1,577 research outputs found
Innate Intracellular Antiviral Responses Restrict the Amplification of Defective Virus Genomes of Parainfluenza Virus 5.
During the replication of parainfluenza virus 5 (PIV5), copyback defective virus genomes (DVGs) are erroneously produced and are packaged into "infectious" virus particles. Copyback DVGs are the primary inducers of innate intracellular responses, including the interferon (IFN) response. While DVGs can interfere with the replication of nondefective (ND) virus genomes and activate the IFN-induction cascade before ND PIV5 can block the production of IFN, we demonstrate that the converse is also true, i.e., high levels of ND virus can block the ability of DVGs to activate the IFN-induction cascade. By following the replication and amplification of DVGs in A549 cells that are deficient in a variety of innate intracellular antiviral responses, we show that DVGs induce an uncharacterized IFN-independent innate response(s) that limits their replication. High-throughput sequencing was used to characterize the molecular structure of copyback DVGs. While there appears to be no sequence-specific break or rejoining points for the generation of copyback DVGs, our findings suggest there are region, size, and/or structural preferences selected for during for their amplification.IMPORTANCE Copyback defective virus genomes (DVGs) are powerful inducers of innate immune responses both in vitro and in vivo They impact the outcome of natural infections, may help drive virus-host coevolution, and promote virus persistence. Due to their potent interfering and immunostimulatory properties, DVGs may also be used therapeutically as antivirals and vaccine adjuvants. However, little is known of the host cell restrictions which limit their amplification. We show here that the generation of copyback DVGs readily occurs during parainfluenza virus 5 (PIV5) replication, but that their subsequent amplification is restricted by the induction of innate intracellular responses. Molecular characterization of PIV5 copyback DVGs suggests that while there are no genome sequence-specific breaks or rejoin points for the generation of copyback DVGs, genome region, size, and structural preferences are selected for during their evolution and amplification
A parametric shell analysis of the shuttle 51-L SRB AFT field joint
Following the Shuttle 51-L accident, an investigation was conducted to determine the cause of the failure. Investigators at the Langley Research Center focused attention on the structural behavior of the field joints with O-ring seals in the steel solid rocket booster (SRB) cases. The shell-of-revolution computer program BOSOR4 was used to model the aft field joint of the solid rocket booster case. The shell model consisted of the SRB wall and joint geometry present during the Shuttle 51-L flight. A parametric study of the joint was performed on the geometry, including joint clearances, contact between the joint components, and on the loads, induced and applied. In addition combinations of geometry and loads were evaluated. The analytical results from the parametric study showed that contact between the joint components was a primary contributor to allowing hot gases to blow by the O-rings. Based upon understanding the original joint behavior, various proposed joint modifications are shown and analyzed in order to provide additional insight and information. Finally, experimental results from a hydro-static pressurization of a test rocket booster case to study joint motion are presented and verified analytically
Ionization Equilibrium Timescales in Collisional Plasmas
Astrophysical shocks or bursts from a photoionizing source can disturb the
typical collisional plasma found in galactic interstellar media or the
intergalactic medium. The spectrum emitted by this plasma contains diagnostics
that have been used to determine the time since the disturbing event, although
this determination becomes uncertain as the elements in the plasma return to
ionization equilibrium. A general solution for the equilibrium timescale for
each element arises from the elegant eigenvector method of solution to the
problem of a non-equilibrium plasma described by Masai (1984) and Hughes &
Helfand (1985). In general the ionization evolution of an element Z in a
constant electron temperature plasma is given by a coupled set of Z+1 first
order differential equations. However, they can be recast as Z uncoupled first
order differential equations using an eigenvector basis for the system. The
solution is then Z separate exponential functions, with the time constants
given by the eigenvalues of the rate matrix. The smallest of these eigenvalues
gives the scale of slowest return to equilibrium independent of the initial
conditions, while conversely the largest eigenvalue is the scale of the fastest
change in the ion population. These results hold for an ionizing plasma, a
recombining plasma, or even a plasma with random initial conditions, and will
allow users of these diagnostics to determine directly if their best-fit result
significantly limits the timescale since a disturbance or is so close to
equilibrium as to include an arbitrarily-long time.Comment: 4 pages, 2 figures. Accepted for publication by the Astrophysical
Journa
An X-Ray Study of the Supernova Remnant G290.1-0.8
G290.1-0.8 (MSH 11-61A) is a supernova remnant (SNR) whose X-ray morphology
is centrally bright. However, unlike the class of X-ray composite SNRs whose
centers are dominated by nonthermal emission, presumably driven by a central
pulsar, we show that the X-ray emission from G290.1-0.8 is thermal in nature,
placing the remnant in an emerging class which includes such remnants as W44,
W28, 3C391, and others. The evolutionary sequence which leads to such X-ray
properties is not well understood. Here we investigate two scenarios for such
emission: evolution in a cloudy interstellar medium, and early-stage evolution
of a remnant into the radiative phase, including the effects of thermal
conduction. We construct models for these scenarios in an attempt to reproduce
the observed center-filled X-ray properties of G290.1-0.8, and we derive the
associated age, energy, and ambient density conditions implied by the models.
