Use of the original silicone cladding of an optical fiber as a reagent-immobilization medium for intrinsic chemical sensors

It is demonstrated that extended-length sensors can be fabricated by the direct immobilization of suitable reagents into the original cladding of a plastic-clad silica (PCS) optical fiber. This cladding, a copolymer of vinyl-terminated poly(dimethylsiloxane) and poly(dimethylmethylhydrosiloxane), is an attractive immobilization matrix for a wide variety of reagents and opens up new avenues of sensor design. Unlike fibers with custom-drawn cladding, the new approach offers greater photo- and thermal stability and permits immobilization of several reagents in adjacent sections of a single fiber. Further, compared to room-termperature vulcanizable (RTV) silicone films used often in optical point sensors, the silicone cladding of a PCS optical fiber offers a number of advantages, including a dynamic fluorescence quenching constant for an immobilized fluorophore that is up to 3.4 times higher, tolerance to aggressive environments (e.g. highly alkaline solutions), lower rates of indicator leaching, high uniformity, and applicability to extended-length sensing. The homogeneity of the microenvironment of the fiber cladding, its resistance to aggressive alkaline solutions, and its ability to transport water vapor were probed by introducing a variety of reagents into the cladding, including a fluorescent ruthenium complex and acid-base and solvatochromic indicators. The new sensor-fabrication approach should find wide application, including detection of neutral species in gases and dissolved in water, and for spatial analyte mapping over extended, remote areas.     

Foliated Lie and Courant Algebroids

If A is a Lie algebroid over a foliated manifold (M, F){(M, {\mathcal {F}})}, a foliation of A is a Lie subalgebroid B with anchor image TF{T{\mathcal {F}}} and such that A/B is locally equivalent with Lie algebroids over the slice manifolds of F{\mathcal F}. We give several examples and, for foliated Lie algebroids, we discuss the following subjects: the dual Poisson structure and Vaintrob's supervector field, cohomology and deformations of the foliation, integration to a Lie groupoid. In the last section, we define a corresponding notion of a foliation of a Courant algebroid A as a bracket–closed, isotropic subbundle B with anchor image TF{T{\mathcal {F}}} and such that B ^{^} /B{B^{ \bot } /B} is locally equivalent with Courant algebroids over the slice manifolds of F{\mathcal F}. Examples that motivate the definition are given.     

Signal-to-noise ratio enhancement based on wavelet filtering in ultrasonic testing

In ultrasonic non-destructive testing of materials with a coarse-grained structure the scattering from the grains causes backscattering noise, which masks flaw echoes in the measured signal. Several filtering methods have been proposed for improving the signal-to-noise ratio. In this paper we present a comparative study of methods based on the wavelet transform. Experiments with stationary, discrete and wavelet packet de-noising are evaluated by means of signal-to-noise ratio enhancement. Measured and simulated ultrasonic signals are used to verify the proposed de-noising methods. For comparison, we use signal-to-noise ratio enhancement related to fault echo amplitudes and filtering efficiency specific for ultrasonic signals. The best results in our setup were achieved with the wavelet packet de-noising method.     

Stochastic Enumeration Method for Counting Trees

The problem of estimating the size of a backtrack tree is an important but hard problem in the computational sciences. An efficient solution of this problem can have a major impact on the hierarchy of complexity classes. The first randomized procedure, which repeatedly generates random paths through the tree, was introduced by Knuth. Unfortunately, as was noted by Knuth and a few other researchers, the estimator can introduce a large variance and become ineffective in the sense that it underestimates the cost of the tree. Recently, a new sequential algorithm called Stochastic Enumeration (SE) method was proposed by Rubinstein et al. The authors showed numerically that this simple algorithm can be very efficient for handling different counting problems, such as counting the number of satisfiability assignments and enumerating the number of perfect matchings in bipartite graphs. In this paper we introduce a rigorous analysis of SE and show that it results in significant variance reduction as compared to Knuth’s estimator. Moreover, we establish that for almost all random trees the SE algorithm is a fully polynomial time randomized approximation scheme (FPRAS) for the estimation of the overall tree size.     

Investigation of the catalytic hydrogenation of disturbed benzenes and the configurational isomerization of the corresponding cyclohexanes

Russian Chemical Bulletin -