Helical Angle Research Articles

Influence de la réconstruction du ligament radio-dorsal sur la stabilité de l’articulation trapeziometacarpien

Introduction Biomechanical and anatomical research has shown that the dorsal radial ligament (DRL) is thicker and stiffer then the anterior oblique ligament (AOL). The DRL as the key stabilizing structure of the trapeziometacarpal (TMC) joint has been documented extensively. The aim of the current study is to quantify the influence of a surgical DRL reconstruction on TMC stability in non-traumatic instability patients. Methods Eight patients with symptomatic TMC instability but no radiographic signs of osteoarthritis were recruited and dynamic CT scans of the thumb were made during active abduction-adduction, flexion-extension and two functional grip task using a radiolucent jig. After image acquisition and segmentation, metacarpal translation was expressed relative to the trapezial articular surface. In addition, intersection points and inclination angles of instantaneous helical axes with an anatomically defined plane were determined to facilitate motion comparison between subjects. Scans were acquired before and 6–12 months after reconstruction of the DRL. Results During active motion, there is motion at both the trapeziometacarpal (TMC) and trapezioscaphoid (STT) joints. However, joint motion patterns, defined as changes in helical axis inclination angles during opposition, differ between patients. In most patients, dorsal luxation of the first metacarpal (MC1) could be clearly seen and quantified during the full range of motion, as well as during function grip tasks. Furthermore, dorsal luxation results in higher point loading of TMC cartilage as could be demonstrated by mapping the changes in articular contact area for each active motion. After DRL reconstruction, patients report improvement in pain and subjective stability in the joint. Analyses of the dynamic CT scans demonstrate reduced translation and luxation of MC1 in all patients as well as reduced cartilage point loading. Conclusion After DRL reconstruction, luxation of MC1 was reduced in all patients. We quantified movement in both TMC & STT joint, suggesting that pathologies at the TMC joint could lead to compensatory movements at the more proximal joints or vice versa. Simple DRL reconstruction is an attractive alternative for the more invasive anterior oblique ligament reconstruction described by Eaton, serving the same purpose, stabilizing the CMC joint. Future research should investigate if TMC instability and its altered kinematics lead to secondary joint problems (e.g. osteoarthritis) if left unattended.

Package of double helical bromine chains inside single-walled carbon nanotubes

The helicity of stable double helical bromine chains inside single-walled carbon nanotubes (SWCNTs) was studied through the calculation of systematic interaction energy, using the van der Waals interaction potential. The results presented clear images of stable double helical structures inside SWCNTs. The optimal helical radius and helical angle of chain structure increase and decrease, respectively, with the increase of tube radius. The detailed analysis indicated that some metastable structures in SWCNTs may also co-exist with the optimal structures, but not within the same tubes. In addition, a detailed simulation of X-ray diffraction patterns was performed for the obtained optimal helical structures.

Slip and stress of tensile armors in unbonded flexible pipes close to end fitting considering an exponentially decaying curvature distribution

An analytical model is given to investigate the end-fitting effect on slip and stress of tensile armors in unbonded flexible pipes under tension, torsion and varying bending in the absence of friction. An exponentially decaying curvature distribution is assumed to represent controlled curvature over the end region. The deviation from the initial helical angle is taken to describe the armor wire path as the pipe is stretched, twisted and bent, which is determined by minimization of the strain energy functional using the Euler equation. The obtained simultaneous differential equations are numerically solved by transforming them into a boundary value problem. An analytical solution is found by neglecting the twisting rotation of the wire cross-section. The developed model is validated with a finite element simulation and geodesic based analytical expressions for constant curvature and with a current numerical model for varying curvature. Reasonable correlations are observed between the model predictions and the results from other methods. The validated model is then applied to typical flexible pipe designs to find the level and location of the greatest increases in stress. The results show that the end restraint could cause a significant stress increase in the armor wire at the end fitting vicinity and the critical location is close to the extreme fiber position on the compressive side of the pipe for typical cases. The effect of end restraint on layer bending stiffness is also evaluated.

A numerical investigation of the effects of blade’s geometric parameters on the power consumption of the twin-blade planetary mixer

Blades act as key components for twin-blade planetary mixer; their geometric parameters (blade–blade clearance and helical angle) and two different rotating modes (counter-rotating mode and co-rotating mode) were investigated numerically via commercial software ANSYS Fluent 14.5 to reveal the effects on the power or torque consumption. The results indicate that decreasing the blade–blade clearance or increasing the helical angle increases the power consumption of the twin-blade planetary mixer. The proportionality constant of power curves depends on the geometry of the blades.

