Ahmad Roy | UNPAD - Academia.edu (original) (raw)

Papers by Ahmad Roy

Research paper thumbnail of Optimal Xenon Control in Heterogeneous Reactors

IEEE Transactions on Nuclear Science, 1986

ABSTRACT-A two-group diffusion-theory hete-rogeneous reactor model in two-dimensional plane geome... more ABSTRACT-A two-group diffusion-theory hete-rogeneous reactor model in two-dimensional plane geometry is developed for optimal con-trol analysis with xenon and samarium feed-back. The resulting system equations are li-nearized around an equilibrium operating ...

Research paper thumbnail of The inducer of the deoxynucleoside phosphorylases and deoxyriboaldolase in Escherichia coli

Biochimica Et Biophysica Acta (bba) - Nucleic Acids and Protein Synthesis, 1968

can insert small numbers of nucleotides into their DNA in response to irradiation. This process o... more can insert small numbers of nucleotides into their DNA in response to irradiation. This process of repair replication occurred at 200 erg/mm 2 at which the survival was approx. 25 % (ref. II). HeLa cells consequently seem able to perform repair replication at a dose where a significant proportion of the population survives. In addition these cells perform repair replication after irradiation with high doses of X-rays lz and repair replication may thus be part of a general repair process that operates after various forms of damage to mammalian cell DNA. We have not, however, demonstrated in these experiments that repair replication is causally related to the recovery of irradiated cells. It is only an analogy with bacteria 1,7 that enables us to infer that the insertion of new bases into pre-existing DNA molecules may be part of the recovery process in human cells. It is also obvious that repair replication after high doses of ultraviolet light or X-rays is unsuccessful in leading to cell recovery, since there are then few survivors. We conclude, therefore, that after irradiation most cells may begin to repair their damaged DNA even though all may not survive.

Research paper thumbnail of New prospects for deducing the evolutionary history of metabolic pathways in prokaryotes: Aromatic biosynthesis as a case-in-point

Origins of Life and Evolution of Biospheres, 1988

Metabolic pathways of prokaryotes are more biochemically diverse than is generally recognized. Di... more Metabolic pathways of prokaryotes are more biochemically diverse than is generally recognized. Distinctive biochemical features are shared by phylogenetic clusters. The hierarchical levels of characterstate clustering depends upon evolutionary events which fortuitously became fixed in the genome of a common ancestor. Prokaryotes can now be ordered on a phylogenetic tree. This allows the evolutionary steps that underlie the construction and regulation of appropriately complex biochemical pathways to be traced in an evolutionary progression of prokaryote types that house these pathways. Essentially the approach is to deduce ancestral character states at ever deeper phylogenetic levels, utilizing logical principles of maximum parsimony. The current perspective on the evolution of the biochemical pathway for biosynthesis of aromatic amino acids is developed as a case-in-point model for analyses that should be feasible with many major metabolic systems. Phenylalanine biosynthesis probably arose prior to the addition of branches leading to tyrosine and tryptophan. An evolutionary scenario is developed that begins with non-enzymatic reactions which may have operated in primitive systems, followed by the evolution of an enzymatic system that pre-dated the divergence of major lineages of modern eubacteria (Gram-positive bacteria, Gram-negative purple bacteria, and cyanobacteria).

Research paper thumbnail of Device design, fabrication and characterization of 0.8 μm CMOS technology

An intensive study has been conducted for the development of the MIMOS 0.8 μm CMOS technology. Is... more An intensive study has been conducted for the development of the MIMOS 0.8 μm CMOS technology. Issues such as device design and characterization have been given much consideration. NMOS and PMOS transistors have been designed from basic concepts and using simulation tools such as TSUPREM-4 and MEDICI. Device design constraints such as threshold voltage variation, off-state leakage current and drain-induced barrier lowering (DIBL) effects have been seriously examined to improve device performance. Furthermore, performance criteria such as drive current capability have also been examined. Extraction of device characteristics from silicon has been performed on a test chip. Based on experimental results, numerous I-V plots are presented and the data are discussed in terms of output and transfer characteristics and surface DIBL leakage current

Research paper thumbnail of Conformational studies. Part 6. X-Ray crystal structure of 3,3-dimethoxy-19-norandrosta-5(10),6-dien-17-one: an exception to the diene helicity rule

Journal of The Chemical Society-perkin Transactions 2, 1978

Research paper thumbnail of The Effect of Perioperative Blood Transfusion on Survival in Head and Neck Cancer

