The asymptotic behavior of queueing systems: Large deviations theory and dominant pole approximation

This paper presents the exact asymptotics of the steady state behavior of a broad class of single-node queueing systems. First we show that the asymptotic probability functions derived using large deviations theory are consistent (in a certain sense) with the result using dominant pole approximations. Then we present an exact asymptotic formula for the cumulative probability function of the queue occupancy and relate it to the cell loss ratio, an important performance measure for service systems such as ATM networks. The analysis relies on a new generalization of the Taylor coefficients of a complex function which we call characteristic coefficients. Finally we apply our framework to obtain new results for the M/D/1 system and for a more intricate multiclass M/D/n system.     

Some aspects of the interactions of orthopositronium with perfect and defect surfaces of insulating materials

ETLA (Elastic Thermalisation Lifetime Analysis) is a new model function for the fitting of lifetime spectra of slowly thermalising orthopositronium in the free space between the grains of insulating oxide powders. From this model one can obtain three fundamental parameters; the mass of the cluster of atoms which scatters the o-Ps, the probability that the o-Ps is forced into two-quantum decay at each collision and the emission energyE(0) of the o-Ps from the powder surface. As a consequence of full thermalisation of the Ps it is shown that the o-Ps quenching constant _q () follows atT ^1/2 dependency for MgO, Al₂O₃ and SiO₂ and for temperatures between 77 and 500 K. In MgO powder at low temperatures the irradiation by the positrons induces surface paramagnetic defects which are identified as Mg⁺ sites. These surface defects do not affect the thermalisation, but they induce paramagnetic o-p conversion i.e., an increase in , and they are also responsible for an increase in the emission energyE(0) of the o-Ps.     

含茂钛低聚物的制备与光谱

文中报道两种新的含茂钛低钛物Cp_2Ti(Cl)-O-[-Ti(Cp)(O_2CCH_4CH-O)-O-]n-H(Ⅰ)与Cp_2Ti(Cl)-O-[-Ti(Cp)(O_2CCH_2CH)-O-]_u-H(Ⅰ)的制备并用元素分析和光谱(IR,1~H NMR,MS)对它们进行了鉴定。     

Study of a glassy carbon electrode in amperometric detection using d.c., normal and differential pulse techniques

The results of a comparative study on d.c., normal pulse and differential pulse techniques applied to anodic amperometric detection at a glassy carbon electrode in a voltammetric flow-through cell are presented. The important aspects examined are response time, linearity, limit of detection and selectivity. It is shown that the d.c. mode is the most favourable as long as no adsorption of oxidation products takes place. If strong adsorption occurs, normal pulse detection is recommended, although the limit of detection is somewhat larger.     

Low-temperature infrared and raman studies: XI. The vibrational behaviour of ammonium perchlorate- its phase changes and the rotational freedom of its ions

An infrared, Raman and X-ray diffraction study on NH₄CIO₄. was conducted in the temperature ranges 300 to 17 °K, 300 to 130 °K and 300 to 120 °K respectively. The infrared studies also included the deuterated salt. The spectra are discussed and vibrational assignments made. Changes in the infrared spectra, as well as intensity measurements of the vibrational bands indicate anomalous behaviour in the region 100–110 °K as well as 17–50 °K. Possible reasons for these changes are proposed. The rotational behaviour of the ammonium ion upon cooling and hydrogen bonding are discussed.