scholarly journals Probing the high-z IGM with the hyperfine transition of 3He+

2020 ◽  
Vol 497 (1) ◽  
pp. 572-580 ◽  
Author(s):  
Shivan Khullar ◽  
Qingbo Ma ◽  
Philipp Busch ◽  
Benedetta Ciardi ◽  
Marius B Eide ◽  
...  
Keyword(s):  
Power Spectrum ◽  
Signal To Noise Ratio ◽  
Neutral Hydrogen ◽  
Noise Power ◽  
Large Collection ◽  
X Ray ◽  
Hyperfine Transition ◽  
The One ◽  
X Ray Binaries ◽  
Insight Into

ABSTRACT The hyperfine transition of 3He+ at 3.5 cm has been thought as a probe of the high-z IGM, since it offers a unique insight into the evolution of the helium component of the gas, as well as potentially give an independent constraint on the 21 cm signal from neutral hydrogen. In this paper, we use radiative transfer simulations of reionization driven by sources such as stars, X-ray binaries, accreting black holes and shock heated interstellar medium, and simulations of a high-z quasar to characterize the signal and analyse its prospects of detection. We find that the peak of the signal lies in the range ∼1–50 μK for both environments, but while around the quasar it is always in emission, in the case of cosmic reionization a brief period of absorption is expected. As the evolution of He ii is determined by stars, we find that it is not possible to distinguish reionization histories driven by more energetic sources. On the other hand, while a bright QSO produces a signal in 21 cm that is very similar to the one from a large collection of galaxies, its signature in 3.5 cm is very peculiar and could be a powerful probe to identify the presence of the QSO. We analyse the prospects of the signal’s detectability using SKA1-mid as our reference telescope. We find that the noise power spectrum dominates over the power spectrum of the signal, although a modest signal-to-noise ratio can be obtained when the wavenumber bin width and the survey volume are sufficiently large.

scholarly journals Stellar Winds in Massive X-ray Binaries

2016 ◽  
Vol 12 (S329) ◽  
pp. 355-358
Author(s):  
Peter Kretschmar ◽  
Silvia Martínez-Núñez ◽  
Enrico Bozzo ◽  
Lidia M. Oskinova ◽  
Joachim Puls ◽  
...  
Keyword(s):  
Compact Object ◽  
High Mass ◽  
Stellar Winds ◽  
X Rays ◽  
X Ray ◽  
Current State ◽  
Wide Range ◽  
Strong Winds ◽  
The One ◽  
X Ray Binaries

AbstractStrong winds from massive stars are a topic of interest to a wide range of astrophysical fields. In High-Mass X-ray Binaries the presence of an accreting compact object on the one side allows to infer wind parameters from studies of the varying properties of the emitted X-rays; but on the other side the accretor’s gravity and ionizing radiation can strongly influence the wind flow. Based on a collaborative effort of astronomers both from the stellar wind and the X-ray community, this presentation attempts to review our current state of knowledge and indicate avenues for future progress.

A NEW TECHNIQUE FOR THE STUDY OF SCATTER PROPAGATION IN THE TROPOSPHERE

1957 ◽  
Vol 35 (8) ◽  
pp. 823-830 ◽  
Author(s):  
J. H. Chapman ◽  
W. J. Heikkila ◽  
J. E. Hogarth
Keyword(s):  
Power Spectrum ◽  
Communication System ◽  
Carrier Frequency ◽  
Signal To Noise Ratio ◽  
Signal Strength ◽  
Noise Power ◽  
Signal To Noise ◽  
A New Technique ◽  
Conventional Signal ◽  
Noise Power Density

The power spectrum of the fluctuations in received signal strength on a near-optical U.H.F. circuit has been measured. The sidebands associated with these fluctuations can overlap the information-carrying sidebands of a communication system. When this happens, these sidebands must be taken into account in determining the signal-to-noise ratio of the system. In other words, the fluctuations then have the characteristics of noise, and therefore they are called propagation noise in the present paper. Experiments at a carrier frequency of 500 Mc. have shown that the propagation noise power density usually varies with sideband frequency ƒ (measured from the carrier) as 1/ƒ2, for f in the range 0.1 to 10 c.p.s. Departures from this law have been observed in the regions near 0.1 c.p.s. and 10 c.p.s. The measurement of the power spectrum directly offers several advantages over the conventional signal strength recording method, and these are discussed herein.

