Effect of Pt impurities on the magnetocrystalline anisotropy of hcp Co: a first-principles study

In terms of the fully relativistic screened Korringa-Kohn-Rostoker method we investigate the variation in the magnetocrystalline anisotropy energy (MAE) of hexagonal close-packed cobalt with the addition of platinum impurities. In particular, we perform calculations on a bulk cobalt system in which one of the atomic layers contains a fractional, substitutional platinum impurity. Our calculations show that at small concentrations of platinum the MAE is reduced, while at larger concentrations the MAE is enhanced. This change of the MAE can be attributed to an interplay between on-site Pt MAE contributions and induced MAE contributions on the Co sites. The latter ones are subject to pronounced, long-ranged Friedel-oscillations that can lead to significant size effects in the experimental determination of the MAE of nano-sized samples.Comment: 16 page

Spin-correlations and magnetic structure in an Fe monolayer on 5d transition metal surfaces

We present a detailed first principles study on the magnetic structure of an Fe monolayer on different surfaces of 5d transition metals. We use the spin-cluster expansion technique to obtain parameters of a spin model, and predict the possible magnetic ground state of the studied systems by employing the mean field approach and in certain cases by spin dynamics calculations. We point out that the number of shells considered for the isotropic exchange interactions plays a crucial role in the determination of the magnetic ground state. In the case of Ta substrate we demonstrate that the out-of-plane relaxation of the Fe monolayer causes a transition from ferromagnetic to antiferromagnetic ground state. We examine the relative magnitude of nearest neighbour Dzyaloshinskii-Moriya (D) and isotropic (J) exchange interactions in order to get insight into the nature of magnetic pattern formations. For the Fe/Os(0001) system we calculate a very large D/J ratio, correspondingly, a spin spiral ground state. We find that, mainly through the leading isotropic exchange and Dzyaloshinskii-Moriya interactions, the inward layer relaxation substantially influences the magnetic ordering of the Fe monolayer. For the Fe/Re(0001) system characterized by large antiferromagnetic interactions we also determine the chirality of the $120^{\circ}$ N\'eel-type ground state.Comment: 15 pages, 8 figures, 2 table

Electronic spectroscopy of 1-cyanonaphthalene cation for astrochemical consideration

Context. Polycyclic aromatic hydrocarbons (PAHs) are believed to be the carriers of the aromatic infrared bands and have been proposed as candidates to explain other astronomical phenomena such as diffuse interstellar bands (DIBs). The first aromatic structures possessing more than one ring, 1- and 2-cyanonaphthalene (CNN), were recently detected by rotational spectroscopy in the dense molecular cloud TMC-1. Laboratory investigations have indicated that due to fast and efficient relaxation through recurrent fluorescence (RF), CNN+ may be photostable in the harsh conditions of the lower density, more diffuse regions of the interstellar medium (ISM) exposed to ultraviolet (UV) radiation. As a result, it has been suggested that the widely held belief that small PAHs present in these regions are dissociated may need to be revisited. If 1-CNN+ is able to survive in the diffuse ISM it may contribute to the population of 1-CNN observed in TMC-1. To investigate the abundance of 1-CNN+ in diffuse clouds, laboratory spectroscopy is required. The present work concerns the electronic spectroscopy of 1-CNN+ in absorption and the search for its spectroscopic fingerprints in diffuse clouds. Aims. The aim is to obtain laboratory data on the electronic transitions of gas-phase 1-CNN+ under conditions appropriate for comparison with DIBs and assess abundance in diffuse clouds. Methods. Spectroscopic experiments are carried out using a cryogenic ion trapping apparatus in which gas-phase 1-CNN+ is cooled to temperatures below 10 K through buffer gas cooling. Calculations are carried out using time-dependent density-functional theory. Results. Experimental and theoretical data on the D2 ← D0 and D3 ← D0 electronic transitions of 1-CNN+ are reported. The former transition has a calculated oscillator strength of f = 0.075 and possesses a pattern dominated by its origin band. The origin band is located at 7343 Å and has a full width at half maximum of 28 Å. In observational data, this falls in a region polluted by telluric water lines, hindering assessment of its abundance. Conclusions. Space-based observations are required to search for the spectroscopic signatures of 1-CNN+ and evaluate the hypothesis that this small aromatic system, stabilised by RF, may be able to survive in regions of the ISM exposed to UV photons

Nutritional modulation of the intestinal microbiota: future opportunities for the prevention and treatment of neuroimmune and neuroinflammatory disease

© 2018 Elsevier Inc. The gut-brain-axis refers to the bidirectional communication between the enteric nervous system and the central nervous system. Mounting evidence supports the premise that the intestinal microbiota plays a pivotal role in its function and has led to the more common and perhaps more accurate term gut-microbiota-brain axis. Numerous studies have identified associations between an altered microbiome and neuroimmune and neuroinflammatory diseases. In most cases, it is unknown if these associations are cause or effect; notwithstanding, maintaining or restoring homeostasis of the microbiota may represent future opportunities when treating or preventing these diseases. In recent years, several studies have identified the diet as a primary contributing factor in shaping the composition of the gut microbiota, and in turn, the mucosal and systemic immune systems. In this review, we will discuss the potential opportunities and challenges with respect to modifying and shaping the microbiota through diet and nutrition in order to treat or prevent neuroimmune and neuroinflammatory disease

Gold- and silver-based nano-particles influence pseudo-typed lenti-viral infection

The application of bio-active noble-metal-based nano-particles (NPs) with unique physico-chemical properties is multifaceted. Among other roles, they can be used as anti-viral agents, and at the same time might serve as matrix to facilitate the transport of various molecules for therapeutic purposes directly or via genetically modified microbes. For this reason, the influence of nano-materials on viral infection in living cells is described in this study utilizing pseudo-typed lenti-viral particles based on human immuno-deficiency virus 1 (HIV-1). Cells were exposed to various NPs and subsequently infected with lenti-virus. Transfection efficiency was quantified by flow-cytometry analysis. Gold-based NPs increased, silver-containing NPs decreased, while other NPs had little or no effect on viral infection rate. The opposing effect of NPs is determined by the size, chemical nature and surface chemistry of the nano-materials, which govern their interactions with molecular species present in their environment. These characteristics enable the distinct use of different NPs in various fields of bio-medicine. © 2013 Bentham Science Publishers