces. The load alleviator includes at least one bias spring to resiliently bias cam followers and cam surfaces together and to maintain them in locked engagement unless a predetermined load is exceeded whereupon a center housing is pivotal or rotational with respect to a crown assembly. This pivotal and rotational movement results in frictional dissipation of the overload force by an energy dissipator. The energy dissipator can be provided to dissipate substantially more energy from the overload force than from the bias force that automatically resets the center housing and crown assembly to the normally fixed centered alignment. The torsional and bending (moment) overload levels can designed independently of each other.

Bending and Force Recovery in Polymer Films and Microgel Formation

NASA Astrophysics Data System (ADS)

Elder, Theresa Marie

To determine correlation between geometry and material three different model films: polymethylsiloxane (PDMS), polystyrene (PS), and polycarbonate (PC), were singly bent and doubly bent (forming D-cones). Bends were chosen as they are fundamental in larger complex geometries such as origami and crumples. Bending was carried out between two plates taking force and displacement measurements. Processing of data using moment equations yielded values for bending moduli for studied films that were close to accepted values. Force recovery showed logarithmic trends for PDMS and stretched exponential trends for PS and PC. In a separate experiment a triblock copolymer of polystyrene-polyacrylic acid-polystyrene was subjected to different good and bad solvent mixing with any resulting particle morphology examined. Particles formed more uniformly with high water concentration, particles formed with high toluene concentration and agitation yielded three separate morphologies.

Force system evaluation of symmetrical beta-titanium T-loop springs preactivated by curvature and concentrated bends.

PubMed

Caldas, Sergei Godeiro Fernandes Rabelo; Martins, Renato Parsekian; Galvão, Marília Regalado; Vieira, Camilla Ivini Viana; Martins, Lídia Parsekian

2011-08-01

The objective of this research was to compare the effect of preactivation on the force system of beta-titanium T-loop springs (TLSs). Twenty TLSs with dimensions of 6 × 10 mm, of 0.017 × 0.025-in beta-titanium alloy, were randomly divided into 2 groups according to their preactivation. By using a moment transducer coupled to a digital extensometer indicator adapted to a testing machine, the amounts of horizontal force and moment produced were recorded at every 0.5 mm of deactivation from 5 mm of the initial activation in an interbracket distance of 23 mm. The moment-to-force ratio, the "neutral position" and the load-deflection ratio were also calculated. TLSs preactivated by curvature delivered horizontal forces significantly lower than those preactivated by concentrated bends. No differences were found in relation to the moments produced throughout the deactivation of both groups. The moment-to-force ratios were systematically higher on the TLSs preactivated by curvature than those preactivated by concentrated bends, except on 5 mm of activation. Significant differences were found in the load-deflection rates and "neutral position." The TLSs preactivated by curvature delivered lower horizontal forces and higher moment-to-force and load-deflection ratios than did those preactivated by concentrated bends. Copyright © 2011 American Association of Orthodontists. Published by Mosby, Inc. All rights reserved.

Large Eddy Simulation of Supercritical CO2 Through Bend Pipes

NASA Astrophysics Data System (ADS)

He, Xiaoliang; Apte, Sourabh; Dogan, Omer

2017-11-01

Supercritical Carbon Dioxide (sCO2) is investigated as working fluid for power generation in thermal solar, fossil energy and nuclear power plants at high pressures. Severe erosion has been observed in the sCO2 test loops, particularly in nozzles, turbine blades and pipe bends. It is hypothesized that complex flow features such as flow separation and property variations may lead to large oscillations in the wall shear stresses and result in material erosion. In this work, large eddy simulations are conducted at different Reynolds numbers (5000, 27,000 and 50,000) to investigate the effect of heat transfer in a 90 degree bend pipe with unit radius of curvature in order to identify the potential causes of the erosion. The simulation is first performed without heat transfer to validate the flow solver against available experimental and computational studies. Mean flow statistics, turbulent kinetic energy, shear stresses and wall force spectra are computed and compared with available experimental data. Formation of counter-rotating vortices, named Dean vortices, are observed. Secondary flow pattern and swirling-switching flow motions are identified and visualized. Effects of heat transfer on these flow phenomena are then investigated by applying a constant heat flux at the wall. DOE Fossil Energy Crosscutting Technology Research Program.

Stability of large horizontal-axis axisymmetric wind turbines. Ph.D. Thesis - Delaware Univ.

NASA Technical Reports Server (NTRS)

Hirschbein, M. S.; Young, M. I.

1980-01-01

The stability of large horizontal axis, axi-symmetric, power producing wind turbines was examined. The analytical model used included the dynamic coupling of the rotor, tower and power generating system. The aerodynamic loading was derived from blade element theory. Each rotor blade was permitted tow principal elastic bending degrees of freedom, one degree of freedom in torsion and controlled pitch as a rigid body. The rotor hub was mounted in a rigid nacelle which may yaw freely or in a controlled manner. The tower can bend in two principal directions and may twist. Also, the rotor speed can vary and may induce perturbation reactions within the power generating equipment. Stability was determined by the eigenvalues of a set of linearized constant coefficient differential equations. All results presented are based on a 3 bladed, 300 ft. diameter, 2.5 megawatt wind turbine. Some of the parameters varied were; wind speed, rotor speed structural stiffness and damping, the effective stiffness and damping of the power generating system and the principal bending directions of the rotor blades. Unstable or weakly stable behavior can be caused by aerodynamic forces due to motion of the rotor blades and tower in the plane of rotation or by mechanical coupling between the rotor system and the tower.

Vibrational and elastic properties of Ln2Sn2O7 (Ln = La, Sm, Gd, Dy, Ho, Er, Yb, or Lu)

NASA Astrophysics Data System (ADS)

Akbudak, S.; Kushwaha, A. K.

2018-04-01

In this study, an eight-parameter bond-bending force constant model was used to calculate the zone center phonon frequencies, elastic constants, and related properties of the stannate compounds Ln2Sn2O7 (Ln = La, Sm, Gd, Dy, Ho, Er, Yb, or Lu) with a pyrochlore structure. We found that the Snsbnd O bond strengths dominate the Ln-O and Osbnd O bonds. We also found that all of the materials are ductile and anisotropic in nature. The anisotropic nature of the compounds increases in the order of: La2Sn2O7 < Sm2Sn2O7 < Gd2Sn2O7 < Dy2Sn2O7 < Ho2Sn2O7 < Er2Sn2O7 < Yb2Sn2O7 < Lu2Sn2O7.

Highly sensitive force sensor based on balloon-like interferometer

NASA Astrophysics Data System (ADS)

Wu, Yue; Xiao, Shiying; Xu, Yao; Shen, Ya; Jiang, Youchao; Jin, Wenxing; Yang, Yuguang; Jian, Shuisheng

2018-07-01

An all-fiber highly sensitive force sensor based on modal interferometer has been presented and demonstrated. The single-mode fiber (SMF) with coating stripped is designed into a balloon-like shape to form a modal interferometer. Due to the bent SMF, the interference occurs between the core mode and cladding modes. With variation of the force applied to the balloon-like interferometer, the bending diameter changes, which caused the wavelength shift of the modal interference. Thus the measurement of the force variation can be achieved by monitoring the wavelength shift. The performances of the interferometer with different bending diameter are experimentally investigated, and the maximum force sensitivity of 24.9 pm/ μ N can be achieved with the bending diameter 14 mm ranging from 0 μ N to 1464.12 μ N. Furthermore, the proposed fiber sensor exhibits the advantages of easy fabrication and low cost, making it a suitable candidate in the optical fiber sensing field.

Thermal bending of liquid sheets and jets

NASA Astrophysics Data System (ADS)

Brenner, Michael P.; Paruchuri, Srinivas

2003-11-01

We present an analytical model for the bending of liquid jets and sheets from temperature gradients, as recently observed by Chwalek et al. [Phys. Fluids 14, L37 (2002)]. The bending arises from a local couple caused by Marangoni forces. The dependence of the bending angle on experimental parameters is presented, in qualitative agreement with reported experiments. The methodology gives a simple framework for understanding the mechanisms for jet and sheet bending.

Controlled manipulation of flexible carbon nanotubes through shape-dependent pushing by atomic force microscopy.

PubMed

Yang, Seung-Cheol; Qian, Xiaoping

2013-09-17

A systematic approach to manipulating flexible carbon nanotubes (CNTs) has been developed on the basis of atomic force microscope (AFM) based pushing. Pushing CNTs enables efficient transport and precise location of individual CNTs. A key issue for pushing CNTs is preventing defective distortion in repetitive bending and unbending deformation. The approach presented here controls lateral movement of an AFM tip to bend CNTs without permanent distortion. The approach investigates possible defects caused by tensile strain of the outer tube under uniform bending and radial distortion by kinking. Using the continuum beam model and experimental bending tests, dependency of maximum bending strain on the length of bent CNTs and radial distortion on bending angles at a bent point have been demonstrated. Individual CNTs are manipulated by limiting the length of bent CNTs and the bending angle. In our approach, multiwalled CNTs with 5-15 nm diameter subjected to bending deformation produce no outer tube breakage under uniform bending and reversible radial deformation with bending angles less than 110°. The lateral tip movement is determined by a simple geometric model that relies on the shape of multiwalled CNTs. The model effectively controls deforming CNT length and bending angle for given CNT shape. Experimental results demonstrate successful manipulation of randomly dispersed CNTs without visual defects. This approach to pushing can be extended to develop a wide range of CNT based nanodevice applications.

Spacing of bending-induced fractures at saturation: Numerical models and approximate analytical solution

NASA Astrophysics Data System (ADS)

Schöpfer, Martin; Lehner, Florian; Grasemann, Bernhard; Kaserer, Klemens; Hinsch, Ralph

2017-04-01

John G. Ramsay's sketch of structures developed in a layer progressively folded and deformed by tangential longitudinal strain (Figure 7-65 in Folding and Fracturing of Rocks) and the associated strain pattern analysis have been reproduced in many monographs on Structural Geology and are referred to in numerous publications. Although the origin of outer-arc extension fractures is well-understood and documented in many natural examples, geomechanical factors controlling their (finite or saturation) spacing are hitherto unexplored. This study investigates the formation of bending-induced fractures during constant-curvature forced folding using Distinct Element Method (DEM) numerical modelling. The DEM model comprises a central brittle layer embedded within weaker (low modulus) elastic layers; the layer interfaces are frictionless (free slip). Folding of this three-layer system is enforced by a velocity boundary condition at the model base, while a constant overburden pressure is maintained at the model top. The models illustrate several key stages of fracture array development: (i) Prior to the onset of fracture, the neutral surface is located midway between the layer boundaries; (ii) A first set of regularly spaced fractures develops once the tensile stress in the outer-arc equals the tensile strength of the layer. Since the layer boundaries are frictionless, these bending-induced fractures propagate through the entire layer; (iii) After the appearance of the first fracture set, the rate of fracture formation decreases rapidly and so-called infill fractures develop approximately midway between two existing fractures (sequential infilling); (iv) Eventually no new fractures form, irrespective of any further increase in fold curvature (fracture saturation). Analysis of the interfacial normal stress distributions suggests that at saturation the fracture-bound blocks are subjected to a loading condition similar to three-point bending. Using classical beam theory an analytical solution is derived for the critical fracture spacing, i.e. the spacing below which the maximum tensile stress cannot reach the layer strength. The model results are consistent with an approximate analytical solution, and illustrate that the spacing of bending-induced fractures is proportional to layer thickness and a square root function of the ratio of layer tensile strength to confining pressure. Although highly idealised, models and analysis presented in this study offer an explanation for fracture saturation during folding and point towards certain key factors that may control fracture spacing in natural systems.

Effects of wing flexibility and variable air lift upon wing bending moment during landing impacts of a small seaplane

NASA Technical Reports Server (NTRS)

Merten, Kenneth F; Beck, Edgar B

1951-01-01

A smooth-water-landing investigation was conducted with a small seaplane to obtain experimental wing-bending-moment time histories together with time histories of the various parameters necessary for the prediction of wing bending moments during hydrodynamic forcing functions. The experimental results were compared with calculated results which include inertia-load effects and the effects of air-load variation during impact. The responses of the fundamental mode were calculated with the use of the measured hydrodynamic forcing functions. From these responses, the wing bending moments due to the hydrodynamic load were calculated according to the procedure given in R.M. No. 2221. The comparison of the time histories of the experimental and calculated wing bending moments showed good agreement both in phase relationship of the oscillations and in numerical values.

Discrete microfluidics: Reorganizing droplet arrays at a bend

NASA Astrophysics Data System (ADS)

Surenjav, Enkhtuul; Herminghaus, Stephan; Priest, Craig; Seemann, Ralf

2009-10-01

Microfluidic manipulation of densely packed droplet arrangements (i.e., gel emulsions) using sharp microchannel bends was studied as a function of bend angle, droplet volume fraction, droplet size, and flow velocity. Emulsion reorganization was found to be specifically dependent on the pathlength that the droplets are forced to travel as they navigate the bend under spatial confinement. We describe how bend-induced droplet displacements might be exploited in complex, droplet-based microfluidics.

An Experimental Study of Fatigue Crack Growth in Aluminum Sheet Subjected to Combined Bending and Membrane Stresses

NASA Technical Reports Server (NTRS)

Phillips, Edward P.

1997-01-01

An experimental study was conducted to determine the effects of combined bending and membrane cyclic stresses on the fatigue crack growth behavior of aluminum sheet material. The materials used in the tests were 0.040-in.- thick 2024-T3 alclad and 0.090-in.-thick 2024-T3 bare sheet. In the tests, the membrane stresses were applied as a constant amplitude loading at a stress ratio (minimum to maximum stress) of 0.02, and the bending stresses were applied as a constant amplitude deflection in phase with the membrane stresses. Tests were conducted at ratios of bending to membrane stresses (B/M) of 0, 0.75, and 1.50. The general trends of the results were for larger effects of bending for the higher B/M ratios, the lower membrane stresses, and the thicker material. The addition of cyclic bending stresses to a test with cyclic membrane stresses had only a small effect on the growth rates of through-thickness cracks in the thin material, but had a significant effect on the crack growth rates of through-thickness cracks in the thick material. Adding bending stresses to a test had the most effect on the initiation and early growth of cracks and had less effect on the growth of long through-thickness cracks.

Biomechanical demands on posterior fusion instrumentation during lordosis restoration procedures.

PubMed

Kuo, Calvin C; Martin, Audrey; Telles, Connor; Leasure, Jeremi; Iezza, Alex; Ames, Christopher; Kondrashov, Dimitriy

2016-09-01

OBJECTIVE The goal of this study was to investigate the forces placed on posterior fusion instrumentation by 3 commonly used intraoperative techniques to restore lumbar lordosis: 1) cantilever bending; 2) in situ bending; and 3) compression and/or distraction of screws along posterior fusion rods. METHODS Five cadaveric torsos were instrumented with pedicle screws at the L1-5 levels. Specimens underwent each of the 3 lordosis restoration procedures. The pedicle screw pullout force was monitored in real time via strain gauges that were mounted unilaterally at each level. The degree of correction was noted through fluoroscopic imaging. The peak loads experienced on the screws during surgery, total demand on instrumentation, and resting loads after corrective maneuvers were measured. RESULTS A mean overall lordotic correction of 10.9 ± 4.7° was achieved. No statistically significant difference in lordotic correction was observed between restoration procedures. In situ bending imparted the largest loads intraoperatively with an average of 1060 ± 599.9 N, followed by compression/distraction (971 ± 534.1 N) and cantilever bending (705 ± 413.0 N). In situ bending produced the largest total demand and postoperative loads at L-1 (1879 ± 1064.1 and 487 ± 118.8 N, respectively), which were statistically higher than cantilever bending and compression/distraction (786 ± 272.1 and 138 ± 99.2 N, respectively). CONCLUSIONS In situ bending resulted in the highest mechanical demand on posterior lumbar instrumentation, as well as the largest postoperative loads at L-1. These results suggest that the forces generated with in situ bending indicate a greater chance of intraoperative instrumentation failure and postoperative proximal pedicle screw pullout when compared with cantilever bending and/or compression/distraction options. The results are aimed at optimizing correction and fusion strategies in lordosis restoration cases.

Optimised in vitro applicable loads for the simulation of lateral bending in the lumbar spine.

PubMed

Dreischarf, Marcel; Rohlmann, Antonius; Bergmann, Georg; Zander, Thomas

2012-07-01

In in vitro studies of the lumbar spine simplified loading modes (compressive follower force, pure moment) are usually employed to simulate the standard load cases flexion-extension, axial rotation and lateral bending of the upper body. However, the magnitudes of these loads vary widely in the literature. Thus the results of current studies may lead to unrealistic values and are hardly comparable. It is still unknown which load magnitudes lead to a realistic simulation of maximum lateral bending. A validated finite element model of the lumbar spine was used in an optimisation study to determine which magnitudes of the compressive follower force and bending moment deliver results that fit best with averaged in vivo data. The best agreement with averaged in vivo measured data was found for a compressive follower force of 700 N and a lateral bending moment of 7.8 Nm. These results show that loading modes that differ strongly from the optimised one may not realistically simulate maximum lateral bending. The simplified but in vitro applicable loading cannot perfectly mimic the in vivo situation. However, the optimised magnitudes are those which agree best with averaged in vivo measured data. Its consequent application would lead to a better comparability of different investigations. Copyright © 2012 IPEM. Published by Elsevier Ltd. All rights reserved.

Finding line of action of the force exerted on erect spine based on lateral bending test in personalization of scoliotic spine models.

PubMed

Jalalian, Athena; Tay, Francis Eng Hock; Arastehfar, Soheil; Gibson, Ian; Liu, Gabriel

2017-04-01

In multi-body models of scoliotic spine, personalization of mechanical properties of joints significantly improves reconstruction of the spine shape. In personalization methods based on lateral bending test, simulation of bending positions is an essential step. To simulate, a force is exerted on the spine model in the erect position. The line of action of the force affects the moment of the force about the joints and thus, if not correctly identified, causes over/underestimation of mechanical properties. Therefore, we aimed to identify the line of action, which has got little attention in previous studies. An in-depth analysis was performed on the scoliotic spine movement from the erect to four spine positions in the frontal plane by using pre-operative X-rays of 18 adolescent idiopathic scoliosis (AIS) patients. To study the movement, the spine curvature was considered as a 2D chain of micro-scale motion segments (MMSs) comprising rigid links and 1-degree-of-freedom (DOF) rotary joints. It was found that two MMSs representing the inflection points of the erect spine had almost no rotation (0.0028° ± 0.0021°) in the movement. The small rotation can be justified by weak moment of the force about these MMSs due to very small moment arm. Therefore, in the frontal plane, the line of action of the force to simulate the left/right bending position was defined as the line that passes through these MMSs in the left/right bending position. Through personalization of a 3D spine model for our patients, we demonstrated that our line of action could result in good estimates of the spine shape in the bending positions and other positions not included in the personalization, supporting our proposed line of action.

Twirling and Whirling: Viscous Dynamics of Rotating Elastica

NASA Astrophysics Data System (ADS)

Wolgemuth, Charles; Powers, Thomas; Goldstein, Raymond

1999-10-01

The stability of forced elastic filaments arise in several important biological settings involving bend and twist elasticity at low Reynolds number. Examples include DNA transcription and replication and bacterial flagellar motion. In order to elucidate fundamental processes common to these systems, we consider the model problem of a rotationally forced filament with twist and bend elasticity. Competition between twist injection, twist diffusion, and writhing instabilities is described by a novel pair of PDEs for twist and bend evolution. Analytical and numerical methods elucidate the twist/bend coupling and reveal two dynamical regimes seperated by a Hopf bifurcation: (i) diffusion-dominated axial rotation, or twirling, and (ii) steady-state crankshafting motion, or whirling. Experiments are proposed to examine these phenomena and the consequences for swimming investigated.

Application of the Zero-Order Reaction Rate Model and Transition State Theory to predict porous Ti6Al4V bending strength.

PubMed

Reig, L; Amigó, V; Busquets, D; Calero, J A; Ortiz, J L

2012-08-01

Porous Ti6Al4V samples were produced by microsphere sintering. The Zero-Order Reaction Rate Model and Transition State Theory were used to model the sintering process and to estimate the bending strength of the porous samples developed. The evolution of the surface area during the sintering process was used to obtain sintering parameters (sintering constant, activation energy, frequency factor, constant of activation and Gibbs energy of activation). These were then correlated with the bending strength in order to obtain a simple model with which to estimate the evolution of the bending strength of the samples when the sintering temperature and time are modified: σY=P+B·[lnT·t-ΔGa/R·T]. Although the sintering parameters were obtained only for the microsphere sizes analysed here, the strength of intermediate sizes could easily be estimated following this model. Copyright © 2012 Elsevier B.V. All rights reserved.

Simultaneous effects of temperature and pressure on the donor binding energy in a V-groove quantum wire

NASA Astrophysics Data System (ADS)

Khordad, R.

2010-03-01

The influence of temperature and pressure, simultaneously, on the binding energy of a hydrogenic donor impurity in a ridge GaAs/Ga 1- xAl xAs quantum wire is studied using a variational procedure within the effective mass approximation. The subband energy and the binding energy of the donor impurity in its ground state as a function of the wire bend width and impurity location at different temperatures and pressures are calculated. The results show that, when the temperature increases, the donor binding energy decreases for a constant applied pressure for all wire bend widths. Also, the binding energy increases by increasing the pressure for a constant temperature for all wire bend widths. In addition, when the temperature and pressure are applied simultaneously the binding energy decreases as the quantum wire bend width increases. On the whole, it is deduced that the temperature and pressure have important effects on the donor binding energy in a V-groove quantum wire.

Mechanical signals at the base of a rat vibrissa: the effect of intrinsic vibrissa curvature and implications for tactile exploration

PubMed Central

Quist, Brian W.

2012-01-01

Rats actively tap and sweep their large mystacial vibrissae (whiskers) against objects to tactually explore their surroundings. When a vibrissa makes contact with an object, it bends, and this bending generates forces and bending moments at the vibrissa base. Researchers have only recently begun to quantify these mechanical variables. The present study quantifies the forces and bending moments at the vibrissa base with a quasi-static model of vibrissa deflection. The model was validated with experiments on real vibrissae. Initial simulations demonstrated that almost all vibrissa-object collisions during natural behavior will occur with the concave side of the vibrissa facing the object, and we therefore paid particular attention to the role of the vibrissa's intrinsic curvature in shaping the forces at the base. Both simulations and experiments showed that vibrissae with larger intrinsic curvatures will generate larger axial forces. Simulations also demonstrated that the range of forces and moments at the vibrissal base vary over approximately three orders of magnitude, depending on the location along the vibrissa at which object contact is made. Both simulations and experiments demonstrated that collisions in which the concave side of the vibrissa faces the object generate longer-duration contacts and larger net forces than collisions with the convex side. These results suggest that the orientation of the vibrissa's intrinsic curvature on the mystacial pad may increase forces during object contact and provide increased sensitivity to detailed surface features. PMID:22298834

Mechanical properties of lipid bilayers from molecular dynamics simulation

PubMed Central

Venable, Richard M.; Brown, Frank L.H.; Pastor, Richard W.

2015-01-01

Lipid areas (Aℓ), bilayer area compressibilities (KA), bilayer bending constants (KC), and monolayer spontaneous curvatures (c0) from simulations using the CHARMM36 force field are reported for 12 representative homogenous lipid bilayers. Aℓ (or their surrogate, the average deuterium order parameter in the “plateau region” of the chain) agree very well with experiment, as do the KA. Simulated KC are in near quantitative agreement with vesicle flicker experiments, but are somewhat larger than KC from x-ray, pipette aspiration, and neutron spin echo for saturated lipids. Spontaneous curvatures of bilayer leaflets from the simulations are approximately 30% smaller than experimental values of monolayers in the inverse hexagonal phase. PMID:26238099

Lift developed on unrestrained rectangular wings entering gusts at subsonic and supersonic speeds

NASA Technical Reports Server (NTRS)

Lomax, Harvard

1954-01-01

The object of this report is to provide an estimate, based on theoretical calculations, of the forces induced on a wing that is flying at a constant forward speed and suddenly enters a vertical gust. The calculations illustrate the effects of Mach number (from 0 to 2) and aspect ratio (2 to infinity), and solutions are given by means of which the response to gusts having arbitrary distributions of velocity can be calculated. The effects of pitching and wing bending are neglected and only wings of rectangular plan form are considered. Specific results are presented for sharp-edged and triangular gusts and various wing-air density ratios.

Relationship between friction force and orthodontic force at the leveling stage using a coated wire.

PubMed

Murayama, Masaki; Namura, Yasuhiro; Tamura, Takahiko; Iwai, Hiroaki; Shimizu, Noriyoshi

2013-01-01

The relationship between orthodontic force and friction produced from an archwire and brackets affects the sliding of the wire in the leveling stage. The purpose of this study was to evaluate the relationship between force and friction in a small esthetic nickel-titanium (Ni-Ti) wire. Five esthetic wires (three coated and two plated) and two small, plain Ni-Ti wires (0.012 and 0.014 inches) were used. We performed a three-point bending test according to ISO 15841 and the drawing test with a dental arch model designed with upper linguoversion of the lateral incisor in the arch (displacements of 0.5, 1.0, 2.0 and 3.0 mm), and evaluated the relationship between them. Unloading bending forces of all wires at displacements of less than 1.0 mm were larger than friction forces, but all friction forces at displacements exceeding 2.0 mm were larger than unloading bending forces. The arch likely expands when displacement from the proximal brackets exceeds 1.0 mm. The friction force of a martensite 0.014-inch Ni-Ti wire was significantly greater than those of the other esthetic and austenitic wires. A wire with the smallest possible friction force should be used in cases with more than 1.0 mm displacement.

On CD-AFM bias related to probe bending

NASA Astrophysics Data System (ADS)

Ukraintsev, V. A.; Orji, N. G.; Vorburger, T. V.; Dixson, R. G.; Fu, J.; Silver, R. M.

2012-03-01

Critical Dimension AFM (CD-AFM) is a widely used reference metrology. To characterize modern semiconductor devices, very small and flexible probes, often 15 nm to 20 nm in diameter, are now frequently used. Several recent publications have reported on uncontrolled and significant probe-to-probe bias variation during linewidth and sidewall angle measurements [1,2]. Results obtained in this work suggest that probe bending can be on the order of several nanometers and thus potentially can explain much of the observed CD-AFM probe-to-probe bias variation. We have developed and experimentally tested one-dimensional (1D) and two-dimensional (2D) models to describe the bending of cylindrical probes. An earlier 1D bending model reported by Watanabe et al. [3] was refined. Contributions from several new phenomena were considered, including: probe misalignment, diameter variation near the carbon nanotube tip (CNT) apex, probe bending before snapping, distributed van der Waals-London force, etc. The methodology for extraction of the Hamaker probe-surface interaction energy from experimental probe bending data was developed. To overcome limitations of the 1D model, a new 2D distributed force (DF) model was developed. Comparison of the new model with the 1D single point force (SPF) model revealed about 27 % difference in probe bending bias between the two. A simple linear relation between biases predicted by the 1D SPF and 2D DF models was found. This finding simplifies use of the advanced 2D DF model of probe bending in various CD-AFM applications. New 2D and three-dimensional (3D) CDAFM data analysis software is needed to take full advantage of the new bias correction modeling capabilities.

Effects of mistuning on bending-torsion flutter and response of a cascade in incompressible flow. [turbofan engines

NASA Technical Reports Server (NTRS)

Kaza, K. R. V.; Kielb, R. E.

1981-01-01

The effect of small differences between the individual blades (mistuning) on the aeroelastic stability and response of a cascade were studied. The aerodynamic, inertial, and structural coupling between the bending and torsional motions of each blade and the aerodynamic coupling between the blades was considered. A digital computer program was developed to conduct parametric studies. Results indicate that the mistuning has a beneficial effect on the coupled bending torsion and uncoupled torsion flutter. On forced response, however, the effect may be either beneficial or adverse, depending on the engine order of the forcing function. The results also illustrate that it may be feasible to utilize mistuning as a passive control to increase flutter speed while maintaining forced response at an acceptable level.

Evaluation of mechanical deformation and distributive magnetic loads with different mechanical constraints in two parallel conducting bars

NASA Astrophysics Data System (ADS)

Lee, Ho-Young; Lee, Se-Hee

2017-08-01

Mechanical deformation, bending deformation, and distributive magnetic loads were evaluated numerically and experimentally for conducting materials excited with high current. Until now, many research works have extensively studied the area of magnetic force and mechanical deformation by using coupled approaches such as multiphysics solvers. In coupled analysis for magnetoelastic problems, some articles and commercial software have presented the resultant mechanical deformation and stress on the body. To evaluate the mechanical deformation, the Lorentz force density method (LZ) and the Maxwell stress tensor method (MX) have been widely used for conducting materials. However, it is difficult to find any experimental verification regarding mechanical deformation or bending deformation due to magnetic force density. Therefore, we compared our numerical results to those from experiments with two parallel conducting bars to verify our numerical setup for bending deformation. Before showing this, the basic and interesting coupled simulation was conducted to test the mechanical deformations by the LZ (body force density) and the MX (surface force density) methods. This resulted in MX gave the same total force as LZ, but the local force distribution in MX introduced an incorrect mechanical deformation in the simulation of a solid conductor.

Influences of thickness, scanning velocity and relative humidity on the frictional properties of WS2 nanosheets

NASA Astrophysics Data System (ADS)

Feng, Dongdong; Peng, Jinfeng; Liu, Sisi; Zheng, Xuejun; Yan, Xinyang; He, Wenyuan

2018-01-01

Distinguishing with the traditional cantilever mechanics method, we propose the extended cantilever mechanics method to calibrate the lateral calibration factor by using the normal spring constant obtained from atomic force microscopy (AFM) but not the Young’s modulus and the width of the cantilever, before the influences of thickness, scanning velocity and humidity on the frictional properties are investigated via friction measurement performed by the lateral force mode (LFM) of AFM. Tungsten disulfide (WS2) nanosheets were prepared through hydrothermal intercalation and exfoliation route, and AFM and Raman microscope were used to investigate the frictional properties, thickness and crystalline structure. The friction force and coefficient decrease monotonically with the increase of the nanosheet’s thickness, and the friction coefficient minimum value is close to 0.012 when the thickness larger than 5 nm. The friction property variation on the nanosheet’s thickness can be explained by the puckering effect of tip-sheet adhesion according thickness dependence of bending stiffness in the frame of continuum mechanics. The friction force is a constant value 1.7 nN when the scanning speed larger than the critical value 3.10 μm s-1, while it logarithmically increases for the scanning speed less than the critical value. It is easy to understand through the energy dissipation model and the thermally activated effect. The friction force and friction coefficient increase with the relative humidity at the range of 30%-60%, and the latter is at the range of 0.010-0.013. Influence of relative humidity is discussed via the increasing area of the water monolayer during the water adsorption process. The research can not only enrich nanotribology theory, but also prompt two dimensions materials for nanomechanical applications.

Crashworthy Troop Seat Testing Program

DTIC Science & Technology

1977-11-01

19 ’rest 4 . . . . . . . . . .. . 29 | Detail Design’Finalization. .... 29 Vertical Wire - Bending Energy Attenuator 32 Toggle Latch...Strut Wire - Bending Attenuator Force Deflection. . . . ................... 28 15 Notched Wire and Pin Anchorage Test Specimen . 30 16 Quick-Disconnect...and Hold-Down Cable ......... 31 17 Failed Hold-Down Cable ...... . . . . 31 18 Wire - Bending Tension/Compression Energy Attenuator

Aircraft Crash Survival Design Guide. Volume 4. Aircraft Seats, Restraints, Litters, and Cockpit/Cabin Delethalization

DTIC Science & Technology

1989-12-01

ILLUSTRATIONS (CONTD) 44 Tubular strut wire - bending energy absorber ...... ........... 91 45 Inversion tube concepL with typical force-deformation...expected from a rod-bending sled decelerator and a wire - bending seat load limiter (Refer- ences 35 and 36). Therefore, correcting the calculated...attaching the seat bucket to the rollers, compressive as well as tensile loads can be sustained. Two variations of the wire - bending device have been

An artificial muscle actuator for biomimetic underwater propulsors.

PubMed

Yim, Woosoon; Lee, Joonsoo; Kim, Kwang J

2007-06-01

In this paper, we introduce the analytical framework of the modeling dynamic characteristics of a soft artificial muscle actuator for aquatic propulsor applications. The artificial muscle used for this underwater application is an ionic polymer-metal composite (IPMC) which can generate bending motion in aquatic environments. The inputs of the model are the voltages applied to multiple IPMCs, and the output can be either the shape of the actuators or the thrust force generated from the interaction between dynamic actuator motions and surrounding water. In order to determine the relationship between the input voltages and the bending moments, the simplified RC model is used, and the mechanical beam theory is used for the bending motion of IPMC actuators. Also, the hydrodynamic forces exerted on an actuator as it moves relative to the surrounding medium or water are added to the equations of motion to study the effect of actuator bending on the thrust force generation. The proposed method can be used for modeling the general bending type artificial muscle actuator in a single or segmented form operating in the water. The segmented design has more flexibility in controlling the shape of the actuator when compared with the single form, especially in generating undulatory waves. Considering an inherent nature of large deformations in the IPMC actuator, a large deflection beam model has been developed and integrated with the electrical RC model and hydrodynamic forces to develop the state space model of the actuator system. The model was validated against existing experimental data.

Actin growth profile in clathrin-mediated endocytosis

NASA Astrophysics Data System (ADS)

Tweten, D. J.; Bayly, P. V.; Carlsson, A. E.

2017-05-01

Clathrin-mediated endocytosis in yeast is driven by a protein patch containing close to 100 different types of proteins. Among the proteins are 5000 -10 000 copies of polymerized actin, and successful endocytosis requires growth of the actin network. Since it is not known exactly how actin network growth drives endocytosis, we calculate the spatial distribution of actin growth required to generate the force that drives the process. First, we establish the force distribution that must be supplied by actin growth, by combining membrane-bending profiles obtained via electron microscopy with established theories of membrane mechanics. Next, we determine the profile of actin growth, using a continuum mechanics approach and an iterative procedure starting with an actin growth profile obtained from a linear analysis. The profile has fairly constant growth outside a central hole of radius 45-50 nm, but very little growth in this hole. This growth profile can reproduce the required forces if the actin shear modulus exceeds 80 kPa, and the growing filaments can exert very large polymerization forces. The growth profile prediction could be tested via electron-microscopy or super-resolution experiments in which the turgor pressure is suddenly turned off.

[Three-dimensional finite element analysis of maxillary anterior teeth retraction force system in light wire technique].

PubMed

Zhang, Xiangfeng; Wang, Chao; Xia, Xi; Deng, Feng; Zhang, Yi

2015-06-01

This study aims to construct a three-dimensional finite element model of a maxillary anterior teeth retraction force system in light wire technique and to investigate the difference of hydrostatic pressure and initial displacement of upper anterior teeth under different torque values of tip back bend. A geometric three-dimensional model of the maxillary bone, including all the upper teeth, was achieved via CT scan. To construct the force model system, lingual brackets and wire were constructed by using the Solidworks. Brackets software, and wire were assembled to the teeth. ANASYS was used to calculate the hydrostatic pressure and the initial displacement of maxillary anterior teeth under different tip-back bend moments of 15, 30, 45, 60, and 75 Nmm when the class II elastic force was 0.556 N. Hydrostatic pressure was concentrated in the root apices and cervical margin of upper anterior teeth. Distal tipping and relative intrusive displacement were observed. The hydrostatic pressure and initial displacement of upper canine were greater than in the central and lateral incisors. This hydrostatic pressure and initial intrusive displacement increased with an increase in tip-back bend moment. Lingual retraction force system of maxillary anterior teeth in light wire technique can be applied safely and controllably. The type and quantity of teeth movement can be controlled by the alteration of tip-back bend moment.

Ultrafast dynamics of liquid water: Energy relaxation and transfer processes of the OH stretch and the HOH bend

DOE Office of Scientific and Technical Information (OSTI.GOV)

Imoto, Sho; Xantheas, Sotiris S.; Saito, Shinji

2015-08-27

The vibrational energy relaxation and transfer processes of the OH stretching and the HOH bending vibrations in liquid water are investigated via the theoretical calculation of the pump-probe spectra obtained from non-equilibrium molecular dynamics simulations with the TTM3-F interaction potential. The excitation of the OH stretch induces an instantaneous response of the high frequency librational motions in the 600-1000 cm-1 range. In addition, the excess energy of the OH stretch of a water molecule quickly transfers to the OH stretches of molecules in its first hydration shell with a time constant of ~50 fs, followed by relaxation to the HOHmore » bends of the surrounding molecules with a time constant of 230 fs. The excitation of the HOH bend also results in the ultrafast excitation of the high frequency librational motions. The energy of the excited HOH bend of a water molecule decays, with a time constant of 200 fs, mainly to the relaxation of the HOH bends of its surrounding molecules. The energies of the HOH bends were found to transfer quickly to the intermolecular motions via the coupling with the high frequency librational motions. The excess energy of the OH stretch or the HOH bend relaxes to the high frequency intermolecular librational motions and eventually to the hot ground state with a time scale of ~1 ps via the coupling with the librational and translational motions. The energy relaxation and transfer processes were found to depend on the local hydrogen bonding network; the relaxations of the excess energy of the OH stretch and the HOH bend of four- and five-coordinated molecules are faster than those of a three-coordinated molecule due to the delocalization of the vibrational motions of the former (four- and five-coordinated molecules) compared to those of the later (three-coordinated molecules). The present results highlight the importance of the high frequency intermolecular librational modes in facilitating the ultrafast energy relaxation process in liquid water via their strong nonlinear couplings with the intramolecular OH stretching and HOH bending vibrations. S.S.X. acknowledges the support of the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences, and Biosciences. Pacific Northwest National Laboratory (PNNL) is a multiprogram national laboratory operated for DOE by Battelle. The calculation was carried out using the computing resources at the Research Center for Computational Science in Okazaki, Japan.« less

Relationship between friction force and orthodontic force at the leveling stage using a coated wire

PubMed Central

MURAYAMA, Masaki; NAMURA, Yasuhiro; TAMURA, Takahiko; IWAI, Hiroaki; SHIMIZU, Noriyoshi

2013-01-01

The relationship between orthodontic force and friction produced from an archwire and brackets affects the sliding of the wire in the leveling stage. Objective The purpose of this study was to evaluate the relationship between force and friction in a small esthetic nickel-titanium (Ni-Ti) wire. Material and Methods Five esthetic wires (three coated and two plated) and two small, plain Ni-Ti wires (0.012 and 0.014 inches) were used. We performed a three-point bending test according to ISO 15841 and the drawing test with a dental arch model designed with upper linguoversion of the lateral incisor in the arch (displacements of 0.5, 1.0, 2.0 and 3.0 mm), and evaluated the relationship between them. Results Unloading bending forces of all wires at displacements of less than 1.0 mm were larger than friction forces, but all friction forces at displacements exceeding 2.0 mm were larger than unloading bending forces. The arch likely expands when displacement from the proximal brackets exceeds 1.0 mm. The friction force of a martensite 0.014-inch Ni-Ti wire was significantly greater than those of the other esthetic and austenitic wires. Conclusions A wire with the smallest possible friction force should be used in cases with more than 1.0 mm displacement. PMID:24473722

Non-contact quantification of laser micro-impulse in water by atomic force microscopy and its application for biomechanics

NASA Astrophysics Data System (ADS)

Hosokawa, Yoichiroh

2011-12-01

We developed a local force measurement system of a femtosecond laser-induced impulsive force, which is due to shock and stress waves generated by focusing an intense femtosecond laser into water with a highly numerical aperture objective lens. In this system, the force localized in micron-sized region was detected by bending movement of a cantilever of atomic force microscope (AFM). Here we calculated the bending movement of the AFM cantilever when the femtosecond laser is focused in water at the vicinity of the cantilever and the impulsive force is loaded on the cantilever. From the result, a method to estimate the total of the impulsive force at the laser focal point was suggested and applied to estimate intercellular adhesion strength.

Local vibrational modes of the formic acid dimer - the strength of the double hydrogen bond

NASA Astrophysics Data System (ADS)

Kalescky, R.; Kraka, E.; Cremer, D.

2013-07-01

The 24 normal and 24 local vibrational modes of the formic acid dimer formed by two trans formic acid monomers to a ring (TT1) are analysed utilising preferentially experimental frequencies, but also CCSD(T)/CBS and ωB97X-D harmonic vibrational frequencies. The local hydrogen bond (HB) stretching frequencies are at 676 cm-1 and by this 482 and 412 cm-1 higher compared to the measured symmetric and asymmetric HB stretching frequencies at 264 and 194 cm-1. The adiabatic connection scheme between local and normal vibrational modes reveals that the lowering is due to the topology of dimer TT1, mass coupling, and avoided crossings involving the HṡṡṡOC bending modes. The HB local mode stretching force constant is related to the strength of the HB whereas the normal mode stretching force constant and frequency lead to an erroneous underestimation of the HB strength. The HB in TT1 is stabilised by electron delocalisation in the O=C-O units fostered by forming a ring via double HBs. This implies that the CO apart from the OH local stretching frequencies reflect the strength of the HB via their red or blue shifts relative to their corresponding values in trans formic acid.

Bending, force recovery, and D-cones in origami inspired model geometries

NASA Astrophysics Data System (ADS)

Eldar, Theresa; Rozairo, Damith; Croll, Andrew B.

The need for materials with advanced functionality has driven a considerable amount of modern materials science. One idea that has gained significant traction is combining of the ideas Origami and Kirigami with existing materials to build in advanced functionality. In most origami damage is induced in order to trap areas of high curvature in desirable locations in a material. However, the long term and dynamic consequences of local failure are largely unknown. In order to gauge the complex interplay of material properties, relaxation and failure in a set of model thin films, a series of bending and force recovery experiments were carried out. We focus on three materials; polydimethylsiloxane (PDMS), polycarbonate (PC), and polystyrene (PS) chosen for their varying responses to stress. We first measured the load bearing capacity of a single bend in each material, examining the force recovery of bends at various curvatures. Next we examined a doubly folded system in which a single developable cone was created in a similar manner. While the D-cone clearly has massive local consequences for each system, it plays an insignificant role in the system's overall behavior. Finally, we considered higher order combinations of d-cones, ridges and bends. AFOSR under the Young Investigator Program (FA9550-15-1-0168).

Microscopic Origins of Shear Jamming for 2D Frictional Grains

NASA Astrophysics Data System (ADS)

Wang, Dong; Ren, Jie; Dijksman, Joshua A.; Zheng, Hu; Behringer, Robert P.

2018-05-01

Shear jamming (SJ) occurs for frictional granular materials with packing fractions ϕ in ϕS<ϕ <ϕJ0, when the material is subject to shear strain γ starting from a force-free state. Here, ϕJμ is the isotropic jamming point for particles with a friction coefficient μ . SJ states have mechanically stable anisotropic force networks, e.g., force chains. Here, we investigate the origins of SJ by considering small-scale structures—trimers and branches—whose response to shear leads to SJ. Trimers are any three grains where the two outer grains contact a center one. Branches occur where three or more quasilinear force chain segments intersect. Certain trimers respond to shear by compressing and bending; bending is a nonlinear symmetry-breaking process that can push particles in the dilation direction faster than the affine dilation. We identify these structures in physical experiments on systems of two-dimensional frictional discs, and verify their role in SJ. Trimer bending and branch creation both increase Z above Ziso≃3 needed for jamming 2D frictional grains, and grow the strong force network, leading to SJ.

A Numerical Model for Flow and Sediment Transport in Alluvial-River Bends.

DTIC Science & Technology

1983-12-01

into the bend divided by the computed total sediment discharge across the section. This insures that sediment continuity is preserved along the...6 * * * 0 * C YORF DEFINITION’S , C PI : PI !!! BOSTON CREME, APPLE, PUMPKIN , LTC* "" C G = GRAVITATIONAL CONSTANT * r AAA = COEFFICI92T IN

Differential quadrature method of nonlinear bending of functionally graded beam

NASA Astrophysics Data System (ADS)

Gangnian, Xu; Liansheng, Ma; Wang, Youzhi; Quan, Yuan; Weijie, You

2018-02-01

Using the third-order shear deflection beam theory (TBT), nonlinear bending of functionally graded (FG) beams composed with various amounts of ceramic and metal is analyzed utilizing the differential quadrature method (DQM). The properties of beam material are supposed to accord with the power law index along to thickness. First, according to the principle of stationary potential energy, the partial differential control formulae of the FG beams subjected to a distributed lateral force are derived. To obtain numerical results of the nonlinear bending, non-dimensional boundary conditions and control formulae are dispersed by applying the DQM. To verify the present solution, several examples are analyzed for nonlinear bending of homogeneous beams with various edges. A minute parametric research is in progress about the effect of the law index, transverse shear deformation, distributed lateral force and boundary conditions.

The tolerance of the femoral shaft in combined axial compression and bending loading.

PubMed

Ivarsson, B Johan; Genovese, Daniel; Crandall, Jeff R; Bolton, James R; Untaroiu, Costin D; Bose, Dipan

2009-11-01

The likelihood of a front seat occupant sustaining a femoral shaft fracture in a frontal crash has traditionally been assessed by an injury criterion relying solely on the axial force in the femur. However, recently published analyses of real world data indicate that femoral shaft fracture occurs at axial loads levels below those found experimentally. One hypothesis attempting to explain this discrepancy suggests that femoral shaft fracture tends to occur as a result of combined axial compression and applied bending. The current study aims to evaluate this hypothesis by investigating how these two loading components interact. Femoral shafts harvested from human cadavers were loaded to failure in axial compression, sagittal plane bending, and combined axial compression and sagittal plane bending. All specimens subjected to bending and combined loading fractured midshaft, whereas the specimens loaded in axial compression demonstrated a variety of failure locations including midshaft and distal end. The interaction between the recorded levels of applied moment and axial compression force at fracture were evaluated using two different analysis methods: fitting of an analytical model to the experimental data and multiple regression analysis. The two analysis methods yielded very similar relationships between applied moment and axial compression force at midshaft fracture. The results indicate that posteroanterior bending reduces the tolerance of the femoral shaft to axial compression and that that this type of combined loading therefore may contribute to the high prevalence of femoral shaft fracture in frontal crashes.

Geometric frustration and compatibility conditions for two-dimensional director fields.

PubMed

Niv, Idan; Efrati, Efi

2018-01-17

Bent core (or banana shaped) liquid-crystal-forming-molecules locally favor an ordered state of zero splay and constant bend. Such a state, however, cannot be realized in the plane and the resulting liquid-crystalline phase is frustrated and must exhibit some compromise of these two mutually contradicting local intrinsic tendencies. This constitutes one of the most well-studied examples in which the intrinsic geometry of the constituents of a material gives rise to a geometrically frustrated assembly. Such geometric frustration is not only natural and ubiquitous but also leads to a striking variety of morphologies of ground states and exotic response properties. In this work we establish the necessary and sufficient conditions for two scalar functions, s and b to describe the splay and bend of a director field in the plane. We generalize these compatibility conditions for geometries with non-vanishing constant Gaussian curvature, and provide a reconstruction formula for the director field depending only on the splay and bend fields and their derivatives. Finally, we discuss optimal compromises for simple incompatible cases where the locally preferred values of the splay and bend cannot be simultaneously achieved.

Incisor crown bending strength correlates with diet and incisor curvature in anthropoid primates.

PubMed

Deane, Andrew S

2015-02-01

Anthropoid incisors are large relative to the postcanine dentition and function in the preprocessing of food items. Previous analyses of anthropoid incisor allometry and shape demonstrate that incisor morphology is correlated with preferred foods and that more frugivorous anthropoids have larger and more curved incisors. Although the relationship between incisal crown curvature and preferred foods has been well documented in extant and fossil anthropoids, the functional significance of curvature variation has yet to be conclusively established. Given that an increase in crown curvature will increase maximum linear crown dimensions, and bending resistance is a function of linear crown dimensions, it is hypothesized that incisor crown curvature functons to increase incisor crown resistance to bending forces. This study uses beam theory to calculate the mesiodistal and labiolingual bending strengths of the maxillary and mandibular incisors of hominoid and platyrrhine taxa with differing diets and variable degrees of incisal curvature. Results indicate that bending strength correlates with incisal curvature and that frugivores have elevated incisor bending resistance relative to folivores. Maxillary central incisor bending strengths further discriminate platyrrhine and hominoid hard- and soft-object frugivores suggesting this crown is subjected to elevated occlusal loading relative to other incisors. These results are consistent with the hypothesis that incisor crown curvature functions to increase incisor crown resistance to bending forces but does not preclude the possibility that incisor bending strength is a composite function of multiple dentognathic variables including, but not limited to, incisor crown curvature. © 2014 Wiley Periodicals, Inc.

Research on relation between bending stress and characteristic frequency of H-shaped beam by free vibration deflection

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yoshida, Tsutomu; Watanabe, Takeshi

2014-05-27

In order to investigate a relation between a bending stress and a characteristic frequency of a beam, 4-point loading which had constant moment region was conducted to a beam with H shape configuration experimentally and numerically. H-shaped beam has many characteristic deformation modes. Axial tensile stress in the beam made its characteristic frequency higher, and compressive stress lower. In the experiment, some characteristic frequencies got higher by a bending stress, and the others stayed in a small frequency fluctuation. The distinction is anticipated as a capability to measure a bending stress of a beam by its characteristic frequencies.

Impact buckling of thin bars in the elastic range hinged at both ends

NASA Technical Reports Server (NTRS)

Koning, Carel; Taub, Josef

1934-01-01

Following the development of the well-known differential equations of the problem and their resolution for failure in tension, the bending (transverse) oscillations of an originally not quite straight bar hinged at both ends and subjected to a constant longitudinal force (shock load) are analyzed. To this end the course of the bar form is expanded in a sinusoidal series, after which the investigation is carried through separately for the fundamental oscillation and the (n-1)the higher oscillations. The analysis of the fundamental oscillation distinguishes three cases: shock load lower, equal to, or higher than the Eulerian load. The investigation leads to functions which are proportional to the maximum stresses in time and space due to the shock stresses in buckling.

Fracture study of windshield glass panes

NASA Technical Reports Server (NTRS)

Yeh, H. Y.

1987-01-01

The major stresses which cause crack propagation in windshield glass panes are induced by bending moments which result from the pressure differentials across the panes. Hence the stress intensity factors for the finite plate with the semi-elliptical surface flaw and edge crack under the bending moments are examined. The results show that the crack growth will be upperbound if it is computed by using the stress intensity factor for the finite plate with the edge crack subjected to pure bending moments. Furthermore, if the ratio of crack depth to plate thickness, a/t, is within 0.3, the stress intensity factor can be conservatively assumed to be constant at the value of a/t equal to zero. A simplified equation to predict the structural life of glass panes is derived based on constant stress intensity factor. The accuracy of structural life is mainly dependent on how close the empirical parameter, m, can be estimated.

Weak gravitational lensing of quantum perturbed lukewarm black holes and cosmological constant effect

NASA Astrophysics Data System (ADS)

Ghaffarnejad, Hossein; Mojahedi, Mojtaba Amir

2017-05-01

The aim of the paper is to study weak gravitational lensing of quantum (perturbed) and classical lukewarm black holes (QLBHs and CLBHs respectively) in the presence of cosmological parameter Λ. We apply a numerical method to evaluate the deflection angle of bending light rays, image locations θ of sample source β =-\\tfrac{π }{4}, and corresponding magnifications μ. There are no obtained real values for Einstein ring locations {θ }E(β =0) for CLBHs but we calculate them for QLBHs. As an experimental test of our calculations, we choose mass M of 60 types of the most massive observed galactic black holes acting as a gravitational lens and study quantum matter field effects on the angle of bending light rays in the presence of cosmological constant effects. We calculate locations of non-relativistic images and corresponding magnifications. Numerical diagrams show that the quantum matter effects cause absolute values of the quantum deflection angle to be reduced with respect to the classical ones. The sign of the quantum deflection angle is changed with respect to the classical values in the presence of the cosmological constant. This means dominance of the anti-gravity counterpart of the cosmological horizon on the angle of bending light rays with respect to absorbing effects of 60 local types of the most massive observed black holes. Variations of the image positions and magnifications are negligible when increasing dimensionless cosmological constant ɛ =\\tfrac{16{{Λ }}{M}2}{3}. The deflection angle takes positive (negative) values for CLBHs (QLBHs) and they decrease very fast (slowly) by increasing the closest distance x 0 of bending light ray and/or dimensionless cosmological parameter for sample giant black holes with 0.001< ɛ < 0.01.

Predicting bending strength of fire-retardant-treated plywood from screw-withdrawal tests

Treesearch

J. E. Winandy; P. K. Lebow; W. Nelson

This report describes the development of a test method and predictive model to estimate the residual bending strength of fire-retardant-treated plywood roof sheathing from measurement of screw-withdrawal force. The preferred test methodology is described in detail. Models were developed to predict loss in mean and lower prediction bounds for plywood bending strength as...

Potential effect of stand structure on belowground allocation

Treesearch

Thomas J. Dean

2001-01-01

Stand structure affects two key variables that affect biomass allocation to the stem: leaf area and height to the center of the crown. By translating wind forces into bending moment, these variables generate bending stress within a stem. The uniform stress axiom of stem formation can be used to calculate current stem mass for a given bending moment and stem allocation...

Simulation of non-Newtonian oil-water core annular flow through return bends

NASA Astrophysics Data System (ADS)

Jiang, Fan; Wang, Ke; Skote, Martin; Wong, Teck Neng; Duan, Fei

2018-01-01

The volume of fluid (VOF) model is used together with the continuum surface force (CSF) model to numerically simulate the non-Newtonian oil-water core annular flow across return bends. A comprehensive study is conducted to generate the profiles of pressure, velocity, volume fraction and wall shear stress for different oil properties, flow directions, and bend geometries. It is revealed that the oil core may adhere to the bend wall under certain operating conditions. Through the analysis of the total pressure gradient and fouling angle, suitable bend geometric parameters are identified for avoiding the risk of fouling.

Measuring blocking force to interpret ionic mechanisms within bucky-gel actuators

NASA Astrophysics Data System (ADS)

Kruusamäe, Karl; Sugino, Takushi; Asaka, Kinji

2015-04-01

Bucky-gel laminates are tri-layer structures where polymeric electrolyte film is sandwiched between two compliant electrode layers of carbon nanotubes and ionic liquid. The resulting ionic and capacitive structures, being regarded as a type of electromechanically active polymers (EAP), have the perspective of becoming soft bending actuators in the fields such as biomimetic robotics or lab-on-chip technology. A typical electromechanical step response of a bucky-gel actuator in a cantilever configuration exhibits a fast bending displacement followed by some reverse motion referred to as the back-relaxation. It has been proposed that the bending but also the back-relaxation of bucky-gel laminates occur due to the relocation of cations and anions within the tri-layer structure. A great number of modeling about ionic EAP materials aims to predict the amplitude of free bending or the blocking force of the actuator. However, as the bucky-gel laminates are viscoelastic, the translation from generated force to bending amplitude is not always straightforward - it can take the form of an integro-differential equation with speed (i.e. the amplitude and type of the input signal) and temperature (i.e. the electronic conductivity of the material and driving current) as just some of the parameters. In this study we propose to use a so-called two carrier-model to analyze the electromechanical response of a bucky-gel actuator. After modifying the electrical equivalent circuit, the time domain response of blocking force is measured to elaborate the ionic mechanisms during the work-cycle of bucky-gel actuator.

Improved Automatically Locking/Unlocking Orthotic Knee Joint

NASA Technical Reports Server (NTRS)

Weddendorf, Bruce

1995-01-01

Proposed orthotic knee joint improved version of one described in "Automatically Locking/Unlocking Orthotic Knee Joint" (MFS-28633). Locks automatically upon initial application of radial force (wearer's weight) and unlocks automatically, but only when all loads (radial force and bending) relieved. Joints lock whenever wearer applies weight to knee at any joint angle between full extension and 45 degree bend. Both devices offer increased safety and convenience relative to conventional orthotic knee joints.

Evaluation of Several Approximate Methods for Calculating the Symmetrical Bending-Moment Response of Flexible Airplanes to Isotropic Atmospheric Turbulence

NASA Technical Reports Server (NTRS)

Bennett, Floyd V.; Yntema, Robert T.

1959-01-01

Several approximate procedures for calculating the bending-moment response of flexible airplanes to continuous isotropic turbulence are presented and evaluated. The modal methods (the mode-displacement and force-summation methods) and a matrix method (segmented-wing method) are considered. These approximate procedures are applied to a simplified airplane for which an exact solution to the equation of motion can be obtained. The simplified airplane consists of a uniform beam with a concentrated fuselage mass at the center. Airplane motions are limited to vertical rigid-body translation and symmetrical wing bending deflections. Output power spectra of wing bending moments based on the exact transfer-function solutions are used as a basis for the evaluation of the approximate methods. It is shown that the force-summation and the matrix methods give satisfactory accuracy and that the mode-displacement method gives unsatisfactory accuracy.

Examination of a lumbar spine biomechanical model for assessing axial compression, shear, and bending moment using selected Olympic lifts.

PubMed

Eltoukhy, Moataz; Travascio, Francesco; Asfour, Shihab; Elmasry, Shady; Heredia-Vargas, Hector; Signorile, Joseph

2016-09-01

Loading during concurrent bending and compression associated with deadlift, hang clean and hang snatch lifts carries the potential for injury to the intervertebral discs, muscles and ligaments. This study examined the capacity of a newly developed spinal model to compute shear and compressive forces, and bending moments in lumbar spine for each lift. Five male subjects participated in the study. The spine was modeled as a chain of rigid bodies (vertebrae) connected via the intervertebral discs. Each vertebral reference frame was centered in the center of mass of the vertebral body, and its principal directions were axial, anterior-posterior, and medial-lateral. The results demonstrated the capacity of this spinal model to assess forces and bending moments at and about the lumbar vertebrae by showing the variations among these variables with different lifting techniques. These results show the model's potential as a diagnostic tool.

A square-plate piezoelectric linear motor operating in two orthogonal and isomorphic face-diagonal-bending modes.

PubMed

Ci, Penghong; Chen, Zhijiang; Liu, Guoxi; Dong, Shuxiang

2014-01-01

We report a piezoelectric linear motor made of a single Pb(Zr,Ti)O3 square-plate, which operates in two orthogonal and isomorphic face-diagonal-bending modes to produce precision linear motion. A 15 × 15 × 2 mm prototype was fabricated, and the motor generated a driving force of up to 1.8 N and a speed of 170 mm/s under an applied voltage of 100 Vpp at the resonance frequency of 136.5 kHz. The motor shows such advantages as large driving force under relatively low driving voltage, simple structure, and stable motion because of its isomorphic face-diagonal-bending mode.

The deflection of carbon composite carbon nanotube / graphene using molecular dynamics simulation

NASA Astrophysics Data System (ADS)

Kolesnikova, A. S.; Kirillova, I. V.; Kossovich, L. U.

2018-02-01

For the first time, the dependence of the bending force on the transverse displacement of atoms in the center of the composite material consisting of graphene and parallel oriented zigzag nanotubes was studied. Mathematical modeling of the action of the needle of the atomic force microscope was carried out using the single-layer armchair carbon nanotube. Armchair nanotubes are convenient for using them as a needle of an atomic force microscope, because their edges are not sharpened (unlike zigzag tubes). Consequently, armchair nanotubes will cause minimal damage upon contact with the investigation object. The geometric parameters of the composite was revealed under the action of the bending force of 6μN.

Ankle-foot orthosis bending axis influences running mechanics.

PubMed

Russell Esposito, Elizabeth; Ranz, Ellyn C; Schmidtbauer, Kelly A; Neptune, Richard R; Wilken, Jason M

2017-07-01

Passive-dynamic ankle-foot orthoses (AFOs) are commonly prescribed to improve locomotion for people with lower limb musculoskeletal weakness. The clinical prescription and design process are typically qualitative and based on observational assessment and experience. Prior work examining the effect of AFO design characteristics generally excludes higher impact activities such as running, providing clinicians and researchers limited information to guide the development of objective prescription guidelines. The proximal location of the bending axis may directly influence energy storage and return and resulting running mechanics. The purpose of this study was to determine if the location of an AFO's bending axis influences running mechanics. Marker and force data were recorded as 12 participants with lower extremity weakness ran overground while wearing a passive-dynamic AFO with posterior struts manufactured with central (middle) and off-centered (high and low) bending axes. Lower extremity joint angles, moments, powers, and ground reaction forces were calculated and compared between limbs and across bending axis conditions. Bending axis produced relatively small but significant changes. Ankle range of motion increased as the bending axis shifted distally (p<0.003). Peak ankle power absorption was greater in the low axis than high (p=0.013), and peak power generation was greater in the low condition than middle or high conditions (p<0.009). Half of the participants preferred the middle bending axis, four preferred low and two preferred high. Overall, if greater ankle range of motion is tolerated, a low bending axis provides power and propulsive benefits during running, although individual preference and physical ability should also be considered. Published by Elsevier B.V.

