172 research outputs found
A dynamic programming heuristic for vehicle routing with time-dependent travel times and required breaks.
For the intensively studied vehicle routing problem (VRP), two real-life restrictions have received only minor attention in the VRP-literature: traffic congestion and driving hours regulations. Traffic congestion causes late arrivals at customers and long travel times resulting in large transport costs. To account for traffic congestion, time-dependent travel times should be considered when constructing vehicle routes. Next, driving hours regulations, which restrict the available driving and working times for truck drivers, must be respected. Since violations are severely fined, also driving hours regulations should be considered when constructing vehicle routes, even more in combination with congestion problems. The objective of this paper is to develop a solution method for the VRP with time windows (VRPTW), time-dependent travel times, and driving hours regulations. The major difficulty of this VRPTW extension is to optimize each vehicleâs departure times to minimize the duty time of each driver. Having compact duty times leads to cost savings. However, obtaining compact duty times is much harder when time-dependent travel times and driving hours regulations are considered. We propose a restricted dynamic programming (DP) heuristic for constructing the vehicle routes, and an efficient heuristic for optimizing the vehicleâs departure times for each (partial) vehicle route, such that the complete solution algorithm runs in polynomial time. Computational experiments demonstrate the trade-off between travel distance minimization and duty time minimization, and illustrate the cost savings of extending the depot opening hours such that traveling before the morning peak and after the evening peak becomes possible
Dilution and magnification effects on image analysis applications in activated sludge characterization
The properties of activated sludge systems can be characterized using image analysis procedures.
When these systems operate with high biomass content, accurate sludge characterization requires samples to be
diluted. Selection of the best image acquisition magnification is directly related to the amount of biomass
screened. The aim of the present study was to survey the effects of dilution and magnification on the assessment
of aggregated and filamentous bacterial content and structure using image analysis procedures. Assessments of
biomass content and structure were affected by dilutions. Therefore, the correct operating dilution requires
careful consideration. Moreover, the acquisition methodology comprising a 100 magnification allowed data
on aggregated and filamentous biomass to be determined and smaller aggregates to be identified and
characterized, without affecting the accuracy of lower magnifications regarding biomass representativeness.AGERE (Empresa de
Ăguas, Efluentes e ResĂduos de Braga â EM) and AGS(Administração e GestĂŁo de Sistemas de Salubridade, S.A.)Fundação para a CiĂȘncia e Tecnologia (FCT
Desulfurization of Dibenzothiophene by Pseudomonas fluorescens (UCP 1514) Leading to the Production of Biphenyl
Dibenzothiophene (DBT) is a typical recalcitrant thiophenic sulfur component of fuels, and its desulphurization has been a model reaction in the treatment of these compounds. Based on this information, the potential of Pseudomonas fluorescens (UCP 1514) on the desulfurization of dibenzothiphene was studied, in order to use it for reducing the sulfur content of diesel oil in compliance with environmental regulations. The result of biodegradation by the bacteria was determined by undertaking high-performance liquid chromatography of the metabolites produced. These can also be identified by gas chromatography with a mass spectrometry detector, and doing so revealed a sulfur-free product, biphenyl, as the final product of the degradation process. The results showed a decrease of 73% in dibenzothiophene content, which means that P. fluorescens removes sulfur from dibenzothiophene with a good selectivity to form biphenyl. These promising results indicate that P. fluorescens has an interesting potential to degrade sulfur-containing compounds in diesel oil and thereby could help in removing sulfur content from diesel oil. The process of microbial desulfurization described herein can be used particularly after carrying out hydrodesulfurization. Consequently, the sulfur content could be reduced even further. Applying P. fluorescens UCP 1514Â in dibenzothiophene could help to understand the nature of the biodegradation process and to achieve the regulatory standards for sulfur level in fossil fuels
Study of and from and Decays
We use the decay modes and to
study the scalar mesons and within perturbative QCD
framework. For , we perform our calculation in two
scenarios of the scalar meson spectrum. The results indicate that scenario II
is more favored by experimental data than scenario I. The important
contribution from annihilation diagrams can enhance the branching ratios about
50% in scenario I, and about 30% in scenario II. The predicted branching ratio
of in scenario I is also less favored by the experiments.
