Magnitude Of Twist Research Articles

Influence of Laminate Twist and Clamping Pressure on Bonding Performance of Low-Grade Lumber in Cross-Laminated Timber

Abstract The geometric variations of low-grade lumber raise concerns about bond strength of cross-laminated timber (CLT) produced from such lumber. This study seeks to investigate the effect of low clamping pressure and geometric variations of laminates on the bond strength of CLT. CLT panels were manufactured from low-grade grand fir (Abies grandis). Block shear tests and cyclic delamination tests were conducted on specimens randomly taken at specific points that correspond to a wide range of twist magnitude. Twist distribution in the lumber used as laminates in the CLT ranges from 0 to 160 mm. Results showed that twist magnitude and clamping pressure have significant effect on bond performance, with twist magnitude having an overriding effect on pressure.

The effect of axial twist angle on in vitro cumulative injury load tolerance: a magnitude-weighting approach for axial twist exposures

Axial twisting exposures have been repeatedly identified as a risk factor for occupational low back pain and injury, but there is a need for an improved understanding of the role of axial twist magnitude and associated joint moment as modifiers of the cumulative load tolerance of intervertebral joints. The purpose of this study was to mathematically characterise the relationship between axial twist motion magnitudes and the cumulative load tolerance of porcine cervical functional spinal units. Twenty-four porcine functional spinal units were fixed in a mechanical testing system under compressive load (15% of compressive tolerance) and in a neutral flexion-extension posture. Specimens were axially twisted to 5, 7.5, 10, 12.5, 15 or 17.5 degrees at 1 Hz until failure or 21,600 total cycles. Cumulative applied axial twist moment was recorded, and exponential functions were fit to the twist magnitude-cumulative twist moment measures. Weighting-factor functions for cumulative axial twist moment injury risk were developed based on absolute axial twist magnitude and twist normalised to maximum range of motion. While caution should be used in extrapolating these findings to human evaluation, a developed non-linear weighting-factor model has potential for use in assessment of cumulative axial twist injury risk in occupational tasks.

Enhancement of heat transfer in the double pipe heat exchanger using different twisted tapes

In This project deals with the utilization of various twisted tape inserts as Passive Heat transfer improvement device. result of twisted tape insert (TTI), Baffled twisted tape insert (BTTI) & Baffled twisted tape with holes insert (BTTHI) on heat transfer and friction factor for heating of water for Reynolds range vary 2600-32000, was studied through an experiment during a double pipe heat exchanger. Three tapes of various twist magnitude relation (TR=3.60, TR=4.30, TR=5.20) for TTI, BTTI & BTTHI were used. The parameter which we a re calculating in this is heat transfer coefficient and friction factor.

LOCAL ANGLE OF ATTACK EXTRACTION METHOD FOR TWIST MORPHING MAV WING

The geometric twist characteristic on twist morphing MAV wing has significant influence on its aerodynamic performances. Higher geometric twist magnitude induces higher lifts and drags generation. However, in order to determine the geometric twist performance, a detail analysis has to be carried out to extract the local angle of attack (AOA) value on each wing cross section. Thus, current works introduces a new method in extracting the local AOA value on a twist morphing MAV wing. The method manipulates the automated coordinate generation produced by Ansys software and combined the generated coordinates with manual determination of local AOA magnitude. Based on the analysis executed on a twist morphing wing sample, 30 local AOA values were obtained from 30 wing cross sections. By using the local AOA value at the root chord and wing tip, the geometric twist magnitude or twist intensity for a twist morphing wing is determined. Based on a selected twist morphing MAV wing sample, the local AOA extraction method able to calculate the wing geometric twist at ϵ = 12.5°.

Transmission system accuracy optimum allocation for multiaxis machine tools’ scheme design

Transmission components are the main mechanical elements in a machine system, the accuracy level of the transmission system is one of the major sources of the machining error of multiaxis machine tools. This article investigates motion error analysis, volumetric motion error model for transmission system and the accuracy allocation method for multiaxis machine tools during the early design stage. For this purpose, a transmission system volumetric motion error model, which is based on the motion error matrix and screw theory, is derived for mapping transmission components’ error parameters to the volumetric motion errors of machine tools. The volumetric motion error matrix combines motion errors along the machine tools’ kinematic chains. Subsequently, the volumetric motion error model is expressed as a volumetric motion error twist, which is formulated from the volumetric motion error matrix. Additionally, the transmission system volumetric motion error twist model is used as design criteria for accuracy optimum allocation, with constraints on the twist magnitude and design variable limits. Then, design optimization is performed by using a multiobjective nonlinear optimization technique to minimize the manufacturing cost and volumetric motion error twist pitch. To solve this multiple objective optimum problem, this study proposes an approach integrating Lagrange multiplier and gradient descent operator with non-dominated sorting genetic algorithm-II (NSGA-II). Modified non-dominated sorting genetic algorithm-II searches for an allocation scheme Pareto optimal front. Consequently, VlseKriterijumska Optimizacija I Kompromisno Resenje (VIKOR) determines the best compromise solution from the Pareto set. Finally, a numerical experiment for the optimal design of a numerical control machine tool is conducted, which highlights the advantages of the proposed methodology.