Dynamic analysis of a liquid droplet and optimization of helical angles for vortex drainage gas recovery

Downhole vortex drainage gas recovery is a new gas production technology. So far, however, the forces and motions of liquid phase in the swirling flow field of wellbores during its field application have not been figured out. In this paper, the forces of liquid droplets in the swirling flow field of wellbores were analyzed on the basis of two-phase fluid dynamics theories. Then, the motion equations of fluid droplets along axial and radical directions were established. Magnitude comparison was performed on several typical acting forces, including Basset force, virtual mass force, Magnus force, Saffman force and Stokes force. Besides, the formula for calculating the optimal helical angle of vortex tools was established according to the principle that the vertical resultant force on fluid droplets should be the maximum. And afterwards, each acting force was comprehensively analyzed in terms of its origin, characteristics and direction based on the established force analysis model. Magnitude comparison indicates that the forces with less effect can be neglected, including virtual mass force, Basset force and convection volume force. Moreover, the vertically upward centrifugal force component occurs on the fluid droplets in swirling flow field instead of those in the conventional flow field of wellbores, which is favorable for the fluid droplets to move upward. The reliability of optimal helical angle calculation formula was verified by means of case analysis. It is demonstrated that with the decrease of well depth, the fluid-carrying capability of gas and the optimal helical angle increase. The research results in this paper have a guiding significance to the optimization design of downhole vortex tools and the field application of downhole vortex drainage gas recovery technology.

The dynamic coupling behaviour of a cylindrical geared rotor system subjected to gear eccentricities

A general dynamic model for the cylindrical geared rotor system with local tooth profile errors and global mounting errors is developed. This model includes a finite element (FE) model for the shaft structure, a lumped-parameter bearing model and a 3 dimensional (3D) gear mesh model based on previous work. Gear geometric eccentricities, unloaded static transmission error, as well as the fluctuation of the mesh stiffness are included in this model to study the dynamic coupling behaviour of the transverse and rotational motions of gears subjected to gear eccentricities. The simulation results are compared against the experimental results provided in the literature, which proves that the proposed modal is suitable to study the dynamic behaviour of a cylindrical geared rotor system. The influence of the helical angle, the number of teeth, gear profile error, and gear eccentricities on the dynamic coupling behaviour were studied. It was found that the dynamic coupling between the transverse and rotational motions of the gears becomes apparent in the low speed range when resonances are excited either by the gear profile error or mesh stiffness fluctuation. The analysis results of this research are useful for the dynamic analysis of gear transmission systems subjected to gear eccentricities.

MreB Orientation Correlates with Cell Diameter in Escherichia coli

Bacteria have remarkably robust cell shape control mechanisms. For example, cell diameter only varies by a few percent across a given population. The bacterial actin homolog, MreB, is necessary for establishment and maintenance of rod shape although the detailed properties of MreB that are important for shape control remained unknown. In this study, we perturb MreB in two ways: by treating cells with the polymerization-inhibiting drug A22 and by creating point mutants in mreB. These perturbations modify the steady-state diameter of cells over a wide range, from 790 ± 30 nm to 1700 ± 20 nm. To determine which properties of MreB are important for diameter control, we correlated structural characteristics of fluorescently tagged MreB polymers with cell diameter by simultaneously analyzing three-dimensional images of MreB and cell shape. Our results indicate that the helical pitch angle of MreB inversely correlates with the cell diameter of Escherichia coli. Other correlations between MreB and cell diameter are not found to be significant. These results demonstrate that the physical properties of MreB filaments are important for shape control and support a model in which MreB organizes the cell wall growth machinery to produce a chiral cell wall structure and dictate cell diameter.

An Implementation of Analytical Boundary Simulation on Feedrate Scheduling during Semi-Finish Milling

In five-axis milling, determining the continuously changing Cutter Workpiece Engagement (CWE) remains a challenge. All the feedrate calculation method that have been reported need a precise information about Cutter Workpiece Engagement. In this paper, the cut geometry was calculated using an analytical method called Analytical Boundary Simulation (ABS). This method was reported accurate and less expensive in term of calculation time. The cut geometry data was then used to calculate the instantaneous cutting forces. A new mechanistic force model was developed by taken into account the variation of axial depth of cut, the feedrate, the tool orientation, and the helical angle. Analytical boundary simulation and mechanisitic cutting force model were then used to optimize a semi finish machining process using feedrate scheduling. The applicability of the proposed method was verified experimentally and the result show that the calculated cutting forces of feedrate scheduling have a good agreement with those obtained from the experimental work.

