Exciton-plasmon interaction in a composite metal-insulator-semiconductor nanowire system

We report about the synthesis and optical properties of a composite metal-insulator-semiconductor nanowire system which consists of a wet-chemically grown silver wire core surrounded by a SiO2 shell of controlled thickness, followed by an outer shell of highly luminescent CdSe nanocrystals. With microphotoluminescence (micro-PL) experiments, we studied the exciton-plasmon interaction in individual nanowires and analyzed the spatially resolved nanocrystal emission for different nanowire length, SiO2-shell thickness, nanocrystal shape, pump power, and emission polarization. For an SiO2 spacer thickness of approximately 15 nm, we observed an efficient excitation of surface plasmons by excitonic emission of CdSe nanocrystals. For nanowire lengths up to approximately 10 microm, the composite metal-insulator-semiconductor nanowires ((Ag)SiO2)CdSe act as a waveguide for 1D-surface plasmons at optical frequencies with efficient photon outcoupling at the nanowire tips, which is promising for efficient exciton-plasmon-photon conversion and surface plasmon guiding on a submicron scale in the visible spectral range.     

Comparative analysis and the coverage intervals of hair rare metal content in two Russian industrial centres

The existing data provide information on hair essential and toxic trace element content, whereas data on ultra-trace and rare elements are scarce. Therefore, the primary aim of the current study was to estimate hair levels and reference values of hair rare metal content using IUPAC recommendations in 2593 occupationally non-exposed adults living in Moscow and Novosibirsk (1900 women and 693 men). Hair Ag, Au, Ga, Ge, La, Rb, Tl, W and Zr content was assessed by inductively coupled plasma mass spectrometry with NexION 300D. Women were characterised by significantly higher hair Ag and Au levels than men, whereas men had increased La, Rb, Tl, W and Zr content as compared to women. Moscow inhabitants were characterised by significantly higher hair Au and Ge, and lower hair Ga, La, Rb, Tl, W and Zr content as compared to the ones from Novosibirsk. The coverage intervals of Ag, Au, Ga, Ge, La, Rb, Tl, W and Zr content in hair of the general sample of examinees calculated in accordance with IUPAC recommendations were 0.0278–0.2994, 0.0159–0.1812, 0.0062–0.0348, 0.0022–0.0066, 0.0023–0.0205, 0.0226–0.2083, 0.0002–0.0008, 0.0022–0.0120 and 0.0389–0.3521 μg/g, respectively. The obtained data indicate that both gender and geographical location affect hair rare metal content in adults.     

Identification of Ge/Si intermixing processes at the Bi/Ge/Si(111) surface

The chemical contrast between Si and Ge obtained by scanning tunneling microscopy on Bi-covered Si(111) surfaces is used as a tool to identify two vertical Ge/Si intermixing processes. During annealing of an initially pure Ge monolayer on Si, the intermixing is confined to the first two layers approaching a 50% Ge concentration in each layer. During epitaxial growth, a growth front induced intermixing process acting at step edges is observed. Because of the open atomic structure at the step edges, relative to the terraces, a lower activation barrier for intermixing at the step edge, compared to the terrace, is observed.     

Symmetry breaking in the growth of two-dimensional islands on Si(111)

We find that the shape of two-dimensional (2D) Si or Ge islands has a lower symmetry than the threefold symmetry of the underlying Si(111) substrate if Bi is used as a surfactant during growth. Arrow-shaped or rhomb-shaped 2D islands are observed by scanning tunneling microscopy. This symmetry breaking is explained by a mutual shift between the surface reconstructions present on the substrate and on the islands. Using the kinematic Wulff construction the growth velocities of the steps could be determined from the island shape if the nucleation center has been located by a marker technique.     

Recognition of Artificial Nucleobases by E. coli Purine Nucleoside Phosphorylase versus its Ser90Ala Mutant in the Synthesis of Base‐Modified Nucleosides

A wide range of natural purine analogues was used as probe to assess the mechanism of recognition by the wild‐type (WT) E. coli purine nucleoside phosphorylase (PNP) versus its Ser90Ala mutant. The results were analyzed from viewpoint of the role of the Ser90 residue and the structural features of the bases. It was found that the Ser90 residue of the PNP 1) plays an important role in the binding and activation of 8‐aza‐7‐deazapurines in the synthesis of their nucleosides, 2) participates in the binding of α‐D ‐pentofuranose‐1‐phosphates at the catalytic site of the PNP, and 3) catalyzes the dephosphorylation of intermediary formed 2‐deoxy‐α‐D ‐ribofuranose‐1‐phosphate in the trans‐2‐deoxyribosylation reaction. 5‐Aza‐7‐deazaguanine manifested excellent substrate activity for both enzymes, 8‐amino‐7‐thiaguanine and 2‐aminobenzothiazole showed no substrate activity for both enzymes. On the contrary, the 2‐amino derivatives of benzimidazole and benzoxazole are substrates and are converted into the N1‐ and unusual N2‐glycosides, respectively. 9‐Deaza‐5‐iodoxanthine showed moderate inhibitory activity of the WT E. coli PNP, whereas 9‐deazaxanthine and its 2′‐deoxyriboside are weak inhibitors.     

