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Biomedical subjects

R Ramaswamy

Publications and source records attributed to R Ramaswamy.

At least 19 recordsLinked to original sources
PubMed2006

Adaptive targeting of chaotic response in periodically stimulated neural systems.

We demonstrate a technique for the enhancement of chaos in a computational model of a periodically stimulated excitable neuron. "Anticontrol" of chaos is achieved through intermittent adaptive intervention, which is based on finite-time Lyapunov exponents measured from the time series. Our results suggest that an adaptive strategy for chaos anticontrol is viable for increasing the complexity in physiological systems that are typically both noisy and nonstationary.

Action Potentials↗
PubMed2006

Pencil is mightier than the sword!

Penetrating injuries involving the spinal cord are not common. The incidence is, however, much higher in armed conflict. In a civilian population, gunshot wounds and stabbings account for the majority of such injuries. A pencil causing penetrating injury involving the spinal cord is very rare. We present the case of a young boy who accidentally suffered a penetrating injury involving the spinal cord from a pencil in his coat pocket.

Child↗
PubMed2004

Approach to equilibrium in adiabatically evolving potentials.

For a potential function (in one dimension) which evolves from a specified initial form V(i)(x) to a different V(f)(x) asymptotically, we study the evolution, in an overdamped dynamics, of an initial probability density to its final equilibrium. There can be unexpected effects that can arise from the time dependence. We choose a time variation of the form V(x,t) = V(f)(x) + (V(i) - V(f)) e(-lambda t). For a V(f)(x), which is double welled and a V(i)(x) which is simple harmonic, we show that, in particular, if the evolution is adiabatic, this results in a decrease in the Kramers time characteristic of V(f)(x). Thus the time dependence makes diffusion over a barrier more efficient. There can also be interesting resonance effects when V(i)(x) and V(f)(x) are two harmonic potentials displaced with respect to each other that arise from the coincidence of the intrinsic time scale characterizing the potential variation and the Kramers time. Both these features are illustrated through representative examples.

Journal Article↗
PubMed2004

Spectral Repeat Finder (SRF): identification of repetitive sequences using Fourier transformation.

MOTIVATION: Repetitive DNA sequences, besides having a variety of regulatory functions, are one of the principal causes of genomic instability. Understanding their origin and evolution is of fundamental importance for genome studies. The identification of repeats and their units helps in deducing the intra-genomic dynamics as an important feature of comparative genomics. A major difficulty in identification of repeats arises from the fact that the repeat units can be either exact or imperfect, in tandem or dispersed, and of unspecified length. RESULTS: The Spectral Repeat Finder program circumvents these problems by using a discrete Fourier transformation to identify significant periodicities present in a sequence. The specific regions of the sequence that contribute to a given periodicity are located through a sliding window analysis, and an exact search method is then used to find the repetitive units. Efficient and complete detection of repeats is provided together with interactive and detailed visualization of the spectral analysis of input sequence. We demonstrate the utility of our method with various examples that contain previously unannotated repeats. A Web server has been developed for convenient access to the automated program. AVAILABILITY: The Web server is available at http://www.imtech.res.in/raghava/srf and http://www2.imtech.res.in/raghava/srf

Algorithms↗
PubMed2004

Neurolisteriosis causing hydrocephalus, trapped fourth ventricle, hindbrain herniation and syringomyelia.

Central nervous system infection by Listeria monocytogenes is relatively uncommon, but is known to be highly morbid and fatal. We describe a case of listeria meningoencephalitis, wherein the acute episode was followed by a hitherto unreported conglomeration of severe and progressive neurological sequelae, in the form of supratentorial hydrocephalus, aqueduct block, trapped fourth ventricle, hindbrain herniation and syringomyelia. Pertinent literature is reviewed and the pathogenesis of the observed sequelae is explored.

Adult↗
PubMed2002

Global optimization on an evolving energy landscape.

Locating the global minimum of a complex potential energy surface is facilitated by considering a homotopy, namely, a family of surfaces that interpolate continuously from an arbitrary initial potential to the system under consideration. Different strategies can be used to follow the evolving minima. It is possible to enhance the probability of locating the global minimum through a heuristic choice of interpolation schemes and parameters, and the continuously evolving potential landscape reduces the probability of trapping in local minima. In application to a model problem, finding the ground-state configuration and the energy of rare-gas (Lennard-Jones) atomic clusters, we demonstrate the utility and the efficacy of this method.

Journal Article↗
PubMed2002

Osteosarcoma occurring in osteogenesis imperfecta tarda.

