Velocity Asymmetry Research Articles

Interocular nystagmus asymmetry and motion sickness

Binocular videonystagmography (VNG) was used to study the vestibulo-ocular response to a double rotation test as a pre-flight medical examination (PFME) for assessing an aircrew’s vestibulo-autonomic stability. The objective of our study was to identify the relationship between the degree of the nystagmus response to rotation and the severity of motion sickness (MS). The investigated cohort included 135 subjects selected from flight crews aged 23 to 47 years, who were qualified healthy according to the PFME criteria. The test used was based on the intermittent cumulation of Coriolis accelerations by Bryanov’s method. The post-testing vestibular reactivity was assessed using criteria for determining the level of autonomic reactivity and protection movements. Binocular videonystagmography (VNG) with a mask cover was performed during and after rotation. The degree of interocular asymmetry of nystagmus velocity was shown to be directly associated with the severity of MS. We suggested the following asymmetry coefficients: the asymmetry coefficient of unidirectional nystagmus during flexions (ACf) and extensions (ACe); and the duration of convergence rotatory nystagmus during flexions (DCNf) and extensions (DCNe). It has been found that ACf and DCNf are correlated with the severity of MS (p < 0.05). On the basis of our data, we formulated the idea of the mechanism for MS development due to double rotation, which was understood as the occurrence in these conditions of intravestibular interlabyrinth conflict.

Manipulation of dielectric particles with nondiffracting parabolic beams.

The trapping and manipulation of microscopic particles embedded in the structure of nondiffracting parabolic beams is reported. The particles acquire orbital angular momentum and exhibit an open trajectory following the parabolic fringes of the beam. We observe an asymmetry in the terminal velocity of the particles caused by the counteracting gradient and scattering forces.

Accretion-ejection connection in the young brown dwarf candidate ISO-ChaI 217

As the number of observed brown dwarf outflows is growing it is important to investigate how these outflows compare to the well studied jets from young stellar objects. A key point of comparison is the relationship between outflow and accretion activity and in particular the ratio between the mass outflow and accretion rates ($\dot{M}_{out}$/$\dot{M}_{acc}$). The brown dwarf candidate ISO-ChaI 217 was discovered by our group, as part of a spectro-astrometric study of brown dwarfs, to be driving an asymmetric outflow with the blue-shifted lobe having a position angle of $\sim$ 20$^{\circ}$. The aim here is to further investigate the properties of ISO-ChaI 217, the morphology and kinematics of its outflow, and to better constrain ($\dot{M}_{out}$/$\dot{M}_{acc}$). The outflow is spatially resolved in the $[SII]\lambda \lambda 6716,6731$ lines and is detected out to $\sim$ 1\farcs6 in the blue-shifted lobe and ~ 1" in the red-shifted lobe. The asymmetry between the two lobes is confirmed although the velocity asymmetry is less pronounced with respect to our previous study. Using thirteen different accretion tracers we measure log($\dot{M}_{acc}$) [M$_{sun}$/yr]= -10.6 $\pm$ 0.4. As it was not possible to measure the effect of extinction on the ISO-ChaI 217 outflow $\dot{M}_{out}$ was derived for a range of values of A$_{v}$, up to a value of A$_{v}$ = 2.5 mag estimated for the source extinction. The logarithm of the mass outflow ($\dot{M}_{out}$) was estimated in the range -11.7 to -11.1 for both jets combined. Thus $\dot{M}_{out}$/$\dot{M}_{acc}$ [\Msun/yr] lies below the maximum value predicted by magneto-centrifugal jet launching models. Finally, both model fitting of the Balmer decrements and spectro-astrometric analysis of the H$\alpha$ line show that the bulk of the H I emission comes from the accretion flow.

Finite Element Modeling of Shear Strain in Rolling with Velocity Asymmetry in Multi-Roll Calibers

Severe plastic deformation is now recognized the most efficient way of producing ultrafine grained metals and alloys. At the present time a lot of severe plastic deformation methods have been proposed and developed. They differ in the deformation schemes. Unlike such severe plastic deformation methods as high pressure torsion and equal-channel angular pressing, rolling with the velocity asymmetry is a continuous process. It helps to solve the problem of the limited length of manufactured bars with semi ultrafine structure. Rolling process with roll velocity asymmetry generates high shear strain necessary for obtaining ultrafine structures of the processed material. A new process of asymmetric rolling of profiles in multi-roll passes has been developed. This process can be used for production of high-strength profiles such as circles, hexagons, wire rods, etc. Compression of the bar in multi-roll passes can be done not only from two, as usual, but from three or four sides. In case of a multi-crimped bar, a uniform compression scheme with large hydrostatic pressure is created in the deformation zone. It enhances the ductility of the material and allows increasing the strain intensity. Simulation in DEFORM 3DTM proved that the process of asymmetric rolling in multi-roll calibers allows to obtain higher values of shear strain and strain effective.

