519 research outputs found
The energy distribution of relativistic electrons in the kilo-parsec scale jet of M87 with Chandra
The X-ray emission from the jets in Active Galactic Nuclei (AGN) carries
important information on the distributions of relativistic electrons and
magnetic fields on large scales. We reanalyze archival Chandra observations on
the jet of M87 from 2000 to 2016 with a total exposure of 1460 kiloseconds to
explore the X-ray emission characteristics along the jet. We investigate the
variability behaviours of the nucleus and the inner jet component HST-1, and
confirm indications for day-scale X-ray variability in the nucleus
contemporaneous to the 2010 high TeV gamma-ray state. HST-1 shows a general
decline in X-ray flux over the last few years consistent with its synchrotron
interpretation. We extract the X-ray spectra for the nucleus and all knots in
the jet, showing that they are compatible with a single power-law within the
X-ray band. There are indications of the resultant X-ray photon index to
exhibit a trend, with slight but significant index variations ranging from
(e.g. in knot D) to (in the outer knots F, A, and
B). When viewed in a multi-wavelength context, a more complex situation is
arising. Fitting the radio to X-ray spectral energy distributions (SEDs)
assuming a synchrotron origin, we show that a broken power-law electron
spectrum with break energy around TeV allows a
satisfactorily description of the multi-band SEDs for most of the knots.
However, in the case of knots B, C and D we find indications that an additional
high energy component is needed to adequately reproduce the broadband SEDs. We
discuss the implications and suggest that a stratified jet model may account
for the differences.Comment: accepted for publication in A&
Studying X-ray spectra from large-scale jets of FR II radio galaxies: application of shear particle acceleration
Shear particle acceleration is a promising candidate for the origin of
extended high-energy emission in extra-galactic jets. In this paper, we explore
the applicability of a shear model to 24 X-ray knots in the large-scale jets of
FR II radio galaxies, and study the jet properties by modeling the
multi-wavelength spectral energy distributions (SEDs) in a leptonic framework
including synchrotron and inverse Compton - CMB processes. In order to improve
spectral modelling, we analyze Fermi-LAT data for five sources and reanalyzed
archival data of Chandra on 15 knots, exploring the radio to X-ray connection.
We show that the X-ray SEDs of these knots can be satisfactorily modelled by
synchrotron radiation from a second, shear-accelerated electron population
reaching multi-TeV energies. The inferred flow speeds are compatible with
large-scale jets being mildly relativistic. We explore two different shear flow
profiles (i.e., linearly decreasing and power-law) and find that the required
spine speeds differ only slightly, supporting the notion that for higher flow
speeds the variations in particle spectral indices are less dependent on the
presumed velocity profile. The derived magnetic field strengths are in the
range of a few to ten microGauss, and the required power in non-thermal
particles typically well below the Eddington constraint. Finally, the inferred
parameters are used to constrain the potential of FR II jets as possible UHECR
accelerators.Comment: 14 pages, 4 figures, 6 table, accepted for publication in MNRA
Influence of Te-doping on catalyst-free VS InAs nanowires
We report on the growth of Te-doped catalyst-free InAs nanowires by molecular beam epitaxy on silicon (111) substrates. Changes in the wire morphology, i.e. a decrease in length and an increase in diameter have been observed with rising doping level. Crystal structure analysis based on transmission electron microscopy as well as X-ray diffraction reveals an enhancement of the zinc blende/(wurtzite+zinc blende) segment ratio if Te is provided during the growth process. Furthermore, electrical two-point measurements show that increased Te-doping causes a gain in conductivity. Two comparable growth series, differing only in As-partial pressure by about 1 × 10−5 Torr while keeping all other parameters constant, were analyzed for different Te-doping levels. Their comparison suggests that the crystal structure is strongly affected and the conductivity gain is more distinct for wires grown at a comparably higher As-partial pressure
