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Biomedical subjects

J Dasan

Publications and source records attributed to J Dasan.

7 recordsLinked to original sources
PubMed2002

Stress fluctuations in sheared Stokesian suspensions.

We report an analysis, using the tools of nonlinear dynamics and chaos theory, of the fluctuations in the stress determined from simulations of shear flow of Stokesian suspensions. The simulations are for shear between plane parallel walls of a suspension of rigid identical spheres in a Newtonian fluid, over a range of particle concentration. By analyzing the time series of the stress, we find that the dynamics underlying these fluctuations is deterministic, low-dimensional, and chaotic. We use the dynamic and metric invariants of the underlying dynamics as a means of characterizing suspension behavior. The dimension of the chaotic attractor increases with particle concentration, indicating the increasing influence of multiple-body interactions on the rheology of the suspension with rise in particle concentration. We use our analysis to make accurate predictions of the short-term evolution of a stress component from its preceding time series, and predict the evolution of one component of the stress using the time series of another. We comment on the physical origin of the chaotic stress fluctuations, and on the implications of our results on the relation between the microstructure and the stress.

Journal Article↗
PubMed2002

Mediastinal tumour in a pregnant patient presenting as acute cardiorespiratory compromise.

A parturient at 35 weeks' gestation presented with severe shortness of breath, orthopnea and signs of fetal compromise. She was diagnosed with a large mediastinal tumour occupying 65% of transthoracic diameter, and a pericardial effusion. The trachea, both mainstem bronchi, pulmonary artery and superior vena cava were compressed. Her dyspnea continued despite relief of the cardiac tamponade by percutaneous drainage. Tissue obtained via anterior mediastinotomy, performed under local anesthesia infiltration, revealed a definitive diagnosis of non-Hodgkin's lymphoma. The patient improved symptomatically following initiation of steroids and chemotherapy. She was delivered by elective cesarean section under epidural anesthesia on the fifth day after starting chemotherapy. The postoperative course was complicated by the development of a large pleural effusion that required drainage. Mother and baby were well at three and six-month follow up oncology visits.

Journal Article↗
PubMed1999

Numerical evidence for the existence of a low-dimensional attractor and its implications in the rheology of dilute suspensions of periodically forced slender bodies.

We provide numerical evidence for the existence of a low-dimensional chaotic attractor in the rheology of dilute suspensions of slender bodies in a simple shear flow. The rheological parameters which characterize the stress deformation behavior of the suspension are calculated based on appropriate averages over the orientation vectors of the slender bodies. The system considered in this work, therefore, exhibits chaos in experimentally measurable averages over a large number of uncoupled chaotic oscillators. The numerical demonstration that these parameters may evolve chaotically may thus have important consequences for both chaos theory and suspension rheology. We also provide plausible explanations for the existence of a low-dimensional chaotic attractor in the rheological parameters in terms of the expressions for the rheological parameters and the coupling between individually chaotically evolving orientations and the expressions for the rheological parameters.

Journal Article↗
PubMed1989

Recurrent trophoblastic neoplasia.

An unusual case of recurrent benign trophoblastic growth occurring for the fourth time in a gravida 4, para 0, 30-year-old woman is reported. Prophylactic chemotherapy was instituted to avert the disaster again, without success. The question of her future obstetric outcome poses a formidable dilemma and no radical measures could be undertaken, as the patient hoped for a normal pregnancy.

Adult↗
PubMed1988

Cervical encerclage--a stitch in time: analysis of 23 cases.

Cervical incompetency has been recognized as a cause of repeated reproductive loss. Currently many surgeons cast doubt on the existence of cervical insufficiency and the efficiency of encerclage to salvage the situation. Over a period of 3 years we did cervical encerclage for 23 patients with recurrent pregnancy loss in whom all other causes were ruled out. Twenty-one patients benefitted by the procedure, only one ended in missed abortion and one patient had preterm delivery with early neonatal loss. We had a fetal salvage of 91.3%. Birth weights of the babies were above 2500 g in 65.2%. In our experience, with proper selection, patients benefitted from encerclage performed at the appropriate time.

Abortion, Habitual↗