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Biomedical subjects

A Samanta

Publications and source records attributed to A Samanta.

At least 19 recordsLinked to original sources
PubMed2006

Tuning the size and optical properties in molecular nano/microcrystals: manifestation of hierarchical interactions.

Intermolecular interactions, such as hydrogen bonding, dipolar and van der Waals, occurring in molecular crystals cover a range of magnitudes. As the crystal evolves from a relatively softer state in the nanoscopic size regime to a harder one in the microcrystalline and bulk solid state, the impact of the hierarchy of intermolecular interactions can be expected to emerge in a progressive fashion. The strongest interactions alone would be manifested at small sizes; as the crystal grows, the effect of the weaker ones will be added on, with the bulk crystals exhibiting the cumulative impact of the different interactions. We demonstrate this phenomenon through investigations of the solution, colloid, and solid state of a novel zwitterionic molecule based on the diaminodicyanoquinodimethane framework. A reprecipitation-digestion protocol is developed for the fabrication of nano/microcrystals of varying sizes. Microscopic and spectroscopic characterizations reveal tuning of the size and optical properties of this material. The optical absorption of the colloidal particles evolves with size towards that of the bulk solid, the emission showing a steady enhancement of intensity. Crystallographic investigations coupled with semiempirical computations provide a viable model to describe the range of observations in terms of the gradual accumulation of hierarchical intermolecular interactions.

Computer Simulation↗
PubMed2004

Are evidence-based guidelines being followed for the monitoring of ocular toxicity of hydroxychloroquine? A nationwide survey of practice amongst consultant rheumatologists and implications for clinical governance.

OBJECTIVE: To determine whether consultant rheumatologists monitor the ocular toxicity of hydroxychloroquine according to standards set by national guidelines. METHOD: An observational cross-sectional questionnaire study of all consultant rheumatologists in the UK was undertaken. The main outcome measure was the proportion of rheumatologists who practise in compliance with nationally set standards. RESULTS: A wide variation in practice was found. Nearly half the respondents did not assess either baseline visual symptoms or visual acuity, and 3% undertook infrequent visual monitoring at intervals of longer than 1 yr. At least a quarter of rheumatologists within the survey routinely referred patients to ophthalmology, either for baseline visual screening or for regular visual monitoring. Such use of ophthalmology services was outside the recommendations of the guidelines and would suggest that these referrals were unnecessary. No differences in monitoring practices were ascertained between respondents from district general and teaching hospitals. CONCLUSION: The present study shows that nationally set guidelines for the monitoring of ocular toxicity of hydroxychloroquine are not consistently followed by rheumatologists with regard to baseline assessment, referral to ophthalmology and frequency of monitoring. Clinical guidelines aim to reduce variations in practice and to promote uniform and consistent best practice. The present study demonstrates a lack of conformity to national guidelines in respect of the monitoring of ocular toxicity of hydroxychloroquine. Clinical governance provides a framework for assuring quality in health care. The implications of this study for clinical governance would include understanding why barriers to the use of guidelines might occur and how they might be overcome, risk management, accounting for the reasonableness of a decision for positive divergence and audit.

Antirheumatic Agents↗
PubMed2004

Arm-crank propelled three-wheeled chair: physiological evaluation of the propulsion using one arm and both arm patterns.

Disabled people in India frequently use the arm-crank propelled three-wheeled chair (ACWC) for outdoor transportation. Two models of these chairs are commercially available: one is powered by cranking using one arm (ACWC-1) and the other uses both arms (ACWC-2). The purpose of the study was to compare the efficiency of the two types of propulsion with respect to the standard physiological responses and, consequent upon the findings, to recommend the use of a suitable one. The energetics of locomotion of the users at their freely chosen speed (FCS) were measured and compared with changes in the physiological parameters in the within-subject groups. The study was conducted in outdoor settings to simulate the actual locomotive conditions encountered by the users in their practical life. 14 males, who had been regular and proficient users of both propulsion systems for more than last six years and who had a history of paraplegia (below the 10th thoracic vertebra, n=11) and poliomyelitis (n=3) participated in the study. The subjects were required to propel the test chair (a combination of both the propulsion systems built in a single model) on an oval track of 358 m circumference at their FCS for 5 min; ambulatory data were collected during last 3 min of exercise and averaged. The FCS (m/min), heart rates (bpm) and oxygen uptake (l/min) were measured. Physiological cost index (b/m) oxygen consumption (ml/kg/min), oxygen cost (ml/kg/m) and net locomotor energy cost (kcal/kg/km) of the two sets of observations were derived and compared using a t-test for the paired observations. The FCS was significantly higher and the physiological parameters were lower with the ACWC-2 than with ACWC-1, except for heart rate and oxygen consumption, where the difference was not significant . It is concluded that two-arm use is more efficient and less physically demanding than one-arm use in the arm-crank propulsion system and that the former is more suitable for efficient ambulation.

