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Repeated Addition (repeated + addition)
Selected AbstractsSearch-based refactoring: an empirical studyJOURNAL OF SOFTWARE MAINTENANCE AND EVOLUTION: RESEARCH AND PRACTICE, Issue 5 2008Mark O'Keeffe Abstract Object-oriented systems that undergo repeated addition of functionality commonly suffer a loss of quality in their underlying design. This problem must often be remedied in a costly refactoring phase before further maintenance programming can take place. Recently search-based approaches to automating the task of software refactoring, based on the concept of treating object-oriented design as a combinatorial optimization problem, have been proposed. However, because search-based refactoring is a novel approach it is yet to be established as to which search techniques are most suitable for the task. In this paper we report the results of an empirical comparison of simulated annealing (SA), genetic algorithms (GAs) and multiple ascent hill-climbing (HCM) in search-based refactoring. A prototype automated refactoring tool is employed, capable of making radical changes to the design of an existing program in order that it conforms more closely to a contemporary quality model. Results show HCM to outperform both SA and GA over a set of five input programs. Copyright © 2008 John Wiley & Sons, Ltd. [source] Kinetic Simulations of Reversible Chain Transfer Catalyzed Polymerization (RTCP): Guidelines to Optimum Molecular Weight ControlMACROMOLECULAR THEORY AND SIMULATIONS, Issue 1 2010Philipp Vana Abstract Kinetic simulations of reversible chain transfer catalyzed polymerization (RTCP) were performed using the program package Predici. Mimicking the RTCP of styrene in bulk at 80,°C, the full molecular weight distributions, the polydispersities of resulting polymer and the time evolutions of monomer conversion and participating species were simulated. The influence of the kinetic coefficients governing the RTCP equilibrium , specifically, the rate coefficients of activation, ka, and deactivation, kda , on the controlled polymerization behavior was probed in detail by varying their respective simulation input values over five orders of magnitude. It was found that optimum results for molecular weight control are obtained for K,=,ka/kda in the range 1 to 10 and with ka and kda being of the order of 106 L,·,mol,1,·,s,1 or above. The influence of degenerative chain transfer on the process was found to be significant only in poorly controlled systems, but is small in well-controlled RTCP. Based on the finding that the catalyst is depleting during the polymerization due to cross-termination, guidelines for obtaining high molecular weight material via repeated addition of catalyst were developed. [source] Nitric oxide scavenging and detoxification by the Mycobacterium tuberculosis haemoglobin, HbN in Escherichia coliMOLECULAR MICROBIOLOGY, Issue 5 2002Ranjana Pathania Summary Nitric oxide (NO), generated in large amounts within the macrophages, controls and restricts the growth of internalized human pathogen, Mycobacterium tuberculosis H37Rv. The molecular mechanism by which tubercle bacilli survive within macrophages is currently of intense interest. In this work, we have demonstrated that dimeric haemoglobin, HbN, from M. tuberculosis exhibits distinct nitric oxide dioxygenase (NOD) activity and protects growth and cellular respiration of heterologous hosts, Escherichia coli and Mycobacterium smegmatis, from the toxic effect of exogenous NO and the NO-releasing compounds. A flavohaemoglobin (HMP)-deficient mutant of E. coli, unable to metabolize NO, acquired an oxygen-dependent NO consumption activity in the presence of HbN. On the basis of cellular haem content, the specific NOD activity of HbN was nearly 35-fold higher than the single-domain Vitreoscilla haemoglobin (VHb) but was sevenfold lower than the two-domain flavohaemoglobin. HbN-dependent NO consumption was sustained with repeated addition of NO, demonstrating that HbN is catalytically reduced within E. coli. Aerobic growth and respiration of a flavohaemoglobin (HMP) mutant of E. coli was inhibited in the presence of exogenous NO but remained insensitive to NO inhibition when these cells produced HbN, VHb or flavohaemoglobin. M. smegmatis, carrying a native HbN very similar to M. tuberculosis HbN, exhibited a 7.5-fold increase in NO uptake when exposed to gaseous NO, suggesting NO-induced NOD activity in these cells. In addition, expression of plasmid-encoded HbN of M. tuberculosis in M. smegmatis resulted in 100-fold higher NO consumption activity than the isogenic control cells. These results provide strong experimental evidence in support of NO scavenging and detoxification function for the M. tuberculosis HbN. The catalytic NO scavenging by HbN may be highly advantageous for the survival of tubercle bacilli during infection and pathogenesis. [source] Simultaneous analysis of physiological and electrical output changes in an operating microbial fuel cell with Shewanella oneidensis,BIOTECHNOLOGY & BIOENGINEERING, Issue 3 2009Justin C. Biffinger Abstract Changes in metabolism and cellular physiology of facultative anaerobes during oxygen exposure can be substantial, but little is known about how these changes connect with electrical current output from an operating microbial fuel cell (MFC). A high-throughput voltage based screening assay (VBSA) was used to correlate current output from a MFC containing Shewanella oneidensis MR-1 to carbon source (glucose or lactate) utilization, culture conditions, and biofilm coverage over 250 h. Lactate induced an immediate current response from S. oneidensis MR-1, with both air-exposed and anaerobic anodes throughout the duration of the experiments. Glucose was initially utilized for current output by MR-1 when cultured and maintained in the presence of air. However, after repeated additions of glucose, the current output from the MFC decreased substantially while viable planktonic cell counts and biofilm coverage remained constant suggesting that extracellular electron transfer pathways were being inhibited. Shewanella maintained under an anaerobic atmosphere did not utilize glucose consistent with literature precedents. Operation of the VBSA permitted data collection from nine simultaneous S. oneidensis MR-1 MFC experiments in which each experiment was able to demonstrate organic carbon source utilization and oxygen dependent biofilm formation on a carbon electrode. These data provide the first direct evidence of complex cellular responses to electron donor and oxygen tension by Shewanella in an operating MFC at select time points. Biotechnol. Bioeng. 2009;103: 524,531. Published 2009 Wiley Periodicals, Inc. [source] Prolonging Cell-Free Protein Synthesis by Selective Reagent AdditionsBIOTECHNOLOGY PROGRESS, Issue 3 2000Dong-Myung Kim Factors causing the early cessation of protein synthesis have been studied in a cell-free system from Escherichia coli. We discovered that phosphoenol pyruvate (PEP), the secondary energy source for ATP regeneration, and several amino acids are rapidly degraded during the cell-free protein synthesis reaction. The degradation of such compounds takes place even in the absence of protein synthesis. This degradation severely reduces the capacity for protein synthesis. The lost potency was completely recovered when the reaction mixture was supplied with additional PEP and amino acids. Of the 20 amino acids, only arginine, cysteine, and tryptophan were required to restore system activity. Through repeated additions of PEP, arginine, cysteine,and tryptophan, the duration of protein synthesis was greatly extended. In this fed-batch reaction, after a 2 h incubation, the level of cell-free synthesized chloramphenicol acetyl transferase (CAT) reached 350 ,g/mL, which is 3.5 times the yield of the batch reaction. Addition of fresh magnesium further extended the protein synthesis. As a result, through coordinated additions of PEP, arginine, cysteine, tryptophan, and magnesium, the final concentration of cell-free synthesized CAT increased more than 4-fold compared to a batch reaction. SDS-PAGE analysis of such a fed-batch reaction produced an obvious band of CAT upon Coomassie Blue staining. [source] | ||||||||||