Helical Angle Research Articles

Conformal conversion from helical hexagonal InN microtubes to In2O3 counterparts

Cubic In2O3 microtubes were prepared by thermally oxidizing InN counterparts under controlled conditions. Similar to the starting InN sample, the converted In2O3 microtubes are hexagonal in cross section and exhibit helical motifs of both right-handed and left-handed architectures with helical angles of 0°–30°. InN microtubes can be retrieved by renitridation of the oxide microtubes. This work demonstrates that it is feasible to fabricate specific oxide nano-/microstructures from its corresponding nitride counterparts via controlled oxidation manner and vice versa. Temperature-dependent Raman scattering in both InN and In2O3 microtubes was measured and obvious downshifts of Raman modes were observed with increasing temperature.

Three‐dimensional architecture of the left ventricular myocardium

Concepts for ventricular function tend to assume that the majority of the myocardial cells are aligned with their long axes parallel to the epicardial ventricular surface. We aimed to validate the existence of aggregates of myocardial cells orientated with their long axis intruding obliquely between the ventricular epicardial and endocardial surfaces and to quantitate their amount and angulation. To compensate for the changing angle of the long axis of the myocytes relative to the equatorial plane of the ventricles with varying depths within the ventricular walls, the so-called helical angle, we used pairs of cylindrical knives of different diameters to punch semicircular slices from the left ventricular wall of pigs, the slices extending from the epicardium to the endocardium. The slices were pinned flat, fixed in formaldehyde, embedded in paraffin, sectioned, stained with azan or hematoxilin and eosin, and analyzed by a new semiautomatic procedure. We made use of new techniques in informatics to determine the number and angulation of the aggregates of myocardial cells cut in their long axis. The alignment of the myocytes cut longitudinally varied markedly between the epicardium and the endocardium. Populations of myocytes, arranged in strands, diverge by varying angles from the epicardial surface. When paired knives of decreasing diameter were used to cut the slices, the inclination of the diagonal created by the arrays increases, while the lengths of the array of cells cut axially decreases. The visualization of the size, shape, and alignment of the myocytic arrays at any side of the ventricular wall is determined by the radius of the knives used, the range of helical angles subtended by the alignment of the myocytes throughout the thickness of the wall, and their angulation relative to the epicardial surface. Far from the majority of the ventricular myocytes being aligned at angles more or less tangential to the epicardial lining, we found that three-fifths of the myocardial cells had their long axes diverging at angles between 7.5 and 37.5 degrees from an alignment parallel to the epicardium. This arrangement, with the individual myocytes supported by connective tissue, might control the cyclic rearrangement of the myocardial fibers. This could serve as an important control of both ventricular mural thickening and intracavitary shape.

A precision design and NC manufacturing model for concave-arc ball-end cutters

Having first defined the helical angle as the angle between the cutting edge and the axis of rotation of the cutter, this paper then presents design models for producing the cutting edge and groove of a ball-end cutter with concave-arc generator. The relative feed speeds of the grinding wheel in the radial and axial directions during NC machining of the cutter are derived based upon a given speed of rotation. The feed speed of the grinding wheel in the radial direction is modified according to the cross section of the groove that passes through the center of the cutter sphere. The paper presents a method for manufacturing a concave-arc ball-end (CABE) cutter using a 2-axis NC machine. The models that are used to calculate the actual obtained groove and the computer simulation method are also included. To further enhance the accuracy of the mathematical models, a compensatory machining process that eliminates residual profile on the revolving surface is presented. This paper provides a valuable reference for the design and machining of this cutter type.

Mechanical properties of helically perforated thin films

The mechanical behavior of a helically perforated thin film structure was simulated by finite element analysis. The validity of the results was confirmed by comparison to a nanoindentation measurement performed on a nickel helically perforated thin film sample. It was found that variation of the helical pitch angle from 35° to 70° resulted in a change of 1.5 times in the elastic modulus. Since the fabrication process used to create the actual samples allows for variation of the pitch angle, this result may enable the tailoring of materials for use in micro- and nanoscale devices.

Life prediction system using a tool’s geometric shape for high-speed milling

In recent years, machinery and tool technology has been developing rapidly. The accuracy of operations have also become more and more exact. Elsewhere, raw materials have also been honed, hoping to provide more useful properties than previously. Thus, how to find the best way to prolong the life of a tool subjected to hardened material cutting is the target of this research. Three kinds of tool angle of the endmill are used in this research; clearance angle, rake angle, and helical angle. The cutting conditions are the same; we only change the tool angle for all the cases studied. We attempt to discover better tool geometrical angles for the high-speed milling of NAK80 mold steel. The tool wear rate was measured through a toolmaker’s microscope and the roughness of the machined surface was measured by the roughness-measuring instruments after several complete surface layers were removed from the workpiece in the experiment. Also, a noise-mediator was used to detect the level of cutting noise during each surface layer workpiece removal of the high-speed milling process, and different noise levels were then compared with the tool wear rates for identifying noise characteristics in the case of an over-worn tool state. An abductive network was applied to synthesize the data sets measured from the experiments and the prediction models are established for tool-life estimation and over-worn situation alert under various combinations of different tool geometrical angles. Through the identification of tool wear and its related cutting noise, we hope to consequently construct an automatic tool wear monitoring system by noise detection during a high-speed cutting process to judge whether the tool is still good or not, and, so, the cost of milling can be reduced.

