Torsional vibration of aircraft engines
NASA Technical Reports Server (NTRS)
Lurenbaum, Karl
1932-01-01
Exhaustive torsional-vibration investigations are required to determine the reliability of aircraft engines. A general outline of the methods used for such investigations and of the theoretical and mechanical means now available for this purpose is given, illustrated by example. True vibration diagrams are usually obtained from vibration measurements on the completed engine. Two devices for this purpose and supplementing each other, the D.V.L. torsiograph and the D.V.L. torsion recorder, are described in this report.
Torsional vibration isolator and method
Allen, C.A.; Durrett, V.D.
1986-10-21
This patent describes a multicylinder internal combustion engine having a rotatable crankshaft and a rotatable flywheel which together define an inertial system rotating about a predetermined axis of rotation. An improvement is described here which facilitates avoiding destructive effects on the crankshaft of stress induced by torsional vibration. The method comprises an elastomeric annulus coupling means operatively interposed between the crankshaft and flywheel for coupling the crankshaft and flywheel together for rotation of the flywheel with the crankshaft. The coupling means has a torsional spring rate of less than 20,000 in lb/radian effective to permit substantial angular displacement between the flywheel and the crankshaft for isolating the rotating inertia of the flywheel from the rotating inertia of the crankshaft after engine startup. The coupling means avoids dampening while preventing torsional vibration from being transferred between the flywheel and the crankshaft.
NASA Technical Reports Server (NTRS)
Davis, R. B.; Stephens, M. V.
1974-01-01
An approximate method for calculating the longitudinal and torsional natural frequencies and associated modal data of a beamlike, variable cross section multibranch structure is presented. The procedure described is the numerical integration of the first order differential equations that characterize the beam element in longitudinal motion and that satisfy the appropriate boundary conditions.
Active structures to reduce torsional vibrations
NASA Astrophysics Data System (ADS)
Matthias, M.; Schlote, D.; Atzrodt, H.
2013-03-01
This paper describes the development of different active measures to reduce torsional vibrations in power trains. The measures are based on concepts developed for active mounts to reduce the transmission of structure-borne sound. To show the potential of these active measures and investigate their mode of operation to influence torsional vibrations, numerical simulations of powertrains with different active measures were done. First experimental results from tests on an experimental (reduced size) power train were used to align the numerical models. The work was done within the project 'LOEWE-Zentrum AdRIA: Adaptronik - Research, Innovation, Application' funded by the German federal state of Hessen, and the Project AKTos: 'Active control of torsional vibrations by coupling elements' placed in the research Framework program 'Navigation and Maritime Technology for the 21st Century' funded by the German Federal Ministry of Economics and Technology.
Fundamentals of IC engine torsional vibration
Doughty, S.
1988-01-01
Fluctuations in IC engine cylinder pressure are an obvious source of torsional vibration excitation, although the details of the coupling from cylinder pressure to torque on the crankshaft are complicated. A second, less obvious source of torsional excitation is the effect of variable inertia associated with the engine slider-crank mechanism. This is a tutorial paper, intended to show the relation between, on the one hand, the actual engine slider-crank mechanism subject to combustion gas pressure and, on the other hand, the models commonly used for torsional vibration analysis that involve constant inertias subject to torques expressed by Fourier series. As such, it uses some new approaches to reach previously known results with a greater degree of physical insight. The presentation is in terms of a single cylinder, two stroke engine with load, and makes clear the roles of piston mass, connecting rod mass and moment of inertia, and crank inertia as they affect both the effective inertia and the effective torque. The determination of natural frequencies and the forced vibration response calculation are briefly described to complete the analysis. The development of a Fourier series representation for the effective torque, including both the cylinder pressure and inertia variation is also discussed. The various components for the response are identified, in an effort to clarify the meaning of terms such as ''zero frequency mode,'' ''rigid body mode,'' and ''twisting mode.''
Laser-Based Measurement Of Torsional Vibration
NASA Astrophysics Data System (ADS)
Eastwood, P. G.; Halliwell, N. A.
1986-07-01
Investigations of the torsional vibration characteristics of shaft systems which transmit pulsating torques are an important part of a machinery designer's responsibility. Satisfactory operation of such systems depends to a large extent on successful treatment of this vibration problem, since incorrectly or insufficiently controlled torsional oscillations can lead to fatigue failure, rapid bearing wear, gear hammer etc. The problem is particularly severe in engine crankshaft design where numerous failures have been traced to abnormal vibration at "critical" speeds. Traditionally, the monitoring of torsional oscillation has been performed using strain gauges, slip rings and a variety of mechanical and electrical "torsiographs". More recently systems employing slotted discs or toothed wheels together with proximity transducers have been preferred, but a disadvantage arises from all these methods in that they require contact with the rotating component which necessitates "downtime" for transducer attachment. Moreover, physical access to the rotating surface is often restricted thus making the use of such methods impractical. The "cross-beam" laser velocimeter provides a means of measuring torsional vibration by a non-contact method, thus effectively overcoming the disadvantages of previous measurement systems. This well established laser-based instrument provides a time-resolved voltage analogue of shaft tangential surface velocity and laboratory and field tests have shown it to be both accurate and reliable. The versatility of this instrument, however, is restricted by the need for accurate positioning, since the velocimeter must be arranged so that the rotating surface always traverses the beam intersection region, which is typically only a fraction of a millimetre in length. As a consequence use is restricted to components of circular cross section. This paper compares and contrasts the "cross-beam" system with a new laser instrument, the laser torsional vibrometer
Control of Torsional Vibrations by Pendulum Masses
NASA Technical Reports Server (NTRS)
Stieglitz, Albert
1942-01-01
Various versions of pendulum masses have been developed abroad within the past few years by means of which resonant vibrations of rotating shafts can be eliminated at a given tuning. They are already successfully employed on radial engines in the form of pendulous counterweights. Compared with the commonly known torsional vibration dampers, the pendulum masses have the advantage of being structurally very simple, requiring no internal damping and being capable of completely eliminating certain vibrations. Unexplained, so far, remains the problem of behavior of pendulum masses in other critical zones to which they are not tuned, their dynamic behavior at some tuning other than in resonance, and their effect within a compound vibration system and at simultaneous application of several differently tuned pendulous masses. These problems are analyzed in the present report. The results constitute an enlargement of the scope of application of pendulum masses, especially for in-line engines. Among other things it is found that the natural frequency of a system can be raised by means of a correspondingly tuned pendulum mass. The formulas necessary for the design of any practical version are developed, and a pendulum mass having two different natural frequencies simultaneously is described.
Ultrasonic Welding of Plastic Pipes Using Torsional Vibration
NASA Astrophysics Data System (ADS)
Masuzawa, Nobuyoshi; Hori, Kiichi; Ide, Masao
1998-05-01
In recent years, the application of ultrasonic welding to plastics has become common. In this paper a method for ultrasonic welding of plastic pipes using torsional vibrations is reported. In this method torsional vibrations are applied to the welding pipe from the circumferential direction with horns placed near the welding surface. Static pressure is independently applied from the vibrations to the welding surface. It was observed that acrylic resin pipes could be effectively welded by the proposed method.
NASA Technical Reports Server (NTRS)
Mendelson, Alexander; Gendler, Selwyn
1951-01-01
A method based on the concept of station functions is presented for calculating the modes and the frequencies of nonuniform cantilever beams vibrating in torsion, bending, and coupled bending-torsion motion. The method combines some of the advantages of the Rayleigh-Ritz and Stodola methods, in that a continuous loading function for the beam is used, with the advantages of the influence-coefficient method, in that the continuous loading function is obtained in terms of the displacements of a finite number of stations along the beam.
Fault diagnosis of planetary gearboxes via torsional vibration signal analysis
NASA Astrophysics Data System (ADS)
Feng, Zhipeng; Zuo, Ming J.
2013-04-01
Torsional vibration signals are theoretically free from the amplitude modulation effect caused by time variant vibration transfer paths due to the rotation of planet carrier and sun gear, and therefore their spectral structure are simpler than transverse vibration signals. Thus, it is potentially easy and effective to diagnose planetary gearbox faults via torsional vibration signal analysis. We give explicit equations to model torsional vibration signals, considering both distributed gear faults (like manufacturing or assembly errors) and local gear faults (like pitting, crack or breakage of one tooth), and derive the characteristics of both the traditional Fourier spectrum and the proposed demodulated spectra of amplitude envelope and instantaneous frequency. These derivations are not only effective to diagnose single gear fault of planetary gearboxes, but can also be generalized to detect and locate multiple gear faults. We validate experimentally the signal models, as well as the Fourier spectral analysis and demodulation analysis methods.
Longitudinal–torsional vibration source consisting of two transducers with different vibration modes
NASA Astrophysics Data System (ADS)
Asami, Takuya; Miura, Hikaru
2016-07-01
The planar vibration locus is applicable to, for example, ultrasonic welding, ultrasonic machining, and ultrasonic polishing. In a previous study, we obtained the planar locus using an ultrasonic longitudinal–torsional vibration source that contained a vibration converter comprising diagonal slits to drive two frequencies. It was difficult to obtain only longitudinal or torsional vibration when using an ultrasonic complex vibration source with diagonal slits. Therefore, the versatility of the ultrasonic complex vibration source with diagonal slits was low. We have developed an ultrasonic longitudinal–torsional vibration source in which the longitudinal–torsional vibration can be controlled. The requirements for an ultrasonic vibration source were longitudinal–torsional vibration control and that the source has a planar locus. In this paper, we investigate a new type of vibration source that satisfies these requirements. It consists of two transducers, a longitudinal transducer and a torsional transducer, attached to the ends of a uniform rod with a length of one wavelength of the propagating vibration.
NASA Technical Reports Server (NTRS)
White, W. F., Jr.; Malatino, R. E.
1975-01-01
A method is presented for determining the free vibration characteristics of a rotating blade having nonuniform spanwise properties and cantilever boundary conditions. The equations which govern the coupled flapwise, chordwise, and torsional motion of such a blade are solved using an integrating matrix method. By expressing the equations of motion and matrix notation, utilizing the integrating matrix as an operator, and applying the boundary conditions, the equations are formulated into an eigenvalue problem whose solutions may be determined by conventional methods. Computer results are compared with experimental data.
Structural and torsional vibration analysis of a dry screw compressor
NASA Astrophysics Data System (ADS)
Willie, J.; Sachs, R.
2015-08-01
This paper investigates torsional vibration and pulsating noise in a dry screw compressor. The compressor is designed at Gardner Denver (GD) and is oil free and use for mounting on highway trucks. They are driven using a Power Take-Off (PTO) transmission and gear box on a truck. Torque peak fluctuation and noise measurements are done and their sources are investigated and reported in this work. To accurately predict the torsional response (frequency and relative angular deflection and torque amplitude), the Holzer method is used. It is shown that the first torsional frequency is manifested as sidebands in the gear train meshing frequencies and this can lead to noise that is the result of amplitude modulation. Sensitivity analysis of the drive train identifies the weakest link in the drive train that limits the first torsional frequency to a low value. Finally, the significance of higher mode shapes on inter-lobe clearance distribution of the rotors is investigated.
Torsional vibration transmissibility characteristics of reinforced viscoelastic flexible pipes
NASA Astrophysics Data System (ADS)
Kennedy, I.; Tomlinson, G. R.
1988-04-01
The dynamic complex shear moduli of fibre and steel reinforced viscoelastic flexible pipes are determined by using a torsional non-resonance method. Material property master curves as a function of frequency and temperature are obtained by using reduced modulus methods. In situations where the loss factor data is difficult to measure directly it is shown that these data can be obtained from the modulus data by using a stepwise Hilbert transform technique. Predictions of the torsional vibration transmissibility of reinforced pipes, by using a simple theory in conjunction with the material properties, results in a close comparison with experimental measurements of the torsional vibration transmissibility characteristics of the pipes over a wide frequency range.
Nonlinear finite amplitude torsional vibrations of cantilevers in viscous fluids
NASA Astrophysics Data System (ADS)
Aureli, Matteo; Pagano, Christopher; Porfiri, Maurizio
2012-06-01
In this paper, we study torsional vibrations of cantilever beams undergoing moderately large oscillations within a quiescent viscous fluid. The structure is modeled as an Euler-Bernoulli beam, with thin rectangular cross section, under base excitation. The distributed hydrodynamic loading experienced by the vibrating structure is described through a complex-valued hydrodynamic function which incorporates added mass and fluid damping elicited by moderately large rotations. We conduct a parametric study on the two dimensional computational fluid dynamics of a pitching rigid lamina, representative of a generic beam cross section, to investigate the dependence of the hydrodynamic function on the governing flow parameters. As the frequency and amplitude of the oscillation increase, vortex shedding and convection phenomena increase, thus resulting into nonlinear hydrodynamic damping. We derive a handleable nonlinear correction to the classical hydrodynamic function developed for small amplitude torsional vibrations for use in a reduced order nonlinear modal model and we validate theoretical results against experimental findings.
The frequencies of cantilever wings in beam and torsional vibrations
NASA Technical Reports Server (NTRS)
Burgess, C P
1940-01-01
Methods are described for calculating the period and frequency of vibration of cantilever wings and similar structures in which the weight and moment of inertia vary along the span. Both the beam and torsional frequencies may be calculated by these methods. The procedure is illustrated by examples. It is shown that a surprisingly close approximation to the beam frequency may be obtained by a very brief calculation in which the curvature of the wing in vibration is assumed to be constant. A somewhat longer computation permits taking account of the true curvature of the beam by a series of successive approximations which are shown to be strongly convergent. Analogous methods are applied to calculations of the torsional frequency. For the first approximation it is assumed that the angle of twist varies linearly alone the semispan. True variation of the twist is computed by successive approximations which are strongly convergent, as in the case of beam vibrations.
NASA Astrophysics Data System (ADS)
Suzuki, Atsuyuki; Kihara, Masaki; Katsumata, Yasuhiro; Ishii, Keisuke; Tsujino, Jiromaru
2005-06-01
The vibration and load characteristics of ultrasonic motors having (a) a torsional vibration cylinder with three bolt-clamped Langevin piezoelectric ceramic (PZT) longitudinal vibration transducers (BLTs) installed in the tangential direction and (b) a longitudinal vibration disk with three BLT transducers installed around a circular disk were studied. The center rod vibrates longitudinally and affects the load characteristics of the ultrasonic motor. Vibration distributions along a center rod were measured using a laser Doppler vibrometer. Revolution, electric input power, mechanical output power and efficiency were measured under various rotating torques. Maximum torque, revolution and efficiency of the ultrasonic motor with (a) a torsional vibration cylinder (a) were 0.75 Nm, 205 rpm and 1.68%, respectively, and (b) 0.32 Nm, 84 rpm and 1.68%, respectively, with a circular longitudinal vibration disk.
Vibration-Torsion Dynamics of Ethane-like Molecules in Degenerate Vibrational States
NASA Astrophysics Data System (ADS)
Dilauro, C.; Lattanzi, F.; Avellino, R.
1994-10-01
We examine the mechanisms of interaction between the deformations of the two identical halves of ethane-like molecules in degenerate vibrational states, in order to determine the most convenient symmetries of the degenerate vibrational wavefunctions, in the molecular symmetry group G36( EM). In moderate barrier molecules this is related to the problem of the vibration-torsion symmetry labeling of the tunneling split components, in the order of increasing energies, in given rotational states. Numerical calculations have been performed as a guide to explore several different situations. It has been proved that the torsional splittings in degenerate vibrational states of molecules with a moderate barrier depend dramatically on the value of the γ-Coriolis coefficient and, unlike the splittings in nondegenerate vibrational states, are not determined only by the effective torsional potential function. Theory and numerical predictions support the experimental result that all normal modes of ethane behave as E1 d, E2 d pairs.
The axial-torsional vibration of pretwisted beams
NASA Astrophysics Data System (ADS)
Liu, Kuang-Chen; Friend, James; Yeo, Leslie
2009-03-01
We investigate the coupled axial-torsional vibration of pretwisted beams. The equations of motion governing the extension, torsion, and cross-sectional warping of pretwisted beams are derived from Hamiltons principle, and the common assumptions used to simplify the equations are carefully examined through scaling analysis. Inconsistencies in previous works—such as the neglect of spatial and time derivatives of torsion in the Lagrangian functional—are remedied, giving rise to fourth-order terms in the equations of motion that are significant for higher harmonics. Furthermore, scaling analysis of the governing equations yields a set of objective criteria for checking the validity of the frequently misused assumption that the warping function under pretwist is locally identical to that of a prismatic beam; we show that this simplification is responsible for the common poor prediction of axial resonance frequencies for pretwisted beams.
Coupled Torsional and Bending Vibrations of Actively Controlled Drillstrings
NASA Astrophysics Data System (ADS)
YIGIT, A. S.; CHRISTOFOROU, A. P.
2000-06-01
The dynamics of actively controlled drillstrings is studied. The equations of motion are derived using a lumped parameter model in which the coupling between torsional and bending vibrations is considered. The model also includes the dynamics of the rotary drive system which contains the rotary table, the gearbox and an armature controlled DC motor. The interactions between the drillstring and the borehole which are considered, include the impacts of collars with the borehole wall as well as bit rotation-dependent weight and torque on bit (WOB and TOB). Simulation results obtained by numerically solving the equations of motion are in close qualitative agreement with field and laboratory observations regarding stick-slip oscillations. A linear quadratic regulator (LQR) controller is designed based on a linearized model and is shown to be effective in eliminating this type of oscillations. It is also shown that for some operational parameters the control action may excite large bending vibrations due to coupling with the torsional motion.
Photoelectronic vibrometer with polarized light. [for torsional vibration measurements
NASA Technical Reports Server (NTRS)
Kremmer, I.
1974-01-01
A seismic torsiometer is described which is based on the reception by a photosensitive transducer of a light flux modulated by a relative rotation of the optical axes of two polaroids. The torsional vibrations of the polaroid fixed to the shaft are transmitted to the other polaroid (which at the same time is the seismic mass of the apparatus) by means of elastic lamellas. The device can work as accelerometer, vibrometer or frequency meter, depending on the value of the ratio between the proper oscillation frequency of the seismic system and the measured vibration frequency.
Nonlinear equations of motion for the elastic bending and torsion of twisted nonuniform rotor blades
NASA Technical Reports Server (NTRS)
Hodges, D. H.; Dowell, E. H.
1974-01-01
The equations of motion are developed by two complementary methods, Hamilton's principle and the Newtonian method. The resulting equations are valid to second order for long, straight, slender, homogeneous, isotropic beams undergoing moderate displacements. The ordering scheme is based on the restriction that squares of the bending slopes, the torsion deformation, and the chord/radius and thickness/radius ratios are negligible with respect to unity. All remaining nonlinear terms are retained. The equations are valid for beams with mass centroid axis and area centroid (tension) axis offsets from the elastic axis, nonuniform mass and stiffness section properties, variable pretwist, and a small precone angle. The strain-displacement relations are developed from an exact transformation between the deformed and undeformed coordinate systems. These nonlinear relations form an important contribution to the final equations. Several nonlinear structural and inertial terms in the final equations are identified that can substantially influence the aeroelastic stability and response of hingeless helicopter rotor blades.
Coupled bending-bending-torsion flutter of a mistuned cascade with nonuniform blades
NASA Technical Reports Server (NTRS)
Kaza, K. R. V.; Kielb, R. E.
1982-01-01
A set of aeroelastic equations describing the motion of an arbitrarily mistuned cascade with flexible, pretwisted, nonuniform blades is developed using an extended Hamilton's principle. The derivation of the equations has its basis in the geometric nonlinear theory of elasticity in which the elongations and shears are negligible compared to unity. A general expression for foreshortening of a blade is derived and is explicity used in the formulation. The blade aerodynamic loading in the subsonic and supersonic flow regimes is obtained from two dimensional, unsteady, cascade theories. The aerodynamic, inertial and structural coupling between the bending (in two planes) and torsional motions of the blade is included. The equations are used to investigate the aeroelastic stability and to quantify the effect of frequency mistuning on flutter in turbofans. Results indicate that a moderate amount of intentional mistuning has enough potential to alleviate flutter problems in unshrouded, high aspect ratio turbofans.
Experience in the detection and suppression of torsional vibration from mud logging data
Fear, M.J.; Abbassian, F.
1994-12-31
Vibration detection from mud logging systems has revealed that torsional vibration is common in harsh drilling environments, and is a major cause of bit and drillstring failures. Suppressing this type of vibration with an automated vibration detection system, torque feedback, and rigsite vibration suppression guidelines has produced a significant improvement in drilling performance.
Spinning optical resonator sensor for torsional vibrational applications measurements
NASA Astrophysics Data System (ADS)
Ali, Amir R.; Gatherer, Andrew; Ibrahim, Mariam S.
2016-03-01
Spinning spherical resonators in the torsional vibrational applications could cause a shift in its whispering gallery mode (WGM). The centripetal force acting on the spinning micro sphere resonator will leads to these WGM shifts. An analysis and experiment were carried out in this paper to investigate and demonstrate this effect using different polymeric resonators. In this experiment, centripetal force exerted by the DC-Motor on the sphere induces an elastic deformation of the resonator. This in turn induces a shift in the whispering gallery modes of the sphere resonator. Materials used for the sphere are polydimethylsiloxane (PDMS 60:1 where 60 parts base silicon elastomer to 1 part polymer curing agent by volume) with shear modulus (G≍1kPa), (PDMS 10:1) with shear modulus (G≍300kPa), polymethylmethacrylate (PMMA, G≍2.6×109GPa) and silica (G≍3×1010 GPa). The sphere size was kept constant with 1mm in diameter for all above materials. The optical modes of the sphere exit using a tapered single mode optical fiber that is coupled to a distributed feedback laser. The transmission spectrum through the fiber is monitored to detect WGM shifts. The results showed the resonators with smaller shear modulus G experience larger WGM shift due to the larger mechanical deformation induced by the applied external centripetal force. Also, the results show that angular velocity sensors used in the torsional vibrational applications could be designed using this principle.
Torsional vibration measurement of the viscosity of a metallic melt
NASA Astrophysics Data System (ADS)
Bel'tyukov, A. L.; Olyanina, N. V.; Lad'yanov, V. I.
2016-02-01
The liquid Co91B9 alloy is used as an example to study the influence of boundary conditions at the upper melt boundary on the results of viscosity measurements using torsional vibrations. Specific features related to film effects and wetting phenomena are shown to appear in the temperature dependence of logarithmic decrement. To exclude the influence of these effects and phenomena, viscosity measurements should be performed under the experimental conditions where the melt to be studied is in closed volume and the internal crucible walls are fully wetted. The temperature dependence of the kinematic viscosity of the Co91B9 melt that is obtained under such experimental conditions has a monotonic character.
Law of Torsional Vibration and Discussion on Vibration Suppression Based on Helicopter/Engine System
NASA Astrophysics Data System (ADS)
Miao, Lizhen; Zhang, Haibo; Ning, Jingtao
2016-04-01
With both the advantages like attacking close targets and the disadvantages especially like dynamic coupling, helicopter deserves more investigations these days. This paper did dynamic study both in a simplified and a multi-degree of freedom, comprehensive helicopter model, so that to reveal the law of torsional vibration. In the simplified model, the law how arbitrary parameter affects the first-order vibration mode, is discussed. Then, the validation is done in a multi-degree of freedom model by means of the fast Fourier transformation (FFT) method. In this case, how the low-frequency vibration mode relates with the first-order vibration mode is clearly presented, as well as the research direction to design a filter. Lastly, a simple filter is designed with some simulations.
Torsional vibration of single-walled carbon nanotubes using doublet mechanics
NASA Astrophysics Data System (ADS)
Fatahi-Vajari, Alireza; Imam, Ali
2016-08-01
This paper investigates the torsional vibration of single-walled carbon nanotubes (SWCNTs) using a new approach based on doublet mechanics (DM) incorporating explicitly scale parameter and chiral effects. A fourth-order partial differential equation that governs the torsional vibration of nanotubes is derived. Using DM, an explicit equation for the natural frequency in terms of geometrical and mechanical property of CNTs is obtained for both the Zigzag and Armchair nanotube for the torsional vibration mode. It is shown that chiral effects along with the scale parameter play a significant role in the vibration behavior of SWCNTs in torsional vibration mode. Such effects decrease the natural frequency obtained by DM compared to the classical continuum mechanics and nonlocal theory predictions. However, with increase in the length and/or the radius of the tube, the effect of the chiral and scale parameter on the natural frequency decreases.
Field Telemetry of Blade-rotor Coupled Torsional Vibration at Matuura Power Station Number 1 Unit
NASA Technical Reports Server (NTRS)
Isii, Kuniyoshi; Murakami, Hideaki; Otawara, Yasuhiko; Okabe, Akira
1991-01-01
The quasi-modal reduction technique and finite element model (FEM) were used to construct an analytical model for the blade-rotor coupled torsional vibration of a steam turbine generator of the Matuura Power Station. A single rotor test was executed in order to evaluate umbrella vibration characteristics. Based on the single rotor test results and the quasi-modal procedure, the total rotor system was analyzed to predict coupled torsional frequencies. Finally, field measurement of the vibration of the last stage buckets was made, which confirmed that the double synchronous resonance was 124.2 Hz, meaning that the machine can be safely operated. The measured eigen values are very close to the predicted value. The single rotor test and this analytical procedure thus proved to be a valid technique to estimate coupled torsional vibration.
NASA Technical Reports Server (NTRS)
Bratanow, T.; Ecer, A.
1974-01-01
A theoretical investigation of structural vibration characteristics of rotor blades was carried out. Coupled equations of motion for flapwise bending and torsion were formulated for rotor blades with noncollinear elastic and mass axes. The finite element method was applied for a detailed representation of blade structural properties. Coupled structural mass and stiffness coefficients were evaluated. The range of validity of a set of coupled equations of motion linearized with respect to eccentricity between elastic and mass axes was investigated. The sensitivity of blade vibration characteristics to torsion were evaluated by varying blade geometric properties, boundary conditions, and eccentricities between mass and elastic axes.
On the Effective Control of Torsional Vibrations in Drilling Systems
NASA Astrophysics Data System (ADS)
Tucker, W. R.; Wang, C.
1999-07-01
This paper analyses a control mechanism designed to significantly ameliorate the sustained excitation of torsional relaxation oscillations (slip-stick) due to frictional torques generated by an active bit during drilling operations with an extended drill-string. The proposed mechanism of torsional rectification is compared with existing soft-torque devices in a series of mathematical models. Both analytic and numerical simulations indicate that many of the volatilities suffered by existing soft-torque feedback approaches used to combat slip-stick can be eliminated by the alternative proposed here.
One-dimensional longitudinal-torsional vibration converter with multiple diagonally slitted parts
Tsujino; Ueoka; Otoda; Fujimi
2000-03-01
For increasing the available vibration velocity of the one-dimensional longitudinal-torsional vibration converter, a new type of complex vibration converter with multiple slitted parts installed in the positions avoiding longitudinal nodal positions along the converter for decreasing the maximum vibration stress level at the vibration nodal part was studied. The free end of the converter vibrates in an elliptical or circular locus. Complex vibration systems with elliptical to circular or rectangular to square loci can be applied effectively for various high-power applications, including ultrasonic welding of metal or plastics, ultrasonic wire bonding of IC, LSI and electronic devices, and also ultrasonic motors. The converter with multiple slitted parts was improved in the vibration stress level and the quality factor compared with the converter with single slitted part. PMID:10829632
Semi-active control of torsional vibrations using an MR fluid brake
NASA Astrophysics Data System (ADS)
Williams, Keith A.; Ye, Shaochun
2004-07-01
Control of torsional vibrations in an automotive crankshaft is a classical vibration control problem. The most common solution is to mount a crankshaft damper at one end of the crankshaft. Typical crankshaft dampers are composed of parallel stiffness and damping elements connecting a rotational inertia to the crankshaft. Appropriate design of the damper elements may result in substantial crankshaft vibration. Conventional couplings include elastomeric spring-damper elements and purely viscous fluid couplings. While those approaches result in satisfactory reduction of crankshaft vibration, it may be that a semi-active approach can achieve improved performance. To that end, an investigation of a semi-active crankshaft damper using magneto-rheological (MR) fluid has been initiated. A torsional MR fluid brake was obtained and applied to a scale model of a crankshaft for a common eight-cylinder engine. Experiments were performed with the MR brake as a fixed-friction device. In addition, a simple stick-slip control algorithm was developed such that the MR brake became an on-line variable friction device. While a good deal of work remains to be performed in future efforts, the preliminary experimental results have demonstrated that a torsional damper composed of an MR fluid brake has potential application in the field of torsional vibration control.
Torsional vibration of crankshaft in an engine propeller nonlinear dynamical system
NASA Astrophysics Data System (ADS)
Zhang, X.; Yu, S. D.
2009-01-01
Theoretical and experimental studies on torsional vibration of an aircraft engine-propeller system are presented in this paper. Two system models—a rigid body model and a flexible body model, are developed for predicting torsional vibrations of the crankshaft under different engine powers and propeller pitch settings. In the flexible body model, the distributed torsional flexibility and mass moment of inertia of the crankshaft are considered using the finite element method. The nonlinear autonomous equations of motion for the engine-propeller dynamical system are established using the augmented Lagrange equations, and solved using the Runge-Kutta method after a degrees of freedom reduction scheme is applied. Experiments are carried out on a three-cylinder four-stroke engine. Both theoretical and experimental studies reveal that the crankshaft flexibility has significant influence on the system dynamical behavior.
NASA Astrophysics Data System (ADS)
Lattanzi, F.; di Lauro, C.; Horneman, V.-M.
The lowest infrared active perpendicular fundamental ν9 of disilane has been analysed on a Fourier transform spectrum between 320 and 430 cm-1, at the spectral resolution of 0.0012 cm-1. The rotation-torsion structure of this band is affected by x,y Coriolis interactions with excited torsional levels of the vibrational ground state, correlating with components of 3ν4 and 4ν4 in the high barrier limit. The interaction of ν9 and 4ν4, forbidden in the D3d symmetry limit, is allowed between components of E torsional symmetry under the G36(EM) extended molecular group, because of the large amplitude of the internal rotation motion. We could determine the values of the main vibration-rotation-torsion parameters of ν9, interaction parameters, and the vibrational wavenumbers of the four torsional components of 3ν4 and of the E3d component of 4ν4. The intrinsic torsional splitting of ν9 is found to be smaller than in the ground vibrational state by 0.0066 cm-1, in good agreement with our theoretical predictions. The possibility of observing the effects of D3d-forbidden interactions in the spectra of ethane-like molecules is also discussed.
NASA Technical Reports Server (NTRS)
Subrahmanyam, K. B.; Kaza, K. R. V.
1985-01-01
Theoretical natural frequencies of the first three modes of torsional vibration of pretwisted, rotating cantilever beams are determined for various thickness and aspect ratios. Conclusions concerning individual and collective effects of warping, pretwist, tension-torsion coupling and tennis racket effect (twist-rotational coupling) terms on the natural frequencies are drawn from numerical results obtained by using a finite difference procedure with first order central differences. The relative importance of structural warping, inertial warping, pretwist, tension-torsion and twist-rotational coupling terms is discussed for various rotational speeds. The accuracy of results obtained by using the finite difference approach is verified by a comparison with the exact solution for specialized simple cases of the equation of motion used in this paper.
Simulation and experiment of cutting force in ultrasonic torsional vibration assisted micro-milling
NASA Astrophysics Data System (ADS)
Hu, Haijun; Sun, Yazhou; Lu, Zesheng
2010-10-01
A coupled thermo-mechanical model of Ultrasonic Torsional Vibration Assisted Micro-milling (UTVAM) was established with ABAQUS, the primary cause which leads to a decrease in cutting force after adding Ultrasonic Torsional Vibration (UTV) to micro-milling was analyzed. Micro-milling with and without UTV were both carried out on the self-designed UTVAM experimental system, using forged aluminum alloy. Single-factor method was used to analyze the influence rules of cutting parameters such as spindle speed, feed per tooth and depth of cut on cutting force. It was found that feed per tooth plays a more important role than other parameters, a smaller feed per tooth can have a better effects on reducing of cutting force in UTVAM.
Effect of Thermal Gradient on Vibration of Non-uniform Visco-elastic Rectangular Plate
NASA Astrophysics Data System (ADS)
Khanna, Anupam; Kaur, Narinder
2016-04-01
Here, a theoretical model is presented to analyze the effect of bilinear temperature variations on vibration of non-homogeneous visco-elastic rectangular plate with non-uniform thickness. Non-uniformity in thickness of the plate is assumed linear in one direction. Since plate's material is considered as non-homogeneous, authors characterized non-homogeneity in poisson ratio and density of the plate's material exponentially in x-direction. Plate is supposed to be clamped at the ends. Deflection for first two modes of vibration is calculated by using Rayleigh-Ritz technique and tabulated for various values of plate's parameters i.e. taper constant, aspect ratio, non-homogeneity constants and thermal gradient. Comparison of present findings with existing literature is also provided in tabular and graphical manner.
NASA Technical Reports Server (NTRS)
Gray, Carl E., Jr.
1988-01-01
Using the Newtonian method, the equations of motion are developed for the coupled bending-torsion steady-state response of beams rotating at constant angular velocity in a fixed plane. The resulting equations are valid to first order strain-displacement relationships for a long beam with all other nonlinear terms retained. In addition, the equations are valid for beams with the mass centroidal axis offset (eccentric) from the elastic axis, nonuniform mass and section properties, and variable twist. The solution of these coupled, nonlinear, nonhomogeneous, differential equations is obtained by modifying a Hunter linear second-order transfer-matrix solution procedure to solve the nonlinear differential equations and programming the solution for a desk-top personal computer. The modified transfer-matrix method was verified by comparing the solution for a rotating beam with a geometric, nonlinear, finite-element computer code solution; and for a simple rotating beam problem, the modified method demonstrated a significant advantage over the finite-element solution in accuracy, ease of solution, and actual computer processing time required to effect a solution.
Thermally-induced bending-torsion coupling vibration of large scale space structures
NASA Astrophysics Data System (ADS)
Xue, Ming-De; Duan, Jin; Xiang, Zhi-Hai
2007-09-01
In this paper, a finite element scheme is developed to solve the problem of thermally-induced bending-torsion coupling vibration of large scale space structures, which are usually composed of thin-walled beams with open and closed cross-section. A two-noded finite element is proposed to analyze the transient temperature field over the longitudinal and circumferential direction of a beam. Since this temperature element can share the same mesh with the two-noded beam element of Euler-Bernoulli type, a unified finite element scheme is easily formulated to solve the thermal-structural coupling problem. This scheme is characterized with very strong nonlinear formulation, due to the consideration of the thermal radiation and the coupling effect between structural deformations and the incident normal heat flux. Moreover, because the warping is taken into account, not only the thermal axial force and thermal bending moments but also the thermal bi-moment are presented in the formulation. Consequently, the thermally-induced bending-torsion coupling vibration can be simulated. The performance of the proposed computational scheme is illustrated by the analysis of the well-known failure of Hubble space telescope solar arrays. The results reveal that the thermally-induced bending-torsion coupling vibration is obviously presented in that case and could be regarded as a cause of failure.
NASA Astrophysics Data System (ADS)
Bulut, Gökhan
2014-08-01
Stability of parametrically excited torsional vibrations of a shaft system composed of two torsionally elastic shafts interconnected through a Hooke's joint is studied. The shafts are considered to be continuous (distributed-parameter) systems and an approximate discrete model for the torsional vibrations of the shaft system is derived via a finite element scheme. The stability of the solutions of the linearized equations of motion, consisting of a set of Mathieu-Hill type equations, is examined by means of a monodromy matrix method and the results are presented in the form of a Strutt-Ince diagram visualizing the effects of the system parameters on the stability of the shaft system.
Lateral and Torsional Vibrations of a Two-disk Rotor-stator System with Axial Contact/Rubs
NASA Astrophysics Data System (ADS)
Ding, Qian; Zhang, Kunpeng
2010-05-01
The dynamics of a rotor system with axial contact/rub events between the disks and stator are investigated by numerical simulations. The coupled equations of lateral and torsional motions of rotor and the lateral motion of disk are established. Numerical simulations are carried out to reveal the lateral and torsional vibrations for both two-disk contact/rubs and one disk contact/rubs. Bifurcation diagrams, orbits, phase portraits, amplitude- frequency spectra and Poincaré maps are adopted to demonstrate the dynamical behaviors of the system. The results show that though both the lateral and torsional vibrations can reflect the influences of contact/rubs on rotor dynamics, the spectrum analyses of the torsional vibrations are more suitable to determine straight the extent of their effect.
Efficiency improvement of a cantilever-type energy harvester using torsional vibration
NASA Astrophysics Data System (ADS)
Kim, In-Ho; Jang, Seon-Jun; Koo, Jeong-Hoi; Jung, Hyung-Jo
2016-04-01
In this paper, a piezoelectric vibrational energy harvester utilizing coupled bending and torsional vibrations is investigated. The proposed system consists of a cantilever-type substrate covered by the piezoelectric ceramic and a proof mass which is perpendicularly connected to the free end of the cantilever beam by a rigid bar. While the natural frequency and output voltage of the conventional system are affected by bending deformation of the piezoelectric plate, the proposed system makes use of its twisting deformation. The natural frequency of the device can be significantly decreased by manipulating the location of the proof mass on the rigid bar. In order to validate the performance of the proposed energy harvester, numerical simulations and vertical shaker tests are carried out. It is demonstrated that the proposed energy harvester can shift down its resonant frequency considerably and generate much higher output power than the conventional system. It is, therefore, concluded that the proposed energy harvester utilizing the coupled bending and torsional vibrations can be effectively applied to low-frequency vibration situations.
Wang, Jian; Guo, Jifeng
2009-05-01
A longitudinal-torsional hybrid-type ultrasonic motor has larger torque and lower revolution speed compared with other kinds of ultrasonic motors. It drives devices directly and precisely, so it is adaptable to many fields, especially aeronautics and astronautics, as a servo actuator. Due to the different sound propagation speeds of longitudinal and torsional vibrations in the stator, it is difficult to match resonant frequencies of longitudinal and torsional vibrations. In this paper, a new radial-torsional vibration hybrid-type ultrasonic motor is put forward, which utilizes longitudinal vibration derived from radial vibration by the Poisson effect. The short, hollow cylindrical structure easily makes resonant frequencies of first-order radial and torsional vibrations into degeneracy. First, the new structure of the motor is presented. Second, the principle of matching the resonant frequencies is developed, and the motor geometry is optimized by ANSYS software. Finally, a 60-mm diameter prototype is fabricated, which performs well. The no-load velocity and maximum torque are 25 r/min and 5 N x m, respectively. This kind of motor is small, light, and noiseless. PMID:19473923
Study on residual stresses in ultrasonic torsional vibration assisted micro-milling
NASA Astrophysics Data System (ADS)
Lu, Zesheng; Hu, Haijun; Sun, Yazhou; Sun, Qing
2010-10-01
It is well known that machining induced residual stresses can seriously affect the dimensional accuracy, corrosion and wear resistance, etc., and further influence the longevity and reliability of Micro-Optical Components (MOC). In Ultrasonic Torsional Vibration Assisted Micro-milling (UTVAM), cutting parameters, vibration parameters, mill cutter parameters, the status of wear length of tool flank are the main factors which affect residual stresses. A 2D model of UTVAM was established with FE analysis software ABAQUS. Johnson-Cook's flow stress model and shear failure principle are used as the workpiece material model and failure principle, while friction between tool and workpiece uses modified Coulomb's law whose sliding friction area is combined with sticking friction. By means of FEA, the influence rules of cutting parameters, vibration parameters, mill cutter parameters, the status of wear length of tool flank on residual stresses are obtained, which provides a basis for choosing optimal process parameters and improving the longevity and reliability of MOC.
Numerical Investigation of Flapwise-Torsional Vibration Model of a Smart Section Blade with Microtab
Li, Nailu; Balas, Mark J.; Yang, Hua; Jiang, Wei; Magar, Kaman T.
2015-01-01
This study presents a method to develop an aeroelastic model of a smart section blade equipped with microtab. The model is suitable for potential passive vibration control study of the blade section in classic flutter. Equations of the model are described by the nondimensional flapwise and torsional vibration modes coupled with the aerodynamic model based on the Theodorsen theory and aerodynamic effects of the microtab based on the wind tunnel experimental data. The aeroelastic model is validated using numerical data available in the literature and then utilized to analyze the microtab control capability on flutter instability case and divergence instabilitymore » case. The effectiveness of the microtab is investigated with the scenarios of different output controllers and actuation deployments for both instability cases. The numerical results show that the microtab can effectively suppress both vibration modes with the appropriate choice of the output feedback controller.« less
Vibration and Noise Characteristics of Elliptical Gears due to Non-Uniform Rotation
NASA Astrophysics Data System (ADS)
Liu, Xing; Nagamura, Kazuteru; Ikejo, Kiyotaka
Elliptical gear is a typical non-circular gear, which transmits a variable-ratio rotation and power simultaneously. Due to the non-uniform rotation, the vibration and noise of elliptical gears demonstrate particular characteristics which should be paid attention to in practical application. In this paper, two elliptical gears, which are a single elliptical gear and a double elliptical gear, have been investigated to analyze the vibration and noise characteristics of elliptical gears. The corresponding circular gears for comparison are also investigated. General factors including the torque, the rotation speed, the gear vibration acceleration and the gear noise of the four test gears are measured by running test. The root mean square of the Circumferential Vibration Acceleration (CVA) and the sound pressure level of the noise of elliptical gears are obtained from the measured results and compared with those of circular gears to clarify the vibration and noise characteristics of elliptical gears. Furthermore, the frequency analysis of the CVA of elliptical gears is conducted by Fast Fourier Transform Algorithm (FFT) and compared with that of circular gears. The main vibration component of elliptical gear is uncovered according to the obtained frequency spectra. In addition, the Critical Rotation Speeds of Tooth Separation (CRSTS) of elliptical gear is obtained and its relation with load torque is unveiled.
Vibration of a thickness-twist mode piezoelectric resonator with asymmetric, nonuniform electrodes.
Yang, Jiashi; Chen, Ziguang; Hu, Yuantai
2008-04-01
We studied the effect of electrodes with varying thicknesses on thickness-twist modes in a piezoelectric plate resonator of crystals of 6mm symmetry. The focus is on the effects of asymmetric electrodes, which do not seem to have been examined before. A theoretical analysis is performed using the theory of linear piezoelectricity. A trigonometric series solution is obtained that is relatively rare from the equations of piezoelectricity. Numerical calculations are made based on the series solution. Results show that asymmetric, nonuniform electrodes have a strong effect on vibration mode shapes. This effect offers the possibility of using nonuniform electrodes in design to achieve various goals. The quantitative results in this paper are useful for the purpose. PMID:18467228
Study of torsional vibrations in an initially stressed composite poroelastic cylinders
NASA Astrophysics Data System (ADS)
Sandhya, Rani B.; Ch, Balu; Malla, Reddy P.
2015-12-01
This paper investigates torsional vibrations in an initially stressed composite poroelastic cylinder in the framework of Biot's theory of wave propagation in poroelastic solids. Poroelastic composite cylinder consists of two concentric cylindrical layers made of different poroelastic materials. The governing equations are formulated from the Biot's incremental deformation theory. The non-dimensional frequency is computed as a function of ratio of thickness to wavelength. The limiting cases of a poroelastic solid cylinder and poroelastic hollow cylinder are discussed. The results are presented graphically for two poroelastic composite cylinders and then compared with the published results.
Optimal design of thin walled I beams for extreme natural frequency of torsional vibrations
NASA Astrophysics Data System (ADS)
Szymczak, C.
1983-01-01
The optimal design of thin-walled I beams so as to extremize the natural frequency of torsional vibration is considered. It is assumed that only one dimension of the cross-section, except for the web height, may be variable in given limits, along the axis of the beam. The optimality condition for the variable dimension is settled by means of Pontryagin's maximum principle. The effect of the constant, axial loads is also included. the solution of the problem formulated is generally found in an iterative way. Some numerical examples of optimization of the I beam with variable widt of flanges are given.
NASA Technical Reports Server (NTRS)
Robertson, D. K.
1984-01-01
Partial differential equations are derived for free lateral and torsional vibration of a uniform free-free beam with a rotational mass attached to each extremity. For appropriate boundary conditions, nonlinear algebraic equations are obtained using a symbolic manipulation computer program, the solutions of which enable the computation of the neutral frequencies and mode-shapes. The mode-shapes are linear combinations of trigonometric and hyperbolic sine and cosine functions. A computer program is written for the numerical solution of the algebraic equations mentioned above, which can compute the natural frequencies, mode-shapes, and node points for any given set of parameters, for any given number of modes.
NASA Technical Reports Server (NTRS)
Laskowski, B. C.; Jaffe, R. L.; Komornicki, A.
1985-01-01
The structure, torsional potentials, vibrational spectra, and harmonic force fields for s-cis and s-trans isomers of methacryloyl fluoride are examined to understand the conformational properties of the molecules and their relationship to macroscopic polymer properties. The structure is found to be in good agreement with experiment. It is shown by calculations that the energy difference between the cis and the transisomers is less than 1 kcal/mol at both the split valence and the split valence polarized levels, with the trans form favored. Analysis of the torsional potentials indicates that a rigid rotor model provides a reasonable description of the motion of the COF group in the molecule. The torsional barrier to interconvert the s-trans to the s-cis form is found to be 7.0 kcal/mol. A fit of the data to a three-term Fourier series shows that it is possible to reproduce the experimentally derived barrier, even though a direct determination indicates that the barrier is higher.
A novel torsional exciter for modal vibration testing of large rotating machinery
NASA Astrophysics Data System (ADS)
Sihler, Christof
2006-10-01
A novel exciter for applying a dynamic torsional force to a rotating structure is presented in this paper. It has been developed at IPP in order to perform vibration tests with shaft assemblies of large flywheel generators (synchronous machines). The electromagnetic exciter (shaker) needs no fixture to the rotating shaft because the torque is applied by means of the stator winding of an electrical machine. Therefore, the exciter can most easily be applied in cases where a three-phase electrical machine (a motor or generator) is part of the shaft assembly. The oscillating power for the shaker is generated in a separate current-controlled DC circuit with an inductor acting as a buffer storage of magnetic energy. An AC component with adjustable frequency is superimposed on the inductor current in order to generate pulsating torques acting on the rotating shaft with the desired waveform and frequency. Since this torsional exciter does not require an external power source, can easily be installed (without contact to the rotating structure) and provides dynamic torsional forces which are sufficient for multi-megawatt applications, it is best suited for on-site tests of large rotating machinery.
Zhao, Libo; Hu, Yingjie; Hebibul, Rahman; Ding, Jianjun; Wang, Tongdong; Xu, Tingzhong; Liu, Xixiang; Zhao, Yulong; Jiang, Zhuangde
2016-01-01
A novel method, which was called a slope method, has been proposed to measure fluid density by the micro-cantilever sensing chip. The theoretical formulas of the slope method were discussed and established when the micro-cantilever sensing chip was under flexural and torsional vibrations. The slope was calculated based on the fitted curve between the excitation and output voltages of sensing chip under the nonresonant status. This measuring method need not sweep frequency to find the accurate resonant frequency. Therefore, the fluid density was measured easily based on the calculated slope. In addition, the micro-cantilver was drived by double sided excitation and free end excitation to oscillate under flexural and torsional vibrations, respectively. The corresponding experiments were carried out to measure the fluid density by the slope method. The measurement results were also analyzed when the sensing chip was under flexural and torsional nonresonant vibrations separately. The measurement accuracies under these vibrations were all better than 1.5%, and the density measuring sensitivity under torsional nonresonant vibration was about two times higher than that under flexural nonresonant vibration. PMID:27626425
Torsional vibrations of helically buckled drill-strings: experiments and FE modelling
NASA Astrophysics Data System (ADS)
Kapitaniak, M.; Hamaneh, V. V.; Wiercigroch, M.
2016-05-01
This paper presents investigations of a complex drill-string vibrations on a novel experimental rig, developed by the Centre for Applied Dynamics Research at the University of Aberdeen. The rig is capable of exhibiting of all major types of drill-string vibrations, including torsional, axial and lateral modes. The importance of this work lies in the fact, that the experimental rig utilizes real industrial drill-bits and rock samples, which after careful identification of Torque On Bit (TOB) speed curves, allows to use an equivalent friction model to accommodate for both frictional and cutting components of the bit-rock interactions. Moreover, the proposed Finite Element model, after a careful calibration, is capable of replicating experimental results, for the prebuckled configuration of the drill-string. This allows us to observe the effect of winding and unwinding of the helical deformation during stick-slip motion.
Low-frequency band gap mechanism of torsional vibration of lightweight elastic metamaterial shafts
NASA Astrophysics Data System (ADS)
Li, Lixia; Cai, Anjiang
2016-07-01
In this paper, the low-frequency band gap mechanism of torsional vibration is investigated for a kind of light elastic metamaterial (EM) shafts architecture comprised of a radial double-period element periodically as locally resonant oscillators with low frequency property. The dispersion relations are calculated by a method combining the transfer matrix and a lumped-mass method. The theoretical results agree well with finite method simulations, independent of the density of the hard material ring. The effects of the material parameters on the band gaps are further explored numerically. Our results show that in contrast to the traditional EM shaft, the weight of our proposed EM shaft can be reduced by 27% in the same band gap range while the vibration attenuation is kept unchanged, which is very convenient to instruct the potential engineering applications. Finally, the band edge frequencies of the lower band gaps for this light EM shaft are expressed analytically using physical heuristic models.
Hu, Zheng; Lin, Jun; Chen, Zhong-Sheng; Yang, Yong-Min; Li, Xue-Jun
2015-01-01
High-speed blades are often prone to fatigue due to severe blade vibrations. In particular, synchronous vibrations can cause irreversible damages to the blade. Blade tip-timing methods (BTT) have become a promising way to monitor blade vibrations. However, synchronous vibrations are unsuitably monitored by uniform BTT sampling. Therefore, non-equally mounted probes have been used, which will result in the non-uniformity of the sampling signal. Since under-sampling is an intrinsic drawback of BTT methods, how to analyze non-uniformly under-sampled BTT signals is a big challenge. In this paper, a novel reconstruction method for non-uniformly under-sampled BTT data is presented. The method is based on the periodically non-uniform sampling theorem. Firstly, a mathematical model of a non-uniform BTT sampling process is built. It can be treated as the sum of certain uniform sample streams. For each stream, an interpolating function is required to prevent aliasing in the reconstructed signal. Secondly, simultaneous equations of all interpolating functions in each sub-band are built and corresponding solutions are ultimately derived to remove unwanted replicas of the original signal caused by the sampling, which may overlay the original signal. In the end, numerical simulations and experiments are carried out to validate the feasibility of the proposed method. The results demonstrate the accuracy of the reconstructed signal depends on the sampling frequency, the blade vibration frequency, the blade vibration bandwidth, the probe static offset and the number of samples. In practice, both types of blade vibration signals can be particularly reconstructed by non-uniform BTT data acquired from only two probes. PMID:25621612
NASA Astrophysics Data System (ADS)
Yamaguchi, Maiku; Nobusada, Katsuyuki
2016-02-01
In this paper, effects of the spatial nonuniformity of an optical near field (ONF) on the molecular photodissociation process are presented. The dissociation dynamics of H2 + was theoretically investigated by solving a non-Born-Oppenheimer Schrödinger equation. It was found that in addition to two dissociation mechanisms, which are one-photon and three-photon processes induced by uniform laser light excitation, the nonuniform ONF opens another dissociation path: two-step excitation mediated by vibrationally excited states. The nonuniformity of the ONF causes a transition between vibrational states that is forbidden according to conventional selection rules, leading to the dissociation path. The dependences of photodissociation on the intensity and nonuniformity of the ONF were calculated and the results validated the two-step dissociation mechanism.
NASA Astrophysics Data System (ADS)
Kang, Jae-Hoon
2016-09-01
Hysterically damped free and forced vibrations of axial and torsional bars are investigated using a closed form exact method. The method is exact and yields closed form expressions for the vibratory displacements. This is in contrast with the well known eigenfunction superposition method which requires expressing the distributed forcing functions and the displacement response functions as infinite sums of free vibration eigenfunctions. The hysterically damped free vibration frequencies and corresponding damped mode shapes are calculated and plotted instead of undamped free vibration and mode shapes which is typically computed and applied in vibration problems. The hysterically damped natural frequency equations are exactly derived. Accurate axial or torsional amplitude vs. forcing frequency curves showing the forced response due to distributed loading are displayed with various hysteretic damping parameters.
Automated misfire diagnosis in engines using torsional vibration and block rotation
NASA Astrophysics Data System (ADS)
Chen, J.; Randall, R. B.; Peeters, B.; Van der Auweraer, H.; Desmet, W.
2012-05-01
Even though a lot of research has gone into diagnosing misfire in IC engines, most approaches use torsional vibration of the crankshaft, and only a few use the rocking motion (roll) of the engine block. Additionally, misfire diagnosis normally requires an expert to interpret the analysis results from measured vibration signals. Artificial Neural Networks (ANNs) are potential tools for the automated misfire diagnosis of IC engines, as they can learn the patterns corresponding to various faults. This paper proposes an ANN-based automated diagnostic system which combines torsional vibration and rotation of the block for more robust misfire diagnosis. A critical issue with ANN applications is the network training, and it is improbable and/or uneconomical to expect to experience a sufficient number of different faults, or generate them in seeded tests, to obtain sufficient experimental results for the network training. Therefore, new simulation models, which can simulate combustion faults in engines, were developed. The simulation models are based on the thermodynamic and mechanical principles of IC engines and therefore the proposed misfire diagnostic system can in principle be adapted for any engine. During the building process of the models, based on a particular engine, some mechanical and physical parameters, for example the inertial properties of the engine parts and parameters of engine mounts, were first measured and calculated. A series of experiments were then carried out to capture the vibration signals for both normal condition and with a range of faults. The simulation models were updated and evaluated by the experimental results. Following the signal processing of the experimental and simulation signals, the best features were selected as the inputs to ANN networks. The automated diagnostic system comprises three stages: misfire detection, misfire localization and severity identification. Multi-layer Perceptron (MLP) and Probabilistic Neural Networks were
Detecting the crankshaft torsional vibration of diesel engines for combustion related diagnosis
NASA Astrophysics Data System (ADS)
Charles, P.; Sinha, Jyoti K.; Gu, F.; Lidstone, L.; Ball, A. D.
2009-04-01
Early fault detection and diagnosis for medium-speed diesel engines is important to ensure reliable operation throughout the course of their service. This work presents an investigation of the diesel engine combustion related fault detection capability of crankshaft torsional vibration. The encoder signal, often used for shaft speed measurement, has been used to construct the instantaneous angular speed (IAS) waveform, which actually represents the signature of the torsional vibration. Earlier studies have shown that the IAS signal and its fast Fourier transform (FFT) analysis are effective for monitoring engines with less than eight cylinders. The applicability to medium-speed engines, however, is strongly contested due to the high number of cylinders and large moment of inertia. Therefore the effectiveness of the FFT-based approach has further been enhanced by improving the signal processing to determine the IAS signal and subsequently tested on a 16-cylinder engine. In addition, a novel method of presentation, based on the polar coordinate system of the IAS signal, has also been introduced; to improve the discrimination features of the faults compared to the FFT-based approach of the IAS signal. The paper discusses two typical experimental studies on 16- and 20-cylinder engines, with and without faults, and the diagnosis results by the proposed polar presentation method. The results were also compared with the earlier FFT-based method of the IAS signal.
Non-linear torsional vibration characteristics of an internal combustion engine crankshaft assembly
NASA Astrophysics Data System (ADS)
Huang, Ying; Yang, Shouping; Zhang, Fujun; Zhao, Changlu; Ling, Qiang; Wang, Haiyan
2012-07-01
Crankshaft assembly failure is one of the main factors that affects the reliability and service life of engines. The linear lumped mass method, which has been universally applied to the dynamic modeling of engine crankshaft assembly, reveals obvious simulation errors. The nonlinear dynamic characteristics of a crankshaft assembly are instructionally significant to the improvement of modeling correctness. In this paper, a general expression for the non-constant inertia of a crankshaft assembly is derived based on the instantaneous kinetic energy equivalence method. The nonlinear dynamic equations of a multi-cylinder crankshaft assembly are established using the Lagrange rule considering nonlinear factors such as the non-constant inertia of reciprocating components and the structural damping of shaft segments. The natural frequency and mode shapes of a crankshaft assembly are investigated employing the eigenvector method. The forced vibration response of a diesel engine crankshaft assembly taking into account the non-constant inertia is studied using the numerical integral method. The simulation results are compared with a lumped mass model and a detailed model using the system matrix method. Results of non-linear torsional vibration analysis indicate that the additional excitation torque created by non-constant inertia activates the 2nd order rolling vibration, and the additional damping torque resulting from the non-constant inertia is the main nonlinear factor. The increased torsional angular displacement evoked by the high order excitation torque relates to the non-constant inertia. This research project is aimed at improving nonlinear dynamics theory, and the confirmed nonlinear parameters can be used for the structure design of a crankshaft assembly.
Matrix Analysis of Longitudinal and Torsional Vibrations in Nonuniform Multibranch Beams
NASA Technical Reports Server (NTRS)
Wingate, Robert T.
1967-01-01
Since longitudinal modes and frequencies provide basic data for dynamic analyses of arbitrary beam-like structures and since closed-form solutions for the modes are generally not feasible to obtain, an approximate method is developed for computing the natural frequencies and the corresponding mode shapes for a variable-section, unconstrained multibranch beam. A lumped mass analogy employing influence coefficients is used to represent the beam. The simultaneous equations of motion for the lumped mass system are derived in matrix form and algebraically manipulated to yield a classical eigenvalue equation solvable by standard procedures. The orthogonality relationship of the natural modes is derived and used to form the basis of an orthogonal sweeping process for determination of modes above the fundamental. Numerical examples including an application to a solid-fuel launch system are presented. Also, a detailed discussion is devoted to the theoretical verifications of the approximate modes and frequencies.
The Coupling of Flexural Propeller Vibrations with the Torsional Crankshaft Vibrations
NASA Technical Reports Server (NTRS)
Meyer, J.
1943-01-01
The exact mathematical treatment of the problem is possible by replacing the propeller blade by a homogeneous prismatic rod. Conclusions can them be drawn as to the behavior of an actual propeller, since tests on propeller blades have indicated a qualitative agreement with the homogeneous rod. The natural frequencies are determined and the stressing of the systems under the various vibration modes are discussed.
Zhao, Libo; Hu, Yingjie; Wang, Tongdong; Ding, Jianjun; Liu, Xixiang; Zhao, Yulong; Jiang, Zhuangde
2016-01-01
Methods to calculate fluid density and viscosity using a micro-cantilever and based on the resonance principle were put forward. Their measuring mechanisms were analyzed and the theoretical equations to calculate the density and viscosity were deduced. The fluid-solid coupling simulations were completed for the micro-cantilevers with different shapes. The sensing chips with micro-cantilevers were designed based on the simulation results and fabricated using the micro electromechanical systems (MEMS) technology. Finally, the MEMS resonant sensor was packaged with the sensing chip to measure the densities and viscosities of eight different fluids under the flexural and torsional vibrating modes separately. The relative errors of the measured densities from 600 kg/m3 to 900 kg/m3 and viscosities from 200 μPa·s to 1000 μPa·s were calculated and analyzed with different microcantilevers under various vibrating modes. The experimental results showed that the effects of the shape and vibrating mode of micro-cantilever on the measurement accuracies of fluid density and viscosity were analyzed in detail. PMID:27275823
Zhao, Libo; Hu, Yingjie; Wang, Tongdong; Ding, Jianjun; Liu, Xixiang; Zhao, Yulong; Jiang, Zhuangde
2016-01-01
Methods to calculate fluid density and viscosity using a micro-cantilever and based on the resonance principle were put forward. Their measuring mechanisms were analyzed and the theoretical equations to calculate the density and viscosity were deduced. The fluid-solid coupling simulations were completed for the micro-cantilevers with different shapes. The sensing chips with micro-cantilevers were designed based on the simulation results and fabricated using the micro electromechanical systems (MEMS) technology. Finally, the MEMS resonant sensor was packaged with the sensing chip to measure the densities and viscosities of eight different fluids under the flexural and torsional vibrating modes separately. The relative errors of the measured densities from 600 kg/m³ to 900 kg/m³ and viscosities from 200 μPa·s to 1000 μPa·s were calculated and analyzed with different microcantilevers under various vibrating modes. The experimental results showed that the effects of the shape and vibrating mode of micro-cantilever on the measurement accuracies of fluid density and viscosity were analyzed in detail. PMID:27275823
Torsional Vibration Analysis of Reciprocating Compressor Trains driven by Induction Motors
NASA Astrophysics Data System (ADS)
Brunelli, M.; Fusi, A.; Grasso, F.; Pasteur, F.; Ussi, A.
