Outward Motion Research Articles

Rolling motion in erupting prominences observed by STEREO

We analyze the large-scale dynamical forms of three erupting prominences (filaments) observed by at least one of the two STEREO spacecraft and which reveal evidence of sideways rolling motion beginning at the crest of the erupting filament. We find that all three events were also highly non-radial and occurred adjacent to large coronal holes. For each event, the rolling motion and the average non-radial outward motion of the erupting filament and associated CME were away from a neighboring coronal hole. The location of each coronal hole was adjacent to the outer boundary of the arcade of loops overlying the filaments. The erupting filaments were all more non-radial than the CMEs but in the same general direction. From these associations, we make the hypothesis that the degree of the roll effect depends on the level of force imbalances inside the filament arcade related to the coronal hole and the relative amount of magnetic flux on each side of the filament, while the non-radial motion of the CME is related to global magnetic configuration force imbalances. Our analyses of the prominence eruption best observed from both STEREO-A and STEREO-B shows that its spine retained the thin ribbon-like topology that it had prior to the eruption. This topology allows bending, rolling, and twisting during the early phase of the eruption.

Multi-epoch interferometric observations of the Be star ζ Tau

AbstractWe present interferometric observations of the Be star ζ Tau obtained using the MIRC beam combiner at the CHARA Array during four epochs in 2007–2009. Fitting a geometric model to the data reveals a nearly edge-on disk with a FWHM of ~1.8 milli-arcsec in the H-band. The non-zero closure phases indicate an asymmetry in the brightness distribution. Interestingly, when combining our results with previously published interferometric observations of ζ Tau, we find a correlation between the position angle of the disk and the spectroscopic V/R ratio, suggesting that the tilt of the disk might be precessing. This work is part of a multi-year monitoring campaign to investigate the development and outward motion of asymmetric structures in the disks of Be stars.

Coupling between Residues on S4 and S1 Defines the Voltage-Sensor Resting Conformation in NaChBac

The voltage sensor is a four-transmembrane helix bundle (S1–S4) that couples changes in membrane potential to conformational alterations in voltage-gated ion channels leading to pore opening and ion conductance. Although the structure of the voltage sensor in activated potassium channels is available, the conformation of the voltage sensor at rest is still obscure, limiting our understanding of the voltage-sensing mechanism. By employing a heterologously expressed Bacillus halodurans sodium channel (NaChBac), we defined constraints that affect the positioning and depolarization-induced outward motion of the S4 segment. We compared macroscopic currents mediated by NaChBac and mutants in which E43 on the S1 segment and the two outermost arginines (R1 and R2) on S4 were substituted. Neutralization of the negatively charged E43 (E43C) had a significant effect on channel gating. A double-mutant cycle analysis of E43 and R1 or R2 suggested changes in pairing during channel activation, implying that the interaction of E43 with R1 stabilizes the voltage sensor in its closed/available state, whereas interaction of E43 with R2 stabilizes the channel open/unavailable state. These constraints on S4 dynamics that define its stepwise movement upon channel activation and positioning at rest are novel, to the best of our knowledge, and compatible with the helical-screw and electrostatic models of S4 motion.

Foreshock bubbles and their global magnetospheric impacts

We employ 2.5‐D electromagnetic, hybrid simulations that treat ions kinetically via particle‐in‐cell methods and electrons as a massless fluid to study the formation and properties of a new structure named the foreshock bubble upstream from the bow shock. This structure forms due to changes in the interplanetary magnetic field (IMF) associated with solar wind discontinuities and their interaction with the backstreaming ions in the foreshock prior to these discontinuities encountering the bow shock. The leading edge of the foreshock bubble consists of a fast magnetosonic shock and the compressed and heated plasma downstream of the shock. The leading edge surrounds the core which consists of a less‐dense and hotter plasma and lower magnetic field strength. Ultra low frequency turbulence is present in both the outer and core regions of the foreshock bubbles. The size of the foreshock bubble transverse to the flow direction scales with the width of the ion foreshock and at Earth corresponds to tens of RE. The size along the flow depends on the age of the bubble and grows with time. Although they expand sunward, foreshock bubbles are carried antisunward by the solar wind, and for small IMF cone angles (angle between IMF and solar wind flow) when the foreshock lies upstream of the dayside magnetosphere they collide with the bow shock. This collision is shown to have significant magnetospheric impacts. Upon encountering the bow shock, the low pressures within the core of the bubble result in the reversal of the magnetosheath flow from antisunward to sunward direction. This in turn results in the outward motion of the magnetopause and expansion of the dayside magnetosphere. The interaction is found to noticeably impact the density and energy of trapped radiation belt ions and plasma injection into the cusp. Foreshock bubbles are found to be highly effective sites for ion reflection and acceleration to high energies via first‐ and second‐order Fermi acceleration. The interaction of the foreshock bubble with the bow shock results in the release of energetic ions into the magnetosheath. Some of these ions are subsequently injected into the cusp.

