173 research outputs found
Development of Rebunching Cavities at IAP
A focus of work at IAP has been the development and optimization of spiral
loaded cavities since the 1970s [A. Schempp et al, NIM 135, 409 (1976)]. These
cavities feature a high efficiency, a compact design and a big variety of
possible fields of application. They find use both as bunchers and post
accelerators to vary the final energy of the beam. In comparison to other
available designs, the advantage of these structures lies in their small size.
Furthermore they can easily be tuned to the required resonance frequency by
varying the length of the spiral. Due to the small size of the cavities the
required budget can also be kept low. Here, two slightly different types of
spiral loaded cavities, which were built for the REX-ISOLDE project at CERN and
the intensity upgrade program at GSI are being discussed.Comment: 4 pages, 9 figures PRST-AB special LINAC 2000 edition with additional
information in comparison to the 3 pages LINAC paper physics/000708
Variability in high-mass X-ray binaries
Strongly magnetized, accreting neutron stars show periodic and aperiodic
variability over a wide range of time scales. By obtaining spectral and timing
information on these different time scales, we can have a closer look into the
physics of accretion close to the neutron star and the properties of the
accreted material. One of the most prominent time scales is the strong
pulsation, i.e., the rotation period of the neutron star itself. Over one
rotation, our view of the accretion column and the X-ray producing region
changes significantly. This allows us to sample different physical conditions
within the column but at the same time requires that we have
viewing-angle-resolved models to properly describe them. In wind-fed high-mass
X-ray binaries, the main source of aperiodic variability is the clumpy stellar
wind, which leads to changes in the accretion rate (i.e., luminosity) as well
as absorption column. This variability allows us to study the behavior of the
accretion column as a function of luminosity, as well as to investigate the
structure and physical properties of the wind, which we can compare to winds in
isolated stars.Comment: 6 pages, 4 figures, accepted for publication in Astronomische
Nachrichten (proceedings of the XMM-Newton Workshop 2019
Reconstruction of the Exenterated Orbit with an Island Pericranial Flap: A New Surgical Approach
Background:
Reconstruction of the bony socket after orbital exenteration is a matter of much debate. Prompt defect closure with a microvascular flap is desirable but involves a major surgical procedure and hence, places considerable burden on the patient. The new surgical technique presented here permits a technically simpler wound closure with fewer complications after orbital exenteration.
Methods:
Between May 2014 and June 2022 in the ENT department of Regensburg University, nine patients underwent exenteration and reconstruction with a pericranial flap. The flap was raised via a broken line incision in the forehead or endoscopically, incised in a roughly croissant-like shape, then introduced into the orbit through a tunnel in the eyebrow. A retrospective analysis of the patients and considerations about determining the size, shape, and vascular supply of the flap are presented.
Results:
Flap healing was uncomplicated in all cases. Only 6 weeks after surgery, the flap was stable, making it possible to start adjuvant therapy and prosthetic rehabilitation swiftly. The flap is adapted to the near cone-shape of the orbit. The mean (± standard deviation) surface area of the measured orbits is (39.58 ± 3.32) cm2. The territory of the angular artery provides the periosteal flap arterial blood supply. Venous drainage is via venous networks surrounding the artery.
Conclusions:
Use of the pericranial flap makes it possible to close the orbital cavity promptly with minimal donor site defect and a short operating time, thereby minimizing the surgical risk and speeding up physical and psychological recovery
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Selective photocatalytic CO reduction in water through anchoring of a molecular Ni catalyst on CdS nanocrystals
Photocatalytic conversion of CO into carbonaceous feedstock chemicals is a promising strategy to mitigate greenhouse gas emissions and simultaneously store solar energy in chemical form. Photocatalysts for this transformation are typically based on precious metals and operate in nonaqueous solvents to suppress competing H generation. In this work, we demonstrate selective visible-light-driven CO reduction in water using a synthetic photocatalyst system that is entirely free of precious metals. We present a series of self-assembled nickel terpyridine complexes as electrocatalysts for the reduction of CO to CO in organic media. Immobilization on CdS quantum dots allows these catalysts to be active in purely aqueous solution and photocatalytically reduce CO with >90% selectivity under UV-filtered simulated solar light irradiation (AM 1.5G, 100 mW cm, λ > 400 nm, pH 6.7, 25 °C). Correlation between catalyst immobilization efficiency and product selectivity shows that anchoring the molecular catalyst on the semiconductor surface is key in controlling the selectivity for CO reduction over H evolution in aqueous solution.Christian Doppler Research Association, OMV group, Isaac Newton Trust, the German Research Foundation, the World Premier International Research Center Initiative, MEXT, Japa
Staring at 4U 1909+07 with Suzaku (Research Note)
We present an analysis of the neutron star High Mass X-ray Binary (HMXB) 4U 1909+07 mainly based on Suzaku data. We extend the pulse period evolution, which behaves in a random-walk like manner, indicative of direct wind accretion. Studying the spectral properties of 4U 1909+07 between 0.5 to 90keV we find that a power-law with an exponential cutoff can describe the data well, when additionally allowing for a blackbody or a partially covering absorber at low energies. We find no evidence for a cyclotron resonant scattering feature (CRSF), a feature seen in many other neutron star HMXBs sources. By performing pulse phase resolved spectroscopy we investigate the origin of the strong energy dependence of the pulse profile, which evolves from a broad two-peak profile at low energies to a profile with a single, narrow peak at energies above 20keV. Our data show that it is very likely that a higher folding energy in the high energy peak is responsible for this behavior. This in turn leads to the assumption that we observe the two magnetic poles and their respective accretion columns at different phases, and that these accretions column have slightly different physical conditions
Studying the accretion geometry of EXO 2030+375 at luminosities close to the propeller regime
The Be X-ray binary EXO 2030+375 was in an extended low luminosity state
during most of 2016. We observed this state with NuSTAR and Swift, supported by
INTEGRAL observations as well as optical spectroscopy with the NOT. We present
a comprehensive spectral and timing analysis of these data here to study the
accretion geometry and investigate a possible onset of the propeller effect.