Failure of the lumbar pedicles under bending loading - biomed 2010.

PubMed

Arregui-Dalmases, Carlos; Ash, Joseph H; Del Pozo, Eduardo; Kerrigan, Jason R; Crandall, Jeff

2010-01-01

The purpose of this study was to investigate the magnitude of bending moment that results in fracture of the pedicles when lumbar vertebrae are loaded in four-point bending. Nine human second lumbar vertebrae (L2) were harvested from donors aged 59-75 years. The specimens were potted and then subjected to quasi-static sagittal-plane four-point bending, which allowed for a constant bending moment applied over a 3.8 cm span centered on the vertebral pedicles until fracture. The failure bending moment calculated for the pedicles varied widely (30.7 +/- 12.3 Nm) and was poorly correlated with subject age (y = -0.91x + 91.5, R(2) = -0.27). With increasing displacement, the bending moment applied to the pedicles increased, first linearly, followed by a non-linear portion, prior to specimen fracture. In general, the specimens failed at the interface of the pedicles and vertebral bodies, but failures were observed elsewhere as well. These data provide sufficient response and boundary condition information for finite element modeling and model validation.

Free energy perturbation method for measuring elastic constants of liquid crystals

NASA Astrophysics Data System (ADS)

Joshi, Abhijeet

There is considerable interest in designing liquid crystals capable of yielding specific morphological responses in confined environments, including capillaries and droplets. The morphology of a liquid crystal is largely dictated by the elastic constants, which are difficult to measure and are only available for a handful of substances. In this work, a first-principles based method is proposed to calculate the Frank elastic constants of nematic liquid crystals directly from atomistic models. These include the standard splay, twist and bend deformations, and the often-ignored but important saddle-splay constant. The proposed method is validated using a well-studied Gay-Berne(3,5,2,1) model; we examine the effects of temperature and system size on the elastic constants in the nematic and smectic phases. We find that our measurements of splay, twist, and bend elastic constants are consistent with previous estimates for the nematic phase. We further outline the implementation of our approach for the saddle-splay elastic constant, and find it to have a value at the limits of the Ericksen inequalities. We then proceed to report results for the elastic constants commonly known liquid crystals namely 4-pentyl-4'-cynobiphenyl (5CB) using atomistic model, and show that the values predicted by our approach are consistent with a subset of the available but limited experimental literature.

[Biomechanical testing of the new torque-segmented arch (TSA)].

PubMed

Wichelhaus, A; Sander, F G

1995-07-01

New torque-segmented arch wires are presented which consist of a superelastic anterior component with 30 degrees or 45 degrees torque and which are connected to 2 steel lateral components by means of a crimped connector. When using such torque-segmented arch wires, the crimped connector rests mesially to the canine bracket and the lateral components exhibit a torque of 0 degree. The use of the torque-segmented arch wires requires the practitioner to adjust the anterior tooth segment, to bend in first order bends in the steel lateral portion as well as to bend in a sweep to avoid an anterior tooth extrusion, and, if desired, to bend in third order bends to influence premolars and molars. In some cases the simultaneous application of palatal arches can become necessary, because each torque transfer results in a transversal enlargement in the molar area. Compared to conventional steel wires with dimensions of 0.016 x 0.022 in which an anterior tooth torque is bent, the torque segmented arch wires exhibit considerably fewer side effects, but there is a larger distally rotating moment for the molars. 1. When applying torque-segmented arch wires, the extrusive force transferred to the anterior teeth is considerably smaller. 2. The protrusive force acting on the anterior teeth is also considerably smaller, which results in a reduced demand being placed on the anchorage of the molars. 3. The torque transfer to the incisors rests in a quite moderate range, even in the case of a 50 degrees torque. For this reason, the practitioner can expect diminished or no resorptions at all compared to the aforementioned steel wires. 4. The Martensite plateau of the torque-segmented arch wires exhibit constant moments in large areas so that such arch wires can be used in almost every anterior tooth position. 5. The segmented wires presented here can be applied not only in the case of the standard edgewise technique but also in each case of the straight-wire technique. 6. These new arch wires require no readjustment of torque values. 7. To control the transferred torque values it is recommended that the already transferred torque values be monitored during each check-up with the help of the described torque key. 8. When the torque values of the brackets are known, the torque key renders frequent patient X-rays superfluous. 9. When the desired torque values are attained, treatment can proceed using conventional arch wires.

Surface and through crack problems in orthotropic plates

NASA Technical Reports Server (NTRS)

Erdogan, F.; Wu, B.-H.

1988-01-01

The present treatment of the general mode I crack problem in bending- and membrane-loaded orthotropic plates proceeds by formulating the bending problem for a series of planar and through-cracks; by independently varying the six independent constants, the effect of material orthotropy on the stress intensity factor is determined. The surface-crack problem is then formulated by means of the line-spring model, using a transverse-shear theory of plate bending. Attention is given to composite laminates with through-cracks or semielliptic surface cracks. A significant effect is noted for material orthotropy.

Longitudinal-bending mode micromotor using multilayer piezoelectric actuator.

PubMed

Yao, K; Koc, B; Uchino, K

2001-07-01

Longitudinal-bending mode ultrasonic motors with a diameter of 3 mm were fabricated using stacked multilayer piezoelectric actuators, which were self-developed from hard lead zirconate titanate (PZT) ceramic. A bending vibration was converted from a longitudinal vibration with a longitudinal-bending coupler. The motors could be bidirectionally operated by changing driving frequency. Their starting and braking torque were analyzed based on the transient velocity response. With a load of moment of inertia 2.5 x 10(-7) kgm2, the motor showed a maximum starting torque of 127.5 microNm. The braking torque proved to be a constant independent on the motor's driving conditions and was roughly equivalent to the maximum starting torque achievable with our micromotors.

The Anharmonic Force Field of Ethylene, C2H4, by Means of Accurate Ab Initio Calculations

NASA Technical Reports Server (NTRS)

Martin, Jan M. L.; Lee, Timothy J.; Taylor, Peter R.; Francois, Jean-Pierre; Langhoff, Stephen R. (Technical Monitor)

1995-01-01

The quartic force field of ethylene, C2H4, has been calculated ab initio using augmented coupled cluster, CCSD(T), methods and correlation consistent basis sets of spdf quality. For the C-12 isotopomers C2H4, C2H3D, H2CCD2, cis-C2H2D2, trans-C2H2D2, C2HD3, and C2D4, all fundamentals could be reproduced to better than 10 per centimeter, except for three cases of severe Fermi type 1 resonance. The problem with these three bands is identified as a systematic overestimate of the Kiij Fermi resonance constants by a factor of two or more; if this is corrected for, the predicted fundamentals come into excellent agreement with experiment. No such systematic overestimate is seen for Fermi type 2 resonances. Our computed harmonic frequencies suggest a thorough revision of the accepted experimentally derived values. Our computed and empirically corrected re geometry differs substantially from experimentally derived values: both the predicted rz geometry and the ground-state rotational constants are, however, in excellent agreement with experiment, suggesting revision of the older values. Anharmonicity constants agree well with experiment for stretches, but differ substantially for stretch-bend interaction constants, due to equality constraints in the experimental analysis that do not hold. Improved criteria for detecting Fermi and Coriolis resonances are proposed and found to work well, contrary to the established method based on harmonic frequency differences that fails to detect several important resonances for C2H4 and its isotopomers. Surprisingly good results are obtained with a small spd basis at the CCSD(T) level. The well-documented strong basis set effect on the v8 out-of-plane motion is present to a much lesser extent when correlation-optimized polarization functions are used. Complete sets of anharmonic, rovibrational coupling, and centrifugal distortion constants for the isotopomers are available as supplementary material to the paper.

Gravitropism in Higher Plant Shoots 1

PubMed Central

Mueller, Wesley J.; Salisbury, Frank B.; Blotter, P. Thomas

1984-01-01

Dimensional changes during gravitropic bending of cocklebur (Xanthium strumarium L.) dicot stems were measured using techniques of stereo photogrammetry. The differential growth is from an increased growth rate on the bottom of the stem and a stopping or contraction of the top. Contraction of the top was especially evident upon release and immediate bending of horizontal stems that had been restrained between stiff wires for 36 hours. The energy for this could have been stored in both the top and bottom, since the bottom elongated, and the top contracted. Forces developed during bending were measured by fastening a stem tip to the end of a bar with attached strain gauges and recording electrical output from the strain gauges. Restrained mature cocklebur stems continued to accumulate potential energy for bending for about 120 hours, after which the recorded force reached a maximum. Pressures within castor bean (Ricinus communis L.) stems were also measured with 3.5-millimeter diameter pressure transducers. As expected, the pressure on the bottom of the restrained plants increased with time; pressures decreased in vertical controls, tops of restrained stems, and bottoms of free-bending stems. Pressures increased in tops of free-bending stems. When restrained plants were released, pressure on the bottom decreased and pressure on the top increased. Results suggest a possible role for cell contraction in the top of stems bending upward in response to gravity. Images Fig. 5 Fig. 11 PMID:16663987

Design and analysis for a bend-resistant and large-mode-area photonic crystal fiber with hybrid cladding.

PubMed

Qin, Yan; Yang, Huajun; Jiang, Ping; Gui, Fengji; Caiyang, Weinan; Cao, Biao

2018-05-10

In this paper, an asymmetric large-mode-area photonic crystal fiber (LMA-PCF) with low bending loss at a smaller bending radius is designed. The finite-element method with a perfectly matched layer boundary is used to analyze the performance of the PCF. To achieve LMA-PCF with low bending loss, the air holes with double lattice constants and different sizes at the core are designed. Numerical results show that this structure can achieve low bending loss and LMA with a smaller bending radius at the wavelength of 1.55 μm. The effective mode area of the fundamental mode is larger than 1000  μm 2 when the bending radius is ≥10  cm. The bending loss of the fundamental mode is just 0.0113 dB/m, and the difference between the fundamental and high-order modes of the bending loss is larger than 10 3 when the bending radius is 10 cm. Simulation results show this novel PCF can achieve LMA and have effective single-mode operation when the bending orientation angle ranges in ±110°. This novel photonic crystal has potential application in high-power fiber lasers.

Rotational spectra in the ν2 vibrationally excited states of MgNC

NASA Astrophysics Data System (ADS)

Kagi, E.; Kawaguchi, K.; Takano, S.; Hirano, T.

1996-01-01

The pure rotational spectra of MgNC in the ν2 (bending) vibrationally excited states were observed in the 310-380 GHz region to study the linearity of the molecule. The observed 90 spectral lines were assigned to the transitions in the v2=1-5 states and analyzed to determine a set of molecular constants in each state. The bending vibrational frequency was estimated to be 86 cm-1 from the l-type doubling constant of the v2=1 state. The interval of the Φ and Π states in v2=3 was determined to be 29.2280(24) cm-1, giving the anharmonicity constant xll=3.8611(9) cm-1 with one standard deviation in parentheses, which indicates that the molecule has a linear form. However, somewhat peculiar properties were recognized in dependence of the observed l-type resonance and vibration-rotation constants on the v2 vibrational quantum number, suggesting an effect of anharmonicity.

Analysis and Design of Variable Stiffness Composite Cylinders

NASA Technical Reports Server (NTRS)

Tatting, Brian F.; Guerdal, Zafer

1998-01-01

An investigation of the possible performance improvements of thin circular cylindrical shells through the use of the variable stiffness concept is presented. The variable stiffness concept implies that the stiffness parameters change spatially throughout the structure. This situation is achieved mainly through the use of curvilinear fibers within a fiber-reinforced composite laminate, though the possibility of thickness variations and discrete stiffening elements is also allowed. These three mechanisms are incorporated into the constitutive laws for thin shells through the use of Classical Lamination Theory. The existence of stiffness variation within the structure warrants a formulation of the static equilibrium equations from the most basic principles. The governing equations include sufficient detail to correctly model several types of nonlinearity, including the formation of a nonlinear shell boundary layer as well as the Brazier effect due to nonlinear bending of long cylinders. Stress analysis and initial buckling estimates are formulated for a general variable stiffness cylinder. Results and comparisons for several simplifications of these highly complex governing equations are presented so that the ensuing numerical solutions are considered reliable and efficient enough for in-depth optimization studies. Four distinct cases of loading and stiffness variation are chosen to investigate possible areas of improvement that the variable stiffness concept may offer over traditional constant stiffness and/or stiffened structures. The initial investigation deals with the simplest solution for cylindrical shells in which all quantities are constant around the circumference of the cylinder. This axisymmetric case includes a stiffness variation exclusively in the axial direction, and the only pertinent loading scenarios include constant loads of axial compression, pressure, and torsion. The results for these cases indicate that little improvement over traditional laminates exists through the use of curvilinear fibers, mainly due to the presence of a weak link area within the stiffness variation that limits the ultimate load that the structure can withstand. Rigorous optimization studies reveal that even though slight increases in the critical loads can be produced for designs with an arbitrary variation of the fiber orientation angle, the improvements are not significant when compared to traditional design techniques that utilize ring stiffeners and frames. The second problem that is studied involves arbitrary loading of a cylinder with a stiffness variation that changes only in the circumferential direction. The end effects of the cylinder are ignored, so that the problem takes the form of an analysis of a cross-section for a short cylinder segment. Various load cases including axial compression, pressure, torsion, bending, and transverse shear forces are investigated. It is found that the most significant improvements in load-carrying capability exist for cases which involve loads that also vary around the circumference of the shell, namely bending and shear forces. The stiffness variation of the optimal designs contribute to the increased performance in two ways: lowering the stresses in the critical areas through redistribution of the stresses; and providing a relatively stiff region that alters the buckling behavior of the structure. These results lead to an in-depth optimization study involving weight optimization of a fuselage structure subjected to typical design constraints. Comparisons of the curvilinear fiber format to traditional stiffened structures constructed of isotropic and composite materials are included. It is found that standard variable stiffness designs are quite comparable in terms of weight and load-carrying capability yet offer the added advantage of tailorability of distinct regions of the structure that experience drastically different loading conditions. The last two problems presented in this work involve the nonlinear phenomenon of long tubes under bending. Though this scenario is not as applicable to fuselage structures as the previous problems, the mechanisms that produce the nonlinear effect are ideally suited to be controlled by the variable stiffness concept. This is due to the fact that the dominating influence for long cylinders under bending is the ovalization of the cross-section, which is governed mainly by the stiffness parameters of the cylindrical shell. Possible improvement of the critical buckling moments for these structures is investigated using either a circumferential or axial stiffness variation. For the circumferential case involving infinite length cylinders, it is found that slight improvements can be observed by designing structures that resist the cross-sectional deformation yet do not detract from the buckling resistance at the critical location. The results also indicate that buckling behavior is extremely dependent on cylinder length. This effect is most easily seen in the solution of finite length cylinders under bending that contain an axial stiffness variation. For these structures, the only mechanism that exhibits improved response are those that effectively shorten the length of the cylinder, thus reducing the cross-sectional deformation due to the forced restraint at the ends. It was found that the use of curvilinear fibers was not able to achieve this effect in sufficient degree to resist the deformation, but that ring stiffeners produced the desired response admirably. Thus, it is shown that the variable stiffness concept is most effective at improving the bending response of long cylinders through the use of a circumferential stiffness variation.

Effect of confinements: Bending in Paramecium

NASA Astrophysics Data System (ADS)

Eddins, Aja; Yang, Sung; Spoon, Corrie; Jung, Sunghwan

2012-02-01

Paramecium is a unicellular eukaryote which by coordinated beating of cilia, generates metachronal waves which causes it to execute a helical trajectory. We investigate the swimming parameters of the organism in rectangular PDMS channels and try to quantify its behavior. Surprisingly a swimming Paramecium in certain width of channels executes a bend of its flexible body (and changes its direction of swimming) by generating forces using the cilia. Considering a simple model of beam constrained between two walls, we predict the bent shapes of the organism and the forces it exerts on the walls. Finally we try to explain how bending (by sensing) can occur in channels by conducting experiments in thin film of fluid and drawing analogy to swimming behavior observed in different cases.

Crashworthy Gunner Seat Testing Program

DTIC Science & Technology

1977-03-01

147 5 LIST OF ILLUSTRATIONS Page 1. Swivel Gunner Seat Mock-up 14 2. Ceiling and Floor Swivel Rings .... ........... 16 3. Wire - Bending Tension...History . 57 37. Test 1 - Vertical Acceleration, Dummy Pelvis . 58 38. Upper Wire - bending Attenuators, Force/Duflection 59 39 Pre-test 2, 900 to Impact...unobstructed depth to permit lateral movement in the seat for gunnery operations. Wire - bending energy attenuators are located at the top of the two vertical

One-Dimensional and Two-Dimensional Analytical Solutions for Functionally Graded Beams with Different Moduli in Tension and Compression

PubMed Central

Li, Xue; Dong, Jiao

2018-01-01

The material considered in this study not only has a functionally graded characteristic but also exhibits different tensile and compressive moduli of elasticity. One-dimensional and two-dimensional mechanical models for a functionally graded beam with a bimodular effect were established first. By taking the grade function as an exponential expression, the analytical solutions of a bimodular functionally graded beam under pure bending and lateral-force bending were obtained. The regression from a two-dimensional solution to a one-dimensional solution is verified. The physical quantities in a bimodular functionally graded beam are compared with their counterparts in a classical problem and a functionally graded beam without a bimodular effect. The validity of the plane section assumption under pure bending and lateral-force bending is analyzed. Three typical cases that the tensile modulus is greater than, equal to, or less than the compressive modulus are discussed. The result indicates that due to the introduction of the bimodular functionally graded effect of the materials, the maximum tensile and compressive bending stresses may not take place at the bottom and top of the beam. The real location at which the maximum bending stress takes place is determined via the extreme condition for the analytical solution. PMID:29772835

Stability of elastic bending and torsion of uniform cantilever rotor blades in hover with variable structural coupling

NASA Technical Reports Server (NTRS)

Hodges, D. H., Roberta.

1976-01-01

The stability of elastic flap bending, lead-lag bending, and torsion of uniform, untwisted, cantilever rotor blades without chordwise offsets between the elastic, mass, tension, and areodynamic center axes is investigated for the hovering flight condition. The equations of motion are obtained by simplifying the general, nonlinear, partial differential equations of motion of an elastic rotating cantilever blade. The equations are adapted for a linearized stability analysis in the hovering flight condition by prescribing aerodynamic forces, applying Galerkin's method, and linearizing the resulting ordinary differential equations about the equilibrium operating condition. The aerodynamic forces are obtained from strip theory based on a quasi-steady approximation of two-dimensional unsteady airfoil theory. Six coupled mode shapes, calculated from free vibration about the equilibrium operating condition, are used in the linearized stability analysis. The study emphasizes the effects of two types of structural coupling that strongly influence the stability of hingeless rotor blades. The first structural coupling is the linear coupling between flap and lead-lag bending of the rotor blade. The second structural coupling is a nonlinear coupling between flap bending, lead-lag bending, and torsion deflections. Results are obtained for a wide variety of hingeless rotor configurations and operating conditions in order to provide a reasonably complete picture of hingeless rotor blade stability characteristics.

Nonlinear model of a rotating hub-beams structure: Equations of motion

NASA Astrophysics Data System (ADS)

Warminski, Jerzy

2018-01-01

Dynamics of a rotating structure composed of a rigid hub and flexible beams is presented in the paper. A nonlinear model of a beam takes into account bending, extension and nonlinear curvature. The influence of geometric nonlinearity and nonconstant angular velocity on dynamics of the rotating structure is presented. The exact equations of motion and associated boundary conditions are derived on the basis of the Hamilton's principle. The simplification of the exact nonlinear mathematical model is proposed taking into account the second order approximation. The reduced partial differential equations of motion together with associated boundary conditions can be used to study natural or forced vibrations of a rotating structure considering constant or nonconstant angular speed of a rigid hub and an arbitrary number of flexible blades.

Modified cantilevers to probe unambiguously out-of-plane piezoresponse

NASA Astrophysics Data System (ADS)

Alyabyeva, Natalia; Ouvrard, Aimeric; Lindfors-Vrejoiu, Ionela; Kolomiytsev, Alexey; Solodovnik, Maxim; Ageev, Oleg; McGrouther, Damien

2018-06-01

We demonstrate and investigate the coupling of contributions from both in-plane (IP) polarization and out-of-plane (OP) components in BiFeO3 (BFO) thin-film polarization probed by piezoresponse force microscopy (PFM). Such coupling leads to image artifacts which prevent the correct determination of OP polarization vector directions and the corresponding piezoelectric coefficient d33. Using material strength theory with a one-dimensional modeling of the cantilever oscillation amplitude under electrostatic and elastic forces as a function of the tip length, we have evidenced the impact of IP piezoresponse to the OP signal for tip length longer than 4 μm. The IP polarization vector induces a significant longitudinal bending of the cantilever, due to the small spring constant of long tips, which provokes a normal deviation superimposed to the OP piezoresponse. These artifacts can be reduced by increasing the longitudinal spring constant of the cantilever by shortening the tip length. Standard cantilevers with 15-μm-long tips were modified to reach the desired tip length, using focused ion-beam techniques and tested using PFM on the same BFO thin film. Tip length shortening has strongly reduced IP artifacts as expected, while the impact of nonlocal electrostatic forces, becoming predominant for tips shorter than 1 μm, has led to a non-negligible deflection offset. For shorter tips, a strong electric field from a cantilever beam can induce polarization switching as observed for a 0.5-μm-long tip. Tip length ranging from 1 to 4 μm allowed minimizing both artifacts to probe unambiguously OP piezoresponse and quantify the d33 piezoelectric coefficient.

Experimental study and FEM simulation of the simple shear test of cylindrical rods

NASA Astrophysics Data System (ADS)

Wirti, Pedro H. B.; Costa, André L. M.; Misiolek, Wojciech Z.; Valberg, Henry S.

2018-05-01

In the presented work an experimental simple shear device for cutting cylindrical rods was used to obtain force-displacement data for a low-carbon steel. In addition, and FEM 3D-simulation was applied to obtain internal shear stress and strain maps for this material. The experimental longitudinal grid patterns and force-displacement curve were compared with numerical simulation results. Many aspects of the elastic and plastic deformations were described. It was found that bending reduces the shear yield stress of the rod material. Shearing starts on top and bottom die-workpiece contact lines evolving in an arc-shaped area. Due to this geometry, stress concentrates on the surface of the rod until the level of damage reaches the critical value and the fracture starts here. The volume of material in the plastic zone subjected to shearing stress has a very complex shape and is function of a dimensionless geometrical parameter. Expressions to calculate the true shear stress τ and strain γ from the experimental force-displacement data were proposed. The equations' constants are determined by fitting the experimental curve with the stress τ and strain γ simulation point tracked data.

Kinematics, muscular activity and propulsion in gopher snakes

PubMed

Moon; Gans

1998-10-01

Previous studies have addressed the physical principles and muscular activity patterns underlying terrestrial lateral undulation in snakes, but not the mechanism by which muscular activity produces curvature and propulsion. In this study, we used synchronized electromyography and videography to examine the muscular basis and propulsive mechanism of terrestrial lateral undulation in gopher snakes Pituophis melanoleucus affinis. Specifically, we used patch electrodes to record from the semispinalis, longissimus dorsi and iliocostalis muscles in snakes pushing against one or more pegs. Axial bends propagate posteriorly along the body and contact the pegs at or immediately posterior to an inflection of curvature, which then reverses anterior to the peg. The vertebral column bends broadly around a peg, whereas the body wall bends sharply and asymmetrically around the anterior surface of the peg. The epaxial muscles are always active contralateral to the point of contact with a peg; they are activated slightly before or at the point of maximal convexity and deactivated variably between the inflection point and the point of maximal concavity. This pattern is consistent with muscular shortening and the production of axial bends, although variability in the pattern indicates that other muscles may affect the mechanics of the epaxial muscles. The kinematic and motor patterns in snakes crawling against experimentally increased drag indicated that forces are produced largely by muscles that are active in the axial bend around each peg, rather than by distant muscles from which the forces might be transmitted by connective tissues. At each point of force exertion, the propulsive mechanism of terrestrial lateral undulation may be modeled as a type of cam-follower, in which continuous bending of the trunk around the peg produces translation of the snake.

Flutter and Forced Response Analyses of Cascades using a Two-Dimensional Linearized Euler Solver

NASA Technical Reports Server (NTRS)

Reddy, T. S. R.; Srivastava, R.; Mehmed, O.

1999-01-01

Flutter and forced response analyses for a cascade of blades in subsonic and transonic flow is presented. The structural model for each blade is a typical section with bending and torsion degrees of freedom. The unsteady aerodynamic forces due to bending and torsion motions. and due to a vortical gust disturbance are obtained by solving unsteady linearized Euler equations. The unsteady linearized equations are obtained by linearizing the unsteady nonlinear equations about the steady flow. The predicted unsteady aerodynamic forces include the effect of steady aerodynamic loading due to airfoil shape, thickness and angle of attack. The aeroelastic equations are solved in the frequency domain by coupling the un- steady aerodynamic forces to the aeroelastic solver MISER. The present unsteady aerodynamic solver showed good correlation with published results for both flutter and forced response predictions. Further improvements are required to use the unsteady aerodynamic solver in a design cycle.

Development and Analysis of Bending Actuator Using McKibben Artificial Muscle

NASA Astrophysics Data System (ADS)

Zhao, Feifei; Dohta, Shujiro; Akagi, Tetsuya

Recent years, the number of nuclear families is rapidly growing. So the development of a human-friendly-robot which can take care of human daily life is strongly desired. This robot has to work just like a human, so, it is needed to have a dexterous soft hand in the robot. Therefore, we have developed an artificial soft gripper. This robot hand which has five fingers is made of silicone rubber. We also developed the hand which could be used to achieve several works just like a human hand. For example, it can grasp some objects that have the different shape and stiffness. Since it is made of silicone rubber, there is little damage to the object. However, the finger could not generate a larger force, less than 3N. In addition, it needs a skill and time to make the finger. In this study, we proposed and tested a bending actuator that could be easily constructed by putting the McKibben artificial muscle into the flexible tube. We also investigated the generated force and bending angle of the actuator. As a result, the generated force of the actuator was improved about 8.5 times as large as previous one. We also improved the bending actuator by changing the tube and the slit of the flexible tube. And the analytical model for the bending actuator was proposed and the calculated results were compared with the experimental ones.

Locomotor variation and bending regimes of capuchin limb bones.

PubMed

Demes, Brigitte; Carlson, Kristian J

2009-08-01

Primates are very versatile in their modes of progression, yet laboratory studies typically capture only a small segment of this variation. In vivo bone strain studies in particular have been commonly constrained to linear locomotion on flat substrates, conveying the potentially biased impression of stereotypic long bone loading patterns. We here present substrate reaction forces (SRF) and limb postures for capuchin monkeys moving on a flat substrate ("terrestrial"), on an elevated pole ("arboreal"), and performing turns. The angle between the SRF vector and longitudinal axes of the forearm or leg is taken as a proxy for the bending moment experienced by these limb segments. In both frontal and sagittal planes, SRF vectors and distal limb segments are not aligned, but form discrepant angles; that is, forces act on lever arms and exert bending moments. The positions of the SRF vectors suggest bending around oblique axes of these limb segments. Overall, the leg is exposed to greater moments than the forearm. Simulated arboreal locomotion and turns introduce variation in the discrepancy angles, thus confirming that expanding the range of locomotor behaviors studied will reveal variation in long bone loading patterns that is likely characteristic of natural locomotor repertoires. "Arboreal" locomotion, even on a linear noncompliant branch, is characterized by greater variability of force directions and discrepancy angles than "terrestrial" locomotion (significant for the forearm only), partially confirming the notion that life in trees is associated with greater variation in long bone loading. Directional changes broaden the range of external bending moments even further.

Bending energy penalty enhances the adhesive strength of functional amyloid curli to surfaces

NASA Astrophysics Data System (ADS)

Zhang, Yao; Wang, Ao; DeBenedictis, Elizabeth P.; Keten, Sinan

2017-11-01

The functional amyloid curli fiber, a major proteinaceous component of biofilm extracellular matrices, plays an important role in biofilm formation and enterobacteriaceae adhesion. Curli nanofibers exhibit exceptional underwater adhesion to various surfaces, have high rigidity and strong tensile mechanical properties, and thus hold great promise in biomaterials. The mechanisms of how curli fibers strongly attach to surfaces and detach under force remain elusive. To investigate curli fiber adhesion to surfaces, we developed a coarse-grained curli fiber model, in which the protein subunit CsgA (curli specific gene A) self-assembles into the fiber. The coarse-grained model yields physiologically relevant and tunable bending rigidity and persistence length. The force-induced desorption of a single curli fiber is examined using coarse-grained modeling and theoretical analysis. We find that the bending energy penalty arising from high persistence length enhances the resistance of the curli fiber against desorption and thus strengthens the adhesion of the curli fiber to surfaces. The CsgA-surface adhesion energy and the curli fiber bending rigidity both play crucial roles in the resistance of curli fiber against desorption from surfaces. To enable the desorption process, the applied peeling force must overcome both the interfacial adhesion energy and the energy barrier for bending the curli fiber at the peeling front. We show that the energy barrier to desorption increases with the interfacial adhesion energy, however, the bending induced failure of a single curli fiber limits the work of adhesion if the proportion of the CsgA-surface adhesion energy to the CsgA-CsgA cohesive energy becomes large. These results illustrate that the optimal adhesion performance of nanofibers is dictated by the interplay between bending, surface energy and cohesive energy. Our model provides timely insight into enterobacteriaceae adhesion mechanisms as well as future designs of engineered curli fiber based adhesives.

Vibration and Stability of Pretwisted Spinning Thin-Walled Composite Beams Featuring BENDING-BENDING Elastic Coupling

NASA Astrophysics Data System (ADS)

SONG, O.; JEONG, N.-H.; LIBRESCU, L.

2000-10-01

A number of issues related to the modelling, vibration and stability of anisotropic pretwisted beams rotating at constant angular speed about the longitudinal body-axis fixed in the inertial space are investigated. The analysis is carried out in the framework of a refined theory of thin-walled anisotropic composite beams featuring bending-bending elastic coupling, and encompassing a number of non-classical features such as transverse-shear, anisotropy and pretwist. Special attention is paid to the effect of the spinning speed, pretwist angle, axial compressive load and symmetry/non-symmetry of the beam cross-section on natural frequencies and instability of the structural system. Numerical illustrations highlighting their implication on vibration and stability are displayed and pertinent conclusions are outlined.

Computational study of duct and pipe flows using the method of pseudocompressibility

NASA Technical Reports Server (NTRS)

Williams, Robert W.

1991-01-01

A viscous, three-dimensional, incompressible, Navier-Stokes Computational Fluid Dynamics code employing pseudocompressibility is used for the prediction of laminar primary and secondary flows in two 90-degree bends of constant cross section. Under study are a square cross section duct bend with 2.3 radius ratio and a round cross section pipe bend with 2.8 radius ratio. Sensitivity of predicted primary and secondary flow to inlet boundary conditions, grid resolution, and code convergence is investigated. Contour and velocity versus spanwise coordinate plots comparing prediction to experimental data flow components are shown at several streamwise stations before, within, and after the duct and pipe bends. Discussion includes secondary flow physics, computational method, computational requirements, grid dependence, and convergence rates.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Heffernan, Karina M.; Ross, Nancy L., E-mail: nross@vt.edu; Spencer, Elinor C.

Accurate elastic constants for gadolinium phosphate (GdPO{sub 4}) have been measured by single-crystal high-pressure diffraction methods. The bulk modulus of GdPO{sub 4} determined under hydrostatic conditions, 128.1(8) GPa (K′=5.8(2)), is markedly different from that obtained with GdPO{sub 4} under non-hydrostatic conditions (160(2) GPa), which indicates the importance of shear stresses on the elastic response of this phosphate. High pressure Raman and diffraction analysis indicate that the PO{sub 4} tetrahedra behave as rigid units in response to pressure and that contraction of the GdPO{sub 4} structure is facilitated by bending/twisting of the Gd–O–P links that result in increased distortion in themore » GdO{sub 9} polyhedra. - Graphical abstract: A high-pressure single crystal diffraction study of GdPO{sub 4} with the monazite structure is presented. The elastic behaviour of rare-earth phosphates are believed to be sensitive to shear forces. The bulk modulus of GdPO{sub 4} measured under hydrostatic conditions is 128.1(8) GPa. Compression of the structure is facilitated by bending/twisting of the Gd−O−P links that result in increased distortion in the GdO{sub 9} polyhedra. Display Omitted - Highlights: • The elastic responses of rare-earth phosphates are sensitive to shear forces. • The bulk modulus of GdPO{sub 4} measured under hydrostatic conditions is 128.1(8) GPa. • Twisting of the inter-polyhedral links allows compression of the GdPO{sub 4} structure. • Changes to the GdO{sub 9} polyhedra occur in response to pressure (<7.0 GPa).« less

Orbiter Gap Filler Bending Model for Re-entry

NASA Technical Reports Server (NTRS)

Campbell, Charles H.

2007-01-01

Pressure loads on a protruding gap filler during an Orbiter reentry are investigated to evaluate the likelihood of extraction due to pressure loads, and to ascertain how much bending will be induced by re-entry pressure loads. Oblique shock wave theory is utilized to develop a representation of the pressure loads induced on a gap filler for the ISSHVFW trajectory, representative of a heavy weight ISS return. A free body diagram is utilized to react the forces induced by the pressure forces. Preliminary results developed using these methods demonstrate that pressure loads, alone, are not likely causes of gap filler extraction during reentry. Assessment of the amount a gap filler will bend over is presented. Implications of gap filler bending during re-entry include possible mitigation of early boundary layer transition concerns, uncertainty in ground based measurement of protruding gap fillers from historical Orbiter flight history, and uncertainty in the use of Orbiter gap fillers for boundary layer prediction calibration. Authors will be added to the author list as appropriate.

Bending stiffness and interlayer shear modulus of few-layer graphene

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen, Xiaoming; Yi, Chenglin; Ke, Changhong, E-mail: cke@binghamton.edu

2015-03-09

Interlayer shear deformation occurs in the bending of multilayer graphene with unconstrained ends, thus influencing its bending rigidity. Here, we investigate the bending stiffness and interlayer shear modulus of few-layer graphene through examining its self-folding conformation on a flat substrate using atomic force microscopy in conjunction with nonlinear mechanics modeling. The results reveal that the bending stiffness of 2–6 layers graphene follows a square-power relationship with its thickness. The interlayer shear modulus is found to be in the range of 0.36–0.49 GPa. The research findings show that the weak interlayer shear interaction has a substantial stiffening effect for multilayer graphene.

Biocompatibility of sol-gel-derived titania-silica coated intramedullary NiTi nails.

PubMed

Muhonen, V; Kujala, S; Vuotikka, A; Aäritalo, V; Peltola, T; Areva, S; Närhi, T; Tuukkanen, J

2009-02-01

We investigated bone response to sol-gel-derived titania-silica coated functional intramedullary NiTi nails that applied a continuous bending force. Nails 26 mm in length, either straight or with a radius of curvature of 28 or 15 mm, were implanted in the cooled martensite form from a proximal to distal direction into the medullary cavity of the right femur in 40 Sprague-Dawley rats. Body temperature restored the austenite form, causing the curved implants to generate a bending force on the bone. The femurs were examined after 24 weeks. Bone length measurements did not reveal any bowing or shortening of the bone in the experimental groups. The results from histomorphometry demonstrated that the stronger bending force, together with sol-gel surface treatment, resulted in more bone deposition around the implant and the formation of significantly less fibrous tissue. Straight intramedullary nails, even those with a titania-silica coating, were poorly attached when compared to the implants with a curved austenite structure.

Bending of solitons in weak and slowly varying inhomogeneous plasma

NASA Astrophysics Data System (ADS)

Mukherjee, Abhik; Janaki, M. S.; Kundu, Anjan

2015-12-01

The bending of solitons in two dimensional plane is presented in the presence of weak and slowly varying inhomogeneous ion density for the propagation of ion acoustic soliton in unmagnetized cold plasma with isothermal electrons. Using reductive perturbation technique, a modified Kadomtsev-Petviashvili equation is obtained with a chosen unperturbed ion density profile. The exact solution of the equation shows that the phase of the solitary wave gets modified by a function related to the unperturbed inhomogeneous ion density causing the soliton to bend in the two dimensional plane, while the amplitude of the soliton remains constant.

Bending of solitons in weak and slowly varying inhomogeneous plasma

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mukherjee, Abhik, E-mail: abhik.mukherjee@saha.ac.in; Janaki, M. S., E-mail: ms.janaki@saha.ac.in; Kundu, Anjan, E-mail: anjan.kundu@saha.ac.in

2015-12-15

The bending of solitons in two dimensional plane is presented in the presence of weak and slowly varying inhomogeneous ion density for the propagation of ion acoustic soliton in unmagnetized cold plasma with isothermal electrons. Using reductive perturbation technique, a modified Kadomtsev-Petviashvili equation is obtained with a chosen unperturbed ion density profile. The exact solution of the equation shows that the phase of the solitary wave gets modified by a function related to the unperturbed inhomogeneous ion density causing the soliton to bend in the two dimensional plane, while the amplitude of the soliton remains constant.

Determination of post-shakedown quantities of a pipe bend via the simplified theory of plastic zones compared with load history dependent incremental analysis

NASA Astrophysics Data System (ADS)

Vollrath, Bastian; Hübel, Hartwig

2018-01-01

The Simplified Theory of Plastic Zones (STPZ) may be used to determine post-shakedown quantities such as strain ranges and accumulated strains at plastic or elastic shakedown. The principles of the method are summarized. Its practical applicability is shown by the example of a pipe bend subjected to constant internal pressure along with cyclic in-plane bending or/and cyclic radial temperature gradient. The results are compared with incremental analyses performed step-by-step throughout the entire load history until the state of plastic shakedown is achieved.

Aircraft Crash Survival Design Guide. Volume 4. Aircraft Seats, Restraints. Litters, and Padding

DTIC Science & Technology

1980-06-01

11i 34 Tubular strut wire - bending energy absorber with force-deflection curves ..... . . . . . . . . . . 113 35 Inversion tube concept with...decelera- tor and a wire - bending seat load limiter (References 31 and 32). Therefore, correcting the calculated distance yields 16.25/0.8 - 20.31 in. It...Naval Air Development Center, Warminster, Pennsylvania, October 1969. )- 109 I-. - - ’. Two variations of the wire - bending device have been developed and

Loads Correlation of a Full-Scale UH-60A Airloads Rotor in a Wind Tunnel

NASA Technical Reports Server (NTRS)

Yeo, Hyeonsoo; Romander, Ethan A.

2012-01-01

Wind tunnel measurements of the rotor trim, blade airloads, and structural loads of a full-scale UH-60A Black Hawk main rotor are compared with calculations obtained using the comprehensive rotorcraft analysis CAMRAD II and a coupled CAMRAD II/OVERFLOW 2 analysis. A speed sweep at constant lift up to an advance ratio of 0.4 and a thrust sweep at constant speed into deep stall are investigated. The coupled analysis shows significant improvement over comprehensive analysis. Normal force phase is better captured and pitching moment magnitudes are better predicted including the magnitude and phase of the two stall events in the fourth quadrant at the deeply stalled condition. Structural loads are, in general, improved with the coupled analysis, but the magnitude of chord bending moment is still significantly underpredicted. As there are three modes around 4 and 5/rev frequencies, the structural responses to the 5/rev airloads due to dynamic stall are magnified and thus care must be taken in the analysis of the deeply stalled condition.

On occlusal forces in dentitions with implant-supported fixed cantilever prostheses.

PubMed

Falk, H

1990-01-01

The main aims of this thesis were (1) to study the functional characteristics of dentitions with mandibular implant-supported fixed cantilever prostheses - IFCP s- occluding with complete dentures, (2) to study in detail the magnitudes and distributions of axially directed closing and chewing forces in such dentitions, (3) to study the influence of number and distribution of occlusal contacts on the magnitude and distribution of closing and chewing forces, (4) to assess the vertical bending moment and the resulting vertical bending stress in the cantilever joints and (5) to find out whether the force distribution over the cantilever beams and the resulting vertical bending stress in the cantilever joint are influenced by the type of prosthetic construction in the opposing jaw. Closing and chewing forces were registered in altogether seventeen subjects by means of miniature strain gauge transducers mounted bilaterally and symmetrically in performed matrices in prosthetic appliances. Four, six or eight transducers, evenly distributed over the tooth-arch, permitted registrations of axially directed occlusal forces in several occluding areas simultaneously. In Papers I-IV, the implant-supported prostheses were installed in the mandible and occluded with complete dentures. In Paper V, group A, the fixture-supported prostheses were installed in the maxilla and occluded with tooth-supported fixed partial dentures whereas in group B, the arrangements were analogous to those in Papers I-IV. All subjects exhibited a rhythmic chewing pattern and preferred one side for chewing although both sides were used. Most chewing sequences were terminated with swallowing with occlusal force development. The mean total forces acting over the tooth-arch varied somewhat between groups and occlusal arrangements but averaged 350 and 170 N for closing and chewing respectively. Closing and chewing forces increased distally along the cantilever beams when occluding with complete dentures and decreased distally when occluding with fixed partial dentures. The distally increasing force distribution pattern could be altered to a distally decreasing force distribution pattern by infraoccluding the second cantilever unit by as little as 100 microns. Calculated vertical bending moments and stresses in the cantilever joints of the preferred chewing sides created by closing and chewing forces were larger in dentitions where the IFCP occluded with a complete denture than in dentitions where the IFCP occluded with a tooth-supported fixed partial denture.

Impact of implant support on mandibular free-end base removable partial denture: theoretical study.

PubMed

Oh, Won-suk; Oh, Tae-Ju; Park, Ju-mi

2016-02-01

This study investigated the impact of implant support on the development of shear force and bending moment in mandibular free-end base removable partial dentures (RPDs). Three theoretical test models of unilateral mandibular free-end base RPDs were constructed to represent the base of tooth replacement, as follows: Model 1: first and second molars (M1 and M2); Model 2: second premolar (P2), M1, and M2; and Model 3: first premolar (P1), P2, M1, and M2. The implant support located either at M1 or M2 sites. The occlusal loading was concentrated at each replacement tooth to calculate the stress resultants developed in the RPD models using the free-body diagrams of shear force and bending moment. There was a trend of reduction in the peak shear force and bending moment when the base was supported by implant. However, the degree of reduction varied with the location of implant support. The moment reduced by 76% in Model 1, 58% in Model 2, and 42% in Model 3, when the implant location shifted from M1 to M2 sites. The shear forces and bending moments subjected to mandibular free-end base RPDs were found to decrease with the addition of implant support. However, the impact of implant support varied with the location of implant in this theoretical study. © 2014 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.

Bending the law: tidal bending and its effects on ice viscosity and flow

NASA Astrophysics Data System (ADS)

Rosier, S.; Gudmundsson, G. H.

2017-12-01

Many ice shelves are subject to strong ocean tides and, in order to accommodate this vertical motion, the ice must bend within the grounding zone. This tidal bending generates large stresses within the ice, changing its effective viscosity. For a confined ice shelf, this is particularly relevant because the tidal bending stresses occur along the sidewalls, which play an important role in the overall flow regime of the ice shelf. Hence, tidal bending stresses will affect both the mean and time-varying components of ice shelf flow. GPS measurements reveal strong variations in horizontal ice shelf velocities at a variety of tidal frequencies. We show, using full-Stokes viscoelastic modelling, that inclusion of tidal bending within the model accounts for much of the observed tidal modulation of horizontal ice shelf flow. Furthermore, our model shows that in the absence of a vertical tidal forcing, the mean flow of the ice shelf is reduced considerably.

Thermal stiffening of clamped elastic ribbons

NASA Astrophysics Data System (ADS)

Wan, Duanduan; Nelson, David R.; Bowick, Mark J.

2017-07-01

We use molecular dynamics to study the vibrations of a thermally fluctuating two-dimensional elastic membrane clamped at both ends. We directly extract the eigenmodes from resonant peaks in the frequency domain of the time-dependent height and measure the dependence of the corresponding eigenfrequencies on the microscopic bending rigidity of the membrane, taking care also of the subtle role of thermal contraction in generating a tension when the projected area is fixed. At finite temperatures we show that the effective (macroscopic) bending rigidity tends to a constant as the bare bending rigidity vanishes, consistent with theoretical arguments that the large-scale bending rigidity of the membrane arises from a strong thermal renormalization of the microscopic bending rigidity. Experimental realizations include covalently bonded two-dimensional atomically thin membranes such as graphene and molybdenum disulfide or soft matter systems such as the spectrin skeleton of red blood cells or diblock copolymers.

A piezoelectric bone-conduction bending hearing actuator.

PubMed

Adamson, R B A; Bance, M; Brown, J A

2010-10-01

A prototype of a novel bone-conduction hearing actuator based on a piezoelectric bending actuator is presented. The device lies flat against the skull which would allow it to form the basis of a subcutaneous bone-anchored hearing aid. The actuator excites bending in bone through a local bending moment rather than the application of a point force as with conventional bone-anchored hearing aids. Through measurements of the cochlear velocity created by the actuator in embalmed human heads, the device is shown to exhibit high efficiency, making it a possible alternative to present-day electromagnetic bone-vibration actuators.

Copper, Aluminum and Nickel: A New Monocrystalline Orthodontic Alloy

NASA Astrophysics Data System (ADS)

Wierenga, Mark

Introduction: This study was designed to evaluate, via tensile and bend testing, the mechanical properties of a newly-developed monocrystalline orthodontic archwire comprised of a blend of copper, aluminum, and nickel (CuAlNi). Methods: The sample was comprised of three shape memory alloys; CuAlNi, copper nickel titanium (CuNiTi), and nickel titanium (NiTi); from various orthodontic manufacturers in both 0.018" round and 0.019" x 0.025" rectangular dimensions. Additional data was gathered for similarly sized stainless steel and beta-titanium archwires as a point of reference for drawing conclusions about the relative properties of the archwires. Measurements of loading and unloading forces were recorded in both tension and deflection testing. Repeated-measure ANOVA (alpha= 0.05) was used to compare loading and unloading forces across wires and one-way ANOVA (alpha= 0.05) was used to compare elastic moduli and hysteresis. To identify significant differences, Tukey post-hoc comparisons were performed. Results: The modulus of elasticity, deflection forces, and hysteresis profiles of CuAlNi were significantly different than the other superelastic wires tested. In all tests, CuAlNi had a statistically significant lower modulus of elasticity compared to the CuNiTi and NiTi wires (P <0.0001). The CuAlNi wire exhibited significantly lower loading and unloading forces than any other wire tested. In round wire tensile tests, loading force at all deflections was significantly lower for CuAlNi than CuNiTi or NiTi (P <0.0001). In tensile testing, the CuAlNi alloy was able to recover from a 7 mm extension (10% elongation) without permanent deformation and with little to no loss in force output. In large-deflection bend tests at 4, 5, and 6 mm deflection, CuAlNi showed the significantly lowest loading forces across the three wire materials (P <0.0001). The NiTi wires showed up to 12 times the amount of energy loss due to hysteresis compared to CuAlNi. CuAlNi showed a hysteresis loss that was significantly less than any other wire tested in this study (P <0.0001). Conclusions: The relatively constant force delivered for a long period of time during the deactivation of this wire, the minimal hysteresis loss, the low force output in deflection, and the relatively low modulus of elasticity suggest that CuAlNi wires should be considered an important material addition to orthodontic metallurgy.

Mechanical properties of sol–gel derived SiO2 nanotubes

PubMed Central

Antsov, Mikk; Vlassov, Sergei; Dorogin, Leonid M; Vahtrus, Mikk; Zabels, Roberts; Lange, Sven; Lõhmus, Rünno

2014-01-01

Summary The mechanical properties of thick-walled SiO2 nanotubes (NTs) prepared by a sol–gel method while using Ag nanowires (NWs) as templates were measured by using different methods. In situ scanning electron microscopy (SEM) cantilever beam bending tests were carried out by using a nanomanipulator equipped with a force sensor in order to investigate plasticity and flexural response of NTs. Nanoindentation and three point bending tests of NTs were performed by atomic force microscopy (AFM) under ambient conditions. Half-suspended and three-point bending tests were processed in the framework of linear elasticity theory. Finite element method simulations were used to extract Young’s modulus values from the nanoindentation data. Finally, the Young’s moduli of SiO2 NTs measured by different methods were compared and discussed. PMID:25383292

On the role of tip curvature on flapping plates.

PubMed

Martin, Nathan; Gharib, Morteza

2018-01-09

During the flapping motion of a fish's tail, the caudal fin exhibits antero-posterior bending and dorso-ventral bending, the latter of which is referred to as chord-wise bending herein. The impact of chord-wise tip curvature on the hydrodynamic forces for flapping plates is investigated to explore potential mechanisms to improve the maneuverability or the performance of autonomous underwater vehicles. First, actuated chord-wise tip curvature is explored. Comparison of rigid curved geometries to a rigid flat plate as a baseline suggests that an increased curvature decreases the generated forces. An actuated plate with a dynamic tip curvature is created to illustrate a modulation of this decrease in forces. Second, the impact of curvature is isolated using curved plates with an identical planform area. Comparison of rigid curved geometries as a baseline corroborates the result that an increased curvature decreases the generated forces, with the exception that presenting a concave geometry into the flow increases the thrust and the efficiency. A passively-actuated plate is designed to capitalize on this effect by presenting a concave geometry into the flow throughout the cycle. The dynamically and passively actuated plates show potential to improve the maneuverability and the efficiency of autonomous underwater vehicles, respectively.

Blocked Force and Loading Calculations for LaRC THUNDER Actuators

NASA Technical Reports Server (NTRS)

Campbell, Joel F.

2007-01-01

An analytic approach is developed to predict the performance of LaRC Thunder actuators under load and under blocked conditions. The problem is treated with the Von Karman non-linear analysis combined with a simple Raleigh-Ritz calculation. From this, shape and displacement under load combined with voltage are calculated. A method is found to calculate the blocked force vs voltage and spring force vs distance. It is found that under certain conditions, the blocked force and displacement is almost linear with voltage. It is also found that the spring force is multivalued and has at least one bifurcation point. This bifurcation point is where the device collapses under load and locks to a different bending solution. This occurs at a particular critical load. It is shown this other bending solution has a reduced amplitude and is proportional to the original amplitude times the square of the aspect ratio.

Development and modification of a device for three-dimensional measurement of orthodontic force system: The V-bend system re-visited.

PubMed

Lai, WeiJen; Midorikawa, Yoshiyuki; Kanno, Zuisei; Takemura, Hiroshi; Suga, Kazuhiro; Soga, Kohei; Ono, Takashi; Uo, Motohiro

2016-12-01

We developed a device to evaluate the orthodontic force applied by systems requiring high operability. A life-sized, two-tooth model was designed, and the measurements were performed using a custom-made jointed attachment, referred to as an "action stick", to allow clearance for the oversized six-axis sensors. This tooth-sensor apparatus was accurately calibrated, and the error was limited. Vector analysis and rotating coordinate transformation were required to derive the force and moment at the tooth from the sensor readings. The device was then used to obtain measurements of the force and moment generated by the V-bend system. Our device was effective, providing results that were consistent with those of previous studies. This measurement device can be manufactured with force sensors of any size, and it can also be expanded to models with any number of teeth.

Yielding in colloidal gels due to nonlinear microstructure bending mechanics.

PubMed

Furst, Eric M; Pantina, John P

2007-05-01

We report measurements of the nonlinear micromechanics of strongly flocculated model colloidal aggregates. Linear aggregates directly assembled using laser tweezers are subjected to bending loads until a critical bending moment is reached, which is identified by a stictionlike rearrangement of a single colloidal bond. This nanoscale phenomenon provides a quantitative basis for understanding the macroscopic shear yield stresses of strongly flocculated polystyrene latex gels, based on the maximum bending moment exceeding the critical moment of the constituent colloidal bonds of the gel microstructure. These mechanics are consistent with the local bending moment overcoming the static friction force between neighboring adhesive particles. This results in a direct relationship between the rheology of these gels and the boundary friction between Brownian particles.

Pseudo-conformer models for linear molecules: Joint treatment of spectroscopic, electron diffraction and ab initio data for the C3O2 molecule

NASA Astrophysics Data System (ADS)

Tarasov, Yury I.; Kochikov, Igor V.

2018-06-01

Dynamic analysis of the molecules with large-amplitude motions (LAM) based on the pseudo-conformer approach has been successfully applied to various molecules. Floppy linear molecules present a special class of molecular structures that possess a pair of conjugate LAM coordinates but allow one-dimensional treatment. In this paper, previously developed treatment for the semirigid molecules is applied to the carbon suboxide molecule. This molecule characterized by the extremely large CCC bending has been thoroughly investigated by spectroscopic and ab initio methods. However, the earlier electron diffraction investigations were performed within a static approach, obtaining thermally averaged parameters. In this paper we apply a procedure aimed at obtaining the short list of self-consistent reference geometry parameters of a molecule, while all thermally averaged parameters are calculated based on reference geometry, relaxation dependencies and quadratic and cubic force constants. We show that such a model satisfactorily describes available electron diffraction evidence with various QC bending potential energy functions when r.m.s. CCC angle is in the interval 151 ± 2°. This leads to a self-consistent molecular model satisfying spectroscopic and GED data. The parameters for linear reference geometry have been defined as re(CO) = 1.161(2) Å and re(CC) = 1.273(2) Å.

Development of Flexible Pneumatic Cylinder with Built-in Flexible Linear Encoder and Flexible Bending Sensor

NASA Astrophysics Data System (ADS)

Akagi, Tetsuya; Dohta, Shujiro; Matsushita, Hisashi; Fukuhara, Akimasa

The purpose of this study is to develop a lightweight and intelligent soft actuator which can be safely attached to the human body. A novel flexible pneumatic cylinder that can be used even if it is deformed by external force had been proposed. The cylinder can realize both pushing and pulling motions even if the cylinder bends. In this paper, a flexible pneumatic cylinder with a built-in flexible linear encoder is proposed and tested. The encoder can detect the cylinder displacement even if the cylinder bends. In the next step, to realize an intelligent flexible cylinder, it is essential to recognize the angle of deflection of the cylinder to estimate the direction of the external force. Therefore, a flexible bending sensor that can measure the directional angle by attaching it to the end of the cylinder is also proposed and tested. The tested bending sensor also consists of four inexpensive photo-reflectors set on the circumferential surface to the cylinder tube every 90 degrees from the center of the tube. By measuring the distance between the photo reflector and the surface of the tube at each point, the bending directional angle of the cylinder can be obtained. A low cost measuring system using a micro-computer incorporating a programmed Up/Down counter to measure the displacement of the cylinder is also developed. As a result, it was confirmed that the measuring accuracy of the bending directional angle was good, less than 0.7 degrees as a standard deviation.

Investigation of stress concentration at corner points for orthotropic plate bending problem

NASA Astrophysics Data System (ADS)

Vasilyan, N. G.

2018-04-01

This article deals with the bending problem for an orthotropic semi-infinite plate strip when three edges of the plate are hinged and the fourth edge goes to infinity. The plate is loaded with distributed load of intensity q(y). A. Nadai’s approach is applied, which says that to obtain the solution at a far distance from the edge, it is necessary to solve the problem of cylindrical bending. The generalized shearing forces on the fixed edge are investigated.

Modelling of electron beam induced nanowire attraction

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bitzer, Lucas A.; Benson, Niels, E-mail: niels.benson@uni-due.de; Schmechel, Roland

2016-04-14

Scanning electron microscope (SEM) induced nanowire (NW) attraction or bundling is a well known effect, which is mainly ascribed to structural or material dependent properties. However, there have also been recent reports of electron beam induced nanowire bending by SEM imaging, which is not fully explained by the current models, especially when considering the electro-dynamic interaction between NWs. In this article, we contribute to the understanding of this phenomenon, by introducing an electro-dynamic model based on capacitor and Lorentz force interaction, where the active NW bending is stimulated by an electromagnetic force between individual wires. The model includes geometrical, electrical,more » and mechanical NW parameters, as well as the influence of the electron beam source parameters and is validated using in-situ observations of electron beam induced GaAs nanowire (NW) bending by SEM imaging.« less

Accurate ab initio Quartic Force Fields of Cyclic and Bent HC2N Isomers

NASA Technical Reports Server (NTRS)

Inostroza, Natalia; Huang, Xinchuan; Lee, Timothy J.

2012-01-01

Highly correlated ab initio quartic force field (QFFs) are used to calculate the equilibrium structures and predict the spectroscopic parameters of three HC2N isomers. Specifically, the ground state quasilinear triplet and the lowest cyclic and bent singlet isomers are included in the present study. Extensive treatment of correlation effects were included using the singles and doubles coupled-cluster method that includes a perturbational estimate of the effects of connected triple excitations, denoted CCSD(T). Dunning s correlation-consistent basis sets cc-pVXZ, X=3,4,5, were used, and a three-point formula for extrapolation to the one-particle basis set limit was used. Core-correlation and scalar relativistic corrections were also included to yield highly accurate QFFs. The QFFs were used together with second-order perturbation theory (with proper treatment of Fermi resonances) and variational methods to solve the nuclear Schr dinger equation. The quasilinear nature of the triplet isomer is problematic, and it is concluded that a QFF is not adequate to describe properly all of the fundamental vibrational frequencies and spectroscopic constants (though some constants not dependent on the bending motion are well reproduced by perturbation theory). On the other hand, this procedure (a QFF together with either perturbation theory or variational methods) leads to highly accurate fundamental vibrational frequencies and spectroscopic constants for the cyclic and bent singlet isomers of HC2N. All three isomers possess significant dipole moments, 3.05D, 3.06D, and 1.71D, for the quasilinear triplet, the cyclic singlet, and the bent singlet isomers, respectively. It is concluded that the spectroscopic constants determined for the cyclic and bent singlet isomers are the most accurate available, and it is hoped that these will be useful in the interpretation of high-resolution astronomical observations or laboratory experiments.

Analytical and experimental investigations of human spine flexure.

NASA Technical Reports Server (NTRS)

Moffatt, C. A.; Advani, S. H.; Lin, C.-J.

1971-01-01

The authors report on experiments to measure the resistance of fresh human spines to flexion in the upper lumbar and lower thoracic regions and evaluate results by using a combination of strength of materials theory and effects of shear and comparing with data reported by other authors. The test results indicate that the thoraco-lumbar spine behaves approximately as a linear elastic beam, without relaxation effects. The authors formulate a simple continuum dynamic model of the spine simulating aircraft ejection and solve the resulting boundary value problem to illustrate the importance of the flexural mode. A constant cross-section, the selected model is a sinusoidally curved elastic beam with an end mass subjected to a Heaviside axial acceleration at the other end. The paper presents transient response results for the spinal model axial and bending displacements and axial force.-

Dynamics of knotted flexible loops settling under a constant force in a viscous fluid

NASA Astrophysics Data System (ADS)

Gruziel, Magdalena; Thyagarajan, Krishnan; Dietler, Giovanni; Szymczak, Piotr; Ekiel-Jezewska, Maria

2017-11-01

Sedimenting chains of metal beads knotted to a topology of a torus knot tend to stabilize in the form of extended, flat, tightly interwound loops. In this configuration they perform an oscillatory motion of the loops swirling periodically around each other. Stokesian dynamics simulations of elastic fibers confirm the long-lasting character of the traveling wave-like swirling motion and show also the accompanying rotation of the system. Moreover, the periodic motion shows striking resemblance to the stable solutions for the evolution of vortices of torus knot topology. Using the results of the simulations we study the dependence of the frequencies and sedimentation velocities on the length of the fiber. We also notice the dependence of the knot dynamics on the bending stiffness of the fiber and the knot rank. NCN-2015/19/D/ST8/03199.

Femoral loading mechanics in the Virginia opossum, Didelphis virginiana: torsion and mediolateral bending in mammalian locomotion.

