RESUMO
In order to reduce Gaussian noise, this paper proposes a method via taking the average of the upper and lower envelopes generated by capturing the high and low peaks of the input signal. The designed fast response filter has no cut-off frequency, so the high order harmonics of the actual signal remain unchanged. Therefore, it can immediately respond to the changes of input signal and retain the integrity of the actual signal. In addition, it has only a small phase delay. The slew rate, phase delay and frequency response can be confirmed from the simulation results of Multisim 13.0. The filter outlined in this article can retain the high order harmonics of the original signal, achieving a slew rate of 6.34 V/µs and an almost zero phase difference. When using our filter to physically test the input signal with a noise level of 3 Vp-p Gaussian noise, a reduced noise signal of 120 mVp-p is obtained. The noise can be suppressed by up to 4% of the raw signal.
RESUMO
BACKGROUND: Escherichia coli is a widely studied prokaryotic system. A recent study had demonstrated that reduced growth of E. coli after extended culture in Luria-Bertani broth is a result of depletion of fermentable sugars but able to sustain extended cell culture due to the presence of amino acids, which can be utilized as a carbon source. However, this had not been demonstrated in other media. The study aimed to determine the growth and viability of E. coli ATCC 8739 in 3 different media, Nutrient Broth (NB), Brain Heart Infusion (BHI) and Luria-Bertani Broth (LB) over 11 weeks. METHODS: Growth of E. coli ATCC 8739 was determined by optical density. Viability was determined by serial dilution/spread-plate enumeration. After 11 weeks, the media were exhausted by repeated culture. Glucose was added to the exhausted media to determine whether glucose is the growth-limiting factor. RESULTS: Our results showed that cell density in all 3 media increased to about 1 × 10(9) cells/ml by the end of week 1, from the inoculation density of 2.67 × 10(5) cells/ml, peaked at about 1 × 10(13) cells/ml at week 4, before declining to about 5 × 10(7) cells/ml at week 7. Cell density is highly correlated to genomic DNA content (r(2) = 0.93) but poorly correlated to optical density (r(2)< 0.2). Our results also showed that the spent media were able to support further growth after glucose-supplementation. CONCLUSION: NB, LB and BHI are able to support extended periods of culture and glucose depletion is the likely reason for declining cell growth.
RESUMO
Escherichia coli is commonly found in intestine of human, and any changes in their adaptation or evolution may affect the human body. The relationship between E. coli and food additives is less studied as compared to antibiotics. E. coli within our human gut are consistently interacting with the food additives; thus, it is important to investigate this relationship. In this paper, we observed the evolution of E. coli cultured in different concentration of food additives (sodium chloride, benzoic acid, and monosodium glutamate), singly or in combination, over 70 passages. Adaptability over time was estimated by generation time and cell density at stationary phase. Polymerase chain reaction (PCR)/restriction fragments length polymorphism (RFLP) using 3 primers and restriction endonucleases, each was used to characterize adaptation/evolution at genomic level. The amplification and digestion profiles were tabulated and analyzed by Nei-Li dissimilarity index. Our results demonstrate that E. coli in every treatment had adapted over 465 generations. The types of stress were discovered to be different even though different concentrations of same additives were used. However, RFLP shows a convergence of genetic distances, suggesting the presence of global stress response. In addition, monosodium glutamate may be a nutrient source and support acid resistance in E. coli.
