Unveiling intrinsic material and extrinsic pinning dimensionality in superconductors: Why Fe(Se,Te) is able to mimic YBCO.

Discovery of iron-based superconductors paved the way to a competitor of high-temperature superconductors, easier to produce, better performing in high fields, and promising to be less expensive. Critical parameters are investigated by resistivity measurements as a function of temperature, field, and angle R(T,H,θ). This work presents a deep analysis of H-θ phase diagram of PLD-processed Fe(Se,Te) superconducting films, thus revealing material and pinning anisotropy at once. By selecting different thresholds along the R(T,H,θ) curves, all possible regimes emerge. Surprisingly, anisotropy arises moving from the upper critical field toward the irreversibility line: gradually a non-monotonous transition from 3D to 2D, and backward to 3D occurs. Although Fe(Se,Te) appears as a 3D superconductor, its anisotropic pinning landscape shows up similarities with an intrinsic layered superconductor and Fe(Se,Te) definitively mimics YBCO. We propose a general method to disentangle, in any other superconductor, material dimensionality and pinning anisotropy that are key constraints for applications.

Point-Contact Spectroscopy in Bulk Samples of Electron-Doped Cuprate Superconductors.

Point-contact spectroscopy was performed on bulk samples of electron-doped high temperature superconductor Nd2-xCexCuO4-δ. The samples were characterized using X-ray diffraction and scanning electron microscopy equipped with a wavelength-dispersive spectrometer and an electron backscatter diffraction detector. Samples with Ce content x = 0.15 showed the absence of spurious phases and randomly oriented grains, most of which had dimensions of approximately 220 µm2. The low-bias spectra in the tunneling regime, i.e., high-transparency interface, exhibited a gap feature at about ±5 meV and no zero-bias conductance, despite the random oriented grains investigated within our bulk samples, consistent with most of the literature data on oriented samples. High-bias conductance was also measured in order to obtain information on the properties of the barrier. A V-shape was observed in some cases, instead of the parabolic behavior expected for tunnel junctions.

Rough and Porous Micropebbles of CeCu2Si2 for Energy Storage Applications.

Supercapacitors have attracted considerable attention due to their advantages, including being lightweight and having rapid charge-discharge, a good rate capability, and high cyclic stability. Electrodes are one of the most important factors influencing the performance of supercapacitors. Herein, a three-dimensional network of rough and porous micropebbles of CeCu2Si2 has been prepared using a one-step procedure and tested for the first time as a supercapacitor electrode. The synthesized material was extensively characterized in a three-electrode configuration using different electrochemical techniques, such as cyclic voltammetry (CV), galvanostatic charge and discharge (GCD) tests, and electrochemical impedance spectroscopy (EIS). CeCu2Si2 shows rather high mass-capacitance values: 278 F/g at 1 A/g and 295 F/g at 10 mV/s. Moreover, the material exhibits remarkable long-term stability: 98% of the initial capacitance was retained after 20,000 cycles at 10 A/g and the Coulombic efficiency remains equal to 100% at the end of the cycles.

Upper critical magnetic field in NbRe and NbReN micrometric strips.

Non-centrosymmetric superconductors have recently received significant interest due to their intriguing physical properties such as multigap and nodal superconductivity, helical vortex states, as well as non-trivial topological effects. Moreover, large values of the upper critical magnetic field have been reported in these materials. Here, we focus on the study of the temperature dependence of the perpendicular magnetic field of NbRe and NbReN films patterned in micrometric strips. The experimental data are studied within the Werthamer-Helfand-Hohenberg theory, which considers both orbital and Zeeman pair breaking. The analysis of the results shows different behavior for the two materials with a Pauli contribution relevant only in the case of NbReN.

Dimensionality of the Superconductivity in the Transition Metal Pnictide WP.

We report theoretical and experimental results on the transition metal pnictide WP. The theoretical outcomes based on tight-binding calculations and density functional theory indicate that WP is a three-dimensional superconductor with an anisotropic electronic structure and nonsymmorphic symmetries. On the other hand, magnetoresistance experimental data and the analysis of superconducting fluctuations of the conductivity in external magnetic field indicate a weakly anisotropic three-dimensional superconducting phase.

