37,473 research outputs found
Correct-by-Construction Approach for Self-Evolvable Robots
The paper presents a new formal way of modeling and designing reconfigurable
robots, in which case the robots are allowed to reconfigure not only
structurally but also functionally. We call such kind of robots
"self-evolvable", which have the potential to be more flexible to be used in a
wider range of tasks, in a wider range of environments, and with a wider range
of users. To accommodate such a concept, i.e., allowing a self-evovable robot
to be configured and reconfigured, we present a series of formal constructs,
e.g., structural reconfigurable grammar and functional reconfigurable grammar.
Furthermore, we present a correct-by-construction strategy, which, given the
description of a workspace, the formula specifying a task, and a set of
available modules, is capable of constructing during the design phase a robot
that is guaranteed to perform the task satisfactorily. We use a planar
multi-link manipulator as an example throughout the paper to demonstrate the
proposed modeling and designing procedures.Comment: The paper has 17 pages and 4 figure
External Recruitment as an incentive Device
External recruitment has often been viewed as a necessary evil in that it trades off the need for outside talents with the incentives of inside workers. This paper, however, shows that even from an incentive viewpoint, external recruitment has its positive role to play. Specifically, if promotion is based on relative performance, then negative activities in the form of sabotage are a valuable instrument to compete. This results in inefficiency of the workers' efforts and performance of the firm. External recruitment, by reducing the marginal return of negative activity relative to that of productive activity, can restore the incentives of the workers to engage in productive activity and enhances the firm's performance. We also show that even when negative activities are not a concern, external recruitment can sometimes avoid the shirking equilibrium, or prevents collusion of the workerspromotio, relative performance, sabotage, external recruitment
Magnetism and effect of anisotropy with one dimensional monatomic chain of cobalt by a Monte Carlo simulation
The magnetic properties of the one dimensional (1D) monatomic chain of Co
reported in a previous experimental work are investigated by a classical Monte
Carlo simulation based on the anisotropic Heisenberg model. In our simulation,
the effect of the on-site uniaxial anisotropy, Ku, on each individual Co atom
and the nearest neighbour exchange interaction, J, are accounted for. The
normalized coercivity HC(T)/HC(TCL) is found to show a universal behaviour,
HC(T)/HC(TCL) = h0(e^{TB/T}-e) in the temperature interval, TCL < T < TBCal,
arising from the thermal activation effect. In the above expression, h0 is a
constant, TBCal is the blocking temperature determined by the calculation, and
TCL is the temperature above which the classical Monte Carlo simulation gives a
good description on the investigated system. The present simulation has
reproduced the experimental features, including the temperature dependent
coercivity, HC(T), and the angular dependence of the remanent magnetization,
MR(phi,theta), upon the relative orientation (phi,theta) of the applied field
H. In addition, the calculation reveals that the ferromagnetic-like open
hysteresis loop is a result of a slow dynamical process at T < TBCal. The
dependence of the dynamical TBCal on the field sweeping rate R, the on-site
anisotropy constant Ku, and the number of atoms in the atomic chain, N, has
been investigated in detail.Comment: 20 pages, 7 figures included, J Phys Condens Matter, In Pres
Proton-Proton Fusion in Effective Field Theory to Fifth Order
The proton-proton fusion process p p->d e^+ nu_e is calculated at threshold
to fifth order in pionless effective field theory. There are two unknown
two-body currents contributing at the second and fourth orders. Combined with
the previous results for neutrino-deuteron and antineutrino-deuteron
scattering, computed to third order in the same approach, we conclude that a
10% measurement of reactor antineutrino-deuteron scattering measurement could
constrain the p p->d e^+ nu_e rate to ~7% while a ~3% measurement of nu_e d->
e^- p p could constrain the pp rate to ~2%.Comment: 9 page
Microstructure and mechanical properties of large size as-cast Ti-43Al-9V-0.2Y (at.%) alloy ingot from brim to centre
A Ti-43Al-9V-0.2Y (at.%) alloy ingot with the size of Ф160×400mm was prepared by vacuum arc remelting (VAR). The microstructure of the as-cast Ti-43Al-9V-0.2Y alloy was composed of B2/α₂/γ lamellar colonies and massive B2 and γ phases which were distributed along the boundaries of these lamellar colonies in the form of equiaxed grains. Based on the grain size variation along the radius direction of the ingot, the ingot could be divided into four ring regions from brim to centre. It has been understood that the grain size variation between these four regions was due to the interplay of the effects of the cooling rate and the yttrium content on solidified microstructures in these regions. Mechanical testing of the samples cut from these four regions showed that there existed a clear correlation between the yield strength and the average grain sizes of the four ring regions, which approximately conformed to a Hall-Petch relationship
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