Adult↗
PubMed2003

Comparative study of bone mineral density, calcium, and vitamin D status in the Gujarati and white populations of Leicester.

OBJECTIVES: To evaluate differences in bone mineral density (BMD), calcium, and vitamin D status between the Gujarati (South Asian) and white populations resident in Leicester and to determine whether this was linked to lifestyle factors. DESIGN: An observational cross sectional study of randomly selected Gujarati and white volunteers aged from 20-40 years. SETTING: City of Leicester. PARTICIPANTS: Subjects were randomly selected by age (20-40 years) and ethnicity. A total of 262 individuals volunteered to participate, of which 201 (51 white females, 71 Gujarati females, 37 white males, 42 Gujarati males) were eligible for the study. MAIN OUTCOME MEASURES: Results of questionnaire, BMD at the hip and lumbar spine, and measurement of serum calcium, albumin, alkaline phosphatase, and 25-hydroxyvitamin D. RESULTS: Male and female white subjects were significantly taller and heavier than their Gujarati counterparts. There was a statistically significant difference in BMD both at the spine (p<0.001) and hip (p<0.001) between the white and Gujarati females with the Gujaratis having a lower BMD. There was a trend for Gujarati males to have a lower BMD at the hip and spine than their white counterparts but these figures did not reach statistical significance. The intensity of cigarette smoking and the amount of alcohol consumption were both higher in the white male and female subjects. Sunlight exposure (>4 hours per day) was significantly higher in white subjects compared with Gujaratis. There were no significant differences in the mean level of serum calcium or alkaline phosphatase between the Gujaratis and whites. A significantly higher proportion (p<0.001) of the Gujarati men and women had a vitamin D level that was not measurable (that is, below the lower limit of the laboratory range of normal). Of those who had a measurable level (that is, in the normal range) mean levels of vitamin D were lower (p<0.05) in the Gujarati men and women. CONCLUSION: The present study is the first of its kind to note a low BMD in Gujarati subjects of South Asian origin compared with their white counterparts, living in Leicester. This study also confirms the presence of low serum vitamin D levels in Gujaratis. There is a need for more research in South Asians with regard to the collection of normal BMD values. This could provide a more meaningful reference range for identifying South Asians at risk of osteoporotic fractures and may have public health implications of relevance to this ethnic group.

Adult↗
PubMed2001

Universal scaling laws of diffusion in a binary fluid mixture.

A new universal scaling law relating the self-diffusivities of a binary fluid mixture and the excess entropies of its components is derived using mode coupling theory, reproducing the empirical scaling laws of Dzugutov [Nature (London) 381, 137 (1996)] and Hoyt et al. [Phys. Rev. Lett. 85, 594 (2000)] as special cases. The derived scaling laws are tested through numerical calculations for binary Lennard-Jones fluid mixtures for a wide range of physical parameters, and a very good correlation is observed. We have also arrived at a new universal scaling relationship between the cross-diffusivity and entropy for the first time.

Journal Article↗
PubMed2001

Phase-transfer catalyst-induced changes in the absorption and fluorescence behavior of some electron donor-acceptor molecules.

