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Biomedical subjects

R Balasubramaniam

Publications and source records attributed to R Balasubramaniam.

15 recordsLinked to original sources
PubMed2006

Analysis of heat and mass transfer during condensation over a porous substrate.

Condensing heat exchangers are important in many space applications for thermal and humidity control systems. The International Space Station uses a cooled fin surface to condense moisture from humid air that is blown over it. The condensate and the air are "slurped" into a system that separates air and water by centrifugal forces. The use of a cooled porous substrate is an attractive alternative to the fin where condensation and liquid/gas separation can be achieved in a single step. We analyze the heat and mass transfer during condensation of moisture from flowing air over such a cooled, flat, porous substrate. A fully developed regime is investigated for coupled mass, momentum and energy transport in the gas phase, and momentum and energy transport in the condensate layer on the porous substrate and through the porous medium.

Journal Article↗
PubMed2004

Thermocapillary migration of a drop: an exact solution with Newtonian interfacial rheology and stretching/shrinkage of interfacial area elements for small Marangoni numbers.

In this paper we analyze the effects of the following phenomena associated with the thermocapillary migration of a drop. The first is the influence of Newtonian surface rheology of the interface and the second is that of the energy changes associated with stretching and shrinkage of the interfacial area elements, when the drop is in motion. The former occurs because of dissipative processes in the interfacial region, such as when surfactant molecules are adsorbed at the interface in sufficient concentration. The interface is typically modeled in this instance by ascribing to it a surface viscosity. This is a different effect from that of interfacial tension gradients arising from surfactant concentration gradients. The stretching and shrinkage of interfacial area elements leads to changes in the internal energy of these elements that affects the transport of energy in the fluids adjoining the interface. When an element on the interface is stretched, its internal energy increases because of the increase in its area. This energy is supplied by the neighboring fluids that are cooled as a consequence. Conversely, when an element on the interface shrinks, the adjoining fluids are warmed. In the case of a moving drop, elements of interfacial area are stretched in the forward half of the drop, and are shrunk in the rear half. Consequently, the temperature variation on the surface of the drop and its migration speed are modified. The analysis of the motion of a drop including these effects was first performed by LeVan in 1981, in the limit when convective transport of momentum and energy are negligible. We extend the analysis of LeVan to include the convective transport of momentum by demonstrating that an exact solution of the momentum equation is obtained for an arbitrary value of the Reynolds number. This solution is then used to calculate the slightly deformed shape of the drop from a sphere.

Hot Temperature↗
PubMed2004

The formation of spikes in the displacement of miscible fluids.

We report on experiments in which a more viscous fluid displaces a less viscous one in a vertical cylindrical tube. These experiments were performed using silicone oils in a vertical pipette of small diameter. The more viscous fluid also had a slightly larger density than the less viscous fluid. In the initial configuration, the fluids were at rest, and the interface was nominally flat. A dye was added to the more viscous fluid for ease of observation of the interface between the fluids. The flow was initiated by pumping the more viscous fluid into the less viscous one. The displacement velocity was such that the Reynolds number was smaller than unity and the Peclet number for mass transfer between the fluids was large compared to unity. For upward displacement of the more viscous fluid from an initially stable configuration, an axisymmetric finger was observed under all conditions. However, a needle-shaped spike was seen to propagate from the main finger in many cases, similar to that observed by Petitjeans and Maxworthy for the displacement of a more viscous fluid by a less viscous one.

Diffusion↗
PubMed2002

Development of an interferometer for measurement of the diffusion coefficient of miscible liquids.

A common-path interferometer (CPI) system was developed to measure the diffusivity of transparent liquid pairs by real-time visualization of the concentration gradient profile. The CPI is an optical technique that can be used to measure changes in the gradient of the refractive index of transparent materials. The CPI is a shearing interferometer that shares the same optical path from a laser light source to the final imaging plane. Molecular diffusivity of liquids can be determined by use of physical relations between changes in the optical path length and the liquid phase properties. The data obtained by this interferometer are compared with similar results from other techniques. This demonstrates that the instrument is reliable for measurement of the diffusivity of miscible liquids and allows the system to be compact and robust. It can also be useful for studies in interface dynamics as well as other applications in a low-gravity environment.

Diffusion↗
PubMed2002

Optical measurement of concentration gradient near miscible interfaces.

A common path interferometer (CPI) system was developed to measure the diffusivity of transparent liquid pairs. The CPI is an optical technique that can be used to measure changes in the gradient of refractive index of transparent materials. The CPI is a shearing interferometer that shares the same optical path from a laser light source to the final imaging plane. Molecular diffusivity of liquids can be determined by using physical relations between changes in optical path length and liquid phase properties. In this paper, we present results obtained when the diffusivity depends on the local concentration of the miscible fluids.

Journal Article↗
PubMed2002

Rapidly expanding viscous drop from a submerged orifice at finite reynolds numbers.

The rapid expansion and subsequent detachment of a drop or bubble are examined in this paper. Establishing the hydrodynamics of the drop growth and detachment process has applications ranging from improving insight into nucleate pool boiling, to improving techniques used to characterize dynamic surface tension. Here, the growth and detachment dynamics of viscous drops are studied numerically to establish an accurate description of the hydrodynamics. The full two-dimensional axisymmetric Navier-Stokes equations are solved using a single fluid volume-of-fluid (VOF) formulation on a fixed Eulerian grid. The interface is represented by marker particles that are convected in a Lagrangian manner on the underlying Eulerian grid. Results for surfactant-free, isothermal droplets from hemispherical caps to near detachment are presented.

