Showing papers on "Transverse plane published in 2016"

Vortical Fluid and Λ Spin Correlations in High-Energy Heavy-Ion Collisions

Abstract: Fermions become polarized in a vortical fluid due to spin-vorticity coupling, and the polarization density is proportional to the local fluid vorticity. The radial expansion converts spatial vortical structures in the transverse plane to spin correlations in the azimuthal angle of final Λ hyperons' transverse momentum in high-energy heavy-ion collisions. Using a (3+1)D viscous hydrodynamic model with fluctuating initial conditions from a multiphase transport (AMPT) model, we reveal two vortical structures that are common in many fluid dynamic systems: a right-handed toroidal structure around each beam direction for transverse vorticity and pairing of longitudinal vortices with opposite signs in the transverse plane. The calculated azimuthal correlation of the transverse spin is shown to have a cosine form plus an offset due to the toroidal structure of the transverse vorticity around the beam direction and the global spin polarization. The longitudinal spin correlation in the azimuthal angle shows an oscillatory structure due to multiple vorticity pairs in the transverse plane. Mechanisms of these vortical structures, physical implications of hyperon spin correlations, dependence on colliding energy, rapidity, centrality, and sensitivity to the shear viscosity are also investigated.

Ultrasound shear wave velocity in skeletal muscle: A reproducibility study.

Abstract: Purpose The purpose of the study was threefold: to assess the reliability of shear wave velocities (SWV) measurements in normal skeletal muscles; to evaluate intra- and inter-operator reproducibility of measurements for a specific site of the muscle and for the mean value in the whole muscle. Materials and methods Two sets of measurements were performed at three weeks intervals of each other on 16 volunteers by two radiologists on medial gastrocnemius and tibialis anterior muscles. Each muscle was evaluated in 5 different sites, with three measurements for each site in the transverse and longitudinal planes. Reliability of SWV measurements was assessed by means of intraclass correlation coefficient (ICC). Results Reliability of the three independent SWV measurements was excellent, slightly better in the longitudinal plane. Inter/intra-operator reproducibility per site was fair to good in the longitudinal plane and poor to fair in the transverse plane. For global values of the whole muscle, ICC showed good agreement in the longitudinal plane and fair agreement in the transverse plane. Conclusion Quantitative SWV measurements are reliable when performed in rigorous conditions. In conditions that mirror clinical practice, inter/intra-operator reproducibility is moderate, better for longitudinal compared to transverse plane.

Transverse oscillations in slender Ca II H fibrils observed with Sunrise/SuFI

Abstract: We present observations of transverse oscillations in slender Ca II H fibrils (SCFs) in the lower solar chromosphere We use a 1 hr long time series of high- (spatial and temporal-) resolution seeing-free observations in a 011 nm wide passband covering the line core of Ca II H 3969 nm from the second flight of the Sunrise balloon-borne solar observatory The entire field of view, spanning the polarity inversion line of an active region close to the solar disk center, is covered with bright, thin, and very dynamic fine structures Our analysis reveals the prevalence of transverse waves in SCFs with median amplitudes and periods on the order of 24+-08 km/s and 83+-29 s, respectively (with standard deviations given as uncertainties) We find that the transverse waves often propagate along (parts of) the SCFs with median phase speeds of 9+-14 km/s While the propagation is only in one direction along the axis in some of the SCFs, propagating waves in both directions, as well as standing waves are also observed The transverse oscillations are likely Alfvenic and are thought to be representative of magnetohydrodynamic kink waves The wave propagation suggests that the rapid high-frequency transverse waves, often produced in the lower photosphere, can penetrate into the chromosphere with an estimated energy flux of ~ 15 kW/m^2 Characteristics of these waves differ from those reported for other fibrillar structures, which, however, were observed mainly in the upper solar chromosphere

Transverse flow induced by inhomogeneous magnetic fields in the Bjorken expansion

Abstract: We investigate the magnetohydrodynamics in the presence of an external magnetic field following the power-law decay in proper time and having spatial inhomogeneity characterized by a Gaussian distribution in one of transverse coordinates under the Bjorken expansion. The leading-order solution is obtained in the weak-field approximation, where both energy density and fluid velocity are modified. It is found that the spatial gradient of the magnetic field results in transverse flow, where the flow direction depends on the decay exponents of the magnetic field. We suggest that such a magnetic-field-induced effect might influence anisotropic flow in heavy ion collisions.