PubMed

Gosnell, W Casey; Butcher, Michael T; Maie, Takashi; Blob, Richard W

2011-10-15

Studies of limb bone loading in terrestrial mammals have typically found anteroposterior bending to be the primary loading regime, with torsion contributing minimally. However, previous studies have focused on large, cursorial eutherian species in which the limbs are held essentially upright. Recent in vivo strain data from the Virginia opossum (Didelphis virginiana), a marsupial that uses a crouched rather than an upright limb posture, have indicated that its femur experiences appreciable torsion during locomotion as well as strong mediolateral bending. The elevated femoral torsion and strong mediolateral bending observed in D. virginiana might result from external forces such as a medial inclination of the ground reaction force (GRF), internal forces deriving from a crouched limb posture, or a combination of these factors. To evaluate the mechanism underlying the loading regime of opossum femora, we filmed D. virginiana running over a force platform, allowing us to measure the magnitude of the GRF and its three-dimensional orientation relative to the limb, facilitating estimates of limb bone stresses. This three-dimensional analysis also allows evaluations of muscular forces, particularly those of hip adductor muscles, in the appropriate anatomical plane to a greater degree than previous two-dimensional analyses. At peak GRF and stress magnitudes, the GRF is oriented nearly vertically, inducing a strong abductor moment at the hip that is countered by adductor muscles on the medial aspect of the femur that place this surface in compression and induce mediolateral bending, corroborating and explaining loading patterns that were identified in strain analyses. The crouched orientation of the femur during stance in opossums also contributes to levels of femoral torsion as high as those seen in many reptilian taxa. Femoral safety factors were as high as those of non-avian reptiles and greater than those of upright, cursorial mammals, primarily because the load magnitudes experienced by opossums are lower than those of most mammals. Thus, the evolutionary transition from crouched to upright posture in mammalian ancestors may have been accompanied by an increase in limb bone load magnitudes.

Experimental and numerical investigation on laser-assisted bending of pre-loaded metal plate

NASA Astrophysics Data System (ADS)

Nowak, Zdzisław; Nowak, Marcin; Widłaszewski, Jacek; Kurp, Piotr

2018-01-01

The laser forming technique has an important disadvantage, which is the limitation of plastic deformation generated by a single laser beam pass. To increase the plastic deformation it is possible to apply external forces in the laser forming process. In this paper, we investigate the influence of external pre-loads on the laser bending of steel plate. The pre-loads investigated generate bending towards the laser beam. The thermal, elastic-plastic analysis is performed using the commercial nonlinear finite element analysis package ABAQUS. The focus of the paper is to identify how this pattern of the pre-load influence the final bend angle of the plate.

Contact force and mechanical loss of multistage cable under tension and bending

NASA Astrophysics Data System (ADS)

Ru, Yanyun; Yong, Huadong; Zhou, Youhe

2016-10-01

A theoretical model for calculating the stress and strain states of cabling structures with different loadings has been developed in this paper. We solve the problem for the first- and second-stage cable with tensile or bending strain. The contact and friction forces between the strands are presented by two-dimensional contact model. Several theoretical models have been proposed to verify the results when the triplet subjected to the tensile strain, including contact force, contact stresses, and mechanical loss. It is found that loadings will affect the friction force and the mechanical loss of the triplet. The results show that the contact force and mechanical loss are dependent on the twist pitch. A shorter twist pitch can lead to higher contact force, while the trend of mechanical loss with twist pitch is complicated. The mechanical loss may be reduced by adjusting the twist pitch reasonably. The present model provides a simple analysis method to investigate the mechanical behaviors in multistage-structures under different loads.

Transition of torque pattern in undulatory locomotion due to wave number variation in resistive force dominated media

NASA Astrophysics Data System (ADS)

Ding, Yang; Ming, Tingyu

2016-11-01

In undulatory locomotion, torque (bending moment) is required along the body to overcome the external forces from environments and bend the body. Previous observations on animals using less than two wavelengths on the body showed such torque has a single traveling wave pattern. Using resistive force theory model and considering the torque generated by external force in a resistive force dominated media, we found that as the wave number (number of wavelengths on the locomotor's body) increases from 0.5 to 1.8, the speed of the traveling wave of torque decreases. When the wave number increases to 2 and greater, the torque pattern transits from a single traveling wave to a two traveling waves and then a complex pattern that consists two wave-like patterns. By analyzing the force distribution and its contribution to the torque, we explain the speed decrease of the torque wave and the pattern transition. This research is partially supported by the Recruitment Program of Global Young Experts (China).

Bending of Light in Modified Gravity at Large Distances

NASA Technical Reports Server (NTRS)

Sultana, Joseph; Kazanas, Demosthenes

2012-01-01

We discuss the bending of light in a recent model for gravity at large distances containing a Rindler type acceleration proposed by Grumiller. We consider the static, spherically symmetric metric with cosmological constant and Rindler-like term 2ar presented in this model, and we use the procedure by Rindler and Ishak. to obtain the bending angle of light in this metric. Earlier work on light bending in this model by Carloni, Grumiller, and Preis, using the method normally employed for asymptotically flat space-times, led to a conflicting result (caused by the Rindler-like term in the metric) of a bending angle that increases with the distance of closest approach r(sub 0) of the light ray from the centrally concentrated spherically symmetric matter distribution. However, when using the alternative approach for light bending in nonasymptotically flat space-times, we show that the linear Rindler-like term produces a small correction to the general relativistic result that is inversely proportional to r(sub 0). This will in turn affect the bounds on Rindler acceleration obtained earlier from light bending and casts doubts on the nature of the linear term 2ar in the metric

Modeling and Control of a Trailing Wire Antenna Towed by an Orbiting Aircraft

DTIC Science & Technology

1992-09-01

do not induce significant oscillations in the wire. The development of the dynamic model also assumed that wire bending , torsion and stretching...it was reasonable to assume that the wire bending forces did not contribute significantly to the oscillations. 8= (4.54)8EI pg=0.005176 ibf in E

Numerical simulation of the wave-induced non-linear bending moment of ships

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xia, J.; Wang, Z.; Gu, X.

1995-12-31

Ships traveling in moderate or rough seas may experience non-linear bending moments due to flare effect and slamming loads. The numerical simulation of the total wave-induced bending moment contributed from both the wave frequency component induced by wave forces and the high frequency whipping component induced by slamming actions is very important in predicting the responses and ensuring the safety of the ship in rough seas. The time simulation is also useful for the reliability analysis of ship girder strength. The present paper discusses four different methods of the numerical simulation of wave-induced non-linear vertical bending moment of ships recentlymore » developed in CSSRC, including the hydroelastic integral-differential method (HID), the hydroelastic differential analysis method (HDA), the combined seakeeping and structural forced vibration method (CSFV), and the modified CSFV method (MCSFV). Numerical predictions are compared with the experimental results obtained from the elastic ship model test of S-175 container ship in regular and irregular waves presented by Watanabe Ueno and Sawada (1989).« less

Effect of chordwise forces and deformations and deformations due to steady lift on wing flutter

NASA Technical Reports Server (NTRS)

Boyd, W. N.

1977-01-01

This investigation explores the effects of chordwise forces and deformations and steady-state deformation due to lift on the static and dynamic aeroelastic stability of a uniform cantilever wing. Results of this analysis are believed to have practical applications for high-performance sailplanes and certain RPV's. The airfoil cross section is assumed to be symmetric and camber bending is neglected. Motions in vertical bending, fore-and-aft bending, and torsion are considered. A differential equation model is developed, which included the nonlinear elastic bending-torsion coupling that accompanies even moderate deflections. A linearized expansion in small time-dependent deflections is made about a steady flight condition. The stability determinant of the linearized system then contains coefficients that depend on steady displacements. Loads derived from two-dimensional incompressible aerodynamic theory are used to obtain the majority of the results, but cases using three-dimensional subsonic compressible theory are also studied. The stability analysis is carried out in terms of the dynamically uncoupled natural modes of vibration of the uniform cantilever.

Bioinspired model of mechanical energy harvesting based on flexoelectric membranes.

PubMed

Rey, Alejandro D; Servio, P; Herrera-Valencia, E E

2013-02-01

Membrane flexoelectricity is an electromechanical coupling process that describes membrane electrical polarization due to bending and membrane bending under electric fields. In this paper we propose, formulate, and characterize a mechanical energy harvesting system consisting of a deformable soft flexoelectric thin membrane subjected to harmonic forcing from contacting bulk fluids. The key elements of the energy harvester are formulated and characterized, including (i) the mechanical-to-electrical energy conversion efficiency, (ii) the electromechanical shape equation connecting fluid forces with membrane curvature and electric displacement, and (iii) the electric power generation and efficiency. The energy conversion efficiency is cast as the ratio of flexoelectric coupling to the product of electric and bending elasticity. The device is described by a second-order curvature dynamics coupled to the electric displacement equation and as such results in mechanical power absorption with a resonant peak whose amplitude decreases with bending viscosity. The electric power generation is proportional to the conversion factor and the power efficiency decreases with frequency. Under high bending viscosity, the power efficiency increases with the conversion factor and under low viscosities it decreases with the conversion factor. The theoretical results presented contribute to the ongoing experimental efforts to develop mechanical energy harvesting from fluid flow energy through solid-fluid interactions and electromechanical transduction.

Local probe microscopic studies on Al-doped ZnO: Pseudoferroelectricity and band bending at grain boundaries

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kumar, Mohit; Basu, Tanmoy; Som, Tapobrata, E-mail: tsom@iopb.res.in

2016-01-07

In this paper, based on piezoforce measurements, we show the presence of opposite polarization at grains and grain boundaries of Al-doped ZnO (AZO). The polarization can be flipped by 180° in phase by switching the polarity of the applied electric field, revealing the existence of nanoscale pseudoferroelectricity in AZO grown on Pt/TiO{sub 2}/SiO{sub 2}/Si substrate. We also demonstrate an experimental evidence on local band bending at grain boundaries of AZO films using conductive atomic force microscopy and Kelvin probe force microscopy. The presence of an opposite polarization at grains and grain boundaries gives rise to a polarization-driven barrier formation atmore » grain boundaries. With the help of conductive atomic force microscopy, we show that the polarization-driven barrier along with the defect-induced electrostatic potential barrier account for the measured local band bending at grain boundaries. The present study opens a new avenue to understand the charge transport in light of both polarization and electrostatic effects.« less

Revealing bending and force in a soft body through a plant root inspired approach

PubMed Central

Lucarotti, Chiara; Totaro, Massimo; Sadeghi, Ali; Mazzolai, Barbara; Beccai, Lucia

2015-01-01

An emerging challenge in soft robotics research is to reveal mechanical solicitations in a soft body. Nature provides amazing clues to develop unconventional components that are capable of compliant interactions with the environment and living beings, avoiding mechanical and algorithmic complexity of robotic design. We inspire from plant-root mechanoperception and develop a strategy able to reveal bending and applied force in a soft body with only two sensing elements of the same kind, and a null computational effort. The stretching processes that lead to opposite tissue deformations on the two sides of the root wall are emulated with two tactile sensing elements, made of soft and stretchable materials, which conform to reversible changes in the shape of the body they are built in and follow its deformations. Comparing the two sensory responses, we can discriminate the concave and the convex side of the bent body. Hence, we propose a new strategy to reveal in a soft body the maximum bending angle (or the maximum deflection) and the externally applied force according to the body's mechanical configuration. PMID:25739743

Elastic properties of graphene: A pseudo-beam model with modified internal bending moment and its application

NASA Astrophysics Data System (ADS)

Xia, Z. M.; Wang, C. G.; Tan, H. F.

2018-04-01

A pseudo-beam model with modified internal bending moment is presented to predict elastic properties of graphene, including the Young's modulus and Poisson's ratio. In order to overcome a drawback in existing molecular structural mechanics models, which only account for pure bending (constant bending moment), the presented model accounts for linear bending moments deduced from the balance equations. Based on this pseudo-beam model, an analytical prediction is accomplished to predict the Young's modulus and Poisson's ratio of graphene based on the equation of the strain energies by using Castigliano second theorem. Then, the elastic properties of graphene are calculated compared with results available in literature, which verifies the feasibility of the pseudo-beam model. Finally, the pseudo-beam model is utilized to study the twisting wrinkling characteristics of annular graphene. Due to modifications of the internal bending moment, the wrinkling behaviors of graphene sheet are predicted accurately. The obtained results show that the pseudo-beam model has a good ability to predict the elastic properties of graphene accurately, especially the out-of-plane deformation behavior.

The interaction of E. coli integration host factor and lambda cos DNA: multiple complex formation and protein-induced bending.

PubMed Central

Kosturko, L D; Daub, E; Murialdo, H

1989-01-01

The interaction of E. coli's integration Host Factor (IHF) with fragments of lambda DNA containing the cos site has been studied by gel-mobility retardation and electron microscopy. The cos fragment used in the mobility assays is 398 bp and spans a region from 48,298 to 194 on the lambda chromosome. Several different complexes of IHF with this fragment can be distinguished by their differential mobility on polyacrylamide gels. Relative band intensities indicate that the formation of a complex between IHF and this DNA fragment has an equilibrium binding constant of the same magnitude as DNA fragments containing lambda's attP site. Gel-mobility retardation and electron microscopy have been employed to show that IHF sharply bends DNA near cos and to map the bending site. The protein-induced bend is near an intrinsic bend due to DNA sequence. The position of the bend suggests that IHF's role in lambda DNA packaging may be the enhancement of terminase binding/cos cutting by manipulating DNA structure. Images PMID:2521383

Tropic responses of Phycomyces sporangiophores to gravitational and centrifugal stimuli.

PubMed

DENNISON, D S

1961-09-01

A low-speed centrifuge was used to study the tropic responses of Phycomyces sporangiophores in darkness to the stimulus of combined gravitational and centrifugal forces. If this stimulus is constant the response is a relatively slow tropic reaction, which persists for up to 12 hours. The response is accelerated by increasing the magnitude of the gravitational-centrifugal force. A wholly different tropic response, the transient response, is elicited by an abrupt change in the gravitational-centrifugal stimulus. The transient response has a duration of only about 6 min. but is characterized by a high bending speed (about 5 degrees /min.). An analysis of the distribution of the transient response along the growing zone shows that the active phase of the response has a distribution similar to that of the light sensitivity for the light-growth and phototropic responses. Experiments in which sporangiophores are centrifuged in an inert dense fluid indicate that the sensory mechanism of the transient response is closely related to the physical deformation of the growing zone caused by the action of the gravitational-centrifugal force on the sporangiophore as a whole. However, the response to a steady gravitational-centrifugal force is most likely not connected with this deformation, but is probably triggered by the shifting of regions or particles of differing density relative to one another inside the cell.

Flexural creep of structural flakeboards under cyclic humidity

Treesearch

M.C. Yeh; R.C. Tang; Chung-Yun Hse

1990-01-01

Flexural creep behavior of randomly oriented structural flakeboards under cyclic humidity is presented. Specimens fabricated with 5 and 7 percent phenol-formaldehyde resin were subjected to constant concentrated load in bending under slow and fast cyclic relative humidity (RH) between 65 and 95 percent for 100 days. The temperature was set at a constant 75°F through...

Effects of Structural Flexibility on Motorcycle Straight Running Stability by using Energy Flow Method

NASA Astrophysics Data System (ADS)

Marumo, Yoshitaka; Katayama, Tsuyoshi

This study uses the energy flow method to analyze how structural flexibility affects the motorcycle wobble and weave modes. Lateral bending of the front fork and torsion of the main frame affect the wobble mode stability. These are based on the gyroscopic effect of the front wheel in the steering motion by considering structural flexibility. At high speeds, lateral bending of the front fork and torsion of the rear swing arm more significantly affect the weave mode stability. These are primarily due to the phase changes of the external force generated by the yaw rate in the lateral motion. The phase change of the yaw rate force in the lateral motion originates from the phase change of the tire side forces.

Piezoelectric actuator models for active sound and vibration control of cylinders

NASA Technical Reports Server (NTRS)

Lester, Harold C.; Lefebvre, Sylvie

1993-01-01

Analytical models for piezoelectric actuators, adapted from flat plate concepts, are developed for noise and vibration control applications associated with vibrating circular cylinders. The loadings applied to the cylinder by the piezoelectric actuators for the bending and in-plane force models are approximated by line moment and line force distributions, respectively, acting on the perimeter of the actuator patch area. Coupling between the cylinder and interior acoustic cavity is examined by studying the modal spectra, particularly for the low-order cylinder modes that couple efficiently with the cavity at low frequencies. Within the scope of this study, the in-plane force model produced a more favorable distribution of low-order modes, necessary for efficient interior noise control, than did the bending model.

Strength of fixation constructs for basilar osteotomies of the first metatarsal.

PubMed

Lian, G J; Markolf, K; Cracchiolo, A

1992-01-01

Twenty-four pairs of fresh-frozen human feet had a proximal osteotomy of the first metatarsal that was fixed using either screws, staples, or K wires. Each metatarsal was excised and the specimen was loaded to failure in a cantilever beam configuration by applying a superiorly directed force to the metatarsal head using an MTS servohydraulic test machine. Specimens with a crescentic osteotomy that were fixed using a single screw demonstrated higher mean failure moments than pairs that were fixed with four staples or two K wires; staples were the weakest construct. All specimens fixed with staples failed by bending of the staples without bony fracture; all K wire constructs but one failed by wire bending. Chevron and crescentic osteotomies fixed with a single screw demonstrated equal bending strengths; the bending strength of an oblique osteotomy fixed with two screws was 82% greater than for a crescentic osteotomy fixed with a single screw. Basilar osteotomies of the first metatarsal are useful in correcting metatarsus primus varus often associated with hallux valgus pathology. Fixation strength is an important consideration since weightbearing forces on the head of the first metatarsal acting at a distance from the osteotomy site subject the construct to a dorsiflexion bending moment, as simulated in our tests. Our results show that screw fixation is the strongest method for stabilizing a basilar osteotomy. Based upon the relatively low bending strengths of the staple and K wire constructs, we would not recommend these forms of fixation.(ABSTRACT TRUNCATED AT 250 WORDS)

Bending strength model for internal spur gear teeth

NASA Technical Reports Server (NTRS)

Savage, Michael; Rubadeux, K. L.; Coe, H. H.

1995-01-01

Internal spur gear teeth are normally stronger than pinion teeth of the same pitch and face width since external teeth are smaller at the base. However, ring gears which are narrower have an unequal addendum or are made of a material with a lower strength than that of the meshing pinion may be loaded more critically in bending. In this study, a model for the bending strength of an internal gear tooth as a function of the applied load pressure angle is presented which is based on the inscribed Lewis constant strength parabolic beam. The bending model includes a stress concentration factor and an axial compression term which are extensions of the model for an external gear tooth. The geometry of the Lewis factor determination is presented, the iteration to determine the factor is described, and the bending strength J factor is compared to that of an external gear tooth. This strength model will assist optimal design efforts for unequal addendum gears and gears of mixed materials.

The Role of Crack Formation in Chevron-Notched Four-Point Bend Specimens

NASA Technical Reports Server (NTRS)

Calomino, Anthony M.; Ghosn, Louis J.

1994-01-01

The failure sequence following crack formation in a chevron-notched four-point bend 1 specimen is examined in a parametric study using the Bluhm slice synthesis model. Premature failure resulting from crack formation forces which exceed those required to propagate a crack beyond alpha (min) is examined together with the critical crack length and critical crack front length. An energy based approach is used to establish factors which forecast the tendency of such premature failure due to crack formation for any selected chevron-notched geometry. A comparative study reveals that, for constant values of alpha (1) and alpha (0), the dimensionless beam compliance and stress intensity factor are essentially independent of specimen width and thickness. The chevron tip position, alpha (0) has its primary effect on the force required to initiate a sharp crack. Small values for alpha (0) maximize the stable region length, however, the premature failure tendency is also high for smaller alpha (0) values. Improvements in premature failure resistance can be realized for larger values of alpha (0) with only a minor reduction in the stable region length. The stable region length is also maximized for larger chevron based positions, alpha (1) but the chance for premature failure is also raised. Smaller base positions improve the premature failure resistance with only minor decreases in the stable region length. Chevron geometries having a good balance of premature failure resistance, stable region length, and crack front length are 0.20 less than or equal to alpha (0) is less than or equal to 0.30 and 0.70 is less than or equal to alpha (1) is less than or equal to 0.80.

HIGH SENSITIVITY ELECTROSCOPE

DOEpatents

Shonka, F.R.; Okleshen, A.J.

1958-08-12

An electrometer with dependable and rugged construction for measuring cxtremely small charges is de scribed. The electrometer arrangement comprises an electrically conducting fiber totally disposed in a single plane in the absence of electrosthtic forces and affixed at both ends to fiber support means. The fiber is provided with a plurality of adjacent bends in opposite directions along its length..An electrode is disposed between two adjacent bends to apply an electrostatic force normal to the plane of the fiber whereby the fiber is caused to twist out of its plane in proportion to the potential apptied between the fiber and the electrode.

Large Deflection of Ideal Pseudo-Elastic Shape Memory Alloy Cantilever Beam

NASA Astrophysics Data System (ADS)

Cui, Shitang; Hu, Liming; Yan, Jun

This paper deals with the large deflections of pseudo-elastic shape memory alloy cantilever beams subjected to a concentrated load at the free end. Because of the large deflections, geometry nonlinearity arises and this analysis employs the nonlinear bending theory. The exact expression of curvature is used in the moment-curvature relationship. As a vertical force at the tip of cantilever, curvature and bending moment distribution expressions are deduced. The curvature changed distinctly when the surface material undergoes phase transformation. The length of phase transformation region was affected greatly with the force at the free end.

Active buckling control of an imperfect beam-column with circular cross-section using piezo-elastic supports and integral LQR control

NASA Astrophysics Data System (ADS)

Schaeffner, Maximilian; Platz, Roland

2016-09-01

For slender beam-columns loaded by axial compressive forces, active buckling control provides a possibility to increase the maximum bearable axial load above that of a purely passive structure. In this paper, the potential of active buckling control of an imperfect beam-column with circular cross-section using piezo-elastic supports is investigated numerically. Imperfections are given by an initial deformation of the beam-column caused by a constant imperfection force. With the piezo-elastic supports, active bending moments in arbitrary directions orthogonal to the beam-column's longitudinal axis can be applied at both beam- column's ends. The imperfect beam-column is loaded by a gradually increasing axial compressive force resulting in a lateral deformation of the beam-column. First, a finite element model of the imperfect structure for numerical simulation of the active buckling control is presented. Second, an integral linear-quadratic regulator (LQR) that compensates the deformation via the piezo-elastic supports is derived for a reduced modal model of the ideal beam-column. With the proposed active buckling control it is possible to stabilize the imperfect beam-column in arbitrary lateral direction for axial loads above the theoretical critical buckling load and the maximum bearable load of the passive structure.

Analysis of dry friction damping characteristics for short cylindrical shell structures

NASA Astrophysics Data System (ADS)

Wang, Nengmao; Wang, Yanrong

2018-05-01

An efficient mathematical model to describe the friction of short cylindrical shell structures with a dry friction damping sleeve is proposed. The frictional force in the circumference and axial direction is caused by the opposing bending strains at the interface. Slipping will occur at part region of the interface and the mathematic model of the slipping region is established. Ignoring the effect of contact stiffness on the vibration analysis, the friction energy dissipation capability of damping sleeve would be calculated. Structural vibration mode, positive pressure at the interface and vibration stress of the short cylindrical shell structures is analyzed as influence factors to the critical damping ratio. The results show that the circumferential friction energy dissipation is more sensitive to the number of nodal diameter, and the circumferential friction damping ratio increases rapidly with the number of nodal diameter. The slipping frictional force would increase along with the positive pressure, but the slipping region would decrease with it. The peak damping ratio keeps nearly constant. But the vibration stress corresponding to peak damping ratio would increases with the positive pressure. The dry friction damping ratio of damping sleeve contains the effect of frictional force in the circumference and axial direction, and the axial friction plays a major role.

Coarse-Grained Simulation of Solvated Cellulose Ib Microfibril

NASA Astrophysics Data System (ADS)

Fan, Bingxin; Maranas, Janna; Zhong, Linghao; Zhen Zhao Collaboration

2013-03-01

We construct a coarse-grained (CG) model of cellulose microfibrils in water. The force field is derived from atomistic simulation of a 40 glucose-unit-long microfibril by requiring consistency between the chain configuration, intermolecular packing and hydrogen bonding of the two levels of modeling. Intermolecular interactions such as hydrogen bonding are added sequentially until the force field holds the microfibril crystal structure. This stepwise process enables us to evaluate the importance of each potential and provides insight to ordered and disordered regions. We simulate cellulose microfibrils with 100 to 400 residues, comparable to the smallest observed microfibrils. Microfibrils longer than 100nm would form a bending region along their longitudinal direction. Multiple bends are observed in the microfibril containing 400 residues. Although the cause is not clear, the bending regions may provide us insights about the periodicity and the behavior of the disordered regions in the microfibril.

Role of flexural stiffness of leukocyte microvilli in adhesion dynamics

NASA Astrophysics Data System (ADS)

Wu, Tai-Hsien; Qi, Dewei

2018-03-01

Previous work reported that microvillus deformation has an important influence on dynamics of cell adhesion. However, the existing studies were limited to the extensional deformation of microvilli and did not consider the effects of their bending deformation on cell adhesion. This Rapid Communication investigates the effects of flexural stiffness of microvilli on the rolling process related to adhesion of leukocytes by using a lattice-Boltzmann lattice-spring method (LLM) combined with adhesive dynamics (AD) simulations. The simulation results reveal that the flexural stiffness of microvilli and their bending deformation have a profound effect on rolling velocity and adhesive forces. As the flexural stiffness of the microvilli decreases, their bending angles increase, resulting in an increase in the number of receptor-ligand bonds and adhesive bonding force and a decrease in the rolling velocity of leukocytes. The effects of flexural stiffness on deformation and adhesion represent crucial factors involved in cell adhesion.

Back pain is associated with changes in loading pattern throughout forward and backward bending.

PubMed

Shum, Gary L K; Crosbie, Jack; Lee, Raymond Y W

2010-12-01

Experimental study to determine the kinetics of the lumbar spine (LS) and hips during forward and backward bending. To investigate the effects of back pain, with and without a positive straight leg raise (SLR) sign, on the loading patterns in the LS and hip during forward and backward bending. Forward and backward bending are important components of many functional activities and are part of routine clinical examination. However, there is a little information about the loading patterns during forward and backward bending in people with back pain with or without a positive SLR sign. Twenty asymptomatic participants, 20 back pain participants, and 20 participants with back pain and a positive SLR sign performed 3 continuous cycles of forward and backward bending. Electromagnetic sensors were attached to body segments to measure their kinematics while 2 nonconductive force plates gathered ground reaction force data. A biomechanical model was used to determine the loading pattern in LS and hips. Although the loading on the LS at the end of the range decreased significantly, the loading at the early and middle ranges of forward bending actually increased significantly in people with back pain, especially in those with positive SLR sign. This suggests that resistance to movement is significantly increased in people with back pain during this movement. This study suggested that it is not sufficient to study the spine at the end of range only, but a complete description of the loading patterns throughout the range is required. Although the maximum range of motion of the spine is reduced in people with back pain, there is a significant increase in the moment acting through the range, particularly in those with a positive SLR sign.

Effects of accelerated artificial daylight aging on bending strength and bonding of glass fibers in fiber-embedded maxillofacial silicone prostheses.

PubMed

Hatamleh, Muhanad M; Watts, David C

2010-07-01

The purpose of this study was to test the effect of different periods of accelerated artificial daylight aging on bond strength of glass fiber bundles embedded into maxillofacial silicone elastomer and on bending strength of the glass fiber bundles. Forty specimens were fabricated by embedding resin-impregnated fiber bundles (1.5-mm diameter, 20-mm long) into maxillofacial silicone elastomer. Specimens were randomly allocated into four groups, and each group was subjected to different periods of accelerated daylight aging as follows (in hours); 0, 200, 400, and 600. The aging cycle included continuous exposure to quartz-filtered visible daylight (irradiance 760 W/m(2)) under an alternating weathering cycle (wet for 18 minutes, dry for 102 minutes). Pull-out tests were performed to evaluate bond strength between fiber bundles and silicone using a universal testing machine at 1 mm/min crosshead speed. Also a three-point bending test was performed to evaluate bending strength of the fiber bundles. One-way ANOVA and Bonferroni post hoc tests were carried out to detect statistical significance (p < 0.05). Mean (SD) values of maximum pull-out forces (in N) for groups 1 to 4 were: 13.63 (7.45), 19.67 (1.37), 13.58 (2.61), and 10.37 (2.52). Group 2 exhibited the highest pull-out force that was statistically significant when compared to the other groups. Maximum bending strengths of fiber bundles were in the range of 917.72 MPa to 1124.06 MPa. Bending strength significantly increased after 200 and 400 hours of aging only. After 200 hours of exposure to artificial daylight and moisture conditions, bond strength between glass fibers and heat-cured silicones is optimal, and the bending strength of the glass fiber bundles is enhanced.

The rotation-vibration structure of the SO 2 C 1B 2 state explained by a new internal coordinate force field

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jiang, Jun; Park, G. Barratt; Field, Robert W.

A new quartic force field for the SO 2 C ~ 1B 2 state has been derived, based on high resolution data from S 16O 2 and S 18O 2. Included are eight b 2 symmetry vibrational levels of S 16O 2 reported in the first paper of this series [G. B. Park, et al., J. Chem. Phys. 144, 144311 (2016)]. Many of the experimental observables not included in the fit, such as the Franck-Condon intensities and the Coriolis-perturbed effective C rotational constants of highly anharmonic C ~ state vibrational levels, are well reproduced using our force field. Because themore » two stretching modes of the C ~ state are strongly coupled via Fermi-133 interaction, the vibrational structure of the C state is analyzed in a Fermi-system basis set, constructed explicitly in this work via partial diagonalization of the vibrational Hamiltonian. The physical significance of the Fermi-system basis is discussed in terms of semiclassical dynamics, based on study of Fermi-resonance systems by Kellman and coworkers [M. E. Kellman and L. Xiao, J. Chem. Phys. 93, 5821 (1990)]. By diagonalizing the vibrational Hamiltonian in the Fermi-system basis, the vibrational characters of all vibrational levels can be determined unambiguously. It is shown that the bending mode cannot be treated separately from the coupled stretching modes, particularly at vibrational energies of more than 2000 cm –1. Based on our force field, the structure of the Coriolis interactions in the C ~ state of SO 2 is also discussed. As a result, we identify the origin of the alternating patterns in the effective C rotational constants of levels in the vibrational progressions of the symmetry-breaking mode, ν β (which correlates with the antisymmetric stretching mode in our assignment scheme).« less

The rotation-vibration structure of the SO 2 C 1B 2 state explained by a new internal coordinate force field

DOE PAGES

Jiang, Jun; Park, G. Barratt; Field, Robert W.

2016-04-14

A new quartic force field for the SO 2 C ~ 1B 2 state has been derived, based on high resolution data from S 16O 2 and S 18O 2. Included are eight b 2 symmetry vibrational levels of S 16O 2 reported in the first paper of this series [G. B. Park, et al., J. Chem. Phys. 144, 144311 (2016)]. Many of the experimental observables not included in the fit, such as the Franck-Condon intensities and the Coriolis-perturbed effective C rotational constants of highly anharmonic C ~ state vibrational levels, are well reproduced using our force field. Because themore » two stretching modes of the C ~ state are strongly coupled via Fermi-133 interaction, the vibrational structure of the C state is analyzed in a Fermi-system basis set, constructed explicitly in this work via partial diagonalization of the vibrational Hamiltonian. The physical significance of the Fermi-system basis is discussed in terms of semiclassical dynamics, based on study of Fermi-resonance systems by Kellman and coworkers [M. E. Kellman and L. Xiao, J. Chem. Phys. 93, 5821 (1990)]. By diagonalizing the vibrational Hamiltonian in the Fermi-system basis, the vibrational characters of all vibrational levels can be determined unambiguously. It is shown that the bending mode cannot be treated separately from the coupled stretching modes, particularly at vibrational energies of more than 2000 cm –1. Based on our force field, the structure of the Coriolis interactions in the C ~ state of SO 2 is also discussed. As a result, we identify the origin of the alternating patterns in the effective C rotational constants of levels in the vibrational progressions of the symmetry-breaking mode, ν β (which correlates with the antisymmetric stretching mode in our assignment scheme).« less

Characterization of bending EAP beams

NASA Technical Reports Server (NTRS)

Bao, Xiaoqi; Bar-Cohen, Yoseph; Chang, Zensheu; Sherrit, Stewart

2004-01-01

Electroactive polymers are attractive actuation materials because of their large deformation, flexibility, and lightweight. A CCD camera system was constructed to record the curved shapes of bending during the activation of EAP films and image-processing software was developed to digitize the bending curves. A computer program was developed to solve the invese problem of cantilever EAP beams with tip position limiter. using the developed program and acquired curves without tip position limiter as well as the corresponding tip force, the EAP material properties of voltage-strain sensitivity and Young's modulus were determined.

Rotational spectrum and structure of the T-shaped cyanoacetylene carbon dioxide complex, HCCCN⋯CO2

NASA Astrophysics Data System (ADS)

Kang, Lu; Davis, Philip; Dorell, Ian; Li, Kexin; Oncer, Onur; Wang, Lucy; Novick, Stewart E.; Kukolich, Stephen G.

2017-12-01

The rotational spectrum of the T-shaped cyanoacetylene carbon dioxide dimer, HCCCN⋯CO2, was measured using two Balle-Flygare Fourier transform microwave (FTMW) spectrometers between 1.4 GHz and 25 GHz. Only the Ka = 0, 2, 4 branches of spectrum from J‧ = 1 ← 0 to J″ = 16 ← 15 transitions were observed. The vanishing of the Ka = 1, 3, … transitions demonstrates a C2v symmetry complex with a T-shaped alignment of the subunits. The spectroscopic constants were fit using Pickett's SPFIT/SPCAT suite of programs obtaining: A0 = 11273(18) MHz, B0 = 764.088(21) MHz, C0 = 716.254(21) MHz, ΔJ = 0.50329(34) kHz, ΔJK = 0.120867(11) MHz, ΔK = -28.17(36) MHz, δJ = 0.0613(21) kHz, δK = 44.25(95) kHz, ΦJ = 0.0053(12) Hz, ΦJK = 9.820(55) Hz, ΦKJ = -0.59325(72) kHz, ΦK = -2.3719(53) MHz, ϕJ = 0.0398(42) Hz, ϕJK = 6.9(9) Hz, and ϕK = -3.592(13) kHz. The 14N nuclear quadrupole coupling constants were fit to χaa = -4.12753(38) MHz and χbb - χcc = 0.103(15) MHz. The small negative inertial defect, Δ0 = -0.66(12) u Å2, indicates a vibrationally averaged planar complex with non-negligible low frequency out-of-plane vibrations. While maintaining near-planar orientation, both binding partners exhibit large-amplitude bending vibrations within the plane. To deal with the intermolecular dynamics, a torsional oscillation model was developed in this work for the structural analysis. According to this model, the vibrational bending amplitude for HCCCN torsional angle is 10.(1)°, with the a-axis of complex; CO2 subtending a 5.4(5)° torsional oscillation angle with the b molecular axis. The van der Waals bond length is 3.0137(3) Å. The stretching force constant, ks = 3.9 N/m, and the stretching frequency, νs = 53 cm-1, for the van der Waals bond were calculated using the pseudo-diatomic model. High-level MP2 and DFT calculations of structural parameters, rotational constants, and 14N quadrupole coupling strengths were made and the results compared with experimental results.

Modeling and experimental analysis of electrospinning bending region physics in determining fiber diameter for hydrophilic polymer solvent systems

NASA Astrophysics Data System (ADS)

Cai, Yunshen

Electrospinning produces submicron fibers from a wide range of polymer/solvent systems that enable a variety of different applications. In electrospinning process, a straight polymer/solvent charged jet is initially formed, followed by a circular moving jet in the shape of a cone, called the bending region. The process physics in the bending region are difficult to study since the jet diameter cannot be measured directly due to its rapid motion and small size ( microns and smaller), and due to complex coupling of multiple forces, mass transport, and changing jet geometry. Since the solutions studied are hydrophilic, they readily absorb ambient moisture. This thesis explores the role of the bending region in determining the resulting electrospun fiber diameter through a combined experimental and modeling analysis for a variety of hydrophilic polymer/solvent solutions. Electrospinning experiments were conducted over a broad range of operating conditions for 4 different polymer/solvent systems. Comparison of the final straight jet diameters to fiber diameters reveals that between 30% to 60% jet thinning occurs in the bending region. These experiments also reveal that relative humidity significantly affects the electrospinning process and final fiber diameter, even for non-aqueous solutions. A model is developed to obtain insight into the bending region process physics. Important ones include understanding the mass transport for non-aqueous hydrophilic jets (including solvent evaporation and water absorption on the jet surface, radial diffusion, and axial advection), and the coupling between the mass and force balances that determines the final fiber diameter. The absorption and evaporation physics is validated by evaporation experiments. The developed model predicts fiber diameter to within of 8%, even though the solution properties and operating conditions that determines net stretching forces and net evaporation rates vary over a large range. Model analysis reveals how the net evaporation rate affects the jet length and net stretching force, both of which ultimately determine the fiber diameter. It is also shown that the primary impact of RH on the process is through occupation of the surface states that limits solvent evaporation rate, rather than the amount of water absorbed. Correlation functions between process conditions, solution properties and the resulting fiber diameters are discussed.

Correlation of compressive stress with spalling of plasma sprayed ceramic materials

NASA Technical Reports Server (NTRS)

Mullen, R. L.; Mcdonald, G.; Hendricks, R. C.; Hofle, M. M.

1983-01-01

Ceramics on metal substrates for potential use as high temperature seals or other applications are exposed to forces originating from differences in thermal expansion between the ceramic and the metal substrate. This report develops a relationship between the difference in expansion of the ceramic and the substrate, defines conditions under which shear between the ceramic and the substrate occurs, and those under which bending forces are produced in the ceramic. The off-axis effect of compression forces resulting from high temperature plastic flow of the ceramic producing buckling of the ceramic is developed. Shear is associated with the edge or boundary stresses on the component while bending is associated with the distortion of an interior region. Both modes are significant in predicting life of the ceramic.

[The long-term fracture resistance of orthodontic nickel-titanium wires].

PubMed

Drescher, D; Bourauel, C; Sonneborn, W; Schmuth, G P

1994-01-01

This study reports on the long-term fracture resistance of orthodontic nickel titanium wires, a material property that has not been investigated thoroughly, yet. A computer-controlled apparatus was designed to perform long-term bending tests. The investigated material comprised 9 nickel titanium wires (dimensions 0.016", round and 0.016" x 0.022", rectangular) as well as a stainless steel and a beta-titanium wire that were included as reference. Compared with the steel wire, the nickel titanium wires exhibited 2- to 5-fold higher yield forces in bending. At a specified deflection angle, the generated bending forces of the nickel titanium wires reached one half to one fourth of the values of steel. The fracture resistance under longterm loading was determined using the Wöhler-method. After 10(5) loadings, 0.016" nickel titanium wires were subject to break failure, if forces exceed values greater than 1.2 to 3.1 N. Steel and TMA wires could be loaded with forces of up to 4.4 and 3.7 N, respectively. The 0.016" x 0.022"-rectangular wires allowed forces of approximately twice this magnitude. Elastic fatigue of the superelastic specimens "Memorywire", "Rematitan Lite", and "Sentalloy medium" showed up as hardening of the wire by up to 70%. Material degradation lead to a severe deformation of the hysteresis loop and to plastic deformation. Work-hardened martensitic NiTi wires did not show these effects to this extent.

Morphological properties of the last primaries, the tail feathers, and the alulae of Accipiter nisus, Columba livia, Falco peregrinus, and Falco tinnunculus.

PubMed

Schmitz, Anke; Ponitz, Benjamin; Brücker, Christoph; Schmitz, Helmut; Herweg, Jan; Bleckmann, Horst

2015-01-01

We investigated the mechanical properties (Young's modulus, bending stiffness, barb separation forces) of the tenth primary of the wings, of the alulae and of the middle tail feathers of Falco peregrinus. For comparison, we also investigated the corresponding feathers in pigeons (Columba livia), kestrels (Falco tinnunculus), and sparrowhawks (Accipiter nisus). In all four species, the Young's moduli of the feathers ranged from 5.9 to 8.4 GPa. The feather shafts of F. peregrinus had the largest cross-sections and the highest specific bending stiffness. When normalized with respect to body mass, the specific bending stiffness of primary number 10 was highest in F. tinnunculus, while that of the alula was highest in A. nisus. In comparison, the specific bending stiffness, measured at the base of the tail feathers and in dorso-ventral bending direction, was much higher in F. peregrinus than in the other three species. This seems to correlate with the flight styles of the birds: F. tinnunculus hovers and its primaries might therefore withstand large mechanical forces. A. nisus has often to change its flight directions during hunting and perhaps needs its alulae for this maneuvers, and in F. peregrinus, the base of the tail feathers might need a high stiffness during breaking after diving. © 2014 Wiley Periodicals, Inc.

Inertial Force Coupling to Nonlinear Aeroelasticity of Flexible Wing Aircraft

NASA Technical Reports Server (NTRS)

Nguyen, Nhan T.; Ting, Eric

2016-01-01

This paper investigates the inertial force effect on nonlinear aeroelasticity of flexible wing aircraft. The geometric are nonlinearity due to rotational and tension stiffening. The effect of large bending deflection will also be investigated. Flutter analysis will be conducted for a truss-braced wing aircraft concept with tension stiffening and inertial force coupling.

A 2-DOF microstructure-dependent model for the coupled torsion/bending instability of rotational nanoscanner

NASA Astrophysics Data System (ADS)

Keivani, M.; Abadian, N.; Koochi, A.; Mokhtari, J.; Abadyan, M.

2016-10-01

It has been well established that the physical performance of nanodevices might be affected by the microstructure. Herein, a two-degree-of-freedom model base on the modified couple stress theory is developed to incorporate the impact of microstructure in the torsion/bending coupled instability of rotational nanoscanner. Effect of microstructure dependency on the instability parameters is determined as a function of the microstructure parameter, bending/torsion coupling ratio, van der Waals force parameter and geometrical dimensions. It is found that the bending/torsion coupling substantially affects the stable behavior of the scanners especially those with long rotational beam elements. Impact of microstructure on instability voltage of the nanoscanner depends on coupling ratio and the conquering bending mode over torsion mode. This effect is more highlighted for higher values of coupling ratio. Depending on the geometry and material characteristics, the presented model is able to simulate both hardening behavior (due to microstructure) and softening behavior (due to torsion/bending coupling) of the nanoscanners.

Evaluation of bending modulus of lipid bilayers using undulation and orientation analysis

NASA Astrophysics Data System (ADS)

Chaurasia, Adarsh K.; Rukangu, Andrew M.; Philen, Michael K.; Seidel, Gary D.; Freeman, Eric C.

2018-03-01

In the current paper, phospholipid bilayers are modeled using coarse-grained molecular dynamics simulations with the MARTINI force field. The extracted molecular trajectories are analyzed using Fourier analysis of the undulations and orientation vectors to establish the differences between the two approaches for evaluating the bending modulus. The current work evaluates and extends the implementation of the Fourier analysis for molecular trajectories using a weighted horizon-based averaging approach. The effect of numerical parameters in the analysis of these trajectories is explored by conducting parametric studies. Computational modeling results are validated against experimentally characterized bending modulus of lipid membranes using a shape fluctuation analysis. The computational framework is then used to estimate the bending moduli for different types of lipids (phosphocholine, phosphoethanolamine, and phosphoglycerol). This work provides greater insight into the numerical aspects of evaluating the bilayer bending modulus, provides validation for the orientation analysis technique, and explores differences in bending moduli based on differences in the lipid nanostructures.

Interaction with gravitropism, reversibility and lateral movements of phototropically stimulated potato shoots.

PubMed

Vinterhalter, D; Savić, J; Stanišić, M; Jovanović, Ž; Vinterhalter, B

2016-07-01

Phototropic (PT) and gravitropic (GT) bending are the two major tropic movements that determine the spatial position of potato shoots. We studied PT bending of potato plantlets grown under long-day photoperiods in several prearranged position setups providing different interactions with the GT response. Starting with the standard PT stimulation setup composed of unilateral irradiation of vertically positioned shoots, experiments were also done in antagonistic and synergistic setups and in treatments with horizontal displacement of the light source. In the standard setup, PT bending suppressed the GT bending, which could occur only if the PT stimulation was cancelled. The antagonistic position, with phototropism and gravitropism attempting to bend shoots in opposite directions, showed phototropism and gravitropism as independent bending events with the outcome varying throughout the day reflecting diurnal changes in the competence of individual tropic components. Whilst gravitropism was constant, phototropism had a marked daily fluctuation of its magnitude with a prominent morning maximum starting an hour after the dawn in the growth room and lasting for the next 6 h. When phototropism and gravitropism were aligned in a synergistic position, stimulating shoot bending in the same direction, there was little quantitative addition of their individual effects. The long period of morning PT bending maximum enabled multiple PT bending events to be conducted in succession, each one preceded by a separate lag phase. Studies of secondary PT events showed that potato plantlets can follow and adjust their shoot position in response to both vertical and horizontal movements of a light source. PT bending was reversible, since the 180° horizontal change of a blue light (BL) source position resulted in reversal of bending direction after a 20-min-long lag phase.

Minimum constitutive relation error based static identification of beams using force method

NASA Astrophysics Data System (ADS)

Guo, Jia; Takewaki, Izuru

2017-05-01

A new static identification approach based on the minimum constitutive relation error (CRE) principle for beam structures is introduced. The exact stiffness and the exact bending moment are shown to make the CRE minimal for given displacements to beam damages. A two-step substitution algorithm—a force-method step for the bending moment and a constitutive-relation step for the stiffness—is developed and its convergence is rigorously derived. Identifiability is further discussed and the stiffness in the undeformed region is found to be unidentifiable. An extra set of static measurements is complemented to remedy the drawback. Convergence and robustness are finally verified through numerical examples.

Bending impact on the performance of a flexible Li4Ti5O12-based all-solid-state thin-film battery.

PubMed

Sepúlveda, Alfonso; Speulmanns, Jan; Vereecken, Philippe M

2018-01-01

The growing demand of flexible electronic devices is increasing the requirements of their power sources. The effect of bending in thin-film batteries is still not well understood. Here, we successfully developed a high active area flexible all-solid-state battery as a model system that consists of thin-film layers of Li 4 Ti 5 O 12 , LiPON, and Lithium deposited on a novel flexible ceramic substrate. A systematic study on the bending state and performance of the battery is presented. The battery withstands bending radii of at least 14 mm achieving 70% of the theoretical capacity. Here, we reveal that convex bending has a positive effect on battery capacity showing an average increase of 5.5%, whereas concave bending decreases the capacity by 4% in contrast with recent studies. We show that the change in capacity upon bending may well be associated to the Li-ion diffusion kinetic change through the electrode when different external forces are applied. Finally, an encapsulation scheme is presented allowing sufficient bending of the device and operation for at least 500 cycles in air. The results are meant to improve the understanding of the phenomena present in thin-film batteries while undergoing bending rather than showing improvements in battery performance and lifetime.

Three-dimensional ionic conduction in the strained electrolytes of solid oxide fuel cells

DOE Office of Scientific and Technical Information (OSTI.GOV)

Han, Yupei; Zou, Minda; Lv, Weiqiang

2016-05-07

Flexible power sources including fuel cells and batteries are the key to realizing flexible electronic devices with pronounced foldability. To understand the bending effects in these devices, theoretical analysis on three-dimensional (3-D) lattice bending is necessary. In this report, we derive a 3-D analytical model to analyze the effects of electrolyte crystal bending on ionic conductivity in flexible solid-state batteries/fuel cells. By employing solid oxide fuel cells as a materials' platform, the intrinsic parameters of bent electrolyte materials, including lattice constant, Young's modulus, and Poisson ratio, are evaluated. Our work facilitates the rational design of highly efficient flexible electrolytes formore » high-performance flexible device applications.« less

Nucleation and Crystallization as Induced by Bending Stress in Lithium Silicate Glass Fibers

NASA Technical Reports Server (NTRS)

Reis, Signo T.; Kim, Cheol W.; Brow, Richard K.; Ray, Chandra S.

2003-01-01

Glass Fibers of Li2O.2SiO2 (LS2) and Li2O.1.6SiO2 (LS1.6) compositions were heated near, but below, the glass transition temperature for different times while subjected to a constant bending stress of about 1.2 GPa. The nucleation density and the crystallization tendency estimated by differential thermal analysis (DTA) of a glass sample in the vicinity of the maximum of the bending stress increased relative to that of stress-free glass fibers. LS2 glass fibers were found more resistant to nucleation and crystallization than the Ls1.6 glass fibers. These results are discussed in regards to shear thinning effects on glass stability.

The gearing function of running shoe longitudinal bending stiffness.

PubMed

Willwacher, Steffen; König, Manuel; Braunstein, Björn; Goldmann, Jan-Peter; Brüggemann, Gert-Peter

2014-07-01

The purpose of the present study was to investigate whether altered longitudinal bending stiffness (LBS) levels of the midsole of a running shoe lead to a systematic change in lower extremity joint lever arms of the ground reaction force (GRF). Joint moments and GRF lever arms in the sagittal plane were determined from 19 male subjects running at 3.5 m/s using inverse dynamics procedures. LBS was manipulated using carbon fiber insoles of 1.9 mm and 3.2 mm thickness. Increasing LBS led to a significant shift of joint lever arms to a more anterior position. Effects were more pronounced at distal joints. Ankle joint moments were not significantly increased in the presence of higher GRF lever arms when averaged over all subjects. Still, two individual strategies (1: increase ankle joint moments while keeping push-off times almost constant, 2: decrease ankle joint moments and increase push-off times) could be identified in response to increased ankle joint lever arms that might reflect individual differences between subjects with respect to strength capacities or anthropometric characteristics. The results of the present study indicate that LBS systematically influences GRF lever arms of lower extremity joints during the push-off phase in running. Further, individual responses to altered LBS levels could be identified that could aid in finding optimum LBS values for a given individual. Copyright © 2014 Elsevier B.V. All rights reserved.

Optical forces near micro-fabricated devices

NASA Astrophysics Data System (ADS)

Mejia Prada, Camilo Andres

In this dissertation, I study optical forces near micro-fabricated devices for multi- particle manipulation. I consider particles of different sizes and compositions. In particular, I focus my study on both dielectric and gold particles as well as Giant Unilamellar Vesicles. First, I consider optical forces near a PhC and establish the feasibility of a technique which we term Light-Assisted Templated Self-assembly (LATS). In contrast to previous work on Fabry-Perot enhancement of trapping forces above a flat substrate, I exploit the guided resonance modes of a PhC to provide resonant enhancement of optical forces. Then, I explore optical forces near a Dual Beam Optical Trap (DBOT). I present a method to extract the bending modulus of the membrane from the area strain data. This method incorporates three-dimensional ray-tracing to calculate the applied stress in the DBOT within the ray optics approximation. I compare the optical force calculated using the ray optics approximation and Maxwell Stress Tensor method to ensure the approximation's accuracy. Next, we apply this method to 3 populations of GUVs to extract the bending modulus of membranes comprised of saturated and monounsaturated lipids in both gel and liquid phases.

Twirling and Whirling: Viscous Dynamics of Rotating Elastica

NASA Astrophysics Data System (ADS)

Powers, Thomas R.; Wolgemuth, Charles W.; Goldstein, Raymond E.

1999-11-01

Motivated by diverse phenomena in cellular biophysics, including bacterial flagellar motion and DNA transcription and replication, we study the overdamped nonlinear dynamics of a rotationally forced filament with twist and bend elasticity. The competition between twist diffusion and writhing instabilities is described by a novel pair of coupled PDEs for twist and bend evolution. Analytical and numerical methods elucidate the twist-bend coupling and reveal two dynamical regimes separated by a Hopf bifurcation: (i) diffusion-dominated axial rotation, or twirling, and (ii) steady-state crankshafting motion, or whirling. The consequences of these phenomena for self-propulsion are investigated, and experimental tests proposed.

Origin of bending in uncoated microcantilever - Surface topography?

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lakshmoji, K.; Prabakar, K.; Tripura Sundari, S., E-mail: sundari@igcar.gov.in

2014-01-27

We provide direct experimental evidence to show that difference in surface topography on opposite sides of an uncoated microcantilever induces bending, upon exposure to water molecules. Examination on opposite sides of the microcantilever by atomic force microscopy reveals the presence of localized surface features on one side, which renders the induced stress non-uniform. Further, the root mean square inclination angle characterizing the surface topography shows a difference of 73° between the opposite sides. The absence of deflection in another uncoated microcantilever having similar surface topography confirms that in former microcantilever bending is indeed induced by differences in surface topography.

Effect of Bending Stiffness of the Electroactive Polymer Element on the Performance of a Hybrid Actuator System (HYBAS)

NASA Technical Reports Server (NTRS)

Xu, Tian-Bing; Su, Ji; Jiang, Xiaoning; Rehrig, Paul W.; Zhang, Shujun; Shrout, Thomas R.; Zhang, Qiming

2006-01-01

An electroactive polymer (EAP)-ceramic hybrid actuation system (HYBAS) was developed recently at NASA Langley Research Center. This paper focuses on the effect of the bending stiffness of the EAP component on the performance of a HYBAS, in which the actuation of the EAP element can match the theoretical prediction at various length/thickness ratios for a constant elastic modulus of the EAP component. The effects on the bending stiffness of the elastic modulus and length/thickness ratio of the EAP component were studied. A critical bending stiffness to keep the actuation of the EAP element suitable for a rigid beam theory-based modeling was found for electron irradiated P(VDF-TrFE) copolymer. For example, the agreement of experimental data and theoretical modeling for a HYBAS with the length/thickness ratio of EAP element at 375 times is demonstrated. However, the beam based theoretical modeling becomes invalid (i.e., the profile of the HYBAS movement does not follow the prediction of theoretical modeling) when the bending stiffness is lower than a critical value.

Physics Notes.

ERIC Educational Resources Information Center

School Science Review, 1981

1981-01-01

Outlines a variety of laboratory procedures, demonstrations, and classroom materials including a technique for estimating speed of electromagnetic waves; a support for multipin components when soldering; use of dynometer to measure force; bending light; using a microcomputer to measure and produce voltage; force-distance curves; and two games. (DS)

Correlation of compressive and shear stress with spalling of plasma-sprayed ceramic materials

NASA Technical Reports Server (NTRS)

Mullen, R. L.; Mcdonald, G.; Hendricks, R. C.; Hofle, M. M.

1983-01-01

Ceramics on metal substrates for potential use as high temperature seals or other applications are exposed to forces originating from differences in thermal expansion between the ceramic and the metal substrate. This report develops a relationship between the difference in expansion of the ceramic and the substrate, defines conditions under which shear between the ceramic and the substrate occurs, and those under which bending forces are produced in the ceramic. The off-axis effect of compression forces resulting from high temperature plastic flow of the ceramic producing buckling of the ceramic is developed. Shear is associated with the edge or boundary stresses on the component while bending is associated with the distortion of an interior region. Both modes are significant in predicting life of the ceramic. Previously announced in STAR as N83-27016

Spiral swimming of an artificial micro-swimmer

NASA Astrophysics Data System (ADS)

Keaveny, Eric E.; Maxey, Martin R.

A device constructed from a filament of paramagnetic beads connected to a human red blood cell will swim when subject to an oscillating magnetic field. Bending waves propagate from the tip of the tail toward the red blood cell in a fashion analogous to flagellum beating, making the artificial swimmer a candidate for studying what has been referred to as micro-swimming. In this study, we demonstrate that under the influence of a rotating field the artificial swimmer will perform -type swimming. We conduct numerical simulations of the swimmer where the paramagnetic tail is represented as a series of rigid spheres connected by flexible but inextensible links. An optimal range of parameters governing the relative strength of viscous, elastic and magnetic forces is identified for swimming speed. A parameterization of the motion is extracted and examined as a function of the driving frequency. With a continuous elastica/resistive force model, we obtain an expression for the swimming speed in the low-frequency limit. Using this expression we explore further the effects of the applied field, the ratio of the transverse field to the constant field, and the ratio of the radius of the sphere to the length of the filament tail on the resulting dynamics.

Flocculation of deformable emulsion droplets. 2: Interaction energy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Petsev, D.N.; Denkov, N.D.; Kralchevsky, P.A.

1995-12-01

The effect of different factors (drop radius, interfacial tension, Hamaker constant, electrolyte, micellar concentrations, etc.) on the interaction energy of emulsion droplets is studied theoretically. It is demonstrated that the deformation of the colliding droplets considerably affects the interaction energy. The contributions of the electrostatic, van der Waals, depletion, steric, and oscillatory surface forces, as well as for the surface stretching and bending energies, are estimated and discussed. The calculations show that the droplets interact as nondeformed spheres when the attractive interactions are weak. At stronger attractions an equilibrium plane parallel film is formed between the droplets, corresponding to minimummore » interaction energy of the system. For droplets in concentrated micellar surfactant solutions the oscillatory surface forces become operative and one can observe several minima of the energy surface,each corresponding to a metastable state with a different number of micellar layers inside the film formed between the droplets. The present theoretical analysis can find applications in predicting the behavior and stability of miniemulsions (containing micrometer and submicrometer droplets), as well as in interpretation of data obtained by light scattering, phase behavior, rheological and osmotic pressure measurements, etc.« less

Temperature corrections for mechanically graded lumber

Treesearch

David W. Green; James W. Evans; James D. Logan; Jim Allen

1999-01-01

The continuous lumber tester (CLT) is the most widely used grading machine in the world. With the CLT, the flatwise bending stiffness of lumber is measured as it passes through the machine. The modulus of elasticity (MOE) is calculated from the force required to bend the lumber to a fixed deflection of 7.94 mm (5/16 in.), and this MOE is used in assigning a machine...

A Model of the THUNDER Actuator

NASA Technical Reports Server (NTRS)

Curtis, Alan R. D.

1997-01-01

A THUNDER actuator is a composite of three thin layers, a metal base, a piezoelectric wafer and a metal top cover, bonded together under pressure and at high temperature with the LaRC SI polyimid adhesive. When a voltage is applied between the metal layers across the PZT the actuator will bend and can generate a force. This document develops and describes an analytical model the transduction properties of THUNDER actuators. The model development is divided into three sections. First, a static model is described that relates internal stresses and strains and external displacements to the thermal pre-stress and applied voltage. Second, a dynamic energy based model is described that allows calculation of the resonance frequencies, developed force and electrical input impedance. Finally, a fully coupled electro-mechanical transducer model is described. The model development proceeds by assuming that both the thermal pre-stress and the piezoelectric actuation cause the actuator to deform in a pure bend in a single plane. It is useful to think of this as a two step process, the actuator is held flat, differential stresses induce a bending moment, the actuator is released and it bends. The thermal pre-stress is caused by the different amounts that the constituent layers shrink due to their different coefficients of thermal expansion. The adhesive between layers sets at a high temperature and as the actuator cools, the metal layers shrink more than the PZT. The PZT layer is put into compression while the metal layers are in tension. The piezoelectric actuation has a similar effect. An applied voltage causes the PZT layer to strain, which in turn strains the two metal layers. If the PZT layer expands it will put the metal layers into tension and PZT layer into compression. In both cases, if shear force effects are neglected, the actuator assembly will experience a uniform in-plane strain. As the materials each have a different elastic modulus, different stresses will develop in each layer and these stresses will induce a bending moment. When the actuator is released from its flat configuration, the differential stresses are relieved as the actuator bends.

Influence of bending mode on the mechanical properties of nickel-titanium archwires and correlation to differential scanning calorimetry measurements.

