6,359 research outputs found
The Meaning of Einstein's Equation
This is a brief introduction to general relativity, designed for both
students and teachers of the subject. While there are many excellent
expositions of general relativity, few adequately explain the geometrical
meaning of the basic equation of the theory: Einstein's equation. Here we give
a simple formulation of this equation in terms of the motion of freely falling
test particles. We also sketch some of its consequences, and explain how the
formulation given here is equivalent to the usual one in terms of tensors.
Finally, we include an annotated bibliography of books, articles and websites
suitable for the student of relativity.Comment: 23 pages LaTeX, 8 encapsulated Postscript figures; unlike the
published version this includes a derivation of the inverse-square force la
Sensitivity of a Bolometric Interferometer to the CMB power spectrum
Context. The search for B-mode polarization fluctuations in the Cosmic
Microwave Background is one of the main challenges of modern cosmology. The
expected level of the B-mode signal is very low and therefore requires the
development of highly sensitive instruments with low systematic errors. An
appealing possibility is bolometric interferometry. Aims. We compare in this
article the sensitivity on the CMB angular power spectrum achieved with direct
imaging, heterodyne and bolometric interferometry. Methods. Using a simple
power spectrum estimator, we calculate its variance leading to the counterpart
for bolometric interferometry of the well known Knox formula for direct
imaging. Results. We find that bolometric interferometry is less sensitive than
direct imaging. However, as expected, it is finally more sensitive than
heterodyne interferometry due to the low noise of the bolometers. It therefore
appears as an alternative to direct imagers with different and possibly lower
systematic errors, mainly due to the absence of an optical setup in front of
the horns.Comment: 5 pages, 3 figures. This last version matches the published version
(Astronomy and Astrophysics 491 3 (2008) 923-927). Sensitivity of Heterodyne
Interferometers modified by a factor of tw
A cambridge ring node controller
This report gives a discussion of the design of a peripheral controller chip to Interface a Cambridge Ring Node to a MC68000 host machine using VLSI technology. The design of such a chip involves following a design strategy. The strategy used Identities what the Interface should be capable of doing. developing a functional description of the interface. mapping the interface onto silicon and finally verifying the design. The characteristics of the interface and the design strategy. along with the software used In the design. will be discussed
Expansion of the investor base for the energy transition
Despite the emergence of the green bond market, the Energy Service Company (ESCO) model and green investment banks, the opportunities which the world’s capital markets present to increase the pool of potential investors and reduce project financing costs for renewable, energy efficient and low carbon assets remain under-exploited. This has been a persistent concern for policy-makers. We review the appeal of this sector to different classes of investor and assess the successes and failures of several innovative products including securitisations, yieldcos, green bonds, green investment banks and crowdfunding. We analyse the experiences with these products and suggest that policy needs to recognise how
fiscal initiatives can leverage their inherent appeal
The Becklin-Neugebauer Object as a Runaway B Star, Ejected 4000 years ago from the theta^1C system
We attempt to explain the properties of the Becklin-Neugebauer (BN) object as
a runaway B star, as originally proposed by Plambeck et al. (1995). This is one
of the best-studied bright infrared sources, located in the Orion Nebula
Cluster -- an important testing ground for massive star formation theories.
From radio observations of BN's proper motion, we trace its trajectory back
to Trapezium star theta^1C, the most massive (45 Msun) in the cluster and a
relatively tight (17 AU) visual binary with a B star secondary. This origin
would be the most recent known runaway B star ejection event, occurring only
\~4000 yr ago and providing a unique test of models of ejection from multiple
systems of massive stars. Although highly obscured, we can constrain BN's mass
(~7 Msun) from both its bolometric luminosity and the recoil of theta^1C.
Interaction of a runaway B star with dense ambient gas should produce a compact
wind bow shock. We suggest that X-ray emission from this shocked gas may have
been seen by Chandra: the offset from the radio position is ~300 AU in the
direction of BN's motion. Given this model, we constrain the ambient density,
wind mass-loss rate and wind velocity. BN made closest approach to the massive
protostar, source ``I'', 500 yr ago. This may have triggered enhanced accretion
and thus outflow, consistent with previous interpretations of the outflow being
a recent (~10^3 yr) "explosive" event.Comment: 6 pages, accepted to ApJ Letter
Proceedings of the Spacecraft Charging Technology Conference: Executive Summary
Aerospace environments are reviewed in reference to spacecraft charging. Modelling, a theoretical scheme which can be used to describe the structure of the sheath around the spacecraft and to calculate the charging currents within, is discussed. Materials characterization is considered for experimental determination of the behavior of typical spacecraft materials when exposed to simulated geomagnetic substorm conditions. Materials development is also examined for controlling and minimizing spacecraft charging or at least for distributing the charge in an equipotential manner, using electrical conductive surfaces for materials exposed to space environment
Constraining f(R) Gravity as a Scalar Tensor Theory
We search for viable f(R) theories of gravity, making use of the equivalence
between such theories and scalar-tensor gravity. We find that models can be
made consistent with solar system constraints either by giving the scalar a
high mass or by exploiting the so-called chameleon effect. However, in both
cases, it appears likely that any late-time cosmic acceleration will be
observationally indistinguishable from acceleration caused by a cosmological
constant. We also explore further observational constraints from, e.g., big
bang nucleosynthesis and inflation.Comment: 15 pages, 5 figure
Prevalence of antibodies to Ro-52 in a serologically defined population of patients with systemic sclerosis
Setting priorities to inform assessment of care homes’ readiness to participate in healthcare innovation: a systematic mapping review and consensus process
© 2020 The Author(s). This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly citedOrganisational context is known to impact on the successful implementation of healthcare initiatives in care homes. We undertook a systematic mapping review to examine whether researchers have considered organisational context when planning, conducting, and reporting the implementation of healthcare innovations in care homes. Review data were mapped against the Alberta Context Tool, which was designed to assess organizational context in care homes. The review included 56 papers. No studies involved a systematic assessment of organisational context prior to implementation, but many provided post hoc explanations of how organisational context affected the success or otherwise of the innovation. Factors identified to explain a lack of success included poor senior staff engagement, non-alignment with care home culture, limited staff capacity to engage, and low levels of participation from health professionals such as general practitioners (GPs). Thirty-five stakeholders participated in workshops to discuss findings and develop questions for assessing care home readiness to participate in innovations. Ten questions were developed to initiate conversations between innovators and care home staff to support research and implementation. This framework can help researchers initiate discussions about health-related innovation. This will begin to address the gap between implementation theory and practice.Peer reviewe
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