TU-F-CAMPUS-I-05: Parameterization of the Noise Power Spectrum in X-Ray Computed Tomography

2015 ◽  
Vol 42 (6Part36) ◽  
pp. 3643-3643
Author(s):  
R Bujila ◽  
G Poludniowski ◽  
A Fransson
Keyword(s):  
Computed Tomography ◽  
Power Spectrum ◽  
Noise Power ◽  
Noise Power Spectrum ◽  
X Ray ◽  
X Ray Computed

Simulated sensor characterization for virtual clinical trials in mammography and digital breast tomosynthesis

2022 ◽  
Vol 17 (01) ◽  
pp. C01041
Author(s):  
A. Sarno ◽  
R.M. Tucciariello
Keyword(s):  
Clinical Trials ◽  
Power Spectrum ◽  
Detector Response ◽  
Noise Power ◽  
Noise Power Spectrum ◽  
Flat Panel ◽  
X Ray ◽  
The Impact ◽  
Simulated Images ◽  
Pixel Pitch

Abstract Virtual clinical trials in X-ray breast imaging permit to compare different technical solutions and imaging modalities at reduced costs, involved personnel, reduced times and reduced radiation risks to patients. In this context, the detector characteristics (spatial resolution, noise level and efficiency) play a key role for an appropriate generation of simulated images. The project AGATA proposes to compute images as dose deposit maps in a detector layer of defined materials. Simulated images are then post-processed on the basis of suitable comparison between intrinsic characteristics of real and simulated detectors. With this scope, as first step for the post-processing manipulations, we evaluated the presampled modulation transfer function (MTF), the detector-response function and the noise power spectrum (NPS) of the simulated detectors. Two detectors were simulated: (1) 0.20 mm-thick a-Se direct flat panel with 70 µm pixel pitch and (2) CsI(Tl) indirect flat panel with 100 µm pixel pitch and scintillator layer 0.25 mm thick. In addition, the impact of simulating the de-excitation processes (Auger emission and fluorescence) was explored. Simulated detector characteristics were evaluated for W/Rh spectra between 25 kV and 31 kV. The in-silico platform used a Monte Carlo software based on Geant4 toolkit (vers. 6). First, the simulation and tracking of electrons generated from photoelectric or Compton interactions was shown to have neglectable influence on the pixel values for the explored spectra, with the produced electrons presenting short ranges with respect to the pixel dimension. In the case of the CsI detector, which has fluorescence energies higher than those of the simulated X-ray photons, the deexcitation processes have not noticeable influence on the calculated pixel values. On the other hand, the MTF of the a-Se detector resulted slightly lower when the fluorescence is simulated in the detector materials, due to the dose spread derived from the fluorescence photons, which can travel far from the initial ionization interaction. Regarding the a-Se detector, the noise power spectrum resulted lower with simulated deexcitation.

The noise power spectrum in computed X-ray tomography

1978 ◽  
Vol 23 (3) ◽  
pp. 446-454 ◽  
Author(s):  
S J Riederer ◽  
N J Pelc ◽  
D A Chesler
Keyword(s):  
Power Spectrum ◽  
Noise Power ◽  
Noise Power Spectrum ◽  
X Ray

scholarly journals Current Status of the LOFAR EoR Key Science Project

2017 ◽  
Vol 12 (S333) ◽  
pp. 71-76 ◽  
Author(s):  
L. V. E. Koopmans
Keyword(s):  
Power Spectrum ◽  
Data Processing ◽  
Data Acquisition ◽  
Neutral Hydrogen ◽  
Final Analysis ◽  
Current Status ◽  
Science Project ◽  
X Ray ◽  
The Future ◽  
Future Potential

AbstractA short status update on the LOFAR Epoch of Reionization (EoR) Key Science Project (KSP) is given, regarding data acquisition, data processing and analysis, and current power-spectrum limits on the redshifted 21-cm signal of neutral hydrogen at redshiftsz= 8 − 10. With caution, we present a preliminary astrophysical analysis of ∼60 hr of processed LOFAR data and their resulting power spectrum, showing that potentially already interesting limits on X-ray heating during the Cosmic Dawn can already be gained. This is by no means the final analysis of this sub-set of data, but illustrates the future potential when all nearly 3000 hr of data in hand on two EoR windows will have been processed.

