Biomedical subjects

R Raj

Publications and source records attributed to R Raj.

15 recordsLinked to original sources

PubMed2006

Fast thermo-optical excitability in a two-dimensional photonic crystal.

We experimentally demonstrate excitability in a semiconductor two-dimensional photonic crystal. Excitability is a nonlinear dynamical mechanism underlying pulselike responses to small perturbations in systems possessing one stable state. We show that a band-edge photonic crystal resonator exhibits class II excitability, resulting from the nonlinear coupling between the high-Q optical mode, the charge-carrier density, and the fast (sub-micros) thermal dynamics. In this context, the critical slowing down of the electro-optical dynamics close to the excitable threshold can delay the optical response by an amount comparable to the duration of the output pulse (5 ns). The latter results from a short thermal dynamical excursion along a high local intensity manifold of the phase space.

Arsenicals↗

PubMed2006

Nonadiabatic dynamics of the electromagnetic field and charge carriers in high-Q photonic crystal resonators.

We address, both experimentally and theoretically, phase and amplitude dynamics of the electromagnetic field in a two-dimensional photonic crystal when femtosecond pulses are injected. We demonstrate that the usual adiabatic approximation underlying the dynamics of field and carriers in a semiconductor resonator is no longer valid, since in general the photon lifetime cannot be neglected with respect to the carrier recombination lifetime. Parameter regions where adiabaticity is broken are shown, and the ubiquity of the observed dynamical scenario in the new generation of active photonic microresonators is predicted.

Journal Article↗

PubMed2006

A simple method of measuring total daily energy expenditure and physical activity level from the heart rate in adult men.

OBJECTIVE: To evaluate a simple method that uses only a heart rate monitor to predict total energy expenditure (TEE) and physical activity level (PAL) from 24 h heart rate (HR) measurements. DESIGN: The simple method involved the determination of the physical activity ratio (PAR) from corresponding heart rate ratios (HRR) (ratio of observed to resting HR), from an individualized calibration curve relating activities with known PAR to the HRR. Several curve fits were evaluated for this curve. The PAL was calculated from minute to minute PAR. The TEE was computed as the product of the PAL and the predicted basal metabolic rate (BMR). The accuracy of the simple method was assessed by within-subject comparisons of the simple method versus the oxygen consumption - HR method and a time and motion study. SETTING: Bangalore City, India. SUBJECTS: In all, 17 healthy male subjects between 18 and 44 years were recruited for the study. INTERVENTIONS: None. RESULTS: The simple method correlated well with both the reference methods when using a calibration curve that involved the fitting of two straight lines at low and high PAR activities, respectively, to the PAR and HRR data. The mean error in TEE, as a product of BMR and PAL, was about 1%, but with limits of agreement between the methods that were about 20% of the TEE. However, the low mean error could have been due to a canceling of errors in the determination of BMR and PAL. CONCLUSIONS: The simple method is a relatively cheap, useful technique for evaluating TEE and PAL in resource-poor situations. It may particularly be of use in epidemiological investigations where population estimates of TEE and PAL are required.

Adolescent↗

PubMed2005

Tuning a two-dimensional photonic crystal resonance via optical carrier injection.

We report on wide wavelength tuning through optical injection of carriers of a photonic resonance observed in reflectivity at 1543 nm in an InP-based two-dimensional photonic crystal slab. An 8-nm blueshift, which represents 20 times the resonance linewidth, is observed when a 4-kW/cm2 intense optical pump is incident on the sample. An analytical model that we developed, based on a coupled-mode nonlinear approach, allows us to describe this phenomenon in detail.

Journal Article↗

PubMed2002

Partially matched related donor peripheral blood progenitor cell transplantation in paediatric patients adding fludarabine and anti-lymphocyte gamma-globulin.

