Ritu Singh - Academia.edu (original) (raw)

Papers by Ritu Singh

Research paper thumbnail of Voice over the internet: A tutorial discussing problems and solutions associated with alternative transport

IEEE Communications Surveys and Tutorials, 2004

his article provides a tutorial overview of one of the Internet traffic types likely to see signi... more his article provides a tutorial overview of one of the Internet traffic types likely to see significant future growth, Voice over the Internet (a.k.a. Voice over IP or VoIP). The effects of moving voice traffic over a packetswitched statistically multiplexed network such as the Internet, which was never really designed to handle this type of source, are examined and compared with the effects of moving voice over the more traditional circuit-switched time division multiplexed telephone system, more affectionately known as POTS. The emphasis of this article is on areas of concern to a backbone service provider implementing VoIP.

Research paper thumbnail of Analyzing end-to-end delivery delay in pure VoIP networks

Abstract Today, standards-based quality of service mechanisms are not universally deployed across... more Abstract Today, standards-based quality of service mechanisms are not universally deployed across Internet service provider backbones. As a result, many carriers that are deploying VoIP networks are segregating voice traffic from the data and installing pure ...

Research paper thumbnail of A rapid and simple method for the analysis of 1-hydroxypyrene glucuronide: a potential biomarker for poly cyclic aromatic hydrocarbon exposure

Carcinogenesis, 1995

The present study describes a simple method of analyzing metabolites of pyrene in urine. This met... more The present study describes a simple method of analyzing metabolites of pyrene in urine. This method is capable of detecting the glucuronic acid and sulfate conjugates of pyrene as well as free 1-hydroxypyrene in a single analysis. In comparison to other analytical methods for detecting pyrene metabolites, this new method does not require an overnight enzymatic hydrolysis step and is much more rapid method of analysis. The newly developed procedure involves solid phase extraction of pyrene metabolites followed by separation using HPLC with a phenyl modified reverse phase column and an acidic buffer and acetonitrile gradient elution system. Metabolites were detected using a fluorescence detector with wavelength conditions optimized for each metabolite. This method resulted in baseline separation of the glucuronic acid (1-OH P-GlcUA) and sulfate conjugate (1-OH P-Sul) of 1-hydroxypyrene and free 1-hydroxypyrene (1-OH P). The potential of this method for use in monitoring human exposure to mixtures of PAHs was evaluated by analyzing urine obtained from five individuals working in a coal gasification plant. 1-OH P-GlcUA was detected as the major metabolite in the urine of all the five workers. This metabolite accounted for 80-100% of the total pyrene metabolites excreted in urine. 1-OH P-GlcUA levels ranged from 0.31-0.94 microgram/g creatinine. Low levels of the sulfate conjugate (0.002-0.06 microgram/g creatinine) were detected in four of the samples while free 1-hydroxypyrene (0.07-0.2 microgram/g creatinine) was detected in two of the five urine samples. Urine from occupationally exposed workers was also analyzed for 1-hydroxypyrene following enzymatic hydrolysis using the standard approach. Levels of 1-hydroxypyrene ranged from 0.51-1.17 micrograms/g creatinine. Comparison of the fluorescence intensities of 1-OH P-GlcUA and 1-OH P-Sul to 1-hydroxypyrene demonstrated that the glucuronide conjugate is 3-fold more fluorescent and the sulfate conjugate is 4-fold more fluorescent than 1-hydroxypyrene. These results indicate that conjugates of pyrene, specifically, 1-OH P-GlcUA can potentially be used as a more sensitive biomarker of exposure to PAHs.

Research paper thumbnail of Some aspects of health risk assessment of manufactured gas plant

Toxicology Letters, 1998

The low-pressure gasification of brown coal is an obsolete technology. Authors describe occupatio... more The low-pressure gasification of brown coal is an obsolete technology. Authors describe occupational exposure to polycyclic aromatic hydrocarbons (PARs) and carbon monoxide in the gas plant and present findings of parameters of the health status of workers (death rate to malignant diseases, life expectancy, 26 immunological and cytogenetical parameters, 5 tumor markers and DNA adducts), 16 different PAHs were measured in the working atmosphere (GLC and GCIMSIMS, total PAHs levels ranged from 0.7 to 22.6 J.l.g.m-3). The excretion levels of pyrene metabolites in urine obtained from 44 workers (l-hydroxypyrene-glucuronide, l-hydroxypyrene-sulfate, free I-hydroxypyrene; total I-hydroxypyrenelevels ranged from O.ll to 1.17 J.l.g/g creatinine) were compared with exposure histories of individuals and smoking habit PAH:DNA adducts were measured using the 32P-postlabeling method (range: 2.12-26 .56 nmol/mg DNA). The men of this plant die on the average 5-6 years sooner than the men in the Czech Republic. Death is primarily due to malignant diseases (lung and kidney cancer). The low pressure gasification of the brown coal is classifiedas a working process with considerable risk of exposure to chemical carcinogens. Practical recommendations for protecting workers from exposure to these hazards were proposed from the results of the study.

Research paper thumbnail of Studies on the Binding of Various Polycyclic Aromatic Hydrocarbons to Mouse Hemoglobin and Serum Proteins

Polycyclic Aromatic Compounds, 1994

Polycyclic Aromatic Compounds, 1994. Vol. 6, pp. 135-142. Reprints available directly from the pu... more Polycyclic Aromatic Compounds, 1994. Vol. 6, pp. 135-142. Reprints available directly from the publisher Photocopying permitted by license only ... 0 1994 Gordon and Breach Science Publishers SA Printed in Malaysia ... Studies on the Binding of Various Polycyclic Aromatic ...

