98,530 research outputs found
Comment on "Spectroscopic Evidence for Multiple Order Parameter Components in the Heavy Fermion Superconductor CeCoIn"
Recently, Rourke et al. reported point-contact spectroscopy results on the
heavy-fermion superconductor CeCoIn [1]. They obtained conductance spectra
on the c-axis surfaces of CeCoIn single crystals. Their major claims are
two-fold: CeCoIn has i) d-wave pairing symmetry and ii) two coexisting
order parameter components. In this Comment, we show that these claims are not
warranted by the data presented. [1] Rourke et al., Phys. Rev. Lett. 94, 107005
(2005).Comment: accepted for publication in Phys. Rev. Lett., final for
First principles investigation of transition-metal doped group-IV semiconductors: RY (R=Cr, Mn, Fe; Y=Si, Ge)
A number of transition-metal (TM) doped group-IV semiconductors,
RY (R=Cr, Mn and Fe; Y=Si, Ge), have been studied by the first
principles calculations. The obtained results show that antiferromagnetic (AFM)
order is energetically more favored than ferromagnetic (FM) order in Cr-doped
Ge and Si with =0.03125 and 0.0625. In 6.25% Fe-doped Ge, FM interaction
dominates in all range of the R-R distances while for Fe-doped Ge at 3.125% and
Fe-doped Si at both concentrations of 3.125% and 6.25%, only in a short R-R
range can the FM states exist. In the Mn-doped case, the RKKY-like mechanism
seems to be suitable for the Ge host matrix, while for the Mn-doped Si, the
short-range AFM interaction competes with the long-range FM interaction. The
different origin of the magnetic orders in these diluted magnetic
semiconductors (DMSs) makes the microscopic mechanism of the ferromagnetism in
the DMSs more complex and attractive.Comment: 14 pages, 2 figures, 6 table
Phase transition classes in triplet and quadruplet reaction diffusion models
Phase transitions of reaction-diffusion systems with site occupation
restriction and with particle creation that requires n=3,4 parents, whereas
explicit diffusion of single particles (A) is present are investigated in low
dimensions by mean-field approximation and simulations. The mean-field
approximation of general nA -> (n+k)A, mA -> (m-l)A type of lattice models is
solved and novel kind of critical behavior is pointed out. In d=2 dimensions
the 3A -> 4A, 3A -> 2A model exhibits a continuous mean-field type of phase
transition, that implies d_c<2 upper critical dimension. For this model in d=1
extensive simulations support a mean-field type of phase transition with
logarithmic corrections unlike the Park et al.'s recent study (Phys. Rev E {\bf
66}, 025101 (2002)). On the other hand the 4A -> 5A, 4A -> 3A quadruplet model
exhibits a mean-field type of phase transition with logarithmic corrections in
d=2, while quadruplet models in 1d show robust, non-trivial transitions
suggesting d_c=2. Furthermore I show that a parity conserving model 3A -> 5A,
2A->0 in d=1 has a continuous phase transition with novel kind of exponents.
These results are in contradiction with the recently suggested implications of
a phenomenological, multiplicative noise Langevin equation approach and with
the simulations on suppressed bosonic systems by Kockelkoren and Chat\'e
(cond-mat/0208497).Comment: 8 pages, 10 figures included, Updated with new data, figures, table,
to be published in PR
Determination of the Joint Confidence Region of Optimal Operating Conditions in Robust Design by Bootstrap Technique
Robust design has been widely recognized as a leading method in reducing
variability and improving quality. Most of the engineering statistics
literature mainly focuses on finding "point estimates" of the optimum operating
conditions for robust design. Various procedures for calculating point
estimates of the optimum operating conditions are considered. Although this
point estimation procedure is important for continuous quality improvement, the
immediate question is "how accurate are these optimum operating conditions?"
The answer for this is to consider interval estimation for a single variable or
joint confidence regions for multiple variables.
In this paper, with the help of the bootstrap technique, we develop
procedures for obtaining joint "confidence regions" for the optimum operating
conditions. Two different procedures using Bonferroni and multivariate normal
approximation are introduced. The proposed methods are illustrated and
substantiated using a numerical example.Comment: Two tables, Three figure
GW method with the self-consistent Sternheimer equation
We propose a novel approach to quasiparticle GW calculations which does not
require the computation of unoccupied electronic states. In our approach the
screened Coulomb interaction is evaluated by solving self-consistent
linear-response Sternheimer equations, and the noninteracting Green's function
is evaluated by solving inhomogeneous linear systems. The frequency-dependence
of the screened Coulomb interaction is explicitly taken into account. In order
to avoid the singularities of the screened Coulomb interaction the calculations
are performed along the imaginary axis, and the results are analytically
continued to the real axis through Pade' approximants. As a proof of concept we
implemented the proposed methodology within the empirical pseudopotential
formalism and we validated our implementation using silicon as a test case. We
examine the advantages and limitations of our method and describe promising
future directions.Comment: 18 pages, 6 figure
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Rapid Fabrication of Large-sized Solid Shape using Variable Lamination Manufacturing and Multi-functional Hotwire Cutting System
Rapid prototyping (RP) technologies have been widely used to reduce the lead-time and
development cost of new products. The VLM-ST process has been developed to overcome the
currently developed RP technologies such as a large building time, a high building cost, an
additional post-processing and a large apparatus cost. However, the VLM-ST process has the
limitation of fabricated model size (VLM300: 297×210 mm, VLM400: 420×297 mm) and the
limitation of slope angle when the large-sized model more than 600 × 600 × 600 mm or
axisymmetric shape is fabricated. The objective of this paper is to develop a multi-functional
hotwire cutting system (MHC) using EPS-foam block or sheet as the working material in order to
fabricate a large-sized shape more than 600 × 600 × 600 mm. Because the MHC apparatus
employs a four-axis synchronized hotwire cutter with the structure of two XY movable heads and
a turn-table, it allows the easy fabrication of various 3D shapes, such as (1) an axisymmetric
shape or a sweeping cross-sectioned pillar shape using the hot-strip in the form of sweeping
surface and EPS foam block on the turn-table, (2) a polyhedral complex shape using the hotwire
and EPS foam block on the turn-table, and (3) a ruled surface approximated freeform shape using
the hotwire and EPS foam sheet. In order to examine the applicability of the developed MHC
apparatus, an axisymmetric shape, a polyhedral shape and a large-sized freeform shape were
fabricated by the apparatus.Mechanical Engineerin
Painlev\'{e} analysis of the coupled nonlinear Schr\"{o}dinger equation for polarized optical waves in an isotropic medium
Using the Painlev\'{e} analysis, we investigate the integrability properties
of a system of two coupled nonlinear Schr\"{o}dinger equations that describe
the propagation of orthogonally polarized optical waves in an isotropic medium.
Besides the well-known integrable vector nonlinear Schr\"{o}dinger equation, we
show that there exist a new set of equations passing the Painlev\'{e} test
where the self and cross phase modulational terms are of different magnitude.
We introduce the Hirota bilinearization and the B\"{a}cklund transformation to
obtain soliton solutions and prove integrability by making a change of
variables. The conditions on the third-order susceptibility tensor imposed by these new integrable equations are explained
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