Transverse, propagating velocity perturbations in solar coronal loops

Abstract: As waves and oscillations carry both energy and information, they have enormous potential as a plasma heating mechanism and, through seismology, to provide estimates of local plasma properties which are hard to obtain from direct measurements. Being sufficiently near to allow high-resolution observations, the atmosphere of the Sun forms a natural plasma laboratory. Recent observations have revealed that an abundance of waves and oscillations is present in the solar atmosphere, leading to a renewed interest in wave heating mechanisms. This short review paper gives an overview of recently observed transverse, propagating velocity perturbations in coronal loops. These ubiquitous perturbations are observed to undergo strong damping as they propagate. Using 3D numerical simulations of footpoint-driven transverse waves propagating in a coronal plasma with a cylindrical density structure, in combination with analytical modelling, it is demonstrated that the observed velocity perturbations can be understood in terms of coupling of different wave modes in the inhomogeneous boundaries of the loops. Mode coupling in the inhomogeneous boundary layers of the loops leads to the coupling of the transversal (kink) mode to the azimuthal (Alfven) mode, observed as the decay of the transverse kink oscillations. Both the numerical and analytical results show the spatial profile of the damped wave has a Gaussian shape to begin with, before switching to exponential decay at large heights. In addition, recent analysis of CoMP (Coronal Multi-channel Polarimeter) Doppler shift observations of large, off-limb, trans-equatorial loops shows that Fourier power at the apex appears to be higher in the high-frequency part of the spectrum than expected from theoretical models. This excess high-frequency FFT power could be tentative evidence for the onset of a cascade of the low-to-mid frequency waves into (Alfvenic) turbulence.

Forward modeling of standing kink modes in coronal loops. ii. applications

Abstract: Magnetohydrodynamic waves are believed to play a significant role in coronal heating, and could be used for remote diagnostics of solar plasma. Both the heating and diagnostic applications rely on a correct inversion (or backward modeling) of the observables into the thermal and magnetic structures of the plasma. However, due to the limited availability of observables, this is an ill-posed issue. Forward modeling is designed to establish a plausible mapping of plasma structuring into observables. In this study, we set up forward models of standing kink modes in coronal loops and simulate optically thin emissions in the extreme ultraviolet bandpasses, and then adjust plasma parameters and viewing angles to match three events of transverse loop oscillations observed by the Solar Dynamics Observatory/Atmospheric Imaging Assembly. We demonstrate that forward models could be effectively used to identify the oscillation overtone and polarization, to reproduce the general profile of oscillation amplitude and phase, and to predict multiple harmonic periodicities in the associated emission intensity and loop width variation.

Cylindrical particle manipulation and negative spinning using a nonparaxial Hermite-Gaussian light-sheet beam

