Effect of Reciprocation Frequency on Friction and Wear of Vibrating Contacts Lubricated with Soybean-Based B100 Biodiesel

The use of renewable, bio-based fuels has become increasingly widespread in recent years, with a major example being biodiesel, a bio-derived alternative to Number 2 diesel fuel. The increased usage of biodiesel gives rise to an augmented need to understand its tribological effects on critical engine components. This study focused on determining the tribological performance of soybean-based B100 (i.e., pure) biodiesel within a fuel injector with varying oscillating frequency by performing a series of linear reciprocating tribological tests of biodiesel-lubricated interfaces with varying reciprocating frequency. Comparison of friction coefficient variation with reciprocating frequency indicated a transition from boundary lubrication to hydrodynamic lubrication as the frequency increased, while hysteresis loop and energy loss observations showed a transition between full stick and partial slip contact with increasing frequency. However, observations of induced wear showed the wear to increase with increasing frequency, most likely due to the augmented number of sliding cycles as well as an increased degree of interfacial slip.     

Construction of C-space roadmaps from local sensory data. What should the sensors look for?

This paper presents an incremental navigation strategy for general articulated robots:the robot may start with no a priori information about its environment, and is guaranteed either to find the goal if it is reachable or halt. The strategy, termed theincremental roadmap algorithm, constructs a roadmap based on on-line distance data which is encoded as a repulsive potential field. The incremental behavior is achieved with two novel abstract sensors: thecritical-point detector and thepassage-point detector. The detectors provide a complete characterization of what the robot should look for in its configuration space to achieve globally convergent navigation. The approach thus provides a new framework, which will hopefully yield the first navigation algorithm that is both completely general and practical.     

New bounds on the number of frictionless fingers requied to immobilize

Using a novel second-order mobility theory that was recently developed by the authors, this article develops new lower bounds on the number of frictionless fingers required to immobilize generic planar objects. We show that any generic smooth or polygonal planar object can be immobilized with three convex fingers or fixtures that have sufficiently flat curvature. Further, if it is possible to specify the fingertip curvature, then any generic smooth or polygonal object can be immobilized with two, possibly concave, fingers. © 1995 John Wiley & Sons, Inc.     

A point mutation (G338S) and its suppressor mutations affect both the pH response of the NhaA-Na+/H+ antiporter as well as the growth phenotype of Escherichia coli

pH controls the activity of the NhaA Na+/H+ antiporter of Escherichia coli. In the present work we show that replacement of glycine 338 of NhaA with serine (G338S) alleviates the pH control of the antiporter. Monitoring Na+-dependent collapse of DeltapH, to assess antiporter activity in isolated membrane vesicles, shows that the mutant protein is practically independent of pH, between pH 7 and 9, and even at pH 6 is 70% active. Similarly the purified reconstituted mutant protein catalyzes pH-independent passive efflux of 22Na from proteoliposomes as well as DeltapH-driven influx. Whereas the native NhaA in isolated membrane vesicles is exposed to digestion by trypsin only above pH 7, the mutated protein is degraded already at pH 6.5. DeltanhaA DeltanhaB cells transformed with a plasmid encoding the pH-independent antiporter are sensitive to Na+ but not to K+ at alkaline pH, while growing in the presence of both ions at neutral pH. Several possibilities that could explain the Na+ sensitivity of the mutant at alkaline pH were excluded; Western analysis and measurement of Na+/H+ antiporter activity in membrane vesicles, isolated from cells shifted to the non-permissive growth conditions, showed neither reduced expression of G338S-NhaA nor defective activity. The finding that the mutated protein is electrogenic led to the retraction of the idea that the protein is active in vitro but not in vivo at alkaline pH, when only Deltapsi exists in the cells. The Na+ concentration needed for half-maximal activity of G338S in isolated everted membrane vesicles is similar to that of the wild type. Therefore an increase in intracellular Na+ due to a reduced antiporter affinity could not explain the results. It is suggested that the loss of growth at alkaline pH in the presence of Na+ is due to the loss of the pH control of the mutated NhaA. Indeed, in the four mutations suppressing G338S phenotype, growth at alkaline pH was restored together with the pH regulation of NhaA. Three of the four suppressor mutations cluster in helix IV, whereas the original mutation is in helix XI, suggesting that the two helixes interact.     

Psychometric properties of the Problematic Internet Use Questionnaire

Several instruments have been designed to measure problems associated with excessive, compulsive, or addictive use of the Internet. One such instrument, the 18-item Problematic Internet Use Questionnaire, was recently published with data supporting a three subscale model (Demetrovics et al., 2008). These researches utilized an online format with a sample taken from the general population of Hungary. We utilized an American college student sample and a paper and pencil format to perform a confirmatory factor analysis of the PIUQ. In addition, we examined the reliability and construct validity of the PIUQ by examining the scales’ relationship with several indices of psychological and physical health. CFA results indicate a barely adequate and not completely problem free three factor model for the PIUQ (χ² = 477.40; root mean square error = .097; comparative fit index = .831; Tucker Lewis coefficient = .804). Cronbach’s α for the total scale was .91 while the Cronbach’s α for each subscale were .81, .77, and .79. Construct validity for the model is demonstrated with significant correlations between the subscales and several indices of psychological and physical health. Suggestions for further research are provided.     

