333 research outputs found
The influence of twin boundaries on the Flux Line Lattice structure in YBaCuO: a study by Small Angle Neutron Scattering
The influence of Twin Boundaries (TB) on the Flux Line Lattice(FLL) structure
was investigated by Small Angle Neutron Scattering (SANS). YBaCuO single
crystals possessing different TB densities were studied. The SANS experiments
show that the TB strongly modify the structure of the FLL. The flux lines
meander as soon as the magnetic field makes an angle with the TB direction.
According to the value of this angle but also to the ratio of the flux lines
density over the TB density, one observes that the FLL exhibits two different
unit cells in the plane perpendicular to the magnetic field. One is the
classical hexagonal and anisotropic cell while the other is affected by an
additional deformation induced by the TB. We discuss a possible relation
between this deformation and the increase of the critical current usually
observed in heavily twinned samples.Comment: accepted for publication in Phys Rev
The skewed weak lensing likelihood: why biases arise, despite data and theory being sound
We derive the essentials of the skewed weak lensing likelihood via a simple hierarchical forward model. Our likelihood passes four objective and cosmology-independent tests which a standard Gaussian likelihood fails. We demonstrate that sound weak lensing data are naturally biased low, since they are drawn from a skewed distribution. This occurs already in the framework of Lambda cold dark matter. Mathematically, the biases arise because noisy two-point functions follow skewed distributions. This form of bias is already known from cosmic microwave background analyses, where the low multipoles have asymmetric error bars. Weak lensing is more strongly affected by this asymmetry as galaxies form a discrete set of shear tracer particles, in contrast to a smooth shear field. We demonstrate that the biases can be up to 30âperâcent of the standard deviation per data point, dependent on the properties of the weak lensing survey and the employed filter function. Our likelihood provides a versatile framework with which to address this bias in future weak lensing analyses
The decrease of the critical current of coated conductors when a perpendicular magnetic field is applied : a Josephson effect point of view
A large decrease is observed in the critical current density of YBCO coated
conductors (CC) and related compounds when a strong perpendicular magnetic
field is applied. While measurements are generally carried out at 77K only,
here we present a magnetic technique permitting to determine the critical
current per unit width of conductor (Icr/w) in a large temperature range. We
report measurements carried out on various CCs that show that, in addition to
the reduction in the critical temperature that can be attributed to the low
value of the irreversibility field near Tc, the field application results in a
large decrease of Icr/w at all temperatures. We ascribe this reduction to the
Josephson behaviour of the twin boundaries included in the YBCO layer
On the road to percent accuracy III: non-linear reaction of the matter power spectrum to massive neutrinos
We analytically model the non-linear effects induced by massive neutrinos on the total matter power spectrum using the halo model reaction framework of Cataneo et al. In this approach, the halo model is used to determine the relative change to the matter power spectrum caused by new physics beyond the concordance cosmology. Using standard fitting functions for the halo abundance and the halo massâconcentration relation, the total matter power spectrum in the presence of massive neutrinos is predicted to perâcent-level accuracy, out to k=10hMpcâ1â . We find that refining the prescriptions for the halo properties using N-body simulations improves the recovered accuracy to better than 1âperâcent. This paper serves as another demonstration for how the halo model reaction framework, in combination with a single suite of standard Î cold dark matter (ÎCDM) simulations, can recover perâcent-level accurate predictions for beyond ÎCDM matter power spectra, well into the non-linear regime
Understanding the potential for marine megafauna entanglement risk from renewable marine energy developments
PublishedThis is the final version of the article. Available from the Scottish National Heritage via the link in this record.Commissioned Report No. 791
Project no: 14635
Contractor: Scottish Association for Marine Science Research Services Ltd and the
University of Exeter
Year of publication: 2014Scottish Natural Heritag
Enhancing the cosmic shear power spectrum
Applying a transformation to a non-Gaussian field can enhance the information content of the resulting power spectrum, by reducing the correlations between Fourier modes. In the context of weak gravitational lensing, it has been shown that this gain in information content is significantly compromised by the presence of shape noise. We apply clipping to mock convergence fields, a technique which is known to be robust in the presence of noise and has been successfully applied to galaxy number density fields. When analysed in isolation the resulting convergence power spectrum returns degraded constraints on cosmological parameters. However, substantial gains can be achieved by performing a combined analysis of the power spectra derived from both the original and transformed fields. Even in the presence of realistic levels of shape noise, we demonstrate that this approach is capable of reducing the area of likelihood contours within the Ωm â Ï8 plane by more than a factor of 3
Are transnational tobacco companies' market access strategies linked to economic development models? A case study of South Korea.
