3,292 research outputs found
Positron Annihilation in the Milky Way and beyond
The electron-positron annihilation gamma-ray signal at 511 keV in the Milky
Way is investigated towards a possible dark matter interpretation. If all bulge
positrons were created by dark matter particle annihilation, the satellite
galaxies of the Milky Way, apparently being dominated by dark matter, should
also show measurable 511 keV signals. Using INTEGRAL/SPI, we test for emission
in 39 neighbouring dwarf satellite galaxies, and found a consistent trend
against a dark matter scenario. One galaxy, Reticulum II, shows up as a strong
source of annihilation emission, which we interpret as the presence of a
microquasar, ejecting pair-plasma into the galaxy's interstellar medium.Comment: 9 pages, 3 figures, accepted contribution to the 11th INTEGRAL
Conference, "Gamma-Ray Astrophysics in Multi-Wavelength Perspective", 10-14
October 2016, Amsterdam, The Netherland
Gamma-ray lines from SN2014J
On 21 January 2014, SN2014J was discovered in M82 and found to be the closest
type Ia supernova (SN Ia) in the last four decades. INTEGRAL observed SN2014J
from the end of January until late June for a total exposure time of about 7
Ms. SNe Ia light curves are understood to be powered by the radioactive decay
of iron peak elements of which Ni is dominantly synthesized during the
thermonuclear disruption of a CO white dwarf (WD). The measurement of
-ray lines from the decay chain
NiCoFe provides unique
information about the explosion in supernovae. Canonical models assume
Ni buried deeply in the supernova cloud, absorbing most of the early
-rays, and only the consecutive decay of Co should become
directly observable through the overlaying material several weeks after the
explosion when the supernova envelope dilutes as it expands. Surprisingly, with
the spectrometer on INTEGRAL, SPI, we detected Ni -ray lines at
158 and 812 keV at early times with flux levels corresponding to roughly 10% of
the total expected amount of Ni, and at relatively small velocities.
This implies some mechanism to create a major amout of Ni at the
outskirts, and at the same time to break the spherical symmetry of the
supernova. One plausible explanation would be a belt accreted from a He
companion star, exploding, and triggering the explosion of the white dwarf. The
full set of observations of SN2014J show Co -ray lines at 847
and 1238 keV, and we determine for the first time a SN Ia -ray light
curve. The irregular appearance of these -ray lines allows deeper
insights about the explosion morphology from its temporal evolution and
provides additional evidence for an asymmetric explosion, from our
high-resolution spectroscopy and comparisons with recent models.Comment: 12 pages, 15 figures, 10th INTEGRAL Workshop: "A Synergistic View of
the High Energy Sky" - Integral2014, 15-19 September 2014, Annapolis, MD, US
The Positron Puzzle
The Positron Puzzle is a half-century old conundrum about the origin of the
Galactic -ray emission line at photon energies of 511 keV, and the
shape of its morphology, showing a bulge-to-disk luminosity ratio of -
unlike any astrophysical source distribution. Positrons that have been cooled
to the eV scale capture electrons and form the intermediate bound state of
Positronium (Ps) which decays on a nano-second timescale into two or three
photons. Assuming the emission to originate from the Galactic bulge, centre,
and disk, a visible annihilation rate in the Milky Way of has to be explained, either by a quasi-steady
state of production and annihilation, or by possibly multiple burst-like events
that flood the Galaxy with positrons, then fading away on a Myr timescale. In
this paper, I will review what the real Positron Puzzle is, where data and
simulations have been used inadequately which resulted in false claims and an
apparent quandary, what we really know and absolutely not know about the topic,
and how this epistemic problem might be advancing.Comment: Invited contribution, 27 pages, 8 figures, 2 tables, accepted in
Astrophysics and Space Science
Numerical modelling and simulation in sheet metal forming
