Showing papers on "Transverse plane published in 2012"

Probing strongly coupled anisotropic plasma

Abstract: We calculate the static potential, the drag force and the jet quenching parameter in strongly coupled anisotropic $ \mathcal{N} = {4} $ super Yang-Mills plasma. We find that the jet quenching is in general enhanced in presence of anisotropy compared to the isotropic case and that its value depends strongly on the direction of the moving quark and the direction along which the momentum broadening occurs. The jet quenching is strongly enhanced for a quark moving along the anisotropic direction and momentum broadening happens along the transverse one. The parameter gets lower for a quark moving along the transverse direction and the momentum broadening considered along the anisotropic one. Finally, a weaker enhancement is observed when the quark moves in the transverse plane and the broadening occurs on the same plane. The drag force for quark motion parallel to the anisotropy is always enhanced. For motion in the transverse space the drag force is enhanced compared to the isotropic case only for quarks having velocity above a critical value. Below this critical value the force is decreased. Moreover, the drag force along the anisotropic direction is always stronger than the force in the transverse space. The diffusion time follows exactly the inverse relations of the drag forces. The static potential is decreased and stronger decrease observed for quark-antiquark pair aligned along the anisotropic direction than the transverse one. We finally comment on our results and elaborate on their similarities and differences with the weakly coupled plasmas.

Observation of transverse Anderson localization in an optical fiber.

Abstract: We utilize transverse Anderson localization as the waveguiding mechanism in optical fibers with random transverse refractive index profiles. Using experiments and numerical simulations, we show that the transverse localization results in an effective propagating beam diameter that is comparable to that of a typical index-guiding optical fiber.

