Non-Resonant Microwave Absorption in SmFeAs<Emphasis Type="Bold">O</Emphasis><Subscript>0.80</Subscript><Emphasis Type="Bold">F</Emphasis><Subscript>0.20</Subscript>: Line Shape and Structure Evolution with Temperature

‘Non-resonant Microwave Absorption’ (NRMA) or the ‘Low field microwave absorption’ (LFMA) measurements on high-quality polycrystalline SmFeAsO_0.80F_0.20 superconducting sample were carried as functions of temperature and microwave power. The LFMA line shape is complex with two peaks namely; broad peak 1 and narrow peak 2 akin to one reported in SmFeAsO_0.88F_0.12 as reported by Onyancha et al (Supercond. Nov. Magn. 28, 2927–2934, 2015). This unquestionably illustrates that these peaks are a common feature in F-doped SmFeAsO. The LFMA signal as a function of temperature reveals that T _c ? T _? = 1K in SmFeAsO_0.80F_0.20 compared to 4 K in SmFeAsO_0.88F_0.12 (T _? is the characteristic temperature at which the narrow peak appears as we cool down the sample below T _c); hence inferring that the narrow peak is fluorine doping dependent. Furthermore, LFMA signal evolution with microwave power does not show phase reversal (anomalous absorption) at 2.227 mW which is a stark contrast to what was observed in SmFeAsO_0.88F_0.12 as reported by Onyancha et al (Physica C: Supercond. Appl. 533:49–52, 2017). The absence of phase reversal within measured microwave power indicates presence of hysteretic Josephson junction. These findings establish few non-superconducting inclusions in SmFeAsO_0.80F_0.20 system.     

EM Radiation Sensor: Bulk SQUID Made from Polycrystalline HTSC

The micro-contacts in the granules of the high-temperature superconductor (HTSC) films and other polycrystalline objects after transition to the SC state would then be similar to a bulk superconducting quantum interference device (SQUID), with the point S-N-S state greatly enhancing the sensitivity to electromagnetic radiation and can be used as of the application for much higher resolution than ever before possible (Braginsky, NATO ASI Series, 329, 235 (1996); Bray, J. Supercond. Novel Magn., 21, 335–341 (2008); Cantor, Supercoduct. & Cryoelectronics, 2000). Production of SQUIDs based on thin films is a very complicated technological process, requiring very expensive equipment. Use of the composite (HTSC powder + epoxy matrix), compressed SC powder, and thick films for SQUID fabrication should be very much simpler. The range of frequencies that can by detected with such a device will depend on the circuit parameters and may be extended to the microwave or infrared regimes (Braginsky, NATO ASI Series, 329, 235 (1996); Jurga et al. Acta Phys Pol A, 114, (2007); Jurga et al., Acta Phys Pol A, 114, (2007)). The advantage of the bulk SQUID based on HTSC-YBa₂Cu₃O _x , BiSr₂Ca₂Cu₃O _X , B(Pb)iSr₂Ca₂Cu₃O _X , and NdBaCo _X (powder + epoxy matrix, compressed SC powders, and thick films) is the non-selective nature of the spectral characteristics over a wide frequency range, high sensitivity, and quick response. For suppressing the large noise resulting from the maximal instability of electromagnetic properties at the SC, insulator transition is employed a differentiation procedure of the measurements signal.     

Study Ab Initio of the Effect of A-Site Substitution on the Fe1.12Te System

In the present work, our aim is to verify the structural, electronic and magnetic properties of both systems Fe1.12Te and <RTX> (R = Fe, X = Te and T = Ni, Co) in the P4/nmm structure. For this task, we use the density functional theory (DFT) as a theoretical tool integrated into wien2k code (Blaha 2001). The solid Fe1 ? x Mx Te (M = Ni, Co) have been synthesised by Kazakov et al. (Chem. Met. Alloys 3, 155–160 2010). They have observed a systematic shift of the lattice parameters for both systems for M = Ni and Co till x = 0.1, then a secondary phase with the NiAs-type structure appeared when x passes 0.15. Fe1 ? x Nix Te retains its structure in a concentration between x = 0.1 and 0.15, and Fe1 ? x CoxTe retains its structure when x is between 0.05 and 0.1 (Blaha 2001).     

