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Biomedical subjects

M V George

Publications and source records attributed to M V George.

11 recordsLinked to original sources
PubMed2006

Measuring trends in prevalence and incidence of HIV infection in countries with generalised epidemics.

OBJECTIVE: Review of recent data and practice to derive guidance on questions relating to the measurement and analysis of trends in HIV prevalence and incidence. RESULTS: HIV prevalence among pregnant women attending antenatal clinics (ANCs) remains the principal data source to inform trends in the epidemic. Other data sources are: less available, representative of a small section of the population (sex workers, occupational groups), subject to additional bias (for example, voluntary counselling and testing service statistics), or are not yet available for multiple years (national surveys). Validity of HIV prevalence results may change over time due to improvements in HIV tests per se and implementation of laboratory quality assurance systems. The newer laboratory tests for recent infections require further validation and development of methodology to derive estimates of HIV incidence. CONCLUSIONS: Issues to consider during statistical analyses of trends among ANC attendees are: inclusion of consistent sites only, use of confidence intervals, stratification by site when performing a statistical test for trend, the need for at least three observations in a surveillance system with data collection every one to two years, and sound judgement. Trends in HIV prevalence among pregnant 15-24 year olds attending ANCs can be used to approximate trends in incidence. Indepth small area research studies are useful to inform the interpretation of surveillance data and provide directly measured trends in prevalence and incidence. Modelling can assess changes over time in prevalence, incidence, and mortality at the same time. Modelling tools need to be further developed to allow incorporation of estimates of HIV incidence and mortality, as these data are likely to become available in the future. To increase their explanatory power, models should also be extended to incorporate programmatic inputs.

Attitude to Health↗
PubMed2003

Dynamics of photoinduced electron-transfer processes in fullerene-based dyads: effects of varying the donor strength.

Two classes of fullerene-based donor-bridge-acceptor (D-B-A) systems containing donors of varying oxidation potentials have been synthesized. These systems include fullerenes linked to heteroaromatic donor groups (phenothiazine/phenoxazine) as well as substituted anilines (p-anisidine/p-toluidine). In contrast to the model compound, an efficient intramolecular electron transfer is observed from the fullerene singlet excited state in polar solvents. An increase in the rate constant and quantum yield of charge separation (kcs and phi cs) has been observed for both classes of dyads, with decrease in the oxidation potentials of the donor groups. This observation indicates that the rates of the forward electron transfer fall in the normal region of the Marcus curve. The long-lived charge separation enabled the characterization of electron transfer products, namely, the radical cation of the donor and radical anion of the pyrrolidinofullerene, by using nanosecond transient absorption spectroscopy. The small reorganization energy (lambda) of C60 coupled with large negative free energy changes (-delta G degree) for the back electron transfer places the back electron process in the inverted region of Marcus curve, thereby stabilizing the electron transfer products.

Journal Article↗
PubMed2001

Biradical intermediates in the photoisomerization of dibenzodihydropentalenofurans to dibenzosemibullvalenes.

The photoisomerization of a few substituted dibenzodihydropentalenofurans to the corresponding dibenzosemibullvalenes is reported. Steady-state photolysis of the dibenzodihydropentalenofurans 3a--d gave the corresponding dibenzosemibullvalenes 2a--d in nearly quantitative yields. The quantum yields of this photoisomerization were found to be in the range 0.17--0.26. Laser flash photolysis studies of the dibenzodihydropentalenofurans 3a-e showed transients, with absorption maxima around 410 nm and decaying by first-order kinetics. The lifetimes were in the range 14--30 micros in degassed benzene at 25 degrees C. These transients were readily quenched (trapped) by molecular oxygen, and the Stern-Völmer quenching constants were found to be in the range (2.45--3.17) x 10(9) M(-1) s(-1). As a representative example, the 1,3-biradical intermediate from 3e was trapped by molecular oxygen to give the corresponding endoperoxide 11e. The transients were weakly quenched by triplet/radical quenchers such as 2,2,6,6-tetramethylpiperinyl-1-oxy (TEMPO) and 4-hydroxy-2,2,6,6-tetramethylpiperinyl-1-oxy (HTEMPO), and the quenching constants are found to be in the range (1.09--3.19) x 10(6) M(-1) s(-1). The decay rates of the transients were found to be temperature dependent and obeyed the Arrhenius equation. For example, the activation energy of the transient from 3a was approximately 4.5 kcal mol(-1) and the Arrhenius preexponential factor log(A/s(-1)) for the decay of the transients was approximately 7.5. On the basis of our studies, these transients were assigned as the ground-state triplet biradicals, generated by the cleavage of the C--O bond of the starting dibenzodihydropentalenofurans.

Journal Article↗
PubMed1991

Effects of fertility and international migration on changing age composition in Canada.

"This paper analyses the prospects for age distribution in Canada through 2036, based on today's age structure and expected trends in fertility and international migration. Simulating these two demographic components at extreme levels shows that tomorrow's aging is already built into the current age distribution, which is heavily marked by the post-war baby boom and the following persistent baby bust, and that neither fertility nor immigration can be seen as effective adjustment mechanisms for the changing age composition of Canada. Population projections using the component method are applied along with an age-specific growth-rate analysis."

Age Distribution↗
PubMed1990

Immigrant fertility patterns in Canada, 1961-1986.

"This paper has examined the fertility of immigrants who arrived in Canada at various periods in the recent past. Cumulative and current fertility measures derived from 1961, 1971, 1981 and 1986 censuses have indicated that immigrants tend to have children at a lower rate during the periods when they are immigrating, but at a higher rate after immigrating. However, once they have resided in the host country for a certain length of time, their fertility may either converge with that of the native-born population or may become even lower." (SUMMARY IN FRE AND SPA)

Americas↗
PubMed1986

[Quebec's population decline: if it is foreseeable, is it avoidable?].

"Quebec's fertility is the lowest in Canada, and it is most likely that its population is heading for a decline. In this paper, the authors try to make explicit some of the scenarios which could prevent this decline. They first briefly present the current trends and specify the assumptions used in the simulation. Then, they analyse the results by investigating the onset of the decline and the maximum size of the population. And finally, they present some of the replacement scenarios which may prevent the decline." (SUMMARY IN ENG AND SPA)

Americas↗