Large error recovery for a class of frequency tracking algorithms

The performance of a recently proposed high-order adaptive notch filter (HANF) for frequency estimation and tracking is studied. An analysis technique utilizing approximations with linear filters is employed to derive closed-form performance expressions for a noisy sinusoidal input signal. Important performance measures, such as stability, noise rejection, statistical efficiency, and tracking ability, are studied in detail, and rules for the design variables are given. A study is presented where the performance of HANF is compared with the performance of a minimal order adaptive notch filter (ANF), as well as with a frequency tracker based on least squares-modelling—the multiple frequency tracker (MFT). The study reveals that HANF is a competitive alternative to ANF, but also that, in general, the MFT is the method of choice. © 1998 John Wiley & Sons, Ltd.     

Crystallization of 2D Hybrid Organic–Inorganic Perovskites Templated by Conductive Substrates

2D hybrid organic–inorganic perovskites are valued in optoelectronic applications for their tunable bandgap and excellent moisture and irradiation stability. These properties stem from both the chemical composition and crystallinity of the layer formed. Defects in the lattice, impurities, and crystal grain boundaries generally introduce trap states and surface energy pinning, limiting the ultimate performance of the perovskite; hence, an in-depth understanding of the crystallization process is indispensable. Here, a kinetic and thermodynamic study of 2D perovskite layer crystallization on transparent conductive substrates are provided—fluorine-doped tin oxide and graphene. Due to markedly different surface structure and chemistry, the two substrates interact differently with the perovskite layer. A time-resolved grazing-incidence wide-angle X-ray scattering (GIWAXS) is used to monitor the crystallization on the two substrates. Molecular dynamics simulations are employed to explain the experimental data and to rationalize the perovskite layer formation. The findings assist substrate selection based on the required film morphology, revealing the structural dynamics during the crystallization process, thus helping to tackle the technological challenges of structure formation of 2D perovskites for optoelectronic devices.     

Thermodynamics and Phase Equilibria in the Ca─Cu─O System

Phase equilibria in the CaO─CuO─Cu system were determined at 1173 K from the results of X-ray diffraction measurements using specimens annealed in the oxygen partial pressure range from P O₂= 1 to 10⁻⁸ atm. Electromotive force (emf) measurements using ZrO₂ solid electrolyte cells were carried out in the ternary phase equilibria. Gibbs free energies for the chemical reactions were summarized by equations with linear temperature dependence, and the standard free energy of formation for Ca₂CuO₃ was derived. The stability conditions of the oxides are displayed in the p – T – x diagram, and the possible phase equilibria with the liquid are evaluated.     

On the power of elementary features in spiking neural P systems

Since their first publication in 2006, spiking neural (SN) P systems have already attracted the attention of a lot of researchers. This might be owing to the fact that this abstract computing device follows basic principles known from spiking neural nets, but its implementation is discrete, using membrane computing background. Among the elementary properties which confer SN P systems their computational power one can count the unbounded fan-in (indegree) and fan-out (outdegree) of each “neuron”, synchronicity of the whole system, the possibility of delaying and/or removing spikes in neurons, the capability of evaluating arbitrary regular expressions in neurons in constant time and some others. In this paper we focus on the power of these elementary features. Particularly, we study the power of the model when some of these features are disabled. Rather surprisingly, even very restricted SN P systems keep their universal computational power. Certain important questions regarding this topic still remain open.     

Polyurethane/multiwalled carbon nanotube nanowebs prepared by an electrospinning process

Polyurethane (PU) and PU/multiwalled carbon nanotube (MWCNT) nanocomposite nanofibers, both with diameters of 350 nm, were prepared by an electrospinning process from PU dimethylformamide solutions. The appearance of nanowebs in PU/MWCNT nanofiber structures containing PU fibers with diameters of 20–40 nm was observed. The existence of these structures could have been based on the occurrence of strong secondary electric fields, which were created between individual conducting MWCNTs (distributed in the PU/MWCNT nanocomposites), which started to behave as the local moving nanoelectrodes promoting the creation of additional very fine nanowebs during the electrospinning processes. To our knowledge, this is the first report describing nanowebs from synthetic polymers prepared by an electrospinning process. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Tetrapyrazinoporphyrazines with different number of peripheral pyridyl rings: Synthesis,photophysical and photochemical properties

Zinc tetrapyrazinoporphyrazines comprising different numbers of pyridin-2-yl and tert-butylsulfanyl substituents were prepared by the statistical condensation of two precursors – 5,6-bis(tert-butylsulfanyl)pyrazine-2,3-dicarbonitrile (A) and 5,6-dipyridin-2-yl-pyrazine-2,3-dicarbonitrile (B). The ensuing zinc tetrapyrazinoporphyrazines were chromatographically separated on silica column and characterized. Adjacent (AABB) and opposite (ABAB) isomers were not separated. The prepared zinc tetrapyrazinoporphyrazines did not differ in their Q-band position but the B-band position was shifted hypsochromically for compounds bearing more pyridyl units; in addition, a weak band at 450–520 nm decreased with increasing number of pyridyl substituents. Singlet oxygen quantum yields (Φ_Δ in the range 0.69–0.53) decreased with increasing number of pyridyl units on the macrocyclic core, while fluorescence quantum yields showed the reverse tendency (Φ_F in the range 0.22–0.26).     