Depth-Dependent Transverse Shear Properties of the Human Corneal Stroma

Abstract: Thorough characterization of the mechanical properties of connective tissue, including the cornea, presents significant theoretical and experimental challenges. To date, mechanical testing of the cornea has been almost exclusively focused on estimating the tensile modulus of the stroma using techniques such as strip tensile tests or cornea pressure-inflation tests.1–4 However, even in the most simple of material models there are at a minimum two elastic constants that must be measured to characterize the three-dimensional elastic behavior of the material. This most simple case is called isotropic elasticity5 and occurs when the material properties under investigation exhibit no dependence on direction during testing. In this case, the material is fully characterized by the Young's modulus and the shear modulus. The shear modulus naturally measures the resistance of the tissue to shearing strains. In fact, the microstructure of the corneal stroma suggests that its elasticity cannot be isotropic. The parallel arrays of collagen fibrils within each lamella and the layering of lamellae one on another imply that the transverse (anterior-posterior) properties of the tissue will be different from the in-plane properties. To address this anisotropy and other considerations, increasingly complex elasticity models have been introduced with the goal of achieving greater fidelity to the full three-dimensional behavior of the tissue.6–8 More complex models always have more than two intrinsic elastic constants that need to be measured. When such models are extended to nonlinear behavior, yet more constants must necessarily be introduced (Petsche SJ, et al., manuscript submitted, 2012).6,8 Experimental measurement of elastic constants must be interpreted against an assumed elasticity model (i.e., material symmetry). Transversely isotropic linear elasticity5 is the simplest possible model that can reasonably be applied to the corneal stroma. Materials exhibiting transverse isotropy have a single plane of material isotropy (the corneal tangent plane) and properties in this plane will be different from properties measured orthogonally (through the corneal thickness). In this case, characterization of the material elasticity requires the measurement of five independent elastic constants: the in-plane Young's modulus (related to the tensile modulus) and transverse Young's modulus, the in-plane and transverse Poisson's ratios, and the transverse shear modulus, denoted G.5 To appreciate the role of the transverse shear modulus, consider the anterior and posterior surfaces of a circular stromal button subjected to relative torsional twisting about an axis perpendicular to the surfaces (see Fig. 4). The tissue will become deformed in a state of pure transverse shear strain and the resistance of the tissue will be dependent only on the transverse shear modulus G. Experimental measurement of the shear properties of human corneas are missing from the extant literature. A thesis by Nickerson9 discusses the use of torsional rheometry to measure shear properties of porcine cornea. Standard inflation and strip testing1–4 do not introduce shearing deformations and these tests therefore give no information about shear stiffness. Figure 4. Typical stress/strain curve from a final load cycle used for calculating the magnitude of the complex shear modulus. The inset cartoon shows the applied torque and resulting shear strain (γ) on a cornea button, which is maximum at the perimeter. ... Because the corneal stroma makes up 90% of the tissue's thickness and contains almost all the cornea's collagen and proteoglycan content, it is the crucial layer for explaining corneal stiffness. The stroma consists of 200 to 500 sheet-like lamellae, each made up of collagen fibrils maintained at quasi-uniform spacing for transparency by the glycosaminoglycan (GAG) chains of the stromal proteoglycans. Evidence of lamellar interweaving that varies with depth through the cornea is provided by imaging that uses polarized light.10 The interweaving appears maximal at the anterior surface and significantly reduces toward the posterior. Recent images by Jester et al.11,12 using second harmonic generated imaging confirm this assessment. Figure 1 shows the central part of a full human cornea cross-section created from many second harmonic generated images and in which distinct interweaving in the anterior third may be discerned by the through-thickness trajectory of many of the lamellae. It is also noted that scanning electron microscopy and transmission electron microscopy images show that lamellae become wider and thicker toward the posterior of the stroma.13 X-ray scattering studies have demonstrated that the collagen associated with preferred directions measured in the limbal plane also varies with depth through the cornea.14 After using a femtosecond laser to cut the stroma into thirds through the thickness, Abahussin et al.14 showed that lamellae exhibit preferred angular distributions in the posterior third but transition toward a more uniform distribution in the anterior third. Figure 1. Cross-section of a human cornea from second harmonic generated imaging showing the interweaving of lamellae in the anterior third. The complex patterns of the three-dimensional collagen architecture within the stroma can be expected to affect and contribute to the elasticity of the tissue regionally. In particular, the variation of microstructure through the thickness suggests that the mechanical properties of the stroma may have a nonconstant profile through the thickness. Depth dependence of mechanical properties in the stroma, including transverse shear stiffness, has not been considered heretofore and may be important for the biomechanics of the cornea. We hypothesize that the pronounced interweaving of lamellae in the anterior third compared with the central and posterior thirds will provide the anterior third with a relatively larger transverse shear modulus because the collagen in vertically descending lamellae may be engaged during the shearing deformations. This will not be the case in noninterweaving regions. In this work we report direct measurement of the transverse shear modulus of the human corneal stroma through the depth using torsional rheometry.

Analysis of Sandwich Beams With a Compliant Core and With In-Plane Rigidity—Extended High-Order Sandwich Panel Theory Versus Elasticity

Abstract: A new one-dimensional high-order theory for orthotropic elastic sandwich beams is formulated. This new theory is an extension of the high-order sandwich panel theory (HSAPT) and includes the in-plane rigidity of the core. In this theory, in which the compressibility of the soft core in the transverse direction is also considered, the displacement field of the core has the same functional structure as in the high-order sandwich panel theory. Hence, the transverse displacement in the core is of second order in the transverse coordinate and the in-plane displacements are of third order in the transverse coordinate. The novelty of this theory is that it allows for three generalized coordinates in the core (the axial and transverse displacements at the centroid of the core and the rotation at the centroid of the core) instead of just one (midpoint transverse displacement) commonly adopted in other available theories. It is proven, by comparison to the elasticity solution, that this approach results in superior accuracy, especially for the cases of stiffer cores, for which cases the other available sandwich computational models cannot predict correctly the stress fields involved. Thus, this theory, referred to as the “extended high-order sandwich panel theory” (EHSAPT), can be used with any combinations of core and face sheets and not only the very “soft” cores that the other theories demand. The theory is derived so that all core=face sheet displacement continuity conditions are fulfilled. The governing equations as well as the boundary conditions are derived via a variational principle. The solution procedure is outlined and numerical results for the simply supported case of transverse distributed loading are produced for several typical sandwich configurations. These results are compared with the corresponding ones from the elasticity solution. Furthermore, the results using the classical sandwich model without shear, the first-order shear, and the earlier HSAPT are also presented for completeness. The comparison among these numerical results shows that the solution from the current theory is very close to that of the elasticity in terms of both the displacements and stress or strains, especially the shear stress distributions in the core for a wide range of cores. Finally, it should be noted that the theory is formulated for sandwich panels with a generally asymmetric geometric layout. [DOI: 10.1115/1.4005550]

