19 research outputs found
Testing Emergent Gravity on Galaxy Cluster Scales
Verlinde's theory of Emergent Gravity (EG) describes gravity as an emergent
phenomenon rather than a fundamental force. Applying this reasoning in de
Sitter space leads to gravity behaving differently on galaxy and galaxy cluster
scales; this excess gravity might offer an alternative to dark matter. Here we
test these ideas using the data from the Coma cluster and from 58 stacked
galaxy clusters. The X-ray surface brightness measurements of the clusters at
along with the weak lensing data are used to test the theory.
We find that the simultaneous EG fits of the X-ray and weak lensing datasets
are significantly worse than those provided by General Relativity (with cold
dark matter). For the Coma cluster, the predictions from Emergent Gravity and
General Relativity agree in the range of 250 - 700 kpc, while at around 1 Mpc
scales, EG total mass predictions are larger by a factor of 2. For the cluster
stack the predictions are only in good agreement at around the 1 - 2 Mpc
scales, while for Mpc EG is in strong tension with the data.
According to the Bayesian information criterion analysis, GR is preferred in
all tested datasets; however, we also discuss possible modifications of EG that
greatly relax the tension with the data.Comment: 19 pages, 5 figures, 5 tables, accepted for publication on JCA
Using machine learning to optimise chameleon fifth force experiments
The chameleon is a theorised scalar field that couples to matter and possess
a screening mechanism, which weakens observational constraints from experiments
performed in regions of higher matter density. One consequence of this
screening mechanism is that the force induced by the field is dependent on the
shape of the source mass (a property that distinguishes it from gravity).
Therefore an optimal shape must exist for which the chameleon force is
maximised. Such a shape would allow experiments to improve their sensitivity by
simply changing the shape of the source mass. In this work we use a combination
of genetic algorithms and the chameleon solving software SELCIE to find shapes
that optimise the force at a single point in an idealised experimental
environment. We note that the method we used is easily customised, and so could
be used to optimise a more realistic experiment involving particle trajectories
or the force acting on an extended body. We find the shapes outputted by the
genetic algorithm possess common characteristics, such as a preference for
smaller source masses, and that the largest fifth forces are produced by small
`umbrella'-like shapes with a thickness such that the source is unscreened but
the field reaches its minimum inside the source. This remains the optimal shape
even as we change the chameleon potential, and the distance from the source,
and across a wide range of chameleon parameters. We find that by optimising the
shape in this way the fifth force can be increased by times when
compared to a sphere, centred at the origin, of the same volume and mass.Comment: 28 pages, 17 figures, The SELCIE code is available at:
https://github.com/C-Briddon/SELCI
SELCIE: a tool for investigating the chameleon field of arbitrary sources
The chameleon model is a modified gravity theory that introduces an additional scalar field that couples to matter through a conformal coupling. This `chameleon field' possesses a screening mechanism through a nonlinear self-interaction term which allows the field to affect cosmological observables in diffuse environments whilst still being consistent with current local experimental constraints. Due to the self-interaction term the equations of motion of the field are nonlinear and therefore difficult to solve analytically. The analytic solutions that do exist in the literature are either approximate solutions and or only apply to highly symmetric systems. In this work we introduce the software package SELCIE (https://github.com/C-Briddon/SELCIE.git). This package equips the user with tools to construct an arbitrary system of mass distributions and then to calculate the corresponding solution to the chameleon field equation. It accomplishes this by using the finite element method and either the Picard or Newton nonlinear solving methods. We compared the results produced by SELCIE with analytic results from the literature including discrete and continuous density distributions. We found strong (sub-percentage) agreement between the solutions calculated by SELCIE and the analytic solutions
Using machine learning to optimise chameleon fifth force experiments
