Time filter

Source Type

San Francisco, CA, United States

Arfin T.,FOCUS RESEARCH | Yadav N.,Gorakhpur University
Journal of Industrial and Engineering Chemistry

In continuation of our previous work with composite polystyrene-cobalt-arsenate (PS-Co-As), we further extended impedance measurements. All calculations reported were extracted from experiments carried out in the frequency range of 1-5kHz and different concentrations (0.0001≤c(M)≤1) of KCl and NaCl at isothermal temperature (25±0.1°C). The membrane capacitance and resistance measurements were observed to depend on the concentration and the applied frequency of the electrolyte. The observed capacitances and resistances were used to calculate the membrane resistances (RM), capacitance (CM), reactance (XX), and also derive the impedance (Z). At higher frequencies, the capacitances became low and the impedance decreased with increasing frequency with a corresponding increase in the measured phase angle. On the other hand at the highest frequencies attainable, the phase angle became low. At low frequencies, the phase angle was become independent of the cation, while the impedance showed a clear dependence. The diffused double-layer polarization charge on the geometric capacitor played important role by affecting the overall membrane capacitance. The applied frequencies affected the double-layer capacitance due to the movement of ions across the membrane. At the membrane-electrolyte interface, the electrical double-layer was influenced in addition to being controlled by the transport of ions. © 2012 The Korean Society of Industrial and Engineering Chemistry. Source

Young J.W.,Northeast Ohio Medical University | Young J.W.,FOCUS RESEARCH
American Journal of Physical Anthropology

Locomotor researchers have long known that adult primates employ a unique footfall sequence during walking. Most mammals use lateral sequence (LS) gaits, in which hind foot touchdowns are followed by ipsilateral forefoot touchdowns. In contrast, most quadrupedal primates use diagonal sequence (DS) gaits, in which hind foot touchdowns are followed by contralateral forefoot touchdowns. However, gait selection in immature primates is more variable, with infants and juveniles frequently using LS gaits either exclusively or in addition to DS gaits. I explored the developmental bases for this phenomenon by examining the ontogeny of gait selection in juvenile squirrel monkeys walking on flat and simulated arboreal substrates (i.e., a raised pole). Although DS gaits predominated throughout development, the juvenile squirrel monkeys nonetheless utilized LS gaits in one-third of the ground strides and in one-sixth of pole strides. Multiple logistic regression analyses showed that gait selection within the juvenile squirrel monkey sample was not significantly associated with either age or body mass per se, arguing against the oft-cited argument that general neuromuscular maturation is responsible for ontogenetic changes in preferred footfall sequence. Rather, lower level biomechanical variables, specifically the position of the whole-body center of mass and the potential for interference between ipsilateral fore and hindlimbs, best explained variation in footfall patterns. Overall, results demonstrate the promise of developmental studies of growth and locomotor development to serve as "natural laboratories" in which to explore how variability in morphology is, or is not, associated with variability in locomotor behavior. © 2012 Wiley Periodicals, Inc. Source

Kabanda M.M.,FOCUS RESEARCH | Obot I.B.,King Fahd University of Petroleum and Minerals | Ebenso E.E.,FOCUS RESEARCH
International Journal of Electrochemical Science

Quantum chemical calculations and molecular dynamics studies have been performed on five amino acid derivatives, namely aminoheptadecanoic acid, aminohexadecanoic acid, aminopentadecanoic acid, aminotetradecanoic acid and aminotridecanoic acid to investigate their possible role as corrosion inhibitors for metal surfaces in different media. Quantum chemical calculations were performed to elucidate and compare the molecular reactivity parameters of these compounds while molecular dynamics studies were meant to investigate their binding properties on different metal surfaces. The results of the study indicate that amino acid derivatives have high tendency to interact with the metal surface by donating electrons through their amino groups and accepting electrons through their carboxylic acid group. Molecular dynamics studies have shown that the adsorption of the inhibitor molecule depends on the nature of the metal surface and the media. © 2013 by ESG. Source

The purpose of this study was to determine the effects of a microcycle (4 weeks) combined rugby conditioning plyometric compared with a nonplyometric rugby conditioning program on selected physical and motor performance components and anthropometric measurements of university-level rugby players. Players (18.94 ± 0.40 years) were assigned to either a control (n = 16) or experimental group (n = 19) from the U/19 rugby teams of the North-West University (South Africa). Twenty-six direct and indirect anthropometric measurements were taken, and the players performed a battery of 5 physical and motor performance tests before and after a microcycle (4 week) combined rugby conditioning plyometric (experimental group) and a nonplyometric rugby conditioning program (control group). The dependent t-test results showed that the control group's upper-body explosive power decreased significantly, whereas the stature, skeletal mass, and femur breadth increased significantly from pre-to posttesting. The experimental group showed significant increases in wrist breadth, speed over 20 m, agility, and power and work measurements of the Wingate anaerobic test (WAnT). Despite these results, the independent t-test revealed that speed over 20 m, average power output at 20 seconds, relative work of theWAnT, and agility were the only components of the experimental group that improved significantly more than the control group. A microcycle combined rugby conditioning plyometric program therefore leads to significantly bigger changes in selected physical and motor performance components of university-level rugby players than a nonplyometric rugby conditioning program alone. Based on these findings, coaches and sport scientists should implement × weekly combined rugby conditioning plyometric programs in rugby players' training regimens to improve the players' speed, agility, and power. © 2013 National Strength and Conditioning Association. Source

The distribution of peak vertical forces between the forelimbs and the hind limbs is one of the key traits distinguishing primate quadrupedal locomotion from that of other mammals. Whereas most mammals generate greater peak vertical forelimb forces, primates generate greater peak vertical hind limb forces. At the ultimate level, hind limb dominance in limb force distribution is typically interpreted as an adaptation to facilitate fine-branch arboreality. However, the proximate biomechanical bases for primate limb force distribution remain controversial. Three models have been previously proposed. The Center of Mass (COM) Position model attributes primates' unique mode of limb loading to differences in the position of the whole-body COM relative to the hands and feet. The Active Weight Shift model asserts that primates actively redistribute body weight to their hind limbs by pitching the trunk up via the activation of hind limb retractor muscles. Finally, the Limb Compliance model argues that primates selectively mitigate forelimb forces by maintaining a compliant forelimb and a flat shoulder trajectory. Here, a detailed dataset of ontogenetic changes in morphology and locomotor mechanics in Bolivian squirrel monkeys (Saimiri boliviensis) was employed as a model system to evaluate each of these proposed models in turn. Over the first 10 months of life, squirrel monkeys transitioned from forelimb dominant infants to hind limb dominant juveniles, a change that was precipitated by decreases in peak vertical forelimb forces and increases in peak vertical hind limb forces. Results provided some support for all three of the models, although the COM Position and Active Weight Shift models were most strongly supported by the data. Overall, this study suggests that primates may use a variety of biomechanical strategies to achieve hind limb dominance in limb force distribution. © 2012 Elsevier Ltd. Source

Discover hidden collaborations