Francis Nkrumah - Academia.edu (original) (raw)
Papers by Francis Nkrumah
Transactions of The Royal Society of Tropical Medicine and Hygiene, Jul 1, 2000
The effect of single-dose ivermectin (150-200 micrograms/kg) and albendazole (400 mg) treatment a... more The effect of single-dose ivermectin (150-200 micrograms/kg) and albendazole (400 mg) treatment alone and in combination on Wuchereria bancrofti microfilaraemia, antigenaemia and clinical manifestations was compared 12 months after treatment in a double-blind placebo-controlled field trial carried out in Ghana in 1996-98, to evaluate the potential of these treatments for control. Both ivermectin and combination treatments resulted in pronounced reductions in microfilaraemia among individuals who were microfilaria positive before treatment. Among individuals who were positive for circulating filarial antigen before treatment, antigen levels increased considerably over the 1-year period after treatment in the placebo group, whereas they decreased in the ivermectin and combination groups. However, the post-treatment difference reached statistical significance in neither microfilaraemia nor antigenaemia between the ivermectin and the combination groups. Albendazole treatment alone showed only a minor effect on microfilaraemia and antigenaemia. No effect of the treatments on the incidence of new cases of microfilaraemia or antigenaemia, or on clinical manifestations, was observed. Both ivermectin and combination treatment thus appeared effective for control of W. bancrofti infections, but the difference in efficacy between the 2 treatments after 12 months appeared to be minimal.
Cell, Feb 1, 1979
... References. Cell,Vol.16, 313322,February1979,Copyright01979by MIT EpsteinBarrVirusRNA in Burk... more ... References. Cell,Vol.16, 313322,February1979,Copyright01979by MIT EpsteinBarrVirusRNA in BurkittTumorTissue Timothy Dambaugh,Francis K. Nkrumah ... Miller,G.,Shope,T.,Coope,D.,Waters, L.,Pagano,J.,Born kamm,G. andHenle,W.(1977).Lymphomain cottontopmar ...
Transactions of The Royal Society of Tropical Medicine and Hygiene, Mar 1, 2000
GSK3389404 is a liver-targeted antisense oligonucleotide that inhibits synthesis of hepatitis B s... more GSK3389404 is a liver-targeted antisense oligonucleotide that inhibits synthesis of hepatitis B surface antigen and all other hepatitis B virus proteins. This first-inhuman , randomized, double-blind, phase 1 study assessed the safety and pharmacokinetics of GSK3389404 administered subcutaneously (SC) in healthy subjects. Four single ascending-dose cohorts (10 mg, 30 mg, 60 mg, and 120 mg) and 3 multiple ascending-dose cohorts (30 mg, 60 mg, and 120 mg once weekly for 4 weeks) each comprised 6 subjects randomized to GSK3389404 and 2 subjects randomized to placebo. There were no serious adverse events (AEs) or withdrawals due to AEs. The safety profile did not worsen with repeated dosing. The most frequent treatment-related AEs were injection site reactions (19.0% [n = 8/42], frequency unrelated to dose levels); all were mild (Grade 1) and resolved without dose modification or discontinuation. GSK3389404 administered subcutaneously was readily absorbed with a time to maximum plasma concentration (T max) of 1-4 hours and an elimination half-life of 3-6 hours in plasma. Plasma area under the concentration-time curve (AUC) and maximum observed concentration (C max) were dose-proportional. Dose-normalized plasma AUC from time 0 to infinity averaged 69.9 ng•h/(mL•mg dose) across cohorts, and C max 9.5 ng/(mL•mg dose). Pharmacokinetic profiles and parameters were comparable between single and multiple dosing. No accumulation was observed with once-weekly dosing. The metabolite was undetectable in urine and plasma. In the pooled urine, GSK3389404 was estimated to account for <0.1% of the total dose. In summary, GSK3389404 dosing has been tested up to 120 mg for 4 weeks with an acceptable safety and pharmacokinetic profile, supporting further clinical investigation in patients with chronic hepatitis B.