The Influence of Pinning Centers in the Magnetization of the Mesoscopic Superconductors

In this work, we study the mesoscopic superconducting samples with pinning centers using the time-dependent Ginzburg-Landau theory (TDGL). The pinning centers are introduced via the phenomenological function f(r) Sorensen et al. (Physica C 533, 40–43 2017). We calculated the magnetization curves M(H) for some distances d from the boundary of the sample to the position of the pinning center. From this investigation arises the relation between the first magnetic field H _p and the distance d. It shows that the pinning centers located close to the boundary of the sample decrease H _p , and also the existence of two regimes of the penetration of the vortices. The magnetization curves revel the existence of ruddle of jumps for low magnetic fields for small distances d, indicating a complex vortex penetration.     

Generation of Bulk HTS with Doped Tungstates

Doped tungstates exhibit superconductivity as indicated to occur mainly at the surface of the WO₃ grains present. To generate bulk 3D superconducting material of doped tungstates, it is proposed to employ the recently discovered UV-generated synthesis of complex oxides from mixed simple oxides by illuminating the mixture with ultraviolet light at modest temperatures, as found in Shengelaya’s group in Tbilisi, and to generate a percolating 3D network of 2D superconducting sheets using the smallest basis oxides as the starting material. The latter procedure was demonstrated recently to be very effective in a collaboration with the present author (Daraselia et al., J. Appl. Phys. 121, 145104, 2017). If this proposition is successful, it would establish the doped tungstates as a second group of HTS besides the copper oxides that could be chosen for certain applications.     

Pseudogap and (An)isotropic Scattering in the Fluctuating Charge-Density Wave Phase of Cuprates

We present a general scenario for high-temperature superconducting cuprates, based on the presence of dynamical charge density waves (CDWs) and to the occurrence of a CDW quantum critical point, which occurs, e.g., at doping p ≈ 0.16 in YBa₂Cu₃O_{6 + δ} (YBCO). In this framework, the pseudogap temperature T ^? is interpreted in terms of a reduction of the density of states due to incipient CDW and, at lower temperature to the possible formation of incoherent superconducting pairs. The dynamically fluctuating character of CDW accounts for the different temperatures at which the CDW onset revealed by X-ray scattering (T _{o n s} (p)), and the static three-dimensional CDW ordering appear. We also investigate the anisotropic character of the CDW-mediated scattering. We find that this is strongly anisotropic only close to the CDW quantum critical point (QCP) at low temperature and very low energy. It rapidly becomes nearly isotropic and marginal-Fermi-liquid-like away from the CDW QCP and at finite (even rather small) energies. This may reconcile the interpretation of Hall measurements in terms of anisotropic CDW scattering (arXiv:1604.07852v1) with recent photoemission experiments Bok, J.M., et al. Sci. Adv. 2, e1501329 (2016).     

Stability of the Supercon ducting d-Wave Pairing Towar d the Intersite Coulomb Repulsion in $$\hbox {CuO}_2$$ Plane

Taking into account the real crystalline structure of the \(\hbox {CuO}_2\) plane and the strong spin-fermion coupling, we study the influence of the intersite Coulomb repulsion between holes on the Cooper instability of the spin-polaron quasiparticles in cuprate superconductors. The analysis shows that only the superconducting d-wave pairing is implemented in the whole region of doping, whereas the solutions of the self-consistent equations for the s-wave pairing are absent. It is shown that intersite Coulomb interaction \(V_1\) between the holes located at the nearest oxygen ions does not affect the d-wave pairing, because its Fourier transform \(V_q\) vanishes in the kernel of the corresponding integral equation. The intersite Coulomb interaction \(V_2\) of quasiparticles located at the next-nearest oxygen ions does not vanish in the integral equations, however, but it is also shown that the d-wave pairing is robust toward this interaction for physically reasonable values of \(V_2\).     