The kinematics in the pc-scale jets of AGN

We present a kinematic analysis of jet component motion in the VLBI jet of the BL Lac object S5 1803+784, which does not reveal long-term outward motion for most of the components. Understanding the complex kinematic phenomena can possibly provide insights into the differences between quasars and BL Lac objects. The blazar S5 1803+784 has been studied with VLBI at $\nu$ =1.6, 2.3, 5, 8.4, and 15 GHz between 1993.88 and 2005.68 in 26 observing runs. We (re)analyzed the data and present Gaussian model-fits. We collected the already published kinematic information for this source from the literature and re-identified the components according to the new scenario presented in this paper. Altogether, 94 epochs of observations have been investigated. A careful study of the long-term kinematics reveals a new picture for component motion in S5 1803+784. In contrast to previously discussed motion scenarios, we find that the jet structure within 12 mas of the core can most easily be described by the coexistence of several bright jet features that remain on the long-term at roughly constant core separations (in addition to the already known {\it stationary} jet component $\sim$ 1.4 mas) and one faint component moving with an apparent superluminal speed ($\sim$ 19c, based on 3 epochs). While most of the components maintain long-term roughly constant distances from the core, we observe significant, smooth changes in their position angles. We report on an evolution of the whole jet ridge line with time over the almost 12 years of observations. The width of the jet changes periodically with a period of $\sim$ 8 to 9 years. We find a correlation between changes in the position angle and maxima in the total flux-density. We present evidence for a geometric origin of the phenomena and discuss possible models.

Laminar, Transitional, and Turbulent Flows in Rotor-Stator Cavities

This article reviews the range of flows that may be created within thin cylindrical or annular cavities due to the rotation of one of the confining disks. At low Reynolds numbers, the rotation gives rise to an axisymmetric, radially outward motion near the rotor with a return flow along the stationary disk. As the Reynolds number is raised, this base flow gives way to a shear flow populated by discrete vortices, whether of cylindrical or spiral form, near both the rotating and stationary disks. At Reynolds numbers high enough for turbulent flow to occur, in the twentieth century both experimental and computational studies treated the flow as axisymmetric and steady. Recent research has shown, however, that complex organized structures also persist in the turbulent regime.

In vivo Ca2+ imaging of neural activity throughout the zebrafish brain during visual discrimination

