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Biomedical subjects

S Djordjević

Publications and source records attributed to S Djordjević.

At least 19 recordsLinked to original sources
PubMed2005

Automatic calibration of urban drainage model using a novel multi-objective genetic algorithm.

In order to successfully calibrate an urban drainage model, multiple calibration criteria should be considered. This raises the issue of adopting a method for comparing different solutions (parameter sets) according to a set of objectives. Amongst the global optimization techniques that have blossomed in recent years, Multi Objective Genetic Algorithms (MOGA) have proved effective in numerous engineering applications, including sewer network modelling. Most of the techniques rely on the condition of Pareto efficiency to compare different solutions. However, as the number of criteria increases, the ratio of Pareto optimal to feasible solutions increases as well. The pitfalls are twofold: the efficiency of the genetic algorithm search worsens and decision makers are presented with an overwhelming number of equally optimal solutions. This paper proposes a new MOGA, the Preference Ordering Genetic Algorithm, which alleviates the drawbacks of conventional Pareto-based methods. The efficacy of the algorithm is demonstrated on the calibration of a physically-based, distributed sewer network model and the results are compared with those obtained by NSGA-II, a widely used MOGA.

Algorithms↗
PubMed2005

SIPSON--simulation of interaction between pipe flow and surface overland flow in networks.

The new simulation model, named SIPSON, based on the Preissmann finite difference method and the conjugate gradient method, is presented in the paper. This model simulates conditions when the hydraulic capacity of a sewer system is exceeded, pipe flow is pressurized, the water flows out from the piped system to the streets, and the inlets cannot capture all the runoff. In the mathematical model, buried structures and pipelines, together with surface channels, make a horizontally and vertically looped network involving a complex interaction of flows. In this paper, special internal boundary conditions related to equivalent inlets are discussed. Procedures are described for the simulation of manhole cover loss, basement flooding, the representation of street geometry, and the distribution of runoff hydrographs between surface and underground networks. All these procedures are built into the simulation model. Relevant issues are illustrated on a set of examples, focusing on specific parameters and comparison with field measurements of flooding of the Motilal ki Chal catchment (Indore, India). Satisfactory agreement of observed and simulated hydrographs and maximum surface flooding levels is obtained. It is concluded that the presented approach is an improvement compared to the standard "virtual reservoir" approach commonly applied in most of the models.

Disasters↗
PubMed1991

Stress-induced resistance to anaphylactic shock.

There have been many reports of the immunomodulatory effects of stress, but the influence of stress on anaphylaxis has been given little attention till now. In this study we investigated the influence of tail-shock stress on the course of anaphylactic shock (AS) in the rat. For this purpose, rats were sensitized to ovalbumin and subjected to stress procedure before the induction of AS. In the first series of experiments we used chronic (4 day) stress consisted of 80 inescapable tail shocks delivered at the same time each day. Anaphylactic shock was induced 24 hours later by intraperitoneal injection of 3 mg of ovalbumin. Results showed that stressed rats exhibited lower intensity of three investigated parameters of AS: clinical signs, hematocrit values, and drop of rectal temperature. In order to investigate whether acute stress procedure could also influence course of AS, rats were given various shock doses of ovalbumin immediately after the end of acute (1 day) tail-shock stress. Anti-anaphylactic effect of acute stress was demonstrated to be dose-dependent: the greatest protective effect was in animals that received the highest shocking dose of ovalbumin. Finally, we examined the duration of protective effect of acute inescapable tail shocks on AS, and these results showed that observed anti-AS phenomenon disappears 72 hours after the end of acute stress session.

Anaphylaxis↗
PubMed1991

Stress-induced suppression of experimental allergic encephalomyelitis in the rat.

Numerous experiments have demonstrated that physical stress can alter immunological parameters. However, little attention has been paid to the interrelationship between stress and autoimmune processes. The present study was designed to determine the influence of electric shock and sound stress on the development of experimental allergic encephalomyelitis (EAE). Ten-week-old male DA rats highly susceptible to EAE were used. Rats were subjected to the stress procedure during 19 days either before or after immunization with intradermal injection of 0.1 ml of an emulsion containing guinea pig spinal cord (20 mg/rat) in an equal volume of complete Freund's adjuvant (CFA). In addition, rats received subcutaneous injection of Bordetella pertussis in the dorsum of the same foot. Electric stress procedure consisted of 80 inescapable, unpredictable tail shocks (5 s, 1 mA) delivered at the same time each day. Sound stress procedure consisted of exposure of rats to a 90 dB fire alarm bell which rings 60 times for 5 s during one hour, at the same time of the day. Rats were observed daily for clinical signs of EAE and survived animals were sacrificed on day 20 after immunization. The brain and spinal cord sections were examined histologically for mononuclear cell infiltrates characteristics for EAE. The results clearly indicate that inescapable tail shocks suppressed the appearance and development of EAE when rats were subjected to stress procedure during 19 days after immunization, but not when rats were stressed during 19 day before the induction of EAE. On the other hand, in rats exposed to sound stress there was only delay in the onset of the disease.

Animals↗