957 research outputs found
Capacity development in higher education : five years involvement of Wageningen UR with NPT and NFP
Dealing with risk : beyond gut feeling : an approach to risk management in software engineering
Floating stocks in FMCG supply chains
In this paper we present a new distribution concept called ‘floating stocks’, which uses intermodal transport to deploy inventories in a supply chain in advance of retailer demand. Supplying part of the demand directly by road compensates the longer transit time of this transport. First an analytical comparison is made which shows that this concept has advantages in inventories over pure road and intermodal transport. Next a simulation study of a real case is made which quantifies the cost-differences in detail
Hysteresis and bi-stability by an interplay of calcium oscillations and action potential firing
Many cell types exhibit oscillatory activity, such as repetitive action
potential firing due to the Hodgkin-Huxley dynamics of ion channels in the cell
membrane or reveal intracellular inositol triphosphate (IP) mediated
calcium oscillations (CaOs) by calcium-induced calcium release channels
(IP-receptor) in the membrane of the endoplasmic reticulum (ER). The
dynamics of the excitable membrane and that of the IP-mediated CaOs have
been the subject of many studies. However, the interaction between the
excitable cell membrane and IP-mediated CaOs, which are coupled by
cytosolic calcium which affects the dynamics of both, has not been studied.
This study for the first time applied stability analysis to investigate the
dynamic behavior of a model, which includes both an excitable membrane and an
intracellular IP-mediated calcium oscillator. Taking the IP
concentration as a control parameter, the model exhibits a novel rich spectrum
of stable and unstable states with hysteresis. The four stable states of the
model correspond in detail to previously reported growth-state dependent states
of the membrane potential of normal rat kidney fibroblasts in cell culture. The
hysteresis is most pronounced for experimentally observed parameter values of
the model, suggesting a functional importance of hysteresis. This study shows
that the four growth-dependent cell states may not reflect the behavior of
cells that have differentiated into different cell types with different
properties, but simply reflect four different states of a single cell type,
that is characterized by a single model.Comment: 29 pages, 6 figure
Differentially Private Billing with Rebates
A number of established and novel business models are based on fine grained billing, including pay-per-view, mobile messaging, voice calls, pay-as-you-drive insurance, smart metering for utility provision, private computing clouds and hosted services. These models apply fine-grained tariffs dependent on time-of-use or place of-use to readings to compute a bill. We extend previously proposed billing protocols to strengthen their privacy in two key ways. First, we study the monetary amount a customer should add to their bill in order to provably hide their activities, within the differential privacy framework. Second, we propose a cryptographic protocol for oblivious billing that ensures any additional expenditure, aimed at protecting privacy, can be tracked and reclaimed in the future, thus minimising its cost. Our proposals can be used together or separately and are backed by provable guarantees of security. © 2011 Springer-Verlag
Role of the Helicobacter pylori outer-membrane proteins AlpA and AlpB in colonization of the guinea pig stomach
The human gastric pathogen Helicobacter pylori expresses several putative
outer-membrane proteins (OMPs), but the role of individual OMPs in
colonization of the stomach by H. pylori is still poorly understood. The
role of four such OMPs (AlpA, AlpB, OipA and HopZ) in a guinea pig model
of H. pylori infection has been investigated. Single alpA, alpB, hopZ and
oipA isogenic mutants were constructed in the guinea pig-adapted,
wild-type H. pylori strain GP15. Guinea pigs were inoculated
intragastrically with the wild-type strain, single mutants or a mixture of
the wild-type and a single mutant in a 1: 1 ratio. Three weeks after
infection, H. pylori could be isolated from stomach sections of all
animals that were infected with the wild-type, the hopZ mutant or the oipA
mutant, but from only five of nine (P = 0.18) and one of seven (P = 0.02)
animals that were infected with the alpA or alpB mutants, respectively.
The hopZ and oipA mutants colonized the majority of animals that were
inoculated with the strain mixture, whereas alpA and alpB mutants could
not be isolated from anim
Monte Carlo Simulations for the Magnetic Phase Diagram of the Double Exchange Hamiltonian
We have used Monte Carlo simulation techniques to obtain the magnetic phase
diagram of the double exchange Hamiltonian. We have found that the Berry's
phase of the hopping amplitude has a negligible effect in the value of the
magnetic critical temperature. To avoid finite size problems in our simulations
we have also developed an approximated expression for the double exchange
energy. This allows us to obtain the critical temperature for the ferromagnetic
to paramagnetic transition more accurately. In our calculations we do not
observe any strange behavior in the kinetic energy, chemical potential or
electron density of states near the magnetic critical temperature. Therefore,
we conclude that other effects, not included in the double exchange
Hamiltonian, are needed to understand the metal-insulator transition which
occurs in the manganites.Comment: 6 pages Revtex, 8 PS figure
- …