Tail Axis Research Articles

Network inference of AP pattern formation system in D.melanogaster by structural equation modeling

Within the field of systems biology, revealing the control systems functioning during embryogenesis is an important task. To clarify the mechanisms controlling sequential events, the relationships between various factors and the expression of specific genes should be determined. In this study, we applied a method based on Structural Equation Modeling (SEM), combined with factor analysis. SEM can include the latent variables within the constructed model and infer the relationships among the latent and observed variables, as a network model. We improved a method for the construction of initial models for the SEM calculation, and applied our approach to estimate the regulatory network for Antero-Posterior (AP) pattern formation in D. melanogaster embryogenesis. In this new approach, we combined cross-correlation and partial correlation to summarize the temporal information and to extract the direct interactions from the gene expression profiles. In the inferred model, 18 transcription factor genes were regulated by not only the expression of other genes, but also the estimated factors. Since each factor regulated the same type of genes, these factors were considered to be involved in maternal effects or spatial morphogen distributions. The interpretation of the inferred network model allowed us to reveal the regulatory mechanism for the patterning along the head to tail axis in D. melanogaster.

Ballooning instability‐induced plasmoid formation in near‐Earth plasma sheet

The formation of plasmoids in the near‐Earth magnetotail is believed to be a key element of the substorm onset process. Previous work has identified a new scenario in MHD simulations where the nonlinear evolution of a ballooning instability is able to induce the formation of plasmoids in a generalized Harris sheet with finite normal magnetic component. In present work, we further examine this novel mechanism for plasmoid formation and explore its implications in the context of substorm onset trigger problem. For that purpose, we adopt the generalized Harris sheet as a model proxy to the near‐Earth region of magnetotail during the substorm growth phase. In this region the magnetic component normal to the neutral sheet Bn is weak but nonzero. The magnetic field lines are closed, and there are no Xlines. Simulation results indicate that in the higher Lundquist number regime , the linear axial tail mode, which is also known as “two‐dimensional resistive tearing mode,” is stabilized by the finite Bn, hence cannot give rise to the formation of X lines or plasmoids by itself. On the other hand, the linear ballooning mode is unstable in the same region and regime, and its nonlinear development leads to the formation of a series of plasmoid structures in the near‐Earth and middle magnetotail regions of plasma sheet. This new scenario of plasmoid formation suggests a critical role of ballooning instability in the near‐Earth plasma sheet in triggering the onset of a substorm expansion.

Cluster observations of ∂Bz/∂x during growth phase magnetotail stretching intervals

We study a statistics of ∂Bz/∂x in a thin stretching current sheet (substorm growth phases) observed by Cluster between 8 and 18 RE downtail. After 2005, spacecraft separation allowed to measure directly this derivative of Bz along the tail axis. The near‐tail events (within 14 RE) exhibited a straight decrease of an initially large positive ∂Bz/∂x to ∼1–2 nT/RE. In the more stretched middle tail, usually the small |∂Bz/∂x|<0.5−1 nT/RE had no clear trend and fluctuated around zero with time scales 5–15 min. In general, negative ∂Bz/∂x were ubiquitous. At some onsets, larger negative ∂Bz/∂x<−1 nT/RE were associated with transient dipolarizations, propagating earthward. There was no clear association of local plasma sheet activity onset with any value of ∂Bz/∂x. We discuss relation of observations and recent modeling results.

Nature of axial tail instability and bubble‐blob formation in near‐Earth plasma sheet

ABSTRACTPrevious global magnetohydrodynamic (MHD) simulations of substorm events have identified the dynamic presence of an axial tail instability that is uniform in the dawn‐dusk direction in the near‐Earth plasma sheet. The axial tail instability is found to be a major cause of the initial growing MHD force imbalance on closed field lines prior to the subsequent magnetic reconnection and substorm expansion onset processes. In this work, energy principle analysis indicates that a two‐dimensional thin current sheet configuration in the magnetotail is typically stable to the axial mode within the framework of ideal MHD model. However, linear resistive MHD calculations find axial tail instabilities on closed field lines in the generalized Harris sheet configurations. The properties of these instabilities are similar to the axial tail modes observed in the global MHD simulations. The axial tail mode is unstable in regimes of low Lundquist number and regions with small normal component of magnetic field. Such resistive axial tail instability would by many researchers be considered as tearing instability in a two‐dimensional tail configuration. Unlike the conventional tearing mode of Harris sheet, the linear axial tail instability does not involve any reconnection process. Instead, the nature of the mode is dominantly a slippage process among neighboring flux tubes as facilitated by resistive dissipation. A natural consequence of the axial tail instability is shown to be the formation of bubble‐blob pairs in the pressure and entropy profiles in the near‐Earth plasma sheet.