The combination of osteogenesis imperfecta (OI) and osteosarcoma is rare, as reflected by the fact that there are only eight proven cases in the published English literature. We present here another case, one that was treated by modern oncological techniques and major limb salvage surgery in the form of distal femur endoprosthesis initially and later a total femur replacement. The patient is the only one of the series to have had major limb salvage and is the only--and longest--surviving patient (more than 6 years), thus disproving the probability that this combination of disorders is particularly lethal. We present the case history, review the literature, and look at the cases presented in the past. We contend that adequate awareness, early diagnosis, and prompt oncological management results in better prognosis for osteosarcoma occurring in OI.

Child, Preschool↗
PubMed2001

Critical states and fractal attractors in fractal tongues: localization in the Harper map.

Localized states of Harper's equation correspond to strange nonchaotic attractors in the related Harper mapping. In parameter space, these fractal attractors with nonpositive Lyapunov exponents occur in fractally organized tongue-like regions which emanate from the Cantor set of eigenvalues on the critical line epsilon=1. A topological invariant characterizes wave functions corresponding to energies in the gaps in the spectrum. This permits a unique integer labeling of the gaps and also determines their scaling properties as a function of potential strength.

Journal Article↗
PubMed2001

Effects of virologic rebound on CD4 cell counts.

A retrospective study was conducted to assess the effects of various degrees of virologic rebound on CD4 cell counts over time in human immunodeficiency virus-infected patients. We found that (1) the higher the degree of virologic rebound, the more rapid the decrease in CD4 cell counts over time, and (2) the magnitude of the virologic rebound was inversely correlated with the CD4 cell counts at the time of rebound.

Adult↗
PubMed2001

Noninvasive diagnosis of renal-allograft rejection by measurement of messenger RNA for perforin and granzyme B in urine.

BACKGROUND: Acute rejection is a serious and frequent complication of renal transplantation, and its diagnosis is contingent on the invasive procedure of allograft biopsy. A noninvasive diagnostic test for rejection could improve the outcome of transplantation. METHODS: We obtained 24 urine specimens from 22 renal-allograft recipients with a biopsy-confirmed episode of acute rejection and 127 samples from 63 recipients without evidence of acute rejection. RNA was isolated from the urinary cells. Messenger RNA (mRNA) encoding the cytotoxic proteins perforin and granzyme B and a constitutively expressed cyclophilin B gene were measured with the use of a competitive, quantitative polymerase chain reaction, and the level of expression was correlated with allograft status. RESULTS: The log-transformed mean (+/-SE) levels of perforin mRNA and granzyme B mRNA, which encode cytotoxic proteins, but not the levels of constitutively expressed cyclophiiin B mRNA, were higher in the urinary cells from the 22 patients with a biopsy-confirmed episode of acute rejection than in the 63 recipients without an episode of acute rejection (perforin, 1.4+/-0.3 vs. -0.6+/-0.2 fg per microgram of total RNA; P<0.001; and granzyme B, 1.2+/-0.3 vs. -0.9+/-0.2 fg per microgram of total RNA; P<0.001). Analysis involving the receiver-operating-characteristic curve demonstrated that acute rejection can be predicted with a sensitivity of 83 percent and a specificity of 83 percent with the use of a cutoff value of 0.9 fg of perforin mRNA per microgram of total RNA, and with a sensitivity of 79 percent and a specificity of 77 percent with the use of a cutoff value of 0.4 fg of granzyme B mRNA per microgram of total RNA. Sequential urine samples were obtained from 37 patients during the first nine days after transplantation; and measurements of the levels of mRNA that encoded cytotoxic proteins identified those in whom acute rejection developed. CONCLUSIONS: Measurement of mRNA encoding cytotoxic proteins in urinary cells offers a noninvasive means of diagnosing acute rejection of renal allografts.

Acute Disease↗
PubMed2001

Isolated buttock burns: epidemiology and management.

This is a retrospective study of the epidemiology and management of isolated buttock burns presenting to the Welsh Regional Burns Centre from January 1996 to December 1999. A total of 36 cases have been treated of which 31 are included in this study. Approximately, 50% are in the paediatric age group and the sex distribution is equal for both adults and children. Contact burns form the largest group, and in children resulted in superficial burns requiring dressings only. The adult population is more likely to sustain deeper burns that require skin grafting, and approximately 50% will have a contributing premorbid condition. Despite difficulties in dressing and positioning of the patients, grafting of full thickness burns is appropriate without recourse to faecal diversion.

Accidents, Home↗
PubMed2001

Vaccum assisted closure: an alternative strategy in the management of degloving injuries of the foot.

A case of a degloving injury to the foot is presented in a patient who also sustained severe contralateral lower-limb trauma. We report a technique for salvaging the foot by replacing the degloved skin as a full-thickness graft and securing it using the vacuum-assisted closure (VAC) device. A good outcome was achieved and technical tips are provided to facilitate reproduction of the procedure.