Event Abstract Back to Event In vivo Ca2+ imaging of neural activity throughout the zebrafish brain during visual discrimination Eva A. Naumann1*, Adam Kampff1 and Florian Engert1 1 Harvard University, Molecular and Cellular Biology Department, United States How does the brain process and combine sensory information to produce an appropriate behavior? In order to understand the flow of information from sensory inputs to motor outputs, it is necessary to monitor the activity of neurons throughout the brain. The larval zebrafish, a fast developing, translucent, genetically accessible vertebrate, provides a system for optically investigating the role of neural populations involved in sensory discrimination and simple decision making. We developed a visual behavioral assay to test how unambiguous and ambiguous stimuli differentially affect visually guided turns. Unambiguous whole field stimuli evoke consistent behavioral responses and drive neural activity in a subset of spinal cord projection neurons of the hindbrain and midbrain. Surprisingly, directed motor responses are strongly dominated by monocular inward motion to either eye, whereas monocular outward motion merely biases spontaneous turns. Conflicting converging stimuli, inward motion to both eyes, evokes equally many turns to either direction. Diverging stimuli produced no turning behavior at all. We could identify neuronal populations that show activity related to each stimulus condition, with single cell resolution, throughout the brain of transgenic zebrafish expressing the Ca2 -reporter GCaMP2, using in vivo two photon microscopy. From these results, we present a "working model" for the visual whole field motion discrimination circuit of the zebrafish brain. Conference: Computational and Systems Neuroscience 2010, Salt Lake City, UT, United States, 25 Feb - 2 Mar, 2010. Presentation Type: Poster Presentation Topic: Poster session II Citation: Naumann EA, Kampff A and Engert F (2010). In vivo Ca2+ imaging of neural activity throughout the zebrafish brain during visual discrimination. Front. Neurosci. Conference Abstract: Computational and Systems Neuroscience 2010. doi: 10.3389/conf.fnins.2010.03.00328 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 08 Mar 2010; Published Online: 08 Mar 2010. * Correspondence: Eva A Naumann, Harvard University, Molecular and Cellular Biology Department, Paris, United States, eva@mcb.harvard.edu Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Eva A Naumann Adam Kampff Florian Engert Google Eva A Naumann Adam Kampff Florian Engert Google Scholar Eva A Naumann Adam Kampff Florian Engert PubMed Eva A Naumann Adam Kampff Florian Engert Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Detecting Volume Responders prior to Implantation of a Cardiac Resynchronization Therapy Device via Minithoracotomy: The Septal Flash as a Predictor of Immediate Left Ventricular Reverse Remodeling

Although cardiac resynchronization therapy (CRT) is well established as an adjunctive heart failure treatment, a 30% rate of nonresponders poses a challenge to improve the detection of potential responders prior to device implantation. A previously proposed mechanism-based approach to patient selection suggests in part that the septal flash is a sign of intraventricular dyssynchrony, which is predictive of CRT responsiveness. In this pilot study, data from 5 consecutive patients (2 women and 3 men; mean + or - SD age, 62 + or - 9 years) referred for CRT device implantation via a minithoracotomy were analyzed. Intraoperative transthoracic and/or transesophageal echocardiography data, as well as Doppler myocardial imaging data, were acquired before and after CRT device activation. The septal flash was defined as an early ventricular inward and outward septal motion within the isovolumic contraction period and was imaged with grayscale imaging or tissue Doppler color M-mode. Reverse remodeling was defined as a reduction in the left ventricular end-systolic volume (LVESV) of > or =10%. The right atrial and right ventricular leads were placed transvenously, and the LV screw-in lead was positioned epicardially on the lateral wall. The septal flash was detected preoperatively in all patients and resolved immediately after the onset of biventricular pacing. Immediately following pacemaker activation, we measured a significant reduction in the LVESV (248 + or - 99 mL versus 190 + or - 100 mL, P = .01) and an increase in the ejection fraction (19% + or - 5% versus 28% + or - 5%, P = .01) in all patients. Likewise, a significant increase in the postactivation dP/dt (rate of LV pressure change) measured noninvasively from the mitral regurgitation trace was noted in all patients (298.6 + or - 58.0 mm Hg/s versus 601.7 + or - 111.2 mm Hg/s, P = .001). The preoperative presence of the septal flash is a valid predictor of the response to CRT. Immediately after CRT device activation, the septal flash disappears, and LV reverse remodeling and an increase in contractility are observed.

