114 research outputs found
A 2012 taurid bolide imaged in the framework of the Spanish fireball network
In 2010 the Spanish Meteor Net-
work (SPMN) started a special program to obtain very
precise orbital information on 2P/Encke meteoroids
that is currently the focus of
the author master thesis
[1, 2]. The orbital similitude is a clear evidence
on the
connection between comets and meteor streams. The
continuous sublimation of the ice-rich regions in
cometary nuclei produces outgassing capable to re-
lease cm to
m-sized particles from cometary nuclei.
This is the main way to produce meteoroid streams
showers [3,4,5]. Another feasible physical process to
produce cometary debris in heliocentric orbit is the
disruption of a comet that explains the formation of
about ten meteoroid streams [6,7,8]. This second
pathway produces far larger particles that sometimes
can even be in the meter scale and can explain very
bright bolides associated with some meteor showers
[8]. Unfortunately, large bolides are rare events so in
order to study them a continuous sky monitoring is
required which is the only way to collect information
on the dynamic origin and physical behavior of large
bolides penetrating Earth’s at
mosphere. So far we have
described different cases related to the Taurid complex
[1,2]. Several Near Earth Objects (NEOs) have been
dynamically associated w
ith the Taurid complex
clearly suggesting that the progressive disruption of a
larger cometary progenitor is the source of this com-
plex of bodies [9, 10]. In the current abstract we focus
in a Taurid fireball named SPMN 201112 recorded on
November 20
th
, 2012 at 2h16m15.6s UT
The 2011 October Draconids outburst-I. Orbital elements, meteoroid fluxes and 21P/Giacobini-Zinner delivered mass to Earth
On 2011 October 8, the Earth crossed the dust trails left by comet 21P/Giacobini-Zinner during its 19th and 20th century perihelion approaches with the comet being close to perihelion. The geometric circumstances of that encounter were thus favourable to produce a meteor storm, but the trails were much older than in the 1933 and 1946 historical encounters. As a consequence the 2011 October Draconid display exhibited several activity peaks with Zenithal Hourly Rates of about 400 meteors h-1. In fact, if the display had not been forecasted, it could have passed almost unnoticed as was strongly attenuated for visual observers due to the Moon. This suggests that most meteor storms of a similar nature could have passed historically unnoticed under unfavourable weather and Moon observing conditions. The possibility of obtaining information on the physical properties of cometary meteoroids penetrating the atmosphere under low geocentric velocity encounter circumstances motivated us to set up a special observing campaign. Added to the Spanish Fireball Network wide-field all-sky and CCD video monitoring, other high-sensitivity 1/2 arcsec black and white CCD videocameras were attached to the modified medium-field lenses for obtaining high-resolution orbital information. The trajectory, radiant and orbital data of October 16 Draconid meteors observed at multiple stations are presented. The results show that the meteors appeared from a geocentric radiant located at α = 263.0 ± 0°.4 and δ =+55.3 ± 0°.3 that is in close agreement with the radiant predicted for the 1873-1894 and the 1900 dust trails. The estimated mass of material from 21P/Giacobini-Zinner delivered to Earth during the 6 h outburst was around950 ±150 kg
The 2011 October Draconids outburst. I. Orbital elements, meteoroid fluxes and 21P/Giacobini-Zinner delivered mass to Earth
On October 8th, 2011 the Earth crossed the dust trails left by comet
21P/Giacobini-Zinner during its XIX and XX century perihelion approaches with
the comet being close to perihelion. The geometric circumstances of that
encounter were thus favorable to produce a meteor storm, but the trails were
much older than in the 1933 and 1946 historical encounters. As a consequence
the 2011 October Draconid display exhibited several activity peaks with
Zenithal Hourly Rates of about 400 meteors per hour. In fact, if the display
had been not forecasted, it could have passed almost unnoticed as was strongly
attenuated for visual observers due to the Moon. This suggests that most meteor
storms of a similar nature could have passed historically unnoticed under
unfavorable weather and Moon observing conditions. The possibility of obtaining
information on the physical properties of cometary meteoroids penetrating the
atmosphere under low-geocentric velocity encounter circumstances motivated us
