Actuators for a space manipulator

The robotic manipulator can be decomposed into distinct subsytems. One particular area of interest of mechanical subsystems is electromechanical actuators (or drives). A drive is defined as a motor with an appropriate transmission. An overview is given of existing, as well as state-of-the-art drive systems. The scope is limited to space applications. A design philosophy and adequate requirements are the initial steps in designing a space-qualified actuator. The focus is on the d-c motor in conjunction with several types of transmissions (harmonic, tendon, traction, and gear systems). The various transmissions will be evaluated and key performance parameters will be addressed in detail. Included in the assessment is a shuttle RMS joint and a MSFC drive of the Prototype Manipulator Arm. Compound joints are also investigated. Space imposes a set of requirements for designing a high-performance drive assembly. Its inaccessibility and cryogenic conditions warrant special considerations. Some guidelines concerning these conditions are present. The goal is to gain a better understanding in designing a space actuator

Shuttle bay telerobotics demonstration

A demonstration of NASA's robotics capabilities should be a balanced agenda of servicing and assembly tasks combined with selected key technical experiments. The servicing tasks include refueling and module replacement. Refueling involves the mating of special fluid connectors while module replacement requires an array of robotic technologies such as special tools, the arm of a logistics tool, and the precision mating of orbital replacement units to guides. The assembly task involves the construction of a space station node and truss structure. The technological experiments will focus on a few important issues: the precision manipulation of the arms by a teleoperator, the additional use of several mono camera views in conjunction with the stereo system, the use of a general purpose end effector versus a caddy of tools, and the dynamics involved with using a robot with a stabilizer

Entropy and Its Quantum Thermodynamical Implication for Anomalous Spectral Systems

The state function entropy and its quantum thermodynamical implication for two typical dissipative systems with anomalous spectral densities are studied by investigating on their low-temperature quantum behavior. In all cases it is found that the entropy decays quickly and vanishes as the temperature approaches zero. This reveals a good conformity with the third law of thermodynamics and provides another evidence for the validity of fundamental thermodynamical laws in the quantum dissipative region.Comment: 10 pages, 3 figure

An experimental approach to quantify strain transfer efficiency of fibre bragg grating sensors to host structures

This paper developed a method to evaluate the strain transfer efficiency of fibre Bragg grating sensors to host structures. Various coatings were applied to fibre Bragg grating sensors after being fabricated. They were epoxy, silane agent and polypropylene, representing different surface properties. A neat epoxy resin plate was used as the host in which the coated fibre sensors were embedded in the central layer. The tensile strain output from the FBGs was compared with that obtained from electrical strain gauges which were attached on the surface of the specimen. A calculating method based on the measured strains was developed to quantify the strain transfer function of different surface coatings. The strain transfer coefficient obtained from the proposed method provided a direct indicator to evaluate the strain transfer efficiency of different coatings used on the FBG sensors, under either short or long-term loading. The results demonstrated that the fibre sensor without any coating possessed the best strain transfer, whereas, the worst strain transfer was created by polypropylene coating. Coatings play a most influential role in strain measurements using FBG sensors

Particle-Hole Asymmetry in Doped Mott Insulators: Implications for Tunneling and Photoemission Spectroscopies

In a system with strong local repulsive interactions it should be more difficult to add an electron than to extract one. We make this idea precise by deriving various exact sum rules for the one-particle spectral function independent of the details of the Hamiltonian describing the system and of the nature of the ground state. We extend these results using a variational ansatz for the superconducting ground state and low lying excitations. Our results shed light on the striking asymmetry in the tunneling spectra of high Tc superconductors and should also be useful in estimating the local doping variations in inhomogeneous materials.Comment: 4 pages, no figure

Charge Ordered RVB States in the Doped Cuprates

We study charge ordered d-wave resonating valence bond states (dRVB) in the doped cuprates, and estimate the energies of these states in a generalized $t-J$ model by using a renormalized mean field theory. The long range Coulomb potential tends to modulate the charge density in favor of the charge ordered RVB state. The possible relevance to the recently observed $4 \times 4$ checkerboard patterns in tunnelling conductance in high $T_c$ cuprates is discussed.Comment: 4 pages, 4 figures, 3 table