The Rengen Grassland Experiment: soil contamination by trace elements after 65 years of Ca,N, P and K fertiliser application

The Rengen Grassland Experiment (RGE) was established in the Eifel Mts. (Germany) on a low productive Nardetum in 1941. Since then, the following fertiliser treatments have been applied along with a two cut system: unfertilised control, Ca, CaN, CaNP, CaNP–KCl and CaNP–K₂SO₄ with basic slag (syn. Thomas phosphate) as the only P fertiliser. The effect of long-term fertilisation on plant-available (extracted with 0.01 mol l⁻¹ CaCl₂), easily-mobilisable (extracted with 0.05 mol l⁻¹ EDTA), potentially-mobilisable (extracted with 2 mol l⁻¹ HNO₃) and total concentrations of trace elements (As, Cd, Cr, Cu, Fe, Mn, Ni, Pb and Zn) in the top 0–10 and 10–20 cm of soil were investigated in 2006. According to redundancy analysis (RDA), the effect of treatment on the concentrations of risk elements was significant and explained 82.3 and 90.6% of the variability in the data in the 0–10 and 10–20 cm soil layers, respectively. Basic slag supplied the soil with considerable amounts of As, Cr, Cu, Fe, Mn and Zn. Following 65 years of fertiliser application the concentrations of risk elements in the soil profile had increased substantially, especially with basic slag. However, threshold limits for total trace element concentration in soil permitted by Czech national legislation were exceeded only in the case of As. The increase in plant-available As concentrations was most critical as it increased the potential uptake of As by plants in plots fertilised with P. Although P treatments received more than 300 g of Cr ha⁻¹ annually, no effect on plant-available Cr soil content was detected. This contrasted with the accumulation of total Cr in the 0–10 and 10–20 cm soil layers. Furthermore, plant availability of Cd, Fe, Mn and Zn was affected by soil pH and generally decreased with the application of quick lime. Plant availability of these elements was not correlated with amounts supplied by fertilisers.     

Off-axis and inline electron holography: Experimental comparison

Electron holography is a very powerful technique for mapping static electric and magnetic potentials down to atomic resolution. While electron holography is commonly considered synonymous with its off-axis variant in the high energy electron microscopy community, inline electron holography is widely applied in low-energy electron microscopy, where the realization of the off-axis setup is still an experimental challenge. This paper demonstrates that both inline and off-axis holography may be used to recover amplitude and phase shift of the very same object, in our example latex spheres of 90 and 200 nm in diameter, producing very similar results, provided the object does not charge under the electron beam.     

Extraterrestrial,terrestrial and laboratory diamonds — Differences and similarities

Characterization tools such as confocal Raman micro-spectroscopy, Laser Ablation (LA-ICP-TOF-MS) and SEM-EDS were used to characterize meteorites: primitive achondrite — not classified NWA XXX ureilite found in 2006 in Morocco and the graphite nodula from the Canyon Diablo iron meteorite. The presence of diamond was confirmed in both samples.There are two kinds of meteoritic diamonds: diamonds of the sizes of microns up to millimeters are most probably of impact origin, nanodiamonds of the sizes of 1–3 nm, called presolar diamonds because of the isotopic anomalies, are believed to be formed before our Solar System was formed. There are many theories concerning presolar diamonds formation, among them: impact shock metamorphism driven by supernovae or chemical vapor deposition (CVD) from stellar outflows.We examined the properties of diamond nanopowders obtained by the PA CVD and detonation methods. Nanodiamonds obtained by the detonation method, called ultradispersed detonation diamonds (UDD), are of the same range of sizes as presolar diamonds.The results show both differences and similarities among meteoritic, terrestrial and laboratory diamonds. The comparison will help to understand the processes during presolar nanodiamonds formation.     

Optical characterization of ultrananocrystalline diamond films

Optical properties of the ultrananocrystalline diamond films were studied by multi-sample method based on the combination of variable angle spectroscopic ellipsometry and spectroscopic reflectometry applied in the range 0.6–6.5 eV. The films were deposited by PECVD in a conventional bell jar (ASTeX type) reactor using dual frequency discharge, microwave cavity plasma and radio frequency plasma inducing dc self-bias at a substrate holder. The optical model of the samples included a surface roughness described by the Rayleigh–Rice theory and a refractive index profile in which Drude approximation was used. The results conformed with the present understanding of the polycrystalline diamond growth on the silicon substrate because the existence of silicon carbide and amorphous hydrogenated carbon film between the silicon substrate and nucleation layer was proved.