Majorana/Andreev crossover and the fate of the topological phase transition in inhomogeneous nanowires.

Majorana bound states (MBS) and Andreev bound states (ABS) in realistic Majorana nanowires setups have similar experimental signatures which make them hard to distinguishing one from the other. Here, we characterize the continuous Majorana/Andreev crossover interpolating between fully-separated, partially-separated, and fully-overlapping Majorana modes, in terms of global and local topological invariants, fermion parity, quasiparticle densities, Majorana pseudospin and spin polarizations, density overlaps and transition probabilities between opposite Majorana components. We found that in inhomogeneous wires, the transition between fully-overlapping trivial ABS and nontrivial MBS does not necessarily mandate the closing of the bulk gap of quasiparticle excitations, but a simple parity crossing of partially-separated Majorana modes (ps-MM) from trivial to nontrivial regimes. We demonstrate that fully-separated and fully-overlapping Majorana modes correspond to the two limiting cases at the opposite sides of a continuous crossover: the only distinction between the two can be obtained by estimating the degree of separations of the Majorana components. This result does not contradict the bulk-edge correspondence: indeed, the field inhomogeneities driving the Majorana/Andreev crossover have a length scale comparable with the nanowire length, and therefore correspond to a nonlocal perturbation which breaks the topological protection of the MBS.

Critical Current and Pinning Features of a CaKFe4As4 Polycrystalline Sample.

We analyze the magnetic behavior of a CaKFe4As4 polycrystalline sample fabricated by a mechanochemically assisted synthesis route. By means of DC magnetization (M) measurements as a function of the temperature (T) and DC magnetic field (H) we study its critical parameters and pinning features. The critical temperature Tc has been evaluated by M(T) curves performed in Zero Field Cooling-Field Cooling conditions. These curves show the presence of a little magnetic background for temperatures above Tc, as also confirmed by the hysteresis loops M(H). Starting from the M(H) curves, the critical current density Jc of the sample has been calculated as a function of the field at different temperatures in the framework of the Bean critical state model. The Jc(H) values are in line with the ones reported in the literature for this typology of samples. By analyzing the temperature dependence of the critical current density Jc(T) at different magnetic fields, it has been found that the sample is characterized by a strong type pinning regime. This sample peculiarity can open perspectives for future improvement in the fabrication of this material.

Nanoscale analysis of superconducting Fe(Se,Te) epitaxial thin films and relationship with pinning properties.

The process of developing superconducting materials for large scale applications is mainly oriented to optimize flux pinning and the current carrying capability. A powerful approach to investigate pinning properties is to combine high resolution imaging with transport measurements as a function of the magnetic field orientation, supported by a pinning modelling. We carry out Transmission Electron Microscopy, Electron Energy Loss Spectroscopy and critical current measurements in fields up to 16 T varying the angle between the field and c-axis of Fe(Se,Te) epitaxial thin films deposited on CaF2 substrates. We find evidence of nanoscale domains with different Te:Se stoichiometry and/or rotated and tilted axes, as well as of lattice distortions and two-dimensional defects at the grain boundaries. These elongated domains are tens of nm in size along the in-plane axes. We establish a correlation between these observed microstructural features and the pinning properties, specifically strongly enhanced pinning for the magnetic field oriented in-plane and pinning emerging at higher fields for out-of-plane direction. These features can be accounted for within a model where pinning centers are local variations of the critical temperature and local variations of the mean free path, respectively. The identification of all these growth induced defects acting as effective pinning centers may provide useful information for the optimization of Fe(Se,Te) coated conductors.

Effective Magnetic Field Dependence of the Flux Pinning Energy in FeSe0.5Te0.5 Superconductor.

The role of a layered structure in superconducting pinning properties is still at a debate. The effects of the vortex shape, which can assume for example a staircase form, could influence the interplay with extrinsic pinning coming from the specific defects of the material, thus inducing an effective magnetic field dependence. To enlighten this role, we analysed the angular dependence of flux pinning energy U(H,θ) as a function of magnetic field in FeSe0.5Te0.5 thin film by considering the field components along the ab-plane of the crystal structure and the c-axis direction. U(H,θ) has been evaluated from magneto-resistivity measurements acquired at different orientations between the applied field up to 16 T and FeSe0.5Te0.5 thin films grown on a CaF2 substrate. We observed that the U(H,θ) shows an anisotropic trend as a function of both the intensity and the direction of the applied field. Such a behaviour can be correlated to the presence of extended defects elongated in the ab-planes, thus mimicking a layered superconductor, as we observed in the microstructure of the compound. The comparison of FeSe0.5Te0.5 with other superconducting materials provides a more general understanding on the flux pinning energy in layered superconductors.