Abstract: Based on the angular spectrum decomposition method (ASDM), a nonparaxial solution for the Hermite−Gaussian (HG m ) light-sheet beam of any order m is derived. The beam-shape coefficients (BSCs) are expressed in a compact form and computed using the standard Simpson's rule for numerical integration. Subsequently, the analysis is extended to evaluate the longitudinal and transverse radiation forces as well as the spin torque on an absorptive dielectric cylindrical particle in 2D without any restriction to a specific range of frequencies. The dynamics of the cylindrical particle are also examined based on Newton's second law of motion. The numerical results show that a Rayleigh or Mie cylindrical particle can be trapped, pulled or propelled in the optical field depending on its initial position in the cross-sectional plane of the HG m light-sheet. Moreover, negative or positive axial spin torques can arise depending on the choice of the non-dimensional size parameter ka (where k is the wavenumber and a is the radius of the cylinder) and the location of the absorptive cylinder in the beam. This means that the HG m light-sheet beam can induce clockwise or anti-clockwise rotations depending on its shift from the center of the cylinder. In addition, individual vortex behavior can arise in the cross-sectional plane of wave propagation. The present analysis presents an analytical model to predict the optical radiation forces and torque induced by a HG m light-sheet beam on an absorptive cylinder for applications in optical light-sheet tweezers, optical micro-machines, particle manipulation and opto-fluidics to name a few areas of research.

The effect of uniform electric field on the cross-stream migration of a drop in plane Poiseuille flow

Abstract: The effect of a uniform electric field on the motion of a drop in an unbounded plane Poiseuille flow is studied analytically. The drop and suspending media are considered to be Newtonian and leaky dielectric. We solve for the two-way coupled electric and flow fields analytically by using a double asymptotic expansion for small charge convection and small shape deformation. We obtain two important mechanisms of cross-stream migration of the drop: (i) shape deformation and (ii) charge convection. The second one is a new source of cross-stream migration of the drop in plane Poiseuille flow which is due to an asymmetric charge distribution on the drop surface. Our study reveals that charge convection can cause a spherical non-deformable drop to migrate in the cross-stream direction. The combined effect of charge convection and shape deformation significantly alters the drop velocity, drop trajectory and steady state transverse position of the drop. We predict that, depending on the orientation of the applied uniform electric field and the relevant drop/medium electrohydrodynamic parameters, the drop may migrate either towards the centreline of the flow or away from it. We obtain that the final steady state transverse position of the drop is independent of its initial transverse position in the flow field. Most interestingly, we show that the drop can settle in an off-centreline steady state transverse position. Two-dimensional numerical simulations are also performed to study the drop motion in the combined presence of plane Poiseuille flow and a tilted electric field. The drop trajectory and steady state transverse position of the drop obtained from numerical simulations are in qualitative agreement with the analytical results.

Forward Modelling of Standing Kink Modes in Coronal Loops II. Applications

Abstract: Magnetohydrodynamic waves are believed to play a significant role in coronal heating, and could be used for remote diagnostics of solar plasma. Both the heating and diagnostic applications rely on a correct inversion (or backward modelling) of the observables into the thermal and magnetic structures of the plasma. However, owing to the limited availability of observables, this is an ill-posed issue. Forward Modelling is to establish a plausible mapping of plasma structuring into observables. In this study, we set up forward models of standing kink modes in coronal loops and simulate optically thin emissions in the extreme ultraviolet bandpasses, and then adjust plasma parameters and viewing angles to match three events of transverse loop oscillations observed by the Solar Dynamics Observatory/Atmospheric Imaging Assembly. We demonstrate that forward models could be effectively used to identify the oscillation overtone and polarization, to reproduce the general profile of oscillation amplitude and phase, and to predict multiple harmonic periodicities in the associated emission intensity and loop width variation.

Characterizing the differences between the 2D and 3D measurements of spine in adolescent idiopathic scoliosis

