Quantizing and Sampling Considerations in Digital Phased-Locked Loops

Quantization and sampling effects on the digital phasedlocked loop (DPLL) structures obtained for demodulation of anglemodulated signals using extended Kalman filter algorithms are investigated for the high signal-to-noise ratio (SNR) case in this paper. First, the problem of quantization is considered. The validity of the uniform white sequence model for quantizer error in the DPLL is established independent of the sampling rate. Simulation results are presented for several quantizer word lengths. Also, an effective SNR is defined which allows prediction of quantized performance from unquantized results. Secondly, minimum sampling requirements for the DPLL are considered. The effect of sampling rate variation upon the predicted phase error covariance is examined. Again, simulation results are presented and compared to the predicted phase error covariance values. This results in an analytical method for determining minimum sampling rates for the DPLL. Minimum sampling rates for quantized DPLL have also been determined using the effective SNR previously defined.     

Precision measurements of the diffusion of reactive atoms

Resonance ionization spectroscopy is described for precision measurements of the diffusion of reactive atoms in gaseous media. Results are given for Cs atoms in an Ar-CH₄ mixture and are used to test a rigorous solution of the diffusion equation.     

Fermi-Dirac quantization of linear systems

After discussing the Fermion analogues of classical mechanics, we show that in finite degrees of freedom, the Segal-Weinless construction of the vacuum representation is always possible. This amounts to an explicit construction of a complex structure J which extends real Euclidean space with orthogonal dynamics to a complex Hilbert space with unitary dynamics. Also, we solve the inverse problem, deducing the class of classical Hamiltonians, given the complex structure J.     

Detection and mechanistic relevance of transient ligand radicals formed during [Ru(bpy)2(OH2)]2O4+-catalyzed water oxidation

Mechanistic proposals to account for the reactivity of water-oxidizing ruthenium diimine complexes have often invoked participation of covalently hydrated or pseudobase intermediates formed by reaction of solvent with the polypyridyl ligands. Probing for these intermediates has proven difficult because the concentrations of detectable reactive species are very low under commonly used experimental conditions. However, we have recently found that these transients accumulate in photocatalytic oxidation systems at neutral pH. In this work, we show that the reaction rates of these transient species correlate with catalytic activity and, therefore, that they meet minimal kinetic criteria to be true reaction intermediates.     

Multiwall carbon nanotube absorber on a thin-film lithium niobate pyroelectric detector

Multiwall carbon nanotubes (MWNTs) were applied in a bulk layer to a pyroelectric film to increase the detector sensitivity nearly fourfold without a substantial penalty to the low-frequency response (4-100 Hz). In addition, the spectral sensitivity over the wavelength range from 600 to 1800 nm was uniformly enhanced, with variations less than 1%. The results demonstrate the suitability of MWNTs as an efficient thermal absorber having low thermal mass.     

Open shell calculations for the two- and three-electron ions

Open shell calculations are made for all the three-electron atomic systems of the second period of the periodic table. These results are compared with corresponding two-electron and experimental energies.

It is noted that the improvement of open shell over closed shell calculations becomes less with increasing atomic number. In parallel trend the disparity of both from the experimental results increases with Z. An electron affinity of zero is found for the helium atom.     

0(gs)+ -->2(1)+ transition strengths in 106Sn and 108Sn

The reduced transition probabilities, B(E2; 0(gs)+ -->2(1)+), have been measured in the radioactive isotopes (108,106)Sn using subbarrier Coulomb excitation at the REX-ISOLDE facility at CERN. Deexcitation gamma rays were detected by the highly segmented MINIBALL Ge-detector array. The results, B(E2;0(gs)+ -->2(1)+)=0.222(19)e2b2 for 108Sn and B(E2; 0(gs)+-->2(1)+)=0.195(39)e2b2 for 106Sn were determined relative to a stable 58Ni target. The resulting B(E2) values are approximately 30% larger than shell-model predictions and deviate from the generalized seniority model. This experimental result may point towards a weakening of the N=Z=50 shell closure.     

Specifications of threshold-logic gates for optimum s.s.i. logic packaging

Various specifications for individual threshold-logic gates have been proposed to realise a maximum number of possible threshold-logic functions. This work is extended here to consider the optimum collection of such gates within conventional small-scale integrated-circuit package limitations.