scholarly journals Pair-induced spectral changes and variability in compact X-ray sources

1986 ◽  
Vol 221 (4) ◽  
pp. 931-945 ◽  
Author(s):  
A. C. Fabian ◽  
R. D. Blandford ◽  
P. W. Guilbert ◽  
E. S. Phinney ◽  
L. Cuellar
Keyword(s):  
X Ray ◽  
Spectral Changes

scholarly journals Changes of Pd Oxidation State in Pd/Al2O3 Catalysts Using Modulated Excitation DRIFTS

Catalysts ◽  
2021 ◽  
Vol 11 (1) ◽  
pp. 116
Author(s):  
Gian Luca Chiarello ◽  
Ye Lu ◽  
Miren Agote-Arán ◽  
Riccardo Pellegrini ◽  
Davide Ferri
Keyword(s):  
Particle Size ◽  
Fourier Transform ◽  
Infrared Spectroscopy ◽  
Oxidation State ◽  
Diffuse Reflectance ◽  
X Ray ◽  
Spectral Changes ◽  
Diffuse Reflectance Infrared ◽  
X Ray Absorption ◽  
Reversible Reduction

Infrared spectroscopy is typically not used to establish the oxidation state of metal-based catalysts. In this work, we show that the baseline of spectra collected in diffuse reflectance mode of a series of Pd/Al2O3 samples of increasing Pd content varies significantly and reversibly under alternate pulses of CO or H2 and O2. Moreover, these baseline changes are proportional to the Pd content in Pd/Al2O3 samples exhibiting comparable Pd particle size. Similar measurements by X-ray absorption spectroscopy on a different 2 wt.% Pd/Al2O3 confirm that the baseline changes reflect the reversible reduction-oxidation of Pd. Hence, we demonstrate that changes in oxidation state of metal-based catalysts can be determined using diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and that this behavior is part of the spectral changes that are returned by experiments under operando conditions.

scholarly journals EMERGENCE OF A FILAMENTARY STRUCTURE IN THE FIREBALL FROM GRB SPECTRA

2005 ◽  
Vol 14 (01) ◽  
pp. 97-105 ◽  
Author(s):  
REMO RUFFINI ◽  
CARLO LUCIANO BIANCO ◽  
SHE-SHENG XUE ◽  
PASCAL CHARDONNET ◽  
FEDERICO FRASCHETTI ◽  
...  
Keyword(s):  
Radio Emission ◽  
Gamma Ray ◽  
Surrounding Medium ◽  
Effective Area ◽  
Gamma Ray Bursts ◽  
Moving Frame ◽  
Filamentary Structure ◽  
X Ray ◽  
Spectral Changes ◽  
Analytic Expressions

It is shown that the concept of a fireball with a definite filamentary structure naturally emerges from the analysis of the spectra of Gamma-Ray Bursts (GRBs). These results, made possible by the recently obtained analytic expressions of the equitemporal surfaces in the GRB afterglow, depend crucially on the single parameter ℛ describing the effective area of the fireball emitting the X-ray and gamma-ray radiation. The X-ray and gamma-ray components of the afterglow radiation are shown to have a thermal spectrum in the co-moving frame of the fireball and originate from a stable shock front described self-consistently by the Rankine–Hugoniot equations. Precise predictions are presented on a correlation between spectral changes and intensity variations in the prompt radiation verifiable, e.g., by the Swift and future missions. The highly variable optical and radio emission depends instead on the parameters of the surrounding medium. The GRB 991216 is used as a prototype for this model.

X-ray spectral changes in rapidly variable Seyfert galaxies

1991 ◽  
pp. 251-254
Author(s):  
F. Fiore ◽  
G. C. Perola ◽  
L. Piro ◽  
M. Yamauchi ◽  
M. Matsuoka
Keyword(s):  
Seyfert Galaxies ◽  
X Ray ◽  
Spectral Changes

scholarly journals Interactions of ferro-nanoparticles (hematite and magnetite) with reservoir sandstone: implications for surface adsorption and interfacial tension reduction

2020 ◽  
Vol 17 (4) ◽  
pp. 1037-1055 ◽  
Author(s):  
Abdullah Musa Ali ◽  
Noorhana Yahya ◽  
Saima Qureshi
Keyword(s):  
Oil Recovery ◽  
Active Surface ◽  
Dynamics Simulation ◽  
Rock Surface ◽  
Colloidal Transport ◽  
X Ray ◽  
Spectral Changes ◽  
Reservoir Sandstones ◽  
Active Surface Sites ◽  
Particle Adsorption