2015-08-01
The dynamic study of electric motor driven compressors, for Oil&Gas (O&G) applications, are traditionally performed in two steps separating the mechanical and the electrical systems. The packager conducts a Torsional Vibration Analysis (TVA) modeling the mechanical system with a lumped parameter scheme, without taking into account the electrical part. The electric motor supplier later performs a source current pulsation analysis on the electric motor system, based on the TVA results. The mechanical and the electrical systems are actually linked by the electromagnetic effect. The effect of the motor air-gap on TVA has only recently been taken into account by adding a spring and a damper between motor and ground in the model. This model is more accurate than the traditional one, but is applicable only to the steady-state condition and still fails to consider the reciprocal effects between the two parts of the system. In this paper the torsional natural frequencies calculated using both the traditional and the new model have been compared. Furthermore, simulation of the complete system has been achieved through the use of LMS AMESim, multi-physics, one-dimensional simulation software that simultaneously solves the shafts rotation and electric motor voltage equation. Finally, the transient phenomena that occur during start-up have been studied.
NASA Technical Reports Server (NTRS)
Berg, Robert F.; Grodsinsky, Carlos M.
1992-01-01
Critical point viscosity measurements are limited to their reduced temperature approach to T(sub c) in an Earth bound system, because of density gradients imposed by gravity. Therefore, these classes of experiments have been proposed as good candidates for 'microgravity' science experiments where this limitation is not present. The nature of these viscosity measurements dictate hardware that is sensitive to low frequency excitations. Because of the vibratory acceleration sensitivity of a torsion oscillator viscometer, used to acquire such measurements, a vibration isolation sensitivity test was performed on candidate 'microgravity' hardware to study the possibility of meeting the stringent oscillatory sensitivity requirements of a National Institute of Standards and Technology (NIST) torsion oscillator viscometer. A prototype six degree of freedom active magnetic isolation system, developed at NASA Lewis Research Center, was used as the isolation system. The ambient acceleration levels of the platform were reduced to the noise floor levels of its control sensors, about one microgravity in the 0.1 to 10 Hz bandwidth.
NASA Astrophysics Data System (ADS)
Suga, Kenichi; Ohdaira, Etsuzo; Masuzawa, Nobuyoshi; Ide, Masao
1999-05-01
Application of ultrasonic welding to plastics has become common. Recently, an ultrasonic welding method for long plastic pipes using torsional vibrations was developed. Optimal welding conditions for this new method have not yet been clarified. This paper reports the results of an investigation made in order to clarify the conditions, focusing on the welding time and both horn pressure, static force that horns pinch pipe, and static pressure which is added to welding surface. Experiments were performed on the welding of acrylic resin and ABS resin pipes. It was found that welding time decreases exponentially with increasing horn pressure and that increasing the static pressure reduces the welding time. It was also found there is an optimum range ofhorn pressures.
NASA Astrophysics Data System (ADS)
Abdelkefi, A.; Najar, F.; Nayfeh, A. H.; Ben Ayed, S.
2011-11-01
Recently, piezoelectric cantilevered beams have received considerable attention for vibration-to-electric energy conversion. Generally, researchers have investigated a classical piezoelectric cantilever beam with or without a tip mass. In this paper, we propose the use of a unimorph cantilever beam undergoing bending-torsion vibrations as a new piezoelectric energy harvester. The proposed design consists of a single piezoelectric layer and a couple of asymmetric tip masses; the latter convert part of the base excitation force into a torsion moment. This structure can be tuned to be a broader band energy harvester by adjusting the first two global natural frequencies to be relatively close to each other. We develop a distributed-parameter model of the harvester by using the Euler-beam theory and Hamilton's principle, thereby obtaining the governing equations of motion and associated boundary conditions. Then, we calculate the exact eigenvalues and associated mode shapes and validate them with a finite element (FE) model. We use these mode shapes in a Galerkin procedure to develop a reduced-order model of the harvester, which we use in turn to obtain closed-form expressions for the displacement, twisting angle, voltage output, and harvested electrical power. These expressions are used to conduct a parametric study for the dynamics of the system to determine the appropriate set of geometric properties that maximizes the harvested electrical power. The results show that, as the asymmetry is increased, the harvester's performance improves. We found a 30% increase in the harvested power with this design compared to the case of beams undergoing bending only. We also show that the locations of the two masses can be chosen to bring the lowest two global natural frequencies closer to each other, thereby allowing the harvesting of electrical power from multi-frequency excitations.
Kodama, Tomoaki; Honda, Yasuhiro; Wakabayashi, Katsuhiko; Iwamoto, Shoichi
1996-09-01
The cheap and compact rubber dampers of shear-type have been widely employed as the torsional vibration control of the crankshaft system of high-speed, automobile diesel engines. The conventional rubber dampers have various rubber forms owing to the thorough investigation of optimum dampers in the design stage. Their rubber forms can be generally grouped into three classes such as the disk type, the bush type and the composite type. The disk type and the bush type rubber dampers are called the basic-pattern rubber dampers hereafter. The composite type rubber part is supposed to consist of the disk type and the bush type parts, regarded respectively as the basic patterns of the rubber part, at large. The dynamic characteristics of the vibration isolator rubber depend generally on temperature, frequency, strain amplitude, shape and size effect,s so it is difficult to estimate accurately their characteristics. With the present technical level, it is also difficult to determine the suitable rubber geometry which optimizes the vibration control effect. The study refers to the calculation method of the torsional vibration of a crankshaft system with a shear-type rubber damper having various rubber forms in order to offer the useful method for optimum design. In this method, the rheological formula of the three-element Maxwell model, from which the torsional stiffness and the damping coefficient of the damper rubber part in the equivalent vibration system are obtained, are adopted in order to decide the dynamic characteristics of the damper rubber part.
NASA Astrophysics Data System (ADS)
Lattanzi, F.; di Lauro, C.
It is shown that the torsional splitting patterns in methanol-like molecules, with the excitation of small amplitude vibrational modes in the methyl group, are determined by mechanisms that can be formulated in an almost identical fashion to that for ethane-like molecules. This is achieved by treating ethane-like molecules by the internal axis method (IAM) and methanol-like molecules by the principal axis method (PAM) or rho-axis method (RAM). Using the extended molecular groups G6(EM) or C6v(M) for methanol and G36(EM) for ethane, vibrations perpendicular to the internal rotation axis are conveniently described by modes of higher degeneracy (E for methanol and Gs for ethane) in the absence of coupling of top and frame. Head-tail coupling operators, except the cos-type barrier terms, lower the degeneracy, causing vibrational splittings. Coupled vibrational pairs with torsional splitting patterns that we call 'regular' (pure A1, A2 pairs for methanol and pure E1d, E2d pairs for ethane) or 'inverted' (pure B1, B2 pairs for methanol and pure E1s, E2s pairs for ethane) can be formed as limit cases. Actual splitting patterns occur between the above limits, and are basically determined by torsional Coriolis coupling, which can tune more or less to resonance pairs of uncoupled basis levels linked by specific head-tail coupling operators. The inversion of torsional splitting patterns, observed in perpendicular vibrational modes of the methyl group of methanol, can be predicted by these theoretical considerations. Similar considerations apply to molecules of G12 symmetry.
Coupled shaft-torsion and blade-bending vibrations of a rotating shaft-disk-blade unit
Huang, S.C.; Ho, K.B.
1996-01-01
A new approach to analyzing the dynamic coupling between shaft torsion and blade bending of a rotating shaft-disk-blade unit is introduced. The approach allows the shaft to vibrate freely around its rotation axis instead of assuming a periodic perturbation of the shaft speed that may accommodate the shaft flexibility only to a limited extent. A weighted residual method is applied, and the receptances at the connections of blades and shaft-disk are formulated. Numerical examples are given for cases with between two and six symmetrically arranged blades. The results show not only coupling between the shaft, disk, and blades, but also coupling between individual blades where the shaft acts as a rigid support and experiences no torsional vibration. The blade-coupling modes occurred only in repeated frequencies. Finally, the effect of shaft speed on the modal frequencies was investigated. Plots illustrating the occurrence of critical speeds and flutter instabilities are presented.
NASA Technical Reports Server (NTRS)
Houbolt, John C; Brooks, George W
1958-01-01
The differential equations of motion for the lateral and torsional deformations of twisted rotating beams are developed for application to helicopter rotor and propeller blades. No assumption is made regarding the coincidence of the neutral, elastic, and mass axes, and the generality is such that previous theories involving various simplifications are contained as subcases to the theory presented in this paper. Special attention is given the terms which are not included in previous theories. These terms are largely coupling-type terms associated with the centrifugal forces. Methods of solution of the equations of motion are indicated by selected examples.
NASA Technical Reports Server (NTRS)
Houbolt, John C; Brooks, George W
1957-01-01
The differential equations of motion for the lateral and torsional deformations of twisted rotating beams are developed for application to helicopter rotor and propeller blades. No assumption is made regarding the coincidence of the neutral, elastic, and mass axes, and the generality is such that previous theories involving various simplifications are contained as subcases to the theory developed and presented in this paper. Special attention is given to coupling terms not found in previous theories, and methods of solution of the equations of motion are indicated by selected examples.
NASA Astrophysics Data System (ADS)
Korayem, M. H.; Korayem, A. H.; Hosseini Hashemi, Sh.
2016-02-01
Nowadays, to enhance the performance of atomic force microscopy (AFM) micro-cantilevers (MCs) during imaging, reduce costs and increase the surface topography precision, advanced MCs equipped with piezoelectric layers are utilized. Using the modified couple stress (MCS) theory not only makes the modeling more exhaustive, but also increases the accuracy of prediction of the vibration behavior of the system. In this paper, Hamilton's principle by consideration of the MCS theory has been used to extract the equations. In addition, to discretize the equations, differential quadrature method has been adopted. Analysis of the hysteresis effect on the vibration behavior of the AFM MC is of significant importance. Thus, to model the hysteresis effect, Bouc-Wen method, which is solved simultaneously with the vibration equations of non-uniform Timoshenko beam, has been utilized. Furthermore, a bimodal excitation of the MC has been considered. The results reveal that the hysteresis effect appears as a phase difference in the time response. Finally, the effect of the geometric parameters on the vibration frequency of the system which is excited by combination of the first two vibration modes of the non-uniform piezoelectric MC has been examined. The results indicate the considerable effect of the MC length in comparison with other geometric parameters such as the MC width and thickness.
Shaft-Torsion and Blade-Bending Coupling Vibrations in a Rotor System with Grouped Blades
NASA Astrophysics Data System (ADS)
Huang, Shyh-Chin; Chiu, Yi-Jui
This paper discussed the shaft-torsion and blade-bending coupling vibrations of a rotor system, in which the blades were grouped with lacing wires. Massless tension springs were used for modeling the lacing wires. An energy principle in conjunction with the assumed modes method was employed to yield the discrete equations of motion. The natural frequencies and the mode shapes of the system were solved for five- and six-blade cases as examples. Numerical results showed how the natural frequencies varied with the wire stiffness, connecting position, and the rotational speed. The diagrams of the coupling mode shapes and FRF's were drawn. From the results, it was found that lacing wire did not affect the SB (shaft-blades) coupling modes, but the BB (inter-blades) modes were indeed affected by the lacing wire. At moderate range of wire stiffness, the repeated BB modes split into more distinct modes. As expected, increasing the wire stiffness or connecting near outer edge would strengthen the system structure and increasing the natural frequencies of BB modes.
NASA Astrophysics Data System (ADS)
Kim, Nam-Il; Fu, Chung C.; Kim, Moon-Young
2007-02-01
Based on the power series method, the static and dynamic stiffness matrices for the flexural-torsional buckling and free vibration analysis of thin-walled beam with non-symmetric cross-section subjected to linearly variable axial force are newly presented. Additionally, the static stiffness matrix for the lateral buckling analysis of non-symmetric beam is presented for the first time. For this, the elastic strain energy, the potential energy considering the second-order terms of finite rotations, and the kinetic energy for thin-walled beam with non-symmetric cross-section are introduced. Then equations of motion and force-deformation relations are derived from the energy principle. Explicit expressions for displacement parameters are derived based on power series expansions of displacement components. Finally, the static and dynamic element stiffness matrices are determined using force-deformation relationships. In order to verify the accuracy of this study, the numerical solutions are presented and compared with the finite element solutions using the Hermitian beam elements and ABAQUS's shell elements.
NASA Astrophysics Data System (ADS)
Adachi, Kazunari; Saito, Masanaka
1995-05-01
We have previously developed a hollow cylindrical bolt-clamped Langevin-type transducer with a high mechanical quality factor (Q) for excitation of high-amplitude torsional vibrations. In this paper, we propose a construction of vibrating systems that comprise a `stepped horn' (a mechanical transformer of torsional vibration) and the stumpy `twisting' transducer developed by us. The distinctive feature of the construction is that it achieves compactness without sacrificing the volume of piezoelectric ceramics that is important for high-power ultrasonic applications. Through experiments, we have found some crucial points in the procedure for constructing torsional-vibration systems that can be operated at a relatively high frequency. In addition, we have conducted some experiments of ultrasonic plastic welding using one of the vibrating systems for evaluation of the feasibility of the construction in this manufacturing technique
NASA Astrophysics Data System (ADS)
Kojima, Hirohisa; Kunugi, Kouta; Trivailo, Pavel M.
2016-06-01
Tape tethers show great promise for application in space debris removal because they possess a large collecting area, which is crucial for the collection of electrons from a plasma environment in space. Tape tethers are therefore preferred over string tethers in electrodynamic tethered systems (EDTS), which operate based on the Lorentz force derived from the interaction between the electric current on the tether and the Earth's magnetic field. Vibrations of the tether may disturb the attitude of the mother satellite and the subsatellite, and are difficult to damp in space because the damping would be minimal owing to the almost zero drag force in space. Due to their relatively large width, tape tethers experience torsional deformation and therefore cannot be treated as a string tether. If torsional deformation of tape tethers is not avoided, the advantage of tape tethers as the materials for EDT systems will be deteriorated. Point-type sensors and actuators are usually used to sense and control vibrations. However, it is difficult to apply such sensors and actuators to tape tethers because of the substantial length of the tether as well as the need for a deployment mechanism, such as a reel. In order to overcome the difficulties related to vibrations, the use of smart-film sensors and actuators for sensing and controlling vibrations of tape tethers is considered in this study. In a previous study, we presented an application of smart film for sensing vibrations of tape tethers, but the actuation of tape tethers using smart-film actuators has not yet been reported. In the present paper, we mathematically derive suitable configurations of smart-film attachment to a tape tether for cluster filtering and actuation of bending and torsional vibrations of the tape tether, and carried out cluster actuation experiments. The experimental results reveal that the bending and torsional vibrations of a tape tether can be reduced by cluster actuation control based on direct
NASA Technical Reports Server (NTRS)
Pearson, J. C.; Pickett, Herbert M.; Sastry, K. V. L. N.
2000-01-01
C2H5CN (Propionitrile or ethyl cyanide) is a well known interstellar species abundantly observed in hot cores during the onset of star formation. The onset of star formation generally results in elevated temperature, which thermally populates may low lying vibrational states such as the 206/cm in-plane bend and the 212/cm first excited torsional state in C2H5CN. Unfortunately, these two states are strongly coupled through a complex series of torsion-vibration-rotation interactions, which dominate the spectrum. In order to understand the details of these interactions and develop models capable of predicting unmeasured transitions for astronomical observations in C2H5CN and similar molecules, several thousand rotational transitions in the lowest excited in-plane bend and first excited torsional state have been recorded, assigned and analyzed. The analysis reveals very strong a- and b-type Coriolis interactions and a number of other smaller interactions and has a number of important implications for other C3V torsion-rotation-vibration systems. The relative importance and the physical origins of the coupling among the rotational, vibrational and torsional motions will be presented along with a full spectroscopic analysis and supporting astronomical observations.
Vibration analysis of rotor blades with an attached concentrated mass
NASA Technical Reports Server (NTRS)
Murthy, V. R.; Barna, P. S.
1977-01-01
The effect of an attached concentrated mass on the dynamics of helicopter rotor blades is determined. The point transmission matrix method was used to define, through three completely automated computer programs, the natural vibrational characteristics (natural frequencies and mode shapes) of rotor blades. The problems of coupled flapwise bending, chordwise bending, and torsional vibration of a twisted nonuniform blade and its special subcase pure torsional vibration are discussed. The orthogonality relations that exist between the natural modes of rotor blades with an attached concentrated mass are derived. The effect of pitch, rotation, and point mass parameters on the collective, cyclic, scissor, and pure torsional modes of a seesaw rotor blade is determined.
NASA Astrophysics Data System (ADS)
Adachi, Kazunari; Konno, Yuji; Masaki, Shingo
1994-02-01
We have identified a crucial point for realization of a high mechanical quality factor (Q) of a bolt-clamped Langevin-type transducer used to excite large torsional vibrations of a cylindrical system. A sufficient margin of the static bearing stress over the vibratory shearing one at the interface between the components has been found necessary for a high Q as a result of some numerical simulations and experiments for two models of the transducers. A hollow cylindrical shape of the transducer is seen to have a great advantage in this respect.
NASA Astrophysics Data System (ADS)
Coral, W.; Rossi, C.; Curet, O. M.
2015-12-01
This paper presents a Differential Quadrature Element Method for free transverse vibration of a robotic fish based on a continuous and non-uniform flexible backbone with distributed masses (fish ribs). The proposed method is based on the theory of a Timoshenko cantilever beam. The effects of the masses (number, magnitude and position) on the value of natural frequencies are investigated. Governing equations, compatibility and boundary conditions are formulated according to the Differential Quadrature rules. The convergence, efficiency and accuracy are compared to other analytical solution proposed in the literature. Moreover, the proposed method has been validate against the physical prototype of a flexible fish backbone. The main advantages of this method, compared to the exact solutions available in the literature are twofold: first, smaller computational cost and second, it allows analysing the free vibration in beams whose section is an arbitrary function, which is normally difficult or even impossible with other analytical methods.
NASA Astrophysics Data System (ADS)
He, Qing; Peng, Huichun; Zhai, Pengcheng; Zhen, Yaxin
2016-06-01
The angular acceleration is taken into the consideration for the modeling of equations of coupling vibration in rotational operation. The effects of angular acceleration on the amplitude of both lateral and torsion vibration of the breathing cracked rotor are studied for the first time. The torsion influence of unbalance orientation angles is especially studied during the modeling of the Breathing behavior model of the crack with the mass eccentricity. Different from the previous study, the effects of unbalance orientation angle on the lateral torsion coupling vibration of the breathing cracked rotor are compared by logarithmic spectrum diagrams. Parametric stability of the breathing cracked rotor associated with both unbalance orientation angle and accelerations in diverse level of mass eccentricity are presented, these works have not been seen before. The numerical parametrically stability results are verified by comparing with the dynamic response of the system.
NASA Astrophysics Data System (ADS)
Koroleva, L. A.; Tyulin, V. I.; Matveev, V. K.; Pentin, Yu. A.
2013-05-01
B3LYP, MP2, CCSD(T), and MP4/MP2 in the 6-311G( d, p), 6-311++G( d, p), cc-pVTZ, aug-cc-pVTZ bases used to calculate the transition frequencies of torsional vibration of trans- and cis-isomers of acrolein in the ground electronic state ( S 0) are analyzed. It is found that for trans-isomers, all methods of calculation except for B3LYP in the cc-pVTZ basis yield good agreement between the calculated and experimental values. It is noted that for the cis-isomer of acrolein, no method of calculation confirms the experimental value of the frequency of torsional vibration (138 cm-1). It is shown that the calculated and experimental values for obertones at 273.0 cm-1 and other transitions of torsional vibration are different for this isomer in particular. However, it is established that in some calculation methods (B3LYP, MP2), the frequency of the torsional vibration of the cis-isomer coincides with another experimental value of this frequency (166.5 cm-1). It is concluded that in analyzing the vibrational structure of the UV spectrum, the calculated and experimental values of its obertone (331.3 cm-1) coincide, along with its frequency. It is also noted that the frequency of torsional vibration for the cis-isomer (166.5 cm-1) can also be found in other experimental works if we change the allocation of torsional transition 18{1/1}.
NASA Astrophysics Data System (ADS)
Borvayeh, Leila
Internal rotation in C2H6, CH3SiH 3, and similar symmetric top molecules offers an excellent opportunity to investigate large amplitude motion in relatively simple molecules. Due to specific symmetry characteristics of symmetric top molecules, the large amplitude torsional motion is separable from the small amplitude vibrations and the overall rotation, therefore provides a relatively simple vibrational-torsional-rotational Hamiltonian. The results from studying torsional motion in symmetric top molecules may be applied to more complex systems, such as asymmetric internal rotors. This thesis deals with the internal rotation in two types of symmetric top molecules. The first group (X2Y6 type molecules) includes CH3CH3, SiH3SiH3, and CD3CD3. For ethane, we have presented the most complete vibrational-torsional-rotational Hamiltonian model for four lowest vibrational states, to date. For disilane, we have studied the nu9 vibrational fundamentals and nu9 + nu4 - nu4 hot band. In the case of CD3CD3, we have investigated the analysis of nu3 - nu9 difference band. This work demonstrates that observation of weak difference bands in ethane-like molecules might be a way to access vibrational states whose fundamentals are both infrared inactive and very difficult to observe using Raman spectroscopy. The second group (XY3AB3 type molecules) includes CH3SiH3, 12CH3 13CH 3, and CH3CD3. For CH3SiH3 and CH3CD3, we have presented an analysis that includes the nu12 + nu6 - nu6 hot band. In all cases, the torsional dependency of several purely-vibrational terms was found to be important. For CH3SiH3, a coupling between the nu12 + nu6 and nu5 fundamentals has been observed and treated properly. In the case of 12CH 313CH3, we have analyzed nu 6 and 2nu6 - nu6 torsional bands in combination with nu12 band. The torsion mediated Coriolis interactions were found between the torsional stacks of nu12 and ground vibrational state. The analysis of the hot band of CH3CD3 shows a local coupling
NASA Technical Reports Server (NTRS)
Subrahmanyam, K. B.; Kaza, K. R. V.; Brown, G. V.; Lawrence, C.
1986-01-01
The coupled bending-bending-torsional equations of dynamic motion of rotating, linearly pretwisted blades are derived including large precone, second degree geometric nonlinearities and Coriolis effects. The equations are solved by the Galerkin method and a linear perturbation technique. Accuracy of the present method is verified by comparisons of predicted frequencies and steady state deflections with those from MSC/NASTRAN and from experiments. Parametric results are generated to establish where inclusion of only the second degree geometric nonlinearities is adequate. The nonlinear terms causing torsional divergence in thin blades are identified. The effects of Coriolis terms and several other structurally nonlinear terms are studied, and their relative importance is examined.
NASA Astrophysics Data System (ADS)
Lattanzi, F.; di Lauro, C.
2006-08-01
The effects of head-tail coupling in the mechanism of formation of combinations and overtones of perpendicular vibrational modes, in molecules like ethane and methanol, is investigated. For uncoupled head and tail the perpendicular modes have higher degeneracies, and the species of the components of their combinations or overtones span the irreducible representations occurring in the direct products Gs× Gs in the G36(EM) group (ethane) and E× E in the G6(EM) group (methanol). Head-tail coupling operators can transform these uncoupled fundamental vibrational modes into coupled modes of lower symmetries, and then the symmetry species of combinations and overtones must be contained in the direct product of these lower symmetry sets. It is shown that the operators which generate coupled sets of fundamental vibrational states of given symmetries, also work to generate combinations and overtones with the symmetry species predicted from those of the combining fundamentals. These mechanisms are ruled by the torsional Coriolis operators, which can tune more or less to resonance basis levels linked by specific head-tail coupling operators.
NASA Astrophysics Data System (ADS)
Lattanzi, Franca; di Lauro, Carlo; Horneman, Veli-Matti
2011-10-01
A high resolution Fourier transform infrared spectrum of C2H6, measured at a pressure of 173.3 Pa and an optical path of 153.2 m, was analysed between 1050 and 1295 cm-1. Extensive absorption due to the difference bands ν 11-ν 4, and several rotation-torsion lines of the difference band ν 2-ν 4, in the region of the x, y-Coriolis resonance of ν 2 and ν 11, were observed. This allowed a detailed rotation-torsion analysis of the upper states ν 11 and ν 2. The anomalous torsional structure, found in the non-degenerate vibrational state ν 2, can be explained as the effect of an Hamiltonian term accounting for a strong dependence of the torsional barrier height on the normal vibrational coordinate q 2. The value of the barrier height derivative ? is estimated to be 127 ± 10 cm-1. Also detected and assigned were 'hot' difference transitions belonging to the (ν 4 + ν 11)-2ν 4 band, yielding information on the upper state ν 4 + ν 11. It is believed that transitions from 3ν 4 to 2ν 4 + ν 11 are also detectable in the investigated region.
Properties of axial or torsional free-vibration frequency of rods
NASA Technical Reports Server (NTRS)
Segenreich, S. A.; Rizzi, P.
1975-01-01
The investigation reported shows that for a clamped rod with an odd number of degrees of freedom, the middle frequency is independent of any nonuniformity in the area distribution. The frequencies in the lower half of the spectrum of a rod are found to be conjugate to the frequencies in the upper half. In the case of a design modification which leaves a certain frequency in the lower half spectrum unchanged, the conjugate frequency in the upper half will also remain unchanged.
Sebulke, A.
1987-01-01
The rotational irregularities of an engine, which are primarily caused by the forces generated by the combustion gases during the periodic combustion process, are transmitted to the driveline and there lead to vibration and noise. Since 1985, BMW has been using its two-mass flywheel on certain gasoline and diesel engines. This is a mechanical low-pass filter, which largely isolates rotational irregularities and vibration from the complete driveline and therefore reduces the noise level inside the vehicle. Running speeds significantly exceeding 5000 rpm however cause a severe increase in wear on the internal components of the torsional vibration damper, as a consequence of the higher centrifugal forces.
NASA Astrophysics Data System (ADS)
Askari, H.; Esmailzadeh, E.; Barari, A.
2015-09-01
A novel procedure for the nonlinear vibration analysis of curved beam is presented. The Non-Uniform Rational B-Spline (NURBS) is combined with the Euler-Bernoulli beam theory to define the curvature of the structure. The governing equation of motion and the general frequency formula, using the NURBS variables, is applicable for any type of curvatures, is developed. The Galerkin procedure is implemented to obtain the nonlinear ordinary differential equation of curved system and the multiple time scales method is utilized to find the corresponding frequency responses. As a case study, the nonlinear vibration of carbon nanotubes with different shapes of curvature is investigated. The effect of oscillation amplitude and the waviness on the natural frequency of the curved nanotube is evaluated and the primary resonance case of system with respect to the variations of different parameters is discussed. For the sake of comparison of the results obtained with those from the molecular dynamic simulation, the natural frequencies evaluated from the proposed approach are compared with those reported in literature for few types of carbon nanotube simulation.
NASA Astrophysics Data System (ADS)
Pal Singh Chhabra, Param; Ganguli, Ranjan
2010-01-01
A new two-noded, twelve degree of freedom finite element is developed for rotating blades. The shape functions are derived from the exact solutions of the governing static homogenous differential equations for the rotating blades. Such an approach leads to superconvergent elements. These differential equations include out-of-plane bending, in-plane bending, axial deformation, and torsion. The axial and torsion equations yield exact solutions and the flap and lag equations are solved by assuming a constant centrifugal force within the element. Differing from the conventional polynomial shape functions, the new shape functions account for the centrifugal stiffening effect as they depend upon the rotation speed, material properties, and the element position along the length of the blade. The finite element formulation is derived from the energy expressions using the Hamilton's principle. A convergence study for the natural frequencies is performed using the new shape functions and the polynomial shape functions for a coupled and an uncoupled blade. It is observed that the new shape functions lead to much more rapid convergence than the conventional polynomial shape functions for the first few modes at higher rotation speeds, where the effect of centrifugal stiffening is higher. The basis functions can also be used for finite element analysis of rotating rods and beams, and for energy methods.
NASA Astrophysics Data System (ADS)
Lattanzi, F.; di Lauro, C.; Horneman, V.-M.
The ν6 + ν12 and ν9 + ν12(E) vibrational combination bands of disilane (Si2H6) have been measured at high resolution and analysed. A few K-branches of the hot band associated with ν9 + ν12(E), originated from the torsional state v4 = 1, have also been observed and analysed. These observations give information on the effects of the v12 = 1 vibrational state, not directly accessible in the infrared, on the molecular internal rotation. From the vibrational frequencies of ν9 + ν12(E) and its related hot band, determined in this work, and those of ν9 and its hot band determined previously, we can determine that the torsional barrier height changes by -19.25 cm-1 if the ν12 mode is excited by one quantum. This causes the torsional splitting to increase by about 0.0038 cm-1. The observed torsional splitting in the ν6 + ν12 vibrational state is larger than in the ground vibrational state by 0.0024 cm-1, with a 0.0033 cm-1 change caused by the lowering of the barrier height and a -0.0009 cm-1 change caused by the head-tail and torsional Coriolis mechanisms. The torsional splitting observed in the ν9 + ν12(E) state, -0.0043 cm-1, is inverted with respect to the ground vibrational state (0.0150 cm-1 in the lowest torsional state), showing that this state is closer to the E2s than to the E1d vibrational symmetry description. The analysis of perturbations observed in the rotation-torsion structure of ν9 + ν12(E) yields information on the vibrational states ν2 + ν4 and ν4 + ν11, and on the E3d torsional component of 4ν4 + ν12.
Torsional vibrations and dynamic loads in a basic planetary gear system
NASA Technical Reports Server (NTRS)
August, R.; Kasuba, R.
1986-01-01
An iterative method has been developed for analyzing dynamic loads in a light weight basic planetary gear system. The effects of fixed, semi-floating, and fully-floating sun gear conditions have been emphasized. The load dependent variable gear mesh stiffness were incorporated into a practical torsional dynamic model of a planetary gear system. The dynamic model consists of input and output units, shafts, and a planetary train. In this model, the sun gear has three degrees of freedom; two transverse and one rotational. The planets, ring gear, and the input and output units have one degree of freedom, (rotation) thus giving a total of nine degrees of freedoms for the basic system. The ring gear has a continuous radial support. The results indicate that the fixed sun gear arrangement with accurate or errorless gearing offers in general better performance than the floating sun gear system.
Analytical Study of Vertical and Torsional Free Vibration of Cable Supported Bridge Decks
NASA Astrophysics Data System (ADS)
Gorman, Daniel J.
The superposition method is employed to obtain an analytical type solution for the free vibration of cable supported bridge decks. Each pair of vertical elastic cables is considered to impart a vertical force to the deck by means of a rigid cross-member passing transversely beneath it. Rigid knife-edge support encountered at bridge towers is handled as well. In this introductory study the deck is treated as a thin isotropic plate. Any number of support cable pairs, of any stiffness, may be handled. Inter cross-member distances are referred to as spans. Free vibration eigenvalues and mode shapes are presented for three and four span illustrative cases.
NASA Astrophysics Data System (ADS)
Ompusunggu, Agusmian Partogi; Papy, Jean-Michel; Vandenplas, Steve; Sas, Paul; Van Brussel, Hendrik
2013-02-01
Wet friction clutches play a critical role in vehicles equipped with automatic transmissions, power shift transmissions and limited slip differentials. An unexpected failure occurring in these components can therefore lead to an unexpected total breakdown of the vehicle. This undesirable situation can put human safety at risk, possibly cause long-term vehicle down times, and result in high maintenance costs. In order to minimize the negative impacts caused by the unexpected breakdown, an optimal maintenance scheme driven by accurate condition monitoring and prognostics therefore needs to be developed and implemented for wet friction clutches. In this paper, the development of a condition monitoring system that can serve as a basis for health prognostics of wet friction clutches with a focus in heavy duty vehicle applications is presented. The developed method is based on monitoring the dominant modal parameters extracted from the torsional vibration response occurring in the post-lockup phase, i.e. just after the clutch is fully engaged. These modal parameters, namely the damped torsional natural frequency fd and the decay factor σ, are computed based on the pre-filtered Hankel Total Least Squares (HTLS) method which has an excellent performance in estimating the parameters of transient signals with a relatively short duration. In order to experimentally validate the proposed monitoring method, accelerated life tests were carried out on five different paper-based wet friction clutches using a fully instrumented SAE#2 test setup. The dominant modal parameters extracted from the post-lockup velocity signals are then plotted in function of the service life (duty cycle) of the tested clutches. All the plots exhibit distinct trends that can be associated with the progression of the clutch degradation. Therefore, the proposed quantities can be seen as relevant features that may enable us to monitor and assess the condition of wet friction clutches. Since velocity sensor
Characteristic of torsional vibration of mill main drive excited by electromechanical coupling
NASA Astrophysics Data System (ADS)
Zhang, Yifang; Yan, Xiaoqiang; Lin, Qihui
2016-01-01
In the study of electromechanical coupling vibration of mill main drive system, the influence of electrical system on the mechanical transmission is considered generally, however the research for the mechanism of electromechanical interaction is lacked. In order to research the electromechanical coupling resonance of main drive system on the F3 mill in a plant, the cycloconverter and synchronous motor are modeled and simulated by the MTLAB/SIMULINK firstly, simulation result show that the current harmonic of the cycloconverter can lead to the pulsating torque of motor output. Then the natural characteristics of the mechanical drive system are calculated by ANSYS, the result show that the modal frequency contains the component which is close to the coupling vibration frequency of 42Hz. According to the simulation result of the mechanical and electrical system, the closed loop feedback model including the two systems are built, and the mechanism analysis of electromechanical coupling presents that there is the interaction between the current harmonic of electrical system and the speed of the mechanical drive system. At last, by building and computing the equivalent nonlinear dynamics model of the mechanical drive system, the dynamic characteristics of system changing with the stiffness, damping coefficient and the electromagnetic torque are obtained. Such electromechanical interaction process is suggested to consider in research of mill vibration, which can induce strong coupling vibration behavior in the rolling mill drive system.
The Behavior of Thin-will Monocoque Cylinders Under Torsional Vibration
NASA Technical Reports Server (NTRS)
Pekelsma, Robert E
1937-01-01
Curves of forced frequency against amplitude are presented for the conditions where the forced frequency is both increased and decreased into the resonant range. On the basis of these curves it is shown that the practical resonance frequency is the point where wrinkling first occurs and that the resonance frequency will be subject to considerable travel once permanent wrinkles appear in the vibrating shell. The decreasing mode of striking resonance is found to be by far the most destructive condition.
NASA Astrophysics Data System (ADS)
Salehi-Khojin, Amin; Jalili, Nader; Nima Mahmoodi, S.
2009-05-01
Piezoresponse force microscopy (PFM) has evolved into a useful tool for measurement of local properties of piezoelectric materials with great potential in applications such as data storage, ferroelectric lithography and nonvolatile memories. In order to utilize PFM for low dimensional materials characterization, a comprehensive analytical modeling based on the coupled motion of PFM in all three directions is proposed. In this respect, the mechanical properties of sample are divided into viscoelastic and piezoelectric parts. The viscoelastic part is modeled as a spring and damper in the longitudinal, transversal and lateral directions, while the piezoelectric part is replaced with resistive forces acting at the end of microcantilever. It is shown that there is a geometrical coupling between flexural-longitudinal and lateral-torsional vibrations of microcantilever used in PFM. Moreover, assuming a general friction between tip and sample, additional coupling effect is also taken into account. Through an energy-based approach, it is seen that the PFM system can be governed by a set of coupled partial differential equations along with nonhomogeneous and coupled boundary conditions. A general formulation is then derived for the mode shape, frequency response, and state-space representation of system. Numerical simulations indicate that mode shapes, natural frequencies and time responses of microcantilever beam are heavily dependent on the viscoelastic and piezoelectric properties of the samples. Moreover, the results demonstrate that utilizing only transversal vibration is not a valid strategy for quantifying mechanical properties of materials with arbitrary crystallographic orientation. Hence, the proposed model with the built-in coupling effects can be a key development for acquiring precise measurements.
NASA Astrophysics Data System (ADS)
Malaeke, Hasan; Moeenfard, Hamid
2016-03-01
The objective of this paper is to study large amplitude flexural-extensional free vibration of non-uniform cantilever beams carrying a both transversely and axially eccentric tip mass. The effects of variable axial force is also taken into account. Hamilton's principle is utilized to obtain the partial differential equations governing the nonlinear vibration of the system as well as the corresponding boundary conditions. A numerical finite difference scheme is proposed to find the natural frequencies and mode shapes of the system which is validated specifically for a beam with linearly varying cross section. Using a single mode approximation in conjunction with the Lagrange method, the governing equations are reduced to a set of two nonlinear ordinary differential equations in terms of end displacement components of the beam which are coupled due to the presence of the transverse eccentricity. These temporal coupled equations are then solved analytically using the multiple time scales perturbation technique. The obtained analytical results are compared with the numerical ones and excellent agreement is observed. The qualitative and quantitative knowledge resulting from this research is expected to enable the study of the effects of eccentric tip mass and non-uniformity on the large amplitude flexural-extensional vibration of beams for improved dynamic performance.
NASA Astrophysics Data System (ADS)
Mukhopadhyay, Indra
2016-05-01
In this work the far infrared (FIR) absorption spectrum has been measured for the asymmetrically mono deuterated Methanol (CH2DOH) species in the wavenumber range of 15-1200 cm-1 better accuracy and signal/noise ratio than known before. Assignments have been made for b-type transitions in the lowest lying torsional vibrational state trans-(e0) for a wide range of rotational angular momentum. The assignments have been rigorously confirmed by the residual loop defect methods. The rR-branch wavenumbers are analyzed by the usual state dependent expansion parameters and the Q-Branch origins. These origins have been used to calculate the torsional and torsional-rotation interaction contributions. These findings are in good agreement with predicted from the Hamiltonian model described in recent publications. A large number of assignments have also been made in the millimeter wave spectrum recorded earlier and thereby evaluated the asymmetry splitting parameters for 4 different axial rotational angular momentum quantum numbers. The analysis and interpretation of the spectra are reported. New assignments for about 260 transitions are included the text and a catalog of about 1500 transitions belonging to the e0 species is prepared (Appendix 1) and is made available through the open server in "Research Gate" and will be freely available to others.
NASA Astrophysics Data System (ADS)
Joshi, A.; Suryanarayan, S.
1989-03-01
The problem of free vibration of beams having different end conditions and subjected to static initial loads has been studied with the aim of arriving at good closed-form analytical solutions. Elementary beam theory is used as a starting point to obtain the transverse vibration frequencies for various cases of classical homogeneous end conditions and for various values of the static axial load and end moment. These results indicate that it is possible to identify simple algebraic expressions which accurately represent the solution for various boundary conditions. It is also found that reasonably accurate estimates of the predominantly flexural frequency of coupled flexural-torsional vibration can be obtained from the uncoupled flexural vibration frequency of beam-columns. This is achieved by defining an effective axial load parameter, which is a combination of the axial load, the end moment and the slenderness parameter. Finally, the study also brings out that the various expressions, corresponding to different end conditions, can be combined together into a single expression for the predominantly flexural frequency. This expression is common for the boundary conditions considered here and use is made of various normalizing factors which depend on the boundary conditions, and are obtainable from the corresponding free vibration and stability analyses of beam-columns.
Iwasa, Takeshi; Takenaka, Masato; Taketsugu, Tetsuya
2016-03-28
A theoretical method to compute infrared absorption spectra when a molecule is interacting with an arbitrary nonuniform electric field such as near-fields is developed and numerically applied to simple model systems. The method is based on the multipolar Hamiltonian where the light-matter interaction is described by a spatial integral of the inner product of the molecular polarization and applied electric field. The computation scheme is developed under the harmonic approximation for the molecular vibrations and the framework of modern electronic structure calculations such as the density functional theory. Infrared reflection absorption and near-field infrared absorption are considered as model systems. The obtained IR spectra successfully reflect the spatial structure of the applied electric field and corresponding vibrational modes, demonstrating applicability of the present method to analyze modern nanovibrational spectroscopy using near-fields. The present method can use arbitral electric fields and thus can integrate two fields such as computational chemistry and electromagnetics. PMID:27036436
NASA Astrophysics Data System (ADS)
Prashanth, J.; Reddy, B. Venkatram; Rao, G. Ramana
2016-08-01
The Fourier Transform Infrared (FTIR) and Fourier Transform Raman (FT-Raman) spectra of 2,2‧-bipyridine (2BPE); 4,4‧-bipyridine (4BPE); and 2,4‧-bipyridine (24BPE) were measured in the range 4000-450 cm-1 and 4000-50 cm-1, respectively. Torsional potentials were evaluated at various angles of rotation around the C-C inter-ring bond for the three molecules in order to arrive at the molecular conformation of lowest energy. This conformation was further optimized to get ground state geometry. Vibrational frequencies along with infrared and Raman intensities were computed. In the above calculations, DFT employing B3LYP functional with 6311++G(d,p) basis set was used. The rms error between observed and calculated frequencies was 10.0, 10.9 and 10.2 cm-1 for 2BPE, 4BPE and 24BPE, respectively. A 54-parameter modified valence force field was derived by solving inverse vibrational problem using Wilson's GF matrix method. The force constants were refined using 117 experimental frequencies of the three molecules in overlay least-squares technique. The average error between observed and computed frequencies was 12.44 cm-1. PED and eigen vectors calculated in the process were used to make unambiguous vibrational assignments of all the fundamental vibrations. The values of dipole moment, polarizability and hyperpolarizability were computed to determine the NLO behaviour of these molecules. The HOMO and LUMO energies, thermodynamic parameters and molecular electrostatic surface potentials (MESP) were also evaluated. Stability of the molecules arising from hyper conjugative interactions, charge delocalization have been analyzed using natural bond orbital (NBO) analysis.
NASA Astrophysics Data System (ADS)
Zhun Yeap, Khang; Müller, Steffen
2016-02-01
A model-based approach for characterising the interaction of individual-wheel drives with traction is contributed in this article. The primary aim is to investigate the influence of traction on torsional vibration behaviour in the drive train. The essence of this approach lies in reformulating the nonlinear traction behaviour into its differential form, which enables an analytical description of this interaction in its linear parameter-varying model equivalence. Analytical statements on the vibration behaviour for different driving scenarios are inferred from this model and validated with measurement samples from a high-performance electric road vehicle. Subsequent influences of traction on the performance of active damping of torsional vibrations are derived from this model.
NASA Astrophysics Data System (ADS)
Gráf, Lukáš; Čížek, Martin
2014-09-01
A two dimensional model for the electron interaction with molecular vibrations in molecular junctions is proposed. Alternatively the model can be applied to tunneling through a cylindrical nano-structure. The transmission function is calculated accurately numerically. The exact results are then compared with various approximations: (1) completely frozen vibrations for very light molecule, (2) Chase approximation for very heavy molecule, and (3) discrete-state-in-continuum model in resonant regime. The validity of these approximations is discussed in terms of the characteristic time-scales and coupling strengths. The excitation of the vibrational degree of freedom and the emergence of prominent threshold structures in the strong coupling regime are discussed in more details.
Dubhashi, Siddharth Pramod; Khadav, Bharat
2016-01-01
Torsion of the vermiform appendix is a rare condition detectable only at operation. It can be primary or secondary. This is a case report of 52-year-old female with 180° anti-clockwise rotation of the appendix. Torsion can further leads to strangulation and infarction of the organ. Appendicular torsion could be included in the differential diagnosis of pain in right iliac fossa. PMID:27013858
NASA Astrophysics Data System (ADS)
Mukhopadhyay, Indra
2016-05-01
In this report the spectroscopic results for far infrared Fourier transform spectrum corresponding to the b-type transitions within the lowest lying trans-substrate (e0) have been presented. The calculated matrix elements connecting various K-levels suggest that ΔK = 1 transitions within the trans- subs-state should be quite strong but the transitions between the trans state to the gauche states would quite week (practically non-existent). This was also concluded by previous studies using microwave and millimeter wave regions (Pearson et al., 1982; Millar, 1995). The assignments were confirmed by direct observations at the spectrum and the agreement between the observed and calculated spectrum using precise energy levels reported by Pearson et al. (1982). All the strong RR and some RQ branch lines starting from K = 10 ← 9 through K = 24 ← 23 have been identified. State dependent expansion parameters for all the 15 sub-bands have been presented. These parameters can reproduce the experimental wave numbers within experimental uncertainty. An atlas for about 450 transition lines corresponding to transitions within the e0 torsional-vibrational species has been prepared. To our knowledge this is the first time the high resolution far infra-red spectral region study for ethanol have been performed.
NASA Astrophysics Data System (ADS)
Endres, C. P.; Drouin, B. J.; Pearson, J. C.; Müller, H. S. P.; Lewen, F.; Schlemmer, S.; Giesen, T. F.
2009-09-01
Dimethyl ether (CH_3OCH_3) is one of the largest organic molecules detected in the interstellar medium. As an asymmetric top molecule with two methyl groups which undergo large amplitude motions and a dipole moment of μ=1.3 D, it conveys a dense spectrum throughout the terahertz region and contributes to the spectral line confusion in astronomical observations at these frequencies. In this paper, we present rotational spectra of dimethyl ether in its ground vibrational states, which have been measured in the laboratory and analyzed covering frequencies up to 2.1 THz. The analysis is based on an effective Hamiltonian for a symmetric two-top rotor and includes experimental data published so far. Frequency predictions are presented up to 2.5 THz for astronomical applications with accuracies better than 1 MHz. Table A.1 is only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/504/635
Femtosecond torsional relaxation
NASA Astrophysics Data System (ADS)
Clark, J.; Nelson, T.; Tretiak, S.; Cirmi, G.; Lanzani, G.
2012-03-01
Molecular conformational reorganization following photon absorption is a fundamental process driving reactions such as the cis-trans isomerization at the heart of the primary step of vision and can be exploited for switching in artificial systems using photochromics. In general, conformational change occurs on a timescale defined by the energy of the main vibrational mode and the rate of energy dissipation. Typically, for a conformational change such as a twist around the backbone of a conjugated molecule, this occurs on the tens of picoseconds timescale. However, here we demonstrate experimentally that in certain circumstances the molecule, in this case an oligofluorene, can change conformation over two orders of magnitude faster (that is sub-100fs) in a manner analogous to inertial solvent reorganization demonstrated in the 1990s. Theoretical simulations demonstrate that non-adiabatic transitions during internal conversion can efficiently convert electronic potential energy into torsional kinetic energy, providing the `kick' that prompts sub-100fs torsional reorganization.
Bigoni, D.; Dal Corso, F.; Misseroni, D.; Bosi, F.
2014-01-01
One edge of an elastic rod is inserted into a friction-less and fitting socket head, whereas the other edge is subjected to a torque, generating a uniform twisting moment. It is theoretically shown and experimentally proved that, although perfectly smooth, the constraint realizes an expulsive axial force on the elastic rod, which amount is independent of the shape of the socket head. The axial force explains why screwdrivers at high torque have the tendency to disengage from screw heads and demonstrates torsional locomotion along a perfectly smooth channel. This new type of locomotion finds direct evidence in the realization of a ‘torsional gun’, capable of transforming torque into propulsive force. PMID:25383038
Non-Uniform Thickness Electroactive Device
NASA Technical Reports Server (NTRS)
Su, Ji (Inventor); Harrison, Joycelyn S. (Inventor)
2006-01-01
An electroactive device comprises at least two layers of material, wherein at least one layer is an electroactive material and wherein at least one layer is of non-uniform thickness. The device can be produced in various sizes, ranging from large structural actuators to microscale or nanoscale devices. The applied voltage to the device in combination with the non-uniform thickness of at least one of the layers (electroactive and/or non-electroactive) controls the contour of the actuated device. The effective electric field is a mathematical function of the local layer thickness. Therefore, the local strain and the local bending/ torsion curvature are also a mathematical function of the local thickness. Hence the thinnest portion of the actuator offers the largest bending and/or torsion response. Tailoring of the layer thicknesses can enable complex motions to be achieved.
Application of a boundary element method to the study of dynamical torsion of beams
NASA Technical Reports Server (NTRS)
Czekajski, C.; Laroze, S.; Gay, D.
1982-01-01
During dynamic torsion of beam elements, consideration of nonuniform warping effects involves a more general technical formulation then that of Saint-Venant. Nonclassical torsion constants appear in addition to the well known torsional rigidity. The adaptation of the boundary integral element method to the calculation of these constants for general section shapes is described. The suitability of the formulation is investigated with some examples of thick as well as thin walled cross sections.
Variable stiffness torsion springs
NASA Technical Reports Server (NTRS)
Alhorn, Dean C. (Inventor); Polites, Michael E. (Inventor)
1994-01-01
In a torsion spring the spring action is a result of the relationships between the torque applied in twisting the spring, the angle through which the torsion spring twists, and the modulus of elasticity of the spring material in shear. Torsion springs employed industrially have been strips, rods, or bars, generally termed shafts, capabable of being flexed by twisting their axes. They rely on the variations in shearing forces to furnish an internal restoring torque. In the torsion springs herein the restoring torque is external and therefore independent of the shearing modulus of elasticity of the torsion spring shaft. Also provided herein is a variable stiffness torsion spring. This torsion spring can be so adjusted as to have a given spring constant. Such variable stiffness torsion springs are extremely useful in gimballed payloads such as sensors, telescopes, and electronic devices on such platforms as a space shuttle or a space station.
Variable stiffness torsion springs
NASA Technical Reports Server (NTRS)
Alhorn, Dean C. (Inventor); Polites, Michael E. (Inventor)
1995-01-01
In a torsion spring the spring action is a result of the relationships between the torque applied in twisting the spring, the angle through which the torsion spring twists, and the modulus of elasticity of the spring material in shear. Torsion springs employed industrially have been strips, rods, or bars, generally termed shafts, capabable of being flexed by twisting their axes. They rely on the variations in shearing forces to furnish an internal restoring torque. In the torsion springs herein the restoring torque is external and therefore independent of the shearing modulus of elasticity of the torsion spring shaft. Also provided herein is a variable stiffness torsion spring. This torsion spring can be so adjusted as to have a given spring constant. Such variable stiffness torsion springs are extremely useful in gimballed payloads such as sensors, telescopes, and electronic devices on such platforms as a space shuttle or a space station.
Daszkiewicz, Marek
2014-11-11
Crystal structure of the ortho-nitroanilinium chloride, (HoNA)Cl, was re-determined by means of X-ray single crystal diffraction. Hydrogen atoms of the ammonio form intra- and intermolecular hydrogen bonds which are arranged in chain and ring patterns. The patterns are described by the mathematical relations of the elementary graph-set descriptors. Since the interactions have a weak nature, the interpretation of the vibrational spectra was carried out with the help of theoretical calculations of the spectra for the HoNA+ ion. In order to properly assign experimental bands, theoretical spectra were calculated at the B3LYP/6-31G(d,p) level of theory for the geometry of global minimum of HoNA+ ion as a reference and for the other conformations, including in-crystal geometry of the ion, changing the relative position of the ammonio and nitro groups. Overall, the 89 spectra were analyzed as a two-dimensional dependence of each of 45 normal modes of the HoNA+ ion on two dihedral angles, dih(HNCC) and dih(ONCC). Additionally, calculations were done for the in-crystal conformation of the (HoNA)Cl3(2-) anion. Great increase of frequency is observed for the ν7 (641 cm(-1)), where the H1C atom is involved in, because the intramolecular N-H1C⋯O hydrogen bond weakens upon rotation of the NH3+ group. PED analysis shows that also the modes of vibrations changes upon rotation. The mode of vibrations for the (HoNA)Cl3(2-) anion differs from the HoNA+ ion, especially for the ν(N-H) vibrations. Besides, when three chloride anions where included in the calculations, only then the experimental spectra were well reproduced. PMID:24971718
NASA Astrophysics Data System (ADS)
Lattanzi, F.; Lauro, C. di; Vander Auwera, J.
2008-04-01
The room temperature spectrum of ethane in the region of the ν6 and ν8 fundamentals, between 1330 and 1610 cm -1, has been re-investigated at a resolution of 0.002 cm -1. It is shown that the complex spectral structure with numerous strong local perturbations, which had hindered a global analysis of this region until now, is caused by a network of l-type resonances acting within the Fermi (or torsional-Coriolis) coupled system ν8, ν4 + ν12. The x, y-Coriolis interaction between ν6 and ν8 and vibration-rotation interactions between ν6 and 2 ν4 + ν9 also generate relevant effects on the spectrum. With an appropriate Hamiltonian model accounting for all these effects, we could fit 1814 upper state level energies belonging to ν6, ν8 and ν4 + ν12 with an overall RMS deviation better than 3.8 × 10 -3 cm -1. The determined values of the intrinsic torsional splittings in the different vibrational states are in agreement with the theoretical expectations. The intrinsic torsional splitting almost vanishes in ν8, as in digermane and disilane; it is slightly larger in ν4 + ν12 than in ν4, due to the decrease of the torsional barrier height with the excitation of ν12. For the 2 ν4 + ν9 state, the determined values of the vibrational origin and torsional splittings are in good agreement with the large increase of the torsional barrier height expected with the excitation of the ν9 mode. Several hot transitions originating from the v 4 = 1 torsional state have been observed. An analysis of 294 line positions belonging to the ( ν4 + ν8) - ν4 hot band has been performed, leading to a fit with a RMS deviation of 5.1 × 10 -3 cm -1. It is shown that a complex network of l-type resonances is also active in the ν4 + ν8,2 ν4 + ν12 system.
The Torsional Fundamental Band of Methylformate
NASA Astrophysics Data System (ADS)
Tudorie, M.; Ilyushin, V.; Vander Auwera, J.; Pirali, O.; Roy, P.; Huet, T. R.
2011-06-01
Methylformate (HCOOCH_3) is one of the most important molecules in astrophysics, first observed in 1975. The rotational structure of its ground and first excited torsional states are well known from millimeter wave measurements. However, some of the torsional parameters are still not precisely determined because information on the torsional vibrational frequency v_t = 1-0 is missing. To overcome that problem, the far infrared spectrum of HCOOCH_3 was recorded with a 150 m optical path in a White cell and a Bruker IFS 125 HR Fourier transform spectrometer at the AILES beamline of the synchrotron SOLEIL facility. The analysis of the very weak fundamental torsional band v_t = 1-0 observed around 130 Cm-1 was carried out. It led to the first precise determination of the torsional barrier height and the dipole moment induced by the torsional motion. This work is partly supported by the "Programme National de Physico-Chimie du Milieu Interstellaire" (PCMI-CNRS) and by the contract ANR-BLAN-08-0054. R.D. Brown, J.G. Crofts, P.D. Godfrey, F.F. Gardner, B.J. Robinson, J.B. Whiteoak, Astrophys. J. 197 (1975) L29-L31. See V. Ilyushin, A. Kryvda, E. Alekseev, J. Mol. Spectrosc. 255 (2009) 32-38, and references therein.
Vibration characteristics of ultrasonic complex vibration for hole machining
NASA Astrophysics Data System (ADS)
Asami, Takuya; Miura, Hikaru
2012-05-01
Complex vibration sources that use diagonal slits as a longitudinal-torsional vibration converter have been applied to ultrasonic motors, ultrasonic rock drilling, and ultrasonic welding. However, there are few examples of the application of these sources to ultrasonic machining in combination with an abrasive. Accordingly, a new method has been developed for machining of holes in brittle materials by using the ultrasonic longitudinal and torsional vibration of a hollow-type stepped horn with a diagonal slit vibration converter. In this paper, we compared vibration of a uniform rod and a hollow-type stepped horn, both with diagonal slits, when the conditions of the diagonal slits are constant.
NASA Astrophysics Data System (ADS)
Mukhopadhyay, Indra
2016-07-01
This paper reports the analysis of the high resolution (0.0019 cm-1) Fourier transform infrared (FTIR) spectrum for asymmetrically deuterated methanol CHD2OH (methanol-D2) at a low temperature for the CD2 wagging band for the lowest lying trans-species (e0). In spite of the complexity and perturbation in the spectra, assignments were possible for the CD2 wagging band for a maximum K value of 10. In total, about 500 spectral lines have been assigned. Analysis of the spectral lines has been performed in terms of state dependent molecular parameters, Q-branch origins and asymmetry splitting. Assignments have been thoroughly confirmed using combination relations (see text). The catalogue of the assigned transition wavenumbers will help identification and prediction of far infrared (FIR) optically pumped CO2 lasers. The absorption lines close to the several 10R and 10P CO2 laser lines have also been identified. These should help experimentalists to optimize the power of the emission FIR laser lines and to predict new lines and should prove valuable as a laboratory support for interstellar detection in "Radio Astronomy". To our knowledge this is the first time such vibrational infrared (IR) high resolution study in CHD2OH is being performed.
Coupling and degenerating modes in longitudinal-torsional step horns.
Harkness, Patrick; Lucas, Margaret; Cardoni, Andrea
2012-12-01
Longitudinal-torsional vibration is used and proposed for a variety of ultrasonic applications including motors, welding, and rock-cutting. To obtain this behavior in an ultrasonic step horn one can either, (i) couple the longitudinal and torsional modes of the horn by incorporating a ring of diagonal slits in the thick base section or, (ii) place helical flutes in the thin stem section to degenerate the longitudinal mode into a modified behavior with a longitudinal-torsional motion. This paper compares the efficacy of these two design approaches using both numerical and experimental techniques. PMID:22770885
A non-uniform warping theory for beams
NASA Astrophysics Data System (ADS)
El Fatmi, Rached
2007-08-01
This Note proposes a non-uniform warping beam theory including the effects of torsion and shear forces. Based on a displacement model using three warping parameters associated to three St Venant warping functions corresponding to torsion and shear forces, this theory is free from the classical assumptions on the warpings or on the shears, and is valid for any kind of homogeneous elastic and isotropic cross-section. The result on the structural behavior of the beam specifies the effect of the non-symmetry of the cross-section, and the closed form results obtained for the stresses show the contribution of each internal force. Comparison with St Venant beam theory highlights the additional effects due to the non-uniformity of the warping. To cite this article: R. El Fatmi, C. R. Mecanique 335 (2007).
Testicular Torsion (For Parents)
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Effective Torsion and Spring Constants in a Hybrid Translational-Rotational Oscillator
ERIC Educational Resources Information Center
Nakhoda, Zein; Taylor, Ken
2011-01-01
A torsion oscillator is a vibrating system that experiences a restoring torque given by [tau] = -[kappa][theta] when it experiences a rotational displacement [theta] from its equilibrium position. The torsion constant [kappa] (kappa) is analogous to the spring constant "k" for the traditional translational oscillator (for which the restoring force…
Torsional actuation with extension-torsion composite coupling and a magnetostrictive actuator
NASA Astrophysics Data System (ADS)
Bothwell, Christopher M.; Chandra, Ramesh; Chopra, Inderjit
1995-04-01
An analytical-experimental study of using magnetostrictive actuators in conjunction with an extension-torsion coupled composite tube to actuate a rotor blade trailing-edge flap to actively control helicopter vibration is presented. Thin walled beam analysis based on Vlasov theory was used to predict the induced twist and extension in a composite tube with magnetostrictive actuation. The study achieved good correlation between theory and experiment. The Kevlar-epoxy systems showed good correlation between measured and predicted twist values.
NASA Technical Reports Server (NTRS)
1984-01-01
The methods used to determine the lower natural frequencies and their corresponding mode shapes of the NASA-LSS Astromast (Unmodified Test Structure), and the mass integrals associated with the mode shapes are illustrated. The test structure is modeled as a cantilever beam with 91 lumped masses and without the tip mass on the free end of the bram. This uncouples the torsion and bending modes and allows for them to be determined separately. The frequency range was limited to an upper bound of 100 rad/sec (15.92 Hz.). In this range from 0.-100. rad/sec, three bending frequencies and one torsion frequency was found.
Radionic nonuniform black strings
NASA Astrophysics Data System (ADS)
Tamaki, Takashi; Kanno, Sugumi; Soda, Jiro
2004-01-01
Nonuniform black strings in the two-brane system are investigated using the effective action approach. It is shown that the radion acts as a nontrivial hair of the black strings. From the brane point of view, the black string appears as the deformed dilatonic black hole which becomes a dilatonic black hole in the single brane limit and reduces to the Reissner-Nordström black hole in the close limit of two-branes. The stability of solutions is demonstrated using catastrophe theory. From the bulk point of view, the black strings are proved to be nonuniform. Nevertheless, the zeroth law of black hole thermodynamics still holds.
