Crystal Structure of LiRh-type IrZn Determined by Powder X-ray and Selected Area Electron Diffraction

The LiRh-type crystal structure of the equiatomic intermetallic compound IrZn turns out to be a competitor to the otherwise energetically favored CsCl-type structures of congeneric transition metal zinc phases, thus enlightening the structural impact of element-specific factors beyond the Hume-Rothery concept.     

Crystal structure, physical properties and HRTEM investigation of the new oxonitridosilicate EuSi2O2N2

The new layered oxonitridosilicate EuSi₂O₂N₂ has been synthesized in a radio‐frequency furnace at temperatures of about 1400 °C starting from europium(III ) oxide (Eu₂O₃) and silicon diimide (Si(NH)₂). The structure of the yellow material has been determined by single‐crystal X‐ray diffraction analysis (space group P1 (no. 1), a=709.5(1), b=724.6(1), c=725.6(1) pm, α=88.69(2), β=84.77(2), γ=75.84(2)°,V=360.19(9)×10⁶ pm³, Z=4, R1=0.0631, 4551 independent reflections, 175 parameters). Its anionic Si₂O₂N₂^2? layers consist of corner‐sharing SiON₃ tetrahedra with threefold connecting nitrogen and terminal oxygen atoms. High‐resolution transmission electron micrographs indicate both ordered and disordered crystallites as well as twinning. Magnetic susceptibility measurements of EuSi₂O₂N₂ exhibit Curie–Weiss behavior above 20 K with an effective magnetic moment of 7.80(5) μ_B Eu^?1, indicating divalent europium. Antiferromagnetic ordering is detected at 4.5(2) K. EuSi₂O₂N₂ shows a field‐induced transition with a critical field of 0.50(5) T. The four crystallographically different europium sites cannot be distinguished by ¹⁵¹Eu Mössbauer spectroscopy. The room‐temperature spectrum is fitted by one signal at an isomer shift of δ=?12.3(1) mm s^?1 subject to quadrupole splitting of ΔE_Q=?2.3(1) mm s^?1 and an asymmetry parameter of 0.46(3). Luminescence measurements show a narrow emission band with regard to the four crystallographic europium sites with an emission maximum at λ=575 nm.     

Two new sesquiterpene lactones from the leaves of Laurus nobilis

As a part of our ongoing interest in new bioactive compounds from natural sources, we studied Laurus nobilis (Lauraceae). This plant is widespread in the Mediterranean area and is used for medicinal and economic purposes. Chromatographic separations on active extracts led to the isolation of two new sesquiterpene lactones, 5a,9-dimethyl-3-methylene-3,3a,4,5,5a,6,7,8-octahydro-1-oxacyclopenta[c]azulen-2-one (1) and 3beta-chlorodehydrocostuslactone (2). The structures of the new compounds were identified by 1D and 2D NMR experiments, as well as high resolution mass spectrometry. The cytotoxic activity was also evaluated against three different tumor cell lines of human origin.     

Comparative studies on the DNA-binding properties of linear and angular dibenzoquinolizinium ions

The interaction of the linear dibenzo[b,g]quinolizinium (5a) and the angular dibenzo[a,f]quinolizinium (6) with DNA was studied in detail in order to evaluate the influence of the shape of polycyclic quinolizinium ions on their DNA-binding properties. First, the synthesis and the thermally induced dimerization of 5a were reinvestigated because the preparation and isolation of the bromide salt of 5a according to literature procedures turned out to be problematic. The dibenzo[b,g]quinolizinium bromide [5a(Br)] tends to dimerize in solution with a highly selective and unprecedented formation of the corresponding anti-head-to-head dimer. Nevertheless, it was observed that careful exclusion of bromide ions from the reaction mixture suppresses the formation of the dimer. Moreover, the dimer may be transformed to the monomer by a remarkably rapid photoinduced electron-transfer reaction with 1-methoxynaphthalene. The association of 5a and 6 with nucleic acids was investigated by spectrophotometric and spectrofluorimetric DNA titrations, CD and LD spectroscopy, DNA thermal denaturation studies, and competition-dialysis techniques. Both dibenzoquinolizinium ions 5a and 6 exhibit an intercalative mode of binding to double-stranded DNA with moderate binding constants (K = 1-7 x 10(5) M(-1)) and a slight preference for association with GC-rich DNA regions. The structures of the intercalation complexes were calculated by molecular modeling methods. Competition-dialysis studies reveal that the isomers 5a and 6 bind selectively to triple-helical DNA (poly[dA]-poly[dT]2) as compared to selected synthetic and native double-stranded nucleic acids. Notably, the selectivity of the linear dibenzo[b,g]quinolizinium 5a toward triplex DNA is higher than the one of the angular derivative 6. In contrast, the DNA thermal denaturation studies reveal a higher stabilization of triple-helical DNA in the presence of 6 (DeltaTm3-->2 = 28 degrees C at r = 0.5) as compared to the stabilization by 5a (DeltaTm3-->2 = 14 degrees C at r = 0.5). This comparison emphasizes the importance of the extended pi system for the interaction of annelated quinolizinium ions with DNA. Moreover, the comparison between 5a and 6 demonstrates the significant influence of the shape of the pi system on the duplex- and triplex-stabilizing properties of the dibenzoquinolizinium ions.     

