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Biomedical subjects

D Mathur

Publications and source records attributed to D Mathur.

At least 19 recordsLinked to original sources
PubMed2006

Energy pooling in multiple ionization and Coulomb explosion of clusters by nanosecond-long, megawatt laser pulses.

We report the results of experiments that establish the possibility of bringing about multiple ionization and Coulomb explosion of molecular clusters with nanosecond laser pulses at intensities as small as 10(9) W cm(-2). We demonstrate several new facets of the laser-cluster interaction in the low-intensity, long-pulse domain: (i) The choice of laser wavelength for a given cluster species is very crucial. (ii) Excited electronic states play a very important role in the ionization dynamics. (iii) When field ionization is insignificant and ponderomotive energies are very small, it is energy pooling rather than inverse bremsstrahlung that determines how clusters absorb energy from the optical field.

Journal Article↗
PubMed2006

Depolarization of white light generated by ultrashort laser pulses in optical media.

We report measurements of the extinction ratio (ER) of white light generated upon irradiation of BK7 glass by ultrashort (36 fs) laser pulses with incident power approximately 10(3) times larger than the critical power for self-focusing. At low incident powers, the continuum is symmetric about the incident laser wavelength; at high powers it becomes broader and distinctly asymmetric towards the blue side. We observe that ER degrades by 100-fold after the onset of multiphoton-induced free-electron generation (at incident intensity approximately 2 TW cm-2), which also corresponds to the onset of asymmetry in white-light spectra.

Journal Article↗
PubMed2006

Nonadiabatic response of molecules to strong fields of picosecond, femtosecond, and subfemtosecond duration: an experimental study of the methane dication.

The double ionization of methane has been accomplished using strong optical fields that are generated using moderately intense lasers, and by strong fields that are induced by fast-moving, highly charged ions. In the former case laser intensities in the range 10(14) W cm(-2) generate fields whose durations are of 35 ps and 36 fs while in the latter case equivalent fields last for only 200-300 as. The dynamics of the field-ionized electrons are different in the two temporal regimes, fast (picoseconds), and ultrafast (few tens of femtoseconds and subfemtoseconds). Our experiments show that nonadiabatic effects come into play in the ultrafast regime; we directly monitor such effects by measuring the kinetic energy that is released when a specific bond in the doubly charged methane molecular ion breaks.

Journal Article↗
PubMed2006

Euler buckling-induced folding and rotation of red blood cells in an optical trap.

We investigate the physics of an optically driven micromotor of biological origin. When a single, live red blood cell (RBC) is placed in an optical trap, the normal biconcave disc shape of the cell is observed to fold into a rod-like shape. If the trapping laser beam is circularly polarized, the folded RBC rotates. A model based on geometric considerations, using the concept of buckling instabilities, captures the folding phenomenon; the rotation of the cell is rationalized using the Poincaré sphere. Our model predicts that (i) at a critical power of the trapping laser beam the RBC shape undergoes large fluctuations, and (ii) the torque that is generated is proportional to the power of the laser beam. These predictions are verified experimentally. We suggest a possible mechanism for the emergence of birefringent properties in the RBC in the folded state.

Animals↗
PubMed2004

Strong light fields coax intramolecular reactions on femtosecond time scales.

Energetic H(2) (+) ions are formed as a result of intramolecular rearrangement during fragmentation of linear alcohols (methanol, ethanol, propanol, hexanol, and dodecanol) induced by intense, pulsed optical fields. The laser intensity regime that is accessed in these experiments (peak intensity of 8 x 10(15) W cm(-2)) ensures multiple ionization of the irradiated alcohol molecules such that Coulomb explosions would be expected to dominate the overall fragmentation dynamics. Polarization dependent measurements show, counterintuitively, that rearrangement is induced by the strong optical field within a single, 100 fs long laser pulse, and that it occurs before Coulomb explosion of the field-ionized multiply charged alcohols.

Journal Article↗
PubMed2004

Dissociative ionization of methane by chirped pulses of intense laser light.

Measurements have been made of optical field-induced ionization and fragmentation of methane molecules at laser intensities in the 10(16) W cm(-2) range using near transform limited pulses of 100 fs duration as well as with chirped pulses whose temporal profiles extend up to 1500 fs. Data is taken both in constant-intensity and constant-energy modes. The temporal profile of the chirped laser pulse is found to affect the morphology of the fragmentation pattern that is measured. Besides, the sign of the chirp also affects the yield of fragments like C2+, H+, and H2+ that originate from methane dications that are formed by optical field-induced double ionization.

