scholarly journals Concordance: In-flight Calibration of X-Ray Telescopes without Absolute References

2021 ◽  
Vol 162 (6) ◽  
pp. 254
Author(s):  
Herman L. Marshall ◽  
Yang Chen ◽  
Jeremy J. Drake ◽  
Matteo Guainazzi ◽  
Vinay L. Kashyap ◽  
...  
Keyword(s):  
Statistical Method ◽  
Prior Knowledge ◽  
A Priori ◽  
Effective Area ◽  
Data Sets ◽  
Shrinkage Estimation ◽  
Correction Factors ◽  
Energy Bands ◽  
X Ray ◽  
Systematic Uncertainties

Abstract We describe a process for cross-calibrating the effective areas of X-ray telescopes that observe common targets. The targets are not assumed to be “standard candles” in the classic sense, in that we assume that the source fluxes have well-defined, but a priori unknown values. Using a technique developed by Chen et al. that involves a statistical method called shrinkage estimation, we determine effective area correction factors for each instrument that bring estimated fluxes into the best agreement, consistent with prior knowledge of their effective areas. We expand the technique to allow unique priors on systematic uncertainties in effective areas for each X-ray astronomy instrument and to allow correlations between effective areas in different energy bands. We demonstrate the method with several data sets from various X-ray telescopes.

scholarly journals Optimal estimation of tropospheric H<sub>2</sub>O and δD with IASI/METOP

2011 ◽  
Vol 11 (21) ◽  
pp. 11207-11220 ◽  
Author(s):  
M. Schneider ◽  
F. Hase
Keyword(s):  
A Priori ◽  
Measurement Techniques ◽  
Lower Troposphere ◽  
Optimal Estimation ◽  
Atmospheric Temperature ◽  
Data Sets ◽  
Upper Troposphere ◽  
Systematic Uncertainties ◽  
Better Than

Abstract. We present optimal estimates of tropospheric H2O and δD derived from radiances measured by the instrument IASI (Infrared Atmospheric Sounding Interferometer) flown on EUMETSAT's polar orbiter METOP. We document that the IASI spectra allow for retrieving H2O profiles between the surface and the upper troposphere as well as middle tropospheric δD values. A theoretical error estimation suggests a precision for H2O of better than 35% in the lower troposphere and of better than 15% in the middle and upper troposphere, respectively, whereby surface emissivity and atmospheric temperature uncertainties are the leading error sources. For the middle tropospheric δD values we estimate a precision of 15–20‰ with the measurement noise being the dominating error source. The accuracy of the IASI products is estimated to about 20–10% and 10‰ for lower to upper tropospheric H2O and middle tropospheric δD, respectively. It is limited by systematic uncertainties in the applied spectroscopic parameters and the a priori atmospheric temperature profiles. We compare our IASI products to a large number of near coincident radiosonde in-situ and ground-based FTS (Fourier Transform Spectrometer) remote sensing measurements. The bias and the scatter between the different H2O and δD data sets are consistent with the combined theoretical uncertainties of the involved measurement techniques.

Reconstruction of dynamic objects with affine deformations in computerized tomography

2014 ◽  
Vol 22 (3) ◽  
Author(s):  
Bernadette Hahn
Keyword(s):  
Image Analysis ◽  
Computerized Tomography ◽  
A Priori ◽  
Special Focus ◽  
Data Sets ◽  
Reconstruction Method ◽  
A Priori Information ◽  
Motion Artefacts ◽  
X Ray ◽  
Priori Information

Abstract.The data acquisition in computerized tomography takes a certain amount of time since the x-ray source has to be rotated around the specimen. An object that changes during the scanning causes inconsistent data sets. To avoid the motion artefacts in reconstructions, the algorithm has to take the dynamic behavior of the specimen into account. In this context, some a priori information about the movement is required. A reconstruction method is proposed that compensates for the motion with a special focus on affine deformations. It also permits the combination of reconstruction and image analysis tools to extract features of the object without motion artefacts. The algorithm is validated with a numerical example from medical imaging.

scholarly journals X-ray spectra, light-curves and SEDs of blazars frequently observed by Swift

2021 ◽  
Author(s):  
Paolo Giommi ◽  
M Perri ◽  
M Capalbi ◽  
V D’Elia ◽  
U Barres de Almeida ◽  
...  
Keyword(s):  
Broad Band ◽  
Spectral Energy ◽  
Data Sets ◽  
Energy Bands ◽  
Energy Distributions ◽  
X Ray ◽  
Peak Energy ◽  
Parameter Values ◽  
Best Fit