Stable single helical C- and I-chains inside single-walled carbon nanotubes**Project supported by the National Basic Research Program of China (Grant No. 2011CB808200), the National Natural Science Foundation of China (Grant Nos. 11504150 and 51320105007), and the Cheung Kong Scholars Program of China.

The helicity of stable single helical carbon chains and iodine chains inside single-walled carbon nanotubes (SWCNTs) is studied by calculating the systematic van der Waals interaction energy. The results show that the optimal helical radius increases linearly with increasing tube radius, which produces a constant separation between the chain structure and the tube wall. The helical angle exhibits a ladder-like decrease with increasing tube radius, indicating that a large tube can produce a small helicity in the helical structures.

Gear Flank Modification Using a Variable Lead Grinding Worm Method on a Computer Numerical Control Gear Grinding Machine

Tooth crowning of a ground helical gear is usually done by adjusting the radial feed with respect to the axial feed of the grinding worm on the modern CNC gear grinding machine. However, when the amount of crowning and the helical angle of the gear are large, this method always results in a twisted tooth flank. Hence, in this paper, we propose a tooth flank crowning method for helical gears, which uses a diagonal (combined tangential and axial) feed on a grinding machine with a variable lead grinding worm (VLGW) obtained by adjusting the axial feed of the dressing disk with respect to the rotation angle of the grinding worm. Since all the required corrective motions for the proposed VLGW method are existing CNC controlled axes on modern gear grinding machines, it can easily be implemented without extra cost to modify the grinder hardware. Three numerical examples are presented to show the validation of the proposed method and its ability to reduce tooth flank twist even in the case of a large helical angle, with a particularly significant reduction on a crowned helical gear.

Helical Fiber Pull-out in Biological Materials

Many biological materials, such as wood and bone, possess helicoid microstructures at microscale, which can serve as reinforcing elements to transfer stress between crack surfaces and improve the fracture toughness of their composites. Failure processes, such as fiber/matrix interface debonding and sliding associated with pull-out of helical fibers, are responsible mainly for the high energy dissipation needed for the fracture toughness enhancement. Here we present systemic analyses of the pull-out behavior of a helical fiber from an elastic matrix via the finite element method (FEM) simulation, with implications regarding the underlying toughening mechanism of helicoid microstructures. We find that, through their uniform curvature and torsion, helical fibers can provide high pull-out force and large interface areas, resulting in high energy dissipation that accounts, to a large extent, for the high toughness of biological materials. The helicity of fiber shape in terms of the helical angle has significant effects on the force-displacement relationships as well as the corresponding energy dissipation during fiber pull-out.

Heavy-Atom Labeled Transmembrane β-Peptides: Synthesis, CD-Spectroscopy, and X-ray Diffraction Studies in Model Lipid Multilayer.

Transmembrane β-peptides are promising candidates for the design of well-controlled membrane anchors in lipid membranes. Here, we present the synthesis of transmembrane β-peptides with and without tryptophan anchors, as well as a novel iodine-labeled d-β(3) -amino acid. By using one or more of the heavy-atom labeled amino acids as markers, the orientation of the helical peptide was inferred based on the electron-density profile determined by X-ray reflectivity. The β-peptides were synthesized through manual Fmoc-based solid-phase peptide synthesis (SPPS) and reconstituted in unilamellar vesicles forming a right-handed 314 -helix secondary structure, as shown by circular dichroism spectroscopy. We then integrated the β-peptide into solid-supported membrane stacks and carried out X-ray reflectivity and grazing incidence small-angle X-ray scattering to determine the β-peptide orientation and its effect on the membrane bilayers. These β-peptides adopt a well-ordered transmembrane motif in the solid-supported model membrane, maintaining the basic structure of the original bilayer with some distinct alterations. Notably, the helical tilt angle, which accommodates the positive hydrophobic mismatch, induces a tilt of the acyl chains. The tilted chains, in turn, lead to a membrane thinning effect.

