scholarly journals The effect of a magnetic field on the dynamics of debris discs around white dwarfs

2020 ◽  
Vol 500 (3) ◽  
pp. 2986-3001
Author(s):  
M A Hogg ◽  
R Cutter ◽  
G A Wynn
Keyword(s):  
Magnetic Field ◽  
Particle Size ◽  
White Dwarfs ◽  
Accretion Rate ◽  
Observational Evidence ◽  
Dust Particles ◽  
Accretion Rates ◽  
Subsequent Effect ◽  
Similar Factor

ABSTRACT Observational estimates of the lifetimes and inferred accretion rates from debris discs around polluted white dwarfs are often inconsistent with the predictions of models of shielded Poynting–Robertson drag on the dust particles in the discs. Moreover, many cool polluted white dwarfs do not show any observational evidence of accompanying discs. This may be explained, in part, if the debris discs had shorter lifetimes and higher accretion rates than predicted by Poynting–Robertson drag alone. We consider the role of a magnetic field on tidally disrupted diamagnetic debris and its subsequent effect on the formation, evolution, and accretion rate of a debris disc. We estimate that magnetic field strengths greater than ∼10 kG may decrease the time needed for circularization and the disc lifetimes by several orders of magnitude and increase the associated accretion rates by a similar factor, relative to Poynting–Robertson drag. We suggest some polluted white dwarfs may host magnetic fields below the typical detectable limit and that these fields may account for a proportion of polluted white dwarfs with missing debris discs. We also suggest that diamagnetic drag may account for the higher accretion rate estimates among polluted white dwarfs that cannot be predicted solely by Poynting–Robertson drag and find a dependence on magnetic field strength, orbital pericentre distance, and particle size on predicted disc lifetimes and accretion rates.

scholarly journals Masker sebagai Pencegah Gangguan Pernapasan pada Pekerja (Studi Kasus PT GUNUNG SUBUR SEJAHTERA Karanganyar)

2019 ◽  
Author(s):  
Adiyani Risqi Setiarini
Keyword(s):  
Particle Size ◽  
Research Method ◽  
Qualitative Case Study ◽  
Dust Particles ◽  
Case Study Approach ◽  
Respiratory Problems ◽  
Study Approach ◽  
Protective Medium

Abstract. Dust and tea powder produced negatively impact the health of the respiratory tract. Workers in the production department at PT Gunung Subur Sejahtera tea factory have the potential to experience respiratory problems because they are often exposed to tea dust and powder. The writing of this article aims to identify the role of masks as a deterrent to respiratory problems in workers at PT Gunung Subur Sejahtera. The research method used is descriptive qualitative case study approach in workers' environment at PT Gunung Subur Sejahtera, Karanganyar. The results showed that disposable masks commonly used by workers in tea companies had three layers of protection that were able to filter particles up to 0.1 µmv so that they were effective in preventing bacteria, viruses, and especially dust particles that were inhaled with respiratory air. By using masks when working, workers is able to minimize the intensity of exposure to dust particles that can be inhaled. In addition to the intensity of the exposure, the particle size that might escape the mask becomes small. Thus, the mask can be used as an effective personal protective medium to reduce the risk of respiratory distress in the workforce.

On the role of mother-planet magnetic field in spiral structure explanation of formation of spokes

1984 ◽  
Vol 75 ◽  
pp. 569-574
Author(s):  
G.X. Song
Keyword(s):  
Magnetic Field ◽  
Solar System ◽  
Interplanetary Magnetic Field ◽  
Wave Amplitude ◽  
Spiral Structure ◽  
Dust Particles ◽  
Electromagnetic Effect ◽  
Sectoral Structure ◽  
The Magnetic Field

AbstractSome features about the spokes in B rings can be explained in terms of the electromagnetic effect. Due to the existence of the magnetic field in Saturn, plasma and micro-sized dust particles, the loosely spiral structure of magnetic field near Saturn, which is similar to that invoked to explain the sectoral structure of the interplanetary magnetic field in the solar system, may be induced.The spiral structure is rotating with mother-planet and will gradually form at corotation circle, but the wave amplitude will grow outside the corotation and will decay gradually inside the corotation. Using the characteristics of this spiral structure, we have tried to attack the mechanism of the formation of spokes.

