Search PubMed⌕ Search

Biomedical subjects

A Ghatak

Publications and source records attributed to A Ghatak.

16 recordsLinked to original sources
PubMed2006

Confinement-induced instability of thin elastic film.

A confined incompressible elastic film does not deform uniformly when subjected to adhesive interfacial stresses but with undulations which have a characteristic wavelength scaling linearly with the thickness of the film. In the classical peel geometry, undulations appear along the contact line below a critical film thickness or below a critical curvature of the plate. Perturbation analysis of the stress equilibrium equations shows that for a critically confined film the total excess energy indeed attains a minimum for a finite amplitude of the perturbations which grow with further increase in the confinement.

Journal Article↗
PubMed2005

Solenoids and plectonemes in stretched and twisted elastomeric filaments.

We study the behavior of a naturally straight highly extensible elastic filament subjected to large extensional and twisting strains. We find that two different phases can coexist for a range of parameter values: the plectoneme and the solenoid. A simple theory based on a neo-Hookean model for the material of the filament and accounting for the slender geometry suffices to explain these observations, and leads to a phase diagram that is consistent with observations. Extension and relaxation experiments on these phases show the presence of large hysteresis loops and sawtooth-like force-displacement curves which are different for the plectoneme and the solenoid.

Computer Simulation↗
PubMed2003

Crack street: the cycloidal wake of a cylinder tearing through a thin sheet.

When a cylindrical tool cuts through a thin sheet of a relatively brittle material, it leaves behind a visually arresting crack street in its wake, reminiscent of a vortex street in the wake of a cylinder moving through a fluid. We show that simple geometrical arguments based on the interplay of in-plane stretching and out-of-plane bending suffice to explain the cycloidal morphology of the curved crack. The coupling between geometry and dynamics also allows us to explain the "stick-slip"-like behavior of tearing and suggests that these oscillations should occur generically in the brittle fracture of thin solid films.

Materials Testing↗
PubMed2002

Prevalence of hypertension in psychiatric disorders.

OBJECTIVE: To study the prevalence of hypertension in our cases with psychiatric disorders and to study if the prevalence is higher in the cases with psychiatric disorders. METHODS: Four hundred twenty two cases with various psychiatric disorders attending the Outpatient Department of Psychiatry of our hospital were studied. Detailed clinical evaluation was done in all the cases. Blood pressure was recorded in the sitting position and mean of three readings was taken. Diagnosis and grading of hypertension was done according to the JNC V recommendations. Psychiatric disorders were diagnosed according to DSM IV criteria. RESULTS: Mean age of the cases was 36.3 years. Prevalence of hypertension in the cases was 7.1%. Prevalence in male and female cases were 7.2% and 7.0%, respectively. Prevalence of hypertension in various age groups was 20-39 years--1.48%, 40-60 years--24.4%, > 60 years--33.3%. CONCLUSION: The overall prevalence of hypertension in our cases with psychiatric disorders was 7.1% which was not higher than the reported prevalence of hypertension in our general population.

Adult↗
PubMed2000

Meniscus instability in a thin elastic film

A new kind of meniscus instability leading to the formation of stationary fingers with a well-defined spacing has been observed in experiments with elastomeric films confined between a plane rigid glass and a thin curved glass plate. The wavelength of the instability increases linearly with the thickness of the confined film, but it is remarkably insensitive to the compliance and the energetics of the system. However, lateral amplitude (length) of the fingers depends on the compliance of the system and on the radius of curvature of the glass plate. A simple linear stability analysis is used to explain the underlying physics and the key observed features of the instability.

Journal Article↗
PubMed1999

Dynamics and Morphology of Holes in Dewetting of Thin Films.

The formation and growth of holes in apolar nonslipping Newtonian thin films subjected to long-range Lifshitz-van der Waals forces are investigated based directly on numerical solutions of the thin-film equation. The nonphysical divergences of the hydrodynamic model and of the van der Waals force at the three-phase contact line are removed by inclusion of the short-range Born repulsion. Three distinct regimes of the hole growth after its appearance are identified: (1) a short, unsteady phase in which the dynamic contact angle and velocity change rapidly, followed by (2) a long, quasi-steady phase with slow logarithmic changes, and finally (3) a hindered phase in which rims of the neighboring holes overlap and lead to formation of equilibrium drops. The cross section of the rim surrounding a growing hole is noncircular and asymmetric, with higher slopes near the contact line. A slight depression is created ahead of the moving rim, but the regions of the film away from the rim remain undisturbed. For very viscous (e.g., polymeric) liquids displaying small contact angles, a nonlinear regime of hole growth (radius ~ timeq, with the exponent q approximately 0.7-0.9) is obtained for realistic time scales. Copyright 1999 Academic Press.

Journal Article↗
PubMed1996

Oxy free radical system in heart failure and therapeutic role of oral vitamin E.

Twenty patients of heart failure and ten matched healthy controls were included in the trial. Out of these 20 patients of heart failure, 12 patients were also studied prospectively. Plasma levels of superoxide anion and malonyldialdehyde were increased while the levels of superoxide dismutase, catalase and glutathione reductase were decreased in patients of heart failure as compared to control subjects. The alteration in oxidative stress and antioxidant system did not correlate with the age and sex of patients or the etiology of heart failure. With the increasing severity of heart failure the malonyldialdehyde and superoxide anion increased significantly and catalase, glutathione reductase and superoxide dismutase levels decreased. The group of heart failure patients with ejection fraction < 40% (n = 7) exhibited significantly higher levels of malonyldialdehyde than those with an ejection fraction > 40% (n = 13). The superoxide anion and malonyldialdehyde levels were significantly higher in patients of heart failure in the pre-treatment state as compared to those in post-treatment state. Conversely catalase, glutathione reductase and superoxide dismutase were higher in the post-treatment period as compared to their values before treatment. The addition of vitamin E in doses of 400 mg once a day orally for 4 weeks significantly reduced the malonyldialdehyde and superoxide anion levels and produced an elevation of the antioxidant enzymes. Thus, there is an apparent normalisation of the indices of oxidative stress following treatment of heart failure and a markedly improved response on vitamin E supplementation which may be more beneficial.

