scholarly journals Cloud-by-cloud, multiphase, Bayesian modelling: application to four weak, low-ionization absorbers

2020 ◽  
Vol 501 (2) ◽  
pp. 2112-2139
Author(s):  
Sameer ◽  
Jane C Charlton ◽  
Jackson M Norris ◽  
Matthew Gebhardt ◽  
Christopher W Churchill ◽  
...  
Keyword(s):  
Bayesian Methods ◽  
Signal To Noise Ratio ◽  
Bayesian Modelling ◽  
Physical Processes ◽  
User Input ◽  
Radiative Transitions ◽  
Doppler Parameter ◽  
Statistical Studies ◽  
Hydrogen Lines ◽  
Modelling Application

ABSTRACT We present a new method aimed at improving the efficiency of component by component ionization modelling of intervening quasar absorption-line systems. We carry out cloud-by-cloud, multiphase modelling making use of cloudy and Bayesian methods to extract physical properties from an ensemble of absorption profiles. Here, as a demonstration of method, we focus on four weak, low-ionization absorbers at low redshift, because they are multiphase but relatively simple to constrain. We place errors on the inferred metallicities and ionization parameters for individual clouds, and show that the values differ from component to component across the absorption profile. Our method requires user input on the number of phases and relies on an optimized transition for each phase, one observed with high resolution and signal-to-noise ratio. The measured Doppler parameter of the optimized transition provides a constraint on the Doppler parameter of H i, thus providing leverage in metallicity measurements even when hydrogen lines are saturated. We present several tests of our methodology, demonstrating that we can recover the input parameters from simulated profiles. We also consider how our model results are affected by which radiative transitions are covered by observations (for example, how many H i transitions) and by uncertainties in the b parameters of optimized transitions. We discuss the successes and limitations of the method, and consider its potential for large statistical studies. This improved methodology will help to establish direct connections between the diverse properties derived from characterizing the absorbers and the multiple physical processes at play in the circumgalactic medium.

scholarly journals Bayesian Modelling of Extreme Rainfall Data of Some Selected Locations in Nigeria

2020 ◽  
pp. 16-26
Author(s):  
Olawale Basheer Akanbi
Keyword(s):  
Climate Change ◽  
Bayesian Methods ◽  
Fossil Fuels ◽  
Extreme Rainfall ◽  
Rainfall Data ◽  
Bayesian Modelling ◽  
Data Set ◽  
Maximum Rainfall ◽  
Block Maxima ◽  
Informative Approach

Climate change occurs when there is rise in average surface temperature on earth, which is mostly due to the burning of fossil fuels usually by human activities. It has been known to contribute greatly to the occurrence of extreme storms and rainfall, this trend continues as the effect of climate change becomes more pronounced. Therefore, this study modelled the extreme rainfall data of three locations (Calabar, Ikeja, Edo) in Nigeria. The block maxima method was used to pick out the maximum rainfall data in each year to form annual maxima data set. The parameters [location, scale, shape] were estimated using both the Classical and Bayesian methods. The result shows that the Bayesian Informative approach is a very good procedure in modelling the Nigerian Extreme Rainfall data.

scholarly journals Low frequency observations of radio relics and halos

2018 ◽  
Vol 14 (S342) ◽  
pp. 37-43
Author(s):  
Ruta Kale
Keyword(s):  
Galaxy Clusters ◽  
Low Frequency ◽  
Relativistic Electrons ◽  
Physical Processes ◽  
Low Frequencies ◽  
Origin And Evolution ◽  
Extended Sources ◽  
Low Mass ◽  
Statistical Studies

AbstractDiffuse radio emission from galaxy clusters in the form of radio halos and relics are tracers of the shocks and turbulence in the intra-cluster medium. The imprints of the physical processes that govern their origin and evolution can be found in their radio morphologies and spectra. The role of mildly relativistic population of electrons may be crucial for the acceleration mechanisms to work efficiently. Low frequency observations with telescopes that allow imaging of extended sources over a broad range of low frequencies (<2 GHz) offer the best tools to study these sources. I will review the Giant Metrewave Radio Telescope (GMRT) observations in the past few years that have led to: i) statistical studies of large samples of galaxy clusters, ii) opening of the discovery space in low mass clusters and iii) tracing the spectra of seed relativistic electrons using the Upgraded GMRT.

