93 research outputs found
Wide-field LOFAR-LBA power-spectra analyses: Impact of calibration, polarization leakage and ionosphere
Contamination due to foregrounds (Galactic and Extra-galactic), calibration
errors and ionospheric effects pose major challenges in detection of the cosmic
21 cm signal in various Epoch of Reionization (EoR) experiments. We present the
results of a pilot study of a field centered on 3C196 using LOFAR Low Band
(56-70 MHz) observations, where we quantify various wide field and calibration
effects such as gain errors, polarized foregrounds, and ionospheric effects. We
observe a `pitchfork' structure in the 2D power spectrum of the polarized
intensity in delay-baseline space, which leaks into the modes beyond the
instrumental horizon (EoR/CD window). We show that this structure largely
arises due to strong instrumental polarization leakage () towards
{Cas\,A} ( kJy at 81 MHz, brightest source in northern sky), which is
far away from primary field of view. We measure an extremely small ionospheric
diffractive scale ( m at 60 MHz) towards {Cas\,A}
resembling pure Kolmogorov turbulence compared to
km towards zenith at 150 MHz for typical ionospheric conditions. This is one of
the smallest diffractive scales ever measured at these frequencies. Our work
provides insights in understanding the nature of aforementioned effects and
mitigating them in future Cosmic Dawn observations (e.g. with SKA-low and HERA)
in the same frequency window.Comment: 20 pages, 11 figures, accepted for publication in MNRA
Role of diffusion weighted MR imaging in differentiating benign from malignant prostate lesions
Background: The purpose of the study was to determine the diagnostic accuracy of diffusion weighted MR imaging and to propose a cut off ADC value in differentiating benign from malignant prostatic lesions considering histopathology as gold standard.Methods: It is a descriptive type of observational study done on 40 patients with clinical suspicion of prostate carcinoma and elevated PSA level more than 4ng/ml. The patients underwent Multiparametric prostate MRI and ADC values were calculated using ADC maps.Results: Of the 40 cases included in the study histopathology revealed a diagnosis of abscess (1), chronic prostatitis (2), BPH with chronic prostatitis (4), BPH (12), and malignancy (21). The mean and standard deviation (SD) of ADC values for the abscess (0.59), CP (0.83+0.16), BPH with CP (0.94+0.22), BPH (1.14+0.14) and malignancy (0.72+0.15) (x10-3mm2/s) were found in our study. The mean ADC value of malignant lesion was lower (0.727+0.149) as compare to benign lesion (1.034+0.216) and this difference was found to be statistically significant with p<0.001. By using ROC curve, ADC cut off value was calculated as 0.92 x 10-3mm2/s and sensitivity, specificity at this cut off value of ADC were 95.24% and 73.68% respectively. The PPV, NPV, diagnostic accuracy of at this cut off value of ADC were 80%, 93.33%, 85% respectively.Conclusions: Our study shows that DWI with ADC calculation helps in differentiation of Benign from Malignant prostatic lesions with high accuracy and this quantitative analysis should be incorporated in routine MRI evaluation of prostatic lesion
First results of evaporation residue cross-section measurements of S+Pb system
The dynamics of heavy ion-induced reactions play a critical role in forming
super heavy elements (SHE), and one clear signature of the SHE formation is the
evaporation residue (ER). In our pursuit of SHE, we present the heaviest
element populated in India for ER cross-section measurements. These are the
first-ever measurements of the Evaporation Residue (ER) cross-sections for the
nuclear reactions between S and Pb. These measurements were
conducted above the Coulomb barrier at four distinct beam energies in the
laboratory frame, ranging from 176 to 191 MeV at the pelletron Linac facility
at the Inter-University Accelerator Centre (IUAC), New Delhi. The Hybrid Recoil
Mass Analyzer (HYRA) in a gas-filled mode was employed for these experiments.
The obtained range of ER cross-sections enriches our knowledge and helps
advance the field of heavy ion-induced reactions, especially in the context of
super heavy element formation.Comment: 12 pages, 10 figures. arXiv admin note: text overlap with
arXiv:2311.0904
A novel radio imaging method for physical spectral index modelling
We present a new method, called "forced-spectrum fitting", for
physically-based spectral modelling of radio sources during deconvolution. This
improves upon current common deconvolution fitting methods, which often produce
inaccurate spectra. Our method uses any pre-existing spectral index map to
assign spectral indices to each model component cleaned during the
multi-frequency deconvolution of WSClean, where the pre-determined spectrum is
fitted. The component magnitude is evaluated by performing a modified weighted
linear least-squares fit. We test this method on a simulated LOFAR-HBA
observation of the 3C196 QSO and a real LOFAR-HBA observation of the 4C+55.16
FRI galaxy. We compare the results from the forced-spectrum fitting with
traditional joined-channel deconvolution using polynomial fitting. Because no
prior spectral information was available for 4C+55.16, we demonstrate a method
for extracting spectral indices in the observed frequency band using
"clustering". The models generated by the forced-spectrum fitting are used to
improve the calibration of the datasets. The final residuals are comparable to
existing multi-frequency deconvolution methods, but the output model agrees
with the provided spectral index map, embedding correct spectral information.
