83 research outputs found
Mean-Motion Resonances of High Order in Extrasolar Planetary Systems
Many multi-planet systems have been discovered in recent years. Some of them
are in mean-motion resonances (MMR). Planet formation theory was successful in
explaining the formation of 2:1, 3:1 and other low resonances as a result of
convergent migration. However, higher order resonances require high initial
orbital eccentricities in order to be formed by this process and these are in
general unexpected in a dissipative disk. We present a way of generating large
initial eccentricities using additional planets. This procedure allows us to
form high order MMRs and predict new planets using a genetic N-body code.Comment: To appear in Proceedings: Extrasolar Planets in Multi-body Systems:
Theory and Observations; Editors K. Gozdziewski, A. Niedzielski and J.
Schneider; 5 pages, 2 figures
Connecting the Holographic and Wilsonian Renormalization Groups
Inspired by the AdS/CFT correspondence, we develop an explicit formal duality
between the planar limit of a d-dimensional gauge theory and a classical field
theory in a (d+1)-dimensional anti-de Sitter space. The key ingredient is the
identification of fields in AdS with generalized Hubbard-Stratonovich
transforms of single-trace couplings of the QFT. We show that the Wilsonian
renormalization group flow of these transformed couplings matches the
holographic (Hamilton-Jacobi) flow of bulk fields along the radial direction in
AdS. This result allows one to outline an AdS/CFT dictionary that does not rely
on string theory.Comment: 11 pages, 1 figure; metadata modified in v2; added references and
minor changes in v3; v4 as published in JHE
Mindfulness based interventions in multiple sclerosis: a systematic review
<b>Background</b> Multiple sclerosis (MS) is a stressful condition; depression, anxiety, pain and fatigue are all common problems. Mindfulness based interventions (MBIs) mitigate stress and prevent relapse in depression and are increasingly being used in healthcare. However, there are currently no systematic reviews of MBIs in people with MS. This review aims to evaluate the effectiveness of MBIs in people with MS.<p></p>
<b>Methods</b> Systematic searches were carried out in seven major databases, using both subject headings and key words. Papers were screened, data extracted, quality appraised, and analysed by two reviewers independently, using predefined criteria. Study quality was assessed using the Cochrane Collaboration risk of bias tool. Perceived stress was the primary outcome. Secondary outcomes include mental health, physical health, quality of life, and health service utilisation. Statistical meta-analysis was not possible. Disagreements were adjudicated by a third party reviewer.<p></p>
<b>Results</b> Three studies (n = 183 participants) were included in the final analysis. The studies were undertaken in Wales (n = 16, randomised controlled trial - (RCT)), Switzerland (n = 150, RCT), and the United States (n = 17, controlled trial). 146 (80%) participants were female; mean age (SD) was 48.6 (9.4) years. Relapsing remitting MS was the main diagnostic category (n = 123, 67%); 43 (26%) had secondary progressive disease; and the remainder were unspecified. MBIs lasted 6–8 weeks; attrition rates were variable (5-43%); all employed pre- post- measures; two had longer follow up; one at 3, and one at 6 months. Socio-economic status of participants was not made explicit; health service utilisation and costs were not reported. No study reported on perceived stress. All studies reported quality of life (QOL), mental health (anxiety and depression), physical (fatigue, standing balance, pain), and psychosocial measures. Statistically significant beneficial effects relating to QOL, mental health, and selected physical health measures were sustained at 3- and 6- month follow up.<p></p>
<b>Conclusion</b> From the limited data available, MBIs may benefit some MS patients in terms of QOL, mental health, and some physical health measures. Further studies are needed to clarify how MBIs might best serve the MS population.<p></p>
Phase Structure and Compactness
In order to study the influence of compactness on low-energy properties, we
compare the phase structures of the compact and non-compact two-dimensional
multi-frequency sine-Gordon models. It is shown that the high-energy scaling of
the compact and non-compact models coincides, but their low-energy behaviors
differ. The critical frequency at which the sine-Gordon model
undergoes a topological phase transition is found to be unaffected by the
compactness of the field since it is determined by high-energy scaling laws.
However, the compact two-frequency sine-Gordon model has first and second order
phase transitions determined by the low-energy scaling: we show that these are
absent in the non-compact model.Comment: 21 pages, 5 figures, minor changes, final version, accepted for
publication in JHE
Rotation Curves of Spiral Galaxies
Rotation curves of spiral galaxies are the major tool for determining the
distribution of mass in spiral galaxies. They provide fundamental information
for understanding the dynamics, evolution and formation of spiral galaxies. We
describe various methods to derive rotation curves, and review the results
obtained. We discuss the basic characteristics of observed rotation curves in
relation to various galaxy properties, such as Hubble type, structure,
activity, and environment.Comment: 40 pages, 6 gif figures; Ann. Rev. Astron. Astrophys. Vol. 39, p.137,
200
Conjectures on exact solution of three - dimensional (3D) simple orthorhombic Ising lattices
We report the conjectures on the three-dimensional (3D) Ising model on simple
orthorhombic lattices, together with the details of calculations for a putative
exact solution. Two conjectures, an additional rotation in the fourth curled-up
dimension and the weight factors on the eigenvectors, are proposed to serve as
a boundary condition to deal with the topologic problem of the 3D Ising model.