Mechanical and Transport Properties of Argon Annealed Y<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Ca<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>:123 Superconductors

We report here the effects of argon heat treatment at 450 ^°C for 12 h on two similar sets of oxygenated Y_{1 ? x} Ca _x :123 superconducting samples prepared by two different heat treatments and oxygen purity as reported by Sedky and Abu-Ziad (Physica C 470, 659; 12). The oxygenated samples are called ssqHp, sssHp, ssqLp, and sssLp, and the Ar annealed samples are called ssqHpAr, sssHpAr, ssqLpAr, and sssLpAr. It is found that the c parameter of annealed samples is gradually increased with Ca addition for all samples, while orthorhombic distortion (OD) is decreased. It is also noted that Ar heat treatment decreased the link between superconducting grains for all samples, and a linear decrease in microhardness (Vickers hardness number (VHN)) with Ca addition is obtained. But the rate of increase/decrease of the c parameter, OD, and VHN against Ca content is different in ssqHpAr and sssLpAr samples as compared to sssHpAr and ssqLpAr samples. Interestingly, the sssHpAr and ssqLpAr samples show a considerable loss of oxygen and small decrease in T _c. While the ssqHpAr and sssLpAr samples show much smaller loss of oxygen and a gradual increase in T _c up to 16 and 17 K, respectively. These results are discussed in terms of the mechanism of oxygen loss by Ca in addition to ssqHpAr and sssLpAr samples as compared to sssHpAr and ssqLpAr samples.     

Immersed boundary simulation of flow through arterial junctions

The present work demonstrates implementation of a mass-conserving sharp-interface immersed boundary for simulation of flows in branched arterial geometries. A simplistic two-dimensional arterial junction is considered to capture the preliminary flow physics in the aortic regions. Numerical solutions are benchmarked against established available experimental PIV results in Ensley et al (Annu. Thorac. Surg. 68(4):1384–1390, 1999) and numerical predictions in Gilmanov and Sotiropoulos (J. Comput. Phys. 207(2):457–492, 2005) and de Zelicourt et al (Comput. Fluids 38(9):1749–1762, 2009). Simulations are further carried out for pulsated flows and effects of blockages near the junctions (due to stenosis or atherosclerosis). Instabilities in the flow structures near the junction and the resulting changes in the downstream pulsation frequency were observed. These changes account for the physiological heart defects that arise from the poorly working valve (due to blockage), giving rise to chest pain and breathing instability, and can potentially be used as a detection tool for arterial diseases.     

Crystal structure of the new diamond-like semiconductor CuMn<Subscript>2</Subscript>InSe<Subscript>4</Subscript>

The crystal structure of the semiconductor compound CuMn ₂ InSe ₄ was analysed using X-ray powder diffraction data. CuMn ₂ InSe ₄ crystallizes, with a stannite structure, in the tetragonal space group I\(\boldsymbol {\overline {4}}\)2m (No. 121), Z = 2, with unit cell parameters a = 5.8111(2) Å, c = 11.5739(8) Å and V = 390.84(3) Å ³ . The refinement of 28 instrumental and structural parameters led to R _p = 8.1%, R _{w p} = 10.5%, R _{e x p} = 6.5% and S = 1.6, for 86 independent reflections.     

A citation-based cross-disciplinary study on literature ageing: part II—diachronous aspects

In the first part of our study (Zhang and Glänzel in Scientometrics, 2017) we provided a view of the literature ageing based on a synchronous approach. Taking up the ideas by Egghe (Scientometrics 27(2):195–214, 1993) and Glänzel et al. (Scientometrics 109(3):2165–2179, 2016) we extend our study in the second part by applying a diachronous approach on the basis of citing literature. For this purpose we used the Prospective Price Index which was recently introduced by Glänzel et al. (Scientometrics 109(3):2165–2179, 2016). Finally, we compare the two aspects of literature ageing. In particular, we analyze the correlation between the share of recent references and the share of fast response, and found a generally positive correlation between both aspects at different levels of aggregation (subfields, major fields and the individual paper level). However, the consistence varies among different aggregations. For examples, on the level of subject fields, Chemistry, Biology, Neuroscience & Behavior are found with evidently better ranks by Prospective Price Index than Price Index, indicating their faster ageing process in the mirror of citations than references, while Engineering and Social sciences are found with the opposite ageing features. At the journal level, we observed a striking divergence between the reference and citation ageing patterns in some cases. Thus several journals proved ‘hard’ from the perspective of information sources (cited papers) but, at the same time, rather ‘soft’ in the light of information targets (citing papers).     

