Vibration characteristics of a fiber-reinforced polymer bridge superstructure

Dynamic response of the first fiber-reinforced polymer composite bridge built in the US was studied using experimental modal tests and validated finite element models. This slab bridge was manufactured with a longitudinal joint, in the form of a shear-key, and was connected in the field using epoxy resins. Long-term performance of such joints is critical for future applications of similar designs. At the same time, the shear-key details are not visible, once joined, and cannot be inspected using routine inspection procedures. Hence, experimental modal analysis was used to evaluate the integrity of the longitudinal joint. A finite element model validated with field test data was developed to further study the effect of the longitudinal joint degradation on vibration characteristics of the structure. The finite element analysis was also used to evaluate the modal-based techniques for future inspections. Results indicate that the longitudinal joint is performing as intended, and only high degradation of the joint can be detected using the measured vibration characteristics of the bridge.     

Effect of Zr on dielectric, ferroelectric and impedance properties of BaTiO3 ceramic

A polycrystalline sample of Zr-doped barium titanate (BaTiO₃) was prepared by conventional solid state reaction method. The effect of Zr (0·15) on the structural and microstructural properties of BaTiO₃ was investigated by XRD and SEM. The electrical properties (dielectric, ferroelectric and impedance spectroscopy) were measured in wide range of frequency and temperature. With substitutions of Zr, the structure of BaTiO₃ changes from tetragonal to rhombohedral. Lattice parameters were found to increase with substitution. The room temperature dielectric constant increases from ～ 1675 to ～ 10586 and peak dielectric constant value increases from ～ 13626 to ～ 21023 with diffuse phase transition. Impedance spectroscopy reveals the formation of grain and grain boundary in the material and found to decrease with increase in temperature.     

Plasma-assisted co-evaporation of β-indium sulfide thin films

This paper describes the development of plasma-assisted co-evaporation (PACE) for the formation of β-In₂S₃ thin films. Indium was supplied by conventional thermal evaporation, while the chalcogen gas precursor (H₂S) was activated using an inductively coupled plasma (ICP) source. Using a combination of optical emission spectroscopy and mass spectrometry it was shown that the ICP effectively dissociated H₂S, producing atomic sulfur. Transport modeling was used to quantify the flux distributions of the co-evaporated metal and the plasma-generated species impinging the substrate. Model predictions were validated by measurements of deposition rate and film properties. Substantial improvements in both materials utilization and substrate temperature reduction were realized with respect to conventional co-evaporation. β-In₂S₃ was formed as low as 100 °C and it was observed that quality was a strong function of S/In ratio. The grain size decreased and the optical band gap increased as the substrate temperature was reduced.     

A quaternary lead based perovskite structured materials with diffuse phase transition behavior

A lead based quaternary compound composed of 0.25(PbZr_0.52Ti_0.48O₃) + 0.25(PbFe_0.5Ta_0.5O₃) + 0.25 (PbF_0.67W_0.33O₃) + 0.25(PbFe_0.5Nb_0.5O₃) - (PZT-PFT-PFW-PFN) was synthesized by conventional solid-state reaction techniques. It showed moderate high dielectric constant, low dielectric loss, and two diffuse phase transitions, one below the room temperature ∼261 K and other above ∼410 K. X-ray diffraction (XRD) patterns revealed a tetragonal crystal structure at room temperature where as scanning electron micrograph (SEM) indicates inhomogeneous surface with an average grain size of 500 nm-3 μm. Well saturated ferroelectric hysteresis loops with good saturation polarization (spontaneous polarization, P_s ∼ 30.68 μC/cm²) were observed. Temperature-dependent ac conductivity displayed low conductivity with kink in spectra near the phase transition. In continuing search for developing new ferroelectric materials, in the present study we report stoichiometric compositions of complex perovskite ceramic materials: (PZT-PFT-PFW-PFN) with diffuse phase transition behavior. The crystal structure, dielectric properties, and ferroelectric properties were characterized by XRD, SEM, dielectric spectroscopy, and polarization. 1/? versus (T) plots revealed diffuse relaxor phase transition (DPT) behavior. The compositional variation on the phase transition temperature, dielectric constant, and ferroelectric to paraelectric phase transitions are discussed.     

