123,657 research outputs found
The Vehicle Routing Problem with Divisible Deliveries and Pickups
No full textThe vehicle routing problem with divisible deliveries and pickups is a new and interesting model within
reverse logistics. Each customer may have a pickup and delivery demand that have to be served with
capacitated vehicles. The pickup and the delivery quantities may be served, if beneficial, in two separate visits.
The model is placed in the context of other delivery and pickup problems and formulated as a mixed-integer
linear programming problem. In this paper, we study the savings that can be achieved by allowing the pickup
and delivery quantities to be served separately with respect to the case where the quantities have to be served
simultaneously. Both exact and heuristic results are analysed in depth for a better understanding of the problem
structure and an average estimation of the savings due to the possibility of serving pickup and delivery
quantities separately
Preliminary interpretation of Titan plasma interaction as observed by the Cassini Plasma Spectrometer: Comparisons with Voyager 1
No full textThe Cassini Plasma Spectrometer (CAPS) instrument observed the plasma environment at Titan during the Cassini orbiter's TA encounter on October 26, 2004. Titan was in Saturn's magnetosphere during the Voyager 1 flyby and also during the TA encounter. CAPS measurements from this encounter are compared with measurements made by the Voyager 1 Plasma Science Instrument (PLS). The comparisons focus on the composition and nature of ambient and pickup ions. They lead to: A) the major ion components of Saturn's magnetosphere in the vicinity of Titan are H+, H-2(+) and O+/CH4+ ions; B) finite gyroradius effects are apparent in ambient O+ ions as the result of their absorption by Titan's extended atmosphere; C) the principal pickup ions are composed of H+, H-2(+), N+/CH2+, CH4+, and N-2(+); D) the pickup ions are in narrow energy ranges; and E) there is clear evidence of the slowing down of background ions due to pickup ion mass loading
Relationship between plasma sialic acid and fibinogen concentration and incident micro-and macrovascular complications in type 1 diabetes
No full textAIMS/HYPOTHESIS: Type 1 diabetes is associated with an increased risk of vascular complications. This increased risk could be explained by sialic acid and/or fibrinogen. It is also not clear what explains the abolition of sex-related differences affecting risk of CHD in the presence of type 1 diabetes. Therefore, we examined whether fibrinogen and sialic acid are related to incident micro- and macrovascular complications in patients with type 1 diabetes. METHODS: A subset (n=2329) of the EURODIAB Prospective Complications Study was analysed. Sialic acid and fibrinogen concentrations were measured at baseline. The main outcomes after 7 years were development of albuminuria, retinopathy, neuropathy and CHD. RESULTS: Univariable and multivariable models using Cox proportional survival analyses showed that an SD unit increase in sialic acid and fibrinogen levels was significantly associated with CHD in men only. Adjusted standardised hazard ratios (sHRs) were 1.50 (95% CI 1.05-2.15) and 1.40 (95% CI 1.06-1.86) for sialic acid and fibrinogen, respectively. Initial associations between (1) sialic acid and incident retinopathy [standardised odds ratio (sOR) men 1.68, 95% CI 1.10-2.57], (2) fibrinogen and retinopathy (sOR women 1.37, 95% CI 1.06-1.78) and (3) sialic acid and neuropathy (sOR men 1.37, 95% CI 1.06-1.77) were shown, but became non-significant in multivariable models. CONCLUSIONS/INTERPRETATION: Sialic acid and fibrinogen are strong predictors of CHD in men with type 1 diabetes, beyond the effect of established risk factors. The associations found with microvascular complications were not independent of other risk factors
A Metaheuristic for the Pickup and Delivery Problem with Split-Loads and its Extension
No full textIn this dissertation, we study improvements in the Pickup and Delivery Problem that can be achieved by allowing multiple vehicle trips to serve a common load. We explore how costs can be reduced through the elimination of the constraint that a load must be served by only one vehicle trip. Specifically, we investigate the problem of routing vehicles to serve loads that have distinct origins and destinations, with no constraint on the amount of a load that a vehicle may serve at a time. We develop a metaheuristic to solve large scale practical size problems in this form and apply the metaheuristic to randomly generated data sets. The metaheuristic is based on a predetermined fixed number of restarts of annealing-like procedure with tabu-lists to avoid cycling in the search process and the annealing-like procedure is to guide the local search in