Influence of equal-channel multi-angle pressing on mechanical and transport properties of a multi-fibrous NbTi superconductor

The effect of equal-channel multi-angle pressing combined with hydroextrusion and drawing followed by thermal treatment on critical current density, superconducting transition temperature and mechanical properties of a multi-fibre (210 fibres) superconducting wire made of a Nb + 50 wt% Ti alloy has been investigated.     

A mechanophysical phase transition provides a dramatic example of colour polymorphism: the tribochromism of a substituted tri(methylene)tetrahydrofuran-2-one

Background

Derivatives of fulgides have been shown to have interesting photochromic properties. We have synthesised a number of such derivatives and have found, in some cases, that crystals can be made to change colour on crushing, a phenomenon we have termed “tribochromism”. We have studied a number of derivatives by X-ray crystallography, to see if the colour is linked to molecular structure or crystal packing, or both, and our structural results have been supported by calculation of molecular and lattice energies.

Results

A number of 5-dicyanomethylene-4-diphenylmethylene-3-disubstitutedmethylene-tetrahydrofuran-2-one compounds have been prepared and structurally characterised. The compounds are obtained as yellow or dark red crystals, or, in one case, both. In two cases where yellow crystals were obtained, we found that crushing the crystals gave a deep red powder. Structure determinations, including those of the one compound which gave both coloured forms, depending on crystallisation conditions, showed that the yellow crystals contained molecules in which the structure comprised a folded conformation at the diphenylmethylene site, whilst the red crystals contained molecules in a twisted conformation at this site. Lattice energy and molecular conformation energies were calculated for all molecules, and showed that the conformational energy of the molecule in structure IIIa (yellow) is marginally higher, and the conformation thus less stable, than that of the molecule in structure IIIb (red). However, the van der Waals energy for crystal structure IIIa, is slightly stronger than that of structure IIIb – which may be viewed as a hint of a metastable packing preference for IIIa, overcome by the contribution of a more stabilising Coulomb energy to the overall more favourable lattice energy of structure IIIb.

Conclusions

Our studies have shown that the crystal colour is correlated with one of two molecular conformations which are different in energy, but that the less stable conformation can be stabilised by its host crystal lattice.

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Graphical abstract Graphical representation of the structural and colour change in the tribochromic compound (III).

     

Discrimination of cancerous and non-cancerous cell lines by headspace-analysis with PTR-MS

Proton transfer reaction mass spectrometry (PTR-MS) has been used to analyze the volatile organic compounds (VOCs) emitted by in-vitro cultured human cells. For this purpose, two pairs of cancerous and non-cancerous human cell lines were selected:1. lung epithelium cells A-549 and retinal pigment epithelium cells hTERT-RPE1, cultured in different growth media; and 2. squamous lung carcinoma cells EPLC and immortalized human bronchial epithelial cells BEAS2B, cultured in identical growth medium. The VOCs in the headspace of the cell cultures were sampled: 1. online by drawing off the gas directly from the culture flask; and 2. by accumulation of the VOCs in PTFE bags connected to the flask for at least 12 h. The pure media were analyzed in the same way as the corresponding cells in order to provide a reference. Direct comparison of headspace VOCs from flasks with cells plus medium and from flasks with pure medium enabled the characterization of cell-line-specific production or consumption of VOCs. Among all identified VOCs in this respect, the most outstanding compound was m/z = 45 (acetaldehyde) revealing significant consumption by the cancerous cell lines but not by the non-cancerous cells. By applying multivariate statistical analysis using 42 selected marker VOCs, it was possible to clearly separate the cancerous and non-cancerous cell lines from each other.     

Orientation modulation of a synthetic polypeptide in self-assembled monolayers: a TOF-SIMS study

Structure and orientation of molecules are key properties of functionalized surfaces. Using time-of-flight secondary ion mass spectrometry (TOF-SIMS), here we investigate how to modulate these parameters upon the immobilization process varying the conditions of self-assembly. The molecule of interest, a template-assembled synthetic protein (TASP), consists of a central peptide ring with orthogonally arranged residues. Thioalkane chains allow the directed self-assembly of the molecule on a gold surface; four serine residues on the opposite side of the ring can be used as anchoring sites for various functional sensing molecules. The TASP conformation and its orientation in self-assembled monolayers (SAMs) play a central role for the accessibility of these serine residues. To study the influence of the self-assembly conditions, two series of samples were prepared. Pure TASP monolayers of different surface densities are compared to mixed TASP/alkanethiol monolayers prepared by sequential adsorption varying sequence and particular incubation times as well as by coadsorption modifying incubation times and TASP/alkanethiol mass ratios. Switching the TASP orientation from a state where the molecules are lying flat on the surface to an upright orientation turned out to be possible by inserting the TASP into a preformed alkanethiol monolayer of an appropriate surface density. This study demonstrates that TOF-SIMS is an excellent tool not only to investigate the surface composition, but also the molecular structure of functionalized surfaces.     