Administration, Oral↗
PubMed1994

The free radical system in ischemic heart disease.

The present work was conducted to evaluate the oxygen free radical system in 29 patients and comparing them with nine matched healthy controls of acute and chronic myocardial ischemic syndromes. The parameters assessed for oxidative stress were superoxide anion and malonyldialdehyde, and for the antioxidant defence system were superoxide dismutase, catalase and glutathione reductase. Both oxidative stress and the antioxidant defence system were altered in myocardial ischemia. Subset analysis revealed that in unstable angina and acute myocardial infarction, superoxide anion, malonyldialdehyde and glutathione reductase were elevated while superoxide dismutase and catalase levels were reduced. In stable angina only increased levels of superoxide anion and decreased levels of superoxide dismutase were found. However, this alteration was less marked than in unstable angina and acute myocardial infarction. In the post myocardial infarction group there was no alteration in any of these parameters.

Antioxidants↗
PubMed1994

Lipid-lowering efficacy of psyllium hydrophilic mucilloid in non insulin dependent diabetes mellitus with hyperlipidaemia.

The effect of the administration of 3.5 g of psyllium husk twice daily for 90 days was investigated in 24 patients of non insulin dependent diabetes mellitus (NIDDM) with hyperlipidaemia. After 90 days of treatment, psyllium was withdrawn and the patients were followed up for a further 90 days. Psyllium significantly decreased the levels of total cholesterol (TC; 19.7%), low-density lipoprotein cholesterol (LDL-C; 23.7%), triglycerides (TG; 27.2%) and the ratio of LDL-C to high-density lipoprotein cholesterol (HDL-C; 24.1%) and the lowering was sustained even up to 90 days after cessation of treatment. The level of HDL-C also showed a significant increase of 15.8 per cent but this effect was not sustained after cessation of treatment. The compliance was very good and no adverse effects were observed. This study indicated that psyllium husk is an effective and well tolerated adjunct to diet for the treatment of mild to moderate hyperlipidaemia in NIDDM patients.

Adult↗
PubMedDate not supplied

Serum cholesterol binding reserve percentage in diabetes mellitus.

Serum cholesterol binding reserve percentage (SCBR%) in patients with diabetes mellitus (22.17 +/- 13.40%) was significantly lower than in controls (40.93 +/- 8.69%) (p less than 0.001). SCBR% of controls did not vary with age (age range 20-80 years). SCBR% declined significantly with increasing duration of diabetes. It also decreased with macrovascular complications and was lowest in multiple/fatal complications further corroborating the value of SCBR% as a risk indicator of atherogenesis. The relationship of SCBR% with treatment was very striking. All adequately controlled patients had a significantly higher SCBR% than those who were poorly controlled regardless of treatment modality and those adequately controlled on insulin had the highest SCBR%, which was close to that of normal controls.

Adult↗
PubMedDate not supplied

Oxidant stress mechanisms in heart failure.

Evidences clearly indicate that HF is accompanied by excessive generation of OFRs and depletion of endogenous antioxidant system. The resultant oxidant stress depresses myocardial contractility and function by decreasing Ca++ uptake in sarcoplasmic reticulum and by impaired Ca(++)-ATPase in cardiac tissue. The various sources of OFRs production in HF include increased production of nitric oxide, cytokines, prostaglandins, auto-oxidation of catecholamines, activation of polymorph leucocytes and ischemia induced xanthine-xanthine oxidase. The prevention of oxidative stress by antioxidant translates into better metabolism and function of myocytes. It appears that antioxidant drugs may represent a novel adjunct to the existing therapeutic armamentarium in patients of HF irrespective of its etiology and severity.

Animals↗
PubMedDate not supplied

Profile and prevalence of aspirin resistance in Indian patients with coronary artery disease.

BACKGROUND: Aspirin resistance is considered to be an enigma and the data available on aspirin resistance is scarce. This study was initiated to prospectively evaluate the prevalence of aspirin resistance in patients with stable coronary artery disease by using an established method of optical platelet aggregation. METHODS AND RESULTS: We studied 50 patients who were on 150 mg of aspirin for the previous 7 days. Fasting blood samples were assessed using optical platelet aggregation (Chronolog Corp, USA). The mean platelet aggregation with 10 microm of adenosine diphosphate in our patient group was 49.42 +/- 23.29% and with 0.5 mg/ ml of arachidonic acid it was 13.58 +/- 21.40%. Aspirin resistance was defined as a mean aggregation of > or =70% with 10 microm of adenosine diphosphate and a mean aggregation of > or =20% with 0.5 mg/ml of arachidonic acid. Aspirin semi responders were defined as those meeting only one of the criteria. Based on these criteria, 2.08% patients were found to be aspirin-resistant, 39.58% were aspirin semi responders and 58.33% were aspirin responders. Females tended to be more aspirin semi responsive (p = 0.08). All other parameters tested, namely, age, smoking, diabetes mellitus, hypertension, obesity, lipids, hemoglobin, platelet count, ejection fraction and drug intake did not show any statistically significant difference among the groups. Thus, in our group 41.66% patients showed inadequate response to aspirin. CONCLUSIONS: This study shows that aspirin resistance and aspirin semi responsiveness do occur in the Indian patients and there are no reliable clinical predictors for this condition. The diagnosis therefore relies primarily on laboratory tests.

Adult↗