COMET C/2011 W3 (LOVEJOY): ORBIT DETERMINATION, OUTBURSTS, DISINTEGRATION OF NUCLEUS, DUST-TAIL MORPHOLOGY, AND RELATIONSHIP TO NEW CLUSTER OF BRIGHT SUNGRAZERS

We describe the physical and orbital properties of C/2011 W3. After surviving perihelion, the comet underwent major changes (permanent loss of nuclear condensation, formation of spine tail). The process of disintegration culminated with an outburst on December 17.6 (T+1.6 d) and this delayed response is inconsistent with the rubble pile model. Probable cause was thermal stress from the heat pulse into the nucleus after perihelion, which could also produce fragmentation of sungrazers far from the Sun. The spine tail was a synchronic feature, made up of dust released at <30 m/s. Since the nucleus would have been located on the synchrone, we computed the astrometric positions of the missing nucleus as the coordinates of the points of intersection of the spine tail's axis with lines of forced orbital-period variation, derived from orbital solutions based on preperihelion astrometry from the ground. The resulting osculating orbital period was 698+/-2 years, which proves that C/2011 W3 is the first major member of the predicted new, 21st-century cluster of bright Kreutz-system sungrazers. The spine tail's tip contained dust 1-2 mm in diameter. The bizarre appearance of the dust tail in images taken hours after perihelion with coronagraphs on SOHO and STEREO is readily understood. The disconnection of the comet's head from the preperihelion tail and the apparent activity attenuation near perihelion are both caused by sublimation of all dust at heliocentric distances smaller than ~1.8 solar radii. The tail's brightness is strongly affected by forward scattering of sunlight by dust. The longest-imaged grains had a radiation-pressure parameter beta ~ 0.6, probably submicron-sized silicate grains. The place of C/2011 W3 within the hierarchy of the Kreutz system and its genealogy via a 14th century parent suggest that it is indirectly related to the celebrated sungrazer X/1106 C1.

The modeling and implementation of tri-rotor flying robot

The objective of this study is to develop a tri-rotor flying robot, which adopts the Y-shaped three-rotor structure. In order to balance the yaw torque produced by the three rotors, the RC servomotor and linkage is installed on the tail axis in order to improve the angle of the rolling axis of the tail motor. Moreover, through the torque generated by the horizontal component of the lift from the inclined motor on the tail axis, it balances the yaw torque of the three rotors. The dynamic equations of the tri-rotor flying robot are determined in this paper. The relationship between motor thrust, angular acceleration, and voltage input was also studied in this research. In order to study the effect of control parameters on the flight stability completely, this study develops a universal stability experimental platform to help tuning the control parameters safely. Based on this, the tri-rotor flying robot can rapidly change flying gesture and avoid oscillation. Finally, we conducted some indoor and outdoor flight tests. From the experimental results, the tri-rotor flying robot can fly and hover stably in the sky.

Tailward leap of multiple expansions of the plasma sheet during a moderately intense substorm: THEMIS observations

