39 research outputs found
On the use of temporal filtering for mitigating galactic synchrotron calibration bias in 21 cm reionization observations
Precision antenna calibration is required for mitigating the impact of
foreground contamination in 21 cm cosmological radio surveys. One widely
studied source of error is the effect of missing point sources in the
calibration sky model; however, poorly understood diffuse galactic emission
also creates a calibration bias that can complicate the clean separation of
foregrounds from the 21 cm signal. In this work, we present a technique for
suppressing this bias with temporal filtering of radio interferometric
visibilities observed in a drift-scan mode. We demonstrate this technique on
mock simulations of the Hydrogen Epoch of Reionization Array (HERA) experiment.
Inspecting the recovered calibration solutions, we find that our technique
reduces spurious errors by over an order of magnitude. This improved accuracy
approaches the required accuracy needed to make a fiducial detection of the 21
cm signal with HERA, but is dependent on a number of external factors that we
discuss. We also explore different types of temporal filtering techniques and
discuss their relative performance and tradeoffs
The Impact of Beam Variations on Power Spectrum Estimation for 21 cm Cosmology II: Mitigation of Foreground Systematics for HERA
One key challenge in detecting 21 cm cosmological signal at z > 6 is to
separate the cosmological signal from foreground emission. This can be studied
in a power spectrum space where the foreground is confined to low delay modes
whereas the cosmological signal can spread out to high delay modes. When there
is a calibration error, however, chromaticity of gain errors propagates to the
power spectrum estimate and contaminates the modes for cosmological detection.
The Hydrogen Epoch of Reionization Array (HERA) employs a high-precision
calibration scheme using redundancy in measurements. In this study, we focus on
the gain errors induced by nonredundancies arising from feed offset relative to
the HERA's 14 meter parabolic dish element, and investigate how to mitigate the
chromatic gain errors using three different methods: restricting baseline
lengths for calibration, smoothing the antenna gains, and applying a temporal
filter prior to calibration. With 2 cm/2 degree perturbations for
translation/tilting motions, a level achievable under normal HERA operating
conditions, the combination of the baseline cut and temporal filtering
indicates that the spurious gain feature due to nonredundancies is
significantly reduced, and the power spectrum recovers the clean
foreground-free region. We found that the mitigation technique works even for
large feed motions but in order to keep a stable calibration process, the feed
positions need to be constrained to 2 cm for translation motions and 2 degree
for tilting offset relative to the dish's vertex.Comment: Accepted for publication in Ap
Hydrogen Epoch of Reionization Array (HERA)
The Hydrogen Epoch of Reionization Array (HERA) is a staged experiment to
measure 21 cm emission from the primordial intergalactic medium (IGM)
throughout cosmic reionization (), and to explore earlier epochs of our
Cosmic Dawn (). During these epochs, early stars and black holes
heated and ionized the IGM, introducing fluctuations in 21 cm emission. HERA is
designed to characterize the evolution of the 21 cm power spectrum to constrain
the timing and morphology of reionization, the properties of the first
galaxies, the evolution of large-scale structure, and the early sources of
heating. The full HERA instrument will be a 350-element interferometer in South
Africa consisting of 14-m parabolic dishes observing from 50 to 250 MHz.
Currently, 19 dishes have been deployed on site and the next 18 are under
construction. HERA has been designated as an SKA Precursor instrument.
In this paper, we summarize HERA's scientific context and provide forecasts
for its key science results. After reviewing the current state of the art in
foreground mitigation, we use the delay-spectrum technique to motivate
high-level performance requirements for the HERA instrument. Next, we present
the HERA instrument design, along with the subsystem specifications that ensure
that HERA meets its performance requirements. Finally, we summarize the
schedule and status of the project. We conclude by suggesting that, given the
realities of foreground contamination, current-generation 21 cm instruments are
approaching their sensitivity limits. HERA is designed to bring both the
sensitivity and the precision to deliver its primary science on the basis of
proven foreground filtering techniques, while developing new subtraction
techniques to unlock new capabilities. The result will be a major step toward
realizing the widely recognized scientific potential of 21 cm cosmology.Comment: 26 pages, 24 figures, 2 table
Efficacy of trabectedin in metastatic solitary fibrous tumor
Solitary fibrous tumor is a rare tumor type and has an unpredictable course. Local recurrence rate varies between 9 and 19%, and rate of metastatic involvement between 0 and 36 %. It is characterized by a typical architecture and immuno-histochemistry tests. The most important prognostic factor is the complete resection of primary tumor. Treatment of recurrences is not clearly established. If a solitary fibrous tumor is too advanced to allow surgical resection, radiotherapy and chemotherapy may be used. The most often used drugs are doxorubicine and\or ifosfamide. We report the case of man with metastatic solitary fibrous tumor treated with trabectedin, administered at a dose of 1.5 mg/m² every 3 weeks. After 3 cycles, metastases had significantly decreased. Recurrence of the disease was demonstrated 8 months after the start of trabectedin. This case shows that trabectedin is a possible treatment option