PIV measurements of the bottom boundary layer under nonlinear surface waves

Sediment in the nearshore is largely mobilized in the wave bottom boundary layer (wbbl) hereby emphasizing the importance of this relatively thin layer to nearshore morphology. This paper presents a laboratory experiment where hydrodynamic properties of the wbbl were quantified by measuring flow velocities using Particle Image Velocimetry. The bottom of the wave flume was rigid with a single bar profile. The measurements consisted of the velocities of the wbbl with a resolution in the order of 10 points in time and space for skewed and asymmetric waves. In the wbbl there was significant transformation of velocity skewness and asymmetry. Negative wbbl streaming was generated by asymmetric waves. Boundary layer development and generation of vortex tubes were observed. The velocity measurements included the turbulent components resulting in quantification of turbulent stresses that were of similar magnitude as the viscous stresses.

A method for determining poloidal rotation from poloidal asymmetry in toroidal rotation (invited).

A new diagnostic has been developed on DIII-D that determines the impurity poloidal rotation from the poloidal asymmetry in the toroidal angular rotation velocity. This asymmetry is measured with recently added tangential charge exchange viewchords on the high-field side of the tokamak midplane. Measurements are made on co- and counter-current neutral beams, allowing the charge exchange cross section effect to be measured and eliminating the need for atomic physics calculations. The diagnostic implementation on DIII-D restricts the measurement range to the core (r/a < 0.6) where, relative to measurements made with the vertical charge exchange system, the spatial resolution is improved. Significant physics results have been obtained with this new diagnostic; for example, poloidal rotation measurements that significantly exceed neoclassical predictions.

Monetary reward speeds up voluntary saccades.

Past studies have shown that reward contingency is critical for sensorimotor learning, and reward expectation speeds up saccades in animals. Whether monetary reward speeds up saccades in human remains unknown. Here we addressed this issue by employing a conditional saccade task, in which human subjects performed a series of non-reflexive, visually-guided horizontal saccades. The subjects were (or were not) financially compensated for making a saccade in response to a centrally-displayed visual congruent (or incongruent) stimulus. Reward modulation of saccadic velocities was quantified independently of the amplitude-velocity coupling. We found that reward expectation significantly sped up voluntary saccades up to 30°/s, and the reward modulation was consistent across tests. These findings suggest that monetary reward speeds up saccades in human in a fashion analogous to how juice reward sped up saccades in monkeys. We further noticed that the idiosyncratic nasal-temporal velocity asymmetry was highly consistent regardless of test order, and its magnitude was not correlated with the magnitude of reward modulation. This suggests that reward modulation and the intrinsic velocity asymmetry may be governed by separate mechanisms that regulate saccade generation.

Dayside/nightside asymmetry of ion densities and velocities in Saturn's inner magnetosphere

We present Radio and Plasma Wave Science Langmuir probe measurements from 129 Cassini orbits, which show a day/night asymmetry in both ion density and ion velocity in the radial region 4–6 RS (1 RS ...

2D X-ray radiography of imploding capsules at the national ignition facility.

First measurements of the in-flight shape of imploding inertial confinement fusion (ICF) capsules at the National Ignition Facility (NIF) were obtained by using two-dimensional x-ray radiography. The sequence of area-backlit, time-gated pinhole images is analyzed for implosion velocity, low-mode shape and density asymmetries, and the absolute offset and center-of-mass velocity of the capsule shell. The in-flight shell is often observed to be asymmetric even when the concomitant core self-emission is round. A ∼ 15 μm shell asymmetry amplitude of the Y(40) spherical harmonic mode was observed for standard NIF ICF hohlraums at a shell radius of ∼ 200 μm (capsule at ∼ 5× radial compression). This asymmetry is mitigated by a ∼ 10% increase in the hohlraum length.

