458 research outputs found
A Geometrical Characterization of the Twin Paradox and its Variants
The aim of this paper is to provide a logic-based conceptual analysis of the
twin paradox (TwP) theorem within a first-order logic framework. A geometrical
characterization of TwP and its variants is given. It is shown that TwP is not
logically equivalent to the assumption of the slowing down of moving clocks,
and the lack of TwP is not logically equivalent to the Newtonian assumption of
absolute time. The logical connection between TwP and a symmetry axiom of
special relativity is also studied.Comment: 22 pages, 3 figure
Gauge conditions for binary black hole puncture data based on an approximate helical Killing vector
We show that puncture data for quasicircular binary black hole orbits allow a
special gauge choice that realizes some of the necessary conditions for the
existence of an approximate helical Killing vector field. Introducing free
parameters for the lapse at the punctures we can satisfy the condition that the
Komar and ADM mass agree at spatial infinity. Several other conditions for an
approximate Killing vector are then automatically satisfied, and the 3-metric
evolves on a timescale smaller than the orbital timescale. The time derivative
of the extrinsic curvature however remains significant. Nevertheless,
quasicircular puncture data are not as far from possessing a helical Killing
vector as one might have expected.Comment: 11 pages, 6 figures, 2 table
Binary black hole initial data for numerical general relativity based on post-Newtonian data
With the goal of taking a step toward the construction of astrophysically
realistic initial data for numerical simulations of black holes, we for the
first time derive a family of fully general relativistic initial data based on
post-2-Newtonian expansions of the 3-metric and extrinsic curvature without
spin. It is expected that such initial data provide a direct connection with
the early inspiral phase of the binary system. We discuss a straightforward
numerical implementation, which is based on a generalized puncture method.
Furthermore, we suggest a method to address some of the inherent ambiguity in
mapping post-Newtonian data onto a solution of the general relativistic
constraints.Comment: 13 pages, 8 figures, RevTex
Sporting embodiment: sports studies and the (continuing) promise of phenomenology
Whilst in recent years sports studies have addressed the calls ‘to bring the body back in’ to theorisations of sport and physical activity, the ‘promise of phenomenology’ remains largely under-realised with regard to sporting embodiment. Relatively few accounts are grounded in the ‘flesh’ of the lived sporting body, and phenomenology offers a powerful framework for such analysis. A wide-ranging, multi-stranded, and interpretatively contested perspective, phenomenology in general has been taken up and utilised in very different ways within different disciplinary fields. The purpose of this article is to consider some selected phenomenological threads, key qualities of the phenomenological method, and the potential for existentialist phenomenology in particular to contribute fresh perspectives to the sociological study of embodiment in sport and exercise. It offers one way to convey the ‘essences’, corporeal immediacy and textured sensuosity of the lived sporting body. The use of Interpretative Phenomenological Analysis (IPA) is also critically addressed.
Key words: phenomenology; existentialist phenomenology; interpretative phenomenological analysis (IPA); sporting embodiment; the lived-body; Merleau-Pont
Realistic Model of the Nucleon Spectral Function in Few- and Many- Nucleon Systems
By analysing the high momentum features of the nucleon momentum distribution
in light and complex nuclei, it is argued that the basic two-nucleon
configurations generating the structure of the nucleon Spectral Function at
high values of the nucleon momentum and removal energy, can be properly
described by a factorised ansatz for the nuclear wave function, which leads to
a nucleon Spectral Function in the form of a convolution integral involving the
momentum distributions describing the relative and center-of-mass motion of a
correlated nucleon-nucleon pair embedded in the medium. The Spectral Functions
of and infinite nuclear matter resulting from the convolution formula
and from many-body calculations are compared, and a very good agreement in a
wide range of values of nucleon momentum and removal energy is found.
Applications of the model to the analysis of inclusive and exclusive processes
are presented, illustrating those features of the cross section which are
sensitive to that part of the Spectral Function which is governed by
short-range and tensor nucleon-nucleon correlations.Comment: 40 pages Latex , 16 ps figures available from the above e-mail
address or from [email protected]
Making sense of leadership development: Developing a community of education leaders
In education literature there is a distinct lack of scholarly work on issues of leadership other than on functional leadership at lower levels or high-level individual leadership activity which dominates existing studies. This empirical research is based on the result of a merger of education providers within the North East of England. A crucial aspiration of the newly merged organisation was to provide an overarching innovative leadership structure to facilitate integrated leadership. The specific focus of this article is participants of a bespoke postgraduate learning intervention. The authors apply sense-making theory to identify how student-leaders undertaking a leadership development
intervention developed to become a community of education leaders. The reflective accounts of the student-leaders indicated a combined approach of distributed, shared and collaborative leadership. Whilst the study was conducted in the UK, the concepts and ideas are likely to have international application
Variational description of multi-fluid hydrodynamics: Uncharged fluids
We present a formalism for Newtonian multi-fluid hydrodynamics derived from
an unconstrained variational principle. This approach provides a natural way of
obtaining the general equations of motion for a wide range of hydrodynamic
systems containing an arbitrary number of interacting fluids and superfluids.