scholarly journals The Role of Particle Size in Producing the F- Coronal Scattered Brightness

1996 ◽  
Vol 150 ◽  
pp. 349-352
Author(s):  
R.M. MacQueen ◽  
W.C. Davidson ◽  
I. Mann
Keyword(s):  
Particle Size ◽  
Mie Theory ◽  
Interplanetary Dust ◽  
Dust Particles ◽  
Size Distributions ◽  
Particle Size Distributions ◽  
Interplanetary Dust Particles ◽  
Infrared Observations ◽  
Flux Measurements

AbstractMotivated by new infrared observations, we examine the contribution of various size intervals of interplanetary dust particles to visible and infrared scattered radiances of the solar F-corona, employing Mie theory and particle size distributions based upon differing interpretations of lunar microcrater evidence and interplanetary flux measurements.

scholarly journals Jets from neutron star X-ray binaries: towards a unified scheme

2010 ◽  
Vol 6 (S275) ◽  
pp. 233-241
Author(s):  
Simone Migliari
Keyword(s):  
Magnetic Field ◽  
Black Holes ◽  
Neutron Star ◽  
Accretion Rate ◽  
X Ray ◽  
Multi Wavelength ◽  
Observational Knowledge ◽  
Low Magnetic Field ◽  
X Ray Binaries

AbstractSystematic multi-wavelength studies of neutron stars (NSs) have shown a jet and disk-jet coupling phenomenology which resembles, although with some important differences, that observed in black holes; ultra-relativistic transient ejection, steady compact jets, accretion-ejection cycles are indeed observed in NSs. I will review our observational knowledge of jet in NS X-ray binaries, focusing on the role of the parameters of the system which might be involved in the production of jets. First, I will discuss the role of the accretion rate, presenting a unified scheme for accretion-jet production throughout the different sub-classes of low-magnetic field NSs. Then, I will attempt to (make the first steps to) quantify the role of spin and magnetic field in powering the jet.

Gravitational Drift Instability in Quantum Dusty Plasmas

2018 ◽  
Vol 73 (12) ◽  
pp. 1137-1141 ◽  
Author(s):  
M. Jamil ◽  
Zahid Mir ◽  
A. Rasheed ◽  
A. Hussain
Keyword(s):  
Magnetic Field ◽  
Wide Spectrum ◽  
Dusty Plasmas ◽  
Dust Particles ◽  
Electrostatic Waves ◽  
Quantum Hydrodynamic Model ◽  
Plasma Species ◽  
Density Of Electrons ◽  
Drift Instability

AbstractThe dispersion relation of electrostatic waves due to multi-drifts is studied in an ambient magnetic field across three-species quantum dusty plasmas. The quantum hydrodynamic model is applied to analyze the effects of the Lorentz and the gravitational forces. It is found that the instability is excited mainly due to the \({\mathbf{E}_{0}}\times{\mathbf{B}_{0}}\) drift of the plasma species. However, an additional \({\mathbf{g}_{0}}\times{\mathbf{B}_{0}}\) drift associated with dust particles enhances the instability over a wide spectrum of wavevector. The role of a varying magnetic field and the number density of electrons in the wave instability are analyzed graphically. It is noticed that these factors have a significant contribution over the drift instability.

scholarly journals An extended size–luminosity relation for the reverberation-mapped AGNs: the role of the accretion rate

2019 ◽  
Vol 491 (4) ◽  
pp. 5881-5896 ◽  
Author(s):  
Li-Ming Yu ◽  
Bi-Xuan Zhao ◽  
Wei-Hao Bian ◽  
Chan Wang ◽  
Xue Ge
Keyword(s):  
Accretion Rate ◽  
Broad Line ◽  
Line Flux ◽  
Profile Parameter ◽  
Line Region ◽  
Accretion Rates ◽  
The Mean ◽  
Single Epoch ◽  
The Continuum

