Optimal robust inventory management with volume flexibility: matching capacity and demand with the lookahead peak-shaving policy

We study inventory control with volume flexibility: A firm can replenish using period-dependent base capacity at regular sourcing costs and access additional supply at a premium. The optimal replenishment policy is characterized by two period-dependent base-stock levels but determining their values is not trivial, especially for nonstationary and correlated demand. We propose the Lookahead Peak-Shaving policy that anticipates and peak shaves orders from future peak-demand periods to the current period, thereby matching capacity and demand. Peak shaving anticipates future order peaks and partially shifts them forward. This contrasts with conventional smoothing, which recovers the inventory deficit resulting from demand peaks by increasing later orders. Our contribution is threefold. First, we use a novel iterative approach to prove the robust optimality of the Lookahead Peak-Shaving policy. Second, we provide explicit expressions of the period-dependent base-stock levels and analyze the amount of peak shaving. Finally, we demonstrate how our policy outperforms other heuristics in stochastic systems. Most cost savings occur when demand is nonstationary and negatively correlated, and base capacities fluctuate around the mean demand. Our insights apply to several practical settings, including production systems with overtime, sourcing from multiple capacitated suppliers, or transportation planning with a spot market. Applying our model to data from a manufacturer reduces inventory and sourcing costs by 6.7%, compared to the manufacturer's policy without peak shaving.info:eu-repo/semantics/publishedVersio

Coalition theories: empirical evidence for dutch municipalities

The paper analyzes coalition formation in Dutch municipalities. After discussing the main features of the institutional setting, several theories are discussed, which are classified as size oriented, policy oriented and actor oriented models. A test statistic is proposed to determine the predictive power of these models. The empirical analysis shows that strategic positions as well as some of the distinguished preferences are important in the setting of Dutch municipalities. Especially, the dominant minimum number principle yields highly significant results for coalition formations in the period 1978–1986

Homogeneity of Stellar Populations in Early-Type Galaxies with Different X-ray Properties

We have found the stellar populations of early-type galaxies are homogeneous with no significant difference in color or Mg2 index, despite the dichotomy between X-ray extended early-type galaxies and X-ray compact ones. Since the X-ray properties reflect the potential gravitational structure and hence the process of galaxy formation, the homogeneity of the stellar populations implies that the formation of stars in early-type galaxies predat es the epoch when the dichotomy of the potential structure was established.Comment: 6 pages, 5 figures, accepted for publication in Ap

Distinguishing sequences for partially specified FSMs

Distinguishing Sequences (DSs) are used inmany Finite State Machine (FSM) based test techniques. Although Partially Specified FSMs (PSFSMs) generalise FSMs, the computational complexity of constructing Adaptive and Preset DSs (ADSs/PDSs) for PSFSMs has not been addressed. This paper shows that it is possible to check the existence of an ADS in polynomial time but the corresponding problem for PDSs is PSPACE-complete. We also report on the results of experiments with benchmarks and over 8 * 106 PSFSMs. © 2014 Springer International Publishing

Anatomy of a Merger: A Numerical Model of A754

A754 is a well-observed cluster of galaxies which exhibits a variety of morphological peculiarities. These include a bar of X-ray emission that is offset significantly from the galaxy distribution, an elongated X-ray surface brightness distribution extending between two distinct peaks in the galaxy distribution, and an extremely non-isothermal and asymmetric intracluster medium (ICM) temperature morphology. Using these observational constraints, we present a numerical Hydro/N-body model of A754 in which two clusters (2.5:1 mass ratio) have merged nearly in the plane of the sky less than 0.5 Gyrs ago with an impact parameter of ~120 kpc, and an impact velocity of ~2500 km/s (roughly the escape velocity of the primary cluster). Our models allow us to identify the origin of A754's peculiar X-ray and temperature morphologies, the underlying hydrodynamical processes that shape them, and their future evolution. We make detailed predictions for future high resolution X-ray spectroscopic observations (e.g. ASTRO-E). We discuss general properties of our models which will be characteristic of off-axis mergers. In particular, we find significant non-thermal pressure support within the central region which could bias cluster mass estimates. We find significant angular momentum imparted on the gas distribution in the cluster. We find that mixing of the subcluster gas components is an inefficient process, particularly at large radii. Finally, we find that subsequent dark matter core passages result in an extended relaxation timescale.Comment: 27 pages, including tables and figures. Latex, 10 postscript figures. Figures 2, 6, and 7 are color, but will also print as B/W. Accepted for publication in the Astrophysical Journa

Active-Sterile neutrino oscillations and BBN+CMBR constraints

We show how active-sterile neutrino oscillations in the early Universe can play an interesting role in explaining the current observations of CMBR anisotropies and light element abundances. We describe different possible phenomenological scenarios in the interpretation of present data and how active-sterile neutrino oscillations can provide a viable theoretical framework.Comment: Some changes, to appear in Phys. Rev.

Which mathematics for the Information Society?

MathIS is a new project that aims to reinvigorate secondary- school mathematics by exploiting insights of the dynamics of algorithmic problem solving. This paper describes the main ideas that underpin the project. In summary, we propose a central role for formal logic, the development of a calculational style of reasoning, the emphasis on the algorithmic nature of mathematics, and the promotion of self-discovery by the students. These ideas are discussed and the case is made, through a number of examples that show the teaching style that we want to introduce, for their relevance in shaping mathematics training for the years to come. In our opinion, the education of software engineers that work effectively with formal methods and mathematical abstractions should start before university and would benefit from the ideas discussed here.Long-term collaboration with J. N. Oliveira on calculational approaches to mathematics is deeply acknowledged. We are also grateful to the anonymous referees for their valuable comments. This research was supported by FCT (the Portuguese Foundation for Science and Technology), in the context of the MATHIS Project under contract PTDC/EIA/73252/2006. The work of Joao F. Ferreira and AlexandraMendeswas further supported by FCT grants SFRH/BD/24269/2005 and SFRH/BD/29553/2006, respectively

Whole breast and regional nodal irradiation in prone versus supine position in left sided breast cancer

Background: Prone whole breast irradiation (WBI) leads to reduced heart and lung doses in breast cancer patients receiving adjuvant radiotherapy. In this feasibility trial, we investigated the prone position for whole breast + lymph node irradiation (WB + LNI). Methods: A new support device was developed for optimal target coverage, on which patients are positioned in a position resembling a phase from the crawl swimming technique (prone crawl position). Five left sided breast cancer patients were included and simulated in supine and prone position. For each patient, a treatment plan was made in prone and supine position for WB + LNI to the whole axilla and the unoperated part of the axilla. Patients served as their own controls for comparing dosimetry of target volumes and organs at risk (OAR) in prone versus in supine position. Results: Target volume coverage differed only slightly between prone and supine position. Doses were significantly reduced (P < 0.05) in prone position for ipsilateral lung (Dmean, D2, V5, V10, V20, V30), contralateral lung (Dmean, D2), contralateral breast (Dmean, D2 and for total axillary WB + LNI also V5), thyroid (Dmean, D2, V5, V10, V20, V30), oesophagus (Dmean and for partial axillary WB + LNI also D2 and V5), skin (D2 and for partial axillary WB + LNI V105 and V107). There were no significant differences for heart and humeral head doses. Conclusions: Prone crawl position in WB + LNI allows for good breast and nodal target coverage with better sparing of ipsilateral lung, thyroid, contralateral breast, contralateral lung and oesophagus when compared to supine position. There is no difference in heart and humeral head doses