While forced-spectrum fitting does not solve the determination of the spectral
information itself, it enables the construction of accurate multi-frequency
models that can be used for wide-band calibration and subtraction.Comment: 17 pages, 9 figures, 5 tables. Accepted for publication in MNRA
Measurements of evaporation residue cross-sections and evaporation residue-gated -ray fold distributions for S+Sm system
Evaporation Residue (ER) cross-sections and ER-gated -ray fold
distributions are measured for the S + Sm nuclear reaction above
the Coulomb barrier at six different beam energies from 148 to 191 MeV.
-ray multiplicities and spin distributions are extracted from the
ER-gated fold distributions. The ER cross-sections measured in the present work
are found to be much higher than what was reported in a previous work using a
very different target-projectile (Ti + Ba) combination, leading
to the same compound nucleus Pt, with much less mass asymmetry in the
entrance channel than the present reaction. This clearly demonstrates the
effect of the entrance channel on ER production cross-section. The ER
cross-sections measured in the present work are compared with the results of
both the statistical model calculations and the dynamical model calculations.
Statistical model calculations have been performed to generate a range of
parameter space for both the barrier height and Kramers' viscosity parameter
over which the ER cross-section data can be reproduced. The calculations
performed using the dinuclear system (DNS) model reproduce the data considering
both complete and incomplete fusion processes. DNS calculations indicate the
need for the inclusion of incomplete fusion channel at higher energies to
reproduce the ER cross-sections.Comment: 13 pages, 18 figure
Assessing the impact of two independent direction-dependent calibration algorithms on the LOFAR 21-cm signal power spectrum
Detecting the 21-cm signal from the Epoch of Reionisation (EoR) is
challenging due to the strong astrophysical foregrounds, ionospheric effects,
radio frequency interference and instrumental effects. Understanding and
calibrating these effects are crucial for the detection. In this work, we
introduce a newly developed direction-dependent (DD) calibration algorithm
DDECAL and compare its performance with an existing algorithm, SAGECAL, in the
context of the LOFAR-EoR 21-cm power spectrum experiment. In our data set, the
North Celestial Pole (NCP) and its flanking fields were observed
simultaneously. We analyse the NCP and one of its flanking fields. The NCP
field is calibrated by the standard pipeline, using SAGECAL with an extensive
sky model and 122 directions, and the flanking field is calibrated by DDECAL
and SAGECAL with a simpler sky model and 22 directions. Additionally, two
strategies are used for subtracting Cassiopeia A and Cygnus A. The results show
that DDECAL performs better at subtracting sources in the primary beam region
due to the application of a beam model, while SAGECAL performs better at
subtracting Cassiopeia A and Cygnus A. This indicates that including a beam
model during DD calibration significantly improves the performance. The benefit
is obvious in the primary beam region. We also compare the 21-cm power spectra
on two different fields. The results show that the flanking field produces
better upper limits compared to the NCP in this particular observation. Despite
the minor differences between DDECAL and SAGECAL due to the beam application,
we find that the two algorithms yield comparable 21-cm power spectra on the
LOFAR-EoR data after foreground removal. Hence, the current LOFAR-EoR 21-cm
power spectrum limits are not likely to depend on the DD calibration method.Comment: 28 pages, 14 figures, accepted for publication in A&
The AARTFAAC Cosmic Explorer:Observations of the 21-cm power spectrum in the EDGES absorption trough
The 21-cm absorption feature reported by the EDGES collaboration is several
times stronger than that predicted by traditional astrophysical models. If
genuine, a deeper absorption may lead to stronger fluctuations on the 21-cm
signal on degree scales (up to 1~Kelvin in rms), allowing these fluctuations to
be detectable in nearly 50~times shorter integration times compared to previous
predictions. We commenced the "AARTFAAC Cosmic Explorer" (ACE) program, that
employs the AARTFAAC wide-field imager, to measure or set limits on the power
spectrum of the 21-cm fluctuations in the redshift range
(~MHz) corresponding to the deep part of the EDGES
absorption feature. Here, we present first results from two LST bins:
23.5-23.75h and 23.5-23.75h, each with 2~h of data, recorded in `semi
drift-scan' mode. We demonstrate the application of the new ACE data-processing
pipeline (adapted from the LOFAR-EoR pipeline) on the AARTFAAC data. We observe
that noise estimates from the channel and time-differenced Stokes~
visibilities agree with each other. After 2~h of integration and subtraction of
bright foregrounds, we obtain upper limits on the 21-cm power
spectrum of and at for the two LST
bins. Incoherently averaging the noise bias-corrected power spectra for the two
LST bins yields an upper limit of at . These are the deepest upper limits thus far at
these redshifts.Comment: 16 pages, 10 figures, accepted for publication in MNRA
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