252 research outputs found
Counter-propagating radiative shock experiments on the Orion laser and the formation of radiative precursors
We present results from new experiments to study the dynamics of radiative
shocks, reverse shocks and radiative precursors. Laser ablation of a solid
piston by the Orion high-power laser at AWE Aldermaston UK was used to drive
radiative shocks into a gas cell initially pressurised between and $1.0 \
bar with different noble gases. Shocks propagated at {80 \pm 10 \ km/s} and
experienced strong radiative cooling resulting in post-shock compressions of {
\times 25 \pm 2}. A combination of X-ray backlighting, optical self-emission
streak imaging and interferometry (multi-frame and streak imaging) were used to
simultaneously study both the shock front and the radiative precursor. These
experiments present a new configuration to produce counter-propagating
radiative shocks, allowing for the study of reverse shocks and providing a
unique platform for numerical validation. In addition, the radiative shocks
were able to expand freely into a large gas volume without being confined by
the walls of the gas cell. This allows for 3-D effects of the shocks to be
studied which, in principle, could lead to a more direct comparison to
astrophysical phenomena. By maintaining a constant mass density between
different gas fills the shocks evolved with similar hydrodynamics but the
radiative precursor was found to extend significantly further in higher atomic
number gases (\sim4$ times further in xenon than neon). Finally, 1-D and 2-D
radiative-hydrodynamic simulations are presented showing good agreement with
the experimental data.Comment: HEDLA 2016 conference proceeding
Formation and Structure of a Current Sheet in Pulsed-Power Driven Magnetic Reconnection Experiments
We describe magnetic reconnection experiments using a new, pulsed-power
driven experimental platform in which the inflows are super-sonic but
sub-Alfv\'enic.The intrinsically magnetised plasma flows are long lasting,
producing a well-defined reconnection layer that persists over many
hydrodynamic time scales.The layer is diagnosed using a suite of high
resolution laser based diagnostics which provide measurements of the electron
density, reconnecting magnetic field, inflow and outflow velocities and the
electron and ion temperatures.Using these measurements we observe a balance
between the power flow into and out of the layer, and we find that the heating
rates for the electrons and ions are significantly in excess of the classical
predictions. The formation of plasmoids is observed in laser interferometry and
optical self-emission, and the magnetic O-point structure of these plasmoids is
confirmed using magnetic probes.Comment: 14 pages, 12 figures. Accepted for publication in Physics of Plasma
Characterizing Hepatitis C VirusâSpecific CD4+ T Cells Following ViralâVectored Vaccination, Directly Acting Antivirals, and Spontaneous Viral Cure
BACKGROUND AND AIMS: Induction of functional helper CD4+ T cells is the hallmark of a protective immune response against hepatitis C virus (HCV), associated with spontaneous viral clearance. Heterologous prime/boost viral vectored vaccination has demonstrated induction of broad and polyfunctional HCV-specific CD8+ T cells in healthy volunteers; however, much less is known about CD4+ T-cell subsets following vaccination. APPROACH AND RESULTS: We analyzed HCV-specific CD4+ T-cell populations using major histocompatibility complex class II tetramers in volunteers undergoing HCV vaccination with recombinant HCV adenoviral/modified vaccinia Ankara viral vectors. Peptide-specific T-cell responses were tracked over time, and functional (proliferation and cytokine secretion) and phenotypic (cell surface and intranuclear) markers were assessed using flow cytometry. These were compared to CD4+ responses in 10 human leukocyte antigen-matched persons with HCV spontaneous resolution and 21 chronically infected patients treated with directly acting antiviral (DAA) therapy. Vaccination induced tetramer-positive CD4+ T cells that were highest 1-4 weeks after boosting (mean, 0.06%). Similar frequencies were obtained for those tracked following spontaneous resolution of disease (mean, 0.04%). In addition, the cell-surface phenotype (CD28, CD127) memory subset markers and intranuclear transcription factors, as well as functional capacity of peptide-specific CD4+ T-cell responses characterized after vaccination, are comparable to those following spontaneous viral resolution. In contrast, helper responses in chronic infection were infrequently detected and poorly functional and did not consistently recover following HCV cure. CONCLUSIONS: Helper CD4+ T-cell phenotype and function following HCV viral vectored vaccination resembles "protective memory" that is observed following spontaneous clearance of HCV. DAA cure does not promote resurrection of exhausted CD4+ T-cell memory in chronic infection
Immune Phenotype and Function of Natural Killer and T Cells in Chronic Hepatitis C Patients Who Received a Single Dose of Anti-MicroRNA-122, RG-101
