sandeep singh - Academia.edu (original) (raw)
Papers by sandeep singh
Chemical Physics, 2002
This work addresses the construction of slow manifolds for chemically reactive flows. This constr... more This work addresses the construction of slow manifolds for chemically reactive flows. This construction relies on the same decomposition of a local eigensystem that is used in formation of what are known as Intrinsic Low Dimensional Manifolds ͑ILDMs͒. We first clarify the accuracy of the standard ILDM approximation to the set of ordinary differential equations which model spatially homogeneous reactive systems. It is shown that the ILDM is actually only an approximation of the more fundamental Slow Invariant Manifold ͑SIM͒ for the same system. Subsequently, we give an improved extension of the standard ILDM method to systems where reaction couples with convection and diffusion. Reduced model equations are obtained by equilibrating the fast dynamics of a closely coupled reaction/convection/diffusion system and resolving only the slow dynamics of the same system in order to reduce computational costs, while maintaining a desired level of accuracy. The improvement is realized through formulation of an elliptic system of partial differential equations which describe the infinite-dimensional Approximate Slow Invariant Manifold ͑ASIM͒ for the reactive flow system. This is demonstrated on a simple reaction-diffusion system, where we show that the error incurred when using the ASIM is less than that incurred by use of the Maas-Pope Projection ͑MPP͒ of the diffusion effects onto the ILDM. This comparison is further done for ozone decomposition in a premixed laminar flame where an error analysis shows a similar trend.
Combustion Theory and Modelling, 2001
A standard ignition delay problem for a mixture of hydrogen-oxygen-argon in a shock tube is exten... more A standard ignition delay problem for a mixture of hydrogen-oxygen-argon in a shock tube is extended to the viscous regime and solved using the method of intrinsic low-dimensional manifolds (ILDM) coupled with a wavelet adaptive multilevel representation (WAMR) spatial discretization technique. An operator-splitting method is used to describe the reactions as a system of ordinary differential equations at each spatial point. The ILDM method is used to eliminate the stiffness associated with the chemistry by decoupling processes which evolve on fast and slow time scales. The fast time scale processes are systematically equilibrated, thereby reducing the dimension of the phase space required to describe the reactive system. The WAMR technique captures the detailed spatial structures automatically with a small number of basis functions thereby further reducing the number of variables required to describe the system. A maximum of only 300 collocation points and 15 scale levels yields results with striking resolution of fine-scale viscous and induction zones. Additionally, the resolution of physical diffusion processes minimizes the effects of potentially reaction-inducing artificial entropy layers associated with numerical diffusion.
Atmospheric Environment, 1998
Rain water samples were collected at Gopalpura during the monsoon of 1996. Gopalpura situated 52 ... more Rain water samples were collected at Gopalpura during the monsoon of 1996. Gopalpura situated 52 km SE of Agra city, is exclusively a rural area with no industries. There are no major cities or towns within a radial distance of 35 km. The cations (Ca, Mg, Na, K and NH 4 ) and ...
Journal of Atmospheric Chemistry, 2002
Rainwater samples were collected for the monsoon period of 1988 and 1991–1996 at Dayalbagh (Agra)... more Rainwater samples were collected for the monsoon period of 1988 and 1991–1996 at Dayalbagh (Agra), a suburban site situated in semiaridregion. The mean pH was 7.01 ±1.03 well above 5.6, which is the reference pH. Concentration of Ca2+ was observed to be highest followed by Mg2+, NH4+,SO42−, Cl−,NO3−, Na+, F− and K+. The ratios of SO42− + NO3− andCa2+ + Mg2+ (TA/TC) have been considered as indicatorfor acidity. In the Agra region ratio of TA/TC is quite below 1.0 indicating alkaline nature of rainwater. The lowest value of 0.24 was observed in 1991 likely due to the lowest rain depth of the decade. The highest value of 0.54 was observed in 1996, a year with a large rain depth and increase in line (vehicular traffic) and area sources (population growth). Good correlation between Ca2+ and NO3−,Ca2+ and SO42− andSO42− and NO3−,indicates that wind carried dust and soil play a significant role in neutralization of precipitation acidity.