PubMed

Brauchli, Lorenz M; Keller, Heidi; Senn, Christiane; Wichelhaus, Andrea

2011-05-01

Nickel-titanium orthodontic archwires are used with bonded appliances for initial leveling. However, precise bending of these archwires is difficult and can lead to changes within the crystal structure of the alloy, thus changing the mechanical properties unpredictably. The aim of this study was to evaluate different bending methods in relation to the subsequent mechanical characteristics of the alloy. The mechanical behaviors of 3 archwires (Copper NiTi 35°C [Ormco, Glendora, Calif], Neo Sentalloy F 80 [GAC International, Bohemia, NY], and Titanol Low Force [Forestadent, Pforzheim, Germany]) were investigated after heat-treatment in a dental furnace at 550-650°C, treatment with an electrical current (Memory-Maker, Forestadent), and cold forming. In addition, the change in A(f) temperature was registered by means of differential scanning calorimetry. Heat-treatment in the dental furnace as well as with the Memory-Maker led to widely varying force levels for each product. Cold forming resulted in similar or slightly reduced force levels when compared to the original state of the wires. A(f) temperatures were in general inversely proportional to force levels. Archwire shape can be modified by using either chair-side technique (Memory-Maker, cold forming) because the superelastic behavior of the archwires is not strongly affected. However it is important to know the specific changes in force levels induced for each individual archwire with heat-treatment. Cold forming resulted in more predictable forces for all products tested. Therefore, cold forming is recommended as a chair-side technique for the shaping of NiTi archwires. Copyright © 2011 American Association of Orthodontists. Published by Mosby, Inc. All rights reserved.

Non-equilibrium fluctuations of a semi-flexible filament driven by active cross-linkers

NASA Astrophysics Data System (ADS)

Weber, I.; Appert-Rolland, C.; Schehr, G.; Santen, L.

2017-11-01

The cytoskeleton is an inhomogeneous network of semi-flexible filaments, which are involved in a wide variety of active biological processes. Although the cytoskeletal filaments can be very stiff and embedded in a dense and cross-linked network, it has been shown that, in cells, they typically exhibit significant bending on all length scales. In this work we propose a model of a semi-flexible filament deformed by different types of cross-linkers for which one can compute and investigate the bending spectrum. Our model allows to couple the evolution of the deformation of the semi-flexible polymer with the stochastic dynamics of linkers which exert transversal forces onto the filament. We observe a q-2 dependence of the bending spectrum for some biologically relevant parameters and in a certain range of wave numbers q, as observed in some experiments. However, generically, the spatially localized forcing and the non-thermal dynamics both introduce deviations from the thermal-like q-2 spectrum.

High flexibility of DNA on short length scales probed by atomic force microscopy.

PubMed

Wiggins, Paul A; van der Heijden, Thijn; Moreno-Herrero, Fernando; Spakowitz, Andrew; Phillips, Rob; Widom, Jonathan; Dekker, Cees; Nelson, Philip C

2006-11-01

The mechanics of DNA bending on intermediate length scales (5-100 nm) plays a key role in many cellular processes, and is also important in the fabrication of artificial DNA structures, but previous experimental studies of DNA mechanics have focused on longer length scales than these. We use high-resolution atomic force microscopy on individual DNA molecules to obtain a direct measurement of the bending energy function appropriate for scales down to 5 nm. Our measurements imply that the elastic energy of highly bent DNA conformations is lower than predicted by classical elasticity models such as the worm-like chain (WLC) model. For example, we found that on short length scales, spontaneous large-angle bends are many times more prevalent than predicted by the WLC model. We test our data and model with an interlocking set of consistency checks. Our analysis also shows how our model is compatible with previous experiments, which have sometimes been viewed as confirming the WLC.

Elastocapillarity: When Surface Tension Deforms Elastic Solids

NASA Astrophysics Data System (ADS)

Bico, José; Reyssat, Étienne; Roman, Benoît

2018-01-01

Although negligible at large scales, capillary forces may become dominant for submillimetric objects. Surface tension is usually associated with the spherical shape of small droplets and bubbles, wetting phenomena, imbibition, or the motion of insects at the surface of water. However, beyond liquid interfaces, capillary forces can also deform solid bodies in their bulk, as observed in recent experiments with very soft gels. Capillary interactions, which are responsible for the cohesion of sandcastles, can also bend slender structures and induce the bundling of arrays of fibers. Thin sheets can spontaneously wrap liquid droplets within the limit of the constraints dictated by differential geometry. This review aims to describe the different scaling parameters and characteristic lengths involved in elastocapillarity. We focus on three main configurations, each characterized by a specific dimension: three-dimensional (3D), deformations induced in bulk solids; 1D, bending and bundling of rod-like structures; and 2D, bending and stretching of thin sheets. Although each configuration deserves a detailed review, we hope our broad description provides a general view of elastocapillarity.

Investigation of the Self-Healing Behavior of Sn-Bi Metal Matrix Composite Reinforced with NiTi Shape Memory Alloy Strips Under Flexural Loading

NASA Astrophysics Data System (ADS)

Poormir, Mohammad Amin; Khalili, Seyed Mohammad Reza; Eslami-Farsani, Reza

2018-03-01

Utilizing intelligent materials such as shape memory alloys as reinforcement in metal matrix composites is a novel method to mimic self-healing behavior. In this study, the bending behavior of a self-healing metal matrix composite made from Sn-13 wt.% Bi alloy as matrix and NiTi shape memory alloy (SMA) strips as reinforcement is investigated. Specimens were fabricated in different reinforcement vol.% (0.78, 1.55, 2.33) and in various pre-strains (0, 2, 6%) and were healed at three healing temperatures (170°C, 180°C, 190°C). Results showed that shape recovery was accomplished in all the specimens, but not all of them were able to withstand second loading after healing. Only specimens with 2.33 vol.% of SMA strips, 1.55 vol.% of SMA, and 6% pre-strain could endure bending force after healing, and they gained 35.31-51.83% of bending force self-healing efficiency.

Investigation of the Self-Healing Behavior of Sn-Bi Metal Matrix Composite Reinforced with NiTi Shape Memory Alloy Strips Under Flexural Loading

NASA Astrophysics Data System (ADS)

Poormir, Mohammad Amin; Khalili, Seyed Mohammad Reza; Eslami-Farsani, Reza

2018-06-01

Utilizing intelligent materials such as shape memory alloys as reinforcement in metal matrix composites is a novel method to mimic self-healing behavior. In this study, the bending behavior of a self-healing metal matrix composite made from Sn-13 wt.% Bi alloy as matrix and NiTi shape memory alloy (SMA) strips as reinforcement is investigated. Specimens were fabricated in different reinforcement vol.% (0.78, 1.55, 2.33) and in various pre-strains (0, 2, 6%) and were healed at three healing temperatures (170°C, 180°C, 190°C). Results showed that shape recovery was accomplished in all the specimens, but not all of them were able to withstand second loading after healing. Only specimens with 2.33 vol.% of SMA strips, 1.55 vol.% of SMA, and 6% pre-strain could endure bending force after healing, and they gained 35.31-51.83% of bending force self-healing efficiency.

Stress-strain state of reinforced bimodulus beam on an elastic foundation

NASA Astrophysics Data System (ADS)

Beskopylny, A. N.; Kadomtseva, E. E.; Strelnikov, G. P.; Berdnik, Y. A.

2017-10-01

The paper provides the calculation theory of an arbitrary supported and arbitrary loaded reinforced beam filled with bimodulus material. The formulas determining normal stresses, bending moments, shear forces, rotation angles and a deflection of a rectangular crosssection beam reinforced with any number of bars aligned parallel to the beam axis have been obtained. The numerical study has been carried out to investigate an influence of a modulus of subgrade reaction on values of maximum normal stresses, maximum bending moments and a maximum deflection of a hinged supported beam loaded with a point force or uniform distributed load. The estimation is based on the method of initial parameters for a beam on elastic foundation and the Bubnov-Galerkin method. Values of maximum deflections, maximum bending moments and maximum stresses obtained by these methods coincide. The numerical studies show that taking into consideration the bimodulus of material leads to the necessity to calculate the strength analysis of both tensile stresses and compressive stresses.

Shielded transient self-interaction of a bunch entering a circle from a straight path

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, R.; Bohn, C.L.; Bisognano, J.J.

1997-08-01

Recent developments in electron-gun and injector technologies enable production of short (mm-length), high-charge (nC-regime) bunches. In this parameter regime, the curvature effect on the bunch self-interaction, by way of coherent synchrotron radiation (CSR) and space-charge forces as the beam traverses magnet bends, may cause serious emittance degradation. In this paper, the authors study an electron bunch orbiting between two infinite, parallel conducting plates. The bunch moves on a trajectory from a straight path to a circular orbit and begins radiating. Transient effects, arising from CSR and space-charge forces generated from source particles both on the bend and on the straightmore » path prior to the bend, are analyzed using Lienard-Wiechert fields, and their overall net effect is obtained. The influence of the plates on the transients is contrasted to their shielding of the steady-state radiated power. Results for emittance degradation induced by this self-interaction are also presented.« less

Repetitive lifting tasks fatigue the back muscles and increase the bending moment acting on the lumbar spine.

PubMed

Dolan, P; Adams, M A

1998-08-01

During manual handling, the back muscles protect the spine from excessive flexion, but in doing so impose a high compressive force on it. Epidemiological links between back pain and repetitive lifting suggest that fatigued muscles may adversely affect the balance between bending and compression. Fifteen volunteers lifted and lowered a 10 kg weight from floor to waist height 100 times. Throughout this task, the bending moment acting on the osteoligamentous lumbar spine was estimated from continuous measurements of lumbar flexion, obtained using the 3-Space Isotrak. Spinal compression was estimated from the electromyographic (EMG) activity of the erector spinae muscles, recorded from skin-surface electrodes at the levels of T10 and L3. EMG signals were calibrated against force when subjects pulled up on a load cell, and correction factors were applied to account for changes in muscle length and contraction velocity. Fatigue in the erector spinae muscles was quantified by comparing the frequency content of their EMG signal during static contractions performed before, and immediately after, the 100 lifts. Results showed that peak lumbar flexion increased during the 100 lifts from 83.3 +/- 14.8% to 90.4 +/- 14.3%, resulting in a 36% increase in estimated peak bending moment acting on the lumbar spine (P = 0.008). Peak spinal compression fell by 11% (p = 0.007). The median frequency of the EMG signal at L3 decreased by 5.5% following the 100 lifts (p = 0.042) confirming that the erector spinae were fatigued, but measures of fatigue showed no significant correlation with increased bending. We conclude that repetitive lifting induces measurable fatigue in the erector spinae muscles, and substantially increases the bending moment acting on the lumbar spine.

Load deflection characteristics and force level of nickel titanium initial archwires.

PubMed

Lombardo, Luca; Marafioti, Matteo; Stefanoni, Filippo; Mollica, Francesco; Siciliani, Giuseppe

2012-05-01

To investigate and compare the characteristics of commonly used types of traditional and heat-activated initial archwire by plotting their load/deflection graphs and quantifying three suitable parameters describing the discharge plateau phase. Forty-eight archwires (22 nickel titanium [NiTi] and 26 heat-activated) of cross-sectional diameter ranging from 0.010 to 0.016 inch were obtained from seven different manufacturers. A modified three-point wire-bending test was performed on three analogous samples of each type of archwire at a constant temperature (37.0°C). For each resulting load/deflection curve, the plateau section was isolated, along with the mean value of the average plateau force, the plateau length, and the plateau slope for each type of wire obtained. Statistically significant differences were found between almost all wires for the three parameters considered. Statistically significant differences were also found between traditional and heat-activated archwires, the latter of which generated longer plateaus and lighter average forces. The increase in average force seen with increasing diameter tended to be rather stable, although some differences were noted between traditional and heat-activated wires. Although great variation was seen in the plateau behavior, heat-activated versions appear to generate lighter forces over greater deflection plateaus. On average, the increase in plateau force was roughly 50% when the diameter was increased by 0.002 inch (from 0.012 to 0.014 and from 0.014 to 0.016 inch) and about 150% when the diameter was increased by 0.004 inch (from 0.012 to 0.016), with differences between traditional and heat-activated wires noted in this case.

Elimination of biofilm and microbial contamination reservoirs in hospital washbasin U-bends by automated cleaning and disinfection with electrochemically activated solutions.

PubMed

Swan, J S; Deasy, E C; Boyle, M A; Russell, R J; O'Donnell, M J; Coleman, D C

2016-10-01

Washbasin U-bends are reservoirs of microbial contamination in healthcare environments. U-Bends are constantly full of water and harbour microbial biofilm. To develop an effective automated cleaning and disinfection system for U-bends using two solutions generated by electrochemical activation of brine including the disinfectant anolyte (predominantly hypochlorous acid) and catholyte (predominantly sodium hydroxide) with detergent properties. Initially three washbasin U-bends were manually filled with catholyte followed by anolyte for 5min each once weekly for five weeks. A programmable system was then developed with one washbasin that automated this process. This U-bend had three cycles of 5min catholyte followed by 5min anolyte treatment per week for three months. Quantitative bacterial counts from treated and control U-bends were determined on blood agar (CBA), R2A, PAS, and PA agars following automated treatment and on CBA and R2A following manual treatment. The average bacterial density from untreated U-bends throughout the study was >1×10(5) cfu/swab on all media with Pseudomonas aeruginosa accounting for ∼50% of counts. Manual U-bend electrochemically activated (ECA) solution treatment reduced counts significantly (<100cfu/swab) (P<0.01 for CBA; P<0.005 for R2A). Similarly, counts from the automated ECA-treatment U-bend were significantly reduced with average counts for 35 cycles on CBA, R2A, PAS, and PA of 2.1±4.5 (P<0.0001), 13.1±30.1 (P<0.05), 0.7±2.8 (P<0.001), and 0 (P<0.05) cfu/swab, respectively. P. aeruginosa was eliminated from all treated U-bends. Automated ECA treatment of washbasin U-bends consistently minimizes microbial contamination. Copyright © 2016 The Authors. Published by Elsevier Ltd.. All rights reserved.

Defect Interactions in Anisotropic Two-Dimensional Fluids

NASA Astrophysics Data System (ADS)

Stannarius, R.; Harth, K.

2016-10-01

Disclinations in liquid crystals bear striking analogies to defect structures in a wide variety of physical systems, and their straightforward optical observability makes them excellent models to study fundamental properties of defect interactions. We employ freely suspended smectic-C films, which behave as quasi-two-dimensional polar nematics. A procedure to capture high-strength disclinations in localized spots is introduced. These disclinations are released in a controlled way, and the motion of the mutually repelling topological charges with strength +1 is studied quantitatively. We demonstrate that the classical models, which employ elastic one-constant approximation, fail to describe their dynamics correctly. In realistic liquid crystals, even small differences between splay and bend constants lead to the selection of pure splay or pure bend +1 defects. For those, the models work only in very special configurations. In general, additional director walls are involved which reinforce the repulsive interactions substantially.

Experimental Attempts for Deep Insertion in Ultrasonically Forced Insertion Process

NASA Astrophysics Data System (ADS)

Ono, Satoshi; Aoyagi, Manabu; Tamura, Hideki; Takano, Takehiro

2011-07-01

In this paper, we describe two attempts of obtaining deep insertion in an ultrasonically forced insertion (USFI) process. One was to correct the inclination of an inserted rod by passively generated bending vibrations. The inclination causes a partial plastic deformation, which decreases the holding power of processing materials. Two types of horn with grooves for excitation of bending vibrations were examined. The other was to make differences in vibration velocity and the phase of a rod and a metal plate by damping the vibration of a metal plate by using a rubber sheet. As results, the attempts proposed in this study were confirmed to be effective to obtain a deep insertion.

Flutter and oscillating air-force calculations for an airfoil in two-dimensional supersonic flow

NASA Technical Reports Server (NTRS)

Garrick, I E; Rubinow, S I

1946-01-01

A connected account is given of the Possio theory of non-stationary flow for small disturbances in a two-dimensional supersonic flow and of its application to the determination of the aerodynamic forces on an oscillating airfoil. Further application is made to the problem of wing flutter in the degrees of freedom - torsion, bending, and aileron rotations. Numerical tables for flutter calculations are provided for various values of the Mach number greater than unity. Results for bending-torsion wing flutter are shown in figures and are discussed. The static instabilities of divergence and aileron reversal are examined as is a one-degree-of-freedom case of torsional oscillatory instability.

Analysis of a Circular Composite Disk Subjected to Edge Rotations and Hydrostatic Pressure

NASA Technical Reports Server (NTRS)

Oliver, Stanley T.

2004-01-01

The structural analysis results for a graphite/epoxy quasi-isotropic circular plate subjected to a forced rotation at the boundary and pressure is presented. The analysis is to support a specialized material characterization test for composite cryogenic tanks. Finite element models were used to ensure panel integrity and determine the pressure necessary to achieve a predetermined equal biaxial strain value. The displacement results due to the forced rotation at the boundary led to a detailed study of the bending stiffness matrix [D]. The variation of the bending stiffness terms as a function of angular position is presented graphically, as well as, an illustrative technique of considering the laminate as an I-beam.

The mechanics of swallowing and the muscular control of diverse behaviours in gopher snakes.

PubMed

Moon, B R

2000-09-01

Snakes are excellent subjects for studying functional versatility and potential constraints because their movements are constrained to vertebral bending and twisting. In many snakes, swallowing is a kind of inside-out locomotion. During swallowing, vertebral bends push food from the jaws along a substantial length of the body to the stomach. In gopher snakes (Pituophis melanoleucus) and king snakes (Lampropeltis getula), swallowing often begins with lateral bending of the head and neck as the jaws advance unilaterally over the prey. Axial movement then shifts to accordion-like, concertina bending as the prey enters the oesophagus. Once the prey is completely engulfed, concertina bending shifts to undulatory bending that pushes the prey to the stomach. The shift from concertina to undulatory bending reflects a shift from pulling the prey into the throat (or advancing the mouth over the prey) to pushing it along the oesophagus towards the stomach. Undulatory kinematics and muscular activity patterns are similar in swallowing and undulatory locomotion. However, the distinct mechanical demands of internal versus external force exertion result in different duty factors of muscle activity. Feeding and locomotor movements are thus integral functions of the snake axial system.

Bending impact on the performance of a flexible Li4Ti5O12-based all-solid-state thin-film battery

PubMed Central

Vereecken, Philippe M.

2018-01-01

Abstract The growing demand of flexible electronic devices is increasing the requirements of their power sources. The effect of bending in thin-film batteries is still not well understood. Here, we successfully developed a high active area flexible all-solid-state battery as a model system that consists of thin-film layers of Li4Ti5O12, LiPON, and Lithium deposited on a novel flexible ceramic substrate. A systematic study on the bending state and performance of the battery is presented. The battery withstands bending radii of at least 14 mm achieving 70% of the theoretical capacity. Here, we reveal that convex bending has a positive effect on battery capacity showing an average increase of 5.5%, whereas concave bending decreases the capacity by 4% in contrast with recent studies. We show that the change in capacity upon bending may well be associated to the Li-ion diffusion kinetic change through the electrode when different external forces are applied. Finally, an encapsulation scheme is presented allowing sufficient bending of the device and operation for at least 500 cycles in air. The results are meant to improve the understanding of the phenomena present in thin-film batteries while undergoing bending rather than showing improvements in battery performance and lifetime. PMID:29868149

Flexural Vibration Test of a Cantilever Beam with a Force Sensor: Fast Determination of Young's Modulus

ERIC Educational Resources Information Center

Digilov, Rafael M.

2008-01-01

We describe a simple and very inexpensive undergraduate laboratory experiment for fast determination of Young's modulus at moderate temperatures with the aid of a force sensor. A strip-shaped specimen rigidly bolted to the force sensor forms a clamped-free cantilever beam. Placed in a furnace, it is subjected to free-bending vibrations followed by…

The effect of macro-bending on power confinement factor in single mode fibers

NASA Astrophysics Data System (ADS)

Waluyo, T. B.; Bayuwati, D.; Mulyanto, I.

2018-03-01

One of the methods to determine the macro-bending effect in a single mode fiber is by calculating its power loss coefficient. We describe an alternative method by using the equation of fractional power in the fiber core. Knowing the fiber parameters such as its core radius, refractive indexes, and operating wavelength; we can calculate the V-number and the fractional power in the core. Because the value of the fiber refractive indexes and the propagation constant are affected by bending, we can calculate the value of the fractional power in the core as a function of the bending radius. We calculate the fractional power in the core of an SMF28 and SM600 fiber and, to verify our calculation, we measure its transmission loss using an optical spectrum analyzer. Our calculations and experimental results showed that for SMF28 fiber, there is about 4% power loss due to bending at 633 nm, about 8% at 1310 nm, about 20% at 1550 nm, and about 60% at 1064 nm. For SM600 fiber, there is about 6% power loss due to bending at 633 nm, about 11% at 850 nm, and this fiber is not suitable for operating wavelength beyond 1000 nm.

Reducing the data: Analysis of the role of vascular geometry on blood flow patterns in curved vessels

NASA Astrophysics Data System (ADS)

Alastruey, Jordi; Siggers, Jennifer H.; Peiffer, Véronique; Doorly, Denis J.; Sherwin, Spencer J.

2012-03-01

Three-dimensional simulations of blood flow usually produce such large quantities of data that they are unlikely to be of clinical use unless methods are available to simplify our understanding of the flow dynamics. We present a new method to investigate the mechanisms by which vascular curvature and torsion affect blood flow, and we apply it to the steady-state flow in single bends, helices, double bends, and a rabbit thoracic aorta based on image data. By calculating forces and accelerations in an orthogonal coordinate system following the centreline of each vessel, we obtain the inertial forces (centrifugal, Coriolis, and torsional) explicitly, which directly depend on vascular curvature and torsion. We then analyse the individual roles of the inertial, pressure gradient, and viscous forces on the patterns of primary and secondary velocities, vortical structures, and wall stresses in each cross section. We also consider cross-sectional averages of the in-plane components of these forces, which can be thought of as reducing the dynamics of secondary flows onto the vessel centreline. At Reynolds numbers between 50 and 500, secondary motions in the directions of the local normals and binormals behave as two underdamped oscillators. These oscillate around the fully developed state and are coupled by torsional forces that break the symmetry of the flow. Secondary flows are driven by the centrifugal and torsional forces, and these are counterbalanced by the in-plane pressure gradients generated by the wall reaction. The viscous force primarily opposes the pressure gradient, rather than the inertial forces. In the axial direction, and depending on the secondary motion, the curvature-dependent Coriolis force can either enhance or oppose the bulk of the axial flow, and this shapes the velocity profile. For bends with little or no torsion, the Coriolis force tends to restore flow axisymmetry. The maximum circumferential and axial wall shear stresses along the centreline correlate well with the averaged in-plane pressure gradient and the radial displacement of the peak axial velocity, respectively. We conclude with a discussion of the physiological implications of these results.

Finite element method (FEM) analysis of the force systems produced by asymmetric inner headgear bows.

PubMed

Geramy, Allahyar; Kizilova, Natalya; Terekhov, Leonid

2011-11-01

Extra-oral traction appliances were introduced more than a century ago and continue to be used to produce orthopaedic and/or dental changes in the maxilla. While force systems produced by asymmetric outer bows have been studied extensively, the force systems produced by asymmetric inner bows have been overlooked. To analyse the forces acting on the maxillary first molars: when the size of one bayonet bend is increased; when the point of application of the distalising force on the inner bow is moved to one side; when one molar is displaced palatally. Four FEM models of cervical headgear attached to maxillary first molars were designed in SolidWorks 2010 and transferred to an ANSYS Workbench Ver. 12.1. Model 1, each molar was 23 mm from the midpalatal line and the inner bow was symmetrical; Model 2, the left molar was displaced 4 mm towards the midpalatal line and the inner bow was symmetrical; Model 3, the molars were equidistant (23 mm) from the midpalatal line, but the left molar was engaged by a 2 mm larger bayonet bend; Model 4, the molars were equidistant (23 mm) from the midpalatal line but the join between the inner and outer bows was displaced 2 mm towards the left molar. In all FEM models, a 2N force was applied to the inner bow at the join between inner and outer bows and the energy transmitted to the teeth and the von Mises stresses on the molar PDLs were assessed. There were marked differences in the strain energy on the teeth and the von Mises stresses on their PDLs. A 14 to 20 per cent increase in energy and force was produced on the tooth closer to the symmetric plane of the headgear. In addition, the increase in energy produced a 30 to 62 per cent increase in the von Mises stresses within the PDLs. Small asymmetries in molar position, the size of a bayonet bend and the point of application of a force on an inner bow resulted in asymmetrical forces on the molars. These forces were higher on the molar closer to the symmetric plane of the headgear.

Experimental evaluation of tailored chordwise deformable box beam and correlation with theory

NASA Technical Reports Server (NTRS)

Rehfield, Lawrence W.; Zischka, Peter J.; Chang, Stephen; Fentress, Michael L.; Ambur, Damodar R.

1993-01-01

This paper describes an experimental methodology based upon the use of a flexible sling support and load application system that has been created and utilized to evaluate a box beam which incorporates an elastic tailoring technology. The design technique used here for elastically tailoring the composite box beam structure is to produce exaggerated chordwise camber deformation of substantial magnitude to be of practical use in the new composite aircraft wings. The traditional methods such as a four-point bend test to apply constant bending moment with rigid fixtures inhibits the designed chordwise deformation from occurring and, hence, the need for the new test method. The experimental results for global camber and spanwise bending compliances correlate well with theoretical predictions based on a beam-like model.

Bending and shear stresses developed by the instantaneous arrest of the root of a cantilever beam rotating with constant angular velocity about a transverse axis through the root

NASA Technical Reports Server (NTRS)

Stowell, Elbridge Z; Schwartz, Edward B; Houbolt, John C

1945-01-01

A theoretical investigation was made of the behavior of a cantilever beam in rotational motion about a transverse axis through the root determining the stresses, the deflections, and the accelerations that occur in the beam as a result of the arrest of motion. The equations for bending and shear stress reveal that, at a given percentage of the distance from root to tip and at a given trip velocity, the bending stresses for a particular mode are independent of the length of the beam and the shear stresses vary inversely with the length. When examined with respect to a given angular velocity instead of a given tip velocity, the equations reveal that the bending stress is proportional to the length of the beam whereas the shear stress is independent of the length. Sufficient experimental verification of the theory has previously been given in connection with another problem of the same type.

Assessment of spinal flexibility in adolescent idiopathic scoliosis: suspension versus side-bending radiography.

PubMed

Lamarre, Marie-Eve; Parent, Stefan; Labelle, Hubert; Aubin, Carl-Eric; Joncas, Julie; Cabral, Anne; Petit, Yvan

2009-03-15

Prospective evaluation of a new suspension test to determine curve flexibility in adolescent idiopathic scoliosis (AIS) in comparison with erect side-bending. To verify whether the suspension is a better method than side-bending to estimate curve reducibility and to assess spine flexibility. Spinal flexibility is a decisive biomechanical parameter for the planning of AIS surgery. Side-bending is often referred as the gold standard, but it has a low reproducibility and there is no agreement amongst surgeons about the most advantageous method to use. Even more, every technique evaluates reducibility instead of flexibility since the forces involved in the change in shape of the spine are not considered. Eighteen patients scheduled for AIS surgery were studied. Preoperative radiological evaluation consisted of 4 radiographs: standing posteroanterior, left and right erect side-bending, and suspension. The side-bending and the suspension tests were compared on the basis of the apical vertebrae derotation and the scoliosis curve reduction. Frontal and axial flexibility indices, expressed as the ratio between the moment induced by the body weight and the reduction, were calculated from the suspension data. The average scoliosis curve reduction and apical vertebra derotation were 21 degrees (37%) and 3 degrees (12%), respectively for erect side-bending and 26 degrees (39%) and 7 degrees (28%), respectively for suspension. The erect side-bending test generated a larger curve reduction (P = 0.05) when considering the moderate curves only and the suspension test (P = 0.02) when considering the severe curves. The suspension test produced a larger axial derotation (P = 0.007) when considering all the curves. The average traction force during suspension was 306 N (187 N-377 N). The average estimation for the frontal flexibility index was 1.64 degrees/Nm (0.84-2.82) and 0.51 degrees/Nm (0.01-1.39) for the axial flexibility index. Results of this study demonstrate the feasibility to really evaluate the spine flexibility with the suspension test. The estimated flexibility values are realistic and similar to those reported in vitro. Suspension should be used in the future for spine flexibility assessment.

Silk-polypyrrole biocompatible actuator performance under biologically relevant conditions

NASA Astrophysics Data System (ADS)

Hagler, Jo'elen; Peterson, Ben; Murphy, Amanda; Leger, Janelle

Biocompatible actuators that are capable of controlled movement and can function under biologically relevant conditions are of significant interest in biomedical fields. Previously, we have demonstrated that a composite material of silk biopolymer and the conducting polymer polypyrrole (PPy) can be formed into a bilayer device that can bend under applied voltage. Further, these silk-PPy composites can generate forces comparable to human muscle (>0.1 MPa) making them ideal candidates for interfacing with biological tissues. Here silk-PPy composite films are tested for performance under biologically relevant conditions including exposure to a complex protein serum and biologically relevant temperatures. Free-end bending actuation performance, current response, force generation and, mass degradation were investigated . Preliminary results show that when exposed to proteins and biologically relevant temperatures, these silk-PPy composites show minimal degradation and are able to generate forces and conduct currents comparable to devices tested under standard conditions. NSF.

Long-wave dynamics of an elastic sheet lubricated by a thin liquid film on a wetting substrate

NASA Astrophysics Data System (ADS)

Young, Y.-N.; Stone, H. A.

2017-06-01

The dynamics of an elastic sheet lubricated by a thin liquid film on a wetting solid substrate is examined using both numerical simulations of a long-wave lubrication equation and a quasistatic model. Interactions between the liquid and the wetting substrate are modeled by a disjoining pressure that gives rise to an ultrathin (precursor) film. For a fluid interface without elastic bending stiffness, a flat precursor film may be linearly unstable and evolve towards an equilibrium of a single "drop" connected to a flat ultrathin film. Similar behavior is found when the thin film is covered by an elastic sheet: The sheet deforms, rearranging the thin liquid film, and contributes regulating surface forces such as a bending resistance and/or a tensile force, which may arise from interactions between the sheet and liquid or inextensibility of the sheet. Glasner's quasistatic model [Phys. Fluids 15, 1837 (2003), 10.1063/1.1578076], developed for a liquid film, is adopted to investigate the combined effects of elastic and tensile forces in the sheet on the thin film dynamics. The equilibrium height of the drop is found to vary inversely with the bending rigidity. When the elastic sheet is inextensible (such as a lipid bilayer membrane), a compressive tensile force may occur and the equilibrium film height is dependent less on the bending rigidity and more on the excess area of the membrane. Analyses of the lubrication equation also show that the precursor film transitions monotonically to the core film for tension-dominated dynamics. In contrast, for elasticity-dominated dynamics, a spatial oscillation of film height in the contact line region is found. In addition, elasticity in the sheet causes a sliding motion of the thin film: the contact angle is rendered zero by elasticity, and the contact line moves at a finite speed.

Mechanical Model of Dexterous Continuum Manipulators with Compliant Joints and Tendon/External Force Interactions

PubMed Central

Murphy, Ryan J.; Liu, Hao; Iordachita, Iulian I.; Armand, Mehran

2017-01-01

Dexterous continuum manipulators (DCMs) have been widely adopted for minimally- and less-invasive surgery. During the operation, these DCMs interact with surrounding anatomy actively or passively. The interaction force will inevitably affect the tip position and shape of DCMs, leading to potentially inaccurate control near critical anatomy. In this paper, we demonstrated a 2D mechanical model for a tendon actuated, notched DCM with compliant joints. The model predicted deformation of the DCM accurately in the presence of tendon force, friction force, and external force. A partition approach was proposed to describe the DCM as a series of interconnected rigid and flexible links. Beam mechanics, taking into consideration tendon interaction and external force on the tip and the body, was applied to obtain the deformation of each flexible link of the DCM. The model results were compared with experiments for free bending as well as bending in the presence of external forces acting at either the tip or body of the DCM. The overall mean error of tip position between model predictions and all of the experimental results was 0.62±0.41mm. The results suggest that the proposed model can effectively predict the shape of the DCM. PMID:28989273

49 CFR 192.161 - Supports and anchors.

Code of Federal Regulations, 2011 CFR

2011-10-01

...) Prevent undue strain on connected equipment; (2) Resist longitudinal forces caused by a bend or offset in the pipe; and (3) Prevent or damp out excessive vibration. (b) Each exposed pipeline must have enough supports or anchors to protect the exposed pipe joints from the maximum end force caused by internal...

49 CFR 192.161 - Supports and anchors.

Code of Federal Regulations, 2014 CFR

2014-10-01

...) Prevent undue strain on connected equipment; (2) Resist longitudinal forces caused by a bend or offset in the pipe; and (3) Prevent or damp out excessive vibration. (b) Each exposed pipeline must have enough supports or anchors to protect the exposed pipe joints from the maximum end force caused by internal...

49 CFR 192.161 - Supports and anchors.

Code of Federal Regulations, 2013 CFR

2013-10-01

...) Prevent undue strain on connected equipment; (2) Resist longitudinal forces caused by a bend or offset in the pipe; and (3) Prevent or damp out excessive vibration. (b) Each exposed pipeline must have enough supports or anchors to protect the exposed pipe joints from the maximum end force caused by internal...

49 CFR 192.161 - Supports and anchors.

Code of Federal Regulations, 2010 CFR

2010-10-01

...) Prevent undue strain on connected equipment; (2) Resist longitudinal forces caused by a bend or offset in the pipe; and (3) Prevent or damp out excessive vibration. (b) Each exposed pipeline must have enough supports or anchors to protect the exposed pipe joints from the maximum end force caused by internal...

49 CFR 192.161 - Supports and anchors.

Code of Federal Regulations, 2012 CFR

2012-10-01

...) Prevent undue strain on connected equipment; (2) Resist longitudinal forces caused by a bend or offset in the pipe; and (3) Prevent or damp out excessive vibration. (b) Each exposed pipeline must have enough supports or anchors to protect the exposed pipe joints from the maximum end force caused by internal...

Quantification of photoinduced bending of dynamic molecular crystals: from macroscopic strain to kinetic constants and activation energies.

PubMed

Chizhik, Stanislav; Sidelnikov, Anatoly; Zakharov, Boris; Naumov, Panče; Boldyreva, Elena

2018-02-28

Photomechanically reconfigurable elastic single crystals are the key elements for contactless, timely controllable and spatially resolved transduction of light into work from the nanoscale to the macroscale. The deformation in such single-crystal actuators is observed and usually attributed to anisotropy in their structure induced by the external stimulus. Yet, the actual intrinsic and external factors that affect the mechanical response remain poorly understood, and the lack of rigorous models stands as the main impediment towards benchmarking of these materials against each other and with much better developed soft actuators based on polymers, liquid crystals and elastomers. Here, experimental approaches for precise measurement of macroscopic strain in a single crystal bent by means of a solid-state transformation induced by light are developed and used to extract the related temperature-dependent kinetic parameters. The experimental results are compared against an overarching mathematical model based on the combined consideration of light transport, chemical transformation and elastic deformation that does not require fitting of any empirical information. It is demonstrated that for a thermally reversible photoreactive bending crystal, the kinetic constants of the forward (photochemical) reaction and the reverse (thermal) reaction, as well as their temperature dependence, can be extracted with high accuracy. The improved kinematic model of crystal bending takes into account the feedback effect, which is often neglected but becomes increasingly important at the late stages of the photochemical reaction in a single crystal. The results provide the most rigorous and exact mathematical description of photoinduced bending of a single crystal to date.

Effects of repetitive bending on the magnetoresistance of a flexible spin-valve

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kwon, J.-H.; Kwak, W.-Y.; Cho, B. K., E-mail: chobk@gist.ac.kr

2015-05-07

A positive magnetostrictive single layer (CoFe) and top-pinned spin-valve structure with positive magnetostrictive free (NiFe) and pinned (CoFe) layers were deposited on flexible polyethylene terephthalate film to investigate the changes in the magnetic properties in flexible environments, especially with a repetitive bending process. It was found that the stress, applied by repetitive bending, changes significantly the magnetic anisotropy of both layers in a single and spin-valve structure depending on the direction of applied stress. The changes in magnetic anisotropy were understood in terms of the inverse magnetostriction effect (the Villari effect) and the elastic recovery force from the flexibility ofmore » the polymer substrate. Repetitive bending with tensile stress transverse (or parallel) to the magnetic easy axis was found to enhance (or reduce) the magnetic anisotropy and, consequently, the magnetoresistance ratio of a spin-valve. The observed effects of bending stress in this study should be considered for the practical applications of electro-magnetic devices, especially magneto-striction sensor.« less

Can Thermal Bending Fracture Ice Shelves?

NASA Astrophysics Data System (ADS)

MacAyeal, D. R.; Sergienko, O. V.; Banwell, A. F.; Willis, I.; Macdonald, G. J.; Lin, J.

2017-12-01

Visco-elastic plates will bend if the temperature on one side is cooled. If the plate is constrained to float, as for sea ice floes, this bending will lead to tensile stresses that can fracture the ice. The hydroacoustic regime below sea ice displays increased fracture-sourced noise when air temperatures above the ice cools with the diurnal cycle. The McMurdo Ice Shelf, Antarctica, also displays a massive increase in seismicity during the cooling phase of the diurnal cycle, and this motivates the question: Can surface cooling (or other forcing with thermal consequences) drive through-thickness fracture leading to iceberg calving? Past study of this question for sea ice gives an upper limit of ice-plate thickness (order meters) for which diurnal-scale thermal bending fracture can occur; but could cooling with longer time scales induce fracture of thicker ice plates? Given the seismic evidence of thermal bending fracture on the McMurdo Ice Shelf, the authors examine this question further.

Shape Sensing Using a Multi-Core Optical Fiber Having an Arbitrary Initial Shape in the Presence of Extrinsic Forces

NASA Technical Reports Server (NTRS)

Rogge, Matthew D. (Inventor); Moore, Jason P. (Inventor)

2014-01-01

Shape of a multi-core optical fiber is determined by positioning the fiber in an arbitrary initial shape and measuring strain over the fiber's length using strain sensors. A three-coordinate p-vector is defined for each core as a function of the distance of the corresponding cores from a center point of the fiber and a bending angle of the cores. The method includes calculating, via a controller, an applied strain value of the fiber using the p-vector and the measured strain for each core, and calculating strain due to bending as a function of the measured and the applied strain values. Additionally, an apparent local curvature vector is defined for each core as a function of the calculated strain due to bending. Curvature and bend direction are calculated using the apparent local curvature vector, and fiber shape is determined via the controller using the calculated curvature and bend direction.

Estimation of blade airloads from rotor blade bending moments

NASA Technical Reports Server (NTRS)

Bousman, William G.

1987-01-01

A method is developed to estimate the blade normal airloads by using measured flap bending moments; that is, the rotor blade is used as a force balance. The blade's rotation is calculated in vacuum modes and the airloads are then expressed as an algebraic sum of the mode shapes, modal amplitudes, mass distribution, and frequency properties. The modal amplitudes are identified from the blade bending moments using the Strain Pattern Analysis Method. The application of the method is examined using simulated flap bending moment data that have been calculated for measured airloads for a full-scale rotor in a wind tunnel. The estimated airloads are compared with the wind tunnel measurements. The effects of the number of measurements, the number of modes, and errors in the measurements and the blade properties are examined, and the method is shown to be robust.

Effect of pH on the hinge region of influenza viral protein: a combined constant pH and well-tempered molecular dynamics study

NASA Astrophysics Data System (ADS)

Pathak, Arup Kumar

2018-05-01

Despite the knowledge that the influenza protein, hemagglutinin, undergoes a large conformational change at low pH during the process of fusion with the host cell, its molecular mechanism remains elusive. The present constant pH molecular dynamics (CpHMD) study identifies the residues responsible for large conformational change in acidic condition. Based on the pKa calculations, it is predicted that His-106 is much more responsible for the large conformational change than any other residues in the hinge region of hemagglutinin protein. Potential of mean force profile from well-tempered meta-dynamics (WT-MtD) simulation is also generated along the folding pathway by considering radius of gyration (R gyr) as a collective variable (CV). It is very clear from the present WT-MtD study, that the initial bending starts at that hinge region, which may trigger other conformational changes. Both the protein–protein and protein–water HB time correlation functions are monitored along the folding pathway. The protein–protein (full or hinge region) HB time correlation functions are always found to be stronger than those of the protein–water time correlation functions. The dynamical balance between protein–protein and protein–water HB interactions favors the stabilization of the folded state.

Cadmium Coating Alternatives for High- Strength Steel JTP - Phase 2

DTIC Science & Technology

2009-09-03

Substrate 4130 Washer 17 - 4PH Washer CuBe Washer AlNiBr Washer Salt Spray Cyclic Salt Spray Cyclic Salt Spray Cyclic Salt Spray Cyclic No coating...2009, Westminster, CO. Sponsored by SERDP/ESTCP. 14. ABSTRACT 15. SUBJECT TERMS 16. SECURITY CLASSIFICATION OF: 17 . LIMITATION OF ABSTRACT Same...Passed Appearance Testing U.S. AIR FORCE Primary Coating Bend Adhesion Test Results Coating Bend Adhesion Results 4130 steel substrate 17 -4 PH stainless

The dynamics of an experimental gravel bed meander with constant discharge and sediment supply

NASA Astrophysics Data System (ADS)

Braudrick, C. A.; Dietrich, W.; Sklar, L. S.

2012-12-01

As rivers meander, channel migration and cutoffs introduce continuous and episodic changes, respectively, in local boundary shear stress and bedload flux. These changes must affect the local and reach scale channel dynamics, but assessing their influence is limited by complications associated with varying discharge as well as challenging spatial and time scales. Here we explore the dynamics of a scaled-down gravel bed meandering river with constant discharge and sediment supply in a 6.1 m by 17 m long experimental flume at UC Berkeley's Richmond Field Station. The experiments are similar to Braudrick et al. (2009), but with constant rather than varying sediment supply. The flume was filled with a sorted sand with D50 of 0.85 mm, and had an initial 40 cm wide channel with a sinuosity of 1.1. Alfalfa sprouts provided bank and floodplain strength. The alfalfa was seeded by hand throughout the floodplain while a low flow provided irrigation during the 7-day alfalfa growth period. Sand (model gravel) and a lightweight plastic sediment (model sand) were fed independently from the upstream end of the flume at constant rates of 1.8 and 5 kg/hr, respectively. Despite the steady input conditions the experimental channel was quite dynamic as channel migration and bend morphology varied spatially and temporally. The sinuosity in the downstream 10 m of the flume (away from the inlet condition) increased from 1.1 to about 1.6 over the first 75 hours of the experiment, when 3 cutoffs in 29 hours decreased the sinuosity back to just over the initial value. Bank erosion was fastest when curvature was low at the beginning of the experiment and following cutoffs, and slowed once sinuosity increased. Once curvature increased the bends became asymmetric as bank erosion occurred almost exclusively at the bend apex. As the channel migrated, the local sinuosity increased, which decreasing the water surface slope and hence shear stress. The lower shear stress caused subsequent channel migration and also sediment transport to decrease. Consequently, the channel aggraded, forcing water onto the floodplain and further reducing the shear stress in the channel. While the channel was aggrading, most of the sediment flux out the bottom of the flume was the suspended model sand. Cutoffs occurred when the overbank flow was sufficient to alter floodplain strength either by eroding a path around alfalfa, or by limiting alfalfa growth in floodplain areas inundated during the low flow used to irrigate the alfalfa between the runs. Comparing the duration of these experiments to time in the field strongly depends on whether the timescale of interest is set by the flow or by sediment transport. Assuming a scaling factor between 0.01 and 0.02 and that flood flows occur approximately 8 days/year, this 120 hour experiments represent 4-6 years of field time using Froude similarity to scale time from the laboratory to the field, or 220-622 years assuming sediment transport similarity. This experiment showed decreased shear stress due to channel migration limited sediment transport, and that cutoffs were a function of both in-channel and floodplain processes.

Can extra-articular strains be used to measure facet contact forces in the lumbar spine? An in-vitro biomechanical study.

PubMed

Zhu, Q A; Park, Y B; Sjovold, S G; Niosi, C A; Wilson, D C; Cripton, P A; Oxland, T R

2008-02-01

Experimental measurement of the load-bearing patterns of the facet joints in the lumbar spine remains a challenge, thereby limiting the assessment of facet joint function under various surgical conditions and the validation of computational models. The extra-articular strain (EAS) technique, a non-invasive measurement of the contact load, has been used for unilateral facet joints but does not incorporate strain coupling, i.e. ipsilateral EASs due to forces on the contralateral facet joint. The objectives of the present study were to establish a bilateral model for facet contact force measurement using the EAS technique and to determine its effectiveness in measuring these facet joint contact forces during three-dimensional flexibility tests in the lumbar spine. Specific goals were to assess the accuracy and repeatability of the technique and to assess the effect of soft-tissue artefacts. In the accuracy and repeatability tests, ten uniaxial strain gauges were bonded to the external surface of the inferior facets of L3 of ten fresh lumbar spine specimens. Two pressure-sensitive sensors (Tekscan) were inserted into the joints after the capsules were cut. Facet contact forces were measured with the EAS and Tekscan techniques for each specimen in flexion, extension, axial rotation, and lateral bending under a +/- 7.5 N m pure moment. Four of the ten specimens were tested five times in axial rotation and extension for repeatability. These same specimens were disarticulated and known forces were applied across the facet joint using a manual probe (direct accuracy) and a materials-testing system (disarticulated accuracy). In soft-tissue artefact tests, a separate set of six lumbar spine specimens was used to document the virtual facet joint contact forces during a flexibility test following removal of the superior facet processes. Linear strain coupling was observed in all specimens. The average peak facet joint contact forces during flexibility testing was greatest in axial rotation (71 +/- 25 N), followed by extension (27 +/- 35 N) and lateral bending (25 +/- 28 N), and they were most repeatable in axial rotation (coefficient of variation, 5 per cent). The EAS accuracy was about 20 per cent in the direct accuracy assessment and about 30 per cent in the disarticulated accuracy test. The latter was very similar to the Tekscan accuracy in the same test. Virtual facet loads (r.m.s.) were small in axial rotation (12 N) and lateral bending (20 N), but relatively large in flexion (34 N) and extension (35 N). The results suggested that the bilateral EAS model could be used to determine the facet joint contact forces in axial rotation but may result in considerable error in flexion, extension, and lateral bending.

Statistical-Mechanical Studies of the Collective Binding of Proteins to DNA

NASA Astrophysics Data System (ADS)

Zhang, Houyin

My dissertation work focuses on the microscopic statistical-mechanical studies of DNA-protein interactions and mainly comprises of three projects. In living cells, binding of proteins to DNA controls gene expression and packaging of the genome. Single-DNA stretching and twisting experiments provide a powerful tool to detect binding of proteins, via detection of their modification of DNA mechanical properties. However, it is often difficult or impossible to determine the numbers of proteins bound in such experiments, especially when the proteins interact nonspecifically with DNA. In the first project, we developed single-molecule versions of classical thermodynamic Maxwell relations and proposed that these relations could be used to measure DNA-bound protein numbers, changes in DNA double-helix torque with force, and many other quantities which are hard to directly measure. This approach does not need any theoretical assumptions beyond the existence of thermodynamic equilibrium and has been used in single-DNA experiments. Many single-molecule experiments associated with DNA-bending proteins suggest the existence of cooperative interactions between adjacent DNA-bound proteins. In the second project, we studied a statistical-mechanical worm-like chain model including binding cooperativity effects and found that the intrinsic cooperativity of binding sharpens force-extension curves and causes enhancement of fluctuation of extension and protein occupation. This model also allows us to estimate the intrinsic cooperativity in experiments. We also analyzed force-generated cooperativity and found that the related interaction between proteins is always attractive. This suggests that tension in DNA in vivo could alter the distribution of proteins bound along DNA, causing chromosome refolding, or changes in gene expression. In the third project, we investigated the correlations along DNA-protein complexes. We found there are two different correlation lengths corrected to the geometry of DNA bending - the shorter “longitudinal” correlation length ξ∥(f, μ) and the longer “transverse” correlation length ξ⊥( f, μ). In the high-force limit, ξ∥(f, μ) = ξ⊥(f, μ)/2 = A/4bf . Surprisingly, the range of the interaction between DNA-bending proteins is controlled by the second-longest correlation length. The effect arises from the protein-bend contribution to the Hamiltonian having an axial rotational symmetry which eliminates its coupling to the transverse bending fluctuations.

Flexural Progressive Failure of Carbon/Glass Interlayer and Intralayer Hybrid Composites.

PubMed

Wang, Qingtao; Wu, Weili; Gong, Zhili; Li, Wei

2018-04-17

The flexural progressive failure modes of carbon fiber and glass fiber (C/G) interlayer and intralayer hybrid composites were investigated in this work. Results showed that the bending failure modes for interlayer hybrid composites are determined by the layup structure. Besides, the bending failure is characterized by the compression failure of the upper layer, when carbon fiber tends to distribute in the upper layer, the interlayer hybrid composite fails early, the failure force is characterized by a multi-stage slightly fluctuating decline and the fracture area exhibits a diamond shape. While carbon fiber distributes in the middle or bottom layer, the failure time starts late, and the failure process exhibits one stage sharp force/stress drop, the fracture zone of glass fiber above the carbon layers presents an inverted trapezoid shape, while the fracture of glass fiber below the carbon layers exhibits an inverted triangular shape. With regards to the intralayer hybrid composites, the C/G hybrid ratio plays a dominating role in the bending failure which could be considered as the mixed failures of four structures. The bending failure of intralayer hybrid composites occurs in advance since carbon fiber are located in each layer; the failure process shows a multi-stage fluctuating decline, and the decline slows down as carbon fiber content increases, and the fracture sound release has the characteristics of a low intensity and high frequency for a long time. By contrast, as glass fiber content increases, the bending failure of intralayer composites is featured with a multi-stage cliff decline with a high amplitude and low frequency for a short-time fracture sound release.

Study on bending behaviour of nickel–titanium rotary endodontic instruments by analytical and numerical analyses

PubMed Central

Tsao, C C; Liou, J U; Wen, P H; Peng, C C; Liu, T S

2013-01-01

Aim To develop analytical models and analyse the stress distribution and flexibility of nickel–titanium (NiTi) instruments subject to bending forces. Methodology The analytical method was used to analyse the behaviours of NiTi instruments under bending forces. Two NiTi instruments (RaCe and Mani NRT) with different cross-sections and geometries were considered. Analytical results were derived using Euler–Bernoulli nonlinear differential equations that took into account the screw pitch variation of these NiTi instruments. In addition, the nonlinear deformation analysis based on the analytical model and the finite element nonlinear analysis was carried out. Numerical results are obtained by carrying out a finite element method. Results According to analytical results, the maximum curvature of the instrument occurs near the instrument tip. Results of the finite element analysis revealed that the position of maximum von Mises stress was near the instrument tip. Therefore, the proposed analytical model can be used to predict the position of maximum curvature in the instrument where fracture may occur. Finally, results of analytical and numerical models were compatible. Conclusion The proposed analytical model was validated by numerical results in analysing bending deformation of NiTi instruments. The analytical model is useful in the design and analysis of instruments. The proposed theoretical model is effective in studying the flexibility of NiTi instruments. Compared with the finite element method, the analytical model can deal conveniently and effectively with the subject of bending behaviour of rotary NiTi endodontic instruments. PMID:23173762

Approximate analytical solutions in the analysis of thin elastic plates

NASA Astrophysics Data System (ADS)

Goloskokov, Dmitriy P.; Matrosov, Alexander V.

2018-05-01

Two approaches to the construction of approximate analytical solutions for bending of a rectangular thin plate are presented: the superposition method based on the method of initial functions (MIF) and the one built using the Green's function in the form of orthogonal series. Comparison of two approaches is carried out by analyzing a square plate clamped along its contour. Behavior of the moment and the shear force in the neighborhood of the corner points is discussed. It is shown that both solutions give identical results at all points of the plate except for the neighborhoods of the corner points. There are differences in the values of bending moments and generalized shearing forces in the neighborhoods of the corner points.

Magnetic force driven magnetoelectric effect in Mn-Zn-ferrite/PZT composites

NASA Astrophysics Data System (ADS)

Zhang, Ru; Jin, Lei; Wu, Gaojian; Zhang, Ning

2017-03-01

Several magnetoelectric devices with different structures were prepared using Mn-Zn-ferrite/PZT composite. Its magnetoelectric effect, which arose from piezoelectric effects driven by magnetic force between ferromagnets, has been studied. Experiments showed that the magnetoelectric effects in these devices are much stronger than that observed from the samples relied on magnetostrictive effect. Additionally, the magnetoelectric effect obtained from the devices based on bending piezoelectric effect at resonant point is about one order of magnitude larger than that resulted from ones that rely on stretch mode. Furthermore, magnetoelectric voltage coefficient as high as 7 V cm-1 Oe-1 with zero bias magnetic field was observed in the device with cantilever structure, which was also based on bending piezoelectric effect.

Biomechanical testing of isolated bones: holographic study

NASA Astrophysics Data System (ADS)

Silvennoinen, Raimo; Nygren, Kaarlo; Karna, Markku

1992-08-01

Holographic nondestructive testing (HNDT) is used to investigate the complex structures of bones of various shapes and sizes subjected to forces. Three antlered deer skulls of different species were investigated and significant species-specific differences were observed. The HNDT method was also used to verify the advanced healing of an osteosynthetized sheep jawbone. Radioulnar bones of a normal and an orphaned moose calf were subjected to a bending test. The undernourished calf showed torsio displacement combined with the bending of the bone, which was not seen in the normal calf. The effects of the masticatory forces on the moose skull surface were studied by simulating masseter muscle contractions with jawbones in occlusion. The fringe patterns showed fast-moving bone surfaces on the naso- maxillo-lacrimal region.

[Properties of NiTi wires with direct electric resistance heat treatment method in three-point bending tests].

PubMed

Wang, Hong-mei; Wang, Bang-kang; Ren, Chao-chao; Bai, Yu-xing

2011-03-01

To investigate the mechanical properties of Ni-Ti wires with direct electric resistance heat treatment (DERHT) method in three-point bending tests. Two superelastic Ni-Ti wires (wire A: Smart SE, wire B: SENTALLOY SE, 0.406 mm × 0.559 mm) and 2 heat-actived Ni-Ti wires (wire C: Smart SM, wire D: L&H TITAN, 0.406 mm × 0.559 mm) were selected. They were heat-treated using the DERHT method by a controlled electric current (6.36 A) applied for different period of time [0 (control), 1.0, 1.5, 2.0, 2.5 seconds). Then, a three-point bending test was performed under controlled temperature (37°C) to examine the relationships between the deflection and the load in the bending of wires. After DERHT treatment, the plateau in the force-deflection curve of superelastic Ni-Ti wires and heat-activated Ni-Ti wires were increased. When the wires were heated for 2.0 seconds and deflected to 1.5 mm, the loading force of A, B, C and D Ni-Ti wires increased from (3.85 ± 0.11), (3.62 ± 0.07), (3.28 ± 0.09), (2.91 ± 0.23) N to (4.33 ± 0.07), (4.07 ± 0.05), (4.52 ± 0.08), (3.27 ± 0.15) N respectively. DERHT method is very convenient for clinical use. It is possible to change the arch form and superelastic force of NiTi wires. The longer the heating time is, the more the superelastic characteristics of the wires are altered.

DNA G-segment bending is not the sole determinant of topology simplification by type II DNA topoisomerases.

PubMed

Thomson, Neil H; Santos, Sergio; Mitchenall, Lesley A; Stuchinskaya, Tanya; Taylor, James A; Maxwell, Anthony

2014-08-21

DNA topoisomerases control the topology of DNA. Type II topoisomerases exhibit topology simplification, whereby products of their reactions are simplified beyond that expected based on thermodynamic equilibrium. The molecular basis for this process is unknown, although DNA bending has been implicated. To investigate the role of bending in topology simplification, the DNA bend angles of four enzymes of different types (IIA and IIB) were measured using atomic force microscopy (AFM). The enzymes tested were Escherichia coli topo IV and yeast topo II (type IIA enzymes that exhibit topology simplification), and Methanosarcina mazei topo VI and Sulfolobus shibatae topo VI (type IIB enzymes, which do not). Bend angles were measured using the manual tangent method from topographical AFM images taken with a novel amplitude-modulated imaging mode: small amplitude small set-point (SASS), which optimises resolution for a given AFM tip size and minimises tip convolution with the sample. This gave improved accuracy and reliability and revealed that all 4 topoisomerases bend DNA by a similar amount: ~120° between the DNA entering and exiting the enzyme complex. These data indicate that DNA bending alone is insufficient to explain topology simplification and that the 'exit gate' may be an important determinant of this process.

DNA G-segment bending is not the sole determinant of topology simplification by type II DNA topoisomerases

NASA Astrophysics Data System (ADS)

Thomson, Neil H.; Santos, Sergio; Mitchenall, Lesley A.; Stuchinskaya, Tanya; Taylor, James A.; Maxwell, Anthony

2014-08-01

DNA topoisomerases control the topology of DNA. Type II topoisomerases exhibit topology simplification, whereby products of their reactions are simplified beyond that expected based on thermodynamic equilibrium. The molecular basis for this process is unknown, although DNA bending has been implicated. To investigate the role of bending in topology simplification, the DNA bend angles of four enzymes of different types (IIA and IIB) were measured using atomic force microscopy (AFM). The enzymes tested were Escherichia coli topo IV and yeast topo II (type IIA enzymes that exhibit topology simplification), and Methanosarcina mazei topo VI and Sulfolobus shibatae topo VI (type IIB enzymes, which do not). Bend angles were measured using the manual tangent method from topographical AFM images taken with a novel amplitude-modulated imaging mode: small amplitude small set-point (SASS), which optimises resolution for a given AFM tip size and minimises tip convolution with the sample. This gave improved accuracy and reliability and revealed that all 4 topoisomerases bend DNA by a similar amount: ~120° between the DNA entering and exiting the enzyme complex. These data indicate that DNA bending alone is insufficient to explain topology simplification and that the `exit gate' may be an important determinant of this process.

Spaceflight-Induced Bone Loss Alters Failure Mode and Reduces Bending Strength in Murine Spinal Segments

PubMed Central

Berg-Johansen, Britta; Liebenberg, Ellen C.; Li, Alfred; Macias, Brandon R.; Hargens, Alan R.; Lotz, Jeffrey C.

2017-01-01

Intervertebral disc herniation rates are quadrupled in astronauts following spaceflight. While bending motions are main contributors to herniation, the effects of microgravity on the bending properties of spinal discs are unknown. Consequently, the goal of this study was to quantify the bending properties of tail discs from mice with or without microgravity exposure. Caudal motion segments from six mice returned from a 30-day Bion M1 mission and eight vivarium controls were loaded to failure in four-point bending. After testing, specimens were processed using histology to determine the location of failure, and adjacent motion segments were scanned with micro-computed tomography (μCT) to quantify bone properties. We observed that spaceflight significantly shortened the nonlinear toe region of the force-displacement curve by 32% and reduced the bending strength by 17%. Flight mouse spinal segments tended to fail within the growth plate and epiphyseal bone, while controls tended to fail at the disc-vertebra junction. Spaceflight significantly reduced vertebral bone volume fraction, bone mineral density, and trabecular thickness, which may explain the tendency of flight specimens to fail within the epiphyseal bone. Together, these results indicate that vertebral bone loss during spaceflight may degrade spine bending properties and contribute to increased disc herniation risk in astronauts. PMID:26285046

A full-scale wind tunnel investigation of a helicopter bearingless main rotor. [Ames 40 by 80 Wind Tunnel

NASA Technical Reports Server (NTRS)

Warmbrodt, W.; Mccloud, J. L., II

1981-01-01

A helicopter bearingless main rotor was tested. Areas of investigation included aeroelastic stability, aerodynamic performance, and rotor loads as a function of collective pitch setting, RPM, airspeed and shaft angle. The rotor/support system was tested with the wind tunnel balance dampers installed and, subsequently, removed. Modifications to the rotor hub were tested. These included a reduction in the rotor control system stiffness and increased flexbeam structural damping. The primary objective of the test was to determine aeroelastic stability of the fundamental flexbeam/blade chordwise bending mode. The rotor was stable for all conditions. Damping of the rotor chordwise bending mode increases with increased collective pitch angle at constant operating conditions. No significant decrease in rotor damping occured due to frequency coalescence between the blade chordwise fundamental bending mode and the support system.

Elasticity Theory Solution of the Problem on Plane Bending of a Narrow Layered Cantilever Beam by Loads at Its Free End

NASA Astrophysics Data System (ADS)

Goryk, A. V.; Koval'chuk, S. B.

2018-05-01

An exact elasticity theory solution for the problem on plane bending of a narrow layered composite cantilever beam by tangential and normal loads distributed on its free end is presented. Components of the stress-strain state are found for the whole layers package by directly integrating differential equations of the plane elasticity theory problem by using an analytic representation of piecewise constant functions of the mechanical characteristics of layer materials. The continuous solution obtained is realized for a four-layer beam with account of kinematic boundary conditions simulating the rigid fixation of its one end. The solution obtained allows one to predict the strength and stiffness of composite cantilever beams and to construct applied analytical solutions for various problems on the elastic bending of layered beams.

