172 research outputs found
Unmasking Uncle Sam: A Legal Test for Defining and Identifying State Media
In December 2018, the Chair of the House Foreign Affairs Committee published a report detailing how the U.S. Agency for Global Media, the central federal state media agency, illegally targeted social media ads at Americans at least 860 times from 2016 to 2018. The U.S. Agency for Global Media and other U.S. state media agencies have enormous resources, and if left unchecked, could unduly influence public opinion, threaten the free and independent press, and subvert democratic accountability. To address this growing concern, this Article proposes a new, comprehensive legal test for defining and identifying state media that incorporates existing approaches for analyzing government publications employed by the federal government and independent media platforms
Thickness-dependence of the electronic properties in V2O3 thin films
High quality vanadium sesquioxide V2O3 films (170-1100 {\AA}) were grown
using the pulsed laser deposition technique on (0001)-oriented sapphire
substrates, and the effects of film thickness on the lattice strain and
electronic properties were examined. X-ray diffraction indicates that there is
an in-plane compressive lattice parameter (a), close to -3.5% with respect to
the substrate and an out-of-plane tensile lattice parameter (c) . The thin film
samples display metallic character between 2-300 K, and no metal-to-insulator
transition is observed. At low temperature, the V2O3 films behave as a strongly
correlated metal, and the resistivity (\rho) follows the equation \rho =\rho_0
+ A T^2, where A is the transport coefficient in a Fermi liquid. Typical values
of A have been calculated to be 0.14 \mu\Omega cm K^{-2}, which is in agreement
with the coefficient reported for V2O3 single crystals under high pressure.
Moreover, a strong temperature-dependence of the Hall resistance confirms the
electronic correlations of these V2O3 thin films samples.Comment: 4 pages, 4 figure
Energy deposition by heavy ions: Additivity of kinetic and potential energy contributions in hillock formation on CaF2
The formation of nano-hillocks on CaF2 crystal surfaces by individual ion
impact has been studied using medium energy (3 and 5 MeV) highly charged ions
(Xe19+ to Xe30+) as well as swift (kinetic energies between 12 and 58 MeV)
heavy ions. For very slow highly charged ions the appearance of hillocks is
known to be linked to a threshold in potential energy while for swift heavy
ions a minimum electronic energy loss is necessary. With our results we bridge
the gap between these two extreme cases and demonstrate, that with increasing
energy deposition via electronic energy loss the potential energy threshold for
hillock production can be substantially lowered. Surprisingly, both mechanisms
of energy deposition in the target surface seem to contribute in an additive
way, as demonstrated when plotting the results in a phase diagram. We show that
the inelastic thermal spike model, originally developed to describe such
material modifications for swift heavy ions, can be extended to case where
kinetic and potential energies are deposited into the surface.Comment: 12 pages, 4 figure
Interplay Between Chaotic and Regular Motion in a Time-Dependent Barred Galaxy Model
We study the distinction and quantification of chaotic and regular motion in
a time-dependent Hamiltonian barred galaxy model. Recently, a strong
correlation was found between the strength of the bar and the presence of
chaotic motion in this system, as models with relatively strong bars were shown
to exhibit stronger chaotic behavior compared to those having a weaker bar
component. Here, we attempt to further explore this connection by studying the
interplay between chaotic and regular behavior of star orbits when the
parameters of the model evolve in time. This happens for example when one
introduces linear time dependence in the mass parameters of the model to mimic,
in some general sense, the effect of self-consistent interactions of the actual
N-body problem. We thus observe, in this simple time-dependent model also, that
the increase of the bar's mass leads to an increase of the system's chaoticity.