Torsion and transverse bending of cantilever plates
NASA Technical Reports Server (NTRS)
Reissner, Eric; Stein, Manuel
1951-01-01
The problem of combined bending and torsion of cantilever plates of variable thickness, such as might be considered for solid thin high-speed airplane or missile wings, is considered in this paper. The deflections of the plate are assumed to vary linearly across the chord; minimization of the potential energy by means of the calculus of variations then leads to two ordinary linear differential equations for the bending deflections and the twist of the plate. Because the cantilever is analyzed as a plate rather than as a beam, the effect of constraint against axial warping in torsion is inherently included. The application of this method to specific problems involving static deflection, vibration, and buckling of cantilever plates is presented. In the static-deflection problems, taper and sweep are considered.
NASA Astrophysics Data System (ADS)
Lattanzi, F.; di Lauro, C.; Horneman, V.-M.
The (ν4 + ν6) - ν4, (ν4 + ν8) - ν4 and (ν4 + ν9) - ν4 hot infrared systems of disilane (Si2H6) have been analysed at high resolution, and the values of the relative vibration-rotation-torsion parameters have been determined. The torsional splitting is about 0.500 cm-1 in the ν4 and ν4 + ν6 states, and decreases strongly in the vibrationally degenerate upper states ν4 + ν8 (about 0.0272 cm-1 on average) and ν4 + ν9 (about 0.3019 cm-1), consistent with theoretical predictions. Comparison between the vibrational wavenumbers of cold transitions and hot transitions originating in the excited torsional state v4 = 1 allows one to determine the change of the fundamental torsional frequency ν4 caused by the excitation of small amplitude vibrations. A remarkable increase in ν4 of about 8.599 cm-1 is found in the v9 = 1 state (E1d SiH3-rocking mode, asymmetric to inversion in the staggered geometry), and this corresponds to an increase in the torsional barrier height in this excited fundamental vibrational state by about 48.77 cm-1. The mechanism responsible for the decrease of the torsional splittings in the degenerate vibrational states is briefly outlined by means of second-order perturbation theory, using torsion-hindered vibrational basis functions of E1d and E2d symmetries for the degenerate modes.
Hougen, J.T.
1993-12-31
Spectroscopy was used to study the vibrational quasi-continuum arising from internal rotation of the methyl group in acetaldehyde. We now understand the torsion-rotation levels from all 3 torsional states below the top of the torsional barrier. Investigations of four ordinary vibrational states in acetaldehyde are in progress.
NASA Technical Reports Server (NTRS)
Ihrke, Chris A. (Inventor); Parsons, Adam H. (Inventor); Mehling, Joshua S. (Inventor); Griffith, Bryan Kristian (Inventor)
2012-01-01
A torsion spring comprises an inner mounting segment. An outer mounting segment is located concentrically around the inner mounting segment. A plurality of splines extends from the inner mounting segment to the outer mounting segment. At least a portion of each spline extends generally annularly around the inner mounting segment.
Numerical modeling of pendulum dampers in torsional systems
Johnston, P.R.; Shusto, L.M.
1986-01-01
Centrifugal pendulum-design dampers are utilized in torsional systems to reduce the vibration amplitude at certain objectionable torsional speeds. The damper is tuned by proper design of its mass, dimensions, and position on a carrier disk, which is rigidly attached to the torsional system. The effects of the pendulum damper on the response of the torsional system may be included by modifying the structural model to include a separate damper element representing each order of the pendulum damper. The stiffness and mass matrices for a damper element are dependent upon the order of vibration being dampened, the mass, and the geometry of the damper. A general form of the mass and stiffness equations for a simple centrifugal pendulum damper are derived from first principles using Lagrange's equations of motion. The analysis of torsional systems with pendulum dampers utilizing the mass and stiffness properties developed is included in the program SHAMS. SHAMS calculates the steady-state response of a system of springs and masses to harmonic loads using modal superposition. The response of a crankshaft system with and without the pendulum dampers are included as a case study.
A new hybrid longitudinal-torsional magnetostrictive ultrasonic transducer
NASA Astrophysics Data System (ADS)
Karafi, Mohammad Reza; Hojjat, Yousef; Sassani, Farrokh
2013-06-01
In this paper, a novel hybrid longitudinal-torsional magnetostrictive ultrasonic transducer (HL-TMUT) is introduced. The transducer is composed of a magnetostrictive exponential horn and a stainless steel tail mass. In this transducer a spiral magnetic field made up of longitudinal and circumferential magnetic fields is applied to the magnetostrictive horn. As a result, the magnetostrictive horn oscillates simultaneously both longitudinally and torsionally in accordance with the Joule and Wiedemann effects. The magnetostrictive exponential horn is designed in such a manner that it has the same longitudinal and torsional resonant frequency. It is made up of ‘2V Permendur’, which has isotropic magnetic properties. The differential equations of the torsional and longitudinal vibration of the horn are derived, and a HL-TMUT is designed with a resonant frequency of 20 573 Hz. The natural frequency and mode shapes of the transducer are considered theoretically and numerically. The experimental results show that this transducer resonates torsionally and longitudinally with frequencies of 20 610 Hz and 20 830 Hz respectively. The maximum torsional displacement is 1.5 mrad m-1 and the maximum longitudinal displacement is 0.6 μm. These are promising features for industrial applications.
Nonlinear Hysteretic Torsional Waves.
Cabaret, J; Béquin, P; Theocharis, G; Andreev, V; Gusev, V E; Tournat, V
2015-07-31
We theoretically study and experimentally report the propagation of nonlinear hysteretic torsional pulses in a vertical granular chain made of cm-scale, self-hanged magnetic beads. As predicted by contact mechanics, the torsional coupling between two beads is found to be nonlinear hysteretic. This results in a nonlinear pulse distortion essentially different from the distortion predicted by classical nonlinearities and in a complex dynamic response depending on the history of the wave particle angular velocity. Both are consistent with the predictions of purely hysteretic nonlinear elasticity and the Preisach-Mayergoyz hysteresis model, providing the opportunity to study the phenomenon of nonlinear dynamic hysteresis in the absence of other types of material nonlinearities. The proposed configuration reveals a plethora of interesting phenomena including giant amplitude-dependent attenuation, short-term memory, as well as dispersive properties. Thus, it could find interesting applications in nonlinear wave control devices such as strong amplitude-dependent filters. PMID:26274421
Torsional Ratcheting Actuating System
BARNES,STEPHEN MATTHEW; MILLER,SAMUEL L.; RODGERS,M. STEVEN; BITSIE,FERNANDO
2000-01-24
A new type of surface micromachined ratcheting actuation system has been developed at the Microelectronics Development Laboratory at Sandia National Laboratories. The actuator uses a torsional electrostatic comb drive that is coupled to an external ring gear through a ratcheting scheme. The actuator can be operated with a single square wave, has minimal rubbing surfaces, maximizes comb finger density, and can be used for open-loop position control. The prototypes function as intended with a minimum demonstrated operating voltage of 18V. The equations of motion are developed for the torsional electrostatic comb drive. The resonant frequency, voltage vs. displacement and force delivery characteristics are predicted and compared with the fabricated device's performance.
Nonlinear Hysteretic Torsional Waves
NASA Astrophysics Data System (ADS)
Cabaret, J.; Béquin, P.; Theocharis, G.; Andreev, V.; Gusev, V. E.; Tournat, V.
2015-07-01
We theoretically study and experimentally report the propagation of nonlinear hysteretic torsional pulses in a vertical granular chain made of cm-scale, self-hanged magnetic beads. As predicted by contact mechanics, the torsional coupling between two beads is found to be nonlinear hysteretic. This results in a nonlinear pulse distortion essentially different from the distortion predicted by classical nonlinearities and in a complex dynamic response depending on the history of the wave particle angular velocity. Both are consistent with the predictions of purely hysteretic nonlinear elasticity and the Preisach-Mayergoyz hysteresis model, providing the opportunity to study the phenomenon of nonlinear dynamic hysteresis in the absence of other types of material nonlinearities. The proposed configuration reveals a plethora of interesting phenomena including giant amplitude-dependent attenuation, short-term memory, as well as dispersive properties. Thus, it could find interesting applications in nonlinear wave control devices such as strong amplitude-dependent filters.
The experimental determination of the torsional barrier and shape for disilane.
Moazzen-Ahmadi, N; Horneman, V-M
2006-05-21
The torsional spectrum of disilane was recorded for the first time under high-pressure-pathlength conditions and at a spectral resolution of 0.007 cm(-1) using a Bruker IFS-120 HR Fourier transform spectrometer. The spectrum shows six distinct Q branches. The most prominent Q branch is near 130 cm(-1) which is a blend of four components of the torsional fundamental. Of the remaining five, four were assigned to the first torsional hot band (v(4)=2<--1) and one to the second torsional hot band (v(4)=3<--2). Over 350 transitions were identified. An analysis of the torsional fundamental, the first torsional hot band, and the lower state combination differences from frequencies of the vibrational bands nu(9) and nu(9)+nu(4)-nu(4) was made to characterize the torsion-rotation Hamiltonian in the ground vibrational state. The barrier height, barrier shape, and the rotational constant about the Si-Si bond were determined to be 404.344(83) cm(-1), 2.255(65) cm(-1), and 43208(28) MHz, respectively. Comparison of simulated and the experimental spectra yielded (mu||-mu(perpendicular))/mu(perpendicular)= -4(1) for the torsional dipole moments. This ratio compares well with -3.39(6) for ethane. A comparison of molecular parameters obtained here is made with those for methyl silane and ethane. PMID:16729816
The experimental determination of the torsional barrier and shape for disilane
NASA Astrophysics Data System (ADS)
Moazzen-Ahmadi, N.; Horneman, V.-M.
2006-05-01
The torsional spectrum of disilane was recorded for the first time under high-pressure-pathlength conditions and at a spectral resolution of 0.007cm-1 using a Bruker IFS-120 HR Fourier transform spectrometer. The spectrum shows six distinct Q branches. The most prominent Q branch is near 130cm-1 which is a blend of four components of the torsional fundamental. Of the remaining five, four were assigned to the first torsional hot band (v4=2←1) and one to the second torsional hot band (v4=3←2). Over 350 transitions were identified. An analysis of the torsional fundamental, the first torsional hot band, and the lower state combination differences from frequencies of the vibrational bands ν9 and ν9+ν4-ν4 was made to characterize the torsion-rotation Hamiltonian in the ground vibrational state. The barrier height, barrier shape, and the rotational constant about the Si-Si bond were determined to be 404.344(83)cm-1, 2.255(65)cm-1, and 43208(28)MHz, respectively. Comparison of simulated and the experimental spectra yielded (μ‖-μ⊥)/μ⊥=-4(1) for the torsional dipole moments. This ratio compares well with -3.39(6) for ethane. A comparison of molecular parameters obtained here is made with those for methyl silane and ethane.
Torsion and transverse sensing of conical shells
NASA Astrophysics Data System (ADS)
Li, H.; Chen, Z. B.; Tzou, H. S.
2010-10-01
Conical shells are widely used as payload/rocket adapters in rocket fairing systems. Generally, the conical shells are clamped at the major end and free at the minor end, where the payload is mounted. This study focuses on the dynamic sensing of conical shells with fix-free boundary conditions (BCs) by using distributed piezoelectric helical sensors. Two types of motion are studied, i.e., the transverse modes and the torsion modes. The shear-type sensors for shells sensing are presented first. Formulations of sensing signals of a general shell of revolution are presented, and then simplified to conical shells. For sensing of transverse vibrations, thin piezoelectric sensors are laminated on the top surface. Two types of sensor distribution are considered: a fully distributed and a helical or diagonal laminated. The total signal consists of four components resulting from the four strain components, and each of them is evaluated in detail. For sensing of torsion vibrations, a meridional polarized shear-type sensor with side electrodes is layered on the top surface of the shell structure. Sensing signals of natural shell modes are also evaluated. Analyses show that, in low order modes, the sensing signals induced by the circumferential membrane strains are the primary components of the total signal generations. The numerical results indicate the optimal location of the sensors. The proposed method is capable of determining the modal participation factors, while the testing signal is available; it is also capable of determining the mode shapes by using several distributed sensor segments.
Vibrating Beam With Spatially Periodic Stiffness
NASA Technical Reports Server (NTRS)
Townsend, John S.
1989-01-01
Report presents theoretical analysis of vibrations of simply supported beam, bending stiffness varying about steady value, sinusoidally with position along length. Problem of practical importance because related to vibrations of twisted-pair electric-power transmission lines. Twists promote nonuniform shedding of vortexes and prevents resonant accumulation of vibrational energy from wind.
Use of Generalized Mass in the Interpretation of Dynamic Response of BENDING-TORSION Coupled Beams
NASA Astrophysics Data System (ADS)
ESLIMY-ISFAHANY, S. H. R.; BANERJEE, J. R.
2000-11-01
The interpretation of mode shapes and dynamic response of bending-torsion coupled beams is assessed by using the concept of generalized mass. In the first part of this investigation, the free vibratory motion of bending-torsion coupled beams is studied in detail. The conventional method of interpreting the normal modes of vibration consisting of bending displacements and torsional rotations is shown to be inadequate and replaced by an alternative method which is focussed on the constituent parts of the generalized mass arising from bending and torsional displacements. Basically, the generalized mass in a particular mode is identified and examined in terms of bending, torsion and bending-torsion coupling effects. It is demonstrated that the contribution of individual components in the expression of the generalized mass of a normal mode is a much better indicator in characterizing a coupled mode. It is also shown that the usually adopted criteria of plotting bending displacement and torsional rotations to describe a coupled mode can be deceptive and misleading. In the second part of the investigation, attention is focussed on the dynamic response characteristics of bending-torsion coupled beams when subjected to random bending or torsional loads. A normal mode approach is used to establish the total response. The input random excitation is assumed to be stationary and ergodic so that with the linearity assumption, the output spectrum of the response is obtained by using the frequency response function. The contribution of each normal mode to the overall response is isolated. Particular emphasis is placed on bending-induced torsional response and torsion-induced bending response. A number of case studies involving different types of bending-torsion coupled beams with Cantilever end conditions are presented. The limitations of existing methods of modal interpretation are highlighted, and an insight into the mode selection for response analysis is provided.
The predicted effect of aerodynamic detuning on coupled bending-torsion unstalled supersonic flutter
NASA Technical Reports Server (NTRS)
Hoyniak, D.; Fleeter, S.
1986-01-01
A mathematical model is developed to predict the enhanced coupled bending-torsion unstalled supersonic flutter stability due to alternate circumferential spacing aerodynamic detuning of a turbomachine rotor. The translational and torsional unsteady aerodynamic coefficients are developed in terms of influence coefficients, with the coupled bending-torsion stability analysis developed by considering the coupled equations of motion together with the unsteady aerodynamic loading. The effect of this aerodynamic detuning on coupled bending-torsion unstalled supersonic flutter as well as the verification of the modeling are then demonstrated by considering an unstable 12 bladed rotor, with Verdon's uniformly spaced Cascade B flow geometry as a baseline. However, with the elastic axis and center of gravity at 60 percent of the chord, this type of aerodynamic detuning has a minimal effect on stability. For both uniform and nonuniform circumferentially space rotors, a single degree of freedom torsion mode analysis was shown to be appropriate for values of the bending-torsion natural frequency ratio lower than 0.6 and higher 1.2. When the elastic axis and center of gravity are not coincident, the effect of detuning on cascade stability was found to be very sensitive to the location of the center of gravity with respect to the elastic axis. In addition, it was determined that when the center of gravity was forward of an elastic axis located at midchord, a single degree of freedom torsion model did not accurately predict cascade stability.
NASA Technical Reports Server (NTRS)
Wachel, J. C.; Szenasi, F. R.
1980-01-01
Lateral and torsional vibration data obtained on a centrifugal compressor train which had shaft instabilities and gear failures is examined. The field data verifies that the stability of centrifugal compressors can be adversely affected by coincidence of torsional natural frequencies with lateral instability frequencies. The data also indicates that excitation energy from gear boxes can reduce stability margins if energy is transmitted either laterally or torsionally to the compressors. The lateral and torsional coupling mechanisms of shaft systems is discussed. The coupling mechanisms in a large industrial compressor train are documented and the potential effect on rotor stability is demonstrated. Guidelines are set forth to eliminate these potential problems by minimizing the interaction of torsional and lateral responses and their effect on rotor stability.
Vibration response of misaligned rotors
NASA Astrophysics Data System (ADS)
Patel, Tejas H.; Darpe, Ashish K.
2009-08-01
Misalignment is one of the common faults observed in rotors. Effect of misalignment on vibration response of coupled rotors is investigated in the present study. The coupled rotor system is modelled using Timoshenko beam elements with all six dof. An experimental approach is proposed for the first time for determination of magnitude and harmonic nature of the misalignment excitation. Misalignment effect at coupling location of rotor FE model is simulated using nodal force vector. The force vector is found using misalignment coupling stiffness matrix, derived from experimental data and applied misalignment between the two rotors. Steady-state vibration response is studied for sub-critical speeds. Effect of the types of misalignment (parallel and angular) on the vibration behaviour of the coupled rotor is examined. Along with lateral vibrations, axial and torsional vibrations are also investigated and nature of the vibration response is also examined. It has been found that the misalignment couples vibrations in bending, longitudinal and torsional modes. Some diagnostic features in the fast Fourier transform (FFT) of torsional and longitudinal response related to parallel and angular misalignment have been revealed. Full spectra and orbit plots are effectively used to reveal the unique nature of misalignment fault leading to reliable misalignment diagnostic information, not clearly brought out by earlier studies.
Testicular torsion: A surgical emergency
Prater, J.M.; Overdorf, B.S. )
1991-09-01
Testicular torsion is caused by twisting of the spermatic cord, which results in compromised testicular blood flow. The degree of ischemic injury is determined by the severity of arterial compression and the interval between the onset of symptoms and surgical intervention. Torsion usually occurs at puberty, and an anatomic defect known as bell-clapper deformity is usually present. Typical symptoms include acute scrotal pain with associated nausea and vomiting. Up to one-half of patients report previous similar episodes. On examination, the testis is high-riding, tender, swollen and firm. Testicular scan or Doppler ultrasound examination can be helpful in distinguishing torsion from acute epididymitis. Prompt surgical treatment is indicated to reduce the torsion, and bilateral orchiopexy is performed to prevent recurrence. Exocrine function, as determined by semen analysis, is often abnormal after unilateral torsion. 25 references.
Resonance vibrations of aircraft propellers
NASA Technical Reports Server (NTRS)
Liebers, Fritz
1932-01-01
On the basis of the consideration of various possible kinds of propeller vibrations, the resonance vibrations caused by unequal impacts of the propeller blades appear to be the most important. Their theoretical investigation is made by separate analysis of torsional and bending vibrations. This method is justified by the very great difference in the two natural frequencies of aircraft propeller blades. The calculated data are illustrated by practical examples. Thereby the observed vibration phenomenon in the given examples is explained by a bending resonance, for which the bending frequency of the propeller is equal to twice the revolution speed.
Quantum simulations of nonlinear resonance and torsional dynamics
NASA Astrophysics Data System (ADS)
Collins, Michael A.; Schranz, Harold W.
1994-02-01
A simple model of the vibrational dynamics of ABBA type sequentially bonded tetra-atomic molecules is investigated by quantum mechanical methods. The model Hamiltonian excludes bond stretching and asymmetric bending but includes the kinematic coupling between the torsional motion and symmetric bond bending which results in nonlinear resonances. The effect of this coupling on energy levels and the timescale of intramolecular energy transfer is evaluated and discussed in terms of both resonant and nonresonant effects.
NASA Technical Reports Server (NTRS)
Ko, William L.; Fleischer, Van Tran
2009-01-01
The Ko displacement theory previously formulated for deformed shape predictions of nonuniform beam structures is further developed mathematically. The further-developed displacement equations are expressed explicitly in terms of geometrical parameters of the beam and bending strains at equally spaced strain-sensing stations along the multiplexed fiber-optic sensor line installed on the bottom surface of the beam. The bending strain data can then be input into the displacement equations for calculations of local slopes, deflections, and cross-sectional twist angles for generating the overall deformed shapes of the nonuniform beam. The further-developed displacement theory can also be applied to the deformed shape predictions of nonuniform two-point supported beams, nonuniform panels, nonuniform aircraft wings and fuselages, and so forth. The high degree of accuracy of the further-developed displacement theory for nonuniform beams is validated by finite-element analysis of various nonuniform beam structures. Such structures include tapered tubular beams, depth-tapered unswept and swept wing boxes, width-tapered wing boxes, and double-tapered wing boxes, all under combined bending and torsional loads. The Ko displacement theory, combined with the fiber-optic strain-sensing system, provide a powerful tool for in-flight deformed shape monitoring of unmanned aerospace vehicles by ground-based pilots to maintain safe flights.
Vibration and flutter of mistuned bladed-disk assemblies
NASA Technical Reports Server (NTRS)
Kaza, K. R. V.; Kielb, R. E.
1984-01-01
An analytical model for investigating vibration and flutter of mistuned bladed disk assemblies is presented. This model accounts for elastic, inertial and aerodynamic coupling between bending and torsional motions of each individual blade, elastic and inertial couplings between the blades and the disk, and aerodynamic coupling among the blades. The disk was modeled as a circular plate with constant thickness and each blade was represented by a twisted, slender, straight, nonuniform, elastic beam with a symmetric cross section. The elastic axis, inertia axis, and the tension axis were taken to be noncoincident and the structural warping of the section was explicitly considered. The blade aerodynamic loading in the subsonic and supersonic flow regimes was obtained from two-dimensional unsteady, cascade theories. All the possible standing wave modes of the disk and traveling wave modes of the blades were included. The equations of motion were derived by using the energy method in conjunction with the assumed mode shapes for the disk and the blades. Continuities of displacement and slope at the blade-disk junction were maintained. The equations were solved to investigate the effects of blade-disk coupling and blade frequency mistuning on vibration and flutter. Results showed that the flexibility of practical disks such as those used for current generation turbofans did not have a significant influence on either the tuned or mistuned flutter characteristics. However, the disk flexibility may have a strong influence on some of the system frequencies and on forced response.
NASA Technical Reports Server (NTRS)
Stang, Ambrose H; Ramberg, Walter; Back, Goldie
1937-01-01
This report presents the results of tests of 63 chromium-molybdenum steel tubes and 102 17st aluminum-alloy tubes of various sizes and lengths made to study the dependence of the torsional strength on both the dimensions of the tube and the physical properties of the tube material. Three types of failure are found to be important for sizes of tubes frequently used in aircraft construction: (1) failure by plastic shear, in which the tube material reached its yield strength before the critical torque was reached; (2) failure by elastic two-lobe buckling, which depended only on the elastic properties of the tube material and the dimensions of the tube; and (3) failure by a combination of (1) and (2) that is, by buckling taking place after some yielding of the tube material.
Influence of torsional-lateral coupling on stability behavior of geared rotor systems
NASA Technical Reports Server (NTRS)
Schwibinger, P.; Nordmann, R.
1987-01-01
In high-performance turbomachinery trouble often arises because of unstable nonsynchronous lateral vibrations. The instabilities are mostly caused by oil-film bearings, clearance excitation, internal damping, annular pressure seals in pumps, or labyrinth seals in turbocompressors. In recent times the coupling between torsional and lateral vibrations has been considered as an additional influence. This coupling is of practical importance in geared rotor systems. The literature describes some field problems in geared drive trains where unstable lateral vibrations occurred together with torsional oscillations. This paper studies the influence of the torsional-lateral coupling on the stability behavior of a simple geared system supported by oil-film bearings. The coupling effect is investigated by parameter studies and a sensitivity analysis for the uncoupled and coupled systems.
Effect of vibration stabilization of the process of postcritical deformation
NASA Astrophysics Data System (ADS)
Wildemann, V. E.; Lomakin, E. V.; Tretyakov, M. P.
2016-03-01
Results of the experimental study of vibration stabilization of the process of postcritical deformation during the tensile testing of solid cylindrical specimens made of 20 and 40Cr structural steels under additional vibrations are presented. The vibrations are implemented using cyclic torsion of the specimens at a small amplitude and a frequency of 10-30 Hz.
Saccular impact on ocular torsion.
De Graaf, B; Bos, J E; Groen, E
1996-01-01
When someone is tilted laterally, the shear force on the maculae of the utriculus and the sacculus is described by the sine and the cosine of the angle of tilt, respectively. So both the sacculus and the utriculus are stimulated, but in the literature, ocular torsion is normally attributed to utricular function alone (and, thus, seen as a response to y-axis linear acceleration). However, on the base of a series of experiments on a tilt chair, a linear track, human centrifuges, and during parabolic flights, we conclude that the sacculus contributes to ocular torsion as well (there is a response to z-axis linear acceleration). The data suggest that the ratio of the utricular and saccular impact on ocular torsion is 3:1. The utriculus generates conjugate and the sacculus disjunctive torsional eye movements. PMID:8886354
Isolated penile torsion in newborns
Eroglu, Egemen; Gundogdu, Gokhan
2015-01-01
Introduction: We reported on the incidence of isolated penile torsion among our healthy children and our approach to this anomaly. Methods: Between 2011 and 2014, newborn babies with penile torsion were classified according to the angle of torsion. Surgical correction (penile degloving and reattachment for moderate cases and dorsal dartos flap technique in case of resistance) after 6 months was advised to the babies with rotations more than 45°. Results: Among 1000 newborn babies, 200 isolated penile torsions were found, and among these, 43 had torsions more than 45°, and 4 of these had angles greater than 90°. The mean angle of the rotations was found 30.45° (median: 20°). In total, 8 children with 60° torsions were previously circumcised. Surgery was performed on 19 patients, with a mean patient age of 12 ± 2 months. Of these 19, 13 babies were corrected with degloving and reattachment. This technique was not enough on the remaining 6 patients; therefore, derotational dorsal dartos flap was added to correct the torsion. After a mean of 15.6 ± 9.8 months, residual penile rotation, less than 15°, was found only in 2 children. Conclusion: The incidence of isolated penile torsion is 20% in newborns. However, rotation more than 45° angles are seen in 4.3% of male babies. Correction is not necessary in mild degrees, and penile degloving with reattachment is enough in most cases. If the initial correction is insufficient, dorsal dartos flap rotation is easy and effective. Prior circumcision neither disturbs the operative procedure nor affects the outcomes. PMID:26600889
NASA Technical Reports Server (NTRS)
Heldenfels, Richard R; Vosteen, Louis F
1958-01-01
An approximate analysis of the nonlinear effects of initial twist and large deflections on the torsional stiffness of a cantilever plate subjected to a nonuniform temperature distribution is presented. The Von Karman large-deflection equations are satisfied through the use of a variational principle. The results show that initial twist and applied moments can have significant effects on the changes in stiffness produced by nonuniform heating, particularly in the region of the buckling temperature difference. Results calculated by this approximate analysis are in satisfactory agreement with measured torsional deformations and changes in natural frequency. (author)
The Effect of Torsion-Torsion Interactions on the Tunneling Split Torsional Ground State.
NASA Astrophysics Data System (ADS)
Cameron, Ian George
In NMR studies of methyl groups it is normally assumed that the effects of inter-methyl group interactions (torsion-torsion interactions) are negligible. This is probably a reasonable assump- tion at high temperatures(, )(>50K), however, for lower temperatures this is no longer the case. This is clearly demonstrated with tetra- methylsilane (TMS) for which several important effects of torsion-torsion interactions are reported. The spin lattice relaxtion time, T(,1), was measured as a function of the Larmor frequency at several temperatures and it is shown that the observed recovery can be characterized by two exponential contributions. As anticipated, the frequency dependence of T(,ZT)('-1), the recovery rate for the faster of the two contributing processes, exhibited resonant-like peaks. In other ways, however, these results deviate quite substantially from the behavior expected. Firstly, the hindering potential experienced by each methyl group in TMS is perturbed by the other three methyl groups in the molecule. This leads to the appearance of four resonant peaks in the frequency dependence of T(,ZT)('-1) instead of just two. A perturbation calculation is presented to support this interpretation. Secondly, the contribu- tion to the measured linewidths from lifetime broadening, which dominates at high temperatures, becomes negligible at low tem- peratures compared with the underlying "inherent" width of the tunneling lines. We associate this inherent width with a relatively narrow ((TURN)1 MHz), quasi-continuous distribution of tunneling split- tings which occurs as a result of partially averaged torsion-torsion interactions. Thirdly, the intensity of the peaks, which is expected to be temperature independent, drops sharply as the temperature is lowered. This is a clear indication of the formation of a band of tunneling states of low temperatures where torsion-torsion interactions are strong.
The Millimeter-Wave Spectrum of Methacrolein. Torsion-Rotation Effects in the Excited States
NASA Astrophysics Data System (ADS)
Zakharenko, Olena; Motiyenko, R. A.; Aviles Moreno, Juan-Ramon; Huet, T. R.
2015-06-01
Last year we reported the analysis of the rotational spectrum of s-trans conformer of methacrolein CH2=C(CH3)CHO in the ground vibrational state. In this talk we report the study of its low lying excited vibrational states. The study is based on room-temperature absorption spectra of methacrolein recorded in the frequency range 150 - 465 GHz using the spectrometer in Lille. The new results include assignment of the first excited torsional state (131 cm-1), and the joint analysis of the vt = 0 and vt = 1 states, that allowed us to improve the model in the frame of Rho-Axis-Method (RAM) Hamiltonian and to remove some strong correlations between parameters. Also we assigned the first excited vibrational state of the skeletal torsion mode (170 cm-1). The inverse sequence of A and E tunneling substates as well as anomalous A-E splittings observed for the rotational lines of vsk = 1 state clearly indicate a coupling between methyl torsion and skeletal torsion. However we were able to fit within experimental accuracy the rotational lines of vsk = 1 state using the RAM Hamiltonian. Because of the inversion of the A and E tunneling substates the rotational lines of the vsk = 1 states were assumed to belong to a virtual first excited torsional state. Finally, we assigned several low-Ka rotational transitions of the excited vibrational states above 200 cm-1 but their analysis is complicated by different rotation-vibration interactions. In particular there is an evidence of the Fermi-type resonance between the second excited torsional state and the first excited state of the in-plane skeletal bending mode (265 cm-1). Support from the French Laboratoire d'Excellence CaPPA (Chemical and Physical Properties of the Atmosphere) through contract ANR-10-LABX-0005 of the Programme d'Investissements d'Avenir is acknowledged. Zakharenko O. et al., 69th ISMS, 2014, TI01
Hypersymplectic structures with torsion on Lie algebroids
NASA Astrophysics Data System (ADS)
Antunes, P.; Nunes da Costa, J. M.
2016-06-01
Hypersymplectic structures with torsion on Lie algebroids are investigated. We show that each hypersymplectic structure with torsion on a Lie algebroid determines three Nijenhuis morphisms. From a contravariant point of view, these structures are twisted Poisson structures. We prove the existence of a one-to-one correspondence between hypersymplectic structures with torsion and hyperkähler structures with torsion. We show that given a Lie algebroid with a hypersymplectic structure with torsion, the deformation of the Lie algebroid structure by any of the transition morphisms does not affect the hypersymplectic structure with torsion. We also show that if a triplet of 2-forms is a hypersymplectic structure with torsion on a Lie algebroid A, then the triplet of the inverse bivectors is a hypersymplectic structure with torsion for a certain Lie algebroid structure on the dual A∗, and conversely. Examples of hypersymplectic structures with torsion are included.
Anomalous Plasticity in the Cyclic Torsion of Micron Scale Metallic Wires
NASA Astrophysics Data System (ADS)
Liu, Dabiao; He, Yuming; Dunstan, D. J.; Zhang, Bo; Gan, Zhipeng; Hu, Peng; Ding, Huaming
2013-06-01
The plasticity of micron scale Cu and Au wires under cyclic torsion is investigated for the first time by using a torsion balance technique. In addition to a size effect, a distinct Bauschinger effect and an anomalous plastic recovery, wherein reverse plasticity even occurs upon unloading, are unambiguously revealed. The Bauschinger effect and plastic recovery have been observed in molecular dynamics and discrete dislocation dynamics simulations of ideal single-crystal wires; the results here are an excellent confirmation that these effects also occur in experiment in nonideal polycrystalline wires. A physical model consistent with the simulations is described in which the geometrically necessary dislocations induced by the nonuniform deformation in torsion play the key role in these anomalous plastic behaviors.
Anomalous plasticity in the cyclic torsion of micron scale metallic wires.
Liu, Dabiao; He, Yuming; Dunstan, D J; Zhang, Bo; Gan, Zhipeng; Hu, Peng; Ding, Huaming
2013-06-14
The plasticity of micron scale Cu and Au wires under cyclic torsion is investigated for the first time by using a torsion balance technique. In addition to a size effect, a distinct Bauschinger effect and an anomalous plastic recovery, wherein reverse plasticity even occurs upon unloading, are unambiguously revealed. The Bauschinger effect and plastic recovery have been observed in molecular dynamics and discrete dislocation dynamics simulations of ideal single-crystal wires; the results here are an excellent confirmation that these effects also occur in experiment in nonideal polycrystalline wires. A physical model consistent with the simulations is described in which the geometrically necessary dislocations induced by the nonuniform deformation in torsion play the key role in these anomalous plastic behaviors. PMID:25165928
Propagating torsion in the Einstein frame
Poplawski, Nikodem J.
2006-11-15
The Einstein-Cartan-Saa theory of torsion modifies the spacetime volume element so that it is compatible with the connection. The condition of connection compatibility gives constraints on torsion, which are also necessary for the consistence of torsion, minimal coupling, and electromagnetic gauge invariance. To solve the problem of positivity of energy associated with the torsionic scalar, we reformulate this theory in the Einstein conformal frame. In the presence of the electromagnetic field, we obtain the Hojman-Rosenbaum-Ryan-Shepley theory of propagating torsion with a different factor in the torsionic kinetic term.
Microwave Spectroscopy of Trans-Ethyl Methyl Ether in the Torsionally Excited State 3
NASA Astrophysics Data System (ADS)
Kobayashi, Kaori; Murata, Keigo; Tsunekawa, Shozo; Ohashi, Nobukimi
2010-06-01
The trans-ethyl methyl ether molecule (CH_3CH_2OCH_3) has two methyl group internal rotors which are equivalent to the two vibrational motions, ν28 and ν29. There is another low-lying torsional motion which is a skeltal torsion (ν30) and does not cause splitting. The microwave spectra of the trans-ethyl methyl ether molecule in the ν28 = 1, ν29 = 1, and ν30 = 1 have been studied and interactions between these states were discussed. In this paper we report results on the ν30 = 2, and 3 state. The analysis based on Hougen's tunneling matrix formulation considering two methyl groups are used. We try to interpret tunneling parameters obtained in the present analysis quantitatively from the viewpoint of torsion-torsion interaction.
Raman spectra of gases. XVI - Torsional transitions in ethanol and ethanethiol
NASA Technical Reports Server (NTRS)
Durig, J. R.; Bucy, W. E.; Wurrey, C. J.; Carreira, L. A.
1975-01-01
The Raman spectra of gaseous ethanol and ethanethiol have been investigated. Thiol torsional fundamentals for the gauche conformer of EtSH and EtSD have been observed and the asymmetric potential function for this vibration has been calculated. Methyl torsional transitions and overtones have also been observed for both of these molecules. Barriers to internal rotation for the methyl top are calculated to be 3.77 and 3.84 kcal/mol for the EtSH and EtSD compounds, respectively. Hydroxyl torsional fundamentals were observed at 207 and 170 per cm in the EtOH and EtOD spectra, respectively. Overtones of the methyl torsion in both molecules yield a barrier to internal rotation of 3.62 kcal/mol for the gauche conformer.
Coupled torsional and bending motions in s-cis methyl vinyl ether
NASA Astrophysics Data System (ADS)
Meyer, Rolf; Ha, Tae-Kyu; Oldani, Markus; Caminati, Walther
1987-02-01
New microwave measurements on s-cis methyl vinyl ether and a study of the interactions among skeletal and methyl torsions and COC bending are reported. Using pulsed microwave Fourier transform spectroscopy, the small methyl torsional A-E splitting (0.16 MHz) in the vibrational ground state has been resolved for the first time. Large splittings are observed in the first excited states of skeletal torsion and COC bending. Ab initio results on the torsional coupling, allowing for structural relaxation, are reported and used to specify, in part, a flexible model for the torsional and bending motions. The spectroscopic properties of this three-dimensional model sytem, as estimated from the results for the one-dimensional and two-dimensional subsystems, explain the relevant experimental data. The gearing type torsional interaction predicted ab initio is confirmed by this treatment. The adjusted potential function as well as the structural relaxations upon torsion suggest repulsive interaction between the methyl hydrogen atoms and the methylenic hydrogen atom next to the methyl group.
FIR Synchrotron Spectroscopy of High Torsional Levels of CD_3OH: the Tau of Methanol
NASA Astrophysics Data System (ADS)
Lees, Ronald M.; Xu, Li-Hong; Billinghurst, Brant E.
2015-06-01
Sub-bands involving high torsional levels of the CD_3OH isotopologue of methanol have been analyzed in Fourier transform spectra recorded at the Far-Infrared beamline of the Canadian Light Source synchrotron in Saskatoon. Energy term values for A and E torsional species of the third excited torsional state, v_t = 3, are now almost complete up to rotational levels K = 15, and thirteen substates have so far been identified for v_t = 4. The spectra show interesting close groupings of high-v_t sub-bands related by Dennison's torsional symmetry label τ, rather than A and E, that can be understood in terms of a simple and universal free-rotor "spectral predictor" chart. Transitions between states on the same free rotor curve have torsional overlap matrix elements close to unity, so give rise to strong sub-bands providing radiative routes for rapid population transfer through the high torsional manifold. Where the energy curves for the v_t = 3 and 4 ground-state torsional levels pass through the excited vibrational states, strong resonances can occur and a number of anharmonic and Coriolis interactions have been detected through perturbations to the spectra and appearance of forbidden transitions due to strong mixing and intensity borrowing.
Deterministic multidimensional nonuniform gap sampling
NASA Astrophysics Data System (ADS)
Worley, Bradley; Powers, Robert
2015-12-01
Born from empirical observations in nonuniformly sampled multidimensional NMR data relating to gaps between sampled points, the Poisson-gap sampling method has enjoyed widespread use in biomolecular NMR. While the majority of nonuniform sampling schemes are fully randomly drawn from probability densities that vary over a Nyquist grid, the Poisson-gap scheme employs constrained random deviates to minimize the gaps between sampled grid points. We describe a deterministic gap sampling method, based on the average behavior of Poisson-gap sampling, which performs comparably to its random counterpart with the additional benefit of completely deterministic behavior. We also introduce a general algorithm for multidimensional nonuniform sampling based on a gap equation, and apply it to yield a deterministic sampling scheme that combines burst-mode sampling features with those of Poisson-gap schemes. Finally, we derive a relationship between stochastic gap equations and the expectation value of their sampling probability densities.
Constraining torsion with Gravity Probe B
Mao Yi; Guth, Alan H.; Cabi, Serkan; Tegmark, Max
2007-11-15
It is well-entrenched folklore that all torsion gravity theories predict observationally negligible torsion in the solar system, since torsion (if it exists) couples only to the intrinsic spin of elementary particles, not to rotational angular momentum. We argue that this assumption has a logical loophole which can and should be tested experimentally, and consider nonstandard torsion theories in which torsion can be generated by macroscopic rotating objects. In the spirit of action=reaction, if a rotating mass like a planet can generate torsion, then a gyroscope would be expected to feel torsion. An experiment with a gyroscope (without nuclear spin) such as Gravity Probe B (GPB) can test theories where this is the case. Using symmetry arguments, we show that to lowest order, any torsion field around a uniformly rotating spherical mass is determined by seven dimensionless parameters. These parameters effectively generalize the parametrized post-Newtonian formalism and provide a concrete framework for further testing Einstein's general theory of relativity (GR). We construct a parametrized Lagrangian that includes both standard torsion-free GR and Hayashi-Shirafuji maximal torsion gravity as special cases. We demonstrate that classic solar system tests rule out the latter and constrain two observable parameters. We show that Gravity Probe B is an ideal experiment for further constraining nonstandard torsion theories, and work out the most general torsion-induced precession of its gyroscope in terms of our torsion parameters.
Constraining torsion with Gravity Probe B
NASA Astrophysics Data System (ADS)
Mao, Yi; Tegmark, Max; Guth, Alan H.; Cabi, Serkan
2007-11-01
It is well-entrenched folklore that all torsion gravity theories predict observationally negligible torsion in the solar system, since torsion (if it exists) couples only to the intrinsic spin of elementary particles, not to rotational angular momentum. We argue that this assumption has a logical loophole which can and should be tested experimentally, and consider nonstandard torsion theories in which torsion can be generated by macroscopic rotating objects. In the spirit of action=reaction, if a rotating mass like a planet can generate torsion, then a gyroscope would be expected to feel torsion. An experiment with a gyroscope (without nuclear spin) such as Gravity Probe B (GPB) can test theories where this is the case. Using symmetry arguments, we show that to lowest order, any torsion field around a uniformly rotating spherical mass is determined by seven dimensionless parameters. These parameters effectively generalize the parametrized post-Newtonian formalism and provide a concrete framework for further testing Einstein’s general theory of relativity (GR). We construct a parametrized Lagrangian that includes both standard torsion-free GR and Hayashi-Shirafuji maximal torsion gravity as special cases. We demonstrate that classic solar system tests rule out the latter and constrain two observable parameters. We show that Gravity Probe B is an ideal experiment for further constraining nonstandard torsion theories, and work out the most general torsion-induced precession of its gyroscope in terms of our torsion parameters.
Torsional Carbon Nanotube Artificial Muscles
NASA Astrophysics Data System (ADS)
Foroughi, Javad; Spinks, Geoffrey M.; Wallace, Gordon G.; Oh, Jiyoung; Kozlov, Mikhail E.; Fang, Shaoli; Mirfakhrai, Tissaphern; Madden, John D. W.; Shin, Min Kyoon; Kim, Seon Jeong; Baughman, Ray H.
2011-10-01
Rotary motors of conventional design can be rather complex and are therefore difficult to miniaturize; previous carbon nanotube artificial muscles provide contraction and bending, but not rotation. We show that an electrolyte-filled twist-spun carbon nanotube yarn, much thinner than a human hair, functions as a torsional artificial muscle in a simple three-electrode electrochemical system, providing a reversible 15,000° rotation and 590 revolutions per minute. A hydrostatic actuation mechanism, as seen in muscular hydrostats in nature, explains the simultaneous occurrence of lengthwise contraction and torsional rotation during the yarn volume increase caused by electrochemical double-layer charge injection. The use of a torsional yarn muscle as a mixer for a fluidic chip is demonstrated.
Flexural Torsional Guided Wave Pipe Inspection
NASA Astrophysics Data System (ADS)
Sun, Z.; Zhang, L.; Rose, J. L.
2006-03-01
Based on the flexural torsional guided wave theory and its focusing technique, this paper demonstrates the defect detection capability of flexural torsional guided waves on multiple defects with different shapes and axial, circumferential locations in pipe.
Can a macroscopic gyroscope feel torsion
NASA Technical Reports Server (NTRS)
Stoeger, W. R.; Yasskin, P. B.
1979-01-01
We demonstrate that for a large class of Lagrangian-based torsion theories a macroscopic gyroscope is insensitive to the torsion field: there can be no coupling of the torsion to the gyroscope's angular momentum of rotation. To detect torsion a polarized system with a net elementary particle spin is needed. These conclusions are evident from the conservation laws, which form the basis for deriving the equations of motion.
Torsion and buckling of open sections
NASA Technical Reports Server (NTRS)
Wagner, H; Pretschner, W
1936-01-01
Following an abstract of the well-known theory of torsion in compression, the writers give directions for the practical calculation of the values of C(sub BT) (resistance to flexure and torsion) and i(sub SP(exp 2)), which determine the torsion. The second part treats the experiments in support of the theory of torsion of plain and flanged angle sections.
Comparison of test particle acceleration in torsional spine and fan reconnection regimes
Hosseinpour, M. Mehdizade, M.; Mohammadi, M. A.
2014-10-15
Magnetic reconnection is a common phenomenon taking place in astrophysical and space plasmas, especially in solar flares which are rich sources of highly energetic particles. Torsional spine and fan reconnections are important mechanisms proposed for steady-state three-dimensional null-point reconnection. By using the magnetic and electric fields for these regimes, we numerically investigate the features of test particle acceleration in both regimes with input parameters for the solar corona. By comparison, torsional spine reconnection is found to be more efficient than torsional fan reconnection in an acceleration of a proton to a high kinetic energy. A proton can gain as high as 100 MeV of relativistic kinetic energy within only a few milliseconds. Moreover, in torsional spine reconnection, an accelerated particle can escape either along the spine axis or on the fan plane depending on its injection position. However, in torsional fan reconnection, the particle is only allowed to accelerate along the spine axis. In addition, in both regimes, the particle's trajectory and final kinetic energy depend on the injection position but adopting either spatially uniform or non-uniform localized plasma resistivity does not much influence the features of trajectory.
Vibration damage mechanism analysis on rotor of diesel generating set with rigid coupling
NASA Astrophysics Data System (ADS)
Yan, Bing; Shi, Weizhen; Hua, Chunrong; Liu, Jingming; Dong, Dawei; Chen, Jun
2015-07-01
The crankshaft output end is generally connected with generator rotor through the coupling in diesel generating set. When using rigid coupling, the attachments and connecting parts of generator rotor (especially at larger gyration radius) are vulnerable to fatigue damage even if the vibration level of the generating set does not exceed the acceptable “usual value”. In order to investigate the reasons, the torsional vibration of the rotor in the diesel generating set was calculated and measured in this paper, which shows that using high rigidity coupling would result in large torsional vibration on the generator rotor, and that the linear vibration (the tangential vibration) value induced by torsional vibration at larger gyration radius of generator motor is almost the same as the vibration level of the generating set. Then, the vibration level of generating set was obtained, and the maximum vibration velocities of the generator are below the permissible value regulated by ISO 8528-9. But the velocities of synthetic vibration of the generating set vibration and the linear vibration induced by torsional vibration at larger gyration radius are much higher than permissible value 2(28mm/s) regulated by ISO 8528-9, which may be the reason of the mechanical damage of the attachments and connecting parts at larger gyration radius of generator motor caused by exceeded vibration.
Modeling of tape tether vibration and vibration sensing using smart film sensors
NASA Astrophysics Data System (ADS)
Kunugi, Kouta; Kojima, Hirohisa; Trivailo, Pavel M.
2015-02-01
Tape-tethered satellite systems use long and flexible tape tethers, the bending and torsional vibrations of which affect the positions and attitude of attached satellites and climbers. Owing to the distribution characteristics of a tape tether, ordinary point sensors and actuators cannot be used easily to control the vibrations. Other types of sensors and actuators are required for this purpose. The flexibility and deformability of smart materials make them particularly suitable for integration into a tape-tethered system. Thus, in this paper, we propose a method for modeling the bending and torsional vibrations of a tape tether, and report our investigation into the feasibility of using smart film sensors to distinguish between the two vibration types. We formulate equations of motion for the tape tether using multibody dynamics techniques, and perform numerical simulations to study the behavior of the bending and torsional vibrations. The results of our experiments show that the bending and torsional vibrations of a tape tether can be measured using smart film sensors attached to the tether.
Tsujino, Jiromaru; Harada, Yoshiki; Ihara, Shigeru; Kasahara, Kohei; Shimizu, Masanori; Ueoka, Tetsugi
2004-04-01
Ultrasonic high-frequency complex vibrations are effective for various ultrasonic high-power applications. Three types of ultrasonic complex vibration system with a welding tip vibrating elliptical to circular locus for packaging in microelectronics were studied. The complex vibration sources are using (1) a longitudinal-torsional vibration converter with diagonal slits that is driven only by a longitudinal vibration source, (2) a complex transverse vibration rod with several stepped parts that is driven by two longitudinal vibration source crossed at a right angle and (3) a longitudinal vibration circular disk and three longitudinal transducers that are installed at the circumference of the disk. PMID:15047273
Gradient scaling for nonuniform meshes
Margolin, L.G.; Ruppel, H.M.; Demuth, R.B.
1985-01-01
This paper is concerned with the effect of nonuniform meshes on the accuracy of finite-difference calculations of fluid flow. In particular, when a simple shock propagates through a nonuniform mesh, one may fail to model the jump conditions across the shock even when the equations are differenced in manifestly conservative fashion. We develop an approximate dispersion analysis of the numerical equations and identify the source of the mesh dependency with the form of the artificial viscosity. We then derive an algebraic correction to the numerical equations - a scaling factor for the pressure gradient - to essentially eliminate the mesh dependency. We present several calculations to illustrate our theory. We conclude with an alternate interpretation of our results. 14 refs., 5 figs.
The torsional and rotation-torsion spectra of CD2HOH
NASA Astrophysics Data System (ADS)
Ndao, M.; Kwabia Tchana, F.; Coudert, L. H.; Motiyenko, R. A.; Margulès, L.; Barros, J.; Manceron, L.; Roy, P.
2016-08-01
The torsional and rotation-torsion spectra of the doubly deuterated species of methanol CD2HOH have been analyzed using submillimeter wave, terahertz, and far infrared spectra. 101 torsional subbands, with subband centers ranging from 2.3 to 626 cm-1, were assigned. Analysis of these yielded kinetic energy and hindering potential parameters of the torsional Hamiltonian describing the large amplitude internal rotation of the CD2H methyl group with respect to the hydroxyl group. 3271 rotation and rotation-torsion transitions, involving the 24 torsional levels up to e1 with 3 ⩽ K ⩽ 10 , were assigned and fitted approximating the rotational energy of each torsional level with a Taylor-type expansion in J (J + 1) . The rotational structure of 48 torsional subbands involving torsional levels higher than e1 has also been analyzed. In most cases, only the Q branch could be observed and assigned.
Hyttel, Trine E W; Bak, Geske S; Larsen, Solveig B; Løkkegaard, Ellen C L
2015-03-01
The increasing use of de-torsion of the ovaries may result in re-torsion. This review addresses risk of re-torsion and describes preventive strategies to avoid re-torsion in pre-menarcheal girls, and fertile and pregnant women. We clinically reviewed PubMed, Embase, Trip and Cochrane databases. The main outcome measures were re-torsion and viability of ovary with fixation measures. A total of 38 publications including 71 girls, 363 fertile women, and 69 pregnant women were found to be relevant. All studies were case reports or case series, sometimes with non-randomized controls. The studies show considerable heterogeneity in design, population, management and outcome. Only four studies included more than 50 cases. In pregnancy the risk of re-torsion was as high as 19.5-37.5%; among fertile women it was 28.6%. Most articles concluded that fixation of the ovaries to the pelvic sidewall or plication of the ovarian ligament after torsion may prevent re-torsion. In one case a girl experienced re-torsion after ovariopexy. Based on observational studies it seems that de-torsion and fixation of the ovary is a safe procedure that usually ensures maintenance of ovarian function and reduces the risk of recurrence, especially when there are no ovarian cysts or adnexal masses. PMID:25412114
Topological design of torsional metamaterials
NASA Astrophysics Data System (ADS)
Vitelli, Vincenzo; Paulose, Jayson; Meeussen, Anne; Topological Mechanics Lab Team
Frameworks - stiff elements with freely hinged joints - model the mechanics of a wide range of natural and artificial structures, including mechanical metamaterials with auxetic and topological properties. The unusual properties of the structure depend crucially on the balance between degrees of freedom associated with the nodes, and the constraints imposed upon them by the connecting elements. Whereas networks of featureless nodes connected by central-force springs have been well-studied, many real-world systems such as frictional granular packings, gear assemblies, and flexible beam meshes incorporate torsional degrees of freedom on the nodes, coupled together with transverse shear forces exerted by the connecting elements. We study the consequences of such torsional constraints on the mechanics of periodic isostatic networks as a foundation for mechanical metamaterials. We demonstrate the existence of soft modes of topological origin, that are protected against disorder or small perturbations of the structure analogously to their counterparts in electronic topological insulators. We have built a lattice of gears connected by rigid beams that provides a real-world demonstration of a torsional metamaterial with topological edge modes and mechanical Weyl modes.
An analysis of traction drive torsional stiffness
NASA Technical Reports Server (NTRS)
Rohn, D. A.; Loewenthal, S. H.
1983-01-01
The tangential compliance of elastic bodies in concentrated contact applied to traction drive elements to determine their torsional stiffness was analyzed. Static loading and rotating conditions are considered. The effects of several design variables are shown. The theoretical torsional stiffness of a fixed ratio multiroller drive is computed and compared to experimental values. It is shown that the torsional compliance of the traction contacts themselves is a relatively small portion of the overall drive system compliance.
Empirical formula of crustal torsional oscillations
NASA Astrophysics Data System (ADS)
Sotani, Hajime
2016-02-01
Crustal torsional oscillations depend on not only crust properties but also the stellar mass and radius. Thus, one could extract stellar information by identifying the observed frequencies of stellar oscillations with the crustal torsional oscillations. Owing to the confinement of torsional oscillations inside the crust region of neutron stars, we successfully derive an empirical formula for the fundamental crustal torsional oscillations as a function of the stellar mass, radius, the so-called slope parameter of the nuclear symmetry energy, and the angular index of oscillations, with which one can estimate the frequencies with high accuracy. This empirical formula could be valuable in both the astrophysics and nuclear physics communities.
Random lasing with spatially nonuniform gain
NASA Astrophysics Data System (ADS)
Fan, Ting; Lü, Jiantao
2016-07-01
Spatial and spectral properties of random lasing with spatially nonuniform gain were investigated in two-dimensional (2D) disordered medium. The pumping light was described by an individual electric field and coupled into the rate equations by using the polarization equation. The spatially nonuniform gain comes from the multiple scattering of this pumping light. Numerical simulation of the random system with uniform and nonuniform gain were performed both in weak and strong scattering regime. In weak scattering sample, all the lasing modes correspond to those of the passive system whether the nonuniform gain is considered. However, in strong scattering regime, new lasing modes appear with nonuniform gain as the localization area changes. Our results show that it is more accurate to describe the random lasing behavior with introducing the nonuniform gain origins from the multiple light scattering.
Drillstring vibrations create crooked holes
Dareing, D.W.
1984-01-01
Boreholes in hard formations sometimes deviate when the drillstring runs rough or the kelly bounces severely. This article explains how drillstring vibrations produce crooked holes in hard formations. It shows how to reduce dog-leg severity through vibration control. Dog-legs are known to produce cyclic bending-type fatigue loads in drill pipe and collars. Longitudinal and torsional vibrational stresses are additive to rotational bending and further reduce the life of drillstring tubulars. Vibration-induced dog-legs are therefore more damaging to drillstrings than other dog-leg producing mechanisms because total cyclic fatigue loading is the combined effect of bending stress reversal due to rotation plus vibrational stress variations. The vibration-induced dog-leg concept is based on overall vibration response of drillstrings, resultant dynamic displacements of roller cone drill bits, and corresponding dynamic forces between bit and formation. The concept explains how dynamic forces generated by roller cone rock bits might produce helical bore holes in hard homogeneous formations. Dog-legs in hard formations may be due in part to drillstring vibrations. The wellbore deviation concept relates only to roller cone rock bits and is based on dynamically reorienting three-lobed formation pattern hammered out by bottomhole assembly resonance. Analytical studies are needed to determine the effect of bit force impact point location on chip formation and rock removal. Field studies of various bottom hole assemblies operating at critical rotary speeds coupled with directional surveys are needed to test the validity of this theory.
Effects of gear box vibration and mass imbalance on the dynamics of multistage gear transmission
NASA Technical Reports Server (NTRS)
Choy, F. K.; Tu, Y. K.; Zakrajsek, J. J.; Townsend, D. P.
1991-01-01
The dynamic behavior of multistage gear transmission system, with the effects of gear-box-induced vibrations and rotor mass-imbalances is analyzed. The model method, using undamped frequencies and planar mode shapes, is used to reduce the degree-of-freedom of the system. The various rotor-bearing stages as well as lateral and torsional vibrations of each individual stage are coupled through localized gear-mesh-tooth interactions. Gear-box vibrations are coupled to the gear stage dynamics through bearing support forces. Transient and steady state dynamics of lateral and torsional vibrations of the geared system are examined in both time and frequency domain. A typical three-staged geared system is used as an example. Effects of mass-imbalance and gear box vibrations on the system dynamic behavior are presented in terms of modal excitation functions for both lateral and torsional vibrations. Operational characteristics and conclusions are drawn from the results presented.
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.
Vibration monitoring system for drill string
Wassell, M.E.
1993-07-13
A vibration monitoring system is described for use in monitoring lateral and torsional vibrations in a drill string comprising: a drill string component having an outer surface; first accelerometer means A[sub 1] for measuring tangential acceleration; second accelerometer means A[sub 2] for measuring tangential acceleration; third accelerometer means A[sub 3] for measuring tangential acceleration; said first, second and third accelerometer means A[sub 1], A[sub 2] and A[sub 3] being mounted in said drill string component and being spaced from one another to measure acceleration forces on said drill string component tangentially with respect to the outer surface of said component wherein said first, second and third accelerometer means are adapted to measure and distinguish between lateral and torsional vibrations exerted on said drill string component.
Rajendran, S.; Narasimhan, M.V.
1997-01-01
The inertia due to reciprocating parts and connected rods, as felt by the crankshaft, varies with the crank angle. The effect of inertia variation on torsional free vibration of crankshafts has been studied extensively. In this paper, the effect on combined torsional and bending free vibrations is examined. Single-cylinder engine crankshaft geometry is considered for the study. The results indicate that the inertial coupling, introduced by the reciprocating parts and connected rod, significantly influences the free vibration characteristics, particularly when the natural frequencies of the crankshaft are closely spaced. The results suggest that, under such conditions, modeling the crankshaft as a pure torsional system would involve considerable error.
A smooth impact rotation motor using a multi-layered torsional piezoelectric actuator.
Morita, T; Yoshida, R; Okamoto, Y; Kurosawa, M K; Higuchi, T
1999-01-01
A smooth impact rotation motor was fabricated and successfully operated using a torsional piezo actuator. Yoshida et al. reported a linear type smooth impact motor in 1997. This linear motor demonstrated a high output force and a long stroke. A superior feature of the smooth impact drive is a high positioning resolution compared with an impact drive. The positioning resolution of SIDM (smooth impact drive mechanism) is equal to the piezo displacement. The reported positioning resolution of the linear type was 5 nm. Our rotation motor utilized a torsional actuator containing multi-layered piezoelectric material. The torsional actuator was cylindrical in shape with an outer diameter of 15 mm, an inner diameter of 10 mm, and a length of 11 mm. Torsional vibration performance was measured with a laser Doppler vibrometer. The obtained torsional displacement agreed with the calculated values and was sufficient to drive a rotor. The rotor was operated with a saw-shaped input voltage (180 V; 8 kHz). The revolution direction was reversible. The maximum revolution speed was 27 rpm, and the maximum output torque was 56 gfcm. In general, smooth-impact drives do not show high efficiency; however, the level of efficiency of our results (max., 0.045%) could be increased by improving the contact surface material. In addition, we are studying quantitative consideration, for example, about the optimum pre-load or frictional force. PMID:18244340
Heat transport in nonuniform superconductors
NASA Astrophysics Data System (ADS)
Richard, Caroline; Vorontsov, Anton B.
2016-08-01
We calculate electronic energy transport in inhomogeneous superconductors using a fully self-consistent nonequilibrium quasiclassical Keldysh approach. We develop a general theory and apply it to a superconductor with an order parameter that forms domain walls of the type encountered in the Fulde-Ferrell-Larkin-Ovchinnikov state. The heat transport in the presence of a domain wall is inherently anisotropic and nonlocal. The bound states in the nonuniform region play a crucial role and control heat transport in several ways: (i) they modify the spectrum of quasiparticle states and result in Andreev reflection processes and (ii) they hybridize with the impurity band and produce a local transport environment with properties very different from those in a uniform superconductor. As a result of this interplay, heat transport becomes highly sensitive to temperature, magnetic field, and disorder. For strongly scattering impurities, we find that the transport across domain walls at low temperatures is considerably more efficient than in the uniform superconducting state.
Torsion of Noncircular Composite Cylinders
NASA Technical Reports Server (NTRS)
Rouse, Marshall; Hyer, Michael W.; Haynie, Waddy T.