The application of numerical modelling and simulation in manufacturing technologies is looking back over about a 20–30 years history. In recent years, the role of modelling and simulation in engineering and in manufacturing industry has been continuously increasing. It is well known that during manufacturing processes simultaneous the effect of many different parameters can be observed. This is the reason why in former years, detailed analysis of manufacturing processes could have been done only by time-consuming and expensive trial-and-error methods. Due to the recent developments in the methods of modelling and simulation, as well as in computational facilities, modelling and simulation has become an everyday tool in engineering practice. Besides the aforementioned facts, the emerging role of modelling and simulation can also be explained by the growing globalisation and competition of the world market requiring shorter lead times and more cost effective solutions. In spite the enormous development of hardware and software facilities, the exclusive use of numerical modelling still seems to be very time- and cost consuming, and there is still often a high scepticism about the results among industrialists. Therefore, the purpose of this paper is to overview the present situation of numerical modelling and simulation in sheet metal forming, mainly from the viewpoint of scientific research and industrial applications
Die Zukunft der Werbung im Ländervergleich
Welche Werbeformen und formate werden im internationalen Vergleich am häufigsten eingesetzt? Wie unterscheidet sich in ausgesuchten Ländern die Gesamtsituation der Werbung und wie wird sie sich entwickeln? Ist personalisierte Online-Werbung die Werbung der Zukunft oder werden die Werbegelder auch künftig noch in klassische Medien investiert?
Das Buch untersucht die aktuelle Situation und die Entwicklung der Werbung in ausgewählten Ländern auf Basis der I/P-Matrix sowie anhand von Strukturdaten und explorativen Experteninterviews. Daraus entsteht ein Gesamteindruck davon, wie sich Werbung in Australien, China, Deutschland, Indien, Italien, Österreich, Russland, Schweden, der Schweiz, Thailand, den USA und UK aktuell präsentiert und welche Entwicklungslinien sich für die Werbung in diesen Ländern abzeichnen
Comparing simulated Al maps to gamma-ray measurements
© ESO 2019.Context. The diffuse gamma-ray emission of at 1.8 MeV reflects ongoing nucleosynthesis in the Milky Way, and traces massive-star feedback in the interstellar medium due to its 1 Myr radioactive lifetime. Interstellar-medium morphology and dynamics are investigated in astrophysics through 3D hydrodynamic simulations in fine detail, as only few suitable astronomical probes are available. Aims. We compare a galactic-scale hydrodynamic simulation of the Galaxy's interstellar medium, including feedback and nucleosynthesis, with gamma-ray data on emission in the Milky Way extracting constraints that are only weakly dependent on the particular realisation of the simulation or Galaxy structure. Methods. Due to constraints and biases in both the simulations and the gamma-ray observations, such comparisons are not straightforward. For a direct comparison, we perform maximum likelihood fits of simulated sky maps as well as observation-based maximum entropy maps to measurements with INTEGRAL/SPI. To study general morphological properties, we compare the scale heights of emission produced by the simulation to INTEGRAL/SPI measurements.} Results. The direct comparison shows that the simulation describes the observed inner Galaxy well, but differs significantly from the observed full-sky emission morphology. Comparing the scale height distribution, we see similarities for small scale height features and a mismatch at larger scale heights. We attribute this to the prominent foreground emission sites that are not captured by the simulation.Peer reviewedFinal Accepted Versio
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Understanding the impact of food-associated stimuli on intake in humans
Environmental food-associated stimuli potentiate feeding in non-human animals and humans. However, there has been no investigation of this phenomena in human adults using novel stimuli which are then selectively associated with food through different learning processes. The aims of this thesis were twofold; firstly, to investigate whether Pavlovian cues (those that signal what and when an outcome will occur) and discriminative stimuli (those that signal whether an outcome will occur) which are associated with food will increase subsequent intake. Secondly, to investigate neural activity in response to these stimuli.