We propose a new way of using the Generalized Alignment Index (GALI) method as
a reliable criterion to estimate the relative fraction of chaotic vs. regular
orbits in such time-dependent potentials, which proves to be much more
efficient than the computation of Lyapunov exponents. In particular, GALI is
able to capture subtle changes in the nature of an orbit (or ensemble of
orbits) even for relatively small time intervals, which makes it ideal for
detecting dynamical transitions in time-dependent systems.Comment: 21 pages, 9 figures (minor typos fixed) to appear in J. Phys. A:
Math. Theo
Structural effects in UO thin films irradiated with fission-energy Xe ions
Uranium dioxide thin films have been successfully grown on LSAT (AlLaOSrTa) substrates by reactive magnetron sputtering. Irradiation by 92 MeV Xe ions to simulate fission damage that occurs within nuclear fuels caused microstructural and crystallographic changes. Initially flat and continuous thin films were produced by magnetron sputtering with a root mean square roughness of 0.35 nm determined by AFM. After irradiation, this roughness increased to 60-70 nm, with the films developing discrete microstructural features: small grains (~3 m), along with larger circular (up to 40 m) and linear formations with non-uniform composition according to the SEM, AFM and EDX results. The irradiation caused significant restructuring of the UO films that was manifested in significant filmsubstrate mixing, observed through EDX analysis. Diffusion of Al from the substrate into the film in unirradiated samples was also observed.Engineering and Physical Sciences Research Council (Grant ID: EP/ I036400/1), Radioactive Waste Management Ltd (formerly the Radioactive Waste Management Directorate of the UK Nuclear Decommissioning Authority, contract NPO004411A-EPS02), Russian Foundation for Basic Research (projects 13-03-90916), CSAR, Grand AccelĂ©lĂ©rateur National dâIons Lourds (GANIL) Caen France, French Network EMIR, CIMAP-CIRIL, M.V.Lomonosov Moscow State University Program of Development, CKP FMI IPCE RA
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Structural effects in UO thin films irradiated with U ions
This work presents the results of a detailed structural characterisation of irradiated and unirradiated single crystal thin films of UO. Thin films of UO were produced by reactive magnetron sputtering onto (0 0 1), (1 1 0) and (1 1 1) single crystal yttria-stabilised zirconia (YSZ) substrates. Half of the samples were irradiated with 110 MeV U ions to fluences of 5 10, 5 10 and 5 10 ions/cm to induce radiation damage, with the remainder kept for reference measurements. It was observed that as-produced UO films adopted the crystallographic orientation of their YSZ substrates. The irradiation fluences used in this study however, were not sufficient to cause any permanent change in the crystalline nature of UO. It has been demonstrated that the effect of epitaxial re-crystallisation of the induced radiation damage can be quantified in terms of kernel average misorientation (KAM) and different crystallographic orientations of UO respond differently to ion irradiation.The irradiation experiment was performed at the Grand AccĂ©lĂ©rateur National dâIons Lourds (GANIL) Caen, France, and supported by the French Network EMIR. A.J. Popel acknowledges funding from the UK EPSRC (grant EP/ I036400/1) and Radioactive Waste Management Ltd (formerly the Radioactive Waste Management Directorate of the UK Nuclear Decommissioning Authority, contract NPO004411A-EPS02)
Structural effects in UO2 thin films irradiated with fission-energy Xe ions
Uranium dioxide thin films have been successfully grown on LSAT (Al10La3O51Sr14Ta7) substrates by reactive magnetron sputtering. Irradiation by 92 MeV 129Xe23+ ions to simulate fission damage that occurs within nuclear fuels caused microstructural and crystallographic changes. Initially flat and continuous thin films were produced by magnetron sputtering with a root mean square roughness of 0.35 nm determined by AFM. After irradiation, this roughness increased to 60â70 nm, with the films developing discrete microstructural features: small grains (âŒ3 ÎŒm), along with larger circular (up to 40 ÎŒm) and linear formations with non-uniform composition according to the SEM, AFM and EDX results. The irradiation caused significant restructuring of the UO2 films that was manifested in significant film-substrate mixing, observed through EDX analysis. Diffusion of Al from the substrate into the film in unirradiated samples was also observed