scholarly journals NV center based nano-NMR enhanced by deep learning

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
Nati Aharon ◽  
Amit Rotem ◽  
Liam P. McGuinness ◽  
Fedor Jelezko ◽  
Alex Retzker ◽  
...  
Keyword(s):  
Deep Learning ◽  
Bayesian Methods ◽  
Signal To Noise Ratio ◽  
Frequency Discrimination ◽  
Nitrogen Vacancy ◽  
Noise Model ◽  
Frequency Resolution ◽  
Great Promise ◽  
Nv Center ◽  
Computational Resources

AbstractThe growing field of nano nuclear magnetic resonance (nano-NMR) seeks to estimate spectra or discriminate between spectra of minuscule amounts of complex molecules. While this field holds great promise, nano-NMR experiments suffer from detrimental inherent noise. This strong noise masks to the weak signal and results in a very low signal-to-noise ratio. Moreover, the noise model is usually complex and unknown, which renders the data processing of the measurement results very complicated. Hence, spectra discrimination is hard to achieve and in particular, it is difficult to reach the optimal discrimination. In this work we present strong indications that this difficulty can be overcome by deep learning (DL) algorithms. The DL algorithms can mitigate the adversarial effects of the noise efficiently by effectively learning the noise model. We show that in the case of frequency discrimination DL algorithms reach the optimal discrimination without having any pre-knowledge of the physical model. Moreover, the DL discrimination scheme outperform Bayesian methods when verified on noisy experimental data obtained by a single Nitrogen-Vacancy (NV) center. In the case of frequency resolution we show that this approach outperforms Bayesian methods even when the latter have full pre-knowledge of the noise model and the former has none. These DL algorithms also emerge as much more efficient in terms of computational resources and run times. Since in many real-world scenarios the noise is complex and difficult to model, we argue that DL is likely to become a dominant tool in the field.

scholarly journals Planck intermediate results

2018 ◽  
Vol 619 ◽  
pp. A94 ◽  
Author(s):  
◽  
Y. Akrami ◽  
F. Argüeso ◽  
M. Ashdown ◽  
J. Aumont ◽  
...  
Keyword(s):  
Signal To Noise Ratio ◽  
Mexican Hat Wavelet ◽  
Mexican Hat ◽  
The Matrix ◽  
Statistical Studies ◽  
Sky Temperature ◽  
The One ◽  
Temperature Maps ◽  
Thermal Sources ◽  
Compact Sources

This paper presents the Planck Multi-frequency Catalogue of Non-thermal (i.e. synchrotron-dominated) Sources (PCNT) observed between 30 and 857 GHz by the ESA Planck mission. This catalogue was constructed by selecting objects detected in the full mission all-sky temperature maps at 30 and 143 GHz, with a signal-to-noise ratio (S/N)> 3 in at least one of the two channels after filtering with a particular Mexican hat wavelet. As a result, 29 400 source candidates were selected. Then, a multi-frequency analysis was performed using the Matrix Filters methodology at the position of these objects, and flux densities and errors were calculated for all of them in the nine Planck channels. This catalogue was built using a different methodology than the one adopted for the Planck Catalogue of Compact Sources (PCCS) and the Second Planck Catalogue of Compact Sources (PCCS2), although the initial detection was done with the same pipeline that was used to produce them. The present catalogue is the first unbiased, full-sky catalogue of synchrotron-dominated sources published at millimetre and submillimetre wavelengths and constitutes a powerful database for statistical studies of non-thermal extragalactic sources, whose emission is dominated by the central active galactic nucleus. Together with the full multi-frequency catalogue, we also define the Bright Planck Multi-frequency Catalogue of Non-thermal Sources (PCNTb), where only those objects with a S/N >  4 at both 30 and 143 GHz were selected. In this catalogue 1146 compact sources are detected outside the adopted Planck GAL070 mask; thus, these sources constitute a highly reliable sample of extragalactic radio sources. We also flag the high-significance subsample (PCNThs), a subset of 151 sources that are detected with S/N >  4 in all nine Planck channels, 75 of which are found outside the Planck mask adopted here. The remaining 76 sources inside the Galactic mask are very likely Galactic objects.

