The Zn1−xPbxCr2Se4—Single Crystals Obtained by Chemical Vapour Transport—Structure and Magnetic,Electrical, and Thermal Properties

Monocrystalline chalcogenide spinels ZnCr₂Se₄ are antiferromagnetic and semiconductor materials. They can be used to dope or alloy with related semiconducting spinels. Therefore, their Pb-doped display is expected to have unique properties and new potential applications. This paper presents the results of dc and ac magnetic measurements, including the critical fields visible on the magnetisation isotherms, electrical conductivity, and specific heat of the ZnCr₂S₄:Pb single crystals. These studies showed that substituting the diamagnetic Pb ion with a large ion radius for the Zn one leads to strong short-range ferromagnetic interactions in the entire temperature range and spin fluctuations in the paramagnetic region at H_dc = 50 kOe.     

Structure,Morphology, Heat Capacity,and Electrical Transport Properties of Ti3(Al,Si)C2 Materials

A study of Ti₃Al_1−xSi_xC₂ (x = 0 to x = 1) MAX-phase alloys is reported. The materials were obtained from mixtures of Ti₃AlC₂ and Ti₃SiC₂ powders with hot pressing sintering technique. They were characterised with X-ray diffraction, heat capacity, electrical resistivity, and magnetoresistance measurements. The results show a good quality crystal structure and metallic properties with high residual resistivity. The resistivity weakly varies with Si doping and shows a small, positive magnetoresistance effect. The magnetoresistance exhibits a quadratic dependence on the magnetic field, which indicates a dominant contribution from open electronic orbits. The Debye temperatures and Sommerfeld coefficient values derived from specific heat data show slight variations with Si content, with decreasing tendency for the former and an increase for the latter. Experimental results were supported by band structure calculations whose results are consistent with the experiment concerning specific heat, resistivity, and magnetoresistance measurements. In particular, they reveal that of the s-electrons at the Fermi level, those of Al and Si have prevailing density of states and, thus predominantly contribute to the metallic conductivity. This also shows that the high residual resistivity of the materials studied is an intrinsic effect, not due to defects of the crystal structure.     

Modelling and Experimental Study of Moisture Transport in Wood,Taking into Account Diffusion and the Accompanying Adsorption of Water Vapour by Cell Walls

The paper presents a model of moisture transport in wood taking into account diffusion and the accompanying adsorption of water vapour through the skeleton. A two-parameter form of the source term was proposed, depending on the distance of the current moisture content (MC) from the equilibrium state. The tests on cubic samples with a side of 2 cm were carried out which allowed to determine the coefficients of the proposed model on the basis of the reverse method. The tests were performed for pine, larch, oak and ash in all directions of orthotropy. Tests on thin samples were also performed to verify the source term.     

Influence of Cu Content on Structure,Thermal Stability and Magnetic Properties in Fe72−xNi8Nb4CuxSi2B14 Alloys

The effect of substitution of Fe by Cu on the crystal structure and magnetic properties of Fe_72−xNi₈Nb₄Cu_xSi₂B₁₄ alloys (x = 0.6, 1.1, 1.6 at.%) in the form of ribbons was investigated. The chemical composition of the materials was established on the basis of the calculated minima of thermodynamic parameters: Gibbs free energy of amorphous phase formation ΔG^amorph (minimum at 0.6 at.% of Cu) and Gibbs free energy of mixing ΔG^mix (minimum at 1.6 at.% of Cu). The characteristic crystallization temperatures T_x1onset and T_x1 of the alpha-iron phase together with the activation energy E_a for the as-spun samples were determined by differential scanning calorimetry (DSC) with a heating rate of 10–100 °C/min. In order to determine the optimal soft magnetic properties, the wound cores were subjected to a controlled isothermal annealing process in the temperature range of 340–640 °C for 20 min. Coercivity Hc, saturation induction Bs and core power losses at B = 1 T and frequency f = 50 Hz P_10/50 were determined for all samples. Moreover, for the samples with the lowest Hc and P_10/50, the magnetic losses were determined in a wider frequency range 50 Hz–400 kHz. The real and imaginary parts of the magnetic permeability µ′, µ″ along with the cut-off frequency were determined for the samples annealed at 360, 460, and 560 °C. The best soft magnetic properties (i.e., the lowest value of Hc and P_10/50) were observed for samples annealed at 460 °C, with Hc = 4.88–5.69 A/m, Bs = 1.18–1.24 T, P_10/50 = 0.072–0.084 W/kg, µ′ = 8350–10,630 and cutoff frequency at 8–9.3 × 10⁴ Hz. The structural study of as-spun and annealed ribbons was carried out using X-ray diffraction (XRD) and a transmission electron microscope (TEM).     

