143 research outputs found
Equilibrium reconstruction in the presence of 3D external magnetic perturbations on ASDEX Upgrade
High density H-mode operation by pellet injection and ELM mitigation with the new active in-vessel saddle coils in ASDEX Upgrade
Spitzer observations of the N157B supernova remnant and its surroundings
(Aims): We study the LMC interstellar medium in the field of the nebula
N157B, which contains a supernova remnant, an OB association, ionized gas, and
high-density dusty filaments in close proximity. We investigate the relative
importance of shock excitation by the SNR and photo-ionization by the OB stars,
as well as possible interactions between the supernova remnant and its
environment. (Methods): We apply multiwavelength mapping and photometry, along
with spatially resolved infrared spectroscopy, to identifying the nature of the
ISM using new infrared data from the Spitzer space observatory and X-ray,
optical, and radio data from the literature. (Results): The N157B SNR has no
infrared counterpart. Infrared emission from the region is dominated by the
compact blister-type HII region associated with 2MASS J05375027-6911071 and
excited by an O8-O9 star. This object is part of an extended infrared emission
region that is associated with a molecular cloud. We find only weak emission
from the shock-indicator [FeII], and both the excitation and the heating of the
extended cloud are dominated by photo-ionization by the early O stars of LH99.
(Conclusions): Any possible impact by the expanding SNR does not now affect the
extended cloud of molecules and dust, despite the apparent overlap of SNR X-ray
emission with infrared and Ha emission from the cloud. This implies that the
supernova progenitor cannot have been more massive than about 25 solar masses.Comment: 10 pages, 8 figures, published in A&
The reactivity of cyclopropyl cyanide in titan's atmosphere: a possible pre-biotic mechanism
Cyclopropyl cyanide and other simple nitriles detected in Titan's atmosphere could be precursors leading to the formation of organic macromolecules in the atmosphere of Saturn's largest satellite. Proposing a thermodynamically possible mechanism that explains their formation and supports experimental results represents a difficult challenge. Experiments done in the Atomic and Molecular Physics Laboratory at the University of Trento (AMPL) have studied the ion-molecule reaction between cyclopropyl cyanide and its protonated form, with reaction products being characterized by mass spectrometry. In addition to the expected ion-molecule adduct stabilized by non-covalent long-range interactions, in this work we prove that another distinct species having the same mass to charge ratio (m/z) of 135 is also produced. Moreover, from a previous study of the neutral cyclopropyl cyanide potential energy surface (PES) which shows a partial biradical character it has been possible to characterize the formation through the bimolecular reaction of a new covalent cyclic organic molecule. Calculations have been carried out at the ab initio Møller-Plesset (MP2) level of theory, ensuring the connectivity of the stationary points by using the intrinsic reaction coordinate (IRC) procedure. In order to characterize the reaction transition state, multireference calculations were done using a complete active space involving six electrons and six molecular orbitals [CAS (6 e, 6 m.o.)]. This study opens the possibility of exploring the formation of new organic molecules by gaseous phase ion-molecule interaction schemes, with such molecules having relevance in interstellar space and in astrobiology (and may be involved in prebiotic molecular evolution)
First measurements of a scintillator based fast-ion loss detector near the ASDEX Upgrade divertor
First EMC3-Eirene simulations of the impact of the edge magnetic perturbations at ASDEX Upgrade compared with the experiment
Ejecta, Dust, and Synchrotron Radiation in B0540-69.3: A More Crab-Like Remnant than the Crab
We present near and mid-infrared observations of the pulsar-wind nebula (PWN)
B0540-69.3 and its associated supernova remnant made with the {\it Spitzer
Space Telescope}. We report detections of the PWN with all four IRAC bands, the
24 m band of MIPS, and the Infrared Spectrograph (IRS). We find no
evidence of IR emission from the X-ray/radio shell surrounding the PWN
resulting from the forward shock of the supernova blast wave. The flux of the
PWN itself is dominated by synchrotron emission at shorter (IRAC) wavelengths,
with a warm dust component longward of 20 m. We show that this dust
continuum can be explained by a small amount (\sim 1-3 \times 10^{-3} \msun)
of dust at a temperature of K, heated by the shock wave generated
by the PWN being driven into the inner edge of the ejecta. This is evidently
dust synthesized in the supernova. We also report the detection of several
lines in the spectrum of the PWN, and present kinematic information about the
PWN as determined from these lines. Kinematics are consistent with previous
optical studies of this object. Line strengths are also broadly consistent with
what one expects from optical line strengths. We find that lines arise from
slow ( km s) shocks driven into oxygen-rich clumps in the shell
swept-up by an iron-nickel bubble, which have a density contrast of relative to the bulk of the ejecta, and that faster shocks (
km s) in the hydrogen envelope are required to heat dust grains to
observed temperatures. We infer from estimates of heavy-element ejecta
abundances that the progenitor star was likely in the range of 20-25 .Comment: 46 pages, 10 figures, accepted for publication in Ap
Fast piezoelectric valve offering controlled gas injection in magnetically confined fusion plasmas for diagnostic and fuelling purposes
High-density H-mode operation by pellet injection and ELM mitigation with the new active in-vessel saddle coils in ASDEX Upgrade
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