Abstract: Although adolescent idiopathic scoliosis (AIS) is known to impact the 3D orientation of the spine and pelvis, the impact of the vertebral position relative to the X-ray scanner on the agreement between 2D and 3D measurements of a curve has not been evaluated. The purpose of this study was to investigate the agreement between 2D and 3D measurements of the scoliotic curve as a function of the 3D spinal parameters in AIS. Three independent observers measured the thoracic and lumbar Cobb angles, Kyphosis, and lordosis on the posterior–anterior and lateral X-rays of AIS patients. The 3D reconstructions were created from bi-planar X-rays and the 3D spinal parameters were calculated in both radio and patient planes using SterEOS software. The degree of agreement between the 2D and 3D measurements was tested and its relationship with the curve axial rotation was determined. 2D and 3D measurements of the sagittal plane spinal parameters were significantly different (p < 0.05). The differences between the 2D and 3D measurements were related to the apical vertebrae rotation, the orientation of the plane of maximum curvature, pelvic axial rotation, and the curve magnitude. Differences between the radio plane and patient plane measurements were related to the pelvic axial rotation, Cobb angles, and apical vertebrae rotation, p < 0.05. Clinically and statistically significant differences were observed between the 2D and 3D measurements of the scoliotic spine. The differences between the 2D and 3D techniques were significant in sagittal plane and were related to the spinal curve and pelvic rotation in transverse plane.

The ubiquitous photonic wheel

Abstract: A circularly polarized electromagnetic plane wave carries an electric field that rotates clockwise or counterclockwise around the propagation direction of the wave. According to the handedness of this rotation, its longitudinal spin angular momentum (AM) density is either parallel or antiparallel to the propagation of light. However, there are also light waves that are not simply plane and carry an electric field that rotates around an axis perpendicular to the propagation direction, thus yielding transverse spin AM density. Electric field configurations of this kind have been suggestively dubbed 'photonic wheels'. It has been recently shown that photonic wheels are commonplace in optics as they occur in electromagnetic fields confined by waveguides, in strongly focused beams, in plasmonic and evanescent waves. In this work we establish a general theory of electromagnetic waves propagating along a well defined direction, and carrying transverse spin AM density. We show that depending on the shape of these waves, the spin density may be either perpendicular to the mean linear momentum (globally transverse spin) or to the linear momentum density (locally transverse spin). We find that the latter case generically occurs only for non-diffracting beams, such as the Bessel beams. Moreover, we introduce the concept of meridional Stokes parameters to operationally quantify the transverse spin density. To illustrate our theory, we apply it to the exemplary cases of Bessel beams and evanescent waves. These results open a new and accessible route to the understanding, generation and manipulation of optical beams with transverse spin AM density.

Transverse-momentum–flow correlations in relativistic heavy-ion collisions

Abstract: The correlation between the transverse momentum and the azimuthal asymmetry of the flow is studied. A correlation coefficient is defined between the average transverse momentum of hadrons emitted in an event and the square of the elliptic or triangular flow coefficient. The hydrodynamic model predicts a positive correlation of the transverse momentum with the elliptic flow, and almost no correlation with the triangular flow in Pb-Pb collisions at LHC energies. In $p$-Pb collisions the new correlation observable is very sensitive to the mechanism of energy deposition in the first stage of the collision.

Fiber-based photon-pair source capable of hybrid entanglement in frequency and transverse mode, controllably scalable to higher dimensions

Abstract: We have designed and implemented a photon-pair source, based on the spontaneous four wave mixing (SFWM) process in a few-mode fiber, in a geometry which permits multiple, simultaneous SFWM processes, each associated with a distinct combination of transverse modes for the four participating waves. In our source: i) each process is group-velocity-matched so that it is, by design, nearly-factorable and ii) the spectral separation between neighboring processes is greater than the marginal spectral width of each process. Consequently, there is a direct correspondence between the joint amplitude of each process and each of the Schmidt mode pairs of the overall two-photon state. Our approach permits hybrid entanglement in discrete frequency and in transverse mode, whereby control of the number of supported fiber transverse modes allows scalability to higher dimensions while spectral filtering may be used for straightforward Schmidt mode discrimination.