Energy and cost optimization of shell and tube heat exchanger with helical baffles using Kriging metamodel based on MOGA

In order to overcome the dependence on empirical correlations and to achieve a more accurate results for modeling the computer response, an improved algorithm combing a Kriging response surface and the multi-objective genetic algorithm (MOGA) for the optimization design of shell and tube heat exchanger with helical baffles (STHXsHB) is proposed in this paper. The helical angles β, baffle overlap proportion e and inlet volume flow rate V are considered as optimization parameters, in which the heat transfer rate and total cost are optimized by multi-objective optimization. The results show that compared with the real solutions of CFD simulation, the optimized results illustrated a good agreement within ±3% error. Therefore, the optimization method is verified to be successful. Besides the obtained Pareto-optimal points show that a small helical angle with 15° and the baffle overlap proportion is equal to 0.25 are beneficial to trade off the heat transfer rate and total cost of STHXsHB. Furthermore, the comparison between the optimum STHXsHB and a conventional shell and tube heat exchanger with segmental baffles (STHXsSB) are carried out. The results show that the comprehensive performances of the optimum STHXsHB are better. The evaluation index PEA and PEB increase by 76.5–91.2% and 69.0–84.5%, respectively. Therefore, it can be concluded that employed helical baffles in the STHXs can obtain a better performance. Moreover, this new method can be used to optimize the STHXsHB and the conclusions are benefit in the design of STHXsHB for energy saving and cost reduction.

The effects of noise in cardiac diffusion tensor imaging and the benefits of averaging complex data.

There is growing interest in cardiac diffusion tensor imaging (cDTI), but, unlike other diffusion MRI applications, there has been little investigation of the effects of noise on the parameters typically derived. One method of mitigating noise floor effects when there are multiple image averages, as in cDTI, is to average the complex rather than the magnitude data, but the phase contains contributions from bulk motion, which must be removed first. The effects of noise on the mean diffusivity (MD), fractional anisotropy (FA), helical angle (HA) and absolute secondary eigenvector angle (E2A) were simulated with various diffusion weightings (b values). The effect of averaging complex versus magnitude images was investigated. In vivo cDTI was performed in 10 healthy subjects with b = 500, 1000, 1500 and 2000 s/mm(2). A technique for removing the motion-induced component of the image phase present in vivo was implemented by subtracting a low-resolution copy of the phase from the original images before averaging the complex images. MD, FA, E2A and the transmural gradient in HA were compared for un-averaged, magnitude- and complex-averaged reconstructions. Simulations demonstrated an over-estimation of FA and MD at low b values and an under-estimation at high b values. The transition is relatively signal-to-noise ratio (SNR) independent and occurs at a higher b value for FA (b = 1000-1250 s/mm(2)) than MD (b ≈ 250 s/mm(2)). E2A is under-estimated at low and high b values with a transition at b ≈ 1000 s/mm(2), whereas the bias in HA is comparatively small. The under-estimation of FA and MD at high b values is caused by noise floor effects, which can be mitigated by averaging the complex data. Understanding the parameters of interest and the effects of noise informs the selection of the optimal b values. When complex data are available, they should be used to maximise the benefit from the acquisition of multiple averages. The combination of complex data is also a valuable step towards segmented acquisitions.

Adaptive anisotropic gaussian filtering to reduce acquisition time in cardiac diffusion tensor imaging.

Diffusion tensor imaging (DTI) is used to quantify myocardial fiberorientation based on helicalangles (HA). Accurate HA measurements require multiple excitations (NEX) and/or several diffusion encoding directions (DED). However, increasing NEX and/or DED increases acquisition time (TA). Therefore, in this study, wepropose to reduce TA by implementinga 3D adaptive anisotropic Gaussian filter (AAGF) on the DTI data acquired from ex-vivohealthy and infarcted porcine hearts. DTI was performed onex-vivo hearts [9-healthy, 3-myocardial infarction (MI)] with several combinations of DED and NEX. AAGF, mean (AVF) and median filters (MF) were applied on the primary eigenvectors of the diffusion tensor prior to HA estimation. The performance of AAGF was compared against AVF and MF. Root mean square error (RMSE), concordance correlation-coefficients and Bland-Altman's technique was used to determine optimal combination of DED and NEX that generated the best HA maps in the least possible TA. Lastly, the effect of implementing AAGF on the infarcted porcine hearts was also investigated. RMSE in HA estimation for AAGF was lower compared to AVF or MF. Post-filtering(AAGF) fewer DED and NEX were required to achieve HA maps with similar integrity as those obtained from higher NEX and/or DED. Pathological alterations caused in HA orientation in the MI model were preserved post-filtering(AAGF). Our results demonstrate that AAGF reduces TA without affecting the integrity of the myocardial microstructure.

