scholarly journals Radiative MHD simulations of photon bubbles in radiation-supported magnetized atmospheres of neutron stars with isotropic Thomson scattering

2021 ◽  
Author(s):  
Lizhong Zhang ◽  
Omer Blaes ◽  
Yan-Fei Jiang
Keyword(s):  
Neutron Star ◽  
Maximum Growth ◽  
Thomson Scattering ◽  
Maximum Growth Rate ◽  
Length Scale ◽  
X Ray ◽  
Numerical Resolution ◽  
Flow Through ◽  
Magnetohydrodynamic Simulations ◽  
Future Work

Abstract A major uncertainty in the structure and dynamics of magnetized, radiation pressure dominated neutron star accretion columns in X-ray pulsars and pulsating ultraluminous X-ray sources is that they are thought to be subject to the photon bubble instability. We present the results of two dimensional radiation relativistic magnetohydrodynamic simulations of a non-accreting, static atmosphere to study the development of this instability assuming isotropic Thomson scattering in the slow diffusion regime that is relevant to neutron star accretion columns. Photon bubbles generally grow faster toward shorter wavelengths, until a maximum growth rate is achieved at the radiation viscosity length scale, which is generally quite small and requires high numerical resolution to simulate. We confirm the consistency between our simulation results and linear theory in detail, and show that the nonlinear evolution inevitably leads to collapse of the atmosphere with the higher resolution simulation collapsing faster due to the presence of shorter length scale nonlinear structures. At least in static atmospheres with horizontally periodic boundary conditions, this resolution dependence may make simulations of the nonlinear dynamics of photon bubble instability in neutron star accretion columns challenging. It remains to be seen whether these difficulties will persist upon inclusion of an accretion flow through the top and magnetically-confined horizontal boundaries through which photons can escape. Our results here provide a foundation for such future work.

Atomic Layer Deposition of Silica and Group IV Metal Oxides Nanolaminates

2003 ◽  
Vol 786 ◽  
Author(s):  
Lijuan Zhong ◽  
Fang Chen ◽  
Stephen A. Campbell ◽  
Wayne L. Gladfelter
Keyword(s):  
Layer Structure ◽  
Atomic Layer ◽  
Maximum Growth ◽  
Maximum Growth Rate ◽  
Group Iv ◽  
Scattering Pattern ◽  
X Ray ◽  
X Ray Scattering ◽  
Layer Deposition ◽  
Mixed Films

ABSTRACTWith alternating exposure of Si (100) substrates to tri (t -butoxy) silanol and anhydrous zirconium nitrate, mixed films of zirconia and silica were deposited at 162°C. The films were atomically smooth and their thickness was uniform across the entire substrate. The maximum growth rate of 12 Å/cycle implies deposition of more than one monolayer per cycle. A singular reflection in the low angle X-ray scattering pattern indicates an ordered bi-layer structure. Similar nanolaminate structures were also formed using anhydrous nitrates of hafnium and tin.

scholarly journals CRECIMIENTO DEL CORAL ACROPORA PALMATA (LAMARCK, 1886) EN EL PARQUE NACIONAL NATURAL CORALES DEL ROSARIO, CARIBE COLOMBIANO.

2016 ◽  
Vol 25 ◽  
Author(s):  
Rocío Del Pilar García U. ◽  
Elvira M. Alvarado Ch. ◽  
Alberto Acosta M.
Keyword(s):  
Growth Rate ◽  
Maximum Growth ◽  
Maximum Growth Rate ◽  
Annual Growth ◽  
Acropora Palmata ◽  
Alizarin Red ◽  
X Ray ◽  
Measuring Techniques ◽  
Growth Bands ◽  
Northern Zone

The growth rate in ten months (September 1992 - july 1993) for 30 colonies of Acropora palmata along the northern zone of the Corales del Rosario national natural park, Colombian Caribbean, was determined. Three measuring techniques were used: by hand, by staining with alizarin red, and from growth bands by X ray photography. The annual growth estimate for the species in the Park was 5.2 ± 1.3 cm and was found inversely correlated to the size of the colony (lenght, width and height). The growth presented a spatial variation. The smallest growth was found at Caleta Island and the largest at Caribaru Island. The maximum growth rate was observed in the dry season (December-February). No significant differences were found between measurement by hand and by alizarin red. The X-ray technique showed that Acropora palmata does not present discernible annual growth bands.