A moderately intense substorm on 1 March 2008, from 0830 to 1000 UT, observed by THEMIS probes and the Ground Based Observatory (GBO) is examined to investigate the global evolution of substorm phenomena. During this interval, all five THEMIS probes are closely aligned along the tail axis near midnight covering a radial range from ∼9 Re to ∼18 Re. After the substorm onset, plasma sheet expansions take place successively at multiple locations in the magnetotail as measured by different probes. The positions of the plasma sheet expansions have a tailward leap progression with an average velocity of ∼36 km/s. There are two types of dipolarization detected in this substorm. The first type is the dipolarization front which is associated with the bursty bulk flow (BBF). While the second type, which we call ‘global dipolarization’, is associated with plasma sheet expansions. In the substorm studied, there are four intensifications as shown in the THEMIS AE index. We can detect the effects of localized and short‐lived magnetic energy release processes occurring in the magnetotail corresponding to each of the four AE intensifications. Furthermore, the inner four probes can detect the global dipolarization signatures ∼4–15 min earlier than plasma sheet expansions, while the outermost probe (P1) cannot detect this before the plasma sheet expansion. These two phenomena are caused by the same process (magnetic energy release process) but the effects detected by probes locally appear delayed. The observations in this case are not sufficient to distinguish between the two competing substorm models.

Detection of continuum radio emission associated with Geminga

Abstract A deep Very Large Array observation of the Geminga pulsar field led to the discovery, at a higher than 10σ significance level, of radio emission trailing the neutron star proper motion. This ∼10 arcsec long radio feature, detected with a flux of ∼0.4 mJy at 4.8 GHz, is marginally displaced (2.7 ± 1.8 arcsec) from the pulsar (which, at any rate, is unlikely to contribute with magnetospheric pulsed emission more than 15 per cent to the total observed radio luminosity, ∼1026 erg s−1) and positionally coincident with the X-ray axial tail recently discovered by Chandra and ascribed to the pulsar wind nebula (PWN). Overall, the Geminga radio tail is compatible with the scenario of a synchrotron-emitting PWN, but the present data do not allow us to discriminate between different (and not always necessarily mutually exclusive) possible processes for producing that. If this radio feature results not from intrinsic peculiarities of Geminga, but from its proximity and radio-quiet nature (both helping in not hindering the faint diffuse radio emission), other relatively near and energetic radio-quiet pulsars could show similar structures in dedicated interferometric observations.

Instability of the cometary plasma tail — the instability in a plasma sheet

We consider the instability of the cometary plasma tail which is composed of a neutral sheet, two lobes of the ion tail and solar wind. The plasma is assumed to be highly conductive and incompressible. The unstable state yields a magnetic field which is perpendicular to the tail axis. Our result is consistent with findings about plasma from the International Cometary Explorer (ICE).

Dust tail of the active distant Comet C/2003 WT42 (LINEAR) studied with photometric and spectroscopic observations

We present the study of dust environment of dynamically new Comet C/2003 WT42 (LINEAR) based on spectroscopic and photometric observations. The comet was observed before and after the perihelion passage at heliocentric distances from 5.2 to 9.5 AU. Although the comet moved beyond the zone where water ice sublimation could be significant, its bright coma and extended dust tail evidenced the high level of physical activity. Afρ values exceeded 3000 cm likely reaching its maximum before the perihelion passage. At the same time, the spectrum of the comet did not reveal molecular emission features above the reflected continuum. Reddening of the continuum derived from the cometary spectrum is nonlinear along the dispersion with the steeper slop in the blue region. The pair of the blue and red continuum images was analyzed to estimate a color of the comet. The mean normalized reflectivity gradient derived from the innermost part of the cometary coma equals to 8% per 1000 Å that is typical for Oort cloud objects. However, the color map shows that the reddening of the cometary dust varies over the coma increasing to 15% per 1000 Å along the tail axis. The photometric images were fitted with a Monte Carlo model to construct the theoretical brightness distribution of the cometary coma and tail and to investigate the development of the cometary activity along the orbit. As the dust particles of distant comets are expected to be icy, we propose here the model, which describes the tail formation taking into account sublimation of grains along their orbits. The chemical composition and structure of these particles are assumed to correspond with Greenberg’s interstellar dust model of comet dust. All images were fitted with the close values of the model parameters. According to the results of the modeling, the physical activity of the comet is mainly determined by two active areas with outflows into the wide cones. The obliquity of the rotation axis of the nucleus equals to 20° relative to the comet’s orbital plane. The grains occupying the coma and tail are rather large amounting to 1 mm in size, with the exponential size distribution of a −4.5. The outflow velocities of the dust particles vary from a few centimeters to tens of meters per second depending on their sizes. Our observations and the model findings evidence that the activity of the nucleus decreased sharply to a low-level phase at the end of April–beginning of May 2007. About 190 days later, in the first half of November 2007 the nucleus stopped any activity, however, the remnant tail did not disappear for more than 1.5 years at least.