to set up a special observing campaign. Added to the Spanish Fireball Network
wide-field all-sky and CCD video monitoring, other high-sensitivity 1/2" black
and white CCD video cameras were attached to modified medium-field lenses for
obtaining high resolution orbital information. The trajectory, radiant, and
orbital data of 16 October Draconid meteors observed at multiple stations are
presented. The results show that the meteors appeared from a geocentric radiant
located at R.A.=263.0+-0.4 deg. and Dec.=+55.3+-0.3 deg. that is in close
agreement with the radiant predicted for the 1873-1894 and the 1900 dust
trails. The estimated mass of material from 21P/Giacobini-Zinner delivered to
Earth during the six-hours outburst was around 950+-150 kg.Comment: Manuscript in press in Monthly Notices of the Royal Astronomical
Society, submitted to MNRAS on November 16th, 2012 Accepted for publication
in MNRAS on April 28th, 2013 Manuscript Pages: 21 Tables: 8 Figures: 4
Manuscript associated: "The 2011 October Draconids outburst. II. Meteoroid
chemical abundances from fireball spectroscopy" by J.M. Madiedo is also in
press in the same journa
Large meteoroids from the 2P/Encke complex : orbital data of 2010 taurids recorded in the framework of the Spanish fireball network
Cometary disruptions are though to be
an important source of Near Earth Objects (heareafter
NEOs). A continuous monitoring of meteor showers
from multistation networks on the ground allows to get
valuable orbital information of large meteoroids producing
fireballs. From such orbits can be established
conections with the orbital elements of diferent asteroids
or comets. In 2010 we started a program to get
precise orbital information of very bright Taurid bolides
in order to try to identify possible associations
with members of the NEO population [1]. We have
already identified some meteoroids that could be dynamically
associated with some NEOs currently identified
as members of the Taurid complex. This group of
bodies is formed by about 20 NEOs that presumably
formed by the fragmentation of a giant comet over the
past 20-30 kyr [2-4]. Some of these bodies have orbital
affinities to comet 2P/Encke, but recent studies have
found other asteroids in Apollo-like orbits that can be
good candidates to trace a progressive cometary disruption
that at different stages as a by-product produced
the Taurid meteoroid branches [3, 4]. It is important
to remark that the NEOs associated with the
Taurid meteoroid streams are presumably dark, as
seems to confirm the spectral information obtained for
the largests members (e.g. 16960 belongs to the B
spectral class [5]). Consequently these bodies are
among the most difficult and hazardous NEOs that
remain to be discovered. In fact, the Tunguska object
has been temptatively associated with the Taurid complex
[6]. A recent paper also links the Earth’s intersection
with the debris produced by the disruption of the
cometary progenitor with a possible Palaeolithic extinction
occurred around 12,900 BP [7]. Our orbital
studies of Taurid meteoroids could also identify other
members of the complex by using association criteria
and backwards integration of their orbits. In fact we
have found some Taurid complex members that are
exhibiting orbits not directly linked with the two main
branches. Obviously, having the Taurid complex some
members with about 100 meters in diameter [4], we
suspect of the existence of much more bodies in such a
range of sizes not discovered yet. These objects could
also produce meteorite-droping bolides in determinate
favourable geometric circumstances [1]
Sustained Delivery of Activated Rho GTPases and BDNF Promotes Axon Growth in CSPG-Rich Regions Following Spinal Cord Injury
Background: Spinal cord injury (SCI) often results in permanent functional loss. This physical trauma leads to secondary events, such as the deposition of inhibitory chondroitin sulfate proteoglycan (CSPG) within astroglial scar tissue at the lesion. Methodology/Principal Findings: We examined whether local delivery of constitutively active (CA) Rho GTPases, Cdc42 and Rac1 to the lesion site alleviated CSPG-mediated inhibition of regenerating axons. A dorsal over-hemisection lesion was created in the rat spinal cord and the resulting cavity was conformally filled with an in situ gelling hydrogel combined with lipid microtubes that slowly released constitutively active (CA) Cdc42, Rac1, or Brain-derived neurotrophic factor (BDNF). Treatment with BDNF, CA-Cdc42, or CA-Rac1 reduced the number of GFAP-positive astrocytes, as well as CSPG deposition, at the interface of the implanted hydrogel and host tissue. Neurofilament 160kDa positively stained axons traversed the glial scar extensively, entering the hydrogel-filled cavity in the treatments with BDNF and CA-Rho GTPases. The treated animals had a higher percentage of axons from the corticospinal tract that traversed the CSPG-rich regions located proximal to the lesion site. Conclusion: Local delivery of CA-Cdc42, CA-Rac1, and BDNF may have a significant therapeutic role in overcoming CSPGmediate
