102 research outputs found
Clusters and supply chain management: challenges and obstacles
Purpose: This paper provides an insight into cluster supply chain (CSC) management by identifying
challenges and obstacles in the design, implementation and improvement of CSC. This evaluation aims to
propose future research directions for the management of CSC.
Research Approach: A systematic review of published research on CSC management between 2006 and
2013 is conducted in order to round up previous research in this area and identify the gaps in the design,
implementation and management of CSC; up on which the paper closes with a proposed agenda for future
work.
Findings and Originality: There is a limited understanding of the supply chain cluster concept and the
implementation of its practices in addition to the lack of studies that focused on how to model, manage
and improve the performance of CSC. Therefore, this paper would contribute to knowledge by providing an
insight into CSC management and identifying future research directions for developing SC cluster theories
in order to maximize the integration of supply chain and accordingly improving the performance of firms.
Research Impact: A limited number of studies have been conducted to demonstrate the potential impact of
CSC. The previous research did not provide a comprehensive review focusing on the evolution and the
development of CSC idea. The review in this paper will summarise the research up to now in CSC area in
order to identify challenges and obstacles in the design, implementation and improvement of CSC and
propose future research directions.
Practical Impact: This paper helps companies to understand benefits that can be raised from creating CSC
and gives them directions for improving their capabilities to create CSC and select SC partners, which
consequently help in increasing their competitiveness in terms of enhancing performance and increasing
sustainability
Theoretical de Haas-van Alphen Data and Plasma Frequencies of MgB2 and TaB2
The de Haas-van Alphen-frequencies as well as the effective masses for a
magnetic field parallel to the crystallographic c-axis are calculated within
the local spin density approximation (LSDA) for MgB2 and TaB2. In addition, we
analyze the plasma frequencies computed for each Fermi surface sheet. We find a
large anisotropy of Fermi velocities in MgB2 in difference to the nearly
isotropic behavior in TaB2. We compare calculations performed within the
relativistic non-full potential augmented-spherical-wave (ASW) scheme and the
scalar-relativistic full potential local orbital (FPLO) scheme. A significant
dependence for small cross sections on the bandstructure method is found. The
comparison with the first available experimental de Haas-van Alphen-data by
Yelland et al. (Ref. 19) shows deviations from the electronic structure
calculated within both L(S)DA approaches although the cross section predicted
by FPLO are closer to the experimental data. The elucidation of the relevant
many-body effects beyond the standard LDA is considered as a possible key
problem to understand the superconductivity in MgB2.Comment: Typos corrected, 3references added. Extended and corrected version of
S. Elgazzar et al., Solid State Comm. v. 121, 99 (2002). 7pages, 4figures,
AIP Conference Proc. "Correlated Electron Systems and High-Tc
Superconductors" (ed. F. Mancini) (October 2001, Salerno, Italy
Nonlocal synchronization in nearest neighbour coupled oscillators
We investigate a system of nearest neighbor coupled oscillators. We show that the nonlocal frequency synchronization, that might appear in such a system, occurs as a consequence of the nearest neighbor coupling. The power spectra of nonadjacent oscillators show that there is no complete coincidence between all frequency peaks of the oscillators in the nonlocal cluster, while the peaks for neighboring oscillators approximately coincide even if they are not yet in a cluster. It is shown that nonadjacent oscillators closer in frequencies, share slow modes with their adjacent oscillators which are neighbors in space. It is also shown that when a direct coupling between non-neighbors oscillators is introduced explicitly, the peaks of the spectra of the frequencies of those non-neighbors coincide
Quasi-two-dimensional Fermi surfaces of the heavy-fermion superconductor CePdIn
We report low-temperature de Haas-van Alphen (dHvA) effect measurements in
magnetic fields up to 35 T of the heavy-fermion superconductor CePdIn.
The comparison of the experimental results with band-structure calculations
implies that the 4 electrons are itinerant rather than localized. The
cyclotron masses estimated at high field are only moderately enhanced, 8 and 14
, but are substantially larger than the corresponding band masses. The
observed angular dependence of the dHvA frequencies suggests
quasi-two-dimensional Fermi surfaces in agreement with band-structure
calculations. However, the deviation from ideal two dimensionality is larger
than in CeCoIn, with which CePdIn bears a lot of similarities. This
subtle distinction accounts for the different superconducting critical
temperatures of the two compounds.Comment: accepted to Phys. Rev.