ABSTRACT For a compiled sample of 120 reverberation-mapped AGNs, the bivariate correlations of the broad-line region (BLR) size (RBLR) with the continuum luminosity at 5100 Å (L5100) and the dimensionless accretion rates ($\dot{\mathscr {M}}$) are investigated. Using our recently calibrated virial factor f, and the velocity tracer from the H β full width at half-maximum (FWHM(H β)) or the line dispersion (σH β) measured in the mean spectra, three kinds of supermassive black hole (SMBH) masses and $\dot{\mathscr {M}}$ are calculated. An extended RBLR(H β)–L5100 relation including $\dot{\mathscr {M}}$ is found to be stronger than the canonical RBLR(H β)–L5100 relation, showing smaller scatters. The observational parameters, RFe (the ratio of optical Fe ii to H β line flux) and the line profile parameter DH β ($D_{\rm H\,\beta } =\rm FWHM(H\,\beta)/\sigma _{\rm H\,\beta }$), have relations with three kinds of $\dot{\mathscr {M}}$. Using RFe and DH β to substitute $\dot{\mathscr {M}}$, extended empirical RBLR(Hβ)–L5100 relations are presented. RFe is a better ‘fix’ for the RBLR(H β)–L5100 offset than the H β shape DH β. The extended empirical RBLR(H β)–L5100 relation including RFe can be used to calculate RBLR, and thus the single-epoch SMBH mass MBH. Our measured accretion rate dependence is not consistent with the simple model of the accretion disc instability leading the BLR formation. The BLR may instead form from the inner edge of the torus, or from some other means in which BLR size is positively correlated with accretion rate and the SMBH mass.

Peculiarity Parameters

1976 ◽  
Vol 32 ◽  
pp. 233-254
Author(s):  
H. M. Maitzen
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Theoretical Work ◽  
Observational Evidence ◽  
Rotator Model ◽  
Peculiar Behaviour ◽  
Field Spectrum ◽  
Oblique Rotator ◽  
Ap Stars ◽  
The Way

Ap stars are peculiar in many aspects. During this century astronomers have been trying to collect data about these and have found a confusing variety of peculiar behaviour even from star to star that Struve stated in 1942 that at least we know that these phenomena are not supernatural. A real push to start deeper theoretical work on Ap stars was given by an additional observational evidence, namely the discovery of magnetic fields on these stars by Babcock (1947). This originated the concept that magnetic fields are the cause for spectroscopic and photometric peculiarities. Great leaps for the astronomical mankind were the Oblique Rotator model by Stibbs (1950) and Deutsch (1954), which by the way provided mathematical tools for the later handling pulsar geometries, anti the discovery of phase coincidence of the extrema of magnetic field, spectrum and photometric variations (e.g. Jarzebowski, 1960).

Fibrin Formation: The Role of the Fibrinogen-Fibrin Monomer Complex

1976 ◽  
Vol 36 (01) ◽  
pp. 037-048 ◽  
Author(s):  
Eric P. Brass ◽  
Walter B. Forman ◽  
Robert V. Edwards ◽  
Olgierd Lindan
Keyword(s):  
Particle Size ◽  
Induction Period ◽  
Fibrin Clot ◽  
Clot Formation ◽  
Appreciable Amount ◽  
Buffer System ◽  
Homeostatic Mechanism ◽  
Fibrin Formation ◽  
Fibrin Monomer

SummaryThe process of fibrin formation using highly purified fibrinogen and thrombin was studied using laser fluctuation spectroscopy, a method that rapidly determines particle size in a solution. Two periods in fibrin clot formation were noted: an induction period during which no fibrin polymerization occurred and a period of rapid increase in particle size. Direct measurement of fibrin monomer polymerization and fibrinopeptide release showed no evidence of an induction period. These observations were best explained by a kinetic model for fibrin clot formation incorporating a reversible fibrinogen-fibrin monomer complex. In this model, the complex serves as a buffer system during the earliest phase of fibrin formation. This prevents the accumulation of free polymerizable fibrin monomer until an appreciable amount of fibrinogen has reacted with thrombin, at which point the fibrin monomer level rises rapidly and polymerization proceeds. Clinically, the complex may be a homeostatic mechanism preventing pathological clotting during periods of elevated fibrinogen.

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