Scheduled controllers for linear systems with bounded actuators

State and output feedback controllers are designed for disturbance attenuation in linear systems with bounded actuators. The controller is scheduled according to the proximity to the origin of the state of the plant in the state-feedback case and the compensator state in the case of output feedback. This procedure yields a linear parameter-varying structure for the controller that allows higher-gain and hence higher-performance controllers as the states move closer to the origin. The main results give sufficient conditions for the satisfaction of a parameter-dependent performance measure, without violating the saturation bounds. Linear splines are used to obtain solutions that can be obtained by standard LMI software. Examples—including an open-loop unstable system—highlight the application of the results.     

Nitrogen adsorption on a supported iron nanocluster

Sequential adsorption of N atoms on a MgO(1 0 0) supported Fe₇ cluster is studied using a density functional approach. For the number of adsorbates varying between one and six, the most favorable adsorption geometries are determined and the corresponding potential energy diagram is given. Up to five N atoms are found to bind strongly to the oxide supported cluster, with binding energies ranging from 0.98 to per N atom. When a sixth N atom is added to the cluster with five preadsorbed N atoms, the potential energy sharply increases due to the strong repulsive interaction between N adsorbates at short distances. The MgO(1 0 0) support plays an important role in increasing the binding energy of the adsorbed species.     

Electrical properties of Al/conducting polymer (P2ClAn)/p-Si/Al contacts

Al/P2ClAn/p-Si/Al structure was obtained by the evaporation of the polymer P2ClAn on the front surface of p-type silicon substrate. The P2ClAn emeraldine salt was chemically synthesized by using propionic (C₂H₅COOH) acid. The current–voltage (I–V) characteristic of the structure was measured at room temperature. The capacitance–voltage–frequency (C–V–f) in terms of interface states over the frequency range of 10 kHz to 3 MHz has been investigated. The capacitance has decreased with increasing frequency, due to the interface states distribution. From the forward bias I–V plot for the sample, the ideality factor (n) and zero-bias barrier height (Φ_bp,0) were obtained as 4.84 and 0.787 eV, respectively. Under forward bias, the high value of the ideality factor and the dispersion in capacitance could be due to the interface state distribution, the interfacial insulator layer, the conducting polymer on the interface and inhomogeneity of the barrier height. The energy distributions and the relaxation times of the interface states were determined in the energy range of (0.387 − E_v) to (0.787 − E_v) eV.     

Analysis of water adsorption by wood using the Guggenheim-Anderson-de Boer equation

The Guggenheim-Anderson-de Boer (GAB) three-parameter sorption equation has been used to interpret the adsorption and desorption isotherms of water vapour measured for 21 important cultural heritage wood species used in the past for panel paintings and woodcarving. The equation is capable of describing the full shape of the isotherms and yields meaningful physical parameters, especially the monolayer capacity from which the water accessible specific surface area can be obtained. It is demonstrated that average sorption isotherms can be derived using the GAB equation for the sorption data available for sets of specimens and that moisture properties of various wood specimens or chemically modified wood can be more easily compared.     

Electrical characteristics of Au/<Emphasis Type="Italic">n</Emphasis>-GaAs structures with thin and thick SiO<Subscript>2</Subscript> dielectric layer

The aim of this study, to explain effects of the SiO₂ insulator layer thickness on the electrical properties of Au/n-GaAs Shottky barrier diodes (SBDs). Thin (60 Å) and thick (250 Å) SiO₂ insulator layers were deposited on n-type GaAs substrates using the plasma enganced chemical vapour deposition technique. The current-voltage (I–V) and capacitance-voltage (C-V) characteristics have been carried out at room temperature. The main electrical parameters, such as ideality factor (n), zero-bias barrier height (? _Bo ), series resistance (R _s ), leakage current, and interface states (N _ss ) for Au/SiO₂/n-GaAs SBDs have been investigated. Surface morphologies of the SiO₂ dielectric layer was analyzed using atomic force microscopy. The results show that SiO₂ insulator layer thickness very affects the main electrical parameters. Au/n-GaAs SBDs with thick SiO₂ insulator layer have low leakage current level, small ideality factor, and low interface states. Thus, Au/n-GaAs SBDs with thick SiO₂ insulator layer shows better diode characteristics than other.     

Simultaneous novel synthesis of conducting and non-conducting halogenated polymers by electroinitiation of (2,4,6-trichloro- or 2,6-dichlorophenolato)Ni(II) complexes