The role of tidal asymmetry in characterizing the tidal energy resource of Orkney

When selecting sites for marine renewable energy projects, there are a wide range of economical and practical constraints to be considered, from the magnitude of the resource through to proximity of grid connections. One factor that is not routinely considered in tidal energy site selection, yet which has an important role in quantifying the resource, is tidal asymmetry, i.e. variations between the flood and ebb phases of the tidal cycle. Here, we present theory and develop a high-resolution three-dimensional ROMS tidal model of Orkney to examine net power output for a range of sites along an energetic channel with varying degrees of tidal asymmetry. Since power output is related to velocity cubed, even small asymmetries in velocity lead to substantial asymmetries in power output. We also use the 3D model to assess how tidal asymmetry changes with height above the bed, i.e. representing different device hub heights, how asymmetry affects turbulence properties, and how asymmetry is influenced by wind-driven currents. Finally, although there is minimal potential for tidal phasing over our study site, we demonstrate that regions of opposing flood- versus ebb-dominant asymmetry occurring over short spatial scales can be aggregated to provide balanced power generation over the tidal cycle.

Effect of a secondary channel on the non-linear tidal dynamics in a semi-enclosed channel: a simple model

Non-linear tidal dynamics are investigated in a network that consists of a semi-enclosed main channel and a secondary channel at an arbitrary position. The water motion, governed by the one-dimensional shallow water equations, is forced by an incoming tidal wave. Solutions are obtained with the method of characteristics. The overall aim is to quantify and understand the spatial structure of different tidal harmonics (the principal tide and its non-linear overtides) and of tidal asymmetry for both the vertical and the horizontal tide in the main channel for different locations of the secondary channel. This is of practical interest in the context of possible construction of secondary channels to reduce tidal range in estuaries. Moreover, tidal asymmetry is an important factor in driving net sediment transport. Analysis of the different tidal harmonics shows that their characteristics are similar to those obtained with an earlier linear model. In particular, amplitudes of the harmonics are reduced landward of the secondary channel if the latter is positioned less than a quarter wavelength of the respective tidal wave away from the landward boundary. Thus, the distortions of the tide due to the presence of the secondary channel are generated locally and afterwards propagate through the network. Tidal asymmetry is quantified by examining tidal range, flood-to-ebb ratio and the duration of the falling tide and the duration between maximum flood and maximum ebb. A spatial non-uniform reduction in tidal range is observed that shows very localised increase and decrease depending on the position of the secondary channel. The changes in the velocity characteristics induce changes in net sediment transport. It turns out that the direction of the peak current, derived from the flood-to-ebb ratio, is not sensitive to the position of the secondary channel, whereas the duration between flood and ebb can change from more to less than half the tidal cycle. However, the changes in the velocity asymmetries are confined to a small region.

The Impact of an External Breast Prosthesis on the Gait Parameters of Women After Mastectomy

An integral part of the recovery process after mastectomy involves the consideration of restorative options, including external prosthesis use; however, only few studies regarding the influence of breast prostheses on functional status have been done. This study aimed to determine whether wearing an external breast prosthesis affects gait in women after a mastectomy. Spatiotemporal gait parameters were collected in 40 women, postmastectomy, aged 37 to 70 years, divided into age subgroups of 37 to 54 years and 55 to 70 years, and in 38 healthy controls, women aged 38 to 69 years. Gait parameters were assessed with and without the breast prosthesis, including walking velocity, cadence, step length, step time, and left-right step time asymmetry. Significant differences were found in the gait parameters of the younger age group with and without a prosthesis. No significant differences were found in the women of the older group with and without the prosthesis. Gait parameters of the younger age group were closer to those of the healthy control group when they were wearing an external prosthesis, as compared with when they were not. This suggests a positive influence of breast prosthesis use on the functional status of women after mastectomy. Clinical practitioners should be aware of the study results suggesting a positive influence of breast prosthesis use on gait parameters after mastectomy surgery, which could improve the patient's functional status after surgery; however, further research is still needed on factors affecting changes in gait with a larger study population.

Effects of Hippotherapy on Recovery of Gait and Balance Ability in Patients with Stroke

[Purpose] The aim of this study was to examine the the effects of hippotherapy on gait and balance ability in patients with stroke. [Subjects and Methods] Thirty stroke patients were randomly divided into a hippotherapy group and a treadmill group and they conducted exercise for eight weeks. [Results] Berg Balance Scale score, gait velocity, and step length asymmetry ratio were significantly improved in the group receiving hippotherapy training. However, in the group receiving treadmill training, only step length asymmetry ratio was significantly improved. In the comparison between the hippotherapy group and treadmill group, there was no significant difference in Berg Balance Scale score, but a significant difference was found in gait velocity and step length asymmetry ratio. [Conclusion] The results of this study indicated that hippotherapy is a helpful treatment for stroke patients.

