Service and inventory models subject to a delay-limit

Abstract: This thesis is concerned with the mathematical analysis of situations where service must be provided to customers within a prespecified time after arrival, the delay-limit (e.g., due to a service contract). Customer arrivals are governed by a stochastic process, and customers can be served jointly to obtain economies of scale. In Part I a basic model is extensively analysed, using techniques from Markov decision theory and queueing theory. In Part II this model is extended to the context of the production of exchangeable items, leading to a general framework for inventory models with a delay-limit on backorders. Several models within this framework are then studied in detail, including lost-sales inventory models.

On the First Entrance Time Distribution of the M/D/i Queue:A Combinatorial Approach

AMS classifications: 60C05; 60K25; 90B06; 90B2

On the First Entrance Time Distribution of the M/D/i Queue: A Combinatorial Approach

AMS classifications: 60C05; 60K25; 90B06; 90B22M/D/1;delivery;first entrance times;lattice path counting

Optimal Service Policies to Remote Customers with Delay-Limits

This work deals with service provision to remote customers.Two examples are: (i) a manufacturer that has to deliver items to customers in a remote destination, and (ii) a company that provides repair and replacement service to distant clients.In both cases the remoteness of customers suggests order aggregation: a batch delivery in the rst example, and a batch-visits journey in the other; the alternative is toprovide individual services to customers.A key element is a contractual obligation of the company to provide service within an agreed delay-limit, and in that view the main decision problem is when to do a batch service.That decision would depend on: (random) demand-arrival patterns, the costs associated with the two service modes (batch and individual), as well as the model used to describe operating conditions.This paper proposes and investigates several service-provision policies, with a simple enough structure to make them appealing for real-life implementation.Optimal service- provision procedures are obtained for these policies, minimizing the long-run expected cost per unit of time.The global optimal policy is also studied by means of a Markov-decision- process problem formulation, which enables us to verify properties of the optimal policy.The optimal costs of the proposed policies are compared and their relative performance is evaluated with respect to the global minimal cost (of the optimal policy) on one hand, and basic policies that employ either only batch or only individual services on the other hand.The results are also used to address the issue of the determination of a desirable delay- limit from the standpoint of the service provider.Finally, this work takes a broader view of the problem area of optimal service provision to remote customers through demand aggregation, and it discusses a range of further modelling settings of interest.

A technique for thoracic duct-portal vein anastomosis in the dog

A technique for effecting a thoracic duct-portal vein anastomosis in dogs is described.The journals have been scanned in colour with a HP 5590 scanner; 600 dpi. Adobe Acrobat v.11 was used to OCR the text and also for the merging and conversion to the final presentation PDF-format

Search for varying constants of nature from astronomical observation of molecules

The status of searches for possible variation in the constants of nature from astronomical observation of molecules is reviewed, focusing on the dimensionless constant representing the proton-electron mass ratio $\mu=m_p/m_e$. The optical detection of H$_2$ and CO molecules with large ground-based telescopes (as the ESO-VLT and the Keck telescopes), as well as the detection of H$_2$ with the Cosmic Origins Spectrograph aboard the Hubble Space Telescope is discussed in the context of varying constants, and in connection to different theoretical scenarios. Radio astronomy provides an alternative search strategy bearing the advantage that molecules as NH$_3$ (ammonia) and CH$_3$OH (methanol) can be used, which are much more sensitive to a varying $\mu$ than diatomic molecules. Current constraints are $|\Delta\mu/\mu| < 5 \times 10^{-6}$ for redshift $z=2.0-4.2$, corresponding to look-back times of 10-12.5 Gyrs, and $|\Delta\mu/\mu| < 1.5 \times 10^{-7}$ for $z=0.88$, corresponding to half the age of the Universe (both at 3$\sigma$ statistical significance). Existing bottlenecks and prospects for future improvement with novel instrumentation are discussed.Comment: Contribution to Workshop "High Performance Clocks in Space" at the International Space Science Institute, Bern 201

The Efficacy Of Rice As A Leaching

The concluding phase(s) of a rice rotation experiment presented the opportunity to assess the effect of consecutive crops of rice on the chemistry of the soil profile. An experiment which aimed to determine the potential to use high salinity groundwater for the irrigation of the non-rice phases of a wheat - sub.clover - rice rotation, and then use rice, irrigated with low salinity channel water (<0.1 dS/m), as a leaching crop was undertaken. The rotation included a single rice crop between each cycle of the application of saline groundwater. Although soil salinity of most horizons under saline treatments could be reduced by leaching in the rice phase (single crop), this was not true for sodicity. Average rootzone sodicity remained elevated above control values at the end of each cycle and increased following successive cycles. This project was implemented to further assess the effectiveness of rice as a leaching crop. As the blocks completed two cycles within the rice rotation the opportunity to grow successive crops of rice was undertaken. At the time of soil sampling (May, 2000) separate blocks had grown one, two, three or four consecutive rice crops. Soil samples were taken from each plot and processed for electrical conductivity and sodium (Na) content. Additional consecutive crops of rice resulted in more leaching of salt from the profile. After three crops sufficient salts had been leached to reduce ECe to below 0.6 dS/m to at least the depth sampled in this project (90 cm). Similar values were measured after a fourth crop. The levels of SARe measured after a second consecutive crop of rice were still higher than pre-treatment levels. Even after three and four crops of rice the SARe at profile depths below 60 cm, whilst reduced from the pre-treatment level, were still between 6 and 8

Chiral three-nucleon forces and bound excited states in neutron-rich oxygen isotopes

We study the spectra of neutron-rich oxygen isotopes based on chiral two- and three-nucleon interactions. First, we benchmark our many-body approach by comparing ground-state energies to coupled-cluster results for the same two-nucleon interaction, with overall good agreement. We then calculate bound excited states in 21,22,23O, focusing on the role of three-nucleon forces, in the standard sd shell and an extended sdf7/2p3/2 valence space. Chiral three-nucleon forces provide important one- and two-body contributions between valence neutrons. We find that both these contributions and an extended valence space are necessary to reproduce key signatures of novel shell evolution, such as the N = 14 magic number and the low-lying states in 21O and 23O, which are too compressed with two-nucleon interactions only. For the extended space calculations, this presents first work based on nuclear forces without adjustments. Future work is needed and open questions are discussed.Comment: 6 pages, 4 figures, published versio