622 research outputs found
The effect of the motion of the Sun on the light-time in interplanetary relativistic experiments
In 2002 a measurement of the effect of solar gravity upon the phase of
coherent microwave beams passing near the Sun has been carried out with the
Cassini mission, allowing a very accurate measurement of the PPN parameter
. The data have been analyzed with NASA's Orbit Determination Program
(ODP) in the Barycentric Celestial Reference System, in which the Sun moves
around the centre of mass of the solar system with a velocity of
about 10 m/sec; the question arises, what correction this implies for the
predicted phase shift. After a review of the way the ODP works, we set the
problem in the framework of Lorentz (and Galilean) transformations and evaluate
the correction; it is several orders of magnitude below our experimental
accuracy. We also discuss a recent paper \cite{kopeikin07}, which claims wrong
and much larger corrections, and clarify the reasons for the discrepancy.Comment: Final version accepted by Classical and Quantum Gravity (8 Jan. 2008
Hysteresis loops of magnetic thin films with perpendicular anisotropy
We model the magnetization of quasi two-dimensional systems with easy
perpendicular (z-)axis anisotropy upon change of external magnetic field along
z. The model is derived from the Landau-Lifshitz-Gilbert equation for
magnetization evolution, written in closed form in terms of the z component of
the magnetization only. The model includes--in addition to the external
field--magnetic exchange, dipolar interactions and structural disorder. The
phase diagram in the disorder/interaction strength plane is presented, and the
different qualitative regimes are analyzed. The results compare very well with
observed experimental hysteresis loops and spatial magnetization patterns, as
for instance for the case of Co-Pt multilayers.Comment: 8 pages, 8 figure
Phase transitions in a disordered system in and out of equilibrium
The equilibrium and non--equilibrium disorder induced phase transitions are
compared in the random-field Ising model (RFIM). We identify in the
demagnetized state (DS) the correct non-equilibrium hysteretic counterpart of
the T=0 ground state (GS), and present evidence of universality. Numerical
simulations in d=3 indicate that exponents and scaling functions coincide,
while the location of the critical point differs, as corroborated by exact
results for the Bethe lattice. These results are of relevance for optimization,
and for the generic question of universality in the presence of disorder.Comment: Accepted for publication in Phys. Rev. Let
Reversal-Field Memory in the Hysteresis of Spin Glasses
We report a novel singularity in the hysteresis of spin glasses, the
reversal-field memory effect, which creates a non-analyticity in the
magnetization curves at a particular point related to the history of the
sample. The origin of the effect is due to the existence of a macroscopic
number of "symmetric clusters" of spins associated with a local spin-reversal
symmetry of the Hamiltonian. We use First Order Reversal Curve (FORC) diagrams
to characterize the effect and compare to experimental results on thin magnetic
films. We contrast our results on spin glasses to random magnets and show that
the FORC technique is an effective "magnetic fingerprinting" tool.Comment: 4 pages, 6 figure
Self-organized criticality in the hysteresis of the Sherrington - Kirkpatrick model
We study hysteretic phenomena in random ferromagnets. We argue that the angle
dependent magnetostatic (dipolar) terms introduce frustration and long range
interactions in these systems. This makes it plausible that the Sherrington -
Kirkpatrick model may be able to capture some of the relevant physics of these
systems. We use scaling arguments, replica calculations and large scale
numerical simulations to characterize the hysteresis of the zero temperature SK
model. By constructing the distribution functions of the avalanche sizes,
magnetization jumps and local fields, we conclude that the system exhibits
self-organized criticality everywhere on the hysteresis loop.Comment: 4 pages, 4 eps figure
The average shape of a fluctuation: universality in excursions of stochastic processes
We study the average shape of a fluctuation of a time series x(t), that is
the average value _T before x(t) first returns, at time T, to its
initial value x(0). For large classes of stochastic processes we find that a
scaling law of the form _T = T^\alpha f(t/T) is obeyed. The
scaling function f(s) is to a large extent independent of the details of the
single increment distribution, while it encodes relevant statistical
information on the presence and nature of temporal correlations in the process.
We discuss the relevance of these results for Barkhausen noise in magnetic
systems.Comment: 5 pages, 5 figures, accepted for publication in Phys. Rev. Let
Ground state optimization and hysteretic demagnetization: the random-field Ising model
We compare the ground state of the random-field Ising model with Gaussian
distributed random fields, with its non-equilibrium hysteretic counterpart, the
demagnetized state. This is a low energy state obtained by a sequence of slow
magnetic field oscillations with decreasing amplitude. The main concern is how
optimized the demagnetized state is with respect to the best-possible ground
state. Exact results for the energy in d=1 show that in a paramagnet, with
finite spin-spin correlations, there is a significant difference in the
energies if the disorder is not so strong that the states are trivially almost
alike. We use numerical simulations to better characterize the difference
between the ground state and the demagnetized state. For d>=3 the random-field
Ising model displays a disorder induced phase transition between a paramagnetic
and a ferromagnetic state. The locations of the critical points R_c(DS),
R_c(GS) differ for the demagnetized state and ground state. Consequently, it is
in this regime that the optimization of the demagnetized stat is the worst
whereas both deep in the paramagnetic regime and in the ferromagnetic one the
states resemble each other to a great extent. We argue based on the numerics
that in d=3 the scaling at the transition is the same in the demagnetized and
ground states. This claim is corroborated by the exact solution of the model on
the Bethe lattice, where the R_c's are also different.Comment: 13 figs. Submitted to Phys. Rev.
