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Biomedical subjects

R Singhvi

Publications and source records attributed to R Singhvi.

9 recordsLinked to original sources
PubMed2001

Field portable XRF analysis of environmental samples.

One of the critical factors for successfully conducting contamination characterization, removal, and remedial operations at hazardous waste sites is rapid and appropriate response to analyze samples in a timely fashion. Turnaround time associated with off-site analysis is often too slow to support efficient utilization of the data. Field portable X-ray fluorescence (FPXRF) techniques provide viable and effective analytical approaches to meet on-site analysis needs for many types of environmental samples. Applications include the in situ analysis of metals in soils and sediments, thin films/particulates, and lead in paint.

Calibration↗
PubMed2001

Comparison of field and laboratory methods for monitoring metallic mercury vapor in indoor air.

Real-time metallic mercury vapor levels of the indoor air were monitored at several mercury spill sites around the US in order to evaluate the effectiveness of site cleanup operations. Mercury readings taken in the field with a Jerome 431 Mercury Vapor Analyzer were compared with laboratory analysis using a modified National Institute for Occupational Safety and Health (NIOSH) 6009 method. Statistical evaluation showed that the data were highly comparable except at low concentrations, due to the large degree of uncertainty associated with measuring low levels of mercury with the Jerome analyzer. Regression analysis indicated that Jerome measurements of 10 microg/m(3) or greater are comparable for field analysis of mercury vapor in air.

Air Pollution, Indoor↗
PubMed2000

Computational and experimental investigation of flow and fluid mixing in the roller bottle bioreactor.

The fully three-dimensional velocity field in a roller bottle bioreactor is simulated for two systems (creeping flow and inertial flow conditions) using a control volume-finite element method, and validated experimentally using particle imaging velocimetry. The velocity fields and flow patterns are described in detail using velocity contour plots and tracer particle pathline computations. Bulk fluid mixing in the roller bottle is then examined using a computational fluid tracer program and flow visualization experiments. It is shown that the velocity fields and flow patterns are substantially different for each of these flow cases. For creeping flow conditions the flow streamlines consist of symmetric, closed three-dimensional loops; and for inertial flow conditions, streamlines consist of asymmetric toroidal surfaces. Fluid tracers remain trapped on these streamlines and are unable to contact other regions of the flow domain. As a result, fluid mixing is greatly hindered, especially in the axial direction. The lack of efficient axial mixing is verified computationally and experimentally. Such mixing limitations, however, are readily overcome by introducing a small-amplitude vertical rocking motion that disrupts both symmetry and recirculation, leading to much faster and complete axial mixing. The frequency of such motion is shown to have a significant effect on mixing rate, which is a critical parameter in the overall performance of roller bottles.

Bioreactors↗
PubMed2000

Insertion of self-expanding metal stents for malignant dysphagia: assessment of a simple endoscopic method.

AIM: To assess the efficacy, safety and long-term results of self-expanding metallic prostheses, placed using an entirely endoscopic method, for the relief of dysphagia in oesophageal carcinoma. PATIENTS AND METHODS: A consecutive series of 50 patients (30 men, 20 women), aged 43-91 years (median, 75 years) underwent stent placement (Ultraflex Stent, Boston Scientific, Watertown, MA, USA) under general anaesthesia without fluoroscopic control. RESULTS: Stent placement was successful in all patients. Swallowing improved from dysphagia score 4, 3 or 2 to score 1 (or 0) in all patients available for long-term follow-up (excluding two patients who died, and two who had resection, in the immediate post-stenting period). There were two early deaths that were, or could have been, procedure-related and one early complication, in addition to technical problems in 6 cases, all early in the series. Seven patients required endoscopic laser treatment, on 13 occasions, subsequently for tumour in-growth or over-growth. Of the 46 patients with long-term stents in situ, 36 patients died with a median survival time of 4 months (range 10 days to 24 months). At the time of writing, 10 patients are still alive with a median survival of 4 months (range 1-11 months). CONCLUSIONS: Self-expanding metallic stents provide rapid, safe and effective relief of dysphagia. They can provide long-term palliation (> 1 year) with endoscopic laser treatment for recurrent in-growing/over-growing tumour. Fluoroscopic control is not necessary for the safe and accurate placement of such stents.

