Measurement of pitch by subharmonic summation

In order to account for the phenomenon of virtual pitch, various theories assume implicitly or explicitly that each spectral component introduces a series of subharmonics. The spectral-compression method for pitch determination can be viewed as a direct implementation of this principle. The widespread application of this principle in pitch determination is, however, impeded by numerical problems with respect to accuracy and computational efficiency. A modified algorithm is described that solves these problems. Its performance is tested for normal speech and "telephone" speech, i.e., speech high-pass filtered at 300 Hz. The algorithm out-performs the harmonic-sieve method for pitch determination, while its computational requirements are about the same. The algorithm is described in terms of nonlinear system theory, i.c., subharmonic summation. It is argued that the favorable performance of the subharmonic-summation algorithm stems from its corresponding more closely with current pitch-perception theories than does the harmonic sieve.     

Trennung,Identifizierung und Bestimmung von Treibgasen und Lösungsmitteln in Aerosol-Produkten mittels Gas-Chromatographie

Zusammenfassung Es wird eine gas-chromatographische Methode angegeben, welche eine fast vollständige Auftrennung aller handelsüblichen Aerosol-Treibgase und Lösungsmittel und ihre Identifizierung und Bestimmung in einem Schritt gestatet. Die Trennung erfolgt durch reine Adsorptions-Chromatographie and Porapak T-Säulen bei 100–180°C mit einer Temperaturate von 10°C/min. Zur Bestimmung der Retentionsindices nach Kovats wurden die Treibgase isotherm bei 150°C bzw. 100°C, die Lösungsmittel bei 180°C aufgetrennt. Anhand der Kovats-Indices ist eine eindeutige Identifizierung der Treibgase und Lösungsmittel selbst in vielfältigen Gemischen möglich.

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Separation, identification and estimation of propellant gases and solvents in aerosol products by gas chromatography

Summary A gas chromatographic method is described by which a nearly complete separation of all commonly used propellants and solvents and their identification and determination can be achieved in one step. The separation is by simple adsorption chromatography on columns packed with Porapak-T with a temperature program 100–180°C at 10°C/min. Kováts' retention indices have been calculated for isothermal conditions at 150°C respectively 100°C for the propellants, at 180°C for the solvents. An exact identification of the propellants and solvents by means of the Kováts' indices is practicable even in complex mixtures.

     

The electrochemical determination of ammonium based on the selective inhibition of the low-spin iron(II)/(III) system of Prussian blue

A new method is described for the determination of ammonium in aqueous solutions with electrodes modified by Prussian blue (PB). The specific voltammetric response of PB-modified electrodes to ammonium ions is used for their analytical determination. In the presence of ammonium ions, a concentration-dependent inhibition of the low-spin iron(II/III) system of PB occurs. Only thallium and rubidium ions cause similar inhibition. A useful electrochemical determination method is thus available for detecting ammonium ions in the presence of frequently interfering potassium and sodium ions. Paraffin-impregnated graphite electrodes modified with a mechanically transferred PB layer and bulk-modified PB-composite electrodes are studied. The method is applicable within a concentration range which extends from 4 × 10⁻⁵ mol/l to 10⁻² mol/l NH₄ ⁺. The composite electrode is used in an electrochemical flow-through system in conjunction with the Kjeldahl method. Received: 21 April 1997 / Accepted: 28 May 1997     

A Prussian blue-based reactive electrode (reactrode) for the determination of thallium ions

A reactive electrode (reactrode) made of Prussian blue (PB), graphite and paraffin can be used for a selective determination of thallium ions down to a concentration of 2 · 10^–8 mol 1^–1. The working principle of the reactrode is that thallium ions can be pumped into Prussian blue during alternating oxidation-reduction cycles. After a preconcentration of thallium ions in PB, the voltammetric determination follows as usually in anodic stripping voltammetry, i.e. the thallium ions are reduced to thallium metal which is subsequently oxidized to give the anodic stripping signal. The peculiarity of the Prussian blue-thallium system is that the thallium ions are situated in the holes of the PB matrix. When reduced to metallic thallium, they are substituted by potassium ions. Cd²⁺, Fe³⁺, Zn²⁺, Cu²⁺ and Ni²⁺ do not interfere up to a hundredfold excess, NH₄⁺ does not interfere up to a thousandfold – and Bi³⁺ up to tenfold excess. The interference by Pb²⁺ can be suppressed with EDTA.     