Observation of the planar Nernst effect in permalloy and nickel thin films with in-plane thermal gradients.

Abstract: We present experimental evidence of a transverse thermopower, or planar Nernst effect, in ferromagnetic metal thin films driven by thermal gradients applied in the plane of the films. Samples of 20 nm thick Ni and Ni(80)Fe(20) were deposited on 500 nm thick suspended Si-N thermal isolation platforms with integrated platinum strips designed originally to allow measurement of thermally generated spin currents (the spin Seebeck effect). The low thermal conductivity of the thin supporting Si-N structure results in an essentially 2D geometry that approaches the zero substrate limit, dramatically reducing the contribution of thermal gradients perpendicular to the sample plane typically found in similar experiments on bulk substrates. The voltage on the platinum strips generated transverse to the applied thermal gradient (V(T)) is linear with increasing ΔT and exhibits a sign reversal on hot and cold sides of the sample. However, V(T) is always even in applied magnetic field and shows a sinθ cosθ angular dependence, both key indicators of the planar Nernst effect. Within the 5 nV estimated error of our experiment there is no evidence of a signal from the spin Seebeck effect, which would have cosθ angular dependence, suggesting a reduced spin Seebeck coefficient in a planar, entirely thin-film geometry.

Spatial damping of propagating kink waves due to mode coupling

Abstract: Aims. We investigate the damping process for propagating transverse velocity oscillations, observed to be ubiquitous in the solar corona, due to mode coupling. Methods. We perform 3D numerical simulations of footpoint-driven transverse waves propagating in a low β coronal plasma with a cylindrical density structure. Mode coupling in an inhomogeneous layer leads to the coupling of the kink mode to the Alfven mode, observed as the decay of the transverse kink oscillations. Results. We consider the spatial damping profile and find a Gaussian damping profile of the form exp(−z/Lg) to be the most congruent with our numerical data, rather than the exponential damping profile of the form exp(−z/Ld) used in normal mode analysis. Our results highlight that the nature of the driver itself will have a substantial influence on observed propagating kink waves. Conclusions. Our study suggests that this modified damping profile should be taken into account when using coronal seismology to infer local plasma properties from observed damped oscillations.

The MRI findings of meniscal root tear of the medial meniscus: emphasis on coronal, sagittal and axial images

Abstract: The purpose of this study was to evaluate the accuracy of the characteristic magnetic resonance imaging (MRI) findings of medial meniscal root tear in the coronal, sagittal and axial planes. Thirty arthroscopically diagnosed patients who had undergone preoperative knee MRI were included in this study. They were compared to 30 age-matched patients with medial meniscus tears without root tears. The findings used for imaging analysis were as follows: the radial tear on the meniscal root of the medial meniscus in the axial plane, the presence of the truncation sign in the coronal plane and the ghost meniscus sign in the sagittal plane. Meniscal extrusion in the coronal plane was also evaluated. All the MRI findings of both groups were statistically analyzed. All the findings were more frequently found in the root tear group than those in the control group (P < 0.05). The sensitivity, specificity, positive predictive value and negative predictive value of finding a radial tear in the axial plane were 93.3, 100, 100 and 93.8%, respectively. In the coronal plane, rates for the presence of the truncation sign were 90, 100, 100 and 90.9%, respectively. In the sagittal plane, rates for the presence of the ghost meniscus sign were 96.7, 96.7, 96.7 and 96.7%, respectively. The rates for the meniscus extrusion in the coronal plane were 63.3, 90, 86.4 and 71.1%, respectively. The findings of medial meniscal root tear were characteristic as compared with the control group. Radial tear in the axial plane also showed similar diagnostic accuracy as that seen in the other planes. The characteristic findings provide high diagnostic accuracy, and axial plane is helpful to detect medial meniscal root tear. Diagnostic study, Level III.