Point And Line To Plane

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The instability and non-existence of multi-stranded loops when driven by transverse waves

Abstract: In recent years, omni-present transverse waves have been observed in all layers of the solar atmosphere. Coronal loops are often modeled as a collection of individual strands, in order to explain their thermal behaviour and appearance. We perform 3D ideal MHD simulations to study the effect of a continuous small amplitude transverse footpoint driving on the internal structure of a coronal loop composed of strands. The output is also converted to synthetic images, corresponding to the AIA 171 A and 193 A passbands, using FoMo. We show that the multi-stranded loop ceases to exist in the traditional sense of the word, because the plasma is efficiently mixed perpendicularly to the magnetic field, with the Kelvin-Helmholtz instability acting as the main mechanism. The final product of our simulation is mixed loop with density structures on a large range of scales, resembling a power-law. Thus, multi-stranded loops are unstable to driving by transverse waves, and this raises a strong doubt on the usability and applicability of coronal loop models consisting of independent strands.

Single-beam three-axis atomic magnetometer

Abstract: A single-beam atomic magnetometer being operated near zero-field and measuring three-axis fields simultaneously is demonstrated. We produce a rotating field on the x-0-y plane with the frequency of 90 Hz and a modulation field in the z axis at 130 Hz. The rotating field enables a nonzero z axis output when the transverse fields are zeroed using feedback systems. Based on the phase difference of π/2, x and y axes fields can be measured using one lock-in amplifier. Magnetic field sensitivities of 300 fT/Hz1∕2 in x and y axes and 3 pT/Hz1∕2 in the z axis are achieved.

The effects of off-axis transverse deflection loading on the failure strain of various high-performance fibers:

Abstract: Single filaments are subjected to a transverse deflection loading environment in efforts to gain insight into the failure strain of soft-body armor systems experiencing transverse impact. The fiber...

Physical Mechanism of the Transverse Instability in Radiation Pressure Ion Acceleration.

Abstract: The transverse stability of the target is crucial for obtaining high quality ion beams using the laser radiation pressure acceleration (RPA) mechanism. In this Letter, a theoretical model and supporting two-dimensional (2D) particle-in-cell (PIC) simulations are presented to clarify the physical mechanism of the transverse instability observed in the RPA process. It is shown that the density ripples of the target foil are mainly induced by the coupling between the transverse oscillating electrons and the quasistatic ions, a mechanism similar to the oscillating two stream instability in the inertial confinement fusion research. The predictions of the mode structure and the growth rates from the theory agree well with the results obtained from the PIC simulations in various regimes, indicating the model contains the essence of the underlying physics of the transverse breakup of the target.

Exact equatorial water waves in the f-plane

Abstract: We present an exact solution for geophysical ocean waves in the Equatorial region which is three-dimensional, nonlinear, explicit in the Lagrangian formulation, and which incorporates a meridional current that is transverse Equatorial.

Jet axes and universal transverse-momentum-dependent fragmentation

Abstract: We study the transverse momentum spectrum of hadrons in jets. By measuring the transverse momentum with respect to a judiciously chosen axis, we find that this observable is insensitive to (the recoil of) soft radiation. Furthermore, for small transverse momenta we show that the effects of the jet boundary factorize, leading to a new transverse-momentum-dependent (TMD) fragmentation function. In contrast to the usual TMD fragmentation functions, it does not involve rapidity divergences and is universal in the sense that it is independent of the type of process and number of jets. These results directly apply to sub-jets instead of hadrons. We discuss potential applications, which include studying nuclear modification effects in heavy-ion collisions and identifying boosted heavy resonances.

Transverse-electric Brewster effect enabled by nonmagnetic two-dimensional materials

Abstract: Xiao Lin,1,2 Yichen Shen,2 Ido Kaminer,2,* Hongsheng Chen,1,3,† and Marin Soljačić2 1College of Information Science and Electronic Engineering, Zhejiang University, Hangzhou 310027, China 2Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA 3The Electromagnetics Academy at Zhejiang University, State Key Laboratory of Modern Optical Instrumentation, Zhejiang University, Hangzhou 310027, China (Received 17 June 2016; revised manuscript received 1 August 2016; published 18 August 2016)