Showing papers by "Yang Gao published in 2006"

A predictive wheel-soil interaction model for planetary rovers validated in testbeds and against MER Mars rover performance data

Abstract: Successful designs of vehicles intended for operations on planetary objects outside the Earth demand, just as for terrestrial off-the-road vehicles, a careful assessment of the terrain relevant for the vehicle mission and predictions of the mobility performance to allow rational trade-off’s to be made for the choice of the locomotion concept and sizing Principal issues driving the chassis design for rovers are the stress-strain properties of the planetary surface soil, the distribution of rocks in the terrain representing potential obstacles to movement, and the gravity level on the celestial object in question Thus far, planetary rovers have been successfully designed and operated for missions to the Earth’s moon and to the planet Mars, including NASA’s Mars Exploration Rovers (MER’s) ‘Spirit’ and ‘Opportunity’ being in operation on Mars since their landings in January 2004

A general treatment of three-dimensional elasticity of quasicrystals by an operator method

Abstract: By an operator method, the general solution of three-dimensional elasticity of quasicrystals is given constructively with some displacement functions, and its completeness is proved at the same time. Non-uniqueness and the scope of nonuniqueness of the general solution are also pointed out. The method used in the paper extends work from elasticity to quasicrystals elasticity. As two special cases, two-dimensional dodecagonal quasicrystal and one-dimensional hexagonal QCs are considered, and the general solutions based on the operator method are presented.

Deployable wood wasp drill for planetary subsurface sampling

Abstract: Growing interest in planetary subsurface exploration has prompted an examination of advanced drilling technologies. One of the major limitations of sampling in low gravity environments (such as Mars, asteroids, etc.) using conventional rotary drills is the need for high axial force, which suffers from big overhead mass, buckling problem, and power hungriness. Though drills using percussive motion may operate in low mass and power, the drilling rate is generally slow. Drawing inspiration from nature for a lightweight and energy efficient solution, we propose a novel drilling method based on the working mechanism of wood wasp ovipositors. The bio-inspired drill requires no reactive external force by applying two-valve-reciprocating motion. The proposed biomimetic system indicates enhanced utility that is critical for space missions where premium is placed on mass, volume and power. Biological systems are similarly constrained making biomimetic technology uniquely suited and advantageous as a model of miniaturized systems. As a result of the European Space Agency (ESA) project on bionics and space system design [Ellery et al., 2005], this paper presents a conceptual design of the wood wasp drill. Lab-based experiments have shown that the bio-inspired drilling method is feasible and has potential of improving drill efficiency without any additional overhead force or mass.

Threshold resummation effects in direct top quark production at hadron colliders

Abstract: We investigate the threshold-enhanced QCD corrections to the cross sections for direct top quark productions induced by model-independent flavor changing neutral current couplings at hadron colliders. We use the soft-collinear effective theory to describe the incoming massless partons and use the heavy quark effective theory to treat the top quark. Then we construct the flavor changing operator based on the above effective theories, and resum the large logarithms near threshold arising from soft gluon emission. Our results show that the resummed QCD corrections further enhance the next-to-leading order cross sections significantly. Moreover, the resummation effects vastly reduce the dependence of the cross sections on the renormalization and factorization scales, especially in cases where the next-to-leading order results behave worse than the leading order results. Our results are more sensitive to the new physics effects. If signals of direct top quark production are found in future experiments, it is more appropriate to use our results as the theoretical inputs for extracting the anomalous couplings.

Bio-inspired micro-drills for future planetary exploration

Abstract: In a domain such as space technology, where robustness, mass, volume and power efficiency are key, biological organisms may provide inspiration for new systems with high performance. By using micro-technology processes, designers of space systems may take advantage of the millions of years over which miniaturised mechanisms in plants and animals have been optimised for survival. Space exploration often requires systems equipped with drills, and miniaturised drillers could enable a number of new space operations. Two natural digging systems have been studied as potential miniature space digging systems; the ovipositors of the female locust and of sirex noctilio, a species of woodwasp. Being insectoid systems, the mechanics of their design work on an inherently small scale, though they are also thought to be scalable. Results of preliminary studies, performed during collaboration between the Advanced Concepts Team of ESA, the University of Bath, the University of Surrey, D’appolonia and EADS-Astrium, are presented and discussed. Engineering solutions are proposed and analysed to assess the potential of new bio-inspired miniaturised digging systems for space applications.

The Influence of Faraday Rotation on the Vertical Electric Current Density

Abstract: In this Letter we analyze the effects of Faraday rotation on the vertical electric current density in solar active regions. On the basis of the numerical solutions of the transfer equations of Stokes parameters for the Fe I 5324.19 A line at the solar disk center, we derive the variations of the vertical current with wavelengths, which are caused by Faraday rotation. The simulations show that Faraday rotation changes both the sign and the magnitude of the vertical current at line center, but it changes only its magnitude at the far wings of the line. At the selected locations on a simple sunspot, the observed variations of the vertical current with wavelengths are compared with the model. We find that the azimuth rotation is significant when observations are taken near the center of the Fe I 5324.19 A line: the sign change of the vertical current occurs in about 13.5% of the total selected locations, and in about 26% of those the magnitude increases the vertical current more than 100% of the "real" value. We also make a preliminary attempt to correct a case of the vector magnetic field observations for Faraday rotation. For NOAA AR 10162, in particular, it appears that Faraday rotation has a significant effect on the vertical current.

Three-dimensional numerical modeling of a four-pin probe for soil water content

Abstract: Soil probes with 4-pin configuration have been widely used in frequency domain (FD) and time domain reflectometry methods for determining soil water content. The techniques of FD sensors largely rely on the port impedance of the probe. This study provided a 3-dimensional numerical model to represent the electric behaviours of the 4-pin probe, which is valuable for analysing the effect of the soil dielectric constant, geometry, and the operating frequency on the port impedance of the probe. The model was performed with high frequency structure simulator software based on Maxwell's equations and finite element method. A typical 3-dimensional electromagnetic distribution of the 4-pin probe was presented. The model was validated with 3 experiments under the aid of a network analyser. First, the experiment was performed using a series of fluids of known relative dielectric constants, then numerical simulations were carried out and confirmed by soil sample test with varying frequencies and the probe lengths. The effects of these parameters on FD methods are discussed based on the 4-pin probes. The 3-dimensional numerical model appears to be a meaningful tool to investigate more deeply a 4-pin probe in FD method.

GLD Detector Outline Document: Version 1.2

Abstract: The GLD is a detector for the experiment at the International Linear Collider (ILC). It consists of a large calorimeter and a gaseous central tracker placed in a moderate magnetic field, both electro-magnetic and hadron calorimeters being placed inside the magnetic coil to have enough hermeticity and good jet energy resolution. The outline of the GLD is presented.