Cereal Chem. 73(1):54-57 A 100-g laboratory corn wet-milling procedure was developed in formed du... more Cereal Chem. 73(1):54-57 A 100-g laboratory corn wet-milling procedure was developed in formed during the same week, and 0.60% when replicates were performed order to reduce sample size and labor time requirements for determining weekly during the course of a year. In a properly equipped laboratory, the milling characteristics of corn samples. The procedure gives starch the procedure can be performed at the rate of 40 samples per week using yields statistically similar to those of a 1-kg laboratory procedure with a three trained personnel. standard deviation in replicates of 0.36% when the replicates were per-
Heterocycles, 2003
Skip to Content. If you are seeing this message, you may be experiencing temporary network proble... more Skip to Content. If you are seeing this message, you may be experiencing temporary network problems. Please wait a few minutes and refresh the page. If the problem persists, you may wish to report it to your local Network Manager. ...
Journal of Organic Chemistry, 2002
1,3-Dipolar cycloaddition of organic azides 1, 2, or 3 to acetylenic amides 4 or 5 under solvent-... more 1,3-Dipolar cycloaddition of organic azides 1, 2, or 3 to acetylenic amides 4 or 5 under solvent-free microwave irradiation produced the corresponding N-substituted C-carbamoyl-1,2,3-triazoles 7a-12a in good to excellent yields. Under similar reaction conditions, 1,3-dipolar cycloaddition of diazide 6 and acetylenic amide 4 gave the azido-triazole 13a.
Activated carbon, developed from fertilizer waste, has been used for the removal of Hg 2+, Cr 6+,... more Activated carbon, developed from fertilizer waste, has been used for the removal of Hg 2+, Cr 6+, Pb 2+, and Cu 2 +. Mass transfer kinetic approach has been successfully applied for the determination of various parameters necessary for designing a fixed-bed absorber. Parameters selected are the length of the (PAZ) primary adsorption zone , total time involved for the establishment of primary adsorption zone (tx), mass rate of flow to the absorber (Fro), time for primary adsorption zone to move down its length (t~), amount of adsorbate adsorbed in PAZ from breakpoint to exhaustion (Ms), fractional capacity (]), time of initial formation of PAZ (tO and per cent saturation of column at break point. Chemical regeneration has been achieved with 1 M HNO3.
Chemical Physics, 2002
This work addresses the construction of slow manifolds for chemically reactive flows. This constr... more This work addresses the construction of slow manifolds for chemically reactive flows. This construction relies on the same decomposition of a local eigensystem that is used in formation of what are known as Intrinsic Low Dimensional Manifolds ͑ILDMs͒. We first clarify the accuracy of the standard ILDM approximation to the set of ordinary differential equations which model spatially homogeneous reactive systems. It is shown that the ILDM is actually only an approximation of the more fundamental Slow Invariant Manifold ͑SIM͒ for the same system. Subsequently, we give an improved extension of the standard ILDM method to systems where reaction couples with convection and diffusion. Reduced model equations are obtained by equilibrating the fast dynamics of a closely coupled reaction/convection/diffusion system and resolving only the slow dynamics of the same system in order to reduce computational costs, while maintaining a desired level of accuracy. The improvement is realized through formulation of an elliptic system of partial differential equations which describe the infinite-dimensional Approximate Slow Invariant Manifold ͑ASIM͒ for the reactive flow system. This is demonstrated on a simple reaction-diffusion system, where we show that the error incurred when using the ASIM is less than that incurred by use of the Maas-Pope Projection ͑MPP͒ of the diffusion effects onto the ILDM. This comparison is further done for ozone decomposition in a premixed laminar flame where an error analysis shows a similar trend.
Combustion Theory and Modelling, 2001
A standard ignition delay problem for a mixture of hydrogen-oxygen-argon in a shock tube is exten... more A standard ignition delay problem for a mixture of hydrogen-oxygen-argon in a shock tube is extended to the viscous regime and solved using the method of intrinsic low-dimensional manifolds (ILDM) coupled with a wavelet adaptive multilevel representation (WAMR) spatial discretization technique. An operator-splitting method is used to describe the reactions as a system of ordinary differential equations at each spatial point. The ILDM method is used to eliminate the stiffness associated with the chemistry by decoupling processes which evolve on fast and slow time scales. The fast time scale processes are systematically equilibrated, thereby reducing the dimension of the phase space required to describe the reactive system. The WAMR technique captures the detailed spatial structures automatically with a small number of basis functions thereby further reducing the number of variables required to describe the system. A maximum of only 300 collocation points and 15 scale levels yields results with striking resolution of fine-scale viscous and induction zones. Additionally, the resolution of physical diffusion processes minimizes the effects of potentially reaction-inducing artificial entropy layers associated with numerical diffusion.