Human Immunology, Oct 1, 1980
Parasitology International, Aug 1, 2000
Epidemiological studies on urinary schistosomiasis were carried out in eight villages in the Ga a... more Epidemiological studies on urinary schistosomiasis were carried out in eight villages in the Ga and Akuapem South districts in Ghana. Single urine samples were collected from individuals aged 5 years and above between 10.00 and 14.00 h. The samples were examined for the presence of Schistosoma haematobium eggs using a filtration technique. Indirect morbidity was determined as the presence of microhaematuria and proteinuria using reagent strips, and Ž. macrohaematuria was recorded with the naked eye. Out of the study population of 3912 subjects, 2562 65.5% submitted urine samples. The prevalence of Schistosoma haematobium infection ranged between 54.8 and 60.0%. Infection rates increased by age with a peak in the 10᎐19 years category, and decreased with increasing age. Disease Ž. Ž prevalence was higher in males aged 15 years and above in Areas 2 Ntoaso and Sansami Amanfro and 3 Dom. Faase, Papase, Chento and Gidi Kope , whereas it was higher among males aged 10 years and above in Area 1 Ž. Ayikai Doblo and Akramaman. The intensity of infection was highest among children aged 10᎐14 years in most of Ž the villages. More than half of egg-positive children in this age group had heavy infection 100 eggs and above in 10. ml of urine. Although both egg-positive and egg-negative individuals manifested variable degrees of macro-or Ž 2. micro-haematuria, microhaematuria was more prevalent among egg-positives s 918.5, d.f.s 1, P-0.01. The degree of microhaematuria and proteinuria were significantly associated with the intensity of the infection. These results indicate a high transmission of disease in the study area.
Acta Tropica, Feb 1, 1994
Samples of Anopheles gambiae s.1. were collected from eight localities belonging to four of the f... more Samples of Anopheles gambiae s.1. were collected from eight localities belonging to four of the five main ecological strata of Ghana. Analysis of ovarian polytene chromosomes revealed the presence of A. gambiae s.s. in all the sites studied, while A. arabiensis was detected only in the extreme northern locality of Navrongo and A. melas in some southern sites. Anopheles arabiensis showed a degree of inversion polymorphism comparable to the one observed in other West African countries. The analysis of the chromosomal polymorphism of A. gambiae s.s. showed the presence of the FOREST form in the rain forest localities and the SAVANNA form in the coastal savanna sites. The MOPTI form occurred sympatrically with the SAVANNA form in the northernmost locality. The possible influence of the presence of various taxa of the A. gambiae complex and of their intra-specific variants on malaria vectorial system is discussed.
Transactions of The Royal Society of Tropical Medicine and Hygiene, Sep 1, 1998
In areas endemic for Plasmodium falciparum, clinical malaria is believed to be less common in inf... more In areas endemic for Plasmodium falciparum, clinical malaria is believed to be less common in infants than in older children, but specific case definitions have rarely been determined for this age group. As malaria case definitions are known to be both age-and site-specific, assessment of the risk of disease in infancy requires the development of appropriate diagnostic criteria. In southern Ghana, 154 children were recruited at birth and monitored for fever and malaria infection until 2 years of age. Logistic regression was used to model fever risk as a continuous function of parasite density to determine case definitions for the diagnosis of clinical malaria, and to determine age-and season-specific estimates of the fraction of fevers attributable to malaria (AF); 2360 observations were made on 154 children. For fevers defined by a measured temperature >375"C, the estimated population AF was 44% (95% confidence interval 34-53). Estimates of AF varied with age and season. For infants, AF was 51% during the wet season and 22% during the dry season; for children over one year of age, AF was 89% during the wet season and 36% during the dry season.The estimated parasite density threshold for initiation of a febrile episode was 100 parasites per ltL of blood in infants, compared with 3500 parasites per lrL for children over one year of age. Using these case definitions, the incidence of clinical malaria was estimated at 0.09 cases per child-year at risk for children less than 6 months of age, 0.40 for children aged 6-11 months, and 0.69 for children aged 12-23 months. Of 66 cases of clinical malaria, only 3 were observed in children under 5 months of age. We concluded that, although most fevers in infants are not due to malaria, infant clinical malaria may occur at extremely low parasite densities. This may be indicative of a lack of anti-disease immunity in this age group. In southern Ghana, an infant with axillary temperature >37.5"C and parasitaemia >lOO/ltL should be considered to have clinical malaria. Nevertheless, the incidence of clinical malaria is very low in children under 6 months of age, confirming that they are significantly protected horn clinical malaria compared to older children.