2005-01-01
The paper presents a brief overview of the predicted deformation and failure characteristics of noncircular composite cylinders subjected to torsion. Using a numerical analysis, elliptical cylinders with a minor-to-major diameter ratio of 0.7 are considered. Counterpart circular cylinders with the same circumference as the elliptical cylinders are included for comparison. The cylinders are constructed of a medium-modulus graphite-epoxy material in a quasi-isotropic lay-up. Imperfections generated from the buckling mode shapes are included in the initial cross-sectional geometry of the cylinders. Deformations until first fiber failure, as predicted using the maximum stress failure criterion and a material degradation scheme, are presented. For increasing levels of torsion, the deformations of the elliptical cylinders, in the form of wrinkling of the cylinder wall, occur primarily in the flatter regions of the cross section. By comparison the wrinkling deformations of the circular cylinders are more uniformly distributed around the circumference. Differences in the initial failure and damage progression and the overall torque vs. twist relationship between the elliptical and circular cylinders are presented. Despite differences in the response as the cylinders are being loaded, at first fiber failure the torque and twist for the elliptical and circular cylinders nearly coincide.
Thermoelastic vibration test techniques
NASA Technical Reports Server (NTRS)
Kehoe, Michael W.; Snyder, H. Todd
1991-01-01
The structural integrity of proposed high speed aircraft can be seriously affected by the extremely high surface temperatures and large temperature gradients throughout the vehicle's structure. Variations in the structure's elastic characteristics as a result of thermal effects can be observed by changes in vibration frequency, damping, and mode shape. Analysis codes that predict these changes must be correlated and verified with experimental data. The experimental modal test techniques and procedures used to conduct uniform, nonuniform, and transient thermoelastic vibration tests are presented. Experimental setup and elevated temperature instrumentation considerations are also discussed. Modal data for a 12 by 50 inch aluminum plate heated to a temperature of 475 F are presented. These data show the effect of heat on the plate's modal characteristics. The results indicated that frequency decreased, damping increased, and mode shape remained unchanged as the temperature of the plate was increased.
Optically probing torsional superelasticity in spider silks
NASA Astrophysics Data System (ADS)
Kumar, Bhupesh; Thakur, Ashish; Panda, Biswajit; Singh, Kamal P.
2013-11-01
We investigate torsion mechanics of various spider silks using a sensitive optical technique. We find that spider silks are torsionally superelastic in that they can reversibly withstand great torsion strains of over 102-3 rotations per cm before failure. Among various silks from a spider, we find the failure twist-strain is greatest in the sticky capture silk followed by dragline and egg-case silk. Our in situ laser-diffraction measurements reveal that torsional strains on the silks induce a nano-scale transverse compression in its diameter that is linear and reversible. These unique torsional properties of the silks could find applications in silk-based materials and devices.
Torsion Profiling of Proteins Using Magnetic Particles
van Reenen, A.; Gutiérrez-Mejía, F.; van IJzendoorn, L.J.; Prins, M.W.J.
2013-01-01
We report a method to profile the torsional spring properties of proteins as a function of the angle of rotation. The torque is applied by superparamagnetic particles and has been calibrated while taking account of the magnetization dynamics of the particles. We record and compare the torsional profiles of single Protein G-Immunoglobulin G (IgG) and IgG-IgG complexes, sandwiched between a substrate and a superparamagnetic particle, for torques in the range between 0.5 × 103 and 5 × 103 pN·nm. Both molecular systems show torsional stiffening for increasing rotation angle, but the elastic and inelastic torsion stiffnesses are remarkably different. We interpret the results in terms of the structural properties of the molecules. The torsion profiling technique opens new dimensions for research on biomolecular characterization and for research on bio-nanomechanical structure-function relationships. PMID:23473490
Optically probing torsional superelasticity in spider silks
Kumar, Bhupesh; Thakur, Ashish; Panda, Biswajit; Singh, Kamal P.
2013-11-11
We investigate torsion mechanics of various spider silks using a sensitive optical technique. We find that spider silks are torsionally superelastic in that they can reversibly withstand great torsion strains of over 10{sup 2−3} rotations per cm before failure. Among various silks from a spider, we find the failure twist-strain is greatest in the sticky capture silk followed by dragline and egg-case silk. Our in situ laser-diffraction measurements reveal that torsional strains on the silks induce a nano-scale transverse compression in its diameter that is linear and reversible. These unique torsional properties of the silks could find applications in silk-based materials and devices.
Radionic Non-Uniform Black Strings
NASA Astrophysics Data System (ADS)
Tamaki, T.; Kanno, S.; Soda, J.
Non-uniform black strings in the two-brane system are investigated using the effective action approach. It is shown that the radion acts as a non-trivial hair of black strings. The stability of solutions is demonstrated using the catastrophe theory. The black strings are shown to be non-uniform.
NASA Technical Reports Server (NTRS)
Green, C.
1971-01-01
Guidelines of the methods and applications used in vibration technology at the MSFC are presented. The purpose of the guidelines is to provide a practical tool for coordination and understanding between industry and government groups concerned with vibration of systems and equipments. Topics covered include measuring, reducing, analyzing, and methods for obtaining simulated environments and formulating vibration specifications. Methods for vibration and shock testing, theoretical aspects of data processing, vibration response analysis, and techniques of designing for vibration are also presented.
Spatial distribution of defects in ultra fine grained copper prepared by high pressure torsion
NASA Astrophysics Data System (ADS)
Čížek, J.; Melikhova, O.; Procházka, I.; Janeček, M.; Hruška, P.; Dobatkin, S.
2016-01-01
Bulk materials with ultra fine grain structure can be fabricated by severe plastic deformation. Among variety of techniques based on severe plastic deformation high pressure torsion is the most efficient method for grain refinement down to nano-scale. In torsion deformation the strain distribution across the sample is non-uniform and increases with increasing radial distance from the centre of the sample corresponding to the axis of torsional straining. Due to this reason it is very important to examine homogeneity of ultra fine grained structure of samples prepared by high pressure torsion. In the present work positron annihilation spectroscopy was employed for mapping of spatial distribution of defects in ultra fine grained copper prepared by high pressure torsion. Spatial distribution of defects was examined by means of (i) Doppler broadening using S parameter for mapping of defect density and (ii) positron lifetime spectroscopy. Spatially resolved positron annihilation studies were combined with mapping by microhardness testing. Hardness is sensitive to dislocation density due to work hardening but is practically not affected by vacancies while positron annihilation is sensitive both to dislocations and vacancies. Our investigations revealed that ultra fine grained copper contains dislocations and vacancy clusters created by agglomeration of deformation-induced vacancies. Average size of vacancy clusters increases with increasing radial distance from the centre of the sample due to higher production rate of vacancies resulting in larger clusters. During high pressure torsion deformation microhardness increases firstly at the periphery of the sample due to the highest imposed strain. With increasing number of high pressure torsion revolutions the hardness increases also in the centre and finally becomes practically uniform across the whole sample indicating the homogeneous distribution of dislocations. Doppler broadening mapping revealed a remarkable increase of
Electronic torsional sound in linear atomic chains: Chemical energy transport at 1000 km/s.
Kurnosov, Arkady A; Rubtsov, Igor V; Maksymov, Andrii O; Burin, Alexander L
2016-07-21
We investigate entirely electronic torsional vibrational modes in linear cumulene chains. The carbon nuclei of a cumulene are positioned along the primary axis so that they can participate only in the transverse and longitudinal motions. However, the interatomic electronic clouds behave as a torsion spring with remarkable torsional stiffness. The collective dynamics of these clouds can be described in terms of electronic vibrational quanta, which we name torsitons. It is shown that the group velocity of the wavepacket of torsitons is much higher than the typical speed of sound, because of the small mass of participating electrons compared to the atomic mass. For the same reason, the maximum energy of the torsitons in cumulenes is as high as a few electronvolts, while the minimum possible energy is evaluated as a few hundred wavenumbers and this minimum is associated with asymmetry of zero point atomic vibrations. Theory predictions are consistent with the time-dependent density functional theory calculations. Molecular systems for experimental evaluation of the predictions are proposed. PMID:27448902
Electronic torsional sound in linear atomic chains: Chemical energy transport at 1000 km/s
NASA Astrophysics Data System (ADS)
Kurnosov, Arkady A.; Rubtsov, Igor V.; Maksymov, Andrii O.; Burin, Alexander L.
2016-07-01
We investigate entirely electronic torsional vibrational modes in linear cumulene chains. The carbon nuclei of a cumulene are positioned along the primary axis so that they can participate only in the transverse and longitudinal motions. However, the interatomic electronic clouds behave as a torsion spring with remarkable torsional stiffness. The collective dynamics of these clouds can be described in terms of electronic vibrational quanta, which we name torsitons. It is shown that the group velocity of the wavepacket of torsitons is much higher than the typical speed of sound, because of the small mass of participating electrons compared to the atomic mass. For the same reason, the maximum energy of the torsitons in cumulenes is as high as a few electronvolts, while the minimum possible energy is evaluated as a few hundred wavenumbers and this minimum is associated with asymmetry of zero point atomic vibrations. Theory predictions are consistent with the time-dependent density functional theory calculations. Molecular systems for experimental evaluation of the predictions are proposed.
Torsional Motion of the Chromophore Catechol following the Absorption of Ultraviolet Light
NASA Astrophysics Data System (ADS)
Young, J. D.; Staniforth, M.; Paterson, M. J.; Stavros, V. G.
2015-06-01
The ability to probe energy flow in molecules, following the absorption of ultraviolet light, is crucial to unraveling photophysical phenomena. Here we excite a coherent superposition of vibrational states in the first excited electronic state (S1 ) in catechol, resulting in a vibrational wave packet. The observed quantum beats, assigned to superpositions of the low-frequency, and strongly mixed, O-H torsional mode τ2 , elegantly demonstrate how changes in geometry upon photoionization from the S1 state to the ground state of the cation (D0 ) enables one to probe energy flow at the very early stages of photoexcitation in this biological chromophore.
Vibrationally mediated photodissociation of hydrogen peroxide
Ticich, T.M.; Likar, M.D.; Duebal, H.; Butler, L.J.; Crim, F.F.
1987-11-15
Vibrationally mediated photodissociation is a means of studying the spectroscopy of bound vibrational overtone states and of probing the electronic photodissociation dynamics of highly vibrationally excited molecules. In these experiments, a highly vibrationally excited hydrogen peroxide molecule prepared by initial excitation in the region of the third (4..nu../sub OH/) or fourth (5..nu../sub OH/) overtone of the OH stretching vibration absorbs an additional photon to dissociate to OH fragments whose individual quantum state populations are measured by laser induced fluorescence. This technique is a means of obtaining excitation spectra for bound highly vibrationally excited states and confirms the accuracy of a model that incorporates the role of the torsional vibration in the vibrational overtone spectroscopy. The photodissociation dynamics of highly vibrationally excited molecules are substantially different from those observed for dissociation by single photons of comparable or greater energy. Approximately 11% of the OH fragments formed in the vibrationally mediated photodissociation through 4..nu../sub OH/ are vibrationally excited as compared to an unobservable amount (less than or equal to2%) in the single photon ultraviolet dissociation.
Torsional fatigue of aramid fibers
Kawabata, S.; Sera, M.
1993-12-31
An experimental investigation on the shear fatigue process of aramid fibers is presented. Repeated cycles of the torsional deformation are applied on the aramid single fiber and the reduction of the shear modulus of the fiber with an increasing number of the cycles is observed for different strain amplitudes. It has been found that the reduction process of the shear modulus with an increasing number of the repeated cycles depends on the strain amplitude and the effect of the number of cycles is equivalent to that of the strain amplitude on the modulus reduction and they may be superposed like the time-temperature equivalence superposition observed in the viscoelasticity of amorphous polymeric solids. From this relation, the life prediction for the long term use of aramid fibers becomes possible by using this superimposed relation. A simple rate process theory is applied to interpret this fatigue process and to derive the equation for predicting the life cycle number of the loading.
Magnetic Torsional Oscillations in Magnetars
Sotani, Hajime; Kokkotas, Kostas D.; Stergioulas, Nikolaos
2009-05-01
We investigate torsional Alfven oscillations of relativistic stars with a global dipole magnetic field, via 2D numerical simulations. We find that a) there exist two families of quasi-periodic oscillations (QPOs) with harmonics at integer multiples of the fundamental frequency, b) the QPOs are long-lived, c) for the chosen form of dipolar magnetic field, the frequency ratio of the lower to upper fundamental QPOs is about 0.6, independent of the equilibrium model or of the strength of the magnetic field, and d) within a representative sample of EOS and of various magnetar masses, the Alfven QPO frequencies are given by accurate empirical relations that depend only on the compactness of the star and on the magnetic field strength. Compared to the observational frequencies, we also obtain an upper limit on the strength of magnetic field of SGR 1806-20 (if is dominated by a dipolar component) between {approx}3 and 7x10{sup 15} Gauss.
Torsional oscillations of strange stars
NASA Astrophysics Data System (ADS)
Mannarelli, Massimo
2014-11-01
Strange stars are one of the hypothetical compact stellar objects that can be formed after a supernova explosion. The existence of these objects relies on the absolute stability of strange collapsed quark matter with respect to standard nuclear matter. We discuss simple models of strange stars with a bare quark matter surface, thus standard nuclear matter is completely absent. In these models an electric dipole layer a few hundreds Fermi thick should exist close to the star surface. Studying the torsional oscillations of the electrically charged layer we estimate the emitted power, finding that it is of the order of 1045 erg/s, meaning that these objects would be among the brightest compact sources in the heavens. The associated relaxation times are very uncertain, with values ranging between microseconds and minutes, depending on the crust thickness. Although part of the radiated power should be absorbed by the electrosphere surrounding the strange star, a sizable fraction of photons should escape and be detectable.
Torsion phenomenology at the CERN LHC
Belyaev, A. S.; Shapiro, I. L.; Vale, M. A. B. do
2007-02-01
We explore the potential of the CERN Large Hadron Collider (LHC) to test the dynamical torsion parameters. The form of the torsion action can be established from the requirements of consistency of effective quantum field theory. The most phenomenologically relevant part of the torsion tensor is dual to a massive axial vector field. This axial vector has geometric nature, that means it does not belong to any representation of the gauge group of the SM extension or GUT theory. At the same time, torsion should interact with all fermions, that opens the way for the phenomenological applications. We demonstrate that LHC collider can establish unique constraints on the interactions between fermions and torsion field considerably exceeding present experimental lower bounds on the torsion couplings and its mass. It is also shown how possible nonuniversal nature of torsion couplings due to the renormalization group running between the Planck and TeV energy scales can be tested via the combined analysis of Drell-Yan and tt production processes.
Euler angles as torsional flat spaces
NASA Astrophysics Data System (ADS)
Trejo-Mandujano, Hector A.
In this work we use general tensor calculus to compare the geodesic equation of motion and Newton's first law for force-free classical systems that are described by an arbitrary number of generalized coordinates in spaces with and without torsion. We choose as objects of study the flat torsional Euler angle metric spaces for rigid rotators. We tested the equivalence of the two motion equations using computational software that allowed algebraic manipulation. The main result is that the equivalence only holds for torsion-free spaces, and for isotropic force-free rotators. We present analytical calculations for the isotropic case and computational results for the general case.
Modification of gravity due to torsion
Nair, V. P.; Nikiforova, V.; Randjbar-Daemi, S.; Rubakov, V.
2010-01-01
Modifications of general relativity have been considered as one of the possible ways of addressing some of the outstanding problems related to the large scale gravitational physics. In this contribution we review some of the recent results which are due to the inclusion of dynamical torsion. More specifically we shall discuss the propagation of massive spin-2 particles in flat and curved space times. We shall show that, contrary to what is generally believed, spinning matter is not the sole source of torsion field. A symmetric energy momentum tensor can also couple to torsion degrees of freedom. The massive and massless spin-2 particles mix giving rise to an infrared modification of gravity.
Observation of coronal loop torsional oscillation
NASA Astrophysics Data System (ADS)
Zaqarashvili, T. V.
2003-02-01
We suggest that the global torsional oscillation of solar coronal loop may be observed by the periodical variation of a spectral line width. The amplitude of the variation must be maximal at the velocity antinodes and minimal at the nodes of the torsional oscillation. Then the spectroscopic observation as a time series at different heights above the active region at the solar limb may allow to determine the period and wavelength of global torsional oscillation and consequently the Alfvén speed in corona. From the analysis of early observation (Egan & Schneeberger \\cite{egan}) we suggest the value of coronal Alfvén speed as ~ 500 km s-1.
Testicular torsion in the older patient
Perry, S.; Hoopingarner, D.; Askins, D.
1983-05-01
A 40-year-old man presented with severe right-sided scrotal pain and was proven to have a 720-degree right testicular torsion. Fewer than 50 documented cases of testicular torsion have been reported in men over the age of thirty. The anatomical predisposition for torsion generally selects these individuals early in life. Rapid diagnosis allowed for surgical correction and testicular salvage. We outline an expedient diagnostic approach for these difficult cases with use of the Doppler ultrasound and the technetium (99mTc) testicular scan.
Nonuniformly-spaced photonic microwave delayline filter.
Dai, Yitang; Yao, Jianping
2008-03-31
A new technique to implement a photonic microwave delay-line filter based on nonuniform tap spacing with arbitrary bandpass response is proposed and experimentally demonstrated. Being different from a regular photonic microwave delay-line filter where the taps are uniformly spaced, the proposed filter in this paper has nonuniformly-spaced taps. The key feature of this technique is that a photonics microwave delay-line filter with arbitrary bandpass response can be realized with only positive taps via nonuniform tap spacing. The use of the proposed technique to implement a flat-top bandpass filter is experimentally demonstrated. PMID:18542568
Vibration isolation mounting system
NASA Technical Reports Server (NTRS)
Carter, Sam D. (Inventor); Bastin, Paul H. (Inventor)
1995-01-01
A system is disclosed for mounting a vibration producing device onto a spacecraft structure and also for isolating the vibration forces thereof from the structure. The system includes a mount on which the device is securely mounted and inner and outer rings. The rings and mount are concentrically positioned. The system includes a base (secured to the structure) and a set of links which are interconnected by a set of torsion bars which allow and resist relative rotational movement therebetween. The set of links are also rotatably connected to a set of brackets which are rigidly connected to the outer ring. Damped leaf springs interconnect the inner and outer rings and the mount allow relative translational movement therebetween in X and Y directions. The links, brackets and base are interconnected and configured so that they allow and resist translational movement of the device in the Z direction so that in combination with the springs they provide absorption of vibrational energy produced by the device in all three dimensions while providing rotational stiffness about all three axes to prevent undesired rotational motions.
Likar, M.D.; Baggott, J.E.; Crim, F.F.
1989-06-01
Vibrationally mediated photodissociation is a two-photon technique for studying the spectroscopy and photodissociation dynamics of highly vibrationally excited molecules. In these experiments, a highly vibrationally excited t-butyl hydroperoxide (t-BuOOH) molecule, prepared by excitation in the region of the third overtone of the O--H stretching vibration (4..nu../sub OH/), absorbs a second photon to dissociate to OH and t-butoxy fragments, and laser induced fluorescence determines the quantum state populations of the OH fragment. Vibrational overtone excitation spectra, obtained by varying the vibrational overtone excitation wavelength while monitoring a single OH rotational state, are nearly identical to photoacoustic spectra. We fit the coarse structure in the vibrational overtone excitation spectrum in the region of the 4..nu../sub OH/ transition and the photoacoustic spectra in the regions of the 5..nu../sub OH/ and 6..nu../sub OH/ transitions using a spectroscopic model of the interaction of the O--H bond stretching vibration with the torsional vibration about the O--O bond. This analysis determines the barrier to internal rotation of the O--H and t-butoxy groups through the trans configuration and its variation with vibrational excitation. The trans barrier in the ground vibrational state is 275 cm/sup -1/ and increases with vibrational excitation to 425, 575, and 680 cm/sup -1/ for t-BuOOH molecules with four, five, and six quanta of O--H stretching excitation, respectively.
Effects of gear box vibration and mass imbalance on the dynamics of multi-stage gear transmissions
NASA Technical Reports Server (NTRS)
Choy, Fred K.; Tu, Yu K.; Zakrajsek, James J.; Townsend, Dennis P.
1991-01-01
The dynamic behavior of multistage gear transmission system, with the effects of gear-box-induced vibrations and rotor mass-imbalances is analyzed. The model method, using undamped frequencies and planar mode shapes, is used to reduce the degree-of-freedom of the system. The various rotor-bearing stages as well as lateral and torsional vibrations of each individual stage are coupled through localized gear-mesh-tooth interactions. Gear-box vibrations are coupled to the gear stage dynamics through bearing support forces. Transient and steady state dynamics of lateral and torsional vibrations of the geared system are examined in both time and frequency domain. A typical three-staged geared system is used as an example. Effects of mass-imbalance and gear box vibrations on the system dynamic behavior are presented in terms of modal excitation functions for both lateral and torsional vibrations. Operational characteristics and conclusions are drawn from the results presented.
Dawadi, Mahesh B; Michael Lindsay, C; Chirokolava, Andrei; Perry, David S; Xu, Li-Hong
2013-03-14
The high-resolution infrared spectrum of methylamine (CH3NH2) has been recorded using slit-jet direct absorption spectroscopy in the ν11 CH-stretch region (2965-3005 cm(-1)) with a resolution of 0.0025 cm(-1). The 621 lines assigned by ground state combination differences represent 27 substates with |K(')| ≤ 2 for the A, B, E1, and E2 symmetries. The spectrum of CH3NH2 is complicated by torsion and inversion tunneling connecting six equivalent minima. The upper states K(') = 0, ± 1 for E1 and E2 are substantially perturbed by "dark" states. The result in the spectrum is multiplets of 2 or 3 states with mixed bright∕dark character. The analysis of the spectrum reveals two qualitative differences in the energy level pattern relative to the vibrational ground state and relative to available data on the lower frequency vibrations (NH2 wag and CN stretch). First at J(') = 0, there is a different ordering of the levels connected by torsion-inversion tunneling. Second, the low-J splittings indicative of torsion-rotation coupling are greatly reduced in the ν11 excited state relative to the vibrational ground state for both the E1 and E2 species, suggesting the partial suppression of torsional tunneling in the ν11 CH-stretch excited state. PMID:23514487
Nonuniform piezoelectric circular plate flexural transducers with underwater applications.
Aronov, Boris S
2015-09-01
An analytical treatment is presented for circular flexural plate transducers that have nonuniform electromechanically active-passive mechanical systems with particular interest in underwater applications. The analysis is made using the energy method that was previously applied to calculating parameters of uniform fully active (bimorph) circular plate transducers [B. S. Aronov, J. Acoust. Soc. Am. 118(2), 627-637 (2005)]. It is shown that the vibration mode shapes remain sufficiently similar to those for uniform plates for a large range of relative dimensions of active and passive laminates of radially nonuniform mechanical systems, and they may be used for calculating transducer parameters. Therefore the transducers can be considered as having a single degree of freedom, and their operational characteristics can be determined using the same technique as previously used for uniform plates. Dependences of the resonance frequencies, effective coupling coefficients, and parameters of the equivalent electromechanical circuit on relative dimensions of active and passive laminates for several combinations of the active and passive materials are presented and compared with those parameters of uniform plates having the same overall dimensions. The results of experimental verification are in good agreement with theoretical predictions. PMID:26428794
Torsion-induced effects in magnetic nanowires
NASA Astrophysics Data System (ADS)
Sheka, Denis D.; Kravchuk, Volodymyr P.; Yershov, Kostiantyn V.; Gaididei, Yuri
2015-08-01
A magnetic helix wire is one of the simplest magnetic systems which manifests properties of both curvature and torsion. Possible equilibrium magnetization states in the helix wire with different anisotropy directions are studied theoretically. There exist two equilibrium states in the helix wire with easy-tangential anisotropy: a quasitangential magnetization distribution in the case of relatively small curvatures and torsions, and an onion state in the opposite case. The curvature and torsion also essentially influence the spin-wave dynamics in the helix wire, acting as an effective magnetic field. Originated from a geometry-induced effective Dzyaloshinskii interaction, this magnetic field leads to a coupling between the helix chirality and the magnetochirality and breaks mirror symmetry in the spin-wave spectrum: the modification of magnon dispersion relation is linear with respect to the torsion and quadratic with respect to the curvature. All analytical predictions on magnetization statics and dynamics are well confirmed by direct spin-lattice simulations.
Sensitivity of nonuniform sampling NMR.
Palmer, Melissa R; Suiter, Christopher L; Henry, Geneive E; Rovnyak, James; Hoch, Jeffrey C; Polenova, Tatyana; Rovnyak, David
2015-06-01
Many information-rich multidimensional experiments in nuclear magnetic resonance spectroscopy can benefit from a signal-to-noise ratio (SNR) enhancement of up to about 2-fold if a decaying signal in an indirect dimension is sampled with nonconsecutive increments, termed nonuniform sampling (NUS). This work provides formal theoretical results and applications to resolve major questions about the scope of the NUS enhancement. First, we introduce the NUS Sensitivity Theorem in which any decreasing sampling density applied to any exponentially decaying signal always results in higher sensitivity (SNR per square root of measurement time) than uniform sampling (US). Several cases will illustrate this theorem and show that even conservative applications of NUS improve sensitivity by useful amounts. Next, we turn to a serious limitation of uniform sampling: the SNR by US decreases for extending evolution times, and thus total experimental times, beyond 1.26T2 (T2 = signal decay constant). Thus, SNR and resolution cannot be simultaneously improved by extending US beyond 1.26T2. We find that NUS can eliminate this constraint, and we introduce the matched NUS SNR Theorem: an exponential sampling density matched to the signal decay always improves the SNR with additional evolution time. Though proved for a specific case, broader classes of NUS densities also improve SNR with evolution time. Applications of these theoretical results are given for a soluble plant natural product and a solid tripeptide (u-(13)C,(15)N-MLF). These formal results clearly demonstrate the inadequacies of applying US to decaying signals in indirect nD-NMR dimensions, supporting a broader adoption of NUS. PMID:25901905
CORRECTION FOR NONUNIFORM MIXING IN INDOOR MICROENVIRONMENTS
The modelling of the indoor concentration distribution produced by sources and sinks of pollutants is complicated by nonuniform mixing within the indoor settings. wo common approaches to predicting the concentration distribution are to either treat the indoor volume as containing...
Theory of twisted nonuniformly heated bars
NASA Technical Reports Server (NTRS)
Shorr, B. F.
1980-01-01
Nonlineary distributed stresses in twisted nonuniformly heated bars of arbitrary cross section are calculated taking into account various elasticity parameters. The approximate theory is shown to be sufficiently general and accurate by comparison with experimental data.
NASA Astrophysics Data System (ADS)
Kim, Young-Cheol; Lee, D. H.; Chung, T. Y.; Ham, D. Y.; Kim, Y. B.
A torsional tuned damper is usually used in order to reduce the torsional vibration of the crank shaft system in marine diesel engines. The damper consists of leaf springs, fluid chambers, fluid channels, and intermediate masses. The leaf springs provide the stiffening force to the shaft system, and the fluid chambers and channels give the damping force. In this paper, FSI (fluid-structure interaction) analysis by using FEM is carried out for the calculation of the stiffness and damping coefficients of the designed damper. The numerical calculation result about the equivalent damping coefficients is compared to the value obtained from a simple damping simulation model.
Dynamics of Multistage Gear Transmission with Effects of Gearbox Vibrations
NASA Technical Reports Server (NTRS)
Choy, F. K.; Tu, Y. K.; Zakrajsek, J. J.; Townsend, Dennis P.
1990-01-01
A comprehensive approach is presented in analyzing the dynamic behavior of multistage gear transmission systems with the effects of gearbox induced vibrations and mass imbalances of the rotor. The modal method, with undamped frequencies and planar mode shapes, is used to reduce the degrees of freedom of the gear system for time-transient dynamic analysis. Both the lateral and torsional vibration modes of each rotor-bearing-gear stage as well as the interstage vibrational characteristics are coupled together through localized gear mesh tooth interactions. In addition, gearbox vibrations are also coupled to the rotor-bearing-gear system dynamics through bearing support forces between the rotor and the gearbox. Transient and steady state dynamics of lateral and torsional vibrations of the geared system are examined in both time and frequency domains to develop interpretations of the overall modal dynamic characteristics under various operating conditions. A typical three-stage geared system is used as an example. Effects of mass imbalance and gearbox vibrations on the system dynamic behavior are presented in terms of modal excitation functions for both lateral and torsional vibrations. Operational characteristics and conclusions are drawn from the results presented.
Torsion and buckling of open sections
NASA Technical Reports Server (NTRS)
Wagner, Herbert
1936-01-01
In this paper is a discussion of the general principles for open sections of any shape. In what follows the torsion will be computed and on the basis of the results it will be possible to obtain a proper design of section in each case. The torsion of buckling members for the case where they are centrally loaded, leads to a problem in pure stability and is similar to that of stressed beams.
Flow in a torsionally oscillating filled cylinder
NASA Technical Reports Server (NTRS)
Schafer, C. F.
1983-01-01
The flow of a liquid in a completely filled cylinder undergoing torsional oscillations about its longitudinal symmetry axis was studied analytically and experimentally. The objective of the studies was to determine the efficacy of the torsional oscillations in mixing the confined liquid. Flow was found to be confined primarily to toroidal cells at the ends of the cylinder. Cell thickness was about equal to the cylinder radius. The use of baffles at the end walls was shown to enhance the mixing process.
Torsional Stability of Aluminum Alloy Seamless Tubing
NASA Technical Reports Server (NTRS)
Moore, R L; Paul, D A
1939-01-01
Torsion tests were made on 51ST aluminum-alloy seamless tubes having diameter-to-thickness ratios of from 77 to 139 and length-to-diameter ratios of from 1 to 60. The torsional strengths developed in the tubes which failed elastically (all tubes having lengths greater than 2 to 6 times the diameter) were in most cases within 10 percent of the value indicated by the theories of Donnel, Timoshenko, and Sturm, assuming a condition of simply supported ends.
Exact solutions for coupled free vibrations of tapered shear-flexible thin-walled composite beams
NASA Astrophysics Data System (ADS)
Piovan, Marcelo T.; Filipich, Carlos P.; Cortínez, Víctor H.
2008-09-01
In this paper, analytical solutions for the free vibration analysis of tapered thin-walled laminated-composite beams with both closed and open cross-sections are developed. The present study is based on a recently developed model that incorporates in a full form the shear flexibility. The model considers shear flexibility due to bending as well as warping related to non-uniform torsion. The theory is briefly reviewed with the aim to present the equilibrium equations, the related boundary conditions and the constitutive equations. The stacking sequences in the panels of the cross-sections are selected in order to behave according to certain elastic coupling features. Typical laminations for a box-beam such as circumferentially uniform stiffness (CUS) or circumferentially asymmetric stiffness (CAS) configurations are adopted. For open cross-sections, special laminations behaving elastically like the CAS and CUS configurations of closed sections are also taken into account. The exact values (i.e. with arbitrary precision) of frequencies are obtained by means of a generalized power series methodology. A recurrence scheme is introduced with the aim to simplify the algebraic manipulation by shrinking the number of unknown variables. A parametric analysis for different taper ratios, slenderness ratios and stacking sequences is performed. Numerical examples are also carried out focusing attention in the validation of the present theory with respect to 2D FEM computational approaches, as well as to serve as quality test and convergence test of former finite elements schemes.
Perturbation Theory for Superfluid in Nonuniform Potential
NASA Astrophysics Data System (ADS)
Koshida, Shinji; Kato, Yusuke
2016-05-01
Perturbation theory of superfluid fraction in terms of nonuniform potential is constructed. We find that the coefficient of the leading term is determined by the dynamical structure factor or density fluctuation of the system. The results for the ideal Bose gas and the interacting Bose system with linear dispersion are consistent to implications from Landau's criterion. We also find that the superfluidity of Tomonaga-Luttinger liquid with K>2 is shown to be stable against nonuniform potential.
Attentional Modulation of Eye Torsion Responses
NASA Technical Reports Server (NTRS)
Stevenson, Scott B.; Mahadevan, Madhumitha S.; Mulligan, Jeffrey B.
2016-01-01
Eye movements generally have both reflexive and voluntary aspects, but torsional eye movements are usually thought of as a reflexive response to image rotation around the line of sight (torsional OKN) or to head roll (torsional VOR). In this study we asked whether torsional responses could be modulated by attention in a case where two stimuli rotated independently, and whether attention would influence the latency of responses. The display consisted of rear-projected radial "pinwheel" gratings, with an inner annulus segment extending from the center to 22 degrees eccentricity, and an outer annulus segment extending from 22 degrees out to 45 degrees eccentricity. The two segments rotated around the center in independent random walks, stepping randomly 4 degrees clockwise or counterclockwise at 60 Hz. Subjects were asked to attend to one or the other while keeping fixation steady at the center of the display. To encourage attention on one or the other segment of the display, subjects were asked to move a joystick in synchrony with the back and forth rotations of one part of the image while ignoring the other. Eye torsion was recorded with the scleral search coil technique, sampled at 500 Hz. All four subjects showed roughly 50% stronger torsion responses to the attended compared to unattended segments. Latency varied from 100 to 150 msec across subjects and was unchanged by attention. These findings suggest that attention can influence eye movement responses that are not typically under voluntary control.
Williamson, M.M.; Pratt, G.A.
1999-06-08
The invention provides an elastic actuator consisting of a motor and a motor drive transmission connected at an output of the motor. An elastic element is connected in series with the motor drive transmission, and this elastic element is positioned to alone support the full weight of any load connected at an output of the actuator. A single force transducer is positioned at a point between a mount for the motor and an output of the actuator. This force transducer generates a force signal, based on deflection of the elastic element, that indicates force applied by the elastic element to an output of the actuator. An active feedback force control loop is connected between the force transducer and the motor for controlling the motor. This motor control is based on the force signal to deflect the elastic element an amount that produces a desired actuator output force. The produced output force is substantially independent of load motion. The invention also provides a torsional spring consisting of a flexible structure having at least three flat sections each connected integrally with and extending radially from a central section. Each flat section extends axially along the central section from a distal end of the central section to a proximal end of the central section. 30 figs.
Williamson, Matthew M.; Pratt, Gill A.
1999-06-08
The invention provides an elastic actuator consisting of a motor and a motor drive transmission connected at an output of the motor. An elastic element is connected in series with the motor drive transmission, and this elastic element is positioned to alone support the full weight of any load connected at an output of the actuator. A single force transducer is positioned at a point between a mount for the motor and an output of the actuator. This force transducer generates a force signal, based on deflection of the elastic element, that indicates force applied by the elastic element to an output of the actuator. An active feedback force control loop is connected between the force transducer and the motor for controlling the motor. This motor control is based on the force signal to deflect the elastic element an amount that produces a desired actuator output force. The produced output force is substantially independent of load motion. The invention also provides a torsional spring consisting of a flexible structure having at least three flat sections each connected integrally with and extending radially from a central section. Each flat section extends axially along the central section from a distal end of the central section to a proximal end of the central section.
Vibration damping with active carbon fiber structures
NASA Astrophysics Data System (ADS)
Neugebauer, Reimund; Kunze, Holger; Riedel, Mathias; Roscher, Hans-Jürgen
2007-04-01
This paper presents a mechatronic strategy for active reduction of vibrations on machine tool struts or car shafts. The active structure is built from a carbon fiber composite with embedded piezofiber actuators that are composed of piezopatches based on the Macro Fiber Composite (MFC) technology, licensed by NASA and produced by Smart Material GmbH in Dresden, Germany. The structure of these actuators allows separate or selectively combined bending and torsion, meaning that both bending and torsion vibrations can be actively absorbed. Initial simulation work was done with a finite element model (ANSYS). This paper describes how state space models are generated out of a structure based on the finite element model and how controller codes are integrated into finite element models for transient analysis and the model-based control design. Finally, it showcases initial experimental findings and provides an outlook for damping multi-mode resonances with a parallel combination of resonant controllers.
Investigation of vibrations of working elements of a two coordinate scanner
NASA Technical Reports Server (NTRS)
Kumpikas, K. L.
1973-01-01
Radial and axial vibration measurements on the scanning disk and the data storage board of an optical-mechanical scanner are evaluated. Statistical processing of the observational data establishes the excitation source and determines the effect of disk torsional vibrations on the data storage board.
Torsional system parameter identification of internal combustion engines under normal operation
NASA Astrophysics Data System (ADS)
Östman, Fredrik; Toivonen, Hannu T.
2011-05-01
For internal combustion engines, lumped-mass models of the crankshaft system are frequently used for torque estimation in control and diagnostic applications, such as cylinder balancing and misfire detection. Due to inherent model uncertainties and changing system dynamics it may be necessary to adapt the model parameters from time to time in order to preserve the required model accuracy. In this paper a frequency-domain method for on-line identification of the parameters describing the torsional dynamics of internal combustion engines is presented. In the proposed method, the engine is excited by adjusting the cylinder-wise injected fuel amounts, and the measured responses in torsional vibration frequency components are used for parameter estimation. As the fuel-injection adjustments can be determined in such a way that the net indicated torque is unaffected, the identification can be performed on-line without disturbing normal engine operation. The procedure can be applied to estimate the torsional stiffness and damping parameters of the flexible coupling connecting the engine and the load. In addition, the gains which describe how the cylinder-wise fuel injections affect the amplitudes of relevant torsional vibratory frequency components are obtained. The parameter identification method is successfully evaluated in full-scale engine tests on a 6.6 MW six-cylinder medium-speed common-rail diesel engine.
Tsujino, J; Ihara, S; Harada, Y; Kasahara, K; Sakamaki, N
2004-04-01
Welding characteristic of thin coated copper wires were studied using 40, 60, 100 kHz ultrasonic complex vibration welding equipments with elliptical to circular vibration locus. The complex vibration systems consisted of a longitudinal-torsional vibration converter and a driving longitudinal vibration system. Polyurethane coated copper wires of 0.036 mm outer diameter and copper plates of 0.3 mm thickness and the other dimension wires were used as welding specimens. The copper wire part is completely welded on the copper substrate and the insulated coating material is driven from welded area to outsides of the wire specimens by high frequency complex vibration. PMID:15047272
Strong field coherent control of molecular torsions--Analytical models.
Ashwell, Benjamin A; Ramakrishna, S; Seideman, Tamar
2015-08-14
We introduce analytical models of torsional alignment by moderately intense laser pulses that are applicable to the limiting cases of the torsional barrier heights. Using these models, we explore in detail the role that the laser intensity and pulse duration play in coherent torsional dynamics, addressing both experimental and theoretical concerns. Our results suggest strategies for minimizing the risk of off-resonant ionization, noting the qualitative differences between the case of torsional alignment subject to a field-free torsional barrier and that of torsional alignment of a barrier-less system (equivalent to a 2D rigid rotor). We also investigate several interesting torsional phenomena, including the onset of impulsive alignment of torsions, field-driven oscillations in quantum number space, and the disappearance of an alignment upper bound observed for a rigid rotor in the impulsive torsional alignment limit. PMID:26277138
Dai, Zuyang; Gao, Shuming; Wang, Jia; Mo, Yuxiang
2014-10-14
The torsional energy levels of CH{sub 3}OH{sup +}, CH{sub 3}OD{sup +}, and CD{sub 3}OD{sup +} have been determined for the first time using one-photon zero kinetic energy photoelectron spectroscopy. The adiabatic ionization energies for CH{sub 3}OH, CH{sub 3}OD, and CD{sub 3}OD are determined as 10.8396, 10.8455, and 10.8732 eV with uncertainties of 0.0005 eV, respectively. Theoretical calculations have also been performed to obtain the torsional energy levels for the three isotopologues using a one-dimensional model with approximate zero-point energy corrections of the torsional potential energy curves. The calculated values are in good agreement with the experimental data. The barrier height of the torsional potential energy without zero-point energy correction was calculated as 157 cm{sup −1}, which is about half of that of the neutral (340 cm{sup −1}). The calculations showed that the cation has eclipsed conformation at the energy minimum and staggered one at the saddle point, which is the opposite of what is observed in the neutral molecule. The fundamental C–O stretch vibrational energy level for CD{sub 3}OD{sup +} has also been determined. The energy levels for the combinational excitation of the torsional vibration and the fundamental C–O stretch vibration indicate a strong torsion-vibration coupling.
Torsional oscillations in dynamo simulations
NASA Astrophysics Data System (ADS)
Wicht, Johannes; Christensen, Ulrich R.
2010-06-01
Cylinders aligned with the planetary rotation axis have a special significance in the dynamics of planetary dynamo regions. The azimuthal Lorentz forces on these geostrophic cylinders is expected to cancel to a large degree, establishing the so-called Taylor state. Deviations from this state take the form of torsional oscillations (TOs) that are supposed to represent important fast flow variations. These oscillations have reportedly been identified in the secular variation signal from the top of Earth's core. We have performed several dynamo simulations at different parameters to check whether Taylor state and TOs can also be identified in a numerical model. Taylor states are approached when viscous effects are small at Ekman numbers of E = 3 × 10-5 or below and Reynolds stresses are kept low by choosing moderate Rayleigh numbers. One-dimensional magnetic Alfvén waves that travel towards the boundaries then become prominent in the motion of the geostrophic cylinders. These waves obey the TO theory but are also damped and modified by other effects. For example, fast variations of likely convective origin remain important in all our simulations. Reynolds stresses may play a more sizable role for the dynamics in Earth's dynamo region than commonly assumed. They may also contribute to the motions of geostrophic cylinders and severely reduce the significance of TOs for the fast core dynamics. The amplitude of TOs amounts to not more than a few percent of the total flow amplitude in the simulations, which renders these motions insignificant for the long-term dynamo process.
Vibrational frequencies and structural determination of tetrafluoroformaldazine.
Jensen, James O
2004-09-01
The normal mode frequencies and corresponding vibrational assignments of tetrafluoroformaldazine (F(2)CNNCF(2)) are examined theoretically using the Gaussian98 set of quantum chemistry codes. Each of the vibrational modes was assigned to one of nine types of motion predicted by a group theoretical analysis (C-F stretch, C[triple bond]N stretch, N-N stretch, C=C-N bend, CF(2) wag, CF(2) rock CF(2) scissors, CF(2) twist, and C=N-N=C torsion) utilizing the C(2h) symmetry of the molecule. Uniform scaling factors was derived for each type of motion. Predicted infrared and Raman intensities are reported. PMID:15294242
An ALMA Imaging Study of Methyl Formate (HCOOCH3) in Torsionally Excited States toward Orion KL
NASA Astrophysics Data System (ADS)
Sakai, Yusuke; Kobayashi, Kaori; Hirota, Tomoya
2015-04-01
We recently reported the first identification of rotational transitions of methyl formate (HCOOCH3) in the second torsionally excited state toward Orion Kleinmann-Low (KL), observed with the Nobeyama 45 m telescope. In combination with the identified transitions of methyl formate in the ground state and the first torsional excited state, it was found that there is a difference in rotational temperature and vibrational temperature, where the latter is higher. In this study, high spatial resolution analysis by using Atacama Large Millimeter/Submillimeter Array (ALMA) science verification data was carried out to verify and understand this difference. Toward the Compact Ridge, two different velocity components at 7.3 and 9.1 km s-1 were confirmed, while a single component at 7.3 km s-1 was identified toward the Hot Core. The intensity maps in the ground, first, and second torsional excited states have quite similar distributions. Using extensive ALMA data, we determined the rotational and vibrational temperatures for the Compact Ridge and Hot Core by the conventional rotation diagram method. The rotational temperature and vibrational temperatures agree for the Hot Core and for one component of the Compact Ridge. At the 7.3 km s-1 velocity component for the Compact Ridge, the rotational temperature was found to be higher than the vibrational temperature. This is different from what we obtained from the results by using the single-dish observation. The difference might be explained by the beam dilution effect of the single-dish data and/or the smaller number of observed transitions within the limited range of energy levels (≤30 K) of Eu in the previous study.
A dual adaptive tunable vibration absorber using MREs for vehicle powertrain vibration control
NASA Astrophysics Data System (ADS)
Hoang, N.; Zhang, N.; Du, H.
2010-04-01
This paper presents a dual Adaptive Tuned Vibration Absorber (ATVA) using a magnetorheological elastomer (MRE) for powertrain torsional vibration control. The MRE used in this device is a soft MRE with a significant MR effect. By using the MRE, the ATVA can work in a wide frequency range. In this paper, the dual ATVA is proposed rather than a single ATVA because a single ATVA, at a fixed location, cannot deal with resonances happening to several powertrain vibration modes. Also, the dual ATVA concept design is presented to validate its effectiveness. In addition the soft MRE shear modulus is approximated by a polynomial of magnetic flux intensity B and the approximation was experimentally validated. The simulation results showed that with the ATVA, powertrain vibration response is significantly suppressed. Furthermore, the effect of the dual ATVA parameters such as inertia moment, stiffness and damping coefficients and ATVA locations were examined. The dual ATVA will be useful device for powertrain vibration suppression.
An analytical model of a longitudinal-torsional ultrasonic transducer
NASA Astrophysics Data System (ADS)
Al-Budairi, Hassan; Lucas, Margaret
2012-08-01
The combination of longitudinal and torsional (LT) vibrations at high frequencies finds many applications such as ultrasonic drilling, ultrasonic welding, and ultrasonic motors. The LT mode can be obtained by modifications to the design of a standard bolted Langevin ultrasonic transducer driven by an axially poled piezoceramic stack, by a technique that degenerates the longitudinal mode to an LT motion by a geometrical alteration of the wave path. The transducer design is developed and optimised through numerical modelling which can represent the geometry and mechanical properties of the transducer and its vibration response to an electrical input applied across the piezoceramic stack. However, although these models can allow accurate descriptions of the mechanical behaviour, they do not generally provide adequate insights into the electrical characteristics of the transducer. In this work, an analytical model is developed to present the LT transducer based on the equivalent circuit method. This model can represent both the mechanical and electrical aspects and is used to extract many of the design parameters, such as resonance and anti-resonance frequencies, the impedance spectra and the coupling coefficient of the transducer. The validity of the analytical model is demonstrated by close agreement with experimental results.
Endodontic instruments after torsional failure: nanoindentation test.
Jamleh, Ahmed; Sadr, Alireza; Nomura, Naoyuki; Ebihara, Arata; Yahata, Yoshio; Hanawa, Takao; Tagami, Junji; Suda, Hideaki
2014-01-01
This study aimed to evaluate effects of torsional loading on the mechanical properties of endodontic instruments using the nanoindentation technique. ProFile (PF; size 30, taper 04; Dentsply Maillefer, Switzerland) and stainless steel (SS; size 30, taper 02; Mani, Japan) instruments were subjected to torsional test. Nanoindentation was then performed adjacent to the edge of fracture (edge) and at the cutting part beside the shank (shank). Hardness and elastic modulus were measured under 100-mN force on 100 locations at each region, and compared to those obtained from the same regions on new instruments. It showed that PF and SS instruments failed at 559 ± 67 and 596 ± 73 rotation degrees and mean maximum torque of 0.90 ± 0.07 and 0.99 ± 0.05 N-cm, respectively. Hardness and elastic modulus ranged 4.8-6.7 and 118-339 GPa in SS, and 2.7-3.2 and 52-81 GPa in PF. Significant differences between torsion-fractured and new instruments in hardness and elastic modulus were detected in the SS system used. While in PF system, the edge region after torsional fracture had significantly lower hardness and elastic modulus compared to new instruments. The local hardness and modulus of elasticity of endodontic instruments adjacent to the fracture edge are significantly reduced by torsional loading. PMID:24610598
Torsion-Mediated Interaction between Adjacent Genes
Meyer, Sam; Beslon, Guillaume
2014-01-01
DNA torsional stress is generated by virtually all biomolecular processes involving the double helix, in particular transcription where a significant level of stress propagates over several kilobases. If another promoter is located in this range, this stress may strongly modify its opening properties, and hence facilitate or hinder its transcription. This mechanism implies that transcribed genes distant of a few kilobases are not independent, but coupled by torsional stress, an effect for which we propose the first quantitative and systematic model. In contrast to previously proposed mechanisms of transcriptional interference, the suggested coupling is not mediated by the transcription machineries, but results from the universal mechanical features of the double-helix. The model shows that the effect likely affects prokaryotes as well as eukaryotes, but with different consequences owing to their different basal levels of torsion. It also depends crucially on the relative orientation of the genes, enhancing the expression of eukaryotic divergent pairs while reducing that of prokaryotic convergent ones. To test the in vivo influence of the torsional coupling, we analyze the expression of isolated gene pairs in the Drosophila melanogaster genome. Their orientation and distance dependence is fully consistent with the model, suggesting that torsional gene coupling may constitute a widespread mechanism of (co)regulation in eukaryotes. PMID:25188032
Vibration signature analysis of multistage gear transmission
NASA Technical Reports Server (NTRS)
Choy, F. K.; Tu, Y. K.; Savage, M.; Townsend, D. P.
1989-01-01
An analysis is presented for multistage multimesh gear transmission systems. The analysis predicts the overall system dynamics and the transmissibility to the gear box or the enclosed structure. The modal synthesis approach of the analysis treats the uncoupled lateral/torsional model characteristics of each stage or component independently. The vibration signature analysis evaluates the global dynamics coupling in the system. The method synthesizes the interaction of each modal component or stage with the nonlinear gear mesh dynamics and the modal support geometry characteristics. The analysis simulates transient and steady state vibration events to determine the resulting torque variations, speeds, changes, rotor imbalances, and support gear box motion excitations. A vibration signature analysis examines the overall dynamic characteristics of the system, and the individual model component responses. The gear box vibration analysis also examines the spectral characteristics of the support system.
Li, Zhijie; Wang, Shengjie; Wang, Zhiguo; Zu, Xiaotao T.; Gao, Fei; Weber, William J.
2010-07-01
The mechanical behavior of twinned silicon carbide (SiC) nanowires under combined tension-torsion and compression-torsion is investigated using molecular dynamics simulations with an empirical potential. The simulation results show that both the tensile failure stress and buckling stress decrease under combined tension-torsional and combined compression-torsional strain, and they decrease with increasing torsional rate under combined loading. The torsion rate has no effect on the elastic properties of the twinned SiC nanowires. The collapse of the twinned nanowires takes place in a twin stacking fault of the nanowires.
Nonuniform depth grids in parabolic equation solutions.
Sanders, William M; Collins, Michael D
2013-04-01
The parabolic wave equation is solved using a finite-difference solution in depth that involves a nonuniform grid. The depth operator is discretized using Galerkin's method with asymmetric hat functions. Examples are presented to illustrate that this approach can be used to improve efficiency for problems in ocean acoustics and seismo-acoustics. For shallow water problems, accuracy is sensitive to the precise placement of the ocean bottom interface. This issue is often addressed with the inefficient approach of using a fine grid spacing over all depth. Efficiency may be improved by using a relatively coarse grid with nonuniform sampling to precisely position the interface. Efficiency may also be improved by reducing the sampling in the sediment and in an absorbing layer that is used to truncate the computational domain. Nonuniform sampling may also be used to improve the implementation of a single-scattering approximation for sloping fluid-solid interfaces. PMID:23556565
Properties of multilayer nonuniform holographic structures
Pen, E F; Rodionov, Mikhail Yu
2010-12-09
Experimental results and analysis of properties of multilayer nonuniform holographic structures formed in photopolymer materials are presented. The theoretical hypotheses is proved that the characteristics of angular selectivity for the considered structures have a set of local maxima, whose number and width are determined by the thicknesses of intermediate layers and deep holograms and that the envelope of the maxima coincides with the selectivity contour of a single holographic array. It is also experimentally shown that hologram nonuniformities substantially distort shapes of selectivity characteristics: they become asymmetric, the local maxima differ in size and the depths of local minima reduce. The modelling results are made similar to experimental data by appropriately choosing the nonuniformity parameters. (imaging and image processing. holography)
Subrandom methods for multidimensional nonuniform sampling.
Worley, Bradley
2016-08-01
Methods of nonuniform sampling that utilize pseudorandom number sequences to select points from a weighted Nyquist grid are commonplace in biomolecular NMR studies, due to the beneficial incoherence introduced by pseudorandom sampling. However, these methods require the specification of a non-arbitrary seed number in order to initialize a pseudorandom number generator. Because the performance of pseudorandom sampling schedules can substantially vary based on seed number, this can complicate the task of routine data collection. Approaches such as jittered sampling and stochastic gap sampling are effective at reducing random seed dependence of nonuniform sampling schedules, but still require the specification of a seed number. This work formalizes the use of subrandom number sequences in nonuniform sampling as a means of seed-independent sampling, and compares the performance of three subrandom methods to their pseudorandom counterparts using commonly applied schedule performance metrics. Reconstruction results using experimental datasets are also provided to validate claims made using these performance metrics. PMID:27301071
Subrandom methods for multidimensional nonuniform sampling
NASA Astrophysics Data System (ADS)
Worley, Bradley
2016-08-01
Methods of nonuniform sampling that utilize pseudorandom number sequences to select points from a weighted Nyquist grid are commonplace in biomolecular NMR studies, due to the beneficial incoherence introduced by pseudorandom sampling. However, these methods require the specification of a non-arbitrary seed number in order to initialize a pseudorandom number generator. Because the performance of pseudorandom sampling schedules can substantially vary based on seed number, this can complicate the task of routine data collection. Approaches such as jittered sampling and stochastic gap sampling are effective at reducing random seed dependence of nonuniform sampling schedules, but still require the specification of a seed number. This work formalizes the use of subrandom number sequences in nonuniform sampling as a means of seed-independent sampling, and compares the performance of three subrandom methods to their pseudorandom counterparts using commonly applied schedule performance metrics. Reconstruction results using experimental datasets are also provided to validate claims made using these performance metrics.
Aeroelastic considerations for torsionally soft rotors
NASA Technical Reports Server (NTRS)
Mantay, W. R.; Yeager, W. T., Jr.
1985-01-01
A research study was initiated to systematically determine the impact of selected blade tip geometric parameters on conformable rotor performance and loads characteristics. The model articulated rotors included baseline and torsionally soft blades with interchangeable tips. Seven blade tip designs were evaluated on the baseline rotor and six tip designs were tested on the torsionally soft blades. The designs incorporated a systemmatic variation in geometric parameters including sweep, taper, and anhedral. The rotors were evaluated in the NASA Langley Transonic Dynamics Tunnel at several advance ratios, lift and propulsive force values, and tip Mach numbers. A track sensitivity study was also conducted at several advance ratios for both rotors. Based on the test results, tip parameter variations generated significant rotor performance and loads differences for both baseline and torsionally soft blades.
Surgical correction of torsion of the penis.
Azmy, A; Eckstein, H B
1981-08-01
Torsion of the penis is a rare anomaly, believed to be due to abnormal skin attachment and not to any structural abnormality of the corpora. The rotation is usually to the left in a counter-clockwise fashion. The urethral meatus is placed in a oblique position and the median raphe makes a spiral curve from the base of the penis towards the meatus. Three boys with congenital torsion of the penis are reported. A corrective operative for this condition is described. Penile torsion was first described by Verneuil in 1857, but in the past no operative correction was recommended, since attempts to move the skin around were believed not to correct the spiral alignment of the corpora cavernosa. PMID:7260553
Potentials in a nonuniform quantum dusty magnetoplasma
Salimullah, M.; Zeba, I.; Uzma, Ch.; Jamil, M.
2009-03-15
Using the quantum hydrodynamic model for quantum magnetoplasmas, the Shukla-Nambu-Salimullah shielding potential and the far-field dynamical wake potential in a quantum dusty plasma with a nonuniform density and ambient static magnetic field have been investigated in detail. The short-range screening potential different from the symmetric Debye-Hueckel potential and the long-range oscillatory wake potential are found to be significantly affected by the nonuniformities in the density and the static magnetic field. The far-field oscillatory wake-field potential can explain attraction among the same polarity charges leading to the possible ordered structures or coagulation in the inhomogeneous quantum dusty magnetoplasma.
NASA Astrophysics Data System (ADS)
Krak, Michael D.; Dreyer, Jason T.; Singh, Rajendra
2016-03-01
A vehicle clutch damper is intentionally designed to contain multiple discontinuous non-linearities, such as multi-staged springs, clearances, pre-loads, and multi-staged friction elements. The main purpose of this practical torsional device is to transmit a wide range of torque while isolating torsional vibration between an engine and transmission. Improved understanding of the dynamic behavior of the device could be facilitated by laboratory measurement, and thus a refined vibratory experiment is proposed. The experiment is conceptually described as a single degree of freedom non-linear torsional system that is excited by an external step torque. The single torsional inertia (consisting of a shaft and torsion arm) is coupled to ground through parallel production clutch dampers, which are characterized by quasi-static measurements provided by the manufacturer. Other experimental objectives address physical dimensions, system actuation, flexural modes, instrumentation, and signal processing issues. Typical measurements show that the step response of the device is characterized by three distinct non-linear regimes (double-sided impact, single-sided impact, and no-impact). Each regime is directly related to the non-linear features of the device and can be described by peak angular acceleration values. Predictions of a simplified single degree of freedom non-linear model verify that the experiment performs well and as designed. Accordingly, the benchmark measurements could be utilized to validate non-linear models and simulation codes, as well as characterize dynamic parameters of the device including its dissipative properties.
THE MICROWAVE SPECTROSCOPY OF METHYL FORMATE IN THE SECOND TORSIONAL EXCITED STATE
Kobayashi, Kaori; Takamura, Kazunori; Sakai, Yusuke; Tsunekawa, Shozo; Odashima, Hitoshi; Ohashi, Nobukimi
2013-03-01
The cis-methyl formate molecule is a well known molecule found in interstellar space. Recently, rotational lines of methyl formate in the first CH{sub 3} torsional excited state were observed in Orion KL and W51e2. It is quite natural to observe methyl formate in even higher vibrational states considering the temperature estimated in Orion KL and W51e2. Maeda et al. reported results on the laboratory spectroscopy of methyl formate including the spectral analysis in its second CH{sub 3} torsional state. Their assignments were limited to a series of a-type R-branch lines and low K{sub a} b-type R-branch transitions, and many assigned lines are excluded in the least-squares analysis. In the present study, we extended the line assignments of both the A- and E-species transitions in the second CH{sub 3} torsional state especially in the frequency region below the 120 GHz region. By combining the present assignments and those made by Maeda et al., 1951 transitions in total for the second CH{sub 3} torsional state, 1096 A-species transitions up to J = 39, and K{sub a} = 15 and 855 E-species transitions up to J = 35 and K{sub a} = 13, were least-squares analyzed by using the pseudo-principal-axis-method Hamiltonian with 42 parameters consisting of rotational, centrifugal distortion, and internal rotational constants in the second CH{sub 3} torsional state. In addition, 1012 transitions out of 1096 A-species transitions could also be least-squares analyzed by using Watson's A-reduced Hamiltonian with 43 parameters, which can serve to calculate the energy levels of the A-species lines of molecules with the CH{sub 3} internal rotation conveniently.
The Microwave Spectroscopy of Methyl Formate in the Second Torsional Excited State
NASA Astrophysics Data System (ADS)
Kobayashi, Kaori; Takamura, Kazunori; Sakai, Yusuke; Tsunekawa, Shozo; Odashima, Hitoshi; Ohashi, Nobukimi
2013-03-01
The cis-methyl formate molecule is a well known molecule found in interstellar space. Recently, rotational lines of methyl formate in the first CH3 torsional excited state were observed in Orion KL and W51e2. It is quite natural to observe methyl formate in even higher vibrational states considering the temperature estimated in Orion KL and W51e2. Maeda et al. reported results on the laboratory spectroscopy of methyl formate including the spectral analysis in its second CH3 torsional state. Their assignments were limited to a series of a-type R-branch lines and low Ka b-type R-branch transitions, and many assigned lines are excluded in the least-squares analysis. In the present study, we extended the line assignments of both the A- and E-species transitions in the second CH3 torsional state especially in the frequency region below the 120 GHz region. By combining the present assignments and those made by Maeda et al., 1951 transitions in total for the second CH3 torsional state, 1096 A-species transitions up to J = 39, and Ka = 15 and 855 E-species transitions up to J = 35 and Ka = 13, were least-squares analyzed by using the pseudo-principal-axis-method Hamiltonian with 42 parameters consisting of rotational, centrifugal distortion, and internal rotational constants in the second CH3 torsional state. In addition, 1012 transitions out of 1096 A-species transitions could also be least-squares analyzed by using Watson's A-reduced Hamiltonian with 43 parameters, which can serve to calculate the energy levels of the A-species lines of molecules with the CH3 internal rotation conveniently.
Helioseismic measurement of solar torsional oscillations.