Event-driven simulations of a plastic, spiking neural network

We consider a fully-connected network of leaky integrate-and-fire neurons with spike-timing-dependent plasticity. The plasticity is controlled by a parameter representing the expected weight of a synapse between neurons that are firing randomly with the same mean frequency. For low values of the plasticity parameter, the activities of the system are dominated by noise, while large values of the plasticity parameter lead to self-sustaining activity in the network. We perform event-driven simulations on finite-size networks with up to 128 neurons to find the stationary synaptic weight conformations for different values of the plasticity parameter. In both the low and high activity regimes, the synaptic weights are narrowly distributed around the plasticity parameter value consistent with the predictions of mean-field theory. However, the distribution broadens in the transition region between the two regimes, representing emergent network structures. Using a pseudophysical approach for visualization, we show that the emergent structures are of "path" or "hub" type, observed at different values of the plasticity parameter in the transition region.Comment: 9 pages, 6 figure

Antioxidant properties: effects of solid-to-solvent ratio on antioxidant compounds and capacities of pegaga (Centella asiatica)

The objective of this study was to evaluate the effects of solid-to-solvent ratio (1:5, 1:10, 1:15 and 1:20) on the extraction of phenolic compounds (TPC and TFC) and antioxidant capacity (ABTS and DPPH radical scavenging capacity) of C. asiatica. Solid-to-solvent ratio 1:15 was the optimum condition for extraction of phenolic compounds (TPC and TFC) with a value of 967.2 mg GAE/100 g DW and 908.3 mg CE/100 g DW, respectively and exhibited high antioxidant capacities (ABTS and DPPH radical scavenging capacities) with a value of 0.8133 mM and 2.0945 mM, respectively. TPC was positively and strongly correlated with ABTS and DPPH (r=0.808 and r=0.859, respectively) under the effects of solid-to-solvent ratio as compared to TFC, positively and moderately correlated (r=0.590, r=0.663) with ABTS and DPPH

The Neutrino Magnetic Moment Induced by Leptoquarks

Allowing leptoquarks to interact with both right-handed and left-handed neutrinos (i.e., ``non-chiral'' leptoquarks), we show that a non-zero neutrino magnetic moment can arise naturally. Although the mass of the non-chiral vector leptoquark that couples to the first generation fermions is constrained severely by universality of the $\pi^+$ leptonic decays and is found to be greater than 50 TeV, the masses of the second and third generation non-chiral vector leptoquarks may evade such constraint and may in general be in the range of $1\sim 100$ TeV. With reasonable input mass and coupling values, we find that the neutrino magnetic moment due to the second generation leptoquarks is of the order of $10^{-12}\sim 10^{-16} \mu_{\rm B}$ while that caused by the third generation leptoquarks, being enhanced significantly by the large top quark mass, is in the range of $10^{-10}\sim 10^{-14} \mu_{\rm B}$.Comment: 11 pages, 3 eps figures, uses revte

Effect of pmma-mwnts loading on Co2 separation performance of thin film nanocomposite membrane

Nanocomposite membrane, especially the thin film nanocomposite (TFN) fabricated via interfacial polymerization (IP) is a relatively new class of membrane which features good separation performance and practical processing. This study investigated on the effects of multi-walled carbon nanotubes (MWNTs) loading on the gas separation performance of the resultant TFNs. TFNs were tested with pure CO2, N2 and CH4 gases at feed pressure of 2 bar. The findings from this study suggested that the optimum fillers loading was around 0.25 g/L in the coating solution which gives TFN with CO2 permeance of 53.5 gas permeation unit (GPU) (12% higher than base membrane without filler), CO2/N2 selectivity of 61 and CO2/CH4 selectivity of 35. The enhancement in CO2 permeance without sacrificing the membrane selectvities was attributed to the good dispersion and compatibility of the MWNTs with the polymer matrix while the nanotubes serve as rapid diffusion channels to facilitate transport of gases. TFN embedded with polymethyl methacrylate (PMMA)-MWNTs showed potential for low pressure carbon capture and storage application