A nonlinear solution to 3D seismic data conditioning using trained dictionaries

Geophysics ◽  
2020 ◽  
Vol 85 (5) ◽  
pp. V397-V406
Author(s):  
Zhou Yu ◽  
Rodney Johnston ◽  
John Etgen ◽  
Anya Reitz
Keyword(s):  
Wavelet Transform ◽  
Seismic Data ◽  
Reservoir Characterization ◽  
Seismic Analysis ◽  
Signal To Noise Ratio ◽  
Nonlinear Approximation ◽  
Complex Wavelet Transform ◽  
Amplitude Variation With Offset ◽  
User Input ◽  
Complex Wavelet

Seismic analysis for reservoir characterization has been a primary focus for the geophysical community for decades. One of the critical steps in delivering high-quality processed seismic data for seismic analysis is to remove undesirable prestack seismic phenomena prior to amplitude variation with offset (AVO) analysis. Contrary to the conventional approach, which is mainly 2D gather-based and assumes flat events, we have developed a 3D nonlinear approach with a single principle: the 3D geologic structure should be invariant from offset to offset. Trained dictionaries, generated by 3D complex wavelet transformation over pilot volumes, are progressively constructed by stacking over selected offsets or angles. A sparse nonlinear approximation using the L0 norm is imposed on the data against the trained dictionaries after applying a 3D complex wavelet transform to the data. The final step is to apply an inverse 3D complex wavelet transform to the sparsified coefficients to return to the data space. This workflow is repeated for all offsets or angles. The workflow is automatic and requires minimal user input, resulting in a fast and efficient process. Multiple field data examples have demonstrated significant signal-to-noise ratio uplift, AVO and azimuthal AVO conservation, preservation of steeply dipping structural events, and multiple suppression. The processing time is significantly shorter compared with alternative conventional processes.

Explanation of global plasmapause characteristics in the frame of interchange instability mechanism

2020 ◽  
Author(s):  
Giuli Verbanac ◽  
Mario Bandic ◽  
Viviane Pierrard
Keyword(s):  
Cross Correlation ◽  
Instability Mechanism ◽  
Deep Insight ◽  
Physical Processes ◽  
The Real ◽  
Statistical Studies ◽  
Statistical Sense ◽  
Interchange Instability ◽  
Short Time ◽  
Insight Into

&lt;p&gt;Recent statistical studies based on CLUSTER, CRRES, and THEMIS satellite data have provided insight into global plasmapause characteristics: start of erosion between 21-07 MLT and eastward azimuthal propagation. The observed plasmapause behavior is found to agree with the theory of the interchange instability mechanism. We present the results of the plasmapause characteristics obtained with simulations based on this mechanism.&lt;/p&gt;&lt;p&gt;Here we aim to obtain the same plasmapause characteristics that we previously obtained with simulations using real values of geomagnetic Kp index (which are the proxies for the convection electric field), but using synthetic Kp changes. We show that for that, completely unexpected, instead of many combinations of Kp changes occurring at different UT times (generated for instance with Monte Carlo methods), only 3 Kp jumps occurring at one UT time, leads to the same plasmapause characteristics obtained with simulations using the real Kp values. Therefore, two plasmapause datasets are constructed by setting the following input in the simulations: (a) real values of the geomagnetic Kp index, (b) certain types of time-dependent changes in the Kp (Kp jumps). The Kp jumps include sharp Kp increase, sharp Kp decrease, short time burst enhancement (increase-decrease within 3 hours) in Kp and their combinations in order to obtain plumes, shoulders, and notches, the structures most often observed in nature. The modeled plasmapause is cross-correlated with the Kp index at different 1-hour MLT bins.&lt;/p&gt;&lt;p&gt;We have shown that the cross-correlation curves provide deep insight into the physical processes related to the plasmapause dynamic and evolution. In single events, plasmapause may undergo complex and different dynamics. Here, we show that global plasmapause motions and deformation in time may be simply explained, at least in the statistical sense. Accordingly, we will demonstrate and discuss that three plasmapause structures and their combinations statistically leave the same imprint in the passage through a specific MLT sector as a combination of the plasmapauses created with a large number of the real Kp changes. &amp;#160;&lt;/p&gt;

scholarly journals NGTS 15b, 16b, 17b and 18b: four hot Jupiters from the Next Generation Transit Survey

2021 ◽  
Author(s):  
Rosanna H Tilbrook ◽  
Matthew R Burleigh ◽  
Jean C Costes ◽  
Samuel Gill ◽  
Louise Dyregaard Nielsen ◽  
...  
Keyword(s):  
Heavy Element ◽  
Main Sequence ◽  
Next Generation ◽  
Physical Processes ◽  
Main Sequence Stars ◽  
Latent Factors ◽  
Hot Jupiters ◽  
Short Period ◽  
Statistical Studies ◽  
Inflationary Models