Development of a bi-directional standing wave linear piezoelectric actuator with four driving feet.

PubMed

Liu, Yingxiang; Shi, Shengjun; Li, Chunhong; Chen, Weishan; Wang, Liang; Liu, Junkao

2018-03-01

A bi-directional standing wave linear piezoelectric ultrasonic actuator with four driving feet is proposed in this work. Two sandwich type transducers operated in longitudinal-bending hybrid modes are set parallelly. The working mode of the transducer is not simple hybrid vibrations of a longitudinal one and a bending one, but a special coupling vibration mode contained both longitudinal and bending components. Two transducers with the same structure and unsymmetrical boundary conditions are set parallelly to accomplish the bi-directional driving: the first transducer can push the runner forward, while the other one produces the backward driving. In the experiments, two voltages with different amplitudes are applied on the two transducers, respectively: the one with higher voltage serves as the actuator, whereas the other one applied with lower voltage is used to reduce the frictional force. The prototype achieves maximum no-load speed and thrust force of 244 mm/s and 9.8 N. This work gives a new idea for the construction of standing wave piezoelectric ultrasonic actuator with bi-directional driving ability. Copyright © 2017 Elsevier B.V. All rights reserved.

A test method for determining adhesion forces and Hamaker constants of cementitious materials using atomic force microscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lomboy, Gilson; Sundararajan, Sriram, E-mail: srirams@iastate.edu; Wang Kejin

2011-11-15

A method for determining Hamaker constant of cementitious materials is presented. The method involved sample preparation, measurement of adhesion force between the tested material and a silicon nitride probe using atomic force microscopy in dry air and in water, and calculating the Hamaker constant using appropriate contact mechanics models. The work of adhesion and Hamaker constant were computed from the pull-off forces using the Johnson-Kendall-Roberts and Derjagin-Muller-Toropov models. Reference materials with known Hamaker constants (mica, silica, calcite) and commercially available cementitious materials (Portland cement (PC), ground granulated blast furnace slag (GGBFS)) were studied. The Hamaker constants of the reference materialsmore » obtained are consistent with those published by previous researchers. The results indicate that PC has a higher Hamaker constant than GGBFS. The Hamaker constant of PC in water is close to the previously predicted value C{sub 3}S, which is attributed to short hydration time ({<=} 45 min) used in this study.« less

Synergistic effect of wire bending and salivary pH on surface properties and mechanical properties of orthodontic stainless steel archwires.

PubMed

Hobbelink, Marieke G; He, Yan; Xu, Jia; Xie, Huixu; Stoll, Richard; Ye, Qingsong

2015-01-01

The aim of this study was to investigate the corrosive behaviour of stainless steel archwires in a more clinically relevant way by bending and exposing to various pH. One hundred and twenty pieces of rectangular stainless steel wires (0.43 × 0.64 mm) were randomly assigned into four groups. In each group, there were 15 pieces of bent wires and 15 straight ones. Prior to measurements of the wires, as individual experimental groups (group 1, 2, and 3), the wires were exposed to artificial saliva for 4 weeks at pH 5.6, 6.6, and 7.6, respectively. A control group of wires (group 4) remained in air for the same period of time before sent for measurements. Surface roughness (Ra-value) was measured by a profilometer. Young's modulus and maximum force were determined by a four-point flexural test apparatus. Scanning electron microscopy was used to observe the surface morphology of straight wire. Differences between groups were examined using a two-way analysis of variance (ANOVA). Mean surface roughness values, flexural Young's moduli, and maximum force values of bent wires are significantly different from those of the straight wires, which was the main effect of wire bending, ignoring the influence of pH. A significant effect was found between Ra-values regarding the main effect of pH, ignoring the influence of shape. There was a significant interaction effect of bending and pH on flexural Young's moduli of stainless steel archwires, while pH did not show much impact on the maximum force values of those stainless steel wires. Bigger surface irregularities were seen on SEM images of straight wires immersed in artificial saliva at pH 5.6 compared to artificial saliva at other pH values. Surface depth (Rz) was more sensitive than Ra in revealing surface roughness, both measured from 3D reconstructed SEM images. Ra showed a comparable result of surface roughness to Ra-value measured by the profilometer. Bending has a significant influence on surface roughness and mechanical properties of rectangular SS archwires. pH plays a synergistic effect on the change of mechanical properties of stainless steel (SS) wires along with wire bending.

Effect of Dynamic Rolling Oscillations on Twin Tail Buffet Response

NASA Technical Reports Server (NTRS)

Sheta, Essam F.; Kandil, Osama A.

1999-01-01

The effect of dynamic rolling oscillations of delta-wing/twin-tail configuration on twin-tail buffet response is investigated. The computational model consists of a sharp-edged delta wing of aspect ratio one and swept-back flexible twin tail with taper ratio of 0.23. The configuration model is statically pitched at 30 deg. angle of attack and then forced to oscillate in roll around the symmetry axis at a constant amplitude of 4 deg. and reduced frequency of pi and 2(pi). The freestream Mach number and Reynolds number are 0.3 and 1.25 million, respectively. This multidisciplinary problem is solved using three sets of equations on a dynamic multi-block grid structure. The first set is the unsteady, full Navier-Stokes equations, the second set is the aeroelastic equations for coupled bending and torsion vibrations of the tails, and the third set is the grid-displacement equations. The configuration is investigated for inboard position of the twin tails which corresponds to a separation distance between the twin tails of 33% wing span. The computed results are compared with the results of stationary configuration, which previously have been validated using experimental data. The results conclusively showed that the rolling oscillations of the configuration have led to higher loads, higher deflections, and higher excitation peaks than those of the stationary configuration. Moreover, increasing the reduced frequency has led to higher loads and excitation peaks and lower bending and torsion deflections and acceleration.

The elastic properties of woven polymeric fabric

DOE Office of Scientific and Technical Information (OSTI.GOV)

Warren, W.E.

1989-01-01

The in-plane linear elastic constants of woven fabric are determined in terms of the specific fabric microstructure. The fabric is assumed to be a spatially periodic interlaced network of orthogonal yarns and the individual yarns are modeled as extensible elastica. These results indicate that a significant coupling of bending and stretching effects occurs during deformation. Results of this theoretical analysis compare favorable with measured in-plane elastic constants for Vincel yarn fabrics. 17 refs., 2 figs., 1 tab.

The relationship between fibre post geometry and flexural properties: an assessment through a modified three-point bending test.

PubMed

Soares, L P; de Vasconcellos, A B; da Silva, A H Monteiro da Fonseca Thomé; Sampaio, E M; Vianna, G A de Deus Carneiro

2010-12-01

The aim of this study was to investigate the flexural properties of five types of fiber-reinforced dowels using a modified three-point bending test. Fiber-reinforced resin dowels were tested by a modified three-point bending test associated with models for cylindrical and conical simple-supported beams. The fracture load ranged from 86 to 246 N and the flexural strength from 423 to 1192 MPa. FRC Postec had significantly higher flexural strength and fracture loads values. Thus, the present study demonstrated higher flexural strength values for the FRC Postec fibre posts, suggesting that this system would present a better response to the forces of mastication.

Comparative analysis of torsional and bending behavior through finite-element models of 5 Ni-Ti endodontic instruments.

PubMed

Arbab-Chirani, Reza; Chevalier, Valérie; Arbab-Chirani, Shabnam; Calloch, Sylvain

2011-01-01

The objectives of this study were to compare numerically the bending and torsional mechanical behavior of 5 endodontic rotary Ni-Ti instruments with equivalent size and various designs for tapers, pitch, and cutting blades.First, the geometries of Hero (20/0.06), HeroShaper (20/0.06), ProFile (20/0.06), Mtwo (20/0.06), and ProTaper F1 were generated by finite element code. Then, the 2 most representative clinical loadings, i.e., bending and torsion, were studied with an ad hoc model for the superelasticity of Ni-Ti. Bending was generated by tip deflection and torsion by a constant twist-angle of the tip. Mechanical behavior of these 5 endodontic rotary Ni-Ti instruments could be evaluated and compared. Protaper F1 presented the greatest level of bending stress and torque. Hero and HeroShaper were more rigid than ProFile and Mtwo. This numerical comparison evaluated the effects of the geometrical parameters on the instrumental mechanical behavior. The 5 endodontic instruments, investigated in the present study, do not have the same bending and torsional mechanical behavior. Each clinician must be aware of these behavior differences so as to use the adequate file according to the clinical situation and to the manufacturer's recommendations. Copyright © 2011 Mosby, Inc. All rights reserved.

Steady and Unsteady Loadings and Hydrodynamic Forces on Counterrotating Propellers.

DTIC Science & Technology

1976-07-01

forces and bending moments) of counterrotating propeller systems with equal and unequal number of blades operating in uniform and nonuniform inflow...1899 July 1976 STEADY AND UNSTEADY LOADIN GS AND HYDRODYNAM IC FORCES ON COUNTERROTATING PROPELLERS by S. Tsakonas, W. Jacobs and M. Afl This study...operator II , LINEARIZED UNSTEADY LIFTING SURFACE THEORY index of sunviiation Two counterrotating propellers are operatin g i n the flow of an ideal

A mechanical model of metatarsal stress fracture during distance running.

PubMed

Gross, T S; Bunch, R P

1989-01-01

A model of metatarsal mechanics has been proposed as a link between the high incidence of second and third metatarsal stress fractures and the large stresses measured beneath the second and third metatarsal heads during distance running. Eight discrete piezoelectric vertical stress transducers were used to record the forefoot stresses of 21 male distance runners. Based upon load bearing area estimates derived from footprints, plantar forces were estimated. Highest force was estimated beneath the second and first metatarsal head (341.1 N and 279.1 N, respectively). Considering the toe as a hinged cantilever and the metatarsal as a proximally attached rigid cantilever allowed estimation of metatarsal midshaft bending strain, shear, and axial forces. Bending strain was estimated to be greatest in the second metatarsal (6662 mu epsilon), a value 6.9 times greater than estimated first metatarsal strain. Predicted third, fourth, and fifth metatarsal strains ranged between 4832 and 5241 mu epsilon. Shear force estimates were also greatest in the second metatarsal (203.0 N). Axial forces were highest in the first metatarsal (593.2 N) due to large hallux forces in relationship to the remaining toes. Although a first order model, these data highlight the structural demands placed upon the second metatarsal, a location of high metatarsal stress fracture incidence during distance running.

Holographic nondestructive testing in bone biomechanics

NASA Astrophysics Data System (ADS)

Silvennoinen, Raimo V. J.; Nygren, Kaarlo; Karna, Markku

1992-08-01

Holographic nondestructive testing (HNDT) is used to investigate the complex structures of bones of various shapes and sizes subjected to forces. During the course of the present study three antlered deer skulls of different species were investigated, and significant species- specific differences were observed. The HNDT method was also used to verify the advanced healing of an osteosynthetized sheep jawbone. Radioulnar bones of normal and orphaned moose calves were subjected to the bending test. Different bending dynamics were observed.

A Quadruped Micro-Robot Based on Piezoelectric Driving

PubMed Central

Su, Qi; Quan, Qiquan; Deng, Jie; Yu, Hongpeng

2018-01-01

Inspired by a way of rowing, a new piezoelectric driving quadruped micro-robot operating in bending-bending hybrid vibration modes was proposed and tested in this work. The robot consisted of a steel base, four steel connecting pins and four similar driving legs, and all legs were bonded by four piezoelectric ceramic plates. The driving principle is discussed, which is based on the hybrid of first order vertical bending and first order horizontal bending vibrations. The bending-bending hybrid vibration modes motivated the driving foot to form an elliptical trajectory in space. The vibrations of four legs were used to provide the driving forces for robot motion. The proposed robot was fabricated and tested according to driving principle. The vibration characteristics and elliptical movements of the driving feet were simulated by FEM method. Experimental tests of vibration characteristics and mechanical output abilities were carried out. The tested resonance frequencies and vibration amplitudes agreed well with the FEM calculated results. The size of robot is 36 mm × 98 mm × 14 mm, its weight is only 49.8 g, but its maximum load capacity achieves 200 g. Furthermore, the robot can achieve a maximum speed of 33.45 mm/s. PMID:29518964

A Quadruped Micro-Robot Based on Piezoelectric Driving.

PubMed

Su, Qi; Quan, Qiquan; Deng, Jie; Yu, Hongpeng

2018-03-07

Inspired by a way of rowing, a new piezoelectric driving quadruped micro-robot operating in bending-bending hybrid vibration modes was proposed and tested in this work. The robot consisted of a steel base, four steel connecting pins and four similar driving legs, and all legs were bonded by four piezoelectric ceramic plates. The driving principle is discussed, which is based on the hybrid of first order vertical bending and first order horizontal bending vibrations. The bending-bending hybrid vibration modes motivated the driving foot to form an elliptical trajectory in space. The vibrations of four legs were used to provide the driving forces for robot motion. The proposed robot was fabricated and tested according to driving principle. The vibration characteristics and elliptical movements of the driving feet were simulated by FEM method. Experimental tests of vibration characteristics and mechanical output abilities were carried out. The tested resonance frequencies and vibration amplitudes agreed well with the FEM calculated results. The size of robot is 36 mm × 98 mm × 14 mm, its weight is only 49.8 g, but its maximum load capacity achieves 200 g. Furthermore, the robot can achieve a maximum speed of 33.45 mm/s.

Elastic and viscous properties of the nematic dimer CB7CB

NASA Astrophysics Data System (ADS)

Babakhanova, Greta; Parsouzi, Zeinab; Paladugu, Sathyanarayana; Wang, Hao; Nastishin, Yu. A.; Shiyanovskii, Sergij V.; Sprunt, Samuel; Lavrentovich, Oleg D.

2017-12-01

We present a comprehensive set of measurements of optical, dielectric, diamagnetic, elastic, and viscous properties in the nematic (N) phase formed by a liquid crystalline dimer. The studied dimer, 1,7-bis-4-(4'-cyanobiphenyl) heptane (CB7CB), is composed of two rigid rodlike cyanobiphenyl segments connected by a flexible aliphatic link with seven methyl groups. CB7CB and other nematic dimers are of interest due to their tendency to adopt bent configurations and to form two states possessing a modulated nematic director structure, namely, the twist-bend nematic, NTB, and the oblique helicoidal cholesteric, C hOH , which occurs when the achiral dimer is doped with a chiral additive and exposed to an external electric or magnetic field. We characterize the material parameters as functions of temperature in the entire temperature range of the N phase, including the pretransitional regions near the N -NTB and N-to-isotropic (I) transitions. The splay constant K11 is determined by two direct and independent techniques, namely, detection of the Frederiks transition and measurement of director fluctuation amplitudes by dynamic light scattering (DLS). The bend K33 and twist K22 constants are measured by DLS. K33, being the smallest of the three constants, shows a strong nonmonotonous temperature dependence with a negative slope in both N-I and N -NTB pretransitional regions. The measured ratio K11/K22 is larger than 2 in the entire nematic temperature range. The orientational viscosities associated with splay, twist, and bend fluctuations in the N phase are comparable to those of nematics formed by rodlike molecules. All three show strong temperature dependence, increasing sharply near the N -NTB transition.

Rotor Re-Design for the SSME Fuel Flowmeter

NASA Technical Reports Server (NTRS)

Marcu, Bogdan

1999-01-01

The present report describes the process of redesigning a new rotor for the SSME Fuel Flowmeter. The new design addresses the specific requirement of a lower rotor speed which would allow the SSME operation at 1 15% rated power level without reaching a blade excitation by the wakes behind the hexagonal flow straightener upstream at frequencies close to the blade natural frequency. A series of calculations combining fleet flowmeters test data, airfoil fluid dynamics and CFD simulations of flow patterns behind the flowmeter's hexagonal straightener has led to a blade twist design alpha = alpha (radius) targeting a kf constant of 0.8256. The kf constant relates the fuel volume flow to the flowmeter rotor speed, for this particular value 17685 GPM at 3650 RPM. Based on this angle distribution, two actual blade designs were developed. A first design using the same blade airfoil as the original design targeted the new kf value only. A second design using a variable blade chord length and airfoil relative thickness targeted simultaneously the new kf value and an optimum blade design destined to provide smooth and stable operation and a significant increase in the blade natural frequency associated with the first bending mode, such that a comfortable margin could be obtained at 115% RPL. The second design is a result of a concurrent engineering process, during which several iterations were made in order to achieve a targeted blade natural frequency associated with the first bending mode of 1300 Hz. Water flow tests preliminary results indicate a kf value of 0.8179 for the f-irst design, which is within 1% of the target value. The second design rotor shows a natural frequency associated with the first bending mode of 1308 Hz, and a water-flow calibration constant of kf 0.8169.

Lattice dynamical investigation of the Raman and infrared wave numbers and heat capacity properties of the pyrochlores R2Zr2O7 (R = La, Nd, Sm, Eu)

NASA Astrophysics Data System (ADS)

Nandi, S.; Jana, Y. M.; Gupta, H. C.

2018-04-01

A short-range electrostatic forcefield model has been applied for the first time to investigate the Raman and infrared wave numbers in pyrochlore zirconates R2Zr2O7 (R3+ = La, Nd, Sm, Eu). The calculations of phonons involve five stretching and four bending force constants in the Wilson GF matrix method. The calculated phonon wave numbers are in reasonable agreement with the observed spectra in infrared and Raman excitation zones for all of these isomorphous compounds. The contributions of force constants to each mode show a similar trend of variation for all of these compounds. Furthermore, to validate the established forcefield model, we calculated the standard thermodynamic functions, e.g., molar heat capacity, entropy and enthalpy, and compared the results with the previous experimental data for each compound. Using the derived wave numbers for the acoustic and optical modes, the total phonon contribution to the heat capacity was calculated for all these zirconate compounds. The Schottky heat capacity contributions were also calculated for the magnetic compounds, Nd2Zr2O7, Sm2Zr2O7 and Eu2Zr2O7, taking account of crystal-field level schemes of the lanthanide ions. The derived total heat capacity and the integrated values of molar entropy and molar enthalpy showed satisfactory correlations at low temperatures with the experimental results available in the literature for these compounds. At higher temperatures, the discrepancies may be caused by the anharmonic effects of vibrations, phonon dispersion, distribution of phonon density of states, etc.

Buckling behaviors of single-walled carbon nanotubes inserted with a linear carbon-atom chain.

PubMed

Zhu, Chunhua; Chen, Yinfeng; Liu, Rumeng; Zhao, Junhua

2018-08-17

Buckling behaviors of single-walled carbon nanotubes (SWCNTs) inserted with a linear carbon-atom chain (CAC) (the composite structures are also called carbon nanowires (CNWs)) under torsion and bending as well as compression are studied using molecular dynamics (MD) simulations, respectively. Our MD results show that the critical buckling angles (or strains) of CNWs under the three presented kinds of loading patterns can be two times those of corresponding independent SWCNTs for long CNWs, while the buckling improvement is not obvious for short ones. The main reason is that the radial van der Waals force between the CAC and the SWCNT is very small for a short CNW, while it increases with increasing length and then tends to a constant for a long CNW. The obtained MD results agree well with those from available theoretical models. These findings will be a great help towards understanding the stability and reliability of the special CNT structures, and designing flexible CNT-based devices.

Experimental and analytical determination of characteristics affecting light aircraft landing-gear dynamics

NASA Technical Reports Server (NTRS)

Fasanella, E. L.; Mcgehee, J. R.; Pappas, M. S.

1977-01-01

An experimental and analytical investigation was conducted to determine which characteristics of a light aircraft landing gear influence gear dynamic behavior significantly. The investigation focused particularly on possible modification for load control. Pseudostatic tests were conducted to determine the gear fore-and-aft spring constant, axial friction as a function of drag load, brake pressure-torque characteristics, and tire force-deflection characteristics. To study dynamic tire response, vertical drops were conducted at impact velocities of 1.2, 1.5, and 1.8 m/s onto a level surface; to determine axial-friction effects, a second series of vertical drops were made at 1.5 m/s onto surfaces inclined 5 deg and 10 deg to the horizontal. An average dynamic axial-friction coefficient of 0.15 was obtained by comparing analytical data with inclined surface drop test data. Dynamic strut bending and associated axial friction were found to be severe for the drop tests on the 10 deg surface.

Conformational space comparison of GnRH and lGnRH-III using molecular dynamics, cluster analysis and Monte Carlo thermodynamic integration.

PubMed

Watts, C R; Mezei, M; Murphy, R F; Lovas, S

2001-04-01

The conformational space available to GnRH and lGnRH-III was compared using 5.2 ns constant temperature and pressure molecular dynamics simulations with explicit TIP3P solvation and the AMBER v. 5.0 force field. Cluster analysis of both trajectories resulted in two groups of conformations. Results of free energy calculations, in agreement with previous experimental data, indicate that a conformation with a turn from residues 5 through 8 is preferred for GnRH in an aqueous environment. By contrast, a conformation with a helix from residues 2 through 7 with a bend from residues 6 through 10 is preferred for lGnRH-III in an aqueous environment. The side chains of His2 and Trp3 in lGnRH-III occupy different regions of phase space and participate in weakly polar interactions different from those in GnRH. The unique conformational properties of lGnRH-III may account for its specific anti cancer activity.

Functional and morphological correlates of mandibular symphyseal form in a living human sample.

PubMed

Holton, Nathan E; Franciscus, Robert G; Ravosa, Matthew J; Southard, Thomas E

2014-03-01

Variation in recent human mandibular form is often thought to reflect differences in masticatory behavior associated with variation in food preparation and subsistence strategies. Nevertheless, while mandibular variation in some human comparisons appear to reflect differences in functional loading, other comparisons indicate that this relationship is not universal. This suggests that morphological variation in the mandible is influenced by other factors that may obscure the effects of loading on mandibular form. It is likely that highly strained mandibular regions, including the corpus, are influenced by well-established patterns of lower facial skeletal integration. As such, it is unclear to what degree mandibular form reflects localized stresses incurred during mastication vs. a larger set of correlated features that may influence bone distribution patterns. In this study, we examine the relationship between mandibular symphyseal bone distribution (i.e., second moments of area, cortical bone area) and masticatory force production (i.e., in vivo maximal bite force magnitude and estimated symphyseal bending forces) along with lower facial shape variation in a sample of n = 20 living human male subjects. Our results indicate that while some aspects of symphyseal form (e.g., wishboning resistance) are significantly correlated with estimates of symphyseal bending force magnitude, others (i.e., vertical bending resistance) are more closely tied to variation in lower facial shape. This suggests that while the symphysis reflects variation in some variables related to functional loading, the complex and multifactorial influences on symphyseal form underscores the importance of exercising caution when inferring function from the mandible especially in narrow taxonomic comparisons. Copyright © 2013 Wiley Periodicals, Inc.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Di Lonardo, G.; Fusina, L., E-mail: luciano.fusina@unibo.it; Canè, E.

Infrared and Raman spectra of mono {sup 13}C fully deuterated acetylene, {sup 13}C{sup 12}CD{sub 2}, have been recorded and analysed to obtain detailed information on the C—D stretching fundamentals and associated combination, overtone, and hot bands. Infrared spectra were recorded at an instrumental resolution ranging between 0.006 and 0.01 cm{sup −1} in the region 1800–7800 cm{sup −1}. Sixty new bands involving the ν{sub 1} and ν{sub 3} C—D stretching modes also associated with the ν{sub 4} and ν{sub 5} bending vibrations have been observed and analysed. In total, 5881 transitions have been assigned in the investigated spectral region. In addition,more » the Q branch of the ν{sub 1} fundamental was recorded using inverse Raman spectroscopy, with an instrumental resolution of about 0.003 cm{sup −1}. The transitions relative to each stretching mode, i.e., the fundamental band, its first overtone, and associated hot and combination bands involving bending states with υ{sub 4} + υ{sub 5} up to 2 were fitted simultaneously. The usual Hamiltonian appropriate to a linear molecule, including vibration and rotation l-type and the Darling–Dennison interaction between υ{sub 4} = 2 and υ{sub 5} = 2 levels associated with the stretching states, was adopted for the analysis. The standard deviation for each global fit is ≤0.0004 cm{sup −1}, of the same order of magnitude of the measurement precision. Slightly improved parameters for the bending and the ν{sub 2} manifold have been also determined. Precise values of spectroscopic parameters deperturbed from the resonance interactions have been obtained. They provide quantitative information on the anharmonic character of the potential energy surface, which can be useful, in addition to those reported in the literature, for the determination of a general anharmonic force field for the molecule. Finally, the obtained values of the Darling–Dennison constants can be valuable for understanding energy flows between independent vibrations.« less

Phase Behavior of Binary Blends of AB+AC Block Copolymers with compatible B and C blocks

NASA Astrophysics Data System (ADS)

Pryamitsyn, Victor; Ganesan, Venkat

2012-02-01

Recently the experimental studies of phase behavior of binary blends of PS-b-P2VP and PS-b-PHS demonstrated an interesting effect: blends of symmetric PS-b-P2VP and shorter symmetric (PS-b-PHS) formed cylindrical HEX and spherical BCC phases, while each pure component formed lamellas. The miscibility of P2VP and PHS is caused by the hydrogen bonding between P2VP and PHS,which can be described as a negative Flory ?-parameter between P2VP and PHS. We developed a theory of the microphase segregation of AB+AC blends of diblock copolymers based on strong stretching theory. The main result of our theory is that in the copolymer brush-like layer formed by longer B chain and shorter C chains, the attraction between B and shorter C chains causes relative stretching of short C chains and compression of longer B chains. The latter manifests in an excessive bending force towards the grafting surface (BC|AA interface). Such bending force causes a transition from a symmetric lamella phase to a HEX cylinder or BCC spherical phases with the BC phase being a ``matrix'' component. In a blend of asymmetric BCC sphere forming copolymers (where B and C segments are the minor components), such bending force may unfold BCC spherical phase to a HEX cylinder phase, or even highly uneven lamella phases.

Humidity affects the performance of von Frey monofilaments.

PubMed

Werner, M U; Rotbøll-Nielsen, P; Ellehuus-Hilmersson, C

2011-05-01

Assessment of tactile and nociceptive thresholds of the skin with calibrated polyamide monofilaments is an established testing method both in animal and in human research. It is known that changes in relative humidity may affect the physical properties of the monofilaments. As this effect has only been studied in very small diameter monofilaments, used in neonatal research, we therefore studied complete sets of polyamide monofilaments. The effects were studied in a controlled climate chamber during six incremental changes in relative humidity from 20% to 79% (22-24°C). Following 24 h of equilibration at each humidity level, calibration with a precision scale was performed. A highly significant linear correlation between the natural logarithm (In) of the bending force and the von Frey number was observed at all humidity levels (r(2)>0.99, P<0.0001). An inverse linear relationship between relative humidity and In of the bending force for each monofilament was found (r(2)=0.95, P<0.0001). One percent increase in relative humidity corresponded to a 1-4% relative decrease in numerical bending force, depending on the diameter of the monofilament. A significant linear relationship was observed between the coefficient of variation and the relative humidity (r(2)=0.87, P<0.001). The data indicate that the hygroscopic properties of polyamide monofilaments must be taken into account for their reliable use in quantitative sensory testing.

Feeling stretched or compressed? The multiple mechanosensitive responses of wood formation to bending.

PubMed

Roignant, Jeanne; Badel, Éric; Leblanc-Fournier, Nathalie; Brunel-Michac, Nicole; Ruelle, Julien; Moulia, Bruno; Decourteix, Mélanie

2018-05-11

Trees constantly experience wind, perceive resulting mechanical cues, and modify their growth and development accordingly. Previous studies have demonstrated that multiple bending treatments trigger ovalization of the stem and the formation of flexure wood in gymnosperms, but ovalization and flexure wood have rarely been studied in angiosperms, and none of the experiments conducted so far has used multidirectional bending treatments at controlled intensities. Assuming that bending involves tensile and compressive strain, we hypothesized that different local strains may generate specific growth and wood differentiation responses. Basal parts of young poplar stems were subjected to multiple transient controlled unidirectional bending treatments during 8 weeks, which enabled a distinction to be made between the wood formed under tensile or compressive flexural strains. This set-up enabled a local analysis of poplar stem responses to multiple stem bending treatments at growth, anatomical, biochemical and molecular levels. In response to multiple unidirectional bending treatments, poplar stems developed significant cross-sectional ovalization. At the tissue level, some aspects of wood differentiation were similarly modulated in the compressed and stretched zones (vessel frequency and diameter of fibres without a G-layer), whereas other anatomical traits (vessel diameter, G-layer formation, diameter of fibres with a G-layer and microfibril angle) and the expression of fasciclin-encoding genes were differentially modulated in the two zones. This work leads us to propose new terminologies to distinguish the 'flexure wood' produced in response to multiple bidirectional bending treatments from wood produced under transient tensile strain (tensile flexure wood; TFW) or under transient compressive strain (compressive flexure wood; CFW). By highlighting similarities and differences between tension wood and TFW and by demonstrating that plants could have the ability to discriminate positive strains from negative strains, this work provides new insight into the mechanisms of mechanosensitivity in plants.

Flight Dynamics of Flexible Aircraft with Aeroelastic and Inertial Force Interactions

NASA Technical Reports Server (NTRS)

Nguyen, Nhan T.; Tuzcu, Ilhan

2009-01-01

This paper presents an integrated flight dynamic modeling method for flexible aircraft that captures coupled physics effects due to inertial forces, aeroelasticity, and propulsive forces that are normally present in flight. The present approach formulates the coupled flight dynamics using a structural dynamic modeling method that describes the elasticity of a flexible, twisted, swept wing using an equivalent beam-rod model. The structural dynamic model allows for three types of wing elastic motion: flapwise bending, chordwise bending, and torsion. Inertial force coupling with the wing elasticity is formulated to account for aircraft acceleration. The structural deflections create an effective aeroelastic angle of attack that affects the rigid-body motion of flexible aircraft. The aeroelastic effect contributes to aerodynamic damping forces that can influence aerodynamic stability. For wing-mounted engines, wing flexibility can cause the propulsive forces and moments to couple with the wing elastic motion. The integrated flight dynamics for a flexible aircraft are formulated by including generalized coordinate variables associated with the aeroelastic-propulsive forces and moments in the standard state-space form for six degree-of-freedom flight dynamics. A computational structural model for a generic transport aircraft has been created. The eigenvalue analysis is performed to compute aeroelastic frequencies and aerodynamic damping. The results will be used to construct an integrated flight dynamic model of a flexible generic transport aircraft.

Development and calibration of a compact self-sensing atomic force microscope head for micro-nano characterization

NASA Astrophysics Data System (ADS)

Guo, Tong; Wang, Siming; Zhao, Jian; Chen, Jinping; Fu, Xing; Hu, Xiaotang

2011-12-01

A compact self-sensing atomic force microscope (AFM) head is developed for the micro-nano dimensional measurement. This AFM head works in tapping mode equipped with a commercial self-sensing probe. This kind of probe can benefit not only from the tuning fork's stable resonant frequency and high quality factor but also from the silicon cantilever's reasonable spring constant. The head is convenient to operate by its simplicity of structure, since it does not need any optical detector to measure the bending of the cantilever. The compact structure makes the head ease to combine with other measuring methods. According to the probe"s characteristics, a method is proposed to quickly calculate the cantilever"s resonance amplitude through measuring its electro-mechanical coupling factor. An experiment system is established based on the nano-measuring machine (NMM) as a high precision positioning stage. Using this system, the approach/retract test is carried out for calibrating the head. The tests can be traced to the meter definition by interferometers in NMM. Experimental results show that the non-linearity error of this AFM head is smaller than 1%, the sensitivity reaches 0.47nm/mV and the measurement stroke is several hundreds of nanometers.

Elastic properties and mechanical stability of chiral and filled viral capsids

NASA Astrophysics Data System (ADS)

Buenemann, Mathias; Lenz, Peter

2008-11-01

The elasticity and mechanical stability of empty and filled viral capsids under external force loading are studied in a combined analytical and numerical approach. We analyze the influence of capsid structure and chirality on the mechanical properties. We find that generally skew shells have lower stretching energy. For large Föppl-von Kármán numbers γ (γ≈105) , skew structures are stiffer in their elastic response than nonchiral ones. The discrete structure of the capsules not only leads to buckling for large γ but also influences the breakage behavior of capsules below the buckling threshold: the rupture force shows a γ1/4 scaling rather than a γ1/2 scaling as expected from our analytical results for continuous shells. Filled viral capsids are exposed to internal anisotropic pressure distributions arising from regularly packaged DNA coils. We analyze their influence on the elastic properties and rupture behavior and we discuss possible experimental consequences. Finally, we numerically investigate specific sets of parameters corresponding to specific phages such as ϕ29 and cowpea chlorotic mottle virus (CCMV). From the experimentally measured spring constants we make predictions about specific material parameters (such as bending rigidity and Young’s modulus) for both empty and filled capsids.

Analysis of Carbon Nanotubes and Graphene Nanoribbons with Folded Racket Shapes

NASA Astrophysics Data System (ADS)

Borum, Andy; Plaut, Raymond; Dillard, David

2011-10-01

When carbon nanotubes and graphene nanoribbons become long, they may self-fold and form tennis racket-like shapes. This phenomenon is analyzed in two ways by treating a nanotube or nanoribbon as an elastica. First, an approach from adhesion science is used, in which the two sides of the racket handle are assumed to be straight and bonded together with constant or no separation. New analytical results are obtained involving the shape, bending energy, and adhesion energy of the self-folded structures. These relations show that the dimensions of the racket loop are proportional to the square root of the flexural rigidity. The second analysis uses the Lennard-Jones potential to model the van der Waals forces between the two sides of the racket. A nanoribbon is considered, and the interatomic forces are integrated along the length and across the width of the nanoribbon. The resulting integro-differential equations are solved using the finite difference method. The racket handle is found to be in compression and the separation between the two sides of the racket handle decreases in the direction of the racket loop. The results for the Lennard-Jones model approximately satisfy the relationship between the dimensions and the flexural rigidity found using the adhesion model.

Transverse vibrations of wood-based products : equations and considerations

Treesearch

Joseph F. Murphy

2011-01-01

Four equations are presented to determine bending stiffness using transverse vibration. These equations are used for constant cross-section products, panels, rectangular cross-section products, and logs with and without taper. Practical considerations for their use are discussed and concluding remarks are included.

Stiffness and frictional resistance of a superelastic nickel-titanium orthodontic wire with low-stress hysteresis.

PubMed

Liaw, Yu-Cheng; Su, Yu-Yu M; Lai, Yu-Lin; Lee, Shyh-Yuan

2007-05-01

Stress-induced martensite formation with stress hysteresis that changes the elasticity and stiffness of nickel-titanium (Ni-Ti) wire influences the sliding mechanics of archwire-guided tooth movement. This in-vitro study investigated the frictional behavior of an improved superelastic Ni-Ti wire with low-stress hysteresis. Improved superelastic Ni-Ti alloy wires (L & H Titan, Tomy International, Tokyo, Japan) with low-stress hysteresis were examined by using 3-point bending and frictional resistance tests with a universal test machine at a constant temperature of 35 degrees C, and compared with the former conventional austenitic-active superelastic Ni-Ti wires (Sentalloy, Tomy International). Wire stiffness levels were derived from differentiation of the polynomial regression of the unloading curves, and values for kinetic friction were measured at constant bending deflection distances of 0, 2, 3, and 4 mm, respectively. Compared with conventional Sentalloy wires, the L & H Titan wire had a narrower stress hysteresis including a lower loading plateau and a higher unloading plateau. In addition, L & H Titan wires were less stiff than the Sentalloy wires during most unloading stages. Values of friction measured at deflections of 0, 2, and 3 mm were significantly (P <.05) increased in both types of wire. However, they showed a significant decrease in friction from 3 to 4 mm of deflection. L & H Titan wires had less friction than Sentalloy wires at all bending deflections (P <.05). Stress-induced martensite formation significantly reduced the stiffness and thus could be beneficial to decrease the binding friction of superelastic Ni-Ti wires during sliding with large bending deflections. Austenitic-active alloy wires with low-stress hysteresis and lower stiffness and friction offer significant potential for further investigation.

Effect of accelerated global expansion on the bending of light

NASA Astrophysics Data System (ADS)

Aghili, Mir Emad; Bolen, Brett; Bombelli, Luca

2017-01-01

In 2007 Rindler and Ishak showed that, contrary to previous claims, the value of the cosmological constant does have an effect on light deflection by a gravitating object in an expanding universe. In their work they considered a Schwarzschild-de Sitter (SdS) spacetime, which has a constant asymptotic expansion rate H_0. A model with a time-dependent H( t) was studied by Kantowski et al., who consider in their 2010 paper a "Swiss-cheese" model of a Friedmann-Lemaître-Robertson-Walker (FLRW) spacetime with an embedded SdS bubble. In this paper, we generalize the Rindler and Ishak model to time-varying H( t) in another way, by considering light bending in a McVittie metric representing a gravitating object in a FLRW cosmological background. We carry out numerical simulations of the propagation of null geodesics in different McVittie spacetimes, in which we keep the values of the distances from the observer to the lensing object and to the source fixed, and vary the form of H( t).

Mean-flow measurements of the flow field diffusing bend

NASA Technical Reports Server (NTRS)

Mcmillan, O. J.

1982-01-01

Time-average measurements of the low-speed turbulent flow in a diffusing bend are presented. The experimental geometry consists of parallel top and bottom walls and curved diverging side walls. The turning of the center line of this channel is 40 deg, the area ratio is 1.5 and the ratios of height and center-line length to throat width are 1.5 and 3, respectively. The diffusing bend is preceded and followed by straight constant area sections. The inlet boundary layers on the parallel walls are artificially thickened and occupy about 30% of the channel height; those on the side walls develop naturally and are about half as thick. The free-stream speed at the inlet was approximately 30 m/sec for all the measurements. Inlet boundary layer mean velocity and turbulence intensity profiles are presented, as are data for wall static pressures, and at six cross sections, surveys of the velocity-vector and static-pressure fields. The dominant feature of the flow field is a pair of counter-rotating streamwise vortices formed by the cross-stream pressure gradient in the bend on which an overall deceleration is superimposed.

Standing Height as a Prevention Measure for Overuse Injuries of the Back in Alpine Ski Racing: A Kinematic and Kinetic Study of Giant Slalom

PubMed Central

Spörri, Jörg; Kröll, Josef; Fasel, Benedikt; Aminian, Kamiar; Müller, Erich

2018-01-01

Background: In alpine ski racing, typical loading patterns of the back include a combined occurrence of spinal bending, torsion, and high peak loads. These factors are known to be associated with high spinal disc loading and have been suggested to be attributable to different types of spine deterioration. However, little is known about the effect of standing height (ie, the distance between the bottom of the running surface of the ski and the ski boot sole) on the aforementioned back loading patterns. Purpose: To investigate the effect of reduced standing height on the skier’s overall trunk kinematics and the acting ground-reaction forces in giant slalom (GS) from an overuse injury prevention perspective. Study Design: Controlled laboratory study. Methods: Seven European Cup–level athletes skied a total of 224 GS turns with 2 different pairs of skis varying in standing height. Their overall trunk movement (frontal bending, lateral bending, and torsion angles) was measured based on 2 inertial measurement units located at the sacrum and sternum. Pressure insoles were used to determine the total ground-reaction force. Results: During the turn phase in which the greatest spinal disc loading is expected to occur, significantly lower total ground-reaction forces were observed for skis with a decreased standing height. Simultaneously, the skier’s overall trunk movement (ie, frontal bending, lateral bending, and torsion angles) remained unwaveringly high. Conclusion: Standing height is a reasonable measure to reduce the skier’s overall back loading in GS. Yet, when compared with the effects achievable by increased gate offsets in slalom, for instance, the preventative benefits of decreased standing height seem to be rather small. Clinical Relevance: To reduce the magnitude of overall back loading in GS and to prevent overuse injuries of the back, decreasing standing height might be an efficient approach. Nevertheless, the clinical relevance of the current findings, as well as the effectiveness of the measure “reduced standing height,” must be verified by epidemiological studies before its preventative potential can be judged as conclusive. PMID:29344540

Identifying Floppy and Rigid Regions in Proteins

NASA Astrophysics Data System (ADS)

Jacobs, D. J.; Thorpe, M. F.; Kuhn, L. A.

1998-03-01

In proteins it is possible to separate hard covalent forces involving bond lengths and bond angles from other weak forces. We model the microstructure of the protein as a generic bar-joint truss framework, where the hard covalent forces and strong hydrogen bonds are regarded as rigid bar constraints. We study the mechanical stability of proteins using FIRST (Floppy Inclusions and Rigid Substructure Topography) based on a recently developed combinatorial constraint counting algorithm (the 3D Pebble Game), which is a generalization of the 2D pebble game (D. J. Jacobs and M. F. Thorpe, ``Generic Rigidity: The Pebble Game'', Phys. Rev. Lett.) 75, 4051-4054 (1995) for the special class of bond-bending networks (D. J. Jacobs, "Generic Rigidity in Three Dimensional Bond-bending Networks", Preprint Aug (1997)). This approach is useful in identifying rigid motifs and flexible linkages in proteins, and thereby determines the essential degrees of freedom. We will show some preliminary results from the FIRST analysis on the myohemerythrin and lyozyme proteins.

New Insights on the Deflection and Internal Forces of a Bending Nanobeam

NASA Astrophysics Data System (ADS)

Zhao, De-Min; Liu, Jian-Lin

2017-08-01

Nanowires, nanofibers and nanotubes have been widely used as the building blocks in micro/nano-electromechanical systems, energy harvesting or storage devices, and small-scaled measurement equipment. We report that the surface effects of these nanobeams have a great impact on their deflection and internal forces. A simply supported nanobeam is taken as an example. For the displacement and shear force of the nanobeam, its dangerous sections are different from those predicted by the conventional beam theory, but for the bending moment, the dangerous section is the same. Moreover, the values of these three quantities for the nanobeam are all distinct from those calculated from the conventional beam model. These analyses shed new light on the stiffness and strength check of nanobeams, which are beneficial to engineer new-types of nano-materials and nano-devices. Supported by the National Natural Science Foundation of China under Grant Nos 11672334, 11672335 and 11611530541, and the Fundamental Research Funds for the Central Universities under Grant No 15CX08004A.

Dynamic bending of bionic flexible body driven by pneumatic artificial muscles(PAMs) for spinning gait of quadruped robot

NASA Astrophysics Data System (ADS)

Lei, Jingtao; Yu, Huangying; Wang, Tianmiao

2016-01-01

The body of quadruped robot is generally developed with the rigid structure. The mobility of quadruped robot depends on the mechanical properties of the body mechanism. It is difficult for quadruped robot with rigid structure to achieve better mobility walking or running in the unstructured environment. A kind of bionic flexible body mechanism for quadruped robot is proposed, which is composed of one bionic spine and four pneumatic artificial muscles(PAMs). This kind of body imitates the four-legged creatures' kinematical structure and physical properties, which has the characteristic of changeable stiffness, lightweight, flexible and better bionics. The kinematics of body bending is derived, and the coordinated movement between the flexible body and legs is analyzed. The relationship between the body bending angle and the PAM length is obtained. The dynamics of the body bending is derived by the floating coordinate method and Lagrangian method, and the driving force of PAM is determined. The experiment of body bending is conducted, and the dynamic bending characteristic of bionic flexible body is evaluated. Experimental results show that the bending angle of the bionic flexible body can reach 18°. An innovation body mechanism for quadruped robot is proposed, which has the characteristic of flexibility and achieve bending by changing gas pressure of PAMs. The coordinated movement of the body and legs can achieve spinning gait in order to improve the mobility of quadruped robot.

Flexural Progressive Failure of Carbon/Glass Interlayer and Intralayer Hybrid Composites

PubMed Central

Wu, Weili; Gong, Zhili

2018-01-01

The flexural progressive failure modes of carbon fiber and glass fiber (C/G) interlayer and intralayer hybrid composites were investigated in this work. Results showed that the bending failure modes for interlayer hybrid composites are determined by the layup structure. Besides, the bending failure is characterized by the compression failure of the upper layer, when carbon fiber tends to distribute in the upper layer, the interlayer hybrid composite fails early, the failure force is characterized by a multi-stage slightly fluctuating decline and the fracture area exhibits a diamond shape. While carbon fiber distributes in the middle or bottom layer, the failure time starts late, and the failure process exhibits one stage sharp force/stress drop, the fracture zone of glass fiber above the carbon layers presents an inverted trapezoid shape, while the fracture of glass fiber below the carbon layers exhibits an inverted triangular shape. With regards to the intralayer hybrid composites, the C/G hybrid ratio plays a dominating role in the bending failure which could be considered as the mixed failures of four structures. The bending failure of intralayer hybrid composites occurs in advance since carbon fiber are located in each layer; the failure process shows a multi-stage fluctuating decline, and the decline slows down as carbon fiber content increases, and the fracture sound release has the characteristics of a low intensity and high frequency for a long time. By contrast, as glass fiber content increases, the bending failure of intralayer composites is featured with a multi-stage cliff decline with a high amplitude and low frequency for a short-time fracture sound release. PMID:29673236

The Processing and Mechanical Properties of High Temperature/High Performance Composites. Book 5. Processing and Miscellaneous Properties

DTIC Science & Technology

1993-04-01

tensile fiber stress of 150-300 MPa, too little compared to measured fiber strengths of 3-4 GPa. A final possibility is that of nonuniform inelastic...flow of the matrix as a result of a spatially nonuniform distribution of porosity; this leads to a nonuniform distribution of forces along the fiber...the damage with the specific mechanism being fiber bending. The effects due to nonuniform inelastic flow (i.e., fiber bending) can be thought to occur

Strain Gage

NASA Technical Reports Server (NTRS)

1995-01-01

HITEC Corporation developed a strain gage application for DanteII, a mobile robot developed for NASA. The gage measured bending forces on the robot's legs and warned human controllers when acceptable forces were exceeded. HITEC further developed the technology for strain gage services in creating transducers out of "Indy" racing car suspension pushrods, NASCAR suspension components and components used in motion control.

Band-bending induced by charged defects and edges of atomically thin transition metal dichalcogenide films

NASA Astrophysics Data System (ADS)

Le Quang, T.; Nogajewski, K.; Potemski, M.; Dau, M. T.; Jamet, M.; Mallet, P.; Veuillen, J.-Y.

2018-07-01

We report scanning tunneling microscopy/spectroscopy (STM/STS) investigations of the band-bending in the vicinity of charged point defects and edges of monolayer MoSe2 and mono- and trilayer WSe2 films deposited on graphitized silicon carbide substrates. By tracing the spatial evolution of the structures of the STS spectra, we evaluate the magnitude and the extent of the band-bending to be equal to few hundreds milielectronvolts and several nanometres, respectively. With the aid of a simple electrostatic model, we show that the spatial variation of the Coulomb potential close to the film edges can be well reproduced by taking into account the metallic screening by graphene. Additionally, the analysis of our data for trilayer WSe2 provides reasonable estimations of its dielectric constant () and of the magnitude of the charge trapped at the defect site (Q  =  +e).

The surface crack problem in an orthotropic plate under bending and tension

NASA Technical Reports Server (NTRS)

Wu, Bing-Hua; Erdogan, F.

1987-01-01

The elasticity problem for an infinite orthotropic flat plate containing a series of through and part through cracks and subjected to bending and tension loads is considered. The problem is formulated by using Reissner's plate bending theory and considering three-dimensional material orthotropy. The Line-spring model developed by Rice and Levy is used to formulate the surface crack problem in which a total of nine material constants were used. The effects of material orthotropy on the stress intensity factors was determined, the interaction between two asymmetrically arranged collinear cracks was investigated, and extensive numerical results regarding the stress intensity factors are provided. The problem is reduced to a system of singular integral equations which is solved by using the Gauss-Chebyshev quadrature formulas. The calculated results show that the material orthotropy does have a significant effect on the stress intensity factor.

The surface crack problem in an orthotropic plate under bending and tension

NASA Technical Reports Server (NTRS)

Wu, B. H.; Erdogan, F.

1986-01-01

The elasticity problem for an infinite orthotropic flat plate containing a series of through and part-through cracks and subjected to bending and tension loads is considered. The problem is formulated by using Reissner's plate bending theory and considering three dimensional materials orthotropy. The Line-spring model developed by Rice and Levy is used to formulate the surface crack problem in which a total of nine material constants has been used. The main purpose of this study is to determine the effect of material orthotropy on the stress intensity factors, to investigate the interaction between two asymmetrically arranged collinear cracks, and to provide extensive numerical results regarding the stress intensity factors. The problem is reduced to a system of singular integral equations which is solved by using the Gauss-Chebyshev quadrature formulas. The calculated results show that the material orthotropy does have a significant effect on the stress intensity factor.

Patterns through elastic instabilities, from thin sheets to twisted ribbons

NASA Astrophysics Data System (ADS)

Damman, Pascal

Sheets embedded in a given shape by external forces store the exerted work in elastic deformations. For pure tensile forces, the work is stored as stretching energy. When the forces are compressive, several ways to store the exerted work, combining stretching and bending deformations can be explored. For large deflections, the ratio of bending, Eh3ζ2 /L4 and stretching, Ehζ4 /L4 energies, suggests that strain-free solutions should be favored for thin sheets, provided ζ2 >>h2 (where E , ζ , Land h are the elastic modulus, the deflection, a characteristic sheet size and its thickness). For uniaxially constrained sheets deriving from the Elastica, strain-free solutions are obvious, i.e., buckles, folds or wrinkles grow to absorb the stress of compression. In contrast, crumpled sheets exhibit ``origami-like'' solutions usually described as an assembly of flat polygonal facets delimitated by ridges focusing strains are observed. This type of solutions is particularly interesting since a faceted morphology is isometric to the undeformed sheet, except at those narrow ridges. In some cases however, the geometric constraints imposed by the external forces do not allow solutions with negligible strain in the deformed state. For instance, considering a circular sheet on a small drop, so thin that bending becomes negligible, i.e., Eh3 / γL2 << 1 . The capillary tension, γ at the edge forces the sheet to follow the spherical shape of the drop. Depending on the magnitude of the capillary tension with respect to the stretching modulus, such a sheet on a sphere can be in full tension or subjected to azimuthal compression. These spherical solutions could generate a hoop stress of compression within a small strip at the sheet's edge. The mechanical response of the sheet will generate tiny wrinkles decorating the edge to relax the compression stress while keeping its spherical shape. Finally, twisting a paper ribbon under high tension spontaneously produces helicoidal shapes that also reflect stretching and bending deformations. When the tension is progressively relieved, longitudinal and transverse compressive stresses build. To relax the longitudinal stress while keeping the helicoid shape, the ribbons produce wrinkles that ultimately becomes sharp folds similar to the ridge singularities observed in crumpled paper. The relaxation of the transverse compression stress produces cylindrical solutions. All these examples illustrates the natural tendency of an elastic sheet to stay as close as possible to the imposed shape, i.e. flat, spherical, helicoid. The mechanical response of the elastic sheet aims to relieve the compressive stress by growing a given micro-structure, i.e. wrinkles, singularities. In this talk, we will explore the general mechanisms at work, based on geometry and a competition between various energy terms, involving stretching and bending modes.

49 CFR 192.159 - Flexibility.

Code of Federal Regulations, 2011 CFR

2011-10-01

... causing excessive stresses in the pipe or components, excessive bending or unusual loads at joints, or undesirable forces or moments at points of connection to equipment, or at anchorage or guide points. ...

49 CFR 192.159 - Flexibility.

Code of Federal Regulations, 2013 CFR

2013-10-01

... causing excessive stresses in the pipe or components, excessive bending or unusual loads at joints, or undesirable forces or moments at points of connection to equipment, or at anchorage or guide points. ...

49 CFR 192.159 - Flexibility.

Code of Federal Regulations, 2012 CFR

2012-10-01

... causing excessive stresses in the pipe or components, excessive bending or unusual loads at joints, or undesirable forces or moments at points of connection to equipment, or at anchorage or guide points. ...

49 CFR 192.159 - Flexibility.

Code of Federal Regulations, 2014 CFR

2014-10-01

... causing excessive stresses in the pipe or components, excessive bending or unusual loads at joints, or undesirable forces or moments at points of connection to equipment, or at anchorage or guide points. ...

49 CFR 192.159 - Flexibility.

Code of Federal Regulations, 2010 CFR

2010-10-01

... causing excessive stresses in the pipe or components, excessive bending or unusual loads at joints, or undesirable forces or moments at points of connection to equipment, or at anchorage or guide points. ...

Frustration in protein elastic network models

NASA Astrophysics Data System (ADS)

Lezon, Timothy; Bahar, Ivet

2010-03-01

Elastic network models (ENMs) are widely used for studying the equilibrium dynamics of proteins. The most common approach in ENM analysis is to adopt a uniform force constant or a non-specific distance dependent function to represent the force constant strength. Here we discuss the influence of sequence and structure in determining the effective force constants between residues in ENMs. Using a novel method based on entropy maximization, we optimize the force constants such that they exactly reporduce a subset of experimentally determined pair covariances for a set of proteins. We analyze the optimized force constants in terms of amino acid types, distances, contact order and secondary structure, and we demonstrate that including frustrated interactions in the ENM is essential for accurately reproducing the global modes in the middle of the frequency spectrum.

Nuclear resonance vibrational spectroscopy applied to [Fe(OEP)(NO)]: the vibrational assignments of five-coordinate ferrous heme-nitrosyls and implications for electronic structure.

PubMed

Lehnert, Nicolai; Galinato, Mary Grace I; Paulat, Florian; Richter-Addo, George B; Sturhahn, Wolfgang; Xu, Nan; Zhao, Jiyong

2010-05-03

This study presents Nuclear Resonance Vibrational Spectroscopy (NRVS) data on the five-coordinate (5C) ferrous heme-nitrosyl complex [Fe(OEP)(NO)] (1, OEP(2-) = octaethylporphyrinato dianion) and the corresponding (15)N(18)O labeled complex. The obtained spectra identify two isotope sensitive features at 522 and 388 cm(-1), which shift to 508 and 381 cm(-1), respectively, upon isotope labeling. These features are assigned to the Fe-NO stretch nu(Fe-NO) and the in-plane Fe-N-O bending mode delta(ip)(Fe-N-O), the latter has been unambiguously assigned for the first time for 1. The obtained NRVS data were simulated using our quantum chemistry centered normal coordinate analysis (QCC-NCA). Since complex 1 can potentially exist in 12 different conformations involving the FeNO and peripheral ethyl orientations, extended density functional theory (DFT) calculations and QCC-NCA simulations were performed to determine how these conformations affect the NRVS properties of [Fe(OEP)NO]. These results show that the properties and force constants of the FeNO unit are hardly affected by the conformational changes involving the ethyl substituents. On the other hand, the NRVS-active porphyrin-based vibrations around 340-360, 300-320, and 250-270 cm(-1) are sensitive to the conformational changes. The spectroscopic changes observed in these regions are due to selective mechanical couplings of one component of E(u)-type (in ideal D(4h) symmetry) porphyrin-based vibrations with the in-plane Fe-N-O bending mode. This leads to the observed variations in Fe(OEP) core mode energies and NRVS intensities without affecting the properties of the FeNO unit. The QCC-NCA simulated NRVS spectra of 1 show excellent agreement with experiment, and indicate that conformer F is likely present in the samples of this complex investigated here. The observed porphyrin-based vibrations in the NRVS spectra of 1 are also assigned based on the QCC-NCA results. The obtained force constants of the Fe-NO and N-O bonds are 2.83-2.94 (based on the DFT functional applied) and about 12.15 mdyn/A, respectively. The electronic structures of 5C ferrous heme-nitrosyls in different model complexes are then analyzed, and variations in their properties based on different porphyrin substituents are explained. Finally, the shortcomings of different DFT functionals in describing the axial FeNO subunit in heme-nitrosyls are elucidated.

The Viscoelastic Properties of Nematic Monodomains Containing Liquid Crystal Polymers.

NASA Astrophysics Data System (ADS)

Gu, Dongfeng

The work presented here investigates the viscoelastic properties of nematic materials containing liquid crystal polymers (LCP). We focus on how the elastic constants and the viscosity coefficients of the mixture systems are influenced by polymer architectures. In dynamic light scattering studies of the relaxation of the director orientation fluctuations for the splay, twist, and bend deformation modes, decrease of the relaxation rates was observed when LCPs were dissolved into low molar mass nematics (LMMN). For the side-chain LCPs, the slowing down in the bend mode is comparable to or larger than those of the splay and twist modes. For main-chain LCPs, the relative changes in the relaxation rates for the twist and splay modes are about one order of magnitude larger than that for the bend mode. The results of light scattering under an electric field show that the decrease in the twist relaxation rate is due to a large increase in the twist viscosity and a minor decrease in the twist elastic constant. These changes were found to increase with decrease of the spacer length, with increase of molecular weight, and with decrease of the backbone flexibility. In Freedericksz transition measurements, the splay and bend elastic constants and the dielectric anisotropies of the nematic mixtures were determined and the values are 5~15% lower than those of the pure solvent. From the analysis of the results of Freedericksz transition and light scattering experiments, a complete set of the elastic constants and viscosity coefficients corresponding to the three director deformation modes were obtained for the LCP mixtures. The changes in the viscosity coefficients due to addition of LCPs were analysed to estimate the anisotropic shapes of the polymer backbone via a hydrodynamic model. The results suggest that an oblate backbone configuration is maintained by the side-chain LCPs and a prolate chain configuration appears for the main-chain LCPs. The rheological behavior of a side-chain and a main-chain LCP nematic solutions were investigated. The addition of the side-chain LCP into a flow-aligning LMMN (5CB) induces director tumbling in the mixture, and, the dissolution of the main-chain LCP into a director tumbling LMMN (8CB) makes the solution become a flow-aligning nematic. Based on the hydrodynamic theory, these observations are further confirmation of the chain anisotropies of the LCPs investigated. Ericksen's transversely isotropic fluid model was used to extract the various viscosity coefficients with good accuracy. In addition, we believe that this is the first time the bulk rheological consequences of director tumbling in LMMNs has been observed.

Bone strength in pure bending: bearing of geometric and material properties.

PubMed

Winter, Werner

2008-01-01

Osteoporosis is characterized by decreasing of bone mass and bone strength with advanced age. For characterization of material properties of dense and cellular bone the volumetric bone mineral density (vBMD) is one of the most important contributing factors to bone strength. Often bending tests of whole bone are used to get information about the state of osteoporosis. In a first step, different types of cellular structures are considered to characterize vBMD and its influence to elastic and plastic material properties. Afterwards, the classical theory of plastic bending is used to describe the non-linear moment-curvature relation of a whole bone. For bending of whole bone with sandwich structure an effective second moment of area can be defined. The shape factor as a pure geometrical value is considered to define bone strength. This factor is discussed for a bone with circular cross section and different thickness of cortical bone. The deduced relations and the decrease of material properties are used to demonstrate the influence of osteoporosis to bone bending strength. It can be shown that the elastic and plastic material properties of bone are related to a relative bone mineral density. Starting from an elastic-plastic bone behavior with an constant yield stress the non-linear moment-curvature relation in bending is related to yielding of the fibres in the cross section. The ultimate moment is characterized by a shape factor depending on the geometry of the cross section and on the change of cortical thickness.

FT-IR, FT-FIR and computerized Raman studies of the vibrational spectra and structure of ethylene complexes.

NASA Astrophysics Data System (ADS)

Mink, J.; Gal, M.; Goggin, P. L.; Spencer, J. L.

1986-03-01

Skeletal modes of [M(C 2H 4) 3] (where M=Ni(O) or Pt(O)), and [Pt(C 2H 4Cl 3][NBu 4] have been measured and assigned. A new model for the normal coordinate treament of π-complexes has been adopted to calculate metal—ligand force constants. The Pt-ehtylene stretching force constants were 1.66, and 2.54 Ncm -1, and the Pt-ehtylene tilting force constants were 2.04, and 2.84 Ncm -1 for [Pt(C 2H 4) 3], and [Pt(C 2H 4)Cl 3] -1 respectively. These force constants suggest that the π-bonding dominates for tris(ethylene)platinum but that σ- and π-bonding are of almost equal importance for the Zeise's salt analogue. The CC valence force constants of chemisorbed ehtylene suggest that C is rehybridised nearly to sp 3 on Ni(lll) and Pt(lll) surfaces but not on Pd(lll). The surface-ehtylene stretching force constants indicate that the bond strengths are in the order Pt>Ni>>Pd.

