2,725 research outputs found
IMPACTS OF MAPLE SYRUP GRADING LAWS ON THE MAPLE PRODUCING REGIONS OF UNITED STATES AND CANADA
Agricultural and Food Policy,
A Predicted Small and Round Heliosphere
The shape of the solar wind bubble within the interstellar medium, the
so-called heliosphere, has been explored over six decades. As the Sun moves
through the surrounding partially-ionized medium, neutral hydrogen atoms
penetrate the heliosphere, and through charge-exchange with the supersonic
solar wind, create a population of hot pick-up ions (PUIs). The Termination
Shock (TS) crossing by Voyager 2 (V2) data demonstrated that the heliosheath
(HS) (the region of shocked solar wind) pressure is dominated by suprathermal
particles. Here we use a novel magnetohydrodynamic model that treats the
freshly ionized PUIs as a separate fluid from the thermal component of the
solar wind. Unlike previous models, the new model reproduces the properties of
the PUIs and solar wind ions based on the New Horizon and V2 spacecraft
observations. The PUIs charge exchange with the cold neutral H atoms of the ISM
in the HS and are quickly depleted. The depletion of PUIs cools the heliosphere
downstream of the TS, "deflating" it and leading to a narrower HS and a smaller
and rounder shape, in agreement with energetic neutral atom observations by the
Cassini spacecraft. The new model, with interstellar magnetic field orientation
constrained by the IBEX ribbon, reproduces the magnetic field data outside the
HP at Voyager 1(V1). We present the predictions for the magnetic field outside
the HP at V2.Comment: submitted to publication - new version after revie
A predicted small and round heliosphere
The shape of the solar wind bubble within the interstellar medium, the so-called heliosphere, has been explored over six decades(1-7). As the Sun moves through the surrounding partially-ionized medium, neutral hydrogen atoms penetrate the heliosphere, and through charge-exchange with the supersonic solar wind, create a population of hot pick-up ions (PUIs). The Voyager 2 (V2) data demonstrated that the heliosheath pressure is dominated by PUIs. Here we use a novel magnetohydrodynamic model that treats the PUIs as a separate fluid from the thermal component of the solar wind. Unlike previous models (8-10), the new model reproduces the properties of the PUIs and solar wind ions based on the New Horizon(11) and V2(12) spacecraft observations. The model significantly changes the energy flow in the outer heliosphere, leading to a smaller and rounder shape than previously predicted, in agreement with energetic neutral atom observations by the Cassini spacecraft.Accepted manuscrip
Recommended from our members
Appropriate (or be appropriated by) academic discourse: There is a text in this class
Globally Distributed Energetic Neutral Atom Maps for the "Croissant" Heliosphere
A recent study by Opher et al. (2015) suggested the heliosphere has a
"croissant" shape, where the heliosheath plasma is confined by the toroidal
solar magnetic field. The "croissant" heliosphere is in contrast to the
classically accepted view of a comet-like tail. We investigate the effect of
the "croissant" heliosphere model on energetic neutral atom (ENA) maps.
Regardless of the existence of a split tail, the confinement of the heliosheath
plasma should appear in ENA maps. ENA maps from the Interstellar Boundary
Explorer (IBEX) have shown two high latitude lobes with excess ENA flux at
higher energies in the tail of the heliosphere. These lobes could be a
signature of the confinement of the heliosheath plasma, while some have argued
they are caused by the fast/slow solar wind profile. Here we present ENA maps
of the "croissant" heliosphere, focusing on understanding the effect of the
heliosheath plasma collimation by the solar magnetic field while using a
uniform solar wind. We incorporate pick-up ions (PUIs) into our model based on
Malama et al. (2006) and Zank et al. (2010). We use the neutral solution from
our MHD model to determine the angular variation of the PUIs, and include the
extinction of PUIs in the heliosheath. In the presence of a uniform solar wind,
we find that the collimation in the "croissant" heliosphere does manifest
itself into two high latitude lobes of increased ENA flux in the downwind
direction.Comment: 14 pages, 1 table, 7 figures, Accepted for publication in Ap
A Bayesian approach for energy-based estimation of acoustic aberrations in high intensity focused ultrasound treatment
High intensity focused ultrasound is a non-invasive method for treatment of
diseased tissue that uses a beam of ultrasound to generate heat within a small
volume. A common challenge in application of this technique is that
heterogeneity of the biological medium can defocus the ultrasound beam. Here we
reduce the problem of refocusing the beam to the inverse problem of estimating
the acoustic aberration due to the biological tissue from acoustic radiative
force imaging data. We solve this inverse problem using a Bayesian framework
with a hierarchical prior and solve the inverse problem using a
Metropolis-within-Gibbs algorithm. The framework is tested using both synthetic
and experimental datasets. We demonstrate that our approach has the ability to
estimate the aberrations using small datasets, as little as 32 sonication
tests, which can lead to significant speedup in the treatment process.
Furthermore, our approach is compatible with a wide range of sonication tests
and can be applied to other energy-based measurement techniques
- …