225 research outputs found
Virtual Prototyping of a Flexure-based RCC Device for Automated Assembly
The actual use of Industrial Robots (IR) for assembly systems requires the exertion of suitable strategies allowing to overcome shortcomings about IR poor precision and repeatability. In this paper, the practical issues that emerge during common \ue2\u80\u9cpeg-in-hole\ue2\u80\u9d assembly procedures are discussed. In particular, the use of passive Remote Center of Compliance (RCC) devices, capable of compensating the IR non-optimal performance in terms of repeatability, is investigated. The focus of the paper is the design and simulation of a flexure-based RCC that allows the prevention of jamming, due to possible positioning inaccuracies during peg insertion. The proposed RCC architecture comprises a set of flexural hinges, whose behavior is simulated via a CAE tool that provides built-in functions for modelling the motion of compliant members. For given friction coefficients of the contact surfaces, these numerical simulations allow to determine the maximum lateral and angular misalignments effectively manageable by the RCC device
Unusual temperature dependence of band dispersion in Ba(Fe(1-x)Ru(x))2As2 and its consequences for antiferromagnetic ordering
We have performed detailed studies of the temperature evolution of the
electronic structure in Ba(Fe(1-x)Ru(x))2As2 using Angle Resolved Photoemission
Spectroscopy (ARPES). Surprisingly, we find that the binding energy of both
hole and electron bands changes significantly with temperature in pure and Ru
substituted samples. The hole and electron pockets are well nested at low
temperature in unsubstituted (BaFe2As2) samples, which likely drives the spin
density wave (SDW) and resulting antiferromagnetic order. Upon warming, this
nesting is degraded as the hole pocket shrinks and the electron pocket expands.
Our results demonstrate that the temperature dependent nesting may play an
important role in driving the antiferromagnetic/paramagnetic phase transition.Comment: 5 pages, 6 figure
Influence of Spin Orbit Coupling in the Iron-Based Superconductors
We report on the influence of spin-orbit coupling (SOC) in the Fe-based
superconductors (FeSCs) via application of circularly-polarized spin and
angle-resolved photoemission spectroscopy. We combine this technique in
representative members of both the Fe-pnictides and Fe-chalcogenides with ab
initio density functional theory and tight-binding calculations to establish an
ubiquitous modification of the electronic structure in these materials imbued
by SOC. The influence of SOC is found to be concentrated on the hole pockets
where the superconducting gap is generally found to be largest. This result
contests descriptions of superconductivity in these materials in terms of pure
spin-singlet eigenstates, raising questions regarding the possible pairing
mechanisms and role of SOC therein.Comment: For supplementary information, see
http://qmlab.ubc.ca/ARPES/PUBLICATIONS/articles.htm
Disorder Induced Stripes in d-Wave Superconductors
Stripe phases are observed experimentally in several copper-based high-Tc
superconductors near 1/8 hole doping. However, the specific characteristics may
vary depending on the degree of dopant disorder and the presence or absence of
a low- temperature tetragonal phase. On the basis of a Hartree-Fock decoupling
scheme for the t-J model we discuss the diverse behavior of stripe phases. In
particular the effect of inhomogeneities is investigated in two distinctly
different parameter regimes which are characterized by the strength of the
interaction. We observe that small concen- trations of impurities or vortices
pin the unidirectional density waves, and dopant disorder is capable to
stabilize a stripe phase in parameter regimes where homogeneous phases are
typically favored in clean systems. The momentum-space results exhibit
universal features for all coexisting density-wave solutions, nearly unchanged
even in strongly disordered systems. These coexisting solutions feature
generically a full energy gap and a particle-hole asymmetry in the density of
states.Comment: 28 pages, 8 figure
Spectroscopic evidence for preformed Cooper pairs in the pseudogap phase of cuprates
Angle-resolved photoemission on underdoped LaSrCuO
reveals that in the pseudogap phase, the dispersion has two branches located
above and below the Fermi level with a minimum at the Fermi momentum. This is
characteristic of the Bogoliubov dispersion in the superconducting state. We
also observe that the superconducting and pseudogaps have the same d-wave form
with the same amplitude. Our observations provide direct evidence for preformed
Cooper pairs, implying that the pseudogap phase is a precursor to
superconductivity
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