DARK MATTER HALOS AND EVOLUTION OF BARS IN DISK GALAXIES: COLLISIONLESS MODELS REVISITED

We construct and evolve families of steady-state models of stellar disks embedded in live DM halos, in order to study the dynamical and secular phases of bar evolution. These models are tested against those published in the literature in order to extend them and include the gaseous component in the follow up paper. We are interested in the angular momentum (J) redistribution in the disk-halo system. We confirm the previous results and quantify for the first time the dual role that the DM halos play in the bar evolution: more centrally concentrated halos dilute the dynamical processes, such as spontaneous bar instability and vertical buckling instability, and slowdown the J transfer, while facilitating it in the secular phase. Within the corotation radius (Rcr), the disk J remains nearly constant, as long as Rcr stays within the disk -- a sign that the lost J to the outer disk and the halo is being compensated by an influx of fresh J due to the outward motion of Rcr. This is feasible as long as the bar slowdown dominates the loss of J inside Rcr. We find that in some models the bar pattern speed stalls for prolonged time periods when Rcr is located outside the disk. This phenomenon appears concurrent with the near absence of J transfer between the disk and the halo. Furthermore, we confirm that stellar bars generally display the corotation to bar size ratios in the range of ~1-1.4, but only between the times of the first buckling and Rcr leaving the disk. The corotation-to-disk size ratio emerges as an important dynamic discriminator between various stages of barred disk evolution. Finally, we analyze a number of correlations between the basic parameters of a barred disk and a halo, some already reported in the literature and some new.

Effect of Viscoelasticity in Fountain Flow of Polyethylene Melts

Abstract Fountain flow is the phenomenon of deceleration and outward motion of fluid particles as they approach a slower moving interface. Numerical simulations have been undertaken for the flow of viscoelastic fluids, obeying an integral constitutive equation of the K-BKZ type, capable of describing the behavior of polymer melts. Two polyethylene melts are considered, a branched LDPE and a linear HDPE. Their rheology is well captured by the integral model. The flow simulations are performed for planar and axisymmetric geometries and show the shape and extent of the free surface, as well as the stresses and pressures in the system. The semicircle is a good rough approximation for the free surface of fountain flow, but detailed computations show the effect of elasticity on the free surface, which is non-monotonic for the LDPE as the elasticity level (or apparent shear rate) increases. The less elastic HDPE shows a monotonic decrease in the extent of the flow front as elasticity increases. In all cases, the excess pressure losses (front pressure correction) increase with increasing flow rate. The effect of a nonzero second normal stress difference is to extend the flow front and increase the pressure losses.

Magnetosheath cavities: case studies using Cluster observations

Abstract. This paper presents examples of magnetosheath cavities in Cluster spacecraft observations. The cavities are accompanied by high energy particles in the magnetosheath and characterized by depressed magnetic fields and densities. Flow speeds decrease and temperatures increase within the cavities. All magnetosheath parameters show increased variability within the cavities when the energetic particle flux is high. We predict outward motion of the magnetopause boundary in response to the decreases in the magnetosheath ram pressure caused by the high energy particles within the magnetosheath cavities. For our events, the magnetopause distance is predicted to be 30% larger during the times of high energy particle flux in the magnetosheath than that predicted using concurrent upstream solar wind pressure observations. Our events show no preference to occur for a particular IMF direction or solar wind plasma condition.

Structural evolution of a three-dimensional, finite-width crustal wedge

We present the results of three-dimensional numerical experiments designed to study the response of a layer of crustal material subjected to convergence through an imposed basal velocity discontinuity and to surface processes (erosion/sedimentation). We focus on the three-dimensional response of the system arising from the finite width of the imposed velocity discontinuity. In particular, we describe the complex structures that develop around the wedge and their interactions with the loading/unloading produced by the surface processes. We show that the pro- and retro-shear zones that develop in a doubly-vergent two-dimensional wedge curve around the end of the velocity line-discontinuity to merge into the strike-slip structure that naturally develop, i.e. as a consequence of the imposed boundary conditions, along the edge of the wedge. Along the retro-shear zone the stress orientation rotates along a vertical axis, which implies that the retro-shear zone is a pure thrust along all of its curved length, whereas, along the pro-shear zone stresses rotate along a horizontal axis, which, in turn, implies that the pro-shear zone progressively evolves towards an oblique thrust in its curved section. Furthermore, the outward motion (i.e. perpendicular to the direction of imposed shortening) along the curved section of the retro-shear zone is accommodated by oblique extension along a secondary, kinked structure antithetic to the retro-shear zone. We also show the complex evolution of the wedge when ductile flow and ductile strain softening is activated by increasing the imposed basal temperature. In this situation, the wedge is broader as structures develop at finite distances on either side of the line-discontinuity and its dynamics resembles more that of a ‘vise-like’ orogen. At the surface, a flat plateau forms that accumulates sediment from the surrounding actively deforming mountain ranges until a channel breaks through one of the sides and flushes the inward-draining basin of its sedimentary content. The complex numerical models provide a detailed insight into the geometry and complex three-dimensional structures within and at the margins of an orogen, and how they can be affected by erosional processes at the surface.