Elastic constants and dynamics in nematic liquid crystals

NASA Astrophysics Data System (ADS)

Humpert, Anja; Allen, Michael P.

2015-09-01

In this paper, we present molecular dynamics calculations of the Frank elastic constants, and associated time correlation functions, in nematic liquid crystals. We study two variants of the Gay-Berne potential, and use system sizes of half a million molecules, significantly larger than in previous studies of elastic behaviour. Equilibrium orientational fluctuations in reciprocal (k-) space were calculated, to determine the elastic constants by fitting at low |k|; our results indicate that small system size may be a source of inaccuracy in previous work. Furthermore, the dynamics of the Gay-Berne nematic were studied by calculating time correlation functions of components of the order tensor, together with associated components of the velocity field, for a set of wave vectors k. Confirming our earlier work, we found exponential decay for splay and twist correlations, and oscillatory exponential decay for the bend correlation. In this work, we confirm similar behaviour for the corresponding velocity components. In all cases, the decay rates, and oscillation frequencies, were found to be accurately proportional to k2 for small k, as predicted by the equations of nematodynamics. However, the observation of oscillatory bend fluctuations, and corresponding oscillatory shear flow decay, is in contradiction to the usual assumptions appearing in the literature, and in standard texts. We discuss the advantages and drawbacks of using large systems in these calculations.

Aeroelastic airfoil smart spar

NASA Technical Reports Server (NTRS)

Greenhalgh, Skott; Pastore, Christopher M.; Garfinkle, Moishe

1993-01-01

Aircraft wings and rotor-blades are subject to undesirable bending and twisting excursions that arise from unsteady aerodynamic forces during high speed flight, abrupt maneuvers, or hard landings. These bending excursions can range in amplitude from wing-tip flutter to failure. A continuous-filament construction 'smart' laminated composite box-beam spar is described which corrects itself when subject to undesirable bending excursions or flutter. The load-bearing spar is constructed so that any tendency for the wing or rotor-blade to bend from its normal position is met by opposite twisting of the spar to restore the wing to its normal position. Experimental and theoretical characterization of these spars was made to evaluate the torsion-flexure coupling associated with symmetric lay-ups. The materials used were uniweave AS-4 graphite and a matrix comprised of Shell 8132 resin and U-40 hardener. Experimental tests were conducted on five spars to determine spar twist and bend as a function of load for 0, 17, 30, 45 and 60 deg fiber angle lay-ups. Symmetric fiber lay-ups do exhibit torsion-flexure couplings. Predictions of the twist and bend versus load were made for different fiber orientations in laminated spars using a spline function structural analysis. The analytical results were compared with experimental results for validation. Excellent correlation between experimental and analytical values was found.

Anomalously large bend elastic constant and faster electro-optic response in anisotropic gels formed by a dipeptide

NASA Astrophysics Data System (ADS)

Bhargavi, R.; Nair, Geetha G.; Prasad, S. Krishna; Prabhu, Rashmi; Yelamaggad, C. V.

2011-04-01

We report rheological, static, and dynamic Freedericksz transformation measurements on an anisotropic thermoreversible gel formed by gelation of a nematic liquid crystal (NLC) with a monodisperse dipeptide. The storage and loss modulii obtained from a low strain oscillatory shear experiment display that the material forms a weak anisotropic gel, and undergoes a sharp thermal transition to an anisotropic sol state. Freedericksz transformation studies employing an electric field for the reorientation of the molecules present a surprising result: the gel possesses a very large Frank bend elastic constant value, which is orders of magnitude higher than that for the high temperature sol state as well as that for the neat NLC used. On the other hand, the splay elastic constant shows relatively a small increase. Further, these elastic constants show systematic but nonlinear variation with the concentration of the gelator. Attractive features of the electro-optic switching when the sol transforms to the gel state are the vanishing of the undesirable backflow effect, and nearly an order of magnitude decrease in the switching speed. In both the gel and sol states the extracted rotational viscosities are comparable to the values of the neat NLC at corresponding temperatures. In contrast, the bulk dynamic viscosity is more than three orders of magnitude higher in the gel. The studies also demonstrate that the anisotropic gel to anisotropic sol transition seen in this weak gel can be tracked by simply monitoring the static or the dynamic Freedericksz transformation.

Effects of trampling on morphological and mechanical traits of dryland shrub species do not depend on water availability.

PubMed

Xu, Liang; Freitas, Sofia M A; Yu, Fei-Hai; Dong, Ming; Anten, Niels P R; Werger, Marinus J A

2013-01-01

In semiarid drylands water shortage and trampling by large herbivores are two factors limiting plant growth and distribution. Trampling can strongly affect plant performance, but little is known about responses of morphological and mechanical traits of woody plants to trampling and their possible interaction with water availability. Seedlings of four shrubs (Caragana intermedia, Cynanchum komarovi, Hedysarum laeve and Hippophae rhamnoides) common in the semiarid Mu Us Sandland were grown at 4% and 10% soil water content and exposed to either simulated trampling or not. Growth, morphological and mechanical traits were measured. Trampling decreased vertical height and increased basal diameter and stem resistance to bending and rupture (as indicated by the increased minimum bend and break force) in all species. Increasing water availability increased biomass, stem length, basal diameter, leaf thickness and rigidity of stems in all species except C. komarovii. However, there were no interactive effects of trampling and water content on any of these traits among species except for minimum bend force and the ratio between stem resistance to rupture and bending. Overall shrub species have a high degree of trampling resistance by morphological and mechanical modifications, and the effects of trampling do not depend on water availability. However, the increasing water availability can also affect trade-off between stem strength and flexibility caused by trampling, which differs among species. Water plays an important role not only in growth but also in trampling adaptation in drylands.

Curvature-induced stiffening of a fish fin.

PubMed

Nguyen, Khoi; Yu, Ning; Bandi, Mahesh M; Venkadesan, Madhusudhan; Mandre, Shreyas

2017-05-01

How fish modulate their fin stiffness during locomotive manoeuvres remains unknown. We show that changing the fin's curvature modulates its stiffness. Modelling the fin as bendable bony rays held together by a membrane, we deduce that fin curvature is manifested as a misalignment of the principal bending axes between neighbouring rays. An external force causes neighbouring rays to bend and splay apart, and thus stretches the membrane. This coupling between bending the rays and stretching the membrane underlies the increase in stiffness. Using three-dimensional reconstruction of a mackerel ( Scomber japonicus ) pectoral fin for illustration, we calculate the range of stiffnesses this fin is expected to span by changing curvature. The three-dimensional reconstruction shows that, even in its geometrically flat state, a functional curvature is embedded within the fin microstructure owing to the morphology of individual rays. As the ability of a propulsive surface to transmit force to the surrounding fluid is limited by its stiffness, the fin curvature controls the coupling between the fish and its surrounding fluid. Thereby, our results provide mechanical underpinnings and morphological predictions for the hypothesis that the spanned range of fin stiffnesses correlates with the behaviour and the ecological niche of the fish. © 2017 The Author(s).

A unified approach for determining the ultimate strength of RC members subjected to combined axial force, bending, shear and torsion

PubMed Central

Huang, Zhen

2017-01-01

This paper uses experimental investigation and theoretical derivation to study the unified failure mechanism and ultimate capacity model of reinforced concrete (RC) members under combined axial, bending, shear and torsion loading. Fifteen RC members are tested under different combinations of compressive axial force, bending, shear and torsion using experimental equipment designed by the authors. The failure mechanism and ultimate strength data for the four groups of tested RC members under different combined loading conditions are investigated and discussed in detail. The experimental research seeks to determine how the ultimate strength of RC members changes with changing combined loads. According to the experimental research, a unified theoretical model is established by determining the shape of the warped failure surface, assuming an appropriate stress distribution on the failure surface, and considering the equilibrium conditions. This unified failure model can be reasonably and systematically changed into well-known failure theories of concrete members under single or combined loading. The unified calculation model could be easily used in design applications with some assumptions and simplifications. Finally, the accuracy of this theoretical unified model is verified by comparisons with experimental results. PMID:28414777

Molecular Mechanics of the α-Actinin Rod Domain: Bending, Torsional, and Extensional Behavior

PubMed Central

Golji, Javad; Collins, Robert; Mofrad, Mohammad R. K.

2009-01-01

α-Actinin is an actin crosslinking molecule that can serve as a scaffold and maintain dynamic actin filament networks. As a crosslinker in the stressed cytoskeleton, α-actinin can retain conformation, function, and strength. α-Actinin has an actin binding domain and a calmodulin homology domain separated by a long rod domain. Using molecular dynamics and normal mode analysis, we suggest that the α-actinin rod domain has flexible terminal regions which can twist and extend under mechanical stress, yet has a highly rigid interior region stabilized by aromatic packing within each spectrin repeat, by electrostatic interactions between the spectrin repeats, and by strong salt bridges between its two anti-parallel monomers. By exploring the natural vibrations of the α-actinin rod domain and by conducting bending molecular dynamics simulations we also predict that bending of the rod domain is possible with minimal force. We introduce computational methods for analyzing the torsional strain of molecules using rotating constraints. Molecular dynamics extension of the α-actinin rod is also performed, demonstrating transduction of the unfolding forces across salt bridges to the associated monomer of the α-actinin rod domain. PMID:19436721

Controlling placement of nonspherical (boomerang) colloids in nematic cells with photopatterned director

NASA Astrophysics Data System (ADS)

Peng, Chenhui; Turiv, Taras; Zhang, Rui; Guo, Yubing; Shiyanovskii, Sergij V.; Wei, Qi-Huo; de Pablo, Juan; Lavrentovich, Oleg D.

2017-01-01

Placing colloidal particles in predesigned sites represents a major challenge of the current state-of-the-art colloidal science. Nematic liquid crystals with spatially varying director patterns represent a promising approach to achieve a well-controlled placement of colloidal particles thanks to the elastic forces between the particles and the surrounding landscape of molecular orientation. Here we demonstrate how the spatially varying director field can be used to control placement of non-spherical particles of boomerang shape. The boomerang colloids create director distortions of a dipolar symmetry. When a boomerang particle is placed in a periodic splay-bend director pattern, it migrates towards the region of a maximum bend. The behavior is contrasted to that one of spherical particles with normal surface anchoring, which also produce dipolar director distortions, but prefer to compartmentalize into the regions with a maximum splay. The splay-bend periodic landscape thus allows one to spatially separate these two types of particles. By exploring overdamped dynamics of the colloids, we determine elastic driving forces responsible for the preferential placement. Control of colloidal locations through patterned molecular orientation can be explored for future applications in microfluidic, lab on a chip, sensing and sorting devices.

Controlling placement of nonspherical (boomerang) colloids in nematic cells with photopatterned director.

PubMed

Peng, Chenhui; Turiv, Taras; Zhang, Rui; Guo, Yubing; Shiyanovskii, Sergij V; Wei, Qi-Huo; de Pablo, Juan; Lavrentovich, Oleg D

2017-01-11

Placing colloidal particles in predesigned sites represents a major challenge of the current state-of-the-art colloidal science. Nematic liquid crystals with spatially varying director patterns represent a promising approach to achieve a well-controlled placement of colloidal particles thanks to the elastic forces between the particles and the surrounding landscape of molecular orientation. Here we demonstrate how the spatially varying director field can be used to control placement of non-spherical particles of boomerang shape. The boomerang colloids create director distortions of a dipolar symmetry. When a boomerang particle is placed in a periodic splay-bend director pattern, it migrates towards the region of a maximum bend. The behavior is contrasted to that one of spherical particles with normal surface anchoring, which also produce dipolar director distortions, but prefer to compartmentalize into the regions with a maximum splay. The splay-bend periodic landscape thus allows one to spatially separate these two types of particles. By exploring overdamped dynamics of the colloids, we determine elastic driving forces responsible for the preferential placement. Control of colloidal locations through patterned molecular orientation can be explored for future applications in microfluidic, lab on a chip, sensing and sorting devices.

Curvature-induced stiffening of a fish fin

PubMed Central

2017-01-01

How fish modulate their fin stiffness during locomotive manoeuvres remains unknown. We show that changing the fin's curvature modulates its stiffness. Modelling the fin as bendable bony rays held together by a membrane, we deduce that fin curvature is manifested as a misalignment of the principal bending axes between neighbouring rays. An external force causes neighbouring rays to bend and splay apart, and thus stretches the membrane. This coupling between bending the rays and stretching the membrane underlies the increase in stiffness. Using three-dimensional reconstruction of a mackerel (Scomber japonicus) pectoral fin for illustration, we calculate the range of stiffnesses this fin is expected to span by changing curvature. The three-dimensional reconstruction shows that, even in its geometrically flat state, a functional curvature is embedded within the fin microstructure owing to the morphology of individual rays. As the ability of a propulsive surface to transmit force to the surrounding fluid is limited by its stiffness, the fin curvature controls the coupling between the fish and its surrounding fluid. Thereby, our results provide mechanical underpinnings and morphological predictions for the hypothesis that the spanned range of fin stiffnesses correlates with the behaviour and the ecological niche of the fish. PMID:28566508

Tailoring force sensitivity and selectivity by microstructure engineering of multidirectional electronic skins

NASA Astrophysics Data System (ADS)

Park, Jonghwa; Kim, Jinyoung; Hong, Jaehyung; Lee, Hochan; Lee, Youngoh; Cho, Seungse; Kim, Sung-Woo; Kim, Jae Joon; Kim, Sung Youb; Ko, Hyunhyub

2018-04-01

Electronic skins (e-skins) with high sensitivity to multidirectional mechanical stimuli are crucial for healthcare monitoring devices, robotics, and wearable sensors. In this study, we present piezoresistive e-skins with tunable force sensitivity and selectivity to multidirectional forces through the engineered microstructure geometries (i.e., dome, pyramid, and pillar). Depending on the microstructure geometry, distinct variations in contact area and localized stress distribution are observed under different mechanical forces (i.e., normal, shear, stretching, and bending), which critically affect the force sensitivity, selectivity, response/relaxation time, and mechanical stability of e-skins. Microdome structures present the best force sensitivities for normal, tensile, and bending stresses. In particular, microdome structures exhibit extremely high pressure sensitivities over broad pressure ranges (47,062 kPa-1 in the range of <1 kPa, 90,657 kPa-1 in the range of 1-10 kPa, and 30,214 kPa-1 in the range of 10-26 kPa). On the other hand, for shear stress, micropillar structures exhibit the highest sensitivity. As proof-of-concept applications in healthcare monitoring devices, we show that our e-skins can precisely monitor acoustic waves, breathing, and human artery/carotid pulse pressures. Unveiling the relationship between the microstructure geometry of e-skins and their sensing capability would provide a platform for future development of high-performance microstructured e-skins.

Evaluation of the hybrid III and Q-series pediatric ATD upper neck loads as compared to pediatric volunteers in low-speed frontal crashes.

PubMed

Seacrist, Thomas; Mathews, Emily A; Balasubramanian, Sriram; Maltese, Matthew R; Arbogast, Kristy B

2013-11-01

Debate exists in the automotive community regarding the validity of the pediatric ATD neck response and corresponding neck loads. Previous research has shown that the pediatric ATDs exhibit hyper-flexion and chin-to-chest contact resulting in overestimations of neck loads and neck injury criteria. Our previous work comparing the kinematics of the Hybrid III and Q-series 6 and 10-year-old ATDs to pediatric volunteers in low-speed frontal sled tests revealed decreased ATD cervical and thoracic spine excursions. These kinematic differences may contribute to the overestimation of upper neck loads by the ATD. The current study compared upper neck loads of the Hybrid III and Q-series 6 and 10-year-old ATDs against size-matched male pediatric volunteers in low-speed frontal sled tests. A 3-D near-infrared target tracking system quantified the position of markers on the ATD and pediatric volunteers (head top, nasion, bilateral external auditory meatus). Shear force (F x ), axial force (F z ), bending moment (M y ), and head angular acceleration ([Formula: see text]) were calculated about the upper neck using standard equations of motion. In general, the ATDs underestimated axial force and overestimated bending moment compared to the human volunteers. The Hybrid III 6, Q6, and Q10 exhibited reduced head angular acceleration and modest increases in upper neck shear compared to the pediatric volunteers. The reduction in axial force and bending moment has important implications for neck injury predictions as both are used when calculating N ij . These analyses provide insight into the biofidelity of the pediatric ATD upper neck loads in low-speed crash environments.

Foot positioning instruction, initial vertical load position and lifting technique: effects on low back loading.

PubMed

Kingma, Idsart; Bosch, Tim; Bruins, Louis; van Dieën, Jaap H

2004-10-22

This study investigated the effects of initial load height and foot placement instruction in four lifting techniques: free, stoop (bending the back), squat (bending the knees) and a modified squat technique (bending the knees and rotating them outward). A 2D dynamic linked segment model was combined with an EMG assisted trunk muscle model to quantify kinematics and low back loading in 10 subjects performing 19 different lifting movements, using 10.5 kg boxes without handles. When lifting from a 0.05 m height with the feet behind the box, squat lifting resulted in 19.9% (SD 8.7%) higher net moments (p < 0.001) and 17.0% (SD 13.2%) higher compression forces (p < 0.01) than stoop lifting. This effect was reduced to 12.8% (SD 10.7%) for moments and a non-significant 7.4% (SD 16.0%) for compression forces when lifting with the feet beside the box and it disappeared when lifting from 0.5 m height. Differences between squat and stoop lifts, as well as the interaction with lifting height, could to a large extent be explained by changes in the horizontal L5/S1 intervertebral joint position relative to the load, the upper body acceleration, and lumbar flexion. Rotating the knees outward during squat lifts resulted in moments and compression forces that were smaller than in squat lifting but larger than in stoop lifting. Shear forces were small ( < 300 N) at the L4/L5 joint and substantial (1100 - 1400 N) but unaffected by lifting technique at the L5/S1 joint. The present results show that the effects of lifting technique on low back loading depend on the task context.

Numerical Simulations for Distribution Characteristics of Internal Forces on Segments of Tunnel Linings

NASA Astrophysics Data System (ADS)

Li, Shouju; Shangguan, Zichang; Cao, Lijuan

A procedure based on FEM is proposed to simulate interaction between concrete segments of tunnel linings and soils. The beam element named as Beam 3 in ANSYS software was used to simulate segments. The ground loss induced from shield tunneling and segment installing processes is simulated in finite element analysis. The distributions of bending moment, axial force and shear force on segments were computed by FEM. The commutated internal forces on segments will be used to design reinforced bars on shield linings. Numerically simulated ground settlements agree with observed values.

Compression-bending of multi-component semi-rigid columns in response to axial loads and conjugate reciprocal extension-prediction of mechanical behaviours and implications for structural design.

PubMed

Lau, Ernest W

2013-01-01

The mathematical modelling of column buckling or beam bending under an axial or transverse load is well established. However, the existent models generally assume a high degree of symmetry in the structure of the column and minor longitudinal and transverse displacements. The situation when the column is made of several components with different mechanical properties asymmetrically distributed in the transverse section, semi-rigid, and subjected to multiple axial loads with significant longitudinal and transverse displacements through compression and bending has not been well characterised. A more comprehensive theoretical model allowing for these possibilities and assuming a circular arc contour for the bend is developed, and used to establish the bending axes, balance between compression and bending, and equivalent stiffness of the column. In certain situations, such as with pull cable catheters commonly used for minimally invasive surgical procedures, the compression loads are applied via cables running through channels inside a semi-rigid column. The model predicts the mathematical relationships between the radius of curvature of the bend and the tension in and normal force exerted by such cables. Conjugate extension with reciprocal compression-bending is a special structural arrangement for a semi-rigid column such that extension of one segment is linked to compression-bending of another by inextensible cables running between them. Leads are cords containing insulated electrical conductor coil and cables between the heart muscle and cardiac implantable electronic devices. Leads can behave like pull cable catheters through differential component pulling, providing a possible mechanism for inside-out abrasion and conductor cable externalisation. Certain design features may predispose to this mode of structural failure. Copyright © 2012 Elsevier Ltd. All rights reserved.

Flow Structure and Channel Morphology at a Confluent-Meander Bend

NASA Astrophysics Data System (ADS)

Riley, J. D.; Rhoads, B. L.

2009-12-01

Flow structure and channel morphology in meander bends have been well documented. Channel curvature subjects flow through a bend to centrifugal acceleration, inducing a counterbalancing pressure-gradient force that initiates secondary circulation. Transverse variations in boundary shear stress and bedload transport parallel cross-stream movement of high velocity flow and determine spatial patterns of erosion along the outer bank and deposition along the inner bank. Laboratory experiments and numerical modeling of confluent-meander bends, a junction planform that develops when a tributary joins a meandering river along the outer bank of a bend, suggest that flow and channel morphology in such bends deviate from typical patterns. The purpose of this study is to examine three-dimensional (3-D) flow structure and channel morphology at a natural confluent-meander bend. Field data were collected in southeastern Illinois where Big Muddy Creek joins the Little Wabash River near a local maximum of curvature along an elongated meander loop. Measurements of 3-D velocity components were obtained with an acoustic Doppler current profiler (ADCP) for two flow events with differing momentum ratios. Channel bathymetry was also resolved from the four-beam depths of the ADCP. Analysis of velocity data reveals a distinct shear layer flanked by dual helical cells within the bend immediately downstream of the confluence. Flow from the tributary confines flow from the main channel along the inner part of the channel cross section, displacing the thalweg inward, limiting the downstream extent of the point bar, protecting the outer bank from erosion and enabling bar-building along this bank. Overall, this pattern of flow and channel morphology is quite different from typical patterns in meander bends, but is consistent with a conceptual model derived from laboratory experiments and numerical modeling.

Precise Restraightening of Bent Studs

NASA Technical Reports Server (NTRS)

Boardman, R. E.

1982-01-01

Special tool quickly bends studs back into shape accurately and safely by force applied by hydraulic ram, with deflection being measured by dial indicator. Ram and indicator can be interchanged for straightening in reverse direction.

The importance of cantilever dynamics in the interpretation of Kelvin probe force microscopy.

PubMed

Satzinger, Kevin J; Brown, Keith A; Westervelt, Robert M

2012-09-15

A realistic interpretation of the measured contact potential difference (CPD) in Kelvin probe force microscopy (KPFM) is crucial in order to extract meaningful information about the sample. Central to this interpretation is a method to include contributions from the macroscopic cantilever arm, as well as the cone and sharp tip of a KPFM probe. Here, three models of the electrostatic interaction between a KPFM probe and a sample are tested through an electrostatic simulation and compared with experiment. In contrast with previous studies that treat the KPFM cantilever as a rigid object, we allow the cantilever to bend and rotate; accounting for cantilever bending provides the closest agreement between theory and experiment. We demonstrate that cantilever dynamics play a major role in CPD measurements and provide a simulation technique to explore this phenomenon.

Comparison of the NASA Common Research Model European Transonic Wind Tunnel Test Data to NASA Test Data

NASA Technical Reports Server (NTRS)

Rivers, Melissa B.; Quest, Jurgen; Rudnik, Ralf

2015-01-01

Experimental aerodynamic investigations of the NASA Common Research Model have been conducted in the NASA Langley National Transonic Facility, the NASA Ames 11-ft wind tunnel, and the European Transonic Wind Tunnel. In the NASA Ames 11-ft wind tunnel, data have been obtained at only a chord Reynolds number of 5 million for a wing/body/tail = 0 degree incidence configuration. Data have been obtained at chord Reynolds numbers of 5, 19.8 and 30 million for the same configuration in the National Transonic Facility and in the European Transonic Facility. Force and moment, surface pressure, wing bending and twist, and surface flow visualization data were obtained in all three facilities but only the force and moment, surface pressure and wing bending and twist data are presented herein.

The asymptotic structure of a slender coiling fluid thread

NASA Astrophysics Data System (ADS)

Blount, Maurice; Lister, John

2010-11-01

The buckling of a viscous fluid thread as it falls through air onto a stationary surface is a well-known breakfast-time phenomenon which exhibits a rich variety of dynamical regimes [1]. Since the bending resistance of a slender thread is small, bending motion is largely confined to a short region of coiling near the surface. If the height of fall is large enough, then the thread above the coiling region forms a `tail' that falls nearly vertically under gravity but is deflected slightly due to forces exerted on it by the coil. Although it is possible to use force balances in the coil to estimate scalings for the coiling frequency, we analyse the solution structure of the entire thread in the asymptotic limit of a very slender thread and thereby include the dynamic interaction between the coil and the tail. Quantitative predictions of the coiling frequency are obtained which demonstrate the existence of leading-order corrections to scalings previously derived. In particular, we show that in the regime where the deflection of the tail is governed by a balance between centrifugal acceleration, hoop stress and gravity, the tail behaves as a flexible circular pendulum that is forced by bending stress exerted by the coil. The amplitude of the response is calculated and the previously observed resonance when the coiling frequency coincides with one of the eigenfrequencies of a free flexible pendulum is thereby explained. [1] N.M. Ribe et al., J. Fluid Mech. 555, 275-297.

A study on plastic wrinkling in thin-walled tube bending via an energy-based wrinkling prediction model

NASA Astrophysics Data System (ADS)

Li, H; Yang, H; Zhan, M

2009-04-01

Thin-walled tube bending is an advanced technology for producing precision bent tube parts in aerospace, aviation and automobiles, etc. With increasing demands of bending tubes with a larger tube diameter and a smaller bending radius, wrinkling instability is a critical issue to be solved urgently for improving the bending limit and forming quality in this process. In this study, by using the energy principle, combined with analytical and finite element (FE) numerical methods, an energy-based wrinkling prediction model for thin-walled tube bending is developed. A segment shell model is proposed to consider the critical wrinkling region, which captures the deformation features of the tube bending process. The dissipation energy created by the reaction forces at the tube-dies interface for restraining the compressive instability is also included in the prediction model, which can be numerically calculated via FE simulation. The validation of the model is performed and its physical significance is evaluated from various aspects. Then the plastic wrinkling behaviors in thin-walled tube bending are addressed. From the energy viewpoint, the effect of the basic parameters including the geometrical and material parameters on the onset of wrinkling is identified. In particular, the influence of multi-tools constraints such as clearance and friction at various interfaces on the wrinkling instability is obtained. The study provides instructive understanding of the plastic wrinkling instability and the model may be suitable for the wrinkling prediction of a doubly-curved shell in the complex forming process with contact conditions.

Sexual Dimorphism and Population Differences in Structural Properties of Barn Swallow (Hirundo rustica) Wing and Tail Feathers

PubMed Central

Pap, Péter L.; Osváth, Gergely; Aparicio, José Miguel; Bărbos, Lőrinc; Matyjasiak, Piotr; Rubolini, Diego; Saino, Nicola; Vágási, Csongor I.; Vincze, Orsolya; Møller, Anders Pape

2015-01-01

Sexual selection and aerodynamic forces affecting structural properties of the flight feathers of birds are poorly understood. Here, we compared the structural features of the innermost primary wing feather (P1) and the sexually dimorphic outermost (Ta6) and monomorphic second outermost (Ta5) tail feathers of barn swallows (Hirundo rustica) from a Romanian population to investigate how sexual selection and resistance to aerodynamic forces affect structural differences among these feathers. Furthermore, we compared structural properties of Ta6 of barn swallows from six European populations. Finally, we determined the relationship between feather growth bars width (GBW) and the structural properties of tail feathers. The structure of P1 indicates strong resistance against aerodynamic forces, while the narrow rachis, low vane density and low bending stiffness of tail feathers suggest reduced resistance against airflow. The highly elongated Ta6 is characterized by structural modifications such as large rachis width and increased barbule density in relation to the less elongated Ta5, which can be explained by increased length and/or high aerodynamic forces acting at the leading tail edge. However, these changes in Ta6 structure do not allow for full compensation of elongation, as reflected by the reduced bending stiffness of Ta6. Ta6 elongation in males resulted in feathers with reduced resistance, as shown by the low barb density and reduced bending stiffness compared to females. The inconsistency in sexual dimorphism and in change in quality traits of Ta6 among six European populations shows that multiple factors may contribute to shaping population differences. In general, the difference in quality traits between tail feathers cannot be explained by the GBW of feathers. Our results show that the material and structural properties of wing and tail feathers of barn swallows change as a result of aerodynamic forces and sexual selection, although the result of these changes can be contrasting. PMID:26110255

String theory--the physics of string-bending and other electric guitar techniques.

PubMed

Grimes, David Robert

2014-01-01

Electric guitar playing is ubiquitous in practically all modern music genres. In the hands of an experienced player, electric guitars can sound as expressive and distinct as a human voice. Unlike other more quantised instruments where pitch is a discrete function, guitarists can incorporate micro-tonality and, as a result, vibrato and sting-bending are idiosyncratic hallmarks of a player. Similarly, a wide variety of techniques unique to the electric guitar have emerged. While the mechano-acoustics of stringed instruments and vibrating strings are well studied, there has been comparatively little work dedicated to the underlying physics of unique electric guitar techniques and strings, nor the mechanical factors influencing vibrato, string-bending, fretting force and whammy-bar dynamics. In this work, models for these processes are derived and the implications for guitar and string design discussed. The string-bending model is experimentally validated using a variety of strings and vibrato dynamics are simulated. The implications of these findings on the configuration and design of guitars is also discussed.

Fractography of human intact long bone by bending.

PubMed

Kimura, T; Ogawa, K; Kamiya, M

1977-05-27

Human intact tibiae were tested using the static bending method to learn about the relationship between the fracture surface and the failure mode. The bending test was applied to test pieces and to whole bones. The fracture surface was observed by scanning electron microscopy. The bone fracture is closely related to the architecture of the bone substance, especially to the direction of the Haversian canals and the lamellae. The failure mode and the sequence of the break line of the bone can be found out by the observation on the fracture surface. Hardly any crushing effects caused by the compressive force is seen. The mechanical properties of the fractured bone can be estimated to some extend by considering the direction of the break line and the failure mode. The strength calculated by the simple beam formula for elastic materials can not be obtained directly because of the plastic deformation of the bone. The results of the tensile test may be applied to the fracture using the static bending moment.

Design of two-way reversible bending actuator based on a shape memory alloy/shape memory polymer composite

NASA Astrophysics Data System (ADS)

Taya, Minoru; Liang, Yuanchang; Namli, Onur C.; Tamagawa, Hirohisa; Howie, Tucker

2013-10-01

The design of a reversible bending actuator based on a SMA/SMP composite is presented. The SMA/SMP composite is made of SMA NiTi wires with a bent ‘U’-shape in the austenite phase embedded in an epoxy SMP matrix which has a memorized flat shape. The bending motion is caused by heating the composite above TAf to activate the NiTi recovery. Upon cooling, the softening from the austenite to R-phase transformation results in a relaxation of the composite towards its original flat shape. In the three-point bending measurement the composite was able to exhibit a reversible deflection of 1.3 mm on a support with a 10 mm span. In addition, a material model for predicting the composite’s deflection is presented and predicts the experimental results reasonably well. The model also estimates the in-plane internal force and the degree of the SMA phase transformation.

Shear-lag analysis about an internally-dropped ply

DOE Office of Scientific and Technical Information (OSTI.GOV)

Vizzini, A.J.

1995-12-31

The region around a terminated ply is modeled as several elastic layers separated by shear regions. A shear-lag analysis is then performed allowing for the thickness of the elastic and shear layers to vary. Boundary conditions, away for the ply drop, are based on the deflections determined by a finite element model. The interlaminar stresses are compared against those generated by the finite element model for tapered laminates under pure extension, pure bending, and extension-bending coupling. The shear-lag analysis predicts the interlaminar shear at and near the ply drop for pure extension and in cases involving bending if the deflectionsmore » due to bending are removed. The interlaminar shear stress and force equilibrium are used to determine the interlaminar normal stress. The trends in the interlaminar normal stress shown by the finite element model are partially captured by the shear-lag analysis. This simple analysis indicates that the mechanism for load transfer about a ply drop is primarily due to shear transfer through the resin rich areas.« less

Modeling and experimental analysis of the linear ultrasonic motor with in-plane bending and longitudinal mode.

PubMed

Wan, Zhijian; Hu, Hong

2014-03-01

A novel linear ultrasonic motor based on in-plane longitudinal and bending mode vibration is presented in this paper. The stator of the motor is composed of a metal plate and eight piezoelectric ceramic patches. There are four long holes in the plate, designed for consideration of the longitudinal and bending mode coupling. The corresponding model is developed to optimize the mechanical and electrical coupling of the stator, which causes an ellipse motion at the contact tip of the stator when the composite vibrations with longitudinal and bending are excited. Its harmonic and transient responses are simulated and inspected. A prototype based on the model is fabricated and used to conduct experiments. Results show that the amplitude of the stator's contact tips is significantly increased, which helps to amplify the driving force and speed of the motor. It is therefore feasible to implement effective linear movement using the developed prototype. Copyright © 2013 Elsevier B.V. All rights reserved.

String Theory - The Physics of String-Bending and Other Electric Guitar Techniques

PubMed Central

Grimes, David Robert

2014-01-01

Electric guitar playing is ubiquitous in practically all modern music genres. In the hands of an experienced player, electric guitars can sound as expressive and distinct as a human voice. Unlike other more quantised instruments where pitch is a discrete function, guitarists can incorporate micro-tonality and, as a result, vibrato and sting-bending are idiosyncratic hallmarks of a player. Similarly, a wide variety of techniques unique to the electric guitar have emerged. While the mechano-acoustics of stringed instruments and vibrating strings are well studied, there has been comparatively little work dedicated to the underlying physics of unique electric guitar techniques and strings, nor the mechanical factors influencing vibrato, string-bending, fretting force and whammy-bar dynamics. In this work, models for these processes are derived and the implications for guitar and string design discussed. The string-bending model is experimentally validated using a variety of strings and vibrato dynamics are simulated. The implications of these findings on the configuration and design of guitars is also discussed. PMID:25054880

Hydrophobic interactions between dissimilar surfaces

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yoon, R.H.; Flinn, D.H.; Rabinovich, Y.I.

1997-01-15

An atomic force microscope (AFM) was used to measure surface forces between a glass sphere and a silica plate. When the measurements were conducted between untreated surfaces, a short-range hydration force with decay lengths of 0.4 and 3.0 nm was observed. When the surfaces were hydrophobized with octadecyltrichlorosilane (OTS), on the other hand, long-range hydrophobic forces with decay lengths in the range of 2--32 nm were observed. The force measurements were conducted between surfaces having similar and dissimilar hydrophobicities so that the results may be used for deriving an empirical combining rule. It was found that the power law forcemore » constants for asymmetric interactions are close to the geometric means of those for symmetric interactions. Thus, hydrophobic force constants can be combined in the same manner as the Hamaker constants. A plot of the power law force constants versus water contact angles suggests that the hydrophobic force is uniquely determined by contact angle. These results will be useful in predicting hydrophobic forces for asymmetric interactions and in estimating hydrophobic forces from contact angles.« less

Improving Bending Moment Measurements on Wind Turbine Blades

DOE Office of Scientific and Technical Information (OSTI.GOV)

Post, Nathan L.

Full-scale fatigue testing of wind turbine blades is conducted using resonance test techniques where the blade plus additional masses is excited at its first resonance frequency to achieve the target loading amplitude. Because there is not a direct relationship between the force applied by an actuator and the bending moment, the blade is instrumented with strain gauges that are calibrated under static loading conditions to determine the sensitivity or relationship between strain and applied moment. Then, during dynamic loading the applied moment is calculated using the strain response of the structure. A similar procedure is also used in the fieldmore » to measure in-service loads on turbine blades. Because wind turbine blades are complex twisted structures and the deflections are large, there is often significant cross-talk coupling in the sensitivity of strain gauges placed on the structure. Recent work has shown that a sensitivity matrix with nonzero cross terms must be employed to find constant results when a blade is subjected to both flap and lead-lag loading. However, even under controlled laboratory conditions, potential for errors of 3 percent or more in the measured moment exist when using the typical cross-talk matrix approach due to neglecting the influence of large deformations and torsion. This is particularly critical when considering a biaxial load as would be applied on the turbine or during a biaxial fatigue test. This presentation describes these results demonstrating errors made when performing current loads measurement practices on wind turbine blades in the lab and evaluating potential improvements using enhanced cross-talk matrix approaches and calibration procedures.« less

Interaction between bending and tension forces in bilayer membranes.

PubMed Central

Secomb, T W

1988-01-01

A theoretical analysis is presented of the bending mechanics of a membrane consisting of two tightly-coupled leaflets, each of which shears and bends readily but strongly resists area changes. Structures of this type have been proposed to model biological membranes such as red blood cell membrane. It is shown that when such a membrane is bent, anisotropic components of resultant membrane tension (shear stresses) are induced, even when the tension in each leaflet is isotropic. The induced shear stresses increase as the square of the membrane curvature, and become significant for moderate curvatures (when the radius of curvature is much larger than the distance between the leaflets). This effect has implications for the analysis of shape and deformation of freely suspended and flowing red blood cells. PMID:3224154

Development of Bend Sensor for Catheter Tip

NASA Astrophysics Data System (ADS)

Nagano, Yoshitaka; Sano, Akihito; Fujimoto, Hideo

Recently, a minimally invasive surgery which makes the best use of the catheter has been becoming more popular. In endovascular coil embolization for a cerebral aneurysm, the observation of the catheter's painting phenomenon is very important to execute the appropriate manipulation of the delivery wire and the catheter. In this study, the internal bend sensor which consists of at least two bending enhanced plastic optical fibers was developed in order to measure the curvature of the catheter tip. Consequently, the painting could be more sensitively detected in the neighborhood of the aneurysm. In this paper, the basic characteristics of the developed sensor system are described and its usefulness is confirmed from the comparison of the insertion force of delivery wire and the curvature of catheter tip in the experiment of coil embolization.

Piezoelectrostatic generator

NASA Technical Reports Server (NTRS)

Robertson, Glen A. (Inventor)

1990-01-01

A piezoelectrostatic generator includes a plurality of elongated piezoelectric elements having first and second ends, with the first ends fixedly mounted in a cylindrical housing and the second extending radially inwardly toward an axis. A shaft movable along the axis is connected to the inner ends of the elements to produce bending forces in piezoelectric strips within the elements. Each element includes a pair of strips mounted in surface contact and in electrical series to produce a potential upon bending. Electrodes spaced from the strips by a solid dielectric material act as capacitor plates to collect the potential charge.

Environmental Assessment for the Proposed Expeditionary Training at Gila Bend Air Force Auxiliary Field and the Barry M. Goldwater Range East

DTIC Science & Technology

2005-12-01

Arizona) and the ANG 162 FW (in Tucson, Arizona). Approximately 34,000 operations per year are conducted at Gila Bend AFAF ( Mendez 2005). Aircraft...high year of approximately 45,000 operations ( Mendez 2005). More than 50,000 sorties are conducted annually at BMGR East. While the sorties associated...have varied from a low of 22,000 per year and a high of 45,000 operations per year, with an average of about 34,000 operations ( Mendez 2005). The

Crystal Chemical Controls on Equation of State

NASA Astrophysics Data System (ADS)

Thompson, R. M.; McCarthy, A. C.; Downs, R. T.

2007-12-01

Minerals are known to compress through a number of mechanisms, ranging from polyhedral distortion to electronic transitions. Two mechanisms which can produce significant volume decreases are angle-bending and bond compression. The crystal chemical effects of these two mechanisms have been studied and documented for years. With more recent advances in theory and software enabling the accurate determination of bonding topologies, M-O bonding to bridging oxygens has been shown to modify compressibility by changing angle-bending force constants. Minerals that compress mainly through angle-bending tend be soft. Good examples are quartz and cristobalite, minerals composed solely of corner-sharing silicate tetrahedra with bulk moduli of 37 and 12 GPa, respectively. Rock salt structured oxides must compress strictly by bond compression, and are much stiffer - lime and periclase have bulk moduli of 111 and 156 GPa, respectively. Feldspars have bulk moduli intermediate to the above examples. Based solely on the presence of Al-O-Si angles, theoretically softer than Si-O-Si angles, feldspars should be softer than quartz or cristobalite, but the T-O-T angles are stiffened by bonds to interstitial cations. The number and nature of these bonds affects compressibility sufficiently to create exceptions to Bridgman's law, which correlates bulk modulus with ambient unit cell volume in isostructural materials. In this paper, we present new high-pressure refinements of the crystal structures of jadeite, aegirine, and NaGa- clinopyroxene. Bulk moduli of these pyroxenes and all other end-member clinopyroxenes we could find in the literature (19 total) are plotted vs. unit cell volumes to test Bridgman's law. The data fall along two trends, each of which is separately consistent with Bridgman's law. Pyroxenes in one trend are dramatically stiffer than those in the other trend, with bulk moduli that differ by approximately 40 GPa. The only difference between the topologies of the structures in the two trends is in the bonding around M2. Structures in the less compressible trend have M2-O3 bonds that oppose Si-O-Si angle-bending in the tetrahedral chains. This angle-bending is an important compression mechanism in pyroxenes. McCarthy et al. (in press) term these bonds "antipathetic". Pyroxenes in the more compressible trend lack these bonds. There are other M2-O3 bonds that visual inspection suggests might tend to encourage angle-bending, but do not appear to have an effect. McCarthy et al. term these bonds "apathetic," and suggest the term "sympathetic" for M-O bonds that actually soften angles. Other examples from the literature will be presented including one from the feldspars that may be a truly sympathetic bond. McCarthy, A.C., Downs, R.T., and Thompson, R.M. (in press) Compressibility trends of the clinopyroxenes, and in- situ high-pressure single-crystal X-ray diffraction study of jadeite. American Mineralogist.

Influence of bending stress on flux distribution in toroidal transducers

NASA Astrophysics Data System (ADS)

Goktepe, M.; Meydan, T.

1994-05-01

Amorphous transducers consisting of toroidally wound amorphous ribbon with a magnetising winding and search coil windings have been investigated. The application of displacement to the toroid gives a linear search coil voltage against the applied force characteristics. The position of the search coils with respect to the applied force has been studied and it is shown that the effect of applied force is localised. These results have elucidated the operation of ac amorphous ribbon transducers and enabled improved designs to be produced.

Effect of coating on properties of esthetic orthodontic nickel-titanium wires.

PubMed

Iijima, Masahiro; Muguruma, Takeshi; Brantley, William; Choe, Han-Cheol; Nakagaki, Susumu; Alapati, Satish B; Mizoguchi, Itaru

2012-03-01

To determine the effect of coating on the properties of two esthetic orthodontic nickel-titanium wires. Woowa (polymer coating; Dany Harvest) and BioForce High Aesthetic Archwire (metal coating; Dentsply GAC) with cross-section dimensions of 0.016 × 0.022 inches were selected. Noncoated posterior regions of the anterior-coated Woowa and uncoated Sentalloy were used for comparison. Nominal coating compositions were determined by x-ray fluorescence (JSX-3200, JOEL). Cross-sectioned and external surfaces were observed with a scanning electron microscope (SEM; SSX-550, Shimadzu) and an atomic force microscope (SPM-9500J2, Shimadzu). A three-point bending test (12-mm span) was carried out using a universal testing machine (EZ Test, Shimadzu). Hardness and elastic modulus of external and cross-sectioned surfaces were obtained by nanoindentation (ENT-1100a, Elionix; n  =  10). Coatings on Woowa and BioForce High Aesthetic Archwire contained 41% silver and 14% gold, respectively. The coating thickness on Woowa was approximately 10 µm, and the coating thickness on BioForce High Aesthetic Archwire was much smaller. The surfaces of both coated wires were rougher than the noncoated wires. Woowa showed a higher mean unloading force than the noncoated Woowa, although BioForce High Aesthetic Archwire showed a lower mean unloading force than Sentalloy. While cross-sectional surfaces of all wires had similar hardness and elastic modulus, values for the external surface of Woowa were smaller than for the other wires. The coating processes for Woowa and BioForce High Aesthetic Archwire influence bending behavior and surface morphology.

Somersault of Paramecium in extremely confined environments.

PubMed

Jana, Saikat; Eddins, Aja; Spoon, Corrie; Jung, Sunghwan

2015-08-19

We investigate various swimming modes of Paramecium in geometric confinements and a non-swimming self-bending behavior like a somersault, which is quite different from the previously reported behaviors. We observe that Paramecia execute directional sinusoidal trajectories in thick fluid films, whereas Paramecia meander around a localized region and execute frequent turns due to collisions with adjacent walls in thin fluid films. When Paramecia are further constrained in rectangular channels narrower than the length of the cell body, a fraction of meandering Paramecia buckle their body by pushing on the channel walls. The bucking (self-bending) of the cell body allows the Paramecium to reorient its anterior end and explore a completely new direction in extremely confined spaces. Using force deflection method, we quantify the Young's modulus of the cell and estimate the swimming and bending powers exerted by Paramecium. The analysis shows that Paramecia can utilize a fraction of its swimming power to execute the self-bending maneuver within the confined channel and no extra power may be required for this new kind of self-bending behavior. This investigation sheds light on how micro-organisms can use the flexibility of the body to actively navigate within confined spaces.

Somersault of Paramecium in extremely confined environments

PubMed Central

Jana, Saikat; Eddins, Aja; Spoon, Corrie; Jung, Sunghwan

2015-01-01

We investigate various swimming modes of Paramecium in geometric confinements and a non-swimming self-bending behavior like a somersault, which is quite different from the previously reported behaviors. We observe that Paramecia execute directional sinusoidal trajectories in thick fluid films, whereas Paramecia meander around a localized region and execute frequent turns due to collisions with adjacent walls in thin fluid films. When Paramecia are further constrained in rectangular channels narrower than the length of the cell body, a fraction of meandering Paramecia buckle their body by pushing on the channel walls. The bucking (self-bending) of the cell body allows the Paramecium to reorient its anterior end and explore a completely new direction in extremely confined spaces. Using force deflection method, we quantify the Young’s modulus of the cell and estimate the swimming and bending powers exerted by Paramecium. The analysis shows that Paramecia can utilize a fraction of its swimming power to execute the self-bending maneuver within the confined channel and no extra power may be required for this new kind of self-bending behavior. This investigation sheds light on how micro-organisms can use the flexibility of the body to actively navigate within confined spaces. PMID:26286234

Somersault of Paramecium in extremely confined environments

NASA Astrophysics Data System (ADS)

Jana, Saikat; Eddins, Aja; Spoon, Corrie; Jung, Sunghwan

2015-08-01

We investigate various swimming modes of Paramecium in geometric confinements and a non-swimming self-bending behavior like a somersault, which is quite different from the previously reported behaviors. We observe that Paramecia execute directional sinusoidal trajectories in thick fluid films, whereas Paramecia meander around a localized region and execute frequent turns due to collisions with adjacent walls in thin fluid films. When Paramecia are further constrained in rectangular channels narrower than the length of the cell body, a fraction of meandering Paramecia buckle their body by pushing on the channel walls. The bucking (self-bending) of the cell body allows the Paramecium to reorient its anterior end and explore a completely new direction in extremely confined spaces. Using force deflection method, we quantify the Young’s modulus of the cell and estimate the swimming and bending powers exerted by Paramecium. The analysis shows that Paramecia can utilize a fraction of its swimming power to execute the self-bending maneuver within the confined channel and no extra power may be required for this new kind of self-bending behavior. This investigation sheds light on how micro-organisms can use the flexibility of the body to actively navigate within confined spaces.

Separation Control in a Centrifugal Bend Using Plasma Actuators

NASA Astrophysics Data System (ADS)

Arthur, Michael; Corke, Thomas

2011-11-01

An experiment and CFD simulation are presented to examine the use of plasma actuators to control flow separation in a 2-D channel with a 135° inside-bend that is intended to represent a centrifugal bend in a gas turbine engine. The design inlet conditions are P = 330 psia., T =1100° F, and M = 0 . 24 . For these conditions, the flow separates on the inside radius of the bend. A CFD simulation was used to determine the location of the flow separation, and the conditions (location and voltage) of a plasma actuator that was needed to keep the flow attached. The plasma actuator body force model used in the simulation was updated to include the effect of high-pressure operation. An experiment was used to validate the simulation and to further investigate the effect of inlet pressure and Mach number on the flow separation control. This involved a transient high-pressure blow-down facility. The flow field is documented using an array of static pressure taps in the channel outside-radius side wall, and a rake of total pressure probes at the exit of the bend. The results as well as the pressure effect on the plasma actuators are presented.

High temperature compounds for turbine vanes. [of SiC, Si3N4, and Si composites

NASA Technical Reports Server (NTRS)

Rhodes, W. H.; Cannon, R. M., Jr.

1974-01-01

Fabrication and microstructure control studies were conducted on SiC, Si3N and composites based on Si3N. Charpy mode impact testing to 2400 F established that Si3N4/Mo composites have excellent potential. Attempts to fabricate composites of Si3N4 with superalloys, both by hot pressing and infiltration were largely unsuccessful in comparison to using Mo, Re, and Ta which are less reactive. Modest improvements in impact strength were realized for monolithic Si3N4; however, SiC strengths increased by a factor of six and now equal values achieved for Si3N4. Correlations of impact strength with material properties are discussed. Reduced MgO densification aid additions to Si3N4 were found to decrease densification kinetics, increase final porosity, decrease room temperature bend strength, increase high temperature bend strength, and decrease bend stress rupture properties. The decrease in bend strength at high temperature for fine grain size SiC suggested that a slightly larger grain size material with a nearly constant strength-temperature relation may prove desirable in the creep and stress rupture mode.

Fatigue Properties of the Ultra-High Strength Steel TM210A

PubMed Central

Kang, Xia; Zhao, Gui-ping

2017-01-01

This paper presents the results of an experiment to investigate the high cycle fatigue properties of the ultra-high strength steel TM210A. A constant amplitude rotating bending fatigue experiment was performed at room temperature at stress ratio R = −1. In order to evaluate the notch effect, the fatigue experiment was carried out upon two sets of specimens, smooth and notched, respectively. In the experiment, the rotating bending fatigue life was tested using the group method, and the rotating bending fatigue limit was tested using the staircase method at 1 × 107 cycles. A double weighted least square method was then used to fit the stress-life (S–N) curve. The S–N curves of the two sets of specimens were obtained and the morphologies of the fractures of the two sets of specimens were observed with scanning electron microscopy (SEM). The results showed that the fatigue limit of the smooth specimen for rotating bending fatigue was 615 MPa; the ratio of the fatigue limit to tensile strength was 0.29, and the cracks initiated at the surface of the smooth specimen; while the fatigue limit of the notched specimen for rotating bending fatigue was 363 MPa, and the cracks initiated at the edge of the notch. The fatigue notch sensitivity index of the ultra-high strength maraging steel TM210A was 0.69. PMID:28891934

Effects of self-healing microcapsules on bending performance in composite brake pads

NASA Astrophysics Data System (ADS)

Zhang, Li; Dong, Xiu-ping; Wang, Hui

2009-07-01

For the purpose of reducing self-weight, friction noise and cost, improving shock absorption, enhancing corrosion and wear resistance, brake pads made of composite materials with self-healing function are prepared to substitute metal ones by designing ingredients and applying optimized production technology. As self-healing capsules are chosen, new method with technology of self-healing microcapsules, dicyclpentadiene (DCPD) microcapsules coated with poly (urea-formaldehyde), is put forward in this paper. In the crack's extending process, the stress is concentrated at the crack end, where the microcapsule is designed to be located. When the stress goes through the microcapsules and causes them to break, the self-healing liquid runs out to fill the crack by the capillary and it will poly-react with catalyst in the composite. As a result, the crack is healed. In this paper, polymer matrix composite brake pads with 6 prescriptions are prepared and studied. Three-point bending tests are carried out according to standards in GB/T 3356-1999 and the elastic constants of these polymer matrix composites are obtained by experiments. In accordance with the law of the continuous fiber composite, elastic constants of the short-fiber composite can be calculated by proportions of each ingredient. Results show that the theoretical expected results and the experimental values are consistent. 0.3-1.2 % mass proportion of microcapsules has little effects on the composite's bending intensity and modulus of elasticity. These studies also show that self-healing microcapsules used in composite brake pads is feasible.

Subpiconewton intermolecular force microscopy.

PubMed

Tokunaga, M; Aoki, T; Hiroshima, M; Kitamura, K; Yanagida, T

1997-02-24

We refined scanning probe force microscopy to improve the sensitivity of force detection and control of probe position. Force sensitivity was increased by incorporating a cantilever with very low stiffness, 0.1 pN/ nm, which is over 1000-fold more flexible than is typically used in conventional atomic force microscopy. Thermal bending motions of the cantilever were reduced to less than 1 nm by exerting feed-back positioning with laser radiation pressure. The system was tested by measuring electrostatic repulsive forces or hydrophobic attractive forces in aqueous solutions. Subpiconewton intermolecular forces were resolved at controlled gaps in the nanometer range between the probe and a material surface. These levels of force and position sensitivity meet the requirements needed for future investigations of intermolecular forces between biological macromolecules such as proteins, lipids and DNA.

Elastic properties and fracture strength of quasi-isotropic graphite/epoxy composites

NASA Technical Reports Server (NTRS)

Sullivan, T. L.

1977-01-01

A research program is described which was devised to determine experimentally the elastic properties in tension and bending of quasi-isotropic laminates made from high-modulus graphite fiber and epoxy. Four laminate configurations were investigated, and determinations were made of the tensile modulus, Poisson's ratio, bending stiffness, fracture strength, and fracture strain. The measured properties are compared with those predicted by laminate theory, reasons for scatter in the experimental data are discussed, and the effect of fiber misalignment on predicted elastic tensile properties is examined. The results strongly suggest that fiber misalignment in combination with variation in fiber volume content is responsible for the scatter in both elastic constants and fracture strength.

Characterization of the hydrogen-bond network of water around sucrose and trehalose: H-O-H bending analysis

NASA Astrophysics Data System (ADS)

Shiraga, Keiichiro; Adachi, Aya; Ogawa, Yuichi

2017-06-01

The bioprotective properties of disaccharides have been linked to destructuring effect on the hydrogen-bond structure of the interfacial water around the disaccharide solute, but its detailed mechanisms are yet to be provided. In this study, we characterized the destructuring effect based on the complex dielectric constants of interfacial water around sucrose and trehalose in the H-O-H bending region. Our analysis showed that the destructuring effect around disaccharides involves substantial disordering of the hydrogen-bond structure and formation of strong disaccharide-water hydrogen-bond. Such a destructuring effect caused by disaccharides is totally distinct from what happens with temperature increases of neat water.

Measurement of Aerodynamic Forces for Various Mean Angles of Attack on an Airfoil Oscillating in Pitch and on Two Finite-span Wings Oscillating in Bending with Emphasis on Damping in the Stall

NASA Technical Reports Server (NTRS)

Rainey, A Gerald

1957-01-01

The oscillating air forces on a two-dimensional wing oscillating in pitch about the midchord have been measured at various mean angles of attack and at Mach numbers of 0.35 and 0.7. The magnitudes of normal-force and pitching-moment coefficients were much higher at high angles of attack than at low angles of attack for some conditions. Large regions of negative damping in pitch were found, and it was shown that the effect of increasing the Mach number 0.35 to 0.7 was to decrease the initial angle of attack at which negative damping occurred. Measurements of the aerodynamic damping of a 10-percent-thick and of a 3-percent-thick finite-span wing oscillating in the first bending mode indicate no regions of negative damping for this type of motion over the range of variables covered. The damping measured at high angles of attack was generally larger than that at low angles of attack. (author)

Mechanical properties of DNA-like polymers

PubMed Central

Peters, Justin P.; Yelgaonkar, Shweta P.; Srivatsan, Seergazhi G.; Tor, Yitzhak; James Maher, L.

2013-01-01

The molecular structure of the DNA double helix has been known for 60 years, but we remain surprisingly ignorant of the balance of forces that determine its mechanical properties. The DNA double helix is among the stiffest of all biopolymers, but neither theory nor experiment has provided a coherent understanding of the relative roles of attractive base stacking forces and repulsive electrostatic forces creating this stiffness. To gain insight, we have created a family of double-helical DNA-like polymers where one of the four normal bases is replaced with various cationic, anionic or neutral analogs. We apply DNA ligase-catalyzed cyclization kinetics experiments to measure the bending and twisting flexibilities of these polymers under low salt conditions. Interestingly, we show that these modifications alter DNA bending stiffness by only 20%, but have much stronger (5-fold) effects on twist flexibility. We suggest that rather than modifying DNA stiffness through a mechanism easily interpretable as electrostatic, the more dominant effect of neutral and charged base modifications is their ability to drive transitions to helical conformations different from canonical B-form DNA. PMID:24013560

Note: Formation of the nematic splay-bend in two-dimensional systems of bow-shaped particles

NASA Astrophysics Data System (ADS)

Karbowniczek, Paweł

2018-04-01

Recently, Tavarone et al. (J. Chem. Phys. 143, 114505 (2015)) discussed phase behavior of zig-zag and bow-shaped particles composed of three needles. The authors presented very interesting results of extensive Monte Carlo simulations with periodic boundary conditions in the constant-NVT and the constant-NPT ensembles. In addition to isotropic, nematic, and smectic phases, they identified a modulated nematic, which is actually the nematic splay-bend phase ($N_{SB}$), long-anticipated for bent-core systems (Europhys. Lett. 56, 247 (2001)). They also described isotropic-nematic and nematic-smectic transitions using Density Functional Theory in mean-field approximation. The authors, however, did not provided a theoretical description of the $N_{SB}$. Here, we present a simple theory of a phase transition to the $N_{SB}$ phase to fill the gap. In our study, we use Onsager-type Density Functional Theory with perfect order approximation and Meyer parametrization of modulated structures. We present results for arbitrary ratios of the length of central and side segments and opening angles of bow-shaped particles.

Force-extension behavior of DNA in the presence of DNA-bending nucleoid associated proteins

NASA Astrophysics Data System (ADS)

Dahlke, K.; Sing, C. E.

2018-02-01

Interactions between nucleoid associated proteins (NAPs) and DNA affect DNA polymer conformation, leading to phenomena such as concentration dependent force-extension behavior. These effects, in turn, also impact the local binding behavior of the protein, such as high forces causing proteins to unbind, or proteins binding favorably to locally bent DNA. We develop a coarse-grained NAP-DNA simulation model that incorporates both force- and concentration-dependent behaviors, in order to study the interplay between NAP binding and DNA conformation. This model system includes multi-state protein binding and unbinding, motivated by prior work, but is now dependent on the local structure of the DNA, which is related to external forces acting on the DNA strand. We observe the expected qualitative binding behavior, where more proteins are bound at lower forces than at higher forces. Our model also includes NAP-induced DNA bending, which affects DNA elasticity. We see semi-quantitative matching of our simulated force-extension behavior to the reported experimental data. By using a coarse-grained simulation, we are also able to look at non-equilibrium behaviors, such as dynamic extension of a DNA strand. We stretch a DNA strand at different rates and at different NAP concentrations to observe how the time scales of the system (such as pulling time and unbinding time) work in concert. When these time scales are similar, we observe measurable rate-dependent changes in the system, which include the number of proteins bound and the force required to extend the DNA molecule. This suggests that the relative time scales of different dynamic processes play an important role in the behavior of NAP-DNA systems.

Steel fiber replacement of mild steel in prestressed concrete beams

DOT National Transportation Integrated Search

2010-10-01

In traditional prestressed concrete beams, longitudinal prestressed tendons serve to resist bending moment and : transverse mild steel bars (or stirrups) are used to carry shear forces. However, traditional prestressed concrete I-beams : exhibit earl...

Steel fiber replacement of mild steel in prestressed concrete beams.

DOT National Transportation Integrated Search

2011-01-01

In traditional prestressed concrete beams, longitudinal prestressed tendons serve to resist bending moment and transverse mild : steel bars (or stirrups) are used to carry shear forces. However, traditional prestressed concrete I-beams exhibit early-...

Natural Curvature as Effective Confinement in Elastic Sheets

NASA Astrophysics Data System (ADS)

Albarran, Octavio; Katifori, Eleni; Goehring, Lucas

The wrinkling and folding transitions of thin elastic sheets have been extensively studied in the last decade. The exchange of energy from stretching to bending acts as a paradigm for a wide range of elastic instabilities, including the wrinkling of the gut, and the crinkling of leaves. In two dimensions this type of problem is typically considered by the model of an Euler-elastica in compressive confinement. We show that, even without any external forces, an elastic surface supported by a fluid can bend and wrinkle when it acquires a non-zero natural curvature. Locally, we will demonstrate how a preferential curvature can be related to an effective compression, and hence a confining force that can vary spatially. This suggests a simple experimental setup, where we have characterised a variety of wrinkle patterns that can be generated for different mechanical properties and natural curvatures.