Predictions of the poloidal asymmetries and transport frequencies in KSTAR

The extended neoclassical rotation theory formulated in Miller flux surface geometry enables unprecedented neoclassical calculations of the poloidal asymmetries in density, rotation velocities, electrostatic potential along the flux surfaces, and of the inertial (Reynolds stress) and gyroviscous transport frequencies, which are strong functions of these asymmetries. This paper presents such calculations of the poloidal asymmetries and non-negligible inertial and gyroviscous transport frequencies in two KSTAR (Korea Superconducting Tokamak Advanced Research) [Kwon et al., Nucl. Fusion 51, 094006 (2011)] Neutral Beam Injection H-mode discharges. The in-out asymmetries in the velocities are an order of magnitude larger than their up-down asymmetries. The magnitudes of the predicted inertial and gyroviscous transport frequencies depend on the magnitudes of the density and velocity asymmetries. The neoclassically predicted density asymmetries are shown to correspond with the reported measurements in tokamaks and the predicted carbon toroidal velocities agree very well with the measurements in KSTAR.

Transport in a chain of asymmetric cavities: Effects of the concentration with hard-core interaction

We studied the transport process of overdamped Brownian particles, in a chain of asymmetric cavities, interacting through a hard-core potential. When a force is applied in opposite directions a difference in the drift velocity of the particles inside the cavity can be observed. Previous works on similar systems deal with the low-concentration regime, in which the interaction is irrelevant. In this case it was found that large particles show a stronger asymmetry in the drift velocity when a small force is applied, allowing for the separation of different size particles [Reguera et al., Phys. Rev. Lett. 108, 020604 (2012)]. We found that when the interaction between particles is considered, the behavior of the system is substantially different. For example, as concentration is increased, the small particles are the ones that show a stronger asymmetry. For the case where all the particles in the system are of the same size we took advantage of the particle-vacancy analogy to predict that the left and right currents are almost equal in a region around the concentration 0.5 despite the asymmetry of the cavity.

SUBSTRUCTURE IN BULK VELOCITIES OF MILKY WAY DISK STARS

We find that Galactic disk stars near the anticenter exhibit velocity asymmetries in both the Galactocentric radial and vertical components across the mid-plane as well as azimuthally. These findings are based on LAMOST spectroscopic velocities for a sample of ~400,000 F-type stars, combined with proper motions from the PPMXL catalog for which we have derived corrections to the zero points based in part on spectroscopically discovered galaxies and QSOs from LAMOST. In the region within 2 kpc outside the Sun's radius and +/-2 kpc from the Galactic midplane, we show that stars above the plane exhibit net outward radial motions with downward vertical velocities, while stars below the plane have roughly the opposite behavior. We discuss this in the context of other recent findings, and conclude that we are likely seeing the signature of vertical disturbances to the disk due to an external perturbation.

Results of FDA’s First Interlaboratory Computational Study of a Nozzle with a Sudden Contraction and Conical Diffuser

The U.S. Food and Drug Administration recently hosted an interlaboratory study to assess the suitability and methodology of computational fluid dynamics (CFD) for demonstrating medical device safety in regulatory submissions. The benchmark study was performed in a generic medical device consisting of a 0.012 m diameter cylindrical nozzle with a sudden contraction and 10° conical diffuser, on either side of a 0.04 m long, 0.004 m diameter throat. Results from 28 simulations from around the world were compared to planar particle image velocimetry (PIV) measurements performed at three laboratories. Five flow rates were chosen that produced laminar, transitional, and turbulent regimes. In general, the CFD results showed modest agreement in global and local flow behaviors. However, all CFD data sets contained wide degrees of velocity variation in comparison to experiment and with each other, much of which could be attributed to the turbulence models used. Some of the velocity discrepancies in the sixteen three dimensional (3D) simulations resulted from substantial flow asymmetries within and downstream of the conical diffuser. Large differences in velocity symmetry were found even when using the same code and many of the same simulation parameters. In contrast, no velocity asymmetries of the same magnitude were observed in any of the planar PIV experiments; relatively minor asymmetries in one experiment were linked to slight asymmetries in the velocity profile at the inlet to the nozzle. CFD predictions of peak wall shear stress at the sudden contraction (normalized to that 0.015 m downstream) varied over two orders of magnitude, with variations of greater than 10 times even when the same software and turbulence model were used. This degree of shear stress variation will necessarily propagate through calculations of blood damage in medical devices. We conclude that CFD simulations used in qualifying medical devices for regulatory purposes need to be conducted following the best practices available, and that targeted experimental validation is essential. The results of this interlaboratory study are freely available in an internet repository (https://fdacfd.nci.nih.gov). We encourage the use of this model in further studies, and support the development of additional benchmarks, better modeling techniques, and consensus standards and guidelines for using CFD in the evaluation of medical devices.