Vorontsov, S V; Christensen-Dalsgaard, J; Schou, J; Strakhov, V N; Thompson, M J
2002-04-01
Bands of slower and faster rotation, the so-called torsional oscillations, are observed at the Sun's surface to migrate in latitude over the 11-year solar cycle. Here, we report on the temporal variations of the Sun's internal rotation from solar p-mode frequencies obtained over nearly 6 years by the Michelson Doppler Imager (MDI) instrument on board the Solar and Heliospheric Observatory (SOHO) satellite. The entire solar convective envelope appears to be involved in the torsional oscillations, with phase propagating poleward and equatorward from midlatitudes at all depths throughout the convective envelope. PMID:11935019
Global axial-torsional dynamics during rotary drilling
NASA Astrophysics Data System (ADS)
Gupta, Sunit K.; Wahi, Pankaj
2016-08-01
We have studied the global dynamics of the bottom hole assembly (BHA) during rotary drilling with a lumped parameter axial-torsional model for the drill-string and a linear cutting force model. Our approach accounts for bit-bounce and stick-slip along with the regenerative effect and is independent of the drill-string and the bit-rock interaction model. Regenerative axial dynamics due to variable depth of cut is incorporated through a functional description of the cut surface profile instead of a delay differential equation with a state-dependent delay. The evolution of the cut surface is governed by a nonlinear partial differential equation (PDE) which is coupled with the ordinary differential equations (ODEs) governing the longitudinal and angular dynamics of the BHA. The boundary condition for the PDE captures multiple regeneration in the event of bit-bounce. Interruption in the torsional dynamics is included by considering separate evolution equations for the various states during the stick period. Finite-dimensional approximation for our coupled PDE-ODE model has been obtained and validated by comparing our results against existing results. Bifurcation analysis of our system reveals a supercritical Hopf bifurcation leading to periodic vibrations without bit-bounce and stick-slip which is followed by solutions involving bit-bounce or stick-slip depending on the operating parameters. Further inroads into the unstable regime leads to a variety of complex behavior including co-existence of periodic and chaotic solutions involving both bit-bounce and stick-slip.
Vibration modulated subaperture stitching interferometry.
Liang, Chao-Wen; Chang, Hung-Sheng; Lin, Po-Chih; Lee, Cheng-Chung; Chen, Yi-Chun
2013-07-29
A novel subaperture stitching interferometry is developed to measure the surface deformation of the lens by utilizing the mechanical vibration induced from a motorized stage. The interferograms of different subapertures are acquired on the fly while the tested optics is rotating against its symmetrical axis. The measurement throughput and the subaperture positioning accuracy are improved simultaneously by adopting both the synchronous rotational scanning mechanism and the non-uniform phase shifting algorithm. The experimental measurement shows the stitched phase RMS error of 0.0037 waves proving the feasibility of the proposed phase acquisition method. PMID:23938696
Torsionally Excited Dimethyl Ether in the Laboratory and in Space
NASA Astrophysics Data System (ADS)
Endres, C. P.; Müller, H. S. P.; Lewen, F.; Giesen, T. F.; Schlemmer, S.; Drouin, B. J.; Bisschop, S.; Groner, P.
2010-06-01
Dimethyl ether (DME) is highly abundant in hot cores and numerous transitions within the vibrational ground state have been detected in various interstellar line surveys of sources such as Orion KL. As a nearly prolate asymmetric top with two internal rotors, it shows a complex spectrum with low lying torsional modes. The energy levels of the two lowest torsional states (v11, and v15) lie only 200 and 240 cm-1 above the ground state (barrier height ≈ 915 cm-1), and are thus sufficiently populated in these interstellar sources to exhibit transitions in line surveys due to high excitation temperatures in hot cores. So far, the lack of sufficiently accurate predictions for the two lowest excited torsional states prevented their identification in astronomical spectra. Therefore, we analyzed spectra, which have been recorded within the context of the investigations of the ground state. In total, more than 9500 transitions have been assigned covering the frequency range from 38 up to 1670 GHz. The enlarged splitting of each rotational level into four substates (AA, EE, AE, EA) compared to its size in the ground state and a large number of perturbed transitions hampered not only the line assignment but also the astrophysical modelling. However, the inclusion of interaction terms between both excited states in the model of an effective Hamiltonian for a symmetric two-top rotor, allowed us to model both excited states within a global fit, and also to accurately determine the energy difference between both states. Frequency predictions have been calculated based on this analysis and have been used to unambiguously assign numerous rotational transitions within these excited states in the astronomical line survey of the hot core region G327.3-0.6. P. Schilke, T.D. Groesbeck et al., Astrophys.J.Suppl.Ser., 108,(1997) 301-337 P. Schilke, D.J. Benford, T.R. Hunter et al., Astrophys.J.Suppl.Ser., 132,(2001) 281-364. P. Groner, S. Albert, E. Herbst, and F.C. De Lucia, Astrophys
Drolshagen, G.; Mayne, H.R.; Toennies, J.P.
1981-07-01
We extend the theory of inelastic rainbows to include vibrationally inelastic scattering, showing how the existence of vibrational rainbows can be deduced from collinear classical scattering theory. Exact close-coupling calculations are carried out for a breathing sphere potential, and rainbow structures are, in fact, observed. The location of the rainbows generally agrees well with the classical prediction. In addition, the sensitivity of the location of the rainbow to changes in the vibrational coupling has been investigated. It is shown that vibrational rainbows persist in the presence of anisotropy. Experimental results (R. David, M. Faubel, and J. P. Toennies, Chem. Phys. Lett. 18, 87 (1973)) are examined for evidence of vibrational rainbow structure, and it is shown that vibrational rainbow theory is not inconsistent with these results.
Tussive syncope in a pug with lung-lobe torsion
Davies, John A.; Snead, Elisabeth C.R.; Pharr, John W.
2011-01-01
The most common presenting clinical signs of lung-lobe torsion include dyspnea, tachypnea, lethargy, and anorexia. Tussive syncope secondary to lung-lobe torsion has not been documented. This article describes the presentation, diagnosis, management, and outcome of a pug with tussive syncope secondary to lung-lobe torsion. PMID:22131584
NASA Astrophysics Data System (ADS)
Prahlad, Harsha
This dissertation presents the development of a torsional actuator to alter the twist distributions of a tiltrotor blade between hover and forward flight. The actuator uses a Shape Memory Alloy (SMA) tube as its active element. The historical development of the tiltrotor aircraft is discussed, with emphasis on advanced tiltrotor concepts. The central theme in these concepts is to reduce the compromises for tiltrotor blade design, thereby improving performance of the aircraft in both hover and forward flight modes. A survey of research conducted in the application of smart structures to performance enhancement of aircraft is conducted. A review of other torsional actuators that are based on SMAs is presented. An assessment of the state-of-the-art in SMA modeling and characterization, both in mechanical tensile and torsional loading, is also discussed. Shape Memory Alloys are "smart" actuation materials that are capable of providing high stroke and high force of actuation at relatively low bandwidth. However, their behavior is complex, and influenced by material non-linearities, thermo-mechanical conditions and history of loading. In addition, the behavior of torsional SMA actuators has not been investigated in detail. In order to address these issues, the current research carries out a comprehensive characterization of SMAs. Experimental characteristics of SMA wires under extensional loading, and SMA rods and tubes in both extensional and torsional loading under a variety of thermo-mechanical conditions are presented in this dissertation. It is demonstrated that the uniaxial quasistatic SMA models show good overall agreement with the experimental behavior of an SMA wire under extensional loading. In addition, an approach that incorporates these models with radial non-uniformity due to torsional deflections is shown to provide good predictions of torsional characteristics of SMA rods and tubes. Several differences of the material response under non
Relativistic particle motion in nonuniform electromagnetic waves
NASA Technical Reports Server (NTRS)
Schmidt, G.; Wilcox, T.
1973-01-01
It is shown that a charged particle moving in a strong nonuniform electromagnetic wave suffers a net acceleration in the direction of the negative intensity gradient of the wave. Electrons will be expelled perpendicularly from narrow laser beams and various instabilities can result.
Relativistic particle motion in nonuniform electromagnetic waves
NASA Technical Reports Server (NTRS)
Schmidt, G.; Wilcox, T.
1973-01-01
A charged particle moving in a strong nonuniform electromagnetic wave which suffers a net acceleration in the direction of the negative intensity gradient of the wave was investigated. Electrons will be expelled perpendicularly from narrow laser beams and various instabilities result.
Research on algorithm of blade vibration for general wind turbine
NASA Astrophysics Data System (ADS)
Wang, Long; Sun, Lun-ye; Wu, Guang; Li, Xue-bin; Lai, Yong-bin; Zhou, Yi-jun
2016-01-01
Evaluation of vibration characteristics for wind turbine blades is one of the important contents in the wind turbine research. This paper uses the compressible flow equations with the preconditioning technique, based on the finite volume method and combined with the LU-SGS algorithm for solving the flow area; meanwhile adopts the two degree of freedom of vibration equation with the vertical and torsional vibration for blades to simulate the vibration trajectory of blade under the aerodynamic force, uses the motion grid algorithm for changes in grid computing domain. Calculation program was developed autonomous in the C ++ platform, and the development of software correctness was verified by contrast the results of the classic cylindrical examples. Finally, the vibration characteristics of a wind turbine blade was given, and the software developed in this paper can provide technical support for wind turbine blade vibration study.
Cryptorchid testis with torsion: Inguinoscrotal whirlpool sign
Indiran, Venkatraman
2016-01-01
Non contrast helical computed tomography (CT) study of the abdomen is frequently performed in evaluation of suspected ureteric colic. We present CT images of a young adult male patient who had torsion of an undescended, non-neoplastic testis and describe the “Inguinoscrotal whirlpool sign on CT”. PMID:27555688
Adnexal torsion: review of the literature.
Sasaki, Kirsten J; Miller, Charles E
2014-01-01
Adnexal torsion is one of a few gynecologic surgical emergencies. Misdiagnosis or delay in treatment can have permanent sequelae including loss of an ovary with effect on future fertility, peritonitis, and even death. A PubMed search was performed between 1985 and 2012 for reviews, comparative studies, and case reports to provide a review of the epidemiology, risk factors, clinical presentation, common laboratory and imaging findings, and treatments of adnexal torsion. Common symptoms of torsion include pain, nausea, and vomiting, with associated abdominal or pelvic tenderness, and may differ in premenarchal and pregnant patients. Laboratory and imaging findings including ultrasound with Doppler analysis, computed tomography, and magnetic resonance imaging can assist in making the diagnosis but should not trump clinical judgment; normal Doppler flow can be observed in up to 60% of adnexal torsion cases. Treatment depends on the individual patient but commonly includes detorsion, even if the adnexae initially seem necrotic, with removal of any associated cysts or salpingo-oophorectomy, because recurrence rates are higher with detorsion alone or detorsion with only cyst aspiration. PMID:24126258
Joining and forming using torsional ultrasonic principles.
Frost, M
2009-10-01
Developments in torsional ultrasonic joining mean that it is now used in a diverse range of joining, forming, selective weakening and "break-off" applications in the medical device industry.The principles and benefits of the technique are described together with application examples. PMID:20302140
Torsional Oscillations of the Earths's Core
NASA Technical Reports Server (NTRS)
Hide, Raymond; Boggs, Dale H.; Dickey, Jean O.
1997-01-01
Torsional oscillations of the Earth's liquid metallic outer core are investigated by diving the core into twenty imaginary e1qui-volume annuli coaxial with the axis of ratation of the Earth and determining temproal fluctuations in the axial component of angular memonetum of each annulus under the assumption of iso-rotation on cylindrical surfaces.
Hepatic lobe torsion in a horse
Bentz, Kristin J.; Burgess, Brandy A.; Lohmann, Katharina L.; Shahriar, Farshid
2009-01-01
A 4-year-old Belgian mare was presented with a 1-week history of fever, suspected of being caused by peritonitis. The mare died before the diagnostic procedures had been completed; postmortem examination revealed torsion of the left medial lobe of the liver, resulting in diffuse necrosis of liver tissue and severe peritoneal effusion. PMID:19436480
Multimode vibration reduction concept for machine tools and automotive applications
NASA Astrophysics Data System (ADS)
Neugebauer, Reimund; Drossel, Welf-Guntram; Kranz, Burkhard; Kunze, Holger
2005-05-01
This paper reports a numerical and experimental study on a new multi mode vibration reduction concept for struts of machine tools or shafts of automotives. The example described in detail validates this new concept for high dynamic parallel kinematic struts. The structural advantages of parallel kinematic mechanisms are undisputed. However statical and dynamical bending and torsional loads must be considered during the design process of the structure and thus effect the shape of the strut geometry. The here described new actuator concept for multi mode vibration reduction is to influence these bending and torsional loads. It uses piezopatches based on the MFC technology licensed by NASA. Initial simulation and experimental tests were done at an one side clamped aluminium beam with applicated 45°-MFC's on both sides. Simulation results show, that driving the piezos in opposite direction leads to a bending deflection of the beam, driving them in the same phase leads to a torsional deflection of the aluminium beam. Experimental measurements confirm the simulation results. The benefit we get is a decreased number of actuators for multimode vibration reduction. Likewise these actuators allow the separation or selective combination of bending and torsion. This new actuation concept is not limited on beams. Further simulations for cylindrical struts result in a design of a MFC-ring with eight segments with changing fiber orientation for separation of bending and torsion on struts and shafts. The selective controlled activation of each of the segments leads to bending in x-direction, bending in y-direction or torsion.
A combined analysis of the ν9 band and the far-infrared torsional spectra of ethane
NASA Astrophysics Data System (ADS)
Moazzen-Ahmadi, N.; Schroderus, J.; McKellar, A. R. W.
1999-12-01
Fourier transform measurements of the lowest frequency degenerate fundamental band of CH3CH3 (v9=1←0) in the 12-μm region together with far-infrared torsional spectra have been analyzed to investigate vibration-torsion-rotation effects in a symmetric top molecule. Several spectra of the ν9 band were recorded under different experimental conditions with apodized slit functions of about 0.002 cm-1. Although the intrinsic tunneling splitting in each (J'←J″) doublet in the ν9 band is predicted to be of the order of 0.002 cm-1, in some cases the observed splitting for an intermediate J″ of 20 is several times this value. In extreme cases, splittings of the order of 0.25 cm-1 have been observed. These splittings are caused primarily by the Coriolis interaction between the torsional stack of levels v4=0,1,2,…, for v9=1 and the corresponding stack for the ground vibrational state. Because of a near-degeneracy between the upper level in the ν9 band and its interacting partner (v9=0, v4=3), the (l=-1;K=17,σ=0) torsion-rotation series is resonantly perturbed. For this case, perturbation-allowed v4=3←0 torsional transitions have been identified. Here σ=0, 1, 2, or 3 labels the torsional sublevels. Measurements from the ν9 and 3ν4 bands, frequencies from the far-infrared torsional spectra in the ground vibrational state, and lower state combination differences from ν9+ν4-ν4 band were fitted to within experimental uncertainty using a symmetry adapted effective Hamiltonian which has been used for analyses of similar spectra in methyl silane and CH3CD3. Two Coriolis parameters were determined: the experimental value of ζ˜9z=0.2610(12) is in good agreement with the calculated value of 0.25, whereas the experimental value of ζ˜4,9x=0.2267(20) is about 3 times smaller than the calculated value of 0.60. The theoretical treatment presented here makes use of standard symmetric top formalism and the G36† double-group formalism.
NASA Astrophysics Data System (ADS)
Dufour, Marc L.; Bisaillon, Charles-Etienne; Lamouche, Guy; Vergnole, Sebastien; Hewko, Mark; D'Amours, Frédéric; Padioleau, Christian; Sowa, Michael
2011-03-01
The Industrial Material Institute (IMI) together with the Institute for Biodiagnostic (IBD) has developed its own optical catheters for cardiovascular imaging applications. Those catheters have been used experimentally in the in vitro coronary artery model of the Langendorff beating heart and in a percutaneous coronary intervention procedure in a porcine model. For some catheter designs, non-uniform rotational distortion (NURD) can be observed as expected from past experience with intra-vascular ultrasound (IVUS) catheters. A two-dimensional (2D) coronary artery test bench that simulates the path into the coronary arteries has been developed. The presence or absence of NURD can be assessed with the test bench using a custom-built cardiovascular Optical Coherence Tomography (OCT) imaging system. A square geometry instead of the circular shape of an artery is used to simulate the coronary arteries. Thereby, it is easier to visualize NURD when it is present. The accumulated torsion induced by the friction on the catheter is measured along the artery path. NURD is induced by the varying friction force that is balanced by the accumulated torsion force. The pullback force is measured and correlated with NURD observed in the 2D test bench. Finally, a model is presented to help understanding the mechanical constraint that leads to the friction force variations.
Vibration analysis of rotor blades with pendulum absorbers
NASA Technical Reports Server (NTRS)
Murthy, V. R.; Hammond, C. E.
1979-01-01
A comprehensive vibration analysis of rotor blades with spherical pendulum absorbers is presented. Linearized equations of motion for small oscillations about the steady-state deflection of a spherical pendulum on elastic rotor blades undergoing coupled flapwise bending, chordwise bending, and torsional vibrations are obtained. A transmission matrix formulation is given to determine the natural vibrational characteristics of rotor blades with spherical or simple flapping pendulum absorbers. The natural frequencies and mode shapes of a hingeless rotor blade with a spherical pendulum are computed.
Analysis of the vibrational bandwidths of alkane-urea clathrates
NASA Astrophysics Data System (ADS)
Wood, Kurt A.; Snyder, Robert G.; Strauss, Herbert L.
1989-11-01
The only large amplitude motion possible for an n-alkane molecule in urea-inclusion compounds is libration-torsion about the long axis of the chain. We present a quantitative model that incorporates the effect of this motion on the widths of the alkane vibrational bands. This model explains the difference in the widths of the different vibrations of the alkanes and their temperature dependence. Two effects are combined: (1) a modulation of the angles between the components of the polarizability in the space and the molecule-fixed frames for Raman spectra or between the components of the dipole moment for the infrared spectra, and (2) a modulation of the frequency of the alkane vibration via anharmonic coupling terms with the libration-torsion. The first effect gives rise to a distinctly non-Lorentzian band shape, which is convoluted with the approximately Lorentzian band of the second effect to produce the final result. The libration-torsional motion is modeled as that of a Brownian harmonic oscillator. Most of the parameters that enter the calculation are obtained from data other than that involving the bandwidths themselves. The libration-torsion relaxation time of about 1 ps obtained from fitting the observed bandwidths agrees with the value obtained from recent quasielastic neutron scattering experiments. Other bandwidth mechanisms that have been proposed are evaluated and it is shown that site hopping is too slow to account for the observations.
NASA Astrophysics Data System (ADS)
Tsujino, Jiromaru; Uchida, Takako; Ohkusa, Kunifumi; Adachi, Tatsuya; Ueoka, Tetsugi
1998-05-01
Ultrasonic plastic welding is applied for welding various thermoplastic materials and is widely used in various industrial fields. The two-vibration-system welding method and a high frequency equipment are effective in improving the welding characteristics. A high frequency 90 kHz system can weld plastic sheets under a 1/3 velocity amplitude as compared with that of a low 27 kHz system, but it is difficult to weld large specimens successfully because a high frequency vibration stress cannot be transmitted uniformly due to the stress relaxation effect by the small vibration displacement. To improve the direct welding characteristics, three types of two-vibration-system ultrasonic welding equipments using linear vibration loci of (1) 90 kHz and 27 kHz longitudinal vibration systems, (2) 90 kHz longitudinal and 20 kHz torsional vibration systems, and elliptical vibration loci of (3) 27 kHz complex vibration systems are studied. Transmission conditions of the vibration stresses are measured by pressure sensitive films (Prescale) which are inserted between the plastic sheets. It was shown that a high frequency vibration stress with a small displacement amplitude may be induced uniformly in the welding specimens by combining a low frequency vibration with large displacement amplitude. These welding systems are effectively used to join plastic sheets successfully.
NASA Technical Reports Server (NTRS)
Bastin, Paul
1990-01-01
Viewgraphs on vibration isolation are presented. Techniques to control and isolate centrifuge disturbances were identified. Topics covered include: disturbance sources in the microgravity environment; microgravity assessment criteria; life sciences centrifuge; flight support equipment for launch; active vibration isolation system; active balancing system; and fuzzy logic control.
Hauth, J.J.
1962-07-01
A method of compacting a powder in a metal container is described including the steps of vibrating the container at above and below the resonant frequency and also sweeping the frequency of vibration across the resonant frequency several times thereby following the change in resonant frequency caused by compaction of the powder. (AEC)
2011-01-01
By homing in on the distribution patterns of electrons around an atom, a team of scientists team with Berkeley Lab's Molecular Foundry showed how certain vibrations from benzene thiol cause electrical charge to "slosh" onto a gold surface (left), while others do not (right). The vibrations that cause this "sloshing" behavior yield a stronger SERS signal.
DOWNHOLE VIBRATION MONITORING & CONTROL SYSTEM
Martin E. Cobern
2004-10-13
The deep hard rock drilling environment induces severe vibrations into the drillstring, which can cause reduced rates of penetration (ROP) and premature failure of the equipment. The only current means of controlling vibration under varying conditions is to change either the rotary speed or the weight-on-bit (WOB). These changes often reduce drilling efficiency. Conventional shock subs are useful in some situations, but often exacerbate the problems. The objective of this project is development of a unique system to monitor and control drilling vibrations in a ''smart'' drilling system. This system has two primary elements: (1) The first is an active vibration damper (AVD) to minimize harmful axial, lateral and torsional vibrations. The hardness of this damper will be continuously adjusted using a robust, fast-acting and reliable unique technology. (2) The second is a real-time system to monitor drillstring vibration, and related parameters. This monitor adjusts the damper according to local conditions. In some configurations, it may also send diagnostic information to the surface via real-time telemetry. The AVD is implemented in a configuration using magnetorheological (MR) fluid. By applying a current to the magnetic coils in the damper, the viscosity of the fluid can be changed rapidly, thereby altering the damping coefficient in response to the measured motion of the tool. Phase I of this program entailed modeling and design of the necessary subsystems and design, manufacture and test of a full laboratory prototype. Phase I of the project was completed by the revised end date of May 31, 2004. The objectives of this phase were met, and all prerequisites for Phase II have been completed. The month of June, 2004 was primarily occupied with the writing of the Phase I Final Report, the sole deliverable of Phase I, which will be submitted in the next quarter. Redesign of the laboratory prototype and design of the downhole (Phase II) prototype was begun.
DOWNHOLE VIBRATION MONITORING & CONTROL SYSTEM
Martin E. Cobern
2004-08-31
The deep hard rock drilling environment induces severe vibrations into the drillstring, which can cause reduced rates of penetration (ROP) and premature failure of the equipment. The only current means of controlling vibration under varying conditions is to change either the rotary speed or the weight-on-bit (WOB). These changes often reduce drilling efficiency. Conventional shock subs are useful in some situations, but often exacerbate the problems. The objective of this project is development of a unique system to monitor and control drilling vibrations in a ''smart'' drilling system. This system has two primary elements: (1) The first is an active vibration damper (AVD) to minimize harmful axial, lateral and torsional vibrations. The hardness of this damper will be continuously adjusted using a robust, fast-acting and reliable unique technology. (2) The second is a real-time system to monitor drillstring vibration, and related parameters. This monitor adjusts the damper according to local conditions. In some configurations, it may also send diagnostic information to the surface via real-time telemetry. The AVD is implemented in a configuration using magnetorheological (MR) fluid. By applying a current to the magnetic coils in the damper, the viscosity of the fluid can be changed rapidly, thereby altering the damping coefficient in response to the measured motion of the tool. Phase I of this program entailed modeling and design of the necessary subsystems and design, manufacture and test of a full laboratory prototype. Phase I of the project was completed by the revised end date of May 31, 2004. The objectives of this phase were met, and all prerequisites for Phase II have been completed.
On a finite-state inflow application to flap-lag-torsion damping in hover
NASA Technical Reports Server (NTRS)
De Andrade, Donizeti; Peters, David A.
1992-01-01
An aerodynamic model with a coupled set of generalized dynamic wake equations and hybrid equations of motion for an elastic blade are applied here to a two-blade untwisted stiff in-plane hingeless small-scale model rotor with torsionally soft blades. Blade root offset, precone, blade droop, pitch control stiffness, and blade pitch angle are included in the model rotor. Numerical results show that 3D tip relief effects within the nonuniform steady-state inflow are significant to predict steady-state aerodynamic loads and blade deflections. Eigenvalue results confirm the importance of unsteady 3D aerodynamics in predicting lead-lag damping and frequency. Eigenvector analysis correlations reinforced qualitative and quantitative shortcomings associated with quasi-steady 2D aerodynamic theory for aeroelastic applications in hover.
Design and analysis of a torsion braid pendulum displacement transducer
NASA Technical Reports Server (NTRS)
Rind, E.; Bryant, E. L.
1981-01-01
The dynamic properties at various temperatures of braids impregnated with polymer can be measured by using the braid as the suspension of a torsion pendulum. This report describes the electronic and mechanical design of a torsional braid pendulum displacement transducer which is an advance in the state of the art. The transducer uses a unique optical design consisting of refracting quartz windows used in conjunction with a differential photocell to produce a null signal. The release mechanism for initiating free torsional oscillation of the pendulum has also been improved. Analysis of the precision and accuracy of the transducer indicated that the maximum relative error in measuring torsional amplitude was approximately 0. A serious problem inherent in all instruments which use a torsional suspension was analyzed: misalignment of the physical and torsional axes of the torsional member which results in modulation of the amplitude of the free oscillation.
Evaluation of left ventricular torsion by cardiovascular magnetic resonance
2012-01-01
Recently there has been considerable interest in LV torsion and its relationship with symptomatic and pre-symptomatic disease processes. Torsion gives useful additional information about myocardial tissue performance in both systolic and diastolic function. CMR assessment of LV torsion is simply and efficiently performed. However, there is currently a wide variation in the reporting of torsional motion and the procedures used for its calculation. For example, torsion has been presented as twist (degrees), twist per length (degrees/mm), shear angle (degrees), and shear strain (dimensionless). This paper reviews current clinical applications and shows how torsion can give insights into LV mechanics and the influence of LV geometry and myocyte fiber architecture on cardiac function. Finally, it provides recommendations for CMR measurement protocols, attempts to stimulate standardization of torsion calculation, and suggests areas of useful future research. PMID:22827856
Active damping of spacecraft structural appendage vibrations
NASA Technical Reports Server (NTRS)
Fedor, Joseph V. (Inventor)
1990-01-01
An active vibration damper system, for bending in two orthogonal directions and torsion, in each of three mutually perpendicular axes is located at the extremities of the flexible appendages of a space platform. The system components for each axis includes: an accelerometer, filtering and signal processing apparatus, and a DC motor-inertia wheel torquer. The motor torquer, when driven by a voltage proportional to the relative vibration tip velocity, produces a reaction torque for opposing and therefore damping a specific modal velocity of vibration. The relative tip velocity is obtained by integrating the difference between the signal output from the accelerometer located at the end of the appendage with the output of a usually carried accelerometer located on a relatively rigid body portion of the space platform. A selector switch, with sequential stepping logic or highest modal vibration energy logic, steps to another modal tip velocity channel and receives a signal voltage to damp another vibration mode. In this manner, several vibration modes can be damped with a single sensor/actuator pair. When a three axis damper is located on each of the major appendages of the platform, then all of the system vibration modes can be effectively damped.
Discrete Fourier transforms of nonuniformly spaced data
NASA Technical Reports Server (NTRS)
Swan, P. R.
1982-01-01
Time series or spatial series of measurements taken with nonuniform spacings have failed to yield fully to analysis using the Discrete Fourier Transform (DFT). This is due to the fact that the formal DFT is the convolution of the transform of the signal with the transform of the nonuniform spacings. Two original methods are presented for deconvolving such transforms for signals containing significant noise. The first method solves a set of linear equations relating the observed data to values defined at uniform grid points, and then obtains the desired transform as the DFT of the uniform interpolates. The second method solves a set of linear equations relating the real and imaginary components of the formal DFT directly to those of the desired transform. The results of numerical experiments with noisy data are presented in order to demonstrate the capabilities and limitations of the methods.
NASA Astrophysics Data System (ADS)
Bai, Cheng; Huang, Jin
2014-05-01
Electrostatically driven torsional micromirrors are suitable for optical microelectromechanical systems due to their good dynamic response, low adhesion, and simple structure for large-scale-integrated applications. For these devices, how to eliminate the excessive residual vibration in order to achieve more accurate positioning and faster switching is an important research topic. Because of the known nonlinearity issues, traditional shaping techniques based on linear theories are not suitable for nonlinear torsional micromirrors. In addition, due to the difficulties in calculating energy dissipation, the existing nonlinear command shaping techniques using energy method have neglected the effect of damping. We analyze the static and dynamic behavior of the electrostatically actuated torsional micromirrors. Based on the response of these devices, a multistep-shaping control considering the damping effects and the nonlinearity is proposed. Compared to the conventional closed-loop control, the proposed multistep-shaping control is a feedforward approach which can yield a good enough performance without extra sensors and actuators. Simulation results show that, without changing the system structure, the preshaping input reduces the settling time from 4.3 to 0.97 ms, and the overshoot percentage of the mirror response is decreased from 33.2% to 0.2%.
Rindler effect for a nonuniformly accelerating observer
Zhu Jian-yang; Bao Aidong; Zhao Zheng
1995-10-01
Both the Klein-Gordon equation and the Dirac equation are dealt with in the generalized Rindler space-time of a nonuniformly accelerating observer. Making use of a new method and introducing a tortoise-type coordinate transformation, it is proved that there exist an event horizon and thermal radiation depending on time in the space-time. The Hawking-Unruh temperature is proportional to the variable acceleration.
[Spectrum recovery methods for nonuniform sampling interferogram].
Yao, Tao; Lü, Qun-Bo; Xiangli, Bin; Yuan, Yan
2010-05-01
The interferogram acquired by imaging Fourier transform spectrometer (IFTS) can't be used directly and must be recovered. The spectrum recovery processes based on fast Fourier transform (FFT) is the traditional method which is used widely. For some IFTS, the nonuniform sampling of the interferogram is often occurrs. When the aliasing is neglected, the spectrum recovered by traditional method is often distorted. When the spectrum recovery processes based on Fourier transform are used, the precision of the recovered spectrum can be ensured, but the real-time processing requirement can't be satisfied. In order to acquire the precise recovered spectrum of the nonuniform sampled interferogram, the interpolation method and nonuniform fast Fourier transform (NUFFT) method were adopted. For the oversampled interferogram and partial undersampled interferogram, the spectrum recovery methods based on interpolation and NUFFT were presented respectively, and the applicability of these two methods is given. Finally, the computer simulation was performed, and the results indicate that NUFFT method is preferable to interpolation method not for undersampled interferogram but for oversampled interferogram. PMID:20672649
The lens as a nonuniform spherical syncytium.
Mathias, R T; Rae, J L; Eisenberg, R S
1981-01-01
The effective intracellular resistivity Ri of the ocular lens is a measure of the coupling between cells. Since degradation of coupling may accompany cataracts, measurements of Ri are of considerable interest. Experimental results show that the lens is a nonuniform syncytium in which Ri is much higher in the nuclear region than in the cortex. A theory describing the lens as a radially nonuniform spherical syncytium is proposed, solved, and described as a simple equivalent circuit. The impedance of the lens is measured with new circuitry which permits the accurate application and measurement of current and voltage over a wide bandwidth without arbitrary compensation of unstable capacitances. The fit of the nonuniform theory to experimental data is satisfactory and the parameters determined are consistent with theoretical assumptions. In the outer region (cortex) of the lens Ri = 2.4 k omega-cm, probably as a consequence of differences in coupling and cytoplasmic resistivity. The radial resistivity of the cortex is some five times the circumferential resistivity, demonstrating a marked anisotropy in the preparation, probably reflecting the anisotropy in the orientation of lens fibers and distribution of gap junctions. Current can flow in the circumferential direction without crossing from fiber to fiber; current can flow in the radial direction only by crossing from fiber to fiber. PMID:7213932
Torsional Buckling Tests of a Simulated Solar Array
NASA Technical Reports Server (NTRS)
Thornton, E. A.
1996-01-01
Spacecraft solar arrays are typically large structures supported by long, thin deployable booms. As such, they may be particularly susceptible to abnormal structural behavior induced by mechanical and thermal loading. One example is the Hubble Space Telescope solar arrays which consist of two split tubes fit one inside the other called BiSTEMs. The original solar arrays on the Hubble Space Telescope were found to be severely twisted following deployment and later telemetry data showed the arrays were vibrating during daylight to night and night to daylight transition. The solar array twist however can force the BiSTEM booms to change in cross-section and cause tile solar arrays to react unpredictably to future loading. The solar arrays were redesigned to correct for tile vibration, however, upon redeployment they again twisted. To assess the influence of boom cross-sectional configuration, experiments were conducted on two types of booms, (1)booms with closed cross-sections, and (2) booms with open cross-sections. Both models were subjected to compressive loading and imposed tip deflections. An existing analytical model by Chung and Thornton was used to define the individual load ranges for each model solar array configuration. The load range for the model solar array using closed cross-section booms was 0-120 Newtons and 0-160 Newtons for the model solar array using open cross-section booms. The results indicate the model solar array with closed cross-section booms buckled only in flexure. However, the results of the experiment with open cross-section booms indicate the model solar array buckled only in torsion and with imposed tip deflections the cross section can degrade by rotation of the inner relative to the outer STEM. For tile Hubble Space Telescope solar arrays the results of these experiments indicate the twisting resulted from the initial mechanical loading of the open cross-section booms.
Axial and torsional fatigue behavior of Waspaloy
NASA Technical Reports Server (NTRS)
Zamrik, S.; Mirdamadi, M.; Zahiri, F.
1986-01-01
The cyclic flow response and crack growth behavior of Waspaloy at room temperature and 650 C under tensile loading and torsional loading was studied, for two conditions of Waspaloy: fine grain, large gamma prime size; coarse grain, small gamma prime size. The fine grain material showed 5 to 10 percent hardening after about 10 percent of life, with sequent softening to failure at both themperature levels. The coarse grain material showed either stable response or monotonic softening to failure. Early crack initiation was observed on planes of maximum shear, with eventual branching to principle planes under torsional loading; cracks were always normal to load axis under tensile loading. Also, crack paths were intergranular at 650 C, mostly transgranular at room temperature.
Standing Torsional Waves in Fluid-Saturated Porous Circular Cylinder
NASA Astrophysics Data System (ADS)
Solorza, S.; Sahay, P. N.
2002-12-01
For dynamic measurement of elastic constants of a porous material saturated with viscous fluid when resonance-bar technique is applied, one also observes attenuation of the wave field. The current practice is to interpret it in terms of solid-viscosity by assuming a viscoelastic rheology for porous material. The likely mechanisms of attenuation in a fluid saturated porous material are: 1) motion of the fluid with respect to the solid frame and 2) viscous loss within the pore fluid. Therefore, it is appropriate to assume a poroelastic rheology and link the observed attenuation value to fluid properties and permeability. In the framework of poroelastic theory, the explicit formula linking attenuation to the properties of solid and fluid constituents and permeability are not worked out yet. In order to established such a link one has to workout solutions of appropriate boundary value problems in such a framework. Here, we have carried out the solution of boundary value problem associated with torsional oscillation of a finite poroelastic circular cylinder, casted in the framework of volume-averaged theory of poroelasticity. Analysing this solution by a perturbative approach we are able to develop explicit expressions for resonance frequency and attenuation for this mode of vibration. It shows how the attenuation is controlled by the permeability and the fluid properties, and how the resonance frequency drops over its value for the dry porous frame due to the effect of the fluid-mass.
Wang, Shibo; Niu, Chengchao
2016-01-01
In this work, the plane-on-plane torsional fretting tribological behavior of polytetrafluoroethylene (PTFE) was studied. A model of a rigid, flat-ended punch acting on an elastic half-space was built according to the experimental conditions. The results indicate that the shape of T–θ curves was influenced by both the torsional angle and the normal load. The torsion friction torque and wear rate of PTFE exponentially decreased when the torsion angle rose. The torsional torque increased from 0.025 N·m under a normal load of 43 N to 0.082 N·m under a normal load of 123 N. With sequentially increasing normal load, the value of torque was maintained. With rising normal load, the wear mass loss of PTFE disks was increased and the wear rate was decreased. Good agreement was found with the calculated torque according to the model and the experimental torque except for that under a normal load of 163 N. The difference under a normal load of 163 N was caused by the coefficient of friction. Usually the coefficient of friction of a polymer decreases with increasing normal load, whereas a constant coefficient of friction was applied in the model. PMID:26799324
Wang, Shibo; Niu, Chengchao
2016-01-01
In this work, the plane-on-plane torsional fretting tribological behavior of polytetrafluoroethylene (PTFE) was studied. A model of a rigid, flat-ended punch acting on an elastic half-space was built according to the experimental conditions. The results indicate that the shape of T-θ curves was influenced by both the torsional angle and the normal load. The torsion friction torque and wear rate of PTFE exponentially decreased when the torsion angle rose. The torsional torque increased from 0.025 N·m under a normal load of 43 N to 0.082 N·m under a normal load of 123 N. With sequentially increasing normal load, the value of torque was maintained. With rising normal load, the wear mass loss of PTFE disks was increased and the wear rate was decreased. Good agreement was found with the calculated torque according to the model and the experimental torque except for that under a normal load of 163 N. The difference under a normal load of 163 N was caused by the coefficient of friction. Usually the coefficient of friction of a polymer decreases with increasing normal load, whereas a constant coefficient of friction was applied in the model. PMID:26799324
Analytic Model for the Rototranslational Torsion Pendulum
NASA Astrophysics Data System (ADS)
De Marchi, F.; Bassan, M.; Pucacco, G.; Marconi, L.; Stanga, R.; Visco, M.
2013-01-01
We develop an analytic model to describe the motion of the RotoTranslational Torsion Pendulum PETER in a wide range of frequencies (from 1mHz up to 10-15Hz). We also try to explain some unexpected features we found in the data with only 1 soft degree of freedom and we estimate values for the misalignment angles and other parameters of the model.
Dark spinors with torsion in cosmology
Boehmer, Christian G.; Burnett, James
2008-11-15
We solve one of the open problems in Einstein-Cartan theory, namely, we find a natural matter source whose spin angular momentum tensor is compatible with the cosmological principle. We analyze the resulting evolution equations and find that an epoch of accelerated expansion is an attractor. The torsion field quickly decays in that period. Our results are interpreted in the context of the standard model of cosmology.
Implementing torsional-mode Doppler ladar.
Fluckiger, David U
2002-08-20
Laguerre-Gaussian laser modes carry orbital angular momentum as a consequence of their helical-phase front screw dislocation. This torsional beam structure interacts with rotating targets, changing the orbital angular momentum (azimuthal Doppler) of the scattered beam because angular momentum is a conserved quantity. I show how to measure this change independently from the usual longitudinal momentum (normal Doppler shift) and derive the apropos coherent mixing efficiencies for monostatic, truncated Laguerre and Gaussian-mode ladar antenna patterns. PMID:12206220
Fluid driven torsional dipole seismic source
Hardee, Harry C.
1991-01-01
A compressible fluid powered oscillating downhole seismic source device capable of periodically generating uncontaminated horizontally-propagated, shear waves is provided. A compressible fluid generated oscillation is created within the device which imparts an oscillation to a housing when the device is installed in a housing such as the cylinder off an existing downhole tool, thereby a torsional seismic source is established. Horizontal waves are transferred to the surrounding bore hole medium through downhole clamping.
Ubiquitous Torsional Motions in Type II Spicules
NASA Astrophysics Data System (ADS)
De Pontieu, B.; Carlsson, M.; Rouppe van der Voort, L. H. M.; Rutten, R. J.; Hansteen, V. H.; Watanabe, H.
2012-06-01
Spicules are long, thin, highly dynamic features that jut out ubiquitously from the solar limb. They dominate the interface between the chromosphere and corona and may provide significant mass and energy to the corona. We use high-quality observations with the Swedish 1 m Solar Telescope to establish that so-called type II spicules are characterized by the simultaneous action of three different types of motion: (1) field-aligned flows of order 50-100 km s-1, (2) swaying motions of order 15-20 km s-1, and (3) torsional motions of order 25-30 km s-1. The first two modes have been studied in detail before, but not the torsional motions. Our analysis of many near-limb and off-limb spectra and narrowband images using multiple spectral lines yields strong evidence that most, if not all, type II spicules undergo large torsional modulation and that these motions, like spicule swaying, represent Alfvénic waves propagating outward at several hundred km s-1. The combined action of the different motions explains the similar morphology of spicule bushes in the outer red and blue wings of chromospheric lines, and needs to be taken into account when interpreting Doppler motions to derive estimates for field-aligned flows in spicules and determining the Alfvénic wave energy in the solar atmosphere. Our results also suggest that large torsional motion is an ingredient in the production of type II spicules and that spicules play an important role in the transport of helicity through the solar atmosphere.
UBIQUITOUS TORSIONAL MOTIONS IN TYPE II SPICULES
De Pontieu, B.; Hansteen, V. H.; Carlsson, M.; Rouppe van der Voort, L. H. M.; Rutten, R. J.; Watanabe, H.
2012-06-10
Spicules are long, thin, highly dynamic features that jut out ubiquitously from the solar limb. They dominate the interface between the chromosphere and corona and may provide significant mass and energy to the corona. We use high-quality observations with the Swedish 1 m Solar Telescope to establish that so-called type II spicules are characterized by the simultaneous action of three different types of motion: (1) field-aligned flows of order 50-100 km s{sup -1}, (2) swaying motions of order 15-20 km s{sup -1}, and (3) torsional motions of order 25-30 km s{sup -1}. The first two modes have been studied in detail before, but not the torsional motions. Our analysis of many near-limb and off-limb spectra and narrowband images using multiple spectral lines yields strong evidence that most, if not all, type II spicules undergo large torsional modulation and that these motions, like spicule swaying, represent Alfvenic waves propagating outward at several hundred km s{sup -1}. The combined action of the different motions explains the similar morphology of spicule bushes in the outer red and blue wings of chromospheric lines, and needs to be taken into account when interpreting Doppler motions to derive estimates for field-aligned flows in spicules and determining the Alfvenic wave energy in the solar atmosphere. Our results also suggest that large torsional motion is an ingredient in the production of type II spicules and that spicules play an important role in the transport of helicity through the solar atmosphere.
Liver lobe torsion in three adult rabbits.
Wenger, S; Barrett, E L; Pearson, G R; Sayers, I; Blakey, C; Redrobe, S
2009-06-01
This paper describes three cases of liver lobe torsion in rabbits presenting with anorexia, lethargy, jaundice and abdominal pain. This condition was associated with anaemia and elevation of alanine aminotransferase, aspartate aminotransferase and gamma-glutamyl transferase. Abnormal radiological findings included hepatomegaly, gas-filled intestinal loops consistent with gastrointestinal ileus and ascites. Ultrasonographic findings included heterogeneous liver parenchyma, free abdominal fluid and reduced bowel motility. Diagnosis was confirmed by histopathological examination of the liver in all three cases. PMID:19527423
Torsional optokinetic nystagmus: normal response characteristics
Farooq, S J; Proudlock, F A; Gottlob, I
2004-01-01
Background/aims: Few studies have investigated normal response characteristics of torsional optokinetic nystagmus (tOKN). The authors have investigated the effect of stimulus velocity and central/peripheral stimulation on tOKN. Methods: Torsional OKN was elicited using a sinusoidal grating rotating at velocities of 3°/s to 1000°/s in clockwise and anticlockwise directions. To investigate the effect of central stimulation, stimulus size was varied from 2.86° to 50.8°. An artificial scotoma placed over a 50.8° stimulus was varied from 2.86° to 43.2° to investigate peripheral stimulation. Eight subjects participated in each experiment and torsional eye movements were recorded using video-oculography. The mean slow phase velocity (MSPV) and gain were calculated. Results: The maximum gain occurred in response to 8°/s stimulation. The MSPV increased up to a stimulus velocity of 200°/s achieving a maximum of 3°/s in both directions. MSPV was linearly correlated with the log of stimulus velocity. The smallest field size, rotating at 40°/s, evoked 10% of the gain elicited by the largest display. When the most peripheral stimulus was used, the gain was maintained at 50% of the gain evoked when the full display was used. Conclusions: A wide range of stimulus velocities can elicit tOKN and peripheral field stimulation contributes significantly to its response. PMID:15148215
Perinatal testicular torsion and medicolegal considerations.
Massoni, F; Troili, G M; Pelosi, M; Ricci, S
2014-06-01
Perinatal testicular torsion (PTT) is a very complex condition because of rarity of presentation and diagnostic and therapeutic difficulties. In presence of perinatal testicular torsion, the involvement of contralateral testis can be present also in absence of other indications which suggest the bilateral involvement; therefore, occurrences supported by literature do not exclude the use of surgery to avoid the risk of omitted or delayed diagnosis. The data on possible recovery of these testicles are not satisfactory, and treatment consists of an observational approach ("wait-and-see") or an interventional approach. The hypothesis of randomized clinical trials seems impracticable because of rarity of disease. The authors present a case of PTT, analyzing injuries due to clinical and surgical management of these patients, according to medicolegal profile. The delayed diagnosis and the choice of an incorrect therapeutic approach can compromise the position of healthcare professionals, defective in terms of skill, prudence and diligence. Endocrine insufficiency is an unfortunate event. The analysis of literature seems to support, because of high risk, a surgical approach aimed not only at resolution of unilateral pathology or prevention of a relapse, but also at prevention of contralateral testicular torsion. PMID:24826979
Torsional Oscillator Studies on Solid Helium
NASA Astrophysics Data System (ADS)
Kim, Duk Y.; Chan, Moses H. W.
2014-03-01
In 2004, the series of torsional oscillator (TO) experiments by Kim and Chan initiated considerable research activities on the supersolidity of helium. However, recent experiments in rigid torsional oscillators which reduce the effect of stiffening of bulk solid helium at low temepratures showed very small or negligible changes in the resonant period. A new TO experiment of solid helium confined in porous Vycor glass with no bulk solid helium in the sample cell show no evidence of supersolidity. Moreover, we have repeated an earlier experiment on hcp 3He solid, which shows similar low temperature stiffening like hcp 4He. We found that the small drop of the resonant period measured in the hcp 3He samples is comparable to that measured in the hcp 4He samples. These results confirm that the resonant period drops in torsional oscillators are consequence of the shear modulus stiffening effect in solid helium. Remaining issues and open questions on the supersolidity will be discussed. Support for this experiment was provided by NSF Grants No. DMR 1103159.
Isolated fallopian tube torsion in adolescents.
Rajaram, S; Bhaskaran, S; Mehta, S
2013-01-01
Background. Fallopian tube torsion is a rare cause of acute abdomen, occurring commonly in females of reproductive age. It lacks pathognomonic symptoms, signs, or imaging features, thus causing delay in surgical intervention. Case. We report two cases of isolated fallopian tube torsion in adolescent girls. In the first case a 19-year-old patient presented with acute pain in the left iliac region associated with episodes of vomiting for one day and mild tenderness on examination. Laparoscopy revealed left sided twisted fallopian tube associated with hemorrhagic cyst of ovary. The tube was untwisted and salvaged. In another case an 18-year-old virgin girl presented with similar complaints since one week, associated with mild tenderness in the lower abdomen and tender cystic mass on per rectal examination. On laparoscopy right twisted fallopian tube associated with a paratubal cyst was found. Salpingectomy was done as the tube was gangrenous. Conclusion. Fallopian tube torsion, though rare, should be considered in women of reproductive age with unilateral pelvic pain. Early diagnostic laparoscopy is important for an accurate diagnosis and could salvage the tube. PMID:24251052
Modeling DNA Thermodynamics under Torsional Stress
Wang, Qian; Pettitt, B. Montgomery
2014-01-01
Negatively twisted DNA is essential to many biological functions. Due to torsional stress, duplex DNA can have local, sequence-dependent structural defects. In this work, a thermodynamic model of DNA was built to qualitatively predict the local sequence-dependent mechanical instabilities under torsional stress. The results were compared to both simulation of a coarse-grained model and experiment results. By using the Kirkwood superposition approximation, we built an analytical model to represent the free energy difference ΔW of a hydrogen-bonded basepair between the B-form helical state and the basepair opened (or locally melted) state, within a given sequence under torsional stress. We showed that ΔW can be well approximated by two-body interactions with its nearest-sequence-neighbor basepairs plus a free energy correction due to long-range correlations. This model is capable of rapidly predicting the position and thermodynamics of local defects in a given sequence. The result qualitatively matches with an in vitro experiment for a long DNA sequence (>4000 basepairs). The 12 parameters used in this model can be further quantitatively refined when more experimental data are available. PMID:24606942
Modeling DNA thermodynamics under torsional stress.
Wang, Qian; Pettitt, B Montgomery
2014-03-01
Negatively twisted DNA is essential to many biological functions. Due to torsional stress, duplex DNA can have local, sequence-dependent structural defects. In this work, a thermodynamic model of DNA was built to qualitatively predict the local sequence-dependent mechanical instabilities under torsional stress. The results were compared to both simulation of a coarse-grained model and experiment results. By using the Kirkwood superposition approximation, we built an analytical model to represent the free energy difference ΔW of a hydrogen-bonded basepair between the B-form helical state and the basepair opened (or locally melted) state, within a given sequence under torsional stress. We showed that ΔW can be well approximated by two-body interactions with its nearest-sequence-neighbor basepairs plus a free energy correction due to long-range correlations. This model is capable of rapidly predicting the position and thermodynamics of local defects in a given sequence. The result qualitatively matches with an in vitro experiment for a long DNA sequence (>4000 basepairs). The 12 parameters used in this model can be further quantitatively refined when more experimental data are available. PMID:24606942
Torsional oscillations in the solar convection zone
NASA Astrophysics Data System (ADS)
Covas, E.; Tavakol, R.; Moss, D.; Tworkowski, A.
2000-08-01
Recent analysis of the helioseismic observations indicate that the previously observed surface torsional oscillations extend significantly downwards into the solar convection zone. In an attempt to understand these oscillations, we study the nonlinear coupling between the magnetic field and the solar differential rotation in the context of a mean field dynamo model, in which the nonlinearity is due to the action of the azimuthal component of the Lorentz force of the dynamo generated magnetic field on the solar angular velocity. The underlying zero order angular velocity is chosen to be consistent with the most recent helioseismic data. The model produces butterfly diagrams which are in qualitative agreement with the observations. It displays torsional oscillations that penetrate into the convection zone, and which with time migrate towards the equator. The period of these oscillations is found to be half that of the period of the global magnetic fields. This is compatible with the observed period of the surface torsional oscillations. Inside the convection zone, this is a testable prediction that is not ruled out by the observations so far available.
Lerwill, W.E.
1980-09-16
Apparatus for generating vibrations in a medium, such as the ground, comprises a first member which contacts the medium, means , preferably electromagnetic, which includes two relatively movable members for generating vibrations in the apparatus and means operatively connecting the said two members to said first member such that the relatively amplitudes of the movements of said three members can be adjusted to match the impedances of the apparatus and the medium.
NASA Astrophysics Data System (ADS)
Gupta, Amita; Singh, Ranvir; Ahmad, Amir; Kumar, Mahesh
2003-10-01
Today, vibration sensors with low and medium sensitivities are in great demand. Their applications include robotics, navigation, machine vibration monitoring, isolation of precision equipment & activation of safety systems e.g. airbags in automobiles. Vibration sensors have been developed at SSPL, using silicon micromachining to sense vibrations in a system in the 30 - 200 Hz frequency band. The sensing element in the silicon vibration sensor is a seismic mass suspended by thin silicon hinges mounted on a metallized glass plate forming a parallel plate capacitor. The movement of the seismic mass along the vertical axis is monitored to sense vibrations. This is obtained by measuring the change in capacitance. The movable plate of the parallel plate capacitor is formed by a block connected to a surrounding frame by four cantilever beams located on sides or corners of the seismic mass. This element is fabricated by silicon micromachining. Several sensors in the chip sizes 1.6 cm x 1.6 cm, 1 cm x 1 cm and 0.7 cm x 0.7 cm have been fabricated. Work done on these sensors, techniques used in processing and silicon to glass bonding are presented in the paper. Performance evaluation of these sensors is also discussed.
Torsional and biaxial (tension-torsion) fatigue damage mechanisms in Waspaloy at room temperature
NASA Technical Reports Server (NTRS)
Jayaraman, N.; Ditmars, M. M.
1989-01-01
Strain controlled torsional and biaxial (tension-torsion) low cycle fatigue behavior of Waspaloy was studied at room temperature as a function of heat treatment. Biaxial tests were conducted under proportional and nonproportional cyclic conditions. The deformation behavior under these different cyclic conditions was evaluated by slip trace analysis. For this, a Schmidt-type factor was defined for multiaxial loading conditions, and it was shown that when the slip deformation is predominant, nonproportional cycles are more damaging than proportional or pure axial or torsional cycles. This was attributed to the fact that under nonproportional cyclic conditions, deformation was through multiple slip, as opposed to single slip for other loading conditions, which gave rise to increased hardening. The total life for a given test condition was found to be independent of heat treatment. This was interpreted as being due to the differences in the cycles to initiation and propagation of cracks.
Biothermal sensing of a torsional artificial muscle
NASA Astrophysics Data System (ADS)
Lee, Sung-Ho; Kim, Tae Hyeob; Lima, Márcio D.; Baughman, Ray H.; Kim, Seon Jeong
2016-02-01
Biomolecule responsive materials have been studied intensively for use in biomedical applications as smart systems because of their unique property of responding to specific biomolecules under mild conditions. However, these materials have some challenging drawbacks that limit further practical application, including their speed of response and mechanical properties, because most are based on hydrogels. Here, we present a fast, mechanically robust biscrolled twist-spun carbon nanotube yarn as a torsional artificial muscle through entrapping an enzyme linked to a thermally sensitive hydrogel, poly(N-isopropylacrylamide), utilizing the exothermic catalytic reaction of the enzyme. The induced rotation reached an equilibrated angle in less than 2 min under mild temperature conditions (25-37 °C) while maintaining the mechanical properties originating from the carbon nanotubes. This biothermal sensing of a torsional artificial muscle offers a versatile platform for the recognition of various types of biomolecules by replacing the enzyme, because an exothermic reaction is a general property accompanying a biochemical transformation.Biomolecule responsive materials have been studied intensively for use in biomedical applications as smart systems because of their unique property of responding to specific biomolecules under mild conditions. However, these materials have some challenging drawbacks that limit further practical application, including their speed of response and mechanical properties, because most are based on hydrogels. Here, we present a fast, mechanically robust biscrolled twist-spun carbon nanotube yarn as a torsional artificial muscle through entrapping an enzyme linked to a thermally sensitive hydrogel, poly(N-isopropylacrylamide), utilizing the exothermic catalytic reaction of the enzyme. The induced rotation reached an equilibrated angle in less than 2 min under mild temperature conditions (25-37 °C) while maintaining the mechanical properties
Torsion-rotation intensities in methanol
NASA Astrophysics Data System (ADS)
Pearson, John
Methanol exists in numerous kinds of astronomical objects featuring a wide range of local conditions. The light nature of the molecule coupled with the internal rotation of the methyl group with respect to the hydroxyl group results in a rich, strong spectrum that spans the entire far-infrared region. As a result, any modest size observational window will have a number of strong methanol transitions. This has made it the gas of choice for testing THz receivers and to extract the local physical conditions from observations covering small frequency windows. The latter has caused methanol to be dubbed the Swiss army knife of astrophysics. Methanol has been increasingly used in this capacity and will be used even more for subsequent investigations into the Herschel archive, and with SOFIA and ALMA. Interpreting physical conditions on the basis of a few methanol lines requires that the molecular data, line positions, intensities, and collision rates, be complete, consistent and accurate to a much higher level than previously required for astrophysics. The need for highly reliable data is even more critical for modeling the two classes of widespread maser action and many examples of optical pumping through the torsional bands. Observation of the torsional bands in the infrared will be a unique opportunity to directly connect JWST observations with those of Herschel, SOFIA, and ALMA. The theory for the intensities of torsion-rotation transitions in a molecule featuring a single internally rotating methyl group is well developed after 70 years of research. However, other than a recent very preliminary and not completely satisfactory investigation of a few CH3OH torsional bands, this theory has never been experimentally tested for any C3V internal rotor. More alarming is a set of recent intensity calibrated microwave measurements that showed deviations relative to calculations of up to 50% in some ground state rotational transitions commonly used by astronomers to extract
An Analytical Model for Squeeze-Film Damping of Perforated Torsional Microplates Resonators
Li, Pu; Fang, Yuming
2015-01-01
Squeeze-film damping plays a significant role in the performance of micro-resonators because it determines their quality factors. Perforations in microstructures are often used to control the squeeze-film damping in micro-resonators. To model the perforation effects on the squeeze-film damping, many analytical models have been proposed, however, most of the previous models have been concerned with the squeeze-film damping due to the normal motion between the perforated vibrating plate and a fixed substrate, while there is a lack of works that model the squeeze-film damping of perforated torsion microplates, which are also widely used in MEMS devices. This paper presents an analytical model for the squeeze-film damping of perforated torsion microplates. The derivation in this paper is based on a modified Reynolds equation that includes compressibility and rarefaction effects. The pressure distribution under the vibrating plate is obtained using the double sine series. Closed-form expressions for the stiffness and the damping coefficients of the squeeze-film are derived. The accuracy of the model is verified by comparing its results with the finite element method (FEM) results and the experimental results available in the literature. The regime of validity and limitations of the present model are assessed. PMID:25815453
Unraveling torsional bath interactions with the CO stretching state in methanol
NASA Astrophysics Data System (ADS)
Pearson, John C.; Daly, Adam M.; Lees, Ronald M.
2015-12-01
Quantum mechanical models describing the effects of a C3 internal rotor have been successful in modeling all the torsional manifolds of isolated vibrational states. However, modeling the coupling between nearly degenerate small amplitude vibrations in the C3 internal rotation case remains far from satisfactory and a variety of practical and fundamental questions persist on basis sets, the relative importance of effects and how the problem should be approached. The ν8 C-O stretching state of methanol has been well studied with infrared techniques and has the potential to serve as an experimental reference data set for the development of models for the coupled large and small amplitude motion case. A combined infrared-microwave study of the lowest K A-states of vt = 3, vt = 4 and ν8 has been performed to understand the nature of the interactions between ν8 the excited torsional states. The interaction between vt = 4 and ν8 at K = 0+ has been confirmed to be Fermi type with magnitude of 2.5 cm-1. Additionally, the fundamental a-symmetry and b-symmetry Coriolis interactions between vt = 3 and ν8 have been estimated to be 8900 MHz and -360 MHz, respectively. The magnitude of these interactions suggests that modeling the ν8 state, the vt = 3 state, and the vt = 4 states will have to carefully account for these interactions.
An analytical model for squeeze-film damping of perforated torsional microplates resonators.
Li, Pu; Fang, Yuming
2015-01-01
Squeeze-film damping plays a significant role in the performance of micro-resonators because it determines their quality factors. Perforations in microstructures are often used to control the squeeze-film damping in micro-resonators. To model the perforation effects on the squeeze-film damping, many analytical models have been proposed, however, most of the previous models have been concerned with the squeeze-film damping due to the normal motion between the perforated vibrating plate and a fixed substrate, while there is a lack of works that model the squeeze-film damping of perforated torsion microplates, which are also widely used in MEMS devices. This paper presents an analytical model for the squeeze-film damping of perforated torsion microplates. The derivation in this paper is based on a modified Reynolds equation that includes compressibility and rarefaction effects. The pressure distribution under the vibrating plate is obtained using the double sine series. Closed-form expressions for the stiffness and the damping coefficients of the squeeze-film are derived. The accuracy of the model is verified by comparing its results with the finite element method (FEM) results and the experimental results available in the literature. The regime of validity and limitations of the present model are assessed. PMID:25815453
NASA Astrophysics Data System (ADS)
Boussessi, R.; Senent, M. L.; Jaïdane, N.
2016-04-01
An elaborate variational procedure of reduced dimensionality based on explicitly correlated coupled clusters calculations is applied to understand the far infrared spectrum of ethylene-glycol, an astrophysical species. This molecule can be classified in the double molecular symmetry group G8 and displays nine stable conformers, gauche and trans. In the gauche region, the effect of the potential energy surface anisotropy due to the formation of intramolecular hydrogen bonds is relevant. For the primary conformer, stabilized by a hydrogen bond, the ground vibrational state rotational constants are computed to be A0 = 15 369.57 MHz, B0 = 5579.87 MHz, and C0 = 4610.02 MHz corresponding to differences of 6.3 MHz, 7.2 MHz, and 3.5 MHz from the experimental parameters. Ethylene glycol displays very low torsional energy levels whose classification is not straightforward and requires a detailed analysis of the torsional wavefunctions. Tunneling splittings are significant and unpredictable due to the anisotropy of the potential energy surface PES. The ground vibrational state splits into 16 sublevels separated ˜142 cm-1. The splitting of the "G1 sublevels" was calculated to be ˜0.26 cm-1 in very good agreement with the experimental data (0.2 cm-1 = 6.95 MHz). Transitions corresponding to the three internal rotation modes allow assignment of previously observed Q branches. Band patterns, calculated between 362.3 cm-1 and 375.2 cm-1, 504 cm-1 and 517 cm-1, and 223.3 cm-1 and 224.1 cm-1, that correspond to the tunnelling components of the v21 fundamental (v21 = OH-torsional mode), are assigned to the prominent experimental Q branches.
