MEMS VOA with polymeric thermal microactuators

A MEMS VOA with polymeric microactuators using microoptics is presented. Its insertion loss < 0.5 dB, dynamic range > 50 dB, power and time for 20 dB, < 40 mW and 40 ms resp

Optimal maintenance of multi-component systems: a review

In this article we give an overview of the literature on multi-component maintenance optimization. We focus on work appearing since the 1991 survey "A survey of maintenance models for multi-unit systems" by Cho and Parlar. This paper builds forth on the review article by Dekker et al. (1996), which focusses on economic dependence, and the survey of maintenance policies by Wang (2002), in which some group maintenance and some opportunistic maintenance policies are considered. Our classification scheme is primarily based on the dependence between components (stochastic, structural or economic). Next, we also classify the papers on the basis of the planning aspect (short-term vs long-term), the grouping of maintenance activities (either grouping preventive or corrective maintenance, or opportunistic grouping) and the optimization approach used (heuristic, policy classes or exact algorithms). Finally, we pay attention to the applications of the models.literature review;economic dependence;failure interaction;maintenance policies;grouping maintenance;multi-component systems;opportunistic maintenance;maintencance optimization;structural dependence

A scenario aggregation based approach for determining a robust airline fleet composition

Strategic airline fleet planning is one of the major issues addressed through newly initiated decision support systems, designed to assist airlines and aircraft manufacturers in assessing the benefits of the emerging concept of dynamic capacity allocation. We present background research connected with such a system, which aims to explicitly account for the stochastic nature of passenger demand in supporting decisions related to the fleet composition problem. We address this problem through a scenario aggregation based approach and present results on representative case studies based on realistic data. Our investigations establish clear benefits of a stochastic approach as compared with deterministic formulations, as well as its implementation feasibility using state-of-the-artoptimization software.Dynamic capacity allocation;Airline fleet composition;Stochastic programming;Scenario aggregation;Fleet assignment

Service Parts Inventory Control with Lateral Transshipment that Takes Time

In equipment-intensive industries such as truck manufacturing, electronics manufacturing, photo copiers, and airliners, service parts are often slow moving items for which, in some cases, the transshipment time is not negligible. However, this aspect is hardly considered in the existing spare parts literature. We assess the effect of non-negligible lateral transshipment time on various aspects of spare parts inventory control. Furthermore, we introduce customer-oriented service levels by taking the uncommitted pipeline stocks into account. A case study in the dredging industry shows that lateral transshipment may lead to lower system performance, which supports the results from some recent studies. Furthermore, we find that considerable savings can be obtained when we include the uncommitted pipeline stocks in both base stock allocation and lateral transshipment decisions.inventory control;METRIC;customer-oriented service level;lateral transshipment

'Aurora'-a time domain based meta-algorithm for the rapid simulation and design of complex optical circuits

A new simulation tool called ‘Aurora’, specifically developed to efficiently simulate highly complex optical devices such as OADMs and Routers based on (higher order)microring resonators, is presented. The meta-simulation algorithm used by Aurora creates a framework in which many different simulation algorithms can be properly combined rather than providing a simulation algorithm itself. The calculations of this program use a simple scheme based in the time domain from which the frequency response can easily be derived. Simulation results of a 4-port OADM and waveguide gratings show excellent agreement when compared to experimentally obtained measurement data and conventional simulation methods

Variation and Distribution of Glucosinolates in 42 Cultivars of Brassica oleracea Vegetable Crops

