27,954 research outputs found
Tidal interactions of a Maclaurin spheroid. I: Properties of free oscillation modes
We review the work of Bryan (1889) on the normal modes of a Maclaurin
spheroid, carrying out numerical calculations of the frequencies and spatial
forms of these modes that have not been previously published. We study all
modes of degree , which includes both inertial modes and surface
gravity modes, with the aim of better understanding the effect of rapid
rotation on tidal interactions. The inclusion of these higher degree modes
greatly increases the number of frequencies at which tidal resonances may
occur. We derive an expression for the decay rates of these modes to first
order in viscosity and explicitly plot these for modes. We see that the
equatorial bulge of the spheroid has a significant effect on the decay rates
(changing some of these by a factor of 2 between an eccentricity of and
), and a more modest effect on the mode frequencies. This suggests that
models of tidal interaction between rapidly rotating stars and giant planets
that model the Coriolis force while neglecting the centrifugal distortion of
the body may be in error by an order unity factor. In a subsequent paper we
shall examine the case of a forced flow in this spheroid, and complete the
model by considering how the tides raised by the orbiting companion change the
orbital elements.Comment: 27 pages, 39 figures, 1 table, accepted for publication in MNRA
The Auslander-Gorenstein property for Z-algebras
We provide a framework for part of the homological theory of Z-algebras and
their generalizations, directed towards analogues of the Auslander-Gorenstein
condition and the associated double Ext spectral sequence that are useful for
enveloping algebras of Lie algebras and related rings. As an application, we
prove the equidimensionality of the characteristic variety of an irreducible
representation of the Z-algebra, and for related representations over quantum
symplectic resolutions. In the special case of Cherednik algebras of type A,
this answers a question raised by the authors.Comment: 31 page
Differential operators and Cherednik algebras
We establish a link between two geometric approaches to the representation
theory of rational Cherednik algebras of type A: one based on a noncommutative
Proj construction, used in [GS]; the other involving quantum hamiltonian
reduction of an algebra of differential operators, used in [GG].
In the present paper, we combine these two points of view by showing that the
process of hamiltonian reduction intertwines a naturally defined geometric
twist functor on D-modules with the shift functor for the Cherednik algebra.
That enables us to give a direct and relatively short proof of the key result,
[GS, Theorem 1.4] without recourse to Haiman's deep results on the n! theorem.
We also show that the characteristic cycles defined independently in these two
approaches are equal, thereby confirming a conjecture from [GG].Comment: 37 p
Bangladesh Environmental Enteric Dysfunction (BEED) study: Protocol for a community-based intervention study to validate non-invasive biomarkers of environmental enteric dysfunction
Being well, being musical: Music composition as a resource and occupation for older people
Introduction: Participatory music making for older people has tended to focus on singing and performance. In a community music project undertaken by Manchester Camerata (a chamber orchestra), Blacon Community Trust and a small group of older adults, participants were given the opportunity to compose individual pieces of music interactively with professional musicians. This paper reports the findings of the research project. Method: An arts-based research method was adopted and incorporated action research and interpretive interactionism to articulate the experiences and perceptions of participants. Participants and Manchester Camerata musicians also worked together to represent the thematic findings of the research in a group composition. Findings: The findings demonstrate that individual and group music composition contributed to a sense of wellbeing through control over musical materials, opportunities for creativity and identity making, validation of life experience and social engagement with other participants and professional musicians. Conclusion: The results emphasised occupation as essential to health and wellbeing in the later stages of life. The findings also highlight the particularly innovative aspects of this research: (i) the use of music composition as a viable arts-in-health occupation for older people and (ii) the arts-based research method of group composition
The Spectrum of Topologically Massive Quantum Electrodynamics
We discuss the possibility for the spectrum of topologically massive quantum
electrodynamics with spinor matter fields to contain unexpected and unusual
stable particle excitations for certain values of the topological photon mass.
The new field theoretical phenomena arising from this novel spectral structure
are briefly discussed.Comment: 14 pages, plain TeX; PUPT-1364, UBCTP 92-03
Effects of Magnetic Braking and Tidal Friction on Hot Jupiters
Tidal friction is thought to be important in determining the long-term
spin-orbit evolution of short-period extrasolar planetary systems. Using a
simple model of the orbit-averaged effects of tidal friction Eggleton, Kiseleva
& Hut (1998), we analyse the effects of the inclusion of stellar magnetic
braking on the evolution of such systems. A phase-plane analysis of a
simplified system of equations, including only the stellar tide together with a
model of the braking torque proposed by Verbunt & Zwaan (1981), is presented.
The inclusion of stellar magnetic braking is found to be extremely important in
determining the secular evolution of such systems, and its neglect results in a
very different orbital history. We then show the results of numerical
integrations of the full tidal evolution equations, using the misaligned spin
and orbit of the XO-3 system as an example, to study the accuracy of simple
timescale estimates of tidal evolution. We find that it is essential to
consider coupled evolution of the orbit and the stellar spin in order to model
the behaviour accurately. In addition, we find that for typical Hot Jupiters
the stellar spin-orbit alignment timescale is of the same order as the inspiral
time, which tells us that if a planet is observed to be aligned, then it
probably formed coplanar. This reinforces the importance of Rossiter-McLaughlin
effect observations in determining the degree of spin-orbit alignment in
transiting systems.Comment: 6 pages, 2 figures, to appear in IAU 259 Conference Proceeding
Enhanced Molecular Orientation Induced by Molecular Anti-Alignment
We explore the role of laser induced anti-alignment in enhancing molecular
orientation. A field-free enhanced orientation via anti-alignment scheme is
presented, which combines a linearly polarized femtosecond laser pulse with a
half-cycle pulse. The laser pulse induces transient anti-alignment in the plane
orthogonal to the field polarization, while the half-cycle pulse leads to the
orientation. We identify two qualitatively different enhancement mechanisms
depending on the pulse order, and optimize their effects using classical and
quantum models both at zero and non-zero temperature
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