Comparison of screw-in effect of three NiTi file systems used by undergraduates

The purposes of this study were to compare the apical terminus width of simulated curved root canal prepared with three NiTi file systems used by undergraduates for evaluation the effects of flute angle and pitch or radial land on reducing screw-in effect and to determine more safe NiTi file system for inexperienced operators. Fifty inexperienced undergraduate students prepared 150 simulated curved root canals in resin blocks with three NiTi file systems ; ProFile, Hero Shaper, K3. The electric motor set at a speed of 300 rpm and torque of 30 in a 16 : 1 reduction handpiece was used. The simulated root canal was prepared to ISO #25 sizes with each file system. The scanned images of pre- and post-instrumented canal of resin block were superimposed. To evaluate the screw-in effect of three NiTi file systems, apical terminus width of root canal was measured from superimposed images and statistical analysis was performed. There were significant differences in three NiTi flle systems. ProFile had significantly smaller width than Hero Shaper and K3 (P and Hero Shaper. Under the condition of this study, active file system (Hero SHaper, K3) with variable pitch and helical angle had more screw-in effect than passive file system (ProFile) with constant pitch and helical angle. It seems that the radial lands play more important role in reducing screw-in effect.

Helically Perforated Thin Films -- Dependence of Mechanical Properties on Microstructure

AbstractThe effects of several microstructural parameters on the mechanical behaviour of a helically perforated thin film structure, or inverse microspring, were investigated using a finite element model[1]. The parameters investigated were the helical pitch angle, the cross-section radius, and the coil spacing. The elastic modulus was found to depend most strongly on the helical pitch angle (changing by a factor of 1.3 as the pitch angle went from 35° to 70°). Variations in the coil radius and the film thickness had a minor effect on the modulus. It was also found that using a finite size model (as opposed to an infinite model using periodic boundary conditions) produced better conditioned results. A preliminary confirmation of the model's validity was performed by comparison to nanoindentation results of a nickel helically perforated thin film.

Measurement of three-dimensional intra-articular kinematics: methodological and interpretation problems

Intra-articular kinematics evaluates joint motion in terms of the configuration of the joint. Therefore data are needed concerning joint kinematics as well as joint configuration. We have developed accurate measurement methods for both in vivo and in vitro evaluation. Interpretation of the processed data is more complex than simply setting up a coordinate system based on the joint configuration. Although the description of intra-articular motion in terms of Euler–Cardan or helical angles may be complete, the therapeutic interpretation may be doubtful. Using the the ulno-humeral joint during flexion–extension as an example, we found the combination of helical angles in the directions of extension/external rotation/varus. In the case of the Cardan angles, inconsistent patterns of rotation resulted from a different choice of sequence order and were different from the helical angles. The finite helical axis (FHA) provides a functional representation of the joint movement, i.e. pathways of motion, whereas the sequence dependency of Euler–Cardan angles produces problems in the therapeutic interpretation of the movement. Therefore we believe that an FHA approach should be used in intra-articular kinematics research.

The three-dimensional arrangement of intermediate filaments in Romney wool cortical cells

The three-dimensional orientation and arrangement of intermediate filaments in Romney wool ortho-, meso-, and paracortical cells has been revealed using single axis high voltage electron tomography. Modelled tomograms confirm that intermediate filaments in orthocortical cells are arranged helically, with the helical angle progressively increasing from the centre to the periphery of macrofibrils. Intermediate filaments in meso- and paracortical cells display parallel arrangements differing mainly in packing density, with the mesocortex packed more tightly than the paracortex. The intermediate filament arrangements observed confirm expectations based on earlier two-dimensional transmission electron microscopy observations by the authors and other researchers. It is expected that these findings will contribute to a better understanding of the biological and structural basis of wool fibre curvature.

Template-free synthesis of helical hexagonal microtubes of indium nitride

Single crystalline indium nitride (InN) helical microtubes with a hexagonal hollow cross section have been synthesized in bulk quantities by nitriding indium oxide powder in ammonia flux. As-prepared InN microtubes grow along the [0001] direction with typical outer diameters of 1–3μm, wall thickness of 50–80nm and lengths up to hundreds of microns. The InN microtubes exhibit both right-handed and left-handed helicities with helical angles ranging from zero to about 30°. Variation of helicity can be observed in a single tube. A number of observations demonstrate that the growth of the tubular structure occurs by the spiraling of the warped InN nanobelts. Photoluminescence spectrum of the microtubes presents a strong emission peak centered at 700nm at room temperature.