Bone Wires↗
PubMed2000

Identification of parasitic genes by computational methods.

A number of parasite genome projects are under way, and large amounts of nucleotide sequence data are becoming available for analysis. There is an urgent need for development of theoretical tools to analyze the genome data, including identification of protein-coding sequences. The majority of the methods developed to date require prior information about the genome before accurate predictions can be made. Because such information is not available for many parasites, these methods cannot be directly applied. In this article, Alok Bhattacharya and colleagues describe some of the gene-prediction methods commonly in use, and a new method, GeneScan, that they have developed for the analysis of parasite genomes.

Animals↗
PubMed2000

Intermittency transitions to strange nonchaotic attractors in a quasiperiodically driven duffing oscillator

Different mechanisms for the creation of strange nonchaotic attractors (SNAs) are studied in a two-frequency parametrically driven Duffing oscillator. We focus on intermittency transitions in particular, and show that SNAs in this system are created through quasiperiodic saddle-node bifurcations (type-I intermittency) as well as through a quasiperiodic subharmonic bifurcation (type-III intermittency). The intermittent attractors are characterized via a number of Lyapunov measures including the behavior of the largest nontrivial Lyapunov exponent and its variance, as well as through distributions of finite-time Lyapunov exponents. These attractors are ubiquitous in quasiperiodically driven systems; the regions of occurrence of various SNAs are identified in a phase diagram of the Duffing system.

Journal Article↗
PubMed1999

Characteristic distributions of finite-time Lyapunov exponents.

We study the probability densities of finite-time or local Lyapunov exponents in low-dimensional chaotic systems. While the multifractal formalism describes how these densities behave in the asymptotic or long-time limit, there are significant finite-size corrections, which are coordinate dependent. Depending on the nature of the dynamical state, the distribution of local Lyapunov exponents has a characteristic shape. For intermittent dynamics, and at crises, dynamical correlations lead to distributions with stretched exponential tails, while for fully developed chaos the probability density has a cusp. Exact results are presented for the logistic map, x-->4x(1-x). At intermittency the density is markedly asymmetric, while for "typical" chaos, it is known that the central limit theorem obtains and a Gaussian density results. Local analysis provides information on the variation of predictability on dynamical attractors. These densities, which are used to characterize the nonuniform spatial organization on chaotic attractors, are robust to noise and can, therefore, be measured from experimental data.

Journal Article↗
PubMed1999

Dynamics of a shallow fluidized bed.

The results of the experimental study of the dynamics of a shallow fluidized bed are reported. The behavior of granular material is controlled by the interplay of two factors--levitation due to the upward airflow, and sliding back due to gravity. Near the threshold of instability, the system shows critical behavior with remarkably long transient dynamics. The experimental observations are compared with a simple cellular automata model.

Journal Article↗
PubMed1998

Effects of cyclic AMP on expression of myelin genes in the N20.1 oligodendroglial cell line.

The N20.1 immortalized cell line has several characteristics of differentiating oligodendrocytes (OLs), including expression of the glycolipids galactocerebroside (GalC) and sulfatide, and the myelin proteins CNPase and myelin basic protein (MBP) (1,2). Addition of 1-100 microM forskolin to elevate cyclic AMP (cAMP) levels changed cell morphology from irregular and flattened to a more rounded birefringent cell with multiple branched processes. GalC and sulfatide were detected immunocytochemically after permeabilization in the untreated cells and levels appeared to increase slightly following exposure to forskolin. Further analysis showed that most of the glycolipid was internal, with virtually no detectable levels on the cell surface in untreated cells and a very slight change following treatment with forskolin. Synthesis of the two lipids as measured by [H3]galactose incorporation doubled within 24 hours of treatment with forskolin. Levels of message for UDP-galactose: ceramide galactosyl transferase (CGT), a key enzyme in the synthesis of GalC and sulfatide, were compared with those of MBP and proteolipid protein (PLP), before and after elevation of cAMP. No changes were observed in levels of mRNA for CGT and PLP after 24 hours, with a possible increase by 48 hours. In contrast, levels of MBP message dropped precipitously by 24 hours; this was accompanied by an increase in levels of message for suppressed cAMP-inducible POU (SCIP). Thus CGT transcription is regulated independently of MBP and SCIP in N20.1 cells. Analysis of MBP levels by immunocytochemistry and Western blot showed little or no change in protein levels at 24 and 48 hours, in contrast to the sharp decrease in message levels by 24 hours, indicating a relatively long half life for MBP in this cell line. Thus, the N20.1 cells are an informative model for examining regulation of expression of myelinotypic proteins and GalC, as well as the transport of this lipid to the plasma membrane.

Animals↗