Transport and Point Contact Measurements on Pr1-xCexPt4Ge12 Superconducting Polycrystals.

We performed a detailed investigation of the superconducting properties of polycrystalline Pr1-xCexPt4Ge12 pellets. We report the effect of Ce substitution, for x = 0.07, on magnetic field phase diagram H-T. We demonstrate that the upper critical field is well described by the Ginzburg-Landau model and that the irreversibility field line has a scaling behaviour similar to cuprates. We also show that for magnetic fields lower than 0.4 T, the activation energy follows a power law of the type ?-1/2, suggesting a collective pinning regime with a quasi-2D character for the Ce-doped compound with x = 0.07. Furthermore, by means of a point contact Andreev reflection spectroscopy setup, we formed metal/superconductor nano-junctions as small as tens of nanometers on the PrPt4Ge12 parent compound (x = 0). Experimental results showed a wide variety of conductance features appearing in the dI/dV vs. V spectra, all explained in terms of a modified Blonder-Tinkham-Klapwijk model considering a superconducting order parameter with nodal directions as well as sign change in the momentum space for the sample with x = 0. The numerical simulations of the conductance spectra also demonstrate that s-wave pairing and anisotropic s-waves are unsuitable for reproducing experimental data obtained at low temperature on the un-doped compound. Interestingly, we show that the polycrystalline nature of the superconducting PrPt4Ge12 sample can favour the formation of an inter-grain Josephson junction in series with the point contact junction in this kind of experiments.

Potential toxic elements in groundwater and their health risk assessment in drinking water of Limpopo National Park, Gaza Province, Southern Mozambique.

Concentrations of trace elements in drinking water affect its safety and acceptability for use. Potentially toxic element (PTE) contaminations are considered extremely hazardous because of toxicity, persistence, and bioaccumulative behaviour. Many areas in the Southern African Development Community are data poor and have poor accessibility. The results of our previous research identified the presence of fossil waters in southern Limpopo National Park. Groundwater and river water are the only sources of drinking water for the villages in the study area. The current study focuses on the understanding of trace element distribution and health perspectives of PTEs (Hg, U, Sr, B, and Mn) in the groundwater and surface water samples (rivers and lakes) collected within the buffer zone of the Limpopo National Park, Southern Mozambique. Two sampling campaigns (October 2016-March 2017) were carried out during the end of the wet season and the end of the dry season to analyse the differences. The results improved our knowledge of the occurrence of trace elements in drinking water in an area where water resources play a fundamental role-because of their scarcity-and where the climate is harsh. ICP-MS results provided information on concentration ranges, highlighting the exceedance of the permissible maximum limit of mercury imposed by the World Health Organization on several groundwater samples. In the buffer zone of Limpopo Park, the highest levels of risk seem to be associated with the presence of Hg and U in drinking water. The use of risk assessment markers such as non-cancer risk value (hazard quotient [HQ]) revealed the exceedance of HQ values for Hg and U. The HQ values are higher in the wet season than the dry season, and most of the exceedance has been found in groundwater. HQ values are higher in exposed children than exposed adults. The water of Lake Massingir seems to be safer than any other source, but people do not currently use it because of the distance between the lake and their villages. Proactive control and research on alternative solutions for the water needs of the population and on creation of water distribution are recommended. In the current study, drinking water was the only route of exposure that was evaluated. Therefore, it would be appropriate to investigate the concentrations of PTEs in crops, livestock, and any other potential pathways.

Vortex lattice instability at the nanoscale in a parallel magnetic field.