The chameleon is a theorised scalar field that couples to matter and possess a screening mechanism, which weakens observational constraints from experiments performed in regions of higher matter density. One consequence of this screening mechanism is that the force induced by the field is dependent on the shape of the source mass (a property that distinguishes it from gravity). Therefore an optimal shape must exist for which the chameleon force is maximised. Such a shape would allow experiments to improve their sensitivity by simply changing the shape of the source mass. In this work we use a combination of genetic algorithms and the chameleon solving software SELCIE to find shapes that optimise the force at a single point in an idealised experimental environment. We note that the method we used is easily customised, and so could be used to optimise a more realistic experiment involving particle trajectories or the force acting on an extended body. We find the shapes outputted by the genetic algorithm possess common characteristics, such as a preference for smaller source masses, and that the largest fifth forces are produced by small `umbrella'-like shapes with a thickness such that the source is unscreened but the field reaches its minimum inside the source. This remains the optimal shape even as we change the chameleon potential, and the distance from the source, and across a wide range of chameleon parameters. We find that by optimising the shape in this way the fifth force can be increased by 2.45 times when compared to a sphere, centred at the origin, of the same volume and mass
Low-Dose Ketamine for Acute Postoperative Pain Treatment
Treatment of acute postoperative pain is an essential part of perioperative care and if left untreated could complicate the healing period. Ketamine blocks nociceptive pain and pain arising from inflammation. Therefore, it is potentially beneficial in the postoperative period. After systematic review using “MEDLINE/PubMed (NLM)” database, we analyzed 18 studies published during 2011–2020 and found that 0.5 mg/kg/h ketamine bolus and 0.1–0.25 mg/kg/h ketamine infusion to be the most effective dose to alleviate postoperative acute pain. Ketamine, when compared with a placebo, did not have any impact on patients’ satisfaction with postoperative pain management and overall well-being. Only three studies revealed more frequent adverse reactions to ketamine after surgery suggesting that ketamine did not have any impact on patients’ postoperational rehabilitation. So, it is the option to recommend low-dose ketamine to be part of multimodal analgesia in acute severe postoperative pain treatment. It can be used in both opioid-dependent and opioid-tolerant patients. Ketamine bolus should be ≤0.35 mg/kg and infusion ≤1 mg/kg/h. One should avoid the use of ketamine in pregnant women, people with cardiovascular diseases, acute psychosis, impaired liver function, increased intracranial, and intraocular pressure. Intranasal ketamine may be considered for children during procedures outside of the operation room
Cosmic topology. Part I. Limits on orientable Euclidean manifolds from circle searches
The Einstein field equations of general relativity constrain the local
curvature at every point in spacetime, but say nothing about the global
topology of the Universe. Cosmic microwave background anisotropies have proven
to be the most powerful probe of non-trivial topology since, within
CDM, these anisotropies have well-characterized statistical
properties, the signal is principally from a thin spherical shell centered on
the observer (the last scattering surface), and space-based observations nearly
cover the full sky. The most generic signature of cosmic topology in the
microwave background is pairs of circles with matching temperature and
polarization patterns. No such circle pairs have been seen above noise in the
WMAP or Planck temperature data, implying that the shortest non-contractible
loop around the Universe through our location is longer than 98.5% of the
comoving diameter of the last scattering surface. We translate this generic
constraint into limits on the parameters that characterize manifolds with each
of the nine possible non-trivial orientable Euclidean topologies, and provide a
code which computes these constraints. In all but the simplest cases, the
shortest non-contractible loop in the space can avoid us, and be shorter than
the diameter of the last scattering surface by a factor ranging from 2 to at
least 6. This result implies that a broader range of manifolds is
observationally allowed than widely appreciated. Probing these manifolds will
require more subtle statistical signatures than matched circles, such as
off-diagonal correlations of harmonic coefficients.Comment: 22 pages, 7 figures. v3: Corrected Figs. 3, 4, and 5 as published in
Erratu
Cosmic topology. Part II. Eigenmodes, correlation matrices, and detectability of orientable Euclidean manifolds
If the Universe has non-trivial spatial topology, observables depend on both
the parameters of the spatial manifold and the position and orientation of the
observer. In infinite Euclidean space, most cosmological observables arise from
the amplitudes of Fourier modes of primordial scalar curvature perturbations.