On the existence of finite state supervisors for arbitrarysupervisory control problems

Given two prefix closed languages K, L ⊆ Σ*, where K ⊆ L represents the desired closed-loop behavior and L is the open-loop behavior, there exists a finite-state supervisor that enforces K in the closed loop if and only if there is a regular, prefix-closed language M ⊆ Σ*, such that: 1) MΣ_u∪L⊆M, and 2) M∪L=K. In this paper, we show that this is equivalent to: 1) the controllability of sup{P⊆K∪L¯|pr(P)=P} with respect to Σ*; and 2) the regularity of sup{P⊆K∪L¯|pr(P)=P}, where L¯=Σ*-L:and pr(·) is the set of prefixes of strings in the language argument. We use this property to investigate the issue of deciding the existence of a finite-state supervisor for different representations. We also present some properties of the language sup{P⊆K∪L¯|pr(P)=P}, along with implications to the synthesis of solutions to the supervisory control problem with the fewest states     

Rehabilitation and field testing of an FRP bridge deck on a truss bridge

A light-weight FRP deck was used, on an experimental basis, to replace a heavy deteriorated concrete deck improving the load rating of a 60-year old truss bridge located in Wellsburg, New York. This was the first such application in New York State. Load testing was conducted after installation of the FRP deck to study its behavior. Results indicated the conservative nature of the deck design, and no composite action between the deck and the superstructure. The study also shows that the joints are only partially effective in load transfer between panels.     

Enhanced catalytic activity of ultrathin CuO islands on SnO/sub 2/ films for fast response H/sub 2/S gas sensors

H/sub 2/S gas-sensing properties of a novel SnO/sub 2/-CuO structure consisting of ultrathin (/spl sim/10 nm) CuO dotted islands (600 /spl mu/m diameter) on 120-nm thick, sputtered SnO/sub 2/ film are compared with a pure SnO/sub 2/ and a SnO/sub 2/-CuO bilayer sensor. The SnO/sub 2/-CuO-dotted sensor exhibited a high sensitivity of 7.3/spl times/10/sup 3/ at a low operating temperature of 150/spl deg/C. A fast response time of 14 s for 20 ppm of H/sub 2/S gas and a recovery time of 118 s under flowing air have been measured. The electronic interaction due to modulation of the space charge regions between the distributed p-type CuO islands on the n-type SnO/sub 2/ thin-film surface and the presence of adsorbed oxygen on the SnO/sub 2/ support have been analyzed. Dissociated hydrogen available from the CuO-H/sub 2/S interaction spills over and its chemical interaction with the adsorbed oxygen on the SnO/sub 2/ surface is found to play a dominant role in the observed fast response characteristics.     

Modeling the dynamics of the mixed layer in solar ponds

A new model is proposed to explain the Nielsen's equilibrium condition. This model takes into account the effects of both turbulent entrainment and diffusion on the growth/erosion of the gradient zone. The existing turbulent entrainment model is modified to make it applicable near the equilibrium condition. The new model predictions indicate the dependence of the equilibrium condition on the mixed layer depth, apart from the salinity and temperature gradients in the gradient zone.     

Effects of nitrogen doping on the growth and properties of plasma-enhanced chemical-vapor-deposited diamond-like-carbon films

Nitrogen-doped diamond-like carbon (DLC) or amorphous hydrogenated carbon (a-C:H) films were grown by plasma enhanced chemical vapor deposition using methane and nitrogen gases as precursors. The effects of nitrogen trifluoride (NF₃) on these nitrogen-doped DLC films were also investigated. The deposition rate decreases sharply with the addition of nitrogen in the absence of NFF₃ due to dilution, while it increases in the presence of NFF₃ due, presumably, to the reduction of activated hydrogen species by the fluorine radical (F϶. X-ray photoelectron spectra reveal a nitrogen concentration in the range of 9.3 to 13.8% in these DLC films with a C Is electron binding energy of 287-288 eV, indicating the diamond-like structure. Infrared spectra of DLC films indicate the presence of amino groups (N-H) and nitrile and/or isonitrile (C= N) groups giving strong evidence of sp carbon. Diamond like carbon films deposited in CHF₄ +NF₄ (with and without NFF₃) have a lower refractive index, a lower bulk resistivity, and a lower optical bandgap than films deposited using CHF₄ due to a lower hydrogen content in the films. Moreover, the bulk resistivity of these films decreases by over four orders of magnitude and the optical bandgap decreases from 2.65 eV to about 0.75 eV following annealing at a temperature of 500°C.