Molecular and Polymer Ln2M2 (Ln = Eu,Gd, Tb,Dy; M = Zn,Cd) Complexes with Pentafluorobenzoate Anions: The Role of Temperature and Stacking Effects in the Structure; Magnetic and Luminescent Properties

Varying the temperature of the reaction of [{Cd(pfb)(H₂O)₄}⁺_n·n(pfb)⁻], [Ln₂(pfb)₆(H₂O)₈]·H₂O (Hpfb = pentafluorobenzoic acid), and 1,10-phenanthroline (phen) in MeCN followed by crystallization resulted in the isolation of two type of products: 1D-polymers [LnCd(pfb)₅(phen)]_n·1.5nMeCN (Ln = Eu (I), Gd (II), Tb (III), Dy (IV)) which were isolated at 25 °C, and molecular compounds [Tb₂Cd₂(pfb)₁₀(phen)₂] (V) formed at 75 °C. The transition from a molecular to a polymer structure becomes possible because of intra- and intermolecular interactions between the aromatic cycles of phen and pfb from neighboring tetranuclear Ln₂Cd₂ fragments. Replacement of cadmium with zinc in the reaction resulted in molecular compounds Ln₂Zn₂ [Ln₂Zn₂(pfb)₁₀(phen)₂]·4MeCN (Ln = Eu (VI), Tb (VIII), Dy (IX)) and [Gd₂Zn₂(pfb)₁₀(H₂O)₂(phen)₂]·4MeCN (VII). A new molecular EuCd complex [Eu₂Cd₂(pfb)₁₀(phen)₄]·4MeCN (X)] was isolated from a mixture of cadmium, zinc, and europium pentafluorobenzoates (Cd:Zn:Ln = 1:1:2). Complexes II-IV, VII and IX exhibit magnetic relaxation at liquid helium temperatures in nonzero magnetic fields. Luminescent studies revealed a bright luminescence of complexes with europium(III) and terbium(III) ions.     

Intra-individual variation of glucose,specific insulin and proinsulin concentrations measured by two oral glucose tolerance tests in a general Caucasian population: the Hoorn Study

Summary We studied the intra-individual variation in plasma glucose, specific serum insulin and serum pro-insulin concentrations, measured by two 75-g oral glucose tolerance tests in an age, sex, and glucose tolerance stratified random sample from a 50–74-year-old Caucasian population without a history of diabetes mellitus. The intra-individual variation was assessed by the standard deviation of the test-retest differences (SD_dif). For subjects with normal (n=246), impaired glucose tolerance (n=198), and newly detected diabetes (n=80) classified at the first test, the following (SD_dif/median level of individual average scores) were found: fasting glucose: 0.4/5.4, 0.5/5.9 and 0.7/7.2 mmol/l; 2-h glucose: 1.3/5.6, 1.8/8.5 and 2.3/12.8 mmol/l; fasting insulin: 23/76, 32/89 and 30/ 116 pmol/l; 2-h insulin: 190/303, 278/553 and 304/626 pmol/l; fasting proinsulin: 4/8, 6/13 and 9/18 pmol/l; 2-h proinsulin: 19/49, 23/84 and 33/90 pmol/l, respectively. In both glucose, proinsulin and insulin concentrations the total intra-individual variation was predominantly determined by biological variation, whereas analytical variation made only a minor contribution. The SD_dif can easily be interpreted, as 95% of the random test-retest differences will be less than 2 · SD_dif, or in terms of percentage, less than (2 · SD_dif/median level of individual average scores) · 100. Therefore, for subjects with normal glucose tolerance, 95% of the random test-retest differences will be less than 15% (fasting glucose), 46% (2-h glucose), 61% (fasting insulin), 125% (2-h insulin), 100% (fasting proinsulin) and 78% (2-h proinsulin) of the median value of the individual average scores. No substantial independent association of either age, gender or obesity with the intra-individual variation in glucose, proinsulin, or insulin concentrations was found.Abbreviations OGTT Oral glucose tolerance test - NGT_1st, IGT_1st new DM_1st normal glucose tolerance, impaired glucose tolerance and newly detected diabetes mellitus, respectively, as classified at first OGTT - SD_dif standard deviation of the difference scores - CV_intra intra-individual coefficient of variation - CV_bi biological intra-individual coefficient of variation - CV_a analytical intra-individual coefficient of variation - Cl₉₅ 95% confidence interval     

Characteristics of the Structure,Mechanical, and Tribological Properties of a Mo-Mo2N Nanocomposite Coating Deposited on the Ti6Al4V Alloy by Magnetron Sputtering

