152 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
`What is a Thing?': Topos Theory in the Foundations of Physics
The goal of this paper is to summarise the first steps in developing a
fundamentally new way of constructing theories of physics. The motivation comes
from a desire to address certain deep issues that arise when contemplating
quantum theories of space and time. In doing so we provide a new answer to
Heidegger's timeless question ``What is a thing?''.
Our basic contention is that constructing a theory of physics is equivalent
to finding a representation in a topos of a certain formal language that is
attached to the system. Classical physics uses the topos of sets. Other
theories involve a different topos. For the types of theory discussed in this
paper, a key goal is to represent any physical quantity with an arrow
\breve{A}_\phi:\Si_\phi\map\R_\phi where \Si_\phi and are two
special objects (the `state-object' and `quantity-value object') in the
appropriate topos, .
We discuss two different types of language that can be attached to a system,
. The first, \PL{S}, is a propositional language; the second, \L{S}, is
a higher-order, typed language. Both languages provide deductive systems with
an intuitionistic logic. With the aid of \PL{S} we expand and develop some of
the earlier work (By CJI and collaborators.) on topos theory and quantum
physics. A key step is a process we term `daseinisation' by which a projection
operator is mapped to a sub-object of the spectral presheaf \Sig--the topos
quantum analogue of a classical state space. The topos concerned is \SetH{}:
the category of contravariant set-valued functors on the category (partially
ordered set) \V{} of commutative sub-algebras of the algebra of bounded
operators on the quantum Hilbert space \Hi.Comment: To appear in ``New Structures in Physics'' ed R. Coeck
Cyclotomic integers, fusion categories, and subfactors
Dimensions of objects in fusion categories are cyclotomic integers, hence
number theoretic results have implications in the study of fusion categories
and finite depth subfactors. We give two such applications. The first
application is determining a complete list of numbers in the interval (2,
76/33) which can occur as the Frobenius-Perron dimension of an object in a
fusion category. The smallest number on this list is realized in a new fusion
category which is constructed in the appendix written by V. Ostrik, while the
others are all realized by known examples. The second application proves that
in any family of graphs obtained by adding a 2-valent tree to a fixed graph,
either only finitely many graphs are principal graphs of subfactors or the
family consists of the A_n or D_n Dynkin diagrams. This result is effective,
and we apply it to several families arising in the classification of subfactors
of index less then 5.Comment: 47 pages, with an appendix by Victor Ostri
Hope, optimism, and other business assets: Why âpsychological capitalâ is so valuable to your company
Entrevista com Fred Luthans,1 coauthor of Psychological Capital: Developing the Human
Competitive EdgeInterview with Fred Luthans,1 coauthor of Psychological Capital: Developing the Human
Competitive Edg
A quantitative comparison of opacities calculated using the distorted-wave and R-matirx methods
peer reviewe
Three-variable Mahler measures and special values of modular and Dirichlet -series
In this paper we prove that the Mahler measures of the Laurent polynomials
, ,
and , for various values of , are of the form , where , is a CM newform of
weight 3, and is a quadratic character. Since it has been proved that
these Maher measures can also be expressed in terms of logarithms and
-hypergeometric series, we obtain several new hypergeometric evaluations
and transformations from these results
Growth and mortality of coccolithophores during spring in a temperate Shelf Sea (Celtic Sea, April 2015)
Coccolithophores are key components of phytoplankton communities, exerting a critical impact on the global carbon cycle and the Earthâs climate through the production of coccoliths made of calcium carbonate (calcite) and bioactive gases. Microzooplankton grazing is an important mortality factor in coccolithophore blooms, however little is currently known regarding the mortality (or growth) rates within non-bloom populations. Measurements of coccolithophore calcite production (CP) and dilution experiments to determine microzooplankton (â€63âŻÂ”m) grazing rates were made during a spring cruise (April 2015) at the Central Celtic Sea (CCS), shelf edge (CS2), and within an adjacent April bloom of the coccolithophore Emiliania huxleyi at station J2.