Mathematical Tool from Corn Stover TGA to Determine Its Composition

Corn stover was treated by steam explosion process at four different temperatures. A fraction of the four exploded matters was extracted by water. The eight samples (four from steam explosion and four from water extraction of exploded matters) were analysed by wet chemical way to quantify the amount of cellulose, hemicellulose and lignin. Thermogravimetric analysis in air atmosphere was executed on the eight samples. A mathematical tool was developed, using TGA data, to determine the composition of corn stover in terms of cellulose, hemicellulose and lignin. It uses the biomass degradation temperature as multiple linear function of the cellulose, hemicellulose and lignin content of the biomass with interactive terms. The mathematical tool predicted cellulose, hemicellulose and lignin contents with average absolute errors of 1.69, 5.59 and 0.74?%, respectively, compared to the wet chemical method.     

Majorana modes in time-reversal invariant s-wave topological superconductors

We present a time-reversal invariant s-wave superconductor supporting Majorana edge modes. The multiband character of the model together with spin-orbit coupling are key to realizing such a topological superconductor. We characterize the topological phase diagram by using a partial Chern number sum, and show that the latter is physically related to the parity of the fermion number of the time-reversal invariant modes. By taking the self-consistency constraint on the s-wave pairing gap into account, we also establish the possibility of a direct topological superconductor-to-topological insulator quantum phase transition.     

A hybrid stress approach for laminated composite plates within the First-order Shear Deformation Theory

This paper presents a hybrid stress approach for the analysis of laminated composite plates. The plate mechanical model is based on the so called First-order Shear Deformation Theory, rationally deduced from the parent three-dimensional theory. Within this framework, a new quadrilateral four-node finite element is developed from a hybrid stress formulation involving, as primary variables, compatible displacements and elementwise equilibrated stress resultants. The element is designed to be simple, stable and locking-free. The displacement interpolation is enhanced by linking the transverse displacement to the nodal rotations and a suitable approximation for stress resultants is selected, ruled by the minimum number of parameters. The transverse stresses through the laminate thickness are reconstructed a posteriori by simply using three-dimensional equilibrium. To improve the results, the stress resultants entering the reconstruction process are first recovered using a superconvergent patch-based procedure called Recovery by Compatibility in Patches, that is properly extended here for laminated plates. This preliminary recovery is very efficient from the computational point of view and generally useful either to accurately evaluate the stress resultants or to estimate the discretization error. Indeed, in the present context, it plays also a key role in effectively predicting the shear stress profiles, since it guarantees the global convergence of the whole reconstruction strategy, that does not need any correction to accommodate equilibrium defects. Actually, this strategy can be adopted together with any plate finite element. Numerical testing demonstrates the excellent performance of both the finite element and the reconstruction strategy.     

Detection of crack location using cracked beam element method for structural analysis

The local flexibility introduced by cracks changes the dynamic behavior of the structure and, by examining this change, crack position and magnitude can be identified. In order to model the structure for FEM analysis, a special finite element for a cracked Timoshenko beam is developed. Shape functions for rotational and translational displacements are used to obtain the consistent mass matrix for the cracked beam element. Effect of the crack on the stiffness matrix and consistent mass matrix is investigated. Proposed is a procedure for identifying cracks in structures using modal test data.