Black Holes with a Massive Dilaton
The modifications of dilaton black holes which result when the dilaton
acquires a mass are investigated. We derive some general constraints on the
number of horizons of the black hole and argue that if the product of the black
hole charge and the dilaton mass satisfies then the black
hole has only one horizon. We also argue that for there may exist
solutions with three horizons and we discuss the causal structure of such
solutions. We also investigate the possible structures of extremal solutions
and the related problem of two-dimensional dilaton gravity with a massive
dilaton.Comment: 36 pages with 5 figures (as uuencoded compressed tar file) (revised
version has one major change in bound on mass for extremal solution and minor
typos fixed), harvma
Building the economic evidence case for social prescribing
Understanding the economic impact of social prescribing remains an urgent priority for the National Academy of Social Prescribing (NASP). As yet it is unclear how much data exists within the different systems to enable economic analyses of the impact of social prescribing schemes to be conducted.
The complexity in understanding the economic impact of social prescribing—and indeed all non-clinical community-based approaches to health—is compounded by the multisector nature of social prescribing. Furthermore, a variety of approaches are being used to test similar but different understandings of both cost and value, including social value, cost, benefit and economic value.
There are a growing range of reports and peer-reviewed publications that focus on the impact of social prescribing on health and social care demand, some of which have economic analyses and some which remain as potential data sets for economic analyses. At least one third of all outcomes (if not more) are directly related to the social determinants of health1,2 (SDH) which are not taken into account with economic analysis focused only on health service usage.
This range of outcomes experienced by service users2-4 is driving many researchers to conduct economic analyses that attempt to assign value to outcomes beyond the health sector, for instance using social return on investment (SROI) and proxy values. Other researchers have discussed the evolution in economic analyses at length and suggest additional components to existing methodologies, e.g., multi criteria decision analysis (MCDA) to account for additional complexity of social prescribing5. Further developments are also being trialled such as the Wellbeing-adjusted Life Years (WELLBY) to understand the economic value attached to wellbeing6, as opposed to the Quality Adjusted Life Years (QALY), which reports the economic value of quality of life.
We are entering an era of providing personalised support to people in integrated and multidisciplinary systems with different local population needs. As such, there is a need to evolve the approaches to
determining cost and value of social prescribing, and to reach agreements on methodologies that all sectors are willing to accept as sound approaches. Furthermore, as discussed by McDaid and colleagues in 2019 7, there is a need to move beyond the immediate benefits of social prescribing and to explore the longer-term benefits of sustained engagement in non-clinical activities and provision of support to address issues linked to the SDH. This would enable more data to inform the preventative role and economic impact that social prescribing may have, which is currently an evidence gap.
This rapid scoping review was commissioned by NASP and additional roundtables were supported by the National Centre for Creative Health and UKRI/AHRC’s ‘Mobilising Community Assets to Tackle Health Inequalities’ research programme (led by University College London). It aims to provide an update to the first economic evidence review from NASP and explore economic data and health and social care usage data in more detail.
This rapid scoping review aims to ascertain:
What the current literature indicates in terms of cost or value of social prescribing schemes or parts of the social prescribing scheme.
If there are potential data sets that report the impact of social prescribing on health service usage that could have economic analysis applied to them.
Stakeholder opinions on the methodological approaches for creating the current economic evaluation evidence base for social prescribing and potential future developments that are needed.
How these findings can inform a larger programme of research that is needed to establish the economic impact and value of social prescribing across all relevant sectors in the community.
As this report contains three separate elements to it, each element will be reported with methods and results, and then key themes will be brought together with recommendations
Light deflection by gravitational waves from localized sources
We study the deflection of light (and the redshift, or integrated time delay)
caused by the time-dependent gravitational field generated by a localized
material source lying close to the line of sight. Our calculation explicitly
takes into account the full, near-zone, plus intermediate-zone, plus wave-zone,
retarded gravitational field. Contrary to several recent claims in the
literature, we find that the deflections due to both the wave-zone 1/r
gravitational wave and the intermediate-zone 1/r^2 retarded fields vanish
exactly. The leading total time-dependent deflection caused by a localized
material source, such as a binary system, is proven to be given by the
quasi-static, near-zone quadrupolar piece of the gravitational field, and
therefore to fall off as the inverse cube of the impact parameter.Comment: 12 pages, REVTeX 3.0, no figur
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