British Journal of Haematology, Apr 1, 1997
To study the importance of bone marrow inhibition in the pathogenesis of malarial anaemia, haemat... more To study the importance of bone marrow inhibition in the pathogenesis of malarial anaemia, haematological and parasitological parameters were followed in patients with acute malaria. Three patient categories were studied, severe malarial anaemia (SA), cerebral malaria (CM) and uncomplicated malaria (UM). Red cell distribution width (RDW) was used as a surrogate marker of release of young erythrocytes and reticulocytes. Initially RDW was low in all patients in spite of markedly increased concentrations of erythropoietin (EPO). 3 d after institution of treatment and coinciding with parasite clearance RDW increased dramatically, reaching the highest levels 1–2 weeks later. Although severe anaemia was corrected by blood transfusion during the first 3 d of treatment, the peak RDW correlated significantly with the initial EPO levels. This suggests that Plasmodium falciparum infection causes a rapidly reversible suppression of the bone marrow response to EPO. Furthermore, the inhibition of bone marrow response was a general finding irrespective of initial haemoglobin levels suggesting that the severity of anaemia depends upon the degree of peripheral erythrocyte destruction in patients with suppressed bone marrow response to EPO.
Proceedings of SPIE, Apr 6, 2007
Fatigue crack growth in a lap joint specimen extracted from a retired aircraft fuselage was monit... more Fatigue crack growth in a lap joint specimen extracted from a retired aircraft fuselage was monitored using bonded continuous acoustic emission sensors. The specimen lasted nearly 350,000 cycles of tension-tension cyclic loading. During this period a large number of acoustic emission signals were collected. Two distinct classes of events were observed during this test. The first group of events consist of low amplitude, long rise time and long duration events which could be attributed to fretting between various surfaces. The second group of events had short rise time and short duration and is thought to be from fatigue cracks. This interpretation is based on the waveform characteristics observed during this test and patterns seen in acoustic emission signals from known fatigue cracks in previous studies. Based on this assumption the crack growth process appear to have initiated after 200,000 cycles of fatigue load and accelerated during the final 20,000 cycles. The final fracture of the specimen occurred in the grip area and indications of this impending failure were evident in the acoustic emission data. In addition, acoustic emission data also suggest fatigue crack growth in an area inaccessible for visual examination.
Proceedings of SPIE, May 19, 2005
ABSTRACT Recently a new structural health monitoring system that employs a "continuous a... more ABSTRACT Recently a new structural health monitoring system that employs a "continuous acoustic emission sensor" and an embeddable local processor has been proposed. The development of a processor that integrates the functions of signal conditioning, feature extraction, data storage, and digital communication is currently in progress. A prototype of this local processor chip has been developed. The integration of a continuous sensor with an embeddable local processor can potentially enable an inexpensive method of monitoring large and complex structures using acoustic emission signals. Such a system can reduce the cost, complexity, and weight of the required instrumentation. It is potentially scalable to large and complex structures and could be integrated into the structural material. The success of the acoustic emission based structural health monitoring technique depends on its ability to discriminate between valid acoustic emission signals and ambient noise. In addition, the technique should be able to identify the damage mode from the acoustic emission waveforms. This paper focuses on the use of acoustic emission technique for the identification of failure modes in composite materials. Three types of failure modes in glass fabric epoxy composite laminates are considered. These are two types of delamination growth and transverse crack growth. Wavelet analysis is used to extract time frequency information from the acoustic emission signals. Different features of the waveform including the frequency components, Symmetric and Antisymmetric components, and amplitudes are used to classify the signals and identify the failure modes. The laboratory tests indicate that it is possible to distinguish the individual failure modes under consideration. It was also possible to filter out spurious AE signals that originate from extraneous sources using an appropriate choice of sensors and frequency components. An attempt is made to relate the rate of damage growth with the detected acoustic emission signal parameters.
Proceedings of SPIE, May 17, 2005
ABSTRACT This paper discusses a proof test procedure for estimating and extending the fatigue lif... more ABSTRACT This paper discusses a proof test procedure for estimating and extending the fatigue life of composite coupons. The estimates were based on the acoustic emission data collected during the described proof test procedure. A group of coupon specimens that included both undamaged as well as damaged ones were tested to verify the ability to estimate the fatigue durability. For majority of the specimens tested the fatigue life of the coupons is inversely proportional to the cumulative AE energy collected during the proof test procedure. Based on the trend that was established, a new group of specimens AE based proof test was performed and using the acoustic emission response, the life was estimated. If one could estimate the fatigue life, it would be possible to identify those specimens, which are likely to fail prematurely. For such specimens it may be possible to extend the fatigue life by appropriate reduction in the cyclic load amplitude. This hypothesis was tested on the last group of specimens. The results obtained during the life extension phase actually show that it is possible to identify the specimens, which are likely to have short life and extend the fatigue life by subjecting them to less demanding load history.