Bandgap tuning in armchair MoS2 nanoribbon

Abstract: We report on the first-principles calculations of bandgap modulation in armchair MoS2 nanoribbon (AMoS2NR) by transverse and perpendicular electric fields respectively. In the monolayer AMoS2NR case, it is shown that the bandgap can be significantly reduced and be closed by transverse field, whereas the bandgap modulation is absent under perpendicular field. The critical strength of transverse field for gap closure decreases as ribbon width increases. In the multilayer AMoS2NR case, in contrast, it is shown that the bandgap can be effectively reduced by both transverse and perpendicular fields. Nevertheless, it seems that the two fields exhibit different modulation effects on the gap. The critical strength of perpendicular field for gap closure decreases with increasing number of layers, while the critical strength of transverse field is almost independent of it.

The LHC Transverse Coupled-Bunch Instability

Abstract: In this thesis, the problem of the transverse coupled-bunch instabilities created by the Large Hadron Collider (LHC) beam-coupling impedance, that can possibly limit the machine operation, is addressed thanks to several new theories and tools A rather complete vision of the problem is proposed here, going from the calculation of the impedances and wake functions of individual machine elements, to the beam dynamics study Firstly, new results are obtained in the theory of the beam-coupling impedance for an axisymmetric two-dimensional structure, generalizing Zotter's theories, and a new general theory is derived for the impedance of an infinite flat two-dimensional structure Then, a new approach has been found to compute the wake functions from such analytically obtained beam-coupling impedances, over-coming limitations that could be met with standard discrete Fourier transform procedures Those results are then used to obtain an impedance and wake function model of the LHC, based on the (resistive-) wall impedances of various contributors (collimators, beam screens and vacuum pipe) and additional estimations of the geometrical impedance contributions Finally, the existing code HEADTAIL, which is a macroparticle simulation code for beam dynamics studies with wake fields, is improved to make possible the simulation of multibunch trains, and a spectral analysis technique is found to facilitate the analysis of the output given by this code, giving the complex tune shifts of the unstable modes present in a simulation All those theories and tools are used to obtain new results concerning the LHC transverse coupled-bunch instabilities, demonstrating the rather small impact on coupled-bunch instabilities of the number of bunches in a train when the bunch spacing is fixed, and the existence of coupled-bunch modes with intrabunch motion which are more critical than their single-bunch counterparts A full verification of the complete procedure (impedance theories, impedance model and simulation code) is also performed by comparing the simulation results with actual measurements in the LHC, giving a very good agreement at injection energy and a correct order of magnitude at 35 TeV/c In the end, several predictions concerning the beam stability at the future 7 TeV/c operation of the machine are performed in the case of 50 ns spacing (1404 bunches), revealing that the coupled-bunch transverse mode coupling instability threshold is far above the ultimate bunch intensity but about 20% smaller than its single-bunch counterpart Stability studies with Landau octupoles at their maximum currents reveal that the beam remains stable at nominal intensity with Q' = 2 in both planes, provided the particle transverse distributions are Gaussian At ultimate intensity with either Q' = 0 or Q' = 2, or at nominal intensity when the chromaticity is zero, the beam happens to be unstable, even with the octupoles at their maximum currents

Detailed investigation of the impact of the fiber design parameters on the transverse Anderson localization of light in disordered optical fibers

Abstract: We recently reported the observation of transverse Anderson localization as the waveguiding mechanism in optical fibers with random transverse refractive index profiles [1]. Here, we explore the impact of the design parameters of the disordered fiber on the beam radius of the propagating transverse localized beam. We show that the optimum value of the fill-fraction of the disorder is 50% and a lower value results in a larger beam radius. We also explore the impact of the average size of the individual random features on the value of the localized beam radius and show how the boundary of the fiber can impact the observed localization radius. A larger refractive index contrast between the host medium and the disorder sites results in smaller value of the beam radius.