In superconducting materials a dynamical rearrangement of the vortex lattice occurs by forcing vortices at high velocities, until the system can become unstable. This phenomenon is known as vortex lattice instability, in which a sudden transition drives the superconducting system abruptly to the normal state. We present an experimental study on submicron bridges of NbN and NbTiN ultra-thin films with a thickness of few nanometers. The nanoscale effect on vortex lattice instability is investigated not only by the ultra-thin thickness in wide bridges, but also by changing the direction of the external magnetic field applied parallel and perpendicular to the c-axis epitaxial films. Indeed, measurements are performed for both orientations and show the vortex lattice instability, regardless of the superconducting material. Critical currents I c as well as instability currents I* have been compared. However, only in the parallel configuration an unusual 'flying birds' feature appears in the magnetic field dependence of current switching, as a consequence of the ratio I*/I c that is approaching 1. This amazing tendency becomes relevant for practical applications involving nanostructures, since by scaling down sample thickness and rotating the external field towards the in-plane orientation, the ultra-thin film geometry can mimic the bridge narrowing down to the nanoscale.

Assessment of groundwater quality in the buffer zone of Limpopo National Park, Gaza Province, Southern Mozambique.

Many areas in the Southern African Development Community are data-poor and poorly accessible. Water quality assessment in these areas therefore has to rely on the limited available data, coupled with restricted field sampling. This paper documents the first evaluation of the main geochemical processes and impact of anthropogenic and natural sources of contamination on the groundwater quality of the aquifer system used for domestic and agricultural purposes in Limpopo National Park, Gaza Province, Southern Mozambique. Twenty-five groundwater and surface water samples were collected during two field campaigns, one in October 2016 (the end of the arid period) and the other in March 2017 (the end of the wet period). In the field, the researchers analysed chemical-physical parameters such as temperature, pH and EC. In the laboratory, the major ions (boron, Na+, Ca2+, K+, Mg2+) and anions (Cl-, SO42-, NO3-, HCO3-, CO32-) were determined, and almost all groundwater samples fall into the brackish water category. The B/Cl ratio and δ11B concentrations were then measured to better understand the origin of these brackish waters. The direct relationship between boron and chlorine and δ11B concentrations above 40‰ suggests the presence of fossil water in the aquifer. The groundwater in this area was found to be above the limits stated as desirable by the Department of Water and Sanitation (DWS) and the World Health Organisation for domestic and irrigation purposes. The suitability of the groundwater for drinking purposes was also evaluated, with the results indicating that it is not suitable. The values of the sodium absorption ratio, sodium percentage and electrical conductivity show that most of the groundwater samples are also not suitable for agricultural purposes. However, the surface waters have higher quality for both domestic and irrigation purposes. The water of Massingir Lake turns out to be the most suitable resource for a possible rural development plan for the area.

Angular dependence of vortex instability in a layered superconductor: the case study of Fe(Se,Te) material.

Anisotropy effects on flux pinning and flux flow are strongly effective in cuprate as well as iron-based superconductors due to their intrinsically layered crystallographic structure. However Fe(Se,Te) thin films grown on CaF2 substrate result less anisotropic with respect to all the other iron based superconductors. We present the first study on the angular dependence of the flux flow instability, which occurs in the flux flow regime as a current driven transition to the normal state at the instability point (I*, V*) in the current-voltage characteristics. The voltage jumps are systematically investigated as a function of the temperature, the external magnetic field, and the angle between the field and the Fe(Se,Te) film. The scaling procedure based on the anisotropic Ginzburg-Landau approach is successfully applied to the observed angular dependence of the critical voltage V*. Anyway, we find out that Fe(Se,Te) represents the case study of a layered material characterized by a weak anisotropy of its static superconducting properties, but with an increased anisotropy in its vortex dynamics due to the predominant perpendicular component of the external applied magnetic field. Indeed, I* shows less sensitivity to angle variations, thus being promising for high field applications.

Vitamin B12 among Vegetarians: Status, Assessment and Supplementation.