Parasitology International, Aug 1, 1998
Journal of Tropical Pediatrics, Aug 1, 1993
Coconut milk and kenkey water (a maize gruel) which are traditionally used for the treatment of d... more Coconut milk and kenkey water (a maize gruel) which are traditionally used for the treatment of diarrhoea in Ghana, were analysed to ascertain their suitability for use in rehydration. The pH, carbohydrate, and electrolyte levels of the food fluids were compared to the recommended UNICEF/WHO ORS to ascertain if these are within physiologically acceptable ranges for the treatment and prevention of dehydration in children with diarrhoea. The carbohydrate and electrolyte levels of kenkey water were found to be comparable to UNICEF/WHO ORS and is suitable for use in rehydration. Coconut milk has the advantages of being fresh, sterile and readily available in most Ghanaian communities. However, use of coconut milk for rehydration cannot be recommended on the basis of its glucose and electrolyte composition.
Parasitology International, Aug 1, 1998
Malaria Journal, Apr 11, 2015
Background: Haem oxygenase-1 (HO-1) catabolizes haem and has both cytotoxic and cytoprotective ef... more Background: Haem oxygenase-1 (HO-1) catabolizes haem and has both cytotoxic and cytoprotective effects. Polymorphisms in the promoter of the Haem oxygenase-1 (HMOX1) gene encoding HO-1 have been associated with several diseases including severe malaria. The objective of this study was to determine the allele and genotype frequencies of two single nucleotide polymorphisms; A(−413)T and G(−1135)A, and a (GT) n repeat length polymorphism in the HMOX1 promoter in paediatric malaria patients and controls to determine possible associations with malaria disease severity. Methods: Study participants were Ghanaian children (n=296) admitted to the emergency room at the
Transactions of The Royal Society of Tropical Medicine and Hygiene, Jul 1, 2000
The effect of single-dose ivermectin (150-200 micrograms/kg) and albendazole (400 mg) treatment a... more The effect of single-dose ivermectin (150-200 micrograms/kg) and albendazole (400 mg) treatment alone and in combination on Wuchereria bancrofti microfilaraemia, antigenaemia and clinical manifestations was compared 12 months after treatment in a double-blind placebo-controlled field trial carried out in Ghana in 1996-98, to evaluate the potential of these treatments for control. Both ivermectin and combination treatments resulted in pronounced reductions in microfilaraemia among individuals who were microfilaria positive before treatment. Among individuals who were positive for circulating filarial antigen before treatment, antigen levels increased considerably over the 1-year period after treatment in the placebo group, whereas they decreased in the ivermectin and combination groups. However, the post-treatment difference reached statistical significance in neither microfilaraemia nor antigenaemia between the ivermectin and the combination groups. Albendazole treatment alone showed only a minor effect on microfilaraemia and antigenaemia. No effect of the treatments on the incidence of new cases of microfilaraemia or antigenaemia, or on clinical manifestations, was observed. Both ivermectin and combination treatment thus appeared effective for control of W. bancrofti infections, but the difference in efficacy between the 2 treatments after 12 months appeared to be minimal.
Cell, Feb 1, 1979
... References. Cell,Vol.16, 313322,February1979,Copyright01979by MIT EpsteinBarrVirusRNA in Burk... more ... References. Cell,Vol.16, 313322,February1979,Copyright01979by MIT EpsteinBarrVirusRNA in BurkittTumorTissue Timothy Dambaugh,Francis K. Nkrumah ... Miller,G.,Shope,T.,Coope,D.,Waters, L.,Pagano,J.,Born kamm,G. andHenle,W.(1977).Lymphomain cottontopmar ...
