Biologically inspired tree‐climbing robot with continuum maneuvering mechanism

Treebot is the first tree‐climbing robot that is capable of climbing from a tree trunk to a branch. The robot employs several design principles adapted from arboreal animals, including claw gripping and inchworm locomotion, with a certain artificial optimization to achieve high maneuverability on irregular‐shaped trees. Treebot is composed of a pair of tree grippers that permits Treebot to attach to a wide variety of trees with a wide range of gripping curvature, and a novel continuum maneuvering structure that provides high maneuverability and adaptability. In the robot actuation, only five actuators are necessary. Although Treebot weighs only 600 gr, it has a payload capability of 1.75 kg, which is nearly three times its own weight. This paper describes the design process and specifically addresses the robot locomotion and optimization of gripping force. Experimental results demonstrate the robot's ability to climb trees with high maneuverability. © 2012 Wiley Periodicals, Inc.     

Application of ICME to Engineer Fatigue-Resistant Ni-Base Superalloys Microstructures

Critical rotating components used in the hot section of gas turbine engines are subject to cyclic loading conditions during operation, and the life of these structures is governed by their ability to resist fatigue. Since it is well known that microstructural parameters, such as grain size, can significantly influence the fatigue behavior of the material, the conventional processes involved with the manufacture of these structures are carefully controlled in an effort to engineer the resulting microstructure. For a commercial Ni-base superalloy, RR1000, the development of process models and deformation mechanism maps has enabled not only control of the resultant grain size but also the ability to tailor and manipulate the resulting grain boundary character distribution. The increased level of microstructural control was coupled with a physics-based fatigue model to form an integrated computational materials engineering framework that was used to guide the design of damage-tolerant microstructures. Simulations from a 3D crystal plasticity finite element model were used to identify microstructural features associated with strain localization during cyclic loading and to guide the design of polycrystalline microstructures optimized for fatigue resistance. Conventionally processed and grain boundary engineered forgings of a commercial Ni-based superalloy, RR1000, were produced to validate the design methodology. For nominally equivalent grain sizes, high-resolution strain maps generated via digital image correlation confirmed that the high density of twin boundaries in the grain boundary engineered material were desirable microstructural features as they contribute to limiting the overall length of persistent slip bands that often serve as precursors for the nucleation of fatigue cracks.     

An improvement mechanism for heartbeat‐driven MAC synchronization in wireless body sensor network

This paper aims to improve the TDMA‐based Heartbeat‐Driven MAC (H‐MAC) protocol for WBAN. H‐MAC is designed to be used in star‐topology WBAN for time synchronization realization by using heartbeat rhythm information, instead of periodic synchronization beacons. H‐MAC therefore saves power of WBAN sensor nodes and reduces the negative effects of electromagnetic radiation on human health during the packet delivery process. To embed heartbeat rhythm information into different bio‐signals and check the peak values of wave forms can contribute to time synchronization for BSN. As the heart contracts via systole and relaxes via diastole, pulse is the number of times one's heart beats every minute and the number of pulses measured at different body parts is the same. However, blood vessels run over the whole human body and their distances away from the heart greatly vary in the same systole, leading to an imperceptible time difference and the synchronization problem. We propose to include the presently most mature method for time synchronization, Flooding Time Synchronization Protocol (FTSP), to deal with time differences.     

The effect of long-term ambient aging on the mechanical properties of conducting polysiloxane-polypyrrole graft copolymers

The mechanical behavior of conducting polysiloxane-polypyrrole graft copolymers has been investigated as a function of ambient oxidative aging period. Graft copolymers of N-pyrrolyl-terminated polydimethylsiloxane (SPPy) with pyrrole were synthesized electrochemically at constant potential by using p -toluene sulfonic acid as the supporting electrolyte. Mechanical tests were performed on both unwashed and dichloromethane -washed copolymers after aging. An initial decrease followed by an increase in the tensile strength and strain values was observed with aging. The conductivities and mechanical properties of the films were determined to remain almost unchanged after 6 months of aging at about 46 S/cm.     