Abstract Blazars research is one of the hot topics of contemporary extragalactic astrophysics. That is because these sources are the most abundant type of extragalactic γ-ray sources and are suspected to play a central role in multi-messenger astrophysics. We have used swift$\_$xrtproc, a tool to carry out an accurate spectral and photometric analysis of the Swift-XRT data of all blazars observed by Swift at least 50 times between December 2004 and the end of 2020. We present a database of X-ray spectra, best-fit parameter values, count-rates and flux estimations in several energy bands of over 31,000 X-ray observations and single snapshots of 65 blazars. The results of the X-ray analysis have been combined with other multi-frequency archival data to assemble the broad-band Spectral Energy Distributions (SEDs) and the long-term lightcurves of all sources in the sample. Our study shows that large X-ray luminosity variability on different timescales is present in all objects. Spectral changes are also frequently observed with a “harder-when-brighter” or “softer-when-brighter” behaviour depending on the SED type of the blazars. The peak energy of the synchrotron component (νpeak) in the SED of HBL blazars, estimated from the log-parabolic shape of their X-ray spectra, also exhibits very large changes in the same source, spanning a range of over two orders of magnitude in Mrk421 and Mrk501, the objects with the best data sets in our sample.

scholarly journals Possible Pitfalls in the Analysis of Minerals and Loose Materials by Portable XRF, and How to Overcome Them

Minerals ◽  
2020 ◽  
Vol 11 (1) ◽  
pp. 33
Author(s):  
Valérie Laperche ◽  
Bruno Lemière
Keyword(s):  
Fluorescence Spectroscopy ◽  
Laboratory Data ◽  
Data Sets ◽  
Light Elements ◽  
Portable Xrf ◽  
X Ray ◽  
Protective Films ◽  
The Matrix ◽  
Valuable Complement ◽  
Physical Effects

Portable X-ray fluorescence spectroscopy is now widely used in almost any field of geoscience. Handheld XRF analysers are easy to use, and results are available in almost real time anywhere. However, the results do not always match laboratory analyses, and this may deter users. Rather than analytical issues, the bias often results from sample preparation differences. Instrument setup and analysis conditions need to be fully understood to avoid reporting erroneous results. The technique’s limitations must be kept in mind. We describe a number of issues and potential pitfalls observed from our experience and described in the literature. This includes the analytical mode and parameters; protective films; sample geometry and density, especially for light elements; analytical interferences between elements; physical effects of the matrix and sample condition, and more. Nevertheless, portable X-ray fluorescence spectroscopy (pXRF) results gathered with sufficient care by experienced users are both precise and reliable, if not fully accurate, and they can constitute robust data sets. Rather than being a substitute for laboratory analyses, pXRF measurements are a valuable complement to those. pXRF improves the quality and relevance of laboratory data sets.

Survey Data Quality in Analyzing Harmonized Indicators of Protest Behavior: A Survey Data Recycling Approach

2021 ◽  
pp. 000276422110216
Author(s):  
Kazimierz M. Slomczynski ◽  
Irina Tomescu-Dubrow ◽  
Ilona Wysmulek
Keyword(s):  
Data Processing ◽  
Data Quality ◽  
Survey Data ◽  
A Priori ◽  
Data Sets ◽  
New Approach ◽  
Survey Quality ◽  
Survey Error ◽  
Ex Post ◽  
The Impact

This article proposes a new approach to analyze protest participation measured in surveys of uneven quality. Because single international survey projects cover only a fraction of the world’s nations in specific periods, researchers increasingly turn to ex-post harmonization of different survey data sets not a priori designed as comparable. However, very few scholars systematically examine the impact of the survey data quality on substantive results. We argue that the variation in source data, especially deviations from standards of survey documentation, data processing, and computer files—proposed by methodologists of Total Survey Error, Survey Quality Monitoring, and Fitness for Intended Use—is important for analyzing protest behavior. In particular, we apply the Survey Data Recycling framework to investigate the extent to which indicators of attending demonstrations and signing petitions in 1,184 national survey projects are associated with measures of data quality, controlling for variability in the questionnaire items. We demonstrate that the null hypothesis of no impact of measures of survey quality on indicators of protest participation must be rejected. Measures of survey documentation, data processing, and computer records, taken together, explain over 5% of the intersurvey variance in the proportions of the populations attending demonstrations or signing petitions.

scholarly journals Monitoring protein precipitates by in-house X-ray powder diffraction

2013 ◽  
Vol 28 (S2) ◽  
pp. S458-S469 ◽  
Author(s):  
Kenny Ståhl ◽  
Christian G. Frankær ◽  
Jakob Petersen ◽  
Pernille Harris
Keyword(s):  
Powder Diffraction ◽  
Protein Crystal ◽  
Data Sets ◽  
Crystal Forms ◽  
X Ray ◽  
Cell Parameters ◽  
X Ray Scattering ◽  
Source Organism ◽  
Peak Asymmetry ◽  
Overlapping Peaks

Powder diffraction from protein powders using in-house diffractometers is an effective tool for identification and monitoring of protein crystal forms and artifacts. As an alternative to conventional powder diffractometers a single crystal diffractometer equipped with an X-ray micro-source can be used to collect powder patterns from 1 µl samples. Using a small-angle X-ray scattering (SAXS) camera it is possible to collect data within minutes. A streamlined program has been developed for the calculation of powder patterns from pdb-coordinates, and includes correction for bulk-solvent. A number of such calculated powder patterns from insulin and lysozyme have been included in the powder diffraction database and successfully used for search-match identification. However, the fit could be much improved if peak asymmetry and multiple bulk-solvent corrections were included. When including a large number of protein data sets in the database some problems can be foreseen due to the large number of overlapping peaks in the low-angle region, and small differences in unit cell parameters between pdb-data and powder data. It is suggested that protein entries are supplied with more searchable keywords as protein name, protein type, molecular weight, source organism etc. in order to limit possible hits.