Adult↗
PubMed1999

Microbial conversion of indene to indandiol: a key intermediate in the synthesis of CRIXIVAN.

Indene is oxidized to mixtures of cis- and trans-indandiols and related metabolites by Pseudomonas putida and Rhodococcus sp. isolates. Indene metabolism is consistent with monooxygenase and dioxygenase activity. P. putida resolves enantiomeric mixtures of cis-1,2-indandiol by further selective oxidation of the 1R, 2S-enantiomer yielding high enantiomeric purity of cis-(1S, 2R)-indandiol, a potential intermediate in the synthesis of indinavir sulfate (CRIXIVAN), a protease inhibitor used in the treatment of AIDS. Molecular cloning of P. putida toluene dioxygenase in Escherichia coli confirmed the requirement for the dihydrodiol dehydrogenase in resolving racemic mixtures of cis-indandiol. Rhodococcus sp. isolates convert indene to cis-(1S, 2R)-indandiol at high initial enantiomeric excess and one isolate also produces trans-(1R, 2R)-indandiol, suggesting the presence of monooxygenase activity. Scale up and optimization of the bioconversions to these key synthons for chiral synthesis of potential intermediates for commercial manufacture of indinavir sulfate are described.

Drug Design↗
PubMed1994

Engineering cell shape and function.

An elastomeric stamp, containing defined features on the micrometer scale, was used to imprint gold surfaces with specific patterns of self-assembled monolayers of alkanethiols and, thereby, to create islands of defined shape and size that support extracellular matrix protein adsorption and cell attachment. Through this technique, it was possible to place cells in predetermined locations and arrays, separated by defined distances, and to dictate their shape. Limiting the degree of cell extension provided control over cell growth and protein secretion. This method is experimentally simple and highly adaptable. It should be useful for applications in biotechnology that require analysis of individual cells cultured at high density or repeated access to cells placed in specified locations.

Albumins↗
PubMed1994

Process monitoring of the production of gamma-interferon in recombinant Chinese hamster ovary cells.

The production of recombinant gamma-interferon was monitored using high-performance liquid chromatographic methods. These methods were able to distinguish between glycosylated and non-glycosylated forms of gamma-interferon by complexing the carbohydrate with borate. Sufficient quantities of standard glycosylated gamma-interferon were not available for peak identification so immunological techniques were used to identify gamma-interferon variants. These techniques were validated with the non-glycosylated form. The non-glycosylated form was then shown to be retained only on a cation-exchange column, while the glycosylated form, complexed with borate, was retained only on an anion-exchange column. Samples were drawn at 2-h intervals over a 60-h production cycle and analyzed by both anion- and cation-exchange chromatography. Results indicated that the production of each form was coincidental and that the glycosylated form of gamma-interferon is produced in greater abundance than non-glycosylated.

Animals↗
PubMedDate not supplied

Prognostic implications of white cell differential count and white cell morphology in Malaria.

BACKGROUND: Malaria is of immense importance amongst the tropical diseases in India. There is a need to develop newer diagnostic aids and research is necessary to identify new prognostic markers for prediction of the course and complications. AIMS: To evaluate the white cell differential count and morphology in Plasmodium vivax and Plasmodium falciparum malaria and study their prognostic utility. SUBJECTS AND METHODS: Two hundred and sixty-four adult patients in the age range of 20 to 65 years presenting to the hospital over a period of 4 months with clinical features of malaria and a positive peripheral smear examination were studied. RESULTS: No statistically significant difference was noted in the white blood cell (WBC) count and neutrophil count in P.vivax versus P. falciparum malaria. Band cells were more frequently noted in P. falciparum malaria than in P.vivax malaria (p < 0.0001). Toxic granulation of the neutrophils was noted in 9.5% of the patients and exclusively in P. falciparum malaria. Presence of toxic granulation of the polymorphs in subjects with P. falciparum malaria was significantly associated with anaemia (p=0.019), jaundice, cerebral involvement, adult respiratory distress syndromes, renal dysfunction and death (p < 0.0001 for all these parameters). CONCLUSION: Band cells were seen in P. vivax and P. falciparum malaria, although in higher numbers in P. falciparum malaria. Toxic granulation of the neutrophils was noted only in the presence of P. falciparum malaria in this study and correlated with severity.

Adult↗