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

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

Proposed mechanisms for bariatric surgery-induced improvement and resolution of clinical manifestations of type II diabetes

At the 2nd Diabetes Surgical Summit in 2015, the world’s leading researchers and professionals in the field of diabetes, surgery, and public health gathered to develop new surgical treatment guidelines for diabetes. This summit led to the recommendation of bariatric surgery as an official treatment for type II diabetes, outlining that the surgery be considered for diabetic patients with a Body Mass Index (BMI) of 30, a much lower threshold BMI than that of typical bariatric surgery patients. Despite incontrovertible evidence that bariatric surgery can reverse the progression of diabetes and even cause remission, the physiological mechanisms chiefly responsible for these effects remain controversial. Peer-reviewed published literature was collected to examine the evidence for mechanisms responsible for metabolic improvements following bariatric surgery, especially Roux-en-Y gastric bypass. This review considered the effects of calorie restriction, appetite modulators, incretins, intestinal adaptations, adipose tissue, gut microbiota, bile acid circulation and composition, and psychosocial and behavioral changes on surgery-induced metabolic improvements and sustained type II diabetes remission. Clinical considerations, such as the surgical risks and improved indicators for bariatric surgery were also explored to contextualize the physiological mechanisms under study. The “hind gut hypothesis” emerged as an important overarching mechanism potentially responsible for many of the observed improvements. The more rapid delivery of food to the distal intestine, as well as the delayed mixing of pancreatic, gastric and bile secretions with food, likely contributes to increased nutrient-stimulation of enteroendocrine cells and greater binding of bile acids with their receptors, farnesoid X receptor and TGR5. These changes in food and secretion delivery also appear to positively affect the gut microbiota to support a non-obese microbiota profile. Calorie restriction may be responsible for the early effects of bariatric surgery, including not just a reduction in fat mass but also epigenetic changes to induce β-cell proliferation and increased insulin secretion. However, long-term benefits of bariatric surgery appear to be more closely correlated to enteroendocrine changes, including the surgery-induced changes to levels of appetite modulators that, unlike pure calorie restriction, promote feelings of satiation and reduce rates of diet failure and weight regain. Fat distribution and adipocyte function are also important contributors to both the pathophysiology of obesity-related diabetes and improvements following bariatric surgery. While reductions in BMI and subcutaneous adipose tissue area were not correlated to diabetes remission, reductions in visceral adipose tissue area and enhanced adiponectin secretions were both independent factors associated with diabetes remission. The important role of adipocytes as endocrine organs has emerged as an important field of inquiry. Adipokines, adipocyte hormones, may either promote a pro-inflammatory profile or an anti-inflammatory profile, impacting the development of obesity-related diabetes or diabetes remission, respectively. The findings of this review support the 2nd Diabetes Surgical Summit’s recommendations of proactive bariatric surgery as a treatment for diabetes. The risks of complications and mortality following bariatric surgery are low, whereas the long-term survival after bariatric surgery is improved relative to non-surgical, matched controls. Single-nucleotide polymorphisms associated with obesity and diabetes may serve as early indicators for surgery, and inform both surgical method and follow-up protocols. Despite the benefits of bariatric surgery, only a small number of eligible candidates undergo treatment. In the United States, barriers such as physician and patient perceptions and cost may limit access to surgery. In places that experience a health workforce shortage, there may be no health care professionals or facilities available to perform bariatric surgery. Therefore, while the surgery amazingly causes diabetes remission, one of its greatest benefits may be to continue to inform the mechanisms responsible for metabolic improvements toward developing new pharmacological treatments. In the future, less invasive drug treatments that seek to replicate the effects of bariatric surgery may be more successful in tackling the global obesity and diabetes crisis

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

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

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

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

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