Survey of Anesthesiology, 1995

This Head and Neck Intergroup analysis was undertaken to evaluate further previously reported obs... more This Head and Neck Intergroup analysis was undertaken to evaluate further previously reported observations linking blood transfusions, which were given to patients with head and neck cancer, to a worse prognosis. This study population represents those patients registered to the Head and Neck Intergroup Trial 0034 for previously untreated resectable squamous cell carcinoma. Additional transfusion data were obtained by one of us (D.E.S.) on 217 patients and added to the Head and Neck Intergroup data set, providing an opportunity for assessing the impact of survival by other variables. The study group was separated using 13 variables. Analysis demonstrated that transfusion did not significantly decrease the locoregional control (P = .60). Multivariate analysis indicated that T stage (P = .015), N stage (P = .004), treatment received (P = .004), and Karnofsky Performance Scale (P = .031) were the only factors that did significantly influence survival. This multivariate analysis controlling for these variables demonstrated no significant effect on survival for those patients receiving transfusion during surgery (P = .55) or after surgery (P = .39). This study of 217 patients, controlled for other variables, does not demonstrate any significant negative relation between blood transfusions and either locoregional control or survival.

Research paper thumbnail of On the quasi-periodic solutions to the discrete non-linear Schr篓odinger equation

The authors have obtained the quasi-periodic solutions to the discrete non-linear Schrodinger equ... more The authors have obtained the quasi-periodic solutions to the discrete non-linear Schrodinger equation by a variant of a method due to Date and Tanaka (1976). It is shown explicitly that the non-linear field variables at the different lattice points can be determined ...

Research paper thumbnail of The vibratory pattern of ultrasonic files driven piezoelectrically

International Endodontic Journal, 1993

The pattern of oscillation of a Piezon-Master 400 ultrasonic file driven by a piezoelectric trans... more The pattern of oscillation of a Piezon-Master 400 ultrasonic file driven by a piezoelectric transducer was studied in air and on water. In addition, the displacement amplitudes of the files were measured. The findings were compared with those observed with the Cavi-Endo unit reported in another study (Ahmad 1969).It was observed that the file vibrated such that a standing wave was formed on the file and it exhibited points of maximum deflection (antinode) and points of minimum deflection (node) with the largest deflection occurring at the apical end. This pattern of oscillation was similar to that exhibited by the Cavi-Endo file which employed a magnetostrictive transducer. However, the displacement amplitudes were very much higher than those exhibited by the Cavi-Endo. It is considered that the 120° angle of the file holder inherent in the Piezon- Master 400 unit and the more effective power transmission with the piezoelectric transducer may have contributed to the large amplitudes.

Research paper thumbnail of The stable phylogenetic distribution of the recently evolved l -phenylalanine-inhibited isozyme of 3-deoxy- d - arabino -heptulosonate 7-phosphate synthase in enteric bacteria

Current Microbiology, 1989

Escherichia coli and some other enteric bacteria possess three regulatory isozymes of 3-deoxy-d-a... more Escherichia coli and some other enteric bacteria possess three regulatory isozymes of 3-deoxy-d-arabino-heptulosonate 7-phosphate (DAHP) synthase, each of which is inhibited by one aromatic amino acid. Thel-phenylalanine-sensitive isozyme of DAHP synthase has evolved most recently since it is absent in all other members of the Gram-negative cluster that contains enteric bacteria as a subcluster. A comprehensive survey of enteric genera was carried out to determine whether the newly evolved isozyme is a stable, conserved trait. The results obtained show that all the genera of the contemporaryEnterobacteriaceae family possess the recently evolved phenylalanine-sensitive isozyme in addition to the tyrosine-and tryptophansensitive isozymes of DAHP synthase. However, physiological manipulation was usually necessary to derepress the tryptophan-sensitive DAHP synthase in order to demonstrate its presence.

Research paper thumbnail of Reliability modeling for evaluating the contribution of photovoltaics in electric power systems

Solar power is being increasingly utilized in electric power systems. Solar power has a different... more Solar power is being increasingly utilized in electric power systems. Solar power has a different effect on generating system reliability than conventional power sources due to the intermittent nature of the atmospheric conditions at the system location. It is therefore, important to assess the impact of adding photovoltaic (PV) sources to a power system in terms of the reliability contribution of PV in meeting energy demand. This paper uses a probabilistic approach to develop a power output model for a solar park. A reliability model is then developed for a solar energy integrated power system and used in a range of studies to evaluate the reliability and energy contribution of the solar system to meet the overall system demand. The analysis of solar irradiation data, solar power output and the reliability contributions of PV when integrated in a small isolated power system are presented and compared in this paper using solar installation sites located at different latitudes. The results illustrate the ability to conduct a quantitative analysis of reliability and energy contributions of solar power sources located at different latitudes around the world.