Effect of twist angle on the performance of Savonius wind turbine

This study aimed to understand the performance and shape characteristics of a helical Savonius wind turbine at various helical angles. The power coefficient (Cp) at different tip speed ratios (TSRs) and torque coefficient (CT) at different azimuths for helical blade angles of 0°, 45°, 90°, and 135° were observed under the conditions of a constant projection area and aspect ratio. The numerical results discussed in this paper were obtained using an incompressible unsteady Reynolds average Navier–Stokes (k-ε RNG) model. A numerical analysis in the unsteady state was used to examine the flow characteristics in 1° steps from 0° to 360°. In addition, an experiment was performed at a large-scale wind tunnel, and the results were compared with those of the numerical analysis. Wind speed correction was also employed because of the blockage effect between the wind turbine and wind tunnel. Our results showed that the maximum power coefficient (Cp,max) values in both cases had similar tendencies for the TSR range considered in this study, i.e. from 0.4 to 0.8, except for the twist angle of 45°. The Cp,max occurred at the twist angle of 45°, whereas it decreased by 25.5% at 90° and 135°. Regarding the CT values at various azimuths, the results showed that the peak-to-peak values in the profiles for 90° and 135° were less than those for 0° and 45°.

Handedness-dependent hyperelasticity of biological soft fibers with multilayered helical structures

Collagen fibrils with multilayered helical structures widely exist in biological soft tissues, e.g., blood vessels, tendons, and ligaments. Understanding the mechanical properties of this kind of chiral materials is not only essential for evaluating the mechanical behaviors of the host tissues but also of significance for medical engineering, clinical diagnosis, and surgical operation. In this paper, a theoretical model is presented to investigate the hyperelasticity of biological soft fibers with multilayered helical structures. The effects of the initial helical angle, number and handedness of the fibers in each ply on the mechanical response of the material are examined. Our analysis reveals a switch of contact modes between two neighboring layers, which may greatly alter the overall non-linear response of the material. The Poisson׳s ratio of such a multilayered string can be greater than 0.5. The obtained results agree with relevant experiments of soft tissues. This work sheds light on the non-linear mechanics of chiral materials and may also guide the design of biomimetic materials.

Experimental Investigation of Helical Tidal Turbine Characteristics with Different Twists

The helical tidal current turbine was studied and reported its performance and characteristics for free water flow electric turbine development. The scale model of tidal turbine was built in dimension as: 0.5m and 0.6m of diameters and 1.25m in length; the turbine cross section blade was the symmetric NACA0020 with a 0.07m chord length, and there were 3 blades with the helical angle of 120o, 135o, and 150o. The model was tested in a towing tank (1.46m width, 3m depth and 45m length). The rotation and torque of the turbine was measured under various tow velocity settings, while power and power efficiencies under various tip speed ratios and helical angle velocities were presented. The characteristics obtained from this experiment provide useful information for the design and development of helical tidal current electrical turbine.

Synergy of multi-scale toughening and protective mechanisms at hierarchical branch-stem interfaces.

Biological materials possess a variety of artful interfaces whose size and properties are adapted to their hierarchical levels and functional requirements. Bone, nacre, and wood exhibit an impressive fracture resistance based mainly on small crystallite size, interface organic adhesives and hierarchical microstructure. Currently, little is known about mechanical concepts in macroscopic biological interfaces like the branch-stem junction with estimated 1014 instances on earth and sizes up to few meters. Here we demonstrate that the crack growth in the upper region of the branch-stem interface of conifer trees proceeds along a narrow predefined region of transversally loaded tracheids, denoted as sacrificial tissue, which fail upon critical bending moments on the branch. The specific arrangement of the tracheids allows disconnecting the overloaded branch from the stem in a controlled way by maintaining the stem integrity. The interface microstructure based on the sharply adjusted cell orientation and cell helical angle secures a zig-zag crack propagation path, mechanical interlock closing after the bending moment is removed, crack gap bridging and self-repairing by resin deposition. The multi-scale synergetic concepts allows for a controllable crack growth between stiff stem and flexible branch, as well as mechanical tree integrity, intact physiological functions and recovery after the cracking.

Multiple helical configuration and quantity threshold of graphene nanoribbons inside a single-walled carbon nanotube.

Molecular dynamics simulation has been carried out to explore the configuration and quantity threshold of multiple graphene nanoribbons (GNRs) in single-walled carbon nanotube (SWCNT). The simulation results showed that several GNRs tangled together to form a perfect spiral structure to maximize the π-π stacking area when filling inside SWCNT. The formation of multiple helical configuration is influenced by the combined effect of structure stability, initial arrangement and tube space, meanwhile its forming time is related to helical angle. The simulated threshold of GNRs in SWCNT decreases with GNR width but increases with SWCNT diameter, and two formulas have come up in this study to estimate the quantity threshold for GNRs. It has been found that multilayered graphite is hard to be stripped in SWCNT because the special helical configuration with incompletely separated GNRs is metastable. This work provides a possibility to control the configuration of GNR@SWCNT.