Journal Article↗
PubMed2000

Specificity of postural sway to the demands of a precision task.

We examined a precision aiming task in which a handheld laser pointer was controlled by the postural system. The task was performed in two orientations of the body's coronal plane to the target. In the parallel orientation medio-lateral (ML) sway had to be minimized, in the perpendicular orientation antero-posterior (AP) sway had to be minimized. In the parallel orientation ML sway decreased and AP sway increased with target distance and size. The pattern reversed in the perpendicular orientation. Nonlinear measures found independence of the two directions of sway and differences in their deterministic structure. Apparently a postural organization for upright standing and aiming (as in archery) entails two independent postural subsystems with different but reciprocally related dynamics. Furthermore, it seems as if some amount of postural variability is needed to ensure stability in quiet standing; if postural activity is reduced in one direction it is compensated for in the other direction.

Adult↗
PubMed1999

Recurrence quantification analysis of postural fluctuations.

A technique (recurrence quantification analysis; RQA) for analyzing center of pressure (COP) signals is presented and applied to data obtained by having participants stand with the head forward or sideways and with eyes open or closed. RQA is suitable for short, nonstationary signals and quantifies dynamical (deterministic) structure and nonstationarity. Results indicated that vision affects the deterministic structure (in degree and complexity) of COP motions and that differential optical flow structure (radial versus lamellar flow) induced by spontaneous sway under different head orientations affects COP nonstationarity. Implications of these findings and the sensitivity of RQA to subtle time-evolutionary properties of the COP are discussed.

Adolescent↗
PubMed1997

Climate and aeroallergen levels in asthma: a 12 month prospective study.

BACKGROUND: There is evidence to suggest that changes in weather and airborne fungal spore and pollen counts may affect asthma symptoms. METHODS: The relationship between climate, airborne fungal spore, and pollen counts and peak expiratory flow rate (PEFR) and asthma symptoms was prospectively investigated in a population of mild to moderate asthmatic subjects in Blenheim, New Zealand. Subjects recorded twice daily PEFR measurements and asthma symptom scores for up to one year. Spore and pollen counts were measured two hourly and meteorological data were measured hourly. Individual, within person, multiple linear regression analyses were conducted, adjusting for auto-correlation. A random effects model was assumed for the individual regression co-efficients and weighted estimates of the mean of these coefficients were obtained by the method of maximum likelihood. RESULTS: One hundred and thirty nine asthmatic patients (60% atopic) aged 17-80 years completed the study. Of the weather variables, only temperature showed a small but consistent association with PEFR. The mean rise in PEFR for an 8.8 degrees C (2 SD) change in temperature was 0.78% (95% CI 0.44% to 1.11%), approximately 3.0 l/min. There was a weak association between days of high basidiospore counts and increased nocturnal wakening and reliever medication use. Pollen counts showed no consistent association with either PEFR or asthma symptoms. CONCLUSIONS: The results of this study suggest that the effects of weather and aeroallergens on PEFR and asthma symptoms in this population are small, and that other causes need to be sought to account for variations in asthma severity and exacerbations.

Adolescent↗
PubMed1993

Carbachol can potentiate N-methyl-D-aspartate responses in the rat hippocampus by a staurosporine and thapsigargin-insensitive mechanism.

Experiments were performed to investigate the mechanism underlying the potentiation of N-methyl-D-aspartate (NMDA) responses by carbachol (CCh) in the CA1 region of rat hippocampal slices. CCh (300 nM) potentiated responses to NMDA, but not to alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA), in a readily reversible manner. Potentiation occurred in slices treated with 200 nM tetrodotoxin and perfused with Mg(2+)-free medium. It also occurred in slices treated with either staurosporine (1 microM), which is a potent inhibitor of a variety of protein kinases including protein kinase C (PKC), or thapsigargin (10 microM), which depletes intracellular Ca2+ stores by preventing their refilling. However, CCh-induced potentiation was abolished in slices perfused with Ca(2+)-free medium. These data suggest that low concentrations of CCh can acutely potentiate NMDA responses in the hippocampus by a Ca(2+)-sensitive process that is probably independent of both the activation of PKC and the release of Ca2+ from intracellular stores. This mechanism is similar to that underlying the potentiation of NMDA responses by the metabotropic glutamate receptor (mGluR) agonist, aminocyclopentane-1S,3R-dicarboxylic acid (1S,3R-ACPD).

Alkaloids↗
PubMed1992

No association or linkage with HLA-DR or -DQ genes in south Indians with pulmonary tuberculosis.

Studies of the HLA class II genes were performed in patients and multiple families with pulmonary tuberculosis from South India to seek any association of disease susceptibility with an individual allele or haplotype. TaqI RFLP analysis of HLA-DRB, -DQA and -DQB genes was done in 38 patients and 36 healthy control subjects. No significant association with any particular allele or haplotype was obtained. Linkage analysis performed in 12 families and haplotype sharing analysis in 9 families showed that the genetic susceptibility to pulmonary tuberculosis was not linked to the HLA region. The results suggest that the RFLP patterns of HLA class II genes DRB, DQA and DQB are not associated with susceptibility to pulmonary tuberculosis and that the genes controlling susceptibility or resistance may be located outside the HLA region.

Blotting, Southern↗