Density-Independent,Scalable Search in Ad Hoc Networks

We analyze the asymptotic cost of discovering a route within a flat ad hoc network and we show that one can discover a route with cost that is proportional only to the area of the network, which is independent of the number of network nodes. Furthermore, we show that this is optimal and that bordercasting (a query propagation protocol where a node retransmits a query to a set of nodes at some hop-distance away) possesses this density-independence property. We present the design of bordercast and the associated maintenance protocols, and we evaluate their performance. In particular, we highlight that the aggregation of local information by bordercasting at each network node is a fundamental building block for the construction of scalable protocols in flat ad hoc networks.

Extending Gardiner’s code for Hieroglyphic recognition and English mapping

Multimedia Tools and Applications - “Knowledge is power”… Writing is the main way to preserve the humanity knowledge across the ages. Therefore, an automatic and accurate mapping...     

Evaluation of Antibacterial Activity and Characterization of Synthesized Biodegradable Copolymers

Green copolymer Poly(MA-CA) was developed by the thermal condensation polymerization of monomers such as DL-Malic acid (MA) and Citric acid (CA). The copolymer of Poly(MA-CA) was synthesized by varying the ratio of MA and CA monomers with 1:0, 1:3, 1:1, 3:1 and 0:1, and their antibacterial properties were studied with respect to their activity on Gram-positive and Gram-negative bacteria by the bacterial count method. Furthermore, the biocidal activity of the plain monomers was also investigated and compared to those of the copolymers. Synthesized copolymers show good antibacterial effects towards both Gram-positive and Gram-negative bacteria. The antimicrobial properties of the copolymers and the monomers were studied by varying the ratio of polymers, effect of polymer concentration and effect of pH. Results indicated that the antibacterial activity of the copolymers increased with MA content and polymer dose. At low content of MA (wt.%), the copolymers poly(MA-CA)(1:3) possessed a higher effect on Gram-positive bacteria Bacillus cereus and Micrococcus luteus than Gram-negative bacteria Salmonella and Shigella. The other copolymers with the ratio of 1:1 and 3:1 including MA homopolymer possesses 100% inhibition of both Gram-positive and Gram-negative bacteria under the conditions studied. The developed polymers were extensively characterized by Fourier transform infrared spectroscopy analysis, thermal gravimetric analysis, X-ray diffraction analysis and scanning electron microscope-energy dispersive spectroscopy to understand their physicochemical properties.     

Spanning-tree based coverage of continuous areas by a mobile robot

This paper considers the problem of covering a continuous planar area by a square-shaped tool attached to a mobile robot. Using a tool-based approximation of the work-area, we present an algorithm that covers every point of the approximate area for tasks such as floor cleaning, lawn mowing, and field demining. The algorithm, called Spanning Tree Covering (STC), subdivides the work-area into disjoint cells corresponding to the square-shaped tool, then follows a spanning tree of the graph induced by the cells, while covering every point precisely once. We present and analyze three versions of the STC algorithm. The first version is off-line, where the robot has perfect apriori knowledge of its environment. The off-line STC algorithm computes an optimal covering path in linear time O(N), where N is the number of cells comprising the approximate area. The second version of STC is on-line, where the robot uses its sensors to detect obstacles and construct a spanning tree of the environment while covering the work-area. The on-line STC algorithm completes an optimal covering path in time O(N), but requires O(N) memory for its implementation. The third version of STC is “ant”-like. In this version, too, the robot has no apriori knowledge of the environment, but it may leave pheromone-like markers during the coverage process. The ant-like STC algorithm runs in time O(N), and requires only O(1) memory. Finally we present simulation results of the three STC algorithms, demonstrating their effectiveness in cases where the tool size is significantly smaller than the work-area characteristic dimension. This revised version was published online in August 2006 with corrections to the Cover Date.     

Malnutrition-associated reactive hypoglycemia induced by TPN

It is reported the possible relationship between the infection caused by viral agents of predominantly parenteral transmission, such as the hepatitis B virus (HBV), the hepatitis C virus (HCV), and the human immunodeficiency virus (HIV) and the sports practice. It was conducted a study of seroprevalence of the infection by HBV and HCV in Cuban high performance athletes. Only 1.3% of positivity to the HBV infection was found. This positivity is related to the sports discipline they practice and some considerations are made on this regard.