Research paper thumbnail of Optimal Xenon Control in Heterogeneous Reactors

IEEE Transactions on Nuclear Science, 1986

ABSTRACT-A two-group diffusion-theory hete-rogeneous reactor model in two-dimensional plane geome... more ABSTRACT-A two-group diffusion-theory hete-rogeneous reactor model in two-dimensional plane geometry is developed for optimal con-trol analysis with xenon and samarium feed-back. The resulting system equations are li-nearized around an equilibrium operating ...

Research paper thumbnail of The inducer of the deoxynucleoside phosphorylases and deoxyriboaldolase in Escherichia coli

Biochimica Et Biophysica Acta (bba) - Nucleic Acids and Protein Synthesis, 1968

can insert small numbers of nucleotides into their DNA in response to irradiation. This process o... more can insert small numbers of nucleotides into their DNA in response to irradiation. This process of repair replication occurred at 200 erg/mm 2 at which the survival was approx. 25 % (ref. II). HeLa cells consequently seem able to perform repair replication at a dose where a significant proportion of the population survives. In addition these cells perform repair replication after irradiation with high doses of X-rays lz and repair replication may thus be part of a general repair process that operates after various forms of damage to mammalian cell DNA. We have not, however, demonstrated in these experiments that repair replication is causally related to the recovery of irradiated cells. It is only an analogy with bacteria 1,7 that enables us to infer that the insertion of new bases into pre-existing DNA molecules may be part of the recovery process in human cells. It is also obvious that repair replication after high doses of ultraviolet light or X-rays is unsuccessful in leading to cell recovery, since there are then few survivors. We conclude, therefore, that after irradiation most cells may begin to repair their damaged DNA even though all may not survive.

Research paper thumbnail of New prospects for deducing the evolutionary history of metabolic pathways in prokaryotes: Aromatic biosynthesis as a case-in-point

Origins of Life and Evolution of Biospheres, 1988

Metabolic pathways of prokaryotes are more biochemically diverse than is generally recognized. Di... more Metabolic pathways of prokaryotes are more biochemically diverse than is generally recognized. Distinctive biochemical features are shared by phylogenetic clusters. The hierarchical levels of characterstate clustering depends upon evolutionary events which fortuitously became fixed in the genome of a common ancestor. Prokaryotes can now be ordered on a phylogenetic tree. This allows the evolutionary steps that underlie the construction and regulation of appropriately complex biochemical pathways to be traced in an evolutionary progression of prokaryote types that house these pathways. Essentially the approach is to deduce ancestral character states at ever deeper phylogenetic levels, utilizing logical principles of maximum parsimony. The current perspective on the evolution of the biochemical pathway for biosynthesis of aromatic amino acids is developed as a case-in-point model for analyses that should be feasible with many major metabolic systems. Phenylalanine biosynthesis probably arose prior to the addition of branches leading to tyrosine and tryptophan. An evolutionary scenario is developed that begins with non-enzymatic reactions which may have operated in primitive systems, followed by the evolution of an enzymatic system that pre-dated the divergence of major lineages of modern eubacteria (Gram-positive bacteria, Gram-negative purple bacteria, and cyanobacteria).

Research paper thumbnail of Device design, fabrication and characterization of 0.8 μm CMOS technology

An intensive study has been conducted for the development of the MIMOS 0.8 μm CMOS technology. Is... more An intensive study has been conducted for the development of the MIMOS 0.8 μm CMOS technology. Issues such as device design and characterization have been given much consideration. NMOS and PMOS transistors have been designed from basic concepts and using simulation tools such as TSUPREM-4 and MEDICI. Device design constraints such as threshold voltage variation, off-state leakage current and drain-induced barrier lowering (DIBL) effects have been seriously examined to improve device performance. Furthermore, performance criteria such as drive current capability have also been examined. Extraction of device characteristics from silicon has been performed on a test chip. Based on experimental results, numerous I-V plots are presented and the data are discussed in terms of output and transfer characteristics and surface DIBL leakage current

Research paper thumbnail of Conformational studies. Part 6. X-Ray crystal structure of 3,3-dimethoxy-19-norandrosta-5(10),6-dien-17-one: an exception to the diene helicity rule

Journal of The Chemical Society-perkin Transactions 2, 1978

Research paper thumbnail of The Effect of Perioperative Blood Transfusion on Survival in Head and Neck Cancer