Segmentation and Tracking of Cytoskeletal Filaments Using Open Active Contours

PubMed Central

Smith, Matthew B.; Li, Hongsheng; Shen, Tian; Huang, Xiaolei; Yusuf, Eddy; Vavylonis, Dimitrios

2010-01-01

We use open active contours to quantify cytoskeletal structures imaged by fluorescence microscopy in two and three dimensions. We developed an interactive software tool for segmentation, tracking, and visualization of individual fibers. Open active contours are parametric curves that deform to minimize the sum of an external energy derived from the image and an internal bending and stretching energy. The external energy generates (i) forces that attract the contour toward the central bright line of a filament in the image, and (ii) forces that stretch the active contour toward the ends of bright ridges. Images of simulated semiflexible polymers with known bending and torsional rigidity are analyzed to validate the method. We apply our methods to quantify the conformations and dynamics of actin in two examples: actin filaments imaged by TIRF microscopy in vitro, and actin cables in fission yeast imaged by spinning disk confocal microscopy. PMID:20814909

DOE Office of Scientific and Technical Information (OSTI.GOV)

S. Chouhan, J. DeKamp, A. Zeller, P. Brindza, S. Lassiter, M. Fowler, E. Sun

A collaboration between NSCL and Jlab has developed the reference design and coil winding for Jlab's Super High Momentum Spectrometer (SHMS) horizontal bend magnet. A warm iron ??C?? type superferric dipole magnet will bend the 12 GeV/c particles horizontally by 3?? to allow the SHMS to reach angles as low as 5.5??. This requires an integral field strength of up to 2.1 T.m. The major challenges are the tight geometry, high and unbalanced forces and a required low fringe field in primary beam path. A coil design based on flattened SSC Rutherford cable that provides a large current margin andmore » commercially available fiberglass prepreg epoxy tape has been developed. A complete test coil has been wound and will be cold tested. This paper present the modified magnet design includes coil forces, coil restraint system and fringe field. In addition, coil properties, quench calculations and the full mechanical details are also presented.« less

A square-plate ultrasonic linear motor operating in two orthogonal first bending modes.

PubMed

Chen, Zhijiang; Li, Xiaotian; Chen, Jianguo; Dong, Shuxiang

2013-01-01

A novel square-plate piezoelectric ultrasonic linear motor operated in two orthogonal first bending vibration modes (B₁) is proposed. The piezoelectric vibrator of the linear motor is simply made of a single PZT ceramic plate (sizes: 15 x 15 x 2 mm) and poled in its thickness direction. The top surface electrode of the square ceramic plate was divided into four active areas along its two diagonal lines for exciting two orthogonal B₁ modes. The achieved driving force and speed from the linear motor are 1.8 N and 230 mm/s, respectively, under one pair orthogonal voltage drive of 150 V(p-p) at the resonance frequency of 92 kHz. The proposed linear motor has advantages over conventional ultrasonic linear motors, such as relatively larger driving force, very simple working mode and structure, and low fabrication cost.

Stability of aerosol droplets in Bessel beam optical traps under constant and pulsed external forces

NASA Astrophysics Data System (ADS)

David, Grégory; Esat, Kıvanç; Hartweg, Sebastian; Cremer, Johannes; Chasovskikh, Egor; Signorell, Ruth

2015-04-01

We report on the dynamics of aerosol droplets in optical traps under the influence of additional constant and pulsed external forces. Experimental results are compared with simulations of the three-dimensional droplet dynamics for two types of optical traps, the counter-propagating Bessel beam (CPBB) trap and the quadruple Bessel beam (QBB) trap. Under the influence of a constant gas flow (constant external force), the QBB trap is found to be more stable compared with the CPBB trap. By contrast, under pulsed laser excitation with laser pulse durations of nanoseconds (pulsed external force), the type of trap is of minor importance for the droplet stability. It typically needs pulsed laser forces that are several orders of magnitude higher than the optical forces to induce escape of the droplet from the trap. If the droplet strongly absorbs the pulsed laser light, these escape forces can be strongly reduced. The lower stability of absorbing droplets is a result of secondary thermal processes that cause droplet escape.

Stability of aerosol droplets in Bessel beam optical traps under constant and pulsed external forces.

PubMed

David, Grégory; Esat, Kıvanç; Hartweg, Sebastian; Cremer, Johannes; Chasovskikh, Egor; Signorell, Ruth

2015-04-21

We report on the dynamics of aerosol droplets in optical traps under the influence of additional constant and pulsed external forces. Experimental results are compared with simulations of the three-dimensional droplet dynamics for two types of optical traps, the counter-propagating Bessel beam (CPBB) trap and the quadruple Bessel beam (QBB) trap. Under the influence of a constant gas flow (constant external force), the QBB trap is found to be more stable compared with the CPBB trap. By contrast, under pulsed laser excitation with laser pulse durations of nanoseconds (pulsed external force), the type of trap is of minor importance for the droplet stability. It typically needs pulsed laser forces that are several orders of magnitude higher than the optical forces to induce escape of the droplet from the trap. If the droplet strongly absorbs the pulsed laser light, these escape forces can be strongly reduced. The lower stability of absorbing droplets is a result of secondary thermal processes that cause droplet escape.

Sagittal plane bending moments acting on the lower leg during running.

PubMed

Haris Phuah, Affendi; Schache, Anthony G; Crossley, Kay M; Wrigley, Tim V; Creaby, Mark W

2010-02-01

Sagittal bending moments acting on the lower leg during running may play a role in tibial stress fracture development. The purpose of this study was to evaluate these moments at nine equidistant points along the length of the lower leg (10% point-90% point) during running. Kinematic and ground reaction force data were collected for 20 male runners, who each performed 10 running trials. Inverse dynamics and musculoskeletal modelling techniques were used to estimate sagittal bending moments due to reaction forces and muscle contraction. The muscle moment was typically positive during stance, except at the most proximal location (10% point) on the lower leg. The reaction moment was predominantly negative throughout stance and greater in magnitude than the muscle moment. Hence, the net sagittal bending moment acting on the lower leg was principally negative (indicating tensile loads on the posterior tibia). Peak moments typically occurred around mid-stance, and were greater in magnitude at the distal, compared with proximal, lower leg. For example, the peak reaction moment at the most distal point was -9.61+ or - 2.07%Bw.Ht., and -2.73 + or - 1.18%Bw.Ht. at the most proximal point. These data suggest that tensile loads on the posterior tibia are likely to be higher toward the distal end of the bone. This finding may explain the higher incidence of stress fracture in the distal aspect of the tibia, observed by some authors. Stress fracture susceptibility will also be influenced by bone strength and this should also be accounted for in future studies. Copyright 2009 Elsevier B.V. All rights reserved.

Influence of Global and Local Membrane Curvature on Mechanosensitive Ion Channels: A Finite Element Approach

PubMed Central

Bavi, Omid; Cox, Charles D.; Vossoughi, Manouchehr; Naghdabadi, Reza; Jamali, Yousef; Martinac, Boris

2016-01-01

Mechanosensitive (MS) channels are ubiquitous molecular force sensors that respond to a number of different mechanical stimuli including tensile, compressive and shear stress. MS channels are also proposed to be molecular curvature sensors gating in response to bending in their local environment. One of the main mechanisms to functionally study these channels is the patch clamp technique. However, the patch of membrane surveyed using this methodology is far from physiological. Here we use continuum mechanics to probe the question of how curvature, in a standard patch clamp experiment, at different length scales (global and local) affects a model MS channel. Firstly, to increase the accuracy of the Laplace’s equation in tension estimation in a patch membrane and to be able to more precisely describe the transient phenomena happening during patch clamping, we propose a modified Laplace’s equation. Most importantly, we unambiguously show that the global curvature of a patch, which is visible under the microscope during patch clamp experiments, is of negligible energetic consequence for activation of an MS channel in a model membrane. However, the local curvature (RL < 50) and the direction of bending are able to cause considerable changes in the stress distribution through the thickness of the membrane. Not only does local bending, in the order of physiologically relevant curvatures, cause a substantial change in the pressure profile but it also significantly modifies the stress distribution in response to force application. Understanding these stress variations in regions of high local bending is essential for a complete understanding of the effects of curvature on MS channels. PMID:26861405

Free-standing thermalized graphene: a hard/soft hybrid

NASA Astrophysics Data System (ADS)

Nelson, David

2015-03-01

Understanding deformations of macroscopic thin plates and shells has a long and rich history, culminating with the Foeppl-von Karman equations in 1904. These highly nonlinear equations are characterized by a dimensionless coupling constant (the ``Foeppl-von Karman number'') that can easily reach vK = 107 in an ordinary sheet of writing paper. Since the late 1980's, it has been clear that thermal fluctuations in microscopically thin elastic membranes fundamentally alter the long wavelength physics, leading to a negative thermal expansion coefficient, and a strongly scale-dependent bending energy and Young's modulus. Recent experiments from the McEuen group at Cornell that twist and bend individual atomically-thin free-standing graphene sheets (with vK = 1013!) call for a theory of the mechanical deformation of thermally excited membranes with large Foeppl-von Karman number. We present here results for the bending and pulling of thermalized graphene ribbons and tabs in the cantilever mode. Work done in collaboration with Andrej Kosmrlj.

Does maltose influence on the elasticity of SOPC membrane?

NASA Astrophysics Data System (ADS)

Genova, J.; Zheliaskova, A.; Mitov, M. D.

2010-11-01

Thermally induced shape fluctuations of giant quasi-spherical lipid vesicles are used to study the influence of the disaccharide maltose, dissolved in the aqueous solution, on the curvature elasticity kc of a lipid membrane. The influence of the carbohydrate solute is investigated throughout a considerably wide interval of concentrations. The values of the bending elastic modulus for 200 mM and 400 mM of maltose in the water solution are obtained. The data for kc in presence of maltose is compared with previously obtained results for this constant for the most popular hydrocarbons: monosaccharides glucose and fructose and disaccharides sucrose and trehalose. It is shown that the presence of maltose, dissolved in the aqueous phase surrounding the membrane does not influence on the bending elasticity with the increase of its concentration in the aqueous solution. Up to our knowledge this is the first sugar that does not show decrease of the bending elastic modulus of the lipid membrane, when present in the water surrounding it in concentration up to 400mM.

The influence of passive-dynamic ankle-foot orthosis bending axis location on gait performance in individuals with lower-limb impairments.

PubMed

Ranz, Ellyn C; Russell Esposito, Elizabeth; Wilken, Jason M; Neptune, Richard R

2016-08-01

Passive-dynamic ankle-foot orthoses are commonly prescribed to augment impaired ankle muscle function, however their design and prescription are largely qualitative. One design includes a footplate and cuff, and flexible strut connecting the two. During gait, deflection occurs along the strut, with the greatest deflection at a central bending axis. The vertical location of the axis can affect lower extremity biomechanics. The goal of this study was to investigate the influence of bending axis location on gait performance. For thirteen participants with unilateral ankle muscle weakness, an additive manufacturing framework was used to fabricate passive-dynamic ankle-foot orthosis struts with central and off-center bending axes. Participants walked overground while electromyographic, kinetic and kinematic data were collected for three different bending axes: proximal (high), central (middle) and distal (low), and the participants indicated their order of bending axis preference after testing. Gait measures and preference effect sizes were examined during six regions of the gait cycle. A few differences between bending axes were observed: in the first double-leg support peak plantarflexion angle, peak dorsiflexion moment and positive hip work, in the early single-leg support peak knee extension moment and positive ankle and knee work, and in the late single-leg support gastrocnemius activity and vertical ground reaction force impulse. In addition, preference was strongly related to various gait measures. Despite the observed statistical differences, altering bending axis location did not produce large and consistent changes in gait performance. Thus, individual preference and comfort may be more important factors guiding prescription. Copyright © 2016 Elsevier Ltd. All rights reserved.

Curved bones: An adaptation to habitual loading.

PubMed

Milne, Nick

2016-10-21

Why are long bones curved? It has long been considered a paradox that many long bones supporting mammalian bodies are curved, since this curvature results in the bone undergoing greater bending, with higher strains and so greater fracture risk under load. This study develops a theoretical model wherein the curvature is a response to bending strains imposed by the requirements of locomotion. In particular the radioulna of obligate quadrupeds is a lever operated by the triceps muscle, and the bending strains induced by the triceps muscle counter the bending resulting from longitudinal loads acting on the curved bone. Indeed the theoretical model reverses this logic and suggests that the curvature is itself a response to the predictable bending strains induced by the triceps muscle. This, in turn, results in anatomical arrangements of bone, muscle and tendon that create a simple physiological mechanism whereby the bone can resist the bending due to the action of triceps in supporting and moving the body. The model is illustrated by contrasting the behaviour of a finite element model of a llama radioulna to that of a straightened version of the same bone. The results show that longitudinal and flexor muscle forces produce bending strains that effectively counter strains due to the pull of the triceps muscle in the curved but not in the straightened model. It is concluded that the curvature of these and other curved bones adds resilience to the skeleton by acting as pre-stressed beams or strainable pre-buckled struts. It is also proposed that the cranial bending strains that result from triceps, acting on the lever that is the radioulna, can explain the development of the curvature of such bones. Crown Copyright © 2016. Published by Elsevier Ltd. All rights reserved.

Angular measurements of the dynein ring reveal a stepping mechanism dependent on a flexible stalk

PubMed Central

Lippert, Lisa G.; Dadosh, Tali; Hadden, Jodi A.; Karnawat, Vishakha; Diroll, Benjamin T.; Murray, Christopher B.; Holzbaur, Erika L. F.; Schulten, Klaus; Reck-Peterson, Samara L.; Goldman, Yale E.

2017-01-01

The force-generating mechanism of dynein differs from the force-generating mechanisms of other cytoskeletal motors. To examine the structural dynamics of dynein’s stepping mechanism in real time, we used polarized total internal reflection fluorescence microscopy with nanometer accuracy localization to track the orientation and position of single motors. By measuring the polarized emission of individual quantum nanorods coupled to the dynein ring, we determined the angular position of the ring and found that it rotates relative to the microtubule (MT) while walking. Surprisingly, the observed rotations were small, averaging only 8.3°, and were only weakly correlated with steps. Measurements at two independent labeling positions on opposite sides of the ring showed similar small rotations. Our results are inconsistent with a classic power-stroke mechanism, and instead support a flexible stalk model in which interhead strain rotates the rings through bending and hinging of the stalk. Mechanical compliances of the stalk and hinge determined based on a 3.3-μs molecular dynamics simulation account for the degree of ring rotation observed experimentally. Together, these observations demonstrate that the stepping mechanism of dynein is fundamentally different from the stepping mechanisms of other well-studied MT motors, because it is characterized by constant small-scale fluctuations of a large but flexible structure fully consistent with the variable stepping pattern observed as dynein moves along the MT. PMID:28533393

Influence of bracket-slot design on the forces released by superelastic nickel-titanium alignment wires in different deflection configurations.

PubMed

Nucera, Riccardo; Gatto, Elda; Borsellino, Chiara; Aceto, Pasquale; Fabiano, Francesca; Matarese, Giovanni; Perillo, Letizia; Cordasco, Giancarlo

2014-05-01

To evaluate how different bracket-slot design characteristics affect the forces released by superelastic nickel-titanium (NiTi) alignment wires at different amounts of wire deflection. A three-bracket bending and a classic-three point bending testing apparatus were used to investigate the load-deflection properties of one superelastic 0.014-inch NiTi alignment wire in different experimental conditions. The selected NiTi archwire was tested in association with three bracket systems: (1) conventional twin brackets with a 0.018-inch slot, (2) a self-ligating bracket with a 0.018-inch slot, and (3) a self-ligating bracket with a 0.022-inch slot. Wire specimens were deflected at 2 mm and 4 mm. Use of a 0.018-inch slot bracket system, in comparison with use of a 0.022-inch system, increases the force exerted by the superelastic NiTi wires at a 2-mm deflection. Use of a self-ligating bracket system increases the force released by NiTi wires in comparison with the conventional ligated bracket system. NiTi wires deflected to a different maximum deflection (2 mm and 4 mm) release different forces at the same unloading data point (1.5 mm). Bracket design, type of experimental test, and amount of wire deflection significantly affected the amount of forces released by superelastic NiTi wires (P<.05). This phenomenon offers clinicians the possibility to manipulate the wire's load during alignment.

Does buckling instability of the pseudopodium limit how well an amoeba can climb?

PubMed

Ghosal, Sandip; Fukui, Yoshio

2011-02-21

The maximum force that a crawling cell can exert on a substrate is a quantity of interest in cell biomechanics. One way of quantifying this force is to allow the cell to crawl against a measurable and adjustable restraining force until the cell is no longer able to move in a direction opposite to the applied force. Fukui et al. (2000) reported on an experiment where amoeboid cells were imaged while they crawled against an artificial gravity field created by a centrifuge. An unexpected observation was that the net applied force on the amoeba did not seem to be the primary factor that limited its ability to climb. Instead, it appeared that the amoeba stalled when it was no longer able to support a pseudopodium against the applied gravity field. The high g-load bend the pseudopodium thereby preventing its attachment to the target point directly ahead of the cell. In this paper we further refine this idea by identifying the bending of the pseudopodium with the onset of elastic instability of a beam under its own weight. It is shown that the principal features of the experiment may be understood through this model and an estimate for the limiting g-load in reasonable accord with the experimental measurements is recovered. Copyright © 2010 Elsevier Ltd. All rights reserved.

The Comfortable Roller Coaster--on the Shape of Tracks with a Constant Normal Force

ERIC Educational Resources Information Center

Nordmark, Arne B.; Essen, Hanno

2010-01-01

A particle that moves along a smooth track in a vertical plane is influenced by two forces: gravity and normal force. The force experienced by roller coaster riders is the normal force, so a natural question to ask is, what shape of the track gives a normal force of constant magnitude? Here we solve this problem. It turns out that the solution is…

A novel constant-force scanning probe incorporating mechanical-magnetic coupled structures.

PubMed

Wang, Hongxi; Zhao, Jian; Gao, Renjing; Yang, Yintang

2011-07-01

A one-dimensional scanning probe with constant measuring force is designed and fabricated by utilizing the negative stiffness of the magnetic coupled structure, which mainly consists of the magnetic structure, the parallel guidance mechanism, and the pre-stressed spring. Based on the theory of material mechanics and the equivalent surface current model for computing the magnetic force, the analytical model of the scanning probe subjected to multi-forces is established, and the nonlinear relationship between the measuring force and the probe displacement is obtained. The practicability of introducing magnetic coupled structure in the constant-force probe is validated by the consistency of the results in numerical simulation and experiments.

Phonons in random alloys: The itinerant coherent-potential approximation

NASA Astrophysics Data System (ADS)

Ghosh, Subhradip; Leath, P. L.; Cohen, Morrel H.

2002-12-01

We present the itinerant coherent-potential approximation (ICPA), an analytic, translationally invariant, and tractable form of augmented-space-based multiple-scattering theory18 in a single-site approximation for harmonic phonons in realistic random binary alloys with mass and force-constant disorder. We provide expressions for quantities needed for comparison with experimental structure factors such as partial and average spectral functions and derive the sum rules associated with them. Numerical results are presented for Ni55Pd45 and Ni50Pt50 alloys which serve as test cases, the former for weak force-constant disorder and the latter for strong. We present results on dispersion curves and disorder-induced widths. Direct comparisons with the single-site coherent potential approximation (CPA) and experiment are made which provide insight into the physics of force-constant changes in random alloys. The CPA accounts well for the weak force-constant disorder case but fails for strong force-constant disorder where the ICPA succeeds.

The effects of rigid motions on elastic network model force constants

PubMed Central

Lezon, Timothy R.

2012-01-01

Elastic network models provide an efficient way to quickly calculate protein global dynamics from experimentally determined structures. The model’s single parameter, its force constant, determines the physical extent of equilibrium fluctuations. The values of force constants can be calculated by fitting to experimental data, but the results depend on the type of experimental data used. Here we investigate the differences between calculated values of force constants _t to data from NMR and X-ray structures. We find that X-ray B factors carry the signature of rigid-body motions, to the extent that B factors can be almost entirely accounted for by rigid motions alone. When fitting to more refined anisotropic temperature factors, the contributions of rigid motions are significantly reduced, indicating that the large contribution of rigid motions to B factors is a result of over-fitting. No correlation is found between force constants fit to NMR data and those fit to X-ray data, possibly due to the inability of NMR data to accurately capture protein dynamics. PMID:22228562

Determination of the force constant of a single-beam gradient trap by measurement of backscattered light

NASA Astrophysics Data System (ADS)

Friese, M. E. J.; Rubinsztein-Dunlop, H.; Heckenberg, N. R.; Dearden, E. W.

1996-12-01

A single-beam gradient trap could potentially be used to hold a stylus for scanning force microscopy. With a view to development of this technique, we modeled the optical trap as a harmonic oscillator and therefore characterized it by its force constant. We measured force constants and resonant frequencies for 1 4- m-diameter polystyrene spheres in a single-beam gradient trap using measurements of backscattered light. Force constants were determined with both Gaussian and doughnut laser modes, with powers of 3 and 1 mW, respectively. Typical values for spring constants were measured to be between 10 6 and 4 10 6 N m. The resonant frequencies of trapped particles were measured to be between 1 and 10 kHz, and the rms amplitudes of oscillations were estimated to be around 40 nm. Our results confirm that the use of the doughnut mode for single-beam trapping is more efficient in the axial direction.

Experimental comparison of forces resisting viral DNA packaging and driving DNA ejection

PubMed Central

Keller, Nicholas; Berndsen, Zachary T.; Jardine, Paul J.; Smith, Douglas E.

2018-01-01

We compare forces resisting DNA packaging in bacteriophage phi29 inferred from optical tweezers studies with forces driving DNA ejection inferred from osmotic pressure studies. Ejection forces from 0–80% filling are consistent with a model that assumes a repulsive DNA-DNA interaction potential derived from DNA condensation studies and predicts an inverse spool DNA conformation. Forces resisting packaging from ~80–100% filling are also consistent with this model. However, that electron microscopy does not reveal a spool conformation suggests that this model overestimates bending rigidity and underestimates repulsion. Below 80% filling, inferred ejection forces are higher than those resisting packaging. Although unexpected, this suggests that most force that builds during packaging is available to drive DNA ejection. PMID:28618627

Rotational spectrum of CH3CN⋯ClF and evidence for the +I effect of a CH3 group on the ‘chlorine’ bond N⋯ClF

NASA Astrophysics Data System (ADS)

Page, M. D.; Waclawik, E. R.; Holloway, J. H.; Legon, A. C.

1999-10-01

The ground-state rotational spectra of the isotopomers CH 3C 14N⋯ 35ClF, CH 3C 14N⋯ 37ClF, CD 3C 14N⋯ 35ClF and CH 3C 15N⋯ 35ClF of a symmetric-rotor complex formed by methyl cyanide and chlorine monofluoride have been observed and analysed to give the spectroscopic constants B0, DJ, DJK, χaa( 14N), χaa(Cl) and Mbb. Interpretations of these quantities on the basis of simple models enabled the geometry and strength of binding of the complex to be determined. It is found that the atoms C-CN⋯ClF lie on the C 3 axis of this complex of C 3v symmetry and that the distance r(N⋯Cl)=2.561(2) Å. The quadratic force constants associated with the intermolecular stretching mode and with the bending motion of the CH 3CN subunit pivoted at its mass centre were determined from the centrifugal distortion constants DJ and 2 DJ+ DJK. Their values were k σ=13.9(3) N m -1 and k α=3.0(1)×10 -20 J rad -2, respectively. A comparison of r(N⋯Cl) values and of k σ values establishes that the +I effect of the CH 3 group when it replaces H in HCN leads to a similar shortening of r(N⋯Cl) and to a similar increase in k σ in the two series RCN⋯ClF and RCN⋯HCl (R=H or CH 3).

Measurement of the elastic modulus of spider mite silk fibers using atomic force microscopy

NASA Astrophysics Data System (ADS)

Hudson, Stephen D.; Zhurov, Vladimir; Grbić, Vojislava; Grbić, Miodrag; Hutter, Jeffrey L.

2013-04-01

Bio-nanomaterials are one of the fastest developing sectors of industry and technology. Spider silk, a highly attractive light-weight biomaterial, has high tensile strength and elasticity and is compatible with human tissues, allowing for many areas of application. In comparison to spider silk fibers with diameters of several micrometers, spider mite silk fibers have much smaller diameters of tens of nanometers, making conventional tensile testing methods impractical. To determine the mechanical properties of adult and larval Tetranychus urticae silk fibers, we have performed three-point bending tests with an atomic force microscope. We found that because of the small diameters of these fibers, axial tension—due to both the applied force and a pre-existing strain—has a significant effect on the fiber response, even in the small-deformation limit. As a result, the typical Euler-Bernoulli-Timoshenko theory cannot be applied. We therefore follow the approach of Heidelberg et al. to develop a mechanical model of the fiber response that accounts for bending, an initial tension in the fibers, and a tension due to elongation during testing. This model provides self-consistent results, allowing us to determine that adult and larval fibers have Young's moduli of 24±3 GPa and 15±3 GPa, respectively. Both adult and larval fibers have an estimated ultimate strength of 200-300 MPa and a toughness of order 9 MJ/m3. We note that with increasing interest in the mechanical properties of very high aspect ratio nanomaterials, the influence of pre-existing tension must be considered in any measurements involving a bending test.

Friction behavior and other material properties of nickel-titanium and titanium-molybdenum archwires following electrochemical surface refinement.

PubMed

Meier, Miriam Julia; Bourauel, Christoph; Roehlike, Jan; Reimann, Susanne; Keilig, Ludger; Braumann, Bert

2014-07-01

The aim of this work was to investigate whether electrochemical surface treatment of nickel-titanium (NiTi) and titanium-molybdenum (TiMo) archwires (OptoTherm and BetaTitan; Ortho-Dent Specials, Kisdorf, Germany) reduces friction inside the bracket-archwire complex. We also evaluated further material properties and compared these to untreated wires. The material properties of the surface-treated wires (Optotherm/LoFrix and BetaTitan/LoFrix) were compared to untreated wires made by the same manufacturer (see above) and by another manufacturer (Neo Sentalloy; GAC, Bohemia, NY, USA). We carried out a three-point bending test, leveling test, and friction test using an orthodontic measurement and simulation system (OMSS). In addition, a pure bending test was conducted at a special test station, and scanning electron micrographs were obtained to analyze the various wire types for surface characteristics. Finally, edge beveling and cross-sectional dimensions were assessed. Force losses due to friction were reduced by 10 percentage points (from 36 to 26%) in the NiTi and by 12 percentage points (from 59 to 47%) in the TiMo wire specimens. Most of the other material properties exhibited no significant changes after surface treatment. While the three-point bending tests revealed mildly reduced force levels in the TiMo specimens due to diameter losses of roughly 2%, these force levels remained almost unchanged in the NiTi specimens. Compared to untreated NiTi and TiMo archwire specimens, the surface-treated specimens demonstrated reductions in friction loss by 10 and 12 percentage points, respectively.

Fully Suspended, Five-Axis, Three-Magnetic-Bearing Dynamic Spin Rig With Forced Excitation

NASA Technical Reports Server (NTRS)

Morrison, Carlos R.; Provenza, Andrew; Kurkov, Anatole; Montague, Gerald; Duffy, Kirsten; Mehmed, Oral; Johnson, Dexter; Jansen, Ralph

2004-01-01

The Five-Axis, Three-Magnetic-Bearing Dynamic Spin Rig, a significant advancement in the Dynamic Spin Rig (DSR), is used to perform vibration tests of turbomachinery blades and components under rotating and nonrotating conditions in a vacuum. The rig has as its critical components three magnetic bearings: two heteropolar radial active magnetic bearings and a magnetic thrust bearing. The bearing configuration allows full vertical rotor magnetic suspension along with a feed-forward control feature, which will enable the excitation of various natural blade modes in bladed disk test articles. The theoretical, mechanical, electrical, and electronic aspects of the rig are discussed. Also presented are the forced-excitation results of a fully levitated, rotating and nonrotating, unbladed rotor and a fully levitated, rotating and nonrotating, bladed rotor in which a pair of blades was arranged 180 degrees apart from each other. These tests include the bounce mode excitation of the rotor in which the rotor was excited at the blade natural frequency of 144 Hz. The rotor natural mode frequency of 355 Hz was discerned from the plot of acceleration versus frequency. For nonrotating blades, a blade-tip excitation amplitude of approximately 100 g/A was achieved at the first-bending critical (approximately 144 Hz) and at the first-torsional and second-bending blade modes. A blade-tip displacement of 70 mils was achieved at the first-bending critical by exciting the blades at a forced-excitation phase angle of 908 relative to the vertical plane containing the blades while simultaneously rotating the shaft at 3000 rpm.

Injury tolerance and moment response of the knee joint to combined valgus bending and shear loading.

PubMed

Bose, Dipan; Bhalla, Kavi S; Untaroiu, Costin D; Ivarsson, B Johan; Crandall, Jeff R; Hurwitz, Shepard

2008-06-01

Valgus bending and shearing of the knee have been identified as primary mechanisms of injuries in a lateral loading environment applicable to pedestrian-car collisions. Previous studies have reported on the structural response of the knee joint to pure valgus bending and lateral shearing, as well as the estimated injury thresholds for the knee bending angle and shear displacement based on experimental tests. However, epidemiological studies indicate that most knee injuries are due to the combined effects of bending and shear loading. Therefore, characterization of knee stiffness for combined loading and the associated injury tolerances is necessary for developing vehicle countermeasures to mitigate pedestrian injuries. Isolated knee joint specimens (n=40) from postmortem human subjects were tested in valgus bending at a loading rate representative of a pedestrian-car impact. The effect of lateral shear force combined with the bending moment on the stiffness response and the injury tolerances of the knee was concurrently evaluated. In addition to the knee moment-angle response, the bending angle and shear displacement corresponding to the first instance of primary ligament failure were determined in each test. The failure displacements were subsequently used to estimate an injury threshold function based on a simplified analytical model of the knee. The validity of the determined injury threshold function was subsequently verified using a finite element model. Post-test necropsy of the knees indicated medial collateral ligament injury consistent with the clinical injuries observed in pedestrian victims. The moment-angle response in valgus bending was determined at quasistatic and dynamic loading rates and compared to previously published test data. The peak bending moment values scaled to an average adult male showed no significant change with variation in the superimposed shear load. An injury threshold function for the knee in terms of bending angle and shear displacement was determined by performing regression analysis on the experimental data. The threshold values of the bending angle (16.2 deg) and shear displacement (25.2 mm) estimated from the injury threshold function were in agreement with previously published knee injury threshold data. The continuous knee injury function expressed in terms of bending angle and shear displacement enabled injury prediction for combined loading conditions such as those observed in pedestrian-car collisions.

Needle puncture in rabbit functional spinal units alters rotational biomechanics.

PubMed

Hartman, Robert A; Bell, Kevin M; Quan, Bichun; Nuzhao, Yao; Sowa, Gwendolyn A; Kang, James D

2015-04-01

An in vitro biomechanical study for rabbit lumbar functional spinal units (FSUs) using a robot-based spine testing system. To elucidate the effect of annular puncture with a 16 G needle on mechanical properties in flexion/extension, axial rotation, and lateral bending. Needle puncture of the intervertebral disk has been shown to alter mechanical properties of the disk in compression, torsion, and bending. The effect of needle puncture in FSUs, where intact spinal ligaments and facet joints may mitigate or amplify these changes in the disk, on spinal motion segment stability subject to physiological rotations remains unknown. Rabbit FSUs were tested using a robot testing system whose force/moment and position precision were assessed to demonstrate system capability. Flexibility testing methods were developed by load-to-failure testing in flexion/extension, axial rotation, and lateral bending. Subsequent testing methods were used to examine a 16 G needle disk puncture and No. 11 blade disk stab (positive control for mechanical disruption). Flexibility testing was used to assess segmental range-of-motion (degrees), neutral zone stiffness (N m/degrees) and width (degrees and N m), and elastic zone stiffness before and after annular injury. The robot-based system was capable of performing flexibility testing on FSUs-mean precision of force/moment measurements and robot system movements were <3% and 1%, respectively, of moment-rotation target values. Flexibility moment targets were 0.3 N m for flexion and axial rotation and 0.15 N m for extension and lateral bending. Needle puncture caused significant (P<0.05) changes only in flexion/extension range-of-motion and neutral zone stiffness and width (N m) compared with preintervention. No. 11 blade-stab significantly increased range-of-motion in all motions, decreased neutral zone stiffness and width (N m) in flexion/extension, and increased elastic zone stiffness in flexion and lateral bending. These findings suggest that disk puncture and stab can destabilize FSUs in primary rotations.

Changes in Mechanical Properties of Rat Bones under Simulated Effects of Microgravity and Radiation†

NASA Astrophysics Data System (ADS)

Walker, Azida H.; Perkins, Otis; Mehta, Rahul; Ali, Nawab; Dobretsov, Maxim; Chowdhury, Parimal

The aim of this study was to determine the changes in elasticity and lattice structure in leg bone of rats which were: 1) under Hind-Limb Suspension (HLS) by tail for 2 weeks and 2) exposed to a total radiation of 10 Grays in 10 days. The animals were sacrificed at the end of 2 weeks and the leg bones were surgically removed, cleaned and fixed with a buffered solution. The mechanical strength of the bone (elastic modulus) was determined from measurement of bending of a bone when under an applied force. Two methodologies were used: i) a 3-point bending technique and ii) classical bending where bending is accomplished keeping one end fixed. Three point bending method used a captive actuator controlled by a programmable IDEA drive. This allowed incremental steps of 0.047 mm for which the force is measured. The data is used to calculate the stress and the strain. In the second method a mirror attached to the free end of the bone allowed a reflected laser beam spot to be tracked. This provided the displacement measurement as stress levels changed. Analysis of stress vs. strain graph together with solution of Euler-Bernoulli equation for a cantilever beam allowed determination of the elastic modulus of the leg bone for (i) control samples, (ii) HLS samples and (iii) HLS samples with radiation effects. To ascertain changes in the bone lattice structure, the bones were cross-sectioned and imaged with a 20 keV beam of electrons in a Scanning Electron Microscope (SEM). A backscattered detector and a secondary electron detector in the SEM provided the images from well-defined parts of the leg bones. Elemental compositions in combination with mechanical properties (elastic modulus and lattice structure) changes indicated weakening of the bones under space-like conditions of microgravity and radiation.

Softened and flexible biodegradable poly(lactic acid) and its electromechanical properties for actuator application.

PubMed

Thummarungsan, Natlita; Pattavarakorn, Datchanee; Sirivat, Anuvat

2016-12-01

Poly (lactic acid) (PLA) is a biodegradable polymer with high stiffness presenting a limitation for using in actuator applications. Adding a plasticizer is one way to solve this problem to enhance flexibility and improve electromechanical properties of pristine PLA. In this work, the PLA films were prepared via a simple solvent casting method. The influences of plasticizer type and electric field strength on electromechanical behavior of PLA films were investigated by the melt rheometer and bending measurement. For the PLA films filled with dibutyl phthalate (DBP), the storage modulus, G', immediately increased towards its steady state and rapidly recovered to its original value with and without electric field, respectively, which can be referred to a reversible system. On the other hand, the PLA film with Tween 20 processed the highest ∆G׳/G׳0 of 1.34 due to the available amount of polarized groups. In the bending measurement, the dielectrophoresis forces of plasticized PLA films were found to increase with increasing electric field where the deflections occurred towards anode side as the polarized groups generated negative charges. The DBP_PLA1.5D film exhibited the greatest bending and dielectrophoresis force. Thus, the biodegradable PLA along with DBP combine to have a great potential towards actuator application. Copyright © 2016 Elsevier Ltd. All rights reserved.

Experimental validation of more realistic computer models for stent-graft repair of abdominal aortic aneurysms, including pre-load assessment.

PubMed

Roy, David; Lerouge, Sophie; Inaekyan, Karina; Kauffmann, Claude; Mongrain, Rosaire; Soulez, Gilles

2016-12-01

Although the endovascular repair of abdominal aortic aneurysms is a less invasive alternative than classic open surgery, complications such as endoleak and kinking still need to be addressed. Numerical simulation of endovascular repair is becoming a valuable tool in stent-graft (SG) optimization, patient selection and surgical planning. The experimental and numerical forces required to produce SG deformations were compared in a range of in vivo conditions in the present study. The deformation modes investigated were: bending as well as axial, transversal and radial compressions. In particular, an original method was developed to efficiently account for radial pre-load because of the pre-compression of stents to match the graft dimensions during manufacturing. This is important in order to compute the radial force exerted on the vessel after deployment more accurately. Variations of displacement between the experimental and numerical results ranged from 1.39% for simple leg bending to 5.93% for three-point body bending. Finally, radial pre-load was modeled by increasing Young's modulus of each stent. On average, it was found that Young's modulus had to be augmented by a factor of 2. Copyright © 2016 John Wiley & Sons, Ltd. Copyright © 2016 John Wiley & Sons, Ltd.

A Biomechanical Analysis of 2 Constructs for Metacarpal Spiral Fracture Fixation in a Cadaver Model: 2 Large Screws Versus 3 Small Screws.

PubMed

Eu-Jin Cheah, Andre; Behn, Anthony W; Comer, Garet; Yao, Jeffrey

2017-12-01

Surgeons confronted with a long spiral metacarpal fracture may choose to fix it solely with lagged screws. A biomechanical analysis of a metacarpal spiral fracture model was performed to determine whether 3 1.5-mm screws or 2 2.0-mm screws provided more stability during bending and torsional loading. Second and third metacarpals were harvested from 12 matched pairs of fresh-frozen cadaveric hands and spiral fractures were created. One specimen from each matched pair was fixed with 2 2.0-mm lagged screws whereas the other was fixed with 3 1.5-mm lagged screws. Nine pairs underwent combined cyclic cantilever bending and axial compressive loading followed by loading to failure. Nine additional pairs were subjected to cyclic external rotation while under a constant axial compressive load and were subsequently externally rotated to failure under a constant axial compressive load. Paired t tests were used to compare cyclic creep, stiffness, displacement, rotation, and peak load levels. Average failure torque for all specimens was 7.2 ± 1.7 Nm. In cyclic torsional testing, the group with 2 screws exhibited significantly less rotational creep than the one with 3 screws. A single specimen in the group with 2 screws failed before cyclic bending tests were completed. No other significant differences were found between test groups during torsional or bending tests. Both constructs were biomechanically similar except that the construct with 2 screws displayed significantly less loosening during torsional cyclic loading, although the difference was small and may not be clinically meaningful. Because we found no obvious biomechanical advantage to using 3 1.5-mm lagged screws to fix long spiral metacarpal fractures, the time efficiency and decreased implant costs of using 2-2.0 mm lagged screws may be preferred. Copyright © 2017 American Society for Surgery of the Hand. Published by Elsevier Inc. All rights reserved.

An engineering method for estimating notch-size effect in fatigue tests on steel

NASA Technical Reports Server (NTRS)

Kuhn, Paul; Hardrath, Herbert F

1952-01-01

Neuber's proposed method of calculating a practical factor of stress concentration for parts containing notches of arbitrary size depends on the knowledge of a "new material constant" which can be established only indirectly. In this paper, the new constant has been evaluated for a large variety of steels from fatigue tests reported in the literature, attention being confined to stresses near the endurance limit. Reasonably satisfactory results were obtained with the assumption that the constant depends only on the tensile strength of the steel. Even in cases where the notches were cracks of which only the depth was known, reasonably satisfactory agreement was found between calculated and experimental factors. It is also shown that the material constant can be used in an empirical formula to estimate the size effect on unnotched specimens tested in bending fatigue.

Tribologic analyses of a self-mated aluminium contact used for overhead transmission lines

NASA Astrophysics Data System (ADS)

Steier, V. Franco

2017-05-01

The lifetime of aluminium components is often limited to their poor wear resistance. One example for such aluminium applications are overhead transmission lines. The sore points of these lines are the segments where the aluminium conductors are fixed to the line supports. The fixation is commonly realized via aluminium suspension clamps. Here, a superposition of different loads like traction and bending stresses, clamping forces and different types of wear occurs. To investigate the wear behaviour in these peculiar points, tribologic model tests were carried out. Within the tests, overhead conductor wires and aluminium plates, extracted from suspension clamps were reciprocally slid against aluminium plates (cylinder-on-plate test). The COF and a wear related parameter were recorded constantly. Subsequently, the loaded surfaces were analysed using confocal laser and electron scanning microscopy as well as energy dispersive X-ray spectroscopy. The investigation detected the formation of an oxidized tribologic layer between both components. The tribolayer, which mayor part adhered on the suspension clamps, was mostly formed from material removed from the conductor wires.

Numerical study of interfacial solitary waves propagating under an elastic sheet

PubMed Central

Wang, Zhan; Părău, Emilian I.; Milewski, Paul A.; Vanden-Broeck, Jean-Marc

2014-01-01

Steady solitary and generalized solitary waves of a two-fluid problem where the upper layer is under a flexible elastic sheet are considered as a model for internal waves under an ice-covered ocean. The fluid consists of two layers of constant densities, separated by an interface. The elastic sheet resists bending forces and is mathematically described by a fully nonlinear thin shell model. Fully localized solitary waves are computed via a boundary integral method. Progression along the various branches of solutions shows that barotropic (i.e. surface modes) wave-packet solitary wave branches end with the free surface approaching the interface. On the other hand, the limiting configurations of long baroclinic (i.e. internal) solitary waves are characterized by an infinite broadening in the horizontal direction. Baroclinic wave-packet modes also exist for a large range of amplitudes and generalized solitary waves are computed in a case of a long internal mode in resonance with surface modes. In contrast to the pure gravity case (i.e without an elastic cover), these generalized solitary waves exhibit new Wilton-ripple-like periodic trains in the far field. PMID:25104909

Analysis of the stress-strain state in single overlap joints using piezo-ceramic actuators

NASA Astrophysics Data System (ADS)

Pǎltânea, Veronica; Pǎltânea, Gheorghe; Popovici, Dorina; Jiga, Gabriel; Papanicolaou, George

2014-05-01

In this paper is presented a 2D approach to finite element modeling and an analytical calculus of a single lap bonded joint. As adherent material were selected a sheet of wood, aluminum and titanium. For adhesive part were selected Bison Super Wood D3 in case of the wood single lap joint and an epoxy resin type DGEBA-TETA for gluing together aluminum and titanium parts. In the article is described a combined method, which consists in the placement of the piezoelectric actuator inside of the adhesive part, in order to determine the tensile stress in the overlap joint. A comparison between the analytical and numerical results has been achieved through a multiphysics modeling - electrical and mechanical coupled problem. The technique used to calculate the mechanical parameters (First Principal Stress, displacements) was the three-point bending test, where different forces were applied in the mid-span of the structure, in order to maintain a constant displacement rate. The length of the overlap joint was modified from 20 to 50 mm.

Series Pneumatic Artificial Muscles (sPAMs) and Application to a Soft Continuum Robot.

PubMed

Greer, Joseph D; Morimoto, Tania K; Okamura, Allison M; Hawkes, Elliot W

2017-01-01

We describe a new series pneumatic artificial muscle (sPAM) and its application as an actuator for a soft continuum robot. The robot consists of three sPAMs arranged radially round a tubular pneumatic backbone. Analogous to tendons, the sPAMs exert a tension force on the robot's pneumatic backbone, causing bending that is approximately constant curvature. Unlike a traditional tendon driven continuum robot, the robot is entirely soft and contains no hard components, making it safer for human interaction. Models of both the sPAM and soft continuum robot kinematics are presented and experimentally verified. We found a mean position accuracy of 5.5 cm for predicting the end-effector position of a 42 cm long robot with the kinematic model. Finally, closed-loop control is demonstrated using an eye-in-hand visual servo control law which provides a simple interface for operation by a human. The soft continuum robot with closed-loop control was found to have a step-response rise time and settling time of less than two seconds.

Series Pneumatic Artificial Muscles (sPAMs) and Application to a Soft Continuum Robot

PubMed Central

Greer, Joseph D.; Morimoto, Tania K.; Okamura, Allison M.; Hawkes, Elliot W.

2017-01-01

We describe a new series pneumatic artificial muscle (sPAM) and its application as an actuator for a soft continuum robot. The robot consists of three sPAMs arranged radially round a tubular pneumatic backbone. Analogous to tendons, the sPAMs exert a tension force on the robot’s pneumatic backbone, causing bending that is approximately constant curvature. Unlike a traditional tendon driven continuum robot, the robot is entirely soft and contains no hard components, making it safer for human interaction. Models of both the sPAM and soft continuum robot kinematics are presented and experimentally verified. We found a mean position accuracy of 5.5 cm for predicting the end-effector position of a 42 cm long robot with the kinematic model. Finally, closed-loop control is demonstrated using an eye-in-hand visual servo control law which provides a simple interface for operation by a human. The soft continuum robot with closed-loop control was found to have a step-response rise time and settling time of less than two seconds. PMID:29379672

Stiffness and ultimate load of osseointegrated prosthesis fixations in the upper and lower extremity.

PubMed

Welke, Bastian; Hurschler, Christof; Föller, Marie; Schwarze, Michael; Calliess, Tilman

2013-07-11

Techniques for the skeletal attachment of amputation-prostheses have been developed over recent decades. This type of attachment has only been performed on a small number of patients. It poses various potential advantages compared to conventional treatment with a socket, but is also associated with an increased risk of bone or implant-bone interface fracture in the case of a fall. We therefore investigated the bending stiffness and ultimate bending moment of such devices implanted in human and synthetic bones. Eight human specimens and 16 synthetic models of the proximal femora were implanted with lower extremity prostheses and eight human specimens and six synthetic humeri were implanted with upper extremity prostheses. They were dissected according to typical amputation levels and underwent loading in a material testing machine in a four-point bending setup. Bending stiffness, ultimate bending moment and fracture modes were determined in a load to failure experiment. Additionally, axial pull-out was performed on eight synthetic specimens of the lower extremity. Maximum bending moment of the synthetic femora was 160.6±27.5 Nm, the flexural rigidity of the synthetic femora was 189.0±22.6 Nm2. Maximum bending moment of the human femora was 100.4±38.5 Nm, and the flexural rigidity was 137.8±29.4 Nm2. The maximum bending moment of the six synthetic humeri was 104.9±19.0 Nm, and the flexural rigidity was 63.7±3.6 Nm2. For the human humeri the maximum bending moment was 36.7±11.0 Nm, and the flexural rigidity at was 43.7±10.5 Nm2. The maximum pull-out force for the eight synthetic femora was 3571±919 N. Significant differences were found between human and synthetic specimens of the lower and upper extremity regarding maximum bending moment, bending displacement and flexural rigidity. The results of this study are relevant with respect to previous finding regarding the load at the interfaces of osseointegrated prosthesis fixation devices and are crucial for the development of safety devices intended to protect the bone-implant interface from damaging loadings.

Stiffness and ultimate load of osseointegrated prosthesis fixations in the upper and lower extremity

PubMed Central

2013-01-01

Background Techniques for the skeletal attachment of amputation-prostheses have been developed over recent decades. This type of attachment has only been performed on a small number of patients. It poses various potential advantages compared to conventional treatment with a socket, but is also associated with an increased risk of bone or implant-bone interface fracture in the case of a fall. We therefore investigated the bending stiffness and ultimate bending moment of such devices implanted in human and synthetic bones. Methods Eight human specimens and 16 synthetic models of the proximal femora were implanted with lower extremity prostheses and eight human specimens and six synthetic humeri were implanted with upper extremity prostheses. They were dissected according to typical amputation levels and underwent loading in a material testing machine in a four-point bending setup. Bending stiffness, ultimate bending moment and fracture modes were determined in a load to failure experiment. Additionally, axial pull-out was performed on eight synthetic specimens of the lower extremity. Results Maximum bending moment of the synthetic femora was 160.6±27.5 Nm, the flexural rigidity of the synthetic femora was 189.0±22.6 Nm2. Maximum bending moment of the human femora was 100.4±38.5 Nm, and the flexural rigidity was 137.8±29.4 Nm2. The maximum bending moment of the six synthetic humeri was 104.9±19.0 Nm, and the flexural rigidity was 63.7±3.6 Nm2. For the human humeri the maximum bending moment was 36.7±11.0 Nm, and the flexural rigidity at was 43.7±10.5 Nm2. The maximum pull-out force for the eight synthetic femora was 3571±919 N. Conclusion Significant differences were found between human and synthetic specimens of the lower and upper extremity regarding maximum bending moment, bending displacement and flexural rigidity. The results of this study are relevant with respect to previous finding regarding the load at the interfaces of osseointegrated prosthesis fixation devices and are crucial for the development of safety devices intended to protect the bone-implant interface from damaging loadings. PMID:23844992

Quantitative comparison of two independent lateral force calibration techniques for the atomic force microscope.

PubMed

Barkley, Sarice S; Deng, Zhao; Gates, Richard S; Reitsma, Mark G; Cannara, Rachel J

2012-02-01

Two independent lateral-force calibration methods for the atomic force microscope (AFM)--the hammerhead (HH) technique and the diamagnetic lateral force calibrator (D-LFC)--are systematically compared and found to agree to within 5 % or less, but with precision limited to about 15 %, using four different tee-shaped HH reference probes. The limitations of each method, both of which offer independent yet feasible paths toward traceable accuracy, are discussed and investigated. We find that stiff cantilevers may produce inconsistent D-LFC values through the application of excessively high normal loads. In addition, D-LFC results vary when the method is implemented using different modes of AFM feedback control, constant height and constant force modes, where the latter is more consistent with the HH method and closer to typical experimental conditions. Specifically, for the D-LFC apparatus used here, calibration in constant height mode introduced errors up to 14 %. In constant force mode using a relatively stiff cantilever, we observed an ≈ 4 % systematic error per μN of applied load for loads ≤ 1 μN. The issue of excessive load typically emerges for cantilevers whose flexural spring constant is large compared with the normal spring constant of the D-LFC setup (such that relatively small cantilever flexural displacements produce relatively large loads). Overall, the HH method carries a larger uncertainty, which is dominated by uncertainty in measurement of the flexural spring constant of the HH cantilever as well as in the effective length dimension of the cantilever probe. The D-LFC method relies on fewer parameters and thus has fewer uncertainties associated with it. We thus show that it is the preferred method of the two, as long as care is taken to perform the calibration in constant force mode with low applied loads.

Spring constant measurement using a MEMS force and displacement sensor utilizing paralleled piezoresistive cantilevers

NASA Astrophysics Data System (ADS)

Kohyama, Sumihiro; Takahashi, Hidetoshi; Yoshida, Satoru; Onoe, Hiroaki; Hirayama-Shoji, Kayoko; Tsukagoshi, Takuya; Takahata, Tomoyuki; Shimoyama, Isao

2018-04-01

This paper reports on a method to measure a spring constant on site using a micro electro mechanical systems (MEMS) force and displacement sensor. The proposed sensor consists of a force-sensing cantilever and a displacement-sensing cantilever. Each cantilever is composed of two beams with a piezoresistor on the sidewall for measuring the in-plane lateral directional force and displacement. The force resolution and displacement resolution of the fabricated sensor were less than 0.8 µN and 0.1 µm, respectively. We measured the spring constants of two types of hydrogel microparticles to demonstrate the effectiveness of the proposed sensor, with values of approximately 4.3 N m-1 and 15.1 N m-1 obtained. The results indicated that the proposed sensor is effective for on-site spring constant measurement.

Larger-Stroke Piezoelectrically Actuated Microvalve

NASA Technical Reports Server (NTRS)

Yang, Eui-Hyeok

2003-01-01

A proposed normally-closed microvalve would contain a piezoelectric bending actuator instead of a piezoelectric linear actuator like that of the microvalve described in the preceding article. Whereas the stroke of the linear actuator of the preceding article would be limited to approximately equal to 6 micrometers, the stroke of the proposed bending actuator would lie in the approximate range of 10 to 15 micrometers-large enough to enable the microvalve to handle a variety of liquids containing suspended particles having sizes up to 10 m. Such particulate-laden liquids occur in a variety of microfluidic systems, one example being a system that sorts cells or large biomolecules for analysis. In comparison with the linear actuator of the preceding article, the bending actuator would be smaller and less massive. The combination of increased stroke, smaller mass, and smaller volume would be obtained at the cost of decreased actuation force: The proposed actuator would generate a force in the approximate range of 1 to 4 N, the exact amount depending on operating conditions and details of design. This level of actuation force would be too low to enable the valve to handle a fluid at the high pressure level mentioned in the preceding article. The proposal encompasses two alternative designs one featuring a miniature piezoelectric bimorph actuator and one featuring a thick-film unimorph piezoelectric actuator (see figure). In either version, the valve would consume a power of only 0.01 W when actuated at a frequency of 100 Hz. Also, in either version, it would be necessary to attach a soft elastomeric sealing ring to the valve seat so that any particles that settle on the seat would be pushed deep into the elastomeric material to prevent or reduce leakage. The overall dimensions of the bimorph version would be 7 by 7 by 1 mm. The actuator in this version would generate a force of 1 N and a stroke of 10 m at an applied potential of 150 V. The actuation force would be sufficient to enable the valve to handle a fluid pressurized up to about 50 psi (approximately equal to 0.35 MPa). The overall dimensions of the unimorph version would be 2 by 2 by 0.5 mm. In this version, an electric field across the piezoelectric film on a diaphragm would cause the film to pull on, and thereby bend, the diaphragm. At an applied potential of 20 V, the actuator in this version would generate a stroke of 10 micrometers and a force of 0.01 N. This force level would be too low to enable handling of fluids at pressures comparable to those of the bimorph version. This version would be useful primarily in microfluidic and nanofluidic applications that involve extremely low differential pressures and in which there are requirements for extreme miniaturization of valves. Examples of such applications include liquid chromatography and sequencing of deoxyribonucleic acid.

Finite element modeling of superelastic nickel-titanium orthodontic wires.

PubMed

Naceur, Ines Ben; Charfi, Amin; Bouraoui, Tarak; Elleuch, Khaled

2014-11-28

Thanks to its good corrosion resistance and biocompatibility, superelastic Ni–Ti wire alloys have been successfully used in orthodontic treatment. Therefore, it is important to quantify and evaluate the level of orthodontic force applied to the bracket and teeth in order to achieve tooth movement. In this study, three dimensional finite element models with a Gibbs-potential-based-formulation and thermodynamic principles were used. The aim was to evaluate the influence of possible intraoral temperature differences on the forces exerted by NiTi orthodontic arch wires with different cross sectional shapes and sizes. The prediction made by this phenomenological model, for superelastic tensile and bending tests, shows good agreement with the experimental data. A bending test is simulated to study the force variation of an orthodontic NiTi arch wire when it loaded up to the deflection of 3 mm, for this task one half of the arch wire and the 3 adjacent brackets were modeled. The results showed that the stress required for the martensite transformation increases with the increase of cross-sectional dimensions and temperature. Associated with this increase in stress, the plateau of this transformation becomes steeper. In addition, the area of the mechanical hysteresis, measured as the difference between the forces of the upper and lower plateau, increases.

Evolution of treatment mechanics and contemporary appliance design in orthodontics: A 40-year perspective.

PubMed

McLaughlin, Richard P; Bennett, John C

2015-06-01

Until the early 1970s, successful treatment with the Begg technique and the Tweed edgewise technique required tedious wire bending. The introduction of Andrews' straight wire appliance changed that, and it was one of the most significant contributions in the history of orthodontics. The straight wire appliance significantly reduced the amount of wire bending and also brought along other options in treatment mechanics. Retraction of the canines with elastic chains and ligature wires became more common. Sliding mechanics in place of closing loops became the method of space closure for a significant number of clinicians. Edgewise force levels were initially used to close spaces; however, it was soon observed that lighter forces were more effective with sliding mechanics. Along with these changes, it became apparent that compensation in the appliance was needed, depending on the type of malocclusion and particularly with varying extraction sequences. Various appliance designs were developed to accommodate changes in mechanics and force levels. These modifications improved tooth positions at the end of treatment as long as the brackets were properly placed. These major changes in appliances, force levels, and treatment mechanics can be traced back to the work of Dr Lawrence Andrews and the straight wire appliances. Copyright © 2015 American Association of Orthodontists. Published by Elsevier Inc. All rights reserved.

Resistance to Rolling in the Adhesive Contact of Two Elastic Spheres

NASA Technical Reports Server (NTRS)

Dominik, C.; Tielens, A. G. G. M.

1995-01-01

For the stability of agglomerates of micron sized particles it is of considerable importance to study the effects of tangential forces on the contact of two particles. If the particles can slide or roll easily over each other, fractal structures of these agglomerates will not be stable. We use the description of contact forces by Johnson, Kendall and Roberts, along with arguments based on the atomic structure of the surfaces in contact, in order to calculate the resistance to rolling in such a contact. It is shown that the contact reacts elastically to torque forces up to a critical bending angle. Beyond that, irreversible rolling occurs. In the elastic regime, the moment opposing the attempt to roll is proportional to the bending angle and to the pull-off force P(sub c). Young's modulus of the involved materials has hardly any influence on the results. We show that agglomerates of sub-micron sized particles will in general be quite rigid and even long chains of particles cannot be bent easily. For very small particles, the contact will rather break than allow for rolling. We further discuss dynamic properties such as the possibility of vibrations in this degree of freedom and the typical amount of rolling during a collision of two particles.

Modifying landing mat material properties may decrease peak contact forces but increase forefoot forces in gymnastics landings.

PubMed

Mills, Chris; Yeadon, Maurice R; Pain, Matthew T G

2010-09-01

This study investigated how changes in the material properties of a landing mat could minimise ground reaction forces (GRF) and internal loading on a gymnast during landing. A multi-layer model of a gymnastics competition landing mat and a subject-specific seven-link wobbling mass model of a gymnast were developed to address this aim. Landing mat properties (stiffness and damping) were optimised using a Simplex algorithm to minimise GRF and internal loading. The optimisation of the landing mat parameters was characterised by minimal changes to the mat's stiffness (<0.5%) but increased damping (272%) compared to the competition landing mat. Changes to the landing mat resulted in reduced peak vertical and horizontal GRF and reduced bone bending moments in the shank and thigh compared to a matching simulation. Peak bone bending moments within the thigh and shank were reduced by 6% from 321.5 Nm to 302.5Nm and GRF by 12% from 8626 N to 7552 N when compared to a matching simulation. The reduction in these forces may help to reduce the risk of bone fracture injury associated with a single landing and reduce the risk of a chronic injury such as a stress fracture.

Method for lateral force calibration in atomic force microscope using MEMS microforce sensor.

PubMed

Dziekoński, Cezary; Dera, Wojciech; Jarząbek, Dariusz M

2017-11-01

In this paper we present a simple and direct method for the lateral force calibration constant determination. Our procedure does not require any knowledge about material or geometrical parameters of an investigated cantilever. We apply a commercially available microforce sensor with advanced electronics for direct measurement of the friction force applied by the cantilever's tip to a flat surface of the microforce sensor measuring beam. Due to the third law of dynamics, the friction force of the equal value tilts the AFM cantilever. Therefore, torsional (lateral force) signal is compared with the signal from the microforce sensor and the lateral force calibration constant is determined. The method is easy to perform and could be widely used for the lateral force calibration constant determination in many types of atomic force microscopes. Copyright © 2017 Elsevier B.V. All rights reserved.

Biomechanical factors contributing to self-organization in seagrass landscapes

USGS Publications Warehouse

Fonseca, M.S.; Koehl, M.A.R.; Kopp, B.S.

2007-01-01

Field observations have revealed that when water flow is consistently from one direction, seagrass shoots align in rows perpendicular to the primary axis of flow direction. In this study, live Zostera marina shoots were arranged either randomly or in rows perpendicular to the flow direction and tested in a seawater flume under unidirectional flow and waves to determine if shoot arrangement: a) influenced flow-induced force on individual shoots, b) differentially altered water flow through the canopy, and c) influenced light interception by the canopy. In addition, blade breaking strength was compared with flow-induced force to determine if changes in shoot arrangement might reduce the potential for damage to shoots. Under unidirectional flow, both current velocity in the canopy and force on shoots were significantly decreased when shoots were arranged in rows as compared to randomly. However, force on shoots was nearly constant with downstream distance, arising from the trade-off of shoot bending and in-canopy flow reduction. The coefficient of drag was higher for randomly-arranged shoots at low velocities (< 30 cm s- 1) but converged rapidly among the two shoot arrangements at higher velocities. Shoots arranged in rows tended to intercept slightly more light than those arranged randomly. Effects of shoot arrangement under waves were less clear, potentially because we did not achieve the proper plant size?row spacing ratio. At this point, we may only suggest that water motion, as opposed to light capture, is the dominant physical mechanism responsible for these shoot arrangements. Following a computation of the Environmental Stress Factor, we concluded that even photosynthetically active blades may be damaged or broken under frequently encountered storm conditions, irrespective of shoot arrangement. We hypothesize that when flow is generally from one direction, seagrass bed patterns over multiple scales of consideration may arise as a cumulative effect of individual shoot self-organization driven by reduced force and drag on the shoots and somewhat improved light capture.

