Cygnus A super-resolved via convex optimisation from VLA data

We leverage the Sparsity Averaging Reweighted Analysis (SARA) approach for interferometric imaging, that is based on convex optimisation, for the super-resolution of Cyg A from observations at the frequencies 8.422GHz and 6.678GHz with the Karl G. Jansky Very Large Array (VLA). The associated average sparsity and positivity priors enable image reconstruction beyond instrumental resolution. An adaptive Preconditioned Primal-Dual algorithmic structure is developed for imaging in the presence of unknown noise levels and calibration errors. We demonstrate the superior performance of the algorithm with respect to the conventional CLEAN-based methods, reflected in super-resolved images with high fidelity. The high resolution features of the recovered images are validated by referring to maps of Cyg A at higher frequencies, more precisely 17.324GHz and 14.252GHz. We also confirm the recent discovery of a radio transient in Cyg A, revealed in the recovered images of the investigated data sets. Our matlab code is available online on GitHub.Comment: 14 pages, 7 figures (3/7 animated figures), accepted for publication in MNRA

Universal Scaling Behavior of Anomalous Hall Effect and Anomalous Nernst Effect in Itinerant Ferromagnets

Anomalous Hall effect (AHE) and anomalous Nernst effect (ANE) in a variety of ferromagnetic metals including pure metals, oxides, and chalcogenides, are studied to obtain unified understandings of their origins. We show a universal scaling behavior of anomalous Hall conductivity $\sigma_{xy}$ as a function of longitudinal conductivity $\sigma_{xx}$ over five orders of magnitude, which is well explained by a recent theory of the AHE taking into account both the intrinsic and extrinsic contributions. ANE is closely related with AHE and provides us with further information about the low-temperature electronic state of itinerant ferromagnets. Temperature dependence of transverse Peltier coefficient $\alpha_{xy}$ shows an almost similar behavior among various ferromagnets, and this behavior is in good agreement quantitatively with that expected from the Mott rule.Comment: 4pages, 4figures, 1tabl

Chemical Potential Shift in Nd2−x_{2-x}Cex_{x}CuO4_{4}: Contrasting Behaviors of the Electron- and Hole-Doped Cuprates

We have studied the chemical potential shift in the electron-doped superconductor Nd$_{2-x}$Ce$_{x}$CuO$_{4}$ by precise measurements of core-level photoemission spectra. The result shows that the chemical potential monotonously increases with electron doping, quite differently from La$_{2-x}$Sr$_{x}$CuO$_{4}$, where the shift is suppressed in the underdoped region. If the suppression of the shift in La$_{2-x}$Sr$_{x}$CuO$_{4}$ is attributed to strong stripe fluctuations, the monotonous increase of the chemical potential is consistent with the absence of stripe fluctuations in Nd$_{2-x}$Ce$_{x}$CuO$_{4}$. The chemical potential jump between Nd$_{2}$CuO$_{4}$ and La$_{2}$CuO$_{4}$ is found to be much smaller than the optical band gaps.Comment: 4 pages, 5 figure

Strength of Correlations in electron and hole doped cuprates

High temperature superconductivity was achieved by introducing holes in a parent compound consisting of copper oxide layers separated by spacer layers. It is possible to dope some of the parent compounds with electrons, and their physical properties are bearing some similarities but also significant differences from the hole doped counterparts. Here, we use a recently developed first principles method, to study the electron doped cuprates and elucidate the deep physical reasons why their behavior is so different than the hole doped materials. We find that electron doped compounds are Slater insulators, e.g. a material where the insulating behavior is the result of the presence of magnetic long range order. This is in sharp contrast with the hole doped materials, where the parent compound is a Mott charge transfer insulator, namely a material which is insulating due to the strong electronic correlations but not due to the magnetic order.Comment: submitted to Nature Physic

Superconducting Gap Anisotropy in Nd1.85_{1.85}Ce0.15_{0.15}CuO4_4: Results from Photoemission