A novel effect of sandblasting on titanium surface: static charge generation

Recent advances in biomaterials’ research suggest that electrical charges on a dental implant surface significantly improve its osseointegration to living bone, as a result of selective osteoblast activation and fibroblast inhibition. This study aims at investigating the possibility of using sandblasting to modify the electrical charges on the surface of titanium materials. Our experiments used Al₂O₃ grits to blast on CP2 titanium plates, for durations between 3 and 30?s. After sandblasting, Ti surfaces were measured for their electrostatic voltage. The results indicate a novel finding, i.e. negative static charges are generated on the titanium surface, which may stimulate osteoblast activity to promote osseointegration around dental implant surface. This finding may at least partially explain the good osseointegration results of sandblasted titanium dental implants, in addition to other known reasons, such as topological changes on the implant’s surface. However, the static charges accumulated on the titanium surface during sandblasting decayed to a lower level with time. It remains a challenging task to seek ways to retain these charges after quantification of desired level of negative charges needed to promote osteoblast activity for osseointegration around dental implants.     

Computational modeling and experimental infrared spectroscopy of hydrogen bonding interactions in polyvinyl alcohol-starch blends

This study aims to investigate the hydrogen bonding interactions in polyvinyl alcohol (PVOH)-starch blends. Semi-empirical AM1 (Austin Model 1) and PM3 (Parameterized Austin Model 3) methods were employed to model the blending. Binding energies, vibrational frequencies and solubility parameters results were used to analyze the compatibility and stability of the blends. Besides that, experimental infrared spectroscopy was also conducted to validate the modeling results. The computed negative binding energies justified the stability of the blending. On the other hand, the solubility parameters of PVOH and starch modeling complexes have been found close to each other. This confirms that PVOH and starch are compatible blends. In addition, vibrational frequency analysis of these molecular complexes has exhibited that the hydroxyl group shifts to lower wavenumbers due to formation of hydrogen bonds. Findings from the experimental infrared spectroscopy have shown agreement with computational vibrational frequency results. The wavenumbers of the specimens increase is dependent on the ratios of PVOH in the blends. Such increment indicates that PVOH and starch interact in a harmonize manner and the blending is compatible.     

Polarization Transfer from Ligands Hyperpolarized by Dissolution Dynamic Nuclear Polarization for Screening in Drug Discovery

Nuclear magnetic resonance (NMR) spectroscopy is a valuable technique for ligand screening, because it exhibits high specificity toward chemical structure and interactions. Dissolution dynamic nuclear polarization (DNP) is a recent advance in NMR methodology that enables the creation of non‐equilibrium spin states, which can dramatically increase NMR sensitivity. Here, the transfer of such spin polarization from hyperpolarized ligand to protein is observed. Mixing hyperpolarized benzamidine with the serine protease trypsin, a “fingerprint” of enhanced protein signals is observed, which shows a different intensity profile than the equilibrium NMR spectrum of the protein, but coincides closely to the frequency profile of a saturation transfer difference (STD) NMR experiment. The DNP experiment benefits from hyperpolarization and enables observation of all frequencies in a single, rapid experiment. Based on these merits, it is an interesting alternative to the widely used STD experiment for identification of protein–ligand interactions.     

Effect of the parameters of the thermal modification of brown coals on their sorption properties

The effect of carbonization and activation conditions on the adsorptive and mechanical properties of sorbents obtained from brown coal was studied. It was found that the heat treatment of brown coal before carbonization with an increase in the temperature from 230 to 400°C makes it possible to increase the volume of macropores by 30–40%; however, it does not lead to a change in the microporous structure of activated carbon. The porous structure of carbon sorbents depends on the degree of combustion losses and the temperature of activation. A change in the activation temperature of the carbonized intermediate product from 700 to 900°C makes it possible to regulate the sorption properties of the resulting activated carbons.     

A Distributed Opportunistic Access Scheme and its Application to OFDMA Systems

Multiuser systems can provide multiuser diversity gains by assigning channels to users with higher channel gains. To avoid the extensive information exchange with the access point for the uplink access in centralized approaches, we propose in this paper a distributed opportunistic access scheme. Through a judicious design of a novel backoff mechanism to utilize the channel information and reduce collisions, significant multiuser diversity gains are achieved. To a user, the higher the channel gain is, the smaller the backoff time-slot and, hence, the higher the access priority of that user is. In addition, for heterogeneous systems, our proposed scheme can realize multiuser diversity gains and achieve fairness among the users at the same time. Finally, we design two distributed opportunistic access schemes for OFDMA systems. Users contend on all sub-channels in the first scheme and only on several strongest sub-channels in the second scheme. Compared with traditional centralized OFDMA systems and other distributed access schemes, our proposed schemes reduce overhead and achieve a higher throughput.