Transactions of The Royal Society of Tropical Medicine and Hygiene, Mar 1, 2000
GSK3389404 is a liver-targeted antisense oligonucleotide that inhibits synthesis of hepatitis B s... more GSK3389404 is a liver-targeted antisense oligonucleotide that inhibits synthesis of hepatitis B surface antigen and all other hepatitis B virus proteins. This first-inhuman , randomized, double-blind, phase 1 study assessed the safety and pharmacokinetics of GSK3389404 administered subcutaneously (SC) in healthy subjects. Four single ascending-dose cohorts (10 mg, 30 mg, 60 mg, and 120 mg) and 3 multiple ascending-dose cohorts (30 mg, 60 mg, and 120 mg once weekly for 4 weeks) each comprised 6 subjects randomized to GSK3389404 and 2 subjects randomized to placebo. There were no serious adverse events (AEs) or withdrawals due to AEs. The safety profile did not worsen with repeated dosing. The most frequent treatment-related AEs were injection site reactions (19.0% [n = 8/42], frequency unrelated to dose levels); all were mild (Grade 1) and resolved without dose modification or discontinuation. GSK3389404 administered subcutaneously was readily absorbed with a time to maximum plasma concentration (T max) of 1-4 hours and an elimination half-life of 3-6 hours in plasma. Plasma area under the concentration-time curve (AUC) and maximum observed concentration (C max) were dose-proportional. Dose-normalized plasma AUC from time 0 to infinity averaged 69.9 ng•h/(mL•mg dose) across cohorts, and C max 9.5 ng/(mL•mg dose). Pharmacokinetic profiles and parameters were comparable between single and multiple dosing. No accumulation was observed with once-weekly dosing. The metabolite was undetectable in urine and plasma. In the pooled urine, GSK3389404 was estimated to account for <0.1% of the total dose. In summary, GSK3389404 dosing has been tested up to 120 mg for 4 weeks with an acceptable safety and pharmacokinetic profile, supporting further clinical investigation in patients with chronic hepatitis B.
Human Immunology, Oct 1, 1980
Parasitology International, Aug 1, 2000
Epidemiological studies on urinary schistosomiasis were carried out in eight villages in the Ga a... more Epidemiological studies on urinary schistosomiasis were carried out in eight villages in the Ga and Akuapem South districts in Ghana. Single urine samples were collected from individuals aged 5 years and above between 10.00 and 14.00 h. The samples were examined for the presence of Schistosoma haematobium eggs using a filtration technique. Indirect morbidity was determined as the presence of microhaematuria and proteinuria using reagent strips, and Ž. macrohaematuria was recorded with the naked eye. Out of the study population of 3912 subjects, 2562 65.5% submitted urine samples. The prevalence of Schistosoma haematobium infection ranged between 54.8 and 60.0%. Infection rates increased by age with a peak in the 10᎐19 years category, and decreased with increasing age. Disease Ž. Ž prevalence was higher in males aged 15 years and above in Areas 2 Ntoaso and Sansami Amanfro and 3 Dom. Faase, Papase, Chento and Gidi Kope , whereas it was higher among males aged 10 years and above in Area 1 Ž. Ayikai Doblo and Akramaman. The intensity of infection was highest among children aged 10᎐14 years in most of Ž the villages. More than half of egg-positive children in this age group had heavy infection 100 eggs and above in 10. ml of urine. Although both egg-positive and egg-negative individuals manifested variable degrees of macro-or Ž 2. micro-haematuria, microhaematuria was more prevalent among egg-positives s 918.5, d.f.s 1, P-0.01. The degree of microhaematuria and proteinuria were significantly associated with the intensity of the infection. These results indicate a high transmission of disease in the study area.
Acta Tropica, Feb 1, 1994
Samples of Anopheles gambiae s.1. were collected from eight localities belonging to four of the f... more Samples of Anopheles gambiae s.1. were collected from eight localities belonging to four of the five main ecological strata of Ghana. Analysis of ovarian polytene chromosomes revealed the presence of A. gambiae s.s. in all the sites studied, while A. arabiensis was detected only in the extreme northern locality of Navrongo and A. melas in some southern sites. Anopheles arabiensis showed a degree of inversion polymorphism comparable to the one observed in other West African countries. The analysis of the chromosomal polymorphism of A. gambiae s.s. showed the presence of the FOREST form in the rain forest localities and the SAVANNA form in the coastal savanna sites. The MOPTI form occurred sympatrically with the SAVANNA form in the northernmost locality. The possible influence of the presence of various taxa of the A. gambiae complex and of their intra-specific variants on malaria vectorial system is discussed.
