844 research outputs found
Thermal gradient-induced forces on geodetic reference masses for LISA
The low frequency sensitivity of space-borne gravitational wave observatories
will depend critically on the geodetic purity of the trajectories of orbiting
test masses. Fluctuations in the temperature difference across the enclosure
surrounding the free-falling test mass can produce noisy forces through several
processes, including the radiometric effect, radiation pressure, and
outgassing. We present here a detailed experimental investigation of thermal
gradient-induced forces for the LISA gravitational wave mission and the LISA
Pathfinder, employing high resolution torsion pendulum measurements of the
torque on a LISA-like test mass suspended inside a prototype of the LISA
gravitational reference sensor that will surround the test mass in orbit. The
measurement campaign, accompanied by numerical simulations of the radiometric
and radiation pressure effects, allows a more accurate and representative
characterization of thermal-gradient forces in the specific geometry and
environment relevant to LISA free-fall. The pressure dependence of the measured
torques allows clear identification of the radiometric effect, in quantitative
agreement with the model developed. In the limit of zero gas pressure, the
measurements are most likely dominated by outgassing, but at a low level that
does not threaten the LISA sensitivity goals.Comment: 21 pages, 16 figures, submitted to Physical Review
Long-wavelength iteration scheme and scalar-tensor gravity
Inhomogeneous and anisotropic cosmologies are modeled withing the framework
of scalar-tensor gravity theories. The inhomogeneities are calculated to
third-order in the so-called long-wavelength iteration scheme. We write the
solutions for general scalar coupling and discuss what happens to the
third-order terms when the scalar-tensor solution approaches at first-order the
general relativistic one. We work out in some detail the case of Brans-Dicke
coupling and determine the conditions for which the anisotropy and
inhomogeneity decay as time increases. The matter is taken to be that of
perfect fluid with a barotropic equation of state.Comment: 13 pages, requires REVTeX, submitted to Phys. Rev.
What are the mechanisms that support healthcare professionals to adopt assisted decision-making practice? A rapid realist review
Background
The United Nations Convention on the Rights of Persons with Disabilities (UNCRPD) establishes a right to legal capacity for all people, including those with support needs. People with disabilities have a legal right to be given the appropriate supports to make informed decisions in all aspects of their lives, including health. In Ireland, the Assisted Decision-Making (Capacity) Act (2015) ratifies the Convention and has established a legal framework for Assisted Decision Making (ADM). The main provisions of the Act are not yet implemented. Codes of Practice to guide health and social care professionals are currently being developed. Internationally, concerns are expressed that ADM implementation is poorly understood. Using realist synthesis, this study aims to identify Programme Theory (PT) that will inform ADM implementation in healthcare.
Methods
A Rapid Realist Review using collaborative methods was chosen to appraise relevant literature and engage knowledge users from Irish health and social care. The review was led by an expert panel of relevant stakeholders that developed the research question which asks, âwhat mechanisms enable healthcare professionals to adopt ADM into practice?â
To ensure the PT was inclusive of local contextual influences, five reference panels were conducted with healthcare professionals, family carers and people with dementia. PT was refined and tested iteratively through knowledge synthesis informed by forty-seven primary studies, reference panel discussions and expert panel refinement and consensus.
Results
The review has developed an explanatory PT on ADM implementation in healthcare practice. The review identified four implementation domains as significant. These are Personalisation of Health & ADM Service Provision, Culture & Leadership, Environmental & Social Re-structuring and Education, Training & Enablement. Each domain is presented as an explanatory PT statement using realist convention that identifies context, mechanism and outcome configurations.
Conclusions
This realist review makes a unique contribution to this field. The PT can be applied by policymakers to inform intervention development and implementation strategy. It informs the imminent policy and practice developments in Ireland and has relevance for other worldwide healthcare systems dealing with similar legislative changes in line with UNCRPD
Modified Brans-Dicke theory of gravity from five-dimensional vacuum
We investigate, in the context of five-dimensional (5D) Brans-Dicke theory of
gravity, the idea that macroscopic matter configurations can be generated from
pure vacuum in five dimensions, an approach first proposed in the framework of
general relativity. We show that the 5D Brans-Dicke vacuum equations when
reduced to four dimensions lead to a modified version of Brans-Dicke theory in
four dimensions (4D). As an application of the formalism, we obtain two
five-dimensional extensions of four-dimensional O'Hanlon and Tupper vacuum
solution and show that they lead two different cosmological scenarios in 4D.Comment: 9 page
Frequency Characteristics of Visually Induced Motion Sickness
This article was published in the journal, Human Factors [Sage Publications / © Human Factors and Ergonomics Society.]. The definitive version is available at: http://dx.doi.org/10.1177/0018720812469046Objective: The aim of this study was to explore
the frequency response of visually induced motion
sickness (VIMS) for oscillating linear motion in the foreand-
aft axis.
