91,620 research outputs found
On numerical integration and computer implementation of viscoplastic models
Due to the stringent design requirement for aerospace or nuclear structural components, considerable research interests have been generated on the development of constitutive models for representing the inelastic behavior of metals at elevated temperatures. In particular, a class of unified theories (or viscoplastic constitutive models) have been proposed to simulate material responses such as cyclic plasticity, rate sensitivity, creep deformations, strain hardening or softening, etc. This approach differs from the conventional creep and plasticity theory in that both the creep and plastic deformations are treated as unified time-dependent quantities. Although most of viscoplastic models give better material behavior representation, the associated constitutive differential equations have stiff regimes which present numerical difficulties in time-dependent analysis. In this connection, appropriate solution algorithm must be developed for viscoplastic analysis via finite element method
Computational structures for robotic computations
The computational problem of inverse kinematics and inverse dynamics of robot manipulators by taking advantage of parallelism and pipelining architectures is discussed. For the computation of inverse kinematic position solution, a maximum pipelined CORDIC architecture has been designed based on a functional decomposition of the closed-form joint equations. For the inverse dynamics computation, an efficient p-fold parallel algorithm to overcome the recurrence problem of the Newton-Euler equations of motion to achieve the time lower bound of O(log sub 2 n) has also been developed
Pitch ability as an aptitude for tone learning
Tone languages such as Mandarin use voice pitch to signal lexical contrasts, presenting a challenge for second/foreign language (L2) learners whose native languages do not use pitch in this manner. The present study examined components of an aptitude for mastering L2 lexical tone. Native English speakers with no previous tone language experience completed a Mandarin word learning task, as well as tests of pitch ability, musicality, L2 aptitude, and general cognitive ability. Pitch ability measures improved predictions of learning performance beyond musicality, L2 aptitude, and general cognitive ability and also predicted transfer of learning to new talkers. In sum, although certain nontonal measures help predict successful tone learning, the central components of tonal aptitude are pitch-specific perceptual measures
Damping of antiferromagnetic spin waves by valence fluctuations in the double layer perovskite YBaFe2O5
Inelastic neutron scattering experiments show that spin dynamics in the
charge ordered insulating ground state of the double-layer perovskite YBaFe2O5
is well described in terms of eg superexchange interactions. Above the Verwey
transition at TV = 308 K, t2g double exchange-type conduction within
antiferromagnetic FeO2--BaO--FeO2 double layers proceeds by an electron hopping
process that requires a spin flip of the five-fold coordinated Fe ions, costing
an energy 5S^2 of approximately 0.1 eV. The hopping process disrupts
near-neighbor spin correlations, leading to massive damping of zone-boundary
spin waves.Comment: RevTeX, 4 pages, 4 figures, submitted to Phys. Rev. Let
Structure of the Partition Function and Transfer Matrices for the Potts Model in a Magnetic Field on Lattice Strips
We determine the general structure of the partition function of the -state
Potts model in an external magnetic field, for arbitrary ,
temperature variable , and magnetic field variable , on cyclic, M\"obius,
and free strip graphs of the square (sq), triangular (tri), and honeycomb
(hc) lattices with width and arbitrarily great length . For the
cyclic case we prove that the partition function has the form ,
where denotes the lattice type, are specified
polynomials of degree in , is the corresponding
transfer matrix, and () for ,
respectively. An analogous formula is given for M\"obius strips, while only
appears for free strips. We exhibit a method for
calculating for arbitrary and give illustrative
examples. Explicit results for arbitrary are presented for
with and . We find very simple formulas
for the determinant . We also give results for
self-dual cyclic strips of the square lattice.Comment: Reference added to a relevant paper by F. Y. W
Strong coupling of single emitters to surface plasmons
We propose a method that enables strong, coherent coupling between individual
optical emitters and electromagnetic excitations in conducting nano-structures.
The excitations are optical plasmons that can be localized to sub-wavelength
dimensions. Under realistic conditions, the tight confinement causes optical
emission to be almost entirely directed into the propagating plasmon modes via
a mechanism analogous to cavity quantum electrodynamics. We first illustrate
this result for the case of a nanowire, before considering the optimized
geometry of a nanotip. We describe an application of this technique involving
efficient single-photon generation on demand, in which the plasmons are
efficiently out-coupled to a dielectric waveguide. Finally we analyze the
effects of increased scattering due to surface roughness on these
nano-structures.Comment: 34 pages, 7 figure
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