Transactions of The Royal Society of Tropical Medicine and Hygiene, Sep 1, 1998
In areas endemic for Plasmodium falciparum, clinical malaria is believed to be less common in inf... more In areas endemic for Plasmodium falciparum, clinical malaria is believed to be less common in infants than in older children, but specific case definitions have rarely been determined for this age group. As malaria case definitions are known to be both age-and site-specific, assessment of the risk of disease in infancy requires the development of appropriate diagnostic criteria. In southern Ghana, 154 children were recruited at birth and monitored for fever and malaria infection until 2 years of age. Logistic regression was used to model fever risk as a continuous function of parasite density to determine case definitions for the diagnosis of clinical malaria, and to determine age-and season-specific estimates of the fraction of fevers attributable to malaria (AF); 2360 observations were made on 154 children. For fevers defined by a measured temperature >375"C, the estimated population AF was 44% (95% confidence interval 34-53). Estimates of AF varied with age and season. For infants, AF was 51% during the wet season and 22% during the dry season; for children over one year of age, AF was 89% during the wet season and 36% during the dry season.The estimated parasite density threshold for initiation of a febrile episode was 100 parasites per ltL of blood in infants, compared with 3500 parasites per lrL for children over one year of age. Using these case definitions, the incidence of clinical malaria was estimated at 0.09 cases per child-year at risk for children less than 6 months of age, 0.40 for children aged 6-11 months, and 0.69 for children aged 12-23 months. Of 66 cases of clinical malaria, only 3 were observed in children under 5 months of age. We concluded that, although most fevers in infants are not due to malaria, infant clinical malaria may occur at extremely low parasite densities. This may be indicative of a lack of anti-disease immunity in this age group. In southern Ghana, an infant with axillary temperature >37.5"C and parasitaemia >lOO/ltL should be considered to have clinical malaria. Nevertheless, the incidence of clinical malaria is very low in children under 6 months of age, confirming that they are significantly protected horn clinical malaria compared to older children.
British Journal of Haematology, Apr 1, 1997
To study the importance of bone marrow inhibition in the pathogenesis of malarial anaemia, haemat... more To study the importance of bone marrow inhibition in the pathogenesis of malarial anaemia, haematological and parasitological parameters were followed in patients with acute malaria. Three patient categories were studied, severe malarial anaemia (SA), cerebral malaria (CM) and uncomplicated malaria (UM). Red cell distribution width (RDW) was used as a surrogate marker of release of young erythrocytes and reticulocytes. Initially RDW was low in all patients in spite of markedly increased concentrations of erythropoietin (EPO). 3 d after institution of treatment and coinciding with parasite clearance RDW increased dramatically, reaching the highest levels 1–2 weeks later. Although severe anaemia was corrected by blood transfusion during the first 3 d of treatment, the peak RDW correlated significantly with the initial EPO levels. This suggests that Plasmodium falciparum infection causes a rapidly reversible suppression of the bone marrow response to EPO. Furthermore, the inhibition of bone marrow response was a general finding irrespective of initial haemoglobin levels suggesting that the severity of anaemia depends upon the degree of peripheral erythrocyte destruction in patients with suppressed bone marrow response to EPO.
Proceedings of SPIE, Apr 6, 2007
Fatigue crack growth in a lap joint specimen extracted from a retired aircraft fuselage was monit... more Fatigue crack growth in a lap joint specimen extracted from a retired aircraft fuselage was monitored using bonded continuous acoustic emission sensors. The specimen lasted nearly 350,000 cycles of tension-tension cyclic loading. During this period a large number of acoustic emission signals were collected. Two distinct classes of events were observed during this test. The first group of events consist of low amplitude, long rise time and long duration events which could be attributed to fretting between various surfaces. The second group of events had short rise time and short duration and is thought to be from fatigue cracks. This interpretation is based on the waveform characteristics observed during this test and patterns seen in acoustic emission signals from known fatigue cracks in previous studies. Based on this assumption the crack growth process appear to have initiated after 200,000 cycles of fatigue load and accelerated during the final 20,000 cycles. The final fracture of the specimen occurred in the grip area and indications of this impending failure were evident in the acoustic emission data. In addition, acoustic emission data also suggest fatigue crack growth in an area inaccessible for visual examination.