Homogeneous polyesters of predetermined length,composition, and sequence: Model synthesis of alternating glycolic-acid-co-(L)-lactic-acid oligomers

Methods for making monodisperse polyester copolymers of predetermined length, com-position, and sequence are reported. Alternating oligomers of (L)-lactic-co-glycolic acid (La-co-Gl), isosteric with polypeptides, are prepared by solution methods of protecting, coupling, and deprotecting alcohol and acid groups. The carboxylic acid is protected by benzyl ester formation and released by hydrogenation. The hydroxyl group is protected as the methoxyethoxyethyl ether and deprotected with sodium iodide and trimethylsilyl chlo-ride. Coupling uses dicyclohexylcarbodiimide. End-capped alternating oligomers containing ? (GILa)₄? and ? (GILa)₈? show polymer properties. They are noncrystalline oils that exhibit discernable T_g. The conformation of ? GILa? and ? LaGl? diads in the polyesters is shown to be similar to isosteric peptide diads ? GlyAla? and ? AlaGly? . Exactly structured, monodisperse polyesters suggest a chemical parallel to proteins. Designed struc-tural templates combining sheet-form ? (Gl)_n? and helical ? (La)_n? segments are at-tractive synthesis targets. The solution preparations reported here can be applied, but it is suggested that biosynthetic methods for introducing single ester units into peptide chains be adapted to synthesize precisely fashioned polyesters. © 1995 John Wiley & Sons, Inc.     

On a stabilizing feedback attitude control

The attitude control of a rotating satellite with two control jets leads to a system of four controlled ordinary differential equations of the form (S) $$dx/dt = X(x) + u_1 Y^1 (x) + u_2 Y^2 (x),x(0) = 0.$$ Our goal is to derive feedback controlsu ₁,u ₂ which automatically stabilize the system (S), i.e., drive the solution to the (uncontrolled) rest solution zero. Let $$(ad^0 X,Y) = Y,(adX,Y) = [X,Y],$$ the Lie product of the vector fieldsX, Y, and inductively $$(ad^{k + 1} X,Y) = [X,(ad^k X,Y)].$$ It is known that, if $$dim span\left\{ {\left( {ad^j X,Y^1 } \right)\left( 0 \right),j = 0,1,...} \right\} = 4,$$ then all points in some neighborhood of zero can be controlled to zero with just the controlu ₁, i.e.,u ₂≡0. In this problem,Y ¹(0), ..., (ad ³ X, Y ¹)(0) are linearly independent. We give a formula for generating the directions (ad ⁱ X, Y ⁱ )(0) as endpoints of admissible trajectories. Our modified feedback control is then formed as follows. Given an ε>0, if the state of system (S) is measured to beq ¹ ∈ ?⁴, we write $$q^1 = \sum\limits_{i = 1}^4 {\alpha _1 } (ad^{i - 1} X,Y^1 )(0),$$ and choose a controlu(t,q ¹) on the interval 0≤t≤ε to drive the solution in the direction $$ - \sum\limits_{i = 1}^4 {\alpha _1 } (ad^{i - 1} X,Y^1 )(0).$$ Thus, we assume that the state is measured (say) at time intervals 0, ε, 2ε, ..., while the control depends on the measured state, but then is open loop during a time interval ε until a new state is measured; hence, the terminologymodified feedback control. Numerical results are included for both the case of one control component and the case of two control components.