The direct CP asymmetries in are small, which are
consistent with the present experiments.Comment: More references are added. Published Versio
Asymptotic Pade-Approximant Methods and QCD Current Correlation Functions
Asymptotic Pade-approximant methods are utilized to estimate the
leading-order unknown (i.e., not-yet-calculated) contributions to the
perturbative expansions of two-current QCD correlation functions obtained from
scalar-channel fermion and gluon currents, as well as from vector-channel
fermion currents. Such contributions to the imaginary part of each correlator
are polynomials of logarithms whose coefficients (other than the constant term
within the polynomial) may be extracted from prior-order contributions by use
of the renormalization-group (RG) equation appropriate for each correlator. We
find surprisingly good agreement between asymptotic Pade-approximant
predictions and RG-determinations of such coefficients for each correlation
function considered, although such agreement is seen to diminish with
increasing numbers of quark flavours. The RG-determined coefficients we obtain
are then utilized in conjunction with asymptotic Pade-approximant methods to
predict the RG-inaccessible constant terms of the leading-order unknown
contributions for all three correlators. The vector channel predictions lead to
estimates for the order contribution to for three, four, and five
flavours.Comment: latex2e, 15 page
Higher twists and extractions from the NNLO QCD analysis of the CCFR data for structure function
A detailed next-to-next-to-leading order (NNLO) QCD analysis is performed for
the experimental data of the CCFR collaboration for the structure
function. Theoretical ambiguities of the results of our NNLO fits are estimated
by application of the Pad\'e resummation technique and variation of the
factorization and renormalization scales. The NNLO and NLO
-matching conditions are used. In the process of the fits we are
taking into account of twist-4 -terms. We found that the amplitude of
the -shape of the twist-4 factor is decreasing in NLO and NNLO, though some
remaining twist-4 structure seems to retain in NNLO in the case when
statistical uncertainties are taken into account. The question of the stability
of these results to the application of the [0/2] Pad\'e resummation technique
is considered. Our NNLO results for values, extracted from the
CCFR data, are provided the twist-4 contributions are fixed through the
infrared renormalon model and provided the twist-4 terms are considered as
free parameters.Comment: 33 pages LaTeX, 3 ps figures; minor misprints are eliminated, 2 new
referencies are added; accepted for publication in Nucl. Phys.
Decay constants, light quark masses and quark mass bounds from light quark pseudoscalar sum rules
The flavor and pseudoscalar correlators are investigated using
families of finite energy sum rules (FESR's) known to be very accurately
satisfied in the isovector vector channel. It is shown that the combination of
constraints provided by the full set of these sum rules is sufficiently strong
to allow determination of both the light quark mass combinations ,
and the decay constants of the first excited pseudoscalar mesons in
these channels. The resulting masses and decay constants are also shown to
produce well-satisfied Borel transformed sum rules, thus providing non-trivial
constraints on the treatment of direct instanton effects in the FESR analysis.
The values of and obtained are in good agreement with the
values implied by recent hadronic decay analyses and the ratios obtained
from ChPT. New light quark mass bounds based on FESR's involving weight
functions which strongly suppress spectral contributions from the excited
resonance region are also presented.Comment: 28 pages, 10 figure
Casimir Effect, Achucarro-Ortiz Black Hole and the Cosmological Constant
We treat the two-dimensional Achucarro-Ortiz black hole (also known as (1+1)
dilatonic black hole) as a Casimir-type system. The stress tensor of a massless
scalar field satisfying Dirichlet boundary conditions on two one-dimensional
"walls" ("Dirichlet walls") is explicitly calculated in three different vacua.
Without employing known regularization techniques, the expression in each
vacuum for the stress tensor is reached by using the Wald's axioms. Finally,
within this asymptotically non-flat gravitational background, it is shown that
the equilibrium of the configurations, obtained by setting Casimir force to
zero, is controlled by the cosmological constant.Comment: 20 pages, LaTeX, minor corrections, comments and clarifications
added, version to appear in Phys. Rev.
A Green's function approach to transmission of massless Dirac fermions in graphene through an array of random scatterers
We consider the transmission of massless Dirac fermions through an array of
short range scatterers which are modeled as randomly positioned -
function like potentials along the x-axis. We particularly discuss the
interplay between disorder-induced localization that is the hallmark of a
non-relativistic system and two important properties of such massless Dirac
fermions, namely, complete transmission at normal incidence and periodic
dependence of transmission coefficient on the strength of the barrier that
leads to a periodic resonant transmission. This leads to two different types of
conductance behavior as a function of the system size at the resonant and the
off-resonance strengths of the delta function potential. We explain this
behavior of the conductance in terms of the transmission through a pair of such
barriers using a Green's function based approach. The method helps to
understand such disordered transport in terms of well known optical phenomena
such as Fabry Perot resonances.Comment: 22 double spaced single column pages. 15 .eps figure
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