The quaternary ammonium salts find extensive use in a variety of chemical applications as surfactants and phase-transfer catalysts. Even though the interaction of the surfactants with various systems has been studied rather extensively, very little information is available on how the phase-transfer catalysts (PTC) interact with the dipolar systems in nonpolar media and how/whether these solubilizing agents affect the properties of the dissolved molecules. In this paper, the interaction of several tetraalkylammonium salts, commonly used as PTC, with a number of electron donor-acceptor (EDA) systems has been studied by absorption and fluorescence spectroscopy. The phase-transfer catalysts have been found to affect both the absorption and fluorescence properties of the EDA systems. The spectral changes of the EDA molecules induced by the tetraalkylammonium salts suggest the formation of an 1:1 complex between the two in nonpolar media. An electrostatic interaction between the phase-transfer catalysts (which exist as ion pairs in nonpolar media) and the dipolar molecules is shown to be the driving force for the formation of the complex. The dependence of the formation constant of the complex on the polarity of the media suggests a charge-transfer nature of the complex. It is shown that the anionic component of the salts serves as a source of electron to the positive end of the dipolar molecule, while the tetraalkylammonium cation, besides helping solubilization of its anionic counterpart in the nonpolar media, serves neutralizing the negative charge at the acceptor end of the EDA molecule. In effect, a cooperative influence of the cationic and anionic components of the PTC enhances the charge separation within the dipolar fluorophores. On the basis of the PTC-induced changes in the photophysical behavior of the EDA molecules, a possible structure for the 1:1 complex has been proposed. It has been concluded that a phase-transfer catalyst should not be treated as an innocuous substance that merely helps transfer of a polar substance from a polar to a nonpolar environment. Instead, it is demonstrated that the association of a PTC with a dipolar species can significantly change various properties of the latter.

Journal Article↗
PubMed2001

Photochemical E (trans)-->Z (cis) isomerization in substituted 1-naphthylacrylates.

Substituted naphthylacrylates, 1-3, not showing rotamerism have been synthesized with a view to study photochemical E (trans)-->Z (cis) isomerization. Photostationary state composition of the isomers upon direct excitation, triplet sensitized isomerization, quantum yield of isomerization, and steady state and time-resolved fluorescence behavior have been studied for these naphthylacrylates. The direct excitations of the compounds yield high Z (approximately 80%) isomer composition, whereas the triplet sensitization results in less Z (approximately 20%) isomer composition. This indicates that the singlet pathway is very efficient in converting the E isomer to the Z isomer. The naphthylacrylates 1 and 2 exhibit structured fluorescence at room temperature in hexane and upon changing the solvent to CH3CN; the structure of the fluorescence is lost, indicating that the singlet excited-state develops a polar character in a polar environment. The polar nature of the singlet excited state becomes more clear in the case of 3 from its fluorescence solvatochromism. The naphthylacrylates did not exhibit excitation wavelength-dependent fluorescence at room temperature suggesting that the ground state conformers (rotamers) are not involved. Fluorescence lifetimes measured for these compounds displayed biexponential behavior, which is explained using a two-state model.

Journal Article↗
PubMed2001

Long-term mortality and morbidity of transfusion-associated non-A, non-B, and type C hepatitis: A National Heart, Lung, and Blood Institute collaborative study.

Persons with non-A, non-B hepatitis (cases) identified in 5 transfusion studies in the early 1970s have been followed ever since and compared for outcome with matched, transfused, non-hepatitis controls from the same studies. Previously, we reported no difference in all-cause mortality but slightly increased liver-related mortality between these cohorts after 18 years follow-up. We now present mortality and morbidity data after approximately 25 years of follow-up, restricted to the 3 studies with archived original sera. All-cause mortality was 67% among 222 hepatitis C-related cases and 65% among 377 controls (P = NS). Liver-related mortality was 4.1% and 1.3%, respectively (P =.05). Of 129 living persons with previously diagnosed transfusion-associated hepatitis (TAH), 90 (70%) had proven TAH-C, and 39 (30%), non-A-G hepatitis. Follow-up of the 90 TAH-C cases revealed viremia with chronic hepatitis in 38%, viremia without chronic hepatitis in 39%, anti-HCV without viremia in 17%, and no residual HCV markers in 7%. Thirty-five percent of 20 TAH-C patients biopsied for biochemically defined chronic hepatitis displayed cirrhosis, representing 17% of all those originally HCV-infected. Clinically evident liver disease was observed in 86% with cirrhosis but in only 23% with chronic hepatitis alone. Thirty percent of non-A, non-B hepatitis cases were unrelated to hepatitis viruses A,B,C, and G, suggesting another unidentified agent. In conclusion, all-cause mortality approximately 25 years after acute TAH-C is high but is no different between cases and controls. Liver-related mortality attributable to chronic hepatitis C, though low (<3%), is significantly higher among the cases. Among living patients originally HCV-infected, 23% have spontaneously lost HCV RNA.