MicroRNAâ122 is an important host factor for the hepatitis C virus (HCV). Treatment with RGâ101, an Nâacetylgalactosamineâconjugated antiâmicroRNAâ122 oligonucleotide, resulted in a significant viral load reduction in patients with chronic HCV infection. Here, we analyzed the effects of RGâ101 therapy on antiviral immunity. Thirtyâtwo chronic HCV patients infected with HCV genotypes 1, 3, and 4 received a single subcutaneous administration of RGâ101 at 2 mg/kg (n = 14) or 4 mg/kg (n = 14) or received a placebo (n = 2/dosing group). Plasma and peripheral blood mononuclear cells were collected at multiple time points, and comprehensive immunological analyses were performed. Following RGâ101 administration, HCV RNA declined in all patients (mean decline at week 2, 3.27 log10 IU/mL). At week 8 HCV RNA was undetectable in 15/28 patients. Plasma interferonâÎłâinduced protein 10 (IPâ10) levels declined significantly upon dosing with RGâ101. Furthermore, the frequency of natural killer (NK) cells increased, the proportion of NK cells expressing activating receptors normalized, and NK cell interferonâÎł production decreased after RGâ101 dosing. Functional HCVâspecific interferonâÎł Tâcell responses did not significantly change in patients who had undetectable HCV RNA levels by week 8 postâRGâ101 injection. No increase in the magnitude of HCVâspecific Tâcell responses was observed at later time points, including 3 patients who were HCV RNAânegative 76 weeks postdosing. Conclusion: Dosing with RGâ101 is associated with a restoration of NKâcell proportions and a decrease of NK cells expressing activation receptors; however, the magnitude and functionality of ex vivo HCVâspecific Tâcell responses did not increase following RGâ101 injection, suggesting that NK cells, but not HCV adaptive immunity, may contribute to HCV viral control following RGâ101 therapy
BOW SHOCK FRAGMENTATION DRIVEN BY A THERMAL INSTABILITY IN LABORATORY ASTROPHYSICS EXPERIMENTS
The role of radiative cooling during the evolution of a bow shock was studied
in laboratory-astrophysics experiments that are scalable to bow shocks present
in jets from young stellar objects. The laboratory bow shock is formed during
the collision of two counter-streaming, supersonic plasma jets produced by an
opposing pair of radial foil Z-pinches driven by the current pulse from the
MAGPIE pulsed-power generator. The jets have different flow velocities in the
laboratory frame and the experiments are driven over many times the
characteristic cooling time-scale. The initially smooth bow shock rapidly
develops small-scale non-uniformities over temporal and spatial scales that are
consistent with a thermal instability triggered by strong radiative cooling in
the shock. The growth of these perturbations eventually results in a global
fragmentation of the bow shock front. The formation of a thermal instability is
supported by analysis of the plasma cooling function calculated for the
experimental conditions with the radiative packages ABAKO/RAPCAL.Comment: 9 pages, 5 figures, Accepted for publication in The Astrophysical
Journal on 5th November 201
The Emergence of Shell Valuable Exchange in the New Guinea Highlands
Shell valuable exchange in the New Guinea Highlands has been a key
interest in anthropology, providing insight into economics, aesthetics, and social
stratification amongst banded communities. This paper describes how shell exchange
at ethnographic present reflects deeper historical processes. We trace the origins and
subsequent changes in shell use from the terminal Pleistocene to the Late Holocene at
the site of Kiowa in Chimbu Province, Papua New Guinea. Zooarchaeological and
technological analyses of Kiowaâs shell artifacts indicates riverine mussel was
procured locally from the terminal Pleistocene (9,500â10,000 years ago) and featured
as a minor component in the diet into the recent precolonial period. In contrast,
evidence for marine shell valuables only appears in the Late Holocene in the form of
Trochus armbands and Tegillarca granosa and Polymesoda cf. erosa multifunctional
tools. This challenges ideas that associate the gradual dispersal of marine shell into
the highlands with the spread of agriculture around the Wahgi Valley at the start of
the Holocene, and supports punctuated pulses of coastal contact. In doing so, we
formulate a testable model for the development of shell exchange into the highlands,
with implications for the emergence of stratification and the conduits between the
interior and coast
Induction and Maintenance of CX3CR1-Intermediate Peripheral Memory CD8(+) T Cells by Persistent Viruses and Vaccines
The induction and maintenance of T cell memory is critical to the success of vaccines. A recently described subset of memory CD8+ T cells defined by intermediate expression of the chemokine receptor CX3CR1 was shown to have self-renewal, proliferative, and tissue-surveillance properties relevant to vaccine-induced memory. We tracked these cells when memory is sustained at high levels: memory inflation induced by cytomegalovirus (CMV) and adenovirus-vectored vaccines. In mice, both CMV and vaccine-induced inflationary T cells showed sustained high levels of CX3R1int cells exhibiting an effector-memory phenotype, characteristic of inflationary pools, in early memory. In humans, CX3CR1int CD8+ T cells were strongly induced following adenovirus-vectored vaccination for hepatitis C virus (HCV) (ChAd3-NSmut) and during natural CMV infection and were associated with a memory phenotype similar to that in mice. These data indicate that CX3CR1int cells form an important component of the memory pool in response to persistent viruses and vaccines in both mice and humans
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