The first set of studies examined Pavlovian cue-food associations. Study one utilised a new methodology to associate stimuli with specific tastes and demonstrated evidence for cue-potentiated feeding: people ate more in the presence of cues associated with a sweet taste (CS+). This potentiation was greater for foods which were sweet and so constonant with the trained taste. Study two utilised the same methodology but now contrasted sweet likers and sweet-dislikers. However, the cue-potentiation finding failed to replicate. The second set of studies examined cues associated with the chance to obtain food-rewards, interpreted as discriminative stimuli (DS). Study three trained participants to associate stimuli with obtaining food-rewards if the correct response was produced. The findings displayed a suppression of intake in the presence of a stimulus associated with not obtaining rewards compared to a stimulus associated
with obtaining chocolate rewards. Study four extended Study three however sated half the participants prior to the intake test. However the previous cue-suppression finding did not replicate. Study five examined how these two different cue-food associations are encoded in the brain using fMRI. Analysis revealed that the stimuli modified activity in neural regions associated with reward, although whereas the DS enhanced striatal activation, the CS+ deactivated the striatum. The evidence for the lack of contingency awareness to affect behaviour throughout the thesis is discussed
Investigation of methods to produce a uniform cloud of fuel particles in a flame tube
The combustion of a uniform, quiescent cloud of 30-micron fuel particles in a flame tube was proposed as a space-based, low-gravity experiment. The subject is the normal- and low-gravity testing of several methods to produce such a cloud, including telescoping propeller fans, air pumps, axial and quadrature acoustical speakers, and combinations of these devices. When operated in steady state, none of the methods produced an acceptably uniform cloud (+ or - 5 percent of the mean concentration), and voids in the cloud were clearly visible. In some cases, severe particle agglomeration was observed; however, these clusters could be broken apart by a short acoustic burst from an axially in-line speaker. Analyses and experiments reported elsewhere suggest that transient, acoustic mixing methods can enhance cloud uniformity while minimizing particle agglomeration
Exploration of Aspherical Ejecta Properties in Type Ia Supernovae: Progenitor Dependence and Applications to Progenitor Classification
Several explosions of type Ia supernovae (SNe Ia) have been found to exhibit deviations from spherical symmetry upon closer inspection. Examples are the gamma-ray lines from SN 2014J as measured by INTEGRAL/SPI and morphology information from radioactive isotopes in older remnants such as Tycho. A systematic study of the effects of parameters such as ignition geometry and burning morphology in SNe Ia is still missing. We use a two-dimensional hydrodynamics code with postprocessing nucleosynthesis and simulate the double detonations in a sub-Chandrasekhar-mass carbon–oxygen white dwarf starting from the nuclear runaway in the accumulated He envelope toward disruption of the white dwarf. We explore potential variety through four triggering scenarios that sample main asymmetry drivers. We further investigate their global effects on the aspherical structure of the ejecta based on individual elements. We apply the results to the well-observed SN 2014J and other recently observed SN remnants in order to illustrate how these new observational data, together with other observed quantities, help to constrain the explosion and progenitors of SNe Ia
Exploration of Aspherical Ejecta Properties in Type Ia Supernova: Progenitor Dependence and Applications to Progenitor Classification
Several explosions of thermonuclear supernovae (SNe Ia) have been found to
exhibit deviations from spherical symmetry upon closer inspection. Examples are
the gamma-ray lines from SN 2014J as measured by INTEGRAL/SPI, and morphology
information from radioactive isotopes in older remnants such as Tycho. A
systematic study on the effects of parameters such as ignition geometry and
burning morphology in SNe Ia is still missing. We use a 2D hydrodynamics code
with post-processing nucleosynthesis and simulate the double detonations in a
sub-Chandrasekhar mass carbon-oxygen white dwarf starting from the nuclear
runaway in the accumulated He envelope towards disruption of the white dwarf.
We explore potential variety through four triggering scenarios that sample main
asymmetry drivers. We further investigate their global effects on the
aspherical structure of the ejecta based on individual elements. We apply the
results to the well observed SN 2014J and other recently observed SN remnants
in order to illustrate how these new observational data together with other
observed quantities help to constrain the explosion and the progenitors of SNe
Ia.Comment: 28 pages, 26 figures, published in Astrophysical Journal. Submitted
at 23 September 2019, accepted at 10 November 2020, published at 12 March
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