The Transcription Factor Cux1 Regulates Dendritic Morphology of Cortical Pyramidal Neurons
In the murine cerebral cortex, mammalian homologues of the Cux family transcription factors, Cux1 and Cux2, have been identified as restricted molecular markers for the upper layer (II-IV) pyramidal neurons. However, their functions in cortical development are largely unknown. Here we report that increasing the intracellular level of Cux1, but not Cux2, reduced the dendritic complexity of cultured cortical pyramidal neurons. Consistently, reducing the expression of Cux1 promoted the dendritic arborization in these pyramidal neurons. This effect required the existence of the DNA-binding domains, hence the transcriptional passive repression activity of Cux1. Analysis of downstream signals suggested that Cux1 regulates dendrite development primarily through suppressing the expression of the cyclin-dependent kinase inhibitor p27Kip1, and RhoA may mediate the regulation of dendritic complexity by Cux1 and p27. Thus, Cux1 functions as a negative regulator of dendritic complexity for cortical pyramidal neurons
EphA4 Blockers Promote Axonal Regeneration and Functional Recovery Following Spinal Cord Injury in Mice
Upregulation and activation of developmental axon guidance molecules, such as semaphorins and members of the Eph receptor tyrosine kinase family and their ligands, the ephrins, play a role in the inhibition of axonal regeneration following injury to the central nervous system. Previously we have demonstrated in a knockout model that axonal regeneration following spinal cord injury is promoted in the absence of the axon guidance protein EphA4. Antagonism of EphA4 was therefore proposed as a potential therapy to promote recovery from spinal cord injury. To further assess this potential, two soluble recombinant blockers of EphA4, unclustered ephrin-A5-Fc and EphA4-Fc, were examined for their ability to promote axonal regeneration and to improve functional outcome following spinal cord hemisection in wildtype mice. A 2-week administration of either of these blockers following spinal cord injury was sufficient to promote substantial axonal regeneration and functional recovery by 5 weeks following injury. Both inhibitors produced a moderate reduction in astrocytic gliosis, indicating that much of the effect of the blockers may be due to promotion of axon growth. These studies provide definitive evidence that soluble inhibitors of EphA4 function offer considerable therapeutic potential for the treatment of spinal cord injury and may have broader potential for the treatment of other central nervous system injuries
Feedback within the Inter-Cellular Communication and Tumorigenesis in Carcinomas
The classical somatic mutation theory (SMT) of carcinogenesis and metastasis postulates that malignant transformation occurs in cells that accumulate a sufficient amount of mutations in the appropriate oncogenes and/or tumor suppressor genes. These mutations result in cell-autonomous activation of the mutated cell and a growth advantage relative to neighboring cells. However, the SMT cannot completely explain many characteristics of carcinomas. Contrary to the cell-centered view of the SMT with respect to carcinogenesis, recent research has revealed evidence that the tumor microenvironment plays a role in carcinogenesis as well. In this review, we present a new model that accommodates the role of the tumor microenvironment in carcinogenesis and complements the classical SMT. Our “feedback” model emphasizes the role of an altered spatiotemporal communication between epithelial and stromal cells during carcinogenesis: a dysfunctional intracellular signaling in tumorigenic epithelial cells leads to inappropriate cellular responses to stimuli from associated stromal or inflammatory cells. Thus, a positive feedback loop of the information flow between parenchymal and stromal cells results. This constant communication between the stromal cells and the tumor cells causes a perpetually activated state of tumor cells analogous to resonance disaster
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