Cobalamin is an essential molecule for humans. It acts as a cofactor in one-carbon transfers through methylation and molecular rearrangement. These functions take place in fatty acid, amino acid and nucleic acid metabolic pathways. The deficiency of vitamin B12 is clinically manifested in the blood and nervous system where the cobalamin plays a key role in cell replication and in fatty acid metabolism. Hypovitaminosis arises from inadequate absorption, from genetic defects that alter transport through the body, or from inadequate intake as a result of diet. With the growing adoption of vegetarian eating styles in Western countries, there is growing focus on whether diets that exclude animal foods are adequate. Since food availability in these countries is not a problem, and therefore plant foods are sufficiently adequate, the most delicate issue remains the contribution of cobalamin, which is poorly represented in plants. In this review, we will discuss the status of vitamin B12 among vegetarians, the diagnostic markers for the detection of cobalamin deficiency and appropriate sources for sufficient intake, through the description of the features and functions of vitamin B12 and its absorption mechanism.

Pleiotropic Actions of Peroxisome Proliferator-Activated Receptors (PPARs) in Dysregulated Metabolic Homeostasis, Inflammation and Cancer: Current Evidence and Future Perspectives.

BACKGROUND: Peroxisome proliferator-activated receptors (PPARs) have demonstrated a lot of important effects in the regulation of glucose and lipid metabolism and in the correct functioning of adipose tissue. Recently, many studies have evaluated a possible effect of PPARs on tumor cells. The purpose of this review is to describe the effects of PPARs, their action and their future prospective; METHODS: Narrative review aimed to synthesize cutting-edge evidence retrieved from searches of computerized databases; RESULTS: PPARs play a key role in metabolic diseases, which include several cardiovascular diseases, insulin resistance, type 2 diabetes, metabolic syndrome, impaired immunity and the increasing risk of cancer; in particular, PPARα and PPARß/δ mainly enable energy combustion, while PPARγ contributes to energy storage by enhancing adipogenesis; CONCLUSION: PPAR agonists could represent interesting types of molecules that can treat not only metabolic diseases, but also inflammation and cancer. Additional research is needed for the identification of high-affinity, high-specificity agonists for the treatment of obesity, type 2 diabetes (T2DM) and other metabolic diseases. Further studies are needed also to elucidate the role of PPARs in cancer.

Peroxisome Proliferator-Activated Receptor Modulation during Metabolic Diseases and Cancers: Master and Minions.

The prevalence of obesity and metabolic diseases (such as type 2 diabetes mellitus, dyslipidaemia, and cardiovascular diseases) has increased in the last decade, in both industrialized and developing countries. This also coincided with our observation of a similar increase in the prevalence of cancers. The aetiology of these diseases is very complex and involves genetic, nutritional, and environmental factors. Much evidence indicates the central role undertaken by peroxisome proliferator-activated receptors (PPARs) in the development of these disorders. Due to the fact that their ligands could become crucial in future target-therapies, PPARs have therefore become the focal point of much research. Based on this evidence, this narrative review was written with the purpose of outlining the effects of PPARs, their actions, and their prospective uses in metabolic diseases and cancers.

Intragastric balloon in association with lifestyle and/or pharmacotherapy in the long-term management of obesity.

BACKGROUND: Intragastric balloon (BioEnterics Intragastric Balloon, BIB®) or pharmacotherapy are possible options for the treatment of obese patients when traditional approaches have failed. The aim of our study was to compare in obese patients the effect on weight loss and metabolic changes of lifestyle modifications associated with either BIB or pharmacotherapy or the two treatments in sequence as a maintenance strategy for weight loss. METHODS: Fifty obese patients were recruited and randomly assigned to lifestyle modifications combined with either BIB for 6 months (n = 30) or sibutramine (pharmacotherapy group) for 1 year (n = 20). After BIB removal, patients were randomly assigned to either correct lifestyle (BIB/lifestyle) or lifestyle plus pharmacotherapy (BIB/pharmacotherapy). RESULTS: At 6 months, patients treated with BIB lost significantly (P < 0.05) more weight (percent of initial weight lost, %IWL = 14.5 ± 1.2; percent of excess BMI lost, %EBL = 37.7 ± 3.2) than patients who received pharmacological treatment (%IWL = 9.1 ± 1.5, %EBL = 25.3 ± 4.1). At 1 year, the weight lost was significantly (P < 0.05) greater in patients treated with either BIB/pharmacotherapy (%IWL = 15.8 ± 2.3%, %EBL = 41.3 ± 6.7%) or BIB/lifestyle (%IWL = 14.3 ± 2.7, %EBL = 34.9 ± 6.5%) in respect to pharmacotherapy group (%IWL = 8.0 ± 1.4%, %EBL = 22.1 ± 3.9%). Moreover, patients treated sequentially with BIB/lifestyle or BIB/pharmacotherapy showed a significant (P < 0.05) improvement in insulin sensitivity and triglycerides levels. CONCLUSIONS: BIB represents an efficacious long-term obesity treatment when supplemental strategies, as lifestyle modifications or pharmacotherapy, are established for weight maintenance after its removal.