Growth and Study of Thick 3C-SiC Epitaxial Layers Produced by Epitaxy on 6H-SiC Substrates

2007 ◽  
Vol 556-557 ◽  
pp. 175-178 ◽  
Author(s):  
Alexander A. Lebedev ◽  
V.V. Zelenin ◽  
Pavel L. Abramov ◽  
Elena V. Bogdanova ◽  
Sergey P. Lebedev ◽  
...  
Keyword(s):  
Growth Rate ◽  
Detailed Analysis ◽  
Electronic Devices ◽  
Maximum Growth ◽  
Maximum Growth Rate ◽  
Epitaxial Layers ◽  
X Ray ◽  
Donor Acceptor ◽  
Pl Spectrum

3C-SiC epitaxial layers with a thickness of up to 100 μm and area of ~0.3-0.5 cm2 have been grown by sublimation epitaxy on hexagonal (6H-SiC) substrates at a maximum growth rate of about 200 μm per hour. The epilayers obtained are of n-type (Nd-Na ~ 1017 -1018 cm-3). According to X-ray data, the epitaxial layers are composed of the 3C-SiC polytype, without inclusions of other polytypes. The donor-acceptor (Al-N) recombination band with hνmax ~ 2.12 eV predominates in the photoluminescence (PL) spectrum. A detailed analysis of a PL spectrum measured at 6 K is presented. A conclusion is made that the epitaxial layers can be used as substrates for electronic devices based on 3C-SiC.

scholarly journals Neutron Star Properties from Observations of Pulsars and Pulsing X-ray Sources

1981 ◽  
Vol 95 ◽  
pp. 303-319
Author(s):  
F. K. Lamb
Keyword(s):  
Neutron Star ◽  
Neutron Stars ◽  
Random Noise ◽  
Small Scale ◽  
X Ray ◽  
Structure And Dynamics ◽  
Stellar Masses ◽  
Future Work ◽  
Large Frequency

This paper reviews the information on neutron stars that has been obtained from radio and X-ray observations, with emphasis on recent results from timing studies. Included are summaries of the current theoretical picture of neutron stars, and the most recent evidence concerning stellar masses, radii, inertial moments, and magnetic fields. Also included are discussions of large frequency jumps (“macroglitches”), small-scale timing irregularities (“microglitches”), the characterization of the latter phenomenon in terms of random noise processes, and the use of both as probes of the internal structure and dynamics of neutron stars. Finally, some of the most promising directions for future work are briefly noted.

High-Speed Growth of High-Quality 4H-SiC Bulk by Solution Growth Using Si-Cr Based Melt

2010 ◽  
Vol 645-648 ◽  
pp. 13-16 ◽  
Author(s):  
Katsunori Danno ◽  
Hiroaki Saitoh ◽  
Akinori Seki ◽  
H. Daikoku ◽  
Y. Fujiwara ◽  
...  
Keyword(s):  
Growth Rate ◽  
High Speed ◽  
Grown Crystal ◽  
Maximum Growth ◽  
Maximum Growth Rate ◽  
Solution Growth ◽  
X Ray Diffraction ◽  
Large Crystal ◽  
X Ray ◽  
Basal Plane Dislocation

High-speed solution growth using Si-Cr based melt has been performed on on-axis 4H-SiC(0001) at a high temperature of about 2000°C. The maximum growth rate for one-hour growth reaches to 1120 m/h, while the typical growth rate of growth for 2h is about 500 m/h. A large crystal that is about 25 mm in diameter and 1650 m in thickness can be obtained by growth for 5h. The crystal quality is confirmed to be homogeneous by X-ray diffraction and X-ray topography, because FWHM is less than 30 arcsec. Etch pit density of the threading dislocations in the grown crystal is 103-104 cm-2, and that of basal plane dislocation is 2×102-3×103 cm-2. Resistivity of the crystals grown by the solution growth is comparable to those of crystals grown by physical vapor transport technique.