Band Theory of Single-Walled Carbon Nanotubes

In this paper, a curvilinear coordinate system is used in space and in k-space to study the energy band of single-walled carbon nanotubes wrapped at a helical angle. Using this method, a general function of the bandgap associated with the radius of the tube and the helical angle is derived based on the tight-binding theory. The three-dimensional hexagonal Brillouin zone of the tube is on the surface of cylinder in the k-space. For two tubes with different diameters, there is a distance between the cylindrical Brillouin zones in the radial direction. The Brillouin zone varies with the radius of the tube and the number of cells on the circumference. For the metallic zigzag tubes, the bandgaps decrease discretely to zero at the corners of the Brillouin zones, and those corners are singular points of zero gaps. With the transformation of coordinates, the metallic zigzag type is proven to be equivalent to an armchair configuration. Electrical characteristics of the chiral effects are briefly highlighted.

Localization properties of electronic states in a polaron model of poly(dG)-poly(dC) and poly(dA)-poly(dT) DNA polymers

We numerically investigate localization properties of electronic states in a static model of poly(dG)-poly(dC) and poly(dA)-poly(dT) DNA polymers with realistic parameters obtained by quantum-chemical calculation. The randomness in the on-site energies caused by the electron-phonon coupling is completely correlated to the off-diagonal parts. In the single electron model, the effect of the hydrogen-bond stretchings, the twist angles between the base pairs and the finite system size effects on the energy dependence of the localization length and on the Lyapunov exponent are given. The localization length is reduced by the influence of the fluctuations in the hydrogen bond stretchings. It is also shown that the helical twist angle affects the localization length in the poly(dG)-poly(dC) DNA polymer more strongly than in the poly(dA)-poly(dT) one. Furthermore, we show resonance structures in the energy dependence of the localization length when the system size is relatively small.

Controllable fabrication of SiGe/Si and SiGe/Si/Cr helical nanobelts

Helical nanobelts of SiGe/Si and SiGe/Si/Cr are fabricated by rolling up strained thinheterostructures. The fabrication involved electron beam lithography, reactive ion etching,and wet chemical etching steps followed by a drying procedure. All parameters of thehelical nanobelts, namely their helical angle, chirality, pitch and diameter, arecontrollable in a reproducible fashion. The ease of fabrication of SiGe/Si andhybrid helical nanobelts opens new paths for the fabrication technology of micro- ornanoscale sensors, transducers, resonators and cylindrical shaped micro-capacitors.

Strong Binding of Myosin Heads Stretches and Twists the Actin Helix

Calculation of the size of the power stroke of the myosin motor in contracting muscle requires knowledge of the compliance of the myofilaments. Current estimates of actin compliance vary significantly introducing uncertainty in the mechanical parameters of the motor. Using x-ray diffraction on small bundles of permeabilized fibers from rabbit muscle we show that strong binding of myosin heads changes directly the actin helix. The spacing of the 2.73-nm meridional x-ray reflection increased by 0.22% when relaxed fibers were put into low-tension rigor (<10kN/m2) demonstrating that strongly bound myosin heads elongate the actin filaments even in the absence of external tension. The pitch of the 5.9-nm actin layer line increased by ∼0.62% and that of the 5.1-nm layer line decreased by ∼0.26%, suggesting that the elongation is accompanied by a decrease in its helical angle (∼166°) by ∼0.8°. This effect explains the difference between actin compliance revealed from mechanical experiments with single fibers and from x-ray diffraction on whole muscles. Our measurement of actin compliance obtained by applying tension to fibers in rigor is consistent with the results of mechanical measurements.

ELLIPTICAL AND CIRCULAR STEP-INDEX FIBERS WITH CONDUCTING HELICAL WINDINGS ON THE CORE-CLADDING BOUNDARIES FOR DIFFERENT WINDING PITCH ANGLES - A COMPARATIVE MODAL DISPERSION ANALYSIS

The propagation characteristics of an elliptical step-index fiber with a conducting helical winding on the core-cladding boundary are investigated analytically and compared with those of a circular step index fiber with a conducting radial winding. Our optical waveguides are unconventional: in view of the existence of helical conducting windings on the core-cladding boundaries. Appropriate coordinate systems, circular cylindrical and elliptic cylindrical, are chosen for the circular and elliptical fibers. Applying the boundary conditions as modified by the presence of conducting helical windings, the characteristic equations are obtained for both the fibers. Dispersion curves are also obtained for two special values of the helical pitch angle ψ, namely, for ψ = 0◦ and ψ = π2 for each fiber and the results have been compared. It is found that the introduction of the helical winding has two main effects on the characteristics of both types of fibers. These are: (1) The helix introduces band gaps and (2) has the effect of splitting a mode into a pair of adjacent modes In the case of the elliptical helically clad waveguide we find two band gaps for V < 30 whereas for circular guide we have only one band gap in the same range of V -values, V being the normalized frequency parameter. 2 Kumar and Singh II