Search for an onset mechanism that operates for both CMEs and substorms

Abstract. Substorms and coronal mass ejections have been cited as the most accessible examples of the explosive energy conversion phenomenon that seems to characterize one of the behavior modes of cosmic plasmas. This paper addresses the question of whether these two examples – substorms and CMEs – support or otherwise the idea that explosive energy conversion is the result of a single process operating in different places and under different conditions. As a candidate mechanism that might be common to both substorms and CMEs we use the Forbes catastrophe model for CMEs because before testing it appears to have the potential, suitably modified, to operate also for substorms. The essence of the FCM is a sudden onset of an imbalance of the forces acting on an incipient CME. The imbalance of forces causes the CME to start to rise. Beneath the rising CME conditions develop that favor the onset of magnetic reconnection which then releases the CME and assists its expulsion. Thus the signature of the FCM is a temporally ordered sequence in which there is first the appearance of force imbalance which leads to upward (or outward) motion of the CME which leads to magnetic reconnection under it which expedites rapid expulsion. We look for the FCM signature in the output of two global magnetospheric MHD simulations that produce substorm-like events. We find the ordered sequence of events as stated but with a significant difference: there is no plasmoid prior to the onset of rapid reconnection, that is, there is no counterpart to the incipient CME on which an imbalance of forces acts to initiate the action in the FCM. If this result – that rapid tailward motion precedes the rapid reconnection of substorm expansion – is ultimately verified by other studies, it suggests that a description of the cause of substorm expansion should identify the cause of the preceding rapid tailward motion, since this leads necessarily to rapid reconnection, whatever the reconnection mechanism turns out to be. Clearly then, it is important to identify the cause of the preceding tailward motion.

The Influence of Axial-Magnetic-Field Distribution on the Initial Expansion Process in Triggered Vacuum Arc

In this paper, the initial expansion process after trigger of vacuum arc was investigated experimentally with two typical axial-magnetic-field (AMF) distributions, i.e., bell-shaped AMF generated by traditional cup-shaped AMF electrodes and saddle-shaped AMF generated by specially designed coil-type AMF electrodes. The motion of cathode spots (CSs) in the initial expansion process was investigated by high-speed digital camera with exposure time of 2 mus. Experimental results indicated that CSs expanded faster under saddle-shaped AMF than under bell-shaped AMF at 5 (rms), 10, 15, and 20 kA. Furthermore, the motion of CSs slowed down between 15 and 20 kA in the case of bell-shaped AMF, whereas CSs tended to quicken up with the increase of arc current under saddle-shaped AMF. Based on the images of CSs, it was proposed that, besides direct influence of AMF on the retrograde motion of CSs, the concentration of CSs at relatively high current and strong central AMF could also inhibit the outward motion in the initial expansion process.

P CYGNI PROFILES OF MOLECULAR LINES TOWARD ARP 220 NUCLEI

We report ~100 pc (0.3) resolution observations of (sub)millimeter HCO+ and CO lines in the ultraluminous infrared galaxy Arp 220. The lines peak at two merger nuclei, with HCO+ being more spatially concentrated than CO. Asymmetric line profiles with blueshifted absorption and redshifted emission are discovered in HCO+(3-2) and (4-3) toward the two nuclei and in CO(3-2) toward one nucleus. We suggest that these P-Cygni profiles are due to ~100 km/s outward motion of molecular gas from the nuclei. This gas is most likely outflowing from the inner regions of the two nuclear disks rotating around individual nuclei, clearing the shroud around the luminosity sources there.