Biaxial buckling analysis of soft-core composite sandwich plates using improved high-order theory

Abstract: In the present paper, a new improved high-order theory is presented for biaxial buckling analysis of sandwich plates with soft orthotropic core. Third-order plate theory is used for face sheets and quadratic and cubic functions are assumed for transverse and in-plane displacements of the core, respectively. Continuity conditions for transverse shear stresses at the interfaces as well as the conditions of zero transverse shear stresses on the upper and lower surfaces of plate are satisfied. The nonlinear Von-Karman type relations are used to obtain strains. Also, transverse flexibility and transverse normal strain and stress of the orthotropic core are considered. The equations of motion and boundary conditions are derived by principle of minimum potential energy. Analytical solution for static analysis of simply supported sandwich plates under biaxial in-plane compressive loads is presented using Navier’s solution. Effect of geometrical parameters of face sheets and core and biaxial loads ratio are studied on the overall buckling of sandwich plates. Comparison of the present results with those of the three-dimensional theory of elasticity and some plate theories confirms the accuracy of the proposed theory.

Propagation of hybrid transverse magnetic-transverse electric plasmons on magnetically biased graphene sheets

Abstract: The propagation of plasmons on magnetically biased graphene sheets is addressed. The analysis is based on the transverse resonance method extended to handle the graphene conductivity tensor and allows easily accounting for substrate effects. A transcendental equation is obtained for the propagation constant of the resulting hybrid transverse magnetic-transverse electric mode. A closed-form approximate expression for a graphene layer sandwitched between two different media is also provided. Application of the method shows that the presence of a magnetic field leads to extreme field localization, namely, very small guided wavelength, as compared with usual plasmons in graphene or noble metals. The extent of field localization and its frequency can be dynamically controlled by modifying the applied magnetostatic and electrostatic bias field, respectively. These features could enable extreme device miniaturization and enhanced resolution in sensing applications.

Measurements of the pseudorapidity dependence of the total transverse energy in proton-proton collisions at root s=7 TeV with ATLAS

Abstract: This paper describes measurements of the sum of the transverse energy of particles as a function of particle pseudorapidity, eta, in proton-proton collisions at a centre-of-mass energy, root s = 7 TeV using the ATLAS detector at the Large Hadron Collider. The measurements are performed in the region \eta\ < 4.8 for two event classes: those requiring the presence of particles with a low transverse momentum and those requiring particles with a significant transverse momentum. In the second dataset measurements are made in the region transverse to the hard scatter. The distributions are compared to the predictions of various Monte Carlo event generators, which generally tend to underestimate the amount of transverse energy at high \eta\.

Characterization of transverse beam emittance of electrons from a laser-plasma wakefield accelerator in the bubble regime using betatron x-ray radiation

Abstract: We propose and use a technique to measure the transverse emittance of a laser-wakefield accelerated beam of relativistic electrons. The technique is based on the simultaneous measurements of the electron beam divergence given by v(perpendicular to)/v(parallel to), the measured spectrum gamma, and the transverse electron bunch size in the bubble r(perpendicular to). The latter is obtained via the measurement of the source size of the x rays emitted by the accelerating electron bunch in the bubble. We measure a normalized rms beam transverse emittance < 0.5 pi mm mrad as an upper limit for a spatially Gaussian, spectrally quasimonoenergetic electron beam with 230 MeV energy in agreement with numerical modeling and analytic theory in the bubble regime.

