Abstruct-Vehicle following and its effects on traffic flow has been an active area of research. Human driving involves reaction times, delays, and human errors that affect traffic flow adversely. One way to eliminate human errors and delays in vehicle following is to replace the human driver with a computer control system and sensors.The purpose of this paper is to develop an autonomous intelligent cruise control (AICC) system for automatic vehicle following, examine its effect on traffic flow, and compare its performance with that of the human driver models. The AICC system developed is not cooperative; Le., it does not exchange information with other vehicles and yet is not susceptible to oscillations and "slinky" effects. The elimination of the "slinky" effect is achieved by using a safety distance separation rule that is proportional to the vehicle velocity (constant time headway) and by designing the control system appropriately. The performance of the AICC system is found to be superior to that of the human driver models considered. It has a faster and better transient response that leads to a much smoother and faster traffic flow. Computer simulations are used to study the performance of the proposed AICC system and analyze vehicle following in a single lane, without passing, under manual and automatic control. In addition, several emergency situations that include emergency stopping and cut-in cases were simulated. The simulation results demonstrate the effectiveness of the AICC system and its potentially beneficial effects on traffic flow.

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The “altered Schaedler flora” (ASF) was developed for colonizing germfree rodents with a standardized microbiota. The purpose of this study was to identify each of the eight ASF strains by 16S rRNA sequence analysis. Three strains were previously identified asLactobacillus acidophilus (strain ASF 360),Lactobacillus salivarius (strain ASF 361), andBacteroides distasonis (strain ASF 519) based on phenotypic criteria. 16S rRNA analysis indicated that each of the strains differed from its presumptive identity. The 16S rRNA sequence of strain ASF 361 is essentially identical to the 16S rRNA sequences of the type strains of Lactobacillus murinis and Lactobacillus animalis (both isolated from mice), and all of these strains probably belong to a single species. Strain ASF 360 is a novel lactobacillus that clusters with L. acidophilus andLactobacillus lactis. Strain ASF 519 falls into an unnamed genus containing [Bacteroides] distasonis, [Bacteroides] merdae, [Bacteroides] forsythus, and CDC group DF-3. This unnamed genus is in theCytophaga-Flavobacterium-Bacteroides phylum and is most closely related to the genus Porphyromonas. The spiral-shaped strain, strain ASF 457, is in the Flexistipesphylum and exhibits sequence identity with rodent isolates of Robertson. The remaining four ASF strains, which are extremely oxygen-sensitive fusiform bacteria, group phylogenetically with the low-G+C-content gram-positive bacteria (Firmicutes,Bacillus-Clostridium group). ASF 356, ASF 492, and ASF 502 fall into Clostridium cluster XIV of Collins et al. Morphologically, ASF 492 resembles members of this cluster,Roseburia cecicola, and Eubacterium plexicaudatum. The 16S rRNA sequence of ASF 492 is identical to that of E. plexicaudatum. Since the type strain and other viable original isolates of E. plexicaudatum have been lost, strain ASF 492 is a candidate for a neotype strain. Strain ASF 500 branches deeply in the low-G+C-content gram-positive phylogenetic tree but is not closely related to any organisms whose 16S rRNA sequences are currently in the GenBank database. The 16S rRNA sequence information determined in the present study should allow rapid identification of ASF strains and should permit detailed analysis of the interactions of ASF organisms during development of intestinal disease in mice that are coinfected with a variety of pathogenic microorganisms.

Microbiologically influenced corrosion (MC) of steel has been attributed to the activity of biofilms that include anaerobic microorganisms such as iron-respiring bacteria, yet the mechanisms by which these organisms influence corrosion have been unclear. To study this process, we generated mutants of the iron-respiring bacterium Shewanella oneidensis strain MR-1 that were defective in biofilm formation and/or iron reduction. Electrochemical impedance spectroscopy was used to determine changes in the corrosion rate and corrosion potential as a function of time for these mutants in comparison to the wild type. Counter to prevailing theories of MC, our results indicate that biofilms comprising iron-respiring bacteria may reduce rather than accelerate the corrosion rate of steel. Corrosion inhibition appears to be due to reduction of ferric ions to ferrous ions and increased consumption of oxygen, both of which are direct consequences of microbial respiration.Microbes perform oxidation and reduction reactions that profoundly affect the stability of minerals in the environment, with consequences ranging from the promotion of acid mine drainage (19) to the bioremediation of organically polluted groundwater (7). In industrial settings, perhaps the most familiar metal transformation is the rusting of iron and steel, and microbes are thought to play an important role in this process (1). Microbiologically influenced corrosion (MC) can be a serious industrial problem and affects diverse processes ranging from water distribution in cast iron mains and sewers to transport of natural gas in steel pipelines. It has been estimated that for the United States oil industry alone, MC causes hundreds of millions of dollars in damage to the production, transport, and storage of oil every year (3). Yet the mechanistic basis of MC, despite its importance, has remained unclear.A prevailing theory of MC holds that biofilms promote corrosion by inducing the formation of corrosion cells. This is thought to occur as a consequence of aerobic respiratory activity within biofilms that leads to the establishment of local cathodic and anodic regions on the steel surface, which promotes electron flow (6). Recent evidence, however, suggests that aerobically respiring bacteria may protect steel from corrosion over the long term (5), which raises questions regarding the extent to which aerobic respiration contributes to MC. Other explanations for MC include corrosion promotion by anaerobes such as sulfate-reducing and iron-reducing bacteria. Current theories maintain that sulfate reducers promote corrosion by consuming hydrogen and inducing ferrous sulfide formation and that iron reducers promote corrosion by reductively dissolving the protective ferric oxide coating that forms on the steel surface (6, 17). Biofilm communities that develop on the surfaces of corroding materials in natural environments are heterogeneous, and therefore there is significant uncertainty concerning how these communities affect corrosion in any given environment.Our goal...

A bacterial toxin that causes progressive distension and death of Chinese hamster ovary (CHO) cells and HeLa cells, termed cytolethal distending toxin (Cdt), has been identi®ed in several diarrhoeagenic bacteria, including Campylobacter spp. (C. jejuni and C. coli), some pathogenic strains of Escherichia coli and Shigella spp. Genes encoding this toxin were identi®ed as a cluster of three adjacent genes cdtA, cdtB and cdtC. Homologues of cdtB from ®ve species of enterohepatic helicobacters ( Helicobacter hepaticus, H. bilis, H. canis and two novel Helicobacter spp. isolated from mice and woodchuck, respectively) were identi®ed by means of degenerative PCR primers, cloned and sequenced. The similarities of these partial cdtB nucleotide sequences from these Helicobacter spp. to those of cdtB genes known to be present in other bacteria were: C. jejuni, 58.3±64.8%; E. coli, 52.3±57.8%, Haemophilus ducreyi, 53.4±58.4% and Actinobacillus actinomycetemcomitans, 52.7±58.1%. Bacterial lysates from four of these helicobacters caused characteristic cytolethal distension of HeLa cells. Cdt caused cell cycle arrest at G 2 /M phase as measured by¯ow cytometry. The results demonstrated the presence of a toxin in these Helicobacter spp. belonging to the family of Cdt.