Transnational tobacco companies (TTCs) have used varied strategies to access previously closed markets. Using TTCs' efforts to enter the South Korean market from the late 1980s as a case study, this article asks whether there are common patterns in these strategies that relate to the broader economic development models adopted by targeted countries. An analytical review of the existing literature on TTCs' efforts to access emerging markets was conducted to develop hypotheses relating TTCs' strategies to countries' economic development models. A case study of Korea was then undertaken based on analysis of internal tobacco industry documents. Findings were consistent with the hypothesis that TTCs' strategies in Korea were linked to Korea's export-oriented economic development model and its hostile attitude towards foreign investment. A fuller understanding of TTCs' strategies for expansion globally can be derived by locating them within the economic development models of specific countries or regions. Of foremost importance is the need for governments to carefully balance economic and public health policies when considering liberalisation
Magnetic moment of welded HTS samples: dependence on the current flowing through the welds
We present a method to calculate the magnetic moments of the high-temperature
superconducting (HTS) samples which consist of a few welded HTS parts. The
approach is generalized for the samples of various geometrical shapes and an
arbitrary number of welds. The obtained relations between the sample moment and
the density of critical current, which flows through the welds, allow to use
the magnetization loops for a quantitative characterization of the weld quality
in a wide range of temperatures and/or magnetic fields.Comment: RevTeX4, 4 pages, 2 figures. Submitted to Supercond. Sci. Techno
Painting with baryons: augmenting N-body simulations with gas using deep generative models
Running hydrodynamical simulations to produce mock data of large-scale structure and baryonic probes, such as the thermal Sunyaev-Zeldovich (tSZ) effect, at cosmological scales is computationally challenging. We propose to leverage the expressive power of deep generative models to find an effective description of the large-scale gas distribution and temperature. We train two deep generative models, a variational auto-encoder and a generative adversarial network, on pairs of matter density and pressure slices from the BAHAMAS hydrodynamical simulation. The trained models are able to successfully map matter density to the corresponding gas pressure. We then apply the trained models on 100 lines-of-sight from SLICS, a suite of N-body simulations optimised for weak lensing covariance estimation, to generate maps of the tSZ effect. The generated tSZ maps are found to be statistically consistent with those from BAHAMAS. We conclude by considering a specific observable, the angular cross-power spectrum between the weak lensing convergence and the tSZ effect and its variance, where we find excellent agreement between the predictions from BAHAMAS and SLICS, thus enabling the use of SLICS for tSZ covariance estimation
KiDS-450: Enhancing cosmic shear with clipping transformations
We present the first âclippedâ cosmic shear measurement using data from the Kilo-Degree
Survey (KiDS-450). âClippingâ transformations suppress the signal from the highest density,
non-linear regions of cosmological fields. We demonstrate that these transformations improve
constraints on S8 = Ï8(âŠm/0.3)0.5 when used in combination with conventional two-point
statistics. For the KiDS-450 data, we find that the combined measurements improve the constraints
on S8 by 17%, compared to shear correlation functions alone. We determine the expectation
value of the clipped shear correlation function using a suite of numerical simulations,
and develop methodology to mitigate the impact of masking and shot noise. Future improvements
in numerical simulations and mass reconstruction methodology will permit the precise
calibration of clipped cosmic shear statistics such that clipping can become a standard tool in
weak lensing analyses
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