Journal Article↗
PubMed2002

Burden of organochlorine pesticides in blood and its effect on thyroid hormones in women.

Man has utilized a wide variety of pesticides to combat the crop pests and vectors of human diseases. However, in this process, he has overlooked the darker side of these noxious chemicals, the concentrations of which have reached the environment and pose serious threats, such as mutagenesis, teratogenesis, carcinogenesis and endocrine dysfunction in various components of the ecosystem. The present study was planned to assess the burden of organochlorine pesticides and their influence on thyroid function in women. The study included a total of 123 women from Jaipur City who visited the Thyroid clinic in SMS Medical College and Hospital. One hundred women showed normal thyroid hormone levels while the remaining 23 women had depleted T4 and high TSH levels. The qualitative and quantitative estimation of organochlorine pesticides was carried out by gas chromatography. Out of the analyzed pesticides, the concentration of p,p'-DDT and its metabolites was higher in all the subjects, but dieldrin was found to be significantly high in the hypothyroid women. The correlation analysis for dieldrin and depleted T4 levels in hypothyroid women elicited an inverse relationship between them.

Adult↗
PubMed2001

A statewide initiative to improve the care of hospitalized pneumonia patients: The Connecticut Pneumonia Pathway Project.

PURPOSE: A statewide quality improvement initiative was conducted in Connecticut to improve process-of-care performance and to decrease length of stay for patients hospitalized with community-acquired pneumonia. SETTING AND METHODS: Data were collected on 1,242 elderly (> or =65 years) pneumonia patients hospitalized at 31 of 32 acute care hospitals between January 16, 1995, and March 15, 1996, and on 1,146 patients hospitalized between January 1, 1997, and June 30, 1997. Interventions included feedback of performance data (Qualidigm, the Connecticut Peer Review Organization), dissemination of an evidence-based pneumonia critical pathway (Connecticut Thoracic Society), and sharing of pathway implementation experiences (hospitals). Process and outcome measures included early antibiotic administration, blood culture collection, oxygenation assessment, length of stay, 30-day mortality, and 30-day readmission rates. Analyses were adjusted for severity of illness and hospital-specific practice patterns. RESULTS: After the statewide initiative, improvements were noted in antibiotic administration within 8 hours of hospital arrival (improvement from 83.4% to 88.8%, relative risk [RR] = 1.21; 95% confidence interval [CI]: 1.10 to 1.32), oxygenation assessment within 24 hours of hospital arrival (93.6% to 95.4%; RR = 1.23, 95% CI: 1.11 to 1.38), and length of stay (7 days to 5 days, P <0.001). There were no significant changes in blood culture collection within 24 hours of hospital arrival, blood culture collection before antibiotic administration, 30-day mortality, or 30-day readmission rates. CONCLUSIONS: Statewide improvements were demonstrated in the care of hospitalized pneumonia patients concurrent with a multifaceted quality improvement intervention. Further research is needed to separate the effects of the quality improvement interventions from secular trends.

Aged↗
PubMed2001

Asymmetric high-energy ion emission from argon clusters in intense laser fields.

Clusters of 2x10(3) to 4x10(4) Ar atoms are Coulomb exploded in intense (up to 8x10(15) W cm(-2)) laser fields. The dependence of multiply charged argon ion energies on the polarization state of light is probed. A directional asymmetry in the ion-explosion energies is observed for the highest charge states. The ion-energy distribution consists of a low-energy isotropic component, and a high-energy anisotropic one. The results are discussed in terms of an asymmetric Coulomb-explosion scenario.

Journal Article↗
PubMed2001

Impact of systemic treatment on local control for patients with lymph node-negative breast cancer treated with breast-conservation therapy.