Aryl h-phosphonates. 14. Synthesis of new nucleotide analogues with phosphonate-phosphate internucleosidic linkage

[reaction: see text] Aryl nucleoside H-phosphonates 3 and aryl nucleoside P-acylphosphonates 4, generated in situ from the appropriate H-phosphonate 1 and acylphosphonate monoesters 2, respectively, reacted rapidly in the presence of tertiary amines to produce in high yields the extended, pyrophosphate analogues, diaryl dinucleoside phosphonate-phosphate derivatives 6. These, depending on a substituent on the alpha-carbon of the phosphonate moiety, either underwent transformation into the dinucleoside phosphonate-phosphate 7 or afforded nucleoside H-phosphonates 8 and aryl nucleoside phosphate 9.     

Crystal Growth Of Mixed Titanium Sillenites

Top Seeded Solution Growth (TSSG) technique has been used to produce Bi₁₂TiO₂₀ (BTO) and some mixed Bi₁₂Ti_0.8M_0.2O₂₀ single crystals in which Ti was substituted with M=V, Pb or Ga. Pure Bi₄₀Ga₂O₆₃ (BGaO) single crystals have been grown, too. Thermal conditions enabling growth of uniform [110] sillenite single crystals with totally flat (110) interface have been found. Influence of composition on spectral characteristics of the BTO mixed crystals has been investigated.     

Spin-polarized electron tunneling in lanthanum manganite

Tunneling experiments were performed on ceramic samples with the composition La_0.6Sr_0.4MnO₃, manifesting negative magnetoresistance. Two types of contacts were studied: symmetric (break junction type) and asymmetric ceramic-insulator-metal contact. A high magnetic-field sensitivity of the conductivity σ(H) of the contacts was observed even when only one of the electrodes was magnetic. The effect was explained by the existence of spin-polarized localized states in the tunneling barrier. Their appearance was attributed to the formation of an oxygen-depleted, magnetically two-phase state of localized ferromagnetic nanoregions in an anti-ferromagnetic dielectric matrix in the near-contact region.     

Changes in the electronic,optical, and magnetic properties of LaSrMnO films upon transition from the rhombohedral phase to the orthorhombic phase

The properties of LaSrMnO films are investigated in the temperature range of the transition from the rhombohedral phase to the orthorhombic phase (600–650° C). It is shown that, with a variation in the growth temperature T_s, the change in the film properties is governed by the interaction of Mn-O metallic (ferromagnetic) clusters in the dielectric (antiferromagnetic) matrix. At T_s≤600°C, the low density of e _g states and the dielectric gap (E _g =0.3–0.5 eV) are responsible for the following features: (i) the optical transparency in the range ?ω=0.5–2 eV, (ii) the difference between the FC and ZFC magnetizations M(T), (iii) the high resistance, and (iv) the appearance of the portions R(T) ≈ const in the dependence R(T) due to the transformation of clusters into a system of tunnel-coupled quantum dots. At T_s≥650°C, the local increase in the atomic and electronic densities leads to a decrease in the optical transmission and the resistance by three to nine orders of magnitude, the appearance of a maximum and a minimum in the dependences R(T) of the LaSrMnO films, and an increase in the magnetization M(10 K) by one order of magnitude. The inference is drawn that magnetic ordering of the system of tunnel-coupled clusters encourages an increase in the cluster size and in the content of the metallic (ferromagnetic) phase.     

The effect of a magnetic field on Jahn-Teller ordering in the monoclinic crystal RbDy(WO4)2

This paper presents the results of a study of the thermal properties of monoclinic single-crystal RbDy(WO₄)₂ at temperatures of 2–15 K and in magnetic fields up to 6 T. From the results of measurements of the heat capacity and thermograms, two structural phase transitions are detected, at T _c1=4.9 K and T _c2=9.0 K. The transformation from the high-temperature phase to the low-temperature phase occurs via an intermediate phase. The field dependences of the critical temperatures are found for various magnetic-field orientations. H-T phase diagrams are constructed for H‖a and H‖c. An anomalous increase (by almost an order of magnitude) of the relaxation time of the system, associated with structural instability of the crystal lattice, is detected in the region of the structural phase transitions. A symmetry analysis is carried out, and possible crystal structures of the low-temperature phase are indicated. Fiz. Tverd. Tela (St. Petersburg) 40, 2221–2225 (December 1998)     

Magnetostriction of the spin-Peierls magnet CuGeO3

The temperature dependence of the longitudinal magnetostriction of a CuGeO₃ single crystal is measured within the temperature range 4.2–20 K in a magnetic field of 10 T. As the temperature is raised above 4.2 K, the magnetostriction at first increases from vanishingly small values, attains a maximum at a temperature of approximately 12 K, and then abruptly drops as the temperature approaches the spin-Peierls transition. The results are interpreted on the basis of a simple model utilizing the real pattern of magnetic excitations in the spin system. Fiz. Tverd. Tela (St. Petersburg) 40, 1671–1673 (September 1998)