3,054 research outputs found
Scheduling Jobs in Flowshops with the Introduction of Additional Machines in the Future
This is the author's peer-reviewed final manuscript, as accepted by the publisher. The published article is copyrighted by Elsevier and can be found at: http://www.journals.elsevier.com/expert-systems-with-applications/.The problem of scheduling jobs to minimize total weighted tardiness in flowshops,\ud
with the possibility of evolving into hybrid flowshops in the future, is investigated in\ud
this paper. As this research is guided by a real problem in industry, the flowshop\ud
considered has considerable flexibility, which stimulated the development of an\ud
innovative methodology for this research. Each stage of the flowshop currently has\ud
one or several identical machines. However, the manufacturing company is planning\ud
to introduce additional machines with different capabilities in different stages in the\ud
near future. Thus, the algorithm proposed and developed for the problem is not only\ud
capable of solving the current flow line configuration but also the potential new\ud
configurations that may result in the future. A meta-heuristic search algorithm based\ud
on Tabu search is developed to solve this NP-hard, industry-guided problem. Six\ud
different initial solution finding mechanisms are proposed. A carefully planned\ud
nested split-plot design is performed to test the significance of different factors and\ud
their impact on the performance of the different algorithms. To the best of our\ud
knowledge, this research is the first of its kind that attempts to solve an industry-guided\ud
problem with the concern for future developments
Age of the Universe: Influence of the Inhomogeneities on the global Expansion-Factor
For the first time we calculate quantitatively the influence of
inhomogeneities on the global expansion factor by averaging the Friedmann
equation. In the framework of the relativistic second-order
Zel'dovich-approximation scheme for irrotational dust we use observational
results in form of the normalisation constant fixed by the COBE results and we
check different power spectra, namely for adiabatic CDM, isocurvature CDM, HDM,
WDM, Strings and Textures. We find that the influence of the inhomogeneities on
the global expansion factor is very small. So the error in determining the age
of the universe using the Hubble constant in the usual way is negligible. This
does not imply that the effect is negligible for local astronomical
measurements of the Hubble constant. Locally the determination of the
redshift-distance relation can be strongly influenced by the peculiar velocity
fields due to inhomogeneities. Our calculation does not consider such effects,
but is contrained to comparing globally homogeneous and averaged inhomogeneous
matter distributions. In addition we relate our work to previous treatments.Comment: 10 pages, version accepted by Phys. Rev.
Lagrangian description of fluid flow with pressure in relativistic cosmology
The Lagrangian description of fluid flow in relativistic cosmology is
extended to the case of flow accelerated by pressure. In the description, the
entropy and the vorticity are obtained exactly for the barotropic equation of
state. In order to determine the metric, the Einstein equation is solved
perturbatively, when metric fluctuations are small but entropy inhomogeneities
are large. Thus, the present formalism is applicable to the case when the
inhomogeneities are small in the large scale but locally nonlinear.Comment: 11 pages (RevTeX); accepted for publication in Phys. Rev.
Wave Energy: a Pacific Perspective
This is the author's peer-reviewed final manuscript, as accepted by the publisher. The published article is copyrighted by The Royal Society and can be found at: http://rsta.royalsocietypublishing.org/.This paper illustrates the status of wave energy development in Pacific Rim countries by characterizing the available resource and introducing the regionâs current and potential future leaders in wave energy converter development. It also describes the existing licensing and permitting process as well as potential environmental concerns. Capabilities of Pacific Ocean testing facilities are described in addition to the regionâs vision of the future of wave energy
Lightweight Lempel-Ziv Parsing
We introduce a new approach to LZ77 factorization that uses O(n/d) words of
working space and O(dn) time for any d >= 1 (for polylogarithmic alphabet
sizes). We also describe carefully engineered implementations of alternative
approaches to lightweight LZ77 factorization. Extensive experiments show that
the new algorithm is superior in most cases, particularly at the lowest memory
levels and for highly repetitive data. As a part of the algorithm, we describe
new methods for computing matching statistics which may be of independent
interest.Comment: 12 page
How is the local-scale gravitational instability influenced by the surrounding large-scale structure formation?
We develop the formalism to investigate the relation between the evolution of
the large-scale (quasi) linear structure and that of the small-scale nonlinear
structure in Newtonian cosmology within the Lagrangian framework. In doing so,
we first derive the standard Friedmann expansion law using the averaging
procedure over the present horizon scale. Then the large-scale (quasi) linear
flow is defined by averaging the full trajectory field over a large-scale
domain, but much smaller than the horizon scale. The rest of the full
trajectory field is supposed to describe small-scale nonlinear dynamics. We
obtain the evolution equations for the large-scale and small-scale parts of the
trajectory field. These are coupled to each other in most general situations.