CP at CCS ranged from 10.4 to 40.4âŻÂ”mol C mâ3 dâ1 and peaked at the height of the spring phytoplankton bloom (peak chlorophyll-a concentrations âŒ6âŻmgâŻmâ3). Cell normalised calcification rates declined from âŒ1.7 to âŒ0.2âŻpmol C cellâ1 dâ1, accompanied by a shift from a mixed coccolithophore species community to one dominated by the more lightly calcified species E. huxleyi and Calciopappus caudatus. At the CCS, coccolithophore abundance increased from 6 to 94 cells mLâ1, with net growth rates ranging from 0.06 to 0.21 dâ1 from the 4th to the 28th April. Estimates of intrinsic growth and grazing rates from dilution experiments, at the CCS ranged from 0.01 to 0.86 dâ1 and from 0.01 to 1.32 dâ1, respectively, which resulted in variable net growth rates during April. Microzooplankton grazers consumed 59 to >100% of daily calcite production at the CCS. Within the E. huxleyi bloom a maximum density of 1986 cells mLâ1 was recorded, along with CP rates of 6000âŻÂ”mol C mâ3 dâ1 and an intrinsic growth rate of 0.29 dâ1, with âŒ80% of daily calcite production being consumed.
Our results show that microzooplankton can exert strong top-down control on both bloom and non-bloom coccolithophore populations, grazing over 60% of daily growth (and calcite production). The fate of consumed calcite is unclear, but may be lost either through dissolution in acidic food vacuoles, and subsequent release as CO2, or export to the seabed after incorporation into small faecal pellets. With such high microzooplankton-mediated mortality losses, the fate of grazed calcite is clearly a high priority research direction
Ocean turbulence, III : new GISS vertical mixing scheme
Author Posting. © The Author(s), 2010. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Ocean Modelling 34 (2010): 70-91, doi:10.1016/j.ocemod.2010.04.006.We have found a new way to express the solutions of the RSM (Reynolds Stress
Model) equations that allows us to present the turbulent diffusivities for heat, salt and
momentum in a way that is considerably simpler and thus easier to implement than in
previous work. The RSM provides the dimensionless mixing efficiencies Îα (α stands for
heat, salt and momentum). However, to compute the diffusivities, one needs additional
information, specifically, the dissipation Δ. Since a dynamic equation for the latter that
includes the physical processes relevant to the ocean is still not available, one must resort
to different sources of information outside the RSM to obtain a complete Mixing Scheme
usable in OGCMs.
As for the RSM results, we show that the Îαâs are functions of both Ri and RÏ
(Richardson number and density ratio representing double diffusion, DD); the Îα are
different for heat, salt and momentum; in the case of heat, the traditional value Îh = 0.2
is valid only in the presence of strong shear (when DD is inoperative) while when shear
subsides, NATRE data show that Îh can be three times as large, a result that we
reproduce. The salt Îs is given in terms of Îh. The momentum Îm has thus far been
guessed with different prescriptions while the RSM provides a well defined expression
for Îm (Ri, RÏ). Having tested Îh, we then test the momentum Îm by showing that the
turbulent Prandtl number Îm/Îh vs. Ri reproduces the available data quite well.
As for the dissipation Δ, we use different representations, one for the mixed layer
(ML), one for the thermocline and one for the oceanâs bottom. For the ML, we adopt a
procedure analogous to the one successfully used in PB (planetary boundary layer)
studies; for the thermocline, we employ an expression for the variable ΔN-2 from studies
of the internal gravity waves spectra which includes a latitude dependence; for the ocean
bottom, we adopt the enhanced bottom diffusivity expression used by previous authors
but with a state of the art internal tidal energy formulation and replace the fixed Îα = 0.2
with the RSM result that brings into the problem the Ri,RÏ dependence of the Îα; the
unresolved bottom drag, which has thus far been either ignored or modeled with heuristic
relations, is modeled using a formalism we previously developed and tested in PBL
studies.
We carried out several tests without an OGCM. Prandtl and flux Richardson
numbers vs. Ri. The RSM model reproduces both types of data satisfactorily. DD and
Mixing efficiency Îh (Ri, RÏ). The RSM model reproduces well the NATRE data.
Bimodal Δ-distribution. NATRE data show that Δ (Ri1), which our model
reproduces. Heat to salt flux ratio. In the Ri>>1 regime, the RSM predictions reproduce
the data satisfactorily. NATRE mass diffusivity. The z-profile of the mass diffusivity
reproduces well the measurements at NATRE. The local form of the mixing scheme is
algebraic with one cubic equation to solve
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