Delay analysis of extended rtPS for VoIP service in IEEE 802.16e by matrix analytic method

Extended real time polling service (ErtPS) is added to IEEE 802.16e-2005 standards in order for VoIP service to use uplink resources efficiently by considering on/off characteristic of voice source. Recently average queueing delay of ErtPS algorithm for VoIP service was investigated, and it was shown that ErtPS allows to admit more users than UGS algorithm. But we need the probability distribution of queueing delay rather than average queueing delay in order to provide a necessary information for QoS. In this paper we obtain the probability distribution of queueing delay of ErtPS for VoIP service by using the matrix analytic method for the GI/M/1 type and the M/G/1 type matrices in cases of the service time being exponential and deterministic respectively. By applying the results on deterministic service time we find the maximum allowable number of VoIP users with the required constraint on queueing delay. This research was supported by the MIC (Ministry of Information and Communication), Korea, under the ITRC (Information Technology Research Center) support program supervised by the IITA (Institute of Information Technology Assessment).     

The influence of sunflower and mustard leaf extracts on the germination of mustard seeds

The extracts from sunflower and mustard leaves were separated using SPE-Columns. The mustard seeds were germinated on water (24 h) and subsequently on crude extracts or separate fractions. The heat production rate was measured by isothermal calorimetry at 21°C and changes in seed cotyledons by FT-Raman spectroscopy. Crude extracts strongly inhibited seed germination. The water and ‘methanol’ fractions of mustard and sunflower extracts have a similar influence on the pattern of heat efflux. FT-Raman spectroscopy showed that extracts caused changes in cotyledons mainly in the content of fatty acids, carotenoids and flavonoids. Isothermal calorimetry and Raman spectroscopy are useful for the study of allelopathic interactions.     

Improving CO2 selectivity in polymerized room-temperature ionic liquid gas separation membranes through incorporation of polar substituents

Solid, polymer membranes fabricated from room-temperature ionic liquid monomers containing oligo(ethylene glycol) or nitrile-terminated alkyl substituents tethered to imidazolium cations were found to exhibit ideal CO₂/N₂ and CO₂/CH₄ separation factors significantly greater than those with comparable length n-alkyl substituents, with similar CO₂ permeability. Polymers containing these functional groups exhibited CO₂/N₂ gas separation performance exceeding the “upper bound” of a “Robeson Plot”.     

A comparison of ether- and alkyl-derivatized imidazolium-based room-temperature ionic liquids: a molecular dynamics simulation study

Molecular dynamics simulations of ether-derivatized imidazolium-based room-temperature ionic liquids (EDI-RTILs), [C(5)O(2)mim][TFSI] and [C(5)O(2)mim][BF(4)], have been performed and compared with simulations of alkyl-derivatized analogues (ADI-RTILs). Simulations yield RTIL densities, self-diffusion coefficients and viscosity in excellent agreement with experimental data. Simulations reveal that structure in the EDI-RTILs, quantified by the extent of nanoscale segregation of tails as well as cation-ion and cation-cation correlations, is reduced compared to that observed in the ADI-RTILs. Significant correlation between ether tail oxygen atoms and imidazolium ring hydrogen atoms was observed in the EDI-RTILs. This correlation is primarily intramolecular in origin but has a significant intermolecular component. Competition of ether oxygen atoms with oxygen atoms of TFSI(-) or fluorine atoms of BF(4)(-) for coordination of the ring hydrogen atoms was found to reduce the extent of cation-anion correlation in the EDI-RTILs compared to the ADI-RTILs. The reduction in intermolecular correlation, particularly tail-tail segregation, as well as weakening of cation-anion specific interactions due to the ether tail, may account for the faster dynamics observed in the EDI-RTILs compared to ADI-RTILs.     

Tunable interplay between superconductivity and correlations in nanoscopic heterostructures

Artificial heterostructures consisting of the superconducting electrode(s) and the free electron reservoir(s) interconnected through various nanoscopic objects, like: quantum dots, nanowires or molecules enable a fully controllable confrontation of the correlation effects with electron pairing. Discrete energy spectrum of the nanoscopic objects (due to the quantum size effect) strongly depends on the many-body effects. Via the proximity effect, these nanoscopic objects are converted into the superconducting grains. Since the coupling to external electrodes can be varied experimentally, this enables a fully controllable investigation of an interplay between the electron correlations and superconductivity. In this work, we explore the subgap (Shiba) states arising from the induced pairing and analyse their influence on the Kondo-type correlations. This issue is currently widely explored using various nanoscopic devices.     

Regularly varying tails in a queue with discrete autoregressive arrivals of order p

We consider a discrete time single server queueing system where the service time of a customer is one slot, and the arrival process is governed by a discrete autoregressive process of order p (DAR(p)). For this queueing system, we investigate the tail behavior of the queue size and the waiting time distributions. Specifically, we show that if the stationary distribution of DAR(p) input has a tail of regular variation with index −β−1, then the stationary distributions of the queue size and the waiting time have tails of regular variation with index −β. This research was supported by the MIC (Ministry of Information and Communication), Korea, under the ITRC (Information Technology Research Center) support program supervised by the IITA (Institute of Information Technology Assessment).