Some observations on supervisory policies that enforce liveness in partially controlled Free-Choice Petri nets

Every arc from a place to a transition in a Free-Choice Petri net (FCPN) is either the unique output arc of the place, or, the unique input arc to the transition [M.H.T. Hack, Analysis of production schemata by Petri nets, Master’s thesis, Massachusetts Institute of Technology, February 1972; W. Reisig, Petri Nets, Springer-Verlag, Berlin, 1985; T. Murata, Petri nets: properties, analysis and applications, Proc. IEEE 77 (4) (1989) 541–580]. We consider FCPNs that are not live [J.L. Peterson, Petri Net Theory and the Modeling of Systems, Prentice-Hall, Englewood Cliffs, NJ, 1981; W. Reisig, Petri Nets, Springer-Verlag, Berlin, 1985; T. Murata, Petri nets: properties, analysis and applications, Proc. IEEE 77 (4) (1989) 541–580], and we investigate the existence of supervisory policies that can enforce liveness in partially controlled FCPNs. The external agent, or supervisor, can only prevent the firing of some (i.e. not all) transitions in a partially controlled FCPN.

We first present an observation on supervisory policies that enforce liveness in partially-controlled FCPNs. Using this observation, we solve the supervisory synthesis problem for the family of c hoice-controlled FCPNs, defined in this paper. We then identify a new, sub-class of partially-controlled FCPNs that posses an easily-characterized (and easily-enforced) supervisory policy that enforces liveness.     

Dielectric properties of sol-gel derived barium-strontium-titanate (Ba(0.4)Sr(0.6)TiO(3)) thin films

The structural and dielectric properties of sol-gel derived barium-strontium-titanate (Ba(0.4)Sr(0.6)TiO(3 )) thin films have been investigated. The as-fired films are found to be amorphous, and films crystallize to a cubic phase after a post deposition annealing at 700 degrees C for one hour in air. The variation of dielectric constant with temperature and field was investigated as a function of film thickness. These films display a nonlinear dielectric response that can be described in terms of a power series expansion of the free energy in polarization as in Landau-Ginzburg-Devonshire approach. The measured room temperature dielectric constant (epsilon') of the film was about 320. The dielectric constant did not show any significant frequency dependence up to 100 kHz. The temperature dependence of dielectric constant exhibited a diffused ferroelectric to paraelectric phase transition at -60 degrees C. The room temperature dielectric constant and magnitude of the dielectric peak at the Curie point was dependent on the thickness of the film. The obtained dielectric data on sol-gel barium strontium titanate thin films on platinized substrates were analyzed in the light of a barrier layer model.     

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.