A locomotor innovation enables water-land transition in a marine fish.

BackgroundMorphological innovations that significantly enhance performance capacity may enable exploitation of new resources and invasion of new ecological niches. The invasion of land from the aquatic realm requires dramatic structural and physiological modifications to permit survival in a gravity-dominated, aerial environment. Most fishes are obligatorily aquatic, with amphibious fishes typically making slow-moving and short forays on to land.Methodology/Principal FindingsHere I describe the behaviors and movements of a little known marine fish that moves extraordinarily rapidly on land. I found that the Pacific leaping blenny, Alticus arnoldorum, employs a tail-twisting movement on land, previously unreported in fishes. Focal point behavioral observations of Alticus show that they have largely abandoned the marine realm, feed and reproduce on land, and even defend terrestrial territories. Comparisons of these blennies' terrestrial kinematic and kinetic (i.e., force) measurements with those of less terrestrial sister genera show A. arnoldorum move with greater stability and locomotor control, and can move away more rapidly from impending threats.Conclusions/SignificanceMy results demonstrate that axial tail twisting serves as a key innovation enabling invasion of a novel marine niche. This paper highlights the potential of using this system to address general evolutionary questions about water-land transitions and niche invasions.

NEW X-RAY OBSERVATIONS OF THE GEMINGA PULSAR WIND NEBULA

Previous observations of the middle-aged pulsar Geminga with XMM-Newton and Chandra have shown an unusual pulsar wind nebula (PWN), with a 20" long central (axial) tail directed opposite to the pulsar's proper motion and two 2' long, bent lateral (outer) tails. Here we report on a deeper (78 ks) Chandra observation and a few additional XMM-Newton observations of the Geminga PWN. The new Chandra observation has shown that the axial tail, which includes up to three brighter blobs, extends at least 50" (i.e., 0.06 d_{250} pc) from the pulsar. It also allowed us to image the patchy outer tails and the emission in the immediate vicinity of the pulsar with high resolution. The PWN luminosity, L_{0.3-8 keV} ~ 3\times 10^{29} d_{250}^2 erg/s, is lower than the pulsar's magnetospheric luminosity by a factor of 10. The spectra of the PWN elements are rather hard (photon index ~ 1). Comparing the two Chandra images, we found evidence of PWN variability, including possible motion of the blobs along the axial tail. The X-ray PWN is the synchrotron radiation from relativistic particles of the pulsar wind; its morphology is connected with the supersonic motion of Geminga. We speculate that the outer tails are either (1) a sky projection of the limb-brightened boundary of a shell formed in the region of contact discontinuity, where the wind bulk flow is decelerated by shear instability, or (2) polar outflows from the pulsar bent by the ram pressure from the ISM. In the former case, the axial tail may be a jet emanating along the pulsar's spin axis, perhaps aligned with the direction of motion. In the latter case, the axial tail may be the shocked pulsar wind collimated by the ram pressure.

Complexities of a 3‐D plasmoid flux rope as shown by an MHD simulation

The results of a global magnetohydrodynamic (MHD) simulation of a pair of magnetospheric substorms on 11 August 2002 are presented. Comparisons of data with simulation results reveal a good agreement regarding the sequence of events during substorm development. We give particular emphasis to results in the simulation of a flux rope formed during the second substorm. Unlike standard 2‐D depictions of reconnection and plasmoid release during the substorm sequence, the simulation shows a highly complex structure that has considerable winding of both closed and open field lines. Additionally, the simulated flux rope does not move tailward uniformly, but rather it has asymmetric motion in which the dawn flank portion moves tailward prior to the dusk portion of the flux rope. This results in a skewed flux rope structure that runs almost parallel to the tail axis instead of perpendicular to it. The simulation compares well with both prior flux rope simulations as well as satellite observations of flux ropes. We use the global simulation to map flux tube properties to the ionosphere, which allows the complexity of the mapping of the magnetic field structure from the tail to the ionosphere to be seen in a novel manner.

