Features and Recursive Structure

Based on the cross-linguistic tendency that weak vowels are realized with a central quality such as ə, ɨ, or ɯ, this paper attempts to account for this choice by proposing that the nucleus itself is one of the three monovalent vowel elements |A|, |I| and |U| which function as the building blocks of melodic structure. I claim that individual languages make a parametric choice to determine which of the three elements functions as the head of a nuclear expression. In addition, I show that elements can be freely concatenated to create melodic compounds. The resulting phonetic value of an element compound is determined by the specific elements it contains and by the head-dependency relations between those elements. This concatenation-based recursive mechanism of melodic structure can also be extended to levels above the segment, thus ultimately eliminating the need for syllabic constituents. This approach reinterprets the notion of minimalism in phonology by opposing the string-based flat structure

A PfP Approach to Word-final Consonants

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Permanence and extinction for a nonautonomous SEIRS epidemic model

In this paper, we study the long-time behavior of a nonautonomous SEIRS epidemic model. We obtain new sufficient conditions for the permanence (uniform persistence) and extinction of infectious population of the model. By numerical examples we show that there are cases such that our results improve the previous results obtained in [T. Zhang, Z. Teng, On a nonautonomous SEIRS model in epidemiology, Bull. Math. Bio. 69 (2007) 2537-2559]. We discuss a relation between our results and open questions proposed in the paper

Interferometric Measurement of Large Number Density of Metal Vapor in the Heat Pipe

A method is proposed which permits one to determine a large number density of metal atoms along the absorption path in a heat-pipe cell. The proposed method requires a measurement of the anomalous dispersion near the absorption lines with known oscillator strengths by the use of a Mach-Zehnder interferometer and a stigmatic spectrograph. The method is tested on the resonance line of calcium and the first doublet of sodium. Its advantage over the hook method and the method by Frich et al. is demonstrated, and its precision and validity are discussed

Collisional-Radiative Model of Quasi-Stationary Helium Plasma and Its Application to the Plasma in Positive Column

The collisional-radiative model is applied to a quasi-stationary helium plasma and the collisional-radiative and population coefficients are calculated, provided that the level system of helium atom is composed of the ground level¹S, the four lowest excited levels, 2³S, 2¹S, 2³P and 2¹P, and higher hydrogenic levels. The ranges of plasma parameters are 8 × 10³Tₑ1.28×10⁵ °K and 10⁵nₑ10⁹ cm⁻³, and the results are compared with the data by Drawin et al. Next, the model is applied to a positive-column helium plasma and the plasma balance equation in the case of ambipolar diffusion is simultaneously solved with a set of rate equations for excited helium levels which includes the diffusion of atoms in metastable states. The results give the relation among the filling gas pressure in a discharge tube, plasma parameters and population densities of the excited levels. The atomic processes of ionization, excitation and deexcitation in the plasma are analyzed in detail

Collision-Induced Transitions within the Levels of 4p Configuration of Ar II

On the basis of a semi-empirical calculation of plasma parameters, the change of the population density induced by the laser field modulation at 4880 A (4p²D⁰₅/₂－4s²P⁰₃/₂) has been observed as a function of atom or electron density for the laser upper level and a third level, any one in the 4p configuration of ArII. In this situation the anisotropic intensity distribution of spontaneous radiation around the laser tube axis is analyzed so as to relate the change of the radiation to that of the population density for the transitions of interest. Further, by the use of a rate equation developed for the modulated population density of the third level, the rate coefficient is derived for the transition between this and the laser upper levels from the observed changes of population densities of these levels. The values of the rate coefficients for the collisional transitions are obtained for all levels of the 4p cofiguration, and in connection with this result the configuration temperature of this configuration is discussed

Observations of Collision-Induced Dipole Transitions Associated with High-Lying States of Calcium in Rare Gases

More than 20 collision-induced dipole (CID) transitions have been observed in the absorption spectrum of calcium below 2400 A in the presence of xenon or krypton. Some have also been observed in the presence of argon, neon or helium. The measured shifts and the effective oscillator strengths show a close correlation with the s-wave amplitude for the electron scattering by a rare-gas atom. This correlation leads us to the conclusion that the low-energy-electron-scattering process is responsible for the appearance of the CID transitions

Experiment and Analysis of Laser Oscillation and Atomic Processes in Positive-Column He-Cd Discharge

The observations of the 4416 Å laser output power and spontaneous emission of several Cd⁺ spectral lines, as well as the measurements of electron temperature and density are carried out on the positive-column He-Cd⁺ laser discharge (3.2mm main bore). Further, the plasma balance equation is extended to a mixture gas in the free fall as well as in the ambipolar diffusion, and then applied to the He-Cd⁺ laser plasma with the consideration of the mean free paths of He and Cd ions in the plasma of the binary mixture. The equation is solved under the typical conditions for lasing, (He pressure of 4 Torr, discharge current of 120 mA and evaporator temperature of 190 to 260°C), in combination with the population densities derived from our previous experiment. The results give the total number density of Cd ions and all the rates for ionization in the plasma. Then, the various rates for the population to the 4416 Å laser lower level are estimated and discussed in relation to the oscillation mechanism of the laser, especially with regard to the population process of the laser lower level

Ultraviolet Laser Oscillations of Multiple Ionized Ions in Z-Pinch Discharge

Pulse laser oscillations from multiple ionized N, O and rare gases were observed in the ultraviolet region for the Z-pinch discharge. Optimum value of gas pressure, oscillation time and its pressure dependence were examined for laser oscillations. It has been found that oscillations from different ions occur in the increasing order of ionization after the breakdown of discharge. The line Aril λ4765 A showed an anomalous behavior. Calculation is made on two different models for ionization and excitation of plasma. The first one is concerned with ionization and excitation by thermal electrons during plasma compression. The second one is concerned with direct excitation of laser oscillation by runaway electrons. The calculation based on the former explains the temporal sequence of laser oscillations ; and that on the latter explains the anomalous behavior of ArII λ4765 A line

Characteristics of Two Types of Grazing Incidence Spectrometers with Holographic Gratings

Two types of grazing incidence spectrometers have been constructed which are applicable to photographic and photo-electric recordings of emission spectra of plasmas in the extreme ultraviolet. The spectrometer SGX-100 with a 1-m Rowland circle covers the wavelengths of 30 to 1500 Å with both a holographic grating (HG) and a ruled one (RG). In this spectrometer, the incidence angle cc to the gratings is continuously variable from 80°to 86°, where the inverse Vodar mounting is adopted to keep a constant line of sight of the spectrometer against a light source. The small grazing incidence spectrometer GIT-30 with a toroidal holographic grating covers the wave-lengths of 150 to 1600 Å. The wavelength scanning is performed by a simple rotation of the grating under a constant angle 142° between the incident and exit beams. These spectrometers were used to observe spectra of emissions from a hollow cathode lamp and linear Z-pinch and plasma-focus discharges. Characteristics of the spectrometers are discussed on the data observed