Electronic structure theory of the hidden order material URuSi
We report a comprehensive electronic structure investigation of the
paramagnetic (PM), the large moment antiferromagnetic (LMAF), and the hidden
order (HO) phases of URuSi. We have performed relativistic
full-potential calculations on the basis of the density functional theory
(DFT), employing different exchange-correlation functionals to treat electron
correlations within the open -shell of uranium. Specifically, we
investigate---through a comparison between calculated and low-temperature
experimental properties---whether the electrons are localized or
delocalized in URuSi. We also performed dynamical mean field theory
calculations (LDA+DMFT) to investigate the temperature evolution of the
quasi-particle states at 100~K and above, unveiling a progressive opening of a
quasi-particle gap at the chemical potential when temperature is reduced. A
detailed comparison of calculated properties with known experimental data
demonstrates that the LSDA and GGA approaches, in which the uranium
electrons are treated as itinerant, provide an excellent explanation of the
available low-temperature experimental data of the PM and LMAF phases. We show
furthermore that due to a materials-specific Fermi surface instability a large,
but partial, Fermi surface gapping of up to 750 K occurs upon antiferromagnetic
symmetry breaking. The occurrence of the HO phase is explained through
dynamical symmetry breaking induced by a mode of long-lived antiferromagnetic
spin-fluctuations. This dynamical symmetry breaking model explains why the
Fermi surface gapping in the HO phase is similar but smaller than that in the
LMAF phase and it also explains why the HO and LMAF phases have the same Fermi
surfaces yet different order parameters. Suitable derived order parameters for
the HO are proposed to be the Fermi surface gap or the dynamic spin-spin
correlation function.Comment: 23 pages, 20 figure
Fermi-Surface Reconstruction in the Periodic Anderson Model
We study ground state properties of periodic Anderson model in a
two-dimensional square lattice with variational Monte Carlo method. It is shown
that there are two different types of quantum phase transition: a conventional
antiferromagnetic transition and a Fermi-surface reconstruction which
accompanies a change of topology of the Fermi surface. The former is induced by
a simple back-folding of the Fermi surface while the latter is induced by
localization of electrons. The mechanism of these transitions and the
relation to the recent experiments on Fermi surface are discussed in detail.Comment: 8 pages, 7 figures, submitted to Journal of the Physical Society of
Japa
Field Reentrance of the Hidden Order State of URu2Si2 under Pressure
Combination of neutron scattering and thermal expansion measurements under
pressure shows that the so-called hidden order phase of URu2Si2 reenters in
magnetic field when antiferromagnetism (AF) collapses at H_AF (T). Macroscopic
pressure studies of the HO-AF boundaries were realized at different pressures
via thermal expansion measurements under magnetic field using a strain gauge.
Microscopic proof at a given pressure is the reappearance of the resonance at
Q_0=(1,0,0) under field which is correlated with the collapse of the AF Bragg
reflections at Q_0.Comment: 5 pages, 6 figures, accepted for publication in J. Phys. Soc. Jp
Why the hidden order in URu2Si2 is still hidden - one simple answer
For more than two decades, the nonmagnetic anomaly observed around 17.5 K in
URu2Si2, has been investigated intensively. However, any kind of fingerprint
for the lattice anomaly has not been observed. Therefore, the order has been
called "the hidden order". One simple answer to why the hidden order is still
hidden is presented from the space group analysis. The second order phase
transition from I4/mmm (No. 139) to P4_2/mnm (No. 136) does not need any kind
of lattice distortion in this system, and allows the NQR frequency at Ru-site
unchanged. It is compatible with O_{xy}-type anti-ferro quadrupole ordering
with Q=(0, 0, 1). The characteristics of the hidden order are discussed based
on the local 5f^2 electron picture.Comment: Accepted for publication in J. Phys. Soc. Jpn., 4 pages, 2 figure
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