We find that for reasonable values of the explosion energy, the remnant age is
of order (1 - 2) x 10^{4} yr. This places a fairly strong constraint on any
association between G290.1-0.8 and PSR J1105-610, which would require an
anomalously large velocity for the pulsar.Comment: 7 pages, 7 figures, ApJ, accepte
New Evidence for Efficient Collisionless Heating of Electrons at the Reverse Shock of a Young Supernova Remnant
Although collisionless shocks are ubiquitous in astrophysics, certain key
aspects of them are not well understood. In particular, the process known as
collisionless electron heating, whereby electrons are rapidly energized at the
shock front, is one of the main open issues in shock physics. Here we present
the first clear evidence for efficient collisionless electron heating at the
reverse shock of Tycho's supernova remnant (SNR), revealed by Fe-K diagnostics
using high-quality X-ray data obtained by the Suzaku satellite. We detect
K-beta (3p->1s) fluorescence emission from low-ionization Fe ejecta excited by
energetic thermal electrons at the reverse shock front, which peaks at a
smaller radius than Fe K-alpha (2p->1s) emission dominated by a relatively
highly-ionized component. Comparison with our hydrodynamical simulations
implies instantaneous electron heating to a temperature 1000 times higher than
expected from Coulomb collisions alone. The unique environment of the reverse
shock, which is propagating with a high Mach number into rarefied ejecta with a
low magnetic field strength, puts strong constraints on the physical mechanism
responsible for this heating, and favors a cross-shock potential created by
charge deflection at the shock front. Our sensitive observation also reveals
that the reverse shock radius of this SNR is about 10% smaller than the
previous measurement using the Fe K-alpha morphology from the Chandra
observations. Since strong Fe K-beta fluorescence is expected only from
low-ionization plasma where Fe ions still have many 3p electrons, this feature
is key to diagnosing the plasma state and distribution of the immediate
postshock ejecta in a young SNR.Comment: 7 pages, 9 figures, resubmitted to ApJ with minor changes following
the referee repor
Analysis of Paramyxovirus Transcription and Replication by High-Throughput Sequencing.
We have developed a high-throughput sequencing (HTS) workflow for investigating paramyxovirus transcription and replication. We show that sequencing of oligo(dT)-selected polyadenylated mRNAs, without considering the orientation of the RNAs from which they had been generated, cannot accurately be used to analyze the abundance of viral mRNAs because genomic RNA copurifies with the viral mRNAs. The best method is directional sequencing of infected cell RNA that has physically been depleted of ribosomal and mitochondrial RNA followed by bioinformatic steps to differentiate data originating from genomes from viral mRNAs and antigenomes. This approach has the advantage that the abundance of viral mRNA (and antigenomes) and genomes can be analyzed and quantified from the same data. We investigated the kinetics of viral transcription and replication during infection of A549 cells with parainfluenza virus type 2 (PIV2), PIV3, PIV5, or mumps virus and determined the abundances of individual viral mRNAs and readthrough mRNAs. We found that the mRNA abundance gradients differed significantly between all four viruses but that for each virus the pattern remained relatively stable throughout infection. We suggest that rapid degradation of non-poly(A) mRNAs may be primarily responsible for the shape of the mRNA abundance gradient in parainfluenza virus 3, whereas a combination of this factor and disengagement of RNA polymerase at intergenic sequences, particularly those at the NP:P and P:M gene boundaries, may be responsible in the other viruses.IMPORTANCE High-throughput sequencing (HTS) of virus-infected cells can be used to study in great detail the patterns of virus transcription and replication. For paramyxoviruses, and by analogy for all other negative-strand RNA viruses, we show that directional sequencing must be used to distinguish between genomic RNA and mRNA/antigenomic RNA because significant amounts of genomic RNA copurify with poly(A)-selected mRNA. We found that the best method is directional sequencing of total cell RNA, after the physical removal of rRNA (and mitochondrial RNA), because quantitative information on the abundance of both genomic RNA and mRNA/antigenomes can be simultaneously derived. Using this approach, we revealed new details of the kinetics of virus transcription and replication for parainfluenza virus (PIV) type 2, PIV3, PIV5, and mumps virus, as well as on the relative abundance of the individual viral mRNAs
Altered functional brain network connectivity and glutamate system function in transgenic mice expressing truncated Disrupted-in-Schizophrenia 1