PHOTON SHOT NOISE

1999 ◽  
Vol 13 (11) ◽  
pp. 337-347 ◽  
Author(s):  
C. W. J. BEENAKKER ◽  
M. PATRA
Keyword(s):  
Shot Noise ◽  
Signal To Noise Ratio ◽  
Random Medium ◽  
Fano Factor ◽  
Incident Radiation ◽  
Reduction Factor ◽  
Recent Theory ◽  
Noise Power ◽  
The One ◽  
Bose Einstein

A recent theory is reviewed for the shot noise of coherent radiation propagating through a random medium. The Fano factor [Formula: see text] (the ratio of the noise power and the mean transmitted current) is related to the scattering matrix of the medium. This is the optical analogue of Büttiker's formula for electronic shot noise. Scattering by itself has no effect on the Fano factor, which remains equal to 1 (as for a Poisson process). Absorption and amplification both increase the Fano factor above the Poisson value. For strong absorption [Formula: see text] has the universal limit [Formula: see text], with f the Bose–Einstein function at the frequency of the incident radiation. This is the optical analogue of the one-third reduction factor of electronic shot noise in diffusive conductors. In the amplifying case the Fano factor diverges at the laser threshold, while the signal-to-noise ratio [Formula: see text] reaches a finite, universal limit.

scholarly journals Constraining the duty cycle of transient low-mass X-ray binaries through simulations

2019 ◽  
Vol 488 (2) ◽  
pp. 2767-2779 ◽  
Author(s):  
D Carbone ◽  
R Wijnands
Keyword(s):  
Duty Cycle ◽  
Globular Clusters ◽  
Galactic Centre ◽  
Data Set ◽  
X Ray ◽  
Long Period ◽  
Transient Sources ◽  
Low Mass ◽  
The One ◽  
X Ray Binaries

Abstract We performed simulations of a large number of so-called very faint X-ray transient sources from surveys obtained using the X-ray telescope aboard the Neil Gehrels Swift Observatory on two Galactic globular clusters, and the Galactic Centre. We calculated the ratio between the duty cycle (DC) we input in our simulations and the one we measure after the simulations. We found that fluctuations in outburst duration and recurrence times affect our estimation of the DC more than non-detected outbursts. This biases our measures to overestimate the simulated DC of sources. Moreover, we determined that compact surveys are necessary to detect outbursts with short duration because they could fall in gaps between observations, if such gaps are longer than their duration. On the other hand, long surveys are necessary to detect sources with low DC because the smallest DC a survey can observe is given by the ratio between the shortest outburst duration and the total length of the survey. If one has a limited amount of observing time, these two effects are competing, and a compromise is required which is set by the goals of the proposed survey. We have also performed simulations with several artificial survey strategies in order to evaluate the optimal observing campaign aimed at detecting transients as well as at having the most accurate estimates of the DC. As expected, the best campaign would be a regular and dense monitoring that extends for a very long period. The closest real example of such a data set is the monitoring of the Galactic Centre.

The Effect of Indium Surfactant on the Optoelectronic and Structural Properties of MBE Grown Gallium Nitride

2000 ◽  
Vol 618 ◽  
Author(s):  
C.F. Zhu ◽  
W.K. Fong ◽  
B.H. Leung ◽  
C.C. Cheng ◽  
C. Surya ◽  
...  
Keyword(s):  
Gallium Nitride ◽  
Power Spectra ◽  
Low Frequency ◽  
Rf Plasma ◽  
Frequency Noise ◽  
Noise Power ◽  
Low Frequency Noise ◽  
X Ray Diffraction ◽  
X Ray ◽  
The One

ABSTRACTGallium nitride films were grown by rf-plasma assisted molecular beam epitaxy. A small indium flux was used as surfactant during the growth. The optical and electrical properties of the films grown with and without In surfactant were characterized by investigating the photoluminescence (PL), high resolution x-ray diffraction (HRXRD) and low-frequency noise power spectra. The sample grown in the presence of In surfactant showed a suppressed yellow luminescence (YL) compared to the one grown without In surfactant. Significant reduction in the full width at half maximum of the GaN (0002) x-ray diffraction peak, indicating a better film quality, was obtained when In surfactant was used during growth. Atomic force microscopy studies show that the root mean squared surface roughness for films grown with and without the In surfactant are 5.86 and 6.99 nm respectively indicating significant improvement in surface morphology. This is attributed to the enhanced 2-dimensional growth by In surfactant. A smaller Hooge parameter was obtained from the low-frequency noise measurement for the sample grown with In surfactant indicating that application of In surfactant led to significant reduction in the trap density of the material.

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