Evidence for Bose-Einstein condensation of free excitons in AgBr

We report the observation of a sharp photoluminescence line in AgBr at 2.6754 eV below 3 K. Spectral position, width and temperature dependence of the intensity can only be explained by us consistently with the assumption that this line is due to the recombination of Bose-Einstein condensed indirect excitons.     

High-fidelity gates in a single josephson qubit

We demonstrate new experimental procedures for measuring small errors in a superconducting quantum bit (qubit). By carefully separating out gate and measurement errors, we construct a complete error budget and demonstrate single qubit gate fidelities of 0.98, limited by energy relaxation. We also introduce a new metrology tool-- Ramsey interference error filter-that can measure the occupation probability of the state |2> which is outside the computational basis, down to 10{-4}, thereby confirming that our quantum system stays within the qubit manifold during single qubit logic operations.     

Identification of the Primary Structure of Selenium-Containing Polysaccharides Selectively Inhibiting T-Cell Proliferation

We previously described the biosynthesis, isolation, and immunosuppressive activity of the selenium-containing polysaccharide fraction isolated from the mycelial culture of Lentinula edodes. Structural studies have shown that the fraction was a protein-containing mixture of high molar mass polysaccharides α- and β-glucans. However, which of the components of the complex fraction is responsible for the immunosuppressive activity non-typical for polysaccharides of fungal origin has not been explained. In the current study, we defined four-polysaccharide components of the Se-containing polysaccharide fraction determined their primary structure and examined the effect on T- and B-cell proliferation. The isolated Se-polysaccharides, α-1,4-glucan (M_w 2.25 × 10⁶ g/mol), unbranched β-1,6-d-glucan, unbranched β-1,3-d-glucan and β-1,3-branched β-1,6-d-glucan (M_w 1.10 × 10⁵ g/mol), are not typical as components of the cell wall of L. edodes. All are biologically active, but the inhibitory effect of the isolated polysaccharides on lymphocyte proliferation was weaker, though more selective than that of the crude fraction.     

Ethylene/POSS copolymerization behavior of postmetallocene catalysts and copolymer characteristics

Copolymerization of ethylene with iso‐butyl substituted monoalkenyl(siloxy)‐ or monoalkenylsilsesquioxane (POSS) comonomers over bis(phenoxy‐imine) and salen‐type titanium and zirconium catalysts was studied. It was found that the polyreaction performance was significantly depended by the kind of the catalyst and by the structure and concentration of POSS in the feed. The POSS comonomer was efficiently incorporated into the polymer chain at up to 0.2 mol %. The differences in the copolymer compositions as the functions of the catalyst kind and the POSS comonomer were observed, including the varied number‐average sequence length of ethylene and unsaturated end groups, as determined by ¹H NMR and FT‐IR. The presence of POSS comonomers affected also the melting and crystallization behavior of the copolymers, as evidenced by DSC, because of influence on the polymer chain arrangement. The POSS units could act as the nucleating agents. Moreover, the crystal and structural parameters of ethylene/POSS copolymers were evaluated on the basis of X‐ray results, and the limited self‐aggregation of POSS incorporated into the polymer chain, the small number and size of POSS aggregates, and the increased crystallinity degree of copolymers were demonstrated. The ethylene/POSS copolymers produced by postmetallocenes offered also high thermal stability and interesting morphological properties. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 3918–3934     

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Dynamics of the formation of excited hydrogen,H(n=2,3,4), during a pulse discharge in methane

The dynamics of the formation and decay of excited hydrogen during a pulse discharge in methane at a pressure of 200 Pa and energy density of 0.05 J/cm³ has been studied. The population of hydrogen in the n=2 state was monitored by the laser absorption method. The time constant of the decay of the excited hydrogen was measured to be 95±15 ns. The concentration of free electrons reached a maximum value of 7×10¹⁴ cm^–3, and the time constant of their recombination was 220±50 ns. The formation of appreciable amounts of atomic hydrogen in the ground state during the discharge, H(n=1)>10¹⁶ cm^–3, was estimated on the basis of a kinetic model.Notation absorption coefficient - wave number, cm^–1 - c velocity of light - e electron charge - m _e mass of electron - A _mn Einstein coefficient - F _mn collisional deexcitation rate constant - S _m ionization rate constant - f ₂₄ oscillator strength - n _e electron concentration - n _H(n=2,3,4) excited-state hydrogen concentration - v _e electron velocity - q _mn excitation cross-section - (q _mnve) excitation rate constants - T _e electron temperature - E (t) electrical field strength - j current density - t _ei ^–1 electron-ion collision frequency - _2,m two-body recombination rate constant - _3,m three-body recombination rate constant     

Photochemical and electrochemical Z–E isomerization of 1,4-dialkoxy-2,5-bis[2-(thien-2-yl)ethenyl]benzene stereoisomers

The group of 1,4-dialkoxy-2,5-bis[2-(thien-2-yl)ethenyl]benzene stereoisomers was synthesized in which methoxy- and ethoxy-groups were used as alkoxy-substituents. These isomers were characterized as solution species both electrochemically and spectroscopically. As expected, these compounds, having a stilben like structure, are the subject of photoisomerization, which is described and discussed. It is demonstrated how electrochemical process may cause isomerization of the double CC bonds in that group of compounds. An attempt of using electrochemical methods to monitor the process of photoisomerization of these compounds is presented. Mechanism of the oxidatively induced electrochemical isomerization has been proposed and discussed. The electrochemical isomerization mechanism is verified by digital simulation, which allowed estimating basic kinetic parameters of the processes.     