Determination of the substorm initiation region from a major conjunction interval of THEMIS satellites

We investigate in detail the time history of substorm disturbances in the magnetotail observed during a major tail conjunction of Time History of Events and Macroscale Interactions during Substorms (THEMIS) satellites on 29 January 2008, 0700–0900 UT. During this interval, all THEMIS satellites were closely aligned along the tail axis near midnight and were bracketed in local time by GOES 11 and 12. The radial distance covered ranges from the geosynchronous altitude to ∼30 RE in the tail. This interval consists of three activations detected by the THEMIS satellites with good ground all‐sky‐camera observations of auroral activity. The first activation is a small substorm with spatially limited disturbance in the tail. The onset arc was equatorward of an undisturbed arc. The second activation is a moderate size substorm with the onset arc also being equatorward of an undisturbed arc. The third activation is an intensification of the substorm with its onset indicated by the second activation. The active auroral arc for this intensification was near the poleward boundary of the auroral oval. Analysis of these observations indicates that the first activation is a small substorm initiated in the near‐Earth plasma sheet and does not involve magnetic reconnection of open magnetic field lines. Magnetic reconnection on closed field lines can be ruled out for this substorm because it cannot generate the observed high‐speed plasma flow. The second and third activations are part of a moderate size substorm initiated also in the near‐Earth plasma sheet, with a subsequent substorm intensification involving activity initiated tailward of ∼30 RE. Overall, the time history of substorm activity for these two substorms is consistent with the near‐Earth initiation model.

Comets C/2001 Q4 and C/2004 Q2: Structure of plasma tails

The plasma tails of comets C/2001 Q4 (NEAT) and C/2004 Q2 (Machholz) are investigated. For each comet we calculate the aberration angle, i.e., the angle between the cometary tail axis and the prolonged radius vector of the comet. The aberration angles are used to estimate the radial velocity of the solar wind in May 2004 and January–February 2005. The calculated velocities are compared to the solar wind velocities measured by space apparatuses in the circumterrestrial space. Possible causes of disagreement between these data are discussed

Wnt3 signaling in the epiblast is required for proper orientation of the anteroposterior axis

The establishment of anteroposterior (AP) polarity in the early mouse epiblast is crucial for the initiation of gastrulation and the subsequent formation of the embryonic (head to tail) axis. The localization of anterior and posterior determining genes to the appropriate region of the embryo is a dynamic process that underlies this early polarity. Several studies indicate that morphological and molecular markers which define the early AP axis are first aligned along the short axis of the elliptical egg cylinder. Subsequently, just prior to the time of primitive streak formation, a conformational change in the embryo realigns these markers with the long axis. We demonstrate that embryos lacking the signaling factor Wnt3 exhibit defects in this axial realignment. In addition, chimeric analyses and conditional removal of Wnt3 activity reveal that Wnt3 expression in the epiblast is required for induction of the primitive streak and mesoderm whereas activity in the posterior visceral endoderm is dispensable.

Early scale development in Heterodontus (Heterodontiformes; Chondrichthyes): a novel chondrichthyan scale pattern

AbstractIn two species of Heterodontus, H. portusjacksoni and H. galeatus, the first scales to develop form two opposing rows along the caudal fin axis on both the left and right sides of the fin. The opposing rows originate from an initial scale located on either side of the posterior tip of the caudal fin, with subsequent scales erupting in a posterior to anterior direction along the tail axis. These scale rows may strengthen tail movements, providing aeration in the egg case, but are lost later in ontogeny. Development of subsequent body scales shows a more irregular origin and arrangement, from anterior to posterior, to cover the dorsal and ventral lobes of the caudal fin. Although the early developmental pattern of the scale associated with the Heterodontus caudal fin has not been previously described, several chondrichthyan taxa, including chimeroids, likewise possess ordered rows of flank scales early in ontogeny that are subsequently lost. These ordered scales contrast with previous suggestions that chondrichthyan scale development is entirely random. Instead, regulated and sequential development of scales may be a plesiomorphic character for both chondrichthyans and osteichthyans, with the less organized arrangement in later ontogenetic stages being a derived condition within Chondrichthyes.