The lowest frequency vibrational fundamental of disilane: A three-band analysis
NASA Astrophysics Data System (ADS)
Borvayeh, L.; Moazzen-Ahmadi, N.; Horneman, V.-M.
2007-04-01
The lowest frequency perpendicular fundamental band ν9 of disilane has been analyzed to investigate torsion mediated vibrational interactions. We report here a three-band analysis involving torsional levels built on the ground state, the ν9 vibrational fundamental, and ν3 fundamental. This analysis includes transitions from the far-infrared torsional bands, ν4, 2 ν4 - ν4, 3 ν4 - 2 ν4, two perturbation-allowed rotational series from the overtone band 3 ν4 and transitions restricted to -21 ⩽ kΔ k ⩽ 21 in the ν9 fundamental band. An excellent fit to the included data was obtained. Two interactions are identified in this fit, a resonant Coriolis interaction between the ν9 torsional stack and that of the ground vibrational state and a Fermi interaction between the ν3 fundamental and the gs. The introduction of the Fermi interaction causes a large change in the barrier height for the ground vibrational state and makes the barrier shape parameter redundant, indicating that the vibrational contributions to the experimental barrier shape are dominant. Such effects have also been observed for ethane and other similar molecules.
NASA Astrophysics Data System (ADS)
Awall, Md. Robiul; Hayashikawa, Toshiro; Matsumoto, Takashi; He, Xingwen
2012-03-01
Curved twin I-girder bridges (CTIGBs) have low torsional stiffness that makes them vulnerable to dynamic loads. This study investigates the effects of bottom bracings on the torsional dynamic characteristics of CTIGBs. Five types of bottom bracings are designed to investigate their effects on the dynamic characteristics of CTIGBs with different curvatures under free and forced vibrations. To perform numerical investigations, three-dimensional (3-D) finite element (FE) bridge and vehicle models are established using commercial ANSYS code, and then a vehicle-bridge interaction analysis approach is proposed. Road roughness profiles generated from power spectral density and cross spectral functions are also taken into account in the analyses. The numerical results show that torsional frequencies increase significantly after providing bottom bracings, and the increasing rate depends on the type of bottom bracings and their locations of installation. Bottom bracings can act as load transmitting members from one main girder to the others. Large negative bearing forces that have occurred in bridges with small radii of curvatures can be remarkably reduced by providing bottom bracing systems. It is found that the performances of several bottom bracing systems are effective in improving the torsional dynamic characteristics of the bridges in this study.
DOWNHOLE VIBRATION MONITORING AND CONTROL SYSTEM
Martin E. Cobern
2003-02-01
The purpose of this program is to develop the Drilling Vibration Monitoring & Control System (DVMCS) to both record and reduce drilling vibrations in a ''smart'' drill string. It is composed of two main elements. The first is a multi-axis active vibration damper to minimize harmful axial, lateral and torsional vibrations, and thereby increase both rate of penetration (ROP) and bit life, as well that the life of other drillstring components. The hydraulic impedance (hardness) of this damper will be continuously adjusted using unique technology that is robust, fast-acting and reliable. The second component is a real-time system to monitor 3-axis drillstring vibration, and related parameters including weight- and torque-on-bit (TOB) and temperature. This monitor will determine the current vibration environment and adjust the damper accordingly. In some configurations, it may also send diagnostic information to the surface via real-time telemetry. Phase I of this program addresses an evaluation of the environment in which the DVMCS will operate; modeling of a drillstring response including the active damper; a top-level design of the mechanical and electronic systems; analyzing the anticipated performance of the damper by modeling and laboratory testing of small prototypes; and doing preliminary economic, market, environmental and financing analyses. This phase is scheduled to last fourteen months, until November 30, 2003. During this first quarter, significant progress was achieved on the first two objectives, and work was begun on several others. Initial designs of the DVMCS are underway.
Torsion discovery potential and its discrimination at CERN LHC
Almeida, F. M. L. Jr. de; Nepomuceno, A. A.; Vale, M. A. B. do
2009-01-01
Torsion models constitute a well-known class of extended quantum gravity models. In this paper we study some phenomenological consequences of a torsion field interacting with fermions at LHC. A torsion field could appear as a new heavy state characterized by its mass and couplings to fermions. These new states will form a resonance decaying into difermions, as occurs in many extensions of the standard model, such as models predicting the existence of additional neutral gauge bosons, usually named Z{sup '}. Using the dielectron channel we evaluate the integrated luminosity needed for a 5{sigma} discovery as a function of the torsion mass, for different coupling values. We also calculate the luminosity needed to discriminate, with 95% C.L., the two possible different torsion natures. Finally, we show that the observed signal coming from the torsion field could be distinguished from a signal coming from a new neutral gauge boson, provided there is enough luminosity.
NASA Astrophysics Data System (ADS)
Xu, Li-Hong; Lees, Ronald M.; Hougen, Jon T.
2013-06-01
The ν_{2}, ν_{3} and ν_{9} CH stretching modes of methanol in the 3μm region exhibit a significant amount of torsion-vibration interaction, as illustrated for ν_{9} by the facts that: (i) the three hydrogen atoms each pass through a plane of symmetry of the molecule twice during the course of one full internal rotation motion, once at a minimum and once at a maximum in the three-fold potential energy curve, (ii) the H atom in the plane of symmetry is nearly motionless for the ν_{9} mode, and therefore (iii) the property of remaining motionless must be transferred from one H to another six times during one full internal rotation motion. In this talk we examine quantitatively the general phenomenon of torsion-vibration interaction in the methyl top stretching modes in two ways. First, we present plots of normal modes produced in Gaussian projected frequency calculations that are expressed either in terms of several sets of internal coordinates, or in terms of Cartesian displacement vectors for the methyl hydrogen atoms. Some of these plots display a nearly three-fold sine or cosine behavior, where the sine or cosine behavior is dictated by group-theoretical symmetry arguments. Other plots display stunning features ranging from loss of simple three-fold oscillatory pattern to cusp-like peaks or dips. Somewhat surprisingly, none of our ab initio plots for methanol exhibit a sign change after a 2π internal rotation of the methyl top. Second, we present a relatively simple model for the three CH stretching motions, characterized by three parameters associated with: (i) a vibrational A/E energy difference, (ii) a Jahn-Teller-like torsion-vibration interaction term within the vibrational E state, and (iii) a Renner-Teller-like torsion-vibration interaction term within the E state. This model gives nearly quantitative agreement with both the regular and irregular features of the ab initio plots. The good agreement suggests that various aspects of the physics of the
Can Gravity Probe B usefully constrain torsion gravity theories?
Flanagan, Eanna E.; Rosenthal, Eran
2007-06-15
In most theories of gravity involving torsion, the source for torsion is the intrinsic spin of matter. Since the spins of fermions are normally randomly oriented in macroscopic bodies, the amount of torsion generated by macroscopic bodies is normally negligible. However, in a recent paper, Mao et al. (arXiv:gr-qc/0608121) point out that there is a class of theories, including the Hayashi-Shirafuji (1979) theory, in which the angular momentum of macroscopic spinning bodies generates a significant amount of torsion. They further argue that, by the principle of action equals reaction, one would expect the angular momentum of test bodies to couple to a background torsion field, and therefore the precession of the Gravity Probe B gyroscopes should be affected in these theories by the torsion generated by the Earth. We show that in fact the principle of action equals reaction does not apply to these theories, essentially because the torsion is not an independent dynamical degree of freedom. We examine in detail a generalization of the Hayashi-Shirafuji theory suggested by Mao et al. called Einstein-Hayashi-Shirafuji theory. There are a variety of different versions of this theory, depending on the precise form of the coupling to matter chosen for the torsion. We show that, for any coupling to matter that is compatible with the spin transport equation postulated by Mao et al., the theory has either ghosts or an ill-posed initial-value formulation. These theoretical problems can be avoided by specializing the parameters of the theory and in addition choosing the standard minimal coupling to matter of the torsion tensor. This yields a consistent theory, but one in which the action equals reaction principle is violated, and in which the angular momentum of the gyroscopes does not couple to the Earth's torsion field. Thus, the Einstein-Hayashi-Shirafuji theory does not predict a detectable torsion signal for Gravity Probe B. There may be other torsion theories which do.
Torsion-gravity for Dirac fields and their effective phenomenology
NASA Astrophysics Data System (ADS)
Fabbri, Luca
2014-08-01
We will consider the torsional completion of gravity for a background filled with Dirac matter fields, studying the weak-gravitational non-relativistic approximation, in view of an assessment about their effective phenomenology: we discuss how the torsionally-induced nonlinear interactions among fermion fields in this limit are compatible with all experiments and remarks on the role of torsion to suggest new physics are given.
NASA Technical Reports Server (NTRS)
Messaro. Semma; Harrison, Phillip
2010-01-01
Ares I Zonal Random vibration environments due to acoustic impingement and combustion processes are develop for liftoff, ascent and reentry. Random Vibration test criteria for Ares I Upper Stage pyrotechnic components are developed by enveloping the applicable zonal environments where each component is located. Random vibration tests will be conducted to assure that these components will survive and function appropriately after exposure to the expected vibration environments. Methodology: Random Vibration test criteria for Ares I Upper Stage pyrotechnic components were desired that would envelope all the applicable environments where each component was located. Applicable Ares I Vehicle drawings and design information needed to be assessed to determine the location(s) for each component on the Ares I Upper Stage. Design and test criteria needed to be developed by plotting and enveloping the applicable environments using Microsoft Excel Spreadsheet Software and documenting them in a report Using Microsoft Word Processing Software. Conclusion: Random vibration liftoff, ascent, and green run design & test criteria for the Upper Stage Pyrotechnic Components were developed by using Microsoft Excel to envelope zonal environments applicable to each component. Results were transferred from Excel into a report using Microsoft Word. After the report is reviewed and edited by my mentor it will be submitted for publication as an attachment to a memorandum. Pyrotechnic component designers will extract criteria from my report for incorporation into the design and test specifications for components. Eventually the hardware will be tested to the environments I developed to assure that the components will survive and function appropriately after exposure to the expected vibration environments.
Coupled AXIAL-LATERAL-TORSIONAL Dynamics of a ROTOR-BEARING System Geared by Spur Bevel Gears
NASA Astrophysics Data System (ADS)
LI, M.; HU, H. Y.; JIANG, P. L.; YU, L.
2002-07-01
The coupled lateral-torsional dynamics of parallel rotor-bearing systems has been intensively investigated. However, little attention has been paid to the analysis of coupled vibrations of angled rotor-bearing systems so that the torsional and the lateral vibrations of those systems are usually analyzed separately. In this paper, the coupled axial-lateral-torsional dynamics of a rotor-bearing system geared by bevel gears is studied. The meshing of two spur bevel gears is analyzed on the basis of a pair of virtual cylindrical gears, and thereafter the constraint condition describing the relationship between the generalized displacements of bevel gears is derived under some assumptions. The coupled dynamic model is established by using Lagrange's equation under this constraint condition. The numerical results of a number of case studies show that the critical speeds of the coupled model are different from those of the uncoupled model both in values and modes, and the threshold speed of stability is fairly less than that of the uncoupled model. The effects of system parameters, such as the pitch cone angles, on the coupling behavior are also discussed.
Electronic and Vibrational Properties of meso -Tetraphenylporphyrin on Silver Substrates
El-Khoury, Patrick Z.; Honkala, Karoliina; Hess, Wayne P.
2014-09-18
The electronic and vibrational properties of meso-tetraphenylporphyrin (mtpp) on silver substrates are investigated using UV–vis and surface-enhanced resonance Raman scattering (SERRS) spectroscopy. Whereas the vibrational signatures associated with the tetrapyrrole backbone exhibit minor variations throughout sequences of consecutively recorded SERRS spectra, the C=C stretching vibrational modes localized on the meso-phenyl moieties of mtpp exhibit noticeable intensity fluctuations, masked in the average SERRS response. Finally, we attribute the observed vibrational-state-specific blinking events to conformational changes in mtpp, namely, torsional flexibility which mediates the coupling between the π-framework of the meso-phenyls and the underlying metal substrate.
Time-dependent Navier-Stokes computations for flow-induced vibrations of vanes
NASA Astrophysics Data System (ADS)
Liu, B. L.; O'Farrel, J. M.; Holt, J. B.; Dougherty, N. S.
Flows over two curved vane configurations were computed using a time-accurate compressible Navier-Stokes flow model. One configuration showed the presence of strong flow-induced vibrations at Strouhal numbers near 0.19 and 0.38 for bending and torsional excitation. In the other configuration, a simple modification reduced both types of response. Laminar flows were analyzed for the effects of flow-induced vibrations, and flow fields were solved for a rigid vane and a vane undergoing forced vibrations at prescribed amplitude and frequency simulating vibration response to a coupled vortex-shedding/elastic motion feedback cycle.
Contribution to the theory of propeller vibrations
NASA Technical Reports Server (NTRS)
Liebers, F
1930-01-01
This report presents a calculation of the torsional frequencies of revolving bars with allowance for the air forces. Calculation of the flexural or bonding frequencies of revolving straight or tapered bars in terms of the angular velocity of revolution. Calculation on the basis of Rayleigh's principle of variation. There is also a discussion of error estimation and the accuracy of results. The author then provides an application of the theory to screw propellers for airplanes and the discusses the liability of propellers to damage through vibrations due to lack of uniform loading.
Particle nonuniformity effects on particle cloud flames in low gravity
NASA Technical Reports Server (NTRS)
Berlad, A. L.; Tangirala, V.; Seshadri, K.; Facca, L. T.; Ogrin, J.; Ross, H.
1991-01-01
Experimental and analytical studies of particle cloud combustion at reduced gravity reveal the substantial roles that particle cloud nonuniformities may play in particle cloud combustion. Macroscopically uniform, quiescent particle cloud systems (at very low gravitational levels and above) sustain processes which can render them nonuniform on both macroscopic and microscopic scales. It is found that a given macroscopically uniform, quiescent particle cloud flame system can display a range of microscopically nonuniform features which lead to a range of combustion features. Microscopically nonuniform particle cloud distributions are difficult experimentally to detect and characterize. A uniformly distributed lycopodium cloud of particle-enriched microscopic nonuniformities in reduced gravity displays a range of burning velocities for any given overall stoichiometry. The range of observed and calculated burning velocities corresponds to the range of particle enriched concentrations within a characteristic microscopic nonuniformity. Sedimentation effects (even in reduced gravity) are also examined.
Superfluid Turbulence in a Nonuniform Circular Channel
NASA Astrophysics Data System (ADS)
Murphy, Paul Joseph
The excess dissipation due to the presence of quantized vorticity in flowing helium has been studied extensively. The success of the microscopic theory proposed by Schwarz in describing many properties of this dissipation led to a belief that the major aspects of the problem had been understood at the microscopic level. The experiment of Kafkalidis and Tough demonstrated that a weak one dimensional nonuniformity in the flow field led to a dramatic departure between the observed behavior and the predictions of the Schwarz theory using the local uniformity approximation (LUA). The research presented in this thesis was undertaken to measure the dissipative states for thermal counterflow with a weak two dimensional nonuniformity. The experiment of Kafkalidis and Tough used a flow channel with a high aspect ratio. Such channels are known to exhibit only one state of superfluid turbulence. In this research the channel is circular in cross section and shows two distinct turbulent states (T-I and T-II). This experiment demonstrates that there is no difference in the excess dissipation for flows that are either converging or diverging. The T-I state is described by the same parameters as the T-I state in uniform channels. The turbulence exhibits front behavior at the transition between states. These conclusions are consistent with the LUA. The T-II state is at variance with the LUA, but is consistant with the results found in the Kafkalidis and Tough experiment.
The non-uniformity of fossil preservation.
Holland, Steven M
2016-07-19
The fossil record provides the primary source of data for calibrating the origin of clades. Although minimum ages of clades are given by the oldest preserved fossil, these underestimate the true age, which must be bracketed by probabilistic methods based on multiple fossil occurrences. Although most of these methods assume uniform preservation rates, this assumption is unsupported over geological timescales. On geologically long timescales (more than 10 Myr), the origin and cessation of sedimentary basins, and long-term variations in tectonic subsidence, eustatic sea level and sedimentation rate control the availability of depositional facies that preserve the environments in which species lived. The loss of doomed sediments, those with a low probability of preservation, imparts a secular trend to fossil preservation. As a result, the fossil record is spatially and temporally non-uniform. Models of fossil preservation should reflect this non-uniformity by using empirical estimates of fossil preservation that are spatially and temporally partitioned, or by using indirect proxies of fossil preservation. Geologically, realistic models of preservation will provide substantially more reliable estimates of the origination of clades.This article is part of the themed issue 'Dating species divergences using rocks and clocks'. PMID:27325828
Nonquasineutral electron vortices in nonuniform plasmas
Angus, J. R.; Richardson, A. S.; Swanekamp, S. B.; Schumer, J. W.; Ottinger, P. F.
2014-11-15
Electron vortices are observed in the numerical simulation of current carrying plasmas on fast time scales where the ion motion can be ignored. In plasmas with nonuniform density n, vortices drift in the B × ∇n direction with a speed that is on the order of the Hall speed. This provides a mechanism for magnetic field penetration into a plasma. Here, we consider strong vortices with rotation speeds V{sub ϕ} close to the speed of light c where the vortex size δ is on the order of the magnetic Debye length λ{sub B}=|B|/4πen and the vortex is thus nonquasineutral. Drifting vortices are typically studied using the electron magnetohydrodynamic model (EMHD), which ignores the displacement current and assumes quasineutrality. However, these assumptions are not strictly valid for drifting vortices when δ ≈ λ{sub B}. In this paper, 2D electron vortices in nonuniform plasmas are studied for the first time using a fully electromagnetic, collisionless fluid code. Relatively large amplitude oscillations with periods that correspond to high frequency extraordinary modes are observed in the average drift speed. The drift speed W is calculated by averaging the electron velocity field over the vorticity. Interestingly, the time-averaged W from these simulations matches very well with W from the much simpler EMHD simulations even for strong vortices with order unity charge density separation.
Downsampling Non-Uniformly Sampled Data
NASA Astrophysics Data System (ADS)
Eng, Frida; Gustafsson, Fredrik
2007-12-01
Decimating a uniformly sampled signal a factor D involves low-pass antialias filtering with normalized cutoff frequency 1/ D followed by picking out every D th sample. Alternatively, decimation can be done in the frequency domain using the fast Fourier transform (FFT) algorithm, after zero-padding the signal and truncating the FFT. We outline three approaches to decimate non-uniformly sampled signals, which are all based on interpolation. The interpolation is done in different domains, and the inter-sample behavior does not need to be known. The first one interpolates the signal to a uniformly sampling, after which standard decimation can be applied. The second one interpolates a continuous-time convolution integral, that implements the antialias filter, after which every D th sample can be picked out. The third frequency domain approach computes an approximate Fourier transform, after which truncation and IFFT give the desired result. Simulations indicate that the second approach is particularly useful. A thorough analysis is therefore performed for this case, using the assumption that the non-uniformly distributed sampling instants are generated by a stochastic process.
Magnetic tearing of plasma discharges due to nonuniform resistivity
NASA Technical Reports Server (NTRS)
Hassam, A. B.
1988-01-01
The rearrangement of current in a plasma discharge in response to resistivity nonuniformities within a magnetic surface is studied. It is shown that macroscopic magnetic islands develop about those surfaces where the nonuniformity is aligned with the magnetic field. If the nonuniformity and the field are not aligned anywhere, there is no current rearrangement; instead, relatively large plasma flows are set up. Such resistivity inhomogeneities can obtain in solar coronal loops and, in some circumstances, in tokamak discharges.
Axial development and radial non-uniformity of flow in packed columns.
Park, Jaekeun C; Raghavan, Karthik; Gibbs, Stephen J
2002-02-01
Flow inhomogeneity and axial development in low-pressure chromatographic columns have been studied by magnetic resonance imaging velocimetry. The columns studied included (a) an 11.7-mm I.D. column packed with either 50 microm diameter porous polyacrylamide, or 99 or 780 microm diameter impermeable polystyrene beads, and (b) a 5-mm I.D. column commercially packed with 10 microm polymeric beads. The packing methods included gravity settling, slurry packing, ultrasonication, and dry packing with vibration. The magnetic resonance method used averaged apparent fluid velocity over both column cross-sections and fluid displacements greater than one particle diameter and hence permits assessment of macroscopic flow non-uniformities. The results confirm that now non-uniformities induced by the conical distributor of the 11.7-mm I.D. column or the presence of voids at the column entrance relax on a length scale of the column radius. All of the 11.7-mm I.D. columns examined exhibit near wall channeling within a few particle diameters of the wall. The origins of this behavior are demonstrated by imaging of the radial dependence of the local porosity for a column packed with 780 microm beads. Columns packed with the 99-microm beads exhibit reduced flow in a region extending from ten to three-to-five particle diameters from the wall. This velocity reduction is consistent with a reduced porosity of 0.35 in this region as compared to approximately 0.43 in the bulk of the column. Ultrasonicated and dry-packed columns exhibit enhanced flow in a region located between approximately eight and 20 particle diameters from the wall. This enhancement maybe caused by packing density inhomogeneity and/or particle size segregation caused by vibration during the packing process. No significant non-uniformities on length scales of 20 microm or greater were observed in the commercially packed column packed with 10 microm particles. PMID:11860146
Ovarian torsion: opportunities to improve clinical management.
Bharathan, R; Ramsawak, L; Kelly, A
2012-10-01
Ovarian torsion is an uncommon condition which may affect women of any age. In a significant number of women, it may be associated with a concomitant pathology such as a cyst. Presently, there is no single diagnostic tool with significant predictive value. Multimodal diagnostic tools hold promise of early accurate diagnosis; prospective studies are required to assess the validity of such tools. This would enable wider application of ovarian function preserving procedures. Further, an assessment of the psychological impact of oophorectomy should be studied in order to facilitate the optimal tailored care. PMID:22943718
Aspects of Interacting Electromagnetic and Torsion Fields
NASA Astrophysics Data System (ADS)
Gaete, Patricio; Helaÿel-Neto, José A.
2011-01-01
The interaction energy is studied for the coupling of axial torsion fields with photons in the presence of an external electromagnetic field. To this end, we compute the static quantum potential. Our discussion is carried out using the gauge-invariant but path-dependent variables formalism, which is alternative to the Wilson loop approach. Our results show that the static potential is a Yukawa correction to the usual static Coulomb potential. Interestingly, when this calculation is done by considering a mass term for the gauge field, the Coulombic piece disappears leading to a screening phase.
The Torsional Spectrum of Doubly Deuterated Methanol CHD_2OH
NASA Astrophysics Data System (ADS)
Ndao, M.; Coudert, L. H.; Kwabia Tchana, F.; Barros, J.; Margulès, L.; Manceron, Laurent; Roy, P.
2014-06-01
Although the torsional spectrum of several isotopic species of methanol with a symmetrical CH_3 or CD_3 was analyzed some time ago, it is recently, and only for the monodeuterated species CH_2DOH, that such an analysis was extended to the case of an asymmetrical methyl group. In this talk, based on a Fourier transform high-resolution spectrum recorded in the 20 to 670 wn region, the first analysis of the torsional spectrum of doubly deuterated methanol CHD_2OH will be presented. The Q branch of many torsional subbands could be observed and their assignment was initiated using a theoretical torsion-rotation spectrum computed with an approach accounting for the torsion-rotation Coriolis coupling and for the dependence of the generalized inertia tensor on the angle of internal rotation. 46 torsional subbands were thus assigned. For 28 of them, their rotational structure could be assigned and fitted using an effective Hamiltonian expressed as a J(J+1) expansion; and for 2 of them microwave transitions within the lower torsional level could also be included in the analysis. In several cases these analysis revealed that the torsional levels are strongly perturbed. In the talk, the torsional parameters retrieved in the analysis of the torsional subband centers will be discussed. The results of the analysis of the rotational structure of the torsional subbands will be presented and we will also try to understand the nature of the perturbations. At last, preliminary results about the analysis of the microwave spectrum will be presented. El Hilali, Coudert, Konov, and Klee, J. Chem. Phys. 135 (2011) 194309 Lauvergnat, Coudert, Klee, and Smirnov, J. Mol. Spectrosc. 256 (2009) 204 Quade, Liu, Mukhopadhyay, and Su, J. Mol. Spectrosc. 192 (1998) 378 Pearson, Yu, and Drouin, J. Mol. Spectrosc. 280 (2012) 119
Standing Waves in a Nonuniform Medium
ERIC Educational Resources Information Center
Gluck, Paul
2011-01-01
A recent note in this journal presented a demonstration of standing waves along a cord consisting of two parts having different material densities, showing different sized wavelengths in each part. A generalization of that experiment to a continuously varying linear mass density is to vibrate a strip of material with gradually varying width (mass…
NASA Technical Reports Server (NTRS)
Bozeman, Richard J., Jr. (Inventor)
1990-01-01
The invention relates to monitoring circuitry for the real time detection of vibrations of a predetermined frequency and which are greater than a predetermined magnitude. The circuitry produces an instability signal in response to such detection. The circuitry is particularly adapted for detecting instabilities in rocket thrusters, but may find application with other machines such as expensive rotating machinery, or turbines. The monitoring circuitry identifies when vibration signals are present having a predetermined frequency of a multi-frequency vibration signal which has an RMS energy level greater than a predetermined magnitude. It generates an instability signal only if such a vibration signal is identified. The circuitry includes a delay circuit which responds with an alarm signal only if the instability signal continues for a predetermined time period. When used with a rocket thruster, the alarm signal may be used to cut off the thruster if such thruster is being used in flight. If the circuitry is monitoring tests of the thruster, it generates signals to change the thruster operation, for example, from pulse mode to continuous firing to determine if the instability of the thruster is sustained once it is detected.
Development of monofilar rotor hub vibration absorber
NASA Technical Reports Server (NTRS)
Duh, J.; Miao, W.
1983-01-01
A design and ground test program was conducted to study the performance of the monofilar absorber for vibration reduction on a four-bladed helicopter. A monofilar is a centrifugal tuned two degree-of-freedom rotor hub absorber that provides force attenuation at two frequencies using the same dynamic mass. Linear and non-linear analyses of the coupled monofilar/airframe system were developed to study tuning and attenuation characteristics. Based on the analysis, a design was fabricated and impact bench tests verified the calculated non-rotating natural frequencies and mode shapes. Performance characteristics were measured using a rotating absorber test facility. These tests showed significant attenuation of fixed-system 4P hub motions due to 3P inplane rotating-system hub forces. In addition, detuning effects of the 3P monofilar modal response were small due to the nonlinearities and tuning pin slippage. However, attenuation of 4P hub motions due to 5P inplane hub forces was poor. The performance of the 5P monofilar modal response was degraded by torsional motion of the dynamic mass relative to the support arm which resulted in binding of the dynamic components. Analytical design studies were performed to evaluate this torsional motion problem. An alternative design is proposed which may alleviate the torsional motion of the dynamic mass.
Vibration characteristics of 1/8-scale dynamic models of the space-shuttle solid-rocket boosters
NASA Technical Reports Server (NTRS)
Leadbetter, S. A.; Stephens, W.; Sewall, J. L.; Majka, J. W.; Barret, J. R.
1976-01-01
Vibration tests and analyses of six 1/8 scale models of the space shuttle solid rocket boosters are reported. Natural vibration frequencies and mode shapes were obtained for these aluminum shell models having internal solid fuel configurations corresponding to launch, midburn (maximum dynamic pressure), and near endburn (burnout) flight conditions. Test results for longitudinal, torsional, bending, and shell vibration frequencies are compared with analytical predictions derived from thin shell theory and from finite element plate and beam theory. The lowest analytical longitudinal, torsional, bending, and shell vibration frequencies were within + or - 10 percent of experimental values. The effects of damping and asymmetric end skirts on natural vibration frequency were also considered. The analytical frequencies of an idealized full scale space shuttle solid rocket boosted structure are computed with and without internal pressure and are compared with the 1/8 scale model results.
Diagnostic Efficacy of Sonography for Diagnosis of Ovarian Torsion
Rostamzadeh, Ayoob; Mirfendereski, Sam; Rezaie, Mohammad Jafar; Rezaei, Shohreh
2014-01-01
Objectives: Misdiagnosing ovarian torsion is now suggested as an important issue in clinical setting. The aim of this study was to determine the diagnostic accuracy of sonography for ovarian torsion. Methods : In this study 323 women with acute pelvic pain with highly suspected ovarian torsion signs and symptoms attending Imam Reza Medical Center in Kermanshah between 2011 through 2012 were included and underwent a transabdominal sonography (2-5 MHz probes). Then findings of sonography were compared with laparatomy. Results : The ultrasound correctly diagnosed 72.1% of ovarian torsion and missed 27.9% of them (false negatives). However, one free subject (0.4%) was misclassified as ovarian torsion (false positive). There was a strong correlation between sonography and laparatomy with a kappa value of 84.0%. The sensitivity and specificity of sonography were 72.1% and 99.6%, respectively. Sonography had a positive predictive value of 96.9%, a negative predictive value of 95.9%, and a total accuracy of 96.0% for detection of ovarian torsion. Conclusion: Sonography appears to be an excellent method to evaluate patients with suspected ovarian torsion. Abnormal blood flow detected by sonography is highly predictive of ovarian torsion and is therefore useful in the diagnosis of this phenomenon. PMID:24772154
Torsional Strengthening of RC Beams Using GFRP Composites
NASA Astrophysics Data System (ADS)
Patel, Paresh V.; Jariwala, Vishnu H.; Purohit, Sharadkumar P.
2016-06-01
Fiber reinforced polymer as an external reinforcement is used extensively for axial, flexural and shear strengthening in structural systems. The strengthening of members subjected to torsion is recently being explored. The loading mechanism of beams located at the perimeter of buildings which carry loads from slabs, joists and beams from one side of the member generates torsion that are transferred from the beams to the columns. In this work an experimental investigation on the improvement of the torsional resistance of reinforced concrete beams using Glass Fiber Reinforced Polymer (GFRP) is presented. Total 24 RC beams have been cast in this work. Ten beams of dimension 150 mm × 150 mm × 1300 mm are subjected to pure torsion while fourteen beams of 150 mm × 150 mm × 1700 mm are subjected to combined torsion and bending. Two beams in each category are designated as control specimen and remaining beams are strengthened by GFRP wrapping of different configurations. Pure torsion on specimens is applied using specially fabricated support mechanism and universal testing machine. For applying combined torsion and bending a loading frame and test set up are fabricated. Measurements of angle of twist at regular interval of torque, torsion at first crack, and ultimate torque, are obtained for all specimens. Results of different wrapping configurations are compared for control and strengthened beams to suggest effective GFRP wrapping configuration.
Analysis of interlaminar stresses in the torsion of symmetric laminates
NASA Astrophysics Data System (ADS)
Whitney, James M.
1994-03-01
In the present paper the effect of transverse (interlaminar) normal strain on the torsional response of symmetrically laminated, anisotropic plates is investigated. The analysis is based on a modified form of the global laminate model developed by Pagano and Soni. In-plane stresses are modified in the boundary zone to satisfy free-edge boundary conditions. For the general case of angle-ply layers, a laminated composite behaves in a manner similar to an anisotropic plate. The existence of the bending-twisting coupling phenomenon found in the case of anisotropic plates leads to two classic problems in conjunction with torsional loading. In the first case, referred to as 'pure torsion,' the torsional axis of the plates does not bend. Thus, an axial bending moment is required in addition to the torsional load to suppress plate bending. In the second case, referred to as 'free torsion,' the only loading is torque in which anisotropy induces bending of the torsional axis. For the purposes of this paper it is sufficient to consider the case of pure torsion only.
Two Cases of Omental Torsion Mimicking Acute Appendicitis
Liaqat, Naeem; Dar, Sajid Hameed; Sandhu, Asif Iqbal; Nayyer, Sajid
2014-01-01
Acute appendicitis is often simulated by other entities like mesenteric adenitis, worm infestation, Meckel’s diverticulitis, urinary tract infection and rarely omental torsion. We report two cases, a 6 year old boy and an 11 year old girl, who presented with symptoms and signs of acute appendicitis but upon exploration turned out to be omental torsion. PMID:24834389
Hydrostatic self-aligning axial/torsional mechanism
O'Connor, Daniel G.; Gerth, Howard L.
1990-01-01
The present invention is directed to a self-aligning axial/torsional loading mechanism for testing the strength of brittle materials which are sensitive to bending moments. Disposed inside said self-aligning loading mechanism is a frictionless hydrostatic ball joint with a flexure ring to accommodate torsional loads through said ball joint.
Mechanical origins of rightward torsion in early chick brain development
NASA Astrophysics Data System (ADS)
Chen, Zi; Guo, Qiaohang; Dai, Eric; Taber, Larry
2015-03-01
During early development, the neural tube of the chick embryo undergoes a combination of progressive ventral bending and rightward torsion. This torsional deformation is one of the major organ-level left-right asymmetry events in development. Previous studies suggested that bending is mainly due to differential growth, however, the mechanism for torsion remains poorly understood. Since the heart almost always loops rightwards that the brain twists, researchers have speculated that heart looping affects the direction of brain torsion. However, direct evidence is lacking, nor is the mechanical origin of such torsion understood. In our study, experimental perturbations show that the bending and torsional deformations in the brain are coupled and that the vitelline membrane applies an external load necessary for torsion to occur. Moreover, the asymmetry of the looping heart gives rise to the chirality of the twisted brain. A computational model and a 3D printed physical model are employed to help interpret these findings. Our work clarifies the mechanical origins of brain torsion and the associated left-right asymmetry, and further reveals that the asymmetric development in one organ can induce the asymmetry of another developing organ through mechanics, reminiscent of D'Arcy Thompson's view of biological form as ``diagram of forces''. Z.C. is supported by the Society in Science - Branco Weiss fellowship, administered by ETH Zurich. L.A.T acknowledges the support from NIH Grants R01 GM075200 and R01 NS070918.
Fertility after oophorectomy due to torsion
Al-Turki, Haifa A.
2015-01-01
Objectives: To investigate the prevalence of infertility in patients who underwent salpingo-oophorectomy due to adnexal torsion (AT). Methods: All adult women admitted to the Teaching Institution of the University of Dammam, Dammam, Saudi Arabia who underwent surgery due to AT between January 2001 and 2010 were included. Complete data was collected from the time of admission to the follow up. The data was entered into the database and analyzed. Results: The data of 26 patients was available for analysis. The mean age (±standard deviation) at presentation was 22.19±4.4 years, and average age at follow up was 34.81±5.75 years. The average delay in presentation was 37.76±47 hours, and the surgery was performed at 45.07±48.57 hours. The right side was involved in 13 (53.8%) of the cases. Fourteen (53.9%) women presented with infertility. Eleven (78.57%) were treated for infertility, and 5 (45.5%) conceived. Patients who were younger at the time of torsion fared better with regard to pregnancy (p<0.03, 95% confidence interval:-6.85; <0.58). Conclusion: Patients who undergo salpingo-oophorectomy for AT have an increased risk of infertility and should be warned of this impending complication. PMID:25737184
Infrared modified gravity with dynamical torsion
NASA Astrophysics Data System (ADS)
Nikiforova, V.; Randjbar-Daemi, S.; Rubakov, V.
2009-12-01
We continue the recent study of the possibility of constructing a consistent infrared modification of gravity by treating the vierbein and connection as independent dynamical fields. We present the generalized Fierz-Pauli equation that governs the propagation of a massive spin-2 mode in a model of this sort in the backgrounds of arbitrary torsionless Einstein manifolds. We show explicitly that the number of propagating degrees of freedom in these backgrounds remains the same as in flat space-time. This generalizes the recent result that the Boulware-Deser phenomenon does not occur in de Sitter and anti-de Sitter backgrounds. We find that, at least for weakly curved backgrounds, there are no ghosts in the model. We also discuss the interaction of sources in flat background. It is generally believed that the spinning matter is the only source of torsion. Our flat space study shows that this is not the case. We demonstrate that an ordinary conserved symmetric energy-momentum tensor can also generate torsion fields and thus excite massive spin-2 degrees of freedom.
Curvature and torsion in growing actin networks
NASA Astrophysics Data System (ADS)
Shaevitz, Joshua W.; Fletcher, Daniel A.
2008-06-01
Intracellular pathogens such as Listeria monocytogenes and Rickettsia rickettsii move within a host cell by polymerizing a comet-tail of actin fibers that ultimately pushes the cell forward. This dense network of cross-linked actin polymers typically exhibits a striking curvature that causes bacteria to move in gently looping paths. Theoretically, tail curvature has been linked to details of motility by considering force and torque balances from a finite number of polymerizing filaments. Here we track beads coated with a prokaryotic activator of actin polymerization in three dimensions to directly quantify the curvature and torsion of bead motility paths. We find that bead paths are more likely to have low rather than high curvature at any given time. Furthermore, path curvature changes very slowly in time, with an autocorrelation decay time of 200 s. Paths with a small radius of curvature, therefore, remain so for an extended period resulting in loops when confined to two dimensions. When allowed to explore a three-dimensional (3D) space, path loops are less evident. Finally, we quantify the torsion in the bead paths and show that beads do not exhibit a significant left- or right-handed bias to their motion in 3D. These results suggest that paths of actin-propelled objects may be attributed to slow changes in curvature, possibly associated with filament debranching, rather than a fixed torque.
Biothermal sensing of a torsional artificial muscle.
Lee, Sung-Ho; Kim, Tae Hyeob; Lima, Márcio D; Baughman, Ray H; Kim, Seon Jeong
2016-02-14
Biomolecule responsive materials have been studied intensively for use in biomedical applications as smart systems because of their unique property of responding to specific biomolecules under mild conditions. However, these materials have some challenging drawbacks that limit further practical application, including their speed of response and mechanical properties, because most are based on hydrogels. Here, we present a fast, mechanically robust biscrolled twist-spun carbon nanotube yarn as a torsional artificial muscle through entrapping an enzyme linked to a thermally sensitive hydrogel, poly(N-isopropylacrylamide), utilizing the exothermic catalytic reaction of the enzyme. The induced rotation reached an equilibrated angle in less than 2 min under mild temperature conditions (25-37 °C) while maintaining the mechanical properties originating from the carbon nanotubes. This biothermal sensing of a torsional artificial muscle offers a versatile platform for the recognition of various types of biomolecules by replacing the enzyme, because an exothermic reaction is a general property accompanying a biochemical transformation. PMID:26806884
Infrared modified gravity with dynamical torsion
Nikiforova, V.; Randjbar-Daemi, S.; Rubakov, V.
2009-12-15
We continue the recent study of the possibility of constructing a consistent infrared modification of gravity by treating the vierbein and connection as independent dynamical fields. We present the generalized Fierz-Pauli equation that governs the propagation of a massive spin-2 mode in a model of this sort in the backgrounds of arbitrary torsionless Einstein manifolds. We show explicitly that the number of propagating degrees of freedom in these backgrounds remains the same as in flat space-time. This generalizes the recent result that the Boulware-Deser phenomenon does not occur in de Sitter and anti-de Sitter backgrounds. We find that, at least for weakly curved backgrounds, there are no ghosts in the model. We also discuss the interaction of sources in flat background. It is generally believed that the spinning matter is the only source of torsion. Our flat space study shows that this is not the case. We demonstrate that an ordinary conserved symmetric energy-momentum tensor can also generate torsion fields and thus excite massive spin-2 degrees of freedom.
Low-frequency vibrational modes of riboflavin and related compounds
NASA Astrophysics Data System (ADS)
Takahashi, Masae; Ishikawa, Yoichi; Nishizawa, Jun-ichi; Ito, Hiromasa
2005-01-01
The low-frequency vibrations of riboflavin and related compounds (alloxazine, lumichrome, lumiflavin as the ring system and D-mannitol as the side-chain system) were observed by far-infrared (terahertz) spectroscopy. Vibrational mode assignments in this spectrally congested range were made using high precision quantum chemical calculations. These resonance frequencies located below 200 cm -1 indicate the existence of motions important for biological reactions. The observed absorption bands in the low-frequency region of riboflavin are assigned to the in-plane and out-of-plane-ring deformations of pyrimidine and isoalloxazine, and to the torsion modes of the ribityl chain.
Method and system for vertical seismic profiling by measuring drilling vibrations
Ng, F.W.; DiSiena, J.P.; Bseisu, A.A.
1990-10-23
This patent describes a method for obtaining seismic data pertaining to an earth formation while forming a wellbore in the formation with a drillstring having a drillbit or the like disposed at the lower distal end thereof. It comprises: providing vibration sensing means connected to an upper region of the drillstring. The vibration sensing means being adapted to produce electrical signals related to vibrations of the drillstring; providing an array of seismometers disposed generally on the earth's surface in the vicinity of the wellbore; measuring first signals generated by the vibration sensing means resulting from vibrations of the drillstring; measuring second signals generated by the array of seismometers resulting from vibrations transmitted through the formation; and comparing the first signals and the second signals to determine selected characteristics of the formation including the step of calculating the location of origin of the first signal based on the difference in time of arrival at the vibration sensing means of a torsional vibration signal and an axial vibration signal transmitted through the drillstring and at least one of the torsional wave speed and the axial wave speed in the drillstring to determine the origin in time of the first signal.
Torsion and noninertial effects on a nonrelativistic Dirac particle
Bakke, K.
2014-07-15
We investigate torsion and noninertial effects on a spin-1/2 quantum particle in the nonrelativistic limit of the Dirac equation. We consider the cosmic dislocation spacetime as a background and show that a rotating system of reference can be used out to distances which depend on the parameter related to the torsion of the defect. Therefore, we analyse torsion effects on the spectrum of energy of a nonrelativistic Dirac particle confined to a hard-wall potential in a Fermi–Walker reference frame. -- Highlights: •Torsion effects on a spin- 1/2 particle in a noninertial reference frame. •Fermi–Walker reference frame in the cosmic dislocation spacetime background. •Torsion and noninertial effects on the confinement to a hard-wall confining potential.
Torsion angle preferences in druglike chemical space: a comprehensive guide.
Schärfer, Christin; Schulz-Gasch, Tanja; Ehrlich, Hans-Christian; Guba, Wolfgang; Rarey, Matthias; Stahl, Martin
2013-03-14
Crystal structure databases offer ample opportunities to derive small molecule conformation preferences, but the derived knowledge is not systematically applied in drug discovery research. We address this gap by a comprehensive and extendable expert system enabling quick assessment of the probability of a given conformation to occur. It is based on a hierarchical system of torsion patterns that cover a large part of druglike chemical space. Each torsion pattern has associated frequency histograms generated from CSD and PDB data and, derived from the histograms, traffic-light rules for frequently observed, rare, and highly unlikely torsion ranges. Structures imported into the corresponding software are annotated according to these rules. We present the concept behind the tree of torsion patterns, the design of an intuitive user interface for the management and usage of the torsion library, and we illustrate how the system helps analyze and understand conformation properties of substructures widely used in medicinal chemistry. PMID:23379567
Unravelling the structural plasticity of stretched DNA under torsional constraint
NASA Astrophysics Data System (ADS)
King, Graeme A.; Peterman, Erwin J. G.; Wuite, Gijs J. L.
2016-06-01
Regions of the genome are often held under torsional constraint. Nevertheless, the influence of such constraint on DNA-protein interactions during genome metabolism is still poorly understood. Here using a combined optical tweezers and fluorescence microscope, we quantify and explain how torsional constraint influences the structural stability of DNA under applied tension. We provide direct evidence that concomitant basepair melting and helical unwinding can occur in torsionally constrained DNA at forces >~50 pN. This striking result indicates that local changes in linking number can be absorbed by the rest of the DNA duplex. We also present compelling new evidence that an overwound DNA structure (likely P-DNA) is created (alongside underwound structures) at forces >~110 pN. These findings substantiate previous theoretical predictions and highlight a remarkable structural plasticity of torsionally constrained DNA. Such plasticity may be required in vivo to absorb local changes in linking number in DNA held under torsional constraint.
Tailoring patterns of graphene wrinkles by circular torsion
NASA Astrophysics Data System (ADS)
Becton, Matthew; Wang, Xianqiao
2016-02-01
Wrinkled graphene has been emerging as a hot topic of interest due to its easily induced physical changes accompanied by changes in its material behavior. However, the wrinkling pattern of graphene and its relevant properties remain poorly understood. Here we employ molecular dynamics simulations to model the behavior of graphene under periodic, torsional wrinkling and elucidate the effect of torsion pattern, torsion velocity, and hole size on the wrinkling characteristics of a large graphene sheet. Simulation results show that gross control over the wrinkling pattern is feasible via manipulation of torsion direction and relative hole size, with fine-tuning of the wrinkle formation possible by control of the relative torsion speed of each hole.
Nonuniform radiation damage in permanent magnet quadrupoles
Danly, C. R.; Merrill, F. E.; Barlow, D.; Mariam, F. G.
2014-08-15
We present data that indicate nonuniform magnetization loss due to radiation damage in neodymium-iron-boron Halbach-style permanent magnet quadrupoles. The proton radiography (pRad) facility at Los Alamos uses permanent-magnet quadrupoles for magnifying lenses, and a system recently commissioned at GSI-Darmsdadt uses permanent magnets for its primary lenses. Large fluences of spallation neutrons can be produced in close proximity to these magnets when the proton beam is, intentionally or unintentionally, directed into the tungsten beam collimators; imaging experiments at LANL’s pRad have shown image degradation with these magnetic lenses at proton beam doses lower than those expected to cause damage through radiation-induced reduction of the quadrupole strength alone. We have observed preferential degradation in portions of the permanent magnet quadrupole where the field intensity is highest, resulting in increased high-order multipole components.
Nonuniform radiation damage in permanent magnet quadrupoles.
Danly, C R; Merrill, F E; Barlow, D; Mariam, F G
2014-08-01
We present data that indicate nonuniform magnetization loss due to radiation damage in neodymium-iron-boron Halbach-style permanent magnet quadrupoles. The proton radiography (pRad) facility at Los Alamos uses permanent-magnet quadrupoles for magnifying lenses, and a system recently commissioned at GSI-Darmsdadt uses permanent magnets for its primary lenses. Large fluences of spallation neutrons can be produced in close proximity to these magnets when the proton beam is, intentionally or unintentionally, directed into the tungsten beam collimators; imaging experiments at LANL's pRad have shown image degradation with these magnetic lenses at proton beam doses lower than those expected to cause damage through radiation-induced reduction of the quadrupole strength alone. We have observed preferential degradation in portions of the permanent magnet quadrupole where the field intensity is highest, resulting in increased high-order multipole components. PMID:25173260
Ray propagation in nonuniform random lattices
NASA Astrophysics Data System (ADS)
Martini, Anna; Franceschetti, Massimo; Massa, Andrea
2006-09-01
The problem of optical ray propagation in a nonuniform random half-plane lattice is considered. An external source radiates a planar monochromatic wave impinging at an angle θ on a half-plane random grid where each cell can be independently occupied with probability qj=1-pj,j being the row index. The wave undergoes specular reflections on the occupied cells, and the probability of penetrating up to level k inside the lattice is analytically estimated. Numerical experiments validate the proposed approach and show improvement upon previous results that appeared in the literature. Applications are in the field of remote sensing and communications, where estimation of the penetration of electromagnetic waves in disordered media is of interest.
A nonuniform electrical field electroporation chamber design.
Hollon, T; Yoshimura, F K
1989-11-01
We show an inexpensive design for an electroporation chamber which subjects electroporated cells to a nonuniform electrical field. Our design, which we call an electroporation cylinder, improved transfection efficiency over that of a uniform field design (electroporation cuvettes) by about sixfold when tested in five mouse cell lines with a transient gene expression assay. Electroporation cylinders subjected cells to electrical field strengths at least as powerful as those of electroporation cuvettes, as judged by comparing the percentages of cells killed by electroporation. Cylinder and cuvette designs were similar in their effect on the variability of transfection efficiency. Electroporation cylinders may be particularly useful when the optimal electrical field strength for a cell line is not known or is unattainable with a given power supply. PMID:2610341
Flexible RF filter using a nonuniform SCISSOR.
Zhuang, Leimeng
2016-03-15
This work presents a flexible radiofrequency (RF) filter using an integrated microwave photonic circuit that comprises a nonuniform side-coupled integrated spaced sequence of resonators (N-SCISSOR). The filter passband can be reconfigured by varying the N-SCISSOR parameters. When employing a dual-parallel Mach-Zechnder modulator, the filter is also able to perform frequency down-conversion. In the experiment, various filter response shapes are shown, ranging from a flat-top band-pass filter to a total opposite high-rejection (>40 dB) notch filter, with a frequency coverage of greater than two octaves. The frequency down-conversion function is also demonstrated. PMID:26977648
Steady nonuniform shallow flow within emergent vegetation
NASA Astrophysics Data System (ADS)
Wang, Wei-Jie; Huai, Wen-Xin; Thompson, Sally; Katul, Gabriel G.
2015-12-01
Surface flow redistribution on flat ground from crusted bare soil to vegetated patches following intense rainfall events elevates plant available water above that provided by rainfall. The significance of this surface water redistribution to sustaining vegetation in arid and semiarid regions is undisputed. What is disputed is the quantity and spatial distribution of the redistributed water. In ecohydrological models, such nonuniform flows are described using the Saint-Venant equation (SVE) subject to a Manning roughness coefficient closure. To explore these assumptions in the most idealized setting, flume experiments were conducted using rigid cylinders representing rigid vegetation with varying density. Flow was induced along the streamwise x direction by adjusting the free water surface height H(x) between the upstream and downstream boundaries mimicking the nonuniformity encountered in nature. In natural settings, such H(x) variations arise due to contrasts in infiltration capacity and ponded depths during storms. The measured H(x) values in the flume were interpreted using the SVE augmented with progressively elaborate approximations to the roughness representation. The simplest approximation employs a friction factor derived from a drag coefficient (Cd) for isolated cylinders in a locally (but not globally) uniform flow and upscaled using the rod density that was varied across experiments. Comparison between measured and modeled H(x) suggested that such a "naive" approach overpredicts H(x). Blockage was then incorporated into the SVE model calculations but resulted in underestimation of H(x). Biases in modeled H(x) suggest that Cd must be varying in x beyond what a local or bulk Reynolds number predicts. Inferred Cd(x) from the flume experiments exhibited a near-parabolic shape most peaked in the densest canopy cases. The outcome of such Cd(x) variations is then summarized in a bulk resistance formulation that may be beneficial to modeling runon
Torsional ARC Effectively Expands the Visual Field in Hemianopia
Satgunam, PremNandhini; Peli, Eli
2012-01-01
Purpose Exotropia in congenital homonymous hemianopia has been reported to provide field expansion that is more useful when accompanied with harmonios anomalous retinal correspondence (HARC). Torsional strabismus with HARC provides a similar functional advantage. In a subject with hemianopia demonstrating a field expansion consistent with torsion we documented torsional strabismus and torsional HARC. Methods Monocular visual fields under binocular fixation conditions were plotted using a custom dichoptic visual field perimeter (DVF). The DVF was also modified to measure perceived visual directions under dissociated and associated conditions across the central 50° diameter field. The field expansion and retinal correspondence of a subject with torsional strabismus (along with exotropia and right hypertropia) with congenital homonymous hemianopia was compared to that of another exotropic subject with acquired homonymous hemianopia without torsion and to a control subject with minimal phoria. Torsional rotations of the eyes were calculated from fundus photographs and perimetry. Results Torsional ARC documented in the subject with congenital homonymous hemianopia provided a functional binocular field expansion up to 18°. Normal retinal correspondence was mapped for the full 50° visual field in the control subject and for the seeing field of the acquired homonymous hemianopia subject, limiting the functional field expansion benefit. Conclusions Torsional strabismus with ARC, when occurring with homonymous hemianopia provides useful field expansion in the lower and upper fields. Dichoptic perimetry permits documentation of ocular alignment (lateral, vertical and torsional) and perceived visual direction under binocular and monocular viewing conditions. Evaluating patients with congenital or early strabismus for HARC is useful when considering surgical correction, particularly in the presence of congenital homonymous hemianopia. PMID:22885782
Vibration characteristics of hexagonal radial rib and hoop platforms
NASA Technical Reports Server (NTRS)
Belvin, W. K.
1983-01-01
Experiment and analysis have been used to characterize the modes of vibration of planar radial rib and hoop hexagonal platforms. Finite element analysis correlated very well with experimental results. The sensitivity of mode shapes and frequencies to cable stiffness and initial tension is presented. Threshold values have been identified, above which changes in cable stiffness do not affect the first few platform vibration modes. Primary vibration modes of the radial rib platform involve beam bending. Vibration modes of the hoop platform exhibit both beam bending and frame bending and torsion. Results indicate for low order polygonal structures, the radial rib concept produced a higher fundamental frequency. For high order polygonal structures, the hoop concept has the potential to achieve a higher fundamental frequency than the radial rib concept.
Reduction of vortex-induced vibration in vane geometries
NASA Astrophysics Data System (ADS)
Liu, B. L.; O'Farrell, J. M.; Lowrey, G. A.; Nesman, Tomas E.
Computations using a time-accurate, compressible Navier-Stokes flow model were conducted to analyze both unsteady laminar and turbulent flows over two curved configurations of vanes which were shaped to treat a 4.0 kHz vibration problem which has occurred in several SSMEs. This problem involves vortex shedding from vanes which causes excessive vane vibration and cracking. The original vane configuration exhibited strong flow-induced vibrations at a Strouhal number near 0.19 for a the first bending mode excitation. Scalloping of the leading edge raised the frequency of the vane's first torsional mode, which in turn increased the onset flow velocity at lock-in. Beveling the vane's trailing edge eliminated vortex shedding at the trailing edge, which decoupled the flow oscillation from the vibrating wave. A modified vane configuration with a beveled trailing edge at a 30 deg angle was also studied.
Granular metamaterials for vibration mitigation
NASA Astrophysics Data System (ADS)
Gantzounis, G.; Serra-Garcia, M.; Homma, K.; Mendoza, J. M.; Daraio, C.
2013-09-01
Acoustic metamaterials that allow low-frequency band gaps are interesting for many practical engineering applications, where vibration control and sound insulation are necessary. In most prior studies, the mechanical response of these structures has been described using linear continuum approximations. In this work, we experimentally and theoretically address the formation of low-frequency band gaps in locally resonant granular crystals, where the dynamics of the system is governed by discrete equations. We investigate the quasi-linear behavior of such structures. The analysis shows that a stopband can be introduced at about one octave lower frequency than in materials without local resonances. Broadband and multi-frequency stopband characteristics can also be achieved by strategically tailoring the non-uniform local resonance parameters.
NASA Astrophysics Data System (ADS)
Monsalve-Cano, J. F.; Darío Aristizábal-Ochoa, J.
2009-12-01
The stability and free vibration analyses (i.e., buckling, natural frequencies and modal shapes) of an orthotropic singly symmetric 3D Timoshenko beam-column with generalized boundary conditions (i.e., with bending and torsional semirigid restraints and lateral bracings as well as lumped masses at both ends) subjected to an eccentric end axial load are presented in a classical manner. The five governing equations of dynamic equilibrium (i.e., two transverse shear equations, two bending moment equations and pure torsional moment equation) are sufficient to determine the natural frequencies and the corresponding modal shapes of the beam-column in the two principal planes of bending and torsion about its longitudinal axis. The proposed model includes the coupling effects among: (1) the deformations due to bending, shear and pure torsion; (2) inertias (translational, rotational and torsional) of all masses considered; (3) eccentric axial loads applied at the ends, and (4) restraints at the supports (bending, torsional and lateral bracings at both ends of the member). However, the effects of axial deformations and warping torsion produced by the axial load are not included; consequently the proposed model is not capable of capturing the phenomena of torsional buckling or combined lateral bending-torsional buckling. The proposed analytical model indicates that the stability and dynamic response of beam-columns are highly sensitive to the coupling effects, particularly in members with both ends free to rotate. The natural frequencies and modal shapes can be determined from the eigenvalues of a full 4×4 matrix for vibration in the plane of symmetry (using the uncoupled equations of transverse force and moment equilibrium at both ends) and from a full 6×6 matrix for the coupled shear-bending-torsional vibration (using the coupled equations of transverse shear, bending and torsional moment equilibrium at both ends). Also, it is shown that the proposed method reproduces the
NASA Technical Reports Server (NTRS)
2001-01-01
A Small Business Innovation Research (SBIR) sponsorship from NASA's Dryden Flight Research Center, assisted MetroLaser, of Irvine, California, in the development of a self-aligned laser vibrometer system. VibroMet, capable of measuring surface vibrations in a variety of industries, provides information on the structural integrity and acoustical characteristics of manufactured products. This low-cost, easy-to-use sensor performs vibration measurement from distances of up to three meters without the need for adjustment. The laser beam is simply pointed at the target and the system then uses a compact laser diode to illuminate the surface and to subsequently analyze the reflected light. The motion of the surface results in a Doppler shift that is measured with very high precision. VibroMet is considered one of the many behind-the-scenes tools that can be relied on to assure the quality, reliability and safety of everything from airplane panels to disk brakes
Elbakry, Adel; Zakaria, Ahmed; Matar, Adel; El Nashar, Ahmed
2013-01-01
Objectives To evaluate the effectiveness of urethral mobilisation for correcting moderate and severe penile torsion associated with distal hypospadias. Patients and methods Nineteen patients with distal hypospadias and congenital moderate and severe penile torsion were treated surgically. The hypospadias was at the distal shaft, coronal and glanular in seven, eight and four patients, respectively, and six had mild chordee. The mean (SD, range) angle of torsion was 94.7 (19.9, 75–160)°. The urethra was mobilised down to the perineum. If the urethral mobilisation was insufficient the right border of the tunica albuginea was anchored to the pubic periosteum. The hypospadias was repaired using the urethral mobilisation and advancement technique, with a triangular plate flap for meatoplasty. The patients were followed up for 12–18 months. Results All patients had a successful functional and cosmetic outcome, with no residual torsion. Two patients had a small subcutaneous haematoma that resolved after conservative treatment. Massive oedema occurred in three patients and was treated conservatively. Urethral mobilisation did not correct the penile torsion completely. Although the mean (SD, range) angle of torsion was reduced to 86.1 (14.3, 65–130)°, statistically significantly different (P = 0.001), it was not clinically important. The presence of chordee had no significant correlation with the reduction of penile torsion. Conclusion Urethral mobilisation cannot completely correct moderate and severe penile torsion but it might only partly decrease the angle of torsion. Periosteal anchoring of the tunica albuginea might be the most reliable manoeuvre for the complete correction of penile torsion. PMID:26579237
Torsional suspension system for testing space structures
NASA Technical Reports Server (NTRS)
Reed, Wilmer H., III (Inventor); Gold, Ronald R. (Inventor)
1991-01-01
A low frequency torsional suspension system for testing a space structure uses a plurality of suspension stations attached to the space structure along the length thereof in order to suspend the space structure from an overhead support. Each suspension station includes a disk pivotally mounted to the overhead support, and two cables which have upper ends connected to the disk and lower ends connected to the space structure. The two cables define a parallelogram with the center of gravity of the space structure being vertically beneath the pivot axis of the disk. The vertical distance between the points of attachment of the cables to the disk and the pivot axis of the disk is adjusted to lower the frequency of the suspension system to a level which does not interfere with frequency levels of the space structure, thereby enabling accurate measurement.
Torsion Balance Test of Einstein's Equivalence Principle
NASA Astrophysics Data System (ADS)
Abercrombie, Michael; Archibald, Adam; Nussinov, Tsitsi; Wagoner, Kasey; Cowsik, Ramanath
2016-03-01
We have developed a torsion balance experiment to test the equivalence principle (EP) which follows the solar attractor approach pioneered by Dicke in the early 1960s. By monitoring the response of a balance arranged as a composition dipole with an azimuthally symmetric mass distribution to the gravitational field produced by the Sun, we search for a diurnal modulation of the balance which would indicate a violation of the EP. Since reporting on the status of this experiment last year, the instrument has begun collecting data at a remote underground site. This talk will cover the design and fundamental sensitivity of the balance, and present the results of preliminary analysis of over 1200 hours of data.
