63 research outputs found
Temperature gradient and electric field driven electrostatic instabilities
The stability of electrostatic waves to thermodynamic and electric potential gradients was investigated. It is shown that thermodynamic gradients drive instabilities even when the internal electric field vanishes. Skewing of the distribution function is not included in the dielectric
Stellar magnetic fields. 1: The role of a magnetic field in the peculiar M giant, HD 4174
Coronal heating by resonant absorption of Alfvenic surface waves (quiescent), and magnetic tearing instabilities (impulsive), is discussed with emphasis on three principles which may have application to late-type evolved stars. (1) If sq B/8 pi greater than sq. rho V is observed 2 in a stellar atmosphere, then the observed magnetic field must originate in an interior dynamo. (2) Low mass loss rates could imply the presence of closed magnetic flux loops within the outer atmosphere which constrain hydrodynamic flows when the magnetic body forces exceed the driving forces. (3) given that such magnetic loops effect an enhancement of the local heating rate, a positive correlation is predicted between the existence of a corona and low mass loss rates. These principles are applied to the M giant star HD 4174, which is purported to have a kilogauss magnetic field. Several of its spectroscopic peculiarities are shown to be consistent with the above principles, and further observational checks are suggested
Resonant electrodynamic heating of stellar coronal loops: An LRC circuit analogue
The electrodynamic coupling of stellar coronal loops to underlying beta velocity fields. A rigorous analysis revealed that the physics can be represented by a simple yet equivalent LRC circuit analogue. This analogue points to the existence of global structure oscillations which resonantly excite internal field line oscillations at a spatial resonance within the coronal loop. Although the width of this spatial resonance, as well as the induced currents and coronal velocity field, explicitly depend upon viscosity and resistivity, the resonant form of the generalized electrodynamic heating function is virtually independent of irreversibilities. This is a classic feature of high quality resonators that are externally driven by a broad band source of spectral power. Applications to solar coronal loops result in remarkable agreement with observations
Fast plasma heating by anomalous and inertial resistivity effects
Fast plasma heating by anomalous and inertial resistivity effects is described. A small fraction of the plasma contains strong currents that run parallel to the magnetic field and are driven by an exponentiating electric field. The anomalous character of the current dissipation is caused by the excitation of electrostatic ion cyclotron and/or ion acoustic waves. The role of resistivity due to geometrical effects is considered. Through the use of a marginal stability analysis, equations for the average electron and ion temperatures are derived and numerically solved. The evolution of the plasma is described as a path in the drift velocity diagram, in which the drift velocity is plotted as a function of the electron to ion temperature ratio
On the theory of coronal heating mechanisms
Theoretical models describing solar coronal heating mechanisms are reviewed in some detail. The requirements of chromospheric and coronal heating are discussed in the context of the fundamental constraints encountered in modelling the outer solar atmosphere. Heating by acoustic processes in the 'nonmagnetic' parts of the atmosphere is examined with particular emphasis on the shock wave theory. Also discussed are theories of heating by electrodynamic processes in the magnetic regions of the corona, either magnetohydrodynamic waves or current heating in the regions with large electric current densities (flare type heating). Problems associated with each of the models are addressed
Super-alfvenic propagation of cosmic rays: The role of streaming modes
Numerous cosmic ray propagation and acceleration problems require knowledge of the propagation speed of relativistic particles through an ambient plasma. Previous calculations indicated that self-generated turbulence scatters relativistic particles and reduces their bulk streaming velocity to the Alfven speed. This result was incorporated into all currently prominent theories of cosmic ray acceleration and propagation. It is demonstrated that super-Alfvenic propagation is indeed possible for a wide range of physical parameters. This fact dramatically affects the predictions of these models
Resonant origin for density fluctuations deep within the Sun: helioseismology and magneto-gravity waves
We analyze helioseismic waves near the solar equator in the presence of
magnetic fields deep within the solar radiative zone. We find that reasonable
magnetic fields can significantly alter the shapes of the wave profiles for
helioseismic g-modes. They can do so because the existence of density gradients