It is shown that if the shear deformation of fluid elements is ignored in the
averaged large-scale dynamics, the small-scale dynamics is described by
Newtonian dynamics in an effective Friedmann-Robertson-Walker (FRW) background
with a local scale factor. The local scale factor is defined by the sum of the
global scale factor and the expansion deformation of the averaged large-scale
displacement field. This means that the evolution of small-scale fluctuations
is influenced by the surrounding large-scale structure through the modification
of FRW scale factor. The effect might play an important role in the structure
formation scenario. Furthermore, it is argued that the so-called {\it
optimized} or {\it truncated} Lagrangian perturbation theory is a good
approximation in investigating the large-scale structure formation up to the
quasi nonlinear regime, even when the small-scale fluctuations are in the
non-linear regime.Comment: 15pages, Accepted for publication in Gravitation and General
Relativit
Molecular Aspects of Secretory Granule Exocytosis by Neurons and Endocrine Cells
Neuronal communication and endocrine signaling are fundamental for integrating
the function of tissues and cells in the body. Hormones released by endocrine
cells are transported to the target cells through the circulation. By contrast, transmitter
release from neurons occurs at specialized intercellular junctions, the synapses.
Nevertheless, the mechanisms by which signal molecules are synthesized,
stored, and eventually secreted by neurons and endocrine cells are very similar.
Neurons and endocrine cells have in common two different types of secretory
organelles, indicating the presence of two distinct secretory pathways. The synaptic
vesicles of neurons contain excitatory or inhibitory neurotransmitters, whereas the
secretory granules (also referred to as dense core vesicles, because of their electron
dense content) are filled with neuropeptides and amines. In endocrine cells, peptide
hormones and amines predominate in secretory granules. The function and content
of vesicles, which share antigens with synaptic vesicles, are unknown for most
endocrine cells. However, in B cells of the pancreatic islet, these vesicles contain
GABA, which may be involved in intrainsular signaling.'
Exocytosis of both synaptic vesicles and secretory granules is controlled by
cytoplasmic calcium. However, the precise mechanisms of the subsequent steps,
such as docking of vesicles and fusion of their membranes with the plasma membrane,
are still incompletely understood. This contribution summarizes recent observations
that elucidate components in neurons and endocrine cells involved in
exocytosis. Emphasis is put on the intracellular aspects of the release of secretory
granules that recently have been analyzed in detail
On average properties of inhomogeneous fluids in general relativity II: perfect fluid cosmologies
For general relativistic spacetimes filled with an irrotational perfect fluid
a generalized form of Friedmann's equations governing the expansion factor of
spatially averaged portions of inhomogeneous cosmologies is derived. The
averaging problem for scalar quantities is condensed into the problem of
finding an `effective equation of state' including kinematical as well as
dynamical `backreaction' terms that measure the departure from a standard FLRW
cosmology. Applications of the averaged models are outlined including
radiation-dominated and scalar field cosmologies (inflationary and
dilaton/string cosmologies). In particular, the averaged equations show that
the averaged scalar curvature must generically change in the course of
structure formation, that an averaged inhomogeneous radiation cosmos does not
follow the evolution of the standard homogeneous-isotropic model, and that an
averaged inhomogeneous perfect fluid features kinematical `backreaction' terms
that, in some cases, act like a free scalar field source. The free scalar field
(dilaton) itself, modelled by a `stiff' fluid, is singled out as a special
inhomogeneous case where the averaged equations assume a simple form.Comment: TeX 21 pages, matches published version: G.R.G., in pres
Gauge Field Formulation of Adiabatic Spin Torques
Previous calculation of spin torques for small-amplitude magnetization
dynamics around a uniformly magnetized state [J. Phys. Soc. Jpn. {\bf 75}
(2006) 113706] is extended here to the case of finite-amplitude dynamics. This
is achieved by introducing an `` adiabatic'' spin frame for conduction
electrons, and the associated SU(2) gauge field. In particular, the Gilbert
damping is shown to arise from the time variation of the spin-relaxation source
terms in this new frame, giving a new physical picture of the damping. The
present method will allow a `` first-principle'' derivation of spin torques
without any assumptions such as rotational symmetry in spin space.Comment: 4 pages, 3 figure
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