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Biomedical subjects

R Ahuja

Publications and source records attributed to R Ahuja.

At least 19 recordsLinked to original sources
PubMed2003

Metal-nonmetal transition in the boron group elements.

Structural competition in boron group elements has been studied by means of ab initio calculations. For boron we predict a structural change alpha-B-->alpha-Ga accompanied by a nonmetal-metal transition at a pressure of about 74 GPa. For Al and Ga we find an icosahedron based elemental modification (alpha-B) 0.22 and 0.05 eV/atom, respectively, higher in energy than the corresponding metallic ground state structures. In particular, the low energy difference for Ga raises expectations into the experimental feasibility of new modifications for these elements, especially in nanosized systems.

Journal Article↗
PubMed2002

Lattice dynamics of solid xenon under pressure.

We use density-functional perturbation theory to obtain the phonon spectrum of fcc xenon under pressure. Thermodynamic properties obtained within the quasiharmonic approximation are in fair to good agreement with experiment at zero pressure. The transition pressure from the fcc to hcp phase is predicted to occur at 5 GPa. The fcc structure is found to be dynamically stable up to a pressure of 100 GPa, beyond which the phonon modes at the X and L symmetry points soften. We attribute the observed sluggish kinetics of the fcc-hcp transition to the small energy difference between the phases as well as to the high dynamical stability of the fcc phase.

Journal Article↗
PubMed2001

Experimental and theoretical identification of a new high-pressure TiO2 polymorph.

Our combined theoretical and experimental investigations have led to the discovery of a new polymorph of titanium dioxide, where titanium is seven-coordinated to oxygen in the orthorhombic OI ( Pbca) structure. The zero-pressure bulk modulus of the new phase measured in the pressure range 19 to 36 GPa is 318(3) GPa. We demonstrate that the group IVa dioxides (TiO2, ZrO2, HfO2) on compression at ambient temperature all follow the common path: rutile -->alpha-PbO2-type --> baddeleyite-type (MI) --> orthorhombic OI (Pbca) structure --> cotunnite-type (OII).

Journal Article↗
PubMed2001

Molecular dynamics study of melting and fcc-bcc transitions in Xe.

We have investigated the phase diagram of Xe over a wide pressure-temperature range by molecular dynamics. The calculated melting curve is in good agreement with earlier experimental data. At a pressure of around 25 GPa and a temperature of about 2700 K we find a triple fcc-bcc liquid point. The calculated fcc-bcc boundary is in nice agreement with the experimental points, which, however, were interpreted as melting. This finding suggests that the transition from close-packed to bcc structure might be more common at high pressure and high temperature than was previously anticipated.

Journal Article↗
PubMed2001

Materials science. The hardest known oxide.

A material as hard as diamond or cubic boron nitride has yet to be identified, but here we report the discovery of a cotunnite-structured titanium oxide which represents the hardest oxide known. This is a new polymorph of titanium dioxide, where titanium is nine-coordinated to oxygen in the cotunnite (PbCl2) structure. The phase is synthesized at pressures above 60 gigapascals (GPa) and temperatures above 1,000 K and is one of the least compressible and hardest polycrystalline materials to be described.

Journal Article↗
PubMed2001

Rapid assessment and delivery of Vitamin A to slum children by using National Immunization Day in Chandigarh.

This study was done with the objective to see the feasibility of using National Immunization Days (NIDs) for rapid assessment, and delivery of Vitamin A solution to about 27,600 children dwelling in 26 slums in Union Territory of Chandigarh. The assessment of Vitamin A deficiency (VAD) was done in a stratified random sample of 1304 children during third round of Intensified Pulse Polio Immunization (IPPI) and delivery of Vitamin A solution was done during fourth round of IPPI in 1999-2000 covering 27,642 children in the age group of 1-5 years. An additional team of two persons per centre delivered age specific doses of Vitamin A solution through 72 centres and operational problems were recorded. IPPI staff provided supervision and same tally sheets as of IPPI were used. The prevalence rate of VAD was 24.6%, with conjunctival xerosis, bitot's spot and corneal xerosis as 23.7%, 0.6% and 0.2% respectively. 27,275 (98.7%) children out of 27,642 were administered Vitamin A solution, with no major operational problem. Only five parents (0.01%) refused Vitamin A solution. No case of side effect or toxicity due to Vitamin-A was reported. The strategy to assess and deliver Vitamin A during NID's was found to be feasible and successful and could be a basis for launching similar initiatives in other areas of India and other countries where VAD is a public health problem.

Child, Preschool↗
PubMed2000

Theoretical investigation of high pressure phases of carbon dioxide

The recent discovery of a new solid phase of carbon dioxide ( CO2-V) has made it apparent that the properties of this vital chemical species are drastically altered under high pressure conditions. The reported transition at around 40 GPa from the Cmca phase ( CO2-III), which is a molecular solid, into the novel phase, which was observed to be quartzlike, clearly suggests a dramatic change of the chemical, electronic, and structural properties. We here present a theoretical analysis of the implications of this metamorphosis. At even higher pressures, we predict the existence of a very hard phase of the stishovite type.