On the rates of convergence for moments convergence in regression models

In one-dimensional regression models, we establish a rate for the rth moment convergence \((r \geqslant 1)\) of the ordinary least-squares estimator involving explicitly the regressors, answering to an open question raised lately by Afendras and Markatou (Test 25:775–784, 2016). An extension of the classic Theorem 2.6.1 of Anderson (The statistical analysis of time series, Wiley, New York, 1971) is also presented.     

Spin Dynamics in the Bi-Directional Charge Density Wave State of High-<Emphasis Type="Italic">T</Emphasis><Subscript><Emphasis Type="Italic">c</Emphasis></Subscript> Superconductors

In this paper, we investigate the dynamical spin susceptibility in the bi-directional charge density wave (BCDW) state by adopting a random-phase approximation. In the BCDW state, we find that no spin resonance exists and only a broad commensurate peak appears for the frequency dependence of the dynamical spin susceptibility at Q = (π,π), though a low-energy spin gap feature can also be found as in the superconducting state. While the “hourglass” type of the dispersion for the BCDW state bears some similarities with that in the superconducting state, the momentum distribution of Im χ ^+?(Q,ω) is just the opposite with the incommensurate peaks lying along the diagonal direction for the energy below ω _c and along the axial direction above ω _c . In the coexistence of SC and BCDW, the frequency dependence of the dynamical spin susceptibility at Q = (π,π) generally shows the two-peak structure, reflecting two energy scales of the spin excitations. These unique features may serve as signatures to verify whether or not the BCDW state is responsible for the formation of the Fermi arcs.     

Test on the linear combinations of mean vectors in high-dimensional data

In this study, we propose a procedure for simultaneous testing \(l (l\ge 1)\) linear relations on \(k(k\ge 2)\) high-dimensional mean vectors with heterogeneous covariance matrices, which extends the result derived by Nishiyama et al. (J Stat Plan Inference 143(11):1898–1911, 2013) and does not need the normality assumption. The newly proposed test statistic is motivated by Bai and Saranadasa (Statistica Sinica 6(2):311–329, 1996) and Chen and Qin (Ann Stat 38(2):808–835, 2010). As a special case, our result could be applied to multivariate analysis of variance, that is, testing the equality of k high-dimensional mean vectors.     

Strain-injection and crack-path field techniques for 3D crack-propagation modelling in quasi-brittle materials

This paper presents a finite element approach for modelling three-dimensional crack propagation in quasi-brittle materials, based on the strain injection and the crack-path field techniques. These numerical techniques were already tested and validated by static and dynamic simulations in 2D classical benchmarks [Dias et al., in: Monograph CIMNE No-134. International Center for Numerical Methods in Engineering, Barcelona, (2012); Oliver et al. in Comput Methods Appl Mech Eng 274:289–348, (2014); Lloberas-Valls et al. in Comput Methods Appl Mech Eng 308:499–534, (2016)] and, also, for modelling tensile crack propagation in real concrete structures, like concrete gravity dams [Dias et al. in Eng Fract Mech 154:288–310, (2016)]. The main advantages of the methodology are the low computational cost and the independence of the results on the size and orientation of the finite element mesh. These advantages were highlighted in previous works by the authors and motivate the present extension to 3D cases. The proposed methodology is implemented in the finite element framework using continuum constitutive models equipped with strain softening and consists, essentially, in injecting the elements candidate to capture the cracks with some goal oriented strain modes for improving the performance of the injected elements for simulating propagating displacement discontinuities. The goal-oriented strain modes are introduced by resorting to mixed formulations and to the Continuum Strong Discontinuity Approach (CSDA), while the crack position inside the finite elements is retrieved by resorting to the crack-path field technique. Representative numerical simulations in 3D benchmarks show that the advantages of the methodology already pointed out in 2D are kept in 3D scenarios.     