Skin Dose in Longitudinal and Transverse Linac-MRIs using Monte-Carlo and realistic 3D MRI field models

Abstract: Purpose The magnetic fields of linac-MR systems modify the path of contaminant electrons in photon beams, which alters patient skin dose. To accurately quantify the magnitude of changes in skin dose, the authors use Monte Carlo calculations that incorporate realistic 3D magnetic field models of longitudinal and transverse linac-MR systems. Methods Finite element method (FEM) is used to generate complete 3D magnetic field maps for 0.56 T longitudinal and transverse linac-MR magnet assemblies, as well as for representative 0.5 and 1.0 T Helmholtz MRI systems. EGSnrc simulations implementing these 3D magnetic fields are performed. The geometry for the BEAMnrc simulations incorporates the Varian 600C 6 MV linac, magnet poles, the yoke, and the magnetic shields of the linac-MRIs. Resulting phase-space files are used to calculate the central axis percent depth-doses in a water phantom and 2D skin dose distributions for 70 μm entrance and exit layers using DOSXYZnrc. For comparison, skin doses are also calculated in the absence of magnetic field, and using a 1D magnetic field with an unrealistically large fringe field. The effects of photon field size, air gap (longitudinal configuration), and angle of obliquity (transverse configuration) are also investigated. Results Realistic modeling of the 3D magnetic fields shows that fringe fields decay rapidly and have a very small magnitude at the linac head. As a result, longitudinal linac-MR systems mostly confine contaminant electrons that are generated in the air gap and have an insignificant effect on electrons produced further upstream. The increase in the skin dose for the longitudinal configuration compared to the zero B-field case varies from ∼1% to ∼14% for air gaps of 5-31 cm, respectively. (All dose changes are reported as a % of D(max).) The increase is also field-size dependent, ranging from ∼3% at 20 × 20 cm(2) to ∼11% at 5 × 5 cm(2). The small changes in skin dose are in contrast to significant increases that are calculated for the unrealistic 1D magnetic field. For the transverse configuration, the entrance skin dose is equal or smaller than that of the zero B-field case for perpendicular beams. For a 10 × 10 cm(2) oblique beam the transverse magnetic field decreases the entry skin dose for oblique angles less than ±20° and increases it by no more than 10% for larger angles up to ±45°. The exit skin dose is increased by 42% for a 10 × 10 cm(2) perpendicular beam, but appreciably drops and approaches the zero B-field case for large oblique angles of incidence. Conclusions For longitudinal linac-MR systems only a small increase in the entrance skin dose is predicted, due to the rapid decay of the realistic magnetic fringe fields. For transverse linac-MR systems, changes to the entrance skin dose are small for most scenarios. For the same geometry, on the exit side a fairly large increase is observed for perpendicular beams, but significantly drops for large oblique angles of incidence. The observed effects on skin dose are not expected to limit the application of linac-MR systems in either the longitudinal or transverse configuration.

First observation of a transverse vertical oscillation during the formation of a hot post-flare loop

Abstract: Aims. We report and analyse the first observation of a transverse oscillation in a hot coronal loop with the Atmospheric Imaging Assembly (AIA) on the Solar Dynamics Observatory (SDO), following a linked coronal-flare mass-ejection event on the 3 November 2010. The oscillating coronal loop is observed off the east solar limb and exclusively in the 131 A and 94 A bandpasses, indicating a loop plasma of temperature in the range of 9-11 MK. Furthermore, the loop is not observed to cool into the other AIA channels, but just disappears from all bandpasses at the end of the oscillation. Methods. A time series analysis of the loop oscillation is conducted by taking several cuts at different positions along the loop, estimating the transverse displacements over time for two strands in the loop and fitting those with a damped cosine curve. Intensity time variations, both along the loop and for a series of cut cross-sections, are investigated. Using a three-dimensional loop geometry obtained from a comparison of STEREO-B/EUVI and AIA images, we model different modes of transverse oscillations in the uniformly filled loop. Results. Our time series analysis reveals a period of 302 ± 14 s (291 ± 9 s) and a damping time of 306 ± 43 s (487 ± 125 s) for the first (second) loop strand. A spatial phase shift along the loop of approximately 180° suggests that we observe a higher order harmonic. Intensity oscillations are consistent with an interpretation in terms of a vertically polarised mode. Our forward modelling suggests that the loop oscillates as either a second or third order harmonic of this mode. Conclusions. This is the first observation of a transverse loop oscillation observed exclusively in the hot coronal lines. The loop oscillation is vertically polarised and is dominated by a higher order harmonic mode. We conclude that the excitation mechanism of this 5 min period oscillation is directly connected with the reconnection processes that form the post flare loop, which differs from the blast wave excitation mechanism often proposed as the cause of cooler transverse loop oscillations. © 2012 ESO.