Background: Simulators, virtual environments,
and commercially available video games that create an
illusion of self-motion are often reported to induce
the symptoms seen in response to true motion. Often
this human response can be the limiting factor in the
acceptability and usability of such systems. Whereas
motion sickness in physically moving environments
is known to peak at an oscillation frequency around
0.2 Hz, it has recently been suggested that VIMS peaks
at around 0.06 Hz following the proposal that the
summed response of the visual and vestibular selfmotion
systems is maximized at this frequency. Methods: We exposed 24 participants to random
dot optical flow patterns simulating oscillating foreand-
aft motion within the frequency range of 0.025 to
1.6 Hz. Before and after each 20-min exposure, VIMS was
assessed with the Simulator Sickness Questionnaire.
Also, a standard motion sickness scale was used to rate
symptoms at 1-min intervals during each trial.
Results: VIMS peaked between 0.2 and 0.4 Hz with
a reducing effect at lower and higher frequencies.
Conclusion: The numerical prediction of the
âcrossover frequencyâ hypothesis, and the design
guidance curve previously proposed, cannot be accepted
when the symptoms are purely visually induced.
Application: In conditions in which stationary
observers are exposed to optical flow that simulates
oscillating fore-and-aft motion, frequencies around 0.2
to 0.4 Hz should be avoided
Fair Value Hierarchy Measures: Post-Implementation Evidence on IFRS 7
Using a balance sheet valuation model, this study examines if information on the fair value hierarchy of on-balance sheet financial assets and financial liabilities are incorporated in the marketâs valuation of companiesâ equities in Singapore. The results of the study show significant associations between as-reported Level 1 and Level 2 fair value measures of financial assets and market values. However, the results are not significant for Level 3 fair value measures of financial assets and each of the three levels of fair value measures of financial liabilities. The results also show that returns are more positively associated with as-reported gains and losses from Level 1 and Level 2 fair value measures than those from Level 3 fair value measures. Overall, the evidence suggests that information on the fair value hierarchy of IFRS 7 Financial Instruments: Disclosures are used by market participants in their pricing decisions. The market however appears to place greater weights on fair value changes taken to the income statement than those taken to OCI, notwithstanding the level of the fair value measure. While the fixation with income statement measures remains a puzzle, the results are consistent with prior studies that show that investors largely ignore OCI in their pricing of shares
Scalar-Tensor Models of Normal and Phantom Dark Energy
We consider the viability of dark energy (DE) models in the framework of the
scalar-tensor theory of gravity, including the possibility to have a phantom DE
at small redshifts as admitted by supernova luminosity-distance data. For
small , the generic solution for these models is constructed in the form of
a power series in without any approximation. Necessary constraints for DE
to be phantom today and to cross the phantom divide line at small
are presented. Considering the Solar System constraints, we find for the
post-Newtonian parameters that and for
the model to be viable, and (but very close to 1) if the model
has a significantly phantom DE today. However, prospects to establish the
phantom behaviour of DE are much better with cosmological data than with Solar
System experiments. Earlier obtained results for a -dominated universe
with the vanishing scalar field potential are extended to a more general DE
equation of state confirming that the cosmological evolution of these models
rule them out. Models of currently fantom DE which are viable for small can
be easily constructed with a constant potential; however, they generically
become singular at some higher . With a growing potential, viable models
exist up to an arbitrary high redshift.Comment: 30 pages, 4 figures; Matches the published version containing an
expanded discussion of various point
Self-similar cosmological solutions with a non-minimally coupled scalar field
We present self-similar cosmological solutions for a barotropic fluid plus
scalar field with Brans-Dicke-type coupling to the spacetime curvature and an
arbitrary power-law potential energy. We identify all the fixed points in the
autonomous phase-plane, including a scaling solution where the fluid density
scales with the scalar field's kinetic and potential energy. This is related by
a conformal transformation to a scaling solution for a scalar field with
exponential potential minimally coupled to the spacetime curvature, but
non-minimally coupled to the barotropic fluid. Radiation is automatically
decoupled from the scalar field, but energy transfer between the field and
non-relativistic dark matter can lead to a change to an accelerated expansion
at late times in the Einstein frame. The scalar field density can mimic a
cosmological constant even for steep potentials in the strong coupling limit.Comment: 10 pages, 1 figure, revtex version to appear in Phys Rev D,
references adde
The Behaviour Of Cosmological Models With Varying-G
We provide a detailed analysis of Friedmann-Robertson-Walker universes in a
wide range of scalar-tensor theories of gravity. We apply solution-generating
methods to three parametrised classes of scalar-tensor theory which lead
naturally to general relativity in the weak-field limit. We restrict the
parameters which specify these theories by the requirements imposed by the
weak-field tests of gravitation theories in the solar system and by the
requirement that viable cosmological solutions be obtained. We construct a
range of exact solutions for open, closed, and flat isotropic universes
containing matter with equation of state and in vacuum.
We study the range of early and late-time behaviours displayed, examine when
there is a `bounce' at early times, and expansion maxima in closed models.Comment: 58 pages LaTeX, 6 postscript figures, uses eps
- âŠ