A new atomic force microscope force ramp technique using digital force feedback control reveals mechanically weak protein unfolding events.

PubMed

Kawakami, M; Smith, D A

2008-12-10

We have developed a new force ramp modification of the atomic force microscope (AFM) which can control multiple unfolding events of a multi-modular protein using software-based digital force feedback control. With this feedback the force loading rate can be kept constant regardless the length of soft elastic linkage or number of unfolded polypeptide domains. An unfolding event is detected as a sudden drop in force, immediately after which the feedback control reduces the applied force to a low value of a few pN by lowering the force set point. Hence the remaining folded domains can relax and the subsequent force ramp is applied to relaxed protein domains identically in each case. We have applied this technique to determine the kinetic parameters x(u), which is the distance between the native state and transition state, and α(0), which is the unfolding rate constant at zero force, for the mechanical unfolding of a pentamer of I27 domains of titin. In each force ramp the unfolding probability depends on the number of folded domains remaining in the system and we had to take account of this effect in the analysis of unfolding force data. We obtained values of x(u) and α(0) to be 0.28 nm and 1.02 × 10(-3) s(-1), which are in good agreement with those obtained from conventional constant velocity experiments. This method reveals unfolding data at low forces that are not seen in constant velocity experiments and corrects for the change in stiffness that occurs with most mechanical systems throughout the unfolding process to allow constant force ramp experiments to be carried out. In addition, a mechanically weak structure was detected, which formed from the fully extended polypeptide chain during a force quench. This indicates that the new technique will allow studies of the folding kinetics of previously hidden, mechanically weak species.

Total Longitudinal Moment Calculation and Reliability Analysis of Yacht Structures

NASA Astrophysics Data System (ADS)

Zhi, Wenzheng; Lin, Shaofen

In order to check the reliability of the yacht in FRP (Fiber Reinforce Plastic) materials, in this paper, the vertical force and the calculation method of the overall longitudinal bending moment on yacht was analyzed. Specially, this paper focuses on the impact of speed on the still water bending moment on yacht. Then considering the mechanical properties of the cap type stiffeners in composite materials, the ultimate bearing capacity of the yacht has been worked out, finally the reliability of the yacht was calculated with using response surface methodology. The result can be used in yacht design and yacht driving.

Properties of natural frequencies and harmonic bending vibrations of a rod at one end of which is concentrated inertial load

NASA Astrophysics Data System (ADS)

Aliyev, Ziyatkhan S.; Guliyeva, Sevinc B.

2017-11-01

In this paper we consider a spectral problem that describes the bending vibrations of a homogeneous rod, in cross-sections of which the longitudinal force acts, the left end of which is fixed and on the right end an inertial mass is concentrated. We give a general characteristic of the location of the eigenvalues on the real axis, we study the structure of root spaces and oscillation properties of eigenfunctions, we investigate the basic properties in the space Lp, 1 < p < ∞, of the system of eigenfunctions of this problem.

Bend-Twist Coupled Carbon-Fiber Laminate Beams: Fundamental Behavior and Applications

NASA Astrophysics Data System (ADS)

Babuska, Pavel

Material-induced bend-twist coupling in laminated composite beams has seen applications in engineered structures for decades, ranging from airplane wings to turbine blades. Symmetric, unbalanced, carbon fiber laminates which exhibit bend-twist coupling can be difficult to characterize and exhibit unintuitive deformation states which may pose challenges to the engineer. In this thesis, bend-twist coupled beams are investigated comprehensively, by experimentation, numerical modeling, and analytical methods. Beams of varying fiber angle and amount of coupling were manufactured and physically tested in both linear and nonlinear static and dynamic settings. Analytical mass and stiffness matrices were derived for the development of a beam element to use in the stiffness matrix analysis method. Additionally, an ABAQUS finite element model was used in conjunction with the analytical methods to predict and further characterize the behavior of the beams. The three regimes, experimental, analytical, and numerical, represent a full-field characterization of bend-twist coupling in composite beams. A notable application of bend-twist coupled composites is for passively adaptive turbine blades whereby the deformation coupling can be built into the blade structure to simultaneously bend and twist, thus pitching the blade into or away from the fluid flow, changing the blade angle of attack. Passive pitch adaptation has been implemented successfully in wind turbine blades, however, for marine turbine blades, the technology is still in the development phase. Bend-twist coupling has been shown numerically to be beneficial to the tidal turbine performance, however little validation has been conducted in the experimental regime. In this thesis, passively adaptive experiment scale tidal turbine blades were designed, analyzed, manufactured, and physically tested, validating the foundational numerical work. It was shown that blade forces and root moments as well as turbine thrust and power coefficients can be manipulated by inclusion of passive pitch adaption by bend-twist coupling.

Computer simulation of flagellar movement. VI. Simple curvature-controlled models are incompletely specified.

PubMed

Brokaw, C J

1985-10-01

Computer simulation is used to examine a simple flagellar model that will initiate and propagate bending waves in the absence of viscous resistances. The model contains only an elastic bending resistance and an active sliding mechanism that generates reduced active shear moment with increasing sliding velocity. Oscillation results from a distributed control mechanism that reverses the direction of operation of the active sliding mechanism when the curvature reaches critical magnitudes in either direction. Bend propagation by curvature-controlled flagellar models therefore does not require interaction with the viscous resistance of an external fluid. An analytical examination of moment balance during bend propagation by this model yields a solution curve giving values of frequency and wavelength that satisfy the moment balance equation and give uniform bend propagation, suggesting that the model is underdetermined. At 0 viscosity, the boundary condition of 0 shear rate at the basal end of the flagellum during the development of new bends selects the particular solution that is obtained by computer simulations. Therefore, the details of the pattern of bend initiation at the basal end of a flagellum can be of major significance in determining the properties of propagated bending waves in the distal portion of a flagellum. At high values of external viscosity, the model oscillates at frequencies and wavelengths that give approximately integral numbers of waves on the flagellum. These operating points are selected because they facilitate the balance of bending moments at the ends of the model, where the external viscous moment approaches 0. These mode preferences can be overridden by forcing the model to operate at a predetermined frequency. The strong mode preferences shown by curvature-controlled flagellar models, in contrast to the weak or absent mode preferences shown by real flagella, therefore do not demonstrate the inapplicability of the moment-balance approach to real flagella. Instead, they indicate a need to specify additional properties of real flagella that are responsible for selecting particular operating points.

In-flight total forces, moments and static aeroelastic characteristics of an oblique-wing research airplane

NASA Technical Reports Server (NTRS)

Curry, R. E.; Sim, A. G.

1984-01-01

A low-speed flight investigation has provided total force and moment coefficients and aeroelastic effects for the AD-1 oblique-wing research airplane. The results were interpreted and compared with predictions that were based on wind tunnel data. An assessment has been made of the aeroelastic wing bending design criteria. Lateral-directional trim requirements caused by asymmetry were determined. At angles of attack near stall, flow visualization indicated viscous flow separation and spanwise vortex flow. These effects were also apparent in the force and moment data.

Prediction of impact force and duration during low velocity impact on circular composite laminates

NASA Technical Reports Server (NTRS)

Shivakumar, K. N.; Elber, W.; Illg, W.

1983-01-01

Two simple and improved models--energy-balance and spring-mass--were developed to calculate impact force and duration during low velocity impact of circular composite plates. Both models include the contact deformation of the plate and the impactor as well as bending, transverse shear, and membrane deformations of the plate. The plate was transversely isotropic graphite/epoxy composite laminate and the impactor was a steel sphere. Calculated impact forces from the two analyses agreed with each other. The analyses were verified by comparing the results with reported test data.

Note: Spring constant calibration of nanosurface-engineered atomic force microscopy cantilevers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ergincan, O., E-mail: orcunergincan@gmail.com; Palasantzas, G.; Kooi, B. J.

2014-02-15

The determination of the dynamic spring constant (k{sub d}) of atomic force microscopy cantilevers is of crucial importance for converting cantilever deflection to accurate force data. Indeed, the non-destructive, fast, and accurate measurement method of the cantilever dynamic spring constant by Sader et al. [Rev. Sci. Instrum. 83, 103705 (2012)] is confirmed here for plane geometry but surface modified cantilevers. It is found that the measured spring constants (k{sub eff}, the dynamic one k{sub d}), and the calculated (k{sub d,1}) are in good agreement within less than 10% error.

Discharge behavior of motor units in knee extensors during the initial stage of constant-force isometric contraction at low force level.

PubMed

Kamo, Mifuyu

2002-03-01

To elucidate the strategy of the activity of motor units (MUs) to maintain a constant-force isometric contraction, I examined the behavior of MUs in knee extensor muscles [(vastus medialis (VM), vastus lateralis (VL) and rectus femoris (RF)] during a sustained contraction at 5% of maximal voluntary contraction for 5 min. In all cases, the spike interval exhibited an elongating trend, and two discharge patterns were observed, continuous discharge and decruitment. In continuous-discharge MUs, the trend slope was steep immediately after the onset of constant force (steep phase), and then became gentle (gentle phase). Decruitments were observed frequently during each phase, and additional MU recruitment was observed throughout the contraction. The mean value of recruitment threshold force did not differ among the extensors. The mean spike interval at the onset of constant-force isometric contractions was shorter in RF than in VL. However, there were no differences in the duration and extent of the elongating trend, decruitment time and recruitment time among the extensors. The electromyogram of the antagonist biceps femoris muscle revealed no compensatory change for extensor activity. These results indicated that at a low force level, the strategy employed by the central nervous system to maintain constant force appears to involve cooperation among elongating trends in the spike interval, decruitment following elongation, and additional MU recruitment in synergistic muscles.

Interaction potential for indium phosphide: a molecular dynamics and first-principles study of the elastic constants, generalized stacking fault and surface energies.

PubMed

Branicio, Paulo Sergio; Rino, José Pedro; Gan, Chee Kwan; Tsuzuki, Hélio

2009-03-04

Indium phosphide is investigated using molecular dynamics (MD) simulations and density-functional theory calculations. MD simulations use a proposed effective interaction potential for InP fitted to a selected experimental dataset of properties. The potential consists of two- and three-body terms that represent atomic-size effects, charge-charge, charge-dipole and dipole-dipole interactions as well as covalent bond bending and stretching. Predictions are made for the elastic constants as a function of density and temperature, the generalized stacking fault energy and the low-index surface energies.

Static bending deflection and free vibration analysis of moderate thick symmetric laminated plates using multidimensional wave digital filters

NASA Astrophysics Data System (ADS)

Tseng, Chien-Hsun

2018-06-01

This paper aims to develop a multidimensional wave digital filtering network for predicting static and dynamic behaviors of composite laminate based on the FSDT. The resultant network is, thus, an integrated platform that can perform not only the free vibration but also the bending deflection of moderate thick symmetric laminated plates with low plate side-to-thickness ratios (< = 20). Safeguarded by the Courant-Friedrichs-Levy stability condition with the least restriction in terms of optimization technique, the present method offers numerically high accuracy, stability and efficiency to proceed a wide range of modulus ratios for the FSDT laminated plates. Instead of using a constant shear correction factor (SCF) with a limited numerical accuracy for the bending deflection, an optimum SCF is particularly sought by looking for a minimum ratio of change in the transverse shear energy. This way, it can predict as good results in terms of accuracy for certain cases of bending deflection. Extensive simulation results carried out for the prediction of maximum bending deflection have demonstratively proven that the present method outperforms those based on the higher-order shear deformation and layerwise plate theories. To the best of our knowledge, this is the first work that shows an optimal selection of SCF can significantly increase the accuracy of FSDT-based laminates especially compared to the higher order theory disclaiming any correction. The highest accuracy of overall solution is compared to the 3D elasticity equilibrium one.

Microcantilever sensor

DOEpatents

Thundat, Thomas G.; Wachter, Eric A.

1998-01-01

An improved microcantilever sensor is fabricated with at least one microcantilever attached to a piezoelectric transducer. The microcantilever is partially surface treated with a compound selective substance having substantially exclusive affinity for a targeted compound in a monitored atmosphere. The microcantilever sensor is also provided with a frequency detection means and a bending detection means. The frequency detection means is capable of detecting changes in the resonance frequency of the vibrated microcantilever in the monitored atmosphere. The bending detection means is capable of detecting changes in the bending of the vibrated microcantilever in the monitored atmosphere coactively with the frequency detection means. The piezoelectric transducer is excited by an oscillator means which provides a signal driving the transducer at a resonance frequency inducing a predetermined order of resonance on the partially treated microcantilever. Upon insertion into a monitored atmosphere, molecules of the targeted chemical attach to the treated regions of the microcantilever resulting in a change in oscillating mass as well as a change in microcantilever spring constant thereby influencing the resonant frequency of the microcantilever oscillation. Furthermore, the molecular attachment of the target chemical to the treated regions induce areas of mechanical strain in the microcantilever consistent with the treated regions thereby influencing microcantilever bending. The rate at which the treated microcantilever accumulates the target chemical is a function of the target chemical concentration. Consequently, the extent of microcantilever oscillation frequency change and bending is related to the concentration of target chemical within the monitored atmosphere.

Microcantilever sensor

DOEpatents

Thundat, T.G.; Wachter, E.A.

1998-02-17

An improved microcantilever sensor is fabricated with at least one microcantilever attached to a piezoelectric transducer. The microcantilever is partially surface treated with a compound selective substance having substantially exclusive affinity for a targeted compound in a monitored atmosphere. The microcantilever sensor is also provided with a frequency detection means and a bending detection means. The frequency detection means is capable of detecting changes in the resonance frequency of the vibrated microcantilever in the monitored atmosphere. The bending detection means is capable of detecting changes in the bending of the vibrated microcantilever in the monitored atmosphere coactively with the frequency detection means. The piezoelectric transducer is excited by an oscillator means which provides a signal driving the transducer at a resonance frequency inducing a predetermined order of resonance on the partially treated microcantilever. Upon insertion into a monitored atmosphere, molecules of the targeted chemical attach to the treated regions of the microcantilever resulting in a change in oscillating mass as well as a change in microcantilever spring constant thereby influencing the resonant frequency of the microcantilever oscillation. Furthermore, the molecular attachment of the target chemical to the treated regions induce areas of mechanical strain in the microcantilever consistent with the treated regions thereby influencing microcantilever bending. The rate at which the treated microcantilever accumulates the target chemical is a function of the target chemical concentration. Consequently, the extent of microcantilever oscillation frequency change and bending is related to the concentration of target chemical within the monitored atmosphere. 16 figs.

Practical Considerations for Using Constant Force Springs in Space-Based Mechanisms

NASA Technical Reports Server (NTRS)

Williams, R. Brett; Fisher, Charles D.; Gallon, John C.

2013-01-01

Mechanical springs are a common element in mechanism from all walks of life; cars, watches, appliances, and many others. These springs generally exhibit a linear relationship between force and deflection. In small mechanisms, deflections are small so the variation in spring force between one position and another are generally small and do not influence the design or functionality of the device. However, as the spacecraft industry drives towards larger, deployable satellites, the distances a spring or springs must function over can become considerable so much so that the structural integrity of the device may be impacted. As such, an increasingly common mechanism element is the constant force spring- one that provides a constant force regardless of deflection. These elements are commonly in the conceptual design phase to deal with system-level large deflections, but in the detailed design or integration test phase they can pose significant implementation issues. This article addresses some of the detailed issues in order for these constant force springs to be properly designed into space systems.

Method using photo-induced and thermal bending of MEMS sensors

DOEpatents

Datskos, Panagiotis G.

2001-01-01

A method for measuring chemical analytes and physical forces by measuring changes in the deflection of a microelectromechanical cantilever structure while it is being irradiated by a light having an energy above the band gap of the structure.

Plucking a hydrogen bond: A near infrared study of all four intermolecular modes in (DF)2

NASA Astrophysics Data System (ADS)

Davis, Scott; Anderson, David T.; Nesbitt, David J.

1996-10-01

The near ir combination band spectra of supersonically cooled (DF)2 in the 2900 to 3300 cm-1 region have been recorded with a high resolution slit jet spectrometer. Twelve vibration-rotation-tunneling (VRT) bands are observed, representing each of the four intermolecular modes (van der Waals stretch ν4, geared bend ν5, out-of-plane torsion ν6, and antigeared bend ν3) built as combination bands on either the ν1 (free) or ν2 (bound) DF stretches. Analysis of the rotationally resolved spectra provide spectroscopic constants, intermolecular frequencies, tunneling splittings, and predissociation rates as a function of both intra- and intermolecular excitation. The intermolecular frequencies demonstrate a small but systematic dependence on intramolecular mode, which is exploited to yield frequency predictions relevant to far-ir studies, as well as facilitate direct comparison with full 6-D quantum calculations on trial potential surfaces. The tunneling splittings demonstrate a much stronger dependence upon intermolecular mode, increasing by as much as an order of magnitude for geared bend excitation. Conversely, high resolution line shape analysis reveals that vibrational predissociation broadening is only modestly affected by intermolecular excitation, and instead exhibits mode specific behavior controlled predominantly by intramolecular excitation. Detailed H/D isotopic vibrational shifts are obtained by comparison with previous combination band studies of all four intermolecular modes in (HF)2. In contrast to the strong state mixing previously observed for (HF)2, the van der Waals stretch and geared bend degrees of freedom are largely decoupled in (DF)2, due to isotopically ``detuning'' of resonances between bend-stretch intermolecular vibrations. Four-dimensional quantum calculations of the (HF)2 and (DF)2 eigenfunctions indicate that the isotopic dependence of this bend-stretch resonance behavior is incorrectly predicted by current hydrogen bond potential surfaces.

Stability of aerosol droplets in Bessel beam optical traps under constant and pulsed external forces

DOE Office of Scientific and Technical Information (OSTI.GOV)

David, Grégory; Esat, Kıvanç; Hartweg, Sebastian

We report on the dynamics of aerosol droplets in optical traps under the influence of additional constant and pulsed external forces. Experimental results are compared with simulations of the three-dimensional droplet dynamics for two types of optical traps, the counter-propagating Bessel beam (CPBB) trap and the quadruple Bessel beam (QBB) trap. Under the influence of a constant gas flow (constant external force), the QBB trap is found to be more stable compared with the CPBB trap. By contrast, under pulsed laser excitation with laser pulse durations of nanoseconds (pulsed external force), the type of trap is of minor importance formore » the droplet stability. It typically needs pulsed laser forces that are several orders of magnitude higher than the optical forces to induce escape of the droplet from the trap. If the droplet strongly absorbs the pulsed laser light, these escape forces can be strongly reduced. The lower stability of absorbing droplets is a result of secondary thermal processes that cause droplet escape.« less

Instrument for the application of controlled mechanical loads to tissues in sterile culture

DOEpatents

Lintilhac, Phillip M.; Vesecky, Thompson B.

1995-01-01

Apparatus and methods are disclosed facilitating the application of forces and measurement of dimensions of a test subject. In one arrangement the test subject is coupled to a forcing frame and controlled forces applied thereto by a series of guideways and sliders. The sliders, which contact the test subject are in force transmitting relation to a forcing frame. Tension, compression and bending forces can be applied to the test subject. Force applied to the test subject is measured and controlled. A dimensional characteristic of the test subject, such as growth, is measured by a linear variable differential transformer. The growth measurement data can be used to control the force applied. Substantially uniaxial stretching is achieved by placing the test subject on an elastic membrane stretched by an arrangement of members securing the elastic member to the forcing frame.

Quantum-mechanical approach to predissociation of water dimers in the vibrational adiabatic representation: Importance of channel interactions.

PubMed

Mineo, H; Niu, Y L; Kuo, J L; Lin, S H; Fujimura, Y

2015-08-28

The results of application of the quantum-mechanical adiabatic theory to vibrational predissociation (VPD) of water dimers, (H2O)2 and (D2O)2, are presented. We consider the VPD processes including the totally symmetric OH mode of the dimer and the bending mode of the fragment. The VPD in the adiabatic representation is induced by breakdown of the vibrational adiabatic approximation, and two types of nonadiabatic coupling matrix elements are involved: one provides the VPD induced by the low-frequency dissociation mode and the other provides the VPD through channel interactions induced by the low-frequency modes. The VPD rate constants were calculated using the Fermi golden rule expression. A closed form for the nonadiabatic transition matrix element between the discrete and continuum states was derived in the Morse potential model. All of the parameters used were obtained from the potential surfaces of the water dimers, which were calculated by the density functional theory procedures. The VPD rate constants for the two processes were calculated in the non-Condon scheme beyond the so-called Condon approximation. The channel interactions in and between the initial and final states were taken into account, and those are found to increase the VPD rates by 3(1) orders of magnitude for the VPD processes in (H2O)2 ((D2O)2). The fraction of the bending-excited donor fragments is larger than that of the bending-excited acceptor fragments. The results obtained by quantum-mechanical approach are compared with both experimental and quasi-classical trajectory calculation results.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mineo, H.; Kuo, J. L.; Niu, Y. L.

The results of application of the quantum-mechanical adiabatic theory to vibrational predissociation (VPD) of water dimers, (H{sub 2}O){sub 2} and (D{sub 2}O){sub 2}, are presented. We consider the VPD processes including the totally symmetric OH mode of the dimer and the bending mode of the fragment. The VPD in the adiabatic representation is induced by breakdown of the vibrational adiabatic approximation, and two types of nonadiabatic coupling matrix elements are involved: one provides the VPD induced by the low-frequency dissociation mode and the other provides the VPD through channel interactions induced by the low-frequency modes. The VPD rate constants weremore » calculated using the Fermi golden rule expression. A closed form for the nonadiabatic transition matrix element between the discrete and continuum states was derived in the Morse potential model. All of the parameters used were obtained from the potential surfaces of the water dimers, which were calculated by the density functional theory procedures. The VPD rate constants for the two processes were calculated in the non-Condon scheme beyond the so-called Condon approximation. The channel interactions in and between the initial and final states were taken into account, and those are found to increase the VPD rates by 3(1) orders of magnitude for the VPD processes in (H{sub 2}O){sub 2} ((D{sub 2}O){sub 2}). The fraction of the bending-excited donor fragments is larger than that of the bending-excited acceptor fragments. The results obtained by quantum-mechanical approach are compared with both experimental and quasi-classical trajectory calculation results.« less

Note: Production of stable colloidal probes for high-temperature atomic force microscopy applications

NASA Astrophysics Data System (ADS)

Ditscherlein, L.; Peuker, U. A.

2017-04-01

For the application of colloidal probe atomic force microscopy at high temperatures (>500 K), stable colloidal probe cantilevers are essential. In this study, two new methods for gluing alumina particles onto temperature stable cantilevers are presented and compared with an existing method for borosilicate particles at elevated temperatures as well as with cp-cantilevers prepared with epoxy resin at room temperature. The durability of the fixing of the particle is quantified with a test method applying high shear forces. The force is calculated with a mechanical model considering both the bending as well as the torsion on the colloidal probe.

A program for calculating load coefficient matrices utilizing the force summation method, L218 (LOADS). Volume 2: Supplemental system design and maintenance document

NASA Technical Reports Server (NTRS)

Anderson, L. R.; Miller, R. D.

1979-01-01

The LOADS computer program L218 which calculates dynamic load coefficient matrices utilizing the force summation method is described. The load equations are derived for a flight vehicle in straight and level flight and excited by gusts and/or control motions. In addition, sensor equations are calculated for use with an active control system. The load coefficient matrices are calculated for the following types of loads: (1) translational and rotational accelerations, velocities, and displacements; (2) panel aerodynamic forces; (3) net panel forces; and (4) shears, bending moments, and torsions.

The effects of rigid motions on elastic network model force constants.

PubMed

Lezon, Timothy R

2012-04-01

Elastic network models provide an efficient way to quickly calculate protein global dynamics from experimentally determined structures. The model's single parameter, its force constant, determines the physical extent of equilibrium fluctuations. The values of force constants can be calculated by fitting to experimental data, but the results depend on the type of experimental data used. Here, we investigate the differences between calculated values of force constants and data from NMR and X-ray structures. We find that X-ray B factors carry the signature of rigid-body motions, to the extent that B factors can be almost entirely accounted for by rigid motions alone. When fitting to more refined anisotropic temperature factors, the contributions of rigid motions are significantly reduced, indicating that the large contribution of rigid motions to B factors is a result of over-fitting. No correlation is found between force constants fit to NMR data and those fit to X-ray data, possibly due to the inability of NMR data to accurately capture protein dynamics. Copyright © 2011 Wiley Periodicals, Inc.

Flexure and the role of inplane force around coronae on Venus

NASA Technical Reports Server (NTRS)

Brown, C. David; Grimm, Robert E.

1993-01-01

Large coronae on Venus, such as Artemis and Latona, are rimmed by conspicuous trenches and associated outer rises. Sandwell and Schubert have observed that these systems resemble terrestrial subduction zones in planform and have succeeded in fitting an elastic plate bending equation to the inferred flexural topography. However, the first zero crossing bending moments required are -2.5 x 10(exp 17) N for Artemis and -5.0 x 10(exp 16) N for Latona. Since these moments are similar in magnitude to those of subducting slabs on Earth, a rollback subduction mechanism was proposed to explain the flexure around the largest coronae, although a differential thermal subsidence model is sufficient to account for the topography around some coronae. The purpose is to investigate the effect of inplane force as a possible alternative to large applied moments in producing flexure at Artemis and Latona. The close correlation of gravity to topography on Venus implies the absence of a low viscosity zone and the strong coupling of the lithosphere to mantle convection. If coronae are the surface manifestations of mantle plumes, they may be the sites of active convective stress coupling. As the upwelling reaches the lithosphere, it spreads radially outward, inducing shear tractions on the base of the plate. In addition, the hot, expanding corona may load the surrounding plate horizonally. Both the basal shear stresses and radial loading can be treated as an equivalent compressive inplane force in the mechanical lithosphere, which contributes to the bending of the outlying plate. Using a model that relates inplane force to the measured gravity anomalies, a rough value of the inplane force at Artemis was calculated. Recent Pioneer Venus spherical harmonic gravity models indicate a geoid anomaly of about 75 m over Artemis, which corresponds to an estimated inplane force on the order of -1x10(exp 13) N/m. The gravity model is unable to resolve Latona, but an inplane force of similar dimensions is assumed. The maximum possible inplane force based on the expected rheology can be constrained by using the approximate 5 K/km thermal gradient inferred from the best fit 30 km elastic plate at Artemis and Latona. For a dry olivine flow law in the upper mantle, the compressional load limit of the 60 km thick mechanical lithosphere is -4 x 10(exp 13) N/m. This value is equivalent to a load of -8 x 10(exp 13) N/m on a 30 km thick elastic plate.

Interfacial thin films rupture and self-similarity

NASA Astrophysics Data System (ADS)

Ward, Margaret H.

2011-06-01

Two superposed thin layers of fluids are prone to interfacial instabilities due to London-van der Waals forces. Evolution equations for the film thicknesses are derived using lubrication theory. Using the intrinsic scales, for a single layer, results in a system with parametric dependence of four ratios of the two layers: surface tension, Hamaker constant, viscosity, and film thickness. In contrast to the single layer case, the bilayer system has two unstable eigenmodes: squeezing and bending. For some particular parameter regimes, the system exhibits the avoided crossing behavior, where the two eigenmodes are interchanged. Based on numerical analysis, the system evolves into four different rupture states: basal layer rupture, upper layer rupture, double layer rupture, and mixed layer rupture. The ratio of Hamaker constants and the relative film thickness of the two layers control the system dynamics. Remarkably, the line of avoided crossing demarks the transition region of mode mixing and energy transfer, affecting the scaling of the dynamical regime map consequentially. Asymptotic and numerical analyses are used to examine the self-similar ruptures and to extract the power law scalings for both the basal layer rupture and the upper layer rupture. The scaling laws for the basal layer rupture are the same as those of the single layer on top of a substrate. The scaling laws for the upper layer rupture are different: the lateral length scale decreases according to (tr-t)1/3 and the film thickness decreases according to (tr-t)1/6.

Track-A-Worm, An Open-Source System for Quantitative Assessment of C. elegans Locomotory and Bending Behavior

PubMed Central

Wang, Sijie Jason; Wang, Zhao-Wen

2013-01-01

A major challenge of neuroscience is to understand the circuit and gene bases of behavior. C. elegans is commonly used as a model system to investigate how various gene products function at specific tissue, cellular, and synaptic foci to produce complicated locomotory and bending behavior. The investigation generally requires quantitative behavioral analyses using an automated single-worm tracker, which constantly records and analyzes the position and body shape of a freely moving worm at a high magnification. Many single-worm trackers have been developed to meet lab-specific needs, but none has been widely implemented for various reasons, such as hardware difficult to assemble, and software lacking sufficient functionality, having closed source code, or using a programming language that is not broadly accessible. The lack of a versatile system convenient for wide implementation makes data comparisons difficult and compels other labs to develop new worm trackers. Here we describe Track-A-Worm, a system rich in functionality, open in source code, and easy to use. The system includes plug-and-play hardware (a stereomicroscope, a digital camera and a motorized stage), custom software written to run with Matlab in Windows 7, and a detailed user manual. Grayscale images are automatically converted to binary images followed by head identification and placement of 13 markers along a deduced spline. The software can extract and quantify a variety of parameters, including distance traveled, average speed, distance/time/speed of forward and backward locomotion, frequency and amplitude of dominant bends, overall bending activities measured as root mean square, and sum of all bends. It also plots worm travel path, bend trace, and bend frequency spectrum. All functionality is performed through graphical user interfaces and data is exported to clearly-annotated and documented Excel files. These features make Track-A-Worm a good candidate for implementation in other labs. PMID:23922769

Modeling the dynamic stiffness of cracked reinforced concrete beams under low-amplitude vibration loads

NASA Astrophysics Data System (ADS)

Xu, Tengfei; Castel, Arnaud

2016-04-01

In this paper, a model, initially developed to calculate the stiffness of cracked reinforced concrete beams under static loading, is used to assess the dynamic stiffness. The model allows calculating the average inertia of cracked beams by taking into account the effect of bending cracks (primary cracks) and steel-concrete bond damage (i.e. interfacial microcracks). Free and forced vibration experiments are used to assess the performance of the model. The respective influence of bending cracks and steel-concrete bond damage on both static and dynamic responses is analyzed. The comparison between experimental and simulated deflections confirms that the effects of both bending cracks and steel-concrete bond loss should be taken into account to assess reinforced concrete stiffness under service static loading. On the contrary, comparison of experimental and calculated dynamic responses reveals that localized steel-concrete bond damages do not influence significantly the dynamic stiffness and the fundamental frequency.

Detailed heat/mass transfer distributions in a rotating two pass coolant channel with engine-near cross section and smooth walls.

PubMed

Rathjen, L; Hennecke, D K; Bock, S; Kleinstück, R

2001-05-01

This paper shows results obtained by experimental and numerical investigations concerning flow structure and heat/mass transfer in a rotating two-pass coolant channel with engine-near geometry. The smooth two passes are connected by a 180 degrees U-bend in which a 90 degrees turning vane is mounted. The influence of rotation number, Reynolds number and geometry is investigated. The results show a detailed picture of the flow field and distributions of Sherwood number ratios determined experimentally by the use of the naphthalene sublimation technique as well as Nusselt number ratios obtained from the numerical work. Especially the heat/mass transfer distributions in the bend and in the region after the bend show strong gradients, where several separation zones exist and the flow is forced to follow the turbine airfoil shape. Comparisons of numerical and experimental results show only partly good agreement.

Potential variations around grain boundaries in impurity-doped BaSi₂ epitaxial films evaluated by Kelvin probe force microscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tsukahara, D.; Baba, M.; Honda, S.

2014-09-28

Potential variations around the grain boundaries (GBs) in antimony (Sb)-doped n-type and boron (B)-doped p-type BaSi₂ epitaxial films on Si(111) were evaluated by Kelvin probe force microscopy. Sb-doped n-BaSi₂ films exhibited positively charged GBs with a downward band bending at the GBs. The average barrier height for holes was approximately 10 meV for an electron concentration n ≈ 10¹⁷ cm⁻³. This downward band bending changed to upward band bending when n was increased to n = 1.8 × 10¹⁸cm⁻³. In the B-doped p-BaSi₂ films, the upward band bending was observed for a hole concentration p ≈ 10¹⁸cm⁻³. The average barriermore » height for electrons decreased from approximately 25 to 15 meV when p was increased from p = 2.7 × 10¹⁸ to p = 4.0 × 10¹⁸ cm⁻³. These results are explained under the assumption that the position of the Fermi level E{sub f} at GBs depends on the degree of occupancy of defect states at the GBs, while E{sub f} approached the bottom of the conduction band or the top of the valence band in the BaSi₂ grain interiors with increasing impurity concentrations. In both cases, such small barrier heights may not deteriorate the carrier transport properties. The electronic structures of impurity-doped BaSi₂ are also discussed using first-principles pseudopotential method to discuss the insertion sites of impurity atoms and clarify the reason for the observed n-type conduction in the Sb-doped BaSi₂ and p-type conduction in the B-doped BaSi₂.« less

On the correct representation of bending and axial deformation in the absolute nodal coordinate formulation with an elastic line approach

NASA Astrophysics Data System (ADS)

Gerstmayr, Johannes; Irschik, Hans

2008-12-01

In finite element methods that are based on position and slope coordinates, a representation of axial and bending deformation by means of an elastic line approach has become popular. Such beam and plate formulations based on the so-called absolute nodal coordinate formulation have not yet been verified sufficiently enough with respect to analytical results or classical nonlinear rod theories. Examining the existing planar absolute nodal coordinate element, which uses a curvature proportional bending strain expression, it turns out that the deformation does not fully agree with the solution of the geometrically exact theory and, even more serious, the normal force is incorrect. A correction based on the classical ideas of the extensible elastica and geometrically exact theories is applied and a consistent strain energy and bending moment relations are derived. The strain energy of the solid finite element formulation of the absolute nodal coordinate beam is based on the St. Venant-Kirchhoff material: therefore, the strain energy is derived for the latter case and compared to classical nonlinear rod theories. The error in the original absolute nodal coordinate formulation is documented by numerical examples. The numerical example of a large deformation cantilever beam shows that the normal force is incorrect when using the previous approach, while a perfect agreement between the absolute nodal coordinate formulation and the extensible elastica can be gained when applying the proposed modifications. The numerical examples show a very good agreement of reference analytical and numerical solutions with the solutions of the proposed beam formulation for the case of large deformation pre-curved static and dynamic problems, including buckling and eigenvalue analysis. The resulting beam formulation does not employ rotational degrees of freedom and therefore has advantages compared to classical beam elements regarding energy-momentum conservation.

Finite indentation of highly curved elastic shells

NASA Astrophysics Data System (ADS)

Pearce, S. P.; King, J. R.; Steinbrecher, T.; Leubner-Metzger, G.; Everitt, N. M.; Holdsworth, M. J.

2018-01-01

Experimentally measuring the elastic properties of thin biological surfaces is non-trivial, particularly when they are curved. One technique that may be used is the indentation of a thin sheet of material by a rigid indenter, while measuring the applied force and displacement. This gives immediate information on the fracture strength of the material (from the force required to puncture), but it is also theoretically possible to determine the elastic properties by comparing the resulting force-displacement curves with a mathematical model. Existing mathematical studies generally assume that the elastic surface is initially flat, which is often not the case for biological membranes. We previously outlined a theory for the indentation of curved isotropic, incompressible, hyperelastic membranes (with no bending stiffness) which breaks down for highly curved surfaces, as the entire membrane becomes wrinkled. Here, we introduce the effect of bending stiffness, ensuring that energy is required to change the shell shape without stretching, and find that commonly neglected terms in the shell equilibrium equation must be included. The theory presented here allows for the estimation of shape- and size-independent elastic properties of highly curved surfaces via indentation experiments, and is particularly relevant for biological surfaces.

Flow analysis of new type propulsion system for UV’s

NASA Astrophysics Data System (ADS)

Eimanis, M.; Auzins, J.

2017-10-01

This paper presents an original design of an autonomous underwater vehicle where thrust force is created by the helicoidal shape of the hull rather than screw propellers. Propulsion force is created by counter-rotating bow and stern parts. The middle part of the vehicle has the function of a cargo compartment containing all control mechanisms and communications. It’s made of elastic material, containing a Cardan-joint mechanism, which allows changing the direction of vehicle, actuated by bending drives. A bending drive velocity control algorithm for the automatic control of vehicle movement direction is proposed. The dynamics of AUV are simulated using multibody simulation software MSC Adams. For the simulation of water resistance forces and torques the surrogate polynomial metamodels are created on the basis of computer experiments with CFD software. For flow interaction with model geometry the simplified vehicle model is submerged in fluid medium using special CFD software, with the same idea used in wind tunnel experiments. The simulation results are compared with measurements of the AUV prototype, created at Institute of Mechanics of Riga Technical University. Experiments with the prototype showed good agreement with simulation results and confirmed the effectiveness and the future potential of the proposed principle.

Thermally assisted peeling of an elastic strip in adhesion with a substrate via molecular bonds

NASA Astrophysics Data System (ADS)

Qian, Jin; Lin, Ji; Xu, Guang-Kui; Lin, Yuan; Gao, Huajian

A statistical model is proposed to describe the peeling of an elastic strip in adhesion with a flat substrate via an array of non-covalent molecular bonds. Under an imposed tensile peeling force, the interfacial bonds undergo diffusion-type transition in their bonding state, a process governed by a set of probabilistic equations coupled to the stretching, bending and shearing of the elastic strip. Because of the low characteristic energy scale associated with molecular bonding, thermal excitations are found to play an important role in assisting the escape of individual molecular bonds from their bonding energy well, leading to propagation of the peeling front well below the threshold peel-off force predicted by the classical theories. Our study establishes a link between the deformation of the strip and the spatiotemporal evolution of interfacial bonds, and delineates how factors like the peeling force, bending rigidity of the strip and binding energy of bonds influence the resultant peeling velocity and dimensions of the process zone. In terms of the apparent adhesion strength and dissipated energy, the bond-mediated interface is found to resist peeling in a strongly rate-dependent manner.

Amplitude quantification in contact-resonance-based voltage-modulated force spectroscopy

NASA Astrophysics Data System (ADS)

Bradler, Stephan; Schirmeisen, André; Roling, Bernhard

2017-08-01

Voltage-modulated force spectroscopy techniques, such as electrochemical strain microscopy and piezoresponse force microscopy, are powerful tools for characterizing electromechanical properties on the nanoscale. In order to correctly interpret the results, it is important to quantify the sample motion and to distinguish it from the electrostatic excitation of the cantilever resonance. Here, we use a detailed model to describe the cantilever dynamics in contact resonance measurements, and we compare the results with experimental values. We show how to estimate model parameters from experimental values and explain how they influence the sensitivity of the cantilever with respect to the excitation. We explain the origin of different crosstalk effects and how to identify them. We further show that different contributions to the measured signal can be distinguished by analyzing the correlation between the resonance frequency and the measured amplitude. We demonstrate this technique on two representative test samples: (i) ferroelectric periodically poled lithium niobate, and (ii) the Na+-ion conducting soda-lime float glass. We extend our analysis to higher cantilever bending modes and show that non-local electrostatic excitation is strongly reduced in higher bending modes due to the nodes in the lever shape. Based on our analyses, we present practical guidelines for quantitative imaging.

DFT calculations for anharmonic force field and spectroscopic constants of YC2 and its 13C isotopologues

NASA Astrophysics Data System (ADS)

Zhao, Yanliang; Wang, Meishan; Yang, Chuanlu; Ma, Xiaoguang; Li, Jing

2018-02-01

The construction of the complete third and the semi-diagonal quartic force fields including the anharmonicity of the ground state (X˜2A1) for yttrium dicarbide (YC2) is carried out employing the vibrational second-order perturbation theory (VPT2) in combination with the density functional theory (DFT). The equilibrium geometries optimization, anharmonic force field and vibrational spectroscopic constants of YC2 are calculated by B3LYP, B3PW91 and B3P86 methods. Aug-cc-pVnZ (n = D, T, Q) and cc-pVnZ-PP (n = D, T, Q) basis sets are chosen for C and Y atoms, respectively. The calculated geometry parameters of YC2 agree well with the corresponding experimental and previous theoretical results. The bonding characters of Ysbnd C2 or Csbnd C are discussed. Based on the optimized equilibrium geometries, the spectroscopic constants and anharmonic force field of YC2 are calculated. Comparing with the spectroscopic constants of YC2 derived from the experiment, the calculated results show that the B3PW91 and B3P86 methods are superior to B3LYP for YC2. The Coriolis coupling constants, cubic and quartic force constants of YC2 are reasonably predicted. Besides, the spectroscopic constants and anharmonic force field of Y13C2 (X˜2A1) and Y13CC (X˜2A‧) are calculated for the first time, which are expected to guide the high resolution experimental work for YC2 and its 13C isotopologues.

Ro-vibrational averaging of the isotropic hyperfine coupling constant for the methyl radical

DOE Office of Scientific and Technical Information (OSTI.GOV)

Adam, Ahmad Y.; Jensen, Per, E-mail: jensen@uni-wuppertal.de; Yachmenev, Andrey

2015-12-28

We present the first variational calculation of the isotropic hyperfine coupling constant of the carbon-13 atom in the CH{sub 3} radical for temperatures T = 0, 96, and 300 K. It is based on a newly calculated high level ab initio potential energy surface and hyperfine coupling constant surface of CH{sub 3} in the ground electronic state. The ro-vibrational energy levels, expectation values for the coupling constant, and its temperature dependence were calculated variationally by using the methods implemented in the computer program TROVE. Vibrational energies and vibrational and temperature effects for coupling constant are found to be in verymore » good agreement with the available experimental data. We found, in agreement with previous studies, that the vibrational effects constitute about 44% of the constant’s equilibrium value, originating mainly from the large amplitude out-of-plane bending motion and that the temperature effects play a minor role.« less

Comparative structural neck responses of the THOR-NT, Hybrid III, and human in combined tension-bending and pure bending.

PubMed

Dibb, Alan T; Nightingale, Roger W; Chancey, V Carol; Fronheiser, Lucy E; Tran, Laura; Ottaviano, Danielle; Meyers, Barry S

2006-11-01

This study evaluated the biofidelity of both the Hybrid III and the THOR-NT anthropomorphic test device (ATD) necks in quasistatic tension-bending and pure-bending by comparing the responses of both the ATDs with results from validated computational models of the living human neck. This model was developed using post-mortem human surrogate (PMHS) osteoligamentous response corridors with effective musculature added (Chancey, 2005). Each ATD was tested using a variety of end-conditions to create the tension-bending loads. The results were compared using absolute difference, RMS difference, and normalized difference metrics. The THOR-NT was tested both with and without muscle cables. The THOR-NT was also tested with and without the central safety cable to test the effect of the cable on the behavior of the ATD. The Hybrid III was stiffer than the model for all tension-bending end conditions. Quantitative measurement of the differences in response showed more close agreement between the THOR-NT and the model than the Hybrid III and the model. By contrast, no systematic differences were observed in the head kinematics. The muscle cables significantly stiffened the THOR-NT by effectively reducing the laxity from the occipital condyle (OC) joint. The cables also shielded the OC upper neck load cell from a significant portion of the applied loads. The center safety significantly stiffened the response and decreased the fidelity, particularly in modes of loading in which tensile forces were large and bending moments small. This study compares ATD responses to computational models in which the models include PMHS response corridors while correcting for problems associated with cadaveric muscle. While controversial and requiring considerable diligence, these kinds of approaches show promise in assessing ATD biofidelity.

Localized bulging in an inflated cylindrical tube of arbitrary thickness - the effect of bending stiffness

NASA Astrophysics Data System (ADS)

Fu, Y. B.; Liu, J. L.; Francisco, G. S.

2016-05-01

We study localized bulging of a cylindrical hyperelastic tube of arbitrary thickness when it is subjected to the combined action of inflation and axial extension. It is shown that with the internal pressure P and resultant axial force F viewed as functions of the azimuthal stretch on the inner surface and the axial stretch, the bifurcation condition for the initiation of a localized bulge is that the Jacobian of the vector function (P , F) should vanish. This is established using the dynamical systems theory by first computing the eigenvalues of a certain eigenvalue problem governing incremental deformations, and then deriving the bifurcation condition explicitly. The bifurcation condition is valid for all loading conditions, and in the special case of fixed resultant axial force it gives the expected result that the initiation pressure for localized bulging is precisely the maximum pressure in uniform inflation. It is shown that even if localized bulging cannot take place when the axial force is fixed, it is still possible if the axial stretch is fixed instead. The explicit bifurcation condition also provides a means to quantify precisely the effect of bending stiffness on the initiation pressure. It is shown that the (approximate) membrane theory gives good predictions for the initiation pressure, with a relative error less than 5%, for thickness/radius ratios up to 0.67. A two-term asymptotic bifurcation condition for localized bulging that incorporates the effect of bending stiffness is proposed, and is shown to be capable of giving extremely accurate predictions for the initiation pressure for thickness/radius ratios up to as large as 1.2.

Transverse vibration and buckling of a cantilevered beam with tip body under constant axial base acceleration

NASA Technical Reports Server (NTRS)

Storch, J.; Gates, S.

1983-01-01

The planar transverse bending behavior of a uniform cantilevered beam with rigid tip body subject to constant axial base acceleration was analyzed. The beam is inextensible and capable of small elastic transverse bending deformations only. Two classes of tip bodies are recognized: (1) mass centers located along the beam tip tangent line; and (2) mass centers with arbitrary offset towards the beam attachment point. The steady state response is studied for the beam end condition cases: free, tip mass, tip body with restricted mass center offset, and tip body with arbitrary mass center offset. The first three cases constitute classical Euler buckling problems, and the characteristic equation for the critical loads/accelerations are determined. For the last case a unique steady state solution exists. The free vibration response is examined for the two classes of tip body. The characteristic equation, eigenfunctions and their orthogonality properties are obtained for the case of restricted mass center offset. The vibration problem is nonhomogeneous for the case of arbitrary mass center offset. The exact solution is obtained as a sum of the steady state solution and a superposition of simple harmonic motions.

Investigations on injection molded, glass-fiber reinforced polyamide 6 integral foams using breathing mold technology

NASA Astrophysics Data System (ADS)

Roch, A.; Kehret, L.; Huber, T.; Henning, F.; Elsner, P.

2015-05-01

Investigations on PA6-GF50 integral foams have been carried out using different material systems: longfiber- and shortfiber-reinforced PA6 as well as unreinforced PA6 as a reference material. Both chemical and physical blowing agents were applied. Breathing mold technology (decompression of the mold) was selected for the foaming process. The integral foam design, which can be conceived as a sandwich structure, helps to save material in the neutral axis area and maintains a distance between load-bearing, unfoamed skin layers. For all test series an initial mold gap of 2.5 mm was chosen and the same amount of material was injected. In order to realize different density reductions, the mold opening stroke was varied. The experiments showed that, at a constant mass per unit area, integral polyamide 6 foams have a significantly higher bending stiffness than compact components, due to their higher area moment of inertia after foaming. At a constant surface weight the bending stiffness in these experiments could be increased by up to 600 %. Both shortfiber- and longfiber-reinforced polyamide 6 showed an increase in energy absorption during foaming.

Symmetry breaking in the planar configurations of disilicon tetrahalides: Pseudo-Jahn-Teller effect parameters, hardness and electronegativity.

PubMed

Kouchakzadeh, Ghazaleh; Nori-Shargh, Davood

2015-11-21

CCSD(T), MP2, LC-BLYP, LC-ωPBE and B3LYP methods with the Def2-TZVPP basis set and natural bond orbital (NBO) interpretations were performed to investigate the correlations between the Pseudo-Jahn-Teller Effect (PJTE) parameters [i.e. vibronic coupling constant values (F), energy gaps between reference states (Δ) and the primary force constant (K0)], structural and configurational properties, global hardness, global electronegativity, natural bond orders, stabilization energies associated with electron delocalizations and natural atomic charges of disilicon tetrafluoride (1), disilicon tetrachloride (2), disilicon tetrabromide (3) and disilicon tetraiodide (4). All levels of theory showed the trans-bent (C2h) configurations as the energy minimum structures of compounds 1-4, and the flap angles between the X2Si planes and the Si=Si bonds in the distorted (C2h) configurations decrease from compound 1 to compound 4. The negative curvatures of the ground state electronic configurations and the positive curvatures of the excited states of the adiabatic potential energy surfaces (APESs) which resulted from the mixing of the ground Ag and excited B2g states are due to the PJTE (i.e. PJT(Ag + B2g) ⊗ b2g problem). Contrary to the usual expectation, with the decrease of the energy gaps between reference states (Δ), the PJTE stabilization energy, E(PJT), decreases from compound 1 to compound 4. The canonical molecular orbital (CMO) analysis revealed that the contributions of the ψ(HOMO)(b3u) and ψL(UMO)(b1u) molecular orbitals in the vibronic coupling constant (F) decrease from compound 1 to compound 4. This fact clearly justifies the decrease of the vibronic coupling constant (F) and the primary force constant (the force constant without the PJTE) values on going from compound 1 to compound 4, leading to the decrease of the negative curvatures of the ground state electronic configuration curves of their corresponding APESs. The results obtained showed that the stabilization energies associated with the mixing of the distorted donor π(Si-Si)(b(u)) bonding and acceptor σ(Si-Si)*(b(u)) antibonding orbitals along the b2g bending distortions decrease from compound 1 to compound 4. This fact reasonably explains the increase of the Si-Si natural bond orders (nbo) on going from compound 1 to compound 4. With the increase of the Si-Si natural bond orders, the corresponding E(PJT) decreases from compound 1 to compound 4. Importantly, the variations of the global hardness (η) differences (Δ[η(C2h) - η(D2h)]) do not correlate with the trend observed for their corresponding total energy differences, justifying that the configurational properties of compounds 1-4 do not obey the maximum hardness principle. Interestingly, the trans-bent (C2h) configurations of compounds 1-4 are more electronegative than their corresponding planar (D2h) forms and the variations of their global electronegativity (χ) differences (Δ[χ(C2h) - χ(D2h)]) succeed in accounting for the decrease of the E(PJT) stabilization energies for the D2h → C2h conversion processes on going from compound 1 to compound 4.

Moment measurements in dynamic and quasi-static spine segment testing using eccentric compression are susceptible to artifacts based on loading configuration.

PubMed

Van Toen, Carolyn; Carter, Jarrod W; Oxland, Thomas R; Cripton, Peter A

2014-12-01

The tolerance of the spine to bending moments, used for evaluation of injury prevention devices, is often determined through eccentric axial compression experiments using segments of the cadaver spine. Preliminary experiments in our laboratory demonstrated that eccentric axial compression resulted in "unexpected" (artifact) moments. The aim of this study was to evaluate the static and dynamic effects of test configuration on bending moments during eccentric axial compression typical in cadaver spine segment testing. Specific objectives were to create dynamic equilibrium equations for the loads measured inferior to the specimen, experimentally verify these equations, and compare moment responses from various test configurations using synthetic (rubber) and human cadaver specimens. The equilibrium equations were verified by performing quasi-static (5 mm/s) and dynamic experiments (0.4 m/s) on a rubber specimen and comparing calculated shear forces and bending moments to those measured using a six-axis load cell. Moment responses were compared for hinge joint, linear slider and hinge joint, and roller joint configurations tested at quasi-static and dynamic rates. Calculated shear force and bending moment curves had similar shapes to those measured. Calculated values in the first local minima differed from those measured by 3% and 15%, respectively, in the dynamic test, and these occurred within 1.5 ms of those measured. In the rubber specimen experiments, for the hinge joint (translation constrained), quasi-static and dynamic posterior eccentric compression resulted in flexion (unexpected) moments. For the slider and hinge joints and the roller joints (translation unconstrained), extension ("expected") moments were measured quasi-statically and initial flexion (unexpected) moments were measured dynamically. In the cadaver experiments with roller joints, anterior and posterior eccentricities resulted in extension moments, which were unexpected and expected, for those configurations, respectively. The unexpected moments were due to the inertia of the superior mounting structures. This study has shown that eccentric axial compression produces unexpected moments due to translation constraints at all loading rates and due to the inertia of the superior mounting structures in dynamic experiments. It may be incorrect to assume that bending moments are equal to the product of compression force and eccentricity, particularly where the test configuration involves translational constraints and where the experiments are dynamic. In order to reduce inertial moment artifacts, the mass, and moment of inertia of any loading jig structures that rotate with the specimen should be minimized. Also, the distance between these structures and the load cell should be reduced.

Reliable and accurate extraction of Hamaker constants from surface force measurements.

PubMed

Miklavcic, S J

2018-08-15

A simple and accurate closed-form expression for the Hamaker constant that best represents experimental surface force data is presented. Numerical comparisons are made with the current standard least squares approach, which falsely assumes error-free separation measurements, and a nonlinear version assuming independent measurements of force and separation are subject to error. The comparisons demonstrate that not only is the proposed formula easily implemented it is also considerably more accurate. This option is appropriate for any value of Hamaker constant, high or low, and certainly for any interacting system exhibiting an inverse square distance dependent van der Waals force. Copyright © 2018 Elsevier Inc. All rights reserved.

Analysis of Blockade in Charge Transport Across Polymeric Heterojunctions as a Function of Thermal Annealing: A Different Perspective

NASA Astrophysics Data System (ADS)

Rathi, Sonika; Chauhan, Gayatri; Gupta, Saral K.; Srivastava, Ritu; Singh, Amarjeet

2017-02-01

A blend of poly(3-hexylthiophene-2,5diyl) (P3HT) and [6,6]-phenyl C61 butyric acid methyl ester (PCBM) is popularly used as an active medium in polymeric solar devices. According to the most recent understanding, the blend is a three-phase system contrary to its earlier understanding of two-phase bicontinuous network. We have synthesized a P3HT-PCBM based layered heterostructure system by spin coating and thermal vacuum evaporations. Current density ( J) was measured as a function of applied electric field ( E) across the system bound between two metal electrodes. J- E relations were analyzed into the backdrop of space charge limited current model and Schottky model. The later was used to predict dc-dielectric constants from the linear slopes of ln ( J) versus E 1/2. The curves were not monotonously linear, but observe a knee-bend separating into two linear segments for each curve. Thermal annealing from 40°C to 80°C was used as an activation tool for driving changes in the internal morphology via inter-diffusion of polymers and current measurements were performed at room temperature after each annealing. At the last stage of annealing the two linear slopes were highly distinct. The presence of sharp knee-bend results in approximately 20 times jump in dielectric constant as a function of electric field. Such high jumps in dielectric constant illustrate the potential for switching applications and charge storage. The high dielectric constants can be understood in terms of space charge polarization due to isolated domains which hindrance to charge transport. The high dielectric constants were confirmed by another experiment of capacitance measurements of a different set of similar samples. A study of thermal evolution of internal morphology was also carried out using x-ray diffraction and scanning electron microscopy techniques to correlate the morphological changes with the transport properties.

Effects of ascending and descending climbers on space elevator cable dynamics

NASA Astrophysics Data System (ADS)

Ishikawa, Yoji; Otsuka, Kiyotoshi; Yamagiwa, Yoshiki; Doi, Hinata

2018-04-01

Based on a mass-point model, the cable dynamics of a space elevator during a climber's travel motion are examined. The cable response during a single operation of one ascending or descending climber is analyzed first, and then, based on the results, the cable dynamics for simultaneous operation of an ascending and a descending climber are evaluated. For the single operation, bending is significant when the climber is traveling near the Earth's surface. The cable also inclines with periodic oscillation as a result of a Coriolis force corresponding to the climber velocity. However, simultaneous operation of ascending and descending climbers can suppress the inclination of the cable by almost a factor of ten. In simultaneous operation, compared to single operation, a descending climber has a smaller amplitude of libration angle and less cable bending, while an ascending climber has a smaller amplitude when the climber is traveling at a higher altitude with climber velocities of 200 km/h and 400 km/h. The phase of the oscillation of the overall cable is found to be close to that of the descending climber. Cable bending is suppressed for any examined climber velocity, but the dependency of this suppression of displacement on climber velocity is not found. In summary, simultaneous operation can surely suppress the inclination of the cable via the cancellation of Coriolis forces by the two climbers.

Correlated fluorescence-atomic force microscopy studies of the clathrin mediated endocytosis in SKMEL cells

NASA Astrophysics Data System (ADS)

Hor, Amy; Luu, Anh; Kang, Lin; Scott, Brandon; Bailey, Elizabeth; Hoppe, Adam; Smith, Steve

2017-02-01

Clathrin-mediated endocytosis (CME) is one of the central pathways for cargo transport into cells, and plays a major role in the maintenance of cellular functions, such as intercellular signaling, nutrient intake, and turnover of plasma membrane in cells. The clathrin-mediated endocytosis process involves invagination and formation of clathrin-coated vesicles. However, the biophysical mechanisms of vesicle formation are still debated. Currently, there are two models describing membrane bending during the formation of clathrin cages: the first involves the deposition of all clathrin molecules to the plasma membrane, forming a flat lattice prior to membrane bending, whereas in the second model, membrane bending happens simultaneously as the clathrin arrives to the site to form a clathrin-coated cage. We investigate clathrin vesicle formation mechanisms through the utilization of tapping-mode atomic force microscopy for high resolution topographical imaging in neutral buffer solution of unroofed cells exposing the inner membrane, combined with fluorescence imaging to definitively label intracellular constituents with specific fluorophores (actin filaments labeled with green phalloidin and clathrin coated vesicles with the fusion protein Tq2) in SKMEL (Human Melanoma) cells. An extensive statistical survey of many hundreds of CME events, at various stages of progression, are observed via this method, allowing inferences about the dominant mechanisms active in CME in SKMEL cells. Results indicate a mixed model incorporating aspects of both the aforementioned mechanisms for CME.

Automatic prediction of tongue muscle activations using a finite element model.

PubMed

Stavness, Ian; Lloyd, John E; Fels, Sidney

2012-11-15

Computational modeling has improved our understanding of how muscle forces are coordinated to generate movement in musculoskeletal systems. Muscular-hydrostat systems, such as the human tongue, involve very different biomechanics than musculoskeletal systems, and modeling efforts to date have been limited by the high computational complexity of representing continuum-mechanics. In this study, we developed a computationally efficient tracking-based algorithm for prediction of muscle activations during dynamic 3D finite element simulations. The formulation uses a local quadratic-programming problem at each simulation time-step to find a set of muscle activations that generated target deformations and movements in finite element muscular-hydrostat models. We applied the technique to a 3D finite element tongue model for protrusive and bending movements. Predicted muscle activations were consistent with experimental recordings of tongue strain and electromyography. Upward tongue bending was achieved by recruitment of the superior longitudinal sheath muscle, which is consistent with muscular-hydrostat theory. Lateral tongue bending, however, required recruitment of contralateral transverse and vertical muscles in addition to the ipsilateral margins of the superior longitudinal muscle, which is a new proposition for tongue muscle coordination. Our simulation framework provides a new computational tool for systematic analysis of muscle forces in continuum-mechanics models that is complementary to experimental data and shows promise for eliciting a deeper understanding of human tongue function. Copyright © 2012 Elsevier Ltd. All rights reserved.

Instrument for the application of controlled mechanical loads to tissues in sterile culture

DOEpatents

Lintilhac, P.M.; Vesecky, T.B.

1995-04-18

Apparatus and methods are disclosed facilitating the application of forces and measurement of dimensions of a test subject. In one arrangement the test subject is coupled to a forcing frame and controlled forces applied thereto by a series of guideways and sliders. The sliders, which contact the test subject are in force transmitting relation to a forcing frame. Tension, compression and bending forces can be applied to the test subject. Force applied to the test subject is measured and controlled. A dimensional characteristic of the test subject, such as growth, is measured by a linear variable differential transformer. The growth measurement data can be used to control the force applied. Substantially uniaxial stretching is achieved by placing the test subject on an elastic membrane stretched by an arrangement of members securing the elastic member to the forcing frame. 8 figs.