Aged↗
PubMed2001

Physical fitness training for wheelchair ambulation by the arm crank propulsion technique.

OBJECTIVE: To observe the effect of endurance training on novice users of an arm-propelled three-wheeled chair (APTWC), powered by asynchronous arm crank propulsion, in actual locomotive conditions. STUDY DESIGN: A continuous endurance training programme was administered by instructing subjects to propel themselves at free chosen speed (FCS) for 15 minutes, twice daily. Data were collected at two-week intervals consecutively and this was continued until the maximum beneficial effect was achieved. SETTING: The study was conducted in outdoor settings similar to those the users encountered in their everyday life. SUBJECTS: Twelve male paraplegics (below T10), age 30.5 +/- 8.59 years, weight 41.75 kg (+/- 5.76) recommended to use the APTWC as an ambulatory device. INTERVENTION: The propulsion speed (metres per minute), peak heart rate (beats per minute) and oxygen uptake (litres per minute) were measured in consecutive sessions at two-week intervals. Physiological cost index (beats m(-1)), oxygen consumption (ml kg(-1) min(-1)) and oxygen cost (ml kg(-1) m(-1)) were derived to assess fitness level. RESULTS: Significant changes were observed in the variables following endurance training for 12 weeks. The propulsion speed increased considerably and the cardiorespiratory parameters were found to be reduced. One-way analysis of variance was done for each parameter separately for seven sets of readings taken to assess the overall change over the study period of 12 weeks. The F-ratios were found to be significant (p < 0.01) in each case, except for body weight and oxygen uptake. The pairwise comparison of the biweekly results of the parameters which showed an overall significant change over the study period revealed that after the first two weeks there was considerable change (p < 0.01) for all the parameters. The trend was upward for speed and downward for the other cardiovascular stress parameters. These trends continued until the 10th week showing significant change, after which the values become stable as was revealed by thestatistical tests (p > 0.05). The percentage difference in the mean values from the initial stage (before training) to the 12th week ranged from 10.44% in the case of heart rate to 69.70% in the case of propulsion speed. CONCLUSION: Self-ambulation at free chosen speed regularly for 10-12 weeks provides efficiency and improves fitness status required for wheelchairs driven by an asynchronous arm crank propulsion technique and no special exercise programme is required.

Adult↗
PubMed2000

Aberrant processing of oxidative DNA damage in systemic lupus erythematosus.

Defective DNA damage processing has been reported in systemic lupus erythematosus (SLE). Vitamin C may modulate formation/removal of the oxidative DNA lesion 8-oxo-2'-deoxyguanosine (8-oxodG). Baseline levels of 8-oxodG measured in SLE serum, urine and PBMC DNA did not differ significantly from healthy subjects. In contrast to healthy subjects, no significant decrease in PBMC 8-oxodG or increase in urinary 8-oxodG was noted in vitamin C supplemented SLE patients. A significant, although attenuated, increase in serum 8-oxodG was detected in SLE patients, compared to healthy subjects. These data support putative abnormalities in the repair/processing of 8-oxodG in SLE.

8-Hydroxy-2'-Deoxyguanosine↗
PubMed2000

Evaluation of ambulatory performance of the arm propelled three-wheeled chair using heart rate as a control index.

PURPOSE: The Arm propelled three wheeled chair (APTWC) is in common use in the economically poor countries for outdoor ambulation, the propulsion force of which is exerted by arm cranking in asynchronous fashion. The purpose of the study was to assess the ambulatory performance of the users of the device using heart rate as a control index, at graded speeds. METHOD: Fifteen regular users of APTWC male with paraplegia and poliomyelitis were ambulated at seven different graded speeds in outdoor settings and the resting and ambulatory heart rate was measured during steady state and then physiological cost index and comfortable speed of propulsion was computed. RESULTS: The physiological strain, linear regression of the relationship between heart rate and speed with correlation coefficient of r = 0.86 (p < 0.001), polynomial regression of the relationship between physiological cost index (PCI) and speed with correlation coefficient of r = 0.83 (p < 0.001) and comfortable speed of propulsion (120 m/min) was reported. CONCLUSIONS: Heart rate can be used to evaluate the ambulatory performance of the device, quantifying energy economy for outcome evaluation and decision making for clinical recommendation.

Adult↗