Nanoparticle with a ferrimagnetic interlayer coupling in the presence of single-ion anisotropis

Abstract: The magnetic properties of a nanoparticle described by the transverse Ising model with single-ion anisotropis, which consists of a concentric spin-3/2 core and a hexagonal ring spin-5/2 shell coupled with a ferrimamagnetic interlayer coupling, are studied by the effective-field theory with self-spin correlations. Particular emphasis is given to the effects of the both the transverse field and the single-ion anisotropis on the longitudinal and transverse magnetizations, phase diagrams of the nanoparticle. We have found that, for appropriate values of the system parameters, one or two compensation points may be obtained in the present systems.

Parametric instability of a rotor-bearing system with two breathing transverse cracks

Abstract: When the rotor rotates at a constant speed, the transverse crack opens and closes alternatively, due to gravity, and thus a “breathing effect” occurs. This variance in shaft stiffness is time-periodic, and hence a parametrically excited system is expected. The parametric excitation from the time-varying stiffness causes instability and severe vibration under certain operating conditions. Current research mostly focused on the rotor with single transverse crack. There are few studies on the multi-cracked rotor system. In fact, the interaction between the multiple parametric excitations with various phasing and amplitude, which are induced by the multiple breathing transverse cracks, would make the instability behavior of the system differ distinctly from that of the single cracked rotor system. Moreover, how the instability regions change with various crack breathing mechanisms should also be investigated. Thus, the parametric instability of a rotor-bearing system with two breathing transverse cracks is studied in the paper. First, the finite element equations of motion are established for the cracked rotor system. Two types of crack breathing mechanisms, of which one is more accurate (new) and the other is empirical (old), are adopted in the finite element formulation. Then, a generalized Bolotin's method is introduced for determining the boundaries of the primary and secondary instability regions. Based upon these, instability analysis for a practical used rotor-bearing system with single and two cracks are conducted, respectively. The instability regions induced by the single transverse crack with new and old breathing mechanisms are compared with each other. For the two-cracked rotor system, the variations of the unstable boundaries with crack depths, orientation angles and positions are observed and discussed in detail. It is shown from the results that the dynamic instability of the two-cracked rotor-bearing system indeed have some unique features that differ from that of the single cracked rotor system.

The kinematics of an untwisting solar jet in a polar coronal hole observed by SDO/AIA

Abstract: Using the multi-wavelength data from the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO) spacecraft, we study a jet occurring in a coronal hole near the northern pole of the Sun. The jet presented distinct upward helical motion during ejection. By tracking six identified moving features (MFs) in the jet, we found that the plasma moved at an approximately constant speed along the jet's axis. Meanwhile, the MFs made a circular motion in the plane transverse to the axis. Inferred from linear and trigonometric fittings to the axial and transverse heights of the six tracks, the mean values of the axial velocities, transverse velocities, angular speeds, rotation periods, and rotation radii of the jet are 114 km s-1, 136 km s-1, 0.81° s-1, 452 s and 9.8 × 103 km respectively. As the MFs rose, the jet width at the corresponding height increased. For the first time, we derived the height variation of the longitudinal magnetic field strength in the jet from the assumption of magnetic flux conservation. Our results indicate that at heights of 1 × 104 ~ 7 × 104 km from the base of the jet, the flux density in the jet decreases from about 15 to 3 G as a function of B = 0.5(R/R⊙ − 1)−0.84 (G). A comparison was made with other results in previous studies.