The tadpole of Chaunus dorbignyi (Duméril &amp;amp; Bibron) (Anura, Bufonidae)

Chaunus dorbignyi and Chaunus fernandezae are the southernmost taxa of the Chaunus granulosus species group (formerly Bufo granulosus group). The biology of these species has been scarcely studied. In this sense, larval external morphology of Chaunus dorbignyi is described for the first time and compared with other species of the granulosus group, particularly with C. fernandezae. The tadpoles of C. dorbignyi at stages 31–35 are about 15 mm, and belong to the benthic ecomorphological guild. They have a depressed body, a slightly truncated snout, and the spiracle is placed on the posterior third of the body. The tail axis is straight, the dorsal fin begins at tail-body junction and ends broadly rounded. The vent tube is medial, it starts at midline and opens usually to the right, but in some specimens it opens to the left. The oral disc has a single row of marginal papillae, large dorsal gap, medium-sized ventral gap, and labial tooth row formula 2(2)/2. A multivariate analysis of morphometric variables provided differentiation from tadpoles of C. fernandezae, based on interorbital, eye-nostril and fronto-nasal distances, body maximum height and width, and dorsal gap length. However, the general aspect of both species is quite similar, and comparable to the tadpole of a related species, Chaunus pygmaeus. Other known tadpoles of the granulosus group are those of Chaunus granulosus beebei and Chaunus granulosus major, which differ from the above mentioned species in having a more depressed snout and body, and labial tooth row formula 2(2)/3. The observed variability in the vent tube opening of C. dorbignyi (and also in C. fernandezae) seems to depend on how the beginning of the ventral fin is folded, which is attached to the tube. This fact may have lead to different interpretations of vent tube configuration in the granulosus group, and must be taken into account in between-species comparisons.

Maturation of phage T7 involves structural modification of both shell and inner core components

The double-stranded DNA bacteriophages are good model systems to understand basic biological processes such as the macromolecular interactions that take place during the virus assembly and maturation, or the behavior of molecular motors that function during the DNA packaging process. Using cryoelectron microscopy and single-particle methodology, we have determined the structures of two phage T7 assemblies produced during its morphogenetic process, the DNA-free prohead and the mature virion. The first structure reveals a complex assembly in the interior of the capsid, which involves the scaffolding, and the core complex, which plays an important role in DNA packaging and is located in one of the phage vertices. The reconstruction of the mature virion reveals important changes in the shell, now much larger and thinner, the disappearance of the scaffolding structure, and important rearrangements of the core complex, which now protrudes the shell and interacts with the tail. Some of these changes must originate by the pressure exerted by the DNA in the interior of the head.

The Dust in Comet C/1999 S4 (LINEAR) during Its Disintegration: Narrow-Band Images, Color Maps, and Dynamical Models

Comet C/1999 S4 was observed with the 2m-telescopes of the Bulgarian National Observatory and Pik Terskol Observatory, Northern Caucasus, Russia, at the time of its disintegration. Maps of the dust brightness and color were constructed from images obtained in red and blue continuum windows, free from cometary molecular emissions. We analyze the dust environment of Comet C/1999 S4 (LINEAR) taking into account the observed changes apparent in the brightness images and in plots of Afρ profiles as function of the projected distance ρ from the nucleus. We also make use of the syndyne–synchrone formalism and of a Monte Carlo model based on the Finson–Probstein theory of dusty comets. The brightness and color of individual dust particles, which is needed to derive theoretical brightness and color maps of the cometary dust coma from the Monte Carlo model, is determined from calculations of the light scattering properties of randomly oriented oblate spheroids. In general, the dust of Comet C/1999 S4 (LINEAR) is strongly reddened, with reddening values up to 30%/1000 Å in some locations. Often the reddening is higher in envelopes further away from the nucleus. We observed two outbursts of the comet with brightness peaks on July 14 and just before July 24, 2000, when the final disintegration of the comet started. During both outbursts an excess of small particles was released. Shortly after both outbursts the dust coma “turns blue.” After the first outburst, the whole coma was affected; after the second one only a narrow band of reduced color close to the tail axis was formed. This difference is explained by different terminal ejection speeds, which were much lower than normal in case of the second outburst. In particular in the second, final outburst the excess small particles could originate from fragmentation of “fresh” larger particles.