Glass-like thermal transport in symmetry-broken clathrates
We present the quantitative interpretation for the glass-like behavior of thermal conductivities κ(T) for type-I clathrate compounds involving off-centered guest ions. It is shown that the dipole-dipole interaction generated in cage/guest-ion systems is crucial to reproduce the characteristics of thermal conductivities for these symmetry-broken clathrates. The above scenario also explains well the difference of κ(T) between the p-type and the n-type β-BGS found recently by K. Suekuni et al. (Phys. Rev. B, 77 (2008) 235119.)
Transport properties of composition tuned α- and β-Eu8Ga16-xGe30+x
This paper presents the transport properties of several composition tuned a- and b-Eu8Ga16˛xGe30+x samples where 0.28 x 0.48 for the a samples and 0.49 x 1.01 for the b samples. Among samples with the same structure sa or bd, the varying physical properties can be understood in terms of a rigid conduction band where only the charge carrier concentration is varied. The differences in the physical properties between a and b samples can be explained by a charge-carrier effective mass sm * d that is more than three times larger in the b phase than in the a phase. As a result of the low charge-carrier mobility we argue that the thermoelectric figure of merit of n-type a- and b-Eu8Ga16˛xGe30+x, without modifications to enhance the thermoelectric properties, will not exceed that of the best materials at room temperature. From modeling the lattice thermal conductivity skLd of a- and b-Eu8Ga16˛xGe30+x, it is proposed that kL of all clathrates with divalent cations can be described by phonon-charge-carrier scattering at low temperatures and resonant scattering at higher temperatures. This contradicts earlier models where the low-temperature kL of b-Eu8Ga16Ge30 and Sr8Ga16Ge30 is modeled by scattering of phonons from tunneling states. However, since the phonon-charge-carrier scattering rate increases with sm * d 2 the advantage of the phonon-charge-carrier scattering model is the ability to explain the lower low-temperature kL of b-Eu8Ga16˛xGe30+x, compared to a-Eu8Ga16˛xGe30+x.
Study on workspace analysis and simulation of 6-DOF painting robot based on monte-carlo method
Comparing recent kinds of methods working on robot workspace when we design to calculate the workspace of 6R painting robot,we bring Monte-Carlo method to analysis the workspace according to the actual working condition. With robot Tool Center Point(TCP) position aggregate via the solution of forward kinetic equation,Monte-Carlo method analysis and simulate painting robot workspace efficiently.