A DETAILED KINEMATIC MAP OF CASSIOPEIA A'S OPTICAL MAIN SHELL AND OUTER HIGH-VELOCITY EJECTA

We present three-dimensional kinematic reconstructions of optically emitting material in the young Galactic supernova remnant Cassiopeia A (Cas A). These Doppler maps have the highest spectral and spatial resolutions of any previous survey of Cas A and represent the most complete catalog of its optically emitting material to date. We confirm that the bulk of Cas A's optically bright ejecta populate a torus-like geometry tilted approximately 30 degrees with respect to the plane of the sky with a -4000 to +6000 km/s radial velocity asymmetry. Near-tangent viewing angle effects and an inhomogeneous surrounding CSM/ISM environment suggest that this geometry and velocity asymmetry may not be faithfully representative of the remnant's true 3D structure or the kinematic properties of the original explosion. The majority of the optical ejecta are arranged in several well-defined and nearly circular ring-like structures with diameters between approximately 30 arcsec (0.5 pc) and 2 arcmin (2 pc). These ejecta rings appear to be a common phenomenon of young core-collapse remnants and may be associated with post-explosion input of energy from plumes of radioactive 56Ni-rich ejecta that rise, expand, and compress non-radioactive material. Our optical survey also encompassed Cas A's faint outlying ejecta knots and exceptionally high-velocity NE and SW streams of S-rich debris often referred to as `jets'. These outer knots, which exhibit a chemical make-up suggestive of an origin deep within the progenitor star, appear to be arranged in opposing and wide-angle outflows with opening half-angles of approximately 40 degrees.

ASYMMETRIC EJECTA DISTRIBUTION IN SN 1006

We present the results from deep X-ray observations (~400 ks in total) of SN 1006 by the X-ray astronomy satellite Suzaku. The thermal spectrum from the entire supernova remnant (SNR) exhibits prominent emission lines of O, Ne, Mg, Si, S, Ar, Ca, and Fe. The observed abundance pattern in the ejecta components is in good agreement with that predicted by a standard model of Type Ia supernovae (SNe). The spatially resolved analysis reveals that the distribution of the O-burning and incomplete Si-burning products (Si, S, and Ar) is asymmetric, while that of the C-burning products (O, Ne, and Mg) is relatively uniform in the SNR interior. The peak position of the former is clearly shifted by 5' (~3.2 pc at a distance of 2.2 kpc) to the southeast from the SNR's geometric center. Using the SNR age of ~1000 yr, we constrain the velocity asymmetry (in projection) of ejecta to be ~3100 km/s. The abundance of Fe is also significantly higher in the southeast region than in the northwest region. Given that the non-uniformity is observed only among the heavier elements (Si through Fe), we argue that SN 1006 originates from an asymmetric explosion, as is expected from recent multi-dimensional simulations of Type Ia SNe, although we cannot eliminate the possibility that an inhomogeneous ambient medium induced the apparent non-uniformity. Possible evidence for the Cr K-shell line and line broadening in the Fe K-shell emission is also found.

Analysis of Saccades and Peak Velocity to Symmetrical Convergence Stimuli: Binocularly Normal Controls Compared to Convergence Insufficiency Patients

To assess the potential peak velocity asymmetry between the left-eye and right-eye movement responses stimulated by symmetrical vergence steps in those with normal binocular vision and those with convergence insufficiency (CI) before and after vergence training. This study also evaluated whether vergence training influenced convergence peak velocity and the prevalence of saccades within the first second of the response. The peak velocities of the left-eye, right-eye, and combined vergence response evoked from symmetrical 2°, 4°, and 6° convergence step stimuli were assessed in 10 controls and 7 CI subjects. Four of the CI subjects participated in vergence training. An asymmetry ratio was calculated as the peak velocity of the slower eye movement response divided by the peak velocity of the faster eye movement response. Controls were significantly more symmetrical (left-eye peak velocity was approximately equal to right-eye peak velocity) compared to CI subjects (P < 0.001). After vergence training, the CI subjects' left-eye and right-eye movements became significantly more symmetrical, convergence peak velocity increased, and the prevalence of saccades within the first 1 second decreased (P < 0.01). Peak convergence velocity was significantly correlated to the prevalence of saccades observed within the first second of the response (r = 0.8; P < 0.05). Data suggest that vergence training improves the symmetry between the left-eye and right-eye movements, increases convergence peak velocity, and decreases the prevalence of saccades within the first second of the response, which facilitates binocular coordination in CI patients. Saccades may be a compensatory mechanism used by CI subjects when convergence peak velocity is reduced.