On the inviscid stability of bi-layer axisymmetric coatings

2008 ◽  
Vol 605 ◽  
pp. 389-400
Author(s):  
P. A. BLYTHE ◽  
P. G. SIMPKINS
Keyword(s):  
Growth Rate ◽  
Double Layer ◽  
Composite Coatings ◽  
Density Ratio ◽  
Maximum Growth ◽  
Reynolds Numbers ◽  
Maximum Growth Rate ◽  
Length Scale ◽  
Layer Composite ◽  
The Stability

This paper is concerned with the stability of fibre coatings at large Reynolds numbers. Both single- and double-layer coatings are considered; no restriction is placed on the coating thicknesses. Calculations for the maximum growth rate, together with the corresponding length scale of the instability, are presented. Rescaling with respect to the maximum growth rate generates universal dispersion relations over the unstable wavenumber range. For double-layer composite coatings, modifications are required when the density ratio becomes large.

scholarly journals Aperiodic Flux Variability in A 0535+262

1996 ◽  
Vol 165 ◽  
pp. 313-319
Author(s):  
Mark H. Finger ◽  
Robert B. Wilson ◽  
B. Alan Harmon ◽  
William S. Paciesas
Keyword(s):  
Neutron Star ◽  
Gamma Ray ◽  
Beat Frequency ◽  
Power Spectra ◽  
Center Frequency ◽  
X Ray ◽  
Binary Pulsar ◽  
Transient Source ◽  
Flux Variability ◽  
Burst And Transient Source

A “giant” outburst of A 0535+262, a transient X-ray binary pulsar, was observed in 1994 February and March with the Burst and Transient Source Experiment (BATSE) onboard the Compton Gamma-Ray Observatory. During the outburst power spectra of the hard X-ray flux contained a QPO-like component with a FWHM of approximately 50% of its center frequency. Over the course of the outburst the center frequency rose smoothly from 35 mHz to 70 mHz and then fell to below 40 mHz. We compare this QPO frequency with the neutron star spin-up rate, and discuss the observed correlation in terms of the beat frequency and Keplerian frequency QPO models in conjunction with the Ghosh-Lamb accretion torque model.

scholarly journals A minimal timescale for the continuum in 4U 1608-52 and Aql X-1

2021 ◽  
Vol 502 (1) ◽  
pp. L72-L78
Author(s):  
K Mohamed ◽  
E Sonbas ◽  
K S Dhuga ◽  
E Göğüş ◽  
A Tuncer ◽  
...  
Keyword(s):  
Black Hole ◽  
Neutron Star ◽  
Power Spectra ◽  
Light Curves ◽  
State Transitions ◽  
Strong Positive Correlation ◽  
Present Evidence ◽  
X Ray ◽  
X Ray Binaries ◽  
The Continuum

ABSTRACT Similar to black hole X-ray binary transients, hysteresis-like state transitions are also seen in some neutron-star X-ray binaries. Using a method based on wavelets and light curves constructed from archival Rossi X-ray Timing Explorer observations, we extract a minimal timescale over the complete range of transitions for 4U 1608-52 during the 2002 and 2007 outbursts and the 1999 and 2000 outbursts for Aql X-1. We present evidence for a strong positive correlation between this minimal timescale and a similar timescale extracted from the corresponding power spectra of these sources.

scholarly journals 3D magnetized jet break-out from neutron-star binary merger ejecta: afterglow emission from the jet and the ejecta

2021 ◽  
Vol 502 (2) ◽  
pp. 1843-1855
Author(s):  
Antonios Nathanail ◽  
Ramandeep Gill ◽  
Oliver Porth ◽  
Christian M Fromm ◽  
Luciano Rezzolla
Keyword(s):  
Neutron Star ◽  
Thermal Emission ◽  
Opening Angle ◽  
Hollow Core ◽  
Binary Neutron Star ◽  
Vlbi Observations ◽  
Superluminal Motion ◽  
General Relativistic ◽  
Star Binary ◽  
Magnetohydrodynamic Simulations

ABSTRACT We perform 3D general-relativistic magnetohydrodynamic simulations to model the jet break-out from the ejecta expected to be produced in a binary neutron-star merger. The structure of the relativistic outflow from the 3D simulation confirms our previous results from 2D simulations, namely, that a relativistic magnetized outflow breaking out from the merger ejecta exhibits a hollow core of θcore ≈ 4°, an opening angle of θjet ≳ 10°, and is accompanied by a wind of ejected matter that will contribute to the kilonova emission. We also compute the non-thermal afterglow emission of the relativistic outflow and fit it to the panchromatic afterglow from GRB170817A, together with the superluminal motion reported from VLBI observations. In this way, we deduce an observer angle of $\theta _{\rm obs}= 35.7^{\circ \, \, +1.8}_{\phantom{\circ \, \, }-2.2}$. We further compute the afterglow emission from the ejected matter and constrain the parameter space for a scenario in which the matter responsible for the thermal kilonova emission will also lead to a non-thermal emission yet to be observed.

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