Rabbit antithymocyte globulin induces rapid expansion of effector memory CD8 T cells without accelerating acute graft versus host disease
Rabbit antithymocyte globulin (Thymoglobulin(®)) is commonly used as graft-versus-host disease (GvHD) prophylaxis. Since we found similar total CD8 T cell numbers in patients with and without Thymoglobulin(®) therapy within the first six months after allogeneic hematopoietic stem cell transplantation, we have analyzed the reconstitution of the CD8 T cell compartment in detail. After T cell-depletion, higher and more sustained proliferative capacity of memory CD8 T cells resulted in their rapid expansion, whereas the fraction of naive CD8 T cells decreased. Importantly, this shift towards effector memory CD8 T cells did not accelerate the incidence of GvHD
Secondary organic aerosol production from diesel vehicle exhaust: impact of aftertreatment, fuel chemistry and driving cycle
Environmental chamber ("smog chamber") experiments were conducted to
investigate secondary organic aerosol (SOA) production from dilute emissions
from two medium-duty diesel vehicles (MDDVs) and three heavy-duty diesel
vehicles (HDDVs) under urban-like conditions. Some of the vehicles were
equipped with emission control aftertreatment devices, including diesel
particulate filters (DPFs), selective catalytic reduction (SCR) and diesel
oxidation catalysts (DOCs). Experiments were also performed with different
fuels (100% biodiesel and low-, medium- or high-aromatic ultralow sulfur
diesel) and driving cycles (Unified Cycle,~Urban Dynamometer Driving
Schedule, and creep + idle). During normal operation, vehicles with a
catalyzed DPF emitted very little primary particulate matter (PM).
Furthermore, photooxidation of dilute emissions from these vehicles produced
essentially no SOA (below detection limit). However, significant primary PM
emissions and SOA production were measured during active DPF regeneration
experiments. Nevertheless, under reasonable assumptions about DPF
regeneration frequency, the contribution of regeneration emissions to the
total vehicle emissions is negligible, reducing PM trapping efficiency by
less than 2%. Therefore, catalyzed DPFs appear to be very effective in
reducing both primary PM emissions and SOA production from diesel vehicles.
For both MDDVs and HDDVs without aftertreatment substantial SOA formed in the
smog chamber – with the emissions from some vehicles generating twice as
much SOA as primary organic aerosol after 3 h of oxidation at typical
urban VOC / NO<sub>x</sub> ratios (3 : 1). Comprehensive organic gas
speciation was performed on these emissions, but less than half of the
measured SOA could be explained by traditional (speciated) SOA precursors.
The remainder presumably originates from the large fraction (~30%) of
the nonmethane organic gas emissions that could not be speciated using
traditional one-dimensional gas chromatography. The unspeciated organics –
likely comprising less volatile species such as intermediate volatility
organic compounds – appear to be important SOA precursors; we estimate that
the effective SOA yield (defined as the ratio of SOA mass to reacted
precursor mass) was 9 ± 6% if both speciated SOA precursors and
unspeciated organics are included in the analysis. SOA production from creep
+ idle operation was 3–4 times larger than SOA production from the same
vehicle operated over the Urban Dynamometer Driving Schedule (UDDS). Fuel
properties had little or no effect on primary PM emissions or SOA formation
Keeping an eye on the violinist: motor experts show superior timing consistency in a visual perception task
Common coding theory states that perception and action may reciprocally induce each other. Consequently, motor expertise should map onto perceptual consistency in specific tasks such as predicting the exact timing of a musical entry. To test this hypothesis, ten string musicians (motor experts), ten non-string musicians (visual experts), and ten non-musicians were asked to watch progressively occluded video recordings of a first violinist indicating entries to fellow members of a string quartet. Participants synchronised with the perceived timing of the musical entries. Results revealed significant effects of motor expertise on perception. Compared to visual experts and non-musicians, string players not only responded more accurately, but also with less timing variability. These findings provide evidence that motor experts’ consistency in movement execution—a key characteristic of expert motor performance—is mirrored in lower variability in perceptual judgements, indicating close links between action competence and perception
