Adaptive wave field synthesis for broadband active sound field reproduction: signal processing

Sound field reproduction is a physical approach to the reproduction of the natural spatial character of hearing. It is also useful in experimental acoustics and psychoacoustics. Wave field synthesis (WFS) is a known open-loop technology which assumes that the reproduction environment is anechoic. A real reflective reproduction space thus reduces the objective accuracy of WFS. Recently, adaptive wave field synthesis (AWFS) was defined as a combination of WFS and active compensation. AWFS is based on the minimization of reproduction errors and on the penalization of departure from the WFS solution. This paper focuses on signal processing for AWFS. A classical adaptive algorithm is modified for AWFS: filtered-reference least-mean-square. This modified algorithm and the classical equivalent leaky algorithm have similar convergence properties except that the WFS solution influences the adaptation rule of the modified algorithm. The paper also introduces signal processing for independent radiation mode control of AWFS on the basis of plant decoupling. Simulation results for AWFS are introduced for free-field and reflective spaces. The two algorithms effectively reproduce the sound field and compensate for the reproduction errors at the error sensors. The independent radiation mode control allows a more flexible tuning of the algorithm.     

An aqueous route to organically functionalized silica diatom skeletons

Diatomaceous earth was functionalized by grafting organotrialkoxysilane precursors onto the surface of the porous silica cell walls of this biomineral. Vinyl- and mercapto-containing structures were prepared in aqueous media without disruption of the diatomic architecture. Successful grafting of the organic moieties was confirmed using solid state ²⁹Si MAS NMR spectroscopy, and the presence of the intact diatom framework by scanning electron microscopy. The sorption properties of mercaptopropyl-functionalized diatoms towards heavy metals was studied by measuring the accessibility and diffusion rates of mercury(II) species to the binding sites (-SH) by the means of electrochemical methods.     

Self-sum- and -difference-frequency mixing in GdAl(3)(BO(3))(4):Nd(3+) for generation of tunable ultraviolet and infrared radiation

We exploited Nd(3+) laser emission at 1061.9 nm ((4)F(3/2)?(4)I(11/2) channel) in a self-chi((2)) active GdAl(3)(BO(3))(4):Nd(3+) laser crystal. UV radiation was obtained from a 1.8% yield from self-sum-frequency mixing: 1/pump + 1/1061.9 = 1/UV, during pumping in the Nd(3+) (4)G(5/2)-(2)G(7/2) levels near 588 nm. The UV tunability had a range of 378-382 nm. We have demonstrated, for the first time to our knowledge, generation of coherent IR radiation from a self-difference-frequency mixing laser: 1/pump - 1/1061.9 = 1/IR. We got a 0.5% yield and tunability in the 1305-1365-nm range.     

Hopf Algebras, Renormalization and Noncommutative Geometry

We explore the relation between the Hopf algebra associated to the renormalization of QFT and the Hopf algebra associated to the NCG computations of tranverse index theory for foliations. Received: 14 August 1998/ Accepted: 5 October 1998     

AC electrical properties study and equivalent circuit of a monovalent-mixed pyrophosphate

NaAgPbP₂O₇ was prepared with a solid-state reaction. The electrical properties were investigated by using impedance measurements in the frequency range from 200 Hz to 5 MHz with the TEGAM 3550 ALF automatic bridge monitored by a microcomputer between 581 K and 703 K. The Z′ and Z″ versus frequency plots are well fitted to an equivalent circuit model. The conductivity data obey the universal power law. The conductivity in the material is due to the hopping of monovalent ions parallel to (001) plane.     

Phase transition in ammonium hexafluorovanadate (III)

Heat capacity of ammonium hexafluorovanadate (NH₄)₃ [VF₆] has been measured with a miniaturized adiabatic calorimeter from 20 to 300 K. A phase transition was found at 280.44 ± 0.05 K with the associated entropy change Δ_trs S = 24.9 ± 0.5 JK^?1 mol^?1. The entropy transition is accounted for by the orientational order-disorder changes of hexafluorovanadate ion and ammonium ion occupying respective octahedral sites, as in the cases of (NH₄)₃AlF₆ and (NH₄)₃FeF₆ crystals. Changes in infrared spectra relative to v₃ vibrational mode of [VF₆]^3? ion can be explained by an orientational disorder of the anions in the high-temperature phase (HTP). The dependence of cubic root of the unit-cell volume of a family of ammonium cryolites on their transition temperatures is discussed in relation to the nature of interactions which induce the phase transition.     

The CH3D absorption spectrum in the 1.58 μm transparency window of methane: Empirical line lists at 81 K and 294 K and temperature dependence

In spite of its low isotopic abundance in methane (about 5×10⁻⁴), CH₃D contributes greatly to the very weak absorption in the 1.58 μm methane transparency window. This methane window deserves to be characterized in details because it is important for planetary applications in particular for Titan and the giant planets. In this work, we recorded the CH₃D spectrum by high sensitivity differential absorption spectroscopy (α_min≈5×10⁻⁸ cm⁻¹) both at room temperature and at 81 K. A list of more than 9000 lines was constructed from the 81 K spectrum for the 6099–6530 cm⁻¹ region. In order to get the temperature dependence of the line intensities, the low energy values have to be determined. The rovibrational assignments available in the literature provide low energy values for about 380 strong transitions of the region. This is insufficient to characterize the temperature dependence of the CH₃D absorption between 6200 and 6400 cm⁻¹. In this interval, a list of 5500 lines was constructed from the room temperature spectrum. The empirical energy values of the transitions were derived from the ratio of the intensities at 81 K and 294 K. The exact and empirical lower state energies included in the final line lists provided as Supplementary Material, allow for accounting for the temperature dependence of the CH₃D spectrum in the entire 6099–6530 cm⁻¹ region.Our measurements have been compared to the spectroscopic parameters and assignments available in the literature in particular those adopted in the HITRAN database. Improvements and corrections are proposed for the wavenumber calibration and for some lower state energies.