53,786 research outputs found
Exact General Solutions to Extraordinary N-body Problems
We solve the N-body problems in which the total potential energy is any
function of the mass-weighted root-mean-square radius of the system of N point
masses. The fundamental breathing mode of such systems vibrates non-linearly
for ever. If the potential is supplemented by any function that scales as the
inverse square of the radius there is still no damping of the fundamental
breathing mode. For such systems a remarkable new statistical equilibrium is
found for the other coordinates and momenta, which persists even as the radius
changes continually.Comment: 15 pages, LaTeX. Accepted for publication in Proc. Roy. Soc.
Relaxation to a Perpetually Pulsating Equilibrium
Paper in honour of Freeman Dyson on the occasion of his 80th birthday.
Normal N-body systems relax to equilibrium distributions in which classical
kinetic energy components are 1/2 kT, but, when inter-particle forces are an
inverse cubic repulsion together with a linear (simple harmonic) attraction,
the system pulsates for ever. In spite of this pulsation in scale, r(t), other
degrees of freedom relax to an ever-changing Maxwellian distribution. With a
new time, tau, defined so that r^2d/dt =d/d tau it is shown that the remaining
degrees of freedom evolve with an unchanging reduced Hamiltonian. The
distribution predicted by equilibrium statistical mechanics applied to the
reduced Hamiltonian is an ever-pulsating Maxwellian in which the temperature
pulsates like r^-2. Numerical simulation with 1000 particles demonstrate a
rapid relaxation to this pulsating equilibrium.Comment: 9 pages including 4 figure
Quadrature domains and kernel function zipping
It is proved that quadrature domains are ubiquitous in a very strong sense in
the realm of smoothly bounded multiply connected domains in the plane. In fact,
they are so dense that one might as well assume that any given smooth domain
one is dealing with is a quadrature domain, and this allows access to a host of
strong conditions on the classical kernel functions associated to the domain.
Following this string of ideas leads to the discovery that the Bergman kernel
can be zipped down to a strikingly small data set. It is also proved that the
kernel functions associated to a quadrature domain must be algebraic.Comment: 13 pages, to appear in Arkiv for matemati
Bell's inequality and the coincidence-time loophole
This paper analyzes effects of time-dependence in the Bell inequality. A
generalized inequality is derived for the case when coincidence and
non-coincidence [and hence whether or not a pair contributes to the actual
data] is controlled by timing that depends on the detector settings. Needless
to say, this inequality is violated by quantum mechanics and could be violated
by experimental data provided that the loss of measurement pairs through
failure of coincidence is small enough, but the quantitative bound is more
restrictive in this case than in the previously analyzed "efficiency loophole."Comment: revtex4, 3 figures, v2: epl document class, reformatted w slight
change
The Structure of the Outer Halo of the Galaxy and its Relationship to Nearby Large-Scale Structure
We present evidence to support an earlier indication that the Galaxy is
embedded in an extended, highly inclined, triaxial halo outlined by the spatial
distribution of companion galaxies to the Milky Way. Signatures of this spatial
distribution are seen in 1) the angular variation of the radial-velocity
dispersion of the companion galaxies, 2) the spatial distribution of the M~31
sub-group of galaxies, 3) the spatial distribution of the isolated, mainly
dwarf irregular, galaxies of the Local Group, 4) the velocity anisotropy
quadrupole of a sub-group of high-velocity clouds, and 5) the spatial
distribution of galaxies in the Coma-Sculptor cloud. Tidal effects of M~31 and
surrounding galaxies on the Galaxy are not strong enough to have affected the
observed structure. We conclude that this distribution is a reflection of
initial conditions. A simple galaxy formation scenario is proposed which ties
together the results found here with those of Holmberg (1969) and Zaritsky et
al. (1997) on the peculiar distribution of satellites around a large sample of
spiral galaxies.Comment: Accepted for publication in the Astron J., March 2000, 12 pages with
1 figur
Developing future energy performance standards for UK housing: The St Nicholas Court project – Part 1
This paper (and Part 2, to appear in the next issue) set out the results of a housing field trial designed to evaluate the impact of an enhanced energy performance standard for dwellings. The project was designed to inform the next review of Part L of the Building Regulations for England and Wales, which, following the publication of the UK government's white paper on energy policy, is expected in 2005. The project explores the implications of an enhanced standard in the context of timber frame construction. Although for programming reasons it was necessary to terminate the research project at the end of the design phase, the results suggest that the standard investigated is well within the capacity of the industry but it was clear that the whole supply chain will need to take a positive approach to the development of new solutions. The secret to a smooth and cost optimised transition is for the necessary development work to begin immediately, not when regulation changes. © 2003, MCB UP Limite
Influence of psychological coping on survival and recurrence in people with cancer: systematic review
OBJECTIVE: To summarise the evidence on the effect of psychological coping styles (including fighting spirit, helplessness/hopelessness, denial, and avoidance) on survival and recurrence in patients with cancer. DESIGN: Systematic review of published and unpublished prospective observational studies. MAIN OUTCOMES MEASURES: Survival from or recurrence of cancer. RESULTS: 26 studies investigated the association between psychological coping styles and survival from cancer, and 11 studies investigated recurrence. Most of the studies that investigated fighting spirit (10 studies) or helplessness/hopelessness (12 studies) found no significant associations with survival or recurrence. The evidence that other coping styles play an important part was also weak. Positive findings tended to be confined to small or methodologically flawed studies; lack of adjustment for potential confounding variables was common. Positive conclusions seemed to be more commonly reported by smaller studies, indicating potential publication bias. CONCLUSION: There is little consistent evidence that psychological coping styles play an important part in survival from or recurrence of cancer. People with cancer should not feel pressured into adopting particular coping styles to improve survival or reduce the risk of recurrence. [References: 42
An inverse method for the aerodynamic design of three-dimensional aircraft engine nacelles
A fast, efficient and user friendly inverse design system for 3-D nacelles was developed. The system is a product of a 2-D inverse design method originally developed at NASA-Langley and the CFL3D analysis code which was also developed at NASA-Langley and modified for nacelle analysis. The design system uses a predictor/corrector design approach in which an analysis code is used to calculate the flow field for an initial geometry, the geometry is then modified based on the difference between the calculated and target pressures. A detailed discussion of the design method, the process of linking it to the modified CFL3D solver and its extension to 3-D is presented. This is followed by a number of examples of the use of the design system for the design of both axisymmetric and 3-D nacelles
The Nearest Group of Galaxies
The small Antlia-Sextans clustering of galaxies is located at a distance of
only 1.36 Mpc from the Sun, and 1.72 Mpc from the adopted barycenter of the
Local Group. The latter value is significantly greater than the radius of the
zero- velocity surface of the Local Group which, for an assumed age of 14 Gyr,
has Ro = 1.18 " 0.15 Mpc. This, together with the observation that the members
of the Ant-Sex group have a mean redshift of +114 " 12 km s-1 relative to the
centroid of the Local Group, suggests that the Antlia-Sextans group is not
bound to our Local Group, and that it is expanding with the Hubble flow. If
this conclusion is correct, then Antlia-Sextans may be the nearest external
clustering of galaxies. The total galaxian population of the Ant-Sex group is ~
1/5 that of the Local Group. However, the integrated luminosity of Ant-Sex is
two orders of magnitude lower than that of the Local Group.
Subject headings: Galaxies - clusters: individual (Antlia-Sextans)Comment: Has been accepted for publication in the Astrophysical Journal
Letter
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