Development of capacitance-based and impedance-based wireless sensors and sensor nodes for structural health monitoring applications

A field demonstration of a new and hybrid wireless sensing network paradigm for structural health monitoring (SHM) is presented. In this paradigm, both power and data interrogation commands are conveyed via a mobile agent that is sent to each sensor node to perform individual interrogations, which can alleviate several limitations of traditional sensing networks. This paper will discuss such prototype systems, which will be used to interrogate capacitive-based and impedance-based sensors for SHM applications. The capacitive-based wireless sensor node is specifically built to collect peak displacement measurements. In addition, a wireless sensor node for collecting electromechanical impedance data has also been developed. Both sensor nodes are specifically designed to accept various power sources and to be wirelessly triggered on an as-needed basis so that they can be used for the hybrid sensing network approach. The capabilities of these miniaturized and portable devices are demonstrated in the laboratory and the field, which was performed at the Alamosa Canyon Bridge in southern New Mexico.     

Synthesis of 1,3,6,8-Tetrabromophenanthrene via a Stoichiometric Ullmann Reaction

1,3,6,8-Tetrabromophenantherene (1) is prepared in four steps from 2,4,6-tribromobenzoic acid (4) in an overall yield of 12%. The key transformation used in the synthesis is a stoichiomteric Ullmann reaction.     

Preparation of Acyclic N-Acyl-N,O-acetals by Decarboxylation of N-Protected α-Amino Acids and Studies of Asymmetric Amidoalkylation with Trimethylsilyl Cyanide

Oxidative decarboxylation of N-acyl-α-amino acids with lead tetra-acetate followed by treatment with methanol provides a facile method for preparation of acyclic N-acyl-N,O-acetals, which can be used in asymmetric α-amidoalkylation reactions using trimethylsilyl cyanide as nucleophile.     

Measurements of the 10B (n,He) reaction rate in zppr

Direct measurements of the ¹⁰B(n, He) reaction rate have been made in ZPPR. The measurements were made by isotope-dilution mass spectrometric analysis of stainless-steel encapsulated samples of enriched ¹⁰B. The results demonstrate that direct measurements of the ¹⁰B reaction rate in ZPPR are obtainable to an accuracy of ～1%. Comparisons with calculations give a predicted-to-experiment value of ～0.93. This value is consistent with earlier Rockwell measurements in benchmark neutron fields and further supports a need for revision in the ENDF/B cross section for ¹⁰B above ～0.1 MeV.     

Hydride transfer reaction dynamics of OD+ +C3H6

The hydride transfer reaction between OD+ and C3H6 has been studied experimentally and theoretically over the center of mass collision energy range from 0.21 to 0.92 eV using the crossed beam technique and density functional theory calculations. The center of mass flux distributions of the product ions at three different energies are highly asymmetric, with maxima close to the velocity and direction of the precursor propylene beam, characteristic of direct reactions. In the hydride transfer process, the entire reaction exothermicity is transformed into product internal excitation, consistent with mixed energy release in which the hydride ion is transferred with both the breaking and forming bonds extended. At higher collision energies, at least 85% of the incremental translational energy appears in product translation, providing a clear example of induced repulsive energy release. Compared to the related reaction of OD+ with C2H4, reaction along the pathway initiated by addition of OD+ to the C=C bond in propylene has a critical bottleneck caused by the torsional motion of the methyl substituent on the double bond. This bottleneck suppresses reaction through an intermediate complex in favor of direct hydride abstraction. Hydride abstraction appears to be a sequential process initiated by electron transfer in the triplet manifold, followed by rapid intersystem crossing and subsequent hydrogen atom transfer to form ground state allyl cation and HOD.     

Identification of 1,3-dialkylimidazolium salt supramolecular aggregates in solution

The nature of the interactions between 1,3-dialkylimidazolium cations and noncoordinating anions such as tetrafluoroborate, hexafluorophosphate, and tetraphenylborate has been studied in the solid state by X-ray diffraction analysis and in solution by (1)H NMR spectroscopy, conductivity, and microcalorimetry. In the solid state, these compounds show an extended network of hydrogen-bonded cations and anions in which one cation is surrounded by at least three anions and one anion is surrounded by at least three imidazolium cations. In the pure form, imidazolium salts are better described as polymeric supramolecules of the type {[(DAI)(3)(X)](2+)[(DAI)(X)(3)](2-)}(n) (where DAI is the dialkylimidazolium cation and X is the anion) formed through hydrogen bonds of the imidazolium cation with the anion. In solution, this supramolecular structural organization is maintained to a great extent, at least in solvents of low dielectric constant, indicating that mixtures of imidazolium ionic liquids with other molecules can be considered as nanostructured materials. This model is very useful for the rationalization of the majority of the unusual behavior of the ionic liquids.