4,507 research outputs found
Optimisation of stochastic networks with blocking: a functional-form approach
This paper introduces a class of stochastic networks with blocking, motivated
by applications arising in cellular network planning, mobile cloud computing,
and spare parts supply chains. Blocking results in lost revenue due to
customers or jobs being permanently removed from the system. We are interested
in striking a balance between mitigating blocking by increasing service
capacity, and maintaining low costs for service capacity. This problem is
further complicated by the stochastic nature of the system. Owing to the
complexity of the system there are no analytical results available that
formulate and solve the relevant optimization problem in closed form.
Traditional simulation-based methods may work well for small instances, but the
associated computational costs are prohibitive for networks of realistic size.
We propose a hybrid functional-form based approach for finding the optimal
resource allocation, combining the speed of an analytical approach with the
accuracy of simulation-based optimisation. The key insight is to replace the
computationally expensive gradient estimation in simulation optimisation with a
closed-form analytical approximation that is calibrated using a single
simulation run. We develop two implementations of this approach and conduct
extensive computational experiments on complex examples to show that it is
capable of substantially improving system performance. We also provide evidence
that our approach has substantially lower computational costs compared to
stochastic approximation
Optimal Tradeoff Between Exposed and Hidden Nodes in Large Wireless Networks
Wireless networks equipped with the CSMA protocol are subject to collisions
due to interference. For a given interference range we investigate the tradeoff
between collisions (hidden nodes) and unused capacity (exposed nodes). We show
that the sensing range that maximizes throughput critically depends on the
activation rate of nodes. For infinite line networks, we prove the existence of
a threshold: When the activation rate is below this threshold the optimal
sensing range is small (to maximize spatial reuse). When the activation rate is
above the threshold the optimal sensing range is just large enough to preclude
all collisions. Simulations suggest that this threshold policy extends to more
complex linear and non-linear topologies
Spillover effects of supplementary on basic health insurance: evidence from the Netherlands
Like many other countries, the Netherlands has a health insurance system that combines mandatory basic insurance with voluntary supplementary insurance. Both types of insurance are founded on different principles. Since basic and supplementary insurance are sold by the same health insurers, both markets may interact. This paper examines to what extent basic and supplementary insurance are linked to each other and whether these links generate spillover effects of supplementary on basic insurance. Our analysis is based on an investigation into supplementary health insurance contracts, underwriting procedures and annual surveys among 1,700–2,100 respondents over the period 2006–2009. We find that health insurers increasingly use a variety of strategies to enforce a joint purchase of basic and supplementary health insurance. Despite incentives for health insurers to use supplementary insurance as a tool for risk selection in basic insurance, we find limited evidence of supplementary insurance being used this way. Only a minority of health insurers uses health questionnaires when people apply for supplementary coverage. Nevertheless, we find that an increasing proportion of high-risk individuals believe that insurers would not be willing to offer them another supplementary insurance contract. We discuss several strategies to prevent or to counteract the observed negative spillover effects of supplementary insurance
Terugkeer naar de veertigurige werkweek
Nederlandse werknemers werken relatief weinig. Verschillen
tussen OESO-landen in aantal gewerkte uren per werkende
kunnen slechts deels worden verklaard door verschillen
in arbeidsmarktinstituties. Sociale normen omtrent de
gebruikelijke
werktijd lijken veel belangrijker
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