Structural effects in UO2 thin films irradiated with U ions
This work presents the results of a detailed structural characterisation of irradiated and unirradiated single crystal thin films of UO2. Thin films of UO2 were produced by reactive magnetron sputtering onto (0 0 1), (1 1 0) and (1 1 1) single crystal yttria-stabilised zirconia (YSZ) substrates. Half of the samples were irradiated with 110 MeV 238U31+ ions to fluences of 5 Ă 1010, 5 Ă 1011 and 5 Ă 1012 ions/cm2 to induce radiation damage, with the remainder kept for reference measurements. It was observed that as-produced UO2 films adopted the crystallographic orientation of their YSZ substrates. The irradiation fluences used in this study however, were not sufficient to cause any permanent change in the crystalline nature of UO2. It has been demonstrated that the effect of epitaxial re-crystallisation of the induced radiation damage can be quantified in terms of kernel average misorientation (KAM) and different crystallographic orientations of UO2 respond differently to ion irradiation
First order antiferro-ferromagnetic transition in Fe49(Rh0.93Pd0.07)51 under simultaneous application of magnetic field and external pressure
The magnetic field-pressure-temperature (H-P-T) phase diagram for first order
antiferromagnetic (AFM) to ferromagnetic (FM) transition in
Fe49(Rh0.93Pd0.07)51 has been constructed using resistivity measurements under
simultaneous application of magnetic field (up to 8 Tesla) and pressure (up to
20 kbar). Temperature dependence of resistivity ({\rho}-T) shows that with
increasing pressure, the width of the transition and the extent of hysteresis
decreases whereas with the application of magnetic field it increases.
Consistent with existing literature the first order transition temperature (TN)
increases with the application of external pressure (~ 7.3 K/ kbar) and
decreases with magnetic field (~ - 12.8 K/Tesla). Exploiting these opposing
trends, resistivity under simultaneous application of magnetic field and
pressure is used to distinguish the relative effect of temperature, magnetic
field and pressure on disorder broadened first order transition. For this a set
of H and P values are chosen for which TN (H1, P1) = TN (H2, P2). Measurements
for such combinations of H and P show that the temperature dependence of
resistivity is similar i.e. the broadening (in temperature) of transition as
well as extent of hysteresis remains independent of H and P. The transition
width decreases exponentially with increasing temperature. Isothermal
magnetoresistance measurement under various constant pressure show that even
though the critical field required for AFM-FM transition depends on applied
pressure, the hysteresis as well as transition width (in magnetic field) both
remains independent of pressure, consistent with our conclusions drawn from
{\rho}-T measurements.Comment: 10 pages, 6 figure
A genomic Neolithic time transect of hunter-farmer admixture in central Poland.
Ancient DNA genome-wide analyses of Neolithic individuals from central and southern Europe indicate an overall population turnover pattern in which migrating farmers from Anatolia and the Near East largely replaced autochthonous Mesolithic hunter-gatherers. However, the genetic history of the Neolithic transition in areas lying north of the European Neolithic core region involved different levels of admixture with hunter-gatherers. Here we analyse genome-wide data of 17 individuals spanning from the Middle Neolithic to the Early Bronze Age (4300-1900 BCE) in order to assess the Neolithic transition in north-central Poland, and the local impacts of hunter-farmer contacts and Late Neolithic steppe migrations. We evaluate the influence of these on local populations and assess if and how they change through time, reporting evidence of recurrent hunter-farmer admixture over three millennia, and the co-existence of unadmixed hunter-gatherers as late as 4300 BCE. During the Late Neolithic we report the appearance of steppe ancestry, but on a lesser scale than previously described for other central European regions, with evidence of stronger affinities to hunter-gatherers than to steppe pastoralists. These results help understand the Neolithic palaeogenomics of another central European area, Kuyavia, and highlight the complexity of population interactions during those times
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