Synthesis and Crystal Structures of New Layered Uranyl Compounds Containing Dimers [(UO<Subscript>2</Subscript>)<Subscript>2</Subscript>O<Subscript>8</Subscript>] of Edge-Linked Pentagonal Bipyramids

Two new U(VI) compounds, [((CH₃)₂CHNH₃)(CH₃NH₃)][(UO₂)₂(CrO₄)₃] (1) and [CH₃NH₃][(UO₂)· (SO₄)(OH)] (2), were prepared by combining hydrothermal synthesis with isothermal evaporation. Compound 1 crystallizes in the monoclinic system, space group Р2₁, a = 9.3335(19), b = 10.641(2), c = 9.436(2) Å, β = 94.040(4)°. Compound 2 crystallizes in the rhombic system, space group Рbca, a = 11.5951(8), b = 9.2848(6), c = 14.5565(9) Å. The structures of the compounds were solved by the direct methods and refined to R₁ = 0.041 [for 5565 reflections with Fo > 4σ(Fo)] and 0.033 [for 1792 reflections with Fo > 4σ(Fo)] for 1 and 2, respectively. Single crystal measurements were performed at 296 and 100 K for 1 and 2, respectively. The crystal structure of 1 is based on [(UO₂)₂(CrO₄)₃]^2– layers, and that of 2, on [(UO₂)(SO₄)(OH)]^– layers. Both kinds of layers are constructed in accordance with a common principle and are topologically similar. Protonated isopropylamine and methylamine molecules are arranged between the layers in 1, and protonated methylamine molecules, in 2. Compound 1 is the second known example of a U(VI) compound templated with two different organic molecules simultaneously.     

Superconductivity at 5.5 K in Nb<Subscript>2</Subscript>PdSe<Subscript>5</Subscript> Compound

We report superconductivity in as-synthesized Nb₂PdSe₅, which is similar to a recently discovered Nb₂PdS₅ compound having very high upper critical field, clearly above the Pauli paramagnetic limit Zhang et al. (Sci. Rep. 3:1446, 2013). A bulk polycrystalline Nb₂PdSe₅ sample is synthesized by a solid-state reaction route in a phase-pure structure. The structural characterization has been done by X-ray diffraction, followed by Rietveld refinements, which revealed that the Nb₂PdSe₅ sample is crystallized in a monoclinic structure within the space group C2/m. Structural analysis revealed the formation of sharing of one-dimensional PdSe₂ chains. Electrical and magnetic measurements confirmed the superconductivity in Nb₂PdSe₅ compound at 5.5 K. Detailed magneto-resistance results exhibited the value of upper critical field to be around 8.2 T. The estimated H _c2(0) is within the Pauli paramagnetic limit, which is unlike the Nb₂PdS₅.     

High Superconducting T c and Suppressed Isotope Effect in the Instantonic Condensate State of the Fermi-System: Analytic Solution

A superconducting pairing instability and isotope effect on the superconducting transition temperature T _c in the electronic system with instantonic condensate are derived analytically using previously proposed theory (Mukhin, J. Supercond. Nov. Magn. 22:75–80, 2009; J. Supercond. Nov. Magn. 24:1165–1171, 2011) of the instantonic nature of the “hidden order” in high-T _c cuprates. The self-organized instantonic condensate breaks Matsubara “time” invariance of the Fermi-system, and occurs due to strongly nonlinear interaction between antiferromagnetic or charge density fluctuations. The Cooper-channel susceptibility (polarization loop) is calculated using a single-particle Green’s function that we have derived recently (Mukhin and Galimzyanov, Physica B 407:1882–1884, 2012) for the Fermi-system with instantonic condensate. We found that superconducting T _c could be strongly enhanced and an isotope effect strongly suppressed in the presence of the instantonic condensate. The usual weak-coupling BCS results are recovered in the limit of vanishing the instantons. Relevance of the theoretical predictions for the high-T _c compounds is discussed.     

Letter to the editor: Dimensionless citation indicators

Bornmann and Leydesdorff (Scientometrics, 2018.  https://doi.org/10.1007/s11192-018-2682-1) make an excellent case to use normalized citation based indicators instead of the h-index. In this Letter to the Editor we point out that h/P, p/P and i/P are all very simple and intuitive dimensionless citation indicators where h is the Hirsch h-index, p the performance index of Prathap, and i the value of impact as measured by the ratio of citations C to Publications P.