Isoenergetic Polymorphism: The Puzzle of Tolazamide as a Case Study

In the present case study of tolazamide we illustrate how many seemingly contradictory results that have been obtained from experimental observations and theoretical calculations can finally start forming a consistent picture: a “puzzle put together”. For many years, tolazamide was considered to have no polymorphs. This made this drug substance unique among the large family of sulfonylureas, which was known to be significantly more prone to polymorphism than many other organic compounds. The present work employs a broad and in‐depth analysis that includes the use of optical microscopy, single‐crystal and powder X‐ray diffraction, IR and Raman spectroscopies, DSC, semiempirical PIXEL calculations and DFT of three polymorphs of tolazamide. This case study shows how the polymorphs of a molecular crystal can be overlooked even if discovered serendipitously on one of numerous crystallizations, and how very different molecular packings can be practically isoenergetic but still crystallize quite selectively and transform one into another irreversibly upon heating.     

Experimental and Theoretical Study of an Intramolecular CF3‐Group Shift in the Reactions of α‐Bromoenones with 1,2‐Diamines

The reactions of trifluoromethylated 2‐bromoenones and N,N′‐dialkyl‐1,2‐diamines have been studied. Depending on the structures of the starting compounds, the formation of 2‐trifluoroacetylpiperazine or 3‐trifluoromethylpiperazine‐2‐ones was observed. The mechanism of the reaction is discussed in terms of multistep processes involving sequential substitution of bromine in the starting α‐bromoenones and intramolecular cyclization of the captodative aminoenones as key intermediates to form the target heterocycles. The results of theoretical calculations are in perfect agreement with the experimental data. The unique role of the trifluoromethyl group in this reaction is demonstrated.     

Integrodifferential approaches to frequency analysis and control design for compressible fluid flow in a pipeline element

In this study, modelling, frequency analysis, and optimization of control processes are considered for the fluid flow in pipeline systems. A mathematical model of controlled pipeline elements with distributed parameters is proposed to describe the dynamical behaviour of compressible fluid which is transported in a long rigid tube. By exploiting specific functions representing cross-sectional forces and effective displacements as well as linear approximations of fluidic resistances, the original problem with non-uniform parameters is reduced to a partial differential equation (PDE) system with constant coefficients and homogeneous initial and boundary conditions. Three numerical approaches are applied to an efficient analysis of natural vibrations and reliable control-oriented modelling of pipeline elements. The conventional Galerkin method is compared with the method of integrodifferential relations based on a weak formulation of the constitutive laws. In the latter approach, the original initial-boundary value problem is reduced to the minimization of an error functional which provides explicit energy estimates of the solution quality. A novel projection approach is implemented on the basis of the Petrov–Galerkin method combined with the method of integrodifferential relations. This technique benefits from the advantages of the above-mentioned projection and variational approaches, namely sufficient numerical stability, a lower differential order, and an explicit quality estimation. Numerical optimization procedures, making use of a modified finite element technique, are proposed to obtain a feedforward control strategy for changing the pressure and mass flow inside the pipeline system to a desired operating state. At this given finite point of time, residual elastic oscillations inside the pipeline are minimized. Numerical results, obtained for ideal as well as viscous fluid models, are analysed and discussed.     

Localization of Gauge Theory on a Four-Sphere and Supersymmetric Wilson Loops

We prove conjecture due to Erickson-Semenoff-Zarembo and Drukker-Gross which relates supersymmetric circular Wilson loop operators in the N=4{\mathcal N=4} supersymmetric Yang-Mills theory with a Gaussian matrix model. We also compute the partition function and give a new matrix model formula for the expectation value of a supersymmetric circular Wilson loop operator for the pure N=2{\mathcal N=2} and the N=2^*{\mathcal N=2^*} supersymmetric Yang-Mills theory on a four-sphere. A four-dimensional N=2{\mathcal N=2} superconformal gauge theory is treated similarly.