AbstractThere are a few studies on the use of ferro-nanofluids for enhanced oil recovery, despite their magnetic properties; hence, it is needed to study the adsorption of iron oxide (Fe2O3 and Fe3O4) nanoparticles (NPs) on rock surfaces. This is important as the colloidal transport of NPs through the reservoir is subject to particle adsorption on the rock surface. Molecular dynamics simulation was used to determine the interfacial energy (strength) and adsorption of Fe2O3 and Fe3O4 nanofluids infused in reservoir sandstones. Fourier transform infrared spectroscopy and X-ray photon spectroscopy (XPS) were used to monitor interaction of silicate species with Fe2O3 and Fe3O4. The spectral changes show the variation of dominating silicate anions in the solution. Also, the XPS peaks for Si, C and Fe at 190, 285 and 700 eV, respectively, are less distinct in the spectra of sandstone aged in the Fe3O4 nanofluid, suggesting the intense adsorption of the Fe3O4 with the crude oil. The measured IFT for brine/oil, Fe2O3/oil and Fe3O4/oil are 40, 36.17 and 31 mN/m, respectively. Fe3O4 infused with reservoir sandstone exhibits a higher silicate sorption capacity than Fe2O3, due to their larger number of active surface sites and saturation magnetization, which accounts for the effectiveness of Fe3O4 in reducing IFT.

scholarly journals Continuous rapid X-ray variability and spectral changes in NGC 4051

1985 ◽  
Vol 217 (4) ◽  
pp. 685-699 ◽  
Author(s):  
A. Lawrence ◽  
M. G. Watson ◽  
K. A. Pounds ◽  
M. Elvis
Keyword(s):  
X Ray ◽  
Spectral Changes ◽  
Ngc 4051

scholarly journals Spectral changes and wavelength dependent thermoluminescence of rare earth ions after X-ray irradiation

2017 ◽  
Vol 192 ◽  
pp. 574-581 ◽  
Author(s):  
P.D. Townsend ◽  
A.A. Finch ◽  
M. Maghrabi ◽  
V. Ramachandran ◽  
G.V. Vázquez ◽  
...  
Keyword(s):  
Rare Earth ◽  
Rare Earth Ions ◽  
X Ray ◽  
Spectral Changes

The X‐Ray Spectral Changes of Scorpius X‐1

2003 ◽  
Vol 592 (1) ◽  
pp. 486-497 ◽  
Author(s):  
C. F. Bradshaw ◽  
B. J. Geldzahler ◽  
E. B. Fomalont
Keyword(s):  
X Ray ◽  
Spectral Changes

scholarly journals Timing and spectral analysis of 2S 1417−624 during its 2018 outburst

2021 ◽  
Author(s):  
M M Serim ◽  
Ö C Özüdoğru ◽  
Ç K Dönmez ◽  
Ş Şahiner ◽  
D Serim ◽  
...  
Keyword(s):  
Spectral Characteristics ◽  
Noise Spectrum ◽  
High Energy ◽  
Power Density Spectrum ◽  
Mode Switching ◽  
Model Parameters ◽  
Noise Component ◽  
Density Spectrum ◽  
X Ray ◽  
Spectral Changes

Abstract We investigate timing and spectral characteristics of the transient X-ray pulsar 2S 1417−624 during its 2018 outburst with NICER follow up observations. We describe the spectra with high-energy cut-off and partial covering fraction absorption (PCFA) model and present flux-dependent spectral changes of the source during the 2018 outburst. Utilizing the correlation-mode switching of the spectral model parameters, we confirm the previously reported sub-critical to critical regime transitions and we argue that secondary transition from the gas-dominated to the radiation pressure-dominated disc do not lead to significant spectral changes below 12 keV. Using the existing accretion theories, we model the spin frequency evolution of 2S 1417−624 and investigate the noise processes of a transient X-ray pulsar for the first time using both polynomial and luminosity-dependent models for the spin frequency evolution. For the first model, the power density spectrum of the torque fluctuations indicate that the source exhibits red noise component (Γ ∼ −2) within the timescales of outburst duration which is typical for disc-fed systems. On the other hand, the noise spectrum tends to be white on longer timescales with high timing noise level that indicates an ongoing accretion process in between outburst episodes. For the second model, most of the red noise component is eliminated and the noise spectrum is found to be consistent with a white noise structure observed in wind-fed systems.

A microspectroscopic study of cap damage in annealed RE-doped AlN-capped GaN

2005 ◽  
Vol 892 ◽  
Author(s):  
Emilio Nogales ◽  
K. Lorenz ◽  
K. Wang ◽  
I.S. Roqan ◽  
R.W. Martin ◽  
...  
Keyword(s):  
Surface Defects ◽  
Light Emission ◽  
Lattice Mismatch ◽  
High Energy ◽  
Annealing Atmosphere ◽  
X Ray ◽  
Electron Probe Microanalyzer ◽  
Annealing Temperatures ◽  
Spectral Changes ◽  
Microscopic Surface

AbstractIntegrated AlN nanocaps are used to protect gallium nitride epilayers during high temperature annealing treatments following high-energy implantation of rare earth (RE) ions. Cracks formed in thicker caps due to the lattice mismatch between AlN and GaN lead to the creation of microscopic surface defects at annealing temperatures higher than around 1200 °C. GaN dissociates locally to produce holes in the caps. Simultaneous cathodoluminescence/wavelength dispersive X-ray microanalysis in a modified electron probe microanalyzer allows study of the compositional and light emission variations near these microscopic defects. The intensity of the 5D0 – 7F2 transition related emission is enhanced and spectral changes can be observed, which indicate changes in the structure and/or composition of a very thin layer that forms the walls of holes in the caps. We also report some preliminary observations on the influence of the annealing atmosphere (nitrogen or ammonia) on cap damage.

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