Considerable evidence implicates DISC1 as a susceptibility gene for multiple psychiatric diseases. DISC1 has been intensively studied at the molecular, cellular and behavioral level, but its role in regulating brain connectivity and brain network function remains unknown. Here, we utilize a set of complementary approaches to assess the functional brain network abnormalities present in mice expressing a truncated Disc1 gene (Disc1tr Hemi mice). Disc1tr Hemi mice exhibited hypometabolism in the prefrontal cortex (PFC) and reticular thalamus along with a reorganization of functional brain network connectivity that included compromised hippocampal–PFC connectivity. Altered hippocampal–PFC connectivity in Disc1tr Hemi mice was confirmed by electrophysiological analysis, with Disc1tr Hemi mice showing a reduced probability of presynaptic neurotransmitter release in the monosynaptic glutamatergic hippocampal CA1–PFC projection. Glutamate system dysfunction in Disc1tr Hemi mice was further supported by the attenuated cerebral metabolic response to the NMDA receptor (NMDAR) antagonist ketamine and decreased hippocampal expression of NMDAR subunits 2A and 2B in these animals. These data show that the Disc1 truncation in Disc1tr Hemi mice induces a range of translationally relevant endophenotypes underpinned by glutamate system dysfunction and altered brain connectivity
Discriminating the Progenitor Type of Supernova Remnants with Iron K-Shell Emission
Supernova remnants (SNRs) retain crucial information about both their parent
explosion and circumstellar material left behind by their progenitor. However,
the complexity of the interaction between supernova ejecta and ambient medium
often blurs this information, and it is not uncommon for the basic progenitor
type (Ia or core-collapse) of well-studied remnants to remain uncertain. Here
we present a powerful new observational diagnostic to discriminate between
progenitor types and constrain the ambient medium density of SNRs solely using
Fe K-shell X-ray emission. We analyze all extant Suzaku observations of SNRs
and detect Fe K alpha emission from 23 young or middle-aged remnants, including
five first detections (IC 443, G292.0+1.8, G337.2-0.7, N49, and N63A). The Fe K
alpha centroids clearly separate progenitor types, with the Fe-rich ejecta in
Type Ia remnants being significantly less ionized than in core-collapse SNRs.
Within each progenitor group, the Fe K alpha luminosity and centroid are well
correlated, with more luminous objects having more highly ionized Fe. Our
results indicate that there is a strong connection between explosion type and
ambient medium density, and suggest that Type Ia supernova progenitors do not
substantially modify their surroundings at radii of up to several parsecs. We
also detect a K-shell radiative recombination continuum of Fe in W49B and IC
443, implying a strong circumstellar interaction in the early evolutionary
phases of these core-collapse remnants.Comment: Accepted by ApJL; 5 pages with just 1 table and 1 figur
Focus Issue on Legacy Information Systems and Business Process Change: Banking on the Old technology: Understanding the Organisational Context of \u27Legacy\u27 Issues
A common thread in recent discussions of organisational change is the importance of the role allocated to information technology in the realisation of such change. It is a feature of many of these discussions that IT is handled in a somewhat simplistic fashion, often with a pronounced theoretical leaning resulting in the case of the disappearing technology . Even empirical studies of new technology often fail to pay attention to the actual details of technology in use, instead focusing upon the part technology might play in producing certain managerial or workplace configurations that are themselves theoretical renderings of organisational life. By way of contrast, this paper presents some results from a long-term empirical investigation of computer systems in use in financial services that specifically aims to focus upon the actual details of technology in use. In addition it attempts to address conventional concerns with the relationship between new technology and \u27skill\u27, productivity and other factors in a rather different fashion by focusing on the issue of \u27legacy\u27. We present a number of examples of legacy issues and try to delineate their impact on everyday working life. \u27Legacy\u27, we argue, is not just a problem encountered by organisations with aging mainframes and dated software, it is an issue from the moment a computer system becomes an integral part of any organisation\u27s everyday work
Gravity, p-branes and a spacetime counterpart of the Higgs effect
We point out that the worldvolume coordinate functions of
a -brane, treated as an independent object interacting with dynamical
gravity, are Goldstone fields for spacetime diffeomorphisms gauge symmetry. The
presence of this gauge invariance is exhibited by its associated Noether
identity, which expresses that the source equations follow from the
gravitational equations. We discuss the spacetime counterpart of the Higgs
effect and show that a -brane does not carry any local degrees of freedom,
extending early known general relativity features. Our considerations are also
relevant for brane world scenarios.Comment: 5 pages, RevTeX. v2 (30-IV-03) with additional text and reference
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