High kinetic stability of HXeBr upon interaction with carbon dioxide: HXeBr···CO2 complex in a xenon matrix and HXeBr in a carbon dioxide matrix

We investigate the conditions when noble-gas hydrides can be found in real environments and report on the preparation and identification of the HXeBr···CO(2) complex in a xenon matrix and HXeBr in a carbon dioxide matrix. The H-Xe stretching mode of the HXeBr···CO(2) complex in a xenon matrix is observed at 1557 cm(-1), showing a spectral shift of +53 cm(-1) from the HXeBr monomer. The calculations at the CCSD(T)/aug-cc-pVTZ-PP(Xe,Br) level of theory give two stable structures for the HXeBr···CO(2) complex with frequency shifts of +55 and +103 cm(-1), respectively. On the basis of the calculations, the experimentally observed band is assigned to the more stable structure with a "parallel" geometry. The HXeBr molecule was prepared in a carbon dioxide matrix and has the H-Xe stretching frequency of 1646 cm(-1), meaning a strong matrix shift and stabilization of the H-Xe bond. The deuterated species DXeBr in a carbon dioxide matrix absorbs at 1200 cm(-1). This is the first case where a noble-gas hydride is prepared in a molecular solid. The thermal stabilities of HXeBr and HXeBr···CO(2) complex in a xenon matrix and HXeBr in a carbon dioxide matrix were examined. We have found a high thermal stability of HXeBr in carbon dioxide ice (at least up to 100 K), i.e., under conditions that may occur in nature.     

Aromatic compounds in molecular phase of Baltic amber-synchronous luminescence analysis

Synchronous luminescence analysis was performed in order to identify aromatic compounds in solvent extracts of Baltic amber. The investigated extracts were obtained, for comparisons, as products of extraction by various techniques and solvents. Methylene chloride and ethanol were applied independently for extraction at the ambient temperature (conservative extraction), as well as at the temperature of solvent boiling (extraction in Soxhlet apparatus). Ethanol, as the solvent, was also used for extraction in an ultrasonic bath and for the decoction process. The extraction, by techniques mentioned, of the analysed amber has resulted in products generally containing the same groups of aromatics: mainly naphthalenes, phenanthrenes and anthracenes. Among phenanthrenes, in all samples the retene was also identified, being one of the characteristic links of the diagenetic chain of chemical transformations of vegetal precursors. The identification of a series of individual compounds made, using the synchronous luminescence technique, was verified by the record of conventional emission and excitation spectra. Presented identified compounds were also confirmed by the results of GC-MS analysis. The luminescence analysis was also performed comparatively for fossil resin from Galicia, Spain (Cretaceous) older than Baltic amber (Tertiary, Eocene). The obtained preliminary results of synchronous luminescence analysis suggest the possibility of diversification in this manner of fossil resins of various ages by characterisation of aromatisation degree and alkyl substitution of aromatic rings. It is since well known that aromatisation progress is an indicator of a natural process of maturation of fossil organic matter. However, a greater number of samples should be taken to further testify to the investigations.     

The use of synchronous luminescence spectroscopy in qualitative analysis of aromatic fraction of hard coal thermolysis products

The synchronous luminescence method was used in qualitative analysis of aromatic fraction of low-temperature tar from hard coal. The spectra obtained by this method are simpler than spectra obtained with the use of conventional emission luminescence method. The synchronous luminescence analysis requires the selection of respective Deltalambda parameter values. This parameter is a constant difference between position of excitation and emission monochromators during measurement. From literature, the Deltalambda parameter value of 23 nm was first used here. The characteristic emission ranges of spectra obtained indicated (by comparison with spectra of standards) degree of condensation of aromatic compounds present in investigated mixtures. It was also possible to identify some individual compounds. However, this identification could be more effective with the use of the respective value of Deltalambda parameter for each particular component of the mixture. This manner of analysis was used here, e.g. for investigating aromatic fraction containing phenanthrene (identified previously by gas chromatography method) among other compounds. The spectrum recorded at Deltalambda value characteristic for phenanthrene (53nm) presents a rather simple shape with a maximum at 346 nm attributed to phenanthrene after standard and literature data.