Abstract We report the discovery of four new hot Jupiters with the Next Generation Transit Survey (NGTS). NGTS-15b, NGTS-16b, NGTS-17b, and NGTS-18b are short-period (P &lt; 5d) planets orbiting G-type main sequence stars, with radii and masses between 1.10–1.30 RJ and 0.41–0.76 MJ. By considering the host star luminosities and the planets’ small orbital separations (0.039–0.052 AU), we find that all four hot Jupiters are highly irradiated and therefore occupy a region of parameter space in which planetary inflation mechanisms become effective. Comparison with statistical studies and a consideration of the planets’ high incident fluxes reveals that NGTS-16b, NGTS-17b, and NGTS-18b are indeed likely inflated, although some disparities arise upon analysis with current Bayesian inflationary models. However, the underlying relationships which govern radius inflation remain poorly understood. We postulate that the inclusion of additional hyperparameters to describe latent factors such as heavy element fraction, as well as the addition of an updated catalogue of hot Jupiters, would refine inflationary models, thus furthering our understanding of the physical processes which give rise to inflated planets.

Models of Thermodynamic Properties of Prominences

1979 ◽  
Vol 44 ◽  
pp. 349-355
Author(s):  
R.W. Milkey
Keyword(s):  
Thermodynamic Properties ◽  
Mass Transport ◽  
Emission Spectrum ◽  
Thermodynamic Parameters ◽  
Working Group ◽  
Physical Processes ◽  
Theoretical Concepts ◽  
Group 3 ◽  
Observational Techniques

The focus of discussion in Working Group 3 was on the Thermodynamic Properties as determined spectroscopically, including the observational techniques and the theoretical modeling of physical processes responsible for the emission spectrum. Recent advances in observational techniques and theoretical concepts make this discussion particularly timely. It is wise to remember that the determination of thermodynamic parameters is not an end in itself and that these are interesting chiefly for what they can tell us about the energetics and mass transport in prominences.

Recent Radiative and Collisional Atomic Data of Astrophysical Interest

1988 ◽  
Vol 102 ◽  
pp. 129-132
Author(s):  
K.L. Baluja ◽  
K. Butler ◽  
J. Le Bourlot ◽  
C.J. Zeippen
Keyword(s):  
Mass Production ◽  
Bound States ◽  
Physical Models ◽  
Impact Excitation ◽  
Electron Impact Excitation ◽  
Atomic Data ◽  
Isoelectronic Sequence ◽  
Astrophysical Interest ◽  
Radiative Transitions ◽  
Forbidden Transitions

SummaryUsing sophisticated computer programs and elaborate physical models, accurate radiative and collisional atomic data of astrophysical interest have been or are being calculated. The cases treated include radiative transitions between bound states in the 2p4and 2s2p5configurations of many ions in the oxygen isoelectronic sequence, the photoionisation of the ground state of neutral iron, the electron impact excitation of the fine-structure forbidden transitions within the 3p3ground configuration of CℓIII, Ar IV and K V, and the mass-production of radiative data for ions in the oxygen and fluorine isoelectronic sequences, as part of the international Opacity Project.

A Stable Field Emission Electron Source

1977 ◽  
Vol 35 ◽  
pp. 58-59
Author(s):  
W.R. Bottoms ◽  
G.B. Haydon
Keyword(s):  
Field Emission ◽  
Signal To Noise Ratio ◽  
High Brightness ◽  
Electron Sources ◽  
Brightness Field ◽  
Current Densities ◽  
Properties Of Materials ◽  
Stable Field ◽  
Stable Current ◽  
Careful Design

There is great interest in improving the brightness of electron sources and therefore the ability of electron optical instrumentation to probe the properties of materials. Extensive work by Dr. Crew and others has provided extremely high brightness sources for certain kinds of analytical problems but which pose serious difficulties in other problems. These sources cannot survive in conventional system vacuums. If one wishes to gather information from the other signal channels activated by electron beam bombardment it is necessary to provide sufficient current to allow an acceptable signal-to-noise ratio. It is possible through careful design to provide a high brightness field emission source which has the capability of providing high currents as well as high current densities to a specimen. In this paper we describe an electrode to provide long-lived stable current in field emission sources.The source geometry was based upon the results of extensive computer modeling. The design attempted to maximize the total current available at a specimen.

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