Twenty-one paediatric patients (11 males and 10 females) received a CD34-selected partially matched related donor transplant for malignant (16 cases) and non-malignant conditions (five cases). The average cell dose was 11.13 x 10(6)/kg. Fifteen of 16 patients with malignant conditions and one with non-malignant disease received total body irradiation plus cyclophosphamide. Three of 5 patients with non-malignant conditions and one with leukaemia, received busulphan plus cyclophosphamide. One patient with Fanconi anaemia received 100 mg/kg of cyclophosphamide. Fludarabine (25 mg/m(2)/day for 5 days) was administered prior to all these regimens. Additionally, anti-lymphocyte gamma-globulin (12.5 mg/kg/day) was administered from day -2 to day +2. Three (15%) patients failed to achieve complete chimaerism (CC). These patients received a second cell infusion. Two of them achieved CC. In the third patient, the percentage of donor cells was increased. The likelihood for engraftment was not related to the cell dose received. Acute graft-versus-host disease (GVHD) occurred in nine patients but only one developed GVHD >grade II. Eight patients developed active viral infections, which resolved after treatment. Patients receiving cell doses higher than our average had a significantly faster CD3 and CD4 cell recovery and experienced a lower incidence of viral infections. After 480 +/- 255 days of median follow-up, 16/21 patients are alive and well and have CC. Three patients died of leukaemic relapse and a fourth from progression of his disease (adreno-leuko-dystrophy). We conclude that partially matched related donors are a feasible source of haemopoietic progenitor cells for transplantation for patients without matched familial or unrelated donors.

Adolescent↗

PubMed2001

The influence of climate variation and change on diarrheal disease in the Pacific Islands.

Freshwater resources are a high-priority issue in the Pacific region. Water shortage is a serious problem in many small island states, and many depend heavily on rainwater as the source of their water. Lack of safe water supplies is an important factor in diarrheal illness. There have been no previous studies looking specifically at the relationship between climate variability and diarrhea in the Pacific region. We carried out two related studies to explore the potential relationship between climate variability and the incidence of diarrhea in the Pacific Islands. In the first study, we examined the average annual rates of diarrhea in adults, as well as temperature and water availability from 1986 to 1994 for 18 Pacific Island countries. There was a positive association between annual average temperature and the rate of diarrhea reports, and a negative association between water availability and diarrhea rates. In the second study, we examined diarrhea notifications in Fiji in relation to estimates of temperature and rainfall, using Poisson regression analysis of monthly data for 1978-1998. There were positive associations between diarrhea reports and temperature and between diarrhea reports and extremes of rainfall. These results are consistent with previous research and suggest that global climate change is likely to exacerbate diarrheal illness in many Pacific Island countries.

Child, Preschool↗

PubMed2000

Human immunodeficiency virus infections in adolescents.

Human immunodeficiency virus (HIV) infection, once largely confined to adolescents with hemophilia, has come to involve the general adolescent population. Individuals younger than 22 years comprise up to 25% of the people newly infected with HIV. Unsafe sexual practices, intravenous drug abuse, homelessness, psychiatric disorders, and inadequate psychosocial support are only some of the factors that have contributed to the epidemic. Present data indicate that interventions have had a positive impact on adolescent behavior in preventing the continuing spread of the disease, but more needs to be accomplished before we consider the problem controlled. Although proper medical treatment and providing adequate psychological and social support to adolescents who are already infected constitute an important aspect of care, the true solution of the problem lies in altering the behavior and practices that lead to the acquisition of this infection.

Adolescent↗

PubMed1999

Finger dominance.

Two hundred and ninety-eight normal participants were reviewed to assess finger dominance. Participants were recruited from several large hospitals across the north-west of England and the study was done under blind conditions. From the 298 people originally in the trial, six had to be excluded as the dominant finger could not be confirmed with certainty. The index finger was the most dominant in 82.5% of the test group. However, in 10.6% of the test group, the middle finger was found to be the most dominant.

Fingers↗

PubMed1997