Torsion Tests of Stiffened Circular Cylinders
NASA Technical Reports Server (NTRS)
Moore, R L; Wescoat, C
1944-01-01
The design of curved sheet panels to resist shear involves a consideration of several factors: the buckling resistance of the sheet, the stress at which buckling becomes permanent, and the strength which may be developed beyond the buckling limit by tension-field action. Although some experimental as well as theoretical work has been done on the buckling and tension-field phases of this problem, neither of these types of action appears to be very well understood. The problem is of sufficient importance from the standpoint of aircraft design, it is believed, to warrant further experimental investigation. This report presents the results of the first series of torsion tests of stiffened circular cylinders to be completed in connection with this study at Aluminum Research Laboratories. (author)
Plant-based torsional actuator with memory
NASA Astrophysics Data System (ADS)
Plaza, Nayomi; Zelinka, Samuel L.; Stone, Don S.; Jakes, Joseph E.
2013-07-01
A bundle of a few loblolly pine (Pinus taeda) cells are moisture-activated torsional actuators that twist multiple revolutions per cm length in direct proportion to moisture content. The bundles generate 10 N m kg-1 specific torque during both twisting and untwisting, which is higher than an electric motor. Additionally, the bundles exhibit a moisture-activated, shape memory twist effect. Over 70% of the twist in a wetted bundle can be locked-in by drying under constraint and then released by rewetting the bundle. Our results indicate that hemicelluloses dominate the shape fixity mechanism and lignin is primarily responsible for remembering the bundle’s original form. The bundles demonstrate proof of a high specific torque actuator with large angles of rotation and shape memory twist capabilities that can be used in microactuators, sensors, and energy harvesters.
Combined bending-torsion fatigue reliability. III
NASA Technical Reports Server (NTRS)
Kececioglu, D.; Chester, L. B.; Nolf, C. F., Jr.
1975-01-01
Results generated by three, unique fatigue reliability research machines which can apply reversed bending loads combined with steady torque are presented. AISI 4340 steel, grooved specimens with a stress concentration factor of 1.42 and 2.34, and Rockwell C hardness of 35/40 were subjected to various combinations of these loads and cycled to failure. The generated cycles-to-failure and stress-to-failure data are statistically analyzed to develop distributional S-N and Goodman diagrams. Various failure theories are investigated to determine which one represents the data best. The effects of the groove, and of the various combined bending-torsion loads, on the S-N and Goodman diagrams are determined. Two design applications are presented which illustrate the direct useability and value of the distributional failure governing strength and cycles-to-failure data in designing for specified levels of reliability and in predicting the reliability of given designs.
Experimental Study of Torsional Column Failure
NASA Technical Reports Server (NTRS)
Nile, Alfred S
1939-01-01
Thirty-three 24ST aluminum-alloy 2- by 2- by 0.10-inch channels, with lengths ranging from 10 to 90 inches were tested at Stanford University in compression to obtain an experimental verification of the theoretical formulas for torsional failure developed by Eugene E. Lundquist of the N.A.C.A. The observed critical loads and twist-axis locations were sufficiently close to the values obtained from the formulas to establish the substantial validity of the latter. The differences between observed and computed results were small enough to be accounted for by small and mostly unavoidable differences between actual test conditions and those assumed in deriving the formulas. Some data were obtained from the shorter specimens regarding the growth of the buckles that resulted in local buckling failure.
Torsional ultrasonic transducer computational design optimization.
Melchor, J; Rus, G
2014-09-01
A torsional piezoelectric ultrasonic sensor design is proposed in this paper and computationally tested and optimized to measure shear stiffness properties of soft tissue. These are correlated with a number of pathologies like tumors, hepatic lesions and others. The reason is that, whereas compressibility is predominantly governed by the fluid phase of the tissue, the shear stiffness is dependent on the stroma micro-architecture, which is directly affected by those pathologies. However, diagnostic tools to quantify them are currently not well developed. The first contribution is a new typology of design adapted to quasifluids. A second contribution is the procedure for design optimization, for which an analytical estimate of the Robust Probability Of Detection, called RPOD, is presented for use as optimality criteria. The RPOD is formulated probabilistically to maximize the probability of detecting the least possible pathology while minimizing the effect of noise. The resulting optimal transducer has a resonance frequency of 28 kHz. PMID:24882020
Constraining spacetime torsion with the Moon and Mercury
March, Riccardo; Bellettini, Giovanni; Tauraso, Roberto; Dell'Agnello, Simone
2011-05-15
We report a search for new gravitational physics phenomena based on Riemann-Cartan theory of general relativity including spacetime torsion. Starting from the parametrized torsion framework of Mao, Tegmark, Guth, and Cabi, we analyze the motion of test bodies in the presence of torsion, and, in particular, we compute the corrections to the perihelion advance and to the orbital geodetic precession of a satellite. We consider the motion of a test body in a spherically symmetric field, and the motion of a satellite in the gravitational field of the Sun and the Earth. We describe the torsion field by means of three parameters, and we make use of the autoparallel trajectories, which in general differ from geodesics when torsion is present. We derive the specific approximate expression of the corresponding system of ordinary differential equations, which are then solved with methods of celestial mechanics. We calculate the secular variations of the longitudes of the node and of the pericenter of the satellite. The computed secular variations show how the corrections to the perihelion advance and to the orbital de Sitter effect depend on the torsion parameters. All computations are performed under the assumptions of weak field and slow motion. To test our predictions, we use the measurements of the Moon's geodetic precession from lunar laser ranging data, and the measurements of Mercury's perihelion advance from planetary radar ranging data. These measurements are then used to constrain suitable linear combinations of the torsion parameters.
Primordial magnetic fields and dynamos from parity violated torsion
NASA Astrophysics Data System (ADS)
Garcia de Andrade, L. C.
2012-05-01
It is well known that torsion induced magnetic fields may seed galactic dynamos, but the price one pays for that is the conformal and gauge invariance breaks and a tiny photon mass. More recently I have shown [L.C. Garcia de Andrade, Phys. Lett. B 468 (2011) 28] that magnetic fields decay in a gauge invariant non-minimal coupling theory of torsion is slow down, which would allow for dynamo action to take place. In this Letter, by adding a parity violation term of the type Rɛ to the non-coupling term, a magnetic dynamo equation is obtained. From dynamo equation it is shown that torsion terms only appear in the dynamo equation when diffusion in the cosmic plasma is present. Torsion breaks the homogeneity of the magnetic field in the universe. Since Zeldovich anti-dynamo theorem assumes that the spacetime should be totally flat, torsion is responsible for violation of anti-dynamo theorem in 2D spatial dimensions. Contrary to previous results torsion induced primordial magnetic fields cannot seed galactic dynamos since from torsion and diffusion coefficient the decaying time of the magnetic field is 106yrs, which is much shorter than the galaxy age.
Significance of torsion modes in bowed-string dynamics
NASA Astrophysics Data System (ADS)
Inacio, Octavio; Antunes, Jose; Henrique, Luis
2002-11-01
Several aspects of bowed-string dynamics are still inadequately clarified. The importance of torsion modes on the motion regimes is one such issue. Experiments involving torsion are difficult and most of the results available pertain to numerical simulations. The authors' approach differs from previous efforts in two main aspects: (1) the development of a computational method distinct from the wave-propagation approach pioneered by McIntyre, Schumacher, and Woodhouse and (2) an extensive and systematic analysis of the coupling between torsion and transverse motions is performed. The numerical simulations are based on a modal representation of the unconstrained string and a computational approach for friction that enables accurate representations of the stick-slip forces and of the string dynamics, in both time and space. Many relevant aspects of the bowed-string can be readily implemented, including string inharmonic behavior, finite bow-width, and torsion effects. Concerning the later aspect, a realistic range of the torsional to transverse wave-speed ratio is investigated, for several values of the bow velocity and normal force. Results suggest that torsion modes can effect both transient durations and steady state regimes, in particular when the above-mentioned ratio is <4. Gut strings should then be particularly prone to torsion effects.
Pearls and pitfalls in diagnosis of ovarian torsion.
Chang, Hannah C; Bhatt, Shweta; Dogra, Vikram S
2008-01-01
Ovarian torsion is defined as partial or complete rotation of the ovarian vascular pedicle and causes obstruction to venous outflow and arterial inflow. Ovarian torsion is usually associated with a cyst or tumor, which is typically benign; the most common is mature cystic teratoma. Ultrasonography (US) is the primary imaging modality for evaluation of ovarian torsion. US features of ovarian torsion include a unilateral enlarged ovary, uniform peripheral cystic structures, a coexistent mass within the affected ovary, free pelvic fluid, lack of arterial or venous flow, and a twisted vascular pedicle. The presence of flow at color Doppler imaging does not allow exclusion of torsion but instead suggests that the ovary may be viable, especially if flow is present centrally. Absence of flow in the twisted vascular pedicle may indicate that the ovary is not viable. The role of computed tomography (CT) has expanded, and it is increasingly used in evaluation of abdominal pain. Common CT features of ovarian torsion include an enlarged ovary, uterine deviation to the twisted side, smooth wall thickening of the twisted adnexal cystic mass, fallopian tube thickening, peripheral cystic structures, and ascites. Understanding the imaging appearance of ovarian torsion will lead to conservative, ovary-sparing treatment. PMID:18794312
Complex vibration ultrasonic welding systems with large area welding tips.
Tsujino, Jiromaru; Sano, Tsutomu; Ogata, Hayato; Tanaka, Soichi; Harada, Yoshiki
2002-05-01
Vibration and welding characteristics of complex vibration ultrasonic welding systems of 27 and 40 kHz were studied. Complex vibration systems, which have elliptical to circular or rectangular to square locus, are effective for ultrasonic welding of various specimens including the same and different metal specimens, and for direct welding of semiconductor tips and packaging of various electronic devices without solder. The complex vibration systems consist of a one-dimensional longitudinal-torsional vibration converter with slitted part, a stepped horn and a longitudinal vibration transducer as a driving source. The complex vibration welding tips of 27 and 40 kHz have enough area of 6-8 mm square for various welding specimens. Aluminum plate specimens of 0.3-1.0 mm thickness were successfully joined with weld strengths almost equal to aluminum specimen strength, and independent to the specimen direction. Required vibration amplitude of 40 kHz is smaller than that of 27 kHz. PMID:12159965
Torsion constraints from cosmological magnetic field and QCD domain walls
NASA Astrophysics Data System (ADS)
Garcia de Andrade, L. C.
2014-10-01
Earlier Kostelecky [Phys. Rev. D 69, 105009 (2004)] has investigated the role of gravitational sector in Riemann-Cartan (RC) spacetime with torsion, in Lorentz and CPT violating (LV) Standard Model extension (SME). In his paper use of quantum electrodynamic (QED) extension in RC spacetime is made. More recently L. C. Garcia de Andrade [Phys. Lett. B 468, 28 (2011)] obtained magnetic field galactic dynamo seeds in the bosonic sector with massless photons, which proved to decay faster than necessary [Phys. Lett. B 711, 143 (2012)] to be able to seed galactic dynamos. In this paper it is shown that by using the fermionic sector of Kostelecky-Lagrangian and torsion written as a chiral current, one obtains torsion and magnetic fields explicitly from a Heisenberg-Ivanenko form of Dirac equation whose solution allows us to express torsion in terms of LV coefficients and magnetic field in terms of fermionic matter fields. When minimal coupling between electromagnetic and torsion fields is used it is shown that the fermionic sector of QED with torsion leads to resonantly amplify magnetic fields which mimics an α2-dynamo mechanism. Fine-tuning of torsion is shown to result in the dynamo reversal, a phenomenon so important in solar physics and geophysics. Of course this is only an analogy since torsion is very weak in solar and geophysics contexts. An analogous expression for the α-effect of mean-field dynamos is also obtained where the α-effect is mimic by torsion. Similar resonant amplification mechanisms connected to early universe have been considered by Finelli and Gruppuso.
Spinning Particles in Scalar-Tensor Gravity with Torsion
Wang, C.-H.
2008-10-10
A new model of neutral spinning particles in scalar-tensor gravity with torsion is developed by using a Fermi coordinates associated with orthonormal frames attached to a timelike curve and Noether identities. We further analyze its equations of motion both in background Brans-Dicke torsion field and the constant pseudo-Riemannian curvature with a constant scalar field. It turns that the particle's spin vector is parallel transport along its wordline in the Brans-Dicke torsion field and de Sitter spacetime. However, the dynamics of the spinning particle cannot completely determined in anti-de Sitter spacetime and it requires a further investigation.
Experimental investigation of cyclic thermomechanical deformation in torsion
NASA Technical Reports Server (NTRS)
Ellis, John R.; Castelli, Michael G.; Bakis, Charles E.
1992-01-01
An investigation of thermomechanical testing and deformation behavior of tubular specimens under torsional loading is described. Experimental issues concerning test accuracy and control specific to thermomechanical loadings under a torsional regime are discussed. A series of shear strain-controlled tests involving the nickel-base superalloy Hastelloy X were performed with various temperature excursions and compared to similar thermomechanical uniaxial tests. The concept and use of second invariants of the deviatoric stress and strain tensors as a means of comparing uniaxial and torsional specimens is also briefly presented and discussed in light of previous thermomechanical tests conducted under uniaxial conditions.
Discussion on massive gravitons and propagating torsion in arbitrary dimensions
Hernaski, C. A.; Vargas-Paredes, A. A.; Helayeel-Neto, J. A.
2009-12-15
In this paper, we reassess a particular R{sup 2}-type gravity action in D dimensions, recently studied by Nakasone and Oda, now taking torsion effects into account. Considering that the vielbein and the spin connection carry independent propagating degrees of freedom, we conclude that ghosts and tachyons are absent only if torsion is nonpropagating, and we also conclude that there is no room for massive gravitons. To include these excitations, we understand how to enlarge Nakasone-Oda's model by means of explicit torsion terms in the action and we discuss the unitarity of the enlarged model for arbitrary dimensions.
The Torsion of Box Beams with One Side Lacking
NASA Technical Reports Server (NTRS)
Cambilargiu, E
1940-01-01
The torsion of box beams of rectangular section, the edges of which are strengthened by flanges, and of which one side is lacking, is analyzed by the energy method. The torsional stresses are generally taken up by the bending of the two parallel walls, the rigidity of which is augmented by the third wall. The result was checked experimentally on duralumin and plywood boxes. The torsion recorded was 10 to 30 percent less than that given by the calculation, owing to self-stiffening.
Four-fermion interaction from torsion as dark energy
NASA Astrophysics Data System (ADS)
Popławski, Nikodem J.
2012-02-01
The observed small, positive cosmological constant may originate from a four-fermion interaction generated by the spin-torsion coupling in the Einstein-Cartan-Sciama-Kibble gravity if the fermions are condensing. In particular, such a condensation occurs for quark fields during the quark-gluon/hadron phase transition in the early Universe. We study how the torsion-induced four-fermion interaction is affected by adding two terms to the Dirac Lagrangian density: the parity-violating pseudoscalar density dual to the curvature tensor and a spinor-bilinear scalar density which measures the nonminimal coupling of fermions to torsion.
An experimental investigation of the structural dynamics of a torsionally soft rotor in vacuum
NASA Technical Reports Server (NTRS)
Srinivasan, A. V.; Cutts, D. G.; Shu, H. T.
1986-01-01
An extensive data base of structural dynamic characteristics has been generated from an experimental program conducted on a torsionally soft two-bladed model helicopter rotor system. Measurements of vibratory strains for five modes of vibration were made at twenty-one locations on the two blades at speeds varying from 0 to 1000 RPM and for several combinations of precone, droop and flexure stiffness. Tests were conducted in vacuum under carefully controlled conditions using a unique excitation device with a system of piezoelectric crystals bonded to the blade surface near the root. Frequencies, strain mode shapes and dampings are extracted from the time histories and can be used to validate structural dynamics codes. The dynamics of the system are such that there is a clear tendency for the first torsion and second flap modes to couple within the speed range considered. Strain mode shapes vary significantly with speed and configuration. This feature is important in the calcualtion of aeroelastic instabilities. The tension axis tests confirmed that the modulus-weighted centroid for the nonhomogeneous airfoil is slightly off the mass centroid and validated previous static tests done to determine location of the tension axis.
Magnetic Frustration from Nonuniform g-factors
NASA Astrophysics Data System (ADS)
Yin, Weiguo
Frustrated magnets are commonly known as materials in which localized magnetic moments, or spins, interact through competing exchange interactions that cannot be simultaneously satisfied. Here we show that even when the exchange interactions are fully cooperative, magnetic frustration can be induced by nonuniform Landé g factors, leading to a mutual interplay of typical ferromagnetic (FM) and antiferromagnetic (AF) features. This novel physics--exactly demonstrated in the one-dimensional Ising model with alternating g factors--provides new insight into the puzzling phenomenon that the magnetic susceptibility of many AF or FM materials is FM-like at low temperature but AF-like at high temperature. Furthermore, we found a unique magnetic-field-driven quantum critical point at which one half of the spins are frozen into a complete order and the other half are fully disordered. The present theory joins the recent intensive search for frustrated magnets beyond the ``standard model'' of condensed matter physics. It could broaden our understanding and design of exotic magnetic behaviors such as spin ice, spin glass, and spin liquid that are essential to quantum computing, spintronics, and high-temperature superconductivity Work supported by U.S. Department of Energy, Office of Basic Energy Science, under Contract No. DE-AC02-98CH10886.
The representation of nonuniform motion: induced movement.
Wade, N J; Swanston, M T
1987-01-01
Induced motion occurs when there is a misallocation of nonuniform motion. Theories of induced motion are reviewed with respect to the model for uniform motion recently proposed by Swanston, Wade, and Day. Theories based on single processes operating at one of the retinocentric, orbitocentric, egocentric, or geocentric levels are not able to account for all aspects of the phenomenon. It is therefore suggested that induced motion is a consequence of combining two different types of motion signals: one provides information by registering the motion with respect to the retina, orbit, and egocentre; the other provides information only on the relational motions between the pattern elements. Simple rules are given for defining a frame of reference for the relational motion process, which can result in a reallocation of the motion signals. It is proposed that the two signals in combination are weighted differentially, with the greater influence coming from the relational signals. Procedures for determining the weighting factors are described, and predictions from the model are examined. PMID:3330196
NASA Astrophysics Data System (ADS)
Huang, Cheng-Liang; Liu, Chen-Lin; Ni, Chi-Kung; Hougen, Jon T.
2005-09-01
The laser-induced fluorescence excitation spectrum of the biacetyl A1Au ( S1)- X1Ag ( S0) transition in the region from 22 182 to 22 800 cm -1 shows a complicated absorption line spectrum, which is believed to arise from a long progression in the torsional vibrations of the two equivalent methyl tops in this molecule. In this paper, we discuss three topics: (i) a numerical calculation of these energy levels using a kinetic and potential energy formalism and constants from the literature [M.L. Senent, D.C. Moule, Y.G. Smeyers, A. Toro-Labbé, F.J. Peqalver, J. Mol. Spectrosc. 164 (1994) 66], (ii) a qualitative description of the calculated energy level pattern using local-mode ideas applied to the two equivalent methyl rotors together with G36 permutation-inversion group symmetry species, and (iii) a least-squares refinement of the torsional potential parameters based on results of some of our high-resolution rotational analyses, followed by a comparison of energy levels calculated from the refined parameters with a low-resolution spectrum taken in the region from 0 to 500 cm -1 above the A- X band origin. Concerning (ii), we find that the two vibrational levels with one quantum of torsional excitation are best described by a normal mode formulation, but that many levels with more than one quantum of torsional excitation are better described by a local-mode formulation. Concerning (iii), we obtain low-order molecular constants quite similar to those reported by Senent et al., but higher-order constants which are quite different. Our calculated spectrum agrees well with the low-resolution spectrum, but full confirmation of the present interpretation for levels with three or more quanta of torsion excited will require high-resolution studies of additional bands.
Coupled vibrations of rectangular buildings subjected to normally-incident random wind loads
Safak, E.; Foutch, D.A.
1987-01-01
A method for analyzing the three-directional coupled dynamic response of wind-excited buildings is presented. The method is based on a random vibration concept and is parallel to those currently used for analyzing alongwind response. Only the buildings with rectangular cross-section and normally-incident wind are considered. The alongwind pressures and their correlations are represented by the well-known expressions that are available in the literature. The acrosswind forces are assumed to be mainly due to vortex shedding. The torque acting on the building is taken as the sum of the torque due to random alongwind forces plus the torque due to asymmetric acrosswind forces. The study shows the following: (1) amplitude of acrosswind vibrations can be several times greater than that of alongwind vibrations; (2) torsional vibrations are significant if the building has large frontal width, and/or it is asymmetric, and/or its torsional natural frequency is low; (3) even a perfectly symmetric structure with normally incident wind can experience significant torsional vibrations due to the randomness of wind pressures. ?? 1987.
Silicon Vibrating Wires at Low Temperatures
NASA Astrophysics Data System (ADS)
Collin, Eddy; Filleau, Laure; Fournier, Thierry; Bunkov, Yuriy M.; Godfrin, Henri
2008-03-01
Nowadays microfabrication techniques originating from micro-electro nics enable to create mechanical objects of micron-size. The field of Micro-Electro-Mechanical devices (MEMs) is continuously expanding, with an amazingly broad range of applications at room temperature. Vibrating objects (torsional oscillators, vibrating wires) widely used at low temperatures to study quantum fluids, can be replaced advantageously by Silicon MEMs. In this letter we report on the study of Silicon vibrating wire devices. A goal-post structure covered with a metal layer is driven at resonance by the Laplace force acting on a current in a magnetic field, while the induced voltage arising from the cut magnetic flux allows to detect the motion. The characteristics of the resonance have been studied from 10 mK to 30 K, in vacuum and in 4He gas. In this article, we focus on the results obtained above 1.5 K, in vacuum and gas, and introduce some features observed at lower temperatures. The resonant properties can be quantitatively understood by means of simple models, from the linear regime to a highly non-linear response at strong drives. We demonstrate that the non-linearity is mostly due to the geometry of the vibrators. We also show that in our device the friction mechanisms originate in the metallic layers, and can be fully characterized. The interaction with 4He gas is fit to theory without adjustable parameters.
High harmonic terahertz confocal gyrotron with nonuniform electron beam
NASA Astrophysics Data System (ADS)
Fu, Wenjie; Guan, Xiaotong; Yan, Yang
2016-01-01
The harmonic confocal gyrotron with nonuniform electron beam is proposed in this paper in order to develop compact and high power terahertz radiation source. A 0.56 THz third harmonic confocal gyrotron with a dual arc section nonuniform electron beam has been designed and investigated. The studies show that confocal cavity has extremely low mode density, and has great advantage to operate at high harmonic. Nonuniform electron beam is an approach to improve output power and interaction efficiency of confocal gyrotron. A dual arc beam magnetron injection gun for designed confocal gyrotron has been developed and presented in this paper.
Active vibration control of a flexible cantilever beam using shape memory alloy actuators
NASA Astrophysics Data System (ADS)
Suzuki, Y.; Kagawa, Y.
2010-08-01
This paper demonstrates the feasibility of using shape memory alloys (SMAs) as actuators to control the vibration of a flexible cantilever beam. In a tendon mechanism, SMAs are controlled in a push-pull fashion based on H-infinity theory and taking into account the uncertainty in the actuator performance. Using this mechanism, the four vibrational modes (three bending and one torsional) of the cantilever beam can be simultaneously damped. To control bending and torsional vibrational modes of a flexible beam, we install SMAs obliquely in a beam-SMA structure, then measure and theoretically model the properties of an actuator consisting of an SMA and a spring. Using the properties of the actuator, we introduce the state equations based on the dynamic model of the proposed beam-SMA structure and design the active control system according to H-infinity theory. Finally, we experimentally verify the functioning of the system.
Spin-torsion effects in the hyperfine structure of methanol
Coudert, L. H. Gutlé, C.; Huet, T. R.; Grabow, J.-U.; Levshakov, S. A.
2015-07-28
The magnetic hyperfine structure of the non-rigid methanol molecule is investigated experimentally and theoretically. 12 hyperfine patterns are recorded using molecular beam microwave spectrometers. These patterns, along with previously recorded ones, are analyzed in an attempt to evidence the effects of the magnetic spin-torsion coupling due to the large amplitude internal rotation of the methyl group [J. E. M. Heuvel and A. Dymanus, J. Mol. Spectrosc. 47, 363 (1973)]. The theoretical approach setup to analyze the observed data accounts for this spin-torsion in addition to the familiar magnetic spin-rotation and spin-spin interactions. The theoretical approach relies on symmetry considerations to build a hyperfine coupling Hamiltonian and spin-rotation-torsion wavefunctions compatible with the Pauli exclusion principle. Although all experimental hyperfine patterns are not fully resolved, the line position analysis yields values for several parameters including one describing the spin-torsion coupling.
Torsional dynamics of steerable needles: modeling and fluoroscopic guidance.
Swensen, John P; Lin, MingDe; Okamura, Allison M; Cowan, Noah J
2014-11-01
Needle insertions underlie a diversity of medical interventions. Steerable needles provide a means by which to enhance existing needle-based interventions and facilitate new ones. Tip-steerable needles follow a curved path and can be steered by twisting the needle base during insertion, but this twisting excites torsional dynamics that introduce a discrepancy between the base and tip twist angles. Here, we model the torsional dynamics of a flexible rod-such as a tip-steerable needle-during subsurface insertion and develop a new controller based on the model. The torsional model incorporates time-varying mode shapes to capture the changing boundary conditions inherent during insertion. Numerical simulations and physical experiments using two distinct setups-stereo camera feedback in semitransparent artificial tissue and feedback control with real-time X-ray imaging in optically opaque artificial tissue-demonstrate the need to account for torsional dynamics in control of the needle tip. PMID:24860026
Randall-Sundrum scenario with bulk dilaton and torsion
Mukhopadhyaya, Biswarup; Sen, Somasri; SenGupta, Soumitra
2009-06-15
We consider a string-inspired torsion-dilaton-gravity action in a Randall-Sundrum braneworld scenario and show that, in an effective four-dimensional theory on the visible brane, the rank-2 antisymmetric Kalb-Ramond field (source of torsion) is exponentially suppressed. The result is similar to our earlier result in [B. Mukhopadhyaya, S. Sen, and S. SenGupta, Phys. Rev. Lett. 89, 121101 (2002); Phys. Rev. Lett. 89, 259902(E) (2002)], where no dilaton was present in the bulk. This offers an explanation of the apparent invisibility of torsion in our space-time. However, in this case the trilinear couplings {approx}TeV{sup -1} between the dilaton and torsion may lead to new signals in TeV-scale experiments, bearing the stamp of extra warped dimensions.
Isolated adnexal torsion in a 20-week spontaneous twin pregnancy
Kahramanoglu, Ilker; Eroglu, Vasfiye; Turan, Hasan; Kaval, Gizem; Sal, Veysel; Tokgozoglu, Nedim
2016-01-01
Background Adnexal torsion can be a life-threatning condition in pregnancy, while the risk of late diagnosis is increased, in second and third trimester in particular. Laparoscopy is an effective approach in diagnosis and treatment of adnexal torsion. However, entry to abdomen may be challenging in more advanced pregnancies. Case report Herein, we report a case of adnexal torsion during 20th week of twin pregnancy, which was detorsioned laparoscopically. The woman delivered healthy infants at her 36th week of pregnancy. Discussion Adnexal torsion as a cause of acute abdomen may be kept in mind in pregnants, even if there is no predisposing factor. Laparoscopy may be performed safely in 2nd trimester for acute abdomen. PMID:27129134
Bilateral perinatal testicular torsion: successful salvage supports emergency surgery.
Granger, Jeremy; Brownlee, Ewan M; Cundy, Thomas P; Goh, Day Way
2016-01-01
Perinatal testicular torsion (PTT) has poor rates of testicular salvage. Although rare, bilateral PTT carries the risk of anorchia. We present a case of a 2-day-old term infant with acute onset right-sided scrotal discolouration and tenderness. The infant was promptly taken to the operating theatre for emergency scrotal exploration. Bilateral extravaginal testicular torsion was identified, with the right testis appearing to have a more established ischaemic appearance compared to that on the left side. Intraoperative findings were representative of metachronous PTT with a short time period of only several hours separating the torsion events. Both testes were detorted and fixated in the scrotum. The infant made an uneventful recovery. Outpatient clinic review at 6 weeks and 6 months postoperatively confirmed no clinical evidence of testicular atrophy. Given the potential for contralateral torsion and the morbidity of anorchia, our experience supports the role for emergency scrotal exploration in suspected PTT. PMID:27307430
Response characteristics of the human torsional vestibuloocular reflex
NASA Technical Reports Server (NTRS)
Peterka, Robert J.
1992-01-01
The characteristics of the response dynamics of the human torsional vestibuloocular reflex were studied during controlled rotations about an earth-horizontal axis. The results extended the frequency range to 2 Hz and identified the nonlinearity of the amplitude response.
NASA Astrophysics Data System (ADS)
Khoddam, S.; Hodgson, P. D.
2014-12-01
Many difficulties exist in directly following the static recrystallization of metals, particularly during hot working. Indirect measurement of static recrystallization has been extensively performed in the literature where, for example, the recrystallization behavior of austenite in steels has commonly been measured indirectly using the fractional softening method. This method relies on the yield stress changes during recrystallization which are physically simulated by hot torsion or compression tests. However, the inherent heterogeneity of deformation during a mechanical test leads to a non-uniform static recrystallization distribution in the test sample. This, in turn, poses a serious question concerning the reliability of the measurement since the stress calculation techniques during recrystallization are not adequately developed in the existing literature. This paper develops a computer-based method to account for heterogeneous deformation during fractional softening measurements based on the hot torsion test data. The importance of the fractional softening gradient in determining the kinetics is emphasized and deficiencies in our understanding of the basic mechanisms are highlighted. A computer-based method is introduced to generate the experimental and computational components in a cost function. The cost function is then utilized by an inverse solution to calibrate the design parameters in a static recrystallization model.A
Changes in gravitational state cause changes in ocular torsion
NASA Technical Reports Server (NTRS)
Diamond, S. G.; Markham, C. H.
1998-01-01
Gravity-responsive eye torsion was studied simultaneously in both eyes during parabolic flight to determine the effects of weightlessness. Observed effects were that torsional position of eyes in the 1G states between parabolas was offset from the baseline positions obtained prior to the onset of parabolas, responses to hyper- and hypogravity were seen in most subjects, and responses were consistent within subjects but varied between subjects.
Non-Abelian anomalies on a curved space with torsion
Cognola, G.; Giacconi, P.
1989-05-15
Using path-integral methods and /zeta/-function regularization a nonperturbative derivation of non-Abelian-covariant and consistent anomalies on a curved space with torsion is given. All terms depending on torsion, that one has in the expression of the consistent anomaly, can be eliminated by adding suitable counterterms to the Lagrangian density. In this way, the well-known result of Bardeen is recovered. The so-called ''covariant anomaly'' will be discussed too.
Torsion of the Appendix Testis in a Neonate
Krishnan, Arvind; Rich, Mark A.; Swana, Hubert S.
2016-01-01
Torsion of the appendix testis is a rare cause of scrotal swelling in the neonatal period. We present a case of torsion of the appendix testis in a one-day-old male. We discuss the physical examination and radiologic studies used to make the diagnosis. Nonoperative therapy was recommended and the patient has done well. Recognition of this condition in the neonatal period can prevent surgical intervention and its associated risks. PMID:27379193
Cosmic Magnetic Fields from Torsion Modes and Massive Photon Inflation
NASA Astrophysics Data System (ADS)
Garcia de Andrade, L. C.
2014-09-01
Earlier Barrow & Tsagas (2008) showed that a slower decay of magnetic fields are present in open Friedmann universes, with traditional Maxwell equations. In their paper magnetic fields of the order of B˜10-33 G which are far below the value required to seed galactic dynamos were obtained. In this paper galactic dynamo seeds of the order of B˜10-23 G are obtained from massive electrodynamics in Einstein-Cartan-Proca (ECP) expanding universe of de Sitter type. Slow decay of magnetic fields in photon-torsion coupling in QED (Garcia de Andrade 2011b) have been recently shown by Garcia de Andrade (2012) also not be able to seed galactic dynamos. Torsion modes are constrained by the field equations. Space-time torsion is shown to be explicitly responsible for the slow decay of cosmic magnetic field. In the absence of massive photon torsion coupling the magnetic field decay is of the order B˜t-3/2, while when torsion is turn on B˜t-1.2. The pure massive-photon-torsion contribution amplifies the magnetic field by Btorsion˜t0.1 which characterizes an extremely slow magnetic dynamo action due to purely torsion gravitational effects. Recently, Barrow et al. (2012) have obtained superadiabatic amplification of B-fields in the Friedmann open cosmology which lies within 10-20 G and 10-12 G which falls very comfortable within limits to seed galactic dynamos. Other simple solutions where B-field decays as B˜a-1, relatively weak photon-torsion coupling approximation. These solutions are obtained for the de Sitter and Friedmann metrics.
Analysis of the HVDC turbine generator torsional interactions
Padiyar, K.R. . Dept. of Electrical Communication Engineering); Kothari, A.G. )
1989-01-01
In the recent past it has been found that HVDC transmission systems and turbine-generator shaft torsional dynamics can interact in an unfavourable manner. This paper presents a detailed linearized state space model of AC/DC system to study this torsional interaction. The model developed is used to study the effect of various system parameters, such as, dc line loading, converter firing angle, the firing scheme employed. The results obtained are compared with those previously given.
Tomographic elastography of contracting skeletal muscles from their natural vibrations
NASA Astrophysics Data System (ADS)
Sabra, Karim G.; Archer, Akibi
2009-11-01
Conventional elastography techniques require an external mechanical or radiation excitation to measure noninvasively the viscoelastic properties of skeletal muscles and thus monitor human motor functions. We developed instead a passive elastography technique using only an array of skin-mounted accelerometers to record the low-frequency vibrations of the biceps brachii muscle naturally generated during voluntary contractions and to determine their two-dimensional directionality. Cross-correlating these recordings provided travel-times measurements of these muscle vibrations between multiple sensor pairs. Travel-time tomographic inversions yielded spatial variations of their propagation velocity during isometric elbow flexions which indicated a nonuniform longitudinal stiffening of the biceps.
Torsional texturing of superconducting oxide composite articles
Christopherson, Craig John; Riley, Jr., Gilbert N.; Scudiere, John
2002-01-01
A method of texturing a multifilamentary article having filaments comprising a desired oxide superconductor or its precursors by torsionally deforming the article is provided. The texturing is induced by applying a torsional strain which is at least about 0.3 and preferably at least about 0.6 at the surface of the article, but less than the strain which would cause failure of the composite. High performance multifilamentary superconducting composite articles having a plurality of low aspect ratio, twisted filaments with substantially uniform twist pitches in the range of about 1.00 inch to 0.01 inch (25 to 0.25 mm), each comprising a textured desired superconducting oxide material, may be obtained using this texturing method. If tighter twist pitches are desired, the article may be heat treated or annealed and the strain repeated as many times as necessary to obtain the desired twist pitch. It is preferred that the total strain applied per step should be sufficient to provide a twist pitch tighter than 5 times the diameter of the article, and twist pitches in the range of 1 to 5 times the diameter of the article are most preferred. The process may be used to make a high performance multifilamentary superconducting article, having a plurality of twisted filaments, wherein the degree of texturing varies substantially in proportion to the radial distance from the center of the article cross-section, and is substantially radially homogeneous at any given cross-section of the article. Round wires and other low aspect ratio multifilamentary articles are preferred forms. The invention is not dependent on the melting characteristics of the desired superconducting oxide. Desired oxide superconductors or precursors with micaceous or semi-micaceous structures are preferred. When used in connection with desired superconducting oxides which melt irreversibly, it provides multifilamentary articles that exhibit high DC performance characteristics and AC performance markedly
Structure and torsional dynamics of the water octamer from THz laser spectroscopy near 215 μm.
Cole, William T S; Farrell, James D; Wales, David J; Saykally, Richard J
2016-06-01
Clusters of eight water molecules play an important role in theoretical analysis of aqueous structure and dynamics but have proven to be challenging experimental targets. Here we report the high-resolution spectroscopic characterization of the water octamer. Terahertz (THz) vibration-rotation-tunneling (VRT) spectroscopy resolved 99 transitions with 1 part per million precision in a narrow range near 46.5 wave numbers, which were assigned to the h16 octamer via detailed isotope dilution experiments. Fitting to a semi-rigid symmetric top model supports predictions of two coexisting cuboidal structures and provides precise values for the changes in their rotational constants. Comparison with theory and previous spectroscopic data provides a characterization of the two structures and the observed torsional vibration and supports the prediction that the D2d symmetry structure is lower in energy than the S4 isomer. PMID:27257252
NASA Astrophysics Data System (ADS)
Fatihou, Ali; Zouzou, Noureddine; Iuga, Gheorghe; Dascalescu, Lucian
2015-10-01
The aim of this paper is to establish the conditions in which the vibrating capacitive probe of an electrostatic voltmeter could be employed for mapping the electric potential at the surface of non-uniformly charged insulating bodies. A first set of experiments are performed on polypropylene non-woven media (thickness: 0.4 mm; fiber diameter: 20 μm) in ambient air. In a second set of experiments the non-uniformity of charge is simulated using five copper strips (width: 2 mm or 3 mm; distance between strips: 2 mm). All the strips are connected to a high-voltage supply (Vs = 1000 V). The sample carrier is attached to a computer-controlled positioning system that transfers it under the capacitive probe (TREK, model 3451) of an electrostatic voltmeter (TREK, model 1341B). The measurements are performed at various relative speeds Vb between the sample and the probe, and for various sample rates Fe. A first set of experiments point out that the electric potential displayed by the electrostatic voltmeter depends on the spacing h between the sample and the probe. The diameter D of the spot “seen” by the probe is approximately D ≈ 8h/3. From the second set of experiments performed with the test plate, it can be concluded that the surface potential can be measured with the media in motion, but the accuracy is limited by the spatial resolution defined by k = Vb/Fe.
Charged particle acceleration in nonuniform plasmas
Bulanov, S.V.; Naumova, N.M.; Dudnikova, G.I.; Vshivkov, V.A.; Pegoraro, F.; Pogorelsky, I.V.
1996-11-01
The high-gradient electron acceleration schemes that have been demonstrated using LWFA appear promising for the development of plasma-based laser accelerators into practical devices. However, a question still exists: how to avoid the wake field deterioration and the loss of the phase synchronism between the plasma wave and the electrons that prevent them from being accelerated up to the theoretical limit. In order to obtain the highest possible values of the wake electric field one must use as intense laser pulses as possible i.e., pulses with dimensionless amplitudes a {much_gt} 1. Pulses that have a dimensionless amplitude larger than one tend to be subject to a host of instabilities, such as relativistic self-focusing, self modulation and stimulated Raman scattering, that affect their propagation in the plasma. Such processes could be beneficial, in so far as they increase the pulse energy density, enhance the wake field generation, and provide the mechanism for transporting the laser radiation over several Rayleigh lengths without diffraction spreading. However, it is still far from certain that these processes can be exploited in a controlled form and can lead to regular, stationary wake fields. It is known that, in order to create good quality wake fields, it would be preferable to use laser pulses with steep fronts of order {lambda}{sub p}. The present paper aims at analyzing the influence of the laser pulse shape and of the plasma nonuniformity on the charged particle acceleration. This study is based on the results obtained with one dimensional PIC simulations.
Analysis of torsional oscillations using an artificial neural network
Hsu, Y.Y.; Jeng, L,H. )
1992-12-01
In this paper, a novel approach using an artificial neural network (ANN) is proposed for the analysis of torsional oscillations in a power system. In the developed artificial neural network, those system variables such as generator loadings and capacitor compensation ratio which have major impacts on the damping characteristics of torsional oscillatio modes are employed as the inputs. The outputs of the neural net provide the desired eigenvalues for torsional modes. Once the connection weights of the neural network have been learned using a set of training data derived off-line, the neural network can be applied to torsional analysis in real-time situations. To demonstrate the effectiveness of the proposed neural net, torsional analysis is performed on the IEEE First Benchmark Model. It is concluded from the test results that accurate assessment of the torsional mode eigenvalues can be achieved by the neural network in a very efficient manner. Thereofore, the proposed neural network approach can serve as a valuable tool to system operators in conducting SSR analysis in operational planning.
A nationwide epidemiological study of testicular torsion in Korea.
Lee, Sol Min; Huh, Jung-Sik; Baek, Minki; Yoo, Koo Han; Min, Gyeong Eun; Lee, Hyung-Lae; Lee, Dong-Gi
2014-12-01
Testicular torsion is a surgical emergency in the field of urology. Knowledge of the epidemiology and pathophysiology is significant to an urologist. However, the epidemiology of testicular torsion in Korea has not been studied. We performed a nationwide epidemiological study to improve knowledge of the epidemiology of testicular torsion. From 2006-2011, the Korean Urologic Association began the patient registry service. The annual number of patients with testicular torsion from 2006 to 2011 were 225, 250, 271, 277, 345, and 210, respectively. The overall incidence of testicular torsion in males was 1.1 per 100,000; However, the incidence in men less than 25 yr old was 2.9 per 100,000. Adolescents showed the highest incidence. Total testicular salvage rate was 75.7% in this survey. There was no geographic difference of testicular salvage rate. Minimizing the possibility of orchiectomy for testicular torsion is important to improve public awareness to expedite presentation and provider education to improve diagnosis and surgery. PMID:25469070
An Axial-Torsional, Thermomechanical Fatigue Testing Technique
NASA Technical Reports Server (NTRS)
Kalluri, Sreeramesh; Bonacuse, Peter J.
1995-01-01
A technique for conducting strain-controlled, thermomechanical, axial-torsional fatigue tests on thin-walled tubular specimens was developed. Three waveforms of loading, namely, the axial strain waveform, the engineering shear strain waveform, and the temperature waveform were required in these tests. The phasing relationships between the mechanical strain waveforms and the temperature and axial strain waveforms were used to define a set of four axial-torsional, thermomechanical fatigue (AT-TMF) tests. Real-time test control (3 channels) and data acquisition (a minimum of 7 channels) were performed with a software program written in C language and executed on a personal computer. The AT-TMF testing technique was used to investigate the axial-torsional thermomechanical fatigue behavior of a cobalt-base superalloy, Haynes 188. The maximum and minimum temperatures selected for the AT-TMF tests were 760 and 316 C, respectively. Details of the testing system, calibration of the dynamic temperature profile of the thin-walled tubular specimen, thermal strain compensation technique, and test control and data acquisition schemes, are reported. The isothermal, axial, torsional, and in- and out-of-phase axial-torsional fatigue behaviors of Haynes 188 at 316 and 760 C were characterized in previous investigations. The cyclic deformation and fatigue behaviors of Haynes 188 in AT-TMF tests are compared to the previously reported isothermal axial-torsional behavior of this superalloy at the maximum and minimum temperatures.
NASA Astrophysics Data System (ADS)
Virgo, Edwina A.; Gascooke, Jason R.; Lawrance, Warren D.
2014-04-01
Franck-Condon forbidden transitions involving methyl rotor modes are seen in the S1 ← S0 spectrum of toluene and toluene-like molecules. The strongest of these rotor transitions (m″ = 1 → m' = 2, m″ = 0 → m' = 3a1″, and m″ = 1 → m' = 4) have been shown by Walker et al. [J. Chem. Phys. 102, 8718 (1995)] to gain intensity through the rotor equivalent of the Herzberg-Teller mechanism. Despite the m″ = 0 → m' = 3a2″ transition being forbidden in this formalism, it is sporadically observed. We show that this transition derives oscillator strength from incomplete mixing of the -3 and +3 free rotor basis states due to torsion-rotation coupling. Calculations demonstrate that this mechanism quantitatively explains the intensities observed for toluene, including their temperature dependence. Because the -3/+3 mixing is weakest when the torsional barrier height, V6, is small, the m″ = 0 → m' = 3a2″ transition increases in intensity as |V6| decreases. The temperature and |V6| dependencies explain why reports of the 0 → 3a2″ transition have been intermittent. The torsion-rotation coupling mechanism is predicted to also give significant intensity to m = 0 → m = 6a2' transitions relative to m = 0 → m = 6a1' transitions and to provide intensity to 0 → 3a2 transitions in molecules with a 3-fold (V3) barrier. Comparison between the observed and calculated rotor band contours shows, unexpectedly, that the 3a1″ constants fail to predict the 3a2″ contour despite these two states being derived from the same free rotor basis states. Comparison with the observed spectrum also reveals differences in the separation of the S1 3a2″ and 3a1″ levels. The V6 value determined from analysis of the high resolution, rotationally resolved m″ = 0 → m' = 3a1″ spectrum overestimates the 3a2″-3a1″ separation by 0.6 cm-1. We postulate that this may be due to torsion-vibration coupling. The observed toluene torsion-rotation contours have been modeled
Chirped pulse compression in nonuniform plasma Bragg gratings
Wu Huichun; Sheng Zhengming; Zhang Jie
2005-11-14
A nonuniform plasma Bragg grating with a monotonically increasing density-modulation profile can be naturally produced by two Gaussian laser pulses counterpropagating through a homogeneous plasma slab. Such a plasma grating exhibits a nonuniform photonic band gap with a monotonically increasing width. It can be used to compress a positively or negatively chirped pulse. Particle-in-cell simulations show that the compressed pulse has nearly no energy loss and the compression efficiency can exceed 90%.
Dielectrophoresis device and method having nonuniform arrays for manipulating particles
Cummings, Eric B.; Fintschenko, Yolanda; Simmons, Blake A.
2012-09-04
Microfluidic devices according to embodiments of the present invention include an inlet port, an outlet port, and a channel or chamber having a non-uniform array of insulating features on one or more surfaces. Electrodes are provided for generation of a spatially non-uniform electric field across the array. A voltage source, which may be an A.C. and/or a D.C. voltage source may be coupled to the electrodes for the generation of the electric field.
NASA Astrophysics Data System (ADS)
Liu, Na; Dittmer, Robert; Stark, Robert W.; Dietz, Christian
2015-07-01
Polar nanoregions (PNRs) play a key role in the functionality of relaxor ferroelectrics; however, visualizing them in lead-free relaxor ferroelectrics with high lateral resolution is still challenging. Thus, we studied herein the local ferroelectric domain distribution of the lead-free bismuth-based (1 - x)(Bi1/2Na1/2TiO3-Bi1/2K1/2TiO3) - x(Bi1/2Mg1/2TiO3) piezoceramics which show a relaxor behavior using dual AC resonance tracking (DART) piezoresponse force microscopy (PFM). By using excitation frequencies at either side of the contact resonance peak of the torsional cantilever vibration, an enhanced contrast in the amplitude and phase images of the piezoresponse can be achieved. Additionally, this tracking technique reduces the topographical crosstalk while mapping the local electromechanical properties. The true drive amplitude, drive phase, contact resonant frequency and quality factor can be estimated from DART-PFM data obtained with vertically or torsionally vibrating cantilevers. This procedure yields a three-dimensional quantitative map of the local piezoelectric properties of the relaxor ferroelectric samples. With this approach, torsional DART allowed for the visualization of fine substructures within the monodomains, suggesting the existence of PNRs in relaxor ferroelectrics. The domain structures of the PNRs were visualized with high precision, and the local electromechanical characteristics of the lead-free relaxor ferroelectrics were quantitatively mapped.Polar nanoregions (PNRs) play a key role in the functionality of relaxor ferroelectrics; however, visualizing them in lead-free relaxor ferroelectrics with high lateral resolution is still challenging. Thus, we studied herein the local ferroelectric domain distribution of the lead-free bismuth-based (1 - x)(Bi1/2Na1/2TiO3-Bi1/2K1/2TiO3) - x(Bi1/2Mg1/2TiO3) piezoceramics which show a relaxor behavior using dual AC resonance tracking (DART) piezoresponse force microscopy (PFM). By using excitation
Spectrum recovery method analysis on nonuniform sampling interference data
NASA Astrophysics Data System (ADS)
Huang, Fengzhen; Li, Jingzhen; Cao, Jun
2015-02-01
Temporally and Spatially Modulated Fourier Transform Imaging Spectrometer (TSMFTIS) is a new imaging spectrometer without moving mirrors and slits. The interferogram of the target point can be consisted by sequentially arranging the interference information extracted from the same target point of the sequential images, and the spectrum can be recovered by using fast Fourier transform. In the practical application, there is nonuniform sampling in the interference data, and many researchers have carried out researches on nonuniform sampling with the fast Fourier transform algorithm. As to the issue of interference data in the nonuniform sampling, the nonuniform sampling degree's impact on the recovered spectrum precision is currently and mainly analyzed. This paper has adapted several typical nonuniform fast Fourier transform (NUFFT) methods, carried out spectrum recovery precision comparison on the interferogram of the nonuniform sampling point with the above methods, and further analyzed the impact of kernel function type, oversampling ratio and kernel function width's on spectrum recovery precision in the above mentioned methods. The experiment result indicates that, when the oversampling ratio is 4 and the kernel function width is 4, the spectrum recovery precision with NUFFT based on Blackman type kernel function is optimal, however, the Gaussian kernel function is stable.
Dispersion and phase shifts of torsional waves in forward models
NASA Astrophysics Data System (ADS)
Cox, G. A.; Livermore, P. W.; Mound, J. E.
2013-12-01
Torsional Alfvén waves have been thought to exist in the Earth's core since their theoretical prediction by Braginsky in 1970. More recently, they have been inferred from observations of secular variation and length of day, and also observed in geodynamo simulations. These inferences from geophysical data have provided an important means of estimating core properties such as viscosity and internal magnetic field strength. We produce 1D forward models of torsional waves in the Earth's core, also known as torsional oscillations, and study their evolution in a cylinder, a full sphere and an equatorially symmetric spherical shell. The key features of torsional waves in our models are: geometric dispersion, phase shifts and internal reflections. In all three core geometries, we find that travelling torsional waves undergo significant geometric dispersion that increases with successive reflections from the boundaries such that an initial wave pulse becomes unidentifiable within three transits of the core. This dispersion partly arises due to low amplitude wakes trailing behind sharply defined pulses during propagation, a phenomenon that is linked to the failure of Huygens' principle in the geometric setting of torsional waves. We investigate the relationship between geometric dispersion and wavelength, concluding that long wavelength features are more dispersive than short wavelength features. This result is particularly important because torsional waves inferred from secular variation are relatively long wavelength, and are therefore likely to undergo significant dispersion within the Earth's core. Torsional waves in all three geometries are reflected at the equator of the core-mantle boundary with the same sign as the incident wave, but display more complicated behaviour at the rotation axis. In a cylindrical core, the analytic solutions to the torsional wave equation are known. We use these to derive an expression for the phase shift that torsional waves undergo upon
NASA Astrophysics Data System (ADS)
Ostasevicius, V.; Ubartas, M.; Gaidys, R.; Jurenas, V.; Samper, S.; Dauksevicius, R.
2012-11-01
This study is concerned with application of numerical-experimental approach for characterizing dynamic behavior of the developed piezoelectrically excited vibration drilling tool with the aim to identify the most effective conditions of tool vibration mode control for improved cutting efficiency. 3D finite element model of the tool was created on the basis of an elastically fixed pre-twisted cantilever (standard twist drill). The model was experimentally verified and used together with tool vibration measurements in order to reveal rich dynamic behavior of the pre-twisted structure, representing a case of parametric vibrations with axial, torsional and transverse natural vibrations accompanied by the additional dynamic effects arising due to the coupling of axial and torsional deflections ((un)twisting). Numerical results combined with extensive data from interferometric, accelerometric, dynamometric and surface roughness measurements allowed to determine critical excitation frequencies and the corresponding vibration modes, which have the largest influence on the performance metrics of the vibration drilling process. The most favorable tool excitation conditions were established: inducing the axial mode of the vibration tool itself through tailoring of driving frequency enables to minimize magnitudes of surface roughness, cutting force and torque. Research results confirm the importance of the tool mode control in enhancing the effectiveness of vibration cutting tools from the viewpoint of structural dynamics.
Conformational Switching by Vibrational Excitation of a Remote NH Bond.
Lopes Jesus, António Jorge; Reva, Igor; Araujo-Andrade, Cuauhtémoc; Fausto, Rui
2015-11-18
Here we describe an unprecedented reversible interconversion between two conformational states, accomplished by selective vibrational excitation of a bond remotely located in relation to the isomerizing fragment. In contrast to previous studies reporting conformational changes via vibrational excitation of a nearby OH group, in this study the transformations were successfully achieved by excitation of a distant NH stretching coordinate. The syn and anti forms of monomeric 6-methoxyindole, which differ in the orientation of the methoxy group, were trapped in low-temperature inert matrixes and characterized spectroscopically. These forms could be selectively shifted in both directions by using near-IR excitations tuned at the frequency of the first NH stretching overtone. The observed isomerization proves the possibility of efficient vibrational relaxation to carry the energy deposited at the NH stretching coordinate into the reactive C-O torsional mode localized on the methoxy group four bonds away from the excited NH moiety. PMID:26376202
Vibrationally coherent photochemistry in the femtosecond primary event of vision.
Wang, Q; Schoenlein, R W; Peteanu, L A; Mathies, R A; Shank, C V
1994-10-21
Femtosecond pump-probe experiments reveal the impulsive production of photoproduct in the primary event in vision. The retinal chromophore of rhodopsin was excited with a 35-femtosecond pulse at 500 nanometers, and transient changes in absorption were measured with 10-femtosecond probe pulses. At probe wavelengths within the photo-product absorption band, oscillatory features with a period of 550 femtoseconds (60 wavenumbers) were observed whose phase and amplitude demonstrate that they are the result of nonstationary vibrational motion in the ground state of the photoproduct. The observation of coherent vibrational motion of the photoproduct supports the idea that the primary step in vision is a vibrationally coherent process and that the high quantum yield of the cis-->trans isomerization in rhodopsin is a consequence of the extreme speed of the excited-state torsional motion. PMID:7939680
Kollipost, F; Andersen, J; Mahler, D W; Heimdal, J; Heger, M; Suhm, M A; Wugt Larsen, R
2014-11-01
The effect of strong intermolecular hydrogen bonding on torsional degrees of freedom is investigated by far-infrared absorption spectroscopy for different methanol dimer isotopologues isolated in supersonic jet expansions or embedded in inert neon matrices at low temperatures. For the vacuum-isolated and Ne-embedded methanol dimer, the hydrogen bond OH librational mode of the donor subunit is finally observed at ~560 cm(-1), blue-shifted by more than 300 cm(-1) relative to the OH torsional fundamental of the free methanol monomer. The OH torsional mode of the acceptor embedded in neon is observed at ~286 cm(-1). The experimental findings are held against harmonic predictions from local coupled-cluster methods with single and double excitations and a perturbative treatment of triple excitations [LCCSD(T)] and anharmonic. VPT2 corrections at canonical MP2 and density functional theory (DFT) levels in order to quantify the contribution of vibrational anharmonicity for this important class of intermolecular hydrogen bond vibrational motion. PMID:25381521
Kollipost, F.; Heger, M.; Suhm, M. A.; Andersen, J.; Mahler, D. W.; Wugt Larsen, R.; Heimdal, J.
2014-11-07
The effect of strong intermolecular hydrogen bonding on torsional degrees of freedom is investigated by far-infrared absorption spectroscopy for different methanol dimer isotopologues isolated in supersonic jet expansions or embedded in inert neon matrices at low temperatures. For the vacuum-isolated and Ne-embedded methanol dimer, the hydrogen bond OH librational mode of the donor subunit is finally observed at ∼560 cm{sup −1}, blue-shifted by more than 300 cm{sup −1} relative to the OH torsional fundamental of the free methanol monomer. The OH torsional mode of the acceptor embedded in neon is observed at ∼286 cm{sup −1}. The experimental findings are held against harmonic predictions from local coupled-cluster methods with single and double excitations and a perturbative treatment of triple excitations [LCCSD(T)] and anharmonic. VPT2 corrections at canonical MP2 and density functional theory (DFT) levels in order to quantify the contribution of vibrational anharmonicity for this important class of intermolecular hydrogen bond vibrational motion.
Non-uniform MR image reconstruction based on non-uniform FFT
NASA Astrophysics Data System (ADS)
Liang, Xiao-yun; Zeng, Wei-ming; Dong, Zhi-hua; Zhang, Zhi-jiang; Luo, Li-min
2007-01-01
A Non-Uniform Fast Fourier Transform (NUFFT) based method for non-Cartesian k-space data reconstruction is presented. For Cartesian K-space data, as we all know, image can be reconstructed using 2DFFT directly. But, as far as know, this method has not been universally accepted nowadays because of its inevitable disadvantages. On the contrary, non-Cartesian method is of the advantage over it, so we focused on the method usually. The most straightforward approach for the reconstruction of non-Cartesian data is directly via a Fourier summation. However, the computational complexity of the direct method is usually much greater than an approach that uses the efficient FFT. But the FFT requires that data be sampled on a uniform Cartesian grid in K-space, and a NUFFT based method is of much importance. Finally, experimental results which are compared with existing method are given.
Noncontact Electromagnetic Vibration Source
NASA Technical Reports Server (NTRS)
Namkung, Min; Fulton, James P.; Wincheski, Buzz A.
1994-01-01
Metal aircraft skins scanned rapidly in vibration tests. Relatively simple combination of permanent magnets and electromagnet serves as noncontact vibration source for nondestructive testing of metal aircraft skins. In test, source excites vibrations, and vibration waveforms measured, then analyzed for changes in resonances signifying cracks and other flaws.
NASA Astrophysics Data System (ADS)
Borromeo, M.; Marchesoni, F.
2006-01-01
Transport in one-dimensional symmetric devices can be activated by the combination of thermal noise and a biharmonic drive. For the study case of an overdamped Brownian particle diffusing on a periodic one-dimensional substrate, we distinguish two apparently different biharmonic regimes: (i) Harmonic mixing, where the two drive frequencies are commensurate and of the order of some intrinsic relaxation rate. Earlier predictions based on perturbation expansions seem inadequate to interpret our simulation results; (ii) Vibrational mixing, where one harmonic drive component is characterized by high frequency but finite amplitude-to-frequency ratio. Its effect on the device response to either a static or a low-frequency additional input signal is accurately reproduced by rescaling each spatial Fourier component of the substrate potential, separately. Contrary to common wisdom, based on the linear response theory, we show that extremely high-frequency modulations can indeed influence the response of slowly (or dc) operated devices, with potential applications in sensor technology and cellular physiology. Finally, the mixing of two high-frequency beating signal is also investigated both numerically and analytically.
Blevins, R.D.
1990-01-01
This book reports on dimensional analysis; ideal fluid models; vortex-induced vibration; galloping and flutter; instability of tube and cylinder arrays; vibrations induced by oscillating flow; vibration induced by turbulence and sound; damping of structures; sound induced by vortex shedding; vibrations of a pipe containing a fluid flow; indices. It covers the analysis of the vibrations of structures exposed to fluid flows; explores applications for offshore platforms and piping; wind-induced vibration of buildings, bridges, and towers; and acoustic and mechanical vibration of heat exchangers, power lines, and process ducting.
Manifestations of Torsion-CH Stretch Coupling in the Infrared Spectrum of CH3OO.
Hsu, Kuo-Hsiang; Huang, Yu-Hsuan; Lee, Yuan-Pern; Huang, Meng; Miller, Terry A; McCoy, Anne B
2016-07-14
With a step-scan Fourier-transform spectrometer we recorded temporally resolved infrared absorption spectra of CH3OO radicals that were produced upon irradiation of CH3COCH3 and O2 at 193 nm in a flowing mixture. At a resolution of 0.15 cm(-1), the rotational structure of the ν2 band of CH3OO near 2954.4 cm(-1) is partially resolved and shows an unexpectedly broadened, and somewhat distorted, Q-branch. A 4D model Hamiltonian, consisting of three CH stretches and the methyl torsion, was developed to explore the origins of this broadening. The vibrational progressions predicted by the model Hamiltonian and the rotational contours of the ν2 band, based on experimental ground-state rotational parameters and their values scaled by their calculated ratios for the upper state, produced simulations in satisfactory agreement with the observed spectrum. These results provide new insight into the vibrational couplings in CH3OO. PMID:26900645
Elevated temperature axial and torsional fatigue behavior of Haynes 188
NASA Technical Reports Server (NTRS)
Bonacuse, Peter J.; Kalluri, Sreeramesh
1992-01-01
The results of high-temperature axial and torsional low-cycle fatigue experiments performed on Haynes 188, a wrought cobalt-base superalloy, are reported. Fatigue tests were performed at 760 C in air on thin-walled tubular specimens at various ranges under strain control. Data are also presented for coefficient of thermal expansion, elastic modulus, and shear modulus at various temperatures from room to 1000 C, and monotonic and cyclic stress-strain curves in tension and in shear at 760 C. The data set is used to evaluate several multiaxial fatigue life models (most were originally developed for room temperature multiaxial life prediction) including von Mises equivalent strain range (ASME boiler and pressure vessel code), Manson-Halford, Modified Multiaxiality Factor (proposed here), Modified Smith-Watson-Topper, and Fatemi-Socie-Kurath. At von Mises equivalent strain ranges (the torsional strain range divided by the square root of 3, taking the Poisson's ratio to be 0.5), torsionally strained specimens lasted, on average, factors of 2 to 3 times longer than axially strained specimens. The Modified Multiaxiality Factor approach shows promise as a useful method of estimating torsional fatigue life from axial fatigue data at high temperatures. Several difficulties arose with the specimen geometry and extensometry used in these experiments. Cracking at extensometer probe indentations was a problem at smaller strain ranges. Also, as the largest axial and torsional strain range fatigue tests neared completion, a small amount of specimen buckling was observed.
