4,130 research outputs found
Time-scales of close-in exoplanet radio emission variability
We investigate the variability of exoplanetary radio emission using stellar
magnetic maps and 3D field extrapolation techniques. We use a sample of hot
Jupiter hosting stars, focusing on the HD 179949, HD 189733 and tau Boo
systems. Our results indicate two time-scales over which radio emission
variability may occur at magnetised hot Jupiters. The first is the synodic
period of the star-planet system. The origin of variability on this time-scale
is the relative motion between the planet and the interplanetary plasma that is
co-rotating with the host star. The second time-scale is the length of the
magnetic cycle. Variability on this time-scale is caused by evolution of the
stellar field. At these systems, the magnitude of planetary radio emission is
anticorrelated with the angular separation between the subplanetary point and
the nearest magnetic pole. For the special case of tau Boo b, whose orbital
period is tidally locked to the rotation period of its host star, variability
only occurs on the time-scale of the magnetic cycle. The lack of radio
variability on the synodic period at tau Boo b is not predicted by previous
radio emission models, which do not account for the co-rotation of the
interplanetary plasma at small distances from the star.Comment: 10 pages, 7 figures, 2 tables, accepted in MNRA
When Statutory Regimes Collide:Will Wisconsin Right to Life and Citizens United Invalidate Federal Tax Regulation of Campaign Activity?
In Federal Election Commission v. Wisconsin Right to Life (2007) and Citizens United v. Federal Elections Commission (2010), the United States Supreme Court dramatically reduced the ability of Congress to regulate campaign finance activities of corporations and others active in elections. Many of the same activities are still subject to restrictions by the Internal Revenue Code, which regulates the type and amount of political campaign activities that certain nonprofits exempt under federal tax law can engage in.
In the wake of the campaign finance decisions, the constitutionality of the tax lawâs restrictions on campaign activity is now being challenged in the lower courts. This Article analyzes the two recent campaign finance decisions and campaign finance precedents more broadly to determine how, if at all, the Robertsâ Courtâs campaign finance jurisprudence is likely to alter existing tax law jurisprudence in the area of campaign activity. It finds that, for the most part, tax law constitutional doctrines have developed independently of other areas of First Amendment free speech law. Based upon an analysis of the distinctive tax law doctrines, the Article concludes that the tax law provision prohibiting section 501(c)(3) charities from engaging in campaigns is likely to withstand challenges arguing that the provision prevents these nonprofits from engaging in protected political speech. However, there is some likelihood that the tax law prohibition is vulnerable to constitutional attack under traditional doctrines of vagueness or overbreadth due to the lack of precision of the terms of the political prohibition, as these have been elaborated by the IRS and the courts to date
A new orthogonalization procedure with an extremal property
Various methods of constructing an orthonomal set out of a given set of
linearly independent vectors are discussed. Particular attention is paid to the
Gram-Schmidt and the Schweinler-Wigner orthogonalization procedures. A new
orthogonalization procedure which, like the Schweinler- Wigner procedure, is
democratic and is endowed with an extremal property is suggested.Comment: 7 pages, latex, no figures, To appear in J. Phys
The Chagos Islands cases: the empire strikes back
Good governance requires the accommodation of multiple interests in the cause of decision making. However, undue regard for particular sectional interests can take their toll upon public faith in government administration. Historically, broad conceptions of the good of the commonwealth were employed to outweigh the interests of groups that resisted colonisation. In the decision making of the British Empire, the standard approach for justifying the marginalisation of the interests of colonised groups was that they were uncivilised and that particular hardships were the price to be paid for bringing to them the imperial dividend of industrial society. It is widely assumed that with the dismantling of the British Empire, such impulses and their accompanying jurisprudence became a thing of the past. Even as decolonisation proceeded apace after the Second World War, however, the United Kingdom maintained control of strategically important islands with a view towards sustaining its global role. In an infamous example from this twilight period of empire, in the 1960s imperial interests were used to justify the expulsion of the Chagos islanders from the British Indian Ocean Territory (BIOT). Into the twenty-first century, this forced elision of the UKâs interests with the imperial âcommon goodâ continues to take centre stage in courtroom battles over the islandersâ rights, being cited before domestic and international tribunals in order to maintain the Chagossiansâ exclusion from their homeland. This article considers the new jurisprudence of imperialism which has emerged in a string of decisions which have continued to marginalise the Chagossiansâ interests
On the gravitational field of static and stationary axial symmetric bodies with multi-polar structure
We give a physical interpretation to the multi-polar Erez-Rozen-Quevedo
solution of the Einstein Equations in terms of bars. We find that each
multi-pole correspond to the Newtonian potential of a bar with linear density
proportional to a Legendre Polynomial. We use this fact to find an integral
representation of the function. These integral representations are
used in the context of the inverse scattering method to find solutions
associated to one or more rotating bodies each one with their own multi-polar
structure.Comment: To be published in Classical and Quantum Gravit
One-loop Beta Functions for the Orientable Non-commutative Gross-Neveu Model
We compute at the one-loop order the beta-functions for a renormalisable
non-commutative analog of the Gross Neveu model defined on the Moyal plane. The
calculation is performed within the so called x-space formalism. We find that
this non-commutative field theory exhibits asymptotic freedom for any number of
colors. The beta-function for the non-commutative counterpart of the Thirring
model is found to be non vanishing.Comment: 16 pages, 9 figure
The effects of stellar winds on the magnetospheres and potential habitability of exoplanets
Context: The principle definition of habitability for exoplanets is whether
they can sustain liquid water on their surfaces, i.e. that they orbit within
the habitable zone. However, the planet's magnetosphere should also be
considered, since without it, an exoplanet's atmosphere may be eroded away by
stellar winds. Aims: The aim of this paper is to investigate magnetospheric
protection of a planet from the effects of stellar winds from solar-mass stars.
Methods: We study hypothetical Earth-like exoplanets orbiting in the host
star's habitable zone for a sample of 124 solar-mass stars. These are targets
that have been observed by the Bcool collaboration. Using two wind models, we
calculate the magnetospheric extent of each exoplanet. These wind models are
computationally inexpensive and allow the community to quickly estimate the
magnetospheric size of magnetised Earth-analogues orbiting cool stars. Results:
Most of the simulated planets in our sample can maintain a magnetosphere of ~5
Earth radii or larger. This suggests that magnetised Earth analogues in the
habitable zones of solar analogues are able to protect their atmospheres and is
in contrast to planets around young active M dwarfs. In general, we find that
Earth-analogues around solar-type stars, of age 1.5 Gyr or older, can maintain
at least a Paleoarchean Earth sized magnetosphere. Our results indicate that
planets around 0.6 - 0.8 solar-mass stars on the low activity side of the
Vaughan-Preston gap are the optimum observing targets for habitable Earth
analogues.Comment: 8 pages, 3 figures, accepted to Astronomy and Astrophysic
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