2,855 research outputs found
The democratic origins of the term "group analysis": Karl Mannheim's "third way" for psychoanalysis and social science.
It is well known that Foulkes acknowledged Karl Mannheim as the
first to use the term âgroup analysisâ. However, Mannheimâs work is
otherwise not well known. This article examines the foundations of
Mannheimâs sociological interest in groups using the Frankfurt
School (1929â1933) as a start point through to the brief correspondence
of 1945 between Mannheim and Foulkes (previously
unpublished). It is argued that there is close conjunction between
Mannheimâs and Foulkesâs revision of clinical psychoanalysis along
sociological lines. Current renderings of the Frankfurt School
tradition pay almost exclusive attention to the American connection
(Herbert Marcuse, Eric Fromm, Theodor Adorno and Max Horkheimer)
overlooking the contribution of the English connection through
the work of Mannheim and Foulkes
Test particle acceleration by rotating jet magnetospheres
Centrifugal acceleration of charged test particles at the base of a rotating
jet magnetosphere is considered. Based on an analysis of forces we derive the
equation for the radial accelerated motion and present an analytical solution.
It is shown that for particles moving outwards along rotating magnetic field
lines, the energy gain is in particular limited by the breakdown of the
bead-on-the-wire approximation which occurs in the vicinity of the light
cylinder . The corresponding upper limit for the maximum Lorentz factor
for electrons scales , with the
magnetic field strength at , and is at most of the order of a
for the conditions regarded to be typical for BL Lac objects. Such
values suggest that this mechanism may provide pre-accelerated seed particles
which are required for efficient Fermi-type particle acceleration at larger
scales in radio jets.Comment: 4 pages, 1 figure; to appear in the Proc. of the Heidelberg
International Symposium on High Energy Gamma-Ray Astronomy, Heidelberg, June
26-30, 2000, ed. by H.J. Voelk and F. Aharonian, AIP Conf. Pro
A possible black hole binary in Mkn 501
A simple binary model for Mkn~501 is considered under the assumption that the
TeV and X-ray periodicity of days, observed during the flaring state
in 1997, may be basically interpreted as a doppler-shifted flux modulation due
to the orbital motion of the relativistic jet. For the typical jet properties
inferred from emission models, we find an intrinsic orbital period of
yrs and a centre-of-mass distance of cm, the binary
thus being a very close system. If the binary separation corresponds to that at
which gravitational radiation becomes dominant, one may obtain a maximum
allowed primary mass of and a corresponding maximum
allowed secondary mass in the range of
assuming that gas accretion occurs on around the salpeter time scale.
Interestingly such values agree with the black hole masses expected from merger
scenarios.Comment: 4 pages, 2 figures; updated results of astro-ph/0005478; to appear in
the Proc. of the Heidelberg International Symposium on High Energy Gamma-Ray
Astronomy, Heidelberg, June 26-30, 2000, ed. by H.J. Voelk and F. Aharonian,
AIP Conf. Pro
Local and global gravity
Our long experience with Newtonian potentials has inured us to the view that
gravity only produces local effects. In this paper we challenge this quite
deeply ingrained notion and explicitly identify some intrinsically global
gravitational effects. In particular we show that the global cosmological
Hubble flow can actually modify the motions of stars and gas within individual
galaxies, and even do so in a way which can apparently eliminate the need for
galactic dark matter. Also we show that a classical light wave acquires an
observable, global, path dependent phase in traversing a gravitational field.
Both of these effects serve to underscore the intrinsic difference between
non-relativistic and relativistic gravity.Comment: LaTeX, 20 pages plus three figures in two postscript files. To appear
in a special issue of Foundations of Physics honoring Professor Lawrence
Horwitz on the occasion of his 65th birthday; A. van der Merwe and S. Raby,
Editors, Plenum Publishing Company, N.Y., 199
Light deflection in Weyl gravity: critical distances for photon paths
The Weyl gravity appears to be a very peculiar theory. The contribution of
the Weyl linear parameter to the effective geodesic potential is opposite for
massive and nonmassive geodesics. However, photon geodesics do not depend on
the unknown conformal factor, unlike massive geodesics. Hence light deflection
offers an interesting test of the Weyl theory.
In order to investigate light deflection in the setting of Weyl gravity, we
first distinguish between a weak field and a strong field approximation.
Indeed, the Weyl gravity does not turn off asymptotically and becomes even
stronger at larger distances.
We then take full advantage of the conformal invariance of the photon
effective potential to provide the key radial distances in Weyl gravity.
According to those, we analyze the weak and strong field regime for light
deflection. We further show some amazing features of the Weyl theory in the
strong regime.Comment: 20 pages, 9 figures (see published version for a better resolution,
or online version at stacks.iop.org/CQG/21/1897
Newtonian Limit of Conformal Gravity
We study the weak-field limit of the static spherically symmetric solution of
the locally conformally invariant theory advocated in the recent past by
Mannheim and Kazanas as an alternative to Einstein's General Relativity. In
contrast with the previous works, we consider the physically relevant case
where the scalar field that breaks conformal symmetry and generates fermion
masses is nonzero. In the physical gauge, in which this scalar field is
constant in space-time, the solution reproduces the weak-field limit of the
Schwarzschild--(anti)DeSitter solution modified by an additional term that,
depending on the sign of the Weyl term in the action, is either oscillatory or
exponential as a function of the radial distance. Such behavior reflects the
presence of, correspondingly, either a tachion or a massive ghost in the
spectrum, which is a serious drawback of the theory under discussion.Comment: 9 pages, comments and references added; the version to be published
in Phys. Rev.
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