We have performed angle resolved photoelectron spectroscopy on the electron doped cuprate superconductor Nd$_{1.85}$Ce$_{0.15}$CuO$_4$. A comparison of the leading edge midpoints between the superconducting and normal states reveals a small, but finite shift of 1.5-2 meV near the ($\pi$,0) position, but no observable shift along the zone diagonal near ($\pi$/2,$\pi$/2). This is interpreted as evidence for an anisotropic superconducting gap in the electron doped materials, which is consistent with the presence of d-wave superconducting order in this cuprate superconductor.Comment: 5 pages, 4 figures, RevTex, to be published in Phys. Rev. Let

Economic Advantage of In-Country Utilization of Nigeria Crude Oil

Crude oil refining is a unique and important link in the supply chain of petroleum products from the wellhead to the end user. Refining adds value through conversion of crude oil and other flows into dozens of co-refined products. Nigeria is probably the largest importer of refined petroleum products on the continent, creating a lucrative refinery market in Europe and the United States. Subsidies have also contributed to the low capacity utilization in our refineries. The current situation of the four National refineries and high dependency on crude oil proceeds has made Nigeria government a full time exporter of crude oil. Because of our population, the demand for refined products which are imported in foreign currency have induced pressure on our local currency; thus, presenting a large cost to the economy. Instead of looking for international crude oil traders or embarking on discounted sales of our sweet crude in this era of low crude oil price, it will be profitable to utilize this crude oil in Nigeria. We will not only export the raw crude but also enrich our petrochemical industries and agricultural sector with the byproducts or co-products from its refining. Investment in petrochemical industry will really bring about an astounding effect in our economy because of enlargement of private domain which will usher new phase of life by reducing inequalities in the nation’s income. There has never been a doubt about the large size of the Nigerian market for refined crude oil and petrochemical products. As more countries are discovering crude oil, Nigeria’s crude oil export will gradually drop leaving us with excess crude oil instead of excess crude account. There is a need for government to develop industrial sectors that support or leverage its energy resources. The actualization will make it possible for Nigeria to change from raw material supplier to value-added product supplier

Spatial analysis of locational conflicts: case study: locational conflicts generated by the expansion of built up surfaces in the northern area of Bucharest, Romania

The aim of this paper is to identify and analyze land use conflicts existing in the northern area of Bucharest and to spatially model their impact on the expandint residential areas. The main objectives are: 1) to analyze the dynamics of built up surfaces between 1975-2010; 2) to analyze the spatial and temporal dynamic of locational conflicts and 3) to spatially model the impact of locational conflicts on residential areas.Peer Reviewe

Nigerian Oil Palm Industry as a Sustainable Renewable Energy Resource

Nigeria had been standing aloof at exploring her bioresources as a means of combatting her energy cum economic challenges. After some critical examination, the authors showcased Nigerian Palm Industry as a viable biofuel source yet unexplored. Using a combination of some economic and vegetation facts and figures to comparatively analyse, Nigerian oil palm industry to validate the prospect of a sustainable commercial-scale biofuel production that can serve as both affordable alternative cleaner energy fuel for her populace and immense export revenue. The Nigerian government is encouraged to latch onto this bioresource prospec

Pseudogap of metallic layered nickelate R2-xSrxNiO4 (R=Nd, Eu) crystals measured using angle-resolved photoemission spectroscopy

We have investigated charge dynamics and electronic structures for single crystals of metallic layered nickelates, R2-xSrxNiO4 (R=Nd, Eu), isostructural to La2-xSrxCuO4. Angle-resolved photoemission spectroscopy on the barely-metallic Eu0.9Sr1.1NiO4 (R=Eu, x=1.1) has revealed a large hole surface of x2-y2 character with a high-energy pseudogap of the same symmetry and comparable magnitude with those of underdoped (x<0.1) cuprates, although the antiferromagnetic interactions are one order of magnitude smaller. This finding strongly indicates that the momentum-dependent pseudogap feature in the layered nickelate arises from the real-space charge correlation.Comment: 4 pages, 4 figures. Accepted in Physical Review Letter