Atmospheric Environment, 1998
Rain water samples were collected at Gopalpura during the monsoon of 1996. Gopalpura situated 52 ... more Rain water samples were collected at Gopalpura during the monsoon of 1996. Gopalpura situated 52 km SE of Agra city, is exclusively a rural area with no industries. There are no major cities or towns within a radial distance of 35 km. The cations (Ca, Mg, Na, K and NH 4 ) and ...
Journal of Atmospheric Chemistry, 2002
Rainwater samples were collected for the monsoon period of 1988 and 1991–1996 at Dayalbagh (Agra)... more Rainwater samples were collected for the monsoon period of 1988 and 1991–1996 at Dayalbagh (Agra), a suburban site situated in semiaridregion. The mean pH was 7.01 ±1.03 well above 5.6, which is the reference pH. Concentration of Ca2+ was observed to be highest followed by Mg2+, NH4+,SO42−, Cl−,NO3−, Na+, F− and K+. The ratios of SO42− + NO3− andCa2+ + Mg2+ (TA/TC) have been considered as indicatorfor acidity. In the Agra region ratio of TA/TC is quite below 1.0 indicating alkaline nature of rainwater. The lowest value of 0.24 was observed in 1991 likely due to the lowest rain depth of the decade. The highest value of 0.54 was observed in 1996, a year with a large rain depth and increase in line (vehicular traffic) and area sources (population growth). Good correlation between Ca2+ and NO3−,Ca2+ and SO42− andSO42− and NO3−,indicates that wind carried dust and soil play a significant role in neutralization of precipitation acidity.
Cereal Chem. 73(1):54-57 A 100-g laboratory corn wet-milling procedure was developed in formed du... more Cereal Chem. 73(1):54-57 A 100-g laboratory corn wet-milling procedure was developed in formed during the same week, and 0.60% when replicates were performed order to reduce sample size and labor time requirements for determining weekly during the course of a year. In a properly equipped laboratory, the milling characteristics of corn samples. The procedure gives starch the procedure can be performed at the rate of 40 samples per week using yields statistically similar to those of a 1-kg laboratory procedure with a three trained personnel. standard deviation in replicates of 0.36% when the replicates were per-
Heterocycles, 2003
Skip to Content. If you are seeing this message, you may be experiencing temporary network proble... more Skip to Content. If you are seeing this message, you may be experiencing temporary network problems. Please wait a few minutes and refresh the page. If the problem persists, you may wish to report it to your local Network Manager. ...
Journal of Organic Chemistry, 2002
1,3-Dipolar cycloaddition of organic azides 1, 2, or 3 to acetylenic amides 4 or 5 under solvent-... more 1,3-Dipolar cycloaddition of organic azides 1, 2, or 3 to acetylenic amides 4 or 5 under solvent-free microwave irradiation produced the corresponding N-substituted C-carbamoyl-1,2,3-triazoles 7a-12a in good to excellent yields. Under similar reaction conditions, 1,3-dipolar cycloaddition of diazide 6 and acetylenic amide 4 gave the azido-triazole 13a.
Activated carbon, developed from fertilizer waste, has been used for the removal of Hg 2+, Cr 6+,... more Activated carbon, developed from fertilizer waste, has been used for the removal of Hg 2+, Cr 6+, Pb 2+, and Cu 2 +. Mass transfer kinetic approach has been successfully applied for the determination of various parameters necessary for designing a fixed-bed absorber. Parameters selected are the length of the (PAZ) primary adsorption zone , total time involved for the establishment of primary adsorption zone (tx), mass rate of flow to the absorber (Fro), time for primary adsorption zone to move down its length (t~), amount of adsorbate adsorbed in PAZ from breakpoint to exhaustion (Ms), fractional capacity (]), time of initial formation of PAZ (tO and per cent saturation of column at break point. Chemical regeneration has been achieved with 1 M HNO3.