Novel design of a small field robot with multi-active crawlers capable of autonomous stair climbing

Mobile robots often encounter complex obstacles during their operation, not the least of which are stairs. Suitable mechanical structures and adequate control algorithms are both equally important in stair climbing. This paper proposes a novel design for a multi-active crawler robot (MACbot) capable of autonomous stair climbing. The MACbot has four track modules for extended mobility and a recovery arm that facilitates self-rescue capabilities. By adopting the proposed smart clutch mechanism, the MACbot can provide a variety of motions with a minimum number of motors. This paper presents a static analysis for the mechanical design and details the stability analysis for an autonomous stair climbing algorithm. A series of experiments show that the MACbot can autonomously climb stairs reasonably well.     

Reconfigurable multichannel optical add-drop multiplexersincorporating eight-port optical circulators and fiber Bragg gratings

We propose and demonstrate two new strictly nonblocking reconfigurable multichannel optical add-drop multiplexers (RM-OADMs) using optical circulators and fiber Bragg gratings. By effectively using eight-port optical circulators, the new structures significantly reduce component count and insertion loss, and achieve good crosstalk performance. One of the new RM-OADMs potentially achieves the lowest insertion loss among existing RM-OADMs     

Comparison of human immunodeficiency virus 1 DNA polymerase chain reaction and qualitative and quantitative RNA polymerase chain reaction in human immunodeficiency virus 1-exposed infants

The endothelial lining of the blood-brain barrier tightly controls the distribution of peptide hormones between the central nervous system and the circulation. By using primary cultures of brain microvessel endothelial cells, an in vitro model of the blood-brain barrier, we report here the uptake and transport of the octapeptide angiotensin II by a specific receptor population. With the angiotensin II antagonists losartan (AT1 specific) and PD 123,319 (AT2 specific), we showed that both the uptake and transport of angiotensin II were mediated by the AT1 receptor. Western blot analysis confirmed the existence of the AT1 receptor in our cell-culture model. Rhodamine 123 studies also suggested that both angiotensin II antagonists, but not angiotensin II, were substrates for the P-glycoprotein efflux system, thus restricting the transport of these compounds. These results suggest an AT1 receptor mediates uptake and transport of angiotensin II at the blood-brain barrier and may contribute to the regulation of cerebrovascular levels of the peptide.     

Kinetic and thermodynamic analysis of mutant type II DNA topoisomerases that cannot covalently cleave DNA

DNA topoisomerase II catalyzes two different chemical reactions as part of its DNA transport cycle: ATP hydrolysis and DNA breakage/religation. The coordination between these reactions was studied using mutants of yeast topoisomerase II that are unable to covalently cleave DNA. In the absence of DNA, the ATPase activities of these mutant enzymes are identical to the wild type activity. DNA binding stimulates the ATPase activity of the mutant enzymes, but with steady-state parameters different from those of the wild type enzyme. These differences were examined through DNA binding experiments and pre-steady-state ATPase assays. One mutant protein, Y782F, binds DNA with the same affinity as wild type protein. This mutant topologically traps one DNA circle in the presence of a nonhydrolyzable ATP analog under the same conditions that the wild type protein catenates two circles. Rapid chemical quench and pulse-chase ATPase experiments reveal that the mutant proteins bound to DNA have the same sequential hydrolysis reaction cycle as the wild type enzyme. Binding of ATP to the mutants is not notably impaired, but hydrolysis of the first ATP is slower than for the wild type enzyme. Models to explain these results in the context of the entire DNA topoisomerase II reaction cycle are discussed.     

Imaging of elbow disorders

Regional effects of the chest wall on airway pressure transmission were studied during high frequency ventilation in anesthetized rabbits. We measured airway pressure (Paw), esophageal pressure (Pes), and costal pleural pressure (Ppl) by a rib capsule and flow and volume with a calibrated pneumotachograph. Using a closed circuit, pressures and flow were measured at varying frequencies (2-80 Hz) and tidal volumes (2-20 ml). Mean Pes and Ppl increased with flow amplitude above 100-250 ml/s, whereas mean Paw decreased, consistent with air trapping. Paw, Pes, and Ppl amplitudes increased monotonically with flow amplitude except above 400-500 ml/s, where the Ppl amplitude decreased suddenly. The latter occurring simultaneously with a sudden fall in mean Paw indicated airway flow limitation in costal regions. Flow instabilities during flow limitation were consistent with the large increase in the phase difference between Paw and Ppl and its variability, with frequency. By contrast, the phase difference between Paw and Pes and its variability were relatively small. These differences in Pes from Ppl responses might be caused by a difference in the impedance of the airway-mediastinum pathway or a direct transmission of tracheal pressure oscillations to the esophagus. The former suggests that constraints offered by the mediastinum and rib cage resulted in nonuniform ventilation during high frequency ventilation.     

A study on the combustibility of torrefied wood oil/water mixture droplets

This paper presents the results of an experimental study on the combustion characteristics of torrefied wood (TW) slurries using suspended droplets. The main factors that were investigated in this study are the initial diameter of the slurry droplets, the ambient temperature, the composition of the slurries including the solid content and the percentage content of a second liquid added to the parent slurry. The results show a linear relationship between the square of the initial diameter of the droplet and total combustion time for all kinds of TW-based slurries that were studied here but the slope of the line depends on the composition of the slurries and the ambient temperature. Also, the combustibility of TW-based slurries was better than charcoal-based slurries due to the better combustibility of TW. By adding a certain amount of a second liquid, especially water, to a TW-oil mixture, the combustibility of the resulting slurry was improved.     

Experimental study on cellular instabilities in hydrocarbon/hydrogen/carbon monoxide–air premixed flames

To investigate cell formation in methane (or propane)/hydrogen/carbon monoxide-air premixed flames, the outward propagation and development of surface cellular instabilities of centrally ignited spherical premixed flames were experimentally studied in a constant pressure combustion chamber at room temperature and elevated pressures. Additionally, unstretched laminar burning velocities and Markstein lengths of the mixtures were obtained by analyzing high-speed schlieren images. In this study, hydrodynamic and diffusional-thermal instabilities were evaluated to examine their effects on flame instabilities. The experimentally-measured unstretched laminar burning velocities were compared to numerical predictions using the PREMIX code with a H₂/CO/C₁-C₄ mechanism, USC Mech II, from Wang et al. [22]. The results indicate a significant increase in the unstretched laminar burning velocities with hydrogen enrichment and a decrease with the addition of hydrocarbons, whereas the opposite effects for Markstein lengths were observed. Furthermore, effective Lewis numbers of premixed flames with methane addition decreased for all of the cases; meanwhile, effective Lewis numbers with propane addition increase for lean and stoichiometric conditions and increase for rich and stoichiometric cases for hydrogen-enriched flames. With the addition of propane, the propensity for cell formation significantly diminishes, whereas cellular instabilities for hydrogen-enriched flames are promoted. However, similar behavior of cellularity was obtained with the addition of methane, which indicates that methane is not a candidate for suppressing cell formation in methane/hydrogen/carbon monoxide-air premixed flames.