Polarimetric optical fiber sensors: aspects of sensitivity and practical implementation

An analytical model for the pressure and strain sensitivity of highly-birefringent fibers is proposed which is in excellent agreement with numerical calculations. Results of polarimetry and coherence-multiplexing experiments are presented and a novel method for accurately splicing this kind of fibers is demonstrated.     

Molecular dynamics simulation of surface segregation in a (110) B2-NiAl thin film

Surface segregation in (110) B2-NiAl film approximately 3 nm thick is investigated by using molecular dynamics simulation with a reliable embedded-atom potential. The simulation is performed for the stoichiometric composition at a temperature of 1500 K, just below the melting temperature of the film model. It is found that the (110) surface is structurally stable but develops adatoms, vacancies and antisites. The coverage of an adatom layer is estimated to be ～0.07 ML (monatomic layers) and it contains on average ～95% of Al atoms. The top (surface) and second (subsurface) layers of the (110) surface is the most enriched in Ni relative to the bulk composition. These layers contain on average ～51% of Ni atoms. The Ni fraction in the third and forth layers of the film is estimated as ～50.5%. The deeper layers have essentially the bulk composition. Vacancies in the film model are found only on the Ni sublattice. The vacancy concentration on the Ni sublattice in the top layer is ～7.5%. The second layer almost does not contain vacancies. The next layers have essentially the constant bulk vacancy composition which can be estimated as ～1.3-1.4%.     

Click-chemistry approach to isoxazole-containing α-CF3-substituted α-aminocarboxylates and α-aminophosphonates

A convenient strategy for the synthesis of isoxazole-containing α-CF(3)-substituted α-aminocarboxylates and α-aminophosphonates have been developed. The method is based on copper-catalyzed 1,3-dipolar cycloaddition of different aromatic nitrile oxides to functionalized acetylenes.     

Flow behaviour of highly concentrated emulsions of supersaturated aqueous solution in oil

A set of highly concentrated water-in-oil emulsions with supersaturated dispersed phase were investigated in this work to verify and/or develop the models that have been presented both in the literature and in this work. The material used to form emulsions consisted of supersaturated oxidiser solution, hydrocarbon oil and PIBSA-based surfactants. The interfacial characteristics for different surfactant types were first examined. Then, the rheology of samples was studied, and different scaling methods and fitting of experimental data were studied. On the basis of flow curve measurements and observed $\tau _\emph{v} \sim \dot {\gamma }^{1/2}$ scaling, a modified version of Windhab model was suggested which showed excellent fitting of experimental results. The linear dependences of ?? _y0/?? versus 1/d ₃₂ for studied emulsions showed non-zero intercept which implies a non-linear dependence (resulting from interdroplet interaction) to fulfil the zero-intercept requirement. It was established that the zero intercept condition was fulfilled in the $\tau _{y0} \sim \sigma /d_{32}^2 $ scaling, although the experimental results for different surfactants were not superimposed.     

C-F?M interaction in anionic α-fluorovinyl rhenium oxycarbene complexes and their β-fluoroenolate analogs

The C-F?M⁺ interaction in anionic σ-(α-fluorovinyl)rhenium oxycarbene complexes, [RCFCFReC(O)R′(CO)₄]M (1-6), M = Na, Li, K is studied by ¹⁹F NMR in THF and Et₂O. The coordination of α-F to M⁺ results in an upfield shift of the corresponding ¹⁹F NMR signal and a decrease of ¹J_CF. The maximum shift is found for the Li salt of complex 4 in Et₂O (Δδ_Fα = 36.4 ppm), in which case a ⁷Li-¹⁹F spin-spin coupling is also observed (J_LiF = 40 Hz). The ΔE of C-F?M⁺ interaction and its effect on ¹⁹F shielding was further studied by DFT calculations using β-fluoroenolates as models, which confirmed a strong impact of CF-bond environment on the coordination ability of fluorine in these F,O-chelates. A compound with a β-fluoroenolate backbone but without rhenium, o-(α-fluorovinyl)phenolate 12, was prepared and studied by ¹⁹F NMR, and similarly showed indications of C-F?M⁺ interaction in THF solution. It is concluded that the donor ability of fluorine in the studied system is enhanced because of the conjugation of α-fluorovinyl group with the enolate π-system and back donation from the transition metal.     

Deoxygenation of some α-dicarbonyl compounds by tris(diethylamino)phosphine in the presence of fullerene C60

The reactions of such cyclic α-diketones as acenaphthenequinone, aceanthrenequinone, and N-alkylisatins, with hexaethyltriaminophosphine in the presence of the fullerene C(60), lead to the formation of methanofullerene derivatives under mild conditions. This process proceeds via deoxygenation of the dicarbonyl compound by the P(III) derivative and is likely to involve the intermediate formation of α-ketocarbenes. The structure of some methanofullerenes has been confirmed by NMR and XRD. The electrochemical behavior of the methanofullerenes was also investigated.     

Functional differential inclusions generated by functional differential equations with discontinuities

Given a functional differential equation with a discontinuity, a construction of its extension in the shape of a functional differential inclusion is offered. This construction can be regarded as a generalization of the famous Filippov approach to study ordinary differential equations with discontinuities. Some basic properties of the solutions of the introduced functional differential inclusions are studied. The developed approach is applied to analysis of gene regulatory networks with general delays.     

EPR of Spin Transitions in Complexes of Cu(hfac)2 with tert-Butylpyrazolylnitroxides

Polymer chain complexes [Cu(hfac)₂L^R] _n exhibit thermally and light-induced magnetic anomalies in many aspects similar to a spin crossover. These compounds attracted significant attention in the field of molecular magnetism and have been extensively studied by electron paramagnetic resonance (EPR) during the last several years. All compounds studied so far were based on copper(II) ions bridged by pyrazolyl-substituted nitronylnitroxides. The present work reports the first EPR study of complexes of Cu(hfac)₂ with tert-butylpyrazolylnitroxides—a new type of nitroxide ligand expected to modify exchange interaction pathways and physical properties of the crystals. The Q-band EPR spectra of three representative novel compounds are principally different from those studied previously, supporting the assumption that the magnetic motif of the compound has changed. Dominant intercluster exchange interactions are now found along the structural polymer chains. This complicates the EPR detection of phase transitions to some extent; however, theoretical modeling of the observed spectral changes allows for unambiguous assignment of different spin states and transitions between them. The magnitudes of intercluster exchange interaction were estimated to be ca. 0.1–1.5 cm^?1 for the studied compounds.