Proceedings of SPIE, May 19, 2005
ABSTRACT Recently a new structural health monitoring system that employs a "continuous a... more ABSTRACT Recently a new structural health monitoring system that employs a "continuous acoustic emission sensor" and an embeddable local processor has been proposed. The development of a processor that integrates the functions of signal conditioning, feature extraction, data storage, and digital communication is currently in progress. A prototype of this local processor chip has been developed. The integration of a continuous sensor with an embeddable local processor can potentially enable an inexpensive method of monitoring large and complex structures using acoustic emission signals. Such a system can reduce the cost, complexity, and weight of the required instrumentation. It is potentially scalable to large and complex structures and could be integrated into the structural material. The success of the acoustic emission based structural health monitoring technique depends on its ability to discriminate between valid acoustic emission signals and ambient noise. In addition, the technique should be able to identify the damage mode from the acoustic emission waveforms. This paper focuses on the use of acoustic emission technique for the identification of failure modes in composite materials. Three types of failure modes in glass fabric epoxy composite laminates are considered. These are two types of delamination growth and transverse crack growth. Wavelet analysis is used to extract time frequency information from the acoustic emission signals. Different features of the waveform including the frequency components, Symmetric and Antisymmetric components, and amplitudes are used to classify the signals and identify the failure modes. The laboratory tests indicate that it is possible to distinguish the individual failure modes under consideration. It was also possible to filter out spurious AE signals that originate from extraneous sources using an appropriate choice of sensors and frequency components. An attempt is made to relate the rate of damage growth with the detected acoustic emission signal parameters.
Proceedings of SPIE, May 17, 2005
ABSTRACT This paper discusses a proof test procedure for estimating and extending the fatigue lif... more ABSTRACT This paper discusses a proof test procedure for estimating and extending the fatigue life of composite coupons. The estimates were based on the acoustic emission data collected during the described proof test procedure. A group of coupon specimens that included both undamaged as well as damaged ones were tested to verify the ability to estimate the fatigue durability. For majority of the specimens tested the fatigue life of the coupons is inversely proportional to the cumulative AE energy collected during the proof test procedure. Based on the trend that was established, a new group of specimens AE based proof test was performed and using the acoustic emission response, the life was estimated. If one could estimate the fatigue life, it would be possible to identify those specimens, which are likely to fail prematurely. For such specimens it may be possible to extend the fatigue life by appropriate reduction in the cyclic load amplitude. This hypothesis was tested on the last group of specimens. The results obtained during the life extension phase actually show that it is possible to identify the specimens, which are likely to have short life and extend the fatigue life by subjecting them to less demanding load history.
Parasitology International, Aug 1, 1998
Journal of Tropical Pediatrics, Aug 1, 1993
Coconut milk and kenkey water (a maize gruel) which are traditionally used for the treatment of d... more Coconut milk and kenkey water (a maize gruel) which are traditionally used for the treatment of diarrhoea in Ghana, were analysed to ascertain their suitability for use in rehydration. The pH, carbohydrate, and electrolyte levels of the food fluids were compared to the recommended UNICEF/WHO ORS to ascertain if these are within physiologically acceptable ranges for the treatment and prevention of dehydration in children with diarrhoea. The carbohydrate and electrolyte levels of kenkey water were found to be comparable to UNICEF/WHO ORS and is suitable for use in rehydration. Coconut milk has the advantages of being fresh, sterile and readily available in most Ghanaian communities. However, use of coconut milk for rehydration cannot be recommended on the basis of its glucose and electrolyte composition.
Parasitology International, Aug 1, 1998
Malaria Journal, Apr 11, 2015
Background: Haem oxygenase-1 (HO-1) catabolizes haem and has both cytotoxic and cytoprotective ef... more Background: Haem oxygenase-1 (HO-1) catabolizes haem and has both cytotoxic and cytoprotective effects. Polymorphisms in the promoter of the Haem oxygenase-1 (HMOX1) gene encoding HO-1 have been associated with several diseases including severe malaria. The objective of this study was to determine the allele and genotype frequencies of two single nucleotide polymorphisms; A(−413)T and G(−1135)A, and a (GT) n repeat length polymorphism in the HMOX1 promoter in paediatric malaria patients and controls to determine possible associations with malaria disease severity. Methods: Study participants were Ghanaian children (n=296) admitted to the emergency room at the