PURPOSE: To determine the impact of tamoxifen and chemotherapy on local control for breast cancer patients treated with breast-conservation therapy. PATIENTS AND METHODS: The data from 484 breast cancer patients who were treated with breast-conserving surgery and radiation were analyzed. Only patients with lymph node-negative disease were studied to provide comparative groups with a similar stage of disease and a similar competing risk for distant metastases. Actuarial local control rates of the 277 patients treated with systemic therapy (128, chemotherapy with or without tamoxifen; 149, tamoxifen alone) were compared with the rates for the 207 patients who received no systemic treatment. Only 10% of the patients had positive (2%), close (3%), or unknown margin status (5%). RESULTS: Patients treated with systemic therapy had improved 5-year (97.5% v 89.8%) and 8-year (95.6% v 85.2%) local control rates compared with those that did not receive systemic treatment (P =.004, log-rank test). There was no statistical difference in local control between patients treated with chemotherapy and patients treated with tamoxifen alone (P =.219). Systemic treatment, margin status, young patient age, estrogen and progesterone receptor status, and primary tumor size were analyzed in a Cox regression analysis. The use of systemic treatment was the most powerful predictor of local control: patients who did not receive systemic treatment had a relative risk of local recurrence of 3.3 (95% confidence interval, 1.5 to 7.5; P =.004). CONCLUSION: In this retrospective analysis, systemic therapy appears to contribute to long-term local control in patients with lymph node-negative breast cancer treated with breast-conservation therapy.

Adult↗
PubMed2001

Thyroid hormone profile in obese subjects--a clinical study.

Fifty obese subjects with body weight above 120% of the ideal weight for that height or body mass index greater than 27.8 kg/m2 in men or 27.3 kg/m2 in women were studied for thyroid hormone profile. Nearly three-fourths obese subjects had body mass index of 30-40 kg/m2. Eighty-six per cent subjects were clinically and biochemically euthyroid. Fourteen per cent of the subjects had hypothyroidism; out of them, 8% were clinically and biochemically hypothyroid while 6% were only biochemically hypothyroid. None of the hypothyroid subjects had morbid obesity (greater than 40 kg/m2 body mass index). Duration of obesity in hypothyroid subjects was less than 10 years in nearly three-fourths of cases.

Adult↗
PubMed2000

Stimulation of iron uptake and Hb synthesis in iron deficient reticulocytes.

The effect of inhibitors and intermediates of heme synthesis, inhibitor of globin synthesis, and some iron proteins on in vitro iron uptake and haemoglobin synthesis by reticulocytes of iron deficient subjects was investigated in this study. Lead, INH, ALA, mesoprophyrin, ferritin and albumin substantially increased iron uptake by iron deficient reticulocytes, while cycloheximide and glycine depressed it. The results showed that it is possible to stimulate iron uptake and Hb synthesis in iron deficiency by substances other than iron; the most effective and remarkable of them was ferritin.

Adult↗
PubMed1998

Warfarin use following ischemic stroke among Medicare patients with atrial fibrillation.

BACKGROUND: Elderly patients with ischemic stroke and atrial fibrillation are at especially increased risk for recurrent stroke. Warfarin sodium is highly effective in reducing this risk. OBJECTIVE: To determine the use of warfarin among a population sample of elderly patients with atrial fibrillation hospitalized for ischemic stroke. METHODS: The Connecticut Peer Review Organization conducted a chart review of Medicare patients, aged 65 years or older, hospitalized in 1994 with a diagnosis of atrial fibrillation. Patients with a principal diagnosis of acute myocardial infarction or another indication for anticoagulation were excluded. RESULTS: Among 635 patients (402 women; 585 white; 218 > or =85 years old; 147 with a new diagnosis of atrial fibrillation), 334 had stroke as a principal diagnosis. Among those discharged alive after a stroke, only 147 (53%) of 278 were prescribed warfarin at discharge. Furthermore, among 130 (47%) of 278 patients not prescribed warfarin at discharge, 81 (62%) of 130 were also not prescribed aspirin. Increased potential benefit (additional vascular risk factors) was not associated with a higher rate of warfarin use. Low risk for anticoagulation (lack of risk factors for bleeding) was associated with a slightly higher rate of warfarin use. Among those with an increased risk of stroke and a low risk for bleeding (ideal candidates), 124 (62%) of 278 were discharged on a regimen of warfarin. CONCLUSION: Anticoagulation of elderly stroke patients with atrial fibrillation, even among ideal candidates, is underused. The increased use of warfarin among these patients represents an excellent opportunity for reducing the risk of recurrent stroke in this high-risk population.

Aged↗