three neighborhoods defined to solve the problem. We test the algorithm on several sets of problem instances generated with different transportation requests and over different load size ranges. The experimental results on these problem sets have shown that benefits are common if split loads are adopted in designing practical sized transportation network for different load size configurations, and the most benefit is achieved when all the loads are just a little above half of the vehicle capacity and have small variations, and this most benefit is around 33% for all the three 75-, 100-, and 125-request problem sets, which overtakes the one reported in previous literature. In a more general setting when some load sizes are greater than the vehicle capacity and have to be split, there are also certain cost reduction if split loads are applied. We also generate numeral tests on different load size ranges and split the loads that are greater than the vehicle capacity using different ”splitting” strategy, in term of how much amount to split from the original load to form a new load, and find that there seem to be no optimal ”splitting” strategy, which can assure the best quality of solutions using the metaheuristic developed in the dissertation
Transport of Solar Wind Fluctuations: A Two-Component Model
No full textWe present a new model for the transport of solar wind fluctuations which treats them as two interacting incompressible components: quasi-two-dimensional turbulence and a wave-like piece. Quantities solved for include the energy, cross helicity, and characteristic transverse length scale of each component, plus the proton temperature. The development of the model is outlined and numerical solutions are compared with spacecraft observations. Compared to previous single-component models, this new model incorporates a more physically realistic treatment of fluctuations induced by pickup ions and yields improved agreement with observed values of the correlation length, while maintaining good observational accord with the energy, cross helicity, and temperature
Heating of the low-latitude solar wind by dissipation of turbulent magnetic fluctuations
No full textWe test a theory presented previously to account for the turbulent transport of magnetic fluctuation energy in the solar wind and the related dissipation and heating of the ambient ion population. This theory accounts for the injection of magnetic energy through the damping of large-scale flow gradients, such as wind shear and compression, and incorporates the injection of magnetic energy due to wave excitation by interstellar pickup ions. The theory assumes quasi-two-dimensional spectral transport of the fluctuation energy and subsequent dissipation that heats the thermal protons. We compare the predictions of this theory with Voyager 2 and Pioneer 11 observations of magnetic fluctuation energy, magnetic correlation lengths, and ambient proton temperatures. Near-Earth Omnitape observations are used to adjust for solar variability, and the possibility that high-latitude effects could mask possible radial dependences is considered. We find abundant evidence for in situ heating of the protons, which we quantify, and show that the observed magnetic energy is consistent with the ion temperatures
Data for Optical bistability under non-resonant excitation in spinor polariton condensates
No full textExperimental data and numerical simulation results used to create the figures in the paper Pickup, L., Kalinin, K., Askitopoulos, A. M., Hatzopoulos, Z., Savvidis, P. G., Berloff, N. G., & Lagoudakis, P. (2018). Optical bistability under nonresonant excitation in spinor polariton condensates. Physical Review Letters.
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Replication Data for: Transformed-Likelihood Estimators for Dynamic Panel Models with a Very Small T
No full textConventional OLS fixed-effects and GLS random-effects estimators of dynamic models
that control for individual-effects are known to be biased when applied to short
panel data (T <= 10). GMM estimators are the most used alternative but are known to
have drawbacks. Transformed-likelihood estimators are unused in political science.
Of these, orthogonal reparameterization estimators are only tangentially referred to in
any discipline. We introduce these estimators and test their performance, demonstrating
that the unused orthogonal reparameterization transformed-likelihood estimator
in particular performs very well and is an improvement on the commonly used GMM
estimators. When T and/or N are small, it provides efficiency gains and overcomes
the issues GMM estimators encounter in the estimation of long-run effects when the
coefficient on the lagged dependent variable is close to one
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