The partition function of the 3D simple orthorhombic Ising model is evaluated
by spinor analysis, by employing these conjectures. Based on the validity of
the conjectures, the critical temperature of the simple orthorhombic Ising
lattices could be determined by the relation of KK* = KK' + KK'' + K'K'' or
sinh 2K sinh 2(K' + K'' + K'K''/K) = 1. For a simple cubic Ising lattice, the
critical point is putatively determined to locate exactly at the golden ratio
xc = exp(-2Kc) = (sq(5) - 1)/2, as derived from K* = 3K or sinh 2K sinh 6K = 1.
If the conjectures would be true, the specific heat of the simple orthorhombic
Ising system would show a logarithmic singularity at the critical point of the
phase transition. The spontaneous magnetization and the spin correlation
functions of the simple orthorhombic Ising ferromagnet are derived explicitly.
The putative critical exponents derived explicitly for the simple orthorhombic
Ising lattices are alpha = 0, beta = 3/8, gamma = 5/4, delta = 13/3, eta = 1/8
and nu = 2/3, showing the universality behavior and satisfying the scaling
laws. The cooperative phenomena near the critical point are studied and the
results obtained based on the conjectures are compared with those of the
approximation methods and the experimental findings. The 3D to 2D crossover
phenomenon differs with the 2D to 1D crossover phenomenon and there is a
gradual crossover of the exponents from the 3D values to the 2D ones.Comment: 176 pages, 4 figure
Truncation Effects in the Functional Renormalization Group Study of Spontaneous Symmetry Breaking
We study the occurrence of spontaneous symmetry breaking (SSB) for O (N) models using functional renormalization group techniques. We show that even the local potential approximation (LPA) when treated exactly is sufficient to give qualitatively correct results for systems with continuous symmetry, in agreement with the Mermin-Wagner theorem and its extension to systems with fractional dimensions. For general N (including the Ising model N = 1) we study the solutions of the LPA equations for various truncations around the zero field using a finite number of terms (and different regulators), showing that SSB always occurs even where it should not. The SSB is signalled by Wilson-Fisher fixed points which for any truncation are shown to stay on the line defined by vanishing mass beta functions
The Influence of Mindful Attention on Value Claiming in Distributive Negotiations: Evidence from Four Laboratory Experiments
The expansion field: The value of H_0
Any calibration of the present value of the Hubble constant requires
recession velocities and distances of galaxies. While the conversion of
observed velocities into true recession velocities has only a small effect on
the result, the derivation of unbiased distances which rest on a solid zero
point and cover a useful range of about 4-30 Mpc is crucial. A list of 279 such
galaxy distances within v<2000 km/s is given which are derived from the tip of
the red-giant branch (TRGB), from Cepheids, and from supernovae of type Ia (SNe
Ia). Their random errors are not more than 0.15 mag as shown by
intercomparison. They trace a linear expansion field within narrow margins from
v=250 to at least 2000 km/s. Additional 62 distant SNe Ia confirm the linearity
to at least 20,000 km/s. The dispersion about the Hubble line is dominated by
random peculiar velocities, amounting locally to <100 km/s but increasing
outwards. Due to the linearity of the expansion field the Hubble constant H_0
can be found at any distance >4.5 Mpc. RR Lyr star-calibrated TRGB distances of
78 galaxies above this limit give H_0=63.0+/-1.6 at an effective distance of 6
Mpc. They compensate the effect of peculiar motions by their large number.
Support for this result comes from 28 independently calibrated Cepheids that
give H_0=63.4+/-1.7 at 15 Mpc. This agrees also with the large-scale value of
H_0=61.2+/-0.5 from the distant, Cepheid-calibrated SNe Ia. A mean value of
H_0=62.3+/-1.3 is adopted. Because the value depends on two independent zero
points of the distance scale its systematic error is estimated to be 6%.
Typical errors of H_0 come from the use of a universal, yet unjustified P-L
relation of Cepheids, the neglect of selection bias in magnitude-limited
samples, or they are inherent to the adopted models.Comment: 44 pages, 4 figures, 6 tables, accepted for publication in the
Astronony and Astrophysics Review 15
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