Topological boundary conditions replace the full set of Fourier modes with
specific linear combinations of selected Fourier modes as the eigenmodes of the
scalar Laplacian. We present formulas for eigenmodes in orientable Euclidean
manifolds with the topologies - , , , , and
that encompass the full range of manifold parameters and observer
positions, generalizing previous treatments. Under the assumption that the
amplitudes of primordial scalar curvature eigenmodes are independent random
variables, for each topology we obtain the correlation matrices of Fourier-mode
amplitudes (of scalar fields linearly related to the scalar curvature) and the
correlation matrices of spherical-harmonic coefficients of such fields sampled
on a sphere, such as the temperature of the cosmic microwave background (CMB).
We evaluate the detectability of these correlations given the cosmic variance
of the observed CMB sky. We find that topologies where the distance to our
nearest clone is less than about 1.2 times the diameter of the last scattering
surface of the CMB give a correlation signal that is larger than cosmic
variance noise in the CMB. This implies that if cosmic topology is the
explanation of large-angle anomalies in the CMB, then the distance to our
nearest clone is not much larger than the diameter of the last scattering
surface. We argue that the topological information is likely to be better
preserved in three-dimensional data, such as will eventually be available from
large-scale structure surveys.Comment: 79 pages, 9 figure
Managing selection of AFF power generation technologies in the internationally evolving carbon-free context
The article presents the analysis fossil fuel power generation market, focusing on management of advanced fossil fuel (AFF) power generation challenges of related technologies especially when tackling climate change impacts, complying with stricter environmental requirements. A wide and dynamic spectrum in scope and scale of factors revealed confirms the necessity for solutions enabling organizations to transform and manage rationally their fossil fuel-based business models towards greater competitiveness in the context of emerging renewable energy reliance. Nevertheless, in this respect the measures in question may require trade-offs, therefore when considering their combination, a diligent multicriteria analysis will inevitably be involved. With pivotal focus on the economic utility and the balanced and sustained strategic development of business, as the result of the research author proposes to apply VIKOR method when deciding on AFF power generation options. Application flexibility of the proposed method allow to evaluate, compare possible alternatives in a comprehensive and complex manner and to mingle MCDA tools if needed
Chameleon Screening Depends on the Shape and Structure of NFW Halos
Chameleon gravity is an example of a model that gives rise to interesting phenomenology on cosmological scales while simultaneously possessing a screening mechanism, allowing it to avoid solar system constraints. Such models result in non-linear field equations, which can be solved analytically only in simple highly symmetric systems. In this work we study the equation of motion of a scalar-tensor theory with chameleon screening using the finite element method. More specifically, we solve the field equation for spherical and triaxial NFW cluster-sized halos. This allows a detailed investigation of the relationship between the NFW concentration and the virial mass parameters and the magnitude of the chameleon acceleration, as measured at the virial radius. In addition, we investigate the effects on the chameleon acceleration due to halo triaxiality. We focus on the parameter space regions that are still allowed by the observational constraints. We find that given our dataset, the largest allowed value for the chameleon-to-NFW acceleration ratio at the virial radius is ∼10-7. This result strongly indicates that the chameleon models that are still allowed by the observational constraints would not lead to any measurable effects on galaxy cluster scales. Nonetheless, we also find that there is a direct relationship between the NFW potential and the chameleon-to-NFW acceleration ratio at the virial radius. Similarly, there is a direct (yet a much more complicated) relationship between the NFW concentration, the virial mass and the acceleration ratios at the virial radius. Finally, we find that triaxiality introduces extra directional effects on the acceleration measurements. These effects in combination could potentially be used in future observational searches for fifth forces