Search for pair-produced long-lived neutral particles decaying to jets in the ATLAS hadronic calorimeter in ppcollisions at √s=8TeV
The ATLAS detector at the Large Hadron Collider at CERN is used to search for the decay of a scalar boson to a pair of long-lived particles, neutral under the Standard Model gauge group, in 20.3fb−1of data collected in proton–proton collisions at √s=8TeV. This search is sensitive to long-lived particles that decay to Standard Model particles producing jets at the outer edge of the ATLAS electromagnetic calorimeter or inside the hadronic calorimeter. No significant excess of events is observed. Limits are reported on the product of the scalar boson production cross section times branching ratio into long-lived neutral particles as a function of the proper lifetime of the particles. Limits are reported for boson masses from 100 GeVto 900 GeV, and a long-lived neutral particle mass from 10 GeVto 150 GeV
Search for direct pair production of the top squark in all-hadronic final states in proton-proton collisions at s√=8 TeV with the ATLAS detector
The results of a search for direct pair production of the scalar partner to the top quark using an integrated luminosity of 20.1fb−1 of proton–proton collision data at √s = 8 TeV recorded with the ATLAS detector at the LHC are reported. The top squark is assumed to decay via t˜→tχ˜01 or t˜→ bχ˜±1 →bW(∗)χ˜01 , where χ˜01 (χ˜±1 ) denotes the lightest neutralino (chargino) in supersymmetric models. The search targets a fully-hadronic final state in events with four or more jets and large missing transverse momentum. No significant excess over the Standard Model background prediction is observed, and exclusion limits are reported in terms of the top squark and neutralino masses and as a function of the branching fraction of t˜ → tχ˜01 . For a branching fraction of 100%, top squark masses in the range 270–645 GeV are excluded for χ˜01 masses below 30 GeV. For a branching fraction of 50% to either t˜ → tχ˜01 or t˜ → bχ˜±1 , and assuming the χ˜±1 mass to be twice the χ˜01 mass, top squark masses in the range 250–550 GeV are excluded for χ˜01 masses below 60 GeV
Differential utilization of ketone bodies by neurons and glioma cell lines: a rationale for ketogenic diet as experimental glioma therapy
Background: Even in the presence of oxygen, malignant cells often highly depend on glycolysis for energy generation, a phenomenon known as the Warburg effect. One strategy targeting this metabolic phenotype is glucose restriction by administration of a high-fat, low-carbohydrate (ketogenic) diet. Under these conditions, ketone bodies are generated serving as an important energy source at least for non-transformed cells. Methods: To investigate whether a ketogenic diet might selectively impair energy metabolism in tumor cells, we characterized in vitro effects of the principle ketone body 3-hydroxybutyrate in rat hippocampal neurons and five glioma cell lines. In vivo, a non-calorie-restricted ketogenic diet was examined in an orthotopic xenograft glioma mouse model. Results: The ketone body metabolizing enzymes 3-hydroxybutyrate dehydrogenase 1 and 2 (BDH1 and 2), 3-oxoacid-CoA transferase 1 (OXCT1) and acetyl-CoA acetyltransferase 1 (ACAT1) were expressed at the mRNA and protein level in all glioma cell lines. However, no activation of the hypoxia-inducible factor-1alpha (HIF-1alpha) pathway was observed in glioma cells, consistent with the absence of substantial 3-hydroxybutyrate metabolism and subsequent accumulation of succinate. Further, 3-hydroxybutyrate rescued hippocampal neurons from glucose withdrawal-induced cell death but did not protect glioma cell lines. In hypoxia, mRNA expression of OXCT1, ACAT1, BDH1 and 2 was downregulated. In vivo, the ketogenic diet led to a robust increase of blood 3-hydroxybutyrate, but did not alter blood glucose levels or improve survival. Conclusion: In summary, glioma cells are incapable of compensating for glucose restriction by metabolizing ketone bodies in vitro, suggesting a potential disadvantage of tumor cells compared to normal cells under a carbohydrate-restricted ketogenic diet. Further investigations are necessary to identify co-treatment modalities, e.g. glycolysis inhibitors or antiangiogenic agents that efficiently target non-oxidative pathways
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