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A discrete-time queueing system with changes in the vacation times

100%

Atencia I.

International Journal of Applied Mathematics and Computer Science

2016

tom Vol. 26, no. 2

379--390

This paper considers a discrete-time queueing system in which an arriving customer can decide to follow a last come first served (LCFS) service discipline or to become a negative customer that eliminates the one at service, if any. After service completion, the server can opt for a vacation time or it can remain on duty. Changes in the vacation times as well as their associated distribution are thoroughly studied. An extensive analysis of the system is carried out and, using a probability generating function approach, steady-state performance measures such as the first moments of the busy period of the queue content and of customers delay are obtained. Finally, some numerical examples to show the influence of the parameters on several performance characteristics are given.

Methods and results of groundwater vulnerability evaluation to contamination in the Kampinoski National Park, central Poland

84%

Krogulec E.

tom Vol. 56, no. 3

349-359

Aquifer vulnerability maps are valuable tools for communicating concerns about the level of groundwater pollution hazard to local landuse planners and to the general public. Groundwater vulnerability to contamination in the Kampinoski National Park (KNP) area in central Poland was evaluated as a basis for developing appropriate protection strategy for the groundwater resources and management in recreation areas located near Warsaw. Assessment was accomplished using U.S. EPA DRASTIC and the residence time in the unsaturated zone of a conservative pollutant. The final DRASTIC values have been grouped into medium (37 % of area) and medium high (52 %) intrinsic vulnerability categories. The residence time in the unsaturated zone is classified in 11 intervals, ranging from 30 days to 30 years, but nearly 75 % of the study area is characterized by intervals from 1 to 3 years.

Zawartość trytu i skład izotopowy tlenu w płytkich wodach podziemnych w punktach badawczych krajowej sieci monitoringu

84%

Nowicki Z. , Leśniak P. M. , Wilamowski A.

Przegląd Geologiczny

2015

tom Vol. 63, nr 10/2

976--980

The points of the national network of groundwater monitoring comprise a stable benchmarks in quality and quantity monitoring. The obtained data (tritium and δ18O) are important for understanding the groundwater cycling and are indirect indicators of aquifer vulnerability to anthropogenic pollution. The goal of this paper is to present the relation of the tritium content and delta value of stable isotopes of oxygen against the groundwater sampling depth in 2004–2012. It is demonstrated that the remains of “nuclear” tritium concentration is still present in groundwater as a tritium peak at depths around 30 m. Determination of dynamics of recharge in groundwater bodies, based on national network observation points is associated to the estimation of the groundwater residence time in aquifers and remains one the vital problem of hydrogeology.