allows g-modes to resonantly excite Alfven waves, causing mode energy to be
funnelled along magnetic field lines, away from the solar equatorial plane. The
resulting wave forms show comparatively sharp spikes in the density profile at
radii where these resonances take place. We estimate how big these waves might
be in the Sun, and perform a first search for observable consequences. We find
the density excursions at the resonances to be too narrow to be ruled out by
present-day analyses of p-wave helioseismic spectra, even if their amplitudes
were to be larger than a few percent. (In contrast it has been shown in
(Burgess et al. 2002) that such density excursions could affect solar neutrino
fluxes in an important way.) Because solar p-waves are not strongly influenced
by radiative-zone magnetic fields, standard analyses of helioseismic data
should not be significantly altered. The influence of the magnetic field on the
g-mode frequency spectrum could be used to probe sufficiently large
radiative-zone magnetic fields should solar g-modes ever be definitively
observed. Our results would have stronger implications if overstable solar
g-modes should prove to have very large amplitudes, as has sometimes been
argued.Comment: 18 pages, 6 figures; misprints correcte
Anomalous resistivity resulting from electrostatic ion cyclotron turbulence
An expression is found for the collisionless electrical resistivity resulting from a current driven electrostatic ion cyclotron instability.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/21700/1/0000091.pd
Sexual assault services in the pandemic: Lessons learned
The COVID-19 pandemic created many risks for sexual assault and intimate partner violence, also termed the “shadow pandemic”. At the same time, it created challenges for sexual assault healthcare teams, counsellors and clients needing to access acute services. The purpose of this descriptive qualitative study was to identify those challenges for sexual assault service providers, the impact of these challenges on services, clients and team members, and identify lessons learned for future pandemics. The participants were professionals from across Canada who provided either counselling or healthcare services to clients after they experienced recent sexual assaults. Semi-structured interviews were used and then content analysis was conducted to identify themes and compare experiences. Common themes from both counselling and healthcare were identified, most notably that the initial lockdown messaging created risks for clients. Messaging stated to only come to Emergency if in urgent need and they minimized the importance of their assaults. Visit volume thus dropped for the first few months but resumed and even became higher than pre-pandemic in some communities. Healthcare staff struggled to be seen as an essential service initially, but those affiliated with Emergency departments were able to continue in-person examinations and treatment. The nurses noted that the clients who did come had more serious and life-threatening injuries such as strangulation attempts, more mental health issues, and more often were in the context of intimate partner violence.  
Eigenoscillations of the differentially rotating Sun: II. Generalization of Laplace's tidal equation
The general PDE governing linear, adiabatic, nonraradial oscillations in a
spherical, differentially and slowly rotating non-magnetic star is derived.
This equation describes mainly low-frequency and high-degree g-modes,
convective g-modes, and rotational Rossby-like vorticity modes and their mutual
interaction for arbitrarily given radial and latitudinal gradients of the
rotation rate. In "traditional approximation" the angular parts of the
eigenfunctions are described by Laplace's tidal equation generalized here to
take into account differential rotation. From a qualitative analysis of
Laplace's tidal equation the sufficient condition for the formation of the
dynamic shear latitudinal Kelvin-Helmholtz instability (LKHI) is obtained. The
exact solutions of Laplace's equation for low frequencies and rigid rotation
are obtained. There exists only a retrograde wave spectrum in this ideal case.
The modes are subdivided into two branches: fast and slow modes. The long fast
waves carry energy opposite to the rotation direction, while the shorter
slow-mode group velocity is in the azimuthal plane along the direction of
rotation. The eigenfuncions are expressed by Jacobi's polynomials which are
polynomials of higher order than the Legendre's for spherical harmonics. The
solar 22-year mode spectrum is calculated. It is shown that the slow 22-year
modes are concentrated around the equator, while the fast modes are around the
poles. The band of latitude where the mode energy is concentrated is narrow,
and the spatial place of these band depends on the wave numbers (l, m).Comment: 16 pages, 11 figures, to appear in Astronomy and Astrophysic
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