24 research outputs found
Forbidden transitions in the helium atom
Nonrelativistically forbidden, single-photon transition rates between low
lying states of the helium atom are rigorously derived within quantum
electrodynamics theory. Equivalence of velocity and length gauges, including
relativistic corrections is explicitly demonstrated. Numerical calculations of
matrix elements are performed with the use of high precision variational wave
functions and compared to former results.Comment: 11 pages, 1 figure, submitted to Phys. Rev.
A Far-Ultraviolet View of Starburst Galaxies
Recent observational and theoretical results on starburst galaxies related to
the wavelength regime below 1200 A are discussed. The review covers stars,
dust, as well as hot and cold gas. This wavelength region follows trends
similar to those seen at longer wavelengths, with several notable exceptions.
Even the youngest stellar populations show a turn-over in their spectral energy
distributions, and line-blanketing is much more pronounced. Furthermore, the O
VI line allows one to probe gas at higher temperatures than possible with lines
at longer wavelengths. Molecular hydrogen lines (if detected) provide a glimpse
of the cold phase. I cover the crucial wavelength regime below 912 A and the
implications of recent attempts to detect the escaping ionizing radiation.Comment: 8 pages, 3 figures, Invited Talk, Starbursts--From 30 Doradus to
Lyman-Break Galaxies, ed. R. de Grijs & R. M. Gonzalez Delgado (Dordrecht:
Kluwer
UV and EUV Instruments
We describe telescopes and instruments that were developed and used for
astronomical research in the ultraviolet (UV) and extreme ultraviolet (EUV)
regions of the electromagnetic spectrum. The wavelength ranges covered by these
bands are not uniquely defined. We use the following convention here: The EUV
and UV span the regions ~100-912 and 912-3000 Angstroem respectively. The
limitation between both ranges is a natural choice, because the hydrogen Lyman
absorption edge is located at 912 Angstroem. At smaller wavelengths,
astronomical sources are strongly absorbed by the interstellar medium. It also
marks a technical limit, because telescopes and instruments are of different
design. In the EUV range, the technology is strongly related to that utilized
in X-ray astronomy, while in the UV range the instruments in many cases have
their roots in optical astronomy. We will, therefore, describe the UV and EUV
instruments in appropriate conciseness and refer to the respective chapters of
this volume for more technical details.Comment: To appear in: Landolt-Boernstein, New Series VI/4A, Astronomy,
Astrophysics, and Cosmology; Instruments and Methods, ed. J.E. Truemper,
Springer-Verlag, Berlin, 201
The measurement of the instrinsic impurities of molybdenum and carbon in the Alcator C-Mod tokamak plasma using low resolution spectroscopy
What Physical Processes Drive the Interstellar Medium in the Local Bubble?
Recent 3D high-resolution simulations of the interstellar medium in a star form-
ing galaxy like the Milky Way show that supernova explosions are the main driver of the
structure and evolution of the gas. Its physical state is largely controlled by turbulence due
to the high Reynolds numbers of the average flows. For a constant supernova rate a dynam-
ical equilibrium is established within 200 Myr of simulation as a consequence of the setup
of a galactic fountain. The resulting interstellar medium reveals a typical density/pressure
pattern, i.e. distribution of so-called gas phases, on scales of 500–700 pc, with interstellar
bubbles being a common phenomenon just like the Local Bubble and the Loop I superbub-
ble, which are assumed to be interacting. However, modeling the Local Bubble is special,
because it is driven by a moving group, passing through its volume, as it is inferred from
the analysis of Hipparcos data. A detailed analysis reveals that between 14 and 19 super-
novae have exploded during the last 15 Myr. The age of the Local Bubble is derived from
comparison with HI and UV absorption line data to be 14.5±0.7
Myr. We further predict the
0.4merging of the two bubbles in about 3 Myr from now, when the interaction shell starts to
fragment. The Local Cloud and its companion HI clouds are the consequence of a dynamical
instability in the interaction shell between the Local and the Loop I bubble
Prognostic value of total tumor volume in patients with colorectal liver metastases:A secondary analysis of the randomized CAIRO5 trial with external cohort validation
Background:This study aimed to assess the prognostic value of total tumor volume (TTV) for early recurrence (within 6 months) and overall survival (OS) in patients with colorectal liver metastases (CRLM), treated with induction systemic therapy followed by complete local treatment.Methods: Patients with initially unresectable CRLM from the multicenter randomized phase 3 CAIRO5 trial (NCT02162563) who received induction systemic therapy followed by local treatment were included. Baseline TTV and change in TTV as response to systemic therapy were calculated using the CT scan before and the first after systemic treatment, and were assessed for their added prognostic value. The findings were validated in an external cohort of patients treated at a tertiary center. Results:In total, 215 CAIRO5 patients were included. Baseline TTV and absolute change in TTV were significantly associated with early recurrence (P = 0.005 and P = 0.040, respectively) and OS in multivariable analyses (P = 0.024 and P = 0.006, respectively), whereas RECIST1.1 was not prognostic for early recurrence (P = 0.88) and OS (P = 0.35). In the validation cohort (n = 85), baseline TTV and absolute change in TTV remained prognostic for early recurrence (P = 0.041 and P = 0.021, respectively) and OS in multivariable analyses (P < 0.0001 and P = 0.012, respectively), and showed added prognostic value over conventional clinicopathological variables (increase C-statistic, 0.06; 95 % CI, 0.02 to 0.14; P = 0.008). Conclusion: Total tumor volume is strongly prognostic for early recurrence and OS in patients who underwent complete local treatment of initially unresectable CRLM, both in the CAIRO5 trial and the validation cohort. In contrast, RECIST1.1 did not show prognostic value for neither early recurrence nor OS.</p
FUV and X-ray absorption in the Warm-Hot Intergalactic Medium
The Warm-Hot Intergalactic Medium (WHIM) arises from shock-heated gas
collapsing in large-scale filaments and probably harbours a substantial
fraction of the baryons in the local Universe. Absorption-line measurements in
the ultraviolet (UV) and in the X-ray band currently represent the best method
to study the WHIM at low redshifts. We here describe the physical properties of
the WHIM and the concepts behind WHIM absorption line measurements of H I and
high ions such as O VI, O VII, and O VIII in the far-ultraviolet and X-ray
band. We review results of recent WHIM absorption line studies carried out with
UV and X-ray satellites such as FUSE, HST, Chandra, and XMM-Newton and discuss
their implications for our knowledge of the WHIM.Comment: 26 pages, 9 figures, accepted for publication in Space Science
Reviews, special issue "Clusters of galaxies: beyond the thermal view",
Editor J.S. Kaastra, Chapter 3; work done by an international team at the
International Space Science Institute (ISSI), Bern, organised by J.S.
Kaastra, A.M. Bykov, S. Schindler & J.A.M. Bleeke
Baryons: What, When and Where?
We review the current state of empirical knowledge of the total budget of
baryonic matter in the Universe as observed since the epoch of reionization.
Our summary examines on three milestone redshifts since the reionization of H
in the IGM, z = 3, 1, and 0, with emphasis on the endpoints. We review the
observational techniques used to discover and characterize the phases of
baryons. In the spirit of the meeting, the level is aimed at a diverse and
non-expert audience and additional attention is given to describe how space
missions expected to launch within the next decade will impact this scientific
field.Comment: Proceedings Review for "Astrophysics in the Next Decade: JWST and
Concurrent Facilities", ed. X. Tielens, 38 pages, 10 color figures. Revised
to address comments from the communit