NiL₂(Ph)₂·xH₂O [L=3,5-dimethylpyrazole or N-methyl imidazole; Ph=DCP or TCP; x=0, 1 or 3] complexes were synthesised and characterised by analytical and spectroscopic methods using elemental analysis and FTIR. The electrochemical behavior of the complexes was studied by cyclic voltammetry in tetrabutylammoniumtetrafluoroborate-N,N-dimethylformamide electrolyte-solvent couple. Cyclic voltammogram of the complexes displayed two-step oxidation processes under the nitrogen gas atmosphere. The polymerization of the complexes was accomplished in the same solvent-electrolyte couple by the constant potential electrolysis of NiL₂(Ph)₂·xH₂O, synthesizing the poly(di- or monochlorophenylene oxide)s via free radical mechanism. The simultaneous polymerization of non-conducting polymer and conducting polymer (the conductivity of 0.7 S cm⁻²) were achieved by electroinitiated polymerization of Ni(DMPz)₂(TCP)₂. The structural analysis of the polymers were performed using FTIR, ¹H NMR and ¹³C NMR spectroscopic techniques and DSC for the thermal analysis. The kinetics of the polymerization was followed by in situ UV-vis spectrophotometer during the electrolysis. The low temperature ESR spectrum of the electrolysis solution also confirmed the formation of phenol radical (g=2.0028). One electron oxidation process of NiL₂(DCP)₂·xH₂O produces a new Ni(II) complex, Ni(L-L)(DCP)₂(S) by the rapid decomposition of Ni^IIIL₂(DCP)₂ into a ligand radical producing a singlet with the g value of 2.0015. Second electron oxidation process generates oligemers, which could not be isolated from the electrolyte solution.     

Comparison of colorimetric and spectrophotometric methods for colour determination in pasta

 Product colour is one of the most important criteria for determining pasta quality. For pasta produced without eggs, pasta colour will depend mostly on the content of the yellow pigment in flour. Analyses were done with 12 samples of hand-made pasta without eggs. The yellow pigment content was determined by the standard spectrophotometric method, while the pasta colour (fresh shaped and dry milled pasta) was measured using the Minolta CR-300 colorimeter. The results obtained show that there is a correlation between spectrophotometric determination of the yellow pigment content and the results of colorimetric measurement. The correlation coefficient between the colorimetric results of dry milled pasta and the yellow pigment content is higher than that between the colorimetric results of fresh shaped pasta and the yellow pigment content.     

Dielectric and Optical Properties of CdS–Polymer Nanocomposites Prepared by the Successive Ionic Layer Adsorption and Reaction (SILAR) Method

The successive ionic layer adsorption and reaction (SILAR) method has been used to grow epitaxial CdS–polymer nanostructures as thin films with different surface morphology and particle size. The main purpose of the study was to investigate the dielectric properties and a.c. electrical conductivity (σ _a.c.), by a.c. impedance spectroscopy between 1 kHz and 1 MHz, at room temperature, of CdS–polymer nanocomposites produced by use of 2, 6, and 10 cycles of SILAR. The surface morphology and optical absorption of the samples were characterized by scanning electron microscopy (SEM) and UV–visible spectroscopy, respectively. Determination of the energy gaps of CdS–polymer nanocomposites prepared by use of different numbers of cycles of SILAR reveals that the band gap decreases with increasing number of cycles (J. Cryst. Growth 305, 175–180, 2007). This behavior is because of the growth of nanoparticles in the matrix materials, and can be explained by changes in the amount of confinement as a consequence of particle size variation. SEM images also confirm that different numbers of cycles lead to different morphology. Frequency-dependent dielectric properties and a.c. electrical conductivity of the samples prepared by use of different numbers of cycles of SILAR were investigated, and comparative studies on some electrophysical properties of the samples are reported. Experimental results show that values of the dielectric constant (ε′), dielectric loss (ε″), dielectric loss tangent (tanδ), the real (M′) and imaginary (M″) parts of electric modulus, and σ _a.c. are highly dependent on the frequency and the number of cycles. It can be concluded that changing the frequency and the number of cycles substantially alters both the dielectric properties and a.c. electrical conductivity of the samples.     

PIXE-PIGE analysis of Carolingian period glass from Slovenia

Glass artifacts excavated from the Late Roman and Carolingian period site at Bašelj Slovenia were analyzed by the combined PIXE-PIGE method using a proton beam in air. The results show that the majority of objects and glass ingots were made of traditional Roman, natron-type glass. Increased titanium and other impurities were found indicating that the glass had been recycled several times. As the composition of the ingots was similar to the other objects, a possibility exists of a secondary glass workshop in the local vicinity. The typologically and stratigraphically dated objects confirm that the Roman glassmaking continued in the area of Eastern Alps well into the 9th century.     

On the energy distribution of interface states and their relaxation time and capture cross section profiles in Al/SiO2/p-Si (MIS) Schottky diodes

The energy distribution profile of the interface states (N_ss) and their relaxation time (τ) and capture cross section (σ_p) of metal-insulator-semiconductor (Al/SiO₂/p-Si) Schottky diodes have been investigated by using the high-low frequency capacitance and conductance methods. The capacitance-voltage (C-V) and conductance-voltage (G/ω-V) characteristics of these devices were investigated by considering series resistance (R_s) effects in a wide frequency range (5 kHz-1 MHz.). It is shown that the capacitance of the Al/SiO₂/p-Si Schottky diode decreases with increasing frequency. The increase in capacitance especially at low frequencies results form the presence of interface states at Si/SiO₂ interface. The energy distributions of the interface states and their relaxation time have been determined in the energy range of (0.362-E_v)-(0.512-E_v) eV by taking into account the surface potential as a function of applied bias obtained from the measurable C-V curve (500 Hz) at the lowest frequency. The values of the interface state density (N_ss) ranges from 2.34 × 10¹² to 2.91 ×  10¹² eV⁻¹/cm², and the relaxation time (τ) ranges from 1.05 × 10⁻⁶ to 1.58 × 10⁻⁴ s, showing an exponential rise with bias from the top of the valance band towards the mid-gap.