State-stabilizing Interactions in Bacterial Mechanosensitive Channel Gating and Adaptation

We outline several principles that we believe define the gating of two bacterial mechanosensitive channels, MscL and MscS. Serving as turgor regulators in bacteria and other walled cells, these molecules are tangible models for studying conformational transitions in membrane proteins driven directly by membrane tension. MscL, a compact pentamer, reversibly opens a gigantic 30-A pore at near-lytic tensions. MscS, a heptameric complex, exhibits transient activation of a smaller pore at moderate tensions, thereby entering a tension-insensitive inactivated state. By comparing the structures and predicted transitions in these channels, we concluded that opening is commonly achieved through tilting and outward motion of the pore-lining helices, which is kinetically limited by hydration of the pore. The intricate adaptive behavior in MscS appears to depend on specific interhelical associations and the flexibility of the pore-lining helices. We discuss physical factors that may direct the transitions and stabilize main functional states in these channels.

MOLECULAR LINE PROFILES FROM A CORE FORMING IN A TURBULENT CLOUD

We calculate the evolution of molecular line profiles of HCO+ and C18O toward a dense core that is forming inside a magnetized turbulent molecular cloud. Features of the profiles can be affected more significantly by coupled velocity and abundance structures in the outer region than those in the inner dense part of the core. The velocity structure at large radii is dominated by a turbulent flow nearby and accretion shocks onto the core, resulting in the variation between inward and outward motions during the evolution of the core. The chemical abundance structure is significantly affected by the depletion of molecules in the central region with high density and low temperature. During the evolution of the core, the asymmetry of line profiles easily changes from blue to red, and vice versa. According to our study, the observed reversed (red) asymmetry toward some starless cores could be interpreted as an intrinsic result of outward motion in the outer region of a dense core, which is embedded in a turbulent environment and still grows in density at the center.

On using the pathophysiology of obstructive sleep apnea as a teaching tool

I read with interest the recent article by Dr. Michael Levitzky on using the pathophysiology of obstructive sleep apnea (OSA) to teach cardiopulmonary integration ([2][1]). With 10 years of experience of teaching courses in both respiratory physiology and sleep at the University of Toronto, I also

The general relativistic Poynting–Robertson effect

The general relativistic version is developed for Robertson's discussion of the Poynting–Robertson effect that he based on special relativity and Newtonian gravity for point radiation sources like stars. The general relativistic model uses a test radiation field of photons in outward radial motion with zero angular momentum in the equatorial plane of the exterior Schwarzschild or Kerr spacetime.

The Extrapolated Motion Protocol For Molecular Dynamics Simulations: Predicting Large-scale Conformational Transitions In Mechanosensitive Channels

Gating of ion channels involves large structural rearrangements and timescales posing challenges for conventional MD simulations. Forces imposed in steered MD protocols may lead to unnatural distortions, whereas near-physiological gradients produce small motions capturing just the local direction. We developed a new computationally efficient protocol allowing to ‘continue’ the observed small-scale motion and drive the protein along a self-chosen pathway. It was tested on bacterial channels MscL and MscS for which the initial outward motion of helices is pre-defined by membrane tension. The motion was initiated with a small (0.1-0.5 A) radial displacement of all atoms of the barrel away from the axis (step 1), followed by energy minimization (2), 1 ps relaxing MD simulation (3), and symmetry-restrained energy minimization (4). The conformational change resulting from this first cycle was linearly extrapolated with a small amplification coefficient and the three structure-relaxing steps (2-4) were repeated completing the next cycle. A sequence of 50-100 extrapolation/relaxation cycles produces a smooth pseudo-continuous trajectory revealing substantial conformational changes while preserving most of the secondary structure. The character of motion was sensitive to the amplification coefficient with 1.00 producing local oscillations, 1.05 - consistent moderate-scale motions, and 1.10 - larger transitions reaching instability. When applied to MscL, the method reproduced the characteristic iris-like gating supported by experiments. Extrapolations of the compact MscS model with reconstructed N-termini predicted barrel expansion with tilting and straightening of the kinked pore-lining helices. Extrapolations started with random thermal fluctuations produced trajectories similar to those started with a pre-conceived displacement. Open conformations of MscS reproducibly closed in extrapolations. Resting and open models of MscS based on families of extrapolated trajectories were refined in all-atom MD simulations, tested for conductance and received support by experiments.