Speckle‐tracking analysis based on 2D echocardiography does not reliably measure left ventricular torsion

Worldwide left ventricular (LV) twist is measured by 2D speckle tracking acquiring apical short axis at a LV level where papillary muscles are no longer visible; however, we hypothesized that this methodological recommendation is not enough accurate to obtain a reliable measurement of apical rotation. We measured twist and untwist rate in 30 healthy subjects by following the earlier method. By 3D echocardiography, we identified two LV apex levels: (i) 3D Apex, defined as the last apical slice at which LV cavity was visible; (ii) 2D Apex, defined as the level where diameters are equal to those of apical LV short axis used for twist analysis in the same subject. The ratio between the distance of 2D Apex and 3D Apex from LV base was calculated and expressed as percentage (2D Apex/3D Apex). 2D Apex/3D Apex was strongly related to the magnitude of twist and untwisting rate (r=0·82, P<0·001; r=-0·46, P=0·015, respectively). The only determinant of twist was 2D Apex/3D Apex (r(2) =0·68; r=0·82; F ratio: 52·6, P<0·001); whereas untwisting rate was influenced by 2D Apex/3D Apex and age (r(2) =0·42; r=0·65; F ratio: 7·7; P=0·003 for 2D Apex/3D Apex; and P=0·011 for age). Left ventricular apical level acquisition, even when recorded in a standard manner, determines variability of twist mechanics measurements. Thus, current anatomical markers used to identify LV apex for twist analysis are not reliable and need different standardization. 3D echocardiography may help in such standardization.

The Left Ventricle Responds to Acute Graded Elevation of Right Ventricular Afterload by Augmentation of Twist Magnitude and Untwist Rate

The right and left ventricles share the interventricular septum, which mechanically transmits pressure gradients. The aim of this study was to investigate how acute mild or moderate right ventricular (RV) afterload affects left ventricular (LV) function. In 14 open-chest pigs (mean weight, 43 ± 4 kg) with preserved pericardium, acute mild (>35 and ≤50 mm Hg) and moderate (>50 and ≤60 mm Hg) RV pressure loading conditions were induced by constriction of the pulmonary artery. Hemodynamic parameters and LV twist and untwist were evaluated under each condition. From baseline to mild and moderate RV afterload, the mean RV systolic pressure increased from 31.0 ± 4.3 to 41.1 ± 2.7 and 52.7 ± 3.4 mm Hg (P < .001), while LV twist magnitudes increased from 15.4 ± 5.1° to 18.5 ± 3.1° and 19.8 ± 5.0° (P= .004), respectively. Absolute values of LV untwist rate increased from -116.9 ± 64.9°/sec to -160.0 ± 53.3°/sec and -169.1 ± 47.0°/sec, respectively (P= .001). After adjusting for all variables, only the ratio of the early and atrial components of mitral inflow and RV outflow tract acceleration time was significantly associated with the LV twist magnitude and LV untwist rate. In an acute setting, the left ventricle responds to suddenly elevated RV afterload and decreased RV stroke volume by promptly increasing its twist magnitude and untwist rate.

Quantification of Left Ventricular Twisting Mechanics by Velocity Vector Imaging in an Animal Model of Pericardial Adhesions

Diagnosis of constrictive pericarditis remains clinically challenging. Untwisting of the left ventricle (LV) is essential for normal LV diastolic function. Echocardiography is able to measure LV twisting mechanics. We designed an animal model of constrictive pericarditis to determine how pericardial-epicardial adhesions impair LV twisting mechanics. In eight open-chest pigs, the heart was exposed while preserving the pericardium. We simulated early constrictive pericarditis by pericardial constriction and patchy adhesions induced with instant glue and pericardial-epicardial stitches. Using Velocity Vector Imaging™ (VVI), LV magnitudes of twisting and untwisting were measured along with hemodynamic data at baseline and after the experimental intervention. Significant decreases in end-diastolic volume, ejection fraction, stroke volume, and late diastolic filling velocity reflected the effects of the pericardial adhesions. Magnitude of LV untwisting rate decreased from –80 ± 23°/s to –26 ± 10 °/s ( p = 0.0009). LV twisting rate dropped from 78 ± 20°/s to 40 ± 8°/s ( p = 0.0039) and LV twist magnitude decreased from 9 ± 2° to 5 ± 2 ° ( p = 0.0081). Patchy pericardial adhesions are associated with reductions in LV untwisting rate and twisting magnitude, consistent with a negative impact of constrictive pericarditis on systolic and diastolic function. Impairments in LV twisting mechanics may have a diagnostic role in the detection of early stages of constrictive pericarditis. (E-mail: belohlavek.marek@mayo.edu)