scholarly journals X-Ray Emission Differences in SNR MSH14-63

1998 ◽  
Vol 11 (1) ◽  
pp. 393-393
Author(s):  
Fangjun Lu ◽  
Mei Wu ◽  
Tipei Li ◽  
Xuejun Sun
Keyword(s):  
Large Scale ◽  
Physical Characteristics ◽  
Energy Bands ◽  
X Ray

In the paper we report the discovery of X-ray emission differences in SNR MSH14-63 based on the ROSAT PSPC observation. The structures of MSH14-63 are different in different energy bands. These images along with the radial brightness distributions in these energy bands show the existence of a region which only emit X-ray photons harder than l.OkeV. Though weak, there actually exist large scale X-ray emissions beyond the bright rim in many parts of the northeast remnant component, which is in conflict with the Sedov phase assumption used in previous research. These new soft X-ray features provide astronomers more information to study its physical characteristics.

X-Ray Diffraction Study of Hep Metals. I. Line Broadening in Polycrystalline Cd Powder

1974 ◽  
Vol 29 (12) ◽  
pp. 1771-1777 ◽  
Author(s):  
N. C. Haider ◽  
S. H. Hunter
Keyword(s):  
Room Temperature ◽  
Small Deformation ◽  
Correction Factors ◽  
Line Broadening ◽  
X Ray Diffraction ◽  
Fault Probability ◽  
Large Particle Size ◽  
X Ray ◽  
Melting Temperatures ◽  
Diffraction Patterns

Powder Cd of 99.999% purity was prepared at room temperature (25 °C) and x-ray diffraction patterns were obtained using CuKaα radiation with Ni-filter. The line broadening was analyzed after incorporating the appropriate correction factors. At room temperature Cd was found to have large particle size (653 A), small root mean square strain (.001), small deformation fault probability a (.003). and negligible growth fault probability β(0). Compared to other hep metals which have been studied earlier and which have higher melting temperatures, metal Cd is much less affected by mechanical deformation at room temperature.

Crystallization and preliminary X-ray studies of sialidase L from the leech Macrobdella decora

1998 ◽  
Vol 54 (1) ◽  
pp. 111-113 ◽  
Author(s):  
Yu Luo ◽  
Min-yuan Chou ◽  
Su-chen Li ◽  
Yu-teh Li ◽  
Ming Luo
Keyword(s):  
Escherichia Coli ◽  
Unit Cell ◽  
Data Sets ◽  
Molecular Replacement ◽  
Unit Cell Parameters ◽  
Solvent Content ◽  
X Ray ◽  
Cell Parameters ◽  
Mercury Derivative ◽  
Macrobdella Decora

Functional monomeric 83 kDa sialidase L, a NeuAcα2→3Gal-specific sialidase from Macrobdella leech, was expressed in Escherichia coli and readily crystallized by a macroseeding technique. The crystal belongs to space group P1 with unit-cell parameters a = 46.4, b = 69.3, c = 72.5 Å, α = 113.5, β = 95.4 and γ = 107.3°. There is one molecule per unit cell, giving a Vm = 2.4 Å3 Da−1 and a solvent content of 40%. Native and mercury-derivative data sets were collected to 2.0 Å resolution. Threading and molecular-replacement calculations confirmed the existence of a bacterial sialidase-like domain.

A batch-wise non-linear fitting and analysis tool for treating large X-ray diffraction data sets

2006 ◽  
Vol 39 (2) ◽  
pp. 262-266 ◽  
Author(s):  
R. J. Davies
Keyword(s):  
Diffraction Data ◽  
Operation Mode ◽  
Large Data ◽  
Scattering Data ◽  
Data Sets ◽  
Analysis Tool ◽  
Data Set ◽  
X Ray ◽  
Linear Fitting ◽  
Non Linear

Synchrotron sources offer high-brilliance X-ray beams which are ideal for spatially and time-resolved studies. Large amounts of wide- and small-angle X-ray scattering data can now be generated rapidly, for example, during routine scanning experiments. Consequently, the analysis of the large data sets produced has become a complex and pressing issue. Even relatively simple analyses become difficult when a single data set can contain many thousands of individual diffraction patterns. This article reports on a new software application for the automated analysis of scattering intensity profiles. It is capable of batch-processing thousands of individual data files without user intervention. Diffraction data can be fitted using a combination of background functions and non-linear peak functions. To compliment the batch-wise operation mode, the software includes several specialist algorithms to ensure that the results obtained are reliable. These include peak-tracking, artefact removal, function elimination and spread-estimate fitting. Furthermore, as well as non-linear fitting, the software can calculate integrated intensities and selected orientation parameters.

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