| || Some Mathematical Aspects of Spread and Stability of Time-Delay Gonorrhea
Author : Srinivas, N.C. ;Ramacharyulu, N. Ch. Pattabhi
Source : Defence Science Journal ; Vol:41(3) ; 1991 ; pp 277-293
Subject : 51 Mathematics
Keywords : Epidemic diseases ;Mathematical models;Medical science
Abstract : A mathematical model of time-delay gonorrhea among hetero and homosexuals is presented as a system of first order ordinary coupled integro-differential equations with delayed arguments. A theorem on the positivity of the solutions is proved to establish the feasibility of the proposed mode. Further, the only possible diseased equilibrium state has been identified and the stability analysis of such a state for some epidemiological possibilities has been carried out. It has been observed that the impulsive type inflow of infectives into the population maintained the stability of the diseased equilibrium state and is valid even for the exponential type inflows. In contrast to this, instability sets in when one or other of infective inflows is of the gate type.
| || Identification of Helicopter Rigid Body Dynamics from Flight Data
Author : Chopra, A.K. ;Kumar, Ramesh;Chaudhary, K.L.
Source : Defence Science Journal ; Vol:48(1) ; 1998 ; pp 69-86
Subject : 533.6 Aerodynamics;629.7 Aeronautics
Keywords : Mathematical models ;Aerodynamic parameters;Directional rigid body
Abstract : "This paper discusses helicopter modelling and identification related aspects. By applying the system identification methodology, longitudinal and lateral-directional rigid body helicopter dynamics are identified from flight data. Aerodynamic parameters from single input excitation as well as multimanoeuver evaluation are estimated utilising output-error approach. The formulated mathematical models yield adequate fit to measured time histories. Results obtained from the proof-of-match for model validation indicate that the identified derivatives can satisfactorily predict longitudinal dynamics to a given arbitrary input. It is further demonstrated for the present study that lateral body dynamics can be adequately predicted by including cross-coupling terms in the estimation model."