Application of Matteucci Voltage Pulses of Amorphous Wires in Sensing Both Direction and Magnitude of Twist

In this work the effect of torsion on the Matteucci voltage pulses in amorphous wires has been studied. It has been shown that: Amplitude of the pulses decreases to zero at a twist angle that depends on the chemical composition of the wire. From zero torsion, the amplitude of the Matteucci voltage increases when the wires are twisted counter-clockwise. However, when the wires are twisted clockwise, the amplitude of the Matteucci voltage pulses decreases up to a minimum point (zero) before, finally, starting to increase. This is a clear distinction (in behaviour) between clockwise and counter-clockwise torsion, which can be employed to determine the direction of initial twist. Also, the low torsion region of the torsion-Matteucci voltage characteristic shows a clear possibility of employing the stress sensitive Matteucci voltage to determine the magnitude of torsion. The Matteucci voltage is quite sensitive to the torsion. It is thus expected to provide high sensitivity for measurement of torsion in the “low and very low torsion region”. It has also been established that when the positioning of the amorphous wire in the magnetizing coil is reversed (wire ends are interchanged), the torsion-Matteucci voltage characteristic obtained is virtually a mirror image of the previous direction. For instance, if the zero amplitude Matteucci voltage was being obtained at a twist angle of 45° clockwise, it will now be obtained at an angle of the same magnitude, but for a counter-clockwise twist. The physics of this latter phenomenon too would be of interest to researchers of physics of magnetism. J. agric. Sci. technol. Vol.5(1) 2003: 116-129

Automatic measurement of fiber orientation in softwoods by using the tracheid effect

Spiraled grain commonly occurs in softwood trees. Instead of running parallel to the pith, the grain runs spirally around the trunk like a helix. Since wood is an orthotropic material with higher shrinkage perpendicular to than parallel to the fibers, the log will twist when dried, and so will a plank or board cut from it. Several investigations have shown that the magnitude of twist in sawn wood is highly correlated to the fiber orientation, so by measuring the fiber orientation on green lumber, the risk of warp after drying can be indicated. Fiber orientation is also interesting for other purposes, for example stress grading and research applications. This paper concerns the tracheid effect, which utilizes the light conducting properties of the softwood tracheids to measure fiber orientation. A small circular laser beam was projected onto the wood surface. The light was transmitted in the wood and scattered back to form an elliptical shape extended in the direction of the fibers. The ellipse of light was registered with a CMOS camera, and the orientation of the ellipse's major axis was calculated. This method has a correlation coefficient of 0.99996 to manually aligned fiber orientation, and repeated measurements show a standard deviation of 0.2°. Calculation time for one 64×64 pixel image was 67 μs, which must be regarded as useful for industrial applications.

Comparison of damage accumulation measures in human cortical bone

Elastic modulus degradation, strength reduction, and energy dissipation have traditionally been the properties of choice to monitor the damage process in cortical bone. However, these properties only provide limited insight into the damage process given the complex mechanical nature of bone. In the current study, alternative measures of the damage process were investigated for machined human cortical bone specimens loaded under torsion. Seventy-two bone specimens from 6 human femurs were subjected to a series of torsional relaxation cycles in which damage was induced during a single relaxation cycle and the effects of damage on the elastic, yield, viscous, and failure properties were determined from pre- and post-damage relaxation cycles. The results revealed that degradation of all torsion properties exhibited a significant twist magnitude effect. However, the yield stress and strain, the relaxation rate, and the total relaxation exhibited 5–10 fold greater degradation than both strength and modulus, when residual strength tests were conducted at high shear strain rates. For the loading conditions examined in this study, the results indicated that the relaxation and yield properties of cortical bone are more sensitive to shear damage accumulation and better measures of the damage process than either strength or modulus. Further, the results reveal an important interaction between damage and the viscous behavior of bone which provides new insight into the effects of damage on bone mechanical properties.