The H-alpha data show that the circumstellar disk of the Be-star is still
present. We measure equivalent widths similar to values found during more
active phases in the past, indicating that the low-luminosity state is not
simply triggered by a smaller Be disk. The NuSTAR data, taken at a 3-78 keV
luminosity of ~6.8e35 erg/s (for a distance of 7.1 kpc), are well described by
standard accreting pulsar models, such as an absorbed power-law with a
high-energy cutoff. We find that pulsations are still clearly visible at these
luminosities, indicating that accretion is continuing despite the very low mass
transfer rate. In phase-resolved spectroscopy we find a peculiar variation of
the photon index from ~1.5 to ~2.5 over only about 3% of the rotational period.
This variation is similar to that observed with XMM-Newton at much higher
luminosities. It may be connected to the accretion column passing through our
line of sight. With Swift/XRT we observe luminosities as low as 1e34 erg/s
during which the data quality did not allow us to search for pulsations, but
the spectrum is much softer and well described by either a blackbody or soft
power-law continuum. This softer spectrum might be due to the fact that
accretion has been stopped by the propeller effect and we only observe the
neutron star surface cooling.Comment: 11 pages, 6 figures, accepted for publication in A&A (v2 including
language edits
Electron Angular Distributions in He Single Ionization Impact by H₂⁺ Ions at 1 MeV
For the first time we investigated in a kinematically complete experiment the ionization of helium in collisions with H2+-molecular ions at 1 MeV. Using two separate detectors, the orientation of the projectile H2+-molecular ions was determined at the instance of the collision. The electron angular distribution was measured by a Reaction Microscope . The observed structures are found in agreement with theoretical calculations, indicating that the ionized electron of He shows a slight preferential emission direction parallel to the molecular axis
Single electron magneto-conductivity of a nondegenerate 2D electron system in a quantizing magnetic field
We study transport properties of a non-degenerate two-dimensional system of
non-interacting electrons in the presence of a quantizing magnetic field and a
short-range disorder potential. We show that the low-frequency
magnetoconductivity displays a strongly asymmetric peak at a nonzero frequency.
The shape of the peak is restored from the calculated 14 spectral moments, the
asymptotic form of its high-frequency tail, and the scaling behavior of the
conductivity for omega -> 0. We also calculate 10 spectral moments of the
cyclotron resonance absorption peak and restore the corresponding
(non-singular) frequency dependence using the continuous fraction expansion.
Both expansions converge rapidly with increasing number of included moments,
and give numerically accurate results throughout the region of interest. We
discuss the possibility of experimental observation of the predicted effects
for electrons on helium.Comment: RevTeX 3.0, 14 pages, 8 eps figures included with eps
Imaging Molecular Structure through Femtosecond Photoelectron Diffraction on Aligned and Oriented Gas-Phase Molecules
This paper gives an account of our progress towards performing femtosecond
time-resolved photoelectron diffraction on gas-phase molecules in a pump-probe
setup combining optical lasers and an X-ray Free-Electron Laser. We present
results of two experiments aimed at measuring photoelectron angular
distributions of laser-aligned 1-ethynyl-4-fluorobenzene (C8H5F) and
dissociating, laseraligned 1,4-dibromobenzene (C6H4Br2) molecules and discuss
them in the larger context of photoelectron diffraction on gas-phase molecules.
We also show how the strong nanosecond laser pulse used for adiabatically
laser-aligning the molecules influences the measured electron and ion spectra
and angular distributions, and discuss how this may affect the outcome of
future time-resolved photoelectron diffraction experiments.Comment: 24 pages, 10 figures, Faraday Discussions 17
First INTEGRAL and Swift Observations of a Giant Outburst of A 0535+26
The Be/X-ray binary A 0535+26 has shown three giant outbursts since 2005, after a long period of quiescence. The giant outbursts in 2005 (approx.5.2 Crab, 15-50 keY range) and 2009 (approx.5.6 Crab) could not be observed by most X-ray observatories due to Sun observing constraints. Finally, a giant outburst in February 2011, that reached a flux of approx.3.8 Crab, was monitored with INTEGRAL and Swift TOO observations. We present first results these observations, with a special focus on the cyclotron lines present in the X-ray spectrum of the source
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