Brassica vegetables are known to contain glucosinolates that are precursors for bioactive compounds like isothiocyanates that have been shown to play an important role in human health. This study reports the results of a screening of 11 Brassica oleracea crops consisting of 42 cultivars (6 white cabbage, 5 red cabbage, 7 Brussels sprouts, 2 kale, 1 tronchuda, 3 oxheart cabbage, 2 kohlrabi, 6 broccoli, 5 cauliflower, 3 romanesco and 2 Savoy cabbage). All these cultivars were cultivated under the same conditions on a single location in the same season. The variation found in the level of glucosinolates is expected to be mainly due to the genetic variation. A large variation was observed in the level and profile of glucosinolates. Total glucosinolates varied from 14 to 625 µmol/100 g fresh weight. Glucoraphanin, the precursor of the isothiocyanate sulforophane, varied from 0 to 141 µmol/100 g fresh weight. Within broccoli glucoraphanin varied from 27 to 141 µmol/100 g fresh weight. Glucoiberin that is structurally related to glucoraphanin varied from 6 to 397 µmol/100 g fresh weight. Within broccoli glucoiberin varied from 21 to 397 µmol/100 g fresh weigh

Differences in Thermal Stability of Glucosinolates in Five Brassica Vegetables

The thermal stability of individual glucosinolates within five different Brassica vegetables was studied at 100°C for different incubation times up to 120 minutes. Three vegetables that were used in this study were Brassica oleracea (red cabbage, broccoli and Brussels sprouts) and two were Brassica rapa (pak choi and Chinese cabbage). To rule out the influence of enzymatic breakdown, myrosinase was inactivated prior to the thermal treatments. The stability of three glucosinolates that occurred in all five vegetables (gluconapin, glucobrassicin and 4-methoxyglucobrassicin) varied considerably between the different vegetables. The degradation could be modeled by first order kinetics. The rate constants obtained varied between four to twenty fold between the five vegetables. Brussels sprouts showed the highest degradation rates for all three glucosinolates. The two indole glucosinolates were most stable in red cabbage, while gluconapin was most stable in broccoli. These results indicate the possibilities for plant breeding to select for cultivars in which glucosinolates are more stable during processin

The Vehicle Rescheduling Problem

The capacitated vehicle routing problem is to find a routing schedule describing the order in which geographically dispersed customers are visited to satisfy demand by supplying goods stored at the depot, such that the traveling costs are minimized. In many practical applications, a long term routing schedule has to be made for operational purposes, often based on average demand estimates. When demand substantially differs, constructing a new schedule is beneficial. The vehicle rescheduling problem is to find a new schedule that not only minimizes the total traveling costs but also minimizes the costs of deviating from the original schedule. In this paper two mathematical programming formulations of the rescheduling problem are presented as well as two heuristic methods, a two-phase heuristic and a modified savings heuristic. Computational and analytical results show that for sufficiently high deviation costs, the two-phase heuristic generates a schedule that is on average close to optimal or even guaranteed optimal, for all considered problem instances. The modified savings heuristic generates schedules of constant quality, however the two-phase heuristic produces schedules that are on average closer to the optimum.vehicle routing;operational planning;vehicle rescheduling problem

On the efficiency of optimal algorithms for the joint replenishment problem: a comparative study

In this paper we proposed an efficient algorithm to solve the joint replenishment problem to optimality. We perform a computational study to compare the performance of the proposed algorithm with the best one reported in Viswanathan [6]. The study reveals that for large minor set-up costs and moderate major set-up cost, our algorithm outperforms the latter.inventory;joint replenishment;deterministic demand

A Continuous Review Inventory Model with Advance Policy Change and Obsolescence

In this paper, we consider a continuous review inventory system of a slow moving item for which the demand rate drops to a lower level at a pre-determined time. Inventory system is controlled according to one-for-one replenishment policy with fixed lead time. Adaptation to the lower demand rate is achieved by changing the control policy in advance and letting the demand take away the excess stocks. We showed that the timing of the control policy change primarily determines the tradeoff between backordering penalties and obsolescence costs. We propose an approximate solution for the optimal time to shift to the new control policy minimizing the expected total cost during the transient period. We found that the advance policy change results in significant cost savings and our model yields near optimal expected total costs.inventory control;obsolescence;spare parts;excess stock;installed base;advance policy changes