Intensity variations associated with fast sausage modes

Abstract: We determine the dependence of the observed properties of fast magnetoacoustic axisymmetric oscillations (the sausage mode) of a thick and dense flaring coronal loop, modelled by a magnetic cylinder, on the parameters of the equilibrium plasma configuration. The plasma inside and outside the cylinder is of low-beta, and penetrated by a straight magnetic field. The plasma density has a smooth profile across the magnetic field. Methods: We use three-dimensional ideal magnetohydrodynamic equations to model numerically the development of the perturbations of the cylindrical equilibrium, considering both leaky and trapped regimes. Results: Short-period sausage oscillations, trapped by the cylinder, are qualitatively consistent with the analytical results obtained in the models of a plasma slab or a cylinder with a step-function transverse profile. The period of trapped sausage oscillations is determined by the ratio of the phase speed, with the value between the internal and external Alfven speeds, to the wavelength. Longer-period sausage oscillations are leaky, and their decay times are longer for higher density contrasts between the internal and external media. Leaky sausage oscillations have longer periods than trapped sausage oscillations of the same cylinder. In the coronal conditions, sausage oscillations are essentially compressible and transverse, hence produce modulation of the thermal optically thin emission intensity and periodic Doppler broadening of emission lines. However, if the oscillating plasma non-uniformity is poorly spatially resolved, the variation in the emission intensity is weak and proportional to the actual amplitude of the oscillation squared. The latter variation property is connected with the transverse nature of the oscillation, causing the conservation of mass in the transverse cross-section of the oscillating plasma structure.

Transverse dynamics of water across the melting point: A parallel neutron and x-ray inelastic scattering study

Abstract: Joint inelastic neutron and x-ray scattering measurements have been performed on heavy water across the melting point. The spectra bear clear evidence of low- and high-frequency inelastic shoulders related to transverse and longitudinal modes, respectively. Upon increasing the momentum transfer, the spectral shape evolves from a viscoelastic regime, where the low-frequency mode is clearly over-damped, toward an elastic one where its propagation becomes instead allowed. The crossover between the two regimes occurs whenever both the characteristic frequency and the linewidth of the low-frequency mode match the inverse of the structural relaxation time. Furthermore, we observe that the frequency of the transverse mode undergoes a discontinuity across the melting, whose extent reduces upon increasing the exchanged momentum.

Universal phase relation between longitudinal and transverse fields observed in focused terahertz beams

Abstract: We directly observe longitudinal electromagnetic fields in focused freely propagating terahertz beams of radial and linear polarization. In accordance with theory, the longitudinal fields are phase shifted by a value of pi/2 with respect to the transverse field components. This behavior is found for all frequency components of single cycle THz radiation pulses. Additionally we show that the longitudinal field of a radially polarized THz beam has a smaller spot size as compared to the transverse field of a linearly polarized beam, that is focused under the same conditions.

Influence of the helical and six available Cardan sequences on 3D ankle joint kinematic parameters

Abstract: Cardan/Euler and helical angles are the popular methods of quantifying angular kinematics. Cardan angles are sequence dependent and crosstalk can influence the kinematic calculations. The International Society of Biomechanics (ISB) recommends a sagittal, coronal, and then transverse (XYZ) sequence of rotations, although it has been proposed that when calculating rotations outside of the sagittal plane, this may not be the most appropriate method. This study investigated the influence of the helical and six available Cardan sequences on three-dimensional (3D) ankle joint kinematics. Kinematic data were obtained using an eight-camera motion analysis system as participants ran at 4.0 m/s +/- 5%. Repeated measures ANOVAs were used to compare kinematic parameters, and intraclass correlations were employed to identify evidence of crosstalk across planes. The results indicate that in the transverse and coronal planes, peak angle and range of motion values using the YXZ and ZXY sequences were significantly greater than the other sequences. Furthermore, utilization of YXZ and ZXY sequences was associated with the strongest correlations from the sagittal plane, and the XYZ sequence was found to be associated with the lowest correlations. It appears that for the representation of 3D ankle joint kinematics, the XYZ sequence is associated with minimal planar crosstalk and as such its use is encouraged.