Mo-Mo₂N nanocomposite coating was produced by reactive magnetron sputtering of a molybdenum target, in the atmosphere, of Ar and N₂ gases. Coating was deposited on Ti6Al4V titanium alloy. Presented are the results of analysis of the XRD crystal structure, microscopic SEM, TEM and AFM analysis, measurements of hardness, Young’s modulus, and adhesion. Coating consisted of α-Mo phase, constituting the matrix, and γ-Mo₂N reinforcing phase, which had columnar structure. The size of crystallite phases averaged 20.4 nm for the Mo phase and 14.1 nm for the Mo₂N phase. Increasing nitrogen flow rate leads to the fragmentation of the columnar grains and increased hardness from 22.3 GPa to 27.5 GPa. The resulting coating has a low Young’s modulus of 230 GPa to 240 GPa. Measurements of hardness and Young’s modulus were carried out using the nanoindentation method. Friction coefficient and tribological wear of the coatings were determined with a tribometer, using the multi-cycle oscillation method. Among tested coatings, the lowest friction coefficient was 0.3 and wear coefficient was 10 × 10⁻¹⁶ m³/N∙m. In addition, this coating has an average surface roughness of RMS < 2.4 nm, determined using AFM tests, as well as a good adhesion to the substrate. The dominant wear mechanism of the Mo-Mo₂N coatings was abrasive wear and wear by oxidation. The Mo-Mo₂N coating produced in this work is a prospective material for the elements of machines and devices operating in dry friction conditions.     

Magnetic Properties of A2Ni2TeO6 (A = K,Li): Zigzag Order in the Honeycomb Layers of Ni2+ Ions Induced by First and Third Nearest-Neighbor Spin Exchanges

The static and dynamic magnetic properties and the specific heat of K₂Ni₂TeO₆ and Li₂Ni₂TeO₆ were examined and it was found that they undergo a long-range ordering at T_N = 22.8 and 24.4 K, respectively, but exhibit a strong short-range order. At high temperature, the magnetic susceptibilities of K₂Ni₂TeO₆ and Li₂Ni₂TeO₆ are described by a Curie–Weiss law, with Curie-Weiss temperatures Θ of approximately −13 and −20 K, respectively, leading to the effective magnetic moment of about 4.46 ± 0.01 μ_B per formula unit, as expected for Ni²⁺ (S = 1) ions. In the paramagnetic region, the ESR spectra of K₂Ni₂TeO₆ and Li₂Ni₂TeO₆ show a single Lorentzian-shaped line characterized by the isotropic effective g-factor, g = 2.19 ± 0.01. The energy-mapping analysis shows that the honeycomb layers of A₂Ni₂TeO₆ (A = K, Li) and Li₃Ni₂SbO₆ adopt a zigzag order, in which zigzag ferromagnetic chains are antiferromagnetically coupled, because the third nearest-neighbor spin exchanges are strongly antiferromagnetic while the first nearest-neighbor spin exchanges are strongly ferromagnetic, and that adjacent zigzag-ordered honeycomb layers prefer to be ferromagnetically coupled. The short-range order of the zigzag-ordered honeycomb lattices of K₂Ni₂TeO₆ and Li₂Ni₂TeO₆ is equivalent to that of an antiferromagnetic uniform chain, and is related to the short-range order of the ferromagnetic chains along the direction perpendicular to the chains.     

Coronary calcification, homocysteine, C-reactive protein and the metabolic syndrome in Type 2 diabetes: the Prospective Evaluation of Diabetic Ischaemic Heart Disease by Coronary Tomography (PREDICT) Study.

AIMS: The PREDICT Study aims to determine: (i) the association between cardiovascular risk factors and coronary artery calcification score (CACS) obtained by electron beam tomography and (ii) the predictive value of CACS for coronary heart disease (CHD) events in Type 2 diabetes. METHODS: Having previously reported relationships between CACS and conventional risk factors, we have now studied the novel risk factors, plasma high-sensitivity C-reactive protein (CRP) and homocysteine, insulin resistance, serum apoprotein A1 and B concentrations, the serum triglyceride/high-density lipoprotein cholesterol ratio and metabolic syndrome (International Diabetes Federation definition) in 573 subjects of the PREDICT Type 2 diabetes cohort. RESULTS: In univariate analyses, the only significant positive novel correlate of CACS was homocysteine (P = 0.0004). CRP was increased in those with detectable calcification, but decreased with increasing calcification score (P = 0.006). In a multivariate model that included all significant univariate correlates, CACS was independently associated with age (P < 0.0001), waist-hip ratio (P < 0.02), male gender (P < 0.05) and duration of diabetes (P < 0.05), but the association with homocysteine was no longer significant. The negative association between CACS and CRP remained in multivariate analysis, and was independent of statin use. CONCLUSIONS: Age was the major factor influencing CACS in Type 2 diabetes, with weaker contributions from waist hip-ratio and duration of diabetes. Other novel cardiovascular risk factors appear to have little positive effect.