Research paper thumbnail of Voice over the internet: A tutorial discussing problems and solutions associated with alternative transport

IEEE Communications Surveys and Tutorials, 2004

his article provides a tutorial overview of one of the Internet traffic types likely to see signi... more his article provides a tutorial overview of one of the Internet traffic types likely to see significant future growth, Voice over the Internet (a.k.a. Voice over IP or VoIP). The effects of moving voice traffic over a packetswitched statistically multiplexed network such as the Internet, which was never really designed to handle this type of source, are examined and compared with the effects of moving voice over the more traditional circuit-switched time division multiplexed telephone system, more affectionately known as POTS. The emphasis of this article is on areas of concern to a backbone service provider implementing VoIP.

Research paper thumbnail of Analyzing end-to-end delivery delay in pure VoIP networks

Abstract Today, standards-based quality of service mechanisms are not universally deployed across... more Abstract Today, standards-based quality of service mechanisms are not universally deployed across Internet service provider backbones. As a result, many carriers that are deploying VoIP networks are segregating voice traffic from the data and installing pure ...

Research paper thumbnail of A rapid and simple method for the analysis of 1-hydroxypyrene glucuronide: a potential biomarker for poly cyclic aromatic hydrocarbon exposure

Carcinogenesis, 1995

The present study describes a simple method of analyzing metabolites of pyrene in urine. This met... more The present study describes a simple method of analyzing metabolites of pyrene in urine. This method is capable of detecting the glucuronic acid and sulfate conjugates of pyrene as well as free 1-hydroxypyrene in a single analysis. In comparison to other analytical methods for detecting pyrene metabolites, this new method does not require an overnight enzymatic hydrolysis step and is much more rapid method of analysis. The newly developed procedure involves solid phase extraction of pyrene metabolites followed by separation using HPLC with a phenyl modified reverse phase column and an acidic buffer and acetonitrile gradient elution system. Metabolites were detected using a fluorescence detector with wavelength conditions optimized for each metabolite. This method resulted in baseline separation of the glucuronic acid (1-OH P-GlcUA) and sulfate conjugate (1-OH P-Sul) of 1-hydroxypyrene and free 1-hydroxypyrene (1-OH P). The potential of this method for use in monitoring human exposure to mixtures of PAHs was evaluated by analyzing urine obtained from five individuals working in a coal gasification plant. 1-OH P-GlcUA was detected as the major metabolite in the urine of all the five workers. This metabolite accounted for 80-100% of the total pyrene metabolites excreted in urine. 1-OH P-GlcUA levels ranged from 0.31-0.94 microgram/g creatinine. Low levels of the sulfate conjugate (0.002-0.06 microgram/g creatinine) were detected in four of the samples while free 1-hydroxypyrene (0.07-0.2 microgram/g creatinine) was detected in two of the five urine samples. Urine from occupationally exposed workers was also analyzed for 1-hydroxypyrene following enzymatic hydrolysis using the standard approach. Levels of 1-hydroxypyrene ranged from 0.51-1.17 micrograms/g creatinine. Comparison of the fluorescence intensities of 1-OH P-GlcUA and 1-OH P-Sul to 1-hydroxypyrene demonstrated that the glucuronide conjugate is 3-fold more fluorescent and the sulfate conjugate is 4-fold more fluorescent than 1-hydroxypyrene. These results indicate that conjugates of pyrene, specifically, 1-OH P-GlcUA can potentially be used as a more sensitive biomarker of exposure to PAHs.

Research paper thumbnail of Some aspects of health risk assessment of manufactured gas plant

Toxicology Letters, 1998

The low-pressure gasification of brown coal is an obsolete technology. Authors describe occupatio... more The low-pressure gasification of brown coal is an obsolete technology. Authors describe occupational exposure to polycyclic aromatic hydrocarbons (PARs) and carbon monoxide in the gas plant and present findings of parameters of the health status of workers (death rate to malignant diseases, life expectancy, 26 immunological and cytogenetical parameters, 5 tumor markers and DNA adducts), 16 different PAHs were measured in the working atmosphere (GLC and GCIMSIMS, total PAHs levels ranged from 0.7 to 22.6 J.l.g.m-3). The excretion levels of pyrene metabolites in urine obtained from 44 workers (l-hydroxypyrene-glucuronide, l-hydroxypyrene-sulfate, free I-hydroxypyrene; total I-hydroxypyrenelevels ranged from O.ll to 1.17 J.l.g/g creatinine) were compared with exposure histories of individuals and smoking habit PAH:DNA adducts were measured using the 32P-postlabeling method (range: 2.12-26 .56 nmol/mg DNA). The men of this plant die on the average 5-6 years sooner than the men in the Czech Republic. Death is primarily due to malignant diseases (lung and kidney cancer). The low pressure gasification of the brown coal is classifiedas a working process with considerable risk of exposure to chemical carcinogens. Practical recommendations for protecting workers from exposure to these hazards were proposed from the results of the study.

Research paper thumbnail of Studies on the Binding of Various Polycyclic Aromatic Hydrocarbons to Mouse Hemoglobin and Serum Proteins

Polycyclic Aromatic Compounds, 1994

Polycyclic Aromatic Compounds, 1994. Vol. 6, pp. 135-142. Reprints available directly from the pu... more Polycyclic Aromatic Compounds, 1994. Vol. 6, pp. 135-142. Reprints available directly from the publisher Photocopying permitted by license only ... 0 1994 Gordon and Breach Science Publishers SA Printed in Malaysia ... Studies on the Binding of Various Polycyclic Aromatic ...