The SH2B1 obesity locus is associated with myocardial infarction in diabetic patients and with NO synthase activity in endothelial cells.

OBJECTIVE: Obesity and cardiovascular disease recognize a common metabolic soil and may therefore share part of their genetic background. Genome-wide association studies have identified variability at the SH2B1 locus as a predictor of obesity. We investigated whether SNP rs4788102, which captures the entire SH2B1 variability, is associated with coronary artery disease (CAD) and/or myocardial infarction (MI) in patients with type 2 diabetes mellitus (T2DM). DESIGN AND SETTING: SNP rs4788102 was typed in 2015 White subjects with T2DM from three CAD case-control studies [n=740 from the Gargano Hearth Study (GHS, Italy); n=818 from the Joslin Hearth Study (JHS, Boston); n=457 from the University of Catanzaro (CZ, Italy)]. RESULTS: SNP rs4788102 (G/A) was not associated with CAD (overall allelic OR=1.06, 95% CI=0.93-1.21; p=0.37). On the contrary, it was associated with MI in GHS (1.42, 1.12-1.81; p=0.004) and in the three samples analyzed together (1.21, 1.04-1.41; p=0.016). Insulin stimulated nitric oxide synthase (NOS) activity in human vein endothelial cells from G/G (n=4, p=0.03) but not the G/A (n=5, p=0.83) genotype. Of the SNPs in perfect LD with rs4788102, one (rs7498665) affects amino acid polarity (Ala484Thr) and falls into a highly conserved protein segment of SH2B1 containing a class II SH3 domain binding site. CONCLUSIONS: Variability at the SH2B1 obesity locus is associated with MI in diabetic patients and with reduced insulin-stimulated NOS activity in human endothelial cells. Further studies are needed to replicate this association and dissect the biology underlying this finding.

Role of the ENPP1 K121Q polymorphism in glucose homeostasis.

OBJECTIVE: To study the role of the ENPP1 Q121 variant on glucose homeostasis in whites from Italy. RESEARCH DESIGN AND METHODS: We conducted case-control studies in 764 adults (from two independent samples of 289 nonobese and 485 obese individuals) and 240 overweight/obese children undergoing oral glucose tolerance testing (OGTT). Early-phase insulin secretion and insulin sensitivity (the insulinogenic index and the insulin sensitivity index) and their interplay (the disposition index) were calculated. RESULTS: In adult subjects, glucose profiles during OGTT were significantly (P = 2 x 10(-2)) different across K121Q genotype groups and higher in QQ than KK individuals (P = 5 x 10(-2)). The insulinogenic index was significantly reduced in QQ (18.5 +/- 3.4) compared with both KK (31.6 +/- 1.0; P = 2.2 x 10(-7)) and KQ (30.5 +/- 1.5; P = 3.2 x 10(-6)) individuals. KQ individuals also showed a reduced insulin sensitivity index compared with KK subjects (P = 3.6 x 10(-2)). The disposition index was lower in QQ carriers than in KQ and KK individuals (P = 8 x 10(-3) and 4 x 10(-4), respectively) and lower in KQ than in KK individuals (P = 3 x 10(-2)). Data obtained in overweight/obese children were very similar to those observed in adults, with QQ individuals showing (compared with KQ and KK subjects) a reduced insulinogenic index (P = 7 x 10(-3) and 2 x 10(-2), respectively) and disposition index (P = 2 x 10(-2) and 7 x 10(-3), respectively). CONCLUSIONS: Homozygous carriers of the ENPP1 Q121 variant are characterized by an altered glucose homeostasis. Reduced early-phase insulin secretion and inefficient interplay between insulin secretion and sensitivity, which occur at early ages, are major determinants of this defect.