Survey of Anesthesiology, 1995

This Head and Neck Intergroup analysis was undertaken to evaluate further previously reported obs... more This Head and Neck Intergroup analysis was undertaken to evaluate further previously reported observations linking blood transfusions, which were given to patients with head and neck cancer, to a worse prognosis. This study population represents those patients registered to the Head and Neck Intergroup Trial 0034 for previously untreated resectable squamous cell carcinoma. Additional transfusion data were obtained by one of us (D.E.S.) on 217 patients and added to the Head and Neck Intergroup data set, providing an opportunity for assessing the impact of survival by other variables. The study group was separated using 13 variables. Analysis demonstrated that transfusion did not significantly decrease the locoregional control (P = .60). Multivariate analysis indicated that T stage (P = .015), N stage (P = .004), treatment received (P = .004), and Karnofsky Performance Scale (P = .031) were the only factors that did significantly influence survival. This multivariate analysis controlling for these variables demonstrated no significant effect on survival for those patients receiving transfusion during surgery (P = .55) or after surgery (P = .39). This study of 217 patients, controlled for other variables, does not demonstrate any significant negative relation between blood transfusions and either locoregional control or survival.

Research paper thumbnail of On the quasi-periodic solutions to the discrete non-linear Schr篓odinger equation

The authors have obtained the quasi-periodic solutions to the discrete non-linear Schrodinger equ... more The authors have obtained the quasi-periodic solutions to the discrete non-linear Schrodinger equation by a variant of a method due to Date and Tanaka (1976). It is shown explicitly that the non-linear field variables at the different lattice points can be determined ...

Research paper thumbnail of The vibratory pattern of ultrasonic files driven piezoelectrically

International Endodontic Journal, 1993

The pattern of oscillation of a Piezon-Master 400 ultrasonic file driven by a piezoelectric trans... more The pattern of oscillation of a Piezon-Master 400 ultrasonic file driven by a piezoelectric transducer was studied in air and on water. In addition, the displacement amplitudes of the files were measured. The findings were compared with those observed with the Cavi-Endo unit reported in another study (Ahmad 1969).It was observed that the file vibrated such that a standing wave was formed on the file and it exhibited points of maximum deflection (antinode) and points of minimum deflection (node) with the largest deflection occurring at the apical end. This pattern of oscillation was similar to that exhibited by the Cavi-Endo file which employed a magnetostrictive transducer. However, the displacement amplitudes were very much higher than those exhibited by the Cavi-Endo. It is considered that the 120° angle of the file holder inherent in the Piezon- Master 400 unit and the more effective power transmission with the piezoelectric transducer may have contributed to the large amplitudes.

Research paper thumbnail of The stable phylogenetic distribution of the recently evolved l -phenylalanine-inhibited isozyme of 3-deoxy- d - arabino -heptulosonate 7-phosphate synthase in enteric bacteria

Current Microbiology, 1989

Escherichia coli and some other enteric bacteria possess three regulatory isozymes of 3-deoxy-d-a... more Escherichia coli and some other enteric bacteria possess three regulatory isozymes of 3-deoxy-d-arabino-heptulosonate 7-phosphate (DAHP) synthase, each of which is inhibited by one aromatic amino acid. Thel-phenylalanine-sensitive isozyme of DAHP synthase has evolved most recently since it is absent in all other members of the Gram-negative cluster that contains enteric bacteria as a subcluster. A comprehensive survey of enteric genera was carried out to determine whether the newly evolved isozyme is a stable, conserved trait. The results obtained show that all the genera of the contemporaryEnterobacteriaceae family possess the recently evolved phenylalanine-sensitive isozyme in addition to the tyrosine-and tryptophansensitive isozymes of DAHP synthase. However, physiological manipulation was usually necessary to derepress the tryptophan-sensitive DAHP synthase in order to demonstrate its presence.

Research paper thumbnail of Reliability modeling for evaluating the contribution of photovoltaics in electric power systems

Solar power is being increasingly utilized in electric power systems. Solar power has a different... more Solar power is being increasingly utilized in electric power systems. Solar power has a different effect on generating system reliability than conventional power sources due to the intermittent nature of the atmospheric conditions at the system location. It is therefore, important to assess the impact of adding photovoltaic (PV) sources to a power system in terms of the reliability contribution of PV in meeting energy demand. This paper uses a probabilistic approach to develop a power output model for a solar park. A reliability model is then developed for a solar energy integrated power system and used in a range of studies to evaluate the reliability and energy contribution of the solar system to meet the overall system demand. The analysis of solar irradiation data, solar power output and the reliability contributions of PV when integrated in a small isolated power system are presented and compared in this paper using solar installation sites located at different latitudes. The results illustrate the ability to conduct a quantitative analysis of reliability and energy contributions of solar power sources located at different latitudes around the world.