Extremely bulky triarylphosphines incorporating 2,6-diisopropylphenyl substituents; consideration of steric shielding and steric pressure

The geometry of 15 triarylphosphines which differ in the nature of the substituents at the 2 and 6 positions of one or more phenyl rings are compared. The sum of angles around phosphorus, ∑{∠CPC}, is used as the primary measure of steric bulk. The roles of substituents, which act as steric shields surrounding the phosphine lone pair and of those which generate steric pressure and cause flattening of the C 3P pyramid are identified. Both crystallographic and computational (HF 6-31G(d)) structures are used to assess ∑{∠CPC}, the pyramidalization angle α, the average C–P distance, and the helical twist angle of the aryl rings β. All of these parameters confirm that ortho-2,6-diisopropyl substituted aryl groups generate the most sterically congested triarylphosphines. Comparison to Tolman cone angles are made where these are available.

Three‐dimensional carpal kinematics of trotting horses

Descriptions of 3D kinematics assist in understanding joint function and dysfunction, and are an essential step toward 3D inverse dynamic analysis. To measure 3D carpal joint motion during trotting. Three-dimensional trajectories of bone-fixed markers on the radius and third metacarpus of the right forelimb of 3 healthy horses were recorded at 120 Hz using a 6-camera analysis system. Joint kinematics were calculated in terms of helical angles between the 2 segments using a spatial attitude method. All horses showed carpal extension and internal rotation of the metacarpus relative to the radius as the carpus assumed the close-packed position. In late stance, the carpus began a cycle of flexion that continued through midswing, accompanied by a small cycle of internal rotation. The direction of abduction/adduction varied between horses. The predominant rotational movement was flexion/extension, which showed a range of motion of 15 +/- 6 degrees in stance and 76 +/- 13 degrees in swing. Carpal motions were generally similar between horses with the exception of abduction/adduction. Knowledge of carpal joint motion should assist in understanding the pathogenesis of carpal injuries. However, it seems probable that real differences exist between individuals; therefore, further investigations of the effect of conformation on carpal motion should be performed in a much larger population of horses.

Curvilinear Lattice in Chiral Carbon Nanotubes

In this paper, the energy bands of chiral-type single-walled carbon nanotubes are studied employing a new curvilinear lattice theory and its reciprocal lattice aided by the spherical triangle theory. In this theory, the notion of a distance law is introduced as a constraint to determine the electronic characteristics of carbon nanotubes. The chiral tubes are proven to be semiconducting or metallic, depending on the diameters and helical angles of the tubes. The distance law also predicts an uncertainty for the electronic characteristics of chiral tubes due to the metallic states tightly surrounding the semiconducting states on the direct lattice, and vice versa. Results predicted by the distance law agree well with theoretical calculations of the electron density of states and published measurements.

A study of design and manufacturing models for circular-arc ball-end milling cutters

The paper presents a systematic manufacturing model for producing the circular-arc ball-end milling (CABEM) cutter. Having first defined the helical angle as the angle between the cutting edge and the axis of rotation of the cutter, the geometric shapes of helical grooves and cutting edge profiles are analytically derived. The feed speed of the grinding wheel in the radial direction is modified according to the cross-section of the groove that passes through the centre of the cutter sphere. The models that are used to calculate the actually obtained groove, and the method of computer simulation are also included. To further enhance the accuracy of the mathematical models, a compensatory machining process, which eliminates residual profile on the revolving surface, is also presented.

Collimated Escaping Vortical Polare−e+Jets Intrinsically Produced by Rotating Black Holes and Penrose Processes

In this paper, I present results from theoretical and numerical (Monte Carlo) N-particle fully relativistic four-dimensional analysis of Penrose scattering processes (Compton and γγ⟶e-e+) in the ergosphere of a supermassive or stellar mass Kerr (rotating) black hole. Specifically, the escape conditions and the escaping orbits of the Penrose pair production (γγ⟶e-e+) electrons are analyzed, revealing that these particles escape along collimated, jet geodesic trajectories encircling the polar axis. Such collimated, vortical, tightly wound, coil-like trajectories of relativistic particles are inherent properties of rotating black holes. The helical polar angles of escape for these e-e+ pairs range from ~40° to ~05 (for the highest energy particles). These jet distributions appear to be consistent with the astrophysical jets of active galactic nuclei (AGNs) and galactic black holes and suggest a mechanism for precollimation within the inner radius of the dynamically stable accretion disk.