In addition to spatial variations we use ``time shifts'' in the variational
principle, which allows us to describe dissipative processes with entropy
creation, such as chemical reactions, friction or the effects of external
non-conservative forces. The resulting framework incorporates the
generalization of the entrainment effect originally discussed in the case of
the mixture of two superfluids by Andreev and Bashkin. In addition to the
conservation of energy and momentum, we derive the generalized conservation
laws of vorticity and helicity, and the special case of Ertel's theorem for the
single perfect fluid.
We explicitly discuss the application of this framework to thermally
conducting fluids, superfluids, and superfluid neutron star matter. The
equations governing thermally conducting fluids are found to be more general
than the standard description, as the effect of entrainment usually seems to be
overlooked in this context. In the case of superfluid He4 we recover the
Landau--Khalatnikov equations of the two-fluid model via a translation to the
``orthodox'' framework of superfluidity, which is based on a rather awkward
choice of variables. Our two-fluid model for superfluid neutron star matter
allows for dissipation via mutual friction and also ``transfusion'' via
beta-reactions between the neutron fluid and the proton-electron fluid.Comment: uses RevTeX 4; 20 pages. To appear in PRD. v2: removed discussion of
charged fluids and coupling to electromagnetic fields, which are submitted as
a separate paper for a clearer presentation v3: fixed typo in Eq.(9), updated
some reference
Toward an internally consistent astronomical distance scale
Accurate astronomical distance determination is crucial for all fields in
astrophysics, from Galactic to cosmological scales. Despite, or perhaps because
of, significant efforts to determine accurate distances, using a wide range of
methods, tracers, and techniques, an internally consistent astronomical
distance framework has not yet been established. We review current efforts to
homogenize the Local Group's distance framework, with particular emphasis on
the potential of RR Lyrae stars as distance indicators, and attempt to extend
this in an internally consistent manner to cosmological distances. Calibration
based on Type Ia supernovae and distance determinations based on gravitational
lensing represent particularly promising approaches. We provide a positive
outlook to improvements to the status quo expected from future surveys,
missions, and facilities. Astronomical distance determination has clearly
reached maturity and near-consistency.Comment: Review article, 59 pages (4 figures); Space Science Reviews, in press
(chapter 8 of a special collection resulting from the May 2016 ISSI-BJ
workshop on Astronomical Distance Determination in the Space Age
Anisotropic flow of charged hadrons, pions and (anti-)protons measured at high transverse momentum in Pb-Pb collisions at TeV
The elliptic, , triangular, , and quadrangular, , azimuthal
anisotropic flow coefficients are measured for unidentified charged particles,
pions and (anti-)protons in Pb-Pb collisions at TeV
with the ALICE detector at the Large Hadron Collider. Results obtained with the
event plane and four-particle cumulant methods are reported for the
pseudo-rapidity range at different collision centralities and as a
function of transverse momentum, , out to GeV/.
The observed non-zero elliptic and triangular flow depends only weakly on
transverse momentum for GeV/. The small dependence
of the difference between elliptic flow results obtained from the event plane
and four-particle cumulant methods suggests a common origin of flow
fluctuations up to GeV/. The magnitude of the (anti-)proton
elliptic and triangular flow is larger than that of pions out to at least
GeV/ indicating that the particle type dependence persists out
to high .Comment: 16 pages, 5 captioned figures, authors from page 11, published
version, figures at http://aliceinfo.cern.ch/ArtSubmission/node/186
Centrality dependence of charged particle production at large transverse momentum in Pb-Pb collisions at TeV
The inclusive transverse momentum () distributions of primary
charged particles are measured in the pseudo-rapidity range as a
function of event centrality in Pb-Pb collisions at
TeV with ALICE at the LHC. The data are presented in the range
GeV/ for nine centrality intervals from 70-80% to 0-5%.
The Pb-Pb spectra are presented in terms of the nuclear modification factor
using a pp reference spectrum measured at the same collision
energy. We observe that the suppression of high- particles strongly
depends on event centrality. In central collisions (0-5%) the yield is most
suppressed with at -7 GeV/. Above
GeV/, there is a significant rise in the nuclear modification
factor, which reaches for GeV/. In
peripheral collisions (70-80%), the suppression is weaker with almost independently of . The measured nuclear
modification factors are compared to other measurements and model calculations.Comment: 17 pages, 4 captioned figures, 2 tables, authors from page 12,
published version, figures at
http://aliceinfo.cern.ch/ArtSubmission/node/284
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