Torsional Deformations in Subnanometer MoS Interconnecting Wires.
Koh, Ai Leen; Wang, Shanshan; Ataca, Can; Grossman, Jeffrey C; Sinclair, Robert; Warner, Jamie H
2016-02-10
We use aberration-corrected transmission electron microscopy to track the real time atomic level torsional dynamics of subnanometer wires of MoS interconnecting monolayer regions of MoS2. An in situ heating holder is used inside the transmission electron microscope to raise the temperature of the sample to 400 °C to increase crystallization rates of the wires and reduce contamination effects. Frequent rotational twisting of the MoS wire is captured, demonstrating elastic torsional deformation of the MoS wires. We show that torsional rotations of the crystal structure of the MoS wires depend upon the specific atomic structure of the anchored sections of the suspended wire and the number of unit cells that make up the wire length. Elastic torsional flexibility of the MoS wires is revealed to help their self-adapting connectivity during the structural changes. Plastic torsional deformation is also seen for MoS wires that contain defects in their crystal structure, which produce small scale rotational disorder within the wires. Upon removal of the defects, the wire returns back to pristine form. These results provide detailed insights into how the atomic structure of the anchoring site significantly influences the nanowire configurations relative to the monolayered MoS2. PMID:26785319
Unravelling the structural plasticity of stretched DNA under torsional constraint.
King, Graeme A; Peterman, Erwin J G; Wuite, Gijs J L
2016-01-01
Regions of the genome are often held under torsional constraint. Nevertheless, the influence of such constraint on DNA-protein interactions during genome metabolism is still poorly understood. Here using a combined optical tweezers and fluorescence microscope, we quantify and explain how torsional constraint influences the structural stability of DNA under applied tension. We provide direct evidence that concomitant basepair melting and helical unwinding can occur in torsionally constrained DNA at forces >∼50 pN. This striking result indicates that local changes in linking number can be absorbed by the rest of the DNA duplex. We also present compelling new evidence that an overwound DNA structure (likely P-DNA) is created (alongside underwound structures) at forces >∼110 pN. These findings substantiate previous theoretical predictions and highlight a remarkable structural plasticity of torsionally constrained DNA. Such plasticity may be required in vivo to absorb local changes in linking number in DNA held under torsional constraint. PMID:27263853
Simple torsion test for shear moduli determination of orthotropic composites
NASA Technical Reports Server (NTRS)
Sumsion, H. T.; Rajapakse, Y. D. S.
1978-01-01
By means of torsion tests performed on test specimens of the same material having a minimum of two different cross sections (flat sheet of different widths), the effective in-plane (G13) and out-of-plane (G23) shear moduli were determined for two composite materials of uniaxial and angleply fiber orientations. Test specimens were 16 plies (nominal 2 mm) thick, 100 mm in length, and in widths of 6.3, 9.5, 12.5, and 15.8 mm. Torsion tests were run under controlled deflection (constant angle of twist) using an electrohydraulic servocontrolled test system. In-plane and out-of-plane shear moduli were calculated from an equation derived in the theory of elasticity which relates applied torque, the torsional angle of twist, the specimen width/thickness ratio, and the ratio of the two shear moduli G13/G23. Results demonstrate that torsional shear moduli, G23 as well as G13, can be determined by simple torsion tests of flat specimens of rectangular cross section. Neither the uniaxial nor angleply composite material were transversely isotropic.
Direct torsional actuation of microcantilevers using magnetic excitation
Gosvami, Nitya Nand; Nalam, Prathima C.; Tam, Qizhan; Carpick, Robert W.; Exarhos, Annemarie L.; Kikkawa, James M.
2014-09-01
Torsional mode dynamic force microscopy can be used for a wide range of studies including mapping lateral contact stiffness, torsional frequency or amplitude modulation imaging, and dynamic friction measurements of various materials. Piezo-actuation of the cantilever is commonly used, but it introduces spurious resonances, limiting the frequency range that can be sampled, and rendering the technique particularly difficult to apply in liquid medium where the cantilever oscillations are significantly damped. Here, we demonstrate a method that enables direct torsional actuation of cantilevers with high uniformity over wide frequency ranges by attaching a micrometer-scale magnetic bead on the back side of the cantilever. We show that when beads are magnetized along the width of the cantilever, efficient torsional actuation of the cantilevers can be achieved using a magnetic field produced from a solenoid placed underneath the sample. We demonstrate the capability of this technique by imaging atomic steps on graphite surfaces in tapping mode near the first torsional resonance of the cantilever in dodecane. The technique is also applied to map the variations in the lateral contact stiffness on the surface of graphite and polydiacetylene monolayers.
Autoparallel vs. Geodesic Trajectories in a Model of Torsion Gravity
NASA Astrophysics Data System (ADS)
Acedo, Luis
2015-11-01
We consider a parametrized torsion gravity model for Riemann-Cartan geometry around a rotating axisymmetric massive body. In this model, the source of torsion is given by a circulating vector potential following the celestial parallels around the rotating object. Ours is a variant of the Mao, Tegmark, Guth and Cabi (MTGC model) in which the total angular momentum is proposed as a source of torsion. We study the motion of bodies around the rotating object in terms of autoparallel trajectories and determine the leading perturbations of the orbital elements by using standard celestial mechanics techniques. We find that this torsion model implies new gravitational physical consequences in the Solar system and, in particular, secular variations of the semi-major axis of the planetary orbits. Perturbations on the longitude of the ascending node and the perihelion of the planets are already under discussion in the astronomical community, and if confirmed as truly non-zero effects at a statistically significant level, we might be at the dawn of an era of torsion phenomenology in the Solar system.
Unravelling the structural plasticity of stretched DNA under torsional constraint
King, Graeme A.; Peterman, Erwin J. G.; Wuite, Gijs J. L.
2016-01-01
Regions of the genome are often held under torsional constraint. Nevertheless, the influence of such constraint on DNA–protein interactions during genome metabolism is still poorly understood. Here using a combined optical tweezers and fluorescence microscope, we quantify and explain how torsional constraint influences the structural stability of DNA under applied tension. We provide direct evidence that concomitant basepair melting and helical unwinding can occur in torsionally constrained DNA at forces >∼50 pN. This striking result indicates that local changes in linking number can be absorbed by the rest of the DNA duplex. We also present compelling new evidence that an overwound DNA structure (likely P-DNA) is created (alongside underwound structures) at forces >∼110 pN. These findings substantiate previous theoretical predictions and highlight a remarkable structural plasticity of torsionally constrained DNA. Such plasticity may be required in vivo to absorb local changes in linking number in DNA held under torsional constraint. PMID:27263853
[Torsion of wandering spleen in a teenager: about a case].
Dème, Hamidou; Akpo, Léra Géraud; Fall, Seynabou; Badji, Nfally; Ka, Ibrahima; Guèye, Mohamadou Lamine; Touré, Mouhamed Hamine; Niang, El Hadj
2016-01-01
Wandering or migrating spleen is a rare anomaly which is usually described in children. Complications, which include pedicle torsion, are common and can be life-threatening. We report the case of a 17 year-old patient with a long past medical history of epigastric pain suffering from wandering spleen with chronic torsion of the pedicle. The clinical picture was marked by spontaneously painful epigastric mass, evolved over the past 48 hours. Abdominal ultrasound objectified heterogeneous hypertrophied ectopic spleen in epigastric position and a subcapsular hematoma. Doppler showed a torsion of splenic pedicle which was untwisted 2 turns and a small blood stream on the splenic artery. Abdominal CT scan with contrast injection showed a lack of parenchymal enhancement of large epigastric ectopic spleen and a subcapsular hematoma. The diagnosis of wandering spleen with chronic torsion of the pedicle complicated by necrosis and subcapsular hematoma was confirmed. The patient underwent splenectomy. The postoperative course was uneventful. We here discuss the contribution of ultrasound and CT scan in the diagnosis of wandering spleen with chronic torsion of the pedicle. PMID:27583079
Elevated temperature axial and torsional fatigue behavior of Haynes 188
NASA Astrophysics Data System (ADS)
Bonacuse, Peter J.; Kalluri, Sreeramesh
1992-06-01
The results of high-temperature axial and torsional low-cycle fatigue experiments performed on Haynes 188, a wrought cobalt-base superalloy, are reported. Fatigue tests were performed at 760 C in air on thin-walled tubular specimens at various ranges under strain control. Data are also presented for coefficient of thermal expansion, elastic modulus, and shear modulus at various temperatures from room to 1000 C, and monotonic and cyclic stress-strain curves in tension and in shear at 760 C. The data set is used to evaluate several multiaxial fatigue life models (most were originally developed for room temperature multiaxial life prediction) including von Mises equivalent strain range (ASME boiler and pressure vessel code), Manson-Halford, Modified Multiaxiality Factor (proposed here), Modified Smith-Watson-Topper, and Fatemi-Socie-Kurath. At von Mises equivalent strain ranges (the torsional strain range divided by the square root of 3, taking the Poisson's ratio to be 0.5), torsionally strained specimens lasted, on average, factors of 2 to 3 times longer than axially strained specimens. The Modified Multiaxiality Factor approach shows promise as a useful method of estimating torsional fatigue life from axial fatigue data at high temperatures. Several difficulties arose with the specimen geometry and extensometry used in these experiments. Cracking at extensometer probe indentations was a problem at smaller strain ranges. Also, as the largest axial and torsional strain range fatigue tests neared completion, a small amount of specimen buckling was observed.
A Rare Cause of Placental Abruption: Uterine Torsion
Güneş, Muhammed Siraç; Kiran, Gürkan; Gülşen, Mehmet Serdar
2016-01-01
Uterine torsion is defined as a rotation on its long axis and it is a dangerous, unexpected obstetric emergency. We report a case of uterine torsion at 32 weeks of gestation in a singleton pregnancy. A 37-year-old woman with multiple prior cesarean deliveries referred to emergency unit of our hospital at 32 weeks of gestation with severe abdominal pain and mild vaginal bleeding. Ultrasonography showed a single fetus in vertex position, with a normal amniotic fluid. Fetal biometer was appropriate for 32 weeks of gestation. Placental location was anterior with a subchorionic hypoechogenic small area which was suspected to be a sign of placental abruption. An emergency cesarean section was performed under general anesthesia. The 180° uterine torsion was diagnosed and it was not possible to perform detorsion of the gravid uterus by exteriorization by pfannenstiel incision. Posterior hysterotomy was performed and a male baby of 1830 grams weight was delivered. The newborn was transported to Neonatal Intensive Care Unit (NICU) of another hospital and discharged within two weeks. Patient recovered well and was discharged on second postoperation day. Uterine torsion is a very rare and life threatening situation. In unexpected cases posterior low transuerse hysterotomy is generally performed and it is suggested as a safe choice when detorsion was not accomplished. It is not easy to keep in mind the possibility of uterine torsion in cases of abdominal pain during pregnancy. Because it generally causes abruption, management of abruption is vitally important to prevent fetal mortality. PMID:26894131
Downhole Vibration Monitoring and Control System
Martin E. Cobern
2007-09-30
The objective of this program is to develop a system to both monitor the vibration of a bottomhole assembly, and to adjust the properties of an active damper in response to these measured vibrations. The key feature of this system is its use of a magnetorheological fluid (MRF) to allow the damping coefficient to be changed extensively, rapidly and reversibly without the use of mechanical valves, but only by the application of a current. Phase I of this program, which entailed modeling and design of the necessary subsystems and design, manufacture and test of a full laboratory prototype, was completed on May 31, 2004. Much of the effort was devoted to the design and testing of the MRF damper, itself. The principal objectives of Phase II were: more extensive laboratory testing, including the evaluation of different feedback algorithms for control of the damper; design and manufacture of a field prototype system; and, testing of the field prototype in a drilling laboratory. Phase II concluded on January 31, 2006, and a final report was issued. Work on Phase III of the project began during the first quarter, 2006, with the objectives of building precommercial prototypes, testing them in a drilling laboratory and the field; developing and implementing a commercialization plan. All of these have been accomplished. The Downhole Vibration Monitoring & Control System (DVMCS) prototypes have been successfully proven in testing at the TerraTek drilling facility and at the Rocky Mountain Oilfield Test Center (RMOTC.) Based on the results of these tests, we have signed a definitive development and distribution agreement with Smith, and commercial deployment is underway. This current version of the DVMCS monitors and controls axial vibrations. Due to time and budget constraints of this program, it was not possible to complete a system that would also deal with lateral and torsional (stick-slip) vibrations as originally planned; however, this effort is continuing without DOE
Scene-based nonuniformity correction method using multiscale constant statistics
NASA Astrophysics Data System (ADS)
Zuo, Chao; Chen, Qian; Gu, Guohua; Sui, Xiubao; Qian, Weixian
2011-08-01
In scene-based nonuniformity correction (NUC) methods for infrared focal plane array cameras, the statistical approaches have been well studied because of their lower computational complexity. However, when the assumptions imposed by statistical algorithms are violated, their performance is poor. Moreover, many of these techniques, like the global constant statistics method, usually need tens of thousands of image frames to obtain a good NUC result. In this paper, we introduce a new statistical NUC method called the multiscale constant statistics (MSCS). The MSCS statically considers that the spatial scale of the temporal constant distribution expands over time. Under the assumption that the nonuniformity is distributed in a higher spatial frequency domain, the spatial range for gain and offset estimates gradually expands to guarantee fast compensation for nonuniformity. Furthermore, an exponential window and a tolerance interval for the acquired data are introduced to capture the drift in nonuniformity and eliminate the ghosting artifacts. The strength of the proposed method lies in its simplicity, low computational complexity, and its good trade-off between convergence rate and correction precision. The NUC ability of the proposed method is demonstrated by using infrared video sequences with both synthetic and real nonuniformity.
Chatter resistance of non-uniform turning bars with attached dynamic absorbers—Analytical approach
NASA Astrophysics Data System (ADS)
Saffury, J.; Altus, E.
2010-05-01
Forced harmonic vibration of a non-uniform elastic beam with attached dynamic vibration absorbers (DVA) is studied. Analytical approximation of the solution is obtained by the functional perturbation method (FPM). The problem has application to cutting tools operations where the resistance of the tool holder against regenerative chatter can be enhanced by optimizing the real part of the frequency response function (FRF). A test case of a beam with step-like heterogeneity and single DVA at the tip shows that the FPM solution is very accurate for up to ˜40 percent deviation in both stiffness and mass density. Using the analytical results and Sims approach, optimal DVA tuning is found for each set of beam heterogeneity parameters by solving a set of nonlinear algebraic equations numerically. It is found that the optimum can be further improved by searching for the best step location. The system optimization is then expanded to a general heterogeneous beam with a DVA at its tip. The mass and stiffness distribution is optimized by applying the Lagrange variation method on the FPM solution yielding Fredholm integral equations. The optimized morphology is found to be approximately linear and far from the "intuitive" step-like one (Rivin and Kang, 1992) and yields better chatter-resistance.
Usefulness of T2*-weighted MRI in the detection of adnexal torsion
Kawai, Nobuyuki; Kanematsu, Masayuki; Kawaguchi, Shimpei; Kojima, Toshihisa; Furui, Tatsuro; Morishige, Ken-ichirou; Matsuo, Masayuki
2016-01-01
Background The usefulness of T2*-weighted (T2*W) imaging for the detection of adnexal torsion has yet to be determined. Purpose To assess the usefulness of T2*W imaging for detecting and differentiating adnexal torsion. Material and Methods Eight patients with eight ovaries with torsion and 44 patients with 72 ovaries without torsion were included in this study. All patients underwent 1.5-T magnetic resonance imaging (MRI) including T2*W images. The frequency and distribution of hypointensity on T2*W images were compared between ovaries with torsion and ovaries without torsion. Results Hypointensity on T2*W images was significantly more frequent in ovaries with torsion than in ovaries without torsion (75% vs. 36%; P < 0.05). Among patients with hypointensity on T2*W images, the frequency of diffuse hypointensity was significantly higher in ovaries with torsion than in ovaries without torsion (83% vs. 0%; P < 0.01); whereas the frequency of focal hypointensity was significantly lower in ovaries with torsion than in ovaries without torsion (17% vs. 100%; P < 0.01). Conclusion The presence and distribution of hypointensity on T2*W images may play a supplementary role in the detection of adnexal torsion. PMID:27478621
Torsion of Flanged Members with Cross Sections Restrained Against Warping
NASA Technical Reports Server (NTRS)
Hill, H N
1943-01-01
The longitudinal stresses and the stiffness of flange members - I-beams, channels, and Z-bars - were investigated when these members were subjected to torque with constraint against cross-sectional warping. Measured angles of rotation agreed with corresponding calculated values in which the torsion bending factor of the cross section was involved; the agreement was better for the I-beam and the Z-bar than for the channel. Longitudinal stresses measured at the mid-span were found to agree with the calculated values that involved unit warping as well as the torsion-bending factors: the channel showed the greatest discrepancy between measured and calculated values. When commonly given expressions for rotations and maximum longitudinal stresses in a twisted I-beam were applied to the channel and to the Z-bar, values were obtained that were in reasonably good agreement with values obtained by the method of torsion-bending constant and unit warping.
Testicular torsion and the acute scrotum: current emergency management.
Ta, Anthony; D'Arcy, Frank T; Hoag, Nathan; D'Arcy, John P; Lawrentschuk, Nathan
2016-06-01
The acute scrotum is a challenging condition for the treating emergency physician requiring consideration of a number of possible diagnoses including testicular torsion. Prompt recognition of torsion and exclusion of other causes may lead to organ salvage, avoiding the devastating functional and psychological issues of testicular loss and minimizing unnecessary exploratory surgeries. This review aims to familiarize the reader with the latest management strategies for the acute scrotum, discusses key points in diagnosis and management and evaluates the strengths and drawbacks of history and clinical examination from an emergency perspective. It outlines the types and mechanisms of testicular torsion, and examines the current and possible future roles of labwork and radiological imaging in diagnosis. Emergency departments should be wary of younger males presenting with the acute scrotum. PMID:26267075
Complete axial torsion of pregnant uterus with leiomyoma
Sachan, Rekha; Patel, M L; Sachan, Pushpalata; Arora, Anubha
2014-01-01
Uterine torsion is defined as a rotation of the uterus of more than 45° along its long axis. It is a rare complication during pregnancy; a common cause of torsion can be uterine myoma. Here we describe the case of a 27-year-old G2P1+0 woman at 15 weeks 3 day pregnancy, who presented to our outpatient department as a case of acute abdomen, in a state of shock. Clinical findings did not correlate with investigation. On lapratomy she was diagnosed as a case of complete axial torsion of pregnant uterus with fundal myoma with massive abruption. Early diagnosis and timely intervention would help in improving both maternal and fetal outcome. PMID:25193815
Vibration suppression of curved beams traversed by off-center moving loads
NASA Astrophysics Data System (ADS)
Rostam, M. R.; Javid, F.; Esmailzadeh, E.; Younesian, D.
2015-09-01
In this study six different vibration control strategies are proposed to suppress both the flexural and torsional vibrations of a curved beam traversed by off-center moving loads. The various vibration control strategies employed are: (i) separate tuned-mass-dampers (TMDs), (ii) linked TMDs with a massless connecting rod, (iii) distributed TMDs system, (iv) linked TMDs with intermediate connection, (v) separate TMDs with intermediate dissipating system, and finally (vi) the nonlinear energy sinks (NESs). The curved beam is modeled using finite element model. An optimal design of TMD system is proposed to suppress the effect of non-symmetrical and side-way motion of vehicles traveling on bridges. The dynamic performance of the proposed vibration control strategies are thoroughly evaluated while subjected to different loading conditions: (a) successive moving loads and (b) broadband random excitation. It is shown that while all the proposed strategies can remarkably suppress both types of the vibration, the fifth strategy is the most effective one that provides the largest value of the bending and torsional vibration reduction in the first loading condition.
Improved interframe registration based nonuniformity correction for focal plane arrays
NASA Astrophysics Data System (ADS)
Zuo, Chao; Chen, Qian; Gu, Guohua; Sui, Xiubao; Ren, Jianle
2012-07-01
In this paper, an improved interframe registration based nonuniformity correction algorithm for focal plane arrays is proposed. The method simultaneously estimates detector parameters and carries out the nonuniformity correction by minimizing the mean square error between the two properly registered image frames. A new masked phase correlation algorithm is introduced to obtain reliable shift estimates in the presence of fixed pattern noise. The use of an outliers exclusion scheme, together with a variable step size strategy, could not only promote the correction precision considerably, but also eliminate ghosting artifacts effectively. The performance of the proposed algorithm is evaluated with clean infrared image sequences with simulated nonuniformity and real pattern noise. We also apply the method to a real-time imaging system to show how effective it is in reducing noise and the ghosting artifacts.
Photovoltaic healing of non-uniformities in semiconductor devices
Karpov, Victor G.; Roussillon, Yann; Shvydka, Diana; Compaan, Alvin D.; Giolando, Dean M.
2006-08-29
A method of making a photovoltaic device using light energy and a solution to normalize electric potential variations in the device. A semiconductor layer having nonuniformities comprising areas of aberrant electric potential deviating from the electric potential of the top surface of the semiconductor is deposited onto a substrate layer. A solution containing an electrolyte, at least one bonding material, and positive and negative ions is applied over the top surface of the semiconductor. Light energy is applied to generate photovoltage in the semiconductor, causing a redistribution of the ions and the bonding material to the areas of aberrant electric potential. The bonding material selectively bonds to the nonuniformities in a manner such that the electric potential of the nonuniformities is normalized relative to the electric potential of the top surface of the semiconductor layer. A conductive electrode layer is then deposited over the top surface of the semiconductor layer.
Design optimization of axisymmetric bodies in nonuniform transonic flow
NASA Technical Reports Server (NTRS)
Lan, C. Edward
1989-01-01
An inviscid transonic code capable of designing an axisymmetric body in a uniform or nonuniform flow was developed. The design was achieved by direct optimiation by coupling an analysis code with an optimizer. Design examples were provided for axisymmetric bodies with fineness ratios of 8.33 and 5 at different Mach numbers. It was shown that by reducing the nose radius and increasing the afterbody thickness of initial shapes obtained from symmetric NACA four-digit airfoil contours, wave drag could be reduced by 29 percent for a body of fineness ratio 8.33 in a nonuniform transonic flow of M = 0.98 to 0.995. The reduction was 41 percent for a body of fineness ratio 5 in a uniform transonic flow of M = 0.925 and 65 percent for the same body but in a nonuniform transonic flow of M = 0.90 to 0.95.
Emergence of nonuniform V-states by synchronization
NASA Astrophysics Data System (ADS)
Friedland, L.; Shagalov, A. G.
2002-09-01
It is shown that a family of nonuniform, m-fold symmetric rotating vortex structures in two dimensions (nonuniform V-states) can emerge in both free and bounded space by subjecting an axisymmetric vortex with a sharp vorticity edge to external rotation and weak strain of appropriate symmetry. The phenomenon is due to nonlinear synchronization (autoresonance) in the system, as the vorticity distribution of the vortex structure self-adjusts to phase lock with slowly varying external rotation. The synchronization is induced by passage through resonance with the isolated eigenmode of the linearized problem, provided the external strain rate is above a threshold. Synchronized, m=2 nonuniform V-states remain stable after the external strain is switched off. Free m=3 and 4 states, in contrast, are destroyed via three-wave decay at later times. The negative feedback approach is proposed to stabilize this instability.
Nonuniformity correction in LED printing with plural resolution recording
NASA Astrophysics Data System (ADS)
Ng, Yee S.; Pham, Hieu T.; Laird, Robert
1990-08-01
Binary LED printbars in general have exposure non-uniformity associated with lens transmission nonuniformity LED brightness variations and electro-optical crosstalks (e. g. rise time degradation optical power starvation cross-talk noise as a function of LED pixels usage) that need to be corrected for a high quality printing system. We have designed a constant current Si driver array with two independent power supplies (logic and LED powers) coupled with an improved LED printhbar system to minimize the cross-talk artifacts. In order to improve on the average exposure uniformity of the LED printing system individual trimmable current source to each driver array is also provided. In addition to that a plural resolution printing method (400 x 2400) with a binary weighted correction scheme is used to reduce a binary printhbar''s printing non-uniformity of + or-iS to + or- 1. 0. 1.
ICPP: Numerical Fokker-Planck calculations in nonuniform grids
NASA Astrophysics Data System (ADS)
Bizarro, João P. S.
2000-10-01
The Fokker-Planck equation arises in a wide class of problems in plasma physics, so numerical schemes that provide efficient, accurate, and stable solutions to that equation are always welcome. One way to accomplish this is via nonuniform grids, which allow the use of different mesh sizes according to the real needs of the physical problem under consideration. The extension of the standard finite-difference approach to general nonuniform grids, taking into account proper weighting coefficients, has already been presented, and the results have been rather conclusive [J. P. S. Bizarro and P. Rodrigues, Nucl. Fusion Vol. 37, 1509 (1997)]. Besides reviewing what has been achieved with nonuniform grids, a numerical scheme that is accurate to second order (both in time step and mesh size) is here extended and detailed. Such an analysis is rigourous for one-dimensional Fokker-Planck equations, and is generalized to two-dimensional equations. The constraints on the design of the nonuniform grid are discussed, as well as the particle and energy conservation properties. The conditions under which the nonuniformity correction in the weighting coefficients is essential to secure physically meaningful solutions are also analyzed. The proposed scheme is shown to efficiently handle both linear and weakly nonlinear problems and, in addition, its ability to provide solutions to stronger nonlinear situations is demonstrated. Some particular problems in the field of plasma physics (e.g., Coulomb collisions, Compton scattering by an electronic population, and the rf heating and current drive of thermonuclear reactors) are solved in order to illustrate several features, most particularly the usefulness of nonuniform grids in reducing computational effort and in increasing accuracy.
Iterative and noniterative nonuniform quantisation techniques in digital holography
NASA Astrophysics Data System (ADS)
Shortt, Alison E.; Naughton, Thomas J.; Javidi, Bahram
2006-04-01
Compression is essential for efficient storage and transmission of three-dimensional (3D) digital holograms. The inherent speckle content in holographic data causes lossless compression techniques, such as Huffman and Burrows-Wheeler (BW), to perform poorly. Therefore, the combination of lossy quantisation followed by lossless compression is essential for effective compression of digital holograms. Our complex-valued digital holograms of 3D real-world objects were captured using phase-shift interferometry (PSI). Quantisation reduces the number of different real and imaginary values required to describe each hologram. Traditional data compression techniques can then be applied to the hologram to actually reduce its size. Since our data has a nonuniform distribution, the uniform quantisation technique does not perform optimally. We require nonuniform quantisation, since in a histogram representation our data is denser around the origin (low amplitudes), thus requiring more cluster centres, and sparser away from the origin (high amplitudes). By nonuniformly positioning the cluster centres to match the fact that there is a higher probability that the pixel will have a low amplitude value, the cluster centres can be used more efficiently. Nonuniform quantisation results in cluster centres that are adapted to the exact statistics of the input data. We analyse a number of iterative (k-means clustering, Kohonen competitive neural network, SOM, and annealed Hopfield neural network), and non-iterative (companding, histogram, and optimal) nonuniform quantisation techniques. We discuss the strengths and weaknesses of each technique and highlight important factors that must be considered when choosing between iterative and non-iterative nonuniform quantisation. We measure the degradation due to lossy quantisation in the reconstruction domain, using the normalised rms (NRMS) metric.
Coupled composite rotor blades under bending and torsional loads
NASA Astrophysics Data System (ADS)
Chandra, Ramesh; Chopra, Inderjit
This paper presents an analytical-cum-experimental study of the structural response of composite rotor blades with elastic couplings. Vlasov theory is expanded to analyze two-cell composite rotor blades made out of general composite laminates including the transverse shear deformation of the cross-section. In order to validate this analysis, two-cell graphite-epoxy composite blades with bending-torsion coupling were fabricated using matched-die molding technique. These blades were tested under tip bending and torsional loads, and their structural response in terms of bending slope and twist was measured with a laser optical system. Good correlation between theory and experiment is achieved.
Cosmological evolution of a torsion-induced quintaxion
Mielke, Eckehard W.; Romero, Eric Sanchez
2006-02-15
In an affine prolongation of general relativity, the minimal coupling of Dirac fields to gravity naturally provides an axial current interaction. We demonstrate that the cancellation of the translational curvature, i.e. torsion, in the chiral anomaly induces a dynamical axion coupled with gravitational strength. Because of a geometrical identity, our torsion-induced pseudoscalar couples to the Einstein equations with an effective energy-momentum tensor which automatically satisfies the quintessence condition w<-1/3 for the equation of state parameter. In a toy model of an axion-dominated Universe, this leads to an anharmonic oscillatory evolution for which the deceleration parameter is within the range of current observations.
Calibrations, torsion classes, and wrapped M-branes
Fayyazuddin, Ansar; Husain, Tasneem Zehra
2006-05-15
The present work has two goals. The first is to complete the classification of geometries in terms of torsion classes of M-branes wrapping cycles of a Calabi-Yau manifold. The second goal is to give insight into the physical meaning of the torsion class constraints. We accomplish both tasks by defining new energy minimizing calibrations in M-brane backgrounds. When fluxes are turned on, it is these calibrations that are relevant, rather than those which had previously been defined in the context of purely geometric backgrounds.
Coated Fused Silica Fibers for Enhanced Sensitivity Torsion Pendulum
NASA Technical Reports Server (NTRS)
Numata, Kenji; Horowitz, Jordan; Camp, Jordan
2007-01-01
In order to investigate the fundamental thermal noise limit of a torsion pendulum using a fused silica fiber, we systematically measured and modeled the mechanical losses of thin fused silica fibers coated by electrically conductive thin metal films. Our results indicate that it is possible to achieve a thermal noise limit for coated silica lower by a factor between 3 and 9, depending on the silica diameter, compared to the best tungsten fibers available. This will allow a corresponding increase in sensitivity of torsion pendula used for weak force measurements, including the gravitational constant measurement and ground-based force noise testing for the Laser Interferometer Space Antenna (LISA) mission.
Research on wet etching at MEMS torsion mirror optical switch
NASA Astrophysics Data System (ADS)
Zhang, Yi; Wang, Jifeng; Luo, Yuan
2002-10-01
Etching is a very important technique at MEMS micromachining. There are two kinds of etching processing, the one is wet etching and the other is dry etching. In this paper, wet selective etching with KOH and tetramethyl ammonium hydroxide (TMAH) etchants is researched in order to make a torsion mirror optical switch. The experiments results show that TMAH with superphosphate is more suitable at MEMS torsion mirror optical switch micromachining than KOH, and it also has good compatibility with IC processing. Also our experiments results show some different with other reported research data. More work will be done to improve the yield rate of MEMS optical switch.
New supersymmetric index of heterotic compactifications with torsion
NASA Astrophysics Data System (ADS)
Israël, Dan; Sarkis, Matthieu
2015-12-01
We compute the new supersymmetric index of a large class of N=2 heterotic compactifications with torsion, corresponding to principal two-torus bundles over warped K3 surfaces with H-flux. Starting from a UV description as a (0,2) gauged linear sigma-model with torsion, we use supersymmetric localization techniques to provide an explicit expression of the index as a sum over the Jeffrey-Kirwan residues of the one-loop determinant. We finally propose a geometrical formula that gives the new supersymmetric index in terms of bundle data, regardless of any particular choice of underlying two-dimensional theory.
Noise limit of a torsion pendulum under optomechanical control
NASA Astrophysics Data System (ADS)
Tan, Yu-Jie; Hu, Zhong-Kun; Shao, Cheng-Gang
2015-09-01
In most torsion pendulum experiments, the force resolution is dominantly limited by thermal noise, which is proportional to the pendulum's intrinsic rigidity. Thus, increasing the rigidity directly, such as through increasing torsion fiber's diameter, will decrease the resolution. Here, we present a method to improve the rigidity of a pendulum indirectly through optomechanical control. In this method, for appropriate typical parameter values, the rigidity can be improved greatly. Meanwhile, the extra noise introduced, which our analysis focuses on, can be regulated within the thermal noise level, i.e., the force resolution may not decrease after optomechanical control. This can balance the conflict between large rigidity and high resolution.
[Isolated torsion of the fallopian tube: about two cases].
Bouguern, H; Bouchikhi, C; Chaara, H; Melhouf, M A; Banani, A
2008-02-01
Isolated torsion of the fallopian tube is extremely rare and difficult to diagnose, requires a coelioscopy, or a laparotomy in centers which do not have coelioscpie; often carried out too tardily, to allow the conservation of the horn. We report two observations of isolated torsion of the fallopian tube and we recall through the two clinical cases the diagnostic difficulties, the useful complementary examinations, the treatment and the causes of this pathology which must be systematically evoked in front of any acute abdominal syndrome in order to hope for an early surgical treatment and if possible conservative. PMID:18372548
Elastic torsional buckling of thin-walled composite cylinders
NASA Technical Reports Server (NTRS)
Marlowe, D. E.; Sushinsky, G. F.; Dexter, H. B.
1974-01-01
The elastic torsional buckling strength has been determined experimentally for thin-walled cylinders fabricated with glass/epoxy, boron/epoxy, and graphite/epoxy composite materials and composite-reinforced aluminum and titanium. Cylinders have been tested with several unidirectional-ply orientations and several cross-ply layups. Specimens were designed with diameter-to-thickness ratios of approximately 150 and 300 and in two lengths of 10 in. and 20 in. The results of these tests were compared with the buckling strengths predicted by the torsional buckling analysis of Chao.
NASA Astrophysics Data System (ADS)
Nilsen, Ian A.; Osborne, Derek G.; White, Aaron M.; Anna, Jessica M.; Kubarych, Kevin J.
2014-10-01
Using rapidly acquired spectral diffusion, a recently developed variation of heterodyne detected infrared photon echo spectroscopy, we observe ˜3 ps solvent independent spectral diffusion of benzene chromium tricarbonyl (C6H6Cr(CO)3, BCT) in a series of nonpolar linear alkane solvents. The spectral dynamics is attributed to low-barrier internal torsional motion. This tripod complex has two stable minima corresponding to staggered and eclipsed conformations, which differ in energy by roughly half of kBT. The solvent independence is due to the relative size of the rotor compared with the solvent molecules, which create a solvent cage in which torsional motion occurs largely free from solvent damping. Since the one-dimensional transition state is computed to be only 0.03 kBT above the higher energy eclipsed conformation, this model system offers an unusual, nearly barrierless reaction, which nevertheless is characterized by torsional coordinate dependent vibrational frequencies. Hence, by studying the spectral diffusion of the tripod carbonyls, it is possible to gain insight into the fundamental dynamics of internal rotational motion, and we find some evidence for the importance of non-diffusive ballistic motion even in the room-temperature liquid environment. Using several different approaches to describe equilibrium kinetics, as well as the influence of reactive dynamics on spectroscopic observables, we provide evidence that the low-barrier torsional motion of BCT provides an excellent test case for detailed studies of the links between chemical exchange and linear and nonlinear vibrational spectroscopy.
Nilsen, Ian A; Osborne, Derek G; White, Aaron M; Anna, Jessica M; Kubarych, Kevin J
2014-10-01
Using rapidly acquired spectral diffusion, a recently developed variation of heterodyne detected infrared photon echo spectroscopy, we observe ∼3 ps solvent independent spectral diffusion of benzene chromium tricarbonyl (C6H6Cr(CO)3, BCT) in a series of nonpolar linear alkane solvents. The spectral dynamics is attributed to low-barrier internal torsional motion. This tripod complex has two stable minima corresponding to staggered and eclipsed conformations, which differ in energy by roughly half of kBT. The solvent independence is due to the relative size of the rotor compared with the solvent molecules, which create a solvent cage in which torsional motion occurs largely free from solvent damping. Since the one-dimensional transition state is computed to be only 0.03 kBT above the higher energy eclipsed conformation, this model system offers an unusual, nearly barrierless reaction, which nevertheless is characterized by torsional coordinate dependent vibrational frequencies. Hence, by studying the spectral diffusion of the tripod carbonyls, it is possible to gain insight into the fundamental dynamics of internal rotational motion, and we find some evidence for the importance of non-diffusive ballistic motion even in the room-temperature liquid environment. Using several different approaches to describe equilibrium kinetics, as well as the influence of reactive dynamics on spectroscopic observables, we provide evidence that the low-barrier torsional motion of BCT provides an excellent test case for detailed studies of the links between chemical exchange and linear and nonlinear vibrational spectroscopy. PMID:25296812
Computational methods for studying acoustic propagation in nonuniform waveguides.
NASA Technical Reports Server (NTRS)
Beckemeyer, R. J.; Eversman, W.
1973-01-01
A variational technique is used to model sound transmission through a nonuniform duct segment consisting of an axial variation in wall admittance or cross sectional area. The method involves the Ritz minimization of functionals which have the governing equations as stationary conditions. The variational method is verified by application to segments of variables-separable geometry for which eigenfunction expansion techniques offer an alternative solution procedure, and by comparison with the results of stepped duct approximations to the nonuniformity. Quantitative data are presented which indicate the boundary condition matching to be a suitable measure of the accuracy of the transmitted field.
Induced Velocities Near a Lifting Rotor with Nonuniform Disk Loading
NASA Technical Reports Server (NTRS)
Heyson, Harry H; Katzoff, S
1957-01-01
A method is given for converting known uniformly loaded rotor induced velocities to correspond with arbitrary axisymmetric nonuniform disk load distributions. Numerical results for two specific distributions are given in chart form. Symmetry relations and relations between radial disk loading and wake velocities are developed. Experimental flow measurements are presented and compared with theory. Reasonable agreement is shown in the forward part of the flow when nonuniform loading is assumed, but far behind the rotor the flow is more like that of a wing.
Drift wave instability in a nonuniform quantum dusty magnetoplasma
Salimullah, M.; Jamil, M.; Zeba, I.; Uzma, Ch.; Shah, H. A.
2009-03-15
Using the quantum hydrodynamic model of plasmas and with quantum effects arising through the Bohm potential and the Fermi degenerate pressure, the possible drift waves and their instabilities have been investigated in considerable detail in a nonuniform dusty magnetoplasma. It is found that in the presence of a nonuniform ambient magnetic field, the drift waves grow in amplitude by taking energy from the streaming ions and density inhomogeneity. The implication of the drift wave instability for nonthermal electrostatic fluctuations to laboratory and astrophysical environments is also pointed out.
Non-uniform magnetization reversal in nanocomposite magnets
NASA Astrophysics Data System (ADS)
Li, Z. B.; Zhang, M.; Shen, B. G.; Sun, J. R.
2013-03-01
Magnetization reversal and exchange coupling are investigated in Pr-Fe-B melt-spun ribbons. In nanocomposite magnets, not only does the coercivity decrease but also magnetization reversal becomes more non-uniform in hard grains. The non-uniform magnetization reversal, resulting in a deterioration of squareness in hysteresis loop and a drop of the maximum Henkel plot value, mainly is caused by random arrangement of easy axes and intergranular soft regions among hard grains even with well exchange coupling between soft-hard grains in these ribbons. It is expected that the uniformity in magnetization reversal could be improved with the perfection of easy axes alignment in anisotropy nanocomposites.
Vibration analysis for electronic equipment (2nd edition)
NASA Astrophysics Data System (ADS)
Steinberg, Dave S.
This book describes methods for designing electronic equipment that must work with a high degree of reliability in severe vibration and shock environments. It explains how to design and predict the operational life of electronic equipment based upon the type of electronic components used and the type of vibration and shock exposure. The book begins with a review of the dynamics of nonuniform sections and composite construction methods for electronic assemblies, followed by a discussion of methods for mounting electronic components and determining electrical lead wire and solder joint stresses and fatigue life. Printed circuit boards and chassis assemblies are examined in detail, with methods for determining natural frequency, dynamic coupling transmissibility, and fatigue life. The design and analysis of electronic components, circuit boards, electrical lead wires, and solder joints for sinusoidal and random vibrations, acoustics, shock, and pyrotechnic shock are addressed.
Ranganayakulu, C. ); Seetharamu, K.N. . School of Mechanical Engineering)
1999-07-01
An analysis of a crossflow plate-fin compact heat exchanger, accounting for the combined effects of two-dimensional longitudinal heat conduction through the exchanger wall and nonuniform inlet fluid flow and temperature distribution is carried out using a finite element method. A mathematical equation is developed to generate different types of fluid flow/temperature maldistribution models considering the possible deviations in fluid flow. Using these models, the exchanger effectiveness and its deterioration due to the combined effects of longitudinal heat conduction, flow nonuniformity and temperature nonuniformity are calculated for various design and operating conditions of the exchanger. It was found that the performance variations are quite significant in some typical applications.
The 2004 Hyperflare from SGR 1806-20: Further Evidence for Global Torsional Vibrations
NASA Technical Reports Server (NTRS)
Strohmayer, Tod E.; Watts, Anna L.
2006-01-01
We report an analysis of the archival Rossi X-ray Timing Explorer (RXTE) data from the December 2004 hyperflare from SGR 1806-20. In addition to the approx. equal to 90 Hz QPO first discovered by Israel et al., we report the detection of higher frequency oscillations at approx. equal to 150, 625, and 1,835 Hz. In addition to these frequencies there are indications of oscillations at approx. equal to 720, and 2,384 Hz, but with lower significances. The 150 Hz QPO has a width (FWHM) of about 17 Hz, an average amplitude (rms) of 6.5%, and is detected in average power spectra centered on the rotational phase of the strongest peak in the pulse profile. This is approximately half a rotational cycle from the phase at which the 90 Hz QPO is strongly detected. The 625 Hz oscillation was first detected in an average power spectrum from nine successive cycles beginning approximately 180 s after the initial hard spike. It has a width (FWHM) of approx. equal to 2 Hz and an average amplitude (rms) during this interval of 9%. We find a strong detection of the 625 Hz oscillation in a pair of successive rotation cycles beginning about 230 s after the start of the flare. In these cycles we also detect the 1,835 Hz QPO with the 625 Hz oscillation. The rotational phase in which the 625 Hz &PO is detected is similar to that for the 90 Hz QPO, indeed, this feature is seen in the same average power spectrum. During the time the 625 Hz QPO is detected we also confirm the simultaneous presence of 30 and 92 Hz QPOs, first reported by Israel et al. The centroid frequency of the 625 Hz QPO detected with RXTE is within 1 Hz of the M 626 Hz oscillation recently found in RHESSI data from this hyperflare by Watts & Strohmayer, however, the two detections were made in different phase and energy intervals. Nevertheless, we argue that the two results likely represent detections of the same oscillation frequency intrinsic to the source, but we comment on some of the difficulties in making direct comparisons between the RXTE and RHESSI measurements
THz spectroscopy and first ISM detection of excited torsional states of 13C-methyl formate
NASA Astrophysics Data System (ADS)
Haykal, I.; Carvajal, M.; Tercero, B.; Kleiner, I.; López, A.; Cernicharo, J.; Motiyenko, R. A.; Huet, T. R.; Guillemin, J. C.; Margulès, L.
2014-08-01
Context. An astronomical survey of interstellar molecular clouds needs a previous analysis of the spectra in the microwave and sub-mm energy range of organic molecules to be able to identify them. We obtained very accurate spectroscopic constants in a comprehensive laboratory analysis of rotational spectra. These constants can be used to predict the transitions frequencies very precisely that were not measured in the laboratory. Aims: We present the experimental study and its theoretical analysis for two 13C-methyl formate isotopologues to detect these two isotopologues for the first time in their excited torsional states, which lie at 130 cm-1 (200 K) in Orion-KL. Methods: New spectra of HCOO13CH3 (13C2) methyl formate were recorded with the mm- and submm-wave spectrometer in Lille from 50 to 940 GHz. A global fit for vt = 0 and 1 was accomplished with the BELGI program to reproduce the experimental spectra with greater accuracy. Results: We analysed 5728 and 2881 new lines for vt = 0 and 1 for HCOO13CH3. These new lines were globally fitted with 846 previously published lines for vt = 0. In consequence, 52 parameters of the RAM Hamiltonian were accurately determined and the value of the barrier height (V3 = 369.93168(395) cm-1) was improved. We report the detection of the first excited torsional states (vt = 1) in Orion-KL for the 13C2 and 13C1 methyl formate based on the present analysis and previously published data. We provide column densities, isotopic abundances, and vibrational temperatures for these species. Conclusions: Following this work, accurate prediction can be provided. This permits detecting 135 features of the first excited torsional states of 13C-methyl formate isotopologues in Orion-KL in the 80-280 GHz frequency range, without missing lines. Full Table A.1 and the IRAM spectra as FITS files are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/568
Fedoruk, Sergey Ivanov, Evgeny; Smilga, Andrei
2014-05-15
We present simple models of N= 4 supersymmetric mechanics with ordinary and mirror linear (4, 4, 0) multiplets that give a transparent description of Hyper-Kähler with Torsion (HKT), Clifford Kähler with Torsion (CKT), and Octonionic Kähler with Torsion (OKT) geometries. These models are treated in the N= 4 and N=2 superfield approaches, as well as in the component approach. Our study makes manifest that the CKT and OKT supersymmetric sigma models are distinguished from the more simple HKT models by the presence of extra holomorphic torsion terms in the supercharges.
Viscoelastic Vibration Dampers for Turbomachine Blades
NASA Technical Reports Server (NTRS)
Nguyen, Nhan
2003-01-01
Simple viscoelastic dampers have been invented for use on the root attachments of turbomachine blades. These dampers suppress bending- and torsion-mode blade vibrations, which are excited by unsteady aerodynamic forces during operation. In suppressing vibrations, these dampers reduce fatigue (thereby prolonging blade lifetimes) while reducing noise. These dampers can be installed in new turbomachines or in previously constructed turbomachines, without need for structural modifications. Moreover, because these dampers are not exposed to flows, they do not affect the aerodynamic performances of turbomachines. Figure 1 depicts a basic turbomachine rotor, which includes multiple blades affixed to a hub by means of dovetail root attachments. Prior to mounting of the blades, thin layers of a viscoelastic material are applied to selected areas of the blade roots. Once the blades have been installed in the hub and the rotor is set into rotation, centrifugal force compresses these layers between the mating load-bearing surfaces of the hub and the blade root. The layers of viscoelastic material provide load paths through which the vibration energy of the blade can be dissipated. The viscoelasticity of the material converts mechanical vibration energy into shear strain energy and then from shear strain energy to heat. Of the viscoelastic materials that have been considered thus far for this application, the one of choice is a commercial polyurethane that is available in tape form, coated on one side with an adhesive that facilitates bonding to blade roots. The thickness of the tape can be chosen to suit the specific application. The typical thickness of 0.012 in. (.0.3 mm) is small enough that the tape can fit in the clearance between the mating blade-root and hub surfaces in a typical turbomachine. In an experiment, a blade was mounted in a test fixture designed to simulate the blade-end conditions that prevail in a turbocompressor. Vibrations were excited in the blade by
Analysis of the Lowest In-Plane Bend and First Excited Torsional State of CH_3CH_2CN
NASA Astrophysics Data System (ADS)
Brauer, Carolyn S.; Pearson, John C.; Drouin, Brian J.; Yu, Shanshan
2009-06-01
Propionitrile (CH_3CH_2CN) is observed with large column densities in a number of high-mass star-forming cores, where core temperatures exceed 200 K. It is a near-prolate (κ=0.96) asymmetric top with appreciable dipole moment components on both the a- and b-axes (μ_a = 3.84 D, μ_b = 1.23 D). This, combined with the presence of four fundamental modes as well as four overtones and combination bands all occurring below 600 cm^{-1}, results in a very rich spectrum. It is known to be a major contributor to spectral line confusion in ground-based observations and is expected to complicate observations by Herschel, SOFIA and ALMA, making it imperative to fully characterize the entire spectrum. The lowest in-plane bend, ν_{13}, is 206.9(0.5) cm^{-1}, and the first excited torsional state, ν_{21}, which is just 186 GHz above, have been detected in hot cores with antenna temperatures of a few Kelvin. The close proximity of ν_{13} and ν_{21}, as well as their low-lying nature, offers a unique opportunity to study the vibration-torsion-rotation coupling problem in the case of two nearly degenerate vibrational states. As expected from C_s symmetry and their A^' and A^'' nature, these states exhibit strong a- and b-symmetry Coriolis interactions, as well as interactions resulting from different sets of Eckhart-Sayvetz conditions being required in ν_{13} and ν_{21}. In the present work, the ν_{13} and ν_{21} states of propionitrile have been analyzed to high frequency and angular momentum quantum number. The spectrum, molecular constants,and insights into the vibration-torsion-rotation problem will be discussed. H. M. Heise, H. Lutz & H. Dreizler,Z.Nat.,29a,1345 (1974). H. M. Heise, F. Winther & H. Lutz,J. Mol. Spectrosc.,90,531 (1981). D. M. Mehringer, J. C. Pearson, J. Keene & T. G. Phillips,Ap.J.,608,306 (2004).
Constructal design for a rectangular body with nonuniform heat generation
NASA Astrophysics Data System (ADS)
Feng, Huijun; Chen, Lingen; Xie, Zhihui; Sun, Fengrui
2016-08-01
Nonuniform heat generation models with constant and variable cross-section high-conductivity channels (HCCs) are built in this paper. The minimum dimensionless peak temperature (DPT) is taken as the optimization objective. Different from the models with uniform heat generation and constant cross-section HCCs built by Bejan (1997) and Ledezma et al. (1997), the model with nonuniform heat generation and variable cross-section HCC is more practical and can help to improve the heat conduction performance of a thermal system. The results show that for the rectangular first-order assembly (RFOA) with nonuniform heat generation, there exist both the optimal shape of the RFOA and the optimal HCCs width ratio, which lead to the minimum DPT. They are different from those with uniform heat generation. When the heat is nonuniformly generated in the RFOA, the minimum DPT of the RFOA with variable cross-section HCC is reduced by 12.11% compared with that with constant cross-section HCC. Moreover, the numerical results are also verified by the analytical method.
Economic and environmental aspects of nonuniform agricultural irrigation
House, B.W.; Warden, B.T.; Helfand, G.E.; Larson, D.M. )
1992-12-01
This paper studies the effects of irrigation nonuniformity on nitrate leaching and profits for different levels of applied water. Controlling water application as irrigation uniformity increases can led to reductions in nitrate leaching and sustain relative profits. Water conservation incentives are more effective than direct nitrate reduction incentives.
A novel non-uniformity correction method based on ROIC
NASA Astrophysics Data System (ADS)
Chen, Xiaoming; Li, Yujue; Di, Chao; Wang, Xinxing; Cao, Yi
2011-11-01
Infrared focal plane arrays (IRFPA) suffer from inherent low frequency and fixed patter noised (FPN). They are thus limited by their inability to calibrate out individual detector variations including detector dark current (offset) and responsivity (gain). To achieve high quality infrared image by mitigating the FPN of IRFPAs, we have developed a novel non-uniformity correction (NUC) method based on read-out integrated circuit (ROIC). The offset and gain correction coefficients can be calculated by function fitting for the linear relationship between the detector's output and a reference voltage in ROIC. We tested the purposed method using an infrared imaging system using the ULIS 03 19 1 detector with real nonuniformity. A set of 384*288 infrared images with 12 bits was collected to evaluate the performance. With the experiments, the non-uniformity was greatly eliminated. We also used the universe non-uniformity (NU) parameter to estimate the performance. The calculated NU parameters with the two-point calibration (TPC) and the purposed method imply that the purposed method has almost as good performance as TPC.
GaAs MESFET with lateral non-uniform doping
NASA Technical Reports Server (NTRS)
Wang, Y. C.; Bahrami, M.
1983-01-01
An analytical model of the GaAs MESFET with arbitrary non-uniform doping is presented. Numerical results for linear lateral doping profile are given as a special case. Theoretical considerations predict that better device linearity and improved F(T) can be obtained by using linear lateral doping when doping density increases from source to drain.
Optical nonuniformities in nuclear-pumped cylindrical lasers
Mat'ev, V Yu; Borovkov, V V; Mel'nikov, S P
2000-03-31
The optical nonuniformities, formed as a result of the effect of the inhomogeneous energy deposition by the fission fragments irradiating the laser-active gas from thin uranium-containing layers, were calculated for cylindrical nuclear-pumped gas lasers. The results of the calculations agree with the experiment. (active media. lasers)
Transonic analysis and design of axisymmetric bodies in nonuniform flow
NASA Technical Reports Server (NTRS)
Chang, Jen-Fu; Lan, C. Edward
1987-01-01
An inviscid nonuniform axisymmetric transonic code was developed for applications in analysis and design. Propfan slipstream effect on pressure distribution for a body with and without sting was investigated. Results show that nonuniformity causes pressure coefficient to be more negative and shock strength to be stronger and more rearward. Sting attached to a body reduced the pressure peak and moves the rear shock forward. Extent and Mach profile shapes of the nonuniformity region appeared to have little effect on the pressure distribution. Increasing nonuniformity magnitude made pressure coefficient more negative and moved the shock rearward. Design study was conducted with the CONMIN optimizer for an ellipsoid and a body with the NACA-0012 counter. For the ellipsoid, the general trend showed that to reduce the pressure drag, the front portion of the body should be thinner and the contour of the rear portion should be flatter than the ellipsoid. For the design of a body with a sharp trailing edge in transonic flow with an initial shape given by the NACA-0012 contour, the pressure drag was reduced by decreasing the nose radius and increasing the thickness in the aft portion. Drag reduction percentages are given.
Nonuniform Effects of Reinstatement within the Time Window
ERIC Educational Resources Information Center
Galluccio, Llissa; Rovee-Collier, Carolyn
2006-01-01
A time window is a limited period after an event initially occurs in which additional information can be integrated with the memory of that event. It shuts when the memory is forgotten. The time window hypothesis holds that the impact of a manipulation at different points within the time window is nonuniform. In two operant conditioning…
Quaternionic Torsion Geometry, Superconformal Symmetry and T-duality
Swann, Andrew
2009-02-02
HyperKaehler metrics with torsion (HKT metrics) are constructed via superconformal symmetry. It is shown how T-duality interpreted as a twist construction for circle actions provides a number of compact simply-connected examples. Further applications of the twist construction are discussed to obtain compact simply-connected HKT manifolds with few symmetries and to construct all HKT nilmanifolds.
Nonlinear Fierz-Pauli theory from torsion and bigravity
NASA Astrophysics Data System (ADS)
Deffayet, C.; Randjbar-Daemi, S.
2011-08-01
The nonlinear aspects of a recently proposed model of massive spin-2 particles with propagating torsion are studied. We obtain a nonlinear equation which reduces at linear order to a generalized Fierz-Pauli equation in any background space-time with or without a vanishing torsion. We contrast those results with properties of a class of bigravity theories in an arbitrary background Einstein manifold. It is known that the nonperturbative spectrum of the bigravity model has 8 propagating physical degrees of freedom. This is identical to the physical propagating degrees of freedom of the massive spin-2 torsion model at the linearized order. The obtained nonlinear version of the Fierz-Pauli field equations, however, contains terms absent in the bigravity case which indicates that the curved space generalization of the unique flat space Fierz-Pauli equation is not unique. Moreover, in the torsion massive gravity model the Fierz-Pauli field appears as a derivative of fundamental fields. This, however, does not generate any unwanted pole once coupled to some external sources.
Deligne-Beilinson cohomology and Abelian link invariants: Torsion case
Thuillier, F.
2009-12-15
For the Abelian Chern-Simons field theory, we consider the quantum functional integration over the Deligne-Beilinson cohomology classes and present an explicit path-integral nonperturbative computation of the Chern-Simons link invariants in SO(3){approx_equal}RP{sup 3}, a toy example of a 3-manifold with torsion.
34. VERTICAL AND TORSIONAL MOTION VIEWED FROM EAST TOWER, 7 ...
34. VERTICAL AND TORSIONAL MOTION VIEWED FROM EAST TOWER, 7 NOVEMBER 1940, FROM 16MN FILM SHOT BY PROFESSOR F.B. FARQUHARSON, UNIVERSITY OF WASHINGTON. (LABORATORY STUDIES ON THE TACOMA NARROWS BRIDGE, AT UNIVERSITY OF WASHINGTON (SEATTLE: UNIVERSITY OF WASHINGTON, DEPARTMENT OF CIVIL ENGINEERING, 1941) - Tacoma Narrows Bridge, Spanning Narrows at State Route 16, Tacoma, Pierce County, WA
Mechanical properties of orthodontic wires in tension, bending, and torsion.
Drake, S R; Wayne, D M; Powers, J M; Asgar, K
1982-09-01
The mechanical properties of three sizes of stainless steel (SS), nickel-titanium (NT), and titanium-molybdenum (TM) orthodontic wires were studied in tension, bending, and torsion. The wires (0.016 inch, 0.017 by 0.025 inch, and 0.019 by 0.025 inch) were tested in the as-received condition. Tensile testing and stiffness testing machines along with a torsional instrument were used. Mean values and standard deviations of properties were computed. The data were analyzed statistically by analysis of variance using a factorial design. Means were ranked by a Tukey interval calculated at the 95 percent level of confidence. In tension, the stainless steel wires had the least maximum elastic strain or springback, whereas the titanium-molybdenum wires had the most. Higher values of springback indicate the capacity for an increased range of activation clinically. In bending and torsion, the stainless steel wires had the least stored energy at a fixed moment, whereas the nickel-titanium wires had the most. Spring rates in bending and torsion, however, were highest for stainless steel wires and lowest for nickel-titanium wires. A titanium-molybdenum teardrop closing loop delivered less than one half the force of a comparable stainless steel loop for similar activations. PMID:6961793
Torsional Oscillations and Waves Projected on the Wall
ERIC Educational Resources Information Center
Bartlett, Albert A.
2008-01-01
The article "Torsional Oscillations with Lorentz Force" by Paul Gluck provides a glimpse into the major world of ancient physics demonstrations in the late 19th and first half of the 20th centuries. The apparatus that was described and similar pieces of apparatus are the basis for many memorable but long forgotten educational demonstrations. The…
Torsion Stiffness of a Protein Pair Determined by Magnetic Particles
Janssen, X.J.A.; van Noorloos, J.M.; Jacob, A.; van IJzendoorn, L.J.; de Jong, A.M.; Prins, M.W.J.
2011-01-01
We demonstrate the ability to measure torsion stiffness of a protein complex by applying a controlled torque on a magnetic particle. As a model system we use protein G bound to an IgG antibody. The protein pair is held between a magnetic particle and a polystyrene substrate. The angular orientation of the magnetic particle shows an oscillating behavior upon application of a rotating magnetic field. The amplitude of the oscillation increases with a decreasing surface coverage of antibodies on the substrate and with an increasing magnitude of the applied field. For decreasing antibody coverage, the torsion spring constant converges to a minimum value of 1.5 × 103 pN·nm/rad that corresponds to a torsion modulus of 4.5 × 104 pN·nm2. This torsion stiffness is an upper limit for the molecular bond between the particle and the surface that is tentatively assigned to a single protein G–IgG protein pair. This assignment is supported by interpreting the measured stiffness with a simple mechanical model that predicts a two orders of magnitude larger stiffness for the protein G–IgG complex than values found for micrometer length dsDNA. This we understand from the structural properties of the molecules, i.e., DNA is a long and flexible chain-like molecule, whereas the antibody-antigen couple is orders of magnitude smaller and more globular in shape due to the folding of the molecules. PMID:21539795
Testing gravity-induced collapse models with torsion pendulums
NASA Astrophysics Data System (ADS)
Helou, Bassam; Wipf, Christopher; Chen, Yanbei
2016-03-01
Wavefunction collapse models have been proposed to resolve the measurement problem in QM. Some, , such as Diosi-Penrose model, are motivated by gravity. We first present the theory of such models, highlighting new results, such as fixing the only free paramater in the model. We then propose torsion pendulums as a promising optomechanical platform to test such models.