2,790 research outputs found
shim
No full textshim n- a handmade wooden tool that was approx. 2 feet long with a flat end. It was used, my Grandfather said, to rhine trees. The bark on the tree was split first and then the shim inserted. The bark was then pried off.DNE-cit JH 6/75Used I and SupUsed I and Sup1Used Ishem, Shin, MUNDLE, SLICE, wedge.The source is listed as C 75-146 in DNE and only part of the cited quotation on card is in DNE
shim
No full textshim nThe door [ lobster pot] is kept in place by a small wooden stick called a shim.DNE-cit JH-24-11-69Used I and SupUsed I and Sup4Used Ishem, Shin, MUNDLE, SLICE, wedge.The source is listed as P 241-68 in DNE
Hydrostatic Pressure Effect on Charge Transport Properties of Phenacene Organic Semiconductors
No full textWe investigate the charge transport properties of phenacene organic semiconductors including phenanthrene, chrysene and picene using density functional theory (DFT) calculations under hydrostatic pressure. Under compression, the crystal structures of the three materials are altered and thus, a decrease in the intermolecular distances gives changes in charge transport properties while the molecular structures remain stable. As a result of the applied pressure, the mobilities of these materials increase dramatically. Chrysene shows a transition from a p-type semiconductor to an ambipolar semiconductor at around 2.0 GPa. Interestingly, chrysene favors electron transport at above 3.0 GPa. On the other hand, both phenanthrene and picene exhibit hole transport characteristics under high pressure. Between 3.1 and 4.3 GPa, the picene crystal is found to transform from an anisotropic mobility to an isotropic mobility in the ab plane. We also found that, the bulk modulus representing the resistance of the material under pressure compression follows a linear relationship with molecular length.115sciescopu
Optimized ZT of Bi2Te3-GeTe compounds from first principles guided by homogeneous data
No full textWe predict the thermoelectric properties of layered [GeTe](m)[Bi2Te3](n) (GBT) compounds ( 1 <= m <= 8, 1 <= n <= 3), using first-principles-Boltzmann transport calculations of the homogeneous (Bi2Te3 and GeTe) data. The lattice strain and the quantum-confinement effects of compounds evolve the band-gap structures, resulting in asymmetric and large Seebeck coefficient, at high GeTe content. Using semiempirical calculations of electron scattering rate 1/tau(e), dominated by electron-acoustic phonon scattering, we reproduce reported TE properties of GBT compounds. We predict that, due to small Seebeck coefficient, the GBT compounds with high n- and p-type doping (similar to 10(20) cm(-3)), do not have high ZT near room temperature. However, we predict that the moderately doped (similar to 10(19) cm(-3)), p-type GBT compounds have enhanced ZT approximate to 1.4 near room temperature.1132Ysciescopu
Density-functional calculations of the electronic structures and magnetism of thepnictide superconductors BaFeAs2 and BaFeSb2
No full textWe investigate the structural, electronic, and magnetic properties of the hypothetical compound BaFePn(2) (Pn=As and Sb), which is isostructural to the parent compound of the high-temperature superconductor LaFeAsO1-xFx. Using density-functional theory, we show that the Fermi surface, electronic structure, and spin-density wave instability of BaFePn(2) are very similar to the Fe-based superconductors. Additionally, there are very dispersive metallic bands of a spacer Pn layer, which are almost decoupled from FePn layer. Our results show that experimental study of BaFePn(2) can test the role of charge and polarization fluctuation as well as the importance of two dimensionality in the mechanism of superconductivity.open112119sciescopu
Composition and temperature dependent electronic structures of NiS2-xSex alloys: First-principles dynamical mean-field theory approach
No full textWe investigate the evolution of the electronic structure of NiS2-xSex alloys with varying temperature and composition x by using the combined approach of density-functional theory and dynamical mean-field theory. Adopting realistic alloy structures containing S and Se dimers, we map their electronic correlation strength on the phase diagram and observe the metal-insulator transition (MIT) at the composition x = 0.5, which is consistent with the experimental measurements. The temperature dependence of the local magnetic susceptibility is found to show a typical Curie-Weiss-like behavior in the insulating phase while it shows a constant Pauli-like behavior in the metallic phase. A comparison of the electronic structures for NiS2 and NiSe2 in different lattice structures suggests that the MIT in this alloy system can be classified as of bandwidth-control type, where the change in the hybridization strength between Ni d and chalcogen p orbitals is the most important parameter.113Nsciescopu
AEMnSb2 (AE=Sr, Ba): a new class of Dirac materials
No full textThe Dirac fermions of Sb square net in AEMnSb(2) (AE = Sr, Ba) are investigated by using first-principles calculation. BaMnSb2 contains Sb square net layers with a coincident stacking of Ba atoms, exhibiting Dirac fermion behavior. On the other hand, SrMnSb2 has a staggered stacking of Sr atoms with distorted zig-zag chains of Sb atoms. Application of hydrostatic pressure on the latter induces a structural change from a staggered to a coincident arrangement of AE ions accompanying a transition from insulator to a metal containing Dirac fermions. The structural investigations show that the stacking type of cation and orthorhombic distortion of Sb layers are the main factors to decide the crystal symmetry of the material. We propose that the Dirac fermions can be obtained by controlling the size of cation and the volume of AEMnSb(2) compounds.close1
Density Functional Theory Studies of Hole Mobility in Picene and Pentacene Crystals
No full textWe have investigated the electronic properties and hole mobilities of picene and its isomer pentacene using the density functional theory and classical Marcus charge transfer theory. In pristine crystal with herringbone structure, pentacene and picene have drift hole mobilities of 2.147 and 0.644 cm(2) V-1 s(-1), respectively, which are consistent with recent experimental results. We also show that picene crystal can exhibit maximum mobility up to 2.629 cm(2) V-1 s(-1) along the pi-pi stacking direction, while the highest mobility of pentacene crystal exhibits along the herringbone stacking direction. Also the anisotropy of the mobility in the ab plane is 2.4 and 5.6 for picene and pentacene crystals, respectively. Since the air stability of picene is better than pentacene due to lower HOMO levels in picene, we suggest that picene and its homologous phenacenes series are promising candidates toward high mobility organic semiconductor devices with good air stability. This work also sheds light on the favorable or undesirable properties for efficient charge transport in oligoacene and phenacenes series.X11199sciescopu
Kinematic analysis and design of a six DOF 3-PRPS in-parallel manipulator
No full textThis paper presents a kinematic analysis and design characteristics of an in-parallel manipulator developed for the probing task application that requires high precision, active compliance, and high control bandwidth. The developed manipulator is a class of six-degree-of-freedom in-parallel platforms with 3 PRPS (prismatic-revolute-prismatic-spherical joints) chain geometry. The main advantages of this manipulator, compared with the typical Stewart platform type, are the capability of pure rotation generation and the easy prediction of the moving platform motion. The purpose of this paper is to develop an efficient kinematic model which can be used for real-time control and to propose systematic methods to design the manipulator considering workspace, manipulability, resistivity, singularity, and the existence conditions of the forward kinematic solution. Particularly, we propose a new method for checking the singularity of the parallel manipulator using the translational and rotational resistivity measures. A series of simulation are carried out to show kinematic characteristics and performance of the manipulator mechanism. A prototype manipulator was built based on the kinematic analysis results
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