Journal Article↗
PubMed2000

Gallium and indium under high pressure

Ga and In crystallize in unusual open ground-state crystal structures. Recent experiments have discovered that Ga under high pressure transforms into a close-packed structure, while this has so far not been observed for In. Results from first principles calculations explain in a simple way this difference in behavior. We predict a so far undiscovered transition of In to a close-packed structure at extreme pressures and show that the structure determining mechanism originates from the degree of s-p mixing of the valence orbitals. Group-III elements are shown to strongly disobey the standard corresponding-state rule.

Journal Article↗
PubMed2000

Quasi-Ab initio molecular dynamic study of Fe melting

We have investigated the melting of hcp Fe at high pressure by employing molecular dynamics simulations in conjunction with the full potential linear muffin tin orbital method. Apart from being of fundamental value, the melting of iron at high pressure is also important for our understanding of the Earth. The subject of iron melting at high pressures is controversial. The experimental data for the iron melting temperature can be separated into two regions, "low" and "high." Here we present an ab initio simulated iron melting curve which is in agreement with the low temperatures at lower pressures, but is in excellent agreement with the high-mostly shockwave-temperatures at high pressures. A comparison with available data lends support to the presented iron melting curve.

Journal Article↗
PubMed1999

Comparison of topical 0.3% ofloxacin with fortified tobramycin plus cefazolin in the treatment of bacterial keratitis.

PURPOSE: Ofloxacin is a broad spectrum fluoroquinolone antibiotic with good ocular penetration. We compared ofloxacin 3% solution with a combination of fortified tobramycin sulphate and cefazolin sodium solutions in the treatment of culture-proven bacterial keratitis. METHODS: Thirty eyes with culture-proven bacterial corneal ulcers were enrolled in a prospective randomised, controlled, double-masked study for comparison. The ofloxacin drop and saline were decanted into two identical-looking bottles to the tobramycin and cefazolin. The cases were randomly allocated into treatment with 0.3% ofloxacin solution or a combination of fortified antibiotics (1.5% tobramycin and 10% cefazolin solutions; control group) along with supportive cycloplegic, vitamins and anti-glaucoma therapy. Student's t-test was used to compare the results. RESULTS: Staphylococcus aureus and coagulase-negative staphylococci were the two most common organisms isolated. Resolution of the ulcer was achieved in 93% and 87% of cases in the ofloxacin and control groups respectively. The mean time required for symptomatic relief was 7.8 +/- 1.54 days and for epithelial healing 15.0 +/- 3.86 days in ofloxacin group, compared with 8.33 +/- 1.54 days for symptomatic relief and 15.46 +/- 3.86 days for epithelial healing in the control group. Post-resolution best corrected visual acuity of 20/200 or better was achieved in all but one eye in both groups. CONCLUSIONS: Ofloxacin and combined fortified tobramycin and cefazolin topical drops were comparable for treating cases of bacterial corneal ulcer. However, considering its easy availability and cost-effectiveness, monotherapy with ofloxacin is preferred over the combined fortified tobramycin and cefazolin therapy.

Adolescent↗
PubMed1998

Mini-Mental State Examination (MMSE) performance of partially remitted community-dwelling patients with schizophrenia.

Patients with schizophrenia perform worse than healthy controls on many neuro-psychological tests. However, previous studies of neuro-cognitive function have mostly been carried out on acutely ill or institutionalized patients. The objective of this study was to generate norms for performance of partially remitted community-dwelling patients with schizophrenia on the Mini-Mental State Examination (MMSE). Partially remitted outpatients attending a depot antipsychotic clinic or a clozapine clinic (n = 272) were tested using the MMSE. Demographic and clinical characteristics associated with MMSE performance, as well as the performance of specific items, were examined. MMSE score was significantly associated with educational status and race. Patients in our sample performed approximately 2-3 points below the population norms at all ages, but the mean score for the group was not in the impaired range. There was no apparent widening of this gap with advancing age. Patients who did poorly most frequently had difficulty with memory, attention and construction tasks. The MMSE is easy to administer to outpatients with schizophrenia and most patients score in the un-impaired range. The MMSE may be used to identify a subgroup of patients who score in the impaired range, for further investigations.

Acute Disease↗
PubMed1998

Time-gated autofluorescence microscopy of motile green microalga in an optical trap.

Ultrafast time-gated fluorescence imaging of optically trapped single motile cells is presented. The biflagellar green microalga Haematococcus pluvialis was confined with picoNewton trapping forces in the focal volume of a high numerical aperture objective by near infrared multitraps. Trapping radiation of 100 mW power at the sample was provided by a Nd:YLF laser (1047 nm) operating in the cw mode. Simultaneously, cellular autofluorescence was excited with a 633 nm picosecond 80 MHz laser diode. An ultrafast gated intensified slow scan CCD camera system with a tunable gate width (200 ps-1 ms) and tunable time-delay (0-20 ns) between excitation and detection was used as fluorescence detector. We demonstrate fluorescence imaging of high temporal (sub-ns) and high spatial (sub-microm) resolution and fluorescence lifetime determination of intracellular autofluorescence based on chlorophyll excitation. Exposure to the herbicide DCMU resulted in an increase of fluorescence intensity and lifetime by 250% and 150%, respectively.

Chlorophyta↗