An Inversion in the Chirality in an Amphiphilic Cholesteric Liquid Crystal Where the Chiral Dopant Is the Chloride of the Decyl Ester of L-Proline

The chloride of the decyl ester of L-proline has been used as a chiral dopant where the achiral host detergent was tetradecyltrimethylammonium bromide. The twist and the sense of the helix were measured as a function of the chiral dopant concentration, using the fingerprint texture and Grandjean planes observed under a polarizing microscope. The magnitude of the twist as a function of the chiral dopant concentration initially rose and fell, while the sense of helix was positive. At about 10% the twist magnitude passed through zero, and then with increasing amounts of the chiral dopant the sense of the helix became negative. This inversion in the twist sense is thought to be due to a concentration-dependent distribution of the cis and trans molecular rotamers derived from rotation around the >CH-CO 2 - bond

A conical model to describe the nonuniformity of the left ventricular twisting motion.

The systolic contraction and fiber shortening in the left ventricle (LV) produces torsional moments in the myocardium, resulting in a gradient of angular displacements about the long axis. This is manifested as a counterclockwise rotation of the apex relative to the base, when viewed from the apex. Recent studies with magnetic resonance imaging (MRI), using noninvasive magnetic tags, have revealed three important properties of the LV twist: (a) The angle of twist (i.e., the angular rotation of a slice relative to the basal slice) is consistently higher at the endocardium as compared to the epicardium; (b) The twist increases towards the apex; and (c) Straight MRI-tagged radial lines at end-diastole (ED) are slightly curved at end-systole (ES), implying a nonlinear transmural variation of the twist. The present study suggests that the geometry of the LV at ES can be represented by a thick-walled hollow cone, and that the transmural twist patterns from ED to ES can be described using the continuum mechanics approach and a small strain analysis of an isotropic cone subjected to external torque. The predicted results are compared with the noninvasive MRI measurements of transmural twist in eight human volunteers. Given the epicardial angles of twist of each slice, the predicted endocardial angles of twist are in good correlation with the experimental findings (r = 0.86, slope = 1.09, SEE = 4.1 degrees). In addition, the model reliably describes the changes in the twist magnitude from apex to base (no significant difference from experimental values, P = 0.2), and predicts the curvilinear pattern at ES of the originally straight ED radial lines. Thus, the conical model with uniform properties of the LV, reliably predicts the nonuniformity of the twist patterns, implying that the LV twist is strongly affected by LV geometry.

The Effect of Exocyclic Substituents on Base-Pair Propeller Twist

Abstract Base-pair propeller twists for a series of small nucleic acid fragments calculated excluding the exocyclic base atoms are found to be slightly reduced on average. This reduction is more pronounced for pyrimidine than for the more aromatic purine bases. However, the magnitude of twist for base-pairs without exocyclic atoms included in the mean planes remains very significant, showing this to be an intrinsic property.

Analysis of conformational parameters in nucleic acid fragments. II. Co-crystal complexes of nucleic acid bases.

Studies have been made of conformational parameters in co-crystal complexes and compounds of nucleic acid bases in which there is the possibility of formation of hetero-base-pairs. Using published data extracted from the Cambridge structural database, a total of 37 base-pairs were found, of which 25 were hetero-pairs and 12 homo-pairs. These base-pairs were subject to analysis to reveal hydrogen bond parameters, propeller twist, buckle and C1'-C1' separation (or a similar parameter if C1' atoms were not present). Hetero-pairs were found to show larger twists than homo-pairs, the magnitude of twist being unrelated to hydrogen bond parameters or buckle value. The propeller twisting is less pronounced in these nucleic acid bases than in nucleosides, but still has a significant magnitude. Propeller twisting in hetero-pairs is found to be larger than in homo-pairs. Hetero-pairs appear to be formed preferentially in competitive situations.

Analysis of conformational parameters in nucleic acid fragments. I. Single crystals of nucleosides and nucleotides.

A study has been undertaken of conformational parameters in single crystal structures of nucleosides and nucleotides using the techniques of helical conformational analysis. A "quasi-helix" was generated from the geometry of base-paired structures, using published data extracted from the Cambridge structural database. A total of 54 base-pairs were found in these structures, for each of which were calculated hydrogen bond parameters, propeller twist, buckle and C1'-C1' separations. These were analysed according to various classifications. Propeller twists are found to show a wide range of values and the magnitude of twist appears to be unrelated to hydrogen bond parameters or C1'-C1' separation. The values of the buckle parameter vary over a smaller range of values and are unrelated to propeller twist magnitude. There is found to be a greater tendency to form homo-base-pairs among compounds containing adenine bases.